Petroleum Chemistry

Prepared By

Dr. Essam M. Hussein

Assistant Professor of Organic Chemistry Chemistry Department

Faculty of Applied Science -Umm Al-Qura University

Introduction

Petroleum - Crude oil:

Petroleum (L. petroleum, from Greek: Πέτρα

(rock) + Latin: oleum (oil)) is a naturally

occurring flammable liquid consisting of a

complex mixture of hydrocarbons of various

molecular weights and other liquid organic

compounds, that are found in geologic

formations under the Earth's surface.

The name Petroleum covers both naturally

occurring unprocessed crude oils and petroleum

products that are made up of refined crude oil.

1- Origins of Oil and Gas

1.a Inorganic Theory:

Inorganic origin source of petroleum was assumed in

nineteenth century by:

(A) Berthelot theory (1866):

. This theory regards petroleum origin that carbonic acid

or carbonates dissolved in ground water acting on

alkali metals present in the earth's interior formed

acetylene and other hydrocarbons.

The formation of acetylene by this reaction was

shown to occur, and the production of other

hydrocarbons was regarded as possible at high

temperature and pressures prevailing at great

depths.

(B) Carbide Theory:

• This theory was originally suggested by

Mendeleev in the early 1800's, and supported by

Mossan, Sabatier and Senderens.

It regards petroleum as of inorganic origin being

formed by the action of steam or water on

metallic carbides in the inner portion of earth's

crust.

The carbide theory describes the formation of

petroleum by the following steps:

(i) Formation of Carbides: The molten metals in the hot interior of the earth came in contact with coal and carbides were formed, thus:

(ii) Action of steam on Carbides: Carbides

reacted with steam under high pressure and at

high temperature forming hydrocarbons.

Al4C3Al(OH)3

CaC2Ca(OH)2

C2H2

+ 12 H2O 4 + 3 CH4

Methane

+ 2 H2O +

Acetylene

(iii) Reduction of Unsaturated Hydrocarbons:

The unsaturated hydrocarbons formed by step (ii)

are reduced with hydrogen in the presence of

metallic catalyst at high temperature.

The hydrogen needed for reduction is obtained by the action of hot metals with steam.

(iv) Polymerization: Unsaturated hydrocarbons

polymerized in the presence of hot metals forming

aromatic hydrocarbons, cycloalkanes, and higher

open-chain hydrocarbons.

He believed that petroleum came from deep within

the earth, noting how petroleum seemed to be

associated with large features of the earth like

mountains and valleys rather than the finer scale

sedimentary deposits.

There are many today who believe in this theory,

and there is some evidence to back them up.

Petroleum and natural gas are frequently found in

geographic patterns of long lines or arcs which are

related more to deep-seated, large-scale structures of

the earth's crust, rather than to smaller-scale

sedimentary deposits.

Hydrocarbon-rich areas tend to be rich at many levels

and extend down to the crystalline basement that

underlies the sediment.

There is no doubt that the carbide theory explains the

formation of petroleum in a rational way but there are

serious objections against it and at present this theory

commands little consideration.

The main facts which go against it are:

(a) Natural petroleum contains sulphur and nitrogen

compounds, chlorophyll, haemen, ect.

The carbide theory fails to explain their presence in

petroleum as they are all essentially of organic origin.

(b) Petroleum contains optically active compounds,

According to the carbide theory, the natural mode of

formation of petroleum is a strict laboratory one and

we know that we cannot get optically active substances

by ordinary synthetic methods in the laboratory.

(c) The presence of the characteristically organic

nitrogen, sulfur and oxygen compounds found in such

crude oil have been studied from this stand point,

cannot well be explained by any reasonable inorganic

theory.

1.b Organic Theory:

The most popular theory is known as the Organic

Theory.

This theory states that oil and gas have biological

origins [Engler 1900]. Small sea creatures from the

days when the earth was mostly covered in water died

and settled to the bottom of the ocean floor.

من *- الماليين عشرات العملية هذه تستغرقالحقل فإن ولذا البترول يتكون حتى السنين

. أخرى مرة يعوض ال ينفذ الذى البترولى

عدة*- على يحتوى قد الواحد البترولى الحقل ( ) مصايد بترولية تراكيب ذات رسوبية طبقات

. والعمر والمصدر الجودة درجة فى مختلفة

النوع *- من كان كلما Kعمرا أقدم البترول كان كلمامن عالية نسبة يعطى حيث جودة األكثر البارافينىمن أقل ونسبة والمتوسطة الخفيفة المقطراتاألحدث للبترول صحيح والعكس الثقيلة المقطرات

.K عمرا

Layer upon layer of silt, sand and clay built up on top of them over time.

Through the process of decay, as well as ever increasing heat and pressure, the former sea creatures were converted to oil and gas.

Over millions of years, continuous pressure actually compressed those layers of silt and clay into layers of rock. This is known as "reservoir rock".

The temperature under the earth's surface increases with the deeper you go underground.

At about 150 F, oil begins to form. Oil formation ceases at about 300 F.

Oil formed at lower temperatures (i.e. closer to the surface) is called immature and is heavy.

Oil formed deeper under the surface is called mature and is light.

At temperatures above 300 F, oil is thermally cracked to produce light gases (i.e. natural gas).

Since temperature increases with depth, natural gas wells are typically drilled much deeper than oil wells.

Another fact that gives weight to Engler's theory is the mineral oil is always found that accompanied with salt and brine, which must have been obtained from sea water.

