Lehrstuhl Technische Chemie

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Optimizing nickel-based hydrocyanation catalysts
(2024) Köhler, Till; Vogt, Dieter; Tiller, Jörg
Nitriles are versatile and highly desired chemical intermediates for a broad range of products. Thus, their economic large-scale production requires highly efficient and selective synthesis. The nickel-catalyzed hydrocyanation of C=C double bonds provides such selective and 100% atom-economical access to nitriles. Nevertheless, the catalysts hitherto lack activity and longevity. The catalytic activity can be increased slightly by using AlCl3 as the Lewis acid, still the overall activity remains unsatisfactory. As there is no literature focused on increasing the cooperativity between the Nickel catalyst and the Lewis acid cocatalyst, first in depth studies are conducted in this thesis. It was found, that adding acetonitrile as a promotor enhances the nickel-Lewis acid cooperation, boosting activity further. Furthermore, it was found that the Lewis acid AlCl3 deactivates the nickel-catalyst reducing catalyst productivity. To increase the catalysts productivity and activity further, the catalyst stability needed investigation. It was found that the extremely oxygen sensitive catalyst requires an optimized experimental procedure to exclude oxygen contamination persisting of septum usage, HCN-addition as a solution and GC-standard addition after the reaction. That way, the full catalytic potential was utilized, resulting in a TOF20 of more than 300,000 h−1. These findings also provide a beneficial insight and help to develop a deeper understanding of current limitations caused by deactivation of the highly sensitive catalyst in nickel-catalyzed hydrocyanations. Conclusively, this catalytic system is applied in hydrocyanation of the renewable C10 1,3-diene β-myrcene under the ptimized procedure, yielding C11-nitriles with excellent selectivity not described in literature to date. It was found that three major products can be formed depending on the choice of ligand, which marks an important step towards the synthetic accessibility of mid-chain nitriles based on renewable resources.
Synthesis strategies towards tagged homogeneous catalysts to improve their separation
(2023-05-11) Diekamp, Justus; Seidensticker, Thomas
The recycling of homogeneous catalysts while keeping them in the homogeneous matrix is an ongoing challenge many reactions face if they are to find industrial applications. While a plethora of different synthetic approaches towards better, recyclable homogeneous catalysts exist, the literature shows a gap when one searches for a concise overview of the different catalyst modifications. This Review is designed to close that gap by summarising the existing synthesis pathways towards polar, non-polar, fluorous, and molecular-weight-enlarged catalysts and by examining their respective synthesis routes with a focus on modular and late-stage approaches. Furthermore, we map out the potential for a generally applicable tag library that allows straightforward catalyst modifications to tune them for each desired recycling strategy.
Selective introduction of nitrogen into bulk chemicals via homogeneously catalyzed reactions
(2024) Hares, Kevin; Vogt, Dieter; Tiller, Jörg
Nitrogen-containing chemical compounds are used everywhere in our day-to-day lives, from high-performance polymers to pharmaceuticals and crop protection. Despite being produced on very large scale, many of their production lines lack efficiency and have a significant impact on the environment. Amides are often synthesized by highly activated coupling agents with an inherently low E-factor. Therefore, developing a catalytic reaction that can produce amides directly from bulk chemicals is highly desired. Primary amines are essential intermediates in the chemical industry, and their selective synthesis is challenging due to their reactive properties. Although they are also produced from bulk feedstock, they require many steps when a renewable substrate is used. This dissertation addresses these challenges by developing and optimizing homogeneous transition metal catalysts. The work is structured into three main parts, each addressing different types of reactions to introduce nitrogen into bulk chemicals: 1. Carbonylative telomerization is a complex chemical reaction that synthesizes amides from simple feedstock molecules, but its high catalyst loading presents a challenge, as well as a limited scope. Both were addressed by optimizing the reaction conditions and adding new dienes and nucleophiles to the reaction portfolio of carbonylative telomerization. 2. Converting fatty esters directly into amines in a one-pot reaction is sought to streamline chemical production, requiring the development of a new catalyst to facilitate the process and improve resource and energy efficiency. Therefore, modified triphos ligands were synthesized and combined with ester amination. 3. The conversion of aldoximes into primary amines, offers a possible alternative to the highly desired hydroamination of alkenes. This is achieved through the combination with hydroformylation, which enables the conversion of alkenes into primary. These contributions offer new efficient ways of introducing nitrogen into bulk feedstock to synthesize more complex amides and primary amines through homogeneous transition metal catalysts.
