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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]

Physical activation of biomass with H 2 O or CO 2 is an important method for producing activated carbon (AC). Activation of biomass with CO 2 or H 2 O follows varied mechanisms and the use of mixed CO 2 /H 2 O might show potential synergistic effects for creating pores. This was investigated by activation of lignin-derived biochar with H 2 O, CO 2 and their mixture. The results demonstrated that H 2 O as an activator was much more effective than CO 2 for generation of pores (804.1 m2g−1 versus 516.1 m2g−1in CO 2), especially mesopores (40% versus 14% in CO 2). This was achieved via enhancing cracking/gasification reactions of the biochar with H 2 O. The synergistic effect of CO 2 and H 2 O for activation of the lignin-derived biochar was insignificant as cracking/gasification reactions were not enhanced, leading to remarkably lower specific surface area of the AC (674.8 m2g−1) than that with H 2 O as an activator alone. Competitive adsorption of CO 2 and H 2 O existed and preferable adsorption of CO 2 hindered deoxygenation of the biochar with H 2 O. The in-situ IR characterization indicated that CO 2 presence suppressed decarbonylation reactions, retaining more oxygen species in form of C O, while it was the opposite in H 2 O. Additionally, activation with H 2 O formed numerous round-shape dents on surface of activated carbon, while the activation with CO 2 formed the characteristic round edges. The AC activated with H 2 O showed superior capability for adsorption of phenol than that activated with CO 2 or mixed H 2 O/CO 2. [Display omitted] • H 2 O is more effective than CO 2 for cracking, forming less activated carbon (AC). • Synergistic effect of CO 2 /H 2 O is insignificant as creating pores are not enhanced via cracking. • Competitive while preferable adsorption of CO 2 hinders activation with H 2 O. • CO 2 is not as active as H 2 O for cracking of C O in intermediates and for creating pores. • AC activated with H 2 O is superior for adsorbing phenol. [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]

CO 2 and H 2 O are two important activators in production of activated carbon (AC) via physical activation method. They could oxidize the carbonaceous species in biochar or biomass via varied mechanisms and might also impact environments as well as the pore structures and evolution of functionalities of AC in different ways. In this study, the activations of the biochar from pyrolysis of cellulose with H 2 O, CO 2 or mixed H 2 O/CO 2 were performed. The results demonstrated that H 2 O as an activator led to higher weight loss than that of CO 2 during the activation, originating from its higher efficiency for oxidation of the aliphatic structures in biochar to –OH and their further removal via deoxygenation or dehydration. Activation with CO 2 made the AC more oxygen-rich, due to the retainment of abundant oxygen-containing functionalities, which suppressed further oxidation of carbon species and led to formation of main micropores. The higher capability of H 2 O for deoxygenation made the AC more carbon-rich with much more developed pore structures as well as higher proportion of mesopores and thus the superior capability for adsorption of phenol. In addition, during the activation in either CO 2 or H 2 O, the unsaturated aldehyde/ketone and C-O-C structures was thermally more stable than lactones, saturated aliphatic acids and aliphatic aldehydes. The life cycle analysis (LCA) suggested that CO 2 activation showed lower impact on environment by reducing emissions and consumption of fossil fuel. [Display omitted] • Carbon yield is lower in activation of biochar from cellulose in H 2 O than in CO 2. • CO 2 makes activated carbon (AC) O-rich, due to lower capability for deoxygenation. • AC obtained with H 2 O has more developed pore structure of mesopores than with CO 2. • C C–C O and C–O–C on AC are more stable than saturated lactones/acids/aldehydes. • LCA indicates that CO 2 activation shows lower impact on environment. [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]

