A Theoretical Analysis of Dissolved-Gas Transfer to the Bulk Liquid in Gas Absorption with a First-Order Reaction

Abstract

A theoretical analysis using the surface-renewal and film-penetration models, which includes gas-phase resistance to mass transfer, is presented for the rate of absorption of a gas and its transfer to the bulk liquid in the case where the solute gas undergoes a first-order chemical reaction in the liquid phase. It reveals that:

a.	The fraction of absorbed gas transported to the bulk liquid depends upon the Hatta number Ha in case of the surface-renewal model and on Ha as well as a dimensionless hydrodynamic parameter in case of the film-penetration model.
b.	The widely assumed law of addition of resistances is valid for the surface-renewal and film-penetration models.
c.	The reaction influences both the overall mass-transfer coefficient and the nature of the driving force, i.e. the increased rate of absorption due to the reaction is not solely due to the enhancement factor multiplying the liquid-phase mass-transfer coefficient for physical absorption as has been conventionally assumed in the literature.

It is also shown that in a gas-liquid reactor the film and surface-renewal models give close predictions for both the rate of absorption and concentration of dissolved gas in the liquid leaving the reactor. For values of Ha ⩾ 0.5, the bulk-liquid concentration of dissolved gas predicted by both models is negligible compared to its interfacial concentration.

Keywords:

• Explicate order
• Film model
• Film-penetration model
• First-order reaction
• Gas absorption
• Implicate order
• Surface-renewal model