A Model Compound Study Of Bio-oil Upgrading In Supercritical Fluids

Biomass. as a renewable energy, plays a significant role in reducing CO2emissions and energy supply. Bio-oil, a liquid product from renewable biomass via liquefaction or pyrolysis, is regarded as a promising renewable energy source and receives more and more attention for the virtue of its environmentally friendly potential. The crude bio-oil is a complicated oxygenated mixture which generally contains a wide variety of acids, phenols, aldehydes, ketones, esters and sugars. As a result, crude bio-oil exhibits some undesired properties such as high water and oxygen content, low heating value, high ignition temperature, high viscosity, strong corrosivity, bad compatibility with the fossil fuel, high residual carbon content, phase separation, and so on.The characteristic of bio-oil hinder its widely use as fuel. In order to enhance its practical application, there must be some ways to improve its quality to become high-grade fuel. At present, the main ways of bio-oil upgrading processes include hydrodeoxygenation, catalytic cracking, catalytic esterification, emulsion reconcile, aqueous-phase reforming and supercritical fluid upgrading technology.Generally speaking, the aim of bio-oil upgrading is to remove oxygen to improve its heating value and thermal stability, such as hydrodeoxygenation, catalytic cracking, and catalytic esterification. However, these techniques, usually halted by catalyst deactivation and reactor clogging, need complicated equipment and excess cost. This paper chooses supercritical fluids as reaction media to upgrade bio-oil through one-step hydrogenation-esterification (OHE) by incorporation and coupling reactions. This new-research objective is to transform a variety of complex and unstable molecules into stable molecules with or without oxygen. The existence of oxygenated hydrocarbons can not only improve the utilization rate of the effective element, reduce the energy consumption, but also improve fuel combustion performance and reduce engine exhaust pollution.A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, with its density close to liquid, and viscosity to gas. It has superior heat and mass transfer characters and can enhance the mix between different materials, form homogeneous reactions, and improve the reaction rate.Hence in this work, the one-step reactions of furfural and acetic acid which were used as model compounds of bio-oil were studied in supercritical fluids(methanol、 ethanol) with the solid super acidic catalyst. In the experiments, HZSM-5, Al2(SiO3)3, SBA-15were used as catalysts carrier. The metal/acid bifunctional catalysts were prepared through the dry impregnation method, including20wt.%Ni/Al2(SiO3)3,20wt.%Ni/SO42-ZrO2/SBA-15,20wt.%Ni/HZSM-5and5wt.%Ni/HZSM-5,10wt.%Ni/HZSM-5,15wt.%Ni/HZSM-5,5wt.%Pt/HZSM-5. The textural properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), and N2temperature programmed adsorption/desorption (N2-TPD), so the distribution of the metal particles on the supports were observed and the surface area of the catalysts was calculated according to the N2adsorption/desorption.The upgrading performances under supercritical conditions were studied through the catalyst comparative experiments. The liquid products were analyzed by gas chromatography-mass spectroscopy (GC-MS) and the recovered catalysts were evaluated by the thermogravimetry (TG), differential thermogravimetry (DTG) after3hours reaction. HZSM-5and ethanol were chosen as the catalyst carrier and solvent. It provides the basis for the crude bio-oil upgrading.Furthermore, the effect of the different supported metal catalysts, temperature, and hydrogen pressure were investigated. The optimized reaction conditions and the general basis for bio-oil upgrading were put forward under supercritical fluid.The reaction in supercritical fluids under pressured H2is the combination of several basic upgrading reactions including hydrodeoxygenation, hydrogenation, catalytic cracking, esterification, and rearrangement. Based on the products analysis, reaction pathway for furfural conversion was discussed in this work.