chapter 2 : the composition of petroleum and its products - composition.pdf · chapter 2 : the...

Petroleum Refining – Chapter 2: Composition of Petroleum and its Products

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Chapter 2 : The Composition of Petroleum and its products

Introduction

• Petroleum is a mixture of compounds - HC’s (C & H).

• Range from CH4 to C85H60.

• Elemental Composition in crude oil1.

Table 2-1: Elemental Composition in crude oil

Element % wt

Hydrocarbon C

H

84 – 87

11 – 14

Non-hydrocarbon

S

N

O

0 – 3

0 – 0.6

Traces

V

Ni

Cu

Traces

Traces

Traces

• Non-hydrocarbon elements (O, S, and N) are present as components of complex molecules

predominantly HC in character.

• Non-hydrocarbon elements (V, Ni, and Cu) are present from filed production operations.

• The boiling point of crude oil ranges from 90 to 1500 ºF.

• Compounds in crude oil are classified as -

- Paraffins and isoparaffins

- Olefins

- Naphthenes

- Aromatics

1 Not to mention, water, salt, sand, sediments, etc.

Prof. Tareq A. Albahri 2018 Kuwait University Chem. Eng. Dep.

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RSH R-S-R' R-S-S-R'

Thiols Sulfides Disulfides

(Mercaptans)

Cyclic Sulfides Thiophene Benzothiophene Dibenzothiophene

Naphthobenzothiophene

Figure 2-1: Examples of simple organic sulfur compounds in crude oil and its products.

(source: Speight, 'the chemistry and technology of petroleum', 1999, p.229 & 710)

ROH R-COOH R-COO

Alkylalcohols Carboxylic acids Carboxylic acid anhydrides

R-O-R' R-COO-R' R-CO-R'

Ethers Carboxylic acid esters Ketones

Diphenylether Tetrahydropyran Furan Benzofuran

Figure 2-2 : Examples of simple organic oxygen compounds in crude oil and its products.

(source: Speight, 'the chemistry and technology of petroleum', 1999, p.233)

SS

S S

S

S

O

OO

O


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R-NH2

Amines aniline

Pyrrole Pyridine Indole Indoline Quinoline

Carbazole Benzoquinoline Benzo carbazole

Figure 2-3: Examples of simple organic nitrogen compounds in crude oil and its products.

(source: Speight, 'the chemistry and technology of petroleum', 1999, p.234 & 711)

Paraffins

• General formula (CnH2n+2)

• Carbon is capable of forming single, double multi-branched chains which give rise to

isomers that have significantly different properties.

• The number for possible isomers increases in geometric progression as the number of atom

increases (Table 2.2).

• Crude oil contains molecules with up to 70-85 carbon atoms, & the number of possible

paraffinic HC’s is very high.


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propane n-butane isobutane n-pentane isopentane neopentane

Figure 2-4 Examples of simple paraffins in crude oil and its products

Table 2-2 : Number of possible paraffinic hydrocarbon isomers.

Molecule Symbol # of paraffin isomers

Methane C1 1

Ethane C2 1

Propane C3 1

Butanes C4 2

Pentanes C5 3

Hexanes C6

Heptanes C7

Octanes C8 17

Nonanes C9

Decanes C10

Undecane C11

Dodecanes C12 355

Tridecanes C13

Tetradecane C14

Pentadecanes C15

Hexadecanes C16

Heptadecanes C17

Octadecanes C18 60,533

Olefins

• Do not naturally occur in crude oils - but are formed during processing in the

thermal/catalytic cracking units like the delayed coker and the FCC.

• They are very similar in structure to paraffins, but at least two of the C atoms are joined by

double bonds.

• The general formula is CnH2n.

• In gasoline boiling range, olefins are desirable because they have a higher RON than

paraffins.

• However, olefins are generally undesirable in finished products, because:


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1. Double bonds are reactive and the compounds are more easily oxidized and

polymerize to form gums and varnishes.

2. Some diolefins, formed during processing, react very rapidly with olefins to form

high MW polymers and form filter plugging compounds.

3. C5 olefins have high reaction rates with compounds in the atmosphere that form

pollutants.

Naphthenes

• Are cycloparaffins in which all the bonds are single.

• The general formula is CnH2n.

• Naphthenes can have paraffin side chains.

• Many types of naphthenes exist in crude oil (Figure 2.4)

• Except for the lower MW compounds, such as cyclopentane and cyclohexane, Naphthenes

are generally not handled as individual compounds. They are classified according to boiling

range, and their properties are determined with the help of correlation factors such as Kw

factor, or CI.


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Cyclopentane Methylcyclopentane Dimethylcyclopentane

Cyclohexane Methylcyclohexane 1,2-dimethylcyclohexane

Decalin n-decylcyclopentane

(Decahydronaphthalene)

Figure 2-5 Examples of simple naphthenes in crude oil and its products

Aromatics

• These are hydrocarbons that contain one or more benzene ring.

