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11.
In order to estimate single solute adsorption isotherms, the nonlinear frequency response (FR) of a chromatographic column is analyzed experimentally and evaluated using the concept of higher order frequency response functions (FRFs) based on the Volterra series and generalized Fourier transform. In this case study, it has been investigated the adsorption of ethyl benzoate on octadecyl silica from a mixture of methanol and water (60:40) as a solvent. Experiments are performed using a standard gradient HPLC unit. For estimation of adsorption isotherms by the nonlinear FR method the column inlet concentration is changed in a nearly sine waveform around several steady-state concentrations. Using this method the first three local derivatives of a single solute adsorption isotherm are estimated from the low frequency asymptotes of the corresponding functions, i.e. the phase and first order derivative of the FRFs. For an accurate estimation of isotherm coefficients periodical experiments should be preformed for frequencies below a certain critical frequency. This is the frequency needed for approaching the low frequency asymptotic behaviour of the corresponding functions close enough, so that errors due to the non-feasibility of experiments with zero frequency can be neglected. Unfortunately, depending on the properties of the system, it can happen (as for the system investigated here) that experiments for the critical frequency would be too long and cannot be realized. In order to study the loss of accuracy of the nonlinear FR method, when it is applied for non-optimal frequencies, experiments are performed for frequencies approximately one order of magnitude higher than the critical frequency required to evaluate the FRF phases. The obtained isotherm model coefficients are compared with the ones estimated using conventional frontal analysis as a reference method. The isotherms determined by two methods are similar, however a closer look reveals that peaks predicted under overloading conditions differ. 相似文献
12.
Zhou Y Sharma N Deshmukh P Lakhman RK Jain M Kasi RM 《Journal of the American Chemical Society》2012,134(3):1630-1641
Here we report a modular strategy for preparing physically cross-linked and mechanically robust free-standing hydrogels comprising unique thermotropic liquid crystalline (LC) domains and magnetic nanoparticles both of which serve as the physical cross-linkers resulting in hydrogels that can be used as magnetically responsive soft actuators. A series of amphiphilic LC pentablock copolymers of poly(acrylic acid) (PAA), poly(5-cholesteryloxypentyl methacrylate) (PC5MA), and poly(ethylene oxide) (PEO) blocks in the sequence of PAA-PC5MA-PEO-PC5MA-PAA were prepared using reversible addition-fragmentation chain transfer polymerization. These pentablock copolymers served as macromolecular ligands to template Fe(3)O(4) magnetic nanoparticles (MNPs), which were directly anchored to the polymer chains through the coordination bonds with the carboxyl groups of PAA blocks. The resulting polymer/MNP nanocomposites comprised a complicated hierarchical structure in which polymer-coated MNP clusters were dispersed in a microsegregated pentablock copolymer matrix that further contained LC ordering. Upon swelling, the hierarchical structure was disrupted and converted to a network structure, in which MNP clusters were anchored to the polymer chains and LC domains stayed intact to connect solvated PEO and PAA blocks, leading to a free-standing LC magnetic hydrogel (LC ferrogel). By varying the PAA weight fraction (f(AA)) in the pentablock copolymers, the swelling degrees (Q) of the resulting LC ferrogels were tailored. Rheological experiments showed that these physically cross-linked free-standing LC ferrogels exhibit good mechanical strength with storage moduli G' of around 10(4)-10(5) Pa, similar to that of natural tissues. Furthermore, application of a magnetic field induced bending actuation of the LC ferrogels. Therefore, these physically cross-linked and mechanically robust LC ferrogels can be used as soft actuators and artificial muscles. Moreover, this design strategy is a versatile platform for incorporation of different types of nanoparticles (metallic, inorganic, biological, etc.) into multifunctional amphiphilic block copolymers, resulting in unique free-standing hybrid hydrogels of good mechanical strength and integrity with tailored properties and end applications. 相似文献
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Menka Petkovska Danijela Antov-Bozalo Ana Markovic Patrick Sullivan 《Adsorption》2007,13(3-4):357-372
Mathematical modeling of an Electric-Swing Adsorption (ESA) system (adsorption cycle with electrothermal desorption step,
performed by direct heating of the adsorbent particles by passing electric current through them), with annular, radial-flow,
cartridge-type fixed-bed and in-vessel condensation, is performed by using Comsol Multiphysics™ software. Three multiphysics
models are built, in order to describe three stages of a compete ESA cycle: adsorption, electrothermal desorption before the
start of condensation and electrothermal desorption with in-vessel condensation. In order to describe the complete ESA cycle
the models for the three stages are integrated, by using a combination of Comsol Multiphysics™ and Matlab™. The models were
successfully used for simulation of separate stages of the process and of the complete ESA cycles, as well as for investigation
of the influences of the main operational parameters on the process performance.
