- Email: [email protected]
Development of a continuous process for the hydroformylation of long-chain olefins in aqueous multiphase systems
Chemical Engineering and Processing 67 (2013) 130–135
Contents lists available at SciVerse ScienceDirect
Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
Development of a continuous process for the hydroformylation of long-chain olefins in aqueous multiphase systems Anke Rost a , Michael Müller b , Tobias Hamerla a , Yasemin Kasaka a , Günther Wozny b,∗ , Reinhard Schomäcker a,∗ a b
Technische Universität Berlin, Institut für Chemie, Fachgebiet Technische Chemie, Sekr. TC-8, Str. des 17. Juni 124, 10623 Berlin, Germany Technische Universität Berlin, Institut für Prozess- und Verfahrenstechnik, Fachgebiet Dynamik und Betrieb, Sekr. KWT 9, Str. des 17. Juni 135, 10623 Berlin, Germany
a r t i c l e
i n f o
Article history: Received 29 May 2012 Received in revised form 28 September 2012 Accepted 8 October 2012 Available online 16 October 2012 Keywords: Miniplant Hydroformylation Water soluble rhodium–ligand-complex SulfoXantPhos Nonionic alkylphenolethoxylate surfactants
a b s t r a c t The challenging task of homogeneous catalysis is the efficient combination of reaction and catalyst recycling. In the hydroformylation of long-chain olefins generally cobalt-based catalysts are used, but in our investigation we used rhodium-based catalysts, because of their higher activity in comparison to cobalt catalysts. In hydroformylation reactions, the recycling of the expensive rhodium catalyst as well as the selectivity to linear aldehydes are very challenging. Multiphase systems offer the possibility to increase the interfacial area during reaction on the one hand and to separate the metal–ligand complexes easily from the organic product phase after reaction, to recycle the expensive catalyst for further reactions, on the other hand. Solubilisers such as surfactants or polar solvents can be used to formulate such a tuneable solvent system. Upon cooling of the reaction mixture, phase separation is achieved. Based on that combination of reaction and phase separation for catalyst recycling, a novel process concept was developed for the hydroformylation of long-chain olefins. In order to show the applicability of that concept in a continuous process a fully automated miniplant was designed. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The hydroformylation reaction or “oxo-reaction” is one of the most important examples for the industrial application of homogeneous catalysis. Otto Roelen discovered this reaction in 1938 at the Ruhrchemie [1]. The olefin reacts with carbon monoxide and hydrogen in presence of a transition metal catalyst to a mixture of linear and branched aldehydes. The concept of two-phase catalysis is a well established process for the hydroformylation of short-chain olefins, like propene, because of their partial solubility in aqueous phase. This concept has been performed in the Ruhrchemie-Rhône-Poulenc-Process since 1984 [2,3]. But longchain olefins, like 1-dodecene, have a too low solubility in water to react at the water–solved catalyst–ligand-complex. Solubilisers such as nonionic surfactants can be used to increase the miscibility of the oil and water phase and to formulate a multiphase system [4–7]. Thereby the hydrophilic metal–ligand-complex is immobilised in the aqueous phase and is insoluble in the organic phase (consisting of olefins and aldehydes) [5]. The multiphase systems offer the possibility for a simple separation of two or
∗ Corresponding authors. E-mail addresses: [email protected] (G. Wozny), [email protected] (R. Schomäcker). 0255-2701/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cep.2012.10.001
three phases by controlling the temperature, which enables the recycling of the expensive rhodium catalyst that is the important factor for a cost efficient process in which the rhodium losses should be keep in the range well below of 1 ppm [4,6]. In our investigations, bidentate water–soluble ligands, like SulfoXanthPhos [8,9], were used in the hydroformylation reaction together with alkyl-phenol-ethoxylates (like Marlophen NP 9 from Sasol) as surfactants. By the use of bidentate ligands for the hydroformylation of long-chain olefins, the selectivity is significantly higher than for monodentate ligands, such as TPP and TPPTS [5,10]. To reduce development time and to be able to gain experimental data and experience on the feasibility of a novel and continuous process, a fully automated miniplant, based on the process control system Simatic PCS7© from Siemens, was built at the Technische Universität Berlin in parallel to the lab scale experiments. Basic knowledge about the reaction and separation is important information that is provided from investigations in the lab, but the miniplant allows over a longer period of time to investigate the activity and stability of the catalyst, the influence of recycle streams on the performance of the hydroformylation as well as the surfactant behaviour under reaction conditions. Furthermore, enrichment effects of trace compounds as well as the process stability can be investigated.
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
131
Fig. 1. Schematic phase diagram of nonionic surfactant [11].
1.1. Phase behaviour The multiphase system is an excellent tool for solubilisation between the aqueous, catalyst containing phase and the substrate phase for the hydroformylation reaction and the separation process accordingly. A schematic phase diagram that characterises a multiphase system is shown in Fig. 1 [11]. Four different states can be found, which are dependent on temperature and concentration of surfactant. At low temperatures a two-phase region (2) is formed, which includes micelles in the water phase. Micelles can solubilise small oil droplets from the organic phase into the aqueous phase. At ¯ two phase region is observed, in which higher temperatures the (2) reverse micelles are formed in the organic phase [11,12]. Reverse micelles can solubilise small amounts of water in the continuous oil phase. In a temperature range between these cases, a three-phase region (3) is formed, which consists of a surfactant-rich-middle phase that can solubilise oil as well as water and two excess phases, a water-rich domain and an oilrich domain. If the concentration of surfactant is increased, a one-phase microemulsion is formed (1). Nonionic surfactants, like nonylphenyl ethoxylates (technical grade from Sasol Marlophen NP 6 or NP 9) or alkylethoxylated (technical grade from Sasol Marlipal O13/200) were used in our investigation to formulate a multiphase system. The hydrophilic properties of these surfactants are dependent on their degree of ethoxylation, which also has a strong influence on their phase behaviour. With an increase in the degree of ethoxylation (it means j in Fig. 2), the three-phase region shifts to higher temperatures [13,15,18]. The composition of the multiphase systems is described by the mass fraction ˛ of the oil (1-dodecene) to the total amount of the mixture of oil and water: moil ˛= (1) moil + mwater
Fig. 2. Photograph of the real three-phase system with most of catalyst (Rhodium SulfoXantPhos) in the surfactant-rich middle phase.
