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ADIGRAT UNIVERSITY

COLLEGE OF ENGINEERING AND TECHNOLOGY

DEPARTMET OF CHEMICAL ENGINEERING

COURSE TITLE MASS TRANSFER UNIT OPERATION

COURSE CODE Cheg3114

PROJECT MASS TRANSFER UNIT OPERATION

NETWORK -SIX

NAME OF STUDENT ID NO SECTION 1

1. LETBRHAN BAHTA………………………….0963/06

2. LETU DESALEGN………………………………0969/06

3. MEKONEN G/WAHID………………………. .1064/06

4. MIHRET G/MESKEL………………………….1121/06

5. MULUBRHAN G/MESKEL…………………….0893/05

6. TEKLAY GODEFA ……………………………..1429/06

7. TEMESGEN ABRAHALEY……………………..1464/06

Submitted to instructor H.T submission date 01/09/08 E.C

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Table content

Topic page

Introduction………………………………………………………………… 3

Chapter one

1. Drying of solid ………………………………………………………………………………4

2. Method of drying………………………………………………………………………….4

3 .mechanism of dryer………………………………………………………………………..5

4. Objective drying………………………………………………………………………………5

5. Application of drying………………………………………………………………………….5

6. Gas vapor mixture………………………………………………………………………….6

7. psychometric term…………………………………………………………………………..7

8. psychometric chart……………………………………………………………………………8

Chapter two

9. Crystallization………………………………………………………………………………10

10. Types of crystallizers………………………………………………………………………10

11, objective of crystallization…………………………………………………………………10

Chapter three

12. Extraction…………………………………………………………………………………12

13. Types extractor……………………………………………………………………………13

14. Objective extraction…………………………………………………………………………14

15. Application of extraction……………………………………………………………….15

16 .Advantage of extraction………………………………………………………………….15

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INTRODUCTION

In ancient time was used to separate two or more phase a different types of unit operation. These

unit operations are in traditional method and requires high amount of energy, poor quality

product and less economical profit. These unit operation was used by

Mineral to separate from its ore

In industry such as food processing, pharmaceutical,

Nowadays, these unit operations were used in modernized method in different corner of world in

industry. These unit operation include

Drying

crystallization

extraction

These unit operation backbone in industry to produce a given raw material in to required product.

The separation of drying convert solid, semisolid or liquid feedstock into solid product by

evaporation of the liquid into vapor phase due heat. drying various feedstock for the following

reason;

for preservation

reduction in cost transportation

easy handling etc.

is a science dealing with the physical law of air –water vapor mixture.it is a field of engineering

concerned with determination of physical and thermodynamic properties of gas

mixture.psychrometric chart it is representation of gas –vapor mixture use a chart to analyze

processing involving moist air and to determine moist air properties.

crystallization is a processes of formation solid precipitate from melt deposited directly from

gas.it also a chemical solid liquid separation technique in which mass transfer of solute from

liquid solution to form pure solid. Crystallization have a several importance.

Extraction the withdrawing of active agent or west substance from solid or liquid mixture with

a liquid solvent. The solvent is not or only partial miscible solid or liquid.

Depending on the phase following types of extraction.

1. Solid-liquid extraction

2. Liquid- liquid extraction

3. Gas-liquid extraction (absorption)

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The main area of extraction is for hydro metallic, for petroleum and pharmaceutical industry.

CHAPTER ONE

Drying of solid

Drying is unit operation in which liquid is separated from solid other than mechanical method.

In other word, the word dry refers to generally removal of moisture from substance.

This process is often used as final production step before packing product.

Dry is often necessary in various industrial operation particularly in chemical processes industry

to remove moisture from wet solid a solution or gas to make it dry and choice of dry medium

depend the chemical nature of the material.

Dryer are used in variety industries such as

Food processing technology

Pharmaceutical

Paper, etc.

