Energy Engineering Lecture

1. Properties of petroleum
products
Energy Engineering
1

2. PROPERTIES OF PETROLEUM PRODUCTS
Elemental (Ultimate) Analysis
➢The analysis of petroleum for the percentages of carbon,
hydrogen, nitrogen, oxygen, and sulfur is perhaps the first method
used to examine the general nature and perform an evaluation, of
a feedstock.
➢The atomic ratios of the various elements to carbon (i.e., H /C, N
/C, O /C, and S/C) are frequently used for indications of the
overall character of the feedstock.
➢It is also of value to determine the amounts of trace elements,
such as vanadium, nickel, and other metals, in a feedstock since
these materials can have serious deleterious effects on catalyst
performance during refining by catalytic processes.
2

3. PROPERTIES OF PETROLEUM PRODUCTS
Elemental (Ultimate) Analysis (cont.)
➢However, it has become apparent, with the introduction of the heavier
feedstocks into refinery operations, that these ratios are not the only
requirement for predicting feedstock character before refining.
➢Of the data that are available, the proportions of the elements in petroleum
vary only slightly over narrow limits:
➢Carbon 83.0 to 87.0%
➢Hydrogen 10.0 to 14.0%
➢Nitrogen 0.1 to 2.0%
➢Oxygen 0.05 to 1.5%
➢Sulfur 0.05 to 6.0%
➢Metals (Ni and V) <1000 ppm
3

4. PROPERTIES OF PETROLEUM PRODUCTS
Density and specific gravity
➢Density is the mass of a unit volume of material at a specified
temperature and has the dimensions of grams per cubic
centimetre.
➢Specific gravity is the ratio of the mass of a volume of the
substance to the mass of the same volume of water and is
dependent on two temperatures, those at which the masses of
the sample and the water are measured.
➢The standard temperatures for a specific gravity in the petroleum
industry in North America are 60 /60 oF.
4

5. Vapor Pressure
➢With decreased atmospheric pressure at high altitudes, the vapor
comes out of the liquid fuel causing vapor locking and difficulty in
starting spark ignition engines.
➢If the vapor pressure of the fuel is too low, starting the engine and
lubricating oil dilution becomes difficult.
➢If the vapor pressure is high that means the flash point is low and
results in danger of fire and explosion, Besides, breathing loss is high.
5

6. Vapour Pressure
➢Lubricants having high vapour pressure will be lost quickly.
➢Vapour pressure of the liquid fuel is reported as Reid Vapour pressure
in psi or mm of Hg at 100 oF.
➢Reid vapor pressure (RVP) is a common measure of the volatility of
gasoline and other petroleum products.
➢It is defined as the absolute vapor pressure exerted by the vapor of the
liquid and any dissolved gases/moisture at 37.8 °C (100 °F) as
determined by the test method ASTM-D-323, which was first developed
in 1930 and has been revised several times (the latest version is ASTM
D323-15a).
6

7. Viscosity
The viscosity of a fluid is a measure of its resistance to ( flow).
Viscosity is an important property because:
➢High viscosity fuel oil can not be properly atomised resulting in loss of
fuel.
➢Highly viscous oil has to be preheated to reduce the viscosity to
minimise the pressure drop in pumping to different refineries from the
oil field.
➢High viscosity lubricating oil reduces its fluidity besides causing undue
friction.
7

8. Viscosity
➢In the cgs system, the unit of viscosity is the poise (p = dynes.s/cm2
or g/cm.s) or which is too larger unit of practical purpose in the oil
industry. Viscosity of oil are therefore conventionally measured in
centipoises (1cp = 0.01 P).
➢Two other terms in common use are kinematic viscosity and fluidity.
➢The kinematic viscosity is the viscosity in centipoises divided by the
density, and the unit is the stoke (cm2/sec), although centistokes
(0.01 cSt) is in more common usage.
➢fluidity is simply the reciprocal of viscosity.
8

9. Viscosity index
➢The viscosity of the oil decreases with increase in temperature.
➢The change in viscosity with change in temperature is expressed by
viscosity index.
➢It is an empirical number indicating the rate of change of viscosity of an oil
from 100 oF to 210 oF.
➢Low viscosity index means a large change in viscosity with change in
temperature.
➢A high viscosity index shows relatively small change in viscosity with
temperature.
9

