Assignment Filtration Adsorption

8/8/2019 Assignment Filtration Adsorption

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Separation processes II

Module CPPT 9004: Separation processes II

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Contents

Object

Introduction

Process Operations

Applicability

Theory

Limitations

Counter current model

Co-current model

Column High and diameter

Modeling

General Process Summary

Conclusions

References

Appendix A

Appendix B

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Object

Part A : Filtration

Filtration and drying are two important unit operations in most pharmaceutical

and chemical processes and are usually carried out in series. In the aspirin

production process you will have conducted mass and energy balances over the

filter. Based on these balances, critically examine a number of filtration options

and select what you consider to be the most suitable types, giving your reasons.

Filtration unit operation:

The stream from the crystalliser is fed to a filtration unit (feed composition is

based on the mass balance performed in Module 9001). Laboratory tests have

given the following data. (Assume an incompressible filter-cake and that the

resistance related to the filter medium and initial layer is negligible)

The filter cake porosity = 0.1

Filtrate specific gravity = 1.0 kg per litre

Specific resistance of the filter-cake, r = 8.0 x 1013 m-2.

Filtrate viscosity, = 1.0 x 10-3

Ns m-2

Design vacuum and pressure filtration units for the required duty. Support your

argument with clear references to both authoritative literature and your design

calculations.

After washing, the filter-cake is pre-dried down to 2.0%w/w water in the

filtration unit before being fed to the dryer.

Part C: Adsorption

Problem No. 1:

Adsorption on 6x10-mesh activated carbon is being considered to recover

methyl ethyl ketone (MEK) from an air stream at 25 oC and 1 atm. The airflow is

12,000 std ft3/min, and the air has 0.4 lb MEK/1000 std ft3. If the superficial

velocity is 0.5ft/s, and an adsorption cycle of at least 8 h is desired, what bed

dimensions should be used? Assume the bulk density of the carbon is 30 lb/ft3.

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Problem No. 2:

Granular carbon is used to remove phenol from an aqueous waste. If 10x20 mesh carbon is used with a superficial velocity of 0.03m/s, estimate the number

of transfer units in a bed 4 m deep. The effective diffusivity in the particles can

be taken as 0.2 times the bulk diffusivity.

Properties of MEK = C4H8O8

T oC 14 25 41.6 79.6P mm Hg 60 100 200 760

= 0.805 g/cm3 at 20 oCM= 72.1Incoming air has 0.40 lb MEK/1000 SCF

==

359/1000

1.72/40.0y 1.99*10 -3 mol fraction MEK

p = 1.99*10-3 (760) =1.51 mm Hg

At 25 oC , p/P= 1.51/100 = 0.0151

If the bed heats up to 40 oC during adsorption,

p/P= 1.51/192= 7.86*10 -3

We have to estimate equilibrium adsorption at 25 oC and 40 oC . From the table

of additive volume increments.

V = 4(14.8) + 8(3.7) +9.9 = 98.7

At 25 oC

(T/V) log (f/fs) = (298/98.7)log(100/1.51)= 5.498

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Using the curve for n-paraffins:

Volume adsorbed =25cm3/100g

W=0.25*0.805=0.20g/g carbon

At 40oC,

(T/V) log (f/fs) = (313/98.7)log(192.1/1.51)= 6.670

W= 0.20*0.805=0.16 g/g carbon

Air flow at bed inlet:

(12000/60)*(298/272) = 218 ft3/s

For uo=0.5 ft/s, area = 436 ft2

For a cylindrical bed:

Dbed = (436*4/)0.5 = 23.6 ft

A rectangular bed 14 ft x 31.1 ft or 16 ft x 27.3 ft could also be used. Check beddepth to see if a horizontal cylinder could be used.

Per ft2 of cross section, MEK adsorbed in 8 h is:

8*0.5*3600*(273/298)*(0.40/1000) = 5.28 lbCarbon needed: 5.28/0.16 = 33lbBed density is 30 lb/ft 3 or 30 lb/ft for 1 ft2

Lmin= 33/30=1.1 ftIf half the bed capacity is used at the breakpoint,a bed 2.2 ft long would suffice.Then a racterngular bed 2-3 ft deep could be placed in the middle of a horizontalcylinder vessel. This would be less expensive than a 23.6 ft diameter cylindricalbed.

Estimate N, the number of transfer units

Dp= (3.327+1.651)/ 2= 2.49 mmAt 25oC l for air = 0.152cm2/s

Re= 0.25152.0

)/48.30*5.0(249.0=

scm

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Introduction

The separation of the components of a liquid mixture by treatment with a

solvent in which one or more of the desired components is preferentially soluble

is known as liquidliquid extractionan operation which is used, for example, in

the processing of coal tar liquids and in the production of fuels in the nuclear

industry, and which has been applied extensively to the separation of

hydrocarbons in the petroleum industry. Extraction is a process that separates

components based on chemical differences. The basic principle behind extraction

involves the contacting of a solution with another solvent that is immiscible with

the original. The solvent is also soluble with a specific solute contained in the

solution. Two phases are formed after the addition of the solvent, due to the

differences in densities and immiscibility. The solvent is chosen so that the

solute in the solution has more affinity toward the added solvent. Therefore

mass transfer of the solute from the solution to the solvent occurs. Further

separation of the extracted solute and the solvent will be necessary. However,

these separation costs may be desirable in contrast to distillation and other

separation processes for situations where extraction is applicable.

It is possible to combine stages A-(bringing the feed mixture and the solvent

into intimate contact) and B-(separation of the resulting two phases) into asingle piece of equipment such as a column which is then operated continuously.

Such an operation is known as differential contacting. Liquidliquid extraction is

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also carried out in stagewise equipment, the prime example being a mixer

settler unit in which the main features are the mixing of the two liquid phases by

agitation, followed by settling in a separate vessel by gravity.[1],[8]

General Extraction Flowsheet

SOLVENT

FEED

EXTRACT

RAFFINATE

Figure 1: Flowsheet for the extraction column.