1.1method of dryer

Dryer can be divided in to two main type based on heating mode

Convective (direct dryer)

Conductive (indirect dryer)

Radiant(radiation)

A, direct dryer (adiabatic)

Unit uses sensible heat of the fluid that contact the solid to provide the heat vaporization of the

liquid.

When, air heating increases the driving force for heat transfer accelerate drying. It is also reduce

relative humidity.

Direct dryer convectively heat a product through direct contact with heated air ,gas or combusted

gas product.

It is direct contact between the material and the drying air to dry material. More than 85%

industrial dryer use convective is convective type.

B, Indirect dryer (none adiabatic)

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Is method of removal of the liquid phase from solid material through the application of heat such

as the heat transfer medium is separated from product to be dried by metal well.

Heat a product through contact with heated well.

It is avoid the direct contact between the material and drying air.

C .radiant dryer this cause duo to radiation heat transfer method sunlight

1.1.2 Mechanism of drying

Drying is complex operation involving transient transfer of heat and mass along with several rate

processes such as chemical transformation or physical transformation which may cause change

product quality as well as mechanism heat and mass transfer.

In some products having relatively high initial moisture content an initial linear reduction of the

average product moisture content as function of time may be observed for limited time.

The drying rate during this period is mostly depend on the rate of heat transfer to material being

dried. Therefore, the maximum achievable drying considered on to be heat transfer limited.

Migration of moisture from the interior of an individual grain to surface .evaporation of moisture

from surface to surrounding.

In money processes improper drying may lead to irreversible damage to product quality and

hence non salable product.

1.1.3 Objective of dryer

Dryers are used for money purpose to decrease the product moisture in order to control the

quality product.

To avoid or eliminate moisture which may lead to corrosion and decrease product

stability.

To make material easy or more suitable for handling.

To reduce the cost of transportation of large volume material.

To improve or keep the good properties of material.e.g flow ability , compressibility

To control the porosity of material

To increase rate crystalize

1.1.4 Application of dryer

Is an energy intensive unit operation in chemical, food, and allied industries. It is always desired

to have low cost.

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Realizing high durability by using brush motor

Increase porosity material

Their application areas are

Cement production

Alcohols and beverage production

Pharmaceutical production,etc

1.2 Gas vapor mixtures (hygrometry)

Is science dealing with the physical laws of air water vapor mixtures.

It is engineering field used to determination of physical and a thermodynamic property of gas

mixture. Atmospheric air normally contains some water vapors. When designing an air condition

system the temperature and moisture content of air to be conditioned. And the same properties of

the air needed to produce the desire air conditioned effect.

The most common system of interest is the mixture water vapor and air. Because of its

application

Heating

Ventilating

Air condition

Properties of gas vapor mixtures are

1) Relative humidity

2) Humidity ratio

3) Absolute humidity

4) Psychromaitic ratio

1. Relative humidity

is properties gas vapor mixture the ratio amount that given amount of air is holding to amount

of moisture that given amount of air can hold.

2. Humidity ratio; is actual weight of water in air water vapor mixture.

That means amount of moisture per unit of dry air.

W=

……………………….1

Where

W=the ratio moisture per dry

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G=the amount weight of dry air

3. Absolute humidity the mass water vapor per unit volume of air containing the water

vapor. That mean, the same as the water vapor density.

4, psychometric ratio ; is the ratio of the heat transfer coefficient to product of mass

transfer coefficient and humid heat at wetted surface.

It may expressed r= hc/ycs…………….(2)

Where r=psychometric ratio, hc=convective heat transfer coefficient,

y=convective mass transfer coefficient

Cs=humid heat

1.3 psychometric term; there so money psychometric term some of these

1. Adiabatic saturation temperature; equilibrium gas temperature reached by unsaturated

vaporizing liquid under adiabatic condition.

N.B for air/water system only it is equal to with wet bulb temperature.

2. Bound moisture; liquid physically/chemically bound solid matrix so as exert a vapor

pressure lower than that of pure liquid at the same temperature.

