Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B7/00—Halogens; Halogen acids
  • C01B7/19—Fluorine; Hydrogen fluoride
  • C01B7/191—Hydrogen fluoride
  • C01B7/195—Separation; Purification
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/38—Separation; Purification; Stabilisation; Use of additives
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/582—Recycling of unreacted starting or intermediate materials

Definitions

• the present invention relates to an improved process for separating and recovering an organic phase (e.g., fluorocarbons) and hydrogen fluoride (HF) from a fluorocarbon/HF mixture, wherein because of the presence or potential formation of an azeotrope or azeotrope-like composition, it is impractical to separate the mixture by conventional distillation. More specifically, the present invention relates to separating a fluorocarbon/HF mixture, by use of a semipermeable membrane unit, into a HF depleted stream and a HF enriched stream that are then further processed individually by distillation.
• an organic phase e.g., fluorocarbons
• HF hydrogen fluoride
• fluorochemicals of commercial interest including chlorofluorocarbons (CFC) , hydrogen-containing chlorofluorocarbons (HCFC) , hydrogen-containing fluorocarbons (HFC) and perfluorocarbons (FC) are typically manufactured by processes involving halogen exchange reactions.
• CFC chlorofluorocarbons
• HCFC hydrogen-containing chlorofluorocarbons
• HFC hydrogen-containing fluorocarbons
• FC perfluorocarbons
• fluorine-donating source is hydrogen fluoride used in the presence of various catalytic compound.
• Such a process may be illustrated by the preparation of monochiorodifluoromethane (HCFC-22) wherein chloroform is the chlorocarbon employed and hydrogen fluoride is the fluorine source according to the following reaction: catalyst
• the catalysts useful in this reaction include various metal oxides and halides and the reaction can be carried out in either vapor or liquid phase.
• the amount of hydrogen fluoride used in the above process is almost always in excess of the stoichiometric amount required and may be as much as a ten-fold excess. Excess hydrogen fluoride is used to increase yields and conversions and to reduce the reaction time.
• the crude reaction stream may contain some unreacted HCC1 , underfluorinated HCCl.F, the desired HCC1F , the by-product HC1 and the unreacted HF.
• HCC1_ and HCC1-F can be recovered for recycling as well as most of the hydrogen fluoride can be recovered by distillation processes.
• the desired product, HCC1F (HCFC-22)
• HCFC-22 and HF form an azeotrope-like mixture (b.p. 50°C at 292.5 psia and essentially constant composition of 97 wt.% HCFC-22 and 3 wt.% HF) .
• Another possible procedure for recovering HCFC-22 from its azeotropic mixture with hydrogen fluoride is to contact the mixture with a concentrated sulfuric acid (as disclosed in U.S. Patent No. 3,873,629) thereby to dissolve the hydrogen fluoride selectively in the sulfuric acid solution.
• a concentrated sulfuric acid as disclosed in U.S. Patent No. 3,873,629
• Such a procedure also requires the additional steps of washing the thus separated HCFC-22 for the removal of the sulfuric acid, dehydration and then distillation.
• the hydrogen fluoride dissolved in the concentrated sulfuric acid can be recovered for recycling by heating the sulfuric acid solution, such a recovery step requires specialized equipment and conditions such as are used in the hydrogen fluoride manufacturing process.
• Van Eijl in U.S. Patent No. 3,947,558 has suggested that hydrogen fluoride can be separated from an organic mixture of fluorinated -C compounds and recovered by selectively absorbing the HF in a glycol in which the HF is soluble, but the fluorinated organic compound is substantially insoluble.
• This process depends upon very selective solubility differences between the fluorinated compounds and hydrogen fluoride.
• Van Eijl even when the fluorinated compound is a perhalo compound, there is a fair degree of solubility of the perhalo compound in the glycol and a fair degree of solubility of the glycol in the perhalo compound.
• the fluorinated compound is a hydrogen-containing chlorofluoro compound, such as HCFC-22
• the solubility of HCFC-22 in the glycol is enhanced as well as the solubility of HF in the glycol-containing HCFC-22 layer and thus the separation process is adversely affected.
• HF can be separated from certain non-azeotrope systems by selective permeation through a membrane.
