Low-cost DETA impregnation of acid-activated sepiolite for CO2 capture

In this paper, a low-cost sepiolite-based adsorbent for CO2 capture was obtained by impregnating DETA into the acid-modified sepiolite. Thermogravimetric analysis, nitrogen adsorption-desorption isotherm, Fourier transform infrared spectroscopy and X-ray diffraction were used for the characterization of the sepiolite supports before and after DETA impregnation. Thermogravimetric analysis was also employed to evaluate the CO2 adsorption performances of the adsorbents. The characterization methods revealed that DETA impregnated into the acid-modified sepiolite effectively. The CO2 adsorption experimental results indicated that acid-activation and amine-loading simultaneously improved the CO2 adsorption capacities of sorbents. For amine-loaded acid-modified sepiolite, low dosage of impregnated amine decreased the CO2 adsorption capacities of sorbents at 35 °C due to the restrictions imposed in the transport and reaction of CO2 due to pore blockage by amines. The highest CO2 adsorption performance attained 1.65 mmol/g with the acid-modified sepiolite with 0.8 g-DETA loading. 95.2% of the adsorption capacity of 0.8-DETA/SH-18 maintains after 4 adsorption-desorption cycles, and the sorbent can be almost fully recovered at 75 °C, pure N2. The kinetic studies showed that for low amine loadings the CO2 adsorption is controlled by micropore blocking. For higher loadings a more complex diffusion and reaction process leads to a two-step adsorption kinetics. By contrast, it can be found that Avrami model is in good accordance with the adsorption kinetics of CO2 on amine-functionalized sepiolite. A cost evaluation indicated that DETA-impregnated sepiolites are cheap adsorbents for CO2 capture.