3.Dew point temperature at which a given unsaturated air vapor mixture becomes saturated.

4. Dry bulb temperature; temperature measured by a dry thermometer immersed in the vapor gas

mixture.

5. Equilibrium moisture content (x*); at a given temperature and pressure ,the moisture content

of moist solid in equilibrium with gas vapor mixture.

6. critical moisture content (XC) ;moisture content at which the drying rate first begin to drop

under constant drying condition. 7. wet bulb temperature ; liquid temperature attained when the large amount of air vapor mixture

is contacted with the surface.

8,Falling rate period ;Drying period (under constant drying conditions) during

which the rate falls continuously in time.

9.Water activity, aw Ratio of vapor pressure exerted by water in solid to that of pure water at the

same temperature.

1oWet bulb temperature, Liquid temperature attained when large amounts of air-vapor mixture

is contacted with the surface. In purely convective drying, drying surface reaches wet bulb

temperature during the constant rat period.

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1.4 PSYCHROMETRIC CHART

Psychometric chart is a graphical representation of psychometric processes of air. And also used

to determine the physical and thermodynamic properties of moist air.

1, Sensible heat; psychometric processes that involves the increase or decrease in the

temperature of air without changing its humidity ratio.

2, heating and humidifying; a psychometrics processes that involves the simultaneous

increase in both dry bulb temperature and humidity ratio of the air.

3, cooling and dehumidifying ; a psychometric processes that involves the removal of water

from the air the air temperature falls below the dew point temperature.

Fig 1.1 psychometric chart

4, Adiabatic(evaporative cooling) a psychometrics process that involves the cooling of air

without heat loss. Sensible heat lost by the air is converted to latent heat in the added water

vapor

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SUMMERY

Drying is one of separation unit operation that remove the moisture of solid, semisolid and

liquid feedstock by helping of heat .drying perhaps the oldest most common and most diverse of

chemical unit operation .why is drying needed?

Easy to handling

Free flowing

To minimize transportation cost

Transport of moisture within solid may occur by the following mechanism of mass transfer

Liquid diffusion; if the wet solid is at a temperature below the boiling point of the liquid.

Vapor diffusion; if the liquid vaporize with in material.

Surface diffusion

Psychometric is a science that studies the physical and thermodynamic properties of gas vapor

mixture.

Psychometrics chart it is graphically representation of psychometrics processes of gas vapor

mixture.

Transport of moisture within the solid may occur by any one or more of the following

mechanisms of mass transfer:

• Liquid diffusion, if the wet solid is at a temperature below the boiling point of the liquid

• Vapor diffusion, if the liquid vaporizes within material

• Surface diffusion (possible although not proven)

• Hydrostatic pressure differences, when internal vaporization rates exceed the rate of vapor

transport through the solid to the surroundings

Psychometric term; there so money psychometric term some of these

Adiabatic saturation temperature,

Bound moisture

Constant rate drying period

Dew point Temperature

Dry bulb temperature

Psychometric chart is a graphical representation of psychometric processes of air. And also used

to determine the physical and thermodynamic properties of moist air.

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CHAPTER TWO

CRYSTALLIZATION

Crystallization is a process of formation of solid precipitate from a solution melt or rarely

deposited directly from gas.

Crystallization is separation and purification technique employed to produce wide variety

materials. Solution is mixture of two or more species that form a homogeneous single phase.

Solution is combination solvent and solute.

The solution to be ready to crystallize must to be supersaturated.

A solution in the solute concentration exceeds equilibrium (saturated) solute concentration at

given temperature known as a supersaturated solution.

There are four main method to generate super saturation are

Temperature change (mainly cooling)

Evaporation of solvent

Chemical reaction and

Change solvent composition

Crystallization from solution can be thought two steps.

Crystal growth (birth)

Nucleation

The birth of new crystal which is called nucleation refers the beginning of the phase separation.

