Specific Features of Formation of Crystalline Silicoaluminophosphates in Grains Based on Kaolin and Phosphoric Acid

Abstract

Transformations of granules based on kaolin and phosphoric acid under the conditions of vapor-phase crystallization at 170°C were studied. Specific features of the individual and cooperative action of a water vapor and a template dipropylamine on the granules were determined. It is shown that the regulation of competing processes of formation of dense non-porous phases (tridymite, cristobalite, berlinite) and microporous crystalline silicoaluminophosphates of structural types ATL and ATN can be carried out by creating transport pores in the volume of the initial granules. The formation of transport pores was provided by using of porogens (hydroxyethyl cellulose and carbon nanospheres) with the subsequent calcination of the granules. The presence of 40- and 60- nm macropores in the porous structure favored intensification of mass-exchange processes occurring within the granules under the vapor-phase crystallization conditions. This led to an increase in the selectivity of crystallization of the materials with crystal structure types AEL and ATN. The morphology of the crystals with the AEL and ATN structure and their chemical composition depend on the porogen used to prepare the starting granules.