Ru, Rh, Ni, Pd Complexes Catalytic Upgrading Of Bio-oil

The crude bio-oil as a low-quality fuel requires upgrading to improve the quality before it is suitable to be applied in a more extensive area. Presently, a number of upgrading routes, such as hydrogenation, cracking, esterification and steaming reforming have been studied to extend the range of possible application, and some progresses were achieved. However, due to the bio-oil's high heat-sensitive property, the current upgrading methods using the tradional heterogeneous catalysts always need severe conditions lead to quick formation of substantial coke or char. The coke or char no only lead to the catalyst deactivate quickly by steadily deposited on catalysts surface or formation inside but also lead to low bio-oil production.The main aim of this study is to establish a mild and efficient bio-oil catalytic upgrading method. According to the result of analysis the high heat-sensitive compounds and their reactive characteristics, the method of using homogeneous metal complex catalytic upgrading of bio-oil was established. The aldehyde in bio-oil as a highly reactive species can reactive with water, alcohols, phenols or each other to form various small molecules, oligomers and resins, particularly in acidic environment the reactions will become more intensively. In this study, firstly, the catalyst RuCl₂(PPh₃)₃ which has been reported shown strong effect on aldehydes hydrogenation was chosen to catalytic hydrogenation of the model aldehydes of bio-oil. The result shown that the conversion rates of these three aldehydes within vanillin were more than 90%, though the temperature less than 100 oC. Subsequently, the ethyl acetate extracted bio-oil which contains a large number of unstable compounds was hydrogenated for investigate the detail compounds transformation. Aldehydes, ketones and phenol with C=C side chain were substaintially converted to more stable compounds. Upgrading of the whole bio-oil has been the difficulty of catalytic refining. Secondly, the Ru,Rh,Pd,Ni complexes with PPh3 ligand were used to catalytic upgrading the whole bio-oil. The effect of various parameters on hydrogenation reaction was disscuessed (T<100 oC, P=2.0-3.0MPa). A main drawback of homogeneous catalyst is the catalyst recycling. Thirdly, the homogeneous cataslyst RuCl₂(PPh₃)₃ and RhCl(PPh₃)₃ which have been tested shown better effect in bio-oil upgrading were further heterogenized on mesoporous MCM-41. The utilization of heterogenized homogeneous metal complex in the whole bio-oil was disscuessed in advance. Meanwhile, the catalysts recyclability and performance were investigated in details. Similar to"neat"metal complex catalyst, the highly reactive aldehydes, phenols were converted to corresponding hydrogenated products with heterogenized metal complex. Moreover, due to the mild conditions, no char or coke formation was found in all experiments.