| Ethylene, propylene and butadiene, which are basic intermediates for a large proportion of the petro-chemical industry, are obtained mainly by thermal cracking of condensing natural gas and distillates such as naphtha and gas oil. There is a worldwide increase in demand on the use of these lighter components of petroleum and it is desirable that heavier feedstock be utilized for olefin production, particularly in China. Because most of Chinese crude is paraffin base crude exemplified by Daqing crude which is of high content of hydrogen and paraffin in heavier distillates, it is a considerable way to produce low carbon olefin by using heavier feedstock. The catalysts for producing ethylene by thermal catalytic pyrolysis and the mechanism of the reaction are investigated in order to improve the selectivity of light olefins and reduce the consumption of feedstock and energy and widen the scope of feedstock.In order to screen the catalysts in the laboratory and simulate the reaction model of riser cracking, a new type of instrument for testing micro-activity of thermal catalytic cracking catalyst by using heavy oil as feedstock is developed. The catalyst inventory and feed quantity of this new unit is between which of small-scale fixed fluidized bed catalytic cracking test unit and heavy oil micro-activity test unit. Steam can be mixed, the reactant is injected into the reactor from the bottom and keep piston flow upward during the reaction. The performance tests show that this unit can be operated steadily with accuracy, repeatability and reproducibility. The calculating loss of material balance is less than 5 m%.Two aspects of the effect of steam on the thermal catalytic cracking reaction are studied. On one hand, when the feed oil is injected at the same speed, the injection of steam that will increase the logarithmic meanvolume and decrease the residence time of the reactant results in the decrease of conversion rate of reaction. On the other hand, steam can be used to restrain the side reaction such as hydrogen transfer reaction so as to increase the yield of light olefins by diluting the concentration of the reactant. In addition, minor steam can react with the feed hydrocarbon resulting in the decrease of coke and the formation of active hydrogen without the increase of hydrogen gas and light saturates that is not desirable.In order to improve the yield of ethylene, the effect of acid-base character of catalysts on the mechanism of thermal catalytic reaction and yield of ethylene are studied by using f3 zeolite ion-exchanged with alkali earth metal Ca and alkali metal K as catalysts compared with quartz, GaO and K2C03. The conversion and yield of ethylene and propylene are not affected by the ion exchange of f3 zeolite with Ca2~. The conversion and yield of propylene decrease with the increase of the exchange degree of K~, while the yield of ethylene is invariable which is mainly produced from thermal cracking reaction. Concluded from product distributions, the cracking reactions catalyzed by basic catalysts GaO and K2C03 proceed via free-radical mechanisms, but conversion of the reactions is close to those catalyzed by quartz. So the cracking reactions catalyzed by basic catalyst proceed via free-radical mechanisms, but the basicity of catalysts is not the cause of free-radical mechanisms.The effect of zeolites ion-exchanged by transition metals on thermal catalytic cracking reaction is studied. The product distributions of the cracking reactions catalyzed by the f3 or ZSM-5 zeolites exchanged with transition metals are different from that catalyzed by corresponding Hzeolites, which means the mechanism of cracking reactions has varied. Group VIII metals Fe, Go, Ni and Cu, Zn are shown to be of strongcatalytic activity of oxidative dehydrogenation, while Ti and Cr are not of oxidative activity. Catalyzed by zeolites or catalyst containing Ag, conversion of thermal catalytic cracking reactions and the yield of ethylene increase while the yield of propylene does not dec...
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