• Grote in U.S. Patent No. 4,661,296 discloses separation of HF from a carbonylation process mixture (e.g., isobutyric acid, water and HF) using a "NAFION" membrane. The disclosed process is an alternative to separation by distillation.
• Tarasenko in U.S. Patent No. 4,424,067 discloses purification of anhydrous HF by removal of AsF_ contaminant by permeation of the HF through non-porous fluoropolymer film. Again no separation of an azeotrope is suggested.
• the present invention provides an improved process for separating and recovering an organic phase containing fluorocarbons (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons and perfluorocarbons) and hydrogen fluoride phase from fluorocarbon/hydrogen fluoride mixtures, particularly mixtures wherein because of the presence or potential formation of an azeotrope or azeotrope-like composition, it is impractical to separate the mixture by conventional distillation.
• the improved method according to the present invention involves the simultaneous use of a membrane separation system in combination with conventional distillation systems, thus producing a hybrid recovery unit.
• this invention provides a process for the separation of a difficult-to-separate azeotrope or azeotrope-like composition consisting essentially of hydrogen fluoride and a C -C fluorocarbon composition.
• the present invention provides a process for separating and recovering an organic phase and an hydrogen fluoride phase from a feed stream of a mixture of fluorocarbons and hydrogen fluoride wherein the mixture is characterized as forming at least one azeotrope or azeotrope-like composition involving at least one fluorocarbon and hydrogen fluoride, comprising the steps of:
• step (c) subjecting the fluorocarbon-depleted hydrogen fluoride permeate stream produced in step (b) to distillation, thus separating and recovering hydrogen fluoride;
• step (d) subjecting the fluorocarbon enriched residual stream produced in step (b) to distillation, thus separating and recovering a fluorocarbon organic phase.
• the fluorocarbon-depleted hydrogen fluoride permeate stream is further characterized as having a hydrogen fluoride concentration above that characteristic of the azeotrope or azeotrope-like composition involving hydrogen fluoride and the fluorocarbon such that the azeotrope or azeotrope-like composition is also separated and recovered in step (c) and wherein the fluorocarbon-enriched residual stream is further characterized as having a hydrogen fluoride concentration below that characteristic of the azeotrope or azeotrope-like composition involving hydrogen fluoride and the fluorocarbon such that the azeotrope or azeotrope-like composition is also separated and recovered in step (d) and wherein the azeotrope or azeotrope-like composition separated and recovered
• the Figure represents a schematic illustration of a typical improved process for recovery of organic vapors according to one embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS
• fluorocarbon refers broadly to any chlorofluorocarbon, hydrochlorofluorocarbon, hydrofluorocarbon, perfluorocarbon (i.e., CFC, HCFC, HFC, and FC, respectively) or mixtures thereof that form or tend to form a mixture with HF that is difficult separate by conventional distillation.
• fluorocarbon is intended to include halocarbons that form or tend to form true azeotropes with HF as well as halocarbons that form or tend to form azeotrope-like compositions with HF.
• the feed stream according to the present invention does not have to be at the azeotrope or azeotrope-like concentration range, per se, but merely capable of forming the difficult-to-separate composition during distillation (all as explained more fully later) .
• azeotrope refers to a constant boiling admixture of one or more fluorocarbons with HF, whose admixture behaves as a single substance, in that the vapor, produced by partial evaporation or distillation of the liquid has the same composition as the liquid, i.e., the admixture distills without compositional change.
• azeotrope-like for purposes of this invention, refers generally to any such mixture of one or more fluorocarbons and HF that exhibits essentially a constant composition on boiling (i.e., distills with little or no change in the composition due to closeness of the boiling points of the components in the mixture or due to some other reasons) .
• fluorocarbons of particular use in the present invention include, by way of example but not limited thereto, the aliphatic halocarbon of 1 to 3 carbon atoms containing at least one fluorine atom substituent.
