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

Abstract

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 (qsat = 6.57 mol kg−1 and ΔHads = − 28.4 kJ mol−1) compared to the CH4 one (qsat = 3.83 mol kg−1 and ΔHads = − 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.