| Biomass is the only renewable carbon resource and can be converted to biofuels through thermo-chemical and bio-chemical methods. Liquid biofuels are promising alternatives in future application since they can be used as transportation fuels to replace traditional petroleum fuels. Crude bio-oil derived from biomass fast pyrolysis has several inferior properties such as high water and oxygen content, low heating value and strong acidity. Therefore it should be upgraded to be high quality biofuel. Based on the support of National Basic Programs and National Natural Science Foundation of China, experimental study on catalytic upgrading of crude bio-oil in supercritical ethanol system was investigated in this work in order to produce stable and combustible oxygenated compounds. The conversion pathway of crude bio-oil production and subsequent upgrading in supercritical ethanol was evaluated using life cycle assessment. Meanwhile the environmental life cycle assessment of crude bio-oil production and hydroprocessing was conducted and compared with the above conversion pathway.Crude bio-oil derived from rice husk fast pyrolysis was first upgraded using2%Pt/10%Ni/HZSM-5in ethanol under hydrogen atmosphere. The results showed that the heating values of dry upgraded bio-oil under all reaction conditions were elevated from21.89MJ/kg of dry crude bio-oil to more than27MJ/kg, and the amount of desired products were increased from56.09%to more than73%. With the increasing of initial hydrogen pressure, the amount of desired products, the yield of dry upgraded bio-oil and the energy efficiency of upgrading process were all raised. Higher initial hydrogen pressure inhibited coke formation on catalyst evidently. With the increasing input mass ratio of ethanol to crude bio-oil, the mass ratio of actual consumed ethanol to dry crude bio-oil and the amount of desired products increased while the reaction of ethanol itself became more obvious. With the increasing of reaction temperature, the amount of desired products decreased and the amount of coke deposited on catalyst increased.Crude bio-oil was then upgraded using5%Pt/SO427ZrO2/SBA-15in ethanol under hydrogen atmosphere. The results indicated that the heating values of dry upgraded bio-oil were elevated to more than27MJ/kg and the amount of desired products were raised to more than75%with the input mass ratio of ethanol to crude bio-oil varying from2to5. Under the conditions of higher initial hydrogen pressure, the amount of desired products, the yield of dry upgraded bio-oil and the energy efficiency of upgrading process were all relatively higher while the amount of coke deposited on catalyst was lower. With higher input mass ratio of ethanol to crude bio-oil, the amount of desired products and the heating value of dry upgraded bio-oil were higher while the amount of desired products was lower. With the increasing of reaction temperature, the amount of desired products decreased while the heating value of dry upgraded bio-oil and the amount of coke deposited on catalyst increased.Based on the selected reaction condition, the influence of different catalysts on upgrading performance was conducted. The results suggested that5%Pd/HZSM-5and5%Pt/SZr had better upgrading performances under the reaction condition (initial hydrogen pressure of2.0MPa, the input mass ratio of5and the reaction temperature of260℃).A life cycle assessment of crude bio-oil production from corn stover fast pyrolysis and upgrading in supercritical ethanol system was conducted based on experimental results. In contrast to1MJ conventional gasoline and diesel production, the outcomes suggested a reduction of96.6%in net non-renewable energy and a reduction of91.4%in net GWP where ethanol consumed in crude bio-oil upgrading was derived from corn stover. By changing ethanol source in crude bio-oil upgrading process to sugarcane bagasse, the results indicated reductions of88.0%and85.7%in net non-renewable energy and net GWP. When corn ethanol was consumed in crude bio-oil upgrading process, reductions of53.1%and31.6%were observed on both environmental aspects. All these results showed better environmental benefits and greater advantage were gained if cellulosic ethanol was introduced in crude bio-oil upgrading process.Combined with Aspen Plus results and GREET software platform, a comparative life cycle assessment of biofuel production from corn stover fast pyrolysis and subsequent hydroprocessing was investigated. All the crude bio-oil produced from fast pyrolysis was upgraded to gasoline and diesel in Case1. In Case2, hydrogen for hydroprocessing was provided by steam reforming of part of aqueous phase of crude bio-oil while the leftover crude bio-oil was hydroprocessed to gasoline and diesel. In Case3, steaming reforming of all aqueous phase of crude bio-oil was conducted to produce hydrogen while the oil phase was hydroprocessed for gasoline and diesel production. Compared with1MJ conventional gasoline and diesel production, the results of all three cases showed great environmental benefits. In contrast to crude bio-oil upgrading in supercritical ethanol system using corn ethanol, all these three cases suggested lower net non-renewable energy and net GWP. If cellulosic ethanol was consumed in crude bio-oil upgrading process, the results showed better environmental benefits over Case1and Case2. Among all the cases studied in this work, Case3performed best on both environmental aspects. |
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