Application of the solvent water in two-phase telomerisation reactions and recycling of the homogeneous palladium catalysts

Article abstract of DOI:10.1039/b820305a

In the chemical industry organic solvents should be avoided wherever possible. They are often toxic to marine organisms and plants as well as to higher organisms and humans. Moreover, volatile organic compounds (VOC) cause air pollution which leads to the

Full text of DOI:10.1039/b820305a

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Application of the solvent water in two-phase telomerisation reactions and
recycling of the homogeneous palladium catalysts†
Arno Behr and Julia Leschinski
Received 13th November 2008, Accepted 9th January 2009
First published as an Advance Article on the web 17th February 2009
DOI: 10.1039/b820305a
In the chemical industry organic solvents should be avoided wherever possible. They are often toxic
to marine organisms and plants as well as to higher organisms and humans. Moreover, volatile
organic compounds (VOC) cause air pollution which leads to the necessity of expensive separation
technologies like waste water or exhaust gas treatments. Solutions for these problems are either the
development of processes without the use of any solvent or the use of environmentally benign
solvents such as water. In this contribution it is shown how versatile water can be, used as a solvent
in homogeneously catalysed processes, for example, telomerisation reactions with methanol,
diethylamine, ethylene glycol and glycerol. In this context another positive effect of the solvent
water is the ecologically and economically required retention of the transition metal catalyst inside
the process. Furthermore, different reactor types, a loop reactor and a mixer-settler reactor, are
presented to cope with the challenges of mass transport limitations and selectivity control in
aqueous biphasic systems.
1
Introduction
disadvantage is the increase of mass transport limitations due
to the additional liquid phase. This problem has to be solved by
special reactor and process design.
In an aqueous catalyst phase a polar soluble catalyst is
needed. One famous example is triphenylphosphine trisulfonate
A transition metal homogeneously catalysed reaction in one
single liquid phase with gaseous reactants leads to some
challenges (Fig. 1a). Firstly, the catalyst must be separated
after the reaction to avoid heavy metal contamination of the
reaction products. Moreover, a recycling method for the catalyst
is required in terms of cost reduction. In the case of gaseous
reactants there can be a mass transport limitation between
the gaseous and liquid phase which can lead to low reaction
rates.
(
TPPTS) (Fig. 2) which is used in the Ruhrchemie-Rh oˆ ne-
1
Poulenc-process and has also been patented for the use in
2
telomerisation reactions.
Fig. 2 Water soluble transition metal catalyst with the ligand triph-
enylphosphine trisulfonate (TPPTS).
Fig. 1 Homogeneous catalysis in single phase and biphasic mode.
If this ligand is used, catalyst separation and recycling can be
done by simple phase separation and recycling of the aqueous
phase. Moreover, polar reactants can also be separated and
recycled in this way.
The catalyst separation and recycling can be implemented
by using the aqueous biphasic technique (Fig. 1b). The main
advantage is the easy catalyst separation but often the main
The telomerisation is defined as the dimerisation of 1,3-dienes
with simultaneous addition of a nucleophile such as water or
alcohols. In Fig. 3 the telomerisation reaction and potential
3
Department of Biochemical and Chemical Engineering, Technical
Chemistry A, Technische Universit a¨ t Dortmund, D-44227, Dortmund,
Germany
This paper was published as part of the themed issue of contribu-
tions from the Green Solvents - Progress in Science and Application
conference held in Friedrichshafen, September 2008.
reactants and products are shown.
It is obvious that the telomerisation is a direct and atom
economic way to unsaturated aliphatic products with interest-
ing applications. In the following, telomerisation reactions of
butadiene with different nucleophiles are presented.
†
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(96% linear telomer) at a moderate palladium leaching of 35–
6
5 ppm in the product phase. Because of the excellent mass
-
3
-1
transport conditions a space-time-yield of 160 kg m
a reaction period of 56 h could be achieved.
h during
9
2
.2 Telomerisation of butadiene with diethylamine
The telomerisation of butadiene with ammonia was already done
10–12
in aqueous biphasic systems to control consecutive reactions.
Telomerisation reactions with secondary amines can even be
conducted in methanol without any methanol conversion. For
example diethylamine is highly active in the telomerisation of
butadiene (Fig. 6) also in the solvent methanol.
