Title of Invention	A PROCESS FOR THE SEPARATION OF HYDROGEN FLUORIDE AND DIFLUOROMETHANE FORM A MIXTURE CONTAINIGN HYDROGEN FLUORIDE AND DIFLUOROMETHANE
Abstract	The invention relates to a process for the separation of hydrogen fluoride (HF) and difluoromethane (F32) from a mixture containing hydrogen fluoride (HF) and difluoromethane (F32). The said process comprises a process selected from fractional distillation, condensation or both, in one or more stages, at least one stage being performed such that there may be obtained a stream whose HF and F32 contents correspond substantially to those of the azeotropic composition, and the said stage being performed, as a function of the intended separation objective, at a pressure chosen so that the partial pressure of the HF + F32 mixture of the said stream (Pa expressed in bars absolute) and the HF content of the said mixture (x in per cent by weight) are linked by the relationship: Pa = 17 -22.9(X+O.821) In (X+O.608) + 56.6 [In (X+O.608)Y (wherein In designates the Naperian logarithm), and recovering the separated hydrogen fluoride and difluoromethane. 57) Abstract:- The invention relates to a process for the of hydrogen fluoride (HF) and difluoromethane (F32) from a mixture containing hydrogen fluoride (HF) and difluoromethane {F32). The said process comprises a process selected from fractional distillation, condensation or both, in one or more stages, at least one stage being performed such that there may be obtained a stream whose HF and F32 contents correspond substantially to those of the isotropic composition, and the said stage being performed, as a function of the intended separation objective, at a pressure chosen so that the partial pressure of the HF + F32 mixture of the said stream (Pa expressed in bars absolute) and the HF content of the said mixture (x in per cent by weight) are linked by the relationship: Pa = 17 - 22.9(X-K).821) In (X+0.608) + 56.6 [ In (X-K).608)]^ (wherein In designates the Nigerians logarithm), and recovering the separated hydrogen fluoride and difluoromethane. PRICE: THIRTY RUPEES

Title of Invention

A PROCESS FOR THE SEPARATION OF HYDROGEN FLUORIDE AND DIFLUOROMETHANE FORM A MIXTURE CONTAINIGN HYDROGEN FLUORIDE AND DIFLUOROMETHANE

Abstract

The invention relates to a process for the separation of hydrogen fluoride (HF) and difluoromethane (F32) from a mixture containing hydrogen fluoride (HF) and difluoromethane (F32). The said process comprises a process selected from fractional distillation, condensation or both, in one or more stages, at least one stage being performed such that there may be obtained a stream whose HF and F32 contents correspond substantially to those of the azeotropic composition, and the said stage being performed, as a function of the intended separation objective, at a pressure chosen so that the partial pressure of the HF + F32 mixture of the said stream (Pa expressed in bars absolute) and the HF content of the said mixture (x in per cent by weight) are linked by the relationship: Pa = 17 -22.9(X+O.821) In (X+O.608) + 56.6 [In (X+O.608)Y (wherein In designates the Naperian logarithm), and recovering the separated hydrogen fluoride and difluoromethane. 57) Abstract:- The invention relates to a process for the of hydrogen fluoride (HF) and difluoromethane (F32) from a mixture containing hydrogen fluoride (HF) and difluoromethane {F32). The said process comprises a process selected from fractional distillation, condensation or both, in one or more stages, at least one stage being performed such that there may be obtained a stream whose HF and F32 contents correspond substantially to those of the isotropic composition, and the said stage being performed, as a function of the intended separation objective, at a pressure chosen so that the partial pressure of the HF + F32 mixture of the said stream (Pa expressed in bars absolute) and the HF content of the said mixture (x in per cent by weight) are linked by the relationship: Pa = 17 - 22.9(X-K).821) In (X+0.608) + 56.6 [ In (X-K).608)]^ (wherein In designates the Nigerians logarithm), and recovering the separated hydrogen fluoride and difluoromethane. PRICE: THIRTY RUPEES

