852
Chemistry Letters Vol.37, No.8 (2008)
Efficient Hydrogenation of Ethyl Lactate to 1,2-Propanediol
over Ru–B/TiO2 in Aqueous Solution
Guang-Yin Fan,1 Ye Zhang,1;2 Ya-Fen Zhou,1 Rui-Xiang Li,ꢀ1 Hua Chen,1 and Xian-Jun Li1
1Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry,
Sichuan University, Chengdu, Sichuan 610064, P. R. China
2Department of Chemistry, Chifeng College, Chifeng 024000, Inner Mongolia, P. R. China
(Received April 14, 2008; CL-080387)
Catalyst Ru–B/TiO2 showed an excellently catalytic per-
perature under the ultrasound agitation. At the end of reaction,
formance for the hydrogenation of ethyl lactate to 1,2-propane-
diol (1,2-PDO) under mild conditions (90 ꢁC and 4.0 MPa H2)
without any additive. Especially, the activity of the catalyst
was greatly improved in aqueous solution. The conversion of
ethyl lactate was up to 98% and the selectivity to 1,2-propane-
diol was over 95%.
the black precipitate was filtered, washed with distilled water,
and dried under vacuum at 60 ꢁC for 10 h. The filtrate was
collected to determine the composition of the catalyst by ICP.
The hydrogenation of ethyl lactate was carried out in a 60-
mL steel autoclave equipped with a glass liner and a magnetic
stirrer. The desired amounts of catalyst, ethyl lactate, and solvent
were charged to the reactor. The autoclave was flushed with pure
hydrogen five times. When the designated reaction temperature
was reached, hydrogen was fed to the desired pressure, the stir-
ring rate was adjusted to 1500 rpm, and reaction timing began.
The contents of ruthenium and boron in catalyst were
determined by ICP (IRIS Intrepid). Transmission electron
microscopy (TEM) was carried out in a JEM-1200 apparatus
at an accelerating voltage of 100 kV. X-ray diffraction spectra
(XRD) were recorded with a PHILIPHS X’Pert MPD and Cu Kꢀ
was used as the radiation source at the voltage of 50 kV and
the current of 30 mA. Samples were scanned in the range of
2ꢁ ¼ 10{90ꢁ at a rate of 0.06ꢁ/s. All liquid samples were
analyzed by gas chromatography (Agilent GC-6890) with a
FID detector and a PEG-20M supelco column (30 m ꢂ
0:25 mm, 0.25-mm film). The conversion and selectivity are
defined as following:
1,2-Propanediol (1,2-PDO) is an important industrial chem-
ical, which is widely used as the raw materials to produce poly-
mers, resins, and functional fluids (antifreeze, deicing). A com-
mercial route to synthesize 1,2-PDO is the hydration of propyl-
ene oxide derived from propylene by either a chlorohydrin proc-
ess or a hydroperoxide process.1,2 Thus, to develop a cleanly and
economically synthetic approach of 1,2-PDO is important. From
renewable feedstocks, hydrogenolysis of glycerol is a useful
route to prepare 1,2-PDO, but a challenging problem for this
route is to look for an efficient catalyst as the reported catalysts
generally show the low activity and selectivity.3–6 Thus, the
direct hydrogenation of lactic acid or lactates, which are easily
obtained by fermentation of renewable sources such as agricul-
tural crops and biomass streams, is a good green route to produce
1,2-PDO. In the hydrogenation of lactates, it is found that nickel
and ruthenium catalysts are effective, but the reaction conditions
are drastic. For example, the hydrogenation over Raney Ni must
be performed in a high H2 pressure of 25 MPa.7–9 To use unsup-
ported ruthenium black as catalyst, the hydrogenation could be
achieved at 150 ꢁC and 27 MPa and only gave a 1,2-propanediol
yield of 84%.10 Over Ru/C, 1,2-propanediol was obtained at the
reaction temperature of 150 ꢁC and hydrogen pressure of
14.5 MPa.11 Recently, it was found that the introduction of tin
was an effective method to improve the hydrogenation activity
of ruthenium-based catalyst,12–14 but the hydrogenation was still
carried out under the conditions of 150 ꢁC and 5.5 MPa. To our
knowledge, an organic solvent is the best choice in order to
obtain a good result for the hydrogenation of lactates to 1,2-
PDO. In the present study, we first found that Ru–B/TiO2
catalyst, prepared by the reduction impregnation method, was
an excellent catalyst for the hydrogenation of ethyl lactates
to 1,2-PDO. Especially, when the safe and environmentally
friendly water was used as a solvent, the hydrogenation could
quickly progress at the low temperature of 90 ꢁC and hydrogen
pressure of 4.0 MPa.
ethyl lactate consumed
C=% ¼
S=% ¼
ꢂ 100
ð1Þ
ð2Þ
ethyl lactate initially charged
defined product
ꢂ 100
ethyl lactate consumed
ICP analysis of the collected filtrate indicated that ruthenium
and boron loading in this catalyst were 7.9 and 8.5 wt %, respec-
tively. The transmission electron micrograph of Ru–B/TiO2
exhibited that ruthenium particles were highly dispersed on TiO2
in a size range of 5–10 nm and the electron diffraction of the
selected metal particle did not show any diffraction spot.17 The
result indicated that the metal particles are amorphous alloy
formed between Ru and B, which is consistent with the reported
result.12 The XRD pattern of Ru–B/TiO2 exhibited no rutheni-
um particles were detected and this also indicated that ruthenium
particles are amorphous and highly dispersed on TiO2.
The effect of solvents on the hydrogenation of ethyl lactate
is shown in Table 1. In all reaction solutions, the detectable by-
products were 1-propanol (n-PP), propionic acid (PA), and lactic
acid (LA). According to the results in Table 1, the conversions in
alcohol solvents are higher than that in n-hexane and dioxane.
The catalytic activity of the catalyst in different solvents
increases in the order of dioxane < n-hexane < ethanol <
2-propanol. Interestingly, an excellently catalytic performance
of RuB/TiO2 was exhibited with water as a solvent. The conver-
Catalyst Ru–B/TiO2 was prepared by a reduction impregna-
tion method. The alcohol solution of 10 mL containing RuCl3
of 1.58 mmol was rapidly added to the flask containing TiO2
(2.0 g), and then the mixture was reduced with an aqueous solu-
tion of NaBH4 (a molar ratio of B to Ru was 10:1) at room tem-
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