Note: Descriptions are shown in the official language in which they were submitted.
7 ~ 5
2~-19-1266
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BACKGROUND OF THE INVENTION
The present invention relates to a carbonyla-
tion process improvement. More particularly, this inven-
tion relates to an improved process scheme wherein at
least a por~ion of the reaction mass from a carbonylation
process can be withdrawn from the reactor and separated
at a lower pressure from a catalyst-con`taining stream
which is recycled to the reactor. In this processing
scheme the catalyst is stabilized in soluble form and any
of the catalyst which may have precipitated is reconverted
to a soluble form.
Recently, processes for producing carboxylic
acids and esters by carbonylating olefins, alcohols, esters,
halides and ethers in the presence of homogeneous catalyst
systems that contain rhodium and halogen components such
as iodine components and bromine components have been dis-
closed and placed into commercial operations. These re-
cently developed processes represent a distinct improve-
ment over the classic carbonylation processes wherein such
feed materials have been previously carbonylated in the
presence of such catalyst systems as phosphoric acid, phos-
phates, activated carbon, heavy metal salts and metal car-
bonyls such as cobalt carbonyl, iron carbonyl and nickel
carbonyl. All of these previously known processes require
$~
7 ~ ~
20-19-1266
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the use of extremely high partial pressures of carbon
monoxide. These previously known carbonylation systems
also have distinc-t disadvantages in that they require
higher catalyst concentrations, longer reac~ion times,
higher temperatures to obtain substantial reaction and
conversion rates that all result in larger and more costly
processing equipment and higher manufacturing costs.
The discovery that rhodium and iodine or bro-
mine containing catalyst systems will carbonylate such
feed materials as olefins, alcohols and esters, halide or
ether deriva~ives of the alcohols at relatively mild pres-
sure and temperature conditions was a distinct contribu-
tion to the carbonylation art. In spite of the vast
superiority of these newly developed catalyst systems, it
has been found that conventio~al processing schemes for
separation of the carbonylation products from the liquid
reaction mass has posted problems of catalyst inactiva-
tion and precipitation from carbon monoxide-deficient
streams.
It has been disclosed to U.S. Patent 3,845,121
that by withdrawing a portion of the liquid reaction mass
from the reactor and passing it to a separation zone of
substantially lower pressure, without the addition of heat,
at least a portion of the carbonylation products can be
vaporized and passed on to purification equipment with much
reduced decomposition of the carbonylation catalyst system.
According to ~his scheme, the carbonylation reaction is
carried out in the reaction zone at a temperature o~ from
about 50 to about 500C and a pressure of from about 345
to about 10340 kPa. By withdrawing a portion of the liquid
reaction mass and passing it to a separation zone that is
maintained at a pressure that is substantially lower than
the pressure in the reactor, at least a portion of the car-
bonylation products will vaporiæe with much reduced decom-
position of the liquid catalyst system. This vaporization
will take place without the addition of heat to the re-
action mass. The unvaporized liquid in the separation zone
725
.3
containing the catalyst system can be recycled to the reactor.
Using this processing scheme, it has been found that
catalyst precipitation may occur, though to a reduced degree,
from liquid streams which are deEicient in carbon monoxide.
Such streams include the stream of reaction mass withdrawn from
the reaction zone, in which CO has been consumed by reaction,
and the liquid cycle stream returned from the separation zone
to the reaction zone.
From U.S. Patent 3,818,060 it is known th~t penta-
valent nitrogen and phosphorous compounds of the form ~NR3 orXP~3 wherein X is oxygen or sulfur may be used as stabilizers
for rhodium catalysts in the liquid phase carbonylation of
ethylenically unsaturated compounds. Also, from U.S. Patent
3,579,552 it is known that, inter alia, phosphines, amines and
trihalostannate compounds form coordination complexes with rho-
dium and carbon monoxide which remain soluble in the carbonyla-
tion of ethylenically unsaturated compounds.
Accordingly, it is an object of this invention to pre-
vent precipitation of the soluble catalyst system from CO-
deficient streams.
Additional objects of this invention will becomeapparent from the following discussion of the invention.
