Amine-functionalized nano-Al₂O₃ adsorbent for CO₂ separation from biogas: Efficient CO₂ uptake and high anti-urea stability

Amine-functionalized adsorbents have become a hot topic in research on CO2 separation from biogas. However, developing superior adsorbents with high adsorption capacity and stable cyclic stability under a CO2 regeneration atmosphere remains difficult. In this study, azeotropic distillation, a green, recyclable method, was used to expand the pores of the nano-Al2O3 support. The pore volume of pore-expanded nano-Al2O3 reached 1.62 cm(3) g(-1), and the derived amine-functionalized nano-Al2O3 adsorbent ('60%PEI@AD-Al2O3') possessed a superior CO2 uptake of 199.4 mg.g(-1) adsorbent with rapid adsorption kinetics. '60%PEI@AD-Al2O3' showed favourable cyclic stability under CO2 regeneration atmosphere with a final CO2 uptake of 133.8 mg.g(-1) adsorbent after 50 cycles, which possessed a competitive CO2 uptake compared with the reported amine-functionalized adsorbents with anti-urea stability. This superior performance is attributed to the large pore volume of the pore-expanded nano-Al2O3 support and the anti-urea stability for '60%PEI@AD-Al2O3', which does not require active amine modification and avoids diluting the active amine content. Furthermore, the effect of water vapour in biogas on adsorption performance was studied. Water vapour could significantly promote CO2 adsorption at low temperatures (<90 degrees C), and it was accompanied by strong water vapour adsorption, which would potentially increase the regeneration energy consumption. Additionally, water vapour could effectively inhibit the formation of urea compounds, further improving the cyclic stability. Because of the facile, scalable preparation method, the synthesised amine-functionalized nano-Al2O3 adsorbent has broad application prospects for CO2 separation.