Note: Descriptions are shown in the official language in which they were submitted.
1 15~256
PRODUCTION OF CARBOXYLIC ESTERS FROM ACYLIUM A2JIONS
FORMED BY CARBONYLATION
BACKGROUND OF THE INVENTION
-
A. Field of the Invention
The invention relates to formation of carboxylic
esters by esterifying acyl fluoriaes and/or chlorides
especially those formed from carbon monoxide, anhydrous
hydrogen fluoride or hydrogen chloride, and an olefin with
one or more double bonds or esters.
B Descri tion of the Prior Art
P
The prior art such as GB 942,367 stresses aqueous
acid catalyst systems for production of carboxylic acid by
carbonylation of compounds having one or more double bonds,
or esters followed by further hydrolysis of the reaction
products with excess water to produce carboxylic acids and
then esterifying acids. In these processes, the aqueous acid
medium is corrosive and expensive equipment is reauired.
TXe prior art problems are overcome by the process described
herein for forming carboxylic esters.
: 20 BRIEF DESCRIPq~ION OF T~IE DRAWING
~ The drawing illustrates one embodiment of the
; esterification-separation process described herein.
SUMMARY OF THE INVENTION
Carboxylic esters, e.g., methyl isobutyrate, are
formed by esterifying with less than the total amount of
alcohol required to react with all of an acylium anion
product, e.g., isobutyryl fluoride, to form the carboxylic
acid ester and to regenerate the anhydrous acid, e.g.,
hydrogen fluoride or hydrogen chloride, The acylium anion
1 15~256
-- 2 --
product, although formed by any reaction, i9 preferably
formed by the reaction of carbon monoxide, an anhydrous
acid described here, e.g., hydrogen fluoride, and an
organic compound capable of reacting with carbon monoxide
and the anhydrous acid, e.g., propylene, under conditions
whereby an acylium anion product, e.g., isobutyryl fluoride,
forms. In other embodiments of the invention, part or all
of the carboxylic acid ester, e.g., methyl isobutyrate, is
separated from the esterified mixture and the remaindçr of
the esterified mixture after part or all of the carboxylic
acid ester is separated therefrom ~e.g., hydrogen fluoride,
unreacted isobutyryl fluoride, unseparated methyl isobuty-
rate) is recycled to react with the organic compound (e.g.,
propylene) to form more acylium anion product ~e.g.,
isobutvryl fluoride). In another embodiment of the inven-
tion, the separation and esterifying are concurrent so that
side reactions are substantially minimized. The anhydrous
acid is separated and is recycled while the acylium anion
product is being esterified. The lower alkyl propionates or
isobutyrates, e.g., methyl isobutyrate, may be oxydehydro-
genated to lower alkyl acrylates or methacrylates, e.g.,
methyl methacrylate.
DESCRIPTION OF T~E INVENTION
The no~el discovered process for producing a
carboxylic acid ester from an acylium anion product com-
prises the step of:
esterifying a mixture comprised of an acylium anion
product (fluoride or chloride), e.g., isobutyr~l fluoride,
especially an acylium anion product formed by the reaction
of carbon monoxide, an acid described hereln and an organlc
compound described herein with less than the total amount of
alcohol described herein required for esterifying all of the
acylium anion product in the mixture to the carboxylic acid
ester, e.g., methyl isobutyrate. This reaction is carried
1 15~2~6
-- 3 --
out under conditions whereby the carboxylic acid ester forms
and the acid is regenerated as described herein.
In other embodiments of the invention, the process
further comprises the step or steps of:
S separating from one ~1) to one hundred (100) percent of
the acid from the esterified mixture and recycling from one
(1) to one hundred (100) percent of the separated acid for
reaction with carbon monoxide and the or~anic compound
described herein to form more of the mixture comprised of
the acylium anion product and the anhydrous acid.
In another embodiment of the invention, the process
can comprise the step of:
separating from one (1) to one hundred (100) percent of
the carboxylic acid ester from the esterified mixture, and
recycling from one (1) to one hundred (100) percent of the
esterification product mixture remaining after separation of
the carboxylic acid ester therefrom, for reaction with carbon
monoxide and the organic compound described herein to form
more of the mixture comprised of the acylium anion product.
