Hydrothermal carbonization of sawdust with the bio-oil of same origin impacts evolution of structures of hydrochar

• Published in: Fuel processing technology 2022-12, Vol.238, p.107516, Article 107516
• Main Authors: Lin, Haisheng, Li, Qingyin, Zhang, Lijun, Zhang, Shu, Hu, Xun
• Format: Article
• Language: English
• Subjects: Bio-oil; Hydrochar; Hydrothermal carbonization; Interactions; Poplar sawdust
• ISSN: 0378-3820; 1873-7188
• DOI: 10.1016/j.fuproc.2022.107516

The high tendency towards polymerization is a bottle-neck issue in upgrading of bio-oil, which, however, is highly desirable in co-hydrothermal carbonization (HTC) of biomass with bio-oil for enhancing production of hydrochar. In this study, co-HTC of bio-oil of the same origin with poplar sawdust was conducted at 180 to 260 °C. The results showed that the HTC in a water medium containing 10% bio-oil could enhanced the yield of hydrochar by ca. 36% at 220 or 260 °C through the cross-polymerization of the sugar-derived furans and ketones/aldehydes as well as the phenolics in bio-oil with the sawdust-derived organics. Furans/sugars in bio-oil showed much more contribution to the increase of hydrochar yield than the phenolics like guaiacol. The highly reactive organics in bio-oil even could react with the crystal region of cellulose at 180 °C, and affected property of hydrochar at especially the higher temperatures by promoting deoxygenation, enhancing carbonization, eliminating polar functionalities like -OH, retaining C=O for continued polymerization, etc. The co-existence of aliphatic organics and phenolics in bio-oil renders the simultaneous formation of highly volatile fraction and aromatic structures in the hydrochar. These created the carbon-rich hydrochar with higher crystallinity, lower hydrophilicity and improved comprehensive combustion index. [Display omitted] •Sugars/furans in bio-oil contribute more than phenolics for enhancing char yield.•Acetic acid in bio-oil catalyzes liquefaction and makes char more fragmentized.•Bio-oil enhances polymerization and deoxygenation, enhancing yield and HHV of char.•Bio-oil presence forms hydrochar of higher crystallinity and improved combustion.•Aliphatics/phenolics involve in volatile and aromatic fractions formation of char.