Pervaporation Separation of Water–Isopropanol Mixtures Using ZSM-5 Zeolite Incorporated Poly(vinyl alcohol) Membranes A. A. Kittur, 1 M. Y. Kariduraganavar, 1 U. S. Toti, 1 K. Ramesh, 2 T. M. Aminabhavi 1 1 Center of Excellence in Polymer Science, Karnatak University, Dharwad 580003, India 2 Department of Physics, Indian Institute of Science, Bangalore 560012, India ABSTRACT: A solution technique was employed to pre- pare ZSM-5 zeolite incorporated poly(vinyl alcohol) (PVA) membranes for the pervaporation separation of water–iso- propanol mixtures. The membranes were characterized by Fourier transform infrared spectroscopy and differential scanning calorimeter. Glass transition temperatures of the membranes varied from 102 to 110°C, with increasing zeolite content of the membrane. The effect of zeolite loading and feed composition on pervaporation performance of the membranes was analyzed. The membrane containing 6 mass % of zeolite gave the highest separation selectivity of 216 for 10 mass % of water containing feed mixture at 30°C. Increase in water selectivity of the membrane was explained as due to a reduction in free volume by increasing zeolite content of the membrane. Separation selectivity and permeation flux data are dependent on water composition of the feed mix- ture, but are comparatively less dependent on temperature. The hindrance of water permeation at higher composition of water in the feed mixture was explained as due to the formation of clusters of water molecules. The overall activa- tion energy and preexponential factors were calculated us- ing Arrhenius equation. Pervaporation data have also been explained on the basis of thermodynamic parameters calcu- lated by using Arrhenius equation as well as relationship proposed by Ping et al. Key words: separation techniques; membranes; zeolites; se- lectivity; activation energy INTRODUCTION Among the many aqueous– organic mixtures, separa- tion of water from its mixture with isopropanol is a challenging task, because the system forms an azeo- trope at 14.7 mass % of water; 1 hence, its separation by conventional distillation is not feasible. In contrast, the pervaporation (PV) separation technique, being en- ergy efficient, has been used widely to separate azeo- tropes even on a large scale. 2–4 In PV, the feed mixture is placed in contact with one side of the membrane while the vapor permeate is removed from the oppo- site side using a vacuum. The chemical potential gra- dient across the membrane is the driving force for the molecular transport. PV has several advantages over the conventional distillation, 5 including reduced en- ergy demand (only a fraction of the liquid is vapor- ized), and is eco-friendly in nature. In PV separation studies of aqueous– organic mix- tures, several types of membranes have been used including those of blends, composites, etc. In an earlier study, 6 the blend membranes of sodium alginate with PVA have been employed to separate water–isopro- panol mixtures. However, flux and selectivity of these membranes were not satisfactory. In an effort to in- crease the flux and selectivity of the membranes, many studies have been made to incorporate metal com- plexes and zeolites in the membranes. 7–11 The zeolite- incorporated polymer membranes have received much attention recently in gas and PV separation studies. 8,9 The incorporation of zeolite or porous fillers in dense membrane can improve the separation per- formance of the membranes 7–11 due to combined effect of molecular sieving action, selective adsorption, and difference in diffusion rates. In addition, zeolites have high mechanical strength, good thermal and chemical stability, and thus, the membranes, when incorpo- rated with these fillers, can be used over the wide range of operating conditions. Silicalite and ZSM-5 zeolites having the MFI-type structures have been widely studied in membrane applications. 12–15 Silicalite is a pure silica zeolite hav- ing straight channels interconnected by zigzag chan- nels. The straight channels in ZSM-5 zeolite are ellip- tical, with an opening of 0.51  0.57 nm, and the Correspondence to: M. Y. Kariduraganavar (mahadevappak@ yahoo.com). Contract grant sponsor: Department of Science and Tech- nology, New Delhi; contract grant number: SP/S1/H-31/ 2000