In another embodiment, the carboxylic esters,
formed by the process described herein, particularly the
lower chain alkylesters of propionic acid and/or isobutyric
acid, such as methyl-propionic acid and methyl isobutyric
acid, are suitable for direct oxydehydroqenation by known
processes to lower alkyl unsaturated esters; such as methyl
acrylate and methyl methacrylate.
REACTANTS TO FORM THE AcyLI~tM ANION PRODUCT
; The acylium anion product described herein, e.g.,
isobutyryl fluoride, may be made by any process, for example,
reaction of isobutyryl chloride or bromide with hydrogen
fluoride to form isobutyryl fluoride, and regeneration of
the hydrogen chloride or hydrogen bromide.
However, a more preferred method is by a carbonyla-
tion reaction of carbon monoxide, an anhydrous acid herein,
1 15~256
and an organic compound described herein. A preferred
carbonylation reaction for making the acylium anion product
is described herein.
The reactants to form the acylium anion product
may be from any source, but must be free from deleterious
materials which interfere with the process described herein.
The total amount of water in the reaction mixture to be
esterified must be less than 0.01 weight ~ to prevent side
reactions of the acylium anion product to.form undesirable
ethers. Preferably the system is anhydrous.
The carbon monoxide may be from any source, but is
preferably substantially free from water so as to maintain
substantially anhydrous reaction conditions. The carbon
monoxide may be diluted with other substances which do not
interfere with the reaction. For example, dry synthesis gas
or coal combustion gas may be used. It is preferred that
dry carbon monoxide itself be used.
The organic compounds are those which are capable
of reacting with carbon monoxide and the anhydrous acid, that
is, carbonylated to form an acyLium anion, for example,
organic esters described herein or olefins having at least
one double bond capable of carbonylating to an acylium anion
product described herein.
The organic esters for the carbonylation reaction
o
are represented by the general formula R - C - O - R',
wherein R is an alkyl of up to twenty carbon atoms, such as
methyl, ethyl, dodecyl, eicosanyl. Preferably the alkyl is
methyl, ethyl, propyl, or isopropyl, with ethyl and isopropyl
being the most preferred. R' is an alkyl of from two to
twenty carbon atoms, such as ethyl, propyl, t-butyl, dodecyl,
eicosanyl. Preferably R' is ethyl or isopropyl, with
isopropyl being the most preferred.
When an organic ester is used in the carbonylation
process described herein, any one of the esters mentioned
1 15~256
- 5 -
herein may be used. It is preferable, however, to use iso-
propyl isobutyrate (2-propanol 2-methylpropionate), ethyl
isobutyrate (ethanol 2-methylpropionate), isopropyl pro-
pionate (2-propanol propionate) or ethyl propionate (ethanol
propionate), and it is especially preferred to use lsopropyl
isobutyrate or ethyl propionate.
Examples of organic compounds having at least one
double bond capable of forming an acylium anion product
therewith (carbonylating to an acylium anion product) which
lQ may be used in the process described herein are olefins of
up to twenty carbon atoms, such as ethylene, propylene,
butenes, 1,3-butadiene, and dodecene. The olefins may be
substituted with alkyl, or aryl, or cycloalkyls, or other
substituents which do not interfere in the process described
herein. Furthermore, the olefins may have multiple double
~onds within the molecule which does not interfere in the
process described herein such as 1,3-butadiene. Preferred
olefins are ethylene, propylene, isobutene, l-butene, 2-
butene, and 1,3-butadiene, and ethylene and propylene are
hi~hly preferred.
Although all of the organic compounds described
herein may be ùsed in the process described herein, propylene,
however, is especially preferred.
The acids used for the preferred process to make
the acylium anion described herein should be substantially
free from water; that is, anhydrous. The term "anhydrous"
as used herein and in the claims refers to acids which are
substantially free from water, e.g., less than 200 ppm of
water, or if water is oresent, it does not interfere with
the reaction to form the acyLium anion, or the carboxylic
ester therefrom.
