University of Science and Technology of Southern Philippines
1st
Cagayan de Oro City
Semester SY 2021 - 2022
TOPIC 7
Liquid FUELS
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Liquid Fuel – Petroleum
Petroleum or crude oil is a naturally occurring brown to black
colored viscous oil formed under the crust of earth, on shore or
off shore. Chemically it is a mixture of various hydrocarbons with
small amounts of N, O, S compounds.
The approximate composition of petroleum:
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C = 80 - 84%
H = 10 - 14 %
S = 0.1 - 0.5 %
N+ O = Negligible
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Classification of Petroleum
1. Paraffinic-base type crude oil
• Contains saturated hydrocarbons from CH4 to C35H72 and a little amount
of naphthalenes and aromatics.
• (e.g. : Pennsylvanian and gulf coast oil)
2. Asphaltic-base type crude oil
• Contains mainly cycloparaffins or naphthalenes with smaller amounts of
paraffins and aromatic hydrocarbons.
• (e.g.: Californian oil)
3. Mixed-base type crude oil
• Contains both paraffinic and asphaltic hydrocarbons and are generally in
the form of semi-solid waxes.
• (e.g. : Mexican oil)
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Processing of Crude Petroleum
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Petroleum is found
deep below the earth
crust.
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The oil is found
floating over salt
water or brine.
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Generally,
accumulation of
natural gas occurs
above the oil.
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Refining of Petroleum
The process of removing impurities and separating out the oil
into various fractions having different boiling points is known
as refining of petroleum.
Refining plants are called oil refineries.
The process of refining involves 3 steps:
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Separation of water
Removal of impurities
Fractional distillation.
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Refining Step 1: Separation of Water
The crude oil from the well is an extremely stable
emulsion of oil and salt water. The crude oil is allowed to
flow between 2 highly charged electrodes, where colloidal
water droplets coalesce to form large drops, which is then
separated out from the oil.
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Refining Step 2: Removal of Impurities
The presence of NaCl and MgCl2 in the crude oil can
corrode the refining equipment, hence these salts are
removed by electrical desalting and dehydration methods.
The sulfur compounds present in the crude oil is removed
by treating the oil with copper(II) oxide, which results in
the formation of copper sulfide, which is then removed by
filtration.
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Refining Step 3: Fractional Distillation
The crude oil is heated to about 400°C, whereby all volatile
substances are evaporated. The hot vapors are then passed
up a fractionating column, which is a tall cylindrical tower
containing a number of horizontal stainless steel trays at short
distances.
When the vapors of the oil go up the fractionating column,
they gradually cool and condense at different heights of the
column. The fractions having higher boiling point condense at
lower trays whereas the fractions having lower boiling points
condense at higher trays.
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Refining Step 3: Fractional Distillation
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Some Important Fractions of Petroleum:
1. Petrol or Gasoline (C5-C9)
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It is a low boiling fraction of petroleum obtained between 40 –
120oC.
It is a mixture of hydrocarbons pentane to nonane (in terms of
carbon atoms C5 - C9).
Its calorific value is about 11,250 kcals/kg.
It is used as fuel in ICE of automobiles and aero planes.
Its antiknock value can be improved by the addition of Tetra Ethyl
Lead (TEL).
It is used as a fuel in IC engine and also used in dry cleaning and
as a solvent.
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Some Important Fractions of Petroleum:
2. Naphtha (C9-C10)
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It is a colorless, light fraction obtained between 1200C to 1800C
during fractional distillation of petroleum. It is a mixture of
hydrocarbons such as nonane and decane.
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Naphtha is also called as white spirit, which is generally used in
dry cleaning and as thinner for varnish, floor and furniture
polishes etc. The lightest portion of the distillate is used as
solvent for fats and rubbers, whereas the heaviest portion of the
same is used as a fuel.
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Some Important Fractions of Petroleum:
3. Kerosene( C10-C16)
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It is relatively a high boiling fraction obtained between 180-250oC
during fractional distillation of petroleum. It is a mixture of
hydrocarbons such as decane to hexadecane approximate
composition is C = 84%, H = 16%, > 0.1% S. Its calorific value is
about 11,100 kcal/kg.
