Method for production of succinic acid and sulfuric acid by paired electrosynthesis

Abstract

A method for the production of succinic acid and sulfuric acid by paired electrolytic synthesis is disclosed in the present invention. The method is described as following: in cathodic compartment of an electrochemical cell separated with cation exchange membrane, maleic acid or maleic anhydride is used as raw material, sulfuric acid as the cathodic reactant and the supporting electrolyte of the reaction system, succinic acid is thus synthesized by the electro-reduction reaction at cathode. In anodic compartment, the aqueous sulfuric acid solution containing iodide ion is used as electrolyte, iodide ion is anodized to form I 2 and I 3 − . SO 2 gas is fed into the circulated anolyte, reacting with I 2 and I 3 − to form sulfuric acid and regenerate iodide ion. Simultaneously the evaporated hydroiodic acid and distilled water are returned to the anolyte circulation system. The cell voltage and the cost of production are reduced significantly.

The invention claimed is: 
     
         1 . A method for the production of succinic acid and sulfuric acid by paired electrolytic synthesis comprising: inside cathodic compartment of an electrochemical cell separated with cation exchange membrane, maleic acid or maleic anhydride is used as raw material, sulfuric acid as the cathodic reactant and the supporting electrolyte of the reaction system, succinic acid is thus synthesized by the electro-reduction reaction at cathode. When the extent of electrolysis reaction reaches a certain degree, catholyte is taken out and post-processed to obtain succinic acid. In anodic compartment, the aqueous sulfuric acid solution containing iodide ion is used as electrolyte, iodide ion is anodized to form I 2  and I 3   − . SO 2  gas is fed into the circulated anolyte, reacting with I 2  and I 3   −  through redox reaction to form sulfuric acid and regenerate iodide ion in anolyte. When the concentration of sulfuric acid in the anolyte reaches a certain degree, the anolyte is taken out to be concentrated to obtain sulfuric acid of high concentration. Simultaneously, the hydroiodic acid and the distilled water evaporated from the anolyte are returned to the anolyte circulation system. 
     
     
         2 . The method of  claim 1 , wherein inside said electrochemical cell, graphite or titanium-supported RuO 2 —TiO 2  electrode is used as anode, lead or lead alloys as cathode. The distance between the cathode and the anode is 5˜50 mm. 
     
     
         3 . The method of  claim 1 , wherein during the process of electrolysis reaction, the concentration of reactants in said catholyte is controlled as following: sulfuric acid 0.5˜3 mol/L, maleic acid 0.5˜3 mol/L; the concentration of reactants in said anolyte as following: sulfuric acid 0.5˜7 mol/L, iodide ion 0.5˜4 mol/L. The molar ratio of the total amount of I 2  and I 3   −  generated through the anodic reaction to SO 2  fed from outside is controlled at 1:(1˜1.5). 
     
     
         4 . The method of  claim 3 , wherein the current density of cathode and anode is controlled at 300˜1200 A/m 2  and 300˜1500 A/m 2 , respectively. 
     
     
         5 . The method of  claim 1 , wherein the post-processing of said catholyte after electrolysis reaction comprising: said catholyte thus obtained is cooled, precipitated, filtered, rinsed, dried to obtain succinic acid; the mother liquor from filtration is returned to said cathodic compartment after supplementing maleic acid or maleic anhydride. 
     
     
         6 . The method of  claim 1 , wherein the temperature of said electrolysis reaction is controlled at the range of 20-70° C. 
     
     
         7 . The method of  claim 1 , wherein the temperature of said electrolysis reaction is controlled at the range of 30-50° C. 
     
     
         8 . The method of  claim 1 , wherein said paired electrolytic synthesis is operated in two modes: batch-type and continuous-type.