Mixed matrix membranes (MMMs) have been considered as an alternative gas separation technique due to their low energy consumption and high selectivity. In previous studies, it was found that silicon rubber MMMs incorporated with polyethylene glycol (PEG) and some diol isomers such as 1,2-, 1,3-, 1,4- and 2,3-butanediol can improve the selectivity and permeation rate of some gases. In this study, solid-liquid-polymer MMMs are prepared by a solution-casting method and then tested for permeation rate of various pure gases (CO2, N2, CH4 and H2) in order to ascertain the selectivity of membranes. The Ultem (polyimide) polymer is selected as a polymer base due to the higher selectivity of gases when compared to the silicon rubber. Activated carbon is selected for stabilizing PEG and diol isomers into its pores avoiding undesirable liquid leakage. The effects of diol isomers and pressure on Ultem-MMM performance have been investigated and will be reported at the meeting.