Separation of mixed amino acids by BMED process using porous SPES and SPSf cation exchange membranes

Porous sulfonated polyethersulfone and polysulfone (SPES and SPSf) cation exchange membranes were prepared by phase inversion process, in which water was used as the coagulation bath at 4   °C or 25   °C. Dense SPES and SPSf cation exchange membranes were also prepared for comparison. Characterizations of the membrane structure, morphology and physico-chemical properties showed that the dense membranes are hydrophobic with large area resistance (>80   Ω   cm 2 ), while the porous membranes are hydrophilic with low area resistance (0.35–18.62   Ω   cm 2 ). The porous SPSf membranes have lower area resistance (0.35–0.81   Ω   cm 2 ) than SPES membranes due to their higher water uptake (289.1–370.1%) and special morphology containing oval-shaped pores in the top skin layer. The membranes are utilized in bipolar membrane electrodialysis (BMED) process to separate the mixed amino acids of l -glutamic acid (Glu) and l -lysine (Lys). Though the dense membranes are unsuitable for electrodialysis experiments due to the large area resistance, the porous membranes have higher recovery ratio and current efficiency than the commercial membrane CMX, for the Lys + can migrate through the porous membranes with lower hindrance. In addition, the SPSf membranes have higher Glu leakage ratio (13.9–15.3%) and lower energy consumption (4.82–6.52   kWh/kg) than the SPES membranes (∼0%, 6.43–9.53   kWh/kg). What’s more, the water permeation can be controlled by membrane materials and pore structures.