• Insufficient removal of organics in chicken bone (CB) at 400 °C forms littles pores. • Effective removal of organics at 650/800 °C obtains mesopore and high cu dispersion. • Carbonaceous residual from CB results in flower-like morphology of Cu/CB catalysts. • Cu/CB-800 with higher cu dispersion and surface area is active for hydrogenation. • Strong adsorption of functional groups over Cu/CB-800 enhances catalytic activity. Metal/biochar catalysts are prepared by direct impregnation of metal salts with biochar produced from pyrolysis. However, the surface structure of the catalyst carrier is affected by the pyrolysis temperature. Different pyrolysis temperatures can produce different pore structures, which can affect the dispersion of active metals. To verify this, Cu/bone biochar catalysts were prepared by directly supporting copper nitrate on the biochar from chicken bone pyrolysis at 400, 500, 650, and 800 °C, respectively. Catalytic performance of Cu/bone biochar catalysts for vanillin hydrogenation was evaluated. The results showed that the hydroxyapatite produced after pyrolysis of chicken bones was relatively stable, which made the catalyst with superior activity and reusability. The catalyst prepared by pyrolysis at a lower temperature had fewer pore structures on its surface, and the active metal Cu was easily sintered. With increasing pyrolysis temperature, organic matter gradually decreased and more pore structures were generated on the surface of the catalyst carrier, which was more conducive to the dispersion of metallic Cu species. The catalyst prepared from the chicken bone pre-pyrolyzed at 800 °C exhibited uniform dispersion of metal Cu, with the average particle size of Cu particles of 11.9 nm, achieving the yield of 91.7 % for 2‑methoxy-4-methyl phenol from hydrogenation of vanillin. In-situ IR characterizations also showed that, with the increase of pyrolysis temperature, the surface functional groups of the catalyst were more conducive to the hydrogenation of vanillin. The effect of pyrolysis temperature on pore structure and dispersion of metallic Cu of metal/biochar catalysts was investigated for conversion of vanillin. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Pre-oxidation enhances specific surface area by 54.6% in CO 2 activation and 30.0% in H 2 O activation. • O 2 breaks rigid structure of biochar, forming activated carbon of microporous with larger diameters. • O 2 promotes conversion of olefinic C = C to aromatic C = C in activation, accelerating aromatization. • Promoting pores formation of O 2 is confirmed in activation of cellulose, pine needle and spirulina. Carbonization plus activation of resulting biochar is a commonly used method for producing activated carbon (AC) from biomass. Nevertheless, carbonization produces biochar of highly aromatic nature, increasing difficulty for creating pores via activation. Herein, O 2 (7.7%) was introduced to pre-oxidize lotus root and other biomasses-derived biochar before being activated with CO 2 or H 2 O for tackling chemical inertness of biochar at 800 °C. The results indicated that O 2 could enhance mass yield of AC (by 16.5% in CO 2 activation and 50.6% in a H 2 O activation) and bio-oil. Moreover, O 2 oxidized organics on AC, forming oxygen-containing aliphatic structures. Such a transformation enhanced reactivity of biochar with CO 2 or H 2 O, facilitating generation of pores. The AC from activation with O 2 -CO 2 was significantly higher than that from CO 2 alone (533.7 m2 g−1 of AC from O 2 -CO 2 activation versus 345.2 m2 g−1 of AC from CO 2 activation). O 2 also could remarkably increase the specific surface area of AC activated with H 2 O by 30.0%. Such an enhancement in pore structures was confirmed in activation of cellulose, pine needle and spirulina with O 2 presence. The pre-oxidation activated biochar destroyed partially rigid structure, facilitating gasification with CO 2 /H 2 O, forming dominantly micropores with enlarged diameters. The characterization with in-situ IR indicated that O 2 could enhance aromatization via aiding formation of aromatic C = C from olefinic C = C, producing AC of more regular alignments of carbon crystals. [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]

[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]

Torrefaction and hydrothermal carbonization (HTC) as important pretreatment methods for processing starch-rich food might affect pyrolysis behaviors of the food waste. This was investigated herein by torrefaction and HTC of rice at 200 ºC and subsequent pyrolysis of the pretreated rice at 600 ºC for probing the influence on evolution of the products. The results indicated that the torrefaction could not remarkably affect yield of the pyrolytic products, but made the torrefied rice more hydrophobic via removing some polar functionalities. The HTC at 200 ºC significantly enhanced overall yield of bio-oil from rice. The HTC also enhanced aromatization degree, making the hydrochar more difficult to crack, reducing the tar yield significantly, increasing the activation energy of 162.3 kJ/mol in pyrolysis of rice to 301.6 kJ/mol in pyrolysis of the hydrochar, and improving combustion performance of the resulting biochar. The HTC could form dominantly microsphere morphology in the hydrochar and biochar. The in-situ IR characterization of the pyrolysis process showed that the torrefaction could induce some deoxygenation reactions to form some aromatics while the HTC pretreatment removed a significant portion of aliphatic structures. Life cycle assessment indicated that HTC pretreatment of rice lowered environmental pollution and fossil fuel depletion during pyrolysis. [Display omitted] • HTC of rice enhances bio-oil production via accelerating degradation of starch. • HTC leads to leaching of inorganics in rice and forms microspheres from starch. • Biochar from HTC-rice with high aromaticity shows superior combustion performance. • HTC pretreatment significantly enhances activation energy for subsequent pyrolysis. • DRIFTS measurement shows that HTC of rice removes majority of aliphatic structures. [ABSTRACT FROM AUTHOR]