hydrocarbon processing manual

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UNION FENOSA gasSEGAS SERVICES

CHAPTER 1

INTRODUCTION TO ORGANIC CHEMISTRY

General Objectives

The student will be able to:1. define “Organic Chemistry” and list the elements commonly found in organic

compounds2. explain the reasons for the large number of organic compounds3. describe the methods of analyzing organic compounds to determine the elements present4. describe the types of bonds formed by carbon and draw structural formulas

5. define “saturated” and “unsaturated” and classify molecules as saturated or unsaturated6. define “functional group” and identify those commonly found in organic compounds7. describe the “intermolecular forces of attraction” that affect the physical properties of

organic compounds

1.1 Organic Chemistry

a) Definition

The terms “inorganic” and “organic” were originally based on the belief thatcompounds found in living organisms contained a vital “life force” and were called“organic”. All other compounds such as minerals and pure elements wereconsidered “inorganic”. Early in the nineteenth century urea was prepared from

ammonium cyanate which disproved the theory.

The modern definition of organic chemistry is “the study of carbon containing

compounds”. There are exceptions to this definition. Graphite, diamond, carbondioxide, sodium carbonate and other compounds do contain carbon but are notconsidered organic. They are derived from minerals and have typical properties of inorganic compounds. However, all compounds that are classified as organic docontain at least one carbon atom. Some examples are listed below:

Inorganic Compounds Organic Compounds

Sodium Chloride (NaCl) Methane (CH4)

Ammonia (NH3) Ethanol (C2H5OH)Sulphuric Acid (H2SO4) Acetic Acid (CH3CO2H)Silver Chloride (AgCl) Chlorobenzene (C6H5Cl)Potassium Phosphate (K 3PO4) Butyl Lithium (C4H9Li)Hydrogen Sulphide (H2S) Methyl Mercaptan (CH3SH)

b) Common Elements

The most common elements found in organic compounds are Carbon, Hydrogen,Oxygen, Nitrogen and Sulphur. Other elements include Phosphorus, halogens(Fluorine, Chlorine, Bromine, Iodine) and metals (Lithium, Magnesium, Lead,

Copper, etc.)

Phase 1SEGAS SERVICES Training Program HYDROCARBON PROCESSING FUNDAMENTALS of 95



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Exercise:

List five compounds that are inorganic and list five compounds that are organic. Find their molecular formulas to see if they contain carbon.

1.2 Number of Organic Compounds

There are over four million known organic compounds and millions more possiblecompounds that have not been made or identified. This can be explained by four factors.

a) Bonding of Carbon to Carbon

Carbon has the ability to form long chains of atoms bonded to each other. Some“polymers” (poly means many and mer means units) like polyethylene containchains over 100,000 carbons long.

Example: Pentadecane (C15H32) Structural Formula

C C C C C C C C C C C C C C C

H

H

H

H

H H

H

H

H H

H

H

H H

H H

H H

H H

H

H

H

HH

H H

H H

H

H

H

b) Bonding of Carbon to Other Elements

Carbon can bond to many other elements including halogens and metals. Eachcarbon can have up to four different elements attached to it.

Example: Bromochlorofluoromethanol (CHBrClFO)

C O

Br

Cl

F

H

c) Multiple Bonds

Carbon can form multiple bonds to itself and other atoms including Oxygen, Nitrogen and Sulphur:

Examples: Ethene (C2 H4) Ethyne (C2 H2)Propanone (C3 H6O)Common Names (Ethylene) (Acetylene) (Acetone)




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C C

H

H H

H

C CH HC

CC

O

HH

H

H

H

H

d) Isomers

The order that atoms are attached to each other (connectivity) and the orientation of the atoms in space determine the physical and chemical properties of the compound.

i) “Structural isomers” have the same molecular formula but differentconnectivity.

Example: Ethanol (C2 H6O) Dimethylether (C2 H6O)

C C

O H

H

H

H

H

H C O C

H

H

H

H

H

H

ii) “Stereoisomers” have the same molecular formula and connectivity but theatoms are orientated differently in space. (This only occurs in certainmolecules.)

Example: trans-2-butene (C4 H8) cis-2-butene (C4 H8)

C

C

C

C

H

H

H

HH

HH

H

C

C C

C

H

H

H

H H

H

H

H

1.3 Elemental Analysis of Organic Compounds

The exact composition of a compound can be determined by analyzing a sample in one

of two ways. The results will provide either an empirical formula or a molecular formula but will not provide the structural formula.

a) Elemental Analysis

Organic compounds can be oxidized using pure oxygen at high temperatures to formcarbon dioxide, water, nitrogen oxides and sulphur oxides. Using a very sensitiveinstrument, a known amount of compound is analyzed and the amount of each

product is measured. The results provide a percentage of carbon, hydrogen, nitrogenand sulphur. Oxygen is measured by pyrolysis in helium and conversion to carbondioxide. From the percentage by mass in the original sample an empirical formulacan be determined.




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Example: The compound C2H5 NOS would be analyzed to contain:

Carbon 26.359% Hydrogen 5.530% Nitrogen 15.370% Oxygen 17.555%Sulphur 35.186%

b) Mass Spectrometry

Organic compounds can be broken down into ions by bombarding them withelectrons under vacuum. The ions are then passed through a magnetic field thatseparates them by their mass to charge ratio. The instrument is so sensitive that themass of the ions can be measured to four decimal places. The largest ion will be the

molecule with one electron missing.The exact composition of this molecular ion can be calculated to determine thenumber of carbon, hydrogen, oxygen, nitrogen atoms present in the molecule. Thismethod can also be used to measure other elements including sulphur, phosphorus,halogens and metals. The results provide the actual molecular formula rather than

just an empirical formula.

Example: The compound C4H6 NO would produce a molecular ion at 84.0449. Other similar compounds are:

CN4O 84.0073 C2 N2O283.9960

C2H2 N3O 84.0198 C2H4 N484.0437C3O3 84.9847 C3H2 NO2 84.0085

1.4 Carbon Bonding

Carbon has an electronegativity of approximately 2.5 which is near the middle of thescale of electronegativities for the elements. As a result, the difference in

electronegativity between carbon and other atoms is less than 1.5 so when carbon bonds to itself or other atoms the bonds are “covalent” (sharing electrons) rather than“ionic” (transfer of electrons to form ions).

a) Number of Bonds to Carbon

Carbon has four “valence electrons” (electrons in the outermost energy level) that ituses to form four covalent bonds. Each covalent bond contains one shared pair of electrons and is represented by one line. The four valence electrons of carbon may

be found in single bonds or multiple bonds. There are four possible situations:

i) Carbon forms four single bonds to four different atoms by sharing one of itselectrons with each atom.




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Examples: Methane (CH4) Methanol (CH3OH)

C H

H

H

H

C O

H

H

H

H

2 electrons are shared

(1 from each atom)

ii) Carbon forms one double bond by sharing two of its electrons with one atom andtwo single bonds by sharing one of its electrons with each other atom.

Examples: Methanal (CH2O) Methanoic Acid (CH2O2)

Common Names (Formaldehyde) (Formic Acid)

C

O

H H

C

O

H O

H


(2 from each atom)

iii) Carbon forms one triple bond by sharing three of its electrons with one atom and

one single bond by sharing one of its electrons with another atom.

Examples: Ethyne (C2H2) Ethanenitrile (C2H3 N)Common Names (Acetylene) (Acetonitrile)

C CH H CN C

H

H

H6 electrons are shared

(3 from each atom)

iv) Carbon bonds to two different atoms by sharing two of its electrons with each of the other atoms. (These compounds are very unstable.)

Examples: Allene (C3H4) Methylisocyanate (C2H3 NO)


(2 from each atom)

C NO C

H

H

HC C

H

C

H

H

H




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b) Types of Bonds to Carbon

The first bond that carbon forms with another atom is called a sigma bond. It is avery strong bond that is hard to break. All single bonds are sigma bonds. When adouble or triple bond is formed weaker bonds called pi bonds are formed. A double

bond contains one sigma and one pi bond. A triple bond contains one sigma and two pi bonds. The types of bonds found in a compound accounts for its chemicalreactivity.

Example: A “double bond” between two carbon atoms.

C Cnucleus

weak pi bond

strong sigma bond

c) Structural Formulas of Organic Compounds

“Decane” has the molecular formula C10H22. There are actually 75 compounds thathave that same molecular formula. “Icosane” has the molecular formula C20H42.There are 366,319 structural isomers with that same molecular formula. Bychanging the connectivity (order that atoms are attached to each other) differentstructural isomers (also known as constitutional isomers) are produced. As a result,the large numbers of organic compounds that have the same molecular formulas

make it necessary to identify each isomer by drawing a unique structural formulaand assigning an appropriate name.To draw structural formulas for organic compounds follow these steps:

i) Draw a chain of carbon atoms with lines representing bonds between atoms.ii) Attach atoms that form more than one bond to the carbon chain.iii) Insert atoms that form more than one bond between carbon atoms in the

chain.iv) Attach atoms that only form one bond. (Halogens rarely bond to O, N, or S.)vi) If there are not enough atoms, make multiple bonds or rings.

Example: C2H5ClO

Step i) There is only one possible way of joining the 2 carbon atoms.

C C

Step ii) There is only one structure with the oxygen attached to a carbon.

C C

O

C C O C C

Oor or




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The oxygen can be attached at any position since the molecules are 3dimensional. Step iii) There is only one structure with the oxygen atom between the carbons.

C O C

Step iv) There are three possible structures that can be drawn.

C C

H

H

H

H

O

Cl

H

C C

H

H

Cl

O

H

H H

+ C O

H

H

H

C Cl

H

H

+

1-chloroethanol 2-chloroethanol chloromethoxymethane

If chlorine is attached to the same carbon as the oxygen it is a different isomer than if it is attached to the other carbon. (The position of chlorine on each carbondoes not matter.)

