Recycling of Spent FCC Catalysts: Conversion of Leached Residues to Zeolite ZSM-5.

The commercial recycling of spent FCC catalyst typically focuses on recovering only 1-3 % of rare-earth elements, with the remaining residues often disposed of in landfills. Here, we present a novel method to close a recycling loop for spent FCC catalyst. The method involves a series of leaching steps: Firstly, the spent catalyst material is leached with HNO3 to remove rare-earth elements such as La; second, solvothermal leaching with HCl removes most of Al and impurities like Fe, Ni and V; finally, a third leaching with H2SO4 removes Ti. The solid residues are then used to synthesize ZSM-5 without the addition of any extra silicon or aluminum sources after mild activation. The impurities in the synthesis gel strongly modify the properties of the zeolite, with ZSM-5 crystals containing higher levels of impurities exhibiting lower crystallinities, surface areas, acidities, cracking activities, as well as larger particle sizes.

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

Alumina-containing binders are widely used for the binding of catalyst particles by spray drying and calcination. As a part of the active matrix, they contribute to the catalytic performance of the resulting catalyst grain during hydrocarbon cracking. In this study, correlations are investigated using different compositions of Al- and Si-based binders (AlCl3 and colloidal silica) together with kaolin as a filler and ZSM-5 zeolite as an active compound. It was demonstrated that the conversion of a 50:50 hexane mixture, the selectivity toward unsaturated hydrocarbons, and the shape-selective conversion of the hexane feed are highly dependent on the amount and distribution of alumina in binder formulations. While silica species are distributed near the outer shell of catalyst grains, the alumina species are distributed evenly as an adhesive between the catalyst compounds ZSM-5 and kaolin. An optimum amount of alumina in binder formulations results in an increasing conversion of hydrocarbon feedstock due to optimum in active-site accessibility but only a slight decrease in shape-selective properties compared to pure ZSM-5, resulting in an optimum yield of light olefins, especially propylene.

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

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 (C3-C5) and gasoline from crude oil fractions with high molecular weight (C16+). 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.

Ethanol to Aromatics on Modified H-ZSM-5 Part II: An Unexpected Low Coking.

In this study a commercial H-ZSM-5 zeolite (Si/Al=11) was post-synthetically modified by a combined dealumination procedure to adjust its catalytic properties for the selective formation of aromatics from ethanol. The solid-state properties of original and modified zeolites are determined by structural, textural and acidity analysis. The formation of aromatics and durability of the zeolites were investigated depending on space velocity or contact time in the catalyst bed. In particular, the formation rate and desorption of aromatics from solid-state surface as well as their tendency to form coke precursors by consecutive build-up reactions determine the formation of coke. Therefore, the rate of build-up and finished aromatization by hydride transfer (pre-determined by the kind, location and geometric arrangement of surface acid sites) and the statistical number of reaction events until final desorption at the specific contact time have to be harmonized to increase aromatics yield and to decrease catalyst decay by coke simultaneously.