The scaling-up of the gas phase catalytic ammoxidation of 2,6-dichlorotoluene (DCT) to 2,6-dichlorobenzonitrile (DCBN) over vanadium phosphate catalyst in a pilot plant was investigated. The focus was led on the process variables that might be critical for designing a commercial manufacturing unit, in particular on evaluation of reaction temperature that may cause hot spots, temperature gradients, etc. Furthermore, catalyst scale-up, catalyst stability and a development of a product separation section particularly for the solid reaction products was studied. The up-scaling of the process using 100 ml of catalyst was investigated both by reactor simulations and catalytic experiments. For reactor simulations, a pseudo-homogeneous model of a fixed bed tubular reactor with negligible axial and radial diffusion operating in the steady-state was applied. The kinetic model based upon the Langmuir-Hinshelwood mechanism was used. The results showed that the temperature control will be crucial in scaling-up of the process. The influence of the reactor geometry, reactor operating conditions and catalyst stability on the reactor performance is discussed. The possibility of an appearance of hot spots in the reactor is addressed. High selectivity of DCBN (85%) can be achieved for an extended period of time. A good agreement between experimental and simulation results is observed. (c) 2008 Elsevier B.V. All rights reserved.