Synthesis of biobased amines via Pd-catalysed telomerisation of the renewable β-myrcene in a water/ethanol multiphase system: catalyst recycling enabled by a self-separating product phase
(2023-07-25) Kampwerth, Anna; Terhorst, Michael; Kampling, Nils; Vogt, Dieter; Seidensticker, Thomas
We developed an aqueous multiphase system for the synthesis of biobased alkyl amines via palladium-catalysed telomerisation based on the terpene β-myrcene. Ethanol was employed as a harmless co-solvent. With this “green” switchable multiphase solvent system, the recycling of the expensive homogeneous catalyst was successfully enabled by self-separating products at room temperature. The total turnover number (TON) was increased to almost 12 000 over 9 runs, with high selectivities towards the desired amine telomer products between 80 and 93% in each run. Furthermore, various amine nucleophiles were successfully used allowing to produce a wide variety of long-chain unsymmetrical alkyl amines with potential applications as, for instance, surfactant precursors or lubricants. In each case, the products self-separated after reaction from the aqueous multiphase system containing the homogeneous palladium catalyst allowing straightforward isolation by simple decantation. Finally, we proved the successful use of spirits (vodka) as solvents in this sustainable amine synthesis.
Continuous production of amines directly from alkenes via cyclodextrin-mediated hydroaminomethylation using only water as the solvent
(2023-03-28) Roth, Thomas; Evertz, Rebecca; Kopplin, Niklas; Tilloy, Sébastien; Monflier, Eric; Vogt, Dieter; Seidensticker, Thomas
Aqueous hydroaminomethylation (HAM) is an atom economical route for the efficient production of amines in one reaction step, starting from basic chemicals like alkenes. Herein we present the first successful establishment of a continuous process for HAM in an aqueous multiphase system. The green mass transfer agents randomly methylated-β-cyclodextrins (CD) enabled the catalytic system consisting of rhodium/sulfoXantphos to achieve high yields of up to 70% with selectivities of up to 80% in several continuous experiments with a total run time of more than 220 h. The key here is that water and products have large polarity differences, but the reaction still proceeds effectively due to the addition of cyclodextrin, which made the application of solvents obsolete. The main achievements in this way were the investigation of the influence of the randomly methylated-β-cyclodextrin concentration on the reaction rate and the selectivity in batch studies and finding promising operating points in the first continuous experiments. In a final experiment, the separation temperature was investigated. It was shown that the catalyst loss in the product phase is enormously small at 0.003% h−1 of the initial mass (0.24% in total), which is the lowest ever reported value for the HAM on this scale. Within a run time of 78 hours, 2.87 kg of tertiary amine were produced using only 0.2 g (>14[thin space (1/6-em)]000[thin space (1/6-em)]:[thin space (1/6-em)]1) of transition metal, while the loss of rhodium per kg of product produced was mostly around 0.15 mg kg−1, suggesting possible economical applicability.
Sodium ethoxide as an environmentally benign and cost-effective catalyst for chemical depolymerization of post-consumer PET waste
(2023-01-19) Javed, Saqib; Ropel, Dennis; Vogt, Dieter
Polyethylene terephthalate (PET) waste is mounting up in the environment due to its poor biodegradability and low recycling rate. Glycolysis is a promising chemical recycling technique to convert PET into its monomer bis(2-hydroxyethyl)terephthalate (BHET). Here, we present our work on the glycolytic depolymerization of post-consumer PET waste using sodium ethoxide (EtONa) as a low-cost catalyst. In order to optimize the reaction in terms of PET conversion and BHET yield, response surface methodology (RSM) based on the Box–Behnken design was applied for the reaction temperature (160–190 °C), the molar ratio of PET : EtONa (50–150), the molar ratio of ethylene glycol to PET (EG : PET) (3–7), the reaction time (2–6 h) and the PET particle size (0.25–1 mm). Based on the experimental results, regression models as a function of significant process parameters were obtained and evaluated by analysis of variance (ANOVA) to predict the depolymerization performance of EtONa. By further optimization and expanding the parameter space beyond the initial upper limits, high PET conversion (98%) and an isolated yield of BHET (76%) were achieved. Under similar conditions, its depolymerization performance was compared to other widely studied catalysts, such as zinc acetate (PET conversion 97%, BHET yield 75%) and cobalt acetate (PET conversion 93%, BHET yield 70%). BHET precipitation without water is also demonstrated and it was found that EG and catalyst recycling is possible at least for 5 recycled runs with persistent conversion. Hence, EtONa is a very promising low-cost catalyst for PET depolymerization which has potential feasibility for a large-scale process.
