DESIGN OF PLANT FOR THE PRODUCTION OF 72000 TONNES/ YEAR OF 2- ETHYLHEXANOL FROM PROPYLENE AND SYNTHESIS GAS
EXECUTIVE SUMMARY
A critical approach is attempted in this project work at realizing the design objectives for
a process plant. Design, being an iterative procedure with a route of procession from the
input or feed to the stated objective(s), amidst intervening constraints, requires a careful,
well- thought- out, comprehensive specifications of the defined or desired requirements.
The stated objective in this case is the design of a 72000 tons/year capacity of a 2-
EthylHexanol (C8H18O) Plant. While many processes exist at producing 2-
EthylHexanol (2- EH), such as the Acetaldehyde Route and others developed by Shell
Corporation etc, the Oxo Process route utilizing propylene and synthesis gas as feed
components was the given route for this design work. However, important modifications
were implemented to the process description for effective process optimization, such as
to improve the conversion of efficiencies of process equipment by aid of recycle
processes.
The oxo synthesis began by reacting propylene feed and synthesis gas (CO + H2) in a
Cobalt Carbonyl (Co2(CO)8) catalyzed hydroformylation reaction. The propylene feed
input of 198.3275 kmols/hr was made up by three streams; Fresh Feed of 152.9 kmols/hr,
recycle streams from cracking unit of 42.9775 kmols/hr, and stripped propylene from
Gas- Liquid Separator 2 of 2.45 kmols/hr.
310.709 kmols/hr of synthesis gas (CO + H2) was supplied together with 218.5415
kmols/hr excess Hydrogen for use in latter processes. The hydroformylation reactor was
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at operating temperature and pressure of 130°C and 350 bar. The design temperature and
pressure however was heuristically accepted as 1.1 times of this value.
The main product of the oxo reactor was n- butyraldehyde with molar flow rate of
141.6840 kmols/hr. A side reaction produced iso- butyraldehyde of 36.1750 kmols/hr,
with a selectivity ratio of 4:1. Alcohols formed from the hydroformylation reaction
included n- butanol (9.0437), and iso butanol of 1.5073 kmols/hr. Other reactions occured
to a small extent yield 136.0750 kg of high molecular weight or heavy end compounds,
representing 1 weight % of the butyraldehyde/ butanol mixture.
A cleaner technology approach to pollution control was adopted for the plant design.
Hence, the need for thorough separation processes and purge streams to remove
extraneous components. From the hydroformylation reactor, the products were separated
with the first Gas- Liquid Separator (GLS 1), which separated the aqueous phase of
cobalt and water from the organic phase components in a process referred to as cobalt
plating. The cobalt was regenerated as an active catalyst, to save cost, and sent back to
the oxo reactor for further reaction. The organic phase of GLS-1 goes for further
separation in a second GLS which stripped the initial reactants (propylene and synthesis
gas) for recycle back to oxo reactor. Liquid phase of n-/iso- butyraldehyde, alcohols,
heavy ends and remnant water exits the GLS 2 operating at 55°C and 1 bar.
A vital separation technique was involved proceeded from GLS-2. A distillation column
1 (DC 1) with 36 trays and made of Ferritic Stainless Steel 430 is employed which gave a
top product of n-/iso- butyraldehyde and bottoms of alcohols etc. Further distillation was
employed to separate normal and iso- butyraldehyde in DC 2. The McCabe Thiele- Plot
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is of stream properties of DC 2 indicated the number of required trays as 42. Tray
thickness and spacing of 3 mm and 457.2 mm was employed for both the enriching and
rectifying section of the 25.89 m heighted DC 2. Sieve hole pitch was 15mm while
diameter was 5mm. Flooding rate of 80% was computed for both sections and it was
ratified that there was no flooding. The Murphee plate efficiency and overall column
efficiency was within acceptable ranges (> 80 %). Log Mean Temperature Difference
(LMTD) for the partial condenser was 31.51°C. Mechanical design specifications for the
DC 2 construction were computed in this report. The top product of DC 2 was mainly
iso- butyraldehyde (35.704 kmols/hr), while the bottoms was mainly n- butyraldehyde
(141.304 kmols/hr) required for 2- EH production.
