A concept for a continuous supercritical drying process for the efficient production of aerogel particles is presented and proven experimentally. A process design involving a countercurrent extraction column with freely sedimenting aerogel particles is proposed and the influence of operating parameters such as temperature, pressure, and CO 2 load on the process is discussed from a theoretical point of view. A proof of concept of the most promising design is demonstrated through the successful countercurrent drying of alginate aerogel particles. At a column length of 1.0 m, dry aerogel particles could be obtained at the bottom of the column with ethanol outlet mass fractions up to 46% at the top of the column. Drying of aerogel particles at a shorter column length of 0.5 m could be achieved by increasing the CO 2 flow rate, resulting in a reduced ethanol outlet mass fraction of 20%. Further development of the continuous drying concept is discussed.
The
first evidence of solvent spillage under subcritical conditions
during aerogel production is presented. The main objective was to
understand the underlying phenomena controlling the solvent extraction
kinetics during autoclave pressurization. Alginate, silica, and polyurethane
as gels and ethanol, methyl ethyl ketone, and ethanol/water as solvents
were investigated. When CO2 diffuses in the gel solvent,
there is a volume expansion of the liquid solvent. This expanded liquid
mixture spills out of the gel and accumulates as a separate liquid
phase at the bottom of the autoclave. A lag time was observed between
the start of the autoclave pressurization and the moment in which
liquid starts to accumulate in the autoclave. The time needed for
the solvent to start accumulating at the bottom of the autoclave is
controlled by capillary forces and the saturation of the CO2-gas phase, on which temperature has an important effect. Low operating
temperature and thereby low solubility of the solvent in the gas phase
is suggested as the factor that enhances the kinetics of solvent removal
at subcritical conditions.
Two new high-performance insulation materials (HPIM) for the usage in buildings are presented. We show how to use and apply the upcoming aerogel products and give examples for structural details. While both materials achieve very low lambda values due to Knudsen-Effect of aerogels, they differ clearly in other key characteristics. SLENTEX® is a slim, mechanically flexible, non-combustible aerogel mat. It is open for water vapor diffusion but water-repellent. It is suitable for applications with strict fire regulations since it is a purely mineral-based product. SLENTITE® is a homogeneous polyurethane-based aerogel insulation board without lamination or encapsulation layers and also vapor open. Its surface adheres to almost any organic or inorganic binder. It can be processed very much like conventional insulation boards. While their handling and application are very similar to other insulation materials, aerogels are however no general-purpose insulation products: due to their sophisticated production process, and thus higher price compared to conventional insulation products, HPIM are best applied as problem solvers. In well-motivated situations, e.g. where space is limited or particular aesthetic requirements apply, they offer cost effective alternatives to standard solutions.
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