Nickel(BiPhePhos)-catalyzed hydrocyanation of styrene - highly increased catalytic activity by optimized operational procedures
(2024-03-21) Köhler, Till; Rienhoff, Bernd; Vogt, Dieter
Nitriles are versatile and highly desired chemical intermediates for a range of products. Their economic large-scale production requires highly efficient and selective synthesis. The nickel- catalyzed hydrocyanation of C=C double bonds provides such selective and 100% atom-economical access to nitriles, but the catalysts hitherto lack activity and longevity. Yet, the literature focusing on increased catalytic activity or optimized operational procedures is scarce, at the least. Here, we present a thorough investigation and optimization of operational procedures using a commercially available diphosphite ligand and styrene as a model substrate. This led us to achieve a TOF20 of more than 300,000 h−1.
Catalytic synthesis of methyl 9,10‐dihydroxystearate from technical feedstocks in continuous flow via epoxidation and hydrolysis
(2022-04-30) Vondran, Johanna; Benninghoff, Tobias; Emminghaus, Anahita Irene; Seidensticker, Thomas
The sequence of the homogeneously Ru-catalyzed epoxidation of methyl oleate and acid-catalyzed hydrolysis of the corresponding epoxide methyl 9,10-epoxy stearate is successfully transferred from batch into flow mode, allowing for the continuous production of methyl 9,10-dihydroxystearate. Thereby, methyl oleate is first converted up to 97% within 14 min at excellent selectivity in the epoxidation using aqueous hydrogen peroxide as the sole oxidant. In the subsequent hydrolysis, a residence time of 10 min is sufficient for quantitative conversion of the epoxide. The desired, pure vicinal diol is isolated upon crystallization from the crude reaction mixture in an integrated process starting from technical grade (91.5%) substrate. The isolated yield is increased upon the addition of water as a green antisolvent from 75% up to 97%. Finally, the concept is transferred to methyl oleate of even lower purity (76%), still obtaining an isolated yield of 66% of the vicinal diol. Thus, the integration of sequential epoxidation and hydrolysis into continuous flow and subsequent crystallization allows for high conversion and selectivities within a total residence time of 27 min, corresponding to a space–time yield of 190 g h−1 L−1 in the epoxidation and 164 g h−1 L−1 in the hydrolysis, respectively. Practical applications: The modular flow setup enables the targeted functionalization toward the epoxide intermediate or the vicinal diol. Both offer versatile applications for the production of polymers, surfactants, or toward further conversion as in oxidative cleavage starting from methyl oleate. The application of flow chemistry offers advantages for the safe handling of hydrogen peroxide even at high temperatures. With fats and oils being natural substances, oleochemicals such as fatty acid methyl esters are typically available in technical purity so that efficient strategies for the isolation of pure products are of need. Crystallization of the product is promising, as additional organic solvents are not required. Thus, using the difference in melting point and solubility behavior of the desired product compared to other compounds is a promising method for the applicability of renewable resource-based substrate mixtures.
Selective synthesis of primary amines by kinetic-based optimization of the ruthenium-Xantphos catalysed amination of alcohols with ammonia
(2022-08-03) Heider, Christian; Pietschmann, Dominik; Vogt, Dieter; Seidensticker, Thomas
The selective synthesis of primary amines directly from several alcohols and ammonia using a homogeneous catalyst based on HRuCl(CO)(PPh3)3 and Xantphos is presented. The key to success was the detailed understanding of all mutually influencing parameters such as temperature, ammonia excess, and substrate concentration. These studies were supported by the determination of the kinetics, which allowed the reaction order to be calculated as 0.7. Furthermore, the kinetic model derived from the mechanism was confirmed. After measuring reaction profiles for all influencing parameters, optimized conditions were obtained, which finally allowed the amination of aliphatic, cyclic, as well as primary and secondary alcohols with selectivities to the desired primary amine exceeding 90 % at quantitative alcohol conversion with only minimal formation of the undesired secondary amines. Furthermore, the catalytic activity of the commercially available and robust Xantphos system was drastically improved, corresponding to a turnover frequency (TOF)>60 h−1 after 30 minutes and a turnover number (TON) of 120.
