Polyurethane (PU) membrane preparation with and without hydroxypropyl-β-cyclodextrin and their pervaporation characteristics

The objective of this research was to synthesize polyurethane (PU) membranes containing hydroxypropyl-β-cyclodextrin (HP-β-CD) and investigate their pervaporation properties on benzene/cyclohexane (Bz/Cx) separation. PU membranes were synthesized from polypropylene oxide (PPO), 4,4′-diphenylmethane diisocyanate (MDI), and 1,4-butanediol (BD) via a two-step polymerization process. The PU and CD/PU hybrid membranes were benzene-selective in nature. The membranes synthesized from lower molecular weight polyol (PPO1000) produced better results than the higher molecular weight polyol (PPO2000) analogue. The sorption selectivity of the membranes in binary mixtures was much higher than the sorption ratio of pure liquids. A competitive sorption mechanism was observed. Membranes containing HP-β-CD yielded higher sorption selectivity due to greater Cx sorption suppression. Incorporating HP-β-CD in the membrane also increased the Bz diffusivity inside the membrane. Thus, HP-β-CD addition plays a two-fold benefit: enhancing the sorption selectivity and increasing the permeation flux on Bz/Cx mixtures. The CD/PU membrane demonstrated excellent Bz permeation flux (much higher flux compared with literature results) while maintaining good separation selectivity.