The Performance of Hollow Fiber Gas Separation Membranes in the Presence of an Aggressive Feed Stream

Abstract

Industrial utilization of polymeric gas separation membranes is predicted to increase significantly over the next 20 years. This growth will be driven by application of membrane based separations to increasingly aggressive feed streams. In this work, the performance of defect-free Matrimid asymmetric hollow fiber membranes in the presence of high pressure carbon dioxide and trace levels of toluene and n-heptane in the feed stream are studied. Specifically, this work shows a significant decrease in the carbon dioxide plasticization pressure and the carbon dioxide permeance prior to plasticization as a result of accelerated physical aging at ambient temperature. Interestingly, sub-Tg thermal annealing at 220 oC reverses the effects of physical aging by increasing the plasticization pressure and the carbon dioxide permeance prior to plasticization for a typical polyimide commonly used in membranes. The performance of Matrimid asymmetric hollow fiber membranes in feed streams contaminated with up to 1200 ppm toluene and 2000 ppm n-heptane is investigated. In the presence of both feed stream contaminants, the productivity and efficiency of the membrane are observed to significantly decrease in this work. These decreases in performance are shown to be the result of antiplasticization, and a free volume based model is developed to correlate the effect of feed stream contamination on membrane performance