Chloromethanes, manufacture

Chlorination of Alkanes. The most direct and economical method for the manufacture of chloromethanes is the thermal free-radical chlorination of methane.176 177 Whereas in the 1940s and 1950s photochlorination was practiced in some plants, thermal chlorination is the principal industrial process today. The product chloromethanes are important solvents and intermediates. Commercial operations perform thermal chlorination at about 400-450°C. Vapor-phase photochemical chlorination of methane may be accomplished at 50-60°C. Fast and effective removal of heat associated with thermally induced free-radical substitution is a crucial point. Inadequate heat control may lead to explosion attributed to the uncontrollable pyrolysis liberating free carbon and much heat ... 

In the manufacture of methyl chloride a mixture of methane and chlorine is mixed with recycled gas and fed into a reactor. The CH4 Cl2 ratio is 4-5. The reactor temperature is maintained by regulating the gas feed rate. In methane chlorination plants, 95-96% chlorine yields and 90-92% methane yields are typical.176 All four chloromethanes are formed with a typical composition of 35 wt% methyl chloride, 45 wt% methylene dichloride, 20 wt% chloroform, and a small amount of carbon tetrachloride.178 The reaction, however, may be regulated so that either mono- or tetrachlorination predominates.177 179 180... 

Conventional processes for the manufacture of dichloromethane are based upon the chlorination of methane or of chloromethane. These reactions have the disadvantage of generating hydrogen chloride as a by-product, and of producing a mixture of all chloromethanes, in addition to dichloromethane. The simple reaction between methanal and phosgene thus... 

Chloromethanes have varied applications in the chemical industry. Methyl chloride is mainly used in the manufacture of silicones, tetramethyl lead, and as a solvent. Methylene chloride (often called methylene dichloride or di-chloromethane, DCM) is a multipurpose solvent, a degreasing agent, and a... 

A few chemicals are based on the direct reaction of methane with other reagents, including carbon disulfide, hydrogen cyanide, chloromethanes, and synthesis gas mixture. A more detailed discussion for chemistry and synthesis can be found in Chapter 4. In this chapter, emphasis will be placed on the environmental aspects of the chemicals and their manufacturing technologies. 

It is now possible to polymerize isobutylene to butyl rubber in toluene instead of the usual chloromethane.215 A new titanium sandwich catalyst does the trick. European manufacturers are phasing out some chloroparaffin lubricants.216 In Japan, rubber is being chlorinated in water instead of carbon tetrachloride.217 This still involves chlorine, but does get rid of the solvent. 1,2-Dimethoxyethane is being used as an alternative to chlorinated solvents for the Schmidt Reaction for conversion of an ester to an amine through an acid azide and a carbamate (3.6).218 This eliminated accidents from polyazides made in situ from methylene chloride or chloroform. 

Once the testing was successfully completed, a CFC dubbed Freon entered the refrigerant market in December 1930. It was manufactured by a joint venture of DuPont, which earlier in the year had acquired a leading maker of chloromethane, and GM. The product was an immediate success and proved highly profitable.21... 

Figure 22.2 Chloromethane is an alkyl halide that Is used In the manufacturing process for silicone products, such as window and door sealants. 

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