8
36
Chemistry Letters 2002
Low Pressure Hydroformylation in the Presence of Alcohol Promoters
y
y
Ãy
Baitao Li, Xiaohong Li, Kenji Asami, and Kaoru Fujimoto
Department of Applied Chemistry, School of Engineering, The University of Tokyo, Tokyo 113-8656
School of Environmental Engineering, The University of Kitakyushu, 1-1 Hibikino, Fukuoka 808-0135
y
(Received May 2, 2002; CL-020382)
Active carbon supported cobalt catalyst was studied for the
hydrocarbon, toluene and THF over Co/A.C., only a small amount
of 1-hexene was converted to 2-hexene, even when the catalyst
was not passivated. The enhanced 1-hexene conversion was
observed over Co/A.C. in alcohol solvents, suggesting that
alcohol solvents dramatically promote the hydroformalytion
reaction under the conditions of 3.0 MPa and 403 K. It is worthy to
note that over the homogeneous catalyst, Co2(CO)8 exhibits high
activity in both methanol and octane, while over the hetero-
geneous catalyst, high activities were observed only in alcohol.
hydroformylation of 1-hexene in the presence of alcohol solvents
at low pressure. The influence of various solvents on the
hydroformylation and the CO conversion vs time on stream were
investigated in detail. It was found that the heterogeneous catalyst
shows excellent activity only in the alcohol solvents.
The emissions (smoke, particulate matter, CO, etc.) from
diesel engine can be diminished by the addition of oxygen-
containing compounds into hydrocarbon fuel. Our research group
is aiming at the production of clean fuel from synthesis gas
a
Table 1. Hydroformylation of 1-hexene in various solvents
b
Solvent
1-hexene
Yield/%
n=i
(
CO þ H2) and olefins, which is the further utilization of products
Conv./% C7-al C7-ol acetal ester isomer
1;2
in the Fischer-Tropsch synthesis. Olefin hydroformylation
process is an old and fundamental route of the synthesis of
aldehydes. The cobalt or rhodium carbonyls have been used as
Benzene
n-Heptane
n-Octane
n-Octanec
THF
Toluene
Methanol
Ethanol
0.3
0.1
0.2
0.2
0.1
0.2
49.2
72.9
74.1
0.1 0.1
0
0
0
0
0
0
0
0
0
0
0
0
0.1
0.1
0.2
0.2
0.1
0.1
14.9
7.6
5.9
—
—
—
—
—
—
0.3
0.4
0.4
0
0
0
0
0.1
0
0
0
0
0
traditionally representative homogeneous catalyst in the hydro-
formylation industrial process.3{5 The drawbacks of homogenous
catalysis, such as the high pressure, the recovery of metal and the
separation problem, inhibit their practical application in the wide
fields. Therefore, most of the researches under low pressure
conditions have been concerned with supported rhodium and
8.8 0.4
28.9 3.8
26.8 3.7
24.8 0.3
31.8 0.8
36.6 1.1
1
-Propanol
6
{11
cobalt catalyst.
n-Octaned
Methanold
a
84.4
80.6
b
67.8
27.4 1.6
0
0
0
38.5 1.3
16.6
11.8
1.0
0.4
Our works focus on the exploration of low pressure process of
hydroformylation. It is quite desirable that synthesis gas and
lower olefins from F-T process can be utilized without any
compression. In this work, hydroformylation was operated in
alcohol solvent at lowerpressure (3.0 MPa) over Co/active carbon
using 1-hexene as model material.
3
1
.0 MPa; 403 K. Ratio of normal C7-aldehyde to i-C7-aldehyde.
c
d
0 wt% Co/active carbon without passivation. Co2(CO)8 (0.06 g)
was used as catalyst.
For heterogeneous catalyst, the conversion of olefin and yield
of oxygenates are largely related to the formation of active metal
The supported active carbon (20–40 mesh) was obtained
2
from Kanto Chemical Co. with surface area of 1071.7 m /g and
3
6
carbonyl species and the formation of Co2(CO)8 requires a
average pore volume of 0.43 cm /g. The support was impregnated
5
higher CO pressure, usually above 7.0 MPa if without any
with aqueous solution of cobalt nitrate. The weight percent of
cobalt metal in catalyst was 10 wt%. The catalyst precursor was
heated in nitrogen flow at 673 K for 4 h and reduced under
hydrogen flow at 673 K for 6 h. The reduced catalyst was
passivated by 1% O2 diluted in N2 flow before use.
solvent. Lower pressure such as 2.0 MPa was not suitable as the
activity was very low under that condition. In case of Co2(CO)8,
the catalyst reaction rate was high but the life was short. After
reaction, the precipitate of Co metal was detected.
When methanol was used as solvent, aldehydes and acetal
1,1-dimethoxy heptane) were main products. Trace amount of
Catalytic reactions were carried out in a semi–batch slurry–
phase reactor with inner volume of 85 ml. The amount of catalyst
was 0.2 g. 120 mmol of 1-hexene was used as a model olefin.
Solvent/1-hexene ¼ 2=1 (molar ratio). The flow rate of syngas
(
ester (heptanoic acid methyl ester) were also formed. The
formations of acetal and ester are shown as follows:
(
CO=H2=Ar ¼ 47:8=48:2=4:0) in the reaction was set to 80 ml/
RCHO þ 2CH OH ! RCHðOCH Þ þ H O
R-CO-Co þ CH3OH ! R-CO-OCH3 þ CoH
ð1Þ
ð2Þ
3
3 2
2
min.
The gaseous products were analyzed by an on-line GC
equipped with an active charcoal column. The liquid products
were analyzed by gas chromatography equipped with a DB-1
column of the J&W Scientific Co.
In the blank test without any solvents or catalyst, no 1-hexene
conversion was observed at 3.0 MPa and 403 K over 10 wt% Co/
A.C. The comparative effects of solvents on the hydroformylation
of 1-hexene are compared in Table 1. In the solvents of benzene,
The CO conversion as a function of reaction time is presented
in Figure 1. For the passivated 10 wt% Co/A.C, an induction
period exists at the beginning of the reaction, while no such period
was showed over 10 wt% Co/A.C. without passivation under the
same reaction condition. We can assume that the induction period
partly involves a reduction process in the presence of methanol
solvent and synthesis gas, which provides more active metallic
Copyright Ó 2002 The Chemical Society of Japan
Li, Baitao
