Thermal regeneration of the metal organic frameworks used in the adsorption of refractory organosulfur compounds from liquid fuels

Abstract

The Metal Organic Framework (MOF) C300 system was used as a sorbent of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from simulated diesel fuel at constant temperature (304 K) and initial sulfur concentration (1724 ppm). Once thermodynamic equilibrium had been reached, thermal regeneration under inert flow within the temperature range 373–473 K was attempted and a second adsorption isotherm was recorded under exactly the same experimental conditions as the previous one. Regeneration at 473 K for all studied organosulfur compounds was only partial as shown by the lower level of adsorption regarding the fresh C300 sorbent. The recovered adsorption capacity was found to be a function of the boiling point of the three adsorbates, which means that the protocol employed to desorb the organosulfur compound (473 K, inert flow) allows only a fraction of the adsorbed phase to be desorbed, smaller for the S-containing molecules with a higher boiling point compound. In addition, it has been observed that the adsorption capacity recovered after the first cycle is maintained for further regeneration cycles. Adsorption of the sulfur compound is very strong, as shown by the slight drop in crystallinity and by the observation of a certain fraction of oxidized species (S(VI) moieties), as confirmed by the photoelectron spectra of the regenerated sorbent.