Pushing boundaries—selective cooling crystallization as tool for selectivity compensation and product purification using a recyclable Pd/Xantphos catalyst in the methoxycarbonylation of methyl 10-undecenoate
(2022-09-30) Vondran, Johanna; Moeschke, Rebecca; Deysenroth, Tabea; Seidensticker, Thomas
The homogeneously catalyzed methoxycarbonylation of methyl 10-undecenoate allows for the synthesis of dimethyl 1,12-dodecandioate as an interesting bio-based drop-in alternative for 1,12-dodecandioic acid as polymer building block. Although the benchmark catalyst system of Pd/1,2-bis((di-tert-butylphosphino)methyl)benzene and methane sulfonic acid is very active and selective, long-term stability over a potential catalyst recycling is limited. In this work, modifications of this catalyst system in terms of protonation of the ligand and its replenishment during recycling are first investigated, proving that the reaction system is tolerant against minor changes. Finally, the commercially available ligand Xantphos, featuring higher stability but comes with a rather low l:b selectivity of 70:30, is applied. However, through the application of cooling crystallization, 58 g product (52% isolated yield) with an overall purity of 94% is obtained from the crude reaction solution without further treatment and a ∑TON of 4000 after ten reaction runs, while catalyst loss into the product is low. Practical Applications: Selective syntheses on the basis of renewable resources are a powerful tool for the production of value products in terms of green chemistry. Thereby, homogeneous transition metal catalysts are beneficial regarding selectivity. However, their separation and recycling are challenging due to their limited stability. The combination of a stable, commercially available catalyst with a selective purification method allows for isolation and purification from a crude reaction mixture without the need for any auxiliary or further purification steps. In this work, cooling crystallization is applied for subsequent purification of the linear diester dimethyl 1,12-dodecandioate. Thereby, a lower selectivity from the methoxycarbonylation reaction using the stable Xantphos ligand is compensated and combined with recycling of the homogeneous catalyst. Thus, the development of an integrated process covering a stable catalyst system in the reaction, and high selectivity in the purification is the key toward an efficient homogeneous catalyst recycling.
Polymer-grade bio-monomers from oleochemicals by combining homogeneous catalysis and selective product crystallization in an integrated process
(2023-09-28) Seifert, Astrid Ina; Wegener, Hannes; Brühl, Katharina; Seidensticker, Thomas; Wohlgemuth, Kerstin
The homogeneously catalyzed methoxycarbonylation of bio-based methyl 10-undecenoate (C11-DME) produces linear 1,12-dimethyl dodecanedioate (l-C12-DME). Subsequent selective product crystallization from the reaction mixture with downstream filtration and washing allows for the generation of the bio-monomer in polymer grade quality (>99.9%). This effective purification enables its direct use, e.g., for bio-based polyamides, without further purification. It separates the expensive homogeneous catalyst dissolved in the liquid phase in its active state for efficient catalyst recycling. We present the complex interactions of process parameters regarding reaction and crystallization-based purification in an integrated catalyst recycling process. Furthermore, we demonstrate that purification of l-C12-DME with >99.9% purity over multiple consecutive recycling runs is possible. However, as the crystallization is highly sensitive towards changing concentrations of by-products and particularly unreacted substrates, this high purity is only achieved by maintaining a stable composition in the reaction mixture using a newly developed system for precise conversion control in the reaction step.
Palladium-catalyzed synthesis of mixed anhydrides via carbonylative telomerization
(2022-05-02) Hares, Kevin; Vogelsang, Dennis; Wernsdörfer, Charlotte S.; Panke, Dennis; Vogt, Dieter; Seidensticker, Thomas
For the first time, mixed carboxylic anhydrides were accessed directly via homogeneous palladium catalysis from 1,3-butadiene and carboxylic acids. Under carbonylative telomerization conditions, the respective mixed 3,8-nonadienoic anhydrides are formed in a single reaction step with yields of up to 82%. These very reactive mixed anhydrides can then be used for consecutive reactions in a one-pot manner and selectively transfer the newly formed unsaturated C9 unit. Possible changes in the proposed mechanism were discussed and in a first example, the mixed anhydrides were utilized to form amides.
