空气中直接捕集CO2技术研究进展

减少碳排放并推动碳中和是应对气候变化、促进经济社会绿色转型的重要途径之一,碳中和技术已成为工业界和学术界的关注焦点。目前碳捕集与封存主要对工业固定源排放的CO₂进行处置捕集,而对占CO₂总排放近50%的分布源CO₂关注度不高。直接空气捕集(direct air capture,DAC)技术不仅可对数以百万计的小型化石燃料燃烧装置以及数以亿计的交通工具等分布源排放的CO₂进行捕集处理,还可有效降低大气中CO₂浓度。介绍了DAC的发展历史、研究现状以及发展趋势,综述了已有DAC技术的工艺流程以及反应装置,对DAC现行工艺中涉及的空气捕捉模块、吸收剂或吸附剂再生模块、CO₂储存模块进行了叙述,对比了几种工艺的优缺点以及吸附剂类型和再生方式,指出DAC技术发展的关键在于研发高效低成本的吸收/吸附材料和设备。分析了DAC吸收/吸附材料的作用原理以及吸附效果,碱性溶液原料成本相对低廉,但再生过程中能耗较高。分子筛及金属有机框架吸附剂虽然再生能耗较低,但对空气中CO₂的吸附容量和吸附选择性表现一般。胺类吸附剂具有较好的吸附能力,由于其再生温度较低,可使用工业废热或少量热能为系统供能;使用胺类吸附剂时吸附和解吸在一个单元中逐步发生,具有更高的效率和操作时间,有望降低DAC系统成本。对比了DAC与其他碳捕集技术的成本并进行了技术经济性分析,DAC成本主要包含运营和维护成本(N_Q&M)、吸附剂材料成本(N_S)和工厂设备的净成本(N_bop);指出目前限制DAC工业化应用的主要因素之一在于吸收/吸附材料和相关工艺成本过高,随着阴离子交换树脂等新型吸附剂的出现和工艺的发展,DAC成本逐年下降。全面探究吸收/吸附材料稳定性、动力学、吸附容量、选择性、再生能量损失等综合性能,研发利于快速装载和卸载吸附剂的相关装置,开发成本低廉的工艺系统是目前DAC领域的发展方向和迫切需求。DAC技术将为减少全球碳排放、实现碳中和提供重要技术支撑。

Research progress on direct capture of CO2 from air

Reducing carbon emissions and promoting carbon neutralization is one of the critical ways to deal with climate change and en?courage the green transformation of economy and society.Carbon neutralization technology has become the focus of industry and academia.At present,carbon capture and storage technology(CCS)is mainly used to treat and capture CO₂ emitted from industrial fixed sources,while the distributed sources,accounting for nearly 50%of total CO₂emissions are not highly concerned.Direct air capture(DAC)technol?ogy can not only capture CO₂ emitted by millions of small-scale fossil fuel combustion devices and hundreds of millions of vehicles,but al?so effectively reduce the concentration of CO₂ in the atmosphere.The development history,research status,and development trend of DAC were introduced.The existing DAC technology process flow and reaction equipment were summarized.The air capture module,absorbent or adsorbent regeneration module and CO₂ storage module involved in DAC current process were described.The advantages and disadvantages of several processes,adsorbent types and regeneration methods were compared.It was pointed out that the key to the development of DAC technology lied in developing high-efficiency and low-cost absorption and adsorption materials and equipment.The functional principle and adsorption effect of DAC absorption/adsorption material was analyzed.The raw material cost of alkaline solution is relatively low,but the energy consumption is high in the regeneration process of alkaline solution.Although the regeneration energy consumption of molecular sieve and metal-organic framework adsorbent is low,the adsorption capacity and adsorption selectivity of CO₂ in air are average.However,amine adsorbents show good adsorption capacity,and industrial waste heat or a small amount of heat energy is used to supply energy for the system because of its low regeneration temperature.In addition,when amine adsorbents are used,adsorption and desorption gradually occur in one unit,which has higher efficiency and operation time,and is expected to reduce the cost of DAC system.The cost of DAC and oth?er carbon capture technologies are compared,and the technical and economic analysis is carried out.The cost of DAC mainly includes op?eration and maintenance costs(N_Q&M),adsorbent material costs(N_S)and net cost of factory equipment(N_bop).One of the main factors lim?iting the industrial application of DAC is the high cost of absorption/adsorption materials and related processes.With the emergence of new adsorbents such as anion exchange resin and the development of technology,the cost of DAC will decrease year by year.It is the current development directions and urgent needs of the DAC field:to comprehensively explore the comprehensive properties of absorption/adsorp?tion materials such as stability,kinetics,adsorption capacity,selectivity,regeneration energy loss,and develop related devices that facilitate rapid loading and unloading of adsorbents,and develop low-cost process systems.DAC technology will provide important technical support for reducing global carbon emissions and achieving carbon neutrality.