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In order to concentrate and separate CO2 from N2-diluted gaseous mixture, the adsorption characteristics and separation performance of various kinds of microporous crystals to be used as adsorbents were investigated. Eight-oxygen-member-ring microporous crystals like zeolite ZSM-34 and silicoaluminophosphate SAPO-34 adsorbed large quantities of CO2 and N2. Metal incorporation in those crystals improved their performance. For ZSM-34 it significantly increased specific surface area and amounts of adsorption, and for SAPO-34 it increased the effective diffusivity to some extent. For Ni-SAPO-34, 2.9% CO2 diluted with N2 could be concentrated to 62.9% and 84.4% at the CO2 recoveries of 33.0% and 20.6%, respectively, by using a pressure swing adsorption (PSA) technique in the pressure range between 10 and 2 kg cm−2 (gauge) and at −75°C.

The performance of various metal ion-exchanged A-type zeolites and metal-incorporated A-type zeolites for O 2 and N 2 adsorption was studied to provide a pressure swing adsorption (PSA) process. Metal-incorporated A-type zeolites adsorbed N 2 in larger quantities than metal ion-exchanged A-type zeolites. Compared with Na-A zeolite, both Cu-incorporated and Ni-incorporated A-type zeolites adsorbed larger quantities of N 2 . The incorporation of Cu or Ni enlarged the pore size of the zeolite, while Fe incorporation reduced it. However, the adsorption volume ratio of O 2 to N 2 could be increased to as high as 4.2 on Fe-incorporated A-type zeolite calcined at 750°C, which was the highest value among the samples tested. The amount of adsorption of O 2 was 38.0 ml g −1 , which was comparable with ordinary Na-A zeolite. The Fe incorporation markedly improved the performance of ordinary Na-A zeolite in O 2 /N 2 separation. Therefore, Fe-incorporated A-type zeolite has a high potential as a good adsorbent for pressure swing adsorption in O 2 /N 2 separation from air.