introduction to separation technology

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Separation Technology (CKD 20103) January 2016

CHAPTER 1s

CHAPTER 1

SEPARATION TECHNOLOGY (CKD 20103)




1.1 Preface

The understanding of the principles and concepts for Separation Technology is essential in

the sense that will enable us to not only identify but as well as choosing the best method in

achieving Separation and Product Recovery while at the same time will also enable us to

identify the type of mixture that we are dealing with. This is because identification the type

of mixture to be separated and choosing the best method for separation is inter related and

dependable with each other. However, it is important to bear in mind that choosing the best

method for separation precede identification of product mixture.

As previously mentioned, it is very important to choose the best and suitable method

for Separation and Product Recovery. For that matter, it is worthwhile to bear in mind that

each and different methods has limitations as well as advantages. With that in mind, it is

important to choose the best and suitable methods which can produce the desired

separation and recover of wanted or desired product from the mixture as specified in the

product’s specification and classification.

With the product limit in terms of the product’s specification and classification,

sometimes, it will be troublesome and difficult to achieve the required specification and

classification by just using only one separation method. In normal cases, more than one

separation methods need to be chosen which compliment to each other in terms of their

respective limitation and enhance each other’s advantages. For that matter, these different

methods of separation can be combined in one big separation system or can be assemble

close to each other with separation process occurs from one step or stage to the other step

until the final step which at the final step the product analysis need to be done to check and

confirmed the product quality meets the product’s specification and classification.

Before we look at each method of Separation in more detail, it is important for us to

know the definition and concept of two classifications of mixture to be separated and thenfollowed by basic concepts in Introduction of Separation Technology. Then, we will look into

different types and General Classifications of Separation Technology.

1.2 Introduction to Separation Process/Technology

1.2.1 Chapter Overview

In this particular chapter, you will be exposed to first and foremost regarding the Purpose

of Separation. In other words, the question of "Why do we need to carry out Separation?

or what is the importance of having Separation Process / Technology? ” will be answered

and discussed in brief. This is then followed by the definition and discussion concerning

the broad classification of mixture which can either be classified as Homogeneous or

Heterogeneous.




Next, this chapter will continue the discussion by looking at two broad categories of

Separation which can be classified as Chemical Separation or Physical Mechanical

Separation. The definition for both categories of Separation will be given in brief. After

that, we will look into specific classifications under both Chemical Separation as well as

Physical Mechanical Separation. Among the specific classifications under Chemical

Separation are Absorption, Distillation, Liquid-Liquid Extraction, Leaching, Membrane

Processing, Crystallization, Adsorption, Evaporation and Ion Exchange. This is then

followed by specific classifications under Physical Mechanical Separation which are

Filtration, Settling and Centrifugation. In this chapter, different definitions for each specific

classification for Chemical Separation as well as Physical Mechanical Separation will be

looked into as given by different reference books which are then followed by a summarized

and simplified definition.

Now let us look at the first part of the chapter which is concerning the Introduction

and Purpose of Separation.

1.2.2 Introduction and Purpose of Separation

In order to understand the concept of Separation Process / Technology, it is important to

KNOW the REASON or PURPOSE of carrying out Separation. The simple basic purpose

of carrying out Separation is of course to SEPARATE or SPLIT a mixture of compound

into two DIFFERENT individual elements with HIGH purity. It means, the individual

elements which has been separated have NONE or VERY MINIMUM amount of mixture

from the other compound.

The EXACT purpose and reason of carrying out Separation as given by reference

material is as shown below:

“Separation processes require the extraction of a desired product at specified purity .”

From the purpose given above, you have to determine the DESIRED product or the

product that you WANT to separate from the mixture. You also need to specify the degree

of purity of the product to be obtained at the end of Separation Process. Therefore, in order

to extract or separate the product that you want from the mixture, you need to choose the

methods of Separation Process or Separation Technology. It is important to bear in mind

that different methods have different capability and limitation and also depends on the

Processing involve in the plant.

Before the Methods of Separation to be discussed in detail, it is important to consider

the type of mixture to be treated or separated into individual components. This is because,the type of mixture to be treated is directly related with the chosen Methods of Separation.

It is the type of mixture which will determine the suitability Methods of Separation to be

applied in order to obtain as high as possible individual component from the mixture.




