Effects of MFI Zeolite Crystal Size on Light Olefins Production in Catalytic Cracking of Hydrocarbon Feedstocks

The paper describes the physicochemical characterization and catalytic testing of MFI zeolites with crystal sizes ranging from 0.15 to 6 mu m supplied by different manufacturers. The physicochemical properties were examined by atomic absorption spectrometry, X-ray fluorescence analysis, scanning electron microscopy, low-temperature nitrogen adsorption, and ammonia temperature-programmed desorption. The MFI zeolites were then added to a cracking catalyst and subjected to catalytic testing in the conversion of cyclohexane and hydrotreated vacuum gas oil (HTVGO). It was found that the conversion of the model cyclohexane feedstock was significantly enhanced when the crystal size of the MFI zeolite added to the cracking catalyst was reduced from the micro- to submicro-scale; on the other hand, an equal downsizing had almost no effect on the conversion of the real HTVGO feed. However, the use of submicrosized MFI crystals in HTVGO cracking decreased the contribution of hydrogen transfer reactions, thus reducing coke deposits.