Full Text	The invention relates to the separation of hydrogen fluoride (HF) and difluoromethane {F32), which is a fluorine compound without effect on the ozone layer and which can therefore be employed as a replacement product for chlorofluorocarbons (CFCs) . In particular the invention relates to the separation of unconverted HF present in the mixtures obtained from the manufacture of F32 by fluorination of methylene chloride with HF. In such manufactures it is economically necessary, on the one hand, to recover the unconverted HP in amhydrous form in order to recycle it to the fluorination reactor and, on the other hand, to recover F32 as free as possible from HF, to facilitate its subsequent final purification. Most chlorofluoro- or fluorohydrocarbons form zoetrope’s with HF; separation of HF and of these compounds is therefore difficult. Various techniques have already been described with the objective of performing this separation. There may be mentioned, for example: - US patent 2 640 086, which relates to the separation of HF and of chlorodifluoromethame and employs chloroform to promote the separation into two phases, an HF-rich phase and an HF-lean phase; - US patent 3 873 629, relating to a continuous process for the separation of HF quid of chlorodifluoromethane and comprising bringing the gaseous mixture of the two constituents into contact countercurrentwise with sulphuric acid; - US patent 3 976 447, which proposes separation of HF from gaseous effluents by absorption-desertion on particles of calcium, barium or strontium chloride; - US patent 4 209 470, which describes a process for separation of HF from its mixtures with 1-chloro-l,1-difluoroethane, in which, to improve the phase separation, an auxiliary liquid is added, consisting entirely or predominantly of 1,1-dichloro-l-fluoroethane; - US patent 5 094 773, relating to the separation of HF from its mixtures with 2,2-dichloro-1,1,1-trifluoroethane and/or 2-chloro-l,1,1,2- tetrafluoroetheuie by phase separation and distillation; - European Patent application EP 0 467 531, which describes a process for separation of 1,1,1,2-tetrafluoroethane from its mixtures with HF and/or 1-chloro-2,2-difluoroethylene by doxible distillation with or without phase separation; - Japanese Patent application JP 5 178 768, which describes the separation of 1,1,1,2- tetrafluoroetheuie from its mixtures with HF by doxible distillation. These various techniques are either uneconomical or inapplicable to the separation of HF sued F32. Inspection of known data on the variations with pressure in the composition of the azeotropes o£ HF and of various chlorofluoro- or fluorohydrocarbons (see Table 1 which follows) shows that the HF content of these azeotropes varies relatively little with pressure. It is found, furthermore, that, in the case of F22 and of F134a, the HF content tends to a limiting value (2.4 and 2.8 % respectively) at elevated pressures. References; 1 - M.A. Zapol'skaya et al., Teor. Snowy Kim. Techs., 1975, pp 3-10 2 - Azeotropic Data, 1973, III, Horsley Lee H., Americium Chemical Society, Advances in Chemistry Series No. 116, page 11 3 - Applicant's internal data 4 - US patent 5 094 773 5 - European Patent application EP 0 467 531 6 - Japanese Patent application JP 5 178 768 It has now been found that, while HF and F32 do form an azeotrope, like most of the chlorofluoro- or fluorohydrocarbons, this HF-F32 azeotrope is singularly characterized (see Table II below) by an HF content which drops considerably when the pressure increases and which becomes very low (lower than 3000 ppm by weight) below 20 bars absolute. From the data in Table II the pressure Pa of the isentropic mixture (expressed in bars absolute) can be represented as a exaction of the HF content x of this mixture (expressed in per cent by weight) by the following relationship: Pa = 17 - 22.9(x+0.821)ln(x+0.608) + 56.6[ln(x+0.608)]’ This special behavior of the HF-F32 azeotrope was quite unexpected and can be exploited, in accordance with the present invention, for carrying out industrially effective separations of HF and of F32, especially in order to recover the unconverted HF present in the mixtures obtained from the manufacture of F32 by fluorination of methylene chloride with HP, and/or to obtain F32 virtually free from HF. According to the present invention, there is therefore provided a process for the separation of hydrogen fluoride (HF) and difluoromethane (F32) from a mixture containing hydrogen fluoride (HF) and difluoromethane (F32) by fractional distillation and/or condensation in one or more stages characterised in that at least one stage of separation is performed to obtain a stream whose HF and F32 contents correspond substantially to those of the isentropic composition, the said stage being performed, as a function of the intended separation objective, at a pressure chosen so that: Pa = 17 - 22.9(x+0.821)ln(x+0.608) + 55.6[ln(x+0.608)]’ in which Pa is the partial pressure of the HF + F3 2 mixture of the said stream in bars absolute. In designates the Naperian logarithm, and x is the HF content of the said stream in per cent by weight, and recovering the separated hydrogen fluoride and difluoromethane in a known manner. The process according to the invention applies not only to the separation of mixtures containing only HF and F32, but also to that of crude mixtures from the manufacture of F32. This manufacture can be performed according to processes that are known per se, which may be: - either of the so-called liquid-phase type, generally catalysed homogeneously by antimony chlorofluorides, - or of the so-called gaseous-phase type, generally catalysed heterogeneously by a solid catalyst based on various metals, for example chromium. In addition to HF and F32, the mixture to be separated according to the invention may therefore include variable proportions of other products or impurities such as, for example, hydrochloric acid, chlorofluoromethane (F31), chlorodifluoromethane (F22), trifluoromethane {F23), chlorine etc. The mixture to be treated may be available at various pressures, may be gaseous or liquid and may contain variable proportions of HF and of F32. The process according to the invention may be carried out according to numerous variants, especially those corresponding to the diagrams of the accompanying Figures 1 to 4. The choice of one variant or another by the manufacturer will depend on the nature of the mixture to be treated amd on the desired objective (recovery of most of the unconverted HF quid/or obtaining F32 virtually free from HF) . Fissure 1 illustrates diagrammatically apparatus applicable in particular to the separation of mixtures consisting essentially of HF and of F32 and in which the HF weight content is of the order of