A theoretical analysis of the capture of greenhouse gases by single water droplet at atmospheric and elevated pressures

Gas absorption by droplets is an important route to reduce greenhouse gas emissions, especially for carbon dioxide. To recognize the fundamental absorption processes of greenhouse gases by single droplets, the mass transport phenomena of greenhouse gas uptake by a quiescent water droplet at atmospheric and elevated pressures are analyzed theoretically and four common greenhouse gases of CO₂, N₂O, CH₄ and O₃ are taken into consideration. On account of piecewise function encountered at the droplet surface, it is impossible to obtain a fully analytical solution for describing the mass transfer process. Instead, a semi-analytical method is developed to predict the mass diffusion between the gas phase and the liquid phase. The obtained results indicate that, by virtue of the four greenhouse gases characterized by low mass diffusion number, the entire mass transfer is controlled by the liquid phase. A unified formula has been successfully established to aid in estimating the dimensionless solute uptake process and the dimensionless aqueous diffusion time of 0.45 is sufficiently long the implement the absorption process. For the ambient temperature and pressure in the ranges of 280–350 K and 1–20 atm, respectively, it is found that increasing the two parameters will intensify the solute absorption amount significantly and the absorption process can be accelerated by increasing temperature.