5. Direct Coal Liquefaction (DCL)
• Direct coal liquefaction starts just prior to World
War II by Germany, continues through the 1950s
and 1960s with the research by the U.S.
• Direct coal liquefaction refers to the direct reaction
of coal with hydrogen to form liquids.
• The hydrogen is also required to increasing the
H/C ratio of the coal as it is liquefied. One of the
key differences between coal and petroleum is the
much lower H/C atomic ratio of coal (0.7 vs 1.5 for
6. • Direct liquefaction involves the addition of
hydrogen to coal in a solvent slurry at elevated
temperature and pressure.
• Coal dissolution is accomplished under high
temperature (~400 0C) and pressure (~1500-3000
psi) with hydrogen and a coal-derived solvent.
8. • The principal products of a direct-liquefaction CTL
plant would be naphtha and middle distillates.
• direct-liquefaction products contain more aromatic
and cyclic hydrocarbons and fewer paraffins, and
they have a lower overall hydrogen content.
• prospective yields are reported to be between 2.7
and 3.0 barrels per ton of as-received coal
• theoretical efficiency can be high…roughly 70-75%
9. Direct Liquefaction Process
• A single-stage direct liquefaction process
process gives distillates via one primary reactor.
• A two-stage direct liquefaction process
processis designed to give distillate products via
two reactor stages in series. The primary function
of the first stage is coal dissolution and is operated
either without a catalyst or with only a low-activity
12. • Coal is slurried with a distillable recycled solvent
that has been rehydrogenated to restore its
hydrogen donation capacity
• The slurry is mixed with H2, preheated and fed to
a simple up-flow tubular reactor that operates at
425-450 ºC and 2575 psig .
• No catalyst is added to liquefaction reactor
• Yields of up to 47% for lignites, 50% for sub-
bituminous coals and 60% for bituminous coals
could be achieved.
14. • This reactor operates at temperatures of 425-
455°C and a pressure of 2900 psig
• H2 is added and the mixture is preheated and fed
to an ebullated bed hydrocracker
• A conventional supported hydrotreating
catalyst, either Ni-Mo or Co-Mo alumina is used.
• As with other processes, yields are dependent on
the coal. >95% overall conversion can be obtained
with suitable coals, with liquid yields up to 50%
15. A two-stage direct liquefaction
• Integrated Two-Stage Liquefaction (ITSL)
• Catalytic Multi-stage Liquefaction (CMSL)
21. Indirect Coal Liquefaction
• In Indirect Liquefaction (IL) coal is first gasified
to form syngas. Syngas is then converted to
liquids by means of a catalyst and Fischer
Tropsch (FT) chemistry
• Synthesis Gas or Syngas –mixture of
CO, H2, CO2, H2O
• theoretical efficiency is lower…roughly 60-65%
22. • The process begins with the gasification of coal
• reacting coal with steam and oxygen at elevated
temperatures (1,000 to 1,500 degrees Celsius)
and moderate pressure(~500 pounds per square
• The naphtha product is basically a very low–
octane (i.e., about 40 octane) gasoline that must
be extensively upgraded before it can be used as
an automotive fuel.
• Conversion of synthesis gas to hydrocarbons is
highly exothermic (i.e., it releases heat).
24. The Methanol-to-Gasoline Coal-
to-Liquids (MTG CTL)
• The front end of an MTG CTL plant would be
similar to that of an FT CTL plant.
CTL of (200 to 300 degrees
steps Celsius, about 750 psi)
from Very exotermic
25. • To better control this heat release,methanol is first
dehydrated to produce dimethyl ether.
• After upgrading and separations, the liquid-fuel
yield of an MTG CTL plant would be about 90-
percent gasoline, with most of the remainder being
• MTG reactor does not produce any of the heavy
hydrocarbons generally found in diesel oil, jet
fuel, and heavy oils and waxes.