Eldorado Collection:http://hdl.handle.net/2003/972024-03-29T14:37:11Z2024-03-29T14:37:11ZActivity-based models to predict kinetics of levulinic acid esterificationKlinksiek, MarcelBaco, SindiLeveneur, SébastienLegros, JulienHeld, Christophhttp://hdl.handle.net/2003/422612024-01-04T23:13:26Z2022-10-20T00:00:00ZTitle: Activity-based models to predict kinetics of levulinic acid esterification
Authors: Klinksiek, Marcel; Baco, Sindi; Leveneur, Sébastien; Legros, Julien; Held, Christoph
Abstract: The solvent is of prime importance in biomass conversion as it influences dissolution, reaction kinetics, catalyst activity and thermodynamic equilibrium of the reaction system. So far, activity-based models were developed to predict kinetics and equilibria, but the influence of the catalyst on kinetics has not been succesfully predicted by thermodynamic models. In this work, the thermodynamic model ePC-SAFT advanced was used to predict the activities of the reactants and of the catalyst at various conditions (temperature, reactant concentrations, γ-valerolactone GVL cosolvent addition, catalyst concentration) for the homogeneously acid-catalyzed esterification of levulinic acid (LA) with ethanol. Different kinetic models were applied, and it was found that the catalyst influence on kinetics could be predicted correctly by simultaneously solving the dissociation equilibrium of H2SO4 catalyst along the reaction coordinate and by relating reaction kinetics to proton activity. ePC-SAFT advanced model parameters were only fitted to reaction-independent phase equilibrium data. The key reaction properties were determined by applying ePC-SAFT advanced to one experimental kinetic curve for a set of temperatures, yielding the reaction enthalpy at standard state urn:x-wiley:14394235:media:cphc202200729:cphc202200729-math-0001 , activation energy urn:x-wiley:14394235:media:cphc202200729:cphc202200729-math-0002 and the intrinsic reaction rate constant k=0.011 s−1 at 323 K, which is independent of catalyst concentration. The new procedure allowed an a-priori identification of the effects of catalyst, solvent and reactant concentration on LA esterification.2022-10-20T00:00:00ZVerallgemeinerte thermodynamische Beschreibung regenerativer GaskreisprozesseKühl, Hans-Detlevhttp://hdl.handle.net/2003/422422023-12-21T23:13:22Z1990-01-01T00:00:00ZTitle: Verallgemeinerte thermodynamische Beschreibung regenerativer Gaskreisprozesse
Authors: Kühl, Hans-Detlev1990-01-01T00:00:00ZModel-based optimization of multi-stage nanofiltration using the solution-diffusion–electromigration modelHubach, TobiasSchlüter, StefanHeld, Christophhttp://hdl.handle.net/2003/420782023-08-25T22:13:22Z2023-08-04T00:00:00ZTitle: Model-based optimization of multi-stage nanofiltration using the solution-diffusion–electromigration model
Authors: Hubach, Tobias; Schlüter, Stefan; Held, Christoph
Abstract: Nanofiltration is well suited to separate monovalent ions from multivalent ions, such as the separation of Li+ and Mg2+ from seawater, a potential lithium source for the production of lithium-ion batteries. To the best of our knowledge, there is no existing work on the optimization of a multi-stage membrane plant that differentiates between different ions and that is based on a validated transport model. This study presents a method for modeling predefined membrane interconnections using discretization along the membrane length and across the membrane thickness. The solution-diffusion–electromigration model was used as the transport model in a fundamental membrane flowsheet, and the model was employed to optimize a given flowsheet with a flexible objective function. The methodology was evaluated for three distinct separation tasks, and optimized operating points were found. These show that permeances and feed concentrations might cause negative rejections and positive rejections (especially for bivalent ions) depending on the ions’ properties and fluxes, thereby allowing for a favorable separation between the ions of different valence at optimized conditions. In an application-based case study for the separation of Li+ and Mg2+ from seawater, the method showed that under optimal conditions, the mol-based ratio of Mg2+/Li+ can be reduced from 2383 to 2.8 in three membrane stages.2023-08-04T00:00:00ZOsmolyte effect on enzymatic stability and reaction equilibrium of formate dehydrogenaseGajardo-Parra, Nicolás F.Akrofi-Mantey, HaroldAscani, MorenoCea-Klapp, EstebanMatias Garrido, JoséSadowski, GabrieleHeld, Christophhttp://hdl.handle.net/2003/413122023-03-27T22:12:59Z2022-11-03T00:00:00ZTitle: Osmolyte effect on enzymatic stability and reaction equilibrium of formate dehydrogenase
Authors: Gajardo-Parra, Nicolás F.; Akrofi-Mantey, Harold; Ascani, Moreno; Cea-Klapp, Esteban; Matias Garrido, José; Sadowski, Gabriele; Held, Christoph