A general extraction column has two input stream and two output streams. The

input streams consist of a solution feed at the top containing the solute to be

extracted and a solvent feed at the bottom which extracts the solute from thesolution. The solvent containing the extracted solute leaves the top of the

column and is referred to as the extract stream. The solution exits the bottom of

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the column containing only small amounts of solute and is known as the

raffinate. Further separation of the output streams may be required through

other separation processes. In this case be practical distillation column forfurther purification of ethanal, from the water ethanal raffinate solution.

Therefore extraction is in many ways complementary to distillation and is

preferable in the following cases: [1],[8]

(a) Where distillation would require excessive amounts of heat, i.e. when the

relative volatility is near unity.

(b) When the formation of azeotropes limits the degree of separation obtainable

in distillation.

(c) When heating must be avoided.

(d) When the components to be separated are quite different in nature

Process Operation

There are certain design variables that must be assigning in an extraction

process. As in many separation processes, the pressure and temperature

conditions play a large role in the effectiveness of the separation. In order for a

good split of the feed the pressure and temperature must be such so as toensure that all components remain in the liquid phase. The process will be

adversely affected if one or more of the components are allowed to become a

vapour, or the extraction may not occur at all if a large enough portion of a

component is allowed to vaporize. In addition, the temperature should be high

enough that the components are all soluble with one another. If extremes in

temperature are present, finding a suitable solvent for extraction can be

problematic. This is however generally not the case since one of the biggest

benefits in the extraction process is that it can be done at ambient pressures

and temperatures. In many applications, a separation process is desired where

an extreme temperature will destroy the desired product such as the

pharmaceutical industry. For these applications, extraction is ideally suited,

since the only temperature requirement is that dictated by the solubility. At this

point the biggest challenge would be finding a suitable solvent for the

extraction. We can also use the pharmaceutical industry in another example for

the benefits of extraction and this has to do with the volumes involved for

effective extraction. The extraction process can become very expensive if the

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solvent needed to be used is costly these expenses can be contained if a batch

process is being used and this is often the case in medicines. In a non-batch

process the solvent would need to be constantly supplied and this would involveeither a huge amount of solvent or another separation process in order to

recycle the solvent. [4]

In this case, we assume:

1. Operating temperature, temperature of entering stream 15oC (ambient).

2. Operating pressure, pressure of entering stream 1 atm (ambient).

3. Feed Flow Rate 1000kg/h.

4. Composition of feed 0.0526 kg Ethanal /kg Toluene in feed,

0526.0950

502 ===

kgToluene

kgEthannalx .

Applicability

It must decide which extractor would be relevant for our situation. The

specifications for each of these different systems are relatively the same. The

design limitations should be placed on each system in order to optimize the

individual process, maximize surface area of mass transfer, and adjust flow

feeds for maximum solute recovery. Generally, there are three main types of

extractors:

1. Mixer-settlers - are used when there will only be one equilibrium stage in the

process. For such a system, the two liquid phases are added and mixed. Due to

their density differences, one phase will settle out and the mixture will be

separated. The downfall to this type of extractor is that it requires a large-

volume vessel and a high liquid demand.

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Figure 2: Example of mixer-settler [2]

2. Contacting columns - are practical for most liquid-liquid extraction systems.

The packings, trays, or sprays increase the surface area in which the two liquid

phases can intermingle. This also allows for a longer flow path that the solutioncan travel through. In the selection of a packing, it is necessary to select a

material that is wetted by the continuous phase. Lastly, the flow in a column

should always be counter-current.

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Figure 3: Example of mixer-settler [2]

3.Centrifugal contractors - are ideal for systems in which the density difference

is less than 4%. In addition, this type of system should be utilized if process

requires many equilibrium stages. In these systems, mechanical devices are

used to agitate the mixture to increase the interfacial area and decrease masstransfer resistance.

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Figure 4: Example of centrifugal contractor [3]

Bellow tabulated advantages and disadvantages for the various extractor types.

Type of extractor Advantages Disadvantages

Mixer-settler - efficient- good contacting- any number of

stages- low head room

- large area to byused

- cost (highoperation and set-up)

Centrifugal extractor - able to separateliquid with smalldensity differences

- short holding time

- high set-up andoperation cost

- not applicable formany stages

Column( without agitation)

- small investmentand operation cost

- difficult to scale-up- less efficient then

mixer-settlers- high head room

Column (with agitation) - low investmentcost

- handle manynumber of stages

- good dispersion

- not applicable forhigh flow ratio

- separation difficultfor small densitiesdifferences

Table 1: Advantages and disadvantages various types of extractors. [4]

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Theory

Usually in a liquid-liquid system there are three components, A, B, and C, in twophases. Substituting into the phase rule gives 3 degrees of freedom. There are 6

variables: temperature, pressure, and four concentrations. Two of the mass

fractions in a phase can be specified with the third determined by the equation:

XA + XB + XC = 1.0

For most situations temperature and pressure are set, therefore the system can

be fixed by setting one concentration in either phase. Ternary Phase diagrams,

triangular coordinates, are used to represent the equilibrium data of three-

component systems. This is shown in figure bellow.

Figure 5: Example of general triangular diagram.

For example the mass fraction xc is designated by the perpendicular distance to

base AB. Furthermore these diagrams are fitted with curves and lines presenting

the equilibrium data for the components in the mixture. A typical phase diagram

is shown in Figure 3. For example the mass fraction xc is designated by the

perpendicular distance to base AB. Furthermore these diagrams are fitted with

curves and lines representing the equilibrium data for the components in the

mixture. A typical phase diagram is shown in figure bellow.

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Figure 6: General Liquid-Liquid phase diagram

The mixture in Figure 3 will separate into two phases following the tie line that

runs through point M. Point A is the raffinate phase and B is the extract phase.