This is probably the story of the origin of oil and gas that we are all familiar with.

However, there are other interesting alternative the hypothesis known as the Inorganic Theory

The main fact that gives weight to Engler's theory (Organic hypotheses):العضوية النشأة نظريات أيدت التى الحقائق

هى:الصخور- 1 طبقات فى الخام البترول وجود

نتيجة النارية الصخور كذلك و الرسوبية. البترول هجرة

األنهار- 2 دلتا أماكن فى البترول وجود. الشواطئ وقرب الخلجان و المائية

وبقايا- 3 األصداف على الخام البترول إحتواء. القديمة الحية الكائنات

مما- 4 البورفيرين مادة على البترول إحتواءللبترول المكونة المواد ترسيب على يدل

. حرارةعالية ودرجة ضغط تحتعند- 5 البترول يشبه سائل إنتاج إمكانية

ودرجة للضغط البحر قاع رواسب تعريض الحرارة.

Chemical Composition of Petroleum

Petroleum, also known as crude oil, is a very

complex mixture consisting of paraffin,

naphthene (cycloparaffin), and aromatic

hydrocarbon as well as nitrogen-, oxygen-,

sulfur- containing compound and traces of a

variety of metal- containing compounds, and

inorganic compounds, over millennia.

The crude oil mixture is composed of the following

groups:

1. Hydrocarbon compounds (compounds made of

carbon and hydrogen).

2. Non-hydrocarbon compounds.

3. Organometallic compounds and inorganic salts

(metallic compounds).

1. Hydrocarbon Compounds

. The principal constituents of most crude oils are

hydrocarbon compounds.

. All hydrocarbon classes are present in the crude

mixture, except alkenes and alkynes.

. This may indicate that crude oils originated

under a reducing atmosphere.

1.1. Alkanes (Paraffins)

Alkanes are saturated hydrocarbons having the general

formula CnH2n+2.

The simplest alkane, methane (CH4), is the principal

constituent of natural gas.

Methane, ethane, propane, and butane are gaseous

hydrocarbons at ambient temperatures

and atmospheric pressure. They are usually found

associated with crude oils in a dissolved state.

. Boiling point and density increase with increasing number of C atoms. . Branched alkanes (iso-alkanes) is very small in quantity. . Boiling point of straight chains > iso-alkanes with the same number of C

. Normal alkanes (n-alkanes, n-paraffins) are straight-

chain hydrocarbons having no branches.

. Branched alkanes are saturated hydrocarbons with an

alkyl substituent or a side branch from the main chain.

NOTE:

A branched alkane with the same number of carbons and hydrogens

as an n-alkane is called an isomer.

For example, butane (C4H10) has two isomers, n-butane and 2-methyl

propane (isobutane). As the molecular weight of the

hydrocarbon increases, the number of isomers also increases.

Pentane (C5C12) has three isomers; hexane (C6H14) has five.

The following shows the isomers of hexane.

C1-C4 (Gases), C5-C15 (Liquids) and C15-C27 (Solids)

1.2. Cycloparaffins (Naphthenes)Saturated cyclic hydrocarbons, normally known as naphthenes, are also part of the hydrocarbon constituents of crude oils. General Formula CnH2n for one ring compounds.

Cycloalkanes have similar properties to alkanes but have higher boiling points.

R

AlkylcyclohexaneCyclopentane Cyclohexane

1.3. Alkenes or Olefins

Unsaturated aliphatic hydrocarbon (e.g. ethylene

or propylene) are rarely formed in crude oil, they

are produced during cracking and conversion

processes.

Aromatics hydrocarbon (Cyclic and polyunsaturated hydrocarbons

containing conjugated double bonds) Alkylaromatics have very high octane number

content in gasoline is limited by environmental regulations –health effects due to high toxicity.

Heteroatom compoundsSulfur compounds

Might be present in inorganic and organic forms. In crude oils sulfur concentration can range from 0.1 to more than 8 weight percent.

The presence on organic sulfur compounds, H2S and elemental sulfur in petroleum can be accounted for in several ways.

Some of them produced from the original organic fragment.

The presence of sulfur compounds could be also explained by thermal reaction between elemental sulfur, or possibly H2S, and the other organic components of the sediments including the hydrocarbons.

These reactions may continue even after the oil has accumulated in the reservoir.

The crudes which contain more than 1% of sulfur are known as high sulfur bearing crudes, but these that contain less than 1% sulfur are known as low sulfur bearing crudes.

Sour crudes contain a high percentage of hydrogen

sulfide. Because many organic sulfur compounds are not

thermally stable, hydrogen sulfide is often produced

during crude processing.

High-sulfur crudes are less desirable because treating

the different refinery streams for acidic hydrogen

sulfide increases production costs.

Most sulfur compounds can be removed from petroleum

streams through hydro-treatment processes, where

hydrogen sulfide is produced and the corresponding

hydrocarbon released.

Hydrogen sulfide is then absorbed in a suitable absorbent

and recovered as sulfur.

Oxygen compounds Oxygen compounds in crude oils are more complex

than the sulfur types.

However, their presence in petroleum streams is not poisonous to processing catalysts.

Many of the oxygen compounds found in crude oils are weakly acidic.

They are carboxylic acids, cresylic acid, and phenol. Naphthenic acids are cyclohexane or cyclopentane derivatives having a carboxyalkyl side chain.

Naphthenic acids in the naphtha fraction

have a special commercial importance and

can be extracted by using dilute caustic

solution.

