Highly efficient and stable PEI@Al2O3 adsorbents derived from coal fly ash for biogas upgrading

Cyclic CO2 adsorption via amine-functional adsorbents is widely accepted as an efficient route for biogas upgrading and CO2 mitigation. However, the fast deactivation and insufficient CO2 uptake are the major drawbacks of this technology. Herein, we developed a green and facile approach, including the recycling of porous nano-Al2O3 support from coal fly ash (CFA) and the impregnation of PEI onto the nano-Al2O3 support with large pore volume, to enhance both the CO2 adsorption capacity and the cyclic stability of amine-functional adsorbents. The as-synthesized 50%PEI@Al2O3 adsorbent possessed a CO2 adsorption capacity of 136 mg galsorbem and showed superior cyclic stability with merely a negligible decay of <0.3% after 10 cycles. Even under the realistic regeneration conditions (at 165 degrees C in pure CO2), it still maintained extremely stable adsorption capacity with a final CO2 uptake of 111 mg gasorbent, markedly increased by 5.5-fold than that of traditional 40%PEI@SiO2 adsorbent. It was concluded that the nano-Al2O3 support was benefical for the resistance of urea linkages formation during the regeneration stage, which would inactivate the functional amidogen. This strategy significantly enhanced the cyclic CO2 uptakes of amine-functional adsorbents through the recycling of CFA-derived nano-Al2O3 support, and is thus a green technology for practical biogas upgrading via CO2 adsorption.