Page 144 - Academic Press Encyclopedia of Physical Science and Technology 3rd Organic Chemistry

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Encyclopedia of Physical Science and Technology EN006K-933 June 29, 2001 12:14

254 Fuel Chemistry

TABLE I Total Primary Energy Consumption sil fuel formation. Global carbon cycle illustrates the fate
and Their Sources carbon in the world. Carbon exists in the world in three
1999 (Quadrillion Btus) major reservoirs: in the atmosphere as CO 2 , in the rocks as
CO −− , and in the oceans, which occupy two thirds of the
3
Source World U.S. planet’s surface, as carbonate (CO −− ) and bicarbonates
3
Petroleum 152.20 37.71 (HCO ). The CO 2 in the atmosphere has a vital role in the
−
3
Natural Gas 86.89 22.1 formation of fossil fuels. The CO 2 in the atmosphere reacts
Coal 84.77 21.7 with water vapor in the presence of sunlight to form the or-
Nuclear 25.25 7.73
ganic matter and oxygen by photosynthesis reaction. The
Hydro Electric 27.29 3
organic matter can be of microscopic plant (phytoplank-
Renewable 2.83 4.37
ton) or microscopic animal (zooplankton) or higher plants.
Total 381.88 96.6
The dead organic matter through decay reaction combines
with oxygen and forms CO 2 and H 2 O. This decay reac-
tion is exactly the reverse of the photosynthesis reaction.
and 10 times, respectively. A vast majority of this energy Fossil fuels have formed by minimization or prevention
(about 85%) comes from fossil fuels. These fuels—coal, of the decay reaction by possibly inundating the organic
oil, natural gas, oil shale, and tar sands were formed over matter by water or covering by sediments. The organic
millions years by compression of organic material (plant matter, microscopic plants and animals, and higher plants,
and animal sources) prevented from decay and buried in is chemically comprised of protiens, lipids, carbohydrates,
the ground. Table I shows the total primary energy use glycosides, resins, and lignin. Of these, lignin is predom-
and the sources. Most of the fuels are used to generate inantly present in higher plants. Other components are
heat and/or power. This chapter deals with the fuels ori- predominantly present in zoo, phytoplankton, and algae
(microscopic organic matter). Coal is a complex material
gin, properties, and utilization methods and chemistry of
composed of microscopically distinguishable, physically
these processes.
distinctive, and chemically different organic substances
called macerals and inorganic substances called minerals.
I. FUELS During the transformation of organic matter to coal,
there is a significant loss in oxygen and moderate loss
Fossil fuels are hydrocarbons comprising of primarily car- of hydrogen with an increase in carbon content by ini-
bon and hydrogen and are classified as solid, liquid, and tial aerobic reactions and subsequent anaerobic reactions.
gaseous based on their physical state. Solid fuels include This process leads to the formation of kerogen. The or-
not only naturally occurring fuels such as wood, peat, lig- ganic matter, which is rich in algae, forms alginitic kero-
nite, bituminous coal, and anthracites, but also certain gen (type I kerogen); whereas the organic matter, which
waste products by human activities like petroleum coke is rich in fatty acids and long-chain hydrocarbons, leads
and municipal solid waste. Approximately 95% of the coal to the formation of liptinic or Type II kerogen. The or-
mined in the United States is combusted in boilers and fur- ganic matter consisting of lignin structure forms Type III
naces to produce heat and/or steam. The other 5% is used kerogen and leads to the formation of coal. Formation of
to produce coke for metallurgical uses. Liquid fuels are kerogen from the organic matter is by a process called
mostly produced in a refinery by refining naturally occur- “diagenesis,” and the transformation of kerogen to fossil
ring crude oil, which include gasoline, diesel, kerosene, fuels is by a process called “catagenesis.” The tempera-
light distillates, and residual fuels oils. Each of these has ture in the earth’s surface increases with depth at a typical
◦
different boiling range and is obtained from a distillation rate of 10–30 C/km. As the temperature and pressure due
process. Gaseous fuels include natural gas, blast furnace to overburden increase, peat is transformed into lignite
gas, coke oven gas, refinery gases, liquefied natural gas, in about 30–50 million years. The primary reactions that
producer gas, water gas and coal gas produced from vari- are believed to occur during this transformation are de-
ous gasification processes. Except for natural gas, most of hydration, decarboxylation, and condensation leading to
the gaseous fuels are manufactured. a loss of oxygen, hydrogen, and some carbon. Progres-
sive transformation of lignite to subbituminous coal to
bituminous coal and then to anthracite occurs in a time
A. Origin of Fossil Fuels
period ranging from 50 to 300 million years. The reac-
Earth is a closed system with respect to carbon, and there- tions responsible for these changes resulting in rapid loss
fore carbon on this planet has to be used and reused. A of hydrogen are dealkylation, aromatization, and conden-
total account of carbon in the world would explain fos- sation. Formation of anthracites from bituminous coals