Operation with Zinc Oxide

Up to about 10 ppm of low molecular weight mercaptans can be removed from natural gas without hydrogen addition, provided that the reaction tempera- 

By increasing the porosity of the absorbent the sulfur absorption can be increased by 200% in the range ambient to 100°C and almost 100% at 200°C.  

Carbonyl sitlfide may be formed ditring natural gas treatment by the reaction of hydrogen sitlfide and carbon dioxide and this can be difficult to remove completely using zinc oxide alone. This is not a problem if a bed of cobalt molybdate catalyst is included in the desulfurizer. It has been shown that lead oxide is an efficient absorbent of earboityl sulfide so the natural lead oxide impurity in some zinc oxides may promote absorption, espeeially if traees of water vapour are present to hydrolyze the carbonyl sulfide. 

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Grain boundary defects are primarily responsible for the operation of zinc oxide (ZnO) varistors, a shortened form of variable resistor. The varistor behaves like an insulator or poor semiconductor at lower electrical field strengths, but at a critical breakdown voltage the resistance decreases enormously and the material behaves like an electrical conductor (Fig. 3.36). When a varistor is connected in parallel with electrical equipment, negligible power flows through it under normal low... 

Validation of the cleaning process has to be done before operating. As difficult to clean objects utensils contaminated with zinc oxide paste (if desired with 3 % brown iron oxide) can be recommended. The validation should be repeated periodically, e.g. yearly, or at any time utensils are not clean after washing up or when new utensils are introduced. Results should be documented. 

Low-Temperature Shift (LTS) catalysts are copper-based catalysts which operate at temperatures as low as 185-225°C [232] [303] [391], They may in principle operate at even lower temperatures, but limited by the dew point of the process gas. The commercial catalysts are typically based on Cu/ZnO/A Os. The active phase is copper in close coimection with zinc oxide. Although the activity relates to the copper surface area, the role of the zinc oxide is still being discussed [216] [232], as is the reaction mechanism [207] [337],... 

Recent work by Flytzani-Stephanopoulos et al. dealt with lanthana and ceria adsorbents, which were operated at high temperatures of up to 800 °C for solid oxide fuel cell applications [299]. However, their adsorption capacity was much lower compared with zinc oxide, in the region of 0.001 g S per g adsorbent. 

The XeroX Copier Machine Model A was announced in 1949, and involved compHcated manual operation. Copies of acceptable quaUty were operator dependent. The Copyflo printer, introduced in 1955, was the first automated xerographic machine and enabled the production of copies on a continuous web of ordinary paper. Early electrophotographic products used paper coated with dye-sensitized zinc oxide Electrofax which had met market resistance in terms of aesthetics and cost, so that in 1958 the total market was only about 100 million (1—3,5). 

In the blast furnace reduction slag-making materials are also added together with a small amount of iron, the function of which is to reduce any sulphide which remains, to the product of the roasting operation to produce a sinter. The sinter is then reduced with coke in a vertical shaft blast furnace in which air is blown tluough tuyeres at the bottom of tire shaft. The temperature in the heartlr where metal is produced must be controlled to avoid the vaporization of any zinc oxide in the sinter. The products of tlris process are normally quite complex, and can be separated into four phases. Typical compositions of these are shown in Table 13.1. 

This continuous process is to be compared with a batch process, such as the Belgian retort process. In this, zinc oxide, free of lead or iron is reduced with carbon to produce zinc vapour, which is condensed in the cold section of the retort. The oxygen potential in this system is very much lower dran in the blast furnace, approximately at the C/CO equilibrium value. A vacuum-operated variant of dris level of reduction is caiTied out to produce zinc vapour which is subsequently converted to zinc oxide before condensation of the metal could take place. 

The impressed current method with metal oxide-coated niobium anodes is usually employed for internal protection (see Section 7.2.3). In smaller tanks, galvanic anodes of zinc can also be used. Potential control should be provided to avoid unacceptably negative potentials. Pure zinc electrodes serve as monitoring and control electrodes in exposed areas which have to be anodically cleaned in the course of operation. Ag-AgCl electrodes are used to check these reference electrodes. 

You might wonder what we would have learned if we had assumed that either of these two cells operates with the reverse reaction. Suppose we had proposed a cell based on oxidation of nickel and reduction of zinc ... 

As an example of the latter technique, Volkman et al. demonstrated the feasibility of using spin-cast zinc oxide nanoparticles encapsulated in 1-dodecanethiol to fabricate a functional transistor.44 The zinc oxide was deposited on a thermally grown silicon dioxide layer on a conventional silicon wafer, with thermally evaporated gold source and drain electrodes. As reported, the process requires very small particles (3nm or less) and a 400 °C forming gas anneal. A similar approach was also reported by Petrat, demonstrating n-channel thin-film transistor operation using a nanoparticle solution of zinc oxide dispersed onto a thermally grown silicon dioxide layer on a conventional... 

French Also known as the Indirect process. A process for making zinc oxide, in the form of a white pigment, from metallic zinc. The zinc is melted and vaporized in a current of carbon monoxide. The vapor is oxidized with air in a second chamber, forming zinc oxide and carbon dioxide. The fume passes through a settling chamber, where oversized particles settle out, and from there go to a bag house, where the product is collected. Confusingly, the French process has been operated by North American Oxide Company, at Clarksville, TN. See also American. 

New Jersey A continuous process for extracting zinc from zinc oxide, made by roasting zinc sulfide ore, by reduction with carbon in a vertical retort. First operated by the New Jersey Zinc Company in Palmerton, PA, in 1929, and introduced into the Avonmouth, UK, works of the Imperial Smelting Company in 1934. 

For example, a COS hydrolysis reactor needs to operate at about 180°C (350°F), the ammonia and acid scrubbers need to be in the vicinity of 40°C (100°F), while the zinc oxide polishers need to be about 370°C (700°F). Thus, gasification systems with cold gas cleanup often become a maze of heat exchange and cleanup systems. 

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