Reaction absorption with chemical

Murphree gas tray rifidency corrected for entrainment, fractional overall tray efficieticy, fractional gas-i iase mass-transfer coefficient for component J, liquid-fdiase mass-transfer coefficient for component J, moIe/L overall mass-transfer coefficient, mole/L  

Prandtl number, ii/k, dimensionless flux of heat transfer, FL/L a constant rate of total beat removal, FL/0 const 

molar latent heat of vaporization of reference substance at temperature FL/mole 

Astarita, G. Mass Transfer with Chemical Reaction, Hsevier, Amsterdam. 1966. 

Danckwerts, P. V. Gas-Liquid Reactions, McGraw-Hill Book Company, New York, 1970. 

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Penetration theoiy often is used in analyzing absorption with chemical reaction because it makes no assumption about the depths of penetration of the various reacting species, and it gives a more accurate result when the diffusion coefficients of the reacting species are not equal. When the reaction process is veiy complex, however, penetration theoiy is more difficult to use than film theory, and the latter method normally is preferred. 

Water generally is used for gases fairly soluble in water, oils for light hydrocarbons, and special chemical solvents for acid gases such as CO9, SO9, and H9S. Sometimes a reversible chemical reaction will result in a veiy high solubility and a minimum solvent rate. Data on actual systems are desirable when chemical reactions are involved, and those available are referenced later under Absorption with Chemical Reaction. ... 

Approximate design equations apphcable only to the case of pure physical desorption are developed later in this sec tion for both packed and plate stripping towers. A more rigorous approach using distiUation concepts may oe found in Sec. 13. A brief discussion of desorption with chemical reac tion is given in the subsec tion Absorption with Chemical Reaction. ... 

A necessary prerequisite to understanding the subject of absorption with chemical reaction is the development of a thorough understanding of the principles involved in physical absorption, as discussed earlier in this section and in Section 5. There are a number of excellent references the subject, such as the book by Danckwerts Gas-Liquid Reactions, McGraw-Hill, New York, 1970) and Astarita et al. Gas Treating with Chemical Solvents, Wiley, New York, 1983). 

While the carbon dioxide/caiistic test method has become accepted, one should use the results with caution. The chemical reaction masks the effect of physical absorption, and the relative values in the table may not hold for other cases, especially distillation applications where much of the resistance to mass transfer is in the gas phase. Background on this combination of physical and chemical absorption may Be found earher in the present section, under Absorption with Chemical Reaction. ... 

F. Gas Absorption with Chemical Reaction—Time-Dependent Bulk Concentration. 346... 

Dynantics of Heat Exchangers, Simple Batch Extraction, Multi-Solute Batch Extraction, Multistage Countercurrent Ctiscade, Extraction Cascade with Backmixing, Countercurrent Extraction Cascade with Reaction, Absorption with Chemical Reaction, Membrane Transfer Processes... 

Only physical absorption from dilute gases has been considered in this section. For a discussion of absorption from concentrated gases and absorption with chemical reaction, the reader should refer to Volume 2, or to the book by Treybal (1980). If the inlet gas concentration is not too high, the equations for dilute systems can be used by dividing the operating line up into two or three straight sections. 

Figure 12.10. Concentration profile for absorption with chemical reaction...

In this paper a transfer model will be presented, which can predict mass and energy transport through a gas/vapour-liquid interface where a chemical reaction occurs simultaneously in the liquid phase. In this model the Maxwell-Stefan theory has been used to describe the transport of mass and heat. On the basis of this model a numerical study will be made to investigate the consequences of using the Maxwell-Stefan equation for describing mass transfer in case of physical absorption and in case of absorption with chemical reaction. Despite the fact that the Maxwell-Stefan theory has received significant attention, the incorporation of chemical reactions with associated... 

Figure 6.3 Gas absorption with chemical reaction (a) rapid second-order reaction and (b) slow pseudo first-order reaction.

The influence of pressure on the mass transfer in a countercurrent packed column has been scarcely investigated to date. The only systematic experimental work has been made by the Research Group of the INSA Lyon (F) with Professor M. Otterbein el al. These authors [8, 9] studied the influence of the total pressure (up to 15 bar) on the gas-liquid interfacial area, a, and on the volumetric mass-transfer coefficient in the liquid phase, kia, in a countercurrent packed column. The method of gas-liquid absorption with chemical reaction was applied with different chemical systems. The results showed the increase of the interfacial area with increasing pressure, at constant gas-and liquid velocities. The same trend was observed for the variation of the volumetric liquid mass-transfer coefficient. The effect of pressure on kia was probably due to the influence of pressure on the interfacial area, a. In fact, by observing the ratio, kia/a, it can be seen that the liquid-side mass-transfer coefficient, kL, is independent of pressure. 

In a number of important industrial processes, it is necessary to carry out a reaction between a gas and a liquid. Usually the object is to make a particular product, for example, a chlorinated hydrocarbon such as chlorobenzene by the re action of gaseous chlorine with liquid benzene. Sometimes the liquid is simply the reaction medium, perhaps containing a catalyst, and all the reactants and products are gaseous. In other cases the main aim is to separate a constituent such as C02 from a gas mixture although pure water could be used to remove CO2, a solution of caustic soda, potassium carbonate or ethanolamine has the advantages of increasing both the absorption capacity of the liquid and the rate of absorption. The subject of gas-liquid reactor design thus really includes absorption with chemical reaction which is discussed in Volume 2, Chapter 12. 

Multiplicity or bifurcation behavior was found to occur in many other systems such as distillation [30], absorption with chemical reaction [31], polymerization of olefins in fluidized beds [32], char combustion [33, 34], the heating of wires [35] and in a number of processes used for manufacturing and processing electronic components [36, 37]. 

When two or more gases are absorbed in systems involving chemical reactions, the system is much more complex. This topic is discussed later in the subsection Absorption with Chemical Reaction. ... 

Characterization of a two phase impinging jets absorber, Part II Absorption with chemical reaction of carbon dioxide in NaOH solution. Chemical Engineering Science, 45 1281-1287. 

Stichlmair and Fair11 and Rose8 are textbooks devoted entirely to design and operation of distillation columns, Ruthven12 considers absorption and Astarita et alP absorption with chemical reaction. Ho14 is a handbook for membrane separations and Guiochon15 considers chromatographic separations. 

Many processes of gas absorption with chemical reaction are set up at high pressures, result of technical and/or economical requirements. That is, for example, processes of hydrocracking and hydrorefining of heavy oils and processes of oxydation of liquid effluents. However, if many chemical systems are found to determine the mass transfer parameters in an industrial reactor at atmospheric pressure by using the chemical method, they become scarce at elevated pressures. Several physical and chemical methods have been proposed chemical methods present some severe drawbacks, since one has to replace the gas-liquid system of interest by another one, presenting different physical properties (specially a different coalescence behaviour). 

Biofilters are chemically enhanced absorbers, and therefore mass transfer limited (see Absorption with Chemical Reaction in Sec. 14). The magnitudes for the Hatta [= Damkohler II = (Thiele modulus)2] numbers are quite low, perhaps below 5. Nevertheless, for design simplicity, mass-transfer limitation is generally assumed to be in the liquid phase (the biofilm). For a single-component biofilter, the simplified biofilter model and design equation is... 

For this example, absorption with chemical reaction gives a 34 percent reduction in the height of the packing relative to absorption without chemical reaction. 

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