TRANSFERRING A TARGET SUBSTANCE BETWEEN TWO LIQUID PHASES

Abstract

The invention relates to a method for transferring a target substance (5), particularly a target molecule (5), between two liquid phases (4, 6; 6, 8; 6, 11), of which at least one phase (4, 6) comprises the target substance (5) to be transferred and at least one phase (4, 8, 11) is an aqueous phase, where at least the aqueous phase (4, 8, 11) is arranged in one of two electrode chambers (1a, 1b, 10a, 10b) which are electroconductively connected, preferably by charge carrier exchange, and separated in terms of the volumes thereof, preferably where the phases (4, 6; 6, 8; 6, 11) are arranged together in one of two electrode chambers (1a, 1b, 10a, 10b) which are electroconductively connected and separated in terms of the volumes thereof, and a pH-value modification is generated by the H and/or OH ions created during the electrolysis in the aqueous phase (4, 8, 11), said modification initiating a transfer process of the target substance (5) between the phases (4, 6; 6, 8; 6, 11). The invention also relates to the use of the method for enrichment and subsequent isolation of the target substance (5).

Claims

1. A method of transferring a target substance (5), particularly a target molecule (5), between two liquid phases (4, 6; 6, 8; 6, 11) of which at least one phase (4, 6) is the target substance (5) to be transferred and at least one phase (4, 8, 11) is an aqueous phase, wherein at least the aqueous phase (4, 8, 11) is in one of two electrode chambers (1a, 1b, 10a, 10b) that are electrically conductively connected, preferably electrically conductively connected by charge carrier exchange, and are separated in terms of the volumes thereof, the phases (4, 6; 6, 8; 6, 11) are transferred together to one of two electrode chambers (1a, 1b, 10a, 10b) that are electrically conductively connected and are separated in terms of the volumes thereof, and are dispersed in the electrode chamber (1a, 1b, 10a, 10b) while the electrolysis is being performed, and a pH-value modification is generated by H and/or OH ions created during the electrolysis in the aqueous phase (4, 8, 11), this modification initiating a transfer process of the target substance (5) between the phases (4, 6; 6, 8; 6, 11).

2. The method according to claim 1, characterized in that, by the aqueous electrolysis taking place between the electrode chambers, a) the target substance (5) is protonated by the H ions created during the electrolysis or deprotonated by the OH ions created during the electrolysis, the transfer process being formed by the dissolution of the target substance (5) in that of the two phases (4, 6, 8, 11) in which the target substance (5) protonated by the electrolysis or the target substance (5) deprotonated by the electrolysis has the higher solubility, or b) the binding of the target substance (5) to a binding partner (6) in one of the phases (6) or the cleaving of the target substance (5) from a binding partner (6) in one of the phases (6) is initiated by the created H+ and/or OH.sup. ions, in particular by pH-value-dependent activation of the binding partner (6) and/or by protonation/deprotonation of the target substance (5).

3. The method according to any one of the preceding claims, characterized in that the target substance (5) is a target molecule (5) that is selected from the group of water-soluble amines, water-soluble amino acids, water-soluble alkanediols and/or water-soluble carboxylic acids.

4. The method according to any one of the preceding claims, characterized in that the non-aqueous phase (6) participating in the material exchange a) comprises an organic solvent (6), in particular is formed by same, in particular wherein the organic solvent (6) is selected from alcohols, esters, ketones, and aliphatic and aromatic hydrocarbons, preferably selected from octanol, kerosene or butyl acetate that are not miscible or are only partially miscible with the aqueous phase (4, 8, 11). b) comprises a reactive binding partner (6) that, depending on the pH value, may enter into reversible bonds with the target substance (5), in particular that is selected from the group of aliphatic amines with at least 10 carbon atoms and organophosphoric acids with 2 to 3 alkyl groups.

5. The method according to any one of the preceding claims, characterized in that the phases (4, 6, 8, 11) are mixed in the electrode chamber (1a, 1b, 10a, 10b) to form a dispersion.

6. The method according to any one of the preceding claims, characterized in that a first phase (4) is formed by an aqueous solution of an acid (5) as target molecule (5) and a second phase (6) a) comprises a reactive extraction agent as a binding partner (6), in particular is formed from same, and/or b) comprises an organic solvent (6), in particular is formed from same such that the acid (5) is protonated in the anode chamber (1a) of both electrode chambers (1a, 1b) and c) is reactively attached to the reactive extraction agent (6), in particular by hydrogen bonds, or d) dissolves in the organic solvent (6), in which the protonated acid (5) has a higher solubility compared to the deprotonated acid (5) and is thereby transferred from the first phase (4) into the second phase (6).

