Wet air oxidation of a direct dye solution catalyzed by CoAlPO4 -5. Performance assessment and kinetic study

Wet air oxidation (WAO) of a prepared direct dye solution was tested by using the CoAIPO4 -5 catalyst. Addition of CoAIPO4 -5 could effectively improve rate of color removal and the activation energy of color removal could decrease from about 110 kJ/mole to about 75 kJ/mole as the catalyst loading was increased from 0.0 g/L to 3.0 g/L. Performance of WAO on color removal would somewhat increase with catalyst loading at 145 degrees C whereas the effect of catalyst loading was not significant at 135 degrees C. With no addition of CoAlPO4 -5, the chemical oxygen demand (COD) value was low. This was due to difficulty of exactly measuring the true COD value of dye solution if the dye was not degraded. Via CoAIPO4 -5, COD of dye solution could be effectively decreased. The rate of COD removal would increase with catalyst loading, oxygen pressure and reaction temperature. Furthermore, a maximum COD value observed, which was due to catalyzed degradation of dye molecule via CoAlPO4 -5, could be characterized by a consecutive reaction scheme. Kinetic study of color removal is expressed as follows: rate = k x [dye](0.8) x W(0.5) x P(n) (145 degrees C) or rate = k x [dye](0.8) x W(0) x P(n) (135 degrees C); where k means rate constant, [] means concentration, W means catalyst loading, P means oxygen pressure and n means uncertain number.