2. Experiments
mixture of CO and H2 (carbon monoxide and hydrogen purchased from Air liquide). All basic chemicals were purchased from Roth or Sigma Aldrich and were used without further purification. The technical grade surfactants were donated from Sasol, Germany. The precursor Rh(acac)(CO)2 was contributed by Umicore, Germany. The water soluble chelating ligand SulfoXantPhos was prepared by Molisa, Germany, according to Van Leeuwen [8]. A typical experiment was carried out using 1-dodecene (180 mmol, 95% pure), water (HPLC-grade) (˛ = 0.6), nonionic surfactant Marlophen NP 9 (nonylphenyl nonylethoxylate) ( = 0.1) and a rhodium concentration of 100 ppm respective to the total mixture. The metal to ligand ratio was between 1:4 and 1:5, the metal to substrate ratio was 1:3600. The water–soluble catalyst complex was prepared from Rh(acac)(CO)2 (0.05 mmol) and the ligand SulfoXantPhos (0.25 mmol) dissolved in 4 ml degassed water; afterwards, the mixture was stirred under nitrogen atmosphere for 24 h. At first the autoclave was filled with 1-dodecene, a part of water and nonionic surfactant, then closed and the reaction mixture was deoxygenated by repeated evacuation and nitrogen purging. Through a dosing valve the water–solved catalyst complex was filled under nitrogen atmosphere in the reactor, the dosing valve was flushed with 6 ml degassed water subsequently. The pressure of syngas was adjusted to 40 bar and the gas dispersion stirrer was adjusted to 1000 rpm. The autoclave temperature was controlled by an oil bath from Huber (CC3). Samples were taken at several time intervals and analysed by gas chromatography (Hewlett Packard) using an RTX-5MS capillary column and an FID analyser. The GC temperature profile is 120 ◦ C held for 5 min constant, a ramp of 10 K/min to 160 ◦ C, held for 2 min constant and finally a ramp of 30 K/min to 340 ◦ C, then held for 15 min constant. After the reaction, the autoclave reactor was cooled down to room temperature (30 min), then depressurised and flushed with nitrogen.
2.1. Experimental set up
3. Results and discussion
All hydroformylation experiments were carried out in a 100 ml stainless steel autoclave from Premex. The synthesis gas (syngas) was dispersed with a gas dispersion stirrer, and consisted of a 1:1
It is important to know the phase behaviour of the multiphase system for achieving high reaction rates and for a better understanding of the parameters needed to design an optimal continuous
and that describes the mass fraction of surfactant in the total amount of the ternary mixture of surfactant, oil and water: =
msurfactant msurfactant + moil + mwater
(2)
132
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
Fig. 3. Phase diagram for nonionic surfactant Marlophen NP 9 – changing the phase behaviour with higher aldehyde concentration ˛ = 0.5.
process. The water–soluble rhodium SulfoXantPhos catalyst complex is highly favoured for the hydroformylation of long-chain olefins in multiphase systems. 3.1. Influence of aldehyde (product) concentration on the phase behaviour In Fig. 3 a hydrophobic shift in the phase behaviour of the investigated multiphase system with increasing aldehyde concentration is shown. We used 1-dodecanal as a model aldehyde substrate. The mass fraction (˛) of oil (1-dodecene and 1-dodecanal as model aldehyde for simulating of conversion X = 0.5) in the mixture with water was 0.5. If the concentration of the aldehyde is increased the three-phase region shifts to lower temperatures and the surfactant concentration for phase transitions to the one-phase microemulsion changes from 27 wt% to 16 wt%. 3.2. Reaction in different regions of the phase diagram We tested the influence of the phase behaviour on the reaction by adjusting the system to three different regions of the phase diagram using three different technical-grade nonionic surfactants (shown in Fig. 4). We expected that the reaction would proceed best in the upper two-phase region, because of the high substrate concentration and also because of the higher partial solubility of syngas in the oil phase [16,17]. ¯ phase system only 7% converHowever, we found that in the (2) sion was achieved after 3 h. Compared to this, in the three-phase system 30% conversion was observed in the same time. In this case we had to decrease the reaction temperature stepwise from 110 ◦ C to 80 ◦ C, because the three-phase region shifted to lower temperature (see also in Section 3.1). If the reaction was performed only at 110 ◦ C and the temperature was held constant, the reaction stopped ¯ phase system was formed after at 11% conversion, because the (2) 60 min. Test conditions: M:L:S = 1:4:3500; M = Rh(acac)(CO)2 , L = SulfoXantPhos, S = 1dodecene, water, ˛ = 0.88; = 0.1 Syngas CO/H2 1:1, p = 40 bar, T = 110 ◦ C, tR = 240 min
Fig. 5 shows the conversion progress when the reaction was performed with addition of the surfactant Marlophen NP9 under the following reaction conditions: the mass oil fraction was ˛ = 0.6; the mass fraction of surfactant was = 0.1 and the ratio of metal to ligand to substrate was 1:5:3600. The hydroformylation started at 110 ◦ C in the three-phase region and after 180 min the reaction rate significantly decreased (circles in Fig. 5) because the 2¯ phase system is formed. So in another run after 3 h we decreased the temperature to 80 ◦ C to follow the shift of the three-phase region to lower temperatures with increasing aldehyde content and the reaction rate accelerated again (squares in Fig. 5). In the third run the hydroformylation was performed at a constant temperature of 80 ◦ C only (triangles in Fig. 5) and the reaction rate was very slow over the whole reaction time. The selectivity was 98:2 for linear to branched aldehyde in all 3 runs. In the light of the miniplant design, a continuous stirred reactor (CSTR) is selected for the hydroformylation of 1-dodecene in a three-phase region working with a reaction temperature of 80 ◦ C and a conversion of about 50%. Around a conversion of 50% only a minor temperature sensitivity to the aldehyde concentration is
Fig. 4. Conversion after 4 h in different regions of phase diagram.
