US 3900372 A
Description (OCR text may contain errors)
nited States Patent C hilds et al.
[ Aug. 19, 1975 RECYCLE OF ACYL FLUORIDE AND ELECTROCHEMICAL FLUORINATION OF ESTERS  Inventors: William V. Childs; Benedict l-l.
Ashe, Jr.; Paul S. Hudson, all of Bartlesville, Okla.
 Assignee: Phillips Petroleum Company,
 Filed: Sept. 16, 1974  Appl. No.: 505,996
 U.S. Cl. 204/81  Int. Cl C07b 9/00  Field of Search 204/81  References Cited UNITED STATES PATENTS 2,317,866 4/1943 Tamele et al. 204/81 Primary ExaminerR. L. Andrews 5 7 ABSTRACT A combination process for the conversion of primary or secondary alkanols to perfluorinated acyl fluorides and/or perfluorinated ketones wherein said alkanols are esterified with acyl fluorides and the resulting par tially fluorinated esters passed to an electrochemical fluorination step to produce perfluorinated esters which are thereafter cleaved on contacting with a source of fluoride ion under reacting conditions. Perfluorinated acyl fluoride resulting from said cleavage is recycled to the esterification step and the remaining perfluorinated acyl fluoride and/or perfluorinated ketone is recovered as product. In an alternative embodiment the perfluorinated ester is transesterified with a primary or secondary alkanol to produce a perfluorinated product, and a partially fluorinated ester resulting therefrom is recycled to the electrochemical fluorination step.
18 Claims, 1 Drawing Figure RECYCLE OF ACYL FLUORIDE AND ELECTROCHEMICAL FLUORINATION OF ESTERS BACKGROUND OF THE INVENTION This invention relates to the production of perfluorinated organic compounds from alkanols.
It is broadly known to utilize electrochemical fluorination techniques to produce specific perfluorinated products from selected feeds. Such techniques to produce some given classes of products have not achieved widespread commercial utilization, however, at least in part due to the difficulty of providing an economically feasible system which can utilize inexpensive feed materials.
SUMMARY OF THE INVENTION It is an object of this invention to provide a process for producing perfluorinated acyl halides and/or perfluorinated ketones utilizing relatively inexpensive starting materials. It is a further object of this invention to continuously produce perfluorinated acyl fluorides for use in producing partially fluorinated esters for subsequent fluorination steps; it is yet a further object of this invention to produce specific perfluorinated ketones employing a mixture of perfluorinated acyl fluorides without the necessity of separating said mixture, and it is yet a further object of this invention to produce hexafluoroacetone; and it is still yet a further object of this invention to generate, in situ, makeup perfluorinated acyl fluoride to compensate for fluoride unavoidably lost, e.g., during the production of perfluorinated ketones from secondary alkanols.
In accordance with this invention, perfluorinated acyl fluoride from the fluoride ion cleavage of a perfluorinated ester is recycled to an esterification step for reaction with primary or secondary alkanols to produce partially fluorinated esters for a subsequent electrochemical fluorination step. In accordance with an alternative embodiment of the invention, partially fluorinated esters from an ester interchange are recycled to an electrochemical fluorination step.
BRIEF DESCRIPTION OF THE DRAWING The drawing, forming a part hereof, is a schematic representation of an electrochemical fluorination unit in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, perfluorinated ketones and/or perfluorinated acyl fluorides are prepared by a multistep process involving the following:
1. Esterification of primary or secondary alkanols with acyl fluorides;
2. Electrochemical fluorination of esters prepared in step (1) to produce perfluorinated esters;
3. Alkali metal fluoride cleavage of the perfluorinated esters prepared in step (2) to produce perfluorinated ketones and/or perfluorinated acyl fluorides; or
3. Cleavage of the perfluorinated esters by HF H +F"catalysis; or 3". Transesterification of the perfluorinated ester with a primary or secondary alkanol to produce a perfluorinated product, hydrogen fluoride, and a partially fluorinated ester recyclable to (2); and
4. Recycle of appropriate perfluorinated acyl fluoride product from step (3) or (3') to sustain esterification step (1).
The use of esters derived from primary alkanols is 5 herein described as Embodiment I whereas Embodiment II involves the use of esters derived from secondary alkanols. In the practice of the present invention, Embodiment I gives rise predominantly to perfluorinated acyl fluorides whereas Embodiment II gives rise to approximately equimolar quantities of perfluorinated ketone and perfluorinated acyl fluoride. The present invention is a combination process consisting of three basic steps (1-3), and a fourth step (4) which, by recycling a product from step (3) to step (1), provides an unobvious cooperation between the three basic steps and thus provides a single integrated process for producing the desired products.
