CO2 Adsorption Behavior of 3-Aminopropyltrimethoxysilane-Functionalized Attapulgite with the Grafting Modification Method

In this study, attapulgite (AT) was treated by high-temperature roasting and hydrochloric acid to form HcAT. It was then modified with 3-aminopropyltrimethoxysilane (APS) through the grafting method to synthesize a new adsorbent, which exhibits relatively low regenerative energy consumption in CO2 adsorption and desorption processes. Scanning electron microscopy (SEM), N2 adsorption–desorption, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis were selected to support the research. The CO2 adsorption process on the adsorbent was studied at different APS loadings and different temperatures. The maximal amount of CO2 adsorbed on the adsorbent is 1.81 mmol/g at 313 K when the APS mass fraction is 30%. The Freundlich isotherm model shows a great correlation with the CO2 adsorption isotherm obtained from the experimental data, and R2 reached up to 0.996. The isosteric heat while CO2 adsorbed on 30%APS-HcAT is calculated as 62.63 kJ/mol. The regeneration cyclic stability of 30%APS-HcAT is excellent, while the CO2 adsorption capacity only decreased by 3.2% after 10 cycles. The energy consumption in the CO2 desorption process was also calculated as 26.875 kJ/mol. Three different kinetic models were selected to fit the experimental data, and two models showed a great fit, which were the pseudo-second and Avrami's fractional order models. The activation energy of 30%APS-HcAT was 38.826 kJ/mol, which can be calculated from the experimental data, and this value is higher compared with those of the other sorbents modified by the impregnation method and also much lower than the value of the chemical absorption process between traditional amine solvents and CO2.