Carbon Dioxide Transfer with Chemical Equilibrium Reactions: An Alternative Mathematical Approach

Abstract

Problem statement: Despite intensive research efforts on CO₂ transfer, mathematical models that describe the dependence of the CO₂ transfer rate on the pH and the degree of rate enhancement due to CO₂ chemical reactions remain unavailable. Approach: Such models are essential for assessing and accurately describing the progress of the CO₂ transfer process. Results: In this study, an alternative view of CO₂ transfer with chemical reactions was used to develop simple mathematical models to describe the pH dependence and degree of enhancement of the CO₂ transfer rate. In the alternative view, the driving force for CO₂ transfer was described in terms of the differences in the concentrations of the various carbonic species in the bulk liquid (i.e., ΔC_Δt(H2CO*3), , ΔC_Δt(HO^-3) and ΔC_Δt(CO^2-3) ) in time (i.e., between time, t, and the time when equilibrium is achieved, t_Eq) rather than in terms of the concentrations gradients across the liquid film. Using the concentration differences in time, simple mathematical models describing the pH dependence of the CO₂ transfer rate and the contributions of the various carbonic species to the rate were formulated. Furthermore, the degree of CO₂ transfer rate enhancement due to CO₂ reactions in water was considered proportional to the sum of the rates of HCO^-₃ and CO^2-₃ transfer. Conclusion/Recommendations: The mathematical models were tested using data from batch and continuous-flow CO₂ transfer experiments, and the results revealed that the mathematical models explained the experimental data in an excellent manner.