Dong-Jang Chang

Wet air oxidation of a reactive dye solution using CoAlPO4-5 and CeO2 catalysts

Wet air oxidation of a prepared reactive dye solution was performed to assess the efficacy of CoAlPO(4)-5 and CeO(2) as catalysts in the reaction. Via adsorption and oxidation of dye, CoAlPO(4)-5 effectively decreased American Dye Manufacturers Institute and chemical oxygen demand (COD) values in the dye solution. At a reaction temperature of 135 degrees C and an applied pressure of 1.0 MPa, color and COD removal were as high as 95% and 90%, respectively, after 2 h. Active sites on the outer surface of CoAlPO(4)-5 are responsible for adsorption and decomposition of dye while active sites in the pores dominate further destruction and oxidation of intermediate products. Since the outer surface only represents a minor part of the total surface, the color removal does not increase appreciably with loading of CoAlPO(4)-5. The CeO(2) catalyst, calcined from cerium chloride under high thermal impact (type A CeO(2)) was very effective in removing color and COD from the solution. This catalyst demonstrated near 100% color removal at temperatures above 135 degrees C and the COD removal could be above 95% at 165 degrees C. With both CoAlPO(4)-5 and CeO(2) catalysts, COD rose and then fell back during the reaction, a feature typical of a consecutive reaction. In contrast to prepared CeO(2), a commercial CeO(2) did not exhibit any catalytic ability for the removal of color and COD. The durability of both CoAlPO(4)-5 and prepared CeO(2) is considered to be fair.

Catalytic wet air oxidation of phenol using CeO2 as the catalyst. Kinetic study and mechanism development

ABSTRACT Using a CeO2 catalyst prepared from CeCl3 ċ 7H2O under high thermal impact, the catalytic wet air oxidation (CWAO) of phenol was effectively implemented. With initial phenol concentrations of between (400 and 2500) mg/L, and at a temperature of 160°C, the rate of phenol conversion increased with increased catalyst loading (0.2 g/L–1.0 g/L) and oxygen pressure (0.5 MPa–1.5 MPa). Even at an initial concentration of 2500 mg/L, conversion of phenol was as high as 95% after 3 h reaction. The effect of phenol concentration, catalyst loading, and oxygen pressure on the initial rate of phenol conversion was evaluated in a kinetic study. The initial rate equation derived from kinetic study is: R o = k 1 × [Ph]1.3–1.4 × W0.5–0.6 × Po 2 0.9–1.1, where k 1 is a rate constant, and [Ph], W and Po 2 refer to phenol concentration, catalyst loading and oxygen pressure, respectively. A free-radical involved reaction mechanism was proposed and an initial rate expression based on this mechanism was derived: R o = k 2 × [Ph]1.5 × W0.5, where k 2 is also a rate constant. Fitting of experimental data with the theoretically derived initial rate equation resulted in good correlation: the coefficient is greater than 0.99.

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 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.

The removal of colloid and dissolved phosphorus by coagulation and membrane microfiltration

Abstract Micro‐filtration has its limitation to remove the dissolved matter and colloids which are smaller than the membrane pore size. Experiments were conducted to develop a preliminary methodology to optimize the operating conditions of membrane hybrid system (coagulation ‐ membrane micro‐filtration) in comparing with the removal of colloidal particles and dissolved phosphorus which are presented in water in particle and dissolved forms, respectively. The results showed that the coagulant dosage could be minimized and high removal efficiency obtained in treating water with colloid particles only. However, for dissolved phosphorus, its removal efficiency is dependent on water alkalinity as well as coagulant dosage and the associated sludge production could not be minimized. To determine the minimum coagulant dosage for the removal of colloidal particles, a few tests of membrane hybrid system were needed. But, to remove dissolved phosphorus, jar test was the only process required to determine the coagulant dosage for meeting effluent standards.

Gas transport properties of CoAlPO4‐5/PC membranes

The transport phenomena of oxygen and nitrogen across a pure polycarbonate (PC) and CoAlPO4-5/PC membranes were studied. Various CoAlPO4-5 membranes with different cobalt content were added to polycarbonate membranes to improve the gas transport performance. Oxygen and nitrogen isotherms were studied. Solubility of oxygen and nitrogen was greatly increased by adding CoAlPO4-5 to the membranes, which also resulted in a higher solubility ratio of oxygen to nitrogen. It might be that a pinhole of the membrane caused the increase in diffusivity and a decrease in selectivity when excess CoAlPO4-5 was added. The results also showed that CoAlPO4-5 with a higher cobalt content would more effectively increase the gas solubility, but make only a minor change in the solubility ratio of oxygen to nitrogen. It was found that the increase in oxygen to nitrogen selectivity was mainly due to an increased diffusivity ratio of oxygen to nitrogen when CoAlPO4-5 was added into the membranes.