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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 Article198 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Preparative chromatography with supercritical fluids. Comparison of simulated moving bed and batch processes(2007-12-28); ; Preparative chromatography is a key technology for the separation of fine chemicals in production scale. Most of the published studies are carried out using liquid solvents as mobile phase. However, the used organic solvents can often be replaced by supercritical fluids. A reduction or renouncement of organic solvents does not only correspond to the trend of the so-called green chemistry-a sustainable, environmentally friendly production of chemical products. But a changeover to chromatography with supercritical fluids can also be reasonable under economic criteria. In this contribution a comparison between the Batch-supercritical fluid chromatography (Batch-SFC) process and the simulated moving bed (SMB)-SFC process is presented. Because of the minor importance of solvent consumption and solvent recovery in SFC, the separation systems were optimized primarily in terms of their specific productivity. For three of the four investigated model systems, the specific productivity of the SMB process is significantly higher than the productivity of the Batch process. Due to the fact, that the process with the higher specific productivity is not inevitably the more economical process, supplementary the costs of the process were considered. Therefore the comparison of the two processes was done from an economic point of view considering the minimum product price that has to be realized to fulfill the defined economic aim. It was found that although the optimized specific productivities of the SMB process were significantly higher than the productivities of the Batch process, the Batch process is the more profitable process for the investigated production rate range between 0.4 and 5 t/a.Publicationtype: Journal Article163 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Adsorption equilibria of α- and δ-tocopherol from supercritical mixtures of carbon dioxide and 2-propanol onto silica by means of perturbation chromatographyFor the determination of adsorption isotherms of dissolved components from supercritical fluids, an experimental equipment has been constructed. It consists of a fluid preparation and two chromatographic units with UV detector and pressure expansion. The equipment allows the performance of peak experiments (injecting samples onto an empty column) as well as perturbation experiments (perturbing the equilibrium in a saturated column). Adsorption isotherms of α- and δ-tocopherol on two unmodified silica gels were determined at a temperature of 313.15 K and pressures of 16.1, 20.0, and 26.1 MPa, respectively. Fluid phase was CO2 with 2-propanol (weight fraction 0.05) as modifier. Parameters of a cubic Hill isotherm were fitted to the data. Ideal adsorbed solution theory (IAST) was applied for prediction of mixture adsorption. Applicability of IAST was tested with perturbation chromatographic experiments using different mixtures. All isotherms show anti-Langmuir behaviour (concave shaped isotherms). These results agree with literature data. Competitive adsorption was successfully predicted by means of the IAS theory.Publicationtype: Journal Article81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Management and control of modifier content in preparative SFC solvent cyclesThe objective of this work was to establish a solvent cycle with a possibility for modifier control in a preparative supercritical fluid chromatography simulated moving bed plant (SFC-SMB). Fourier transform infrared (FTIR) spectroscopy and flame ionization detection (FID) have been investigated for measuring alcohol concentrations in supercritical carbon dioxide. The integration of these in-line techniques into a modifier control schema allowed the operation of a closed loop SFC-SMB cycle. The applicability of the developed control concept for usage of 2-propanol in supercritical carbon dioxide has been verified by an experimental test series involving an eight column SFC-SMB plant. Different process variations have been compared in terms of energy and solvent consumption. Hereby, savings of almost all CO2 and 76% modifier could be achieved.Publicationtype: Journal Article82 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , New aspects on adsorption from supercritical fluid phases(2006-09); Adsorption from a high pressure gaseous phase, containing as one major component a supercritical fluid is discussed. The fundamentals are presented as a basis of the modelling of the adsorption equilibria. Experimental techniques for determination of adsorption isotherms are presented and examples are given. The modelling of the adsorption isotherms is an essential aspect, e.g. since during application in a chromatographic process, multiple processes of adsorption and desorption are occurring, which are influenced by kinetics, but are mainly determined by thermodynamic equilibrium. In this work the modelling is carried out using the adsorption isotherm proposed by Hill. The application of adsorption processes comprises recovery from the gas phase. Decaffeination and purification of synthetic tocopherol acetate are presented as