离子液体中阴阳离子的特性对其吸收二氧化硫的影响

Effect of Anionic and Cationic Characteristic on the SO_2 Absorption Performance of Ionic Liquids

SO_2是一种无色、有强烈刺激性气味的气体,弥散在空气中的SO_2对人体健康、生态环境有着严重的危害,是导致空气质量不断恶化的主要大气污染物之一。人为造成的SO_2污染物的主要来源有燃料燃烧、工业生产、交通运输等,其中燃料燃烧占70%。因此,削减和控制燃料燃烧所产生的SO_2的排放是我国能源利用和环保领域的重要研究方向,烟气脱硫是应对烟气中SO_2排放的有效途径。湿法烟气脱硫是目前应用最广泛的方法,占世界安装烟气脱硫机组总容量的85%,采用该方法处理的烟气占总处理量的80%。在湿法烟气脱硫技术中比较实用的主要包括钙法脱硫、有机胺脱硫、海水脱硫。其中,钙法脱硫的脱硫效率高,对煤种的适应性较强,但是脱硫会产生CaSO_4沉淀,降低经济效益;有机胺脱硫的系统腐蚀性小,副产品可生产硫酸,但是胺易挥发,造成吸收剂损失和环境污染;海水法脱硫的工艺简单、运行可靠,但其应用受到地域的影响,并且对环境也会产生一定的影响。离子液体是一种新兴的绿色介质,它具有环保、可再生、结构可调控的优点,为解决传统工艺中的污染问题提供了新方案。在离子液体吸收气体的过程中,吸收液不会因其挥发性而蒸发进入气相,并且可以在较低的温度下完成吸收解吸循环。离子液体的这些优良特性使其在SO_2吸收方面有着极广阔的应用前景。目前,研究者们已合成了一系列胍盐类、咪唑类、醇胺类、吡啶类等离子液体,探究其吸收SO_2的性能与机理,并根据其结构可设计的特点,在离子液体中的阴阳离子上引入各类官能团(如氰基、醚基、氨基、卤素),合成满足特定需求的离子液体,使其高效、可逆、低耗地吸收SO_2。本文总结了近年来各类离子液体吸收SO_2的性能和机理,为系统地认识离子液体在SO_2分离领域的应用提供了帮助;重点阐明了离子液体中阴阳离子的种类、官能化,尤其是酸碱性对其吸收SO_2的影响,这为调整离子液体酸碱性、合理设计离子液体的结构,探索离子液体吸收SO_2的机理,改善其对SO_2的吸收性能有着重要的价值。最后指出了目前研究中存在的问题并且对未来新型离子液体的合成进行了展望。

Sulfur dioxide(SO 2)is a kind of colorless and intensely irritating gas.When dispersing in the air,SO 2 will threaten the human health,do harm to the environment,and deteriorate air quality.The main sources of man-made SO 2 pollution are fuel combustion,industrial production,transportation and so forth.Among them,fuel combustion accounts for 70%.Therefore,minimizing and controlling SO 2 emission from fuel combustion are primary research directions in the field of energy utilization and environmental protection in China.Flue gas desulfurization(FGD)is considered as an effective way to remove SO 2.Currently,the wet flue gas desulfurization is the most popular method for flue gas treatment.Wet flue gas desulfurization installation accounts for 85%of the total installed capacity of flue gas desulfurization units in the world,and the amount of flue gas treated by wet flue gas desulfurization accounts 80%of the total treatment capacity.There are mainly practical techniques for the wet flue gas desulfurization,including calcium,organic amine and seawater desulfurization.Among them,calcium desulfurization can remove SO 2 efficiently and has strong adaptability to different kinds of coal.However,there are large amounts of by-product CaSO 4 formed in the process,which leads to the low economic efficiency.The organic amine desulfurization is of less system corrosion,and the byproduct can be used to produce sulfuric acid,but the amine is volatile,resulting in loss of absorbent and second pollution.Seawater desulfurization is a simple and reliable method for SO 2 removal,whereas its application is limited by the geographical location and has an adverse impact on environment.Ionic liquid(IL)is an emerging green medium with the advantages of environment protective,reproducible and structure tunable which provides a new method for solving the pollution problems of traditional processes.Especially,ILs have a promising application prospect in gas separation,because there is no weight loss for ILs during the absorption process and the cycle of gas absorption and desorption can be conducted at a lower temperature.This excellent SO 2 absorption performance of ILs endows them with great potential for SO 2 capture.Currently,researchers have synthesized a series guanidinium,imidazoles,alkanolamines and pyridine-based ILs,for SO 2 absorption.The SO 2 absorption performance and mechanism of ILs have been also explored.Based on the tunable structure,functional groups,such as cyano,ether,amino and halogen are introduced into the anion and cation of ILs to synthesized the ILs with specific ability,aiming at making desulfurization process efficient,reversible and energy-saving.In this article,the properties and mechanism of SO 2 absorption by various types of ILs in recent years are reviewed,which provides a systematic understanding of the ILs application in the field of SO 2 absorption.The effects of anion and cation species,functionalization,especially acidity and alkalinity on the absorption of SO 2 in ILs are emphasized.It is of great value to adjust the acidity and basicity of ILs,to design the structure of ILs,to explore the mechanism of SO 2 absorption by ILs,and to improve the absorption properties of SO 2.Finally,the problems existing in the current research are pointed out and the prospects for the synthesis of new type ILs for SO 2 absorption are also discussed.