Carbonylation of methyl acetate in the presence of polymeric rhodium-containing catalysts

Article abstract of DOI:10.1023/A:1015447408651

New catalytic systems based on RhCL3 and polymeric nitrogen- and oxygen-containing supports were proposed for the carbonylation of methyl acetate to acetic anhydride. The catalytic systems possess a high activity typical of homogeneous catalysts. The high activity is retained upon the repeated use of the catalyst separated from the reaction products. The nitrogen-containing polymers of the chitosan type serve as cocatalysts. In their presence, the induction period disappears, and the catalytically active species are stabilized, thus enabling the replacement of expensive LiI for cheaper salts of this metal.

Full text of DOI:10.1023/A:1015447408651

Russian Chemical Bulletin, International Edition, Vol. 51, No. 2, pp. 259—262, February, 2002
259
Carbonylation of methyl acetate in the presence of polymeric
rhodiumꢀcontaining catalysts

N. V. Kolesnichenko, A. E. Batov, N. A. Markova, and E. V. Slivinsky
A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences,
29 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 230 2224
New catalytic systems based on RhCl3 and polymeric nitrogenꢀ and oxygenꢀcontaining
supports were proposed for the carbonylation of methyl acetate to acetic anhydride. The
catalytic systems possess a high activity typical of homogeneous catalysts. The high activity is
retained upon the repeated use of the catalyst separated from the reaction products. The
nitrogenꢀcontaining polymers of the chitosan type serve as cocatalysts. In their presence, the
induction period disappears, and the catalytically active species are stabilized, thus enabling
the replacement of expensive LiI for cheaper salts of this metal.
Key words: carbonylation, methyl acetate, rhodiumꢀcontaining catalysts.
MeI (1 mL), AcOH (4 mL), and AcOMe (14.5 mL). The temꢀ
perature was risen to 190 °C and the pressure was increased
to 5 MPa.
Reaction products were analyzed on a Chromꢀ5 chromatoꢀ
graph (packed column 2.5 m, Porapak Q, flameꢀionization deꢀ
tector, nitrogen as carrier gas, T = 150 °С). According to the
GLC data, Ac2O is the only reaction product. Conversion of
AcOMe was determined as the difference between the concenꢀ
trations of AcOMe in the initial reaction mixture and reaction
products.
Stability of the catalytic system was estimated from the reacꢀ
tion rate upon the catalyst recycle after the removal of the reacꢀ
tion products.
The content of Rh in the polymer before and after the reacꢀ
tion was determined by atomicꢀabsorption spectrophotometry.
Two main commercial processes for acetic anhydride
production are presently available1,2: from acetic acid
through ketene at 750 °C and from acetaldehyde by its
oxidation. Both processes are uneconomical, which leads
to a high cost of acetic anhydride. Among alternative
methods for its production, the Eastman Co. process is of
most interest, viz., AcOMe homogeneous carbonylation
in the presence of RhCl3.3 Carbonylation of AcOMe by
this method occurs in the presence of MeI and anꢀ
hydrous LiI under a gas mixture pressure of 5 MPa
(95% СО + 5% Н2) and at 190 °C.
The purpose of this work is to develop a new variant
of AcOMe carbonylation to Ac2O in the presence of
Rhꢀcontaining polymeric catalytic systems. Natural
(chitosan, chitin, and polyglucin) and synthetic polymers
(styrene copolymers containing pyrrolidinopyridine
(STPP) and pyridylmaleimide (STPM) groups) were used
as ligands (Table 1).
Results and Discussion
The study of the influence of polymeric supports
(chitosan and polyglucin) containing various heteroatꢀ
oms on the catalytic properties of RhCl3 (Fig. 1) showed
that in the presence of RhCl3 without a macroligand the
reaction occurs with a low rate and a considerable inducꢀ
tion period. The reaction is ceased after 4 h at an AcOMe
conversion of ∼36%. When polyglucin is used as a polyꢀ
meric support, the reaction occurs similarly, i.e., the inꢀ
duction period is observed, and the catalytic system also
exhibits low activity. A different situation is observed in
the presence of the RhCl3—chitosan system. Although
the reaction rate increases insignificantly, the induction
period disappears, and after 4 h the reaction rate remains
virtually unchanged. Thus, chitosan not only accelerates
the formation of the catalytically active Rh speciees but
also stabilizes them. It is known4 that LiI is needed to
Experimental
Carbonylation of AcOMe was conducted at 190 °C and a
pressure of 5 MPa in a glass reactor placed in a stainless steel
autoclave. The reaction mixture was magnetically stirred. The
reaction rate was monitored by the amount of the absorbed gas
(95 vol.% СО + 5 vol.% H2), which was measured from the
pressure drop in a calibrated vessel, from which the gas was
supplied to the reactor with consuming, and determined as a
ratio of the number of moles of the gas mixture to the time (min)
and volume of the catalytic solution.
The catalytic system was prepared directly in the reactor
from RhCl3•4H2O (0.038 mmol), macroligand (chitosan, chitin,
polyglucin, and STPM or STPP) at different L : Rh ratios (L is
the structural unit of the macroligand) (Table 2), LiI (0.006 mol),
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 246—249, February, 2002.
1066ꢀ5285/02/5102ꢀ259 $27.00 © 2002 Plenum Publishing Corporation