In accordance with Embodiment I of a combination esterification-electrochemical fluorination-fluoride ion cleavage process for the production of perfluorinated acyl fluorides, suitable esters to the electrochemical fluorination step are prepared by reacting C to C primary alkanols such as methanol, ethanol, n-propanol, n-butanol, 3-methylbutanol, n-hexanol, n-decanol and the like with C to C preferably C to C acyl fluorides such as acetyl fluoride, carbonyl fluoride, and trifluoroacetyl fluoride. These esters are perfluorinated in the electrochemical fluorination step and then cleaved with an alkali metal fluoride to yield approximately two mols of perfluorinated acyl fluoride per mol of perfluorinated ester. Two different perfluorinated acyl fluorides are produced from perfluorinated esters containing different numbers of carbon atoms in the alkyl and acyl portions. Sufiicient perfluorinated acyl fluoride is conveniently recycled to the esterification step to sustain the overall process.
Although it is not intended to limit the scope of the instant invention unduly, the following simplified schematic representations describe some specific examples of Embodiment I of the present invention process:
A. EMBODIMENT I:
Conversion of primary alkanols to perfluoroacyl halides a. Scheme No. l: Ester feedstocks containing different numbers of carbon atoms in the acyl and alkyl portions (l) Esterification Step 0 ll ll CH (CH OH CF CF CH (CH OCCF HF Primary Perfluorinated Partially Fluorinated Alkanol Acyl Fluoride Ester (n-Hexyl (n-I-Iexanol) (Trifluoroacetyl Trifluoroacetate) 5 5 Fluoride) (2) Electrochemical Fluorination Step 0 0- ll ECF ll CH (CH OCCF C- CF (CF OCCF ell Partially Perfluorinated Ester Fluorinated (Perfluoro-n-hexyl Ester Feedstock Trifluoroacetate) (n-Hexyl Trifluoroacetate (3) Alkali Metal Fluoride Cleavage of Perfluorinated Ester to Give two Different Perfluorinated Acyl Fluorides ll l n CF (CF ),-,OCCF CF (CF CF CF CF Perfluorinated Perfluorinated Perfluorinated Ester Acyl Fluoride Acyl Fluoride (Perfluoro-n-hexyl (Perfluoro-n- (Trifluoroacetyl Trifluoroacetatc) hexanoyl Fluoride) Fluoride) In theory, sufficient perfluorinated acyl fluoride, i.e., trifluoroacetyl fluoride, should be produced in the cleavage step (3) to sustain the esterification step (1). However, some fluorine values are lost in some byproducts such as carbon tetrafluoride and carbonyl flu- 5 oride and therefore, additional trifluoroacetyl fluoride for make-up must come to the esterification step 1 from some alternate source such as trifluoroacetyl fluoride make-up stream, by purchase, etc. The C perfluorinated acyl fluoride produced in Scheme No. 1 can be hydrolyzed to give the valuable C perfluorinated acid. It is contemplated that a single perfluorinated acyl fluoride can be prepared in the instant process by employing an ester feedstock containing equal numbers of carbon atoms in the acyl and alkyl portions of the ester as shown in the following schematic representation:
A. EMBODIMENT I b. Scheme No. 2: Ester feedstocks containing the same number of carbon atoms in the acyl and alkyl portions.
ll Cli CH CH O--CCF CF Partially Fluorinated Ester Feedstock (n-Propyl Perfluoropropanoate) (3) Alkali Metal Fluoride Cleavage of Perfluorinated Ester To Give a Single Perfluorinated Acyl Fluoride 2 cr cr cr Perfluorinated Acyl Fluoride (Perfluoropropanoyl Fluoride) Sufficient perfluorinated acyl fluoride, i.e., perfluoropropanoyl fluoride, is produced in the cleavage step (3) to sustain the esterification step (1) and if desirable the balance of the perfluorinated acyl fluoride, e.g., perfluoropropanoyl fluoride, can be hydrolyzed to a valuable perfluorinated carboxylic acid, e.g., perfluoropropanoic acid.
Furthermore, in accordance with Embodiment I, the reaction of carbonyl fluoride with primary alkanols in a 1:1 molar ratio can be utilized to prepare suitable fluoroformate ester feedstocks.
