Cobalt-molybdenum-zinc oxide

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

In addition to the above, preparation in w/o microemulsions of nanoparticles of various other types of compounds, viz. silica-coated iron oxide, Fe203-Ag nanocomposite, oxides of ytrium, erbium, neodymium, vanadium and cobalt, titanates of barium and lead, ferrites of barium, strontium, manganese, cobalt and zinc, oxide superconductors, aluminates, zirconium silicate, barium tungstate, phosphates of calcium, aluminium and zinc, carbonates of calcium and barium, sulphides of molybdenum and sodium, selenides of cadmium and silver etc. have been reported. Preparative sources and related elaboration can be found in [24]. 

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. 

Although all of the above elements catalyze hydrogenation, only platinum, palladium, rhodium, ruthenium and nickel are currently used. In addition some other elements and compounds were found useful for catalytic hydrogenation copper (to a very limited extent), oxides of copper and zinc combined with chromium oxide, rhenium heptoxide, heptasulfide and heptaselen-ide, and sulfides of cobalt, molybdenum and tungsten. 

The raw minerals mined from natural deposits comprise mixtures of different specific minerals. An early step in mineral processing is to use crushing and grinding to free these various minerals from each other. In addition, these same processes may be used to reduce the mineral particle sizes to make them suitable for a subsequent separation process. Non-ferrous metals such as copper, lead, zinc, nickel, cobalt, molybdenum, mercury, and antimony are typically produced from mineral ores containing these metals as sulfides (and sometimes as oxides, carbonates, or sulfates) [91,619,620], The respective metal sulfides are usually separated from the raw ores by flotation. Flotation processes are also used to concentrate non-metallic minerals used in other industries, such as calcium fluoride, barium sulfate, sodium and potassium chlorides, sulfur, coal, phosphates, alumina, silicates, and clays [91,619,621], Other examples are listed in Table 10.2, including the recovery of ink in paper recycling (which is discussed in Section 12.5.2), the recovery of bitumen from oil sands (which is discussed further in Section 11.3.2), and the removal of particulates and bacteria in water and wastewater treatment (which is discussed further in Section 9.4). 

In the steam-reforming process, any sulfur compounds present in the hydrocarbon feedstock have to be removed because the nickel-containing catalysts are sensitive to poisons. This is either achieved by hydrodesulfurization (see Hydrodesulfurization Hydrodenitrogenation), generally with a combination of cobalt-molybdenum and zinc oxide... 

Iron-chromium oxide catalysts, reduced with hydrogen-containing in the conversion plants, permit reactions temperatures of 350 to 380°C (high temperature conversion), the carbon monoxide content in the reaction gas is thereby reduced to ca. 3 to 4% by volume. Since, these catalysts are sensitive to impurities, cobalt- and molybdenum-(sulfide)-containing catalysts are used for gas mixtures with high sulfur contents. With copper oxide/zinc oxide catalysts the reaction proceeds at 200 to 250°C (low temperature conversion) and carbon monoxide contents of below 0.3% by volume are attained. This catalyst, in contrast to the iron oxide/chromium oxide high temperature conversion catalyst, is, however, very sensitive to sulfur compounds, which must be present in concentrations of less than 0.1 ppm. 

Alumina catalysts activated by additions of dehydrogenating catalysts, e.g., nickel oxide, copper oxide or sulfide, zinc oxide or sulfide, cobalt selenide, zinc phosphate, cadmium tungstate, mixtures of the oxides of zinc and tungsten, of cadmium and molybdenum, etc., are claimed to be superior in the formation of acetaldehyde from mixtures of steam and acetylene at 350° to 400° C.l-la Zinc oxide catalysts may be activated in a similar way by the addition of small amounts of molybdates or molybdic acid, and are effective at 300° to 350° C.121b... 

The elements beryllium, magnesium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zinc, zirconium, molybdenum, silver, cadmium, tin, thallium, lead, and bismuth mainly occur in the crystal structures of rock-forming silicates and oxides of the common rocks in the Earths crust. These elements - with the exception of magnesium, iron, titanium, chromium, and zirconium - are trace elements in the minerals. They follow certain rules as reported by Goldschmidt (1954) in their ten-... 

Many enzymes incorporate one or more metal ions as essential parts of their structure. Different metalloenzymes make use of ions of magnesium, calcium, manganese, iron, cobalt, copper, zinc, or molybdenum. For example, the molecule of alcohol dehydrogenase (molecular mass 87000 d), which catalyzes the oxidation of ethanol to acetic acid in the human liver, contains two atoms of zinc, and the amylase in human saliva contains an atom of calcium (Ca" " ). Some enzyme molecules contain several metal atoms, which may be of different kinds. An example is cysteamine oxidase, which catalyzes the oxidation of cysteamine, HSCH2CH2NH2 this enzyme contains an atom of iron, an atom of copper, and an atom of zinc. 

In cases where the natural gas contains stable organic sulfur compounds, it is necessary to use a hydrogenation catalyst, such as cobalt-molybdenum, ahead of the zinc oxide bed to... 

For desulfurization of naphtha, a more complicated process is required. Hydrodesulfurization quite often is used. About 0.5 mole of H2 is mixed with 1 mole of vaporized naphtha or 250 scf (Standard Cubic Feet) per barrel, depending upon the sulfur and olefin content. The mixture is preheated to 320 "C and passed over a cobalt-molybdenum catalyst, where the olefins are hydrogenated to paraffin hydrocarbons and the sulfur compounds are reduced to H2S. The gas then is passed over a sulfur adsorbent such as iron or zinc oxide. It may or may not be necessary to condense the naphtha, depending upon the amount of hydrogen used and the need to remove it from the naphtha. 

As mentioned above, approximately 7% of the total sulfur present in lead ore is emitted as S02. The remainder is captured by the blast furnace slag. The blast furnace slag is composed primarily of iron and silicon oxides, as well as aluminum and calcium oxides. Other metals may also be present in smaller amounts, including antimony, arsenic, beryllium, cadmium, chromium, cobalt, copper, lead, manganese, mercury, molybdenum, silver, and zinc. This blast furnace slag is either recycled back into the process or disposed of in piles on site. About 50 to 60% of the recovery furnace output is slag and residual lead, which are both returned to the blast furnace. The remainder of this dross furnace output is sold to copper smelters for recovery of the copper and other precious metals. 

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