Carbonylation of methanol and dimethyl ether in ionic liquids

Article abstract of DOI:10.1134/S0965544114040070

Carbonylation of methanol and dimethyl ether in various acidic ionic liquids (ILs) over catalysts containing rhodium complexes has been investigated. It has been shown that the presence of the H₂PO ₄ ^- anion in IL leads to a significant increase in the rate of carbonylation of methanol and dimethyl ether to methyl acetate and acetic acid. Ionic liquids and conditions under which a conversion of 92% with a 80% selectivity for methyl acetate is achieved have been selected. The catalytic system proposed can be reused without loss of activity.

Full text of DOI:10.1134/S0965544114040070

ISSN 0965ꢀ5441, Petroleum Chemistry, 2014, Vol. 54, No. 4, pp. 283–287. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © A.L. Maksimov, D.V. Losev, Yu.S. Kardasheva, E.A. Karakhanov, 2014, published in Neftekhimiya, 2014, Vol. 54, No. 4, pp. 282–286.
Carbonylation of Methanol and Dimethyl Ether in Ionic Liquids
A. L. Maksimov, D. V. Losev, Yu. S. Kardasheva, and E. A. Karakhanov
Faculty of Chemistry, Moscow State University, Moscow, Russia
eꢀmail: kar@petrol.chem.msu.ru
Received January 31, 2014
Abstract—Carbonylation of methanol and dimethyl ether in various acidic ionic liquids (ILs) over catalysts
containing rhodium complexes has been investigated. It has been shown that the presence of the H2PO4–
anion in IL leads to a significant increase in the rate of carbonylation of methanol and dimethyl ether to
methyl acetate and acetic acid. Ionic liquids and conditions under which a conversion of 92% with a 80%
selectivity for methyl acetate is achieved have been selected. The catalytic system proposed can be reused
without loss of activity.
Keywords: carbonylation, methanol, dimethyl ether, ionic liquid, methyl acetate, acetic acid
DOI: 10.1134/S0965544114040070
The manufacture of acetic acid and its derivatives containing ILs for this process as applied to the carboꢀ
by the carbonylation of methanol and dimethyl ether
(DME) is currently one of the most widely used indusꢀ
trial processes of basic organic synthesis. Methanol
carbonylation has become the main process for proꢀ
ducing acetic acid, gradually displacing the technolꢀ
ogy based on the oxidation of ethylene. At the same
time, the carbonylation of DME, whose production
rapidly grows, is considered to hold promise as a proꢀ
cess for the production of methyl acetate and acetic
anhydride [1, 2].
nylation of methanol and ethylene was patented by
Eastman [10, 11].
In this paper we present the results of a study of the
carbonylation of methanol and DME, showing that
acidic ionic liquids in the presence of different proꢀ
moters (methyl iodide, iodineꢀcontaining ILs) are
promising for the enhancement of the reaction.
Traditionally, the carbonylation of methanol is carꢀ
ried out on a rhodium or iridium complex in the presꢀ
ence of methyl iodide [3]. In this case, the separation
and reactivation of the catalyst are complicated and
the concentration of the iodine promoter used is quite
high [4]. Furthermore, for the catalyst deactivation
rate to be reduced, a significant amount of water needs
to be present in the system, which also complicates the
isolation of the products [1, 2]. The alternative can be
immobilization of the active complex on a cationꢀ
exchange support or in an ionic liquid [5–7]. Reducꢀ
tion in the concentration of methyl iodide or even its
abandonment can be achieved through the use of acid
catalysts based on zeolites or heteropoly acids [8, 9].
In this case, the process involves the acidꢀcatalyzed
activation of methanol and carbon monoxide.
EXPERIMENTAL
Rhodium(III) trichloride RhCl3
etonatodicarbonylrhodium(I) Rh(acac)(CO)2, and
ꢀmethylimidazole (Aldrich) were used without furꢀ
⋅
3H2O, acetylacꢀ
N
ther purification. 1H NMR spectra were recorded on a
Varian XRꢀ400 spectrometer with an operating freꢀ
quency of 400 MHz. GLC analysis was carried out on
a HewlettꢀPackard chromatograph with FID, a 30ꢀm
capillary column coated with the SEꢀ30 phase, and
helium as the carrier gas at a column temperature proꢀ
grammed from 25 to 200°С, using the internal stanꢀ
dard method. The products were identified using a gas
chromatography–mass spectrometry technique on a
FinniganꢀMATꢀITDS instrument at an ionization
energy of 70 eV and a source temperature of 220°С.
