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Azeo Distillation with LL Extractor


© 2000 AEA Technology plc - All Rights Reserved. Chem 9_3.pdf

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Workshop An azeotropic azeotropic mixture of Benzene and and Cyclo-Hexane Cyclo-Hexane is to be separated in a distillation column using Acetone as the entrainer. Nearly pure Benzene is produced from the bottom of the column, while a near azeotropic mixture of Acetone and Cyclo-Hexane is produced overhead. overhead. The overhead mixture will be s eparated in a Liquid-Liquid extractor using water as the solvent, with Cyclo-Hexane Cyclo-Hexane being recovered as the overhead product. The Acetone/Water mixture will then be separated in a vacuum tower with the Acetone and Water products being recycled through the flowsheet.

The process will be separated into four sections, the Azeotrope tower, the Liquid-Liquid extractor, the Solvent Recovery tower and finally the recycling system.

The problem could be solved with a single set of interaction parameters. However, the problem may be solved more accurately by using one set of binary coefficients which will predict the liquid phase splitting in the Extractor, Extractor, and another set which will predict VLE behaviour in the Distillation Columns.

Learning Objectives Once you have completed this section, you will be able to:

• Impo Import rt Flu Fluid id Packag ackages es • Mod Model el Azeotr Azeotropi opic c Distilla Distillatio tion n Columns Columns • Model Liquid-Liq Liquid-Liquid uid Extracti Extraction on Columns Columns

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Process Overview

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Azeotropic Distillation Column

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Azeotropic Distillation Column

Solvent Recovery Tower

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Building the Simulation Defining the Simulation Basis Two Fluid Packages will be used in this example. Both Fluid Packages will use the UNIQUAC Activity Model, Model , and contain the components Benzene, Benzene, Cyclohexane, Cyclohexane , Acetone and H2O. The first Fluid Package ( VLE( VLEBASIS), BASIS), will use the default library VLE binary interaction parameters and UNIFAC estimated parameters. The second Fluid Package (LLE( LLEBASIS), BASIS), will replace those interaction coefficients with UNIFAC UNIFAC LLE estimated binary coefficients and those regressed from HYSYS Conceptual Design Application Application. 1. 2.

Add Add the the first first Flui Fluid d Pack Package age in in the the usual usual mann manner er and and cha change nge the default name to VLE to VLE Basis. Basis. On the Binary Coeffs tab, Coeffs tab, view the binary coefficients for the UNIQUAC activity UNIQUAC activity model.

The binary coefficients for the Cyclohexane/Water pair Cyclohexane/Water pair are not available from the database, so it is necessary to obtain them by estimation or from another source. In this example, the binary coefficients for the Cyclohexane/Water pair in the VLE Basis will be es timated by the UNIFAC VLE estimation method. Press the Unknowns Only button button to estimate this pair. The second Fluid Package (for the Liquid-Liquid Extractor) will be imported.

Ensure that VLE Basis is is the Default Fluid Package when you leave the Basis Environment.

1.

On the Fluid Pkgs tab Pkgs tab of the Simulation Basis Manager, press the Import button button and import the Fluid Package LLEBasis.fpk . This file should be located on the course disk supplied with this material.

2.

Press the View button button to see the new Fluid Package. Go to the Binary Coeffs tab Coeffs tab to view the binary coefficients.

If you examine the LLE Coefficients for VLE Basis and LLE Basis you will see they are different, because they have been taken from di fferent sources. VLE Basis will Basis will be used for most of the simulation, while LLE Basis will Basis will be used as the Fluid Package for the Liquid-Liquid Extractor. Enter the Simulation Environment. Environment.

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Adding the Feed Stream 1.

Ente Enterr the the foll follo owin wing str stream eam Azeo Feed Feed as follows:

In this cell...

Enter...

Conditions Stream Name

Azeo Feed

Temperature

77°C (170°F)

Pressure

101.3 kPa (14.7 psia)

Mass Flow

85 kg/h (190 lb/hr)

Composition - Mass Frac Benzene

0.518

Cyclohexane

0.482

2.

Enter the stream Acetone as Acetone as follows:

In This Cell...

Enter...

Conditions Stream Name

Acetone

Temperature

55°C (130°F)

Pressure

101.3 kPa (14.7 psia)

Mass Flow

95 kg/h (215 lb/hr)

3.

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Enter ter a mass ass fr fracti actio on of 1.0 for 1.0 for Acetone Acetone..


Azeotrope Tower Published documentation on this process indicates that the overhead composition from the Azeotrope Tower Tower is a near azeotropic mixture of Acetone and Cyclohexane. Cyclohexane. Using Using less Acetone Acetone than is necessary to produce the azeotrope wi ll prevent the original Benzene/Cyclohexane Benzene/Cyclohexane azeotrope from being separated.

