Strontium chloride modified Nieuwland catalyst in the dimerization of acetylene to monovinylacetylene

Article abstract of DOI:10.14233/ajchem.2014.17994

SrCl₂ was used as a co-catalyst of CuCl in Nieuwland catalyst and CuCl as the main catalyst, NH₄Cl as the solubilizer, water as the solvent and a certain amount of hydrochloric acid, thereby forming Sr-Cu bimetallic cooperative catalysis reaction systems for C₂H₂ dimerization. Under the optimum condition, the acetylene conversion is 13 % and monovinylacetylene selectivity can reach to 94 %.

Full text of DOI:10.14233/ajchem.2014.17994

Asian Journal of Chemistry; Vol. 26, No. 23 (2014), 8211-8214
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.17994
Strontium Chloride Modified Nieuwland Catalyst in the Dimerization of Acetylene to Monovinylacetylene
*
*
JUN-LONG LU, JIAN-WEI XIE , HAI-YUE LIU, PING LIU, ZHI-YONG LIU and BIN DAI
School of Chemistry and Chemical Engineering/Key Laboratory for Green Processing of Chemical Engineering of Xinjiang Bingtuan, Shihezi
University, North 4th Road, Shihezi 832003, P.R. China
*Corresponding authors: Fax: +86 993 2057270; Tel: +86 993 2057213; E-mail: cesxjw@gmail.com
Received: 13 May 2014;
Accepted: 23 July 2014;
Published online: 15 November 2014;
AJC-16327
SrCl2 was used as a co-catalyst of CuCl in Nieuwland catalyst and CuCl as the main catalyst, NH4Cl as the solubilizer, water as the solvent
and a certain amount of hydrochloric acid, thereby forming Sr-Cu bimetallic cooperative catalysis reaction systems for C2H2 dimerization.
Under the optimum condition, the acetylene conversion is 13 % and monovinylacetylene selectivity can reach to 94 %.
Keywords: Strontium chloride, Nieuwland catalyst, Acetylene dimerization, Monovinylacetylene.
In recent years, studies related to C2H2 dimerization have
attracted significant attention. Osakada and co-workers3
investigated the structure of Nieuwland catalyst in solid state
and in solution and their results revealed that the Cu compounds
are CuCl and K2CuCl3 in solid state and KCuCl2 is the dominant
component in solution. Han and co-workers reported the
composition of the precipitate which is often formed in the
C2H2 dimerization reaction. Their results indicated that the
precipitate is composed of CuCl·2C2H2·1/5NH3 obtained from
the aqueous Nieuwland catalyst6 and 2CuCl·3C2H2·1/
3CH3CH2NH2·1/7C3H7NO in anhydrous N,N-dimethyl-
formamide (DMF)7. They also studied the effect of solvent on
catalytic performance and the highest yield of monovinyl-
acetylene have been obtained when DMF was used as solvent,
which contribute to its strong coordination ability to Cu(I)8.
Tao and co-workers reported that urea9, LaCl310, or CeCl311
can improve monovinylacetylene selectivity, when they were
used as co-catalyst to the Nieuwland catalyst. Mechanistic
studies on dimerization of C2H2 with Nieuwland catalyst were
conducted by Fukuzumi and co-workers12-14. The results indi-
cated that deprotonation of the C2H2 π-complex to form the σ-
complex with the Nieuwland catalyst was the rate-determining
step and it was important to avoid any further reaction of Cu(I)-
monovinylacetylene π-complex with the C2H2 π-complex,
which leads to the formation of the trimeri-zation product.
Although significant improvements have been achieved
in C2H2 dimerization reaction, the drawbacks such as low C2H2
conversion and low monovinylacetylene selectivity also exist7.
Herein, we report our efforts in finding Sr-Cu bimetallic coope-
rative catalysis reaction systems for C2H2 dimerization. In the
catalyst system, CuCl was used as the main catalyst, SrCl2
INTRODUCTION
The dimerization of C2H2 is an important industrial process
for the production of monovinylacetylene (MVA), a starting
material used in C2H2-based processes for chloroprene rubber
production1. Although largely being superseded in many
developed countries by butadiene-based processes, C2H2
dimerization is still an important process for chloroprene
production in locations where coal-based economies remain
active, such as in China. In addition, monovinylacetylene can
also be used to produce other important chemical products,
such as 4-chlorophthalic anhydride, benzene, styrene and
butanedione2. A Nieuwland catalyst composed of CuCl and
KCl or NH4Cl in acidic aqueous solution has long been used
for C2H2 dimerization on an industrial scales3. Crystallographic
studies of the solid products recovered from Nieuwland
aqueous solutions of CuCl and NH4Cl have revealed that the
active components in Nieuwland catalyst are chlorocuprates
(CumCln-(n-m))4.
Dimerization of C2H2 with Nieuwland catalyst is usually
conducted in a bubbling bed reactor. Acetylene gas is conti-
nuously introduced into a liquid catalyst solution and the
unreacted C2H2, monovinylacetylene and other by-products
flow out of the reactor together. All of the possible reactions
are shown in Table-1. Monovinylacetylene is the dimerization
product of C2H2, and C2H2 or monovinylacetylene can also
react with H2O and HCl to yield several by-products, such as
vinyl chloride, acetaldehyde, 2-chloro-1,3-butadiene and 1,5-
hexadien-3-yne. The main side reaction is C2H2 trimerization,
which can be considered as the further reaction of mono-
vinylacetylene with C2H25.

