Catalytic wet oxidation

A 5 wt.% CoOx/Ti02 catalyst gave the most promising activity for continuous catalytic wet oxidation of trichloroethylene at 310 K with a unsteady-state behavior up to 1 h. The catalyst after the oxidation possessed a Co 2p3/2 main peak at 779.8 eV, while the peak was obtained at 781.3 eV for a fiosh sample. Only reflections for C03O4 were indicated for these samples upon XRD measurements. The simplest model for nanosized C03O4 particles existing with the fi"esh catalyst could reasonably explain the transient activity behavior. 

Wastewaters containing chlorinated hydrocarbons (CHCs) are very toxic for aquatic system even at concentrations of ppm levels [1] thus, appropriate treatment technologies are required for processing them to non-toxic or more biologically amenable intermediates. Catalytic wet oxidation can offer an alternative approach to remove a variety of such toxic organic materials in wet streams. Numerous supported catalysts have been applied for the removal of aqueous organic wastes via heterogeneous wet catalysis [1,2]. 

Although catalytic wet oxidation of acetic acid, phenol, and p-coumaric acid has been reported for Co-Bi composites and CoOx-based mixed metal oxides [3-5], we could find no studies of the wet oxidation of CHCs over supported CoO catalysts. Therefore, this study was conducted to see if such catalysts are available for wet oxidation of trichloroethylene (TCE) as a model CHC in a continuous flow fixal-bed reactor that requires no subsequent separation process. The supported CoOx catalysts were characterized to explain unsteady-state behavior in activity for a certain hour on stream. 

Figure 2. Removal of TOC(—) and color(—) during the catalytic wet oxidation of the real dyehouse effluent with lOg 10wt% CU/AI2O3...

Figure 6. Removal of TOC( ) and color(A) during catalytic wet oxidation of a real dyehouse effluent with 10wt% CU/AI2O3 in the continuous flow system.

Wet oxidation is a process where organic contaminants in liquids or soils are extracted into an aqueous phase and reacted with an oxidant at high temperature (220-290°C) and pressures (100-250 bar) to promote rapid destruction. Laari et al. [67] evaluated the efficiency of wet oxidation for the treatment of TMP processing waters. The major objective of this research was to reduce the concentration of lipophilic wood extractives (LWE) and to treat concentrated residues from evaporation and membrane filtration by low-pressure catalytic wet oxidation. 

For example, the most noteworthy disadvantage of catalytic wet oxidation is the severe catalyst deactivation (Larachi el al., 1999). Hamoudi el al. (1998, 1999) systematically studied the deactivation of Mn02/Ce02 catalyst during wet catalytic oxidation of phenol and the catalyst-surface modifications. It was observed that deactivation was induced mainly by the formation of carbonaceous deposits on the catalyst surface. Ohta et al. (1980) reported that the size of the catalyst particles affected the stabilization of catalytic activity. For granular particles of supported copper oxide, the catalytic activity was decreased after each inn, even after six successive experiments. In contrast, for larger particles the catalytic activity was stabilized after the first three runs. 

Chang CJ, Li S, Ko C. Catalytic wet oxidations of Phenol and p-Chlorophenol-contaminated waters. J Chem Technol Biotechnol 1995 64 245-252. 

CALIPHOX A catalytic wet oxidation process for destroying organic wastes in water, using atmospheric oxygen as the oxidant. The organic material is preconcentated by adsorption on activated carbon, and then desorbed using hot water. Developed at the National Institute of Chemistry in Slovenia. 

An obvious disadvantage is the high energy requirement for attaining process conditions. Lower operation costs and safety risks can be achieved with more moderate conditions by adding selected catalysts (catalytic wet oxidation). 

A STUDY ON CATALYTIC WET OXIDATION OF SIMULATED WASTEWATER SUCCINIC ACID AQUEOUS SOLUTION WITH Ru/TiOj CATALYST... 

Luck F., A review of industrial catalytic wet oxidation processes. Catal. Today, 27 (1996) pp. 195-202. 

Qin J. Y., Zhang Q. L., Karl. T. Chuang K. T., Catalytic wet oxidation of p-chlorophenol over supported noble metal catalysts. Appl. Catal. B Environ., 29 (2001)pp. 115-123. 

Removal of pollutants from waste waters (Catalytic wet oxidation)... 

Whether heterogeneous catalysts are practically used widely or not depends sorely on the their stability. If the problems concerning poisoning by carbonaceous deposits and leaching of the catalyst components are solved, catalytic wet-oxidation (CWO) process will have a highly promising future. 

The use of CeOs-based materials in catalysis has attracted considerable attention in recent years, particularly in applications like environmental catalysis, where ceria has shown great potential. This book critically reviews the most recent advances in the field, with the focus on both fundamental and applied issues. The first few chapters cover structural and chemical properties of ceria and related materials, i.e. phase stability, reduction behaviour, synthesis, interaction with probe molecules (CO. O2, NO), and metal-support interaction — all presented from the viewpoint of catalytic applications. The use of computational techniques and ceria surfaces and films for model catalytic studies are also reviewed. The second part of the book provides a critical evaluation of the role of ceria in the most important catalytic processes three-way catalysis, catalytic wet oxidation and fluid catalytic cracking. Other topics include oxidation-combustion catalysts, electrocatalysis and the use of cerium catalysts/additives in diesel soot abatement technology. 

Figure 10. Proposed pathways for catalytic wet oxidation of phenol Pt/Al203 catalyst.

Catalytic wet oxidation of phenol was carried out with lwt% Pt/AlaOa and lwt% Pt/Ce02 in a batch reactor operated at 423 K and 1.4 MPa. 

Figure 5.5 Experimental and predicted concentration profiles for combined thermolysis, catalytic, and non-catalytic wet oxidation of high-strength alcohol distillery liquor over Mn02/Ce02 catalyst. Adopted from Ref. ...

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