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The crystallization of L-menthol in water was investigated, with the intent of understanding the effect that liquid-liquid phase separation (LLPS) has on the properties of product crystals. First the binary phase diagram was measured, comprising both solid-liquid and liquid-liquid equilibrium regions. Subsequently, a calibration for the online monitoring of solid and liquid-liquid suspension densities was performed using Raman spectroscopy, thus enabling the detection of LLPS and crystallization. By using the obtained phase diagram, an initial composition lying within the LLPS region, was selected to perform cooling crystallization. Crystallization was monitored online using Raman spectroscopy, and after crystallization occurred the solution was filtered, solids were air dried, ground, and subsequent offline characterization was performed using DSC, XRD, and Karl-Fisher. It was shown that crystallization followed by LLPS led to the formation of the most stable polymorphic form, yet those solids contained solvent inclusions. The initial amount of inclusions was shown to be a function of operating conditions, namely cooling rate and suspension density.

A method to derive explicit binary isotherms following the ideal adsorbed solution (IAS) theory is proposed. The method is applicable to any pair of single-component isotherms, as long as they fulfill a set of conditions, as described in this report. Examples of some isotherms fulfilling such conditions are: Langmuir, anti-Langmuir, Brunauer-Emmett-Teller (BET), and quadratic. Following the method proposed in this report, three previously unreported explicit binary isotherms, quadratic-BET, quadratic-Langmuir, and quadratic-anti-Langmuir, while following the IAS framework, could be derived. This work presents the method and the binary isotherms derived through this method.

The feasibility and efficiency of wet-nanogrinding of three drug substances (miconazole, itraconazole, etravirine) with similar elastic and plastic properties proved to depend primarily on the adequate electrostatic and steric stabilization of the nanoparticles and the specific energy input. Particle stabilization was provided by sodium dodecyl sulfate (SDS) and hydroxypropylcellulose. The specific energy input was defined by the grinding time, grinding bead size, and stirrer tip speed. Miconazole and itraconazole exhibited similar milling behavior, whereas etravirine nanosuspensions revealed agglomerates and increasing viscosity with increasing specific energy input. Agglomeration and viscosity increase were successfully counteracted by increasing the SDS concentration in the nanosuspension from 0 to 0.125 %. Under the provision of proper particle stabilization, the three drug substances could be nanosized to a mean size of ∼ 130 nm, with 90 % of all particles being smaller than ∼ 250 nm.

An experimental setup based on a static micromixer is used to determine nucleation and growth kinetics of L-asparagine monohydrate precipitated via antisolvent addition. Mixing in static micromixers was characterized previously using competitive-parallel reactions and computational fluid dynamics (Lindenberg et al., Chem Eng Sci. 2008;63:4135–4149). In this work, the mixer setup is used to determine nucleation and growth kinetics of L-asparagine at high supersaturations, i.e., true kinetics which are not affected by transport limitations. The method is based on measuring the particle size distribution obtained at different residence times. A population balance equation model of the process is used for the design of a continuous precipitation process. Finally, an analysis of the characteristic time scales of nucleation, growth, and mixing shows that, under the conditions in this study, mixing is much faster than precipitation and that the two processes can be decoupled. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Co(salen) [cobaltous bis(salicylaldehyde)ethylenediamine] complexes are well-known O2 carriers in solution. In the solid phase, these complexes exhibit some O2 binding but detailed studies have been complicated because few of the known polymorphs of Co(salen) actually bind O2. The O2 binding results for nanoparticulate Co(salen) are presented in this study. Rod-shaped Co(salen) nanoparticles, roughly 100 nm in diameter, were recrystallized by spraying a methylene chloride solution of commercially obtained Co(salen) into supercritical carbon dioxide. Temperature-programmed desorption, thermogravimetric analysis, and a Rubotherm magnetic suspension balance measurements reveal a reversible O2 uptake of ∼1.51 mmol/(g nanoparticles) at 25°C, consistent with a binding stoichiometry involving a bridging peroxo unit between two Co centers. In contrast, no measurable O2 uptake was observed with the commercial Co(salen). These results clearly show the potential for bottom-up design of nanoparticulate metal complexes for enhanced O2 storage and other applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Tissue engineering scaffolds require a controlled pore size and structure to host tissue formation from cell populations. Supercritical carbon dioxide (scCO2) processing can be used to form porous scaffolds in which the escape of CO2 from a plasticized polymer melt generates gas bubbles that shape the pores. The process is difficult to control with respect to changes in final pore size, porosity, and interconnectivity, while the solubility of CO2 in the polymers strongly affects the foaming process. An in-depth understanding of polymer CO2 interaction will enable a successful scaffold processing. Amorphous poly(DL-lactic acid) (PDLLA) and poly(lactic acid-co-glycolic acid) (PLGA) polymers are attractive candidates for fabricating scaffolds. In this study, CO2 sorption and swelling isotherms at 35 °C and up to 200 bar on a variety of homo- and copolymers of lactic acid and glycolic acids are presented. Sorption is measured through a gravimetric technique using a suspension microbalance and swelling by visualization. The obtained results are modeled using the Sanchez-Lacombe equation of state. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 483–496, 2008

