Use of Adsorbents For Recovery of Acetic Acid From Aqueous Solutions Part I – Factors Governing Capacity

Measurements have been made of the preferential uptake of acetic acid from aqueous solutions onto activated carbons and polymeric sorbents. Interpretation of the data shows that adsorption properties are determined by surface area and chemical effects. For styrene-divinylbenzene macroreticular resins, adsorption densities are nearly identical to those at the liquid-vapor interface, indicating that adsorption behavior is dominated by aqueous-phase non-idealities. The capacities of basic polymeric sorbents can be interpreted in terms of the degree of saturation of basic groups, and in terms of relative basicities, which were gauged through Gutmann Donor Numbers, the solvatochromic basicity parameters of Kamlet, et al., Hammett Parameters, and values of pK_a determined by titration. Low solvatochromic acidity parameter or Acceptor Number is also important for capacity, so as to reduce competitive sorption of water. The adsorption properties of activated carbons with different surface densities of heteroatoms can be rationalized through a simple model based upon the existence of a uniform, selective adsorption layer. Differences in the degree of surface heterogeneity are probably also important. The effect of the pH of the aqueous phase upon capacity can be interpreted through a two-solute competitive adsorption model, involving ionized and un-ionized species.