Absorption with chemical reaction

There are many industrial applications where a gaseous species is transferred from a gas mixture into a liquid phase containing one or more reagents with which the dissolved gas can react. Examples include liquid-phase processes such as hydrogenations, oxidations, halogenations... or gas scrubbing processes (H ₂ S, SO ₂ , NO _x , Cl ₂ , HCI, HF, VOCs (*)...) in air pollution control, or even biological processes or pure product manufacturing processes.

The absorber's overall performance, in terms of efficiency and selectivity, depends on the phenomena involved:

• thermodynamic equilibria at the interface (solubilities) ;

• transport laws in phases (diffusivities) ;

• transfer laws near interfaces (transfer coefficients, interfacial areas) ;

• kinetics of chemical reactions (reaction diagrams, kinetic constants, reaction orders).

Depending on the system under consideration, and in particular on the characteristic transfer, transport or reaction times, the absorber will have to be chosen either on the basis of its performance in terms of material transfer, or on the basis of the volume of liquid involved. Consequently, the absorbers used in industry come in a wide variety of shapes:

• tubular reactors with bubbles, drops, falling film, packing, trays ;

• reactors with mechanically agitated vessels ;

• jet or venturi engines.

The aim of this article is to provide the essential tools for choosing an absorber and implementing it under optimum hydrodynamic and energetic conditions. Operation is of course linked to the various parameters of the phenomena involved. Secondly, the sizing and extrapolation of the reactor require the establishment of a mathematical model including a theory of absorption with chemical reaction in line with reality and well adapted to the target objective.

That's why we're presenting :

• the theory of absorption with chemical reaction, which is necessary to establish the reactor model;

• techniques for measuring the material transfer parameters used in this model.