260
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 2, February, 2002
Kolesnichenko et al.
Table 1. Structure and molecular weight (M) of
XCO/mol L–1
6
macroligands
3
4
5
Macroligand
M
Natural ligands
3
2
1
Chitosan
60000
4
1
2
Chitin
60000
60000
0
1
2
3
4
5
6
t/h
Fig. 1. Absorption of CO (XCO) as a function of the duration (t)
of AcOMe carbonylation (190 °C, 5 MPa) in the presence of
various catalytic systems: RhCl3•4H2O (1); RhCl3—polyglucin
(2), RhCl3—LiI (3), RhCl3—chitosan (4), RhCl3—LiI—polyꢀ
glucin (5), and RhCl3—LiI—chitosan (6).
Polyglucin
Synthetic ligands
increase the rate of AcOMe carbonylation in the presence
of RhCl3. LiI performs several functions: first, it decreases
the induction period of the reaction due to the faster
transformation of the inactive RhIII into active RhI; secꢀ
ond, changes the reaction route due to which the liberaꢀ
tion of MeI is strongly accelerated (oxidative addition of
MeI is the rateꢀdetermining stage of the process) and
virtually excludes the formation of HI, which favors the
STPM
STPP
70000
70000
–
transformation of the catalytically active Rh(CO)2I2
–
complexes into inactive Rh(CO)2I4
.
Indeed, when LiI is added to both RhCl3 and the
RhCl3—polyglucin system, the induction period disapꢀ
pears, the reaction rate significantly increases, and after
6 h the conversion of AcOMe reaches ∼90%. In the presꢀ
ence of the RhCl3—chitosan—LiI system, the reaction
rate also increases, and after 6 h the conversion of AcOMe
becomes >95% (see Fig. 1).
Table 2. Influence of RhCl3 modified by various macroligands
on the initial carbonylation rate of AcOMe (r0)
Thus, chitosan accelerates the transition of the inacꢀ
tive Rh form to the active species, due to which the inꢀ
duction period disappears, and stabilizes the catalytically
active species.
Macroligand
Ratio
N : Rh
r0•102/mol L–1 min–1
Fresh
Catalyst after
catalyst
removal
of products
The Rhꢀcatalyst is deactivated mainly due to the acꢀ
cumulation of I2, formed by the thermal decomposition
of AcI, and НI, which is the product of the reaction of
AcI with AcOH. Both deactivating agents (I2 and HI)
favor5 the transition of active species to inactive. Unlike
polyglucin, chitosan and other Nꢀcontaining polymers
(STPP and STPM) capable of binding HI and AcI accuꢀ
mulated in the system to form quaternary ammonium
STPP
STPM
Chitin
Chitosan
Chitosan
Chitosan
RhCl3
16
16
24
15
30
60
—
3.5
1.8
2.0
3.2
3.3
3.3
3.5
2.5
1.0
—
—
—
—
—