The total acid content of most crudes is

generally low, but many reach as much as

3%, as in some California crudes.

OHOH

Phenol CreasolsNaphthols

CH3

OH

Nitrogen compounds

The nitrogen bases are present as minor constituents in

petroleum

( 0.1 wt %). They have no special significant except to

indicate the presence of proteins in the original organic

material.

They appear to be present in largest amounts in some

of the geologically younger oils. They may be of either

type or neutral type; e.g.

Metallic compounds They are present either as inorganic salts or organometallic

compounds.

a- Inorganic Salts Many metals occur in crude oils. Some of the more

abundant are sodium, calcium, magnesium, aluminum, iron, vanadium, and nickel, such as sodium and magnesium chlorides, Calcium and magnesium can form salts or soaps with carboxylic acids.

These compounds act as emulsifiers, and their presence is undesirable.

Although metals in crudes are found in trace amounts, their presence is harmful and should be removed.

b- Organometallic Compounds Nickel and vanadium are present also in the form of

the organometalllic compounds (porphyrins).

Porphyrins are non-basic nitrogen compounds. The porphyrin ring system is composed of four pyrrole rings joined by =CH- groups.

The entire ring system is aromatic. Many metal ions can replace the pyrrol hydrogens and form chelates.

The chelate is planar around the metal ion and resonance results in four equivalent bonds from the nitrogen atoms to the metal.

Almost all crude oils and bitumens contain delectable amounts of vanadyl and nickel porphyrins.

The following shows a porphyrin structure:

N

NH HN

N

N

N N

N

X

Petroporophyrin Metallic Petroporophyrin

X = Mg Chlorophyll

= Fe Haemoglobin

= Co Vitamin B12

= V, Ni Petroporophyrins

: البترول تصنيف Classification of Crude Oil:

متعددة بأساليب البترول تصنيف على إتم ماالطبيعية خواصه على أو الكيميائى تركيبهحسب البترول يصنف المثال سبيل وعلى

ومتوسط خفيف الى لزوجته و النوعية كثافتةالى الهيدروكربونية مكوناته وحسب وثقيلأسفلتى أو وأروماتى ونافثينى بارافينى

Paraffinic, Naphthenic, Asphaltic الى أومختلط أو القاعدة أسفلتى أو القاعدة بارافينى

القاعدة مهجن أو ,ParaffinicالقاعدةAsphaltic, Mixed or Hybrid Base Oils

Physical properties of crude oil

الكيميائى وتكوينه البترولى المنتج نوعية تحديد يمكن: مثل والكيميائية الطبيعية الخواص بعض بدراسة

ال- 1 : Sulfur content كبريتيالمحتوى

كلما البترول خام جودة المركبات إتقل نسبة زدادت. صحيح والعكس الكبريتية

فى الكبريت نسبة زيادة عليها تترتب التى األثار: البترول خام

.a أجزاء كل فى مستمرة بصفة التأكل تسببالمحركات.

.b غاز الجوية SO3و SO2يتكون الرطوبة مع وباإلتحادفى التأكل يسبب والذى الكبريتيك حمض يتكون

. الحديدية والمواسير المحركات

الجازولين- فى وخاصة األوكتان رقم تقليل على يعمل جويصبح جودته من يقلل .مما للسيارات كوقود صالح غير

تقطير- من المنتجة العضوية المركبات قدرة من يقلل دتفاعالت وجود الى يؤدى مما الذوبان على البترول

. األساسى التفاعل الى باإلضافة أخرى جانبية

أكثر- ـه مركبات تكوين على تساعد الكبريت نسبة زيادةفى تتركز ثقيلة صمغية مركبات لتكوين يؤدى مما Kتعقيدا

.( واألسفلت ( المازوت الثقيلة المقطرات

النوعية- 2 والكثافة :الكثافة

Density and spacific gravity-:

. الحجوم وحدة كتلة هى The mass of unit الكثافةvolume

كتلة الى السائل كتلة بين النسبة هى النوعية الكثافة. الحرارة درجة نفس عند الماء من الحجم نفس

Density = mass / Volume

Fg ra tS p

A P I

6 0/6 0.

5.1 3 15.1 4 1

Relative density = density of pet. fraction / density of water at the same temperature.

API gravity:

3. Aniline Point:

The aniline point is a physical characteristic of

hydrocarbon compounds, such as oils, and refers to the

minimum temperature at which the hydrocarbon and

the same amount of the compound aniline (C5H5NH2)

are perfectly miscible.

At temperatures below this point, a

mixture of the compound and an equal

volume of aniline will not dissolve

together.

The result of a test, called the aniline test,

gives chemists this information about a

hydrocarbon, including certain details

about its composition, such as the relative

content of aromatic chemicals and

various paraffins.

The aniline point of a liquid will vary, depending upon the

relative concentration of aromatic compounds dissolved in

it. Generally, a higher aniline point means a relatively low

level of dissolved aromatics. By using reference materials

for a pure sample of a given substance and comparing the

aniline point of the pure sample to that of the test sample, a

chemist can calculate the amount of aromatics in the test

sample with a high degree of accuracy.

• Increase by increasing carbon atoms in the paraffinic

carbon chain

• Increase by increasing side chains in the paraffinic carbon

chain

• Decrease by increasing aromatic content.

Arrange the following compounds according to increasing in

their Aniline point.

