Method for dehumidifying humid gas mixtures using ionic liquids

Abstract

The invention relates to a process for dehumidifying a moist gas mixture. The invention further relates to an apparatus for dehumidifying a moist gas mixture and to the use of said apparatus in the process according to the invention.

Claims

1. A process for dehumidifying a moist gas mixture G in an apparatus V.sub.1, comprising the steps of: (a) contacting the moist gas mixture G with a liquid absorption medium A.sub.VE comprising at least one salt selected from the group consisting of: Q.sup.+(RO).sub.2PO.sub.2.sup.; (Q.sup.+).sub.2ROPO.sub.3.sup.2; and Q.sup.+M.sup.+ROPO.sub.3.sup.2; wherein the liquid absorption medium A.sub.VE at least partially absorbs water from the moist gas mixture G, to obtain a liquid absorption medium A.sub.VE1 having an elevated water content compared to the liquid absorption medium A.sub.VE and a gas mixture G.sub.1 having a relatively low water content compared to the moist gas mixture G; (b) at least partially removing water from the liquid absorption medium A.sub.VE1 to obtain a liquid absorption medium A.sub.VE2 having a relatively low water content compared to the liquid absorption medium A.sub.VE1; wherein the apparatus V.sub.1 at least partially comprises a surface made of an aluminium material of construction O.sub.Al and in the apparatus V.sub.1, at least one of the liquid absorption media selected from the group consisting of A.sub.VE, A.sub.VE1, A.sub.VE2 contacts the surface made of O.sub.Al via at least one contact surface; and wherein: Q.sup.+ is a 1,3-dialkylimidazolium in which the alkyl groups are, independently of one another, unbranched or branched C.sub.1-C.sub.6 alkyl groups; R is an unbranched or branched C.sub.2-C.sub.6 alkyl group; and M.sup.+ is an alkali metal ion.

2. The process of claim 1, wherein R is selected from the group consisting of: an ethyl group and a n-butyl group.

3. The process of claim 1, wherein Q.sup.+ is selected from the group consisting of 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, 1-n-butyl-3-methylimidazolium.

4. The process of claim 3, wherein the salt is selected from the group consisting of: 1,3-diethylimidazolium diethylphosphate; 1-ethyl-3-methylimidazolium diethylphosphate; and 1-n-butyl-3-methylimidazolium di-n-butylphosphate.

5. The process of claim 1, wherein the liquid absorption medium A.sub.VE is an aqueous solution in which the total weight of all salts of structure Q.sup.+(RO).sub.2PO.sub.2.sup., (Q.sup.+).sub.2ROPO.sub.3.sup.2 and Q.sup.+M.sup.+ROPO.sub.3.sup.2 is at least 70 wt % based on the total weight of the aqueous solution.

6. The process of claim 1, wherein said process is carried out in continuous fashion.

7. The process of claim 2, wherein: a) Q.sup.+ is selected from the group consisting of 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, 1-n-butyl-3-methylimidazolium; and b) the liquid absorption medium A.sub.VE is an aqueous solution in which the total weight of all salts of structure Q.sup.+(RO).sub.2PO.sub.2.sup., (Q.sup.+).sub.2ROPO.sub.3.sup.2 and Q.sup.+M.sup.+ROPO.sub.3.sup.2 is at least 70 wt % based on the total weight of the aqueous solution.

