RU2455272C2 - Methods for geometric isomerisation of halogenated olefins - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to a method of converting cis-1,3,3,3-tetrafluoropropene to trans-1,3,3,3-tetrafluoropropene, involving: a) feeding the starting material into a reactor, said material containing cis-1,3,3,3-tetrafluoropropene and b) bringing said starting material into catalytic reaction conditions which are effective for converting at least part of said cis-1,3,3,3-tetrafluoropropene in said material to trans-1,3,3,3-tetrafluoropropene, wherein said conditions involve action on said material of a catalyst based on a metal selected from a group consisting of halogenated metal oxides, Lewis acids in form of metal halides, zero-valence metals and combinations thereof at reaction temperature from about 25°C to about 600°C.

EFFECT: achieving high degree of conversion and high selectivity of said reaction.

12 cl, 3 tbl, 3 ex

Description

FIELD OF TECHNOLOGY

This invention relates to methods for geometric isomerization of halogenated olefins. According to some aspects, this invention relates to methods for the conversion of cis-C ₂ -C ₆ fluoroolefins to trans-C ₂ -C ₆ fluoroolefins.

BACKGROUND OF THE INVENTION

Among halogenated olefins, tetrafluoropropenes are known to be suitable for use in various fields. For example, U.S. Patent Application No. 10/694273, which is assigned to the assignee of the present invention and incorporated by reference in this application, describes the use of CF ₃ CH = CFH as a cooling agent with a low overall heating potential, as well as a blowing agent for use in connection with the formation of various types of foams. In addition, CF ₃ CH = CFH can also be functionalized to produce various compounds as intermediates suitable for the preparation of industrial chemical agents. Applicants, however, have concluded that some geometric isomers of halogenated olefins are more preferred than others in some embodiments. For example, the trans form of tetrafluoropropene is preferable for some cooling areas than the cis form. Applicants have also found that many of the currently used methods for producing halogenated olefins, and in particular tetrafluoropropene, lead to a mixture of geometric isomers. As a result, the applicants concluded that there is a need for methods that are capable of converting one geometric isomer of a halogenated olefin into a more desirable other geometric isomer.

US patent No. 6734332, Slaugh et al., Provides a method for enriching a product stream with one geometric isomer with respect to another. More specifically, in this patent, a stream containing a mixture of geometric olefin isomers (cis and trans forms) is introduced into the addition reaction zone, where it is contacted with a linear polyaromatic compound, which tends to preferentially bind to the desired shape of the geometric isomer. The adduct thus formed is then easily separated from the less desirable geometric shape, and then the adduct dissociates and is released to form a stream enriched in the more desirable geometric shape. However, one of the disadvantages of this method is that it does not provide further quantities of the desired geometric shape. This method includes sufficiently large stages, which are associated with the costs of separating existing geometric shapes from one another.

US Pat. No. 5,672,803 describes a method for selectively producing a transgeometric isomer of non-conjugated diolefins. This method involves reacting an isomerizable non-conjugated diolefin with a combination of other olefin compounds under catalytic conditions to selectively form a trans-non-conjugated diolefin isomer. The patent states that the preferred catalyst is rhenium, tungsten, molybdenum, cobalt, tantalum, niobium and chromium are also described as potential reaction catalysts. However, one of the drawbacks of this method is that it is rather complex, as it requires some molecular products to be fed into the reaction system. This is a disadvantage not only from the point of view of increasing the complexity of the process scheme, but also from the point of view of raw material costs and the need for equipment for subsequent isolation. In addition, the method described in US Pat. No. 5,672,803 is limited to the isomerization of non-conjugated diene olefins.

The effectiveness of transition metal chlorides as isomerization catalysts was studied by K. Endo, S. Okayama, and T. Otsu in connection with the polymerization of cis-2-butene combined with isomerisation of the monomer.

Applicants are not aware of any published method for the isomerization of the cis form to the trans form of halogenated C ₂ -C ₆ olefins, this invention is based, at least in part, on the recognition of the need to create such a method and to create effective methods for performing such isomerization, in particular the conversion of cis-1,3,3,3-tetrafluoropropene to obtain trans-1,3,3,3-tetrafluoropropene.

SUMMARY OF THE INVENTION

Applicants have developed a method for converting isomerizable halogenated C ₂ -C ₆ olefins from one geometric shape to a more preferred geometric shape.

