A Textbook on: Engineering Chemistry

TTHHEE MMAANNAAGGEEMMEENNTT CCOONNSSOORRTTIIUUMM

First Edition: 2012-13 onwards

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can be emailed to tmcnagpur@gmail.com

1/e 2012-13

onwards

[© 2012-13 Onwards: TMC Textbook on EC] Page 2

Preface

The purpose of this textbook is to present an introduct ion to th e subject of

Engineering Chemistry of Bachelor of Engineering (BE) Semester -I. The book

contains the sy llabus from bas ics of the subjects going into the intricacies of the

subjects.

All the concepts have been explained with relevant examples and diagrams to

make it interes t ing for the readers.

An at tempt is made here by the experts of TMC to ass is t the students by way of

providing Study text as per the curriculum with non -commercial cons iderat ions.

We owe to many websites and their free contents; we would like to specially

acknowledge contents of website www.wikipedia.com and various authors

whose writings formed the basis for this book. We acknowledge our thanks to

them .

At the end we would l ike to say that there is a lw ays a room for improvement in

whatever we do. We would appreciate any suggest ions regarding this study

material from the readers so that the contents can be made more interest ing and

meaningful. Readers can email their queries and doubts to tmcnagpur@gmail.com.

We shall be glad to help you immediately.

Edited and Compiled by :

Team TMC Nagpur

[© 2012-13 Onwards: TMC Textbook on EC] Page 3

Syllabus and TMC Contents

Unit Syllabus and TMC Contents Page

1 Water Technology: Hardness of water and types of hardness

Domestic water treatment: Brief discussion of coagulation and sterilization

using UV. Ozone, chlorine, Break point chlorination.

Softening of water-principle, reactions, advantages, limitations and Comparison

of – Lime-Soda process, Zeolite process, and de-mineralization process.

Boiler Troubles-(causes, effect on boiler operation and methods of prevention) –

Carry over-priming and foaming; Scales and sludges, caustic embrittlement,

boiler corrosion; internal conditioning-phosphate, carbonate, calgon conditioning.

Numerical based on lime-soda and Zeolite process.

Desalination-using electro dialysis and reverse osmosis processes.

Waste water treatment (introduction and importance) – Brief idea about tertiary

treatment methods.

05

2 Corrosion Science: Introduction, Causes and Consequence of corrosion, brief idea

about electrochemical & galvanic series, Factors influencing corrosion: a) Nature

of metal b) Nature of environment,

Chemical and electrochemical corrosion, Mechanisms of electrochemical

corrosion; Pilling Bed worth rule; Differential aeration theory of corrosion.

Types of Corrosion – Pitting, inter granular, stress, waterline and galvanic

corrosion.

Corrosion Prevention – a) Design and material selection b) Cathodic and anodic

protection, c) Protective surface coatings- tinning, galvanizing and powder

coating, metal cladding and electroplating.

75

3 Construction Materials : Cement: Portland cement – Raw material, Dry and wet

process of manufacture, Proportion and role of microscopic constituents,

Additives of cement ,Setting and hardening of cement; heat of hydration,

soundness;

117

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Types of cement ( characteristics & applications ) – White, High alumina, Low

heat ,Rapid hardening cement, Ready Mix Concrete, fly ash as cementing

material( properties, advantages, limitations & application)

4 Green Chemistry and Battery Technology: Green Chemistry: Introduction,

Principles and significance, industrial application (supercritical fluids as Solvents,

Example-super critical CO2 ), Biocatalysis and concept of carbon credits.

Battery Technology: Types of batteries, primary, secondary and reverse batteries,

important definition-energy density, power density. a) Secondary Battery:

Lithium ion, Nickel-Cadmium b) Fuel cell application, advantages and limitation

(Example: Alkaline fuel Cell).

149

Bibliography and further readings;

Model Question Paper

180

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Unit1: Water Technology

Introduction

Water is the most abundant, familiar and important of all compounds that occur in nature. It is found in the

liquid state as water of lakes, rivers and oceans, in the solid state as thick layers of ice in Polar Regions and as

water vapour in air. It is this water vapour that returns to the earth as rain, fog, snow and dew.

Water is the very essence of life of almost all plants and animals. A proper balance between its consumption

and excretion is vital to prevent dehydration of living organism.

