Petroleum Refining and

Petrochemicals
• Refinery: An oil refinery or petroleum refinery is an industrial process
plant where crude oil is transformed and refined into useful products
• Crude oil: Naturally occurring unrefined petroleum product
• Reservoir: The Society of Petroleum Engineers recognizes three main
categories of oil reserves.
1.Possible reserves: extraction of oil under 50-percent, but higher than
10-percent.
2.Proven reserves: extraction of oil, at a 90-percent or above.
3.Probable reserves: are those with the likelihood of recovery for
between possible and proved reserves, or over 50-percent but under
90-percent.
 Extraction of Crude oil

1 2
3
4
 6
5
 Kerogen
• Solid organic matter in sedimentary rock.
➢ Have odd carbon number.

➢ It is non extractable using solvents.

➢ It is also called mother substance for shale.

➢ Organic matter→ Kerogen → Crude oil

• Classification of kerogen
 Carbon Preference Index
• It is the measure of age of oil
• Deep oils have less CPI than shallow ones
• Recent origin …… 4 to 5
• Ancient Bitumen…..1
 Composition of Petroleum

• Crude oil consists 84-87 wt % carbon,11-14% Hydrogen, 0-3%

Sulphur, 0 – 2 wt % oxygen, 0 – 0.6 wt % nitrogen and metals
ranging from 0 – 100 ppm.
• Based on chemical analysis and existence of various functional
groups, refinery crude can be broadly categorized into
1. Paraffins: Paraffins refer to alkanes
obtained as a gas fraction from the crude distillation
unit.
Olefins:
olefins refer to Alkenes such as ethylene, propylene and butylenes
etc.

They are not found in mentionable quantities in crude oil but are
encountered in some refinery processes such as alkylation.
Naphthenes:
Naphthenes or cycloalkanes such as cyclopropane, methyl cyclohexane
are also present in the crude oil.
These compounds are not aromatic and hence do not contribute much
to the octane number.
Therefore, in the reforming reaction, these compounds are targeted to
generate aromatics which have higher octane numbers than the
naphthenes.
Aromatics:
Aromatics such as benzene, toluene o/m/p-xylene are also available in the
crude oil. These contribute towards higher octane number products and the
target is to maximize their quantity in a refinery process.
Evaluation of petroleum
Crude is classified into mainly three type
• Paraffinic base
• Mixed or intermediate
• Naphthenic base

Mallison Classified crude on the basis of residue left after distillation

• >5% paraffins…..paraffinic base
• 2-5 % paraffins….mixed base
• <2% paraffins…. Naphthenic base

1. API gravity
2. U. O. P. characterization factor
3. Correlation index
4. Distillation
• API Gravity: density of petroleum oil is express in terms of API gravity
141.5
API = - 131.5
𝑆𝑃.𝐺𝑟𝑎𝑣𝑖𝑡𝑦

Classification of crude oil on the basis of API gravity

Light crudes: API > 38
Medium crudes: 38 > API > 29
Heavy crudes: 29 > API > 8.5
Very heavy crudes: API < 8.5

• Characterization factor:
➢ There are several correlation between yield, aromacity and paraffinicity of crude
oil but the two most widely used are
1. UOP and waston characterization factor (Kw)
2. Correlation index (CI)
•

100
Distillation
• Fractionation
➢ determines the yield of the products that can be obtained from
crude oil when it is processed in the refinery.
• A light crude oil will produce higher amounts of gasoline than a
heavier crude oil.
• Different standard distillation tests can be performed on crude oil or
petroleum fractions.
True Boiling Point analysis
• This type of distillation is commonly used due
to the accuracy of the results obtained by this
method which is very close to that obtained via
real distillation or industrial distillation.
• In general this type of distillation is carried out
by two steps:
• 1. under atmospheric pressure (1% distilled
every 2 min)
• 2. Under vacuum pressure
• At least 10 -15 trays are with reflux condition to
give accurate results.
• This test allows for the collection of sample cuts
at different boiling point ranges. These cuts can
be subjected to physical and chemical
measurements.
True Boiling Point curve (TBP)

