Potential Approach for Fractionating Oxygenated Aromatic Compounds from Renewable Resources

Abstract

Various oxygenated aromatic compounds (OACs) could be obtained from renewable resources if separations were available to fractionate the complex mixtures. We examined adsorption for the fractionation of OACs into (i) acids, (ii) phenols, (iii) alcohols, and (iv) compounds lacking hydrogen-bond donating ability. Specifically, we studied adsorption from a nonpolar solvent onto a neutral acrylic ester sorbent. The acid, 3-phenylpropionic acid, exists in hexane as monomers and self-associated (e.g., dimeric) species. Phenomenological evidence indicates that monomers can adsorb but that adsorption competes with solution-phase dimerization. Previous studies indicate that phenols and alcohols adsorb through a hydrogen-bonding mechanism, while OACs lacking hydrogen-bond donating ability (i.e. aldehydes, ketones, esters, and ethers) adsorb weakly. Isotherms show that these four classes of OACs adsorb with significantly different affinities. Desorption is achieved by exploiting deprotonation reactions in an aqueous desorption phase and that the acids and phenols can be selectively desorbed based on differences in their pKa's. A potential approach for fractionating renewable OACs is considered.