Fast Adsorption Kinetics of CO2 on Solid Amine Sorbent Measured Using Microfluidized Bed Thermogravimetric Analysis

CO2 adsorption kinetics on a solid amine sorbent are important for material development, reactor design, and process optimization. Most published adsorption kinetics of a solid amine sorbent have been measured using thermogravimetric analysis experiments (TGA) or adsorption columns, which can include additional diffusion limitations and tend to underestimate the adsorption uptake rates. In this study, the CO2 adsorption kinetics on a solid amine sorbent are measured by a novel microfluidized bed thermogravimetric analysis (MFB-TGA) method, which can achieve real-time weight measurement of a solid amine sorbent in a fluidizing state with similar mass and heat transfer characteristics in a fluidized bed reactor. The experimental data from MFB-TGA is analyzed with a reactor model, and the effects of the gas exchange between the bubble phase with the emulsion phase and the gas diffusion around solid amine sorbent particles on the adsorption uptake rate are evaluated. The apparent adsorption kinetics are described by a two-stage model of the linear driving force model (LDF). The effects of the particle size, temperature, and CO2 concentration on the apparent adsorption kinetics of a solid amine sorbent in the MFB-TGA are investigated and compared with that measured by regular TGA. It is observed that the adsorption of CO2 on a solid amine sorbent in the initial stage is fast, and after the initial fast stage, a second slower stage takes place, resulting in slower adsorption rates. CO2 adsorption on a solid amine sorbent in the initial stage is very fast, and the adsorption rate can approach 0.2 mmol/g/s. Additionally, the adsorption rate constants do not change with temperature or CO2 concentration, and the adsorption process is first order on CO2 concentration. This developed MFB-TGA provides a new method for measuring fast adsorption kinetics occurring inside a fluidized bed reactor.