Aging of carbon membranes under different environments

Carbon membranes were obtained by the carbonisation (700 degreesC) of a thin phenolic resin film deposited on the inner face of porous alumina tubes. The carbon membranes were stored in different environments lair, nitrogen and propylene) and the modification of their separation properties (permeance and permselectivity) with time was analysed periodically. It was observed that with time membranes stored in air undergo severe gas permeance losses. By contrast permselectivities increase slightly. The gas permeance losses of carbon membranes stored under nitrogen are much lower with respect to those stored in air. Storage of carbon membranes in propylene has a positive effect on permeance whereas permselectivities decrease slightly. Attempts to recover the permeances of air-aged carbon membranes have demonstrated that they can only partially be regenerated by means of heat treatment. The results indicate that the use of carbon membranes to separate gas mixtures containing oxygen (i,e, air) shows serious problems whereas the separation of oxygen-free gas mixtures (i.e. olefin/paraffin, n-butane/i-butane, hydrogen/hydrocarbons, etc.) is a more reliable option. (C) 2001 Elsevier Science Ltd. All rights reserved.