Cation exchange PVA/SPPO/SiO2 membranes with double organic phases for alkali recovery

Cation exchange hybrid membranes are prepared from sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO), polyvinyl alcohol (PVA) and tetraethoxysilane (TEOS). The membranes contain double organic phases of PVA and SPPO, and thus can combine their advantages of organic solvent resistance and ion exchange property. The SPPO phase is encapsuled in PVA/SiO2 matrix, and thus the crosslinking degree of PVA/SiO2 matrix decreases. The hybrid membranes have the ion exchange capacities (IECs) of 0.44–1.34 mmol/g, and are stable in ethanol. The ethanol uptake (ER) is in the range of 1.3–21.3%, and the swelling degree in 65 °C ethanol is in the range of 7.5–54.5%. The membranes have the tensile strength (TS) of 30–70 MPa, with the elongation at break (Eb) of 5–13%. The initial decomposition temperatures are all higher than 220 °C. Diffusion dialysis (DD) test indicates that, the membranes can be potentially applied for alkali recovery. The dialysis coefficient of NaOH (UOH) is in the range of 0.007–0.013 m/h, and the highest separation factor (S) can reach up to 181. The DD performance may be influenced by three aspects, including membrane hydrophilicity, IEC and the interstices between PVA and SPPO phases. Methods of aldehyde crosslinking and ethanol swelling are compared to enhance membrane stability, and the ethanol swelling is more beneficial to DD process.