Premodified Sepiolite Functionalized with Triethylenetetramine as an Effective and Inexpensive Adsorbent for CO2 Capture

In this work, industrial grade sepiolite (IG-SEP) was premodified with hydrochloric acid, and then premodified sepiolite (SEP) was impregnated with triethylenetetramine (TETA) to create a novel TETA functionalized SEP adsorbent. The effects of TETA loading and adsorption temperature on CO2 adsorption capacity, as well as the CO2 adsorption isotherm and cyclic regenerability were investigated. Results show that, when SEP was optimized at 30 wt % TETA (SEP-TETA-30%), the adsorbent attained a CO2 adsorption capacity as high as 1.93 mmol/g at 50 °C with fast adsorption kinetics and good regenerability. The Freundlich model was best able to fit the experimental adsorption isotherm, and the isosteric heat of adsorption at high CO2 coverage was 28 kJ/mol. The presence of moisture in simulated gas has a positive effect on the adsorption capacity, with less harm to adsorption stability. The adsorbent samples were further characterized by N2 adsorption/desorption, scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The increased surface area and pore volume of the SEP allow for effective immobilization of TETA within its channels. A kinetic study demonstrated that the experimental adsorption data for SEP-TETA-30% were well fitted by the pseudo-second-order model. More importantly, an index of cost efficiency was proposed to evaluate the practicability and competitiveness of amine-impregnated adsorbents. The cost efficiency of SEP-TETA-30% adsorbent was estimated as 0.19 mol CO2/$, which was higher than reported adsorbents, suggesting that the TETA functionalized SEP (SEP-TETA-30%) composite is a promising adsorbent for cyclic postcombustion CO2 capture processes.