Integrated Study On Solid Superacid Catalyst For Normal Paraffin Isomerization

Recently, solid superacid catalysts, e.g. SO₄^2-/M_xO_y and S₂O₈^2-/M_xO_y solid superacid catalysts,have attracted much attention of the researchers, due to their strong acidity, thermal stability, environmentally friendly and excellent catalytic activity.The solid superacid catalyst Pd-SO₄^2-/ZrO₂-WO₃ was prepared by adding noble metal Pd and using WO₃ as an secondary oxide. The new catalyst was studied using n- pentane isomerization as a probe reaction on high pressure microreactor of 10ml continuous flow fixed-bed with online chromatogram unit. In order to study the effects of preparation methods on catalytic activity, the catalysts were characterized by X-ray diffraction(XRD), FTIR, scanning electron microscope(SEM), specific surface area measurements(BET), thermogravimetry-differential thermal analysis(TG-DTA) and NH₃ temperature- programmed desorption(NH₃-TPD). The way of adding Al₂O₃, quantity of Al₂O₃, content of Pd, activation temperature were researched in the article. The catalytic activity of the Pd-SO₄^2-/ZrO₂-WO₃ solid superacid catalyst with the mass fractions of 13% WO₃ and 0.05% Pd which was activated at 300℃was found to be the best. When the catalyst was reacted at the conditions of isomerization temperature of 260℃,space velocity of 1.0h-1,H2/ n-pentane molar ration of 4.0 and reaction pressure of 2.0MPa, the yield of isopentane remain above 35.0% and the selectivity was kept higher than 95.3%within 80h .The Pd-S₂O₈^2-/ZrO₂-Al₂O₃ solid superacid catalyst was prepared by adding noble metal Pd and using Al₂O₃ as an secondary oxide and studied using n- pentane isomerization as a probe reaction in the section two of this article. The catalysts were characterized by X-ray diffraction(XRD), FTIR, specific surface area measurements(BET), thermogravime - try-differential thermal analysis(TG-DTA) and NH₃ temperature- programmed desorption(NH₃-TPD). The effects of preparation methods on catalytic activity such as the quantity of Al₂O₃, calcination temperature, concentration of (NH4)2S2O8, content of Pd, activation temperature and activation time were investigated respectively and the deactivation phenomenon was studied simultaneously. The catalytic activity of the Pd-S₂O₈^2-/ZrO₂-Al₂O₃ solid superacid catalyst with the mass fractions of 2.5% Al₂O₃ and 0.05% Pd which was calcinated at 650℃was found to be the best. The n-pentane conversion attained 67.8%, and the isopentane yield reached 64.3%, when the catalyst was employed at the following reaction conditions; temperature 230 oC,space velocity 1.0 h-1,H2/n-pentane molar ratio 4.0 and reaction pressure 2.0 MPa.