~a~v~
-3a-
SUMMARY OF THE INVENTION
The present invention iæ an improvement in a carbonyl-
ation process wherein at least one reactant selected from the
group consisting of an alcohol, an ester derivative of said al-
cohol, a halide derivative of said alcohol and an ether deriva-
tive of said alcohol is reacted with carbon monoxide in a li-
quid phase in a reaction zone in the presence of a catalyst
system that contains (a) a rhodium component, and (b) an iodine
or bromine component. Such a process further includes the
steps of passing at least a portion of the liquid reaction mass
in which the carbon monoxide has been depleted from the
reaction zone to a separation zone and recycling the remaining
liquid reaction mass from the separation zone to the reaction
zone. In accordance with an embodiment oE the present
inYentiOn, the improvement in the above process comprises
adding to the process an amount of a compound of an element
selected from tin, germanium, antimony or an alkali metal
soluble in the reaction mass, said amount being sufficient to
maintain the rhodium component in soluble formO
In a carbonylation process, generally at least
a portion of the carbonylation products are separated
from the liquid reaction mass at a reduced CO partial
pressure in a separation zone. From this separa-
~ S 20-19-1266
tion zone, an unvaporized liquid stream which is enriched
in the catalyst system components is withdrawn and recycled
~o the reaction zone for reus~ in the carbonylation pro-
ces~. A recycle pump is employed to increase the pressure
of this liquid stream to enable its transfer back into the
high pressure reaction zone.
Under the conditions of reduced CO partial pres-
sure existing in the separation zone and piping connecting
the separation zone to the reaction zone, a small portion
lQ of the catalyst system may decompose, forming an insoluble
rhodium containing precipitate. According to the present
invention, a compo~md of tin, germanium, antimony or an
alkali metal is employed as a catalyst stabilizer for rho-
dium catalysts in the carbonylation of methanol. Prefer-
ably, the stabilizer compound is employed in a molar ratioof at least about 0.5 to the rhodium present.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention is directed to the recently de-
veloped carbonylation processes wherein oleins, alcohols
and ester, halide and other derivatives of the alcohols
are reacted with carbon monoxide in a liquid phase system
in the presence of a homogeneous catalyst system that con-
tains (a) a rhodium, and (b) an iodine or bromine compon-
ent.
This invention solves the catalyst precipitation
problems which may be encountered in the process of separa-
tion of the carbonylation products from the liquid mass
which involves withdrawing at least a portion of the liquid
reaction mass from the reactor and passing it to a separa-
tion zone that is maintained at a substantially lower pres-
sure. The lower pressure in the separation zone results
in the vaporization at at least a portion of the carbony-
lation products which are then withdrawn from the separa-
tion zone in the vapor form. The unvaporized liquid in the
separation zone containing the stable catalyst system can
then be recycled to the reactor for reuse in the carbony-
lation process~ According to this invention, the rhodium
carbonyl halide catalys~ complex is s~abilized by addition
)'7~
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of a compound of tin, germanium, antimony or an alkali
metal. The stabilizer compound is preferably employed in
a molar ratio of at least 0.5 to the rhodium present.
When reference is made to the "catalyst system"
throughout this disclosure of this invention, it means a
catalyst system that forms on combining two distinct compo-
nents in the presence of carbon monoxide. The two essen-
tial catalyst precursor materials are (a) a rhodium, and
(b) an iodine or bromine component while C0 is a third com-
ponent.
Rhodium components suitable for use as constitu-
ents in the catalyst are described and set Ollt in U.S.
Patent 3,845,121.
The iodine or bromine precursor component of the
catalyst system used herein may be in combined form with
the rhodium as1 for instance, one or more ligands in a co-
ordination compound of the rhodium. However, it is gener-
ally preferred to have an excess of the iodine or bromine
present in the reaction system over the iodine or bromine
that exists as ligands of the rhodium compounds. The bro-
mine or iodine precursor can be in the form of elemental
bromine or iodine as well as combinations of bromine or
iodine such as hydrogen iodide, hydrogen bromide, alkyl
iodide, alkyl bromide, aryl iodide, aryl bromide, iodide
salts, bromide salts and the like. Suitable non-limiting
examples of such compounds of bromine and iodine include
methyl iodide, methyl bromide, ethyl iodide, ethyl bro-
mide, sodium iodide, potassium iodide, sodium bromide,
potassium bromide, ammonium iodide, ammonium bromide and
the like.
