Zinc oxide desulfurizer

The role of Co-Mo based hydrogenation catalysts is to convert organic sulfur compounds to H2S. The catalyst itself has limited ability for the removal of produced H2S, and only (1%3%) sulfur can be adsorbed by these catalysts even under equilibrium conditions. Thus, zinc oxide is used to remove H2S after hydrogenation procedure in industry. Some organic sulfur compounds can also be removed simultaneously by zinc oxide. 

Simultaneously, some organic sulfur compounds are also absorbed by zinc oxide. 

Thermodynamically, the above-mentioned reactions are irreversible at the temperature range of 200°C-400°C, and therefore sulfur can be removed completely. 

Iron oxide is another important desulfurizer and its reaction mechanism is the same as that of zinc oxide. Because the reaction conditions, e.g., steam content, must be controlled strictly when iron oxide is used. Zinc oxide is widely used in industry although the price of iron oxide is lower. 

Desulphurization is a typical gas-solid absorbing reaction on zinc oxide. Sulfur adsorption capacity with the mass fraction of sulfur absorbed per gram catalyst is about one percent if only surface zinc oxide is reactive. Therefore, the desulphmiza-tion performance of zinc oxide adsorbent not only depends on the content of zinc oxide, but also on the utilization ratio of zinc oxide (related to porous structme and surface area), and thereby preparation conditions. It is commonly proposed that the zinc oxide prepared from zinc carbonate possesses small crystal size, high smface areas and therefore good desulphurization performances. 

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During ammonia synthesis, the major reactions of production and purification of synthesis gas and the synthesis of ammonia, all are carried out over different catalysts. At least eight kinds of catalysts are used in the whole process, where natural gas or naphtha is used as feedstock and steam reforming is used to produce synthesis gas. These catalysts are Co-Mo hydrogenation catalyst, zinc oxide desulfurizer, primary- and secondary-steam reforming catalysts, high- and low-temperature shift catalysts, methanation catalyst and ammonia synthesis catalyst etc (Table 1.1). 

The eight kinds of catalysts may be roughly classified as protective catalysts and economic catalysts . Co-Mo hydrogenation catalyst and zinc oxide desulfurizer are the protective catalysts for the primary steam reforming catalysts. The high-temperature shift catalyst protects the low-temperature shift catalyst, and the methanation catalyst are the protective catalyst for ammonia synthesis catalyst. The catalysts for primary- and secondary-steam reforming, low-temperature shift and ammonia synthesis are responsible for the conversions of raw materials and the yield of products, and have direct effect on economic benefits of the whole plant, and are thus called as economic catalysts. The amount of catalysts used depends on the process and raw material. Table 1.2 represents the amount of the eight kinds of catalysts used in the different processes. The total volume of the catalysts is about 330 m in every plant, while there are only two kinds of catalysts with the volume of about 100-140 m when heavy oil or coal is used as raw material. Both shift... 

Composition, structure, and preparation. Zinc oxide desulfurizer is... 

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

ELSE [Extremely low sulphur emission] A flue-gas desulfurization process in which the sulfur dioxide is absorbed by zinc oxide. Developed by Amoco, United States. 

At least one developer is developing a liquid-phase fuel desulfurizer cartridge that will be used to remove sulfur prior to fuel vaporization. Other developers remove the sulfur immediately after vaporization and prior to the reforming. Hydrogen needs to be recirculated to the removal device to convert the sulfur species to H2S so that it can be entrapped on zinc oxide, a complication. 

Zinc oxide is used as a raw material for many products stearates, phosphates, chromates, bromates, organic dithiophosphates, and ferrites (ZnO, MnO, Fe203). It is used as a source of zinc in animal feeds and in electrogalvanization. It is also used for desulfurizing gases. 

