Lecture # 1

MECHANICAL SEPARATIONS:

September 06, 2009 1MECHANICAL SEPARATIONS

Prepared by:A.N.TabishLab. Engineer / Lecturer

Department of Chemical Engineering UET, City Campus, Lahore

i. Filtration vi. Clarification

1. Introduction to Separation processes:

2. Role of mechanical separations in Chemical Processing:

3. Discussion of Mechanical separations processes:

Course Contents:

i. Filtration

ii. Sedimentation

iii. Centrifugal Separation

iv. Magnetic and Electrostatic Separations

v. Flotation

vi. Clarification

vii. Tabling

viii.Jigging

ix. Sonic Agglomeration

September 06, 2009 2MECHANICAL SEPARATIONS

Introduction:

Separation: [1]

A technique that transform a mixture of substancesinto two or more products differing in composition.

Separating Agents:

September 06, 2009 MECHANICAL SEPARATIONS 3

Separating Agents:

• Energy input (heat, pressure, electricity, magnetism, kinetic or potential energy)

• Withdrawal of energy (cooling, freezing)

• Matter (filter, membrane, chemicals)

Mechanism of Separation:

Mixing:

Spontaneous, natural process accompanied by increase in

entropy and randomness. Second Law of Thermodynamics

states that all natural processes take place so as to increase the

entropyor randomnessof theuniverse.

September 06, 2009 MECHANICAL SEPARATIONS 4

entropyor randomnessof theuniverse.

Separation:

Reverse of mixing, demixing. Equivalent of thermodynamic

work has to supplied to cause the separation to occur.

Separation process is the technology of unmixing and

isolating the wanted product or products economically, feasibly and

without harming the environment

Critical separations in human body:

September 06, 2009 MECHANICAL SEPARATIONS 5

• Separation of oxygen from air and of CO2 from blood in

the lungs

• Selective removal of water and waste products of

metabolism from blood in the kidneys

Role of separation processes in Chemical Industry:

1. Isolating valuable chemicals from mixtures,

2. Removing impurities from raw materials,

3. Purification of products,

4. Environmental Protection by removing contaminants and

September 06, 2009 MECHANICAL SEPARATIONS 6

pollutants from effluent stream

1. Chemical Reactions

2. Separation of chemicals

3. Separation of phases

Key operations in Chemical Plant: [2]

September 06, 2009 MECHANICAL SEPARATIONS 7

Typical chemical plant layout

Primary factors effecting separations:

Size: Filtration, screening, Chromatography

Diffusivity: Reverse Osmosis

Ionic Charge: Ion Exchange

September 06, 2009 MECHANICAL SEPARATIONS 8

Vapor Temperature, Pressure:

Distillation

Solubility: Solvent Extraction, Absorption

Density:Gravity sedimentation, Centrifugal separation

1. Equilibration separations: (equilibration of two

immiscible phases which have different compositions at

equilibrium)

Classification of Separation Technology: [3]

• distillation, • chromatography,

September 06, 2009 MECHANICAL SEPARATIONS 9

• distillation,

• evaporation,

• extraction,

• leaching,

• chromatography,

• absorption and

stripping,

2. Rate / gradient based separations:(differences

in transport rate through some medium under the influence of

an imposed force, resulting from a gradient in pressure,

temperature, composition,electric potential, or the like)

• membrane separation,

• reverse osmosis

• electro dialysis and

• gas separationsby

September 06, 2009 MECHANICAL SEPARATIONS 10

3. Mechanical separations:(heterogeneous feed consisting of

more than one phase of matter. These simply serve to separate

phases from each other)

• reverse osmosis

• ultra filtration,

• dialysis,

• gas separationsby

membrane permeation

September 06, 2009 MECHANICAL SEPARATIONS 11

Separation Processing:

Mass Transfer Operations: Mechanical Separations:

Classification of Separation Technology:

Based on physical differences, such as density, size, or shape

Based on transfer of material between phases

September 06, 2009 MECHANICAL SEPARATIONS 12

Applicable tohomogeneous solutions

Applicable to Heterogeneous mixtures

such as density, size, or shapematerial between phases

Sedimentation, FiltrationFlotation, Clarification

Absorption, drying,distillation, solvent extraction

Mass transfer operations are characterized by the movement of one substance through another on a molecular scale.

Homogeneous (Single Phase) systems:

A second phase must generally be developed before

Mass Transfer operations:

A second phase must generally be developed before

separation of chemical species can be achieved economically.

Second phase can be created by:

1. ESA (Energy Separating agent e.g. Distillation

2. MSA (Mass Separating agent) e.g. Liq-Liq Extraction

September 06, 2009 MECHANICAL SEPARATIONS 13

Key techniques in Mass Transfer operations:

Gas (Vapor) – liquid contact:Gas Absorption

Liquid – Liquid Contact:

Using Mass Separating Agent (MSA):

September 06, 2009 MECHANICAL SEPARATIONS 14

Liquid – Liquid Contact:Liq-Liq Extraction

Solid – Liquid Contact:Leaching, Crystallization

Gas – Solid Contact:Drying with dry gas stream

September 06, 2009 MECHANICAL SEPARATIONS 15

Mechanical Separations:

Mechanical separation operations depend on differences in bulk properties, such as density or particle size, to bring about the separation of different components of a mixture.

Some specific examples for foods include:

Mechanical Separations in Food Industry:

September 06, 2009 MECHANICAL SEPARATIONS 16

1. clarification of juices,

2. wine and beer;

3. removal of excess pulp from fruit juice;

4. separation of solvents from oil seed meal;

5. separation of water from oils;

6. removal of dust from air;

Mechanical Separations in Food Industry:

September 06, 2009 MECHANICAL SEPARATIONS 17

Advantages of Mechanical Separations:

• Relatively less Energy Requirements Utilities)• Ease of Operation• Ease of Maintenance (But not in all)• No special Feed pretreatment required

Dis-Advantages of Mechanical Separations:

September 06, 2009 MECHANICAL SEPARATIONS 18

• Not applicable for separating Components in homogeneous phase

• They are not versatile i.e. in same state may be one element can be separated and other can not

• Applicable to low flow rates

[1] Binay K. Dutta “Principles of mass transfer and separation processes”pp.3

[2] Ernest J. Henley, and J.D. Seader“ Equilibrium-Stage Separation operations in chemical engineering” , pp. 4

[3] Shouci Lu, Robert, and J. Pugh, K. S. Eric Forssberg“Interfacial separation of particles” , pp. 2

References:

“Interfacial separation of particles” , pp. 2

September 06, 2009 MECHANICAL SEPARATIONS 19

Note:

Purpose of providing all these references is to facilitate the students to study the mentioned topic in detail