Column section membrane systems

B.3.2 Generating Profiles for Hybrid Column For demonstration purposes, it will initially be assumed that operation will occur at 4 = 0.8. In order to display the profiles obtainable for this design, and npvalues were arbitrarily chosen. Furthermore, for the design to be feasible, it is required that the profiles of each section, including the membrane, intersect in the same order and direction as that of liquid flow in the system. Figure 9.14 shows the column and membrane profiles for operation at tai =40 with ni =5. 

The most recent variation of FIA is the so-called lab-on-a-valve (LOV) technology introduced by Ruzicka. The LOV idea incorporates an integrated microconduit on top of the selection valve u.sed in SIA. The nii-croconduit is designed to handle all the unit operations needed for a given analytical procedure. Mixing points for analyte and reagents, column reactors, bead reactors, separation columns, and membranes can all be accommodated within the LOV system. In some cases, microfluidic flow systems are used in ways similar to those described in the next section. 

Most of the chiral membrane-assisted applications can be considered as a modality of liquid-liquid extraction, and will be discussed in the next section. However, it is worth mentioning here a device developed by Keurentjes et al., in which two miscible chiral liquids with opposing enantiomers of the chiral selector flow counter-currently through a column, separated by a nonmiscible liquid membrane [179]. In this case the selector molecules are located out of the liquid membrane and both enantiomers are needed. The system allows recovery of the two enantiomers of the racemic mixture to be separated. Thus, using dihexyltartrate and poly(lactic acid), the authors described the resolution of different drugs, such as norephedrine, salbu-tamol, terbutaline, ibuprofen or propranolol. 

MA systems can easily add a module to increase membrane capacity or resolution. Alternatively, the series addition of a traditional chromatography column for improvement of capacity or resolution is seldom practiced. Thus, membrane chromatography offers the chromatographer a new flexibility of easy expansion of inadequate systems. Alternatively, the easy connectibility also enables a simple way to couple multiple units of different chemistries for a mixed-mode separation.43 The next section describes these configurations in greater details. 

Our main concern here is to present the mass transfer enhancement in several rate-controlled separation processes and how they are affected by the flow instabilities. These processes include membrane processes of reverse osmosis, ultra/microfiltration, gas permeation, and chromatography. In the following section, the different types of flow instabilities are classified and discussed. The axial dispersion in curved tubes is also discussed to understand the dispersion in the biological systems and radial mass transport in the chromatographic columns. Several experimental and theoretical studies have been reported on dispersion of solute in curved and coiled tubes under various laminar Newtonian and non-Newtonian flow conditions. The prior literature on dispersion in the laminar flow of Newtonian and non-Newtonian fluids through... 

Experiments were conducted with a permeator composed of 35 silicone rubber capillaries (pressurized internally). Results are presented for the binary systems O2-N2 (air), CO2-N2, CO2-O2, and the multicomponent system C02-CH -N2. Particular attention is given to separation of the C02 CH -N2 mixture in a stripper, conditions for observing composition minima in the enriching section, inherent simulation difficulties in modeling the membrane column, variation of experimental parameters, and local HMU variation along the column. 

Some further special technical aspects should be mentioned. The intensive mixture of the two liquid phases is an important condition for obtaining high reaction rates. This mixing can be achieved in bubble columns, tray columns or in stirred-tank reactors. In the few publications on industrially realized two-phase reactions the stirred tank reactor is always cited, but without detailed information on the stirring device. One further possible way to increase the mass transfer between the two liquid phases is by the influence of sonification. Cornils et al. applied this technique in the hydroformylation of hexene or diisobutene and found a considerable increase in the turnover numbers [93]. Another possibility for increasing the mass transfer may be by the use of microemulsions and micellar systems [94], which can be reached by addition of certain surfactants. This aspect is discussed in Sections 3.2.4 and 4.5. The separation of catalyst compounds in two-phase systems in combination with membranes has been studied recently by Muller and Bahrmann [95],... 

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