MXPA97001185A - Process for the production of pentafluoroet - Google Patents

Abstract

The present invention relates to a process for recovering pentafluoroethane by subjecting a mixture comprising at least pentafluoroethane and chloropentafluoroethane for an extractive distillation step to obtain pentafluoroethane containing substantially no chloropentafluoroethane, whose process is characterized by the supply of the mixture to the distillation step extractive, the supply, as an extractant to the extractive distillation stage, nitromethane, obtaining a mixture comprising pentafluoroethane and the extractant which together constitute a main component of the mixture as a lower product of the extractive distillation stage, or a mixture comprising pentafluoroethane as a main component of the mixture as a distilled product of the extractive distillation step

Description

PROCESS FOR THE PRODUCTION OF PENTAFLUOROETHANE TECHNICAL FIELD The present invention relates to a process for producing pentafluoroethane by separating the pentafluoroethane from a mixture comprising at least pentafluoroethane (sometimes referred to as HFC-125) and chloropentafluoroethane ( which is sometimes referred to as CFC-115) using extractive distillation in which a specific compound is used as an extraction compound (or solvent). Such a mixture may be, for example, a reaction product of a pentafluoroethane production process by fluorination of tetrachlorethylene.

BACKGROUND OF THE INVENTION HFC-125 is a useful compound which can be a substitute for the flon which does not contain chlorine and is used as a cooling medium, a forming agent, a propellant and so on. The fluorination of tetrachlorethylene is used as a process for the production of HFC-125. In such a process, dichlorotetrafluoroethane, dichlorotrifluoroethane, hexafluoroethane, CFC-115 and so on are produced as by-products. Among these, CFC-115 has a boiling point of -38.7 ° C which is considerably close to a boiling point of HFC-125 (-48.5 ° C) as a target product. In addition, a relative volatility between these two compounds is close to one. Particularly when a REF: 24048 mixture contains HFC-125 at a concentration of not less than 95 mol% (thus, CFC-115 is not more than 5 mol%), the relative volatility is about 1.04. Therefore, it requires a distillation apparatus that has many plates to separate the HFC-125 at its highest concentration from such a mixture, by using a conventional distillation operation, which generally means that separation by distillation is extremely difficult . In the present specification, the relative volatility (a) is defined as follows, when a solution consisting essentially of at least two components A and B in question (a boiling point of the component A < a boiling point of component B ) is in a vapor-liquid equilibrium state: where XA is a molar fraction of the lowest boiling component A in the liquid phase, XB is a molar fraction of the highest boiling component B in the liquid phase , A is a molar fraction of the lower boiling component A in the vapor phase which is equilibrated with the liquid phase and and e is a molar fraction of the highest boiling component B in such a phase. The extractive distillation has been used as a process of separation of a component of a mixture of a system of which the relative volatility is close to one. With respect to the separation of a mixture of HFC-125 and CFC-115, for example, US Patent No.

No. 5,087,329 discloses an extractive distillation process which utilizes a fluorocarbon containing from 1 to 4 carbon atoms as an extraction solvent. In the process described in U.S. Patent No. 5,087,329, a relative volatility between HFC-125 and CFC-115 is about 1.2 based on the calculation when using the figures shown in Example 1 thereof. Thus, in order that a concentration of CFC-125 is increased from HFC-125 / CFC-115 = 7/93 (% in mol /% in mol) to HFC-125 / CFC-115 = 99.7 / 0.3 (% in mol /% mol) when using distillation, approximately 40 theoretical plates are required. The number of theoretical plates were calculated as explained later in this.

