The Effects of both Hydrocarbon and Water Vapour Contamination of Natural Gas Streams upon Polymeric Membrane Performance
Membrane systems for the removal of CO2 from natural gas streams have received much attention from the industry. Polymeric membranes are the most popular membranes for such an application because of their high performance, ease of synthesis, long life, thermal stability, mechanical strength and chemical resistance. Among polymers, 6FDA based polyimide membranes show high permeabilities and permselectivities. However, most published studies on these membranes have been conducted with pure gases in the absence of any contaminants. It is important to replicate the actual gas stream in the laboratory and conduct studies in the presence of contaminants such as hydrocarbons, water and sulphur compounds. These contaminants may restrict the performance of a membrane and result in premature ageing and membrane failure during operation. Conversely, a better understanding of the effects of changing contaminant levels will allow for the improved design of pre-treatment systems to remove these contaminants prior to the membrane system.
Our research is aimed at understanding the impact of hexane and water on 6FDA-Durene polyimide membrane performance. Different compositions of these impurities are being tested. For a mixed methane/carbon dioxide feed at 10 atm pressure and 35 ºC, the results show that both permeability and selectivity of the membrane are reduced substantially upon exposure to hexane vapors over the course of 3-4 hours. The possibility of membrane regeneration after exposure to such contaminants is also being studied. Preliminary results show that membranes can be partially regenerated by purging under a continuous stream of hot N2