Fig. 3 Telomerisation reactions.
13
2
Results and discussion
In this contribution we will present reactions of 1,3-butadiene
with mono-functionalised nucleophiles such as mono-alcohols
and secondary amines which were conducted in a jet loop
reactor. Moreover, reactions with multi-functionalised alcohols
in mixer-settler-units will be shown. A detailed discussion of
various nucleophiles and dienes can be found in our latest review
Fig. 6 Telomerisation of butadiene with diethylamine.
4
on telomerisation.
This reaction showed a mass transfer limitation in an aqueous
biphasic system in semi-batch experiments in a stirred tank
2
.1 Telomerisation of butadiene with methanol
14
reactor, where the reaction rate increased with increasing stirrer
velocity. Because of this restriction the reaction was conducted
in the loop reactor which was already used in the telomerisation
with methanol (Fig. 5). In this reactor type the butadiene intake
was very high and could be further increased by increasing
temperature and volume flow through the loop (Fig. 7).
The telomerisation with methanol leads to methoxyoctadienes
which can be used as intermediates in the production of 1-octene
as a comonomer in the production of LLDPE (Fig. 4).
5–7
Fig. 4 Production of 1-octene via telomerisation.
If the reaction is conducted with gaseous butadiene in an
aqueous catalyst phase (>10 wt% water) containing palladium
and the ligand TPPTS, there are three phases in total. The
reaction products (telomers) form a second liquid phase. To
enhance mass transport, a continuously operated loop reactor
8,9
was used as shown in Fig. 5.
Fig. 7 Butadiene intake in the continuous telomerisation with
14
diethylamine.
The application of the loop reactor led to an increase of space-
-
3
-1
-3
-1
time-yield from 45 kg m
h
to 152 kg m
h
at a catalyst
◦
concentration of only 0.005 mol% palladium at 60 C.
2
.3 Telomerisation of butadiene with ethylene glycol
If multifunctional nucleophiles are used, control of selectivity is a
major challenge. Due to various possibilities of functionalisation
the product distribution is rather broad, especially if the reaction
is carried out in monophasic systems. Fig. 8 shows the possi-
bility of undesired consecutive reactions of the monotelomers
to ditelomers for the example of ethylene glycol.
To increase the selectivity towards the monotelomers, the
aqueous biphasic technique could be applied to utilise the in
situ extraction effect. The monotelomers are extracted into the
organic phase formed by liquid butadiene and are therefore
separated from the aqueous catalyst phase avoiding consecutive
Fig. 5 Loop reactor for telomerisation.
15
Gaseous and liquid reactants as well as the catalyst phase are
mixed intensively inside a jet mixer. They react inside the heated
loop and the phases can be separated by simple phase separation.
The mixing behaviour is excellent and reaction and product
separation are continuously operated. Moreover, catalyst and
reactants can be recycled and the chemoselectivity was above
9
9% for more than 50 h. The regioselectivity was also very high
6
10 | Green Chem., 2009, 11, 609–613
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Table 1 Comparison of the monophasic and biphasic telomerisation
important features so that the polarity differences between the
two phases should be as high as possible. The reaction should
take place in the middle step of the reactor cascade so that a
decreased polarity difference is beneficial.
a15
of butadiene with ethylene glycol
Yield %
Products
Single liquid phase
Aqueous biphasic catalysis
In the so-called “cross-counter-current-mode” of the mixer-
settler-cascade butadiene is added directly before the separation
of the product (step 3) to increase the polarity difference again.
During the reaction, ethylene glycol is converted so that the
aqueous phase leaving step 3 is very polar. However, also the
product phase is more polar due to the product formation. That
is the reason why additional butadiene is added before step 3. In
the reaction step (step 2) ethylene glycol is added to decrease
the polarity of the catalyst phase thus also decreasing mass
transport limitations. Fresh butadiene is also added in step 1
where the catalyst is separated to increase the separation quality
here. The process was run continuously for more than 30 h with
a yield of 75% of monotelomer at a palladium leaching of only
monotelomers
ditelomers
dimers
60
20
10
80
<1
<1
a
T = 80 C, t = 4 h.
19 ppm.
