Enhanced CO2 capture by binary systems of pyridinium-based ionic liquids and porous ZIF-8 particles

Absorption and adsorption technology as widely used methods have been reported for carbon dioxide (CO2) separation. In order to combine the advantages of absorption and adsorption methods, ionic liquids (ILs) as absorption function and zeolitic imidazolate framework-8 (ZIF-8) as adsorption function were integrated into a slurry to efficiently capture CO2 by the absorption-adsorption method. In this study, two pyridinium-based ILs, [C4Py][NTf2] and [C4Py][N(CN)2] were synthesized, and mixed with different concentration of ZIF-8 to form hybrid slurries. CO2 solubility in the different hybrid slurries at temperatures from 303.15 to 333.15 K was measured. The results indicated that CO2 solubility increases significantly with increasing pressure and decreases with increasing temperature. Moreover, CO2 solubility increases with the increase of ZIF-8 content, indicating that the addition of ZIF-8 into ILs can obviously enhance CO2 solubility. CO2 solubility in the ZIF-8/[C4Py][NTf2] slurry increases by 24% compared with the corresponding pure IL at 303.15 K and 1.80 MPa. The absorption-adsorption mechanism was studied using FT-IR and NMR spectroscopy. It was demonstrated that CO2 absorption and adsorption in the ZIF-8/ILs hybrid slurries is a physical process. Furthermore, the ZIF-8/[C4Py][NTf2] slurry can also keep the stable absorption performance after five consecutive absorption and desorption cycles. Considering the excellent capacity, thermal stability and recyclability, the porous materials/ILs slurry will provide new insight to CO2 capture compared with the conventional absorbents.