H3C

H2C

CH2

H2C

CH2

CH3

H3CCH

CH2

H2C

CH3

CH3

H3CCH H

C

CH3

CH3

CH3

I II

IIIIV

4. Flash Point

The flash point of a volatile material is the lowest temperature

at which it can vaporize to form an ignitable mixture in air.

Measuring a flash point requires an ignition source

5. Fire Point

The fire point of a fuel is the temperature at which the vapour

produced by that given fuel will continue to burn for at least 5

seconds after ignition by an open flame. At the flash point, a

lower temperature, a substance will ignite briefly, but vapor

might not be produced at a rate to sustain the fire.

5- Viscosity :-

Kinematic viscosity: a measure of the time for a fixed volume of

liquid to flow by gravity through a capillary. The cgs

(centimeter-gram-second) unit of kinematic viscosity is the

stoke which has the dimensions centimeters-squared per

second. In the petroleum industry kinematic viscosity is usually

expressed in centistokes, cSt, so that 1 St = 100 cSt.

Kinematic viscosity, cSt = C . t

C = calibration constant of the viscometer, cSt/s, and

t = flow time, s.

where:

Dynamic viscosity:- (sometimes called absolute viscosity) is

numerically the product of kinematic viscosity and the density of

the liquid, both at the same temperature. The cgs unit of dynamic

viscosity is the poise, P, which has the dimensions grams per

centimeter per second. It is the force required to move a unit plane

surface over another plane surface at unit velocity when surfaces

are separated by a layer of fluid of unit thickness.

ρ = density, g/cm3 (Note 6) at same temperature as kinematic viscosity, and

ν = kinematic viscosity, cSt.

Dynamic viscosity, cP = ρ . νwhere:

<

Paraffinic-base oil has lower viscosity (higher quality) and vice-versa.

- Viscosity increased by rings increased

- Viscosity increased by side-chains increased at the same carbon atoms.

CH3H3C

H3C

H2CH2C CH3

<

HC CH2 H2C CH3

>

- Viscosity in olefinic hydrocarbons is lower than viscosity of paraffinic hydrocarbons.

Absolute viscosity (dynamic viscosity) provides a measure of a

fluid’s internal resistance to flow. For liquids, viscosity

corresponds to the informal notion of "thickness".

For example, honey has a higher viscosity than water.

Arrange the following compounds according to decreasing in their

viscosity.

HC

HC

CH3 H2C

H2C

CH3

H2CCH3

CH3

CH3

CH3H3C

I II

IIIIV

6- Pour point :-

The pour point of a liquid is the temperature at which it becomes

semi solid and loses its flow characteristics. In crude oil a high

pour point is generally associated with a high paraffin content,

typically found in crude deriving from a larger proportion of

plant material.

7- Freezing Point:

The melting point of a solid is the temperature at which it

changes state from solid to liquid at atmospheric pressure. At the

melting point the solid and liquid phase exist in equilibrium. The

melting point of a substance depends on pressure and is usually

specified at standard pressure. When considered as the

temperature of the reverse change from liquid to solid, it is

referred to as the freezing point or crystallization point.

Jet fuel

Jet fuel or aviation turbine fuel (ATF) is a type of aviation fuel

designed for use in aircraft powered by gas-turbine engines. It is

colorless to straw-colored in appearance. The most commonly

used fuels for commercial aviation are Jet A and Jet A-1, which

are produced to a standardized international specification. The

only other jet fuel commonly used in civilian turbine-engine

powered aviation is Jet B, which is used for its enhanced cold-

weather performance.

Jet fuel is a mixture of a large number of different hydrocarbons.

The range of their sizes (molecular weights or carbon numbers)

is restricted by the requirements for the product, for example,

the freezing point or smoke point.

It should be free of sulfur compounds (octane number = 100)

Types of Jet fuel:

1- Kerosene-type jet fuel (including Jet A and Jet A-1) has a

carbon number distribution between about 8 and 16 (carbon

atoms per molecule), (boiling range 150-250).

2- Jet B is a fuel in the gazoline-kerosene region that is used

for its enhanced cold-weather performance. However, Jet B's

lighter composition makes it more dangerous to handle. For this

reason it is rarely used, except in very cold climates. A blend of

approximately 30% kerosene (C8-C16) and 70% gasoline (C4-

C12), it is known as wide-cut fuel. It has a very low freezing

point of −60 °C (−76 °F) and a low flash point as well. It is

primarily used in some military aircraft. It is also used in Canada

because of its freezing point.

Distillation is a process of separating the component substances

from a liquid mixture by selective vaporization and

condensation.

Distillation

1. Simple distillation

simple distillation is effective only when the liquid boiling points

differ greatly (rule of thumb is 25 °C) or when separating liquids

from non-volatile solids or oils. For these cases, the vapor

pressures of the components are usually different enough that the

distillate may be sufficiently pure for its intended purpose.

2. Fractional Distillation

For many cases, the boiling points of the components in the

mixture will be sufficiently close. Therefore, fractional distillation

must be used in order to separate the components by repeated

vaporization-condensation cycles within a packed fractionating

column.

Perkin triangle distillation setup

1: Stirrer bar/anti-bumping

granules 2: Still pot 3:

Fractionating column 4:

Thermometer/Boiling point

temperature 5: Teflon tap 1 6: Cold

finger 7: Cooling water out 8:

Cooling water in 9: Teflon tap 2 10:

Vacuum/gas inlet 11: Teflon tap 3

12: Still receiver

3. Vacuum distillation

Some compounds have very high boiling points. To boil such

compounds, it is often better to lower the pressure at which such

compounds are boiled instead of increasing the temperature.

