Role of ZDC/S ratio for pervaporative separation of organic liquids through modified EPDM membranes: rational mechanistic study of vulcanization

Abstract

Ethylene propylene diene monomer (EPDM) was crosslinked by conventional (CV), semi-efficient (SEV) and efficient (EV) vulcanization techniques with different weight ratios of accelerator (A) and sulphur (S) to report three new crosslinked membranes designated as EPDMCV, EPDMSEV and EPDMEV, respectively. These membranes were characterized through measurements of crosslink density and mechanical properties: XRD, TGA, DTG, FTIR, FESEM and EDX. All possible EPDM based mono-, di- and poly-sulphide vulcanized products formed from crosslinking precursors in sulphur-only and accelerated sulphur vulcanization mechanisms through radical and/or ionic paths have been incorporated to remove ambiguity of the reaction mechanism. These membranes were used for pervaporative separation of toluene/methanol mixtures, up to 26 wt% of toluene in methanol. A new approach of optimizing membrane efficiency for pervaporative separation using different weight ratios of A/S, which can affect the crystallinity of the rubber membranes, were studied by measuring flux, separation factor (SF), activation energy of permeation and interaction parameters (IPs). To avoid confusion in understanding the membrane property variations with different sets of conditions, the intrinsic membrane properties like partial permeability and membrane selectivity (MS) were also studied. With increases in the A/S weight ratios from EPDMCV to EPDMEV, the vulcanization system resulted in higher degrees of crosslink density and permeation selectivity of toluene. These membranes showed an excellent balance of normalized flux (0.43 ± 0.011 kg μm m⁻² h⁻¹) and SF (254.73 ± 6.37) at 5.24 wt% of toluene in a feed at 30 °C.