From tandem to catalysis – organic solvent nanofiltration for catalyst separation in the homogeneously W-catalyzed oxidative cleavage of renewable methyl 9,10-dihydroxystearate
(2022-04-25) Vondran, Johanna; Peters, Marc; Schnettger, Alexander; Sichelschmidt, Christian; Seidensticker, Thomas
Feasibility of oxidative cleavage of methyl oleate in a homogeneous reaction, facilitating the subsequent recovery of the catalyst from a single phase, is a challenge. Using the high molecular catalyst phosphotungstic acid (2880 Da) as an affordable catalyst offers potential for membrane separation. To gain insight into side-reactions, the intermediate methyl 9,10-dihydroxystearate was first applied as a model substrate. Thus, the stability of the intermediate methyl 9,10-epoxystearate and the vicinal diol was significantly improved under reaction conditions. Oxidative cleavage of the vicinal diol as a stable intermediate is very promising reaching an overall selectivity of 90% and a selectivity towards the cleavage carboxylic acids of 80%, considering dilution and acidity as the most important parameters. Retention of the catalyst via organic solvent nanofiltration was investigated and we retained 94% of the catalyst in the monophasic system as the first step towards a process concept for a product purification or catalyst recycling strategy.
Rhodium-catalysed reductive amination for the synthesis of tertiary amines
(2020-08-09) Bianga, Jonas; Kopplin, Niklas; Hülsmann, Jonas; Vogt, Dieter; Seidensticker, Thomas
A procedure for the synthesis of tertiary amines via reductive amination of aldehydes with molecular hydrogen as a reducing agent using homogeneous rhodium catalysis is presented. Using an amine to aldehyde ratio of 4/1 enabled the synthesis of tertiary amines from nine different aldehydes and nine different secondary amines with selectivities up to 99% and turnover frequencies (TOF) up to 7200 h−1. The reaction showed a high tolerance against alcohol and ester functions allowing the formation of multifunctional molecules. In addition, secondary amines can also be produced by this synthesis. For all compounds, activities were determined by hydrogen gas-uptake. In order to increase the sustainability and efficiency of the procedure, a dosing strategy has been successfully developed. Using the determined reaction indicators enabled the stoichiometric use of aldehydes and amines without significant loss of selectivity.
Improving aqueous biphasic hydroformylation of unsaturated oleochemicals using a jet-loop-reactor
(2019-10-10) Herrmann, Norman; Bianga, Jonas; Palten, Markus; Riemer, Tim; Vogt, Dieter; Dreimann, Jens M.; Seidensticker, Thomas
In two case studies, the reaction performance of the aqueous biphasic hydroformylation of two industrially relevant oleochemicals, namely methyl 10-undecenoate (case 1) and methyl oleate (case 2), is significantly improved by the use of a Jet-Loop Reactor concept. Based on previously reported studies, only the two green and benign co-solvents, 1-butanol and isopropanol are applied, respectively, in the absence of any additional auxiliary. Both reactions benefit highly from using this special piece of equipment, specifically designed for improving gas–liquid–liquid mixing to create large interfacial areas with no moving internals. In case 1, the loading of the co-solvent 1-butanol is successfully reduced. For the first time significant yields (>40% after 1 h) are obtained in the absence of any co-solvent, which is very beneficial, since aldehyde products and substrate form a pure product phase enabling straightforward separation. In case 2, the loading of the substrate methyl oleate is successfully increased from 6 to 30 wt% still showing satisfying productivity. At 15 wt%, the yield of the desired internal aldehydes in the jet-loop reactor is increased by a factor of five compared to a stirred tank reactor after 3 h.
Improvement of productivity for aqueous biphasic hydroformylation of methyl 10-undecenoate
(2019-09-26) Bianga, Jonas; Herrmann, Norman; Schurm, Lasse; Gaide, Tom; Dreimann, Jens M.; Vogt, Dieter; Seidensticker, Thomas
The overall productivity of the aqueous biphasic hydroformylation of the castor oil-derived methyl 10-undecenoate is increased. To increase the reaction rate, the miscibility of water and the fatty compound is increased by addition of the green solvent 1-butanol as co-solvent. For the first time, the concentration of solvents, substrate, and product within the reaction process is experimentally examined in a biphasic system under 20 bar pressure of synthesis gas and 140 °C. A reactor to get samples of both phases is developed to determine the quarternary mixture of the reaction system presented in a four-dimensional tetrahedron diagram. With the knowledge gained about the reaction and its drivers, it is possible to increase the efficiency of the reaction process reported so far. With simultaneously high reaction rates (turn over frequency = >5000 h−1), the space–time yield of the reaction reaches values of >120 g L−1h−1 and can be improved significantly without negatively affecting catalyst leaching.
