Monitoring of crystallization processes during synthesis of zeolite A by in situ 27Al NMR spectroscopy

In situ 27Al NMR spectroscopy has been used for monitoring of crystallization processes during synthesis of zeolite A. Changes of relative intensity and width at half-width of NMR lines originated from solid and liquid phase during crystallization were observed. The line at 79 ppm originated from liquid phase was selected for monitoring of crystallization processes. Kinetic analysis is performed using modified Sharp and Hancock equation. Depending on batch composition, obtained values of parameter n of 1.06 and 1.08 indicate contribution of both diffusion and phase boundary controlled mechanisms, while the synthesis with values of n ranged from 1.89 to 3.09 obey the Avrami–Erofe’ev nucleation and crystal growth model. Exceptions from usual monotonic decay of signal intensity originated from liquid phase observed in some synthesis could be explained by terms of autocatalytic nucleation model.