SUMMARY OF THE INVENTION A process has been studied in which HFC-125 is effectively separated from a mixture comprising HFC-125 and CFC-115 by using extractive distillation and it was found that when a mixture comprising at least HFC -125 and CFC-115 is subjected to extractive distillation, HFC-125 is effectively separated (for example by using a distillation column that has a very small number of theoretical plates) of the mixture when using, as a component (or solvent) of extraction of at least one compound (thus, as a single compound or a mixture of the compounds) selected from an alcohol containing from 1 to 4 carbon atoms, a ketone containing from 3 to 7 carbon atoms, an ether containing from 2 to 6 carbon atoms and nitromethane or at least one compound selected from a hydrocarbon containing from 3 to 8 carbon atoms, trichlorethylene and carbon tetrachloride. Thus, the present invention provides a process for separating HFC-125 from a mixture comprising at least HFC-125 and CFC-115 by subjecting the mixture to extractive distillation to obtain HFC-125 in which a concentration of CFC- 115 is relatively low and preferably highly concentrated HFC-125 which does not substantially contain CFC-115, characterized in that at least one compound selected from an alcohol containing from 1 to 4 carbon atoms, a ketone containing from 3 to 7. carbon atoms, an ether containing from 2 to 6 carbon atoms and nitromethane, or at least one compound selected from a hydrocarbon containing from 3 to 8 carbon atoms, trichlorethylene and carbon tetrachloride is used as an extraction solvent . That is, the present invention provides a process for producing pentafluoroethane in which the pentafluoroethane is separated from a mixture comprising at least pentafluoroethane and chloropentafluoroethane, which together constitute a major component of the mixture, by subjecting the mixture to extractive distillation to obtain a mixture which contains pentafluoroethane as a main component and which does not substantially contain chloropentafluoroethane, which process is characterized in that: at least one compound selected from an alcohol containing from 1 to 4 carbon atoms, a ketone containing from 3 to 7 carbon atoms, an ether containing from 2 to 6 carbon atoms, or at least one compound selected from a hydrocarbon containing from 3 to 8 carbon atoms, trichlorethylene and carbon tetrachloride is used as a solvent of extracting the extractive distillation, and a mixture comprising pentafluoroethane and the dissolvent Extraction, which together constitute a main component of the mixture, is obtained as a bottom product, provided that at least one compound selected from the alcohol containing 1 to 4 carbon atoms, the ketone containing 3 at 7 carbon atoms, the ether containing 2 to 6 carbon atoms and nitromethane, is used as the extraction solvent, or a mixture comprising pentafluoroethane as the main component is obtained as a distilled product, provided that less a compound selected from the hydrocarbon containing from 3 to 8 carbon atoms, trichlorethylene and carbon tetrachloride is used as the extraction solvent.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a flow diagram of a mode of a separation process in which the process according to the present invention is carried out; and Figure 2 shows a flow chart of another embodiment of a separation process in which the process according to the present invention is carried out. In the drawings, the reference numbers denote the following elements, respectively: 1. Extractive distillation apparatus 2. Mixture which contains HFC-125 and CFC-115 3. Extraction solvent 4. Distilled product 5. Bottom product 6. Distilled product 7. Bottom product 8. Heat exchanger 9. Distillation apparatus for the separation of HFC-125 11. Extractive distillation apparatus 12. Mixture which contains HFC-125 and CFC-115 13. Extraction solvent 14. Distilled product 15. Bottom product 16. Distilled product 17. Bottom product 18. Heat exchanger 19. Distillation apparatus for recovery of extraction solvent DETAILED DESCRIPTION OF THE INVENTION In the present specification, the term "principal component" means that an amount of the other component instead of the main component is relatively small. It is sufficient that a quantity of the main component does not. is concretely less than 50%, more specifically not less than 60% and for example not less than 80%. Further, in the present specification, the term "substantially" means that a mixture is ultimately obtained in which the pentafluoroethane is a major component, for example a mixture in which a concentration of the pentafluoroethane is not less than 90% by weight, preference not less than 9.9% by weight and more preferably not less than 99.99% by weight. In the present process, when at least one compound selected from the alcohol containing 1 to 4 carbon atoms, the ketone containing from 3 to 7 carbon atoms, the ether containing from 2 to 6 carbon atoms and nitromethane is used as the extraction solvent, a mixture is