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60
Chemistry Letters Vol.38, No.6 (2009)
Selective Conversion of Glycerol into 1,2-Propanediol at Ambient Hydrogen Pressure
Ã1
1
2
3
Satoshi Sato, Masaki Akiyama, Kanichiro Inui, and Masahiro Yokota
Graduate School of Engineering, Chiba University, Yayoi, Inage-ku, Chiba 263-8522
1
2
Chisso Petrochemical Corporation, 5-1 Goi-kaigan, Ichihara 290-8551
3
Chisso Corporation, 2-2-1 Otemachi, Chiyoda-ku, Tokyo 100-8105
(Received February 17, 2009; CL-090170; E-mail: satoshi@faculty.chiba-u.jp)
The vapor-phase reaction of glycerol was performed over a
OH
OH
-
H O
2
copper–alumina catalyst at ambient hydrogen pressure. Glycerol
was converted into 1,2-propanediol (PDO) through dehydration–
hydrogenation via hydroxyacetone (HA). We also found that
HO
OH
HO
0
.1 MPa H2
1,2-PDO was produced at the selectivity higher than 93 mol %
in hydrogen flow at gradient temperatures: the dehydrogenation
Scheme 1.
ꢀ
into HA was catalyzed at around 180–200 C, while the follow-
ing hydrogenation into 1,2-PDO was catalyzed by Cu–alumina
be an efficient catalyst for the reverse hydrogenation at temper-
ꢀ
atures lower than 210 C.
ꢀ
catalyst at around 145–160 C.
In this paper, we report that the transformation of glycerol
into 1,2-PDO was performed over alumina-supported copper
catalyst at ambient hydrogen pressure, and that 1,2-PDO was
selectively formed from glycerol at gradient temperatures
(Scheme 1).
A commercially available catalyst, such as Cu/Al2O3
(N242) with CuO content of 55 wt %, was purchased from Nikki
Chemical Co., Ltd., Japan. The reaction of glycerol was per-
formed in a fixed-bed down-flow reactor with an inner diameter
of 17 mm at ambient hydrogen pressure and temperatures be-
The catalytic conversion of carbon-neutral biomass into use-
ful chemicals is expected to be a potential solution to the severe
1
,2
global environmental pollution problem. Renewable biomass
fuels, such as bioethanol and biodiesel fuel (BDF), i.e., fatty acid
methyl esters, are attracting much attention worldwide. Glyc-
erol, a by-product of BDF production for ca. 10 mass % of BDF
produced, is one of such promising renewable resources. Its
quantity increases as the amount of BDF produced is increased.
Recently, quite a number of studies on the reaction of glyc-
ꢀ
tween 135 and 250 C. A catalyst with 75 to 650-mm granule size
was placed in the reactor. After the temperature of the catalyst
bed had been maintained at a prescribed temperature in hydro-
gen flow for 1.0 h, a 30 wt % aqueous solution of glycerol was
2
–4
5–16
erol have appeared in reviews and research papers.
In liq-
uid-phase hydrogenolysis under hydrogen pressure, glycerol is
converted into 1,2-PDO and 1,3-PDO in the presence of support-
3
À1
fed into the reactor at the feed rate of 1.8 cm h , which corre-
sponded to 5.9 mmol of glycerol per hour. The liquid product
5
6–8
8,9
ed Rh, Ru, or Pt. In the vapor-phase hydrogenolysis of
glycerol, Cu catalyzes 1,2-PDO formation in the presence of
ꢀ
that was collected in a dry ice–acetone trap (at À80 C) every
1
0–13
high hydrogen pressure.
elevated hydrogen pressure,
Since the hydrogenolysis requires
–11
hour was analyzed on a gas chromatograph (FID-GC, Shimadzu
GC-8A) using a 60-m capillary column (TC-WAX, GL Science,
Japan).
5
side reactions occur to form
several by-products, including ethylene glycol (EG), propanol,
lactic acid, and propanoic acid. Hydroxyacetone (HA) is an in-
termediate product in the conversion of glycerol into 1,2-PDO
through the dehydration–hydrogenation reactions. Over Cu
Figure 1 shows changes in the catalytic conversion of glyc-
erol with reaction temperature. The conversion attained 100%
ꢀ
at temperatures higher than 190 C. The selectivity to 1,2-PDO
ꢀ
catalysts, however, 1,2-PDO selectivity higher than 90 mol %
low temperatures and high hydrogen pressures
was maximum at 190 C, while that to HA was minimum at
the same temperature. The selectivity to EG increased slowly
with increasing reaction temperature. The highest yield of 1,2-
is attained:1
2,13
favor the shift of equilibrium from HA to 1,2-PDO and reduce
1
3
ꢀ
the formation of by-products resulting from HA side reactions.
PDO was attained at 190 C. The changes in the selectivities
One effective operation is a two-step process composed of
dehydration under vacuum and hydrogenation under hydrogen
pressure.1
to HA and 1,2-PDO suggest that the hydrogenation of HA into
1,2-PDO is favored at low temperatures.
Figure 2 shows changes in the catalytic conversion of glyc-
3,15
ꢀ
It is known that copper works as a dehydrogenation catalyst
7
erol with H2 flow rate at 210 C and ambient pressure. The re-
sults indicate that 1,2-PDO is favored at high H2 flow rate even
at ambient pressure. The selectivity to 1,2-PDO became constant
18
for polyols, such as 1,2-1 and 1,3-diols. However, glycerol can
1
4–16
be dehydrated into HA over copper metal catalysts.
be noted that copper metal catalyzes the dehydration of glycerol
It should
3
À1
at H2 flow rates above 360 cm min , which corresponded to
glycerol/H2 = 1/141. The selectivity to EG increased slowly
with increasing H2 flow rate. Therefore, the hydrogenation of
HA into 1,2-PDO should be operated at temperatures lower than
ꢀ
to produce HA with selectivity higher than 90 mol % at 250 C,
and that no dehydrogenation proceeds to form dihydroxyace-
tone.1 1,2-PDO is dehydrogenated to form HA in the presence
of inert carrier gas over copper catalysts, and the dehydrogena-
4,16
ꢀ
190 C to shift the equilibrium to the right side.
Hydrogenation of carbonyl compounds, such as acetone and
1
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tion is controlled by equilibrium. This reminds us that 1,2-
PDO is favored at high hydrogen partial pressure even at ambi-
ent pressure. As copper metal works as a catalyst for the dehy-
1
9
propanal, is an exothermic reaction. Thus, in the hydrogenoly-
sis of glycerol, the second-step hydrogenation would favor low
temperatures thermodynamically. Actually, the reverse reaction,
ꢀ
17
drogenation of 1,2-PDO into HA at 210 C, it is expected to
Copyright ꢀ 2009 The Chemical Society of Japan
Sato, Satoshi