Abstract: Osmolytes are well-known biocatalyst stabilisers as they promote the folded state of proteins, and a stabilised biocatalyst might also improve reaction kinetics. In this work, the influence of four osmolytes (betaine, glycerol, trehalose, and trimethylamine N-oxide) on the activity and stability of Candida bondinii formate dehydrogenase cbFDH was studied experimentally and theoretically. Scanning differential fluorimetric studies were performed to assess the thermal stability of cbFDH, while UV detection was used to reveal changes in cbFDH activity and reaction equilibrium at osmolyte concentrations between 0.25 and 1 mol kg−1. The thermodynamic model ePC-SAFT advanced allowed predicting the effects of osmolyte on the reaction equilibrium by accounting for interactions involving osmolyte, products, substrates, and water. The results show that osmolytes at low concentrations were beneficial for both, thermal stability and cbFDH activity, while keeping the equilibrium yield at high level. Molecular dynamics simulations were used to describe the solvation around the cbFDH surface and the volume exclusion effect, proofing the beneficial effect of the osmolytes on cbFDH activity, especially at low concentrations of trimethylamine N-oxide and betaine. Different mechanisms of stabilisation (dependent on the osmolyte) show the importance of studying solvent–protein dynamics towards the design of optimised biocatalytic processes.2022-11-03T00:00:00ZPrediction of pH in multiphase multicomponent systems with ePC-SAFT advancedAscani, MorenoPabsch, DanielKlinksiek, MarcelGajardo-Parra, NicolásSadowski, GabrieleHeld, Christophhttp://hdl.handle.net/2003/413102023-03-27T22:12:59Z2022-06-30T00:00:00ZTitle: Prediction of pH in multiphase multicomponent systems with ePC-SAFT advanced
Authors: Ascani, Moreno; Pabsch, Daniel; Klinksiek, Marcel; Gajardo-Parra, Nicolás; Sadowski, Gabriele; Held, Christoph
Abstract: Proton activity, which is usually expressed as a pH value, is among the most important properties in the design of chemical and biochemical processes as it determines the dissociation of species in aqueous mixtures. This article addresses the prediction of pH values in multiphase systems based on the IUPAC definition via proton activity. The required proton activity coefficients were predicted using the thermodynamic equation of state ePC-SAFT advanced. The developed framework considers reaction equilibria and phase equilibria (vapor–liquid and liquid–liquid) to predict pH in the equilibrated liquid phases.2022-06-30T00:00:00ZThe melting properties of D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose and their solubility in water: a revisionChua, Yeong ZenDo, Hoang Tam JosephKumar, AartiHallermann, MoritzZaitsau, DzmitrySchick, ChristophHeld, Christophhttp://hdl.handle.net/2003/409462022-06-09T22:13:21Z2021-12-28T00:00:00ZTitle: The melting properties of D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose and their solubility in water: a revision
Authors: Chua, Yeong Zen; Do, Hoang Tam Joseph; Kumar, Aarti; Hallermann, Moritz; Zaitsau, Dzmitry; Schick, Christoph; Held, Christoph
Abstract: Saccharides are still commonly isolated from biological feedstock by crystallization from aqueous solutions. Precise thermodynamic data on solubility are essential to optimize the downstream crystallization process. Solubility modeling, in turn, requires knowledge of melting properties. In the first part of this work, following our previous work on amino acids and peptides, D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose were investigated with Fast Scanning Calorimetry (FSC) in a wide scanning rate range (2000 K·s−1 to 10000 K·s−1). Using the experimental melting properties of saccharides from FSC allowed successfully modeling aqueous solubility for D-sucrose and D-α-galactose with the equation of state PC-SAFT. This provides cross-validation of the measurement methods to determine accurate experimental melting properties with FSC. Unexpectedly, the experimental FSC melting temperatures, extrapolated to zero scanning rates for thermal lag correction, were higher than results determined with DSC and available literature data. To clarify this inconsistency, FSC measurements towards low scanning rates from 10000 K·s−1 to 1 K·s−1 (D-α-glucose, D-β-fructose, D-sucrose) overlapping with the scanning rates of DSC and literature data were combined. At scanning rates below 1000 K·s−1, the melting properties followed a consistent non-linear trend, observed in both the FSC and the literature data. In order to understand the non-linear decrease of apparent melting temperatures with decreasing heating rate, the endothermic peaks were investigated in terms of isoconversional kinetics. The activation energies in the non-linear dependency region are in the range of 300<EA<600kJ∙mol−1. These values are higher than the