WO1993010875A1

WO1993010875A1 - Recovery of substantially pure anhydrous hydrogen fluoride (hf) from mixtures comprising acyl fluorides or water

Info

Publication number: WO1993010875A1
Application number: PCT/US1992/009059
Authority: WO
Inventors: Timothy R. Ryan; Thomas A. Curtis
Original assignee: Hoechst Celanese Corporation
Priority date: 1991-11-27
Filing date: 1992-11-16
Publication date: 1993-06-10
Also published as: MX9206832A

Abstract

The present invention pertains to a method for separating essentially anhydrous hydrogen fluoride from a mixture comprising HF and water by contacting the mixture with an acyl fluoride to convert the water to the corresponding carboxylic acid and then separating HF from the carboxylic acid. Further, the invention pertains to a method for separating HF from a mixture comprising HF and an acyl fluoride. This latter separation method can be practiced if an azeotrope can be formed between HF and the acyl fluoride, and the azeotrope boils at a temperature at least 5 °C higher than the individual boiling points of both the HF and the acyl fluoride. This latter separation method is particularly useful when the acyl fluoride has a boiling point lower than that of HF or within about 10 °C higher than HF so that other methods of separating HF from the acyl fluoride are difficult.

Description

RECOVERY OF SUBSTANTIALLY PURE ANHYDROUS

HYDROGEN FLUORIDE (HF) FROM MIXTURES COMPRISING

ACYL FLUORIDES OR WATER

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to separating HF from a mixture which includes water and HF. This invention also relates to a method of separating hydrogen fluoride

(HF) from an acyl fluoride having a boiling point close to that of HF or below that of HF.

This invention more particularly relates to an improved process for recovery of HF from product mixtures including HF and water or HF and acyl fluoride, as well as various organic compounds. Most particularly, the present invention relates to processes for recovering HF from product mixtures resulting from the Friedel-Crafts acylation of an aromatic compound with an acylating agent which may be an acyl fluoride, a carboxylic acid anhydride, a free carboxylic acid, or a combination of the acylating agents, wherein HF is employed as a catalyst. Such mixtures are produced in an improved process for the production of 4-isobutylacetophenone (4- IBAP).

2. Description of the Related Art

In U.S. Patent 4,990,681, we disclosed a method of separating HF from a mixture including HF complexed with an aromatic ketone in which the keto carbon atom is directly bonded to an aromatic ring carbon atom, as with 4-IBAP. The 4-IBAP is an intermediate in the process for the production of ibuprofen, a widely used, nonsteroidal anti-inflammatory drug. According to this method, which is conveniently carried out in a stripping column, a product mixture comprising such aromatic ketone complexed with HF, a carboxylic acid complexed with HF (if anhydride was used as all or part of an acylating agent), and uncomplexed HF, is fed to a point near the top of the stripping column. Below the feed point of that product mixture, a carboxylic acid anhydride is fed to the stripping column at one or more points. The uncomplexed hydrogen fluoride is substantially stripped between the feed points of the product mixture and the anhydride. The anhydride is reacted with residual HF below the feed point of the anhydride to form an acyl fluoride and a carboxylic acid. The acyl fluoride is stripped from the mixture. The HF and acyl fluoride are withdrawn from the top of the column and recycled to the reactor for further participation in the Friedel-Crafts acylation. The aromatic ketone product is withdrawn from the bottom of the column.

U.S. Patent 4,990,681 further describes prior art relating to Friedel-Crafts acylations and to a solvent assisted distillation process. This '681 patent is incorporated by reference herein for all purposes as if set forth verbatim.

In the Friedel-Crafts' reactions described in the ' 681 patent, the product mixture may include water. Even if the product mixture does not include water, the HF removal column creates both water and acyl fluoride in some zones of the column by dehydration of the carboxylic acid. For example, where the carboxylic acid is acetic acid, the reaction is:

HF + HoAc + H₂O + AcF In the process we described in the ' 681 patent, this formation of water may be suppressed by the addition of excess acetic anhydride. The excess acetyl fluoride produced in that system is inconsequential, because acetyl fluoride is a reactant that is returned with HF to the reactor. Even the exact stoichiometric addition of acetic anhydride to an HF/H₂O stream, to convert it to an HF/acetic acid stream, results in the net production of acetyl fluoride, due to the dehydration reaction described above.

However, for reactions requiring HF, but not requiring an acyl fluoride, an HF removal column of the type described in the '681 patent results in an acyl fluoride buildup in the HF recycle stream or the formation of undesired acylation products.

U.S. Patent 4,038,310 issued July 26, 1977 to Bjornson et al., describes a method of producing a perfluorocarboxylic acid and an acyl fluoride via an electrochemical process. A small amount of an alkanoic acid anhydride is added to react with impurities such as HF, water, and carbonyl fluoride which would otherwise remain with the product and complicate its recovery.

Accordingly, it is an object of this invention to provide a method by which HF can be separated from an acyl fluoride which boils at a temperature which makes separation from HF difficult. This includes acyl fluorides which boil at temperatures lower than the boiling temperature of HF or at temperatures slightly higher than HF, for example, within about 10°C higher than the boiling temperature of HF. Many condensation reactions catalyzed by hydrogen fluoride produce water in moderate amounts, and, as mentioned, water can be created in a hydrogen fluoride removal column by dehydration of a carboxylic acid such as acetic acid. It is very difficult to separate HF from water by distillation because water forms a high boiling, corrosive azeotrope (38% HF in water) which presents severe disposal problems.

Accordingly, it is an object of this invention to provide a method by which hydrogen fluoride can be separated from water.

It is an additional object of this invention to provide a method for separating HF from a mixture comprising HF and an organic compound, such as alkanes, alkenes, aromatic compounds and the like, and in particular from aromatic compounds such as an aromatic ketone in which the keto carbon atom is directly bonded to an aromatic ring, for example, 4-IBAP, and in this method, recover substantially pure anhydrous HF. It is further an object of this invention to provide a unitary method for the production of aromatic ketone in which the keto carbon atom is directly bonded to an aromatic atom, such as, for example, 4-IBAP, in which substantially pure anhydrous HF is separated from a product mix and recycled to a Friedel-Crafts reactor for reuse.

