Catalytic Hydrogenation Of Levulinic Acid To Produce Gamma-valerolactone Over Nickel-based Catalysts

With the increasing consumption of coal, petroleum and other petroleum resources, it is urgent to search for sustainable resources. Biomass is a kind of abundant and renewable resources. Due to the complicated structure of biomass, however, it is difficult to be efficiently converted to liquid fuels and various chemicals. Gamma-valerolactone (GVL), a rising platform compound, is regarded as a bridge between biomass resources and bio-based liquid fuels and chemicals, which is favorable for the efficient utilization of biomass.Gamma-valerolactone can be synthesized by the hydrogenation of bio-based levulinic acid (LA). Recent studies mainly focused on the research field using noble metal catalysts for hydrogenation. The reports on non-noble metal catalysts were sparse. The high cost of noble metal catalyst binders the industrialization of GVL production. Pointing at this issue, the nickel based catalysts were developed to catalyze the hydrogenation of LA to GVL. The catalysis mechanism and regularity of hydrogenation were demonstrated. An efficient and low-cost approach for the preparation of GVL was established.Firstly, nickel supported on zirconium dioxide (Ni/ZrO2) with different nickel loading was prepared by the co-precipitation method. N2 physisorption, X-Ray diffraction and transmission electron microscope analysis were used for the characterization of the catalysts. The activity of the catalysts was evaluated, and then the effects of different nickel loading, reaction temperature, hydrogen pressure and solvent were also investigated. The results showed that high LA conversion could be achieved with the catalyst of high nickel loading. The conversion rate, however, increased first and then decreased as the nickel loading increased. High reaction temperature could accelerate the reaction speed without decreasing the selectivity of the product. In the range of experiments, hydrogen pressure would not affect the reaction. Compared to water, dioxane could facilitate the conversion of levulinic acid. In dioxane, the conversion of levulinic acid with 30% Ni/ZrO2 was 99.1% after reacted for 9 h at 200℃ under 3 MPa hydrogen pressure.Then, aluminium oxide was selected as the support of nickel. Nickel supported on aluminium oxide catalysts (Ni/Al2O3) with different nickel loading were prepared by the co-precipitation method. A series of characterizations were used for the catalysts, and the catalytic activity were evaluated. The effects of different nickel loading, reaction temperature, hydrogen pressure and catalyst loading were also investigated. The results showed that high nickel loading of the catalyst is favorable for high conversion of LA. High temperature could remarkably speed up the reaction rate. With the increase of hydrogen pressure, the conversion of levulinic acid increased at first and then kept stable. Decreasing the loading of the catalyst, the conversion of levulinic acid decreased rapidly. After that,40% Ni/Al2O3 was selected to conduct the test for reusability. The result showed that the catalyst lost activity in water but good catalytic activity can be kept in dioxane. In dioxane, under 3 MPa hydrogen pressure, 40% Ni/Al2O3 as catalyst, the conversion of levulinic acid was 100% and the selectivity of gamma-valerolactone was 99.2% after reacted for 2 h at 180℃.At last, to further improve the catalytic efficiency of catalyst, MgO was added to Al2O3. Nickel supported on magnesium oxide-aluminium oxide (Ni/MgO-Al2O3) with different nickel loading and different carrier component were prepared by the co-precipitation method. A series of characterizations were used for the catalysts, and then the catalytic activity was evaluated. The effect of nickel loading on the catalytic activity was consistent with the two kinds of catalyst above. The effect of support composition on the catalyst activity was investigated. The results showed that MgO-Al2O3 was a better support compared to MgO or Al2O3. The proportion of MgO and Al2O3, however, did not show unambiguous regularity to impact the catalytic activity.40% Ni/MgO-Al2O3(Mg:Al=1:1) was selected to conduct the test for reusability. The conversion of LA slightly decrease after used by 4 times, but the selectivity was stable. In dioxane, under 3 MPa hydrogen pressure,40% Ni/MgO-Al2O3 as the catalyst, a LA conversion of 100% was achieved within 1 h at 160℃. Combining the results of characterizations and reactions, the mechanism of hydrogenation was demonstrated, and the effect of hydrogen pressure, solvent and support on reaction was also discussed.