Wet oxidation of an azo dye: Lumped kinetics in batch and mixed flow reactors

Oxidation of a dilute aqueous solution of a model azo dye pollutant (Orange II) was studied in batch and continuous well-mixed (CSTR) reactors. Both r eactors operate at 200 - 250 degrees C, and total pressures up to 50 bar an d at oxygen partial pressure from 10 to 30 bar. The model pollutant concent rations were in a range between 100 and 1,000 mg/L, which may be found in i ndustrial wastewaters. The dye oxidation undergoes a parallel-consecutive r eaction pathways, in which it first decomposes thermally and oxidatively to aromatic intermediates and via organic acids to the final product carbon d ioxide. To develop a kinetic equation capable of predicting organic carbon reduction, all organic species present in solution were lumped by total org anic carbon (TOC). The lumped oxidation rate in batch reactor exhibited sec ond-order behavior, whereas in the CSTR it was found linearly proportional to its TOC concentration. The lump behavior in batch reactor was dominated by the refractory low molecular mass aliphatic acids formed during the oxid ation.