Crosslinked PVA-based hybrid membranes containing di-sulfonic acid groups for alkali recovery

Hybrid cation exchange membranes (CEMs) are prepared from polyvinyl alcohol (PVA), 3-mercaptopropyltriethoxysilane (MPTES) and benzaldehyde disulfonic acid disodium salt (BADSANa), which contains several functional groups like -OH, -SH/ -Si(OC2H5)3 and -SO3Na/ -CHO, etc. The availability of -CHO and -Si(OC2H5)3 groups are of immense importance as they can be easily cross-linked with PVA-OH groups through the acetal and sol-gel reaction. The -SH groups are further oxidized into the -SO3H groups in the presence of Fenton's reagent or ozone to make the membrane matrix charged. It has been observed that membrane hydrophilicity and ion exchange capacities gradually increase with the dosage of BADSANa and MPTES. The tensile strength of prepared membranes is in the range of 5.8-30.9 MPa while the elongation at break (Eb) of 118.9-447.2%. The short-term thermal stability is ranged between 165 and 275 °C. The alkali resistance is acceptable at room temperature. Diffusion dialysis (DD) process shows that if the prepared membranes are oxidized by Fenton's reagent, the dialysis coefficients of NaOH (UOH) in NaOH /NaAlO2 solution are in the range of 2.8-23.4 mm/h along with the separation factors (S) in between 4.6 and 20.0. The optimized membrane (M6B2-F) has both the highest S value of 20.0 and UOH as 23.4 mm/h. The similar separation performance can be achieved if the membranes are oxidized by ozone instead of Fenton's reagent. The ozone oxidation, the organic solvent free preparation, and the favorable DD performances may provide new clues for designing new cation exchange hybrid membranes for alkali recovery.