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Microwave pyrolysis features with different heating mechanisms and heat transfer directions from traditional pyrolysis with furnace heating, which might impact evolution of volatiles and nature of biochar in varied ways. This was investigated in this study by pyrolysis of wet and dried banana peel with microwave heating and furnace heating at 400 and 600 °C in a fixed-bed reactor. The results showed that microwave pyrolysis could drastically promote gasification of volatiles to form significantly more gases like H 2 via dehydrogenation and CO via cracking and decarbonylation. This was especially evident in the pyrolysis of wet banana peel with abundant water as the heat transfer medium. The dominance of cracking/gasification of volatiles in microwave pyrolysis was due to the rapid heating and the minimized heat transfer limitation, which suppressed the secondary condensation and thus diminished the formation of bio-oil and biochar. Microwave pyrolysis also favored the cracking of the cellulose/hemicellulose-derived aliphatic organics via cracking but promoted the formation of phenolics via cracking of lignin in banana peel. Moreover, the excessive cracking reactions in the microwave pyrolysis led to the biochar of more excellent thermal stability, lower abundance of oxygen-containing functionalities like C O and more rugged morphology than that with furnace heating source. [Display omitted] [ABSTRACT FROM AUTHOR]

Pyrolysis of biomass typically involves intensive dehydration, cracking, secondary condensation, etc. It is known that these reactions could be accelerated or suppressed with externally added acidic/basic sites presenting on surface of a biomass feedstock, which is expected to impact evolution of pyrolytic products and pyrolysis kinetics. This was investigated herein by pyrolysis of the poplar sawdust loaded with H 2 SO 4 or NaOH at 600 °C. The results indicated that H 2 SO 4 presence enhanced charring of the volatiles including sugars, sugar-derivatives and some lignin-derivatives via dehydration, polymerization, etc. This enhanced biochar production while diminished bio-oil formation and abundance of most of the organics in bio-oil including carboxylic acids, heavy tar (i.e. π-conjugated aromatics), etc. Nevertheless, H 2 SO 4 did not lead to substantial removal of hydrogen and oxygen in the biochar, but increased the activation energy (Ea) of the pyrolysis from 162.6 kJ/mol in pyrolysis of unloaded sawdust to 194.7 kJ/mol. In converse, NaOH promoted cracking/gasification of biochar and the volatiles including heavy tar, forming dominantly gases. NaOH presence also made structures of the semi-char (biochar precursor) more fragmented, reducing the Ea for pyrolysis to 135.7 kJ/mol. The in-situ IR characterization of the pyrolysis process showed that H 2 SO 4 promoted removal of -OH via dehydration or transformation to C O and the further condensation of C O, but not dehydrogenation of -C-H. NaOH promoted mainly deoxygenation and cracking of the sugary structures but not dehydration of -OH to carbonyls. [Display omitted] • H 2 SO 4 enhances charring to form more biochar, while NaOH promotes cracking to gas. • Both H 2 SO 4 and NaOH diminish tar formation via condensation to solids or cracking. • Charring-H 2 SO 4 reserves H and O in biochar, while cracking-NaOH enhances aromatization. • Activation energy in pyrolysis is enhanced with H 2 SO 4 , while decreased with NaOH. • DRIFTS shows H 2 SO 4 does not promote dehydrogenation, while NaOH suppresses dehydration. [ABSTRACT FROM AUTHOR]

