Study On The Characteristic Products From Catalytic And Thermal Cracking Reaction And Their Reaction Paths

The formation of dry gas during the process of catalytic cracking has been paying attention and carrying investigation presented in the literature. Using the heavy fraction of FCC naphtha as feedstock, the experiments were conducted in a fixed-fluidized bed reactor over inert quartz sand and acidic catalysts respectively in a reaction temperature range of300-700℃. The results showed that formed dry gas was almost totally attributed to the monomolecular reaction taking place over the acidic catalysts at a reaction temperature below525℃; both catalytic cracking and thermal cracking reactions occurred in the temperature of525-600℃; and thermal cracking reaction was predominated under the reaction temperature higher than600℃. The volume composition in dry gas produced by monomolecular cracking reaction from high to low was in the order of ethylene>methane> hydrogen>ethane, which was entirely different from the dry gas composition formed by thermal cracking reaction over the quartz sand. On the basis of the above experiment results, more experiments for monomolecular cracking reaction were systematically carried over different type catalysts in the temperature range of400-520℃, and the composition of the dry gas were investigated.The results showed that the formations of ethylene, methane, hydrogen and ethane were from four different reaction paths respectively. The four reaction paths over different type catalysts were also distinctly dissimilar. According to the experiment results, the Cracking mechanism Ratio(CMR) has been revised as CMR=(H2+Ci+C2)/i-C4°and was correlated with the ratio of strong Bronsted acid to weak Bronsted. Therefore the ratio of the monomolecular cracking reaction to the bimolecular cracking reaction over different acidic catalysts could be more accurately distinguished. The proportions of the types of cracking reaction, characterized by the formation of propane, n-butane, i-butane and i-butene, performed tby the monomolecular cracking reaction, the bimolecular cracking reaction and the hydrogen transfer reaction were calculated.