• fluorocarbon will include chlorofluorocarbon, hydrogen-containing chlorofluorocarbon, perfluorocarbon and hydrogen-containing fluorinated hydrocarbon of from 1 to 3 carbon atoms and mixtures thereof. More specifically, fluorocarbons of particular interest include:
• chlorodifluoromethane (CHC1F 2 , HCFC-22) difluoromethane t CH 2 F 2 f HFC " 32)
• HCFC-124) pentafluoroethane, (CF..CHF , HFC-125) 1,1,2,2-tetrafluoroethane CHF 2 CHF 2 , HFC-134) 1,1,1,2-tetrafluoroethane (CF 3 CH 2 F, HFC-134a) 1,1-dichloro-l-fluoroethane (CC1 2 FCH 3 , HCFC-141b) l-chloro-l,l-difluoroethane (CC1F 2 CH_, HCFC-142b) 2-chloro-l,l,1-trifluoroethane (CF 3 CH 2 C1, HCFC-133a)
• the improved process of the present invention is particularly useful in separating and recovering mixtures of fluorocarbons in the presence of HF.
• commercial production of a fluorocarbon involves a sequential fluorination of a starting chlorocarbon resulting in a distribution of reaction products and intermediates, all of which tend to make the mixture even more complex and difficult to isolate and recover by conventional separation techniques.
• various mixture of the 120 hydrofluoroethane series are frequently found together such as a mixture of HCFC-123, HCFC-124 and HFC-125 or a mixture of HCFC-124 and HFC-125.
• the present invention provides a separation process for difficult-to-separate fluorocarbon composition containing hydrogen fluoride which process does not require addition of any extraneous components, does not alter any of the components of the fluorocarbon composition and which does not create any additional waste disposal problems.
• the difficult-to-separate fluorocarbon composition is initially treated with a selected non-porous, semi-permeable polymer membrane which provides two components, each of which is enriched in one or the other of the components in the original composition (i.e., either the organic phase or hydrogen fluoride phase) .
• Subsequent treatment such as distillation of the two compositions, can then provide the components of the original composition in essentially purified forms.
• HCFC-22 chlorodifluoromethane
• HCFC-22 is usually manufactured by the process of fluorinating chloroform with excess HF in the presence of certain metallic compounds as catalysts, e.g., antimony halide.
• a mixture of HCFC-22 and HF is obtained which cannot be separated readily by distillation into pure components since HCFC-22 and HF form an azeotropic mixture containing about 97 wt.% HCFC-22 and 3 wt.% HF.
• such an azeotrope mixture is usually treated with an aqueous alkali solution to remove HF from the mixture; the HCFC-22 layer is then washed, dried and distilled to provide purified HCFC-22.
• Such a process results in the loss of HF for recycling back to the manufacturing process and additionally creates a problem of fluoride disposal.
• the above azeotropic mixture of HCFC-22 and HF is typically continuously introduced into a membrane separation unit 10. via inlet 12. as the fluorocarbon/HF feed stream.
• the feed stream make contacted with selected non-porous, semi-permeable polymer membrane 14_.
• the separation unit JLTJ produces a permeate stream exiting via line 16_ wherein the concentration of HF is enriched typically about ten-fold or more relative to its composition in the azeotrope feed concentration.
• a non-permeate residual stream is continuously withdrawn via line 18. wherein the HF concentration is proportionally depleted relative to the original feed composition respective flow rates.
• HCFC-22/HF azeotrope illustration a typical feed stream to the membrane unit JLO. would be at approximately 25°C and about 200 psig and would contain about 3 wt.% HF.
• the residual stream exiting outlet .18 would have a HF concentration reduced to around 0.3 wt.% representing substantial one-pass recovery.
• purified fluorocarbon and purified HF can be recovered by subsequent distillation steps.
• the permeate composition exiting the membrane unit JLQ via line 16 can be distilled in column 2J).
• the small amount of fluorocarbon/HF azeotrope being distilled overhead is then recycled via line .24. to the feed side of the permeation unit 10 and essentially purified HF can is recovered as distillation bottom via line 26_.
• the HF from the distillation column 20 can be recycled to the HCFC-22 manufacturing process.
• the non-permeate residual composition exiting the membrane unit 10 via line 18. is distilled in column 22.- The small amount of fluorocarbon/HF azeotrope being distilled over head is recycled via line 18. to the feed side of the permeation unit 10. and purified fluorocarbon (HCFC-22) is recovered via line 3_0 from the distillation bottom.
• HCFC-22 purified fluorocarbon
• both HF and HCFC-22 can be subjected to further purification if desirable.