Preferred aspects of this method include converting a C ₂ -C ₆ cis olefin to a trans form, comprising subjecting the cis form of the compound, preferably contained in a stream, to conditions that are effective for converting at least about 50% and even more preferably at least about 70% of the cis form of the compound into a trans form of the compound. In preferred embodiments, the C ₂ -C ₆ olefin contains tetrafluoropropene with the conversion of cis-1,3,3,3-tetrafluoropropene (cis-HFO-1234ze), preferably with a high degree of conversion and with high selectivity in trans-1,3,3, 3-tetrafluoropropene (trans-HFO-1234ze). One important element of such preferred options arises from the applicants ’discovery of the fact that certain catalysts that are used as directed in this application are able to efficiently achieve such a high degree of conversion and selectivity for such reactions.

Thus, according to preferred embodiments, conditions that are effective to achieve the desired high degree of conversion and high selectivity include the action on the feedstock of a catalyst based on a metal selected from the group consisting of halide-containing metal oxides, metal halides of Lewis acids, zero-valence metals and their combinations, preferably under reaction conditions, including reaction temperature and residence time, which are effective for conversion at least at about 5% of the cis form of the compound to other compounds and to achieve selectivity for the compound transform of at least about 70%.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present invention provides methods and compositions of catalysts suitable for use in these methods for the isomerization of certain hydrocarbons, especially fluoroolefins in the cis form of a molecule, into a trans form. More specifically, preferred embodiments of the invention relate to the conversion of fluorinated olefin compounds containing at least one fluorine atom as a substituent and a second fluorine atom or fluorine-containing group (e.g., CF ₃ ) in the form of cis-one to the other via an olefinic double bond and conversion of such a molecule in a form in which the first fluorine is located in the trans position - relative to the second substituent - fluorine or fluorine-containing group (e.g., CF _3), i.e. the substituents are located in trans Orme in relation to each other.

Although the method and catalyst according to this invention can be easily adapted for use in general for fluoroolefins, according to preferred aspects of the present invention, the methods and catalysts are adapted for use in connection with the conversion of fluorinated olefins containing three carbon atoms, and more particularly such compounds with three carbon atoms, containing only fluorine atoms as substituents, even more specifically to the conversion of tetrafluoropropenes.

It is proposed that various streams be used as feed for the preferred reaction step of the invention. For example, in some embodiments of the invention, the feed stream that contains the cis form of the compound to be converted may contain relatively low concentrations of the compound, for example, less than about 50% by weight, or possibly even 1% by weight. However, in general, in many embodiments, it is more preferable that the feed stream containing the cis form of the compound undergoing conversion contain rather high concentrations of the cis compound. Thus, in preferred embodiments, the feed stream in accordance with preferred aspects of the invention comprises at least about 5% by weight of the cis form of the compound, more preferably at least about 7% by weight, and even more preferably at least about 10% by weight the weight of the cis form of the compound.

It is believed that a variety of other compounds and materials that do not adversely affect the preferred conversion and selectivity of the present invention can be contained in the feed stream entering the reaction step of the invention. For example, the stream supplied to the reaction step of the invention may be an upstream stream that can be produced in an industrial plant for producing fluorinated olefins. According to one proposed variant of the present invention, the feed stream entering the reaction step is an effluent stream or at least a portion of the stream leaving after one or more upstream reactions when product stream (s) containing unreacted halogenated alkanes are obtained and cis olefins, more particularly unreacted fluorinated and / or chlorinated propanes and cis forms of fluorinated propenes. As a specific example, you can cite a patent application with file number H0013287-4511, which is filed in parallel with this application and is included as a reference, which describes a method involving the reaction of one or more of the following fluorinated alkanes: chlorotetrafluoropropane (HCFC-244) and pentafluoropropane (HFC-245), including all isomers of each of these compounds, but preferably 1-chloro-1,3,3,3-tetrafluoropropane (HCFC-244fa), 1,1,1,3,3-pentafluoropropane (245fa) and 1,1,1,2,3-pentafluoropropane (245eb) to give HFC-tetrafluoropropene. The reaction product often contains some unreacted starting material and a combination of cis-1,3,3,3-tetrafluoropropene and trans-1,3,3,3-tetrafluoropropene together with a halogenated compound such as HF. One aspect of the preferred embodiments of the invention includes the conversion of the cis form of the fluorinated olefin in such a stream and / or other similar streams that have been processed (by separation, for example) using this or a similar reaction product stream into a trans form, preferably with a degree of conversion equal to at least about 1%, more preferably at least about 70% and even more preferably about 90%, while achieving selectivity for the trans form of the compound, p implicit at least about 80%, even more preferably at least about 95%, and according to certain particularly preferred embodiments of about 98%.

