Adsorption of organic compounds in vapor, liquid, and aqueous solution phases on hydrophobic aerogels

The kinetics and equilibrium capacity for adsorption of six volatile organic compounds (VOCs) in the vapor, pure liquid, and aqueous solution phases on commercially available hydrophobic silica aerogel granules (Cabot Nanogel) were studied at room temperature. Very different rates of adsorption were observed depending on whether the vapor, liquid, or solution phases were used. Adsorption of vapor is very slow due to the extremely low thermal conductivity of the aerogel. Effects of heat of adsorption are minimal for the liquid and solution phases, and the faster adsorption rates observed in these two cases are controlled by the mass transport of the organic compounds, either by capillary flow for the adsorption of liquids, or by vapor diffusion/adsorption for the adsorption of the organic compounds from water solutions. The equilibrium adsorption capacities of the aerogel were measured and compared to other sorbents for similar VOCs for the three different phases. The adsorption capacity of the commercial aerogel from the vapor phase studied in this work is higher than that of two other hydrophobic aerogels that were synthesized in the laboratory using supercritical drying, and much higher than that of two commercial sorbents (silica gel and activated carbon). The volumetric sorption capacities of all of the organic liquids studied on Nanogel are all around 16 mL/g. The equilibrium adsorption capacities of the six VOCs from aqueous solution increase in the following order: benzene < trichloroethylene < toluene < chlorobenzene < p-xylene and o-xylene.