硅酸锂材料的制备及其高温二氧化碳吸收性能研究

发布时间：2018-04-16 16:28

  本文选题：硅酸锂 + 二氧化碳　； 参考：《中国矿业大学》2017年硕士论文

【摘要】：燃煤电站是CO_2的主要排放源,捕集和回收燃煤烟气中的CO_2是缓解CO_2排放危机最直接有效的手段。硅酸锂作为一种高温CO_2吸附剂,具有吸附容量大、循环性能稳定以及成本合理等优点,被认为是目前能够高温脱除燃煤烟气CO_2的有潜力捕集材料。本文主要针对常规固态制备方法合成的硅酸锂吸附剂捕获CO_2活性较弱、反应速率较慢,难以达到实际应用需求的缺点,开展优良吸附剂的制备研究,并使用X-射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)、N2吸附仪和热重分析仪(TG)等手段对合成样品的物相组成、结构特征及吸附性能进行表征,系统研究吸附剂的高温CO_2吸附性能。研究的主要内容如下:(1)利用碳包裹的原理,在溶胶-凝胶法的基础上合成得到一种高效的高温CO_2吸附剂(CSG-Li_4Si O_4)。柠檬酸在整个合成过程中既作为螯合剂使硅与锂的前驱体得到充分的混合,也作为碳包裹中的碳源,可以有效的抑制硅酸锂晶体结构的增大。分别与固固反应和溶胶-凝胶法合成的硅酸锂进行对比,发现利用碳包裹法能够合成纯度高、晶粒尺寸小、比表面积较大的硅酸锂吸附剂,其拥有更高的吸附量,更快的吸附速率和更好的吸附稳定性,其最大吸附量可以达到34.2wt.%。(2)采用溶胶-凝胶法制备分别掺杂有K、Mg、Cr和Ce金属元素的Li_4Si O_4吸附剂。结果表明,所有掺杂金属元素(K、Mg、Cr、Ce)都能够融入硅酸锂的晶格中,但对Ce而言,其掺杂难度更大。Ce的掺杂能够有效抑制晶体团聚,同时掺杂后形成的Ce O_2能够有效改善硅酸锂吸附剂颗粒形貌,提高吸附剂吸附性能。Ce2-Li_4Si O_4在纯CO_2、690℃条件下,10min内最大吸附量可达34.57wt.%,对其进行循环吸附性能测试,在10次吸附/解吸循环后,其吸附容量并未出现明显衰减,样品具有良好的可再生能力。(3)采用一种“简单”的水合-掺杂NaCl方法制备硅酸锂吸附剂,以提高其在低浓度CO_2下的吸附性能。Li_4Si O_4材料的水合产物主要是Li OH和Li2Si O3,水合后再生得到的HC样品颗粒粒径有所减小,这将有助于CO_2的吸附,其对应的CO_2吸附量为13.7wt.%,是SS样品的两倍多。掺杂Na Cl后,一方面,有利于制备得到小粒径和大比表面积的硅酸锂颗粒,显著地促进了化学吸附过程。另一方面,在吸收CO_2过程中,共掺杂的Na Cl诱导形成熔融相,能够显著降低CO_2扩散阻力。水合和Na Cl掺杂均能有效提高吸附剂性能。通过对水合Na Cl掺杂量的研究发现,掺杂量越大,吸附剂的吸收速率越快,但过量的Na Cl(5wt.%)会导致杂质的形成,从而降低吸附容量。综合判断最佳添加剂比例为3wt.%,HC-3Na最大吸附量高达34.2wt.%。对HC-3Na进行循环吸附性能测试,在10次吸附/解吸循环后,其吸附容量并未出现衰减,维持着32wt.%左右,样品具有良好的可再生能力。
[Abstract]:Coal-fired power station is the main emission source of CO_2. Collecting and recovering CO_2 from coal-fired flue gas is the most direct and effective means to alleviate the CO_2 emission crisis.As a high temperature CO_2 adsorbent, lithium silicate has the advantages of large adsorption capacity, stable cycling performance and reasonable cost. It is considered to be a potential trapping material for removing CO_2 from coal-fired flue gas at high temperature.In this paper, the preparation of lithium silicate adsorbent, which was synthesized by conventional solid-state preparation method, was mainly aimed at the disadvantages of weak CO_2 activity and slow reaction rate, which was difficult to meet the practical application requirements, so the research on the preparation of excellent adsorbent was carried out.The phase composition, structure and adsorption properties of the synthesized samples were characterized by means of X-ray powder diffractometer (XRD), scanning electron microscope (SEM) and thermogravimetric analyzer (TG). The adsorption properties of the adsorbent at high temperature were studied systematically.The main contents of this study are as follows: (1) based on the sol-gel method, a high temperature CO_2 adsorbent, CSG-Li _ 4Si _ 2O _ 4, has been synthesized by using the principle of carbon encapsulation.Citric acid can be used as a chelating agent to make the precursor of silicon and lithium fully mixed and as a carbon source in carbon encapsulation, which can effectively inhibit the increase of crystal structure of lithium silicate.Compared with solid reaction and sol-gel method, lithium silicate adsorbents with high purity, small grain size and large specific surface area can be synthesized by carbon encapsulation method.With faster adsorption rate and better adsorption stability, the maximum adsorption capacity can reach 34.2wt.0.The Li_4Si O _ 4 adsorbent doped with K _ (mg) Cr and ce metal elements was prepared by sol-gel method.The results show that all the doped metal elements (K _ 2O _ 3) can be incorporated into the lattice of lithium silicate, but for ce, the doping of 路ce can effectively restrain the crystal agglomeration.At the same time, ce _ O _ 2 formed by doping can effectively improve the morphology of lithium silicate adsorbent particles and improve the adsorbability of the adsorbent. Ce2-Li4SiO _ 4 can reach the maximum adsorption capacity of 34.57 wt.In 10 minutes at pure CO_2690 鈩，

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