Vapour phase catalytic oxidation of 2-methylpropene over bismuth molybdate catalysts.

Abstract

The vapor phase air oxidation of 2-methylpropene to methacrolein was investigated in an isothermal integral flow reactor at 1.15 atmospheric pressure, in the temperature range 390°C-560°C. Bismuth molybdate supported on zirconium oxide, an n-type catalyst was used. The effect of various process variables, namely the feed ratio of oxygen to 2-methylpropene, reaction temperature, and the reciprocal of space velocity on the conversion of olefin and the product distribution was investigated. It was observed that an increase in the conversion of 2-methylpropene was always accompanied with a decrease in the selectivity. In most cases the selectivity for methacrolein increased with the increasing feed ratio of oxygen to 2-methyl-propene (0.6 to 2.0). Relatively lower temperature was found to favor the selectivity of methacrolein. Though the conversion of 2-methylpropene, the yield of methacrolein and carbon dioxide increased rapidly at longer contact time, it was hardly affected in the range of shorter contact time. Out of the several models proposed for the oxidation of 2-methylpropene over bismuth molybdate catalyst. The most suitable one appear to be the one in which the rate determining step is the surface reaction between adsorbed olefin and oxygen on different active sites, the rate of reaction can expressed by the equation r=KSKHPH 1+KHPH+KMPM ˙KOPO 1+KOPO where KS, KH, KO and KM are temperature dependent constants.