In situ ion substitution of sodium gluconate: Comparison of bipolar membrane electrodialysis and electro-membrane reactor for producing gluconic acid

Based on the home-made cation-exchange membrane (CEM) and bipolar membrane (BPM), electrodialysis with bipolar membrane (EDBPM) and electro-membrane reactor with three compartments (EMR-3) were developed to achieve in situ ion substitution and recovery of gluconic acid (GLH) from its sodium salt. Physicochemical and electrochemical properties of CEM and BPM were studied to assess their suitability under standard operating conditions. Results showed that the proposed EMR-3 proved a promising tool for in situ ion substitution of GLNa with high current efficiency: CE (93%), and low energy consumption (1.28 kWh/kg of GLH produced). The EMR-3 process performances were dependent on GLNa feed concentration in the central compartment (CC), applied current density and electrochemical properties of CEM/BPM. Furthermore, high CE, recovery of GLH and low energy consumption of EMR-3 in comparison with EDBPM revealed its ion substitution of GLNa. It was concluded that EMR-3 is a more efficient process in comparison with EDBPM for in situ ion substitution of GLNa producing GLH. The production of NaOH as a byproduct in the cathode stream is a spinoff of the EMR-3 and EDBPM.