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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]

Highlights • Effect of pre-reforming by Fe/bio-char catalyst on bio-oil reforming was studied. • Fe/bio-char pre-reforming increases the H 2 and CO yields from bio-oil reforming. • Fe/bio-char catalyst promotes the transformation of aromatics into light compounds. • Less coke was formed on Ni-based catalyst due to Fe/bio-char catalyst at 550–600 °C. • Pre-reforming promotes the formation of NiO and NiAl 2 O 4 on Ni-based catalyst. Abstract Ni-based catalyst is prone to the deactivation by coke deposition during the catalytic steam reforming of bio-oil. In order to optimize catalytic activity of the Ni-based catalyst, a two-stage catalytic reforming scheme was proposed whereby a low-temperature (350–600 °C) pre-reforming process with a less expensive catalyst was introduced prior to the Ni-based catalyst. To study this scheme, the reforming experiments with different combinations of Fe/bio-char (in the first stage) and Ni-Ca/γ-Al 2 O 3 (in the second stage) were conducted. In addition to the quantification of product yields, the tar and gas were characterized with an ultraviolet (UV) fluorescence spectroscopy, a gas chromatography/mass spectrometer (GC/MS) and a gas chromatography (GC). The results indicate that significant proportions of naphthalenes and polycyclic aromatics in the intermediate volatiles turned into furans, phenols and non-aromatics, which are easier to be reformed on Ni-based catalysts, via the Fe/bio-char pre-reforming, resulting in the increase of the final H 2 and CO yields of the overall process. At high pre-reforming temperatures (550–600 °C), the coke formation on Ni-based catalyst was significantly inhibited due to the Fe/bio-char pre-reforming. In addition, the results indicate that the spent Ni-based catalyst had more free NiO and NiAl 2 O 4 spinel than the fresh one, suggesting that the increase in the catalytic activity of Ni-based catalyst during the reforming process was promoted by Fe/bio-char pre-reforming. [ABSTRACT FROM AUTHOR]

• Eggshell-modified biochar shows prominent phosphorous adsorption performance. • Chemical adsorption process is the controlled step for eggshell-modified biochar. • Ca-P precipitation, hydrogen bonding, electrostatic attraction are adsorption step. • Adsorbed phosphates are mainly distributed inside pore size range of 15–50 nm. Biochar modified with calcium source is acted as an effective adsorbent for phosphorous recovery. In this research, eggshell is used as a low-cost and environmentally friendly calcium source to replace chemical reagents such as CaCO 3 , Ca(OH) 2 and CaCl 2 used in the modified biochar production. Biochar derived from rape straw and modified with eggshell shows prominent phosphorous adsorption performance (e.g., equilibrium adsorption amount, 109.7 mg/g). The kinetic and isotherm analysis demonstrate that chemical adsorption process is performed as the main controlled step for the modified biochar adsorption, and the phosphate adsorption process is composed of both monolayer adsorption and multi-layer adsorption. Moreover, it is found from the physicochemical structures comparison before and after phosphate adsorption that Ca-P precipitation, hydrogen bonding and electrostatic attraction are identified as main adsorption mechanisms. In addition, the adsorbed phosphates are mainly distributed inside the space with pore sizes of 15–50 nm. [ABSTRACT FROM AUTHOR]

A study was carried out in both inert and CO 2 atmosphere to investigate the interaction mechanism of K 2 CO 3 with graphite and coal char during the catalytic gasification of coal char. The formation of K 2 CO 3 catalytic precursors was identified by using series of different techniques. The results obtained in an inert atmosphere show that the interaction between K 2 CO 3 and carbon readily took place at low temperature. For the K 2 CO 3 loaded graphite, the intermediate of C n K clusters formed by the interactions of K 2 CO 3 with carbon prevented the evaporation of K at low temperature. At temperatures above 800 °C, however, the C n K clusters were unstable, and decomposed to release K through vaporization. On the contrary, for the K 2 CO 3 loaded demineralized coal char, due to the presence of oxygen groups, K was tightly bonded to carbon during heating, forming a complex precursor containing O and K with high thermal stability. The reaction pathway of carbon-K 2 CO 3 interactions in an inert atmosphere are proposed for both char and graphite. The results of DRIFTs experiment suggest that CO 2 is chemisorbed by the K- catalytic precursors during CO 2 gasification to form potassium phenolate species and a covalently bound carbonate group (dimethyl carbonate). It is believed that these species act as active intermediates in the gasification process. [ABSTRACT FROM AUTHOR]