It is a plot of the boiling points of almost

pure components, contained in the crude or
fraction of the crude oil.
ASTM Distillation
• The distillation of petroleum cuts is done in a simple distillation
apparatus which does not have a fractionation column.
• For light cuts (gasoline, kerosene, diesel and heating oil) the
distillation is run at atmospheric pressure under ASTM D86 test.
Thermal Properties of Petroleum Fractions
• Specific heat: For petroleum fraction is 0.3-0.85.
Lighter fraction : higher values
➢ With increasing density specific heat decreases.
1
➢ Sp. Heat = (0.4024 + 0.00081t)
𝜌
• With API gravity, temperature and characterization factor (K) for oils
only the Sp. Heat correlation is given below:
Sp. Heat = [0.355+1280 (oAPI) 10-6 + (503 + 1.17× oAPI) (32+1.8t) 10-6)
(0.05K+0.41)]
K = Characterisation factor, t= temperature oC
• Heat of combustion :
3
➢ Hydrogen is distinct for its heat of combustion. i.e. 183.6 x 10 kJ/kg

➢ Higher hydrogen content fractions designed to have more heat of combustion.

➢ In the order of paraffins to aromatics the heat of combustion decreases.

➢ sherman-kropff relationship showing heat content with API

o

Heating value kJ/kg = 43,434 + 93.2 (API - 10 )

• Latent heat of vaporisation:

Latent heat for a fraction varies with the temperature at which vaporisation take place.
Related to molecular weight, oAPI and molal average boiling point.
The relationship is expressed as:
L = λ LB *(T/TB)
L= latent heat at any temperature (T absolute)
LB = latent heat at any temperature (TB absolute)
λ = correction factor depends upon reduced temperature
• Latent heat of fusion :
➢ The heat of fusion is approximately 50% of latent heat of

vaporisation.
➢ Waxy distillates and waxes – 167-170 KJ/Kg.

• Thermal expansion:
➢ Like all liquids, petroleum fractions also suffer in loss of density due to

thermal expansion.
➢ Coefficient of expansion is required to find out the volume of the

container and this is related to API gravity.

Gravity range API Mean coeff. Of expansion (change in volume for 1Oc)
0-14.9 0.00063
15-34.9 0.00072
89-93.9 0.00153
94-100 0.00162
• Spontaneous ignition temperatures
➢ The temperature at which a material can catch fire and burn continuously without the aid of
external firing agencies.
➢ Paraffins have less ignition temperatures.

➢ Aromatics have high ignition temperatures

• Viscosity and viscosity index

• Important property of all lube oils.
• In all refinery operations instead of absolute viscosity kinematic viscosity used.
• Kinematic viscosity = Viscosity absolute/Sp. Gravity
• Laboratory viscometer like U-tube , fenske, redwood, engler give kinematic viscosity.
• Lubricants are specified by property namely viscosity index, indicates the variation characteristics
of viscosity with temperatures.
VI= (L-U / L-H) x 100
L = viscosity of a reference oil of zero viscosity index At 37.8 oC
H = viscosity of a reference oil of 100 viscosity in At 37.8 oC
U = viscosity of test sample at 37.8 oC
Gaseous from Petroleum
• Natural gas:
1. Readily available in nature.
2. Contains mainly varying proportions of methane and other dry gas fractions like ethane and propane to a small
extent.
3. Some inerts like CO2, N2 and noble gases are present.
4. Proportion of methane 85-98%

• Associated gas:
1. Obtained from oil reservoir
2. Consist methane and some extent of ethane and propane.

• Dissolve gas
1. Gas may be present in the liquid hydrocarbons mainly in the dissolve state depending upon the formation pressure.
Casing head.
• Casing head gas:
1. Similar to natural gas
2. Contains less % of methane and high % of ethane and propane.
3. It is a by product of oil production.
• Refinery off gas:
1. This gas is formed in cracking and reforming operations due to the thermal
degradation of liquid hydrocarbons.
Contain Impurities like CO2, N2, mercaptons, H2S, water vapour, suspended impurities.
M+E = Dry gas
P+B = Wet gas
• Liquified Petroleum Gas:
1. The gas that is vented from refinery distillation unit, is processed and conveniently
stored after liquefaction.
2. Stored in vapor liquid mixture
3. Key points: ease of handling, smoke lessness, good and steady heating rates.
• LPG is produced in many grades as listed below:
1. Predominantly butanes
2. Butane-propane mixtures (mainly butanes)
3. Butane-propane mixtures (equal volumes)
4. Butane-propane mixtures (more propane)
5. Less butane - propane mixture
6. Predominantly propane
Gasoline
• Gasoline and petrol is a transparent petroleum derives liquid that is used
primarily as a fuel internal combustion engine.
• This is a highly volatile known as motor spirit.
• Different type of gasoline product produced in refineries and almost 90%
consumed by automobile industry and rest aviation industry.

