Mass transfer phenomena in the processing of biopolymer aerogels: in situ study and modeling
Aerogels based on bio-polymers and especially those which are based on naturally available proteins are a new class of highly porous material. Their enormous potential for the food- or pharma-sectors as low-calorie ingredients, taste masking materials, selective adsorbents or as packaging material, are based on their biocompatibility and porosity. The (i) solvent exchange and the subsequent (ii) drying process in compressed carbon dioxide (CO2) are the two crucial process steps during the generation of bio-polymer-based aerogels. The kinetics of both process steps in combination with the thermodynamics relevant for the gel’s interior, determine the costs as well as the quality of the product.Within this project, concentration profiles are determined in the gels’ interior and outside the gels during the solvent exchange and drying processes using optical measurement techniques. Internal and external mass transfer resistances are derived from the concentration profiles. The found resistances are correlated with the properties of the obtained gels and the flow conditions around the gels and are reflected in mass transfer models for porous material. Based on these models the solvent exchange as well as the drying process can be optimized with respect to the costs and quality of the product.