E-diesel is a synthetic diesel fuel created by

Audi Audi AG () is a German automotive manufacturer of luxury vehicles headquartered in Ingolstadt, Bavaria, Germany. As a subsidiary of its parent company, the Volkswagen Group, Audi produces vehicles in nine production facilities worldwide. Th ...

for use in automobiles. Currently, e-diesel is created by an Audi research facility in partnership with a company named Sunfire. The fuel is created from

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

, water, and electricity with a process powered by

renewable energy Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...

sources to create a liquid

energy carrier An energy carrier is a substance (fuel) or sometimes a phenomenon (energy system) that contains energy that can be later converted to other forms such as mechanical work or heat or to operate chemical or physical processes. Such carriers includ ...

called blue crude (in contrast to regular

crude oil Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...

) which is then refined to generate e-diesel. E-diesel is considered to be a

carbon-neutral fuel Carbon-neutral fuel is fuel which produces no net-greenhouse gas emissions or carbon footprint. In practice, this usually means fuels that are made using carbon dioxide (CO2) as a feedstock. Proposed carbon-neutral fuels can broadly be grouped in ...

as it does not extract new carbon and the energy sources to drive the process are from carbon-neutral sources. As of April 2015, an

Audi A8 The Audi A8 is a full-size luxury sedan manufactured and marketed by the German automaker Audi since 1994. Succeeding the Audi V8, and now in its fourth generation, the A8 has been offered with both front- or permanent all-wheel drive—and in s ...

driven by Federal Minister of Education and Research in Germany is using the e-diesel fuel.

Catalytic conversions

Sunfire, a

clean technology Clean technology, in short cleantech, is any process, product, or service that reduces negative environmental impacts through significant energy efficiency improvements, the sustainable use of resources, or environmental protection activities. Cle ...

company, operates a pilot plant in

Dresden, Germany Dresden (, ; Upper Saxon: ''Dräsdn''; wen, label= Upper Sorbian, Drježdźany) is the capital city of the German state of Saxony and its second most populous city, after Leipzig. It is the 12th most populous city of Germany, the fourth la ...

. The current process involves

high-temperature electrolysis High-temperature electrolysis (also HTE or steam electrolysis) is a technology for producing hydrogen from water at high temperatures. Efficiency High temperature electrolysis is more efficient economically than traditional room-temperature elect ...

sources to split water into

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

. The next two chemical processes to create a liquid

called blue crude are done at a temperature of and a pressure of . In a conversion step, hydrogen and carbon dioxide are used to create

syngas Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principly used for producing ammonia or methanol. Syngas is combustible and can be used as ...

with water as byproduct. The syngas, which contains

carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...

and hydrogen, reacts to generate the blue crude. * Sunfire power-to-liquids system: Base products are carbon dioxide (CO₂) and water (H₂O) :1st step: Electrolysis of Water ( SOEC) −water is split into hydrogen and oxygen. :2nd step: Conversion Reactor ( RWGSR) −hydrogen and carbon dioxide are inputs to the Conversion Reactor that outputs hydrogen, carbon monoxide, and water. :3rd step: F-T Reactor −hydrogen and carbon monoxide are inputs to the F-T Reactor that outputs paraffinic and olefinic hydrocarbons, ranging from methane to high molecular weight waxes. The final step is also known as

Fischer–Tropsch process The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperat ...

which was first developed in 1925 by German chemists Franz Fischer and Hans Tropsch. After the blue crude is produced, it can be refined to create e-diesel on site, saving the fuel and other infrastructure costs on crude transportation. As of April 2015, Sunfire has a capability to produce a limited amount of fuel at a day. There is a plan to increase the production to an industrial scale. Audi also partners with a company named Climeworks which manufactures

Direct Air Capture Direct air capture (DAC) is a process of capturing carbon dioxide () directly from the ambient air (as opposed to capturing from point sources, such as a cement factory or biomass power plant) and generating a concentrated stream of for seques ...

technology. Climeworks technologies can absorb atmospheric carbon dioxide which is chemically captured at the surface of a

sorbent A sorbent is a material used to absorb or adsorb liquids or gases. Examples include: *A material similar to molecular sieve material, which acts by adsorption (attracting molecules to its surface). It has a large internal surface area and good t ...

until it becomes saturated. At that point, the sorbent is introduced with heat in a

desorption Desorption is the physical process where a previously adsorbed substance is released from a surface. This happens when a molecule gains enough energy to overcome the activation barrier of the bounding energy that keeps it in the surface. There ...

cycle to drive out the high-purity carbon dioxide that can be used during the conversion step of the blue crude generation process. The atmospheric carbon dioxide capturing process has 90% of energy demand in the form of low-temperature heat and the rest from electrical energy for pumping and control. The combined plant of Climeworks and Sunfire in Dresden became operational in November 2014. A plant on

Herøya Herøya is a peninsula in the municipality of Porsgrunn, Norway. It is located between the fjords of Frierfjord to the west and Gunneklevfjord to the east, at the mouth of Telemarksvassdraget. The name stems from the Old Norse word "her-eyjar" m ...

in Norway, producing 10 million liters per year, is being considered, as from a fertilizer plant is readily available and electricity is relatively cheap in Norway.

Properties

As much as eighty percent of blue crude can be converted into e-diesel. The fuel contains no

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

aromatics Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past grouping ...

, and has a high

cetane number Cetane number (cetane rating) is an indicator of the combustion speed of diesel fuel and compression needed for ignition. It plays a similar role for diesel as octane rating does for gasoline. The CN is an important factor in determining the quali ...

. These properties allow it to be blended with typical fossil diesel and used as a replacement fuel in automobiles with

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...

