Acetone Reactor Design Complete Project

Project title Preparation of acetone via the dehydrogenation of isopropyl alcohol (IPA). Problem Statement Acetone is typically produced in commercial quantities as a by-product during the formation of phenol. However, acetone manufactured thus generally contains small amounts of the reactant benzene and the desired product phenol. In the past, these impurities were deemed to be within allowable limits. However, recent downward revisions of these limits by the US Food and Drug Administration has made alternative processes (which do not involve benzene) more attractive. We wish to design of one such alternative process to produce 45000 tons of 99.9 mol% pure acetone per year, using isopropyl alcohol as the reactant (via the dehydrogenation of isopropyl alcohol). Design a simplified chemical reactor for the production of acetone.

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1. Acetone Introduction  Acetone belongs to ketone family (dimethyl ketone) with scientific name 2Propanone.  In 2010, the worldwide production capacity for acetone was estimated at 6.7 million tons per year.  The United States had the highest production capacity with 1.56 million tons per year (2010)  The second largest production is in Taiwan and followed by China (2010).  It is a common building block in organic chemistry.

(Structural formula of acetone)

1.1 Product Description: Acetone is a clear, colorless, low-boiling, flammable and volatile liquid characterized by rapid evaporation and a faintly aromatic, sweetish odor. It readily mixes with most organic solvents and mixes completely with water. 1.2 Product Uses: Roughly 75% of the available acetone is used to produce other chemicals, and 12% is used as a solvent. Applications range from surface coatings, films and adhesives to cleaning fluids and pharmaceutical applications. Some consumer and commercial applications include         

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Lacquers for automotive/furniture finishes. Cellulose acetate films and fibers. Photographic films and plates casting. Coatings and inks. Resin thinners and clean-up operations. General purpose cements. Degreasing and degumming agents. Paint, varnish, lacquer strippers. Nail polish removers.

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1.3 Physical Hazard Information: Acetone is a highly flammable material in both the liquid and vapor forms, has a relatively high vapor pressure, and should be handled only with adequate ventilation and in areas where ignition sources have been removed (e.g. matches and unprotected light switches). The flash point for acetone is -4ºF /-20ºC. 1.4 Projected demand for acetone: There is about 7% increment in the requirement of the acetone worldwide. With this increasing demand the requirement of the acetone in some upcoming years is: Year

Project Demand (million Tones)

2010

6.7

2011

7.2

2012

7.9

2013

8.4

2014

9.0

2015

9.63

2016

10.3

2017

11.02

1.5 Capacity: The capacity of the desired plant to produce acetone is 45000 tons per year. The capacity data of some previous years is:

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Year

Quantity (Tones)

Year

Quantity (Tones)

2004

31000

2008

39000

2005

32000

2009

40000

2006

34000

2010

42000

2007

36000

2011

45000

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2. Methods for the preparation of acetone: Acetone is prepared by following of the three methods: 2.1 Cumene Process for Phenol and Acetone: This process converts two relatively cheap starting materials, benzene and propylene, into two more valuable ones, phenol and acetone. Other reactants required are oxygen from air and small amounts of a radical initiator. Cumene process is a process of producing phenol (C6H5-OH) and acetone (CH3-CO-CH3) from benzene (C6H6) and propene (C3H6).

The term stems from isopropyl benzene or cumene (C6H5-CH(CH3)2), the intermediate material during the process. 2.2 By the direct oxidation of propylene using air: Acetone can also be produced by the direct oxidation of propylene using air. In this process the catalysis consists of a solution of copper chloride containing small quantities of palladium chloride. The reaction takes place under a moderate pressure and at 100°C. It is exothermic by 61 kcal/mole of acetone produced. The overall reaction is as follows:

Propylene

Oxygen

Acetone

2.3 By the dehydrogenation of isopropyl alcohol: In this process, an aqueous solution of isopropyl alcohol is fed into the reactor, where the stream is vaporized and reacted over a solid catalyst. The reactions occurring within the reactor are as follows: → Isopropyl alcohol

acetone

hydrogen

The primary advantage of this process is that the acetone produced is free from trace aromatic compounds, particularly benzene. For this reason, acetone produced from IPA is favored by the pharmaceutical industry. Group # 5