8212 Lu et al.
Asian J. Chem.
TABLE-1
REACTIONS IN THE DIMERIZATION OF C2H2
CATALYSED BY NIEUWLAND CATALYST
absorption bottle containing NaOH solution and then into a
Shimadzu GC-2014C chromatogram equipped with GDX-301
chromatography column and flame ionization detector for
analysis.
Formula
Number
(1)
HC≡CH + HC≡CH → CH2=CHC≡CH
Analytical methods: The conversion of C2H2 (XA) and
the selectivity to monovinylacetylene (SMVA), which are the
criteria of catalytic performance, are obtained using the
following equations:
(2)
HC≡CH + HCl → CH2=CHCl
(3)
HC≡CH + H2O → CH3CHO
(4)
CH2=CHC≡CH + HCl → CH2=CHCCl=CH2
HC≡CH + CH2=CHC≡CH → CH2=CHC≡CCH=CH2
(5)
XA = [(ϕ2 + ϕ3 + 2ϕ4 + 2ϕ5 + 3ϕ6)/(ϕ1 + ϕ2 + ϕ3 + 2ϕ4 +
2ϕ5 + 3ϕ6)] × 100 %
SMVA = [2ϕ4/(ϕ2 + ϕ3 + 2ϕ4 + 2ϕ5 + 3ϕ6)] × 100 %
(1)
(2)
as co-catalyst, NH4Cl as the solubilizer and a certain amount
of hydrochloric acid was added to the catalyst solution to
achieve an acidic aqueous environment.
where, ϕ1, ϕ2, ϕ3, ϕ4, ϕ5 and ϕ6 are considered as the volume
fraction of acetylene, vinyl chloride, acetaldehyde, monovinyl-
acetylene, 2-chloro-1,3-butadiene and 1,5-hexadien-3-yne (DVA)
in the gas product.
EXPERIMENTAL
Reaction vessel: The gas-liquid C2H2 dimerization was
performed in a self-designed glass reaction vessel, which is
similar to a straight cool condenser, contained a cylindrical
gas distributor and a coaxial glass tubes with various diameter.
The gas distributor caused the gas to scatter into small bubbles,
thus increasing the gas-liquid contact area. The thermosta-
tically controlled water flowed through the interspaces of the
internal and external tubes to achieve the desired reaction
temperature and to remove excess heat as a result of the exo-
thermic reaction of the C2H2 dimerization.
RESULTS AND DISCUSSION
SrCl2 (10 mol %, based on CuCl), a low-cost and water-
soluble salt, was initially added to the Nieuwland catalyst
solution for C2H2 dimerization and the results were shown in
Fig. 2. When SrCl2 was employed as additive, the Nieuwland
catalyst remained as a homogeneous solution without forming
precipitates and the C2H2 conversion and monovinylacet-ylene
selectivity are kept at 15 and 92 %, respectively. Compared
with traditional Nieuwland catalyst, there was slight decrease
in C2H2 conversion, but significant increase in monovinyl-
acetylene selectivity. This could be contributed to the SrCl2-
Nieuwland catalyst increased the reaction energy barrier of
monovinylacetylene and C2H2 to form DVA, which enhanced
the monovinylacetylene selectivity15.
Catalyst preparation and catalytic reaction: A
schematic diagram of the C2H2 dimerization system is shown
in Fig. 1. The pipeline was purged with nitrogen for 0.5 h
before the reaction to remove air in the system. An equivalent
mole of NH4Cl (based on CuCl) and 15 mL distilled water
were added to the reaction vessel at 80 °C under nitrogen.
After the mixture bubbled for about 10 min, SrCl2 was added
and then CuCl and HCl (0.3 wt. %) were added under nitrogen
for at least 20 min until it dissolved, then the catalyst was
obtained. Acetylene was successively passing through a filter
to remove trace impurities, a calibrated mass flow controller
to limit the C2H2 flow, a K2Cr2O7 solution to eradicate H2S and
PH3 and a NaOH solution to eradicate the acidic gas and then
it flowed into a pre-heated glass reaction vessel, which con-
tained the catalyst. The exit gas mixture passed through an
50
45
40
35
30
25
20
15
10
5
100
90
80
70
60
50
40
30
20
10
0
Selectivity of MVA (%)
SrCl2
SrCl2
0 mol %
10 mol %
1
3
2
Conversion of C2H2 (%)
N2
SrCl2
SrCl2
5
0 mol %
10 mol %
C2H2
0
1
0
1
2
3
4
6
7
8
9
Time (h)
Fig. 2. Influence of Nieuwland catalyst modified with SrCl2 to C2H2
dimerization
8
GC
7
Considering that the addition of SrCl2 had an obvious
catalytic effect on the Nieuwland catalyst, the loading of SrCl2
was then investigated. As shown in Fig. 3, increasing the
amount of SrCl2 from 0 to 15 mol % led to a lower C2H2 conver-
sion from 21 to 12 %. Meanwhile, the monovinylacetylene
selectivity increased from 83 to 92 % when the molar percen-
tage of SrCl2 from 0 to 10 mol %. However, the selectivity
decreased to 88 % when the molar percentage of SrCl2
increased to 15 %. With regard to C2H2 conversion, monovinyl-
5
5
4
6
Fig. 1. Schematic diagram of the C2H2 dimerization system. 1 = valve, 2 =
gas filter, 3 = mass flow controller, 4 = K2Cr2O7 solution, 5 = NaOH
solution, 6 = gas distributor, 7 = reactor, 8 = gas chromatography

