Three-chamber electrolytic cell for the production of alkali metal alkoxides

Abstract

The present invention relates, in a first aspect, to an electrolysis cell having three chambers, wherein the middle chamber is separated from the cathode chamber by a solid-state electrolyte permeable to cations, for example NaSICON, and from the anode chamber by a diffusion barrier. The invention is characterized in that the middle chamber comprises internals.The electrolysis cell according to the invention solves the problem that a concentration gradient forms in the middle chamber of the electrolysis cell during the electrolysis, which leads to locally lowered pH values and hence to damage to the solid-state electrolyte. The internals result in vortexing of the electrolyte solution as it flows through the middle chamber during the electrolysis, which prevents the formation of a pH gradient.In a second aspect, the present invention relates to a process for producing an alkali metal alkoxide solution in the electrolysis cell according to the invention.

The invention claimed is: 
     
         1 . An Electrolysis cell E <100> comprising at least one anode chamber K A  <101>, at least one cathode chamber K K  <102> and at least one interposed middle chamber K M  <103>,
 wherein K A  <101> comprises an anodic electrode E A  <104> and an outlet A KA  <106>, 
 wherein K K  <102> comprises a cathodic electrode E K  <105>, an inlet Z KK  <107> and an outlet A KK  <109>, 
 wherein K M  <103> comprises an inlet Z KM  <108>, is divided from K A  <101> by a diffusion barrier D <110> and is divided from K K  <102> by an alkali metal cation-conducting solid-state electrolyte F K  <111>, 
 wherein K M  <103> and K A  <101> are connected to one another by a connection V AM  <112> through which liquid can be routed from K M  <103> into K A  <101>, 
 wherein the middle chamber K M  <103> comprises internals <120>, wherein the internals <120> are configured to lead to turbulence and vortexing in an electrolyte L 3  <114> that flows through the middle chamber K M  <103>. 
 
     
     
         2 . The electrolysis cell E <100> according to  claim 1 , wherein the alkali metal ion-conducting solid-state electrolyte F K  <111> has a structure of the formula M I   1+2w+x−y+z M II   x M III   x Zr IV   2−w−x−y  M V   y  (SiO 4 ) z (PO 4 ) 3−z ,
 where M I  is selected from Na +  and Li + , 
 M II  is a divalent metal cation, 
 M III  is a trivalent metal cation, 
 M 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 0≤x<2,0≤y<2,0≤w<2,0≤z<3, 
 and where w, x, y, z are chosen such that 1+2w+x−y+z≥0 and 2−w−x−y≥0. 
 
     
     
         3 . The electrolysis cell E <100> according to  claim 1 , wherein the internals <120> are selected from the group consisting of trays, structured packings, unstructured packings. 
     
     
         4 . The electrolysis cell E <100> according to  claim 1 , wherein the internals <120> comprise at least one material selected from rubber, plastic, glass, porcelain, metal. 
     
     
         5 . The electrolysis cell E <100> according to  claim 1 , wherein the connection V AM  <112> is formed within the electrolysis cell E <100>. 
     
     
         6 . The electrolysis cell E <100> according to  claim 1 , wherein the internals <120> account for a proportion ζ of 1% to 99% of the volume encompassed by the middle chamber K M ,
 wherein ζ=[(V O −V M )/V O ]*100, 
 and wherein V O  is the maximum volume of liquid that can be accommodated by the middle chamber K M  <103> if it does not comprise internals <120>, 
 and wherein V M  is the maximum volume of liquid that can be accommodated by the middle chamber K M  <103> if it comprises internals <120>. 
 
     
     
         7 . The electrolysis cell E <100> according to  claim 1 , wherein internals <120> interrupt the direct pathway in the middle chamber K M  between inlet Z KM  <108> and connection V AM  <112> according to the thread test stated in the description. 
     
     
         8 . The process for producing a solution L 1  <115> of an alkali metal alkoxide XOR in the alcohol ROH in an electrolysis cell E <100> according to  claim 1 ,
 wherein the process comprises the following steps (a), (b) and (c) that proceed simultaneously: 
 (a) a solution L 2  <113> comprising the alcohol ROH is routed through K K  <102>, 
 (b) a neutral or alkaline, aqueous solution L 3  <114> of a salt S comprising X as cation is routed through K M  <103>, then via V AM  <112>, then through K A  <101>, 
 (c) voltage is applied between E A  <104> and E K  <105>, 
 which affords the solution L 1  <115> at the outlet A KK  <109>, with a higher concentration of XOR in L 1  <115> than in L 2  <113>, 
 and which affords an aqueous solution L 4  <116> of S at the outlet A KA  <106>, with a lower concentration of S in L 4  <116> than in L 3  <114>, 
 wherein X is an alkali metal cation and R is an alkyl radical having 1 to 4 carbon atoms. 
 
     
     
         9 . The process according to  claim 8 , wherein X is selected from the group consisting of Li + , Na + , K + . 
     
     
         10 . The process according to  claim 8 , wherein S is a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X. 
     
     
         11 . The process according to  claim 8 , wherein R is selected from the group consisting of methyl and ethyl. 
     
     
         12 . The process according to  claim 8 , wherein L 2  <113> comprises the alcohol ROH and an alkali metal alkoxide XOR. 
     
     
         13 . The process according to  claim 12 , wherein the mass ratio of XOR to alcohol ROH in L 2  <113> is in the range from 1:100 to 1:5. 
     
     
         14 . The process according to  claim 12 , wherein the concentration of XOR in L 1  <115> is 1.01 to 2.2 times higher than in L 2  <113>. 
     
     
         15 . The process according to  claim 8 , which is performed at a temperature of 20 to 70° C. and a pressure of 0.5 to 1.5 bar. 
     
     
         16 . The process according to  claim 8 , wherein the flow rate of the electrolyte L 3  <114> through the middle chamber K M  <103> is varied during the performance of step (b).