U.S. patent number 3,900,372 [Application Number 05/505,996] was granted by the patent office on 1975-08-19 for recycle of acyl fluoride and electrochemical fluorination of esters.
This patent grant is currently assigned to Phillips Petroleum Company. Invention is credited to Benedict H. Ashe, Jr., William V. Childs, Paul S. Hudson.
United States Patent |
3,900,372 |
Childs , et al. |
August 19, 1975 |
Recycle of acyl fluoride and electrochemical fluorination of
esters
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 partially 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.
Inventors: |
Childs; William V.
(Bartlesville, OK), Ashe, Jr.; Benedict H. (Bartlesville,
OK), Hudson; Paul S. (Bartlesville, OK) |
Assignee: |
Phillips Petroleum Company
(Bartlesville, OK)
|
Family
ID: |
24012746 |
Appl.
No.: |
05/505,996 |
Filed: |
September 16, 1974 |
Current U.S.
Class: |
205/430 |
Current CPC
Class: |
C25B
3/28 (20210101) |
Current International
Class: |
C25B
3/00 (20060101); C25B 3/08 (20060101); C07b
009/00 () |
Field of
Search: |
;204/81 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Andrews; R. L.
Claims
What is claimed is:
1. A process for producing perfluorinated acyl fluorides comprising
in combination:
1. 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 esterification; 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.sub.1
to C.sub.10 primary alkanol and said acyl fluoride is a C.sub.1 to
C.sub.10 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.degree.
to 220.degree.C.
5. A method according to claim 1 wherein said cleavage is carried
out by means of contacting said perfluorinated ester with an HF
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
esterification 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 wherein said alkanol is a C.sub.1
to C.sub.10 secondary alkanol and said acyl fluoride is a C.sub.1
to C.sub.10 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 80.degree.
to 220.degree.C
11. A method according to claim 7 wherein said cleavage is carried
out by passing said perfluorinated ester over an HF 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 transesterification
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.
Description
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.sup.++F.sup.-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 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.sub.1 to C.sub.10 primary alkanols such as
methanol, ethanol, n-propanol, n-butanol, 3-methylbutanol,
n-hexanol, n-decanol and the like with C.sub.1 to C.sub.10,
preferably C.sub.1 to C.sub.3, 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. Sufficient
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. 1: Ester feedstocks containing different numbers of
carbon atoms in the acyl and alkyl portions ##EQU1## 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 by-products such as carbon tetrafluoride and carbonyl
fluoride 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.sub.6 perfluorinated acyl fluoride produced
in Scheme No. 1 can be hydrolyzed to give the valuable C.sub.6
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. ##EQU2## 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
(c) Scheme No. 3: Fluoroformate esters as fluorination feedstocks
##EQU3## Carbonyl fluoride from step (3) is returned to the
esterification step (1) 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 U.S. 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
##EQU4## In theory, sufficient acyl fluoride (carbonyl fluoride)
should be produced in the cleavage step (3) to sustain the
esterification step (1). The loss of any fluorine values to various
fluorine containing by-products can be made up with carbonyl
fluoride from some other source such as by the electrochemical
fluorination of CO, by purchase, etc. The C.sub.8 perfluorinated
acyl fluoride can be hydrolyzed to the valuable C.sub.8
perfluorinated carboxylic acid.
In accordance with Embodiment II of the present invention,
secondary alkanols containing three to ten carbon atoms such as
isopropanol, 2-butanol, 3-hexanol, 4-methyl-2-pentanol, 2-octanol,
4-decanol and the like are reacted with C.sub.1 to C.sub.10,
preferably C.sub.1 to C.sub.3, acyl fluorides such as acetyl
fluoride, carbonyl fluoride, trifluoroacetyl 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
secondary 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 II of the present invention process:
B. EMBODIMENT II:
Conversion of secondary alkanols to perfluoroketones (a) Scheme No.