The equilibrium sorption and swelling behavior in supercritical CO2 of poly(D,L-lactic acid) and poly(lactic-co-glycolic acid) has been studied at a temperature Of 35 degrees C and at pressures up to 200 bar. Sorption was measured through a gravimetric technique and swelling by visualization. From these data, the behavior of the different polymers can be compared. in terms of partial molar volume of CID, in the polymer matrix, all the polymers exhibit a behavior typical of rubbery systems. The experimental results have been modeled using the Sanchez-Lacombe equation of state, which is able to represent the actual behavior of the polymer-CO2 systems with reasonable accuracy.

The novel feature of the presented simulated moving bed (SMB) controller is its capability to make use of the average outlet concentration of the product streams over a cycle as feedback information, i.e., 'cycle to cycle' control. Its effectiveness is confirmed experimentally on an eight-column four-section laboratory SMB unit, which is used to separate a binary mixture of the nucleosides, uridine and guanosine. The performance of the 'cycle to cycle' SMB control scheme is also demonstrated by several SMB simulation runs that are chosen to test the robustness of the controller. Furthermore, the case where measurements have a time delay is presented. The results illustrate that the 'cycle to cycle' controller is able to meet the products' purity specifications and operate the process optimally with minimal information about the system regardless of the disturbances that might take place during the operation.

This work presents a new procedure to determine the nucleation kinetics during the reactive precipitation of an organic substance. The new method has been applied to the pH-shift precipitation of L-glutamic acid upon mixing of an aqueous monosodium glutamate solution with hydrochloric acid. The induction time has been measured precisely in a stirred batch reactor by the combination of two in-situ measurement techniques, namely ATR-FTIR spectroscopy (attenuated total reflection Fourier Transform technique) and Focused Beam Reflectance Measurement (FBRM). It is shown that ATR-FTIR is a suitable tool to measure the concentrations of the different L-glutamic acid ions, and can be used to determine the starting time of the process when the desired supersaturation is established in the reactor. The onset of particle formation is detected through FBRM. The precipitated polymorph is identified using in-situ Raman spectroscopy and Particle Vision & Measurement (PVM). Finally, the induction time is used together with the independently measured growth kinetics to determine the nucleation rate.

The equilibrium sorption and swelling behavior of four different polymers—poly(methyl methacrylate), poly(tetrafluoroethylene), poly(vinylidene fluoride), and the random copolymer tetrafluoroethylene–perfluoromethylvinylether–in supercritical CO2—are studied at different temperatures (from 40 to 80 °C) and pressures (up to 200 bar). Swelling is measured by visualization, and sorption through a gravimetric technique. From these data, the behavior of amorphous and semicrystalline polymers can be compared, particularly in terms of partial molar volume of CO2 in the polymer matrix. Both poly(methyl methacrylate) and the copolymer of tetrafluoroethylene exhibit a behavior typical of rubbery systems. On the contrary, polymers with a considerable degree of crystallinity, such as poly(tetrafluoroethylene) and poly (vinylidene fluoride), show larger values of partial molar volume. These can be related to the limited mobility of the polymer chains in a semicrystalline matrix, which causes the structure to “freeze” during the sorption process into a nonequilibrium state that can differ significantly from the actual thermodynamic equilibrium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1531–1546, 2006

The behavior of a chromatographic column where a single solute is fed in the presence of a suitable modifier is analyzed in the context of equilibrium theory. In particular, the pulse propagation of the solute, whose retention depends on the modifier concentration, has been analyzed as a full-fledged binary problem by the method of hodograph transformation applied to the pair of quasilinear differential equations. It has been shown that all possible operating conditions can be summarized with respect to the modifier concentration into three cases. These have been solved analytically by constructing the solution first in the hodograph plane, and then mapping it onto the physical plane using the method of characteristics. The peculiar properties of the derived hodograph plane were explained, and their impact on the pulse propagation for the three different cases has been elucidated. For the cases of intermediate adsorptivity of the modifier, the occurrence of solute peaks with infinitely high concentrations; that is, solute impulse, has been proven as well as the phenomena of double solute peaks.