enthalpy of sublimation for D-α-glucose, indicating that the non-linear behavior does not have a physical nature but attributes to chemical processes corresponding to the decomposition of molecular compounds within the crystal lattice before melting. The melting properties reported in the literature, commonly determined with conventional methods such as DSC, lead to inaccurate results due to the decomposition of these biomolecules at low heating rates. In addition, the FSC results at lower scanning rates coincide with results from DSC and literature in the overlapping scanning rate range, further validating the accuracy of FSC measurements to determine reliable melting properties of thermally labile biomolecules. The experimental FSC melting properties determined at higher scanning rates are considered as the correct equilibrium melting properties, which are not influenced by any chemical processes. The combination of FSC and PC-SAFT opens the door to model solubility of solid compounds that commonly decompose before melting.2021-12-28T00:00:00ZPrediction of salting-out in liquid-liquid two-phase systems with ePC-SAFT: effect of the Born term and of a concentration-dependent dielectric constantAscani, MorenoHeld, Christophhttp://hdl.handle.net/2003/408492022-04-12T22:12:53Z2021-03-26T00:00:00ZTitle: Prediction of salting-out in liquid-liquid two-phase systems with ePC-SAFT: effect of the Born term and of a concentration-dependent dielectric constant
Authors: Ascani, Moreno; Held, Christoph
Abstract: Knowledge on phase equilibria is of crucial importance in designing industrial processes. However, modeling phase equilibria in liquid-liquid two-phase systems (LLTPS) containing electrolytes is still a challenge for electrolyte thermodynamic models and modeling still requires a lot of experimental input data. Further, modeling electrolyte solutions requires accounting for different physical effects in the electrolyte theory, especially the change of the dielectric properties of the medium at different compositions and the related change of solvation free energy of the dissolved ions. In a previous work, the Born term was altered by combining it with a concentration-dependent dielectric constant within the framework of electrolyte Perturbed-Chain Statistical Associating Fluid Theory (ePC-SAFT), and hence called ‘ePC-SAFT advanced’. In the present work, ePC-SAFT advanced was validated against liquid-liquid equilibria (LLE) of LLTPS water+organic solvents+alkali halides as well as aqueous two-phase systems containing the phase formers poly (propylene glycol) and an ionic liquid. All the ePC-SAFT parameters were used as published in the literature, and each binary interaction parameter between ion-solvent was set to zero. ePC-SAFT advanced allowed quantitatively predicting the salt effect on LLTPS without adjusting binary interaction parameters, while classical ePC-SAFT or meaningless mixing rules for the dielectric constant term failed in predicting the phase behavior of the LLTPS.2021-03-26T00:00:00ZPerformance improvements in Stirling cycle machines by a modified appendix gap geometrySauer, JanKühl, Hans-Detlevhttp://hdl.handle.net/2003/408082022-03-18T23:12:53Z2021-09-20T00:00:00ZTitle: Performance improvements in Stirling cycle machines by a modified appendix gap geometry
Authors: Sauer, Jan; Kühl, Hans-Detlev
Abstract: In this contribution, the optimization potential of the seal geometry in Stirling machines is explored both numerically and analytically, leading to a significant reduction of the related losses which are often referred to as appendix gap losses. These are induced by the narrow gap between the displacer and the cylinder and have mostly been underestimated so far. A recent experimental investigation revealed large optimization potentials by reduction of the seal and cylinder wall diameter near the seal, resulting in reduced appendix gap losses and further indirect positive effects. In this work, these experimental findings could be reproduced by a one-dimensional differential simulation model at a fully satisfyingaccuracy. Furthermore, these investigations reveal that the optimum geometry is largely machine-dependent. To provide an easily applicable design rule for this optimum geometry, a refined analytical model for the mass flow at the top of the gap is derived, which is based on a phasor analysis and a linearized mass balance that also accounts for changes in the spatial mean gas temperature in the gap. The optimum design predicted by this model is very close to numerical optimization results and sufficiently accurate under practical aspects. Furthermore, this model contributes to a better theoretical understanding of the loss mechanisms in the gap.2021-09-20T00:00:00ZNew thermodynamic activity-based approach allows predicting the feasibility of glycolysisGreinert, ThorstenVogel, KristinaMaskow, ThomasHeld, Christophhttp://hdl.handle.net/2003/405972021-12-09T23:12:59Z2021-03-17T00:00:00ZTitle: New thermodynamic activity-based approach allows predicting the feasibility of glycolysis
