CC Our Daily Lives
HEMISTRY IN USE
Petroleum
Petroleum, or crude oil, was discovered in the United States
(Pennsylvania) in 1859 and in the Middle East (Iran) in 1908.
It has been found in many other locations since these initial
discoveries and is now pumped from the ground in many
parts of the world. Petroleum consists mainly of hydrocar-
bons. Small amounts of organic compounds containing
nitrogen, sulfur, and oxygen are also present. Each oil field
produces petroleum with a particular set of characteristics.
Distillation of petroleum produces several fractions.
Gasoline is much in demand, so higher hydrocarbons (C 12
and up) are “cracked” to increase the amount of gasoline that
can be made from a barrel of petroleum. The hydrocarbons
are heated, in the absence of air and in the presence of a cat-
alyst, to produce a mixture of smaller alkanes that can be used
in gasoline. This process is called catalytic cracking.
The octane number(rating) of a gasoline indicates how
smoothly it burns and how much engine “knock” it produces.
(Engine knock is caused by premature detonation of fuel in
the combustion chamber.) 2,2,4-trimethylpentane, isooctane,
has excellent combustion properties and was arbitrarily as-
signed an octane number of 100. Heptane, CH 3 (CH 2 ) 5 CH 3 ,
has very poor combustion properties and was assigned an oc-
tane number of zero.isooctane (octane number100)CH 3 C CH 2 CH CH 3CH 3CH 3CH 3Mixtures of these two were prepared and burned in test
engines to establish the octane scale. The octane number of
such a mixture is the percentage of isooctane in it. Gasolines
burned in standard test engines are assigned octane numbers
based on the compression ratio at which they begin to knock.
A 90-octane fuel produces the same amount of knock as the
90% isooctane/10% heptane mixture. Branched-chain com-
pounds produce less knock than straight-chain compounds.
The octane numbers of two isomeric hexanes areCH 3 (CH 2 ) 4 CH 3
hexane (octane number25)(CH 3 ) 3 CCH 2 CH 3
2,2-dimethylbutane (octane number92)Petroleum FractionsFraction* Principal Composition Distillation Range (°C)natural gas C 1 –C 4 below 20
bottled gas C 5 –C 6 20–60
gasoline C 4 –C 12 40–200
kerosene C 10 –C 16 175–275
fuel oil, diesel oil C 15 –C 20 250–400
lubricating oils C 18 –C 22 above 300
paraffin C 23 –C 29 mp 50–60
asphalt — viscous liquid
(“bottoms fraction”)
coke — solid*Other descriptions and distillation ranges have been used, but all are similar.CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3
heptane (octane number0)Petroleum refinery towers.