Biomass hydrothermal conversion under CO2 atmosphere: A way to improve the regulation of hydrothermal products.

In this study, batched hydrothermal experiments on corn stalk were conducted at 240-330 °C under CO2 or inert (N2) atmosphere. The distribution and characteristics of gaseous, solid, and liquid products were analyzed in detail to comprehensively investigate the effects of CO2 on the hydrothermal conversion of biomass, especially on the cellulose and lignin in biomass. The results demonstrate that compared with N2, CO2 slightly increased the liquid and gas yields and significantly improved the control effect of temperature on bio-oil components. Under CO2 atmosphere, bio-oil achieved effective enrichment of ketones and phenols at 240 °C and 300 °C, respectively, and their highest relative contents reached 44.8% and 62.0%, respectively. In addition, the hydrochar obtained under CO2 atmosphere showed higher crystallinity, which is conducive to its subsequent utilization. This study explored the feasibility of introducing CO2 into the biomass hydrothermal process to realize the high-value utilization of biomass waste and the reuse of CO2.