Effective and selective removal of carbazole from model bitumen-derived fuel via adsorption using amine-grafted metal–organic frameworks

The high nitrogen content of bitumen is a major disadvantage because nitrogenous species disturb deep desulfurization and provoke air pollution. Here, denitrogenation of model bitumen-derived fuel (n-octane and toluene mixtures composed of carbazole (CBZ) and dibenzothiophene (DBT)), through selective adsorption of nitrogen-containing compounds (NCCs), was studied firstly using a MOF, MIL-101(Cr) (named M101), especially after functionalization with ethylenediamine (ED) or diethylenetriamine (DETA). The maximum adsorption capacity (Q₀) of M101-DETA for CBZ (per unit BET surface area) was 1.4 and 2.1 times that of M101-ED and M101, respectively, confirming the efficiency of the MOF in CBZ adsorption increased with increasing the number of amino groups on the MOF. This tendency was also observed in the model fuel containing both CBZ and DBT. Moreover, M101-DETA interacted more strongly with CBZ than DBT. All the observed results could be explained mainly with hydrogen bonding that was supported by a computational calculation and XPS analysis. Therefore, amine-functionalized MOFs such as M101-DETA (showing a high maximum adsorption capacity of 277.8 mg of CBZ/g) can be suggested as potential/recyclable materials for effective and selective removal of NCCs from fuels with a high concentration of SCCs.