Membrane gas separation of Fischer-Tropsch gases

Abstract

Membrane-based gas separation has attracted considerable interest over the past few years because of its low energy consumption and cost-effective separation. Many studies have been conducted related to amorphous silica membrane. This membrane has been reported to perform well with respect to separating various gases including the Sasol Fischer Tropsch gases Hydrogen, Methane and Carbon dioxide. This study is devoted to the investigation of the performance of a commercially available amorphous silica membrane for the separation of a typical Fischer Tropsch gas mixture. For both single and binary permeation experiments performed, it was found that the membrane permeation of the gases Hydrogen, Methane and Carbon dioxide is independent of the transmembrane pressure. As far as temperature is concerned, it was established that the permeation of the three gases is inversely dependent on an increase in operating temperature. This was observed for both single and binary permeation experiments. In general, higher fluxes were achieved if the gases were fed directly onto the support (shell side feed). Selectivity towards Hydrogen was not significantly influenced by any of the operating parameters investigated (temperature, trans-membrane pressure, membrane orientation). The overall conclusions that were made based on the results obtained are that this membrane can essentially be classified as a Knudsen-type membrane, since selectivity values are in the region of Knudsen transport. The selectivity values are thus not large enough to qualify this membrane as a successful gas separation membrane. It was however, established that this membrane may perform more effectively if used for pervaporation application purposes.