Page 22 - Synthetic Fuels Handbook

10 CHAPTER ONE

In the process, methanol is first made from methane (natural gas) in a series of three
reactions:

Steam reforming: CH + H O → CO + 3H ΔrH =+206 kJ/mol
4 2 2
Water shift reaction: CO + H O → CO + H 2 ΔrH =+206 kJ/mol
2
2
Methanol synthesis: 2H + CO → CH OH ΔrH =−92 kJ/mol
2
3
Overall: CO + CO + 5 H → 2 CH OH + H O + heat
2
2
2
3
The methanol is then converted to gasoline by a dehydration step to produce dimethyl
ether:
2CH OH → CH OCH + H O
3
2
3
3
This is then further dehydrated over a zeolite catalyst, ZSM-5, to give gasoline.
n+2CH OH → CH (CH ) CH + n+2H O
3
2
3
3
2 n
Many of the methods for the production of fuels from coal (as well as the conversion of
coal to syngas) release carbon dioxide in the conversion process, far more than is released
in the production of liquid fuels from petroleum. If these methods were adopted to replace
declining petroleum supplies, carbon dioxide emissions would be greatly increased on a
global scale. Hence, carbon dioxide sequestration has been proposed to avoid releasing it
into the atmosphere, though no pilot projects have confirmed the feasibility of this approach
on a wide scale. Sequestration, however, may well add to the costs of synthetic fuels.
Fischer-Tropsch synthesis from natural gas is another established technology. Further
expansion is planned for the year 2010, the bulk of this capacity being located in the Middle
East (Qatar) (Chemical Market Reporter, 2004; IEA, 2004). The conversion efficiency is
about 55 percent, with a theoretical maximum of about 78 percent. Due to the energy loss,
this process makes only economic sense for cheap stranded gas. As the cost for liquefied
natural gas transportation declines and demand increases, the importance or need for such
options may also decline.
1.2.3 Oil Shale
Oil shale is a fine-grained sedimentary rock containing relatively large amounts of organic
matter (called kerogen), an organic sediment (Fig. 1.2) from which significant amounts of
shale oil and combustible gas can be extracted by destructive distillation (Longwell, 1990;
Scouten, 1990; Lee, 1991; Bartis et al., 2005).
Oil shale, or the kerogen contained therein, does not have definite geological definition
or a specific chemical formula. Different type of oil shale vary by the chemical consist, type
of kerogen, age, and depositional history, including the organisms from which they were
derived. Based upon environment of deposition, oil shale could be divided into three groups
which are of terrestrial (land) origin, lacustrine (lake) origin, and marine (sea) origin.
The term oil shale is a misnomer. It does not contain oil nor is it commonly shale. The
organic material is chiefly kerogen, and the shale is usually a relatively hard rock, called
marl. Properly processed, kerogen can be converted into a substance somewhat similar to
petroleum. However, the kerogen in oil shale has not gone through the oil window by which
petroleum is produced and to be converted into a liquid hydrocarbon product, it must be
heated to a high temperature. By this process the organic material is converted into a liquid,
which must be further processed to produce oil which is said to be better than the lowest