Authors: Greinert, Thorsten; Vogel, Kristina; Maskow, Thomas; Held, Christoph
Abstract: Thermodynamic feasibility analyses help evaluating the feasibility of metabolic pathways. This is an important information used to develop new biotechnological processes and to understand metabolic processes in cells. However, literature standard data are uncertain for most biochemical reactions yielding wrong statements concerning their feasibility. In this article we present activity-based equilibrium constants for all the ten glycolytic reactions, accompanied by the standard reaction data (standard Gibbs energy of reaction and standard enthalpy of reaction). We further developed a thermodynamic activity-based approach that allows to correctly determine the feasibility of glycolysis under different chosen conditions. The results show for the first time that the feasibility of glycolysis can be explained by thermodynamics only if (1) correct standard data are used and if (2) the conditions in the cell at non-equilibrium states are accounted for in the analyses. The results here will help to determine the feasibility of other metabolisms and to understand metabolic processes in cells in the future.2021-03-17T00:00:00ZPartitioning of water-soluble vitamins in biodegradable aqueous two-phase systemsWysoczanska, KamilaDo, Hoang TamSadowski, GabrieleMacedo, Eugénia A.Held, Christophhttp://hdl.handle.net/2003/403292021-07-19T22:13:03Z2020-07-14T00:00:00ZTitle: Partitioning of water-soluble vitamins in biodegradable aqueous two-phase systems
Authors: Wysoczanska, Kamila; Do, Hoang Tam; Sadowski, Gabriele; Macedo, Eugénia A.; Held, Christoph
Abstract: Partition coefficients (K) of vitamins (riboflavin, nicotinic acid, nicotinamide, folic acid, cyanocobalamin) in aqueous two-phase systems (ATPS) composed by polyethylene glycol (PEG 4000, PEG 6000) and organic salt (sodium citrate and sodium tartrate) at T = 298.15 K and p = 1 bar have been studied. Data on liquid–liquid equilibria of the ATPS considered in this study have been taken from the literature (PEG-Na3Citrate) or measured in this work (PEG-Na2Tartrate) for PEG 4000 and PEG 6000 at T = 298.15 K and p = 1 bar. The experimental K values were validated by electrolyte perturbed-chain-statistical associating fluid theory predictions. The neutral cyanocobalamin has the highest K values among all studied vitamins at any ATPS studied in this work. This finding contrasted with expectations based on literature data which let assume that charged species have typically the highest K values in the considered ATPS. Thus, besides the typically strong charge–charge interactions especially specific forces (e.g., hydrogen bonding) explains the strong PEG-cyanocobalamin interaction resulting in the high K values.2020-07-14T00:00:00ZIn-silico screening of lipid-based drug delivery systemsBrinkmann, JoschaExner, LaraLuebbert, ChristianSadowski, Gabrielehttp://hdl.handle.net/2003/402632021-06-17T22:12:52Z2020-11-23T00:00:00ZTitle: In-silico screening of lipid-based drug delivery systems
Authors: Brinkmann, Joscha; Exner, Lara; Luebbert, Christian; Sadowski, Gabriele
Abstract: Purpose:
This work proposes an in-silico screening method for identifying promising formulation candidates in complex lipid-based drug delivery systems (LBDDS).
Method:
The approach is based on a minimum amount of experimental data for API solubilites in single excipients. Intermolecular interactions between APIs and excipients as well as between different excipients were accounted for by the Perturbed-Chain Statistical Associating Fluid Theory. The approach was applied to the in-silico screening of lipid-based formulations for ten model APIs (fenofibrate, ibuprofen, praziquantel, carbamazepine, cinnarizine, felodipine, naproxen, indomethacin, griseofulvin and glibenclamide) in mixtures of up to three out of nine excipients (tricaprylin, Capmul MCM, caprylic acid, Capryol™ 90, Lauroglycol™ FCC, Kolliphor TPGS, polyethylene glycol, carbitol and ethanol).
Results:
For eight out of the ten investigated model APIs, the solubilities in the final formulations could be enhanced by up to 100 times compared to the solubility in pure tricaprylin. Fenofibrate, ibuprofen, praziquantel, carbamazepine are recommended as type I formulations, whereas cinnarizine and felodipine showed a distinctive solubility gain in type II formulations. Increased solubility was found for naproxen and indomethacin in type IIIb and type IV formulations. The solubility of griseofulvin and glibenclamide could be slightly enhanced in type IIIb formulations. The experimental validation agreed very well with the screening results.
