Selective Adsorption of Neutral Nitrogen Compounds from Fuel Using Ion-Exchange Resins

Adsorptive removal of hydrodesulfurization inhibitors, that is, nitrogen-containing compounds (N-compounds), was studied using model fuel which contains carbazole and dibenzothiophene in an n-dodecane-toluene mixture over ion-exchange resins (IXRs) in batch and in fixed-bed adsorption systems. The adsorptive capacity and selectivity for neutral N-compounds were examined. The high affinity for neutral N-compounds present in hydrocarbon feed was explained by hydrogen bonding between the chloride anion (with nonbonding electrons) and the neutral N-compounds. However, the presence of a flat charged cation, that is, N-alkylated pyridinium, is essential to ensure the adsorption of neutral N-compounds. The regeneration of the sorbent could be easily performed using polar organic solvent like methanol. Commercially available IXR bearing pyridinium chloride functionality (HPQ) was further evaluated with straight-run fuel oil. The N/S selectivity decreases, but analysis of the adsorbed compounds by gas chromatography/mass spectroscopy (GC/MS) shows that no paraffin and no monoaromatics were adsorbed. The results obtained provided new insight into the fundamental understanding of the adsorption mechanism of neutral N-compounds from hydrocarbon feed.