The Binary extension extension is available on our website. www.aeat.software.com

The flow of Acetone required to separate this azeotrope and produce a mixture near azeotropic Cyclo-Hexane/Acetone, can be calculated from the azeotrope composition, (0.688 Acetone and 0.312 CycloHexane mass fractions). These values can be obtained through HYSYS Conceptual Design Application Application or the HYSYS Extension Binary Plots. Plots. The T-x-y diagrams for the Benzene/Cyclo-hexane and Acetone/Cyclohexane binaries are shown here:

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Calculation for Required Acetone Flow Then, for an initial mass flowrate of the Azeo Feed stream of 85 kg/h with the given composition, composition, the the amount of Acetone Acetone required required will be 90.34 kg/h (85*0.482*0.688/0.312). kg/h (85*0.482*0.688/0.312). A slightly greater flow will be used (95 kg/h {210 lb/hr}) lb/hr} ) to ensure separation of the Benzene/Cyclohexan Benzene/Cyclohexane e azeotrope.

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Adding the Azeotropic Distillation Column 1.

Insert a Distillation Column with Column with the following data:

In This Cell...

Enter...

Connections Column Name

T-100

No. of Stages

28

Condenser Energy Stream

Q-Cond

Inlet Streams

Azeo Feed, Stage 6 Acetone, Stage 21

Condenser Type

Total

Overhead Liquid

A ze o L i q

Bottoms Liquid Outlet

B en z e n e

Reboiler Energy Stream

Q Reb

Pressures Delta P

0

Condenser

95 kPa (13.75 psia)

Reboiler

101.3 kPa (14.7 psia)

Temp. Estimates Condenser

55°C (130°F)

Reboiler

80°C (175°F)

Specifications

Because we expect an azeotrope to be present in this column, we must check the Azeotropic box box on the Solver page.

Benzene Recovery in Reboiler

0.998

Acetone Recovery in Cond

0.998

Reflux Ratio (Estimate)

10.0

Azeo Liq Draw (Estimate)

130 kg/h (285 lb/hr)

2.

On the Parameters tab, Parameters tab, Solver page, Solver page, check the Azeotropic the Azeotropic box and supply a Fixed Damping Factor of 0.5.

3.

Run the column.

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The Liquid-Liquid Extractor Liquid-liquid extraction is used as an alternative to distillation in situations where distillation distillation is either ineffective or very difficult. These situations can be found in a ll process industries. The extraction of penicillin from fermentation broth and the extraction of aromatics from lube oil fractions are two industrial examples. Extraction based on chemical differences is sometimes preferable to distillation, which is separation based on relative volatilities. Some examples of situations when extraction extraction is preferred are are listed below: below:

• Excessive Excessive amounts amounts of heat heat are required required for for distillat distillation ion - relative relative volatility of the components is near one • Separation Separation via via distilla distillation tion is limit limited ed due to the the formatio formation n of azeotropes • The high high temperatu temperatures res of distil distillati lation on cannot cannot be withstoo withstood d by the components, even under vacuum conditions • There are only only small small amounts amounts of solute solute in the the feed feed solution solution • The componen components ts to be separat separated ed are extre extremely mely diffe different rent in in nature Extraction involves involves the separation of a solute from a feed solution by mixing in a solvent in which the solute is preferentially preferentially soluble. In addition, the solvent must be insoluble, or have a limited solubility in the feed solution. The extraction operation, on a stage by stage basis, can therefore be discussed in terms of two processes:

• The mixing mixing of a feed feed solution, solution, a solve solvent, nt, and any any external external feeds feeds • The separati separation on of the two two immisci immiscible ble liquid liquid phases phases which which result result from the mixing HYSYS models the liquid-liquid extraction process using countercurrent flow in a column similar to the absorber template.

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Azeo Di Distillation wi with LL Extractor

Property Package The Liquid-Liquid Extractor cannot be used with the following property packages:

Use only property packages that support 2 liquid phases.

• • • • • • • • • •

Wilson Antoine BraunK10 Esso Esso Tabul abular ar Steam Amine Chao-Seader Gra Grayson yson-S -Str tree eed d Sour PR Sour SRK

Activity Models Models are recommended recommended for most most applications. applications.

Overhead Estimate You You will not be required required to provide an estimate for the Overhead Product Flow. The Extractor will generate an estimate from a mole weighted TP-Flash TP-Flash of the combined tower tower feeds.

Column Sizing Utility The column sizing utility in HYSYS is designed for columns with vapour and liquid traffic; therefore, it is not applicable to the Extractor unit operation.