Several other tie lines are shown. Point P represents the point where the two

phases are the same, this is known as the Plait point. The area of the two-phase

region and the path of the tie lines depend on the equilibrium data for the

system. These graphs change due to variables such as the components used in

the system, temperature, and pressure.

Equilibrium data

The equilibrium condition for the distribution of one solute between two liquid

phases is conveniently considered in terms of the distribution law. Thus, at

equilibrium, the ratio of the concentrations of the solute in the two phases is

given by CE/CR= K where K is the distribution constant. This relation will apply

accurately only if both solvents are immiscible, and if there is no association or

dissociation of the solute. If the solute forms molecules of different molecular

weights, then the distribution law holds for each molecular species. Where the

concentrations are small, the distribution law usually holds provided no chemicalreaction occurs. The addition of a new solvent to a binary mixture of a solute in

a solvent may lead to the formation of several types of mixture:

1. A homogeneous solution may be formed and the selected solvent is then

unsuitable.

2. The solvent may be completely immiscible with the initial solvent.

3. The solvent may be partially miscible with the original solvent resulting in the

formation of one pair of partially miscible liquids.

4. The new solvent may lead to the formation of two or three partially miscible

liquids. [1]

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For the purpose of this exercise I assume that toluene and water are immiscible

and the distribution coefficient or K-value is 2.20 i.e. y = 2.2x, where y = kg

ethanal/kg water and x = kg ethanal/kg toluene.

EXTRACTION COLUMN

F XA , in F XA, out

W Yout

W Y in

Figure 7: Scheme of the extraction process.

Limitations

1. Suitable Solvent [4]

- Solvent partially soluble with the carrier.

- Feed components immiscible with the solvent.

- Solute is soluble in the carrier and at the same time completely or partially

soluble in the solvent.

- Different densities than the feed components for a phase separation to

facilitate and maintain the capacity of the extractor high.

- Extremely high selectivity for the solute for the solvent to dissolve the

maximum amount of solute and the minimum amount of the carrier.

- Large distribution coefficient to reduce the theoretical number of stages

contributing to a greater efficiency

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- Low viscosity increases the capacity of the extraction column and does not

allow for the settling rate of dispersion to be slow.

- Chemically stable and inert toward other components of the system- Low cost, non-toxic, and non-flammable.

2. Equipment

- Interfacial tension and Viscosity

- High interfacial tension and viscosity leads to more power being supplied to

maintain rapid mass transfer throughout the extraction process.

- Low interfacial tension and viscosity leads to the formation of an emulsion.

3. Temperature preferred to be higher since solubility increases, but

temperature not higher than the critical solution temperature.

4. Pressure for condensed system must be maintained below the vapour

pressure of the solutions such that a vapour phase will not appear and interrupt

liquid equilibrium.

5. Separation may only occur for compositions in the region between the feedcomposition and that apex of the carrier.


Step 1: Determine the minimum solvent-to-feed ratio (S/F)min. This calculation

needs to be completed to find the extract composition.

To find the minimum flow rate the slope from the equation need to be

calculated:

42.2)005.00526.0(

)0115.0(

)(

)(

12

12=

=

=

xx

yySLOPE

s

a=

42.2

Where a = 950 kg, therefore minimum flow rate:

hrkgS /39342.2

950min ==

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393 kg/hr is the minimum flow rate of water to achieve required purity of

toluene. Though to design extractor operating with this flow rate, will required a

large number of stages. The equilibrium curve is draw based on the equationgiven as y = 2.2x .

Counter current minimum water flow rate

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.01 0.02 0.03 0.04 0.05 0.06

kg ethanal/kg toluene

kgethanal/kgwater

equlibrium 0.0526 Smin 0.005

Figure 8: Operating line for minimum water flow.

To choose proper operating conditions, a few different water flow rates will be

examine, and the results ware plotted. First step in this operation is todetermine the slope for each of the vary water flow rates.

For 400 kg/hr water flow rate slope will be:

38.2400

950==Slope

Using formula for the slope:

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)(

)(

12

12

xx

yySLOPE

= where, x1= 0.005, x2= 0.0526, y1= 0, we can determine

unknown y2.

)005.00526.0(

)0(38.2

2

=

y

y2= 0.113

Tabulated data for different water flow rates for counter current model.

Flow ratewater [kg]

Flow rateA [kg] Slope XN XF y1 y2

400 950 2.38 0.005 0.0526 0 0.113600 950 1.58 0.005 0.0526 0 0.075800 950 1.19 0.005 0.0526 0 0.0571000 950 0.95 0.005 0.0526 0 0.0451200 950 0.79 0.005 0.0526 0 0.0381400 950 0.68 0.005 0.0526 0 0.0321600 950 0.59 0.005 0.0526 0 0.0281800 950 0.53 0.005 0.0526 0 0.0252000 950 0.48 0.005 0.0526 0 0.023

Table 2: Results for vary water flow rate for counter current model.

The plot was created using Excel spreadsheet, as seen on next page on figure 9.

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Counter current vary water flow rates

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.01 0.02 0.03 0.04 0.05 0.06


kgethanal/k

gwate

equlibrium 0.0526 0.005 400 kg/hr water

600 kg/hr water 800 kg/hr water 1000 kg/hr water 1200 kg/hr water


Figure 9: Operating lines for vary flow rates of water

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Step 2: Calculate the number of stages. From graphic method steping off on the

plot from operating line to equilibrium line. This procedure should be repeateduntil stages have been constructed to x1, the raffinate composition.

Counter current vary water flow rates

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.01 0.02 0.03 0.04 0.05 0.06


kgethanal/kgwater


600 kg/hr water 1000 kg/hr water 2000 kg/hr water

12

34

56

78

9

1011

12

13

14

15

16

1718

Figure 10: Graphical method for determining the number of stages for the

counter current flow with water flow at 400kg/hr.

As can be seen for the flow water flow rate 400 kg/hr, which is close to amount

of minimum solvent = 393, the number of stages is 18.