1.3 General Types of Mixtures

Basically, the types of mixture can be divided into two parts which are known as

Homogeneous Mixture and Heterogeneous Mixture.

1.3.1 Homogeneous Mixture

Homo actually refers to the word same or similar . Therefore, in the context of this

subject, Homogeneous Mixture can be defined as the type of mixture by which the

components of mixture are in the same phase with respect to each other . By here, it

means that if you refer to liquid mixture, it means that all the components inside the mixture

are in liquid form. Same goes if you refer to solid mixture or gaseous mixture. So, it can be

said that all the components inside the mixture are in solid form or in gaseous form

respectively.

1.3.2 Heterogeneous Mixture

On the other hand, Hetero means different or not the same. For that matter,

Heterogeneous Mixture can be defined as the type of mixture by which the

components of mixture are NOT in the same phase with respect to each other .

Therefore, it can be said that, if you refer to Solid - Liquid mixture, it means that the

mixture consist of one component of mixture in Solid form while the other component is in

Liquid form. The same goes if you refer to Solid - Vapour/Gas mixture or Vapour/Gas -

Liquid mixture. From here, it can be said that one component is in Solid form while the other

component is in Vapour or Gas form and one component is in Vapour or Gas form while

the other component is in Liquid form respectively.

At this point onwards, it is important if you can distinguish or differentiate betwee

Homogeneous Mixture and Heterogeneous Mixture. This is very essential and important in

order to understand the concept which will be discussed under each Methods of Separation.

In addition, as previously mentioned in the preceding page, the type of mixture is directly

related to the type of Method of Separation to be implemented. In fact, it can be said that it

is the FIRST STEP before choosing and implementing Separation Technology methods to

achieve separation and purity of product.

Now, let us look at the Methods of Separation which is given briefly in the following

page. These Methods of Separation basically can be divided into Chemical Separation and

Mechanical Separation. First we will look at the brief definition of Chemical Separation and

Mechanical Separation. Then, we will look at some examples of Chemical and Mechanical

Separation.




1.4 Classifications of Separation Process

Separation Process basically can be generally classified or divided into two (2) types, which

are Chemical Separation and Mechanical Separation. The respective definition of these

two methods as well as examples of methods under Chemical Separation and Mechanical

Separation will be shown respectively as given in the below paragraphs.

1.4.1 Chemical Separation

Now, let us look at the first method of separation which is Chemical Separation. The

description of Chemical Separation from reference material can be given as below:

“Chemical Separation is carried out based upon physical chemical properties

differences in the molecules themselves and on mass transfer of the molecules. The

mixtures are separated into two phase because of the molecular differences. In Chemical

Separation, in order to separate or remove one or more of the compounds from its original

mixture, it must be contacted with another phase. ”

Based on the description given above, it can be understood that:

1. In terms of Physical Chemical Properties Differences, it means that the mixtures

consist of compounds with different Physical and Chemical properties.

2. Mass Transfer is the mechanism whereby the molecules are moved from one mixture

to another mixture.

3. Two Phase is concerning the state of the mixture either in Solid, Liquid and Gas or

Vapour. This is related with the arrangement of the atoms or molecules for a compound

which has been covered in General Chemistry (CLD 10004).

In order to separate or extract a compound from the mixture, another medium or

phase is required in order for a transfer to occur. The medium or another phase could be

Solid, Liquid and Gas or Vapour which truly depends on the method of Separation Process

or Technology.

In the PREVIOUS page, we have looked into brief description of Chemical Separation

which is one of two general classifications of Separation Technology or Process. Some

examples on method of separation under Chemical Separation are as given below:

Absorption Distillation Liquid-Liquid Extraction

Stripping Evaporation Leaching

Adsorption Drying Crystallization

Membrane Processing Ion Exchange

Now, we will look at brief description for each method of separation. The detail

principles and operation as well as application will be given in the next and coming chapters.

Let us look at brief definition for Absorption.




Absorption

There are different descriptions of Absorption which can be given as follows which are

based on referenced materials:

1. “When the two contacting phases are a gas and liquid the unit operation is called

absorption. Solute A is absorbed from the gas phase into a liquid phase. Involvesmolecular or turbulent diffusion. Mass transfer of a solute A thorough a stagnant non-

diffusity gas B into a stagnant liquid C.”

