Hydrogenation Of Levulinic Acid In Supercritical Carbon Dioxide System

γ-valerolactone is regarded as a promising renewable platform molecule as its excellent properties and wide applications, such as widely used in fuel additive, solvent and liquid fuel, etc. To produceγ-valerolactone through hydrogenation of levulinic acid, the renewable platform molecule, is of a chemical process with widely application prospect. In addition, the carbon dioxide as a kind of environmental friendly medium, can replace the organic solvents to use in various kinds of catalytic reactions, and the catalytic hydrogenation is one of the most widely researched reactions. For the reactions in supercritical carbon dioxide, the CO₂ pressure and phase behavior present significant impact on activity and selectivity of catalytic hydrogenations. Research on the influncing regularity and mechanism of CO₂ pressure is a hot topic in the field of catalytic reaction in green solvents, and it is still a challenging research topic.In this thesis, the hydrogenation of levulinic acid toγ-valerolactone was studied with a homogeneous RuC l2（PPh₃）₃ catalyst in supercritical CO₂（scCO₂）. We mainly discussed the influence of CO₂ pressure on hydrogenation activity and product selectivity. The molecular interaction between carbon dioxide and reactant molecules of levulinic acid in the reaction process was discussed by using the high-pressure in-situ FTIR spectra. Moreover, the interaction between the RuC l2（PPh₃）₃ and carbon dioxide molecules was studied by FTIR and UV–vis measurements. Finally, we revealed the nature of activity changes of RuC l2（PPh₃）₃ catalyst and explained the effects of CO₂ pressure on the total conversion of the present levulinic acid hydrogenation in scCO₂.The experimental results showed that, the total conversion of levulinic acid increased with increasing of CO₂ pressure, which was enhanced from 78% to 99%. Based on the results of high-pressure in-situ FTIR spectra of levulinic acid, the interaction between CO₂ and the substrate was very weak; it had less influence on the levulinic acid hydrogenation activity. However, the results of FTIR spectra and UV–vis spectra of RuC l2（PPh₃）₃ catalyst suggested the presence of CO₂ could change the structure of RuC l2（PPh₃）₃ catalyst, it turned into a highly active RuHC l（CO）（PPh₃）₃ catalyst under the H2 reducing atmosphere in scCO₂. On the contrary, RuC l2（PPh₃）₃ turned into a low activity RuH2（PPh3）4 catalyst under the H2 reducing atmosphere without CO₂. In addition, we examined the effect of system acidity and phase behavior also, the results showed less influence of these two parameters on the activity of levulinic acid hydrogenation.