The anhydrous acids which may be used for the
described process are:
hydrogen fluoride (hydrofluoric acid) tHF) and
hydrogen chloride (hydrochloric acid) tHCl).
1 15~256
-- 6 --
The most preferred anhydrous acld for the process described
herein is hydroaen fluoride (hydrofluoric acid).
ALCOHOLS FOR ESTERIFYING THE ACYLIUM ANION PRODUCT
The alcohols used for the esterification process
described herein may be any primary or secondary alcohol
which does not decompose under the esterification and separa-
tion conditions, and which generates the anhydrous acid
without reacting with the regenerated acid. Examples of
such alcohols are alkanols of up to twenty aarbon atoms.
Preferred alkanols are those having up to five carbon atoms.
Highly preferred alcohols are methanol, ethanol, and propanol.
The most preferred alcohol is methanol.
REACTION CONDITIONS TO FORM THE ACYLIUM ANION PRODUCT
The reaction of carbon monoxide, with an organic
compound described herein and an anhydrous acid described
herein, can occur at temperatures of from zero degree Centi-
grade (0C) to one hundred degrees Centigrade ~100C), the
upper temperature bein~ determined by side product formation.
For the reaction between the preferred reactants described
herein, the temperature can be from forty degrees Centiarade
(40C) to eighty degrees Centigrade (80C), but preferably
it is at about sixty degrees Centigrade (60C). The carbon
monoxide pressure can vary from 14.? psia to about 6,000 psia,
or to 10,000 psia, but generally it is from 500 psia to 5,000
psia, and preferably from l,500 psia to 3,000 psia, the pres-
sure being increased as required for the solubility of carbon
monoxide in the anhydrous acid and to incrsase the productivity
of the reactor.
The mole ratio of anhydrous acid to the organic
compound described herein should be from ~:l to 100:1, but
generally it is from 10:1 to 20:1 and preferably about 15:1.
The mole ratio of carbon monoxide to the organic compound
described herein is from l:l to 5:1 or higher, but preferably
1 15~256
- 7 -
it is from 1.5:1 to 1:1 and the maximum correspondc to the
saturation limit of carbon monoxide in the reaction mixture
during and at the end of the reaction.
All of the carbon monoxide and anhydrous acid,
e.g., anhydrous hydrogen fluoride, which is to be reacted
with the organic com~ound, should be thoroughly mixed prior
to contacting with the organic compound descxibed herein,
e.g., propylene. The organic compound is then reacted while
mixing with the premixed carbon monoxide and acid. Generally,
the reaction depending upon the pressure and the temperature,
will occur within minutes to form an acylium anion product,
e.g., isobutyryl fluoride. The organic compound itself can
be diluted with carbon monoxide or inert diluents, e.g.,
methane, ethane, propane, prior to reaction with the anhydrous
acid.
The reaction can be conducted in a semi-batch
reactor, plu~ flow reactor, back mix reactor ~CSTR), or other
reactor known to those skilled in the art, ~ut the preferred
reactor is a plug flow reactor.
THE ESTERIFICATION PROCESS mo FORM THE CAR~OXYLIC ACID ~STERS
The esterification reaction of the acylium anion
product, e.g., isobutyryl fluoride, with an alcohol, particu-
larly, methanol, can occur at temperatures from twenty degrees
- Centigrade (20C) to one hundred fifty degrees Centigrade
(150~C) and at pressures from one (1) bar (14.7 psia) to
three hundred forty (340) bars (5,000 psia), but normally it
occurs at temperatures from forty degrees Centigrade (40C)
to seventy degrees Centigrade (70~C) and pressures at three
and three tenths (3.3) bars (50 psia) to six and seven tenths
(6.7) bars (100 psia). The temperature and pressure beinq
set to avoid the decomposition of the intended products, and
to facilitate product separations.
It is preferred that the reactants be stirred during
esterification. In many cases, when rapid mixing is used,
.
115~256
the esterification reaction with the concurrent regeneration
of the anhydrous acid, e.g., HF, can be completed within
seconds to minutes.
