A Plant Design Project on Production of
Gasoline by Sulphuric Acid Alkylation of Olefins
Session: 2010-2014
Project Advisors
Prof. Dr. Syed Nadir Hussain
Project Members
Zain Ul Abidin CE-M10-02
Ahmed Javed PG-M10-03
Umar Draz CE-M10-24
Ali Hasnain CE-M10-47
Institute of Chemical Engineering and Technology
UNIVERISITY OF THE PUNJAB
LAHORE-PAKISTAN
STATEMENT BY THE AUTHORS
We hereby declare that this submission is our own work and to the best of our
knowledge, it contains no material previously published or written by another
person, no material which to a substantial extent has been accepted for the
award of our other degree or diploma at any educational institution, except
where due acknowledgement is made in the thesis.
Signatures Date
Approved by: Supervisor:
Prof. Engr. Dr. Syed Nadir Hussain,
Institute of Chemical Engineering & Technology, Faculty of Engineering &
Technology, University of the Punjab.
Signature Date
Director:
Prof. Dr. Amir Ijaz,
Institute of Chemical Engineering & Technology, Faculty of Engineering &
Technology, University of the Punjab.
Signature Date
DEDICATION
To Almighty Allah; for His daily blessings, make all
our work possible.
To our Parents; who are full of sympathy and
everlasting love.
To Prof. Engr. Dr. Syed Nadir Hussain ; for his
fatherly behavior and inspiring guidance.
To our dearest homeland, Pakistan.
ABSTRACT
Light Ends are the valuable products of a Petroleum refinery, their utilization as
a refinery fuel is not an effective solution; considering economic, product slate
and environmental factors. Alkylated Gasoline is one of the most promising
additions to refinery's Gasoline pool, with its High Octane number and added
advantages of Lower sulfur, Lower RVP, Lower Drivability Index, No Aromatic
Contents.
The new environmental regulations are forcing refineries to adapt new
technologies to reduce the sulfur, aromatics contents while increasing the
products quality and reducing emissions for Gasoline. There are number of
ways by which these requirements can be met, and Alkylation is one of the
best method that a refinery can adopt, not only to meet new environmental
regulations, but also to increase the quality of Gasoline Pool by positively
affecting the Refinery economic end because of the utilization of the light ends,
that are converted to a more valuable Gasoline product.
The installation of Alkylation unit is quite feasible, as considerable amount of
Light ends can be obtained from petroleum refinery's number of processes, like
FCCU, Plat-forming Unit, Coker, Thermal Cracking, Gasoline Stabilization Unit
etc
The Alkylated Gasoline can be produced using different patented processes
available, depending on the type of catalyst or the technology offered by a
specific company. The properties of the Gasoline produced using these
processes depends on the type of feed available for the process, the relevant
processes taking place in refineries from which light ends are obtained, the
catalyst type used, the operating temperature & pressure conditions & several
other factors.
The H2SO4 Alkylation Process of Exxon Mobil with Auto-refrigeration
technology is used; all the calculations of Material & Energy are performed
with the designing of some important equipment as well. Consideration is
given to related factors for the safety of the environment and people working
and residing near the plant area.
5
ACKNOWLEDGMENTS
I have only the pearls of my eyes to admire the blessings of the Compassionate
and Omnipotent because the words are bound, knowledge is limited and the
time is short to express HIS dignity. We are immeasurably grateful to Almighty
Allah, the Propitious, the Benevolent and Sovereign, who has endowed our
brain and instable instinct contraction of knowledge and body to accomplish
our work in the form of this dissertation, whose blessing and glory flourished
our thoughts, thrived our ambitions, granted us talented teachers, affectionate
parents, sweet sisters, loving brothers and exceptional friends.
Trembling lips and wet eyes praise for The Last Prophet Hazrat Muhammad
(PBUH) for enlightening our conscience with the essence of faith in ALMIGHT
ALLAH, enabling us to recognize the Oneness of our creator, and showed us
the right path for the success. Faithfulness in the performance of small duties
gives us strength to adhere to difficult determinations that life will someday
force us to make.
"The ink of the scholar is more holy than the blood of the martyr."
The work presented in this thesis was accomplished under the sympathetic
attitude, fatherly behavior, animate direction, observant pursuit, scholarly
criticism, sheering perspective and enlightened supervision of Prof. Dr. Engr.
Syed Nadir Hussain, Institute of chemical Engineering and Technology,
University of the Punjab for his thorough analysis and rigorous critique
improved not only the quality of this thesis, but also our overall understanding.
We are also very grateful to his ever inspiring guidance, keen interest, scholarly
comments and constructive suggestions during the course of our studies.
We appreciate his valuable comments and suggestions to make this work
complete. We deem it our utmost pleasure in expressing our cordial gratitude
with the strategic command at every step. His valuable suggestion will always
serve as beacon of light throughout the course of our studies.
We owe a great debt of gratitude to our worthy Director Prof. Dr. Amir Ijaz, for
his kind, loving positive thoughtful criticism, keen personal interest, sincere
6
advice, vital instructions throughout the course of our studies besides his very
busy schedule. We fervently extent my zealous thanks to him, also for creating
a healthy & beautiful environment.
7
NOMENCLATURE
SYMBOL DESCRIPTION UNIT V volume of the reactor m
3
V volume of catalyst m3
Viscosity Cp
hi inside heat transfer coefficient W/m2.oC
hs shell side heat transfer coefficient W/m2.oC
U overall heat transfer coefficient W/m2.oC
P Density kg/m3
CP specific heat kJ/kmol.K
AP pressure drop Bar
T Temperature C L Length M
Do outer diameter of tube Mm
Di inner dia ot tube Mm Dp dia of the particle Mm
Dd dia of the dispersed phase um
Ut terminal falling velocity m/s
G mass velocity kg/s.m2
M mass flow rate kg/h q
Heat Watt
R gas constant m3.Pa/mol.C
Nt number of tubes -
Re Reynolds number - g
acceleration due to gravity m/s2
S Voidage E total entrainment (kg/sec)
H Enthalpy (kJ/kgmol C) Ad down comer area (m
2)
Ah hole area (m2)
An net area (m2)
AT total area (m2)
Ada area under down comer apron (m2)
Df flow width normal to liquid flow (m)
D diameter of tower (m)
R reflux ratio
Rm minimum reflux ratio
a relative volatility
UOP Universal Oil Products
HF Hydrofluoric Acid
8
Table of Contents
1.1 WHAT IS GASOLINE? ................................................................................. 24
1.2 BACKGROUND & USES .............................................................................. 24
1.3 OCTANE RATING ....................................................................................... 25
1.4 PHYSICAL PROPERTIES OF GASOLINE ........................................................ 26
1.5 WHAT IS ALKYLATION? ............................................................................. 26
1.6 HISTORY OF ALKYLATION .......................................................................... 27
1.7 ALKYLATION FEEDSTOCKS ......................................................................... 28
1.8 TYPES OF ALKYLATION PROCESSES ........................................................... 29
1.8.1 THERMAL ALKYLATION ........................................................................ 29
1.9 CATALYTIC ALKYLATION ............................................................................ 30
1.10 TYPES OF ACID CATALYSTS USED IN ALKYLATION ..................................... 30
1.10.1 SULPHURIC ACID ALKYLATION PROCESS .............................................. 30
1.10.2 HF ALKYLATION ................................................................................... 32
1.11 COMPARISON OF H2SO4 & HF ................................................................... 33
1.11.1 FEED AVAILABILITY AND PRODUCT REQUIREMENTS ........................... 34
1.11.2 SAFETY & ENVIRONMENTAL CONSIDERATIONS ................................... 34
1.11.3 OPERATING COSTS .............................................................................. 36
1.11.4 UTILITY COSTS ..................................................................................... 36
1.11.5 CATALYST AND CHEMICAL COSTS ........................................................ 37
1.11.6 CAPITAL INVESTMENT ......................................................................... 37
1.11.7 MAINTENANCE .................................................................................... 38
1.12 H2SO4 VS. HF SUMMARY ........................................................................... 38
2 CHAPTER # 2: ..................................................................................... 40
2.1 METHODS OF H2SO4 ALKYLATION MANUFACTURE ................................... 40
2.2 EFFLUENT REFRIGERATION ....................................................................... 40
2.2.1 CASCADE AUTOREFRIGERATION.......................................................... 41
2.3 PROCESS VARIABLES ................................................................................. 42
9
2.3.1 REACTION TEMPERATURE ................................................................... 42
2.3.2 ACID STRENGTH .................................................................................. 42
2.3.3 ISOBUTANE CONCENTRATION ............................................................. 43
2.3.4 OLEFINS SPACE VELOCITY .................................................................... 43
2.4 ALKYLATION CHEMISTRY .......................................................................... 43
2.4.1 REACTION MECHANISM ...................................................................... 43
3 CHAPTER # 3: ..................................................................................... 46
3.1 CAPACITY & BASIS .................................................................................... 46
3.2 EQUATION OF MATERIAL BALANCE .......................................................... 46
3.3 REACTOR (R-101) ...................................................................................... 47
3.3.1 MATERIAL IN ....................................................................................... 47
3.3.2 REACTIONS .......................................................................................... 48
3.3.3 MATERIAL OUT .................................................................................... 49
3.4 PHASE SEPARATOR (PS-101) ..................................................................... 50
3.4.2 MATERIAL IN ....................................................................................... 50
3.4.3 MATERIAL OUT: ................................................................................... 51
3.5 DISTILLATION COLUMN (DC-101) ............................................................. 52
3.5.2 MATERIAL IN ....................................................................................... 52
3.5.3 MATERIAL OUT .................................................................................... 52
3.6 DISTILLATION COLUMN (DC-102) ............................................................. 54
3.6.2 MATERIAL IN ....................................................................................... 54
3.6.3 MATERIAL OUT .................................................................................... 55
3.7 BALANCE TO MIXING POINT ..................................................................... 55
4 CHAPTER # 4: ..................................................................................... 57
4.1 ENERGY BALANCE EQUATION ................................................................... 57
4.2 HEAT OF REACTIONS................................................................................. 57
4.2.1 At 298K ............................................................................................... 57
4.2.2 REACTION 1 ......................................................................................... 57
4.2.3 REACTION 2 ......................................................................................... 57
10
4.2.4 REACTION 3 ......................................................................................... 58
4.2.5 Heats of Formation Data: Hf (kJ/gmol): Vol. 6 .................................... 58
4.3 REACTOR (R-101) ...................................................................................... 59
4.3.1 Table 16: Stream 3+13: ....................................................................... 59
4.3.1.1 Table 17: Stream 4+14: ....................................................................... 60
4.3.2 Heat of Reaction Added At 298 K ........................................................ 60
