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Item type:Publication, Access status: with files , Electrical Capacitance Volume Tomography (ECVT) for Characterization of Additively Manufactured Lattice Structures (AMLS) in Gas-Liquid Systems(Multidisciplinary Digital Publishing Institute (MDPI), 2021-09-08); ; ; ; Against the background of current and future global challenges, such as climate change, process engineering requires increasingly specific solutions adapted to the respective problem or application, especially in gas–liquid contact apparatuses. One possibility to adjust the conditions in this kind of apparatuses is an intelligent and customized structuring, which leads to consistent fluid properties and flow characteristics within the reactor. In the course of this, the interfacial area for mass transfer, as well as residence times, have to be adjusted and optimized specifically for the respective application. In order to better understand and advance the research on intelligent customized additively manufactured lattice structures (AMLS), the phase distributions and local gas holdups that are essential for mass transfer are investigated for different structures and flow conditions. For the first time a tomographic measurement technique is used, the Electrical Capacitance Volume Tomography (ECVT), and validated with the volume expansion method and a fiber optical needle probe (A2PS-B-POP) for an air-water system for different modes of operation (with or without co-current liquid flow in empty or packed state). The ECVT proved to be particularly useful for both in the empty tube and the packed state and provided new insights into the phase distributions occurring within structured packings, which would have led to significantly underestimated results based on the visual reference measurements, especially for a densely packed additively manufactured lattice structure (5 mm cubic on the tip). Particularly for the modified structures, which were supposed to show local targeted differences, the ECVT was able to resolve the changes locally. The additional use of a pump for co-current flow operation resulted in slightly higher fluctuations within the ECVT data, although local events could still be resolved sufficiently. The final comparison of the empty tube at rest data with a fiber optical needle probe showed that the results were in good agreement and that the local deviations were due to general differences in the respective measurement techniques.Publicationtype: Journal ArticleScopus© Citations 5 159 313 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Development and validation of retention models in supercritical fluid chromatography for impregnation process design(Multidisciplinary Digital Publishing Institute (MDPI), 2021-07-31); ; ; ; The retention factor is the key quantity for the thermodynamic analysis of the retention mechanism in chromatographic experiments. In this work, we measure retention factors for moderately polar solutes on four silica-based porous matrices as stationary phases by supercritical fluid chromatography. Elution of the solutes is only possible with binary mixtures of supercritical carbon dioxide (sc-CO₂) and modifier (methanol) due to the low polarity of pure sc-CO₂. The addition of modifiers makes the retention mechanism more complex and masks interactions between solute and stationary phase. In this work, we develop and validate several retention models that allow the obtaining of retention factors in modifier-free sc-CO₂. Such models pave the way for quantifying adsorption interactions between polar solutes and non-swellable porous matrices in pure sc-CO₂ based on retention data obtained in sc-CO₂-modifier mixtures. The obtained information will thereby facilitate the understanding and design of impregnation processes, which are often performed in modifier-free conditions.Publicationtype: Journal Article147 229 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Retention characteristics of silica materials in carbon dioxide/methanol mixtures studied by inverse supercritical fluid chromatography(2019-03-15); ; ; ; In this work, inverse supercritical fluid chromatography was applied to characterize the surface of four silica materials (three commercial Kromasils and one silica aerogel) from chromatographic retention data. Retention factors at various pressures (150-300 bar), temperatures (25-60 °C) and modifier concentrations (5-20 vol.% methanol in CO2) for a set of representative 17 solutes were correlated with the solute properties by the linear solvation energy relationships (LSER). Two types of the LSER models were identified based on different criteria. Firstly, a generally valid model with two descriptors concerning dipolarity/polarizability and solute hydrogen-bonding acceptor ability was constructed. Secondly, a group of specific models for each particular silica material was proposed. According to the statistical analysis of the modeling results, the acid-basic interactions were demonstrated to have a major contribution to the retention for all studied silicas. The intensity of these interactions decreases with increasing methanol concentration in the mobile phase, possibly due to the mixed mechanism of competitive adsorption of the modifier on silanol groups and modification of mobile phase property. Moreover, retention factors measured under constant conditions (p, T, methanol concentration) for a pair of the materials were found to be proportional in logarithmic scale implying the transferability of the adsorption free energies and the adsorption constants across four studied silica materials.Publicationtype: Journal Article186 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Supercritical fluid chromatographic separation on preparative scale and in continuous mode(2018-04-01); Chromatography with supercritical fluids (SFC) is a powerful tool for carrying out separations of substances with very similar structure and volatility, such as isomers of various kinds. In this contribution, we discuss the separation process aiming at the recovery of products on a much larger scale than analytical. Nevertheless, for developing such a process, the separation is carried out first on analytical scale to determine optimum operating conditions and