Gas-liquid phase reaction:
The theoretical basis of gas-liquid phase reaction is mainly laid by the work of Japanese scholar Jiro An Tian in 1928- 1932. When gas phase reactant A reacts with liquid phase reactant B, it is assumed that B does not volatilize.
According to the double-membrane theory (see interphase mass transfer), it can be considered that the reaction has gone through the following steps: reactant A with partial pressure pA is transferred from the gas phase main body to the gas-liquid interface, where the partial pressure of gas phase A is P and the concentration of liquid phase is C, and they are in phase equilibrium; The reactant A is introduced into the liquid phase from the gas-liquid interface, and A with concentration of CA reacts with B with concentration of CB in the liquid phase.
The liquid product produced by the reaction is transferred along the direction of decreasing concentration, and the gas product is transferred to the interface; The gas phase product is transferred to the gas phase main body.
Application of gas-liquid reaction;
It is mainly used for directly preparing products, such as preparing acetaldehyde by oxidizing ethylene in acetic acid solution of PDC L2-Cu2cl2, and preparing cumene hydroperoxide by oxidizing cumene with air. Chemical absorption is used to remove one or more components in the gas phase, such as removing acid gases such as carbon dioxide and hydrogen sulfide from semi-water gas with alkali liquor, and removing carbon monoxide from synthesis gas with cuprammonia solution.
Two-mode theory for judging the principle of gas-liquid reaction;
Basic argument:
There is a stable phase interface between the contacted gas and liquid fluid, and there are thin and stable gas films or liquid films near the two sides of the interface, and solute passes through these two films in the form of molecular diffusion. The gas and sensitive liquid on the interface are in equilibrium. There is no mass transfer resistance at the phase interface. There is no mass transfer resistance in the main area of gas-liquid two-phase outside the membrane layer, that is, the concentration gradient (or partial pressure gradient) is zero.
Double-membrane theory simplifies the whole interphase mass transfer process to the molecular diffusion process of solute through two effective membranes.
Matters needing attention in dual-mode theory:
We must pay attention to the correct collocation of absorption coefficient and driving force in each rate equation and the consistency of their units. The reciprocal of the absorption coefficient is the absorption resistance, and the expression of resistance should also correspond to the expression of driving force.
All absorption rate equations are only applicable to describe the rate relationship on any cross section in the absorption tower under steady-state operation, and cannot be directly used to describe the absorption rate of the whole tower. On different sections in the tower, the composition of gas phase and liquid phase is different, and the absorption rate is also different.