Vol. 26, No. 23 (2014)
Strontium Chloride Modified Nieuwland Catalyst in the Dimerization of Acetylene to Monovinylacetylene 8213
30
28
26
24
22
20
18
16
14
12
10
8
100
98
0 mol %
5 mol %
0 mol %
5 mol %
10 mol %
15 mol %
10 mol %
15 mol %
96
94
92
90
88
86
84
82
80
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
Time (h)
Time (h)
Fig. 3. Effect of SrCl2 mole percentage to C2H2 dimerization
acetylene selectivity and the separation by-product of industrial
production, we adopted the SrCl2 molar percentage of 10
mol % in the subsequent experiment to achieve higher mono-
vinylacetylene selectivity.
increasing temperature is beneficial to the C2H2 conversion
and monovinylacetylene selectivity in reaction temperature
from 70 to 80 °C. However, both C2H2 conversion and mono-
vinylacetylene selectivity decreased when the temperature
increased to 85 °C, which may be probably due to the catalyst
deactivation.
We subsequently tested the effect of CuCl mass percentage
of SrCl2-Nieuwland catalyst (25, 30, 35 and 37 wt. %) and the
results are illustrated in Fig. 4. Given that 40 wt. % CuCl
concentration of the catalyst solution was not prepared because
of the insolubility of CuCl, we employed the 37 wt. % concen-
tration instead. The results indicate that C2H2 conversion
increased with the increasing CuCl concentration from 25 to
37 wt. %. However, there was a slight increase of monovinyl-
acetylene selectivity from 25 wt. % CuCl to 30 wt. % CuCl
and an obviously decrease from 30 wt. % CuCl to 37 wt. %
CuCl. The optimal CuCl mass percentage of the total catalyst
is 30 wt. %, with 13 % C2H2 conversion and 94 % monovinyl-
acetylene selectivity.
The effect of C2H2 space velocity was investigated in the
range between 120 and 240 h-1 and the results were summarized
in Fig. 6. The increase of space velocity of acetylene led to a
decrease of C2H2 conversion and the conversion was similar
to those at space velocities of 160 and 200 h-1. An obvious
decrease in C2H2 conversion was found at the space velocity
of 240 h-1, which is probably due to the incomplete reaction
caused by the shorter residence time in the catalyst solution at
higher gas space velocity. Moreover, monovinylacetylene
selectivity increased with the increase of space velocity from
120 to 200 h-1 and then decreased when the space velocity
increased to 240 h-1. At a space velocity of 200 h-1, the highest
selectivity and good C2H2 conversion are achieved.
Fig. 5 showed the effect of temperature on SrCl2-
Nieuwland catalyst catalyzing C2H2 dimerization reaction. The
17
16
15
14
13
12
11
10
100
98
96
94
92
90
88
86
84
82
80
25 Wt. %
35 Wt. %
30 Wt. %
37 Wt. %
25 Wt. %
35 Wt. %
30 Wt. %
37 Wt. %
9
8
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
Time (h)
Time (h)
Fig. 4. Effect of CuCl mass percentage to C2H2 dimerization