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
133
Fig. 7. Dynamic phase separation behaviour for = 0.05, ˛ = 0.5, X = 0.5 at 74 ◦ C.
Fig. 5. Hydroformylation with Marlophen NP9 under different test conditions.
observed. Under steady state operation conditions in a CSTR no further change in the phase behaviour will occur and assure stable and optimal reaction conditions. 4. Dynamics of separation To optimise the separation of the catalyst and the product from the three-phase system, which shows the highest activity in the hydroformylation reaction, the separation dynamics had to be determined. Therefore, for a sample with this composition, the phase separation process was investigated. The separation progress of each single phase was observed and recorded in steps of 30 s as can be seen in Fig. 6. The graph shows the results for the surfactant Marlophen NP9 ( = 0.05, ˛ = 0.5, X = 0.5, 1-dodecene and 1-dodecanal) for a temperature of 71 ◦ C. As can be seen the separation of this mixture into the individual phases occurs very fast at
this temperature. After about three minutes the separation reaches almost equilibrium compositions. All three phases appear transparent, which is a sign for a completed separation of the three-phase mixture. In addition to the separation time a further criterion is the volume fraction of the separated phases. A small middle phase is desired in order to recycle only a minimum amount of product in parallel to a quantitative separation of the catalyst from the product. The catalyst is mainly located in the middle phase, but also in the aqueous phase. The excess ligand is mainly found in the aqueous phase. In Fig. 7 the results for the same mixture are shown for 74 ◦ C. Here it can be seen that especially the separation of the organic phase is poor so that most of the product remains in the surfactant-rich middle-phase. This is an example of a phaseseparation-behaviour that is not desired. The comparison of these two examples also shows once more how difficult it is to handle this multiphase system, because of the strong dependency on temperature. Even within the three-phase-region the separation quality of each phase differs strongly within small temperature ranges, in this case within 3 K. For the envisioned downstream separation design the phase behaviour and separation dynamics at a temperature of 71 ◦ C is preferred. With the preliminary investigations it
Fig. 6. Dynamic phase separation behaviour for = 0.05, ˛ = 0.5, X = 0.5 at 71 ◦ C.
134
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
Fig. 8. Process concept for the hydroformylation of long-chain olefins.
is possible to plan a continuously operation separation unit like a decanter. 5. Process concept Due to the decreasing solubility of alkenes in the aqueous phase with increasing length of carbon chains, the hydroformylation of higher olefins in two-phase systems is not yet established in industry. In literature, there is no report on the development of a continuous process for the hydroformylation of higher olefins with rhodium catalysts in multiphase systems. Thus, the aim was to create a novel process concept which enables the production of long-chain aldehydes (meaning carbon chains longer or equal to C8) in a continuous process as it is shown schematically in Fig. 8. At first, the hydroformylation reaction of C12-olefins takes place in a continuous stirred tank reactor (CSTR) according to the process conditions that were found to be best during the experimental investigation (Section 2). The reaction is performed within a multiphase system under pressured syngas (H2 /CO), where a non-ionic surfactant (Marlophen NP9/Sasol) is applied to increase the miscibility of the oil- and the catalyst-containing water phase. In the second step the valuable catalyst is separated by means of phase separation and is then recycled to the reactor. This is a very challenging step, because phase separation behaviour, as shown in Fig. 3, referred to as the Kahlweit’s fish, strongly depends on temperature, but also on aldehyde and surfactant concentrations [14,19]. To realise the desired separation behaviour an appropriate temperature has to be chosen. So far, good separation results were achieved within the three-phase-area. Due to high catalyst costs a second catalyst separation step, e.g. an ultra filtration or a further extraction step is possibly needed to reduce the losses to a minimum (lower then 1 ppm) and to ensure economic feasibility of the overall process. Finally, the product components have to be separated from the unreacted olefins to obtain a pure product and to recycle the olefins. 6. Miniplant design Based on the novel process concept a miniplant was designed at the chair of process dynamics and operation at the Technische Universität Berlin to investigate the continuous process in an early phase of research. Hereby, one of the main targets was to design the miniplant to be as flexible as possible to handle a wide range of process flows, temperatures, pressures as well as different feed materials. In the first step a Process Flow Diagram (PFD) was developed that is shown in Fig. 9. There, the process is displayed in more detail. Basically it can be subdivided into three sections: a feed section, the reactor section composed of a mixer/settler system, and a product separation section.
