Shape-tailorable amine grafted silica aerogel microsphere for CO₂ capture

The purpose of this study was to prepare a proof-of-concept CO₂ adsorbing material based on a new amine grafted silica aerogel microsphere (AGSAM) that could be used on both fixed and fluidized beds. A low-cost water glass and environment-friendly water were used as precursor and solvent of the silica aerogel, respectively. The silica aerogel microsphere (SAM) was prepared by dropping the siliceous solution into hot oil bath. The effect of the pH value of the siliceous solution, stirring speed and stirring paddle position on the sphericity and size of the SAM was investigated. The SAM with good sphericity was obtained when the pH value was 5.69–5.79. The mean diameter of the SAM decreased from 5 to 1 mm when the stirring speed increased from 1000 to 2000 rpm. The SAM with excellent sphericity was prepared when the paddle was placed on the top of the oil bath. When the paddle was placed at the middle and bottom of the oil bath, some liquid drops aggregated together and formed large aggregations. AGSAM was obtained by grafting the amine groups onto the framework of the silica gel microsphere. The CO₂ adsorption capacity of the AGSAM was 1.04 mmol g^-1 with 1% CO₂ at 300 mL min^-1. The AGSAM with 4, 3.2, 2 and 1 mm in diameters had the fluidizing velocities of 0.531, 0.425, 0.265 and 0.159 m s^-1, respectively. The AGSAM with different sizes met different fluidizing conditions.