Abstract:

The migration and transformation path and characteristics of organic nitrogen during hydrothermal carbonization at different temperature were studied by using sludge and soybean protein. The nitrogen balance of the whole process showed that with the hydrothermal carbonization temperature increase from 150℃ to 240℃, the ratio of residual nitrogen in hydrochar to total nitrogen in sludge decreased from 68.9% to 29.8%. Proportion of nitrogen transferred to tar and aqueous solution increased from 4.2% to 35.0% and 18.8% to 30.4%, respectively, while the nitrogen in gas only counted for less than 0.02%. The main transformation path of proteins in sludge was to produce amines in tar, then water-soluble organic nitrogen, NH₃ and NH${}_{\mathrm{4}}^{+}$ successively through decompose and hydrolysis. The reaction degree increased with the increase of temperature. More stable heterocyclic nitrogen compounds such as pyrrole and pyridine were formed through Maillard, Mannich and other reactions at high temperature. The residual nitrogen-containing substances in hydrochar include undecomposed protein, heterocyclic nitrogen, quaternary nitrogen and a small amount of nitrile. Nitrogen species in tar were amine and heterocyclic nitrogen compounds, while nitrile is not presented. The aqueous solution is dominated by organic nitrogen, followed by a large amount of NH${}_{\mathrm{4}}^{+}$. The nitrogen-containing gas released is mainly HCN.

Key words: sludge, renewable energy, protein, hydrothermal, transformation

摘要：

利用污泥与大豆蛋白研究了不同温度下水热碳化过程中有机氮迁移转化路径和规律，氮元素全过程平衡分析结果表明随着水热碳化温度由150℃升高至240℃，焦炭中残留的氮占污泥总氮比例由68.9%下降至29.8%，焦油中由4.2%升高至35.0%，水溶液中则由18.8%提升至30.4%，含氮气体释放量低于0.02%。原污泥中蛋白质主要转化路径为通过分解转化和水解反应依次产生焦油态胺类、水溶性有机氮、NH₃和NH${}_{\mathrm{4}}^{+}$，反应程度随温度上升而加深。胺类在高温下通过美拉德、曼尼希等反应形成较稳定的吡咯、吡啶等杂环氮。焦炭中残留的含氮物质包括未分解的蛋白质、杂环氮以及季氮和少量腈类；焦油中的含氮物质为胺类氮和杂环氮，无腈类氮出现；水溶液中以有机氮为主，其次有大量NH${}_{\mathrm{4}}^{+}$；释放的含氮气体主要为HCN。

关键词: 污泥, 再生能源, 蛋白质, 水热, 转化