The critical feature of the esterification reaction
S is maintaining the mole ratio of alcohol, e.g., methanol, to
the acyLium anion product below 1:1; that is, the total
amount of alcohol reacted with the mixture comprised of the
acylium anion product must be less than the amount of alcohol
required for all of the acylium anion product to form the
carboxylic acid ester.
The total amount of alcohol may be injected into
the mixture comprised of the acylium anion product, but
preferably the alcohol is added in partial amounts into the
mixture comprised of the acylium anion product. The esteri-
fication step is exothermic, and thus cooIing may be required.The mixture may also contain carbon monoxide, unreacted
organic compound, anhydrous acid, and carboxylic acid ester.
Preferably the mixture contains anhydrous acid, particularly
when the acylium anion product is isobutyryl fluoride. When
the acylium anion product such as isobutyryl fluoride is
esterified, the ratio of the amount of anhydrous acid, e.g.,
hydrogen fluoride, to isobutyryl fluoride is in the range
from 0.01 to 95.5 parts by weight of anhydrous hydrogen
fluoride (AHF) to 99.09 to 4.5 parts by weight of isobutyryl
fluoride (IBF), but preferably from 10.0 to 90.0 parts by
weight of AHF to 90 to lO parts by weight of I9F. The amount
of anhydrous acid, e.g., hydrogen fluoride, in the mixture
is dependent upon the efficient operation of the process,
and the ease o~ se~arating the anhydrous acid, e.~., hydrogen
fluoride, from the product mixture comprised of the acylium
anion product, e.g., isobutyryl fluoride, hydrogen fluoride,
carbon monoxide, and alkyl isobutyrate, such as methyl
iso~utyrate.
After the esterification reaction is complete,
; 35 which depends upon the reaction conditions from one (1) to
1 15~256
g
one hundred ~100) percent of the carboxylic acid ester
formed is separated from the product mixture of the esteri-
fication reaction. Preferably from eighty (80) to one
hundred (100) percent of the carboxylic acid ester is
separated, and the remaining esterified product mixture
is recycled for further reaction with the reactants to form
more acylium anion product. This recycle stream may contain
carbon monoxide and/or anhydrous acid and/or unreacted
organic compound and/or the unesterified acylium anion
product.
In another embodiment of the invention, from one
(1) to one hundred (100) percent (preferably from eighty (80)
to one hundred (100) percent) of the anhydrous acid is
separated from the esterification product mixture and is
recycled back for reaction to form more acylium anion product.
The recycle stream may contain small amounts of unseparated,
unesterified acylium anion product and/or carboxylic and
; ester and/or unreacted organic compound.
The separation can be by any of the known methods
of separation, such as distillation or solvent extraction.
Preferably, distillation is used.
The preferred embodiment for producing the
carboxy}ic acid esters described herein comprises: Esteri-
fying an organic acylium anion product, described herein,
with an alcohol, described herein, under substantially
anhydrous conditions and separating the carboxylic acid ester,
unreacted alcohol, anhydrous acid, and unreacted acylium
anion product under conditions whereby the esterification
continues to substantial completion.
The process can further comprise esterifying while
separating eighty ~80) percent to one hundred ~100) percent
of the anhydrous acid ~preferably ninety ~0) percent to one
hundred ~100) percent) and recycling the separated anhydrous
acid to form more acylium anion product.
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-- 10 --
The process preferably can further comprise esteri-
fying while separating from the esterification mixture from
ninety (90) percent to one hundred (100) percent of the
carboxylic acid ester, and from eighty (80) percent to one
hundred (100) percent of the anhydrous acid, and recycling
the separated anhydrous acid to form more acylium anion
product.
Preferably the separating while esterifying occurs
by distilling the esterification reaction mixture under
conditions whereby the esterification of the acyLium anion
product continues to substantial completion; that is, from
eighty (80) percent to one hundred (100) percent of the
acylium anion product is esterified to a carboxylic acid
ester, and preferably from ninety (90) percent to one hundred
(100) percent. The distilling conditions are such that the
formation of side products is substantially reduced. Also
the distilling conditions are such that the halogen acids
especially HF are removed so as to substantially reduce the
formation of halogenated side products. Preferably the
esterification yields are substantially from eighty (80)
percent to one hundred (100) percent, with ninetv (90)
percent to one hundred (100) percent being highly preferred.
