The use of fossil fuels has been essential to the development of society, but has also contributed partly to global warming. For example, carbon dioxide emissions from fossil fuels and industries have increased by 60% since 1990, calling for the recycling of modern biomass in the context of a carbon neutral economy. Here we review the hydrothermal conversion of biomass into biofuels, chemicals and biomaterials with emphasis on subcritical water properties, hydrolysis of biomass, steam explosion, fractionation, carbonization, liquefaction, gasification, and fractionation of bio-oil. We observe that hydrothermal conversion of biomass in the presence of water at subcritical conditions produces value-added compounds with high process efficiency. Subcritical water allows rapid reaction rates, low mass transfer resistance, and gas-like diffusivity.

化石燃料的使用对于社会发展至关重要，但也部分加剧了全球变暖。例如，自1990年以来，化石燃料和工业的二氧化碳排放量增加了60%，呼吁在碳中和经济的背景下回收现代生物质。在这里，我们回顾了生物质水热转化为生物燃料、化学品和生物材料，重点是亚临界水性质、生物质水解、蒸汽爆炸、分馏、碳化、液化、气化和生物油分馏。我们观察到，在亚临界条件下，在水存在下，生物质的水热转化会产生具有高工艺效率的增值化合物。亚临界水具有快速的反应速率、低的传质阻力和类似气体的扩散性。