2. “For gas absorption, the gas contains a desired component, say A. A liquid solvent which

has specific affinity only to A is then contacted with the gas stream, and a fraction of A

coming into the absorber is "absorbed " by the entering liquid. Ideally, the chosen solvent

should have low volatility such that almost none of the solvent escapes with the gas. The

fraction absorbed is again strongly dependent on the operating temperature and

pressure, where lower temperature and higher pressure is more desirable. The solvent

containing absorbed A is then passed to another separation unit such as a distillation

column to finally separate the two.”

3. “A widely used alternative to Distillation for the separation of a solute from a gas stream

is Absorption. In this separation process, the gas mixture is contacted with a liquid

solvent which preferentially absorbs one or more components from the gas stream.

Liquid flow rate, temperature and pressure are the variables that must be set in this

separation process. ” (Peters, Timmerhaus & West : Plant Design An Economics

For Chemical Engineers).

From the brief description, it can be said that the method of Absorption involves two

phases which are GAS or VAPOUR and LIQUID. Also, from the description above it can be

simplified that:

“If the desired component of GAS or VAPOUR is to be separated or extracted from the

mixture of gases, a LIQUID will be used as a SOLVENT to ABSORP the desired gas into

the liquid. This process is called ABSORPTION .”

Stripping

There are basically two brief descriptions concerning the process of Stripping which are

as given below:

1. “The reverse of Absorption is called stripping or desorption, and the same theories

and basic principles hold.” (Geankoplis : Transport Process And Separation

Process Principles)

2. “Once a solute is dissolved in a solvent, it is often necessary to separate the solute

from the absorbent in a stripping operation to recycle the solvent back to absorber.”

(Peters, Timmerhaus & West : Plant Design An Economics For Chemical

Engineers).




From the two descriptions given in previous page, it can be said that the Stripping also

involves TWO phases which are LIQUID that consist of mixture between liquid solvent

being used for Absorption and solute which is being Absorbed into the solvent and

VAPOUR that is to Desorbed or Stripped the solute. In other words, it can be said that:

“Stripping or Desorption is the REVERSE process of Absorption whereby the liquid

mixture from Absorption process is to be SEPARATED by using Vapour which is to

DESORP the solute from the Liquid mixture into the Vapour. This is done in order to

REGAIN the Liquid solvent to be recycled or reused for Absorption process.”

Distillation

There are different descriptions concerning the process of Distillation which are as given

below:

1. “A volatile vapor phase and a liquid phase that vaporize are involved. Distillation of an

ethanol-water solution where the vapor contains a concentration of ethanol greater thanin the liquid. In the distillation of crude petroleum, various fractions such as gasoline,

kerosene and heating oils are distilled off.”

2. “ Distillation is similar in concept to evaporation, but allows the capture of the substance

which evaporated. Distillation is the process of heating a liquid to its boiling point,

condensing the vapors back to a liquid (by cooling), and then collecting the liquid

distillate. Since different substances have different boiling points, control of the

temperature allows a separation to occur. As an example, crude oil is refined into

various products such as naphtha, gasoline, kerosene, fuel oil, and lubricating oil

through a fractional distillation process.”

3. “The heavy phase is liquid while the light phase is vapor. For the binary case, say a

mixture of compounds A and B, separation depends strongly on the relative volatilities

of each component. If both have the same volatility then separation via distillation is not

effective. However, as will be shown later, the volatilities depend on the vapor pressures

at the operating temperature and the column pressure used.”

4. “The creation or addition of another phase in Distillation is obtained by the repeated

vaporization and condensation of the fluid. The separation process exploits the

differences in vapour pressure of the key components in the mixture to initiate the

separation. ” (Peters, Timmerhaus & West : Plant Design An Economics For

Chemical Engineers).

Based on the three brief descriptions of Distillation, it can be seen that the separation

of desired compound involve ONE phase only which is in LIQUID phase. Therefore, it can

be simplified or concluded that:




“ DISTILLATION involves the Separation of desired compound based on their

DIFFERENCE in BOILING POINT and VOLATILITY . The MORE volatile compound will

vapourize and then condensed before being collected while the LESS volatile compound

will remain in the column.”