To maximize output of 2- EH, the iso- butanal obtained from DC 2 operation was routed
through a cracking/ conversion process to produce original reactants. The 6461 L
capacity cracker unit had operating specifications of 275°C and 1 bar, but designed at 1.1
bar and 302.5 °C and made of Low- Alloy Steel material for good heat retention. A
recycle process was proposed for the cracker unit which had a limited conversion yield of
80%. Aldol condensation with 2 % w/w aqueous NaOH (9.2 kmols/ hr) took place on the
n- butanal product from DC 2. The Aldol condenser reactor produced 69.946 kmols/hr of
2- Ethyl hexanal, an intermediate reactant for 2- EH. (Improved recycle process for the
90% Efficient Aldol Condenser was also proposed). Subsequently, 2- Ethylhexanal
undergoes hydrogenation to give 69.247 kmols/ hr of 2- Ethyl hexanol, recovery rate of
99.8 % and 99% wt purity.
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Process design for the 2- EH also involved the control and instrumentation of the
processes and equipment to achieve the design objectives and safety. Control of operating
conditions of the oxo reactor was described, with preferred controller as Proportional
Integral Derivative (PID) Controller. A PID controller was chosen for operation to
eliminate the challenge of runaway temperature increase by the derivative component and
the offset error by the integral component. Simulation results suggested the
hydroformylation (HFR) vessel temperature was kept at safe operating condition using
coolant stream and a Temperature controller (TC) with Controller Gain Kc = 2 and
Settling Time Ti = 5min. A controller scheme was also designed for level control to avoid
the splashing of the reactants and prevent the mixing of pure tops from the bottoms. The
proposed controller was proportional controller which can tolerate offset. This controller
allows offset depending on the magnitude of the controller gain which is the only
controller parameter to be varied in this case. HFR liquid level was kept at safe fill of
85% using a bottom product valve (BPV) and a PID level controller (LC) with Kc = 2
and Ti = 10min. The mass flow rates of propylene stream and synthesis gas stream going
into hydroformylation reactor (HFR) were controlled by propylene stream valve (PV) and
synthesis gas stream valve (SGV) respectfully using a PID controller of 0.1 Kc
(Controller gain) and 5min integral time for both streams.
An acceptable design must present a process that is capable of operating under conditions
which will yield a profit. A simple costing procedure is carried out for the 2- EH Plant to
determine if the design is feasible economically or not based on certain estimates.
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Estimates were prepared using data and Chemical Engineering cost index method in
Literature, considering Port Harcourt (Rivers State, Nigeria) as the location of the plant.
Old cost information was obtained and extrapolated using the Index Method to the
present 2012 costs. These costs were then converted to Naira using appropriate foreign
exchange rates.
The Purchased Cost of Equipment (PCE) was valued at #428,171,790, while the Physical
Plant Costs (PPC) or direct costs was obtained by the factorial costing method at 3.4
times PCE, and valued at #1,455,784,086. Indirect costs were the expenses which are
not directly involved with material and labor which included design and engineering,
contractor’s fee etc, and were valued at #650,602,838.70k. The Fixed Capital Investment
(FCI) was obtained by summing up the direct and indirect costs, and valued at
#2,106,386,925.70k. The Working Capital was 15% of the FCI and both gave the Total
Capital Investment of #2,442,344,964.81k.
The start- up cost, or for first- run of plant for production, was valuated at 15% of TC1.
With a selling price at #130.56k, the 72,000 tons/year 2- Ethylhexanol plant is expected
to have a net profit of ##5,146,221,476.
Finally, procedures for safe operation and start- up of the 72000 tons/year 2-
Ethylhexanol Plant were documented.