Once the pressure is lowered to the vapor pressure of the

compound (at the given temperature), boiling and the rest of the

distillation process can commence.

This technique is also very useful for compounds which boil

beyond their decomposition temperature at atmospheric pressure

and which would therefore be decomposed by any attempt to

boil them under atmospheric pressure.

Dimethyl sulfoxide

usually boils at 189

°C. Under a vacuum,

it distills off into the

receiver at only 70

°C.

4. Steam distillation

Like vacuum distillation, steam distillation is a method for distilling

compounds which are heat-sensitive.[18] The temperature of the steam is

easier to control than the surface of a heating element, and allows a high

rate of heat transfer without heating at a very high temperature. This

process involves bubbling steam through a heated mixture of the raw

material. By Raoult's law, some of the target compound will vaporize (in

accordance with its partial pressure). The vapor mixture is cooled and

condensed, usually yielding a layer of oil and a layer of water.

Crude Oil Pretreatment (Desalting)

Description

Crude oil often contains water, inorganic salts, suspended solids, and

water-soluble trace metals. As a first step in the refining process, to

reduce corrosion, plugging, and fouling of equipment and to prevent

poisoning the catalysts in processing units, these contaminants must

be removed by desalting (dehydration).

The two most typical methods of crude-oil desalting, chemical and

electrostatic separation use hot water as the extraction agent.

In chemical desalting, water and chemical surfactant

(demulsifies) are added to the crude, heated so that salts and

other impurities dissolve into the water or attach to the water,

and then held in a tank where they settle out.

Electrical desalting is the application of high-voltage

electrostatic charges to concentrate suspended water globules in

the bottom of the settling tank. Surfactants are added only when

the crude has a large amount of suspended solids. Both methods

of desalting are continuous.

feed

stoc

k

primary flash column

Heater

Gases

Light Oil

Naphtha

Heavy naphtha

Kerosene

Diesel fuel oil

Atmospheric distillation

stripper

Vacuum

Vacuum distillation

Gas oil

Light

Medium

Heavy

Asphalt

Lu

bri

cati

ng

oils

150-250o

200-350o

20-70o 45-200o

220-400o

over 400o

Fractional Distillation of Crude Oil

تقطير لوحدة مخططالبترول

سوالر

التشحيم زيوت

Refining end-products

Light distillates

•Liquid petroleum gas (LPG) [C1-C4]

•Gasoline (also known as petrol) [C4-C12]

•Heavy Naphtha

•Light Naphtha

Middle distillates

•Kerosene [C8-C16]

•Automotive and rail-road diesel fuels [C12-C18]

•Residential heating fuel

•Other light fuel oils

Heavy distillates

•Heavy fuel oils

•Bunker fuel oil and other residual fuel oils

نوع المقطرات

متوسط ذرات عددالكربون

متوسط درجة الحرارة

المقطرات

غازية نواتج C1-C4 غازات غازات

سائلة نواتج

C5-C6 20-70 أثير بترولى

C4-C12 45-200 جازولين

C8-C15 150-250 كيروسين

C12-C18 200-350 سوالر

C15-C32 220-400 ديزل

الوقود زيتC16-C22 من 400أعلى ثقيل ديزل

C18-C24 صلبة مواد مقطرات شمعية

How to get motor fuel (Gasoline)?

1- Distillation of crude oil and heavy distilled to get gasoline.

2- Thermal Cracking processes of heavy distillates: gasoline

output from this process contain olefinic hydrocarbons

needs to saturate the olefinic bonds by hydrogenation and

disposal of sulfur and nitrogen compounds.

3- Re-distillation of heavier fractions : it is carry out in the

presence of a catalyst at high temperatures and pressures.

4- Isomerization of gasoline: compounds containing 5-6

carbon atoms as it turns straight-chain hydrocarbons (with

lower octane number) to branched-chain hydrocarbons (with

high octane number and lower boiling points) and carry out

in the presence of catalyst such as aluminum chloride

promoted with HCl.

5- Polymerization: is the process of converting light olefin

gases including ethylene, propylene, and butylene into

hydrocarbons of higher molecular weight and higher octane

number that can be used as gasoline blending stocks.

Catalytic Cracking

Introduction Catalytic cracking breaks complex hydrocarbons into

simpler molecules in order to increase the quality and quantity of lighter, more desirable products and decrease the amount of residuals.

This process rearranges the molecular structure of hydrocarbon compounds to convert heavy hydrocarbon feedstock into lighter fractions such as kerosene, gasoline, LPG, heating oil, and petrochemical feedstock.

Catalytic cracking is similar to thermal cracking except that catalysts facilitate the conversion of the heavier molecules into lighter products.

Use of a catalyst (a material that assists a chemical reaction but does not take part in it) in the cracking reaction increases the yield of improved-quality products under much less severe operating conditions than in thermal cracking.

Typical temperatures are from 850°-950° F at much lower pressures of 10-20 psi.

The catalysts used in refinery cracking units are typically solid materials (zeolite, aluminum hydrosilicate, treated bentonite clay, fuller's earth, bauxite, and silica-alumina) that come in the form of powders, beads, pellets or shaped materials called extrudites.

