KINETICS AND REACTION NETWORK IN PROPANE AMMOXIDATION TO ACRYLONITRILE ON V-SB-AL BASED MIXED OXIDES

The kinetics of propane ammoxidation to acrylonitrile on a V-Sb-Al based mixed oxide catalyst are described by a Langmuir-Hinshelwood approach, six parallel reactions of formation (propylene, acrylonitrile, carbon oxides, acetonitrile, HCN, and C2 hydrocarbons), three reactions of consecutive transformation of the intermediate propylene to acrylonitrile, acetonitrile and HCN, five decomposition reactions of intermediate products to carbon oxides, and one reaction of decomposition of ammonia. The kinetics were studied in a quartz tubular flow reactor operating both in differential and integral conditions, using propane, oxygen, and ammonia concentrations in the 0-20% range and reaction temperatures in the 680-810 K range. Acrylonitrile forms principally from the intermediate propylene, and the limiting factor in the formation of acrylonitrile is the relative slowness of this step compared to the others and the higher rate of propylene oxidation to carbon oxides as compared to that of acrylonitrile to CO(x). The maximum yields and selectivities to acrylonitrile obtained were in the 35-40 and 50-60% ranges, respectively, for propane conversions in the 60-80 and 40-50% ranges, respectively. The relevance of the kinetic information in determining the best reaction conditions and performance using different possible feedstocks is also discussed.