obtained as a bottom product which contains pentafluoroethane and the extraction solvent together constituting a main component of the mixture as described above, preferably a mixture in which a concentration of the chlorofluoropentane does not is more than 0.1% by weight and more preferably a mixture in which a concentration of chloropentafluoroethane is not more than 0.01% by weight. In this case, there is no limitation on a composition of a distilled product, provided that the ratio of chloropentafluoroethane to pentafluoroethane in the bottom product is reduced from an original ratio of the same, preferably reduced to no more than 1 / 10 of the original ratio and more preferably be reduced to no more than 1/100 of the original ratio. The distilled product may contain chloropentafluoroethane as a major component thereof, may contain pentafluoroethane as a major component thereof or may contain chloropentafluoroethane and pentafluoroethane which together constitute a major component thereof, with the condition described above. In the present process, when at least one compound selected from the hydrocarbon containing from 3 to 8 carbon atoms, trichlorethylene and carbon tetrachloride is used as the extraction solvent, a mixture is obtained as a distilled product which contains pentafluoroethane as a main component thereof as described above, preferably a mixture in which a concentration of the pentafluoroethane is not less than 99.9% by weight. In this case, there is no limitation on a composition of a bottom product, provided that a ratio of pentafluoroethane to chloropentafluoroethane in the distilled product is increased from an original ratio of the same, preferably increased to not less than 10 times. the original ratio and more preferably increase to not less than 100 times the original ratio. The bottom product may contain chloropentafluoroethane and the extraction solvent, which together constitute a major component of the phono product, or may contain chloropentafluoroethane, pentafluoroethane and the extraction solvent which together constitute a major component of the bottom product, with the condition described above. In one embodiment of the present invention, the mixture is of a binary system which consists substantially of HFC-125 and CFC-115. In another embodiment of the present invention, the bottom product thus obtained, for example one which contains the extraction solvent and pentafluoroethane, which together constitute a major component of the bottom product or one which contains chloropentafluoroethane and the extraction solvent which together constitute a main component of the bottom product, it is subjected to distillation, to separate it in the extraction solvent and pentafluoroethane or chloropentafluoroethane, whereby the extraction solvent is recovered, which can be supplied and reused in the step of extractive distillation. In the present specification, the extractive distillation use uses in the meaning which is used in general in the field, in particular the field of chemical engineering; for example it means a distillation operation which is characterized in that the addition of a third component to a mixture of a binary system facilitates the separation of the mixture due to a relative volatility that is considerably deviated from one, by means of the third component, of otherwise separation would be difficult when using conventional distillation. In the present invention, the alcohol containing 1 to 4 carbon atoms means a compound having 1 to 4 carbon atoms, which forms a main chain and which contains at least one hydroxyl group, such as an alcohol aliphatic that has 1 to 4 carbon atoms. Concretely, methanol, ethanol, butanol, propanol, pentafluoropropanol, C2F5CH2OH), tetrafluoropropanol (HCF2CF2CH2? H), ethylene glycol, propanediol and trifluoroethanol can be exemplified. In the present invention, the ketone containing from 3 to 7 carbon atoms means a ketone which is represented by the general formula: R1-CO-R2 (wherein R1 and R2 are aliphatic hydrocarbon groups which may be the same or different from each other, respectively). Concretely, acetone, diethyl ketone and dimethyl ethyl ketone can be exemplified. In the present invention, the ether containing from 2 to 6 carbon atoms means an ether which is of the general formula: R O-R2 (wherein Ri and R2 are aliphatic hydrocarbon groups which may be the same or different from each other) yes, respectively). Concretely, diethyl ether, dimethyl ether, methyl ethyl ether and dipropyl ether can be exemplified. In the present invention, the hydrocarbon containing from 3 to 8 carbon atoms includes a cyclic hydrocarbon and a chain hydrocarbon. The cyclic hydrocarbon means one which contains at least one cyclic structure. Concretely, cyclohexane, cyclopentane, cyclopropane and cyclobutane can be exemplified as a saturated cyclic hydrocarbon. As an unsaturated cyclic hydrocarbon, an aromatic hydrocarbon such as benzene can be exemplified. The chain hydrocarbon also includes a saturated hydrocarbon