7. The method according to claim 6, characterized in that the first phase (4) is taken from a fermentation reactor (9) and, after performing the transfer of the target molecule (5) to the second phase (6), is returned into the fermentation reactor (9) via a cathode chamber (1b) electrically associated with the anode chamber (1a) during or after performance of the electrolysis.

8. The method according to any one of the preceding claims, characterized in that a first phase (6) a) is formed by a complex (7) of a reactive extraction agent (6) as binding partner (6) and a protonated acid (5) bound thereto, in particular by hydrogen bonds, as target molecule (5) or b) is formed by an organic solvent (6) in which a protonated acid (5) is dissolved c) comprises a mixture of reactive extraction agent (6) and organic solvent (6) and one or both of the effects mentioned in a) or b) occur and the second phase comprises water (8, 11), the protonated acid (5) being deprotonated in the cathode chamber (10a) of both electrode chambers (10a, 10b) and d) is cleaved from the reactive extraction agent (6) by breaking of the bonds, preferably hydrogen bonds, and/or e) dissolves in the aqueous phase (8, 11), in particular due to a higher solubility of the deprotonated acid (5) in the second phase (8, 11) compared to the protonated acid (5) in the second phase (8, 11), and is hereby transferred from the first phase (6) into the second phase (8, 11).

9. The method according to claim 8, characterized in that the second phase (11) is transferred into an anode chamber (10b) of an electrolysis unit (10), in particular into the anode chamber (10b) that is electrically associated with the cathode chamber (10a) mentioned in claim 8, and, by lowering the pH value in the second phase (11) by electrolysis carried out due to the pH-value-dependent solubility of the acid (5) in water, the acid (5) is crystallized, in particular after which the second phase (11) separated from the crystallized acid (5) is returned into the cathode chamber (10a).

10. The method of transferring a target molecule (5) between two liquid phases (4, 6, 8, 11), in which a method according to claim 8 or 9 is carried out temporally after or simultaneously with a method according to claim 6 or 7 and the second phase (6) of the method according to claim 6 or 7 forms the first phase (6) of the method according to claim 8 or 9.

11. The method according to claim 10, characterized in that the target molecule (5) is transferred from an aqueous phase (4) into an aqueous phase (8, 11) by the method steps performed in succession, with the concentration in the last aqueous phase (8, 11) being increased.

12. The method according to any one of the preceding claims, characterized in that the anode chamber (1a) and the cathode chamber (10a) are electrode chambers of different electrolysis units (1, 10).

13. The method according to any one of the preceding claims, characterized in that the oxygen created during an electrolysis process is used for the oxygen supply of a fermentation reactor (9).

14. The method according to any one of the preceding claims, characterized in that the target molecule (5) present in aqueous solution of a phase (4), in particular the first phase (4), has at least one pH-value-sensitive functional group, optionally with further functional groups, which gives the target molecule (5) a pH-dependent solubility and/or allows it to bind pH-dependently to the reactive agent (6), the group preferably being a carboxyl group, the target molecule (5) further preferably being a saturated or unsaturated water-soluble carboxylic acid with 1 to 7 carbon atoms.

15. The method according to any of the preceding claims, characterized in that the binding partner (6) in the phase, in particular the second phase (6), is selected from aliphatic amines with at least 10 carbon atoms, preferably tributylamine, trioctylamine and/or tridodecylamine, or organophosphoric acids in the form of linear or branched alkyl phosphates with 2 to 3 alkyl groups, each alkyl group having 1 to 10 carbon atoms, preferably tributyl phosphate and/or di-(2-ethylhexyl)phosphoric acid.

16. Use of the method according to any one of the above claims for the enrichment and subsequent isolation of the target substance (5) according to any one of the preceding claims, in particular of saturated or unsaturated carboxylic acids with at least one carboxyl group that is optionally substituted, optionally with oxygen-containing functional groups, preferably by using the pH-value-dependent solubility to bring about a crystallization or precipitation of the target substance in solid form.

Description

[0070] Embodiments of the invention will be described below.