several per cent. Such a mixture can be obtained downstreeun of manufacture of F32 after distillation of hydrochloric acid. According to this embodiment the mixture to be separated is fed continuously via the conduit 1 into a conventional distillation column and is subjected to distillation conducted at a pressure above 6 bars absolute, preferably above 10 bars absolute. A stream 2 is obtained at the top of the column via the condenser (cold) 21, of HF-F32 azeotrope in which the HF weight content is lower than 2.2% (value at 6 bars absolute) , but may be much lower at higher pressure. A stream 3 is obtained at the bottom of the column, consisting of HF which is in excess in relation to the azeotrope and virtually free from F32. A recoiled 22 generates vapor which is reintroduced at the bottom of the column. In the light of TeQjle II above it will be \understood that the distillation pressure (higher than 6 bars eibsolute} is to be chosen as a function of the desired target purity of the F32 collected at the top,-its residual HF content will be proportionally lower the higher the distillation pressure. Since HF-F32 azeotropes of very low HF content have boiling points very close to that of F32 (-51.7°C), distillation according to this estbodiment is very easy and makes it possible, with low reflux ratios, of the order of 1 or less, to obtain at the top the azeotrope which is practically free from excess HF and at the bottom HF practically free from F32. The distillation according to this embodiment can also be applied to the treatment of a crude mixture containing, besides HF and F32, other products or impurities such as F31, methylene chloride and the like. In this case the F31 or the CHjCl, move to the bottom of the claim with the HF, while F32 with a low or even very low HF content is obtained at the top. Figure 2 shows diagrammatically apparatus for use in a modification of the above method. This also applies to the separation of mixtures consisting essentially of HF and of F32 to obtain virtually pure F32 and to recover HF in anhydrous form. The process carried out according to Figure 2, which includes two distillation stages, may be advantageously employed when, for any reasons (economical or other), the required target purity for F32 is not reached by a single distillation according to the process of Figure In the embodiment according to Figure 2 the mixture to be separated is first introduced via conduit 1 to a first column where it is subjected to distillation at an elevated pressure above 6 bars absolute, preferably above 10 bars absolute. An HF-F32 azeotrope of relatively low HF content (less than 2.2% by weight) is obtained at the top via the condenser (cold) 23 and most of the excess HF, free from F32, at the bottom. A reboiler 24 generates vapour which is reintroduced at the bottom of the first column. The azeotrope obtained at the top is next introduced via the conduit 2 into a second column and subjected to distillation conducted at a lower pressure than that in the first distillation. At the top of the second distillation column an HF-F32 azeotrope is obtained via the condenser (cold) 25 with a relatively high HF content, which is recycled via the conduit 4 to the feed of the first Collin. A stream 5 of F32 virtually free from HF is obtained at the bottom of the second column. A reboiler 26 generates vapour which is reintroduced at the bottom of the second column. Such a system is obviously proportionally more efficient the greater the pressure difference between the two distillations. The separation between the HF-F32 azeotrope and F32, performed in the second distillation column, is more difficult than that performed in the first column between the azeotrope and HF. This separation requires a higher recoiling ratio, for example of the order of 3 to 4, depending on the F32 purity required; it is made easier by a low pressure, preferably below 10 bars absolute. As in the case of the process according to Figure 1, the embodiment according to Figure 2 may also be applied to the treatment of a crude mixture containing, besides HF and F32, other products or impurities (F31, Cecile,, and the like) which are recovered with HF at the bottom of the first distillation Colin. Figure 3 illustrates diagrammatically apparatus for use more particularly in connection with the manufacture of F32 by reaction of methylene chloride with HF in liquid phase in a conventional plant including a liquid phase reactor 27 fed with fresh HF end CE’Cl: via conduits 11 and 12 and a return device. The reaction products, which leave the reactor in gaseous form and include HCl, F32, HF med various impurities, are introduced via conduit 13 into a return column carrying a condenser (cold) 28 above. HCl, F32 and a proportion of unconverted HF leave in gaseous form at the top of the column, while most of the heavier organic products and the remaining unconverted HF are returned to the reactor via conduit 14. In the method according to Figure 3 the objective of the separation between HF and F32, performed in the return device, is to minimize the outflow of HF accompanying the F32 produced and to recycle as much HF as possible directly to the reactor. To achieve the recruited objective in this separation the price’s 4p’rding to the invention consists in conducting the return at a pressure above 12 bars absolute, preferably between 16 and 50 bars absolute. Despite the presence of HCl, the maximum HF content of the HF-F32-HC1 mixture leaving the reaction system by conduit 15 dovmstreaun of the condenser corresponds substantially to the HF content of the HF-F32 azeotrope under the partial pressure of the HF-F32 mixture, this partial pressure being equal to the difference between the total pressure and the partial pressure of HCl. As the HF content of the azeotrope decreases strongly when the pressure increases, the maximum HF content of the HF-F32-HC1 mixture leaving the reaction system decreases strongly when the total pressure at which the return is conducted increases. Thus, when operating at a pressure above 12 bars ejaculate, the HF content of the stream leaving the reaction system by conduit 15 is not more than 2.5% by weight, which corresponds broadly to the objective of returning most of the unconverted HF to the reactor. Yet another method of carrying out the process according to the invention is illustrated with reference to the apparatus shown diagrammatically in Figure 4. This concerns more particularly the manufacture of F32 by reaction of methylene chloride with HF in gaseous phase. At the outlet of the gas phase reactor 29, fed with fresh HF and CH,C1, by conduits 11 and 12, a gaseous mixture of F32, HCl, HF, F31 and Chicly is obtained, which is introduced by conduit 13 into a conventional distillation