Crystallization kinetics of Sn-MFI molecular sieve formation by dry gel conversion method

• Crystallization kinetics of Sn-MFI by dry gel conversion and hydrothermal method.
• Dry gel conversion (DGC) method shortens the induction period.
• Effect of H2O and Si/Sn mole ratio on kinetics of Sn-MFI was studied by DGC method.
• Existence of critical humidity plays an important role in DGC method.
• Experimental data fit well to the Avrami equation.

The conversion of amorphous stannosilicate dry gel into crystalline molecular sieve with MFI structure (Sn-MFI) was achieved by dry gel conversion (DGC) method at 413, 443 and 473 K. For comparison purpose, Sn-MFI molecular sieve with similar SiO2/SnO2 mole ratio was also obtained by hydrothermal crystallization route. Crystallization curves were established by conducting time dependant studies on progressive crystallization processes for both the systems. The values of activation energy of nucleation (En), activation energy of crystallization (Ec), and their pre-exponential factors (ln An, ln Ac respectively) were calculated from Arrhenius plots. Compared to the hydrothermal method, shorter induction period was observed when DGC method was employed. Both the En (49.70 kJ/mol) and Ec (52.82 kJ/mol) for DGC method were found to be lower than that of the En (55.70 kJ/mol) and Ec (60.23 kJ/mol) for hydrothermal method. The kinetics parameters viz. K and q were derived from kinetic expressions and DGC method showed higher value of K and lower value of q compared to hydrothermal crystallization method at identical temperature. Various DGC method parameters such as water content at the bottom of autoclave and SiO2/SnO2 mole ratio have shown the influence on the kinetics of crystallization of Sn-MFI.

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