Separation of xylene mixtures using polyurethane-zeolite composite membranes

Fractionation of o- and p-xylene isomeric mixtures was performed using pervaporation (PV) with polyurethane (PU) membranes containing ZSM zeolite. The xylene vapor sorption isotherms exhibited a Henry's law relationship in this PU-zeolite blend. In binary solutions the individual xylene uptake was also proportional to the solvent composition. Although incorporating zeolite into the PU-zeolite membrane rendered a decrease in xylene solubility as compared with that sorbed in the PU film without zeolite addition, the diffusion coefficient and diffusivity selectivity increases enhanced the separation efficiency using the PU-zeolite blend. The PU-zeolite membrane outperformed other membrane materials in terms of resulting permeability and selectivity. The effects of operating temperature and zeolite concentration on the permeability and selectivity of PV processing were studied. Increasing the operating temperatures enhanced the xylene fluxes. The activation energy was 3.55 kJ/mol for o-xylene and 16.14 kJ/mol for p-xylene. The xylene flux and selectivity were increased with increasing zeolite content.