Challenges of Modeling Steam Cracking of Heavy Feedstocks

Reyniers, Marie‐Françoise; Marin, Guy

doi:10.2516/ogst:2007084

Cited by 76 publications

(65 citation statements)

References 54 publications

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“…However, the methyl radical, due to its small size (mobility) and instability (reactivity), has been used as a prototype for carbonaceous radicals that are known to enhance coke growth. Coke growth models [5][6][7] that have been widely accepted have shown the prominent effect of methyl radical induced hydrogen abstraction on naphtha cracking.…”

Section: Resultsmentioning

confidence: 99%

“…Elementary radical reactions leading to coke growth. [5][6][7] Scheme 2. Industrially applied phosphorus-containing additives, in order of decreasing efficiency for coke inhibition.…”

Section: Introductionmentioning

confidence: 99%

“…[5][6][7][8][9] Numerous computational studies were conducted on the elementary reaction steps involved in thermal cracking and coke formation. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Thermodynamic and kinetic data obtained through theoretical calculations on individual reaction steps proposed in a coking model (Scheme 1) [5][6][7] showed the initial hydrogen abstraction reaction to be the rate-determining step in the coke-formation process. [16,22] An extended theoretical assessment of a reference reaction, namely, methyl radical induced hydrogen abstraction from benzene, [25] was followed by studies on larger polyaromatic surfaces, for both unsubstituted [26] and methyl-substituted aromatic compounds.…”

Section: Introductionmentioning

confidence: 99%

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Competitive Reactions of Organophosphorus Radicals on Coke Surfaces

Çatak

Hemelsoet

Hermosilla

et al. 2011

Chemistry A European J

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The efficacy of organophosphorus radicals as anticoking agents was subjected to a computational study in which a representative set of radicals derived from industrially relevant organophosphorus additives was used to explore competitive reaction pathways on the graphene-like coke surface formed during thermal cracking. The aim was to investigate the nature of the competing reactions of different organophosphorus radicals on coke surfaces, and elucidate their mode of attack and inhibiting effect on the forming coke layer by use of contemporary computational methods. Density functional calculations on benzene and a larger polyaromatic hydrocarbon, namely, ovalene, showed that organophosphorus radicals have a high propensity to add to the periphery of the coke surface, inhibiting methyl radical induced hydrogen abstraction, which is known to be a key step in coke growth. Low addition barriers reported for a phosphatidyl radical suggest competitive aptitude against coke formation. Moreover, organophosphorus additives bearing aromatic substituents, which were shown to interact with the coke surface through dispersive π-π stacking interactions, are suggested to play a nontrivial role in hindering further stacking among coke surfaces. This may be the underlying rationale behind experimental observation of softer coke in the presence of organophosphorus radicals. The ultimate goal is to provide information that will be useful in building single-event microkinetic models. This study presents pertinent information on potential reactions that could be taken up in these models.

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Section: Resultsmentioning

confidence: 99%

“…Elementary radical reactions leading to coke growth. [5][6][7] Scheme 2. Industrially applied phosphorus-containing additives, in order of decreasing efficiency for coke inhibition.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Competitive Reactions of Organophosphorus Radicals on Coke Surfaces

Çatak

Hemelsoet

Hermosilla

et al. 2011

Chemistry A European J

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“…For this purpose, a molecular reconstruction algorithm, termed SR-REM, has been developed during previous works [21][22][23][24][25]. This algorithm results from the coupling of two methods, Stochastic Reconstruction (SR) [21,26,27] and Reconstruction by Entropy Maximisation (REM) [21,[28][29][30].…”

Section: Molecular Representation Of Vacuum Residuesmentioning

confidence: 99%

Development of a General Modelling Methodology for Vacuum Residue Hydroconversion

