Evidence of the »Memory« Effect of Amorphous Aluminosilicate Gel Precursors by Simulation of Zeolite Crystallization Processes Using the Population Balance Method

There is abundant experimental evidence that most, or even all zeolite nuclei are formed in the aluminosilicate gel and/or gel/liquid interface by a linking of specific subunits during gel precipitation and/or ageing. Since the nuclei (particles of quasicrystalline phase) cannot grow inside the gel matrix, they start to grow after being »released« from the gel dissolved during the crystallization, i.e. when they are in full contact with the liquid phase (autocatalytic nucleation). Based on these findings it was assumed that the rate of autocatalytic nucleation depends on the rate of gel dissolution as well as on the number and distribution of nuclei in the gel matrix, but that crystal size distribution in the crystalline end product depends exclusively on the number and distribution of nuclei in the gel matrix and not on the crystallization conditions, or even on the treatment of aluminosilicate gel precursor prior to crystallization. This so called »memory« effect of amorphous aluminosilicate precursors was evidenced by simulation of zeolite crystallization under different conditions, using the population balance method