UPGRADING OF EXTRA-HEAVY CRUDE-OIL BY DIRECT USE OF METHANE IN THE PRESENCE OF WATER - DEUTERIUM-LABELED EXPERIMENTS AND MECHANISTIC CONSIDERATIONS

The upgrading of Orinoco Belt extra-heavy crude oil by reaction by met hane in the absence of catalysts (thermal conditions) using water as a dditive was studied. The reaction of Hamaca crude oil (water content 4 .3 wt%) with methane in a batch reactor at 380 degrees C and 11 MPa fo r 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 degrees C), 60% con version of the > 540 degrees C fraction and 11.3% reduction of sulfur with respect to the original crude. Compared with the methane experime nt, reaction under nitrogen (control experiment) led to a product with higher viscosity (2.6 Pa s), only 54% conversion of the heavy fractio n 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 H-1 and D- 2 n.m.r. analysis, the most probable pathway is a free-radical mechani sm which involves incorporation of methane via production of methyl ra dicals. Reactions with a dehydrated crude oil (< 1 wt% H2O) under meth ane and nitrogen gave similar results (2.4 Pa s, 45% conversion and 8% sulfur removal), indicating that the presence of water enhances metha ne incorporation into the upgraded products. The beneficial effects of water in the CH4 upgrading experiments can be explained by the reacti on of OH. with methane, with the concomitant production of methyl radi cals to continue the chain process.