Contactors categories

Material Absorbent Membrane Contactor Categories/Applications Advantages Disadvantages O O... 

The second type of mass-exchange units is the differential (or continuous) contactor. In this category, the two phases flow through the exchanger in continuous contact throughout without intermediate phase separation and recontacting. Examples of differential contactors include packed columns (Fig. 2.6), spray towers (Fig. 2.7), and mechanically agitated units (Fig. 2.8). 

Many types of countercurrent equipment (e.g., packed columns) do not contain discrete compartments and therefore cannot be treated as combinations of discrete stages (Fig. 5b). The term differential contactor is used to describe this category, and a somewhat different design... 

As mentioned earlier, membrane blood oxygenators probably would qualify as the earliest form of membrane contactors. Reference [11] is a good illustration of a hollow fiber device. However, most work on liquid-gas membrane contactor over the years has focused mainly on two categories (1) separation, purification, and treatment of water or aqueous media and (2) absorption of gaseous species from air either for purification or for recovery, which will be discussed separately. Applications in multiple markets and industries have been investigated in each category. 

Membrane contactor applications in the liquid-liquid extraction field fall in two categories (1) removal of unwanted species from water and (2) removal and recovery of valuable species from water. Many investigations have been conducted over the year by academia as well as by industry. Below we are providing some samples from the wide range of applications reported in hterature. The examples presented are divided roughly into three sections (a) biotech and pharmaceutical products, (b) industrial chemicals and VOC, and (c) metals. 

Class 1 equipment are also called column-type equipment. Under this category, there are the various multiphase contactors. Gas-liquid contactors include bubble columns, packed bubble columns, internal-loop and external-loop air-lift reactors, sectionalized bubble columns, plate columns, and others. Solid-fluid (liquid or gas) contactors include static mixers, fixed beds, expanded beds, fluidized beds, transport reactors or contactors, and so forth. For instance, fixed-bed geometry is used in unit operations such as ion exchange, adsorptive and chromatographic separations, and drying and in catalytic reactors. Liquid-liquid contactors include spray columns, packed extraction... 

In the process industries, low viscosity Newtonian liquids predominate so this chapter concentrates on these. Even within this category, the performance of gas-liquid contactors can be influenced by poorly understood surface phenomena, which particularly affect bubble size and coalescence, so is not yet predictable from first principles. 

Using classification 1, most industrial contactors may be classified in three broad categories with a number of variations in each (Van Krevelen, 1950) ... 

Note that contactors in category A are common to gas-liquid and liquid-liquid reactions. The main difference stems from the need for phase separation in liquid-liquid reactions. A few common designs are shown in Figure 16.4. The design of liquid-liquid extractors in general has been well treated by Laddha and Degaleesan (1976) and the general subject of mass transfer by Taylor and Krishna (1993). 

Liquid-level measurements are relatively straightforward, and the transducers fall into the categories of contactor noncontact. Measurements maybe continuous, in which the liquid level is monitored continuously throughout its operating range, or point, in which the liquid level is determined to be above or below some predetermined level. 

Motor starters can be divided into three basic types (manual, magnetic, and electronic operation) and three categories (full voltage/across the line, reduced voltage, and multispeed). Starters consist of a contactor to switch the electrical load and an overload relay which provides protection for the motor. 

Two categories of methods are commonly used for organic and hybrid membrane characterization. The first ones, named static characterizations, are aimed at the description of the structure and texture of membranes while the second ones named dynamic characterizations describe membranes at work, in other words the transfer of fluids and solutes through the membrane top-layer. Both static an dynamic characterization methods are important for a thorough understanding of single mass transport and even of the additional functions of the membranes (contactor, reactor...). 

Venturi scrabbers, ejectors, and most spray chambers are, at best, single stage contactors. Cocurrent contactors also fall into this category. The theoretically ideal performance of such units is to produce gas and liquid products that are in equilibrium actual hardware can only... 

The membrane contactors in all four categories were primarily developed for separation and purification. However, they are being increasingly exploited for the purposes of reaction-separation, separation-reaction, and so forth. Membrane contactors can therefore function as separator-reactors as well as reactor-separators. 

Membranes are used nowadays typically for the purification and separation of gases in several industrial processes. The role of catalysts in the development of membrane reactors (MRs) has in many cases been ignored in some levels, as the research has been concentrated on the membrane and development of new membranes. There is, however, a need for a catalyst in the MR to perform the desired reaction. The MRs containing a catalyst have been classified in three categories, namely extractor, distributor and contactor reactors (Miachon and Dalmon, 2004 van Dyk et ai, 2003). These reactor types are presented in Fig. 11.1. 

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