عنوان مقاله [English]
Introduction: Sulfur is one of the elements in fossil fuels converted to sulfur dioxide when burned in a car engine, which is one of the most important air pollutants. The release of sulfur in existence petroleum and oil products into the air will lead to a serious environmental crisis. In addition, it has many side effects on human health and other living organisms. Complications such as sore throat and eye irritation and its acidic properties for living organisms are obvious consequences. Air pollution, acid rain, greenhouse effects, and other global environmental crises are due to pollutants such as sulfur in petroleum products and petrochemical industries.
Materials and Methods: In the present study, the adsorption capacity of an organic sulfurized compound from a diesel fuel model containing 300 ppm thiophene was evaluated on zeolite 13x modified with 3% by weight of copper metal. Moreover, the effect of three parameters of contact time (15, 30, 60, and 120 min), the amount of adsorbent (0.5, 1, 2.5, and 3.5 g), and temperature (25, 40, 50, and 60 °C) was evaluated in a batch system. First, in order to activate the adsorbent surface cations, zeolite x13 was washed with deionized water and 0.1 M copper nitrate salt and then copper nanoparticles were loaded on it.
Results: The maximum adsorption capacity achieved in 60 minutes with 2.5 g of adsorbent at ambient temperature; based on which the amount of thiophene for adsorbents modified with copper nanoparticles decreased from 300 to 138 ppm. The adsorption results showed that an increase of more than 2.5 g of adsorbent would not cause a significant change in the adsorption efficiency. As a result, the optimal amount of adsorbent in this study considered as 2.5 g. In other words, the adsorption efficiency in the test performed by zeolite modified with copper nanoparticles after increasing 1 g of adsorbent (from 2.5 to 3.5 g) was less than 1%. In addition, FTIR, SEM, and N2 physisorption studies showed that the adsorbent had a spherical, regular structure that will maintain this structure after nanoparticle loading. Studies have shown that the contact time is an equilibrium variable that this behavior was attributed to the exotherm of the process and its increase after reaching the equilibrium point will no longer have a significant effect on the adsorption capacity. Furthermore, adding 5% by weight of toluene or normal hexane to the cyclohexane and thiophene solution will reduce the removal of thiophene due to the formation of thiophene alkyls on the active sites of the adsorbent and the blockage of the cavities.
Conclusion: The process of adsorption of thiophene from thiophene solution in cyclohexane is physical and reversible, so the adsorbent can be retrievable, which is an extraordinary advantage. Adsorption isotherms were evaluated using common Langmuir, Freundlich, and Temkin models at ambient temperature with a mixing time of 1 hr and an adsorbent of 2.5 g with different amounts of solution. The results were highly consistent with the Freundlich isotherms and physical adsorption. Examination of the thermodynamics of adsorption showed that the reaction is exothermic, so according to Le Chatelier's principle, the progress of the reaction decreases with increasing temperature. Negative entropy also reflects the fact that the degree of freedom at the solid-solution surface decreases during adsorption. Finally, it can be concluded that zeolite modified with copper nanoparticles will show better performance for desulfurization of diesel fuel model.