Production of N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid by BMED process using porous P84 co-polyimide membranes

Anion exchange membranes are prepared by phase inversion of P84 co -polyimide to obtain porous structure, and then chemically modified by branched polyethylenimine. The porous membranes are compared with a dense P84 membrane. The dense membrane is hydrophobic with large area resistance (>85   Ω   cm 2 ), while the porous membranes are hydrophilic with low area resistance (2.4–3.5   Ω   cm 2 ), lower than that of commercial membrane CJMA-3 (6.0   Ω   cm 2 ). The ion exchange capacities are in the range of 0.83–0.86   mmol/g and the water uptake values are 90–130%, both of which are higher than those of dense P84 membrane and CJMA-3 membrane (0.5–0.6   mmol/g; 15–20%). The P84 co -polyimide membranes are utilized in bipolar membrane electrodialysis (BMED) process to produce N -2-hydroxyethylpiperazine- N ′-2-ethanesulfonic acid (HEPES). The porous membranes can decrease the transport resistance of HEPES − ions and yield high recovery ratio and current efficiency, while the dense membrane is unsuitable for BMED . The output of HEPES is increased significantly if the membranes have finger- or tear-like pores, as well as higher ion exchange capacity. The HEPES − recovery ratios are 52.3–61.6% after running 6   h under 40   V, which are higher than that of membrane CJMA-3 (46.5%). The current efficiency can reach up to 86.1% and the energy consumption is only 3.92   kWh/kg by using the optimal porous membrane M-1, which are better than membrane CJMA-3 (65.5%, 5.15   kWh/kg). Hence, the porous membranes have high potential for producing organic acid with high molecular weight.