RU2461539C2 - Method of producing fluorinated alkanes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to versions of a method of producing a fluorinated alkane. One of the versions comprises the following steps: (a) bringing at the first reaction step, a source stream containing fluorinated olefin and hydrogen into contact with a first amount of catalyst to obtain at least a first effluent stream containing fluorinated alkane, unreacted fluorinated olefin and hydrogen. The fluorinated olefin is fed to the first reaction step at a rate which is at least 60% higher than the throughput of the catalyst at the first reaction step, and results in the conversion of fluorinated olefin to fluorinated alkane which ranges from 10 to 60%. Then (b) at one or more additional reaction steps, bringing the effluent stream into contact with a second amount of catalyst to obtain fluorinated alkane, wherein the second amount is an amount for achieving conversion of the fluorinated olefin which is higher than the conversion of fluorinated olefin at the first reaction step (a), where the fluorinated olefin is a compound of formula (I): (CX_nY_3-n)(CR¹ _aR² _b)_zCX=CH_mX_2-m (I) and the fluorinated alkane is a compound of formula (II): (CX_nY_3-n(CR¹ _aR² _b)_zCHXCH₂X (II), where: each X independently denotes Cl, F, I or Br; each Y independently denotes H, Cl, F, I or Br; each R¹ independently denotes H, Cl, F, I or Br or an unsubstituted or halogen-substituted methyl or ethyl radical; each R² independently denotes H, Cl, F, I, Br or an unsubstituted or halogen-substituted methyl or ethyl radical; n equals 1, 2 or 3; a and b are each equal to 1 of 2, provided that a+b=2; m equals 0, 1 or 2; and Z equals 0, 1, 2 or 3.

EFFECT: use of the present invention enables to simultaneously achieve high efficiency and selectivity.

14 cl, 2 ex, 2 dwg

Description

The fluorinated alkane class has many and many uses, including use as chemical intermediates, as blowing agents and refrigerants.

Several methods are known for producing fluorinated alkanes, especially fluorocarbons (HFCs). For example, see Chem. Abstract 55: 349 p. (ILKnunyants, MPKrasuskaya and EIMysov, Izvest. Akad. Nauk SSSR, Otdel. Khim. Nauk, 19060, 14 (2), which describes the reduction of a fluorinated olefin, in particular CF ₃ CF = CFH over a palladium catalyst (Pd - Al ₂ O ₃ ) at room temperature to achieve a selectivity for the saturated analogue (CF ₃ CHFCH ₂ ) of about 60% and a selectivity for CF ₃ CFHCH ₃ of about 30%. In Chem. Abstract 125: 167319 (JP 08165256 A2 ) describes the reduction of CF ₃ CF = CF _{2 with} hydrogen in the liquid phase using palladium catalysts supported on BaSO ₄ and / or activated carbon.

Applicants have discovered that the methods described above have disadvantages and / or are not as effective and / or not so economically feasible as to be applied on an industrial scale. For example, applicants have found that it is generally difficult, expensive, or impossible, following the instructions given only in the publications cited above, to carry out a process that would simultaneously provide a high degree of conversion and a high degree of selectivity for the desired fluorinated alkane. The applicants also came to the conclusion that none of the publications mentioned above even discloses problems arising from the implementation of known methods, which consist either in low selectivity for the desired fluorinated alkane and / or in productivity which is unacceptable from an economic point of view on an industrial scale. In other words, known methods, in general, tend to achieve high selectivity in such methods only due to low productivity. While such methods may be acceptable for non-industrial cases, applicants believe that such processes are unfavorable for obtaining industrial products and, in contrast to conventional methods, have created methods that at the same time are capable of providing high performance and high selectivity.

SUMMARY OF THE INVENTION

Applicants provide, according to one aspect of the invention, methods for the synthesis of fluorinated alkanes and preferably fluorinated alkanes containing from three to six carbon atoms and preferably having a degree of fluorine substitution of from about 3 to about 5.

