Denitrogenation through Adsorption to Sulfonated Metal-Organic Frameworks

Sulfonic acid functionalized MIL-101(Cr) (S-MIL-101(Cr)) are obtained by sulfonation of MIL-101(Cr) (Cr3F(H2O)(2)O[(O2C)-C6H4-(CO2)](3)center dot nH(2)O (n similar to 25)) using triflic anhydride and sulfuric acid. The amount of sulfonic groups in the framework can be controlled by changing the molar ratio of MIL-101(Cr), triflic anhydride, and sulfuric acid. The sulfonated samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, nitrogen physical adsorption/desorption, acid-base potentiometric titration, and thermogravimetric analysis (TGA). The results show that the sulfonated samples retain the general structure of MIL-101(Cr), but the specific areas and pore diameters decrease. The sulfonated samples formed with between 0.21 and 0.42 mmol.g(-1) of sulfonic acid groups. The adsorptive denitrogenation of a model fuel by different S-MIL-101(Cr) samples was investigated in batch adsorption experiments. Sulfonation can strengthen the interactions between nitrogen-containing compounds (NCCs) and the adsorbent. The sample obtained using a molar ratio of n(MIL-101(Cr)):n(H2SO4):n(Tf2O)=1:3:4.5 had the largest adsorption capacity for quinoline and indole. Compared with the bare MIL-101(Cr), this sulfonated material showed enhancement of the maximum adsorption capacity by 12.2% and 6.3% for quinoline and indole, respectively. Regeneration of the used adsorbent was conducted by washing with ethanol, and the adsorptive capacity for NCCs from the model-fuel showed no obvious decrease after three cycles of use.