Swelling behavior of palygorskite–polyacrylamide hybrid membrane in xylene mixtures and its pervaporation performance for separating the xylene isomers

Palygorskite–polyacrylamide (PGS–PAM) hybrid materials were synthesized via intercalation polymerization initiated by redox initiator consisting of modified PGS (reducer) and ceric salt Ce4+ (oxidant), and used as pervaporation membranes. The swelling behavior of hybrid membranes was investigated in single xylene isomer (p-xylene, m-xylene and o-xylene), binary xylene isomer mixtures (p-/o-xylene (the mixtures of p- and o-xylene), o-/m-xylene (the mixtures of o- and m-oxylene) and p-/m-xylene (the mixtures of p- and m-xylene)) and ternary isomer mixture (p-/m-/o-xylene (the mixtures of p-, m- and o-xylene)). A maximum value of degree of swelling at equilibrium (DSequilibrium) in single xylene isomer at 30 °C exhibited for the hybrid membrane with 1.92 wt% PGS. Negative deviation and both negative and positive deviations of the DSequilibrium based on the addition rule existed in binary or ternary xylene isomer mixtures respectively for hybrid membranes with different PGS content at 30 °C. Also, a maximum value of separation factor of the hybrid membrane revealed for each pair of binary xylene isomer mixtures when the PGS content was 1.92 wt% in the hybrid membrane. A reversion of the preferential selectivity and a high permeation activation energy of the hybrid membrane occurred at the concentration region with high p-xylene content in the p-/m-xylene binary xylene isomer mixtures. The swelling behavior and pervaporation performance of PGS–PAM hybrid membranes were discussed in terms of the entrapping channel in the PGS for the potential introduction of xylene isomers, the interaction between xylene isomers in feed and the solution–diffusion mechanism in the pervaporation process.