Catalytic Hydrogenation Of Furfural As Model Compound Of Bio-oil Under Mild Conditions

Energy is the material foundation of human society. It is the basic motivation for the development of human and economic growth. Nowadays, the fossil fuels are the most important energy of the world with more than 80% use ratio. The exhaustion and environmental pollution caused by fossil fuels, such as green house, ozone hole and acid rain are threatening the sustainable development of human society. It is urgent to find environmental friendly and renewable alternative resource. In diverse new energy, biomass energy has attracted more and more attention in recent years due to renewability, low pollution, zero emission of CO2, wide distribution and large reserve of raw material. The main ways of biomass utilization are converted into gas, solid and liquid fuels. Among them, bio-oil from biomass fast pyrolysis and then converted into high quality liquid fuels by catalytic upgrade are considered as one of the most effective ways. However, bio-oil has some drawbacks, such as high water content, high oxygen content, low heating value, high viscosity, strong acidity and instability. It is different from fossil fuel in nature and cannot be used directly as vehicle fuel. It can meet the requirements by upgrade. Among various upgrade methods, catalytic hydrogenation has gain much attention beacuse it can improve the stability of bio-oil.Bio-oil is a complex and highly oxygenated mixture, in which furfural has high content. Furfural is very reactive at high temperature and easily reacts with phenolic, aldehydes and alcohols compounds existed in bio-oil to form polymer by polymerization and condensation reactions. This decreases not only the catalyst life but also the carbon efficiency of bio-oil. Converting the reactive aldehyde functional group of furfural (a model compound for aldehyde in bio-oil) into stable products at low temperature is a key step in bio-oil upgrading. In this dissertation, we take the catalytic hydrogenation of furfural efficiently at room temperature as the goal and prepare a series of Pt, Pd-based catalysts with the support of carbon nanotubes. The main results are shown as follows:1. The liquid phase hydrogenation of furfural had been studied over TiO2, ZrO2, CeO2, La2O3, AC and MWNT supported Pt catalysts. The experiments found that among these catalysts, Pt/MWNT catalyst showed the highest conversion of furfural and selectivity of furfuralcohol under the same reaction conditions. The conversion of furfural was 97.2% and the selectivity of furfuralcohol was 92.1% over l%Pt/MWNT catalyst at 100℃ under 3MPaH2 with the reaction time of 5h. This is related to the MWNT special physical and chemical properties, such as electrical characteristics, pore structure and adsorption performances.2. The influence of various reaction conditions on the catalytic hydrogenation of furfural over Pt/MWNT catalyst were investigated systematically. Through the investigation of reaction temperature, reaction time, hydrogen pressure, Pt loading, catalyst dosage and furfural loading, the obtained optimal reaction conditions were as follows:25 ℃,5h,3MPaH2, 1%Pt/MWNT 0.1g and 0.5mL furfural. Under the optimal reaction conditions,92.6% for the conversion of furfural and 85.8% for the selectivity of furfuralcohol were obtained. Polar solvent was favorable for the enhancement of the catalyst activity. The conversion of furfural was just slightly decreased from 92.6% to 83.7% after the 1%Pt/MWNT catalyst was recycled for three times, which indicated the catalyst with excellent stability.3. Effect of different reaction conditions on the catalytic hydrogenation of furfural over Pd/MWNT catalyst were studied systematically. The experiments found that different noble metal supported catalysts can lead to different products distribution. The main furfural hydrogenation product was partial hydrogenation product of furfuralcohol over 1%Pt/MWNT catalyst, but total hydrogenation product of tetrahydrofurfuryl alcohol over 1%Pd/MWNT catalyst. The conversion of furfural was 83.5%and the selectivity of tetrahydrofurfuryl alcohol was 91.8% over l%Pd/MWNT catalyst at 25℃ under 3MPaH2 with the reaction time of 5h. According to the investigation of a series of reaction conditions, we proposed the reaction mechanism of furfural hydrogenation over 1%Pd/MWNT catalyst:most of tetrahydrofurfuryl alcohol was produced by direct hydrogenation of furfural, only a few was catalytic hydrogenation of furfural via furfuralcohol and then further hydrogenation.