Enhanced coalbed methane recovery (ECBM) increases the recovery of the methane present in a coal seam by injecting CO2 at high pressure. It is attractive from two perspectives, the valuable methane recovered and the storage of the greenhouse gas CO2 for geological times. In the framework of a feasibility study for the Sulcis Coal Province in Italy, the adsorption of pure CO2 and CH4 on dry coal has been measured at 45 and 60°C, using a magnetic suspension balance with in situ density measurement. The results show that the CO2 adsorption isotherms on coal are similar to those for other standard adsorbents such as silica gel and activated carbon. From the excess adsorption isotherms, the absolute adsorption is calculated using the assumption of constant volume of the adsorbed phase. As expected, CO2 get adsorbed more than CH4 in all cases. The Sulcis coal can uptake CO2 at the reservoir conditions in an amount of about 10% of its mass. © 2006 American Institute of Chemical Engineers Environ Prog, 2006

Interest in producing large amounts of plasmid DNA (pDNA) has increased in the last decade as a result of the advances made in gene therapy and DNA vaccines. The last stage of the manufacturing process involves a purification scheme guaranteeing a safe and stable product, considering the authorities' recommendations. This work studies the first step of the purification scheme, i.e., a group separation step based on size exclusion chromatography and using the simulated moving bed technology (SMB). The cleaning in place, crucial for the process validation, is implemented into the SMB in the so-called CIP-SMB configuration. Experiments were designed using the simple approach of triangle theory. The feed consisted of a clarified cleared lysate. The results indicate that total recovery of pDNA is possible and that the productivity can be tuned considering the trade-off with purity. Detailed simulations were used to validate these results after a cleared lysate model was established.

Thermodynamic properties of the enantiomers of the Troger's base as crystals and in ethanol solutions have been studied by means of a suite of analytical techniques. We report the melting diagrams of the two enantiomers, providing evidence for the formation of a solid racemic compound. We present also ternary equilibrium data about the solubility of the two enantiomers in ethanol at 25°, 35°, and 50°. The melting-diagram data are described well by the SchroederVan Laar and PrigogineVieland equations, when the melting temperatures and enthalpies of pure enantiomer and of the racemic compound are provided and with the assumption that the melting behavior is ideal. The ternary equilibrium data were well-described when nonideality of mixtures of ethanol and the enantiomers is accounted for in terms of the non-random two liquids (NRTL) model. Finally, we present the newly determined X-ray crystal structure of an orthorhombic form of the pure Troger's base (+)-enantiomer.

The PowerFeed process is a modification of the simulated moving bed (SMB) technique, where the flow rates in the unit are allowed to change during a switching period following a predefined pattern. Through multiobjective optimization, using a genetic algorithm, it is shown that PowerFeed achieves better performances than SMB in several cases of interest for applications. Moreover, its experimental feasibility and effectiveness is assessed by running and comparing SMB and PowerFeed separations of the enantiomers of α-ionone, on a cyclodextrin based chiral stationary phase.

Simulated moving-bed reactors (SMBR) combine chemical reaction and adsorptive separation within one single unit. Toward the design of this rather complex unit, guidelines for the proper choice of the operating parameters, that is, the flow-rate ratios and the Damkohler numbers within the different sections, have recently been devised based on a mathematical analysis of a linear-model system. For nonlinear systems, though, the influence of the operating parameters on the unit performance is less well understood. In this work, the interplay between the operating conditions and unit performance is investigated through numerical simulations and experiments, focusing on the influence of the feed stream composition. As a model system, the synthesis of methylacetate from methanol and acetic acid, catalyzed by a sulfonated ion-exchange resin, is considered. The experiments were carried out in an SMB reactor of miniplant scale. In addition, the reliability of the model predictions is evaluated by comparing the numerical simulation results with experimental data. It is shown through simulations that optimal performance is achieved where the feed to the SMBR is constituted of an equimolar mixture of the two reactants. Simulations and experimental results allow for an understanding of such a result.

