Study On Clean Production Of Organic Acids By Using Electrodialysis With Bipolar Membranes (EDBM)

This thesis comprises two sections. The first section deals with the competition between organic anions through anion exchange membranes, and the second verifies the feasibility of simultaneously regenerating formic acid and carbonic acid from oxalate discharge by using two-compartment EDBM. The conclusions drawn on the basis of the experiments are as follows:When EDBM is applied to the production of acetic, oxalic, and citric acids, the voltage drop across the stack decreases with an increase in the limit equivalent conductance of anion. Acid yield increases as salt concentration and current density increases. The permselectivity of the tested anions referenced to acetate ions are as follows: TOH-CH3COO- =0.1062, TC6H5O73-CH3COO-=2.481, and TCH3COO-OH- =9.416. Obviously, theanion exchange membrane has a permselectivity for anions in the following order: OH->CH3COO->C2O42->C6H5O73-. The higher the permselectivity, the more the anion migrates and the more the acid is produced. For BP-A configuration, as current density and salt concentration decreases, current efficiency increases and energy consumption decreases. The highest current efficiency could attain 75%; the energy consumptions of acetic acid, oxalic acid and citric acids were 3.8-15.7, 7.3-21.1, 8.1-22.7 k Wh kg-1, respectively. The highest current efficiency could attain 75%. The energy consumption had the following order: EBP-A>EBP-A-C>EBP-C, and Eacetic acid>Eoxalic acid>Ecitric acid.The best configuration was BP-C.It is feasible to simultaneously regenerate formic and carbonic acids from oxalate discharge by using two-compartment electrodialysis. The process performances were evaluated by considering such factors as the molar ratio of sodium formate to sodium carbonate, and current density. The results indicated that current efficiency could attain 72% and 21% for the generation of formic acid and carbonic acid, respectively. The energy consumption was 4.3-16.6 kWh kg-1 for formic acid and 20.1-96.3 kWh kg-1 for carbonic acid. When the molar ratio of sodium formate to sodium carbonate was in the range of 0.5-2, formate anions would be the main current carriers through the anion exchange membrane, and the molar concentration of formic acid could achieve 12 times that of carbonic acid in the product solution. This can be mainly ascribed to the high permselectivity of the anion exchange membrane for formate anions. Notably, a third competitive species - OH- - is not negligible in the acid reclaiming system by using EDBM.