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Figure 11: Graphical method for determining the number of stages for the counter current flow with water flow at

600kg/hr,1000 kg/hr, 2000 kg/hr.

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From the plot on the previous page, it is obvious by increasing amount of our

wash solvent decrees number of stages necessary to approach required purity of

our raffinate toluene in this case. Tabulated results for vary water flow rate vsnumber of stages.

Number of stages Solvent water used [kg/hr]18 4004 6003 10002 2000

Table 3: Number of stages versus water flow.

number of stages versu water flow for counter current model

0

2

4

6

8

10

12

14

16

18

20

0 500 1000 1500 2000 2500

Water flow [kg/hr]

numberof

stages

number of stages versu waterflow

Table 12: Plot number of stages versus water flow for counter current model.

Co-current model

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For the co-current flow if the distribution law is followed, then the equilibrium

curve becomes a straight line given by y = mx. The material balance on the

solute may then be rewritten as:Ax2 = Ax1 + Sy1 = Ax1 + Smx1 = (A + Sm)x1

and the number of stages is given by:

n = (log(x1/x2))/log[A/(A + Sm)]

Using the same formula for the slope:

)(

)(

12

12

xx

yySLOPE

=

where, x1= 0.005, x2= 0.0526, y2= 0, can be determine

unknown y1.

Tabulated data for different water flow rates for co-current model.

Flowratewater[kg]

Flowraet A[kg] Slope Xn Xf Slope y1 y2

400 950 2.38 0.005 0.0526 -2.38 0.113 0

600 950 1.58 0.005 0.0526 -1.58 0.075 0

800 950 1.19 0.005 0.0526 -1.19 0.057 0

1000 950 0.95 0.005 0.0526 -0.95 0.045 0

1200 950 0.79 0.005 0.0526 -0.79 0.038 0

1400 950 0.68 0.005 0.0526 -0.68 0.032 0

1600 950 0.59 0.005 0.0526 -0.59 0.028 0

1800 950 0.53 0.005 0.0526 -0.53 0.025 0

2000 950 0.48 0.005 0.0526 -0.48 0.023 0

Table 4: Results for vary water flow rates for co-current model.

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Co-current extraction model

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.01 0.02 0.03 0.04 0.05 0.06


kgethanal/kg

water




Figure 13: Operating lines for vary water flow rates for co-current model.

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The number of stages can be determined from graphic method, by stepping off

on the plot prom operating line to equilibrium line. This procedure should be

repeated until stages have been constructed to x1, the raffinate composition.

Co-current extraction model - number of stages

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.01 0.02 0.03 0.04 0.05 0.06


kgethanal/kg

water



1

2

34

56

Figure 14: Graphical method for determining the number of stages for the

co-current flow with water flow at 400kg/hr.

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Figure 15: Graphical method for determining the number of stages for the co-current flow with water flow at 600kg/hr,

1000kg/hr, 1400kg/hr, 2000kg/hr.

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As can be observed from the plot on the previous page, the number of stages

for different water flow rates, changes as in the table bellow.

Water flow rate [kg/hr] Number of stages400 6600 51000 51400 42000 3

Table 5: Tabulated data for graphic method for estimation of number of stages

in co-current model

0

1

2

3

4

5

6

7

0 500 1000 1500 2000 2500

Water flow[kg/hr]

numberofstage

number of stages vs water flow

rate for co-current model

Table 16: Plot number of stages versus water flow for co - current model.

Column High and diameter

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After completing all estimation calculations, and choosing the best operating

conditions, the extraction column diameter, and height, can be determined as

well as the estimation operating cost. As shown in next few steps.

Step A: Determination of Extraction Column Diameter [4]

For the counter-current flow the diameter of the column must be big enough to

allow two phases to flow through the column without flooding. The column

diameter for liquid liquid devices can be estimate based on number of variables

including:

1. Individual phase flow rates

2. Density differences between the two phases

3. Interfacial tension

4. Direction of mass transfer

5. Viscosity and density of continuous phase

6. Geometry of internals

Column diameter can be determined through scale-up of laboratory test

analysis. The experimental data are obtained by: testing unit system with

components of concern in the laboratory or pilot plants on the really small scale.The superficial velocities are measure in each phase. The sum of these velocities

may be assumed to hold constant for larger scaled-up commercial units.

Collected data will be used to calculate diameter of column.

Step B. Determining the Height of the Column

We can determine height based on HETS (Height Equivalent to a Theoretical

Stage) it can be applied directly to determine column height from the number of

equilibrium stages. The HETS depends on the physical properties such as;

interfacial tension, phase viscosities, density difference between phases.

Total Height = (HETS)(Number of Equilibrium Stages)

Step C. Costs estimation

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The total cost of the extraction is directly related to the extraction design

variables and type of extraction equipment applied. The variables that affecting

the economic balance are:- at fixed solvent feed ratio, the amount of solvent extracted increases with

increased number of trays. Hence, the value of the unextracted solute may be

balanced against the cost of the extraction equipment required to recover it.

- for a fixed extent of reaction, the number of stages required decreases as the

solvent rate or reflux ratio increases. The capacity of the equipment necessary

for handling the larger liquid flow must increase with the larger reflux rate.

Hence, the cost of the equipment passes through a minimum when the

minimum numbers of stages are utilized.

- when reflux ratio and solvent rates are increased the extract solutions become

more dilute. Therefore, the cost of solvent removal is increased as well as the

operating cost for increased utilities.

As a result of these economic balances the total investment and operating costs

must achieved a minimum at the optimum solvent reflux rate. Additional cost

must be considered for the recovery of the saturated raffinate product as well as

the extract.

