基于藻类的水热液化产油技术被认为是潜在的微藻能源化利用的重要技术之一。而微藻基生物油中的含氮化合物,特别是含氮杂环化合物的种类分布和含量决定后续提质工艺的难度和能耗。因此,本文综述了微藻水热液化过程中氮元素的来源及其迁移转化机理。发现氮元素来自于微藻原料中的蛋白质(氨基酸)、磷脂以及色素,主要来自氨基酸。氨基酸在水热过程中发生复杂的化学反应,包括氨基酸分子内的脱羧基、脱氨基、脱水、脱硫、内环化、内酰胺、反羟醛缩合和断链反应,两个氨基酸分子间的二聚或聚合反应,氨基酸与还原糖的美拉德反应,氨基酸与脂肪酸的氨解反应,以及不饱和中间产物之间的聚合或缩合反应,进而产生氨氮、胺类、酰胺类、哌嗪二酮类和含氮杂环等多种含氮化合物。这些含氮化合物主要分布在生物油和水相产物中,生物油中氮元素存在形式主要是杂环氮、胺类氮和腈类氮三类,而水相氮主要是氨氮、杂环氮和酰胺类氮三类。水相氮和油相氮之间存在明显的迁移转化,通过调控水热液化过程中水相氮组成,将影响微藻水热液化所产生物油的氮元素种类和含量。The bio-oil derived from hydrothermal liquefaction of microalgae is recognized as one of the significant potential techniques for the energy-oriented utilization. The variety and content of nitrogen-containing compounds, particularly nitrogen-containing heterocyclic compounds, in bio-oil determine the difficulty and energy consumption of subsequent upgrading processes. Therefore, this paper reviews the sources of the nitrogen element and its migration and transformation mechanisms during the hydrothermal liquefaction of microalgae. It is discovered that nitrogen primarily originates from proteins or amino acids, phospholipids, and pigments in feedstock, with amino acids being the main contributor. During the hydrothermal process, amino acids undergo complex chemical reactions, including decarboxylation, deamination, dehydration, desulfurization, intramolecular cyclization, lactamization, retro-aldol condensation, and chain scission within amino acid molecule, dimerization or polymerization between two amino acid molecules, Maillard reactions between amino acids and reducing sugars, ammonolysis reactions between amino acids and fatty acids, as well as polymerization or condensation reactions among unsaturated intermediates. These reactions lead to the formation of various nitrogen-containing compounds such as ammonia, amines, amides, piperazine-2,3-diones, and nitrogen-containing heterocycles. These nitrogen-containing compounds are predominantly distributed in the bio-oil and aqueous phase products. In bio-oil, the nitrogen element
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