An optimized process for treating sodium acetate waste residue: Coupling of diffusion dialysis or electrodialysis with bipolar membrane electrodialysis

The sodium acetate waste residue produced by insecticide factories contains mostly CH3COONa (similar to 76.6 wt%) and other organic impurities, and had been treated by bipolar membrane electrodialysis (BMED) to generate CH3COOH and NaOH. Nevertheless, the energy consumption was high (22.3 kWh/kg for CH3COOH and 29.7 kWh/kg for NaOH) and the purity of products was insufficient, as the total organic carbon (TOC) was 1.61 g/L and 0.16 g/L in acid and base compartments respectively. Accordingly, the BMED was coupled with diffusion dialysis (DD) or electrodialysis (ED) here to obtain an optimized process. The DD or ED was used to purify the waste residue, which had the advantage of low energy consumption or high capacity. Then the purified solution was taken for BMED to produce C3COOH and NaOH. The coupled process showed that the product purities were improved, and the apparent energy consumption (E-app) was reduced. Coupling of BMED with DD process could have the output of 0.33 mol/L CH3COOH and 0.35 mol/L NaOH, current efficiency of 85.5% for CH3COOH and 93.7% for NaOH. The TOC values were 0.52 g/L and 0.04 g/L in acid and base compartments respectively, and the E-app for BMED process was reduced to 11.7 kWh/kg CH3COOH and 16.0 kWh/kg NaOH. Meanwhile, the BMED process after coupling with ED had Eapp of 7.4 kWh/kg CH3COOH and 10.4 kWh/kg NaOH, and could yield products with TOC values of 0.13 g/L and 0.01 g/L in acid and base compartments respectively. In summary, the optimized DD-BMED or ED-BMED process for treating sodium acetate waste residue has significant advantages as compared with direct BMED process. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.