Various basic nitrogen compounds removal from model diesel by adsorption with allochroic silica gel

The allochroic silica gel was used for adsorptive denitrification from model diesel containing known amounts of quinoline, aniline or pyridine with a total nitrogen concentration 960.56 μg/g. The adsorptive removal of quinoline in model diesel with alumina, diatomite, silica gel and allochroic silica gel was investigated. The experiment results indicate that the adsorptive denitrification performance of allochroic silica gel is more superior to that of other three adsorbents, implying that the CoCl₂ in allochroic silica gel can significantly improve the performance of denitrification. The silica gel and allochroic silica gel were characterized with X-ray diffraction (XRD), nitrogen adsorption and NH₃-TPD. The XRD results indicate that the two samples are of an amorphous structure. Silica gel and allochroic silica gel have the average pore diameter of 18.46 and 1.80 nm, the Brunauer-Emmett-Teller (BET) surface area of 437.86 and 623.39 m²/g, and the pore volume of 0.9724 and 0.3442 m³/g, respectively. The results of NH₃-TPD show that the acidity of allochroic silica gel is much stronger than that of silica gel which greatly enhances the adsorptive denitrification. Also, the influence of particle size, adsorption temperature, adsorption time, adsorbent to oil mass ratio and aromatic compounds on the adsorptive denitrification of allochroic silica gel was investigated. The adsorptive denitrification for different model diesels by allochroic silica gel is ordered as:aniline > pyridine > quinoline. Adsorption time has almost no influence on the removal of three nitrogen compounds. Adsorption temperature, particle size and aromatic compounds in the model diesel have little impact on the removal of aniline and pyridine, but have evident influences on the removal of quinoline. The adsorbent to oil ratio has a significant effect on the adsorptive denitrification, especially for quinoline. The experimental results suggest that the N-Co bond between Co in allochroic silica gel and N atom in the nitrogen compounds plays a significant role. Furthermore, the allochroic silica gel could be easily regenerated to recover its adsorptive denitrification for quinoline and pyridine by calcination once or several times, but except aniline.