Hydrothermal carbonization of rape straw: Effect of reaction parameters on hydrochar and migration of AAEMs

• Published in: Chemosphere (Oxford) Vol. 291; no. Pt 1; p. 132785
• Main Authors: Cheng, Chen, He, Qing, Ismail, Tamer M., Mosqueda, Alexander, Ding, Lu, Yu, Junqin, Yu, Guangsuo
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-03-2022
• Subjects: AAEMs; Biomass; Carbon; Heating; Hydrochar; Hydrothermal carbonization; Kinetics; Metals, Alkaline Earth; Structure; Temperature; AAEMs; Hydrochar; Kinetics; Hydrothermal carbonization; Structure
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2021.132785

Hydrothermal carbonization (HTC) can improve biomass quality in both physical and chemical aspects for energy application. This study aims to investigate the characteristics and reactivities of rape straw (RS) hydrochars. Hydrochars were prepared at 160–240 °C with residence time of 15–120 min. Mass yield, energy yield, microstructure, functional group and migration of alkali and alkaline earth metals (AAEMs) were studied to evaluate the influence of different conditions on properties of hydrochar. The results showed that O/C and H/C ratio decreased, while the higher heating value (HHV) increased with increasing temperature and residence time. The effect of increasing temperature on hydrochar properties was more significant than residence time. The structure was changed, and hydrochar possessed a more stable form after the aromatization reaction. For the gasification reactivity of hydrochar, decomposition rate curves showed that the peak of pyrolysis and gasification moved to a higher temperature region with the increasing of HTC temperature because of the developed aromatic structures in hydrochar. The pyrolysis activation energy decreased from raw RS 71.68 to 41.03 kJ/mol in 240 °C, while gasification activation energy increased from 80.42 to 251.30 kJ/mol. Moreover, it was found that HTC can reduce the content of AAEMs efficiently and the best removal condition is 200 °C. Ca content dropped to a minimum value at 200 °C and then increased at higher temperature which may be caused by well-developed pore structure in hydrochars. This study provides basic data for comprehensive utilization of rape straw and migration mechanism of AAEMs in HTC process.
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•The effects of HTC on RS structure and reactivity were quantitatively studied.•Temperature effect was more obvious than residence time during HTC.•Effects of HTC on kinetics of pyrolysis and gasification were studied separately.•Energy yield reached max at 180 °C, while AAEMs reached minimum at 200 °C.•The migration behavior of total and active AAEMs is studied.