The solute of molecule has formed the smallest sized particle possible under the conditions

present. The next stage of the crystallization processes is for the nuclei to grow large by

addition of solute molecule from the supersaturated solution. This part crystallization processes

is known as crystal growth. Crystal growth along with nucleation control the final particle size

distribution obtained in a system.

In addition the condition rate of crystal growth has significant impact on the product purity

2.1 step of crystallization

Modeling of crystal growth in solution crystallization is often done by two step model. The

The overall growth can expressed

RG=Kd(Cb-Ci)…………………….(diffusion step)

RG=Kr(Ci-C*)r

…...…………………………………………(integration step)

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The two step method is totally ignoring by the effect heat transfer on the crystal growth kinetics.

RG=(Cb-C*)g…………………..overall

Where (Cb-C*) is supersaturation

RG=Kd(Cb-Ci) =kd⌈ ⌉ ( ) _(Ci*- )

RG=Kd⌊ – ( )

⌋

where Ci* and Cb* are the saturation concentrations evaluated at the interface and bulk

temperatures, respectively.

2.2 TYPES OF CRYSTALIZER

There are crystallizers of batch and continuous operation. Crystallizers depending on the system

of cooling classified in to two.

1. Air cooled crystallizers

2. Water cooled crystallizers

1. Air cooled crystallizers; the massecuite is cooled by circulation of air from the wall of

crystallizer and the surface of the massecuite.

The cooling effect is slow. Nowadays the air cooled crystallizers are commonly used for storing

high massecuite is not favored.

2. Water cooled crystallizers; is type of crystallizer can be classified in two

Water jacketed

Cooling coil of rotating type

2.3 OBJECTIVE OF CRYSTALLIZATION

Crystallization is used for various purposes.

To form solid crystal

To eliminate unwanted material

Forcing further exhaustion of mother liquor

SUMMERY

Crystallization is a process of separation and purification technique employed to produce wide

variety material. Crystallization may be defined as a phase change crystalline product is obtained

from a solution

There are four main methods to generate super saturation that are the following

• Temperature change (mainly cooling),

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• Evaporation of solvent,

• Changing the solvent composition

Crystallization from solution has two steps.

Crystal growth

Nucleation

The birth of new crystal which is called nucleation refers the beginning of the phase separation.

The solute of molecule has formed the smallest sized particle possible under the conditio

Application to ant insolvent crystallization. Concentration feedback control has been applied to

ant solvent batch crystallization processes

There are crystallizers of batch and continuous operation. Crystallizers depending on the system

of cooling classified in to two.

Air cooled crystallizers

Water cooled crystallizers

Crystallization is used for various purposes.

To form solid crystal

To eliminate unwanted material

Forcing further exhaustion of mother liquor

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CHAPTER 3

EXTRACTION

Extraction is withdrawing of active agent or west substances from solid or liquid mixture with

liquid solvent.by intensive contact active agent transfer from solid or liquid mixture into solvent.

After the mixing the two phases are separated which happen either gravity or centrifugal force.

3.1 Types extraction; there are three types extraction method depend on the phase.

These are

Solid –liquid extraction

Liquid-liquid extraction

Gas-liquid extraction (absorption)

3.2 selection of solvent

the solvent for extraction has to withdraw the active agent from mixture in order to enhance the

rate extraction.

Selectivity; only the active agent has to be extracted no further substances which mean

that high selectivity required.

Capacity to reduce the amount necessary solvent capacity of solvent has to be high.

Miscibility; to achieve simple regeneration of the solvent the miscibility of solvent and

primary solvent has to be law.

Recovery solvent; the has to be separated from extract phase easily to produce solvent

free active agent.

Low price

No toxic or less

Corrosion; if the solvent is corrosive price for construction increase.

3.3 Type of extractor; extractor is anequipment used to separate the same or different

phase.

There is several type of extractor.

