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Industrial by-products upgraded into fuel

18 October 2011 Suomen Akatemia (Academy of Finland)

Researchers have achieved good results in using waste and other excess products from industry to develop new and innovative fuels for transport. Working within the Academy of Finland’s research programme Sustainable Energy (SusEn), researchers have studied the processing of both biobutanol and biogas into transport fuels. Biobutanol can be produced from by-products of the food industry and the pulp and paper industry, which makes it a suitable candidate for replacing petrol as a fuel. Methane derived from biogas is also a top candidate for a fuel substitute, as shown in life-cycle assessment, which measures the entire production chain.

“Butanol is a very energy-efficient alternative and, like ethanol, lends itself well for industrial-scale production,” says Professor Ulla Lassi from the University of Oulu, who has been working on a research project investigating the use of biobutanol as a transport fuel. Butanol production is a microbiological process where raw material is converted into sugars and further processed using microbes. The microbes efficiently turn carbon compounds into butanol. Butanol contains more carbon than ethanol does and is therefore also more energy-efficient.

Lassi’s project has also studied the production of butanol via chemical synthesis, which uses novel catalyst materials to convert compounds such as glycerol, methanol or ethanol into alcohols such as butanol, pentanol and alcohol mixes. These are directly suitable as liquid fuels. According to Lassi, using glycerol in fuel production could be quite cost-efficient, as it is a by-product of biodiesel.

There are a number of challenges in the microbiological production of butanol. One of the main challenges concerns the digestion of the raw material to fermentable sugars. In addition, the multi-stage fermentation is in itself a very complex process. Another major challenge is that the fermentation process is inhibited by high solvent contents, which combined with instability in solvent production may also cause a drop in microbial activity.

Lassi explains: “Recent breakthroughs in butanol fermentation techniques have partly solved these problems. However, if we want to produce new liquid fuels, we need completely new chemical synthesis routes and catalyst development.”

The research project investigating the production of biobutanol involves researchers from the University of Oulu and Åbo Akademi University.

Once landfill gas, now fuel

Another research project within the SusEn research programme has looked at the use of biogas as a transport fuel. As a joint Finnish-Chilean effort, the researchers studied the upgrading of landfill gas into fuel. “In recent years, interest in using biogas technology in the utilisation of industrial by-products for energy purposes has increased considerably. Some countries have already introduced this technology on a large scale,” says Professor Jukka Rintala, the principal investigator of the project.

Biogas can be produced from many different materials ranging from biodegradable waste to energy crops. “The biogas produced in this process is a versatile source of energy. It can be used for heat and electricity, be processed into vehicle fuel or fed into the natural gas grid. In addition, the residual material, the so-called digestate, from the process can be used as fertilizer or soil conditioner,” Rintala explains.

Methane derived from biogas has been shown to be one of the most suitable candidates for use as biofuel, thanks to its sustainable production chain. Methane also meets the EU’s criteria for sustainable biofuels, which will take effect in a few years’ time.

The experiments in Rintala’s project were carried out at the Mustankorkea Waste Treatment Facility in Jyväskylä and they particularly focused on the fate and removal of trace compounds of biogas. “Biogas can be used as a biofuel once its methane content is raised above 95 per cent. In our research, we used water absorption, which yielded a methane content of 80–90 per cent. The rest is carbon dioxide and nitrogen.”

Nitrogen does not cause any damage to car engines, but it does lower the energy content of biogas. “To reach a higher methane content through this process, we should prevent the access of nitrogen in the gas collection system in the landfill. Carbon dioxide does not damage engines either, but it lowers the energy value of biogas,” says Rintala.

Rintala would like to see more research on the effects of process parameters on the costs of biogas upgrading and the effects of pressurisation on compound removal. “As a rule, the only criterion for biomass is that it can be broken down by microbes under oxygen-free conditions. Of course, the composition of feedstocks does affect the composition of the biogas produced and also the chosen method of purification. Landfill gases are generally thought of as being the most difficult ones to upgrade into fuel.”

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