A. EMBODIMENT I (0) Scheme No. 3: Fluoroformate esters as fluorination feedstocks (l) Esterrficatron Step ll CH CH CH CH OH COF CH (CH OCF HF Primary Acyl Partially Fluorinated Alkanol Fluoride Ester (n-Butyl (mButanol) (Carbonyl Fluoroformate) Fluoride) (3) Alkali Metal Fluoride Cleavage of Perfluorinated Ester to Give Two Different Acyl Fluorides O O O u m u u CF (CF OCF CF CF CF CF FCF Perfluorinated Perfluorinated Acyl Fluoride Ester (Perfluoro Acyl Fluoride (Carbonyl n-butyl Fluoro- (Perfluoro-nfluoride) formate) butyryl Fluoride) Carbonyl fluoride from step (3) is returned to the esterification step l with any added carbonyl fluoride necessary to sustain the esterification step of the cyclic process. Make-up carbonyl fluoride can be prepared by the electrochemical fluorination of CO in accordance with the teaching of US. Pat. No. 3,461,050. The perfluoro-n-butyryl fluoride product can be hydrolyzed to the valuable perfluoro-n-butyric acid.
Alternatively, two mols of the primary alkanol with one mol of carbonyl fluoride in the esterification step (1) gives one mol of carbonate ester suitable for use in the instant process as described below.
A. EMBODIMENT I (d) Scheme No. 4: Carbonate esters as fluorination feedstocks (l) Esterification Step 0 Primary Acyl Carbonate Ester Alkanol Fluoride (Di-n-octyl Carbonate) (n-Octanol) (Carbonyl Fluoride) (2) Electrochemical Fluorination Step Carbonate Ester (Di-n-octyl carbonate) Perfluorinated Carbonate Ester (Di-n-perfluorooctyl Carbonate) 3) Alkali Metal Fluoride Cleavage of Perfluorinated Ester to Give Two Different Acyl Fluorides hexanol, 4-methyl-2-pentanol, 2-octanol, 4-decanol and the like are reacted with C, to C preferably C to C acyl fluorides such as acetyl fluoride, carbonyl fluoride, trifluoroaeetyl fluoride and the like to give ester feedstocks for the electrochemical fluorination step resulting after cleavage, in the production of perfluorinated ketones and perfluorinated acyl fluorides. The perfluorinated acyl fluoride products can be selectively separated from the effluent and recycled to prepare additional ester feedstocks to the electrochemical fluorination step by reaction with the appropriate sec ondary alkanol. The perfluorinated ketone compounds can be separated and used as chemical intermediates to prepare fluorine-containing alkanols or used in special applications as dielectric agents.
Although not intended to limit the scope of the instant process unduly, the following simplified schematic representation describes an example of Embodiment ll of the present invention process:
B. EMBODIMENT ll:
Conversion of secondary alkanols to perfluoroketones (a) Scheme No. 5:
( l Estcrifieation Step OH (H) (IIH O I ll CH CHCH CF CF H(|f-0--CCli-, HF
Secondary Acyl Fluoride Partially Fluorinatcd Alkanol (Trifluoro- Ester (lsopropyl (lsoproacetyl Trifluoroacetatc) panol) Fluoride) (2) Electrochemical Fluorination Step CH 0 CF 0 l Cell I CH CF Partially Perfluorinatcd Ester Fluorinated (Heptafluoroisopropyl Ester Trifluoroacctatc (isopropyl Trifluoroacetate) (3) Alkali Metal Fluoride Cleavage of Perfluorinated Ester to Give Equimolar Amounts of Perfluorinated Ketone and Perfluorinated Acyl Fluoride The perfluorinated ketone, e.g., hexafluoroacetone, is separated for use as a dielectric or hydrogenated to the valuable alcohol 1,1,l,3,3,3-hexafluoroisopropanol. The perfluorinated acyl fluoride product, .e.g., trifluoroacetyl fluoride, is conveniently recycled to sustain the esterification step (1).
In a manner completely analogous to that shown for Embodiment l schemes No. 3 and No. 4, secondary alkanols can also be converted to perfluoroketones in processes wherein carbonyl fluoride is the acyl halide intermediate and wherein the fluoroformate and/or carbonate esters of secondary alkanols are the ester intermediates.
