低阶煤和生物质水热碳化特性及水热炭功能化改性研究进展

Research progress on the hydrothermal carbonization characteristics of low rank coal and biomass and the functionalization modification of hydrochar

低阶煤中大量含氧官能团赋予其强亲水性,导致孔隙表面吸收大量水分,从而增加运输成本,能源转化效率降低,因此低阶煤的清洁低碳高效转化备受关注。水热碳化反应能耗较低,可直接处理高含水率有机固体物质,是一种绿色低碳高效经济的低阶煤提质技术;而生物质作为可代替化石燃料的可再生能源,水热碳化也可大幅提高其利用率。低阶煤与生物质共水热碳化时,二者会产生一定的协同效应,相较于单一水热碳化具有更高的产率和碳保留率。对水热炭进行功能化改性,可以进一步丰富其孔隙结构,增加材料表面的官能团,进而制备出性能优异的功能性炭材料,用于CO_(2)和SO_(2)等气体吸附。综述了低阶煤和生物质单独水热碳化及共水热碳化特性,分析生物质水热碳化主要影响因素;同时对水热炭活化改性和掺杂改性方法进行了总结,比较了氮、硫掺杂及硫氮共掺杂方式、掺杂机制及改性水热炭应用范围。此外,还对改性水热炭对CO_(2)和SO_(2)吸附性能等进行了综述,探讨了多孔炭表面吸附CO_(2)和SO_(2)的机理;最后对低阶煤和生物质共水热碳化以及水热炭低成本制备气体吸附剂等未来发展方向进行了展望。

The abundant oxygen-containing functional groups in low rank coal endow it with strong hydrophilicity,and cause the pore surface to absorb a large amount of water,which makes the transportation costs increasing and energy conversion efficiency reducing.Therefore,the clean,low-carbon and efficient conversion of low rank coal has attracted more and more attentions.Hydrothermal carbonization is a green,low-carbon,efficient,and economical low-rank coal upgrading technology.It consumes low energy and can treat organic solid substances with high moisture content directly.As a renewable energy source,biomass can replace fossil fuels.Through hydrothermal carbonization,the quality of biomass can be improved significantly.During co-hydrothermal carbonization of low rank coal and biomass,there will be a certain synergistic effect between them,and compared to hydrothermal carbonization of low rank coal or biomass alone,co-hydrothermal carbonization can result in higher yield and carbon retention ratio.Furthermore,functionalization modification of hydrochar can further enrich its pore structure,increase the functional groups on the material surface,and obtain high-performance functional carbon materials for gas adsorption such as CO_(2) and SO_(2).In this paper,the hydrothermal carbonization characteristics of low rank coal,biomass and their mixture were reviewed,and the main influencing factors of biomass hydrothermal carbonization were analyzed.The activation and doping modification methods of hydrochar were also summarized,and the doping methods,mechanisms and application scope of nitrogen,sulfur doping,and co-doping hydrochar were compared.Moreover,the adsorption performance of modified hydrochar for CO_(2) and SO_(2) was also introduced,and the mechanism of CO_(2) and SO_(2) adsorption on the surface of porous carbon were described.At the end,the future development directions of co-hydrothermal carbonization of low rank coal and biomass were suggested,as well as for the low-cost preparation of gas adsorbents using hydrochar.