The feed section offers the possibility to mix all three liquid feed-materials, the olefin, the surfactant and the aqueous catalyst solution, independently to the reactor. The maximum, minimum, and operation design flow rates can be seen from Table 1. Each storage container (B01, B02, B03) comprises a maximum volume of 15 litres. The volume- and mass-flow of every single component is measured by a Coriolis flow metre, which facilitates precise measurements even for small liquid flows or for different feed materials. By means of flow controlled piston pumps the liquid feed is brought into the reactor (C01), where a maximum pressure difference of up to 100 bar has to be overcome. For the gas feed supply there are two options to guarantee maximum flexibility. The first one is, to add a predefined mixture of syngas directly to the reactor. At first, a mixture of 50 vol.% CO and 50 vol.% H2 is applied. To increase flexibility it is also possible to mix up the syngas from pure CO and H2 to vary those parameters to investigate the influence of different composition of syngas on the reaction. By means of the syngas flow from the gas reservoirs, the pressure of the mixer/settler-system is controlled. The mixer/settler section represents the core of the miniplant, because here both challenging steps take place. Both units, the reactor and the liquid–liquid separator (decanter), were designed for a maximum pressure of 100 bar and a maximum temperature of 140 ◦ C. In the thermostated double walled reactor all the liquid and gaseous feed materials are brought in contact by means of a gas dispersion stirrer. Due to the hazard potential of the syngas and the high pressures, the reactor volume of one litre was designed to be as small as possible. During continuous operation the syngas is added from top of the reactor and the liquid feed from the bottom. Depending on the liquid feed flow, residence times of up to 6 h can be adjusted. The products leave the reactor (C01) by an overflow, directly entering the liquid–liquid separation unit. Also, by means of a temperature-controlled decanter (X01), the multiphase mixture can be separated into two or even three liquid phases. The heavier surfactant/water phase, which includes most of the catalyst, is then recycled to the reactor, whereas the organic product phase is released in a flash tank (X02), prepared for further product downstreaming processes. Altogether, more than 40 sensors and 30 actuators are required for measuring, controlling and observing temperatures, pressures Table 1 Plant design flows. Plant design flows [g/h]
1-Dodecene Surfactant Water/catalyst CO H2 H2 /CO
Min.
Operation
Max.
20 10 1 10 1 10
61.75 61.75 6.5 28 2 30
4000 400 200 400 200 400
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
135
Fig. 9. Process Flow Diagram of the hydroformylation miniplant.
and process flows. The miniplant is fully automated and can be run by one or two operators by means of the process control system Simatic PCS7© of Siemens. To guarantee a safe plant operation, while working with flammable and hazardous gases and liquids at high pressures and temperatures, strict safety regulations were set according to a HAZOP-Analysis that was carried out. All the applied instrumentation and control devices satisfy European Explosion Protection Directives – 94/9/EG ATEX. 7. Conclusions We found a reaction medium for the hydroformylation of longchain olefins with a water–soluble rhodium complex. The bidentate rhodium-SulfoXantPhos catalyst shows a good activity and high selectivity (98:2 for linear to branched aldehyde). We identified the three phase region to be the optimal state for reaction and separation. The parallel process development is distinguished for the investigation of the stability using active rhodium species and of the influence of recycle streams. The metal–ligand ratio, the concentration and choice of the surfactant, and the water–oil-ratio are important parameters for the optimisation of a value-adding process. The partition coefficients of the different compounds in the single phases have to be evaluated to adequately describe the system. A possible realisation of this process is depicted in Fig. 8. We obtained basic information on the behaviour of multiphase systems to enable the design of the overall process on miniplant scale. Now we also have equipment for long term experiments. The first investigation in the miniplant was with only water and water, oil with surfactant. The first hydroformylation reaction of 1-dodecene is coming soon. Acknowledgments Financial support of the SFB TR 63, is gratefully acknowledged. The surfactants were provided by Sasol and the rhodium precursor
from Umicore. The donations are gratefully acknowledged. We thanks Simon Kamaryt (TUB) for his results obtained during preparation of his diploma thesis. References [1] O. Roelen, Chemische Verwertungsgesellschaft Oberhausen m.b.H., DE 849.543 (1938/1952), US 2.327.066, 1943. [2] C.W. Kohlpaintner, R. Fischer, B. Cornils, Applied Catalysis A 221 (2001) 219–255. [3] B. Cornils, E. Wiebus, Chemical Engineering and Technology 66 (1994) 916–923. [4] B. Cornils, M. Beller, C.D. Frohning, C.W. Kohlpaintner, Journal of Molecular Catalysis A 104 (1995) 17–85. [5] M. Haumann, R. Koch, P. Hugo, R. Schomäcker, Applied Catalysis A 225 (2002) 239–249. [6] A. Behr, Angewandte homogene Katalyse, vol. 18, Wiley-VCH, Weinheim, 2008, pp. 252–269. [7] A. Behr, Angewandte homogene Katalyse, Wiley-VCH, Weinheim, 2008, 19.2, pp. 275–276. [8] M. Schreuder Goedheijt, P.C.J. Kramer, P.W.N.M. Van Leeuwen, Journal of Molecular Catalysis A: Chemical 134 (1990) 243–249. [9] P.W.N.M. Van Leeuwen, C. Claver, Rhodium catalyzed Hydroformylation, Kluwer Academic Publishers, Dordrecht, 2002. [10] S.L. Desset, S.W. Reader, D.J. Cole-Hamilton, Green Chemistry 11 (2009) 630–637. [11] R. Schomäcker, M. Schwarze, H. Nowothnick, A. Rost, T. Hamerla, Chemie Ingenieur Technik 83 (2011) 1343–1355. [12] G. Bode, M. Lade, R. Schomäcker, Chemie Ingenieur Technik 71 (1999) 877–881. [13] M. Kahlweit, R. Strey, G. Busse, Journal of Physical Chemistry 94 (1990) 3881–3894. [14] M. Kahlweit, E. Lessner, R. Strey, Journal of Physical Chemistry 87 (1983) 5032–5040. [15] C.C. Miyagawa, J. Kupka, A. Schumpe, Journal of Molecular Catalysis A: Chemical 234 (2005) 9–17. [16] B. Cornils, W.A. Herrmann, Aqueous-Phase organometallic catalysis, WileyVCH, Weinheim, 2004, 364-409 6.1 2. [17] R.M. Desphande, H. Purwanto, H. Delmas, Industrial and Engineering Chemistry Research 35 (1995) 3927–3933. [18] T. Sottmann, R. Strey, in: J. Lyklema (Ed.), Microemulsions In Fundamental of Interface and Colloid Science, vol. 5, Elsevier, London, 2005. [19] V.-R. Hanke, W. Knoche, E. Dutkiewicz, Journal of the Chemical Society, Faraday Transactions 1 83 (1987) 2847–2856.
