Page 23 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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1. INTRODUCTION 3
in Iraq. As in January 1, 2002, the total number of world oil
maturation, and in-situ alteration of petroleum.
wells was 830 689, excluding shut or service wells (OGJ, Dec. interconversion schemes may occur during the formation,
22, 2003). Estimates of world oil reserves in 1967 were at Paraffins are also called alkanes and have the general for-
418 billion and in 1987 were at 896 billion bbl, which shows mula of C n H 2n+2 , where n is the number of carbon atoms.
an increase of 114% in this period [5]. Two-thirds of these Paraffins are divided into two groups of normal and isoparaf-
reserves are in the Middle East, although this portion de- fins. Normal paraffins or normal alkanes are simply written
pends on the type of oil considered. Although some people as n-paraffins or n-alkanes and they are open, straight-chain
believe the Middle East has a little more than half of world saturated hydrocarbons. Paraffins are the largest series of hy-
oil reserves, it is believed that many undiscovered oil reser- drocarbons and begin with methane (CH 4 ), which is also rep-
voirs exist offshore under the sea, and with increase in use resented by C 1 . Three n-alkanes, methane (C 1 ), ethane (C 2 ),
of the other sources of energy, such as natural gas or coal, and n-butane (C 4 ), are shown below:
and through energy conservation, oil production may well
continue to the end of the century. January 2000, the total H H H H H H H
amount of gas reserves was about 5.15 × 10 15 scf, and ⏐ ⏐ ⏐ ⏐ ⏐ ⏐ ⏐
9 H ⎯ C ⎯ H H ⎯ C ⎯ C ⎯ H H ⎯ C ⎯ C ⎯ C ⎯ C ⎯ H
its production in 1999 was about 200 × 10 scf/d (5.66 ×
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3
9
10 sm /d) through some 1500 gas plants [3]. In January H H H H H H H
2004, according to OGJ (Dec. 22, 2003, p. 44), world natu-
ral gas reserves stood at 6.068 × 10 15 scf (6068.302 trillion
scf). This shows that existing gas reserves may last for some Methane Ethane n-Butane
70 years. Estimated natural gas reserves in 1975 were at
3
2.5 × 10 15 scf (7.08 × 10 13 sm ), that is, about 50% of current (CH 4 ) (C 2 H 6 ) (C 4 H 10 )
reserves [6]. In the United States, consumption of oil and gas
in 1998 was about 65% of total energy consumption. Crude The open formula for n-C 4 can also be shown as CH 3
oil demand in the United State in 1998 was about 15 million CH 2 CH 2 CH 3 and for simplicity in drawing, usually the
bbl/d, that is, about 23% of total world crude production [3]. CH 3 and CH 2 groups are not written and only the carbon–
Worldwide consumption of natural gas as a clean fuel is on carbon bonds are drawn. For example, for a n-alkane com-
the rise, and attempts are underway to expand the trans- pound of n-heptadecane with the formula of C 17 H 36 , the
fer of natural gas through pipelines as well as its conver- structure can also be shown as follows:
sion to liquid fuels such as gasoline. The world energy con-
sumption is distributed as 35% through oil, 31% through
coal, and 23% through natural gas. Nearly 11% of total
world energy is produced through nuclear and hydroelectric -Heptadecane (C 17 H 36 )
sources [1].
The second group of paraffins is called isoparaffins; these
are branched-type hydrocarbons and begin with isobutane
(methylpropane), which has the same closed formula as n-
1.1.1 Hydrocarbons
butane (C 4 H 10 ). Compounds of different structures but the
In early days of chemistry science, chemical compounds were same closed formula are called isomers. Three branched or
divided into two groups: inorganic and organic, depending isoparaffin compounds are shown below: --`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
on their original source. Inorganic compounds were obtained
from minerals, while organic compounds were obtained from CH 3 CH 3 CH 3
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living organisms and contained carbon. However, now or- CH 3 | CH CH 3 CH 3 | CH CH 2 | | CH 3 CH 3 CH CH 2 | CH 2 | CH 2 | CH 2 | CH 3
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ganic compounds can be produced in the laboratory. Those
organic compounds that contain only elements of carbon (C)
isobutane isopentane (methylbutane) isooctane (2-methylheptane)
and hydrogen (H) are called hydrocarbons, and they form
the largest group of organic compounds. There might be as (C 4 H 10 ) ( C 5 H 12 ) ( C 8 H 18 )
many as several thousand different hydrocarbon compounds
in petroleum reservoir fluids. Hydrocarbon compounds have In the case of isooctane, if the methyl group (CH 3 )isat-
a general closed formula of C x H y , where x and y are integer tached to another carbon, then we have another compound
numbers. The lightest hydrocarbon is methane (CH 4 ), which (i.e., 3-methylheptane). It is also possible to have more than
is the main component in a natural gas. Methane is from a one branch of CH 3 group, for example, 2,3-dimethylhexane
group of hydrocarbons called paraffins. Generally, hydrocar- and 2-methylheptane, which are simply shown as following:
bons are divided into four groups: (1) paraffins, (2) olefins,
(3) naphthenes, and (4) aromatics. Paraffins, olefins, and
naphthenes are sometime called aliphatic versus aromatic
compounds. The International Union of Pure and Applied
Chemistry (IUPAC) is a nongovernment organization that
provides standard names, nomenclature, and symbols for dif-
2-Methylheptane (C 8 H 18 ) 2,3-Dimethylhexane (C 8 H 18 )
ferent chemical compounds that are widely used [7]. The
relationship between the various hydrocarbon constituents Numbers refer to carbon numbers where the methyl group
of crude oils is hydrogen addition or hydrogen loss. Such is attached. For example, 1 refers to the first carbon either

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