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.