SUMMARY OF THE INVENTION

In accordance with this invention, essentially anhydrous hydrogen fluoride (HF) is separated from a mixture comprising HF and water, by contacting the mixture with an acyl fluoride to convert the water to the corresponding carboxylic acid, and then separating HF from the carboxylic acid.

Further in accordance with this invention, HF is separated from a mixture comprising HF and acyl fluoride. Applicants have discovered it is possible to separate HF from acyl fluorides previously thought to be inseparable from HF if an azeotrope can be formed between the HF and the acyl fluoride, and the azeotrope boils at a temperature at least 5°C higher than the boiling point of both the HF and the acyl fluoride. The method of the present invention is particularly useful when the acyl fluoride boils at a temperature below that of HF or within about 10°C higher than HF, because separation of HF from such an acyl fluoride is particularly difficult. Not all acyl fluorides will form an azeotrope of the kind required with HF, but knowing that it is possible to form such an azeotrope, one skilled in the art can determine with minimal experimentation whether the present invention can be practiced.

The separation is accomplished by heating a mixture comprising HF and the acyl fluoride, under conditions that produce a vapor enriched in HF over that of remaining liquid mixture. Such remaining liquid mixture includes the above-described azeotrope. The HF-enriched vapor is separated from the liquid mixture and then condensed. This vaporization/condensation cycle is repeated until vapor produced is substantially pure HF. Separation is typically accomplished in an apparatus such as a stripping column, where HF/acyl fluoride mixtures are maintained in lower sections of the column, with pure HF withdrawn overhead. In further accordance with this invention, in a continuous separation of HF from a mixture using a separation apparatus such as a stripping column, HF is separated from a feed mixture coprising at least HF, an organic compound and, optionally, water, using a process of the kind described above. Carboxylic acid anhydride is added to the feed mixture being fed to the stripping column, while maintaining distillation conditions sufficient to sustain a reaction between the anhydride and HF in the feed mixture to form the corresponding acyl fluoride and carboxylic acid; an azeotrope of HF and the acyl fluoride is formed; and subsequent separation and removal of HF is accomplished as described above. Any water is reacted with sufficient acyl fluoride or the mentioned anhydride, or both, to convert the water to the corresponding carboxylic acid, and if the acyl fluoride is reacted, to also form HF.

In one preferred embodiment of the present invention, the method provides for recovering essentially anhydrous HF from a feed mixture comprising HF, an organic compound and water. The method, which is carried out in a continuous manner, comprises:

(a) providing a feed mixture comprising HF, an organic compound and water; (b) contacting an anhydride of a carboxylic acid with HF and water in the feed mixture under conditions effective to form the acyl fluoride and the corresponding carboxylic acid of the anhydride; (c) contacting the acyl fluoride with water in the feed mixture under conditions effective to form the corresponding carboxylic acid and HF;

(d) vaporizing HF and acyl fluoride present after step (c) to form a vapor enriched in HF and a liquid enriched in acyl fluoride, said liquid comprising an azeotrope of HF and acyl fluoride,

(e) separating the liquid from the HF enriched vapor; and said liquid comprising an azeotrope of HF and acyl fluoride,

(f) repeating the vaporization step (d) and separation step (e) until esentially anhydrous HF vapor is obtained . Steps (d) and (e) can be repeated until substantially pure (95-100% HF), essentially anhydrous HF vapor is obtained.

An additional step (g) is typically carried out, wherein the anhydrous HF obtained is continually removed. In a particular, preferred embodiment of this method, the invention is used in the production of an aromatic ketone in which the keto carbon atom is directly bonded to an aromatic ring atom. This method comprises:

(a) subjecting an aromatic compound to a Friedel- Crafts acylation with an acylating agent in a reactor in the presence of HF which is used as a catalyst and a solvent for the aromatic ketones so produced;

(b) feeding an HF-rich stream originating from such step (a) reactor, and containing at least HF and the aromatic ketone, to a middle distillation zone of a distillation apparatus, at one or more points, as an HF-rich mixture;

(c) feeding a carboxylic acid anhydride at one or more points to a zone in the distillation apparatus which permits contact of the anhydride with HF and any water present in the feed stream of step (b);

(d) controlling the feeding steps (b) and (c), while operating the distillation apparatus in a manner such that i) the anhydride reacts with HF present in the HF-rich feed stream to form the corresponding acyl fluoride and carboxylic acid, ii ) the acyl fluoride, the carboxylic acid anhydride, or both react with water present in the distillation apparatus to form HF, the corresponding carboxylic acid or both; iii) an azeotrope, or stable maximum boiling mixture, is formed between HF and the acyl fluoride from which HF is to be separated, which azeotrope boils at a temperature higher than both HF and the acyl fluoride; iv) HF and the acyl fluoride which enter the distillation apparatus as a feed or which are produced within the apparatus form an azeotropic mixture such that HF in excess of the azeotropic composition, having a lower boiling point, is more easily vapori zed and migrates preferentially to the top of the distillation apparatus; v) substantially pure, essentially anhydrous HF is separated and collected within the distillation apparatus; and vi ) aromatic ketone and carboxylic acid, being higher boiling than other components in the mixture, migrate preferentially to the bottom of the distillation apparatus, from which they can be withdrawn. An additional step is typically carried out wherein the aromatic ketone is separated from the carboxylic acid. This can be done within the distillation apparatus used for the anhydrous HF and acyl fluoride separation if desired. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of an integrated process illustrating a preferred embodiment of the invention. Figure 2 shows is a plot of the mole fraction of acetyl fluoride in the vapor phase (Y axis) against the mole fraction in liquid phase (X axis) of an HF-acetyl fluoride mixture, as described in Example 1.

Figure 3 is a composition profile of AcF/HF solutions under the conditions of refluxing as set forth in Example 2.

Figure 4 is a plot of the mole fraction of acetyl fluoride in HF in vapor phase (Y axis) against the mole fraction of it in liquid phase (X axis), as described in Example 3.

