Gas separation

Gas mixtures can be separated using different types of membranes. Compared to cryogenic methods, membranes offer high selectivities and are also more energy-efficient, since no phase transition is necessary.

Oxygen separation with perovskite capillary membranes

Typical geometry of a perovskite hollow fiber membrane
© Fraunhofer IGB
Typical geometry of a perovskite hollow fiber membrane. Outer diameter: 900 μm, inner diameter: 600 μm, length: 30 cm.

In recent years, mixed-conducting perovskites have increasingly come into focus as membrane materials for the selective separation of oxygen from gas mixtures. In order to combine the special material properties of mixed-conducting perovskites with an effective specific membrane surface, we have developed oxygen-conducting perovskite capillary membranes at Fraunhofer IGB. Compared to conventional geometries (disks, tubes, multi-channel elements), these membranes have the highest packing density (separation area per volume) and extremely low material consumption.

Hydrogen separation with palladium-coated alumina capillary membranes

Scanning electron microscope image of a PdAG-coated hollow fibre membrane.
© Fraunhofer IGB
Scanning electron microscope image of a PdAG-coated hollow fibre membrane

Palladium and its alloys can incorporate hydrogen in the form of hydrides in the metal lattice. We have developed palladium-coated alumina capillary membranes for the separation of hydrogen. This achieves a high specific separation area. Very thin, gas-tight palladium (alloy) layers can be produced by electroless plating.

CO₂ separation

For the separation of CO2 from other gases we use different separation principles.

 

Size exclusion using metal organic frameworks (MOF)

For separation by size exclusion, we use so-called metal-organic frameworks (MOF), which we can incorporate into mixed-matrix membranes. These then have porous structures of defined size in the lower nanometer range, which can be used for gas separation.

Absorption using ionic liquids

We also use ionic liquids (IL), which can absorb CO2 with high capacity. If these are soaked into porous membranes via capillary forces, these carrier-supported liquid membranes can be used for CO2 removal.

Reference projects

MAVO MEGA – Functional membranes for save and energy efficient gas separation

 

So far, the industrial use of technical separation membranes has been largely set to liquid filtration and less to gas separation. In the MEGA project, mixed‑matrix membranes were developed at the Fraunhofer IGB in cooperation with three other Fraunhofer institutes, which have great potential for gas separation due to their improved separation properties compared to pure polymer coatings.