Stage Efficiencies The HYSYS Extraction algorithm models the Extractor as a staged tower, tower, allowing you to specify either ideal stages or actual stages with efficiencies.

Side Draw If you require a Side Draw on the Extractor, you can choose to draw either the Light or Heavy phase from a stage. HYSYS will perform a three phase flash on the entire contents of the stage to produce the conditions and composition of the specified draw.

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The purpose of the Liquid-Liquid Extractor is to determine the required solvent flow flow (in this case water) which will cause a mixture to phase split, forming two liquid phases. A rough estimation of the solvent flow can be obtained by using a Mixer, and then examining the phase separation while varying the solvent flow. However, because the extractor is divided into stages, the flow determined can only be used as an estimate. Use a flow of 200 kg/h (440 lb/hr) of lb/hr) of Water. 1.

Ente Enterr tthe he foll follo owing wing data data for for tthe he stre stream am Wate Waterr:

In This Cell...

Enter...

Conditions

12

Stream Name

Water

Temperature

25°C (77°F)

Pressure

101.3 kPa (14.7 psia)

Mass Flow

200 kg/h (440 lb/hr)

Mass Fraction H 20

1.0


2.

Add the Liquid-Liquid Extractor with Extractor with the following data:

In this cell...

Enter...

Connections

The Temperature Estimates for Stages 2-19 can be supplied on the Parameters tab, tab, Profiles page of the column property view.

Column Name

T-101

No. of Stages

20

Top Stage Inlet

Water

Bottom Stage Inlet

Azeo Liq

Ovhd Light Liquid

CycloC6

Bottoms Heavy Liquid

Rich Solv

Pressures Top Stage

101.3 kPa (14.7 psia)

Bottom Stage

101.3 kPa (14.7 psia)

Temperature E stimates Top Stage

25°C (77°F)

Stages 2-18

25°C (77°F)

Stage 19

28°C (82°F)

Stage 20

33°C (91°F)

3.

On the Parameters tab, Parameters tab, Profiles page, Profiles page, supply an estimate of 48 kg/h (105 (105 lb/hr) for lb/hr) for the overhead light liquid.

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4.

Go to the Basis Environment and select LLE Basis as Basis as the Fluid Package for the Liquid-Liquid Extractor. Return to the Simulation Environment. Environment .

5.

Run the column.


Adding the Solvent Recovery Tower Tower The Solvent Recovery tower, which separates the Acetone from the Water, Water, presents presents a difficult separation separation at atmospheric atmospheric pressure. pressure. To To keep the number of stages reasonable, an overhead pressure of 53 kPa will be used. (Once again the data was obtained from HYSYS Conceptual Design Application Application). 1.

Add Add the the Solv Solven entt Rec Reco overy very Tower wer as as a Distillation Column with Column with the following data:

In This Cell...

Enter...

Connections Column Name

T-102

No. of Stages

20

Inlet Streams

RichSolv, Stage 17

Condenser Type

Total

Overhead Liq

AcetRich

Bottoms Liquid Outlet

H2O Rich

Condenser Energy Stream

RecCond Q

Reboiler Energy Stream

RecReb Q

Pressures Condenser Pressure

53 kPa (7.75 psia)

Reboiler Pressure

56 kPa (8 psia)

Temperature E stimates Condenser

35°C (95°F)

Reboiler

80°C (175°F)

Specifications Reflux Ratio

7

Acetone Recovery (Cond)

0.9998

2.

Supp upply a Dam Damp ping ing Fac Facto torr of of 0.8. 0.8.

3.

Run the column.

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Solvent Recycles Finally, the two products from the Solvent Recovery tower have to be recycled to the previous two towers. Because of the temperature and pressure of the Solvent Recovery tower, each recycle stream will require a Pump and a Cooler/Heater operation to return the stream to the necessary tower conditions.

Add a Pump Add a Pump to Pump to the stream H2O Rich with Rich with the following information: information: In This Cell...

Enter...

Connections Name

P-100

Inlet

H2O Rich

Outlet

H2O Atm

Energy

Q 10 0

Parameters Adiabatic Efficiency

75%

The pressure of stream H2O Atm is 101.3 kPa (14.7 psia). psia).

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Add a Cooler Add a Cooler Cooler downstream downstream of P-100 P-100 with the following following information: information: In This Cell...

Enter...

Connections Name

E-100

Inlet

H2O Atm

Energy

Q 102

Outlet

H2O Cool

Parameters Delta P

0 kPa

The temperature of stream H2O Cool is 25°C (77°F). (77°F).

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Add the Second Pump Add another another Pump Pump from from the T-102 product T-102 product with the following information: In This Cell...

Enter...

