Dynamic capacity of desiccants based on modified alumina at elevated pressures

Abstract

Alumina desiccants obtained by extrusion molding of plastic pastes based on pseudoboehmite or bayerite-containing hydroxides including those modified by sodium and potassium ions were studied. The hydroxides were synthesized by hydration of the product of centrifugal thermal activation of gibbsite under mild conditions. The physicochemical and structural-mechanical properties of the desiccants (fresh and after nine adsorption–regeneration cycles) were studied. The dynamic capacity was determined at a pressure of 3MPa under conditions designed to model the industrial conditions. The sample obtained from bayeritecontaining hydroxide had a higher dynamic capacity than the sample obtained from pseudoboehmite-containing hydroxide at close texture and strength characteristics of adsorbents. Modification of the samples obtained from pseudoboehmite-containing hydroxide with potassium and sodium ions leads to decreased granule stability and increased volume, average pore size, and dynamic capacity. The potassium-modified sample of the desiccant had dynamic capacity as high as that of the sample obtained from bayerite-containing hydroxide at low load. After the cyclic tests, the phase composition, alkaline impurity contents, specific surface area, and crushing strength of the samples did not change within the error of determination. It was found that the prepared desiccants were highly stable in many adsorption–desorption cycles and the minimum dew point of –80°C could be reached during the drying.