【作者】 罗小燕；

【导师】 王从敏；

【作者基本信息】 浙江大学 ， 化学， 2014， 博士

【摘要】 近年来,大气中二氧化碳(CO2)气体含量随着工业的迅速发展不断增加而引起的“全球气候变暖”问题,已经引起了全世界的关注。离子液体(IL)由于它的一些独特性质如蒸汽压低、液程宽、溶解力强、结构性能可调等一系列优良特性,已成为捕集CO2的良好吸收剂。氨基功能化IL首次被合成应用于选择性的捕集CO2之后,一系列改性的氨基功能化ILs被合成并改善吸收CO2的能力。但仍然存在吸收容量低、粘度太大等问题。因此,需要发展新的ILs碳捕集的方法。本文先设计合成一系列唑类、羟基吡啶型阴离子功能化ILs用于高容量的吸收CO2,然后对ILs吸收CO2中结构引起的熵效应进行了初步的探索,最后针对如何避免氨基功能化ILs吸收CO2后粘度大幅度增加的问题,提出使用分子内氢键代替分子间氢键使体系不形成氢键网络结构。首先,我们针对目前氨基功能化IL吸收CO2后形成大量的分子间氢键网络结构,造成体系粘度急剧增加,阻碍气体的传质问题,提出了使用不含质子氢的sp2杂化的N阴离子如唑类或者酚羟基阴离子用于CO2的捕集,由于其不合有形成强的氢键的H来源,避免了氢键网络结构的生成,因此吸收速率非常快。另外对阴离子的碱性进行调控,可以调节其吸收CO2的容量及吸收焓变,从而优化得到等摩尔吸收、低吸收焓变的体系[P66614][Triz]。由此出发,更进一步的提出通过阴离子的电荷离域到与其共轭的基团增加IL的作用位点数,来提高CO2吸收容量的新方法。基于此思想我们设计合成了含两个作用位点的羟基吡啶型和咪唑吡啶型ILs。量化计算的结果表明羟基吡啶环上π电子的离域作用,使得阴离子上的氮原子上的电荷密度比吡啶分子的大很多,能够跟CO2产生化学反应。从谱学上也可以看到酚羟基和毗啶基这儿两种化学吸收的CO2。这类ILs有着非常高的CO2吸收容量,通过设计可达1.65mol CO2/mol IL,远远高于两个点位单独作用的总和,存在多位点的协同效应。该类ILs也显示了良好的循环性能,是具有潜力的CO2捕集剂。对于ILs吸收CO2热力学方面,吸收焓变对吸收容量的影响的研究较多,但是从理论上分析,吸收容量是由吸收焓变和熵变共同影响的,由于CO2跟ILs的作用较强,熵变的影响往往不如焓变突出,因此大家对熵变的影响不明确。针对这方面的空白,我们设计了具有不同空间结构的ILs研究其空间结构对熵变的影响。通过量化计算和实验分析发现分子结构的不同会造成了分子间的作用方式不同,通过原位红外、变温红外的分析得出分子间氢键对熵变的影响很大,从而影响体系吸收CO2的行为。此外,氨基功能化ILs吸收CO2造成粘度的急剧上升主要是体系间形成了大量的分子间氢键网络结构。分子内氢键是除分子间氢键外的另一种氢键形式,但是分子内氢键只是在单个分子内部形成较稳定的氢键,对粘度的影响没有分子间氢键明显。因此我们通过对氨基功能化ILs的结构设计,引入能跟H形成氢键的N或O使其刚好能与分子中的H形成分子内氢键,我们发现在氨基上取代酰基后,其吸收CO后粘度反而有所下降。通过氨基上接入不能跟H形成分子内氢键的甲基作对比,发现甲基取代的氨基功能化ILs吸收CO2之后粘度剧烈增加。综上所述,本文设计合成了几类新型阴离子功能化ILs应用于碳捕集中,除了发展具有CO2吸收容量大、稳定性高和循环使用性好的新型ILs外,还对其中的热力学进行了系统的分析,为设计性能良好的气体吸收剂提供了新的思路与方法,为离子液体的酸性气体捕集打下了一定的基础。更多还原

