基于有机官能团与重金属耦合调控的污泥亚/超临界分级水热液化制清洁生物油机制

Sewage sludge as a biomass waste is very harmful to the environment due to its higher moisture content and complex pollutants. Hydrothermal liquefaction (HTL) of sewage sludge has drawn much attention because of the higher energy recovery efficiency and its environmental friendly. This project proposed a novel method of sub-supercritical HTL of sewage sludge based on a two-stage process, and further study on the mechanism of clean bio-oil production coupling control of organic functional groups and heavy metals. Firstly, subcritical water pretreatment is proposed to separate most of the heavy metals with the structure damage of sludge floc and hydrolysis of organics. Experimental study will be done to reveal the supercritical HTL pathways and regulation control of organic functional groups of typical organic components (protein, carbohydrates, and fat) in sludge. Supercritical HTL of organics from sludge pretreatment will be carried out in order to investigate the effect of different parameters on their liquefaction behavior and optimization method of regulation of functional groups. Meanwhile, the migration, morphology distribution, and regulation mechanism of heavy metals (Cu/Zn/Pb) during the HTL process will be carried out as well as to explore the competition reaction mechanism of heavy metals between functional groups and phosphorus based on quantum chemistry. At last, overall analysis and optimization methods of sewage sludge HTL to clean bio-oil will be proposed based on energy recovery and evaluation of comprehensive pollution control. The investigation of this project is to explore a new way in the sludge conversion to clean biofuels, which will provide scientific guidance for this kind of environment-enhancing energy.

污泥作为高含水率及复杂污染物的生物质废物具有严重的环境危害。水热液化制取生物油因其环境友好和能量转化效率高而成为研究热点。本项目提出基于分级处理的污泥亚/超临界水热液化制生物油的新思路，进一步开展有机官能团与重金属耦合调控制备清洁生物油机理研究。首先开展亚临界水热预处理实现污泥絮体结构破坏与有机质水解，并实现大部分重金属的分离去除。研究蛋白质、糖类和脂类等污泥中典型有机组分的单独超临界水热液化机理与有机官能团调控规律；探讨不同因素对有机提取物超临界水热液化产物生成及有机官能团调控的优化方法；基于量子化学探索生物油中重金属与有机官能团及无机磷酸盐的竞争反应机制，揭示典型重金属（Cu/Zn/Pb）的迁移转化、形态分布及调控机理研究；构建基于能量转化率、综合污染控制评价的污泥水热液化制备清洁生物油的整体优化方法。本研究将探索污泥类生物质转化为清洁生物燃料的新途径，为该类环境增值能源提供科学支持。

本项目探究了市政污泥水热液化过程中各类工况条件对清洁生物油制备的影响并明晰了大量的微观反应机理。.项目研究表明表面活性剂和水热法可以有效释放污泥中的结合水。复配表面活性剂与水热联合预处理比单一预处理的生物油收率高103.3%，并且能够有效降低生物油成分的复杂程度。热预处理可以促进酯交换反应和脱氨基反应，在提升102.7%的酯的同时降低生物油中51.7%的氮。十六烷基三甲基溴化铵(CTAB)通过促进卤代反应使生物油中的烃类物质增加226.7%，此外经过联合预处理后生物油的热值会提高4.99 MJ/kg。.在反应过程中，随温度和时间的增加，重金属以更稳定的形态富集在固相残渣中，环境风险最多降低95.7%。重金属与氮在低温阶段形成−N:…M2+共价键，同时Cu使芳香族化合物减少50%，其他金属能够减少20%以上的含氧化合物。除此之外，重金属在高温下生成金属氧化物。.甲醇-水作为混合溶剂时，污泥两段连续水热液化（260℃-40min-340℃-40min）的生物油产率高达42.2%。Ni和Co负载HZSM-5催化剂能够明显提升生物油分子的氢含量并降低氮和氧的含量，同时增强了多环含氮化合物向胺类、酰胺类物质的转化。另外，利用模型化合物明晰了水热液化过程中有机质转化机理以及氮元素迁移转化路径，并提出生物油收率的贡献率可以按照脂质>蛋白质>碳水化合物顺序排序。.以污泥的水热液化过程为基础，将副产物水相作为溶剂进行循环利用后，生物油产率从17.9%被提高至30.5%，能量回收率从40.3%提高至61.7%，同时水相的循环利用直接导致水相COD下降了24.9%。在生物油的水热液化过程中，CO2气氛能够增加38.6%的短链生物油分子占比，并降低生物油中15%的酸含量；通过化学酸碱沉淀法，提取出固相残渣中的金属离子制备成硝酸盐催化剂后，最多能够降低生物油中32.1%的N含量。这实现了污染控制和资源再利用的双重目的。