8. The process of claim 1, wherein said process is carried out using an apparatus V.sub.2 for dehumidifying a moist gas mixture, wherein said apparatus comprises the components: a) a liquid absorption medium A.sub.VO comprising at least one salt selected from the group consisting of: Q.sup.+(RO).sub.2PO.sub.2.sup.; (Q.sup.+).sub.2ROPO.sub.3.sup.2; and Q.sup.+M.sup.+ROPO.sub.3.sup.2; b) at least one water absorption unit W.sub.abs2 for contacting the moist gas mixture with the liquid absorption medium A.sub.VO; c) at least one water desorption unit W.sub.des2 which comprises a heat exchanger W.sub.x2 and is set up for at least partially removing water from a liquid absorption medium A.sub.VO; and d) a circuit U.sub.2 which connects the water absorption unit W.sub.abs2 with the water desorption unit W.sub.des2 and by means of which the liquid absorption medium A.sub.VO may be circulated; wherein at least one of the components W.sub.abs2, W.sub.des2, and U.sub.2 at least partially comprises a surface made of an aluminium material of construction O.sub.Al; and wherein disposed in the apparatus V.sub.2 is at least one contact surface at which the liquid absorption medium A.sub.VO contacts the surface made of O.sub.Al; and wherein: Q.sup.+ is a 1,3-dialkylimidazolium where the alkyl groups are independently of one another unbranched or branched C.sub.1-C.sub.6 alkyl groups; R is an unbranched or branched C.sub.2-C.sub.6 alkyl group; and M.sup.+ is an alkali metal ion.

9. The process of claim 8, wherein R is selected from the group consisting of: an ethyl group and a n-butyl group.

10. The process of claim 9, wherein: a) Q.sup.+ is selected from the group consisting of 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, 1-n-butyl-3-methylimidazolium; and b) the liquid absorption medium A.sub.VE is an aqueous solution in which the total weight of all salts of structure Q.sup.+(RO).sub.2PO.sub.2.sup., (Q.sup.+).sub.2ROPO.sub.3.sup.2 and Q.sup.+M.sup.+ROPO.sub.3.sup.2 is at least 70 wt % based on the total weight of the aqueous solution.

11. An apparatus V.sub.2 for dehumidifying a moist gas mixture, comprising the components: a) a liquid absorption medium A.sub.VO comprising at least one salt selected from the group consisting of: Q.sup.+(RO).sub.2PO.sub.2.sup.; (Q.sup.+).sub.2ROPO.sub.3.sup.2; and Q.sup.+M.sup.+ROPO.sub.3.sup.2; b) at least one water absorption unit W.sub.abs2 for contacting the moist gas mixture with the liquid absorption medium A.sub.VO; c) at least one water desorption unit W.sub.des2 which comprises a heat exchanger W.sub.x2 and is set up for at least partially removing water from a liquid absorption medium A.sub.VO; and d) a circuit U.sub.2 which connects the water absorption unit W.sub.abs2 with the water desorption unit W.sub.des2 and by means of which the liquid absorption medium A.sub.VO may be circulated; wherein at least one of the components W.sub.abs2, W.sub.des2, and U.sub.2 at least partially comprises a surface made of an aluminium material of construction O.sub.Al; and wherein disposed in the apparatus V.sub.2 is at least one contact surface at which the liquid absorption medium A.sub.VO contacts the surface made of O.sub.Al; and wherein: Q.sup.+ is a 1,3-dialkylimidazolium where the alkyl groups are independently of one another unbranched or branched C.sub.1-C.sub.6 alkyl groups; R is an unbranched or branched C.sub.2-C.sub.6 alkyl group; and M.sup.+ is an alkali metal ion.

12. The apparatus V.sub.2 of claim 11, wherein R is selected from the group consisting of: an ethyl group and a n-butyl group.

13. The apparatus V.sub.2 of claim 11, wherein Q.sup.+ is selected from the group consisting of 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, 1-n-butyl-3-methylimidazolium.

14. The apparatus V.sub.2 of claim 13, wherein the salt is selected from the group consisting of: 1,3-diethylimidazolium diethylphosphate; 1-ethyl-3-methylimidazolium diethylphosphate; and 1-n-butyl-3-methylimidazolium di-n-butylphosphate.

15. The apparatus V.sub.2 of claim 11, wherein A.sub.VO is an aqueous solution in which the total weight of all salts of structure Q.sup.+(RO).sub.2PO.sub.2.sup., (Q.sup.+).sub.2ROPO.sub.3.sup.2 and Q.sup.+M.sup.+ROPO.sub.3.sup.2 is at least 70 wt % based on the total weight of the aqueous solution.

16. The apparatus V.sub.2 of claim 11, wherein at least one of the components W.sub.abs2, and W.sub.des2 is a falling film.

