Experimental Study Of Catalytic Hydrogenation Of Phenol As A Model Compound For Bio-oil

Biomass energy, as a new type energy, is environmental friendly, making it an attractive alternative energy source. In China, there is abundance of biomass. Therefore the development and utilization of biomass energy is significative to the energy security of China. Biomass can converted to liquid fuel named bio-oil through the technology of pyrolysis liquefaction. Bio-oil is the most promising renewable energy to substitute the conventional fossil fuel. But bio-oil is a viscous, acidic, and polar liquid with a low heating value, making it, in most cases, unsuitable as an engine fuel directly. These unfavorable characteristics are all associated with high levels of oxygen containing compounds in the oil. An urgent necessity to upgrade the bio-oil is demanding. Catalyst hydrogenation is an effective way for bio-oil upgrading. At present, some research about the catalyst hydroteatment of bio-oil or oxygen-containing compounds in bio-oil, such as phenol, have been reported. But most of these research are focused on the pathway of hydrodeoxygenation(HDO)of phenol with different catalysts and the hydrogenation activity of these catalysts. The research about the variation of the conversion rate of reactants and the yields of the products with reaction conditions is less reported. In addition, the solvents used present are mainly dodecane, n-decane and n-hexane. Most of them are toxic and non-renewable, so their the application and popularization are limited. Compared with these solvents, ethanol is non-toxic and renewable. Although supercritical ethanol has been proved to be an effective reaction media for bio-oil upgrading, the study of the hydrotreatment of aromatic compounds in supercritical ethanol is less reported. Based on the current situation, this work conducted an investigation on the catalyst hydrogenation process of phenol as bio-oil model compound with noble metal catalysts (Pt/C and Pd/C) in supercritical ethanol, and made an comparison of the hydrogenation activity between different catalysts, Pt/C, Pd/C, Ru/C and Ni/SiO2-Al2O3.The kinetic model for predicting the conversion rate of phenol was established.Main conclusion of this work are:(1) The higher temperature, higher hydrogen pressure, and longer reaction time led to the higher conversion rate of phenol in the hydrotreatment of phenol with platinum supported on carbon in supercritical ethanol system. And the effect of temperature was more efficient. Based on the above, a kinetic model for predicting the conversion rate of phenol was established. The model could provide accuracy for predicting the conversion rate of phenol at different process conditions (R2=0.989). The results of kinetic investigation indicated that the reaction order of the catalytic hydrogenation of phenol in supercritical ethanol was two, and the activation energy was51.7KJ·mol-1, which can provide guidance for controlling the reaction process and improving the conversion rate of phenol in bio-oil upgrading.(2) The analysis result of products of hydrotreatment of phenol with Pt/C catalyst in supercritical ethanol showed that Pt/C catalyst was not effective for the hydrogenation of phenol. It may be that the catalyst adsorbed ethanol first, which led to ethylation reaction between phenol and ethanol, and the reaction of phenol and hydrogen was inhibited. In spite of this, the kinetic investigation of the phenol conversion rule would provide guidance for the research of hydrogenation process of bio-oil and other model compounds in it.(3) Another noble metal catalyst, palladium supported on carbon, was researched for the hydrotreatment of phenol. The palladium catalyst was effective for the hydrotreatment of phenol in the supercritical ethanol showed by the analysis of the liquid product, including ethoxy cyclohexane, cyclohexane, cyclohexanol and cyclohexanone. In the water system, Pd/C could still keep its high hydrogenation activity. The influence of temperature and hydrogen pressure on the reaction were discussed. The results showed that high temperature was benefit for the conversion of phenol. But the lower temperature was benefit for the formation of cyclohexane, cyclohexanone and cyclohexanol. At the same reaction time, higher temperature led to the higher concentration of benzene at the temperature range of300℃～400℃. The Pd/C catalyst was stable, and the catalyst recycling twice still kept high hydrogenation activity. Pd/C catalyst has a certain recovery value.(4) The products of hydroteatment process of phenol with three different kinds of Lewis acid (AlCl3, ZnCl2and LnCl3) and Pd/C catalyst were analyzed. The results showed that ZnCl2and LnCl3could inhibited the hydrogenation activity of the Pd/C catalyst, but the Pd/C and AlCl3catalyst was still effective for the hydroteatment of phenol. (5) The ruthenium catalyst supported on carbon and nickel catalyst supported on silicon dioxide and aluminium oxide were studied. The analysis results of the liquid products showed that Ru/C and Ni/SiO2-Al2O3almost had no hydrogenation activity in the supercritical ethanol. This indicated that the two kinds of catalysts were not effective in the supercritical ethanol for the hydrogenation process for upgrading.(6) In general, Pd/C was superior hydrogenation catalyst in the supercritical ethanol system and water system though the comparison of the hydrogenation activity of the various catalysts mentioned above.