Liquid - Liquid Extraction

There are three descriptions concerning the method of Liquid-Liquid Extraction from a

referenced material which are as given below:

1. “When the two phases are liquids, where a solute or solutes are removed from one

liquid phase to another liquid phase.”

2. “A solution containing the desired component A and solvent C is mixed with another

liquid B. A fraction of A is then "extracted" from C into B. However, B can not be

completely miscible with C . The greater the immiscibility between B and C , the better.

Also, the B-rich phase containing A has to be easier to separate than the C -rich phase,otherwise the whole extraction scheme becomes unnecessary.”

3. “Liquid - Liquid Extraction is a process often selected to separate Azeotropes and

components with overlapping boiling points. The extraction process requires the

addition of a solvent in which one or more of the components in the mixture are soluble.

Components in the liquid mixture are separated based on their different solubilities in

the solvent. ” (Peters, Timmerhaus& West :Plant Design An Economics For

Chemical Engineers).

As given in the title, there is only ONE phase involve which is LIQUID phase. The basic

principle being used for this method is the SOLUBILITY. Therefore, the concept of Liquid

- Liquid Extraction can be summarized or concluded as follows:

“A desired compound in the mixture and in LIQUID phase is to be separated or extracted.

To achieve this, a solvent also in LIQUID phase need to be used. The criteria of choosing

the solvent is based on the desired compound has high SOLUBILITY towards the solvent.

This approach is known as LIQUID - LIQUID EXTRACTION ."

Leaching

There are four brief descriptions concerning the method of Leaching from three different

referenced materials:

1. “The process of Leaching occurs if a fluid is being used to extract a solute from a solid .".

2. “Leaching refers to the extraction of a soluble constituent from a solid by means of a

solvent.” (Coulson & Richardson Volume 2).

3. “This is the method of removing one constituent from a solid by a means of a liquid

solvent.” (McCabe, Smith & Harriott : Unit Operations).

4. “In order to separate the desired solute constituent or remove an undesirable solute




component from the solid phase, the solid is contacted with a liquid phase. The two

phases are in intimate contact and the solute or solutes can diffuse from the solid to the

liquid phase, resulting in a separation of the components originally in the solid. This

separation process is called Liquid - Solid Leaching or simply Leaching .” (Peters,

Timmerhaus & West : Plant Design An Economics For Chemical Engineers).

Based on the four different and similar descriptions given in previous page, it is

important to realize that SOLVENT used is in the form of LIQUID, while the mixtures which

consist of the desired and undesired compound is in the form of SOLID. To conclude the

brief description of Leaching:

“If a process of EXTRACTING solute which is the desired compound in the form of SOLID

from its SOLID MIXTURE with the usage of a solvent in the form of LIQUID, then the

process is called LEACHING or SOLID EXTRACTION ."

Membrane Processing

There are three brief descriptions concerning Membrane Processing as one method of

separation under Chemical Separation which is listed below:

1. “The relatively thin, solid membrane controls the rate of the movement of molecules

between 2 phases.”

2. “This is the method of separating gaseous or liquid mixtures by the usage of semi

permeable membranes which act like a filter. This membrane allows one or more

constituents of the mixture to pass through more readily than the others.” (McCabe,

Smith & Harriott : Unit Operation).

3. “This type of separation is accomplished with the use of specially prepared membranes

that selectively permit one or more components of a feed stream to pass through the

barrier while retarding the passage of other components in the feed stream.” (Peters,

Timmerhaus & West : Plant Design An Economics For Chemical Engineers).

Based on the two brief descriptions given in previous page, it can be seen that the

membrane is basically in the form of SOLID while the desired compound is in the form of

either LIQUID or GAS in the mixture of LIQUID or GAS respectively. Therefore, the

description of Membrane Processing can be given as:

“The method of SEPARATING the desired compound from the mixture by the usage of a

MEMBRANE FILTER which ONLY ALLOWS the DESIRED compound to pass through

and left behind the other compound in the mixture. This method is known as MEMBRANE

PROCESSING ."

Crystallization

For the brief description of the method Crystallization, there are four descriptions based




on the referenced material which can be given as follows:

1. “Solute components soluble in a solution can be removed from the solution by adjusting

the conditions, such as temp. or concentration so the solubility of one or more solute

components is exceeded and they crystallize out as a solid phase.”