17. The apparatus V.sub.2 of claim 11, comprising a further heat exchanger W.sub.y2 positioned so that liquid absorption medium A.sub.VO sent from the water absorption unit W.sub.abs2 to the water desorption unit W.sub.des2 is suppliable with heat from liquid absorption medium A.sub.VO, said medium being conducted away from the water desorption unit W.sub.des2.

18. The apparatus of claim 12, wherein: a) Q.sup.+ is selected from the group consisting of 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, 1-n-butyl-3-methylimidazolium; and b) the liquid absorption medium A.sub.VE is an aqueous solution in which the total weight of all salts of structure Q.sup.+(RO).sub.2PO.sub.2.sup., (Q.sup.+).sub.2ROPO.sub.3.sup.2 and Q.sup.+M.sup.+ROPO.sub.3.sup.2 is at least 70 wt % based on the total weight of the aqueous solution.

19. The apparatus of claim 18, comprising a further heat exchanger W.sub.y2 positioned so that liquid absorption medium A.sub.VO sent from the water absorption unit W.sub.abs2 to the water desorption unit W.sub.des2 is suppliable with heat from liquid absorption medium A.sub.VO, said medium being conducted away from the water desorption unit W.sub.des2.

20. An absorption heat pump, comprising the apparatus V.sub.2 of claim 11, as further components, a condenser, an evaporator and a coolant, wherein the coolant is water.

Description

(1) The FIGS. 1 and 2 elucidated hereinbelow show preferred embodiments of the process according to the invention and the apparatus according to the invention.

(2) FIG. 1 (abbreviated to FIG. 1) shows an embodiment of the apparatus V.sub.2/V.sub.1 according to the invention.

(3) The apparatus V.sub.2 shown in FIG. 1 comprises a water absorption unit W.sub.abs2 <103> (with optional additional heat exchanger W.sub.z2 <104>) to which a conduit <101> leads and from which a conduit <102> leads away, a water desorption unit W.sub.des2 which comprises a heat exchanger W.sub.x2 <108> and a water desorber <109> and to which conduit <111> leads and from which conduits <110>, <112> and <113> lead away, and a circuit U.sub.2 formed from conduits <106>, <111> and <113> or <106>, <111>, <112> and <105> (in each case optionally with conduit <114>). The apparatus in FIG. 1 may also optionally comprise a further heat exchanger W.sub.y2 <107> to which conduits <106> and <112> lead and from which conduits <105> and <111> lead away. In addition the apparatus also comprises a liquid absorption medium A.sub.VO. Said medium is disposed in one or more of the abovementioned components water absorption unit W.sub.abs2, water desorption unit W.sub.des2, circuit U.sub.2. Water absorption unit W.sub.abs2 <103> may optionally also comprise an additional heat exchanger W.sub.z2 <104>. Apparatus V.sub.2, in particular at least one of the components selected from the group consisting of water absorption unit W.sub.abs2, water desorption unit W.sub.des2, circuit U.sub.2, at least partially comprises a surface made of an aluminium material of construction O.sub.Al and there is at least one contact surface at which the liquid absorption medium A.sub.VO contacts the surface made of an aluminium material of construction O.sub.Al. Optionally circuit U.sub.2 may also additionally comprise a pump for conveying the liquid absorption medium.

(4) Apparatus V.sub.1 corresponds to apparatus V.sub.2 without absorption medium A.sub.VO, wherein in the figure description for FIG. 1 and FIG. 2 the terms U.sub.2, W.sub.abs2, W.sub.des2, W.sub.x2, W.sub.y2, W.sub.z2 are to be replaced by U.sub.1, W.sub.abs1, W.sub.des1, W.sub.x1, W.sub.y1, and W.sub.z1 respectively.

