Activated carbon-based CO2 uptake evaluation at different temperatures: The correlation analysis and coupling effects of the preparation conditions. Issue 40 (September 2020) - Yu, Peng
Graphical abstract: Highlights: CO2 uptake evaluation was conducted based on Response Surface Methodology. The activation temperature determined the yield of pitch-based activated carbon. The analysis of variance quantified coupling effects of the preparation conditions. The key factors to determine CO2 uptake vary with the adsorption temperature. It's inappropriate to predict CO2 uptake at 75 °C using CO2 uptake data at 25 °C. Abstract: As potential CO2 adsorbents, carbon materials have recently gained attention because of their low energy penalty, abundant sources and good stability. In this study, the response surface methodology (RSM) was used to guide the pitch-based activated carbon preparation and CO2 adsorption at different temperatures. Based on this experimental design, the correlations of CO2 uptakes at different temperatures, as well as the coupling effects of the preparation conditions on CO2 uptake, were analyzed by mathematical modelling. The obtained optimal carbon sample AC650-1.25-2.5 showed a high atmospheric CO2 uptake of 3.15(±0.14), 2.05(±0.02), and 1.37(±0.11) mmol/g at 25 °C, 50 °C, and 75 °C, respectively. Furthermore, the analysis of variance confirmed that the key factor to determine CO2 uptake at 25 °C was the activator ratio, contributing to 77.8 % of the total variance; however, it gradually shifted to the activation temperature and its coupling effect with other factors for CO2 uptake at 75 °C. The linear regression and significance test of CO2 uptakes showed that using CO2 uptake at 25 °C to predict the uptake at 50 °C was feasible; however, it failed to work when predicting the CO2 uptake at 75 °C. The good linear relationship of CO2 uptakes at similar adsorption temperatures benefited from the existence of sharable effective pore width. It was also concluded that the strict requirement for extremely narrow ultra-micropores led to the non-coincidence of suitable preparation conditions, corresponding to a good CO2 uptake at different adsorption temperatures; this further led to the bad predictability when the adsorption temperature varied greatly.