The invention relates to a pretreatment process for improving the filling of a chamber with solid particles, in which said solid particles are mixed before loading of said solid particles into the chamber with at least one lubricant that is solid at ambient temperature chosen from saturated fatty acids having 14 or more carbon atoms, metal salts of saturated fatty acids having 14 or more carbon atoms, esters of fatty acids having 14 or more carbon atoms, fatty alcohols having 14 or more carbon atoms, linear N-alkanes having 16 or more carbon atoms in solid form, fumaric acid, talc, sodium stearoyl fumarate, the lubricant being introduced at a content of between 0.01% and 1% relative to the total weight of the mixture of solid particles and lubricant. The invention also relates to the use of the process for the pretreatment of particles of adsorbents for the separation of xylenes.