Three-phase contactor

Schlosser, S. and Sabolova, E. (2002) Three phase contactor with distributed U-shaped bundles of hollow fibers for pertraction. Journal of Membrane Science, 210,331. 

The enhancement in the bed-wall heat transfer coefficients in bubble columns as well as the two- and three-phase contactors as compared to the single phase pipe flow is likely because of the strong circulation flow pattern in the continuous phase. 

Gas-flowing solids-fixed bed contactors can be used either as two-phase continuous contactors between flowing solids and gas where the fixed bed structure can be specially designed for distribution of both flowing phases or as three-phase contactors where the fixed bed has an active role (e.g., catalyst bed). 

Figure 213. Four different configurations with a porous membrane in a membrane reactor for selective oxidation (a) packed-bed enclosed membrane reactor (b) membrane with catalytic activity as contactor (c) flow-through configuration (d) three-phase contactor.

The term three-phase fluidization requires some explanation, as it can be used to describe a variety of rather different operations. The three phases are gas, liquid and particulate solids, although other variations such as two immiscible liquids and particulate solids may exist in special applications. As in the case of a fixed-bed operation, both co-current and counter- current gas-liquid flow are permissible and, for each of these, both bubble flow, in which the liquid is the continuous phase and the gas dispersed, and trickle flow, in which the gas forms a continuous phase and the liquid is more or less dispersed, takes place. A well established device for countercurrent trickle flow, in which low-density solid spheres are fluidized by an upward current of gas and irrigated by a downward flow of liquid, is variously known as the turbulent bed, mobile bed and fluidized packing contactor, or the turbulent contact absorber when it is specifically used for gas absorption and/or dust removal. Still another variation is a three-phase spouted bed contactor. 

Efficient contact is produced between the phases in agitated gas-liquid contactors and, therefore, this type of equipment can also be useful for those absorption and stripping operations for which conventional plate or packed towers may not be suited. It may also be useful where the operation involves the contact of three phases—say, gas, liquid, and suspended solids. The latter application could be represented by the low-pressure polymerization of ethylene with solid catalysts (F5). 

The 1970 s also brought about increased use of three-phase systems in environmental applications. A three-phase fluidized bed system, known as the Turbulent Bed Contactor, was commercially used in the 1970 s to remove sulfur dioxide and particulates from flue gas generated by coal combustion processes. This wet scrubbing process experienced several... 

The formulation of the three phases must be such that the liquid membrane extracts the solute from one of the phases and the third phase strips it from the membrane. Thus extraction and stripping take place in the same contactor, and the stripping phase is where the solute is accumulated, instead of the organic phase as in the case of conventional solvent extraction. This allows for a middle phase of small volume that, being thin, behaves like a membrane. 

H F contactors with planar elements with flowing head of fibers and crossflow of one phase in three and more phases contactor have been suggested in a patent [35] and their scheme is shown in ref. [8]. A two-phase H F contactor with planar elements was developed at TNO and tested in pilot plants [36, 37]. Reviews on two-phase HF contactors are presented in refs. [27, 38-40]. Mass-transfer characteristics of two-phase contactors are presented in ref. [30]. Three-phase HF contactors for pertraction are described in refs. [6-9, 41]. They are not produced commercially. 

Related to the experimental studies performed in our laboratory, in this review packed-bed membrane reactors were discussed. It should be mentioned that there are significant investigational activities devoted to study catalytically active membranes where the catalyst is deposited in either the membrane pores or on the inner or outer surface of the tubes [11]. Another similarly interesting and promising principle is based on using the Contactor type of membrane reactors, where the reactants are fed from different sides and react within the membrane [79]. Significant efforts have been made to exploit this principle for heterogeneously catalyzed gas-liquid reactions (three-phase membrane reactors) [80, 81]. 

Figure 1.9 Arc energy A, nitrous oxide production S and yield y of nitrous oxides in a contactor with contacts operated in air at normal ambient pressure, switching off a three-phase system with 1000 V, 260A rms at 50cps, versus the ratio resistance R to impedance Z (or versus the phase angle

Vladisavljevic and Mitrovic [50] developed a three-phase hollow hber membrane contactor with frame elements. The module consists of stacks of polygonal plates containing internal frames packed with hollow hbers and an external frame where headers for the inlet and outlet of the fluids flowing inside the hbers are provided. Plates can be monoaxial or biaxial, allowing two- and three-phase contact, respectively. Authors calculated, both at mbe and shell side, the pressure drops of this system. At the same huid how rate, the pressure drop at the shell side was lower than that of the mbe side and proportional to the gas how rate. The pressure drops at the mbe side were mainly related to the local obstacles in the module rather than the resistance in the hbers. 

Vladisavljevic GT and Mitrovic MV. Pressure drops and hydraulic resistances in a three-phase hoUow fiber membrane contactor with frame elements. Chem. Eng. Proc. 2001 40 3-11. 

Figure 5.12 Scheme ofthe hollow-fiber contactor of three phases with crossflow of LM phase (1) body of element, (2, 3) hollow fiber in downstream and upstream part, (4, 3) inlet and outlet chamber, (6,7) inlet and outlet tube, (8) flowing head, (9) central baffle, F feed, E LM phase, R strip solution. From Ref. [25] with permission. 

In Chapter 2 we discussed a number of studies with three-phase catalytic membrane reactors. In these reactors the catalyst is impregnated within the membrane, which serves as a contactor between the gas phase (B) and liquid phase reactants (A), and the catalyst that resides within the membrane pores. When gas/liquid reactions occur in conventional (packed, -trickle or fluidized-bed) multiphase catalytic reactors the solid catalyst is wetted by a liquid film as a result, the gas, before reaching the catalyst particle surface or pore, has to diffuse through the liquid layer, which acts as an additional mass transfer resistance between the gas and the solid. In the case of a catalytic membrane reactor, as shown schematically in Fig. 5.16, the active membrane pores are filled simultaneously with the liquid and gas reactants, ensuring an effective contact between the three phases (gas/ liquid, and catalyst). One of the earliest studies of this type of reactor was reported by Akyurtlu et al [5.58], who developed a semi-analytical model coupling analytical results with a numerical solution for this type of reactor. Harold and coworkers (Harold and Ng... 

Fig. 30. Contacting patterns and contactor types for gas-liquid-solid reactors, (a) Co-current downflow trickle bed. (b) Countercurrent flow trickle bed. (c) Co-current downflow of gas, liquid, and catalyst, (d) Downflow of catalyst and co-current upflow of gas and liquid, (e) Multi-tubular trickle bed with co-current flow of gas and liquid down tubes with catalyst packed inside them coolant on shell side, (f) Multi-tubular trickle bed with downflow of gas and liquid coolant inside the tubes, (g) Three-phase fluidized bed of solids with solids-free freeboard, (h) Three-phase slurry reactor with no solids-free freeboard, (i) Three-phase fluidized beds with horizontally disposed internals to achieve staging, (j) Three-phase slurry reactor with horizontally disposed internals to achieve staging, (k) Three-phase fluidized bed in which cooling tubes have been inserted coolant inside the tubes. (1) Three-phase slurry... 

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