Generally, it is preferred that the amount of
iodine precursor material added to the reactlon system
will be in an amount such that the atomic ratio of the
iodine or bromine to the rhodium is about 2:1. Prefera-
bly, the a-tomic ratio of the iodine or bromine to the rho-
dium will be in a range of 5:1 to 5000:1. A more pre-
ferred atomic ratio of the iodine or bromine to the rho-
dium is 10:1 to 2500:1O
~B~ 7~5
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Suitable sources o:E tin stabilizer components in-
clude, but are not limited to tin metal, stannous chlor-
ide, stannous oxide, organo tin compounds such as tetral-
kyl tin, stannic chloride, stannic oxide, stannous acetate
and the like. The valence of the tin in the tin component
may be 0, 2 or 4.
Other suitable stabilizer compounds, according
to this invention, include but are not limited to the ha~
lides, acetates, oxides, salts and the like of germanium,
antimony and al~ali metals.
The catalyst system forms by combining the fore-
going rhodium and halogen in the presence of carbon mon-
oxide in a liquid reaction medium. The liquid reaction
medium employed may include any solvent compatible with
the catalyst system and may include pure alcohols or mix-
tures of the alcohol feedstock and/or the desired carboxyl-
ic acid and/or esters of these two compounds. However,
the preferred solvent or liquid reaction medium for the
process of this invention is the desired carbonylation pro-
ducts such as the carboxylic acid and/or ester of the acid
and an alcohol. Water is also often in the reaction mix-
ture to exert a beneficial effect upon the reaction rate.
Suitable feedstock materials for the process are
set out in U.S. Patent 3,845,121.
Methanol and ethylene are two of the most pre-
ferred feedstocks that are utilized in the practice of our
invention.
In carrying out the carbonylation reaction, the
above-mentioned feedstocks are intimately contacted with car-
bon monoxide in a liquid reaction medium that contains the
above-mentioned catalyst system. The catalyst system can be
preformed outside of the reactor by combining the necessary
catalyst precursors or it can be formed in situ.
Generally, the catalyst will be employed in such amounts as
to provide a concentration of soluble rhodium in the
reaction medium of from about 10 ppm to about 3000 ppm de-
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20-19-1266
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pending upon ~he equipment size, desired reaction time and
other factors. The carbon monoxide reactant can be sparged
into the reactor in such a manner as to intimately contact
the carbon monoxide with the reactants in the reaction
mass. The pressure in the reactor will generally be main-
tained in the range of -from 345 to about 10340 kPa. As
disclosed in the prior art, the foregoing known carbony-
lation process is carried out at a temperature range of
from about 50C to about 500C with a preferred temperature
range of from about 100 to about 250C. The optimu~ tem-
perature and pressure maintained in ~he reactor will vary
depending upon the reactants and the particular catalyst
system utilized. The catalyst, feedstock materials and
general reaction parameters set out in the foregoing dis-
cussion are known inthe art.
A portion of the liquid phase reaction mass is
withdrawn from the reactor and passed to a separation zone
that is maintained at a pressure that is lower than the
reactor pressure. This pressure reduction will cause at
least a portion of the carbonylation products to vaporize
and separate from the unvaporized residue of the liquid
reaction mass. The aforementioned catalyst system will
remain in this residue of unvaporized liquid reaction mass
and can be recycled to the reactor.
Generally, it is preferred that the separation
zone be maintained at a pressure of at least 138 kPa lower
than the pressure in the reactor. The pressure in the
reaction is usually in the range of about 345 to 10340 kPa.
Thus, the separation zone is maintained at a pressure less
than 10200 kPa. It has been found that the separation
zone can be maintained at very low pressure, even approach-
ing a complete vacuum; however, it is usually desirable
that the separation zone be maintained at a positive pres-
sure to eliminate vapor compression equipment and the like
in handling the vaporized carbonylation products that are
withdrawn from the separation zone. By maintaining pres-
sure differential of at least 138 kPa between the reactor
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20-19-1266
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and the separation zone, a substantial amount of the car-
bonylation products can be vaporized from the liquid reac-
tion mass.
The exac~ pressure of the separation zone will
vary, depending on ~he temperature and pressure maintained
in the reactor. It is important that the pressure differ-
ential between the separation zone and the reactor be at
least 138 kPa to insure vaporization o a substantial por-
tion of thP carbonylation products in the separation zone.
It is also important that the total pressure in the separa-
tion zone be less than the vapor pressure of the carbony-
lation products in the liquid reaction mass withdrawn from
the reactor at the temperature of the liquid reac~ion mass.
