利用碱金属氢化物与气态小分子化合物反应制备清洁燃料的研究

发布时间：2018-05-13 10:12

本文选题：碱金属氢化物 + 还原　；参考：《扬州大学》2015年硕士论文

【摘要】：高效储氢是将氢能经济变为现实的关键,但作为清洁能源的氢气存储仍有不少瓶颈。由于氢气危险性高且体积能量密度较低,所以传统的高压储存和低温储存对于实际中的运输应用并不是最好的方法,也因如此,氢气与二氧化碳制备作为清洁燃料的甲烷也受到了发展限制。碱金属氢化物由于其较高的储氢能力且具有极强的还原性而被认为是理想的氢载体。前人研究指出碱金属氢化物与NH3反应这类可逆储氢材料能在温和条件下自动放出氢气,是一种具有前途的储氢材料。相关放氢反应如下：MH+NH3→MNH2+H2 (M=Li, Na,和K) (1)在这些系统中,LiH-NH3系统具有最高的储氢能力(8.1 wt%),而且由于其是自发放热反应[14],此系统可在相对较低的温度下进行。然而此系统的反应动力学相对于实际应用来说太慢,寻找一种MH-NH3储氢材料的核心问题在于如何获得高储氢容量的同时还要兼具优良的吸／放氢动力学性能。首先本论文系统地研究了不同尺寸下的LiH与氨气反应的放氢性能以及球磨后LiH在50-200 ℃下的放氢反应以便探究设计出更好的动力学性能,重要的是,各种钾化合物能够作为潜在的催化剂被用于提高LiH-NH3体系的放氢反应动力学性能,研究表明,LiH-NH3反应体系的放氢反应动力学性能会随着LiH晶粒尺寸的减小或者反应温度的提高而得到明显的改善,KBr, KCl, KF和KOH作为钾化合物的添加也能有效地增强其放氢反应动力学,在所添加的钾化合物中,KBr的改善效果最好。其次,本文也系统地研究了KH掺杂的LiH-NH3、LiH-LiNH2系统和掺杂KH和KNH2的LiNH2体系,前人研究表明这些体系具有较好的吸放氢性能,研究发现KLi3(NH2)4是一种极易在掺杂钾化合物的Li-N-H系统吸放氢过程中形成的重要中间体。本文进一步揭示了KH与LiNH2及KNH2和LiNH2之间的固相反应能同时在球磨和加热条件下促进三元氨基化合物KLi3(NH2)4的生成。另外,本文成功地利用球磨法合成出了单相的KLi3(NH2)4并且对其放氨和吸氢性能进行了研究,TPD实验表明KLi3(NH2)4的放氨速率要快于LiNH2,吸氢实验结果也表明LiNH2、KLi3(NH2)4、KNH2的吸氢反应动力学活性依次递增。最后,本文利用还原性强、密度低的碱金属氢化物设计出了碱金属氢化物与CO2甲烷化或固碳产氢的反应,如下列方程式所示：4LiH+CO2→2Li2O+C+2H2→2Li2O+CH4 (2) 4NaH+3CO2→2Na2CO3+C+2H2→2Na2CO3+CH4 (3)上述甲烷化反应不仅具有较负的自由能及反应焓变(-515—890KJ/mol,以LiH为例),而且为强放热反应,这些特点决定了MH-CO2体系有望成为具有高能量密度、在温和条件下自发甲烷化的能源材料,本文也首次验证了二氧化碳能够被碱金属氢化物还原捕捉且仅通过加热反应就能在合适的温度下生成甲烷与氢气的混合气体,在混合气体中的甲烷摩尔分数与二氧化碳甲烷化的产率受到反应温度、压强及反应时间的影响,通过对碱金属氢化物与二氧化碳反应的机理分析表明,在反应过程中生成的无定型的单质碳作为中间体对二氧化碳甲烷化的程度有重要的影响,在本体系中通过催化剂的引入来降低反应温度是当前工作的重点。
[Abstract]:Hydrogen storage is the key to the transformation of hydrogen energy into reality. However, there are still many bottlenecks in the storage of hydrogen as a clean energy source. Because of the high hydrogen risk and low volume energy density, traditional high pressure storage and low temperature storage are not the best methods for the actual transport application, and the hydrogen and carbon dioxide are also prepared. Methane is also restricted by the development of clean fuel. The alkali metal hydride is considered as an ideal hydrogen carrier because of its high hydrogen storage capacity and strong reducibility. Previous studies have pointed out that the reversible hydrogen storage materials such as alkali metal hydride and NH3 can release hydrogen under mild conditions, which is a promising reservoir. Hydrogen material. Related dehydrogenation reactions are as follows: MH+NH3 - MNH2+H2 (M=Li, Na, and K) (1) in these systems, the LiH-NH3 system has the highest hydrogen storage capacity (8.1 wt%), and because it is a self distributed thermal reaction [14], the system can be carried out at relatively low temperatures. However, the reaction kinetics of this system is too slow relative to the actual application. The core problem of finding a MH-NH3 hydrogen storage material is how to obtain high hydrogen storage capacity and also have excellent absorption / desorption kinetics. First, the performance of LiH and ammonia reaction under different sizes and the hydrogen release reaction of LiH at 50-200 C after ball milling are systematically studied in this paper