CHEN401 - Tutorial 1 - Review on Physical & Chemical Properties & Classification.pdf

Petroleum Refining Engineering

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Petroleum Process Engineering, 2011-2012 4

INTRODUCTION
5
Crude Oil - Introduction

Petroleum ‘ Petra Oleum ’
 Petroleum ‘Rock Oil’ is a naturally occurring
underground oil, also referred to as ‘Crude
Oil’.
 Petroleum is a complex mixture of
Hydrocarbons in addition to some
impurities*.
 Q: What are Hydrocarbons? What is the
classification of Hydrocarbons? ANS
* Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical
composition of the material or compound.
6

Petroleum ‘ Petra Oleum ’
 Petroleum is called a fossil fuel because it is
formed from the bodies of ancient organisms –
primarily one celled plants and animals.
 When these creatures died, their remains
accumulated at bottoms of ancient lakes or seas,
along with sand and other sediments.
 Over time, a combination of pressure, heat, and
bacterial action transformed the deposits into
sedimentary rock.The incorporated organic
matter was transformed into simpler chemicals,
such as hydrocarbons, water, carbon dioxide,
hydrogen sulfide, and others.
7

Petroleum Reservoir
8
 If the surrounding rock was porous, liquids and gases
could migrate, either up to the surface or into a
reservoir that was capped by impermeable rock or a
dome of salt.
 Today, when petroleum geologists look for oil, they
actually are looking for structures that might be traps
for liquid hydrocarbons.

10
The Petroleum Industry
 The petroleum industry has three key business
segments.
Crude Oil Refining Product
Exploration & Distribution
Production & Sales
Upstream Downstream

Petroleum Refining
11
 Upgrading of crude oil into products tailored to
meet specific consumer needs is what we mean
by petroleum refining.
 Petroleum refineries have goal to convert as
much of the barrel of crude oil into
transportation fuels which is economically
practical.
 Commercial Amount: is the estimated amount
of petroleum that can cover its extraction
expenses.

Petroleum Refining
 Crude Oil passes through various refinery
operations (physical and chemical processes) to
eventually produce final usable products.
 The relative amounts of these products
compared to their prices determine the crude
value.
 The key step in refining is distillation.
 Distillation is the separation of materials based
on differences in their volatility (as indicated by
their boiling points).
 The following illustration shows a crude tower
in addition to some product uses; 12

Petroleum
 General types of Petroleum:
◦ Gaseous → Natural Gas
◦ Liquid → Crude Oil (contains also dissolved
gases and bitumen)
◦ Semi-Solid/Solid → Asphalt (Bitumen)
 Petroleum Uses:
In the raw form; neither crude oil nor natural
gas has any direct uses.
14

Petroleum – Products/Uses
 General uses of petroleum products:
◦ Fuel ( e.g. Gasoline and Diesel Fuels )
◦ Source of heat ( e.g. Kerosene and Fuel Oil )
◦ Lubricants ( Lubricating Oil )
◦ Raw materials for petrochemical industries
( e.g. plastics, rubber, and fibers )
15

PHYSICAL PROPERTIES
16

Physical Properties
 In order to get more familiar with crude oil, lets
explore some of its important physical
properties
 Usually the physical and chemical properties of
the crude (and products) determine their value
in the market and used to ‘Characterize the Oil’
 Some properties are more important than the
others as specs for certain products
17

Physical Properties – Sp. Gr.
 Q: What is specific gravity? ANS
 Def. API : Stands for American Petroleum
Institute and used as a measure rather
than specific gravity.
 What is the difference between API and
Specific gravity?
18
5
.
131
.
.
5
.
141
−
=
Gr
Sp
API

 Specific gravity is unit less while API has a
special unit (Degree API)
 Sometimes they are reported as API(T/T)
or sp.gr. (T/T) whereT is the temperature
where the crude and reference fluid
density are measured
 Are API and sp. gr. directly measurable?
What is the device used?
19

 A hydrometer device is used to measure
specific gravity, and a calibrated
hydrometer can also be used to directly
measure the API
20

 Notice that:
API α 1/sp. gr.
 They are both an indication of the oil
price where,
◦ The higher the API, the lower the sp. gr. and
hence, the lighter the oil components (Which
are higher in price) and the higher the crude
price.And vice versa
21

