Advanced adsorbents for the separation of the ortho- and para-hydrogen spin isomers at cryogenic temperatures

Abstract

Improved adsorbent types and compositions have been developed for the challenging separation of the ortho- and para-hydrogen spin isomers at 77 K. From a systematic study of commercially available adsorbent types, it has been found that zeolites of type X offer the largest capacity and selectivity towards ortho-hydrogen and that performance is significantly impacted by the cation type and the number of cations present in the zeolite. For the present separation improved performance was obtained with larger Group I cations, especially K and Cs. Another key property of the adsorbents addressed in the present work is the need to control the adsorbent composition to avoid unwanted catalytic conversion of the para- to ortho-hydrogen. A common source of unwanted catalytic activity in many adsorbent compositions was identified as the presence of unwanted transition metal impurities, especially iron associated with the natural clays, commonly employed as binding agents in the commercial agglomerated zeolite products. To avoid this, equivalent adsorbent compositions were agglomerated instead using colloidal silica binding agents which successfully minimize back conversion of the para- to ortho-hydrogen and produced adsorbents with higher capacities and selectivities for the ortho component at the test temperature of 77 K. These advanced adsorbents can be applied in more efficient hydrogen liquefaction processes.