Research on urea linkages formation of amine functional adsorbents during CO₂ capture process

Amine functional adsorbents as a promising choice for practical CO₂ capture applications had attracted extensive interest, but the formation of urea linkages between amine functional adsorbents and CO₂ is extremely adverse to its development for practical application. Therefore, through learning the mechanism of urea linkages formation between amine functional adsorbents and CO₂ will be useful to promote its practical application. Temperature and moisture are two key factors influencing the formation of urea linkages between amine functional adsorbents and CO₂. In this study, we found that temperature obviously affected the kinetics of the formation of urea linkages, and three key temperature points were discerned; when the temperature reached 95, 115, and 121 ºC, the urea linkages formation rate obviously increased. Especially at 121 ºC, the formation rate would reach a very high extent that led to serious degradation of amine functional adsorbents, and badly damaged the cyclic adsorption stability of amine functional adsorbents. Temperature not only influenced the kinetics of the urea linkages formation, but also influenced the types of urea linkages, and the proportion of different types of urea linkages varied with changes in temperature. Moisture is another important factor that affected the formation of urea linkages; the presence of moisture could inhibit the dehydration of carbamic acid and carbamate and obviously alleviate the degradation of amine functional adsorbents, but moisture could not thoroughly eliminate the formation of urea linkages.