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Bio-oil derived from fast pyrolysis of oil palm empty fruit bunch (EFB) was catalytically reformed inside a stainless steel multichannel tubular reactor using steam and air as reforming agents. The catalyst used, denoted as Fe/AC, was an iron catalyst loaded on the coconut shell-derived activated carbon (AC) prepared by a new approach of impregnating iron from an aqueous solution onto the AC in a stepwise manner. Results indicate that a stepwise impregnation was able to minimise the agglomeration of iron particles on AC surface, allowing high loading of iron onto the AC without severely affecting Fe dispersion and catalyst pore properties. The highly reducible, highly efficient catalyst produced in this study was able to lower the concentration of tar in producer gas to lower than 100 mg/Nm3. The best composition of the burnable product gas was obtained with iron loading of 15 wt%, reaction temperature of 800 °C, steam-to-carbon molar ratio (S/C) of 1.0 and air equivalence ratio (ER) of 0.1, with gas composition of 33.5% H2, 21.0% CO, 14.0% CH4, 18.8% CO2 and 1% C2 hydrocarbons and a cold gas efficiency of 78.5%. [ABSTRACT FROM AUTHOR]

Stable free radicals are the long-lived macromolecule radicals formed in pyrolysis, and their reactions play an essential role in biochar formation. The alkali and alkaline earth metals (AAEMs) in biomass might be involved in the radical reactions during pyrolysis. Figuring out the effect of AAEMs on the reactions of stable free radicals can further understand the radical reaction mechanism and the formation of biochar in pyrolysis. In this paper, the in-situ electron paramagnetic resonance (EPR) spectroscopy was used to detect the stable free radicals in cocoanut pyrolysis, and the effect of AAEMs was analysed by the comparative experiments. The results indicate that the stable free radicals in nascent chars, which are generated from the thermal decomposition of biomass, could react and couple with each other. The AAEMs in biomass improve the activity of stable free radicals and promote the radical-radical coupling during high-temperature pyrolysis above 400 °C, which inhibits the condensation of aromatic structure and generates more weak bonds in hot nascent char. After stopping the heating, the weak bonds will be broken by cooling stress, thus inducing radical reactions and further changing the char structure. • In-situ EPR detection was used to study stable radicals during biomass pyrolysis. • Effect of alkali and alkali earth metals on stable radical reactions was analysed. • Nascent char formed in pyrolysis has secondary reaction after volatiles releasing. • Alkali and alkali earth metals promote coupling of stable radicals during pyrolysis. • Unstable structures formed by stable radicals coupling can be broken during cooling. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass can be converted to biochar, bio-oil and gas through reactions of non-volatile stabilised free radicals (SFRs) and volatile radicals during thermal conversion. In the process, the interactions between radicals from different biomass components play an essential role. Figuring out the interactions of radicals during pyrolysis holds the key to revealing the interaction mechanism of biomass components. In this study, the evolution of SFRs during the co-pyrolysis of cellulose and lignin was explored using in-situ electron paramagnetic resonance (EPR) detection. The interactions of cellulose- and lignin-derived radicals were analysed based on the variation of SFRs, thermogravimetric behavior and Raman spectrum measurement. The results indicate that the interactions of radicals influence char yield, char structure and the SFRs evolution during pyrolysis. The interaction of volatile radicals and SFRs increases the char yield and promotes the condensation of aromatic structure in biochar. At temperatures above 400 °C, the interaction between cellulose- and lignin-derived SFRs leads to the coupling of radicals, which forms an unstable structure in the hot nascent biochar. In the subsequent cooling process, the weak bonds from interactions may break due to the structure shrinkage, which promotes radical reactions and further changes the char structure. • Interactions during co-pyrolysis improve char yield and stabilised radicals content. • The relationship between stabilised radicals and char carbon skeleton was studied. • The interaction of stabilised radicals in nascent char causes the radicals coupling. • The weak bonds from interaction break to promote radical reactions during cooling. [ABSTRACT FROM AUTHOR]

