BREAK-RESISTANT PARTITION WALL COMPRISING SOLID ELECTROLYTE CERAMICS FOR ELECTROLYTIC CELLS

Abstract

The present invention relates, in a first aspect, to a dividing wall W suitable for use in an electrolysis cell E. The dividing wall W comprises a frame element R that forms an edge element R.sub.R and a separating element R.sub.T. The frame element R comprises two opposite parts R.sub.1 and R.sub.2, with at least two alkali metal cation-conducting solid-state electrolyte ceramics F.sub.A and F.sub.B disposed therebetween. The separating element R.sub.T lies between alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W and separates these from one another. It is a feature of the invention that the two parts R.sub.1 and R.sub.2 are secured to one another by at least one securing element B.sub.R at the edge element R.sub.R and at least one securing element B.sub.T at the separating element R.sub.T.

Compared to the cases according to the prior art in which the dividing wall W encompasses the solid-state electrolyte in one piece, this arrangement is firstly more flexible since the individual ceramics have more degrees of freedom available in order to react to fluctuations in temperature, for example by shrinkage or expansion. This increases stability with respect to mechanical stresses in the ceramic. At the same time, the mechanical stability of the arrangement of the at least two solid-state electrolyte ceramics between the parts R.sub.1 and R.sub.2 is increased in that the parts R.sub.1 and R.sub.2 are secured to one another both at the edge element R.sub.R and at the separating element R.sub.T by at least one securing element B.sub.R or B.sub.T.

In a second aspect, the present invention relates to an electrolysis cell E encompassing a cathode chamber K.sub.K divided by the dividing wall W from the adjacent chamber, which is the anode chamber K.sub.A or a middle chamber K.sub.M of the electrolysis cell E.

In a third aspect, the present invention relates to a process for producing an alkali metal alkoxide solution in the electrolysis cell E according to the second aspect of the invention.

Claims

1. A dividing wall W <16> comprising one side S.sub.KK <161> having the surface O.sub.KK <163> and, opposite the side S.sub.KK <161>, a side S.sub.A/MK <162> having the surface O.sub.A/MK <164>, wherein the dividing wall W <16> encompasses a frame element R <2> composed of two opposite parts R.sub.1 <201> and R.sub.2 <202>, with at least two alkali metal cation-conducting solid-state electrolyte ceramics F.sub.A <18> and F.sub.B <19> disposed therebetween, wherein R.sub.1 <201> is directly contactable via the surface O.sub.KK <163>, wherein R.sub.2 <202> is directly contactable via the surface O.sub.A/MK <164>, wherein the frame element R <2> forms an edge element R.sub.R <20> and a separating element R.sub.T <17>, wherein the edge element R.sub.R <20> at least partly bounds the surfaces O.sub.KK <163> and O.sub.A/MK <164>, and wherein the separating element R.sub.T <17> lies between alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W <16> and separates these from one another, such that the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W <16> are directly contactable both via the surface O.sub.KK <163> and via the surface O.sub.A/MK <164>, wherein R.sub.1 <201> and R.sub.2 <202> are secured to one another by at least one securing element B.sub.R <91> at the edge element R.sub.R <20>, and R.sub.1 <201> and R.sub.2 <202> are secured to one another by at least one securing element B.sub.T <92> at the separating element R.sub.T <17>.

2. The dividing wall W <16> according to claim 1, wherein the at least one securing element B.sub.R <91> and the at least one securing element B.sub.T <92> are in one-piece form together with at least one of parts R.sub.1 <201> and R.sub.2 <202>.

3. The dividing wall W <16> according to claim 1, wherein the at least one securing element B.sub.R <91> and the at least one securing element B.sub.T <92> are each in the form of mutually engaging hooks B.sub.H <93>.

4. The dividing wall W <16> according to claim 1, comprising at least four alkali metal cation-conducting solid-state electrolyte ceramics F.sub.A <18>, F.sub.B <19>, F.sub.C <28> and F.sub.D <29>.

5. Dividing wall W <16> according to claim 4, wherein the separating element R.sub.T <17> takes the form of a cross or grid.

6. The dividing wall W <16> according to claim 1, wherein the frame element R <2> comprises a material selected from the group consisting of plastic, glass, wood.

7. The dividing wall W <16> according to claim 1, wherein the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W <16> independently have a structure of the formula $M_{1+2w+x-y+z}^I{M}_w^{\mathrm{II}}{M}_x^{\mathrm{III}}{\mathrm{Zr}}_{2-w-x-y}^{IV}{M_y^V\left({\mathrm{SiO}}_4\right)}_z{\left({\mathrm{PO}}_4\right)}_{3-z},$ where M.sup.I is selected from Na.sup.+ and Li.sup.+, M.sup.II is a divalent metal cation, M.sup.III is a trivalent metal cation, M.sup.V is a pentavalent metal cation, the Roman indices I, II, III, IV, V indicate the oxidation numbers in which the respective metal cations exist, and w, x, y, z are real numbers, where 0x<2, 0y<2, 0w<2, 0z<3, and where w, x, y, z are chosen such that 1+2w+xy+z0 and 2wxy0.

8. An electrolysis cell E <1> comprising at least one anode chamber K.sub.A <11> having at least one inlet Z.sub.KA <110>, at least one outlet A.sub.KA <111>, and an interior I.sub.KA <112> comprising an anodic electrode E.sub.A <113>, at least one cathode chamber K.sub.K <12> having at least one inlet Z.sub.KK <120>, at least one outlet A.sub.KK <121>, and an interior I.sub.KK <122> comprising a cathodic electrode E.sub.K <123>, and optionally at least one interposed middle chamber K.sub.M <13> having at least one inlet Z.sub.KM <130>, at least one outlet A.sub.KM <131> and an interior I.sub.KM <132>, where I.sub.KA <112> and I.sub.KM <132> are then divided from one another by a diffusion barrier D <14>, and A.sub.KM <131> is connected by a connection V.sub.AM <15> to the inlet Z.sub.KA <110>, such that liquid can be passed from I.sub.KM <132> into I.sub.KA <112> via the connection V.sub.AM <15>, where in the cases in which the electrolysis cell E <1> does not comprise a middle chamber K.sub.M <13>, I.sub.KA <112> and I.sub.KK <122> are divided from one another by a dividing wall W <16> according to claim 1, in the cases in which the electrolysis cell E <1> comprises at least one middle chamber K.sub.M <13>, I.sub.KK <122> and I.sub.KM <132> are divided from one another by a dividing wall W <16> according to claim 1, wherein the alkali metal cation-conducting solid-state ceramics encompassed by the dividing wall W <16> directly contact the interior I.sub.KK <122> on the S.sub.KK side <161> via the surface O.sub.KK <163>, and in the cases in which the electrolysis cell E <1> does not comprise a middle chamber K.sub.M <13>, the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W <16> directly contact the interior I.sub.KA <112> on the S.sub.A/MK <162> side via the surface O.sub.A/MK <164>, in the cases in which the electrolysis cell E <1> comprises at least one middle chamber K.sub.M <13>, the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W <16> directly contact the interior I.sub.KM <132> on the S.sub.A/MK <162> side via the surface O.sub.A/MK <164>.

9. The electrolysis cell E <1> according to claim 8 which does not comprise a middle chamber K.sub.M <13>.

10. The electrolysis cell E <1> according to claim 8 which comprises at least one middle chamber K.sub.M <13>.

11. The electrolysis cell E <1> according to claim 10, wherein the connection V.sub.AM <15> is formed within the electrolysis cell E <1>.

12. A process for producing a solution L.sub.1 <21> of an alkali metal alkoxide XOR in the alcohol ROH, where X is an alkali metal cation and R is an alkyl radical having 1 to 4 carbon atoms, () wherein the following steps (1), (2), (3) that proceed simultaneously are conducted in the electrolysis cell E <1> according to claim 9: (1) a solution L.sub.2 <22> comprising the alcohol ROH is routed through K.sub.K <12>, (2) a neutral or alkaline, aqueous solution L.sub.3 <23> of a salt S comprising X as cation is routed through K.sub.A <11>, (3) voltage is applied between E.sub.A <113> and E.sub.K <123>.

13. The process according to claim 12, wherein X is selected from the group consisting of Li.sup.+, Na.sup.+, K.sup.+.

14. The process to claim 12, wherein S is a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X.

15. The process according to claim 12, wherein R is selected from the group consisting of methyl and ethyl.

16. A process for producing a solution L.sub.1 <21> of an alkali metal alkoxide XOR in the alcohol ROH, where X is an alkali metal cation and R is an alkyl radical having 1 to 4 carbon atoms, () wherein the following steps (1), (2), (3) that proceed simultaneously are conducted in the electrolysis cell E <1> according to claim 10: (1) a solution L.sub.2 <22> comprising the alcohol ROH is routed through K.sub.K <12>, (2) a neutral or alkaline, aqueous solution L.sub.3 <23> of a salt S comprising X as cation is routed through K.sub.M <13>, then through V.sub.AM <15>, then through K.sub.A <11>, () voltage is applied between E.sub.A <113> and E.sub.K <123>, which affords the solution L.sub.1 <21> at the outlet A.sub.KK <121>, with a higher concentration of XOR in L.sub.1 <21> than in L.sub.2 <22>, and which affords an aqueous solution L.sub.4 <24> of S at the outlet A.sub.KA <111>, with a lower concentration of S in L.sub.4 <24> than in L.sub.3 <23>.

17. The process according to claim 16, wherein X is selected from the group consisting of Li.sup.+, Na.sup.+, K.sup.+.

18. The process according to claim 16, wherein S is a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X.

19. The process according to claim 16, wherein R is selected from the group consisting of methyl and ethyl.

Description

3. FIGURES

3.1 FIGS. 1 A and 1 B

[0046] FIG. 1 A (=FIG. 1 A) shows a non-inventive electrolysis cell E. This comprises a cathode chamber K.sub.K <12> and an anode chamber K.sub.A <11>.

[0047] The cathode chamber K.sub.K <12> comprises a cathodic electrode E.sub.K <123> in the interior I.sub.KK <122>, an inlet Z.sub.KK <120> and an outlet A.sub.KK <121>.

[0048] The anode chamber K.sub.A <11> comprises an anodic electrode E.sub.A <113> in the interior I.sub.KA <112>, an inlet Z.sub.KK <110> and an outlet A.sub.KA <111>.

[0049] The two chambers are bounded by an outer wall <80> of the two-chamber cell E. The interior I.sub.KK <122> is also divided from the interior I.sub.KA <112> by a dividing wall consisting of a sheet of a NaSICON solid-state electrolyte F.sub.A <18> which is selectively permeable to sodium ions. The NaSICON solid-state electrolyte F.sub.A <18> extends over the entire depth and height of the two-chamber cell E. The dividing wall has two sides S.sub.KK <161> and S.sub.A/MK <162>, the surfaces O.sub.KK <163> and O.sub.A/MK <164> of which contact the respective interior I.sub.KK <122> or I.sub.KA <112>.

[0050] An aqueous solution of sodium chloride L.sub.3 <23> with pH 10.5 is introduced via the inlet Z.sub.KA <110>, counter to the direction of gravity, into the interior I.sub.KA <112>.

[0051] A solution of sodium methoxide in methanol L.sub.2 <22> is routed into the interior I.sub.KK <122> via the inlet Z.sub.KK <120>.

[0052] At the same time, a voltage is applied between the cathodic electrode E.sub.K <123> and the anodic electrode E.sub.A <113>. This results in reduction of methanol in the electrolyte L.sub.2 <22> to give methoxide and H.sub.2 in the interior I.sub.KK <122> (CH.sub.3OH+e.sup..fwdarw.CH.sub.3O.sup.+ H.sub.2). At the same time, sodium ions diffuse from the interior I.sub.KA <112> through the NaSICON solid-state electrolyte F.sub.K <18> into the interior I.sub.KK <122>. Overall, this increases the concentration of sodium methoxide in the interior I.sub.KK <122>, which affords a methanolic solution of sodium methoxide L.sub.1 <21> having an elevated sodium methoxide concentration compared to L.sub.2 <22>.

[0053] In the interior I.sub.KA <112>, the oxidation of chloride ions takes place to give molecular chlorine (Cl.sup..fwdarw. Cl.sub.2+e.sup.). In the outlet A.sub.KA <111>, an aqueous solution L.sub.4 <24> is obtained, in which the content of NaCl is reduced compared to L.sub.3 <23>. Chlorine gas (Cl.sub.2) in water, according to the reaction Cl.sub.2+H.sub.2O.fwdarw.HOCl+HCl, forms hypochlorous acid and hydrochloric acid, which give an acidic reaction with further water molecules. The acidity damages the NaSICON solid-state electrolyte F.sub.A <18>.

[0054] FIG. 1 B (=FIG. 1 B) shows a further non-inventive electrolysis cell E. This three-chamber cell E comprises a cathode chamber K.sub.K <12>, an anode chamber K.sub.A <11> and an interposed middle chamber K.sub.M <13>.

[0055] The cathode chamber K.sub.K <12> comprises a cathodic electrode E.sub.K <123> in the interior I.sub.KK <122>, an inlet Z.sub.KK <120> and an outlet A.sub.KK <121>.

[0056] The anode chamber K.sub.A <11> comprises an anodic electrode E.sub.A <113> in the interior I.sub.KA <112>, an inlet Z.sub.KK <110> and an outlet A.sub.KA <111>.

[0057] The middle chamber K.sub.M <13> comprises an interior I.sub.KM <132>, an inlet Z.sub.KM <130> and an outlet A.sub.KM <131>.