Connections Name

P-101

Inlet

Acet Rich

Outlet

Acet Atm

Energy

Q 101

Parameters Adiabatic Efficiency

75%

The pressure of Acet Atm is 101.3 kPa (14.7 psia). psia) .

Add a Heater Add a Heater Heater operation downstre downstream am of Acet of Acet Atm with Atm with the following information: In This Cell...

Enter...

Connections Name

E-101

Inlet

Acet Atm

Energy

Q 10 3

Outlet

Acet Warm

Parameters Delta P

0 kPa

The temperature of Acet Warm is 55°C (130°F). (130°F).

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Adding the Recycles Make-up streams are necessary to compensate for the losses of Acetone and Water in the process product streams. To calculate the exact amount that is lost in the products, Balance operations operations are used. These are not real operations but only mathematical ways of obtaining the make-up values. A Mole Balance Balance operation operation will be used to create create two streams (Rec (Rec Acet and Rec Water) Water) with the same flowrates and compositions as the tower product streams Benzene and Benzene and CycloC6, CycloC6, respectively. These streams are then sent to a Component Splitter and split into two streams: one containing the product and the other containing traces of the lost solvent. The streams containing the lost solvents are the make-up streams which will be mixed with the recycled streams streams from the solvent solvent Recovery Tower.

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Add the Balance Operations Add two Balance Balance operations operations with the following following data: In This Cell...

Enter...

Connections Name

BAL-1

Inlet Streams

Be n z e n e

Outlet Streams

Rec Acet

1. 2.

On the Parameters tab, Parameters tab, specify the Balance Type as Type as Mole. Mole. Spec Specif ify y the the Tem Tempe pera ratu ture re and and Pre Pressu ssure re of of Rec Acet to Acet to be 55°C (130°F) and (130°F) and 101.3 kPa (14.7 psia).

3.

Add Add the the second second balan balance ce oper operati ation on with with the the follo followin wing g information.

In This Cell...

Enter...

Connections Name

BAL-2

Inlet Streams

CycloC6

Outlet Streams

Rec H2O

1. 2.

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On the Parameters tab, Parameters tab, specify the Balance Type as Type as Mole. Mole. Spec Specif ify y the the Tem Tempe pera ratu ture re and and Pre Pressu ssure re of of Rec H2O to H2O to be 25°C (77°F)and (77°F)and 101.3 kPa (14.7 psia). psia).


Add the Component Splitters Add two Component Splitters with Splitters with the following information: information: In This Cell...

Enter...

Connections Name

X-100

Inlets

Rec H2O

Overhead Outlet

H2O Make-up

Bottoms Outlet

Frac CycloC6

Parameters Overhead Pressure

101.3 kPa (14.7 psia)

Bottoms Pressure

101.3 kPa (14.7 psia)

Splits Benzene

0

CycloC6

0

Acetone

1.0

H2O

1.0

Specify the temperature of one of of the product streams to be 25°C (77°F). (77°F) . The temperature in the other stream will be calculated from the energy balance around the operation.

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In This Cell...

Enter...

Connections Name

X-101

Inlets

Rec Acet

Overhead Outlet

Acet Make-up

Bottoms Outlet

Frac Benzene

Parameters Overhead Pressure

101.3 kPa (14.7 psia)

Bottoms Pressure

101.3 kPa (14.7 psia)

Splits Benzene

0

CycloC6

0

Acetone

1.0

H2O

1.0

Specify the temperature of the product streams to be 55°C (130°F). (130°F).

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Add the Mixer Operations Add two Mixer operations Mixer operations with the following information: In This Cell...

Enter...

Connections Name

MIX-100

Inlets

Acet Warm Acet Make-up

Outlet

Acet to Rec

Connections Name

MIX-101

Inlets

H2O Cool H2O Make-up

Outlet

H2O to Rec

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Add the Recycles The input for the recycles is shown below. Note that because of the nature of the process, the Flow Tolerance is Tolerance is set to 1 and the Composition Tolerance is Tolerance is set to 1. The Recycles are installed as Simultaneous. Simultaneous . Put the case in Hold mode Hold mode before adding the recycles. In This Cell...

Enter...

Connections Name

RCY-1

Inlet

H2O to Rec

Outlet

Water

Parameters Vapour Fraction Fraction

10.0

Temperature

10.0

Pressure

10.0

Flow

1.0

Enthalpy

10.0

Composition

1.0

Connections Name

RCY-2

Inlet

Acet to Rec

Outlet

Acetone

Parameters

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Vapour Fraction Fraction

10.0

Temperature

10.0

Pressure

10.0

Flow

1.0

Enthalpy

10.0

Composition

1.0


Press the Go button Go button to begin calculations. Having completed the recycles and converged the whole flowsheet, operations can be opened again in order to be examined.

Save your case!

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