• Char structure was investigated via characterization of its extraction and residue. • Effects of pellet sizes on char structure were weakened by temperatures. • Polymerisation of extract is account for the structural difference of pellet chars. • Aromatisation degree of pellet char is related to its surface-area-to-volume ratio. Char structure can reflect the pyrolysis characteristics and affect the efficiency of gasification and combustion processes, while biomass pellet size and shape are critical for the heat and mass transfer, which in turn influence greatly char structure. The aim of this study is to experimentally study and compare the effect of aspect ratio (diameter/length) on char structure during the pyrolysis of sawdust pellet. Cylindrical sawdust pellets with similar masses and volumes but different diameters (6, 8, 12, 16 mm) were pyrolysed at various temperatures. The chars were separated into two phases (liquid extraction, solid residue) via microwave-assisted extraction. Experimental results show that the pellet with a low aspect ratio had a large char yield because of intra-particle volatile-char interaction especially at low temperature, while there was an optimum aspect ratio due to the change of residence time. The pellet with a high aspect ratio had an intense polymerisation, resulting in the formation of fused aromatic rings in char and residue. By increasing aspect ratio, there was a lowest surface area. This means that less heat entered from surface, and low thermal conductivity caused a slow decomposition. Due to large heat and mass transfer residence, more aromatic molecules with small weight formed in extracts of char, especially at high temperature. Besides, an increase in temperature weakened the differences in structural features of the pellet char caused by different aspect ratios. [ABSTRACT FROM AUTHOR]

In pyrolysis of biomass pellet, heterogeneity in char is almost inevitable, due to the intra-particle mass/heat transfer limitation. In this study, the effects of temperature (350–600 °C) and aspect ratio of a cylindrical sawdust pellet (Diameter = 6, 8, 12, or 16 mm) on the heterogeneity of char structure at radial and axial directions were investigated with a micro-Raman spectroscopy. Based on the spatial distribution of Raman band area ratios, heterogeneity index was proposed to quantify the degree of heterogeneity in char structures. Results show that the heterogeneity exists in both radial and axial directions and could be weakened by the increase of temperature or enlarging the variance between radius and height of the pellet through enhancing the average heat and mass transfer inside the pellet. The heterogeneity index of different biochar decreased with increasing surface-area-to-volume ratio. The char structures was the most heterogeneous (HI(A D /A G) = 5.399 × 10−5, HI(A D /A (Gr+Vr+Vl)) = 2.359 × 10−5) for the pellet with a diameter of 8 mm. • Effects of temperature and aspect ratio on heterogeneity in char were investigated. • The heterogeneity of char structure at radial and axial directions was quantified. • A heterogeneity index was proposed to reflect heterogeneous structure in char. • The heterogeneity of pellet char could be weakened by the increase of temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coke formation during bio-oil pyrolysis was inhibited via Ni/Al 2 O 3 mixing. • Influence of Ni/Al 2 O 3 mixing on aromatic structures of products was investigated. • Interaction among AF, LDO and Ni/Al 2 O 3 during bio-oil pyrolysis was revealed. • Mechanism for bio-oil pyrolysis with Ni/Al 2 O 3 mixing was proposed. Bio-oil can be converted to chemicals, carbon material, or syngas by various thermochemical processes which are always preceded with the pyrolysis step. In bio-oil pyrolysis, coke formation is almost inevitable, causing difficulties for further processing. In this study, bio-oil was mixed with Ni/Al 2 O 3 before it was fed for pyrolysis. Interesting results were observed whereby the effect of Ni/Al 2 O 3 mixing on coke formation shifted from promoting to inhibiting with increasing pyrolysis temperature. When the temperature was higher than 700 °C, contrary to the cases without mixing, the apparent decreases in coke yield were observed (e.g., the coke yield decreased by 10% at 800 °C). Comparative studies on bio-oil and its lignin-derived oligomer fraction indicated that the catalytic cracking of small molecules could enhance the formation of hydrogen radicals, which promoted thermal decomposition of lignin-derived oligomers, thus inhibiting coke formation via polymerization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polymerization electro-initiates on cathode surface, and propagates in bio-oil bulk phase. • Large molecules (MW > 800 Da) originally existed in bio-oil contributes to polymerization. • Aromatics, furans and levoglucosan are important polymerization reactants. • Increasing reaction time and current density can enhance polymerization of bio-oil. • Polymer layer forms on anode surface by polymerization. The electrochemical method provides a green route to upgrade bio-oil, but it is still challenged by the issue of bio-oil polymerization which restrains its application. This study investigates the polymerization behaviors of the bio-oil during its electrochemical upgrading under various current densities and different reaction time using macrophotography and multiple characterizations. The results show that the polymerization is not only electro-initiated on the cathode surface, but also electro-propagated in the bulk solution. The large molecules (MW > 800 Da) originally existed in the bio-oil are consumed in the polymerization. The small molecules (MW < 800 Da) can be produced from the polymerization of aromatics with 1–3 rings, furans and levoglucosan through cycloaddition, dehydration and demethoxylation. These small molecules can directly form solid products (coke) rather than leading to the increase of the large molecules. The polymerization can be enhanced by the increasing current density and reaction time. The rate of bio-oil polymerization can surpass the rate of coke formation as the reaction proceeds. The polymer layer also forms on the anode surface by polymerization during the electrochemical upgrading of bio-oil. [ABSTRACT FROM AUTHOR]

