Methanol economy
The methanol economy is a suggested future economy in which methanol and dimethyl ether replace fossil fuels as a means of energy storage, ground transportation fuel, and raw material for synthetic hydrocarbons and their products. It offers an alternative to the proposed hydrogen economy or ethanol economy.
In the 1990s, Nobel prize winner George A. Olah advocated a methanol economy; in 2006, he and two co-authors, G. K. Surya Prakash and Alain Goeppert, published a summary of the state of fossil fuel and alternative energy sources, including their availability and limitations, before suggesting a methanol economy.
Methanol can be produced from a wide variety of sources including still-abundant fossil fuels as well as agricultural products and municipal waste, wood and varied biomass. It can also be made from chemical recycling of carbon dioxide.
Uses
Fuel
Methanol is a fuel for heat engines and fuel cells. Due to its high octane rating it can be used directly as a fuel in flex-fuel cars using existing internal combustion engines. Methanol can also be burned in some other kinds of engine or to provide heat as other liquid fuels are used. Fuel cells, can use methanol either directly in Direct Methanol Fuel Cells or indirectly.Feedstock
Methanol is already used today on a large scale to produce a variety of chemicals and products. Global methanol demand as a chemical feedstock reached around 42 million metric tonnes per year as of 2015. Through the methanol-to-gasoline process, it can be transformed into gasoline. Using the methanol-to-olefin process, methanol can also be converted to ethylene and propylene, the two chemicals produced in largest amounts by the petrochemical industry. These are important building blocks for the production of essential polymers and like other chemical intermediates are currently produced mainly from petroleum feedstock. Their production from methanol could therefore reduce our dependency on petroleum. It would also make it possible to continue producing these chemicals when fossil fuels reserves are depleted.Production
Today most methanol is produced from methane through syngas. Trinidad and Tobago is currently the world's largest methanol exporter, with exports mainly to the United States. The natural gas that serves as feedstock for the production of methanol comes from the same sources as other uses. Unconventional gas resources such as coalbed methane, tight sand gas and eventually the very large methane hydrate resources present under the continental shelves of the seas and Siberian and Canadian tundra could also be used to provide the necessary gas.The conventional route to methanol from methane passes through syngas generation by steam reforming combined with partial oxidation. New and more efficient ways to convert methane into methanol are also being developed. These include:
- Methane oxidation with homogeneous catalysts in sulfuric acid media
- Methane bromination followed by hydrolysis of the obtained bromomethane
- Direct oxidation of methane with oxygen
- Microbial or photochemical conversion of methane
- Partial methane oxidation with trapping of the partially oxidized product and subsequent extraction on copper and iron exchanged Zeolite
Methanol can be synthesized from carbon and hydrogen from any source, including still available fossil fuels and biomass. CO2 emitted from fossil fuel burning power plants and other industries and eventually even the CO2 contained in the air, can be a source of carbon. It can also be made from chemical recycling of carbon dioxide, which Carbon Recycling International has demonstrated with its first commercial scale plant. Initially the major source will be the CO2 rich flue gases of fossil-fuel-burning power plants or exhaust from cement and other factories. In the longer range however, considering diminishing fossil fuel resources and the effect of their utilization on earth's atmosphere, even the low concentration of atmospheric CO2 itself could be captured and recycled via methanol, thus supplementing nature’s own photosynthetic cycle. Efficient new absorbents to capture atmospheric CO2 are being developed, mimicking plants' ability. Chemical recycling of CO2 to new fuels and materials could thus become feasible, making them renewable on the human timescale.
Methanol can also be produced from CO2 by catalytic hydrogenation of CO2 with H2 where the hydrogen has been obtained from water electrolysis. This is the process used by Carbon Recycling International of Iceland. Methanol may also be produced through CO2 electrochemical reduction, if electrical power is available. The energy needed for these reactions in order to be carbon neutral would come from renewable energy sources such as wind, hydroelectricity and solar as well as nuclear power. In effect, all of them allow free energy to be stored in easily transportable methanol, which is made immediately from hydrogen and carbon dioxide, rather than attempting to store energy in free hydrogen.
or with electric energy
The necessary CO2 would be captured from fossil fuel burning power plants and other industrial flue gases including cement factories. With diminishing fossil fuel resources and therefore CO2 emissions, the CO2 content in the air could also be used. Considering the low concentration of CO2 in air improved and economically viable technologies to absorb CO2 will have to be developed. For this reason, extraction of CO2 from water could be more feasible due to its higher concentrations in dissolved form. This would allow the chemical recycling of CO2, thus mimicking nature’s photosynthesis.
Advantages
In the process of photosynthesis, green plants use the energy of sunlight to split water into free oxygen and free hydrogen. Rather than attempt to store the hydrogen, plants immediately capture carbon dioxide from the air to allow the hydrogen to reduce it to storable fuels such as hydrocarbons and polyalcohols. In the methanol economy, any process which similarly produces free hydrogen, proposes to immediately use it "captively" to reduce carbon dioxide into methanol, which, like plant products from photosynthesis, has great advantages in storage and transport over free hydrogen itself.Methanol is a liquid under normal conditions, allowing it to be stored, transported and dispensed easily, much like gasoline and diesel fuel. It can also be readily transformed by dehydration into dimethyl ether, a diesel fuel substitute with a cetane number of 55.
