甘氨酸水热液化原位拉曼光谱观测及反应动力学分析

随着社会经济的飞速发展，能源短缺问题在世界范围内日益突显。目前，开发利用可再生能源已被我国列为能源发展的优先领域。藻类植物蕴含丰富的生物质能，同时又具有光合效率高、固碳能力强、生长速度快、来源分布广等优势，是公认的可持续绿色清洁能源的发展方向。甘氨酸是藻类水热液化过程中的重要过程反应物，其液化过程中的热动力学性质是认识和优化藻类水热液化技术的基础要素，通过研究甘氨酸水热液化过程可为分析复杂的生物质水热液化反应奠定基础。研究基于熔融石英毛细管反应器（FSCR）高温高压可视反应腔，结合Linkam FTIR600控温台与Andor激光拉曼光谱仪联用，对甘氨酸水溶液在270~290 ℃（压力同于实验环境温度下水饱和蒸气压）条件下的液化过程运用拉曼光谱分析技术开展了原位研究。通过观测5 Wt%甘氨酸溶液中C—C伸缩振动峰（897 cm-1）、C—N 伸缩振动峰（1 031 cm-1）和COO-反对称伸缩峰（1 413 cm-1）在液化过程中的相对拉曼强度变化，深入分析了温度及反应时间对甘氨酸溶液各官能团热分解的影响。运用Avrami的反应动力学模型分析，获取了量化温度对甘氨酸分子中骨架碳链ν（C—C）的特征振动模式热解过程影响的活化能，357 kJ·mol-1，和不同实验温度下的反应速率常数k等一系列相关参数，定量地揭示了甘氨酸液化过程的热动力学性质。实验中发现，在设定相同的液化反应时间（10 min）内，当温度低于290 ℃时，降温后反应腔内能观测到甘氨酸水溶液中ν（C—C），ν（C—N），ν_as（COO-）的特征峰，而温度高于290 ℃时则不然，表明甘氨酸的完全液化温度约为290 ℃。该研究运用高温高压可视化实验技术，结合原位拉曼光谱分析技术，厘清了甘氨酸水热液化过程中的不同温度下特征官能团拉曼峰强的变化规律，为深入了解藻类水热液化过程机理、推进生物质能的开发利用提供必要的实验依据，具有重要的科学意义和现实意义。

In Situ Raman Study and Kinetic Analysis of Hydrothermal Liquefaction of Glycine

With the rapid development of social economy, the problem of energy shortage is becoming more and more prominent in the world. At present, the development and utilization of renewable energy has been listed as the priority area of energy development in China. Algae plants contain abundant biomass energy, and have advantages such as high photosynthetic efficiency, strong carbon fixation capacity, fast growth rate, and wide distribution of sources, which is recognized as the development direction of sustainable green and clean energy. Glycine is an important derivative product in the process of algal hydrothermal liquefaction. The thermomechanical properties of glycine during liquefaction are the basic elements to understand and optimize the technology of algal hydrothermal liquefaction. The study of glycine hydrothermal liquefaction process can lay a foundation for the analysis of complex biomass hydrothermal liquefaction reaction. In this study, based on the high temperature and high pressure visible reactor of fused silicon capillary reactor (FSCR), combined with Linkam FTIR600 temperature control platform and Andor laser Raman spectrometer, the liquefaction process of glycine aqueous solution at 270~290 ℃ (pressures approximate to the saturated vapor pressure of water at ambient temperatures) was studied in situ by Raman spectroscopy. The effects of temperature and reaction time on the thermal decomposition of functional groups of glycine solution were analyzed by observing the relative Raman intensity changes of C—C stretching vibration peak (897 cm-1), C—N stretching vibration peak (1 031 cm-1) and C—O—O antisymmetric peak (1 413 cm-1) during liquefaction. The activation energy, 357 kJ·mol-1, and reaction rate constant k at different temperatures were obtained by using Avrami kinetic model. The thermodynamic properties of glycine liquefaction process were quantitatively determined. It is found that within the same liquefaction reaction time (10 min), when the temperature is lower than 290 ℃, the ν(C—C), ν(C—N), ν_as(COO-) characteristic peak of glycine aqueous solution can be observed in the reaction chamber after cooling, but not when the temperature is higher than 290 ℃, indicating that the complete liquefaction temperature of glycine is about 290 ℃. The present study, based on the high-temperature and high-pressure visualization technology combined with in-situ Raman spectroscopy analyses, reveals the variation of the Raman peak intensities of characteristic functional groups of glycine at different temperatures during the hydrothermal liquefaction and provides deep insights into the pathway of hydrothermal liquefaction of algae. It is of great scientific and practical significance to understand the mechanism of algal hydrothermal liquefaction and promote the development and utilization of biomass energy.