Conclusion:
The API solubility individually depends on the choice of excipients. The proposed in-silico-screening approach allows formulators to quickly determine most-appropriate types of lipid-based formulations for a given API with low experimental effort.2020-11-23T00:00:00ZOdd–even effect for efficient bioreactions of chiral alcohols and boosted stability of the enzymeBülow, MarkSchmitz, AlexaMahmoudi, TermehSchmidt, DanaJunglas, FabianJaniak, ChristophHeld, Christophhttp://hdl.handle.net/2003/392392020-08-19T01:40:53Z2020-07-29T00:00:00ZTitle: Odd–even effect for efficient bioreactions of chiral alcohols and boosted stability of the enzyme
Authors: Bülow, Mark; Schmitz, Alexa; Mahmoudi, Termeh; Schmidt, Dana; Junglas, Fabian; Janiak, Christoph; Held, Christoph
Abstract: We describe a holistic approach for achieving a nearly quantitative conversion for an enzymatic reaction while simultaneously increasing the long-term stability of the enzyme. The approach provided chemical control of bioreactions by utilizing newly synthesized tetrahydrothiophene-based ionic liquids (THT ILs). We showcased its power by using THT-ILs as additives at a low concentration (only 10 mmol L−1) in the alcohol dehydrogenase (ADH)-catalyzed synthesis of methylated 1-phenylethanol (Me-PE). We discovered an “odd–even” effect of the IL-cation chain length: Me-PE displayed beneficial interactions with THT ILs having odd-numbered chain lengths and deleterious interactions with those having even-numbered chain lengths. An intermolecular thermodynamic simulation of the bulk phase and critical micelle concentration investigations of the local surroundings of the THT-ILs proved the occurrence of these interactions, and these two methods confirmed the odd–even effect from different perspectives. Additionally, storing the ADH enzyme in pure THT IL at room temperature allowed for a boosted long-term stability of the enzyme (500 times greater than that in aqueous buffer) without the need for freezing.2020-07-29T00:00:00ZAmorphous-amorphous phase separation in API/polymer formulationsLuebbert, ChristianHuxoll, FabianSadowski, Gabrielehttp://hdl.handle.net/2003/385172020-01-14T02:40:55Z2017-02-15T00:00:00ZTitle: Amorphous-amorphous phase separation in API/polymer formulations
Authors: Luebbert, Christian; Huxoll, Fabian; Sadowski, Gabriele
Abstract: The long-term stability of pharmaceutical formulations of poorly-soluble drugs in polymers determines their bioavailability and therapeutic applicability. However, these formulations do not only often tend to crystallize during storage, but also tend to undergo unwanted amorphous-amorphous phase separations (APS). Whereas the crystallization behavior of APIs in polymers has been measured and modeled during the last years, the APS phenomenon is still poorly understood. In this study, the crystallization behavior, APS, and glass-transition temperatures formulations of ibuprofen and felodipine in polymeric PLGA excipients exhibiting different ratios of lactic acid and glycolic acid monomers in the PLGA chain were investigated by means of hot-stage microscopy and DSC. APS and recrystallization was observed in ibuprofen/PLGA formulations, while only recrystallization occurred in felodipine/PLGA formulations. Based on a successful modeling of the crystallization behavior using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), the occurrence of APS was predicted in agreement with experimental findings.2017-02-15T00:00:00ZExperimental investigation of displacer seal geometry effects in Stirling cycle machinesSauer, JanKühl, Hans-Detlevhttp://hdl.handle.net/2003/383892019-11-22T02:40:48Z2019-11-05T00:00:00ZTitle: Experimental investigation of displacer seal geometry effects in Stirling cycle machines
Authors: Sauer, Jan; Kühl, Hans-Detlev
Abstract: This contribution deals with an experimental investigation of the optimization potential of Stirling engines and similar regenerative machines by an enhanced design of the cylinder liner and the seal. The latter is mounted at the bottom end of the gap surrounding pistons and displacers that separate cylinder volumes at different temperature levels. The thermal loss associated with this gap may amount to more than 10% of the heat input into these machines. Mostly, its design is reduced to an estimation of the optimum width by analytical models, which usually do not account for further relevant optimization parameters, such as a step in the cylinder wall. However, a recently developed, enhanced analytical model predicts that