Membranes module formats

Applications Membranes create a boundary between different bulk gas or hquid mixtures. Different solutes and solvents flow through membranes at different rates. This enables the use of membranes in separation processes. Membrane processes can be operated at moderate temperatures for sensitive components (e.g., food, pharmaceuticals). Membrane processes also tend to have low relative capital and energy costs. Their modular format permits rehable scale-up and operation. This unit operation has seen widespread commercial adoption since the 1960s for component enrichment, depletion, or equilibration. Estimates of annual membrane module sales in 2005 are shown in Table 20-16. Applications of membranes for diagnostic and bench-scale use are not included. Natural biological systems widely employ membranes to isolate cells, organs, and nuclei. 

The first step in downstream processing is the separation of the product-rich phase from the second phase and the biocatalyst. This may be simplified if the enzyme is immobilized or if a membrane module is included in the experimental set-up. In the case of emulsion reactors, centrifugation for liquid phase separation is a likely separation process [58], although the small size of droplets, the possibility of stable emulsion formation during the reaction, particularly if surface-active... 

Recirculate the solution. The solution should be recirculated at about 35 gpm per pressure vessel. In other words, for an 8-pressure vessel stage with 8-inch diameter membrane modules, the recirculation rate should be 8 times 35 gpm or 280 gpm. Recirculation should be conducted using as little pressure as possible, thereby minimizing the formation of permeate. If permeate is generated, it increases the likelihood of re-deposition of removed species on the membrane.1 If the cleaning solution comes out dark, it should be discarded and a new batch should be prepared. Temperature and pH should be monitored and adjusted during the recirculation as needed. Recirculation should continue for about 45 to 60 minutes. 

Fig. 9.15. Proposed mechanism by which P-glycoprotein (P-gp) secretes substrates. (1) Passive drug uptake across cell membrane. (2a) Formation of hydrophobic channel (pore) between the intracellular and extracellular space. (2b) Flippase activity, whereby the drug is flipped from the inner leaflet to the outer leaflet of the cell membrane. (2c) Vacuum cleaner model, in which drug interacts with P-gp in the lipid bilayer and is subsequently secreted back into the extracellular space. (From Matheney C, Lamb M, Brouwer K, et al. Pharmacokinetics and pharmacodynamic implications of P-glycoprotein modulation. Reviews of Therapeutics 2001 21 778-796 with permission.)...

The unexpected results of Sablani et al. [17] (i.e., less turbulence with smaller spacer thickness) may be best explained by an excellent paper by Schwinge et al. [82], The latter employed computational fluid dynamics (CFD) in a study of unsteady flow in narrow spacer-filled channels for spiral-wound membrane modules. The flow patterns were visualized for different filament configurations incorporating variations in mesh length and filament diameter and for channel Reynolds numbers, Re y, up to 1000. The simulated flow patterns revealed the dependence of the formation of... 

The majority of a membrane system cost is associated with the large compressors required to pressurize the permeate stream and feed pretreatment operations required to remove heavy hydrocarbon and water vapor impurities only about 10%-25% of the total system cost is associated with the membrane module [27]. Membranes for CO2 removal applications are typically fabricated in either hollow fiber or spiral wound format. Hollow fiber approach has the advantage of greater membrane area per unit volume and greater operational flexibility and module fabrication cost [28]. 

Manufacture of gas-separation membrane modules is largely a machine-assisted, labor-intensive operation. Polymer dopes are typically prepared batchwise with sufficient hold time to insure uniformity. The membrane performance is largely controlled by the polymer precipitation step and very dependent upon phase behavior and precipitation kinetics. Thus, it is essential that processing conditions be maintained as uniformly and as constant as possible if product quality and uniformity is to be preserved. For this reason, membrane-fihn formation and hollow-fiber spinning processes are usually operated continuously or for extended run times. Since the intermediate film or fiber must eventually be converted into discrete items, the continuous process is typically interrupted by collection of the membrane formed on spools or fiber skeins where it may be inventoried briefly before batch processing into the final assembly resumes. 

The common approach to maintain minimal polarization is to operate at high shear rates [103] however, this can be harmful to biocatalysts. To decrease gel-layer formation in the surface of the membrane, Hakoda and co-workers [178] applied an electric field of 50 and 100 V to a ceramic membrane module used in the lipolysis of triolein in a reversed micellar system. These authors reported a slight increase in the filtration flux (about 15%), without deleterious effects on enzyme stability for an operation time length of 12 h. The electrokinetic phenomena leading to the observations occurred even in apolar media, since small amounts of water or surfactant were present in such media [178]. 

G. Pearce, Fouling behaviour for different module formats in membrane filtration applications for surface water treatment, Desal. Water Treat. 8 (1-3) (2009) 36-38. 

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