A Generalized Mechanistic Kinetic Model for the Hydroisomerization and Hydrocracking of Long-Chain Paraffins

Abstract

A mechanistic kinetic model has been developed for the three-phase hydroisomerization and hydrocracking of long-chain paraffins in which rate-determining steps are assumed to occur on both acid and metal sites of the bifunctional catalyst. The frequency factors for the acid site elementary steps are modeled using the single-event concept and the corresponding activation energies using the Evans−Polanyi relationship. The rate coefficients for the dehydrogenation reactions on the metal sites of the catalyst are classified into five different classes depending on the nature (i.e., primary, secondary, or tertiary) of the carbon atoms forming the double bond. The model contains 14 independent parameters for the hydroisomerization and hydrocracking of heavy paraffins. These parameters are estimated from experimental data on the three-phase isothermal hydrocracking of n-hexadecane in a tubular reactor. A number of reactor simulations have been performed for various operating conditions and hydrocarbons of different chain lengths. The effect of the relative metal to acid activity of the catalyst on the isomerization and cracking selectivities and on the carbon number distribution of the products is discussed in detail.

Fischer-Tropsch Waxes UpgradingviaHydrocracking and Selective Hydroisomerization

“…1.4). Recently, a detailed kinetic model has been developped for the three-phase hydrocracking of heavy paraffins in wich the rate-determining step is assumed to occur on both acid and HD/DHD sites of the catalyst ("non ideal" hydrocracking catalyst) [24]. This review will be limited to the features of ideal bifunctional catalysis.…”

NiMo/Al₂O₃ Promoted Hybrid Catalysts of Nanosized Alumina and Beta Zeolite for Hydrocracking with Isomerization

“…Except for the changes in the conversion and the cracking selectivity between SiO2/ Al2O3 molar ratios of 16 and 25, no large differences were observed for catalysts containing beta zeolite with different SiO2/Al2O3 molar ratios. The optimum SiO2/ Al2O3 molar ratio was found to be about 25 : cracking selectivity, : iso-selectivity, : average carbon number of cracked products.…”

Hydrocracking of Fischer‐Tropsch waxes: Kinetic modeling via LHHW approach

“…This shift was possible because the rate constants for the elementary steps are independent on the carbon number. 14 The authors state that the model can be easily extended to the HDK of FischerTropsch waxes.…”