this loss may be significantly reduced by such a step. In this work, this design was realized and investigated experimentally according to this prediction by modification of the cylinder liner and the seal of an extensively tested laboratory-scale machine. The results confirm that such a design actually reduces the thermal loss substantially, presumably by reducing the cyclic mass flows through the open end of the gap. Additionally, it even improves the net power output due to a reduced volumetric displacement by the piston or displacer, resulting in smaller flow losses and thermal regenerator losses, whereas the pressure amplitude remains virtually unchanged, contrary to initial expectations. This has led to the remarkable conclusion that the design of most Stirling engines is possibly suboptimal in this respect and may be improved a posteriori by a minor modification; i.e., a reduction of the effective displacer seal diameter.2019-11-05T00:00:00ZPredicting the solubility of pharmaceutical cocrystals in solvent/anti-solvent mixturesLange, LindaHeisel, StefanSadowski, Gabrielehttp://hdl.handle.net/2003/383002019-10-26T01:40:45Z2016-05-07T00:00:00ZTitle: Predicting the solubility of pharmaceutical cocrystals in solvent/anti-solvent mixtures
Authors: Lange, Linda; Heisel, Stefan; Sadowski, Gabriele
Abstract: In this work, the solubilities of pharmaceutical cocrystals in solvent/anti-solvent systems were predicted using PC-SAFT in order to increase the efficiency of cocrystal formation processes. Modeling results and experimental data were compared for the cocrystal system nicotinamide/succinic acid (2:1) in the solvent/anti-solvent mixtures ethanol/water, ethanol/acetonitrile and ethanol/ethyl acetate at 298.15 K and in the ethanol/ethyl acetate mixture also at 310.15 K. The solubility of the investigated cocrystal slightly increased when adding small amounts of anti-solvent to the solvent, but drastically decreased for high anti-solvent amounts. Furthermore, the solubilities of nicotinamide, succinic acid and the cocrystal in the considered solvent/anti-solvent mixtures showed strong deviations from ideal-solution behavior. However, by accounting for the thermodynamic non-ideality of the components, PC-SAFT is able to predict the solubilities in all above-mentioned solvent/anti-solvent systems in good agreement with the experimental data.2016-05-07T00:00:00ZCatalytic low-temperature dehydration of fructose to 5-hydroxymethylfurfural using acidic deep eutectic solvents and polyoxometalate catalystsKörner, SamAlbert, JakobHeld, Christophhttp://hdl.handle.net/2003/382882022-01-24T13:02:48Z2019-10-09T00:00:00ZTitle: Catalytic low-temperature dehydration of fructose to 5-hydroxymethylfurfural using acidic deep eutectic solvents and polyoxometalate catalysts
Authors: Körner, Sam; Albert, Jakob; Held, Christoph
Abstract: HMF synthesis typically requires high temperature and is carried out in aqueous solutions. In this work, the low-temperature dehydration of fructose to HMF in different deep eutectic solvents (DES) was investigated. We found a very active and selective reaction system consisting of the DES tetraethyl ammonium chloride as hydrogen bond acceptor (HBA) and levulinic acid as hydrogen bond donor (HBD) in a molar ratio of 1:2 leading to a maximum HMF yield of 68% after 120 h at 323 K. The DES still contained a low amount of water at the initial reaction, and water was also produced during the reaction. Considering the DES properties, neither the molar ratio in the DES nor the reaction temperature had a significant influence on the overall performance of the reaction system. However, the nature of the HBA as well as the acidity of the HBD play an important role for the maximum achievable HMF yield. This was validated by measured yields in a DES with different combinations of HBD (levulinic acid and lactic acid) and HBA (choline chloride and tetra-n-alkyl ammonium chlorides). Moreover, addition of vanadium containing catalysts, especially the polyoxometalate HPA-5 (H8PV5Mo7O40) leads to drastically increased reaction kinetics. Using HPA-5 and the DES tetraethyl ammonium chloride—levulinic acid we could reach a maximum HMF yield of 57% after only 5 h reaction time without decreasing the very high product selectivity.2019-10-09T00:00:00ZSimultaneous prediction of cosolvent influence on reaction equilibrium and Michaelis constants of enzyme-catalyzed ketone reductionsWangler, AntonHüser, AlineSadowski, GabrieleHeld, Christophhttp://hdl.handle.net/2003/380702019-05-24T01:40:49Z2019-04-04T00:00:00ZTitle: Simultaneous prediction of cosolvent influence on reaction equilibrium and Michaelis constants of enzyme-catalyzed ketone reductions
