1,721,153 research outputs found
Optimal operation of simulated moving-bed units for non-linear chromatographic separations - II. Bi-Langmuir isotherm
No full textSeveral important theoretical results have been previously obtained to predict the behaviour of continuous chromatographic separation units in the case of Langmuirian type of isotherms. Concerning separation of binary mixtures in a non-adsorbable carrier with SMB units, stoichiometric and non-stoichiometric Langmuir and modified Langmuir have been considered in the frame of equilibrium theory. For these isotherms explicit constraints on the operating parameters have been found to achieve complete separation (M. Mazzotti, G. Storti, M. Morbidelli, J. Chromatogr. A 769 (1997) 3; M. Mazzotti, G. Storti, M. Morbidelli, AIChE J, 42 (1996) 2784; M. Mazzotti, M. Pedeferri, M. Morbidelli, in: Chiral Europe '96 Symposium, Spring Innovations Limited, Stockport, UK, 1996); the design of the SMB unit was then reduced to the analysis of the so-called region of complete separation for the operating parameters. In this paper, the same result is presented for the bi-Langmuir case, which can avoid the constant selectivity limit of the Langmuir isotherms. Langmuir and bi-langmuir isotherms fitting the same set of data taken from the literature were then used here to show the difference in the prediction of the region of complete separation. Finally an analysis of non-linearity effects on performance parameters is presented as a useful criterion for optimization of the separation performances. (C) 1998 Elsevier Science B.V
Impure cultures. Interfacing science, technology, and humanities
No full textIn 2008 the University of Bologna has launched a new
international Ph.D. program in Science, Technology, and Humanities
(from 2010: Science, Cognition, and Technology), in cooperation with the universities of Exeter, in England, and Konstanz, in Germany. This is the first academic program in Italy that opens up a space for the dialogue between humanities, science studies, and the sciences. The program is sustained by the international collaboration
of faculty from a broad spectrum of disciplines, from the sciences
to the humanities. This volume documents the early activity of
the Bologna doctoral program by collecting work-in-progress essays by
some of its graduate students and by some of their colleagues based at the University of Exeter
Simulated moving-bed units with extra-column dead volume
No full textSimulated moving-bed (SMB) technology is attracting increased interest for application to the separation of pharmaceuticals and fine chemicals, particularly to enantioseparations. Unlike the large-scale UOP Sorbex process, these small-scale units rise a series of HPLC columns, and the volume of the connecting lines may become comparable to the volume of the columns. In this work the effect of extra-column dead volume on SMB performance is analyzed, with the aim of providing a conceptual framework to account for it. In particular guidelines to design SMB operating conditions with nonnegligible extra-column dead volumes to achieve the desired separation performance are provided. These ave quantitatively assessed through comparison with the results obtained using a detailed SMB model which accounts for extra-column dead volumes. The model allows the extent and the role of extra-column band broadening due to the presence of dead volumes to be evaluated. A set of experimental results on a laboratory SMB unit is discussed in light of the theoretical findings
3D fourier reconstruction of irregularly sampled seismic Gathers : analysis of the extended model resolution matrix
No full textFourier reconstruction is basically a linear inverse problem that attempts to recover the Fourier spectrum of the seismic wave-field from irregularly sampled data along the spatial coordinates. The estimated Fourier coefficients are then used to reconstruct the data in a regular grid via a standard inverse Fourier transform (IDFT or IFFT). Unfortunately, this kind of inverse problem is usually under-determined and illconditioned. For this reason the Fourier reconstruction with minimum norm (FRMN) adopts a weighted damped least-squares inversion to retrieve a unique and stable solution. In this work we show how damping can introduce deleterious artifacts on the reconstructed 3D data. To quantitatively describe this issue, we introduce the concept of extended resolution matrix (ERM) and we formulate the reconstruction problem as an appraisal problem. Through the simultaneous analysis of the ERM and of the noise term, we can assess the validity of the reconstructed data and verify the possible bias introduced by the inversion process. Also, we can guide the parametrization of the forward problem to minimize the occurrence of unwanted artifacts. Real data from a 3D marine common shot gather are used to discuss our approach and to show the results of FMNR reconstruction
Analysis of sample-solvent induced modifier-solute peak interactions in biochromatography using equilibrium theory and detailed simulations
No full textSimulated moving-bed chromatography and its application to chirotechnology
No full textThe increased awareness of the differences in biological activity of the two enantiomers of a chiral drug has raised the demand for enantiomerically pure products, particularly in the pharmaceutical industry. Simulated moving-bed chromatography can be used for the separation of the two enantiomers of a chiral molecule, which is feasible at all production scales, from laboratory to pilot to production plant. The use of non-enantioselective synthesis of racemic mixtures and simulated moving-bed enantiomer separation might make the development process of a new chiral drug substantially shorter and cheaper
Dispersion analysis of leaky guided waves in fluid-loaded waveguides of generic shape
No full textA fully coupled 2.5D formulation is proposed to compute the dispersive parameters of waveguides with arbitrary cross-section immersed in infinite inviscid fluids.
