- Dimethyl ether
Dimethyl ether Identifiers Abbreviations DME CAS number PubChem ChemSpider UNII EC number UN number 1033 KEGG MeSH ChEBI ChEMBL RTECS number PM4780000 Beilstein Reference 1730743 Jmol-3D images Image 1 Properties Molecular formula C2H6O Molar mass 46.07 g mol−1 Exact mass 46.041864814 g mol-1 Appearance Colourless gas Odor Typical Density 1.97 mg cm-3 Melting point
-141 °C, 132 K, -222 °F
-24 °C, 249 K, -11 °F
Solubility in water 71 g dm-3 (at 20 °C) log P 0.022 Vapor pressure >100 kPa Dipole moment 1.30 D Thermochemistry Std enthalpy of
o298 -184.1 kJ mol-1 Std enthalpy of
o298 -1.4604 MJ mol-1 Specific heat capacity, C 65.57 J K-1 mol-1 Hazards MSDS External MSDS GHS pictograms GHS signal word Danger GHS hazard statements GHS precautionary statements , EU Index 603-019-00-8 EU classification F+ R-phrases S-phrases , , , NFPA 704 Flash point -41 °C Autoignition
350 °C Explosive limits 27% Related compounds Related ethers Diethyl ether
Related compounds Ethanol
Supplementary data page Structure and
n, εr, etc. Thermodynamic
Solid, liquid, gas
Spectral data UV, IR, NMR, MS (what is: /?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Dimethyl ether (DME), also known as methoxymethane, is the organic compound with the formula CH3OCH3. The simplest ether, it is a colourless gas that is a useful precursor to other organic compounds and an aerosol propellant. When combusted, DME produces minimal soot and CO, though HC and NOx formation is significant. DME can act as a clean fuel when burned in engines properly optimized for DME.
Today, DME is primarily produced by converting hydrocarbons sourced from natural gas or coal via gasification to synthesis gas (syngas). Synthesis gas is then converted into methanol in the presence of catalyst (usually copper-based), with subsequent methanol dehydration in the presence of a different catalyst (for example, silica-alumina) resulting in the production of DME. As described, this is a two-step (indirect synthesis) process that starts with methanol synthesis and ends with DME synthesis (methanol dehydration). The same process can be conducted using organic waste or biomass. Approximately 50,000 tons were produced in 1985 in Western Europe by using the methanol dehydration process. Alternatively, DME can be produced through direct synthesis, using a dual catalyst system that permits both methanol synthesis and dehydration in the same process unit, with no methanol isolation and purification, a procedure that by eliminating the intermediate methanol synthesis stage, the licensors claim promises efficiency advantages and cost benefits.
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.
The largest use of DME is currently (2010) as substitute for propane in LPG used as fuel in household and industry. The largest use of DME for this purpose is in China. DME has two other primary applications: as a propellant in aerosol canisters, and as a precursor to dimethyl sulfate. As an aerosol propellant, DME is useful as a somewhat polar solvent. It can also be used as a refrigerant.
- CH3OCH3 + SO3 → (CH3O)2SO2
- (CH3)2O + 2 CO + H2O → 2 CH3CO2H
Laboratory reagent and solvent
DME is a low-temperature solvent and extraction agent, applicable to specialised laboratory procedures. Its usefulness is limited by its low boiling point (−23 °C), but the same property facilitates its removal from reaction mixtures. DME is the precursor to the useful alkylating agent, trimethyloxonium tetrafluoroborate.
DME is a promising fuel in diesel engines, petrol engines (30% DME / 70% LPG), and gas turbines owing to its high cetane number, which is 55, compared to diesel's, which is 40–53. Only moderate modification are needed to convert a diesel engine to burn DME. The simplicity of this short carbon chain compound leads during combustion to very low emissions of particulate matter, NOx, CO. For these reasons as well as being sulfur-free, DME meets even the most stringent emission regulations in Europe (EURO5), U.S. (U.S. 2010), and Japan (2009 Japan). Mobil is using DME in their methanol to gasoline process.
DME is being developed as a synthetic second generation biofuel (BioDME), 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.
The image below illustrates some of processes from various raw materials to DME.
In 2009 a team of university students from Denmark won the Urban Concept/Internal Combustion class at the European Shell Eco Marathon (The Shell Eco Marathon is an unofficial World Championship for mileage) with a vehicle running on 100% DME. 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 
Unlike other alkyl ethers, DME resists autoxidation. DME is also relatively non-toxic, although it is highly flammable.
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