DESIGN OF A PLANT FOR PRODUCTION OF 36,000kg/day OF METHYL ETHYL KETONE BY VAPOUR PHASE CATALYTIC DEHYDROGENATION OF 2-BUTANOL
A
DESIGN PROJECT
Presented to
The Department of Chemical Engineering Covenant University, Canaan Land, Ota, Ogun State, Nigeria
BY
OKOYE CHIOMA CHIDIMMA (11CF011991) MEMBER OF TEAM COVENANT
In Partial Fulfilment of the requirements for the Degree Bachelor of Engineering (Honours) in Chemical Engineering Covenant University, Canaan Land, Ota, Ogun State, Nigeria
MARCH 2016
i
CERTIFICATION This is to certify that the design project entitled “DESIGN OF A PLANT FOR PRODUCTION OF 36,000kg/day OF METHYL ETHYL KETONE BY VAPOUR PHASE CATALYTIC DEHYDROGEN
OF
2-BUTANOL”submitted
to
the
Department
of
Chemical
Engineering,Covenant University,Canaaland,Ota ,Ogun State,Nigeria,is a record of the original design carried out by Group“Covenant” Members in the Department of Chemical Engineering.
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DEDICATION First of all, I dedicate this report to the Almighty God who kept and sustained me throughout this period of this project. I would also like to dedicate this report to the staff of Chemical Engineering Department for their guidance and support throughout this project. Lastly, this report is also dedicated to my family, Mr. Sunday Okoye ,Mrs.Chioma Okoye,Onyinye Okoye and Chinonye Okoye, my friends and loved ones who provided me with support throughout this experience.
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Department of Chemical Engineering, Covenant University, Canaan Land, Ota, Ogun State, Nigeria. November 10, 2015. The Head, Department of Chemical Engineering, Covenant University, Canaan Land, Ota, Ogun State, Nigeria. Dear Sir,
LETTER OF TRANSMITTAL In accordance with the regulations of the Department of Chemical Engineering, School of chemical & Petroleum Engineering, College of Engineering and Covenant University, Canaan Land, Ota, Ogun State, Nigeria, we the members of group “COVEANANT”, do hereby submit a Design Project entitled “DESIGN OF A PLANT FOR THE PRODUCTION OF 36,000KG/DAY OF METHYL ETHYL KETONE BY VAPOUR PHASE CATALYTIC DEHYDROGENATION OF 2-BUTANOL”in partial fulfilment of the requirements for the award of the Bachelor of Engineering (Honours) Degree in Chemical Engineering at Covenant University, Canaan Land, ota, Ogun State, Nigeria. Yours faithfully,
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ACKNOWLEDGEMENT The Design project on the preparation of MEK from DEHYDROGENATION of 2-Butanol was a great chance for learning and professional development. I consider myself as a very lucky individual as I was provided with an opportunity to be part of a team that designs a plant for the preparation of MEK from Dehydrogenation of 2-Butanol. I want to use this opportunity to express my deepest gratitude and special thanks to my Supervisor Engr.Ojewumi,Miss Babatunde and the Covenant Team whose support, guidance and encouragement was a source of inspiration throughout the execution of this project. I give absolute thanks to God Almighty, whose glory and honor, brought me to the successful conclusion of this project and for keeping me safe through all the difficult times, for granting me wisdom and for always being faithful in my times of need, I give Him all the glory
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TABLE OF CONTENTS CONTENTS
PAGE
TITLE PAGE
i
CERTIFICATION
ii
DEDICATION
iii
LETTER OF TRANSMITTAL
iv
ACKNOWLEDGEMENT
v
TABLE OF CONTENTS
vi
LIST OF TABLES
vii
LIST OF FIGURES
viii
LIST OF SYMBOLS
ix
LIST OF APPENDICES
x
ABSTRACT
xi
CHAPTER ONE
13
1.0 INTRODUCTION
13
1.1 BACKGROUND OF STUDY
13
1.1.1
PHYSICAL AND CHEMICAL PROPERTIES OF 2-BUTANOL 16
1.1.2
PHYSICAL AND CHEMICAL PROPERTIES OF MEK
18
1.1.3
INDUSTRIAL APPLICATION OF MEK
21
1.2 AIM AND OBJECTIVE OF WORK
22
1.3 SIGNIFICANCE OF WORK
23
1.4 SCOPE OF WORK
23
1.5 LIMITATION OF WORK
24
CHAPTER TWO
25
2.0 THEORETICAL PRINCIPLES AND LITERATURE REVIEW
25
2.1 THEORETICAL PRINCIPLES
25
2.1.1
PRINCIPLE OF DISTILLATION
25
2.1.2
COMPRESSORS
27 vi
2.1.3
LIQUID LIQUID EXTRACTION
29
2.1.4
SEPARATOR
31
2.1.5
VAPOUR PRESSURE
32
2.1.6
PRINCIPLE OF ABSORPTION
33
2.1.7
PRINCIPLE OF VAPOURISATION
34
2.1.8
CATALYSIS
36
2.1.9
HEAT TRANSFER
36
2.1.10 CONDENSATION
38
2.2 LITERATURE REVIEW 2.2.1 2.2.2
39
SELECTION OF PROCESS ROUTE
39
REVIEW OF PAST WORKS ON MEK PRODUCTION FROM
DEHYDROGENATION OF 2-BUTANOL.
42
CHAPTER THREE
43
3.0 MATERIAL BALANCES FOR THE PLANT
43
3.1 INTRODUCTION
43
3.2 DESCRIPTION OF THE PROCESS
43
3.3 ASSUMPTION MADE
47
3.4 MATERIAL BALANCE
48
CHAPTER FOUR
54
4.0 ENERGY BALANCE FOR THE PLANT
54
4.1 INTRODUCTION
54
4.2 ENERGY BALANCE
56
REFERENCES
62
APPENDICES
64
A: MATERIAL BALANCES
64
B: ENERGY BALANCE
73
vii
LIST OF TABLES Table
Name
Page
Table 1.1-
Physical Properties of MEK
19
Table 1.2 –
Industrial application of MEK
22
Table 3.1 –
Material Balance across Reactor
48
Table 3.2 –
Material Balance across Partial Condenser
49
Table 3.3 –
Material Balance across Absorption Column
50
Table 3.4 –
Material Balance across Extraction Column
52
Table 3.5 –
Material Balance across Solvent Recovery Unit
52
Table 3.6 –
Material Balance across Distillation Column
53
Table 4.1 –
Energy Balance across Preheater
56
Table 4.2 –
Energy Balance across Vaporizer
57
Table 4.3 –
Energy Balance across Superheater 1
57
Table 4.4 –
Energy Balance across Compressor
57
Table 4.5 –
Energy Balance across Superheater 2
58
Table 4.6 –
Energy Balance across Reactor
58
Table 4.7 –
Energy Balance across Condenser
59
Table 4.8 –
Energy Balance across Absorber
60
Table 4.9 –
Energy Balance across Solvent Recovery Unit
60
Table 4.10 –
Energy Balance across Distillation Column
61
Table 4.11 –
Energy Balance across Cooler system
61
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LIST OF FIGURES Figure 1.1: Molecular Structure of MEK
15
Figure 1.2: Structure of 2-butanol
16
Figure 1.3: Chemical reaction of 2-butanol to give butane.
17
Figure 1.4: oxidation reaction of 2-butanol using KMnO4 as oxidizing agent.
17
Figure 1.5: Chemical reaction of MEK
19
Figure 1.6: Reaction of MEK with ammonia and hydrogen
20
Figure 1.7: Reaction of MEK with acetylene.
20
Figure 1.8: Halo form
20
Figure 1.9: Chemical reaction of MEK with hydrogen peroxide
21
Figure 2.1: Diagram of a Distillation Column
26
Figure 2.2: liquid liquid extraction column
29
Figure 2.3: A vapour liquid separator
32
Figure 2.4: A boiling point diagram shows how the equilibrium compositions of the components in a liquid mixture vary with temperature at a fixed pressure.
33
Figure 2.5: Heat exchanger
38
Figure 2.6: Dehydrogenation of 2-Butanol
40
Figure 3.1: Block flow Diagram of MEK production
40
Figure 3.2: Process Flow Diagram for production of MEK
46
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Symbols
LIST OF SYMBOLS Meaning
λ
Heat of Vaporization
α
Relative Volatility
R
Reflux Ratio
H
Enthalpy
Cp
Heat Capacity
D
Distillate rate
B
Bottoms rate
F
Feed rate
M
Mass flow
T
Temperature
Qc
Condenser heat
QR
Reboiler heat
Q
Heat
x
LIST OF APPENDICES
APPENDIX A: MATERIAL BALANCES CALCULATIONS
64
APPENDIX B: ENERGY BALANCES CALCULATIONS
73
xi
ABSTRACT This project was performed in order to design a plant required for the production of Methyl Ethyl Ketone of 99.9% purity at a continuous rate of 36,000 kg/day. The design shows all the processes involved and the unit operations required to achieve the product by converting the raw material 2-Butanol to Methyl Ethyl Ketone. Both material and energy balances was carried out across the various unit operations for the process. A detailed work on the material and energy balance calculations is contained in this report
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CHAPTER ONE 1. INTRODUCTION Process design can be the design of new facilities or it can be the modification or expansion of existing facilities. The design starts at a conceptual level and ultimately ends in the form of fabrication and construction plans. It is an innovation activity gaps in the industrial world and provide lasting and innovative solutions to the gaps. The activity aimed at providing the most economically feasible and effective procedure to either manufacture a new or an existing product.in this case MEK (methyl Ethyl ketone),which is an important industrial solvent. Chemical engineering has consistently been one of the highest paid engineering professions. There is a demand for chemical engineers in many sectors of industry, including the traditional processing industries: chemicals, polymers, fuels, foods, pharmaceuticals, and paper, as well as other sectors such as electronic materials and devices, consumer products, mining and metals extraction, biomedical implants, and power generation. The reason that companies in such a diverse range of industries value chemical engineers so highly is the following: I.
The creation of plans and specifications and the prediction of the financial outcome if the plans were implemented is the activity of chemical engineering design. Design is a creative activity, and as such can be one of the most rewarding and satisfying activities undertaken by an engineer. The design does not exist at the start of the project. The designer begins with a specific objective or customer need in mind and, by developing and evaluating possible designs, arrives at the best way of achieving that objective—be it a better chair, a new bridge, or for the chemical engineer, a new chemical product or production process. When considering possible ways of achieving the objective, the designer will be constrained by many factors, which will narrow down the number of possible designs
II.
Starting from a vaguely defined problem statement such as a customer need or a set of experimental results, chemical engineers can develop an understanding of the important underlying physical science relevant to the problem and use this understanding to create a plan of action and set of detailed specifications which, if implemented, will lead to a predicted financial outcome. 13
III.
Before the commencement of work, the designer is supposed to provide as complete, and as simple, a statement of the necessities as possible. If in any case the requirement (need) arises from outside the design group, from a customer or from another department, then the designer will have to elucidate the real requirements through discussion. When writing specifications for others, such as for the mechanical design or purchase of a piece of equipment, the design engineer should be aware of the restrictions (constraints) that are being placed on other designers. A well-thought-out, comprehensive specification of the requirements for a piece of equipment defines the external constraints within which the other designers must work.
