Dimethyl ether, also known as methoxymethane, is the organic compound
with the formula CH3OCH3, simplified to C2H6O. The simplest ether, it is a
colorless gas that is a useful precursor to other organic compounds and an
aerosol propellant and is being studied as a future energy option. It is an
isomer of ethanol. Production
Approximately 50,000 tons were produced in 1985 in Western Europe by dehydration
of methanol: 2 CH3OH →2O + H2O
The required methanol is obtained from synthesis gas. In principle, the
methanol could be obtained from organic waste or biomass. Other possible
improvements call for a dual catalyst system that permits both methanol
synthesis and dehydration in the same process unit, with no methanol isolation
and purification. Both the one-step and two-step processes
above are commercially available. Currently, there is more widespread
application of the two-step process since it is relatively simple and
start-up costs are relatively low. It is worth mentioning that there is a
developing one-step liquid-phase process.
Applications The largest use of dimethyl ether is as
the feedstock for the production of the methylating agent, dimethyl sulfate,
which entails its reaction with sulfur trioxide:
CH 3OCH
3 + SO 3 → (CH
3) 2SO
This application consumes several thousand tons of dimethyl ether
annually. Dimethyl ether can also be converted
into acetic acid using carbonylation technology related to the Monsanto
acetic acid process: (CH
3) 2O + 2 CO + H2O → 2 CH3COOH
= Laboratory reagent and solvent= Dimethyl ether is a low-temperature
solvent and extraction agent, applicable to specialised laboratory procedures.
Its usefulness is limited by its low boiling point), but the same property
facilitates its removal from reaction mixtures. Dimethyl ether is the
precursor to the useful alkylating agent, trimethyloxonium
tetrafluoroborate. = Niche applications=
A mixture of dimethyl ether and propane is used in an over-the-counter device to
treat warts, by freezing them. Dimethyl ether is the main constituent
of freezer spray, used as a low temperature source in field testing of
electronic components. Research
= Fuel= A potentially major use of dimethyl
ether is as substitute for propane in LPG used as fuel in household and
industry. It is also a promising fuel in diesel
engines, petrol engines, and gas turbines. For diesel engines, an
advantage is the high cetane number of 55, compared to that of diesel fuel from
petroleum, which is 40–53. Only moderate modifications are needed to convert a
diesel engine to burn dimethyl ether. The simplicity of this short carbon
chain compound leads during combustion to very low emissions of particulate
matter, NOx, and CO. For these reasons as well as being sulfur-free, dimethyl
ether meets even the most stringent emission regulations in Europe, U.S.,
and Japan. Mobil uses dimethyl ether in their methanol to gasoline process.
Dimethyl ether is being developed as a synthetic second generation biofuel,
which can be manufactured from lignocellulosic biomass. Currently the
EU is considering BioDME in its potential biofuel mix in 2030; the Volvo
Group is the coordinator for the European Community Seventh Framework
Programme project BioDME where Chemrec's BioDME pilot plant based on black liquor
gasification is nearing completion in Piteå, Sweden.
In 2009 a team of university students from Denmark won the Urban
Concept/Internal Combustion class at the European Shell Eco Marathon with a
vehicle running on 100% dimethyl ether. The vehicle drove 589 km/liter, fuel
equivalent to gasoline with a 50 ccm 2-stroke engine operating by the Diesel
principle. As well as winning they beat the old standing record of 306 km/liter,
set by the same team in 2007. = Processes=
The image below illustrates some of processes from various raw materials to
dimethyl ether. = Refrigerant=
Dimethyl ether is considered a refrigerant with ASHRAE refrigerant
designation R-E170. Dimethyl ether is also used in refrigerant blends with
e.g. ammonia, carbon dioxide, butane and propene.
Safety Unlike other alkyl ethers, dimethyl
ether resists autoxidation. Dimethyl ether is also relatively non-toxic,
although it is highly flammable. References
ewcontent.cgi?article=1955&context=iracc comdefaultattachments/eurammon12engl.pdf
External links The International DME Association