Preferred methods of the invention include reacting a starting fluorinated olefin containing substantially the same number of carbon atoms as the desired fluorinated alkane and the same degree of fluorine substitution. Preferably, the starting fluorinated olefin is reacted under conditions that are effective to produce a reaction product containing one or more fluorinated alkanes having the same number of carbon atoms as the olefin. According to one preferred aspect of the present invention, this olefin conversion step includes a reaction, which is sometimes referred to in this description for convenience, but without limitation, as multi-stage reduction or hydrogenation.

According to one aspect of the invention, such methods preferably include the steps of:

a) hydrogenating an olefin compound of the formula (I)

by carrying out a multi-stage reaction under conditions effective for the formation of at least one fluorinated alkane of the formula (II)

Where

each X is independently Cl, F, I or Br;

each Y is independently H, Cl, F, I or Br;

each R ¹ independently represents H, Cl, F, I, Br or an unsubstituted or halogen-substituted methyl or ethyl radical;

each R ² independently represents H, Cl, F, I, Br or an unsubstituted or halogen-substituted methyl or ethyl radical;

n is 1, 2 or 3;

a and b are each equal to 1 or 2, provided that a + b = 2;

m is 0, 1 or 2 and

z is 0, 1, 2 or 3.

In some preferred embodiments, the reagent of formula (I) comprises an olefin with three carbon atoms of formula (IA), where z is 0, namely an olefin

and the result is an alkane with three carbon atoms of the formula (IIA)

where X, Y, n and m are all indicated above.

According to some very preferred aspects of the invention, the terminal carbon atom in the compounds of formulas (I) or (IA), which is saturated, is completely replaced by fluorine (for example, n at the saturated terminal carbon atom is 3 and each X at such a carbon atom is F) and even more preferably n is 3 and each X in the compound is F.

According to such preferred aspects, when there are three carbon atoms, the compound of formula (IA) is preferably fluoropropene containing from three to six substituent fluorine atoms, and possibly other compounds with substituents representing halogen atoms, including, for example, hexafluoropropene (then there is z is 0, n is 3, m is 0 and all X are F) or pentafluoropropene (i.e., z is 0, n is 3, m is 1 or all X is F), and the compound of formula (IIA) is preferably selected from a group consisting of one or more of the following fluorinated alkanes thereof: chlorotrifluoropropane (HCFC-244) and pentafluoropropane (HFC-245), and hexafluoropropane (HFC-236), including all isomers of each of these compounds, but preferably 1-chloro-1,3,3,3- tetrafluoropropane (HCFC-244 fa), 1,1,1,3,1-pentafluoropropane (HFC-245fa), 1,1,1,2,3-pentafluoropropane (HFC-245eb) and 1,1,1,2, 3,3-hexafluoropropane (HFC-236ea).

In preferred embodiments, conversion step (a), wherein the olefin is converted to alkane, is carried out under conditions that are effective to obtain a conversion of the compound of formula (I) at least about 40%, more preferably at least about 55%, and , even more preferably at least equal to about 70%. In some preferred embodiments, the conversion is at least about 90% and, more preferably, about 99%.

Further, according to some preferred embodiments, the conversion of the compound of formula (I) to produce the compound of formula (II) is carried out under conditions that are effective to obtain the compound of formula (II) with a selectivity of at least about 60%, more preferably equal to at least about 80% and, even more preferably, equal to at least about 90% and, even more preferably, equal to about 100%.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a diagram of a process of which this multi-stage conversion is a part.

Figure 2 shows a diagram of a semischematic process in accordance with one embodiment of a multi-stage hydrogenation step according to this invention.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention will be described below in connection with FIG. 1, which shows that a feed stream 1 containing at least one fluorinated olefin having a fluorine substitution degree N is supplied to a first conversion step 50 in accordance with this invention . Conversion step 50 preferably also includes a feed stream 2 containing a reducing agent. Conversion step 50 preferably includes one or more reaction vessels, at least one of which preferably contains a reduction or hydrogenation catalyst, wherein streams 1 and 2 are introduced into the vessel (s) under conditions that are effective to achieve the desired conversion in the multi-stage reaction step described in this application.