(5) The process according to the invention will now be illustratively described with reference to apparatus V.sub.1 using FIG. 1:

(6) A stream moist gas mixture G (said stream may moist air, moist natural gas or moist gas mixture originating from the evaporator of an absorption chillersee also FIG. 2 with regard to this option) is supplied via conduit <101> to a water absorption unit W.sub.abs1 <103> and contacted there with the liquid absorption medium A.sub.VE supplied to the water absorption unit W.sub.abs1 <103> via the conduit <105> or via the conduit <113>. The water absorption unit W.sub.abs1 <103> may be any of the water absorbers cited hereinabove for W.sub.abs1, in particular a falling-film. Contacting, in the water absorption unit W.sub.abs1 <103>, gas mixture G supplied via conduit <101> with the liquid absorption medium A.sub.VE supplied via the conduit <105> or via the conduit <113> affords a liquid absorption medium A.sub.VE1 having an elevated water content compared to the liquid absorption medium A.sub.VE and a stream of a gas mixture G.sub.1 discharged via the conduit <102>, G.sub.1 having a relatively low water content compared to the moist gas mixture G. Depending on the application G.sub.1 is in particular dehumidified air or dehumidified natural gas. The water absorption unit W.sub.abs1 <103> may optionally also comprise an additional heat exchanger W.sub.z1 <104>. Preferably via the conduits <106>, <111> and the heat exchanger W.sub.y1 <107> (or, when heat exchanger W.sub.y1 <107> is not employed, via conduits <106>, <111> and <114>) the liquid absorption medium A.sub.VE1 is then passed to the water desorption unit W.sub.des1 composed of the heat exchanger W.sub.x1 <108> and the water desorber <109>. The water-laden liquid absorption medium A.sub.VE1 may additionally be supplied with heat in the optional heat exchanger W.sub.y1 <107>. The at least partial removal of water from liquid absorption medium A.sub.VE1 is then carried out in the water desorber <109> to afford a liquid absorption medium A.sub.VE2 having a relatively low water content compared to the liquid absorption A.sub.VE1. The water removed is then discharged from the water desorber <109> as liquid or vapour, preferably as vapour, via conduit <110>. The liquid absorption medium A.sub.VE2 is then discharged from the water desorber <109> and returned to the water absorption unit W.sub.abs1 <103>. This may either be carried out directly, i.e. via the conduit <113> which is shown in dashed form in FIG. 1. Alternatively and preferably the liquid absorption medium A.sub.VE2 may also be supplied via the conduit <112> to the optional heat exchanger W.sub.y1 <107> in which the liquid absorption medium A.sub.VE1 supplied via conduit <106> to the optional heat exchanger W.sub.y1 <107> is supplied with heat from the liquid absorption medium A.sub.VE2 supplied via conduit <112> to the optional heat exchanger W.sub.y1 <107>. Once the concentrated liquid absorption medium A.sub.VE2 has been supplied to the water absorption unit W.sub.abs1 via conduit <105> or <113> said medium is reused as A.sub.VE for at least partially dehumidifying the gas stream in a new cycle. It is essential to the invention that in this process the apparatus according to FIG. 1, preferably at least one of the components selected from the group consisting of water absorption unit W.sub.abs1 <103> (in FIG. 1 said unit comprises the heat exchanger <104>), water desorption unit W.sub.des1 (in FIG. 1 said unit comprises the heat exchanger <108>), circuit U.sub.1 (composed in FIG. 1 of the conduits <106>, <111>, <113>, or <106>, <111>, <112>, <105>, and in each case optionally also conduit <114>) at least partially comprises a surface made of an aluminium material of construction O.sub.Al and that disposed in the apparatus is at least one contact surface at which at least one of the liquid absorption media A.sub.VE, A.sub.VE1, A.sub.VE2 contacts the surface made of an aluminium material of construction O.sub.Al.

(7) FIG. 2 (abbreviated as FIG. 2) shows in schematic fashion an absorption chiller into which an apparatus V.sub.2 is integrated. The constituents <101> to <114> are shown as for the apparatus V.sub.2 described in FIG. 1. Additionally, the absorption chiller in FIG. 2 also comprises a condenser <211> which is connected to the water desorption unit W.sub.des2 <109> via the conduit <110> and is set up for condensing water at least partially removed from the liquid absorption medium A.sub.VO in the water desorption unit W.sub.des2. Condenser <211> preferably also comprises a heat exchanger <212> with which cooling water may be supplied.

