Chlorination thermal

Thermal asphalt Thermal blacks Thermal bonding Thermal chlorination Thermal coatings Thermal comfort Thermal conductivity... 

Dehydrochlorination of 1,1,2-trichloroethane [25323-89-1] produces vinyHdene chloride (1,1-dichloroethylene). Addition of hydrogen chloride to vinyHdene chloride in the presence of a Lewis acid, such as ferric chloride, generates 1,1,1-trichloroethane. Thermal chlorination of 1,2-dichloroethane is one route to commercial production of trichloroethylene and tetrachloroethylene. 

Chlorine free radicals used for the substitutioa reactioa are obtaiaed by either thermal, photochemical, or chemical means. The thermal method requites temperatures of at least 250°C to iaitiate decomposition of the diatomic chlorine molecules iato chlorine radicals. The large reaction exotherm demands close temperature control by cooling or dilution, although adiabatic reactors with an appropriate diluent are commonly used ia iadustrial processes. Thermal chlorination is iaexpeasive and less sensitive to inhibition than the photochemical process. Mercury arc lamps are the usual source of ultraviolet light for photochemical processes furnishing wavelengths from 300—500 nm. 

Thermal Cracking. Thermal chlorination of ethylene yields the two isomers of tetrachloroethane, 1,1,1,2 and 1,1,2,2. Introduction of these tetrachloroethane derivatives into a tubular-type furnace at temperatures of 425—455°C gives good yields of trichloroethylene (33). In the cracking of the tetrachloroethane stream, introduction of ferric chloride into the 460°C vapor-phase reaction zone improves the yield of trichloroethylene product. 

Thermal chlorination of methane was first put on an industrial scale by Hoechst in Germany in 1923. At that time, high pressure methanol synthesis from hydrogen and carbon monoxide provided a new source of methanol for production of methyl chloride by reaction with hydrogen chloride. Prior to 1914 attempts were made to estabHsh an industrial process for methanol by hydrolysis of methyl chloride obtained by chlorinating methane. 

Chlorination of Methane. Methane can be chlorinated thermally, photochemicaHy, or catalyticaHy. Thermal chlorination, the most difficult method, may be carried out in the absence of light or catalysts. It is a free-radical chain reaction limited by the presence of oxygen and other free-radical inhibitors. The first step in the reaction is the thermal dissociation of the chlorine molecules for which the activation energy is about 84 kj/mol (20 kcal/mol), which is 33 kJ (8 kcal) higher than for catalytic chlorination. This dissociation occurs sufficiendy rapidly in the 400 to 500°C temperature range. The chlorine atoms react with methane to form hydrogen chloride and a methyl radical. The methyl radical in turn reacts with a chlorine molecule to form methyl chloride and another chlorine atom that can continue the reaction. The methane raw material may be natural gas, coke oven gas, or gas from petroleum refining. 

Three industrial processes have been used for the production of ethyl chloride hydrochlorination of ethylene, reaction of hydrochloric acid with ethanol, and chlorination of ethane. Hydrochlorination of ethylene is used to manufacture most of the ethyl chloride produced in the United States. Because of its prohibitive cost, the ethanol route to ethyl chloride has not been used commercially in the United States since about 1972. Thermal chlorination of ethane has the disadvantage of producing undesired by-products, and has not been used commercially since about 1975. 

Thermal chlorination of ethane is generally carried out at 250—500°C. At ca 400°C, a free-radical chain reaction takes place ... 

Ethyl chloride can also be used as a feedstock to produce 1,1,1-trichloroethane by thermal chlorination at temperatures of 375—475°C (49), or by a fluidized-bed reactor at similar temperatures (50). 

Dichloroethane is also one of the iatermediate products of high temperature thermal chlorination of ethane or ethyl chloride. In ethane chlorination, the reaction proceeds through ethyl chloride as an iatermediate (12). 1,1-Dichloroethane itself is usually an iatermediate ia the productioa of viayl chloride and of 1,1,1-tfichloroethane by thermal chlorination or photochlofination (13). 

