Process for purifying a gas stream using a contactor parallel passages presenting a conservation performance

A process for purifying a gas stream comprising at least one first compound selected from compounds of the first group consisting of water, ammonia, aromatic, alkane hydrocarbons, alkene or alkyne having at least 5 carbon atoms , aldehydes, ketones, halogenated hydrocarbons, hydrogen sulfide, hydrogen chloride and at least a second and a third compound selected from the compounds of the second group consisting of helium, hydrogen, the nitrogen, oxygen, argon, carbon monoxide, carbon dioxide, lower hydrocarbons C5, by adsorption to variable pressure (PSA), using at least one main adsorber comprising at least one switch passages parallel, characterized in that the first compound is at least partially stopped at the upstream of said main adsorber.