Fuel
Reforming
gasification
Sulfur
removal
DME - MeOH
synthesis
reactor
H 2
Purification
DME
CO 2 removal
Feedstock
CO 2

Natural gas

Biomass

Coal
O 2 , H 2 O
H 2 O
176
Alternative Fuels for Transportation
Depending on the process catalyst selected and the conditions of the reactions, Reactions 6.5 through 6.7 can occur either in one reactor or Reactions
6.5 and 6.6 can occur in a single reactor, and the DME can be produced by
dehydrating the methanol produced in Reaction 6.7 in a separate reactor.
These processes are shown schematically in Figures 6.4 and 6.5.
A calculation of the energy efficiency of the direct production of DME
from natural gas using the above process, results in an ideal cold gas efficiency (heating value of product relative to heating value of input gas) of
82.8%. Thus, there is an energy loss inherent in the production process, even
Figure 6.4
Schematic diagram of the direct DME production process, where DME is produced directly
from syngas in the synthesis reactor.
Fuel
Feedstock
Natural gas
Biomass
Coal
Sulfur
removal
Reforming
gasification
CO 2
MeOH
Synthesis
reactor
H 2
Purification
DME
CO 2 removal
H 2 O
O 2 , H 2 O
Methanol
Dehydration
Figure 6.5
The two-step process for making DME, involving the separate production of methanol, which
is dehydrated to form DME.