Preparation Of Aluminum-Based Solid Amine CO₂ Adsorbent Derived From Coal Fly Ash And Its Application In Biogas Purification

Biogas purification to produce bio-natural gas is of strategic significance for relieving Chinese energy pressure and achieving carbon neutrality goals.Compared with traditional biogas purification technologies,solid amine adsorbents have potential advantages in terms of CO2 separation efficiency,energy consumption,equipment requirements and environmental impact.However,the disadvantages such as incompatibility between adsorption performance and cyclic stability,mutual constraints between adsorbent performance and preparation cost,and lack of scalable production capacity,limit the application of solid amine adsorbents in the field of biogas purification.From the perspective of preparing high-performance solid amine adsorbents with the advantages of CO2 adsorption capacity,cyclic stability,preparation cost and bulk production,this paper innovatively proposed that highaluminum coal fly ash was used as raw material to recover aluminum and prepare coal fly ash derived aluminum-based solid amine adsorbent.The effects of nanoAl2O3 support’s pore structure and surface chemical properties on the adsorbent’s adsorption performance and cyclic stability were systematically explored.And the relative performance of the adsorbent in the actual biogas composition was further investigated.Thus,this strategy provides a theoretical basis for the application of solid amine adsorbent in biogas purification project.The main conclusions of this paper were as follows:Considering the lack of scalable production capacity and poor cyclic stability of solid amine adsorbent,the preparation technology of aluminum-based solid amine adsorbent derived from coal fly ash was innovatively proposed.The effect rules and mechanisms of key synthesis parameters on the pore structure of coal fly ash derived nano-Al2O3 were systematically investigated,and the role of nano-Al2O3 support pore structure in preparing adsorbent via impregnating PEI was elaborated.The prepared aluminum-based solid amine adsorbent showed a CO2 adsorption capacity of 136 mg·g-1.More importantly,there were abundant Lewis acid sites on the surface of nano-Al2O3,resulting in a spontaneous cross-linking process between nano-Al2O3 support and the organic amine(PEI)in aluminum-based solid amine adsorbent.This cross-linking could effectively inhibit the formation of urea compounds,thereby improving the cyclic stability of the aluminum-based solid amine adsorbent.Under CO2 regeneration atmosphere,the adsorbent still showed a CO2 uptake of 112 mg·g1 after 50 cycles,with a mere 16.5%decay,significantly increased by 5.5-fold than that of traditional silicon-based solid amine adsorbent.Considering the limit of CO2 adsorption capacity for aluminum-based solid amine adsorbent due to small pore volume of nano-Al2O3 support,azeotropic distillation and alcohol washing were used to expand the pore volume of nano-Al2O3.The pore-expanded nano-Al2O3 was used as support to prepare the pore-expanded aluminum-based solid amine adsorbent.The prepared adsorbent exhibited excellent CO2 adsorption performance,with a saturated adsorption capacity of more than 195 mg·g-1,exceeding the excellent solid amine adsorbent standard of 176 mg·g-1.The adsorbent also had an ability to rapidly adsorb CO2,reaching a CO2 uptake of 180 mg·g-1 within 10 min.What’s more,the adsorbent still showed superior anti-urea cyclic stability,with only 6.2%decay post 10 cycles.The influence and mechanism of impurity components(H2O,O2 and H2S)in biogas on aluminum-based solid amine adsorbent were further investigated,and the feasibility study of the adsorbent application in biogas purification project was also evaluated.Although H2O didn’t promote CO2 adsorption under the optimal operating condition of aluminum-based solid amine adsorbent,it could prevent the dehydration process of carbamate or carbamate,and thus effectively inhibited the formation of urea compounds during the regeneration process,as well as improved the cyclic stability for the adsorbent.Furthermore,H2O could provide a partial concentration gradient driving force to promote the regeneration of the adsorbent.Under the optimal operating condition,the adsorbent showed excellent cyclic stability in the CO2 regeneration atmosphere,with only 6.3%decay post 50 cycles.Both O2 and H2S have little interference on the CO2 adsorption performance and cyclic stability of the adsorbent under the optimal operating condition.Finally,in the simulated biogas purification process,the aluminum-based solid amine adsorbent exhibited excellent adsorption performance,with an initial breakthrough CO2 uptake of 159 mg·g-1.Simultaneously,a bio-natural gas product with CH4 purity over 95%could be obtained in the purification process,meeting the needs of multiple areas.