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This study focuses on the effects of interactions among bio-oil components on the formation of aromatic structures of bio-oil during its thermal treatment processes at various temperatures and heating rates. A bio-oil sample and its extracted fractions were pyrolyzed in a fixed-bed reactor at 300–800 °C at different temperatures and heating rates. The results show that the pyrolytic products (including the yields and aromatic structures) from raw bio-oil and its extracted fractions are significantly different, which proves the existence of the interactions between the aromatic components and light components of the bio-oil. Additionally, those interactions are determined by the pyrolysis temperature and heating rate to different extents, which further leads to the evolution of aromatic structures during the pyrolysis of bio-oil. For example, owing to the presence of the aromatic-poor fraction, the aromatic compounds (especially ≥ 2 rings) from the pyrolysis of bio-oil are less than that of the aromatic-rich fraction at relatively low temperatures (≤ 500 °C), especially at slow heating rates. This is because the polymerization, as the main interactions, promotes the transformation of more aromatic compounds (over wide range of ring sizes) into coke at these conditions. At fast heating rates, among the complex interactions, the self-gasification of bio-oil is intensified at high temperatures (≥ 700 °C), resulting in lower secondary coke yields and tar yields as well as the concentration of aromatic compounds (especially ≥ 2 rings). [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]

[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]

• 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]

Abstract: Bark constitutes an important part of any woody biomass to be used for the production of second generation biofuels and chemicals. Pyrolysis followed by biorefinery is a promising technology for the efficient utilisation of all components from a woody crop. While significant efforts have been devoted to the investigation of the pyrolysis characteristics of wood, relatively less is known about the pyrolysis behaviour of bark. This study aims to clarify the effects of temperature on the yields and composition of bio-oil from the pyrolysis of eucalypts bark. The bark of mallee, a type of eucalypt grown for soil amendment in Western Australia, was pyrolysed between 300 and 580°C at fast heating rates in a fluidised-bed pyrolysis unit. The bio-oil liquid products separate into two phases. The bio-oil liquid products were analysed by GC–MS, Karl-Fischer titration, UV-fluorescence spectroscopy, ICP-OES and thermogravimetric analysis (TGA). These results are compared, when appropriate, to those obtained from the wood fraction. [Copyright &y& Elsevier]