(8) The absorption chiller shown in FIG. 2 also comprises an evaporator <214> connected to the condenser <211> via a conduit <216> (which may optionally comprise a throttling means <213>) and connected via the conduit <101> with the water absorption unit W.sub.abs2. The evaporator <214> is set up to evaporate condensed water from the condenser. Additionally, the evaporator <214> can further preferably also comprise a heat exchanger <215> which supplies a medium, heat being drawn off from the medium to thus evaporate the condensed water (for example a coolant conduit with, in particular, water as coolant, this coolant being passed into the evaporator <214>).

(9) In an embodiment of the process according to the invention (described hereinbelow with reference to apparatus V.sub.1 using FIG. 2) moist gas mixture G originating from evaporator <214> is passed via the conduit <101> to the water absorption unit W.sub.abs1 <103>. The water removed in water desorption unit W.sub.des1 is supplied via the conduit <110> to the condenser <211> in which said water is recondensed. A cooling water circuit as heat exchanger <212> installed in the condenser is optionally likewise used therefor. The condensed water is then supplied via a conduit <216> to the evaporator <214> in which the evaporation of water is effected in particular at low pressures thus bringing about a cooling effect. This may optionally also be effected using a throttling means <213>. This achieves a cooling action in the evaporator <214> and, for example, coolant may be cooled via the heat exchanger <215>. The water vapour generated is then returned to the water absorption unit W.sub.abs1 <103> via conduit <101>.

(10) The examples which follow are intended to elucidate the present invention without limiting said invention in any way.

EXAMPLES

(11) The following test series were carried out:

(12) 1. Test Series: E1, V1-V4

(13) 1.1 Chemicals Employed EMIM DEP (=ethylmethylimidazolium diethylphosphate) was obtained from Sigma Aldrich.

(14) EMIM HSO.sub.4 (=ethylmethylimidazolium hydrogensulphate) was obtained from Sigma Aldrich.

(15) LiCl was obtained from Sigma Aldrich.

(16) MMIM.sup.+H.sup.+ ROPO.sub.3.sup.2 where R=ethyl group (dimethylimidazolium hydrogen monoethylphosphate) was obtained as follows:

(17) Added to a cryostat at 5 C. were methylamine (4.8 mol), formaldehyde (2.4 mol) and monoethyl phosphate (2.4 mol). The mixture was stirred for 1 h before glyoxal (2.4 mol) was added. The volatile constituents were subsequently removed under reduced pressure using a rotary evaporator to obtain the pure substance.

(18) 1.2 Test Procedure

(19) At 70 C. and under air, aluminium plates (highest purity aluminium, purity >99.0%) having dimensions of 3 cm7 cm and a thickness of 3 mm were immersed in 350 ml of the respective solution. The liquid was stirred during the test to ensure uniform flow of the liquid around the metal plates. Determination of the removal rates (removal rate=loss due to corroded aluminium, reported in Table 1 in the unit g/m.sup.2*year) was carried out gravimetrically after chemical and mechanical removal of the corrosion products from the immersed aluminium plates. The results are shown in Table 1 which follows.

(20) 1.3 Results

(21) TABLE-US-00001 TABLE 1 test solution employed removal rate V1 EMIM HSO.sub.4 (80 wt % in H.sub.2O) 7548 V2 LiCl (30 wt % in H.sub.2O) 575 V3 H.sub.2O 130 V4 MMIM.sup.+ H.sup.+ ROPO.sub.3.sup.2 where R = 353 ethyl (80 wt % in H.sub.2O) E1 EMIM DEP (80 wt % in H.sub.2O) 33

(22) As is apparent from the results in Table 1 corrosion is markedly lower when using the liquid absorption medium cited in E1 than for the liquid absorption media employed in V1-V4. The use of liquid absorption media according to the invention thus surprisingly makes it possible to reduce the corrosion of aluminium compared to the liquid absorption media otherwise employed in the prior art.

