Hydrogenation of Hydrocarbons through Partial Oxidation in Supercritical Water

Abstract

We propose a new process for the hydrotreatment of heavy oils in supercritical water (SCW). The discussion in this paper is composed of three parts: (1) hydrogenation through water-gas shift reaction in supercritical water, (2) selective formation of carbon monoxide by partial oxidation in supercritical water and through combinations of these two, and (3) hydrogenation of hydrocarbons through their partial oxidation in supercritical water. In the experiments involving hydrogenation of dibenzothiophene, carbazole, and naphthalene, faster hydrogenation rates could be obtained in a CO−SCW atmosphere than in a H2−SCW atmosphere. Even in the case of a H2−CO2−SCW atmosphere, similarly faster reaction rates were obtained, which suggests that an intermediate species of the water-gas shift reaction is the actual reason for the high hydrogenation rates. Partial oxidation experiments were conducted for hexylbenzene and n-hexadecane. The selectivity of CO increased with increasing density of water, while CO2 was the main product of the gas-phase reaction. Partial oxidation of dibenzothiophene (with a sulfur-treated NiMO/Al2O3 catalyst) and n-hexadecane (without catalysts) were also examined. Hydrodesulfurization of dibenzothiophene proceeds effectively in water. For n-hexadecane oxidation, the alkane/alkene ratio increased with increasing water density. The observed product distribution is probably due to the production of carbon monoxide, which is followed by the formation of active hydrogenating species via the water-gas shift reaction. This work demonstrates that hydrogenation reactions can be greatly accelerated in supercritical water through the use of either direct introduction of carbon monoxide or in situ formation of carbon monoxide through the partial oxidation of hydrocarbons.

A Review of Laboratory-Scale Research on Upgrading Heavy Oil in Supercritical Water

“…The technique of SCWO is well known, not only because of the destruction of hazardous organic materials into CO2 and H2O [82,83], but also because hydrogenation can proceed without the supply of additional molecular hydrogen [84,85]. In SCW, CO, forming the partial oxidation of hydrocarbon, will undergo a WGS reaction to form in situ hydrogen [85].…”

“…The partial SCWO of some model hydrocarbon compounds [84][85][86][87][88][89][90][91] and asphalt [59] showed that the in situ hydrogen is more active than molecular hydrogen in the case of the hydrogenation of hydrocarbon. Sato et al [42] reported the effects of reaction temperature, water/oil ratio, and air pressure as an oxygen source, on the formation of coke.…”

Upgrading of Heavy Oil by Hydrogenation through Partial Oxidation and Water-gas Shift Reaction in Supercritical Water

“…First, partial oxidation of hydrocarbons formed aldehyde and ketone, which then decomposed to form CO. In the case of partial oxidation of hexylbenzene at 673 K, the selectivity of CO also tended to increase with increasing water density 5), 6) , similar to the partial oxidation of n-hexadecane. The partial oxidation of methane in SCW using a temperature-controlled flow type reactor was examined using O2/CH4 molar ratio of 0.03 at 673 K under 20 to 30 MPa that corresponded to water density of 0.1 to 0.47 g/cm 3 8) .…”

“…The hydrogenation of dibenzothiophene 5) , carbazole 6) and naphthalene 6) proceeded with NiMo/Al2O3 in SCW at 673 K in the presence of CO (SCW CO), H2 (SCW H2) , H2 C O2 ( S C W H2 C O2) a n d . Hydrodesulfurization of benzothiophene and dibenzothiophene proceeds in emulsions with dispersed Mo in subcritical and supercritical water.…”

“…Partial oxidation of heavy oil is important to supply CO for hydrogenation through the WGSR. Figure 1 shows the concept of upgrading of heavy oil through partial oxidation and the WGSR in SCW 5), 6) . First, partial oxidation of heavy oil occurs to form CO. Next, CO reacts with water in the reaction field to produce active hydrogen through the WGSR.…”