• Test for gasoline

➢ ASTM Distillation

➢ Reid vapor pressure

➢ Octane number

➢ Gum content

➢ Sulfur content
ASTM Distillation
Reid vapor pressure:
• VP for all volatile components are measured by RVP apparatus at
(38oC ± 0.1 oC).
• LPG, naptha, jet fuels, are tested like this.
• Mostly VP is higher than indicated RVP and variation of different
fraction is different.
• During testing following Correction is applied for accommodating
changes in water vapour pressure corresponding to temperature
variation from air to bath temperature.
(𝑃𝑎 − 𝑃𝑡)(𝑡−𝑇)
• Correction: 𝑜 - (PT - 𝑃𝑡)
𝑇𝐾

Pa : atmos. Pressure
Pt: vapour pressure
T: temperature
PT: vapour pressure
• Octane number:
➢ Octane number is used in SI engine or CI engine.

➢ Octane number is used to represent fuel.

➢ More octane number more fuel will resist to detonation.

➢ More octane number more fuel will resist to combustion.

➢ How to rate octane number

➢ Octane number is a mixture of iso octane and normal heptane.

• Gum content:
➢ Motor gasoline are often stored for six months or even longer before use.

➢ It is essential that they should not undergo any deleterious change under storage
condition.
➢ Gasoline remain free from deposits during discharge from the fuel tank of a
vehicle.
➢ Otherwise deposits are build up in the tank, fuel lines and in valves and cause
extensive choking.
➢ Gasoline manufactured by cracking processes contain unsaturated components
which may oxidized during storage and formed undesirable oxidation product.
➢ Gum formation appears to be the results of chain reaction initiated by radicals
which is mostly take place during refining and handling operations.
➢ Gum is two kind 1.existent-gum 2. potential gum

1.existent-gum: ASTM.
2. potential gum: oxidizing the sample with oxygen under restricted conditions.
• Sulfur content:
➢ Sulfur is responsible for corrosion

➢ Effect of overcoming sulfur components is done by adding more lead.

➢ More TEL required if more sulfur component is available in gasoline.

➢ The effect of sulfur on lead is predicted by the relation

L = (a0-a /a0) *100

a0 = TEL present in gasoline with sulfur compounds
a = TEL present in gasoline free sulfur compounds
L= % TEL excess required to boost the octane number of sour gasoline
to the same extent as sweet gasoline
Additives in gasoline
• Modern gasoline engine have been designed for efficient use of
gasoline.
• Different types of additives are blended into gasoline infact in an
petroleum fraction to give interrupted and smooth service. This
additives are divided into
1. Anti-icing and detergent
2. Inhibitors
3. Combustion aids
4. Colors and dyes.
 Kerosene
➢ Kerosene is employed as fuel and illuminant.
➢ These fraction have boiling range 150-250oC.

• Test and properties of kerosene

• Flash point and fire point
• Smoke point
• Sulfur content
• Aniline point

• Flash point and fire point

• Flash point: lowest temperature at which vapors of the material will ignite
when give an ignition source. (kerosene: 37-65oC)
• Fire point: lowest temperature at which oil ignite and continue to burn for
at least five seconds after ignition by an open flame (kerosene: 40-78oC)
• Fire is more than 5 oC of flash.
Flash point and fire point
• Smoke point: Maximum height of flame in millimeter at which given oil will burn
without giving a smoke. (kerosene: 18mm)
➢ It is indication of clean burning quality of kerosene.
➢ Illumination depends upon the flame dimension although it is nit related to flame
height.
➢ Many paraffins are gifted with better flame heights but illumination may be poor.
➢ Different flame height is obtained because of presence of different components such
as paraffins, napthenes, and aromatics
➢ Aromatics contribute in smoke. So, removal of aromatic which increase the smoke
point.
➢ By knowing the composition smoke point is predicted by using given

SP = 0.48P+0.32N+0.20A

• Sulfur content:
High sulfur content is harmful due to its combustion products.
Maximum permissible amount of sulfur is 0.13% in all kerosene

• Aniline point:
This test indicates qualitatively the amount of aromatics present in kerosene
• Sulfur content:
• High sulfur content is harmful due to its combustion products.
• Maximum permissible amount of sulfur is 0.13% in all kerosene

• Aniline point:
• Aniline point of the oil is the lowest temperature at which the oil is completely
miscible with an equal volume of aniline.
• This test indicates qualitatively the amount of aromatics present in kerosene.