(23) 2. Test Series: E2, E3, V5

(24) This effect is corroborated by the test series which follows.

(25) 2.1 Chemicals Employed

(26) EMIM DEP (=ethylmethylimidazolium diethylphosphate) was obtained from Sigma Aldrich.

(27) MMIM.sup.+K.sup.+ROPO.sub.3.sup.2 where R=ethyl (=dimethylimidazolium potassium monoethylphosphate) was obtained as follows: Added to a cryostat at 5 C. were methylamine (4.8 mol), formaldehyde (2.4 mol) and monoethyl phosphate (2.4 mol). The mixture was stirred for 1 h before glyoxal (2.4 mol) was added. The volatile constituents were subsequently removed under reduced pressure using a rotary evaporator and the pH of the pure substance thus obtained was adjusted from 7.0 to 7.5 with 50 wt % aqueous potassium hydroxide solution.

(28) MMIM MeSO.sub.3 (=dimethylimidazolium methylsulphonate) was obtained as follows: Added to a cryostat at 5 C. were methylamine (4.8 mol), formaldehyde (2.4 mol) and methanesulphonic acid (2.4 mol). The mixture was stirred for 1 h before glyoxal (2.4 mol) was added. The volatile constituents were subsequently removed under reduced pressure using a rotary evaporator to obtain the pure substance.

(29) 2.2 Test Procedure

(30) At 70 C. and under air, aluminium plates (highest purity aluminium; purity >99.0%) having dimensions of 3 cm7 cm and a thickness of 3 mm were immersed in 350 ml of the respective solution. The liquid was stirred during the test to ensure uniform flow of the liquid around the metal plates.

(31) Tests E2, E3, V5 employed wet chemical evaluation by measurement of Al in the medium with ICP-OES (inductively coupled plasma optical emission spectrometry). The determined aluminium content in the solution was extrapolated to the mass of the aluminium plates employed. The results are shown in Table 2 which follows.

(32) 2.3 Results

(33) Table 2

(34) TABLE-US-00002 TABLE 2 mg of dissolved aluminium per test solution employed g of aluminium V5 MMIM MeSO.sub.3 (80 wt % in water) 1,040 E2 MMIM.sup.+ K.sup.+ ROPO.sub.3.sup.2 where R = 0,001 ethyl (80 wt % in water) E3 EMIM DEP (80 wt % in water) 0,011

(35) As is apparent from the results in Table 2, use of the liquid absorption media according to the invention makes it possible to reduce the corrosion of aluminium compared to the liquid absorption media otherwise employed in the prior art.

(36) 3. Test Series E4, E5, V6, V7

(37) 3.1 Chemicals Employed

(38) EMIM DEP (=ethylmethylimidazolium diethylphosphate) was obtained from Sigma Aldrich.

(39) EMIM DMP (=ethylmethylimidazolium dimethylphosphate) was obtained from Sigma Aldrich.

(40) 3.2 Test Procedure

(41) 3 drops of the respective solution were dropped onto an aluminium plate (highest purity aluminium, purity >99.0%) having dimensions of 3 cm7 cm and a maximum thickness of 3 mm. The contact angle determination was carried out according to SOP 1827. The results are shown in Table 3 which follows.

(42) 3.3 Results

(43) Table 3

(44) TABLE-US-00003 TABLE 3 test solution employed Contact angle () E4 EMIM DEP (90 wt % in water) 45.7 E5 EMIM DEP (80 wt % in water) 53 V6 EMIM DMP (90 wt % in water) 86 V7 EMIM DMP (80 wt % in water) 90.4

(45) The results show that the absorption media according to the invention (E4, E5) exhibit a small contact angle compared to those of the prior art (V6, V7) and thus ensure good heat conduction in the process according to the invention/for the apparatus according to the invention. This is shown in the comparisons of E4 with E6 and E5 with E7. The use of imidazolium salts with diethylphosphate as counterion as opposed to dimethylphosphate as counterion surprisingly achieves a smaller contact angle to the aluminium-containing surface. This results in improved surface wetting and thus to greater and more efficient heat exchange in the case of diethyl phosphate.