In the practice of the present inventive process, fluorine values are generally lost to some extent in the form of carbon tetrafluoride and carbonyl fluoride byproducts. Therefore, in Embodiment ll, e.g., insufficient acyl fluoride is produced in the fluoride ion cleavage step (3) to sustain the esterification step (1). The additional acyl fluoride required to sustain the esterification step l can be conveniently made-up" by the use of minor amounts of a primary alkanol such as ethanol as shown below:
Make-Up" Trifluoroacetyl Fluoride Stream Based on Ethanol l Esterification Step O 0 ll ll CH CH OH CF CF Ci-I CH OCCF; HF Ethanol Trifluoroacctyl Ethyl Trifluoro- Fluoride p acetate (2) Electrochemical Fluorination Step ll ECF ll CH,,CH OCCF CF;,CF -OCCF Ethyl Trifluoroacetate Perfluoroethyl Trifluoroacetate (3) Alkali Metal Fluoride Cleavage of Perfluorinatcd Ester to Give Perfluorinated Acyl Fluoride By inspection of the above representation, it can be seen that each mol of perfluoroethyl trifluoroacetate cleaves to two mols of trifluoroaeetyl fluoride. Hence, one mol of trifluoroaeetyl fluoride results in the cleavage step (3) for each mol of ethanol used in the esterification step (1). Thusly, a suitable trifluoroaeetyl fluoride level can be maintained in this manner to sustain the esterification step of the present process. Alternatively, ethyl trifluoroacetate, prepared separately, can be admixed with, e.g., isopropyl trifluoroacetate and fed to the ECF cell. However, it is particularly convenient to provide a feedstream comprising a mixture of a suitable primary alkanol suchas ethanol and a suitable secondary alkanol such as isopropanol to be fed directly to the esterification step of the inventive process such that sufficient trifluoroaeetyl fluoride for recycle would be produced in the cleavage step of said process.
As mentioned earlier, carbonyl fluoride can be the acyl fluoride intermediate in the Embodiment ll of the process for converting the secondary alkanols to fluoroformate or carbonate esters and ultimately to perfluoroketones. However, even if other acyl fluorides, such as trifluoroaeetyl fluoride, are present in the system, minor amounts of carbonyl fluoride can be generated in situ as a result of the decomposition of some intermediate and/or product compounds. This byproduct quantity of carbonyl fluoride need not be separated and removed from the process.
For example, in the use of the present invention to produce hexafluoroacetone and trifluoroaeetyl fluoride, one can recycle a mixture of by-produet carbonyl fluoride along with the trifluoroaeetyl fluoride to the esterification step. As shown in the foregoing schemes, mixtures of the resulting trifluoroacetate and fluoroformate esters of isopropanol can be used in Embodiment II to produce a mixture of hexafluoroacetone, trifluoroaeetyl fluoride and carbonyl fluoride (a by-product not shown in the above simplified equations). This technique eliminates the necessity of making the difficult separation of carbonyl fluoride and trifluoroaeetyl fluoride before recycling the acyl fluoride to the esterification step and also minimizes the loss of fluorine values from the process.
This is because the mixture of carbonyl fluoride and trifluoroacetyl fluoride can be reacted with a secondary alkanol to give a corresponding mixture of partially fluorinated esters as follows, e.g., and
This mixture of partially fluorinated esters can be recycled to the electrochemical fluorination cell to give perfluorinated esters as follows, e.g.,
O cr, :1 CF
K II cFoccF On fluoride ion cleavage, each of these perfluorinated esters gives the desired perfluorinated ketone,
plus a mixture of, e.g.,
coF cr cr which can be used to start the cycle over again.
In the esterification step of the present process, the alkanol and acyl fluoride are reacted either batchwise or continuously under suitable conditions of temperature, pressure, and contact time as is known in the art to give the desired ester product. Generally, the alkanol and acyl fluoride are used in an approximately 1:1 molar ratio except in reactions involving the use of carbonyl fluoride directed toward the preparation of carbonate esters wherein two mols of alkanol are used per mol of carbonyl fluoride. The use of an acid acceptor such as pyridine is preferred in the formation of the carbonates but the use of an acid acceptor is optional in the preparation of the trifluoroacetates produced by the reaction of alkanol and trifluoroacetyl fluoride. Generally the use of an acid acceptor such as alkali metal carbonate is preferred for use in the preparation of acetates produced by the reaction of alkanol and acetyl fluoride. Fluoroformates and carbonates are prepared by the direct interaction of carbonyl fluoride and alkanol. It is presently preferred to use an acid acceptor in the preparation of the carbonate esters.
