Pervaporation membrane module design

Pervaporation is a separation process in which a liquid mixture contacts a selective membrane. Some of the liquid evaporates across the membrane. A vacuum pump or an inert gas sweep then removes this vapor from the other side of the membrane. Finally, it is collected by a condenser. This process has selectivity not only from evaporation but also from the membrane. Thus, extremely high selectivities are possible.; Our research has been in three main areas: flat sheet membrane modules, lumen flow hollow fiber modules, and external flow hollow fiber modules.; We conducted pervaporation experiments on flat sheet modules to gain property data for a polydimethylsiloxane (PDMS) membrane separating chloroform from water. These experiments gave us the ideal separation as well as the permeability of chloroform in PDMS. This permeability turns out to be concentration dependent.; We experimented with several different lumen flow hollow fiber designs, measuring their performance. By varying the liquid velocity, we measured the membrane resistance and the liquid boundary layer resistance. Using the flat sheet results with nitrogen permeability, we calculated a membrane resistance, finding it to be similar to the measured value. We found a correlation for the boundary layer resistance of lumen flow in the transitional region from laminar to turbulent that is reproducible although differing from other mass transfer results.; External flow, however, offers greater potential for small boundary layers. We constructed an external flow module using baffles to direct the liquid flow back and forth across the fibers as it flowed down the module, since cross flow offers the best mass transfer. We characterized the performance of this design, finding it to be dominated by cross flow mass transfer, which agrees with other heat and mass transfer experiments.; We also carried out experiments evaluating the effect of vapor resistance on separation. We looked at both the location of vacuum and the addition sweep to the vacuum. We found that, even under extreme conditions, these had no effect. We concluded that the vapor side resistance is negligible.; We examined the effect of polydispersity mathematically. Polydispersity reflects the fact that hollow fibers in a module differ from one another. We analyzed several forms of diameter variation between fibers finding it to reduce the performance of the module. Coating thickness variation could either improve or hinder the performance depending on conditions. We found that diameter variation within one fiber improves the performance.; From this research we suggested the optimal design and operating parameters for pervaporative VOC remediation.