Carbon dioxide and Methane experimental Henry's law constants assessment in alkaline scrubbing solutions deployed for biogas upgrading at moderate pressure and temperature

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.