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3. Comparison between processes and selection of process: Cumene process

Propylene oxidation process

Isopropyl alcohol dehydrogenation process Primary product is phenol Acetone is the primary Acetone is the primary Acetone is by product product product Purity of acetone is low Purity is high Purity is high --Propylene used should be 99% Aqueous solution of the pure isopropyl alcohol can be used Conversion to acetone is low Conversion to acetone is low Conversion to acetone is high Worldwide production method Not used worldwide Worldwide production method Unconverted benzene present Not a dangerous compound Not a dangerous compound along with acetone is present along with acetone present along with acetone dangerous to some process To purify acetone large Less separation process Less separation process number of separation required and production cost is required and production cost is processes are required which low low increase the production cost  Major disadvantage of the production of acetone from cumene process is that some amount of reactant benzene is present along with desired product which is toxic.  The disadvantage of production of acetone from propylene oxidation process is that propylene required for the process should be 99 % pure.  So our process for the production of acetone is dehydrogenation of isopropyl alcohol.

4. Introduction of desired process: 4.1 Chemical reaction: The reaction occurs in vapor phase at a temperature of 350 °C and a pressure of 1.8 – 2 bars in the presence of catalyst. ( )

Isopropyl alcohol

→

( )

Acetone

( )

Hydrogen

4.2 Side reactions: At a temperature lower than 325 °C the following reaction is more expected to occur, and ether (di-isopropyl ether) is obtained as the product instead of acetone.

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( )

(

Isopropyl alcohol

)

(

)

(

Di-isopropyl ether

()

)

Water

At the higher temperature (>350 °C), dehydration reaction is expected to be significant and propylene is formed. ( )

Isopropyl alcohol

( )

( )

Propylene

Water

So the suitable temperature conditions for the reaction is between 325 °C to 350 °C 4.3 Selection of catalyst: Trial and error experimentation and scientific analysis provide guidance for the selection of the catalyst. There are some categories of the catalyst which are suitable for some purpose. For example platinum, copper and related metals elements such as palladium are known to catalyze hydrocarbon oxidation and dehydrogenation. Since our desired reaction is the dehydrogenation reaction of hydrocarbon (isopropyl alcohol), so the catalyst used for the process belong to this category. One of the factors considered in the selection of catalyst is their turn over frequency (TOF). 4.3.1 Turn over frequency: Turn over frequency of the catalyst is defined as the amount of reactant converted into product by the catalyst in the unit time. For most relevant industrial applications, the turnover frequency is in the range of 10−2 - 102 s−1  The turnover frequency of cu chromites catalyst is 0.026 per second  The TOF of carbon supported copper is 0.052 per second double than that of the cu chromites catalyst.  Platinum (with a turnover frequency of 0.66 per second) metal has the high TOF for this process but it is expensive.  So the suitable catalyst for this process is carbon supported copper. 4.4 Reaction kinetics: The reaction to form acetone from isopropyl alcohol is endothermic with a standard heat of reaction 62.9 kJ/mol. The reaction is kinetically controlled and occurs in the vapor phase over a catalyst. The reaction kinetics for this reaction is first order with respect to the concentration of alcohol and can be estimated from the following equation: [ With Ea = 72.38 MJ/Kmol and Group # 5

]

ko = 3.51 × 105 m3 gas/m3 bulk catalyst. s (Ch.E-308) Chemical Reactor Design

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5. Physical properties of reactants and products: Property

Water

Acetone

Isopropyl alcohol

Hydrogen

Molecular Weight(kg/kmol)

18

58

60

2

Freezing Point(°C)

0

-95

-88.5

- 259.2

Boling Point(°C)

100

56.2

82.2

-252.8

Critical Temperature (°C)

647.3

508.1

508.3

33.2

Critical Pressure (bar)

220.5

47

47.6

13

Critical Volume (m3/min)

0.056

0.209

0.220

0.065

Liquid Density(kg/m3)

998

790

786

71

Heat of Vaporization(J/mol)

40683

29140

39858

904

Standard Enthalpy of Formation at 298K(kJ/kmol)

-242.0

20.43

-272.60

0

Standard Gibbs Energy of Formation at 298K (kJ/kmol)

