Detailed kinetic model for hexyl sulfide pyrolysis and its desulfurization by supercritical water

Authors

Caleb A. Class, Butler UniversityFollow
AnGayle K. Vasiliou, Middlebury College
Yuko Kida, Dow Chemical Company
Michael T. Timko, Worcester Polytechnic InstituteFollow
William H. Green, Massachusetts Institute of TechnologyFollow

Document Type

Article

Publication Date

2019

DOI

10.1039/c9cp00234k

Additional Publication URL

https://pubs.rsc.org/en/content/articlelanding/2019/cp/c9cp00234k#!divAbstract

Abstract

A detailed reaction network is proposed for the pyrolysis and desulfurization of hexyl sulfide in the presence or absence of both supercritical water (SCW) and hexadecane, but without any added H₂ or catalyst, for T = 400–450 ^oC. The new kinetic model is developed using the Reaction Mechanism Generator (RMG) software where most of the rate coefficients are derived from quantum chemical calculations. We previously reported that pentane, carbon monoxide and carbon dioxide are major products of hexyl sulfide desulfurization in SCW, but not in the anhydrous pyrolysis of hexyl sulfide. The observation of CO and CO₂ in the reaction products indicates that water effectively acts as a hydrogen source; presumably this assists in sulfur reduction to H₂S. Kinetic parameters for several of the important reactions are calculated using transition state theory and quantum chemical calculations at the CBSQB3 level of theory and then further refined using CCSD(T)-F12//cc-pVTZ-F12 single point energies. Predictions from the new kinetic model agree with factor-of-2 accuracy with new and previously published experimental data for hexyl sulfide conversion and for yields of most major products, either neat or in a hexadecane solvent, both in the presence and absence of SCW. Flux analysis was then used to identify the most important reaction steps, and sensitivity analysis was used to propose reactions that should be studied further in the future to decrease the model’s uncertainty. This study establishes the molecular role of water as diluent, hydrogen bond donor, and reductant in the decomposition of hexyl sulfide. Future work to add molecular weight growth pathways to the model would lead to a more complete mechanism, resulting in improved predictions of product yields.

Rights

This article is published in Physical Chemistry Chemical Physics. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence

Recommended Citation

Class, Caleb A.; Vasiliou, AnGayle K.; Kida, Yuko; Timko, Michael T.; and Green, William H., "Detailed kinetic model for hexyl sulfide pyrolysis and its desulfurization by supercritical water" (2019). Scholarship and Professional Work – COPHS. 257.
https://digitalcommons.butler.edu/cophs_papers/257