Differential Adsorption of Phenol Derivatives onto a Polymeric Sorbent:  A Combined Molecular Modeling and Experimental Study

Abstract

Oxygenated aromatic compounds (OACs) are used for the synthesis of a variety of commercial products. Lignin from wood and other plant products are potential sources of OACs, but it is difficult to separate the mixtures of OACs found in digests of these raw materials. One promising separation approach involves the use of selective adsorption resins, such as the acrylic ester sorbent XAD-7. It has been shown previously that this sorbent binds the para isomer of one OAC, methoxyphenol, more favorably that the ortho isomer when hexane is used as the solvent. The present study uses a combination of molecular modeling and experiment to elucidate the mechanism of this selectivity. The calculations yield good agreement with experimental binding affinities and indicate that hydrogen bonding is the dominant mode of adsorption of para-methoxyphenol onto XAD-7 from hexane. In contrast, ortho-methoxyphenol appears to form an intramolecular hydrogen bond that weakens the intermolecular hydrogen bond to the sorbent. As a consequence, ortho-methoxyphenol binds less strongly, and its association is dominated by van der Waals interactions and three-centered hydrogen bonds. This result is supported by quantum mechanical calculations and infrared spectroscopic experiments. It is also found that when water is the solvent, hydrogen bonding becomes an insignificant adsorption mechanism, and both molecules bind to the resin via nonpolar interactions. This explains the loss of selectivity that is observed in both experiment and calculation.

Adsorptive removal of phenol from aqueous phase by using a porous acrylic ester polymer

“…Such specific interaction may play a positive role in phenol adsorption from aqueous solution [22], however, it will be effectively weakened in aqueous solution due to the competitive effect of water [17].…”

“…In China these polymeric adsorbents have been widely used in industrial settings for removal and even recovery of organic pollutants including phenolic compounds from chemical effluents [10][11][12]. As a family of polymeric adsorbents, acrylic ester polymer has been demonstrated for effective removal of phenolic compounds from the organic mixtures mainly through the hydrogen bonding interaction between the hydroxyl group of phenolic compounds and the carboxyl group fixed in the matrix of the polymeric adsorbent [15,17]. However, we have little knowledge of any studies involving the removal of phenolic compounds from aqueous phase by using an acrylic ester sorbent as adsorbent [18].…”

Enhanced Hydrogen Bonding for the Adsorptive Recovery and Separations of Oxygenated Aromatic Compounds from Renewable Resources

“…40,41 In previous studies, we used ethylpropionate (EP) as a small-molecule analogue of the acrylic ester's binding site. 6,7,28,42 Experimentally, we used infrared (IR) spectroscopy to measure shifts in the O-H stretching frequency that result from hydrogen bonding. Often, the frequency shift (∆ν OH ) correlates with the strength of the hydrogen bond.…”

Modeling Molecular Recognition: Theory and Application

“…We have studied the role of intra-versus intermolecular hydrogen bonding in the differential adsorption of OAC's onto XAD-7 from hexane for six phenol derivatives (32,33,34) (Figure 2). Applying spectroscopic and computational methods directly to adsorption onto the acrylic ester resin is difficult because the sorbent is not readily soluble in hexane and the structure of the sorbent surface is incompletely characterized.…”