-228.77

62.76

-173.5

0

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6. Conversion with temperature change The conversion of isopropyl alcohol to acetone with temperature is: Temperature (°C) 300 310 320 330 340 350

Conversion % 46.3 55.4 64.6 73.4 83.5 90.0

7. Flow sheet:

7.1 Description of the process: 7.1.1 Feed drum: Feed drum is a kind of tank used for the mixing of the recycle stream and feed stream. Recycle stream concentration is assumed to be same with the feed stream. Feed stream is at room temperature (25 °C) and at a pressure of 2 bars, which is assumed to be constant. The temperature of recycle stream calculated as 111.50 °C from the energy balance around the isopropyl alcohol distillation column. The temperature of the leaving stream from the feed drum calculated as 32.890 °C, by the energy balance around feed drum. 7.1.2 Vaporizer: In the vaporizer molten salt is used for heating. The temperature at the entrance of the unit is the temperature of the mixture leaving the feed drum, which is 32.890 °C. And the leaving temperature is the bubble point temperature of the mixture, which is 109.50 °C. The pressure is 2 bars, and assumed to be constant. Group # 5

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7.1.3 Heater: Since the temperature leaving the vaporizer is not enough for the reaction to carry out. Due to which a pre-heater is used to maintain the temperature of the feed stream to the reaction temperature of 350 °C which is the reaction temperature. The unit is working at 2 bars, and assumed to be constant. The entrance and leaving temperatures are 109.50°C and 350 °C. 7.1.4 Reactor: The reactor is the starting point for the calculations. The temperature values for the entering and leaving streams is 350 °C, (i-e the process is isothermal). The reaction takes place inside is endothermic, for this reason the reactor has to be heated. For heating, molten salt is used from the furnace. 7.1.5 Cooler: The entrance temperature of the cooler is 350 °C and leaving temperature is 94.70 °C. (Temperature is calculated by using energy balance). For cooling purpose water is used. By using refrigerant better results may be obtained. But since it costs too much, due to which it isn’t chosen as the cooling material. From the temperature values it’s easily seen that the load is on the cooler not on the condenser, for this process. But in reality the unit cannot cool that much, and the load is mostly on the condenser. In this process, the mixture cooled down to its dew point. The pressure is 1.5 bars, and assumed to be constant. 7.1.6 Condenser: The temperature of the entering stream is the dew point and the leaving temperature is the bubble point of the mixture. In the condenser water is used as cooling material. 7.1.7 Flash unit: Flash unit is operating isothermally, for this reason temperature is not changed. It is 81 °C in the entrance and exit. From trial and error method, (V / F) value is found to be 0.2. The entrance temperature of the unit is the bubble point of the mixture, but if it is its dew point the (V/F) value should be much higher. In the flash unit the hydrogen is flashed out from the mixture of isopropyl alcohol, water and acetone. Along with hydrogen some amount of acetone and isopropyl alcohol is also flashed out. In order to recover these, a scrubber unit is used. 7.1.8 Scrubber: Scrubber operated adiabatically. Water entering the unit is at atmospheric temperature (i-e 25 °C). The temperature of the off gas, including hydrogen and a very little amount of acetone, is between 40-50 °C. The temperature of the leaving stream (containing water, acetone and isopropyl alcohol) is found to be 28.10 °C from the energy balance around the scrubber. The streams leaving the scrubber and flash unit are mixed together before entering the acetone column. The temperature leaving the flash unit and scrubber are 81 °C and 28.10 °C respectively. The temperature of the mixture is found to be 45.0 °C. This result is obtained by using energy balance around the mixing point.

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7.1.9 Acetone distillation column: The acetone column is used to separate the acetone from the mixture. The entrance temperature is 45 °C. The leaving temperatures for the top and bottom product are 102.3 °C and 105 °C, respectively, which are the bubble and dew points. Top product of the unit includes acetone (99wt% of acetone which is desired). From the bottom isopropyl alcohol, water and a very little amount of, 0.1 %, acetone is discharged. 7.1.10 Isopropyl alcohol column: In this distillation column, isopropyl alcohol and water are separated. The entrance temperature is 105 °C. The leaving temperatures of the top and bottom products are both111.50 °C. The top product is recycled to the feed drum. For this reason it’s assumed to have the same concentration with the feed stream. The bottom product is pure water and it’s thrown away. Since its temperature is very high it cannot be recycled to the scrubber. But if a cooler is used, a recycle can be used. 7.2 Description f the process in the reactor

