木质纤维素类生物质水热炭化机理及水热炭应用进展

Hydrothermal carbonization of the lignocellulosic biomass and application of the hydro-char

通过水热炭化方法(HTC)制备纤维类生物质炭材料,是当前废弃生物质高值化处理的一种方式。生物质具有种类繁多、结构复杂的特点,在不同的水热条件下涉及水解、降解、聚合等复杂反应。制备的水热炭性质如形貌、孔结构、表面官能团分布等受原料物理化学结构和水热反应条件影响较大,而水热炭的性质直接影响水热炭的应用。木质素炭化需要较高的水热强度,生成的水热炭石墨化程度和稳定性更高,可应用于导电、耐高温材料等领域;纤维素、半纤维素相对于木质素炭化温度低,更易形成多孔结构,获得更高的比表面积。另外二者因富含羟基,制备的水热炭表面具有丰富的含氧官能团,有利于通过静电吸附、离子交换等过程实现污染物吸附,进一步应用于环境治理等领域。水热温度主要影响炭化程度和水热炭得率,而水热时间则对水热炭形貌具有更明显的作用。通过改性可以定向调控水热炭性能,扩大其应用领域范围。为明晰不同条件下水热炭的结构变化,本文综述了纤维类生物质的种类、原料组成及水热条件对水热炭结构的影响,深入分析了水热炭生成机理,探讨了生物炭改性方法,归纳了生物炭在不同领域的应用并展望了未来的发展方向和前景,为生物质基水热炭研究提供参考。

Hydrothermal carbonization(HTC)is an efficient way to convert the lignocellulosic biomass to high-value added products.The wide variety of lignocellulosic biomass has complex physiochemical structures,resulting in complicated reactions including hydrolysis,degradation,and polymerization during HTC at different conditions.Characteristics of the hydro-char,such as morphology,pore structure,and the surface functional groups distribution are determined not only by the structure of the raw materials but also the hydrothermal reaction conditions,and directly affect the application of hydro-char.Lignin carbonization requires higher hydrothermal strength than cellulose and hemicellulose.In addition,the resulted hydro-char has a higher degree of graphitization and stability.It could be used as electrical and high temperature resistant materials.Compared to lignin,cellulose and hemicellulose can form porous structure more easily.In the meanwhile,they are rich in hydroxyl groups,the prepared hydro-char has abundant oxygen-containing functional groups,which is beneficial to the electrostatic adsorption and ion exchange.The generated biochar can be applied to the fields of environmental treatment.The hydrothermal temperature mainly affects the degree of carbonization and the yield of hydro-char,while the reaction time affects the morphology of the hydro-char obviously.The properties of hydro-char can be regulated by modification to expand its application.In this paper,the relationship among the composition of raw materials,HTC conditions and the structural characters of hydrothermal products were reviewed;the mechanism of carbonization process was deeply analyzed;the modification methods of hydro-char were discussed;the application of hydro-char in different fields was summarized;and the further development directions of HTC were proposed to provide a reference for the research of biomass-based hydro-char.