examples. For the separation of tocopherols and sterols (from natural sources) the selective action of a sequence of adsorption and desorption steps is further discussed. Then, the application of preparative supercritical fluid chromatography (SFC) is investigated. The elution chromatography is compared to the simulated moving bed technology (SMB-SFC).Publicationtype: Journal Article87 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Enantioseparation of 1-phenyl-1-propanol by supercritical fluid-simulated moving bed chromatography(Science Direct, 2005-03-08); ; ; ; The enantioseparation of 1-phenyl-1-propanol through the supercritical fluid-simulated moving bed (SF-SMB) process is studied. Non-linear isotherms were measured on an analytical column, and used together with the triangle theory for SMB design to select operating conditions for the SF-SMB. Experiments were carried out on a pilot-scale SF-SMB plant at conditions that corresponded to the non-linear range of the isotherm. Under conditions of low feed concentration, complete separation (extract purity=99.5%; raffinate purity=98.4%) was achieved. Under conditions of larger feed concentration, the best separation corresponded to an extract purity of 98.0% and a raffinate purity of 94.0%, and yielded a productivity of 110g of racemate per kg stationary phase per day.Publicationtype: Journal Article113 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Separation of ibuprofen enantiomers by supercritical fluid simulated moving bed chromatographyThe continuous separation of R(-)-ibuprofen and S(+)-ibuprofen by supercritical fluid simulated moving bed chromatography has been developed. First, experiments were performed at a low concentration level. Therefore, a starting set of operating parameters was calculated using the "triangle theory," which has been developed in the frame of equilibrium theory. Subsequently, the feed concentration was increased. A dynamic simulation program, based on a plug flow model with axial dispersion and linear mass transfer resistance, was used to predict the effect of operating variables on the process performance. Adsorption isotherms were determined with the elution by a characteristic point method. The experimental results were compared both with the model predictions based on the triangle theory and with the results of simulations.Publicationtype: Journal Article91 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Separation of stereoisomers in a simulated moving bed-supercritical fluid chromatography plantThe combination of two techniques, simulated moving bed (SMB) and supercritical fluid chromatography (SFC), leads to an apparatus with unique features. Besides the known advantages of the SMB process, like reduced solvent consumption and its continuity, the use of supercritical carbon dioxide as the mobile phase offers an easy product recovery by depressurizing the supercritical fluid. Details of a SMB-SFC plant are presented for the first time. Due to the large number of process parameters a simulation of the SMB process is necessary to achieve optimal operating conditions. The most important thermodynamic information for a SMB process is the adsorption isotherms. Therefore, isotherms for two phytol isomers are measured and correlated. A fast dynamic model for the simulation of SMB is used to calculate the region of complete separation taking different column configurations and the compressibility of the mobile phase into account.Publicationtype: Journal Article81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Solubilities of the fat-soluble vitamins A, D, E, and K in supercritical carbon dioxide(1997-01-13); Solubilities of eight different species of the fat-soluble vitamins A, D, E, and K in supercritical carbon dioxide were measured at (313, 333, and 353) K and over a pressure range of 20 MPa to 35 MPa. Solubilities have been determined by an analytical method using the direct coupling of an equilibrium cell to a supercritical fluid Chromatographic system with UV detection. The solubilities of all fat-soluble vitamins in supercritical carbon dioxide under the conditions investigated are in the range of 10 g/kg, except for β-carotene (provitamin A), which is 3 orders of magnitude less soluble. With increasing molecular mass of the vitamin, its solubility in supercritical carbon dioxide decreases. At constant temperature, the solubility of all substances increases with increasing density. At constant density, a rue of temperature results in an increase in solubility. This is caused by the increasing vapor pressure of the solid.Publicationtype: Journal Article106 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Regeneration Methods for Caffeine-Loaded CO₂(1995-10-01); ; ; Supercritical gas extraction for the decaffeination of green coffee beans has become an established method in the last decade. However, because of the commercial aspects in this field, few research results on applications have been published. In this publication, three different methods for the regeneration of caffeine-loaded CO2 are presented: depressurization, adsorption with activated carbon, and absorption with water. For all these methods, phase equilibrium experiments with pure caffeine were done. Furthermore, pilot-plant experiments were performed to decaffeinate green coffee beans.Publicationtype: Journal Article894