Membrane processes hollow fiber membranes

Compared to batch processes, continuous processes often show a higher space-time yield. Reaction conditions may be kept within certain limits more easily. For easier scale-up of some enzyme-catalyzed reactions, the Enzyme Membrane Reactor (EMR) has been developed. The principle is shown in Fig. 7-26 A. The difference in size between a biocatalyst and the reactants enables continuous homogeneous catalysis to be achieved while retaining the catalyst in the vessel. For this purpose, commercially available ultrafiltration membranes are used. When continuously operated, the EMR behaves as a continuous stirred tank reactor (CSTR) with complete backmixing. For large-scale membrane reactors, hollow-fiber membranes or stacked flat membranes are used 129. To prevent concentration polarization on the membrane, the reaction mixture is circulated along the membrane surface by a low-shear recirculation pump (Fig. 7-26 B). 

Nonselective membranes can assist enantioselective processes, providing essential nonchiral separation characteristics and thus making a chiral separation based on enantioselectivity outside the membrane technically and economically feasible. For this purpose several configurations can be applied (i) liquid-liquid extraction based on hollow-fiber membrane fractionation (ii) liquid- membrane fractionation and (iii) micellar-enhanced ultrafiltration (MEUF). 

In the present study, we fabricated hollow fiber membrane modules and performed experiments at several conditions. The energy consumption of this process is compared to those of conventional gas absorption processes and membrane gas separation processes. 

Pertraction A process for removing organic pollutants from industrial wastewater. The water is contacted with an organic solvent via a hollow-fiber membrane. Developed in 1994 by TNO Institute for Environmental and Energy Technology, in collaboration with Tauw Environmental Consultancy and Hoechst. 

High-pressure gas separation, hollow-fiber membrane modules for, 15 823 High pressure liquid chromatography (hplc), 9 234 21 275 in herbicide analysis, 13 312 polymer analysis using, 19 566 High-pressure methanol, production process, 16 300-301 High pressure methods, specialized, 13 430-431... 

Low polarity plasticizers, 74 479 Low power package, 74 863 Low pressure catalytic processes, 20 151 Low pressure chemical vapor deposition (LPCVD), 5 807, 811-812 Low-pressure gas separation, spiral-wound membrane modules for, 75 823-824 Low pressure hollow-fiber membranes, 76 24-26... 

Ekiner, O.M. and Kulkarni, S.S. (2003) Process for making mixed matrix hollow fiber membranes for gas separation. US Patent 5,553,805. 

In the supported liquid membrane process, the liquid membrane phase impregnates a microporous solid support placed between the two bulk phases (Figure 15.1c). The liquid membrane is stabilized by capillary forces making unnecessary the addition of stabilizers to the membrane phase. Two types of support configurations are used hollow fiber or flat sheet membrane modules. These two types of liquid membrane configuration will be discussed in the following sections. 

The process design principles of SLM, non-dispersive extraction, and hybrid hquid membrane systems need to be understood through bench scale experiments using feed solution of practical relevance. While the economic analysis of an ELM process can be performed from small scale experiments, such an analysis is difficult for other LM systems. In particular, availability and cost of hollow fiber membranes for commercial application are not known apriori. A simple rule of thumb for cost scale-up may not be apphcable in the case of an HE membrane. Yet we feel that the pilot plant tests would be adequate to make realistic cost benefit analysis of a liquid membrane process, since the volume of production in )8-lactam antibiotic industries is usually low. 

Hollow fiber membranes are primarily homogeneous. In use, their lower permeability is compensated for by large surface per unit volume of vessel. Fibers are 25-250 pm outside dia, wall thickness 5-50 pm. The cross section of a vessel for reverse osmosis may have 20-35 million fibers/sqft and a surface of 5500-9000 sqft/cuft of vessel. Recently developed hollow fibers for gas permeation processes have anisotropic structures. 

Research on separation processes demonstrated that hydrophobic oilladen surfactant was efficiently regenerated through the use of state-of-the-art hollow fiber membrane columns. Specifically, the hydrophobic oil dodecane was effectively separated from the surfactant system SDBS/IPA/NaCl (Table VI). This separation was accomplished by counterflowing the oil/surfactant solution, comprised of 10.3 ml. dodecane per 100ml. of SDBS/IPA/NaCl solution, with the extraction solvent squalane. These results demonstrate the ability to effectively regenerate and reuse these surfactant systems. 