Water cannot be produced or added as and when required by any technological means. The major

constituent of water in any case is H2O which is the internal medium for almost all organisms, and principal

external medium for several organisms. Although biological and physio-chemical properties of the pure

chemical water are fascinating, its use or consumption determines its importance. Water is the substance

which is present in all the three states of matter, i.e. gaseous, liquid and solid within the ranges of

temperature and pressure common to the earth.

The availability of a water supply adequate in terms of both quantity and quality is essential for its use or

consumption for different purposes like human use, crop production, industry etc.

Many industrial and domestic water users are concerned about the hardness of their water. Hard water

requires more soap and synthetic detergents for home laundry and washing, and contributes to scaling in

boilers and industrial equipment. Hardness is caused by compounds of calcium and magnesium, and by a

variety of other metals. Water is an excellent solvent and readily dissolves minerals it comes in contact with.

As water moves through soil and rock, it dissolves very small amounts of minerals and holds them in

solution. Calcium and magnesium dissolved in water are the two most common minerals that make water

"hard."

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Specification for Water

Different uses of water demand different specifications:

i) Textile Industry: Textile industry needs frequent dyeing of clothes and the water used by this industry

should be soft and free from organic matter. Uniform dyeing is not possible with hard water as it decreases

the solubility of acidic dyes. If water contains Fe, Mn, colour or turbidity, it causes uneven dyeing and leaves

stains on fabrics. Hence, water should be free from these impurities.

ii) Laundries: Laundries require soft water free from colour, Mn and Fe because hardness increases the

consumption of soaps. Salts of Fe and Mn impart a grey or yellow shade to the fabric.

iii) Boilers: Boilers require water of zero hardness otherwise; heat transfer is hindered by scale formation.

Untreated water can also lead to corrosion of boiler materials.

iv) Paper Industry: Paper Industry require water free from SiO2 (as it produces cracks in the paper);

Turbidity (Fe and Mn as they affect the brightness and colour of the paper); Alkalinity (consumes alum and

increases the cost of production); Hardness (as Ca and Mg salts increase the ash content of the paper.)

v) Beverage: Beverages require which isn't alkaline as it destroys or modifies the taste as it tends to

neutralize the fruit acids.

vi) Dairies and Pharmaceutical Industries: Such industries require ultra pure water which should be

colourless, tasteless, odourless and free form pathogenic organisms.

Water needs to be treated to remove all the undesirable impurities. Water treatment is the process by

which all types of undesirable impurities are removed from water and making it fit for domestic or

industrial purposes.

Hardness of water and types of hardness

Hard water is water that has high mineral content (in contrast with “soft water”). Hard water is generally

not harmful to one's health, but can pose serious problems in industrial settings, where water hardness is

monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that handles water. In

domestic settings, hard water is often indicated

by a lack of suds formation when soap is

agitated in water. Wherever water hardness is a

concern, water softening is commonly used to

reduce hard water's adverse effects.

People whose water comes from places with lots

of limestone or chalk have hard water.

Remember that limestone and chalk are both

made up mainly from calcium carbonate. So,

perhaps hard water is produced when calcium

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carbonate dissolves in the water.

Hard water is a very common problem, affecting water in more than 85% of the country. It is a result of the

dissolved minerals calcium, magnesium and manganese. With an increase in these minerals, the following

are seen:

Soap scum in sinks and bathtubs

Bathtub rings

Spots on dishes or shower doors

Reduced foaming and cleaning abilities of soaps and detergents

Dingy and yellowed clothes with soapy residues that require extra rinsing to remove

Clogged pipes from buildup of minerals

Increased water heating costs from buildup of minerals, reducing efficiency of water heaters

Possible skin infections from bacteria trapped in pores underneath soap scum

Definition

Water which does not produce lather with water is known as hard water. It is due to some of the salts

dissolved into the water. When we treat the water with soap, it gets precipitated in the form of insoluble salts

of calcium and magnesium.

CaCl2 + 2C17 H35 COONa → (C17 H35 COO)2 Ca +2NaCl

(From soap) (Soap) (Insoluble precipitate)

Whereas,

The soft water when treated with soap produces more lather and consumes less soap and this is due to the

absence of dissolved salts of Ca & Mg in water.

