Meng Pan,Jiajun Zheng,Yujian Liu,Weiwei Ning,Huiping Tian,Ruifeng Li
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.
ABSTRACT Mesoporous high-silica zeolite Y with advantages of improved accessibility of acid sites and mass transport properties is highly desired catalytic materials for oil refinery, fine chemistry and emerging biorefinery. Here, we report the direct synthesis of mesoporous high-silica zeolite Y (named MSY, SiO 2 /Al 2 O 3 ≥ 9.8) and their excellent catalytic cracking performance. The obtained MSY materials are mesoporous single crystals with octahedral morphology, abundant mesoporosity and excellent (hydro)thermal stability. Both the acid concentration and acid strength of H-form MSY are obviously higher than those of commercial ultra-stable Y (USY), which should be attributed to the uniform Al distribution of MSY zeolite. The H-MSY displays an obviously reduced deactivation rate and improved catalytic activity in the cracking reaction of bulky 1,3,5-triisopropylbenzene (TIPB), as compared with its mesoporogen-free counterpart and USY. In addition, H-MSY was investigated as catalyst for the cracking of industrial heavy oil. The MSY-based catalyst (after aging at 800 o C in 100% steam for 17 h) exhibits superior conversion (7.64% increase) and gasoline yield (16.37% increase) than industrial fluid catalytic cracking (FCC) catalyst under the investigated conditions.
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