Examples of gas-liquid reactors

In the following examples, the aim is to illustrate how the chemical reaction is coupled with the mass transfer processes. To this end the reactor operating characteristics such as kL, a, eL, and the gas-liquid physical properties such as the Henry law constant and liquid-phase diffusivity will be used but the details of their calculation will not be considered. 

The design of packed column reactors is very similar to the design of packed columns without reaction (Volume 2, Chapter 12). Usually plug flow is assumed for both gas and liquid phases. Because packed columns are used for fast chemical reactions, often the gas-side mass transfer resistance is significant and needs to be taken into account. The calculation starts on the liquid side of the gas-liquid interface where the chemical reaction rate constant is compounded with the liquid side mass transfer coefficient to give a reaction-enhanced liquid-film mass transfer 

+ OH = HCOj 2 = 9.5 x 103 m3/kmol s (In a solution of NaOH this reaction is followed instantaneously by  

Solubility of CO, Henry law constant 25 bar m3/kmol (2.5 x 10 Nm/kmol) Equipment performance characteristics (see Volume 2, Chapter 12)  

Effective interfacial area of packing 280 m2/m3 Film mass transfer coefficients  

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The discussion is centered around gas-liquid reactors. If the dissolved gas content exceeds the amount needed for the reaction, the liquid may be first saturated with gas and then sent through a stirred tank or tubular reactor as a single phase. If the residence times for the liquid and gas are comparable, both gas and liquid may be pumped in and out of the reactor together. If the gas has limited solubility, it is bubbled through the reactor and the residence time for gas is much smaller. Figure 19-29 provides examples of gas-liquid reactors for specific processes. 

Figure 4.10.11 shows examples of gas-liquid reactors. Gas is usually dispersed in the liquid by a bubble column, tray column, or a stirring reactor with pressurized gas. Liquid is dispersed in the gas by means of a jet type washer or a spray tower. Liquid in the form of a thin film is exposed to a gas by a falling film reactor or a tricHe reactor with filter elements. Details of the interplay of chemical reaction and mass transfer are given in Section 4.4. 

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