C17H35 COONa + H2O → NaOH + 2C17H35 COOH

Types of Hardness:

1. Temporary Hardness: Temporary hardness is caused by a combination of calcium ions and bicarbonate

ions in the water. It is due to the presence of bicarbonates of calcium and magnesium. It can be easily

removed by boiling. It can be removed by boiling the water or by the addition of lime (calcium hydroxide).

Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of

solution, leaving water that is softer upon cooling.

Boil

Ca (HCO3)2 → CaCO3 ↓+ CO2 ↑+ H2 O

Boil

Mg (HCO3)2 → MgCO3 ↓+ CO2↑ + H2O

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Temporary Hardness:

Calcium bicarbonate: Ca (HCO3)2 Mol.wt : 162gm/mole

Magnesium bicarbonate: Mg (HCO3)2 Mol.wt : 146gm/mole

2. Permanent Hardness: Permanent hardness is hardness (mineral content) that cannot be removed by

boiling. It is usually caused by the presence of calcium and magnesium sulfates and/or chlorides in the

water, which become more soluble as the temperature rises. This type of hardness cannot be removed by

boiling. This is due to the presence of chlorides and sulphates of calcium and magnesium. The hardness can

be removed by the addition of some agents.

Permanent Hardness:

Calciumchloride CaCl2 Mol.wt : 111gm/mole

Magnesiumchloride MgCl2 Mol.wt : 95gm/mole

Calciumsulphate CaSO4 Mol.wt : 136gm/mole

Magnesiumsulphate MgSO4 Mol.wt : 120 gm/mole

How is hardness expressed?

Water hardness is, unfortunately, expressed in several different units, and thus it is often necessary to

convert from one unit to another when making calculations. The most commonly used units include grains

per gallon (gpg), parts per million (ppm), and milligrams per liter (mg/L).

The grain per gallon is based on the old English system of weights and measures. It is based on the average

weight of a dry kernel of grain (or wheat). The part per million is a weight to weight ratio. For example, one

ppm of calcium means 1 pound of calcium in 1 million pounds of water, or 1 gram of calcium in 1 million

grams of water. Since pure water weighs 1000 grams per liter, the mg/L is the same as the ppm in the dilute

solutions present in most raw and treated water.

Units of Hardness:

1. Parts per million (ppm)

2. Milligrams per litre (mg/l)

3. Degree French (ºFr)

4. Degree Clark (ºCl)

Relationship: 1ppm = 1mg/L = 0.1 ºFr = 0.07 ºCl

To convert To Multiply by

Grains per gallon Milligrams per liter 17.12

Milligrams per liter Grains per gallon 0.05841

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The hardness of water is referred to by three types of measurements: grains per gallon, milligrams per liter

(mg/L), or parts per million (ppm). Typically, the water produced by Fairfax Water is considered

"moderately hard" to "hard." The table below is provided as a reference.

Water Hardness Scale Grains Per

Gallon Milligrams Per Liter (mg/L)or Parts Per

Million (ppm)

Classification

less than 1.0 less than 17.1 Soft

1.0 - 3.5 17.1 - 60 Slightly Hard

3.5 - 7.0 60 - 120 Moderately Hard

7.0 - 10.5 120 - 180 Hard

over 10.5 over 180 Very Hard

Since calcium carbonate is one of the more common causes of hardness, total hardness is usually reported in

terms of calcium carbonate concentration (mg/L as CaCO3), using either of two methods:

a) Calcium and magnesium hardness.

b) Carbonate and non-carbonate hardness.

(a) Hardness caused by calcium is called calcium hardness, regardless of the salts associated with it.

Likewise, hardness caused by magnesium is called magnesium hardness. Since calcium and magnesium are

normally the only significant minerals that cause hardness, it is generally assumed that:

Total Hardness = Calcium Hardness + Magnesium Hardness

(mg/L as CaCO3) (mg/L as CaCO

3) (mg/L as CaCO

3)

= 2.50 X Calcium concentration + 4.12 X Magnesium concentration

(mg/L as Ca2+

) (mg/L as Mg2+

)

(b) Carbonate hardness is primarily caused by the carbonate and bicarbonate salts of calcium and

magnesium. Non-carbonate hardness is a measure of calcium and magnesium salts other than carbonate and

bicarbonate salts, such as calcium sulfate, CaSO4, or magnesium chloride, MgCl

2. Total hardness is expressed

as the sum of the carbonate hardness and non-carbonate hardness.