1.1 BACKGROUND OF STUDY Methyl ethyl ketone (MEK), also known as 2-butanone, is a colorless organic liquid with an acetone-like odor and has a low boiling point. It is miscible partially with water and many conventional organic solvents and also forms azeotropes with a number of organic liquids. MEK can be produced using dehydrogenation of secondary butyl alcohol and as a byproduct of butane oxidation. For the purpose of this study, the dehydrogenation of secondary butyl alcohol will be considered. (Arora & Sharma, November 2015) MEK may be irriating to eyes,mucos membrances,and in high concentrations,narcotic .MEK is similar to but more irritating than acetone.the vapor is irritating to mucos membrances and conjunctiva.no serious poisonings were reported in man except for dermatitis.dermatitis can result if excessive repeated prolonged skin contact occurs.Minor skin contacts have been shown to cause no evidence of irritation .MEK can recognized at 25ppm by its odor,which is similar to acetone but more irritating.the warning properties prevent inadvertent exposure to toxic levels. MEK is used industrially as a solvent in the manufacture of adhesives, protective coatings, inks and magnetic tapes. It is also the preferred extraction solvent for dewaxing lube oil. In addition to industrial uses, methyl ethyl ketone is also used in various household products, including paints, paint removers, varnishes and glues. Methyl ethyl ketone may enter the environment during its production, transport and use. It may also be released from vehicle exhausts, natural sources and during the breakdown of other chemicals. MEK is distinguished by its exceptional solvency, which enables it to formulate higher-solids protective coatings. The 14
molecular formula of methyl ethyl ketone is CH3COCH2CH3; its molecular structure is given as:
Figure 1.1: Molecular Structure of MEK (wikipedia, wikipedia/MEK-molecularstructure, 2015) Because of MEK’s high reactivity, it is estimated to have a short atmospheric lifetime of approximately eleven hours. For the general population, exposure to methyl ethyl ketone can occur from cigarette smoking. People may also breathe in small amounts when using household products that contain methyl ethyl ketone. If exposed to methyl ethyl ketone, the potential adverse health effects that may occur depend on the way people are exposed and the amount to which they are exposed. Breathing in high levels of methyl ethyl ketone vapour can cause irritation of the nose, throat and lungs and chest tightness. Ingestion may cause inflammation of the mouth and stomach upsets. Methyl ethyl ketone can be absorbed into the body following through inhalation, ingestion or prolonged skin exposure causing headache, dizziness, tiredness, slurred speech, low temperature, fitting and coma. Heart problems and high levels of blood sugar can also occur. (Arora & Sharma, November 2015)
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1.1.1 PHYSICAL AND CHEMICAL PROPERTIES OF 2-BUTANOL 1.1.1.1
PHYSICAL PROPERTIES:
2-Butanol is a secondary alcohol with formula C4H7OH which is produced in a two (2)-step process from hydration of butanes. It can also be manufactured industrially by the hydration of 1butene in the presence of sulphuric acid. It is used as solvent for paints and resins, manufacture of industrial cleaners, perfumes; it serves as a flavoring agent. Physical properties are:
Colorless liquid
Strong alcoholic odour
Flash point below 26oC
Boiling point at 99.5oC
Melting point: −115 °C
Density: 0.808 g/mL at 25 °C
Vapor density : 2.6 (vs air)
Vapor pressure : 12.5 mm Hg ( 20 °C)
Refractive index: n20/D 1.397(lit.)
Water Solubility : 12.5 g/100 mL (20 ºc) (wikipedia, 2-Butanol, 2015)
Figure 1.2: Structure of 2-butanol
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1.1.1.2
CHEMICAL PROPERTIES
2-butanol which is a secondary alcohol has molecular formula of C4H10O and molecular mass 74.12 gmol-1. It can be easily oxidized as well as undergo elimination (dehydration) and substitution reactions. 2-butanol is dehydrated (removal of H2O) on heating with concentrated sulphuric acid to give butane.
Figure 1.3: Chemical reaction of 2-butanol to give butane. 2-butanol are oxidized, by dehydrogenation, to form butanal and butanone respectively. The oxidation can be achieved using oxidizing agents such as KMnO4 or K2Cr207.The reactions involve the loss of the -OH hydrogen together with a hydrogen atom from the adjacent alkyl group.
Figure 1.4: oxidation reaction of 2-butanol using KMnO4 as oxidizing agent. 2-butanol undergoes substitution reaction when reacted with sodium. The acidic part of the OH group shows up in their reaction with reactive metals (such as sodium) to liberate hydrogen gas. Specifically, in relation to our study, and the production of Methyl Ethyl Ketone. A notable reaction undergone is the dehydration reaction which when carried out on the 2-butanol, an elimination reaction in regards to the molecules present in the compound is observed. (wikipedia, 2-Butanol, 2015)
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1.1.2 PHYSICAL AND CHEMICAL PROPERTIES OF MEK 1.1.2.1
PHYSICAL PROPERTIES
MEK is a low boiling solvent with an atmospheric boiling point of 175.3 0F (79.60C). Methyl Ethyl Ketone (MEK) is a chemically stable compound also known as 2-butanone. MEK is a flammable, colorless liquid possessing a typical ketonic odor. It has very good solvent properties, a fast evaporation rate, and is miscible with organic solvents. Some of the physical properties are listed below.
Boiling point at 1 atm, 0C Azeotrope with water, bp, 0C Wt.% ketone in vapor Auto ignition temperature, 0C Coefficient of cubic expansion, per 0C Critical pressure, atm Critical temperature , 0C Density, g/mL at 200C Dielectric constant Dipole moment, debye units Electrical conductivity, mho Boiling point at 1 atm, 0C Azeotrope with water , bp, 0C Wt.% ketone in vapor Auto ignition temperature, 0C Coefficient of cubic expansion, per 0C Critical pressure, atm Critical temperature , 0C Density, g/mL at 200C Dielectric constant Dipole moment, debye units Electrical conductivity, mho conductivity, mho Freezing point, 0C Heat of combustion, cal/g Heat of fusion, cal/g Heat of vaporization, cal/g
79.6 73.4 88.7 515.6 0.00119 43 260 0.8037 18.51 2.74 5.0 x 10-8 79.6 73.4 88.7 515.6 0.00119 43 260 0.8037 18.51 2.74 5.0 x 10-8 5.0 x 10-8 -86.3 8084 24.7 106 18
Molecular weight Refractive index nD Ketone in water Water in ketone Solubility parameter Specific heat, cal/g 0C Surface tension, dyn/cm
72.104 1.3791 26.3 11.8 9.3 0.549 24.6
Table 1.1: Physical properties of MEK (Arora & Sharma, November 2015)
1.1.2.2
CHEMICAL PROPERTIES
Methyl Ethyl ketone can be widely utilized in chemical synthesis. Its reactivity centers around the carbonyl group and its adjacent hydrogen atoms. Condensation, ammonolysis, halogenations, and oxidation can be carried out under the proper conditions. Some typical reactions are described below.
Figure 2.5: Chemical reaction of MEK Self-Condensation: Aldol condensation of 2 moles of MEK yields a hydroxy ketone, which readily dehydrates to an unsaturated ketone: Condensation with other Compounds: Reaction with aldehydes gives higher ketones, as well as ketals and cyclic compounds, depending on reaction conditions. β - ii ketones are produced by the condensation of MEK with aliphatic esters. MEK condenses with glycols and organic oxides to give derivatives of dioxolane. Sec-Butyl amine is formed by reacting MEK with aqueous ammonia and hydrogen: 19
Figure 1.6: Reaction of MEK with ammonia and hydrogen. An excess of MEK in this reaction will produce di-sec-butyl amine. Reacting MEK with acetylene gives methyl pentynol, a hypnotic compound:
Figure 1.7: Reaction of MEK with acetylene. (Arora & Sharma, November 2015)
Halo form reaction: This is a chemical reaction where a halo form (CHX3, where X is a halogen) is produced by the exhaustive halogenation of a methyl ketone (a molecule containing the R–CO–CH3 group) in the presence of a base. R may be alkyl or aryl. The reaction can be used to produce chloroform (CHCl3), bromoform (CHBr3), or iodoform (CHI3). This reaction was traditionally used as a chemical test for qualitative organic analysis to determine the presence of a methyl ketone, or a secondary alcohol oxidizable to a methyl ketone through the iodoform test. In organic chemistry, this reaction may be used to convert a terminal methyl ketone into the analogous carboxylic acid. (L. Cao, 2015)
Figure 1.8: Halo form reaction 20
Miscellaneous Reactions Oxidation of MEK with oxygen produces diacetyl, a flavoring material. Chlorination yields mixtures of several monochloro and dichloride derivatives in various percentages depending on reaction conditions. The reaction of MEK with hydrogen peroxide gives a mixture of peroxides and hydro peroxides which is used to cure polyester resins at room temperature:
Figure 1.9: Chemical reaction of MEK with hydrogen peroxide MEK peroxides are widely used as catalysts for the polymerization of polyester resins at room temperature. The condensation product of MEK and m-phenyl diamine is an efficient curing agent for epoxy resins. MEK and cobalt acetate function together as a specific catalyst for single-stage oxidation of p-xylene to terephthalic acid. Aliphatic monoketones, such as MEK also function as catalysts in the polymerization of polyethylene terephthalate where, it is claimed, they speed condensation times and cause less yellowing of the polymer than antimony trioxide. MEK is also used in the preparation of complex catalysts used in the syndiotacic polymerization of α- olefins such as propylene. Phenol, glyoxal, formaldehyde, acetaldehyde, furfuraldehyde, and other chemicals can be reacted with MEK to form resins useful for adhesives, coatings, molded products, and electrical insulation. MEK reacts with acrylonitrile to produce a dinitrile, which upon hydrogenation produces amines. (Perona, 2004)
1.1.3 INDUSTRIAL APPLICATION OF METHYL ETHYL KETONE (MEK) 1.1.3.1 as a solvent: Butanone is an effective and common solvent and is used in processes involving gums, resins, and cellulose acetate and nitrocellulose coatings and in vinyl films. For this reason it finds use in the manufacture of plastics, textiles, in the production of paraffin wax, and in household products such as lacquer, varnishes, paint remover, a denaturing agent for denatured alcohol, 21
glues, and as a cleaning agent. It has similar solvent properties to acetone but has a significantly slower evaporation rate. Butanone is also used in dry erase markers as the solvent of the erasable dye. (wikipedia, industrial application of MEK, 2015) 1.1.3.2 as a welding agent: As butanone dissolves polystyrene, it is sold as "polystyrene cement" for use in connecting together parts of scale model kits. Though often considered an adhesive, it is actually functioning as a welding agent in this context. (wikipedia, industrial application of MEK, 2015)
MEK is consumed in large quantities in a variety of industries. Some industries and their various application of MEK is listed below. INDUSTRY Adhesive manufacture Electroplating Electroplating Laboratory chemicals Machinery manufacture and repair Metal degreasing Paint manufacture Paint stripping Paper coating Pesticide manufacturing (insecticides) Printing
APPLICATION Carpet adhesive solvents Cold-cleaning solvents Vapor degreasing solvents Solvents-extraction Solvents Solvents Solvents Solvents Solvents Solvents Solvents for flexography and gravure printing
Table 1.2: industrial application of MEK (Arora & Sharma, November 2015)
1.2 AIM AND OBJECTIVES OF THE DESIGN PROJECT The aim of this design is to design a plant with a capacity of 36,000kg/day that produces Methyl Ethyl Ketone (MEK) of 99.9% purity by vapour phase catalytic dehydrogenation of 2butanol. The objectives of the design project are to:
Design a plant for the continuous production process of MEK;
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1.3
Use cost efficient and optimal energy methods for production;
Obtain a high percentage purity of the product;
Incorporate zinc-oxide brass as the reaction catalyst;
Calculate the material and energy balances of the plant;
Obtain mechanical and chemical design of the plant; and
Perform HAZOP analysis of process equipment’s
SIGNIFICANCE OF WORK Methyl Ethyl Ketone (MEK) is a highly useful and sought after solvent whose application
cut across so many industries such as paints,coating, printing and machinery industries. The design project would to a large extent bring clearer insight on the use of vapour phase dehydrogenation of 2-butanol to maximise the production of MEK.
