With the general worldwide availability of light "sweet" crude
oil continuing its decades long downtrend, crude oil prices have recently
risen to the vicinity of $30/b. Increasingly stringent emissions specifications
for diesel fuel is further reducing yields and increasing the cost of diesel
fuel derived from conventional petroleum refinery operations, while the demand
for diesel fuel is increasing rapidly in some regions. Proven world natural
gas reserves, which currently represent about 83% of the energy equivalence
of proven oil reserves, have been growing at a faster rate. In some remote
locations, wellhead costs of "stranded" natural gas have been estimated
to be below $0.25/MM Btu.
Interest has therefore been increasing in possible "clean" substitutes
for conventional diesel fuel derived from natural gas feedstock. Because of
its high cetane rating and low toxicity, dimethyl ether (DME) currently appears
to be a leading candidate for such a substitute fuel. DME also appears to
be advantageous as an alternative fuel for electric power generation via combined
cycle gas turbines. Since the vapor pressure of DME is comparable to liquefied
petroleum gas (LPG), it is believed that existing LPG transportation, storage,
and handling facilities could be applied to DME with relatively minor modifications.
The focus of this review is DME production technology under development by
Toyo Engineering Corporation (TEC), which appears to be ready for commercialization.
Their technology is based on methanol dehydration, where methanol is produced
as an intermediate from natural gas. Using their proprietary DME reactor synthesis
technology, "jumbo" DME production capacities as high as 7,000 t/d
are claimed to be possible in a single reactor train.