The protein lysozyme has been precipitated as amorphous nanoparticles from a DMSO solution using dense carbon dioxide as antisolvent, by applying the so-called gas antisolvent recrystallization technique in a 400-mL precipitator. The objective is to investigate the possibility of tuning the particle properties by changing the key process parameters, namely, antisolvent addition rate, initial solute concentration, and temperature. It is shown that none of these operating parameters has a major effect on the average particle size or the particle size distribution. The former is mostly between 200 and 300 nm and exhibits no evident trend. The latter is always unimodal and rather narrow and exhibits increasing agglomeration at higher temperature and initial solute concentration. Up to 75% of the protein activity measured in the starting crystalline material is retained by the precipitated amorphous nanoparticles. The present experimental results compare well with data about the same system obtained in a different experimental setup, which were previously reported in the literature, thus pointing at the reproducibility and robustness of GAS antisolvent recrystallization. Moreover, these are consistent with the theoretical understanding of gas antisolvent recrystallization as achieved by using a recently developed model of the process.

Simulated Moving Bed reactors (SMBR) combine chemical reaction and adsorptive separation within one single continuous and countercurrent unit. This integration promises substantial improvements in process performance, especially when applied to equilibrium-limited reactions involving such heat-sensitive products as fine chemicals and pharmaceuticals. In this work, the interplay among the relevant process design parameters (dimensionless ratios of the fluid and solid flow rates, and the Damkohler numbers for each section of the unit) is investigated. For this, an analytical solution of differential mass-balance equations for the corresponding true countercurrent process (TCC), using as a model system the reaction A⇌B+C with each species exhibiting linear adsorption behavior, was developed. Based on this solution, criteria were derived for the optimum process design with respect to productivity and solvent consumption. Comparing these results with numerical simulations of an SMBR unit shows that the TCC model does not apply to SMBR units with a finite number of columns per section, that is, units of practical relevance, because the two units exhibit different residence time distributions and, hence, lead to different degrees of conversion.

Thermodynamic models for aqueous Ba 2+ -SO 4 2- -Na + -Cl - -solutions are compared in their accuracy to predict ion activities in saturated and supersaturated solutions. The Pitzer and the Bromley model are employed, taking into account ion pair formation of barium sulfate. Such models are then used to describe particle nucleation and growth, and finally they are imbedded in a mechanistic mixing-precipitation model for a single feed semibatch process. The effect of the key operating parameters on the mean particle size is analyzed through simulations. The results are compared with previous experimental data, thus highlighting the significance of a proper choice of the thermodynamic model.

The Focused Beam Reflectance Measurement (FBRM) technique provides on-line and in situ information about the chord length distribution (CLD) of a population of particles in dispersion. The effect of changing the focal point position on the measured CLD is experimentally analyzed by carrying out single particle FBRM determinations in both pure water and a dispersion of fines. The results allow some general conclusions to be drawn about optimal focal point positions.

The simulated moving-bed (SMB) chromatographic separation of the Troger's base enantiomers with ethanol as eluent on microcrystalline triacetate cellulose was studied. An experimental technique to design nonlinear SMB separations with few column experiments is presented. This shortcut technique allows the rigorous solution of the Equilibrium Theory model to be approximated without knowing the adsorption equilibria, and therefore can be useful in developing new separations. The predictions of the shortcut method are compared with the experimental results of the SMB separation. The effect of the feed concentration and of the nonideal contributions, such as mass-transfer resistance and extracolumn band broadening, are elucidated.

The scale-up of the HPLC separation of the enantiomers of the flavour norterpenoid ketones α-ionone and α-damascone from analytical to preparative scale was achieved using the chromatographic simulated moving bed (SMB) technique. Commercial HPLC columns, with heptakis-(2,3,6-per-O-methyl)-β-cyclodextrin bound to silica gel as chiral stationary phase, were employed for the separation. High-purity enantiomers of both chiral compounds have been obtained with a rather satisfactory productivity. Copyright © 2002 John Wiley & Sons, Ltd.

