Model catalysts hydrocarbon conversions

The model includes fundamental hydrocarbon conversion kinetics developed on fresh catalysts (referred to as start-of-cycle kinetics) and also the fundamental relationships that modify the fresh-catalyst kinetics to account for the complex effects of catalyst aging (deactivation kinetics). The successful development of this model was accomplished by reducing the problem complexity. The key was to properly define lumped chemical species and a minimum number of chemical reaction pathways between these lumps. A thorough understanding of the chemistry, thermodynamics, and catalyst... 

Davis, S.M., Zaera, F. and Somorjai, G.A. (1982) The reactivity and composition of strongly adsorbed carbonaceous deposits on platinum. Model of the working hydrocarbon conversion catalyst. J. Catal., 77, 439. 

Subsequent hydride transfer and metal catalyzed dehydrogenation steps lead to benzene. Qualitatively, the hydrocarbon conversion over bifunctional catalysts can thus be described as a reaction network using two types of sites. The reactions taking place on the Bronsted sites are similar to those in liquid acids, as described in the first part of this paper a second group of reactions takes place on the metal sites these steps are identical with those observed on the same metal in the absence of acid sites. Mills et al. devised a simple model... 

S.M. Davis, F. Zaera, and G.A. Somorjai. The Reactivity and Composition of Strongly Adsorbed Carbonaceous Deposits on Platinum. Model of the Working Hydrocarbon Conversion Catalyst. J. Catal. ll A >9 (1982). 

Kolbel et al. (K16) examined the conversion of carbon monoxide and hydrogen to methane catalyzed by a nickel-magnesium oxide catalyst suspended in a paraffinic hydrocarbon, as well as the oxidation of carbon monoxide catalyzed by a manganese-cupric oxide catalyst suspended in a silicone oil. The results are interpreted in terms of the theoretical model referred to in Section IV,B, in which gas-liquid mass transfer and chemical reaction are assumed to be rate-determining process steps. Conversion data for technical and pilot-scale reactors are also presented. 

However, the detailed description of the FT product distribution together with the reactant conversion is a very important task for the industrial practice, being an essential prerequisite for the industrialization of the process. In this work, a detailed kinetic model developed for the FTS over a cobalt-based catalyst is presented that represents an evolution of the model published previously by some of us.10 Such a model has been obtained on the basis of experimental data collected in a fixed bed microreactor under conditions relevant to industrial operations (temperature, 210-235°C pressure, 8-25 bar H2/CO feed molar ratio, 1.8-2.7 gas hourly space velocity, (GHSV) 2,000-7,000 cm3 (STP)/h/gcatalyst), and it is able to predict at the same time both the CO and H2 conversions and the hydrocarbon distribution up to a carbon number of 49. The model does not presently include the formation of alcohols and C02, whose selectivity is very low in the FTS on cobalt-based catalysts. 

In this study, a new mathematical model was developed to predict the experimental TPA behaviors with reaction, and it was incorporated with additional adsorption model of extended Langmuir-Freundlich equation (ELF). LDFA approximation and external mass transfer coefficient proposed by Ullah, et. al. were used [3]. Also, rate expression of power law model was employed [4]. The parameters used in the power model were obtained directly from the conversion data of hydrocarbons on adsorber or light off catalyst [S]. In this study, to get numerical solutions for the proposed model, orthogonal collocation method and DVODE package were employed [6]. 

Experimental number distributions (Fig. 16) and chain termination probabilities (/3 and jSn) (Fig. 17) on Co catalysts at low values of bed residence time (<2 s, <10% CO conversion) are accurately described by the model. We reported previously a similar agreement on Ru catalysts (4). The model quantitatively describes the observed curvature of carbon number distribution plots (Fig. 16) and also the constant values of j3/y and the decreasing values of )3o observed as hydrocarbon size increases (Fig. 17). Such effects arise from the higher intrapellet fugacity and the higher residence time of larger a-olefins within transport-limited pellets. 

Since zeolites are typical acid-base catalysts, their acid-base properties are of great importance in investigating the catalytic decomposition of hydrocarbons. Three methods — titration, temperature-programmed desorption, and characterization by test reaction — are employed to measure acid-base properties. In this study, n-hexane was used as a model hydrocarbon and its decomposition over HY, HCeY, HSmY, and HCuY zeolites was investigated. Depending on the metal exchanged, n-hexane conversion and product distribution were observed to vary in the higher ccmversion r ion. The relation between product distribution and the acid-base properties of the zeolites are discussed. 

The difference in the catalytic activity between model compounds and real feedstocks is the most visible evidence for the influence of feedstock components on HDS catalysts. Some researchers have shown that an increase of 30-50°C in temperature is required for a commercial catalyst to achieve the same conversions of DBT, 4-MDBT, and 4,6-DMDBT in light gas oil as compared to the model compounds when dissolved in a hydrocarbon solvent. Inhibition of... 

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