Membranes Packed columns

Use of w/o-MEs for transport in liquid emulsion membrane separations Perforated rotating disk contactor Spray column Packed column... 

The lowest theoretical interparticular volume of perfectly packed uniformly sized spherical beads is calculated to be about 26% of the total available volume. In practice, even the best packed columns still contain about 30-40% void volume in addition to the internal porosity of the beads. The problem of interparticular volume does not exist in systems in which a membrane is used as the separation medium. Both theoretical calculations and experimental results clearly document that membrane systems can be operated in a dead-end filtration... 

Referring to point a, in desalination the content of oxygen and carbon dioxide in the water affects the material life of the plant (because of corrosion problems), as well as the pH and the conductivity of water. Usually, these gases are removed by stripping in a packed column and the final water p H is adjusted by means of caustic soda. By using membrane contactors, there is no need for chemicals, with a consequent reduction of the environmental impact. 

When, on the other hand, a nondifferentially pumped system is used, direct coupling generally will be impossible. In that case either an open split device or a carrier gas separator must be installed. When using a jet or membrane separator, one should keep in mind that these devices have been designed for packed columns. Thus, make-up gas must be added to the column effluent to restore optimal working pressure and purge unswept volumes. 

Separative flow often occurs in a packed bed—typically a tube filled with a granular material. Chromatography in packed columns is the most important example of packed-bed flow. Similar flow is found in porous membranes used for membrane separation. The fluid flowing through such media can be a gas, a liquid, or a supercritical fluid. 

Wells DA, Lensmeyer GL, and Wiebe DA. Particle-loaded membranes as an alternative to traditional packed-column sorbents for drug estraction—in-depth comparative-study. J. Chromatogr. Sci. 1995 33 386-392. 

Suppressor devices include packed column suppressors, hollow-fiber membrane suppressors, micromembrane suppressors, suspension postcolumn reaction suppressors, autoregenerated electrochemical suppressors, and so forth. 

Some of the drawbacks that packed column suppressors have were eliminated when hollow-fiber membrane suppressors were introduced in 1981. These were found to be even more convenient and efficient, with low dead volume and high capacity, and they are dynamically regenerated. Eluent passes through the... 

For analytical LC, standard packed columns (4-8 mm I.D.), capillary packed colunms (50-100 pm I.D.), and microbore packed colunms (0.5-1.5 mm I.D.) are used widely. Colunm sizes depend on the application, e.g., analytical, preparative, or commercial separations. Special configurations also exist, including membrane chromatography modules (stacks and hollow fibers) that offer lower pressure drops and easier scale-up than packed beds. 

The transfer of mass within a fluid mixture or across a phase boundary is a process that plays a major role in various engineering and physiological applications. Typical operations where mass transfer is the dominant step are falling film evaporation and reaction, total and partial condensation, distillation and absorption in packed columns, liquid-liquid extraction, multiphase reactors, membrane separation, etc. The various mass transfer processes are classified according to equilibrium separation processes and rate-governed separation processes. Fig. 1 lists some of the prominent mass transfer operations showing the physical or chemical principle upon which the processes are based. 

Where K a is the mass transfer coefficient, C is the VOC concentration in the solvent in equilibrium with the vapor phase, C is the actual solvent VOC concentration, and J is the flux of the VOC. Raising the temperature will cause C to approach zero. For the dilute VOC in the solvent, small values of C cause the flux to approach zero and separation does not occur. By using membranes with their large area to volume ratio, the mass transfer coefficient can be increased by an order of magnitude or more compare to a conventional packed column (33). This increase in area will enhance flux despite small values of C, thus making the separation more feasible. The VLE data needed to evaluate the MASX/MADS process are currently being collected. It is expected that this process wiU perform well. 

Wells, D.A. Lensmeyer, G.L. Wiebe, D.A. Particle-Loaded Membranes as an Alternative to Traditional Packed-Column Sorbents for Drug Extraction—In Depth Comparative Study, J. Chromatogr. Sci. 33, 386-392 (1995). 

The performance of the continuous membrane column was characterized earlier (28) in a manner analogous to the transfer unit concept for packed columns. The expressions developed for NMU (difficulty of separation) and HMU (efficiency) were... 

A semipermeable membrane which is selective for the analyte that travels on to the MS can be used at the interface. This is used in particular for packed column GC where the carrier gas flow rates are higher than those used with capillary columns. 

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