Contents lists available at SciVerse ScienceDirect
Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
Development of a continuous process for the hydroformylation of long-chain olefins in aqueous multiphase systems Anke Rost a , Michael Müller b , Tobias Hamerla a , Yasemin Kasaka a , Günther Wozny b,∗ , Reinhard Schomäcker a,∗ a b
Technische Universität Berlin, Institut für Chemie, Fachgebiet Technische Chemie, Sekr. TC-8, Str. des 17. Juni 124, 10623 Berlin, Germany Technische Universität Berlin, Institut für Prozess- und Verfahrenstechnik, Fachgebiet Dynamik und Betrieb, Sekr. KWT 9, Str. des 17. Juni 135, 10623 Berlin, Germany
a r t i c l e
i n f o
Article history: Received 29 May 2012 Received in revised form 28 September 2012 Accepted 8 October 2012 Available online 16 October 2012 Keywords: Miniplant Hydroformylation Water soluble rhodium–ligand-complex SulfoXantPhos Nonionic alkylphenolethoxylate surfactants
a b s t r a c t The challenging task of homogeneous catalysis is the efficient combination of reaction and catalyst recycling. In the hydroformylation of long-chain olefins generally cobalt-based catalysts are used, but in our investigation we used rhodium-based catalysts, because of their higher activity in comparison to cobalt catalysts. In hydroformylation reactions, the recycling of the expensive rhodium catalyst as well as the selectivity to linear aldehydes are very challenging. Multiphase systems offer the possibility to increase the interfacial area during reaction on the one hand and to separate the metal–ligand complexes easily from the organic product phase after reaction, to recycle the expensive catalyst for further reactions, on the other hand. Solubilisers such as surfactants or polar solvents can be used to formulate such a tuneable solvent system. Upon cooling of the reaction mixture, phase separation is achieved. Based on that combination of reaction and phase separation for catalyst recycling, a novel process concept was developed for the hydroformylation of long-chain olefins. In order to show the applicability of that concept in a continuous process a fully automated miniplant was designed. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The hydroformylation reaction or “oxo-reaction” is one of the most important examples for the industrial application of homogeneous catalysis. Otto Roelen discovered this reaction in 1938 at the Ruhrchemie [1]. The olefin reacts with carbon monoxide and hydrogen in presence of a transition metal catalyst to a mixture of linear and branched aldehydes. The concept of two-phase catalysis is a well established process for the hydroformylation of short-chain olefins, like propene, because of their partial solubility in aqueous phase. This concept has been performed in the Ruhrchemie-Rhône-Poulenc-Process since 1984 [2,3]. But longchain olefins, like 1-dodecene, have a too low solubility in water to react at the water–solved catalyst–ligand-complex. Solubilisers such as nonionic surfactants can be used to increase the miscibility of the oil and water phase and to formulate a multiphase system [4–7]. Thereby the hydrophilic metal–ligand-complex is immobilised in the aqueous phase and is insoluble in the organic phase (consisting of olefins and aldehydes) [5]. The multiphase systems offer the possibility for a simple separation of two or
∗ Corresponding authors. E-mail addresses: [email protected] (G. Wozny), [email protected] (R. Schomäcker). 0255-2701/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cep.2012.10.001
three phases by controlling the temperature, which enables the recycling of the expensive rhodium catalyst that is the important factor for a cost efficient process in which the rhodium losses should be keep in the range well below of 1 ppm [4,6]. In our investigations, bidentate water–soluble ligands, like SulfoXanthPhos [8,9], were used in the hydroformylation reaction together with alkyl-phenol-ethoxylates (like Marlophen NP 9 from Sasol) as surfactants. By the use of bidentate ligands for the hydroformylation of long-chain olefins, the selectivity is significantly higher than for monodentate ligands, such as TPP and TPPTS [5,10]. To reduce development time and to be able to gain experimental data and experience on the feasibility of a novel and continuous process, a fully automated miniplant, based on the process control system Simatic PCS7© from Siemens, was built at the Technische Universität Berlin in parallel to the lab scale experiments. Basic knowledge about the reaction and separation is important information that is provided from investigations in the lab, but the miniplant allows over a longer period of time to investigate the activity and stability of the catalyst, the influence of recycle streams on the performance of the hydroformylation as well as the surfactant behaviour under reaction conditions. Furthermore, enrichment effects of trace compounds as well as the process stability can be investigated.
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
131
Fig. 1. Schematic phase diagram of nonionic surfactant [11].
1.1. Phase behaviour The multiphase system is an excellent tool for solubilisation between the aqueous, catalyst containing phase and the substrate phase for the hydroformylation reaction and the separation process accordingly. A schematic phase diagram that characterises a multiphase system is shown in Fig. 1 [11]. Four different states can be found, which are dependent on temperature and concentration of surfactant. At low temperatures a two-phase region (2) is formed, which includes micelles in the water phase. Micelles can solubilise small oil droplets from the organic phase into the aqueous phase. At ¯ two phase region is observed, in which higher temperatures the (2) reverse micelles are formed in the organic phase [11,12]. Reverse micelles can solubilise small amounts of water in the continuous oil phase. In a temperature range between these cases, a three-phase region (3) is formed, which consists of a surfactant-rich-middle phase that can solubilise oil as well as water and two excess phases, a water-rich domain and an oilrich domain. If the concentration of surfactant is increased, a one-phase microemulsion is formed (1). Nonionic surfactants, like nonylphenyl ethoxylates (technical grade from Sasol Marlophen NP 6 or NP 9) or alkylethoxylated (technical grade from Sasol Marlipal O13/200) were used in our investigation to formulate a multiphase system. The hydrophilic properties of these surfactants are dependent on their degree of ethoxylation, which also has a strong influence on their phase behaviour. With an increase in the degree of ethoxylation (it means j in Fig. 2), the three-phase region shifts to higher temperatures [13,15,18]. The composition of the multiphase systems is described by the mass fraction ˛ of the oil (1-dodecene) to the total amount of the mixture of oil and water: moil ˛= (1) moil + mwater
Fig. 2. Photograph of the real three-phase system with most of catalyst (Rhodium SulfoXantPhos) in the surfactant-rich middle phase.