[0071] FIG. 1 shows an electrolysis unit 1 with an anode chamber 1a and a cathode chamber 1b. The two chambers are separated in terms of the volumes thereof so that no unintentional convective exchange of the phases between the two chambers may take place. However, the chambers are connected to each other for charge carrier equalization, so that electrolysis may be performed via an anode 2a, a cathode 2b and a power supply 3.

[0072] In the anode chamber 1a there is an aqueous first phase 4 that comprises an acid 5 dissolved in water. When electrolysis is being performed, hydrogen ions (protons) are created at the anode, resulting in protonation of the acid 5 in the aqueous first phase 4 and the acid attaching itself to the reactive extraction agent 6 by hydrogen bonding that at the same time forms the second phase 6 or is at least contained in it. In this illustration, the two phases are shown one on top of the other and thus floating one on top of the other, which is merely symbolic for visualization of the phases. According to the invention, it is preferred to disperse the two phases 4 and 6 for the extraction to be performed, for example in the anode chamber 1a or even before.

[0073] The addition via the hydrogen bond therefore produces the complex 7 in the second phase 6 according to the first equation in FIG. 1. For example, the first phase 4 may be taken from a fermentation reactor to extract the acid formed by fermentation from this phase. The electrolysis causes a pH value shift below the acid number of this acid.

[0074] FIG. 1 shows exchange arrows in the upper region of the two electrode chambers between the opposite upper phases of the anode chamber 1a and cathode chamber 1b. This does not mean that these two chambers are connected to each other with regard to a possible material exchange, but that may be provided in accordance with the method to transfer this phase 6, for example convectively, into the cathode chamber 1b after an initial extraction of the acid 5 into the phase 6, in order to there carry out a back-extraction into an aqueous phase 8.

[0075] Then, in a subsequent step or, if necessary, a step that may also be performed in parallel, OH.sup. ions are created by performing electrolysis in the cathode chamber 1b, which leads to deprotonation and breaking of the hydrogen bonds in phase 6, so that the acid 5 bound to the reactive extraction agent 6 is cleaved and deprotonated. Due to a higher solubility of the deprotonated acid 5 in the aqueous phase 8 of the cathode chamber 1b, the deprotonated acid dissolves and is enriched or concentrated there compared to the aqueous phase 4.

[0076] After cleaving, the phase 6 and thus the reactive extraction agent may be transferred back into the anode chamber 1a according to the arrows in order to perform the two method steps cyclically. During electrolysis, the pH value in the cathode chamber 1b is increased above the acid number of the aqueous solution, i.e. of the phase 8. In the cathode chamber as well, it is preferred to disperse the two phases 6 and 8 in order to obtain the largest possible surface area between the phases.

[0077] In the cathode chamber the reaction takes place according to equation 2 that shows that after electrolysis in this chamber performing the dissociation of the formed complex 7, the phase 6 corresponds substantially to the original reactive extraction agent.

[0078] FIG. 2 shows a further embodiment of the method of the extraction and crystallization of a fermentation acid from a fermentation reactor 9. This comprises a first phase 4 that is introduced through pipes into an anode chamber 1a of an electrolysis unit 1 and comprises the acid 5 in aqueous solution. As in the embodiment of FIG. 1, the reactive extraction agent 6 is provided as the second phase 6 in the anode chamber 1a, i.e. this phase is formed predominantly, if not entirely, by the pure reactive extraction agent 6.

[0079] In the anode chamber 1a, the very same protonation reaction takes place as described with reference to FIG. 1 and visualized by equation 1 at the bottom of FIG. 2, i.e. the acid 5 is attached to the reactive extraction agent 6 by protonation via hydrogen bonds in order to again form in this case as well the complex 7 formed by hydrogen bonds.

[0080] After this first extraction of the acid 5 into the second phase 6, FIG. 2 shows that the first phase 4, from which the acid is extracted, is fed back into the fermentation reactor 4 via the cathode chamber 1b, and electrolysis in the cathode chamber 1b causes the pH value of the aqueous phase 4, which is lowered during the protonation reaction, to be adjusted by the OH.sup. ions in the cathode chamber before being fed back into the fermentation vessel 9, i.e. to be raised, preferably to the pH value that is present in the fermentation vessel 9. In this way the first phase 4 may be circulated between the fermentation vessel 9 and the anode chamber 1a.

[0081] The second step of the method described here involves transferring the phase 6 that now consists substantially of the complex 7 or at least predominantly comprises same, into a cathode chamber 10a of a second electrolysis unit 10.

