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Study On Catalytic Pyrolysis Of FCC Gasoline And Kinetic Model For Two-Stage Riser Fluid Catalytic Cracking

Posted on:2009-04-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y B LiuFull Text:PDF
GTID:1101360278460777Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
Two-stage riser catalytic pyrolysis for maximizing propylene technology (TMP) is a new technology developed based on the TSRFCC. Special catalytic pyrolysis catalyst LTB-2 was used in this technology. The technology can maximize propylene yield and produce high octane gasoline simultaneously. In this paper, a series of basic studies for this technology were carried out in fixed bed-chromatograph equipment, and the advantage of TSRFCC was analyzed according to the kinetic model.Although propylene is the goal product of catalytic pyrolysis process, it can carry on secondary reaction either on ZSM-5 catalyst or on USY catalyst. Ethylene and butene are dominant products. There are some aromatic products, too. Lower temperature is advantageous to propylene transformation. The channel of ZSM-5 zeolite can repress the hydro transfer reaction because it is very narrow. There are two ways for aromatization of propylene under catalytic pyrolysis conditions. One is through hydro transfer and anther is through dehydrogenation. Aromatization of propylene through dehydrogenation is dominant on ZSM-5 zeolite, and toluene is primary product. Aromatization of propylene through hydro transfer is dominant on USY zeolite, and xylene is primary product.Catalytic pyrolysis of some alkenes, alkanes and naphthenes of gasoline fraction were studied. The reaction mechanisms for different hydrocarbons were analyzed. Under the catalytic pyrolysis conditions, monomolecular cracking is the dominant reaction for 2-methyl -2-butene. Ethylene is also the product formed by the catalytic cracking. Reactions of 1-hexene, 1-heptene and 2-methyl -1-hexene are monomolecular cracking. The C-C bonds near the carbon chain center are easy to crack. Cracking of alkanes follow the protolytic cracking-βscission mechanism. Reaction rate of 1-heptene is faster than the rate of 2-methyl-1-hexene and 1-hexene on ZSM-5 catalyst. Reaction rate of 2-methylpentane is faster than rate of n-hexane, too. But the reaction rate of n-octane is faster than the rate of 2-methylheptane, and the rate of 2-methylheptane is faster than the rate of isooctane. Catalytic pyrolysis rate of alkenes is approximately the rate of alkanes 10 times.Olefins are the dominant reactants in catalytic pyrolysis of gasoline. An 8-lump kinetic model for catalytic pyrolysis of gasoline was developed. Reaction network for catalytic pyrolysis of gasoline was determined based on the reaction law of propylene and light hydrocarbons. Parameters were evaluated by the Nonlinear Least Square Fitting method from the experimental data. Reaction heat of secondary reaction of gasoline was calculated. The reaction heat for upgrading of FCC gasoline is 80~150 kJ·kg-1, while the reaction heat for catalytic pyrolysis of FCC gasoline is 370~620 kJ·kg-1. It is higher than the reaction heat of FDFCC process. Reaction conditions can change the conversion of gasoline and the product distribution, and then cause the changes of the reaction heat. With the rise of reaction temperature, increase of the ratio of catalyst to oil, and prolongation of residence time,the reaction heat increases at the experimental conditions. If the ratio of catalyst to oil is large enough, the reaction heat changes slowly with the increasing of ratio of catalyst to oil.In order to analyze the advantage of TSRFCC, a 6-lump reaction kinetic model of TSRFCC was developed. The model was solved by Runge-Kutta method. Calculation results showed that the yields of diesel, gasoline and LPG increase firstly and then decrease along with the increasing of conversion. The selectivity of diesel decreases when the conversion increases. TSRFCC can increase diesel and gasoline yield and selectivity, however, decrease dry gas and coke yields. Ratio of diesel to gasoline also increases. The first stage conversion affects products yield and selectivity of two-stage riser FCC technology. If the total conversion is the same, the yields of diesel and gasoline are increasing and then decreasing along with the increasing of first stage riser conversion. If diesel oil and gasoline, or diesel oil, gasoline and LPG are goal products, TSRFCC can reach higher conversion, and the yield of goal product are higher, too.
Keywords/Search Tags:Catalytic pyrolysis, Propylene, Gasoline, Reaction heat, TSRFCC
PDF Full Text Request
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