Wet oxidation

About: Wet oxidation is a research topic. Over the lifetime, 3094 publications have been published within this topic receiving 61536 citations.

Oxidation of silicon carbide in a wet atmosphere

Abstract: The effects of water vapour on oxidation of pressureless-sintered silicon carbide containing alumina as a densifying aid were studied in a wet air flow with 10, 20, 30 and 40vol% H2O at 1300° C for 100h. The oxidation kinetics were determined in a wet air flow with 20 vol % H2O and in a dry air flow at 1300° C for times up to 360 h. The weight gain on oxidation showed an increasing tendency with increasing water vapour content. Water vapour in the atmosphere strongly influenced oxidation and accelerated the reaction. Oxidation in a wet atmosphere proceeded in a diffusion-controlled manner, in the same process as that for the dry atmosphere. No remarkable differences were noticed in the microstructure of the oxide layer and the surface roughness between the samples oxidized under the four wet conditions, but the surface roughness increased with increasing oxidation time. Water vapour evidently accelerated the devitrification of amorphous silica and promoted oxidation. Oxidation in a wet atmosphere (10 to 40 vol % H2O for 100 h and 20 vol % H2O up to 360 h) had a slight degrading effect on the flexural strength. The microstructure or surface roughness of the oxide layer formed during oxidation presumably had very little effect on the room-temperature strength.

Catalytic wet air oxidation of aqueous ammonia with activated carbon

Abstract: The oxidation of aqueous ammonia to nitrogen by the catalytic wet air oxidation (CWAO) process with activated carbon as catalyst was studied. A commercial activated carbon CUDU1000 chemically modified by oxidation with HNO3 and/or reduction with H2 was used. The characterization of the activated carbons was carried out by N2 adsorption, thermal programmed decomposition (TPD), Fourier transformed infrared (FTIR) spectroscopy, Boehm titration and zero point charge (ZPC) techniques. Studies of aqueous ammonia adsorption on the activated carbons under atmospheric conditions showed that carboxylic, lactonic and anhydride surface groups increase both the rate and capacity of adsorption. The oxidized carbons had lower activity towards selective aqueous ammonia oxidation in CWAO process because of a strong ammonia adsorption. However, hydrogenated activated carbons had higher activity for selective aqueous ammonia oxidation. It is establish that a strong ammonia adsorption takes place onto carboxylic, lactonic and/or anhydride surface groups while the quinonic surface groups are responsible of the catalytic activity shown by these carbons.

Fe-zeolites as catalysts for chemical oxidation of MTBE in water with H2O2

Abstract: The heterogeneous catalytic wet oxidation of methyl tert-butyl ether (MTBE) with hydrogen peroxide, catalyzed by the iron-containing zeolites Fe-ZSM5 and Fe-Beta, was studied at ambient conditions and pH 7. The kinetics of MTBE degradation could be well-fitted to a pseudo-first-order model. Using Fe-ZSM5, the dependence of the reaction rate constant on hydrogen peroxide and catalyst concentration was determined. Furthermore, the formation and oxidation of tert-butyl alcohol and tert-butyl formate as intermediates of MTBE oxidation were studied. A comparison of the reaction rates of MTBE, trichloroethylene and diethyl ether in the Fe-ZSM5/H 2 O 2 system revealed that adsorption plays a positive role for the degradation reaction. Comparing the two types of Fe-containing zeolites applied in this study, Fe-Beta showed a lower catalytic activity for H 2 O 2 decomposition and also MTBE degradation. However, in terms of utilization of H 2 O 2 for MTBE degradation Fe-Beta is advantageous over Fe-ZSM5. This could be explained by the stronger adsorptive enrichment of MTBE on the Fe-Beta zeolite. This study shows that Fe-containing zeolites are promising catalysts for oxidative degradation of MTBE by H 2 O 2 .

Catalytic wet air oxidation of dye pollutants by polyoxomolybdate nanotubes under room condition

Abstract: In order to develop a catalyst with high activity and stability for catalytic wet air oxidation of pollutant dyes at room condition, a new polyoxometalate Zn1.5PMo12O40 with nanotube structure was prepared using biological template. The structure and morphology were characterized using infrared (IR) spectra, UV–vis diffuse reflectance spectra (DR-UV–vis), elemental analyses, X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). And the degradation of Safranin-T (ST), a hazardous textile dye, under air at room temperature and atmospheric pressure was studied as a model experiment to evaluate the catalytic activity of this polyoxomolybdate catalyst. The results show that the catalyst has an excellent catalytic activity in treatment of wastewater containing 10 mg/L ST, and 98% of color and 95% of chemical oxygen demand (COD) can be removed within 40 min. And the organic pollutant of ST was totally mineralized to simple inorganic species such as HCO3−, Cl− and NO3− during this time (total organic carbon (TOC) decreased 92%). The structure and morphology of the catalyst under different cycling runs show that the catalyst are stable under such operating conditions and the leaching tests show negligible leaching effect owning to the lesser dissolution. So this polyoxomolybdate nanotube is proved to be a heterogeneous catalyst in catalytic wet air oxidation of organic dye.