Although streams 1 and 2 in FIG. 1 are shown for convenience in the form of separate streams, this is done just for convenience in the form of separate streams, this is done just for convenience and this does not limit the present invention. For example, in some embodiments, the streams may be connected outside the vessel and then introduced together into the vessel, or, in other embodiments, stream 1 and stream 2 may each include several separate streams, each of which is introduced into the vessel (s) at different times and / or different places. This very condition is used and applies here in all cases of using the term "stream" both in the text and in the figures, unless otherwise indicated.

A preferred conversion step 50 results in a stream of at least one reaction product 3 that contains a fluorinated alkane according to the invention. Some or all of stream 3 can be used, for example, as a reagent in conversion stage 51, where the fluorinated alkane in stream 3 is converted to a fluorinated olefin having a fluorine substitution degree of N-1, followed by a separation step 52 in accordance with the invention described more fully in the accompanying application with file number H0013287.

Although it is claimed that the recovery step of the invention may be carried out periodically, it is preferred that the recovery step is carried out as a substantially continuous operation. In addition, while it is possible that the reduction reaction in some embodiments included a liquid phase, according to preferred embodiments, the reduction reaction includes and, even more preferably, consists of at least two reaction stages in the vapor phase.

Regarding the number of reaction stages, the applicants unexpectedly found that the full degree of conversion and selectivity can be achieved with relatively high levels and / or with relatively high productivity by using at least two reaction stages, while the first reaction stage is carried out under conditions which are effective to achieve a first, rather low degree of conversion to produce a reaction stream in a first reaction step, and at least a second reaction step that is carried out and supplying at least a portion of said stream from the first stage and under conditions that are effective to achieve a second degree of conversion greater than said first magnitude of the degree of conversion. It is preferable to control the reaction conditions in each of the first and second stages in order to achieve the desired degree of conversion in accordance with this invention. As used herein, the term “reaction conditions” includes means for monitoring any one or more process parameters that can be changed by the operator to achieve conversion of the starting material according to the conditions described herein. For example, without limitation, the conversion of the starting material can be monitored or controlled by monitoring or controlling any one or more of the following parameters: reaction temperature, reagent flow rate, presence of diluent, amount of catalyst present in the reaction vessel, shape and size of the reaction vessel, reaction pressure and any combination of these and other process parameters that are available and known to specialists in this field in light of this description. Applicants have found that in some preferred embodiments, the conversion control step in the first stage of the hydrogenation reaction is carried out by consciously selecting the type and amount of catalyst in the first reaction stage relative to the feed rate of one or more reactants and / or by consciously selecting and adjusting the reaction temperature and, preferably by deliberate selection and control of both of these process parameters. Selecting the amount of catalyst to be used in the first reaction step preferably includes determining the amount of catalyst theoretically necessary before 100% conversion of the starting material is achieved. This determination can be made by any and all known methods suitable for this purpose, which are obvious to a person skilled in the art, taking into account the explanations contained in this application. In addition, the step of selecting the amount of catalyst may also include bench, pilot or similar experiments to determine the amount of the particular catalyst used in the process and necessary to convert 100% of the starting material, taking into account the feed rate of the starting reagents and other process parameters that have been selected. According to preferred variants of the invention, the present invention, taking into account the above definition, then includes providing, in the first stage of the reaction, an amount of catalyst that is substantially lower than the amount required for 100% conversion, and is preferably so low as to achieve the degree of conversion of the starting material an olefin equal to from about 10% to about 60%, more preferably from about 10% to about 40%, and even more preferably from about 10% to 25%. Again, experts in this field know that the stage of selecting the amount of catalyst may further include conducting additional bench, pilot or other experience with a reduced amount of catalyst and accordingly controlling the amount of catalyst. Obviously, such studies and definitions can be carried out without unnecessary experiments based on the guidelines contained in this application.

