Silicone fluids manufacture

Silicon fluid manufacture has been described by Gutoff [47] (see Figs. 1 and 2). Batch (Fig. 1) and continuous (Figs. 2 and 3) process flow diagrams are also shown. Another continuous silicone oil process was described by Kirk and is shown in Fig. 3. 

Fig. 1 Batch process for silicone fluid manufacture. [Reprinted from R Cutoff, J. Ind. Eng. Chem. 49, 1807 (1957). Copyright 1957 by the American Chemical Society. Reprinted by permission of the copyright owner.]...

Silicone Fluids. Sihcone fluids are used in a wide variety of appHcations, including damping fluids, dielectric fluids, poHshes, cosmetic and personal care additives, textile finishes, hydraiflic fluids, paint additives, and heat-transfer oils. Polydimethylsiloxane oils are manufactured by the equihbrium polymerisation of cycHc or linear dimethyl silicone precursors. Trifunctional organosilane end groups, typically trimethylsilyl (M), are used, and the ratio of end group to chain units (D), ie, M/D, controls the ultimate average molecular weight and viscosity (112). Low viscosity fluids,... 

The chemistry of silicone halides was recently reviewed by Collins.13 The primary use for SiCU is in the manufacturing of fumed silica, but it is also used in the manufacture of polycrystalline silicon for the semiconductor industry. It is also commonly used in the synthesis of silicate esters. T richlorosilane (another important product of the reaction of silicon or silicon alloys with chlorine) is primarily used in the manufacture of semiconductor-grade silicon, and in the synthesis of organotrichlorosilane by the hydrosilylation reactions. The silicon halohydrides are particularly useful intermediate chemicals because of their ability to add to alkenes, allowing the production of a broad range of alkyl- and functional alkyltrihalosilanes. These alkylsilanes have important commercial value as monomers, and are also used in the production of silicon fluids and resins. On the other hand, trichlorosilane is a basic precursor to the synthesis of functional silsesquioxanes and other highly branched siloxane structures. 

Many women who have received silicone-fluid-filled breast implants have claimed to suffer from implant-related diseases, apparently caused by small leakages of the fluid into the body tissue. Successful lawsuits on those grounds in the United States have driven Dow Corning, the principal manufacturer of the implants, to file for bankruptcy protection. Food and Drug Administration Commissioner David A. Kessler, however, has reported to a congressional subcommittee that, as of July, 1995, there was no scientific evidence that silicone implants are a significant cause of disease. See M. S. Reisch and R. L. Rawls, Silicone gel breast implants. Chem. Eng. News, December 11, 10-17 (1995). 

Methyl chloride is an important industrial product, having a global annual capacity of ca. 900 000 tons. Its primary use is for the manufacture of more highly chlorinated materials such as dichloromethane and chloroform and for the production of silicone fluids and elastomers. It is usually manufactured by the reaction of methanol with hydrogen chloride with a suitable acid catalyst, such as alumina. To develop a site-specific reaction mechanism and a kinetics model for the overall process, one first needs to identify all the reagents present at the catalyst surface and the nature of their interactions with the surface. The first step in the reaction is dissociative adsorption of methanol to give adsorbed methoxy species. Diffuse reflectance IR spectroscopy (29d) showed the expected methoxy C-H stretch and deformations, but an additional feature, with some substructure, at 2600 cm was... 

The silicone fluids are normally chain-blocked linear polymers, manufactured by ring-opening polymerization, as described in Section 3.4. The dimethylsiloxane polymers are by far the most important, but to make fluids for high-temperature use, phenytmethylsiloxane units are also included in the polymer. 

Silicon dioxide is initially rendered hydrophobic in one of a variety of proprietary processes specific to a particular manufacturer. It is then slowly mixed with the silicone fluids in a formulation. After mixing, the simethicone is milled to ensure uniformity. 

Normally, organic fluids (hydrocarbons and silicones) are used to attain a temperature between 200° C and 400° C. A great degree of information can be obtained from the fluid manufacturers as well as other published literature. Different chemistries that are utilized for these applications are discussed below. ° ° ... 