Step v) Molecular formula C2H4. Molecular formula C2H4O.

C C

H

H

H

H

C C

H

H

O

H

H + C C

H

O

HH

H

Exercise:

Draw structural formulas for organic compounds with the following molecular formulas.1. C5H12 (3) 2. C4H8 (5) 3. C3H6BrCl (5) 4. C3H9 N (4) 5. C3H6O (9)

1.5 Saturated and Unsaturated Compounds

Compounds that contain only single bonds between the atoms are called “saturated”while compounds that contain double or triple bonds are called “unsaturated”.These terms are used when describing petroleum constituents. Most compounds foundin oil and gas contain only hydrogen and carbon atoms bonded together with single

bonds. These are called “Saturated Hydrocarbons”. Some of the compounds containhydrogen and carbon with double or triple bonds between the carbons. These are called




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“Unsaturated Hydrocarbons”. The terms are based on the fact that hydrogen (H2) can be chemically reacted with the unsaturated compounds until they are saturated.

Example: Ethene (C2H4) reacts with Hydrogen (H2) to form Ethane (C2H6)

C C

H

H H

H

+ H2 C C

H

H

H

H

H

HUnsaturated Hydrocarbon Saturated Hydrocarbon

Exercise:

Identify each of the following compounds as “saturated” or “unsaturated”.

O C

C

H

H

H

H

C C

C

H

Cl

H

H

H

H

C

H

H

C C

C

H

HH

H

H

H

HN

H

H

C C CH

H

H

H

1.6 Functional Groups in Organic Compounds

A “functional group” is an atom or group of atoms in a molecule that determines the physical and chemical properties of the molecule. Molecules that contain only carbonand hydrogen and have only single bonds between the carbon atoms are not consideredto have any functional groups. These are the “alkanes” which make up the bulk of compounds found in gas and oil. The following table summarizes the most commonfunctional groups found in organic compounds.




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Functional

Group

Structure Description Example

Alkane

C C

Only carbon andhydrogen atoms.All atoms are joined

by only single bonds.

Ethane (Component in gas.)

C C

H

H

H

H

H

H

Alkene

C C

Only carbon andhydrogen atoms. At leasttwo carbon atoms are

joined by a double bond.

Ethene (Common Name:Ethylene)

C C

H

H H

H

Alkyne C C

Only carbon andhydrogen atoms. At leasttwo carbon atoms are

joined by a triple bond.

Ethyne (Common Name:Acetylene)

C CH H

AromaticC

C

C

C

C

C

Rings of carbon atomscontaining alternatingsingle and double bonds.

Benzene (Product of petroleumrefining)

C

C

C

C

C

C

H

H

H

H

H

H

Organohalide

C X

One or more halogens(Fluorine, Chlorine,Bromine or Iodine)attached to a carbon.

Dichloromethane (Solventmade from gas.)

CCl

H

H

Cl

Alcohol C O

H

An oxygen attached to a

carbon with a hydrogenattached to the oxygen.

Methanol (Common Name:

Methyl Alcohol) Solvent

CH

H

H

O

H

Ether C O C

An oxygen atomattached to two carbons.

Dimethyl ether.

C O C

H

H

H

H

H

H




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Functional

Group

Structure Description Example

Thiol

C S

H

An sulphur attached to acarbon with a hydrogenattached to the sulphur.

Methyl mercaptan (Compoundadded to gas to give it odor.)

CH

H

H

S

H

Sulfide

C S C

An sulphur atomattached to two carbons.

Dimethylsulphide.

C S C

H

H

H

H

H

H

Amine C N

H

H A nitrogen attached toone, two or three carbons

Methylamine

CH

H

H

N

H

H

Aldehyde

C O

HAn oxygen atom witha double bond to a carbonatom. At least one

hydrogen atom is also bonded to the carbon.

Methanal (Common name:Formaldehyde)

C O

H

H

Ketone C

O

C C

An oxygen atom witha double bond to a carbonatom. Two other carbonatoms are also bonded tothe carbon.

Propanone (Common name:Acetone)

C

O

C C

H

H

H H

H

H

CarboxylicAcid

C

O

O H

Two oxygen atoms

bonded to a carbon. Oneof the oxygen atoms by adouble bond and one by asingle bond. The oxygenwith a single bond is also

bonded to a hydrogenatom.

Methanoic acid (Common

name: Formic Acid)

C

O

O HH




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Ester C

O

O C

Two oxygen atoms

bonded to a carbon. Oneof the oxygen atoms by adouble bond and one by asingle bond. The oxygenwith a single bond is also

bonded to a carbon atom.

Methyl Methanoate (Common

name: Methyl Formate)

C

O

OH C H

H

H

Amide

C

O

N

One oxygen atom and onenitrogen atom bonded to acarbon. The oxygen atom

by a double bond and thenitrogen atom by a single

bond. The nitrogen is also

bonded to a hydrogen or carbon atoms.

Methanamide (Common name:Formamide)

C

O

N HH

H

Nitrile C N

One nitrogen atom bonded to a carbon atom by a triple bond.

Ethanenitrile (Common name:Acetonitrile)

C NCH

H

H

Example: Monoethanolamine (C2H7 NO) contains two functional groups.

C

H

H

NC

H

O

H

H

H

H

Alcohol Amine

Example: 4-aminobenzoic acid (C7H7 NO2) contains three functional groups.

Amine C

C

C

C

C

C

H H

HH

N

H

H

C

O

OH Carboxylic Acid

Aromatic




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Exercise:Identify the functional groups in each of the following molecules.

C

C

C

C

C

C

H H

OH

H C

O

O

CC

OH

H

H

H C

C

C

C

C

C

H

H H

HH

C

C C

O

HH

H

C

C

C

C

C

C

Cl

H Cl

HH

O C C

OH

O

H

H

C

C

C

C

C

C

H H

HH

OH N C C

OH

H

H

H

1.7 Forces Affecting Physical Properties of Organic Compounds

A “physical property” is any characteristic of a compound that can be measuredwithout a change in chemical composition. The most important physical properties of organic compounds related to the petroleum industry include: melting point, boiling

point, solubility, density and viscosity. These physical properties depend on theattractive forces between the molecules. The term “intermolecular force of attraction”means the attractive forces between molecules. The stronger the attractive forces

between molecules, the higher the melting point and the higher the boiling point.Solubility also depends on the strength of attractive forces between molecules. The term

“like dissolves like” refers to the fact that solute molecules with weak attractive forceswill dissolve in solvent molecules that also have weak attractive forces.

a) London Dispersion Forces

The weakest intermolecular force of attraction between organic molecules is called“London Dispersion Forces”. At any point in time the electrons are not locatedequally around the nucleus of atoms. As a result there is a “temporary dipole” or unequal balance between positive and negative around atoms. An example is theHelium atoms shown below.




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p+p+e-

e-

- +temporary dipole

p+p+e-

e-

- +temporary dipole

Attractive Force

b) Dipole-Dipole Attraction

A stronger intermolecular force of attraction between organic molecules is called“Dipole-Dipole Attraction”. In molecules containing polar covalent bonds (bonds

between atoms that have a difference in electronegativity of greater than 0.5) there isa “permanent dipole” or unequal balance between positive and negative around theatom. An example is the formaldehyde molecules shown below.

permanent dipole-+

C O

H

H

e-

e-

e-

e-

permanent dipole

Attractive Force

-+

C O

H

H

e-

e-

e-

e-

c) Hydrogen Bonding

The strongest intermolecular force of attraction between organic molecules is called“Hydrogen Bonding”. In organic molecules with a hydrogen atom bonded to an

oxygen or nitrogen there is a very strong “permanent dipole”. An example is thewater molecules shown below.

permanent dipole-+

permanent dipole

Attractive Force

-+

e-

e-

OH

He-

e-

e-

e-

OH

He-

e-




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Chapter Exercises:

1. Which of the following is not an organic compound ?a. C6H5Cl

b. C3H6O2

c. C20H42

d. FeCl3

e. BrCH2F

2. Which of the following is a factor in explaining the large number of organic compounds ?a. Carbon can only bond to metals.

b. Carbon can form multiple bonds to itself and other atoms.

c. Carbon can only form bond to four other carbon atoms.d. Only one compound can have the molecular formula C10H22.e. Organic compounds must not contain any carbon atoms.

3. What is the percentage of carbon by mass in the compound C10H20?a. 10.000 %

b. 14.383 %c. 33.333 %d. 50.000 %e. 85.617 %.

4. When a carbon atom is bonded to three other atoms which of the following is true?a. It forms four single bonds.

b. It forms three single bonds and one triple bond.c. It forms two single bonds and one double bond.d. It forms one single bond and one triple bond.e. It forms two double bonds and one single bond.

