Air separation by pressure swing adsorption with a high capacity carbon

Abstract

Nitrogen is produced by separating air in a pressure swing adsorption process using a high capacity kinetically O.sub.2 selective material as the adsorbent. An example of such an adsorbent is a carbon molecular sieve made from coconut shell char. Such a coconut shell char having a high oxygen volumetric capacity is provided by crushing and sizing coconut shells to form granules which are then heated in flowing inert gas at a temperature ramp rate of about 2 to 12.degree. C. per minute to a peak temperature of 775 to 900.degree. C. which is then held so that the total heating time is up to 8 hours and thereafter the granular char is cooled in an inert gas atmosphere. The granular char thus produced is kinetically selective for O.sub.2 over N.sub.2 without further modification to narrow the openings of its micropores and has an oxygen volumetric capacity in excess of 8.0 cc/cc at 1 atm. and ambient temperature. Further modification of this char is provided by contacting it with an oxidizing atmosphere of carbon dioxide or a mixture of inert gas and carbon dioxide, H.sub.2 O or O.sub.2 at temperatures ranging from 650.degree. to 900.degree. C. until the gasified char has been altered so that its volumetric oxygen capacity is greater than 9.0 cc/cc at 1 atm. and ambient temperature.