As synthetic fuels (engl. Synthetic fuel, synfuel), certain fuels referred to, which (from conventional fuels diesel , gasoline , kerosene , etc.) are distinguished by a more expensive production method (change in the chemical structure). A characteristic of some is the replacement of crude oil as a raw material source. The XtL fuels, for example, can have similar properties to conventional fuels, but use natural gas ( GtL ), coal ( CtL ) or biomass ( BtL ) as raw materials . Other types of synthetic fuels allow an increase in the performance of the combustion engine ( methanol , ethanol, etc.) or are used for special tasks, such as rocket fuel ( hydrazine , syntin, etc.). Very different definitions are used. In some cases, gaseous fuels ( hydrogen , methane ), oil products from unconventional raw material sources ( oil sand , oil shale ) and others are also counted among the synthetic fuels.
Definition of the term "synthetic fuel"
Different definitions for “synthetic fuel” are in use. On the one hand, “synthetic” means that the fuel is produced artificially. Conventional fuels, on the other hand, are mostly produced by separating the complex crude oil into individual fractions ( distillation , rectification ) without the components being chemically changed. Various chemical processes can be used in the manufacture of artificial fuels. On the other hand, “synthetic” can be used to emphasize that the fuel was produced by chemical processes known as synthesis , i.e. the production of a higher compound from several lower compounds. This definition applies in particular to XtL fuels, in which the raw material is first broken down into a synthesis gas made up of lower compounds (H 2 , CO etc.) in order to produce higher hydrocarbons from it ( Fischer-Tropsch synthesis ). However, synthesis does not only take place with XtL fuels. Chemical processes can also be part of the manufacturing process for conventional fuels. For example, very long-chain hydrocarbons can be broken down into shorter-chain products, such as those found in gasoline or diesel, by so-called cracking . Thus, depending on the definition, it may not be possible to distinguish it clearly from synthetic fuels. Another example is biodiesel , where a chemical change occurs when it is produced from methanol and triacylglycerides , but the product is still usually not counted among the synthetic fuels.
There is therefore no precise definition. Most of the time, however, the term “synthetic fuel” is restricted to XtL fuels.
Types of synthetic fuels
The various synthetic fuels differ from conventional fuels, mostly made from petroleum. Depending on the type of synthetic fuel, these properties are determined by the raw material used, the manufacturing process, energy content, combustion behavior, etc.
XtL fuels (“X-to-liquid”) are liquid fuels with similar properties and composition to conventional, petroleum-based fuels. Other raw material sources (gas, coal, biomass) can be developed. Since the product is used in common internal combustion engines and can be sold via the existing infrastructure ( filling station network ), it is easier to launch it than for example with electric vehicles .
The manufacturing process begins with the production of synthesis gas and the subsequent synthesis of various hydrocarbons using Fischer-Tropsch synthesis . Another method is the Bergius Pier method . Similar to crude oil in a petroleum refinery , the product is separated into fractions by distillation and rectification. Among other things , gasoline , diesel and aircraft fuels can be produced. Their properties are similar or better than those of petroleum-based fuels. The lack of nitrogen and sulfur compounds and aromatic hydrocarbons , for example, contributes to lower pollutant emissions. Since the manufacturing process is energy-intensive, there can also be ecological disadvantages, for example due to higher CO 2 emissions.
Liquid fuels made from natural gas are referred to as GtL fuels ("gas-to-liquid"). Mostly natural gas is used for this, which is extracted far from the market, often as a by-product of oil extraction. Using the accompanying natural gas is often uneconomical because of the high transport costs, so that the gas is often flared. By converting it into GtL, the energy density is increased many times over, so that the transport can now be economical. Fuels with low proportions of GtL are offered on the German market.
CtL fuels (“coal-to-liquid”) are made from coal. The complex production is becoming increasingly economical, since the oil price shows an upward trend and coal can be mined inexpensively. The production capacities are therefore currently being expanded significantly. Because of the high CO 2 emissions, however, the CtL fuels are heavily criticized.
BtL fuels (“biomass-to-liquid”, also known as synthetic biofuel ) are made from biomass. Since plant residues ( straw , wood waste) and renewable raw materials (Nawaros) can be used as raw materials , the CO 2 emissions are significantly lower than with conventional fuel. However, the limited potential is criticized due to the high space requirement and the competition for space , as well as the high production costs. A first plant from Choren Industries (Freiberg), which, according to forecasts, should generate around 0.3% of German fuel requirements at 15,000 t / a, could not be operated economically. On July 6, 2011, the preliminary insolvency administration was ordered for the assets of Choren Industries GmbH.
Examples of other synthetic fuels
Numerous other types of fuel are known as synthetic fuels:
Synthesis gas products
In addition to the XtL fuels, other fuels can also be produced from synthesis gas:
- Methanol is mainly produced from synthesis gas.
- Dimethyl ether (DME) is produced via the intermediate step methanol.
- SNG ( Synthetic Natural Gas ) can be based on synthesis gas.
- Hydrogen (H 2 ) can be obtained from synthesis gas, among other things. Since no synthesis step is necessary for this, it is not necessarily referred to as a synthetic fuel.
- Oxymethylene ethers are produced from synthesis gas using formaldehyde and methanol
Numerous types of fuel for special tasks are produced using chemical processes. They are used in their pure form or are added to conventional fuel or other synthetic components:
- Acetone can be used as an admixture for internal combustion engine fuel.
- Hydrazine is used, among other things, as a rocket fuel.
- Benzene is made from coal or petroleum. Since it is poisonous, its importance as a pure fuel or fuel additive has greatly decreased.
- MTBE ( tert -butyl methyl ether) is a synthetic additive to petrol that increases the knock resistance .
- ETBE ( tert-butyl ethyl ether) has the same function as MTBE, but is not produced from fossil raw materials.
- Definition of Synfuel in the IEA report Tracking Industrial Energy Efficiency and CO 2 Emissions . ( Memento of the original from March 31, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) Paris 2007.
- Chemnitz District Court, file number: 14 IN 1970/11.
- Automotive industry: Choren is broke ( Memento from July 22, 2012 in the web archive archive.today ).
- Synthetic fuels from synthesis gas ( Memento of the original dated August 28, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Analysis of the VDL (2005).