Gas-liquid-solid multiphase

Small bubbles and flow uniformity are important for gas-liquid and gas-liquid-solid multiphase reactors. A reactor internal was designed and installed in an external-loop airlift reactor (EL-ALR) to enhance bubble breakup and flow redistribution and improve reactor performance. Hydrodynamic parameters, including local gas holdup, bubble rise velocity, bubble Sauter diameter and liquid velocity were measured. A radial maldistribution index was introduced to describe radial non-uniformity in the hydrodynamic parameters. The influence of the internal on this index was studied. Experimental results show that The effect of the internal is to make the radial profiles of the gas holdup, bubble rise velocity and liquid velocity radially uniform. The bubble Sauter diameter decreases and the bubble size distribution is narrower. With increasing distance away from the internal, the radial profiles change back to be similar to those before contact with it. The internal improves the flow behavior up to a distance of 1.4 m. 

Liu, W., Mini-structured Catalyst Bed for Gas-Liquid-Solid Multiphase Catalytic Reaction, AIChEJ, 2002, July, pp. 1519-1532. 

Matsushita Y, Ohba N, Suzuki T et al (2008) Photocatalytic reduction of CO2 in a photocatalytic microreactor under gas-liquid-solid multiphase-flow condition excited by 365-nm UV-LEDs. Catal Today 132 153-158... 

Photocatalytic oxidation of p-chlorophenol and toluene under gas-liquid-solid multiphase flow conditions was investigated using a photocatalytic microreaction system [160]. By loading both gaseous and liquid samples simultaneously into a microchannel with a photocatalytic titanium dioxide thin layer therein, a gas-liquid-solid multiphase annular flow was generated. The reaction yield was greatly enhanced with decreasing thickness of liquid layer because of improved efficiency of interaction and mass transfer between different phases. 

Many gas-liquid-solid multiphase reactions, such as the hydration of propene, catalytic hydrogenation of nitrate, chloroform dehalogenation, and H2O2 synthesis by H2 + O2 reaction in solution, are generally limited by the diffusion of the volatile reactant. Retention of homogeneous catalysts and efficient gas-liquid mass transfer are the key properties of such reaction systems. Both can be well achieved in the contactor-type MRs. 

Table 2.10 Gas-liquid-solid multiphase reactions in porous membrane reactors...

Table 2.10 summarizes the application of porous MRs in gas-liquid-solid multiphase reactions. Operation of the high-pressure membrane contactor requires precision measurement and control. The activity and selectivity of the process may be controlled through controlling the dosage of gas reactant. 

Kreutzer, M.T. et al. (2005) Multiphase monolith reactors chemical reaction engineering of segmented flow in microchannels. 7th International Conference on Gas-Liquid and Gas-Liquid-Solid, 2005,... 

Advances in multiphase reactors for fuel industry are discussed in this work. Downer reactors have some advantages over riser reactors, but suffer from some serious shortcomings. The coupled reactors can fully utilize the advantages of the riser and the downer. For fuel industry that involves gas-liquid-solid system, slurry bed reactors especially airlift reactors are preferred due to their performance of excellent heat control and ease of seale up. For high-pressure processes, the spherical reactor is promising due to its special characteristics. 

A fundamental division of multiphase reactors may be made, depending on whether the solid phase is present as a moving-or as a fixed bed. In principle, one gas-liquid-solid reactor with the fixed bed of solids can be operated in three ways, depending upon the relative orientation of the superficial gas-mass G and superficial liquid-mass L flow-rates (see Figure 5.2-1). 

This reaction is an example of a heterogeneous reaction with a solid catalyst with one reactant principally in solution and another in the gas phase the gas-liquid-solid mixture has to be mixed thoroughly to promote conversion (see Chapter 5 for more detailed consideration of multiphase reactions). Compared with the examples above, the measurement of the hydrogen uptake delivers an additional signal, which can also be used for the determination of reaction parameters. 

In fact, extremum tendencies expressing the dominant mechanisms in systems like turbulent pipe flow (Li et al, 1999), gas-liquid-solid flow (Liu et al, 2001), granular flow, emulsions, foam drainages, and multiphase micro-/nanoflows also follow similar scenarios of compromising as in gas-solid and gas-liquid systems (Ge et al., 2007), and therefore, stability conditions established on this basis also lead to reasonable descriptions of the meso-scale structures in these systems. We believe that such an EMMS-based methodology accords with the structure of the problems being solved, and hence realize the similarity of the structures between the physical model and the problems. That is the fundamental reason why the EMMS-based multi-scale CFD improves the... 

Multiphase systems (gas-liquid, liquid-solid, liquid-liquid, gas-liquid-solid)... 