[0058] The interior I.sub.KA <112> is connected to the interior I.sub.KM <132> via the connection V.sub.AM <15>.

[0059] The three chambers are bounded by an outer wall <80> of the three-chamber cell E. The interior I.sub.KM <132> of the middle chamber K.sub.M <13> is also divided from the interior I.sub.KA <122> of the cathode chamber K.sub.K <12> by a dividing wall consisting of a sheet of a NaSICON solid-state electrolyte F.sub.A <18> which is selectively permeable to sodium ions. The NaSICON solid-state electrolyte F.sub.A <18> extends over the entire depth and height of the three-chamber cell E. The dividing wall has two sides S.sub.KK <161> and S.sub.A/MK <162>, the surfaces O.sub.KK <163> and O.sub.A/MK <164> of which contact the respective interior I.sub.KK <122> or I.sub.KM <132>.

[0060] The interior I.sub.KM <132> of the middle chamber K.sub.M <13> is additionally divided in turn from the interior I.sub.KA <112> of the anode chamber K.sub.A <11> by a diffusion barrier D <14>. The NaSICON solid-state electrolyte F.sub.A <18> and the diffusion barrier D <14> extend over the entire depth and height of the three-chamber cell E. The diffusion barrier D <14> is a cation exchange membrane (sulfonated PTFE).

[0061] In the embodiment according to FIG. 1 B, the connection V.sub.AM <15> is formed outside the electrolysis cell E, especially by a tube or hose, the material of which may be selected from rubber, metal and plastic. The connection V.sub.AM <15> can guide liquid from the interior I.sub.KM <132> of the middle chamber K.sub.M <13> into the interior I.sub.KA <112> of the anode chamber K.sub.A <11> outside the dividing wall W.sub.A <80> of the three-chamber cell E. The connection V.sub.AM <15> connects an outlet A.sub.KM <131> that penetrates the outer wall W.sub.A <80> of the electrolysis cell E at the base of the middle chamber K.sub.M <13> to an inlet Z.sub.KA <110> that penetrates the outer wall W.sub.A <80> of the electrolysis cell E at the base of the anode chamber K.sub.A <11>.

[0062] An aqueous solution of sodium chloride L.sub.3 <23> with pH 10.5 is introduced via the inlet Z.sub.KM <130>, in the direction of gravity, into the interior I.sub.KM <132> of the middle chamber K.sub.M. The connection V.sub.AM <15> formed between an outlet A.sub.KM <131> from the middle chamber K.sub.M <13> and an inlet Z.sub.KA <110> to the anode chamber K.sub.A <11> connects the interior I.sub.KM <132> of the middle chamber K.sub.M <13> to the interior I.sub.KA <112> of the anode chamber K.sub.A <11>. Sodium chloride solution L.sub.3 <23> is routed through this connection V.sub.AM <15> from the interior I.sub.KM <132> into the interior I.sub.KA <112>. A solution of sodium methoxide in methanol L.sub.2 <22> is routed into the interior I.sub.KK <122> via the inlet Z.sub.KK <120>.

[0063] At the same time, a voltage is applied between the cathodic electrode E.sub.K <123> and the anodic electrode E.sub.A <113>. This results in reduction of methanol in the electrolyte L.sub.2 <22> to give methoxide and H.sub.2 in the interior I.sub.KK <122> (CH.sub.3OH+e.sup..fwdarw.CH.sub.3O.sup.+ H.sub.2). At the same time, sodium ions diffuse from the interior I.sub.KM <132> of the middle chamber K.sub.M <13> through the NaSICON solid-state electrolyte F.sub.A <18> into the interior I.sub.KK <122>. Overall, this increases the concentration of sodium methoxide in the interior I.sub.KK <122>, which affords a methanolic solution of sodium methoxide L.sub.1 <21> having an elevated sodium methoxide concentration compared to L.sub.2 <22>.

[0064] In the interior I.sub.KA <112>, the oxidation of chloride ions takes place to give molecular chlorine (Cl.sup..fwdarw. Cl.sub.2+e.sup.). At the outlet A.sub.KA <111>, an aqueous solution L.sub.4 <24> is obtained, in which the content of NaCl is reduced compared to L.sub.3 <23>. Chlorine gas (Cl.sub.2) in water, according to the reaction Cl.sub.2+H.sub.2O.fwdarw.HOCl+HCl, forms hypochlorous acid and hydrochloric acid, which give an acidic reaction with further water molecules. The acidity would damage the NaSICON solid-state electrolyte F.sub.A <18>, but is restricted to the anode chamber K.sub.A <11> by the arrangement in the three-chamber cell, and hence kept away from the NaSICON solid-state electrolyte F.sub.K <18> in the electrolysis cell E. This considerably increases the lifetime thereof.

3.2 FIGS. 2 A and 2 B

[0065] FIG. 2 A (=FIG. 2 A) shows an inventive dividing wall W <16>. The side S.sub.KK <161> with the surface O.sub.KK <163> lies in the plane of the drawing, and the side S.sub.A/MK <162> with the surface O.sub.A/MK <164> not visible in FIG. 2 A lies behind the plane of the drawing.

[0066] The dividing wall W <16> comprises two NaSICON solid-state electrolyte ceramics F.sub.A <18> and F.sub.B <19> disposed between a frame element R <2>. The frame element R <2> comprises two parts R.sub.1 <201> and R.sub.2 <202>, between which the ceramics F.sub.A <18> and F.sub.B <19> are disposed. The frame element R <2> here forms an edge element R.sub.R <20> and a separating element R.sub.T <17>. The separating element R.sub.T <17> lies between the NaSICON solid-state electrolyte ceramics F.sub.A <18> and F.sub.B <19> and separates these from one another. The separating element R.sub.T <17> is the part of the frame element R <2> shown in shaded form in FIGS. 2 A and 2 B. The edge element R.sub.R <20> is the part of the frame element R <2> shown in non-shaded form in FIGS. 2 A and 2 B. The two frame parts R.sub.1 <201> and R.sub.2 <202> in the region of the edge element R.sub.R <20> are secured to one another by eight securing elements B.sub.R <91>, and in the region of the separating elements R.sub.T <17> by a securing element B.sub.T <92>. The views drawn show cross sections Q.sub.RR <165> and Q.sub.RT <166> through the dividing wall W <16> that are elucidated in detail in FIGS. 3 A to 3 C. Q.sub.RR <165> and Q.sub.RT <166> intersect the dividing wall W <16> at right angles to the surface O.sub.KK <163> in the region of one of the two solid-state electrolyte ceramics F.sub.A <18> and F.sub.B <19>.

[0067] FIG. 2 B (=FIG. 2 B) shows another embodiment of an inventive dividing wall W <16>. This corresponds to the embodiment shown in FIG. 2, except that it comprises four NaSICON solid-state electrolyte ceramics F.sub.A <18>, F.sub.B <19>, F.sub.C <28>, F.sub.D <29>, with F.sub.A <18>, F.sub.B <19>, F.sub.C <28> and F.sub.D <29> being disposed between the frame parts R.sub.1 <201> and R.sub.2 <202>. The separating element R.sub.T <17> has the shape of a cross. The two frame parts R.sub.1 <201> and R.sub.2 <202> in the region of the edge element R.sub.R <20> are secured to one another by twelve securing elements B.sub.R <91>, and in the region of the separating elements R.sub.T <17> by three securing elements B.sub.T <92>. The side S.sub.KK <161> with the surface O.sub.KK <163> lies in the plane of the drawing, and the side S.sub.A/MK <162> with the surface O.sub.A/MK <164> not visible in FIG. 2 B behind the plane of the drawing.

3.3 FIGS. 3 A to 3 C

[0068] FIGS. 3 A to 3 C each show, above the continuous dotted line, a detail view of the cross section Q.sub.RR <165> shown in FIGS. 2 A and 2 B in the region of the edge element R.sub.R <20> of the dividing wall W <16>. FIGS. 3 A and 3 B also show, below the continuous dotted line, a detail view of the cross section Q.sub.RT <166> shown in FIGS. 2 A and 2 B in the region of the separating element R.sub.T <17> of the dividing wall W <16>. The side S.sub.KK <161> having the surface O.sub.KK <163> is on the right-hand side of FIG. 3 A; the side S.sub.A/MK <162> having the surface O.sub.A/MK <164> is on the left-hand side of FIG. 3 A.

[0069] In FIG. 3 A (=FIG. 3 A), the solid-state electrolyte ceramic F.sub.A <18>, in the cross section Q.sub.RR <165>, is disposed between the two frame parts R.sub.1 <201> and R.sub.2 <202> that form the frame element R.sub.R <20> here. These may exist in one piece or separately from one another, as indicated by the dotted line. They are preferably separate from one another. They are secured to one another by a screw as securing element B.sub.R <91> and clamp the solid-state electrolyte ceramic F.sub.A <18> between them. A seal Di <40> is preferably provided between the two frame parts R.sub.1 <201> and R.sub.2 <202> and the solid-state electrolyte ceramic F.sub.A <18>.

[0070] In the cross section Q.sub.RT <166>, the two solid-state electrolyte ceramics F.sub.A <18> and F.sub.B <19> are disposed between the two frame parts R.sub.1 <201> and R.sub.2 <202> which form the separating element R.sub.T <17> here. They are secured to one another by a screw as securing element B.sub.T <92> and clamp the solid-state electrolyte ceramics F.sub.A <18> and F.sub.B <19> between them, preferably with provision of a seal Di <40>.

[0071] FIG. 3 B (=FIG. 3 B) illustrates a further embodiment of each of the two cross sections Q.sub.RR <165> and Q.sub.RT <166>. This corresponds to the embodiment shown in FIG. 3 A, except that the two securing elements B.sub.R <91> and B.sub.T <92> are formed by hooks B.sub.H <93>. These hooks may be in one-piece form (as shown here) together with the respective frame part R.sub.1 <201> or R.sub.2 <202>, or be bonded thereto. They engage with one another and enable securing of the two frame parts R.sub.1 <201> and R.sub.2 <202> to one another.

[0072] FIG. 3 C (=FIG. 3 C) illustrates a further embodiment of the cross section Q.sub.RR <165>. This corresponds to the embodiment shown in FIG. 3 A, except that the edge element R.sub.R <20> forms rounded corners.

3.4 FIGS. 4 A and 4 B

[0073] FIGS. 4 A (=FIG. 4 A) and 4 B (=Fig. B A) each show an electrolysis cell E <1> according to the second aspect of the invention. These each correspond to the electrolysis cell shown in FIG. 1 A, except that a dividing wall W <16> separates the interior I.sub.KK <122> of the cathode chamber K.sub.K <12> from the interior I.sub.KA <112> of the anode chamber K.sub.A <11>. The dividing wall is that shown in FIG. 2 A or 2 B.

[0074] In this case, in the embodiment according to FIG. 4 A, a screw is used as securing elements B.sub.R <91> and B.sub.T <92>. The cross section Q.sub.RR <165> in the region of the edge element R.sub.R <20> of the dividing wall W <16> and the cross section Q.sub.RT <166> in the region of the separating element R.sub.T <17> of the dividing wall W <16> is in each case as described in FIG. 3 A.

[0075] In the embodiment according to FIG. 4 B, mutually engaging hooks B.sub.H <93> are used as securing elements B.sub.R <91> and B.sub.T <92>. The cross section Q.sub.RR <165> in the region of the edge element R.sub.R <20> of the dividing wall W <16> and the cross section Q.sub.RT <166> in the region of the separating element R.sub.T <17> of the dividing wall W <16> is in each case as described in FIG. 3 B.

3.5 FIGS. 5 A and 5 B

[0076] FIG. 5 A (=FIG. 5 A) shows an electrolysis cell E <1> according to the second aspect of the invention. This corresponds to the electrolysis cell shown in FIG. 1 B, except that a dividing wall W <16> separates the interior I.sub.KK <122> of the cathode chamber K.sub.K <12> from the interior I.sub.KM <132> of the middle chamber K.sub.M <13>. The dividing wall W <16> is that shown in FIG. 2 A or 2 B. In this case, in the embodiment according to FIG. 4 A, a screw is used as securing elements B.sub.R <91> and B.sub.T <92>. The cross section Q.sub.RR <165> in the region of the edge element R.sub.R <20> of the dividing wall W <16> and the cross section Q.sub.RT <166> in the region of the separating element R.sub.T <17> of the dividing wall W <16> is in each case as described in FIG. 3 A.

[0077] FIG. 5 B (=FIG. 5 B) shows an electrolysis cell E <1> according to the second aspect of the invention. This corresponds to the electrolysis cell E <1> shown in FIG. 5 A with the following two differences:

[0078] 1. The connection V.sub.AM <15> from the interior I.sub.KM <132> of the middle chamber K.sub.M <13> to the interior I.sub.KA <112> of the anode chamber K.sub.A <11> is formed not outside the electrolysis cell E <1>, but rather inside through a perforation in the diffusion barrier D <14>. This perforation may be made in the diffusion barrier D <14> or may already have been present therein from the outset in the production of the diffusion barrier D <14> (for example in the case of textile fabrics such as filter cloths or metal weaves).

[0079] 2. In the embodiment according to FIG. 5 B, mutually engaging hooks B.sub.H <93> are used as securing elements B.sub.R <91> and B.sub.T <92>. The cross section Q.sub.RR <165> in the region of the edge element R.sub.R <20> of the dividing wall W <16> and the cross section Q.sub.RT <166> in the region of the separating element R.sub.T <17> of the dividing wall W <16> is in each case as described in FIG. 3 B.

