To investigate the initial chemical events associated with high-temperature gas-phase oxidation of hydrocarbons, we have expanded the ReaxFF reactive force field training set to include additional transition states and chemical reactivity of systems relevant to these reactions and optimized the force field parameters against a quantum mechanics (QM)-based training set. To validate the ReaxFF potential obtained after parameter optimization, we performed a range of NVT−MD simulations on various hydrocarbon/O2 systems. From simulations on methane/O2, o-xylene/O2, propene/O2, and benzene/O2 mixtures, we found that ReaxFF obtains the correct reactivity trend (propene > o-xylene > methane > benzene), following the trend in the C−H bond strength in these hydrocarbons. We also tracked in detail the reactions during a complete oxidation of isolated methane, propene, and o-xylene to a CO/CO2/H2O mixture and found that the pathways predicted by ReaxFF are in agreement with chemical intuition and our QM results. We o...

ReaxFF Reactive Force Field for Molecular Dynamics Simulations of Hydrocarbon Oxidation

Note: Chevron, Energy Technology Company, 100 Chevron Way, Richmond, California 94802-0627 Reference EPFL-ARTICLE-200588doi:10.1021/cr8002642 URL: http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/cr8002642 URL: http://pubs.acs.org/doi/pdfplus/10.1021/cr8002642 Record created on 2014-08-14, modified on 2017-05-12

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

The invention relates to a process for the manufacture of diesel range hydrocarbons wherein a feed is hydrotreated in a hydrotreating step and isomerised in an isomerisation step, and a feed comprising fresh feed containing more than 5 wt % of free fatty acids and at least one diluting agent is hydrotreated at a reaction temperature of 200-400° C., in a hydrotreating reactor in the presence of catalyst, and the ratio of the diluting agent/fresh feed is 5-30:1.

Process for the manufacture of diesel range hydrocarbons

Nanoparticle technology for heavy oil in-situ upgrading and recovery enhancement: Opportunities and challenges

The implications of the fundamentals of shape selectivity for the development of catalysts for the petroleum and petrochemical industries

A fundamental kinetic model for hydrocracking of C8 to C12 alkanes on Pt/US-Y zeolites

A kinetic model for hydrocracking of an industrial feedstock, fully incorporating the carbenium ion chemistry, was developed. Individual hydrocarbons in the reaction network were relumped into 8 lumps per carbon number: n-alkane, mono-, di- and tri-branched alkanes, mono-, di-, tri- and tetraring cycloalkanes. The rate coefficient of a reaction in the relumped network resulted from the product of the rate coefficients of the elementary reaction steps with lumping coefficients. The former were obtained from regressions on gas-phase hydrocracking data of model components. Lumping coefficients were calculated based on the assignment of all (cyclo)alkanes and the corresponding carbenium ions to structural classes comprising species with identical thermodynamic properties. The simulation of an industrial reactor with vacuum gas-oil feed revealed the relative unimportance of transfer limitations for hydrocracking of saturated hydrocarbons and the model's ability to detail the influence of process conditions on the product composition.

Kinetics for hydrocracking based on structural classes: Model development and application

A mixture of n -paraffins as well as a hydrotreated gasoil were hydrocracked over a Pt/ZSM-22 and a Pt/USY zeolite catalyst in a three phase reactor with complete internal mixing operated under industrially relevant conditions. The distribution of the isomerization products obtained from the n -paraffin mixture and the hydrotreated gasoil on Pt/ZSM-22 shows that pore-mouth and key–lock catalysis are operative, although the selective formation of branching at the end of the carbon chain is less pronounced. Ethylbranching is suppressed in liquid as well as vapor phase conditions. The cracked products obtained on Pt/ZSM-22 for both feedstocks contain a high amount of linear paraffins in comparison to the amount observed for hydrocracking on Pt/USY. This indicates that similar to vapor phase operations, the scission of the bond in the β position of the positively charged secondary carbon atom towards a new secondary carbenium ion (s,s β-scission) is also the dominant cracking mechanism for operations in liquid phase. The differences between vapor and liquid phase operations of Pt/ZSM-22 are attributed to differences in the adsorption modes of the molecules.

Hydrocracking and isomerization of n-paraffin mixtures and a hydrotreated gasoil on Pt/ZSM-22: confirmation of pore mouth and key–lock catalysis in liquid phase

A single-event kinetic model is applied to the hydrocracking of cycloalkane model components on two bifunctional Pt/US-Y zeolites over a wide range of experimental conditions (T = 493−573 K, P = 10−50 bar, molar H2-to-hydrocarbon ratio = 50−300). Values for the standard activation entropies of the elementary steps were obtained from transition state theory, while independently determined Henry coefficients were used to describe the physisorption. Values for the composite activation energies, i.e., the sums of the protonation enthalpies of the alkene intermediates and the activation energies of the elementary carbenium ion transformations, were obtained from a regression of the experimental data. The composite activation energies for intra-ring alkyl shifts vary from 21 to 25 kJ/mol, which is higher than those for the corresponding acyclic alkyl shifts, which vary from 10 to 16 kJ/mol. The composite activation energies for cyclic protonated cyclopropane branching reactions range between 27 and 40 kJ/mol an...

Single-Event Rate Parameters for the Hydrocracking of Cycloalkanes on Pt/US-Y Zeolites

The kinetics of paraffins hydrocracking are developed in terms of elementary steps and single events, thus substantially reducing the number op parameters with respect to an adequate lumping or molecular approach. Plausible assumptions and thermodynamic constraints further reduce the number of independent rate coefficients to 10. These were determined from an experimental program with judiciously chosen C8-paraffins.

GG Martens

Papers

A fundamental kinetic model for hydrocracking of C8 to C12 alkanes on Pt/US-Y zeolites

Kinetics for hydrocracking based on structural classes: Model development and application

Hydrocracking and isomerization of n-paraffin mixtures and a hydrotreated gasoil on Pt/ZSM-22: confirmation of pore mouth and key–lock catalysis in liquid phase

Single-Event Rate Parameters for the Hydrocracking of Cycloalkanes on Pt/US-Y Zeolites

Kinetic Modeling of Paraffins Hydrocracking based upon Elementary Steps and the Single Event Concept.