The reaction occurring in the reactor is in vapor phase. So the isopropyl alcohol is first vaporized and then passed from the reactor. The process is continuous. Since the dehydrogenation of the isopropyl alcohol is the endothermic reaction, so heat has o be supplied to the reactor to maintain the temperature at 350 °C. For heating purpose the molten salt is used. The molten salt is circulated through the small scale furnace where it is heated and its temperature is raised above the 350 °C and this heated molten salt is used to provide the heat to the reaction during the process. In order to heat the molten salt in the furnace, natural gas is burned in the furnace in the limited amount and this amount of heat is used to heat the molten salt which in turn provides the heat to the reaction.

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8. Selection of the type of reactor used in the process: 8.1 Choice of reactor (Batch, CSTR or PFR) Selection of the reactor type for a given process is subjected to a number of considerations a) Temperature and pressure of the reaction. b) Need for removal or addition of the reactants and products. c) Required pattern of the product delivery. d) Catalyst use consideration such as requirement for solid catalyst particle and contact with fluid reactants and products. e) Relative cost of the reactor. Some guideline for the reactor selection is:  For conversion up to 90%, the performance of five or more CSTRs connected in series approaches to that of PFR.  Batch reactors are best suited for small scale production, very slow reactions or those requiring intensive monitoring and control. For large operations CSTR or PER is used  CSTRs are used for slow liquid phase and slurry reactions. For gas phase reactions PER is more preferable.  For endothermic reactions the plug flow reactor is used. For exothermic reaction that has a large temperature raise during the reaction, recycle reactors are the best choice.  For small

⁄

mixed flow reactor is used. For large

⁄

plug flow reactor is

best choice. Since our reaction is the gaseous phase and endothermic reaction so the choice is the plug flow reactor. 8.2 Choice of the bed (Fixed, fluidized or moving) Use of the catalyst requires modifications to basic reactor design to fixed bed reactors, moving bed reactors or fluidized bed reactors. 8.2.1 Fixed bed reactors: These are used in the heterogeneous catalyst reactions and pressure drop across the bed is small. The design of the fixed bed reactor is very easy as compared to the moving bed and fluidized bed reactors. Their size is also compact as compared to other fluidized Group # 5

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bed and moving bed reactors. The energy requirement is also small because no amount of energy is needed as in fluidized bed and moving bed required to fluidize or move the bed. 8.2.2 Fluidized bed reactors: These are the reactors with a gas phase working fluid that requires gas flow around and across the fine particles at a rate sufficient to fluidize the particles suspended within the reactor. Since the catalyst bed has to be fluidized so the energy requirement in these reactors is large. Pressure drop is also large as compared to the fixed bed reactors because the pressure is dissipated to fluidize the bed. The volume of the reactor required is also large as compared to fixed bed reactor, because the void spaces between the fluidized beds occupy the more volume. 8.2.3 Moving bed reactor: These units are fluid reactors used where the fluid contain solid particles that can be separated from the suspension fluid. Mostly suitable for liquid phase reactions or where the slurry travels through the reactor. Moving bed reactors are not preferred for the gas phase reactions. In these reactors the pressure drop is the greater among all. From above points we see that the suitable reactor for our process is fixed bed plug flow reactor, with the reaction occurring in the tubes and the heat exchanging material flowing outside the tubes.

9. Design steps for the reactor: Standard design steps for the reactor are given below: a) Collect together all the kinetic and thermodynamic data on the desired reaction and the side reactions (if present). The kinetic data required for reactor design will normally be obtained from laboratory or pilot plant studies. Values will be needed for the rate of reaction over a range of operating conditions: pressure, temperature, and flow-rate and catalyst concentration. b) Collect the physical property data required for the design. c) Identify the predominant rate-controlling mechanism: kinetic, mass or heat transfer. d) Choose a suitable reactor type, based on experience with similar reactions, or from the laboratory and pilot plant work. e) Make an initial selection of the reactor conditions to give the desired conversion and yield. f) Size the reactor and estimate its performance. Exact analytical solutions of the design relationships are rarely possible; semi empirical methods based on the analysis of idealized reactors will normally have to be used. g) Select suitable materials of construction. h) Make a preliminary mechanical design for the reactor: the vessel design, heat-transfer surfaces, internals and general arrangement. i) Cost the proposed design, capital and operating, and repeat steps 4 to 8, as necessary, to optimize the design. Group # 5

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The design of the reactor must satisfy the following requirements: i.