[0080] The separating element R.sub.T <17> is the part of the frame element R <2> shown in shaded form in FIGS. 6 A and 6 B.

3.6 FIGS. 6 A and 6 B

[0081] FIG. 6 A (=FIG. 6 A) shows a further embodiment of an inventive dividing wall W <16> in a top view of the side S.sub.KK <161> having the surface O.sub.KK <163> (on the left), and then as a side view of the detail that results from the curved clamp in the viewing direction of the arrow.

[0082] This comprises four NaSICON solid-state electrolyte ceramics F.sub.A <18>, F.sub.B <19>, F.sub.C <28> and F.sub.D <29>, which are disposed between two halves R.sub.1 <201> and R.sub.2 <202> of a frame element R <2>. The frame element R <2> here forms an edge element R.sub.R <20> and a separating element R.sub.T <17>. The separating element R.sub.T <17> is cross-shaped and lies between the NaSICON solid-state electrolyte ceramics F.sub.A <18>, F.sub.B <19>, F.sub.C <28> and F.sub.D <29>, and separates these from one another. The separating element R.sub.T <17> is the part of the frame element R <2> shown in shaded form in FIGS. 6 A and 6 B. The edge element R.sub.R <20> is the part of the frame element R <2> shown in non-shaded form in FIGS. 6 A and 6 B. The two frame parts R.sub.1 <201> and R.sub.2 <202> in the region of the edge element R.sub.R <20> are secured to one another by a securing element B.sub.R <91>, and in the region of the separating elements R.sub.T <17> by a securing element B.sub.T <92>. They may optionally be connected to one another via a hinge <50>. A rubber ring as seal Di <40> is preferably provided in each case between the respective solid-state electrolyte ceramic F.sub.A <18>, F.sub.B <19>, F.sub.C <28> and F.sub.D <29> and the two frame parts R.sub.1 <201> and R.sub.2 <202>. The rings that function as seal Di <40> are given as dotted outlines in the front view on the left-hand side of FIG. 6 A.

[0083] FIG. 6 B (=FIG. 6 B) shows a further embodiment of an inventive dividing wall W <16>. This corresponds to the embodiment described in FIG. 6 A, except that it comprises nine NaSICON solid-state electrolyte ceramics F.sub.A <18>, F.sub.B <19>, F.sub.C <28>, F.sub.D <29>, F.sub.E <30>, F.sub.F <31>, F.sub.G <32>, F.sub.H <33>, F.sub.I <34>. In addition, the frame element R <2> additionally has four bulges <60> each with a hole <61> (rabbits' ears), with which the dividing wall can be secured, for example, to a cathode chamber K.sub.K <12> with appropriate designs.

4. DETAILED DESCRIPTION OF THE INVENTION

4.1 Dividing Wall W

[0084] The present invention relates in a first aspect to a dividing wall W. This is especially suitable as a dividing wall in an electrolysis cell, especially an electrolysis cell E.

[0085] In one aspect, the present invention thus also relates to an electrolysis cell comprising the dividing wall W, especially an electrolysis cell E comprising the dividing wall W.

[0086] The dividing wall W comprises at least two alkali metal cation-conducting solid-state electrolyte ceramics (alkali metal cation-conducting solid-state electrolyte ceramic is abbreviated hereinafter as ASC) F.sub.A and F.sub.B, separated from one another by a separating element R.sub.T.

[0087] The dividing wall W comprises two sides S.sub.KK and S.sub.A/MK that are opposite one another, meaning that side S.sub.A/MK is opposite side S.sub.KK (and vice versa). The two sides S.sub.KK and S.sub.A/MK especially comprise planes that are essentially parallel to one another.

[0088] The geometry of the dividing wall W is otherwise subject to no further restriction, and may be matched in particular to the cross section of the electrolysis cell E in which it is used. For example, it may have the geometry of a cuboid and hence have a rectangular cross section, or the geometry of a frustocone or cylinder and accordingly a circular cross section.

[0089] Optionally, the dividing wall W may also have the geometry of a cuboid with rounded corners or bulges which may in turn have holes. The dividing wall W then has bulges (rabbit's ears) by which the dividing wall W can be fixed to electrolysis cells, or else the two frame parts R.sub.1 and R.sub.2 of the dividing wall W can be fixed to one another.

[0090] The side S.sub.KK of the dividing wall W has the surface O.sub.KK, and the side S.sub.A/MK of the dividing wall W has the surface O.sub.A/MK.

[0091] The dividing wall W encompasses a frame element R. This comprises two opposite parts, preferably halves, R.sub.1 and R.sub.2, with at least two alkali metal cation-conducting solid-state ceramics F.sub.A and F.sub.B disposed therebetween. R.sub.1 is directly contactable via the surface O.sub.KK; R.sub.2 is directly contactable via the surface O.sub.A/MK.

[0092] The frame element R forms a frame element R.sub.R and a separating element R.sub.T, with the frame element R.sub.R bounding and preferably fully surrounding the surfaces O.sub.KK and O.sub.A/MK, and with the frame element R.sub.T lying between alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W and separating these from one another, [0093] such that the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W are directly contactable both via the surface O.sub.KK and via the surface O.sub.A/MK.

[0094] What is meant by the feature dividing wall is that the dividing wall W is liquid-tight. This means that the ASCs and the frame element R gaplessly adjoin one another. Thus, no gaps exist between frame element R and the ASCs encompassed by the dividing wall W, through which aqueous solution, alcoholic solution, alcohol or water could flow from the S.sub.KK side to the S.sub.A/MK side or vice versa.

[0095] If there are two or more pairs of opposite sides via the surfaces of which the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W and the respective part R.sub.1 or R.sub.2 are directly contactable, the pair of opposite sides referred to as S.sub.KK and S.sub.A/MK in the context of the invention is preferably that pair which encompasses the greatest surface areas O.sub.KK and O.sub.A/MK. If the surface areas encompassed by two pairs of opposite sides are the same, the person skilled in the art can select one pair as S.sub.KK and S.sub.A/MK with surfaces O.sub.KK and O.sub.A/MK.

[0096] Among dividing walls W where there are two or more pairs of opposite sides via the surfaces of which the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W and the respective part R.sub.1 or R.sub.2 are directly contactable, preference is given to the dividing walls W where the surface areas encompassed by the respective pair of opposite sides are different, in which case the pair of opposite sides referred to as S.sub.KK and S.sub.A/MK in the context of the invention is that which encompasses the greatest surface areas O.sub.KK and O.sub.A/MK.

[0097] The dividing wall W according to the first aspect of the present invention also includes embodiments in which the dividing wall W comprises more than two ASCs, for example four or nine or twelve ASCs.

[0098] In the dividing wall W, all ASCs encompassed by the dividing wall W are separated from one another by the separating element R.sub.T of the frame element R, meaning that no ASC directly adjoins another ASC, that is without a frame element R being in between.

[0099] The dividing wall W is further characterized in that the ASCs encompassed by the dividing wall W are directly contactable both via the surface O.sub.KK and via the surface O.sub.A/MK.

[0100] What is meant by directly contactable with regard to the ASCs encompassed by the dividing wall W is that some of the surfaces O.sub.KK and O.sub.A/MK are formed by the surface of the ASCs encompassed by the dividing wall W, meaning that the ASCs encompassed by the dividing wall W are directly accessible at the two surfaces O.sub.KK and O.sub.A/MK, such that they can be wetted at the two surfaces O.sub.KK and O.sub.A/MK, for example, with aqueous solution, alcoholic solution, alcohol or water.

[0101] What this means for the arrangement of the ASCs in the dividing wall W is that, for each ASC encompassed by the dividing wall W, there is a route from the surface O.sub.KK on the side S.sub.KK to the surface O.sub.A/MK on the side S.sub.A/MK that leads completely through the respective ASC.

[0102] The two frame elements R.sub.1 and R.sub.2 are directly contactable via the surfaces O.sub.KK and O.sub.A/MK.

[0103] What is meant by directly contactable with regard to the frame part R.sub.1 encompassed by the dividing wall W is that part of the surface O.sub.KK is formed by the surface of the frame part R.sub.1, meaning that the frame part R.sub.1 is directly accessible at the surface O.sub.KK, such that it can be wetted at the surface O.sub.KK, for example, with aqueous solution, alcoholic solution, alcohol or water.

[0104] What is meant by directly contactable with regard to the frame part R.sub.2 encompassed by the dividing wall W is that part of the surface O.sub.A/MK is formed by the surface of the frame part R.sub.2, meaning that the frame part R.sub.2 is directly accessible at the surface O.sub.A/MK, such that it can be wetted at the surface O.sub.A/MK, for example, with aqueous solution, alcoholic solution, alcohol or water.

[0105] What this means more particularly for the arrangement of the frame element R in the dividing wall W is that there is a route from the surface O.sub.KK on the side S.sub.KK to the surface O.sub.A/MK on the side S.sub.A/MK that leads through the R.sub.1 part and then through the R.sub.2 part (and possibly through a seal Di), but not through an ASC.

[0106] In a preferred embodiment of the dividing wall W in the first aspect of the invention, 50% to 95%, more preferably 60% to 90%, even more preferably 70% to 85%, of the surface O.sub.KK is formed by the ASCs encompassed by the dividing wall W, with the rest of the surface O.sub.KK even more preferably being formed by the frame part R.sub.1.

[0107] In a preferred embodiment of the dividing wall W in the first aspect of the invention, 50% to 95%, more preferably 60% to 90%, even more preferably 70% to 85%, of the surface O.sub.A/MK is also formed by the ASCs encompassed by the dividing wall W, with the rest of the surface O.sub.A/MK even more preferably being formed by the frame part R.sub.2.

[0108] In a preferred embodiment, the dividing wall W, especially between frame element R and the ASCs, comprises a seal Di (shown, for example, in FIGS. 3 A,3 B and 3 C). This ensures in a particularly efficient manner that the dividing wall W is liquid-tight. The seal Di may be selected by the person skilled in the art for the respective ASC or the respective frame element R.

[0109] The seal Di especially comprises a material selected from the group consisting of elastomers, adhesives, preferably elastomers.

[0110] A useful elastomer is especially rubber, preferably ethylene-propylene-diene rubber (EPDM), fluoropolymer rubber (FPM), perfluoropolymer rubber (FFPM), or acrylonitrile-butadiene rubber (NBR).

[0111] The seal Di is preferably selected such that it is compressed when the two frame parts R.sub.1 and R.sub.2 are secured to one another and the ASCs are arranged between the two frame parts R.sub.1 and R.sub.2. This further increases the integrity of the dividing wall W.

[0112] In a preferred embodiment, the dividing wall W comprises at least four ASCs F.sub.A, F.sub.B, F.sub.C and F.sub.D, and even more preferably comprises exactly four ASCs F.sub.A, F.sub.B, F.sub.C and F.sub.D.

[0113] In a further preferred embodiment, the dividing wall W comprises at least nine ASCs F.sub.A, F.sub.B, F.sub.C, F.sub.D, F.sub.E, F.sub.F, F.sub.G, F.sub.H and F.sub.I, and even more preferably comprises exactly nine ASCs F.sub.A, F.sub.B, F.sub.C, F.sub.D, F.sub.E, F.sub.F, F.sub.G, F.sub.H and F.sub.I.

[0114] In a further preferred embodiment, the dividing wall W comprises at least twelve ASCs F.sub.A, F.sub.B, F.sub.C, F.sub.D, F.sub.E, F.sub.F, F.sub.G, F.sub.H, F.sub.I, F.sub.J, F.sub.K and F.sub.L, and even more preferably comprises exactly twelve ASCs F.sub.A, F.sub.B, F.sub.C, F.sub.D, F.sub.E, F.sub.F, F.sub.G, F.sub.H, F.sub.I, F.sub.J, F.sub.K and F.sub.L.

[0115] This inventive arrangement of at least two ASCs alongside one another in the dividing wall W, compared to the conventional dividing walls in the prior art electrolysis cells, results in a further direction of spread for the ASCs in the event of the fluctuations in temperature that arise in the operation of the electrolysis cell. In the prior art electrolysis cells, the NaSICON sheets that function as dividing walls are framed by the outer walls of the electrolysis cell or by solid plastic frames. It is not possible in this way to dissipate the mechanical stresses that occur in the event of expansion within the NaSICON, which can lead to fracture of the ceramic.

[0116] By contrast, the individual ASCs within the dividing wall W in the first aspect of the invention adjoin the separating element R.sub.T, and, in the case of the ASCs at the edge of the surfaces O.sub.KK and O.sub.A/MK, also adjoin the frame element R.sub.R, which leads to advantageous effects, both of which increase the long-term stability of the ASC: [0117] each ASC has a further available degree of freedom, i.e. a dimension in which it can expand. As well as expansion in z direction (i.e. beyond the thickness of the ceramic sheet at right angles to the plane of the dividing wall W), expansion in x and/or y direction is now also possible, i.e. in horizontal and vertical direction within the plane of the dividing wall W. This direction of expansion does not exist, or is at least greatly restricted, when the ASCs, for example as a solid sheet, span the cross section of the electrolysis cell and adjoin the solid wall of the electrolysis cell. [0118] compared to a dividing wall of equal size consisting solely of one ASC, the division into multiple small ASCs has the effect that the stresses that occur within the smaller ASCs are also smaller in absolute terms, can be dissipated more rapidly and hence cannot as quickly build up to a stress that leads to the fracture of the ASC.

[0119] As a result, the tendency to fracture is distinctly reduced for the divided ASCs in the dividing wall W compared to the use of one sheet.

