The range of applications and the different types of aerogels are diverse and steadily growing. Whereas the general production process can be divided into three major steps for all aerogel types: 1) Gelation Step 2) Solvent Exchange 3) Supercritical drying. Due to high demands on time and energy as well as the necessity to use high pressure technology equipment, the supercritical drying step causes comparatively high costs, which could be reduced via different process optimization strategies.
So far, supercritical drying is carried out in time-consuming batch processes, which are energy and cost-inefficient. In previous works, it was shown, that continuous supercritical drying of wet gel particles is possible for the production of dry aerogel powders. Therefore, are counter-current 1 m high column was set up. To be able to convey the particles into the column, excess solvent is used. The particle suspension enters the column at the top. During their fall through the column, particles are dried and leave the column at the bottom in a completely dry state. The supercritical CO2 enters the column at the bottom and exits at the top, loaded with the extracted solvent. The excess solvent of the suspension also enters the column. Therefore, a solvent profile will build up inside the column, increasing the system's complexity.
A deeper understanding of the system needs to be developed to improve the process and make it even more efficient. Crucial for a successful drying is the residence time of the particles in the column, which needs to be longer than the drying time on the one hand. But short enough to provide an efficient process on the other hand. Many parameters influence the residence time, e.g. the process parameters like pressure, temperature, CO2 flow, or particle flow. Additionally, particle parameters like density, porosity and particle diameter play a major role. To determine the residence time, two view cells at the top and the bottom of the column are installed. With the help of fluorescent particles, which are used as tracers and a python program to track those particles, the residence time can be experimentally determined.
In this work, the residence times for various particles with several process parameters are to be obtained. Based on experimental empirical data, a model with Comsol will be built, to be able to calculate optimized process parameters for all different kinds of Aerogels.