 Higher API, more paraffinic crude, higher
yields of gasoline
(high API gravity, low carbon, high hydrogen)
 Lower API, more aromatic crude, lower
yields of gasoline
 Q: Which is denser, oil or water? ANS
22

Physical Properties – Color
 Crude oil color varies with its components
where the lighter the oil (higher amount of
light components) the lighter the color and
vice versa
 The color varies between pale yellow (light
oil) to dark brown (heavy oil)
23

Physical Properties – Color
 Below are different colors for different oil
samples;
 Q: Which has the highest price? ANS
24
Very light crude, Australia Heavy crude, North Sea Very heavy crude, Venezuela

Physical Properties – odor
 Usually oil has a pleasant smell due to the
presence of aromatics and it increases as the
% aromatics increases
 However, some impurities add an unpleasant
smell to the oil when they exist in high
amounts (Ex: Sulfur and Nitrogen
compounds)
25

Physical Properties –Viscosity
 Viscosity is a measure the resistance of a
fluid to flow and thus, is an important
property since oil is transferred in pipelines
for long distances
 There are several measures of viscosity
stated on the next slide,
26

1. DynamicViscosity (μ or η):
◦ Its SI unit is PaS or kg/mS
◦ While the most common unit is the CGS
unit (Poise)
◦ 1 Poise is equivalent to 1 gm/cmS
◦ Another common unit is the cP or centi-
poise
◦ 1 PaS = 10 Poise = 1000 cP
27

2. KinematicViscosity (ν):
◦ In some cases we are concerned by the
ratio between viscous forces (dynamic
viscosity) to the inertial forces
(characterized by the density) thus we use
the kinematic viscosity, where:
◦ Measuring units:
 1 m2/S = 10,000 stoke = 106 centi-stokes
 1 stoke = 1 cm2/S
28

3. Saybolt UniversalViscosity:
◦ The common unit used in the petroleum
field and obtained directly by the
viscometers is the second
◦ Viscosity in this scale is defined as: It is the
time that 60 cm3 of oil takes to flow through
a calibrated tube at a controlled
temperature –starting at a standard level.
◦ The unit used is based on the device specs
itself…
29

◦ Two saybolt instruments are used:
1. Saybolt universal (Unit: SSU or SUS)
2. Saybolt furol -has a wider orifice- (Unit: SSF or
SFS)
◦ When the flowing time surpasses 600
seconds, Saybolt Furol Second should be
used instead of Saybolt Universal Second.
i.e. it is used for heavy fractions
◦ The tube diameter in the two scales is such
that the Furol viscosity is one-tenth of the
Universal viscosity
30

4. Redwood UniversalViscosity:
◦ The Redwood device is used in the same
way as the saybolt device except that it has
different specs
◦ Two devices are used as well;
1. Redwood I ( Unit: Sec.Red I )
2. Redwood II ( Unit: Sec.Red II )
 Converting to kinematic viscosity
◦ KinematicViscosity = at – b/t, where a and b
are constants based on the device
31

 MeasuringViscosity:
1. Redwood scale
2. Saybolt scale
 Both devices have the same general idea
explained in the next slide;
32

33

Physical Properties – Phosphorescence
 Is the ability of matter to emit radiations
previously received, example: light energy
 This ability is present in crude oil due to the
presence of phosphorus compounds, since the
origin of crude oil is plant and animal remains
(according to the organic theory)
 The feature works as an indication of the
presence of crude oil during the prospecting
phase
34

Flash Point
 For a hydrocarbon or a fuel, it is the minimum
temperature at which vapor pressure of the
hydrocarbon is sufficient to produce the vapor
needed for the ignition of the hydrocarbon with
the air with the presence of an external source,
i.e., spark or flame
 The standard procedure to measure the Flash
point is ASTM D93
 Fractions in vacuum tower are the least
combustible. They are the heaviest.
35

Flash Point
 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
36

Fire Point
 Defined as the minimum temperature at which
the hydrocarbon will continue to burn for at
least 5 s after being ignited by a flame.
37

Auto Ignition Temperature
 It is the minimum temperature at which
hydrocarbon vapor when mixed with air can
spontaneously ignite without the presence of
any external source.
 Values of auto ignition temperature are
generally higher than flash point.
 This is particularly important from a safety
point of view when hydrocarbons are
compressed.
 Standard test is ASTM D 2155.
38