4.1.1 Frame Element R

[0120] The frame element R comprises two opposite parts R.sub.1 and R.sub.2, with the at least two alkali metal cation-conducting solid-state ceramics F.sub.A and F.sub.B encompassed by the dividing wall W disposed therebetween. This arrangement can be effected in any manner familiar to the person skilled in the art. In a particular embodiment, the two parts R.sub.1 and R.sub.2 clamp the ASCs between them, preferably using a seal Di that additionally stabilizes the ASCs in the frame element R. In another preferred embodiment, the ASCs are bonded to the two frame parts R.sub.1 and R.sub.2. Adhesives KI used for the purpose may be any of the adhesives familiar to the person skilled in the art that are stable under the conditions of the electrolysis. Preferred KIs include at least one substance selected from epoxy resins, phenolic resins.

[0121] The dividing wall W may have a hinge by which the two parts R.sub.1 and R.sub.2 of the frame element R can be opened and closed.

[0122] The frame element R especially comprises a material selected from the group consisting of plastic, glass, wood. More preferably, the frame element R comprises plastic.

[0123] Even more preferably, the plastic is one selected from the group consisting of polypropylene, polystyrene, polyvinylchloride.

[0124] In a preferred embodiment, a seal Di is provided between frame element R and the ASCs encompassed by the dividing wall W. This improves the liquid-tightness of the dividing wall W.

[0125] The frame element R forms an edge element R.sub.R and a separating element R.sub.T.

4.1.1.1 Separating Element R.SUB.T

[0126] Separating element R.sub.T refers to that region of the frame element R that lies between at least two ASCs and separates these from one another. The separating element R.sub.T as a region of the frame element R is formed by the two parts R.sub.1 and R.sub.2.

[0127] A suitable separating element R.sub.T which is formed by the frame element R is any body by means of which the respective ASCs can be arranged separately from one another. The ASCs here gaplessly adjoin the separating element R.sub.T in order not to impair the function of the dividing wall W which, in the electrolysis cell E, is to divide the cathode chamber in a liquid-tight manner from the adjacent middle chamber or anode chamber.

[0128] The shape of the separating element R.sub.T can be chosen by the person skilled in the art, especially depending on the number and shape of the ASCs encompassed by the dividing wall W.

[0129] If the dividing wall W comprises two or three ASCs, for example, these may each be separated by a land disposed between the ASCs as a separating element R.sub.T (see, for example, FIG. 2 A).

[0130] If the dividing wall W comprises four or more ASCs, these may be separated by a separating element R.sub.T in the form of a cross (see FIGS. 2 B and 6 A) or grid (see FIG. 6 B).

[0131] It is preferable that the dividing wall W comprises at least four ASCs, and even more preferable that the separating element R.sub.T is then in the form of a cross or grid, since all three dimensions are then fully available to the ASCs for thermal expansion/shrinkage.

[0132] The separating element R.sub.T here is especially shaped in such a way that the respective ASC can be fitted or clamped into the separating element. This can already be implemented in a corresponding manner in the production of the dividing wall W.

[0133] The separating element R.sub.T preferably comprises a material selected from the group consisting of plastic, glass, and wood. More preferably, the separating element R.sub.T comprises plastic.

[0134] Even more preferably, the plastic is one selected from the group consisting of polypropylene, polystyrene, polyvinylchloride (PVC). PVC also includes post-chlorinated polyvinylchloride (PVC-C).

4.1.1.2 Edge Element R.SUB.R

[0135] The frame element R forms not only the separating element R.sub.T but also an edge element R.sub.R. The edge element R.sub.R as a region of the frame element R is formed by the two parts R.sub.1 and R.sub.2. The edge element R.sub.R (as distinct from the separating element R.sub.T) is that region of the frame element R which is not disposed between the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, i.e. does not separate these from one another.

[0136] The edge element R.sub.R bounds the surfaces O.sub.KK and O.sub.A/MK at least partly, preferably completely. What this means is more particularly: The edge element R.sub.R surrounds the surfaces O.sub.KK and O.sub.A/MK at least partly, preferably completely.

[0137] The edge element R.sub.R here may or may not be part of the surfaces O.sub.KK and O.sub.A/MK. The edge element R.sub.R is preferably part of the surfaces O.sub.KK and O.sub.A/MK.

[0138] The edge element R.sub.R is especially directly contactable or not directly contactable via the surfaces O.sub.KK and O.sub.A/MK.

[0139] The edge element R.sub.R is preferably directly contactable via the surfaces O.sub.KK and O.sub.A/MK. In this preferred embodiment, the edge element R.sub.R as part of R.sub.1 is directly contactable via the surface O.sub.KK, and as part of R.sub.2 is directly contactable via the surface O.sub.A/MK. [0140] What is meant by not directly contactable with regard to the edge element R.sub.R encompassed by the dividing wall W is that the edge element R.sub.R is formed exclusively as at least part of the surfaces of those sides of the dividing wall W which are not the sides S.sub.KK and S.sub.A/MK. More particularly, the edge element R.sub.R in that case forms at least 1%, more preferably at least 25%, more preferably at least 50%, even more preferably 100%, of the surface areas of the sides of the dividing wall W that are not the sides S.sub.KK and S.sub.A/MK. [0141] What is meant by directly contactable with regard to the frame element R.sub.R encompassed by the dividing wall W is that part of the surface O.sub.KK is formed by the surface of the frame element R.sub.R, meaning that the frame element R.sub.R is directly accessible at the surface O.sub.KK, such that it can be wetted at the surface O.sub.KK, for example, with aqueous solution, alcoholic solution, alcohol or water. [0142] What is also meant by directly contactable with regard to the frame element R.sub.R encompassed by the dividing wall W is that part of the surface O.sub.A/MK is formed by the surface of the frame element R.sub.R, meaning that the frame element R.sub.R is directly accessible at the surface O.sub.A/MK, such that it can be wetted at the surface O.sub.A/MK, for example, with aqueous solution, alcoholic solution, alcohol or water. What this means for the arrangement of the edge element R.sub.R in the dividing wall W is that there is a route from the surface O.sub.KK on the side S.sub.KK to the surface O.sub.A/MK on the side SA/MK that leads completely through the edge element R.sub.R. [0143] This includes the following embodiments: [0144] a portion of the edge of the surfaces O.sub.KK and O.sub.A/MK is formed by the edge element R.sub.R [0145] the edge of the surfaces O.sub.KK and O.sub.A/MK is formed completely by the edge element R.sub.R (as shown in FIGS. 2 A, 2 B, 6 A, 6 B). [0146] The edge element R.sub.R here may additionally be formed as at least part of the surfaces of those sides of the dividing wall W that are not the sides S.sub.KK and S.sub.A/MK. More particularly, the edge element R.sub.R forms at least 1%, more preferably at least 25%, more preferably at least 50%, even more preferably 100%, of the surface areas of the sides of the dividing wall W that are not the sides S.sub.KK and S.sub.A/MK.

[0147] FIG. 2 A and FIG. 2 B show, for example, embodiments in which the edge element R.sub.R completely forms the surfaces of those sides of the dividing wall W which are not the sides S.sub.KK and S.sub.A/MK.

[0148] The edge element R.sub.R preferably comprises a material selected from the group consisting of plastic, glass, wood. More preferably, the edge element R.sub.R comprises plastic.

[0149] Even more preferably, the plastic is one selected from the group consisting of polypropylene, polystyrene, polyvinylchloride (PVC). PVC also includes post-chlorinated polyvinylchloride (PVC-C).

[0150] In a further preferred embodiment, the edge element R.sub.R and the separating element R.sub.T comprise the same material, and both even more preferably comprise plastic, which is even more preferably selected from polypropylene, polystyrene, polyvinylchloride, PVC-C.

[0151] In a preferred embodiment, at least part of the separating element R.sub.T is formed in one piece with at least part of the frame element R.sub.R. What this means more particularly is that at least part of the separating element R.sub.T merges into the edge element R.sub.R.

[0152] The embodiment of an edge element R.sub.R has the further advantage that it functions as part of the outer wall in the electrolysis cell E. This part of the dividing wall W does not make contact with the solutions in the respective interior I.sub.KK, I.sub.KA or I.sub.KM, and it would therefore be a waste to form this part of the dividing wall W with a solid-state electrolyte ceramic. In addition, the part of the dividing wall W which is clamped between the outer wall or forms part thereof is subjected to forces that the brittle solid-state electrolyte ceramic might not withstand. Instead, a fracture-resistant and cheaper material is thus selected for the frame element R.

4.1.2 Securing Elements B.sub.R and B.sub.T

[0153] The dividing wall W in the first aspect of the invention is characterized in that R.sub.1 and R.sub.2 are secured to one another by at least one securing element B.sub.R at the edge element R.sub.R, and R.sub.1 and R.sub.2 are secured to one another by at least one securing element B.sub.T at the separating element R.sub.T.

[0154] What is meant by at the edge element R.sub.R in this context is in the region of the edge element R.sub.R.

[0155] What is meant by at the separating element R.sub.T in this context is in the region of the separating element R.sub.T.

[0156] Suitable securing elements B.sub.R and B.sub.T are all means familiar to the person skilled in the art for securing the two frame parts R.sub.1 and R.sub.2 to one another.

[0157] These securing elements B.sub.R and B.sub.T are especially selected from hinges, clamps, nails, screws, hooks, preferably from screws, hooks, most preferably hooks.

[0158] The securing elements B.sub.R and B.sub.T may be made from a material familiar to the person skilled in the art.

[0159] They preferably comprise a material selected from the group consisting of plastic, glass, wood. Particular preference is given to plastic.

[0160] Even more preferably, the plastic is one selected from the group consisting of polypropylene, polystyrene, polyvinylchloride, PVC-C.

[0161] Even more preferably, the at least one securing element B.sub.R and the at least one securing element B.sub.T are each in the form of mutually engaging hooks B.sub.H. In the state secured to one another, these hooks especially then span the dividing wall W.

[0162] For this purpose, as B.sub.T, mutually opposing pairs of hooks B.sub.H are advantageously each formed on the mutually facing sides of the two frame parts R.sub.1 and R.sub.2 in the region of the separating element R.sub.T, and these engage with one another, preferably reversibly, on arrangement of the ASCs between the frame parts R.sub.1 and R.sub.2. It will be apparent that, for this embodiment, the edge element R.sub.R must be directly contactable via the surfaces O.sub.KK and O.sub.A/MK.

[0163] For this purpose, as B.sub.R, mutually opposing pairs of hooks B.sub.H are advantageously each formed on the mutually facing sides of the two frame parts R.sub.1 and R.sub.2 in the region of the edge element R.sub.R, and these engage reversibly with one another on arrangement of the ASCs between the frame parts R.sub.1 and R.sub.2.

[0164] Mutually facing sides of the two frame parts R.sub.1 and R.sub.2 relates to the sides of the two frame parts the surface of which is not directly contactable via the surface O.sub.KK in the case of R.sub.1, and the surface of which is not directly contactable via the surface O.sub.A/MK in the case of R.sub.2. These are especially the surfaces R.sub.1 and R.sub.2 that make contact with the ASCs and/or the seal Di in the dividing wall W.

[0165] The securing means B.sub.R and B.sub.T, especially the hooks, are preferably in one-piece form with at least one of the parts R.sub.1 and R.sub.2 (FIG. 3 B).

[0166] In another preferred embodiment, the at least one securing element B.sub.R and the at least one securing element B.sub.T are each in the form of mutually engaging hooks B.sub.H.

[0167] In a preferred embodiment, hooks B.sub.H are formed on both frame parts R.sub.1 and R.sub.2 in the region of the separating element R.sub.T and in the region of the edge element R.sub.R in such a way that they engage when the ASCs are arranged between the frame parts R.sub.1 and R.sub.2 and hence secure the frame parts R.sub.1 and R.sub.2 to one another. Even more preferably, this is reversible, meaning that the hooks B.sub.H can be detached from one another. This can be achieved, for example, in that the hooks are designed so as to be movable with respect to one another.

[0168] The mounting of the securing means B.sub.R and B.sub.T both on the edge element R.sub.R and on the separating element R.sub.T surprisingly improves the stability of the dividing wall W. The use of securing means in the region not just of the edge element R.sub.R but also of the separating element R.sub.T makes it possible to introduce compression forces not just at the outer corners but over the entire area of the frame element R.

4.1.3 Alkali Metal Cation-Conducting Solid-State Electrolyte Ceramic (ASC)

[0169] A useful alkali metal cation-conducting solid-state electrolyte ceramic F.sub.A, F.sub.B etc. encompassed by the dividing wall W is any solid-state electrolyte through which cations, especially alkali metal cations, even more preferably sodium cations, can be transported from the S.sub.A/MK side to the S.sub.KK side. Such solid-state electrolytes are known to the person skilled in the art and are described, for example, in DE 10 2015 013 155 A1, in WO 2012/048032 A2, paragraphs [0035], [0039], [0040], in US 2010/0044242 A1, paragraphs [0040], [0041], in DE 10360758 A1, paragraphs [014] to [025]. They are sold commercially under the NaSICON, LiSICON, KSICON name. A sodium ion-conducting solid-state electrolyte is preferred, and this even more preferably has an NaSICON structure. NaSICON structures usable in accordance with the invention are also described, for example, by N. Anantharamulu, K. Koteswara Rao, G. Rambabu, B. Vijaya Kumar, Velchuri Radha, M. Vithal, J Mater Sci 2011, 46, 2821-2837.

