Product quality and catalyst deactivation in a four day catalytic fast pyrolysis production run†
Catalytic fast pyrolysis of pine sawdust was successfully carried out in VTT's 20 kg h−1 Process Development Unit using a spray dried HZSM-5 catalyst. Approximately 250 kg of partially deoxygenated pyrolysis oil was produced over a period of four days. The catalytically produced pyrolysis oil had an average moisture content of 8.3 wt%, and average carbon and oxygen contents of 72.0 and 21.5 wt% on a dry basis, respectively. Approximately 24% of the original biomass carbon was present in the pyrolysis oil, whereas 14% of carbon was in the form of aqueous side products, which totaled approximately 600 kg. The pyrolysis oil contained a high amount of lignin derived water-insoluble material, as well as 6.4 wt% of aromatic hydrocarbons. The majority of the carbohydrate derived products, i.e. acids, aldehydes, ketones and sugar-type compounds, were found in the aqueous product fraction. While the quality of pyrolysis oil remained quite stable during the four day experiment, distinct changes were observed in the properties and the behavior of the catalyst. Coke formation was heaviest at the beginning of the experiment, and then subsided over time. Catalyst micropore area and volume also decreased during the experiment. This transformation was accompanied by apparent changes in the crystallinity and the structure of the catalyst. Scanning electron microscope images of the catalyst also revealed clear physical damage to the particles. Biomass alkali metals also deposited on the catalyst, and the spent catalyst contained a total of 1.1 wt% of Ca, K, Mg and P after the experiment. A linear correlation was observed between catalyst alkali metal content and acidity, which indicated that biomass alkalis substituted the proton functionalities of the HZSM-5 acid sites.