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CONTENTS
Title Page i
Letter of Transmittal ii
Executive Summary iii
Contents viii
List of Tables xvii
List of Figures xix
Abbreviations xxi
CHAPTER ONE: INTRODUCTION 1
1.1 Background 1
1.2 2- Ethylhexanol Properties and Uses 4
1.2.1 Physical and chemical properties 4
1.2.2 Environmental fate 4
1.2.3 Uses of 2- Ethylhexanol 6
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CHAPTER TWO: LITERATURE REVIEW 8
2.1 Choice of Synthesis Route 8
2.1.1 Acetaldehyde route 8
2.1.2 Aldox process 9
2.1.3 Shell process 9
2.1.4 Oxo process 10
2.2 Specifications, Analytical, and Test Methods 14
2.3 Process Selection 15
2.4 Process Description 18
2.4.1 Problem statement 18
2.4.2 The process 18
2.4.3 Feed specifications 20
2.4.4 Utilities 20
2.5 Scope of the Design Work 20
2.5.1 Process design 20
2.5.2 Chemical engineering design 21
2.5.3 Mechanical design 21
2.5.4 Control system 21
2.5.5 Cost estimate 21
2.6 Data Supplied 22
2.6.1 Chemical reactions 22
2.6.2 Boiling points at 1 bar 23
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2.6.3 Solubilities of gases at 30 Bar in the liquid
phase of the first gas-liquid separator 23
2.6.4 Vapor-liquid equilibrium of the butyraldehydes
at 1 atm 24
CHAPTER THREE: PROPOSAL 25
3.1 Process Description 25
3.1.1 Hydroformylation reactor 25
3.1.2 Gas liquid separator 1 (GLS-1) 28
3.1.3 Gas liquid separator 2 (GLS- 2) 28
3.1.4 Distillation column 1 (DC 1) 29
3.1.5 Distillation column 2 (DC 2) 29
3.1.6 Cracker unit 29
3.1.7 Aldol reactor 30
3.1.8 Hydrogenation reactor 30
3.2 Miscellaneous Equipment 31
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CHAPTER FOUR: PROCESS DESIGN BALANCES 34
4.1 Material Balance 35
4.1.1 Hydrogenation 38
4.1.2 Aldol reactor 39
4.1.3 Distillation column (DC 2) 40
4.1.4 Cracker 43
4.1.5 Distillation column (DC) 1 44
4.1.6 Oxo reactor 45
4.1.7 Gas- liquid separator (GLS) 1 50
4.1.8 Gas- liquid separator (GLS) 2 53
4.1.9 Material balance analysis 53
4.2 Energy Balance 56
4.2.1 Hydroformylation reactor 56
4.2.2 Cracker 64
4.2.3 Energy balance analysis 68
CHAPTER FIVE: EQUIPMENT SCHEDULE AND P&ID 69
5.1 Design Conditions and Physical Properties of Oxo Reactor 69
5.2 Design Conditions and Physical Properties of Cracker 71
5.3 Design Conditions and Physical Properties of
Aldol Condenser 73
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5.4 Design Conditions and Physical Properties of
Hydrogenation Reactor 74
5.5 Capacity of Storage Tanks 75
5.5.1 Propylene feed storage tank 75
5.5.2 Synthesis gas storage tank 77
5.5.3 Hydrogen gas storage tank 77
5.4.4 2-Ethyl hexanol product storage tank 78
5.6 Materials of Construction 79
CHAPTER SIX: CHEMICAL ENGINEERING DESIGN 84
6.1 Plate Hydraulics 91
6.1.1 Enriching section 91
6.1.2 Stripping section 102
6.2 Condenser Preliminary Calculations 111
6.3 Summary of Chemical Engineering Design of DC 2 119
6.4 Notations 119
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CHAPTER SEVEN: MECHANICAL DESIGN OF N- AND ISO-
BUTYRALDEHYDE DISTILLATION COLUMN 124
7.1 Specification Details 124
7.1.1 Shell 124
7.1.2 Calculation of stresses 126
7.1.3 Design of skirt support 132
7.1.4 Design of skirt bearing plate 136
7.2 Mechanical Design for the Condenser 140
7.2.1 Shell side 140
7.2.2 Tube side 145
CHAPTER EIGHT: INSTRUMENTATION SCHEDULE AND
CONTROL SCHEME 151
8.1 Background 151
8.2 Control of the Reactor System Temperature 152
8.2.1 Sensor 154
8.2.2 The controller 155
