Dimethyl ether (or DME) has quite a few names, but it is more popularly known as dimethyl oxide or wood ether. DME has physical properties that are similar to those of propane and butane. It is a colorless, gaseous, organic compound that has a characteristic sweet “ether” scent. DME has very low toxicity and is not a known carcinogen. It does not corrode metals. When released into the atmosphere, it decomposes after about a day or so. At room temperature, DME can be easily condensed into a liquid by increasing the pressure to between 5 and 6 bar (75 psi). It burns in open air with a clean, blue flame similar to that of natural gas or petroleum gases (i.e., propane and butane).
DME has been used since the early 1960s as an aerosol propellant in various cosmetic, personal care, and household products such as hairsprays, shaving creams, and insect sprays. It is also used as a solvent for paints, food products, agricultural pesticides, etc.
DME is currently being manufactured from natural gas and gasified coal or waste biomass. The currently favored “indirect” method converts these raw materials first to synthetic gas (carbon monoxide and hydrogen) and then to methanol. The methanol is then dehydrated to get DME. This multi-step process is relatively simple and inexpensive to set up on a commercial scale. A “direct” syngas-to-DME process is currently being developed by various entities.
Synthesized DME is currently being utilized on a large scale mostly as an LPG (liquefied petroleum gas) supplement in China where DME is mixed with LPG at a ratio of about 1:4. This mix is suitable for cooking or heating with standard LPG gas stoves, ovens, and heaters. Used for this purpose alone, DME could have a very substantial commercial potential in Asia, Latin America, and Africa where piped natural gas is not commonly available. But DME as a diesel fuel substitute could have an even larger commercial potential, worldwide. DME can even replace natural gas as fuel for power generation. DME can also be used as a feedstock for manufacturing other high-value petrochemicals, such as olefins.
If manufactured on a sufficiently large scale, the cost of DME would depend mostly on the cost of extracting and transporting natural gas, coal, and waste biomass. LPG prices generally follow those of light crude oil, from which propane and butane are typically extracted. Natural gas is sold as piped natural gas (at low pressures) or as compressed natural gas (CNG) and liquefied natural gas (LNG). Piped natural gas for household cooking and heating is much less expensive compared to CNG or LNG. CNG requires expensive high-strength containers and high-pressure pumps while LNG requires very costly thermally shielded (usually Dewar-type) containers and cryogenic cooling equipment. The storage and transport equipment requirements for DME are just about the same as those for LPG, which (unlike CNG and LNG) does not require expensive high-pressure or cryogenic pumps and containers. DME, therefore, could potentially cost much less than CNG and LNG, as well as LPG.
Synthesized DME manufactured on a large scale can be a used as a diesel fuel substitute because DME: (1) would have a lower retail price compared to diesel; (2) has a higher cetane number (55 to 60) than typical diesels and can therefore improve a diesel engine's efficiency; (3) is much less toxic to humans, plants, and animals than diesel; (4) burns more thoroughly and cleanly (no soot) than diesel because of its extremely low to zero sulfur content and because of the oxygen atom in its molecule; (5) decomposes easily in water and air and does not accumulate in the atmosphere; (6) does not harm the ozone layer; (7) can be stored and transported using the same facilities as that for LPG or propane and butane fuels.
The only significant disadvantage of DME as a diesel-fuel substitute is that it lacks the lubricity and viscosity of diesel oil. An unmodified diesel engine that is run on pure DME would suffer from excessive wear and tear on its piston oil rings, cylinder sleeves, etc. Replacing standard piston and cylinder gaskets and seals, fuel delivery systems, and fuel tanks with DME-compatible components would be necessary.
DME production would be ideal for countries that have plentiful coal or natural gas resources, or that have extensive waste biomass collection systems. About 5 million tons of DME are already being produced yearly (mostly in China). Brazil, Japan, and South Korea also have DME production facilities. Meanwhile, major plants are being constructed in Egypt, India, Indonesia, Iran, and Uzbekistan. Sweden has just set up a commercial-scale DME plant that utilizes waste biomass (black liquor) from paper mills.
Other Middle Eastern countries, notably Qatar, as well as Australia, Canada, Kazakhstan, Malaysia, Norway, Poland, Russia, Thailand, Turkey, Turkmenistan, United States, Venezuela, and several countries in the African continent including Algeria, Libya, and Nigeria are also looking into DME production. Truck maker Volvo has already developed DME-compatible diesel engines, fuel tanks, and fuel-delivery systems.