The article was published on the Estonian news portal Novaator. 

Humans have probably been using fuels for thousands of years. At first, mainly wood, agricultural waste, and dried manure was used, depending on what was available. Since the 17th century, people have been using coal, which was mainly used in England at the end of the 18th century and beginning of the 19th century. Oil and its products were added in the middle of the 19th century. Coal and oil are used as energy sources to this day.

Fat, herbaceous plants, and sugar beets could also be used

If we focus on fuels that could also be widely used in transport, we should take a closer look at gaseous and liquid fuels. So far, oil products such as petrol, diesel, and compressed and liquefied gas have predominated. In principle, however, liquid fuels could be produced from almost anything that contains carbon – biomass (e.g. wood, herbaceous plants, oil plants, algae, sugar cane, corn, sugar beet), plastic, food waste, agricultural waste (e.g. straw, manure, fat), or rubbish.

Broadly speaking, production methods can be divided into biochemical and chemical. In the first case, the carbon in the source material is converted into so-called biogas, ethanol or a mixture of fatty acids using enzymes or micro-organisms.

In the second case, a carbon-rich substance is gasified at a high temperature of 800–1000 °C to produce syngas. This in turn can be used immediately as a fuel or further processed to produce alcohols, methane or petrol, and diesel. The use of pyrolysis can also be considered here, in which case a substance rich in organic matter is mainly turned into liquid fuels, which could also be used as a raw material for the chemical industry instead of incineration.

The increasing role of hydrogen

Hydrogen, which is being proposed as an alternative to oil-based energy sources, will play an increasingly important role in the future. Hydrogen is produced industrially either from water by electrolysis – and if we use wind or solar energy, we get so-called green hydrogen – or from methane by steam evaporation. The latter is the most prevalent today, but needs non-renewable resources.

In addition, laboratory experiments are under way to produce hydrogen with the help of microorganisms, which in the course of their life produce hydrogen from biomass, i.e. from their own food. This has also led to combined microbial electrolysis cells that produce hydrogen from degradation products of microbes such as acetic acid. In this case, unfortunately, carbon dioxide (CO2) is also produced, which the modern society is trying to avoid.

Finally, let's take a brief look at the possible future role of CO2. Carbon dioxide itself is also a widespread carbon-rich raw material and thus a source of carbon, for example in the production of fuels. It can also be used to make various products such as methanol, methane, petrol, and diesel. In Iceland, for example, methanol is already produced using geothermal energy, demonstrating that this process could be introduced in other parts of the world.

The future with wind, solar, and nuclear energy

It can be assumed that in the future, our energy sources will be various combinations of wind, solar and nuclear energy and the main energy sources will be electricity, hydrogen, and carbon-rich liquid fuels from biomass or carbon dioxide.

*As of October, the researchers of Tallinn University of Technology answer the questions of readers of the ERR science news portal Novaator on topics that require clarification or are of current interest.