Composite aluminum oxide adsorbent modified by calcium chloride

A series of samples of two-component adsorbents of the composition "CaCh/AhO3" with the content of the hygroscopic salt CaCl2 from 8.6 to 15.5 wt. % were synthesized. Samples were obtained by impregnation of aluminum oxide granules from an excess of an aqueous solution of CaCl2, which had the shape of a cylinder with average dimensions - length l = 4-5 mm, diameter d = 3.0 mm. The initial aluminum oxide was obtained using the method of centrifugal thermal activation of hydrargillite (gibbsite). After hydration of the product of centrifugal activation in an acidic environment, drying, grinding and peptising, aluminum oxide granules were formed, followed by calcination of the extrudate at a temperature of 500 °C for 4 hours. The resulting source oxide is a mixture of y-AhO3 (90 wt. %) and bayerite (10 wt. %). Changes in the phase composition and texture characteristics of samples modified with hygroscopic salt depending on their CaCl2 content were studied. It is noted that after modification the samples of the diffraction pattern disappears at the phase bayerite. The specific surface area decreases with increasing CaCl2 content in samples from 290 m²/g for the initial sample to 96 m²/g for the sample with the maximum CaCl2 content. In the samples increases, the average pore diameter and decreases the value of total pore volume that may be due to blocking of the pores at the stage of synthesis due to deposition of salt during drying of the adsorbent. The mechanical strength of granules with a low salt content is less than that of the original sample, but with an increase in the salt content, its increase to 6.8 MPa is observed. In contrast to the original sample for all modified samples, the adsorption capacity for water vapor does not reach an equilibrium value even after more than 5 hours from the start of the experiment. This may be due to the occurrence of slow chemical reaction between water and the dispersed salt. For composite samples, an increase in the water adsorption capacity was observed with an increase in the content of the hygroscopic salt CaCl2, which indicates its determining role in the water sorption process. Sufficiently high values of the speed constants, strength and adsorption characteristics were typical for samples with a salt content of CaCl2 from 13.8 wt. %. and higher.

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