NOVELTY - The adsorbent particle is of basically ellipsoidal form, with a first axis A-A of length (a), a second axis B-B of length (b) and a third axis C-C of length (c). The three axes are orthogonal and the lengths are such that ab=c and the ratio a/b is such that 1.05 a/b 2.50. Gas separation by adsorption using such particles. Installation for gas separation using such particles    USE - Separation of gases by adsorption    ADVANTAGE - The elliptical shape of the particles retains much of the crushing strength of more common spheroidal particles, but increases the surface to volume ratio and therefore the adsorption efficiency    DETAILED DESCRIPTION - The particle is an ellipsoid of revolution with b+c, preferably free of projecting ridges. The ratio a/b is between 1.08 and 2. The adsorbant particle includes at least one zeolite, preferably of faujasite type and/or a bonding agent, preferably an inert bonding agent including at least one clay. The faujasite exchanged with mono- di- or trivalent alkali metal or alkali earth metal cations, preferably lithium, manganese, nickel, cobalt, barium, calcium, zinc, copper, magnesium, strontium or iron cations. The adsorbant particle contains at least 85% lithium and/or calcium cations with a zeolite of type X or LSX. The length of the first axis (a) is between 0.4 and 3mm, and/or (b) is between 0.3 and 2.9mm and/or (c) is between 0.3 and 2.9mm.    Use of such particles for separating a gas flow by adsorption where at least one component is preferentially adsorbed onto at least one of the particles. PSA gas separation process. The gas to be separated contains nitrogen and at least one less polar component, in particular oxygen and/or hydrogen, the gas is preferably nitrogen and oxygen and the process is preferably VSA. Alternatively, the gas to be separated is a mixture of hydrogen and at least one of carbon dioxide, carbon monoxide, nitrogen and hydrocarbons, in particular methane, and preferably the gas is a syngas. Alternatively, the gas to be separated is air containing an impurity such as carbon dioxide, carbon monoxide, water vapor, hydrogen and hydrocarbons, in particular methane. Installation for gas separation operating the above process, with one to three adsorbers of which at least one contains the above adsorbant particles, preferably an adsorber with a radial geometry.    DESCRIPTION OF DRAWING(S) - Dimensions of particle.