Alcohol is used as fuel


Lexicon> Letter E> Ethanol

Definition: the most common form of alcohol

Alternative terms: ethyl alcohol, spirit

Molecular formula: C2H5OH

English: ethanol

Category: Energy sources

Author: Dr. Rüdiger Paschotta

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Original creation: 01/26/2013; last change: 02/21/2021


Ethanol (also Ethyl alcohol or spirit) is the most common form of alcohol - the form of alcohol that is also found in alcoholic beverages such as wine and beer (potable alcohol).

density0.79 kg / l
calorific value26.8 MJ / kg = 7.4 kWh / kg,
21.2 MJ / l = 5.9 kWh / l
Calorific value29.7 MJ / kg = 8.25 kWh / kg,
23.4 MJ / l = 6.5 kWh / l

At room temperature and normal pressure, ethanol is a colorless liquid with a boiling point of 78 ° C. The ethanol molecule has the chemical formula C.2H5OH; it is similar to the ethane molecule, but there is an additional oxygen atom between the carbon atom and one of the hydrogen atoms.

Ethanol is a cell poison and, if taken in large quantities, can cause severe alcohol poisoning. However, it is much less toxic than the chemically related methanol.

Ethanol is highly flammable and burns clean to carbon dioxide and water in the air. It can thus serve as an energy source, for example as fuel for gasoline engines, also for admixture with gasoline (see below), and as fuel, e.g. B. in the form of denatured alcohol. The calorific value of pure ethanol is 26.8 MJ / kg or 21.2 MJ / l.

Manufacture of ethanol

Drinking alcohol is produced through the fermentation of sugars or starches from biological materials, i.e. through the activity of bacteria and yeast. Ethanol, which is also used as an energy source, is often obtained by fermenting biomass. Part of the energy in the biomass is lost and carbon dioxide is produced. Suitable starting materials are, for. B. corn, sugar beet and wood waste. Since these are biological substances, one speaks of Bioethanol - which does not mean that the production has to be particularly environmentally friendly. After all, bioethanol is one of the renewable energy sources.

The concentration of ethanol in fermentation is limited to around 15% because the microorganisms responsible for fermentation die at higher concentrations. The concentration can then be increased to over 90% by distillation. In industry, the more sophisticated process is the Entrainer rectification used to get to much higher concentrations.

Ethanol can also be produced industrially, e.g. B. from ethene (C.2H4) and water (H2O) with the help of sulfuric acid or phosphoric acid as a catalyst. Other possibilities are the catalytic hydrogenation of acetaldehyde and the production of carbon monoxide and hydrogen. Ethanol produced in such a way is called Industrial alcohol used, e.g. B. as a solvent or as a fuel. For example, denatured ethanol is used as Denatured alcohol sold that can be used in camping stoves. Ethanol is also often used as a disinfectant or preservative.

Taxation and Denaturation

Ethanol is subject to the spirits tax unless it can be proven that it is used for purposes other than human consumption. Ethanol intended for other purposes is denatured for the addition of certain bad-tasting and difficult-to-remove substances in order to prevent abuse for human consumption (bypassing the spirits tax).

Bioethanol admixtures for gasoline

Ethanol can be used in its pure form as a fuel for gasoline engines, but also as an additive to gasoline. For example, the type Super E10 contains ten percent by volume of bioethanol. This admixture has advantages, but also disadvantages and problems. The article on gasoline explains this.

In its pure form, ethanol is used relatively rarely as a fuel. For use in gasoline engines, it offers some significant advantages over gasoline, in particular a very high knock resistance (RON 114), a high specific evaporation heat (improved internal cooling and thus a better filling level of the engine) and a comparatively high exhaust gas quality. However, various adjustments to engines are necessary for the use of ethanol. For example, many of the plastics that are often used in engines do not tolerate concentrated alcohols and, due to the low vapor pressure, the cold start behavior can only be sufficiently robust with supportive measures, for example by preheating the intake air. An engine that has been completely optimized for the use of ethanol (with a high compression ratio and correspondingly high efficiency) can work quite energy-efficiently, but can then no longer be operated with gasoline. For such reasons, it is more advantageous to use bioethanol mostly as an admixture to gasoline, which is consumed in very large quantities. Only comparatively minor adjustments to the motors are necessary for this.

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See also: bioethanol, methanol, fuel, gasoline, energy carriers, renewable energy
as well as other articles in the energy source category