Study On Hydrogenation System Of Phenanthrene

The processing of heavy oil becomes more and more important, since the petroleum resource around the world is becoming heavier and inferior. As potential coking component, polycyclic aromatics exist in heavy distillate oil extensively. And Polycyclic aromatics with two or more aromatic rings have disadvantageous effect on product quality. Hydrogenation of heavy oil is considered as the most important procedure for turning heavy oil into light oil. But currently the conversion of polycyclic aromatics has some shortcomings, such as high costs and low value-added products. Lowering hydrogen consumption and optimizing products should be the developing trend. So researchers around the world endeavor to develop new hydrogenation catalysts and study new hydrogenation technology. The main object of this paper is to do systematic research on the fundamental reaction mechanism, thermodynamics and kinetics of polycyclic aromatics hydrogenation, and to provide reference for the developing of new hydrogenation catalyst, technology and procedure.Based on reviewing published papers, this paper carried out the study on thermodynamics and kinetics of polycyclic aromatics selective hydrogenation with phenanthrene as model compound. The activity stability and the influence of internal and external diffusion were investigated before the intrinsic kinetic experiments in the continuous fixed-bed micro-reactors. Effects of space velocity, reaction pressure and temperature on the reaction selectivity of phenanthrene hydrogenation with NiMo/Al2O3 and CoMo/Al2O3 catalysts were systematically investigated, and the trend of experimental result was analyzed.Thermodynamics of phenanthrene hydrogenation was estimated based on group contribution method and contrast method, where Joback method and Constantinous-Gani method were used to estimate critical properties. The estimated thermodynamic parameters were compared with available literature value, and the estimation results fit the literature well. The comparison result showed that Joback method is more suitable for the estimation of critical temperature and critical volume, and Constantinous-Gani method is more suitable for the estimation of critical pressure. And the corresponding temperature and pressure with maximum equilibrium dihydrophenathrene concentration were decided. The accuracy of the estimation method was further validated with experimental equilibrium concentration which was achieved in a non-gradient high-pressure autoclave. The thermodynamic research provides equilibrium conversion under different reaction conditions as the basis for suitable selective hydrogenation conditions of phenanthrene, and the method is also useful reference for the thermodynamic research of other polycyclic aromatics hydrogenation system.Referring to the published literature, three different reaction networks were proposed for the phenanthrene hydrogenation to investigate the possibility of different reaction routes. Langmuir-Hinshelwood-Hougen-Watson adsorption theory was adopted to deduce kinetic equations. The reaction rate constants, activation energy and adsorption constants were estimated by BFGS optimization method, and different reaction networks were compared and screened. First, four different assumption about the status of reactants inside the reactor were proposed, then compared and screened with the calculation connected with three different reaction networks. The results showed the fourth assumption which treating hydrogen as gas, reactant and solvent as partial vaporized, and the concentration of reactants based on the total volumetric flow rate, is more reasonable than the other assumptions. And the reaction network 1 (phenanthrene hydrogenation network proposed by A. R. Beltramone, et al.) is the best among the three tested networks.The reaction rate constants, reaction activation energy and adsorption constants for phenanthrene hydrogenation system on two different catalysts were calculated, and the calculation value of component concentration was compared with experimental data. The simulation result was quite good which showed the reliability and feasility of research method on kinetics. And the further discussion on the calculation result revealed some important conclusion.The calculation result about CoMo catalyst showed:The hydrogenation rate constant of the middle aromatic ring of phenanthrene with CoMo catalyst is higher than that of side aromatic ring; the adsorption constant of phenanthrene on CoMo catalyst is higher than that of hydrogenation products, and the result of adsorption competition is that phenanthrene occupies more active sites of catalyst than other molecules; the reaction activation energy of tetrahydrophenathrene to 1,10-octahydrophenanthrene is the highest. In summary, the hydrogenation reaction of phenanthrene on CoMo catalyst tends to stay in the stage of partial hydrogenation, and perhydrophenanthrene does not appear in the hydrogenation products with CoMo catalyst. It is beneficial for selective hydrogenation, hydrogen consumption control, and high added-value product production.The calculation result about NiMo catalyst showed:The hydrogenation rate constant of the side aromatic ring of phenanthrene with NiMo catalyst is little higher than that of middle aromatic ring; the adsorption constant of phenanthrene on NiMo catalyst is the highest, and the adsorption constants of other molecules decrease with undergoing of further hydrogenation; but the difference between adsorption constants of molecules on NiMo catalyst is not as much as that on CoMo catalyst; the reaction activation energy of reaction decreases with the undergoing of further hydrogenation, which is also favorable for the further hydrogenation reactions. Perhydrophenanthrene does appear in the hydrogenation products with NiMo catalyst.Finally, the hydrogenation result of phenanthrene on CoMo and NiMo catalysts was fully compared and analyzed, which showed that CoMo catalyst is more suitable for selective hydrogenation, and NiMo catalyst is more suitable for hydrogenation with heavy or full depth.The full investigation of phenanthrene hydrogenation system is beneficial for the further understanding on the reaction mechanism of polycyclic aromatics hydrogenation. The analysis on selective hydrogenation of phenanthrene provides reference for developing new selective hydrogenation catalyst for polycyclic aromatics, as well as deciding suitable reaction conditions for selective hydrogenation. The research in this paper has its own theoretical meaning and application value.