Another classification of chemical reactors is according to the phases being present, either single phase or multiphase reactors. Examples of multiphase reactors are gas liquid, liquid-liquid, gas solid or liquid solid catalytic reactors. In the last category, all reactants and products are in the same phase, but the reaction is catalysed by a solid catalyst. Another group is gas liquid solid reactors, where one reactant is in the gas phase, another in the liquid phase and the reaction is catalysed by a solid catalyst. In multiphase reactors, in order for the reaction to occur, components have to diffuse from one phase to another. These mass transfer processes influence and determine, in combination with the chemical kinetics, the overall reaction rate, i.e. how fast the chemical reaction takes place. This interaction between mass transfer and chemical kinetics is very important in chemical reaction engineering. Since chemical reactions either produce or consume heat, heat removal is also very important. Heat transfer processes determine the reaction temperature and, hence, influence the reaction rate. 

Classification by Phase Despite the generic classification by operating mode, reactors are designed to accommodate the reactant phases and provide optimal conditions for reaction. Reactants may be fluid(s) or solid(s), and as such, several reactor types have been developed. Singlephase reactors are typically gas- (or plasma- ) or liquid-phase reactors. Two-phase reactors may be gas-liquid, liquid-liquid, gas-solid, or liquid-solid reactors. Multiphase reactors typically have more than two phases present. The most common type of multiphase reactor is a gas-liquid-solid reactor however, liquid-liquid-solid reactors are also used. The classification by phases will be used to develop the contents of this section. 

Multiphase reactors include, for instance, gas-liquid-solid and gas-liq-uid-liquid reactions. In many important cases, reactions between gases and liquids occur in the presence of a porous solid catalyst. The reaction typically occurs at a catalytic site on the solid surface. The kinetics and transport steps include dissolution of gas into the liquid, transport of dissolved gas to the catalyst particle surface, and diffusion and reaction in the catalyst particle. Say the concentration of dissolved gas A in equilibrium with the gas-phase concentration of A is CaLt. Neglecting the gas-phase resistance, the series of rates involved are from the liquid side of the gas-liquid interface to the bulk liquid where the concentration is CaL, and from the bulk liquid to the surface of catalyst where the concentration is C0 and where the reaction rate is r wkC",. At steady state,... 

Additional information on mechanically agitated gas-liquid-solid reactors can be obtained in van t Riet and Tramper (Basic Bioreactor Design, Marcel Dekker, 1991), Ramachandran and Chaudhari (Three-Phase Catalytic Reactors, Gordon and Breach, 1983), and Gianetto and Silveston (Multiphase Chemical Reactors, Hemisphere, 1986). Examples... 

For more details see Shah (Gas-Liquid-Solid Reactor Design, McGraw-Hill, 1979) and Hofmann [Hydrodynamics and Hydrodynamic Models of Fixed Bed Reactors, in Gianetto and Silveston (eds.), Multiphase Chemical Reactors, Hemisphere 1986]. 

During an experiment in a multiphase system, the tracer should not be transferred from one phase to another phase. For example, a gaseous tracer used in a gas-liquid reactor should not be absorbed by liquid and a liquid tracer used to measure the liquid-phase RTD curve should not be volatile. Similarly, a solid tracer used to measure the RTD curve for the solid phase in a gas-liquid- solid slurry reactor should not dissolve in the liquid, etc. 

The analysis and design of multiphase reactors is probably the most widely researched subject in the area of chemical reaction engineering at the present time. While the subject of two-phase reactor design (i.e., gas-solid and gas-liquid) has been extensively reviewed in numerous texts, no similar treatment of three-phase (i.e., gas-liquid-solid) reactor design is available. 

In many multiphase (gas-liquid, gas-solid, liquid-liquid and gas-liquid-solid) contactors, a large degree of circulation of both discrete and continuous phases occurs. This circulation causes a good degree of mixing and enhances heat and mass transfer between fluid and walls. The degree of circulation depends on a number of parameters such as the size of equipment, the nature of the phases involved, velocities of various phases, nature of the internals within the equipment and many others. 

Many types of multiphase flow exist (i.e., gas-liquid, gas-solid, liquid-liquid, gas-liquid-solid) where within one type of flow several possible flow regimes exist. In Fig. 10 (Ishii, 1975) a classification is given for two-phase flow. 

Laboratory batch reactors can be single-phase (e.g., gas or liquid), multiphase (e.g., gas-liquid or gas-liquid-solid), and catalytic or non-catalytic. In this section we limit the discussion to operation at isothermal conditions. This eliminates the need to consider energy, and due to the uniform composition the component material balances are simple ordinary differential equations with time as the independent variable. 

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