(672c) Forced Dynamic Operation: Propene Ammoxidation over Bismuth Molybdate-Based Catalysts

Ammoxidation (AMO) of propene over bismuth molybdate (BMO)-based catalysts to produce acrylonitrile (ACN) has been used since the 1950s. Acrylonitrile is the precursor to polyacrylonitrile (PAN), which can in turn be manufactured into acrylic fiber or carbon fiber (CF). CF is used in many applications due to its lightweight and high tensile strength nature. As the demand for CF is growing rapidly, manufacturing capacity of ACN is bound to increase. Instead of building in large-scale production, which is costly, small-scale production could be more economic.

Forced dynamic operation (FDO) utilizing feed modulation is suitable for small-volume reactors. In FDO, the reactor is operated such that the composition is periodically changed to achieve enhanced product selectivity and yield. One intuitive aspect in improving yield via FDO is the utilization of lattice oxidation. BMO-based catalysts are well-known for their dynamic oxygen storage capacity (DOSC). However, exactly how DOSC impacts FDO for this reaction is not well-established.

In this work, we applied FDO for AMO over transition metal promoted BMO (denoted HM-BMO).FDO schemes with changing compositions of reactant gases (C₃H₆, NH₃ and O₂) and conditions (cycle period, duty cycle) were tested to identify the best pathway in improving ACN yield. We found a higher than steady state ACN productivity in an FDO scheme that periodically switches between the normal feed and an O₂ feed (Fig. 1a). The so-called ACN “spikes” indicate FDO parameters could be adjusted so that the time-averaged ACN yield can exceed those of steady-state operation (SSO). We also found that the DOSC of the BMO-based catalysts is correlated with ACN productivity in FDO. By tuning promoter element ratios, the FDO performance can be optimized (Fig. 1b). Our results show that FDO can provide promising ACN production rates compared with SSO, potentially contributing to the pursuit of economic modular ACN manufacturing.