8214 Lu et al.
Asian J. Chem.
100
17
98
96
16
15
70 °C
80 °C
75 °C
85 °C
94
92
90
88
86
14
13
12
11
10
9
70 °C
80 °C
75 °C
85 °C
84
82
80
8
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
Time (h)
Time (h)
Fig. 5. Effect of reaction temperature to C2H2 dimerization
17
16
15
14
13
12
11
10
9
100
98
96
94
92
90
88
86
84
82
80
120 h–1
200 h–1
160 h–1
240 h–1
120 h–1
200 h–1
160 h–1
240 h–1
8
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
Time (h)
Time (h)
Fig. 6. Effect of C2H2 space velocity to C2H2 dimerization
3. K.I. Nishiwaki, M. Kobayashi, T. Takeuchi, K. Matuoto and K. Osakada,
J. Mol. Catal. Chem., 175, 73 (2001).
Conclusion
In conclusion, dimerization of C2H2 was successfully
demonstrated using SrCl2 as co-catalyst of Nieuwland catalyst.
Under optimal experimental conditions (10 mol % SrCl2, 30
wt. % CuCl, 80 °C and 200 h-1), the C2H2 conversion was 13 %
and monovinylacetylene selectivity reached to 94 %, which
was beneficial for the subsequent separation of monovinyl-
acetylene and the by-products in industrial production.
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ACKNOWLEDGEMENTS
The authors acknowledge the National Basic Research
Program of China (973 Program) (No. 2012CB722603), the
Doctor Foundation of Xinjiang Bingtuan (No. 2012BB010)
and the National Natural Science Foundation of China (No.
21463021) for their financial support.
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