Biomass pellet is a popular fuel, and pyrolytic char can be a promised carbon material, further understanding char structural evolution can promote its utilization. To deeply investigate the evolution of char chemical structure and its heterogeneity during biomass pellet pyrolysis process, a new method was developed to fragment the char in space, and the chemical structures of the fragmented sections were analyzed by a micro-Raman spectroscopy (equipped with a 532 nm laser). The first-order Raman spectra (800–1800 cm−1) of varied positions of sawdust pellet pyrolytic char were curve-fitted with 10 Gaussian bands to reveal the temporal and spatial evolutions. The results indicate that pyrolysis of sawdust pellet can be divided into two stages: i) the decomposition of raw biomass (temperature heterogeneity in pellet remains); ii) the condensation reactions of aromatic ring systems (temperature in pellet becomes uniform). The axial and radial heterogeneity of char chemical structure is mainly caused by heat transfer when the whole pellet temperature is uniform during heating. While mass transfer, in accordance with volatile diffusion, can eliminate the heterogeneity of char chemical structure by volatile-char interaction. The combined effects of heat and mass transfer lead to a heterogeneity in pellet char chemical structure. • An expanded Raman method by combining micro positioning and analysis was developed. • Chemical structure heterogeneity of sawdust pellet pyrolytic char was quantified. • Temporal and spatial evolutions of pyrolytic char chemical structure were revealed. • Combined effects of heat and mass transfer on char chemical structure were found. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is an attractive, green technology for the management of sewage sludge. In this study, low-value secondary sewage sludge was subjected to an HTC treatment in a 1 L batch hydrothermal reactor and transformed into a high-energy-density hydrochar under varying HTC conditions (temperature of 150–300 °C, carbonization time of 30–150 min and a solid loading of 10–30%). The resulting hydrochar fuel characteristics were analyzed for ultimate and proximate analyses, functional group composition and energetic parameters. It was found that the hydrochar yield decreased with the increasing HTC temperature and reaction time, primarily due to the loss of organic volatile matter and functional groups. Under the optimum conditions of 150 °C, 30 min of carbonization time and 30% solid loading, 80.56% of the hydrochar was recovered, providing a maximum energy yield of 90.32% and a high heating value of 18.49 MJ/kg. Compared to the raw sewage sludge (H/C ratio of 2.67 and O/C ratio of 0.51), the hydrochar also had lower H/C and O/C atomic ratios of 1.42 and 0.18, respectively. The results suggest that significant dehydration and decarboxylation during the HTC treatment of sewage sludge have resulted in the formation of carbonaceous hydrochar with energetic properties close to the sub-bituminous coals. [ABSTRACT FROM AUTHOR]

The electrochemical method is becoming a promising approach to deliver the bio-oil upgrading objective at room temperature. However, it still faces the coke formation issue because of the easy polymerization nature of bio-oil. Interactions among components impact the polymerization during the electrochemical upgrading of bio-oil. This study investigates the effects of interactions between the aromatic-rich and aromatic-poor fractions (ARFs and APFs) of the bio-oil on polymerization under various reaction time and current densities. Coke yield differences provide direct evidence of the existence of interactions between ARFs and APFs during the electrochemical upgrading process. Our results indicate that the coke yields and its condensation level are decreased by the interactions. The surface area, pore volume and the functionalities content of the coke are increased by the interactions. In addition to polymerization, more types of reactions including hydrogenation and esterification are induced by the interactions, resulting in more types of products and less coke. The interactions can inhibit polymerization by consuming the coke precursors before their condensation. The interactions can also inhibit the anodic adsorption and oxidation, thus depressing polymerization and coke formation. Investigating the impacts of interactions between aromatic-rich and aromatic-poor fractions on polymerization of bio-oil in chronoamperometric electrochemical upgrading. [Display omitted] • Interactions of aromatic-rich and -poor fractions in bio-oil is proven existed in electrolysis. • Aromatic-poor fractions end-cap the reactive chains of polymerization precursors. • Interactions weaken the anodic adsorption and polymerization of bio-oil. • Interactions decrease the yields, surface areas and pore volumes of the coke. [ABSTRACT FROM AUTHOR]