4.3.3 Total Heat of Reaction: ........................................................................ 60
4.3.4 Latent Heat Required To Vaporize the Mixture ................................... 60
4.4 PHASE SEPARATOR (PS-101) ..................................................................... 61
4.5 ACROSS COMPRESSOR ............................................................................. 62
4.5.2 Balance ............................................................................................... 63
4.5.3 63
4.5.4 kJ ......................................................................................................... 63
4.6 ACROSS HEAT EXCHANGER HX-102 (CONDENSER) ................................... 63
4.6.2 Vapor Stream After Compression enters in cooler condenser: ............ 63
4.6.3 Balance: .............................................................................................. 63
4.7 ACROSS DE-PROPANIZER DC-102.............................................................. 64
4.8 ACROSS PUMP (STREAM 6)....................................................................... 65
Stream 6 in:............................................................................................................ 65
4.8.2 Table 25: Stream 6 out: ....................................................................... 65
4.9 ACROSS HEAT EXCHANGER HX-108 .......................................................... 66
Stream 6 in:............................................................................................................ 66
4.9.1.1 Table 27: Stream 6 out: ....................................................................... 66
4.10 ACROSS DE-ISOBUTANIZER DC-101 .......................................................... 67
4.10.1.1 Table 29: Stream 11: ........................................................................... 67
4.10.1.2 Table 30: Stream 7: ............................................................................. 67
4.11 AT MIXING POINT ..................................................................................... 68
4.11.1.1 Table 32: Stream 1: ............................................................................. 68
4.11.2 Table 33: Stream 2: ............................................................................. 69
4.11.2.1 Table 34: Stream 12: ........................................................................... 69
11
4.11.3 Balance: .............................................................................................. 69
5 CHAPTER # 5: ..................................................................................... 70
5.1 HEAT EXCHANGER .................................................................................... 70
5.2 TYPES OF HEAT EXCHANGERS ................................................................... 70
5.3 HEAT-TRANSFER FLUIDS ........................................................................... 70
5.4 HEAT-EXCHANGER EVALUATION AND SELECTION .................................... 71
5.5 SHELL AND TUBE HEAT EXCHANGER ......................................................... 74
5.5.1 Tube diameter:.................................................................................... 74
5.5.2 Tube thickness: ................................................................................... 74
5.5.3 Tube length: ........................................................................................ 74
5.5.4 Tube pitch: .......................................................................................... 75
5.6 CONSTRUCTION OF 1-2 SHELL AND TUBE HEAT
EXCHANGER 75
5.6.1 Shell .................................................................................................... 75
5.6.2 Tubes .................................................................................................. 76
5.6.3 Tube sheets ......................................................................................... 76
5.7 TUBE TO TUBE-SHEET ATTACHMENT ........................................................ 77
5.8 NOZZLES 77
5.8.2 IMPINGEMENT PLATE.......................................................................... 78
5.8.3 TUBE-SIDE CHANNELS ......................................................................... 78
5.8.4 CHANNEL COVERS ............................................................................... 78
5.8.5 PASS DIVIDER ...................................................................................... 78
5.9 BAFFLES 78
5.9.1 CLASSIFICATION OF BAFFLES: .............................................................. 79
5.9.2 Transverse Baffles: .............................................................................. 79
5.9.3 Segmental Baffles:............................................................................... 79
5.9.4 BAFFLE SPACING ................................................................................. 80
5.9.5 Disk and doughnut baffle .................................................................... 80
5.9.6 Orifice baffle ....................................................................................... 81
5.9.7 Longitudinal baffles ............................................................................. 81
12
5.9.8 Flanged joints ...................................................................................... 82
5.9.9 Flanged Joint Types ............................................................................. 82
5.9.10 TUBE PITCH ......................................................................................... 82
5.10 THERMO HYDRAULIC DESIGN PROCEDURE............................................... 83
5.10.1 Shell and Tube Heat Exchanger ........................................................... 83
5.10.2 SHELL SIDE CALCULATION ................................................................... 83
5.10.3 TUBE SIDE CALCULATION .................................................................... 83
5.11 DESIGN DATA............................................................................................ 86
5.11.1 Fluid 1: Process stream ....................................................................... 86
5.11.2 Fluid 2 : Cooling Utility (25 % Brine Soln.) ............................................ 86
5.11.3 Unknowns: .......................................................................................... 86
5.11.4 Heat Duty ............................................................................................ 86
5.11.5 Flowrate .............................................................................................. 86
5.11.6 Flowrate Of Utility ............................................................................... 87
5.12 PHYSICAL PROPERTIES .............................................................................. 87
5.12.1 Process Stream : .................................................................................. 87
5.12.2 Brine Solution : .................................................................................... 87
5.13 ASSUME OVERALL COEFFICIENT, U0.......................................................... 87
5.14 MEAN TEMPERATURE DIFFERENCE .......................................................... 87
5.15 HEAT TRANSFER AREA .............................................................................. 88
5.16 DECIDE THE EXCHANGER LAYOUT ............................................................ 88
5.17 INDIVIDUAL H.T.C ..................................................................................... 89
5.17.1 TUBE SIDE CALCULATION .................................................................... 89
5.17.2 Mass Vel: ............................................................................................. 90
5.17.3 Linear Vel: ........................................................................................... 90
5.17.4 Renould's # :........................................................................................ 90
5.17.5 Prandle # : ........................................................................................... 90
5.18 SHELL SIDE CALCULATION ......................................................................... 90
5.18.1 Mass Velocity ...................................................................................... 91
5.18.2 Linear Velocity..................................................................................... 91
13
5.18.3 Equivalent Diameter............................................................................ 91
5.18.4 Reynold Number: ................................................................................ 91
5.18.5 Prandle Number: ................................................................................. 91
5.19 OVERALL CO-EFFICIENT UO ....................................................................... 91
5.20 PRESSURE DROP P .................................................................................. 92
5.20.1 TUBE SIDE ........................................................................................... 92
5.20.2 SHELL SIDE .......................................................................................... 93
6 CHAPTER # 6: ..................................................................................... 96
6.1 CHEMICAL REACTORS ............................................................................... 96
6.2 TYPES OF REACTORS ................................................................................. 96
6.3 SELECTION OF REACTOR ........................................................................... 96
6.4 WHY WE SELECTED CSTR? ........................................................................ 97
6.5 SOME IMPORTANT ASPECTS OF THE CSTR................................................ 97
6.6 PFR (PLUG FLOW REACTOR) ..................................................................... 98
6.7 CSTR (CONTINUOUS STIRRED-TANK REACTOR) ........................................ 98
6.8 SELECTION OF IMPELLER .......................................................................... 100
6.8.1 Based on: ............................................................................................ 100
6.9 DESIGN OF CASCADE AUTOREFRIGERATED REACTOR ............................... 101
6.10 VOLUME OF REACTOR .............................................................................. 101
6.11 VOLUME OF REACTION ZONE ................................................................... 101
6.12 VOLUME OF SETTLING ZONE .................................................................... 102
6.13 LENGTH AND DIAMETER ........................................................................... 103
6.14 BAFFLES 103
6.15 IMPELLER DESIGN ..................................................................................... 103
6.15.1 Conditions ........................................................................................... 103
6.16 REYNOLDS NUMBER ................................................................................. 104
6.17 POWER CONSUMPTION............................................................................ 104
6.18 TYPES OF HEAD COVERS ........................................................................... 104
6.19 MECHANICAL DESIGN ............................................................................... 105
14
6.19.1 SHELL THICKNESS ................................................................................ 105
6.19.2 ELLIPSOIDAL HEAD THICKNESS ............................................................ 105
6.20 MATERIAL OF CONSTRUCTION ................................................................. 106
6.20.1 FOR REACTOR...................................................................................... 106
6.20.2 FOR IMPELLER BLADES ........................................................................ 106
6.20.3 FOR BAFFLES ....................................................................................... 106
6.21 SPECIFICATION SHEET ............................................................................... 107
7 CHAPTER 7:........................................................................................ 108
7.1 CHOICE BETWEEN PLATE AND PACKED COLUMN ..................................... 108
7.2 CHOICE OF PLATE TYPE ............................................................................. 109
7.3 NATURE OF FEED ...................................................................................... 113
7.4 PINCH TEMPERATURE............................................................................... 113
7.4.1 Pinch temperature: ............................................................................. 113
7.5 MINIMUM REFLUX RATIO ......................................................................... 114
7.5.2 Colburns Method: .............................................................................. 114
7.6 NUMBER OF PLATES ................................................................................. 114
7.6.1 Gilliland Method: ................................................................................ 115