The Focused Beam Reflectance Measurement (FBRM) technique provides on-line and in-situ information about the chord length distribution of a population of particles in dispersion. This is rather promising for applications such as crystal size distribution control in crystallization processes. The objective of this study is to deepen the understanding of the characteristics of the FBRM measurement. On the one hand, a model is presented, which allows in principle to transform particle size distributions (PSD) into chord length distributions (CLD). On the other hand, measurements with particles in suspension show the critical dependence of the measurement on the optical properties of the system. A special technique has been developed to measure CLDs of single particles. These measurements clarify some of the above effects, detect possible over- and underestimations of particle size and give indications about how to interpret and exploit on-line CLD spectra.

Operating conditions for the separation of a binary mixture using a nonadsorbable eluent through simulated moving-bed technology were designed. The results obtained using equilibrium theory for adsorption described by Langmuir models lead to the definition of explicit constraints on the operating parameters to operate the unit in the desired regime of separation. A more general approach was able to produce the same result for a larger class of isotherms. The physical and mathematical conditions defining this larger class of isotherms are discussed, as well as the algorithms necessary to calculate the region of complete separation. Applications to the bi-Langmuir isotherm and the ideal adsorbed solution model, which are more flexible than the Langmuir model and can describe systems where selectivity changes with composition, are discussed. A shortcut method to get an explicit, though approximate, solution is proposed and its accuracy is discussed.

A kinetic model suitable to deal with the case of branched polymers produced in emulsion both in the case of chain transfer to polymer and propagation to terminal double bond is briefly presented and numerically solved through the method of the moments. Thanks to the “numerical fractionation” approach, the whole molecular weight distribution of the polymer is evaluated while accounting for the compartmentalized nature of the system. The results of some illustrative calculations concerning the effects upon the molecular properties of the final polymer of starved semibatch monomer feed policies, addition of a chain transfer agent and propagation to terminal double bond are discussed.

The separation of a multicomponent mixture in a countercurrent adsorptive separation unit is analyzed. A procedure for the optimal and robust design of the operating conditions of the unit is developed in the frame of equilibrium theory, where the adsorption equilibria are described through the constant selectivity nonstoichiometric Langmuir model, while mass-transfer resistances and axial dispersion are neglected. This allows for extending the results previously obtained for systems characterized by either the linear or stoichiometric Langmuir isotherm to cases where the adsorbates exhibit rather different loading capacities. Analogies and differences among these three equilibrium models with respect to the criteria for the choice of operating conditions of countercurrent separation units are discussed. A comparison between model predictions and experimental data assesses the reliability and accuracy of the theoretical results achieved in this work.

The adsorption separation of a multicomponent mixture in a four-section countercurrent separation unit is analyzed. A procedure for the optimal and robust design of the unit is developed in the frame of equilibrium theory, where adsorption equilibria are described through the constant selectivity stoichiometric model, while mass-transfer resistances and axial dispersion are neglected. A set of conditions obtained defines a region in the operating parameters space where the unit achieves complete separation. In the case of binary separations, with a desorbent having any adsorptivity with respect to the components to be separated, the boundaries of this region are obtained explicitly. In the general multicomponent case, a numerical procedure is needed. An approximate shortcut method devised allows to obtain explicit and reliable relationships for estimating the boundaries of the exact region. The results provide a very convenient tool not only to analyze the role of the desorbent in determining the separation performance, but to find both optimal and robust operating conditions. Comparison between model predictions and experimental data assesses the reliability and accuracy of the theoretical findings.

The separation of a binary mixture, using a third component having intermediate adsorptivity as desorbent, in a four section countercurrent adsorption separation unit is considered. A procedure for the optimal and robust design of the unit is developed in the frame of Equilibrium Theory, using a model where the adsorption equilibria are described through the constant selectivity stoichiometric model, while mass-transfer resistances and axial mixing are neglected. By requiring that the unit achieves complete separation, it is possible to identify a set of implicity constraints on the operating parameters, that is, the flow rate ratios in the four sections of the unit. From these constraints explicit bounds on the operating parameters are obtained, thus yielding a region in the operating parameters space, which can be drawn a priori in terms of the adsorption equilibrium constants and the feed composition. This result provides a very convenient tool to determine both optimal and robust operating conditions. The latter issue is addressed by first analyzing the various possible sources of disturbances, as well as their effect on the separation performance. Next, the criteria for the robust design of the unit are discussed. Finally, these theoretical findings are compared with a set of experimentalmore » results obtained in a six port simulated moving bed adsorption separation unit operated in the vapor phase.« less

