| Propylene and C4olefins are the most useful and important basic organicchemicals in the petrochemical industry. In recent years, with the recovery offinancial crisis and wide application of downstream derivatives of propylene and C4olefins, the demand for propylene and C4olefins continues to increase. Moreover,with the development of cracking feedstocks conversed into light fraction, propyleneand C4olefins in short supply in China. These situations can promote the research ofnew technology or methods of production of propylene and C4olefins. Traditionalsteam thermal pyrolysis process can provide richer resources of C4fraction, but itsmain products are ethylene. Therefore, the process cannot meet the demand forpropylene production, which has exceeded the growth rate of ethylene. Moreover, theprocess has many deficiencies or disadvantages, among which the most prominent isthe energy consumption. Catalytic cracking process can better overcome thesedrawbacks of traditional steam thermal pyrolysis process. Although the main productsof the catalytic cracking process are propylene and ethylene, C4olefins especially theresources of diolefins are scarce. This paper is to study the ideas or methods ofproduction of propylene and C4olefins by choosing a non-traditional crackingfeedstock and improving the reaction catalysts on the basis of catalytic crackingprocess.First of all, through the4×4orthogonal experiment, the experiment of catalyticpyrolysis of n-heptane in the self-made fixed bed micro-reactor on the HZSM-5molecular sieve (the Si/Al is50) has been investigated the best operating conditionsof molecular sieve catalyst and fixed bed micro-reactor. The results reveal that theoperation pressure and time of tablet press is15MPa and10min respectively;Catalyst bed height is2.5cm; Catalyst particle size is180μm-250μm. Moreover, wealso investigated the performance of heavy naphtha catalytic cracking to propyleneand C4olefins on the commonly used molecular sieve, the results confirm that theperformance of heavy naphtha catalytic cracking into C3-C4olefins over the series ofHZSM-5molecular sieve is most outstanding and prominent. Secondly, through the analyses of components in the heavy naphtha, we chooseseveral representative alkanes as cracking feedstock to study the effect of calcinationprocess conditions (temperature, time) on the performance of the catalytic cracking ofC3-C4olefins over the different Si/Al ratio of HZSM-5molecular sieve catalysts.These results indicate that the performance of ethyl-cyclohexane catalytic cracking onHZSM-5(200), as well as those of n-octane and n-heptane catalytic cracking onHZSM-5(200), is outstanding. However, the performance of iso-octane catalyticcracking on HZSM-5is extremely poor. The effect of calcination process conditionson the performance of heavy naphtha catalytic pyrolysis to produce propylene and C4olefins was studied over HZSM-5(200). The results show that when calcinatoryunder conditions of700℃and2hr, the heavy naphtha catalytic cracking canachieve the best performance to produce the propylene and C4olefins.Finally, the influence of heavy naphtha catalytic cracking of the yield ofpropylene and C4olefins was carried out on the load molecular sieve catalyst, whichhave been modified by volumetric impregnation method with phosphorus, transitionmetal (platinum, rhenium) and rare earth metal elements of the cerium, yttrium, loadin different Si/Al ratio of HZSM5molecular sieve (the Si/Al ratio is80and200). Theresults show that comparing with non-modified HZSM-5molecular sieve, themodified R-HZSM-5counterpart not only improves the yields of target products, butalso increases the productive selectivity by a large margin. Among these modifiedR-HZSM-5molecular sieves, the preferment or effect of catalytic pyrolyses of heavynaphtha to C3-C4olefins on the R-HZSM-5molecular sieve catalyst lording the rareearth metals (cerium, yttrium) is the most outstanding, followed by transition metal,finally to non-metallic element phosphorus (P). |
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