Zinc impregnated carbons

The process is carried out in the gas phase at a temperatures above 160°C. The reaction is exothermic, so heat control in the production process is important. Vinylacetate is used as intermediate in a large number of production processes. The catalysts can be produced by impregnation of an activated carbon with zinc acetate, followed by drying. The zinc concentration is in the order of 11 up to 13%. The optimal activated carbon support is a high steam activated and acid washed 3 or 4 mm extrudate like the NORIT RX 3 EXTRA or NORIT RX 4 EXTRA. Important characteristics of the impregnated carbon are ... 

Preactivated and Water-Activated Types. A typical preactivated industrial-type zinc/air cell, the Edison Carbonaire cell, is manufactured in a 1100-Ah size and is available in two-and three-eell configurations, as illustrated in Fig. 38.12. The cell case and cover are molded from a tinted transparent acrylic plastic. The construction features are shown in Fig. 38.13 identifying the wax-impregnated carbon cathode block, the solid zinc anodes, and the lime-filled reservoir. These cells normally have a bed of lime to absorb carbon dioxide and to remove soluble zinc compounds from solution and precipitate them as calcium zincate. They are made with transparent cases so that the electrolyte level and the state of charge can be monitored visually. The state of charge can be monitored by observing the condition of the zinc plates and the condition of the lime bed. The bed turns darker as it is converted to zincate. 

Figure 31. However, the oxidation resistance can be improved by impregnation with inhibitors, especially zinc phosphate, which prevents weight loss to about 600°C (32,49). At higher temperatures up to 1400°C, SiC coatings are proving successful, if repeated but only short-time heating is considered (56), as in the case of a reentry space vehicle. An SiC-impregnation process using tetraethylorthosilicate (TEOS) was used to impregnate the "all-carbon parts of the space shuttle COLUMBIA (9).

Table V. Effect of Light and Humidity0 on Book Papers Impregnated with Zinc Carbonate...

Activation always involves some form of chemical attack. However, chemical activation is a term often used to indicate the prior impregnation of the precursor with a chemical agent such as phosphoric acid or zinc chloride before heat treatment. Physical activation, on the other hand, signifies the heat treatment of the char in a mildly reactive atmosphere such as steam or carbon dioxide. This type of process is preferably referred to as thermal activation (Baker, 1992). The apparent distinction between chemical and physical is somewhat unsatisfactory for two reasons first, it implies a fundamental difference in the mechanism of activation and second, it does not allow for the many procedures which involve both types of treatment. 

The same authors [118] reduced CO2 using carbon gas diffusion electrodes impregnated with metal (cobalt(II), copper, zinc, or manganese) phthalocyanine. High... 

Most types of metallic ions are not appreciably adsorbed by activated carbon, unless special conditions are provided. Co-adsorbates are often useful. Thus, mercaptobenzothiazole will enable carbon to remove lead and zinc from an aqueous solution. Usually, the carbon is impregnated with the co-adsorbate before use, but, in some cases, the co-adsorbate can be added directly to the solution. Appropriate control of the pH is often necessary to accomplish selective adsorption and to provide a subsequent desorption. 

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