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Pyrolysis of the aromatic-poor and aromatic-rich fractions of bio-oil: Characterization of coke structure and elucidation of coke formation mechanism

2019; Elsevier BV; Volume: 239; Linguagem: Inglês

10.1016/j.apenergy.2019.01.253

1872-9118

Zhe Xiong, Syed Shatir A. Syed‐Hassan, Xun Hu, Junhao Guo, Jihua Qiu, Xingyu Zhao, Sheng Su, Song Hu, Yi Wang, Jun Xiang,

Biodiesel Production and Applications

Coke formation is one major problem during thermal conversion of bio-oil and its main components. Fundamental knowledge about the evolution of the structure of cokes is a prerequisite towards a deep understanding of coking of bio-oil. This study investigates the structure (morphology, elemental composition, O-containing functional groups and aromatic structures) of cokes generated from the pyrolysis of aromatic-rich fraction (ARF) and the aromatic-poor fraction (APF) of bio-oil. The effects of interactions of ARF and APF on properties of the coke formed during the pyrolysis of bio-oil are also studied. The results show that the cokes from the pyrolysis of APF (APF-cokes) are sponge-like while the cokes from the pyrolysis of ARF (ARF-cokes) have a dense structure. The matrix of cokes from the pyrolysis of the whole bio-oil (oil-cokes) is similar to the matrix of ARF-cokes, while its surface is similar to that of APF-cokes, which should be due to the interactions between different bio-oil fractions. The APF-cokes contain more CO, OH and CO functional groups than the ARF-cokes due to the higher O content of APF. Moreover, the interactions between ARF and APF can promote more O-containing species to be transformed as CO, OH and CO functional groups in the oil-cokes. The aromatic rings of ARF-cokes and APF-cokes can be cracked to form smaller ring systems at 300–500 °C, while it is opposite for the oil-cokes because the aromatic structures formed via the interactions between ARF and APF are more stable. At higher temperatures (>500 °C), the interactions (e.g. self-gasification) lead to the highly condensed cokes, while the secondary cokes, which are spherical particles, are preferentially consumed by the steam.