Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2000-09-26
2002-06-11
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S178000, C570S179000, C570S180000
Reexamination Certificate
active
06403849
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for obtaining purified perfluorocarbon compositions.
BACKGROUND
Perfluorocarbons such as perfluorooctane, known as fluorinerts, can be used as cleaning agents for electronics and other precision instruments. Perfluorocarbons can be prepared by electrochemical fluorination (ECF). Perfluorocarbons may be prepared with increased yields, greater efficiency and lower waste by electrochemically fluorinating trifluoromethyl-substituted aromatic compounds. For example, perfluorodimethylcyclohexane (PDMCH), which may be applicable to a wider range of uses than perfluorooctane by virtue of its lower pouring point, can be prepared by fluorinating its trifluoromethyl-containing aromatic counterpart, hexafluoroxylene (HFX), by the Simons process. The fluorination process results in a composition (or a mixture) containing primarily PDMCH and a small amount of HFX. Using physical methods such as fractional distillation to separate traces of HFX impurity from PDMCH is difficult, since HFX forms an azeotrope with PDMCH. Although prolonging the fluorination process may eventually reduce the amount of HFX in the PDMCH composition, this practice is not cost effective.
SUMMARY
Industrial cleaning applications require that a very low amount of HFX (less than about 100 ppm) be present in the final perfluorocarbon product, so there exists a need to obtain perfluorocarbon compositions with high purity. Due to the difficulties in obtaining high purity perfluorocarbon compositions, it is desirable to develop a method to conveniently and economically remove substantially all aromatic impurities from the perfluorocarbon composition.
In general, the invention relates to a method for obtaining a perfluorocarbon composition that is substantially free of aromatic impurities such as, for example, aromatic compounds containing a trifluoromethyl substituent. The method uses a chemical reaction to change the aromatic impurities, making them separable by physical methods by taking advantage of more advantageous solubility and/or boiling point, the absence of an azeotrope, and the like. The perfluorocarbon is substantially or completely unaffected by the chemical reaction and remains unchanged.
In one aspect, the invention features a method for obtaining a purified perfluorocarbon composition (i.e., a perfluorocarbon composition that is substantially free of aromatic impurities). The method includes providing a crude composition containing a perfluorocarbon and an aromatic impurity; and contacting the crude composition with a solubility-increasing reagent selected from the group consisting of concentrated sulfuric acid and oleum to convert the aromatic impurity into an aromatic compound having an acid functionality to form a first composition. Preferably, the aromatic compound having an acid functionality is removed from the first composition to form a purified perfluorocarbon composition.
In a second aspect, the invention also features a method for obtaining a perfluorocarbon composition that is substantially free of an aromatic impurity. The method includes providing a crude composition containing a perfluorocarbon and an aromatic impurity selected from the group consisting of 1,3-bis(trifluoromethyl)benzene, 1,4-bis(trifluoromethyl)benzene, trifluoromethylbenzene and mixtures thereof; contacting the crude composition with concentrated sulfuric acid or oleum at a temperature from about 100° C. to about 200° C.; and contacting the resulting composition with an alkaline aqueous solution to remove the aromatic impurities.
In a third aspect, the invention features a method for obtaining a perfluorocarbon composition that is substantially free of an aromatic impurity. The method includes fluorinating an aromatic compound to form a crude composition comprising a perfluorocarbon and an aromatic impurity; contacting the crude composition with a solubility-increasing reagent to convert the aromatic impurity into an aromatic compound having an acid functionality to form a first composition, wherein the solubility-increasing reagent is selected from the group consisting of sulfuric acid and oleum; and removing the aromatic compound having an acid functionality to form a purified composition comprising a perfluorocarbon.
In a fourth aspect, the invention features a method for purifying a perfluorocarbon composition. The method includes providing a crude composition containing a perfluorocarbon and an aromatic impurity; contacting the crude composition with a solubility-increasing reagent to form a first composition comprising a perfluorocarbon and an aromatic compound with an acid functionality; and removing the aromatic compound with an acid functionality to form a purified perfluorocarbon composition, wherein the aromatic compound and the aromatic impurity are present in the purified perfluorocarbon composition at a total concentration of less than about 100 ppm.
In a fifth aspect, the invention features a method for purifying a perfluorocarbon composition. The method includes providing a crude composition comprising a perfluorocarbon and an aromatic impurity, wherein the aromatic impurity has at least one unsubstituted ring carbon atom; contacting the crude composition with a solubility increasing reagent to form a first composition comprising a perfluorocarbon and an aromatic compound with an acid functionality; and contacting the first composition with an alkaline solution; and separating the alkaline solution to remove the aromatic compound with an acid functionality and form a second composition, wherein the second composition contains perfluorocarbons that are substantially free of aromatic impurities.
A purified perfluorocarbon composition prepared by each of the methods set forth above is also within the scope of this invention.
The invention also features a composition containing at least one of 1,3-perfluorodimethylcyclohexane and 1,4-perfluorodimethylcyclohexane, wherein the composition is substantially free of aromatic impurities. Such impurities are selected from the group consisting of 1,3-bis(trifluoromethyl)benzene, 1,4-bis(trifluoromethyl)benzene, and trifluoromethylbenzene and their total amount in the composition is no more than about 100 ppm; preferably, no more than 10 ppm; more preferably, no more than 1.0 ppm; most preferably no more than 0.1 ppm.
The details of one or more embodiments of the invention are set forth in the description below. Other features and advantages of the present invention will be apparent from the following description of the preferred embodiments, and also from the appending claims.
DETAILED DESCRIPTION
The invention relates to an efficient and economical method for obtaining a perfluorocarbon composition that is substantially free of an aromatic impurity, in particular, a trifluoromethyl-aromatic impurity. As used herein, a composition that is “substantially free” of a material means that the amount of the material is negligible in the composition, i.e., less than about 100 ppm. The purified perfluorocarbon compositions of the invention contain one or more perfluorocarbon compounds at a combined concentration of at least about 80 wt %, preferably at least about 99 wt %, and more preferably at least about 99.99 wt %, of the total weight of the composition. The purified fluorocarbon compositions of the invention also contain one or more aromatic impurities at a concentration of no more than about 100 ppm (based on the total weight of the composition).
The perfluorocarbons in the present composition are organic compounds in which all C—H bonds have been replaced by C—F bonds. In a preferred embodiment, the perfluorocarbon is selected from the group consisting of perfluoroalkanes (e.g., perfluorohexane, perfluoroheptane, or perfluorooctane), perfluorocycloalkanes (e.g., 1,3-perfluorodimethylcyclohexane, 1,4-perfluorodimethylcyclohexane, or perfluoromethylcyclohexane), and a mixture thereof. Preferably, the perfluorocarbon is 1,3-perfluorodimethylcyclohexane, 1,4-perfluorodimethylcyclohexane, perfluorooctane or a mixture thereof
Qiu Zai-Ming
Zhang Zhongxing
3M Innovative Properties Company
Fagan Lisa M.
Siegel Alan
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