0.9
Mole fraction, conversion
260°C, 50 bar
DME conv
xCO
xDME
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
xH 2
xCO 2
xH 2 O
xMeOH
0.0
0.5
1.0
1.5
2.0
2.5
3.0
H 2 /CO
179
Dimethyl Ether
This could occur in a case where the catalyst is not sensitive to the water gas
reaction.
The maximum overall conversion to DME in the direct process with complete equilibrium occurs at hydrogen to carbon ratio of 1.0, which is the stoichiometric mixture for the conversion of syngas to DME according to Reaction
6.6. For the methanol conversion, the maximum conversion is at a H 2 /CO
ratio = 2.0, again the stoichiometric value, this time according to Reaction 6.5.
If the water gas equilibrium reaction is not active, the conversion of the direct
DME process has about the same H 2 /CO ratio for maximum conversion as
methanol. The highest overall conversion is found for the direct process with
a H 2 /CO ratio = 1. The direct process at this stoichiometry would fit well
with coal, since it has a low amount of hydrogen, while the indirect process
with separate methanol production fits better with natural gas, which has a
high amount of hydrogen. As seen above, the H 2 /CO ratio can be controlled
by adding steam, or by gasifying with CO 2 . The importance of the water
gas shift, Reaction 6.6, is shown by the lower conversion and the shift in
the H 2 /CO ratio for maximum conversion when it is not active. For a direct
formation of DME with a hydrogen rich syngas, the slow water gas reaction gives a slightly higher conversion than with the water gas reaction at the
H 2 /CO ratio of about 2.
The equilibrium reaction products are also a function of the ratio of
hydrogen to carbon in the syngas. The product distribution for the direct conversion process with a H 2 /CO ratio of 1.0 is shown in Figure 6.8. As expected
from the conversion effectiveness, the yield of DME is highest at a H 2 /CO
of 1.0, the stoichiometric condition. When this ratio is less than one, there
Figure 6.8
Conversion of syngas to DME and the equilibrium composition of the products of Reactions
6.5, 6.6, and 6.7 shown as a function of hydrogen to carbon ratio of the syngas. The temperature
is 260°C and the pressure 50 atm.
Mole fraction, conversion
260°C, 50 bar
DME conv
xCO
xDME
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
xH 2
xCO 2
xH 2 O
xMeOH
0.0
0.5
1.0
1.5
2.0
2.5
3.0
H 2 /CO
179
Dimethyl Ether
This could occur in a case where the catalyst is not sensitive to the water gas
reaction.
The maximum overall conversion to DME in the direct process with complete equilibrium occurs at hydrogen to carbon ratio of 1.0, which is the stoichiometric mixture for the conversion of syngas to DME according to Reaction
6.6. For the methanol conversion, the maximum conversion is at a H 2 /CO
ratio = 2.0, again the stoichiometric value, this time according to Reaction 6.5.
If the water gas equilibrium reaction is not active, the conversion of the direct
DME process has about the same H 2 /CO ratio for maximum conversion as
methanol. The highest overall conversion is found for the direct process with
a H 2 /CO ratio = 1. The direct process at this stoichiometry would fit well
with coal, since it has a low amount of hydrogen, while the indirect process
with separate methanol production fits better with natural gas, which has a
high amount of hydrogen. As seen above, the H 2 /CO ratio can be controlled
by adding steam, or by gasifying with CO 2 . The importance of the water
gas shift, Reaction 6.6, is shown by the lower conversion and the shift in
the H 2 /CO ratio for maximum conversion when it is not active. For a direct
formation of DME with a hydrogen rich syngas, the slow water gas reaction gives a slightly higher conversion than with the water gas reaction at the
H 2 /CO ratio of about 2.
The equilibrium reaction products are also a function of the ratio of
hydrogen to carbon in the syngas. The product distribution for the direct conversion process with a H 2 /CO ratio of 1.0 is shown in Figure 6.8. As expected
from the conversion effectiveness, the yield of DME is highest at a H 2 /CO
of 1.0, the stoichiometric condition. When this ratio is less than one, there
Figure 6.8
Conversion of syngas to DME and the equilibrium composition of the products of Reactions
6.5, 6.6, and 6.7 shown as a function of hydrogen to carbon ratio of the syngas. The temperature
is 260°C and the pressure 50 atm.