Supercritical drying of aerogels using CO2: Effect of extraction time on the end material textural properties

Aerogel technology provides high added-value lightweight materials with outstanding textural properties (i.e., high surface area and open porosity). Aerogels are obtained from wet gels by using a suitable drying technology, usually supercritical drying process, able to avoid the pore collapse phenomenon in order to keep intact the porous texture of the wet material. In this sense, the study of the kinetic profile of the gel supercritical drying is regarded as a key aspect to be considered in the specific case of the design of aerogel-based systems. In this work, the drying profile with supercritical carbon dioxide (scCO2) of alcogels (in ethanol) was determined using a customized supercritical fluid extraction equipment. The drying of alcogels from different precursors (inorganic-silica-, organic-starch-), densities (silica aerogel of densities 0.08 and 0.15 g/cm3) and morphologies (cylindrical monoliths, microspheres) was studied. Depending on the nature of the gel precursor, the extent of drying (i.e., drying time duration) gave significant differences in the end textural properties of the dried gel.

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► Aerogel sc-drying was studied regarding process kinetics and material properties.
► Diffusion is not the only mass transfer phenomenon involved in the sc-drying.
► Gel drying kinetics was influenced by the minimum diffusion path length.
► Si-aerogel textural properties were not improved above a threshold drying time of 2 h.
► Long sc-drying times is detrimental for the textural properties of starch aerogels.