We believe that catalytic systems based on ionic liqꢀ
uids (ILs), a new type of solvent that can immobilize
an anionic active complex with the simultaneous
introduction of acid groups and iodide ions, are parꢀ
ticularly promising in this regard. The fruitfulness of
this approach has been demonstrated for supported
ILs [6]. A technology comprising the use of iodineꢀ
The components of the mixtures were separated on a
SEꢀ30 capillary column of a 30 m length and a
0.25 mm internal diameter at temperature proꢀ
grammed from 25 to 200
°С.
The ionic liquids used in the study are shown below
283

284
MAKSIMOV et al.
tation. Yield 99%. 1H NMR (400 MHz, D2O):
, ppm:
δ
1.80–1.97 (m, 2H), 2.89 (t, 2H), 3.21–3.31 (m, 2H),
7.1–7.6 (m, 15H).
H2PO4–
N
N
HCO3–
N
H2PO4–
Synthesis of [Ph3P(CH2)3SO3Н][H2PO4]. This IL
was prepared as the previous one, except that 1 mol of
orthophosphoric acid was used instead of 2 mol of triꢀ
fluoroacetic acid and the mixture was dried in a vacꢀ
uum for 10 h. Yield 99%. 1H NMR (400 MHz, D2O):
N
N
N
+
+
+
НMIM H2PO4
BMIM H2PO4 BMIM HCO3
δ
, ppm: 1.80–1.97 (m, 2H), 2.89 (t, 2H), 3.21–3.31
(m, 2H), 7.1–7.6 (m, 15H).
MIMPrSO3 H+OTf–][TfOH
according to the procedure described in [16].
ylimidazole (1.67 mL, 21 mmol) in 40 mL of acetone
was placed in a 250ꢀmL flask and cooled to
HOSO2CF3
–OSO2CF3
HOSO2CF3
–OSO2CF3
P+
N
[
]
was synthesized
ꢀmethꢀ
N
N
+
SO3H
SO3H
0°C.
Slowly, a solution of 2.5 g (21 mmol) of 1,3ꢀpropansulꢀ
tone in 40 mL of acetone was added dropwise with
stirring. The mixture was further stirred for 5 days at
room temperature. The precipitate was washed with
MIMPrSO3H OTf
⋅
TfOH
PPh3PrSO3H OTf
H2PO4–
⋅
TfOH
toluene and dried in a vacuum at 60°C. To the zwitteꢀ
rion obtained, 99% trifluoroacetic acid was added in a
molar ratio of 1 : 2. The mixture was stirred for 2 h at
P+
40°C
(until complete dissolution of the zwitterion).
, ppm: 1.80–
SO3H
Yield 99%. 1H NMR (400 MHz, D2O):
δ
1.97 (m, 2H), 2.89 (t, 2H), 3.21–3.31 (m, 2H), 7.1–
7.6 (m, 15H).
PPh3PrSO3 ⋅ H3PO4
General Procedure of Catalytic Experiments
Synthesis Procedures
syntheses of [BMIM][Cl]
BMIM][HCO3] [13], and [BMIM][H2PO4] [14]
were performed according to the procedures reported
in the literature.
The reaction was carried out in a Parr Instrument
0.1ꢀL autoclave equipped with a turbine stirrer
(1500 rpm), a pressure sensor, and a temperature conꢀ
trol device at a carbon monoxide pressure of 1 to
The
[12],
[
4 MPa and a temperature of 80 to 240
clave was charged with an appropriate amount of
methanol or, after precooling the autoclave to –40
°С. The autoꢀ
Synthesis of [HMIM][H2PO4] was conducted in a
way similar to that described in [14]. A 10.1ꢀg portion
of [HMIM][Cl] (0.05 mol) was dissolved in a minimal
amount of water, and 3.3 mL (0.05 mol) of 85% phosꢀ
phoric acid was slowly added. The mixture was stirred
for 30 min at room temperature and then for 2 h at
°C,
DME; an ionic liquid; the iodine promoter; and
acetylacetonatodicarbonylrhodium. Then, the autoꢀ
clave was filled with carbon monoxide to the working
pressure and heated to the desired temperature. The
reaction was run with continuous stirring for a preset
time (3–15 h). After cooling the autoclave to room
temperature, the pressure was reduced to atmospheric.
Product analysis was carried out by GLC with massꢀ
spectrometric identification.
90°C. Water was evaporated in a vacuum at 90°C to a
constant weight of the residue. The product was a visꢀ
1
cous pale yellow liquid. Yield 97%. H NMR
(400 MHz, D2O): , ppm : 0,16 (s, 3H), 1,18ꢀ1,69 (m,
δ
8H), 3.74 (s, 3H), 4 05 (t, 2H), 6.98 (m, 1H), 7.33 (m,
1H), 8.66 (s, 1H).
