Membrane gas separation processes for permeate purification.

摘要

The use of membrane gas separation processes has grown tremendously during the past few decades. The largest commercial application is the production of nitrogen from air. However, membranes are being considered for other separations as well including carbon dioxide removal from methane, carbon dioxide sequestration from flue gas, and hydrogen purification.; For gas separations, the membranes used are most commonly in the form of fine hollow fibers. A bundle of hollow fibers is enclosed in a case to form a module. The module allows one to control the flows inside and outside the fibers separately and is the mass transfer equivalent of a traditional shell and tube heat exchanger.; Various module design factors such as size, arrangement, contacting pattern, and fiber properties have a significant impact on module performance. The effects of many design factors are well understood but the effects of fiber property variation are not.; Past work has demonstrated that variations in membrane selectivity, permeance, and diameter are detrimental to performance. However, this work has focused on processes that produce a high purity retentate. The effects on processes that produce a high purity permeate have not been studied. Permeate purification differs substantially from retentate purification in that module staging is commonly used to increase efficiency.; The thesis is divided into four parts. First, the effects of fiber property variation on permeate production with a single module for lumen and shell feed are studied. The model is validated with experimental measurements of oxygen production from air. Second the effects of fiber property variation on a staged module system for permeate production are studied. Third, the staged module simulation is used to evaluate the potential of membrane processes for hydrogen purification. Fourth, a novel two-membrane staged design is compared with single-membrane staged designs. Two-membrane designs use two different membrane materials that selectively permeate different components of the feed mixture. Performance comparisons are made for hydrogen purification from carbon dioxide.; While the results presented here are for oxygen and hydrogen purification, the work is applicable to all membrane systems used to produce a high-purity permeate product.