Therefore, according to preferred options, the stage of controlling the conversion of the first stage in the reactor includes feeding the olefin reagent to the first stage of the reaction in such an amount that the catalyst contained in the first stage of the reaction exceeds at least 60-90%. Applicants have found, without being bound by any particular theory, that the use of such an excess of reagent in the first stage of the reaction allows the starting materials to serve as a medium for removing heat. Since the reduction or hydrogenation according to this invention is generally exothermic, usually substantially exothermic, the use of such an excess of starting material contributes, according to preferred embodiments, to maintaining the temperature in the reactor below the temperature that will be achieved if an excess of starting material is not used, provided that that all other process parameters will be the same.

Applicants have found that the step of maintaining a very low conversion of the reactant in the first reaction step of the present invention has a positive effect on the selectivity of the reaction with respect to the desired alkane.

In other words, although the degree of conversion that is achieved in the first stage of the reaction is adjusted to a value that is much lower than the desired value in the reduction stage, the applicants have found that a greater amount of the starting material is converted to the desired alkane in the first stage of the reaction (i.e., higher selectivity is achieved ) by adjusting the degree of conversion as described above. More specifically, in many embodiments, it is preferred that the selectivity for the desired alkane in the first reaction step is at least about 80%, more preferably at least about 90%, and even more preferably at least about 95% and according to many preferred options about 97% or higher.

In some preferred embodiments, the step of controlling the degree of conversion in the first reaction step also includes removing heat of reaction by cooling at least a portion of the reaction mixture. It is obvious that specialists in this field are able to use many tools and mechanisms to carry out such cooling based on the information contained in this application without unnecessary experiments, and all such tools and mechanisms are included in the scope of this invention.

According to preferred embodiments, at least a portion of the stream leaving the first reaction stage, immediately or possibly after further processing, is fed to the second reaction stage, in which the unreacted fluorinated olefin remaining in the stream leaving the first reaction stage is converted to fluorinated alkane according to this invention. More specifically, it is preferable that the second reaction step or subsequent reaction steps, if any, are carried out under conditions that are effective for converting the fluorinated olefin contained in the stream fed to the second reaction step with a conversion degree that is higher than and, preferably, significantly higher than the degree of conversion in the first stage of the reaction. In some preferred embodiments, for example, the degree of conversion in the second reaction step is from about 20% to about 99%, to a large extent depending on the total number of reaction steps used to achieve complete conversion. For example, in the case of variants of a system with two reaction stages, the conversion in the second reaction stage is preferably more than 95% and, even more preferably, about 100%. However, as is apparent to those skilled in the art from this description, such a two-step reaction may not be sufficient to obtain the desired selectivity for fluorinated alkane. In such cases, according to the present invention, the conversion step may include more than two reaction steps, in some embodiments there may be up to 10 or more steps.

In preferred embodiments, the fluorinated olefin conversion step of the present invention comprises about four reaction steps. Although it is obvious that the specific parameters used at each stage of the reaction can vary widely according to this invention, depending on many factors, including the type of fluorinated alkane to be obtained, the feeds and other specific process parameters, the table shows the preferred and more preferred embodiments of the present invention (it should be borne in mind that the word “about” should appear before all numbers in the table).

For purposes of illustration, but without limitation, one embodiment of several reaction steps in accordance with a preferred reduction step is shown in FIG. 2. Although the reduction step 50 may be carried out periodically or semi-continuously, it is preferable that the reduction step 50 be continuous, as shown in FIG. 2. Figure 2 shows that the reactor 50A in the first stage contains a catalyst in an amount effective to achieve a conversion of the fluorinated olefin contained in stream 1 equal to from about 10% to about 60% according to this invention. In preferred embodiments, the first reaction step of the invention, for example, vessel 50A, is provided with means for cooling the reaction mixture (not shown). For example, the reaction vessel 50A may be a jacketed reaction vessel in which the space between the vessel and the jacket contains a cooling medium to remove heat from the reactor. Of course, other means can be used to cool the reaction mixture, such as an internal cooling coil, additional cooling diluent of the reaction mixture, and the like.

