Abstract: A process for removing nitrogen oxides, as well as water and carbon dioxide, from gas streams containing at least 0.2 ppm by volume of nitrogen oxides by passing the gas stream through an alumina adsorbent and a zeolite adsorbent, preferably 13X-zeolite. The process has utility in front end cleanup of air prior to cryogenic distillation of the air where nitrogen oxides would otherwise freeze under the cryogenic processing.

Abstract: Temperature swing adsorption to remove CO.sub.2 from a gas stream is conducted using alumina to adsorb all the water and at least most of the carbon dioxide from the gas stream. Optionally a downstream zone of zeolite may be provided to remove further carbon dioxide and hydrocarbons.

Abstract: A process for the adsorption of at least carbon dioxide, water and oxides of nitrogen and preferably acetylene from a feed gas, comprises contacting the feed gas with an adsorbent mixture of a zeolite and an alumina. The process may be operated as a swing adsorption process comprising contacting the gas with the adsorbent at a first temperature and pressure to adsorb at least carbon dioxide, water and oxides of nitrogen therefrom and periodically regenerating the adsorbent by reducing the pressure and or increasing the temperature to which the adsorbent is exposed.

Abstract: Pressure swing apparatus comprises at least three parallel beds of adsorbent operated on cycles of being on-line to adsorb contaminant from a feed gas stream under pressure, being depressurized, being regenerated by a purge gas, and being repressurised. Feed gas is transferred from a depres-surising bed to a repressurizing bed to reduce switch loss and repressurization is extended to occupy at least 50% of the cycle to smooth the feed gas output.

Abstract: Pressure swing adsorption to remove CO.sub.2 from a gas stream is conducted using an improved alumina obtained by impregnating a starting alumina with a basic solution having a pH of at least 9, e.g. of a basic compound such as KHCO.sub.3, and drying at a temperature low enough to avoid decomposing the basic compound to a form which adsorbs CO.sub.2 such that the compound does not regenerate under reduced pressure purging.