No abstract

The transformation of crude bio-oil to hydrocarbons has been studied in an online thermal catalytic process that is comprised of two steps: the thermal treatment reactor, followed by the catalytic reactor. The deposition of pyrolytic lignin formed by the polymerization of biomass-derived products is enhanced in the thermal step. Volatiles are processed in a fluidized-bed reactor with a catalyst that is hydrothermally stable and selective for aromatic production, which is based on a HZSM-5 zeolite modified by the incorporation of 1 wt % of nickel. The effect of operating conditions (temperature, space time, and time-on-stream), as well as feedstock ratio, on bio-oil conversion, product lump yields, and the selectivity of aromatics has been studied. These conditions also have a significant effect on deactivation, which is attributed to coke deposit on the catalyst. The temperature-programmed oxidation (TPO) curves of coke combustion allow the identification of two fractions: one of thermal origin (pyrolytic lignin) and the other of catalytic origin, whose formation is dependent on the concentration of oxygenates in the reaction medium. A feed with 60 wt % methanol, at 450 °C, with a space time of 0.371 (g of catalyst) h (g of oxygenates)−1 allows one to obtain 90 wt % conversion of the bio-oil in the feed in the catalytic transformation step, with a selectivity of aromatics of 0.4 (benzene, toluene, xylenes (BTX) selectivity of 0.25). These results remain almost constant in the first hour of reaction. The yields of CO and CO2 are low, because their formation is attenuated by co-feeding methanol.

Abstract:The results of the catalytic transformation on HZSM-5 zeolite of mixtures of components of biomass pyrolysis oil in the 673-723 K temperature range are evidence of the need for previously separating certain components (aldehydes, oxyphenols and furfural) that undergo severe thermal degradation by forming carbonaceous deposits at the reactor inlet ducts and on the catalyst itself. The deactivation of the catalyst is a consequence of the deposition of two different types of coke: one of catalytic origin (similar to that generated in the transformation of methanol and bioethanol) and the other of thermal origin, which is produced by the aforementioned degradation. The remaining oxygenate components react to each other with synergistic effect, which means that their reactivity is higher than that of the pure components. The results show that the aqueous fraction of biomass pyrolysis oil may be transformed into hydrocarbons on acid catalysts similarly to the more familiar transformation of methanol and bioethanol.

BACKGROUND: The catalytic processes for valorizing the bio-oil obtained from lignocellulosic biomass pyrolysis face the problem that a great amount of carbonaceous material is deposited on the catalyst due to the polymerization of phenolderived compounds in the crude bio-oil. This carbonaceous material blocks the catalytic bed and contributes to rapid catalyst deactivation. This paper studies an on-line two-step process, in which the first one separates the polymerizable material and produces a reproducible material whose valorization is of commercial interest.

The valorization of crude bio-oil by catalytic transformation into hydrocarbons has been carried out in an online two-step (thermal-catalytic) process. The deposition of pyrolytic lignin, formed by polymerization of biomass-derived products, is enhanced in the thermal step. Volatiles are processed in a fluidized bed reactor with a catalyst that is hydrothermally stable and selective for olefin production, which has been based on a HZSM-5 zeolite. A study has been made of the effect of operating conditions (methanol content in the feed of bio-oil/methanol, temperature, space time, and time on stream) on bio-oil conversion, product lump yields and the selectivity of each individual C 2 -C 4 olefin. These conditions also have a significant effect on deactivation, which is attributed to coke deposited on the catalyst. The TPO curves of coke combustion identify two fractions: one of thermal origin (pyrolytic lignin) and the other of catalytic origin, whose formation depends on the concentration of oxygenates in the reaction medium. A feed with 50 wt % of methanol, at 500 °C, with space time of 0.371 (g of catalyst) h (g of methanol) -1 allows a 94 wt % conversion of the bio-oil in the feed, with a selectivity of C 2 -C 4 olefins of 48 wt % (50 wt % is propene) and low yields of CO and CO 2 (its formation is attenuated by cofeeding methanol).