Description
Shale oil is a type of crude oil extracted from
sedimentary shale formations by heating the shale to 425–
535°C (800–1000°F). The specific gravity of shale oil ranges
from 0.9 to 1.0, which exceeds that of natural crude oil. Two
methods are used to extract the oil from the shale. The shale can
be excavated, crushed, and fed into retorts for heating (retorting)
and extraction. Alternatively, shafts can be driven into the
shale formation and the shale is heated in situ. Only about 75–
110 l (20–30 gallons) of oil can be extracted from a metric ton
of shale. The oil extracted from oil shale is somewhat similar to
oil pumped from conventional oil wells, but shale oil extraction
is more complex and expensive than convention oil
extraction processes.
Shale oil has been extracted from the earth and employed
for various uses since ancient times. As early as 1637, shales in
Sweden were roasted over wood fires to extract potassium
aluminum sulfate, a salt used in tanning leather and for fixing
colors in fabrics. Late in the 1800s, oil shales were retorted on
a small scale for hydrocarbon recovery. Production continued
until 1966 when it was discontinued because of the availability
of cheaper supplies of petroleum crude oil.
Oil shale deposits in France and Scotland were exploited
commercially as early as the mid-1800s. As many as 20 beds of
oil shale were mined in Scotland at different times. Mining
continued during the 1800s and by 1881 oil shale production
had reached 1 million metric tons per year. Between 1 and 4
million metric tons of oil shale were mined yearly in Scotland
from 1881 to 1955 when production began to decline, then
ceased in 1962. Canada produced some shale oil from deposits
in New Brunswick and Ontario starting in the mid-1800s.
Common products made from oil shale in these early operations
were kerosene and lamp oil, paraffin, fuel oil, lubricating
oil and grease, and ammonium sulfate.
The oil-bearing component of the shale is called kerogen.
Kerogen is a bitumen-like solid material
consisting of approximately 75% carbon, 10% hydrogen, 2.5%
nitrogen, 1.0% sulfur, and the balance oxygen. Kerogen is
a mixture of aliphatic and aromatic hydrocarbons of humic and
algal origin. It was formed millions of years ago by deposition
of silt and organic debris on lake beds and sea bottoms.
Shale oil differs from crude oil from other sources in that it
contains significant amounts of nitrogen (about 35%), oxygen (about 20%), and sulfur (about 5%) compounds. Nitrogen
compounds include pyridine, quinoline, amines, pyrrole, and
indole. The major oxygen-containing compounds are phenols,
carboxylic acids, and ketones. Sulfur compounds found in
shale oil include sulfides, thiols, and thiophenes.
The remainder of shale oil consists of hydrocarbons. An
analysis of shale oil from the western United States found 12%
isoalkenes and cycloalkenes, 6% polycyclic aromatic hydrocarbons
(PAHs), 6% normal olefins, 6% normal alkanes, and
4% monocyclic aromatic compounds. After fractionating and
refining, the oil yields about 20% gasoline, 30% kerosene, 30%
gas oil, and 20% lube oils.
Oil shale is found worldwide, but the largest deposits are in
the Green River Formation that covers portions of Colorado,
Utah, and Wyoming in the United States. Oil reserves in this
formation have been estimated to range from 1.2 to 1.8 trillion
barrels. Not all of these reserves are recoverable, but about
800 000 million barrels could be extracted from this formation
using currently available technologies. At the present rate of oil
consumption in the United States, this represents about a 400-
year supply.
Uses
Shale oil, as mentioned above, is used in the production of
gasoline, kerosene, gas oil, and lube oils. Other products that
can be made from shale oil include varnishes, pitches, and
mastics. The latter products are employed as solvents and glues,
and as starting materials for the printing and rubber products
industries. Sulfonated shale oils (e.g., Ichthyol) have found
uses as pharmaceutical agents for the treatment of skin diseases
such as eczema and psoriasis, rheumatic diseases, and even for
the treatment of blunt trauma. Human testing has shown that
sulfonated shale oils are without significant side effects and are
as effective as hydrocortisone in treating inflammatory lesions
of the skin.
Environmental Fate
Releases of shale oil components to the environment can
occur in several ways during the extraction, processing, and
transport of this material. The more volatile components of
shale oil can be released to the atmosphere especially during
the retorting process when heat is applied to the shale.
Workers at shale processing plants and, to a lesser extent,
people residing near those operations can be exposed to the
lighter volatile organic chemical components of shale oil
released into the air. Spills or other accidental releases of shale
oil and its components can threaten wildlife and adversely
impact aquatic organisms if the material reaches surface
waters. In some areas, spills of oil could reach shallow aquifers
thus affecting ground water. Soil contamination is an obvious
result of such spills as well.