select stationary phase, mobile phase, and co-solvent (modifier), if necessary. Determination of isotherms is helpful for simulating the separation process. Verification of the separation process includes the recycling of the mobile phase. The chromatographic process can be a batch process in the elution mode, or a continuous process, approximated as simulated moving bed (SMB). The batch SFC process, although using a higher quantity of mobile phase is less cost intensive than the SFC-SMB process.Publicationtype: Journal Article197 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of chemical nature of carrier materials on the dissolution behavior of racemic ibuprofen(2018-02); ; ; The poor aqueous solubility of ibuprofen due to its hydrophobicity limits the bioavailability of the drug in the aqueous environment of the human body. Therefore particle deposition experiments were performed with ibuprofen and different carrier materials. Furthermore, the dissolution behavior of the untreated ibuprofen and the ibuprofen loaded carriers has been investigated at 310 K and pH = 2.0 and pH = 5.5. The results of this investigation demonstrate that drug loadings up to 50 wt% drug onto silica materials could be achieved and that the drug loading increases nearly linear with increasing surface area of the silica materials. Furthermore, the study reveals that the highest dissolution rate was obtained with β-cyclodextrin and that the dissolution rate of all materials investigated increases with increasing pHvalue.Publicationtype: Journal Article220 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Modeling adsorption on energetically heterogeneous surfaces with an extended SAFT-VR approach(2018); Adsorption equilibria of methanol/carbon dioxide mixtures on plain silica particles at 308 K and pressures of 10.1 MPa, 12.7 MPa, 15.1 MPa and 20.1 MPa were measured with the frontal analysis by characteristic points (FACP) method using supercritical fluid chromatography. The data show a bimodal adsorption energy distribution and cannot be sufficiently modeled with a two-dimensional SAFT-VR approach. Therefore, an extension of SAFT-VR is proposed to model adsorption on heterogeneous surfaces and applied to the presented data. It can be described by the extended model with very low ARDs between 1.0% and 2.4%.Publicationtype: Journal Article123 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Measuring and modeling adsorption equilibria of non-volatile compounds dissolved in supercritical carbon dioxide on nanoparticles using dynamic methods(2016-07); Adsorption equilibria of benzoic acid and ibuprofen on AlO(OH) nanoparticles were measured for the first time using a dynamic method, frontal analysis. Possible techniques for creating packed beds of nanoparticles are presented and their suitability for different chromatographic adsorption measurement methods is discussed. Benzoic acid adsorption was measured at 40 °C and 16 MPa on AlO(OH) solid and hollow spheres, ibuprofen adsorption was measured at 40 °C and varying pressures of 10, 15 and 20 MPa on AlO(OH) hollow spheres. A dry packing method was used to create packed beds for the adsorption experiments. The experimental data was modeled with a Peng-Robinson EoS/RAST/BET approach, which shows excellent agreement with the data. The model is discussed as a way to model adsorption in high pressure drop packed beds.Publicationtype: Journal Article69 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Supercritical fluid simulated moving bed chromatography for the separation of ethyl linoleate and ethyl oleateSupercritical fluid-simulated moving bed (SF-SMB) chromatography is an attractive technology thanks to the outstanding performance of continuous countercurrent adsorption processes in combination with the tunability of eluent strength of supercritical CO 2. This work focuses on the process development steps of simulated moving bed chromatography for the separation of ethyl linoleate and ethyl oleate on silica gel using supercritical carbon dioxide under linear conditions. Adsorption isotherms of the components of interest were determined at analytical scale and applied together with the equilibrium theory for the design of a two-step SF-SMB process for the separation of the fatty acid ethyl esters. Results of the experimental validation of the continuous chromatographic separation of ethyl linoleate and ethyl oleate are shown and discussed in detail.Publicationtype: Journal Article235 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Solubilities and adsorption equilibria of β-carotene in supercritical and near-critical fluidsA systematic investigation of solubility and adsorption equilibria of β-carotene in carbon dioxide and propane, respectively, at elevated pressures was carried out. Investigated at (303, 313, and 323) K and over a pressure range from (3.2 to 13.4) MPa, the solubility of β-carotene in propane was in the range of (110 to 450) mg·kg-1 propane and approximately 2 orders of magnitude higher than that in supercritical carbon dioxide. Adsorption equilibria of β-carotene in carbon dioxide with a modifier and in propane were studied on nonpolar chromatographic adsorbents. Concerning adsorption equilibria of β-carotene in carbon dioxide with 2-propanol as a modifier, the loading decreases with increasing modifier content and increasing pressure. Regarding the adsorption equilibrium of β-carotene in propane, the loading achieved is much lower than in carbon dioxide due to the higher solubility of β-carotene in propane.Publicationtype: Journal Article86 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Partitioning of organic biocides between wood and supercritical carbon dioxideThe degree of interaction between selected organic biocides (tebuconazole, propiconazole, and IPBC) and wood under supercritical conditions was investigated using a supercritical fluid chromatograph. The biocides were carried through a sawdust column by CO2 at various conditions. Retention times differed markedly both between the examined biocides and between physical conditions. Tebuconazole showed a higher affinity for wood than the other biocides. For all biocides, wood affinity was highest and, thus, fluid affinity lowest, at lowest pressures.Publicationtype: Journal Article101