527 Q8 Ch5 Membranes

For the membrane separation of a CO₂+N₂ mixture with dilute CO₂ concentration, the membrane must be selective for

• CO₂

• N₂

• (Membranes cannot be used in this case.)

Which schematic shows a semi-permeable membrane?

• 
• 

Since the pressure difference between the feed and permeate sides of a membrane can be up to 20 atm, the membrane thickness should be large to enjoy mechanical strength.

• True

• False

Consider the application of natural gas purification, i.e., separation of CH₄ and CO₂. Which gas should be the "Retentate"?

• CH₄

• CO₂

• Either gas. It doesn't matter.

Membrane performance is judged by

• its permeance alone.

• its selectivity alone.

• both its permeance and selectivity.

Consider a mixture of CO₂ and CH₄. A membrane is selective to CO₂, if

• CO₂ diffusivity is higher than that of CH₄, but CO₂ solubility is lower.

• CH₄ diffusivity is higher than that of CO₂, but CH₄ solubility is lower.

• both diffusivity and solubility of CO₂ are higher than those of CH₄.

• both diffusivity and solubility of CH₄ are higher than those of CO₂.

Which one of these materials can be used to selectively separate CO₂ from a mixture of natural gas and CO₂?

(check all that applies; no partial credit)

• Ethyl cellulose

• Poly (methyl methacrylate)

• PMDA-4,4'-ODA polyimide

• Polysulfone

• Cellulose acetate

The higher the temperature, the more selective a membrane becomes.

• True

• False

If a membrane is highly permeable to a gas, it is also highly selective to this gas.

• True

• False

CO₂ is more soluble in polymer membranes with a high concentration of polar groups.

• True

• False