The esterification process is normally carried out in the temperature range of 80C to +C and, if desirable, in the absence of any diluent. For example, trifluoroacetyl fluoride in the vapor form can be passed directly into isopropanol at -C to 0C to give high yields of the ester isopropyl trifluoroacetate. This esterification product contains hydrogen fluoride by product but is suitable to be passed to the electrochemical fluorination step of the present process. For the preparation of acetates requiring the use of acid acceptors, it may be convenient to employ low boiling perhalogenated solvents such as l,l,2-trichloro-l,2,2- trifluoroethane to provide a system which can be refluxed under mild temperature conditions to effect the esterification. The product ester from such runs can be isolated and purified by methods well known in the art as extraction, extractive distillation, fractionation, etc.
The fluoroformates prepared by the use of carbonyl fluoride are generally prepared at low temperature conditions such as -20C to 0C. The carbonyl fluoride vapor is passed directly into the cold alkanol. The soformed fluoroformates are readily converted to carbonates by adding an acid acceptor such as pyridine and sufficient alkanol to provide two mols of alkanol per mol of carbonyl fluoride and allowing the tempera ture to increase to about 25C. The fluoroformates and carbonates containing hydrogen fluoride are sufficiently pure to be passed to the electrochemical fluorination step of the present process.
The esterification reaction can be carried out over the time period of a few minutes to several hours. The reaction rates to fluoroformates and trifluoroacetates are rapid and for all practical purposes the esterifications are complete after the desired weight of the gaseous acyl fluoride has been absorbed by the alkanol reactant.
The esterification reaction is conveniently carried out at atmospheric pressure or slightly less than atmospheric pressure as it is desirable to manipulate the often very volatile reactants and products at low temperatures.
Since hydrogen fluoride is produced as a by-product in the esterification step it is desirable to carry out this step in apparatus which is inert to HF such as monel, KEL-F fluorocarbon polymer, and the like.
In the electrochemical fluorination step of the present process, the electrochemical fluorination is carried out generally within the broad teaching of US. Pat. Nos. 3,511,760, 3,511,762 and 3,71 1,396. The electrochemical fluorination step can be carried out over a broad range of temperatures and pressures limited only by the freezing point and the vapor pressure of the specific l-lF-containing electrolyte system such as the KF'2HF electrolyte. It is preferred that the electrochemical fluorination process be carried out at temperatures such that the vapor pressure of the electrolyte is less than about 50 mm Hg. Presently, the preferred temperature range is about to about 120C.
Current densities are preferably in the range of 3OO milliamperes per square centimeter of anode geometric surface area but current densities in the range of 50-1000 milliamperes per square centimeter are suitable. In general, current densities will be high enough so that anodes of moderate size can be employed yet low enough so that the anode is not corroded or disintegrated. Voltages in the range of 4 to 20 volts per unit cell can be used.
Feed rates to the electrochemical fluorination cell vary over a broad range, however, in general the upper limit on flow rate will be that beyond which the feedstock begins to escape from the porous carbon anode into the bulk of the electrolyte. The lower limit of the feed rate will be determined by the requirement to supply the minimum amount of feedstock sufficient to prevent evolution of free fluorine. Generally gaseous feedstock flow rates within the range of 3 to 600 preferably 12 to 240 ml (STP) per minute per square centimeter of anode cross-sectional area are satisfactory. In terms of anode area, gaseous feed rates in the range of 0.5 to milliliters per minute per square centimeter of anode geometric surface area are suitable.
The feedstock and products obtained therefrom ar retained in the cell for a period of time which is usually less than one minute. This is because the feed is introduced into the bottom of the anode and the product taken out the top in a continuous operation as opposed to a batch process. Unconverted feed and partially fluorinated materials can be recycled to the cell for the production of more highly fluorinated products. In the present process the perfluorinated ester can be fractionated from the cell effluent and passed to the alkali metal fluoride cleavage step (3). i r
In the alkali metal fluoride cleavage step of the present process, the perfluorinated ester, fractionated from the electrochemical fluorination cell effluent, is contacted with a bed of an alkali metal fluoride such as sodium fluoride maintained in the temperature range of 80 to 220C under conditions to give a mixture of perfluorinated ketone and/or perfluorinated acyl fluoride. Partially fluorinated ester intermediates in the electrochemical fluorination cell effluent should be recycled to the electrochemical fluorination cell because such intermediates on contact with sodium fluoride at an elevated temperature are highly fragmented to lower molecular weight materials. Some cleavage of the perfluorinated ester takes place in the electrochemical fluorination cell in the temperature range ofabout 100C. Operation of the alkali metal fluoride bed at about 100C effects the cleavage of the perfluorinated ester and the fluoride bed absorbs any HF which may be in the ester feed whereas operation of the alkali metal fluoride bed at about 200C effects the cleavage of the perfluorinated ester but the bed does not absorb the HP at this higher temperature.
