Hydrothermal treatment (HTT) is a promising way of upgrading biomass as a solid fuel and precursor of carbon materials by eliminating or transforming carbohydrates and also leaching alkali and alkaline earth metallic (AAEM) species. This study investigated steam gasification of a woody biomass that had been upgraded by HTT at 250°C. HTT removed 87−97% of AAEM species from the biomass. The char from the pyrolysis of the treated biomass underwent gasification, obeying first-order kinetics with respect to the mass of char over the entire range of conversion. This kinetics arose from non-catalytic gasification. AAEM species remaining in the char had no catalytic activity. The specific surface area of char increased monotonically with its conversion from 500 to well above 2000 m 2 /g. The non-catalytic nature of the gasification was responsible for such a significant surface area development. The surface area was, however, not a factor influencing the rate of gasification. The presence of the inherent AAEM catalyst and that of the extraneous potassium catalyst altered the kinetics of gasification to zeroth order while suppressing the surface-area development not only creating but also consuming micropores. The surface area was not a kinetic factor for the catalytic gasification.

A sequence of briquetting of biomass solids (bamboo, larch and mallee) at temperature and mechanical pressure of respectively, and carbonization at 900°C produces coke with tensile strength (TS) of 5-19 MPa. Introduction of heat treatment in hot-compressed water (i.e., hydrothermal treatment; HT) of the biomass prior to the briquetting increases TS up to 44, 57 and 42 MPa for the bamboo, larch and mallee, respectively. TS of coke is correlated well and positively with the coke/briquette bulk density ratio, and HT increases the ratio if operated under appropriate conditions. The efficacy of HT is attributed primarily to increase in the coke yield on a basis of the briquette mass. HT hydrolytically removes highly volatile cellulosic material (i.e., cellulose and hemicellulose), transforms it into solid that contributes to coke as effectively as lignin, and thereby increases the mass yield of coke by a factor of 1.4 to 2.1. HT also enhances the plasticizability of the biomass during the briquetting by degradation of the lignin to reasonable extent, and then promotes particles' coalescence/fusion and densification of the briquettes. Applying mechanical pressure over a range of 12-114 MPa to the briquetting of a solid from HT of the bamboo at 240°C successfully results in production of coke with TS of 41-44 MPa.

Removal of alkali and alkaline earth metallic (AAEM) species, in particular, that of potassium, is an effective way to upgrade rice husk, because its combustion and gasification often suffer from the formation of potassium silicate with a low softening or fusion temperature. This work has been investigating the leaching of AAEM species with a bio-oil (BO) from the pyrolysis of the parent rice husk. The leaching with BO, which had a pH of 2.59, gave removal rates of K and Na equivalent to or higher than those with an aqueous solution of hydrogen chloride (HCl aqueous) or acetic acid (AcOH aqueous) at pH of 2. The leaching abilities of BO in terms of the removal rates of Mg and Ca were equivalent to HCl aqueous at pH 0 and AcOH aqueous at pH < 2, respectively. Such performances of BO arose from the presence of not only AcOH with a concentration of 6 wt % but also phenolic compounds (phenol, alkylphenols, and methoxyphenols). The phenols permeated into the organic matrix of the rice husk, forming hydrophobic interactions as well as hydrogen bonds with macromolecules, making the matrix more accessible to AcOH and water, and thereby promoting the leaching of organically bound AAEM species. The result of the leaching test with a simulated BO quantitatively demonstrated the role of the phenolic compounds as the leaching promoter.

Binderless briquetting of lignite at 100-200°C and subsequent carbonization produces formed coke with tensile strength (ST) of 5-40 MPa, while the briquetting often requires mechanical pressure over 100 MPa. High reactivity is another feature of the lignite-derived coke, and this arises from highly dispersed metallic species such as alkali/alkaline-earth metallic species and ferrous/ferric ones that catalyze CO2 gasification. This work investigated effects of leaching of those metallic species in aqueous solution of hydrochloric acid, acetic acid or oxalic acid on the reactivity and ST of resulting coke from a lignite. The leaching at pH ≤ 1 removed catalytic metallic species near completely, reducing the coke reactivity by a factor of 8-15. The reduced reactivity was similar to the reactivity of coke from a typical coking coal. The leaching at pH ≤ 2.2 increased ST from 6 to 13 MPa for briquetting at 200°C and 32 MPa. The performance of leaching with oxalic acid, of that solution had pH of 0.75 at 1 mol/L, was much better than that with acetic acid. This work also examined another type of leaching, oxidation of the lignite in aqueous solution of hydrogen peroxide, which produced organic mono-/di-acids in-situ from the oxidation of aromatic carbons of the lignite. The degree of reduction of the coke reactivity was between that for leaching at pH of 1 and 2. The degradation of macromolecules enhanced plasticizability of the lignite under briquetting and increased ST of the resulting coke to 22 MPa.

