Upgrading of extra-heavy crude oil by direct use of methane in the presence of water: Deuterium-labelled experiments and mechanistic considerations

• Published in: Fuel (Guildford) 1995, Vol.74 (8), p.1162-1168
• Main Authors: Ovalles, Cesar, Hamana, Antonia, Rojas, Iraima, Bolívar, Rafael A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Crude oil, natural gas and petroleum products; Energy; Exact sciences and technology; Fuels; heavy crude; methane; Processing of crude oil and oils from shales and tar sands. Processes. Equipment. Refinery and treatment units; upgrading
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/0016-2361(95)00071-C

The upgrading of Orinoco Belt extra-heavy crude oil by reaction by methane in the absence of catalysts (thermal conditions) using water as additive was studied. The reaction of Hamaca crude oil (water content 4.4 wt%) with methane in a batch reactor at 380°C and 11 MPa for 4 h led to a decrease of two orders of magnitude in the viscosity of the upgraded product (from 500 to 1.99 Pa s at 30°C), 60% conversion of the > 540°C fraction and 11.3% reduction of sulfur with respect to the original crude. Compared with the methane experiment, reaction under nitrogen (control experiment) led to a product with higher viscosity (2.6 Pa s), only 54% conversion of the heavy fraction and only 8.3% sulfur reduction. These results indicate that methane was involved in the upgrading reactions and most probably behaved as a source of hydrogen for the thermal processes. According to 1H and 2D n.m.r. analysis, the most probable pathway is a free-radical mechanism which involves incorporation of methane via production of methyl radicals. Reactions with a dehydrated crude oil (< 1 wt% H 2O) under methane and nitrogen gave similar results (2.4 Pa s, 45% conversion and 8% sulfur removal), indicating that the presence of water enhances methane incorporation into the upgraded products. The beneficial effects of water in the CH 4 upgrading experiments can be explained by the reaction of OH ∗ with methane, with the concomitant production of methyl radicals to continue the chain process.