The aviation of the future will need carbon-based fuel for long-haul flights. This is because today's jet fuel has a very high energy density compared to alternative energy carriers such as hydrogen and electrical energy. However, this type of fuel does not have to come from fossil oil but can be produced from renewable carbon sources such as biomass. This could be, for example, wood, slaughter waste, or food waste from private households.
Through a technology called biomass gasification, the biomass reacts with steam or oxygen at high temperatures (typically 700-900 °C) and is broken down into simple molecules such as hydrogen and carbon monoxide (synthesis gas). The synthesis gas can further be assembled into long hydrocarbons (aviation fuel). However, the synthesis gas also contains tar, which must be removed before the gas can be used. The tar substances can be removed through decomposition at high temperatures, or under milder conditions using a catalyst. A catalyst is a material that increases the rate of a chemical reaction.
Through research associated with Bio4Fuel's WP 4.2, PhD student Ask Sødahl Lysne has worked on developing nickel-cobalt-based catalysts that remove tar from synthesis gas through a process called steam reforming. With the help of the catalyst, the tar substances react with steam and form hydrogen and carbon monoxide (more synthesis gas). The catalysts are produced in the laboratory, then characterized and tested in an experimental setup where effects of the catalyst's composition, as well as factors such as tar composition, temperature and steam concentration can be studied.
By combining the active metals nickel and cobalt, the lifetime of the catalyst can be increased, compared to a traditional nickel catalyst. This is because cobalt reduces the amount of deactivating carbon compounds formed on the catalyst's surface.
The catalyst effectively removes the tar substances in the synthesis gas and produces a clean gas ready for further use. Through systematic screening of operating conditions, critical limits for temperature and tar concentration have been identified, which are decisive for the catalyst's performance and lifetime. The composition of the tar is also important, where heavier tar components form strongly deactivating carbon compounds in the catalyst. This is important knowledge for the future integration of biomass gasification and catalytic steam reforming.