For example, if at the temperature and pressure of the re-
actor the carbonylation products to be vaporized have avapor pressure of 1380 kPa, the separation zone should be
operated at a pressure of less than 12~0 kPa. Preferably,
the separation zone of this invention will be operated at
a pressure of from about 69 to 1380 kPa. Most preferably,
the separation zone will be operated at a pressure of about
100 to 690 kPa.
The separation zone should be large enough ~o
allow the liquid reaction mass that is passed to it from
the reactor to be maintained in said separation zone for
a suficient period o~ time to vaporize the desired car-
bonylation products, prior to recycling the unvaporized
liquid containing ~he homogeneous catalyst system back to
the reactor. Usually, a residuce time of at least one
minute in the separation zone is sufficient.
Following separation of the desired carbonyla-
tion products, the unvaporized liquid portion of the reac-
tion mass containing any precipitated catalyst decomposition
products leaves the separation zone and is introduced into
the suction of a recycle pump which increases the pressure
of this stream sufficiently to permit its injection back
into the reaction zone.
3~7~S . 20-19 -1266
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The piping ~hrough which a portion of the reac-
tion mass is withdrawn from the reaction zone, as well as
the piping thTough which the liquid recycle stream is
~ransferred back to the reaction zone by the recycle pump,
will be at substantially the pressure of the reaction zone.
As used herein, "substantially the pressure of the reaction
~one" means the reaction zone pressure plus or minus pres-
sure changes caused by fluid flow through the respective
lines. ,,
Depending upon the temperature and pressure of
the transfer piping, a minor amount of the carbonylation
catalyst system according to the prior art (i.e., not in-
cluding ~he stabilizer component of the present invention,
may decompose and precipitate from the liquid in the piping.
The catalyst system is believed to comprise a carbonyl com-
plex of the rhodium component and ~he halide component
and it is further believed that carbon monoxide may be
abstracted from a portion of the carbonyl'complex form of
the catalyst system converting some of the catalyst to an
insoluble form which may comprise a rhodium halide. Be- I
cause the rhodium component of the catalyst system is quite
expensive, it is desirable to recover any traces of pre-
cipitated catalyst for return to the reaction zone and re-
use.
~ According to the present invention, the rhodium
catalyst is maintained in soluble form in these caTbon
monoxide deficient portions of the process by addition to
the system of a compound of tin germanium, antimony or an
alkali metal.
~' The stabilizer compound is employed in a molar
ratio of at least abou* O.i to the rhodium present in the
catalyst system. The stabilizer compound may be injected
into the caTbonylation reaction system at any convenient
point, but is pre~erably injected into the transfer piping
leading from the carbonylation reactor to the separation
zone, or int~o the piping which conducts the catalyst-
20-19-1266
-10
containing recycle stream from the separation zone back
to the reactor, in order to insure complete mixing of the
stabilizer with the catalyst-containing liquid system.
The practice of this invention is illustrated
by the following examples which should not be construed
as limiting the invention in any way.
In the following examples a stock solution was
prepared which simulated the liquid recycle stream which
is returned from the separation zone to the carbonylation
reac~or in a typical acetic acid plant. Included in this
solution were traces of iron, nickel, chromium and molyb-
denum which are normally found in acetic acid plants as
corrosion products. The stock solution employed acetic
acid as the solvent and contained the following:
Iron 0.025 moles/liter
Nickel 0.02 " ~
Chromium 0.016 " "
Molybdenum 0.01 " "
Water 9.5 " "
Total iodides 0.5 " "
Labile methyl 0.35 " "
groups (methyl
iodide+methanol
-~methyl acetate)
EXAMPLE 1
To establish a base run in which no tin com-
ponent stabilizer was present, the following experiment
was performed. About 650 milliliters of the stock solu-
tion described above plus a rhodium solution and hydrogen
iodide was charged into a 1500 milliliter stirred auto-
clave and pressured with carbon monoxide to a pressure of
791 kPa. The contents were heated with stirr{ng and when
a temperature of 150-155C was reached methanol and methyl
iodide were added. The autoclave contents were then im-
mediately cooled to 125-128C under a pressure of 205
kPa, refluxed, and were sampled and found to contain 444
parts per million (ppm) dissolved rhodium.