1.4
SCOPE OF WORK This Report tries to show how economics, safety, environmental considerations and
operability influence the choices taken in conveyig the task to fulfilment and also the various contributions made by the various areas of study which includes; •
Process Design- this area involves a well detailed Process flow Diagrams (PFD), Detailed
Equipment lists, An estimated cost list for the equipment, a detailed material balance and an overall Energy balance for all the plant items. •
Mechanical Design- Provision of recommendations on the mechanical design of the
secondary alcohol vaporizer, absorber, distillation column etc and preparation of mechanical design specifications for key processes •
Chemical Engineering Design- Preparation of a detailed chemical Engineering design of
all items of equipment and a design specification sheet for all the items.
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1.5
LIMITATIONS OF WORK
The limitation of this design project is that one is limited to only use one process of producing methyl ethyl ketone which is the vapor phase catalytic dehydrogenation of 2Butanol
MEK has come under fire due to some of its properties. It has been touted of being toxic to the ozone layer thereby leading to global warming; it has also been linked to being carcinogenic even though this has not been proved. Some countries have placed MEK on their Hazard control lists.
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CHAPTER TWO 2. THEORETICAL PRINCIPLES AND LITERATURE REVIEW 2.1 THEORETICAL PRINCIPLES 2.1.1PRINCIPLES OF DISTILLATION: Distillation is separation process based on a strategy of isolating the constituents of mixture (either a fluid or gaseous). It is a physical process and not a chemical process utilizing the difference in the boiling temperatures of the constituents to separate them from the each other. In this project, we are dealing with alcoholic distillation, a way of separating secondary alcohol, 2buatanol can be separated from Methyl ethyl ketone (MEK) based on the boiling points (79.64 °C (175.35 °F; 352.79 K) for MEK and 98 to 100 °C; 208 to 212 °F; 371 to 373 K for 2-butanol). (wikipedia, 2-Butanol, 2015) Distillation can take place either in pure components also known as a complete separation or in a partial separation. Distillation in the production of methyl ethyl ketone for dehydrogenation of 2butanol as a separation process is inevitable. Also, distillation separation of components from a liquid mixture depends on certain characteristics of the components such as differences in boiling points of the individual components, concentrations of the components present, depends on the vapour pressure characteristics of liquid mixtures, difference in volatility between the components. (Tham, 2009)
3 Relative Volatility Relative volatility is a measure comparing the vapor pressures of the components in a liquid mixture of chemicals. (https://en.wikipedia.org/wiki/Relative_volatility, Retrieved October 2015). For a liquid mixture of two components (called a binary mixture) at a given temperature and pressure, the relative volatility is defined as: (𝑦 ⁄𝑥 )
𝛼 = (𝑦 𝑖 ⁄𝑥𝑖 ) = 𝐾𝑖 ⁄𝐾𝑗 𝑗
𝑗
Where, = the relative volatility of the more volatile component to the less volatile component
25
= the vapor–liquid equilibrium concentration of component in the vapor phase = the vapor–liquid equilibrium concentration of component in the liquid phase = the vapor–liquid equilibrium concentration of component
in the vapor phase
= the vapor–liquid equilibrium concentration of component
in the liquid phase
= Henry's law constant (also called the K value or vapor-liquid distribution ratio) of a component
Figure 2.1: Diagram of a Distillation Column
26
2.1.2 COMPRESSORS Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible; while some can be compressed, the main action of a pump is to pressurize and transport liquids. (Perry et al, 2007) 2.1.2.2TYPES OF COMPRESSORS 2.1.2.3 CENRTIFUGAL COMPRESSORS Centrifugal compressors use a rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants. (Dixon, 1978) Their application can be from 100 horsepower (75 kW) to thousands of horsepower. With multiple staging, they can achieve high output pressures greater than 10,000 psi (69 MPa). Many large snowmaking operations (like ski resorts) use this type of compressor. They are also used in internal combustion engines as superchargers and turbochargers. Centrifugal compressors are used in small gas turbine engines or as the final compression stage of mediumsized gas turbines. (Aungier,2000) 2.1.2.4 DIAGONAL COMPRESSORS Diagonal or mixed-flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to an axial rather than radial direction. 2.1.2.5 RECIPROCATING COMPRESSORS Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors well over 1,000 hp (750 kW) are commonly found in large industrial 27
and petroleum applications. Household, home workshop, and smaller job site compressors are typically reciprocating compressors 1½ hp or less with an attached receiver tank. (Bloch et al, 1996) Other types of compressors include:
IONIC LIQUID PISTION COMPRESSORS
ROTARY SCREW COMPRESSORS
ROTARY VANE COMPRESSORS
SCROLL COMPRESSORS
DIAPHGRAM COMPRESSORS
AIR BUBBLE COMPRESSOR
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2.1.3 LIQUID LIQUID EXTRACTION: Liquid–liquid extraction (LLE) consists in transferring one (or more) solute(s) contained in a feed solution to another immiscible liquid (solvent). The solvent that is enriched in solute(s) is called extract. The feed solution that is depleted in solute(s) is called raffinate.
Figure 2.2: liquid liquid extraction column (wikipedia/liquid liquid extraction column, 2015) Liquid–liquid extraction is a basic technique in chemical laboratories, where it is performed using a variety of apparatus, from separatory funnels to countercurrent distribution equipment.This type of process is commonly performed after a chemical reaction as part of the work-up. The term partitioning is commonly used to refer to the underlying chemical and physical processes involved in liquid–liquid extraction, but on another reading may be fully synonymous with it. The term solvent extraction can also refer to the separation of a substance from a mixture by preferentially dissolving that substance in a suitable solvent. In that case, a soluble compound is separated from an insoluble compound or a complex matrix. (chemwiki, 2015)
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Solvent extraction is used in nuclear reprocessing, ore processing, the production of fine organic compounds, the processing of perfumes, the production of vegetable oils and biodiesel, and other industries. Liquid–liquid extraction is possible in non-aqueous systems: In a system consisting of a molten metal in contact with molten salts, metals can be extracted from one phase to the other. This is related to a mercury electrode where a metal can be reduced, the metal will often then dissolve in the mercury to form an amalgam that modifies its electrochemistry greatly. For example, it is possible for sodium cations to be reduced at a mercury cathode to form sodium amalgam, while at an inert electrode (such as platinum) the sodium cations are not reduced. Instead, water is reduced to hydrogen. A detergent or fine solid can be used to stabilize an emulsion, or third phase In solvent extraction, a distribution ratio is often quoted as a measure of how well-extracted a species is. The distribution ratio (D) is equal to the concentration of a solute in the organic phase divided by its concentration in the aqueous phase. Depending on the system, the distribution ratio can be a function of temperature, the concentration of chemical species in the system, and a large number of other parameters. Note that D is related to the ΔG of the extraction process. In solvent extraction, two immiscible liquids are shaken together. The more polar solutes dissolve preferentially in the more polar solvent, and the less polar solutes in the less polar solvent. After performing liquid-liquid extraction, a quantitative measure must be taken to determine the ratio of the solution’s total concentration in each phase of the extraction. This quantitative measure is known as the distribution ratio or distribution coefficient. (chemwiki, 2015) Separation factors: The separation factor is one distribution ratio divided by another; it is a measure of the ability of the system to separate two solutes. For instance, if the distribution ratio for nickel (DNi) is 10 and the distribution ratio for silver (DAg) is 100, then the silver/nickel separation factor (SFAg/Ni) is equal to DAg/DNi = SFAg/Ni = 10. (chemwiki, 2015)
30
Decontamination factor: This is used to express the ability of a process to remove a contaminant from a product. For instance, if a process is fed with a mixture of 1:9 cadmium to indium, and the product is a 1:99 mixture of cadmium and indium, then the decontamination factor (for the removal of cadmium) of the process is 0.11 / 0.01 = 11 (chemwiki, 2015) 2.1.4 PRINCIPLES OF SEPARATION: In chemistry and chemical engineering, a separation process, or a separation technique, or simply a separation, is a method to achieve any mass transfer phenomenon that converts a mixture of substances into two or more distinct product mixtures (which may be referred to as fractions) at least one of which is enriched in one or more of the mixture's constituents. In some cases, a separation may fully divide the mixture into its pure constituents. Separations are carried out based on differences in chemical properties or physical properties such as size, shape, mass, density, or chemical affinity, between the constituents of a mixture. They are often classified according to the particular differences they use to achieve separation. (wikipedia, 2015) SEPARATOR: A vapor–liquid separator is a device used in several industrial applications to separate a vapor–liquid mixture. A vapor–liquid separator may also be referred to as a flash drum, knockout drum, knock-out pot, compressor suction drum or compressor inlet drum. When used to remove suspended water droplets from streams of air, it is often called a demister. Method of operation: For the common variety, gravity is utilized in a vertical vessel to cause the liquid to settle to the bottom of the vessel, where it is withdrawn. In low gravity environments such as a space station, a common liquid separator will not function because gravity is not usable as a separation mechanism. In this case, centrifugal force needs to be utilized in a spinning centrifugal separator to drive liquid towards the outer edge of the chamber for removal. Gaseous components migrate towards the center.
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For both varieties of separator, the gas outlet may itself be surrounded by a spinning mesh screen or grating, so that any liquid that does approach the outlet strikes the grating, is accelerated, and thrown away from the outlet. The vapor travels through the gas outlet at a design velocity which minimizes the entrainment of any liquid droplets in the vapor as it exits the vessel. The feed to a vapor–liquid separator may also be a liquid that is being partially or totally flashed into a vapor and liquid as it enters the separator. (MIT, 2015)
Figure 2.3: A vapour liquid separator (wikipedia, 2015)
2.1.5 Vapor Pressure The vapor pressure of a liquid at a particular temperature is the equilibrium pressure exerted by molecules leaving and entering the liquid surface. (Tham, 2009) Special points regarding vapor pressure are as follows:
Energy input raises vapor pressure
Vapor pressure is related to boiling
The ease with which a liquid boils depends on its volatility 32
The vapor pressure and hence the boiling point of a liquid mixture depends on the relative amounts of the components in the mixture.
Distillation occurs because of the differences in the volatility of the components in the liquid mixture.
Boiling Point Diagram Boiling point diagram shows how the equilibrium compositions of the components in a liquid mixture vary with temperature at a fixed pressure.
