Composite catalysts of Pt/SO42--ZrO2 and Pt/WO3-ZrO2 for producing high octane isomerizate by isomerization-cracking of long paraffins

Isomerization-cracking of long paraffins to produce octane enhancers for the gasoline pool is a complex refinery operation that needs simultaneous adjustment of the molecular size of the feed (cracking) and skeletal branching (isomerization). As both reactions are acid-catalyzed it is very difficult to adjust the acidity distribution of a single catalyst to have a proper balance. In this work the used catalyst is a mixture of an isomerization catalyst (Pt/WO3-ZrO2) (PtWZ) and a cracking catalyst (Pt/SO42--ZrO2) (PtSZ), working at the same reaction conditions. The tests were performed using n-hexadecane as a model feedstock. The screening of pressure and temperature conditions indicates that the best match for both catalysts is 20 atm and 225 degrees C. Stable activity levels for both catalysts can only be achieved at a H-2/n-C-16 ratio of 10. An adequate space velocity for increasing the yield to iC(5-9) and preventing consecutive cracking is 18.4 h(-1). At this process conditions mixtures (PtWZ+PtSZ) that contain 25% or 50% PtSZ have a better product distribution, with the maximum displaced to higher carbon numbers, with a reduced yield to isobutane and light gasses. Operation points lie on a monotonic curve of octane number gain (Delta RON) as a function of the yield of light gasses (C1-4) that indicates that RON gains can only be obtained at the expense of the liquid yield. (C) 2012 Elsevier B.V. All rights reserved.