MODELING

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In chemical engineering, as well as in other scientific and technical domains,

where one or more materials are physically or chemically transformed, a process

is represented in its abstract form . The global process could be characterized byconsidering the inputs and outputs. As input variables (also called independent

process variables, process command variables, process factors or simple

factors), we have deterministic and random components. From a physical

viewpoint, these variables concern materials, energy and state parameters, and

of these, the most commonly used are pressure and temperature. The

deterministic process input variables, contain all the process variables that

strongly influence the process exits and that can be measured and controlled so

as to obtain a designed process output. The chemical reactions that take place

over a broad range of temperatures and pressures are extraordinarily diverse.

From the modelling viewpoint, this complexity results in a considerable number

of process and non-process parameters with an appreciable quantity of internal

links, as well as in very complex equations describing the process state. When

we build a model, some phenomena are simplified and consequently some

parameters are disregarded or distorted in comparison with their reality. In

addition, some of the relationships between the parameters could be neglected.Based on the set of simulation of processes, we have the simulation of a

physical process, which, in fact, is a small-scale experimental process

investigation. In other words, to simulate a process at laboratory-scale, we use

the analysis of a more affordable process which is similar to experimental

investigation. [5]

Modelling can be successfully used to:[5]

. reduce manufacturing costs

. reduce time and costs in all stages of the process life-cycle

. increase process efficiency

. allow a better and deeper understanding of the process and its

operation

. be used as support for the solutions adopted during the process

development and exploitation

. ensure an easy technological transfer of the process

. increase the quality of process management

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. reveal abilities to handle complex problems

. contribute to reducing pollution

. improve the safety of the plants

. market new products faster

. reduce waste emission while the process is being developed

. improve the quality of the products

. ensure a high quality of training of the operators.

1.ASPEN MODELS

A few of the choices are described here. The key decision must be make is what

model to use for the liquid phase activity coefficient. The Help/Physical Property

Methods/Choosing a Property Method menu gives advice about which

thermodynamic model is recommended for different applications. In the liquid

phase, the simplest option is an ideal liquid, with an activity coefficient equal to

1.0. That choice leads to Raoults law, which may suffice for similar chemicals.Other models include regular solution theory using solubility parameters

(although not in Aspen Plus), NRTL, Electrolyte NRTL, UNIFAC, UNIQUAC, Van

Laar, and Wilson. Characteristics of the models are:[6]

1. The Electrolyte NRTL is especially suited for acid gas adsorption, which

includes the removal of carbon dioxide and hydrogen sulfide from a gas stream.

Refineries routinely use this process when making hydrogen. This is also one

way of capturing carbon dioxide from a power plant to capture and sequester it.

2. The UNIFAC model is a group contribution method that allows the model

parameters to be estimated using the molecular structure of each chemical.

When experimental data is not available, this is the only method that can be

used.

3. The UNIQUAC model uses binary parameters, which must be determined from

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experimental data. Once found, however, the same parameters can be used in

multicomponent mixtures of three or more chemicals.

4. Both UNIFAC and UNIQUAC can be used when two liquid phases or

azeotropes are present.

5. The Van Laar options are less recommended in Aspen Plus; they are simpler

to use than the others, but less successful in general. In Aspen Plus the ease of

use is immaterial since someone else has created the program.

6. The Wilson equation is an option if there is only one liquid phase, and it does

handle azeotropes.

The simulations ware run based on two models, as they ware the most

applicable for the system of interest: UNIFAC and UNIQUAC.


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Overall flowsheet for extraction counter current mode in ASPEN , as seen bellow.

6

7

8

9

B 1

Figure 17: Extraction flowsheet counter current mode.

Where:

Stream 6 Water

Stream 7 - Feed

Stream 8 - Extract

Stream 9 - Raffinate

B1- Extraction Unit

The run of the sensitivity simulation was based on vary water flow rate, whichwas applied for a different number of stages in column. The comparison of

results obtained using different models types, based on information provide by

ASPEN Help Library Tool. Column was set-up in two modes: UNIFAC and

UNIQUAC, temperature = 15oC (ambient), pressure = 1 Atm (ambient).

On the next page tabulated data.

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Table 6: Tabulated data for ASPEN simulation n-stages vary water flow rate, table 1.UNIFAC mode.

2

STAGES

WATER TOLUEN ETHANAL 1 ETHANAL 2

3

STAGES

WATER TOLUEN ETHANAL 1 ETHANAL 2KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR

480 949.7442 24.29787 25.70213 480 949.7356 26.67466 23.32534580 949.6974 27.68861 22.31139 580 949.6857 30.77106 19.22894680 949.6515 30.54623 19.45377 680 949.6382 34.20682 15.79318780 949.6074 32.96297 17.03703 780 949.5932 37.03377 12.96623880 949.5646 35.00795 14.99205 880 949.5494 39.32546 10.67454

980 949.5231 36.74245 13.25756 980 949.5075 41.17444 8.8255571080 949.4825 38.21617 11.78383 1080 949.4667 42.66185 7.3381531180 949.4422 39.47256 10.52744 1180 949.4271 43.86082 6.1391791280 949.4025 40.55028 9.449717 1280 949.3874 44.82659 5.1734061380 949.3635 41.48076 8.51924 1380 949.3493 45.61447 4.3855291480 949.3243 42.28418 7.715817 1480 949.311 46.25578 3.7442161580 949.2855 42.98369 7.016307 1580 949.2732 46.78379 3.2162091680 949.2475 43.59771 6.402294 1680 949.2356 47.22009 2.7799151780 949.2092 44.13655 5.863455 1780 949.1978 47.58292 2.4170841880 949.1715 44.61274 5.38726 1880 949.1603 47.88706 2.1129411980 949.1337 45.03417 4.96583 1980 949.1233 48.1437 1.8562992000 949.1261 45.11266 4.887341 2000 949.116 48.19015 1.809848

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4

STAGES

WATER TOLUEN ETHANAL 1 ETHANAL 2

5

STAGES

WATER TOLUEN ETHANAL 1 ETHANAL 2KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR

480 949.7314 27.82472 22.17528 480 949.7313 27.82126 22.17874580 949.6794 32.45003 17.54997 580 949.6796 32.45437 17.54563680 949.6302 36.33282 13.66718 680 949.6303 36.33481 13.66519780 949.5839 39.45853 10.54147 780 949.5839 39.45944 10.54056880 949.5401 41.89971 8.100288 880 949.54 41.90028 8.099716980 949.4977 43.76311 6.236886 980 949.4982 43.76568 6.234318

1080 949.4578 45.17746 4.822539 1080 949.4578 45.17708 4.8229221180 949.4181 46.24061 3.75939 1180 949.4185 46.24196 3.7580431280 949.3798 47.04437 2.955626 1280 949.3802 47.04483 2.955171380 949.342 47.65511 2.34489 1380 949.3419 47.65458 2.3454241480 949.3045 48.12135 1.878653 1480 949.3044 48.12109 1.878911580 949.2674 48.48126 1.518742 1580 949.2674 48.48107 1.5189261680 949.23 48.76071 1.239287 1680 949.2302 48.76108 1.2389211780 949.1934 48.98069 1.019305 1780 949.1929 48.98037 1.0196291880 949.1565 49.15472 0.84528 1880 949.1564 49.15465 0.8453461980 949.1192 49.2935 0.706496 1980 949.1194 49.29358 0.7064172000 949.1119 49.31784 0.682159 2000 949.1119 49.31784 0.682162

Table 7: Tabulated data for ASPEN simulation n-stages vary water flow rate, table 2.UNIFAC mode.

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Toluen v s water v ary water flo

47 0

67 0

87 0

1070

1270

1470

1670

1870

949.1 949.2 949.3 949.4 949.5 949.6 949.7 949.8

Toluene [kg/h

Wa

ter[kg/hr] 2 stage

3 stage

4 stage

5 stage

Figure 18: Plot for results toluene Vs water for UNIFAC mode.

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Bellow collected data for toluene versus ethanal in extract stream for 2, 3, 4,and 5 stages in UNIFAC mode.

Sensitivity S-1 Results Summary

TOLUEN KG/HR

KG/HR

949.05 949.1 949.15 949.2 949.25 949.3 949.35 949.4 949.45 949.5 949.55 949.6 949.65 949.7 949.75 949.8

25.0

30.0

35.0

40.0

45.0

50.0

ETH1

Figure 19: Toluene Vs Ethanal in extract stream for 2 stages, UNIFAC mode.


TOLUEN KG/HR

KG/H

R

949.05 949.1 949.15 949.2 949.25 949.3 949.35 949.4 949.45 949.5 949.55 949.6 949.65 949.7 949.75 949.8

25.0

30.0

35.0

40.0

45.0

50.0

ETH1


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TOLUEN KG/HR

KG/HR

949.05 949.1 949.15 949.2 949.25 949.3 949.35 949.4 949.45 949.5 949.55 949.6 949.65 949.7 949.75 949.8

25.0

30.0

35.0

40.0

4

5.0

50.0

ETH1



ETH1 KG/HR

KG/HR

22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0 30.0 31.0 32.0 33.0 34.0 35.0 36.0 37.0 38.0 39.0 40.0 41.0 42.0 43.0 44.0 45.0 46.0 47.0 48.0 49.0 50.0

949.1

949

.2

949.3

949.4

949.5

949.6

949.7

949.8

TOLUEN


Sensitivity test was repeated for the same variables, using UNIQUAC mode. Onthe next page tabulated data.

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2

STAGES

WATER TOLUEN ETH1 ETH2

3

STAGES

WATER TOLUEN ETH1 ETH2KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR

480 949.759 7.76179 42.23821 480 949.7589 7.932407 42.06759580 949.7083 9.258436 40.74156 580 949.7083 9.529974 40.47003680 949.658 10.71364 39.28636 680 949.6576 11.10162 38.89838780 949.6077 12.13846 37.86154 780 949.6068 12.64101 37.35899880 949.5574 13.50642 36.49358 880 949.5564 14.1679 35.8321980 949.5071 14.82227 35.17773 980 949.5054 15.64362 34.35638

1080 949.4572 16.10266 33.89734 1080 949.4551 17.10797 32.892031180 949.4072 17.32702 32.67298 1180 949.4047 18.52515 31.474851280 949.3571 18.50375 31.49625 1280 949.3544 19.89388 30.106121380 949.3071 19.62506 30.37494 1380 949.3042 21.24955 28.750451480 949.2579 20.74037 29.25963 1480 949.2539 22.52621 27.473791580 949.208 21.7648 28.2352 1580 949.2035 23.77485 26.225151680 949.1582 22.75903 27.24097 1680 949.153 24.98476 25.015241780 949.109 23.72184 26.27816 1780 949.1035 26.12244 23.877561880 949.0598 24.65211 25.34789 1880 949.0538 27.24526 22.754741980 949.0105 25.52951 24.47049 1980 949.0039 28.29413 21.705872000 949.0002 25.69364 24.30636 2000 948.9943 28.51686 21.48314

Table 8: Tabulated data for ASPEN simulation n-stages vary water flow rate, table 1.UNIQUAC mode.