Figure 2.4: A boiling point diagram shows how the equilibrium compositions of the components in a liquid mixture vary with temperature at a fixed pressure. (Tham, 2009)
The boiling point of A is that at which the mole fraction of A is 1. The boiling point of B is that at which the mole fraction of A is 0. In this example, A is the more volatile component and therefore has a lower boiling point than B. The upper curve in the diagram is called the dew-point curve while the lower one is called the bubble-point curve. The dew-point is the temperature at which the saturated vapour starts to condense. The bubble-point is the temperature at which the liquid starts to boil. The region above the dew-point curve shows the equilibrium composition of the superheated vapour while the region below the bubble-point curve shows the equilibrium composition of the sub-cooled liquid. (Tham, 2009) The difference between liquid and vapour compositions is the basis for distillation operations. 2.1.6 PRINCIPLES OF ABSORPTION: Absorption, or gas absorption, is a unit operation used in the chemical industry to separate gases by washing or scrubbing a gas mixture with a suitable liquid. The absorbent used for this project is water. 33
The fundamental physical principles underlying the process of gas absorption are the solubility of the absorbed gas and the rate of mass transfer. One or more of the constituents of the gas mixture dissolves or is absorbed in the liquid and can thus be removed from the mixture. In some systems, this gaseous constituent forms a physical solution with the liquid or the solvent, and in other cases, it reacts with the liquid chemically. (wikipedia, absorption_chemistry, 2015) The purpose of such scrubbing operations may be any of the following: gas purification (e.g., removal of air pollutants from exhausts gases or contaminants from gases that will be further processed), product recovery, or production of solutions of gases for various purposes. Gas absorption is usually carried out in vertical counter current columns. The solvent is fed at the top of the absorber, whereas the gas mixture enters from the bottom .The absorbed substance is washed out by the solvent and leaves the absorber at the bottom as a liquid solution . The solvent is often recovered in a subsequent stripping or desorption operation. This second step is essentially the reverse of absorption and involves counter current contacting of the liquid loaded with solute using and inert gas or water vapor. (Terry, 2015) The absorber may be a packed column, plate column, spray column , venturi scrubbers , bubble column , falling films , wet scrubbers ,stirred tanks. Tray absorbers are used in applications where tall columns are required, because tall, random-type packed towers are subject to channeling and maldistribution of the liquid streams. Plate towers can be more easily cleaned. Plates are also preferred in applications having large heat effects since cooling coils are more easily installed in plate towers and liquid can be withdrawn more easily from plates than from packings for external cooling. Tray columns have got some disadvantage. These are slow reaction rate processes, higher pressure drops than packed beds and plugging and fouling may be occur. (Terry, 2015) 2.1.7 PRINCIPLES OF VAPOURIZATION: A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another one by heat transfer. The term is most commonly used to describe transitions between solid, liquid and gaseous states of matter, and, in rare cases, plasma. A phase of a
34
thermodynamic system and the states of matter have uniform physical properties. The change from liquid to gas is vapourization. Vaporization happens at any boiling point. It occurs in two forms; Evaporation and Boiling. It is a phase transition from the liquid phase to vapor (a state of substance below critical temperature and critical pressure) that occurs at temperatures below the boiling temperature at a given pressure. Evaporation usually occurs on the surface. Evaporation may occur when the partial pressure of vapor of a substance is less than the equilibrium vapour pressure. We define the evaporation process as one that starts with a liquid product and ends up with a more concentrated, but still liquid and still pumpable concentrate as the main product from the process. It occurs at the liquid’s surface. (Adams, 1926) The major requirement in the field of evaporation technology is to maintain the quality of the liquid during evaporation and to avoid damage to the product. This may require the liquid to be exposed to the lowest possible boiling temperature for the shortest period of time. The most common types of evaporators are: 1.
Falling Film Evaporators
2.
Rising Film Evaporators
3.
Forced Circulation Evaporators
4.
Plate Evaporators Boiling is a phase transition from the liquid phase to gas phase that occurs at or above the
boiling temperature. Boiling, as opposed to evaporation, occurs below the surface.
Boiling is a
rapid vaporization that occurs at or above the boiling temperature and at or below the liquid's surface.
35
The boiling point corresponds to the temperature at which the vapour pressure of the liquid equals the atmospheric pressure. If the liquid is open to the atmosphere (that is, not in a sealed vessel), it is not possible to sustain a pressure greater than the atmospheric pressure, because the vapour will simply expand until its pressure equals that of the atmosphere. For this reason, boiling point varies with the pressure of the environment. Evaporation is a surface phenomenon whereas boiling is a bulk phenomenon. (wikipedia, vapourization, 2015) 2.1.8 CATALYSIS: Catalysts are substances that speed up a reaction but which are not consumed by it and do not appear in the net reaction equation. In addition, catalysts affect the forward and reverse rates equally; this means that catalysts have no effect on the equilibrium constant and thus on the composition of the equilibrium state. (sciencezen, 2015) Catalysts function by allowing the reaction to take place through an alternative mechanism that requires a smaller activation energy. This change is brought about by a specific interaction between the catalyst and the reaction components. Recall that the rate constacnt of a reaction is an exponential function of the activation energy, so even a modest reduction of E a can yield an impressive increase in the rate. Catalysts are conventionally divided into two categories: homogeneous and heterogeneous. Enzymes, natural biological catalysts, are often included in the former group, but because they share some properties of both but exhibit some very special properties of their own they are treated here as a third category. (chemwiki/catalysis, 2015)
2.1.9 HEAT TRANSFER Basics of Heat Transfer In the simplest of terms, the discipline of heat transfer is concerned with only two things: temperature, and the flow of heat. Temperature represents the amount of thermal energy available, whereas heat flow represents the movement of thermal energy from place to place. (Efunda, 2015)
36
On a microscopic scale, thermal energy is related to the kinetic energy of molecules. The greater a material's temperature, the greater the thermal agitation of its constituent molecules (manifested both in linear motion and vibrational modes). It is natural for regions containing greater molecular kinetic energy to pass this energy to regions with less kinetic energy. Several material properties serve to modulate the heat transferred between two regions at differing temperatures. Examples include thermal conductivities, specific heats, material densities, fluid velocities, fluid viscosities, surface emissivity, and more. Taken together, these properties serve to make the solution of many heat transfer problems an involved process. (Efunda, 2015) Heat Transfer Mechanisms Heat transfer mechanisms can be grouped into 3 broad categories namely: 1. Conduction 2. Convection 3. Radiation. Conduction: Regions with greater molecular kinetic energy will pass their thermal energy to regions with less molecular energy through direct molecular collisions, a process known as conduction. In metals, a significant portion of the transported thermal energy is also carried by conductionband electrons. (wikipedia, conduction, 2015) Convection: When heat conducts into a static fluid it leads to a local volumetric expansion. As a result of gravity-induced pressure gradients, the expanded fluid parcel becomes buoyant and displaces, thereby transporting heat by fluid motion (i.e. convection) in addition to conduction. Such heatinduced fluid motion in initially static fluids is known as free convection. (wikipedia, wikipedia/convection, 2015) Radiation: All materials radiate thermal energy in amounts determined by their temperature, where the energy is carried by photons of light in the infrared and visible portions of the electromagnetic spectrum. When temperatures are uniform, the radiative flux between objects is in equilibrium
37
and no net thermal energy is exchanged. The balance is upset when temperatures are not uniform, and thermal energy is transported from surfaces of higher to surfaces of lower temperature. (wikipedia, wikipedia/radiation, 2015) Heat exchanger is a device built for heat transfer from one medium to another. Diagram of a Heat exchanger is shown below.
Figure 2.5: Heat exchanger Heat exchanger (Alaqua, 2015)
2.1.9 CONDENSATION: Condensation is the change of the physical state of matter from gas phase into liquid phase. It can also be defined as the change in the state of water vapor to liquid water when in contact with a liquid or solid surface or cloud condensation nuclei within the atmosphere. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition. Condensation is deposition of a liquid or a solid from its vapour, generally upon a surface that is cooler than the adjacent gas. A substance condenses when the pressure exerted by its vapour exceeds the vapour pressure of the liquid or solid phase of the substance at the temperature of the surface where condensation occurs. Heat is released when a vapour condenses. Unless this heat is removed, the surface temperature will increase until it is equal to that of the surrounding vapour.
38
Partial condensation is a separation operation used when the feed mixture consists of different chemical species that have different tendencies to condensate/evaporate (different boiling point). By removing heat from a gas feed mixture, part of components will condensate, thus the partial condensation. The liquid has the tendency to go on the bottom of the fraction column and the vapors will have the tendency to separate from the liquid and move to the top of the column. The property that makes this separation possible is the volatility of the components. A component with a higher volatility will evaporate faster, and thus has the tendency to move up to the top of the column. The components with a lower volatility will remain on the bottom of the column, as a liquid phase. The main problem with this kind of separation is that usually, the components have a low volatility range which means it is quite difficult to perform the operation of separation through only one partial condensation/vaporization process. (WW2010, 2015) 2.2 LITERATURE REVIEW 2.2.1 SELECTION OF PROCESS ROUTE: There are various ways in which MEK can be produced some of the methods are listed below and emphasis made on the preferred one. 1. Vapor phase catalytic dehydrogenation of 2- Butanol. 2. Liquid phase oxidation of n-Butane. 3. Direct oxidation of n-Butanes, Hoechst-Wacker process. 4. Direct oxidation of n-Butanes, Maruzen process Commercially, MEK is predominantly produced by the catalytic dehydrogenatio of SBA in vapor phase over ZnO or Brass catalyst. It can, however be produced by the selective direct oxidation of the olefin in a variety of processes, including the HoechstWacker-type process employing a palladium(II) catalyst . Most MEK (88%) is produced today by dehydrogenation of 2-butanol. 2-butanol can be easily produced by the hydration of n-butenes(from petrochemically produced C4 raffinates). The 39
remaining MEK is produced by process in which liquid butane is catalytically cracked giving both acetic acid and MEK. The vapor phase dehydrogenation process gives high conversion of 2-butanol and high selectivity of MEK of about 95 mole%. Other advantages of this process include better yield, longer catalyst life, simple production separation and lower energy consumption. Of all the processes, it has been found that dehydrogenation of 2-butabol has more advantages and is more economical compared to other processes, so this process has been selected for design. The process is further explained below. VAPOR PHASE DEHYDROGENTAION OF 2-BUTANOL: MEK is prepared by vapor phase dehydrogenation of 2-butanol. A 2 step process from butanes , which are first hydrated to give 2-butanol, is used. The dehydrogenation of 2-butanol is an exothermic reaction (51 KJ/Kgmol). The reaction is as follows.
Figure2.6: Dehydrogenation of 2-butanol. The equilibrium constant for 2-butanol can be calculated as follows: log Kp = -2790/T + 1.51*log T + 1.856 Where T = reaction temperature, K
Kp= equilibrium constant, bar.
The MEK concentration in the reaction mixture increases and reaches its maximum at approximately 3500C. Copper, Zinc or Bronze are used as catalysts in gas phase dehydrogenation. Commercially used catalysts are reactivated by oxidation, after 3 to 6 months use. They have a life expectance of several years.
40
Sec-butyl alcohol is dehydrogenated in a multiple tube reactor, the reaction heat being supplied by heat transfer oil. The reaction products leave the reactor as gas and are split into crude MEK and hydrogen on cooling. The hydrogen is purified by further cooling. The crude MEK is separated from uncreated reactants and by-products by distillation. LIQUID PHASE OXIDATION OF n-BUTANE MEK is produced as a by-product in the liquid phase oxidation of n-butane to acetic acid. Autoxidation of n-butane takes place in the liquid phase according to the radical mechanism yielding MEK as an intermediate and acetic acid as end-product with mass ratio 0.2:1.0 by non-catalyzed liquid phase oxidation at 180oC and 53 bars with remixing. Continuous oxidation under plug flow conditions at 150oC, 65 bars and a residence time of 2-7 minutes forms MEK and acetic acid at a mass ratio of 3:1. DIRECT OXIDATION OF n-BUTENES (HOECHST-WACKER PROCESS)
In direct oxidation of n-butanes by Hoechst-Wacker process, oxygen is transferred in a homogenous phase on to n-butenes using redox salt pair, PdCl2 / CuCl2. 95 per cent conversion of nbutanes can be obtained with MEK selectivity of about 86 percent. Disadvantages of the process are:
Formation of chlorinated butanone and n-butryaldehyde; and
Causes corrosion due to free acids.
