The effects of gas bubbling from a solution

When the evolving gas flow is relatively small, the nucleation of bubbles may become a limiting factor, particularly in deep liquid layers. This may be a problem when the chemical reaction is reversible (e.g., esterifications). Mechanical stirring or stripping with an inert gas may be helpful (section 4.6.1.3). Another alternative is the use of a liquid film reactor (section 4.6.3.1). 

Evolving gas from viscous liquids in bubble reactors may give rise to viscous foams and entrainment that will limit the reaction rate, especidly on a larger scale. A spray column may be the first alternative (section 4.6.2.1). If cooling is also required effective measures are costly. For this purpose thin film evaporators (section 4.63.1) or scraped surface evaporators can be effective. For very viscous liquids one may consider batch kneaders or extruders with vapour ports. 

An evolving gas may partly cover solid surfaces present in the reactor, and reduce the contact with the reactive liquid. In many electrolysis cells, metal gauze electrodes (or carbon blocks with holes) are us to allow the gas to escape. An interesting concept was demonstrated by Ravoo (1970) who used an electrolysis cell in the form of a centrifuge, with a gauze for the outer electrode. In this arrangement the evolved gas was removed effectively. 

When the solid is a catalyst, a trickle flow reactor may be an alternative for relatively high gas/liquid flow ratios (section 4.723). 

---