Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HOE 84/H 022
This invention relates to a process for making acetic an-
hydride and, if desired, acetic acid by reacting methyl acetate
and/or dimethylether and, if desired, methanol with carbon mon-
oxide, optionally in the presence of water, at temperatures of
350 to 575 K, under pressures of 1 to 300 bar in the presence
of a catalyst system containing noble metals belonging to group
VIII of the Periodic System of the elements, or their compounds,
iodine and/or its compounds and, if desired, carbonyl-yielding
non noble metals of groups IV, V, VI, VII or VIII of the Perio-
dic system of -the elements, or their compounds and, if desired,
an aliphatic carboxylic acid having from 1 to 4 carbon atoms,
which comprises using a catalyst system containing tetrabutyl-
phosphonium iodide as an additional promoter.
German Specification DE 24 50 965 C2 describes a process
for making acetic anhydride from methyl acetate and carbon mon-
oxide, if desired in the presence of 5 - 50 vol. % hydrogen,
under pressures of 1 to 500 bar and at temperatures of 50 to
250C in contact with catalysts containing noble metals belong-
ing to group VIII of the Periodic system of the elements, or
20. their compounds and iodine and/or its compounds and optionally
also carbonyl-yielding metals, e,g. Co, Ni or Fe. The iodine
compounds mentioned include quaternary ammonium and phosphonium
compounds, such as tetramethylammonium iodide and tetraethyl-
phosphonium iodide. These two compounds are however not very
useful for the catalyst system as they are liable to deposit due
to their high melting points and minor solubility, and there-
fore do not permit the catalyst solution to be cycled continuous-
ly. Still further additional catalyst constituents include alkyl
and aryl phosphines,such as tri-n-butylphosphine and triphenyl-
3û phosphine.
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German Specification DE 26 10 036 C2 describes a comparableprocess for making monocarboxylic anhydrides, wherein however a
metal belonging to groups IVa, Va or VIa of the Periodic System,
preferably chromium, is used together with the noble metal of
5 group VIII of tha Periodic System, an iodide as well as an or-
ganonitrogen or organophosphorus compound containing trivalent
nitrogen or phosphorus.
The process described in German Specification DE 26 10 036
C2 is seriously handicapped by the fact that the metal compounds
10 and daughter products of the multiple promoter are ex-tensively
insoluble in boiling acetic anhydride so that the circulation of
the catalyst system invariably necessary for continuous opera-
tion is rendered very difficult or even made impossible. In
addition, these insoluble compounds have been found unduly to
15 affect the separation of acetic anhydride from the catalyst.
Indeed, on subjecting the reaction mixture to distillative work
up, chromium salts commence de-positing on the evaporator, and -the
transfer of heat is sensitively affected. As a result, it is
necessary for the evaporator temperature to be increased natural-
20 ly with considerable impairment of the catalyst system.
German Specification DE 29 39 839 A1 describes a processfor making acetic anhydride in the presence of a noble metal-
containing catalyst system containing a quaternary organophos-
phorus compound and a zirconium compound soluble in the reaction
25 mixture as additional constituents. The quaternary organophos-
phorus compounds are adducts of organic phosphines and methyl
iodide. The melting point, even of rather useful tributylmethyl-
phosphine, is however as high as almost 140C. This fact makes
it invariably necessary, in the interest of maintaining fusion,
30 for the catalyst solution to be separated at an equally high
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temperature subjecting the catalyst system to considerable
thermal stress. For these reasons it is not possible to reduce
the temperature and separate the catalyst solution under milder
conditions, e.g. under reduced pressure, as the step of reduc-
ing the temperature involves the risk of sudden crystallization.The lnvention as described herein which provides for an
outstanding catalyst activity, expressed in g acetic anhydride
obtalned per g elemental noble metal per hour, permits these
disadvantages to be set aside as the catalyst solution can be
separated from the reaction product under conditions more favor-
able than heretofore by the use of tetrabutylphosphonium iodide
having a melting point o~ 103C. As has unexpectedly been found
tetrabutylphosphonium iodide is reliably stable under the reac-
tion conditions whereas corresponding quaternary phosphonium
iodides having 5 carbon atoms and more undergo decomposition
with formation of corresponding methyl-substituted phosphonium
iodides. Quaternary phosphonium iodides having less than 4 car-
bon atoms in the respective substituent should conveniently not
be used because of their high melting points of 200C and more.
2û Further preferred and optional features of the present i.n-
vention provide:
a) for the catalyst system noble me-tal(compound)/iodine(com-
pound)/carbonyl-yielding non noble metal(compound)/carboxy-
lic acid/tetrabutylphosphonium iodide to be used in an
atomic or molar ratio oE 1:(1-1400):(0-10):(0-2000):
(1-12ûO);
b) for methyl acetate, methanol and water or dimethylether,
methanol and water to be used in a molar ratio of 1:(0-S):
( O - 1 ) ;
c) for a carbon monoxide/hydrogen mixture containing up to
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10 vol. % hydrogen to be used.
