Poly (acrylonitrile-co-methyl acrylate) copolymer designated as PANMA was used for making pervaporation membrane. This membrane was used for separation of acetic acidwater mixtures over the concentration range of 8099.5 wt% acetic acid in water. Interaction parameters based on FloryHuggins lattice model and engaged species induced clustering (ENSIC) model was used to explain swelling of the membranes. Coupling in sorption was explained in terms of activity coefficient of water and acid in feed and membrane using FloryHuggins model and also by interpolating ENSIC parameters. Flow coupling in pervaporation was also determined from phenomenological deviation coefficients. Intrinsic membrane properties like partial permeability and membrane selectivity of the solvents were also determined. Diffusion coefficient and plasticization coefficient of the solvents were obtained using a modified solutiondiffusion model. The copolymer membrane showed high flux and water selectivity for highly concentrated acid. Thus, at 30 degrees C temperature 120 wt% water in feed was concentrated to 8284 wt% water in permeate and for 0.95 wt% water in feed, the membrane showed thickness normalized flux and water selectivity of 1.71 kg m2 h1 m and 409, respectively. OLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers