Effects of hydrolysis and oxidative hydrolysis pretreatments on upgrading of the water-soluble fraction of bio-oil via decarboxylation

Yuan Zhang, Yong Wang, Hongyou Cui, Pingping Zhao, Feng Song, Xiuyu Sun, Yujiao Xie, Weiming Yi and Lihong Wang

Applied Energy, 2018, vol. 226, issue C, 730-742

Abstract: Conversion of the carboxylic acids in bio-oil into ketones via decarboxylation is a highly efficient approach for bio-oil upgrading. However, the char formation during decarboxylation is due to the existence of a considerable amount of pyrolytic sugars in bio-oil, which severely weakens the upgraded bio-oil yield and the energy efficiency. In this paper, two pretreatment approaches, hydrolysis and oxidative hydrolysis, were employed to solve this problem. The pyrolytic sugars in bio-oil were firstly enriched into the water-soluble fraction through water extraction, followed by hydrolysis or oxidative hydrolysis pretreatment before decarboxylation. With the aid of hydrolysis pretreatment, the upgraded bio-oil yield was increased from 27.55 to 30.74%, and the energy efficiency was increased from 77.59 to 88.67% after decarboxylation, whereas the char yield was decreased from 5.67 to 3.81% in comparison with the results without hydrolysis. In the case of oxidative hydrolysis pretreatment, the upgraded bio-oil yield and the energy efficiency were further enhanced to be 32.68% and 92.70% respectively, while the char yield was drastically decreased to only 1.15%. To clarify the effect of the pretreatment, two pentoses and four hexoses were used to investigate the reaction pathways for their conversion in the water-soluble fraction during hydrolysis or oxidative hydrolysis pretreatment. The experimental results showed that hydrolysis of the water-soluble fraction could effectively convert pyrolytic sugars to carboxylic acids. In contrast, oxidative hydrolysis could convert not only the pyrolytic sugars, but also most of the aldehydes and ketones in the water-soluble fraction into carboxylic acids. The reaction pathways for conversion of pentose and hexose into organic acids via oxidative hydrolysis were also investigated.

Keywords: Bio-oil; Pyrolytic sugars; Hydrolysis; Oxidative hydrolysis; Decarboxylation (search for similar items in EconPapers)
Date: 2018
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DOI: 10.1016/j.apenergy.2018.06.043

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