Page 24 - Adsorption Technology & Design, Elsevier (1998)

Adsorbents 21

process application is the production of high purity nitrogen from air by
pressure swing adsorption.
Despite the fact that much of the early work was based on polymeric
precursors, the first industrial manifestation of pressure swing adsorption
technology with carbon molecular sieves in the 1970s was based on Bergbau
Forschung's coal-derived material which was manufactured by modifying
the underlying carbon pore structure by depositing carbon in the pore
mouths through the cracking of an organic material (J0ntgen et al. 1981).
This development was followed by a competitive CMS from Japan, which
was again based on pore structure modification by carbon deposition but this
time using a coconut shell char precursor (Ohsaki and Abe 1984). More
recently there has been a resurgence of interest in the production of new
CMS materials with the emphasis being placed on higher pore volume
precursors combined with the use of chemical vapour deposition using
organics such as iso-butylene for improving the oxygen to nitrogen
selectivity (Cabrera et al. 1993).

2.3 CARBONIZED POLYMERS AND RESINS

Resins such as phenol formaldehyde and highly sulphonated styrene/divinyl
benzene macroporous ion exchange resins can be pyrolysed to produce
carbonaceous adsorbents which have macro-, meso- and microporosity.
Surface areas may range up to 1100 m2/g. These adsorbents tend to be more
hydrophobic than granular activated carbon and therefore one important
application is the removal of organic compounds from water.

2.4 BONE CHARCOALS

Animal bones can be carbonized to produce adsorbent materials which have
only meso- and macropores and surface areas around 100 m2/g. The pore
development activation step used with activated carbons is dispensed with.
The surface is carbon and hydroxyl apatite in roughly equal proportions and
this dual nature means that bone charcoals can be used to adsorb metals as
well as organic chemicals from aqueous systems. Decolourizing sugar syrup
is another application.