Effects of water vapour on CO2 capture with vacuum swing adsorption using activated carbon

• CO2 capture on activated carbon from wet flue gas streams.
• Fundamental isotherms and kinetic data obtained.
• Vacuum swing adsorption cycling conducted to determine effect on CO2 capture.

The capture of CO2 with adsorption processes is greatly complicated by the presence of high water levels in most process and flue gas streams. One option is to use activated carbon of appropriate hydrophobicity. The interaction of water and CO2 on carbon materials in VSA processes is therefore of great interest and it is this feature which the current study addresses.The adsorption equilibrium isotherms of H2O, CO2 and N2 on activated carbon (coconut shell Acticarb GC1200) were measured over the range 25–60 °C and 0–1 bar. The Type V isotherm exhibited by water required a non-Langmuir type representation. In this case, Rutherford’s extended CMMS model was employed to describe water adsorption. Breakthrough experiments as well as one bed vacuum swing adsorption studies were undertaken to investigate the impact of water on CO2 adsorption and its eventual impact on a separation process. Simulations were also conducted to help interpret the data. Our analysis showed that there was little effect of CO2 and water on each other’s adsorption on the carbon material beyond the dilution effect on partial pressure of each component. The single bed vacuum swing experiment showed almost identical recovery and purity of CO2 in the presence of water as in the dry case. However, the presence of water required additional pumping energy and led to an increase in CO2 capture energy of about 35%. There is a need to improve carbon materials to further exclude water without substantially decreasing CO2 capacity and selectivity.