7.7 EFFICIENCY OF THE COLUMN ................................................................... 115
7.8 FEED PLATE ............................................................................................... 116
7.8.1 Kirkbride Method: ............................................................................... 116
7.9 COLUMN DIAMETER: DC CALCULATION .................................................... 116
7.10 FLOODING VELOCITY ................................................................................ 117
7.10.1 Maximum volumetric flow rate of vapors: .......................................... 117
7.10.2 Net area required: ............................................................................... 117
7.10.3 Column Cross sectional Area: .............................................................. 118
7.10.4 Diameter Of Column: .......................................................................... 118
7.11 PROVISIONAL PLATE DESIGN .................................................................... 118
7.11.1 Column Area ....................................................................................... 118
7.11.2 Downcomer Area ................................................................................ 118
15
7.11.3 Net area .............................................................................................. 118
7.11.4 Active area .......................................................................................... 118
7.11.5 Hole area............................................................................................. 118
7.11.6 Assumptions: ...................................................................................... 118
7.12 WEEP POINT ............................................................................................. 119
7.12.1 WEIR LENGTH ...................................................................................... 119
7.12.2 WEIR LIQUID CREST ............................................................................. 119
7.12.3 WEEP POINT ........................................................................................ 119
7.13 PLATE PRESSURE DROP ............................................................................. 120
7.13.1 DRY PLATE PRESSURE DROP ................................................................ 120
7.13.2 orifice co-efficient ............................................................................... 120
7.13.3 Dry Head ............................................................................................. 120
7.13.4 Residual Head ..................................................................................... 120
7.13.5 Total Head loss .................................................................................... 120
7.13.6 Total Dry Pressure Drop ...................................................................... 120
7.14 DOWNCOMER LIQUID BACKUP ................................................................ 121
7.14.1 Area Of Apron ..................................................................................... 121
7.14.2 Head loss in Down Comer: .................................................................. 121
7.14.3 DownComer Backup ............................................................................ 121
7.15 RESIDENCE TIME ....................................................................................... 121
7.16 ENTRAINMENT ......................................................................................... 121
7.17 NUMBER OF HOLES PER PLATE ................................................................. 122
7.18 HEIGHT OF THE COLUMN ......................................................................... 122
7.19 SPECIFICATION SHEET ............................................................................... 123
8 CHAPTER 8 ......................................................................................... 124
8.1 INTRODUCTION ........................................................................................ 124
8.2 ENVIRONMENTAL EFFECTS ....................................................................... 125
8.2.1 EFFECTS OF SULPHURIC ACID ON HEALTH ........................................... 125
8.2.2 EFFECTS OF SULPHURIC ACID ON ENVIRONMENT ............................... 125
16
8.2.3 ACID RAIN ........................................................................................... 125
8.2.4 MSDS OF H2SO4 .................................................................................. 125
8.2.5 Product Identification ......................................................................... 125
8.3 Chemical Formula: H2SO4 in H2O Product Codes: .................................. 126
8.3.1 Composition/Information on Ingredients ............................................ 126
8.4 Hazards Identification ............................................................................... 126
8.5 Risk of cancer depends on duration and level of
exposure. SAFETY DATA(tm): ........................................................................... 127
8.6 Potential Health Effects: ........................................................................... 127
Inhalation: 127
Ingestion: 127
8.6.1 Skin Contact: ....................................................................................... 127
8.6.2 Eye Contact: ........................................................................................ 128
8.6.3 Chronic Exposure: ............................................................................... 128
8.6.4 Aggravation of Pre-existing Conditions:............................................... 128
8.7 FIRST AID MEASURES ................................................................................ 128
Inhalation: 128
Ingestion: 128
8.7.1 Skin Contact: ....................................................................................... 128
8.7.2 Eye Contact: ........................................................................................ 128
8.8 FIRE FIGHTING MEASURES ........................................................................ 129
Fire: 129
Explosion: 129
8.8.1 Fire Extinguishing Media: .................................................................... 129
8.8.2 Special Information: ............................................................................ 129
8.9 ACCIDENTAL RELEASE MEASURES ............................................................ 129
8.10 HANDLING AND STORAGE ........................................................................ 129
8.11 PHYSICAL AND CHEMICAL PROPERTIES .................................................... 130
Stability: 130
8.11.1 Hazardous Decomposition Products: ................................................... 130
17
8.11.2 Hazardous Polymerization: .................................................................. 130
Incompatibilities: ................................................................................................... 130
8.11.3 Conditions to Avoid: ............................................................................ 131
8.12 ECOLOGICAL INFORMATION ..................................................................... 131
8.12.1 Environmental Fate: ............................................................................ 131
8.12.2 Environmental Toxicity: ....................................................................... 131
8.13 MSDS OF GASOLINE .................................................................................. 131
8.14 HAZARDS IDENTIFICATION ........................................................................ 131
8.14.1 Eyes ..................................................................................................... 131
8.14.2 Skin ..................................................................................................... 131
8.14.3 Ingestion ............................................................................................. 132
8.14.4 Inhalation ............................................................................................ 132
8.15 WARNING: ................................................................................................ 132
8.15.1 Chronic Effects and Carcinogenicity .................................................... 132
8.15.2 Medical Conditions Aggravated By Exposure ....................................... 133
8.16 FIRST AID MEASURES ................................................................................ 133
8.16.1 Eyes ..................................................................................................... 133
8.16.2 Skin ..................................................................................................... 133
8.16.3 Ingestion ............................................................................................. 133
8.16.4 Inhalation ............................................................................................ 133
8.17 FIRE FIGHTING MEASURES ........................................................................ 133
8.17.1 Flammable Properties: ........................................................................ 133
8.17.2 Fire and Explosion Hazards .................................................................. 134
8.17.3 Extinguishing Media ............................................................................ 134
8.17.4 Fire Fighting Instructions ..................................................................... 134
8.18 ACCIDENTAL RELEASE MEASURES ............................................................ 135
8.18.1 Activate facility spill contingency or emergency plan. ......................... 135
8.19 HANDLING AND STORAGE ........................................................................ 135
8.19.1 Handling Precautions .......................................................................... 135
8.19.2 Storage Precautions ............................................................................ 136
18
8.19.3 Work/Hygienic Practices ..................................................................... 136
8.20 PHYSICAL AND CHEMICAL PROPERTIES .................................................... 137
8.20.1 Appearance ......................................................................................... 137
8.20.2 Odour .................................................................................................. 137
8.20.3 Odour Threshold ................................................................................. 137
8.20.4 Basic Physical Properties ..................................................................... 137
8.21 STABILITY AND REACTIVITY ....................................................................... 138
8.21.1 Stability: .............................................................................................. 138
8.21.2 Conditions to Avoid ............................................................................. 138
8.21.3 Incompatible Materials ....................................................................... 138
8.21.4 Hazardous Decomposition Products .................................................... 138
9 CHAPTER # 9: ..................................................................................... 138
9.1 INSTRUMENTATION AND PROCESS CONTROL .......................................... 138
9.2 TEMPERATURE MEASUREMENT AND CONTROL ....................................... 139
9.3 PRESSURE MEASUREMENT AND CONTROL............................................... 139
9.4 FLOW MEASUREMENT AND CONTROL ..................................................... 139
9.5 CONTROL SCHEME OF DISTIALLATION COLUMN ...................................... 140
9.5.1 Objectives: .......................................................................................... 140
9.5.2 Manipulated variables: ........................................................................ 140
9.5.3 Loads or disturbances: ........................................................................ 140
9.5.4 Control scheme ................................................................................... 141
9.5.5 Advantage ........................................................................................... 141
9.5.6 Disadvantage ...................................................................................... 141
10 141
11 CHAPTER # 10 .................................................................................... 142
11.2 Fixed Cost: ................................................................................................ 145
11.3 Annual Production Cost: ........................................................................... 146
11.4 Processing Cost / Liter: ............................................................................. 146
11.5 Profit per annum: ..................................................................................... 146
19
11.6 Economic Evaluation: ............................................................................... Error! Bookmark not defined.