Figure 5 is the composition profile of HF/AcF mixtures contained in a distillation column under the procedures described in Example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention provides a method for separating hydrogen fluoride (HF) from a mixture comprising HF and an acyl fluoride. A requirement of the method is that an azeotrope (stable complex having a maximum boiling point) be formed between HF and the acyl fluoride from which the HF is to be separated. The azeotrope formed must boil at a temperature at least 5°C higher (greater) than the boiling point of HF and the acyl fluoride. Preferably the azeotrope boils at a temperature about 20°C higher than the HF and the acyl fluoride from which the HF is to be separated, for economy in use of the method. In a collateral aspect of this invention, an azeotrope of HF and water is prevented from forming in an HF distillation by contacting any water present with an acyl fluoride and/or a carboxylic acid anhydride; to convert the water to the corresponding carboxylic acid and to form HF. HF is separated from the carboxylic acid as part of the method for separating HF from an acyl fluoride and other organic compounds.

In a preferred embodiment of the present invention, the method is used to prevent the formation of an HF - H₂O azeotrope in a reaction system which utilizes HF as a catalyst and as a solvent. The acyl fluoride used is acetyl fluoride, and the carboxylic acid formed is acetic acid. The equation showing the reaction which provides for removal of water from the overall reaction system is as follows: R' COF + H₂O -→ R' COOH + HF (1)

The HF produced, along with that already present, must subsequently be separated from acetyl fluoride present in the reaction system.

Typically the separation method is applied to an overall reaction system comprising a feed stream containing at least HF and various additional organic compounds. As a part of operating the overall system, acetic anhydride would be added to the feed stream, while maintaining distillation conditions sufficient to sustain a reaction between the anhydride and HF in the feed to form AcF and acetic acid (HOAc). These conditions are also sufficient to sustain the formation of an azeotropic mixture of HF and AcF in which the composition does not change on vaporization. HF and AcF are generated, contacted with the mixture of HF and AcF, and HF is removed as a vapor overhead. The HOAc acts as a solvent for various organic compound(s), from which it may subsequently be separated by distillation.

In these methods, the vapor generated and removed overhead is HF, and the AcF comprises about 40-55 wt% of the azeotropic mixture of HF and AcF. There are other mixtures of HF and AcF present in the vicinity of the azeotropic mixture in the distillation apparatus, which mixtures contain AcF at higher or lower concentrations than the AcF concentration in the azeotropic mixture. However, these mixtures of HF and AcF represent transition states which can vary depending on distillation apparatus operating conditions. For the method to operate efficiently, the system is operated in a manner to provide the minimal formation of the azeotropic mixture necessary to provide for removal of any water present in the system and to permit the desired HF separation from other components within the overall reaction system. The pressures may range from about 50 mm Mercury to about 100 psig, and temperatures at such pressures will fall within a range from about -40°C to about 100°C. Distillation of HF and AcF may be carried out in any distillation vessel suitable for the purpose. Thus, the vessel may or may not contain interior surfaces serving to implement condensation and revaporization of the constituents of the reacting composition, e.g., packing, trays, and the like. However, for continuous or semi-continuous operation, the use of a fractionating column, e.g., a packed column or a column containing trays is especially suitable.

The invention may be more particularly described in reference to Figure 1, which illustrates a distillation apparatus 10. A mixture of HF, organic compounds, and water is fed through line 11 to the middle zone of distillation apparatus 10. A reboiler 12 of apparatus 10 vaporizes acetic acid, which is fed into a lower zone (in terms of column height) of the apparatus, to provide the heat necessary to enable a majority of HF in the feed stream to be vaporized and removed from the overhead of apparatus 10. Acetic anhydride (Ac₂O) is fed into apparatus 10 through line 14 at or below the feed points 11 for the HF, organics and (optionally) water feed, and above the acetic acid vapor feed 13. The acetic anhydride reacts with the remaining HF in base and/or lower part of the column to produce low boiling AcF and removes HF from the base of apparatus 10. The apparatus conditions are sustained effective to permit the AcF produced in apparatus 10 to form a stable, maximum boiling azeotrope (or mixture of HF and AcF having an unchanging composition on vaporization) in an upper zone of the column of apparatus 10. Presence of this azeotrope of HF and AcF permits excess HF to be withdrawn from the top of the apparatus through line 15, while the HF-AcF high-boiling mixture comprising the azeotrope remains in the apparatus. The high boiling HF- AcF mixture is optionally withdrawn through line 16 as a sidestream from the upper zone of the apparatus, and advantageously is circulated to one or both of the middle zones of the column of apparatus 10 or to a reactor for use in a Friedel-Crafts acylation in the presence of HF as a catalyst and solvent. If recycled to react with water in the feed stream, or with water in the apparatus, the reaction is according to equation (1) set forth above.

Organic compounds, including desired products, are carried down the apparatus column in acetic acid solution and withdrawn from the base of the apparatus through, line

17, where the desired products may be separated by subsequent distillation.

In the integration in this method of separation of hydrogen fluoride and acetyl fluoride, with prevention of formation of the water-hydrogen fluoride azeotrope, the feed which enters apparatus 10 through line 11 is obtained by subjecting an aromatic compound to a Friedel- Crafts alkylating or acylating agent in a reactor in the presence of liquid HF as a catalyst and solvent for an aromatic compounds produced by such alkylation or acylation. Thus, in a preferred application of our invention, substantially pure, anhydrous HF is recoverable from an HF-rich product mix which, includes aromatic ketones derived from acylations.

