Membrane contactors designs

Stanojevic M, Lazarevic B, and Radic D. Review of membrane contactors designs and applications of different modules in industry. FME Trans. 2003 31 91-98. 

These gas transfer membranes or membrane contactors employ microporous polypropylene hollow fiber membranes arranged in a modular design. Oxygenated water flows on the shell side of the hollow fibers, and a strip gas (such as nitrogen) or a vacuum is applied to the inside (lumenside), with the hollow fibers acting as a support medium for intimate contact between the water and gas phases. 

The availability of new membrane processes such as membrane contactors and catalytic membrane reactors, the progresses in membrane-fouling control and the development of new membranes with well-controlled structures and properties, are recognized as key factors for the design of alternative production systems. 

Referring to the membrane module design, it has a big influence on the membrane-contactor efficiency, because it affects the pressure drops of the streams (and, thus, the operating pressures and flowrates), and their fluidodynamic (which means the mass and heat transport resistances of the phases). Furthermore, for hollow-fiber modules it is essential to ensure a uniform packing, in order to have... 

The design of the first commercial modules has allowed the commercial application of membrane contactors for some specific operations. This is the case of the Membrana-Charlotte Company (USA) that developed the LiquiCel modules, equipped with polypropylene hollow fibers, for the water deoxygenation for the semiconductor industry. LiquiCel modules have been also applied to the bubble-free carbonation of Pepsi, in the bottling plant of West Virginia [18], and to the concentrations of fruit and vegetable juices in an osmotic distillation pilot plant at Melbourne [19]. Other commercial applications of LiquiCel are the dissolved-gases removal from water, the decarbonation and nitrogenation in breweries, and the ammonia removal from wastewater [20]. 

Flat-membrane contactors have been specifically designed and commercialized by GVS SpA (Italy) for air dehumidification processes [23]. 

On the air side calibrated thermocouples to measure temperature at different locations in the cell two capacitive hygrometers on the evaporator a humidity controller designed to deliver a maximum vapor flow rate of lOkg/h have been installed. A liquid flowmeter to measure the volumetric flow rate of the aqueous desiccant solution at the membrane contactor outlet was used. All instruments are connected to a data logger. 

Process conditions have been optimized in order to obtain the best possible efficiency and cost. It has been shown that membrane contactors can be advantageously used to capture C02 from flue gases containing about 25% by volume of C02 and to obtain in the decarbonated gas maximum 3% of C02 mole (i.e. 88% capture of C02). It has been proven that the contactors can capture up to 6 m3/h of C02 per m2 of membrane. In Table 22.2 results of a design of a potential industrial plant treating 300 000 m3/h of flue gas are reported. 

The combination of molecular separation with a chemical reaction, or membrane reactors, offers important new opportunities for improving the production efficiency in biotechnology and in the chemical industry. With regard to the future of biotechnology and pharmaceutical processes, the availability of new high-temperature-resistant membrane contactors offers an important tool for the design of alternate production systems appropriate for sustainable growth. 

FIGURE 2.5 Primary design options for membrane contactors. 

When hydrophobic membranes are used (olefins are preferred because of their low cost), the aqueous absorbent cannot penetrate through the pores and the membrane is gas filled whereas if hydrophilic membranes are employed, the membrane is liquid filled (Figures 38.1 and 38.2). Latter situation is preferred only if the reaction between the gaseous species and the absorbent solution is fast or instantaneous if not, it is better to work with a gas-filled membrane, to reduce mass-transfer resistances. The module design and flow configuration also play an important role in defining the membrane contactors efficiency. This aspect is discussed in detail in Section 38.5. 

Patents on new module designs have been recently presented. Nitto Denko (Japan) patented a spiral wound design for membrane contactor applications [51]. The system includes a central feed pipe around which one or more membranes are wound. Tests on water ozonation demonstrated that it is possible to achieve a concentrahon of ozone 10% higher than in hollow hber. 

All these improvements coupled to further enhancements in the lifetime of the membranes and their compatibility with absorbents, as well as in the mass-transfer design, will allow to extend the use of membrane contactors in industrial productions. 

These membrane systems, mainly provided in the form of low cost hollow fibres, offer a high interfacial area, significantly greater than most traditional absorbers, between two phases to achieve high overall rates of mass transfer. Furthermore, whereas the design of the conventional devices is restricted by limitations in the relative flows of the fluid streams, membrane contactors give an active area which is independent of the liquid fluid dynamics. 

Valenzuela, P., Auspont, J., Basualto, C., Tapia, C., Sapag, J. (2005). Use of a surfactant liquid membrane contactor for zinc uptake from an acid aqueous effluent. Chemical Engineering Research and Design 83 247-255. 

E. Drioli, E. Curcio, G. Di Profio, State of the art and recent progresses in membrane contactors, Transactions ofIChemE, Part A Chemical Engineering Research and Design 83(A3) (2005) 223-233. 

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