Supercritical Water desulfurization of crude oil

Abstract

Supercritical Water (SCW) desulfurization was investigated for both model sulfur compounds and Arab Heavy crude. In part 1, the reactions of alkyl sulfides in SCW were studied. During hexyl sulfide decomposition in SCW, pentane and CO+CO₂ were detected in addition to the expected six-carbon products. A multi-step reaction sequence for hexyl sulfide reacting with SCW is proposed which explains the surprising products. Intermediate studies were performed to confirm that the key intermediate hexanal forms and rapidly decomposes to pentane and CO. In part 2, Arab Heavy crude was treated with SCW and analyzed with comprehensive gas chromatography (GCxGC) coupled with two detectors, sulfur chemiluminescence detector (SCD) and a flame ionization detector (FID). SCD is a sulfur specific detector that allowed detailed analysis of the reactions that occur during SCW treatment of real fuel mixtures. It was shown that SCW treatment had two effects on sulfur compounds: cracking of heavy sulfur compounds into smaller compounds, mainly benzothiophenes (BT) and dibenziophenes (DBT), and cracking of long alkyl chains on these BTs and DBTs causing a shift to lower molecular weight BTs and DBTs. SCW was found to be ineffective in breaking the stable aromatic rings of these thiophenic compounds. Work in this thesis shed light into molecular level reactions during SCW treatment rather than changes in bulk properties which are often reported in work in the field of SCW desulfurization.