Study On The Process And Kinetics For Electro-Synthesis Of Glyoxlic Acid From Oxalic Acid

Glyoxylic acid is one of the most important chemicals and intermediate, which is widely used in the field of chemical engineering especially in Pharmaceuticals. In this paper, industrial oxalic acid is taken as the raw material, and the experiments is carried out continuously in an ion-exchange membrane electrolytic bath with certain reaction-area surface of single pole and larger volume of the electrolyte. The optimally technical conditions for practice is primarily studied. Further more, the mechanism of the electrolysis process has been investigated, then a macroscopically kinetic model is built.First of all, the experiments were carried out in an electrolytic bath of one ion-exchange membrane and two chambers with electrolysis area 10 cm×10 cm .The influences of flow rate on current efficiency, the influences of electrode material, cation exchange membrane, and condition of electrolysis including the concentration of the materials, the current density, temperature, and the time of electrolysis on the process were studied. The results show that efficiency is better when NF-1 is cation exchange membrane, lead electrode is cathode and Ta-Ir electrode is anode. In the optimized condition of electrolysis is NF-1 cation exchange membrane, lead electrode as cathode and Ta-Ir electrode as anode ,under temperature 25 ℃,current density 1000 A/m~2 , flow rate 2 L/min, and electrolysis time 4.5 h. Under this condition, the electrical energy cost is 3038.9 Kwh/t. These data are of value for industrial design.The mass-transfer coefficient was calculated and compared with the chemical reaction kinetic constants under the temperature of 17-30℃ and the electric current density 800～1400 A/m~2 with other conditions the optimums, which shows that the electro-chemical reaction is the rate-determining step of the whole process. Four possible electro-chemical reaction mechanism were examined, and the most reasonable mechanism is decided as follows,Which A stands for oxalic acid, B for glyoxylic acid, and D for glycollic acid. The kinetic equations from glyoxylic acid to glyoxylic acid are:Which,The mean relative deviation of the calculation of the correlation equation is less than 2.02%, and the models has a good value for the industrial application.