The aromatic ketones contemplated to be purified by the process of this invention have the formula:

R

YnAr-C=O where Ar is the residue of benzene, naphthalene or biphenyl, whose hydrogen atoms are substituted with the keto carbon atom and Y's indicated in the formula, n is an integer in the range of 0-5 for benzene, 0-7 for naphthalene and 0-9 for biphenyl, the Y's are the same or different and are each, for example, but not by way of limitation, sulfhydryl, halide, alkyl, hydroxy, alkoxy, acyloxy, or alkylthio, the latter four substituents containing from 1 to 18 carbon atoms, and R is an alkyl group containing 1 to 18 carbon atoms, phenyl or naphthyl. Preferably, R is methyl, ethyl, propyl, or phenyl and most preferably methyl, such that the aromatic ketone being purified is an aromatic methyl ketone. A group of aromatic ketones particularly suited to being purified by the process of this invention are alkyl, alkoxy or hydroxy aromatic ketones such that, in the foregoing formula, Y is alkyl or alkoxy containing 1 to 4 carbon atoms, or hydroxy, n is 1, R is methyl, and Ar is 1, 4-phenylene; 2, 6-naphthylene; 2, 1-naphthylene; 5-phenyl-1, 2-phenylene; 3-phenyl-1, 4-phenylene; or 3- methyl-1, 4-phenylene; with the ketocarbon occupying the first stated numbered position of Ar when the positions are not equivalent. Most preferably Ar is 1, 4-phenylene or 2, 6-naphthalene, and the aromatic ketone being purified is 4-isobutylacetophenone (4-IBAP), 4- hydroxyacetophenone (4-HAP), 6-hydroxy-2-acetonaphthone (6, 2-HAN), 6-methoxy-2-acetonaphthone, or 4- methylacetophenone (4-MAP).

Another group of aromatic ketones suitable for purification by the process of this invention are the benzophenones, wherein Ar in the foregoing formula is a benzene residue and R is phenyl, e.g., benzophenone and

2, 3, 4-trihydroxybenzophenone.

The compositions containing an aromatic ketone and

HF which are treated to separate and recover substantially pure anhydrous HF from these components utilizing the process of this invention are obtained, for example, as effluents from the production of aromatic ketones, e.g., 4-IBAP, by the Friedel-Crafts acylation of an aromatic compound, e.g., isobutylbenzene, using HF as solvent/catalyst.

Such Friedel-Crafts reaction is shown in the following equation: HF

(CH₃)CHCH₂ + CH₃COX

(CH₃) CHCH₂ COCH₃ + HX

where "X" is the residue minus the acetyl group of an effective acetylating agent. Acetylating agents which may be used are, for example, acetyl fluoride (X = F), acetic anhydride (X = - - - OCOCH₃) and acetic acid (X = - - - OH). Mixtures of acetylating agents may also be used and form in situ if certain acetylating agents such as acetic anhydride, are used. The acetic anhydride reacts with isobutylbenzene (IBB) to form 4-IBAP and acetic acid which is also an acetylating agent. Moreover, acetic anhydride also reacts with HF to form acetyl fluoride, another acetylating agent and acetic acid. Acetyl fluoride if present will also react with water of reaction to form HF and acetic acid. A large excess of HF is used as solvent/-extractant/catalyst, e.g., about 7 to 80 moles per mole of IBB/4-IBAP. It is preferable that HF is the only inorganic fluoride present in significant quantity, i.e., there is no other inorganic fluoride present, e.g., BF₃, in such quantity as would materially change the basic and novel characteristics of the process. Expressed another way, the inorganic fluoride present in any of the compositions involved in the method of the invention preferably "consists essentially" of hydrogen fluoride.

The acetylation reaction may be carried out at a temperature, for example, of about 40°C to about 100°C, at a pressure which prevents boiling, for example, a pressure of about 35 to 150 psig over a residence time of, for example, about 0.3 to about 4 hours.

The product of the reactor may pass through a finishing zone of the reactor or may be sent to a separate finishing reactor to maximize the conversation of IBB to 4-IBAP. Such finishing zone may be operated at a temperature (typically about 45°C to about 80°C) and at a pressure similar to those of the reactor and, for a residence time, for example of about 0.1 to 4 hours, preferably about 0.5 to 2 hours.

The product stream withdrawn from the reactor system contains free, i.e., substantially uncomplexed HF, and HF which is complexed with 4-IBAP and, if acetyl fluoride, acetic anhydride or acetic acid is used as all or part of the acetylating agent, also contains HF, water and/or acetic acid, respectively, which is formed as a byproduct of the acetylation reaction. Some of the acetic acid present also tends to form a complex with HF. Additionally, the product stream may also contain unreacted isobutylbenzene (IBB), acetyl fluoride (AcF), acetic acid (HOAc) and acetic anhydride (Ac₂O), depending on the extent of the reaction or initial stoichiometric ratios employed.

As in our invention in the '681 patent, in one preferred embodiment of the present invention, an HF-rich product mix such as that just described, comprising HF, organics and water is reacted with a carboxylic acid anhydride. The reaction is indicated by the following equation:

(R' CO)₂O + HF -→ R' COF + R' COOH (2)

In the formulas of this equation, R' is any suitable organic radical, e.g., alkyl or aryl such as phenyl but is preferably an alkyl group of 1 to 3 carbon atoms so that the anhydride is, for example, acetic anhydride, propionic anhydride or isobutyric anhydride, resulting in the formation of the corresponding fluorides and free carboxylic acids. The R' CO- group is an acyl group.

The mixture comprising HF, organics (e.g., aromatic ketones) and water is preferably heated, before coming in contact with anhydride, at a temperature below that at which the aromatic ketone tends to decompose in the presence of HF, e.g., a temperature of about 30°C to about 155°C, at a pressure of about 0 to about 25 psig, so as to separate most of the excess HF, i.e., that which is above the amount necessary to complex with the aromatic ketone and carboxylic acid present. After the initial HF separation, the mixture is contacted with a carboxylic acid anhydride which reacts with residual HF to produce the corresponding acyl fluoride and free carboxylic acid. The acyl fluoride can be easily stripped from the ketone because of its much lower boiling point, while the free carboxylic acid usually can be readily separated from the ketone in a subsequent distillation operation. The foregoing process can be carried out as consecutive batch operations. Preferably, however, it is carried out continuously or semi-continuously in a distillation apparatus or stripping column, wherein the mixture comprising HF, organics (e.g., aromatic ketones) and typically water, is added to the middle of the column and anhydride is added at one or more points lower on the column of the distillation apparatus. Heat is added to the distillation apparatus to maintain temperatures such that the excess, uncomplexed HF is stripped from the mixture in that part of the column above the point at which the anhydride is added, so that uncomplexed HF doesn't contact the anhydride. The reaction between anhydride and HF below the point at which the anhydride is added proceeds at a satisfactory rate, and the resulting acyl fluoride is also substantially completely separated from the aromatic ketone.

