Catalyst continued wetting

Determination of surface chemical states of CoOj/TiOi catalysts for continuous wet TCE oxidation... 

Some slurry processes use continuous stirred tank reactors and relatively heavy solvents (57) these ate employed by such companies as Hoechst, Montedison, Mitsubishi, Dow, and Nissan. In the Hoechst process (Eig. 4), hexane is used as the diluent. Reactors usually operate at 80—90°C and a total pressure of 1—3 MPa (10—30 psi). The solvent, ethylene, catalyst components, and hydrogen are all continuously fed into the reactor. The residence time of catalyst particles in the reactor is two to three hours. The polymer slurry may be transferred into a smaller reactor for post-polymerization. In most cases, molecular weight of polymer is controlled by the addition of hydrogen to both reactors. After the slurry exits the second reactor, the total charge is separated by a centrifuge into a Hquid stream and soHd polymer. The solvent is then steam-stripped from wet polymer, purified, and returned to the main reactor the wet polymer is dried and pelletized. Variations of this process are widely used throughout the world. 

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. 

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. 

All the supported catalysts used gave TCE conversions less than 20% for the wet oxidation at 310 K, except for the 5 wt.% CoOx/Ti02, which had a steady-state conversion of 45% via a transient behavior in activity up to 1 h on stream (Fig. 1). Subsequently, there was negligible TCE conversion for the bare Ti02 during continuous operating hours near 6. 

From an operations and maintenance perspective the system has also been excellent. Over the first several months of operation, the RCC experienced mnltiple process npsets that resnlted in as mnch as 20-30% of the catalyst inventory being carried ont of the regenerator and into the wet scrubbing system. The wet scrubber readily handled all of these process upsets. The operation of the scrubber was not interrupted. The system continued to operate. 

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