11.6.1 Cash Flow diagram: ............................................................................. Error! Bookmark not defined.
11.7 Pay Back Period: ....................................................................................... Error! Bookmark not defined.
11.8 Discounted Pay Back Period: .................................................................... Error! Bookmark not defined.
11.9 Net present value: .................................................................................... Error! Bookmark not defined.
11.10 Profitability index: ..................................................................... Error! Bookmark not defined.
12 APPENDIX .......................................................................................... 148
12.1 APPENDIX A-1 ........................................................................................... 148
12.2 149
12.3 APPENDIX A-2 ........................................................................................... 149
12.4 APPENDIX A-3 ........................................................................................... 150
12.5 150
12.6 APPENDIX A-4 ........................................................................................... 151
12.7 APPENDIX A-5 ........................................................................................... 152
12.8 APPENDIX A-6 ........................................................................................... 153
12.9 APPENDIX A-7 ........................................................................................... 154
12.10 APPENDIX B-1 ............................................................................ 155
12.11 APPENDIX B-2 ............................................................................ 156
12.12 APPENDIX B-3 ............................................................................ 157
12.13 APPENDIX B-4 ............................................................................ 158
12.14 APPENDIX B-5 ............................................................................ 159
12.15 Appendix B-6 ............................................................................. 160
12.16 APPENDIX C-1 ............................................................................ 161
20
CHAPTER # 01:
INTRODUCTION
1.1 WHAT IS GASOLINE?
A volatile mixture of flammable liquid hydrocarbons
derived chiefly from crude petroleum and used principally as a fuel for
internal-combustion engines. Gasoline is a complex mixture of over 500
hydrocarbons that may have between 5 to 12 carbons. Smaller amounts of
alkane cyclic and aromatic compounds are present. Gasoline has a typical
boiling range from 100 to 400F (38 to 205C) as determined by the ASTM
method.
Alkylate gasoline is the product of the reaction of
isobutane with propylene, butylene, or pentylene to produce branched-chain
hydrocarbons in the gasoline boiling range. Alkylation of a given quantity of
olefins produces twice the volume of high octane motor fuel as can be
produced by polymerization. In addition, the blending octane (PON) of alkylate
is higher and the sensitivity (RON _ MON) is significantly lower than that of
polymer gasoline.
1.2 BACKGROUND & USES
Before internal-combustion engines were invented in the mid 19th century,
gasoline was sold in small bottles as a treatment against lice and their eggs. At
that time, the word Petrol was a trade name. This treatment method is no
longer common, because of the inherent fire hazard and the risk of dermatitis.
Gasoline was also sold as a cleaning fluid to remove grease stains from
clothing. Gasoline was also used in kitchen ranges and for lighting, and is still
available in a highly purified form, known as camping fuel or white gas, for use
in lanterns and portable stoves.
The invention and development of the automobile as primary mode of
personal transportation required a parallel development of the fuels that
would power the automobiles. Hydrocarbon fuels were an integral component
of society in the 19th century as a source of light. Automobile engines
demanded unprecedented amounts of petroleum. The early refiners could
convert only a small proportion of their crude oil to gasoline - the rest was
wasted or spilled to the environment.
1.3 OCTANE RATING
The octane number or rating of gasoline is a measure of its resistance to knock.
The octane number is determined by comparing the characteristics of a
gasoline to isooctane (2,2,4-trimethylpentane) and n-heptane. Isooctane is
assigned an octane number of 100. It is a highly branched compound that
burns smoothly, with little knock. On the other hand, n-heptane, a straight
chain, un-branched molecule is given an octane rating of zero because of its
bad knocking properties.
Straight-run gasoline (directly from the refinery distillation column) has an
octane number of about 70. In other words, straight-run gasoline has the same
knocking properties as a mixture of 70% isooctane and 30% heptanes. Many of
these compounds are straight chain alkanes. Cracking, Isomerization, and other
refining processes can be used to increase the octane rating of gasoline to
about 90. Anti-knock agents may be added to further increase the octane
rating.
The octane rating became important as the military sought higher output
for aircraft engines in the late 1930s and the 1940s. A higher octane rating
allows a higher compression ratio or supercharger boost, and thus higher
temperatures and pressures, which translate to higher power output. Some
scientists even predicted that a nation with a good supply of high octane
gasoline would have the advantage in air power. These requirements lead to
the production of high octane gasoline by alkylation of olefins.
1.4 PHYSICAL PROPERTIES OF GASOLINE
Property Gasoline
Chemical Formula C4 to C12
Molecular Weight 100-105
Specific gravity, 60 F/60 F 0.720.78
Density, lb/gal @ 60 F 6-6.5
Boiling temperature, F 80-437
Heating values
>Lower (Btu/lb) 18,676
>Higher (Btu/lb) 20,004
Freezing point, F -40
Viscosity, mm2/s
>@104 F 0.5-0.6
>@68 F 0.8-1.0
Auto ignition temperature, F -45
Specific heat, Btu/lb F 0.4
1.5 WHAT IS ALKYLATION?
The addition of an alkyl group to any compound is an alkylation reaction but in
petroleum refining terminology the term alkylation is used for the reaction of
low molecular weight olefins with an iso-paraffins to form higher molecular
weight iso-paraffins (collectively called alkylate).
Alkylation is an important refining process for the production of alkylates a
high-octane gasoline blending component. Alkylate product is a mixture of
branched hydrocarbons of gasoline boiling range. Alkylate has a motor octane
(MON) of 90-95 and a research octane (RON) of 93-98. Because of its high
octane number and low vapor pressure, alkylate is considered an excellent
blending component for gasoline.
1.6 HISTORY OF ALKYLATION
Alkylation is a twentieth century refinery innovation. Developments in
petroleum processing in the late 1930s and during World War II were directed
toward production of high-octane liquids for aviation gasoline. The sulfuric acid
process was introduced in 1938, and hydrogen fluoride alkylation was
introduced in 1942.
Humble Oil built the first commercial H2SO4 alkylation unit in 1938 at Baytown,
Texas. Alkylation for aviation gasoline grew rapidly with the Allies war effort.