It remains challenging to develop a techno-economically feasible method to remove alkali and alkaline earth metal species (AAEMs) from rice husk (RH), which is a widely available bioresource across the world. In this study, the AAEMs leaching effect of aqueous phases of both bio-crude prepared by hydrothermal liquefaction (AP-HT) and bio-oil prepared by pyrolysis (AP-Pyro) of RH were systematically investigated. The results indicated that although the acidity of AP-HT and AP-Pyro are much lower than that of HCl, they performed a comparable removal efficiency on AAEMs (Na: 56.2%, K: 96.7%, Mg: 91.0%, Ca: 46.1% for AP-HT, while Na: 58.9%, K: 96.9%, Mg: 94.0%, Ca: 86.3% for AP-Pyro) with HCl. The presence of phenolics in bio-oil could facilitate the penetration of water and organic acids into the inner area of RH cells, thus enhancing the AAEMs removal via chelate reactions. The thermal stability of leached RH during thermochemical conversions was studied via TG and Py-GC-MS. The results showed that the heat conduction efficiency in leached RH was enhanced with a high pyrolysis rate, resulting in a narrow carbon chain distribution (C5–C10) of derived chemical compounds.

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BACKGROUND The interaction mechanism between adsorbent and adsorbate is of great significance in the adsorption process. Activated biochar, prepared from pine sawdust using CO2 and H2O as activator, was employed to adsorb methylene blue in printing and dyeing pollutants. The pore structure, carbon structure of the aromatic ring system and functional groups were investigated though characterization analysis, and the adsorption kinetics and possible adsorption mechanism were also studied. RESULTS The activated biochar prepared using CO2 activation had greater specific surface area, pore structure and surface oxygen‐containing functional groups than that prepared using H2O, which was more conductive to improving its adsorption capacity. The electrostatic interaction between the surface oxygen‐containing functional groups and the π–π interaction formed in the aromatic rings enhanced the adsorption capacity of activated biochar for methylene blue. CONCLUSIONS The adsorption process of methylene blue by activated biochar was spontaneous, and it conformed to pseudo‐second‐order kinetic characteristics and the Langmuir adsorption isotherm equation. It was a monolayer adsorption and the maximum adsorption capacity was about 160 mg g−1. Activated biochar as an adsorbent for wastewater treatment has promise for application and development prospects. © 2021 Society of Chemical Industry (SCI).

The simple incineration of wood-based panels (WBPs) waste generates a significant amount of NOx, which has led to urgency in developing a new method for treating the N-containing biomass residues. This work aims to examine the N evolution and physiochemical structural changes during the co-pyrolysis of fiberboard and glucose, where the percentage of glucose in the feedstock was varied from 0% to 70%. It was found that N retention in chars was monotonically increased with increasing use of glucose, achieving ~60% N fixation when the glucose accounted for 70% in the mixture. Pyrrole-N (N-5) and Pyridine-N (N-6) were preferentially formed at high ratios of glucose to fiberboard. While the relevant importance of volatile–char interactions to N retention and transformation could be observed, the volatile–volatile reactions from the two feedstocks played a vital role in the increase in abundance of glucose. With the introduction of glucose, the porous structure and porosity in chars from the co-pyrolysis were dramatically altered, whereas the devolatilization of glucose tended to generate larger pores than the fiberboard. The insignificant changes in carbon structure of all chars revealed by Raman spectroscopy would practically allow us to apply the monosaccharides to the WBPs for regulating N evolution without concerns about its side effects for char carbon structures.