Female waste picker at sisdole landfill in Kathmandu, Nepal. Photo: Tina Schoolmeester

Science and technology

A new study has explained how fuel can be produced from renewable sources such as waste wood and straw. The findings of the research were published in the journal 'Frontiers in Energy Research' in collaboration with the researchers at Straubing Campus for Biotechnology and Sustainability of the Technical in Munich (TUM) and Lappeenranta-Lahti University of Technology (LUT) in Finland.

According to the latest assessment report from the Intergovernmental Panel on Climate Change, a considerable reduction in CO2 emissions is required to limit the consequences of climate change. Renewable electricity would be one way to reduce carbon emissions from the area of transportation.

The study developed a new process for the production of ethanol, an established fuel that decarbonizes the transportation sector and can be a building block to reduce emissions of CO2 over the long term.

Ethanol is usually produced through the fermentation of sugars from starchy raw materials such as corn, or from lignocellulosic biomass, such as wood or straw.

Accordingly, offcut materials from the area of forestry are used together with hydrogen. The hydrogen is produced by separating water into hydrogen and oxygen with the use of electricity -- in other words, with the use of water electrolysis. In the future, this will allow the excess electricity to be used for the production of ethanol.

"The overall process mainly consists of technically mature sub-processes. However, the composition of the process steps and the final step -- the hydrogenation of acetic acid to produce ethanol -- are new," said Daniel Kluh, a doctoral student at the Professorship of Renewable Energy Systems at the TUM Straubing Campus.

The researchers have also assessed the economic feasibility. "The prices we have calculated are based on assumptions for raw materials and energy. We are not using any current market prices. The calculation basis of our prices for the components in the chemical system is the year 2020," said Kluh.

The lowest cost for ethanol in the modelling was 0.65 euros per litre, with biomass costs of 20 euros per megawatt-hour, electricity costs of 45 euros per megawatt-hour, and a production volume of approximately 42 kilotons of ethanol per year.

"With the current lignocellulosic ethanol production options, the costs are therefore competitive. The price of ethanol is very sensitive to the costs of electricity, and fluctuates between 0.56 and 0.74 euros per litre," explains Assistant Professor Kristian Melin of LUT in Finland.

One reason for the high profitability is that the ethanol yield is much higher compared to the traditional fermentation-based bioethanol process from straw or wood. This process produces 1350 to 1410 litres of ethanol, compared to only 200 to 300 litres of ethanol for the traditional process per dry ton of biomass.

The study is also focusing on the variable geographical positioning of production sites, which would enable a degree of independence from suppliers to be achieved. "Countries with a high potential for waste wood and green electricity, such as Finland or even Canada, can serve as producers of acetic acid, which, in the final process step, is hydrogenated to produce ethanol," said Prof. Tuomas Koiranen of LUT.

"In the future, countries like Germany will hopefully have a green electricity mix and will be able to carry out the hydrogenation of acetic acid to ethanol at a domestic level. However, Germany does not have the waste wood potential for large-scale biomass gasification which is required for the synthesis of acetic acid," added Prof. Matthias Gaderer, Professor of Renewable Energy Systems at TUM.

With the use of green electricity to power the electrolysis, this process can produce a low CO2 fuel that has a greenhouse gas reduction potential of 75 per cent in comparison with a fossil fuel such as gasoline. Ethanol is established as a fuel.

It can be used in the form of both E-10 gasoline, with 10 per cent ethanol in the fuel mixture for regular automobiles, as is already the case, or as ED95, which is 95 per cent ethanol, as a diesel substitute for heavy goods transportation.

With their process simulation, the scientists have demonstrated the competitiveness of the process. "To commercialize this product, it is necessary to further improve the degree of technological maturity. The next steps could entail further catalyst developments, a reactor design and the construction and operation of a pilot system," said Prof. Gaderer.

Source: ANI