The stream 3A leaving the first reaction step is preferably, but not necessarily further cooled before being introduced into the second reaction step, such as the reaction vessel 50B, for example by using a heat exchanger 60A. In some embodiments, it may be desirable for the heat exchanger 60A and / or one or more heat exchangers 60B and 60C located downstream to be able to add heat to the effluent before it is introduced into the next reaction step. This ability is desirable according to some variants, since in general, although not exclusively, it is preferable that the degree of conversion at each subsequent reaction step is higher than at the previous step. In order to achieve this result, it may be desirable and / or necessary to increase the temperature of one or more streams of the starting materials in order to increase the reaction temperature in the next reaction step. Of course, it will be apparent to those skilled in the art that many tools and mechanisms are available to control the temperature at all subsequent stages of the reaction, and all such tools and mechanisms are included in the scope of this invention and can be used to control the degree of conversion in the reaction stage according to this invention.

The size and shape and other characteristics of the reaction vessel itself can vary widely according to this invention, and the vessel associated with each stage may be different or the same as the vessel associated with the reaction stages located upstream and downstream. In addition, it is believed that all stages of the reaction can proceed in one vessel, provided that the means and mechanisms necessary to regulate the degree of conversion are provided. For example, in some embodiments, it may be desirable to use one tubular reactor for each reaction step, provided that the degree of conversion is contemplated throughout the tubular reactor by consciously selecting the amount and / or distribution of catalyst in the reactor. In this case, it is possible to further control the degree of conversion in different sections of the same tubular reactor by controlling the amount of heat removed or added to different sections of the tubular reactor.

Those skilled in the art can easily select the type of catalyst (s) used (s) for the hydrogenation step of this invention, taking into account the information contained in this application. For example, in some embodiments, it is preferable that at least one, but preferably at all stages of the reaction, a palladium-based catalyst be used either alone or in combination with other catalysts. In this regard, at one or more reaction stages according to this invention, one or more hydrogenation catalysts described in US Pat. No. 5,679,875 can be used. In some preferred embodiments, the catalyst is preferably palladium on carbon as a support, for example, on a carbon mesh.

Thus, some variations of these methods include contacting a fluorinated olefin represented by Formula I and a hydrogenation agent such as H ₂ with a first amount of catalyst in a first reaction step to produce a reaction stream containing unreacted fluorocarbon (s) fluorinated olefin and hydrogenation agent. Contacting at least a portion of this first effluent with a second amount of catalyst in a second reaction step to produce fluorocarbon, wherein the second amount of catalyst is greater than the first amount of catalyst, and the conversion of the fluorinated olefin is greater in the second reaction step.

The following examples are illustrative of the invention. However, it should be noted that the invention is not limited to the specific details given in the examples.

EXAMPLES

Comparative example C-1: the reaction of hexafluoropropene and hydrogen in one stage

0.2 g of 1% Pd / C (4-6 mesh) mixed with nichrome particles of the same size with are loaded into a small one-stage reactor with an external jacket connected to a circulation cooling bath and with a temperature of 31 ° C. the goal of obtaining a total volume of the catalyst layer equal to 1 cm ³ .

Before the introduction of hydrogen and gaseous hexafluoropropene, the temperature of the layer at first is about 21 ° C. However, when hydrogen (0.37 m / h) and hexafluoropropene (0.26 m / h) are introduced, the temperature of the layer rises in about 1 minute to almost 70 ° C.

Comparative example C-2: the reaction of hexafluoropropene and hydrogen in one stage

A small amount of 1% Pd / C was charged into the same small jacketed one-stage reactor as in Example 1. Pre-mixed hydrogen and hexafluoropropene and introduced into the reactor. The temperature of the catalyst bed is stabilized at 69 ° C. The exhaust gases are analyzed to determine the degree of conversion and selectivity for CF ₃ CHFCF ₂ H. The average degree of conversion is 93.2% and the average selectivity is 95.7%.