In another inventive though less preferred embodiment of the present process, the cleavage and esterification steps can be essentially combined. This can be accomplished by introducing the suitable alkanol, either a primary or secondary alkanol depending upon the ultimate products desired, into the process at a point in which it contacts the perfluorinated ester. Such a convenient point is the electrochemical fluorination cell effluent from which the partially fluorinated products have been removed for recycle to the cell.
The contacting of the alkanol with the perfluorinated ester is carried out under transesterification conditions such that at least a substantial amount of perfluoroketone or perfluoroacyl fluoride is produced. Such products are formed through the rapid decomposition of the corresponding unstable perfluoroalcohols which are formed as intermediates. Other products of this transesterification step are hydrogen fluoride and the ester of the feed alkanol and the corresponding acyl fluoride. The ester is separated and introduced as the primary feed to the cell and the perfluoroketone or perfluoroacyl fluoride is separated from the hydrogen fluoride and removed from the process as product. The hydrogen fluoride is returned to the process for ultimate con- :CFOCCFG CH3CHCH3 version in the cell. For example the ester interchange and subsequent decomposition can be as follows:
CE, CF n cHoCCF HF FIG. 1 shows a simplified schematic representation of the present invention process. The suitable alkanol or mixture of alkanols is introduced as primary feedstock into the process through line 32. Make-up amounts of the suitable fluorides, if used, are introduced through line 34. The alkanol and acyl fluoride pass into esterification zone 95 where they contact recycle acyl fluoride from line 28 and form the fluorinatable ester. Esterification zone 95 can comprise one or more reactors and can include related heating means, hold tanks, separations means, control means, and other apparatus suitable for producing the desired fluorinatable ester stream.
The fluorinatable ester is passed through line 36, and combined with partially fluorinated recycle ester from line 18, and then passed into electrochemical fluorination zone 45 in which it contacts an PIP-containing electrolyte under electrolysis conditions suitable for producing a perfluorinated ester. Hydrogen fluoride, another principal feedstock, is introduced intotheprocess through line 12. Electrochemical fluorination zone 45 can comprise one or more cells together with associated electrodes, control apparatus, power supply, etc.,
' suitable forffluorinating the feed ester at maximum conversion consistent 'with minimum by-product formation.
By-product hydrogen exits the electrochemical fluorination zone (by means not shown) and fluorinated organic effluent passes from the electrochemical fluorination zone 45 to separation zone 55 via line 16. Separation Zone 55 can comprise one or more separation means such as fractionators which are sufficient to separate partially fluorinated esters. Such partially fluorinated esters are passed from separation zone 55 through line 18 for recycle to electrochemical fluorination zone 45. I
A perfluoroester-containing stream passes from separation zone 55 to cleavage zone 65 which can comprise one or more reactors with associated support apparatus in which the pcrfluoroester can contact a solid alkali metal fluoride under conditions suitable to substantially cleave the ester into perfluoroketone and/or perfluoroacyl fluoride'products. The cleavage products exit the cleavage zone 65 via line22 and are passed into separation zone 75. Separation zone can comprise one or more conventional separation units such as fractionators, extractors, adsorption units, etc., which are suitable for isolation and recovery of the desired products of the process.
A perfluoroacyl fluoride-containing stream is passed from separation zone 75 via line 26 to separation zone in which by-products are separated and removed from the process through line 30. Recycle acyl fluorides pass from separation zone 85 via line 28 and are introduced into esterification zone 95.
Hydrogen fluoride will generally be carried out of electrochemical fluorination zone 45 to some degree but can be separated from organic products by conventional means such as adsorption at one or more convenient points (not shown) in the process and recycled back to the fluorination zone.