The small molecular organics in bio-oil could not be effectively transformed into hydrocarbons with long aliphatic chains or aromatic rings via hydrotreatment, but they could be reformed with steam to generate hydrogen for the hydrotreatment. In this study, the pyrolysis of cellulose coupled with steam reforming of volatiles of small molecular size were performed at 400–600 °C over Ni/Al 2 O 3 catalyst, which is termed as a pyro-reforming process for simultaneous production of hydrogen and heavy organics for further production of biofuels. The results indicated that the effective reforming of small volatiles became dominant at 600 °C. The coke formed at the low temperatures was mainly polymeric coke of aliphatic nature with low thermal stability, low carbon crystallinity, high reactivity towards oxidation and high hydrophilicity. Increase of temperature to 600 °C reduced the formation of coke (from maximum of 15.0%–12.8%) and suppressed the formation of polymeric coke by promoting gasification of precursors of coke. This enhanced formation of catalytic coke with amorphous morphology as well as defective ring structures. However, homogeneous polymerization of volatiles also took place, forming amorphous coke between catalyst particles. Formation of polymeric coke should be tackled for the successful implementation of pyro-reforming process. [Display omitted] • Pyro-reforming of cellulose to H 2 and heavy organics occurs effectively at 600 °C. • Coke formed at 400 °C is polymeric, originating from polymerization of volatiles. • More thermally stable catalytic coke while less polymeric coke forms at 600 °C. • Ratio of aliphatic coke decreases at higher temperature, but it is not negligible. • Homogeneous polymerization of volatile occurs and fills gap of catalyst particles. [ABSTRACT FROM AUTHOR]

[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]

Hydrothermal carbonization (HTC) is a process for enhancing energy content of biomass through deoxygenation reactions, effectiveness of which depends on composition of biomass. Thermal pretreatment could induce structural change of biomass and thus affects the chemical inertness/reactivity in HTC. This was investigated herein by HTC of the pine needles, thermally treated at 250 or 350 °C with/without presence of 11.5% O 2 , at 250 °C for 10 h. The results showed that pretreatment at 250 °C could increase overall yield of hydrochar in subsequent HTC, due to the enhanced aromatization and the resistance towards fragmentation in HTC. Nonetheless, the HTC worked on biochar formed at 250 °C, facilitating deoxygenation to remarkably decrease O/C ratio. In comparison, the pretreatment at 350 °C removed substantial amount of volatile fractions, significantly increasing chemical inertness of resulting char-350 during the followed HTC. Oxygen presence induced oxidation reactions in pretreatment, forming more bio-oil/gases and making resulting hydrochar more hydrophilic. Especially, oxidation at 250 °C formed more aliphatic structures that could be easier removed during followed HTC, enhancing thermal stability of resulting hydrochar. Although a portion of cellulose retained in the biochar obtained from pretreatment at 250 °C, the elimination of aliphatics suppressed formation of spheric structures of hydrochar, while retained original fibrous structures from pine needles. [Display omitted] • Pine needle pretreated at 250°C is more inert in HTC, generating more hydrochar. • HTC barely works the sample pretreated at 350°C, due to removing most of volatiles. • Pretreatment at 250°C retains cellulose crystals, which are removed at 350°C. • O2-pretreatment makes hydrochar thermally more stable via removing more aliphatics. • Pretreatment at even 250°C suppresses formation of hydrochar of spheric structures. [ABSTRACT FROM AUTHOR]

Bio-oil is a complex mixture of organics and each group of chemicals has a varied response to pyrolysis temperatures. This was investigated via the staged pyrolysis of poplar sawdust, cellulose, and lignin by consecutively increasing temperature to 250, 350, 450, and 550 °C, respectively. The results showed that 350 °C was the boundary temperature for formation of majority of organics from sawdust and cellulose and more than half of organics from lignin. The further increase of temperature to 550 °C mainly promoted the aromatization of reaction intermediates from aliphatic components. The staged pyrolysis also facilitated the charring reactions, generating the bio-oil with more light organics including anhydrate sugars, ketones, aldehydes, and phenolics. The enhanced charring reactions promoted the carbonization reactions via deoxygenation, making biochar carbon-rich and thermally more stable. Additionally, the staged pyrolysis also impacted the morphologies and evolution of the functionalities of biochar via influencing the volatile-char interactions. [Display omitted] • Staged pyrolysis of various feedstocks forms the majority of bio-oil at 350 °C. • Increasing temperature promotes mainly aromatization of reaction intermediates. • Staged pyrolysis of cellulose/sawdust produces more sugars, ketones/aldehydes. • Staged pyrolysis forms more light organics in bio-oil via charring reactions. • Staged pyrolysis forms biochar of higher C content, stability, and hydrophilicity. [ABSTRACT FROM AUTHOR]

