The major limitation of biogas upgrading is the interfacial CO 2 mass transfer to the aqueous phase when an absorption process is deployed. Accurate Henry’s law constants are crucial for the design and operation of biogas upgrading systems; which are usually inferred from literature data obtained under non-representative, high pressure, high temperature, and different ionic strength. In this work, Henry’s law constants (C G /C L ) were experimentally evaluated for the main components of biogas such as CO 2 and CH 4 both in pure form and in gaseous mixture. We used alkaline media at moderate conditions of temperatures (10, 25 and 35°C), pressures (from 1.8 to 3.8 atm) and an ionic strength of 0.6, conditions relevant for the biogas upgrading based on microalgae. A carbonated medium (CM) and a modified Zarrouk medium (MZM) were used as solvents, where effective Henry’s law constants (C CO2G /C IC ) of CO 2 besides new values for equilibrium constants of the CO 2 •H 2 O system, were also assessed. A potentiometric method was implemented in a closed system. The assessed equilibrium constants were slightly higher than those reported in water, demonstrating that these differences impact the CO 2 solubility estimation. In basic CM (pH≈9) the effective Henry’s law constants for CO 2 decreased up three times, while the Henry’s law constants for CH 4 increased up 2.5 times both compared with water, indicating higher and lower solubility respectively . These results justify the separation of CO 2 to obtain biomethane when biogas is scrubbed by similar alkaline media under moderate state conditions.
Ramírez-Lozano et al. (Sun,) studied this question.