2. Experiments
mixture of CO and H2 (carbon monoxide and hydrogen purchased from Air liquide). All basic chemicals were purchased from Roth or Sigma Aldrich and were used without further purification. The technical grade surfactants were donated from Sasol, Germany. The precursor Rh(acac)(CO)2 was contributed by Umicore, Germany. The water soluble chelating ligand SulfoXantPhos was prepared by Molisa, Germany, according to Van Leeuwen [8]. A typical experiment was carried out using 1-dodecene (180 mmol, 95% pure), water (HPLC-grade) (˛ = 0.6), nonionic surfactant Marlophen NP 9 (nonylphenyl nonylethoxylate) ( = 0.1) and a rhodium concentration of 100 ppm respective to the total mixture. The metal to ligand ratio was between 1:4 and 1:5, the metal to substrate ratio was 1:3600. The water–soluble catalyst complex was prepared from Rh(acac)(CO)2 (0.05 mmol) and the ligand SulfoXantPhos (0.25 mmol) dissolved in 4 ml degassed water; afterwards, the mixture was stirred under nitrogen atmosphere for 24 h. At first the autoclave was filled with 1-dodecene, a part of water and nonionic surfactant, then closed and the reaction mixture was deoxygenated by repeated evacuation and nitrogen purging. Through a dosing valve the water–solved catalyst complex was filled under nitrogen atmosphere in the reactor, the dosing valve was flushed with 6 ml degassed water subsequently. The pressure of syngas was adjusted to 40 bar and the gas dispersion stirrer was adjusted to 1000 rpm. The autoclave temperature was controlled by an oil bath from Huber (CC3). Samples were taken at several time intervals and analysed by gas chromatography (Hewlett Packard) using an RTX-5MS capillary column and an FID analyser. The GC temperature profile is 120 ◦ C held for 5 min constant, a ramp of 10 K/min to 160 ◦ C, held for 2 min constant and finally a ramp of 30 K/min to 340 ◦ C, then held for 15 min constant. After the reaction, the autoclave reactor was cooled down to room temperature (30 min), then depressurised and flushed with nitrogen.
2.1. Experimental set up
3. Results and discussion
All hydroformylation experiments were carried out in a 100 ml stainless steel autoclave from Premex. The synthesis gas (syngas) was dispersed with a gas dispersion stirrer, and consisted of a 1:1
It is important to know the phase behaviour of the multiphase system for achieving high reaction rates and for a better understanding of the parameters needed to design an optimal continuous
and that describes the mass fraction of surfactant in the total amount of the ternary mixture of surfactant, oil and water: =
msurfactant msurfactant + moil + mwater
(2)
132
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
Fig. 3. Phase diagram for nonionic surfactant Marlophen NP 9 – changing the phase behaviour with higher aldehyde concentration ˛ = 0.5.
process. The water–soluble rhodium SulfoXantPhos catalyst complex is highly favoured for the hydroformylation of long-chain olefins in multiphase systems. 3.1. Influence of aldehyde (product) concentration on the phase behaviour In Fig. 3 a hydrophobic shift in the phase behaviour of the investigated multiphase system with increasing aldehyde concentration is shown. We used 1-dodecanal as a model aldehyde substrate. The mass fraction (˛) of oil (1-dodecene and 1-dodecanal as model aldehyde for simulating of conversion X = 0.5) in the mixture with water was 0.5. If the concentration of the aldehyde is increased the three-phase region shifts to lower temperatures and the surfactant concentration for phase transitions to the one-phase microemulsion changes from 27 wt% to 16 wt%. 3.2. Reaction in different regions of the phase diagram We tested the influence of the phase behaviour on the reaction by adjusting the system to three different regions of the phase diagram using three different technical-grade nonionic surfactants (shown in Fig. 4). We expected that the reaction would proceed best in the upper two-phase region, because of the high substrate concentration and also because of the higher partial solubility of syngas in the oil phase [16,17]. ¯ phase system only 7% converHowever, we found that in the (2) sion was achieved after 3 h. Compared to this, in the three-phase system 30% conversion was observed in the same time. In this case we had to decrease the reaction temperature stepwise from 110 ◦ C to 80 ◦ C, because the three-phase region shifted to lower temperature (see also in Section 3.1). If the reaction was performed only at 110 ◦ C and the temperature was held constant, the reaction stopped ¯ phase system was formed after at 11% conversion, because the (2) 60 min. Test conditions: M:L:S = 1:4:3500; M = Rh(acac)(CO)2 , L = SulfoXantPhos, S = 1dodecene, water, ˛ = 0.88; = 0.1 Syngas CO/H2 1:1, p = 40 bar, T = 110 ◦ C, tR = 240 min
Fig. 5 shows the conversion progress when the reaction was performed with addition of the surfactant Marlophen NP9 under the following reaction conditions: the mass oil fraction was ˛ = 0.6; the mass fraction of surfactant was = 0.1 and the ratio of metal to ligand to substrate was 1:5:3600. The hydroformylation started at 110 ◦ C in the three-phase region and after 180 min the reaction rate significantly decreased (circles in Fig. 5) because the 2¯ phase system is formed. So in another run after 3 h we decreased the temperature to 80 ◦ C to follow the shift of the three-phase region to lower temperatures with increasing aldehyde content and the reaction rate accelerated again (squares in Fig. 5). In the third run the hydroformylation was performed at a constant temperature of 80 ◦ C only (triangles in Fig. 5) and the reaction rate was very slow over the whole reaction time. The selectivity was 98:2 for linear to branched aldehyde in all 3 runs. In the light of the miniplant design, a continuous stirred reactor (CSTR) is selected for the hydroformylation of 1-dodecene in a three-phase region working with a reaction temperature of 80 ◦ C and a conversion of about 50%. Around a conversion of 50% only a minor temperature sensitivity to the aldehyde concentration is
Fig. 4. Conversion after 4 h in different regions of phase diagram.