Methane is the most difficult alkane to chlorinate. The reaction is initiated by chlorine free radicals obtained via the application of heat (thermal) or light (hv). Thermal chlorination (more widely used industrially) occurs at approximately 350-370°C and atmospheric pressure. A typical product distribution for a CH4/CI2 feed ratio of 1.7 is mono- (58.7%), di-(29.3%) tri- (9.7%) and tetra- (2.3%) chloromethanes. 

Thermal capacity rate, 13 253 Thermal-chemical decomposition of ozone, 17 770-773 Thermal chlorination, of ethane, 10 588 Thermal coefficient of expansion (TCE),... 

Carbon tetrachloride is produced by exhaustive chlorination of a variety of low molecular weight hydrocarbons such as carbon disulfide, methanol, methane, propane, and ethylene dichloride (CEH 1985 lARC 1979). It is also produced by thermal chlorination in the production of tetrachloroethylene. Since the U.S. Food and Drug Administration banned the sale of carbon tetrachloride in any product used in the home, its production initially declined at approximately 8% a year from 1974 to 1981 (HSDB 1992). From 1981 to 1988 the United States consistently produced between 573-761 million pounds (260,000-350,000 metric tons) of carbon tetrachloride per year (C EN 1992 SRI 1988 USITC 1986). Carbon tetrachloride production dropped to 413 million pounds (187,000 metric tons) per year in 1990, and to 315 million pounds (143,000 metric tons) in 1991 (C EN 1992, 1993 USITC 1986, 1991). Carbon tetrachloride is currently manufactured at five facilities in the United States Akzo Chemical, Inc., New York, New York Dow Chemical Company, Midland, Michigan Vulcan Materials Company, Birmingham, Alabama Occidental Chemical Corporation, Dallas, Texas and LCP Chemicals, West Virginia Inc., Moundsville, West Virginia (USITC 1991 HSDB 1992). 

During slow thermal chlorination, elimination of HC1 from the monochloride with the resultant formation of an alkene followed by chlorine addition may be the dominant route to yield dichloroalkanes. This mechanism, however, is negligible in rapid thermal or photochemical reactions. 

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 ... 

Since free-radical chlorination is a nonselective process, overchlorination may be a problem in the manufacture of ethyl chloride. Temperature-induced pyrolysis to yield ethylene and hydrogen chloride may occur, too. A fluidized-bed thermal chlorination reactor may be used to overcome these problems. The best selectivity achieved in the temperature range of 400-450°C is 95.5% with a chlorine to ethane ratio of 1 5. 

The so-called integrated ethyl chloride process combines the abovementioned synthesis with an addition reaction. Hydrogen chloride formed in the thermal chlorination process is used in a separate step to add to ethylene, making the manufacture of ethyl chloride more economical. 1,1,1-Trichloroethane is an exceptional product in free-radical chlorination of higher hydrocarbons since the same carbon... 

Thermal chlorinations were carried out similarly except that a solvent was not used. Chlorine was introduced in the dark below the surface of the rapidly stirred paraffin at 80°C. The temperature quickly rose to 120 to 125°C. for the balance of the reaction period. Chlorine was not absorbed as efficiently as it was in the photochemical chlorinations. After the reaction was complete, chloroform was added to facilitate washing of the product. 

Thermal chlorinations were carried out at 125°C. and photochemical chlorina-tions at about 35°C. No posttreatment was employed other than removal of dissolved hydrogen chloride, followed by the removal of solvents, if present, by heating under vacuum. No difference in plasticizer properties was observed for chlorinated n-paraffins made by the two methods. 

The chlorination of saturated hydrocarbons can be induced by light, but also can be carried out at temperatures of about 300° in the dark. Under such circumstances the mechanism is similar to that of light-induced chlorination, except that the chlorine atoms are formed by thermal dissociation of chlorine molecules. Solid carbon surfaces catalyze thermal chlorination, possibly by aiding in the cleavage of the chlorine molecules. 