EXAMPLE 1

Vapor Liquid Equilibrium

The existence of an azeotrope of HF and AcF and an estimate of its composition was determined using a 300 cc stirred autoclave with both vapor and liquid sampling ports. One of the AcF/HF components was charged to the autoclave and the second component was added by pressure- addition from a 150 cc sample bomb. The data was collected at constant temperature, about 61-63°C (33-45 psig). Samples of the vapor and liquid in the autoclave were collected and analyzed as the composition of the liquid phase was changed. The procedure used was:

1. 100 g AcF was charged to a pressure vessel or

"bomb". A source of pressurized nitrogen was then connected to the bomb so that nitrogen could be used to pressure AcF from the bomb into an autoclave. The bomb was placed on balance to allow approximate determination of the amount of AcF added.

2. 50 g HF was then charged to an autoclave. The autoclave was heated to 60°C., producing an internal pressure of about 45 psig. The contents of the autoclave were stirred slowly except when AcF additions were being made.

3. 5-10 g of AcF were added to the HF in the autoclave while holding the temperature in the autoclave at 60°C. After addition of the AcF, the contents of the autoclave were allowed to equilibrate with stirring for about 10 min. The vapor sample line was purged with small amount of sample to clear the line, and the contents of the autoclave were allowed to equilibrate for 5 more minutes.

4. A 2 g sample was taken for analysis from both the liquid and vapor phases in the autoclave; temperature and pressure in the autoclave were noted. Samples were taken into ice, neutralized with KOH solution, and analyzed by ion chromatography for OAc ^-- and F ^--.

5. Repeat additions of AcF were made until the AcF in the bomb was used up. After each addition sampling was repeated in the manner described in 3, above.

The results from Example 1 are given in Table I and plotted in Figure 2. Figure 2 is a plot of the mole fraction of AcF in the vapor (Y) against the mole fraction in the liquid (X) and shows a high boiling azeotrope at approximately 21 mol% AcF (45 wt % AcF).

(a) F=fluoride, OAc = acetate, AcF = acetyl fluoride

(b) Normalized wt% AcF = wt% AcF x [100\ (wt% HF = wt% AcF), where mole AcF is calculated from normalized wt% AcF.

(a) F=fluoride, OAc = acetate, AcF = acetyl fluoride

(b) Normalized wt% AcF = wt% AcF x [100\(wt% HF = wt% AcF), where wt% HF = [wt% F - (19/62) x (wt% AcF] x 20/19.

(c) nAcF/nTot = mole fraction AcF + mole AcF/ (mole HF-=mole AcF), where mole AcF is calculated from normalized wt% AcF. EXAMPLE 2

Separation of HF from HF/AcF at Total Reflux Distillations

Several HF/AcF mixtures were distilled at total reflux using a 2 inch diameter distillation column having 16 Oldershaw-type trays over a hat tray above a reboiler. The column pressure was set at 40 psig which gave column temperatures ranging from about 60°C to about 70°C. The reflux rate was 27-29 g/min, chosen to avoid both weeping and flooding.

As the refluxing column came to equilibrium, liquid samples were taken along the column from the base to the overhead to monitor the separation of HF from the HF/AcF mixture. The HF acted as a light in this system and was readily separated from the AcF/HF solutions in the base. Column temperature and composition profiles are shown in Table II and Figure 3.

Tray efficiencies were assumed to be about 50%. Nine theoretical stages (16 X 50% + 1 for reboiler) were needed to separate pure HF from 47 wt% AcF. Thedetectable limit for AcF in HF ranged from 0.2 wt% to 0.5 wt%. As the composition in the base approached 47%, the composition profile in the lower part of the column became flat (Figure 3), which indicated that the azeotropic composition was near 47 wt% AcF. The azeotrope composition could only be estimated at 45-50 wt% AcF due to analytical and sampling variability, but it was in general agreement with the vapor-liquid equilibrium (VLE) data obtained from the autoclave in Example 1. The actual separations achieved at total, reflux (Table II) required 4.5, 6, and 7.5 stages (50% tray eff. + 1 for reboiler) to achieve a composition mole fraction of AcF equal to 0.002 (0.6 wt% AcF).

Thus, Examples 1 and 2 show that HF and AcF form a high boiling azeotrope at approximately 45-50 wt% AcF, and separation of HF from 47% AcF solution occurs at total reflux in a 16 tray column at 40 psig, with no detectable AcF (0.5 wt%) found in HF at tray 13.

(a) F = fluoride (c) nAcF/nTot = mole fraction AcF = mole AcF/(molc HF + mole AcF),

OAc = acetate where mole AcF is calculated from normalized wt % AcF

AcF = acetyl fluoride

(d) dp = differential press across trays in column in inches of water.

(b) Normalized wt % AcF = wt % AcF x [ 100 / (wt % HF + wt % AcF)] L = liquid reflux returned to the top of the column.

Where wt % HF = [wt % F - (19/62) x (wt % AcF)] x 20/19, D = liquid distillate removed as condensed overhead product.

F = feed to column.

EXAMPLE 3

Low Pressure Vapor Liquid Equilibrium Using the same apparatus and procedures as described in Examples 1 and 2, the vapor liquid equilibrium (VLE) for HF/AcF was determined. Liquid and vapor compositions were determined at 35°C (P = 4-16 psig) as the composition of the liquid was changed. The results are given in Table III. A plot of the mole fraction AcF in the vapor phase (Y) vs. the mole fraction in the liquid phase (X) is shown in Figure 4. A high boiling azeotrope is indicated at X=0.22 (45-50 wt% AcF), comparable to the azeotrope found earlier at 65°C and 40 psig.

