School of Energy Science and Engineering, Central South University, Changsha, Hunan 410083, China.
College of Resources and Environment, Hunan Agricultural University, Changsha, 410128, Hunan, China.
Sci Total Environ. 2021 Feb 20;756:143679. doi: 10.1016/j.scitotenv.2020.143679. Epub 2020 Dec 1.
Biomass is a type of renewable and sustainable resource that can be used to produce various fuels, chemicals, and materials. Nitrogen (N) in biomass such as microalgae should be reduced if it is used to produce fuels, while the retention of N is favorable if the biomass is processed to yield chemicals or materials with N-containing functional groups. The engineering of the removal and retention of N in hydrochar during hydrothermal carbonization (HTC) of biomass rich in protein is a research hot spot in the past decade. However, the N transformation during HTC has not yet been fully understood. In order to mediate the migration and transformation of N in hydrochar, the present review overviewed i) the characteristics of hydrochar and the original feedstock, ii) the possible N transformation behavior and mechanisms, and iii) the effect of factors such as feedstock and pyrolysis parameters such as temperature on hydrochar N. The high temperature and high protein content promote the dehydration, decarboxylation, and deamination of biomass to produce hydrochar solid fuel with reduced N content, while the Millard and Mannich reactions for lignocellulosic biomass rich in carbohydrate (cellulose, hemicellulose, and lignin) at medium temperatures (e.g., 180-240 °C) significantly promote the enrichment of N in hydrochar. The prediction models can be built based on properties of biomass and the processing parameters for the estimation of the yield and the content of N in hydrochar.
生物质是一种可再生和可持续的资源，可用于生产各种燃料、化学品和材料。如果将生物质（如微藻）用于生产燃料，则应减少生物质中的氮（N），而如果将生物质加工成含 N 官能团的化学品或材料，则保留 N 是有利的。在富含蛋白质的生物质的水热碳化（HTC）过程中，工程上需要去除和保留水热炭中的氮，这是过去十年的研究热点。然而，HTC 过程中的 N 转化尚未得到充分理解。为了调节水热炭中 N 的迁移和转化，本综述综述了：i）水热炭和原始原料的特性，ii）可能的 N 转化行为和机制，以及 iii）原料和热解参数（如温度）等因素对水热炭 N 的影响。高温和高蛋白含量促进生物质的脱水、脱羧和脱氨作用，产生 N 含量降低的水热炭固体燃料，而富含碳水化合物的木质纤维素生物质（纤维素、半纤维素和木质素）在中温（例如，180-240°C）下的 Maillard 和 Mannich 反应则显著促进了水热炭中 N 的富集。可以根据生物质的性质和加工参数建立预测模型，用于估算水热炭的产率和 N 含量。
