Vapor-phase carbonylation of dimethoxymethane over H-faujasite

Full text of DOI:10.1002/anie.200900464

Angewandte
Chemie
DOI: 10.1002/anie.200900464
Carbonylation
Vapor-Phase Carbonylation of Dimethoxymethane over H-Faujasite**
Fuat E. Celik, Tae-Jin Kim, and Alexis T. Bell*
The carbonylation of formaldehyde or formaldehyde deriv-
atives has been investigated as a means for producing glycolic
[
1–8]
acid and its esters/ethers.
These products can be converted
readily into ethylene glycol, an important industrial chemical
used in polyester synthesis. Previous investigations of these
reactions have been carried out in the liquid phase, and have
required high carbon monoxide pressures (tens to hundreds
of atmospheres) to overcome the low solubility of carbon
monoxide. It has also been observed that at lower carbon
monoxide pressures, the reaction of formaldehyde with itself,
the Cannizzaro disproportionation reaction, becomes the
dominant process.
We report herein the first example of the vapor-phase
carbonylation of dimethoxymethane (DMM), the dimethyl
acetal of formaldehyde. Using H-Faujasite (H-FAU; an acid
zeolite) as the catalyst, it was possible to produce methyl
methoxyacetate (MMAc) by the reaction in Equation 1 with a
CH OCH OCH þ CO ! CH OCH COOCH
ð1Þ
3
2
3
3
2
3
selectivity of up to 79% and a yield of up to 20% based on
DMM. MMAc is an ether/ester of glycolic acid, and can be
converted into glycolic acid and then ethylene glycol by
hydrolysis and hydrogenation. Alternatively, MMAc can be
reduced directly to 2-methoxyethanol, an industrial solvent.
Disproportionation of DMM to produce dimethyl ether
(
DME) and methyl formate (MF) [Eq. (2)] was the only
Figure 1. The effect of reaction temperature on a) the rates (R) of
MMAc (*), DME (&), and MF (^) formation, and b) DMM conver-
sion (&; left-hand axis), and selectivity of MMAc from DMM (*;
right-hand axis). PCO =1.99 atm, PDMM =0.017 atm, total gas flow
competing process observed.
2
CH
3
OCH
2
OCH
3
! 2 CH
3
OCH
3
þ HCOOCH
3
ð2Þ
3
ꢀ1
3
ꢀ1
rate=100 cm min at pressure, 200 cm min at STP.
The effects of temperature on the rate of DMM carbon-
ylation to MMAc and the rate of DMM disproportionation to
DME and MF are shown in Figure 1a.
conversion of DMM increased with increasing temperature,
the selectivity of DMM conversion into MMAc reached a
maximum at 373 K.
The products DME and MF were formed in a ratio
DME:MF close to two, consistent with the stoichiometry of
Equation (2). This observation and the absence of formalde-
hyde in the reaction products indicate that DMM decom-
position to DME and formaldehyde did not occur. The rate of
MMAc formation reached a maximum at 393 K, whereas the
rate of DMM disproportionation increased monotonically
with increasing temperature. As seen in Figure 1b, while the
The rate of DMM carbonylation and the selectivity of
DMM conversion into MMAc increased with increasing
carbon monoxide partial pressure (PCO) while the DMM
pressure was kept roughly constant (Figure 2a and b). The
maximum rate and the MMAc selectivity shifted to lower
temperatures as PCO increased, with the selectivity maximum
occurring 20–30 K lower than the rate maximum. A maximum
selectivity of 79% was reached at 2.99 atm CO pressure and
3
73 K. Although the maximum rate increased nearly linearly
[
*] F. E. Celik, Dr. T. J. Kim, Prof. A. T. Bell
Chemical Engineering, University of California, Berkeley
Berkeley, CA 94720 (USA)
Fax: (+1)510-642-4778
E-mail: bell@cchem.berkeley.edu
with CO pressure, the maximum selectivity began to level off
at CO pressures between 1.99 and 2.99 atm (see Supporting
Information). DMM conversion increased with increasing
PCO, as the carbonylation rate increased, while the dispro-
portionation rate stayed roughly constant.
[
**] This work was supported by the Methane Conversion Cooperative
funded by BP.
Figure 3a shows that for a fixed CO pressure the rate of
DMM disproportionation increased with increasing DMM
partial pressure (PDMM), while the rate of carbonylation went
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200900464.
Angew. Chem. Int. Ed. 2009, 48, 4813 –4815
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Communications
Figure 2. The effect of reaction temperature on a) the rate of MMAc
formation at different CO pressures as labeled, and b) the selectivity of
MMAc from DMM at different CO pressures as labeled. P =0.013–
Figure 3. The effect of DMM partial pressure on a) the rate (R) of
MMAc (*), DME (&), and MF (^) formation, and b) DMM conver-
sion (&; left-hand axis), and selectivity of MMAc from DMM (*;
DMM
3
ꢀ1
0
3
.019 atm, total gas flow rate=100 cm min at pressure, 100–
00 cm min at standard temperature and pressure (STP).