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4

STAGES

WATER TOLUEN ETH1 ETH2

5

STAGES

WATER TOLUEN ETH1 ETH2KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR KG/HR

480 949.759 7.968364 42.03164 480 949.7592 7.991244 42.00876580 949.7084 9.592094 40.40791 580 949.7084 9.604901 40.3951680 949.6571 11.17303 38.82697 680 949.6576 11.21473 38.78527780 949.6067 12.78024 37.21976 780 949.6067 12.81812 37.18188880 949.5557 14.34613 35.65387 880 949.5561 14.42265 35.57735980 949.5052 15.9139 34.0861 980 949.5047 15.98823 34.01177

1080 949.4548 17.45886 32.54114 1080 949.4539 17.56418 32.435821180 949.4037 18.96508 31.03492 1180 949.4035 19.15834 30.841661280 949.3529 20.44868 29.55132 1280 949.3525 20.69463 29.305371380 949.3022 21.89732 28.10268 1380 949.3017 22.19923 27.800771480 949.252 23.33526 26.66474 1480 949.2515 23.73277 26.267231580 949.2009 24.69912 25.30088 1580 949.2008 25.16638 24.833621680 949.1517 26.04809 23.95191 1680 949.1499 26.6151 23.38491780 949.1009 27.33494 22.66506 1780 949.0998 28.02938 21.970621880 949.0509 28.58773 21.41227 1880 949.0496 29.34275 20.657251980 949.0008 29.7772 20.2228 1980 948.9983 30.61331 19.386692000 948.9904 30.00157 19.99843 2000 948.9893 30.91345 19.08655

Table 9: Tabulated data for ASPEN simulation n-stages vary water flow rate, table 2.UNIQUAC mode.

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Toluene vs water for UNIQUAC mode

450

650

850

1050

1250

1450

1650

1850

948.98 949.18 949.38 949.58 949.78 949.98

Toluene [kg/hr]

Water[kg/hr] 2 stages

3 stages

4 stages

5 stages

Figure 23: Plot for results toluene Vs water flow rate for UNIQUAC mode.

Bellow collected data for toluene versus ethanal in extract stream for 2, 3, 4,and 5 stages in UNIQUAC mode.


ETH1 KG/HR

KG/HR

6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0

949.1

949.2

949.3

949.4

949.5

949

.6

949.7

949.8

TOLUEN

Figure 24: Toluene Vs Ethanal in extract stream for 2 stages, UNIQUAC mode.

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ETH1 KG/HR

KG/HR

6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0

949.0

949.1

9

49.2

949.3

949.4

949.5

949.6

949.7

949.8

TOLUEN



TOLUEN KG/HR

KG/HR

948.95 949.0 949.05 949.1 949.15 949.2 949.25 949.3 949.35 949.4 949.45 949.5 949.55 949.6 949.65 949.7 949.75 949.8 949.85

10.0

15.0

20.0

25.0

30.0

35.0

ETH1


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TOLUEN KG/HR

KG/HR

948.95 949.0 949.05 949.1 949.15 949.2 949.25 949.3 949.35 949.4 949.45 949.5 949.55 949.6 949.65 949.7 949.75 949.8 949.85

10.0

15.0

20.0

25.0

3

0.0

35.0

ETH1


Comparison UNIFAC VS UNIQAC model

0

500

1000

1500

2000

2500

948.8 949 949.2 949.4 949.6 949.8

Toluene [kg/hr]

Water[kg/hr]

UNIFAC

UNIQUAC

Figure 28: Comparison of UNIFAC and UNIQAC modes, based on 2 stagessensitivity test.

Co current mode

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For co-current mode, ware run few different run with vary flow of wash solvent,

as well as vary number of stages. Set up for co current run was as describe:

mixer to which fresh feed and solvent stream ware introduced, was followed by

settler, from which extract was collected at the bottom, and the raffinate from

the top was send it to the nest stage, so in that case to next mixer unit.

Operating conditions ware applied as describe for counter current flow,

temperature= 15oC , and the pressure = 1 atmosphere. Use of Aspen Plus was

based on UNIFAC model. Bellow next page, general flow shets, and table

results, for 2, 3, 4 stages separation unit with vary water flow rates: 500, 1000,1500 [kg/hr] respectively.

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Figure 29: 2 stages co-current mixer settler separation unit.

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Table 10: 2 stages co-current mixer settler separation unit results for 500[kg/hr] water flow rate.

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Co-current mode is mostly used in batch operation. Batch extractors have

traditionally been used in low capacity multi-product plants such as are typical in

the pharmaceutical and agrochemical industries. For washing and neutralization

operations that require very few stages, co-current operation is particularly

practical and economical and offers a great deal of flexibility. The extraction

equipment is usually an agitated tank that may also be used for the reaction

steps. In these tanks, solvent is first added to the feed, the contents are mixed,

settled and then separated. Single stage extraction is used when the extraction

is fairly simple and can be achieved without a high amount of solvent. If more

than one stage is required, multiple solvent-washes are given. Though operation

in co-current mode offers more flexibility, it is not very desirable due to the high

solvent requirements and low extraction yields. The co-current operation is

mostly used in low capacity multi-product batch plants. For larger volume

operation and more efficient use of solvent, counter current mixer-settlers or

columns are employed. Counter current operation conserves the mass transfer

driving force and hence gives optimal performance.

Comparison of co-current and counter current model

0

2

4

6

8

10

12

14

16

18

20

0 500 1000 1500 2000

water flow [kg/hr]

numberofstage

co-current

counter current

Figure 32: Comparison of counter and co-current modes.

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General Process Summary

EXTRACTION

COLUMN

DISTILLATION

COLUMN

FEED

SOLVENT=WATER

EXTRACT

ETHANAL

WATER

RAFFINATE

Figure 33: General process flowsheet.

After extraction process, we will have extract containing 99.5% of toluene and

0.5% of ethanal, and raffinate on the bottom of the extraction column

containing 0.5% of toluene, water and 99.5% of ethanal. Raffinate will be sent it

to distillation column for recovery and purification of the ethanal. As water-

ethanal system doesnt create azeotrope solution, it will be easy to separate.

The boiling point of the ethanal = 20.2 oC, and the boiling point of the water =

100 oC. [11] the feed our raffinate will be introduced to distillation column at

temperature of 20 oC, liquid at boiling point, with no vapour. Drawing a

equilibrium curve for water ethanal system, based on the Antoine coefficients

which can be found in chemical engineering books. From the curve we are able

to compute the mass balance on the process. Composition on the top and the

bottom of the column is required, to step off the number of stages required to

achieve specific purity. The stepping off starts at the feed of around 20%(data

taken from Aspen Simulation counter current mode, water flow=480[kg/hr], and

finishing at point giving a distillation composition of 99%(as this is required

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ethanal-acetaldehyde composition). Next step is to find reflux ratio, the equation

can be used:

q =1+

)( TfTbCp L

Where:

Cp L =Specific Heat capacity of liquid

Tb = Bubble point

Tf = Feed temp

=Latent heat of vaporisation.