column carrying a condenser (cold) 3 0 above to obtain, on the one hand, at the top, a stream 15 consisting essentially of HCl and F32 and, on the other hand, at the bottom, a stream consisting essentially of HF and of under fluorinated organics (F31, CEjCl,) which is recycled to the reactor by conduit 14. A reboiler 31 generates vapour which is reintroduced at the bottom of the column. In mamufacture of this type the objective of the separation between HF and F32 which is performed in the distillation column is to minimize the HF content of the screen 15 so as to recycle most of the unconverted HF to the reaction. To meet this objective the process according to the invention consists in conducting the distillation at a pressure above 12 bars absolute, preferably between 16 and 50 bars absolute. As in the case of the in liquid phase, the maximum HF content in the strata 15 leaving the reaction system corresponds substantially to the HF content of the HF-F32 azeotrope under the partial pressure of the HF-F32 mixture and decreases strongly with increase in the operating pressure. The following examples illustrate the invention without limiting it. The percentages shown are expressed on a weight basis. EXAMPLE 1 The characteristics of the HF-F32 azeotrope indicated in the above Tamale II have been determined by measuring the composition of the gas phase of various mixtures of HF and F32 after bringing them to equilibrium at different pressures. The equilibration is carried out in a 102-ml stainless steel receptacle equipped with a dip pipe and a gas phase outlet. The HF-F32 mixture being studied is prepared by weighing, HF and F32 being introduced separately. HF is introduced first into the receptacle placed beforehand in a bath thermostated at -20°C and evacuated, then the receptacle is weighed and the operation is repeated for the introduction of F32, the total volume of liquid in the receptacle representing 80 ml. After filling, the receptacle is closed and then replaced in the thermostated bath and taken to the pressure being studied. Temperature measurement and analysis of the mixture are performed 12 hours after the pressure and temperature have stabilized. The analysis is carried out by gas chromatography on a sample of the gas phase from the mixture at equilibrivim, each analysis being performed three times before the mixture is taken to a higher pressure or products are recharged. The series of measurements performed has been collected in the following . At each pressure a of measurements are available which straddle the azeotrope and therefore make it possible to determine it. EXAMPLE 2 In accordance with the diagram in Facture 1, a mixture of HF and of F32, containing 10 % of HF is separated at 16 bars absolute in a distillation column of 10 theoretical plates. The following tassel summarizes the operating conditions and the results obtained. EXAMPLE 3 A mixture of HF and of F32, containing 10 % of HF is separated in the device according to Figure 2. The first distillation is performed at 16 bars absolute and the second at 6 bars absolute. The first column has 10 theoretical plates. The second has 2 8 and is fed at the 22nd plate. The operating conditions and the results obtained are summarized in the following table: EXAMPLE 4 The operation is carried out at 20 bars dissolute in accordance with the diagreun in Figure 3. The return column has 6 theoretical plates. The following table summarizes the operating conditions and the results obtained. The overall conversion ratio of HF in this reaction system is 97.5 %. EXAMPLE 5 Fluorination of methylene chloride in gaseous phase at 20 bars absolute is performed in the device according to the diagram in Figure 4. The reactor is fed continuously with fresh reactants (HF and F32) and by recycling the stream 14 originating from the foot of the distillation column which has 13 theoretical plates. The following table summarizes the operating conditions and the results obtained. We Claim;- 1. A process for the separation of hydrogen fluoride (HF) and difluoromethane (F32) from a mixture containing hydrogen fluoride (HF) and difluoromethane (F32) by fractional distillation and/or condensation in one or more stages characterised in that at least one stage of separation is performed to obtain a stream whose HF and F32 contents correspond substantially to those of the azeotropic composition, the said stage being performed, as a fiction of the intended separation objective, at a pressure chosen so that: Pa = 17 - 22.9(x+0.821)ln(x+0.608) + 56.6[ln(x+0.608)] in which Pa is the partial pressure of the HF + F32 mixture of the said stream in bars absolute. In designates the Naperian logarithm, and x is the HF content of the said stream in per cent by weight, and recovering the separated hydrogen fluoride and difluoromethane in a known manner. 2. The process according to Claim 1 for the separation of a mixture containing essentially hydrogen fluoride (HF) and difluoromethane (F32) which process comprises stibjecting the mixture to distillation carried out at a pressure above 6 bars absolute. 3. The process according to Claim 2, wherein the distillation is carried out at a pressure above 10 bars absolute. 4. The process according to Claim 3, wherein the HF-F32 azeotrope of low HF content, obtained at the top of the distillation, is subjected to a second distillation conducted at a lower pressure them that of the first distillation and the HF-F32 azeotrope of higher HF content, obtained at the top of the second distillation, is recycled to the first distillation. 5. The process according to Claim 4, wherein the second distillation is performed at a pressure below 10 bars absolute. 6. The process according, to Claim 1 wherein the gaseous mixture is obtained from the production of difluoromethane (F32) by fluorination of methylene chloride with hydrogen fluoride (HF) in the liquid phase, which process coarsest subjecting the gaseous mixture containing F32, HF, and HCl to a fractional return or condensation operation at a pressure above 12 bars desolate. 7. The process according td Claim 1 wherein the gaseous mixture is obtained from the production of difluoromethane (F32) by fluorination of methylene chloride with hydrogen fluoride (HF) in the gas phase, which process comprises subjecting the gaseous mixture containing F32, HF and HCl to distillation at a pressure above 12 bars absolute. 8. The process according to Claim 6 or 7 wherein the separation is carried out at a pressure between 16 and 50 bars eibsolute. 9. A process for the separation of hydrogen fluoride (HF) and difluoromethane (F32) from a mixture containing hydrogen fluoride (HF) and difluorom ethane (F32) substantially as herein described with reference to the accompanying drawings.

