EXPERIMENTAL EVALUATION OF SELECTIVITY IN SLOW AROMATIC CHLORINATIONS

A dispersion plug flow reactor model (DPFR) has been derived and experimentally verified to predict product distribution and selectivity for commercial aromatic halogenation reactions. From the model recommendations for process modifications to reduce the amounts of undesirable byproducts arising from similar reactions can be obtained. The selectivity of the monochlorinated product is shown to depend on kinetic and hydrodynamic parameters, mixing in the reactor and chlorine solubility. The pertinent variables are arranged in five dimensionless groups which include the kinetic and hydrodynamic Damkohler Numbers, the Peclet Number, ratio of the rate constants and the ratio of chlorine solubility to the inlet aromatic concentration.

A micro pilot plant which duplicates industrial conditions for benzene and toluene chlorination was constructed to test the DPFR model. Chlorination studies were performed under a range of conditions. Hydrodynamic parameters required for the model were obtained from published correlations. The model prediction of selectivity agreed within 8% for all the experimental results, and actually better than 5% for most runs.

A graphical technique which provides recommendations for reducing the dichlorinated products is presented along with examples for both the design of a reactor, and troubleshooting of an existing reactor system.