In gas-liquid operations

Monolithic catalyst carriers are state-of-the-art in exhaust gas cleaning, for example in automobiles, DeNOx or removal of VOCs. To minimize diffusion length and to increase the geometric surface area, monoliths with small-diameter channels have been developed which can be produced easily by extrusion, followed by calcination. In the past few years the application of monoliths in gas-liquid operation has been investigated intensively [10-13]. 

Multiple impellers are often used in gas-liquid operations. Assuming that the lowest impeller is used for the primary gas dispersion, the upper ones are not loaded by all the gas entering through the spar-ger F lo] Pqj. purpose of power demand estimation, it can be assumed that upper impellers experience about half the total gas rate. Correlations to estimate... 

Rational process design of liquid-liquid extractors (or reactors) is in many ways similar to those of equipment used in gas-liquid operations. The latter is discussed in some detail by Alper in this Proceedings (15). The important design parameter is the time of reaction for a specified level of conversion in the case of batch and semi-batch operations and volume (or height) for the continuous mode of operation. The required data include firstly hold-ups, interfacial... 

So far, all the features mentioned parallel those seen in gas-liquid operations. Liquid-liquid systems, however, present some special challenges, which set them apart from their gas-liquid counterparts and make it much more difficult to predict the performance of an extrachon column. 

All these gas-liquid-particle operations are of industrial interest. For example, desulfurization of liquid petroleum fractions by catalytic hydrogenation is carried out, on the industrial scale, in trickle-flow reactors, in bubble-column slurry reactors, and in gas-liquid fluidized reactors. 

The production of alcohols by the catalytic hydrogenation of carboxylic acids in gas-liquid-particle operation has been described. The process may be based on fixed-bed or on slurry-bed operation. It may be used, for example, for the production of hexane-1,6-diol by the reduction of an aqueous solution of adipic acid, and for the production of a mixture of hexane-1,6-diol, pentane-1,5-diol, and butane-1,4-diol by the reduction of a reaction mixture resulting from cyclohexane oxidation (CIO). 

Gas-phase reactions catalyzed by solid catalysts are normally carried out in gas-particle operation in either fixed or fluidized beds. The possibility of using gas-liquid-particle operations for such reactions is, however, of interest in certain cases, particularly if the presence of a liquid medium for the transfer of heat or mass is desirable. 

Epoxides such as ethylene oxide and higher olefin oxides may be produced by the catalytic oxidation of olefins in gas-liquid-particle operations of the slurry type (S7). The finely divided catalyst (for example, silver oxide on silica gel carrier) is suspended in a chemically inactive liquid, such as dibutyl-phthalate. The liquid functions as a heat sink and a heat-transfer medium, as in the three-phase Fischer-Tropsch processes. It is claimed that the process, because of the superior heat-transfer properties of the slurry reactor, may be operated at high olefin concentrations in the gaseous process stream without loss with respect to yield and selectivity, and that propylene oxide and higher... 

The two models commonly used for the analysis of processes in which axial mixing is of importance are (1) the series of perfectly mixed stages and (2) the axial-dispersion model. The latter, which will be used in the following, is based on the assumption that a diffusion process in the flow direction is superimposed upon the net flow. This model has been widely used for the analysis of single-phase flow systems, and its use for a continuous phase in a two-phase system appears justified. For a dispersed phase (for example, a bubble phase) in a two-phase system, as discussed by Miyauchi and Vermeulen, the model is applicable if all of the dispersed phase at a given level in a column is at the same concentration. Such will be the case if the bubbles coalesce and break up rapidly. However, the model is probably a useful approximation even if this condition is not fulfilled. It is assumed in the following that the model is applicable for a continuous as well as for a dispersed phase in gas-liquid-particle operations. 

Discussed in the following section will be such data and other information regarding the elementary process steps in gas-liquid-particle operations as have appeared in the chemical engineering literature. 

The absorption of reactants (or desorption of products) in trickle-bed operation is a process step identical to that occurring in a packed-bed absorption process unaccompanied by chemical reaction in the liquid phase. The information on mass-transfer rates in such systems that is available in standard texts (N2, S6) is applicable to calculations regarding trickle beds. This information will not be reviewed in this paper, but it should be noted that it has been obtained almost exclusively for the more efficient types of packing material usually employed in absorption columns, such as rings, saddles, and spirals, and that there is an apparent lack of similar information for the particles of the shapes normally used in gas-liquid-particle operations, such as spheres and cylinders. 

In addition, it was concluded that the liquid-phase diffusion coefficient is the major factor influencing the value of the mass-transfer coefficient per unit area. Inasmuch as agitators operate poorly in gas-liquid dispersions, it is impractical to induce turbulence by mechanical means that exceeds gravitational forces. They conclude, therefore, that heat- and mass-transfer coefficients per unit area in gas dispersions are almost completely unaffected by the mechanical power dissipated in the system. Consequently, the total mass-transfer rate in agitated gas-liquid contacting is changed almost entirely in accordance with the interfacial area—a function of the power input. 

Uses Research chemical. Derived from industrial and experimental coal gasification operations where the maximum concentrations detected in gas, liquid, and coal tar streams were 28, 4.1, and 18 mg/m , respectively (Cleland, 1981). 

Similarly, the superficial velocity v or vq of the gas throughput as an intensity quantity is a reliable scale-up criterion only in mass transfer in gas/liquid systems in bubble columns. In mixing operations in bubble columns, requiring the whole liquid content be back mixed (e.g., in homogenization), this criterion completely loses its validity (10). 

Earlier studies in mass transfer between the gas-liquid phase reported the volumetric mass-transfer coefficient kLa. Since kLa is the combination of two experimental parameters, mass-transfer coefficient and mterfacial area, it is difficult to identify which parameter is responsible for the change of kLa when we change the operating condition of a fermenter. Calderbank and Moo-Young (1961) separated kta by measuring interfacial area and correlated mass-transfer coefficients in gas-liquid dispersions in mixing vessels, and sieve and sintered plate column, as follows ... 

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