Carbonylation of methyl acetate on Rh catalysts
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 2, February, 2002
261
XCO/mol L–1
XCO/mol L–1
1
1
a
3.0
4
4
2
3
2
3
2.5
2.0
1.5
1.0
0.5
3
2
1
0
0
1
2
3
4
5
t/h
30
60
90
t/min
XCO/mol L–1
Fig. 2. Absorption of CO (XCO) as a function of the duration (t)
AcOMe carbonylation (190 °C, 5 MPa) in the presence of
various catalytic systems: RhCl3—LiI—chitosan—MeI (1),
RhCl3—LiI—MeI (2), RhCl3—LiI—chitosan—HI (3), and
RhCl3—LiI—HI (4).
1
2
3
b
3
2
1
salts,6 preventing the thermal decomposition of the latter
to evolve I2.
The specificity of the mutual influence of HI and
chitosan in this reaction was studied. The replacement of
MeI by HI decreases considerably the reaction rate in the
presence of RhCl3 and the RhCl3—chitosan system
(Fig. 2). In both cases, the initial rates are virtually the
same; however, in the absence of chitosan, after 4 h the
catalyst activity decreases, and after 6 h the reaction is
entirely ceased, and the conversion of AcOMe does not
exceed 80%. By contrast, in the presence of chitosan, the
reaction rate remains almost unchanged, and after 6 h the
conversion of AcOMe becomes >90%. These data conꢀ
firm the fact that chitosan aligns the deactivating role of
HI by the formation of quaternary ammonium salts.
The influence of various Li salts on the catalytic propꢀ
erties of the Rhꢀcontaining catalysts was studied. As can
be seen in Fig. 3, a, the replacement of LiI by Li2CO3 or
LiOAc in the system without chitosan decreases the reacꢀ
tion rate. This can be attributed to a deficient of the I–
ions, which decreases the rate of MeI formation in the
reaction of LiI with AcOMe. In the case of Li2CO3, water
and HI, which deactivate the Rh catalyst, can also be
formed in the system.
0
30
60
90
t/min
Fig. 3. Influence of various Li salts on the activity of the
RhCl3•4H2O (a) и RhCl3—chitosan systems (b): LiI (1), AcOLi
(2), and Li2CO3 (3).
Thus, the use of chitosan as a support allows cheaper
Li salts to be introduced as a promoter.
The study of the influence of various nitrogenꢀconꢀ
taining polymers and the molar N : Rh ratio for chitosan on
the initial carbonylation rate (r0) (see Table 2) showed that
only STPP has the same high activity as chitosan, which
is not inferior to that of the homogeneous RhCl3—LiI
catalytic system. In addition, in the case of chitosan, the
carbonylation rate is independent of the N : Rh molar
ratio in an interval from 15 to 60. After the reaction prodꢀ
ucts were separated from the catalyst and the latter was
repeatedly applied, its activity decreased. This is associꢀ
ated with a loss of some portion of the polymeric catalyst
when STPP or STPM is used as the support due to partial
dissolution in the liquid phase. In the case of chitin and
chitosan, this is due to a loss of Rh (by more than an order
of magnitude), which was confirmed by atomicꢀabsorpꢀ
tion spectroscopy.
Quite different situation is observed in the case of the
polymeric catalyst (Fig. 3, b). The reaction rates are alꢀ
most equal when all three salts are used. The accelerating
function of chitosan is possibly carried out through its
capability of alkylating MeI at the N atom. The coordinaꢀ
tion of the alkylated macroligand with the catalytically
active Rh(CO)2I2– complex favors the oxidative addition
of MeI to the Rh atom.
Another variant of recycle of the catalytic system was
studied for chitosan. The reaction products were sepaꢀ

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Kolesnichenko et al.
r0•102/mol L–1 min–1
that chitosan can retain the alkylated and acylated forms
and coordinate with active anionic Rh complexes stabiꢀ
lizing them.
The data obtained in this work show that the nitrogenꢀ
containing polymers (viz., chitosan and STPP) enhance
the performance of the Rh catalyst in AcOMe carboꢀ
nylation due to an increase in the rate of formation of the
active species and their stabilization. In addition, these
polymers allow the replacement of expensive LiI for
cheaper Li salts.
3
2
1
References
0
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3. PCT Int. Appl. WO 82 01, 704; Chem. Abstrs., 1982, 97,
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1990 (Engl. Transl.)].
1
2
3
4
n
Fig. 4. Influence of the number of catalytic cycles (n) on the
initial rate of AcOMe carbonylation (r0) (RhCl3—LiI—chitosan
system, 190 °C, 5 MPa) in a series of successive experiments
with the intermediate separation of the reaction products from
the catalyst.
rated from the catalyst by distillation, the vat residue conꢀ
taining the Rh complex, polymer, and LiI was returned to
the reactor, and AcOMe carbonylation was repeated. As
can be seen in Fig. 4, for this variant of recycle, the
activity of the catalytic system is retained and even someꢀ
what increases in subsequent experiments. This indicates
Received March 12, 2001;
in revised form August 1, 2001