Competitive Reactions of Organophosphorus Radicals on Coke Surfaces

Abstract

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.

A First‐Principles Study on the Interaction between Alkyl Radicals and Graphene

“…The electronic adsorption energy is 17.0 kcal mol −1 at the M06L/6‐31G* level of theory. A similar result was obtained by Catak et al 49. for the adsorption of P(C 6 H 5 ) 2 radicals at the center of ovalene.…”

PPV Polymerization through the Gilch Route: Diradical Character of Monomers

“…Geometry optimizations for the transition states as well as reactant and product complexes involved in the dimerization, propagation, and side-product formation steps were performed in the gas phase by using the M06-2X/6-31 + G(d,p) level of theory.T he M06-2X functional was particularly chosen due to its known ability to successfully describe dispersive interactions, [43] such as the stacking interactions that may exist between p-quinodimethane units in the current study.M oreover,M 06-2X is also known as an efficient functional for main-group thermochemistry and kinetics. [58,59] Harmonic vibrational frequencies were computed at the same level of theory and used to provide thermal corrections to the Gibbs free energies as well as to confirm the nature of the stationary points. The intrinsic reaction coordinate (IRC) paths were traced to verify the two minima associated with each transition state on the potential energy surface.…”

Insight in the activity and diastereoselectivity of various Lewis acid catalysts for the citronellal cyclization

“…In the case of ATPH, the M06-2X hybrid functional [54,55] is a good choice to accurately quantify the adsorbate-ligand interactions and ligand-ligand interactions because it is used especially for medium range non-covalent interactions. In this functional, double Hartree−Fock exchange is included to improve the description of non-covalent interactions [56,57]. Furthermore, the double-zeta Pople basis set 6-311+g(d,p) was applied for subsequent energy refinements in case of ATPH.…”