Separation And Upgrading Of Bio-oil

The bio-oils produced by fast pyrolysis of wood has the potential to used as a substitute for traditional liquid fuel, such as gasoline and diesel oil; however, the crude bio-oils appear to be not good in quality just because of it's high water content, instability and corrosion. Here, mechanism study of bio-oil upgrading was performed to improve the quality of bio-oils under the support of National Natural Science Foundation of China.On the basis of an assessment of the existing separation technologies, molecular distillation method is chosen to separate bio-oil into three fractions: light, medium and heavy fraction. Experimental results showed that molecular distillation technology was particularly suitable for bio-oil separation because the maximum yield of light and mid fraction could reach up to 85% and no obvious coke and polymerization were found.Based on the analysis of physical and chemical properties of bio-oil, light fraction has the property of strong acidity, poor stability and good fluidness, which is mainly composed of ketones, aldehydes and acids; medium fraction has less mobility and low water content, which accounts for small part of bio-oil; and heavy fraction, without volatile substance, appears in black solid and relatively high in heat value. The effect of distillation temperature on chemical composition of each fraction was studied according to the chemical composition category. Moreover, statistical calculation showed that molecular distillation is successful in the bio-oil separation. A series of experiments on pyrolysis kinetics of three fractions were done on a thermogravimetric balance to measure weight loss curves both in the air and nitrogen at a low heating rate. The change of TG and DTG curves were well explained according to the physical and chemical characterization of each fraction. The kinetic models of fractions pyrolysis were brought forward and the dynamic parameters were obtained. The kinetic model is in good agreement with experimental data. On the basis of model reaction study of acetic acid and ethanol, the research on the esterification of bio-oil was carried out on three kinds of strong acidic cation exchange resins. The catalytic esterification improved light fraction in physical characterization. The analysis of gas chromatography-mass Spectrometry showed that the chemical properties of bio-oil after upgrading were different from original oil in which most of volatile organic acids were converted into esters. Besides that, acetalization of some components in bio-oil was promoted by the strong acidic catalyst simultaneously. Hydrotreatment of light fraction was performed on the model compounds and light fraction under the catalysis of Ru/γ-Al2O3 catalyst. Seven model compounds were hydrogenated to determine the reaction mechanism of main components of light fraction. The effect of reaction parameters on the product distribution was also investigated based on the experiment of hydrogenation of light fraction. It was found that mild hydrogenation over Ru/γ-Al2O3 can significantly reduce instability of light fraction.The activity and stability of 1-hydroxy-2-propanone, furfural, eugenol and acetic acid were studied by DMol3 program. And the parameters of the geometry, atomic net charges, the atomic frontier electron densities and Fukui index were obtained. The reaction process and products deduce from the calculation were well consonant with experimental results.