5. Compounds that have the same molecular formulas but different connectivity are knownas “structural isomers”.a. True

b. False

6. Draw four possible structural isomers for the compound C4H9Cl.

7. Which of the following compounds is “unsaturated”?

C

C

C

C

C

C

H

H

H

HH

H

H

HH

H H

H

C

S

C

H

H

HH

H

H

C O

Br

Cl

F

H

C

C

C

O

H

H

H

H

H

H




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8. What is the functional group that contains one oxygen atom attached to two carbons?a. Alcohol

b. Sulfidec. Ester d. Organohalidee. Ether

9. Circle and identify the three functional groups found in each of the following molecules:

C

O

N

C C

H

C C CCC

OH

H H

H

H

H

H

H

H

H

HH

C

O

C

CC

H

CCO CS

HHH

H

H

H

H

HH

H

H

O

10. What is the intermolecular force of attraction between the molecules of methanol shown below?

CH

H

H

O

H C H

H

H

O

H

11. Which of the following physical properties in not affected by the intermolecular forcesof attraction?

a. melting point b. boiling pointc. color d. solubilitye. viscosity

Chapter 2




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Structure, Nomenclature and Classification of Hydrocarbons

General Objectives

The student will be able to:1. define, write molecular formulas and describe the shapes of “alkanes” and

“cycloalkanes”2. draw expanded, condensed and bond line structural formulas of alkanes and

cycloalkanes3. name alkanes and cycloalkanes using the IUPAC system and common names4. define, write molecular formulas and describe the shapes of “alkenes” and

“cycloalkenes”5. define “stereoisomer” and “geometric isomer” and identify “cis” and “trans” isomers.6. draw and name alkenes and cycloalkenes including “cis/trans” and common names7. define, write molecular formulas and describe the geometry of “alkynes”8. draw and name alkyne compounds using the IUPAC system and common names9. define “aromatic”, describe the geometry and identify aromatic systems10. draw and name aromatics as well as substituted aromatics and heterocyclics

2.1 Alkanes and Cycloalkanes

a) Definition

The terms “alkane” and “paraffin” both refer to compounds which:i) contain only hydrogen and carbon atoms (hydrocarbon)ii) have only single bonds between carbon atoms (saturated)iii) have open chains of carbon atoms (not cyclic)

The alkanes may have a single continuous chain of carbon atoms (unbranched) or there may be side chains bonded to the main chain of carbons (branched).

The terms “cycloalkane”, “naphthene” and “cycloparaffin” all refer to compoundswhich:

i) contain only hydrogen and carbon atoms (hydrocarbon)ii) have only single bonds between carbon atoms (saturated)

iii) have one ring of carbon atoms (cyclic)The cycloalkanes may have a single ring of carbon atoms (unsubstituted) or theremay be side chains bonded to the main ring of carbons (substituted)

b) Molecular Fomulas

Regardless of the amount of branching all “alkanes” or “paraffins” have the generalmolecular formula CnH2n+2 where “n” is a whole number (1,2,3,…)

Example: C4H10 is the molecular formula for both butane and isobutane




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C C

C

H

HH

H

H

H

HC

H

HH

C C

H

H

H

H

C

H

H

C

H H

H

H

butane (unbranched) isobutane (branched)

Regardless of the amount of branching all “cycloalkanes” or “naphthenes” have thegeneral molecular formula CnH2n where “n” is a whole number (1,2,3,…)

Example: C6H12 is the molecular formula for cyclohexane and methylcyclopentane

C

C

C

C

C

C

H

H

H

H

HHH

H

H

HHH

C

C

C

C

C

C

H

H

H

H

HH

H

H

H

H H

H

cyclohexane (unsubstituted) methylcyclopentane (substituted)

c) Geometry of Alkanes and Cycloalkanes

The three dimensional structure of organic compounds is related to the number of other atoms that are bonded to them. The “Valence-Shell Electron-Pair Repulsion”theory (VSEPR) can be used to determine the geometry of each atom. The theory is

based on the pairs of electrons (each bond is a pair of negative electrons) repellingeach other. All alkane carbons have four other atoms (carbon or hydrogen) attachedto them. The furthest apart that four pairs of electrons can get from each other is

109.5o

. The result is a tetrahedron (a pyramid with 3 sides and a base that match).

Example: Methane (CH4) has 4 hydrogen atoms attached to the carbon.




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In the “expanded” format all atoms and all bonds are shown with minimal attention paid to bond angles and bond lengths. Often the unshared pairs of electrons onoxygen, nitrogen, sulphur and halogens are also shown. This format is used to makesure that each atom has the correct number of electrons.

Examples: Pentane (C5H12) Monoethanolamine (C2H7 NO)

C

H

H

NC

H

O

H

H

H

H

: :

:C C C C C

H

H

H

H

H H

H

H

H H

H

H

b) Condensed Structural Formulas

In the “condensed” format the hydrogen atoms are written next to the carbon,nitrogen, oxygen or sulphur atom without showing the bonds to them (The actual

position of the hydrogen atoms may be before or after the atom that they are bondedto.) The unshared pairs of electrons on oxygen, nitrogen, sulphur and halogens may

be shown. This format is faster to use while still showing all of the atoms in themolecule. The bond angles and lengths are more accurate in representing the threedimensional structure.

Examples: heptanol (C7H16O) cyclohexene (C6H10)

CH3

CH2

CH2

CH2

CH2

CH2

CH2

OH CH

CH

CH2

CH2

CH2

CH2

c) Bond Line Formulas

In the “bond line” format carbon atoms (and the hydrogen atoms attached to them)are not shown. Only the bonds between the carbon atoms are shown as lines. Theunshared pairs of electrons on oxygen, nitrogen, sulphur and halogens are not

shown. This format is much faster to use but requires practice to keep track of theatoms. The bond angles and lengths are more accurate in representing the threedimensional structure of the carbons in the molecule.

Examples: Butane(C4H10) Propanone(C3H6O) Monoethanolamine(C2H7 NO)

OOH

NH2

At the end of each line there is a carbon with the correct number of hydrogen atoms.




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d) Combinations of Formats for Drawing Structural Formulas

Often the “bond line” format is used for cycloalkanes while carbon branches areshown using a condensed format. Sometimes this is also done for open chains.

Examples: Methylcyclopentane(C6 H12) 2,4-Dimethyloctane (C10 H22)

CH3

CH3CH3

Another format used in “writing” condensed structures of alkanes is to combine a

number of similar groups and show them as a single unit (in brackets). Branchesmay also be shown as units (in brackets) following the carbon atom that is bonded tothem.

Examples: Hexane (C6H14) 2,3-Dimethylbutane (C6 H14)

CH3(CH2)4CH3 CH3CH(CH3)CH(CH3)CH3

CH3

CH2

CH2

CH2

CH2

CH3 CH3

CH

CH

CH3

CH3

CH3

2.3 Nomenclature of Alkanes and Cycloalkanes

Just like the different ways of drawing structures of organic compounds, there are avariety of ways to name organic compounds. The most widely used system of nomenclature was developed by the International Union of Pure and Applied Chemistry(IUPAC). Another common system is derived from the primary functional group in themolecule. Other systems are derived from a unique structure, a particular use or aspecial property.

Example: One of the isomers of C3H6O has three different names: “Propanone”(IUPAC), “Dimethylketone” (Functional Group) and “Acetone” (Common)

CH3

CCH3

O

"Prop" (3 carbons)

"one" or ketone

Methyl (1 carbon

attached to a

chain or group)

"an" (single

bonds between

carbons)

a) International Union of Pure and Applied Chemistry (IUPAC) System




CONSORTIUM


The IUPAC system has three parts to each name. The “parent” or “root” of the namedescribes the number of carbon atoms in the main or “parent” chain. The “suffix” or ending describes the types or bonds between carbon atoms in the chain as well as themost important functional group attached to the main carbon chain. The “prefix” or

beginning describes any atoms or groups of atoms that have substituted for hydrogenatoms on the main chain.

Example: 4-chlorobutanol can be divided into the three parts:

CH2

CH2

CH2

CH2ClOH

"butan" (4 carbons joined by single bonds)

"ol" (alcohol) is the most

important functional group

"4-chloro"(chlorine replaces

hydrogen on the

fourth carbon)

i) Parent CodesThe codes that represent the number of carbons in a chain are shown below:

Code

Number

of

Carbons

Code

Number

of

Carbons

Code

Number

of

Carbons

Code

Number

of

Carbons

meth 1 hex 6 undec 11 hexadec 16

eth 2 hept 7 dodec 12 heptadec 17

prop 3 oct 8 tridec 13 octadec 18 but 4 non 9 tetradec 14 nonadec 19

pent 5 dec 10 pentadec 15 icos 20

ii) SuffixThe codes that represent the most important functional group are shown below:

Code

Functional

Group Code

Functional

Group Code

Functional

Group

*ane alkane thiol thiol nitrile nitrile

*ene alkene ol alcohol amide amide*yne alkyne one ketone oate ester

amine amine al aldehyde oicacid

carboxylicacid

*these codes are always used either by themselves or with other codes whenthere is more than 1 functional group.

Examples: Propane Propene Propanol Propenol




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CH3

CH2CH3 CH2

CHCH3 CH3

CH2CH2

OHCH2

CHCH2

OH

ii) PrefixThe codes that represent the most important prefixes are shown below:

*Code Atom or Group Structure

cyclo “Parent” or “main” chain of carbonsis in a ring

CH2

CH2CH2

cyclopropane

methyl 1 carbon branch CH3

ethyl 2 carbon branch CH2 CH3

propyl 3 carbon branch (attached by an endcarbon)

CH2 CH2CH3

isopropy 3 carbon branch (attached by themiddle carbon) CH

CH3

CH3

butyl 4 carbon branch (attached by an endcarbon)

CH2

CH2

CH2

CH3

sec-butyl 4 carbon branch (attached by a carbonsecond from the end)

CH CH2

CH3

CH3

isobutyl 3 carbon branch with a 1 carbon branch attached to the second carbon (attached by an end carbon)

CH2 CH

CH3

CH3

t-butyl 3 carbon branch with a 1 carbon branch attached to the second carbon (attached by the central carbon) C

CH3

CH3

CH3

vinyl 2 carbon branch that has a double bond between the carbons CH CH

2

phenyl 6 carbon aromatic ring (attached byany of the carbon atoms)

CH CH

C CH

CH CH

fluoro a fluorine atom F

chloro a chlorine atom Cl

bromo a bromine atom Br

iodo an iodine atom I

methoxy 1 oxygen with 1 carbon (attached bythe oxygen) O CH3




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* The underlined letters are used in determining alphabetical order in a name.Except for the “cyclo” prefix, all atoms or groups of atoms must be preceded bythe number of the carbon atom that they are attached to in the parent chain. If there is more than one identical group, the terms “di”(2), “tri”(3), “tetra”(4) and“penta”(5) are used to indicate the number of identical groups. The prefixes(with their numbers) are listed in alphabetical order in front of the parent name.

