Study On Solid Superacid Catalyst For N-alkanes Isomerization

Recently, solid superacid catalysts, e.g. SO₄²-/ ZrO₂-Al₂O₃,have attracted much attention of the researchers, due to their strong acidity, thermal stability, environmentally friendly and excellent catalytic activity.The paper studied SO₄²-/ZrO2 which has the strongest acidity among the solid superacid catalysts of SO₄²-/MxOy. It presents the methods of preparation and the application of solid superacid catalyst SO₄²-/ZrO2 for n-pentane isomerization. The solid superacid catalyst Pt-SO₄²-/ZrO₂-Al₂O₃ was prepared by adding noble metal and using Al2O3 as an secondary oxide. The catalyst was evaluated with n-pentane as feed 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 way of adding Al2O3, quantity of Al2O3, calcination temperature, kind of impregnated solutions, way of adding H₂SO₄, concentration of H₂SO₄, aging temperature, content of Pt, activation temperature and activation time were investigated respectively. The optimal reaction conditions for isomerization, such as weight hourly space velocity, temperature, pressure and hydrogen/hydrocarbon mole ratio were determined.The results show that the performance of catalyst for alkyl isomerization can be improved by adding an secondary oxide and noble metal Pt. The sample, whose quantity of Al2O3 is 5.0%, using coprecipitation method, impregnating in the H₂SO₄ solution of 0.5mol/L, calcinating at 650℃, aging temperature is lower than room temperature, content of Pt is 0.1% , activated at 300℃for 3h, is best for the reaction of alkyl isomerization. With the catalyst prepared under the optimized condition and reacting at the conditions of temperature of 200℃, pressure of 2.0 MPa, space velocity of 1.5 h-1 and H2/n-pentane molar ration of 4.0, the n-pentane conversion is 72.85%, iso-pentane yield is 67.63%, isopentane selectivity is 92.84% and liquid product yield is 94.78%.