Adsorptive denitrogenation of model fuels with porous metal-organic framework (MOF) MIL-101 impregnated with phosphotungstic acid: effect of acid site inclusion.

A metal-organic framework (MOF) MIL-101 was impregnated with phosphotungstic acid (PWA) and used as an adsorbent in liquid phase adsorption of nitrogen-containing compounds (NCCs) from a model fuel. The model fuel contained one sulfur-containing compound (SCC), benzothiophene (BT); one basic NCC, quinoline (QUI); and one neutral NCC, indole (IND). In both MIL-101 and PWA-impregnated MIL-101s, NCC adsorption selectivity was very high compared to the SCC selectivity. Additionally, the adsorption capacity of basic QUI increased by 20% with only 1% PWA impregnation in MIL-101. The adsorption of a neutral compound, IND, was slightly reduced with PWA impregnation in the MOF. The adsorption capacity/selectivity can be remarkably improved by a slight modification of MOFs, for example, to impart acidity. The MOF impregnated with PWA may be very interesting in commercial denitrogenation, especially for coal-derived fuels which contain mainly basic NCCs, by adsorption since the selectivity for NCCs (compared to SCCs) over the adsorbent is very high and the adsorbent can be reused many times.