Full Text

The invention relates to the separation of hydrogen fluoride (HF) and difluoromethane {F32), which is a fluorine compound without effect on the ozone layer and which can therefore be employed as a replacement product for chlorofluorocarbons (CFCs) . In particular the invention relates to the separation of unconverted HF present in the mixtures obtained from the manufacture of F32 by fluorination of methylene chloride with HF. In such manufactures it is economically necessary, on the one hand, to recover the unconverted HP in amhydrous form in order to recycle it to the fluorination reactor and, on the other hand, to recover F32 as free as possible from HF, to facilitate its subsequent final purification.
Most chlorofluoro- or fluorohydrocarbons form zoetrope’s with HF; separation of HF and of these compounds is therefore difficult. Various techniques have already been described with the objective of performing this separation. There may be mentioned, for example:
- US patent 2 640 086, which relates to the separation of HF and of chlorodifluoromethame and employs chloroform to promote the separation into two phases, an HF-rich phase and an HF-lean phase;
- US patent 3 873 629, relating to a continuous process for the separation of HF quid of chlorodifluoromethane and comprising bringing the gaseous mixture of the two constituents into contact

countercurrentwise with sulphuric acid;
- US patent 3 976 447, which proposes separation of HF from gaseous effluents by absorption-desertion on particles of calcium, barium or strontium chloride;
- US patent 4 209 470, which describes a process for separation of HF from its mixtures with 1-chloro-l,1-difluoroethane, in which, to improve the phase separation, an auxiliary liquid is added, consisting entirely or predominantly of 1,1-dichloro-l-fluoroethane;
- US patent 5 094 773, relating to the separation of HF from its mixtures with 2,2-dichloro-1,1,1-trifluoroethane and/or 2-chloro-l,1,1,2-
tetrafluoroetheuie by phase separation and distillation;
- European Patent application EP 0 467 531, which describes a process for separation of 1,1,1,2-tetrafluoroethane from its mixtures with HF and/or 1-chloro-2,2-difluoroethylene by doxible distillation with or without phase separation;
- Japanese Patent application JP 5 178 768, which describes the separation of 1,1,1,2-
tetrafluoroetheuie from its mixtures with HF by doxible distillation.
These various techniques are either uneconomical or inapplicable to the separation of HF sued F32.
Inspection of known data on the variations

with pressure in the composition of the azeotropes o£ HF and of various chlorofluoro- or fluorohydrocarbons (see Table 1 which follows) shows that the HF content of these azeotropes varies relatively little with pressure. It is found, furthermore, that, in the case of F22 and of F134a, the HF content tends to a limiting value (2.4 and 2.8 % respectively) at elevated pressures.

References;
1 - M.A. Zapol'skaya et al., Teor. Snowy Kim. Techs.,
1975, pp 3-10
2 - Azeotropic Data, 1973, III, Horsley Lee H.,
Americium Chemical Society, Advances in Chemistry Series No. 116, page 11
3 - Applicant's internal data
4 - US patent 5 094 773
5 - European Patent application EP 0 467 531
6 - Japanese Patent application JP 5 178 768
It has now been found that, while HF and F32 do form an azeotrope, like most of the chlorofluoro- or fluorohydrocarbons, this HF-F32 azeotrope is singularly characterized (see Table II below) by an HF content which drops considerably when the pressure increases and which becomes very low (lower than 3000 ppm by weight) below 20 bars absolute.
From the data in Table II the pressure Pa of the isentropic mixture (expressed in bars absolute) can

be represented as a exaction of the HF content x of this mixture (expressed in per cent by weight) by the following relationship:
Pa = 17 - 22.9(x+0.821)ln(x+0.608) + 56.6[ln(x+0.608)]’

