engleski

Effects of lyophilization on amorphous aluminosilicate precursors

Lyophilization or freeze drying is a process in which water is removed from a material after it is frozen and placed under vacuum, allowing the ice to change directly from solid to vapor without passing through a liquid phase.1, 2 In this work, we investigated the influence of lyophilization amorphous aluminosilicate gel on zeolite crystallization kinetics. For this purpose, freshly prepared gel (2.66 Na2O  Al2O3  1.66 SiO2  504.92 H2O) was freeze-dried in aliquots (500 ml Dewar flask). The Dewar flask with gel were frozen in liquid air and the frozen gel were placed into the drying chamber of lyophilizator and cooled to -46  C. Drying was performed at a pressure of 7.8  10-2 mbar for 14 h. The system (freeze dried gel dispersed in the water) was transferred into stainless-steel reaction vessel preheated at 80  C and mixed at the same temperature with magnetic stirrer until complete transformation to zeolite A. Kinetics of nucleation, crystal growth and entire process of crystallization were analyzed by population balance method. Analysis of the experimental results (changes in the concentrations CAl of aluminum and CSi of silicon in the liquid phase as well as the dimension Dm of the largest crystals of zeolite A during crystallization) and particle size distribution analysis shows that the freeze drying process of amorphous aluminosilicate gel affects the rate of crystallization and crystal size. The process of lyophilization resulted in the decrease of particle size and in the increase of crystallization rate.

Amorfni alumosilikatni prekursor; liofilizacija; zeolit

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