Pervaporation of methanol/MTBE/C5 ternary mixtures through the CA membrane

The pervaporation separation properties for the MTBE/C5/methanol ternary system and three corresponding binary mixtures were measured with a cellulose acetate membrane. It was found that there are very high pervaporation properties for methanol/C5 (the flux of methanol >430 g/m2.h). However, the flux of methanol for methanol/MTBE is lower than 90 g/m2.h. The methanol concentrations in the permeate are similar for the two binary mixtures. From the result of ternary mixtures, the flux of methanol decreased from about 450 to 100 g/m2.h, with an increase of MTBE concentration in the feed from 5 to 50 wt%, and there is a strong accompany effect between methanol and MTBE. Based on Fick’s law and the accompany effect, the models of pervaporation flux and quasi-phase equilibrium of permeate components for the ternary mixture were advanced. The calculated values agreed with the experiment results. The models will be useful for separation process design of the MTBE/C5/methanol ternary mixture.

1. The high separation efficiencies can be obtained for the methanol/C5 mixture through the CA membrane. However, for the methanol/MTBE mixture, there are a low methanol flux and a high separation selectivity, and the membrane cannot be used for separation of MTBE/C5 mixture. 2. For the methanol/MTBE/C5 ternary mixture, the flux of methanol will decrease, with increasing MTBE concentration in the feed. There is an accompany effect between methanol and MTBE. 3. The calculated values of the flux model and the quasi-phase equilibrium agree with the experiment results. The average errors are less Bij — Accompany coefficient of component j to i in the binary mixture Bijk — Accompany coefficient of component j and k to i in the ternary mixture — Distribution coefficient of component i Cij between the conjoint layers of the membrane D — Diffusion coefficient of the component in the membrane, g.mm/m2.h Fij — Constant, defined by Cij and ki J — Flux, g/m2.h Ki — Permeability coefficient of component i in the membrane, g.mm/m2h — Adsorption coefficient of the component ki in the membrane surface l — Membrane thickness, mm Pi, Pis — Partial pressure and saturation pressure of component i, respectively, kPa Si — Proportionality constant between molar fraction and partial pressure of component i, 1/KPa Vi, VT — Molar volume of component i and total volume, respectively, cm3/mol xi — Mass fraction of component i in the feed Xi — Mass fraction of component i in the membrane — Mass fraction of component i in the yi permeate α — Separation factor δ — Hansen’s solubility parameter, MPa1/2 ηi — Selection coefficient of component i in the membrane µ — Chemical potential ϕi — Volume fraction of component i