Dimethyl ether

Dimethyl ether, also known as methoxymethane, oxybismethane, methyl ether, wood ether, and DME, is a colorless gaseous ether with an ethereal odor. Dimethyl ether gas is water soluble. It has the formula CH₃OCH₃ or as its empirical formula C₂H₆O (which it shares with ethanol). Dimethyl ether is used as an aerosol spray propellant, and is used in conjunction with propane to give a thermic expansion that lowers temperature to -60°C. This property is usefull in cryogenic freezing of common warts found on the human body. Dimethyl ether is also a clean-burning alternative to liquified petroleum gas, liquified natural gas, diesel and gasoline. It can be made from natural gas, coal, or biomass.

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Production

Conventional DME production uses the methanol dehydration method.^[1] For mass production of DME as a fuel other methods are being considered, the main one being DME synthesis from hydrogen and CO gas, also known as syngas.^[2]

DME can be produced from methanol by combining two methanol molecules to produce a DME molecule and a water molecule.^[3] This is a reversible reaction.^[3] This can be shown in the following equation:

methanol → dimethyl ether + water

2CH₃OH → CH₃OCH₃ + H₂O

There are various companies developing this method of DME production, the most active one being JFE Holding in Japan.^{[citation needed]} The DME-synthesis method has a better overall efficiency because with methanol dehydration,^{[citation needed]} the methanol is firstly produced from a base source such as LPG, NG or coal via synthesis and then this is converted into DME.^{[citation needed]} This method attempts to cut out the intermediate methanol production and produce DME from LPG, NG, coal or even biomass in one process.^{[citation needed]}

DME production from solid raw materials such as biomass and coal requires more processes than DME production from gases such as NG and LPG. This is because the solid materials need go through the gasification process to produce the syngas required for the DME-synthesis. To allow for more efficient gasification the biomass and coal have various preparation processes; such as chipping of the biomass or producing slurry of the coal. To ensure that the DME produced is clean there are various gas scrubbing, cleaning and purification processes. DME production from methane can simply use a methane reforming method to produce the syngas for the DME synthesis.

The image below shows a simple representation of the various processes from raw materials to DME.

Applications

DME is used as:^[4]

• A refrigerant
• A (co-)blowing agent for foam
• A propellant for aerosol products
• A solvent
• An extraction agent
• A chemical reaction medium
• A fuel for welding cutting and brazing
• A multi-purpose fuel

As a fuel

DME can be used as a fuel in diesel engines,^[5] petrol engines (30% DME / 70% LPG) and gas turbines. It works particularly well in diesel engines due to its high cetane number, which is greater than 55 compared to diesel which is 38-53.^[6]

Currently the EU is considering DME in its potential biofuel mix in 2030.^[7]

Solvent

Like ammonia (NH₃), dimethyl ether can be condensed (liquified) and used as a solvent. Clearly there are limitation on the maximum temperature (e.g. the boiling/reflux temperature i.e. -23°C) which the solvent can be used. One advantage of using dimethyl ether as a solvent is that is readily removed by evaporation, especially from a product which has a relatively low boiling point.

References

1. ^ demeon.com, production process
2. ^ JFE-holdings.co.jp, dme
3. ^ ^{a b} gov.br, dehydration catalyst
4. ^ demeon.com, Akzo Nobel DME
5. ^ nycomb.se, Nycomb Chemicals company
6. ^ topsoe.com, Haldor Topsoe Chemicals Company
7. ^ refuel.eu, EU Refuel biofuel project