HYDROCHLOROFLUOROCARBON

Rednctive dechlorination of fluorinated substrates has been observed for both methanogens and snlfate-redncing bacteria. 

In anaerobic microcosms, l,l,2-trichloro-l,2,2-trifiuoroethane (CFC-113) was transformed by successive reductive dechlorination to l,2-dichloro-l,2,2-trifiuoroethane (HCFC-123a), and under methanogenic conditions to l-chloro-l,2,2-trifiuoroethane (HCFC-133) and l-chloro-l,l,2-triflnoroethane (HCFC-133b) without evidence for the reductive replacement of fluorine (Fignre 7.70b) (Lesage et al. 1992). 

l-Trifiuoro-2,2-dichloroethane (HCFC-123) was recalcitrant in aerobic soils, but underwent reductive dechlorination anaerobically to prodnce l,l,l-trifiuoro-2-chloroeth-ane (Oremland et al. 1996). 

The production of carbon monoxide from trichloroflnoromethane catalyzed by cytochrome P450c nj proceeded through intermediate formation of the dichloroflnorocarbene (Li and Wackett 1993) (Fignre 7.70c). Other reactions included (3-elimination from l,l,l-trichloro-2,2,2-trifiuorethane (Fignre 7.70c). Pseudomonas putida strain G786 (pGH-2) was constructed to contain both the 

FIGURE 7.70 (a) Metabolism of trichlorofluoromethane by Methanosarcina barkeri, (b) transformation of 

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The 1990 Clean Air Act regulates the production and use of CFCs, hydrochlorocarbons, hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbon (HFC) substitutes. CFC and halon (Class I substances) usage is to be phased out in steps until total phaseout occurs on January 1,... 

In this sequence the Cl also acts as a catalyst and two molecules are destroyed. It is estimated that before the Cl is finally removed from the atmosphere in 1—2 yr by precipitation, each Cl atom will have destroyed approximately 100,000 molecules (60). The estimated O -depletion potential of some common CFCs, hydrofluorocarbons, HFCs, and hydrochlorofluorocarbons, HCFCs, are presented in Table 10. The O -depletion potential is defined as the ratio of the emission rate of a compound required to produce a steady-state depletion of 1% to the amount of CFC-11 required to produce the 1% depletion. The halons, bromochlorofluorocarbons or bromofluorocarbons that are widely used in fire extinguishers, are also ozone-depleting compounds. Although halon emissions, and thus the atmospheric concentrations, are much lower than the most common CFCs, halons are of concern because they are from three to ten times more destmctive to O, than the CFCs. 

Production of hydrogen fluoride from reaction of Cap2 with sulfuric acid is the largest user of fluorspar and accounts for approximately 60—65% of total U.S. consumption. The principal uses of hydrogen fluoride are ia the manufacture of aluminum fluoride and synthetic cryoHte for the Hall aluminum process and fluoropolymers and chlorofluorocarbons that are used as refrigerants, solvents, aerosols (qv), and ia plastics. Because of the concern that chlorofluorocarbons cause upper atmosphere ozone depletion, these compounds are being replaced by hydrochlorofluorocarbons and hydrofluorocarbons. 

North American HF production capacity has declined since the early 1980s and several smaller producers, such as Harshaw and Essex, have closed plants. Production is expected to continue to decline in the short term because of chlorofluorocarbon (CPC) cutbacks, but is expected to rebound later in the 1990s as replacement hydrochlorofluorocarbons are introduced to the marketplace. 

Table 4. Physical Properties of Aliphatic Hydrochlorofluorocarbons (HCFCs) ...

CFC-113, CF2CICFCI2, or the hydrochlorofluorocarbons (HCFCs) such as HCFC-123, CF2CHCI2, HCFC-141b, or CH2CFCI2, are miscible in all proportions with the perfluoro compounds at 25°C. Typical solubiHty data are shown in Table 2. 

CFG = chlorofluorocarbon HCFC = hydrochlorofluorocarbon see Fluorine compounds,organic-aliphatic. 

Trichloroethylene is being evaluated by the industry as a precursor in the production of hydrochlorofluorocarbons (HCEC), the replacement products for the chlorofluorocarbons impHcated in the depletion of the stratospheric ozone. At this time it is too early to project any estimates or probabihties for potential volume changes as a result of this opportunity (23). 

As you know, most countries are phasing out certain refrigerants to lessen damage to the ozone layer. The chemicals being phased out are chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Replacements are hydrofluorocarbons (HFCs) and certain blends. The DuPont web site (www.dupont.com) gives the handy Table I of recommended replacement refrigerants for various applications. 

Decision allocating production and import quotas for methyl bromide, import quotas for hydrobromofluorocarbons and consumption quotas for hydrochlorofluorocarbons for the period 1 January to 31 December 1995... 

FONT 360 , glyphosate, 70 FORANE , hydrochlorofluorocarbons, 70 Fomialdehyde, 70 Fomialdehyde cyanohydrin, 70 Fomiamide, 70 Fomiic acid, 70... 

The production of chlorofluoro- and hydrochlorofluorocarbons expanded rapidly after 1945, reaching about 1 milbon tons in 1986 despite a drop m production in the late 1970s, when the United States and several other countnes banned the use of chlorofluorocarbons as aerosol propellants In the early 1990s, production and consumpaon are in decline... 

Although many syntheses of chlorofluorocarbons and hydrochlorofluorocarbons have been published, those actually used in manufacturing processes are limited. By far the most important is the original Swarts reaction [5]. 

Table 1 lists the chlorocarbon feedstocks for the produedon of the major chlorofluorocarbons and hydrochlorofluorocarbons... 

Table 1. Chlorocarbon Feedstocks for the Production of the Major Chlorofluorocarbons and Hydrochlorofluorocarbons...

Perhaps the most significant recent issue for the industry was the phase-out of CFCs as blowing agents resulting from the Montreal Protocol (1987) and Clean Air Act (1990).19 These regulations mandate specific timelines for discontinuation and, since foams comprise the bulk of polyurethane applications, have prompted a worldwide search for alternatives. Hydrochlorofluorocarbons, HFCs, and hydrocarbons (HCs) are now the blowing agents of choice. Which one is... 

Several of the commercially available 16,000 chlorinated and brominated compounds have already been regulated or harmed, CFCs, DDT and chlorinated biphenyls are typical examples. Many others are being phased out according to the Montreal Protocol on Substances that Deplete the Ozone Layer. This includes chlorinated solvents, methyl bromide and halons (e.g. CF3Br). The milder ozone destroyers, hydrochlorofluorocarbons (HCFCs) will also, eventually, be phased out. 

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