Multiphasic aqueous hydroformylation of 1-alkenes with micelle-like polymer particles as phase transfer agents
(2018-06-27) Bibouche, Bachir; Peral, Daniel; Stehl, Dmitrij; Söderholm, Viktor; Schomäcker, Reinhard; von Klitzing, Regine; Vogt, Dieter
Micelle-like polymer particles have been applied in aqueous multiphasic hydroformylation reactions of long chain alkenes. These colloids act as phase transfer agents for the nonpolar substrates and as carriers for the catalyst bearing sulfonated ligands by electrostatic attraction. The catalyst performance and the phase separation were optimized with special focus on the conversion, selectivity and catalyst recovery, as those are key points in multiphasic systems to achieve a feasible industrial process. The effect on the catalyst performance of the number of sulfonate groups and electron withdrawing trifluoromethyl groups in the ligand has been studied. The approach was successfully demonstrated for 1-alkenes from 1-hexene to 1-dodecene. For 1-octene, a TOF of more than 3000 h−1 could be achieved at a substrate to catalyst ratio of 80 000, while keeping the rhodium and phosphorous leaching below 1 ppm. In repetitive batch experiments the catalyst was recycled four times, yielding an accumulated TON of more than 100 000 for 1-octene.
Sustainable process development for olefin carbonylation reactions
(2017) Gaide, Tom; Behr, Arno; Mecking, Stefan
The development of sustainable processes and the implementation of renewable raw materials are increasingly important for the chemical industry. In particular, homogeneous catalysis is a key technology in this context since it allows for atom economic and selective syntheses under mild reaction conditions. In this work, two important tasks in process development for homogeneously catalysed carbonylation reactions were investigated: Recycling of known homogeneous transition metal catalysts Development of new catalytic systems for the conversion of substrates based on renewable raw materials in tandem reactions As a recycling strategy for homogeneous transition metal catalysts, the use of thermomorphic multicomponent solvent (TMS) systems was systematically investigated in four steps: 1. Development of a new solvent selection strategy for TMS systems 2. Application of TMS systems in the conversion of technical grade feedstocks 3. Application of TMS systems in the conversion of renewable feedstocks 4. Application of TMS systems in reactions with inherently limited degrees of freedom in the solvent choice The results of these investigations led to the development of a guideline for process development for homogeneously catalyzed reactions in thermomorphic multicomponent solvent systems. Three new catalytic systems were developed for the conversion of substrates based on renewable raw materials in tandem hydroformylations. In the hydroaminomethylation and the reductive hydroformylation, two of the novel catalyst systems allow for a direct conversion of the intermediately formed aldehydes. This makes their purification superfluous, which is of great advantage from an economic and ecologic point of view. The newly developed catalyst system for the isomerising hydroformylation of unsaturated fatty acid methyl esters opens a new way for the synthesis of valuable products from renewable raw materials.
Temperaturgesteuertes Katalysatorrecycling für die homogen katalysierte Hydroformylierung langkettiger Alkene
(2013-10-18) Brunsch, Yvonne; Behr, Arno; Agar, David W.; Schomäcker, Reinhard