This special behavior of the HF-F32 azeotrope was quite unexpected and can be exploited, in accordance with the present invention, for carrying out industrially effective separations of HF and of F32, especially in order to recover the unconverted HF present in the mixtures obtained from the manufacture of F32 by fluorination of methylene chloride with HP, and/or to obtain F32 virtually free from HF.
According to the present invention, there is therefore provided a process for the separation of hydrogen fluoride (HF) and difluoromethane (F32) from a mixture containing hydrogen fluoride (HF) and difluoromethane (F32) by fractional distillation and/or condensation in one or more stages characterised in that at least one stage of separation is performed to obtain a stream whose HF and F32 contents correspond substantially to those of the isentropic composition, the said stage being performed, as a function of the

intended separation objective, at a pressure chosen so that:
Pa = 17 - 22.9(x+0.821)ln(x+0.608) + 55.6[ln(x+0.608)]’
in which Pa is the partial pressure of the HF + F3 2 mixture of the said stream in bars absolute. In designates the Naperian logarithm, and x is the HF content of the said stream in per cent by weight, and recovering the separated hydrogen fluoride and difluoromethane in a known manner.
The process according to the invention applies not only to the separation of mixtures containing only HF and F32, but also to that of crude mixtures from the manufacture of F32. This manufacture can be performed according to processes that are known per se, which may be:
- either of the so-called liquid-phase type,
generally catalysed homogeneously by antimony
chlorofluorides,
- or of the so-called gaseous-phase type,
generally catalysed heterogeneously by a solid catalyst
based on various metals, for example chromium.
In addition to HF and F32, the mixture to be separated according to the invention may therefore include variable proportions of other products or impurities such as, for example, hydrochloric acid, chlorofluoromethane (F31), chlorodifluoromethane (F22), trifluoromethane {F23), chlorine etc. The mixture to be treated may be available at various pressures, may be gaseous or liquid and may contain variable proportions of

HF and of F32.
The process according to the invention may be carried out according to numerous variants, especially those corresponding to the diagrams of the accompanying Figures 1 to 4. The choice of one variant or another by the manufacturer will depend on the nature of the mixture to be treated amd on the desired objective (recovery of most of the unconverted HF quid/or obtaining F32 virtually free from HF) .
Fissure 1 illustrates diagrammatically apparatus applicable in particular to the separation of mixtures consisting essentially of HF and of F32 and in which the HF weight content is of the order of several per cent. Such a mixture can be obtained downstreeun of manufacture of F32 after distillation of hydrochloric acid.
According to this embodiment the mixture to be separated is fed continuously via the conduit 1 into a conventional distillation column and is subjected to distillation conducted at a pressure above 6 bars absolute, preferably above 10 bars absolute.
A stream 2 is obtained at the top of the column via the condenser (cold) 21, of HF-F32 azeotrope in which the HF weight content is lower than 2.2% (value at 6 bars absolute) , but may be much lower at higher pressure. A stream 3 is obtained at the bottom of the column, consisting of HF which is in excess in relation to the azeotrope and virtually free from F32. A recoiled 22 generates vapor which is reintroduced at the bottom of the column.

In the light of TeQjle II above it will be \understood that the distillation pressure (higher than 6 bars eibsolute} is to be chosen as a function of the desired target purity of the F32 collected at the top,-its residual HF content will be proportionally lower the higher the distillation pressure.
Since HF-F32 azeotropes of very low HF content have boiling points very close to that of F32 (-51.7°C), distillation according to this estbodiment is very easy and makes it possible, with low reflux ratios, of the order of 1 or less, to obtain at the top the azeotrope which is practically free from excess HF and at the bottom HF practically free from F32.
The distillation according to this embodiment can also be applied to the treatment of a crude mixture containing, besides HF and F32, other products or impurities such as F31, methylene chloride and the like. In this case the F31 or the CHjCl, move to the bottom of the claim with the HF, while F32 with a low or even very low HF content is obtained at the top.
Figure 2 shows diagrammatically apparatus for use in a modification of the above method. This also applies to the separation of mixtures consisting essentially of HF and of F32 to obtain virtually pure F32 and to recover HF in anhydrous form. The process carried out according to Figure 2, which includes two distillation stages, may be advantageously employed when, for any reasons (economical or other), the required target purity for F32 is not reached by a single distillation according to the process of Figure

In the embodiment according to Figure 2 the mixture to be separated is first introduced via conduit 1 to a first column where it is subjected to distillation at an elevated pressure above 6 bars absolute, preferably above 10 bars absolute. An HF-F32 azeotrope of relatively low HF content (less than 2.2% by weight) is obtained at the top via the condenser (cold) 23 and most of the excess HF, free from F32, at the bottom. A reboiler 24 generates vapour which is reintroduced at the bottom of the first column. The azeotrope obtained at the top is next introduced via the conduit 2 into a second column and subjected to distillation conducted at a lower pressure than that in the first distillation. At the top of the second distillation column an HF-F32 azeotrope is obtained via the condenser (cold) 25 with a relatively high HF content, which is recycled via the conduit 4 to the feed of the first Collin. A stream 5 of F32 virtually free from HF is obtained at the bottom of the second column. A reboiler 26 generates vapour which is reintroduced at the bottom of the second column.
Such a system is obviously proportionally more efficient the greater the pressure difference between the two distillations. The separation between the HF-F32 azeotrope and F32, performed in the second distillation column, is more difficult than that performed in the first column between the azeotrope and HF. This separation requires a higher recoiling ratio, for example of the order of 3 to 4, depending on the