Authors: Wangler, Anton; Hüser, Aline; Sadowski, Gabriele; Held, Christoph
Abstract: Understanding and quantification of cosolvent influences on enzyme-catalyzed reactions are driven by a twofold interest. On the one hand, cosolvents can simulate the cellular environment for deeper understanding of in cellulo reaction conditions. On the other hand, cosolvents are applied in biotechnology to tune yield and kinetics of reactions. Further, cosolvents are even present inherently, for example, for reactions with cofactor regeneration or for enzymes that need cosolvents in a function of a stabilizer. As the experimental determination of yield and kinetics is costly and time consuming, this work aims at providing a thermodynamic predictive approach that might allow screening cosolvent influences on yield and Michaelis constants. Reactions investigated in this work are the reduction of butanone and 2-pentanone under the influence of 17 wt % of the cosolvent polyethylene glycol 6000, which is also often used as a crowder to simulate cellular environments. The considered reactions were catalyzed by a genetically modified alcohol dehydrogenase (ADH 270). Predictions of cosolvent influences are based on accounting for a cosolvent-induced change of molecular interactions among the reacting agents as well as between the reacting agents and the solvent. Such interactions were characterized by activity coefficients of the reacting agents that were predicted by means of electrolyte perturbed-chain statistical associating fluid theory. This allowed simultaneously predicting the cosolvent effects on yield and Michaelis constants for two-substrate reactions for the first time.2019-04-04T00:00:00ZStandard Gibbs energy of metabolic reactions: III the 3-phosphoglycerate kinase reactionWangler, AntonKlein-Schmidt, ChristinaSadowski, GabrieleHeld, Christophhttp://hdl.handle.net/2003/380302022-01-24T12:54:50Z2018-02-12T00:00:00ZTitle: Standard Gibbs energy of metabolic reactions: III the 3-phosphoglycerate kinase reaction
Authors: Wangler, Anton; Klein-Schmidt, Christina; Sadowski, Gabriele; Held, Christoph
Abstract: The glycolytic pathway is one of the most studied metabolic pathways to date. This work focuses on determining the standard Gibbs energy of reaction (ΔRg0) of the first adenosine triphosphate-yielding reaction step of glycolysis, namely, the 3-phosphoglycerate kinase (PGK) reaction. Trustworthy values of ΔRg0 are required for thermodynamic approaches to determine single reaction conversions or even fluxes of metabolic reactions. In literature, the observed ΔRg0,obs values are usually determined directly from the experimental equilibrium composition data without accounting for the nonideality of the reaction mixture. That is the reason why the observed ΔRg0,obs values do not present consistent standard data as they are a function of the concentration, pH, and pMg. In this work, a combination of experimentally determined equilibrium composition data and activity coefficients of the reacting agents was used to determine ΔRg0 values for the temperatures 303, 313, and 323 K at pH 7. The activity coefficients were predicted with the thermodynamic model electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT). The ePC-SAFT parameters were taken from literature or fitted to new experimental osmotic coefficients. At 313.15 K, a value for ΔRg0 of −16.2 ± 0.2 kJ/mol was obtained. This value is about 4 kJ/mol less negative than what is usually considered as an accepted standard value. The reason behind this discrepancy was found to be the activity coefficients of the reacting agents, which dramatically influence the equilibrium position of the PGK reaction. On the basis of the temperature-dependent ΔRg0 values, the standard enthalpy of reaction was determined and found to be ΔRh0 = −49 ± 9 kJ/mol.2018-02-12T00:00:00ZNew experimental melting properties as access for predicting amino-acid solubilityHeld, ChristophChua, Yeong ZenDo, Hoang TamSchick, ChristophZaitsau, Dzmitryhttp://hdl.handle.net/2003/380262019-04-29T22:10:16Z2018-02-07T00:00:00ZTitle: New experimental melting properties as access for predicting amino-acid solubility
Authors: Held, Christoph; Chua, Yeong Zen; Do, Hoang Tam; Schick, Christoph; Zaitsau, Dzmitry
