Denitrogenation and desulfurization of model diesel fuel using functionalized polymer: Charge transfer complex formation and adsorption isotherm study

- Application of functionalized polymers in petroleum refining.
- Role of fluorenone derived π-acceptor in forming charge transfer complexes.
- Equilibrium binding capacities and adsorption affinities have been determined.
- Thermodynamic properties revealed the favorable nature of adsorption.

This study is a perquisite to the fundamental understanding of the adsorption of heterocyclic nitrogen and sulfur compounds present in petroleum feedstock over fluorenone derived π-acceptor functionalized polymers. Quinoline (basic nitrogen compound), 9-ethylcarbazole (non-basic nitrogen compound) and dibenzothiophene (sulfur compound) were scanned to study the adsorptive denitrogenation and desulfurization of model diesel fuel. Batch reactor was used to compare the adsorption capacity and selectivity of these compounds at three sets of temperature (298 K, 313 K and 328 K). Total Nitrogen/Sulfur analyzer measured the change in nitrogen and sulfur content of the model fuels after adsorption over π-acceptor, 2,4,5,7-tetranitro-9-fluorenone (TENF) functionalized polymer. 60% extraction of total nitrogen compounds was obtained in one step, whereas the sulfur reduction was only 23% from a mixed model feed containing 700 ppm each of nitrogen and sulfur compounds. Charge transfer complexes were easily detected by the appearance of new bands in the visible region of UV-vis absorption spectrum. Adsorption isotherms facilitated the measurement of equilibrium binding capacities and adsorption affinities for this novel adsorbent. Functionalized polymer contributed towards higher adsorption of quinoline as compared to carbazole derivative and dibenzothiophene. Adsorption of these compounds was found to be reversible and multilayer over the heterogeneous surface of the functionalized polymer. At 298 K, maximum adsorption capacity increases as follows: quinoline > dibenzothiophene > 9-ethylcarbazole. Calculation of the thermodynamic properties revealed that the adsorption is favorable and spontaneous in nature. Molar enthalpies were calculated between −3.9 and −22 kJ/mol; which are characteristic of the electron donor acceptor complexes.

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