[0170] In a preferred embodiment of the dividing wall W, the alkali metal cation-conducting solid-state ceramics encompassed by the dividing wall W independently have an NaSICON structure of the FORMULA M.sup.I.sub.1+2w+xy+z M.sup.II.sub.w M.sup.III.sub.x ZR.sup.IV.sub.2wxy M.sup.V.sub.Y (SiO.sub.4).sub.z (PO.sub.4).sub.3z. [0171] M.sup.I here is selected from Na.sup.+, Li.sup.+, preferably Na.sup.+. [0172] M.sup.II here is a divalent metal cation, preferably selected from Mg.sup.2+, Ca.sup.2+, Sr.sup.2+, Ba.sup.2+, CO.sup.2+, Ni.sup.2+, more preferably selected from CO.sup.2+Ni.sup.2+. [0173] M.sup.III here is a trivalent metal cation, preferably selected from Al.sup.3+, Ga.sup.3+, Sc.sup.3+, La.sup.3+, Y.sup.3+, Gd.sup.3+, Sm.sup.3+, Lu.sup.3+, Fe.sup.3+, Cr.sup.3+, more preferably selected from Sc.sup.3+, La.sup.3+, Y.sup.3+, Gd.sup.3+, Sm.sup.3+, especially preferably selected from Sc.sup.3+, Y.sup.3+, La.sup.3+. [0174] M.sup.V here is a pentavalent metal cation, preferably selected from V.sup.5+, Nb.sup.5+, Ta.sup.5+.

[0175] The Roman indices I, II, III, IV, V indicate the oxidation numbers in which the respective metal cations exist. [0176] w, x, y, z are real numbers, where 0x<2, 0y<2, 0w<2, 0z<3, [0177] and where w, x, y, z are chosen such that 1+2w+xy+z0 and 2wxy0.

[0178] Even more preferably in accordance with the invention, the NaSICON structure has a structure of the formula Na.sub.(1+v)Zr.sub.2Si.sub.vP.sub.(3v)O.sub.12 where v is a real number for which 0 v3. Most preferably, v=2.4.

[0179] In a preferred embodiment of the dividing wall W according to the first aspect of the invention, the ASCs encompassed by the dividing wall W have the same structure.

4.1.4 Production of the Dividing Wall W

[0180] The dividing wall W can be produced by methods known to the person skilled in the art.

[0181] For example, the ASCs encompassed by the dividing wall W may be inserted into an appropriate casting mould, optionally with seals, and the frame element R may be cast by means of liquid plastic and then left to solidify (injection-moulding method). In the course of solidification, this then surrounds the ASCs. The securing elements B.sub.T and B.sub.R may be provided in one casting by a suitable shape on the frame element R (and are then in one-piece form therewith). In this embodiment, mutually engaging hooks B.sub.H in particular are suitable as securing means.

[0182] Alternatively, the frame element R or the frame parts R.sub.1 and R.sub.2 are cast separately. The securing elements B.sub.T and B.sub.R may be provided in one casting by a suitable shape on the frame element R (and are then in one-piece form therewith). In this embodiment, mutually engaging hooks B.sub.H in particular are suitable as securing means.

[0183] Alternatively, the ASCs, optionally with the seal Di, can be arranged between the frame parts R.sub.1 and R.sub.2, and then the securing elements B.sub.T and B.sub.R can be attached. Suitable examples for this purpose are screws or nails that are driven through suitable cutouts in the frame parts R.sub.1 and R.sub.2 and secure these to one another.

4.2 Electrolysis Cell E

[0184] The dividing wall W in the first aspect of the invention is suitable as a dividing wall in an electrolysis cell E.

[0185] In a second aspect, the present invention therefore relates to an electrolysis cell E comprising [0186] at least one anode chamber K.sub.A having at least one inlet Z.sub.KA, at least one outlet A.sub.KA, and an interior I.sub.KA comprising an anodic electrode E.sub.A, [0187] at least one cathode chamber K.sub.K having at least one inlet Z.sub.KK, at least one outlet A.sub.KK, and an interior I.sub.KK comprising a cathodic electrode E.sub.K, [0188] and optionally at least one interposed middle chamber K.sub.M having at least one inlet Z.sub.KM, at least one outlet A.sub.KM and an interior I.sub.KM, [0189] where I.sub.KA and I.sub.KM are then divided from one another by a diffusion barrier D, and A.sub.KM is connected by a connection V.sub.AM to the inlet Z.sub.KA, such that liquid can be passed from I.sub.KM into I.sub.KA via the connection V.sub.AM,
where [0190] in the cases in which the electrolysis cell E does not comprise a middle chamber K.sub.M, I.sub.KA and I.sub.KK are divided from one another by a dividing wall W according to the first aspect of the invention, [0191] in the cases in which the electrolysis cell E comprises at least one middle chamber K.sub.M, I.sub.KK and I.sub.KM are divided from one another by a dividing wall W according to the first aspect of the invention,
characterized in that
the alkali metal cation-conducting solid-state ceramics encompassed by the dividing wall W, and especially also the separating element R.sub.T, directly contact the interior I.sub.KK on the side S.sub.KK via the surface O.sub.KK,
and [0192] in the cases in which the electrolysis cell E does not comprise a middle chamber K.sub.M, the alkali metal cation-conducting solid-state ceramics encompassed by the dividing wall W, and especially also the frame element R, directly contact the interior I.sub.KA on the side S.sub.A/MK via the surface O.sub.A/MK, [0193] in the cases in which the electrolysis cell E comprise at least one middle chamber K.sub.M, the alkali metal cation-conducting solid-state ceramics encompassed by the dividing wall W, and especially also the frame element R, directly contact the interior I.sub.KM on the side S.sub.A/MK via the surface O.sub.A/MK.

[0194] The electrolysis cell E in the second aspect of the invention comprises at least one anode chamber K.sub.A and at least one cathode chamber K.sub.K, and optionally at least one interposed middle chamber K.sub.M. This also includes electrolysis cells E having more than one anode chamber K.sub.A and/or cathode chamber K.sub.K and/or middle chamber K.sub.M. Such electrolysis cells in which these chambers are joined to one another in the form of modules are described, for example, in DD 258 143 A3 and US 2006/0226022 A1.

[0195] The electrolysis cell E in the second aspect of the invention, in a preferred embodiment, comprises an anode chamber K.sub.A and a cathode chamber K.sub.K, and optionally an interposed middle chamber K.sub.M.

[0196] The electrolysis cell E typically has an outer wall W.sub.A. The outer wall W.sub.A is especially made from a material selected from the group consisting of steel, preferably rubberized steel, plastic, especially from Telene (thermoset polydicyclopentadiene), PVC (polyvinylchloride), PVC-C (post-chlorinated polyvinylchloride), PVDF (polyvinylidenefluoride). W.sub.A may especially be perforated for inlets and outlets. Within W.sub.A are then the at least one anode chamber K.sub.A, the at least one cathode chamber K.sub.K and, In the embodiments in which the electrolysis cell E comprises one, the at least one interposed middle chamber K.sub.M.

4.2.1 Cathode Chamber K.SUB.K

[0197] The cathode chamber K.sub.K has at least one inlet Z.sub.KK, at least one outlet A.sub.KK, and an interior I.sub.KK comprising a cathodic electrode E.sub.K.

[0198] The interior I.sub.KK of the cathode chamber K.sub.K is divided from the interior I.sub.KA of the anode chamber K.sub.A by the dividing wall W in the first aspect of the invention, if the electrolysis cell E does not comprise a middle chamber K.sub.M. The interior I.sub.KK of the cathode chamber K.sub.K is divided from the interior I.sub.KM of the middle chamber K.sub.M by the dividing wall W in the first aspect of the invention, if the electrolysis cell E comprises at least one middle chamber K.sub.M.

4.2.1.1 Cathodic Electrode E.SUB.K

[0199] The cathode chamber K.sub.K comprises an interior I.sub.KK which in turn comprises a cathodic electrode E.sub.K. A useful cathodic electrode E.sub.K of this kind is any electrode familiar to the person skilled in the art that is stable under the conditions of the process according to the invention in the third aspect of the invention. These are described, in particular, in WO 2014/008410 A1, paragraph [025] or DE 10360758 A1, paragraph [030]. This electrode E.sub.K may be selected from the group consisting of mesh wool, three-dimensional matrix structure and balls. The cathodic electrode E.sub.K especially comprises a material selected from the group consisting of steel, nickel, copper, platinum, platinized metals, palladium, carbon-supported palladium, titanium. Preferably, E.sub.K comprises nickel.

[0200] In the embodiments of the electrolysis cell E according to the second aspect of the invention in which it comprises a middle chamber K.sub.M, this is between the anode chamber K.sub.A and the cathode chamber K.sub.K.

4.2.1.2 Inlet Z.sub.KK and Outlet A.sub.KK The cathode chamber K.sub.K also encompasses an inlet Z.sub.KK and an outlet A.sub.KK. This enables addition of liquid, for example the solution L.sub.2, to the interior I.sub.KK of the cathode chamber K.sub.K, and removal of liquid present therein, for example the solution L.sub.1. The inlet Z.sub.KK and the outlet A.sub.KK are attached here to the cathode chamber K.sub.K in such a way that the liquid comes into contact with the cathodic electrode E.sub.K as it flows through the interior I.sub.KK of the cathode chamber K.sub.K. This is the prerequisite for the solution L.sub.1 to be obtained at the outlet A.sub.KK in the performance of the process according to the invention in the third aspect of the invention when the solution L.sub.2 of an alkali metal alkoxide XOR in the alcohol ROH is routed through the interior I.sub.KK of the cathode chamber K.sub.K.

[0201] The inlet Z.sub.KK and the outlet A.sub.KK may be attached to the electrolysis cell E by methods known to the person skilled in the art, for example by means of holes in the outer wall and corresponding connections (valves) that simplify the introduction and discharge of liquid.

4.2.2 Anode Chamber K.SUB.A

[0202] The anode chamber K.sub.A has at least one inlet Z.sub.KA, at least one outlet A.sub.KA, and an interior I.sub.KA comprising an anodic electrode E.sub.A.

[0203] The interior I.sub.KA of the anode chamber K.sub.A, if the electrolysis cell E comprises a middle chamber K.sub.M, is divided from the interior I.sub.KM of the middle chamber K.sub.M by a diffusion barrier D.

[0204] If electrolysis cell E does not comprise a middle chamber K.sub.M, the interior I.sub.KA of the anode chamber K is divided from the interior I.sub.KK of the cathode chamber K.sub.K by the dividing wall W.

4.2.2.1 Anodic Electrode E.SUB.A

[0205] The anode chamber K.sub.A comprises an interior I.sub.KA which in turn comprises an anodic electrode E.sub.A. A useful anodic electrode E.sub.A of this kind is any electrode familiar to the person skilled in the art that is stable under the conditions of the process according to the invention in the third aspect of the invention. These are described, in particular, in WO 2014/008410 A1, paragraph [024] or DE 10360758 A1, paragraph [031]. This electrode E.sub.A may consist of one layer or consist of multiple planar layers parallel to one another that may each be perforated or expanded. The anodic electrode E.sub.A especially comprises a material selected from the group consisting of ruthenium oxide, iridium oxide, nickel, cobalt, nickel tungstate, nickel titanate, precious metals such as, in particular, platinum, supported on a support such as titanium or Kovar (an iron/nickel/cobalt alloy in which the individual components are preferably as follows: 54% by mass of iron, 29% by mass of nickel, 17% by mass of cobalt). Further possible anode materials are especially stainless steel, lead, graphite, tungsten carbide, titanium diboride. Preferably, the anodic electrode E.sub.A comprises a titanium anode coated with ruthenium oxide/iridium oxide (RuO.sub.2+IrO.sub.2/Ti).

4.2.2.2 Inlet Z.sub.KA and Outlet A.sub.KA

[0206] The anode chamber K.sub.K also encompasses an inlet Z.sub.KA and an outlet A.sub.KA. This enables addition of liquid, for example the solution L.sub.3, to the interior I.sub.KA of the cathode chamber K.sub.A, and removal of liquid present therein, for example the solution L.sub.4. The inlet Z.sub.KA and the outlet A.sub.KA are attached here to the anode chamber K.sub.A in such a way that the liquid comes into contact with the anodic electrode E.sub.A as it flows through the interior I.sub.KA of the anode chamber K.sub.A. This is a prerequisite for the solution L.sub.4 to be obtained at the outlet A.sub.KA in the performance of the process according to the invention in the third aspect of the invention when the solution L.sub.3 of a salt S is routed through the interior I.sub.KA of the cathode chamber K.sub.A.

[0207] The inlet Z.sub.KA and the outlet A.sub.KA may be attached to the electrolysis cell E by methods known to the person skilled in the art, for example by means of holes in the outer wall and corresponding connections (valves) that simplify the introduction and discharge of liquid. The inlet Z.sub.KA, in particular embodiments in which the electrolysis cell E comprises a middle chamber K.sub.M, may also be within the electrolysis cell, for example in the form of a perforation in the diffusion barrier D.

4.2.3 Optional Middle Chamber K.SUB.M

[0208] The electrolysis cell E in the second aspect of the invention preferably has a middle chamber K.sub.M. The optional middle chamber K.sub.M lies between cathode chamber and K.sub.K anode chamber K.sub.A. It comprises at least one inlet Z.sub.KM, at least one outlet A.sub.KM and an interior I.sub.KM.