Examples: 3-ethyl-4-isopropyloctane 2,2,3-trimethylbutane

CH3

C

CH

CH3

CH3CH3

CH3

1

2

3

4

butane

methyl

methylmethyl

1

2

3

4

5

6

7

8

ethyl

isopropyl

octane

CH3

CH2

CH

CH

CH2

CH2

CH2

CH3

CH2

CH3

CHCH3CH3

To name organic compounds using the IUPAC system the following steps should beused to develop a correct name:

i) Find the longest continuous chain of carbon atoms. (This is not necessarily astraight chain.) If there is more than one possibility, choose the one with themost branches (substituents).

ii) Write the parent name. If it is a cyclic put the prefix “cyclo” directly in front of the parent name.

iii) Number the carbon in the chain from the end closest to the first branch(substituent). If there is more than one branch, number the chain so that eachsubsequent branch has the lowest number.

iv) Write the names of the branches (substituents) in alphabetical order in front of the parent name. Be sure to include the number of the carbon atom that each

branch (substituent) is attached to as well as the proper term for more than oneidentical branch (substituent). Use commas to separate any numbers and dashesto separate any numbers from letters.

Example:

CH3

CH2

CH CH

CH2 CH

CH2

CH2 CH3

CH3 CH3

CH2

CH3

1

2

3 4

5 6

7 8

9

i) The longest continuous chain of carbon atoms is nine.




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CH3

CH2

CH

CH2

CH

CH3

CH CH3CH3CH3

CH

CH2

CH2

C

CH2

CH2

CHCH3

CH3CH3

CH3

CH3CH2

CH2CH2

CH

CH

CH3

CH2CH2

CH2CH3

CH3

CH3

CHCH

CH2

CH

CH2

CH

CH3

CH3

CH3CH3

CH3

b) Functional Group System

The Functional Group system has only two parts to each name. The “parent”describes the most important functional group in the compound. The “prefix” or

beginning describes the atoms or groups of atoms that are bonded to the parentfunctional group. This system is limited to simple compounds that do not havemany branches (substituents). It is not often used on hydrocarbons.

Example: Dimethylketone can be divided into the two parts:

CH3

CCH3

O"ketone" (functional group)

"Di"(2 units) "methyl"(1 carbon chains attached to the functional group)

Example: methyl-t-butylether (MTBE) has two branches attached to an oxygen:

CH3

O

C

CH3

CH3

CH3

"ether" (functional group)

"methyl"(1 carbon chain)

"t-butyl"(3 carbons attached by the

center carbon and a 1 carbon branch)

c) Common Names

Some organic compounds that have complex IUPAC names are often referred to bya more simple name. There is no real system involved in determining the names.Many of the compounds encountered in the oil and gas industry are referred to bytheir common names. One of the structural isomers of C8H18 that is used in rating




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gasolines is commonly referred to as “isooctane”. The IUPAC name is 2,2,4-trimethylpentane.The unbranched isomer of C16H34 (hexadecane) is called “cetane” which is used inrating diesel fuel.

CH3

CCH2

CHCH3

CH3

CH3

CH3

CH3(CH2)14CH3

“isooctane” “cetane”

2.4 Alkenes and Cycloalkenes

a) Definitions

The terms “alkene” and “olefin” both refer to compounds which:i) contain only hydrogen and carbon atoms (hydrocarbon)ii) have at least one double bond between two of the carbon atoms (unsaturated)iii) have open chains of carbon atoms (not cyclic)

The alkenes may have a single continuous chain of carbon atoms (unbranched) or there may be side chains bonded to the main chain of carbons (branched).

The terms “cycloalkene” and “cycloolefin” both refer to compounds which:i) contain only hydrogen and carbon (hydrocarbon)ii) have at least one double bond between two of the carbon atoms (unsaturated)iii) have one ring of carbon atoms (cyclic)

The cycloalkenes may have a single ring of carbon atoms (unsubstituted) or theremay be side chains bonded to the main ring of carbons (substituted)

b) Molecular Formulas

Regardless of the amount of branching all “alkenes” or “olefins” have the generalmolecular formula CnH2n where “n” is a whole number (1,2,3,…)

Example: C4H8 is the molecular formula for both butene and isobutene

C C

C

H

HH

H

H

CH

HH

C C

H

H

C

H

H

C

H H

H

H

butene (unbranched) isobutene (branched)




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Regardless of the amount of branching all “cycloalkenes” or “cycloolefins” have thegeneral molecular formula CnH2n-2 where “n” is a whole number (1,2,3,…)

Example: C6H10 is the molecular formula for cyclohexene and 1-methylcyclopentene

C

C

C

C

C

C

H

H

H

H

HH

H

H

HH

C

C

C

C

C

CH

H

HH

H

H

H

H H

H

cyclohexene (unsubstituted) 1-methylcyclopentene (substituted)

c) Geometry of Alkenes and Cycloalkenes

All alkene carbons have three other atoms (carbon or hydrogen) attached to them.The double bond electrons act similar to a single bond. The furthest apart that thedouble and single bonds can get from each other is 120o. The resulting geometry iscalled trigonal planar. (a planar or flat triangle).

Example: Ethene (C2H4) has a double bond between the carbon atoms.

120o 120o

120o

120o 120o

120o

H

H

C C

H

H

When carbon chains are drawn the atoms are placed to indicate the bond angles thatmore closely match the 120o.

Example: Propene (C3H6) has a double bond between the first two carbons.

(Lines show bonds in the plane, wedges show bonds coming out of the plane and dashes show bonds going behind the plane.)

C CC

H

H

H

HH

H C CC

H

H H

HH

H

In cycloalkenes the bond angles are affected by the number of carbon atoms in thering and are not exactly 120o. The smaller the ring, the further from 120o which

makes the compounds less stable. Cyclopropene is very unstable.




CONSORTIUM


Example: Cyclohexene (C6H10) has 6 carbons that form a “twisted chair” shape.

H

H

H

H

H

H

H

H

HH

C

C

C

C

CC

CH2

CH

CH2

CH

CH2

CH2

2.5 Stereoisomers in Alkenes, Cycloalkenes and Cycloalkanes

When comparing the structure of organic compounds it is sometimes necessary toconsider the three dimensional structures. Compounds that seem to be the same in twodimensions may actually be different. These differences can affect the chemical and

physical properties of the molecules. The existence of stereoisomers can bedemonstrated using a person’s hands. Both hands have four fingers and a thumbconnected to them but there is a difference between a “right hand” and a “left hand”.The orientation of the fingers, thumb, wrist and palm are actually mirror images of eachother. Some but not all molecules may have mirror image isomers (called“enantiomers”).

a) Definitions

Stereoisomers are compounds which have the same molecular formula and the same“connectivity” but the “orientation of atoms in space” are not the same. There areseveral types of stereoisomers but only one type is relevant to the hydrocarbonindustry. This type of isomer is referred to as a “geometric isomer”.“Geometric isomers” are compounds with the same molecular formula and sameconnectivity but the orientation or the atoms in space are different because of restricted rotation of the bonds in the molecules. In an open chain alkane there isfree rotation of all the bonds in the molecule. (Even at room temperature the atomsare moving all the time and the shape of the molecule is changing.) Because thecarbon atoms form a ring in a cyclic alkane, they can no longer rotate 360o. In bothopen chain and cyclic alkenes the rotation is restricted by the ring and double bond.

Example: The single bond between the carbons in ethane has free rotation.

C C

H

H

H H

H

H




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c) Stereoisomers in Alkenes and Cycloalkenes

Since the carbon atoms of a double bond can not rotate freely, any atoms or branchesof atoms attached to the carbons of the double bond will also be restricted to oneside of the plane of the double bond. When atoms or branches of atoms are attachedto each carbon of the double bond they will either be on the same side “cis” or onopposite sides “trans”. (The double bonds in the ring of cycloalkenes with less thannine carbon atoms are always “cis” so they are not included in the names.)

Example: cis-2-butene vs trans-2-butene

CH3

C C

CH3

H H

CH3

C C

CH3H

H

Because all 4 carbons are in the plane, wedges and dashes are not used.

Exercise:

Identify each of the following isomers shown below as “cis” or “trans”.

CH3

CH2

C

C

CH3

H

H

C

CH2

CH2

CH2

C

CH3

CH3

HH

CH3

CH2

C C

CH2

CH3

H H

CH2

CH2

C

C

CH2

CH3

CH3

HH

2.6 Drawing and Naming Alkenes and Cycloalkenes


In the IUPAC system, any compound with a double bond in the parent chain has thesuffix code “ene”. To indicate where the double bond is in the chain, the number of the first carbon involved in the double bond is placed either directly in front of the

“ene” suffix code or directly in front of the parent code. If the double bond is between the first and second carbon it is not necessary to include the number “1” but




CONSORTIUM


Example: Vinyl chloride Polyvinyl chloride

CH2 CH

Cl

CH2 CH

Cl

100,000

Exercise:

Draw structural formulas for each of the following organic compounds.1. 4-methyl-2-pentene 2. 1-ethyl-3-isopropylcyclohexene

3. 5-t-butyl-1,3-decadiene 4. trans-4-nonene5. 2,5,5-trimethyl-2-heptene 6. cis-1-isobutyl –4-propylcyclohexane

2.7 Alkynes

a) Definitions

The terms “alkyne” and “acetylene” both refer to compounds which:i) contain only hydrogen and carbon atoms (hydrocarbon)ii) have at least one triple bond between two of the carbon atoms (unsaturated)iii) have open chains of carbon atoms

The alkynes may have a single continuous chain of carbon atoms (unbranched) or there may be side chains bonded to the main chain of carbons (branched).Cycloalkynes do not easily form in carbon chains less than eight carbons long andare very unstable.

b) Molecular Formulas

Regardless of the amount of branching all “alkynes” or “acetylenes” have thegeneral molecular formula CnH2n-2 where “n” is a whole number (1,2,3,…)

Example: C4H6 is the molecular formula for 1-butyne and 2-butyne

C CH C

H

H

C

H

H

H

C CC C

H

H

H

H

H H

1- butyne 2-butyne

c) Geometry of Alkynes and Cycloalkynes

All alkyne carbons have two other atoms (carbon or hydrogen) attached to them. Thetriple bond electrons act similar to a single bond. The furthest apart that the triple




CONSORTIUM


and single bonds can get from each other is 180o. The resulting geometry is calledlinear.