10. Viscosity index
➢Viscosity index of an oil is determined by measuring its viscosity at two
temperatures and comparing the results with those for a standard oil of V.I. =
100 and for a standard oil of V.I. = 0.
➢The viscosity index is calculated by the following formula:
V.I. = (L - U)/ (L - H) x 100
U = Viscosity of oil sample at 100 oF
L = Viscosity of a standard oil of V.I. = 0 at 210 oF
H = Viscosity of a standard oil of V.I. = 100 at 210 oF
10

11. Viscosity index
➢Viscosity index measures the paraffinity of an oil.
➢Lubricating oil should in general have high viscosity index.
➢Viscosity index improvers ( e.g. polybutene) are used for improving it.
➢High V.I. oils are called multigrade oils.
11

12. Flash point
➢The flash point of petroleum or a petroleum product is the temperature to
which the product must be heated under specified conditions to give off
sufficient vapor to form a mixture with air that can be ignited momentarily by
a specified flame.
➢Flash point is an important parameter for safety considerations, especially
during storage and transportation of volatile petroleum products (i.e., LPG,
light naphtha, gasoline).
➢The surrounding temperature around a storage tank should always be less
than the flash point of the fuel to avoid possibility of ignition.
12

13. Flash point
➢For products with flash point below 40 oC (104 oF), special precautions are
necessary for safe handling.
➢Flash point should not be mistaken with fire point, which is defined as the
minimum temperature at which the hydrocarbon will continue to burn for at
least 5 s after being ignited by a flame.
13

14. Flash point
➢The flash point of a petroleum product is also used to detect contamination.
➢A substantially lower flash point than expected for a product is a reliable
indicator that a product has become contaminated with a more volatile
product, such as gasoline.
➢The flash point is also an aid in establishing the identity of a particular
petroleum product.
➢Combustible liquid a liquid with a flash point in excess of 37.8 oC (100 oF),
but below 93.3 oC (200 oF).
➢Flammable liquid a liquid having a flash point below 37.8 oC (100 oF).
Flash point less than 23 oC is dangerous and highly inflammable.
14

15. flash point
➢The permissible conditions for storage and use are different for products
with flash points below 23 oC (e.g. gasoline), between 23 and 66 oC ( e.g.
kerosene), and above 66 oC ( e.g. fuel oil and gas oil).
➢The oils of the first category ( F.P below 23 oC ) are regarded as dangerous,
highly inflammable for transportation and storage and are subjected to strict
Govt. regulations.
➢Fuel oil with flash point 66 oC are regarded as “safe”.
➢Besides oil volatility and inflammability limits of the vapour air mixture, the
flash points also depends upon the design of the apparatus, the test
procedure and the barometric pressure.
15

16. Fire point
➢The fire point is the temperature to which the product must be heated under
the prescribed conditions of the method to burn continuously when the
mixture of vapor and air is ignited by a specified flame.
➢It is the lowest temperature at which vapours given off by oil ignites and
continues to burn for at least 5 s.
➢In most cases fire points is 5-40 oC higher than flash point and is determined
in the same apparatus as for flash point determination.
➢It gives as an idea of fire hazards during the storage and use of oil.
➢It is customary to determine both the temperature, although the lower
temperature ( Flash point) is itself a measure of fire risk of an oil.
16

17. Auto ignition temperature
➢Autoignition temperature is the minimum temperature at which hydrocarbon
vapor when mixed with air can spontaneously ignite without the presence of
any external source.
➢Values of autoignition temperature are generally higher than flash point. This
is particularly important from a safety point of view when hydrocarbons are
compressed.
17

18. Cloud point
➢This property is related to the flow of crude oil and its products at low
temperature.
➢Cloud point is the lowest temperature at which wax crystals begin to form by
a gradual cooling under standard conditions.
➢When an oil is cooled at a specified rate, the temperature at which it
becomes cloudy or hazy is called the cloud point of the oil.
➢This haziness is due to the separation of crystals of wax or increase of
viscosity at low temperature.
18

19. Cloud point
➢Cloud point is important for fuel oils which have to pass through unheated
filters of fine mesh.
➢Low cloud point products are desirable under low-temperature conditions.
➢Wax crystals can plug the fuel system lines and filters, which could lead to
stalling aircraft and diesel engines under cold conditions e.g. a jet plane may
be exposed to -60 oC and if solid wax separates from fuel oil the carburettor
may be blocked up.
➢Cloud points are measured for oils that contain paraffins in the form of wax
and therefore for light fractions (naphtha or gasoline) no cloud point data are
reported.
19