It is proposed to carry out the isomerization step using a variety of process parameters and conditions, taking into account the indications contained in this application, for example, it is proposed that the isomerization step according to some non-preferred embodiments be carried out in the liquid phase. However, according to many variations of the present invention, it is preferred that this reaction step is carried out in the gas phase, preferably in the presence of a catalyst, preferably a metal catalyst.

Applicants have found that the high desired values of the degree of conversion of the cis form to trans form and selectivity, especially and preferably using the feed streams described above, can be obtained by a suitable choice of operating parameters, including, but not limited to, type of catalyst, reaction temperature and residence time in the reactor. Preferably, the values of these parameters are described below.

Applicants have found that three common types of catalysts used in accordance with this invention are very desirable and effective, which allow a high degree of conversion and selectivity to be achieved. More specifically, preferred embodiments of the processes of the invention typically include cis-acting a metal-based catalyst compound selected from the group consisting of halogenated metal oxides, metal halides — Lewis acids, zero-valence metals, and combinations of these compounds.

With regard to catalysts comprising halogenated metal oxides and / or metal-Lewis acid halides, it is preferred that the metal is and preferably consists of one or more metals selected from transition metals, boron group metals, rare earth metals, VA group metals, alkali metals metals, alkaline earth metals and their combinations.

Although many transition metals can be used as a metal in the catalysts of the present invention, it is generally preferred that the catalyst includes a transition metal selected from the group consisting of transition metals with an atomic number of from about 21 to about 57 and transition metals with an atomic number of 77 (iridium) or 78 (platinum). As for catalysts that contain a metal selected from the group of boron, those metals are preferred which have an atomic number of from about 13 to about 81, and among them, Ti and Al are particularly preferred. For catalysts containing a metal selected from alkaline earth metals, Mg is preferred. For catalysts that contain a metal selected from Group VA metals, Sb is preferred. References to the Periodic Table are given in this application under the CAS (Chemical Abstracts Service) version of the Periodic Table of the Elements. For catalysts that contain a metal selected from among alkali metals, those metals having an atomic number of from about 3 to about 37 are preferred, metals with an atomic number of from about 3 to about 19 are particularly preferred. For catalysts containing a metal selected from rare earth metals, cerium is preferred. Of course, it is believed that any metal and all combinations of the above metals and other metals not mentioned in this application can be used in accordance with this invention.

In the case of catalysts which are halogenated metal oxides (which are sometimes referred to as HMO catalysts for convenience) and Lewis acid catalysts (which are referred to below as LA catalysts for convenience), it is generally preferred that the catalysts contain a transition metal or Al, preferably also so that in the case of a transition metal, it is selected from the group consisting of transition metals with an atomic number of from about 21 to about 57 and mixtures thereof.

Of the transition metals for use in HMO and LA catalysts, Group VIB metals are preferred, Cr is particularly preferred among this group. In general, in the case of HMO and LA catalysts that contain a transition metal, it is preferable to select a metal from the group consisting of Cr, Mo, V, Nb, Fe, La, Ni, Zn, and combinations thereof. In general, in the case of HMO and LA catalysts that contain a rare earth metal, the metal is preferably Ce. In general, in the case of HMO and LA catalysts that include boron, the metal is preferably selected from Al, Ti, and combinations thereof. In the case where the HMO and LA catalysts include an alkaline earth metal, Mg is the preferred metal. In the case of HMO and LA catalysts including alkali metals, it is preferable to select a metal from Li, Na, K and combinations thereof.

It is believed that the metals used in the catalysts HMO and LA, according to this invention can be used in any available oxidation state. In some embodiments, it is preferred that the metals are used in accordance with the following oxidation states:

Cr ³⁺ and Cr ⁶⁺

Mo ⁶⁺

V ⁵⁺

Nb ⁵⁺

Sb ⁵⁺

Ti ⁴⁺

Zr ⁴⁺

Ce ⁴⁺

Al ³⁺

Fe ³⁺

La ³⁺

Mg ²⁺

Ni ²⁺

Zn ²⁺

Li ⁺

Na ⁺

K ⁺

In general, halogen can be used as a component that is included in the HMOs of this invention. However, it is preferable that the HMO catalyst according to this invention is a fluorinated metal oxide, more preferably a fluorinated transition metal oxide and even more preferably a fluorinated transition metal oxide, where the metal is selected from the group consisting of Cr, Mo, V, Nb, Fe, La, Ni, Zn, and combinations thereof, and in some embodiments fluorinated chromium oxide is particularly preferred. The agent and the conditions used to process the metal oxide in order to obtain a catalyst for HMO can vary widely according to this invention. In some embodiments, it is preferable to treat the metal oxide with one or more of the following halogenating agents: HF, F ₂ , HCl, Cl ₂ , HBr, Br ₂ , HI, I ₂ ; and their combination. In some embodiments, the halogenating agent includes one or more of HF, F ₂ , HCl, Cl ₃ , HBr, Br _2, and a combination thereof, even more preferably HF, F ₂ , HCl, Cl ₂ and a combination thereof, and even more preferably HF, F ₂ and their combination.

In general, any coordinating component may be used as the component that is included in the LA of the invention. However, it is preferable that the LA catalyst of the present invention comprise a Lewis acid halide, more preferably a Lewis acid halide, where the halogen is selected from F, Cl, Br, I and combinations thereof, more preferably from F, Cl, Br and combinations thereof, even more preferably from F, Cl and combinations thereof, and most preferably the halogen is F. In some particularly preferred embodiments, the Lewis acid catalyst is a halide, preferably a fluoride derived from a transition metal and, yes more preferably, the Lewis acid is a halide derived from a transition metal selected from the group consisting of Cr, Mo, V, Nb, Fe, La, Ni, Zn and combinations thereof, with Cr and Fe being preferred in some embodiments. The agent and conditions used to prepare the LA catalysts of this invention can vary widely. In some embodiments, it is preferred that the LA catalyst be prepared, for example, by dissolving in an aqueous halide salt, followed by evaporation and calcination. According to one specific, but not limiting example, the process for preparing a catalyst includes: 1) dissolving metal hydroxides, metal oxides and / or carbonates, preferably in an aqueous HF solution (preferably in a 49% aqueous HF solution) with stirring in a container of Teflon®; 2) evaporation of the solution to dryness; 3) firing the dried sample at elevated temperature for a sufficiently long period of time, preferably in the presence of an inert gas such as N ₂ ; and 4) optionally, but it is preferable to obtain particles of the material thus obtained, preferably by grinding, to form a finely divided powder and then it is preferable to obtain tablets of the desired shape.

Regarding neutral metal-based catalysts (sometimes referred to as NM catalysts), it is preferred that they include one or more metals selected from Groups VIII and IB, with Co and Pd being preferred in some embodiments.

The specific form of the catalyst can also vary widely. For example, the catalysts of this invention may contain other components, some of which can improve the activity and / or viability of the composition of the catalyst. Preferred catalysts according to some variants can be activated by compounds of molybdenum, vanadium, tungsten, silver, iron, potassium, cesium, rubidium, barium, or combinations thereof. The catalyst may contain other additives, such as binders and lubricants, to ensure the physical integrity of the catalyst during granulation or molding of the catalyst to obtain the desired forms. Suitable additives include magnesium stearate, charcoal and graphite. When binders and / or lubricants are added to the catalyst, they typically comprise about 0.1-5% by weight of the catalyst. In addition, the catalyst can be used without a carrier or on a carrier, or using a combination of these forms. According to the invention, all types of carriers known to those skilled in the art can be used. For example, any of the catalysts described herein may be supported on one or more materials, including but not limited to carbon, activated carbon, graphite, silicon dioxide, alumina, fluorinated graphite, fluorinated alumina, and combinations of any two or more of these materials.

Before use, the catalyst can be activated either by treating HF in the case of HMO and LA catalysts or by treating H ₂ in the case of NM catalysts at elevated temperatures. After application for some time in the method of the invention, the activity of the catalyst may decrease. When this happens, the catalyst can be reactivated. The reactivation of the catalyst can be carried out by any known method, for example by passing air or oxygen diluted with nitrogen over the catalyst at temperatures from about 100 ° C to about 400 ° C, preferably from about 200 ° C to about 375 ° C for a period of time from about 0.5 h to about 3 days followed by treatment with either HF at temperatures from about 25 ° C to about 400 ° C, preferably from about 200 ° C to about 350 ° C in the case of HMO and LA catalysts, or H ₂ at temperatures from about 100 ° C to about 400 ° C, preferably from about 200 ° C. to about 350 ° C. in the case of NM catalysts.