【Abstract】 Recently, the discharge of carbon dioxide (CO2) into the atmosphere duing to the rapid development of industry has attracted a wide attention for their intribution to climate change. Ionic liquids (ILs) have developed as potentional CO2absorbent for their unique properties such as negligible vapor pressure, wide liquid range, superior dissolved ability, and their tunable structures and properties. Followed by the first reported example of CO2chemisorption by an amino-functionalized IL, lots of works fock on optimizing the CO2capacity of amino-based ILs, but low capacity, high viscosity do exist. Thus, the development of ILs for improving CO2capture is highly desired. In this manuscript, we designed a series of azole and hydrxypydridine-based anion functionalized ILs with high CO2capacity, besides, we tried to investigate the entropy effect design on CO2capture through the ILs’structure. Taking advantage of intramolecular hydrogen bond insteads of intermolecular hydrogen bond network to avoid the sharp increase of viscosity of amino-functionalized ILs.One disadvantage of amine-functionalized ILs is its low absorption kinetics due to the relatively high viscosity of the IL during the absorption of CO2for the formation of hydrogen bond network. We developed azole-based ILs with sp2hybridization of N such as azole anion and phenolate interaction with CO2. The azole-based ILs with improved properties such as scanty active hydrogen for strong hydrogen-bond formation, fast absorption rate, ect. The stability, absorption capability, and absorption enthalpy of ILs can be facilely tuned by varying the anions with different pKa values. Thus, highly stable basic ILs [P66614][Triz] for CO2capture with desirable enthalpy of absorption and high absorption capacity can be achieved. We further put forward ILs with multiple site cooperative interactions through conjugation effect of electron to enhance capacity of CO2. Based on this assumption, we present a new method for carbon capture by several hydroxypyridine-based ILs with two kinds of different interacting sites including pyridine and phenolate. Quantum mechanical calculations and spectroscopic investigations demonstrate that such a high capacity originate from the cooperative multiple site interactions between the electronegative nitrogen and oxygen atoms in the anion. The results show that an extremely high capacity up to1.65mol CO2per mol IL can be achieved, in addition, excellent reversible process by those ILs can provide a potential alternative for CO2capture.There are lots of works investigated the effect of enthalpy on the capacity of CO2capture by ILs, however, the CO2capacity not only depends on the reaction enthalpy based on the eqution△G=△H-T△S that the entropy is another parallel factor. For CO2chemisorption, the enthalpic change would be far greater than entropic change, which makes the entropy not obvious. It is not clear how the entropy effect on CO2chemisorption. We designed some isomeric anion functionalized ILs with substituent in different position to investigate the effect of structure on entropy of CO2capture. Viscosity measurements, spectroscopic investigations, and quantum chemical calculations showed that such a unique behavior originated from the entropic effect, which was induced by the intermolecular hydrogen bonding in these ionic liquids.The sharp increase of viscosity of amino-functionalized ionic liquids through CO2capture is duing to the formation of intermolecular hydrogen bond networks. As we know, hydrogen bond includes intermolecular and intramolecular hydrogen bond, the latter would not form the strong interaction among moleculars and not infulence the viscosity of the system very much. Based on this assumption, we introduce atom N or O to the amino-functionalized ILs, we expect the N or O in the just right position and can form intramolecular hydrogen bond with H of NH or NCOOH after CO2capture. We found the viscosity of amino-functionalized ILs with acetyl group tethered at the amino have slightly decrease during the CO2capture process, while with methy group tethered at the amino, the viscosity increase violently.Summary, we developped several class of anion-functionalized ILs for CO2capture, on the basis of the relationship between CO2absorption performance and the structure of the ILs, high capacity, low absorption enthalpy, rapid absorption kinetics, and excellent reversibility can be achieved by tuning the structure of the ILs, and we did a preliminary exploration on thermodynamics, which offer new strategy for enhancing the performace of gas absorbent.更多还原