(a) F = fluoride, OAc = acetate, AcF = acetyl fluoride.

(b) Normalized wt% AcF = wt% AcF x [100/wt% HF + wt% AcF)].

(c) nAcF/nTot = mole fraction AcF = AcF/(mole HF + mole AcF), where mole AcF is calculated from normalized wt % AcF. EXAMPLE 4

Low Pressure Separation of HF from HF/AcF at Total Reflux Using the procedures of Example 2, distillation of HF from a 20 wt% and a 35 wt% AcF solution was performed. As the refluxing column came to equilibrium, liquid samples were taken from the base, overhead, and several trays. The results are set forth in Table IV.

Variable AcF content throughout the column was seen for the 20% data, indicating the column had not yet reached equilibrium. The composition profile with 35 wt% AcF in the base was more uniform, and showed only 0.4 wt% AcF at tray 4. Further analysis of the base by gas chromatography showed the acetyl component to be AcF had no appreciable HOAc present. Examples 3 and 4 show that VLE data for HF/AcF mixtures is essentially the same at 35°C and 65°C. HF and AcF form a high boiling azeotrope at 45-55 wt% AcF at both temperatures. The demonstrated separation of HF from AcF solutions shows a single distillation column may be used to separate HF from acetic acid and organic products while simultaneously producing acetyl fluoride to be used for converting water to acetic acid.

(a) F ' = fluoride. OAc = acetate , ACF = acetyl fluoride.

(b) Normalized wt % AcF - wt % AcF x [100 / (wt % HF + wt %

AcF)].

(c) nAcF/nTot = mole fraction AcF = AcF/ [mole HF + mole AcF). where mole AcF is calculated from normalized wt % AcF.

(d) L = reflux rate = liquid reflux returned to the top of the column.

dp = differential pressure across trays in column in inches of water. EXAMPLE 5

Continuous Separation of HF from HF/AcF Mixtures

Two continuous distillation runs were made at 40 psig.

Reflux ratio = 3.3. The first run was performed with 10.3% AcF as feed to the hat tray of the column used in Example 2. Using a feed rate of 15.1 g/min. and a reflux ratio (L/D) of 3.3, the AcF was concentrated in the base to 21.8% AcF while only HF was detected in the overhead. An AcF mass balance based on the measured flows predicted 19 wt% AcF concentration in the base, which was within the measurement errors. Table V and Figure 5 show the composition profile of the column. After 3 hours there was only a small change in the two sets of profiles taken 30 minutes apart, showing that the column was close to steady state operation. Separation of pure HF was easily achieved with no AcF detected at tray 7 (4.5 theoretical stages).

Reflux ratio = 1.7. A 6.8% AcF solution was fed to tray 4 of the column at 14.2 g/min. Using a reflux ratio of 1.7, the AcF was concentrated to about 30% in the base of the column, and again no AcF was detected in the overhead. Table V and Figure 6 show the composition profiles of the column. Using the data in Table V, the calculated number of stages needed for the separation was

9 at R= 1.7.

Thus, continuous distillation of 6-10% AcF solutions in a 16 tray column at reflux ratios of 2-3 resulted in pure HF overhead (less than 0.5% AcF) and 20-30% AcF in the base.

(a) F = fluoride, OAc = acetate, AcF = acetyl fluoride.

(b) Nomialized wt % AcF = wt % AcF x [ 100 / (wt % HF + wt % AcF)].

where wt % HF = [wt % F - (19/62) x (wt % AcF)| x 20/19.

(c) nAcF/nTot = mole fraction AcF = mole AcF/(mole HF + mole AcF),

where mole AcF is calculated from normalized wt % AcF.

(d) dp = differential pressure across trays in column in inches of water.

L = liquid reflux returned to the top of the column.

D = liquid distillate removed as condensed overhead product. O-i

EXAMPLE 6

Distillation of HF/HOAc/AcF with Sidestream Takeoff According to the VLE data from Examples 1 and 3, a stable zone of AcF/HF should be generated in a distillation column between the base composition of HOAc and the overhead composition of HF. In order to confirm this phenomenon and test its stability, a solution of Ac₂O in HF was fed to a distillation column configured as in Figure 1.

A solution of 10% Ac₂O in HF was distilled. The feed was located at tray 10 and a liquid side stream takeoff was at tray 13 of the 16 tray column. The reboiler of the column was loaded with HOAc and slowly warmed until the HOAc began to reflux up the column. When the vapors reached tray 7, anhydrous HF was added as reflux to the top of the column. The liquid side stream takeoff was then started at 2.2 g/min. from tray 13 and the feed of AcF/HOAc/HF was started at 7 g/min to Tray 10. A temperature profile of the column (Figure 7) showed that as the AcF-HF azeotrope was formed, the temperatures above the AcF feed point began to rise. Removal of AcF from the sidestream at tray 13 prevented AcF from rising up the column. Samples taken from the trays during steady state column operation were analyzed for fluoride and acetate, and confirmed that the base of the column contained only a few % fluoride while the overhead product was 99+% HF (Table VI). Analysis of tray 13 by gas chromatography confirmed that the acetate found in the top of the column was due to AcF and not HOAc .

Addition of more theoretical stages to the bottom of the column with injection of Ac₂O reduces fluoride to the 0-50 ppm level. More theoretical stages at the top of the column allows recovery of 100% HF overhead. These results show formation of a stable AcF-containing zone in the HF removal column, and they further show removal of AcF/HF mixtures via a sidestream can be accomplished, the AcF being available for reactions such as acylations or conversion of water to acetic acid.

