Electrolytic method to make alkali alcoholates using ion conducting alkali electrolyte/separator
Alkali alcoholates, also called alkali alkoxides, are produced from alkali metal salt solutions and alcohol using a three-compartment electrolytic cell. The electrolytic cell includes an anolyte compartment configured with an anode, a buffer compartment, and a catholyte compartment configured with a cathode. An alkali ion conducting solid electrolyte configured to selectively transport alkali ions is positioned between the anolyte compartment and the buffer compartment. An alkali ion permeable separator is positioned between the buffer compartment and the catholyte compartment. The catholyte solution may include an alkali alcoholate and alcohol. The anolyte solution may include at least one alkali salt. The buffer compartment solution may include a soluble alkali salt and an alkali alcoholate in alcohol.
1. A method for producing alkali alcoholate, comprising:
(a) providing an electrolytic cell comprising:
an alkali ion conducting solid electrolyte configured to selectively transport alkali ions, the solid electrolyte positioned between an anolyte compartment configured with an anode and a buffer compartment, and
a porous separator configured to transport alkali ions, the separator positioned between the buffer compartment and a catholyte compartment configured with a cathode;
(b) introducing a first solution comprising alkali alcoholate and alcohol into the catholyte compartment of the electrolytic cell such that said first solution is in communication with the porous separator and the cathode;
(c) introducing a second solution comprising at least one alkali salt into the anolyte compartment of the electrolytic cell such that said second solution is in communication with the alkali ion conducting solid electrolyte and the anode;
(d) feeding a third solution comprising alkali alcoholate, alcohol and alkali salt into the buffer compartment;
(e) applying an electric potential to the electrolytic cell to cause alkali ions to pass through the alkali ion conducting solid electrolyte into the second buffer compartment and to cause alkali ions from the buffer compartment to diffuse through the porous separator into the catholyte compartment and to form alkali alcoholate in the catholyte compartment, wherein the alkali ion concentration in the buffer compartment remains substantially constant;
(f) maintaining the concentration of the alkali alcoholate in the catholyte compartment of the electrolytic cell between about 2% by weight and about 28% by weight of the contents of the catholyte compartment; and
(g) removing alkali alcoholate from the catholyte compartment.
2. The method according to claim 1 wherein the separator is porous ceramic or a polymer separator material.
3. The method according to claim 1 wherein the separator is alkali ion conducting solid electrolyte.
4. The method according to claim 1 wherein the alkali ion conducting solid electrolyte is a specific alkali ion conductor.
5. The method according to claim 1 , wherein the alcohol comprises one of the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, tert-amyl alcohol and combinations thereof.
6. The method according to claim 1 , wherein the alkali alcoholate comprises one of the group consisting of alkali methoxide, alkali ethoxide, alkali n-propoxide, alkali isopropoxide, alkali n-butoxide, alkali tert-butoxide, alkali tert-amoxide of sodium, lithium and potassium.
7. The method according to claim 1 , wherein the first solution and the third solution contain an alkali alcoholate selected from the group consisting of alkali methoxide, alkali ethoxide, alkali n-propoxide, alkali isopropoxide, alkali n-butoxide, alkali tert-butoxide, alkali tert-amoxide of sodium, lithium and potassium.
8. The method according to claim 1 , wherein the first solution and the third solution contain an alkali alcoholate comprising an alkali metal selected from Na, K and Li and mixtures thereof, in alcohol.
9. The method according to claim 1 , wherein the third solution contains an alkali salt of MX, where M is an alkali metal selected from Na, K, Li, and mixtures thereof, and X is an anion including, but not limited to, F − , Cl − , Br − , I − , OH − , NO 3 − , NO 2 − , SO 4 −2 , ClO 3 − , ClO 4 − , H 3 C 2 O 2 − , HCO 3 − , CO 3 −2 , HCOO − , PO 4 −3 , and C 6 H 5 O 7 −3 , and mixtures thereof.
10. The method according to claim 1 , wherein the second solution contains an alkali salt of MX, where M is an alkali metal selected from Na, K, Li, and mixtures thereof, and X is an anion including, but not limited to, F, Cl − , Br − , I − , OH − , NO 3 − , NO 2 − , SO 4 −2 , ClO 3 − , ClO 4 − , H 3 C 2 O 2 − , HCO 3 − , CO 3 −2 , HCOO − , PO 4 −3 , and C 6 H 5 O 7 −3 , and mixtures thereof.