CALCULATED ILLUSTRATIVE EMBODIMENT An illustrative method for carrying out one specific embodiment of the process of this invention is de scribed below with reference to FIG. 1. The system discussed is based on Embodiment II, scheme No. 5 which shows the production of hexafluoroacetone with recycle of the trifluoroacetyl fluoride product to the esterification reactor. In the FIGURE the numerals have the following meanings:
Recycle Stream and Fresh Ester Feedstock Line 12 Hydrogen Fluoride Inflow 45 Electrochemical Fluorination (ECF) Zone 16 Electrochemical Fluorination Cell Effluent 55 Fractionation Column 18 Partially Fluorinated Ester Intermediates Recycle to ECF Zone 20 Perfluorinated Ester, CF COF Stream 65 Alkali Metal Fluoride Cleavage Reactor 22 Effluent from Alkali Metal Fluoride Cleavage Reactor 75 Fractionation Column 24 Perfluorinated Ketone Product 26 Trifluoroacetyl Fluoride, CF COF Stream 85 Fractionation Column 30 CF COF Stream 28 Trifluoroacetyl Fluoride Line 95 Esterification Reactor 32 lsopropanol Feed Line 34 Make-up Trifluoroacetyl Fluoride Feed Line Referring now to FIG. 1, the invention will be more fully explained with respect to producing hexafluoroacminor amounts of carbon tetrafluoride and carbonyl fluoride are passed to column 75 to separate hexafluoroacetone product as bottoms through conduit 24. The trifluoroacetyl fluoride, carbon tetrafluoride and carbonyl fluoride are taken overhead through conduit 26 to fractionation column 85. In column 85 the lower boiling carbonyl fluoride and carbon tetrafluoride are passed overhead through line 30 and the trifluoroacetyl fluoride is passed via conduit 28 to the esterification reactor 95 for conversion to additional isopropyl trifluoroacetate feedstock. Optionally, some or all of the carbonyl fluoride present in line 26 can be combined with the trifluoroacetyl fluoride and passed via line 28 into the esterification zone.
In a calculated run assuming a 25% per pass hydrogen replacement in the electrochemical fluorination zone, Table I indicates the approximate compositions of the streams shown in FIG. 1. One mole of heptafluoroisopropyl trifluoroacetate counts as one mole of hexafluoroacetone and one mole of trifluoroacetyl fluoride. The amount of hydrogen fluoride carried from the ECF zone will vary considerably depending on a number of parameters but approximately 1 mol of HF should pass through line 16 per hour. The values in Table l are based on the assumption' of a steady state operation at a current level of 536 amperes (1O Faradays/hour) with a current efficiency of 90% for the conversion of C-H to CF.
The cleavage zone contains beds of granular sodium fluoride maintained at about 150C. In the esterifi cation zone, the temperature is maintained at about 0C with a residence time of about 30 minutes.
TABLE I PRODUCTION OF HEXAFLUOROACETONE AND TRIFLUOROACETYL FLUORIDE BY THE ALKALI METAL FLUORIDE CLEAVAGE OF HEP'TAFLUOROISOPROPYL TRIFLUOROACETATE Components (Flow Rate Moles/Hour) l0 l2 l6 I8 20 22 24 26 28 30 32 34 36 Hydrogen 4.50 4.50 4.50 4,50 4,50 lsopropyl Trifluoroacetutc 0.90 0.257 0.257 0.643 Partially Fluorinated lsopropyl Trifluoroacctatcs 2.50 2.50 2.50 Trifluoroacctyl Fluoride 0.579 0.579 0.579 0.579 0.579 0.064 Licglts (CF,. C F C F 0. I93 0. I93 0. I93 0.096 0.097 0.097 C Hexafluoroacetone 0.5 l4 0.514 0.5 l 4 0.5 l4 lsopropanol (1643 etone. lsopropanol and make-up trifluoroacetyl fluoride are introduced, respectively, through conduits 32 and 34 into the esterification reactor 95. The product ester isopropyl trifluoroacetate is passed through line 36 to enter the electrochemical fluorination zone 45 through line 10 along with any partially fluorinated ester intermediates conveyed into line 36 by conduit 18. Hydrogen fluoride enters the electrochemical fluorination cell through conduit 12 and products of the electrochemical fluorination step are passed to fractionation column 55 through line 16. Fractionation column 55 is operated so as to take perfluorinated ester (heptafluoroisopropyl trifluoroacetate), and byproducts carbonyl fluoride and carbon tetrafluoride overhead through conduit 20 to an alkali metal fluoride cleavage reactor 65. Partially fluorinated ester intermediates are recycled to the electrochemical fluorination cell through line 18. In the cleavage reactor 65 the perfluorinated ester is cleaved to hexafluoroacetone and trifluoroacetyl fluoride. These products along with Under these conditions the principal streams of the process will contain the specific components and in the approximate amounts shown in Table I wherein the stream numbers correspond to those of FIG. 1.