EXAMPLE 7

Distillation of HF Containing Water

A solution of 2.8% H₂O in HF was fed at tray 13 of the

16 tray column used in the foregoing examples. The reboiler of the column was loaded with HOAc and slowly warmed until the HOAc began to reflux up the column. When the vapors reached tray 7, anhydrous HF was added as reflux to the top of the column. After about 30 minutes, the composition of the tower was predominantly HOAc in the base and HF at the top. Ac₂O was added to tray 7 in order to generate AcF in the column according to equation (2). The temperatures in the top of the column began to increase as the AcF-HF azeotrope was formed. When tray temperatures showed a significant amount of AcF in the column, HF containing 2.8% water was fed to tray 13. The rate of Ac₂O addition into the column was adjusted to be equimolar with water in the HF feed. After 90 minutes of stable operation a set of column profile samples was taken. A second set of column profile samples was taken before the unit was shut down. The results are shown in Table VII. The composition profiles were consistent with the temperature profiles. Very little fluoride was found in the base samples. Water analysis could not be done on the top trays, but the lower trays showed a small amount of water. No acetate was found in the overhead samples and temperatures at the top of the column were consistent with an anhydrous HF overhead product. Lack of AcF in the overhead implies reaction (1) was operative in the mid section of the tower.

The material balance shown in Table VII indicated a possible slight excess of Ac₂O being fed during the run (0.012 mole Ac₂O per 0.011 mole H₂O in the feed). Recovery of 1.4 g/min from the base matched well with the Ac₂O being fed. HF recovered as distillate was less than expected,

5.5 g/min vs. 6.5 expected. Unavoidable losses of HF out the vent of the column make up a part of this difference.

Thus, in this example, a single distillation column was used to remove 2.8% water from HF by converting the water to HOAc and distilling the HF overhead. HOAc, depleted in fluoride, was recovered from the base.

Claims

WHAT IS CLAIMED IS:

1. A method of separating hydrogen fluoride (HF) from an acyl fluoride which comprises heating HF and an acyl fluoride under conditions effective to permit separation of HF from said acyl fluoride and to form an azeotropic mixture of said HF and said acyl fluoride which azeotropic mixture boils at a temperature at least 5°C higher than the individual boiling temperatures of both HF and said acyl fluoride.

2. The method of Claim 1, wherein the boiling point of said acyl fluoride is at a lower temperature than the boiling point of HF or within about 10°C higher than the boiling point of HF, under the same conditions.

3. The method of Claim 1, wherein said azeotropic mixture of HF and said acyl fluoride comprises from about 40 to 55 weight percent of said acyl fluoride.

4. The method of Claim 3, wherein said acyl fluoride is acetyl fluoride.

5. The method of Claim 1, wherein said conditions include a pressure from about 50 mm Hg to about 100 psig, and said conditions include a temperature within the range from about -40°C to about 100°C.

6. The method of Claim 1 wherein said separation comprises a distillation conducted in distillation apparatus having a single column.

7. A method of preventing formation of a hydrogen fluoride (HF) and water azeotrope in a separation system wherein HF is separated from other components of a mixture, said method comprising the steps of:

(a) contacting water present in said separation system with an acyl fluoride, a carboxylic acid anhydride, or both, to react with any water to form the corresponding carboxylic acid of said anhydride, and if acyl fluoride is reacted, also to form HF; and

(b) separating said HF from said carboxylic acid.

8. The method of Claim 7 including an additional separatin wherein said acyl fluoride is separated from said HF, which additional separation comprises: heating said HF and said acyl fluoride under conditions effective to form an azeotropic mixture of said HF and said acyl fluoride and to form essentially anhydrous vapor enriched in HF over that remaining in a liquid mixture which comprises said azeotropic mixture, and separating said vapor enriched in HF from said liquid mixture.

9. The method of Claim 7, wherein said acyl fluoride is acetyl fluoride and said carboxylic acid is acetic acid.

10. A method of separating hydrogen fluoride (HF) from a feed stream comprising HF and an organic compound, which method comprises:

(a) adding a carboxylic acid anhydride to said feed stream or to a mixture comprising said feed stream while maintaining separation system conditions which provide

(i) reaction between said carboxylic acid anhydride and HF in said feed stream or said mixture comprising said feed stream, to form an acyl fluoride and the corresponding carboxylic acid, said carboxylic acid acting as a solvent for said organic compound,

(ii) vaporizing HF and said acyl fluoride to form an HF-enriched vapor and a liquid enriched in said acyl fluoride, said liquid comprising an azeotrope of HF and said acyl fluoride;

(iii) separating said HF-enriched vapor from said liquid enriched in said acyl fluoride; and (b) removing said HF enriched vapor.

11. The method of Claim 10, wherein said carboxylic acid anhydride is acetic acid and said acyl fluoride is acetyl fluoride.

12. A continuous method for separating essentially anhydrous HF from a feed mixture comprising HF, an organic compound and water, said method comprising: a) providing a feed mixture comprising HF, an organic compound and water; b) contacting an anhydride of a carboxylic acid with HF and water in said feed mixture under conditions effective to form the acyl fluoride and the corresponding carboxylic acid of said anhydride; c) contacting said acyl fluoride or said anhydride, or both, with any water in said feed mixture under conditions effective to form the corresponding carboxylic acid of said anhydride, and if acyl fluoride is reacted, also to form HF; d) vaporizing HF and acyl fluoride present after step (c) to form an HF-enriched vapor and a liquid enriched in acyl fluoride, said liquid comprising an azeotrope of HF and said acyl fluoride; and e) separating said HF-enriched vapor from said liquid comprising said azeotrope of HF and said acyl fluoride.

13. The method of Claim 12, wherein said step (d) vaporization step and said (e) separating step are repeated until essentially anhydrous HF vapor is obtained.

14. The method of Claim 13, wherein said steps (d) and

(e) are repeated until substantially pure, essentially anhydrous HF vapor is obtained.

15. The method of Claim 13 or Claim 14, wherein said essentially anhydrous HF obtained is continually removed.

16. The method of Claim 12, wherein said feed mixture is fed to one or more points of a distillation apparatus comprising a column, said anhydride is fed at one or more points to said column at or below said feed point or points for said feed mixture, and said distillation apparatus is operated at conditions such that

(i) at least a portion of the HF present in said column is separated from other compounds present in said column at or below the feed point or points of said feed mixture, (ii) said anhydride reacts with residual HF remaining after (i), at or below the feed point or points of said anhydride, to form said acyl fluoride and said corresponding carboxylic acid of said anhydride; and

(iii) said acyl fluoride or said anhydride, or both, react with any water in said distillation apparatus column to form said carboxylic acid of said anhydride and if acyl fluoride is reacted, also to form HF.