2. “ Precipitation or Crystallization is a process in which a solution is cooled until a solute

precipitates to form a solid phase (which is called a precipitate). The two-phase mixture

may then be further separated by decantation or filtration. The word crystallize is more

specific and is used when the solid forms crystals rather than an amorphous solid

(powder or granules). Crystals have well-formed planar faces and a regular geometric

shape.”

3. “A solution is heated to evaporate the solvent and is then cooled through careful

temperature schedules to obtain predetermined crystal size and composition. Then the

slurry is either passed through a series of settling tanks or filtration units.”

4. “Under certain operating conditions, dissolved materials in solution are recoverable insolid form by precipitation upon cooling, removal of the solvent or the addition of

precipitating agents.”(Peters, Timmerhaus & West : Plant Design An Economics

For Chemical Engineers).

Based on the four brief descriptions of Crystallization or also known as Precipitation,

it is important to realize that INITIALLY the mixture which contains the desired compound

is in the form of LIQUID. Then, the temperature is adjusted so that the desired compound

become SOLID. The definition of Crystallization can be summarized as follows:

“ CRYSTALLIZATION is the method of separation whereby the mixture which consists of

desired compound is in liquid form. The temperature is adjusted by either one of thefollowing methods:

The temperature is INCREASED to vapourize the undesired compound and left with

desired compound which is then COOLED until it turns to SOLID. Finally, the

crystals are collected by using Filtration.

The temperature of the mixture is DECREASED in order to SOLIDIFY the desired

compound which is then filtered from the mixture.”

Adsorption

There are basically two descriptions concerning the method of Adsorption as given in the

referenced materials which are as follows:

1. “One or more components in a gas stream are adsorbed on the surface of the pres of

a solid adsorbent and the separation is obtained.”

2. “Adsorption is a separation process in which certain components of a fluid phase are

transferred to the surface of a solid adsorbent.”




3. “The selective adsorption of components on an adsorbent followed by removal of these

components through regeneration forms the basis for adsorption.”


Engineers).

Based on the brief description, it is important to bear in mind that the mixture as well

as the desired compound is in the form of LIQUID or GAS. Meanwhile, the medium where

the desired compound is to be transferred is in the form of SOLID. Therefore, the method

of Adsorption can be summarized as:

“ ADSORPTION is a process whereby the desired compound in the mixture of LIQUID or

GAS will be separated from other compound by the usage of an Adsorbent which is in the

form of SOLID."

Evaporation

There are different descriptions of Evaporation which can be given as follows which arebased on referenced materials:

1. “Evaporation refers to removal of relatively large amounts of water from material. In

Evaporation, the water is removed as vapour at its boiling point . In Evaporation, the

vapour from a boiling liquid solution is removed and a more concentrated solution

remains. In the majority of cases, the separation process called Evaporation refers to

the removal of water from an aqueous solution.” (Geankoplis : Transport Process

And Separation Process Principles).

2. “In Separation Technology, Evaporators may be considered as liquid dryers or

concentrators that separate solvents from a solution by Evaporation. In most cases, the

solvent is water. Evaporation, as a separation process, is distinct from Distillation in that

the solute is nonvolatile and a high degree of separation can be achieved in one stage.”


Engineers).

Based on two brief descriptions concerning Evaporation, it can be understood that the

mixture is in Liquid form or a Homogenous type of mixture. Therefore, the concept of

Evaporation can be summarized as follows:

“ EVAPORATION is a method of REMOVING Water which acts as a solvent or Organic

solvent from the liquid mixture. The evaporated Water or Organic solvent is DISCARDED

or DISPERSED to the atmosphere and leaving the desired product in MORECONCENTRATED form. ”

Ion Exchange

There are different descriptions of Ion Exchange which can be given as follows which are

based on referenced materials:




1. “ Ion Exchange is also similar to Adsorption in that solid particles are used in the

separation process and regeneration is necessary. However, a chemical reaction is

involved.” (Peters, Timmerhaus & West : Plant Design An Economics For Chemical

Engineers).

2. “ Ion Exchange processes are basically chemical reactions between ions in solution

and ions in an insoluble solid phase. The technique used in Ion Exchange so closely

resemble those used in Adsorption that for the majority of engineering purposes Ion

Exchange can be considered as a special case of Adsorption. In Ion Exchange, certain

ions are removed by the Ion Exchange solid. Since electro neutrality must be

maintained, the solid releases replacement ions to the solution.” (Geankoplis :

Transport Process And Separation Process Principles).

