FR2989374A1 - Preparing hydrofluoropropene/hydrofluorobutene in form of isomer E, involves subjecting mixture of isomer E and Z and hydrofluoropropene/hydrofluorobutene to thermal treatment or isomerizing the mixture at temperature of specified range - Google Patents

Abstract

Preparing hydrofluoropropene or hydrofluorobutene in the form of isomer E, comprising subjecting a mixture of isomers E and Z of hydrofluoropropene or hydrofluorobutene to a thermal treatment or isomerizing a mixture of isomers of hydrofluoropropene or hydrofluorobutene at a temperature of 100-500[deg] C, preferably 150-450[deg] C.

Description

The present invention relates to a process for the preparation of an olefinic compound in the form of a specific isomer. It relates more particularly to a process for preparing a hydrofluoropropene or hydrofluorobutene compound in the isomeric form E (ie, trans isomer).

In general, the processes for producing a compound existing in at least two isomeric forms lead to mixtures. Often, these isomers have so different toxicities and properties that it is necessary to separate and purify them before possible use. There may be mentioned in particular the case of 1-chloro-3,3,3,4-trifluoropropene which exists in the cis (Z) and trans (E) form with an increased toxicity of the cis isomer. Hydrofluoropropene or hydrofluorobutene compounds are likely to replace hydrofluorocarbons in various applications such as refrigeration, blowing agent and solvents because they are less harmful to the environment. There is therefore a real need to specifically manufacture an isomer of these hydrofluoropropenes or hydrofluorobutenes. The present invention therefore provides a process for producing a hydrofluoropropene or hydrofluorobutene in the form of an E isomer comprising at least one step during which a mixture of E and Z isomers of said hydrofluoropropene or hydrofluorobutene are subjected to a heat treatment step , hereinafter referred to as isomerization step, at a temperature between 100 and 500 ° C, preferably between 150 and 450 ° C. The Z isomer preferably represents at least 10 mol% of the mixture to be treated, more particularly at least 45 mol% and advantageously at least 70 mol%.

The isomeric mixture can come directly from a process for producing said hydrofluoropropene or hydrofluorobutene or after a step of separating the mixture to recover the E isomer. According to one embodiment of the invention, the isomerization step may be made from a mixture containing essentially Z isomer.

As hydrofluoropropene, there may be mentioned in particular 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd), 1,3,3,3-tetrafluoropropene (HFO-1234ze) and 1,2,3,3, 3-pentafluoropropene (HFO-1225ye). As hydrofluorobutene, there may be mentioned in particular hexafluorobutenes such as 1,1,1,4,4,4, -hexafluoro-2-butene (HF0-1336mzz), 1,2,3,3,4,4, -hexafluoro-2 butene, 1,2,3,4,4,4, 2-hexafluoro-butene, 1,3,3,4,4,4, 2-hexafluoro-butene, tetrafluorobutenes such as 1,4,4,4 2-tetrafluoro-2-butene, 1,3,4,4-tetrafluoro-2-butene, 1,3,3,4-tetrafluoro-2-butene, 1,2,4,4-tetrafluoro-2-butene, 1, 2,3,4-tetrafluoro-2-butene and 1,2,3,3-tetrafluoro-2-butene, and chlorohexafluorobutenes such as 1-chloro, 1,3,3,4,4,4-hexafluorobutene, 1-chloro, 1,2,3,4,4,4-hexafluorobutene, 1-chloro, 1,2,3,3,4,4-hexafluorobutene, 1-chloro, 2,3,3,4,4 , 4-hexafluorobutene, 2-chloro, 1,3,3,4,4,4-hexafluorobutene, 3-chloro, 1,2,3,4,4,4-hexafluorobutene, 4-chloro, 1,2,3 , 3,4,4-hexafluorobutene, and heptafluorobutenes such as 1,2,3,3,4,4,4-heptafluoro-2-butene. The process according to the present invention is particularly suitable for the isomerization of hydrofluorobutene-1, especially cis-HFO-1336mzz in transH F0-1336mzz. According to a preferred embodiment of the invention, the process comprises at least one step during which a stream containing essentially 1,1,1,4,4,4-trans-2-hexafluoro butene or a mixture of cis and trans isomers of 1,1,1,4,4,4-hexafluoro-2-butene is subjected to the aforementioned heat treatment to give mainly E isomer (E-HFO-1336mzz). The boiling point of the E-HFO-1336mzz isomer is about 8 ° C, while the boiling point of the Z-HFO-1336mzz isomer is about 31 ° C. In addition, the Z isomer is flammable. Although it is not necessary, the isomerization step according to the present invention can be carried out in the presence of a catalyst.

