The application of response surface methodology to optimize the amination of activated carbon for the preparation of carbon dioxide adsorbents

In this comparative study, the application of response surface methodology (RSM) in predicting and optimizing the amination conditions of activated carbon adsorbent toward CO ₂ adsorption was investigated. The adsorbents were prepared based on the central composite design (CCD) with three independent variables (i.e., amination temperature, amination time, and the use of pre-heat treated (HTA) or pre-oxidized (OXA) sorbent as the starting material), and the responses studied were CO ₂ adsorption and desorption capacity. Two quadratic models were developed to calculate the optimum amination conditions of activated carbon that provide a compromise between the studied responses (dependent variables). From the analysis of variance (ANOVA), the temperature of ammonia treatment was found to be the most important factor; it had a positive influence on CO ₂ adsorption capacity but a negative effect on desorption capacity. The optimal point indicated by numerical optimization corresponded to an OXA sorbent that had been aminated at 425°C for 2.1 h. The activated carbon modified at optimum conditions had a CO ₂ adsorption capacity of 26.47 mg/g and a CO ₂ desorption capacity of 95.4%. The experimental values of the responses were in good agreement with the amounts predicted by the regression models, indicating that the developed models could adequately predict the responses from the amination variables. The stable adsorption/desorption performance of the optimal activated carbon adsorbent during cyclical operations showed its potential for practical applications.