Effect of sequential catalyst regeneration in catalytic fast pyrolysis of biomass

Fast pyrolysis is a thermochemical process that contributes to the conversion of biomass into a variety of fuels and chemicals. The process aims to produce a liquid mixture of organic molecules called bio-oil. To improve the quality of crude bio-oil in relation to biofuel applications, biomass fast pyrolysis can be carried out in the presence of suitable catalysts. Catalyst particles can be introduced to the reactor (in situ) for the removal of oxygen and the catalytic cracking of high molecular weight compounds in the pyrolysis vapours. The primary goal of this work was to investigate the effects of a repeatedly regenerated ZSM-5 based FCC catalyst on the fast pyrolysis product yields (e.g. organics, water, carbonaceous solids and non-condensable gases), non-condensable gas compositions, bio-oil compositions and the elemental distribution over various pyrolysis products and to gain an insight of the underlying mechanisms. Experiments were performed in a newly designed laboratory scale mechanical agitated bed reactor at a fixed reaction temperature of 500 °C. The experimental reproducibility of the setup has been checked by repetition of several non-catalytic and in situ experiments under identical conditions. The catalyst containing bed material obtained from in situ experiments were successively reacted and regenerated (eight cycles performed in total) to observe the effect of catalyst regeneration on the products and on the catalyst itself. Along the reaction/regeneration sequence, the yield of organics increased, while water, carbonaceous solids and non-condensable gases decreased. The trends in the pyrolysis product yields of converging to that of non-catalytic levels were observed which revealed that the influence of the catalyst slowly declined. The main observation was that the catalyst partially loses its activity along the regeneration sequence due to catalyst poisoning by ash components and the degradation of the physical and the chemical structure of the catalyst during several regeneration cycles