The process of this invention should preferably be effected
at temperatures of 400 to 475 K under pressures of 20 to ~50
bar. 0.0001 to 0.01 mol noble metal of group VIII of the Perio-
dic System of the elements, or its sompounds should preferablybe used per mol methyl acetate and/or dlmethylether. It is also
advantageous to use the catalyst system noble metal(compound)/
iodine(compound)/carbonyl-yielding non noble metal(compound)/
carboxylic acid/tetrabutylphosphonium iodide in an atomic or
10 molar ratio of 1:(10-300):(0-8):(0-600):(10-300). The carboxy-
lic acid if used, preferably is acetic acid.
All of the metals belonging to group VIII of the Periodic
System of the elements (Ru, Rh, Pd, Os, Ir, Pt) can be used as
Ihe catalyst. Rhodium however is most active. It and all other
15 metals should be used in form of compounds which are soluble
: under the reaction conditions and form the active noble metal/
carbonyl-complex, e.g. RhCl3 . 3 H20, ! Rh(CO)~Cl 72~
/ Pd(C0)2I_72, IrCl3, Pd(CH3C02)2, PdC12, Pd(C5H702)2-
Methyl iodide but also acetyl iodide or hydrogen iodide are
20 the compounds which should preferably be used as iodine compounds.
The non noble metals of groups IV, V, VI, VII and VIII,
forming carbonyl complexes which may optionally be used as pro-
moters should conveniently be used in form of readily soluble
compounds, e.g. acetyl acetonate or carbonyl, in -the reaction.
25 Compounds of the metals Ti, Zr, V, Nb, Ta, Cr, ~o, W, Mn, Re,
Fe, Co or Ni are preferably used.
The process of this invention can be effected continuously
or discontinuously as more fully described in the following:
.. The mixture to undergo reaction is placed in an autoclave
30 of stainless steel (Hastelloy~B2) and reacted under the condi-
~d~ Mark
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tions described. Unreacted carbon monoxide and hydrogen, if any,are cycled whereas a small partial stream thereof (off-gas) is
allowed to escape from the system. Fresh carbon monoxide optio-
nally admixed with hydrogen is metered into the cycle gas at
5 the same rate as it is consumed. Quantities oE fresh methyl
acetate and/or dimethylether and me-thanol, if any, and/or water,
corresponding to the conversion rate, are admitted to the reac-
tor. Reaction mixture issues from the reactor at the same rate
as feed materials are added. In a short-way evaporator, the
reaction mixture is separated from the catalyst system which is
recycled into the reactor. The low boilers (methyl acetate, di-
methylether, methyl iodide) are separated in a first column and
recycled to the reactor. The still product of the first column
is worked up in two further columns to give acetic acid and
. 15 acetic anhydride.
Example 1
250 9 methyl acetate, 1.6 9 RhC13 . 3H20, 60 9 methyl iodide
and 70 9 tetrabutylphosphonium iodide were placed in a Hastelloy
autoclave; next, a pressure of 25 bar was established by inject-
ing C0. The whole was heated to the reaction temperature of 455K and a total pressure of 50 bar was established and maintained
o.ver a period of 50 minutes by continuous injection of C0. After
cooling with release of pressure, the reaction mixture was ana-
lyzed gas-chromatographically and found to contain 276 9 acetic
anhydride, corresponding to 1766 9 Ac20 per gram Rh per hour.
Example 2
200 9 dimethylether, 1.6 9 RhCl3 . 3H20, 7û 9 methyl iodide
and 80 9 tetrabutylphosphoni.um iodide were reacted with carbon
monoxide in the Hastelloy autoclave at 455 K under a pressure of
60 bar. After a reaction period of 15 minutes, the reac-tion mix-
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ture was found to contain 228 9 acetic anhydride and 156 9 methyl
acetate, corresponding to 1459 9 Ac20 per gram Rh per hour.
Example 3
300 9 methyl acetate, 1.6 9 RhC13 . 3H20, 90 9 methyl iodide,
70 9 acetic acid and 70 9 tetrabutylphosphonium iodide were react-
ed with carbon monoxide in an autoclave at 453 K under a pressure
of 50 bar. After a reaction period of 15 minutes, the reaction
mixture was found to contain 298 9 ace-tic anhydride, correspond
: ing to 1907 9 Ac20 per 9 Rh per hour.
Example 4
280 9 methyl acetate, 2 9 Pd(OAc)2, 70 9 methyl iodide and
100 9 tetrabutylphosphonium iodide were reacted with C0 in a
Hastelloy autoclave at 460 K under a pressure of 50 bar. After
65 minutes, 203 9 acetic anhydride, corresponding to 193 9 Ac20
per 9 Pd per hour, was obtained.