In 1939, six petroleum companies formed a consortium to pool their alkylation
technology and develop both sulfuric acid and HF acid processes for 100
octane aviation fuel. The first commercial HF alkylation unit started up in 1942.
During the war 60 alkylation units were built. Half were built with sulfuric acid
as the catalyst and half with HF.
Following World War II, most alkylation operations were discontinued
although a few refiners continued to use the process for aviation and premium
automobile gasoline.
In the mid-1950s, use of higher performance automotive engines required the
refining industry to both increase gasoline production and quality. The
development of catalytic reforming, such as UOP Plat forming, provided
refiners with an important refining tool for production of high octane gasoline.
However, the motor fuel produced in such operations, called reformate, is
highly aromatic with a higher sensitivity (the spread between research and
motor octane) and a lower lead response than alkylate.
Many refiners expanded their alkylation operations and began to broaden the
range of olefin feeds to both existing and new alkylation units to include
propylene and occasionally even some pentenes along with the butenes.
With the phase-out of leaded gasoline and the advent of environmental
gasoline the lead response of alkylate is no longer valued, but the importance
of alkylate and its production have both grown because of its other properties.
Its high unleaded motor octane, low volatility, low-sulfur, and nearly zero
olefins and aromatics make alkylate critical to the production of quality
environmental gasoline.
Licensors of motor fuel HF Alkylation processes are UOP LLC and Phillips.
Licensors of H2SO4 alkylation processes are Exxon Mobil and Stratco
Engineering.
1.7 ALKYLATION FEEDSTOCKS
Olefins and isobutane are used as alkylation unit feedstock. The chief
sources of olefins are catalytic cracking and coking operations. Butenes and
propene are the most common olefins used, but pentenes (amylenes) are
included in some Olefins can be produced by dehydrogenation of paraffins,
and isobutane is cracked commercially to provide alkylation unit feed.
Hydrocrackers and catalytic crackers produce a great deal of the
isobutene used in alkylation but it is also obtained from catalytic reformers,
crude distillation, and natural gas processing. In some cases, normal butane is
isomerized to produce additional isobutane for alkylation unit feed. Olefins and
iso-butane obtained usually in Refinery are given in table.
1.7.1.1 Table 1: Olefins and isobutane production from
different units
LV %
Iso-Butane
Olefins
Hydro-cracker
3
-
FCC
6
15
Coker
1
15
Hydrotreater
1
-
Reformer
2
-
Isomerization
1
-
Crude Unit
0.5
-
1.8 TYPES OF ALKYLATION PROCESSES
There are two main types of alkylation processes,
Thermal alkylation
Catalytic alkylation
1.8.1 THERMAL ALKYLATION
Alkylation can be done without the use of catalysts. But a very high
temperature and pressure conditions are required i.e.
T = 950 OF
P = 3000-5000psi
In this process iso-butane along with ethylene is used as raw materials. This is a
vapor phase process and no catalysts are used, but it is commercially not
favorable.
1.9 CATALYTIC ALKYLATION
Catalytic alkylation of iso-paraffin involves addition of tertiary hydrogen to an
olefin. This process occurs at low temperature (30-100oC) and pressure.
1.9.1.1 Table 2: COMPARISON BETWEEN THERMAL
AND CATALYTIC ALKYLATION
THERMAL ALKYLATION CATALYTIC ALKYLATION
It takes place at high temperature and pressure without the aid of catalyst.
It takes place at much lower temperature pressure with the aid of catalyst.
It occurs with both normal and iso-paraffins.
It occurs with paraffins containing tertiary carbon atom.
In this process, ethylene reacts more readily than higher molecular weight olefins.
In this process, the higher molecular weight olefins react more readily than ethylene.
Thermal alkylation is of little importance in refinery operation.
Catalytic process has economic advantage with better selectivity and milder operating conditions that make them preferred for commercial processing.
1.10 TYPES OF ACID CATALYSTS USED IN ALKYLATION
Sulphuric acid
Hydrofluoric acid
1.10.1 SULPHURIC ACID ALKYLATION PROCESS
Two sulphuric acid alkylation processes are commonly available. These are the
auto-refrigeration process licensed by Exxon and the effluent refrigeration
process licensed by Stratford Engineering Corporation. The major difference
between the two processes is in the reactor design. In the auto-refrigeration
process, the evaporation of iC4 and Propane induces cooling of the emulsion in
the reactor. In the effluent refrigeration process, a refrigeration unit provides
cooling to the reactor. The auto-refrigeration unit is shown in Figure 1.
UmarHighlight
1.10.1.1.1 Figure 1: Auto refrigeration unit:
The olefin is fed to the first reactor in the cascades, together with the recycled
acid and refrigerant. Recycled and make-up isobutanes are distributed to each
reactor. Evaporated gases are compressed and fed back to the reactor along
with the fresh olefin feed which is also cooled by this stream. The reactor
operates at a pressure of 90 kPa (10 psig) and at a temperature of 5 oC (40 oF)
for up to 40 min.
In the Stratco process, the reactor is operated at a higher pressure of 420 kPa
(60 psig), to prevent evaporation of hydrocarbon, and at a temperature of 10 oC (50 oF). The effluent refrigeration process uses a single Stratco reactor
design as shown in Figure 2. An impeller emulsifies the hydrocarbonacid
mixture for about 2035 min.
1.10.1.2 Figure 2: Effluent refrigeration unit:
1.10.2 HF ALKYLATION
This is highly successful process for combining iso-butane and iso-butane
involves the recirculation of about 6 parts of iso-butane to 1 part of iso-butane.
A temp of 75-105 oF and a Pressure of 100-150psig is maintained on the
reaction contractor. The acid is currently dried, about 6% of heavy oils are
removed, and acid consumption is 0.20lb per barrel of alkylates produced.
Plain carbon steel is used throughout except that some rundown lines are
constructed of Monel metal. The cycle time efficiency is said to be 96%.The
basic advantage of HF Alkylation process over H2SO4 alkylation process is that
acid recovery is easy.
Two hydrofluoric acid (HF) alkylation processes are commonly available. These
are the Phillip process and the UOP process. The HF processes have no
mechanical stirring as in the sulphuric acid processes. The low viscosity of HF
and the high solubility of isobutane in the acid allow for a simpler design. The
emulsion is obtained by injecting the hydrocarbon feed into the continuous HF
phase through nozzles at the bottom of a tubular reactor. Reaction
temperature is about 30 oC (86 oF), allowing for the use of water as a coolant to
the reactor. The two processes are quite similar. The flow diagram of the
Phillips process is shown in Figure 3. The residence time in the reactor is 2040
s. The hydrocarbon phase is sent to the main fractionation column to obtain
stabilized alkylate. H2SO4 alkylation processes are favored over the HF
processes because of the recent concern about the mitigation of HF vapors. HF
is a very hazardous material for humans because it can penetrate and damage
tissue and bone.
1.10.2.1 Figure 3: HF Alkylation unit:
1.11 COMPARISON OF H2SO4 & HF
A process comparison of H2SO4 and HF alkylation processes shows that neither
has an absolute advantage over the other. From a safety an environmental
standpoint, H2SO4 has a clear advantage over HF. Economics of the processes
are sensitive to base conditions for feed stocks and operating conditions, as
well as refined product pricing. Thus, the actual choice for a particular location
is governed by a number of site-specific factors that require a detailed analysis.
Commercial alkylation catalyst options for refiners today consist of
hydrofluoric (HF) and sulfuric (H2SO4) acids. In some areas of the world, HF is
no longer considered an acceptable option for a new unit due to concerns over
safety; however, this is not the case everywhere. Due to site-specific
differences in utility economics, feed and product values, proximity to acid
regeneration facilities, etc, both H2SO4 and HF alkylation technologies should
be evaluated. The evaluation criteria can be divided into the following
categories:
Feed Availability and Product Requirements.
Safety and Environmental Considerations.
Operating Costs.
Utilities.
Catalyst and Chemical Costs. And Capital Investment
Maintenance.
1.11.1 FEED AVAILABILITY AND PRODUCT REQUIREMENTS
Historically, butylenes from the FCC were the traditional olefins fed to the
alkylation unit. Today, alkylation units are using a broader range of light olefins
including propylene, butylenes and amylenes. Alkylate composition and
octanes from pure olefins are quite different for each catalyst as shown in
Table for light olefin alkylate octanes.