and an unsaturated hydrocarbon and specifically normal octane and normal hexene can be exemplified. As a mixture thereof, the use of petroleum ether or petroleum benzine are particularly preferable. Extraction solvents have been studied as described above, which are used in the separation process of HFC-125 from the mixture comprising HFC-125 and CFC-115 by extractive distillation and measurements of relative volatilities between the HFC-125 and the CFC-115 which are shown in table 1 below: Table 1 Component Volatility relation extraction extraction *) relative () (1) Dichlorotrifluoroethane **) 0.85 1.2 (2) Dichloropentafluoropropane 0.67 1.2 (3) Tetrachloroethylene 1.33 1.2 (4) Dichloromethane 2.12 0.9 (5) Methanol 1.60 0.4 (6) Ethanol 1.5 0.5 (7) Propanol 1.2 0.76 (8) Butanol 1.4 0.86 (9) Pentafluoropropanol 1.2 0.88 (10) Tetrafluoropropanol 1.6 0.65 (11) Acetone 0.5 0.4 (12) Cyclohexane 1.6 1.7 (13) Cyclopentane 1.5 1.9 (14) Trichlorethylene 2.0 1.4 (15) Carbon tetrachloride 1.6 1.5 (16) Normal octane 1.4 1.8 (17) Benzine oil 4.7 2.1 (18) Petroleum ether 4.0 2.1 (19) Diethyl ether 1.4 0.7 (20) Nitromethane 1.4 0.4 *) Relation of the extraction solvent = weight of the extraction / weight component of ( HFC-125 + CFC-115) **) Extraction solvent described in U.S. Patent No. 5,087,329. When the measurements in Table 1 are obtained, the following procedure was used: After a sealed container was evacuated to an almost vacuum pressure, predetermined quantities of HFC-125, CFC-115 and the extraction solvent were charged to the vessel. , which was allowed to reach a state of vapor-liquid equilibrium at a temperature of 20 ° C. Then, the liquid phase and the vapor phase were analyzed by gas chromatography to obtain the compositions of both phases as molar fractions. The relative volatility a was calculated using the following equation a = (yA? A) (yB xB) - As clearly seen from table 1, when the alcohol having 1 to 4 carbon atoms, the ketone having 3 at 7 carbon atoms, the ether having from 2 to 6 carbon atoms or nitromethane, which are represented by the compound (5) to (11), (19) or (20) in table 1, is used as the extraction solvent, the relative volatility is considerably less than 1. In addition, when the hydrocarbon having from 3 to 8 carbon atoms, trichlorethylene or carbon tetrachloride, which are represented by the compounds (12) to (18) in Table 1 is used as the extraction solvent, the relative volatilities are considerably greater than one. Accordingly, when HFC-125 is to be separated from the mixture of HFC-125 and CFC-115 by extractive distillation by using a compound (5) to (20) in Table 1 as the extraction solvent, it is expected that the separation is carried out by using a distillation apparatus which includes a much smaller number of theoretical plates than a conventional apparatus. In general, when a mixture comprising HFC-125 and CFC-115 is subjected to a distillation operation, HFC-125 is concentrated to an enrichment section (an upper side of a column) since its boiling point is lower than that of CFC-115. However, when the relative volatility is less than 1, for example when one or more compounds from (5) to (11) and (19) and (20) are used as the extraction solvent, CFC-115 is concentrated at upper side of the column. On the other hand, when one or more compounds from (12) to (18) are used as the extraction solvent, HFC-125 is concentrated to the top side of the column since the distillation apparatus, as is usual due to volatility relative, is greater than 1. In the same way as in the case when the data are obtained in table 1, the effects of a composition of the mixture of HFC-125 and CFC-115 and a ratio of the solvent have been studied. of extraction on relative volatility for the case in which the mixture of HFC-125 and CFC-115 is subjected to extractive distillation by using methanol as the extraction solvent and the results shown in Table 2 below are obtained. Table 2 (in the case where methanol is used as the extraction component) Percent by weight of Volatility Ratio HFC-125 / CFC-115 extraction *) relative 9999..9988 // 00..001177 1.5 0.47 99.84 / 0.164 2.1 0.48 97.8 / 2.2 3.0 0.26 97.8 / 2.2 1.6 0.39 97.8 / 2.2 0.8 0.57 97 8 / 2.2 0.2 0.77 80 9 / 19.1 1.2 0.48 38.3 / 61.7 1.2 0.48 *) Relation of extraction solvent = weight of methanol / weight of HFC -125 + CFC-115) It has been confirmed from the results of table 2 that alpha () is considerably less than one in all weight ratios, such that the addition of methanol to the mixture of HFC-125 and CFC-115 at various ratios of the extraction solvent leads to the effective separation of CFC-115 as a volatile component, ie methanol is preferable as the solvent of extraction when the separation of the mixture of HFC-125 / CFC-115 is carried out when using extractive distillation. Then, the separation process of the present invention will be compared later in the present with the example described in the North American patent No. 5,087,329 regarding the number of theoretical plates of an extractive