Adsorption of short-chain alcohols by hydrophobic silica aerogels

The hydrophobic silica aerogel Cabot Nanogel TLD302 was evaluated as an adsorbent for recovering 2-5 carbon n-alcohols from aqueous solutions. Whereas intraparticle transport limitations restricted adsorption under dilute conditions, at higher concentrations, improved surface wetting resulted in facile "pore intrusion" and ∼5-fold increases in adsorption capacity for all alcohols. To promote surface wetting and pore intrusion at lower concentrations, partial oxidation of TLD302 was performed by heat treatment to create a series of novel aerogel materials with tunable surface hydrophobicities. An optimum surface oxidation state was found to exist wherein pore intrusion under dilute conditions was achieved while still balancing high adsorption affinity. Lastly, the optimized aerogel adsorbent was used to recover n-butanol from a Clostridium acetobutylicum ATCC 824 fermentation broth. Relative to model solutions, no loss of adsorption affinity or capacity was observed, indicating that competitive coadsorption by other media components was not a performance-limiting factor.