• one of the columns can be eliminated and a single column in combination with the membrane unit can be employed and should be considered an equivalent process for purposes of this invention.
• the non-porous, semi-permeable polymer film useful in the present invention for the permeation step of the process may be any hydrogen fluoride-resistant polymeric material which can be formed into a thin non-porous film and exhibits the desired selective permeability as defined latter.
• the polymers are fluorinated polymers and include, among others, fluorinated ethylene-propylene copolymers, poly(ethylene-chloro- trifluoroethylene) , poly(chlorotrifluoroethylene) , poly(tetrafluoroethylene) , copolymers of ethylene and tetrafluoroethylene, poly(vinylidene fluoride) , poly(perfluorovinyl ethers) and the like.
• fluorinated polymers containing groups such as carboxyl or sulfonyl such as described in U.S.
• perfluorinated membranes useful in the present invention are the fluorinated polymers containing sulfonic acid groups sold under the name "NAFION" by Du Pont and derived from ⁇ opolymerizing tetrafluorethylene and a perfluorovinylether which contains a sulfonic acid group or derivative thereof.
• NAFION fluorinated polymers containing sulfonic acid groups sold under the name "NAFION" by Du Pont and derived from ⁇ opolymerizing tetrafluorethylene and a perfluorovinylether which contains a sulfonic acid group or derivative thereof.
• the preferred membranes are characterized structurally as copolymers containing the following recurring units:
• the salt or partial salt forms (e.g., -SO Na and -SO K) of the above polymer are found to be equally effective in achieving the desired selective permeability.
• the semipermeable membrane unit (the permeator) useful in the present invention can be generally any such device as well known in the art, including by way of example, but not limited thereto, semipermeable membrane thin layer of film (i.e., the so-called plate and frame unit), spiral wound membrane, hollow fiber semipermeable membrane or the like (including combinations of such devices) .
• semipermeable membrane thin layer of film i.e., the so-called plate and frame unit
• spiral wound membrane i.e., the so-called plate and frame unit
• hollow fiber semipermeable membrane or the like including combinations of such devices
• the necessary preferential permeation rate for the hydrogen fluoride through the barrier membrane relative to the permeation rate for fluorocarbon phase can be satisfied and/or confirmed by considering the increase in HF concentration in the permeate relative to the concentration of HF in the feed stream.
• This parameter for purposes of this invention hereinafter referred to as selectivity, can vary from as little as a three but is more typically 10 or greater and is frequently higher than 20. Preferably this selectivity should be 10 or greater.
• turbulent flow of a HF/HCFC-22 mixture in a thin layer across the permeation membrane a separation is achieved which gave as much as twenty-fold increase in the HF concentration in the permeate.
• the turbulent flow for purposes of this invention is characterized by a Reynolds Number of at least 2,000. Such a concentration increase by permeation provides a good potential for the separation of HF from HCFC-22.
• a mixture of HF and HCFC-22 was prepared in a cylinder and appropriate valves were installed to monitor the flow of HCFC-22/HF out of the cylinder.
• the feed from the cylinder entered the permeation device through a 1/16" stainless steel tubing located directly opposite the feed outlet so that the HCFC-22/HF mixture from the feed tube would move across the membrane surface and then exit the device via the second stainless steel tubing.
• the gas exiting the permeation device was contacted with a column containing ultra-pure potassium carbonate to trap HF and HCFC-22 was collected in a polyethylene or a stainless steel cylinder. After the separation run was finished, the column containing potassium carbonate was disconnected, and the potassium carbonate was dissolved in a known volume of deionized water.
• the fluoride ion content was determined and expressed as HF.
• HCFC-22 was determined by gas chromatography. Suitable valves were provided in the exit stream to control pressure, feed flow, etc.
• the permeate stream coming through the membrane was passed into a column containing ultra-pure potassium carbonate to trap HF and then HCFC-22 was collected in an evacuated stainless steel cylinder.
• the analysis of the potassium carbonate for fluoride and of HCFC-22 in the collection cylinder provided a composition of the permeate.
• Material balance was made by comparing the total weight of the HF in the permeate and the non-permeate and the total weight of HCFC-22 in the permeate and the non-permeate with the total amount of HF and HCFC-22 taken from the original feed cylinder.
