Progress on CO2-induced inactivation of solid amine adsorbents 固态胺吸附剂的CO2诱导性失活难题研究进展

Climate warming caused by massive CO emission is a global problem facing mankind. The carbon capture and storage (CCS) technology can substantially reduce CO emissions from heavy industries, such as power, steel, cement and chemical industries. By eliminating billions of tonnes of CO from fossil fuels, CCS can help limit the increase in global temperatures to under 2°C by the end of the century. The CCS technology has rapidly developed to include several technologies, such as liquid ammonia absorption, physical adsorption, membrane separation and solid amine adsorption. Solid amine adsorption, in particular, can be used to capture CO from flue gas and air, and separate it from biogas or syngas because of its various advantages, such as high CO selectivity, low energy consumption during regeneration, the ability to process large amounts of CO, and the non-corrosive equipment used. By designing the pore structure of the support material, a solid amine adsorbent can adsorb more than 5 mmol/g of CO at a time. However, to understand its commercial potential, the adsorbent should be stable over hundreds of adsorption-desorption cycles to ensure a longer lifetime and lower CO capture cost. The cyclic stability of adsorbents is seriously hindered by CO-induced inactivation, which occurs during their regeneration. To obtain highly pure CO, adsorbents are regenerated under a CO atmosphere instead of an inert atmosphere, but the urea groups formed when CO reacts with amine molecules are too stable to release CO, hampering the reusability of the adsorbent. In this paper, we focus on the challenges posed by CO-induced inactivation of solid amine adsorbents as well as discuss the inactivation process, its critical factor and its mechanism. We also analyse the current preventive strategies employed to tackle this problem. CO-induced inactivation widely occurs in different types of solid amine adsorbents, with an inactivation rate of more than 70% in 10 cycles. The regeneration temperature is a critical factor in this process. When the regeneration temperature exceeds 120°C, the solid amine adsorbents form several urea groups, resulting in prolific CO-induced inactivation. Mechanistically, the carbamic acid intermediate formed when a primary amine reacts with CO gets easily dehydrated to generate isocyanate, which can subsequently form urea group by combining with another primary or secondary amine. The dehydration of carbamic acid to form isocyanate, thus, plays a key role in the formation of urea groups. The formation of urea can be effectively inhibited by decreasing the amount of primary amines in the adsorbent, reducing the regeneration temperature, and increasing the water vapour content in the regeneration atmosphere. Accordingly, three strategies to inhibit urea formation were proposed: Organic amine modification (primary amines conversion into secondary amines), water vapour repression (inhibition of dehydration) and the use of support materials cross-linking organic amines (change the primary amine properties). Nevertheless, the challenges associated with CO-induced inactivation, including high regeneration temperatures and the non-compatibility of CO adsorption capacity with cyclic stability, still plague solid amine adsorbents. Finally, potential solutions that can facilitate the industrial application of this process have been discussed.