Physical and chemical properties of petroleum

Physical & chemical properties of Petroleum…

What is petroleum.
 Petroleum:
A latin word “petra” means rock and “oleum” means
oil therefore “rock oil”
 Hydrocarbons
Hydrocarbon generaly another term used with word
petroleum for any of its forms. The most important
substances present are hydrocarbons, which are
compounds containing only two elements, hydrogen
and carbon also small amount of Oxygen, Sulpher
and Nitrogen (NSO compounds).
 Mostly in oils the hydrogen and carbon comprises
95% to 99% of the total.

Chemical properties of
Petroleum
Hydrocarbons are found in nature in many
different forms, mainly as:
Liquid Petroleum: known as “crude oil” to
distinguish it from “refined oil” . It is most
important commercially.
Natural Gas: which is the lighter fraction of
hydrocarbons, can be free or dissolved.
Asphalt, Tar, Pitch: these are solid or semi-
solid forms of hydrocarbons, the heavy
fraction.

Hydrocarbon Series
 A saturated hydrocarbon (sometime called
Alkane) is one which the valence of all the carbon
atoms is satisfied by single bonds For each carbon
atom is connected to each other carbon atom by a
single covelant bond e.g Parrafins.
 An unsaturated hydrocarbon is one in which the
valence of some of the carbon atom is not satisfied
by single bond, so that these atoms are connected
to one another with two or more covelant bonds
e.g Benzene.
 It is generally agreed that Hydrocarbons of Four
different Series or Types are present in important
Quantities in Petroleum.

Parafins
Paraffins are also called alkanes and have the
general formula of CnH2n+2,
where n is the number of carbon atoms.
Paraffins from C1 to C40 usually appear in crude oil
and represent up to 20% of crude by volume. Since
paraffins are fully saturated (no double bond), they are
stable and remain unchanged over long periods of
geological time.

Napthenes
 Naphthenes or cycloparaffins are ring or
cyclic saturated hydrocarbons with the general
formula of CnH2n.
 Thermodynamic studies show that naphthene
rings with five and six carbon atoms are the most
stable naphthenic hydrocarbons. The content of
cycloparaffins in petroleum may vary up to 60%.

Aromatics
 Aromatics are an important series of
hydrocarbons found in almost every petroleum
mixture from any part of the world.
 This series of aromatics is called alkylbenzenes
and have a general formula of CnH2n-6 (where n ≥
6).
 Its example are Benzene C6H6

Asphaltenes
 They are composed of fused benzene-ring
network, but they contain impurity atoms and
are not true hydrocarbons.These impurities are
the high in moleculer weight compound
previously referred to as NSO compounds.
 Asphaltenes are heavy compounds of crude
oil and the major components in many natural
tars and asphalts.

Chemical composition of typical
Petroleum
Element Natural Gas Crude oil Asphalt
Carbon 65-80 82-87 80-85
Hydrogen 1-25 12-15 9-11
Sulphar 0.2 0.1-6 2-8
Nitrogen 1-15 0.1-2 0-2
Oxygen 0 0.1-5 0

Classification of crude oils
 Crude oil may be classified by their relative
enrichment in the four hydrocarbon groups or
series describe above.most normal crude oils
fall within only three of these fields.They can
be either.
1. Paraffinic oil: rich in paraffins.
2) Paraffinic-Nephthenic Oil: They can have
nearly equal amounts of Paraffins and
naphthenese which togeather make up more
than 50% of the crude.
3) Aromatic intermediate Oil: They can have
subequal amount of Paraffins and nephthenes,
which total less than 50% and the composition
is dominated by the aromatics and

Physical properties…
The physical properties are most commonly used
in petroleum are as under:
 Density
 Specific gravity
 Volume
 Viscosity
 Refractive index
 Fluoresence
 Optical activity
 Colour
 Odour
 Boiling point

Specific Gravity
 Specific gravity of oil generally lies in between
0.73 and very slightly above 1.0
 Paraffin oils are commonly lies asphalt base
oils almost in variably high. The gravity is
conventionally signified by the Greek letter rho
ρ.
 The gravity was formerly express in degrees of
the European Beaumé scale read directly
hydrometer this means the degree goes up as
the density goes down. The high gravity is not
a heavy oil.

