Experimental investigation of CO2 adsorption using adsorbents derived from residual char of agricultural waste gasification

This study proposed a novel approach, suggesting a cascading utilization of agricultural residues for both energy generation and the production of CO2 adsorbents through gasification. Gasification was carried out employing a 20 kWe commercial gasification system with macadamia nut shell, bagasse, and rice straw. Subsequently, postgasification residues were meticulously collected, analyzed and utilized for CO2 adsorption experiments. Among these residual chars, macadamia nut shell demonstrated the highest CO2 adsorption capacity, followed by bagasse, while rice straw showed moderate performance. In laboratory conditions (25 degrees C, 1 bar, without the influence of ambient moisture or CO2 diffusion constraint), the post-gasification residue from macadamia nut shell achieved a CO2 adsorption capacity of 2.8 mmol g-1, followed by bagasse (2.4 mmol g-1). Transitioning to more practical conditions (25 degrees C, 1 bar, considering the influence of ambient moisture and CO2 diffusion limitations within an adsorbent bed), the macadamia nut shell and bagasse residual chars reached 2.7 mmol g-1 and 2.3 mmol g-1, respectively. Moreover, these chars exhibited noteworthy CO2/N2 selectivity and recyclability, making them comparable to various advanced CO2 adsorbents investigated in prior studies. The superior performance of the macadamia nut shell-derived residual char can be attributed to its highest microporous/ultramicroporous volumes and concentrations of basic and aromatic functional groups on the char's surface. The results of this study open up the potential for different strategies in combining the production of energy and affordable and upscalable CO2 adsorbents for industrial applications.