Extraction Of Sulfur Impurities From Gasoline Through Hollow Fiber Membrane Contactor

Organosulfur impurities present in gasoline produce SOx in automotive exhaust and therefore lead to severe environmental problems. Worldwide concerns over environment have promoted an increasing interest both in academia and industry for deep desulfurization of Fluid Catalytic Cracked (FCC) gasoline.As a membrane based extraction technique, hollow fiber membrane contactor (HFMC) possesses advantageous and potential for desulfurization of FCC gasoline, in which the separation mechanism is based on the potentials (concentrations) difference of the solute between the liquid feed side and the extract side of the membrane.The main advantages of this technique are: dispersion-free operation, independent variation in phase flow rates, no requirement of density difference between phases, ability to handle systems that form emulsions, and a very high interfacial area per unit volume, especially in the hollow-fiber modules. Mass transfer in membrane pores is controlled by diffusion.With n-octane/mercaptan/thiophene as the primary components making up model gasoline, the fundamental problems related to the mass transfer mechanism, mathematical model and contributing factors in the desulfurization process of simulated gasoline by highly hydrophilic cellulose HFMC were investigated. Firstly, NaOH solution was selected as the extractant for mercaptan removal from gasoline. The effects of various extractants, concentration ofNaOH solution, oil/extracting phase volumetric flowrates, oil to extractant volumetric ratios, and oil flowing patterns (in the tube or shell side) on the efficiency of RSH removal were investigated. The experimental results indicated that the chemical extraction had high efficiency up to 99%, and the oil phase resistance controlled the mass transfer. When 3%(wt) NaOH solution was employed as the extractant, the oil phase resistance 1/kf contributed more than 95% to the overall mass transfer resistance of RSH. Furthermore, a mathematical model (Lévêque-Graetz equations) of KOV was set up. It was well fit with the experimental results.Secondly, methanol was selected as the extracting solvent for thiophene removal from gasoline. A mathematical model was also set up for this system. It was well fit with the experimental results. When the extracting flowrate higher than 20mL·min-1, the resistance of polymer membrane contributed more than 90% to the overall mass transfer resistance of thiophene.Finally, in order to investigate the commercial application potential of cellulose HFMC in petroleum industry, a mixed methanol-dilute caustic solvent (containing 80%wt methanol and 2%wt NaOH) and oil/solvent ratio 5:1 were employed to desufurize from real FCC gasoline. This novel and capital-avoiding system performed as high sulfur removal efficiency as 84.76%, much higher than conventional extraction tech.Above all, the extraction performance was stable relatively during the long time operation, which indicated that membranes made from cellulose possess characteristics of solvent resistance, anti-fouling and alkali resistance.