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It is mainly used as a domestic fuel in stoves and lamps.
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It is also used as jet engine fuel and for making oil gas.
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Some Important Fractions of Petroleum:
4. Diesel (C15-C18)
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It is also a high boiling fraction obtained between 250-320oC
during fractional distillation of petroleum. It is a mixture of
hydrocarbons such as C15H32 to C18H38. Its calorific value is about
11,000 kcal/kg.
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It is used as a very good diesel engine fuel.
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Some Important Fractions of Petroleum:
5. Heavy oil or Residual fuel oil (C17 – C30)
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The left over portion of petroleum after distilling off all the lighter
fractions are called Fuel Oil.
• The approximate composition of fuel oil is C = 86%, H =
12%, S = 1%, H2O = 0.6%; sediments = 0.4%.
• Its calorific value is about 9200 kcal/kg.
The following fractions are obtained on further vacuum
distillation of the fuel oil.
i) Light fuel oil = 350 -420oC
ii) Heavy neutral oil = 420-500oC
It is used as fuel for ships and also used in metallurgical
furnaces.
Gasoline is also obtained from oil by cracking process.
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Some Important Fractions of Petroleum:
6. Asphalt
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Asphalts are obtained by:
i) The oxidation of residual heavy oil in presence of air at
higher
temperature.
ii) The deep vacuum distillation of residual heavy oil.
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Asphalts are available in the market in liquid, semi-solid and
solid forms.
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It is used for road making and making water-proofing roofs.
It is also used for the manufacture of water proofing concrete
and water proofing paints.
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Standard Ignition Temperature and Flash Point
Standard Ignition Temperature (SIT)
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It is the lowest temperature that a fuel will ignite without the help
of any external flame or ignition source.
Flash Point
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It is the lowest temperature at which a fuel can be heated so
that the vapor gives off flashes when an open flame is passed
over it.
This gives an indication of the flammability of the fuel.
Its significance is in the safety aspects of storing and handling
the fuel.
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Fire Point and Smoke Point
Fire Point
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It is the temperature to which the oil must be heated so that the
vapor pressure is sufficient to maintain the flame after the flame
source is removed.
Smoke Point
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It is an arbitrary scale related to the height of the flame of the
fuel burning in a standard lamp without smoking.
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Cracking
Cracking is defined as the decomposition of high boiling
hydrocarbons of high molecular weight into smaller, low boiling
hydrocarbons of low molecular weight.
The crude oil on fractional distillation yields only about 15 - 20
% gasoline. This is known as Straight Run Gasoline.
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Cracking
During cracking:
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Straight chain alkanes are converted into branched chain
hydrocarbons.
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Saturated hydrocarbons are converted into mixture of
Saturated and Unsaturated hydrocarbons.
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Aliphatic alkanes are converted into cyclic alkanes.
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All hydrocarbons obtained by cracking have lower boiling
point than the parent hydrocarbons.
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TypesTwo
of Cracking
in Use
Types of
Cracking in Use:
1. Thermal Cracking
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In this process, the heavy oil is subjected in high temperature
and pressure, when the bigger hydrocarbon molecules break
down to give smaller molecules of the paraffins, olefins, and
hydrogen.
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The cracked products are then separated by fractional
distillation.
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Types of Cracking in Use
2. Catalytic Cracking
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In this process, cracking is carried out in the presence of
a catalyst at a lower temperatures and pressures. The
catalysts like aluminum silicate, Al2SiO3, or alumina Al2O3,
used in cracking gives higher yield and better quality of
gasoline
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Knocking
The rate of ignition of the fuel gradually increases and the final
portion of the fuel-air mixture gets ignited instantaneously
producing an explosive sound known as knocking.
Knocking property of the fuel reduces the efficiency of engine.
So a good gasoline should resist knocking.
