Study On Inhibition Of Hydrogen Transfer Reaction In Butene Catalytic Cracking

The effect of catalyst pore structure, acidity and reaction temperature, space velocity and facing-water on the restriction of H-transfer reaction in butene catalytic cracking was studied in a small fixed bed reactor. Regeneration stability of the self-made ZSM-5crystal nucleus catalyst was characterized by ammonia temperature-programmed desorption(NH3-TPD) and N2physical adsorption. The results obtained are following:(1) Large amount of alkanes and aromatics generated by the side reaction of hydrogen transfer in butene catalytic cracking decrease the selectivity and yield of ethylene and propylene. ZSM-5, ITQ-2, MCM-22and Mordcnite/β were chosen as catalyst in the catalytic cracking of butenes for their different acidity, pore structure and channels. Mordenite/β catalyst with a small pore volume and without strong acid sites restrain the side-reaction of hydrogen transfer effectively.(2) The decrease of ZSM-5catalyst acidity caused by elements modification leads to a decrease of butenes conversion and the production of dry gas, propane, butane and C5+liquid, an increase of the selectivity and yield of propylene. Although the modification reduce the acidity of ZSM-5and restrain the side-reactions of hydrogen-transfer and dehydrogenation reactions to produce aromatics, but the acid strength and density of catalyst after modification was different.(3) Under the condition of steam, the hydrogen-transfer reaction was restrained and the selectivity and yield of propylene were promoted. The selectivity and yield of propylene were54.1%and34.0%respectively as the steam to hydrocarbon ratio was0.78. The butenes conversion was sharply reduced and the selectivity and yield of propylene were reduced under excess steam. Therefore, an appropriate ratio of steam to butene is importance to the reaction of butenes catalytic cracking as the diluent is water steam.(4) ZSM-5crystal nucleus catalyst could effectively constrain hydrogen transfer reaction in the catalytic cracking of butenes without element modification and steam dilution. The results indicated that ZSM-5crystal nucleus catalyst shows perfect catalytic performance in the catalytic cracking of butenes. The conversion of butene was75.99%, the selectivity and yield of propylene was46.24%and35.33%respectively at the reaction conditions are500℃,3.85h-1and atmosphere pressure. ZSM-5crystal nucleus catalyst displayed very good regeneration stability.