Adsorptive Denitrogenation of Fuel over Metal Organic Frameworks: Effect of N-Types and Adsorption Mechanisms

Abstract

This work investigates adsorptive denitrogenation (ADN) of fuels over metal organic frameworks using a combined experimental/computational approach. MIL-101(Cr) shows high ADN capacities at low concentrations, ascribing to the sites on MIL-101(Cr) offering the strongest adsorption. Adsorption capacity of MIL-101(Cr) is higher for basic quinoline than that for nonbasic indole due to a greater adsorption strength of quinoline (−61.31 kJ/mol) than indole (−38.33 kJ/mol). Adsorption selectivity of various types of compounds in fuels follows the order of organonitrogen ≫ organosulfur > naphthalene, in good agreement with the order of adsorption strength as BEN (−62 ∼ −34 kJ/mol) < BES (−32 ∼ −24 kJ/mol) < BENap (−21.65 kJ/mol), suggesting MIL-101(Cr) is a highly selective adsorbent for ADN. ADN is negligibly affected by polyaromatic hydrocarbons, but suppressed by oxygenate cosolvent, that is, tetrahydrofuran to varied extents, depending on the varied adsorption mechanisms affected by N-types, including N-basicity, positive charge on H bound to N, and H-substitution.