Simultaneous regeneration of formic acid and carbonic acid from oxalate discharge by using electrodialysis with bipolar membranes (EDBM)

The feasibility was tested on simultaneous generation of formic acid and carbonic acid from oxalate discharge by using two-compartment electrodialysis with bipolar and anion exchange membranes. 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.