Adsorption (2008) 14: 415–422 DOI 10.1007/s10450-007-9100-y Capture of CO 2 from high humidity flue gas by vacuum swing adsorption with zeolite 13X Gang Li · Penny Xiao · Paul Webley · Jun Zhang · Ranjeet Singh · Marc Marshall Received: 30 April 2007 / Revised: 29 September 2007 / Accepted: 27 December 2007 / Published online: 16 January 2008 © Springer Science+Business Media, LLC 2008 Abstract Capture of CO 2 from flue gas streams using ad- sorption processes must deal with the prospect of high hu- midity streams containing bulk CO 2 as well as other impu- rities such as SO x , NO x , etc. Most studies to date have ig- nored this aspect of CO 2 capture. In this study, we have ex- perimentally examined the capture of CO 2 from a 12% syn- thetic flue gas stream at a relative humidity of 95% at 30 °C. A 13X adsorbent was used and the migration of the water and its subsequent impact on capture performance was eval- uated. Binary breakthrough of CO 2 /water vapor was per- formed and indicated a significant effect of water on CO 2 adsorption capacity, as expected. Cyclic experiments indi- cate that the water zone migrates a quarter of the way into the column and stabilizes its position so that CO 2 capture is still possible although decreased. The formation of a wa- ter zone creates a “cold spot” which has implications for the system performance. The recovery of CO 2 dropped from 78.5% to 60% when moving from dry to wet flue gas while the productivity dropped by 22%. Although the concentra- tion of water leaving the bed under vacuum was 27%(vol), the low vacuum pressure prevented condensation of water in this stream. However, the vacuum pump acted as a con- denser and separator to remove bulk water. An important consequence of the presence of a water zone was to ele- vate the vacuum level thereby reducing CO 2 working ca- pacity. Thus although there is a detrimental effect of water G. Li · P. Xiao · P. Webley ( ) · J. Zhang · R. Singh Cooperative Research Centre for Greenhouse Gas Technologies, Department of Chemical Engineering, Monash University, Wellington Road, Clayton, Victoria 3800, Australia e-mail: paul.webley@eng.monash.edu.au M. Marshall School of Chemistry, Monash University, Wellington Road, Clayton, Victoria 3800, Australia on CO 2 capture, long term recovery of CO 2 is still possible in a single VSA process. Pre-drying of the flue gas steam is not required. However, careful consideration of the impact of water and accommodation thereof must be made partic- ularly when the feed stream temperature increases resulting in higher feed water concentration. Keywords CO 2 capture · Pressure swing adsorption · Humid flue gas Abbreviations L Length of bed (mm) P Pressure (kPa) T Temperature (°C) Z Dimensionless distance u Interstitial velocity (mm/s) t Time (s) z Axial distance along adsorption bed (mm) τ Dimensionless time 1 Introduction Carbon dioxide is the most significant greenhouse gas emit- ted from human activities and contributes to global warm- ing. As a result there has been wide spread efforts to mit- igate and control these emissions. One practical method to reduce carbon dioxide emissions is geo-sequestration which involves capturing carbon dioxide from flue gases and in- jecting it directly into underground geological formations. VSA (vacuum swing adsorption) is a promising technology for the capture of CO 2 from flue gas streams since it has a number of advantages such as relatively low power con- sumption and ease of operation.