Separation of acetic acid/water mixtures by pervaporation with composite membranes of sodium alginate active layer and microporous polypropylene substrate

A new kind of composite membrane for the pervaporation dehydration of acetic acid was prepared by casting sodium alginate (NaAlg) solution onto a microporous polypropylene membrane (MPPM) which possessed well-controlled porosity and excellent solvent resistance. The MPPM surface was modified by N2 plasma prior to the fabrication of the corresponding NaAlg-based composite membrane in order to improve its compatibility with the NaAlg active layer. The active layer of the NaAlg/MPPM composite membrane was then cross-linked with multivalent ions. This cross-linking behavior restricted the mobility of the polymer chains in the active layer and accordingly increased their relaxation time. Interestingly, the activation energy of the pervaporation process increased linearly with the relaxation time. Pervaporation results indicated that the prepared composite membranes exhibited desirable separation properties, and a good compromise between flux and separation factor was observed. For the separation of an 80/20 wt% acetic acid/water mixture at 50 °C, the Ca2+ cross-linked composite membrane (Ca-Alg/MPPM) displayed a separation factor of 631 and a flux of 653 g/m2 h, which surpassed most NaAlg-based homogeneous membranes and other composite membranes reported in the literature. These results suggest that the prepared composite membranes have promising potential for acetic acid dehydration.