Enhancing Hydrothermal Stability of ZSM-5 Cracking Additives with Aluminum Phosphates

Abstract

The production of well-shaped, spherical, and hydrothermally stable catalyst additives is a complex task in catalytic cracking. Industrial solutions often involve the use of phosphate materials. In this work, we prepared a spherical catalyst grain by spray-drying zeolite (ZSM-5) and kaolin filler with three different aluminum phosphate binders. The phosphate binders were used as pure binders and in combination with colloidal silica. We prepared the aluminum phosphate binders from boehmite and phosphoric acid with three different P/Al ratios. All of these can effectively bind the catalyst components to spherical particles. We demonstrated that various combinations of aluminum phosphate binders with colloidal silica can modify the catalyst’s porosity, acidity, stability, and hydrocarbon cracking properties. Finally, we found that the use of a silica-containing aluminum phosphate binder and a total P/Al ratio below 1 is necessary to avoid pore blockage by phosphates and to reduce the acidity of the catalyst. As a result, the aluminum phosphate binder can improve both the hydrothermal stability of the zeolite and the catalyst grains as well as the yield of light olefins in hexane cracking test reactions.