17. The method of Claim 12, wherein said liquid comprising said azeotrope of HF and said acyl fluoride is circulated from the location at which it forms in said distillation apparatus column to another location within said column or to a reactor for use in a Friedel-Crafts acetylation wherein HF is used as a catalyst and solvent.

18. The method of Claim 12, wherein said organic compound and said carboxylic acid of said anhydride are withdrawn from a location in said distillation apparatus column which is below the location at which said liquid comprising said azeotrope of HF and said acyl fluoride forms and below the location to which said liquid comprising said azeotrope is circulated, if applicable.

19. The method of Claim 12, wherein said conditions include a pressure which is from about 0 to 80 psig and wherein the temperature in said distillation apparatus column is in the range from about 10°C to about 200°C.

20. A method of recovering essentially anhydrous hydrogen fluoride (HF) from a feed containing at least HF and water, which comprises:

(a) contacting acetic anhydride with HF in said feed under conditions effective to form acetyl fluoride (AcF) and acetic acid (HOAc),

(b) contacting said AcF or said anhydride, or both, with water in said feed under conditions effective to form HOAc, and if the AcF is reacted, also to form HF,

(c) vaporizing HF and any AcF not consumed in step (b) from said HOAc,

(d) forming a liquid mixture of HF and AcF not consumed in step (b) having a composition which does not change on vaporization, and

(e) removing HF vapor generated in step (c) and not consumed in step (d) overhead.

21. The method of Claim 20 in which said AcF is from about 45 to about 55 weight percent of said liquid mixture formed in step (d).

22. The method of Claim 20 in which steps (a) and (b) occur in a contacting zone and step (d) occurs in a distillation zone having a lower average temperature than said contacting zone.

23. The method of Claim 22 in which said contacting zone is in a first distillation column and said distillation zone is in a second distillation column.

24. The method of Claim 22 in said contacting zone and said distillation zone are in a single distillation column.

25. The method of Claim 22 in which said feed is fed at one or more points to said contacting zone, said anhydride is fed at one or more points to said contacting zone at or below said feed point or points for said mixture, and said contacting zone is operated at conditions such that

(i) the HF is in part stripped from said feed below the feed point or points of said feed,

(ii) said anhydride reacts with unstripped

HF in below the feed point or points of said anhydride to form said AcF and HOAc, and

(iii) AcF or said anhydride, or both, react with any water in said reaction zone to HOAc, and if AcF is reacted, also to form HF.

26. The method of Claim 25 in which said liquid mixture having said unchanging composition upon vaporization is circulated from said distillation zone to said reaction zone or to a reactor for use in a Friedel-Crafts acetylation in the presence of HF as a catalyst and solvent.

27. The method of Claim 20 in which said conditions include a pressure which is from about 0 to 80 psig and the temperature in said distillation zone is in the range from about 10°C to about 80°C.

28. A method of separating hydrogen fluoride (HF) from a mixture including HF, an organic compound and water, which comprises

(a) feeding said mixture to a middle zone of a single distillation column,

(b) feeding acetic acid (HOAc) vapor to a lower zone of said column to strip overhead a portion of the HF in said mixture in said lower and middle zones, (c) feeding acetic anhydride to said column at or below the feeds for said mixture and above said HOAc vapor feed and controlling conditions effective to sustain

(i) reaction of said anhydride with unstripped HF from said feed to form acetyl fluoride (AcF) and HOAc,

(ii) reaction of the water from said feed with sufficient of said AcF or said anhydride, or both, to convert the water to HOAc, and if the AcF is reacted, to also form HF, and

(iii) formation of a stable maximum boiling mixture of HF and AcF having a composition which does not change on vaporization in an upper zone of the column,

(d) withdrawing only HF from the top of the column,

(e) withdrawing HOAc and said organic compound from the base of the column, and

(f) withdrawing said high boiling complex from said upper zone of the column and circulating it to one or both of said middle zone of the column or to a reactor for use in a Friedel-Crafts acetylation in the presence of HF as a catalyst and solvent.

29. The method of Claim 28 in which said AcF is from about 40 to about 55 weight percent of said stable maximum boiling complex.

30. The method of Claim 29 in which said conditions include a temperature in the range from 10°C to about 200°C and a pressure in the range from 0 to about 100 psig.

31. A method for producing an aromatic ketone in which the keto carbon atom is directly bonded to an aromatic ring atom, comprising

(a) subjecting an aromatic compound to a

Friedel-Crafts acylation with an acylating agent in an reactor in the presence of a liquid hydrogen fluoride (HF) as a catalyst and solvent for an aromatic ketone produced by such acylation having a keto carbon atom directly bonded to the aromatic ring of said compound,

(b) feeding a HF-rich stream originating from said reactor and containing at least HF and said aromatic ketone to a middle distillation zone in one or more points, (c) feeding acetic anhydride at one or more points to a distillation zone at or below said point or points of feed of said HF-rich stream,

(d) operating said distillation zones and a higher distillation zone having an average temperature lower than said middle distillation zone at conditions such that

(i) a portion of HF in said HF-rich feed is stripped overhead,

(ii) said anhydride reacts with unstripped

HF to form acetyl fluoride (AcF) and acetic acid (HOAc),

(iii) AcF or said anhydride, or both, react with any water in said distillation zones to form HOAc, and if AcF reacts with said water, also to form HF, and

(iv) AcF and HF form a stable maximum boiling mixture having a composition which does not change on vaporization in said higher distillation zone,

(e) withdrawing said high boiling complex from said higher distillation zone and recycling it to one, or both, of said middle distillation zone and said reactor, (f) withdrawing HF from the top of said higher distillation zone and recycling it to said reactor,

(g) withdrawing said aromatic ketone and said

HOAc from the base of said lower distillation zone, and

(h) separating said aromatic ketone from said

HOAc.