distillation column, which are required for example when going to obtain HFC-125 (for example a mixture of HFC-125 (99.9 mol%) / CFC-115 (0.1 mol%)) concentrate of a mixture of HFC-125 (90 mol%) / CFC (10%) in mol). The process described in the North American patent described above requires approximately 26 theoretical plates in order to produce a superior distillate product of concentrated HFC-125 (for example concentrate to a mixture of HFC-125 (99.9 mol%) / CFC-115 ( 0.1% in mol)). In this case the calculation is carried out assuming that the relative volatility is 1.2. On the contrary, when according to the present process, when the extraction solvent such as those from (12) to (18) is used, which makes the relative volatility greater than one, the required number of theoretical plates is approximately eight. . In this case, the calculation is carried out assuming that the relative volatility is 1.9. When according to the process herein, the extraction solvent such as those from (5) to (11) and (19) and (20) is used, which makes * the relative volatility less than one, the CFC- 115 is concentrated to the top side of the column as a low boiling component. When the column has approximately six theoretical plates, a mixture of the extraction solvent and HFC-125 which is concentrated at a ratio of HFC-125 (99.9 mol%) / CFC-115 (0.1 mol%) as a distilled product it is produced as a bottom product, while a mixture is produced in which the concentration of CFC-115 is increased from its original concentration to a ratio of HFC-125 (80% in mol) / CFC-115 (20% in mol). In this case, the calculation is carried out assuming that the relative volatility is 0.4 The required number of theoretical plates (N) to which reference is made in the present in the above, is calculated according to the following equation: aN = (yw / Xw) / (yD / Xo) where is the relative volatility, XQ is the mole fraction of HFC-125 in a higher distillate, xw is the mole fraction of HFC-125 in a bottom product (or inert), and D is the molar fraction of CFC-115 in a higher distillate and yw is a mole fraction of CFC-115 in a bottom (or inert) product. When the extraction solvent is used which makes the relative volatility less than one, the HFC-125 must be separated from the extraction solvent to finally obtain HFC-125 alone, since the bottom product of the extractive distillation stage contains the extraction solvent as described above. This separation step is easily carried out with a conventional distillation operation by using a packed column or packed column, since the difference in boiling point is large between the HFC-125 and the extraction solvent. Thus, HFC-125 is effectively separated from the mixture comprising at least HFC-125 and CFC-115 by using the combination of the extractive distillation operation with the distillation operation, after which the solvent is separated of extraction. Also, when the extraction solvent is used which makes the relative volatility greater than one, the bottom product of the extractive distillation step contains the extraction solvent as described above. In this case, the target HFC-125 is produced as the distillate product of the extractive distillation stage and thus, any treatment of the bottom product is possible. Preferably, the extraction solvent is recovered from the bottom product when using for example distillation and reused in the extractive distillation step. If the mixture to be separated contains a third component in addition to HFC-125 and CFC-115, the only difference is that the third component behaves in conjunction with HFC-125 and / or CFC-115 depending on the boiling point of the third component. Thus, even if the third component is contained in the mixture, the HFC-125 is separated from the CFC-115 when carrying out the extractive distillation by using the tile extraction solvent according to the present invention. In addition with respect to the reuse of the extraction solvent in the extractive distillation step, when the extraction solvent described in US Patent No. 5,087,329 is used, the CFC-115 is concentrated to the bottom product and the extraction solvent is also recover from the distillation fund. This means that the extraction solvent contains a large amount of CFC-115, which requires complete separation of the CFC-115 for the reuse of the extraction solvent. If only a small amount of the CFC-115 remains in the extraction solvent, the CFC-115 can be finally added to the extractive distillation stage, whereby the extraction efficiency can be deteriorated and the required number of theoretical plates can be increase. In fact, it is estimated that the required number of theoretical plates of a distillation apparatus would be from about 10 to 20 in order to separate the CFC-115 while the separation efficiency is not deteriorated. In this regard, this is also applicable when the cyclic hydrocarbon is used as the extraction solvent in the process of the present invention. On the other hand, in the process according to the present invention, in