Comparative example C-3: the reaction of hexafluoropropene and hydrogen in one stage

Example C-2 was repeated using the same one-stage reactor, but the temperature of the circulating liquid was reduced to 21 ° C. The temperature of the catalyst layer was stabilized and was 61.5 ° C. Under these conditions, the degree of conversion decreased to 88.6%, and the selectivity increased to 97.0%.

Examples 1 and 2: multi-stage recovery reactions

The reactors used in the following examples are multi-stage reactors consisting of sections of pipes of 40, 316 SS assortment of 1.5 inches.

The amount of catalyst used for loading at each stage of the reaction is calculated by determining the productivity of the catalyst (g of converted feed per g of catalyst per hour). Productivity is determined using a small reactor. Then, the desired production rate is set equal to about 10 pounds per hour, which allows you to determine the total amount of catalyst required for 100% conversion. Using this information, the amount of catalyst needed to convert 10-15% olefin in the first reactor is calculated.

The catalyst loading in the following examples was:

Section 1 (1.5 inch × 1 foot): 10g of catalyst (.. 1 wt% Pd on 4-8 mesh carbon), the rest is filled with packing SS _^1/4 inch, uniformly distributed in the catalyst layer.

Section 2 (1.5 inches × 2 feet): 25 g of catalyst distributed as in section 1.

Section 3 (1.5 inches × 3 feet): 73.4 g of catalyst with 1200 cm ^{3 of} packing, distribution as in section 1.

Section 4 (1.5 inches × 4 feet): 158 g of catalyst distributed in 1,400 cm ^{3 of} packing. The total amount of catalyst is 267 g.

Hexafluoropropene was introduced into a multi-stage reactor and continuous reduction was carried out for 58 hours, during which the average feed rate was 14.5 lb / h (or approximately 16.4 l / min). The average hydrogen feed rate is 25 l / min. Samples were taken at various points along a series of reactors to determine the degree of conversion and selectivity. After the second stage, the degree of conversion is about 40%; after the fourth stage of the reaction, the degree of conversion is 99.5%, and the selectivity to CF ₃ CHFCF ₂ H is 99%. The temperature of the gases leaving the stages is 66 ° C for the first stage, 104 ° C for the second stage, 173 ° C for the third stage and 100 ° C for the fourth stage. The maximum temperature at any stage of the reaction is about 230 ° C. The first bath has a temperature of 55 ° C, and the second bath - 111 ° C.

Example 2: multi-stage recovery of 1,2,3,3,3-pentafluoropropene-1

1,2,3,3,3-pentafluoropropene-1 is hydrogenated using the same reactor as in Example 1, with a feed rate of 25 l / min. Samples were taken at different points along the reaction to determine the degree of conversion and selectivity. After the second reactor, the degree of conversion is about 54%. After the fourth reactor, the degree of conversion is 100% with a selectivity for CF ₃ CHFCH ₂ F equal to 98%. The temperature immediately at the outlet of the gases leaving the reactors is 99 ° C for the first reactor, 95 ° C for the second reactor, 173 ° C for the third reactor and 104 ° C for the fourth reactor. The maximum temperature in any reactor is about 240 ° C. The temperature in the first bath is 59 ° C, the temperature of the second bath is 116 ° C.

The above examples and the description of the preferred options should be considered as illustrating, but not as limiting, the invention defined by the claims. Obviously, without going beyond the scope of the invention defined by the claims, various variations and combinations of the features mentioned above can be used. Such variations are not considered to be outside the scope of the invention, and they are all included in the scope of this invention.