Methanol is water-soluble: An accidental release of methanol in the environment would cause much less damage than a comparable gasoline or crude oil spill. Unlike these fuels, methanol is biodegradable and totally soluble in water, and would be rapidly diluted to a concentration low enough for microorganism to start biodegradation. This effect is already exploited in water treatment plants, where methanol is already used for denitrification and as a nutrient for bacteria. Accidental release causing groundwater pollution has not been thoroughly studied yet, though it is believed that it might undergo relatively rapid.
Comparison with hydrogen
Methanol economy advantages compared to a hydrogen economy:- Efficient energy storage by volume, as compared with compressed hydrogen. When hydrogen pressure-confinement vessel is taken into account, an advantage in energy storage by weight can also be realized. The volumetric energy density of methanol is considerably higher than liquid hydrogen, in part because of the low density of liquid hydrogen of 71 grams/litre. Hence there is actually more hydrogen in a litre of methanol than in a litre of liquid hydrogen, and methanol needs no cryogenic container maintained at a temperature of -253 °C.
- A liquid hydrogen infrastructure would be prohibitively expensive. Methanol can use existing gasoline infrastructure with only limited modifications.
- Can be blended with gasoline.
- User friendly. Hydrogen is volatile, and its confinements uses high pressure or cryogenic systems.
- Less losses : Hydrogen leaks more easily than methanol. Heat will evaporate liquid hydrogen, giving expected losses up to 0.3% per day in storage tanks..
Comparison with ethanol
- Can be made from any organic material using proven technology going through syngas. There is no need to use food crops and compete with food production. The amount of methanol that can be generated from biomass is much greater than ethanol.
- Can compete with and complement ethanol in a diversified energy marketplace. Methanol obtained from fossil fuels has a lower price than ethanol.
- Can be blended in gasoline like ethanol. In 2007, China blended more than of methanol into fuel and will introduce methanol fuel standard by mid-2008. M85, a mixture of 85% methanol and 15% gasoline can be used much like E85 sold in some gas stations today.
Disadvantages
- High energy costs currently associated with generating and transporting hydrogen offsite.
- Presently generated from natural gas still dependent on fossil fuels.
- Energy density one half of that of gasoline and 24% less than ethanol
- Handling
- * If no inhibitors are used, methanol is corrosive to some common metals including aluminum, zinc and manganese. Parts of the engine fuel-intake systems are made from aluminum. Similar to ethanol, compatible material for fuel tanks, gasket and engine intake have to be used.
- * As with similarly corrosive and hydrophilic ethanol, existing pipelines designed for petroleum products cannot handle methanol. Thus methanol requires shipment at higher energy cost in trucks and trains, until new pipeline infrastructure can be built, or existing pipelines are retrofitted for methanol transport.
- * Methanol, as an alcohol, increases the permeability of some plastics to fuel vapors. This property of methanol has the possibility of increasing emissions of volatile organic compounds from fuel, which contributes to increased tropospheric ozone and possibly human exposure.
- Low volatility in cold weather: pure methanol-fueled engines can be difficult to start, and they run inefficiently until warmed up. This is why a mixture containing 85% methanol and 15% gasoline called M85 is generally used in ICEs. The gasoline allows the engine to start even at lower temperatures.
- With the exception of low level exposure, methanol is toxic. Methanol is lethal when ingested in larger amounts. But so are most motor fuels, including gasoline and diesel fuel. Gasoline also contains small amounts of many compounds known to be carcinogenic. Methanol is not a carcinogen, nor does it contain carcinogens. However, methanol may be metabolized in the body to formaldehyde, which is both toxic and carcinogenic. Methanol occurs naturally in small quantities in the human body and in edible fruits.
- Methanol is a liquid: this creates a greater fire risk compared to hydrogen in open spaces as Methanol leaks do not dissipate. Methanol burns invisibly unlike gasoline. Compared to gasoline, however, methanol is much safer. It is more difficult to ignite and releases less heat when it burns. Methanol fires can be extinguished with plain water, whereas gasoline floats on water and continues to burn. The EPA has estimated that switching fuels from gasoline to methanol would reduce the incidence of fuel related fires by 90%.
Literature
- F. Asinger: Methanol, Chemie- und Energierohstoff. Akademie-Verlag, Berlin, 1987,,.
- Martin Bertau, Heribert Offermanns, Ludolf Plass, Friedrich Schmidt, Hans-Jürgen Wernicke: Methanol: The Basic Chemical and Energy Feedstock of the Future: Asinger's Vision Today, 750 Seiten, Verlag Springer; 2014,
- †George A. Olah, Alain Goeppert, G. K. Surya Prakash, Beyond Oil and Gas: The Methanol Economy – Third, Updated and Enlarged Edition, Wiley-VCH, 2018,.