Methanol fuel is an alternative biofuel for internal combustion and other engines, either in combination with gasoline or independently. Methanol (CH3OH) is less expensive to sustainably produce than ethanol fuel, although it is more toxic than ethanol and has a lower energy density than gasoline. Methanol is safer for the environment than gasoline, is an anti-freeze agent, prevents dirt and grime buildup within the engine, has a higher ignition temperature and can withstand compression equivalent to that of super high-octane gasoline. It can readily be used in most modern engines. To prevent vapor lock due to being a simple, pure fuel, a small percentage of other fuel or certain additives can be included. Methanol may be made from fossil fuels or renewable resources, in particular natural gas and coal, or biomass respectively. In the case of the latter, it can be synthesized from CO2 (carbon dioxide) and hydrogen. The vast majority of methanol produced globally is currently made with gas and coal. However, projects, investments, and the production of green-methanol has risen steadily into 2023. Methanol fuel is currently used by racing cars in many countries and has seen increasing adoption by the maritime industry. In 2022, the worldwide biomethanol market was around 120 million USD. Most of it is currently made from biomass. Companies investing significantly in biomethanol production and research include Enerkem, Södra, Methanex, Alberta Pacific, and BASF.
History and production During the 1973 oil crisis, methanol produced from coal was suggested as a fuel to replace gasoline. In 2005, George A. Olah proposed a "methanol economy" based on energy storage in synthetically produced methanol. In most countries, methanol is currently usually produced from syngas, obtained from steam reforming of methane (the chief constituent of natural gas). In China, which produced around 60% of the world's methanol in 2014, it is made primarily from coal. However, to be viable as an environmentally friendly fuel, it will need to be produced from renewable feedstocks, the most significant of which is biomass. Methanol produced from biomass is sometimes called biomethanol. Biomethanol is primarily produced by gasification of biomass. Like traditional methanol production, this produces syngas. After removing hydrogen sulfide and carbon dioxide (sweetening), which form as side products during the gasification step, methanol can be made using conventional methods. This route can offer renewable methanol production from biomass at efficiencies up to 75%. Production methods using carbon dioxide as a feedstock have also been proposed. This method involves reacting the carbon dioxide with hydrogen gas at high temperatures and pressures in the presence of a copper-based catalyst. The main drawback of this approach is the difficulty of isolating carbon dioxide and hydrogen gas in the required large volumes and high purity. A small amount of methanol is produced annually using carbon dioxide captured from industrial flue gas.
Uses
Internal combustion engine fuel Because of methanol's high octane rating of 114, it can achieve a higher thermal efficiency and power output compared to gasoline in engines developed for methanol use. However, it is also less volatile and burns at a lower temperature than gasoline, making it more difficult to start and warm up an engine in cold weather. In addition, its relatively low specific energy of around 17 MJ/kg (compared to 34 MJ/kg for gasoline) and air-to-fuel ratio of 6.4:1 mean that it suffers from higher fuel consumption than hydrocarbon fuels. Because it produces more water vapor when burned (similar to hydrogen combustion engines) and some acidic byproducts, increased wearing of engine components is likely. It may contain soluble contaminants like chloride ions, which makes it more corrosive. Insoluble contaminants, such as aluminum hydroxide, itself a product of corrosion by halide ions, clog the fuel system over time. Methanol is also hygroscopic, meaning it absorbs water vapor from the atmosphere. Because absorbed water dilutes the fuel value of the methanol (although it suppresses engine knock), and may cause phase separation of methanol-gasoline blends, containers of methanol fuels must be kept tightly sealed. Compared to gasoline, methanol is more tolerant to exhaust gas recirculation (EGR), which improves fuel efficiency of the internal combustion engines utilizing Otto cycle and spark ignition. An acid, albeit weak, methanol attacks the oxide coating that normally protects the aluminium from corrosion:
6 CH3OH + Al2O3 → 2 Al(OCH3)3 + 3 H2O The resulting methoxide salts are soluble in methanol, resulting in a clean aluminium surface, which is readily oxidized by dissolved oxygen. Also, the methanol can act as an oxidizer:
6 CH3OH + 2 Al → 2 Al(OCH3)3 + 3 H2 This reciprocal process effectively fuels corrosion until either the metal is eaten away or the concentration of CH3OH is negligible. Methanol's corrosivity has been addressed with methanol-compatible materials and fuel additives that serve as corrosion inhibitors. Organic methanol, produced from wood or other organic materials (bioalcohol), has been suggested as a renewable alternative to petroleum-based hydrocarbons. Low levels of methanol can be used in existing vehicles with the addition of cosolvents and corrosion inhibitors.
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