Co-hydrothermal carbonization (co-HTC) of microalgae and lignocellulosic biomass has high potential for producing nitrogen-rich carbon materials (hydrochar) with relatively high yield. The synergistic effect, hydrochar structure evolution and nitrogen transformation mechanism during the co-HTC process were depicted in depth. The results of the co-HTC process showed that the positive synergy between biomass and microalgae could improve the hydrochar yield and facilitate incorporation of nitrogen into the hydrochar aromatic heterocycles structures. Moderate reaction conditions were beneficial for co-HTC hydrochar nitrogen enrichment and porosity increment, and the optimal nitrogen content and specific surface area reached 3.50% and 5.91 m/g in co-HTC hydrochars at 240 °C and 1 h. Severe reaction conditions could enhance the formation of stable heterocyclic nitrogen species (reaching 54% at 300 °C). The hydrochar structure evolution and nitrogen transformation mechanism during co-HTC process could be generally divided into two stages. The first stage took place from 180 to 260 °C, and the nitrogen-rich secondary chars could be formed by the interaction of the hydrolysis intermediates. The second stage occurred from 260 to 300 °C, and the previously formed secondary char would be gradually decomposed. This study provides theoretical guidance for regulating the co-HTC process to produce nitrogen-rich carbon materials.

中文翻译：

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微藻与生物质共水热碳化过程中水炭结构演化特征及氮转化机制

微藻和木质纤维素生物质的共水热碳化（co-HTC）具有以相对高产率生产富氮碳材料（水炭）的巨大潜力。深入描述了co-HTC过程中的协同效应、水炭结构演化和氮转化机制。 co-HTC过程的结果表明，生物质和微藻之间的正协同作用可以提高水炭产量并促进氮结合到水炭芳香杂环结构中。温和的反应条件有利于co-HTC水热炭的氮富集和孔隙率增加，在240℃和1h下，co-HTC水热炭的最佳氮含量和比表面积分别达到3.50%和5.91 m/g。严酷的反应条件可以增强稳定杂环氮的形成（300°C 时达到 54%）。 co-HTC过程中的水炭结构演化和氮转化机制一般可分为两个阶段。第一阶段发生在180至260℃，通过水解中间体的相互作用形成富氮的二次焦。第二阶段发生在260～300℃，之前形成的二次炭逐渐分解。该研究为调控co-HTC工艺生产富氮碳材料提供了理论指导。