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 Omega cm(2)), while the porous membranes are hydrophilic with low area resistance (2.4-3.5 Omega cm(2)), lower than that of commercial membrane CJMA-3 (6.0 Omega 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. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.