Adsorption separation of low concentrations of CO₂ and NO₂ by synthetic zeolites

The CO₂ equilibrium adsorption and breakthrough activity of CO₂-NO₂ mixtures on A- and faujasite-type zeolites and Na- and proton-type (HM) mordenites were studied to determine the appropriate zeolite for separation of low-concentration mixtures of CO₂ and NO₂. Adsorption of CO₂ correlated with the polarity of the zeolites as a result of dominant adsorption via interaction of the quadrupole moment and polar surface sites. Competitive adsorption of NO₂ and CO₂ gives nearly zero breakthrough times for CO₂ on 5A- and faujasite-type zeolites and HM. Adsorption separation of CO₂ and NO₂ by zeolites depends on the NO₂ adsorptivity, which is determined not only by surface polar sites but also by pore geometry and dimension. 13X had the greatest NO₂ adsorptivity, but the thermal instability in NO₂ adsorptive sites is the main obstacle for its use as a substrate for the separation of CO₂ and NO₂. Sufficient protonation of NaM leads to zero CO₂ adsorption and still keeps a great NO₂ adsorption. Because of the thermal stability and low NO₂ desorption temperature, HM is the most promising adsorbent for separation of CO₂ and NO₂ using the thermal-swing adsorption method.