Effect of the operation variables on the wettability of membrane and the performance in membrane distillation process

Abstract

In this study, membrane distillation was investigated to develop an effective separation process of dilute volatile organic compound from aqueous stream, and purification process for water/nonvolatile mixture. This study consisted of three branches, First, the wettability of hydrophobic membranes was investigated to determine the upper limit concentration of isopropanol using direct contact membrane distillation. The effect of operation variables on the wettability factor of membrane was also investigated. Second, the effect of operation variables on the flux and selectivity in air gap membrane distillation was investigated. A predictive model was also proposed based on the first principles of heat and mass transfer. Third, the effect of operation variables on the removal rate of isopropanol from aqueous solution was investigated using vacuum membrane distillation. The analysis of experimental results was performed by the evaluation of overall mass transfer coefficients. Details of each branch were summarized as follows. A simple method is described for the determination of the wettability of polyvinylidenefluoride (PVDF) and polytetrafluoroethylene (PTFE) membranes used in membrane distillation modules. This very simple in-situ method in termed the “pH method”. A wettability factor which varies from 0 to 1 is defined, and this factor is determined by the measurements of pH in feed and permeate reservoir. With water/isopropanol mixtures, effects such as the feed temperature, the pore size and the surface energy of membrane were shown to seriously affect wettability of flat membranes. Using this technique, the isopropanol concentration start to be wetted $C_{p,pc}$, were determined with different operating conditions. On PTFE 0.2㎛ membrane, a value of $C_{p,pc}$ was about 410 g/L at 37℃,and the value of $C_{p,pc}$ is reduced with increasing feed temperature. Membrane distillation was investigated as a possible technique for separation of nonvolatile/volatile co...