DIRECT OXIDATION OF n-BUTANES, MARUZEN PROCESS
The Maruzen process is similar to the Hoechst-Wacker process except that oxygen is transferred by an aqueous solution of palladium sulphate and ferric sulphate. The process is commercially good to get MEK via direct oxidation of n-butenes, but is generally not accepted due to formation of undesirable by products. The process is patented and not much information is available.
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2.2.2 REVIEW OF PAST WORKS ON MEK PRODUCTION FROM DEHYDROGENATION OF 2-BUTANOL. 1. Dehydrogenation of Sec-Butanol to Methyl Ethyl Ketone over Cu-ZnO Catalysts Prepared by Different Methods: Co-precipitation and Physical Mixing Cu-ZnO catalysts prepared by co-precipitation and physical mixing methods were characterized to investigate the roles of ZnO by X-ray diffraction (XRD), N2O chemisorption decomposition and evaluated for the vapour-phase dehydrogenation of sec-butanol (SBA) to methyl ethyl ketone (MEK). ZnO not only could disperse Cu species, but also prevent Cu0 from sintering. Cu-ZnO catalyst by co-precipitation method exhibited excellent reactivity. (Yun Feng Hu, 2013) 2. The production of methyl ethyl ketone from n-butene In this preliminary design the production of methyl ethyl ketone (MEK) from normal butene, with secondary butyl alcohol (SBA) as intermediate, is described. This design is split into two parts. In the first part SBA is obtained from n-butene by absorption in sulphuric acid, followed by hydrolysis with water. Sulphuric acid and SBA are separated in a stripper. The sulphuric acid is reconcentrated and recycled to the absorber. The SBA is purified in an azeotropic distillation unit, using di-isobutylene as entrained. In the second part of the design, SBA is vaporized and fed to a multitubular, isothermal reactor, filled with a Cu/Ni on SiO2 catalyst. The SBA is dehydrogenized; forming MEK and hydrogen. The hydrogen is purified and sold as a valuable by-product. The MEK is purified in two fractionation columns and obtained with a purity of 99.1 wt."-%. The capacity of the plant is 33,731 tons of MEK per year. An economic evaluation shows that this plant can pay itself back within approximately 1.5 to 2 years. (A.H. Amer, 1988)
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CHAPTER 3 3.0 MATERIAL BALANCES FOR THE PROCESS 3.1 INTRODUCTION: Material balances are the basis of process design. A material balance taken over the complete process will determine the quantities of raw materials required and products produced. Balances over individual process units set the process stream flows and compositions. Material balances are also useful tools for the study of plant operation and trouble shooting. They can be used to check performance against design; to extend the often limited data available from the plant instrumentation; to check instrument calibrations; and to locate sources of material loss. All mass/material balances are based on the principle of conservation of mass that is massr can neither be created nor destroyed with an exception of nuclear processes according to Einstein’s equation; E=mc2. The general conservation equation for any process system can be written as: Material out − Material in + Generation − Consumption = Accumlation For a steady state process the accumulation term is zero and thus for a continuous steady state process, the general balance equation for any substance involved in the process can be written as: Material in + Generation = Material out + Consumption If no chemical reaction takes place, material balance is computed on the basis of chemical compounds mass basis that are used whereas if a chemical reaction occurs molar units are used. Also it is worthwhile to note that when a reaction occurs an overall balance is not appropriate but a reactant balance (a compound balance) is. a.
PROCESS DESCRIPTON
Pre-Heater
In the dehydrogenation of 2-butanol, the cold feed of 2-Butanol is mixed with recycle stream and then pumped from the feed tank to a steam heater and heated up to 373°K (stream1), the heating medium being used is dry saturated steam at 140°C. 43
Vaporizer
This Stream 1 is further fed to thermo-syphon vaporizer which is heated by the reactor vapor. The heating medium in vaporizer is heated reaction products discharged from the reactor at 673°K i.e. (Stream 5) and itself gets cooled down to 425°K.
Knock-Out Drum
Stream 2 is further fed to knockout drum to remove entrained liquid which is recycled back to the vaporizer. Knockout drum consists of a hollow vertical drum having inclined sieve plates known as demister for the passage of clean gas. Separation in knock-out drum is based on the principle of density difference of the liquid and the clean gas.
Super-Heater 1
The dry alcohol vapours are fed to the super-heater 1 where they are heated to increase the temperature of the vapours to 573K. The vapours are heated with the help of flue gases at high temperature of 813K.
Compressor
The superheated vapours are then compressed with the help of a compressor to increase the pressure as well as increasing the temperature of the vapours.
Super-Heater 2
The compressed vapours are then fed to the super-heater 2 to increase the vapours temperature of 773K with the help of flue gases at 813K high temperature.
Reactor
The superheated vapours are fed to the reactor in which the butanol is dehydrated to produce MEK and hydrogen, according to the reaction: CH3CH2CH3CHOH
CH3CH2CH3CO + H2
The conversion of alcohol to MEK is 90 per cent and the yield is taken as 100 per cent. Initially, preheated vapours of secondary-butyl alcohol are passed through a reactor (Step 1) containing a catalytic bed of zinc oxide or brass (zinc-copper alloy) which is maintained between 400°C and 44
500°C. A mean residence time of two to eight seconds at normal atmospheric pressures is required for conversion from secondary-butyl alcohol to MEK.
Partial Condenser
The reaction product from the reactor are cooled to a suitable temperature in the vaporizer and the cooled products are then fed to the condenser where almost 80% of the MEK and unreacted 2-butanol are condensed and sent to the distillation column while the non-condensable hydrogen with the un-condensed MEK and unreacted 2-butanol are sent to the absorber.
Absorption Column
In the absorption column the uncondensed MEK and alcohol are absorbed in water. Around 98 per cent of the MEK and alcohol can be considered to be absorbed in this unit, giving a 10 per cent w/w solution of MEK. The water feed to the absorber is recycled from the next unit, the extractor. The vent stream from the absorber, containing mainly hydrogen, are dried and used as a furnace fuel.
Extraction Column
In the extraction column the MEK and alcohol in the solution from the absorber are extracted into tri-chloro-ethylane (TCE). The raffinate, water containing around 0.5 per cent w/w MEK, is recycled to the absorption column. The extract, which contains around 20 per cent w/w MEK, and a small amount of butanol and water, is fed to the solvent recovery.
Solvent Recovery
In the solvent recovery, the unit separates the MEK and alcohol from the solvent TCE. The solvent containing a trace of MEK and water is recycled to the extraction column. The bottom product is solvent, i.e. 1, 1, 2-trichloroethane and the distillate from this column (Stream 15) is MEK and alcohol. The recovery of solvent is 99.9%. The solvent is first cooled down to room temperature and then fed to the extraction column.
Distillation Column
The distillate from the solvent recovery column is fed to this distillation column along with the condensate from partial condenser containing MEK and 2-Butanol, which is mixed first and then 45
fed into the column. The distillate is MEK and the bottom product is 2-Butanol. The 2-Butanol discharged from the bottom of the column will be sent back to the feed tank.
46
FLOW SHEET FOR THE PRODUCTION OF METHYL ETHYL KETONE Make up water
6 169KPa 642 K 2 142KPa 373 K
11 150KPa 300 K
13' 13 121KPa 300 K
18 101KPa 303 K
16
14 300 K
2-butanol feed
17 141 KPa 308 K
P-78
Pre-heater Storage
1 145KPa 298 K
1' 144KPa 373 K
MEK Storage Separator
Vaporizer
Reactor Absorber
3 133KPa 373 K
Pump 3' 131KPa 573 K
5 353KPa 773 K
Cooler
12 101KPa 310 K
15
Distillation Column
Superheater 1 4 355KPa 583 K
Compressor
10 156KPa 335 K
Superheater 2
7 163KPa 398 K
9 299 K
8
Partial Condenser
Solvent Recovery Column
E-34
Liq-Liq Extraction Column
Separator 19
Figure 3.2 Process flow diagram for production of MEK
3.3 ASSUMPTIONS MADE 1. Material loss between the steam heater and the second super-heater is negligible. 2. Only 98% of the MEK and 2-butanol entering the absorption column is absorbed. 3. MEK is 10% of the absorption product. 4. The raffinate from the extraction column contains 99.5% water, 0.5% MEK and no 2butanol. 5. The extract contains 20% MEK. 6. No spillage across any unit operation. 7. Perfect separation in the absorption column 8. Perfect separation of TCE in the extraction column
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3.4 MATERIAL BALANCE ACROSS ALL UNIT OPERATIONS Choosing a Basis: The correct choice of the basis for a calculation will often determine whether the calculation proves to be simple or complex. A time basis was chosen in which the results will be presented. The basis for calculations was chosen as 1 hour and thus results will be presented in kg/h. Reactor
2-butanol XF
X (kg)
MEK
Reactor
2-butanol H2
XR
MATERIAL BALANCE ACROSS REACTOR IN Components
Mass Flow
OUT %
Components
(kg/hr) MEK 2 Butanol H2 TOTAL
Mass Flow
%
(kg/hr)
0
0
1720.2
100
0
0
1720.2
100
MEK
1506.34
87.567
2 Butanol
172.02
10
H2
41.84
2.432
TOTAL
1720.2
100
TABLE 3.1: MATERIAL BALANCE ACROSS REACTOR Partial Condenser
MATERIAL BALANCE ACROSS PARTIAL CONDENSER IN Components
Mass Flow
OUT %
Components 48
Mass Flow
%
(kg/hr)
(kg/hr) MEK
MEK
1506.33
87.567 condensable
1205.07
70.054
301.27
17.514
137.62
8.000
34.4
1.999
41.84
2.432
1720.2
100
MEK noncondensable 2 Butanol 2 Butanol
172.02
10 condensable 2 Butanol noncondensable
H2
41.84
TOTAL
2.432 H2
1720.2
100 TOTAL
TABLE 3.2: MATERIAL BALANCE ACROSS PARTIAL CONDENSER Absorption Column: MEK= 0.00803𝑥
K
H2O= 1.597𝑥
MEK= 0.17513𝑥 2-Butanol = 0.02x
Absorption column 2
MEK= 0.02(0.17513𝑥) Butanol= 0.0004𝑥
H2=0.024324𝑥
H2= 0.024324𝑥
MEK=0.0035𝑥
MEK= 0.1716𝑥 + 0.00803𝑥 = 0.1796𝑥 H2O= 1.597𝑥 and 2 − 𝑏𝑢𝑡𝑎𝑛𝑜𝑙 = 0.0196𝑥
MATERIAL BALANCE ACROSS ABSORPTION COLUMN IN Components
Mass Flow
OUT %
Components
49
Mass Flow
%
(kg/hr)
(kg/hr) MEK to
MEK noncondensable
extraction 301.27
9.599 column
308.95
9.844
6.02
0.192
MEK raffinate stream
13.81
0.440 MEK to drier
2 Butanol
2 Butanol to
non-
extraction
condensable
34.4
1.096 column
33.716
1.074
2 Butanol to drier H2
41.84 1.333
H2 to drier
0.6881
0.022
41.84
1.333
H2O to H2O raffinate stream
extraction 2747.16
87.532 column
2747.16
87.532
0.1059
0.003
3138.48
100
Negligible losses TOTAL
3138.48
100
TABLE 3.3: MATERIAL BALANCE ACROSS ABSORPTION COLUMN
50
Extraction column: : MEK = 0.00803𝑥
Raffinate H2O= 1.597𝑥 B MEK= 0.1796𝑥
Extractor
2-butanol= 0.0196x
MEK= 0.17157𝑥
ϑ
Q
2-butanol= 0.0196𝑥
H2O= 1.597𝑥
TCE= 0.667𝑥
R = TC R- Recycle from next operation (TCE)
MATERIAL BALANCE ACROSS EXTRACTION COLUMN IN Components
Mass Flow
OUT %
Components
(kg/hr)
Mass Flow
%
(kg/hr) MEK to solvent
MEK
308.95
7.291 recovery
295.135
6.965
13.81
0.326
MEK to absorption column 2 Butanol to solvent 2 Butanol H2O
33.716 2747.16
0.7957 recovery 64.834 H2O
TCE from
TCE to
recycle
solvent
stream
1147.4
27.079 recovery
33.716
0.7957
2747.16
64.834
1147.4
27.079
Negligible losses 51
0.005
0.0001
TOTAL
4237.226
100
4237.226
100
TABLE 3.4: MATERIAL BALANCE ACROSS EXTRACTION COLUMN Solvent Recovery Unit:
TCE= 0.667𝑥
MEK= 0.17157𝑥
2-Butanol = 0.0196x
Solvent Recovery Unit
MEK= 0.17157𝑥 2-Butanol= 0.0196𝑥
TCE= 0.667𝑥
MATERIAL BALANCE ACROSS SOLVENT RECOVERY UNIT (DISTILLATION COLUMN 1) IN Components
Mass Flow
OUT %
Components
(kg/hr)
Mass Flow
%
(kg/hr)
MEK
295.135
19.992
MEK
295.135
19.992
2 Butanol
33.716
2.284
2 Butanol
33.716
2.284
TCE
1147.4
77.724
TCE
1147.4
77.724
1476.251
100
TOTAL
TOTAL
1476.251
100
TABLE 3.5: MATERIAL BALANCE ACROSS SOLVENT RECOVERY UNIT (DISTILLATION COLUMN 1)
52
Distillation Column: MEK= (0.17157𝑥 + 0.70054𝑥)
Distillation Column
= 0.872𝑥
1500kg/hr. (flow rate as given)
2-Butanol= 0.0196𝑥 + 0.08𝑥 = 0.0996𝑥 2-Butanol (recycled back to the reactor)
MATERIAL BALANCE ACROSS DISTILLATION COLUMN IN Components
Mass Flow
OUT %
Components
(kg/hr)
%
(kg/hr)
MEK condensable
Mass Flow
99.9% pure 1205.07
72.093 MEK
1500.2
89.749
MEK from solvent recovery unit
295.135
17.656 2 Butanol
2 Butanol condensable
back to 137.62
8.233 storage tank
171.33
10.249
2 Butanol from solvent recovery unit
33.716
2.017 Negligible losses
TOTAL
1671.541
100 TOTAL
0.011 1671.541
TABLE 3.6: MATERIAL BALANCE ACROSS DISTILLATION COLUMN Detailed calculations are shown in Appendix B.