1.11.1.1 Table 3: Types of olefins
Types of Olefin RON
MON
HF H2SO4 HF H2SO4
Propylene 91-93 91-92 89-91 90-92
1-Butene 90-91 97-98 88-89 93-94
2-Butene 96-97 97-98 92-93 93-94
Iso-Butene 94-95 94-95 91-92 92-93
Amylenes 90-92 89-92 88-89 88-90
1.11.2 SAFETY & ENVIRONMENTAL CONSIDERATIONS
Safety and environmental concerns are extremely important when choosing an
alkylation technology. A huge concern is the large volume of LPG present
within the unit. Refineries must protect against conditions that could lead to
LPG releases and potential fire hazards. All of the alkylation technologies being
evaluated have similar volumes of hydrocarbon within the unit. In addition,
neither acid catalyst impacts the flammability of LPG; therefore, no one
technology has an advantage over another in this regard.
Another major safety concern is the acid catalyst used to promote the
reaction. Both HF and H2SO4 acids are hazardous materials, however, HF is
considerably more dangerous. In the United States, HF has been identified as a
hazardous air pollutant in current federal and state legislation. Sulfuric acid has
not. HF and H2SO4 represent an ever-present danger to personnel working on
alkylation units. Contact with either HF or H2SO4 can result in chemical burns.
However, HF burns tend to be more severe, since the fluoride ion penetrates
the skin and destroys deeper layers of tissue. If not treated, it may even cause
dissolution of the bone. In addition, inhalation of HF vapors may cause
pulmonary edema and, in severe cases, may result in death. The volatility of
the acid at ambient conditions is a chief concern. HF is a toxic, volatile gas at
these conditions, while H2SO4 is a toxic liquid. Therefore, H2SO4 is much easier
to contain in the event of an accidental release. The hazardous nature of both
materials has been known and respected for years. In more densely populated
areas of the world, safety and environmental concerns of HF usage have given
H2SO4 alkylation a notable advantage.
In 1986, tests were conducted in the Nevada desert to determine the dangers
of a possible HF liquid release. Under conditions similar to those that exist in
an alkylation unit, lethal concentrations of an HF aerosol were present up to 8
km (5 miles) from the release points. It was during these tests that HF releases
were observed to be much more dangerous than anticipated. Due to the risk,
many refiners are implementing water mitigation and detection devices in an
effort to remove any HF that would vaporize in the event of a release. With
water/HF ratios of 40:1, nearly 90% of the HF can be removed. However, these
systems are expensive and there is the concern that the water sprays could
become inoperative as a result of an accident. In addition, details have not yet
been obtained, or at least reported, on the fate of the HF that is not removed
by the water sprays. For a major leak (200 lb/s 100 kg/s) that might result from
a 4 inch (10 cm) hole at process conditions, water systems are thought to be
less effective. Major HF leaks have been rare in the industry, and when they
have occurred, there has usually been a major fire event that has dissipated
the HF cloud as it formed. However, the impact of a major HF release should
always be considered.
Following a number of HF incidents in the 1980s, and in view of the impact
that the Bhopal and Valdez calamities had on the companies concerned, many
refiners have carried out Quantified Risk Assessment studies to identify the risk
associated with specific HF units. In terms of offsite impact, an unmitigated HF
unit will usually generate by far and away the largest element of the risk
associated with the site. Tests conducted in 1991 by Quest Consultants, Inc.
showed that the potential for a H2SO4 aerosol formation from an alkylation
unit release is highly unlikely. Several tests were performed under a variety of
conditions resembling those observed in an alkylation unit. The tests provided
conditions favorable to the formation of airborne particles. However, the
released acid did not remain airborne, and an aerosol was not formed
1.11.3 OPERATING COSTS
Operating costs for H2SO4 technologies tend to be spread equally amongst
steam, electric power and acid costs. With the HF process, most operating
costs are associated with high pressure steam or fuel requirements for the
isostripper reboiler. This reboiler provides thermal de-fluorination of the
alkylate product, in addition to providing the required reboiler duty.
1.11.4 UTILITY COSTS
Utility costs tend to favor the H2SO4 systems. Many HF units require isobutene-
to-olefin ratios on the order of 13 - 15/1 to produce an acceptable octane
product. Other HF units and many H2SO4 units develop conditions of mixing
and recycle optimization such that they produce similar octane products with
isobutane to olefin ratios on the order of 7 - 9/1. Clearly the latter, better-
designed units operate with significantly lower fractionation costs. Today,
many HF units are operating below the design isobutene-to olefin ratio, but to
obtain the required octane, due to increasingly tight gasoline specifications,
these ratios will need to be increased back to design ratios. The H2SO4 process
employs either electric or turbine drives for the reactors and compressor to
optimize refinery utilities. Horsepower input to the HF reaction zone is lower
than to the H2SO4 reaction zone. In addition, the HF process does not require
refrigeration.
1.11.5 CATALYST AND CHEMICAL COSTS
Catalyst and chemical costs favor HF units, with the main difference being acid
cost. Although HF is more expensive, much less is used, and, can be
regenerated on site. The operating cost of H2SO4 alkylation depends heavily on
reactor design, feed pretreatment, residual contaminants, and the cost and
availability of H2SO4 regeneration. Presently, refiners can either regenerate the
catalyst on site or send it to an outside regenerator. The latter choice is very
common in the United States, where most refiners are not too distant from
H2SO4 manufacturers who can regenerate spent acid at a reasonable cost. On-
site acid regeneration is much more common outside the U.S, due to the lack
of regional commercial acid regeneration facilities. Over 25% of the new
alkylation units built outside the United States in the last five years have
elected to build on-site regeneration facilities. Some regenerators have greatly
reduced acid regeneration cost by providing total sulfur handling facilities for
refiners.
1.11.6 CAPITAL INVESTMENT
It has been over ten years since a comparative cost analysis was conducted
between HF and H2SO4 alkylation technologies. Changes in peripheral
equipment to both technologies have changed dramatically in the past ten
years, and the impact of these on capital investment will be discussed later in
this section. When the above referenced cost estimate was performed there
was objectively no real difference in installed costs between the two
technologies. Since that time, there have been no improvements in either
technology that would warrant a significant change in the cost advantage of
one technology over the other. The separate studies performed by
independent consulting firms (Pace Engineering and Chem Systems) found that
the cost for H2SO4 and HF alkylation units were comparable.
Installed Capital Cost ($MM)
Alkylate Production (BPD) H2SO4 HF
5000 14.9 14.5
7000 18.8 18.2
It is not surprising that the two processes are competitive on a capital cost
basis, when one considers the basic process differences. The H2SO4 process has
a more expensive reactor section and requires refrigeration. However, equal
costs are realized in the HF unit by the need for feed driers, product treating,
regeneration equipment and more exotic metallurgy. In addition, most refiners
will require a dedicated cooling system for an HF unit, to remove the risk of
site-wide corrosion in the case of an HF leak.
It should be noted that these capital cost estimates do not account for the
additional safety and mitigation equipment now required in HF units. Due to
the possible hazardous aerosol formation when the HF catalyst is released as a
superheated liquid, expensive mitigation systems are now required in many
locations throughout the world where HF is used as an alkylation catalyst.
Consequently, capital costs for a grassroots HF unit are greater by $2-5 million
(U.S.) depending upon the degree of sophistication of the mitigation design.
1.11.7 MAINTENANCE
Maintenance costs and data are difficult to obtain on a comparable basis. HF
units have much more peripheral equipment (feed driers, product treaters,
acid regeneration column and an acid-soluble oil neutralizer); thus, more
pieces of equipment to operate and maintain. H2SO4 units have larger pieces of
equipment, such as the compressor and reactor, but maintenance costs are
generally lower. Unit downtime to prepare for a full unit turnaround can take
longer for HF units, since the reactor-settler system and all the fractionators
must be neutralized before maintenance work can proceed. In H2SO4 units,
only the reactor-settler system requires neutralization. In addition, extensive
safety equipment (breathing apparatus, etc.) is required whenever
maintenance is performed with a potential of HF release.
1.12 H2SO4 VS. HF SUMMARY
A process comparison of the alkylation processes shows that neither has an
absolute advantage over the other. From a safety and environmental
standpoint, H2SO4 has a clear advantage over HF. Economics of the processes
are sensitive to base conditions for feed stocks and operating conditions, as
well as refined product pricing. Thus, the actual choice for a particular refinery
is governed by a number of site-specific factors, which require a detailed
analysis.
