PRINCIPLE OF SELECTIVE PERMEATION
FUNCTIONAL PRINCIPLE OF SEPURAN® MEMBRANES FOR GAS SEPARATION
Gas separation membranes work according to the principle of selective permeation through the membrane surface. The permeation rate of each gas depends on its solubility in the membrane material and on the diffusion rate of the gas.
Gases with high solubility and small molecules pass through the membrane very quickly. Less soluble gases with larger molecules take more time to permeate the membrane. In addition, different membrane materials separate differently. The driving force needed to separate gases is achieved by means of a partial pressure gradient.
Partial pressure gradient
The driving force for a gas to permeate through a membrane is the partial pressure difference; in other words, the partial gradient between the inside of the hollow fiber (retentate side) and the outside of the hollow fiber (permeate side). The greater the difference, the more gas permeates through the membrane. For example, if carbon dioxide and methane are being separated, as is the case with biogas upgrading, carbon dioxide permeates through the membrane very quickly while the methane tends to be held back.
The separation capability through the membrane is unaffected by process conditions – even with partial pressures of up to 20 bar, which is the case in biogas upgrading.