The thermodynamic inhibition study of two biological osmoprotectants on methane hydrate

• L-proline and betaine are outstanding environmental-friendly THIs. • Betaine is more potent than L-proline and ethylene glycol at the same mole fraction. • Betaine forms stronger H-bonds with water than L-proline and ethylene glycol. • Stronger H-bonds between THIs with water led to more potent hydrate inhibition. L-proline (PRO) and betaine are osmoprotectants that protect various plant species in extreme environments such as drought, salinity, extreme temperatures, ultraviolet radiation, and heavy metals. In this work, the phase equilibrium conditions of methane hydrates were examined in the presence of PRO and betaine. The results showed that both PRO and betaine were outstanding effective thermodynamic inhibitors for methane hydrate. And betaine showed stronger inhibition than PRO at the same concentration. Additionally, the Gaussian 09 program was used to predict the hydrogen bond energies between PRO, betaine, and ethylene glycol with water molecules. The results demonstrated that betaine showed stronger interactions with water than PRO, which was in agreement with the experimental data of methane hydrate phase equilibrium.