11. The method according to claim 1 , wherein introducing a second solution into the catholyte compartment comprises a continuous operation.
12. The method according to claim 1 , wherein introducing a first solution into the anolyte compartment comprises a continuous operation.
13. The method according to claim 1 , wherein introducing a third solution into the buffer compartment comprises a continuous operation.
14. The method according to claim 1 , wherein introducing a first solution into the catholyte compartment comprises recycling at least a portion of the solution received from the catholyte compartment back into the catholyte compartment.
15. The method according to claim 1 , wherein introducing a second solution into the anolyte compartment comprises recycling at least a portion of the solution received from the anolyte compartment back into the anolyte compartment.
16. The method according to claim 1 , wherein introducing a third solution into the buffer compartment comprises recycling at least a portion of the solution received from the buffer compartment back into the buffer compartment.
17. The method according to claim 1 , wherein the concentration of the alkali alcoholate in the catholyte compartment of the electrolytic cell is maintained between about 2% by weight and about 20% by weight of the contents of the catholyte compartment.
18. The method according to claim 1 , wherein the concentration of the alkali alcoholate in the catholyte compartment of the electrolytic cell is maintained between about 5% by weight and about 13% by weight of the contents of the catholyte compartment.
19. The method according to claim 1 wherein the electrolytic cell is operated at a temperature of about 25° C. to about 50° C.
20. The method according to claim 1 wherein the electrolytic cell is operated at a temperature of about 40° C. to about 70° C.
21. The method according to claim 1 wherein the separator between the buffer compartment and the catholyte compartment is a porous polyethylene separator.
22. The method according to claim 1 wherein the separator between the buffer compartment and the catholyte compartment is a porous polypropylene, organic or ceramic oxide, material.
23. The method according to claim 1 wherein the separator between the buffer compartment and the catholyte compartment comprising an alkali ion conducting solid electrolyte.
24. The method according to claim 1 wherein the alkali ion conducting solid electrolyte separating the buffer compartment from the anolyte compartment is an organic or a polymer ion exchange membrane.
25. The method according to claim 1 wherein the alkali ion conducting solid electrolyte separating the buffer compartment from the anolyte compartment is a solid alkali metal ion super ion conducting material, wherein the alkali metal is Na, K, or Li.
26. The method according to claim 1 , wherein the alkali ion conducting solid electrolyte separating the buffer compartment from the anolyte compartment comprises a material having the formula M 1+x Zr 2 Si x P 3-x O 12 where 0≦x≦3, where M is Na, K, or Li.
27. The method according to claim 3 , wherein the alkali ion conducting solid electrolyte comprises a material having the formula Na 1+x Zr 2 Si x P 3-x O 12 where 0≦x≦3.
28. The method according to claim 3 , wherein the alkali ion conducting solid electrolyte comprises a material having the formula M 5 RESi 4 O 12 where M is Na, K, or Li, where RE is Y, Nd, Dy, or Sm, or any mixture thereof.
29. The method according to claim 3 , wherein the alkali ion conducting solid electrolyte comprises a non-stoichiometric alkali-deficient material having the formula (M 5 RESi 4 O 12 ) 1−δ (RE 2 O 3 .2SiO 2 ) δ , where M is Na, K, or Li, where RE is Nd, Dy, or Sm, or any mixture thereof and where δ is the measure of deviation from stoichiometry.
30. The method according to claim 3 wherein the said alkali ion conducting solid electrolyte is beta-alumina.
31. The method according to claim 1 , wherein the anolyte solution comprises a pH of greater than about 4.
32. The method according to claim 1 , wherein the buffer compartment solution comprises a pH of greater than about 4.
33. The method according to claim 1 , wherein the alkali ion conducting solid electrolyte operates at a current density of between about 20 mA/cm 2 and about 180 mA/cm 2 .
34. The method according to claim 1 , wherein the alkali ion conducting solid electrolyte operates at a current density of about 100 mA/cm 2 .
35. The method according to claim 3 wherein the alkali ion conducting solid electrolyte comprises a monolithic flat plate, a monolithic tube, a monolithic honeycomb, or supported structures of the foregoing.
36. The method according to claim 3 , wherein the alkali ion conducting solid electrolyte comprises a layered alkali ion conducting ceramic-polymer composite membrane, comprising sodium ion-selective polymers layered on alkali ion conducting ceramic solid electrolyte materials.