Chemical factors:

The design must provide sufficient residence time for the desired reaction to proceed to the required degree of conversion. ii.

Mass transfer factors:

For example with heterogeneous reactions the reaction rate may be controlled by the rates of diffusion of the reacting species; rather than the chemical kinetics. iii.

Heat transfer factors:

Removal or addition of the heat of the reaction. iv.

Safety factors

The confinement of hazardous reactants and products, and the control of the reaction and the process conditions.

10. Feed to the reactor: Feed used for the preparation of the acetone is 87% weight solution of the isopropyl alcohol. Here we are using the 87 weight percent solution of the isopropyl alcohol because commercially isopropyl alcohol is available in two grades. i. ii.

Anhydrous 87% by weight.

Due to which we are using the 87 weight percent solution of isopropyl alcohol.

11. Material balance across the reactor: Start calculation from the reactor. Basis: 100 kgmol/hr of the isopropyl alcohol are entering in the reactor. Since the solution used for the preparation of acetone is 87%. So the number of moles of water entering in the reactor is calculated as:

(

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)

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(

)

Acetone Hydrogen Water Isopropyl alcohol

→ At a temperature of 350 °C the conversion is 90%. So

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From material balance Mass in

=

Mass out

Mass of water in + Mass of IPA in = Mass of water out + Mass of IPA out + Mass of acetone out + Mass of hydrogen out 6000 + 896.5

=

5220 + 180 + 600 + 896.5

6896.5 kg/hr

=

6896.5 kg/hr

So the material balance is justified.

Summary of material balance:

Component

Acetone Hydrogen IPA Water

Number of moles entering in reactor 100 kgmol/hr 49.8 kgmol/hr

Mass of component entering in reactor 6000 kg/hr 896.5 kg/hr

Number of moles leaving from reactor 90 kgmol/hr 90 kgmol/hr 10 kgmol/hr 49.8 kgmol/hr

Mass of component leaving from reactor 5220 kg/hr 180 kg/hr 600 kg/hr 896.5 kg/hr

From the 100 kmol/hr of the isopropyl alcohol entering in the reactor the amount of the acetone produced per year is 45700 tons, which is very close to the desired amount of the product. So we are not applying the material balance again, but using these calculations in the process. So, By using 100 moles of the isopropyl alcohol per hour the amount of acetone produced is 45700 ton per year.

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12. Energy Balance across the reactor: The reaction occurring in the reactor is isothermal at the temperature of 350 °C

Temperature at inlet = 350 °C

Temperature at outlet = 350 °C

Component Acetone Hydrogen IPA Water

Number of moles entering in reactor 100 kgmol/hr 49.8 kgmol/hr

Number of moles leaving from reactor 90 kgmol/hr 90 kgmol/hr 10 kgmol/hr 49.8 kgmol/hr

Heat of formation of components -216.685 KJ/gmol 0 -272.290 KJ/gmol -241.826 KJ/gmol

12.1 Calculations at the inlet of reactor Reference temperature = 25 °C Inlet temperature = 350 °C Sensible heat at inlet ∫ (

)

∫(

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Components In

IPA Water

Moles In ni

Standard heat of formation

kgmol 100 49.8

Heat of Sensible phase change heats

( )

KJ/gmol -272.290 -241.826

KJ/gmol 39.858 40.65

KJ/gmol 20.014 10.476

KJ

12.2 Calculations at the outlet of reactor Reference temperature = 25 °C Outlet temperature = 350 °C Sensible heat at outlet ∫(

)

∫ (

)

∫(

)

∫ ( )

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Components Moles Out Out nout

Acetone IPA Hydrogen Water

kgmol 90 10 90 49.8

Standard heat of formation KJ/gmol -216.69 -272.290 0 -241.826

Heat of Sensible phase change heats

( )

