Desulfurization of fossil fuels with supercritical water (SCW) has been the focus of several studies over the past few decades.  This process does not require the use of any catalyst, eliminates the need for hydrogen feed, and minimizes coke formation.  Past research has shown that it has the potential to be a viable commercial process.  However, the exact desulfurization mechanism in SCW is largely unknown. In order to gain mechanistic understanding of SCW desulfurization, the reactivity and product distribution of hexyl sulfide has been investigated. Most notably, the product distribution of hexyl sulfide decomposition in the presence of SCW was found to be significantly different than in the absence of water. In the presence of SCW, hexyl sulfide decomposes mainly into hexane, hexene, CO, CO2 and pentane with sulfur being removed as hydrogen sulfide. When SCW is absent hexyl sulfide does not produce pentane, CO or CO2. The observation of CO and CO2   as products only when water is present, suggests that water reacts with hexyl sulfide during its decomposition, providing a hydrogen source for sulfur removal.            To support the experimental findings a detailed reaction network for SCW desulfurization is proposed using the automated Reaction Mechanism Generator (RMG). Multiple pathways to generate the aforementioned products from hexyl sulfide are proposed, and kinetic parameters for the included reactions are calculated using transition state theory and quantum chemical calculations at the CBS-QB3 and CCSD(T)-F12 levels of theory.  Using these rate parameters, as well as previously calculated data for hydrocarbon and sulfur kinetics, a reaction mechanism was built using RMG for the reaction of hexyl sulfide to H2S. Predictions from this model are compared with results from experiments.

Desulfurization of hexyl sulfide in the presence of supercritical water

245th National Meeting (2013)

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