Evaluation and application of iron-modified clay adsorbents for clean fuel production in the frame of desulfurization technology

Abstract This study investigated clay adsorbents for benzothiophene sulfone (BTO) removal through oxidative desulfurization. Bentonite-Fe 3+ (BF3), Fe 6+ (BF6), activated clay-Fe 3+ (ACF3), and Fe 6+ (ACF6) were synthesized via impregnation of raw bentonite (BR) and raw activated clay (ACR) with Fe 3+ and Fe 6+ ions. Fourier transform infrared analysis identified the functional groups before and after impregnation and sulfur adsorption. The proposed mechanism involves covalent bonding between double-bonded oxygen of the sulfone and the oxygen of the hydroxyl group on the surface of the adsorbent. Scanning electron microscopy was then used to observe the adsorbent morphology. This showed that iron impregnation resulted in the conglomeration of particles, lowering the available surface area. This was confirmed with the Brunauer, Emmett, and Teller analysis as the specific surface area decreased in the following order: raw > Fe 3+ > Fe 6 . Experiments were done in batch with model oil using toluene and BTO, where adsorption time, temperature, and adsorbent dosage were varied to test their effect on BTO removal. Calculations using kinetic models showed that clay adsorbent and BTO systems closely follow the pseudo-second order model, indicating that the reaction rate is limited by the chemisorption rate. Equilibrium isotherms showed that BTO onto BF3 and ACR systems align with the Freundlich model, which suggests that BTO is adsorbed heterogeneously. The BTO and BR, BF6, ACF3, and ACF6 systems closely follow the Dubinin-Radushkevich model, suggesting that sulfones are removed through micropore filling. Thermodynamic studies showed that the clay adsorbent and BTO systems are endothermic and non-spontaneous.