20. pour point
➢The temperature at which oil just ceases to flow ( or pour) is called the
pour point.
➢Pour point of a petroleum fraction is the lowest temperature at which
the oil will pour or flow when it is cooled without stirring.
➢It determines the temperature below which an oil can not be used as
lubricant.
➢Pour point represents the lowest temperature at which an oil can be
stored and still capable of flowing under gravity. When temperature is
less than pour point of a petroleum product it cannot be stored or
transferred through a pipeline.
20

21. Pour point
➢To determine the pour point, the oil is cooled in the test jar with every
3 oC fall in temperature tilted to observe the flow of oil.
➢The temperature at which it doesn’t flow even when the test tube is
kept horizontal for 5 s is taken as the pour point.
➢Naphthenes and the aromatics have lower pour point than paraffins.
21

22. Freezing point
➢It is the temperature at which fuel oil freezes completely and can not
flow at all.
➢This is important in case of aviation gasoline because of the high
altitudes where low temperatures are encountered, the fuel supply
from the fuel tank to the engine may be impeded due to choking of
the pipeline if the freezing point of the fuel oil is not sufficiently low.
➢Paraffins possess high freezing points than Naphthenes and
aromatics.
➢Aviation gasoline should have freezing point below 60 oC to avoid
trouble due to crystal formation in the feed line and filters.
22

23. Smoke point
➢These properties of kerosene determine the suitability of kerosene as
a fuel and as an illuminant.
➢The smoke point (SP) is a maximum flame height of the flame in mm
without smoke formation when kerosene is burned under closely
controlled conditions in a standard wick-fed lamp.
➢A high smoke point indicates a fuel with low smoke-producing
tendency.
➢Smoke point is a characteristic of aviation turbine fuels and kerosenes
and indicates the tendency of a fuel to burn with a smoky flame.
23

24. Smoke point
➢Paraffins are desirable in kerosene as it has got the highest smoke
point whereas aromatics are undesirable as it has got the lowest
smoke point.
➢Higher amount of aromatics in a fuel causes a smoky characteristic for
the flame.
➢Standard smoke point for Kerosene is 20-30mm.
➢Aromatics are hence removed from kerosene to improve smoke point.
24

25. Aniline point
➢ Aniline point for a hydrocarbon or a petroleum fraction is defined as
the minimum temperature at which equal volumes of liquid
hydrocarbon and aniline are miscible.
➢Since aromatics dissolve aniline ( itself an aromatic) more readily than
paraffins or iso-paraffins, the higher the aniline point, lower the
aromatics and higher the paraffin contents with very high cetane
number making the oil suitable for the diesel engine.
➢Aniline point for an oil also gives an indication of the possible
deterioration of rubber sealing, packing etc. in contact with the oil.
25

26. Aniline point
➢The aromatics have a tendency to dissolve natural rubber and certain
types of synthetic rubber. Therefore in such cases, a low aromatic
content in the lubricant ( e.g. a high aniline point) is desirable.
➢ The aniline point is important in characterization of petroleum
fractions and analysis of molecular type. The aniline point is also used
as a characterization parameter for the ignition quality of diesel fuels.
➢Aniline point of cetane C16H34 is 95 oC and for hexyl benzene is -12 oC.
➢Hence, higher the aniline point, better the diesel fuel and the lubricant.
26

27. Diesel Index
➢An alternative method of expressing the quality of the diesel oil is by
use of the “ Diesel Index”.
𝐷𝑖𝑒𝑠𝑒𝑙 𝐼𝑛𝑑𝑒𝑥 =
𝐴𝑛𝑖𝑙𝑖𝑛𝑒 𝑝𝑜𝑖𝑛𝑡 𝑜
𝐹 ×𝐴𝑃𝐼 𝑔𝑟𝑎𝑣𝑖𝑡𝑦
100
➢Diesel index is roughly related with the cetane number as
➢Diesel Index = Cetane number + 3
➢The use of diesel index does not necessarily used for the determining
the cetane number but it is used for the quality of diesel.
27

