高蛋白藻分段式水热液化制备低N生物油的基础研究

Hydrothermal liquefaction is favorable for bio-oil production from algae, since drying is not needed and all constituents of algae can be effectively utilized. But the high N-containing heterocyclic compounds in product oil is difficult to catalytic degraded and tends to poison the catalyst. A two-stage hydrothermal liquefaction method, including low-temperature hydrolysis combining with moderated-temperature liquefaction, is proposed for utilization of protein-rich algae which is the most common kind of algae. Briefly, part of nitrogen in algae is enriched into aqueous liquid via low-temperature hydrolysis, which can prevent hydrolysis products of protein from reacting with reducing sugar (hydrolyzed from saccharide ) and fatty acid (hydrolyzed from lipids), thus decreases the production of N-containing compounds (i.e. heterocyclic compounds and amides) and the nitrogen content of algae bio-oil at source. This project mainly focuses on: (1) mechanism on hydrothermal liquefaction of protein; (2) decomposition pathway and denitrification mechanism of protein-rich algae during low-temperature hydrolysis; (3) liquefaction mechanism of hydrolyzed residue at moderated-temperature liquefaction; (4) Coupling relationship and regulation mechanism between low temperature hydrolysis and moderated-temperature liquefaction. In light of theory and experiments, special attention is paid for the transferring pathway of the nutrient N and integrated optimization of the whole process. The results serve as fundamental basis for production of bio-oil with a low-nitrogen content from protein-rich algae and other nitrogen-rich materials. It is of great significance in academy and practice.

海藻水热液化制备生物油具有无须干燥、充分利用原料组分等优势，但产物中N杂环化合物含量高，在后续提质中极难催化降解且极易造成催化剂中毒。本研究针对普遍存在的一类海藻资源−高蛋白藻，提出“低温水解-中温液化”分段式水热液化的工艺路线，通过低温水解将一部分N富集在水相，控制蛋白质水解产物与还原糖（糖类水解产物）或长链脂肪酸（油脂水解产物）发生反应，从源头减少生物油中的N杂环化合物和脂肪胺类。研究内容包括：①蛋白质水热降解机理；②高蛋白藻低温水解路径及脱N机理；③固体藻渣中温液化特性及成油机制；④低温水解-中温液化之间的耦合关系及调控机制。通过理论和实验的有机结合，重点解析反应过程中营养元素N的迁移转化路径及“高蛋白藻-低温水解-中温液化-低N生物油”之间的耦合调控机制。预期成果可为高蛋白藻水热液化制备低N生物油提供基础依据，也可为其他高含氮原料的水热液化提供参考，具有重要的学术价值和实际意义。

本研究针对高蛋白藻类生物质，基于“低温水解-中温液化”分段式水热液化的工艺，开展了高蛋白藻分段式水热液化制备低N生物油的基础研究。选取典型氨基酸和葡萄糖分别为蛋白质和糖类的模型化合物，利用石英毛细管反应器，考察了其在反应温度150-300°C和时间15-120min下的转化规律和产物分布特性，提出了苯丙氨酸与葡萄糖反应路径，解析了蛋白质的水热液化机理。选取不同种类的高蛋白藻（硅藻、小球藻和螺旋藻）为原料，利用间歇式水热反应釜进行了水热低温预处理研究，考察了反应温度120-250°C和时间5-60min下的各相产物产率，重点研究了C、N元素产物的分布特性和赋存形态，解析了高蛋白藻低温水解路径及脱N机理。针对低温水热预处理固体产物-固相藻渣，在深入考察其热降解特性的基础上，研究了在反应温度250-380°C和时间30-60min下的产物分布，重点分析了目标产物生物油的产率及组分特性，阐述了固体藻渣的中温液化特性及成油机制；基于以上研究，解析了高蛋白藻低温水解-中温液化之间的耦合关系及调控机制。结果证明，高蛋白藻经低温水解预处理通过脱氨反应能有效将一部分营养元素N富集在水相，抑制了蛋白质水解产物与糖类水解产物或油脂水解产物发生反应，进而从源头减少生物油中的N杂环化合物和脂肪胺类。本研究成果可为高蛋白藻水热液化制备低N生物油提供基础依据，也可为其他高含氮原料的水热液化提供参考，具有重要的学术价值和实际意义。