Eine wichtige technologische Herausforderung der homogenen Katalyse besteht darin eine effiziente Trennung von Produkt und Katalysator zu gewährleisten, um das wertvolle Katalysatormetall zu rezyklieren. Der Einsatz des Verfahrenskonzeptes der thermomorphen Mehrkomponenten-Lösungsmittelsysteme (TML-Systeme) ermöglicht nach der homogen katalysierten Reaktion eine temperaturgesteuerte Abtrennung und das Recycling des homogenen Katalysators mittels Phasenseparation. Ziel dieser Arbeit ist deshalb die experimentelle Untersuchung der homogen katalysierten Hydroformylierung langkettiger Alkene unter Anwendung des Verfahrenskonzeptes der TML-Systeme. Als Modellreaktion wurde insbesondere die Rhodium-katalysierte Hydroformylierung des langkettigen 1-Dodecens zu n-Tridecanal mit dem Liganden Biphephos in dem TML-Referenzsystem DMF/Decan betrachtet. Im Sinne einer ganzheitlichen Prozessentwicklung sind grundlegende, systematische Untersuchungen zum Katalysatorsystem, zu TML-Systemen sowie zur Reaktion und Phasenseparation im Labormaßstab erfolgt. Vor allem der Ligand besitzt einen entscheidenden Einfluss auf die Aktivität, Selektivität und Stabilität des homogenen Metallkatalysators. Im Rahmen dieser Dissertation wurde der Fokus auf die systematische Untersuchung der Katalysatorabtrennung gelegt. Um ein wirtschaftlich rentables Verfahren zu ermöglichen, ist eine möglichst vollständige Rückführung des Katalysators erforderlich. Daher wurde in dieser Arbeit untersucht, ob das Katalysatorleaching beeinflusst werden kann, welche Einflussfaktoren signifikant sind und wie es insbesondere effektiv minimiert werden kann. Es wurde nachgewiesen, dass neben dem Austrag der Katalysatorphase auch das Substrat, die Katalysatorkonzentration und das in der Reaktion entstehende Produkt einen Einfluss auf das unerwünschte Katalysatorleaching ausüben. Darüber hinaus bestimmt das Produkt maßgeblich das Phasenverhalten und somit das Betriebsfenster von TML-Systemen. Erfolgreich angewendet wurde das Konzept der TML-Systeme in Recycling-experimenten, in denen die Katalysatorphase nach dem Phasenseparationsschritt rezykliert wurde. Durch Absenkung der Separationstemperatur konnte die Effizienz der Trennung von Produkt und Katalysator gesteigert werden. Erstmalig wurde ein Katalysatorrecycling in 30 Recyclingzyklen durchgeführt und damit experimentell die Langzeitstabilität des Rhodiumkatalysators nachgewiesen. Darüber hinaus trugen die im Rahmen dieser Arbeit gewonnenen Erkenntnisse zum Design und dem Bau einer kontinuierlichen Miniplant für die Rhodium-katalysierte Hydroformylierung langkettiger Alkene in TML-Systemen bei.
Immobilisation of non-selective catalysts in permselective microcapsules
(2012-10-25) Pachariyanon, Pavadee; Agar, David W.; Wichmann, Rolf
Mikrokapseln sind Partikel mit Abmessungen im Mikro- bzw. Millimeterbereich, in denen eine aktive Substanz in einer schützenden Hülle oder Matrix eingeschlossen wird. Die Mikroverkapselung ist eine besondere Methode zur Verkapselung dieser neuartigen, kleinen Partikel. Sie dient entweder der Stabilisierung, der Immobilisierung, der geregelten Freisetzung oder dem verbesserten Handling der aktiven Komponente. Des Weiteren ermöglicht die Mikroverkapselung eine gezielte Manipulation der Selektivität von immobilisierten, mikroverkapselten Katalysatoren durch die Einstellung des Permselektivitätsverhaltens der Mikrokapselmembran. Damit können solche „Mikromembranreaktoren“ als ein permselektives Tool zur Prozessintensivierung verwendet werden. Die Mikroverkapselung findet ihre Anwendung in einem großen Bereich der Industrie, Ingenieurwissenschaft, Medizin, Biotechnik und Forschung. Ihre aktuelle Entwicklung konzentriert sich auf detaillierte Untersuchungen der permselektiven Eigenschaften der Mikrokapseln. In der vorliegenden Arbeit werden permselektive Polyacrylamid-Alginat-(pAAm-Alg)-Mikrokapseln untersucht, die eine flüssige Kern-Lösung enthalten. Zur Herstellung der hohlen Mikrokapseln kam eine doppelkonzentrische Düse mit verschiedenen intrinsischen und extrinsischen Parametern zum Einsatz. Der äquivalente Durchmesser und die Kreisform der Mikrokapseln wurden unter Verwendung der Bildanalyse-Software ImageJ bestimmt, wobei ihre Membrandicke mithilfe eines Stereo-Mikroskops beobachtet und gemessen worden ist. Es hat sich herausgestellt, dass die mittlere Größe und die Anzahl der hergestellten Mikrokapseln mit einer Zunahme von Vernetzer- und Monomer-Konzentration abnahmen, während der äquivalente Durchmesser mit einer Zunahme der Initiator-Konzentration zunahm. Der Einfluss von unterschiedlichen Konzentrationen an Vernetzer, Monomer