Oxygen by-product

In future designs, the oxygen

by-product A by-product or byproduct is a secondary product derived from a production process, manufacturing process or chemical reaction; it is not the primary product or service being produced. A by-product can be useful and marketable or it can be consid ...

may be combined with

renewable natural gas Renewable natural gas (RNG), also known as sustainable natural gas (SNG) or biomethane, is a biogas which has been upgraded to a quality similar to fossil natural gas and having a methane concentration of 90% or greater. By increasing the concentr ...

in the

oxidative coupling of methane Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene i ...

: : 2 + → + 2 The reaction is

exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...

(∆H = -280 kJ/mol) and occurs at high temperatures (750–950 ˚C). The yield of the desired products is reduced by non-selective reactions of

methyl radical Methyl (also systematically named trihydridocarbon) is an organic compound with the chemical formula (also written as •). It is a metastable colourless gas, which is mainly produced ''in situ'' as a precursor to other hydrocarbons in the petrol ...

s with the reactor surface and oxygen, which produces carbon monoxide and carbon dioxide by-products. Another ethylene production initiative developed by the European Commission through the Seventh Framework Programme for Research and Technological Development is the OCMOL process, which is the Oxidative Coupling of Methane (OCM) and simultaneous Reforming of Methane (RM) in a fully integrated reactor.

Biocatalytic conversions

Audi also partnered with a now-defunct United States company,

Joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...

, to develop ''Sunflow-D'' as e-diesel for Audi. Joule's planned plant in

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

involved the use of

genetically modified Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of Genetic engineering techniques, technologies used to change the gene ...

microorganisms in bright sunlight to act as

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

for the conversion of carbon dioxide and salty water into

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...

s. The process could be modified for longer molecular chains to produce

alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which ...

s in order to create synthetic diesel. Joule was the first company to patent a modified organism that continuously secretes hydrocarbon fuel. The organism is a single-celled cyanobacterium, also known as blue-green algae, although it is technically not an algae. It produces the fuel using photosynthesis, the same process that multi-cellular green plants use, to make sugars and other materials from water, carbon dioxide, and sunlight.

Similar initiatives

There are other initiatives to create synthetic fuel from carbon dioxide and water, however they are not part of Audi's initiatives and the fuels are not called e-diesel. The

water splitting Water splitting is the chemical reaction in which water is broken down into oxygen and hydrogen: :2 H2O → 2 H2 + O2 Efficient and economical water splitting would be a technological breakthrough that could underpin a hydrogen economy, base ...

methods vary. *

Concentrated solar power Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight into a receiver. Electricity is generated when ...

**2004 Sunshine-to-Petrol –

Sandia National Laboratories Sandia National Laboratories (SNL), also known as Sandia, is one of three research and development laboratories of the United States Department of Energy's National Nuclear Security Administration (NNSA). Headquartered in Kirtland Air Force Ba ...

. **2013 NewCO2Fuels – New Fuels Ltd ( IL) and

Weizmann Institute of Science The Weizmann Institute of Science ( he, מכון ויצמן למדע ''Machon Vaitzman LeMada'') is a public research university in Rehovot, Israel, established in 1934, 14 years before the State of Israel. It differs from other Israeli unive ...

. **2014 Solar-Jet Fuels – Consortium partners

ETH Zurich (colloquially) , former_name = eidgenössische polytechnische Schule , image = ETHZ.JPG , image_size = , established = , type = Public , budget = CHF 1.896 billion (2021) , rector = Günther Dissertori , president = Joël Mesot , ac ...

Royal Dutch Shell Shell plc is a British multinational oil and gas company headquartered in London, England. Shell is a public limited company with a primary listing on the London Stock Exchange (LSE) and secondary listings on Euronext Amsterdam and the New Yo ...

, DLR, Bauhaus Luftfahrt, ARTTIC. *

High-temperature electrolysis High-temperature electrolysis (also HTE or steam electrolysis) is a technology for producing hydrogen from water at high temperatures. Efficiency High temperature electrolysis is more efficient economically than traditional room-temperature elect ...

**2004 Syntrolysis Fuels –

Idaho National Laboratory Idaho National Laboratory (INL) is one of the national laboratories of the United States Department of Energy and is managed by the Battelle Energy Alliance. While the laboratory does other research, historically it has been involved with nu ...

and Ceramatec, Inc. (US). **2008 WindFuels – Doty Energy (US). **2012 Air Fuel Synthesis – Air Fuel Synthesis Ltd (UK). **2013 Green Feed –

Ben-Gurion University of the Negev Ben-Gurion University of the Negev (BGU) ( he, אוניברסיטת בן-גוריון בנגב, ''Universitat Ben-Guriyon baNegev'') is a public research university in Beersheba, Israel. Ben-Gurion University of the Negev has five campuses: the ...

and Israel Strategic Alternative Energy Foundation (I-SAEF). **2014 E-diesel The U.S. Naval Research Laboratory (NRL) is designing a power-to-liquids system using the Fischer-Tropsch Process to create fuel on board a ship at sea, with the base products carbon dioxide (CO₂) and water (H₂O) being derived from sea water via "An Electrochemical Module Configuration For The Continuous Acidification Of Alkaline Water Sources And Recovery Of CO₂ With Continuous Hydrogen Gas Production".

References

External links

Sustainable Transportation Fuels from Off-Peak Wind Energy, , and WaterOptions to dissociate for sustainable sunlight-to-fuel pathwaysPerspectives in electrolysis and recyclingChemical Processes for a Sustainable Future - ch 8. Renewable Energy, {{chem, C, O, 2 and an Anthropogenic Carbon Cycle
Audi Synthetic fuels Renewable energy *