| Refinery catalytic cracking of mixed C4 hydrocarbons was one of the effective ways to increase propylene yield. This thesis with the refinery mixed C4 hydrocarbon as raw material, studied systematically the modified catalysts, the optimization of reaction conditions and the reaction mechanism.Based on the mechanism of butene dimerization-cracking, isobutane and butene alkylation and 2-butene and ethylene disproportionation, we proposed the main reaction paths of mixed C4 hydrocarbon catalytic cracking process, as well as the main reactions and the major side reations, and thermodynamic analysis of theirs. Thus providing theoretical guidance to screen catalyst and optimize the process conditions.In this experiment, we studied the influence of HZSM-5 sieve Si-Al ratio on mixed C4 hydrocarbon cracking properties, and selected the best Si-Al ratio was 200. With Si-Al ratio 200 of HZSM-5 as the carrier, a series of different modified catalysts were prepared, selected excellent catalytic activity of La-HZSM-5 and Ce-HZSM-5 zeolite catalyst, and studied the influence of modified materials on the performance of the modified catalyst, La-HZSM-5 and Ce-HZSM-5 molecular modification of the best material content were 0.099g/g·cat and 0.051g/g·cat.With La-HZSM-5 and Ce-HZSM-5 molecular sieve as a catalyst optimized process conditions, we studied the influence of feed flow rate investigated, reaction temperature and water-hydrocarbon ratio(m) on mixed C4 hydrocarbon cracking performance. The optimal conditions were:feed flow rate 40ml/min, reaction temperature 480℃and water-hydrocarbon ratio 0.3. Under the optimum conditions, Ce-HZSM-5 molecular sieve cracking performance is superior to La-HZSM-5, conversion and propylene selectivity of 67.15% and 72.44%, P/E =7.1.Catalyst had a longer service life, its inactivation was mainly due to carbon covering the active site. The catalyst regeneration temperatures were 400℃and 550℃. Regenerated catalyst still remained fresh catalyst activity. |
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