Example: Ethyne (C2H2) has a triple bond between the carbon atoms.

C CH

180o

180o

180o

180o

H

When carbon chains are drawn the atoms are drawn to indicate the bond angles thatmore closely match the 180o.

Example: 1-Octyne (C8H14) has a triple bond between the first two carbons.

CH2

CH2

CH2

CH2

CH2

C

CH

CH3

8. Drawing and Naming Alkynes


In the IUPAC system, any compound with a triple bond in the parent chain has thesuffix code “yne”. To indicate where the triple bond is in the chain, the number of the first carbon involved in the triple bond is placed either directly in front of the“yne” suffix code or directly in front of the parent code. If the triple bond is

between the first and second carbon it is not necessary to include the number “1” butit can be included. There are no stereoisomers involving the triple bond of alkynes.Examples: Pent-2-yne (2-Pentyne) Hexyne (1-Hexyne)

CH3 C C CH2

CH3 CH

C

CH2

CH2

CH2

CH3

The position of the triple bond is more important than the positions of any branchesor substituents. As a result, an open chain alkyne must be numbered from the endclosest to the triple bond. If the first carbon of the triple bond is the same number of carbons from either end of the open chain, then the chain is numbered like a

branched alkane so that the first branch is on the lowest number carbon. Even if there is a longer chain of carbon atoms without the double bond, the parent chain

must contain the triple bond.




CONSORTIUM


Examples: 4-methyl-2-pentyne 2-methyl-3-hexyne

CH3

C C CH

CH3

CH3

CH3

CH C C CH2

CH3CH3

If there are two triple bonds in the compound, then the suffix “adiyne” must be usedalong with the numbers for the first carbon of each double bond.

Example: 1,4-pentadiyne

CH

C

CH2

C

CH

If a compound contains a double and a triple bond the suffix used is “enyne”. Thenumber of the first carbon of the double and triple bond are usually placed in thesuffix to indicate the positions. If the number of carbons from the end of the chain tothe double and triple bonds are the same, then the chain is numbered from the end

closest to the double bond.

Examples: hex-4-en-1-yne hex-2-en-4-yne

CH3

CH

CH

C

C

CH3

CH3

CH CH

CH2 C CH

b) Common Names for Alkynes

The simplest alkyne has only two carbon atoms triple bonded to each other. Thiscompound (“ethyne” in the IUPAC system) is also known as “acetylene”. In thefunctional group system for common names, the two carbon atoms are treated as the

parent and named “acetylene”. Any carbon chains attached to the carbons arenamed as branches or substituents.

Examples: Acetylene Dimethylacetylene (2-butyne)

CH CH C CCH3 CH3




CONSORTIUM


Exercise:

Draw structural formulas for each of the following organic compounds.1. 4-ethyl-2-heptyne 2. 5-isopropyl-3-octyne3. 6-sec-butyl-4-decyne 4. 2,4-nonadiyne5. 2,6-dimethylhept-3-yne 6. ethylpropylacetylene

9. Aromatic Hydrocarbons

a) Definitions

The term “aromatic hydrocarbon” refers to compounds which:i) contain only hydrogen and carbon atoms (hydrocarbon)ii) have electrons evenly shared over all carbon atomsiii) have flat rings of carbon atoms

Although the original term “aromatic” was used to describe the pleasant smell of certain compounds, the term is currently used to describe unusually stable cycliccompounds. The simplest aromatic hydrocarbon that has been studied extensively is“benzene”. This compound has a ring of six carbon atoms. Each carbon atom hasone hydrogen atom and two other carbon atoms attached.

Chemists who first studied benzene suggested that there were three single and threedouble bonds alternating in the ring producing the structure 1,3,5-cyclohexatriene. Itwas later discovered that all of the bonds between carbon atoms in the ring wereidentical. This unusual characteristic is referred to as the delocalization of electronsand is responsible for the stability of the compound.

Examples: 1,3,5-cyclohexatriene benzene(theoretical structure) (actual structure)

C

C

C

C

C

C

H

H

H

H

H

H

C

C

C

C

C

C

H

H

H

H

H

H




CONSORTIUM


b) Geometry

Because all of the carbons are similar to those in alkenes, the benzene ring is a flat molecule with the hydrogen atoms and carbon atoms all in the same plane. This isquite different from cyclohexane that has a “chair” shape with all the carbon atomshaving only single bonds.

Example: Benzene ring tipped up at the back to show planar structure.

c) Identifying Aromatic Hydrocarbons

Most aromatic hydrocarbons contain one or more rings of six carbons. They may beshown with single and double bonds or with a single circle in the middle of theatoms. There are often branches attached to the rings in place of hydrogen atoms.

Examples: Benzene Naphthalene Biphenyl

CH

CH

CH

CH

CH

CH

CH

CH

CH

CH

C

CCH

CH

CH

CH

C

CH

CH

CH

CH

CH C

CH

CH

CH

CH

CH

2.10 Drawing and Naming Aromatic Compounds


The IUPAC system has accepted the names “benzene”, “naphthalene” (not to beconfused with “naphthenes” which is a general term for cycloalkanes), and“anthracene” for aromatic fused ring systems containing 1,2 and 3 rings. Thecarbons in the ring are named as the parent chain and any branches or substituentsattached are named the same way as branches on cycloalkanes. Since the rings areall planar, there are no stereoisomers involving the aromatic rings.




CONSORTIUM


C

CH

CH

CH

CH

CH SH C

CH

CH

CH

CH

C OHCH3

C

C

CH

CH

CH

CH

CH3

NO2

Exercise:

Draw structural formulas for each of the following organic compounds.1. 1,2,4-triethylbenzene 2. 4-isobutyltoluene3. p-dichlorobenzene 4. m-propylphenol5. 2-t-butylaniline 6.2,4,6-trinitrotoluene(TNT)

Chapter 2 Exercises:

1. Which of the following is the molecular formula for an “alkane” or “paraffin”?a. C6H6

b. C3H6

c. C10H22

d. C2H3Cle. C4H10O

2. Which of the following terms best describes the geometry of an “alkane” carbon ?a. tetrahedron

b. trigonal planar c. linear f. planar g. octahedron

3. What format used to draw structural formulas shows all atoms, all bonds and unsharedelectrons ?a. bond line

b. condensedc. expandedd. semicondensede. isotopic notation

4. Which of the following represents the compound with the molecular formula C4H10 ?

CH2

CH

CH2

CH3

CH3

CH

CH3

CH3

CH2

CH2

CH2

CH2

CH3

C

C

CH3

a. b. c. d.




CONSORTIUM


CH3CCH2 C

CH2C

CH3

CH3

CH3

a. 2,2-dimethyl-5-heptyne d. 6,6-dimethyl-2-heptene b. 5-t-butyl-2-pentyne e. t-butylmethylacetylenec. 6,6-dimethyl-2-heptyne

11. What is the IUPAC name for the following compound?

C

CH

CH

CH

C

CH

CH2

CH2

CH2

CH

CH3

CH3

CH3

a. o-dipropylbenzene d. m-isobutylpropylbenzene b. p-butylisopropylbenzene e. 1-isopropyl-3-isobutylbenzenec. 1-butyl-3-isobutylbenzene

Chapter 3




CONSORTIUM


Composition of Natural Gas and Oil

3.1. Natural Gas – Well Head Gas

In the reservoir, crude oil almost always contains dissolved methane and other lighthydrocarbons that are released when the pressure on the oil is reduced (i.e. bringing the oil fromthe high pressure reservoir to the surface separator). As the gas evolves, the remaining crude oilliquid volume decreases; this is known as shrinkage. The gas produced is called associated

gas, separator gas or solution gas, etc.

Natural gas produced from a gas reservoir may contain small amounts of heavier hydrocarbons

that are separated as a liquid called condensate. Natural gas containing condensate is said to bewet gas. Conversely, if no condensate forms when the gas is produced to surface, the gas iscalled dry gas.

The main constituent of natural gas is methane, which is used as fuel for residential andindustrial applications (furnaces, heaters, steam generation, etc.). When natural gas comes fromthe reservoir, it may have any of the following constituents:

Class Component Formula Shorthand

Hydrocarbons Methane CH4 C1

Ethane C2H6 C2Propane C3H8 C3i-Butane iC4H10 iC4n-Butane nC4H10 nC4i-Pentane iC5H12 iC5n-Pentane nC5H12 nC5

Cyclopentane C5H10

Hexanes andheavier

C6+

Inert Gases Nitrogen N2 N2Helium HeArgon A

Hydrogen H2 H2Oxygen O2 O2

Acid Gases HydrogenSulfide

H2S H2S

CarbonDioxide

CO2 CO2

Sulphur compounds

Mercaptans R-SH

Sulfides R-S-R’

Disulfides R-S-S-R’Water Vapor H2O




CONSORTIUM


Liquid Slugs Free water or brine

CorrosioninhibitorsMethonal CH3OH

Solids Millscale andrust

Iron sulfide FeSReservoir fines

(sand)

Remember that it is the methane (and ethane) that are desirable as heating fuel or commercial

“natural gas”. The heavier components have an undesirable effect of raising its hydrocarbondew point to an unacceptable temperature.

