The adsorption of multinuclear phenolic compounds on activated carbon

Pure compounds, whose structures model that of phenol-formaldehyde resins, were synthesized and their adsorption from ethanol solvent on activated carbon examined. Two series of compounds were studied, (i) those with methylene linkages substituted in only the ortho- positions relative to the phenolic hydroxyl group (the ortho- series), and (ii) those in which all para- positions together with sufficient ortho- positions were used to synthesize the compounds (the para- series). Successive coupling of phenolic units to bis-(2-hydroxyphenyl)-methane and bis-(4-hydroxyphenyl)-methane resulted in tetra-, hexa-, and octa-nuclear species, which are referred to as tetramer, hexamer, and octamer, respectively, with the appropriate prefix (ortho- or para-). Experimental adsorption isotherms could be fitted to the Langmuir equation. From the maximum amounts adsorbed for each compound, it was shown that ortho-linked species were adsorbed to a greater extent than their para-linked analogues. This could be attributed to ethanol being a better solvent for the para-linked compounds relative to the ortho- series. The differences in behavior toward solvent could be attributed to the presence of strong intramolecular hydrogen bonding in the ortho-linked compounds, an interaction minimal (or absent) in the para-linked series. This conclusion is supported by results from molecular modeling and intrinsic viscosity measurements for the compounds of interest. (C) 1996 Academic Press, Inc.