[0209] The interior I.sub.KA of the anode chamber K.sub.A, if the electrolysis cell E comprises a middle chamber K.sub.M, is divided from the interior I.sub.KM of the middle chamber K.sub.M by a diffusion barrier D. A.sub.KM is then also connected to the inlet Z.sub.KA by a connection V.sub.AM, such that liquid can be guided from I.sub.KM into I.sub.KA through the connection V.sub.AM.

4.2.3.1 Diffusion Barrier D

[0210] The interior I.sub.KM of the optional middle chamber K.sub.M is divided from the interior I.sub.KA of the anode chamber K.sub.A by a diffusion barrier D and divided from the interior I.sub.KK of the cathode chamber K.sub.K by the dividing wall W.

[0211] The material used for the diffusion barrier D may be any which is stable under the conditions of the process according to the invention in the third aspect of the invention and prevents or slows the transfer of protons from the liquid present in the interior I.sub.KA of the anode chamber K.sub.A to the interior I.sub.KM of the optional middle chamber K.sub.M.

[0212] The diffusion barrier D used is especially a non-ion-specific dividing wall or a membrane permeable to specific ions. The diffusion barrier D is preferably a non-ion-specific dividing wall.

[0213] The material of the non-ion-specific dividing wall is especially selected from the group consisting of fabric, which is especially textile fabric or metal weave, glass, which is especially sintered glass or glass frits, ceramic, especially ceramic frits, membrane diaphragms, and is more preferably a textile fabric or metal weave, especially preferably a textile fabric. The textile fabric preferably comprises plastic, more preferably a plastic selected from PVC, PVC-C, polyvinylether (PVE), polytetrafluoroethylene (PTFE).

[0214] If the diffusion barrier D is a membrane permeable to specific ions, what this means in accordance with the invention is that the respective membrane promotes the diffusion of particular ions therethrough over other ions. More particularly, what this means is membranes that promote the diffusion therethrough of ions of a particular charge type over ions of the opposite charge. Even more preferably, membranes permeable to specific ions also promote the diffusion of particular ions of one charge type over other ions of the same charge type therethrough.

[0215] If the diffusion barrier D is a membrane permeable to specific ions, the diffusion barrier D is especially an anion-conducting membrane or a cation-conducting membrane.

[0216] According to the invention, anion-conducting membranes are those that selectively conduct anions, preferably selectively conduct particular anions. In other words, they promote the diffusion of anions therethrough over that of cations, especially over protons; even more preferably, they additionally promote the diffusion of particular anions therethrough over the diffusion of other anions therethrough.

[0217] According to the invention, cation-conducting membranes are those that selectively conduct cations, preferably selectively conduct particular cations. In other words, they promote the diffusion of cations therethrough over that of anions; even more preferably, they additionally promote the diffusion of particular cations therethrough over the diffusion of other cations therethrough, more preferably still that of cations that are not protons, more preferably sodium cations, over protons.

[0218] What is meant more particularly by promote the diffusion of particular ions X over the diffusion of other ions Y is that the coefficient of diffusion (unit: m.sup.2/s) of ion type X at a given temperature for the membrane in question is higher by a factor of 10, preferably 100, preferably 1000, than the coefficient of diffusion of ion type Y for the membrane in question.

[0219] If the diffusion barrier D is a membrane permeable to specific ions, it is preferably an anion-conducting membrane since this particularly efficiently prevents the diffusion of protons from the anode chamber K.sub.A into the middle chamber K.sub.M.

[0220] The anion-conducting membrane used is especially one selective for the anions encompassed by the salt S. Such membranes are known to and can be used by the person skilled in the art.

[0221] The salt S is preferably a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X, even more preferably a halide.

[0222] Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.

[0223] The anion-conducting membrane used is preferably one selective for halides, preferably chloride.

[0224] Anion-conducting membranes are described, for example, by M. A. Hickner, A. M. Herring, E. B. Coughlin, Journal of Polymer Science, Part B: Polymer Physics 2013, 51, 1727-1735, by C. G. Arges, V. Ramani, P. N. Pintauro, Electrochemical Society Interface 2010, 19, 31-35, in WO 2007/048712 A2, and on page 181 of the textbook by Volkmar M. Schmidt, Elektrochemische Verfahrenstechnik: Grundlagen, Reaktionstechnik, Prozessoptimierung [Electrochemical Engineering: Fundamentals, Reaction Technology, Process Optimization], 1st edition (8 Oct. 2003).

[0225] Even more preferably, anion-conducting membranes used are accordingly organic polymers that are especially selected from polyethylene, polybenzimidazoles, polyether ketones, polystyrene, polypropylene and fluorinated membranes such as polyperfluoroethylene, preferably polystyrene, where these have covalently bonded functional groups selected from NH.sub.3.sup.+, NRH.sub.2.sup.+, NR.sub.3.sup.+, NR.sup.+; PR.sub.3.sup.+, where R is alkyl groups having preferably 1 to 20 carbon atoms, or other cationic groups. They preferably have covalently bonded functional groups selected from NH.sub.3.sup.+, NRH.sub.2.sup.+ and NR.sub.3.sup.+, more preferably selected from NH.sub.3.sup.+ and NR.sub.3.sup.+, even more preferably NR.sub.3.sup.+.

[0226] If the diffusion barrier D is a cation-conducting membrane, it is especially a membrane selective for the cations encompassed by the salt S. Even more preferably, the diffusion barrier D is an alkali metal cation-conducting membrane, even more preferably a potassium and/or sodium ion-conducting membrane, most preferably a sodium ion-conducting membrane.

[0227] Cation-conducting membranes are described, for example, on page 181 of the textbook by Volkmar M. Schmidt, Elektrochemische Verfahrenstechnik: Grundlagen, Reaktionstechnik, Prozessoptimierung, 1st edition (8 Oct. 2003).

[0228] Even more preferably, cation-conducting membranes used are accordingly organic polymers that are especially selected from polyethylene, polybenzimidazoles, polyether ketones, polystyrene, polypropylene and fluorinated membranes such as polyperfluoroethylene, preferably polystyrene and polyperfluoroethylene, where these bear covalently bonded functional groups selected from SO.sub.3.sup., COO.sup., PO.sub.3.sup.2 and PO.sub.2H.sup., preferably SO.sub.3.sup. (described in DE 10 2010 062 804 A1, U.S. Pat. No. 4,831,146).

[0229] This may be, for example, a sulfonated polyperfluoroethylene (Nafion with CAS number: 31175-20-9). These are known to the person skilled in the art, for example from WO 2008/076327 A1, paragraph [058], US 2010/0044242 A1, paragraph [0042] or US 2016/0204459 A1, and are commercially available under the Nafion, Aciplex F, Flemion, Neosepta, Ultrex, PCSK trade names. Neosepta membranes are described, for example, by S. A. Mareev, D. Yu. Butylskii, N. D. Pismenskaya, C. Larchet, L. Dammak, V. V. Nikonenko, Journal of Membrane Science 2018, 563, 768-776.

[0230] If a cation-conducting membrane is used as diffusion barrier D, this may, for example, be a polymer functionalized with sulfonic acid groups, especially of the formula P.sub.NAFION below, where n and m may independently be a whole number from 1 to 10.sup.6, preferably a whole number from 10 to 105, more preferably a whole number from 10.sup.2 to 10.sup.4.

##STR00001##

4.2.3.2 Inlet Z.sub.KM and Outlet A.sub.KM

[0231] The optional middle chamber K.sub.M also encompasses an inlet Z.sub.KM and an outlet A.sub.KM. This enables addition of liquid, for example the solution L.sub.3, to the interior I.sub.KM of the middle chamber K.sub.M, and transfer of liquid present therein, for example the solution L.sub.3, to the anode chamber K.sub.A.

[0232] The inlet Z.sub.KM and the outlet A.sub.KM may be attached to the electrolysis cell E by methods known to the person skilled in the art, for example by means of holes in the outer wall and corresponding connections (valves) that simplify the introduction and discharge of liquid. The outlet A.sub.KM may also be within the electrolysis cell, for example in the form of a perforation in the diffusion barrier D.

4.2.3.3 Connection V.SUB.AM

[0233] In the electrolysis cell E according to the second aspect of the invention, the outlet A.sub.KM is connected to the inlet Z.sub.KA by a connection V.sub.AM in such a way that liquid can be guided from I.sub.KM into I.sub.KA through the connection V.sub.AM.

[0234] The connection V.sub.AM may be formed within the electrolysis cell E and/or outside the electrolysis cell E, and is preferably formed within the electrolysis cell.

[0235] 1) If the connection V.sub.AM is formed within the electrolysis cell E, it is preferably formed by at least one perforation in the diffusion barrier D. This embodiment is preferred especially when the diffusion barrier D used is a non-ion-specific dividing wall, especially a metal weave or textile fabric. This functions as a diffusion barrier D and, on account of the weave properties, has perforations and gaps from the outset that function as connection V.sub.AM.

[0236] 2) The embodiment described hereinafter is preferred especially when the diffusion barrier D used is a membrane permeable to specific ions: In this embodiment, the connection V.sub.AM is formed outside the electrolysis cell E, preferably formed by a connection of A.sub.KM and Z.sub.KA that runs outside the electrolysis cell E, especially in that an outlet A.sub.KM through the outer wall W.sub.A is formed from the interior of the middle chamber I.sub.KM, preferably at the base of the middle chamber K.sub.M, the inlet Z.sub.KM more preferably being at the top end of the middle chamber K.sub.M, and an inlet Z.sub.KA through the outer wall W.sub.A is formed in the interior I.sub.KA of the anode chamber K.sub.A, preferably at the base of the anode chamber K.sub.A, and these are connected by a conduit, for example a pipe or a hose, preferably comprising a material selected from rubber and plastic. The outlet A.sub.KA is then more preferably at the top end of the anode chamber K.sub.A.

[0237] Outlet A.sub.KM at the base of the middle chamber K.sub.M means that the outlet A.sub.KM is attached to the electrolysis cell E in such a way that the solution L.sub.3 leaves the middle chamber K.sub.M in the direction of gravity.

[0238] Inlet Z.sub.KA at the base of the anode chamber K.sub.A means that the inlet Z.sub.KA is attached to the electrolysis cell E in such a way that the solution L.sub.3 enters the anode chamber K.sub.A counter to gravity.

[0239] Inlet Z.sub.KM at the top end of the middle chamber K.sub.M means that the inlet Z.sub.KM is attached to the electrolysis cell E in such a way that the solution L.sub.3 enters the middle chamber K.sub.M in the direction of gravity.

[0240] Outlet A.sub.KA at the top end of the anode chamber K.sub.A means that the outlet A.sub.KA is mounted on the electrolysis cell E in such a way that the solution L.sub.4 leaves the anode chamber K.sub.A counter to gravity.

[0241] This embodiment is particularly advantageous and therefore preferred when the outlet A.sub.KM is formed by the outer wall W.sub.A at the base of the middle chamber K.sub.M, and the inlet Z.sub.KA by the outer wall W.sub.A at the base of the anode chamber K.sub.A. This arrangement makes it possible in a particularly simple manner to remove gases formed in the anode chamber K.sub.A from the anode chamber K.sub.A with L.sub.4, in order to separate them further.

[0242] When the connection V.sub.AM is formed outside the electrolysis cell E, Z.sub.KM and A.sub.KM are especially arranged at opposite ends of the outer wall W.sub.A of the middle chamber K.sub.M (i.e., for example, Z.sub.KM at the base and A.sub.KM at the top end of the electrolysis cell E or vice versa) and Z.sub.KA and A.sub.KA are arranged at opposite ends of the outer wall W.sub.A of the anode chamber K.sub.A (i.e. Z.sub.KA at the base and A.sub.KA at the top end of the electrolysis cell E or vice versa), as shown more particularly in FIG. 5 A. By virtue of this geometry, L.sub.3 must flow through the two chambers K.sub.M and K.sub.A. It is possible here for Z.sub.KA and Z.sub.KM to be formed on the same side of the electrolysis cell E, in which case A.sub.KM and A.sub.KA are automatically also formed on the same side of the electrolysis cell E. Alternatively, Z.sub.KA and Z.sub.KM may be formed on opposite sides of the electrolysis cell E, in which case A.sub.KM and A.sub.KA are then automatically also formed on opposite sides of the electrolysis cell E.

[0243] 3) When the connection V.sub.AM is formed within the electrolysis cell E, this may especially be ensured in that one side (side A) of the electrolysis cell E, which is the top end or the base of the electrolysis cell E, preferably the top end as shown in FIG. 5 B, comprises the inlet Z.sub.KM and the outlet A.sub.KA, and the diffusion barrier D extends proceeding from this side (side A) into the electrolysis cell E, but does not quite reach up to the side (side B) of the electrolysis cell E opposite side A, which is then the base or the top end of the electrolysis cell E, and at the same time covers 50% or more of the height of the three-chamber cell E, preferably 60% to 99% of the height of the three-chamber cell E, more preferably 70% to 95% of the height of the three-chamber cell E, even more preferably 80% to 90% of the height of the three-chamber cell E, more preferably still 85% of the height of the three-chamber cell E. Because the diffusion barrier D does not touch side B of the three-chamber cell E, a gap thus arises between diffusion barrier D and the outer wall W.sub.A of side B of the three-chamber cell E. In that case, the gap is the connection V.sub.AM. By virtue of this geometry, L.sub.3 must flow completely through the two chambers K.sub.M and K.sub.A.

[0244] These embodiments best ensure that the aqueous salt solution L.sub.3 flows past the acid-sensitive solid-state electrolyte before it comes into contact with the anodic electrode E.sub.A, which results in the formation of acids.