ESTERIFICATION REACTOR AMD SEPARATOR
A schematic diagram of a preferred esterification
and separation apparatus is shown in Figure 1, which is
adaptable to the esterification process described herein,
but is especially useful for the esterification of isobutyryl
fluoride with methanol to methyl isobutyrate. The acylium
anion product, e.g., isobutyryl fluoride source 20, is fed
30 by line 30 through the metering pump 32 via line 34, valve 36
and line 38, into the esterification reactor 40 where it
reacts with the alcohol, e.g., methanol. The alcohol is fed
from the alcohol feed source 42 through the metering pump 44
'
2 5 6
-- 11 --
to the esterification reactor 40 via lines 46, valve 48, and
line 50. The feed of the acylium anion product (e.g.,
isobutyryl fluoride) and alcohol (e.g., methanol) enter the
esterification reactor 40 through dispersion nozzles (not
shown) connected to lines 38 and S0 respectively. The
esterification reactor 40 can be equipped with baffles or
other means for insuring rapid mixing of the reactants.
The reaction mixture from the esterification reactor 40
enters the distillation column 52 via line 42 at point 56
which is located between the reflux entry point 58 and above
the removal point 60 of the liquid phase. The distillation
column 52 is operated to remove the unreacted organic carbon
monoxide acid anion, e.g., isobutyryl fluoride, the unreacted
alcohol, e.g., methanol, and the regenerated acid, e.g.,
lS hydrogen fluoride, and to cause the esterification reaction
which begins in the esterification reactor 40 to be completed
within the distillation column 52. This distillation column
52 shown in Figure 2 with its feed and take off points is
particularly applicable to the substantially anhydrous
methanol esterification of isobutyryl fluoride. However,
the feed and take off points can readily be modified as known
to those skilled in the art so as to be adaoted to anhydrous
esterification by other alcohols. For example, if the boiling
point of the ester is below that of the anhydrous acid, the
take off of ester would be at the top of the column while
that of the anhydrous acid would be below.
The liquid phase containing unreacted alcohol
(methanol) and/or acylium anion addition product (e.g.,
isobutyryl fluoride) and/or hydrogen fluoride and~or ester
(e.g., methyl isobutyrate) is removed at take off point 60
and passes through line 62 into the heat exchanger 64 where
it is cooled if necessary and passes through line 66 into
; metering pump 68 through line 70 into the esterification
reactor 40. The acylium anion product, e.g., isobutyryl
fluoride, combines to react with the alcohol, e.g., methanol,
1 15~256
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during the stripping operation which occurs between the feedpoint 56 and the liquid stream take ofC point 60, so that it
is substantially converted to the ester, e.g., methyliso-
butyrate, which moves downward through the stripping section
and is removed from the distillation column 52 at outlet 72
and passes through line 74 into storage container 76. A
slip of the crude product passing through line 74 can be
returned via line 78 through heat exchanger 80 and line a2
to reenter at 84 into the distillation column 52. The anhy-
drous acid (e.g., hydrogen fluoride) which is regenerated bythe esterification reaction passes up and through the distil-
lation column S2 and is removed overhead at outlet 86, and
passes through line 88 in the heat exchanger 90 where it is
partially or totally condensed, and passes through line 92
into separator 94. The anhydrous acid (e.g., hydrogen
fluoride) passes through line 96 into storage unit 98 or 102
for reuse to make more acylium anion product. The separator
bottoms pass out of the separator bottom via line 96 and
part or all return via line 9~ to the distillation column at
point 58 for reflux. Operation of the condenser and separator
can be specified by those ski~lled in the art to assist in
the removal of impurities and/or side products which are
either more or less volatile than hydrogen fluoride (HF).