8.2.3 The control valve 155
8.2.4 The cooling process 157
8.3 Control Scheme for the Liquid Level within the Reactor 158
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CHAPTER NINE: COST ESTIMATION AND ECONOMIC
EVALUATION OF THE PROCESS 160
9.1 Background 160
9.2 Cost Estimate of Plant Equipment 161
9.3 Estimation of Purchased Costs of Equipment (PCE) 162
9.4. Estimation of Total Investment Cost 171
9.4.1 Direct costs 171
9.4.2 Indirect costs 173
9.5 Estimation of Total Production Cost 175
9.6 Profitability Analysis 180
CHAPTER TEN: PLANT START- UP AND OPERATING
PROCEDURES 182
10.1 Background 182
10.2 General Principles 185
10.3 Start- Up 190
10.3.1 Preparation prior to initial start-up 191
10.3.1.1 Operational check-out 192
10.3.1.2 Hydrostatic testing 193
10.3.1.3 Final inspection of vessels 196
10.3.1.4 Flushing of lines 197
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10.3.1.5 Instruments 201
10.3.1.6 Acid cleaning of compressor lines 202
10.3.1.7 General notes for dry-out
and boil-out 202
10.3.1.8 Catalyst loading 203
10.3.1.9 Tightness test 203
10.3.2 Normal start-up procedures 204
10.3.2.1 Prestart-up check list 205
10.3.2.2 Make area safe 206
10.3.2.3 Utilities commissioning 206
10.3.2.4. Establish flow in the unit 206
10.3.2.5 Adjust operation to obtain quality 207
10.4 Performance Trails 207
10.5 Safety Practices 208
10.6 Shut Down and Emergency Procedures 209
10.6.1 Scheduled shutdown 210
10.6.2 Maintenance shutdown 211
10.6.3 Emergency shutdown 212
10.6.4 Reactor trips 212
10.6.5 Shutting down to a standby condition 212
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REFERENCES 213
APPENDICES 218
APPENDIX A: Mechanical Drawings for Distillation Column (DC) 2 219
APPENDIX B: Material Safety Data Sheet (MSDS) for 2- EthylHexanol 240
APPENDIX C: Simulation Graphs for Control Scheme of Oxo Reactor 248
APPENDIX D: Commissioning System File (Abridged) 254
APPENDIX E: Possible Problems, Analysis and Appropriate Action 267
CHAPTER ONE
INTRODUCTION
1.1 Background
2-Ethylhexanol (2-EH) is a clear, colourless liquid with a characteristic odour, which has
been described as sweet and floral (Genium, 1999; WHO, 1993) and as intense and
unpleasant (HSDB, 2004; Verschueren, 2001). This compound occurs naturally in food
(e.g., corn, olive oil, tobacco, tea, rice, apricots, plums, apples, nectarines, tamarind grapes,
and blueberries) and is also used as a flavor additive in foods (WHO, 1993). In the
atmosphere, 2-ethylhexanol occurs as a vapor. This compound is combustible and will
react violently with oxidizing materials and strong acids. 2-Ethylhexanol is soluble in
organic solvents but only moderately soluble in water.
The chemical formula, structure, registry numbers, synonyms and trade names for 2-ethyl
hexanol are provided in Table 1 (NIST, 2003).
2-Ethylhexanol is formulated by petrochemical synthesis (WHO, 1993). 2-Ethylhexanol is
also a valuable intermediate in the chemical and petrochemical industry. It ranks after the
lighter alcohols (methanol to butanol) as the most important synthetic alcohol. The main
outlet for 2-ethylhexanol (2-EH) is the production of phthalate plasticizers, such as di-octyl
phthalate (DOP), which are used in the manufacture of polyvinyl chloride (PVC). The next
largest outlet for 2-EH is for the manufacture of the acrylate esters which are used in 2
adhesives and surface-coating materials such as acrylic paints, in printing inks and as
impregnating agents.