Degradation of the polyisobutene chain takes place parallel to the chlorination. This is shown in Figure 5, where the molecular weight Mn is plotted vs. the absorbed radiation dose. A similar effect was observed by McNeill and McGuchan (4) for the thermal chlorination of polyisobutene, which they explained by reaction of a polymer radical formed in the chlorination process ... 

The structure of the chlorinated products obtained is not yet clear. McNeill and McGuchan concluded from NMR data that, in the thermal chlorination process, both methyl and methylene groups were chlorinated but that the methylene groups were more readily substituted and that even some disubstitution of the methylene groups occurred. We studied our products by infrared-spectroscopy Figure 6 shows the spectra of four chlorinated polyisobutenes with increasing chlorine content. 

Vinyl chloride and chloroprene (2-chlorobuta- 1,3-diene) are among the major intermediates which are produced industrially on the 100,000 tonnes/year scale by thermal chlorination or oxychlorination of ethylene or butadiene. 

Hoechst, GB 1400855,1975, Process for the manufacture of cUoromethanes by thermal chlorination... 

You should already be familiar with the mechanism for the thermal chlorination of methane. We will use Figure 1.17 to review briefly the net equation, the initiation step, and the propagation steps of the monochlorination of methane. Figure 1.18 shows the energy profile of the propagation steps of this reaction. 

A much smaller amount is produced by the thermal chlorination of ethane. This direct chlorination may be run in conjunction with another process, such as oxychlorination, which can use the byproduct HCI as feed. 

Ttie second large-scale use of methane is its halogenation [I], where chlorine and fluorine are the most important halogens for methane substitution. Chloro-methanes aie formed by thermal chlorination or catalyzed uxychlorination of methane. Monochlorination is controlled by using a ten-fold excess of methane. 

Thermal chlorination (400-500°) in the absence of catalysts and light is a chain reaction initiated by thermal dissociation of Cl2.328 Details of laboratory apparatus for this method of chlorination, which is particularly important for alkanes of lower molecular weight, are given in Asinger s book324d and by Hass.329 The procedure can be used to convert alkanes into monochlorides and to chlorinate the latter further. 

Carbon skeleton rearrangements do not occur during either photochemical or thermal chlorinations if pyrolysis temperatures are avoided. Every possible monochloride derivative without such rearrangement is always form. As far as is known, this generalization extends also to the polychlorides. 

One of the advantages of liquid-phase thermal chlorination is that, because of the lower temperatures involved, the pyrolysis is almost com-... 

Dichlorination proceeds by two mechanisms (a) loss of hydrogen chloride followed by addition of chlorine to the resulting olefin and (h) progressive substitution. Slow thermal chlorination favors mechanism 1, whereas with rapid liquid-phase or vapor-phase single-pass thermal reaction or low-temperature photochemical conditions, mechanism 1 is substantially eliminated. 

The thermal chlorination of methane is carried out on a large scale in this country by Dow Chemical Company, Diamond Alkali Company, and Allied Chemical Dye Corporation, Solvay Process Division. High-purity methane is mixed with cycle gas and then with chlorine and the mixture introduced into a packed reactor heated to 350-400 C, where chlorine is completely reacted in the excess of hydrocarbon and chlorinated hydrocarbon. The effluent gases contain excess methane and all the chlorinated methanes, which may be separated after condensation by fractional distillation. When reaction temperatures are increased, a competing reaction develops with the formation of perchloroethylene. 

Chlorobutanes. Chlorobutanes can be obtained by diverse procedures, such as (1) the liquid-phase or thermal chlorination of butane, (2) addition of chlorine or hydrogen chloride to butenes, (3) reaction of hydrochloric acid with butanols and butylene glycols, (4) chlorination of chlorobutenes and chlorobutadienes, and (5) hydrochlorination of tetramethylene oxide (tetrahydrofuran) and butadiene. 

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