Cloud Point
 It is the lowest temperature at which wax
crystals begin to form by a gradual cooling
under standard conditions.
 At this temperature the oil becomes cloudy
and the first particles of wax crystals are
observed.
 The standard procedure to measure the cloud
point is ASTM D2500.
39

Cloud Point
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.
Cloud points are measured for oils that
contain paraffin in the form of wax and
therefore for light fractions (naphtha or
gasoline) no cloud point data are reported
40

Pour Point
 The minimum temperature at which the oil will
seize to flow for 5 seconds
 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.
 It is a rough indicator of the relative paraffinicity and
aromaticity of the crude.
 The lower the pour point, the lower the paraffin
content and the greater the content of aromatics.
41

Freezing Point
 For a pure compound the freezing point is the
temperature at which liquid solidifies at 1 atm
pressure.
 A pure substance has the same freezing point
 For petroleum mixtures, there are ranges of
freezing points versus percent of the mixture
frozen.
42

44
• API
• Odor
• Color
• Viscosity
• Flash point
• Fire Point
• Auto ignition Point
• Cloud Point
• Pour Point
• Freezing Point

CHEMICAL COMPOSITION
45

46
Chemical Composition – Main
 As mentioned before in the introduction crude
oil consists mainly of:
1. Hydrocarbon compounds
2. Impurities (Non Hydrocarbon compounds)
 An average crude contains about:

47
 The properties of the hydrocarbons depend on
the number and arrangement of the carbon and
hydrogen atoms in the molecules.
 Hydrocarbons containing up to four carbon
atoms are usually gases.
 Those with 5 to 19 carbon atoms are usually
liquids and those with 20 or more are solids.

 Notes:
◦ Alkanes  Paraffins
◦ Alkenes  Olefins
◦ Alkynes are not originally present in crude oil,
where as alkenes are present to some extent
◦ Crude oil consists essentially from paraffins
and naphthenes, while aromatics are found in
lower %’s and olefins are found as traces
(sometimes they are formed during
processing of the crude)
48

Chemical Composition – Impurities
 Remember that not all impurities are
harmful
 The following lines show some famous
impurities that are found with crude
oil/crude oil fractions
1. Sulfur compounds
◦ The sulfur content is expressed as percent
sulfur by weight and varies from less than
0.1% to greater than 5%.
49

1. Sulfur compounds
◦ If sulphur content < 0.5% => "sweet crude".
◦ If sulphur content > 2.5% => "sour crude".
◦ A crude with a sulfur content between these
two endpoints is => "intermediate".
◦ Crudes with greater than 0.5% sulfur
generally require more extensive processing
than those with lower sulfur content.
◦ Sulfur content and API gravity are two
properties which have had the greatest
influence on the price of crude oil, 50

Sulphur compounds are the most serious
impurities due to the following reasons:
1. They cause a bad odor
2. The result in poisoning the catalyst used in
petroleum processing.
What is catalyst poisoning?
3. They decrease the effect of TEL (Tetra Ethyl Lead)
in increasing the octane number of gasoline
4. They have a corrosive effect whether during the
oil field refining processes or further refining in
refineries or even later upon using final petroleum
fractions 51

◦ Sulfur compounds are classified according to
their corrosive effect as follows:
1. Active Sulfur Compounds:They carry out
corrosion on cold ( i.e. before the combustion of
the fraction starts).Thus these compounds are
capable of causing corrosion to tanks, pipes,
pump…etc during the transportation of crude oil
 The active sulfur compounds are Mercaptans –Thiols- ( R-
SH ) where the most simple mercaptan is the H2S
 A higher example of mercaptans:
52
Methanethiol
Methyl Mercaptan
Mercaptomethane

2. Inactive Sulfur Compounds:They result in a
corrosion effect only after combustion, thus they
have a very dangerous effect on the engines, the
following is a list of these compounds;
 Sulfides ( R-S )
 Sulfates ( R-SO4 )
 Thio Ether ( R-S-R )
 Alkyl Di Sulfides ( R-SS-R)
 ThioPhene
53

2. Nitrogen compounds
◦ Found at very low percentages, most
common compounds are;
 Pyridine
 Quinoline
54

◦ Their Effect:
1. Increase the bad odor effect of sulfur compounds
2. Have a corrosive effect
3. Result in catalyst poisoning
55

