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

Abstract

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 (>85Ωcm2), while the porous membranes are hydrophilic with low area resistance (2.4–3.5Ωcm2), lower than that of commercial membrane CJMA-3 (6.0Ωcm2). The ion exchange capacities are in the range of 0.83–0.86mmol/g and the water uptake values are 90–130%, both of which are higher than those of dense P84 membrane and CJMA-3 membrane (0.5–0.6mmol/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 6h under 40V, 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 3.92kWh/kg by using the optimal porous membrane M-1, which are better than membrane CJMA-3 (65.5%, 5.15kWh/kg). Hence, the porous membranes have high potential for producing organic acid with high molecular weight.