Removal of CO? from Natural Gas by Polyimide Membrane In the Presence of Heavy Hydrocarbon

Carbon dioxide, heavy hydrocarbon, hydrogen sulfide, water vapor and toluene are the common impurities found in raw natural gas that can bring detrimental effects on the performanceof membrane. The heavy hydrocarbon contamination can cause the loss of flux and membrane performance and thus it is imperative for pretreatment of the natural gas feed stream to remove the contaminants. This project is to study the effect of heavy hydrocarbon on the polyimide membrane performance in separating gas CO2 from natural gas feed stream at designed operating parameters, i.e. feed pressure, temperature and C02 concentration in feed. Liquid Pentane (C5H12) is used as a basis to simulate the presence of heavy hydrocarbon in the experiments. Gas permeation experiments have been conducted in laboratory to study the effect of pentane on Polyimide membrane performance. It is proven that permeance of C02 and CH4will decrease with an increase in operating pressure at feed side in both dry and wet condition. The CO2/CH4 selectivity increases with an increase in feed pressure. Higher operating temperatures increased C02 and CH4 permeance but decreased CO2/CH4 selectivity of polyimide membrane. An increase in CO2 concentrationin feed compositionincreases the losses of hydrocarbon but reduced C02, CH4 permeance and C02/CH4 selectivity. The decrease of membrane permeance and selectivity with an increase in C02 concentration in the feed compositionis due to the plasticization and coupling effect. The pentane presence in the feed gas caused swelling or plasticization of polyimide membrane and lead to the reduction in membrane selectivity. It was concluded that the presence of pentane as heavy hydrocarbon in natural gas stream contributed to the loss of membraneselectivity and caused the separationperformance of the membranesystem become less efficient