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Octane Number or Octane Rating
It is introduced to express the knocking characteristics of
petrol. It has been found that n-heptane knocks very badly and
hence, its anti-knock value has been given zero (0). On the
other hand, iso-octane gives very little knocking and so, its
anti-knock value has been given 100.
Octane number is defined as the percentage of iso-octane
present in a mixture of iso-octane and n-heptane.
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Cetane Number or Cetane Rating
It is introduced to express the knocking characteristics of
diesel. Cetane has a very short ignition lag and hence its
cetane number is taken as 100. On the other hand, 2-methyl
naphthalene has a long ignition lag and its cetane number is
taken as zero (0).
Cetane number is defined as the percentage of hexadecane
(n-cetane) present in a mixture of hexadecane and 2-methyl
naphthalene, which has the same ignition lag as the fuel under
test.
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Improvement of Antiknock Characteristics
The octane number of fuel can be improved by:
1. Blending petrol of high octane number with
petrol of low octane number, so that the octane
number of the latter can be improved
2. The addition of anti-knock agents
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TOPIC 7
Gaseous FUELS
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Gaseous Fuels
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Gaseous Fuel – Natural Gas
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Natural gas is always found above the oil in the oil wells.
It is also called Marsh gas.
It consists of methane and other saturated hydrocarbons.
The average composition of natural gas is as follows :
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Methane = 88.5 %
Ethane = 5.5 %
Propane = 4 %
Butane = 1.5%
Pentane = 0.5%
If natural gas contains lower hydrocarbons like methane and ethane
it is called lean or dry gas. In the natural gas contains higher
hydrocarbons like propane, butane along with methane it is called
rich or wet gas.
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Gaseous Fuel – Water or Blue Gas
Water gas essentially a
mixture of combustible gases
like CO, H2 with a little non
combustible gases like CO2
and N2.
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Gaseous Fuel – Producer Gas
It is prepared by passing air
mixed with a little steam over a
red hot coal (or) a coke bed
maintained at above 1100° C in a
special reactor called ‘‘ Gas
Producer’’.
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Gaseous Fuel – Liquified Petroleum Gas (LPG)
It is a mixture of propane and butane.
It is obtained as one of the top fractions in the fractional
distillation of petroleum.
It is easily liquefied and so can be economically stored and
transported in cylinders.
The approximate composition is as follows:
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N-Butane = 70 %
Isobutane = 17 %
N-Propane = 11 %
Butylene and Ethane = 2 %
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Biofuels
Biogas: from animal manure, other organic wastes, energy
crops
Bioethanol/Ethanol: from sugar/starch
Biodiesel: from vegetable oils, animal fats
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TOPIC 7
BIOFUELS
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Bioethanol vs Biodiesel
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Power Alcohol
When ethyl alcohol is used as fuel in an internal
combustion engine, it is called power alcohol.
Generally, ethyl alcohol is used as a 5-25% mixture
with petrol.
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Philippines: Biofuels Act of 2006
• Develop and utilize indigenous renewable and sustainablysourced clean energy to reduce dependence on imported oil.
• Mitigate toxic and greenhouse gas emissions.
• Increase rural employment and income.
• Ensure the availability of alternative and renewable clean
energy without any detriment to the natural ecosystem,
biodiversity and food reserves of the country.
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Philippines: Biofuels Act of 2006
• At present, 5% ethanol and 2.5% biodiesel.
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REFERENCES
REFERENCES
R. Mukhopadhyay & S. Datta. Engineering Chemistry.
Syed Shabudeen P.S. Fuels and Combustion. Retrieved from
https://www.researchgate.net/publication/265602602
K. Sesha Maheswaramma. Engineering Chemistry.
J. A. Moulijn, M. Makkee, A.E. Van Diepen. Chemical Process Technology.
H. Schobert. Chemistry of Fossil Fuels and Biofuels.
Wiley Critical Content. Petroleum Technology. Volume 1-2 .
J.G. Speight. The Chemistry and Technology of Petroleum.
C.S. Hsu & P.R. Robinson. Springer Handbook of Petroleum Technology.
L.J. Gonzaga. Lectures 5-9 Fuels. [Powerpoint Slides].
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