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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
The direct process, also called the direct synthesis, Rochow process, and Müller-Rochow process is the most common technology for preparing organosilicon compounds on an industrial scale. It was first reported independently by Eugene G. Rochow and Richard Müller in the 1940s.[1][2]
The process involves copper-catalyzed reactions of alkyl halides with elemental silicon, which take place in a fluidized bed reactor. Although theoretically possible with any alkyl halide, the best results in terms of selectivity and yield occur with chloromethane (CH3Cl). Typical conditions are 300 °C and 2–5 bar. These conditions allow for 90–98% conversion for silicon and 30–90% for chloromethane. Approximately 1.4 Mton of dimethyldichlorosilane (Me2SiCl2) is produced annually using this process.[3]
Few companies actually carry out the Rochow process, because of the complex technology and high capital requirements. Since the silicon is crushed prior to reaction in a fluidized bed, the companies practicing this technology are referred to as silicon crushers.[4]
The relevant reactions are (Me = CH3):
Dimethyldichlorosilane (Me2SiCl2) is of particular value (precursor to silicones), but trimethylsilyl chloride (Me3SiCl) and methyltrichlorosilane (MeSiCl3) are also valuable.[5]: 371
The mechanism of the direct process is still not well understood, despite much research. Copper plays an important role, and almost certainly forms an intermetallic with the approximate composition Cu3Si.[6] This intermediate facilitates the formation of the Si-Cl and Si-Me bonds. It is proposed that close proximity of the Si-Cl to a copper-chloromethane "adduct" allows for formation of the Me-SiCl units. Transfer of a second chloromethane allows for the release of the Me2SiCl2. Thus, copper is oxidized from the zero oxidation state and then reduced to regenerate the catalyst.[1]
The chain reaction can be terminated in many ways. These termination processes give rise to the other products that are seen in the reaction. For example, combining two Si-Cl groups gives the SiCl2 group, which undergoes Cu-catalyzed reaction with MeCl to give MeSiCl3.[1]
In addition to copper, the catalyst optimally contains promoter metals that facilitate the reaction. Tin is necessary, and synergistic with zinc; but extremely minute quantities of many other promoter metals appear to influence the reaction. Among the many promoter metals, iron, aluminum, titanium, manganese, nickel, lead, phosphorus,[7] antimony, magnesium, calcium, bismuth, arsenic, and cadmium have been mentioned.[1][3]
The major product for the direct process should be dichlorodimethylsilane, Me2SiCl2. However, many other products are formed. Unlike most reactions, this distribution is actually desirable because the product isolation is very efficient.[1] Each methylchlorosilane has specific and often substantial applications. Me2SiCl2 is the most useful. It is the precursor for the majority of silicon products produced on an industrial scale. The other products are used in the preparation of siloxane polymers as well as specialized applications.[1]
Dichlorodimethylsilane is the major product of the reaction, as is expected, being obtained in about 70–90% yield. The next most abundant product is methyltrichlorosilane (MeSiCl3), at 5–15% of the total. Other products include Me3SiCl (2–4%), MeHSiCl2 (1–4%), and Me2HSiCl (0.1–0.5%).[1]
The Me2SiCl2 is purified by fractional distillation. Although the boiling points of the various chloromethylsilanes are similar (Me2SiCl2: 70 °C, MeSiCl3: 66 °C, Me3SiCl: 57 °C, MeHSiCl2: 41 °C, Me2HSiCl: 35 °C), the distillation utilizes columns with high separating capacities, connected in series. The purity of the products crucially affects the production of siloxane polymers, otherwise chain branching arises.[1]
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
The direct process, also called the direct synthesis, Rochow process, and Müller-Rochow process is the most common technology for preparing organosilicon compounds on an industrial scale. It was first reported independently by Eugene G. Rochow and Richard Müller in the 1940s. The process involves copper-catalyzed reactions of alkyl halides with elemental silicon, which take place in a fluidized bed reactor. Although theoretically possible with any alkyl halide, the best results in terms of selectivity and yield occur with chloromethane (CH3Cl). Typical conditions are 300 °C and 2–5 bar. These conditions allow for 90–98% conversion for silicon and 30–90% for chloromethane. Approximately 1.4 Mton of dimethyldichlorosilane (Me2SiCl2) is produced annually using this process. Few companies actually carry out the Rochow process, because of the complex technology and high capital requirements. Since the silicon is crushed prior to reaction in a fluidized bed, the companies practicing this technology are referred to as silicon crushers.
Dynamic business process management (dynamic BPM) is a solution which enables enterprises to react to changing conditions of operation (both interior and/or exterior) and cater to the individual needs of their clients in a timely fashion (and even provide a practically instant response in case of critical conditions), in accordance with process adaptations executed in real time by their direct process owners with access to the codified knowledge of their enterprises. The concept of a dynamic BPM is an extension of traditional (static) business process management tailored to learning organizations.
In the iron and steel industry, direct reduction is a set of processes for obtaining iron from iron ore, by reducing iron oxides without melting the metal. The resulting product is pre-reduced iron ore. Historically, direct reduction was used to obtain a mix of iron and slag called a bloom in a bloomery. At the beginning of the 20th century, this process was abandoned in favor of the blast furnace, which produces iron in two stages (reduction-melting to produce cast iron, followed by refining in a converter). However, various processes were developed in the course of the 20th century and, since the 1970s, the production of pre-reduced iron ore has undergone remarkable industrial development, notably with the rise of the Midrex process. Designed to replace the blast furnace, these processes have so far only proved profitable in certain economic contexts, which still limits this sector to less than 5% of world steel production.
The Krupp–Renn process was a direct reduction steelmaking process used from the 1930s to the 1970s. It used a rotary furnace and was one of the few technically and commercially successful direct reduction processes in the world, acting as an alternative to blast furnaces due to their coke consumption. The Krupp–Renn process consumed mainly hard coal and had the unique characteristic of partially melting the charge. This method is beneficial for processing low-quality or non-melting ores, as their waste material forms a protective layer that can be easily separated from the iron. It generates Luppen, nodules of pre-reduced iron ore, which can be easily melted down. The first industrial furnaces emerged in the 1930s, firstly in Nazi Germany and then in the Japanese Empire. During the 1950s, new facilities were constructed, notably in Czechoslovakia and West Germany. The process was discontinued in the early 1970s, with a few nuances. It was unproductive, intricate to master, and only pertinent to certain ores. In the beginning of the 21st century, Japan modernized the process to manufacture ferronickel, which is the sole surviving variant.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Shirley Chisholm, elected in 1968.
