Methanol, an alcohol, is a liquid fuel that can be used in internal-combustion engines to power vehicles. During the late 1980s, it was seen as a route to diversifying the fuels for the U.S. transportation system; natural gas from remote fields around the world would be converted into methanol and transported to the United States. This strategy was seen by energy planners as a way to convert what was, at that time, cheap remote natural gas (on the order of $1 per thousand cubic feet) into a marketable product. Currently, however, while methanol is produced primarily from natural gas, it is used principally as a commodity chemical.

Methanol has a higher octane rating than gasoline does and is therefore a suitable neat fuel for internal-combustion engines (for example, in racing cars). In practical terms, the penetration of methanol into a transportation system for LDVs that are fueled primarily by gasoline would require flexible-fuel vehicles that could run on a mixture of gasoline and methanol. Further, the use of a mixture of 85 percent methanol (M85) and gasoline would avoid the cold-start problem caused by methanol’s low volatility. However, methanol has about half the energy density of gasoline, which affects the driving range that a vehicle can achieve on a full tank of the fuel.

Other drawbacks of methanol include its corrosive, hydrophilic, and toxic nature and its harmfulness to human health in particular if ingested, absorbed through the skin, or inhaled. Methanol could thus potentially create environmental, safety, health, and liability issues for fuel station owners. In addition, introducing a new fuel such as methanol on a large scale would require the construction of a new distribution system and the use of flexible-fuel vehicles that could run on a mixture of gasoline and methanol. One means of avoiding these infrastructural barriers would be to convert the methanol to gasoline using the MTG process.

Dimethyl Ether

Dimethyl ether (DME) is a liquid fuel with properties similar to that of liquefied petroleum gas (LPG). It produces lower CO and CO2 emissions when burned, compared to gasoline and diesel, because of its modest carbon-to-hydrogen ratio. Because DME contains oxygen, it also requires a lower air-to-fuel ratio than do gasoline and diesel. DME has a thermal efficiency higher than that of diesel fuel (Kim et al., 2008), which could enable a higher-efficiency engine design. The presence of oxygen in the structure of DME also minimizes soot formation (Arcoumanis et al., 2008). Other exhaust emissions, such as unburned hydrocar-

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