53
0.00066 100
CHAPTER 4 a. ENERGY BALANCE FOR THE PLANT 4.1 INTRODUCTION ENERGY BALANCES As with mass, energy can be considered to be separately conserved in all but nuclear processes. The conservation of energy, however, differs from that of mass in that energy can be generated (or consumed) in a chemical process. Material can change form, new molecular species can be formed by chemical reaction, but the total mass flow into a process unit must be equal to the flow out at the steady state. The same is not true of energy. The total enthalpy of the outlet streams will not equal that of the inlet streams if energy is generated or consumed in the processes; such as that due to heat of reaction. Energy can exist in several forms: heat, mechanical energy, electrical energy, and are the total energy that is conserved. In process design, energy balances are made to determine the energy requirements of the process: the heating, cooling and power required. In plant operation, an energy balance (energy audit) on the plant will show the pattern of energy usage, and suggest areas for conservation and savings. A general equation can be written for the conservation of energy: Accumulation = Energy In + Generation − Consumption − Energy out This is a statement of the first law of thermodynamics. An energy balance can be written for any process step. Chemical reaction will evolve energy (exothermic) or consume energy (endothermic). For steady-state processes the accumulation of both mass and energy will be zero. The energy balance was carried out around cooler condenser and the second distillation column. In chemical processes the kinetic and potential energy terms are usually small compared with heat and work terms, and can normally be neglected. If the kinetic and potential energy terms are neglected the energy equation reduces to 54
H2 − H1 = Q − W For many processes the work term will be zero, or negligibly small, and equation above reduces to the simple heat balance equation: Q = H2 − H1 Where heat is generated in the system; for example in a chemical reactor: Q = QP + QS QS = Heat generated in the system. If heat is evolved (exothermic processes) QS is taken as positive, and if heat is absorbed (endothermic processes) it is taken as negative. QP = Process heat added to the system to maintain required system temperature. Hence: QP = H2 − H1 − QS H1 = enthalpy of the exit stream H2 = enthalpy of the outlet stream. For a practical reactor, the heat added (or removed) Qp to maintain the design reactor temperature will be given by: QP= Hproducts − Hreactants − Qr Where Hproducts is the total enthalpy of the product streams, including unreacted materials and byproducts, evaluated from a datum temperature of 25°C; Hreactants is the is the total enthalpy of the feed streams, including excess reagent and inerts, evaluated from a datum of 25°C;
55
Qr is the total heat generated by the reactions taking place, evaluated from the standard heats of reaction at 25°C (298 K). This equation can be written in the form: Tout
QP = ∑ ∫
Tout
ni cpi dT − ∑ ∫
Tref
ni cpi dT − ∑[−∆H ° rxn ] × mol of product formed
Tref
Cp = A + BT + CT 2 + DT 3 4.2 ENERGY BALANCE ACROSS ALL UNIT OPERATIONS: ENERGY BALANCE ACROSS COLD FEED PREHEATER Components
HEAT LOST
Component
HEAT GAINED
ENERGY
Heat lost by
%
ENERGY
FLOW
FLOW
(kJ/hr)
(kJ/hr)
335400
100
dry saturated
Heat load on
%
335400
100
335400
100
pre heater
steam TOTAL
335400
100
TABLE 4.1: ENERGY BALANCE ACROSS COLD FEED PREHEATER
ENERGY BALANCE ACROSS VAPORIZER Components
HEAT LOST
Component
HEAT GAINED
ENERGY
Heat lost by
%
ENERGY
FLOW
FLOW
(kJ/hr)
(kJ/hr)
958000
100
Heat gained
reaction
by 2-butanol
products
feed liquid 56
958000
%
100
TOTAL
958000
100
958000
100
TABLE 4.2: ENERGY BALANCE ACROSS VAPORIZER
ENERGY BALANCE ACROSS SUPER HEATER 1 Components
HEAT LOST
Component
HEAT GAINED
ENERGY
Heat lost by
%
ENERGY
FLOW
FLOW
(kJ/hr)
(kJ/hr)
538000
100
flue gas
Heat gained
%
538000
100
538000
100
by 2-butanol feed vapour
TOTAL
538000
100
TABLE 4.3: ENERGY BALANCE ACROSS SUPER HEATER 1
ENERGY BALANCE ACROSS COMPRESSOR ENERGY
Heat lost by
%
ENERGY
FLOW
FLOW
(kJ/hr)
(kJ/hr)
168650
100
compression
Heat gained
%
168650
100
168650
100
by 2-butanol feed vapour
TOTAL
168650
100
TABLE 4.4: ENERGY BALANCE ACROSS COMPRESSOR
ENERGY BALANCE ACROSS SUPER HEATER 2 Components
HEAT LOST
Component 57
HEAT
GAINED ENERGY
Heat lost by
%
ENERGY
FLOW
FLOW
(kJ/hr)
(kJ/hr)
704000
100
flue gas
Heat gained
%
704000
100
704000
100
by 2-butanol feed vapour
TOTAL
704000
100
TABLE 4.5: ENERGY BALANCE ACROSS SUPER HEATER 2
ENERGY BALANCE ACROSS REACTOR Components
HEAT LOST
Component
HEAT GAINED
ENERGY
Heat lost due
%
ENERGY
FLOW
FLOW
(kJ/hr)
(kJ/hr)
1160000
100
Heat gained
to reaction,
by reactor,
Qr
Qp
TOTAL
1160000
%
1160000
100
1160000
100
TABLE 4.6: ENERGY BALANCE ACROSS REACTOR
ENERGY BALANCE ACROSS CONDENSER Components
HEAT LOST
Component
HEAT GAINED
ENERGY
Heat lost due
%
ENERGY
FLOW
FLOW
(kJ/hr)
(kJ/hr)
304000
26.32946475
Heat gained 58
1154600
%
100
to reduction
by cooling
in vapor
water
temperature, Q1 Heat lost due
742000
64.26468041
108600
9.405854842
1154600
100
to condensation, Q2 Heat loss due to further cooling of vapor, Q3 TOTAL
1154600
100
TABLE 4.7: ENERGY BALANCE ACROSS CONDENSER
ENERGY BALANCE ACROSS ABSORBER Components
HEAT LOST
Component
HEAT GAINED
ENERGY
Heat of
%
ENERGY
FLOW
FLOW
(kJ/hr)
(kJ/hr)
137000
52.9120964
condensation
Heat gained
%
242299.512
93.58084041
13819.3335
5.337298586
1944.0519
0.750831106
857.1026
0.331029893
by water
of MEK Heat of
22300
8.612698903
condensation
Heat gained by MEK
of alcohol Heat of
120
Heat gained
solution Heat loss due
by alcohol 99500
38.42885833
negligible 59
to off gases TOTAL
losses 258920
100
258920
100
TABLE 4.8: ENERGY BALANCE ACROSS ABSORBER
ENERGY BALANCE ACROSS SOLVENT RECOVERY UNIT Components
HEAT LOST
Component
HEAT GAINED
ENERGY
Heat Lost by
%
ENERGY
FLOW
FLOW
(kJ/hr)
(kJ/hr)
75000
15.46391753
feed
Heat gained
%
272000
56.08247423
52300
10.78350515
160350
33.06185567
350
0.072164948
485000
100
by condensate
Heat lost by
410000
84.53608247
utility steam
Heat gained by distillate Heat gained by bottom product
0
negligible losses
TOTAL
485000
100
TABLE 4.9: ENERGY BALANCE ACROSS SOLVENT RECOVERY UNIT
ENERGY BALANCE ACROSS DISTILLATION COLUMN Components
HEAT LOST
Component
HEAT GAINED
Heat Lost by feed
161000
5.768541741
Heat gained by condensate 60
2415000
86.46443179
Heat lost by
2630000
94.23145826
utility steam
Heat gained
340300
12.18378722
37756
1.351780988
by distillate Heat gained by bottom product
negligible
2056
0.073665353
2791000
100
0
losses TOTAL
2793056
100
TABLE 4.10: ENERGY BALANCE ACROSS DISTILLATION COLUMN
ENERGY BALANCE ACROSS COOLER SYSTEM Heat lost by
233100
90.13921114
distillate
Heat gained
258600
100
258600
100
by cooling water
Heat lost by
25500
9.860788863
258600
100
bottoms product TOTAL
TABLE 4.11: ENERGY BALANCE ACROSS COOLER SYSTEM Detailed calculations are shown in Appendix B
61
References 1. (2015, November 3). Retrieved from sciencezen: http://www.sciencezen.com/partialcondensation 2. Alaqua. (2015). Heat Exchanger. (Alaqua Inc) Retrieved November 7, 2015, from Alaqua Inc: http://www.alaquainc/heat_exchanger.com 3. Arora, D., & Sharma, M. (November 2015). Methyl Ethyl Ketone: A TechnoCommercial Profile. Jaypee Institute of Engineering and Technology, Department of chemical engineering. 4. britannica. (2015, November 5). Retrieved from condenser: httption://www.britannica.com/condenser 5. catalysis. (2015, November 5). Retrieved from chemwiki: http://www.chemwiki.ucdavis.edu/complex_reactions/catalysis 6. Davis, A. (2005). Reciprocating compressor basics. In A. Davis, Reciprocating compressor basics. Noria corporation . 7. Efunda. (2015). Heat transfer:overview. Retrieved November 7, 2015, from Efunda: http://www.efunda.com/formulae/heat_transfer/home/overview.cfm 8. https://en.wikipedia.org/wiki/2-Butanol. (October 2015). wikipedia/2-Butanol. (wikipedia, Foundation Inc) Retrieved November 3, 2015, from wikipedia: https://en.wikipedia.org/wiki/2-butanol 9. https://en.wikipedia.org/wiki/Relative_volatility. (Retrieved October 2015). Relative Voaltility. 10. Perry, R.H & Green D.W. (2007). Perry chemical engineering handbook. Mc Graw Hill. 11. rhum-agricole. (Retrieved October,2015., October). Distillation. 12. S.L, D. (1978). compressors. In Fluid Mechanics, Thermodynamics of turbomachinery (third ed). Pergamon Press. 13. Tham, M. T. (2009). Distillation. Distillation Principles.