The discretization of the waveguide is performed by means of a Semi-Analytical Finite Element (SAFE) approach, whereas a 2.5D BEM formulation is used to model the impedance of the surrounding infinite fluid. The kernels of the boundary integrals contain the fundamental solutions of the space Fourier-transformed Helmholtz equation, which governs the wave propagation process in the fluid domain. Numerical difficulties related to the evaluation of singular integrals are avoided by using a regularization procedure. To improve the numerical stability of the discretized boundary integral equations for the external Helmholtz problem, the so called CHIEF method is used.
The discrete wave equation results in a nonlinear eigenvalue problem in the complex axial wavenumbers that is solved at the frequencies of interest by means of a contour integral algorithm. In order to separate physical from non-physical solutions and to fulfill the requirement of holomorphicity of the dynamic stiffness matrix inside the complex wavenumber contour, the phase of the radial bulk wavenumber is uniquely defined by enforcing the Snell-Descartes law at the fluid-waveguide interface.
Three numerical applications are presented. The computed dispersion curves for a circular bar immersed in oil are in agreement with those extracted using the Global Matrix Method. Novel results are presented for viscoelastic steel bars of square and L-shaped cross-section immersed in water
Supercritical fluid simulated moving bed chromatography
No full textContinuous chromatographic separation processes have gained increasing industrial importance for fine chemical and pharmaceutical applications. These are based on the simulated moving bed (SMB) technology, of which the implementation using a supercritical eluent (SF-SMB) is dealt with in this work. Criteria for the choice of the operating conditions of SF-SMBs to achieve optimal separation performance are derived. Through these a thorough analysis of the two operating modes of these units, isocratic and pressure gradient mode, is made. The theoretical findings are supported by comparison with experimental data previously published in the literature. (C) 1997 Elsevier Science B.V
Experimental investigation of the behavior of gas phase simulated moving beds
No full textThe preparative, continuous gas chromatographic separation of the enantiomers of the inhalation anaesthetic enflurane has been studied on a chiral stationary phase based on octakis(3-O-butanoyl-2,6-di-O-n-pentyl)-gamma-cyclodextrin, dissolved in polysiloxane SE-54 and coated on Chromosorb particles. This has been carried out in a gas chromatographic simulated moving bed (GC-SMB) unit, equipped with eight columns, yielding a total volume of 1.128 1. With reference to this particular system, the separation performance and the behavior of GC-SMB units have been analyzed in depth. We have varied the internal flow-rates in the four sections of the unit in the range between about 1 and about 5 std 1/min, the temperature between 20 and 45 degreesC, the switch time between about 2 and about 14 min, and the feed concentration in the range 0.32-0.90 mol%. Similarities and differences in the behavior of GC-SMBs as compared to conventional liquid phase SMBs have been described, and discussed. Operating conditions leading to more than 99% purity in one or both outlet stream have been identified, together with those achieving optimal throughput. Under such optimal conditions, about 20 g of each enflurane enantiomer with enantiomeric purity larger than 98% have been prepared. (C) 2002 Elsevier Science B.V. All rights reserved
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