 Beaumé value ,with the density standardize to
15.6 °C, is given by the equation.
Be=(140/ ρ )-130
 The Beaumé scale was long ago superseded
by the scale of the American Petroleum
Institute, called the API Scale. The relation
between two scales is given by:
API value=(1.010 71*Be)-0.107 14
in relation to the density, this is equivalent to
API value=(141.5/ ρ)-131.5

 The value of API Gravity is high correspond to
low Specific Gravity.
And the low API Gravity value correspond to
High Specific Gravity.
Between oils in the same reservoir rocks but
in separate traps.
And between oils within the same reservoir
rocks but different structural position.

 The most favorite grade of crude oil is about 37°
API, equivalent to a relative density of 0.84.
 Very light crude above 40° API, occur in large
quantity in Algeria, south eastern Australia and in
some Indonesian and Andean fields.
 Very heavy crudes dominant production from
California, Mexico,Venezuela and Sicily.
Gravity of Crude oil at different
temperature..

Gravity at 60 °F change in gravity for
each
1°F change in T.
Specific
gravity
API Specific
gravity
0.90 25.7 0.00036
0.80 45.4 0.00039
0.70 70.6 0.00049

Colors
 Paraffinic oils are light color: Yellow to
Brown by transmitted light.
Asphalt-base oils are commonly brown to
black; many of them are known as “Black
oils”. Color is commonly
determined with the Saybolt Colorimeter.

Refractive Index
 Absolute refractive index (RI) of a
substance is the inverse ratio of the speed
of light. The range of
refractive indices for petroleum is
from1.42 to 1.48.
The lower indices are the lighter oils.
The refractive index is dependent on the
density of the oils, the heavy (lower API
Gravity) oils have the higher indecies.

Refractive Indices of Representative
Oils
API Degrees Density Refractive
Index
6 1.029 1.566
32 0.918 1.509
44 0.802 1.448
58 0.742 1.417
72 0.691 1.390

Fluorescence
 The all oils show more or less
fluorescence. The aromatic oils
being the most fluorescent. The
fluorescent colors of crude oils range from
Yellow through Green to Blue.
 Fluorescence is observed under ultraviolet
radiation that most generally used for
Petroleum having wavelengths of 2,537
and 3,650 angstrom unit.

Odor
 Due to the light hydrocarbons some oils is
agreeable like gasoline odor.
 Aromatics impart pleasant odors.
 Oils containing sulphur and certain
nitrogen compounds usually a
disagreeable odor.

Viscosity.
 Viscosity is the internal friction of fluid causing it is
resistant put change of form.(viscosity is
conventionally defied by the Greek letter eta, η).
 It is the ratio of stress to shear per unit time.
Shear with liquid is not a constant but is
proportional to time
 viscosity is defined by the ratio,
 force*distance / area*velocity
 The CGS unit of viscosity is the poise which is
too larger unit of practical purpose in the oil
industry. Viscosity of oil are therefore
conventionally measured in centipoises.
 Such a unit is a saybolt universal second(SUS):

 SUS = viscosity in centipoises*4.635 / relative
density
 Hydrocarbons having viscosity higher then
10,000 mPa are now to be called natural tar.
 A useful indicator of the viscosity of a crude oil
is it pour point. This is the lowest temperature
at which the crude will flow under described
controlling conditions. pour point is above 40
degree(more than 100 F) a relatively common
among crudes having highest contents of
paraffin's wax.

Volume
 Oil in the reservoir contains dissolved gas,
and the volume of the solution depends
upon the formation gas-oil ratio and the
reservoir pressure.
 Gas may be dissolved in oils under
increasing pressure and increase the
volume in solution.
 The volume of liquid petroleum, at
constant pressure.

 The volume of surface equivalent gas will
dissolve in a unit volume of reservoir oil.
Increases as the reservoir pressure increases
until the oil is finally saturated with gas and no
more gas will dissolve in the oil.

Boiling Point
 Atmospheric true boiling point (TBP) data are
obtained through distillation of a petroleum mixture
using a distillation column with 15-100 theoretical
plates at relatively high reflux ratios (1-5 or greater).
 The high degree of fractionation in these
distillations gives accurate component distributions for
mixtures. The lack of standardized apparatus and
operational procedure is a disadvantage, but variations
between TBP data reported by different laboratories for
the same sample are small.

ASTMD 86 and TBP curves for a
kerosene sample.

Physical and chemical properties of petroleum

Physical and chemical properties of petroleum

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