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Application of vanadium -based catalyst in the in mixed ethylbenzene dehydrogenation process

Author: ZhangXueBin
Tutor: DongWenSheng
School: Shaanxi Normal University
Course: Applied Chemistry
Keywords: Ethylbenzene Dehydrogenation Styrene Vanadium pentoxide Supported Catalysts
CLC: TQ203.2
Type: Master's thesis
Year: 2008
Downloads: 106
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Abstract


Dehydrogenation of hydrocarbons has been the subject of one of the most challenging of the oil and chemical industry, which is characterized by the thermodynamic equilibrium of the reaction conversion rate limit. Styrene is an important basic organic chemical raw materials, widely used in the production of plastics, resins and rubber. Currently, the global styrene annual production capacity of more than 25 million tons, of which more than 90% ethylbenzene dehydrogenation of production. The main disadvantage of the existing process is the reaction temperature and the water / hydrocarbon is high and the energy consumption, the equilibrium conversion is low, is difficult to recover the large heat of condensation of water vapor contained in the separator, therefore, research and development of new alternative dehydrogenation process necessary. The oxidative dehydrogenation of ethylbenzene with low energy consumption, not equilibrium conversion restrictions, since the 1970s found that certain forms of carbon exhibit excellent catalytic activity for oxidative dehydrogenation of ethylbenzene, researchers devoted great enthusiasm. However, the new technology styrene selectivity is poor, a large number of by-products a serious impediment to the process of industrial applications. Use greenhouse gas CO 2 selective oxidation of ethylbenzene to styrene is a research focus in recent years, the role in the preparation of the catalyst, the choice of the reaction conditions and CO 2 mechanism and other aspects of their predecessors has done a lot of work. However, the process is still strong endothermic reaction, energy consumption by thermodynamic equilibrium restriction and catalyst deactivation due to surface carbon deposition serious. If a part of the oxygen is introduced in the system, on the one hand, by the oxidation reaction can be supplied to part of the energy of the system, thereby reducing the energy consumption of the system; on the other hand, can eliminate the catalyst surface of carbon, thereby improving the stability of the catalyst. Based on the above thinking, the paper prepared by incipient wetness impregnation of a series of V 2 O 5 / gamma-Al 2 O (V / Al) and additives modified catalyst was investigated catalyst the CO 2 atmosphere under the oxidation of ethylbenzene dehydrogenation in the system leads to O 2 < / sub> catalyst structure and catalytic properties of. The main findings are as follows: 1. V / Al catalyst prepared by impregnation V load, and for mild oxidation in the CO 2 atmosphere ethylbenzene dehydrogenation reaction. Investigated the type of catalyst for ethylbenzene and of CO 2 of the conversion rate and the styrene selectivity of the reaction at atmospheric pressure, 550 ° C, EB airspeed 20.4 mmool / g · cat · h conditions. Experimental results show that the V / Al catalyst in the type V load, V (8% wt.) / Al catalyst showing good ethylbenzene dehydrogenation activity. As the the V load increases, the increase in the initial activity of the catalyst in the CO 2 oxidation of ethylbenzene dehydrogenation process, but the stability of the catalyst deteriorates, in CO 2 oxide pass into a small amount of ethylbenzene process the O 2 can effectively inhibit the deactivation of the catalyst to maintain high catalyst activity and stability. 2. Prepared by impregnation with a variety of additives modified V / Al catalyst, the experiment proved auxiliaries from the the ethylbenzene dehydrogenation activity of the catalyst active role in the EB conversion rate improved to some extent. In the additive modified catalyst V-Sb/Al ethylbenzene dehydrogenation activity, high styrene selectivity and ethylbenzene conversion and good stability, where V (8%) Sb ( 9%) / Al catalyst. Pass a small amount of O 2 CO 2 Oxidation of Ethylbenzene process, so that the initial activity of the catalyst decreased, slowed down but the catalyst deactivation rate, to improve the catalyst stability. 3. In this paper, temperature-programmed reduction reaction (XPR), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction analysis (XRD) and the N 2 physical adsorption on the catalyst before and after reaction were characterized characterization The results show that the V / Al catalyst surface of the V component exist in a highly dispersed form, mainly due to deactivation of the catalyst caused by the change in composition of the catalyst surface and the surface of the coke, coke caused by the decrease of the catalyst surface area and pore volume, especially micropore size complete loss. Add additives able to further improve the degree of dispersion of the active ingredient in the carrier surface, and modulating the pH of the catalyst surface, thereby facilitating the adsorption and activation of the reaction gas, is conducive to improved performance of the catalytic reaction. Additives Sb modified V / Al catalyst in the formation of V 1.1 Sb 0.9 the O 4 middle phase may is V-SB / Al-active centers of the catalyst. CO 2 oxidation of ethylbenzene in the process of adding a small amount the O 2 and the surface of the catalyst coke can be effectively suppressed, while stabilizing the surface of the catalyst composition, in order to maintain a high activity and stability.

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