Conversely, natural gas usually has some nitrogen included, which has no heating value. Theheavier ends may be required to compensate for the diminished heat value of the gas. When thenitrogen content is too high, cryogenic processing (extreme cold) may be required to remove it.This is very expensive and could render a gas field uneconomic to produce.

Depending on the composition of the gas, a gas plant may be built in the field to remove theheavier ends. If enough producers are leaving small quantities of propane and butane etc. in the

pipeline gas, a “straddle plant” may be built downstream to remove these components. Straddle

plants must process huge volumes of gas to recover enough heavy ends to make themeconomical. LNG plants are a type of “straddle plant” designed to take preprocessed gas

in a pipeline and liquefy it for transportation or petrochemical feedstock.

Acid gases; Hydrogen sulfide (H2S) and carbon dioxide (CO2) must be removed to specifiedminimum levels before the gas is pipelined or fed into an LNG plant. This process is termedsweetening and there are various methods employed in gas plants to do this.

Produced gas is regarded as saturated with water even if no liquid water is produced. This water must be removed or “dehydrated ”. LNG plants have strict hydrocarbon, water, and CO2

specifications to prevent the formation of solids in the cryogenic (very cold) conditions of

an LNG plant.

3.2. Field Processing of Natural Gas

Field processing is the treatment of gas soon after it has reached the surface and left the wellhead. It generally consists of two distinct categories of operations:

1. Separation of the gas/liquid/water well effluent into its individual phases.




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2. Removal of impurities from the separated phases to meet sales /transportation/reinjection specifications and/or environmental regulations.

The individual unit operations that may be required include:

• Basic field-processing

• Prevention of hydrate formation

• Separation of free liquids and solids from the gas

• Sweetening (removing H2S, CO2)

• Dehydration using TEG, solid desiccants, LTX and CaCl2

• Condensate recovery and HC dew-point control

• Compression

• Flow measurement

• Pipeline transport of natural gas

3.3. Natural Gas Specifications

3.3.1. Product Specifications – Gas Feedstock to an LNG Plant

As a producer, the gas from the reservoir must be processed in the field to meet specificationsset out by the pipeline or LNG plant. These specifications ensure that the gas sold to market has

predictable qualities such as heating value, corrosion tendency and water dew point. Thesespecifications are usually the feedstock to the LNG plant.

There are many types of gas plants producing a variety of products and to differentspecifications Three types of plants are:

Liquefied Natural Gas (LNG) Plants typically liquefy the C1 and C2 components of natural gas.

Liquefied Petroleum Gases (LPG’s) are the C3 and C4 components.

Natural Gas Liquids (NGL’s) are the C3, C4, and C5+ components.

Natural gas has to be highly process before it enters an LNG plant – the impurities of CO2, H2Sand water must be removed almost completely before liquefaction takes place because thesecomponents are solids at the temperatures and pressures found in an LNG plant. Similarly the

NGL fractions of Natural Gas should also be removed before the C1 and C2 components areliquefied.




CONSORTIUM


3.3.2. Quality requirements for gas received by gas plants are as follows:

1. Free of sand, dust, gums, crude oil, contaminants, impurities and other objectionablesubstances;

2. Hydrocarbon dew point less than minus ten (-10) degrees Celcius at operating pressures;

3. Not more than twenty three (23) milligrams of Hydrogen Sulphide per one (1) cubic metre;

4. Not more than one hundred fifteen (115) milligrams of total sulphur per one (1) cubic metre;

5. Not more than two (2) percent by volume of carbon dioxide;

6. Not more than sixty five (65) milligrams of water vapour per one (1) cubic metre;7. Water dew point less than minus ten (-10) degrees Celcius at operating pressures greater

than 8275 kPa;

8. Not to exceed forty nine (49) degrees Celsius in temperature;

9. As free of oxygen as possible (in no cases to exceed 0.4% by volume);

10. Minimum Gross Heating Value of thirty six (36) megajoules per cubic metre.

Summary:

Component Specification

HC dew point < -10oC @ operating pressureWater dew point < -10oC @ pressure exceeding 8275

kPa

H2S 23 mg/m3 (max)

Total Sulphur 115 mg/m3 (max)

CO2 2% vol (max)

Water vapour 65 mg/m3 (max)

O2 0.4% vol (max)

Temp 49oC (max)

Gross Heating

Value

36 MJ/m3

Notes:

Water content:

Water vapour must be removed in a dehydration process. The most typical is glycoldehydration, but many plants use a dry desiccant technology such as mole sieves to removewater. If free water forms, it may form hydrates and is also very corrosive in the presence of carbon dioxide.




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Calculate:

Component Mol % Fraction of a

m3

Gross Heat

Value kJ/m3

Total Gross

Heating value

(kJ/m3)

C1 85 37,708

C2 4 66,065

C3 1 93,936

n-C4 1 121,794

N2 5 0

CO2 4 0

Total 100 1.00

Is this gas suitable for pipeline?

Depending on the pressure, temperature and composition of the gas, surface facilities aredesigned to process the specific gas from the field. Rarely are any two fields processed exactlythe same.

Within each process (separation, dehydration, etc.) there are many variables and many options

on the technology and hardware that can be used.

3.4. Sampling and Analysis

Gas is often sampled at various locations in the process. Initially, the most important sample provided is the wellhead or “raw gas” sample. This will provide the necessary information for the entire design of the gas processing facilities.

Since almost all natural gas is considered to be water saturated in the reservoir, dehydration isessential. If gas is not dehydrated, liquid water will drop out as soon as the gas is cooled.

Compression is also normally required to get the gas from the field to the plant or to get the gasfrom the plant into the pipeline.

Other facilities such as methanol injection, sweetening, and refrigeration will depend on thecomposition of the gas.

• The probability of hydrate formation depends on H2S levels, C2+ content, pressure and

temperature.

• The hydrocarbon dew point temperature depends on the composition of the gas. If too

many C3+ fractions are present in the gas, they will liquefy at an undesirable

temperature.




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• If H2S is present in a level above 16ppm, it must be removed. CO2 must also be removedif it is above 2%.

• High levels of inerts such as helium (rare) or nitrogen (common) will lower the heating

value of the gas. Nitrogen may have to be removed through cryogenics if the economics

are profitable.

Samples are taken from the process in many locations to determine the efficiency of the process

or to troubleshoot a piece of hardware.

3.5. DISCUSSION

1. What processes will be required to prepare a gas for pipeline if the composition is 98%

methane, 1% ethane and 1% Hydrogen Sulphide?

2. What processes will be required to prepare a gas for pipeline if the composition is 80%methane, 5% ethane, 5% propane, 3% isobutane, 3% n-butane and 4% C5

+?

3. What processes will be required to prepare a gas for pipeline if the composition is 65%

methane, 8% ethane, 15% condensate liquids, 5% Hydrogen Sulphide, and 7% Carbon

Dioxide. Free water is produced in some of the wells.




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Chapter4

Plant Processing of Natural Gas

The raw product often referred to as Natural Gas comes from two main sources – gas fields wherethe hydrocarbon leaving the well head is predominantly gas with some associated liquids or from oilfield where the gas (often called solution gas) escapes from the crude oil when the pressure isreduced.

Natural gas must be preconditioned very close to the wellhead before it can be taken to a gas plantfor further processing. The gas product from a standard gas plant is the feedstock to an LNG plant.

4.1 Field Processing of Natural Gas

Two essential processes occur very quickly after the gas, gas/oil mixture reach the surface from thereservoir – gas liquid separation and dehydration.

4.1.1. Gas-Liquid Separation

Separation of liquids. This is usually carried out in horizontal or vertical separators that oftencontain baffles to promote the coalescence of the liquid droplets that are carried in the gas

stream. These liquids are referred to as condensate and are usually stored at the well site for

later removal by truck.

4.1.2. Separation Principles

• Separation of well stream liquids is by far the most common of all field processing operations

and at the same time, one of the most critical.

• Well effluent is a complex mixture of liquid and gaseous hydrocarbons, with water and other

impurities often present.




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• It is necessary to separate hydrocarbon liquids and water from the hydrocarbon gas.

• The separation of natural gas, liquid hydrocarbons, and impurities is accomplished by various

field processing methods which include:i) gravityii) heatiii) mechanicaliv) electricalv) chemical

4.1.3. Separation Processes

A combination of these methods is used to separate hydrocarbon gas, liquid and water phases.

1) Gravity

- simplest and most common method in use today.- dependant upon the principle that the liquid components have a greater density than the gas

components.- water present is usually heavier than the hydrocarbon liquid and therefore settles due to

gravity.

2) Impingement

- relies upon the difference in momentum between a gas particle and a liquid droplet.- takes place when liquid-laden gas approaches an obstacle and liquid droplets impinge upon

the barrier and increase in size.- the effects of gravity become significant and the drop falls to the liquid section of the

vessel.

3) Centrifugal

- occurs when the stream to be separated rotates at high velocities inside a vessel.- centrifugal force moves the liquid to the wall of the vessel where it coalesces and drains to

the liquid section by gravity.- Allows a smaller vessel to be used than other types.

There are two main classes of separation: Two Phase and Three Phase

Two Phase Separation

- one combined raw product separated into two distinct products; hydrocarbon gas andhydrocarbon liquids.

- has an application mainly in fields with little or no produced water.

Three Phase Separation

- Splits the raw well effluent into three distinct phases or products; hydrocarbon gas,hydrocarbon liquid and water

- Used where free water is produced with the oil or gas stream.




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- used when there is either a very high GOR (scrubbers) or a very low GOR.- the inlet stream enters near the midpoint of the vessel.- can provide either two phase separation or three phase separation.