• Aromatics can have paraffin side chains and can form a mixed structure with naphthenes.

• These mixed types have many of the chemical & physical characteristics of both of the

parent compounds (the aromatic and the paraffin), but generally are classified according to

the parent cyclic compound.

.


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Benzene Toluene o-xylene m-xylene p-xylene cumene

Naphthalene Indan Tertahydronaphthalene Diphenyl

Diphenylmethane Anthracene Phenanthrene

o-terphenyl m-terphenyl p-terphenyl

Pyrene Chrysene Flourene

Figure 2-6: Examples of simple aromatic hydrocarbons in crude oil and its products

.


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Composition of Petroleum Distillates

Figure 2-7: Principal petroleum products, their boiling range temperatures and their number of

carbon atoms.


2-9

Table 2-3 Boiling point and carbon number range for petroleum products

No. Petroleum product Boling Point (°C) Carbon Number

1 LPG (-120) - 40 C3 – C4

2 Gasoline (-10) - 230 C4 – C13

3 Naphtha 40 - 180 C5 – C11

4 WS 120 - 220 C8 – C12

5 Jet Fuel 140 - 250 C9 – C13

6 Lamp Oils 180 - 310 C10 – C17

7 Diesel Fuel & Home Heating oil 200 - 380 C11 – C23

8 Paraffins 360 - 480 C22 – C33

9 Base Stocks 380 – 610 C23 – C55

10 Heavy Fuels 375+ C23 +

11 Waxes 490 - 650 C36 – C60

12 Asphalts 570 + C45 +


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Table 2-4 : Compounds Completely Identifiable in Naphtha by a Detailed Hydrocarbon GC analyzer1.

No Model Compound No Model Compound

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

Propane

Isobutane

n-Butane

2,2-Dimethylpropane (Neopentane)

Isopentane

n-Pentane

2,2-Dimethylbutane (Neohexane)

Cyclopentane

2,3-Dimethylbutane

2-Methylpentane

3-Methylpentane

n-Hexane

2,2-Dimethylpentane

Methylcyclopentane

2,4-Dimethylpentane

2,2,3-Trimethylbutane

Benzene

3,3-Dimethylpentane

Cyclohexane

2-Methylhexane

2,3-Dimethylpentane

1,1Dimethylcyclohexane

3-Methylhexane

1-trans-3-Dimethylcyclopentane

1-cis-3-Dimethylcyclopentane

3-Ethylpentane

1-trans-2-Dimethylcyclopentane

2,2,4-Trimethylpentane (Isooctane)

n-Heptane

Methylcyclohexane

2,2-Dimethylhexane

Ethylcyclopentane

2,5-Dimethylhexane

2,4-Dimethylhexane

1-trans-2-cis-4-Trimethylcyclopentane

2,3,4-Trimethylpentane

1-trans-2-cis-3-Trimethylcyclopentane

2,3,3-Trimethylpentane

Toluene

2,3-Dimethylhexane

2-methyl-3-Ethylpentane

2-Methylheptane

4-Methylheptane

3,4-Dimethylhexane

1-cis-2-cis-4-trans-Trimethylcyclopentane

3-Methylheptane

1-methyl-2-Ethylcyclopentane

1-trans-4-Dimethylcyclohexane

1,1-Dimethylcyclohexane

1-cis-3-Dimethylcyclohexane

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

1-methyl-cis-2-Ethylcyclopentane

1-methyl-trans-3-Ethylcyclopentane

1-methyl-cis-3-Ethylcyclohexane

1-ethyl-1-Methylcyclopentane

1-trans-2-Dimethylcyclohexane

n-Octane

Isopropylcyclopentane

C9 Paraffin

C9 Paraffin

2,2,5-Trimethylhexane




3,4-Dimethyheptane

2,4-Dimethylheptane

1-cis-2-Dimethylcyclohexane

n-Propylcyclopentane

Ethylcyclopentane

1-cis-2-Dimenthylcyclohexane

1,1,3-Trimethylcyclohexane

2,5-Dimethylheptane

3,3-Dimethylheptane

3,5-Dimethylheptane

2,4-Dimethylheptane


Ethylbenzene

1-cis-3-cis-5-Trimethylpentane




m-Xylene

p-Xylene

2,3-Dimethylheptane

1-cis-2-trans-4-Trimethylcyclohexane

1-cis-2-trans-4-cis-Trimethylcyclohexane

3,4-Dimethylheptane

3-methyl-Ethylhexane

4-Ethylheptane

4-Methyloctane

2-Methyloctane

C9 Paraffin

3-Methyloctane

C9 Paraffin

o-Xylene

C9 Paraffin

1-methyl-2-Propylcyclopentane

1-methyl-trans-4-Ethylcyclohexane

1-methyl-cis-4-Ethylcyclohexane

C9 Paraffin

3,3-Diethylpentane

1 Source; Detailed Hydrocarbon Gas Chromatography Analyzer.


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Table 2-4: continued. No Model Compound No Model Compound

