Synthesis Of SPEEK Cation Exchange Membrane And Its Application In Preparing Thioglycolic Acid By Electroreduction

Organic electrosynthesis is promising new synthesis technology to avoid the contamination produced by traditional organic synthesis.As the key part of organic electrosynthesis equipment,ion exchange membrane currently used in organic electrosynthesis are perfluorinated polymers such as Nafion.Even though such membranes have demonstrated good performance and long-term stability,their high cost and low current efficiency make them unpractical for large-scale production.Sulfonated poly(arylene ether ether ketones)(SPEEK)base cation exchange membrane have been studied due to their good mechanical properties,thermal stability and ion-exchange capacities(IEC).Usually SPEEK membranes as proton exchange membrane were used in proton exchange membrane fuel cells,and it was rarely used in organic electrosynthesis.In this paper,4,4-dichlorobenzophenone and 4,4-difluorobenzophenone were sulfonated successfully using fuming sulfuric acid(～50%SO₃).The substitution position of the sulfonic group were confirmed by FT-IR,¹H NMR and ¹H-¹H COSY. These monomers and Bisphenol A were converted to SCPEEK and SPEEK by nucleophilic displacement polycondensation in the presence of potassium carbonate in DMSO or in DMAc.We found it is difficult for SCPEEK to be film forming.SPEEK was selected as the material of cation exchange membrane.The chemical structures of the polymers were confirmed by FT-IR and ¹H NMR.According to the properties of SPEEK membranes with different sulfonation degree(DS),the SPEEK membrane with DS of 120%exhibited water content of 26.45 %,IEC of 2.0225 meq/g and good tensile strength,thermal stability,dimensional stability,H⁺ penetrability.So SPEEK120 membrane was chosen as Electrolysis Diaphragm in the electrolysis cell to produce thioglycolic acid(TGA).The influences of temperature,current density,the time of electrolysis and concentration of anolyte on the reaction were studied.The experiment result showed that the mixture of TGA and DTDGA as electrolyte in the cathodic room,30%H₂SO₄ as anolyte,lead electrode as cathode and anode,the reactive temperature was 30℃,current density was 15 mA/cm², electrolysis time was 60 min.Under this condition,the current efficiency was up to 59.89%.Comparing with the traditional zinc powder reduction method,the electroreduction technology saved the costly zinc powder and eliminated the pollution to environment.