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4.2.3. Horizontal Separators

- most common application is in streams with relatively high gas/oil ratios.- gas/liquid interface area is large which results in a quicker gas breakout- the double barrel type consists of an upper separation section and a lower liquid

retention and level control chamber.- Tend to require a large “footprint” so space can be a limitation (offshore for example.)




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6) Presence of H2S or CO2 is conducive to hydrate formation since these acid gases are moresoluble in water than hydrocarbons.

Now, if you consider the first 2 points and the second 6, some of the techniques which could beused to inhibit the formation of hydrates are:

• Raise the temperature so it doesn’t hit its hydrate formation temperature

• Lower the pressure so it doesn’t hit its hydrate formation temperature.

• Remove the water so it doesn’t hit its water dew point conditions.

These techniques are all used to some degree. Line heaters are used to keep the gas temperaturehigh. Keeping the pressure low is often not an option but restrictions which cause a sudden pressuredrop and subsequent drop in temperature are avoided. Dehydration units are used at the wellsite andat plants to remove the water. Another technique used to lower the hydrate formation temperatureis:

• Chemical injection to depress hydrate formation temperature.

Many chemicals depress the temperature at which hydrates and/or ice form. Ammonia and brinewere used in the past, but the current choice is either a glycol or methanol. Methanol is the commonfield choice for our situations and glycol would tend to be used in a plant refrigeration system.

4.4. Dehydration - Overview

removal of water associated with the production of natural gas.

prevents hydrates and reduces corrosion.

Prepares gas for further processing (e.g. cryogenic)

Removal of free water to prevent accumulations and promote single-phase pipeline flow.

• Three major methods of gas dehydration are commonly used:

a) Absorption (wet)

i) triethylene glycol (TEG)∗

ii) diethylene glycol (DEG)

b) Adsorption (dry)

TEG is by far the most common glycol used in dehy’s (probably 90 to 95%). DEG may be used in fields where

minimal gas is available for heating the glycol; DEG does not have to be heated to as high a temperature torelease the water.




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4.4.2. Process Description

Gas Stream:

a. Gas enters inlet separator and liquids are removed.

b. Gas enters contacting tower and starts upward through a chimney tray.

c. The gas passes through the trays or packing, contacting glycol as it travels. The water inthe gas has an affinity for the glycol and attaches to it.

d. The gas exits the tower through a mist eliminator to the next process or to the flowline.

Glycol Stream:

a. Lean glycol in the accumulator is pumped to the top of the contactor tower.

b. The glycol picks up water from the gas as it travels down from tray to tray (or through the packing).

c. The glycol exits as rich glycol, is warmed through the accumulator and is dumped into thestripping column of the reboiler.

d. The rich glycol is heated in the reboiler by a natural gas flame in a burner tube. Thetemperature causes the water to vaporize and exit the stripping tower (where it contactsmore incoming rich glycol).

e. The lean glycol spills over into the accumulator ready for its next pass through thecontacting tower.




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4.4.3. Dehydrator Components

Inlet Scrubber

- simple two phase separator used to remove water and liquid hydrocarbons from the wet gasstream.

Glycol - Gas Contactor

- vessel in which wet gas is contacted with lean glycol.

- utilizes counter-current flow: gas upward and lean glycol downward.

- trays exist in the contactor (valve or bubble cap) to increase the contact time between the wet

gas and lean glycol.

- mist extractor is located at the top of the vessel to remove any glycol entrained in the gas.

- lean glycol is pre-cooled by a double pipe heat exchanger prior to entering the vessel (glycol canabsorb more water at cooler temps).

- Glycol should enter the dehy at about 10o hotter than the gas temperature. If it is too hot, it canlead to foaming and inefficient dehydration, and if it is too cold, hydrocarbons can condense inthe glycol.

Filter and Pump

- rich glycol exits the bottom of the contactor and is filtered prior to entering a pump.

- filter removes solid components from glycol in order to protect the pump and decreaseoperational problems with fouling of the dehy. unit.

- the hydraulic pump utilizes rich glycol from the contactor as the power fluid to pump leanglycol from the surge tank to the contactor.

Stripping Still

- the warm rich glycol enters the stripping still after being preheated in a heating coil (tubeside) in the surge tank.

- The stripping still is usually filled with ceramic packing or structured packing to improvethe surface area contact of the water vapour with the rich glycol.

- allows any glycol vapors to be condensed to eliminate losses.

- water vapor exits the top of the stripping still.

- Fins on the stripping still condenser section cool the vapor to help drop out any glycol whichmay be entrained or vaporized in the water vapor. A temperature just above the boiling point of water is optimal for the condensing section.

Reboiler

- vessel in which rich glycol is heated to 175 – 200o

C to vaporize water.




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- Dry stripping gas (usually fuel gas) is injected into a column between the reboiler andaccumulator

- The dry gas mixes with the lean glycol (99%) and strips out more water. Glycol concentrationsof 99.9% can be achieved.

- The gas enters the reboiler and exits with the water vapour.

- The cost to operate a Stahl column must be weighed against the benefits. The costs are fuel gas(and hydrocarbon to the environment).

Heat Exchange/Surge Tank

- regenerated glycol leaves the reboiler through an overflow pipe and enters the shell side of the Surge Tank.

- the lean glycol is cooled by the rich glycol on the tube side of the exchanger.

- the surge tank is a liquid accumulator for the glycol pump to ensure the pump receives auninterrupted supply of glycol.

- A sweet gas blanket is often maintained in the vapour space above the glycol in theaccumulator. A slight pressure is held which prevents oxygen from the atmosphere and water vapour from the reboiler from entering.




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v) Most expensive option for dehydration

4.5.2. Desiccant Cycle

As the wet gas passes the desiccant, the water is picked up in the pore spaces of the solid.During the adsorption cycle, the bed is operating in three zones:

The Saturation or Equilibrium Zone:

- the upper portion of the bed is saturated and in equilibrium with the wet gas. It is no longer active.

The Middle or Mass Transfer Zone (MTZ)

- This portion of the bed is picking up water as the gas passes by.

- If the bed is operated too long, the MTZ moves to the bottom of the vessel and“breakthrough” occurs.

The Bottom or Active Zone:

- This is the portion of the bed which is waiting to be used.

- The gas which is passing by this portion of the bed has already been dried in the upper

portion.

• regeneration will start just before the water content of the the outlet gas from a tower on

adsorption reaches an unacceptable level.

• under operating conditions the gas velocity through the adsorbing tower should be 0.1 - 0.25

m/s.

• in order to maximise the adsorbing ability of the desiccant, the gas temperature should be

kept within the 25oC - 40oC range.

4.5.3. Desiccant Bed Life

• Desiccant is expected to last 3-5 years, depending on the conditions of operation.

• New desiccant is more efficient at accepting water than older desiccant.

• This means it picks up more water and the reaction is faster with new desiccant.

• When designing systems, desiccant capacity should be calculated using 3-5 year old

product.

• For example, new mole sieve could accept 20 kg of water for every 100 kg of desiccant.

Design estimates should use a lower figure of 13 kg of water for every 100 kg of desiccant.




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• Separator should be sized to handle surge capacity. Poor separator design can cause

problems in the treating facilities.Contactor

• Sour gas enters the bottom of the tower and moves upward through the trays

• H2S and CO2 in the gas react with the liquid amine solution and are removed from the gas

stream.

• The reaction is often assisted by placing fresh lean amine on various trays down the tower.

This ensures that the gas will contact lean amine a few times as it moves up the tower.(Thisis not shown on the diagram).

• As the sweet gas leaves the tower, it is often contacted with water to remove any amine that

has vapourized and is travelling with the gas. The top 2 or 3 trays may be used for thisfunction. This is considered a “water wash” section of the tower.

• The water wash is often used if the contactor temperature is especially high or if MEA is

used as the amine.

Outlet Separator

• The sweetened gas is passed through a separator to remove any amine solution (or liquid

water) that may be travelling with the gas flow

• The gas is now saturated with water and must proceed through dehydration facilities to lower

the water dew point before sale.

Rich Amine

The amine picks up H2S and CO2 in the contactor tower.

Flash Drum

• From the contactor, the amine may enter a flash drum to allow any hydrocarbon an

opportunity to leave the amine solution.

Heat Exchanger (HTEX)

• The rich amine passes through a heat exchanger where it picks up heat from the hotter lean

amine on its way to the contactor.

• Since this service is clean, plate and frame exchangers can be used, but often a more

common shell and tube exchanger is put in service.

Stripper

• The rich amine enters the stripper, where hot acid gas and steam heat the rich amine,

removing the H2S and CO2 that is bound into the product.

Reboiler

• The amine at the bottom of the stripper tower is heated to 105oC – 140oC (depending on the

type of amine being used).




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• This causes the acid gas/amine reaction to reverse and the acid gas vapourizes with steam

from the amine solution.• The acid gas/steam vapour re-enters the stripper and contacts new rich amine on its way out

the top. Amine carried with the acid gas/steam vapour tends to reunite with the rich liquidamine thereby removing it from the vapour flow.

Condenser

• After leaving the top of the stripper tower, the acid gas/steam vapour is cooled to remove

heat and condense out the water from the flow.

• The water is separated in a reflux drum and returned to the stripper tower as a liquid.

• The acid gas vapour is sent downstream to a Sulphur Recovery Unit (SRU).

•If the plant has a gas sulphur inlet rate of less than 1 tonne/day (this is a very small amount),the acid gas may be incinerated. Burning the H2S creates SO2 which is a monitored pollutant.

Reclaimer

• a reclaimer may be used in MEA or DGA service.

• A reclaimer heats a slipstream of the amine from the reboiler to higher temperatures. In

MEA service, a caustic solution is added to increase the pH of the mixture.

• This higher temperature (and higher pH) cleans out some products of “side reactions” and an

amine sludge is created. This must be disposed of properly.

