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., ΔCΔt(H2CO*3), , ΔCΔt(HO-3) and ΔCΔt(CO2-3) ) in time (i.e., between time, t, and the time when equilibrium is achieved, tEq) 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 CO2-3 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.
Highlights
Carbon dioxide exchange across the gas/liquid interface is related to numerous natural and engineered processes and as such, the topic is of multidisciplinary interest in the scientific community[1,2,3,4,5,6]
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
There are no mathematical models to describe the degree of enhancement of the CO2 transfer rate as a function of pH due to chemical reactions involving hydration of CO2 and acid-base ionization reactions leading to the formation of HCO3− and CO32−
Summary
Carbon dioxide exchange across the gas/liquid interface is related to numerous natural and engineered processes and as such, the topic is of multidisciplinary interest in the scientific community[1,2,3,4,5,6]. The theory and mathematics describing CO2 transfer have generally evolved in agreement with earlier concepts describing the process in natural and engineered systems[7,8,9,10]. There are no mathematical models that explicitly and accurately describe the dependence of the CO2 transfer rate on the pH. There are no mathematical models to describe the degree of enhancement of the CO2 transfer rate as a function of pH due to chemical reactions involving hydration (de-hydration) of CO2 and acid-base ionization reactions leading to the formation (or removal) of HCO3− and CO32−. The main objective of the study was to develop simple mathematical models to describe the dependence of the CO2 transfer rate on the pH and the degree of rate enhancement due to chemical reactions
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