5: ##EQU5## The perfluorinated ketone, e.g., hexafluoroacetone, is
separated for use as a dielectric or hydrogenated to the valuable
alcohol 1,1,1,3,3,3-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 I
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 by-products. Therefore, in
Embodiment II, 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 (1) can be conveniently "made-up" by the use of
minor amounts of a primary alkanol such as ethanol as shown below:
##EQU6##
By inspection of the above representation, it can be seen that each
mol of perfluoroethyl trifluoroacetate cleaves to two mols of
trifluoroacetyl fluoride. Hence, one mol of trifluoroacetyl
fluoride results in the cleavage step (3) for each mol of ethanol
used in the esterification step (1). Thusly, a suitable
trifluoroacetyl 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 such
as ethanol and a suitable secondary alkanol such as isopropanol to
be fed directly to the esterification step of the inventive process
such that sufficient trifluoroacetyl 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 II 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 trifluoroacetyl 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 by-product 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 trifluoroacetyl fluoride, one can recycle a
mixture of by-product carbonyl fluoride along with the
trifluoroacetyl 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, trifluoroacetyl
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
trifluoroacetyl 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 ##EQU7## This mixture of partially fluorinated
esters can be recycled to the electrochemical fluorination cell to
give perfluorinated esters as follows, e.g., ##EQU8##
On fluoride ion cleavage, each of these perfluorinated esters gives
the desired perfluorinated ketone, e.g., ##EQU9## plus a mixture
of, e.g., ##EQU10## 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 -80.degree.C to +20.degree.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 -40.degree.C to 0.degree.C 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
1,1,2-trichloro-1,2,2-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 -20.degree.C to 0.degree.C. The
carbonyl fluoride vapor is passed directly into the cold alkanol.
The so-formed 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 temperature to increase to about 25.degree.C. 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 U.S. Pat. Nos. 3,511,760, 3,511,762 and
3,711,396. 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
HF-containing electrolyte system such as the KF.sup.. 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 70.degree. to about
120.degree.C.
Current densities are preferably in the range of 100-300
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 10
milliliters per minute per square centimeter of anode geometric
surface area are suitable.
The feedstock and products obtained therefrom are 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).
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.degree. to 220.degree.C 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 of about 100.degree.C.
Operation of the alkali metal fluoride bed at about 100.degree.C
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 200.degree. C effects the
cleavage of the perfluorinated ester but the bed does not absorb
the HF 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
conversion in the cell. For example the ester interchange and
subsequent decomposition can be as follows: ##EQU11##
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 HF-containing electrolyte under electrolysis conditions
suitable for producing a perfluorinated ester. Hydrogen fluoride,
another principal feedstock, is introduced into the process through
line 12. Electrochemical fluorination zone 45 can comprise one or
more cells together with associated electrodes, control apparatus,
power supply, etc., suitable for fluorinating 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.
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 perfluoroester 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 line 22 and are passed into separation zone
75. Separation zone 75 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 85 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 described 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:
10 -- 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.sub.4, COF.sub.2 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.sub.4, COF.sub.2 Stream
85 -- Fractionation Column
30 -- CF.sub.4, COF.sub. 2 Stream
28 -- Trifluoroacetyl Fluoride Line
95 -- Esterification Reactor
32 -- Isopropanol 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 hexafluoroacetone. Isopropanol 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 by-products 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 minor 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 45 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 1 are based on the assumption of a steady state operation at
a current level of 536 amperes (10 Faradays/hour) with a current
efficiency of 90% for the conversion of C-H to C-F.
The cleavage zone contains beds of granular sodium fluoride
maintained at about 150.degree.C. In the esterification zone, the
temperature is maintained at about 0.degree.C with a residence time
of about 30 minutes.
TABLE I
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PRODUCTION OF HEXAFLUOROACETONE AND TRIFLUOROACETYL FLUORIDE BY THE
ALKALI METAL FLUORIDE CLEAVAGE OF HEPTAFLUOROISOPROPYL
TRIFLUOROACETATE Components (Flow Rate Moles/Hour) 10 12 16 18 20
22 24 26 28 30 32 34 36
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Hydrogen 4.50 4.50 4.50 4.50 4.50 Isopropyl Trifluoroacetate 0.90
0.257 0.257 0.643 Partially Fluorinated Isopropyl Trifluoroacetates
2.50 2.50 2.50 Trifluoroacetyl Fluoride 0.579 0.579 0.579 0.579
0.579 0.064 Lights (CF.sub.4, C.sub.2 F.sub.6, C.sub.3 F.sub.8,
COF.sub.2...) 0.193 0.193 0.193 0.096 0.097 0.097 Hexafluoroacetone
0.514 0.514 0.514 0.514 Isopropanol 0.643
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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 .
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