[0245] According to the invention, base of the electrolysis cell E is the side of the electrolysis cell E through which a solution (e.g. LU in the case of A.sub.KM in FIG. 5 A) exits from the electrolysis cell E in the same direction as gravity, or the side of the electrolysis cell E through which a solution (e.g. L.sub.2 in the case of Z.sub.KK in FIGS. 5 A and 5 B and L.sub.3 in the case of A.sub.KA in FIGS. 4 A and 4 B) is supplied to the electrolysis cell E counter to gravity.

[0246] According to the invention, top end of the electrolysis cell E is the side of the electrolysis cell E through which a solution (e.g. L.sub.4 in the case of A.sub.KA and L.sub.1 in the case of A.sub.KK in FIGS. 5 A and 5 B) exits from the electrolysis cell E counter to gravity, or the side of the electrolysis cell E through which a solution (e.g. L in the case of Z.sub.KM in FIGS. 5 A and 5 B) is supplied to the electrolysis cell E in the same direction as gravity.

4.2.4 Arrangement of the Dividing Wall W in the Electrolysis Cell E

[0247] The dividing wall W is arranged in the electrolysis cell E in such a way that the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R, directly contact the interior I.sub.KK on the side S.sub.KK via the surface O.sub.KK.

[0248] This means that the dividing wall W is arranged within the electrolysis cell E such that, when the interior I.sub.KK on the side S.sub.KK side is completely filled with solution L.sub.4, the solution L.sub.4, via the surface O.sub.KK, then makes contact with all alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R via part R.sub.1, such that ions (e.g. alkali metal ions such as sodium, lithium) from all ASCs encompassed by the dividing wall W can enter the solution L.sub.4.

[0249] In addition, the dividing wall W, in the embodiments in which the electrolysis cell E does not comprise a middle chamber K.sub.M, is arranged in the electrolysis cell E such that the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R, make direct contact with the interior I.sub.KA on the side S.sub.A/MK via the surface O.sub.A/MK.

[0250] What this means is as follows: in the embodiments in which the electrolysis cell E does not comprise a middle chamber K.sub.M, the dividing wall W adjoins the interior I.sub.KA of the anode chamber K.sub.A. In these embodiments, the dividing wall W is arranged within the electrolysis cell E such that, when the interior I.sub.KA on the side S.sub.AM/K is completely filled with solution L.sub.3, the solution L.sub.3, via the surface O.sub.A/MK, then makes contact with all alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R via part R.sub.2, such that ions (e.g. alkali metal ions such as sodium, lithium) from the solution L.sub.3 can enter any ASC encompassed by the dividing wall W.

[0251] In addition, the dividing wall W, in the cases in which the electrolysis cell E comprises at least one middle chamber K.sub.M, is arranged in the electrolysis cell E such that the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and especially also the frame element R, make direct contact with the interior I.sub.KM on the side S.sub.A/MK via the surface O.sub.A/MK.

[0252] What this means is as follows: in the embodiments in which the electrolysis cell E comprises at least one middle chamber K.sub.M, the dividing wall W adjoins the interior I.sub.KM of the middle chamber K.sub.M. In these embodiments, the dividing wall W is arranged within the electrolysis cell E such that, when the interior I.sub.KM on the side S.sub.AM/K is completely filled with solution L.sub.3, the solution L.sub.3, via the surface O.sub.A/MK, then makes contact with all alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R via part R.sub.2, such that ions (e.g. alkali metal ions such as sodium, lithium) from the solution L.sub.3 can enter any ASC encompassed by the dividing wall W.

[0253] In a preferred embodiment of the electrolysis cell E in the second aspect of the invention, at least 50%, especially at least 70%, preferably at least 90%, most preferably 100%, of the portion of the surface O.sub.KK which is formed by ASCs makes contact with the interior I.sub.KK.

[0254] In a preferred embodiment of the electrolysis cell E without a middle chamber in the second aspect of the invention, at least 50%, especially at least 70%, preferably at least 90%, most preferably 100%, of the portion of the surface O.sub.A/MK which is formed by ASCs makes contact with the interior I.sub.KA.

[0255] In a preferred embodiment of the electrolysis cell E with at least one middle chamber in the second aspect of the invention, at least 50%, especially at least 70%, preferably at least 90%, most preferably 100%, of the portion of the surface O.sub.A/MK which is formed by ASCs makes contact with the interior I.sub.KM.

4.3 Process According to the Invention

[0256] The present invention relates, in a third aspect, to a process for producing a solution L.sub.1 of an alkali metal alkoxide XOR in the alcohol ROH, where X is an alkali metal cation and R is an alkyl radical having 1 to 4 carbon atoms. The process according to the third aspect of the invention is conducted in an electrolysis cell E in the second aspect of the invention.

[0257] X is preferably selected from the group consisting of Li.sup.+, K.sup.+, Na.sup.+, more preferably from the group consisting of K.sup.+, Na.sup.+. Most preferably, X=Na.sup.+.

[0258] R is preferably selected from the group consisting of n-propyl, iso-propyl, ethyl and methyl, more preferably from the group consisting of ethyl and methyl. R is most preferably methyl. 4.3.1 Process according to the invention in an electrolysis cell E without a middle chamber K.sub.MIn the cases in which the electrolysis cell E does not comprise a middle chamber K.sub.M, the steps (1), (2), (3) that proceed simultaneously are conducted.

4.3.1.1 Step (1)

[0259] In step (1), a solution L.sub.2 comprising the alcohol ROH, preferably comprising an alkali metal alkoxide XOR and alcohol ROH, is routed through K.sub.K.

[0260] Solution L.sub.2 is preferably free of water. What is meant in accordance with the invention by free of water is that the weight of water in solution L.sub.2 based on the weight of the alcohol ROH in solution L.sub.2 (mass ratio) is 1:10, more preferably 1:20, even more preferably 1:100, even more preferably 0.5:100.

[0261] If solution L.sub.2 comprises XOR, the proportion by mass of XOR in solution L.sub.2, based on the overall solution L.sub.2, is especially >0% to 30% by weight, preferably 5% to 20% by weight, more preferably 10% to 20% by weight, more preferably 10% to 15% by weight, most preferably 13% to 14% by weight, at the very most preferably 13% by weight.

[0262] If solution L.sub.2 comprises XOR, the mass ratio of XOR to alcohol ROH in solution L.sub.2 is especially in the range of 1:100 to 1:5, more preferably in the range of 1:25 to 3:20, even more preferably in the range of 1:12 to 1:8, even more preferably 1:10.

4.3.1.2 Step (2)

[0263] In step (2), a neutral or alkaline, aqueous solution L.sub.3 of a salt S comprising X as cation is routed through K.sub.A.

[0264] The salt S is preferably a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X, even more preferably a halide.

[0265] Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.

[0266] The pH of the aqueous solution L.sub.3 is >7.0, preferably in the range of 7 to 12, more preferably in the range of 8 to 11, even more preferably 10 to 11, most preferably 10.5.

[0267] The proportion by mass of salt S in solution L.sub.3 is preferably in the range of >0% to 20% by weight, preferably 1% to 20% by weight, more preferably 5% to 20% by weight, even more preferably 10% to 20% by weight, most preferably 20% by weight, based on the overall solution L.sub.3.

4.3.1.3 Step (3)

[0268] In step (3), a voltage is then applied between E.sub.A and E.sub.K.

[0269] This results in transfer of current from the charge source to the anode, transfer of charge via ions to the cathode and ultimately transfer of current back to the charge source. The charge source is known to the person skilled in the art and is typically a rectifier that converts alternating current to direct current and can generate particular voltages via voltage transformers.

[0270] This in turn has the following consequences: [0271] the solution L.sub.1 is obtained at the outlet A.sub.KK with a higher concentration of XOR in L.sub.1 than in L.sub.2, [0272] an aqueous solution L.sub.4 of S is obtained at the outlet A.sub.KA, with a lower concentration of S in L.sub.4 than in L.sub.3.

[0273] In step (3) of the process according to the third aspect the invention, in particular, such a voltage is applied that such a current flows such that the current density (=ratio of the current supplied to the electrolysis cell to the area of the solid-state electrolyte in contact with the anolyte present in the anode chamber K.sub.A) is in the range from 10 to 8000 Nm.sup.2, more preferably in the range from 100 to 2000 Nm.sup.2, even more preferably in the range from 300 to 800 Nm.sup.2, and even more preferably is 494 Nm.sup.2. This can be determined in a standard manner by the person skilled in the art. The area of the solid-state electrolyte in contact with the anolyte present in the anode chamber K.sub.A is especially 0.00001 to 10 m.sup.2, preferably 0.0001 to 2.5 m.sup.2, more preferably 0.0002 to 0.15 m.sup.2, even more preferably 2.83 cm.sup.2.

[0274] It will be apparent that step (3) of the process according to the third aspect of the invention is conducted when the chamber K.sub.A is at least partly laden with L.sub.3 and K.sub.K is at least partly laden with L.sub.2, such that both L.sub.3 and L.sub.2 come into contact with the ASCs encompassed by the dividing wall W and especially also come into contact with the frame element R.

[0275] The fact that transfer of charge takes place between E.sub.A and E.sub.K in step (3) implies that K.sub.K and K.sub.A are simultaneously laden with L.sub.2 and L.sub.3 respectively, such that they cover the electrodes E.sub.A and E.sub.K to such an extent that the circuit is complete.

[0276] This is the case especially when a liquid stream of L.sub.3 is routed continuously through K.sub.A and a liquid stream of L.sub.2 through K.sub.K, and the liquid stream of L.sub.3 covers electrode E.sub.A and the liquid stream of L.sub.2 covers electrode E.sub.K at least partly, preferably completely.

[0277] In a further preferred embodiment, the process according to the third aspect of the invention is performed continuously, i.e. step (1) and step (2) are performed continuously, while applying voltage as per step (3).

[0278] After performance of step (3), solution L.sub.1 is obtained at the outlet A.sub.KK, wherein the concentration of XOR in L.sub.1 is higher than in L.sub.2. If L.sub.2 already comprised XOR, the concentration of XOR in L.sub.1 is preferably 1.01 to 2.2 times, more preferably 1.04 to 1.8 times, even more preferably 1.077 to 1.4 times, even more preferably 1.077 to 1.08 times, higher than in L.sub.2, most preferably 1.077 times higher than in L.sub.2, where the proportion by mass of XOR in L.sub.1 and in L.sub.2 is more preferably in the range from 10% to 20% by weight, even more preferably 13% to 14% by weight.

[0279] An aqueous solution L.sub.4 of S is obtained at the outlet A.sub.KA, with a lower concentration of S in L.sub.4 than in L.sub.3.

[0280] The concentration of the cation X in the aqueous solution L.sub.3 is preferably in the range of 3.5 to 5 mol/l, more preferably 4 mol/l. The concentration of the cation X in the aqueous solution L.sub.4 is more preferably 0.5 mol/l lower than that of the aqueous solution L.sub.3 used in each case.

[0281] More particularly, steps (1) to (3) of the process according to the third aspect of the invention are conducted at a temperature of 20 C. to 70 C., preferably 35 C. to 65 C., more preferably 35 C. to 60 C., even more preferably 35 C. to 50 C., and that a pressure of 0.5 bar to 1.5 bar, preferably 0.9 bar to 1.1 bar, more preferably 1.0 bar.

[0282] In the course of performance of steps (1) to (3) according to the third aspect of the process according to the invention, hydrogen is typically formed in the cathode chamber K.sub.K, which can be removed from the cell together with solution L.sub.1 via outlet A.sub.KK. The mixture of hydrogen and solution L.sub.1 can then, in a particular embodiment of the present invention, be separated by methods known to the person skilled in the art. When the alkali metal compound used is a halide, especially chloride, it is possible for chlorine or another halogen gas to form in the anode chamber K.sub.A, and this can be removed from the cell together with solution L.sub.4 via outlet A.sub.KK. In addition, it is also possible for oxygen or/and carbon dioxide to form, which can likewise be removed. The mixture of chlorine, oxygen and/or CO.sub.2 and solution L.sub.4 can then, in a particular embodiment of the present invention, be separated by methods known to the person skilled in the art. It is then likewise possible, after the chlorine, oxygen and/or CO.sub.2 gases have been separated from solution L.sub.4, to separate these by methods known to the person skilled in the art.

4.3.2 Process According to the Invention in an Electrolysis Cell E with a Middle Chamber K.sub.M

[0283] In the cases in which the electrolysis cell E comprises at least one middle chamber K.sub.M, the steps (1), (2), (3) that proceed simultaneously are conducted.

[0284] It is preferable that the electrolysis cell E comprises at least one middle chamber K.sub.M, and then the steps (1), (2), (3) that proceed simultaneously are conducted.

4.3.2.1 Step (1)

[0285] In step (1), a solution L.sub.2 comprising the alcohol ROH, preferably comprising an alkali metal alkoxide XOR and alcohol ROH, is routed through K.sub.K.

[0286] Solution L.sub.2 is preferably free of water. What is meant in accordance with the invention by free of water is that the weight of water in solution L.sub.2 based on the weight of the alcohol ROH in solution L.sub.2 (mass ratio) is 1:10, more preferably 1:20, even more preferably 1:100, even more preferably 0.5:100.

[0287] If solution L.sub.2 comprises XOR, the proportion by mass of XOR in solution L.sub.2, based on the overall solution L.sub.2, is especially >0% to 30% by weight, preferably 5% to 20% by weight, more preferably 10% to 20% by weight, more preferably 10% to 15% by weight, most preferably 13% to 14% by weight, at the very most preferably 13% by weight.

