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.ru-mb/zro <sub> 2 </ Sub> Catalytic Benzene Selective Hydrogenation To Cyclohexene Dynamics Study

Posted on:2004-04-23Degree:MasterType:Thesis
Country:ChinaCandidate:X L YangFull Text:PDF
GTID:2191360095950217Subject:Industrial Catalysis
Abstract/Summary:PDF Full Text Request
Cyclohexene can be hydrated to cyclohexanol and be oxidized to cyclohexanone and adipic acid. It is of great synthetic and industrial interest for selective hydrogenation of benzene to cyclohexene, by which the procedure of e -caprolactam and adipic acid is shortened. In recent thirty years, many chemical industry corporations in developed countries such as America, German and Japan have importantly being attached to the catalysts study of selective hydrogenation of benzene to cyclohexene. There are eight corporations and one study institute which study the catalysts of benzene selective hydrogenation to cyclohexene in Japan. In 1989, Asahi Chemical Industry Corporation in Japan built Nylon-66 product line, in which the critical path is selective hydrogenation of benzene to cyclohexene. Asahi Chemical Industry Corporation still does its efforts to study the new catalytic system now. Moreover they will apply for patents in Japan, China and Europe when they make a further progress. The product line was introduced to China in 1995. It is of great significance to assimilate the foreign advanced technology and study the catalysts of selective hydrogenation of benzene to cyclohexene and exploit the novel catalysts of ours. Now, there are two disadvantages of the industrial ruthenium catalyst for selective hydrogenation of benzene to cyclohexene. One is that zinc sulphate as additive is an kind of strong acid salt, so the equipments must be able to resist strong corrosion; the other is the yield of cyclohexene only reaches about thirty percent. In order to enhance the yield and selectivity of cyclohexene effectively, it must depend on high selective catalysts to cyclohexene and relevant kinetics factors. So, it is significant to study the kinetics and mechanism of the selective hydrogenation of benzene to cyclohexene.The kinetics and reaction mechanism of liquid-phase selective hydrogenation of benzene to cyclohexene on Ru-M-B/ ZrOi catalysts have been systematically studied in this paper. The TPD of benzene on the catalysts has also been studied. This paper stresses on the study of macroscopic kinetics of the reaction. The macroscopic kinetics parameters such as reaction order, rate constant, apparent activation energy and pre-exponential factor have been obtained. It hasbeen proved that benzene hydrogenation is a consecutive reaction. It was concluded that the benzene conversion is first order with respect to benzene, and with respect to hydrogen, it is second order at low hydrogen pressure, fraction order at middle hydrogen pressure and zero order at high hydrogen pressure; while the cyclohexene hydrogenation to cyclohexane is zero order with respect to cyclohexene, and with respect to hydrogen, it is second order at low hydrogen pressure, fraction order at middle hydrogen pressure and zero order at high hydrogen pressure. The apparent activation energies of benzene conversion and cyclohexene hydrogenation are 32.63KJ mol-1 and 21.13KJ mol-1, respectively at high hydrogen pressure. The pre-exponential factors of the two steps are 735min-1 and 478mol L-1min-1, respectively. Based on these results, the kinetic equations of benzene hydrogenation to cyclohexene in each step were given.According to the macroscopic kinetics studies, two kinds of reaction mechanism have been drawn out which obey Langmuir-Hinshelwood model. The equations are obtained in a straightforward manner subject to the assumptions that there are two different kinds of active sites on the catalyst surface; benzene and hydrogen are adsorbed on the two different active sites, respectively, which also obey Langmuir adsorption istotherm; Surface reactions of benzene conversion and cyclohexene hydrogenation are two rate-determining steps.The TPD analysis indicates that there is only one kind of active sites on the catalyst surface which adsorb benzene. The desorption active energy is obtained through calculation. The results may supply some information to draw out the reaction mechanism.The studies of selective hydrogenation of ben...
Keywords/Search Tags:selective hydrogenation of benzene, catalysts, kinetics, reaction order, rate constant, reaction mechanism
PDF Full Text Request
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