~3~7 ~ S
20-19-1266
The autoclave contents were sampled periodi-
cally and analyæed for dissolved rhodium. The results of
these analyses were as follows:
Time Ater Methanol ppm Dissolved % af Original
Addition (minutes? _Rhodium Dissolved Rhodium
63249 56
93166 37
15379 18
This experiment clearly demo~strates tha~ in
the absence of a catalyst stabilizer the rhodium rapidly
precipitates from the solution in the autoclave.
EX~MPLE 2
Using the equipment and procedure of Example 1,
the base case run was repeated except that the autoclave
solution contained 0.00512 mols/liter of anhydrous SnC14.
Total iodine and total labile methyl groups were as in
Example 1 initially. Initial dissolved rhodium was 434
ppm. Samples were taken and analyzed periodically while
the temperature was maintained at 125-126C and the fol-
lowing results obtained.
Time After Methanol ppm Dissolved % of Original
Addition (minutes) Rhodium Dissolved Rhodium
62 462 106
128 462 106
These results clearly indicate that the tin
stabilizer greatly retarded the rate of rhodium precipita-
tion from the autoclave solution.
EXAMPLES 3-7
~0 To show the variety of tin components which
may be used ~s stabilizers, the experiment of Example 1
was repeated except that the autoclave solution contained
the tin components shown in the following Table as a stabi-
lizer. The initial total iodine level and the initial
total labile methyl groups were as in Example 1 and the
initial dissolved rhodium was as shown in the Table. Peri-
odic samples for dissolved rhodium gave the results shown.
In all cases, the tin component was present in a concen-
tration of 0.0045 moles/liter, except in Example 3 th~
tin component concentration was 0.0046 moles/liter.
3~1t7~5
20 - 19 -1266
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20-19~1266
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EXAMPLE 8
Usîng the equipment and procedure of Example 1,
the base case run was repeated except that the autoclave
solution contained 0.0045 mols/liter of GeI4. Total io-
dine and total labile methyl groups were as in Example 1initially. After 85 minutes at a temperature of 128-129C,
the solution was analyzed and found to contain 379 ppm
dissolved rhodium or 85% of the original dissolved rhodium.
These results clearly indicate that the stabili-
zer greatly retarded the rate of rhodium precipitation fromthe autoclave solution.
EXAMPLE 9
The experiment of Example 1 was repeated except
that the autoclave solution contained 0.2 mols/liter of
lithium acetate and 0.7 mols/liter total iodide. Auto-
clave temperature was 126-128C. Periodic sampling for
dissolved rhodium gave the following results:
Time After Methanol ppm Dissolved % of Original
Addition (minutes) Rhodium Dissolved rhodium
61 318 72
91 249 56
C~
20-19-1266
-14-
EXAMPLE 10
The experiment of Example 1 was repeated using
as a stabilizer 0.2 mole/liter of potassium iodide. After
124 minutes of refluxing at 128-129C, the solution was
analyzed and found to contain 228 ppm or 51% of the origi-
nal dissolved rhodium.
EXAMPLE 11
To establish another base run under different
conditions in which no stabilizer was present, the follow-
ing experiment was performed. About 650 milliliters of astock solution containing 0.027 moles/liter iron, 0.019
moles/liter nickel, 0.014 moles/liter chromium, 0.007
moles/liter molybdenum, 1.40 moles/liter total iodide,
8.9 moles/liter water and 1.44 moles/liter labile methyl
groups using acetic acid as the solvent plus a rhodium so-
lution and hydrogen iodide was charged into a 1500 mil-
liliter stirred autoclave and pressured with carbon monox-
ide to a pressure of 791 kPa. The contents were heated
with stirring and when a temperature of 185C was reached
methanol and methyl iodide were added. Temperature was
maintained at 185C.
The autoclave contents, which ini~ially con-
tained 416 ppm dissolved rhodium, were sampled and ana-
lyzed for dissolved rhodium after 61 minutes. Dissolved
rhodium ran 168 ppm or 40% of the original.
Again, this experiment clearly demonstrates
that in the absence of a catalyst stabilizer the rhodium
rapidly precipitates from the solution in the autoclave.
EXAMPLES 12-14
The procedure of Example 11 was repeated using
the stock solution of that Example and using the stabili-
zer compounds shown in the following Table. The results
were as shown below.
s
20-19 -1266
-15 -
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