Journal of Membrane Science, Vol.92, No.3, 257-265, 1994
Selective Permeation of Carbon-Dioxide Through Plasma-Polymerized Membrane from Diisopropylamine
For the purpose of the selective separation of CO2 over CH4, plasma polymerized membranes were prepared. They were multilayer composite membranes consisting of a top plasma polymer layer and a substrate consisting of a silicone skin layer and a porous polyimide support. As monomer, diisopropylamine was mainly used in order to utilize the acid-base interaction between CO2 and amino groups. The separation coefficient and the permeation rate obtained were 17 and 1.5 X 10(-10) kmol/m2 s Pa ( = 4.5 X 10-4 cm3/cm2 s cmHg). This high permeation rate was characteristic of the plasma polymerized membrane which can be made very thin. The effects of the plasma conditions such as power input, monomer flow rate and plasma deposition time on the membrane properties were investigated in detail. It is suggested that the permeation of CO2 can be explained by the partial immobilization model based on the acid-base interaction between CO2 and amino groups incorporated into the membranes. The obtained membrane was stable for as long as 25 days. The structures of the plasma polymers were analyzed by FT-IR and XPS measurements. The change of the selectivity corresponded well to the changes of the amounts of nitrogen incorporated into the membrane.