Adsorption of Diols on Silica Gel Modified by Phenylboronic Acid

Abstract

Diols are key intermediate materials for polymers. Conventional distillation techniques for the separation of diols require a substantial energy input. Alternatively, in this paper we examine an adsorption technique to recover and separate diols. Silica gels modified by boronate were used as a selective adsorbent for diols. First, using potentiometric titration, we examined the number and pK_a of the active site included in the gels. The values of the pK_a of the boronate were larger than that of phenylboronic acid. From the adsorption experiments on the resin, we found that main adsorption mechanism was a complex formation between neutral boronic acid and the diols. A pH value smaller than pK_a (=10) of boronate is desirable for the adsorption of diols. Silica gels modified by phenylboronic acid effectively adsorbed the hydrophobic diols. The adsorption capacity of vicinal and 1,3-diols were similar.