• the permeate can be distilled to remove HCFC-22 as HCFC-22/HF azeotrope, leaving behind essentially pure HF, and similarly the non-permeate fraction can also be distilled to remove the HF as HCFC-22/HF azeotrope, leaving behind the essentially pure HCFC-22.
• the permeate will be 378 g/hr. of which 228 g (60.3 wt.%) was HF. This permeate stream will then be distilled to provide 154 g/hr. of distillate of the azeotropic composition (2.8 wt.% HF and 97.2 wt.% HCFC-22) and a distillation residue of substantially pure HF at a rate of 224 g/hr.
• the non-permeate from the permeation separation will be 20,736 g/hr. of which 363 g (1.75 wt.%) will be HF and 20,373 g (98.25 wt.%) will be HCFC-22.
• Distillation of this non-permeate stream provides 12,960 g/hr. of an azeotropic mixture of which 363 g is HF and 12,597 g is HCFC-22.
• the distillation residue is substantially pure HCFC-22 at a rate of 7776 g per hour.
• the azeotropic distillates from both the distillation of the permeate and the non-permeate is to be recycled to the feed side of the permeation separator.
• the present separation process is advantageously carried out as a continuous process and, as this Example illustrates, an azeotropic mixture of HF and HCFC-22 can be completely separated into its pure components with little or no contribution to fluoride waste disposal problems.
• the permeate was 121 g/hr. of which 101 g (83 wt.%) will be HF and 20 g (17 wt.%) will be organics. This permeate stream will then be distilled to provide 21 g/hr. of distillate of the azeotrope-like compositions (5 wt.% HF and 95 wt.% organics) and a distillation residue of substantially pure HF at a rate of 100 g/hr.
• the non-permeate from the permeation separator will be 2,714.3 g/hr. of which 40.7 g (1.5 wt.%) will be HF and 2,673.6 g (98.5 wt.%) will be organics. Distillation of this non-permeate stream will provide 814 g/hr. of an azeotrope-like mixture of which 40.7 g will be HF and 773.3 g will be organics.
• the distillation residue will be substantially pure organics at a rate of 1,900 g/hr. which can be further separated into individual organic components by simple conventional distillation.
• the azeotropic distillates from both the distillation of the permeate and the non-permeate are recycled to the feed side of the permeation separator.
• the present separation process is advantageously carried out as a continuous process and, as this Example illustrates, an azeotrope-like mixture of (HFC-125 & HCFC-124)/HF can be separated into pure components with little or no contribution to the fluoride waste disposal problem.
• the above compositions of (HFC-134a & HCFC-124)/HF will be passed over the permeation membrane at a rate of 2,000 g/sq.ft./hr. or a total rate of 17,377 g/hr. at ambient temperature (about 20°C) , feed pressure about 65 psig and permeate pressure of about 22" Hg vac.
• feed rate 122 g HF and 17,257 g of organics will be introduced into the permeator per hour.
• the permeate will be 17.6 g/hr. of which 14 g (80 wt.%) will be HF and 3.6 g (20 wt.%) will be organics.
• the permeate stream will then be distilled to provide 3.6 g/hr. of distillate of the azeotrope-like compositions (0.7 wt.% HF and 99.3 wt.%) organics) and a distillation residue of substantially pure HF at a rate of 14 g/hr.
• the non-permeate from the permeation separator will be 17,359 g/hr. of which 108 g (0.62 wt.%) will be HF and 17,251 g (99.38 wt.%) will be organics. Distillation of this non-permeate stream will provide 15,375 g/hr. of an azeotrope-like mixture of which 108 g will be HF and 15,267 g will be organics. The distillation residue will be substantially pure organics at a rate of 1,984 g/hr., which can be further separated into individual organic components by simple conventional distillation.
• the present separation process is advantageously carried out as a continuous process and, as this Example illustrates, an azeotrope-like mixture of (HFC-134a & HCFC-124)/HF can be separated into pure components with little or no contribution to the fluoride waste disposal problem.

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• Chemical & Material Sciences (AREA)
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• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Separation Using Semi-Permeable Membranes (AREA)

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• 1991
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