Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2001-05-09
2002-07-02
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S178000
Reexamination Certificate
active
06414203
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for treating 1,1,1,3,3-pentafluoropropane (R245fa). Particularly, this invention relates to a method for reducing the content of unsaturated impurities including halogenated hydrocarbons having an unsaturated bond (hereinafter referred to as unsaturated impurities) such as 1-chloro-3,3,3-trifluoropropene (R1233zd) contained in R245fa.
BACKGROUND ART
R245fa is an essential substance having extensive uses including a replacement for 1,1-dichloro-1-fluoroethane (R141b) which is used as e.g. a foaming agent. As disclosed in WO 96/01797, a method for producing such R245fa is known as an industrially effective method, wherein 1,1,1,3,3-pentachloropropane (R240fa) is fluorinated in a liquid phase, preferably, in the presence of an antimony catalyst.
However, it is known that R245fa produced by the above-mentioned method, in many cases, contains a total amount of from 300 to 20,000 ppm (weight) unsaturated impurities such as 1-chloro-3,3,3-trifluoropropene (R1233zd), 1,3,3,3-tetrafluoropropene (R1234ze), 1,2-dichloro-3,3,3-trifluoropropene (R1223x), 1-chloro-1,3,3,3-tetrafluoropropene (R1224zb), 2-chloro-1,3,3,3-tetrafluoropropene (R1224xe) and 2-chloro-3,3,3-trifluoropropene (R1233xf).
The specification of the Panel for Advancement of Fluorocarbon Test (PAFT II) stipulates that the above-mentioned unsaturated impurities, namely halogenated hydrocarbons having an unsaturated bond, should be reduced to not more than 20 ppm in a total amount.
However, among these unsaturated impurities, there are so many compounds having boiling points close to that of R245fa which is an objective compound. Therefore, it is difficult to separate these compounds from R245fa by a usual distillation treatment. Particularly, it is difficult to separate R1233zd from R245fa by means of distillation. If the concentration of R1233zd is reduced by such distillation to the limiting point stipulated by the above-mentioned PAFT II, the distillation yield of R245fa is extremely lowered, which will lead to a large increase in its production cost.
In general, as a method for separating a saturated halogenated hydrocarbon from unsaturated impurities such as unsaturated halogenated hydrocarbons having physical properties similar to those of the saturated hydrocarbon, a method has been recommended wherein a certain extent of separation is carried out by means of distillation, and then, the remaining unsaturated impurities are removed by means of a chemical method. Heretofore, such various chemical methods have been proposed. For example, U.S. Pat. Nos. 2,999,855 and 4,129,603 disclose an oxidation method using aqueous potassium permanganate as an effective method.
In addition, European Patent 370,688 discloses a decomposition method of unsaturated impurities in a gas phase using a metal oxide such as hopcalite. Further, JP-A-5-32567 discloses a method wherein unsaturated compounds are reacted with chlorine gas in the presence of a catalyst such as &ggr;-alumina and activated carbon to convert unsaturated compounds to their chloride compounds.
Further, WO97/37955 discloses a method wherein unsaturated impurities such as the above-mentioned R1233zd contained in R245fa are removed by chlorination with chlorine gas under light irradiation.
However, those conventional methods have the following disadvantages and thus can not be satisfied. Namely, the method using an aqueous solution of potassium permanganate disclosed in U.S. Pat. No. 2,999,855 have problems from an industrial viewpoint as described below: Potassium permanganate is relatively expensive; Disposal treatment of manganese, heavy metal, compound, is required. The objective saturated halogenated hydrocarbon is moved to an aqueous solution phase of potassium permanganate, which will lead to the loss of the saturated halogenated hydrocarbon.
Further, in the method disclosed in the European Patent 370,688, a life time of the metal oxide is relatively short such as 204 hours at longest, and the activity of the metal oxide is also not sufficient, because the unsaturated impurities to be removed remain in substantial quantity even after carrying out the method.
Further, JP-A-5-32567 discloses a method in a broad concept wherein the unsaturated impurities are reacted with chlorine gas in the presence of the catalyst such as &ggr;-alumina and activated carbon to convert them to their chlorinated compounds, which will be then removed. However, R245fa, an objective compound in the method of the present invention, has a relatively low stability against an alkali in comparison with the compounds disclosed in said patent. Therefore, their dehalogenation reactions are likely to occur, and at the same time, their chlorination reactions are also likely to occur in the presence of chlorine gas. Accordingly, it can not be expected by those skilled in the art whether this method is applicable to a case of R245fa.
Further, in the method disclosed in WO97/37955, wherein the impurities are removed by chlorination using chlorine gas under irradiation of light, it is difficult to control such reaction due to a photochlorination reaction. As a result, byproducts caused by the chlorination of R245fa are generated in relatively large amount. For example, the results shown in Table 1 of the Example shows that R235fa, a chlorinated compound of R245fa, will be generated in an amount of not less than 1%, when R1233zd, an unsaturated impurity, is reduced to not more than 100 ppm. Further, when the fluorinated compound which is obtained by the reaction of R240fa with hydrogen fluoride is employed, it is required to remove hydrogen fluoride before the above chlorination reaction, since the light irradiation lamp made of glass is corroded by the remaining hydrogen fluoride.
The object of the present invention is to provide a new effective treating method of R245fa wherein the amounts of R1233zd and/or the above-mentioned other unsaturated impurities are reduced by converting them to other harmless compounds, while the loss of R245fa, an objective compound, is maintained at a minimum level during its treatment.
The another object of the present invention is to provide a new effective treating method of R245fa wherein R1233zd and/or the above-mentioned other unsaturated impurities contained in R245fa are converted to other harmless compounds, which are then removed, whereby the purity of R245fa, an objective compound, can be increased.
DISCLOSURE OF THE INVENTION
The present invention, which has been made to attain the above-mentioned objects, is to provide a method for treating R245fa, which comprises contacting R245fa containing unsaturated impurities including R1233 and/or other halogenated hydrocarbons having a unsaturated bond in a gas phase with chlorine gas in the presence of an activated carbon catalyst, whereby said unsaturated impurities are converted to the chlorine addition compounds to reduce the content of said unsaturated impurities.
In accordance with the present invention, when R245fa is contacted in a gas phase with chlorine gas in the presence of an activated carbon catalyst, preferably, an activated carbon catalyst having an ash content of not more than a particular value, the side reactions can be suppressed at a minimum level in comparison with a case wherein other catalysts such as alumina are employed. The above side reactions are such that R245fa is subjected to a dehydrohalogenation reaction to produce an unsaturated compound, and that R245fa itself is chlorinated to produce chlorinated byproducts such as R235fa. These facts are newly found by the present inventors, and the present invention is based on such facts.
BEST MODE FOR CARRYING OUT THE INVENTION
The details of the present invention will be described with referring to Examples in the following.
R245fa to be treated by the present invention contains unsaturated impurities including chain or cyclic halogenated hydrocarbons having an unsaturated bond such as a double bond and a triple bond between their carbon atoms. Such unsaturated impurities include R1233zd a
Ohnishi Keiichi
Okamoto Hidekazu
Asahi Glass Company Limited
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Siegel Alan
LandOfFree
Method of treating 1,1,1,3,3-pentafluoropropane does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of treating 1,1,1,3,3-pentafluoropropane, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of treating 1,1,1,3,3-pentafluoropropane will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2901769