The views and conclusions contained herein are those of the author and should not be interpreted as necessarily representing
the official policies or endorsements, either expressed or implied, of the Air Force Office of Scientific Research or the
U.S. Government. 相似文献
15.
Milica Ilić Menka Petkovska Andreas Seidel-Morgenstern 《Journal of chromatography. A》2009,1216(33):6108-6118
This paper demonstrates an experimental application of the nonlinear frequency response (FR) method extension to determine adsorption isotherms of binary mixtures. This method, based on the analysis of the response of a chromatographic column subjected to the sinusoidal inlet concentration changes, is shown to be an alternative for isotherm determination. The critical issue related to the successful application of the method is to reach experimentally the low frequency asymptotic behaviour of the corresponding frequency response functions (FRFs). Although, there are different possibilities to perform periodical inlet concentration changes, in this paper only simultaneous changes for both components were considered. The adsorption of phenol and 2-phenylethanol on octadecyl silica was analyzed experimentally using a mixture of methanol and water as a solvent. Parameters of competitive isotherms were also estimated for comparison using the classical perturbation method. Despite certain differences between competitive isotherms estimated with the two methods that were found, the obtained results show the potential of the nonlinear FR method for measuring competitive isotherms. 相似文献
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Milica Ilić Menka Petkovska Andreas Seidel-Morgenstern 《Journal of chromatography. A》2009,1216(33):6098-6107
In this work adsorption equilibria of binary mixtures are quantified analyzing the nonlinear frequency response of a chromatographic column. Local partial derivatives of an isotherm model can be estimated for certain steady-states from the low frequency asymptotes of the corresponding frequency response functions (FRFs). The required FRFs correspond to two different compounds and the type of the imposed inlet concentration changes, e.g. periodical inlet concentration changes of only one compound or of both of them. For an accurate determination of isotherm parameters, it is necessary to approach as close as possible the low frequency asymptotic behaviour of these functions. Based on principles valid for the FRFs corresponding to the adsorption of a single solute, frequencies needed to reach the low frequency asymptotes of the functions of interest for estimating competitive isotherms are defined in this paper. The relation between the accuracy of the isotherm parameters determined and numbers and types of periodical inlet concentration changes and steady-states analyzed is also evaluated. 相似文献
18.
Ljubica T. Petkovska 《光谱学快报》2013,46(3):283-300
Carbon-dioxide spectra of some higher transitions in the 9-11μm region were studied. Spectra of the sequence ([10°1,02°1]I,II - 00°2) and hot (0111 - 1110) bands were calculated as a function of temperature. the positions of the ro-vibrational transitions and their intensities were determined as a function of temperature. for lines in hot and sequence transitions whose positions are close to some of the regular lines ([l000,0200]I,II - 00°1)1 absorption coefficients of adjacent lines were calculated as functions of line center distances and temperature. the resulting values of the absorption coefficient for conditions of constant pressure or constant volume were determined. 相似文献
19.
Bojan B. Radak Ljubica T. Petkovska epan S. Miljani Raymond T. Bailey Francis R. Cruickshank David Pugh 《Journal of Chemical Sciences》1991,103(3):409-412
Spectra of coincidence of CH3C1 IR absorption with CO2-laser emission were recorded by a photoacoustic detection method in the whole range of CO2-laser emission. The samples were neat gas and mixtures with argon, at several pressures (10 to 600Torr) so that pressure
effects could be observed. The results show that argon affects absorption of CO2-laser emission quite differently from neat chloromethane, both regarding the most prominent coincidences and background absorption. 相似文献