Chemistry

Polymer chemistry

Polycarbonate

Permeation

Hydrogen

Solubility

Polymer

Methane

Biochemistry

Supercritical fluid

Organic chemistry

Gas separation

Semipermeable membrane

Engineering

Membrane

Chemical engineering

Trends in polymer science

Polymeric membranes for the separation ofsupercritical gases are typically glassy and achieve high selectivity by a size-sieving mechanism. This property permits some polymers to be more than 100 times more permeable to hydrogen (kinetic diameter = 2.89A) than to methane (kinetic diameter = 3.8A), despite the fact that hydrogen solubility is markedly lower than methane solubility. The permeation properties of glassy polymers for the separation of supercritical gases follow an immutable trade-off relationship : polymers that are more permeable tend to be less selective and vice versa. In contrast, new gas. separation applications, such as removal of higher hydrocarbons from natural gas for dew-point and heating-value control, removal of higher hydrocarbons from hydrogen streams, and separation of valuable or toxic organic vapors from air or nitrogen streams, generally require membranes that are more permeable to the larger, more condensable components in a mixture (i.e. vapors) than to smaller supercritical ga...

Separation of gases using solubility-selective polymers