28. Octane Number
• An octane rating, or octane number, is a standard measure of a fuel's ability
to withstand compression in an internal combustion engine without
detonating. The higher the octane number, the more compression the fuel
can withstand before detonating.
➢This is a property of gasoline which is used in a spark ignition engine and
expressed its knocking characteristics.
➢When a gasoline is made to operate at high load and low speed, a sort of
rattling noise may develop from the combustion chamber resulting from
unsteady and uncontrolled combustion.
➢This noise is called knocking or detonation.
➢Knocking is harmful to engine and its parts are set to vibration, thereby
reducing the life of the engine.
➢Knocking depends on the quality of fuel also. 28

29. Octane Number
➢It has been found that n-heptane knocks very badly so its anti knock
property has been arbitrarily taken as zero and iso-octane gives very
little knocking so its anti knock value has been taken as 100.
➢Octane number of the fuel is defined as “ the % by volume of the iso-
octane in a mixture of n-heptane and iso-octane, with the same
knocking tendency as fuel.
➢Thus if the sample of gasoline gives as much knocking as a mixture of
80 parts of iso octane and 20 parts of n- heptane, its octane number is
80.
29

30. Octane Number
➢Higher the octane number, better is the fuel as maximum permissible
power increases with the octane number besides causing minimum
knocking.
➢Octane number of the hydrocarbon fuels increases in the order n-
paraffins- olefins- naphthenes- iso-paraffins- aromatics.
➢To determine the octane number of a fuel, it is burnt in a standard
engine for the purpose and the knock is measured by a knockmeter.
➢This is compared with the standard knockmeter readings of fuels of
different octane numbers to determine the octane number of desired
fuel.
30

31. Octane Number
The typical antiknock agents in use are:
➢Tetraethyllead (still in use as a high octane additive)
➢Alcohol
➢Methylcyclopentadienyl manganese tricarbonyl (MMT)
➢Ferrocene
➢Iron pentacarbonyl
➢Toluene
➢Iso-octane
➢BTEX - a hydrocarbon mixture of benzene, toluene, xylene and ethyl-
benzene, also called gasoline aromatics.
31

32. Cetane Number
➢It is the characteristic property of diesel and is used to indicate its
quality and performance in compression ignition engines.
➢For diesel engines, the fuel must have a characteristic that favours
auto-ignition. The ignition delay period can be evaluated by the fuel
characterization factor called cetane number (CN). The shorter the
ignition delay period the higher CN value.
➢In case of diesel engine, the fuel should ignite as soon as it is injected
into the cylinder.
32

33. Cetane Number
➢If it does not ignite instantaneously, ( the time lag between fuel
injection and fuel ignition is called ignition delay period) abnormal
combustion takes place resulting in shock waves, due to fluctuating
pressure rise in the cylinder.
➢With diesel of long ignition delay period, much of the charge is
injected into the cylinder before ignition is initiated., causing violent
combustion, sudden increase in pressure and rough and bumpy
running. This is called diesel knock.
33

34. Cetane Number
➢Cetane C16H34 has a very small ignition delay period hence it is given
a cetane number rating of 100.
➢α-methyl naphthalene has a very high ignition delay period, hence it is
given a rating of zero.
➢Cetane number of diesel oil is the percentage by volume of cetane in
a cetane/ α-methyl naphthalene mixture that has the same ignition
delay period and performance in a standard compression ignition
engine as that of the fuel.
34

35. Cetane Number
➢Cetane number increases in the order, aromatics < iso paraffins <
Naphthenes < olefins < n- paraffins.
➢The result is that the oil of high octane number has a low cetane
number and vice versa.
➢Cetane number of diesel fuels can be improved by adding additives
such as 2-ethyl-hexyl nitrate or other types of alkyl nitrates.
35

36. Calorific Value
The calorific value of a liquid fuel is measured in a bomb calorimeter, which
measure directly the gross calorific value at constant volume.
Sulfur content
Sulfur exists in all liquid fuels, but it is present to a significant degree in
residual fuel oils.
When burnt, sulfur forms SO2 and SO3 which are major sources of air pollution
Specific Heat
A knowledge of the specific heat of the liquid is important in handling liquid
fuels since the residual oils all have to be heated before they can be atomized,
and the heavier grades must be stored in a heated tank if they are to flow
freely into the distribution pipework.
36