Defect-engineered metal-organic frameworks for carbon dioxide capture

自工业革命以来，人类开始通过提取和燃烧越来越多的化石燃料来严重干扰自然碳循环，导致大气中以前所未有的速度释放大量二氧化碳，导致气候变化。为了缓解气候变化的影响，最近制定的《巴黎协定》设定了到2100年将全球平均气温上升控制在2摄氏度以内的目标。这将需要将自1860年以来所有人为来源的累计二氧化碳排放量保持在8400亿吨以下。如果全球碳排放继续像过去十年那样增长，那么2摄氏度的碳预算将在2035年耗尽。这就要求寻找替代能源和可持续的过程来实现向低碳经济的过渡。二氧化碳捕获、储存和利用(CCSU)被认为是在化石燃料逐步淘汰的同时减少二氧化碳排放的关键技术之一。这项技术的大规模采用取决于其效率和经济可行性，要求不断开发能够将优异性能与长期稳定性和可负担性相结合的新材料。理想的二氧化碳捕集吸附剂(CC)应该具有较高的质量吸收能力，对二氧化碳的选择性高于其他气体，能够以较低的能量损失进行再生，并且在各种工作周期中都是稳定的。来自大型点源(如燃煤或燃气发电厂和工业设施)的CC是最具吸引力的选择。这些来源约占全球排放量的一半，它们产生的浓缩二氧化碳气流与直接空气二氧化碳捕集相比更容易处理。该项目旨在通过利用锆基金属有机骨架(Zr-MOF)中的缺陷使其具有广泛的氨基来开发用于CC的新型固体吸着剂。ZR-MOF是一类由六核氧化锆-氢氧化物簇合物和羧酸盐连接物连接而成的结晶性和高孔性材料。它们因其非凡的稳定性而吸引人，特别是在有水的情况下，这使它们适合于实际应用。与其他脱附剂相比，裸Zr-MOF对CO2的吸附能力中等。已经证明，使用带有待定氨基的有机连接物或通过将乙醇胺接枝到金属簇上来官能化Zr-MOF可以增加它们对二氧化碳的亲和力。然而，这些方法在范围上相当有限。Zr-MOF中的缺陷是活性中心，可以被利用来引入以其他方式不能插入到多孔结构中的官能团。用不同性质的氨基(脂肪族、芳香族、杂环族)对有缺陷的Zr-MOF进行官能化处理，可以考察和评估一大组参数对其CC性能的影响。由此产生的缺陷工程MOF将是一个新型、稳定和多功能的固体吸附剂库，具有可调的物理化学性质，用于CC。塔塔钢铁公司将作为工业合作伙伴参与该项目。这将为拟议的研究提供一个极好的案例研究，因为塔尔博特港的钢铁厂是英国最大的工业二氧化碳排放者，塔塔钢铁致力于解决这一问题。在该项目期间开发的材料将在与从高炉煤气中提取CC相关的条件下进行测试。这种气体主要由氮气(45%-50%)、一氧化碳(20%-25%)、二氧化碳(20%-25%)和氢气(05%)组成，由于热值低，通常是燃烧的。去除二氧化碳将使高炉中富含CO的气流循环，用于还原铁矿石，并将捕获的二氧化碳转化为有用的化学品。

Since the Industrial Revolution, mankind has started to heavily interfere with the natural carbon cycle by extracting and burning increasingly larger amounts of fossil fuels, which has led to release huge amounts of CO2 in the atmosphere at an unprecedented rate, causing climate change. In order to mitigate the effects of climate change, the recently established Paris Agreement sets the goal of limiting the rise in the average global temperature to 2 degrees by 2100. This will require keeping cumulative CO2 emissions from all anthropogenic sources since year 1860 to less than 840 gigatons of carbon. If global carbon emissions continue to grow as they have in the last decade, the 2 degrees carbon budget will be spent by year 2035. This dictates to look for alternative energy sources and sustainable processes to enable the transition to a low-carbon economy.CO2 capture, storage and utilisation (CCSU) is regarded as one of the key technologies to reduce CO2 emissions while fossil fuels are progressively phased out. Adoption of this technology on a large scale depends on its efficiency and economic viability, demanding the constant development of new materials able to combine excellent performances with long-term stability and affordability. The ideal sorbent for CO2 capture (CC) should have high mass uptake capacity, be selective towards CO2 over other gases, be able to be regenerated with a low energy penalty and be stable over various working cycles. CC from large point sources, such as coal- or gas-fired power plants and industrial facilities, is the most attractive option. These sources are responsible for about half of the global emissions and they generate concentrated CO2 streams that are easier to treat, if compared with direct air CO2 capture.This project aims at developing new solid sorbents for CC by exploiting defects in zirconium-based metal-organic frameworks (Zr-MOFs) to functionalise them with a wide range of amino groups. Zr-MOFs are a class of crystalline and highly porous materials constructed from the connection of hexanuclear zirconium oxide-hydroxide clusters and carboxylate linkers. They are attractive for their remarkable stability, especially in the presence of water, which makes them suitable for practical applications. The CO2 adsorption capacity of bare Zr-MOFs is moderate, if compared to that of other sorbents. Functionalisation of Zr-MOFs using organic linkers with pending amino groups or through grafting of ethanolamine to the metal clusters has been demonstrated to increase their affinity for CO2. However, these methods are rather limited in scope. Defects in Zr-MOFs are reactive sites and can be exploited to introduce functional groups that cannot be otherwise inserted in the porous structure. Functionalisation of defective Zr-MOFs with amino groups of different nature (aliphatic, aromatic, heterocyclic) will allow to investigate and evaluate the influence of a large set of parameters on their CC performances. The resulting defect-engineered MOFs will be a library of novel, stable and versatile solid sorbents with tuneable physical-chemical properties for application in CC.Tata Steel will be part of this project as an industrial partner. This will provide an excellent case study for the proposed research, because the steelworks in Port Talbot are the largest industrial CO2 emitter in the UK and Tata Steel is committed to address this issue. The materials developed during this project will be tested in conditions relevant to CC from blast furnace gas. This gas is mainly composed of N2 (45-50%), CO (20-25%), CO2 (20-25%) and H2 (0-5%) and is normally flared, due to its low calorific value. Removal of CO2 would allow to recycle the CO-rich stream in the blast furnace for reduction of iron ore and to convert the captured CO2 into useful chemicals.