Construction and practical application of a novel zeolite catalyst for hierarchically cracking of heavy oil
The conversion of the heavy fractions of crude oil into transportation fuels and chemical feedstocks is still a severe challenge for fluid catalytic cracking (FCC) technology, in which geometrical parameters of the catalyst are of key importance to the accessibility for reactant and product molecules to travel through the pore space. Here a new core-shell zeolite catalyst with hierarchical pore network from macro- via meso- to micropores is developed by controlling overgrowth of another zeolite shell on the surface of a commercial Y-zeolite. The zeolite shell is a distinctive nano ZSM-5 crystals. The core-shell zeolite catalyst has a high thermal and hydrothermal stability because of high crystallinity, which can meet the industrial requirements. More importantly, the heavy oil can be cracked by the designed zeolite catalyst step-by-step into the required products. The meso- and macroporous shell facilitates pre-cracking the large molecules in heavy oil into moderate ones which can directly diffuse into the micropores of the Y-zeolite to be cracked selectively into the desired products. Both the pore structure network and acid sites distribution of the core-shell zeolite catalyst in the FCC processing are completely harmonious. As a practical example, the catalytic cracking of VGO heavy oil is actualized over the new catalyst. The results showed that the conversion of heavy oil and the yield of gasoline increased by 1.8 wt% and 8.9 wt% respectively, LPG decreased by 6.9 wt%, iso -paraffins and olefins in gasoline fraction increased by 5.21 wt% and 6.31 wt% respectively, aromatics decreased by 11.55 wt%, because of the graduated cracking in core-shell zeolite and returned isomerization in nano ZSM-5, compared with commercially industrial FCC catalyst.
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