Desulfurization Of Methyl Tert Butyl Ether (MTBE) Using Heterogeneous Zeotype Adsorbents

This work mainly involved the investigation of the methyl tertiary butyl ether (MTBE) desulfurization by adsorption. For the purpose of reducing the sulfur content from liquid hydrocarbon fuels further, an adsorption desulfurization process by loading CuBr2 on bentonite for removing propylmercaptan (PM) and dimethyl sulfide (DMS) was investigated under ambient conditions in this work. A saturated sulfur capacity as high of 196 mg S/g adsorbent when the bentonite was loaded with 15 wt% Cu(Ⅱ), calcined at 150℃ was demonstrated. The results revealed that the adsorption capacity of PM and DMS were enhanced significantly due to the addition of CuBr2 on the bentonite. Loading amount of Cu(Ⅱ) and baking temperature of CuBr2 modified bentonite, which influence the desulfurization capability were investigated. The adsorbents were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Pyridine-FTIR spectroscopy. The Pyridine-FTIR spectroscopy showed that a certain amount of Lewis acid could contribute to increasing the adsorption capacity. Spectral shifts of the v(C-S) and v(Cu-S) vibrations were detected with the Raman spectrum in the Cu(Ⅱ) complexe which is a product of CuBr2 react with DMS. According to hybrid orbital theory and complex adsorption reaction, the desulfurization of PM and DMS on CuBr2 modified bentonite is contributed to multilayer intermolecular forces and S-M (σ) bonds.Secondly the objective is also to find an economically attractive method instead of distillation for desulfurization of MTBE. Zeolites, including X, Y, β, MCM-41 and ZSM-5, were studied for this purpose. MTBE is found to have strong inhibiting effect on desulfurization by adsorption with zeolites. And only ZSM-5 made an excellent desulfurization performance in MTBE solution, withstanding its inhibiting effect. Study on effect of ZSM-5 with different particle size showed the shape-selectivity is responsible for the selective adsorption of DMDS rather than MTBE. A high sulfur removal capacity (35.4 mg S/g adsorbent) has been observed for ZSM-5 with 7 wt% Ag+ loading prepared in kneading method, tested in model MTBE feedstock. And for AgZSM-5 the optional calcination temperature was found to be 450℃. Characterization by thermal analysis (TGA-DSC) demonstrates the adsorption on AgZSM-5 occurred via multilayer intermolecular forces and S-M bonds. AgZSM-5 could desulfurize 96 mL of commercial MTBE from initial 55.6 to 10 ppmw. Results of Pyridine-adsorption FTIR spectra show the Lewis acid sites play a positive role on the adsorption. The selectivity has been explained by the shape-selective effect of NaZSM-5 and the direct S-M interaction Results of equilibrium isothermal adsorption show it can be represented by the Freundlich model.Regeneration test showed the adsorbent prepared in kneading method is reusable, and the decline of sulfur capacity was due to the loss of Ag+ species. Fixed-bed test in industrial MTBE stream revealed the gradual loss of Ag+ species as TOS increased. Ag-ZSM-5 adsorbent prepared in AE method was found to be sufficient to withstand the loss and then leading to a more stable desulfurization performance.