| As the only renewable energy which could be directly converted into liquid fuels, biomass has attracted widely attention and it has a great value for energy security and sustainable development of our country. Fast pyrolysis of biomass is a simple and efficient technique for biomass conversion and this technology is a promising technical route for biomass application. As the product of biomass pyrolysis, low-grade bio-oil just could be used as fuels of industrial furnaces directly and it must be upgraded to be suitable as a biofuel for internal combustion engines. Based on the above background, this paper worked on catalytic upgrading of bio-oil to improve the bio-oil fuel quality and utilization efficiency of biomass.The stability of bio-oil could be improved by the addition of small molecule alcohols, which was beneficial for catalytic upgrading of bio-oil. Viscosity-temperature and thermal response characteristics of bio-oil/alcohol mixtures had significant effect on the upgrading of bi-oil and it was necessary to study furtherly. Choosing methanol to represent the low molecular weight alcohols, the experiments on viscosity-temperature characteristics of bio-oil/methanol mixture were carried out during30～80℃with0-70%methanol. Based on the results, the semi-empirical formula was established by the regression analysis depending on the Andrade equation, with the average error of2.8%and the maximum error of8.2%compared with our experiment results. Thermal response characteristics of bio-oil/methanol mixture were investigated by self-designed measuring device during initial heating temperature difference of12-32℃with0-70%methanol. The semi-empirical formula was established by the regression analysis based on lumped heat capacity method, which had the average error of4.52%during the main part of our experiments.Catalytic upgrading of bio-oil often requires harsh reaction conditions, which was unfavorable for highly thermosensitive bio-oil leading to coking and deactivation of catalysts. In order to enhance heat and mass transfer, reduce bio-oil residence time and the influence of thermal istability during upgrading of bio-oil, air-atomization was introduced. Based on self-designed two-channel air-atomizing nozzle, the process of air-atomization could be divided into two parts, and the atomization models were established, respectively. Firstly, the liquid rings were formed by liquid film shedding with the high-speed air flows. Then, the liquid rings were broken into droplets under the influences of growing unstable disturbances on the gas-liquid interface. Based on the structure parameters of self-designed two-channel air-atomizing nozzle, liquid film shedding model was established according to the statics and dynamics analysis on inviscid and viscous liquid films depending on free jet theory and the influences of gas speed, liquid speed and liquid viscosity on liquid ring thickness and speed were investigated. According to linear perturbation model (LPM) and empirical correction on gas speed with liquid-gas interaction, the liquid-ring-broken model was set up and the influences of gas speed, liquid speed and viscosity were discussed.Poor thermalstability of bio-oil was partly caused by considerable compounds with unsaturated carbon-carbon and carbon-oxygen bond, which were active for polymerization and condensation reactions under an elevated temperature, leading to poor miscibility of bio-oil’s components, high viscosity and even phase separation. Mesoporous MCM-41and SBA-15were used as the supports of amorphous alloy catalysts. NiMoB/MCM-41and NiMoB/SBA-15were prepared by ultrasound-assisted reduction of nickel-ammonia complex with borohydride in aqueous solution. Mild hydrogenations of bio-oil and its model compound furfural were carried out at various conditions, resulting in less unsaturated compounds and improved stability. Moreover, recycles of these two supported catalysts and unsupported NiMoB were carried out and the deactivations of supported and unsupported catalysts were discussed. The results indicated that1-hydroxy-2-propanone, furfural and2-methoxy-4-vinylphenol in bio-oil were converted to relevant alcohols and saturated phenols under mild conditions and the maximum conversion rates were45.7%,71.5%, and57.1%, respectively. These two supported amorphous alloys exhibited much higher catalytic activity and stability than the unsupported one, especially for NiMoB/MCM-41. The deactivations of these catalysts were mainly caused by reduction of surface active species, transition from amorphous to crystalline state and coke deposited on the surface of catalysts.As the heavy phase had the maximum energy density of bio-oil, simple removal of it could lead to much lower energy utilization efficiency. The heavy phase was mainly composed of oligomers from lignin pyrolysis, which were high-molecular-weight, technology dependent, easy to polymerization and condensation under elevated temperature. Lignin oligomers were the most difficult components for efficient conversion and utilization, which was unfavorable for bio-oil’s application. In view of incomplete lignin’s structure of bio-oil’s heavy phase, lignin and lignin model compounds were used as the representative of lignin oligmers. Photocatalytic degradation of lignin and its model compounds under visible light irradiation were conducted to generate mono-phenolic products. This approach is a promising combined conversion technique of biomass and solar energy, which could achieve an efficient conversion from lignin oligomers into high-value mono-phenolic products and improve the utilization efficiency of bio-oil. Two types of CdS/TiO2were respectively prepared by microemulsion-mediated solvothermal hydrolyzation (CdS/TiO2(SH)) and in-situ sulfurization under supercritical conditions (CdS/TiO2(SS)). The photodegradation reactions of three lignin monomer compounds, αβ-O-4dimer compound and kraft pine lignin (Indulin AT) were carried out at room temperature in alkaline aqueous system by visible light irradiation. Quantitative results showed that the degradation rate of isoeugenol was the highest. The pH of alkaline aqueous lignin solution was reduced during the photodegradation of lignin, and several mono-phenolic compounds were included in the degraded products and vanillin was the main product. The maximum concentration ratio of mono-phenolic compounds was0.376mg/L. β-O-4ether bond, Cα-Cβ, Cβ-Cγ cleavage and α-carbon, β-carbon oxidation were conducted during the photodegradation of kraft lignin. |
PDF Full Text Request