Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2001-06-11
2003-03-18
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S262000
Reexamination Certificate
active
06534688
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the stabilization of polychlorinated alkanes against dehydrochlorination. More particularly, the present invention relates to the prevention or reduction of dehydrochlorination of 1,1,1,3,3-pentachloropropane when heated in the presence of iron(III) contamination by the addition of monomethyl ether hydroquinone.
2. Brief Description of Art
The Montreal Protocol of 1987 placed a ban on certain substances that deplete the ozone layer, especially chlorofluorocarbons (CFC's). To hasten the elimination of CFC production and use, the Protocol allowed for certain fluorocarbon products (HCFC's) to be used as “bridge replacements.” Although these bridge replacements are considerably more ozone friendly than CFC's, they are intended to be transitional and not permanent replacements. Fluorocarbon producers are actively pursuing replacement candidates known as “third generation fluorocarbons.” These third generation fluorocarbons will require hydrochlorocarbon feedstocks.
The second largest U.S. fluorochemical end-use market, next to refrigeration, is for blowing agents utilized in the manufacture of various synthetic plastic formed products. CFC-11 was the dominant product in this market; however, it has been replaced by the bridge-fluorocarbon HCFC-141b. Because current regulations require foam manufacturers to transition away from HCFC-141b by the year 2003, new third generation fluorocarbon products must be developed and commercialized.
Several fluorochemical producers have targeted fluorocarbon 1,1,1,3,3-pentafluoropropane, utilizing 1,1,1,3,3-pentachloropropane (5CP) as the hydrochlorocarbon feedstock, as the primary replacement product for foam blowing applications. The commercial production of 5CP results in a product which is purified through a series of distillation steps. The presence of iron catalyst used in the reaction to produce 5CP, however, allows for the possibility of iron contamination of the product purification section of such a commercial plant. In addition, many non-ferrous alloys actually contain small amounts of iron which can contribute trace quantities of iron to process streams if any corrosion occurs.
Polychlorinated alkanes such as 1,1,1,3,3-pentachloropropane are known to be susceptible to dehydrochlorination in the presence of iron(III). Since iron is or may be present in the process operation steps downstream from the reactor, a need therefore exists to reduce or prevent dehydrochlorination of 5CP in the presence of iron(III).
Various additives are known to be useful to prevent the oxidation and/or polymerization of halogenated compounds such as polychlorinated alkanes in the presence of air or various metals. One such compound, monomethyl ether hydroquinone, also known as MEHQ or p-methoxyphenol, is well known as an additive for halogenated compounds to prevent oxidation and/or polymerization.
Kita et al ( JP Kokai 50088007, “Stabilization of 1,1,1-Trichloro-ethane”) and Marsden et al (GB 1265567, “Stabilizers for 1,1,1-Trichloro-ethane”), for example, describe the use of MEHQ to stabilize 1,1,1-trichloroethane against oxidation in the presence of aluminum. Nakatsukasa et al (JP 47011045 B4, “Stabilization of Trichloroethylene or Tetrachloroethylene”), Campbell et al (DE 2008617, “Stabilized Trichloroethylene”), and others, describe the use of MEHQ to stabilize trichloroethylene and/or tetrachloroethylene against heat, light, air, humidity, and contact with metals. Numerous authors also disclose the use of MEHQ to inhibit polymerization of vinyl monomers, including vinyl chloride, vinylidene chloride, or other vinyl group-containing monomers (e.g., JP Kokai 48092310 to Oshima et al, “Vapor-Phase Polymerization inhibition of vinylidene chloride”; DE 2148185 to Fruhwirth et al, “Polymerization inhibitor for vinyl group-containing aliphatic, aromatic, and heterocyclic compounds”; U.S. Pat. No. 3,696,050 to Wert et al, “Polymerization inhibitors for vinyl monomers and unsaturated polyesters”; U.S. Pat. No. 3,346,551 to Moakes, “Stabilization of vinylidene chloride”). However, these documents describe MEHQ as preventing oxidation, hydrolysis, or polymerization; suppression of dehydrochlorination is not mentioned.
Several patents also teach stabilization of fluorinated alkanes with MEHQ. These fluoroalkanes are used in vapor degreasing applications or cleaning of circuit boards. However, MEHQ is used to prevent oxidation, hydrolysis, or polymerization, rather than dehydrochlorination. See, for example, Cook et al (U.S. Pat. No. 4,961,870, “Azeotrope-like compositions of 1,1,2-trichloro-1,2,2-trifluoro-ethane, 1,2-dichlorethylene, and alkanol having 3 to 7 carbon atoms”) and Gorski (U.S. Pat. No. 4,804,493, “Stabilized azeotrope or azeotrope-like composition of 1,1,2-trichloro-1,2,2-trifluoroethane and trans-1,2-dichloroethylene for cleaning circuit boards” and U.S. Pat. No. 4,803,009 A, “Stabilized azeotrope or azeotrope-like composition of 1, 1,2-trichloro-1,2,2-trifluoroethane, methanol, and 1,2-dichloroethylene for cleaning circuit boards”).
Brooks et al (U.S. Pat. No. 5,683,554, “F141B Crude Stabilization”) discloses the addition of various compounds, including MEHQ, to prevent the formation of 1,1-difluoro-1-chloroethane (F142b) when heating 1,1-dichloro-1-fluoroethane (F141b) in a distillation column. In the background disclosure, it is postulated that 142b “results from a breakdown of 141b to 1130 (1,1-dichloroethylene) and HF which, in turn, reacts with 141b to produce 142b.” However, suppression of dehydrochlorination is not mentioned, even though these compounds contain chlorine. Instead, only the formation of F142b, not dehydrohalogenation of 141b, is disclosed.
In view of the susceptibility of polychlorinated alkanes such as 1,1,1,3,3-pentafluoropropane (5CP) to dehydrochlorination in the presence of iron(III), a need therefore continues to exist to provide a process which suppresses the dehydrochlorination of such polychlorinated alkanes.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process which suppresses the dehydrochlorination of polychlorinated alkanes. The process preferably reduces or prevents the dehydrochlorination of polychlorinated alkanes when heated in the presence of iron(III), or the dehydrochlorination of polychlorinated alkanes under storage conditions. More particularly, in a preferred embodiment, the process reduces or prevents the dehydrochlorination of 1,1,1,3,3-pentachloropropane (5CP) when heated in the presence of iron(III). In another preferred embodiment, the process reduces or prevents the dehydrochlorination of 1,1,1,3,3-pentachloropropane (5CP) under storage conditions.
In accordance with one aspect of the present invention, a process is provided which suppresses the dehydrochlorination of a polychlorinated alkane when heated in the presence of iron(III) by adding an effective amount of a phenol compound to suppress dehydrochlorination. A process is also provided which suppresses the dehydrochlorination of a polychlorinated alkane under storage conditions by adding an effective amount of a phenol compound to suppress dehydrochlorination.
In accordance with another aspect of the invention, the process of the invention provides the addition of an effective amount of a phenol compound which is unsubstituted or substituted in one or more ring positions during the production, manufacture or storage of a polychlorinated alkane to suppress dehydrochlorination due to the presence of iron(III) contamination. Crude polychlorinated alkanes are usually prepared in a reaction vessel using a suitable catalyst system. The catalyst is subsequently removed from the crude product. The product is then sent to one or more fractionating columns for purification. At least two columns will typically be utilized for such product purification. Dehydrochlorination of the desired product due to iron(III) contamination may occur in any or all of the columns utilized in such a process. F
Burns, Daone, Swecker & Mathis, L.L.P.
Siegel Alan
Vulcan Chemicals
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