捕获烟气中二氧化碳的多孔固体强碱新材料

Combustion of fossil fuels emits huge amounts of carbon dioxide, contributing to global climate changes. Therefore it is necessary to trap CO2 from flue gas. However, most of CO2-capture methods, including commercial liquid amine, carbon-based adsorbent and amine-modified mesoporous materials are carried out at relative low temperature, generally below 373 K, but the temperature of flue gas vent usually exceeds 423 K, which also makes zeolites and hydrotalcite are flaccid. Thus, it is crucial to develop new functional material to trap CO2 from flue gas at high temperature. .To meet the exigent requirement of capturing the CO2 in flue gas vent, new functional materials with the optimized structure and high activity as well as the convenient regeneration will be designed and fabricated in this investigation, in order to trap CO2 quickly but release CO2 at tolerable higher temperature, along with a high stability for recycle uses. Magnesia is chosen as the main component to fabricate the new efficient CO2 capturers through various particular methods: it will be in situ coated on the special mesoporous silica host that has the thin pore wall through the well-connected procedures, resulting in the new composite with plenty of the high dispersed and active MgO guest nano-particles. Alternatively, the guest MgO and/or CaO nano-particles will be wrapped/capsules in the silica hosts such as micro-capsules to capture and release CO2 target within the geometrically confined microenvironment, keeping the high dispersion of the guest in recycle use. Other strategy is to directly synthesize the porous or hollow micro-spheric magnesia through peculiar assembly procedures, elevating the accessibility of basic active sites and promoting the capture of CO2 through wrapping other active species such as CaO, which is the formidable challenge facing not only the capture of CO2 but also the fabrication of porous solid strong basic materials. .Apart from the studies in synthesis, the actual performance of new CO2-capturer will be assessed around 423 K with different gas flux along with various temperatures, and the influences of impurity in gas stream such as SO2, NOx and moisture are analyzed, in order to provide some candidates for controlling the CO2 pollution in the flue gas with a relatively high temperature. Besides, one aim of our research is to get patent in synthesis of new basic functional materials.

针对烟气排放温度下高效捕获CO2的需求，研制优化排布-分散高比例活性组分的固体碱新材料，使之既能快速接触CO2而发生反应进行捕获，又能降低逆反应所需高温、释放CO2而再生，还能具有结构稳定性以应对循环使用的需求。拟选择氧化镁为主要活性组分、控制它的分布和表面性质：减轻介孔硅分子筛等支撑体的自重并提高分散量，结合原位镀饰、微晶嵌插和外延生长等技术引入氧化镁并控制其分散状态；调控微胶囊型介孔硅的结构，分隔储存氧化镁以及氧化钙等组分以捕获烟气里的CO2。提出氧化镁可控成孔-包藏氧化钙等其它组分的固体强碱研制新思路，提升在较高温度下捕获CO2的效率。在不同流量、403-473 K温度区间研究CO2捕获剂的性能，考察模拟烟气里水蒸气、SOx和/或NOx对于捕获剂的总捕获-去除能力和实验室条件下循环使用的影响。为攻克排放烟气中CO2由于温度过高而难以被吸附去除的难题提供实验依据，形成独立知识产权。

在工业烟气排放温度下（中温，可达403-473 K）捕获CO2是环境保护的难题，因为这个温度区间下CO2在大多数固体碱上发生脱附而不是吸附，使用超强碱材料捕获CO2又存在着再生能耗问题。研制新材料中温捕获CO2是固体碱研究面临的挑战，不仅要求提高活性组分在复合捕获剂里的比重、减少主体/载体的比例，而且要求活性组分能够充分接触CO2以捕获之；活性组分的高比例和高分散度是提高捕获效率的关键所在。2013年1月至2016年12月，我们在国家自然科学基金的资助下，选定MgO为活性组分，通过两条技术路线进行了“捕获烟气中二氧化碳的多孔固体强碱新材料”研究。在研制主-客体类型吸附材料方面：共沉淀法制备介孔MgO-Al2O3促使35 wt%的氧化镁微晶插入氧化铝框架，水汽存在下其CO2吸附量在473 K可达131 mg g-1。将醋酸镁负载于椰壳活性炭后分解，促使氧化镁微晶相高度分散，423 K的CO2瞬时捕获量是MgO/SiO2的5倍；还提出了贴近烟气排放状态的CO2瞬时吸附新方法。研制新型碱性离子液并固载在多孔氧化铝上，首次实现离子液在393 K对于CO2的等摩尔吸附。在研制氧化镁自身造孔新材料方面：溶胶-凝胶法合成了单块泡沫状氧化镁，比表面达130 m2 g-1，473 K时吸附CO2可达78 mg g-1。提出了制备高比表面氧化镁材料的新概念：在醋酸镁碳化过程中原位形成的MgO-C混合粒子促成氧化镁微晶相高度分散，比表面可达336 m2 g-1（孔容0.34 cm3 g-1），并具有介孔结构；在473 K的CO2静态吸附里的吸附量可达44.8 mg g-1，超过文献报道的最高值。提出“同晶取代法”增加MgO表面缺陷和碱性的新理念：微波碳化法使得镁-锌离子发生同晶取代，提高MgO的强碱位比例达到79%，超过通常MgO约25倍。还构筑了Cu-MgO多功能固体碱，利用CuO被还原的体积收缩提升MgO活性位的暴露度，进一步提高中温CO2吸附量。.合同任务完成，4年内发表SCI论文15篇（其中包括J. Mater. Chem. A三篇， ACS Appl. Mater. Interf. 三篇，Chem. Euro. J.一篇，J. Hazard. Mater.一篇， Micropr. Mesopr. Mater. 三篇），学术专著两篇，培养研究生9名，毕业博士生4名和硕士生1名。