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
133
Fig. 7. Dynamic phase separation behaviour for = 0.05, ˛ = 0.5, X = 0.5 at 74 ◦ C.
Fig. 5. Hydroformylation with Marlophen NP9 under different test conditions.
observed. Under steady state operation conditions in a CSTR no further change in the phase behaviour will occur and assure stable and optimal reaction conditions. 4. Dynamics of separation To optimise the separation of the catalyst and the product from the three-phase system, which shows the highest activity in the hydroformylation reaction, the separation dynamics had to be determined. Therefore, for a sample with this composition, the phase separation process was investigated. The separation progress of each single phase was observed and recorded in steps of 30 s as can be seen in Fig. 6. The graph shows the results for the surfactant Marlophen NP9 ( = 0.05, ˛ = 0.5, X = 0.5, 1-dodecene and 1-dodecanal) for a temperature of 71 ◦ C. As can be seen the separation of this mixture into the individual phases occurs very fast at
this temperature. After about three minutes the separation reaches almost equilibrium compositions. All three phases appear transparent, which is a sign for a completed separation of the three-phase mixture. In addition to the separation time a further criterion is the volume fraction of the separated phases. A small middle phase is desired in order to recycle only a minimum amount of product in parallel to a quantitative separation of the catalyst from the product. The catalyst is mainly located in the middle phase, but also in the aqueous phase. The excess ligand is mainly found in the aqueous phase. In Fig. 7 the results for the same mixture are shown for 74 ◦ C. Here it can be seen that especially the separation of the organic phase is poor so that most of the product remains in the surfactant-rich middle-phase. This is an example of a phaseseparation-behaviour that is not desired. The comparison of these two examples also shows once more how difficult it is to handle this multiphase system, because of the strong dependency on temperature. Even within the three-phase-region the separation quality of each phase differs strongly within small temperature ranges, in this case within 3 K. For the envisioned downstream separation design the phase behaviour and separation dynamics at a temperature of 71 ◦ C is preferred. With the preliminary investigations it
Fig. 6. Dynamic phase separation behaviour for = 0.05, ˛ = 0.5, X = 0.5 at 71 ◦ C.
134
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
Fig. 8. Process concept for the hydroformylation of long-chain olefins.
is possible to plan a continuously operation separation unit like a decanter. 5. Process concept Due to the decreasing solubility of alkenes in the aqueous phase with increasing length of carbon chains, the hydroformylation of higher olefins in two-phase systems is not yet established in industry. In literature, there is no report on the development of a continuous process for the hydroformylation of higher olefins with rhodium catalysts in multiphase systems. Thus, the aim was to create a novel process concept which enables the production of long-chain aldehydes (meaning carbon chains longer or equal to C8) in a continuous process as it is shown schematically in Fig. 8. At first, the hydroformylation reaction of C12-olefins takes place in a continuous stirred tank reactor (CSTR) according to the process conditions that were found to be best during the experimental investigation (Section 2). The reaction is performed within a multiphase system under pressured syngas (H2 /CO), where a non-ionic surfactant (Marlophen NP9/Sasol) is applied to increase the miscibility of the oil- and the catalyst-containing water phase. In the second step the valuable catalyst is separated by means of phase separation and is then recycled to the reactor. This is a very challenging step, because phase separation behaviour, as shown in Fig. 3, referred to as the Kahlweit’s fish, strongly depends on temperature, but also on aldehyde and surfactant concentrations [14,19]. To realise the desired separation behaviour an appropriate temperature has to be chosen. So far, good separation results were achieved within the three-phase-area. Due to high catalyst costs a second catalyst separation step, e.g. an ultra filtration or a further extraction step is possibly needed to reduce the losses to a minimum (lower then 1 ppm) and to ensure economic feasibility of the overall process. Finally, the product components have to be separated from the unreacted olefins to obtain a pure product and to recycle the olefins. 6. Miniplant design Based on the novel process concept a miniplant was designed at the chair of process dynamics and operation at the Technische Universität Berlin to investigate the continuous process in an early phase of research. Hereby, one of the main targets was to design the miniplant to be as flexible as possible to handle a wide range of process flows, temperatures, pressures as well as different feed materials. In the first step a Process Flow Diagram (PFD) was developed that is shown in Fig. 9. There, the process is displayed in more detail. Basically it can be subdivided into three sections: a feed section, the reactor section composed of a mixer/settler system, and a product separation section.