Example 5
250 9 methyl acetate, 0.8 9 RhC13 . 3H20, 5 9 zirconium
acetyl acetonate, 90 9 methyl iodide, 90 9 acetic acid and 120 9
tetrabutylphosphonium iodide were rPacted with C0 in a Hastelloy
autoclave at 458 K under 70 bar. After a reaction period of 25
minutes, 282 9 acetic anhydride, corresponding to 2165 9 Ac20
per gram Rh per hour, was found to have been obtained.
Example 6
280 9 methyl acetate, 1.8 9 RhC13 . 3H20, 8 9 vanadium hexa-
carbonyl, 90 9 methyl iodide and 70 9 tetrabutylphosphonium iodide
were reacted with C0 in a Hastelloy autoclave at 460 K under 50
bar. After a reaction period of 15 minutes, 292 9 acetic anhydride,
corresponding to 1661 9 Ac20 per 9 Rh per hour was found to have
been obtained.
. 6
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Example 7
250 9 methyl acetate, 1.6 g RhCl3 . 3H20, 7 9 chromhexacar-
bonyl, 80 9 methyl iodide and 75 9 tetrabutylphosphonium iodide
were reacted with C0 in a Hastelloy autoclave at 450 K under 60
bar. After 14 minutes, 294 9 acetic anhydride, corresponding to
2016 9 Ac20 per gram Rh per hour, was obtained.
Example 8
250 9 methyl acetate, 1.6 9 RhCl3 . 3H20, lû 9 dirheniumde-
cacarbonyl, 150 9 methyl iodide, 75 9 acetic acid and 100 9 te-
trabutylphosphonium iodide were reacted with C0 in a Hastelloyautoclave at 453 K under 60 bar. After 15 minutes, the reaction
mixture was found to contain 286 9 acetic anhydride, correspond-
ing to 1830 gram Ac20 per gram Rh per hour.
Example 9
280 9 methyl acetate, 2 9 Pd(OAc)2, 10 9 dicobaltoctacar-
bonyl, 60 9 methyl iodide and 100 9 tetrabutylphosphonium iodide
were reacted with C0 in a Hastelloy autoclave at 450 K under 80
bar. After 25 minutes, the reaction mixture was ~ound to contain
248 9 acetic anhydride, corresponding to 628 9 Ac20 per gram Pd
per hour.
Example 10
250 9 methyl acetate, 50 9 methanol, 1,6 9 RhCl3 . 3H20,
100 9 methyl iodide and 70 9 tetrabutylphosphonium iodide were
reacted with C0 in a Hastelloy autoclave at 455 K under 50 bar.
25 After a reaction period of 15 minutes, 288 9 acetic anhydride
and 94 9 acetic acid, corresponding to 1843 g Ac20 per gram Rh
per hour and 601 9 acetic acid per gram Rh per hour, were
obtained.
Example 11
200 9 dimethylether, 50 9 methanol, 1.6 9 RhC13 . 3H20,
5~
90 9 methyl iodide and 90 9 tetrabutylphosphonium iodide were
reacted with C0 in a Hastelloy autoclave at 458 K under 60 bar.
After a reaction period of 15 minutes, 242 9 acetic anhydride,
146 9 methyl acetate and 94 9 acetic acid, corresponding to
1549 9 Ac20 per gram Rh per hour and 601 9 acetic acid per gram
Rh per hour, were obtained.
Example 12
300 9 dimethylether, 1.8 9 RhCl3 . 3H20, lûO g methyl
iodide, 100 9 acetic acid and 80 9 tetrabutylphosphonium iodide
were reacted with a C0/H2-mixture containing 5 vol. % H2 in a
Hastelloy autoclave at 458 K under 80 bar. After 15 minutes,
340 9 acetic anhydride was obtained together with 160 9 methyl
acetate, 70 9 ethylidene diacetate and 30 9 additionally formed
acetic acid, corresponding to 1935 9 Ac20 per gram Rh per hour
and 171 9 acetic acid per gram Rh per hour.
Example 13
200 9 methyl acetate, 300 9 methanol, 1.6 9 RhCl3 . 3H20,
100 9 methyl iodide and 75 9 tetrabutylphosphonium iodide were
reacted with C0 in a Hastelloy autoclave at 455 K under 50 bar.
20 After a reaction period of 18 minutes, 220 9 acetic anhydride
and 208 9 acetic acid, corresponding to 1173 9 Ac20 per gram
Rh per hour and 1109 g acetic acid per gram Rh per hour, were
obtained.
Example 14
300 9 methyl acetate, 36 9 water, 70 9 hydrogen iodide,
1.6 9 RhCl3 . 3H20 and 80 9 tetrabutylphosphonium iodide were
reacted with C0 in a Hastelloy autoclave at 458 K under 40 bar.
After a reaction period of 14 minutes, 122 9 acetic anhydride
and 273 9 acetic acid, corresponding to 836 9 Ac2û per gram Rh
30 per hour and 1872 9 ace-tic acid per gram Rh per hour, were ob-
tained.
