METHOD FOR PRODUCING LACTIC ACID

Abstract

The invention is directed to a method for producing lactate. The method of the invention comprises electrochemically oxidising a catalyst at an anode, and using oxidised catalyst to oxidise propylene glycol and form lactate, thereby reducing the said oxidised catalyst.

Claims

1. A method of producing lactate, the method comprising oxidising electrochemically a catalyst at an anode to form an oxidised catalyst, and oxidising propylene glycol with the oxidised catalyst to form lactate, thereby reducing the said oxidised catalyst.

2. The method according to claim 1 wherein the catalyst is chosen from the group consisting of NiOOH, CoOOH, bicyclic nitroxyl derivates, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), and a derivative thereof.

3. The method according to claim 1, wherein the catalyst is an organic homogeneous catalyst.

4. The method according to claim 1, wherein the catalyst is immobilised on the anode.

5. The method according to claim 1, wherein the catalyst is dissolved or dispersed in anode electrolyte.

6. The method according to claim 1, which method is carried out at a temperature of 10-40 C.

7. The method according to claim 1, wherein pH is kept within a range of 9-14.

8. The method according to claim 1, which method is carried out at a pressure of 51-152 kPa.

9. The method according to claim 1, wherein a cathode comprises a material selected from the group consisting of Au, carbon, Co, Cr, Cu, Fe, Ir, Mo, Ni, Pb, Pd, Pt, Ru, Ta, Ti and alloys thereof.

10. The method according to claim 1, wherein the anode comprises a material selected from the group consisting of Au, Ag, carbon, Co, Cr, Cu, Fe, Ir, Mo, Ni, Pb, Pd, Pt, Ru, Ta, Ti, and alloys thereof.

11. The method according to claim 1, wherein an anode potential of 0.4-1.4 V vs. SCE is applied.

12. The method according to claim 1, wherein said method is carried out in an electrochemical cell comprising the anode in an anode electrolyte solution comprising propylene glycol, and a cathode in a cathode electrolyte solution, wherein the cathode is in electrical communication with the anode.

13. The method according to claim 12, wherein electrolyte solvents in the anode electrolyte solution and cathode electrolyte solution are the same.

14. The method according to claim 12, wherein electrolyte solvents in the anode electrolyte solution and cathode electrolyte solution are different.

15. The method according to claim 12, wherein the electrolyte solvents in the anode electrolyte solution and cathode electrolyte solution are aqueous.

16. The method according to claim 12, wherein the electrolyte solvents in the anode electrolyte solution and cathode electrolyte solution are non-aqueous.

17. The method according to claim 1, which method is carried out in a two-compartment electrochemical cell with an anode electrolyte solution and a cathode electrolyte solution, wherein the anode electrolyte solution and the cathode electrolyte solution are separated by a membrane, such as a semi-permeable membrane, a diaphragm or a porous pot.

18. The method according to claim 1, wherein said method further comprises a step of converting produced lactate into lactic acid, such as by adding an acid.

19. The method according to claim 18, wherein the method is adapted to predominantly produce D-lactic acid or L-lactic acid, such as by using L-lactate dehydrogenase enzyme (E.C. 1.1.1.27).

20. The method according to claim 1, wherein molecular hydrogen is formed at a cathode by reduction of water.

21. The method according to claim 1, wherein oxygen is reduced to hydrogen peroxide at a cathode.

22. The method according to claim 21 wherein said hydrogen peroxide is used for oxidation of propylene glycol to lactic acid and/or pyruvic acid.

23. The method according to claim 1, which method is carried out at a temperature of 15-35 C.

24. The method according to claim 1, wherein pH is kept within a range of 10-12.

25. The method according to claim 1, which method is carried out at a pressure of 81-122 kPa.

26. The method according to claim 1, which method is carried out at a pressure of 91-111 kPa.

27. The method according to claim 1, wherein an anode potential of 0.7-1.1 V vs. SCE is applied.

28. The method of claim 2 wherein the bicyclic nitroxyl derivate is selected from the group consisting of 2-azaadamantane N-oxyl (AZADO), and 9-azabicyclo[3.3.1]nonane N-oxyl (ABNO).

29. The method of claim 2 wherein the derivative is selected from the group consisting of: 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-MeO-TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (4-oxo-TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO), 4-benzoyloxy-2,2,6,6-tetra-methylpiperidine-1-oxyl (BnO-TEMPO), 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxyl (AcNH-TEMPO), 4-acetamino-2,2,6,6-tetramethylpiperidine-1-oxyl (AA-TEMPO), 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO), N,N-dimethylamino-2,2,6,6-tetramethylpiperidine-1-oxyl (NNDMA-TEMPO), 3,6-dihydro-2,2,6,6-tetramethyl-1(2H)-pyridinyloxyl (DH-TEMPO), and bis(2,2,6,6-tetramethyl-piperidine-1-oxyl-4-yl)sebacate (TINO).

Description

EXAMPLE

[0050] A H-cell, made from glass, was used for electrolysis. An anion exchange membrane was used to separate the compartments. The anolyte (100 ml) consisted of 0.5 M boric acid at pH 9.2 (by addition of NaOH), 7.5 mM TEMPO and 5.0 mM propylene glycol. The catholyte (100 ml) consisted of 0.1 M NaOH. The electrolysis was performed under nitrogen atmosphere and room temperature. The working electrode consisted of a graphite rod, the counter electrode of a spirally wound platinum wire and the reference electrode was a saturated calomel electrode (SCE). Electrolysis was performed at +0.8 V vs. SCE. Samples were taken during electrolysis and analysed by HPLC running on an Aminex HPX-8711 column and a RID detector. The results are shown in the table below.

TABLE-US-00001 Time Propylene glycol Sodium lactate [hours] [mM] [mM] 0 5.26 0 0.35 4.03 0.53 0.67 3.72 0.95 1 3.46 1.32 2 2.75 2.27 3 2.18 2.97 4 1.70 3.45 5 1.35 3.76 6 1.06 4.03
After 6 hours of operation 80% propylene glycol conversion was achieved with a selectivity of 95% towards sodium lactate.