3. “ Ion Exchange is a chemical reaction wherein an ion from solution is exchanged for a

similarly charged ion attached to an immobile solid particle.” (Mohd. Adi Abdul Hadi,

Mohd Azri, Mohd Helmy & Idris : Ion Exchange Separation).

Based on three brief desriptions concerning the concept of Ion Exchange, therefore, itcan be summarized as follows:

“Ion Exchange is a SPECIAL case of Adsorption since it is SIMILAR with Adsorption but

with the DIFFERENCE by having CHEMICAL REACTION between IONS of solution with

ions of Solid Particle or Ion Exchange Resin. As a result of the chemical reaction, the ions

of solution exchange with ions of Solid Particle based on SIMILARLY CHARGED Ions.”

Drying

There are basically two brief descriptions concerning the principle and concept of Drying

which are as shown below:

1. “Drying generally means removal of relatively small amounts of water from material. In

Drying, the water is usually removed as a vapour by air.’ (Geankoplis : Transport

Process And Separation Process Principles).

2. “The main purpose of this separation process is to remove liquid from a liquid - solid

system to produce a dry solid. Generally, the liquid removed is water, but drying can

also be used to separate organic liquids from solids.” (Peters, Timmerhaus & West :

Plant Design An Economics For Chemical Engineers).

Therefore, from the two brief descriptions given above, it can be seen that the mixtures

for Drying is basically a Heterogeneous which is SOLID and LIQUID. For that matter, the

concept of Drying can be summarized as follows:




“Drying generally involves the method of REMOVING water or organic solvents from the

wet Solids at a specified MOISTURE CONTENT . The water or organic solvents being

removed to the atmosphere is in the form of VAPOUR .”

Now, we have FINISHED our brief discussion concerning each method of

separation under CHEMICAL SEPARATION. In the NEXT section, we will look at somebrief description concerning the Mechanical Separation as well as the methods of

separation.

1.4.2 Mechanical Separation

Now, let us turn our attention to the next method of separation which is known as Physical

Mechanical Separation or simply Mechanical Separation. The description of Mechanical

Separation as given by referenced material is as shown below:

“ Mechanical Separation is carried out by using mechanical physical forces and will beacting on particles, liquids or mixtures of particles and liquids. Among the Mechanical

Physical Forces are gravitational, centrifugal, mechanical and kinetic forces. As a

result, particles and or fluids are separated because of the different effects produced on

them by these forces.”

By referring to the statement given above regarding Mechanical Separation, it can be

understood that Mechanical Physical Forces such as gravitational, centrifugal,

mechanical as well as kinetic forces are applied to solids, liquids or mixture of both solids

and liquids in order to cause separation of desired product.

In order to achieve Mechanical Separation, the specific methods used are as listedbelow:

Filtration Settling & Sedimentation

Centrifugal Settling Centrifugal Filtration

Now, let us look at briefly the concept of using these three methods of Mechanical

Separation starting with Filtration.

Filtration

There are basically two brief descriptions concerning the principle and concept of Filtration

as given by reference materials which are as shown below:

1. “ In Filtration, a pressure difference is set up that causes the fluid to flow through small

holes in a screen or cloth which block the passage of the large solid particles; these, in

turn, build up on the cloth as a porous cake.” (Geankoplis : Transport Process And

Separation Process Principles).




2. “ In this mode of separation, solid particles in a liquid or gas are removed by passing the

mixture through a porous medium that retains the particles and passes the fluid ."

( Peters, Timmerhaus & West: Plant Design An Economics For Chemical

Engineers).

As a summary, the concept of Filtration as given in the reference material can be

given as follows:

“Filtration is used to separate a solid from a liquid or solid from gas. In this case, the

mixture is poured through a porous medium (often filter paper), in which the size of the

pores allows liquids or gas and dissolved solutes to pass through but retains solid

particles. This is essentially like using a strainer, but with much smaller openings. The clear

liquid phase obtained is called the filtrate.”

