Other Production Methods

Many other procedures have been used to produce catalysts  

1 Carbothermal Reduction of Silica This process is based on the following equation 

According to the reaction mechanism proposed by Weimer [36] the reaction takes place in several steps  

The initial reaction with formation of gaseous SiO at points of direct contact between C and Si02 requires temperatures above 1600°C at atmospheric 

This process has been used in the early 1960s to fabricate pure ultrafine pSiC powders especially suited for the semiconductor and pigment industry [37,38]. During the first step of the General Electric Process [37] a silica gel is formed by hydrolysis of silicon tetrachloride in an aqueous solution of sugar (sucrose). Upon dehydratization at 300°C the sugar pyrolizes and an intimate amorphous carbon/amorphous silica mixture is obtained which is subsequently fired at 1800°C in an inert atmosphere to form pSiC. 

2 Synthesis from the Elements Prochazka [39] synthesized submicron pSiC powder with a surface area of 7 m g using direct reaction of high-purity silicon powder with carbon-black at temperatures between 1500 and 1650°C, but saw little densification with boron and carbon additions, suggesting that free sihcon is detrimental to densification. 

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In 1988 diaphragm cells accounted for 76% of all U.S. chlorine production, mercury cells for 17%, membrane cells for 5%, and all other production methods for 2%. Corresponding statistics for Canadian production are diaphragm cells, 81% mercury cells, 15% and membrane cells, 4% (5). for a number of reasons, including concerns over mercury pollution, recent trends are away from mercury cell production toward the more environmentally acceptable membrane cells, which also produce higher quality product and have favorable economics. 

Dichloroethane is produced commercially through the reaction of hydrogen chloride and vinyl chloride at 20°-55°C in the presence of an aluminum, ferric, or zinc chloride catalyst (Grayson 1978). Other production methods include the direct chlorination of ethane, the reaction of PCI s with acetaldehyde as a by-product during the manufacture of chloral (Browning 1965), and as intermediate in the production of vinyl chloride and 1,1,1-trichloroethane by photochlorination (Windholz 1983). 

The arc method of production was vastly improved after these original observations, and numerous other production methods were developed [96-99], including methods which primarily promoted the growth of single wall carbon nanotubes (SWNTs) [99-101]. As implied by the name, SWNTs are nanotubes which consist of only one layer of carbon atoms. 

Similarly, certain other criteria of reservoir suitability may be mitigated. For example, application of thermal methods can be advantageous in reservoirs of low viscosity petroleum if the latter contain great amounts of paraffin. In such cases, the employment of some other production method may lead to an inadmissible reduction in formation temperature. The restrictions placed on maximum permissible formation pressures are dictated by technical limitations of installations used in steam and/or air injection during thermal treatment. As regards viscosities, thermal methods should be restricted to crude oil of less than 1,000 centipoise. 

Here is a listing of other production methods besides the three processes described for production of elastomer moldings. 

Most commercially available PVC is polymerized with radical initiators by a hquid-phase suspension process. In other production methods, the material is formed with a free-radical initiator via mass polymerization, emulsion polymerization, or solution polymerization processes. PVC is mostly a pure head-to-tail polymer with predominantly a syndiotactic structure, but exhibiting low crystallinity. 

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