F32 purity required; it is made easier by a low pressure, preferably below 10 bars absolute.
As in the case of the process according to Figure 1, the embodiment according to Figure 2 may also be applied to the treatment of a crude mixture containing, besides HF and F32, other products or impurities (F31, Cecile,, and the like) which are recovered with HF at the bottom of the first distillation Colin.
Figure 3 illustrates diagrammatically apparatus for use more particularly in connection with the manufacture of F32 by reaction of methylene chloride with HF in liquid phase in a conventional plant including a liquid phase reactor 27 fed with fresh HF end CE’Cl: via conduits 11 and 12 and a return device. The reaction products, which leave the reactor in gaseous form and include HCl, F32, HF med various impurities, are introduced via conduit 13 into a return column carrying a condenser (cold) 28 above. HCl, F32 and a proportion of unconverted HF leave in gaseous form at the top of the column, while most of the heavier organic products and the remaining unconverted HF are returned to the reactor via conduit 14.
In the method according to Figure 3 the objective of the separation between HF and F32, performed in the return device, is to minimize the outflow of HF accompanying the F32 produced and to recycle as much HF as possible directly to the reactor. To achieve the recruited objective in this separation the price’s 4p’rding to the invention consists in

conducting the return at a pressure above 12 bars absolute, preferably between 16 and 50 bars absolute.
Despite the presence of HCl, the maximum HF content of the HF-F32-HC1 mixture leaving the reaction system by conduit 15 dovmstreaun of the condenser corresponds substantially to the HF content of the HF-F32 azeotrope under the partial pressure of the HF-F32 mixture, this partial pressure being equal to the difference between the total pressure and the partial pressure of HCl. As the HF content of the azeotrope decreases strongly when the pressure increases, the maximum HF content of the HF-F32-HC1 mixture leaving the reaction system decreases strongly when the total pressure at which the return is conducted increases. Thus, when operating at a pressure above 12 bars ejaculate, the HF content of the stream leaving the reaction system by conduit 15 is not more than 2.5% by weight, which corresponds broadly to the objective of returning most of the unconverted HF to the reactor.
Yet another method of carrying out the process according to the invention is illustrated with reference to the apparatus shown diagrammatically in Figure 4. This concerns more particularly the manufacture of F32 by reaction of methylene chloride with HF in gaseous phase. At the outlet of the gas phase reactor 29, fed with fresh HF and CH,C1, by conduits 11 and 12, a gaseous mixture of F32, HCl, HF, F31 and Chicly is obtained, which is introduced by conduit 13 into a conventional distillation column carrying a condenser (cold) 3 0 above to obtain, on the

one hand, at the top, a stream 15 consisting essentially of HCl and F32 and, on the other hand, at the bottom, a stream consisting essentially of HF and of under fluorinated organics (F31, CEjCl,) which is recycled to the reactor by conduit 14. A reboiler 31 generates vapour which is reintroduced at the bottom of the column.
In mamufacture of this type the objective of the separation between HF and F32 which is performed in the distillation column is to minimize the HF content of the screen 15 so as to recycle most of the unconverted HF to the reaction. To meet this objective the process according to the invention consists in conducting the distillation at a pressure above 12 bars absolute, preferably between 16 and 50 bars absolute.
As in the case of the in liquid phase, the maximum HF content in the strata 15 leaving the reaction system corresponds substantially to the HF content of the HF-F32 azeotrope under the partial pressure of the HF-F32 mixture and decreases strongly with increase in the operating pressure.
The following examples illustrate the invention without limiting it. The percentages shown are expressed on a weight basis.
EXAMPLE 1
The characteristics of the HF-F32 azeotrope indicated in the above Tamale II have been determined by measuring the composition of the gas phase of various

mixtures of HF and F32 after bringing them to equilibrium at different pressures.
The equilibration is carried out in a 102-ml stainless steel receptacle equipped with a dip pipe and a gas phase outlet. The HF-F32 mixture being studied is prepared by weighing, HF and F32 being introduced separately. HF is introduced first into the receptacle placed beforehand in a bath thermostated at -20°C and evacuated, then the receptacle is weighed and the operation is repeated for the introduction of F32, the total volume of liquid in the receptacle representing 80 ml. After filling, the receptacle is closed and then replaced in the thermostated bath and taken to the pressure being studied. Temperature measurement and analysis of the mixture are performed 12 hours after the pressure and temperature have stabilized.
The analysis is carried out by gas chromatography on a sample of the gas phase from the mixture at equilibrivim, each analysis being performed three times before the mixture is taken to a higher pressure or products are recharged.
The series of measurements performed has been collected in the following . At each pressure a of measurements are available which straddle the azeotrope and therefore make it possible to determine it.

