Research on upgrading of bio-oil in supercritical alcohols shows a potential to produce vehicle fuels from bio-crude. However, the separation of solvent alcohols and upgraded oil remains a problem. In this paper, biocrude derived from fast pyrolysis of rice husk was upgraded in supercritical CO2 with the catalysts of Pd, Ru, Pt (supported on activated carbon), in order to recycle the solvent from upgraded oil spontaneously. Results reveal that increase of reaction temperature promotes both esterification reaction and hydrogenation reaction, while increase of initial H2 pressure promotes the conversion of aldehydes, but decrease the conversion of phenols and sugars. On this basis, the production process of fast pyrolysis and supercritical CO2 upgrading was established and simulated with Aspen plus software. Through life cycle inventory analysis, the environmental impact of this process were studied, and then compared with upgrading in supercritical ethanol. The result shows weaknesses centered in the agricultural production and upgrading process. At last, the analytic hierarchy process is used to consider the weights of various environmental indicators to obtain a comprehensive LCA result. The final results display a slightly better environmental impact potential than that of ethanol.
Keywords bio-oil upgrading, supercritical CO2, life cycle assessment(LCA), the analytic hierarchy process(AHP)