The upgrading of bio-oil by catalytic transformation upon acidic catalysts is aimed at adapting its composition to that of conventional fuel, or at obtaining petrochemical raw materials, such as olefins and aromatics. A further alternative of growing interest for bio-oil upgrading is catalytic reforming for obtaining H2. The viability of any of these alternatives requires minimizing both the plugging problems that arise in the reactor when the bio-oil is fed and the rapid deactivation of the catalyst, which are associated with the thermal degradation of the lignocellulosic components. In this paper, the catalytic transformation of bio-oil (obtained by fast pyrolysis of vegetable biomass) in a fluidized bed reactor upon a Ni-HZSM-5 zeolite catalyst has been studied, and special attention has been paid to the design of the feed preheating zone. Operation in a single-unit (U-shaped steel tube) for the thermal treatment of the bio-oil (in the downward zone of the U-tube) and its catalytic transformation (in a fluidized bed located in the upward zone of the U-tube) has been compared with operation in a two-unit system, where both steps are carried out in separate units connected through a thermostated line (U-shaped tube for thermal treatment, followed by a fluidized bed reactor for catalytic transformation). It has been proven that a separate step of thermal treatment prior to the catalytic transformation notably improves the global process of bio-oil upgrading. Firstly, it contributes to minimizing coke deposition on the acidic catalyst, mainly the deposition of "thermal" coke (which is associated with the thermal degradation of the bio-oil components at high temperatures), leading to an important attenuation of catalyst deactivation. Secondly, the bio-oil components degraded in the thermal treatment can subsequently be subjected to another upgrading treatment (by steam activation or pyrolysis) in order to obtain a high quality char, which involves upgrading the entire bio-oil.
©2011 Walter de Gruyter GmbH & Co. KG, Berlin/Boston
