news / 2013-10-30

MEM-OXYCOAL: Ceramics reduce energy needed to separate air

Cryogenic air separation, a process employed to produce oxygen, requires a lot of energy. This high energy consumption impairs the efficiency of a number of industrial processes and procedures used to separate carbon dioxide from exhaust gases. In the context of the MEM-OXYCOAL research project headed by RWTH Aachen University, scientists have developed membranes that improve the energy efficiency of oxygen separation.

Member of the research staff working at a high-temperature oven at RWTH Aachen University. Source: IPC, RWTH Aachen

The membranes are entirely non-porous. In contrast to their porous counterparts, high-temperature membranes do not require pores for the oxygen separation process. Oxygen is separated via the integration of molecular oxygen from the air into the crystalline structure of the oxide membrane material. This works on the basis that the oxygen becomes a component of the membrane material during the integration process while other components of the air are not being integrated.


In contrast to other membrane types, high-temperature membranes also achieve one-hundred per cent selectivity for oxygen even at high throughput rates – provided they are free of pores and fractures. Project partners under the EU GREEN-CC project, which was launched in September 2013, are working to improve long-term stability and the oxygen throughput rate.


Air separation – potential applications

High-energy cryogenic air separation processes are used in industries that require pure oxygen, for instance in the manufacture of steel and glass, in oxidation processes for the chemical industry or in medical applications.


A further area of application is CO2 separation in the energy conversion context. Several technical approaches are suitable to reduce the carbon dioxide emissions during the combustion of biomass, coal and gas. Under the oxyfuel process, combustion takes place in a pure oxygen environment. This has a clear advantage in terms of carbon dioxide separation: During combustion only carbon dioxide and water vapour arise that can easily be separated while the gas mixture cools down. However, due to the large amount of energy that has so far been required to produce pure oxygen, the oxyfuel process would reduce the efficiency of a coal-fired power plant by approx. ten percent. The development of ceramic membranes promises to reduce this loss of efficiency. The membranes can also be used in the pre-combustion process. After the gasification of coal or biomass, pure oxygen is needed for partial oxidation.

Cryogenic air separation

With cryogenic air separation, oxygen is extracted from air by means of liquefaction. The Linde process is available for the large-scale generation of oxygen. This makes it possible to manufacture both gaseous and liquid oxygen and nitrogen as well as argon.

Project management MEM-OXYCOAL

Prof Dr Manfred Martin

Institut für Physikalische Chemie

RWTH Aachen

Landoltweg 2

52056 Aachen

Telefon: +49(0)241 8094712

Fax: +49(0)241 8092128


The project partners are working on improving the long-term stability and the oxygen flux in the subsequent GREEN-CC, EU project, which started in September 2013.