Membrane contactors advantages

Contactors have a number of advantages compared to simple liquid/gas absorb-er/strippers or liquid/liquid extractors. Perhaps the most important advantage is high surface area per volume. The contact area of membrane contactors compared to traditional contactor columns is shown in Table 13.2. Membrane contactors provide 10-fold higher contactor areas than equivalent-sized towers. This makes membrane... 

Additionally, membranes have the unique advantage of allowing the simultaneous contact with two different media, at each membrane side, creating compartments with different properties. Therefore, membranes offer the potential to promote the spatial organization of catalytic compartments and selective barriers. This feature is used with advantage in new concepts of membrane multiphasic (bio)reactors and membrane contactors. 

When compared to conventional systems (such as strippers, scrubbers, distillation columns, packed towers, bubble columns, evaporators, etc.), membrane contactors present several advantages, as reported in Figure 20.3. However, some drawbacks have also to be taken into account, as shown in Figure 20.4. 

As previously reported, membrane contactors present interesting advantages with respect to traditional units. Moreover, they well respond to the main targets of the process intensification, such as to develop systems of production with lower equipment-size/production-capacity ratio, lower energy consumption, lower waste production, higher efficiency. In order to better identify the potentialities of membrane contactors in this logic, they have been recently compared to traditional devices for the sparkling-water production in terms of new defined indexes [24]. In particular, the comparison has been made at parity of plant capacity and quality of final product. The metrics used for the comparison between membranes and traditional units are ... 

However, industrial applications have been limited mostly because these new membrane-based systems have not been proven extensively at the industrial level and their advantages have not been quantified in industrial terms, as is the case for traditional consolidated technologies. This fact has discouraged industries from applying these systems in large plants. Therefore, demonstration tests are needed in order to be able to fully exploit the commercial potential of the membrane contactor technology. 

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. 

As mentioned in Table 2.2, one unique feature of membrane contactors is the ability to operate without the aid of gravity. This, along with the advantage of smaller sizes for contactor systems, has led to the interest in possible use of this technology in microgravity and confined spaces such as spacesuits, manned spacecrafts, and space station. Primary apphcations are (1) separating gas and liquid phases in microgravity and (2) removal of unwanted gas species from liquids [62-64]. 

Membrane contactors (MCs) represent another interesting frontier in the application of membrane technology in seawater desalination. Gas-liquid application for addition/extraction of selected gasses or operation like membrane crystallization has been recognized in some new experimental works, as important ways for improve efficiency and get some advantages for the overall desalination processes [5,6]. 

General advantages of facilitated transport membranes are improved selectivity, increased flux and, especially if compared with membrane contactors, the possibility to use expensive carriers. The specific prerequisites, advantages and disadvantages connected the mobile carriers, are reported in Table 7.1. So far, mainly conventional liquid membranes have been loaded with different mobile carrier systems to obtain facilitated transport properties [3]. Problems encountered are (evaporative) loss of solvent and carrier, temperature limitations, a too large membrane thickness and therefore too low permeabilities as weU as a limited solubility of the carrier in the liquid medium. The low fluxes achieved have, untU now, limited their application... 

As a standard appliance in the extraction of uranium, a multistage mixer-settler arranganent with concurrent flow of two phases, water and organic, is used. It can be replaced by novel design with membrane contactors that avoid the constraints of conventional systems. Manbrane extraction used for uranium recovery has many advantages over conventional methods, like no fluid-fluid dispersion, no emulsion... 

Similarly to partially overlapping channels, microchannels with mesh contactors (Figure 7.2h) are used to create the partial contact of fluids. The advantage of these contactors is that both modes of operation, cocurrent and countercurrent, can be apphed. Besides, the flow is stabilized because of the solid support between two fluids. The solid contactors are porous membrane [9, 10] and metal sheets with sieve-like structure [11]. Similarly to parallel flow, the mass transfer in both cases is only by diffusion and the flow is under laminar flow regime dominated by capillary forces. The membrane contactor has the advantage of being flexible with respect to the ratio of two fluids. In addition to flow velocities, the mass transfer is a function of membrane porosity and thickness. In another type of microextractor, two microchaimels are separated by a sieve-like wall architecture to achieve the separation of two continuous phases. However, the hydrodynamics in both types of contactors is more complex because of interfadal support and bursting of fluid... 

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