Selective Production of Aromatics by Crude Bio-oil Valorization with a Nickel-Modified HZSM-5 Zeolite Catalyst

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.

Application, Deactivation, and Regeneration of Heterogeneous Catalysts in Bio-Oil Upgrading

“…Thermal coke was formed by condensation-degradation and polymerization reactions of bio-oil oxygenated compounds derived from lignin pyrolysis in step A [76]. The methanol and bio-oil mixture was transformed into aromatic hydrocarbons present in the hydrocarbon pool via direct deoxygenation, dehydration, decarboxylation, decarbonylation, and cracking reactions using a Ni/HZSM-5 catalyst in step B [79]. Some hydrocarbons contained in the hydrocarbon pool were transformed to C 2-4 olefins through oligomerization-cracking reactions in step C [80].…”

“…C 2-4 olefins were then transformed to C 5+ aliphatics and C 5+ aromatics through alkylation, oligomerization and hydrogen transfer reactions in step D [81]. The C 5+ aliphatics and C 5+ aromatics then undergo rearrangement and condensation reactions to form alkylaromatics and polyaromatics that comprise the catalytic coke in step E [77,79]. Some hydrocarbons present in the hydrocarbon pool were directly converted to catalytic coke through oligomerization, cyclization, aromatization, and condensation reactions that were catalyzed by acid sites of Ni/HZSM-5 catalyst in step F [76].…”

High-Efficiency Separation of Bio-Oil

“…Besides, some thermally sensitive compounds, such as pyrolitic lignin, might undergo aggregation to form a precipitate, which would block the reactor and lead to deactivation of the catalyst. Consequently, efforts have been made to avoid this phenomenon by separating these compounds through thermal pre-treatment (Valle et al, 2010). Therefore, to maintain the stability and high performance of the cracking process, it is necessary to obtain fractions suitable for cracking by separation of bio-oil, to achieve the partial conversion of bio-oil into hydrocarbon fuels.…”

Aromatic Hydrocarbon Generation from a Simulated Bio-oil Fraction by Dual-stage Hydrogenation-cracking: Hydrogen Supply and Transfer Behaviors

“…However, direct cracking of bio-oil faces problems of low aromatic hydrocarbon yield and severe coking (Vitolo et al 1999). There are two main reasons for the coke (carbonaceous deposit) formation: the presence of large molecular weight compounds in bio-oil, such as phenolic oligomers (pyrolytic lignin), which are nonvolatile and have low cracking reactivity, resulting in easy carbonaceous deposition in the catalytic bed (Valle et al 2010); and the hydrogen-poor composition, namely the high unsaturation degree that leads to the low integral H/C ratios of final products and also favors the formation of coke (Zhang et al 2011).…”

“…However, because the hydrogenlacking property of this fraction is not improved, proper hydrogen supply is still required to adjust the H/C ratio of the final products. Researchers found that by coprocessing with hydrogen-rich chemicals, such as alcohols, the cracking behaviors of bio-oil components could be improved (Valle et al 2010;Mentzel and Holm 2011). In the authors' previous studies alcohols were also introduced as the coreactants (Wang et al 2012a(Wang et al , 2013aWang et al 2014b).…”