Polymeric adsorbents versus activated carbons

In many respects, activated carbons meet these requirements and today a vast assortment of microporous and macroporous activated carbons are commercially available. These sorbents are very attractive due to their low cost, particularly if prepared by pyrolysis of natural raw materials. The main advantage of carbonaceous materials consists in their high adsorption capacity with respect to a variety of organic compounds. 

Comprehensive Analytical Chemistry, Volume 56 ISSN 0166-526X, DOI 10.1016/S0166-526X(10)56010-1 

Polymeric adsorbents, particularly macroporous styrene—divinylbenzene (DVB) copolymers, are free from these drawbacks of activated carbons. The heat of adsorption onto the polymeric adsorbents is significandy lower and, accordingly, the regeneration of polymers proceeds under much milder conditions. As a rule, the copolymers have no functional groups (apart from those specially introduced) that are capable of catalyzing chemical transformation of an adsorbate. However, in contrast to activated carbons, the specific surface area of most polymeric adsorbents is not very high therefore, their sorption capacity is lower, often making the use of macro-porous polystyrene-type adsorbents unprofitable. This circumstance impelled scientists to develop new types of polymeric materials with an enhanced 

Up to now four main groups of hypercrosslinked sorbents have been developed and intensively tested. The first group, Styrosorb 1, incorporates laboratory samples of nanoporous (microporous) single-phase sorbents prepared by intensive post-crosslinking Hnear polystyrene of about 300,000 Da molecular weight, dissolved in ethylene dichloride, with monochlorodi-methyl ether or p-xylylene dichloride. The irregular particles of these sorbents have pores with a diameter of about 20—30 A and display an apparent specific surface area as high as 1000—1500 m g. The pore volume of Styrosorb 1 materials usually amounts to 0.4—O.Scm g. 

The third group, Styrosorb 2, represents nanoporous single-phase polymers derived from spherical beads of gel-type styrene copolymers with largely 0.7% DVB, post-crosslinked in swollen state with monochlorodimethyl ether. The size of the micropores is approximately 10—30 A, and the apparent specific surface area reaches very large values of 1000—1900 m /g, which is comparable to the range of the best activated carbons. On the other hand, the pore volume of these materials is rather small, 0.2—0.3 cm /g. 

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