A)There are three basic functions in the catalytic cracking process:

Reaction: Feedstock reacts with catalyst and cracks into different hydrocarbons;

R-CH2-CH2-R` + catalyst R-CH2-CH+-R`

R-CH2-CH+-R`-H+

R-CH=CH-R'

The intermediate alkene may cyclized by internal addition of a carbonium ion to a double bond may occur (Catalytic reforming):

RR

+

R

+

-H+

R

etc.

R

+

R

etc.

Dealkylation of alkyl benzenes may occur without ring degradation below 500° C

CH2 -R

+ R-CH2+

b- Regeneration: Catalyst is reactivated by burning off coke.

c- Fractionation: Cracked hydrocarbon stream is separated into various products.

Types of Catalytic Cracking Processes

The two types of catalytic cracking processes are fluid catalytic cracking (FCC), moving-bed catalytic cracking, and Thermofor catalytic cracking (TCC).

The catalytic cracking process is very flexible, and operating parameters can be adjusted to meet changing product demand.

In addition to cracking, catalytic activities include dehydrogenation, hydrogenation, and isomerization.

Thermal Cracking Description

Because the simple distillation of crude oil produces amounts and types of products that are not consistent with those required by the marketplace, subsequent refinery processes change the product mix by altering the molecular structure of the hydrocarbons.

One of the ways of accomplishing this change is through "cracking," a process that breaks or cracks the heavier, higher boiling-point petroleum fractions into more valuable products such as gasoline, fuel oil, and gas oils.

The two basic types of cracking are thermal cracking, using heat and pressure, and catalytic cracking.

Tow general types of reaction occur during thermal cracking1. The decomposition of large molecules into small

molecules (primary reactions):

CH3-CH2-CH2-CH3 CH4 CH3-CH=CH2+

butane methane propene

CH3-CH2-CH2-CH3 CH3-CH3 +

butane ethane ethylene

CH2=CH2

2. Reactions by which some of the primary product interact to form higher molecular weight materials (secondary reactions):

ethylene

+

ethylene butene

or

+ R`-CH=CH2 tar, heavy oil, coke

CH2=CH2 CH2=CH2 CH3-CH2-CH=CH2

R-CH=CH2

The first thermal cracking process was developed around 1913.

Distillate fuels and heavy oils were heated under pressure in large drums until they cracked into smaller molecules with better antiknock characteristics.

However, this method produced large amounts of solid, unwanted coke.

This early process has evolved into the following applications of thermal cracking: visbreaking, steam cracking, and coking.

Isomerization Isomerization converts n-butane, n-pentane and n-

hexane into their respective isoparaffins of substantially higher octane number.

The straight-chain paraffins are converted to their branched-chain counterparts whose component atoms are the same but are arranged in a different geometric structure.

The catalyst used may be aluminum chloride promoted with HCl

or a platinum containing catalyst.

A l C l 3 + H C l [ A l C l 4 ] - H +

H3C

H2C

CH2

CH3 RH3C

HC

CH2

CH3

- R-H H3C

CH

CH2

CH3

H3C

C

CH3

CH3H3C

H2C

CH2

CH3

H3C

HC

CH2

CH3

H3C

CH

CH3

CH3

+

Paraffins are isomerized by means of the formation and rearrangement of a carbocation.

Polymerization Polymerization in the petroleum industry is the process

of converting light olefin gases including ethylene, propylene, and butylene into hydrocarbons of higher molecular weight and higher octane number that can be used as gasoline blending stocks.

Polymerization combines two or more identical olefin molecules to form a single molecule with the same elements in the same proportions as the original molecules.

Polymerization may be accomplished thermally or in the presence of a catalyst at lower temperatures.

Polymerization

H2C

HC

CH3H2C

HC

CH2

CHCH3

CH3

H2H2SO4

H3C

H2C

CH2

CHCH3

CH3

H2CC

CH3

CH3

H2CC

CH2

CH3

C

CH3

CH3

CH3

H3CCH

CH2

CH3

CCH3

CH3

CH3H2

H2SO4

2

2

propene

iso-butene

2-methylpentane

2,2,4-trimethylpentane

iso-octaneOctane No. = 100

Alkylation

Introduction Alkylation combines low-molecular-weight olefins

(primarily a mixture of propylene and butylene) with isobutene in the presence of a catalyst, either sulfuric acid or hydrofluoric acid.

The product is called alkylate and is composed of a mixture of high-octane, branched-chain paraffinic hydrocarbons.

Alkylate is a premium blending stock because it has exceptional antiknock properties and is clean burning.

The octane number of the alkylate depends mainly upon the kind of olefins used and upon operating conditions.

Alkylation

H3C

H2C

HC

CH3

CH3

CH2CH

H3C

H3C CH3

CH2C

CH3

CH

CH3H3C

H3C

+H2SO4

or HF

H2CC

CH3

CH3 CH3

CH2CH

H3C

H3C CH3

CH2C

CH3

C

CH3H3C

H3C+H2SO4

or HF

iso-butene iso-pentane

propene

2,2,3,3-tetramethylpentane

2,3,3-trimethylpentane

In a normal spark-ignition engine, the air-fuel mixture is heated

due to being compressed and is then triggered to burn

(relatively) slowly by the spark plug and ignition system. If it is

heated and/or compressed too much, then it will explode when

triggered (detonate), or even self-ignite before the ignition

system sparks. This causes much higher pressures than engine

components are designed for and can cause a "knocking" or

"pinging" sound. Knocking can cause major engine damage if

severe.

