Effect of Tetralin, Decalin and Naphthalene as Hydrogen Donors in the Upgrading of Heavy Oils

Abstract

Abstract Nowadays the upgrading of heavy crude oils is achieved by thermal cracking or hydrocracking, which are based on the carbon rejection and hydrogen addition routes. These processes have several problems yet to be solved, such as coke deposition both on the reactor walls and on the catalyst, low quality of products and low efficiency of usage of hydrogen. Thus, an efficient technology for the production of high quality distillates from heavy oils or residua has not been developed yet. An interesting alternative for improving the yield of valuable liquid products in the hydroprocessing of heavy feeds is the use of hydrogen donors (usually polycyclic naphthenic-aromatic or naphthenic compounds that can be reversibly hydrogenated-dehydrogenated in the reacting mixture). The molecules of the hydrogen donors are dehydrogenated, transferring hydrogen atoms to the heavy hydrocarbons in the oil, thus improving the quality of the cracked products and minimizing the polymerization of the heavier molecules via a free radicals mechanism. This work is focused on the effect of tetralin, decalin and naphthalene as hydrogen donors (Hdonors) in the thermal cracking of a Mexican heavy crude oil (12.1 °API) in the presence of hydrogen or methane as reducing agents. Experiments were carried out in a batch reactor under relatively mild conditions, 1.1 MPa initial pressure and 693 K temperature. The results indicate that the combination of these H-donors and reducing agentsleads to significant reductions in the yield of coke, compared to those obtained using only the reducing agents under the same conditions. The improvements in the API gravity, the viscosity and the distillates yield (as determined by GC-simulated distillation) upon treatment are nearly the same with or without H-donors, confirming that the primary cracking reactions depend mainly on the temperature of reaction and are not appreciably affected by the presence of reducing agents or hydrogen donors. The reduction in the yield of coke was similar for tetralin, decalin and naphthalene.