(247b) Propene Ammoxidation over Bismuth Molybdate (BMO)-Based Catalysts: Effects of Feed Modulation and Transition Metal Addition

Acrylonitrile production through ammoxidation (AMO) of propene over bismuth molybdate (BMO)-based catalysts has been used commercially for decades. With carbon fiber needs predicted to grow over the next several years, and acrylonitrile a precursor to polyacrylonitrile, which is in turn a precursor for carbon fiber, acrylonitrile manufacturing will need to increase to meet demand. Instead of building the traditional large-scale production facility, modular, smaller-scale production may prove more economic and would provide quicker response to market demands.

With smaller reactors, forced dynamic operation (FDO), or periodic operation, can be used to tune catalyst surface properties. This is less practical for large-scale facilities, where thermal and momentum inertias would dampen periodic changes in input conditions. One intuitive aspect in improving yield via FDO is the leveraging lattice oxygen in the catalyst. BMO-based catalysts are known to have reactive lattice oxygen and could impact acrylonitrile production.

Here, we used FDO for propene ammoxidation over transition metal promoted BMO catalysts and a commercially-supplied BMO-based catalyst. FDO schemes with changing compositions of reactant gases, cycle period and duty cycle were compared with ACN yield as the measure. Higher than steady-state ACN productivity was observed under some FDO conditions, specifically those with a higher than stoichiometric amount of oxygen in one of the phases. We observed acrylonitrile formation “spikes” at the transition between phases, and these were the main contributors to the improved yields. We also correlated the dynamic oxygen storage capacity, measured using propene oxidation, to acrylonitrile productivity during FDO. Different transition metal ratios led to changes in the spike formation and ultimately acrylonitrile yields. These were also correlated to the dynamic oxygen storage capacity, and also described by changes in compositional phases.