PLASTICIZATION-RESISTANT GLASSY POLYIMIDE MEMBRANES FOR CO2 CO4 SEPARATIONS/

It is known that CO2 acts as a plasticizer in CO2/CO4 membrane separat ions at elevated pressures. The polymer matrix swells upon sorption of CO2, accelerating the permeation of CH4. As a consequence, the polyme r membrane loses its selectivity. To overcome this effect, plasticizat ion should be minimized. We succeeded in stabilizing the polymer membr ane by a thermal treatment. For this purpose the polyimide Matrimid 52 18 is used as model polymer. In single gas experiments with CO2, the u ntreated membrane normally shows a minimum in its pressure dependence on permeability, whereas the treated membranes do not. Membrane perfor mances for CO2/CO4 gas mixtures showed that the plasticizing effect in deed accelerates the permeation of methane. The heat treatment clearly suppresses this undesired methane acceleration Additionally to the pu re and mixed gas permeation results, process calculations reveal valua ble information as to what extent the stabilized membranes show improv ed membrane performance. The favourable performance of the stabilized membrane can be attributed to less methane loss and therefore a higher recovery, resulting in higher profit from gas sales. (C) 1998 Elsevie r Science B.V. All rights reserved.