Study On Solid Superacid Catalyst For Light Alkanes Isomerization

Solid superacids is a new type of catalytic materials, which have been deyeloped in recent years. Solid superacid catalysts S2O82-/ZrO2-Al2O3 have broad application prospects, and have become one of the hot spots in the field of catalysis,because they have many obvious advantages, such as high catalytic activity, good selectivity, simple preparation methods, not polluting the environment, not corroding equipments, reusing.The paper studied S2O82-/ZrO2 which has the strongest acidity among the solid superacid catalysts of S2O82-/MxOy. The solid superacid catalyst Pt-S2O82-/ZrO2-Al2O3 was prepared by adding noble metal Pt and using Al2O3 as a secondary oxide. It mainly studied the methods of preparation and the application of solid superacid catalyst Pt-S2O82-/ZrO2-Al2O3for n-pentane isomerization. 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, calcination time, kind of impregnated solutions, way of adding (NH4)2S2O8, concentration of (NH4)2S2O8, soaking time of (NH4)2S2O8, 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, mole ratio of hydrogen and hydrocarbon were determined.These catalysts were analysed by modern analysis methods,such as XRD,IR,BET.The results showed that the sample, whose quantity of Al2O3 was 2.5%, content of Pt was 0.1%, using coprecipitation method, impregnated in the (NH4)2S2O8 solution of 0.75mol/L for 6h, calcinated at 600℃for 3h, activated at 300℃for 3h, was best for the reaction of n-pentane isomerization. With the catalyst prepared under the optimized condition and reacting at the conditions of temperature of 220℃, pressure of 2.0 MPa, space velocity of 1.5 h-1 and hydrogen/n-pentane molar ratio of 4.0, the n-pentane conversion was 78.25%, iso-pentane yield was 74.85%, isopentane selectivity was 95.65% and liquid product yield was 96.42%.