About DME
DME (Di-Methyl Ether) is a substance of which the chemical formula is shown by CH3OCH3. DME is a colorless gas at ambient temperature as its boiling point is -25.1℃. As its saturated vapor pressure is as low as 0.6Mpa, it is easily liquefied. As the physical properties of DME are similar to those of propane and butane, main components of Liquid Petroleum Gas (LPG), the storage and handling technology of LPG is applied to DME.
When DME was introduced as spray propellant, it had already been confirmed that its toxicity is low and its negative environmental impact is small. As for the safety evaluation for voluminous distribution of DME, detailed examinations were later conducted and it was concluded that DME is as safe as LPG.
As DME has no carbon-carbon bond, no soot is generated on burning. It doesn't contain sulfur not to emit SOX. It is rich in hydrogen and CO2 emission per calorie is little, and NOX emission is little. It is "Next generation's clean energy carrier" of which the negative environmental impact is extremely small.
DME can be produced from wide range of raw materials; not only from the fossil resources such as natural gas and coal, but also from the renewable resources such as biomass and hydrogen generated by photovoltaic electricity.
Like LPG and natural gas, DME is expected to be a new energy that can be used for wide usage such as home fuel, power generation fuel, diesel engine fuel, and furthermore fuel for the fuel cell.
Physical properties of DME
Fundamental physical properties of DME as fuel are shown in comparison to other relating fuels.
| Property | DME | Methane | Propane | Methanol | Gas oil |
|---|---|---|---|---|---|
| Chemical Formula | CH3OCH3 | CH4 | C3H8 | CH3OH | - |
| Boiling point (℃) | -25.1 | -161.5 | -42.0 | 64.6 | 180〜360 |
| Liquid density (g/cm3,20℃) | 0.67 | - | 0.49 | 0.79 | 0.84 |
| Gas density (vs. AIR) | 1.59 | 0.55 | 1.52 | - | - |
| Saturated vapor pressure (MPa,25℃) | 0.6 | - | 0.9 | - | - |
| Auto-ignition point (℃) | 235 | 650 | 470 | 450 | 250 |
| Explosion limit (%) | 3.4〜27 | 5〜15 | 2.1〜9.4 | 5.5〜36 | 0.6〜7.5 |
| Cetane number | 55〜60 | 0 | 5 | 5 | 40〜55 |
| Lower Heating value (MJ/kg) | 28.8 | 50.2 | 46.4 | 20.1 | 42.7 |
| Lower Heating value (MJ/m3) | 59.2 | 35.8 | 90.9 | - | - |
Quality standard of DME
The examination of DME quality standardization has been progressing in consideration of DME production method, DME distribution method, and conditions on DME utilization equipment, and JIS standard K2180 of fuel DME was issued in March, 2013. JIS of DME fuel for the vehicle is at present under examination.
International Standard ISO of fuel DME is now under examination and expected to be issued in 2014.
JIS standard K2180 of fuel DME is shown.
| Item | Unit | Standard value |
|---|---|---|
| DME purity | mass % | 99.5 or more |
| Methanol | mass % | 0.050 or less |
| Water | mass % | 0.030 or less |
| Hydrocarbon (C4 or less) | mass % | 0.050 or less |
| Carbon dioxide | mass % | 0.10 or less |
| Carbon monoxide | mass % | 0.010 or less |
| Methyl formate | mass % | 0.050 or less |
| Ethyl methyl ether | mass % | 0.20 or less |
| Residue after evaporation | mass % | 0.0070 or less |
| Total sulfur | mg/kg | 3.0 or less |