Membrane Gas Separation

9 
Air Enrichment by Polymeric 
Magnetic Membranes
Zbigniew J. Grzywna , Aleksandra Rybak and Anna Strzelewicz
Faculty of Chemistry, Silesian University of Technology, Gliwice, Poland
9.1
Introduction 
Nowadays, obtaining cheap high purity gases or enriched gas mixtures (the air, in particu-
lar) is a very important problem in industry and medicine as well as in everyday life [1] . 
Methods for air separation or oxygen enrichment can be divided into two groups [2,3] : 
cryogenic and non - cryogenic. The gaseous oxygen and nitrogen market is dominated by 
cryogenic distillation of air, and vacuum swing adsorption [4] . Of the non - cryogenic 
methods, selective adsorption on zeolites and carbon adsorbents are available [5,6] , and 
more and more attention is attracted to the membrane separation techniques [7,8] . The 
success of polymeric membranes has been largely based on their mechanical and thermal 
stability, along with good gas separation properties. The process of membrane separation 
is continuous, has a low capital cost, low power consumption, and the membranes, at 
least in gas separation, do not require regeneration [3] . In the case of gas separation two 
groups of factors have to be taken into account: solution - diffusion properties of membrane 
materials and molecular size differences of components. For similar - sized molecules such 
as oxygen and nitrogen, permselectivities P (O 
2
)/ P (N 
2
) are usually less than 10 in tradi-
tional polymer membranes, and it prevents the high degree of oxygen enrichment easily 
achieved in the cryogenic industry. In this situation a certain breakthrough was needed. 
Different approaches have been applied to improve performance of polymeric mem-
branes, e.g. use of carbon molecular sieving (CMS) membranes or application of mixed 
matrix membranes [9 – 11] . Further development resulted in higher O 
2
/N 
2
selectivity of 

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Membrane Gas Separation
membranes (up to 14 [12 – 14] , i.e. about 80% of oxygen in the permeate or oxygen 
enriched stream). Efforts in various directions performed by another group [15 – 23] did 
not result in creation of very selective polymeric membranes. 
The challenge with air, when separation by polymer membrane is concerned, is to 
provide conditions for differences (other than sorption and diffusion properties) in mass 
transport between oxygen and nitrogen. The idea of ‘ magnetic membranes ’ was intro-
duced, and described briefl y, only recently [24 – 26] , based on the observation that oxygen 
and nitrogen have quite different magnetic properties, i.e. oxygen is paramagnetic whereas 
nitrogen diamagnetic, which gives a real chance for their separation. This idea can be 
utilized in at least two ways: magnets dispersed in a membrane ( ‘ magnetic membranes ’ ), 
and a magnetic fi eld applied on both sides of the permeation cell ( ‘ magnetic cell ’ ). Of 
course, using both would be the most effective.