In another embodiment of the invention, it is
possible to add via line 104 a secondary solvent to act as
stripping agent to enhance the removal of the acylium anion
addition product (e.g., isobutyryl flu!oride) from the ester,
e.g., methyl isobutyrate, thereby eliminating the exchanger
64 and placing the entire energy load on exchanger 90.
In anotner embodiment o~ the invention, the level
of point 60 can be selected so as to eliminate exchanger 64
and placing the entire energy load on exchanger 90.
In another embodiment of the invention, a solvent
is added co-currently with the alcohol, e.g., methanol, into
the esterification reactor 40, to assist in diluting and
mixing the alcohol in the reaction mixture and to enhance
1 156256
- 13 -
the stripping of the regenerated anhydrous acid ~e.g., HF),
and is removed through purge 102. The solvent used is inert
to the reactants under the reaction and separation condi-
tions, and does not azeotrope with the ester, e.g., methyl-
isobutyrate or the anhydrous acid, hydrogen fluoride, andhas a boiling point which is intermediate between the anhy-
drous acid, e.g., HF, and the ester, e.g., methyl isobutyrate,
so that separation is enhanced, preferably the solvent has a
low heat of vaporization. Useful solvents for the esteri-
fication and separation of isobutyryl fluoride esterifiedwith methanol are the hydrofluoroalkanes, having up to twenty
carbon atoms, but preferably those of up to five carbon atoms.
EXAMPLES
, .
The following examples will illustrate the inven-
tion described herein.
The following procedure was used to study theesterification of isobutyryl fluoride based on less than
the amount of methanol required to esterify all of the iso-
butyryl fluoride to methyl isobutyrate, under semiadiabatic
conditions.
A two-liter Hastello~ C Parr reactor, equipped with
a methanol delivery system (used nitrogen at 500 psia), a
thermocouple connected to a continuous temperature recorder,
and an air motor and stirrer adjusted to rotate at 1,000
revolutions per minute, was charged with a weighed amount of
reactant anhydrous hydrogen fluoride (if used) and isobutyryl
fluoride (maintained at dry ice-acetone temperature). After
charging, the reactants and reactor are brought to the pre-
selected temperature, and the temperature recorder i9 star~ed.
The weighed amount of methanol (less than the amount required
for reaction of all of the isobutyryl fluoride) is then
injected into the reactor. The initial temperature of the
methanol was at room temperature. After esterification was
complete, the mixture was analyzed by gas chromatography.
* Trade Mark
i
1 15625~
- 14 -
From the temperature-time recording, the temperature rises
were noted. Generally, the first was attributed to the heat
of mixing, and the second was attributed to the esterifica-
tion reaction.
s Example I
isobutyryl fluoride, IBF (419.3 arams; 4.66 moles)
at 26C was esterified by injecting 131.2 grams of methanol
(at 21 a C). The reaction mixture temperature initially
dropped then rose to 64.6C over the next 5.25 minutes. The
reaction was complete, and GC analysis showed only anhydrous
hydrogen fluoride tl82 grams; 4.1 moles) and methyl isobuty-
rate (418.2 grams; 4.1 moles) formed, with 50.3 grams (0.56
moles) of isobutyryl fluoride was unreacted.
Example II
A mixture of 46.6 grams of anhydrous hydrogen
fluoride (10 wt. percent) and 422.6 grams of isobutyryl
fluoride (90 wt. percent) at 29.3C was esterified with 133
grams of methanol at 21C. ~The methanol was added in one
slug.) A temperature rise of 20.7C was obser~ed, followed
20 by temperature to 128C over the next 38.4 seconds. The
reaction was complete, the GC analvsis showed methyl isobuty-
rate (416.0 grams), anhydrous HF (134.3 grams), and unreacted
; isobutyryl fluoride (51.8 grams).
Example III
A mixture of 540.4 grams anhydrous hydrogen fluoride
and 59.9 grams isobutyryl fluoride at 30C Centigrade was
esterified by adding 18.6 grams of methanol (at 22C) in one
slug. Under these conditions, after 1.5 9econds, the
temperature rose continuously from 30C to 49.5~C. The
reaction was complete, the analysis showed that 58.2 grams
of methyl isobutyrate was formed. The amount of anhydrous
HF wa~ 552.7 grams, and the unreacted iso~utyryl fluoride
was 8.0 grams.
