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, for example a membrane selective for cations or anions. The invention is characterized in that the middle chamber comprises a mechanical stirring device. 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. With the aid of the mechanical stirring device, it is possible to stir the electrolyte solution in the middle chamber during the electrolysis. This leads to mixing of the electrolyte solution in the middle chamber, 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.

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 a mechanical stirring device < 120 >. 
 
     
     
         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   w  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 mechanical stirring device < 120 > comprises a propeller aligned parallel to the alkali metal cation-conducting solid-state electrolyte F K  < 111 >. 
     
     
         4 . The electrolysis cell E < 100 > according to  claim 1 , wherein the connection V AM  < 112 > is formed within the electrolysis cell E < 100 >. 
     
     
         5 . The electrolysis cell E < 100 > according to  claim 1 , wherein the mechanical stirring device < 120 > accounts 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 a mechanical stirring device < 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 the mechanical stirring device < 120 >. 
 
     
     
         6 . The electrolysis cell E < 100 > according to  claim 1 , wherein the mechanical stirring device < 120 > interrupts 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. 
     
     
         7 . 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 >, while the mechanical stirring device < 120 > stirs the solution L 3  < 114 > in K M  < 103 >, 
 (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. 
 
 
     
     
         8 . The process according to  claim 7 , wherein X is selected from the group consisting of Li + , Na + , K + . 
     
     
         9 . The process according to  claim 7 , wherein S is a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X. 
     
     
         10 . The process according to  claim 7 , wherein R is selected from the group consisting of methyl and ethyl. 
     
     
         11 . The process according to  claim 7 , wherein L 2  < 113 > comprises the alcohol ROH and an alkali metal alkoxide XOR. 
     
     
         12 . The process according to  claim 11 , wherein the mass ratio of XOR to alcohol ROH in L 2  < 113 > is in the range from 1:100 to 1:5. 
     
     
         13 . The process according to  claim 11 , wherein the concentration of XOR in L 1  < 115 > is 1.01 to 2.2 times higher than in L 2  < 113 >. 
     
     
         14 . The process according to  claim 7 , which is performed at a temperature of 20 to 70° C. and a pressure of 0.5 to 1.5 bar. 
     
     
         15 . The process according to  claim 7 , wherein the stirrer speed of the mechanical stirring device < 120 > is varied during the performance of step (b).