Search

[Display omitted] • Pyro-reforming of sawdust co-produces H 2 and heavy organics effectively above 550℃. • Small acids and ketones are reformed while furans, anhydrate sugars, phenols retain. • Coking from cracking/polymerization of volatiles reached the maximum at 500℃. • Dominant reforming at 650℃ aids coke elimination and forms nanotube coke. • Coke at lower temperature is amorphous and more aliphatic with low crystallinity. In hydrotreatment of bio-oil, it is difficult to convert the aliphatic compounds with the carbon number less than four into liquid fuel via hydrodeoxygenation. Thus, ideally, the very light organics of bio-oil could be reformed to generate hydrogen for further upgrading the heavier organics in bio-oil to biofuel or fine chemicals. In this study, the pyrolysis of poplar sawdust coupled with the simultaneously steam reforming of the bio-oil (pyro-reforming) were studied over Ni/SBA-15 catalyst at the medium temperature range from 450 to 650 °C for transforming mainly the light aliphatic compounds into H 2. The results showed that the effective steam reforming of the aliphatic compounds like carboxylic acid and small aldehydes/ketones took place to remarkable extent from 550 °C, while the furans, anhydrate sugars, light phenols and heavy phenolics of fused ring structures could be largely retained in the resulting bio-oil. Coking reached the maximum with increasing temperature to 500 °C from cracking/polymerization of the volatiles. Further increase of temperature to 650 °C accelerated steam reforming and gasification of precursors of coke, shifting the morphology of coke from amorphous form to unregular carbon nanotube structures (stringed beads-like) and making the coke more aromatic and more resistant to oxidation. Nevertheless, in overall, the coke produced from 450 to 650 °C was aliphatic with low C/H ratio, low thermal stability and low crystallinity, originating from the significant contribution from the aliphatic compounds in the bio-oil for coking. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reactions of volatile and biochar fill pores via forming carbon deposit on biochar. • Aliphatic of cellulose are more reactive than phenolics of lignin with biochar. • Volatile-char interaction consumes aldehydes/ketones and π-conjugated organics. • Volatile-char interaction dominate pore formation instead of activation with H 2 O/CO 2. • Interaction aids deoxygenation, forming C-rich biochar of higher energy yield. CO 2 and H 2 O are commonly used oxidants for activation of carbonaceous feedstock, which are also major products in biomass pyrolysis. The heated CO 2 and H 2 O from pyrolysis might be used directly to activate biochar without cooling down. This was investigated in a reactor with dual fixed beds with biochar on the bottom and biomass feedstock (poplar sawdust, cellulose, or lignin) of the same origin on top. The CO 2 and H 2 O together with the volatiles generated at 700 °C from the top bed passed through the lower-bed biochar for activation. The results indicated that, except for CO 2 and H 2 O, the volatiles from pyrolysis of upper-bed biomass were highly reactive with the lower-bed biochar, especially for the cellulose-derived aliphatic volatiles. This formed carbonaceous deposit and enhanced the yield of biochar at expense of the volatiles (i.e. aldehydes/ketones and heavy organics of large π-conjugated structures), leading to lower yields of bio-oil. The carbonaceous deposit formed via cracking and/or polymerization filled the pores and substantially decreased the surface specific area by 99.9 % for sawdust-biochar, 87.4 % for cellulose-biochar, and 33.1 % for lignin-biochar. The volatile-char interaction, instead of the activation with CO 2 and H 2 O, dominated the pore development of biochar. Additionally, the interaction of volatiles with biochar enhanced deoxygenation, producing the carbon-rich biochar of higher heating value and energy yield. [ABSTRACT FROM AUTHOR]