High nitrogen content in Spirulina platensis -derived bio-oil is a highly undesirable feature in upgrading of bio-oil to biofuel via hydrodeoxygenation. However, the nitrogen species could be potentially used as dopant for tailoring the catalytic behaviors of metallic sites in heterogeneous catalysts. In this study, the nitrogen species in the bio-oil from hydrothermal carbonization (HTC) of Spirulina platensis was used to modify Co-based catalyst for enhancing their catalytic activity for hydrogenation of o -chloronitrobenzene (o -CNB). The results showed that the introduction of N species not only promoted dispersion of Co particles via formation of Co–N sites, but also generated extra pores and significantly increased H 2 uptake. The abundant Co–N sites, high dispersion of Co and higher surface area of N-doped catalyst (CoFeAl–N) jointly contributed to the enhanced catalytic activity for hydrogenation of o -CNB, achieving the yield of 90.3% for o -chloroaniline (o -CA) and lowering the activation energy from 63.0 kJ mol−1 (with N-free CoFeAl catalyst) to 55.1 kJ mol−1. The effectiveness of introducing nitrogen for enhancing catalytic activity for hydrogenation of o -CNB was also confirmed in the experiments for doping Co/Al 2 O 3 (prepared via impregnation) and CoAl (prepared via co-precipitation) catalysts with the Spirulina platensis derived bio-oil. Spirulina platensis derived bio-oil was used as N dopant for modifying cobalt catalysts for the hydrogenation of o-chloronitrobenzene. [Display omitted] • Functionalizing CoFeAl with N from Spirulina platensis bio-oil enhances Co dispersion. • N species react with Co, forming Co–N sites, increasing H 2 uptake by 71.5%. • N species enhances interaction with –NO 2 , lowering E a (12.5%) for hydrogenation. • CoFeAl–N achieves higher o -chloroaniline yield (90.3%) than N-free catalyst (6.0%). • Co–N sites, high dispersion of Co and developed pores enhance the hydrogenation activity. [ABSTRACT FROM AUTHOR]

Bio-oil as a carbon source can be used to prepare hybrid metal@carbon material while the polymerization of which generally prevents metals from exposure. In this study, melamine was used as a structural regulating agent for preparing Co/N/C catalyst via heating the mixture of cobalt nitrate, melamine and bio-oil for hydrogenation of o-chloronitrobenzene (o-CNB). The results showed that the Co species was encapsulated in the carbon structure from cross-polymerization of melamine and bio-oil at 600 °C. The further heating to 900 °C led to decomposition of melamine-derived substance, and meanwhile cobalt oxide was reduced and confined in the resulting carbon structure. The formed metallic Co catalyzed the growth of long carbon nanotube with cobalt on the tip, forming the Co/N/C catalyst of higher specific surface area (128.2 m2/g) and metallic Co dispersion (3.7%), rendering the superior activity for hydrogenation of o-CNB with the yield of o-chloroaniline up to 90.2%. The encapsulation or exposure of Co species was closely related to relative ratio of bio-oil and melamine in the catalyst precursors. Additionally, leaching of cobalt, due to dechlorination of o-CNB, was found to be an issue of Co/N/C catalyst but not for that of Ni/N/C catalyst. [Display omitted] • Heating mixture of CoNO 3 , bio-oil and melamine produces pin-like Co/N/C catalyst. • Bio-oil acts as a source of carbon skeleton to confine Co from aggregation. • Complexation with Co is essential for dispersion of Co in Co/N/C. • Balance of bio-oil and melamine determines exposure and access of metallic Co. • Catalyst obtained at 900 °C minimizes Co encapsulation, rendering superior activity. [ABSTRACT FROM AUTHOR]