which the extraction solvent is used as the compound (5) to (11) and (19) or (20), which makes the relative volatility lower from one, for example, the bottom product of the extractive distillation stage does not substantially contain CFC-115, so that it is sufficient to separate only the HFC-125 from the extraction solvent. Accordingly, although the HFC-25 remains in the extraction solvent at a concentration of few percentages and such extraction solvent is reused in the extractive distillation stage, almost no effect is observed on the efficiency of the extraction. Thus, the number of theoretical plates of the distillation apparatus required for the recovery of the extraction solvent is only about 2 to 5. From this point of view, it is preferable in the process of the present invention to use at least one selected component. of the alcohol containing 1 to 4 carbon atoms, the ketone containing from 3 to 7 carbon atoms, the ether containing from 2 to 6 carbon atoms and nitromethane as the extraction solvent. The extractive distillation process using the compound as the extraction solvent according to the present invention can be carried out in any distillation apparatus which is conventionally used as a column of dishes, packed column and so on. There are no specific limitations as to the various conditions of the distillation apparatus (such as an operating temperature, an operating pressure, a reflux ratio, a total number of dishes of the distillation apparatus, levels of the dishes of the distillation apparatus. mixing and feeding the extraction solvent and so on) and the appropriate conditions are selected depending on the separation sought. Since HFC-125 and CFC-115 have considerably low boiling points, it is generally preferred to carry out extractive distillation under a pressurized condition. The operating pressure it can be, for example, in the range between 0 and 30 kg / cm 2 (gauge pressure) and preferably in the range between 10 and 20 kg / cm 2 (gauge pressure). The temperatures at the top and bottom of the distillation apparatus are determined depending on the operating pressure and the compositions of the distilled product and the bottom product. In order to carry out the distillation operation considering from the economic point of view the operating temperatures of a condenser and a reboiler, the temperature in the upper part of the distillation apparatus is preferably in the range between -40 and 50 ° C and the temperature at the bottom of the distillation apparatus is preferably in the range between -20 and 70 ° C. The process of the present invention can be carried out in a batch mode or in a continuous mode. Although in some cases, the process can be carried out in a semi-continuous mode, where the separation and / or feeding is carried out intermittently, the extraction solvent must be supplied continuously to the distillation apparatus . In the process of the present invention, a ratio (S / F) of an amount (S) of the extraction solvent to an amount (F) of the feed mixture (ie HFC-125 and CFC-115) has an effect about the extent of the separation. In general, the ratio can be appropriately selected depending on the composition of HFC-125 / CFC-115 of the mixture to be subjected to the extraction distillation, a permissible concentration of CFC-115 which remains in the separated HFC-125 and so on A required number of theoretical plates of the extractive distillation apparatus ~ can be appropriately selected in combination with the selection of the ratio (S / F). The preferable separation can usually be achieved with the ratio based on the weight in the range between about 0.1 and 20 and preferably in the range between about 1 and 10. The following example can be shown: A mixture of CFC-115 (1 % in mol) and HFC-125 (99% in mol) is subjected to extractive distillation by using the extraction solvent selected from compounds (5) to (11) and (19) and (20), whereby the CFC-115 is distilled at an increased concentration of 10 mol% (thus, 90 mol% of HFC-125) and also a stream of HFC-125 is finally obtained, of which the concentration of CFC-115 is no more 0.1% mole (thus, more than 99.9% mole of HFC-125) after removal of the extraction solvent. In order to achieve this separation, it is sufficient that the required number of theoretical plates in the extractive distillation is in the range of, for example, about 5 to 30 and the weight ratio of the extraction solvent to the mixture consisting of HFC -125 and CFC-115 is in the range of, for example, approximately 1 to 10.