Resorcinol–formaldehyde carbon xerogel as selective adsorbent of carbon dioxide present on biogas

A carbon xerogel obtained by carbonization of a resorcinol–formaldehyde polymer which was synthesized using Cs₂CO₃ as catalyst was employed as CO₂ selective adsorbent for biogas upgrading. The material presented a large narrow micropore volume (W₀(CO₂) = 0.34 cm³ g⁻¹) and macropore volume; as expected for a carbon xerogel, these macropores are very regular in size. The CO₂ preferential adsorption onto this material was tested by analysing adsorption equilibrium isotherms of both gases (CO₂ and CH₄) and breakthrough curves at different inlet concentrations. Equilibrium studies showed a large CO₂ uptake (q_sat = 6.57 mol kg⁻¹ and ΔH_ads = − 28.4 kJ mol⁻¹) compared to the CH₄ one (q_sat = 3.83 mol kg⁻¹ and ΔH_ads = − 19.6 kJ mol⁻¹) revealing a high CO₂ to CH₄ selectivity, especially at low pressures. Dynamic adsorption of both gases at different concentrations demonstrated the excellent performance of the prepared xerogel in biogas upgrading by selective adsorption of CO₂. The adsorbent was tested in binary dynamic adsorption to estimate its performance when both gases are present; the carbon xerogel was able to completely separate them.