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Dimethyl ether

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Dimethyl ether, also known as DME or methoxymethane, is a simple organic compound. It has the chemical formula CH3OCH3. This means it is made of two methyl groups connected by an oxygen atom. It is a colorless gas that serves many important roles in science and industry. DME is considered the simplest type of ether. Because of its unique properties, it acts as a building block for making other chemicals. It also works as a propellant in spray cans and as a potential fuel for engines.

DME process diagram
DME process diagram

There are several ways to produce dimethyl ether. One common commercial method is the dehydration of methanol. In this two-step process, methanol is first obtained from synthesis gas, also called syngas. Then, water is removed from the methanol to create the DME. Some researchers are developing a one-step liquid-phase process to make this more efficient. This new method would allow methanol synthesis and dehydration to happen in a single unit. This would remove the need to isolate and purify the methanol separately.

Another important way to make this gas is through biomass. This produces a synthetic second-generation biofuel known as BioDME. BioDME can be made from lignocellulosic biomass, which is plant material. It can also be produced from methane or biogas found in agricultural, food, or animal waste. Even shale gas or natural gas can be used. In Sweden, a pilot plant in Piteå uses black liquor gasification to study this. The Volvo Group coordinates the BioDME project as part of a European Community program.

Chemrec 5 - small
Chemrec 5 - small

Scientists first synthesized dimethyl ether in 1835. Two researchers, Jean-Baptiste Dumas and Eugene Péligot, created it. They did this by distilling methanol and sulfuric acid. Later, the gas changed how the world moved food. In 1876, a French engineer named Charles Tellier used a methyl-ether refrigerating plant on a cargo ship. He named the ship Le Frigorifique. It successfully carried refrigerated meat from Argentina. By 1877, another ship called the Paraguay used an improved plant designed by Ferdinand Carré to run the same route.

Chemrec 5 - small
Chemrec 5 - small

Today, dimethyl ether has many specific industrial applications. It is a primary feedstock used to create dimethyl sulfate. This happens when DME reacts with sulfur trioxide. It can also be turned into acetic acid through carbonylation technology. In laboratories, DME serves as a low-temperature solvent and an extraction agent. While its low boiling point limits some uses, it makes the gas very easy to remove from reaction mixtures. It is also used to create the alkylating agent trimethyloxonium tetrafluoroborate.

In daily life, you might encounter DME in niche products. A mixture of DME and propane is used in "freeze spray" to treat warts. It is also a component in high-temperature "Map-Pro" blowtorch gas blends. You can find it as a propellant in aerosol products like hair spray, bug spray, and some glues. It even serves as a refrigerant, designated as R-E170 by ASHRAE. It can be used alone or blended with substances like ammonia, carbon dioxide, butane, or propene.

DME process diagram
DME process diagram

Researchers are very interested in DME as a clean fuel. It can replace propane in LPG used for homes and industry. It is also a promising fuel for gas turbines and diesel engines. DME has a high cetane number of 55. This is higher than the 40 to 53 range found in many petroleum diesel fuels. Because it has a short carbon chain, it burns with very low emissions of particulate matter. It is also sulfur-free. This allows it to meet strict emission regulations in the U.S., Europe, and Japan.

Chemrec 5 - small
Chemrec 5 - small

One remarkable example of its efficiency occurred at the European Shell Eco Marathon. A vehicle running on 100% dimethyl ether drove 589 km per liter. This beat the previous record of 306 km per liter. While the gas is useful, it must be handled with care because it is highly flammable. In 1948, a leak of 30 tonnes at a BASF factory in Ludwigshafen led to an explosion. This event resulted in 200 deaths and destroyed one-third of the plant. However, unlike other alkyl ethers, dimethyl ether is notable for resisting autoxidation, making it more stable in certain conditions.

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