[0082] In this cathode chamber 10a there is the transferred phase 6 as well as another phase 11, for example water or at least an aqueous phase comprising water. As a result of the OH.sup. ion release taking place here, the acid 5 is cleaved from the complex 7 and the acid bound in the complex is deprotonated, so that the deprotonated acid 5 is transferred into the phase 11 due to its better solubility in water compared to the protonated acid and is enriched, i.e. concentrated, there. The phase 11 thus forms an aqueous phase in which the acid 5 is enriched compared to the aqueous phase 4.

[0083] FIG. 2 shows that the phase 6 is returned to the anode chamber 1a of electrolysis unit 1 after breaking up the complex 7 in order to be able to perform the extraction process repeatedly with this phase. The phase 11 concentrated with the acid 5 is transferred from the cathode chamber 10a of the electrolysis unit 10 to its anode chamber 10b, where in this aqueous phase 11 a pH value shift to lower pH values occurs due to the release of hydrogen ions in this chamber. Since the solubility of the acid 5 in the aqueous phase 11 is pH-value-dependent and, in particular, has a lower solubility at lower pH values than at higher pH values, the pH-value decrease in the anode chamber leads to crystallization of the acid.

[0084] The acid may thus be removed as a solid from the anode chamber 10b and, for example, may be routed to its desired application.

[0085] FIG. 2 shows that the phase 11 may be transferred back into the cathode chamber of the second electrolysis unit 10 after the process of crystallization in order to perform a back-extraction in the cycle, as described previously.

[0086] It is thus clear that the various phases 4, 6 and 11 may each be circulated. The extraction, back-extraction and crystallization may thus be carried out continuously.

[0087] The back-extraction in the cathode chamber 10a is carried out according to equation 2 below FIG. 2 and is thus identical to FIG. 1. The crystallization in the anode chamber is described by equation 3 of FIG. 2.

[0088] The following example describes the electrochemically initiated back-extraction of itaconic acid from trioctylamine and demonstrates its feasibility.

[0089] Test Description:

[0090] For the back-extraction, 20 ml TOA loaded with itaconic acid and 130 ml of 1M KCl solution are added to the cathode chamber, and 130 ml of 1M KCl solution are added to the anode chamber. As anode, a titanium sheet with 7.5 cm.sup.2 active area is used, and as cathode a nickel sheet with 7.5 cm.sup.2 active area is used. Both chambers are convectively separated from each other by a porous glass filter. Before starting the electrolysis, the system is dispersed for 25 min to determine the initial concentration. Before starting the electrolysis, a concentration of 17.3 g/l of itaconic acid and a pH value of 3.5 is measured in the aqueous phase of the cathode chamber. Subsequently, a current flow of 0.75 A is generated for 60 min by applying a voltage of 15-25 V. After completion of the electrolysis, the concentration of itaconic acid in the aqueous phase of the cathode chamber is 24.42 g/l and the pH value is 4.3. In the non-optimized test setup, a Faraday efficiency of the extraction of 51% of the extracted amount of itaconic acid relative to the maximum amount of acid extractable by the transferred charge carrier amount was achieved. The concentration of itaconic acid was measured by HPLC (Agilent Technologies 1100) on an organic acid resin column with RI and DAD detector.

[0091] In the following example, the electrochemically initiated back-extraction of succinic acid with trioctylamine-1-octanol is described and its feasibility demonstrated.

[0092] Extraction of Succinic Acid:

[0093] For the extraction, 160 g of 0.5 M K.sub.2SO.sub.4 solution with 10 g succinic acid and a pH value of 7 set by KOH are added into the anode chamber. At the same time, 200 g of 0.5 M K.sub.2SO.sub.4 solution with 1.5 g succinic acid are added into the cathode chamber. Then, 35 g trioctylamine-1-octanol with a ratio of 0.4:0.6% m are added into the anode chamber and brought into contact with the aqueous phase by stirring. A platinum-coated titanium electrode with 7.5 cm.sup.2 active area is used as the anode, and a nickel sheet with 7.5 cm.sup.2 active area is used as the cathode. Both chambers are convectively separated from each other by a porous glass filter. Before starting the electrolysis, the system is dispersed for 25 min to determine the initial concentration. Before starting the electrolysis, a concentration of 45.11 g/l succinic acid and a pH value of 7 is measured in the aqueous phase of the anode chamber.

