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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]

This study experimentally investigates the gasification of nickel-preloaded oil palm biomass as an alternative catalytic approach to produce clean syngas. To eliminate the use of catalyst support, nickel was added directly to the oil palm mesocarp fiber via ion-exchange using an aqueous solution of nickel nitrate. Nickel species was found to disperse very well on the biomass at a nano-scale dispersion. The presence of the finely dispersed nickels on biomass enhanced syngas production and reduced tar content in the producer gas during the air gasification of biomass. It is believed that nickel particles attached on the biomass and its char promote the catalytic cracking of tar on their surface and supply free radicals to the gas phase to enhance the radical-driven gas-phase reactions for the reforming of high molecular weight hydrocarbons. The unconsumed nickel-containing char shows great potential to be re-utilised as a catalyst to further enhance the destruction of tar components in the secondary tar reduction process. [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]

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]

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]

• Volatile–char interactions are important for the evolution of pyrolysis volatile. • Surface functional group on char contributes to volatile–char interactions. • CNT favors the cleavage of C–O bond in the β–5 dimer to produce dimeric products. • CNT–NH 2 promotes the breakage of C−C bonds in the β–5 dimer to yield monomers. This study investigated the interactions between volatile and char during biomass pyrolysis at 400 °C, employing a β–5 lignin dimer and amino-modified graphitized carbon nanotube (CNT–NH 2) as their models, respectively. The results demonstrated that both –NH 2 and its carrier (CNT) facilitated the conversion of the β–5 dimer, which significantly increased from 9.7% (blank run), to 61.6% (with CNT), and to 96.6% (with CNT–NH 2). CNT mainly favored the breakage of C–O bond in the feedstock to produce dimers with a yield of 55.5%, while CNT–NH 2 promoted the cleavage of both C–O and C–C bonds to yield monomers with a yield up to 63.4%. Such significant changes in the pyrolysis behaviors of the β–5 lignin dimer after the introduction of CNT–NH 2 were considered to be mainly caused by hydrogen-bond formations between –NH 2 and the dimeric feedstock/products, in addition to the π–π stacking between CNT and aromatic rings. [ABSTRACT FROM AUTHOR]