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According to Ashford’s Chemicals Dictionary (2011), the production of 2- Ethylhexanol
has recorded an average annual growth rate of 2.5% from 1986 – 2000. The future of 2-
ethylhexanol demand lies in the demand for phthalates such as DOP; the largest volume
phthalate ester; and is expected to remain flat or decline slightly due to competition from
other phthalates and environmental pressure. An issue for 2-EH producers is that DOP has
been dogged by health hazard and environmental concerns, and phthalates in general are
under pressure. On the positive side, there is increasing demand for other derivatives of 2-
EH, in particular 2-ethylhexyl acrylate.
3
The industrial production of 2-ethylhexanol is by a three-step process involving the aldol
self-condensation of n-butyraldehyde followed by dehydration and hydrogenation. The n-
butyraldehyde was originally obtained from acetaldehyde via ethylene but this has been
superseded by the oxo process from propylene.
Today, nearly all 2-EH is produced by catalytic hydroformylation of propylene with
synthesis gas (carbon monoxide and hydrogen). The catalytic process now mostly uses
rhodium catalysts rather than the older cobalt hydro carbonyl catalysts.
The esters of 2-Ethylhexanol with dicarboxylic acids are excellent plasticisers for synthetic
resins and rubbers and include phthalates, adipates and sebacates .Its main application is as
a feedstock in the manufacture of low volatility esters, the most important of which is di-
(2-ethylhexyl) phthalate (DOP or DEHP). Other plasticizers that can be obtained from 2-
Ethylhexanol are the corresponding ester of adipic acid and para- hydroxylbenzoic acid.
2-Ethylhexanol is also used as a solvent and has a particular niche use in the formation of
lacquers and coatings when slow evaporation is desired. 2-Ethylhexanol is also an excellent
defoaming agent for use in the photographic, varnish, rubber latex, textile printing and
ceramic industries and can be used to advantage wherever foaming is undesirable.
2-Ethylhexanol is manufactured using the OXO process involving hydroformylation of
propylene to n-butyraldehyde followed by an Aldol condensation and reduction to produce
the ethyl hexanol.
4
1.2 2- Ethylhexanol Properties and Uses
2-Ethylhexanol (2-EH) is a clear, colorless, mobile and neutral liquid with a characteristic
odor. It is miscible with most common organic solvents, but its miscibility with water is
very limited. It enters into the reactions that are typical for primary alcohols. For instance,
it readily forms esters with various acids. 2- Ethylhexanol is the oldest, best known and
most widely used of the synthetically made higher aliphatic alcohols.
1.2.1 Physical and chemical properties
The distinct physical and chemical properties of 2-ethylhexanol are summarized in Table 2.
1.2.2 Environmental fate
During commercial operations, 2-ethylhexanol is typically released to the environment as
an air emission or in wastewater. In the atmosphere, vapor phase 2-ethylhexanol is
degraded by photochemically produced hydroxyl radicals. In water, 2- ethylhexanol will
volatilize to air or undergo biodegradation, it is not expected to adsorb to sediments or
bioconcentrate in aquatic receptors. If released to soil 2- ethylhexanol will likely volatilize
from the surface or migrate to water, adsorption to soil is not significant.
A summary of the environmental fate and half-lives for 2-ethylhexanol is provided in Table
3 (HSDB, 2004). Appendix B gives the Material Safety Data Sheet (MSDS) for safe
handling of 2- Ethylhexanol.
5
Table 2: Physical and Chemical Properties of 2-Ethylhexanol (NIST, 2003)
Property Value Reference
Molecular Weight 130.23g/mol Verschueren, 2001
Physical State Liquid Verschueren, 2001
o
Melting Point -76 C
o
Boiling Point 183.5 C Verschueren, 2001
Specific gravity (liquid) 0.8344 at 20˚Genium, 1999
C
Specific gravity (gas) (air=1) 4.49 Genium, 1999
Vapour Pressure 0.05 mmHg at 20˚C Verschueren, 2001
0.20 mmHg at 20˚C Lewis, 1997
Solubility Soluble in organic solvents Genium, 1999
Solubility in water 880 mg/l at 25˚HSDB, 2004
C
Verschueren, 2001
1000 mg/l at 20˚C
53
Henry's Law Constant 2.65 x10- atm-m/mol Genium, 1999
Octanol water p
.