Table 2 Comparison of the monophasic and biphasic telomerisations
23,24
of butadiene with glycerol
a
Yield %
b
c
Products
Single liquid phase
Aqueous biphasic catalysis
Fig. 8 Telomerisation of butadiene with ethylene glycol.
monotelomers
ditelomers
octadienols
45
30
—
70
1
<5
reactions to the ditelomers. Table 1 shows that by using aqueous
biphasic catalysis the yield of monotelomers increases from 60%
to 80% whereas the yield of ditelomers decreases from 20% to
nearly 0%.
a
T = 90 ◦C, 600 min , nbuta diene/nglycerol = 2. t = 60 min, solvent:
-1
b
c
isopropanol. 6 h.
Due to the biphasic system the reaction proceeds more
selectively, however the reaction rate is decreased due to
mass transport limitations. Therefore, a three-step mixer-settler-
16–18
process was developed
to overcome this problem (Fig. 9).
In the first and the last step separation properties are the most
Fig. 9 Cross-counter-current mode in the telomerisation with ethylene
glycol.
Fig. 11 Flow diagram for the continuous telomerisation of butadiene
with glycerol.
16,17
Fig. 10 Telomerisation of butadiene with glycerol.
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◦
-1
Fig. 12 Continuous telomerisation of butadiene with glycerol (T = 90 C, 1000 min , 0.077 mol% Pd, 0.03 mol% inhibitor, 0.13 mol% phosphonium
salt, m(But) = 20 g/h, m (Gly)/m (Water, t = 0) = 1, P/Pd = 7).
29
2
.4 Telomerisation of butadiene with glycerol
recycling loops were closed so that unconverted substrates could
be reused.
The use of glycerol as a nucleophile leads to numerous products
which are shown in Fig. 10.
Besides linear and branched monotelomers there can also be
consecutive reactions towards di- and tritelomers especially in
monophasic systems.
ates in the production of surfactants or defoaming agents,
that a high selectivity towards these products is highly desirable.
Once again, an aqueous biphasic reaction leads to an increased
selectivity towards the mono-substituted products (Table 2).
As in the reaction with ethylene glycol, the monotelomers
are extracted by the organic phase containing liquid butadiene
and consecutive reactions are avoided. In the aqueous biphasic
reaction there is the possibility of 2,7-octadienol formation,
which is the telomer of butadiene and water, but Table 2 shows
that this product is formed in yields below 5%. Further by-
products which are undesired especially in technical processes
are butadiene dimers, oligomers and polymers which cause
fouling inside the process equipment. A further requirement for
an economic technical process is the catalyst stability, which has
to be enhanced to save catalyst costs. In order to analyse these
3
Conclusions
The green solvent water is a perfect solvent in liquid–liquid-
two-phase catalysis. This technique could be applied at different
telomerisation reactions in a mixer-settler-arrangement as well
as in a loop reactor. The processes were run continuously
at low palladium leaching and unconverted substrates were
recycled which leads to very economic processes. Moreover,
mass transport limitations and selectivity could be controlled by
choosing the right reactor and process concepts. All processes
were conducted without additional organic solvents so that costs
for waste water treatment or solvent recovery could be saved and
the environment is not polluted.
19,20
Monotelomers are valuable intermedi-
2
1,22
so
2
3,24
25
Acknowledgements
We would like to thank Umicore AG & Co. KG, especially
Dr. Ralf Karch, for providing noble metal catalysts and OXEA-
group for TPPTS as well as Cognis Oleochemicals, especially Dr.
Alfred Westfechtel, for providing glycerol as well as financial and
scientific support. Moreover, we would like to thank the German
Federal Ministry of Food, Agriculture and Consumer Pro-
tection, Deutsche Forschungsgemeinschaft (German Research
Foundation) and Fonds der Chemischen Industrie for financial
support of the projects.
2
6,27
aspects, a continuous process was developed (Fig. 11)
realised in a miniplant.
and
28,29
Liquid butadiene and glycerol are mixed in a reaction step
followed by liquid/liquid-phase separation, where the catalyst
and unconverted glycerol are recycled to the reactor. The organic
phase is fed into a flash-unit where unconverted butadiene
evaporates and the liquid products can be removed. Butadiene
is liquefied and fed into the reactor.
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