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

2,2,6-Trimethylheptane


n-Nonane

1-methyl-1-Ethylcyclohexane

C10 Paraffin

C10 Paraffin

Isopropylbenzene (Cumene)

tert-Butylcyclopentane

tert-Butylbenzene

Isobutylcyclopentane

C10 Paraffin

C10 Paraffin

1-methyl-4-Isopropylcyclohexane

Sec-Butylcyclopentane

1-cis-2-cis-3-cis-Trimethylcyclohexane

n-Butylcyclopentane

1-methyl-2-Ethylcyclohexane

3-Methylnonane

C10 Paraffin

n-Propylbenzene

n-Propylcyclohexane

C9-Aromatic

C9Aromatic

m-Ethyltoluene

p-Ethyltoluene

1,3,5-Trimethylbenzene

C10 Paraffin

C10 Paraffin

2-Methylnonane

0-Ethyltoluene

2,2-Dimethyloctane

3,6-Dimethyloctane

C10 Paraffin

C10 Paraffin

1,2,4-Trimethylbenzene (Psuedocumene)

1-cis-methyl-3-Ethylcyclohexane

1-trans-methyl-2-Ethylcyclohexane

1-trans-2-methyl-Propylcyclohexane

C10 Paraffin

C10 Paraffin

1-methyl-Ethylbenzene

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

1-ethyl-2,3-Dimethylcyclohexane

Isobutylbenzene

n-Decane

C11 Paraffin

C11 Paraffin

1,2,3-Trimethylbenzene (Hemimellitene)

C11 Paraffin

C11 Paraffin

C11 Paraffin

C11 Paraffin

4-Methyldecane

1-methyl-2-Isopropylbenzene (o-Cymene)

C10 Naphthene

sec-Butylbenzene

C11 Paraffin

n-Butylbenzene

C10 Aromatic

1-methyl-4-Propylbenzene


C10 Aromatic

Isobutylcyclohexane

C11 Paraffin

5-Methyldecane

1,4-Diethylbenzene

C10 Aromatic

C10 Aromatic


C11 Paraffin

C11 Paraffin

trans-1-methyl-2-(4-methylpentyl)-Cyclopentane

C11 Paraffin

C11 Paraffin

2-ethyl-1,4-Dimethylbenzene

C10 Aromatic

1,4-dimethyl-2-Ethylbenzene

n- Undecane

C11 Paraffin

1,2,4,5-Tetramethylbenzene

1,2-dimethyl-4-Ethylbenzene

C11 Paraffin

C11 Aromatic


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Composition of Vacuum Residue

• Vacuum residue contains thousands of complex (high molecular weight, high boiling point)

hydrocarbons and organic compounds.

• This is divided into three main fractions.

1. Oil fraction.

2. Resin fraction

3. Asphaltene fraction.

Figure 2-8: Separation of vacuum residue.

1. Oil fraction.

- Highly paraffinic.

- Usually contains no metals.

- Has lower S and N content than the vacuum residue.

2. Resin fraction

- Contains certain condensed-ring aromatics

- Has substantial amount of paraffinic structure

- Sulfur concentrations are approximately the same as the vacuum residue (from which they

are derived)

- Contain 10-20 %wt of the metals in the crude.

- Serves as a solvent for the asphaltenes

MW ≈ 600 – 5,000 (solution techniques)

MW ≈ 60 – 500 (mass spectrometer)

3. Asphaltene fraction.

- Very low H/C ratio.

- Contains 80-90% of the metals in crude (Ni, V).

- Consists of highly condensed aromatic ring compounds

MW ≈ 5,000 – 10,000 (solution techniques)

MW ≈ 500 – 1000 (mass spectrometer)

C3 EXTRACTIONVacuum Residue

C5/C6/C7 EXTRACTION

Oil + C3

Resin + C5/C6/C7

Asphaltene

(insoluble in C3 - C7)


2-13

Figure 2-9: Hypothetical asphaltene molecule structure

S

S

Paraffinic side chain

Sheets of highly condensed ring structure (3-5)

Naphthenic rings

Valence

bonds

hetro atom

(N, S, O, V, Ni)


2-14

References

1. David R. Lide, CRC Handbook of Chemistry and Physics, 82nd ed, CRC Press, 2001. (QD

65 C7 2001-2002)

2. James Speight, The Chemistry and Technology of Petroleum, CRC Press, 1999.

3. Klaus H. Altgelt and Boduszynski, Composition and analysis of heavy petroleum fractions,

CRC Press, 1993.

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