Nanotechnology in cleanrooms

Medicines must be produced in sterile conditions. Industry and research organisations use hydrogen peroxide for disinfection and sterilization but the extremely reactive oxidizing agent must not come into contact with humans, reagents and products. Therefore researchers at the Institute of Chemistry and Bioanalytics working with Skan AG have developed a catalyst system to break down hydrogen peroxide more efficiently. The nanotechnology- based manufacturing process is simple and scalable.

In the pharmaceutical industry, product purity is everything. To ensure this quality, strict conditions must be met during production, packaging and analysis; micro-organisms and germs must not come into contact with pharmaceutical products. In cleanroom environments therefore, both industry and research use so-called containments: isolators and workbenches, separated from the ambient air by filter systems which can be decontaminated automatically. For their disinfection and sterilization, pharmacists and food technicians use evaporated hydrogen peroxide. The H2O2 molecule is a very reactive oxidant due to an oxygen-oxygen single bond; it reliably destroys bacteria and other microorganisms. There is a catch though: hydrogen peroxide reacts just as quickly with other organic substances, including active ingredients in medicines. To avoid this, an insulator must not contain any hydrogen peroxide when in use.

The traditional method of removing hydrogen peroxide from the isolator is by ventilation with large quantities of sterile air. In order not to simply discharge this air and hydrogen peroxide mix into the environment, it is circulated in a closed system through a catalyst which converts the remaining hydrogen peroxide into harmless water and oxygen. However, conventional catalysts do not work efficiently unless the air is warm and a powerful fan is needed to overcome the high pressure differential of about 1100 Pascals and penetrate the catalyst. These temperature and pressure criteria increase energy consumption and therefore costs.

In order to reduce air volume, energy costs and time, a team of researchers led by Uwe Pieles at the Institute of Chemistry and Bioanalytics (ICB), in collaboration with the market leader in insulators, Skan AG, have developed a more effective technology. In a project funded by the Swiss Nanoscience Institute and the Commission for Technology and Innovation, the new process was ready for the market within four years. Pieles and his team have succeeded by using nanotechnology. Instead of applying the catalyst on a solid support material as before, the researchers coated porous ceramic spheres with a layer of metallic nanoparticles and the catalyst. The porosity of the carrier material creates an enormous surface area and thus much more capacity for catalysis. For example, a 50 x 50 cm module with the new technology achieves a surface area of about one hundred soccer fields. “The layer can only be a few nanometers thick, otherwise the pores would become clogged. However, it cannot be too thin, or sufficient catalysis does not take place”, explains the director of the ICB, Gerhard Grundler. The exhaust air penetrates from the insulator into the pores; the large surface area guarantees a high hydrogen peroxide decomposition rate.

In order to find the right catalyst, research- ers analysed and tested various materials using computer simulations. During simulated ageing experiments for example, the research team found a metal compound that can be used for more than ten years. “A good catalyst does not wear out with time because it is not involved in the reaction but only mediates between the reagent and the product”, says Grundler. In addition to the search for the right catalyst, the HLS researchers also solved the problem of packing the material as closely as possible into a catalyst module. As a result, they were able to reduce the pressure at which the exhaust air is forced through the catalyst by 80%. Finding the right combination of catalyst, carrier material and packing density makes the higher efficiency possible. Grundler explains: “The highly efficient catalyst allows us to circulate the air: we extract the air from the isolator and after catalysis it is sent back. The heat thus remains in the building and is not wasted.” This makes the catalyst process independent of a complex ventilation system and the insulator can be used much more flexibly.