Increasing the Productivity of Colloidal Zeolite Beta by Posthydrolysis Evaporation

Colloidal beta zeolite is typically synthesized by the reaction of a clear precursor sol at temperatures below 100 °C. The process usually suffers from limited batch productivity with a long reaction time, because of the large amount of water used in the precursor sol. Reducing the water content is expected to shorten the reaction time, enhance the productivity, and reduce the particle size, but proper procedures are required to achieve a supersaturated, but pourable, composition. A precursor sol having a record low H2O/SiO2 ratio has been prepared by the addition of a posthydrolysis evaporation step. Compared to a conventional composition, which took 14 days to produce >100-nm particles at 60% yield of ∼55-nm redispersible zeolite beta particles in only 6 days. The formation of beta zeolite and the evolution of its particle size during the 90 °C reaction confirmed that aggregation always occurred before colloidal zeolite particles could be extracted. On the other hand, the “amorphous” residue was also found to be microporous, suggesting that it might be smaller zeolite particles that were undetectable by XRD and did not settle even with the high-speed centrifugation employed.