Occupational Hygiene in the
Oil & Gas Industry
Day 1 – Section 3
Basic Petroleum Chemistry
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Introduction
Composition Of Crude And Petroleum Products
1. Names of hydrocarbons and their
groupings into hydrocarbon types.
2. Most important physical and chemical
properties of specific hydrocarbons.
3. General chemical nature of crude petroleum
and the refining operations which produce the
petroleum products.
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PARAFFINS
• Formula = Cn.H(2n+2) where n = the number of
Carbon atoms
• Crude petroleum and its products contain
compounds of carbon and hydrogen.
• Carbon has a combining power (bonds) of 4
and hydrogen has a combining power (bond)
of 1.
• Simplest hydrocarbon molecule contains one
Carbon atom and 4 hydrogen atoms and is
C1H4 known as METHANE. Natural Gas
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Ethane C2H6
Methane CH4
Propane C3H8
iso-Butane C4H10
n-Butane C4H10
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OLEFINS
• Formula = C(n).H(2n) where n = the number of
Carbon atoms
• BUTENE C4H8 known as Butene-1 one double
linkage (bond) on
• Double, or even a triple linkage between
carbon atoms. This type of linkage increases
chemical activity.
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NAPHTHENES
• Naphthene or cyclic structure - carbon atoms
form a ring with only two linkages available for
hydrogen or substation (described later).
• The simplest form is 3 carbons
CYCLOPROPANE C3H6
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Cyclohexane C6H12
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AROMATICS
• Combination of hydrogen and carbon based
on a six carbon atoms ring with an unsaturated
type linkage.
BENZENE C6H6
• Benzene is a known carcinogen and requires
special health considerations.
• Benzene in gasolines is generally limited to 1%
or less
• Series of compounds known as AROMATICS
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Benzene C6H6
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Toluene C7H8
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ortho Xylene C8H10
meta Xylene C8H10
para Xylene C8H10
Xylene isomers
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Two aromatic rings can join to form Naphthalene
Three aromatic rings can join to form Anthracene
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Four or more aromatic rings can join to
form ‘Polynuclear Aromatics’
C20H12 Benzo(a)pyrene which is a
potential carcinogen.
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PONA
• Paraffins, Olefins, Naphthenes and Aromatics.
(PONA)
• Petroleum chemists and engineers use PONA
to describe the broad composition various
refinery hydrocarbon streams (or distillation
cuts or boiling ranges) and their approximate
“PONA” composition.
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Summary of Product Types from Petroleum
Carbon
Number
C1-C4
Boiling Range
Deg. C
Deg. F
<0
<30
Name
Natural gas (LNG), Liquified Petroleum
Gas (LPG)
C4-C12
0-200
30-392
Gasoline, Naphtha
C12-C15
200-300
392-572
Kerosene, Jet Fuel
C15-C25
300-400
572-750
Gas Oil, Heating Oil, Diesel, Lube Oil
>400
>750
>C25
Residuum, Asphalt (Bitumen), Paraffin
Wax
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Other hydrocarbon derivatives
• Oxygen – specifically hydroxyl group – OH produce
ALCOHOLS
• Methane becomes Methanol
• Ethane becomes Ethanol (found in wines, spirits and
beer)
• Propane becomes Propanol (or Isopropanol used in
hand cleaners).
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Sulphur Compounds
• Hydrogen Sulphide H2S – a special case- Toxic
Gas
• Aliphatic Sulphides – Mercaptans R-SH
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Aliphatic Sulphides
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CHEMICAL REACTIONS IN A REFINERY
Gasoline Treating
• Mercaptans are mixed with Caustic solution (Sodium
Hydroxide NaOH) to react and produce an organic
sodium sulphide which is soluble in water and
removed.
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Cracking Reaction
• Fluidized Catalytic Cracker (FCC) or Thermofor
Catalytic Cracker (TCC). T
• Catalyst ‘cracks’ or breaks longer hydrocarbon
molecules into smaller fractions
• Produces wide range of hydrocarbons from gases
through to heavy residuum
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Alkylation Reaction
• Reaction of two gases Isobutane with
Butene/Propylene to produce Alkylate
• Alkylate- gasoline blend stock high octane (RON
100) used in motor gasolines & aviation gasolines.
• Catalyst - Sulphuric acid or Hydrofluoric acid
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Isomerization Reaction
• Changes straight chain paraffins into isomers which
have higher octane rating
• normal Pentane (octane 68) into Isopentane (octane
92)
• Gasoline blend stock
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Dehydrocyclization Reaction
• Changes straight chain paraffin into a ring or cyclic
formation (aromatic) with increase in octane rating
• Normal Heptane C7H16 (octane zero) transformed
into Toluene (octane 120)
• Valuable gasoline blend stock.
• Hydrogen gas produced - used in other processes.
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Hydrogenation – Sulphur removal
• Breaking the molecule and converting the
sulphur radical into hydrogen sulphide and
joining the hydrogen atoms to the free
linkages (bonds)
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Sulphur Recovery
• Hydrogen sulphide gas is converted into elemental
yellow sulphur by burning in air to convert to Sulphur
Dioxide SO2
• SO2 then reacted with Alumina catalyst to produce
elemental sulphur.
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Naphthene Dehydrogenation
• Catalyst & temperature break hydrogen from cyclic
structure Cyclohexane to form Benzene and 6
Hydrogen atoms
• Octane increase 83 to 100+.
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Oxidiser Reaction - Bitumens
• Reacts heavy vacuum treated residuum with air to
polymerise heavy hydrocarbons (heavier molecules)
• Produces bitumen for road making.
• Two hydrogen atoms stripped off and reacted with air
(oxygen) to produce water (steam)
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End of Section 3
Basic Petroleum Chemistry
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