Pre-ignition and knocking

Octane number (Octane rating)Octane number (Octane rating)  

Measure of the ignition quality of gas (gasoline or petrol).

Higher this number, the less susceptible is the gas to 'knocking'

(explosion caused by its premature burning in the combustion

chamber) when burnt in a standard (spark-ignition internal

combustion) engine.

Octane number denotes the percentage (by volume) of iso-octane

(a type of octane) in a combustible mixture (containing iso-

octane and normal-heptane) whose 'anti-knocking' characteristics

match those of the gas being tested.

The octane rating of gasoline is measured in a test engine and is

defined by comparison with the mixture of 2,2,4-trimethylpentane

(iso-octane) and heptane that would have the same anti-knocking

capacity as the fuel under test: the percentage, by volume, of 2,2,4-

trimethylpentane in that mixture is the octane number of the

fuel.

For example, petrol with the same knocking characteristics as a

mixture of 90% iso-octane and 10% heptane would have an

octane rating of 90.

Isooctane (upper) has an octane rating of 100

whereas n-heptane has an octane rating of 0.

In the older vehicles, high octane numbers were achieved by

adding lead tetraethyl [(Et)4Pb] to the gas (the 'leaded gas'), a

pollutant that contributes to lead poisoning (see Lead). In the

newer vehicles, the same result is achieved by the engine design

that increases turbulence in the combustion chamber, and/or by

adding aromatic hydrocarbons (such as xylenes) and oxygenates

(oxygen-containing compounds such as alcohols) to the gas (the

'unleaded gas').

. Branched-chain paraffinic hydrocarbons have high octane

number than straight-chain paraffinic hydrocarbons. The

straight-chain paraffins are converted to their branched-chain

paraffins to increase the octane number (isomerization process).

. Aromatic and alkyl aryl hydrocarbons have very high octane

number, addition of aromatic compounds (toluene, xylene, etc.)

to gasoline to raise its octane rating is limited by environmental

regulations –health effects due to high toxicity.

. Olefinic hydrocarbons have high octane number

. Sulfur compounds decrease the octane number.

Compound Structure Octane No.

n-heptane zero

3-methylhexane 52

3-ethylpentane 65

1-methylcyclohexane 74.8

2-methyl-1-hexene 90.4

2,3-dimethylpentane 91.1

2,4-dimethyl-1-pentene 99.2

2,2,3-trimethylbutane 100

toluene 100

يزداد*- األوكتان رقمالتفرعات بزيادة

يزداد*- األوكتان رقمالمجموعات بزيادة

األوليفينية

Arrange the following hydrocarbon according to increasing

in their octane number 1-) 2,2,3-trimethylbutane , 2-methyl-1-hexene , n-heptane , 3-ethylpentane

2-) 1-methylcyclohexane , toluene , n-heptane , 2,4-dimethylpentane

Cetane number

Cetane number or CN is an indicator of the combustion speed

of diesel fuel. It is an inverse of the similar octane rating for

gasoline (petrol). The CN is an important factor in determining

the quality of diesel fuel. Cetane number is an inverse function of

a fuel's ignition delay, the time period between the start of

injection and the first identifiable pressure increase during

combustion of the fuel.

Cetane is a colorless, liquid hydrocarbon (C16H34) that ignites

easily under compression. For this reason, it was given a base

rating of 100.The cetane number of diesel fuel is measured in a test engine and is

defined by comparison with the mixture of cetane (C16H34) and

heptamethylnonane that would have the same anti-knocking capacity

as the fuel under test: the percentage, by volume, cetane in that

mixture is the cetane number or CN of the deisel fuel (normaly

40-55).

Diesel Index = (density X Aniline point 0F) / 150

ºF = 1.8 ºC + 32

Effect of sulfur compounds on petroleum productsA- In gasoline:

1- Sulfur compounds are generally of low octane ratings.

2- May tend to decrease the response of the fuel to (Et)4Pb.

3- In cracked products certain sulphur compounds act as catalysts

for polymerization and condensation reaction, thus acceleration

gum formation and adversely affecting the storage stability.

4- The presence of SO2 and SO3 in the exhaust gases contribute

to air pollution.

5- Plays a big role in corrosion problems (during-transportation

and storage).

B- In kerosene

The presences of sulfur compounds in illumination kerosene

contribute to smoky flames, besides air pollution problems.

For cooking purpose, the presence of sulfur compounds has

corrosion problems as well as air pollution.

C- In solar and diesel fuels

The same problems of corrosion and air pollution, besides the

storage stability problems, are encountered.

D- In fuel oils (mazout)

In boilers and furnaces:

1- S, V, and Na form the hard scales on the boiler tubes, specially in

the superheated section, which decrease the heat transfer

coefficient. Trials to remove this hard scale endanger the metal of

the tubes.

2- The dew point of the flue gases increase with increase of the SO2

and SO3 contents. Hence, in presence of high of SO2 and SO3

contents the flue gases should leave the chimney at relatively higher

temperatures.

Both these effects tend to lower the thermal efficiency of the boiler.

Sweetening operations

Hydrogen sulphide H2S and light mercaptoans are the main

contributes in this respect.Hydrogen sulphide could be easily lowered through an alkali wash.

2NaOH + H2S Na2S + 2 H2O

Mercaptans were dealt with in another way. They were

converted through oxidation into disulphides. Yet the sulphur

content remained the same.

Such operations have been called sulfur sweetening processes.

