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Conversion of Methyl Lactate to
Acrylates over Modified
NaY Zeolite Catalysts
Conversion
MA
Atsushi Takahashi,1 Naomi Shibasaki-Kitakawa,2
and Tadahiro Fujitani*1
MeOH
CO2
1Interdisciplinary Research Center for Catalytic Chemistry,
National Institute of Advanced Industrial Science and
Technology (AIST), 1-1-1 Higashi, Tsukuba,
Ibaraki 305-8565
AA
AD
10
CO
0
5
15
K content /wt%
2Department of Chemical Engineering, Tohoku University,
6-6-07 Aoba-Yama, Aoba-ku, Sendai, Miyagi 980-8579
Figure 1. K content dependence of product distribution of
reaction of methyl lactate over K/NaY zeolites. ; AD,
acetaldehyde, ; AA, acrylic acid, ; MA, methyl acrylate,
; MeOH, methanol, ; CO, ; CO2. Open symbols
indicate data for a sample prepared by ion exchange.
E-mail: t-fujitani@aist.go.jp
Received: June 22, 2015; Accepted: August 3, 2015;
Web Released: November 15, 2015
Reaction conditions: temperature, 350 °C; methyl lactate
¹3
concentration, 10 vol %; W/F, 1.0 © 10¹2 g min cm
.
The catalytic activity of alkali metal- and alkaline earth
metal-modified NaY zeolites for production of acrylic acid
and methyl acrylate from methyl lactate was investigated.
The reaction pathways and the role of the alkali metals in
acrylate production are discussed.
received. The zeolites were impregnated with hydroxide salts of
alkali metals (LiOH¢H2O, NaOH, KOH, and CsOH¢H2O) and
hydroxide or nitrate salts of alkaline earth metals (Mg(NO3)2¢
6H2O, Ca(NO3)2¢4H2O, Sr(OH)2, and Ba(OH)2¢H2O) by
means of the incipient wetness method. All catalysts were
dried in air at 100 °C for 10 h prior to use.
Reactions of ML were carried out in a continuous-flow
fixed-bed tubular reactor at atmospheric pressure. ML was
vaporized with a heater, and the vapor was diluted with N2 to a
ML concentration of 10 vol %. The reaction temperature was
350 °C. The catalyst temperature was monitored with a thermo-
couple in the catalyst bed. Oxygenated reaction products were
analyzed by means of an online gas chromatograph equipped
with a hydrogen-flame ionization detector and a TC-FFAP
column, and CO and CO2 were analyzed with a thermal
conductivity detector and a Shincarbon ST column (Shinwa
Chemical Industries, Japan). Product yields were calculated on
a carbon number basis.
Acrylic acid (AA) and acrylic acid esters are the primary
building blocks of acrylate polymers and plastics. Currently,
AA is manufactured mainly by two-step oxidation of propyl-
ene, a process that is totally dependent on a nonrenewable
fossil resource. Therefore, the development of a novel process
that is both sustainable and economically viable would be of
great importance. One possible process is the formation of AA
by dehydration of lactic acid (LA) or methyl lactate (ML). New
fermentation-based technologies for producing LA from starch
hydrolysates make LA a viable feedstock for chemical pro-
duction.1 Furthermore, a new chemical process for the conver-
sion of cellulose to LA and its derivatives, mainly ML, has
been developed.2
There have been numerous reports of the dehydration of LA
to AA over catalysts such as sulfates,3 phosphates,3-6 mixtures
of sulfates and phosphates,7 NaY zeolites, and NaY zeolites
modified with potassium (K).8,9 In contrast, there have been
only a few reports dealing with catalyst systems for ML dehy-
dration. NaY modified with K by means of an ion-exchange
method has been shown to catalyze the dehydration of ML
to methyl acrylate (MA) in a relatively high yield (38%).10
However, the reaction mechanism and the nature of the active
sites for ML dehydration are not well understood.
In the present work, we carried out the dehydration of ML to
MA and AA over NaY zeolite catalysts and studied how the
catalyst activity was affected by modification with alkali and
alkaline earth metals. The reaction pathways and the active
sites for ML dehydration are discussed.
We examined the effect of K content on the catalytic activity
of K-modified NaY zeolites (K/NaY) (Figure 1). ML conver-
sion over unmodified NaY zeolites was 86%, and the AA and
MA selectivities were 43% and 10%, respectively. Both ML
conversion and MA selectivity increased (reaching maxima of
98% and 53%, respectively) with increasing K content up to
5 wt %, whereas AA selectivity was unchanged. CO and CO2
were produced as by-products of the reaction. We confirmed
acetaldehyde and methanol as the counter-part chemicals of CO
formation (decarbonylation) and CO2 formation (decarboxyla-
tion) by GC measurements. The CO selectivity was 5% over
unmodified NaY zeolites, and the selectivity decreased with
increasing K content (no CO was produced at 10 wt % K);
whereas CO2 production increased with increasing K content.
Decarbonylation of LA to form CO is reported to occur on
acidic sites, whereas CO2 is produced by decarboxylation of
LA on basic sites.11 Over NaY zeolites, the conversion of LA to
Na-form Y zeolites (NaY; JRC-Z-Y-5.3, SiO2/Al2O3 = 5.3)
were obtained from the Catalysis Society of Japan and used as
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