3. Oxygen Compounds
◦ Like oxides, carbonates…ETC
◦ Generally they have no harmful effect.
4. Phosphorus Compounds
◦ They are responsible for the effect of
phosphorescence which is useful for
prospecting oil reservoirs
◦ Hence, we consider them as useful
impurities
56

5. Mineral Salts and Mineral Elements
◦ The mineral salts like (NaCl, MgCl2) are
found dissolved in the water accompanying
the oil
◦ They have a dangerous electrolytic
corrosion effect, and thus they have to be
removed
◦ Such salts are usually removed through
washing by water then separating
Water/Salts layer from oil layer through
gravity settling
57

◦ Mineral elements like (vanadium and nickel)
are also present and they catalyze the
electrolytic reaction
58

Exercise
Apply the different types of hydrocarbons on a
compound made of 8 carbon atoms:
Q)What is the name, molecular formula and
structural formula of each type ?
59

CLASSIFICATION OF
CRUDE OIL
60

Introduction
 Why do we need a
classification/characterization technique
for crude oil?
 Classification of crude oil is based on its
chemical constitution
61

Methods of Crude Oil Classification
 PONA Analysis
 USBM
 UOP Characterization Factor

Classification Techniques - PONA
63
PONA
Paraffines
Olefins
Naphthenes
Aromatics
1. PONA Analysis

PONA Analysis
 PONA (Parrafins-Olefins-Naphthenes-
Aromatics) Analysis
 PONA analysis shows the relative
concentrations of major hydrocarbon groups in
the crude oil
 It is a general rough method based on the
chromatographic analysis for the hydrocarbons
present.

Classification Techniques - PONA
◦ Results expected:
 Paraffinic base
 Naphthenic base
 Mixed base
65
Gasoline chromatograph

Classification Techniques - USBM
2. U.S.B.M.
66
USBM
United
States
Bureau
of
Mines

◦ So, we can do a classification based on the API
of a Boiling Range
◦ In this method, two boiling ranges (Key
Fractions) are chosen:
 KI (250 – 275 ˚C), Atm. P
 KII (275 – 300 ˚C), 40 mmHg
◦ The first word of the name of the base applies
to gasoline and lower fractions while the
second word applies to lubricants and higher
boiling points of the crude oil.
◦ For each fraction API is measured and the
criteria in the following slide is applied 67

◦ For KI
 API ≥ 40 (PBC)
 40 > API > 33 (MBC)
 API ≤ 33 (NBC)
◦ For KII
 API ≥ 30 (PBC)
 30 > API > 20 (MBC)
 API ≤ 20 (NBC)
◦ Result form: ( KI base followed by KII base)
68

◦ Results expected
69
No. KI KII Result
1 PBC PBC PBC
2 PBC MBC PBC-MBC
3 PBC NBC PBC-NBC*
4 MBC PBC MBC-PBC
5 MBC MBC MBC
6 MBC NBC MBC-NBC
7 NBC PBC NBC-PBC*
8 NBC MBC NBC-MBC
9 NBC NBC NBC
* Not practically found yet

◦ Further sub-divisions can be added upon
measuring pour point
◦ If cloud point of KII is below 5 ˚F, the class
name is appended by “Wax Free”
70

Classification Techniques - UOP
3. UOP orWatson Characterization Factor
71
UOP
Universal
Oil
Products

◦ Analogous to USBM, this method is based
on two properties:
 Average Molal Boiling Point (AMBP) - R
 Sp. Gravity(60/60 ˚F) (S) - Unitless
, Where:
◦ AMBP is obtained from a distillation curve
like the ASTM D86
◦ VABP: Volumetric Average Boiling Point
72

◦ Advantages of this technique:
 Dependant on both BP and S
 Providing a number that can be used for
correlating physical properties and used
simulation
73

 In contrast to individual hydrocarbons which boils
at specific temperature, petroleum cuts which are
continuous mixtures, have wide boiling range.
Therefore, we use the concept of average boiling
point.
 The average molal boiling point is defined as A
pseudo boiling point for a mixture calculated as the
summation of individual mole fraction-boiling point
(in degrees Rankine) products.

 However, it is very difficult to determine the mole
fraction of each component, so the MABP is
difficult to be determined. So the volumetric
average boiling point is determined and correlated
to give the MABP:
 Where theVABP =

Characterization Factor
 Xvi is the volumetric fraction of component i, at its
boiling pointTi in Kelvin. Since it is difficult to
determine the volumetric fraction of each
component and its definite boiling point.
 VABP is determined from ASTM D86 distillation
curve.

