Hydrothermal liquefaction (HTL) of biomass, especially that of high moisture such as microalgae, macroalgae, sludge, manure, and food waste, for the production of bio-oil has been widely concerned worldwide. However, the contents of nitrogen (N) in these biomasses are commonly high, and 20–40% of the N in the raw biomasses would distribute into bio-oil during the HTL process, resulting in a high content of N in bio-oil, sometimes up to 10 wt%. The combustion of N-rich bio-oil will probably induce massive emission of nitrogen oxides. The transformation behavior of N has not yet been fully understood, and the denitrogenation is a critical issue during bio-oil production and upgrading. This review comprehensively summarized the effects of the type, composition, and pretreatment of biomass and HTL processing parameters, such as temperature, residence time, solid loading, reaction solvent, extraction solvent/procedure, and catalyst, on the N content of bio-oil. The N conversion mechanisms in the HTL process were also clarified. Research gaps were identified, and future research directions were finally proposed to achieve the production of bio-oil with low N content.

用于生产生物油的生物质，尤其是高水分的生物质的水热液化（HTL），例如生物藻油的热液化（HTL）。但是，这些生物质中的氮（N）含量通常很高，在HTL过程中，原始生物质中的20％至40％的氮会分配到生物油中，从而导致生物油中的氮含量很高。 ，有时可达10 wt％。富氮生物油的燃烧可能会导致大量排放氮氧化物。N的转化行为尚未完全了解，脱氮是生物油生产和升级过程中的关键问题。这篇综述全面总结了生物质的类型，组成和预处理以及HTL处理参数（例如温度，停留时间，固体载量，反应溶剂，萃取溶剂/程序和催化剂对生物油中N含量的影响。还阐明了HTL过程中的N转换机制。确定了研究空白，并最终提出了未来的研究方向，以实现低氮含量生物油的生产。