The feed section offers the possibility to mix all three liquid feed-materials, the olefin, the surfactant and the aqueous catalyst solution, independently to the reactor. The maximum, minimum, and operation design flow rates can be seen from Table 1. Each storage container (B01, B02, B03) comprises a maximum volume of 15 litres. The volume- and mass-flow of every single component is measured by a Coriolis flow metre, which facilitates precise measurements even for small liquid flows or for different feed materials. By means of flow controlled piston pumps the liquid feed is brought into the reactor (C01), where a maximum pressure difference of up to 100 bar has to be overcome. For the gas feed supply there are two options to guarantee maximum flexibility. The first one is, to add a predefined mixture of syngas directly to the reactor. At first, a mixture of 50 vol.% CO and 50 vol.% H2 is applied. To increase flexibility it is also possible to mix up the syngas from pure CO and H2 to vary those parameters to investigate the influence of different composition of syngas on the reaction. By means of the syngas flow from the gas reservoirs, the pressure of the mixer/settler-system is controlled. The mixer/settler section represents the core of the miniplant, because here both challenging steps take place. Both units, the reactor and the liquid–liquid separator (decanter), were designed for a maximum pressure of 100 bar and a maximum temperature of 140 ◦ C. In the thermostated double walled reactor all the liquid and gaseous feed materials are brought in contact by means of a gas dispersion stirrer. Due to the hazard potential of the syngas and the high pressures, the reactor volume of one litre was designed to be as small as possible. During continuous operation the syngas is added from top of the reactor and the liquid feed from the bottom. Depending on the liquid feed flow, residence times of up to 6 h can be adjusted. The products leave the reactor (C01) by an overflow, directly entering the liquid–liquid separation unit. Also, by means of a temperature-controlled decanter (X01), the multiphase mixture can be separated into two or even three liquid phases. The heavier surfactant/water phase, which includes most of the catalyst, is then recycled to the reactor, whereas the organic product phase is released in a flash tank (X02), prepared for further product downstreaming processes. Altogether, more than 40 sensors and 30 actuators are required for measuring, controlling and observing temperatures, pressures Table 1 Plant design flows. Plant design flows [g/h]
1-Dodecene Surfactant Water/catalyst CO H2 H2 /CO
Min.
Operation
Max.
20 10 1 10 1 10
61.75 61.75 6.5 28 2 30
4000 400 200 400 200 400
A. Rost et al. / Chemical Engineering and Processing 67 (2013) 130–135
135
Fig. 9. Process Flow Diagram of the hydroformylation miniplant.
and process flows. The miniplant is fully automated and can be run by one or two operators by means of the process control system Simatic PCS7© of Siemens. To guarantee a safe plant operation, while working with flammable and hazardous gases and liquids at high pressures and temperatures, strict safety regulations were set according to a HAZOP-Analysis that was carried out. All the applied instrumentation and control devices satisfy European Explosion Protection Directives – 94/9/EG ATEX. 7. Conclusions We found a reaction medium for the hydroformylation of longchain olefins with a water–soluble rhodium complex. The bidentate rhodium-SulfoXantPhos catalyst shows a good activity and high selectivity (98:2 for linear to branched aldehyde). We identified the three phase region to be the optimal state for reaction and separation. The parallel process development is distinguished for the investigation of the stability using active rhodium species and of the influence of recycle streams. The metal–ligand ratio, the concentration and choice of the surfactant, and the water–oil-ratio are important parameters for the optimisation of a value-adding process. The partition coefficients of the different compounds in the single phases have to be evaluated to adequately describe the system. A possible realisation of this process is depicted in Fig. 8. We obtained basic information on the behaviour of multiphase systems to enable the design of the overall process on miniplant scale. Now we also have equipment for long term experiments. The first investigation in the miniplant was with only water and water, oil with surfactant. The first hydroformylation reaction of 1-dodecene is coming soon. Acknowledgments Financial support of the SFB TR 63, is gratefully acknowledged. The surfactants were provided by Sasol and the rhodium precursor
from Umicore. The donations are gratefully acknowledged. We thanks Simon Kamaryt (TUB) for his results obtained during preparation of his diploma thesis. References [1] O. Roelen, Chemische Verwertungsgesellschaft Oberhausen m.b.H., DE 849.543 (1938/1952), US 2.327.066, 1943. [2] C.W. Kohlpaintner, R. Fischer, B. Cornils, Applied Catalysis A 221 (2001) 219–255. [3] B. Cornils, E. Wiebus, Chemical Engineering and Technology 66 (1994) 916–923. [4] B. Cornils, M. Beller, C.D. Frohning, C.W. Kohlpaintner, Journal of Molecular Catalysis A 104 (1995) 17–85. [5] M. Haumann, R. Koch, P. Hugo, R. Schomäcker, Applied Catalysis A 225 (2002) 239–249. [6] A. Behr, Angewandte homogene Katalyse, vol. 18, Wiley-VCH, Weinheim, 2008, pp. 252–269. [7] A. Behr, Angewandte homogene Katalyse, Wiley-VCH, Weinheim, 2008, 19.2, pp. 275–276. [8] M. Schreuder Goedheijt, P.C.J. Kramer, P.W.N.M. Van Leeuwen, Journal of Molecular Catalysis A: Chemical 134 (1990) 243–249. [9] P.W.N.M. Van Leeuwen, C. Claver, Rhodium catalyzed Hydroformylation, Kluwer Academic Publishers, Dordrecht, 2002. [10] S.L. Desset, S.W. Reader, D.J. Cole-Hamilton, Green Chemistry 11 (2009) 630–637. [11] R. Schomäcker, M. Schwarze, H. Nowothnick, A. Rost, T. Hamerla, Chemie Ingenieur Technik 83 (2011) 1343–1355. [12] G. Bode, M. Lade, R. Schomäcker, Chemie Ingenieur Technik 71 (1999) 877–881. [13] M. Kahlweit, R. Strey, G. Busse, Journal of Physical Chemistry 94 (1990) 3881–3894. [14] M. Kahlweit, E. Lessner, R. Strey, Journal of Physical Chemistry 87 (1983) 5032–5040. [15] C.C. Miyagawa, J. Kupka, A. Schumpe, Journal of Molecular Catalysis A: Chemical 234 (2005) 9–17. [16] B. Cornils, W.A. Herrmann, Aqueous-Phase organometallic catalysis, WileyVCH, Weinheim, 2004, 364-409 6.1 2. [17] R.M. Desphande, H. Purwanto, H. Delmas, Industrial and Engineering Chemistry Research 35 (1995) 3927–3933. [18] T. Sottmann, R. Strey, in: J. Lyklema (Ed.), Microemulsions In Fundamental of Interface and Colloid Science, vol. 5, Elsevier, London, 2005. [19] V.-R. Hanke, W. Knoche, E. Dutkiewicz, Journal of the Chemical Society, Faraday Transactions 1 83 (1987) 2847–2856.