From the statement given above, it can be understood that the method of Filtration is

used to SEPARATE a mixture which contains SOLIDS and LIQUIDS for Solid Liquid

Mixture but also used to separate mixture which contains SOLIDS and GASEOUS for Solid

Gaseous Mixture. Solid is the desired product while Liquid is an unwanted product for thecase of Solid Liquid Mixture.

For the case of Solid Gaseous Mixture, Solid is again the desired product while

Gaseous is an unwanted product. Therefore, in order to achieve separation, the Solid and

Liquid or Solid and Gas need to be separated by the usage of a POROUS MEDIUM such

as Filter Paper. The concept of Filtration is about the same with Membrane Processing in

the Chemical Separation. The DIFFERENCE is that Membrane Processing is used to

separate LIQUID mixture as well as GASEOUS mixture whereas Filtration is used to

separate mixture which contains SOLID and LIQUID or SOLID and GAS.

Settling

There are basically two brief descriptions given by referenced material which can be shown

as follows:

1. “In Settling and Sedimentation, the particles are separated from the fluid by gravitational

forces acting on particles of various sizes and densities.” (Geankoplis: Transport

Process and Separation Process Principles).

2. “In Settling processes, solid particles or liquid drops are separated from a fluid by

gravitational forces acting on the particles or drops. The fluid can be a liquid or a gas.”

(Peters, Timmerhaus & West: Plant Design An Economics For ChemicalEngineers).

To summarize the concept of Settling based from the statements given by two referenced

material, the description can be given as below:

“Settling or also known as GRAVITATIONAL SETTLING is a method of separating SOLIDS

from the mixture of SOLIDS and LIQUID by the usage of gravitational force. Here, the Solid




which has higher density will obviously slowly drop to the bottom of the container or tank

which is then sucked by pumps to separate the Solid by the usage of Filter .”

Here, it can be seen that the method of Settling cannot stand on its own. This method

needs to come together with Filtration in order to achieve complete separation of solids from

the filtrate or the liquid remains of the mixture.

Centrifugal Settling

There are basically two brief descriptions given based on referenced materials which can

be given as follows:

1. “In Centrifugal Separations, the particles are separated from the fluid by centrifugal

forces acting on particles of various sizes and densities.” (Geankoplis : Transport

Process And Separation Process Principles).

2. “Use of centrifugal force increases the force acting on the particle and permits morerapid separation times. Beside solids separation from liquids, it is also sometimes used

to separate two liquids with different densities by centrifugation. ” ( Peters, Timmerhaus

& West : Plant Design An Economics For Chemical Engineers ).

As a summary, the concept of Centrifugation which is based on referenced material can be

given as below:

“Centrifugation is the process of separating a suspended solid in a liquid by high speed

rotation which result in centrifugal force acting on the particle or more denser liquid.”

Based on the statement given above, it can be seen that the mixture contains SOLIDSand LIQUIDS or can also Liquids with DIFFERENT DENSITIES. Solid with higher density

is the desired product. If the method of Settling allows the desired product which is the solids

to drop slowly by gravitational force, Centrifugation is a method of separating the solid from

the liquid by rotating the tank or vessel in high speed. As a result, water will be removed

outward and at the top while the solid will be removed at the bottom of Centrifugal Separator.

This concept is similar to our usage of Spinning in Washing Machine.

Centrifugal Filtration

It is unfortunate at the time of writing that not much description is given for this type of

Mechanical Separation. However, there is only one brief description which can be given asfollows:

“In the second type of centrifugal separation process, centrifugal filtration occurs, which is

similar to ordinary filtration, where a bed or cake of solids builds up on a screen, but

centrifugal force is used to cause the flow instead of a pressure difference." (Geankoplis :

Transport Process And Separation Process Principles).




Based on the statement given above, it can be understood that there is not much

different as compared to Filtration as been mentioned earlier. This is because this method

also deals with either Heterogeneous mixture of Solid - Liquid or Solid - Vapour or Gas. The

only difference is concerning the causes of flow with Pressure Difference is applied for

normal Filtration but obviously Centrifugal Force is used for Centrifugal Filtration type.

By now, we have FINISHED our discussions concerning the basic concept of

CHEMICAL SEPARATION and MECHANICAL SEPARATION. In the NEXT TOPIC, we will

look at SOLID - LIQUID SEPARATION which involves DRYING and FILTRATION .

introduction to separation technology

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