Ethanol as a petrol substitute: how to turn wood into fuel

The use of bioethanol as fuel reduces the emission of greenhouse gases such as CO2. Up until now, bioethanol has been produced almost exclusively from sugar cane and corn starch and has therefore competed with the production of food and fodder. But ethanol can also be obtained from lignocellulose such as wood, which is potentially available in large quantities in Switzerland.

Because the process is technically more demanding, it has not been economically viable in large-scale production. The project has now shown that the existing biotechnical process can be improved. The key task is to degrade the lignin because it inhibits the conversion of complex carbohydrates (cellulose and hemicellulose) into simple sugars. This was achieved by adding lignin-degrading fungi strains to the reactor.

The production of biofuel from biomass that could potentially be used as food or fodder is politically not desirable in Switzerland. But wood, of which the country has a plentiful supply, could be used as a raw material for second-generation biofuels. The disadvantage of wood is that it contains lignin, which hampers the degradation of cellulose and hemicellulose into monosaccharides. If wood waste is to be used to produce bioethanol at an industrial scale, the conversion of cellulose and hemicellulose into simple sugars must be made easier and become much cheaper.

Lignin-rich wood, e.g. beech wood, is difficult to convert into ethanol using biotechnology. For this reason, the researchers added lignin-degrading fungi strains to the microbes that had been used so far. As a result, the production and reaction rate were improved and less energy was used in the pre-treatment stage.

To reduce the climate impact and make better use of Swiss wood, it makes sense to replace petrol and diesel with ethanol made from wood. The studied process offers the potential to produce ethanol sustainably and in decentralised facilities. This would keep the road miles of the necessary biomass minimal.

Using the process, it was possible to obtain maximum yields of sugar and ethanol while reducing the input of energy to a minimum. A two-stage process was used to maximise the amount of hemicellulose obtained and minimise the production of inhibitors.

A newly constructed reactor with a 3.6 litre capacity showed that the process also functions in a stirred-tank reactor, which is favoured by the industry and can be upscaled.

The project did not only improve the output, it also reduced the energy input. In addition, the consolidation of the process made it more economically viable.

Enhanced direct fermentative production of chemicals from forestry residues in a membrane biofilm reactor by enzymatic in-situ delignification