so as to explore the design of better motion. It is important that all kinds of potassium compounds can be used as potential catalysts to improve the kinetic properties of the hydrogen release reaction of LiH-NH3 system. The study shows that the kinetic properties of the LiH-NH3 reaction system will be greatly improved with the decrease of LiH grain size or the increase of reaction temperature, KBr, KCl, KF and KOH. The addition of potassium compounds can also effectively enhance the kinetics of its hydrogen release reaction. In the added potassium compound, KBr has the best improvement effect. Secondly, the KH doped LiH-NH3, LiH-LiNH2 system and LiNH2 system doped with KH and KNH2 are systematically studied. The previous studies show that these systems have better hydrogen absorption properties. It is found that KLi3 (NH2) 4 is an important intermediate in the process of absorbing and releasing hydrogen in the Li-N-H system with potassium compounds. This paper further reveals that the solid state reaction between KH and LiNH2 and KNH2 and LiNH2 can promote the formation of the three element amino compound KLi3 (NH2) 4 under the ball milling and heating conditions. In addition, the ball milling is successfully used in this paper. A single phase KLi3 (NH2) 4 was synthesized and its ammonia and hydrogen absorption properties were studied. The TPD experiment showed that the rate of ammonia release of KLi3 (NH2) 4 was faster than LiNH2. The experimental results of hydrogen absorption showed that LiNH2, KLi3 (NH2) 4, KNH2 increased the kinetic activity of hydrogen absorption reaction in turn. Finally, the design of alkali metal hydride with strong reducibility and low density was designed in this paper. The reaction of alkali metal hydride with CO2 methanation or carbon sequestration, as shown in the following equation: 4LiH+CO2 to 2Li2O+C+2H2 to 2Li2O+CH4 (2) 4NaH+3CO2 to 2Na2CO3+C+2H2 to 2Na2CO3+CH4 (3), the above methanation reaction not only has a negative free energy and reaction enthalpy change (-515 890KJ/mol, LiH for example), but also a strong exothermic reaction, Some characteristics determine that the MH-CO2 system is expected to be an energy material with high energy density and spontaneous methanation under mild conditions. This paper also first verified that carbon dioxide can be captured by the reduction of alkali metal hydride and can produce methane and hydrogen gas at the appropriate temperature only by heating reaction, and in the mixture gas. The rate of methane mole fraction and carbon dioxide methane is affected by reaction temperature, pressure and reaction time. Through the analysis of the reaction mechanism of the alkali metal hydride and carbon dioxide, it is shown that the amorphous carbon produced in the reaction process has an important influence on the degree of carbon dioxide methanation. It is the focus of the current work to reduce the reaction temperature through the introduction of catalysts.

【学位授予单位】：扬州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ116.2

【相似文献】