The Adsorption of Multinuclear Phenolic Compounds on Activated Carbon

Abstract 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.