62
14. Treybal, R. .. (1981). Mass transfer operations. In R. .. Treybal, Mass transfer operations/absorption (pp. 275,281,282). McGraw hill . 15. wikipedia. (2015, november 5). Retrieved from liquid liquid extraction column: http://en.wikipedia.org 16. wikipedia. (2015, November 3). Retrieved from separators: http://www.wikipedia.org 17. wikipedia. (2015). wikipedia/convection. (wikipedia, foundation inc) Retrieved November 6, 2015, from wikipedia: https://en.wikipedia.org/wiki/Convection 18. wikipedia. (2015, Novenmber 4th). wikipedia/MEK-molecular-structure. Retrieved from Wikipedia: www.wikipedia.com 19. wikipedia. (2015). wikipedia/radiation. (wikipedia, foundation) Retrieved November 6, 2015, from wikipedia: https://en.wikipedia.org/wiki/Radiation
63
APPENDICES A.
MATERIAL BALANCE:
The material balance was done around the following units: Reactor
2-butanol XF
MEK
Reactor
X (kg)
2-butanol H2 XR
RMM of 2-butanol =74 Moles of 2-butanol =
X(kg) 74
= 0.01351x
Moles of the2-Butanol that reacted 0.90 × 0.01351x = 0.012162x From the equation: CH3CH2CH3CHOH
Yields
CH3CH2CH3CO + H2
Mole ratio for the reaction is 1:1 Hence moles of the MEK reacting is 1 × (0.012162x) = 0.012162x Mass of MEK then is 0.012162x ×72=0.875676x 10
Mass of 2-butanol is 100 × x = 0.10x Mass of then H2 is 0.012162×2=0.024324x X (kg)
Reactor
MEK = 0.87567𝑥 2-Butanol=0.10𝑥 H2 =0.024324𝑥
64
All the components leaving the reactor are discharged directly into the cooler condenser for the next operation. Partial-condenser
Condensate (which is then directly sent to the final purification column) comprises: 80% MEK= 0.8×0.875676x = 0.70054x 80% 2-Butanol=0.80× 0.10x = 0.08x Incondensable stream comprises: 20% MEK=0.2 × 0.875676x = 0.175135x 20% 2-Butanol= 0.2 × 0.10x = 0.02x 100% H2=0.024324x
MEK =
0.875676x
Partialcondenser
(Non-condensable)
2-Butanol=012𝑥
MEK= 0.01369𝑥 2-Butanol= 0.02𝑥
H2=0.024324𝑥 H2=0.024324𝑥
(Condensate) MEK= 0.70054x 2-butanol= 0.08x
65
MEK =0.175135𝑥
Absorption column:
MEK= 0.5% = 0.005𝐾 H2O= 99.5% = 0.995𝐾
(Non-condensable) MEK= 0.175135𝑥 2-Butanol= 0.02𝑥
K Absorption MEK column
𝑀𝐸𝐾 = 0.02(0.175135𝑥) 2-Butanol= 0.02(0.02𝑥) H2=0.024324𝑥 J
H2=0.024324𝑥
J MEK = 0.98(0.175135𝑥) + 0.005𝐾 = 0.1𝐽 2-Butanol= 0.98(0.02𝑥) H2O=?
75
MEK balance around the absorption column
0.175135x + 0.005K = 0.02(0.175135X) + 0.1J 0.175135x + 0.005K = 0.003503X + 0.1J J = 1.716x + 0.05K
Overall balance (0.024324x + 0.02x + 0.175135x) + K = 1.716x + 0.05k + (0.024324x + 0.0004x + 0.003503x) k = 1.605x Performing a new balance around the absorption column to express the k -value in terms of x in the above equations gives the following values:
66
MEK= 0.00803𝑥
K
H2O= 1.597𝑥
MEK= 0.17513𝑥
Absorption column 2
2-Butanol = 0.02x
MEK= 0.02(0.17513𝑥) Butanol= 0.0004𝑥
H2=0.024324𝑥
H2= 0.024324𝑥
MEK= 0.1716𝑥 + 0.00803𝑥 = 0.1796𝑥 H2O= 1.597𝑥 and 2 − 𝑏𝑢𝑡𝑎𝑛𝑜𝑙 = 0.0196𝑥
Raffinate: MEK= 0.005K = 0.005(1.605x) = 0.00803x H2O= 0.995K = 0.995(1.605x) = 1.597x Stream J: MEK= 0.1J = 0.1{1.716x + 0.05(1.605x)} = 0.1796x H2O= 1.597x 2-butanol = 0.0196x
67
MEK=0.0035𝑥
Extraction column : MEK = 0.00803𝑥
Raffinate H2O= 1.597𝑥 B Extractor
MEK= 0.1796𝑥 2-butanol= 0.0196x H2O= 1.597𝑥
ϑ
Q
MEK= 0.17157𝑥 2-butanol= 0.0196𝑥 TCE= 0.667𝑥
R = TC R- Recycle from next operation (TCE)
MEK Balance around the extractor 0.1796x = 0.00803x + 0.2𝛝 ϑ= 0.858x Overall balance 𝐑+𝐐= 𝛝+𝐁 1.7962x + 𝐑 = 1.605x + 0.858x 𝐑 = 0.667x TCE = 0.858x − (0.17157x + 0.0196x) = 0.667x (Which is approximately = 𝐑)
68
Solvent Recovery Unit
For this unit operation, the balances were obtained from the previous unit operation i.e. the extraction column and are indicated in the block diagram below.
TCE= 0.667𝑥
MEK= 0.17157𝑥
2-Butanol = 0.0196x
Solvent Recovery Unit
MEK= 0.17157𝑥 2-Butanol= 0.0196𝑥
TCE= 0.667𝑥
Distillation Column The material balance for the second distillation column is given as follows;
MEK= (0.17157𝑥 + 0.70054𝑥)
= 0.872𝑥
Distillation Column
1500kg/hr (flow rate as given)
2-Butanol= 0.0196𝑥 + 0.08𝑥 = 0.0996𝑥 2-Butanol (recycled back to the reactor)
Balancing around this gives:
69
MEK: 0.872x = 1500 x=
1500 = 𝟏𝟕𝟐𝟎. 𝟐𝐤𝐠 0.872
2-Butanol: 0.0996x x = 0.0996(1720.2) = 𝟏𝟕𝟏. 𝟑𝟑𝐤𝐠 (Returning to the reactor)
CALCULATION OF ACTUAL MASS OF THE COMPONENTS IN ALL THE STREAMS
The streams are indicated in the diagrams above. 1) Reactor From the balances carried out in the previous exercise the value of X was obtained as 1720.2kg based on the 1 hour basis. In = out Entering stream: XF + XR= X where: XF = feed and XR = feed as recycle Leaving streams: MEK = 0.87567x = 0.87567 × 1720.2 = 𝟏𝟓𝟎𝟔. 𝟑𝟑 𝐤𝐠 70
2-butanol = 0.10x = 0.10 × 1720.2 = 𝟏𝟕𝟐. 𝟎𝟐 𝐤𝐠 H2= 0.024324x = 0.024324 × 1720.2 = 𝟒𝟏. 𝟖𝟒 𝐤𝐠 2) Cooler condenser In = out Entering Stream MEK = 0.87567x = 0.87567 × 1720.2 = 𝟏𝟓𝟎𝟔. 𝟑𝟑 𝐤𝐠 2-butanol = 0.10x = 0.10 × 1720.2 = 𝟏𝟕𝟐. 𝟎𝟐 𝐤𝐠 H2= 0.024324x = 0.024324 × 1720.2 = 𝟒𝟏. 𝟖𝟒 𝐤𝐠
Leaving Stream MEK = 0.70054x = 0.70054 × 1720.2 = 𝟏𝟐𝟎𝟓. 𝟎𝟕 𝐤𝐠 2-butanol= 0.08x = 0.08 × 1720.2 = 𝟏𝟑𝟕. 𝟔𝟐 𝐤𝐠 Non-condensable MEK= 0.175135x = 0.175135 × 1720.2 = 𝟑𝟎𝟏. 𝟐𝟕 𝐤𝐠 2-Butanol = 0.02x = 0.02 × 1720.2 = 𝟑𝟒. 𝟒 𝐤𝐠 H2= 0.024324x = 0.024324 × 1720.2 = 𝟒𝟏. 𝟖𝟒 𝐤𝐠 3) Absorption column Entering stream: MEK= 0.175135x = 0.175135 × 1720.2 = 𝟑𝟎𝟏. 𝟐𝟕 𝐤𝐠 2-Butanol = 0.02x = 0.02 × 1720.2 = 𝟑𝟒. 𝟒 𝐤𝐠 71
H2= 𝟒𝟏. 𝟖𝟒 𝐤𝐠 Raffinate stream: MEK 0.00803x = 0.00803 × 1720.2 = 𝟏𝟑. 𝟖𝟏 𝐤𝐠 H2O: 1.597x = 1.597 × 1720.2 = 𝟐𝟕𝟒𝟕. 𝟏𝟔 𝐤𝐠 Leaving stream: MEK 0.1796x = 0.1796 × 1720.2 = 𝟑𝟎𝟖. 𝟗𝟓 𝐤𝐠 H2O 1.597x = 1.597 × 1720.2 = 𝟐𝟕𝟒𝟕. 𝟏𝟔 𝐤𝐠 2-butanol = 0.0196x = 0.0196 × 1720.2 = 𝟑𝟑. 𝟕𝟏𝟔 𝐤𝐠 H2= 𝟒𝟏. 𝟖𝟒 𝐤𝐠 MEK 0.0035x = 0.0035 × 1720.2 = 𝟔. 𝟎𝟐 𝐤𝐠 4) Extractor Entering stream: MEK 0.1796x = 0.1796 × 1720.2 = 𝟑𝟎𝟖. 𝟗𝟓 𝐤𝐠 H2O 1.597x = 1.597 × 1720.2 = 𝟐𝟕𝟒𝟕. 𝟏𝟔 𝐤𝐠 2-butanol = 0.0196x = 0.0196 × 1720.2 = 𝟑𝟑. 𝟕𝟏𝟔 𝐤𝐠 Recycle stream = TCE (Trichloroethane) TCE: 0.667x = 0.667 × 1720.2 = 𝟏𝟏𝟒𝟕. 𝟒𝐤𝐠 Leaving stream: MEK:0.17157x = 0.17157 × 1720.2 = 𝟐𝟗𝟓. 𝟏𝟑𝟓𝐤𝐠 2-butanol 0.0196x = 0.0196 × 1720.2 = 𝟑𝟑. 𝟕𝟏𝟔𝐤𝐠 72
5) Solvent Recovery Unit Entering stream: MEK: 0.17157x = 0.17157 × 1720.2 = 𝟐𝟗𝟓. 𝟏𝟑𝟓𝐤𝐠 2-butanol 0.0196x = 0.0196 × 1720.2 = 𝟑𝟑. 𝟕𝟏𝟔𝐤𝐠 Leaving stream: MEK: 0.17157x = 0.17157 × 1720.2 = 𝟐𝟗𝟓. 𝟏𝟑𝟓𝐤𝐠 2-butanol 0.0196x = 0.0196 × 1720.2 = 𝟑𝟑. 𝟕𝟏𝟔𝐤𝐠 TCE: 0.667x = 0.667 × 1720.2 = 𝟏𝟏𝟒𝟕. 𝟒𝐤𝐠 (This is recycled back into the extractor) 6) Distillation column 2 In = out Entering stream: MEK: 0.17157x + 0.70054x = 0.872x 2-butanol: 0.0196x + 0.08x = 0.0996x (this is recycled back to the reactor) Leaving stream 99.99% pure MEK at 1500kg/hr. B. ENERGY BALANCE: The energy balance was done around the following units
73
ENERGY BALANCE ACROSS THE CONDENSER:-
MEK=301.27𝑘𝑔
MEK= 1506.33 kg MEK = 0.8554𝑥 2-butanol =172.02 kg 2-Butanol=012𝑥 H2 =41.84kg
(Non-condensable) 2-Butanol= 34.4 𝑘𝑔
Coolercondenser
H2=0.02376𝑥
H2= 41.84 𝑘𝑔
Condensate MEK =1205.07 𝑘𝑔 2-butanol= 137.62 𝑘𝑔
The vapor enters condenser at 141.50C (414.5K) at 1 bar pressure. Liquid and the vapor leaving the condenser are in equilibrium. At the MEK mole fraction x = 0.88 of the condensate we get both liquid and vapor temperature from the T- x- y diagram. 299.6K = liquid temperature, 335.7K = vapor temperature We take cooling water enters at 250C and leaving at 280C
Cpmix = 2.24 KJ/kg.