As a result of these factors, nearly 90% of new units licensed since 1990 have
selected H2SO4 alkylation technology over HF.
2 CHAPTER # 2:
PROCESS DESCRIPTION
On the basis of the above discussion we select ultimately H2SO4 alkylation
process.
2.1 METHODS OF H2SO4 ALKYLATION MANUFACTURE
Methods for H2SO4 production is classified on the basis of reactors types
EFFLUENT REFRIGERATION
CASCADE AUTOREFRIGERATION
2.2 EFFLUENT REFRIGERATION
The effluent refrigeration process is licensed by Stratford Engineering
Corporation. The effluent refrigeration process (Stratco) uses a single-stage
reactor in which the temperature is maintained by cooling coils. The reactor
contains an impeller that emulsifies the acidhydrocarbon mixture and re-
circulates it in the reactor. Average residence time in the reactor is on the
order of 20 to 25 minutes. Emulsion removed from the reactor is sent to a
settler for phase separation. The acid is re-circulated and the pressure of the
hydrocarbon phase is lowered to flash vaporize a portion of the stream and
reduce the liquid temperature to about 30F (1C). The cold liquid is used as
coolant in the reactor tube bundle. The flashed gases are compressed and
liquefied then sent to the depropanizer where LPG grade propane and recycle
isobutane are separated. The hydrocarbon liquid from the reactor tube bundle
is separated into isobutane, n-butane, and alkylate streams in the
deisobutanizer column. The isobutane is recycled and n-butane and alkylate
are product streams. A separate distillation column can be used to separate
the n-butane from the mixture or it can be removed as a side stream from the
deisobutanizing column. The choice is a matter of economics because including
a separate column to remove the n-butane increases the capital and operating
costs. Separating n-butane as a side stream from the deisobutanizing can be
restricted because the pentane content is usually too high to meet butane
sales specifications. The side stream n-butane can be used for gasoline
blending. In this type of reactor there are chances of
Degradation of alkylate
Polymerization may occur at a high level
Compressor demands for the effluent refrigeration process are larger
2.2.1 CASCADE AUTOREFRIGERATION
The major alkylation processes using sulfuric acid as a catalyst are the auto-
refrigeration process, licensed by Exxon Research and Engineering (similar to a
process previously licensed by the M. W. Kellogg Company), The major
differences between the auto-refrigeration and effluent refrigeration
processes are in the reactor designs and the point in the process at which
propane and isobutane are evaporated to induce cooling and provide the
process refrigeration required. The auto-refrigeration process uses a
multistage cascade reactor with mixers in each stage to emulsify the
hydrocarbonacid mixture. Olefin feed or a mixture of olefin feed and
isobutane feed is introduced into the mixing compartments and enough mixing
energy is introduced to obtain sufficient contacting of the acid catalyst with the
hydrocarbon reactants to obtain good reaction selectivity. The reaction is held
at a pressure of approximately 10 psig (69 kPag) in order to maintain the
temperature at about 40F (5C). In the Stratco, or similar type of reactor
system, pressure is kept high enough [4560 psig (310420 kPag)] to prevent
vaporization of the hydrocarbons. In the Exxon process, acid and isobutane
enter the first stage of the reactor and pass in series through the remaining
stages. The olefin hydrocarbon feed is split and injected into each of the
stages. Exxon mixes the olefin feed with the recycle isobutane and introduces
the mixture into the individual reactor sections to be contacted with the
catalyst. The gases vaporized to remove the heats of reaction and mixing
energy are compressed and liquefied, the liquefied hydrocarbon is sent to a
depropanizer column for removal of the excess propane which accumulates in
the system. The liquid isobutane from the bottom of the depropanizer is
pumped to the first stage of the reactor. The acidhydrocarbon emulsion from
the last reactor stage is separated into acid and hydrocarbon phases. The acid
is removed from the system for reclamation, and the hydrocarbon phase is
then sent to a deisobutanizer. The deisobutanizer separates the hydrocarbon
feed stream into isobutane (which is returned to the reactor), n-butane, and
alkylate product. Although high amount of iso-butane is required to maximize
the conversion and high power input is also needed to achieve better mixing
but acid consumption values are lesser and high quality Alkylate is produced.
2.3 PROCESS VARIABLES
The most important process variables are.
Reaction temperature
Acid strength
Isobutane concentration
Olefin space velocity.
Changes in these variables affect both product quality and yield.
2.3.1 REACTION TEMPERATURE
Reaction temperature has a greater effect in sulfuric acid processes than in
those using hydrofluoric acid. Low temperatures mean higher quality and the
effect of changing sulfuric acid reactor temperature from (4 to 23C) is to
decrease product octane from one to three numbers depending upon the
efficiency of mixing in the reactor. In hydrofluoric acid alkylation, increasing
the reactor temperature from 60 to 125F (16 to 52C) degrades the alkylate
quality about three octane numbers. In sulfuric acid alkylation, low
temperatures cause the acid viscosity to become so great that good mixing of the
reactants and subsequent separation of the emulsion is difficult. At temperatures
above 70F (21C), polymerization of the olefins becomes significant and yields
are decreased. For these reasons the normal sulfuric acid reactor temperature is
from 40 to 50F (5 to 10C) with a maximum of 70F (21C) and a minimum of
30F (1C). For hydrofluoric acid alkylation, temperature is less significant and
reactor temperatures are usually in the range of 70 to 100F (21 to 38C).
2.3.2 ACID STRENGTH
It has varying effects on alkylate quality depending on the effectiveness of
reactor mixing and the water content of the acid. In sulfuric acid alkylation, the
best quality and highest yields are obtained with acid strengths of 93 to 98% by
weight of acid, 1 to 2% water. The water concentration in the acid lowers its
catalytic activity about 3 to 5 times as much as hydrocarbon diluents.
2.3.3 ISOBUTANE CONCENTRATION
Higher ratios of isobutane to olefins in the feed streams to the reactor
minimize the undesired polymerization reactions. The quality of alkylates
hence increases as the ratios increases. Alkylation plants employing H2SO4 as
the catalyst often operate in the range of 5:1 to 8:1.
2.3.4 OLEFINS SPACE VELOCITY
It is defined as gallon per hour of olefin feed divided by the gallons of acid
catalyst instantaneously resident in the true reaction zone. As the space
velocity decreases octane no of alkylate goes to maximum value.
2.4 ALKYLATION CHEMISTRY
The alkylation reaction combines light C3-C5 olefins with isobutane in the
presence of a strong acid catalyst. Although alkylation can take place at high
temperature without catalyst, the only processes of commercial importance
involve low to moderate temperatures using either sulfuric or hydrofluoric
acid.
2.4.1 REACTION MECHANISM
It is accepted that alkylation of isobutane with C3 C5 olefins involves a series of
consecutive and simultaneous reactions occurring through carbocation
intermediates. A generalized reaction scheme for butene alkylation can be
summarized as follows.
The first step is the addition of a proton to the olefin to form a
t-butyl cation.
This reaction with sulfuric acid results in the production of alkyl sulfates.
Occasionally alkyl sulfates are called esters. Propylene tends to form much
more stable alkyl sulfates than either C4 or C5 olefins. With either 1-butene or 2-
butene, the sec-butyl cation formed may isomerize via methyl shift to give a
more stable t-butyl cation.