Claims (14)

1. A method of producing a fluorinated alkane, comprising the steps of:
(a) bringing into contact in the first reaction stage a feed stream containing a fluorinated olefin and hydrogen with a first amount of catalyst to produce at least a first effluent comprising a fluorinated alkane, unreacted fluorinated olefin and hydrogen,
moreover, the fluorinated olefin is fed to the first reaction stage at a rate that is at least 60% higher than the productivity of the catalyst present in the first reaction stage, and leads to the conversion of the fluorinated olefin to fluorinated alkane, comprising from 10 to 60%;
(b) bringing into contact at one or more additional reaction stages a first effluent with a second amount of catalyst to produce a fluorinated alkane, the second amount of catalyst being an amount to achieve a degree of conversion of the fluorinated olefin greater than the degree of conversion of the fluorinated olefin in the first reaction stage ( but),
where the fluorinated olefin is a compound of formula (I):

and fluorinated alkane is a compound of formula (II):

where each X independently represents Cl, F, I or Br; each Y independently represents H, Cl, F, I or Br; each R ¹ independently represents H, Cl, F, I, Br or an unsubstituted or halogen-substituted methyl or ethyl radical; each R ² independently represents H, Cl, F, I, Br or an unsubstituted or halogen-substituted methyl or ethyl radical; n is 1, 2 or 3; a and b are each equal to 1 or 2, provided that a + b = 2; m is 0, 1 or 2; and z is 0, 1, 2, or 3. 2. The method according to claim 1, characterized in that the fluorinated olefin is hexafluoropropene. 3. The method according to claim 1, characterized in that the fluorinated olefin is pentafluoropropene. 4. The method according to claim 1, characterized in that the fluorinated alkane is chlorotrifluoropropane (HCFC-244). 5. The method according to claim 1, characterized in that the fluorinated alkane is pentafluoropropane (HFC-245). 6. The method according to claim 1, characterized in that the fluorinated alkane is hexafluoropropane (HFC-236). 7. The method according to claim 1, characterized in that the fluorinated alkane comprises 1,1,1,2,3-pentafluoropropane (HFC-245eb). 8. The method according to claim 1, characterized in that each of the contacting steps involves the use of palladium on a carbon support. 9. The method according to claim 1, in which the fluorinated olefin is fed to the first reaction stage at a rate that is at least 90% higher than the productivity of the catalyst present in the first stage. 10. The method according to claim 1, in which the conversion of the specified fluorinated olefin in the second reaction stage is from 20% to 99%. 11. The method according to claim 1, in which the conversion of the specified fluorinated olefin in the second reaction stage is more than 95%. 12. The method according to claim 1, in which the stage of contacting (b) is carried out in one additional reaction stage. 13. The method according to claim 1, in which the contacting step (b) is carried out in three additional reaction stages. 14. A method of producing a fluorinated alkane, comprising the steps of:
(a) selecting a first amount of a pre-selected catalyst, which is theoretically required for the reduction of a fluorinated olefin with a conversion of 10 to 60%;
(b) bringing into contact at the first reaction stage an initial stream containing a fluorinated olefin and hydrogen with a first amount of catalyst to obtain at least a first effluent containing a fluorinated alkane, unreacted fluorinated olefin and hydrogen, wherein the degree of conversion of the fluorinated olefin to fluorinated alkane is from 10% to 60%;
(c) bringing into contact at one or more additional reaction stages a first effluent with a second amount of catalyst to produce a fluorinated alkane, the second amount of catalyst being an amount to achieve a degree of conversion of the fluorinated olefin greater than the degree of conversion of the fluorinated olefin in the first reaction stage,
where the fluorinated olefin is a compound of formula (I):

and fluorinated alkane is a compound of formula (II):

where each X independently represents Cl, F, I or Br;
each Y independently represents H, Cl, F, I or Br;
each R ¹ independently represents H, Cl, F, I, Br or an unsubstituted or halogen-substituted methyl or ethyl radical; each R ² independently represents H, Cl, F, I, Br or an unsubstituted or halogen-substituted methyl or ethyl radical; n is 1, 2 or 3; a and b are each equal to 1 or 2, provided that a + b = 2; m is 0, 1 or 2; and z is 0, 1, 2, or 3.

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