Oliveira

Verstraete

KoIb

2013

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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Re´sume´-De´veloppement d'une me´thodologie ge´ne´rale de mode´lisation pour l'hydroconversion de re´sidu sous vide -Ce travail porte sur le de´veloppement d'une me´thodologie de mode´lisation cine´tique de proce´de´s de raffinage, et plus particulie`rement de proce´de´s pour la conversion de re´sidus sous vide. L'approche propose´e permet de surmonter le manque de de´tail mole´culaire des fractions pe´trolie`res et de simuler la transformation des mole´cules de la charge en mole´cules de l'effluent au moyen d'une proce´dure en deux e´tapes. Dans la premie`re e´tape, un me´lange synthe´tique de mole´cules repre´sentant la charge du proce´de´est ge´ne´re´par une me´thode de reconstruction mole´culaire appele´e SR-REM. Dans la seconde e´tape, une me´thode de Monte-Carlo cine´tique est utilise´e pour simuler les re´actions de conversion sur ce me´lange de mole´cules. La reconstruction mole´culaire a e´te´applique´e a`plusieurs re´sidus pe´troliers et est illustre´e pour un re´sidu sous vide Athabasca (Canada). La me´thode de Monte-Carlo cine´tique est ensuite de´crite en de´tail. Afin de valider cette approche stochastique, un mode`le de´terministe regroupe´pour la conversion de re´sidu sous vide a e´te´simule´en utilisant l'algorithme de simulation stochastique de Gillespie. Malgre´le fait que les deux approches sont fonde´es sur des hypothe`ses tre`s diffe´rentes, l'algorithme de simulation stochastique simule les re´actions de conversion avec la meˆme pre´cision que l'approche de´terministe. En utilisant des voies re´actionnelles au niveau mole´culaire, l'approche de simulation stochastique fournit ainsi des informations de´taille´es sur la composition de l'effluent et est brie`vement illustre´e pour l'hydrocraquage du re´sidu sous vide d'Athabasca.Abstract -Development of a General Modelling Methodology for Vacuum Residue Hydroconversion -This work concerns the development of a methodology for kinetic modelling of refining processes, and more specifically for vacuum residue conversion. The proposed approach allows to overcome the lack of molecular detail of the petroleum fractions and to simulate the transformation of the feedstock molecules into effluent molecules by means of a two-step procedure. In the first step, a synthetic mixture of molecules representing the feedstock for the process is generated via a molecular reconstruction method, termed SR-REM molecular reconstruction. In the second step, a kinetic Monte-Carlo method (kMC) is used to simulate the conversion reactions on this mixture of molecules. The molecular reconstruction was applied to several petroleum residues and is illustrated for an Athabasca (Canada) vacuum residue. The kinetic Monte-Carlo method is then described in detail. In order to validate this stochastic approach, a lumped deterministic model for vacuum residue conversion was simulated using Gillespie's Stochastic Simulation Algorithm. Despite the fact that both approaches are based on very different hypotheses, the stochastic simulation algorithm simulates

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“…Therefore, a lot of research has been performed to obtain a better understanding of the reaction network, and hence a reliable prediction of the run length in terms of various process conditions of an industrial furnace. [1][2][3] The global process of thermal cracking and coke formation is known to proceed through a complex radical reaction network, and generates thousands of reactive intermediates and products. To allow a facile and rapid investigation of the aforementioned process conditions, kinetic models have been developed.…”

Section: Introductionmentioning

confidence: 99%

A DFT‐Based Investigation of Hydrogen Abstraction Reactions from Methylated Polycyclic Aromatic Hydrocarbons

2008

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The growth of polycyclic aromatic hydrocarbons (PAHs) is in many areas of combustion and pyrolysis of hydrocarbons an inconvenient side effect that warrants an extensive investigation of the underlying reaction mechanism, which is known to be a cascade of radical reactions. Herein, the focus lies on one of the key reaction classes within the coke formation process: hydrogen abstraction reactions induced by a methyl radical from methylated benzenoid species. It has been shown previously that hydrogen abstractions determine the global PAH formation rate. In particular, the influence of the polyaromatic environment on the thermodynamic and kinetic properties is the subject of a thorough exploration. Reaction enthalpies at 298 K, reaction barriers at 0 K, rate constants, and kinetic parameters (within the temperature interval 700-1100 K) are calculated by using B3LYP/6-31+G(d,p) geometries and BMK/6-311+G(3df,2p) single-point energies. This level of theory has been validated with available experimental data for the abstraction at toluene. The enhanced stability of the product benzylic radicals and its influence on the reaction enthalpies is highlighted. Corrections for tunneling effects and hindered (or free) rotations of the methyl group are taken into account. The largest spreading in thermochemical and kinetic data is observed in the series of linear acenes, and a normal reactivity-enthalpy relationship is obtained. The abstraction of a methyl hydrogen atom at one of the center rings of large methylated acenes is largely preferred. Geometrical and electronic aspects lie at the basis of this striking feature. Comparison with hydrogen abstractions leading to arylic radicals is also made.

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Challenges of Modeling Steam Cracking of Heavy Feedstocks

Cited by 76 publications

References 54 publications

Competitive Reactions of Organophosphorus Radicals on Coke Surfaces

Competitive Reactions of Organophosphorus Radicals on Coke Surfaces

Development of a General Modelling Methodology for Vacuum Residue Hydroconversion

A DFT‐Based Investigation of Hydrogen Abstraction Reactions from Methylated Polycyclic Aromatic Hydrocarbons

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