It is believed that the methods of the invention, taking into account this description, can be adapted for use at a wide variety of reaction temperatures. For example, in preferred embodiments, the reaction temperature may be from about 25 ° C to about 600 ° C. Used in this description, the term "reaction temperature" refers to the average temperature in the catalyst bed, unless otherwise indicated. In some preferred embodiments, the reaction temperature is from about 50 ° C to about 350 ° C, and even more preferably from about 75 ° C to about 300 ° C.

Although a wide variety of temperatures can be used according to this invention, the applicants have unexpectedly found that extremely good properties with respect to the degree of conversion and / or selectivity and preferably both properties can be obtained at a temperature in the preferred range of from about 75 ° C to about 350 ° C. more preferably from about 90 ° C. to 250 ° C. and even more preferably from about 90 ° C. to about 110 ° C. When it is said that these preferred ranges are generally used in the conversion reactions of the invention, in some embodiments they provide particularly good results, for example, in the case of isomerization of C ₂ -C ₆ fluoroolefins, more preferably C ₃ -C ₄ fluoroolefins and even more preferably tetrafluoropropenes. Thus, in some embodiments, when the isomerization reactions include or preferably consist essentially of converting cis-HFO-1234ze to trans-HFO-1234ze, it is preferred that the reaction temperature is from about 90 ° C to about 250 ° C.

It is assumed that when carrying out the processes of the invention, pressure can be applied over a wide range. Nevertheless, in certain preferred embodiments the reaction is conducted at a pressure ranging from a vacuum of about 5 torr to about 200 lb / ^in2.

For the implementation of the preferred reactions of the invention, various contact times can be used. However, in some preferred embodiments, the residence time is preferably from about 0.5 s to about 600 s.

According to preferred aspects of the invention, the cis form of the convertible compound is contained in the feed stream, the conversion step comprises one or more reaction vessels, at least one of which preferably contains the catalyst of the invention, and introducing the feed stream into the vessel (s) under conditions that are effective to achieve the desired degree of conversion. It should be noted that the term "stream" used in this description is not limited to one stream, it is believed that according to some options, the individual streams can be connected outside the vessel and then introduced together into the vessel, or alternatively, the individual streams can constitute the feedstock and each of them is introduced into the vessel (s) at different times and / or in different places. This condition applies throughout the text when applying the term “stream”, unless otherwise specified.

The following examples are provided to illustrate the present invention. However, it should be noted that the present invention is not limited to the specific details indicated in the examples.

EXAMPLES

Example 1: Isomerization of cis-1234ze over Fluorinated Cr ₂ O ₃ as a Catalyst

Fluorinated Cr ₂ O _{3 is} used as a catalyst (20 cm ³ by volume). A mixture of 85.3% cis-1234ze and 14.7% HFC-245fa is passed over this catalyst at a rate of 12 g / h at the temperatures indicated in Table 1 below. As shown in this Table, with the exception of 30 ° C, the catalyst provides cis conversion -1234ze, equal to about 80%, and selectivity for trans-1234ze about 95% at all indicated temperatures. These results show that fluorinated Cr ₂ O ₃ is a very active catalyst and selective for the conversion of cis-1234ze to trans-1234ze according to this invention.

Table 1 Cis-1234ze isomerization over fluorinated Cr ₂ O ₃ The reaction temperature, ° C The degree of conversion of cis-1234ze,% Selectivity for trans-1234ze,% thirty 5.8 one hundred one hundred 91.0 one hundred 150 87.8 one hundred 200 84.7 99 250 82,4 99 275 81.5 97.2

Example 2: Isomerization of cis-1234ze over a Lewis acid (metal halide) as a catalyst

The catalysts used in this example 2 include a number of metal halides on and without support, namely AlF ₃ , FeF ₃ , 10.0 wt.% FeCl ₃ / AC and 10.0 wt.% LiCl / AC. During the reaction, 20 cm ^{3 of} each catalyst was used. A mixture of 85.3% cis-1234ze / 14.7% 245fa was passed over each of the four catalysts at a rate of 12 g / h at temperatures ranging from 200 to 300 ° C. As shown in Table 2, at a temperature of 200 ° C., AlF ₃ provided a cis-1234ze conversion of approximately 85% and a trans-1234ze selectivity of approximately 99%; at 300 ° С FeFe ₃ ensured that the degree of cis-1234ze conversion was approximately 80% and the trans-1234ze selectivity was 100 ° С. The FeCl ₃ / AC catalyst provided a conversion of less than 30% and a selectivity of less than 90%. These results show that metal fluorides as catalysts are more active in the isomerization of cis-1234ze than metal chlorides.