[
Ph3P(CH2)3SO3Н][H2PO4] and [PPh3PrSO3H+
OTf–][TfOH] were prepared analogously to the proꢀ
RESULTS AND DISCUSSION
cedure described in [15].
As a medium for carbonylation, a number of acidic
Synthesis of [PPh3PrSO3H+ OTf–][TfOH]. 1,3ꢀ ILs were used, both superacidic (containing trifluoroꢀ
Propansultone (4.14 g) and triphenylphosphine (8.9 g) sulfonic acid and the sulfo group in the IL cation) and
taken in the molar ratio of 1 : 1 were placed in a 100ꢀmL somewhat less acidic liquids containing hydrogen
flask and dissolved in toluene. The solution was phosphate or hydrogen carbonate anions (Fig. 1). The
refluxed for 12 h at 90°C with continuous stirring. data presented in Table 1 show that the maximum
After cessation of heating, the solvent was distilled off selectivity for methyl acetate is achieved using the
on a rotary evaporator until complete dryness of the superacidic ILs, for which the formation of acetic acid
resulting white amorphous precipitate of the zwitteꢀ hardly takes place during the reaction at 130°С. The
rion. A 3ꢀg portion of the zwitterion was placed in a highest values of methanol conversion are achieved for
flask, and 1.4 mL of 99% CF3SO3H was added. The the imidazole ILs containing the dihydrogen phosꢀ
reaction was run for 2 h at 40°C with continuous agiꢀ phate or the hydrogen carbonate anion.
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CARBONYLATION OF METHANOL AND DIMETHYL ETHER IN IONIC LIQUIDS
285
For [HMIM][H2PO4], a conversion of 92% and a
methyl acetate selectivity of 80% were achieved at
%
80
Methanol
Methyl acetate
Acetic acid
130°C. Elevation of the temperature to 190°С expectꢀ
edly led to an increase in the yield of acetic acid in all
cases. Apparently, the influence of the anion [A] on
the catalyst activity is associated with the formation of
an intermediate complex in which this anion replaces
one of the iodide ions (Rh(CO)2I[A]). It is known [16]
that admixture of an acetate leads to a significant
enhancement of the methanol carbonylation rate due
to the formation of the intermediate complex
60
40
20
0
[
Rh(CO)2I(CH3COO)], which is highly amenable to
oxidative addition of methyl iodide. In IL media, the
anions that are a part of the ILs can form complexes of
this type.
It should be noted that the activity of the rhodium
complex in methanol carbonylation in the presence of
the IL [HMIM][H2PO4] with the dihydrogen phosꢀ
phate anion was significantly higher than in its absence
0.5
1.0
1.5
2.0
2.5
3.0
P
3.5
MPa
,
СО
(Table 2). The product yield at 130°C in the convenꢀ
tional (solventless) system was 18 to 35%, whereas that
in the presence of methylimidazolium dihydrogen
Fig. 1.Effect of pressure on the reaction of carbonylation
of methanol.
Reaction conditions: 3 h, 190
°C, [СH OH]/[CH I] = 6.25,
3 3
[HMIM][H PO ] 0.45 mol,
=
[
Rh(acac)(CO) ]
=
2
4
2
phosphate was 90–92%. At a temperature of 190°C,
0.004 mmol.
the main difference in activity was associated with the
yield of acetic acid: it was significantly lower than that
for the conventional system. The presence of water (up
to 10% by volume) during the carbonylation catalyzed
by a rhodium complex is necessary for maintaining a
high catalyst activity and stability. However, this gives
rise to the problem of isolation of the final products
(acetic acid, methyl acetate) capable of forming an
azeotrope with water.
acetic acid increases and the amount of methyl acetate
decreases with the reaction time.
We also studied the effect of concentration and
nature of iodineꢀcontaining additives on the rate of the
reaction in the presence of acidic ILs (Table 3). As can
be seen from the data, the best results are achieved
using methyl iodide and iodine and somewhat less
Increasing the pressure also leads to enhancement decent results, with potassium iodide. With the other
of the carbonylation rate and, hence, an increase in promoters, the reaction rate is significantly lower.
the yield of acetic acid (Fig. 2). Note that amount of Apparently, the methyl iodide formation rate is low in
Table 1. Carbonylation of methanol in the medium of various ionic liquids
Yield, %
Ionic liquid
T
, °C
Conversion, %
CH3OC(O)CH3
CH3COOH
[MIMPrSO3H][HSO4
]
130
190
190*
130
190
130
190
130
190
190
190
25
18
50
73
45
73
91
92
95
94
84
25
18
50
25
35
70
54
73
42
37
23
0
0
[MIMPrSO3H+OTf–][TfOH]
[PPh3PrSO3H+ OTf–][TfOH]
[Ph3P(CH2)3SO3H][H2PO4]
[HMIM][H2PO4]
0
2
10
3
37
19
53
57
61
[
BMIM][HCO3]
[BMIM][H2PO4]
Reaction conditions: [CH OH]/[CH I] = 6.25, 3 h,
p
= 2MPa, [IL] = 0.45 mol, [Rh(acac)(CO) ] = 0.004 mmol; *15 h.
