Binder Selection to Modify Hydrocarbon Cracking Properties of Zeolite-Containing Composites

Abstract

Activity, selectivity, and deactivation behavior of catalyst materials determine their efficiency in hydrocarbon conversion processes. For hydrocarbon cracking, the industrial catalyst is an important parameter in reaction technology to produce valuable compounds, e.g. , light olefins (C 3 –C 5 ) and gasoline from crude oil fractions with high molecular weight (C 16+ ). One strategy to enhance the catalytic activity for precracking is increasing the matrix activity, which depends on the used binder and additives. In this work, three binders (water glass, aluminum chloride, and a mixture of colloidal silica with aluminum dihydrogen phosphate) were used in combination with active zeolite Y, kaolin as filler, and ZSM-5 as additive to produce composite materials. Specific surface area and surface acidity measurements were combined with catalytic testing of the formulated samples in order to find the relation between the catalyst morphology and its activity. In addition, constraint index was used as a control parameter for the determination of the shape-selective properties and their correlation with the catalytic activity. The results show that the binders determine the porosity of the matrix and so the accessibility to zeolite pores and active sites. Matrixes with low porosity and activity enhance coke production and deactivate faster than matrixes with mesopores. Furthermore, ZSM-5 modifies the individual morphological and catalytic effects of the binders. Everything considered, the small crystals of ZSM-5 together with mesopores increase the olefins yield, reduce coking, and therefore enhance the performance of the final grain.

Crucial Role of Silica-Alumina Binder Mixtures for Hydrocarbon Cracking with ZSM-5 Additives

“…Although the acidity of a pure alumina binder from AlCl 3 is slightly higher than that of a pure silica binder as determined by ammonia desorption experiments, its correlation to acidity properties is weak. More importantly, the silica (LUDOX) used tends to form outer particle shells after spray drying, covering active and shape-selective ZSM-5, which confirms our previous studies . The investigations demonstrate that only small amounts of alumina in the mainly silica-based binder prevent the grain from shelling and ensure the access of hydrocarbon molecules to the active surface.…”

“…More importantly, the silica (LUDOX) used tends to form outer particle shells after spray drying, covering active and shape-selective ZSM-5, which confirms our previous studies. 28 The investigations demonstrate that only small amounts of alumina in the mainly silica-based binder prevent the grain from shelling and ensure the access of hydrocarbon molecules to the active surface. The resulting good olefin yield in catalytic tests is due to an optimization between the suppression of excessive subsequent conversion steps after propylene formation from hexanes while still maintaining good accessibility of active sites and, thus, good activity.…”