Impregnation via supercritical CO2 - what we know and what we need to know

Impregnation of solid materials has drawbacks such as low diffusion, long contact times, and overdosing of impregnates causing pollution and high consumption of additives that can be overcome with CO2-intensified processes. Wood is already protected against biological deterioration in industrial scale by supercritical impregnation. Industrial plants for dyeing of fabrics are built in Asia at present. A number of processes are far advanced - giving hope for numerous applications in the coming years. In a process analysis addressing the unit operations mixing, sorption, expansion, and pretreatment advantageous design features for processes and products using pressurized CO2 are summarized. Four examples - impregnation of hip implants, of polycarbonate with silver nitrate, of nuts with antioxidants and reactive impregnation (tanning) of leather − illustrate that commercially competitive solutions can be derived and scaled up. Boundary conditions and empirical rules are suggested how CO2 can be used to generate impregnated materials.