Heat loss to reduction in vapor temperature from 459K to 335.7K
Q1= 1720.2 x 2.24 x (414.5 - 335.7) = 3.04 x 105 KJ/ hr
Heat loss due to condensation Total mass condensed= 1205.07 + 137.62 = 1342.7kg 74
Q2 = 1342.7 x 552.5 KJ/kg = 7.42 x 105 KJ/hr
Heat loss due to further cooling of a part of vapor is Q3 = 1342.7 x 2.24 x (335.7 – 299.6) = 1.086 x 105 KJ/hr
Total heat lost = Q = Q1 + Q2 + Q3 = (4.75 + 7.42 + 1.086) x 105 KJ/hr = 11.546 x 105 KJ/hr
Heat gained by cooling water = Heat lost by Vapor 11.546 ×105
Mass flow of cooling water = 4.2×(28−25) = 9.16 x 104 kg / h
ENERGY BALANCE ACROSS THE ABSORBER:MEK= 13.8𝑘𝑔
K
MEK= 301.27𝑘𝑔 2-Butanol =34.4kg
H2O= 2747.16𝑘𝑔
Absorption column
MEK= 0.02(0.17513𝑥) Butanol= 6.88𝑘𝑔 MEK=6.02𝑘𝑔
H2= 41.8𝑘𝑔
H2=41.8𝑘𝑔 MEK= 308.95𝑘𝑔 H2O= 2747.16𝑘𝑔 and 2 − 𝑏𝑢𝑡𝑎𝑛𝑜𝑙 = 33.7𝑘𝑔
75
H2O= 2747.16𝑘𝑔 and 2 − 𝑏𝑢𝑡𝑎𝑛𝑜𝑙 = 33.7𝑘𝑔
Heat of condensation of MEK = 308.95 x 435.2 = 1.37 x 105 KJ/hr
Heat of condensation of alcohol is = 33.7 x 550.6 = 0.223 x 105 KJ/hr
Heat of solution = (308.95 + 33.7) x 0.35 = 0.00120 x 105 KJ/hr. Heat gained by off gases from 320C to 62.4 Mean Cp = 1.89KJ/kg = (41.8 + 6.88 + 6.02) x 1.89 x (62.4 –32) = 0.995 x 105 KJ/hr. Total heat released = 2.59 x 105 KJ/hr.
Heat gained by irrigating liquor a) Water: 2747.16 x 4.2 x (T – 300) b) MEK: 308.95 x 2.13 x ( T-300 ) c) Alcohol: 33.7 x 2.747 x (T- 300 ) Total heat gained = 0.123 x 105 (T-300) KJ/hr
Heat released = heat gained = > 2.59 x 105 = 0.123 x 105 (T – 300) 76
= > T = 321K
ENERGY BALANCE ACROSS THE EXTRACTION COLUMN:It is assume that the extraction process is isothermal. All that streams come at 500C and leaves at 500C.
ENERGY BALANCE ACROSS THE SOLVENT RECOVERY UNIT:Entering stream: MEK: 0.17157𝑥 = 0.17157 × 1720.2 = 𝟐𝟗𝟓. 𝟏𝟑𝟓𝒌𝒈 2-butanol 0.0196𝑥 = 0.0196 × 1720.2 = 𝟑𝟑. 𝟕𝟏𝟔𝒌𝒈 TCE: 0.667𝑥 = 0.667 × 1720.2 = 𝟏𝟏𝟒𝟕. 𝟒𝒌𝒈 Total Mass = 1476.25kg Leaving stream: MEK: 0.17157𝑥 = 0.17157 × 1720.2 = 𝟐𝟗𝟓. 𝟏𝟑𝟓𝒌𝒈 2-butanol 0.0196𝑥 = 0.0196 × 1720.2 = 𝟑𝟑. 𝟕𝟏𝟔𝒌𝒈 TCE: 0.667𝑥 = 0.667 × 1720.2 = 𝟏𝟏𝟒𝟕. 𝟒𝒌𝒈 (This is recycled back into the extractor) Stream Temperatures were obtained from HYSYS Simulation. From x-y diagram we get Rm = 0.38. R= 2Rm = 0.76
Feed: 2-butanol =
33.716 74
= 0.4556𝑘𝑚𝑜𝑙/ℎ𝑟
77
MEK =
TCE =
295.135 72
1147.4 133.5
= 4.1𝑘𝑚𝑜𝑙/ℎ𝑟
= 8.6𝑘𝑚𝑜𝑙/ℎ𝑟
Total = 13.1556 kmol /hr
Mole fraction of MEK 4.1
XMEK = 13.1556 = 0.312 Feed temperature = 500C F . HF = 𝑀 × 𝐶𝑝𝑚𝑖𝑥 × 𝑇 = 1476.25 x 1.018 x (50) F . HF = 0.75 x 105 KJ/hr
Distillate:Alcohol =
MEK =
33.716 74
295.135 72
= 0.4556𝑘𝑚𝑜𝑙/ℎ𝑟
= 4.1𝑘𝑚𝑜𝑙/ℎ𝑟
Total = 4.556kmol/hr
D = 4.556 kmol/hr 4.1
Mole fraction of MEK, XMEK = 4.556 = 0.90 From the HYSYS Simulation, distillate temperature = 700C 78
Cp mix = 2.273 KJ/kg D. HD = 𝑀 × 𝐶𝑝𝑚𝑖𝑥 × 𝑇 = 328.851 x 2.273 x 70 = 0.523 x 105 KJ/hr
Bottoms: TCE =
1147.4 133.5
= 8.6𝑘𝑚𝑜𝑙/ℎ𝑟
Total = 8.6 kmol/hr From the HYSYS simulation, the temperature obtained, T = 1250C (bottoms)
Cp TCE = 1.118 KJ/kgK B. HB = 𝑀 × 𝐶𝑝𝑚𝑖𝑥 × 𝑇 = 1147.4 × 1.118 × 125 = 1.6035 x 105 KJ/hr
Condenser :Qc = V x (Hv - HL) Qc = 𝑉 × ∆𝐻 V = (1 + R ) x D D = 4.556 kmole/hr V = ( 1 + 0.76 ) x 4.556 = 8.02 kmole/hr. 𝑉 × ∆𝐻
4
79
= 2.72 x105 KJ/hr Qc = 2.72 x105 KJ/hr 2.72×105
Cooling water requirement = 4.186×(42−24) = 3.61x 103 kg/hr
Reboiler:Overall heat balance F. HF + QB = Qc + D.HD + B. HB QB = Qc + D . HD + B. HB - F. HF QB = DHD + B. HB + Qc – FHF QB = 0.523 x 105 + 1.6035 x 105 + 2.72 x105 - 0.75 x 105 QB = 4.1 x 105 KJ/hr
Utility steam supplied at Medium pressure (MP) is available at 3.302 bar steam temperature = 410 K
Steam requirement is =
4.1 ×105 2152
= 190.5 kg/hr
80
ENERGY BALANCE ACROSS THE DISTILLATION COLUMN:-
QC
F=1671.33kg/h XF=0.88
R
D=1500kg/h XD=0.999
QR
B=171.33kg/h XB=0.001
Taking reflux ratio (R.R) = 2.8 (obtained from HYSYS) Total energy balance equation is: HF+QR=QC+HD+HB Condenser: Qc = V x λ 81
V = (1 +R) x D V = (1 + 2.8) x 1500 V= 5700kg/hr Qc = 5700 x 423.7 = 2.415 x 106KJ/hr 2.415 ×106
So, mass flow rate of cooling water = 4.186 ×(42−24) = 3.205 x 104 kg/h Reboiler: QB = DHD + BHB + Qc - FHF FHF = 𝑀 × 𝐶𝑝𝑚𝑖𝑥 × 𝑇 = 1671.33 x 2.241 x (43) F.HF = 1.61 x 105 KJ/hr DHD = 𝑀 × 𝐶𝑝𝑚𝑖𝑥 × 𝑇 = 1500 x 2.394 x 94.76 = 3.403 x 105 KJ/hr BHB = 𝑀 × 𝐶𝑝𝑚𝑖𝑥 × 𝑇 = 171.33 × 2.862 × 77 = 0.37756 x 105 KJ/hr QB = 26.3 x 105 KJ/hr
Utility Steam supplied at medium pressure (MP) Steam available at = 3.302 bar. Steam temperature = 410 k
Steam requirement =
26.3 ×105 2152
= 1222.12 kg/hr. 82
ENERGY BALANCE AROUND COOLER SYSTEM
Distillate & the residue both has to be cooled
Distillate Heat load to cool the distillate from 94.76 to 29.850C =1500 × 2.394 × (94.76 − 29.85) = 2.331 x 105 KJ/hr. 2.331 ×105
So, cooling water requirement,= 4.187 ×(42−24) =3093 kg/hr
For 2-Butanol Recycle 2-butanol is 77 to 250C Heat load = 171.33 × 2.862 × (77 − 25) = 2.55 x 104 KJ/hr 2.55 ×104
Cooling water requirement = 4.187(42−24) = 338.3 kg/hr.
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