Modification Of NaY Zeolites And Their Properties Of Adsorption Desulfurization Of Thiophene In Model Gasoline

Increasing attention has been focused on the quality of transportation fuels,such as diesel and gasoline,because they pose serious threats to the environment and air quality.Countries around the world have a strict standard of sulfur content of transportation fuels,so there is a great scientific interest to develop effective deep desulfurization methods to remove sulfur compounds from fuels.In this paper,Zn-modified adsorbents were successfully prepared by liquid-phase ion exchange method.X-ray powder diffraction（XRD）,inductively coupled plasma atomic emission spectrometry（ICP-AES）,N₂ adsorption-desorption（BET）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）were used to characterize the prepared adsorbents.The effects of different Zn source modification,ion exchange time and ion exchange temperature on the desulfurization performance of ZnY zeolites were studied by static adsorption desulfurization method.The adsorption conditions,adsorption time,adsorption temperature,adding aromatics and adding olefins were also studied.When ion exchange using Zn（Ac）₂,ion exchange concentration of 0.1 mol/L,ion exchange at60℃for 10 hours,Zn（Ac）₂-Y exhibit the best performance for the desulfurization of model gasoline.Adsorption sulfur capacity reached 21.12 mgS/g and thiophene removal rate reached 56.01%after 120 min adsorption at 50℃with model gasoline oil containing thiophene（adsorbents/model gasoline ratio of 0.02 g/m L）.In this paper,the desulfurization performance of adsorbent also was tested with model gasoline containing a certain amount of competitive components（toluene and n-hexene）.The results showed that the desulfurization performance of adsorbents was significantly decreased with the addition of toluene and n-hexene in the model gasoline.The effect of toluene was more significant than that of n-hexene.Zn（Ac）₂-Y have a higher adsorption capacity than Zn（NO₃）₂-Y and ZnSO₄-Y.Toluene and n-hexene affect the mechanism of adsorption desulfurization is different.there are some donation of electron charges transfer from theπorbital of TP to the vacant s orbital of Zn²⁺,simultaneously,back-donation of electron charges transfer from the d orbitals of Zn²⁺to theπ*orbital of TP.The toluene contain benzene ring structure,for which forms the competitive adsorption with TP,leading to a sharp drop of sulfur adsorption capacity.The acid catalyzed alkylation by 1-hexene of TP and the generated complex mixture of bulky alkylthiophenes would adsorb on the surface active sites of the adsorbent and block the pores.In addition,the adsorption kinetics,thermodynamics and equilibrium isothermal adsorption of NaY and ZnY were also studied.The adsorption equilibrium,adsorption kinetics and adsorption thermodynamics data were calculated by Freundlich,Langmuir,Toth adsorption model,first order and second order kinetic equation,and thermodynamic equation,respectively.Mass transfer and intra-particle diffusion models were also evaluated to fit the kinetic of the adsorption process and to determine the mechanism of it.The equilibrium data are fitted Langmuir,Freundlich and Toth isotherms.It is indicated from calculated determination coefficient（R²）that the equilibrium isothermal adsorption follows Toth isotherms well.The second order kinetic model provides the best fit to both NaY and Zn Y zeolite adsorbents.The transfer of thiophene from the solution to the surface of the adsorbent is a very rapid process.As the intra-particle diffusion advance,the diffusion rate gradually decreases until equilibrium,and the intra-particle diffusion is the rate-controlling step.The enthalpy（ΔH）of NaY and ZnY were less than 0 indicate the exothermic nature of the adsorption process.The Gibbs free energy（ΔG）increases with increasing temperature,indicating that the desulfurization process is a spontaneous process.