Desulfurization reactions in the 1,2-series are encountered among derivatives of both oxathiins and dithiins. 1,2-Oxathiin 2,2-dioxides extrude sulfur dioxide at elevated temperature over zinc oxide, iron or copper oxide to give the corresponding furan (66HC(21 -2)789) [cf. Section 2.26.3.1.2). Copper is a good catalyst for the extrusion of sulfur and sulfur dioxide from dibenzo[c,e3[l,2]dithiin (40) and its dioxide respectively to give dibenzothiophene (66HC(21-2)968). 

Natural gas feedstock enters the fuel processing subsystem at about 63 psig (4,5 atm). The fuel is first processed in hydrodesulfurizing unit (HDS) and zinc-oxide (ZnO) beds lo remove any sulfur compounds. The desulfurized fuel is mixed with process steam and preheated to about 850°F (454cC) before entering the reformer, which consists of reactor tubes containing a... 

In the actual process (Figure 10-5), the natural gas feedstock must first be desulfurized in order to prevent catalyst poisoning or deactivation. The desulfurization step depends upon the nature of the sulfur-containing contaminants and can vary from the more simple ambient temperature adsorption of the sulfur-containing materials on activated charcoal to a more complex high-temperature reaction with zinc oxide to catalytic hydrogenation followed by zinc oxide treatment. 

Brief Process Description of Davy s Latest High Efficiency Design. Natural gas is desulfurized over an activated carbon bed or zinc oxide to remove sulfur below 0.2 ppm, suitable for natural gas reforming. 

There are many methods for the desulfurization of nature gas, which can be classified into dry desulfurization, wet desulfurization, and catalytic adsorption. In the dry desulfurization, some solid sorbents, such as iron oxide, zinc oxide, activated carbon (AC), zeolites, and molecular sieves, are used. In wet desulfurization method, liquid-phase chemical/physical solvent absorption systems are usually used for scrubbing H2S amine-based processes are subject to equipment corrosion, foaming, amine-solution degradation, and evaporation, and require extensive wastewater treatment. As a result, this sulfur removal technology is complex and capital intensive,44 although the processes are still employed widely in the industry. The desulfurization of coal gasification gas will be reviewed in detail in Section 5.5. In the catalytic-adsorption method, the sulfur compounds are transformed into H2S by catalytic HDS or into elemental sulfur or SOx by selective catalytic oxidation (SCO), and then, the reformed H2S and SOx are removed by the subsequent adsorption. 

Natural gas or light hydrocarbons that serve as feed gas in the synthesis of ammonia contain sulfur compounds that act as poisons for the nickel catalyst used in synthesis gas production. Hydrogen sulfide and mercaptans are the dominant sulfur species in natural gas, while the light hydrocarbons may contain higher boiling sulfur species. A fixed-bed reactor containing zinc oxide is often used to desulfurize the feed gas. The chemical reaction with hydrogen sulfide is... 

Considerable effort has been expended over the last few years to extend the use of zinc oxide to the desulfurization of coal-derived gases. Harrison has described these efforts. The much higher inlet sulfur concentrations in this application require that the sorbent be regenerated so that it can be used for multiple cycles. 

In the production of hydrogen, pressurized natural gas is desulfurized over active carbon or hot zinc oxide, mixed with steam to give the required steam-to-feedstock carbon molar ratio (typically three to one) and then steam-reformed. 

Zinc Oxide. New ammonia plants use zinc oxide (ZnO) beds to desulfurize entirely or provide the final step for the feedstock and operate as per the following reaction ... 

Impurities such as chlorine, arsenic, and nickel used in the manufacturing process tend to shorten the life of the catalyst. The usual methods for desulfurization are by activated carbon adsorption at about 15 to 50°C or oxidation with zinc oxide or both. The use of zinc oxide is often preferred when large quantities of mercaptans and highly condensable hydrocarbons are present, which may quickly saturate the catalysts. The main function of the zinc oxide is to remove the hydrogen sulfide, mercaptans and chlorine. Combining activated carbon and zinc oxide is very effective in removing the different types of sulfide compounds. 

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