und Initiator auf die Kreisform der Mikrokapseln war geringfügig. Mit Zufuhr von Druckluft in das System sank der äquivalente Durchmesser der Mikrokapseln dramatisch, wobei die Anzahl der erzeugten Mikrokapseln erheblich anstieg. Die Membrandicke der Mikrokapseln erhöhte sich proportional zur Zunahme des äquivalenten Durchmessers der Mikrokapseln. Um die Transporteigenschaften (Durchlässigkeit) und den Molekulargewichtschwellenwert (Molecular weight cut-off MWCO) der pAAm-Alg-Mikrokapselmembranen zu bestimmen, Kurzfassung V die Informationen über die Porosität und indirekt auch über die Struktur der Mikrokapseln zu liefern, sind Diffusionsexperimente durchgeführt worden. Der Einfluss auf den Diffusionskoeffizienten von Dextran T1 und Glucose wurde für verschiedene Konzentrationen des Monomers Acrylamid (AAm), des Vernetzers N,N-Methylen-Bis-Acrylamid (Bis-AAm), des Initiators und des Silica-Additivs ermittelt. Die Diffusionskoeffizienten wurden mittels der Crank-Methode bestimmt, um die instationäre Diffusion aus einer endlich verdünnten Lösung in die Mikrokapseln zu untersuchen. Es ist beobachtet worden, dass die Diffusionskoeffizienten mit Zunahme von AAm-, Bis-AAm- und Silica-Additiv-Konzentrationen abnahmen, wobei die Veränderung der Initiator-Konzentration nur eine mäßige Auswirkung zeigte. Dementsprechend konnte die Porengröße der pAAm-Alg-Mikrokapselmembran allein durch die Einstellung der vorher erwähnten Parameter manipuliert werden. Ein breites Spektrum gelöster Stoffe - Glucose, Maltose, Dextran T1, Insulin, a-Lactalbumin und Trypsin - wurde verwendet, um den Molekulargewichtschwellenwert der pAAm-Alg-Mikrokapseln zu ermitteln. Es hat sich ergeben, dass der Molekulargewichtschwellenwert einer pAAm-Alg-Mikrokapsel 1 bis 5,7 kDa beträgt. Dieses deutet darauf hin, dass die pAAm-Alg-Mikrokapsel als eine größenselektive Mikrokapsel für Substrate in diesem Molekulargewichtsbereich angewendet werden kann. Zur Bestimmung der spezifischen und selektiven Eigenschaften verkapselter Enzyme in einer pAAm-Alg-Mikrokapselmembran wurden multi-kompetitive enzymatische Reaktionen durchgeführt. Die von der Lipase M.Miehei (MML) katalysierte Umesterung verschiedener Kettenlängen von Fettsäureethylestern (C2-C14) und Alkoholen mit unterschiedlichen Größen, wurde als Testreaktionssystem gewählt. Während das freie Enzym eine hohe Selektivität für den Fettsäureethylester mit einer langen Kettenlänge (ab C8-Ethylester) und Butanol aufwies, lieferte das verkapselte Enzym eine hohe Selektivität für den Fettsäureethylester mit einer kurzen Kettelänge (C4- und C6-Ethylester) und Methanol. Dies ist auf die hydrophilen Eigenschaften der pAAm-Alg-Mikrokapselmembran zurückzuführen. Die Regelung der selektiven Eigenschaften der pAAm-Alg-Mikrokapselmembran erfolgte durch das Einbringen verschiedener Konzentrationen des hydrophoben Comonomers Isopropyl-Acrylamid (IPPAAm) in die Mikrokapselhülle. Dazu wurden die multi-kompetitiven enzymatischen Reaktionen wiederholt. Die Resultate zeigten, dass die Kurzfassung VI Eigenschaften der Mikrokapsel durch die Modifizierung der Mikrokapselmembran geringfügig beeinflusst wurden. Bei niedrigen Konzentrationen von IPPAAm wies das verkapselte Enzym eine hohe Selektivität für den Fettsäureethylester mit einer kurzen Kette (C4- und C6-Ethylester) auf, wobei ein höherer Prozentsatz an IPPAAm (höher als 2,5%) eine Umsetzung der langkettigen Fettsäureethylester (ab C8-Ethylester) begünstigt. Dies beruht auf den hydrophoben Eigenschaften des IPPAAm-Monomers. Die modifizierte Mikrokapsel mit einer 10%-IPPAAm-Konzentration zeigte eine hohe Selektivität für das kleine Alkohol-Molekül (Methanol). Die Wiederverwendbarkeit wurde anhand der Durchführung mehrfacher Reaktionszyklen der verkapselten Enzyme in pAAm-Alg-Mikrokapseln getestet. Die verkapselten Enzyme wiesen sogar nach fünf Reaktionszyklen (insgesamt 240 Stunden) noch ca. 90% ihrer anfänglichen katalytischen Aktivität auf. Damit ist von einer hohen Stabilität der Mikrokapseln auszugehen.

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