Research On Upgrading Of Bio-oil To Advanced Liquid Fuel

Upgrading of bio-oil to stable and combustible oxygenated organics in supercritical fluids (methanol or ethanol) is superior to converntional upgrading methods in terms of low H2 consumption and high liquid yield. However, high solvent consumption caused by high solvent to bio-oil ratio hampered the application of this upgrading method. Besides, the reaction mechanisms of compounds in bio-oil which are crucial for the optimization of this upgrading approach during supercritical upgrading are not clear. In this paper, the reaction mechanisms were clarified by model compound. Based on the results, the supercritical upgrading process was optimized. Moreover, a new upgrading approach was proposed. The consumption of ethanol was extremely low and the properties of upgraded products by this method were superior to that obtained by supercritical upgrading.Firstly, the reaction mechanisms of compounds in bio-oil were clarified using acetic acid, furfural, and guaiacol as model compound. The effects of reaction conditions, catalyst supports, and active metals were analyzed.Based on the results obtained by model compounds, low temperature hydrogenation followed by supercritical upgrading in ethanol (HS) was proposed to decrease the consumption of ethanol and direct upgrading in supercritical ethanol (DS) was also conducted as a comparison. The consumption of ethanol in HS was slightly lower than that in DS. For both methods, the physical properties (heating value, pH) as well as GC-MS results of bio-oil were improved greatly. The effect of catalyst was analyzed in direct supercritical upgrading with 2:1 of ethanol to bio-oil ratio. Compared with Ru/HZSM-5, C-supported catalysts (Pt/C, Pd/C, and Ru/C) gave better upgrading performance. Over the C-supported catalysts, the heating value increased from 21.45 MJ/kg to about 30 MJ/kg and the pH value increased from 3.13 to about 5.5. The ratio of ethanol to bio-oil was further reduced to about 1:1 by solvent recovery and reutilization. The relative content of desired products particularly that of esters increased with the recovered solvent. The stability of catalyst in supercritical upgrading was also studied.To further decrease the consumption of solvent, hydrogenation-esterification was proposed. N-butanal, acetic acid, and phenol were selected to represent aldehydes, acids, and phenols, respectively. To convert these compounds into stable and combustible oxygenated organics (alcohols and esters), separate hydrogenation-esterification (SHE) of n-butanal, phenol, and acetic acid was carried out.100% conversions of n-butanal and phenol were achieved over C-supported catalysts (Ru/C, Pt/C, and Pd/C) with high selectivity to desired products. With the catalysis of SO42-/ZrO2/SBA-15, the yields of butyl acetate and cyclohexyl acetate were 75.89% and 30.97% respectively, which were higher than those over HZSM-5. Based on the results, one-pot hydrogenation-esterification (OHE) of n-butanal, phenol and acetic acid was tested. In OHE, yields of desired products (alcohols and esters) reached 95%, which were higher than those in SHE.Pyrolytic lignin, the water insoluble fraction in bio-oil, was characterized by 2D 1H-13C HSQC and quantitative 13C NMR techniques. The hydrogenation of pyrolytic lignin was conducted with a Ru/TiO2 catalyst at temperatures ranging from 25℃ to 150℃ with higher temperatures showing higher levels of hydrogenation. Coke formation and catalyst deactivation were detected across the range of temperatures tested. A three step hydrogenation scheme at 150℃ was utilized to promote further hydrogenation and resulted in a reduction of aromatic carbons from 64.61% to 16.68% where a single step resulted in a reduction from 64.61% to 38.45% aromatic carbons. Coke formation during the second and third hydrogenation steps was greatly reduced. Further fractionation of pyrolytic lignin into low and high molecular weight fractions and hydrogenation of those fractions found coke formation to be twice as much with the high molecular weight fraction over the low molecular weight fraction.A new upgrading approach was proposed based on the previous results. Bio-oil was first fractionated to aqueous fraction and water insoluble fraction (pyrolytic lignin) by water extraction. The aqueous fraction was upgraded by hydrogenation and pyrolytic lignin was upgraded by hydrogenation-catalytic cracking. After hydrogenation, the relative content of desired products (alcohols/ethers and esters) reached as high as 91.01%. The cracking of pyrolytic lignin as well as hydrogenated pyrolytic lignin was conducted by Py-GCMS. The products from pyrolytic lignin cracking were mainly phenols, while alcohols made up about 55% of the total peak area in the products from hydrogenated pyrolytic lignin cracking. With the catalysis of HZSM-5, the peak area percentage of aromatics was over 80%, while aromatics accounts for 67.9% of the total peak area with the rest being alkanes over HY.In this paper, bio-oil was upgraded to advanced liquid fuels by two methods, supercritical upgrading and fractionation upgrading. For both methods, the entire processes from biomass to advanced liquid fuels were estabilished by using Aspenplus and the energy efficiency was calculated. The energy efficiency of biomass fast pyrolysis-fractionation upgrading was about 39%, which was almost equivalent to the other approach. However, the advantages of biomass pyrolysis-fractionation upgrading were simpler process, milder reaction condition and superior properties of refined oil.