.
1 156256
- 15 -
Example IV
The following continuous process can be conducted
to produce methyl isobutyrate by the process described
herein.
A plug flow reactor is used for the ormation of
isobutyric acid _rom propene. It is formed from a forty (40)
foot tube having a one-half (1/2) inch internal diameter,
with a premix section of about five (5) feet and equipped
with injection points at five-foot inter~als and a heater.
The carbonylation reaction is conducted at 50C and 2,800
psig, with propene, anhydrous hydrogen fluoride and carbon
monoxide in a mole ratio of 1.0:14:1.3, at a flow rate of
3.2 lbs per hour (1.52 kilograms per hour). The anhydrous
hydrogen fluoride and carbon monoxide is injected into the
premix section where they are thoroughly mixed, and the
propene is injected into the mixture of anhydrous hydrogen
fluoride and carbon monoxide at five-foot intervals, with the
final addition being 30 feet from the beginning of the
reactor. After the reaction is complete, at the 35-foot
injection point, methanol is injected into the reactor where
the esterification occurs preferably at the rate at which
esterification occurs and methyl isobutyrate is formed. The
amount of methanol injected is less than the amount of iso-
butyryl fluoride formed. This section of the reactor where
the esterification occurs is maintained at approximately 40C
and at a pressure of 100 psig. The methylisobutyrate is
separated from the final product mixture by simple distilla-
tion, and the remaining isobutyryl fluoride, carbon monoxide
and anhydrous hydrogen fluoride is recycled with the carbon
monoxide and anhydrous hydroqen fluoride that are being
in~ected into the premix section o.f the reactor.
In another embodiment of the continuous reaction,
prior to esterification, the product mixture containing the
acylium anion product (isobutyryl fluoride) is passed to a
separation unit where the excess carbon monoxide and from
1 156256
- 16 -
ten to ninety percent of the excess anhydrous hydrogen
1uoride is removed, and recycled, while the remaining
product mixture preferably having 10 part~ by weight of
anhydrous hydrogen fluoride to 90 parts by weight of iso-
butyryl fluoride is esterified as described herein followedby separation of methylisobutyrate and recycling of the
remaining product mixture of unreacted isobutyryl fluoride
and anhydrous hydrogen fluoride.
FORMATION OF METHYLACRYLIC ACID OR METHYL METHAC~YLIC ACID
The methyl ester of the carboxylic acid of propionic
acid or isobutyric acid formed from acylic anion product,
e.g., propionyl fluoride or isobutyryl fluoride, after
esterification, as described herein, can be oxydehydro-
genated by the process described in U.S. patents 3,585,248;
3,585,249; 3,585,250; 3,634,494; 3,6~2,654, 3,660,514;
3,766,191; 3,781,336; 3,7~4,483; 3,855,279, 3,91~,673;
3,948,959; 3,968,149, 3,975,301; 4,029,695; 4,061,673;
4,081,465; 4,088,602; and British patent 1,447,593.
Preferably the catalyst is comprised of iron,
phosphorous, and oxygen as defined by the empirical formula,
Fe Px z~ where relative to one (1) atom of Fe, x represents
from 0.25 to 3.5 atoms of phosphorous, and z represents the
number of oxygen atoms required to satisfy the valence
requirements of the catalyst. More preerred catalysts are
those described in U.S. patent 3,948,959, which have a
promoter represented by Mey wherein Me represents the
promoter of Li, Na, R, Rb, Ce, Mg, Ca, Sr, Ba, and mixtures
thereof, and y represents the number of promoter atoms
relative to one atom o iron and is from 0.01 to 2Ø The
methyl acrylate or methyl methacrylate is then separated by
techniques known in the art, e.g., distillation in the
presence of a polymerization inhibitor, or by extraction.
, While the invention has been described with refer-
ence to specific details of certain illustrative embodiments,
1 15~256
it is not intended that it shall be limited thereby except
insofar as such details appear in the accompanying claims.