Oxidative Processes

Oxidative treatment processes are, in fact, processes that have

been developed to convert the objectionable-smelling

mercaptans to the less objectionable disulfide by oxidation:

SH O2 R4R + 2R S . S + 2 H2O

Mercaptan (thiol)

disulfide

However, disulfides tend to reduce the tetraethyllead

susceptibility of gasoline, and recent trends are toward processes

that are capable of completely removing the mercaptans.

a- Doctor sweetening process

Treatment of gasoline with alkaline sodium plumbite (doctor

solution) in the presence of a small amount of free sulfur. A

black precipitate of lead sulfide is formed, and the material,

which has improved odor, has been rendered sweet.

Na2PbO2 Pb(SR)2

Pb(SR)2 S PbS R2S2

2RSH + + 2NaOH

+ +

2NaOH + PbO Na2PbO2 + H2OSodium plumbite

Regeneration of Doctor’s solution:

PbS + O2 PbSO4

PbSO4 + 2NaOH PbO + Na2SO4 + H2O

PbO was isolated and then treated with NaOH solution to form sodium plumbite.

b- Hypochlorite Sweetening Process

The main reaction will be

RSH NaOCl RSSR NaCl+ + + H2O2

In this process the H2S or elemental sulphur should be present in

the feedstock, otherwise elemental sulphur will be produced.

Cracked products are not suitable feedstock for this process,

because of the powerful oxidizing effect in a considerable loss in

the yields as well as the decrease of the octane number of the

product.

c- Copper Sweetening Process:

RSH CuCl2 RSSR Cu2Cl22 + 2 + + 2HCl

H2S & elemental sulfur should be removed as well from the

feedstock for the process.

Regeneration could be represented as follows:

Cu2Cl2 CuCl2 H2O++ 2HCl + 1/2 O2 2

It should be mentioned that sweetening operations are applied only to gasoline.

Synthesis of Petroleum

1- Bergius Process

The Bergius process is a method of production of liquid

hydrocarbons for use as synthetic fuel by hydrogenation of

high-volatile bituminous coal at high temperature and

pressure.

Catalyst is typically added to the mixture. A number of

catalysts have been developed over the years, including

tungsten or molybdenum sulfides

The reaction occurs at between 400 to 500 °C and 20 to 70

MPa hydrogen pressure. The reaction produces heavy oils,

middle oils, gasoline, and gases. The overall reaction can be

summarized as follows:(

(where x = Degrees of Unsaturation)

2- Fischer-Tropsch Process

The Fischer–Tropsch process is a collection of chemical

reactions that converts a mixture of carbon monoxide and

hydrogen into liquid hydrocarbons.

The Fischer–Tropsch process involves a series of chemical

reactions that produce a variety of hydrocarbons, ideally having

the formula (CnH(2n+2)). The more useful reactions produce

alkanes as follows:(

(2n + 1) H2 + n CO → CnH(2n+2) + n H2O

Conversion – Alteration or Arrangement Processes

Process Name Action Method Purpose Feedstock(s) Product(s)

Catalytic reforming

Alteration/ dehydration

Catalytic Upgrade low-octane naphtha

Coker/hydro-cracker naphtha

High octane, Reformate/aromatic

Isomerization

Rearrange Catalytic Convert straight chain to branch

Butane, pentane, hexane

Isobutane/ pentane/ hexane

Hydrocracking Process

R-CH2-CH2-CH2-CH3 R-CH3 + [CH3-CH=CH2]

CH3-CH2-CH3

catalytic

cracking

hydrogenation

Branched – chain paraffins undergo demethanation:

CH3-CH2CH-CH2-CH3

CH3

CH3-CH2CH2-CH2-CH3 + CH4(1) catalytic cracking(2) hydrogenation

Naphthenes undergo ring scission followed by saturation of each end .

For example methyl-cyclopentane is converted to 2-methylpentane or 3-methylpentane or n-hexane

CH3

H2

CH3-CH2-CH2-CH-CH3

CH3

or

CH3-CH2-CH-CH2-CH3

CH3

or

CH3-CH2-CH2-CH2-CH2-CH3

Polynuclear hydrocarbons also undergo hydrocracking to finally produce paraffins (> C6)

1- Arrange the following compounds according to increasing of their octane number. a)- 2,2,3-trimethylbutane, 2-methyl-1-hexene, n-heptane, 3-ethylpentane. b)- 1-methylcyclohexane, toluene, n-heptane, 2,4-dimethylpentane.

2-Briefly, discuss the following. a- Effect of sulfur compounds on gasoline (petrol). b- Sweeting process. c- Carbide theory of the origin of petroleum. d- Organic theory of the origin of petroleum.3- Predict the thermal cracking products of n-pentane, n-hexane, and n-heptane.4- Predict the hydrocracking products of n-pentane, n-hexane, and n-heptane, methylcyclohexane.

األوكتان رقم حسب Kتصاعديا Kترتيبا التالية البترولية المنتجات رتب 2,2,3-trimethylbutane , 2-methyl-1-hexene , n-heptane , 3-ethylpentane

1-methylcyclohexane , toluene , n-heptane , 2,4-dimethylpentane

: ممايأتى كل ناقشi. الجازولين- فى البترول نواتج على الكبريتية المركبات تأثير

ii . التحلية- Sweetening processعملياتiii. البترول– نشأة أصل فى الكاربيد نظريةIV -البترول نشأة أصل فى العضويه النظريةV -البترول خام فى الكبريت نسبة زيادة عليها تترتب التى األثار

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