3
3
CO
2
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286
MAKSIMOV et al.
Table 2. Carbonylation of methanol in the ionic liquid
this case, thus determining the low activity. But a
reduced amount of iodine causes a much smaller fall
in activity than that of methyl iodide. Note that an
acidic IL in combination with tetrabutylammonium
iodide provides not only the necessary conversion, but
also a high selectivity for methyl acetate in the carboꢀ
nylation of methanol at a high temperature and a high
CO pressure.
[HMIM][H2PO4]
Yield, %
Water, Conversion,
T
, °C
mol
%
CH3OC(O)CH3 CH3COOH
Solventꢀfree
130
–
18
35
82
27
18
35
73
26
–
–
A substantial advantage of the proposed catalyst
system is its ease of reuse, since all of the catalyst
remains in the ionicꢀliquid phase. Data on the reuse of
–*
–*
9*
the system at 190°C for various reaction times are preꢀ
190
130
9
sented in Fig. 3. It is seen that activity substantially
increased during the second and third cycle and did
not change any further. This behavior can be due to the
buildup of iodide anions in the solution of the ionic
liquid.
1
0.45 M [HMIM][H2PO4]
130
190
–
9
92
90
95
90
92
75
73
50
42
36
29
17
19
We also explored the possibility of synthesis of
methyl acetate from DME in an IL medium. A careꢀ
fully measured amount of DME was introduced into
the system by freezing it directly in the autoclave. The
results are shown in Table 4.
40
–
53
9
54
18
27
63
Under the conventional carbonylation conditions
(row 1), a substantially greater amount of methanol is
produced and the methyl acetate selectivity is low.
Apparently, the conversion of DME in carbonylation
over a rhodium catalyst proceeds as follows:
58
Reaction conditions: [CH OH]/[CH I] = 6.25, 3 h, p = 2MPa,
CO
[Rh(acac)(CO) ] = 0.004 mmol; * [RhCl ⋅ 3H O] = 0.01 mM.
3
3
2
3 2
Table 3. Effect of iodineꢀcontaining additives on methanol carbonylation in the [HMIM][H2PO4] medium
Yield, %
Iodineꢀcontaining additive
[CH3OH]/[I–]
Conversion, %
CH3OC(O)CH3
CH3COOH
CH3I
CH3I
CH3I*
KI
6.2
24
95
48
26
85
91
92
86
5
42
48
26
63
29
42
8
53
–
–
22
62
50
6
24
6.2
6.2
24
I2
I2
HI
6.2
6.2
6.2
24
(CH3)4NI
(C2H5)4NI
Bu4NI
Bu4NI
Bu4NI**
5
–
–
–
–
5
7
7
12
83
12
12
17
75
6.2
6.2
Reaction conditions: 3 h, 190
5 h, = 5 MPa.
°
C,
p
= 2 MPa, [HMIM][H PO ] = 0.45 mol, [Rh(acac)(CO) ] = 0.004 mmol; * 130°C, ** 190
°
C,
CO
2
4
2
p
CO
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CARBONYLATION OF METHANOL AND DIMETHYL ETHER IN IONIC LIQUIDS
Table 4. Carbonylation of dimethyl ether
287
Yield, %
Medium
DME/CH3I
Conversion, %
CH3OH
CH3OC(O)CH3
CH3COOH
H2O
[HMIM][H2PO4]
6.22
6.22
1.4
60
100
96
20
4
15
64
65
25
32
26
5
Reaction conditions: 3 h, 190
°C,
p
= 2 MPa, [HMIM][H PO ] = 0.45 mol; [Rh (acac)(CO) ] = 0.004 mmol; [(CH ) O] = 0.04 mol.
CO 2 4 2 3 2
+
amount of an iodine promoter. It has been found that
the catalyst system can be repeatedly used without loss
of activity.
H
CH3OCH3
–
I
CH3OH + CH3I
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Fig. 3. Reuse of the catalyst system. Reaction conditions:
3 h, 190 C, = 2 MPa, [СH OH]/[CH I] = 6.25,
[HMIM][H PO ] = 0.45 mol, [Rh(acac)(CO) ] =
°
р
СО
4
3
3
2
2
0.004 mmol.
Translated by S. Zatonsky
PETROLEUM CHEMISTRY Vol. 54
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2014