Hydrothermal Liquefaction of Cornstalk by Reusing Pyroligneous Acid: Synergistic Effects on Biocrude Oil Formation and Solid Residue Accumulation

• Published in: Energy & fuels 2022-01, Vol.36 (1), p.435-449
• Main Authors: Li, Yanmei, Tian, Chunyan, Zhang, Nianze, Zhao, An, Bai, Xueyuan, Yi, Weiming, Fu, Peng
• Format: Article
• Language: English
• Subjects: Bioenergy, Biofuels, and Biorefinery
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.1c03093

The reuse of process wastewater as a reaction medium in hydrothermal liquefaction (HTL) of biomass to enhance biocrude oil (BO) production has been investigated, but the interaction between the biomass and process wastewater has rarely been studied. In the present work, pyroligneous acid (PA) was used as the reaction medium and substrate during the HTL process of cornstalk (CS). Hydrothermal conversion of PA itself, HTL of CS with water, and coliquefaction of CS and PA were carried out in a high-temperature and high-pressure batch reactor. Effects of reaction temperature and PA on the yields and characteristics of products were investigated. The PA itself was hydrothermally converted into BO, solid residue (SR), an aqueous phase, and gases. Reaction temperature had a strong influence on the product distribution during the coliquefaction of CS and PA but little influence on products during PA hydrothermal conversion. The highest BO yield from PA hydrothermal conversion occurred at 300 °C (28.96 wt %). For the coliquefaction of CS and PA, the highest experimental BO yield was 31.29 wt % at 300 °C, exceeding its corresponding theoretical value by 3.28 wt %; the experimental SR yield at 350 °C was 13.01 wt %, with the highest increase of 3.34 wt % compared to its corresponding theoretical value. The synergistic effects of CS and PA occurred at high temperatures (300 and 350 °C), promoting BO formation and strengthening SR accumulation, possibly due to the interactions among the compounds dissolved in PA and the components of CS. The BOs obtained from CS and PA coliquefaction had similar C, H, and O contents and higher heating values (HHVs) than those of HTL of CS, suggesting that the reuse of PA in HTL did not compromise the oil quality. Compared with the HTL of CS with water, CS and PA coliquefaction resulted in reduced concentrations of phenols, N-containing compounds, and organic acids and higher concentrations of ketones, alcohols, and hydrocarbons. Hence, PA clearly affected the distribution of organic components in BOs. In addition, more carbonaceous SRs were produced from coliquefaction with C and O contents of 65.14–70.23 and 23.94–29.89 wt %, respectively, and HHVs of 22.77–26.99 MJ/kg.