𝑆 𝑖 * 𝐷 𝑖 * ∆𝑝 𝛿𝑚 (1) where J is the flux of diffusing species normalized for the membrane surface area (mol/s m 2 ), Si is the solubility of the permeant i (mol/m 3 Pa), Di is the diffusion coefficient of the permeant in the material (m 2 /s), ∆p is the pressure difference between the high and low-pressure side, and δm is the membrane thickness.