Classification Techniques - ASTM
77
ASTM
American
Society
for
Testing
and
Materials

◦ Several Types of curves showing BP vs
Volume are available, including
 TBP Curve
 ASTM D-86 Curve
◦ ASTM D-86 is the most used in labs
◦ Such curves are used to obtain some specs
for the crude/fraction (Example: obtaining
theVABP) and do prepare a crude/fraction
assay
78

◦ The experimental setup is shown below
79

◦ Procedure:
1. Make sure the experimental setup is correct
2. Fill the distillation flask will 100 ml of the crude
3. Start heating at constant rate and watch the
temperature increase
4. Record the temperature at which the first droplet
falls in the receiving flask (IBP)
5. Keep recording volumes every 10 °C increase
6. Record the temp. at the final droplet (FBP)
7. Measure the remaining volume in the distillation
flask
80

◦ Definitions:
1. Recovery: the total volume obtained at the FBP
2. Residue: the amount of the liquid that remained
in the distillation flask
3. Loss: InitialVolume – (Recovery + Residue)
4. % DistilledVolume:
81

◦ Results:
1. Repeat the experiment if the %loss is greater than
2%
2. Draw the temperature on the y-axis versus the
%volume distilled on the x-axis
◦ The next slide shows a sample ASTM D-86
curve
82

83

Characterization Factor
 Then calculate theVABP:
 Use the mentioned correlation to get MABP,
 and then determine the characterization factor.
 The following criteria applies:
 K ≥ 12.2 , PBC
 K ≤ 11.4, NBC
 11.4 < K< 12.2, MBC

Answers to section questions
 Slide 5:
◦ Hydrocarbons are compounds that consist
entirely from carbon and hydrogen
◦ Side chains might contain other atoms
(impure hydrocarbons)
◦ They are generally classified into:
1. Saturated Hydrocarbons (Paraffins)
2. Unsaturated Hydrocarbons (Olefins and Alkynes)
3. Cycloalkanes (Naphthenes)
4. Aromatic Hydrocarbons
85

 Follow Slide 5:
1. Paraffins
 Composed entirely from single bonds, can either
be found linear (normal) or branched (iso)
 General Molecular Formula: CnH2n+2
 Example: Ethane C2H6
86

 Follow Slide 5:
2. Olefins
 Unsaturated hydrocarbons
 Has one or more double bonds (Alkenes) or
triple bonds (Alkynes) between carbon atoms
 Due to their high reactivity, olefins are not
common in natural crude oil.
 General Molecular Formulae and Examples:
 Alkenes: CnH2n , Ex: Ethylene (Ethene) C2H4
 Alkynes: CnH2n-2 , Ex: Acetylene (Ethyne) C2H2
87

 Follow Slide 5:
3. Naphthenes
 They contain one or more saturated carbon rings
 General Molecular Formula: CnH2(n+1-g) where g is
the number of rings, for a single ring (CnH2n)
 Example: Hexane C6H12
88

 Follow Slide 5:
4. Aromatics:
 They are unsaturated hydrocarbons that contain
at least one benzene ring (simplest possible
aromatic hydrocarbon)
 General Molecular Formula for a benzene ring:
(CnH2n-6)
 Example: Benzene C6H6
89

 Follow Slide 5:
Hetero-atom Compounds
 When present in organic compounds, atoms other
than carbon and hydrogen are called hetero-atoms.
 Sulfur, Nitrogen, Oxygen and Metals are minor
constituents of crude oil
 When burned in vehicles or power plants, high-
sulfur fuels cause acid rain. For many refining
processes, sulfur is a catalyst poison.
 Nitrogen and metals also are catalyst poisons.
 Therefore,We must remove hetero-atoms from
intermediate streams and finished products.
90

 Slide 17:
◦ Specific Gravity: is the ratio between the
density of a substance to the density of a
reference fluid at a specific temperature and
pressure
◦ The reference fluid for gases is air while for
liquids and solids is water
91

 Slide 21:
◦ Depends on the Oil composition, Most
crudes are lighter than water except for
some very heavy crudes that might
approach the density of water
92
 Slide 23:
◦ The Australian crude has the highest price
being the lighter in color, thus the lighter in
density and higher API, meaning that it
contains a higher % of the valuable light
components

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