Modification Of Zsm-5 Zeolite For Catalytic Pyrolysis

Catalytic thermal cracking technology, making use of VGO and residue as feedstock and solid acid catalyst which consists of ZSM-5 zeolite as major activity components, is a new process of producing low-carbon olefines composed of ethylene and propylene mainly under certain condition in FCC plant. This paper concerns the small-scale test and industrial amplification test in activity components of catalytic thermal cracking catalyst respectively, as well as the initial research in reaction mechanism.Utilizing alkaline earth metals Ca, Mg, etc., Ib family metals Ag, Cu, etc., and the nitrate of VIII family metals Fe, Co, Ni, etc., and adopting dip-moulding and ion exchange method,ZSM-5 zeolite is modified, and its physical and chemical characteristics is indicated by XRD, SEM, MAS NMR and IR.Catalytic thermal cracking performance of modified ZSM-5 zeolite is evaluated through pure hydrocarbon impulsive micro-reaction pilot unit. The test results indicate that C2 components yield is improved, but the yield of C3 components decreased as the increase of reaction temperature. While the content of metal oxide in modified zeolite increases, the yield of both C2 and C3 components are enhanced, and zeolite of modified by Ib family metals has better selectivity.Catalytic thermal cracking tests of metal modified zeolite are carried out in heavy oil micro-reaction unit. Test results show that zeolite modified by Ib family metals has much higher ethylene yield, as well as the yield of propylene at the same time, and the second one modified by VIII family metals have very excellent dehydrogenation ability, lower olefine yield and obvious carbon accumulation, and the third one modified by alkaline earth results lower yield of both ethylene and propylene.On the basis of small-scale test, industrial amplification tests are executed, and the synthesized samples of catalytic thermal cracking catalyst are applied in commercial application test. The application effects are excellent.Upon test foundations, reaction mechanism of catalytic thermal cracking is explored. The distribution of acid site in zeolite determines ethylene yield of catalytic thermal cracking reaction. Ethylene yield improves with the increases of L-acid site amounts in zeolite. Therefore, not only can L-acid site catalyze the carbonium ion reaction, but also promote free radical reaction under different temperature condition and acid strength respectively. The types of metal loaded in zeolite and its electronegativity are the reasons that cause the transformation of L-acid sites. The more negativity of alkaline earth metal and VIII family metal corresponds to higher ethylene yield, while the case of Ib family metal is the reverse.