Table 2. Cis-1234ze isomerization over a Lewis acid catalyst (metal halide) Catalyst The reaction temperature, ° C The degree of conversion of cis-1234ze,% Selectivity for trans-1234ze,% Alf ₃ 200 85,2 99.3 FeF ₃ 300 80.9 one hundred 10.0 wt.% FeCl ₃ / AC 300 27.1 87.8 10.0 wt.% LiCl / AC 300 0.6 94.6

Example 3: Isomerization of cis-1234ze over a Neutral Metal Based Catalyst

The catalysts used in example 3 include two catalysts - Pd and Co on activated carbon, both of which contain 0.5 wt.% Metal. During the reaction, 20 cm ^{3 of} each catalyst is used. A mixture of 85.3% cis-1234ze / 14.7 245fa was passed over each of the catalysts at a rate of 12 g / h at a temperature of 350 ° C. As can be seen from Table 3, both catalysts provided a cis-1234ze conversion rate of about 45% and a trans-1234ze selectivity of about 98%. These results show that the metals Pd and Co have some activity in the process of conversion of cis-1234ze to trans-1234ze.

Table 3. CIS-1234ze isomerization over a neutral metal catalyst Catalyst The reaction temperature, ° C The degree of conversion of cis-1234ze,% Selectivity for trans-1234ze,% 0.5 wt.% Pd / AC 350 46.9 98.5 0.5 wt.% Co / AC 350 45.0 98.2

Claims (11)

1. A method of converting cis-1,3,3,3-tetrafluoropropene to trans-1,3,3,3-tetrafluoropropene, comprising:
a) providing in the reactor a feedstock comprising cis-1,3,3,3-tetrafluoropropene, and
b) introducing said feedstock into a catalytic reaction that is effective for converting at least a portion of said cis-1,3,3,3-tetrafluoropropene in said feed into trans-1,3,3,3-tetrafluoropropene, wherein these conditions include the action on the specified raw materials of a catalyst based on a metal selected from the group consisting of halogenated metal oxides, Lewis acids in the form of metal halides, zero-valence metals and their combinations at a reaction temperature of from about 25 ° C to about 600 ° C. 2. The method according to claim 1, characterized in that the metal in the halogenated metal oxide is selected from the group consisting of: (1) transition metals with an atomic number from about 21 to about 57, (2) metals from group IIIA with an atomic number from about 13 to about 81; (3) metals from the group VA with an atomic number from about 51 to about 83; (4) rare earth metals such as cerium; (5) alkali metals from the group IA with an atomic number from about 3 to about 37 , (6) alkaline earth metals from group IIA with an atomic number of from about 12 to about 56, and (7) combinations of any two and whether more than these metals. 3. The method according to claim 1, characterized in that the metal in the halides of metals that are Lewis acids is selected from the group consisting of: transition metals with an atomic number from about 21 to about 57, (2) metals from group IIIA with an atomic number from about 13 to about 81; (3) metals from the group VA with an atomic number from about 51 to about 83; (4) rare earth metals such as cerium; (5) alkali metals from the group IA with an atomic number from about 3 to about 37, (6) alkaline earth metals from group IIA with an atomic number from about 12 to about 56, and (7) comb nations any two or more of these metals. 4. The method according to claim 1, characterized in that the catalyst comprises a metal from group VIII or IB, and wherein said metal is contained in a form that has an oxidation state of zero. 5. The method according to claim 1, characterized in that the reaction conditions are effective for converting at least about 5% of the cis form and to achieve selectivity in the trans form of at least about 70%. 6. The method according to claim 1, characterized in that the raw material in the reactor contains at least about 5% by weight of the specified cis form. 7. The method according to claim 1, characterized in that the raw material in the reactor contains at least about 10% by weight of the specified cis form. 8. The method according to claim 1, characterized in that the feed in the reactor includes unreacted halogenated propanes and the cis form of fluorinated propenes. 9. The method according to claim 1, characterized in that the reaction conditions are effective for converting at least about 70% of the cis form and to achieve a trans form selectivity of at least about 70%. 10. The method according to claim 9, characterized in that the reaction conditions are effective for converting at least about 90% of the cis form and to achieve selectivity in the trans form of at least equal to about 80%. 11. The method according to claim 9, characterized in that the reaction conditions are effective for converting at least about 95% of the cis form and to achieve selectivity for the trans form of at least equal to about 98%.