Alginate aerogels as adsorbents of polar molecules from liquid hydrocarbons: Hexanol as probe molecule

Ionotropic gels of alginate, a polysaccharide, can be easily converted to aerogels of high surface area. The potential of alginate aerogels as adsorbents for trace polar contaminants in hydrocarbon feedstocks is evaluated, n-hexanol being used as a polar probe molecule. The influence of the nature of the gelling cation has been studied by testing Ca-, Ba-, Ni-, Co-, and Cu-alginate aerogels and a gel of alginic acid, formed by proton exchange of Na-alginate. Adsorption capacity can reach 15% hexanol (w/w) without any swelling of the gel. The amount adsorbed in the monolayer allows to evaluate the surface area of the adsorbent and confirms that the immersion in hydrocarbon does not modify the size and the dispersion of the polysaccharide fibrils. The comparison of the surface density of adsorbate with the structure of the surface indicates that hexanol is adsorbed on alginic acid by the formation of hydrogen bonds between the alcohol heads and two hydroxyls of the polymer surface. In the case of alginates gelled by divalent cations, stronger adsorption sites allows completion of a monolayer at lower concentrations of the polar molecule.