Ammoxidation of 2,6-dichloro toluene—From first trials to pilot plant studies

The scaling-up of the gas phase catalytic ammoxidation of 2,6-dichloro toluene (DCT) to 2,6-dichloro benzonitrile (DCBN) over a promoted vanadium phosphate (VPO) catalyst from first lab-scale experiments to pilot plant runs is reported. First experiments in a row of conversions of isomeric dichloro toluenes using simple, non-promoted VPO catalysts only show poor yield and selectivity. In particular, DCT ammoxidation is hindered due to bulky chlorine substituents probably preventing a sufficient interaction of the methyl group and lattice oxygen and/or N-containing surface species. Improved synthesis of VPO catalyst with the addition of promoters and γ-alumina or titania leads to significant increase in DCT conversion and DCBN yield. A Cr containing vanadyl pyrophosphate catalyst admixed with titania (anatase) showed conversion up to 97% with DCBN yields of ca. 80%. The same catalyst was also used for pilot plant runs, usually in the form of 5 mm × 3.5 mm shaped tablets that were prepared from a larger batch of solid synthesis. The scaling-up of the process using 100 ml of catalyst was investigated both by catalytic experiments and reactor simulations. The results showed that the temperature control will be crucial in scaling-up. Validation of simulation results with that of experimental results was also checked and a good agreement between measured and simulated results is observed.