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be explained in detail with reference to Figure 1 by way of example, in which methanol is used as the extraction solvent, which makes the relative volatility between HFC-125 and CFC-115 less than 1. A mixture comprising HFC-125 and CFC-115 (for example HFC-125 / CFC-115 = 90% mol / 10 mol%) is supplied to the extractive distillation apparatus 1, which is operated under a pressurized condition (for example 15 Kg / cm2 (manometric) For example, an apparatus having the number of theoretical plates of about ten is used as the distillation apparatus 1. Methanol 3 is supplied to the apparatus of distillation 1 (for example, on the first theoretical plate from the top) An amount of methanol is for example approximately five times by weight of that of mixture 2. When, under those conditions, the mixture is supplied for example about the fifth theoretical dish or from the top and a reflux ratio is set for ten, whereby a mixture of HFC-125 / CFC-115 (for example 10% mol / 90 mol%) is extracted from the top as a product distilled 4 In addition, a mixture containing methanol and HFC-125 / CFC-115 (for example 99.9% mol / O.1% mol) is extracted from the bottom as a bottom product 5 (the methanol concentration is 85%). %). Then, the bottom product is supplied to a distillation apparatus 9 which is operated under a pressurized condition (for example 12 Kg / cm 2 (gauge) and the HFC-125 is obtained as a distilled product 6 from the top, the which does not substantially contain neither methanol nor CFC-115 Methanol which does not substantially contain HFC-125 is recovered from the bottom of distillation apparatus 9 as a bottom product 7, which is supplied to extractive distillation apparatus 1 for reused as the extraction solvent - The methanol to be reused can be supplied to the distillation apparatus 1 optionally after it is heated or cooled as required through a heat exchanger 8. In the process of the present invention, the level of the plate on which the extraction solvent is supplied is preferably above the plate on which the mixture is supplied in any of the extraction components. n that is used. Thus, the plate on which a reflux is returned and the plate on which the extraction solvent is supplied can be the same. Optionally, the plate on which the mixture is fed and the plate on which the extraction solvent is supplied may be the same. Alternatively, before the mixture is fed to the distillation apparatus, it can be mixed with the extraction solvent and then the resulting mixture can be supplied to the distillation apparatus. Specifically, when methanol is used as the extraction solvent, it is more preferable to supply methanol on a plate which is located at about 3 to 5 theoretical plates above a plate on which the mixture is supplied. By using the apparatus and operating conditions as described above, HFC-125 which does not substantially contain CFC-115 can be separated from the mixture which contains HFC-125 and CFC-115. Next, the present invention will be explained in detail with reference to Figure 2, by way of another example in which cyclopentane is used as the extraction solvent, which makes the relative volatility between HFC-125 and CFC-115 greater than 1 as in the case of compounds (12) to (18). A mixture 12 comprising HFC-125 and CFC-115 (e.g.

HFC-125 / CFC-115 = 90% mol / 10 mol%) is supplied to an extractive distillation apparatus 11, which is operated under a pressurized condition (for example 15 Kg / cm2 (manometric). an apparatus having the number of theoretical plates of about twenty is used as the distillation apparatus 11. The cyclopentane 13 is supplied to the distillation apparatus 11 (e.g., on the fifth theoretical plate from the top). An amount of cyclopentane is for example about three times by weight of that of mixture 12. When, under those conditions, mixture 12 is supplied for example on the thirteenth theoretical plate from the top and a reflux ratio is fixed for ten, whereby a mixture of HFC-125 / CFC-115 (eg 99.9% mol / 0 mol%) is extracted from the top as a distilled product 14. In addition, a mixture containing cyclopentane and HFC-125 / CFC-115 (for example 10% mol / 90% mol) is extracted from the bottom as a bottom product 15 (the concentration of cyclopentane is 70%). Then, the product from the bottom is supplied to a distillation apparatus 19 which is operated under a pressurized condition (for example 12 Kg / cm 2 (gauge)) and a mixture of HFC-125 and CFC-115 (10%) is obtained. n mol / 90% mol) as a distilled product 16 of the upper part, which does not substantially contain cyclopentane. The cyclopentane which substantially does not contain either HFC-125 or CFC-115 is recovered from the bottom of the distillation apparatus 19 as a bottom product 17, which is supplied to the extractive distillation apparatus 11 to be reused as the extraction solvent . The cyclopentane to be reused can optionally be supplied to the distillation apparatus 11 after it is heated or cooled as required through a heat exchanger 18. The level of the cyclopentane-supplied dish is preferably above of a dish on which the mixture is supplied as described above. It is more preferable to supply cyclopentane on a plate which is located at about 7 to 10 theoretical plates above a plate on which the mixture is fed. By using the apparatus and operating conditions as described above, HFC-125 which does not substantially contain CFC-115 can be separated from the mixture which contains HFC-125 and CFC-115.