EXAMPLE 2
In accordance with the diagram in Facture 1, a mixture of HF and of F32, containing 10 % of HF is separated at 16 bars absolute in a distillation column of 10 theoretical plates.
The following tassel summarizes the operating conditions and the results obtained.

EXAMPLE 3
A mixture of HF and of F32, containing 10 % of HF is separated in the device according to Figure 2. The first distillation is performed at 16 bars absolute and the second at 6 bars absolute. The first column has 10 theoretical plates. The second has 2 8 and is fed at the 22nd plate.
The operating conditions and the results obtained are summarized in the following table:

EXAMPLE 4
The operation is carried out at 20 bars dissolute in accordance with the diagreun in Figure 3. The return column has 6 theoretical plates.
The following table summarizes the operating conditions and the results obtained.

The overall conversion ratio of HF in this reaction system is 97.5 %.
EXAMPLE 5
Fluorination of methylene chloride in gaseous phase at 20 bars absolute is performed in the device according to the diagram in Figure 4. The reactor is fed continuously with fresh reactants (HF and F32) and by recycling the stream 14 originating from the foot of the distillation column which has 13 theoretical plates.
The following table summarizes the operating conditions and the results obtained.

We Claim;-
1. A process for the separation of hydrogen
fluoride (HF) and difluoromethane (F32) from a mixture
containing hydrogen fluoride (HF) and difluoromethane
(F32) by fractional distillation and/or condensation in
one or more stages characterised in that at least one
stage of separation is performed to obtain a stream whose
HF and F32 contents correspond substantially to those of
the azeotropic composition, the said stage being
performed, as a fiction of the intended separation
objective, at a pressure chosen so that:
Pa = 17 - 22.9(x+0.821)ln(x+0.608) + 56.6[ln(x+0.608)]
in which Pa is the partial pressure of the HF + F32 mixture of the said stream in bars absolute. In designates the Naperian logarithm, and x is the HF content of the said stream in per cent by weight, and recovering the separated hydrogen fluoride and difluoromethane in a known manner.
2. The process according to Claim 1 for the separation of a mixture containing essentially hydrogen fluoride (HF) and difluoromethane (F32) which process comprises stibjecting the mixture to distillation carried out at a pressure above 6 bars absolute.
3. The process according to Claim 2, wherein the distillation is carried out at a pressure above 10 bars absolute.
4. The process according to Claim 3, wherein the HF-F32 azeotrope of low HF content, obtained at the

top of the distillation, is subjected to a second distillation conducted at a lower pressure them that of the first distillation and the HF-F32 azeotrope of higher HF content, obtained at the top of the second distillation, is recycled to the first distillation. 5. The process according to Claim 4, wherein the second distillation is performed at a pressure below 10 bars absolute.
6. The process according, to Claim 1 wherein the gaseous mixture is obtained from the production of difluoromethane (F32) by fluorination of methylene chloride with hydrogen fluoride (HF) in the liquid phase, which process coarsest subjecting the gaseous mixture containing F32, HF, and HCl to a fractional return or condensation operation at a pressure above 12 bars desolate.
7. The process according td Claim 1 wherein the gaseous mixture is obtained from the production of difluoromethane (F32) by fluorination of methylene chloride with hydrogen fluoride (HF) in the gas phase, which process comprises subjecting the gaseous mixture containing F32, HF and HCl to distillation at a pressure above 12 bars absolute.
8. The process according to Claim 6 or 7 wherein the separation is carried out at a pressure between 16 and 50 bars eibsolute.

9. A process for the separation of hydrogen fluoride (HF) and difluoromethane (F32) from a mixture containing hydrogen fluoride (HF) and difluorom ethane (F32) substantially as herein described with reference to the accompanying drawings.

Documents:

162-mas-95 abstract.pdf

162-mas-95 claims.pdf

162-mas-95 description (complete).pdf

162-mas-95 drawings.pdf

162-mas-95 form-1.pdf

162-mas-95 form-26.pdf

162-mas-95 form-4.pdf

162-mas-95 others document.pdf

162-mas-95 others.pdf

162-mas-95 correspondence-others.pdf

162-mas-95 correspondence-po.pdf

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Patent Number

188512

Indian Patent Application Number

162/MAS/1995

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

11-Jul-2003

Date of Filing

13-Feb-1995

Name of Patentee

M/S. ELF ATOCHEM S.A

Applicant Address

4 AND 8 COURS MICHELET, LA DEFENSE 10, PUTEAUX

Inventors:

#	Inventor's Name	Inventor's Address
1	JEAN-MICHEL GALLAND	1 DOMAINE DES ESSARTS, 69390 VERNAISON
2	DOMINIQUE ROUZIES	30 RUE DE 1'ARBRE SEC, 69001 LYON

PCT International Classification Number

B 01D 3/36

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA