Research On Distillation Of Methanol-Water In Hollow Fibers

A membrane contactor is a device that achieves gas/liquid orliquid/liquid mass transfer without dispersion of one phase with another.It is a bran-new, more effective and environmental mass transfer method.In this experiment, non-porous polyether sulfone hollow fibers (with a5pro polydimethylsiloxane coating) were used as structured packing inthe distillation of methanol-water solutions. In this novel membranecontactor, liquid flowed through the lumens of the fibers, and vaporflowed counter currently outside the fibers. The main studies of this thesishave been focused on the feasibility of distillation in hollow fibers andthe mass transport phenomenon of this new hollow fiber membranecontactor, including the study of the operation limit, the development ofthe model of the gas diffusion through the microporous membrane, thecalculating of mass transfer coefficients and the comparing of the hollowfiber contactors with no or two baffles in shell.Experiments involving separation of three kinds of methanol-waterby the hollow fiber membrane contactor were performed. The resultsshowed that the new membrane contactor gave better, more productive separations than traditional packing in distillation. The minimal HETP ofhollow fibers could reach as low as 5 cm, and the contactor worked wellabove the limit where flooding normally occurs in conventional cases.The membrane contactor and another similar contactor which lumen wasinstalled with two baffles have been compared. The results and the theoryanalysis showed that operating with two baffles is steadier; baffles helpmodule to get a higher mass-transfer coefficient, in the same meaning,have a smaller mass-transfer resistance. The overall mass-transfercoefficient and individual mass-transfer coefficients based on the gas sideand liquid side were calculated respectively. The theoretical analysisindicated that resistance in the liquid is responsible for about half of thetotal resistance. At last, this paper especially discusses the contradictionbetween theoretical mass-transfer coefficient and experimental value.