Silicones are manufactured on a very large scale in 19 75 about 24000 tonnes of silicon were converted into chlorosilanes for this purpose in the USA alone. About half the production is of methylsilicone fluids Me,SiO(SiMe O) SiMe, (n up to 3000). The rest consists of resins, rubbers and some composites which include copolymers, blends and laminates. 

Silicones have a wide variety of applications (Figure 22.27). Due to the strong Si—O and Si—C bonds, silicones are generally imreactive and can be synthesized to perform in temperature ranges of 75°F to 400°F. Silicone oils can be found in cosmetics, car wax, and hydrauhc fluids. The silicone elastomers are used for medical tubing, heart valve implants, electrical tape, caulk, and gaskets. Silicone resins are used to insulate electrical equipment and in the molding process of electronic circuit boards. These examples represent only a small portion of the uses for silicone compounds. Because of this extensive use, several hundred thousand tons of silicones are manufactured each year. 

As expected, the major producers of PAO, esters, PIB and alkylaromatics are integrated petroleum eompanies that supply conventional mineral oil base stocks and petrochemicals as well as various synthetic base stocks. PAG, phosphate esters and silicone fluids are manufactured by chemical companies that produce these fluids on a much larger scale mainly for other applications. Their use as lubricant base stocks is only a fraction of the total market. Table 1 summarizes the major synthetic base stock producers. 

Silicon fluids Methylsilicone fluid is the most common product, with relatively constant viscosity over a range of temperatures and it exhibits shear stability with high pumping pressure. Industrial apphcations of siHcon fluids include uses in fermentation adhesives, and sealant manufacturing. 

In 1962, Cronin and Gerow implanted silicone shells into dogs, which was a significant change in breast augmentation. The breast implant was crosslinked and reinforced silicone rubber shell that encapsulated a silicone gel or saline solution. The silicone gel comprised crosslinked silicone elastomer, mainly PDMS and a low molecular weight silicone fluid (also PDMS). There were many variations in the PDMS functionalities by different manufacturers to attain desired gel properties. Saline-filled implants were first manufactured as Simaplast in 1965 but did not have the same confluence due to the water-like viscosity of saline as compared to a more viscous gel. 

Pressure-sensitive adhesives (PSAs) based on acrylic, natural rubber and silicone are employed primarily for ease of application. To name Just a few applications, PSAs bond decals to surfaces, interior decorative surfaces to interior panels, interior trim pieces in place directly or hook and loop tape for the same purpose, structural shims in place during manufacturing and acoustic (sound deadening) materials to body skin interior surfaces. Tape products with pressure-sensitive adhesive on one or both surfaces are used for such functions as cargo compartment sealing, as a fluid barrier to prevent spills and leaks in the lavatories and... 

Used industrially for the manufacture of organophosphorus compounds (Insecticides, dyes, pharmaceuticals, defoliants) as well as esters for plasticizers, gasoline additives, and hydraulic fluids used in industry as a chlorinating agent, catalyst, dopant for semiconductor grade silicon, fire retarding agent, and solvent in cryoscopy. 

Uses Coolant and refrigerant herbicide and fumigant organic synthesis-methylating agent manufacturing of silicone polymers, pharmaceuticals, tetramethyl lead, synthetic rubber, methyl cellulose, agricultural chemicals and nonflammable films preparation of methylene chloride, carbon tetrachloride, chloroform low temperature solvent and extractant catalytic carrier for butyl rubber polymerization topical anesthetic fluid for thermometric and thermostatic equipment. 

Table 5.1 summarizes the uses of lime. Lime is used as a basic flux in the manufacture of steel. Silicon dioxide is a common impurity in iron ore that cannot be melted unless it combines with another substance first to convert it to a more fluid lava called slag. Silicon dioxide is a Lewis acid and therefore it reacts with the Lewis base lime. The molten silicate slag is less dense than the molten iron and collects at the top of the reactor, where it can be drawn off. Over 100 lb of lime must be used to manufacture a ton of steel. 

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