KJ/gmol 30.2 39.858 40.65

KJ/gmol 33.940 22.6 9.466 11.388

KJ

Energy balance equation is: [(

) ]

Here kinetic and potential energies are neglect able with no work done and no accumulation of heat. So the general energy balance equation becomes:

∑

∑

This shows that in order to carry out the reaction we have to supply the 6.3111 ×106 KJ of heat on the basis of 100 kg-mol of isopropyl alcohol entering in the reactor. 12.3 Supply of the heat: From the energy balance calculations, it is also seen that the reaction is endothermic and we have to supply the heat to the process. This heat is supplied by the use of the molten salt:

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From energy balance Energy supplied by the molten salt

(

= Energy absorbed by the reacting fluid

)

The mass flow rate and the temperature are selected and optimized and that values of the flow rate and temperature are selected which makes the process most efficient at minimum cost. From this relation we see that the inverse relation exist between the mass flow rate of the salt and the inlet temperature of the salt. By increasing the inlet temperature of the salt, mass flow rate has to be decreased to exchange 6.3111 × 106 KJ of heat. Similarly if we decrease the inlet temperature of the salt then mass flow rate has to be increased to exchange this amount of heat. So a suitable value of both temperature and mass flow rate has to be selected to make the process optimum.

13. Design of reactor The reactor used in the process is fixed bed plug flow reactor. 13.1 Performance equation for the reactor: The performance equation for the fixed bed plug flow reactor is: ∫ Where W is the weight of the catalyst. is the flow rate of the isopropyl alcohol. rate of the reaction. The weight of the catalyst is found from this performance equation.

is the

Since the rate equation of reaction is

In the form of conversion the rate equation becomes Group # 5

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(

)

Where [

]

By putting the values of conversion from 0 to 1 in rate equation we obtain the values of . From this we find the values of 1/ . Plot the graph between and 1/ , the weight of catalyst can be calculated. 13.2 Table of and

and

From the rate equation: ⁄

Group # 5

0

0.0061

163.9344

0.1

0.004990909

200.3643

0.2

0.004066667

245.9016

0.3

0.003284615

304.4496

0.4

0.002614286

382.5137

0.5

0.002033333

491.8033

0.6

0.001525

655.7377

0.7

0.001076471

928.9617

0.8

0.000677778

1475.41

0.9

0.000321053

3114.754

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13.3 Graph between Graph between

⁄

and

and ⁄

3500

3000

2500

(1/-rA)

2000

1500

1000

500

0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Conversion (XA)

From this the area under the curve = 730 So ∫ 13.4 Weight of catalyst Weight of catalyst = W =

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× 730 = 100 × 730 = 73000 kg

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13.5 Volume of catalyst

From the general gas equation the concentration of IPA = 13.6 Space time The time needed to treat the one reactor volume is called the space time.

13.7 Catalyst particles size The following shapes of catalyst are frequently used in applications:  20-100 µm diameter spheres for fluidized-bed reactors.  0.3-0.7 mm diameter spheres for fixed-bed reactors.  0.3-1.3 cm diameter cylinders with a length-to-diameter ratio of 3-4.  Up to 2.5 cm diameter hollow cylinders or rings. The void fractions for the spherical particles is between 0.4 to 0.41 The diameter of the copper particles selected (from the literature) = 0.3 mm with the void fractions (Porosity = φ) of 0.4 13.8 Volume of reactor

13.9 Number of tubes The preferred lengths of the tubes (according to the TEMA standard) should be is 6ft, 8ft, 12ft, 16ft, 20ft and 24ft (7.32 m). So Group # 5

Length of tube selected = 20 ft = 7.32 m (Ch.E-308) Chemical Reactor Design

Page 22

To calculate tube diameter As we know that to prevent deviation from plug flow assumption ⁄

Assuming Diameter of tube = 70 mm ⁄

⁄

(

)

13.10 Height of reactor (Shell) Allowance of the reactor height is 20% - 50% of the shell height. For our system assuming the allowance for shell is 20% of the tube height. So (

)

13.11 Diameter of reactor Diameter of the shell is calculated by using the Harvey equation. Harvey equation is: [(

) ]

(

)(

)

( ) Where

The tubes used in triangular form. For triangular form

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By putting all these values in the Harvey and solving, we have