The membrane separation processes described above represent the bulk of the industrial membrane separation industry. Another process, dialysis, is not used industrially but is used on a large scale in medicine to remove toxic metabolites from blood in patients suffering from kidney failure. The first successful artificial kidney was based on cellophane (regenerated cellulose) dialysis membranes and was developed in 1945. Over the past 50 years, many changes have been made. Currently, most artificial kidneys are based on hollow-fiber membranes formed into modules having a membrane area of about 1 m2 the process is illustrated in Figure 1.7. Blood is circulated through the center of the fiber, while isotonic... 

P.S. Puri, Continuous Process for Making Coated Composite Hollow Fiber Membranes, US Patent 4,863,761 (September, 1989). 

Removal of carbon dioxide is the only membrane-based natural gas separation process currently practiced on a large scale—more than 200 plants have been installed, some very large. Most were installed by Grace (now Kvaerner-GMS), Separex (UOP) and Cynara and all use cellulose acetate membranes in hollow fiber or spiral-wound module form. More recently, hollow fiber polyaramide (Medal) membranes have been introduced because of their higher selectivity. 

Another type of gas exchange process, developed to the pilot plant stage, is separation of gaseous olefin/paraffin mixtures by absorption of the olefin into silver nitrate solution. This process is related to the separation of olefin/paraffin mixtures by facilitated transport membranes described in Chapter 11. A membrane contactor provides a gas-liquid interface for gas absorption to take place a flow schematic of the process is shown in Figure 13.11 [28,29], The olefin/paraffin gas mixture is circulated on the outside of a hollow fiber membrane contactor, while a 1-5 M silver nitrate solution is circulated countercurrently down the fiber bores. Hydrophilic hollow fiber membranes, which are wetted by the aqueous silver nitrate solution, are used. 

While both of these devices use hollow fiber membranes similar to the primary components of kidney dialyzer units, the difference between the two techniques lies in how the analyte undergoes mass transport into the device. Microdialysis sampling is a diffusion-based separation process that requires the analyte to freely diffuse from the tissue space into the membrane inner lumen in order to be collected by the perfusion fluid that passes through the inner lumen of the fiber. Ultrafiltration pulls sample fluid into the fiber lumen by applying a vacuum to the membrane (Figure 6.1). 

In an attempt to overcome the significant difficulties that the presence of water vapor poses to the analysis of very volatile compounds, purge-and-membrane extraction techniques have been developed that largely prevent the introduction of water into the analytical system. Typical implementations of this form of sample introduction have been called by its developers membrane extraction with a sorbent interface (MESI),97 or membrane introduction mass spectrometry (MIMS).98 " They are based on a silicone hollow-fiber membrane that is inserted into the sample to be monitored, and the passing of a certain volume of inert gas through the membrane. Volatile compounds permeate the membrane and are swept to the adsorbent trap from which they are desorbed into the GC. This method of sample introduction is particularly suited for field and process monitoring and for dirty samples, since it prevents any nonvolatile compounds from entering the analytical system.100... 

Figure 17.3, the reactant was fed into the solvent, while the product was extracted in water. The lipase was immobilized by entrapment method on asymmetric PAN hollow-fiber membranes. The process was run for several years with modules for the production plant of 60 m2 of active membrane area. 

The following processes can be described as selective therapeutic plasmapheresis. In a first step, blood is withdrawn from the patient and separated by crossflow filtration in a hollow-fiber membrane cartridge water and some plasma solutes are transferred through a semipermeable membrane under a convection process. The transmembrane pressure applied from blood to filtrate compartment ensures flow and mass transfers. Then, the filtrate perfuses the adsorption columns where toxins are retained and is finally mixed with blood cells and other plasma components before returning to the patient (Figure 18.11). 

A Hollow-Fiber Membrane Extraction Process for Recovery and Separation of Lactic Acid from Aqueous Solution... 

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