• Fe/activated char shows high performance on bio-oil upgrading. • The fresh catalysts favor the production of aromatic hydrocarbons. • The regenerated catalysts by active agents facilitate the production of phenols. • The catalyst regeneration promotes the formation of γ-Fe 2 O 3 on the char surface. Char-supported metals as catalysts has attracted much attention due to the renewability and structural controllability of char. However, such catalysts can not be regenerated by the conventional calcination method, which is widely used in industy. In this study, the catalytic performance of char-supported Fe on bio-oil upgrading during pyrolysis of pine wood was first investigated. It was found that the typical components (acids, ketones, furans, etc) in bio-oil were completely converted to aromatic hydrocarbons over char-supported Fe, in which char acted not only as a support but also as a catalyst for the converison of bio-oil to phenols. Then, the spent char-supported Fe catalyst was regenerated by CO 2 or steam gasification. The results showed that only phenols could be produced over both CO 2 and steam regenerated catalysts, which was caused by the changes in carbon structure and surface functional groups of char as well as the species of Fe. The CO 2 regenerated catalyst was rich in C O groups and α-Fe 2 O 3 , while the H 2 O regenerated one mainly contained O C O groups and Fe/FeO. [ABSTRACT FROM AUTHOR]

Antibiotics are extensively used in treating infectious diseases for both humans and animals. However, they are generally not fully digested in the body and are released as active compounds into aquatic systems through domestic sewage treatment plants, where they can cause chronic toxicity and some potentially major health and environmental risks. Many researchers reported that conventional wastewater treatment processes cannot completely eradicate antibiotic residue and that these residues may be discharged to the receiving rivers and streams. Adsorption was claimed to be able to remove these contaminants even at low concentrations and under a variety of pH conditions. Biomass-based adsorbent materials have recently been used to remove antibiotics due to their wide availability, eco-friendly nature, good surface characteristics, and low cost. This study conducted a systematic review of biomass-based carbon adsorbents used for antibiotic removal. The surface chemistry and maximum antibiotic adsorption capacities were reviewed and discussed based on the type of biomass and chemical modification. The effect of influential variables such as pH, initial concentration of antibiotics and adsorbent dosage was also discussed in detail. After the screening process, four articles were found to be suitable for the detail analysis on reusable efficiency. Results of the detail analysis shows coconut shell and sawdust based-carbon adsorbent could remove antibiotics with 89% reusable efficiency after the fourth cycle of reuse. Overall, this systematic review ascribes the research work for synthesizing an excellent performance of biomass-based carbon adsorbent. • A systematic review on chemically modified biomass-based carbon adsorbent for the removal of antibiotics in water. • The performance of carbon adsorbent depends on the chemical and physical properties of the adsorbent surface. • Chemical modification is effective to enhance adsorption capacity for antibiotics removal. • Reusable efficiency of 89% is possible after four cycles of antibiotics removal. [ABSTRACT FROM AUTHOR]

• Char activity in volatile-char interactions varies with biomass components. • Xylan char rich in C O group is the most active for (benzyloxy)benzene conversion. • Char C(sp2) O group promotes the breaking of C(sp3) O in (benzyloxy)benzene. • Char C(sp3) O group promotes the breaking of C(sp2) O in (benzyloxy)benzene. • Lignin char is highly selective to monomers due to the abundant C O group. Char activity is a critical factor for the interactions between char and volatile, which are recognized to determine the final product distribution from biomass pyrolysis. To clarify the effect of biomass composition on char activity, the interactions between (benzyloxy)benzene as a volatile model compound and char samples obtained from cellulose, xylan, and lignin were studied. The (benzyloxy)benzene conversion increased from 0.64 % for no char to 6.31 %, 6.98 % and 53.5 % for lignin char, cellulose char, and xylan char, respectively, which were mainly derived from the contribution of surface C O groups and surface defects in the carbon structure. Especially, surface C(sp2) O groups and C(sp3) O groups on char respectively favored the breakage of C(sp3) O and C(sp2) O bonds in (benzyloxy)benzene. Despite the low activity, lignin char showed high selectivity to monomeric products due to the high content of surface C O groups, which were considered to induce the production of hydrogen radicals to stabilize the resulting intermediates. The findings of this study prove that the volatile-char interaction could be adjusted facilely by changing the hemicellulose content during feedstock pretreatments. [ABSTRACT FROM AUTHOR]