These initiation reactions are required to generate a high level of ions but
become less important at steady state. Typically, this can be observed as a
higher rate of acid consumption initially when using fresh acid. The t-butyl
cation is then added to an olefin to give the corresponding C8 carbocation:
2.4.1.1.1 Figure 4: PROCESS FLOW DIAGRAM
3 CHAPTER # 3:
MATERIAL BALANCE
3.1 CAPACITY & BASIS
10000 BPSD of Alkylate Produced
Since 1m3 = 6.29bbls & Density of Alkylate = 720 kg/m3
Avg. Molecular Mass of Alkylate = 113.85 kg/kmol
Alkylate = 47694.75 kg/hr
= 418.92 kmol/hr
Basis: 1 hr Operation
3.2 EQUATION OF MATERIAL BALANCE
At steady State,
Overall Material Balance can be given by equation,
3.3 REACTOR (R-101)
3.3.1 MATERIAL IN
3.3.1.1 Table 4: Stream 3 = 383658.1 kg
Component kmol Kg
Butane 412.67 23109.52
Isobutane 5105.61 296128.2
n-butane 1033.82 59961.67
Propene 6.20 260.48
Propane 95.42 4198.26
Sum 6653.76 383658.1
3.3.1.1.1 Figure 5: Reactors single step:
3.3.1.2 Table 5: Stream 13 = 4769.4 kg
Substance kmol Kg
H2SO4 47.69 4674.01
Water 5.23 95.38
Sum 52.99 4769.4
3.3.2 REACTIONS
REACTION 1
C4H8 (l) + iC4H10 (l)C8H18 (l) H298= -90.572 kJ/gmol
REACTION 2
C3H6 (l) + iC4H10 (l) C7H16 (l) H298 = -83.81 kJ/gmol
REACTION 3
C3H6 (l) + 2iC4H10 (l) C3H8 (l) + C8H18 (l) H298 = -79.16 kJ/gmol
From Patent
At 12 oC & 25 Psig, Conversion to Alkylate according is:
Reaction 1 98.51%
Reaction 2 0.341%
Reaction 3 1.149%
3.3.3 MATERIAL OUT
3.3.3.1 Table 6: Stream 4 = 383659.3 kg
Component kmol kg
Isobutane 4682.54 271588
nbutane 1033.94 59968.54
propane 100.19 4408.68
alkylate 418.92 47694.04
Sum 6235.61 383659.3
3.3.3.2 Table 7: Stream 14 = 4769.4 kg
Component kg
Spent Acid 4769.4
Balance:
Stream 3 = 383658.1 kg Stream 13 = 4769.4 kg
Total Material In = 383658.1 + 4769.4 = 388427.5 kg
Stream 4 = 383659.3 kg
Stream 14 = 4769.4 kg
Total Material Out = 383659.3 + 4769.4 = 388428.7 kg
3.4 PHASE SEPARATOR (PS-101)
3.4.1.1.1 Figure 6: phase separators single step:
3.4.2 MATERIAL IN
3.4.2.1 Table 8: Stream 4 = 383659.3 kg
Component kmol kg
Isobutane 4682.54 271588
nbutane 1033.94 59968.54
propane 100.19 4408.68
alkylate 418.92 47694.04
Sum 6235.61 383659.3
3.4.3 MATERIAL OUT:
3.4.3.1 Table 8: Stream 5 = 122417.2 kg
Component kmol kg
Isobutane 1791.62 103914.1
nbutane 271.96 15773.91
propane 62.02 2729.183
Sum 2125.61 122417.2
3.4.3.2 Table 9: Stream 6 = 261242.1 kg
Component kmol kg
Isobutane 2890.93 167673.9
nbutane 761.97 44194.63
propane 38.17 1679.49
alkylate 418.92 47694.04
Sum 4109.99 261242.1
Balance: Stream 4 = 5+6
Stream 4 = 383659.3 kg
Stream 5+6 = 122417.2 + 261242.1= 383659.1 k
3.5 DISTILLATION COLUMN (DC-101)
3.5.1.1.1 Figure 7: De-isobutanizer:
3.5.2 MATERIAL IN
3.5.2.1 Table 10: Stream 6 = 261242.1 kg
Component kmol kg
Isobutane 2890.93 167673.9
nbutane 761.97 44194.63
propane 38.17 1679.49
alkylate 418.92 47694.04
Sum 4109.99 261242.1
3.5.3 MATERIAL OUT
3.5.3.1 Table 11: Stream 11 = 203308.9 kg
Component kmol kg
Isobutane 2886.16 167397.2
n-butane 590.20 34232.16
propane 38.17 1679.49
Sum 3514.53 203308.9
3.5.3.2 Table 12: Stream 7 = 57933.24 kg
Component kmol kg
n-butane 171.75 9962.46
Isobutane 4.77 276.73
Alkylate 418.92 47694.04
Sum 595.44 57933.23
Balance:
Stream 6 = 7 + 11
Stream 6 =261242.1 kg
Stream 7+8+11 = 57933.24 + 203308.9= 261242.14 kg
3.6 DISTILLATION COLUMN (DC-102)
3.6.1.1.1
3.6.1.1.2 Figure 8: De-propanizer:
3.6.2 MATERIAL IN
3.6.2.1 Table 13: Stream 5 = 122417.2 kg
Component kmol kg
Isobutane 1791.62 103914.1
nbutane 271.96 15773.91
propane 62.02 2729.183
Sum 2125.61 122417.2
3.6.3 MATERIAL OUT
3.6.3.1 Table 14: Stream 10 = 1259.62 kg
Component kmol kg
Propane 28.62 1259.62
3.6.3.2 Table 15: Stream 9 = 121157.6 kg
Component kmol kg
Isobutane 1791.62 103914.1
nbutane 271.96 15773.92
propane 33.39 1469.56
Sum 2096.98 121157.6
Balance: Stream 5 = 9 + 10
Stream 5 = 122417.2 kg
Stream 9 + 10 = 1259.62 + 121157.6= 122417.22 kg
3.7 BALANCE TO MIXING POINT
Stream 1 + Stream 2 + Stream 12 = Stream 3
Total Amount = Stream 1 + 2 + 12
= 28560.58 + 30631.06 + 324466.5 = 383658.14 kg
3.7.1.1 Table 15: Flow rates of different streams
Stream 1
Stream 2
Stream 12
Component kmol kg
kmol kg
kmol kg
Butene
412.67 23109.52
nbutane
85.87 4980.665
85.77 4974.926
862.17 50006.08
propene
6.20 260.483
propane
4.77 209.9131
19.07 839.2908
71.57 3149.057
Iso Butane
427.87 24816.84
4677.78 271311.3
Sum
509.51 28560.58
532.71 30631.06
5611.52 324466.5
4 CHAPTER # 4:
ENERGY BALANCE
4.1 ENERGY BALANCE EQUATION
At steady State,
Overall Energy Balance can be given by equation,
4.2 HEAT OF REACTIONS
4.2.1 At 298K
4.2.2 REACTION 1
C4H8 (g) + iC4H10 (l) C8H18 (l) H298 = -90.572 kJ/gmol
H298 = -223.9 - (-134.5 + 1.172) = -90.572 kJ/gmol
4.2.3 REACTION 2
C3H6 (g) + iC4H10 (l) C7H16 (l) H298 = -83.81 kJ/gmol
H298 = -197.9-(-134.5 + 20.41) = -83.81 kJ/gmol
4.2.4 REACTION 3
C3H6 (g) + 2iC4H10 (l) C3H8 (l) + C8H18 (l) H298 = -79.16 kJ/gmol
H298 = -223.9 103.85 (20.41 2(134.5)) = -79.16 kJ/gmol
4.2.5 Heats of Formation Data: Hf (kJ/gmol): Vol. 6
C3H6 (g) = 20.41 C3H8 (l) = -103.85
C4H8 (g) = 1.172 C8H18 (l) = -223.9
iC4H10 (l) = -134.5 C7H16 (l) = -197.9
4.2.5.1.1 Figure 9: Graphical Representation of Hess Law
4.3 REACTOR (R-101)
4.3.1 Table 16: Stream 3+13:
T= 12oC & let Tref. = 25oC
Component Cp (kJ/kmol K) kmol H (kJ)
Propene 66.92 6.20 5395.504
propane 76.96 95.41 95461.71
butene 93.51 412.67 501665.9
butane 105.82 1033.82 1422218
isobutane 106.52 5105.65 7070434
H2SO4 140.97 47.69 87405.2
Water 24.65 5.29 1698.173
H1: 9.18E+06 kJ
4.3.1.1 Table 17: Stream 4+14:
T= 12oC & let Tref. = 25oC
Component Cp (kJ/kmol K) kmol H(kJ)
propane 76.96 100.19 -100246.29
butane 105.822 1033.94 -1422380.91
isobutane 106.52 4682.55 -6484507.20
2,2,4,Tmpentane 196.47 417.24 -1065710.48
2,3,Dmpentane 183.49 1.67 -3995.63
H2SO4 140.97 47.69 -87405.19
Water 24.65 5.29 -1698.17
H2: -9.17E+06 kJ
4.3.2 Heat of Reaction Added At 298 K
H298 = (-90572*412.67) + (-79160*4.57) + (-83810*1.675)
= -3.8E+07 kJ
