Monoethanolamine-Modified Attapulgite-Based Amorphous Silica for the Selective Adsorption of CO2 from Simulated Biogas

Biogas upgrading technology is important for increasing the heating value of biogas through selective adsorption of CO2. In this work, a series of new monoethanolamine (MEA)-modified attapulgite (ATP)-based amorphous silica (a-SiO2) sorbents with a large surface area and oxygen vacancies were prepared by the impregnation method for the selective adsorption of CO2 from simulated biogas. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and N2 adsorption–desorption results indicated that MEA with suitable loading was anchored onto the external surface of a-SiO2, which could improve the dispersion of rodlike fibers of ATP. MEA loading and reaction temperature optimization experiments showed that the 50MEA/a-SiO2 sorbent achieved the highest CO2 adsorption capacity of 2.14 mmol/g with an amine efficiency of 5.22 mmol/g and 0.32 mol/mol at 60 °C. Furthermore, only a 6.3 and 4.7% reduction of CO2 adsorption capacity occurred after five adsorption–desorption cycles under simulated biogas at 30 and 60 °C adsorption, respectively, indicating that the sorbent has good regenerability and thermal stability. The chemical adsorption was proved to be the CO2 adsorption mechanism of MEA-modified ATP-based a-SiO2 sorbent by XRD and FTIR testing.