The catalyst may comprise a transition metal oxide or a derivative or a halide or an oxyhalide of such a metal. Examples of catalysts are FeCl 3, chromium oxyfluoride, chromium oxides (optionally subjected to fluorination treatments), chromium fluorides and mixtures thereof. Other possible catalysts are the carbon-supported catalysts which are based on antimony and on aluminum (AlF 3, Al 2 O 3, aluminum oxyfluoride, aluminum fluoride). In general, catalysts which can be used are chromium oxyfluoride, fluoride and aluminum oxyfluoride and supported or non-supported catalysts containing a metal such as Cr, Ni, Zn, Ti, V, Zr, Mo, Ge, Sn, Pb, Mg. Reference may also be made to the documents WO 2007/079431 in p.7, 1.1-5 and 28-32, EP 0939071 in paragraph [0022], WO 2008/054781 in p.9 I.22-p.10 1.34, WO 2008/040969 in claim 1, all incorporated herein by reference. Prior to use, the catalyst may be activated, typically with air, oxygen, or chlorine and / or with HF under appropriate conditions.

In a preferred embodiment, a mixed catalyst containing both chromium and nickel is used. The molar ratio Cr: Ni, in metallic elements, is generally from 0.5 to 5, for example from 0.7 to 2, for example of about 1. The catalyst may comprise, by weight, from 0.5 to 20 % of chromium and 0.5 to 20% of nickel, preferably 2 to 10% of each metal. The metal may be present in metallic form or in the form of a derivative, in particular oxide, halide or oxyhalide. These derivatives, in particular halides and halides oxides, are obtained by activation of the catalytic metal. Although activation of the metal is not necessary, it is preferred. The support is preferably prepared from aluminum, for example alumina, activated alumina or aluminum derivatives. These derivatives include aluminum halides and aluminum oxide halides, for example as described in US 4,902,838, or obtained by activation. The catalyst may comprise chromium and nickel in activated or unactivated form, on a support which has been subjected to activation or not. Reference can be made to WO 2009/118628, and particularly to the description of the catalyst of p. 1.30 on p.7, 1.16, which is hereby incorporated by reference.

According to another particularly preferred embodiment, the catalyst may also be high surface area Cr, which is preferably unsupported. The catalyst may contain a low content of one or more co-catalysts such as Co, Zn, Mn, Mg and Ni salts. A preferred cocatalyst is Ni. Another preferred cocatalyst is Zn. Another preferred cocatalyst is Mg. A description of the high surface area Cr catalyst is disclosed in WO 2009/158321, p. 4 and 6. Acidic catalysts such as Lewis acids may also be suitable. According to a particularly preferred embodiment of the invention, the isomerization step is carried out in the absence of the catalyst. The isomerization step according to the present invention is preferably carried out at atmospheric pressure or higher. The pressure can reach 35 bar absolute, even 100 bar.

The isomerization step may be carried out in a heated enclosure, for example any type of reactor or separation column. When this isomerization step in implementation in the gas phase, the heated enclosure can partially or completely contain an inert lining or a catalyst.

The residence or contact time, defined as the volume of the chamber or the volume of catalyst divided by the total flow rate of the reagents and inert, adjusted to the operating conditions of pressure and temperature, may be between 0.1 and 50h and preferably between 0.5 and 10h.

According to the present invention, the conversion of the Z isomer to the E isomer is preferably greater than 50% and advantageously greater than 70%. The isomer selectivity E is preferably at least 80%, advantageously at least 95%.

The process according to the present invention can be carried out batchwise, semi-continuously or continuously. Embodiment Figure 1 shows an embodiment of the invention. A stream S2 comprising a mixture of isomers E and Z-HFO-1336mzz is introduced continuously into a reactor (1) and heated at a temperature of 250 ° C. under a pressure of 40 bar. The flow S3 at the outlet of the reactor, enriched in isomer Z, is then subjected to a distillation step to give at the top of the column a flow S4 containing the E isomer. A flow S5 containing the Z isomer is withdrawn at the bottom of the reactor. the distillation column. Part S6 of this stream is recovered and another S7 is recycled to the reactor. The flow S2 results from the addition 51 of isomers mixed from a manufacturing unit of the HFO-1336mzz and the flow S7 so as to maintain the flow S2 is at 98.9 mol% in Z-HFO-1336mzz. Under these conditions, the flow S3 contains 75 mol% of E-HFO-1336mzz and 25 mol% of Z-HFO-1336mzz. The E-HFO-1336mzz isomer recovered at the top of the distillation column (2) can then be purified using the known separation methods (distillation, molecular sieve purification, for example) to obtain a commercial grade. 35

Claims (1)

1) A method for producing a hydrofluoropropene or hydrofluorobutene E isomer form comprising at least one step during which a mixture of isomers E and Z of said hydrofluoropropene or hydrofluorobutene are subjected to a heat treatment step, called by the following isomerization step, at a temperature between 100 and 500 ° C, preferably between 150 and 450 ° C. Process according to Claim 1, characterized in that the Z isomer represents at least 10% of the mixture to be treated, preferably at least 45 mol% and advantageously at least 70%. Process according to Claim 1 or 2, characterized in that the hydrofluorobutene is 1,1,1,4,4,4-hexafluoro-2-butene. Process according to any one of the preceding claims, characterized in that the treatment stage is carried out at a pressure of between 1 and 100 bar absolute. Process according to any one of the preceding claims, characterized in that the treatment step is carried out in the presence or in the absence of a catalyst. Process according to any one of the preceding claims, characterized in that the catalyst is an oxide, halide, oxyhalide or transition metal derivatives. 102) 3) 15 4) 20 5) 25 6)