Example When using an extractive distillation column equipped with a condenser in its upper part, a mixture of HFC-125 and CFC-115 (= 99/1 (w / w)) is treated. The distillation column had a diameter of 10 m and 10 theoretical plates (the real number was 15) and was put into operation under a pressure of approximately 7 Kg / cm2 (gauge) (at the top of the column). Methanol is supplied to the second plate from the top as the extraction solvent and the mixture to be distilled is fed at a temperature of 38 ° C on the fifth plate from the top. Concentrated CFC-115 is extracted, which contains HFC-125 as a distilled product from the top. This operation is carried out at a reflux ratio of 200. A mixture of HFC-125 and methanol is extracted from the bottom at a temperature of 45 ° C which does not substantially contain CFC-115. The mass balance of the previous operation is shown in table 3 below: Table 3 Vel. of flow (% by weight (% by weight) (% by total weight (Kg / hr) of) HFC-125 of) CFC-115 of) methanol (Input) Dissolve. extraction (methanol) 50 100 Mixture HFC-125 / CFC-1 15 10 99 1 (Output) Distilled product 1 89 9.9 1.1 Bottom product 59 14.9 9.9 1.1 The bottom product extracted from the bottom of the distillation apparatus which contained HFC-125 and methanol and a small amount of CFC-115 is supplied to another distillation apparatus having a diameter of 80 mm and 5 theoretical plates (the number real of plates was 7) which was put into operation under an operating pressure of 5 Kg / cm2 (gauge) and a reflux ratio of 10, by which the HFC-125 / CFC-115 (weight / weight is obtained ) of the upper part and methanol as a bottom product. The concentration of CFC-115 in the bottom product contained no more than 0.01% by weight. This methanol can be reused as the extracting solvent of the extractive distillation.

It is noted that in relation to this date, the best method to carry out the aforementioned invention is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims (14)

1. Claims 1. A process for producing pentafluoroethane by subjecting a mixture comprising at least pentafluoroethane and chloropentafluoroethane to an extractive distillation step, to obtain pentafluoroethane which substantially does not contain chloropentafluoroethane, which process is characterized in that it comprises: supplying the mixture to the extractive distillation step, providing, as an extraction solvent to the extractive distillation step, at least one compound selected from: an alcohol containing from 1 to 4 carbon atoms, a ketone containing from 3 to * 7 atoms of carbon, an ether containing from 2 to 6 carbon atoms and nitromethane or at least one compound selected from a hydrocarbon containing from 3 to 8 carbon atoms, trichlorethylene and carbon tetrachloride, and obtaining a mixture comprising pentafluoroethane and the extraction solvent, which together constitute the main component of the as a bottom product of the extractive distillation stage or a mixture comprising pentafluoroethane as a main component of the mixture as a product distilled from the extractive distillation stage.
2. 2. The process according to claim 1, characterized in that the mixture and the extraction solvent are mixed together, which mixture is then supplied to the extractive distillation stage.
3. 3. The process according to claim 1 or 2, characterized in that a weight ratio (S / F) of the extraction solvent (S) used in the extractive distillation step to pentafluoroethane and chloropentafluoroethane (F) which are contained in the mixture to be supplied to the extractive distillation stage, it is in the range of between 0.1 and 10.
4. 4. The process according to any of claims 1 to 3, characterized in that the pentafluoroethane is separated by distillation from the mixture as the bottom product comprising pentafluoroethane and the extraction solvent which together constitute the main component of the mixture, by which a mixture which contains the extraction solvent as a main component thereof is recovered and reused in the extractive distillation stage.
5. 5. The process according to any of claims 1 to 3, characterized in that a mixture is obtained as a bottom product, comprising the extraction solvent, chloropentafluoroethane and optionally pentafluoroethane, which together constitute a main component of the mixture while the mixture comprising pentafluoroethane as the main component thereof as the distilled product and the first mixture is distilled to separate the chloropentafiuoroethane and optionally pentafluoroethane, whereby a mixture which contains the extraction solvent as a main component thereof is recovers and reuses in the extractive distillation stage.
6. 6. The process according to any of claims 1 to 4, characterized in that the extraction solvent causes the relative volatility (a) between pentafluoroethane and chloropentafluoroethane is not greater than one.
7. 7. The process according to any of claims 1 to 4, characterized in that the extraction solvent is methanol.
8. 8. The process according to any of claims 1 to 4, characterized in that the extraction solvent is acetone.
9. 9. The process according to any of claims 1 to 3 and 5, characterized in that the extraction solvent is cyclopentane.
10. 10. The process according to any of claims 1 to 4 and claim 6, characterized in that the extraction solvent is diethyl ether.
11. The process according to any of claims 1 to 4 and claim 6, characterized in that the extraction solvent is nitromethane.
12. 12. The process according to any of claims 1 to 3 and claim 5, characterized in that the extraction solvent is normal octane.
13. The process according to any of claims 1 to 3 and claim 5, characterized in that the extraction solvent is petroleum benzine.
14. 14. The process according to any of claims 1 to 3 and claim 5, characterized in that the extraction solvent is petroleum ether.