Abstract: The properties of melting are required for the prediction of solubility of solid compounds. Unfortunately, direct determination of the enthalpy of fusion and melting temperature by using conventional DSC or adiabatic calorimetry is often not possible for biological compounds due to decomposition during the measurement. To overcome this, fast scanning calorimetry (FSC) with scanning rates up to 2 × 104 K s−1 was used in this work to measure the melting parameters for L-alanine and glycine. The enthalpy of fusion and melting temperature (extrapolated to zero heating rate) were ΔfusH = (22 ± 5) kJ mol−1 and Tfus = (608 ± 9) K for L-alanine, and ΔfusH = (21 ± 4) kJ mol−1 and Tfus = (569 ± 7) K for glycine. These melting properties were used in the modeling framework PC-SAFT to predict amino-acid solubility in water. The pure-component PC-SAFT parameters and one binary parameter were taken from literature, in which these parameters were fitted to solubility-independent thermodynamic properties such as osmotic coefficients or mixture densities. It was shown that this allowed accurately predicting amino-acid solubility in water over a broad temperature range. The combined methodology of PC-SAFT and FSC proposed in this work opens the door for predicting solubility of molecules that decompose before melting.2018-02-07T00:00:00ZOxalic acid – phase behavior of a cocrystal and hydrate forming componentSchleinitz, Mikohttp://hdl.handle.net/2003/356802016-12-02T03:00:14Z2016-01-01T00:00:00ZTitle: Oxalic acid – phase behavior of a cocrystal and hydrate forming component
Authors: Schleinitz, Miko2016-01-01T00:00:00ZAnalyse von Verbesserungspotentialen der Gaserzeugung eines PEMFC-HausenergiesystemsFunke, Matthiashttp://hdl.handle.net/2003/274612015-08-12T20:17:12Z2010-11-10T00:00:00ZTitle: Analyse von Verbesserungspotentialen der Gaserzeugung eines PEMFC-Hausenergiesystems
Authors: Funke, Matthias
Abstract: In den privaten Haushalten kann ein Brennstoffzellen-Hausenergiesystem wegen der hohen
Stromkennzahl einen erheblichen Beitrag zur angestrebten Reduzierung der CO2-Emissionen
und des Primärenergiebedarfs leisten. Wesentlicher Bestandteil des Brennstoffzellensystems ist
die Gaserzeugung und Gasreinigung zur Produktion von CO-freiem Wasserstoff aus Erdgas. Die
bestehenden Prototypen der Gasprozessoren erreichen bislang noch nicht die avisierten Wirkungsgrade
und Standzeiten. Daher ist eine stetige Weiterentwicklung erforderlich.
Ziel dieser Arbeit war daher, mittels Simulationsrechnungen die Möglichkeiten zu untersuchen,
die Gaserzeugungseinheit einer Hausenergieversorgungsanlage durch konstruktive und verfahrenstechnische
Veränderungen energetisch und sicherheitstechnisch zu verbessern.
Zu diesem Zweck wurde ein Modell der Gaserzeugung entwickelt, das die konstruktiven Gegebenheiten
detailliert berücksichtigt und alle Energieflüsse innerhalb des Systems hinreichend genau
erfasst (mehrdimensionales Modell).
Zur Untersuchung der verbesserten Energiezufuhr in den Reformierungsreaktor wurden verschiedene
konstruktive Varianten zur Beheizung des Reaktors geprüft, um den Energieeintrag in
den Reformer an der Stelle zu erhöhen, wo die Reaktionsgeschwindigkeit und entsprechend der
Energiebedarf am größten sind.
Großes Potential zur Steigerung der Effizienz des Gaserzeugungssystems bietet die Rückführung
des Anodenrestgases auf den Reformerbrenner. Bei dieser Rezirkulation können allerdings Probleme
wie z. B. Schwankungen in der Anodenrestgasmenge und Zusammensetzung auftreten,
welche in allen Betriebszuständen beherrschbar sein müssen. Für den Normalbetrieb, für das
Anfahren und für unvorhergesehene Störfälle wurden stationäre und dynamische Simulationen
durchgeführt, mit denen die sicherheits- und verfahrenstechnischen Grenzen der Anodenrestgasrückführung
ermittelt wurden.
Anhand von weiteren Simulationsrechnungen erfolgte eine Optimierung der Wärmeintegration
und daraus resultierend die Entwicklung eines neuen Wärmeübertragernetzwerkes. Auf Grundlage
dieser Ergebnisse wurde schließlich ein Vorschlag für eine Neukonstruktion des Gaserzeugungssystems
erarbeitet, der die wesentlichen Schwachstellen des bestehenden Systems beseitigt.
Durch vergleichende Simulationsrechungen konnte belegt werden, dass sich der Wirkungsgrad
der Gaserzeugung durch konstruktive Veränderungen, aber auch durch Optimierung der Betriebsparameter,
noch erheblich steigern lässt.2010-11-10T00:00:00ZWärmetransformationsprozesse ohne PhasenumwandlungKühl, Hans-Detlevhttp://hdl.handle.net/2003/27982015-08-12T19:06:31Z2004-09-16T00:00:00ZTitle: Wärmetransformationsprozesse ohne Phasenumwandlung
Authors: Kühl, Hans-Detlev2004-09-16T00:00:00Z