13.12 Verification of the assumptions All the values assumed can be verified from the length to diameter ratio of the given reactor and the pressure drop calculations. If the value of length to diameter ratio and pressure drop lies within the limit of the fixed bed plug flow reactor then the design is accepted, otherwise we have to perform the calculations again with the different assumptions. 13.12.1 Length to diameter ratio For the plug flow reactor the length to diameter ratio lies between 3-5. For the desired reactor Length = 10.248 m Diameter = 2.15 m ⁄

Length to diameter ratio for desired reactor = = 4.766

For the desired reactor the length to diameter ratio is 4.766 lies between the allowable limit. So the design is satisfactory. 13.12.2 Pressure drop calculation For the fixed bed reactor to operate economically the pressure drop along the length of the reactor should be less than the 10% of the operating pressure. The pressure drop along the length of the packed bed is calculated by using the Ergun equation. The Ergun equation is: (

)

(

)

Where

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⁄ ⁄ ⁄

By putting all the values in the Ergun equation:

The operating pressure is 2 bars. The pressure drop along the length of the reactor is less than the 10% of the operating pressure. So the design is accepted. 13.12.3 Volume of tubes In plug flow reactor where the reacting fluid is inside the tubes, the volume of tubes should be greater than the volume of the reactor. So In the desired reactor

This is greater than the reactor volume. So all the conditions are satisfied and design is accepted.

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14.Mechanical design of the reactor 14.1 Thickness of the reactor: An estimate of the thickness of the shell is obtained from the diameter of the shell. The wall thickness of any vessel should not be less than the values given below; the values include a corrosion allowance of 2 mm:

Vessel Diameter (m)

Minimum thickness (mm)

1

5

1-2

7

2-2.5

9

2.5-3

10

3-3.5

12

Since the diameter of the vessel is 2.15 m, so from the above table the thickness of the shell is 9mm. Thickness of the reactor shell = 9mm 14.2 Head selection and design The ends of a cylindrical vessel are closed by heads of various shapes. The principal types used are: 1. Flat plates and formed flat heads 2. Hemispherical head 3. Ellipsoidal head 4. Torispherical head

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Flat head Applicable to low pressure Cheapest from all types

Torispherical head Used up to the operating pressure of 15 bar Above 10 bars their cost should be compared with that of an equivalent ellipsoidal head

Ellipsoidal head Above 15 bars ellipsoidal head is used Economical within pressure limits

Hemispherical head Used for very high pressures Capital cost is high

So the right choice of head is Torispherical head. Thickness of head is calculated by: (

)

Where

(

(

√

)

) (

)

So by putting the values of all the variables the value of thickness of head is:

14.3 Vessel Supports: The method used to support a vessel will depend on the size, shape, and weight of the vessel; the design temperature and pressure and the vessel location and arrangement. Types of supports:  Saddle support (for horizontal vessels)  Brackets support (for vertical vessels) Group # 5

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 Skirt support (for vertical vessels, particularly where the length is high and effect of wind is prominent) For the desired reactor “Bracket supports” are used.

Bracket Support 15. Specification Sheet

Group # 5

Equipment

Reactor

Type of reactor

Multi-tubular fixed bed reactor

Operating temperature

350 °C

Operating pressure

2 bar

Volume of reactor

13.6 m3

Volume of catalyst

8.16 m3

Weight of catalyst

73000 Kg

Number of tubes

485

Shell height

10.248 m

Diameter of shell

2.15 m

Thickness of shell

9 mm

Head type

Torispherical head

Support type

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16. References  www.che.cemr.wvu.edu/publications/projects/acetone/acetone-a.PDF  http://www.owlnet.rice.edu/~ceng403/gr1998/acetone.html  http://www.scribd.com/doc/30134032/Isopropyl-Alcohol  www.annualreviews.org/doi/pdf/.../annurev.matsci.35.100303.12073  www.jbrwww.che.wisc.edu/home/jbraw/chemreacfun/.../slides-masswrxn.p  Gael D. Ulrich P. T. Vasudevan “A Guide to Chemical Engineering Process Design and Economics” 2nd ed, Process publishing, 1993  Plant design and economics for chemical engineers by Timmerhaus 5th edition  Chemical engineering design by Coulson and Richardson’s volume 6, 4th edition

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