Urea for CO2 Capture: a Theoretical Investigation

Climate change and global warming are two of the biggest issues facing
modern science. The atmospheric carbon dioxide concentration has increased
rapidly since the industrial revolution, and finding novel technologies to support
carbon capture, storage and utilisation (CCSU) is vital in reducing the risk
of catastrophic climate change. Urea is a low-cost, bio-based material that is
produced in large quantities every year. It has been hypothesised that urea
shows the pre-requisite chemical functionality to perform as an adsorbent for
carbon capture. This study examines the adsorption of CO2 on the most common
surfaces observed in phase I, phase III and phase IV of urea. Density functional
theory was used to relax the crystalline geometries, and results showed that
ambient phase urea is the most stable crystal morphology. Furthermore, grand
canonical Monte Carlo was used to simulate both single component CO2 and
mixed component CO2/N2 adsorption isotherms. Results indicate that the (001)
surface of phase I urea has the highest overall selectivity and adsorption capacity
towards CO2. At 298 K and 1 bar, the (001), (100) and (010) surfaces showed
excess adsorption capacities of 0.250, 0.061, and 0.184 mmol/g respectively. The
results showed that crystalline urea shows relatively poor performance when
compared to other physical adsorbents such as activated carbons and zeolites.