After completing mass balance for distillation column and energy balance,

diameter, and high can be estimate.

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CONCLUSION

As we have seen in the sections above, there are a number of factors affecting

extraction performance. Laboratory and pilot plant testing using actual feed and

solvent help in optimization. The study could often be an iterative cycle

involving laboratory testing followed by process simulation and design. In most

industrial extractors, there is usually a good scope for optimizing solvent usage

and energy consumption. The extraction model, which I used for separation

ethanal/toluene/water is continuous process, counter current mode. The counter

current mode of operation outperforms the co-current mode. This is

demonstrated in a case study presented. This process was chosen because the

system operating with high quantity flow rate. Also I have used vary information

and methods for describing the material balance, designed of extraction column,

flow diagram. The system will operate at ambient pressure and temperature

which will be equal respectively 15oC and 1 atmosphere for the extraction

column. Based on the UNIQUAC Aspen model using binary parameters, which

are determine from experimental data. The same parameters can be used in

multicomponent mixtures of three components i.e. toluene / ethanal / water.

General design process required determination of solvent- water flow [kg/hr],

basic design of the system, number of stages, and equipment required. Based

on the run simulations in Aspen Plus, I will suggest counter current flow with 2

stages centrifugal extractor. As we can see from the results simulation for Aspen

counter current Sensitivity test, the best effectively we will achieve when we will

use 480-580 [kg/hr] of solvent- water, used in two stages step. I will suggest

Pod liquid-liquid centrifugal extractor and separator, as seen on the figure on

the next page.

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Figure 34 : The Podbielniak Contactor

The Podbielniak is providing differential counter current extraction in a compact

hermetic rotor. Is used successfully for more than fifty years to solve extraction

problems in the chemical process industry, the Pod can provide up to 5

theoretical stages in one unit and can separate liquids with a specific gravity

difference as low as 0.01. The Pod has a bright future in new technologies as

indicated by ongoing research in non-conventional applications. [10] Counter

current configuration increase extraction efficiency at a given flow rate ratio.

Using Pod as an extractor we can reduces solvent usage and operating costs

while producing better product at higher yields in a safer environment. Complete

enclosure will provide safer operations process, the possibility of product

contamination will be reduced. Large interfacial area, and high flow rate will

shorten residence time when necessary. More stable then other types because

of horizontal orientation reduce possibility for formation of emulsion.

Introduce further separation process applies only for recovery of ethanal,

implement distillation reduce solvent and solute losses.

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REFERENCES

1. Coulson and Richardsons CHEMICAL ENGINEERING VOLUME 2,5th Edition

Particle Technology and Separation Processes,2002.

2. http://www.halwachs.de

3. http://www.bjtoptec.com

4. Seader,J.D. and Henley, E.J. Separation Process Principles. John Wiley

and Sons, 1998.

5. Chemical Engineering: Modelling, Simulation and Similitude Tanase Gh.Dobre, Jos G. Sanchez Marcano ,2007.

6. INTRODUCTION TO CHEMICAL ENGINEERING COMPUTING, BRUCE A.

FINLAYSON, PH.D., A JOHN WILEY & SONS, INC., PUBLICATION, 2006.

7. http://www.akpetrochem.com

8. Unit Operations, Warren L. McCabe, Jul;ian C. Smith, Peter Harriott,

2001.

9. CHOPEY,N.P. Handbook of chemical engineering calculations

10. http://www.pharmaceuticalonline.com/article.mvc/Podbielniak-

Contactor-A-Unique-Liquid-Liquid-0003?VNETCOOKIE=NO

11. http://en.wikipedia.org

63
http://www.halwachs.de/solvent-extraction.htmhttp://www.bjtoptec.com/en/sbxs2.asp?id=177http://eu.wiley.com/WileyCDA/Section/id-302479.html?query=Tanase+Gh.+Dobrehttp://eu.wiley.com/WileyCDA/Section/id-302479.html?query=Tanase+Gh.+Dobrehttp://eu.wiley.com/WileyCDA/Section/id-302479.html?query=Jos%C3%A9+G.+Sanchez+Marcanohttp://www.akpetrochem.com/http://www.pharmaceuticalonline.com/article.mvc/Podbielniak-Contactor-A-Unique-Liquid-Liquid-0003?VNETCOOKIE=NOhttp://www.pharmaceuticalonline.com/article.mvc/Podbielniak-Contactor-A-Unique-Liquid-Liquid-0003?VNETCOOKIE=NOhttp://en.wikipedia.org/http://www.halwachs.de/solvent-extraction.htmhttp://www.bjtoptec.com/en/sbxs2.asp?id=177http://eu.wiley.com/WileyCDA/Section/id-302479.html?query=Tanase+Gh.+Dobrehttp://eu.wiley.com/WileyCDA/Section/id-302479.html?query=Tanase+Gh.+Dobrehttp://eu.wiley.com/WileyCDA/Section/id-302479.html?query=Jos%C3%A9+G.+Sanchez+Marcanohttp://www.akpetrochem.com/http://www.pharmaceuticalonline.com/article.mvc/Podbielniak-Contactor-A-Unique-Liquid-Liquid-0003?VNETCOOKIE=NOhttp://www.pharmaceuticalonline.com/article.mvc/Podbielniak-Contactor-A-Unique-Liquid-Liquid-0003?VNETCOOKIE=NOhttp://en.wikipedia.org/


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Appendix A

Acetaldehyde specification

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Appendix B

Toluene specification

Documents

Assignment Filtration Adsorption