Lean Amine

• A lean amine stream from the bottom of the reboiler (or bottom of the tower) is pumped back

to the contactor.

• The lean amine is often passed through a charcoal filtration system to remove entrained

solids

• If anti-foam additives are added to the system, the charcoal filters will remove them, so they

should be taken off-line during addition.

• The lean amine must be cooled to approximately 6oC warmer than the inlet gas temperature

before it enters the contactor.

5.4 Sulphur Recovery

5.4.1 Acid Gas Options

• The acid gas stream from the sweetening unit contains mainly H2S and CO2. The proportion

of each will depend on the inlet gas composition and the type of amine that you are using.

• The H2S in the acid gas is very toxic (and smelly) so it could not possibly be released to the

atmosphere without some further processing.

The options facing an operator are:




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1. Re-inject the acid gas into a formation.2. Burn the acid gas, converting the H2S into SO2. Release the SO2 to the atmosphere.3. Convert the H2S into elemental sulphur (S). Sell the sulphur into the world market.

The most common method of converting H2S into S is the Claus process.

5.4.2 Modified Claus Process

• If H2S is reacted with oxygen (burned), it will form SO 2 and water. This is a very

exothermic reaction – it creates a lot of heat. Even though SO2 is not as deadly as H2S, itis still a pollutant that can have adverse health effects in high concentrations. Thereforecreating SO2 is undesirable.

• The “Modified Clause Process” was developed in 1937 and involves a Combustion

Reaction & Catalytic Reaction (in stages)• The combustion reaction occurs in a reaction furnace where acid gas from the sweetening

system is reacted with oxygen to form H2O and SO2,But….

• Only 1/3 of the H2S is converted. This means that only enough oxygen (air) is fed into

the reaction to convert 1/3 of the H2S stream to SO2.

• This gas is then cooled and any pure sulphur that has formed is condensed out.

• The gas mixture is then reheated and fed into a vessel with a catalyst bed of activated

alumina. The remaining H2S and SO2 react with each other to form elemental sulphur (S)and H2O.

• 2H2S + SO2 →

2H2O + 3S

• This creates more heat as the reaction occurs. Therefore, as the gas mixture leaves the

first catalytic reactor, it is cooled and sulphur condenses out and drains to a holding tank (usually heated with steam coils and located underground).

• The remaining gas is again reheated and enters a second reactor where the same reaction

takes place.

• Depending on the amount of conversion required, 3 or 4 reactor vessels may be

employed. (Four reactors is uncommon)




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EXERCISE:

1. What does acid gas consist of?

2. Why would a low concentration of H2S in the acid gas cause the plant to have lower efficiencies per reactor?

3. How many Claus reactors would be required for a plant with a 25 tonne per day of sulphur inlet rate?

4. How many for a 50 tonne per day inlet rate?

5. How do you know when a reactor needs regeneration? What happens to the catalyst tocause it to become less active?

5.5 LPG Recovery

In a gas plant, the liquefied petroleum gas components C3 and C4 are usually removed beforethe dry “sales gas” leaves the plant. This “sales gas” is typically the feed to an LNG plant andis mainly C1 and C2 that is to be liquefied. There are two main methods of removing the LPGfraction from a gas stream – 1. refrigeration process and 2. lean oil adsorption. Only therefrigeration process will be discussed.

5.5.1 Refrigeration Process

Refrigerant (usually propane) is placed into a heat exchanger, a “chiller” in this case, where it isallowed to boil. The heat required to boil (latent heat of vaporization) the propane is extractedfrom the natural gas which is flowing through pipes that are in contact with the propane. Thisdrops the temperature of the natural gas causing liquid hydrocarbons and liquid water to formand drop out.

Propane is chosen as the refrigerant as it:- Is relatively inexpensive

- Is readily available- Has good thermodynamic properties




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A typical refrigeration with EG injection process flow looks like this:

5.5.2 The Propane Refrigeration Cycle

If we now look specifically at the propane cycle, knowing how much duty is expected of it fromthe previous calculations:

Chiller

Compressor

Condenser

Accumulator

Expansion Valve

Cold Vapour

hot vapour

cool l iq

cool l iquid

cold l iq +vap

cold,boiling liq




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-5.5.3.8 Insulation

- All lines and vessels between the throttling valve and the compressor suction should be insulated.

5.5.3.9 Materials of Construction

- As soon as temperatures are expected to reach minus 29oC and lower, a differentANSI code is used for the pipe specs. This special code ensures that the piping andequipment is able to withstand the temperatures and pressures expected.

5.6 Ethane Stripping and LNG Processing

Ethane stripping is often carried out cryogenically in "straddle plants" that sit on gas trunk lines. C2H6 is then sent to ethane crackers to provide ethylene for the petrochemical

industry.

LNG processing liquefies both the C1 and C2 components of natural gas using several typesof processes, the most common being turbo-expansion as shown below.

A typical ethane extraction plant is shown below – this process will be covered in asubsequent course in the training program.




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Chapter 6

Composition of Crude Oil

Crude oil consists primarily of a large variety of hydrocarbons and of some heterocompounds,i.e. compounds containing sulfur, nitrogen and oxygen. Compounds containing metals,

primarily nickel (Ni) and vanadium (V) may also be present.

In addition, the produced crude oil may contain water, dissolved gases, salt and sand. Thesehave to be removed before the actual petroleum is subjected to refinery processes.

Because of the geological age of petroleum, the most reactive compounds that might have been

present at some time, have already reacted away. In the hydrocarbon series, the more stablecompounds are alkanes (paraffins) including cycloalkanes, and the aromatics. Therefore, themajor building blocks of molecules found in petroleum are based on alkane, cycloalkane andaromatic (especially polyaromatic) structures. Typically, a given molecule might containstructural elements from each of these compound types. As mentioned above, sulfur, nitrogenand oxygen may also be present in these compounds.

The more reactive hydrocarbons, i.e. alkenes (carbon-carbon double bonds) and alkynes(carbon-carbon triple bonds) are not present in crude oil compounds. However, they might beformed as the crude is being subjected to chemical reactions during refinery processes.

6.1 Elemental Composition:

Carbon and hydrogen content:Crude oil being composed mostly of hydrocarbons, the carbon content and the hydrogencontent of crude oil are of interest. Typical values are

Wt%

Carbon 83.5 – 86

Hydrogen 11 – 14

Often, the atomic H/C ratio is used describe a stream. This approach is being used for crudeoil streams and for product streams.

For example:

Formula Name Atomic H/C ratioC10H22 decane 22 / 10 = 2.2

C10H8 naphthalene 8 / 10 = 0.8

CH4 methane 4 / 1 = 4




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Sulfur is removed to product specification levels during the refining process.

Exercise:

Write the chemical structure for a thiophene, thioether and a mercaptan (thiol). (Consult thesection on organic chemistry. Thioethers are the sulfur analogues of ethers).

Nitrogen content:The nitrogen content of crude is typically low falls in the range of 0.1 – 1 wt%. In general, theheavier the oil, the higher its nitrogen content.

Nitrogen is mostly present in ring structures, i.e. pyridine, quinoline and pyrrole structures.

Nitrogen is removed to product specification levels during the refining process.

Oxygen content:The oxygen content of crude oil is generally low. Considerable discrepancy exists in thereported numbers due to the difficulty in determining the oxygen content. Usually, thereported oxygen values represent the difference to mass balance closure after C, H, N,and S have been measured. In this approach, the value reported for oxygen contains thecombined errors for these measurements.

A direct oxygen determination is also possible, but is a complex procedure.

Oxygen is mostly present as part of a phenol structure.

Oxygen is removed to product specification levels during the refining process.

Metal content (mostly Ni and V)Metal content is typically in the ppm (parts per million) range, as opposed to the percent rangeused for C, H, N, and S.

Typical ranges are:

ppm

Ni 2.5 - 140

V 3 - 1500

These metals are removed during the refining process.

Salt contentSalt (mostly NaCl) is often associated with crude oil. Although salt is not soluble inhydrocarbons, it can be present as very small solid particles, or it can be dissolved in thewater that is often present in the oil.




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6.2.1 Chemical properties used for classifying crude:

The hydrocarbon type is often used to describe a crude oil. A common thought is that thehydrocarbon type used in the name of the oil is the main component of an oil of this type. It isimportant to realize that, in each type, hydrocarbons other types are also present. Also, therewill be compounds containing sulfur, nitrogen, metals, etc.

i) Hydrocarbon type:

According to the hydrocarbon type, one can distinguish between:

• Paraffinic crudes

o Typically more than 5 % of the residuum consists of paraffins• Naphthenic crudes

o Less than 2 % paraffins in residue

• Mixed crudes

o Paraffin content in residue: 2 – 5 %

ii) Sulfur content:

Sulfur is present in a chemically bonded form, i.e. not as elemental sulfur. Sulfur can also be present as part of H2S dissolved in the crude oil. The classification is made on the basisof sulfur that is incorporated in the sulfur containing organic compounds (mercaptans,thiophenes, etc.) that are in the crude oil.

• Sour crude

o Sulfur content > 0.5 wt%

• Sweet crude

o Sulfur content < 0.5 wt%

6.2.2 Physical properties used for classifying crude

i) Density

Density has long been used to describe crude oil. Different scales can be used to describethe density, namely the metric scale (in g/cm3 or in kg/m3) or the API (AmericanPetroleum Institute) scale. The density is a function of temperature: the standardtemperature is 15.6 oC or 60 oF).

oAPI = (141.5 / sp. gr. 60/60) – 131.5

The specific gravity (sp. gr.) represents the value of the density of the oil in questiondivided by the density of water. This value being a ratio, is dimensionless.

Specific gravity (sp. gr.) = density of sample / density of water


hydrocarbon processing manual

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