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Carbon-neutral fuels can refer to a variety of energy fuels or energy systems which have no net greenhouse gas emissions or carbon footprint. One class is synthetic fuel (including methane, gasoline, diesel fuel, jet fuel or ammonia〔Leighty and Holbrook (2012) ("Running the World on Renewables: Alternatives for Transmission and Low-cost Firming Storage of Stranded Renewable as Hydrogen and Ammonia Fuels via Underground Pipelines" ) ''Proceedings of the ASME 2012 International Mechanical Engineering Congress & Exposition'' November 9–15, 2012, Houston, Texas〕) produced from sustainable or nuclear energy used to hydrogenate waste carbon dioxide recycled from power plant flue exhaust gas or derived from carbonic acid in seawater. Other types can be produced from renewable energy sources such as wind turbines, solar panels, and hydroelectric power plants.〔 (Review.)〕〔 (Review.)〕〔 (Review.)〕 Such fuels are potentially carbon-neutral because they do not result in a net increase in atmospheric greenhouse gases.〔 (Review.)〕 Until captured carbon is used for plastics feedstock, carbon neutral fuel synthesis is the primary means of carbon capture and utilization or recycling.〔(Conference on Carbon Dioxide as Feedstock for Chemistry and Polymers ) (Essen, Gerrmany, October 10–11, 2012; (post-conference program ))〕 To the extent that carbon-neutral fuels displace fossil fuels, or if they are produced from waste carbon or seawater carbonic acid, and their combustion is subject to carbon capture at the flue or exhaust pipe, they result in negative carbon dioxide emission and net carbon dioxide removal from the atmosphere, and thus constitute a form of greenhouse gas remediation.〔 (Review.)〕〔 (Review.)〕 Such power to gas carbon-neutral and carbon-negative fuels can be produced by the electrolysis of water to make hydrogen used in the Sabatier reaction to produce methane which may then be stored to be burned later in power plants as synthetic natural gas, transported by pipeline, truck, or tanker ship, or be used in gas to liquids processes such as the Fischer–Tropsch process to make traditional fuels for transportation or heating.〔 (Review.)〕 Carbon-neutral fuels are used in Germany and Iceland for distributed storage of renewable energy, minimizing problems of wind and solar intermittency, and enabling transmission of wind, water, and solar power through existing natural gas pipelines. Such renewable fuels could alleviate the costs and dependency issues of imported fossil fuels without requiring either electrification of the vehicle fleet or conversion to hydrogen or other fuels, enabling continued compatible and affordable vehicles.〔 A 250 kilowatt synthetic methane plant has been built in Germany and it is being scaled up to 10 megawatts. ==Production== Carbon-neutral fuels are synthetic hydrocarbons. They can be produced in chemical reactions between carbon dioxide, which can be captured from power plants or the air, and hydrogen, which is created by the electrolysis of water using renewable energy. The fuel, often referred to as electrofuel, stores the energy that was used in the production of the hydrogen. Coal can also be used to produce the hydrogen, but that would not be a carbon-neutral source. Carbon dioxide can be captured and buried, making fossil fuels carbon-neutral, although not renewable. Carbon capture from exhaust gas can make carbon-neutral fuels carbon negative. Other hydrocarbons can be broken down to produce hydrogen and carbon dioxide which could then be stored while the hydrogen is used for energy or fuel, which would also be carbon-neutral. The most energy-efficient fuel to produce is methanol, which is made from a chemical reaction of a carbon-dioxide molecule with three hydrogen molecules to produce methanol and water. The stored energy can be recovered by burning the methanol in a combustion engine, releasing carbon dioxide, water, and heat. Methane can be produced in a similar reaction. More energy can be used to combine methanol or methane into larger hydrocarbon fuel molecules.〔 Researchers have also suggested using methane to produce dimethyl ether. This fuel could be used as a substitute for diesel fuel due to its ability to self ignite under high pressure and temperature. It is already being used in some areas for heating and energy generation. It is nontoxic, but must be stored under pressure. Octane and ethanol can also be produced from carbon dioxide and hydrogen. All synthetic hydrocarbons are generally produced at temperatures of 200–300 °C, and at pressures of 20 to 50 bar. Catalysts are usually used to improve the efficiency of the reaction and create the desired type of hydrocarbon fuel. Such reactions are exothermic and use about 3 mol of hydrogen per mole of carbon dioxide involved. They also produce large amounts of water as a byproduct.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Carbon-neutral fuel」の詳細全文を読む スポンサード リンク
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