A Study On Hydrogenation Of Levulinic Acid To γ-Valerolactone In Different Solvents

Biomass is a renewable energy and carbon-based chemical source. The conversion of biomass to carbon-based chemicals and liquid fuels in green solvents has important environmental and practical significance. Levulinic acid (LA) conversion into y-valerolactone (GVL) is a key step of biomass conversion. Strong acid, alkali and enzymes are uesed in traditional hydrogenation of Levulinic acid into y-valerolactone. The use of those volatile organic and corrosive solvents leads to low product yield, long reaction time, and environmental issues.Ionic liquid (IL) and supercritical CO2 (scCO2) have the unique physical and chemical properties. ILs, scCO2 and water are considered as the three major green solvents in chemical reactions. Ionic liquids, supercritical CO2, and IL/scCO2 biphasic system have been studied extensively in metal-catalyzed hydrogenation.In this study, Hydrogenation of levulinic acid (LA) to y-alerolactone (GVL) in several "green" solvents has been studied systemically. A hydrogenation reaction kinetic model has been established. A possible reaction mechanism was proposed. The effects of water on the hydrogenation, hydrogenation in different solvents (ionic liquid, supercritical CO2 and IL/scCO2 biphasic system) have been studied, respectively.This paper mainly includes the follo wings:1. Under the condition of without solvent, the effects of the reaction conditions, including stirring, temperature, reaction time, H2 pressure were studied. The overall hydrogenation reaction rate is zero-order and first-order with respect to levulinic acid and hydrogen pressure and the activation energy is 33.0kJ/mol. A possible reaction mechanism was proposed.2. By adding different contents of water to the reaction system, the influence of water content on the hydrogenation was investigated. Introduction of water to the system is unfavorable to the hydrogenation, by decreasing the solubility of H2 in the liquid.3. Hydrogenation were investigated in three ionic liquids:[bmim]PF6,[bmim]BF4 and TMGBF4. The effect of hydrogen pressure, reaction time, ionic liquid and catalyst on the hydrogenation were investigated. The results shows that the presence of ionic liquids [bmin]PF6 can significantly increase the rate of hydrogenation.4. After hydrogenation in ionic liquids, the product can be extracted by scCO2 at pressures of 16-17 MPa. After reaction, ionic liquid-catalyst system can be regenerated under vacuum by drying in oven. It can be reuse 3 times without no significant catalyst deactivation. 5. By adding different pressures of CO2 to the reaction system, the effects of temperature, CO2 pressure, H2 pressure on the hydrogenation reaction were investigated. At Low CO2 pressure, the hydrogenation has a low reaction rate. At higher CO2 pressure,the reaction rate was increased with the increase of CO2 pressure.6. Hydrogenation of levulinic acid to y-valerolactone in scCO2 and in IL/scCO2 biphasic system have been studied. The effects of CO2 partial pressure and H2 partial pressure have been investigated. The results show that the presence of of IL can enhance the hydrogenation reaction rate at low CO2 pressure ((0-10 MPa)) and higher CO2 pressure (>15 MPa).