Such as

1. Single step mixer-separator

2. Mixer-settler-cascade

3. Centrifugal extractor

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1. Single step mixer –separator; it is simplest extraction equipment which operated

continuous or discontinuous. The transfer of the agent from one phase in to other phase take

place in the mixer the separation of the two phases is done in the separator by gravity force.

Advantage

-High efficiency per step - low apparatus height

-High operating area - insensible for suspended substances

Limitation

-High ground area necessary -high energy required and regulating effort

-high solvent cost

2. Mixer –settler-cascade; adding more mixer-settler unit cascade is obtained. This unit can

operate in counter current.

3 .centrifugal extractor; this exist of rotating drum where the heavier phase is transported to

the periphery and the lighter phase to the center.

This means centrifugal force is responsible the counter current flow of the phase.

Advantage

High through put

Short residence time by fasting of equilibrium

Disadvantage

High cost for investment

3.4 Mechanism of extraction

The extraction material is no homogenous substances but exist of a lot of capillary. At the

beginning the solvent enter the capillaries and solute extract. A solution with high concentration

is produced. Because of diffusion a concentration change between the solution in extraction

material and solution surrounding the solid particle take places.at the end of extraction processes

still a certain amount of solution consist of solvent and extracted substance is retained in the

solid amount of particle because of adhesive forces.

3.5 Objective of extraction

Extractions have been used for different purpose.

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To separate active agent from solvent

To eliminate the undesired product from required one

To control quality product

Requirement of extraction; to transfer high amount agent from the starting phase into the extract

the extraction equipment has fulfill the following point.

High mass transfer coefficient which is achieved in most case by high relative velocities

between the two phases.

No axial remixing

Fast and complete phase separation

3.6 Application of extraction; extraction have being a lot of application area.

The main area of extraction

For hydro metallic processes

For pharmaceutical industry

For petroleum industry and for cleaning west water to separate solved compound. When

we see the application extraction in pharmaceutical industry.

Typical applications of extraction in bioprocessing include:

1. Purification of antibiotics

2. Purification of alkaloids

3. Protein purification using aqueous two-phase systems

4. Purification of peptides and small proteins

5. Purification of lipids

6. Purification of DNA

The photonics processes is used to for extraction in biotechnology.(e.g. for production

antibiotics) in the herbal drug industry, in the food ,essential oil and so.

3.7Advantage of extraction

The main advantages of extractions are

It is less threating to the environment

It require minimum electrical energy

The solvent are completely recycled within the system.

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SUMMERY

Extraction is withdrawing of active agent or west substances from solid or liquid mixture with

liquid solvent.by intensive contact active agent transfer from solid or liquid mixture into solvent.

An extraction process makes use of the partitioning of a solute between two immiscible or

partially miscible phases. When the extraction takes place from one liquid medium to another,

the process is referred to as liquid-liquid extraction. There are three types extraction method

depends on the phase. These are

Solid –liquid extraction

Liquid-liquid extraction

Gas-liquid extraction (absorption)

There is several type of extractor.

Such as

A.Single step mixer-separator

B. Mixer-settler-cascade

Centrifugal extractor

D. column without energy

Typical applications of extraction in bioprocessing include:

Purification of antibiotics

Purification of alkaloids

Protein purification using aqueous two-phase systems

Purification of peptides and small proteins

Extractions have been used for different purpose.

To separate active agent from solvent

To eliminate the undesired product from required one

To control quality product

The main advantages of extractions are

It is less threating to the environment

It require minimum electrical energy

The solvent are completely recycled within the system.

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REFERENCES

1)Keey, R.B., 1992, Drying of Loose and Particulate Materials, Hemisphere, Washington

2)Miura K, Miura T, Ohtani S. Heat and Mass Transfer to and From Droplets. American

Journal of Chemical Engineers, Symposium series 1977; 73 (163).

3) R.E Treybal mass transfer operation 3rd

edition