3
ꢀ1
right-hand axis). T=383 K, P =1.0 atm, P=2.0 atm (balance He),
CO
3
ꢀ1
3
ꢀ1
total gas flow rate=100 cm min at pressure, 200 cm min at STP.
selectivity to MMAc increased as a function of time until
reaching their steady-state values.
through a maximum. Figure 3b demonstrates that both DMM
conversion and selectivity to MMAc decreased with increas-
ing DMM pressure. These data indicate that higher DMM
pressures favor disproportionation over carbonylation, as
could be inferred from the stoichiometry of the reactions in
Equations (1) and (2). For this reason, DMM pressure was
kept low in all experiments, usually between 0.01 atm and
The observed rate of DMM carbonylation is comparable
to that reported for the carbonylation of DME over H-
[
9]
MOR. At 438 K, the turnover frequency for DME carbon-
ꢀ
1
ylation to methyl acetate was approximately 0.2 h at
approximately 2 atm of CO and increased to approximately
ꢀ1
1.1 h at approximately 10 atm of CO with selectivity
approaching 100%. By contrast, the turnover frequency for
DMM carbonylation to MMAc over H-FAU reported herein
0
.02 atm. Figure 3b suggests that even higher selectivities and
conversions could have been achieved at DMM partial
pressures below 0.01 atm.
Taken together the results presented in Figures 1–Figure 3
show that the selectivity of DMM conversion into MMAc
increases with increasing PCO/PDMM ratio and that the overall
rate of MMAc formation could be increased by increasing
ꢀ
1
was approximately 13 h at approximately 1 atm of CO and
413 K with 35% selectivity, and increased to approximately
ꢀ1
32 h at approximately 3 atm of CO and 393 K with 69%
selectivity. A MMAc selectivity of 79% from DMM was
ꢀ
1
achieved with a turnover frequency of approximately 24 h at
approximately 3 atm of CO and 373 K. These observations
are consistent with the higher reactivity of formaldehyde and
its acetals relative to those of ethers.
PCO at a fixed PDMM
.
With increasing space time (number of Al centers within
the catalyst sample divided by the total gas volumetric flow
rate), the conversion of DMM increased but the MMAc
selectivity remained nearly constant (see Supporting Infor-
mation). While the rate of MMAc formation per mole of Al
loaded into the reactor decreased with increasing space time,
higher yields of MMAc could be achieved without sacrificing
selectivity by operating at higher space times.
The maximum MMAc selectivity of 79% achieved in the
present study using a vapor-phase reaction is comparable to
that reported previously for formaldehyde carbonylation
using solid acids and carbon monoxide pressures of 314 atm
[
3]
[5]
(79%) and 238 atm (81%) in liquid-phase reactions with
solid acid resin catalysts.
After an initial transient period of approximately 120 min,
the catalyst showed stable steady-state activity and selectivity
for at least 24 h. During the transient period, activity and
In conclusion, we have shown that high-selectivity, vapor-
phase, carbonylation of DMM to MMAc can be achieved at
low pressure using H-FAU as the catalyst. DMM dispropor-
4
814
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Angewandte
Chemie
ꢀ1
tionation to DME and MF can be minimized by keeping the
ratio of PCO to PDMM high.
was held constant at 0.27 (mmol Al) minL except where noted
otherwise. When varied, changes in space time were accomplished by
increasing the amount of catalyst used in the experiment.
Selectivities to MMAc from DMM are reported on the basis of
mole of carbon using the following formula: 3(mole of MMAc
formed)/[2(mole of DME formed) + 2(mole of MF formed) + 3(mole
of MMAc formed)]. The selectivity to MMAc from CO was 100%.
Experimental Section
NH -faujasite (Si/Al = 30, Zeolyst), was heated for 3 h at 773 K
4
ꢀ1
3
ꢀ1
+
(
2 Kmin ramp rate) in 100 cm min dry air to convert it into the H
form and remove water. Characterization by FT-IR using a Thermo
Nicolet Nexus 6700 FTIR spectrometer showed no evidence for
extra-framework aluminum formation following catalyst pretreat-
ment (see Supporting Information).
Received: January 24, 2009
Revised: March 17, 2009
Published online: May 18, 2009
Reactions were carried out using 0.05 g of catalyst in a 6.35 mm
outer diameter (OD) quartz reactor tube with an expansion in the
middle (ca. 12.7 mm OD) packed with quartz wool to hold the
catalyst in place. A quartz-sheathed K-type thermocouple was placed
in direct contact with the catalyst bed. The catalyst was pretreated for
Keywords: acid catalysis · carbonylation · formaldehyde ·
heterogeneous catalysis · zeolites
.
3
ꢀ1
3
h at 773 K in dry air (100 cm min ) to remove residual moisture,
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and cooled to reaction temperature. CO (99.99% pure research
grade, Praxair) was bubbled through a stainless steel saturator filled
with DMM (99%, Sigma–Aldrich) and chilled to provide the desired
vapor pressure. Additional CO or He was mixed with the saturator
exit flow to set the desired CO/DMM ratio and the total gas
volumetric flow rate. Reaction products were analyzed using an
Agilent 6890n GC equipped with an HP-PLOT Q capillary column
connected to a flame ionization detector. Experiments at elevated
pressure were carried out by throttling a needle valve located
downstream from the reactor.
Activity and selectivity data were collected as a function of
temperature by increasing the reaction temperature at a fixed
reactant composition and flow rate. Each temperature was held
constant for 45 min.
The total gas flow rate in the reactor was maintained at
3
ꢀ1
1
00 cm min at the reaction pressure, resulting in gas flow rates
3
ꢀ1
between 100 and 300 cm min at STP. The reactor space time,
calculated on the basis of mole of aluminum in the zeolite framework,
Angew. Chem. Int. Ed. 2009, 48, 4813 –4815
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4815