While this invention has been described in detail for the purpose of illustration, it is not to be construed as limited thereby but is intended to cover all changes and modifications within the spirit and scope thereof.
What is claimed is:
A process for producing perfluorinated acyl fluorides comprising in combination:
I. contacting a primary alkanol with an acyl fluoride under esterification conditions to produce a partially fluorinated ester;
2. passing said partially fluorinated ester to an electrochemical fluorination cell to produce a perfluorinated ester;
3. cleaving said perfluorinated ester to produce said perfluorinated acyl fluorides and acyl fluoride for recycle;
4. recycling a portion of said acyl fluoride from step (3) to step (1) to sustain said esteriflcation; and
5. recovering a portion of said perfluorinated acyl fluoride as product.
2. A process according to claim 1 wherein said alkanol is a C to C primary alkanol and said acyl fluoride is a'C, to C acyl fluoride.
3. A process according to claim 1 wherein said alkanol is selected from the group consisting of n-hexanol, n-propanol, n-butanol, and n-octanol and said acyl fluoride is selected from trifluoroacetyl fluoride, perfluoropropanoyl fluoride and carbonyl fluoride.
4. A process according to claim 1 wherein said cleavage is carried out by passing said perfluorinated ester over an alkali metal fluoride catalyst at a temperature within the range of 80 to 220C.
5. A method according to claim 1 wherein said cleavage is carried out by means of contacting said perfluorinated ester with an HP catalyst.
6. A method according to claim 1 wherein said electrochemical fluorination step is carried out by passing feed into the bottom of an anode and taking the product out of the top in a continuous operation so that the residence time for the feed and products within the cell is less than 1 minute.
7. A process for producing perfluorinated ketones comprising in combination:
1. contacting a secondary alkanol with an acyl fluoride under esteriflcation conditions to produce a partially fluorinated ester;
2. passing said partially fluorinated ester to an electrochemical fluorination cell to form a perfluorinated ester;
3. cleaving said thus formed perfluorinated ester to produce said perfluorinated ketone and perfluorinated acyl fluoride;
4. recycling said perfluorinated acyl fluoride from said step (3) to said step (1) to sustain esterification; and
5. recovering said perfluorinated ketone as product.
8. A method according to claim 7'wh erein said alkanol is a C to C secondary alkanol and said acyl fluoride is a C to C acyl fluoride.
9. A method according to claim 7 wherein said alkanol is isopropanol and said acyl fluoride is acetyl fluoride.
10. A method according to claim 7 wherein said cleavage is carried out by passing said perfluorinated ester over an alkali metal fluoride catalyst at a temperature within the range of to 220C 11. A method according to claim 7 wherein said cleavage is carried out by passing said perfluorinated ester over an HP catalyst.
12. A method according to claim 7 wherein make-up acyl fluoride is produced by passing a minor amount of a primary alkanol into the esterification step.
13. A method according to claim 12 wherein said primary alkanol is ethanol, said secondary alkanol is isopropanol and said acyl fluoride is trifluoroacetyl fluoride.
14. A method according to claim 13 wherein said electrochemical fluorination is carried out by passing said partially fluorinated ester to the bottom of an anode and recovering product from top of said anode in a continuous operation, the contact time for feed and products within the cell being less than 1 minute.
15. A method according to claim 7 wherein said electrochemical fluorination is carried out by passing said partially fluorinated ester to the bottom of an anode and recovering product from top of said anode in a continuous operation, the contact time for feed and products within the cell being less than 1 minute.
16. A process for producing perfluorinated products comprising in combination:
A. passing a partially fluorinated ester to an electrochemical fluorination cell to form a perfluorinated ester;
B. contacting said perfluorinated ester under transes terification conditions with a primary or secondary alkanol to produce said perfluorinated product, hydrogen fluoride and a partially fluorinated ester; and
C. recycling said partially fluorinated ester to said step (A).
17. A process according to-claim 16 wherein said alkanol is a secondary alkanol and said product is a ketone.
18. A process according to-claim 16 wherein said alkanol is isopropanol and ketone is hexafluoroacetone. =l