[0094] Then, by applying a voltage of 15-25 V, a current flow of 0.57 A is generated for 325 min. After completion of the electrolysis, the concentration of succinic acid in the aqueous phase of the anode chamber is 33.40 g/l and the pH value is 4.84. In the non-optimized test setup, a Faraday efficiency of the extraction of 61% of the protonated substance amount of succinic acid was achieved relative to the maximum substance amount of acid that may be protonated due to the transferred charge carrier amount. The succinic acid concentration was measured by HPLC (Agilent Technologies 1100) on an Organic Acid Resin column with RI and DAD detector.

[0095] Back-Extraction:

[0096] For the back-extraction, 40 g of trioctylamine-1-octanol loaded with succinic acid in a ratio of 0.4:0.6% m and 160 g of 0.5 M K.sub.2SO.sub.4 solution are added into the cathode chamber and 200 g of 0.5 M K.sub.2SO.sub.4 solution are added into the anode chamber. A platinum-coated titanium electrode with 7.5 cm.sup.2 active area is used as the anode, and a nickel sheet with 7.5 cm.sup.2 active area is used as the cathode. Both chambers are convectively separated from each other by a porous glass filter. Before starting the electrolysis, the system is dispersed for 25 min to determine the initial concentration. Before starting the electrolysis, a concentration of 22.31 g/l succinic acid and a pH value of 2.76 is measured in the aqueous phase of the cathode chamber. Subsequently, a current flow of 0.4 A for 280 min is generated by applying a voltage of 15-20 V. After completion of the electrolysis, the concentration of succinic acid in the aqueous phase of the cathode chamber is 32.53 g/l and the pH value is 6.3.

[0097] The functionality is demonstrated by two tests relating to the crystallization of dicarboxylic acids (itaconic acid and succinic acid).

[0098] An itaconic acid solution with a pH value of 4.1 was prepared for the itaconic acid crystallization by adding potassium hydroxide solution (50% by weight) at a load of 0.32 g.sub.IA/g.sub.H20. Then, electrolyte (EL) K.sub.2SO.sub.4 was added, resulting in a loading of 0.07 g.sub.EL/g.sub.H2O in the phase. 180 ml of the aqueous phase was homogeneously mixed with a stirrer for 8.5 h. The electrolysis was carried out with a mixed metal anode made of titanium with a ruthenium oxide coating from Magenta Special Anodes B.V. and a nickel cathode at a voltage of 20-25 V. The temperature was kept constant at 15 C. with a Lauda E100 thermostat. The mass of crystalline itaconic acid and an optical image of the crystals in transmitted light with an Olympus BH-2 microscope with an Olympus DP25 camera and their purity are used to check the functionality. Additionally, efficiency parameters of the electrochemical system are given.

[0099] Result: 2.65 g.sub.IA could be recovered. Transmitted light microscope images are shown in FIG. 3. FIG. 3A shows a crystallizate magnified 40 times, FIGS. 3B and 3C show a crystallizate magnified 60 times. The specific current was on average 0.025 A/cm.sup.2 with an anode-specific conversion of 0.031 g/cm.sup.2 h. A Faraday efficiency of 43.74% was able to be achieved.

[0100] For the succinic acid crystallization, a succinic acid solution with a pH value of 4.144 was prepared by adding potassium hydroxide solution (50% by weight) at a load of 0.187 g.sub.sA/g.sub.H2O Then, electrolyte (EL) K.sub.2SO.sub.4 was added, resulting in a loading of 0.033 g.sub.EL/g.sub.H2O in the phase. 300 ml of the aqueous phase was homogeneously mixed with a stirrer for 2 h. The electrolysis was carried out with a mixed metal anode made of titanium with a ruthenium oxide coating from Magenta Special Anodes B.V. and a nickel cathode at a voltage of 20 V. The temperature was kept constant at 15 C. by the Lauda E100 thermostat. The mass of crystalline succinic acid and an optical image of the crystals in transmitted light with the Olympus BH-2 microscope with the Olympus DP25 camera and their purity are used to check the functionality. In addition, efficiency parameters of the electrochemical system are given.

[0101] Result: 0.962 g.sub.IA could be obtained. Transmitted light microscope images are shown in FIG. 4. This shows the succinic acid crystallizate with 40 magnification. The purity of the crystals obtained corresponds to 89.4%. The average specific current was 0.034 A/cm.sup.2 with an anode-specific conversion of 0.048 g/cm.sup.2 h. A Faraday efficiency of 32.34% was able to be achieved.