WET AIR OXIDATION OF A DIRECT DYE SOLUTION CATALYZED BY CoAlPO₄-5. PERFORMANCE ASSESSMENT AND KINETIC STUDY

Abstract

Wet air oxidation (WAO) of a prepared direct dye solution was tested by using the CoAlPO₄-5 catalyst. Addition of CoAlPO₄-5 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°C whereas the effect of catalyst loading was not significant at 135°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 CoAlPO₄-5, 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 × [dye]^0.8 × W ^0.5 × P ⁿ (145°C) or rate = k × [dye]^0.8 × W ⁰ × P ⁿ (135°C); where k means rate constant, [ ] means concentration, W means catalyst loading, P means oxygen pressure and n means uncertain number.

Keywords:

• CoAlPO₄-5
• COD removal
• Color removal
• Kinetic study
• Wet air oxidation

ACKNOWLEDGMENT

The authors are grateful to National Science Council of R. O. C. for financial support (NSC 89-2211-E-041-010).