[0288] If solution L.sub.2 comprises XOR, the mass ratio of XOR to alcohol ROH in solution L.sub.2 is especially in the range of 1:100 to 1:5, more preferably in the range of 1:25 to 3:20, even more preferably in the range of 1:12 to 1:8, even more preferably 1:10.

4.3.2.2 Step (2)

[0289] In step (2), a neutral or alkaline aqueous solution L.sub.3 of a salt S comprising X as cation is routed through K.sub.M, then via V.sub.AM, then through K.sub.A.

[0290] The salt S is preferably a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X, even more preferably a halide.

[0291] Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.

[0292] The pH of the aqueous solution L.sub.3 is >7.0, preferably in the range of 7 to 12, more preferably in the range of 8 to 11, even more preferably 10 to 11, most preferably 10.5.

[0293] The proportion by mass of salt S in solution L.sub.3 is preferably in the range of >0% to 20% by weight, preferably 1% to 20% by weight, more preferably 5% to 20% by weight, even more preferably 10% to 20% by weight, most preferably 20% by weight, based on the overall solution L.sub.3.

4.3.2.3 Step (3)

[0294] In step (3), a voltage is then applied between E.sub.A and E.sub.K.

[0295] This results in transfer of current from the charge source to the anode, transfer of charge via ions to the cathode and ultimately transfer of current back to the charge source. The charge source is known to the person skilled in the art and is typically a rectifier that converts alternating current to direct current and can generate particular voltages via voltage transformers.

[0296] This in turn has the following consequences: [0297] the solution L.sub.1 is obtained at the outlet A.sub.KK with a higher concentration of XOR in L.sub.1 than in L.sub.2, [0298] an aqueous solution L.sub.4 of S is obtained at the outlet A.sub.KA, with a lower concentration of S in L.sub.4 than in L.sub.3.

[0299] In step (3) of the process according to the third aspect the invention, in particular, such a voltage is applied that such a current flows such that the current density (=ratio of the current supplied to the electrolysis cell to the area of the solid-state electrolyte in contact with the anolyte present in the middle chamber K.sub.M) is in the range from 10 to 8000 Nm.sup.2, more preferably in the range from 100 to 2000 Nm.sup.2, even more preferably in the range from 300 to 800 Nm.sup.2, and even more preferably is 494 Nm.sup.2. This can be determined in a standard manner by the person skilled in the art. The area of the solid-state electrolyte in contact with the anolyte present in the middle chamber K.sub.M is especially 0.00001 to 10 m.sup.2, preferably 0.0001 to 2.5 m.sup.2, more preferably 0.0002 to 0.15 m.sup.2, even more preferably 2.83 cm.sup.2.

[0300] It will be apparent that step (3) of the process according to the third aspect of the invention is conducted when the two chambers K.sub.M and K.sub.A are at least partly laden with L.sub.3, and K.sub.K is at least partly laden with L.sub.2, such that both L.sub.3 and L.sub.2 come into contact with the solid-state electrolytes encompassed by the dividing wall W and especially also come into contact with the frame element R.

[0301] The fact that transfer of charge takes place between E.sub.A and E.sub.K in step (3) implies that K.sub.K, K.sub.M and K.sub.A are simultaneously laden with L.sub.2 and L.sub.3 such that they cover the electrodes E.sub.A and E.sub.K to such an extent that the circuit is complete.

[0302] This is the case especially when a liquid stream of L.sub.3 is routed continuously through K.sub.M, V.sub.AM and K.sub.A and a liquid stream of L.sub.2 through K.sub.K, and the liquid stream of L.sub.3 covers electrode E.sub.A and the liquid stream of L.sub.2 covers electrode E.sub.K at least partly, preferably completely.

[0303] In a further preferred embodiment, the process according to the third aspect of the invention is performed continuously, i.e. step (1) and step (2) are performed continuously, while applying voltage as per step (3).

[0304] After performance of step (3), solution L.sub.1 is obtained at the outlet A.sub.KK, wherein the concentration of XOR in L.sub.1 is higher than in L.sub.2. If L.sub.2 already comprised XOR, the concentration of XOR in L.sub.1 is preferably 1.01 to 2.2 times, more preferably 1.04 to 1.8 times, even more preferably 1.077 to 1.4 times, even more preferably 1.077 to 1.08 times, higher than in L.sub.2, most preferably 1.077 times higher than in L.sub.2, where the proportion by mass of XOR in L.sub.1 and in L.sub.2 is more preferably in the range from 10% to 20% by weight, even more preferably 13% to 14% by weight.

[0305] An aqueous solution L.sub.4 of S is obtained at the outlet A.sub.KA, with a lower concentration of S in L.sub.4 than in L.sub.3.

[0306] The concentration of the cation X in the aqueous solution L.sub.3 is preferably in the range of 3.5 to 5 mol/l, more preferably 4 mol/l. The concentration of the cation X in the aqueous solution L.sub.4 is more preferably 0.5 mol/l lower than that of the aqueous solution L.sub.3 used in each case.

[0307] More particularly, steps (1) to (3) of the process according to the third aspect of the invention are conducted at a temperature of 20 C. to 70 C., preferably 35 C. to 65 C., more preferably 35 C. to 60 C., even more preferably 35 C. to 50 C., and at a pressure of 0.5 bar to 1.5 bar, preferably 0.9 bar to 1.1 bar, more preferably 1.0 bar.

[0308] In the course of performance of steps (1) to (3) according to the third aspect of the process according to the invention, hydrogen is typically formed in the cathode chamber K.sub.K, which can be removed from the cell together with solution L.sub.1 via outlet A.sub.KK. The mixture of hydrogen and solution L.sub.1 can then, in a particular embodiment of the present invention, be separated by methods known to the person skilled in the art. When the alkali metal compound used is a halide, especially chloride, it is possible for chlorine or another halogen gas to form in the anode chamber K.sub.A, and this can be removed from the cell together with solution L.sub.4 via outlet A.sub.KK. In addition, it is also possible for oxygen or/and carbon dioxide to form, which can likewise be removed. The mixture of chlorine, oxygen and/or CO.sub.2 and solution L.sub.4 can then, in a particular embodiment of the present invention, be separated by methods known to the person skilled in the art. It is then likewise possible, after the chlorine, oxygen and/or CO.sub.2 gases have been separated from solution L.sub.4, to separate these by methods known to the person skilled in the art.

4.3.2.4 Additional Advantages of Steps (1) to (3)

[0309] This performance of steps (1) to (3) brings further surprising advantages that were not to be expected in the light of the prior art. Steps (1) to (3) of the process according to the invention protect the acid-labile solid-state electrolyte from corrosion without, as in the prior art, having to sacrifice alkoxide solution from the cathode space as buffer solution. Thus, the process according to the invention is more efficient than the procedure described in WO 2008/076327 A1, in which the product solution is used for the middle chamber, which reduces the overall conversion.

5. EXAMPLES

5.1 Comparative Example 1

[0310] Sodium methoxide (SM) was produced via a cathodic process, with supply of 20% by weight NaCl solution (in water) in the anode chamber and of 10% by weight methanolic SM solution in the cathode chamber. The electrolysis cell consisted of three chambers that corresponded to those shown in FIG. 1 B. The connection between middle chamber and anode chamber was established by a hose mounted at the base of the electrolysis cell. The anode chamber and middle chamber were separated by a 2.83 cm.sup.2 anion exchange membrane (Tokuyama AMX, ammonium groups on polymer). Cathode chamber and middle chamber were separated by a ceramic of the NaSICON type with an area of 2.83 cm.sup.2. The ceramic had a chemical composition of the formula Na.sub.3.4Zr.sub.2.0Si.sub.2.4P.sub.0.6O.sub.12.

[0311] The anolyte was transferred through the middle chamber into the anode chamber. The flow rate of the anolyte was 1 I/h, that of the catholyte was 90 ml/h, and a current of 0.14 A was applied. The temperature was 35 C. The electrolysis was conducted for 500 hours at a constant voltage of 5 V. It was observed that a pH gradient developed in the middle chamber over a prolonged period, which is attributable to the migration of the ions to the electrodes in the course of the electrolysis and the spread of the protons formed in further reactions at the anode. This local increase in pH is undesirable since it can attack the solid-state electrolyte and can lead to corrosion and fracture of the solid-state electrolyte specifically in the case of very long periods of operation.

[0312] In addition, there is expansion and shrinkage of the NaSICON ceramic on account of the heating and cooling effects when the electrolysis cell is repeatedly started up and shut down. In addition, the NaSICON membrane may be displaced within the cell. This is problematic since the tendency of the ceramic to fracture is enhanced and can lead to leakage of electrolyte from the middle chamber into the cathode chamber, which waters down the electrolysis product. In addition, this can lead to leaks in the outer wall of the cell, which leads to leakage of electrolyte to the outside.

5.2 Comparative Example 2

[0313] Comparative Example 1 was repeated with a two-chamber cell comprising just one anode chamber and one cathode chamber, with the anode chamber separated from the cathode chamber by the ceramic of the NaSICON type (FIG. 1 A). This electrolysis cell thus did not contain any middle chamber. This is reflected in even faster corrosion of the ceramic compared to the comparative example 1, which leads to a rapid rise in the voltage curve. With a starting voltage value of <5 V, this rises to >20 V within 100 hours.

5.3 Inventive Example 1

[0314] Comparative Example 1 is repeated using an electrolysis cell according to FIG. 5 A in which a dividing wall comprising two NaSICON ceramics in a frame is inserted and secured with screws.

[0315] This arrangement reduces the extent of the expansion and shrinkage processes, which contributes to the service life of the ceramic and results in a cleaner product solution since the leakage is prevented.

5.4 Comparative Example 3

[0316] Comparative Example 2 is repeated using an electrolysis cell according to FIG. 5 B in which a dividing wall comprising four NaSICON ceramics in a frame is inserted and secured with hooks as shown in FIG. 7 A. The difference is, however, that the securing element B.sub.T <92> (in cross section <166> in FIG. 5 B) is omitted.

[0317] This arrangement reduces the extent of the expansion and shrinkage processes, which contributes to the service life of the ceramic and results in a cleaner product solution since the leakage is prevented. However, it is observed that the frame R is flexible in the region of the separating element R.sub.T, and hence the stability of the dividing wall W in this region is low.

5.5 Inventive Example 2

[0318] Comparative Example 3 is repeated, with attachment of a securing element B.sub.T <92> (mutually engaging hooks) in the region of the separating element R.sub.T. This distributes compression forces over the entire surface of the respective side of the dividing wall, which increases the stability of the dividing wall.

5.6 Result

[0319] The alleviation of the tensions within the solid-state electrolyte ceramics in the expansion and shrinkage processes which result from the repeated electrolysis cycles leads to an extension of the lifetime of the electrolysis chamber. In the execution according to Inventive Examples 1 and 2, these effects are reduced, which increases the stability of the solid-state electrolyte.

[0320] In addition, by comparison with Comparative Example 3, the stability of the dividing wall W is increased by homogeneous distribution of the compression forces exerted by the frame element on the ceramics in the dividing wall, by providing a securing element B.sub.T in the region of the separating element R.sub.T.

[0321] The use of a three-chamber cell according to the invention in the process according to the invention also prevents the corrosion of the solid-state electrolyte, and at the same time there is no need to sacrifice alkali metal alkoxide product for the middle chamber and the voltage is kept constant. These advantages that are already apparent from the comparison of the two Comparative Examples 1 and 2 underline the surprising effect of an electrolysis cell according to the invention comprising at least one middle chamber and the process conducted therein.

TABLE-US-00001 6. Reference symbols in the figures Electrolysis cell E <1> Anode chamber K.sub.A <11> Inlet Z.sub.KA <110> Outlet A.sub.KA <111> Interior I.sub.KA <112> Anodic electrode E.sub.A <113> Cathode chamber K.sub.K <12> Inlet Z.sub.KK <120> Outlet A.sub.KK <121> Interior I.sub.KK <122> Cathodic electrode E.sub.K <123> Middle chamber K.sub.M <13> Inlet Z.sub.KM <130> Outlet A.sub.KM <131> Interior I.sub.KM <132> Diffusion barrier <14> Connection V.sub.AM <15> Dividing wall W <16> Side S.sub.KK <161> Side S.sub.A/MK <162> Surface O.sub.KK <163> Surface O.sub.A/MK <164> Cross section through edge element R.sub.R Q.sub.RR <165> Cross section through separating Q.sub.RT <166> element R.sub.T Solid-state electrolyte ceramic F.sub.A <18> Solid-state electrolyte ceramic F.sub.B <19> Solid-state electrolyte ceramic F.sub.C <28> Solid-state electrolyte ceramic F.sub.D <29> Solid-state electrolyte ceramics F.sub.E, F.sub.F, <30>, <31>, <32>, F.sub.G, F.sub.H, .sup.<33>, <34> F.sub.I Frame element R <2> Edge element R.sub.R <20> Separating element R.sub.T <17> Frame part R.sub.1 <201> Frame part R.sub.2 <202> Seal Di <40> Hinge <50> Bulge (rabbit's ear) <60> Additional hole <61> Outer wall W.sub.A <80> Securing element B.sub.R <91> Securing element B.sub.T <92> Hook B.sub.H <93> Alkali metal alkoxide XOR in the L.sub.1 <21> alcohol ROH Solution comprising the alcohol ROH L.sub.2 <22> Neutral or alkaline, aqueous solution L.sub.3 <23> of a salt S comprising X as cation Aqueous solution of S, where L.sub.4 <24> [S].sub.L4 < [S].sub.L3.