Steam catalytic cracking of crude oil over novel hierarchical zeolite–containing mesoporous silica–alumina core-shell catalysts

Abstract

The direct conversion of crude oil to basic chemicals was studied over novel core-shell structured ZSM-5 zeolite containing mesoporous silica-alumina (MSA) composites. A template-directed sol-gel method in an alkaline medium was used to prepare a core-shell structured ZSM-5 containing MSA composites employing CTAB as template, tetraethyl orthosilicate (TEOS), and aluminum sulfate. This approach resulted in the formation of a uniform mesoporous silica-alumina shell around the zeolite crystal. The shell thickness (tune in the 8–26 nm range) and its alumina content were controlled by varying the TEOS/zeolite and TEOS/aluminum sulfate ratios. The physicochemical properties and steam catalytic cracking performance of Arab Extra Light (AXL) crude oil were investigated to enhance the yield of C2-C4 light olefins. For comparative study, conventional and mesoporous silica-alumina composites were mixed with kaolin (50%), steam deactivated (810 °C for 6 h) and tested in a fixed-bed reactor operated at 675 °C, residence time of 10 s and steam/oil ratio (g/g) of 0.5. The optimized mesoporous silica-alumina composite Z30 @ MSA (TEOS/zeolite = 0.85 and TEOS/aluminum sulfate = 15.86) had improved textural characteristics, moderate acidity, and AXL crude oil cracking potential at higher conversion (~70%) and selectivity towards light olefins (49.4%) than the unmodified ZSM-5(30). The mesoporous core-shell composite's distinct reaction pattern resulted in the formation of a unique mesoporous silica-alumina core-shell catalyst, which eased the rapid diffusion of desired products from intra-framework channels while inhibiting the formation of coke deposits.