Simulated moving bed (SMB) chromatography has become a key separation technology in the areas of pharmaceutical and biotechnology industry thanks to its high productivity and short process development times. Today, modeling, design, and optimization of the SMB process are regarded to be well established. On the other hand, long term robust/optimized operation of the process is still an open issue. The common practice is to operate the SMB units under suboptimal operating conditions in order to gain the necessary robustness. The operating parameters are tuned manually by experienced operators in order to maintain the product specifications in the long term. Therefore, as SMB applications spread, the SMB process control problem becomes increasingly important. Recently, we have proposed an on-line optimization based SMB control scheme that allows exploiting the full economic potential of the SMB technology on the basis of minimal information. This work addresses the experimental implementation of the developed control concept on an eight-column four-section laboratory SMB unit that is used to separate the binary mixture of nucleosides uridine and guanosine. The performance of the SMB control scheme is demonstrated via several experimental controlled SMB runs that are designed to challenge the robust performance of the controller. The reported results aim to demonstrate that the controller is able to deliver the products with the specified purities and to optimize the process performance despite uncertainties in the system behavior and disturbances taking place during the operation. © 2006 American Institute of Chemical Engineers AIChE J, 2006

The interpretation of chord length distributions (CLDs) is essential in many fields and has been discussed by various authors. Here, the technique of the Focused Beam Reflectance Measurement (FBRM) is considered as on-line and in-situ measurement device of the CLD of particle dispersions and emulsions. Though useful in general, this measurement cannot be converted directly into a particle size distribution (PSD), unless the physics of the measurement method is described and accounted for. In this work we present a new tool to carry out such a conversion once the particle shape is known a priori and can be fixed, which is based on a two step procedure: (1) the computation of a matrix that converts the PSD of a population of particles with given shape into the corresponding CLD using a 3-dimensional geometric model; (2) the calculation of the PSD from the resulting linear matrix equation for the measured CLD. Here, the method of Projections onto Convex Sets (POCS) is applied to solve the PSD restoration problem, which is a mathematically ill-posed inverse problem. We study the effect of particle shape and matrix dimension on the ill-posed character of the inverse problem. A detailed error analysis of the CLD allows for a predictive description of a posteriori constraints in the POCS framework. We discuss the application of this method to the characterization of simulated test cases and experimentally obtained data.

Struktur-Eigenschaftsbeziehungen polydisperser fraktaler Stoffsysteme Dr. U. Katzel (E-Mail: uwe.kaetzel@merck.de), Dr. T. Gottschalk-Gaudig, Dr. M. Stintz, Dr. H. Barthel Merck KGaA, Zentrale Verfahrensentwicklung, ZVE-I, Frankfurter Strase 250, D-64293 Darmstadt Wacker-Chemie AG, Werk Burghausen, Johannes-Hess-Strase 24, D-84480 Burghausen Institut fur Verfahrenstechnik und Umwelttechnik, Arbeitsgruppe Mechanische Verfahrenstechnik, Technische Universitat Dresden, D-01062 Dresden DOI: 10.1002/cite.200750628

We consider a hyperbolic system of two first order partial differential equations that can be used to describe nonlinear chromatography, and the corresponding Riemann initial value problems. It can be shown that these equations admit classical solutions made of constant states separated by continuous (simple wave) or discontinuous (shock) transitions, but also – for exactly specified initial states – singular solutions. Such solutions are due to the occurrence of an overcompression condition that leads to the formation of a spike travelling at constant speed and increasing strength in space. Such singular solution can be observed by solving numerically a regularized form of the original equations, but eludes the application of techniques proposed in the literature to study singular shocks and delta-shocks, which share with the system studied here its overcompressive character. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ren etabliert sind, wurden neuerdings Ruckspulungen mit sehr hoher Frequenz eingesetzt. Besonders wirksam erwies sich die schnelle Ruckspulung in Kombination mit aus Silicium-Wafer hergestellten Filterscheiben der niederlandischen Firma FluXXion B.V., s. Abb. Die hochfrequente Ruckspulung wird zurzeit am IVT erforscht. Dabei werden sowohl der Einfluss der hochfrequenten Ruckspulung auf die Permeatleistung untersucht als auch Modelle zur Beschreibung des Transportprozesses entwickelt.