Total hardness = Carbonate hardness + Non-carbonate hardness

(mg/L as CaCO3) (mg/L as CaCO

3) (mg/L as CaCO

3)

The amount of carbonate and non-carbonate hardness depends on the alkalinity of the water.

When a laboratory reports a value for total hardness of, for instance, 150 mg/l as CaCO3, this indicates that

the combined effect of the different hardness causing agents is the same as if the water contained exactly 150

mg/l of CaCO3.

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There are advantages and disadvantages for people who live in hard water areas.Some of the advantages

and disadvantages of hard water are as follows:

Disadvantage of hard water

1. Domestic:

Hard water affects cleaning ability of soap.

When hard water is used for washing, large amount of soap is consumed.

2. Industrial:

Hard water can cause "Scaling" inside the pipes that transport water. Therefore if we use hard water

in turbines and heat exchangers, their pipes will be corroded

3. Health:

Hard water when used for drinking for long period can lead to stomach disorders. Especially hard

water contains magnesium sulphate can weaken the stomach permanently.

Advantages of hard water

1. Some people prefer the taste.

2. Calcium ions in the water are good for children's teeth and bones.

3. It helps to reduce heart disease.

4. Some brewers prefer using hard water for making beer.

5. A coating of lime scale inside copper pipes, or especially old lead pipes, stops poisonous salts dissolving

into water.

Softening of water

Hard water is a problem for millions of households across the country. Hard water is water that has high

mineral content. Due to the minerals present in hard water, the sides of pipe lines are clogged. Over a period

of time, deposits and build up prevent water to flow like it should, pipes becomes too small to allow fast

passage of water. Once the holes become smaller, the pressure in pipes increases so much that there is a high

risk of the lines deteriorating or may burst. Softened water still contains all the natural minerals that we

need. It is only deprived off its calcium and magnesium contents, and some sodium is added during the

softening process.

Water softening is the reduction of the concentration of calcium, magnesium, and certain other

metal cations in hard water. These "hardness ions" can cause a variety of undesired effects including

interfering with the action of soaps, the buildup of lime scale, which can foul plumbing, and galvanic

corrosion. Conventional water-softening appliances intended for household use depend on an ion-exchange

resin in which hardness ions are exchanged for sodium ions. Water softening may be desirable where the

source of water is hard.

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The process whereby we remove or reduce the hardness of water irrespective of whether it is temporary

or permanent is termed as ‘softening’ of water. Water softening is very essential since hard water is

unsuitable for domestic as well as industrial use. Water can be made soft by external as well internal

treatment.

To remove hardness from water, three methods are used on a large scale:

(1) Lime-Soda process

(2) Zeolite process or Permutit process

(3) De-mineralization process or Ion-exchange process

Principle

It is the process by which hard water is converted to soft water by removing inorganic impurities in it as an

insoluble precipitate. Hard water can be of two types, temporary and permanent. They can soften as

follows:

Temporary hard water is softened by:

● Simple boiling; calcium/magnesium bicarbonates are precipitated as insoluble carbonates

Permanent hard water is softened by adding:

● Washing soda (sodium carbonate).

. ● Lime (calcium hydroxide) and washing soda mixture.

● Ammonia

● Sodium hydroxide

● Sodium tetraborate (Borax)

● Trisodium phosphate

Permanent hard water contains sulphates and chlorides of calcium or magnesium. Boiling the water does not

remove them. Only addition of the substances listed above will remove them and make the water soft.

1. Lime-Soda process

Lime-Soda is a process used in water treatment to remove hardness from water. This process is now

obsolete but was very useful for the treatment of large volumes of hard water.

Chemical precipitation is one of the more common methods used to soften water. The chemicals normally

used are lime (calcium hydroxide, Ca(OH)2) and soda ash (sodium carbonate, Na

2CO

3). Lime is used to

remove the chemicals that cause the carbonate hardness. Soda ash is used to remove the chemicals that cause

the non-carbonate hardness.

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When lime and soda ash are added, the hardness-causing minerals form nearly insoluble precipitates. When

calcium hardness is

removed in a chemical

softener, it is precipitated

as calcium carbonate

(CaCO3). When

magnesium hardness is

removed in a chemical

softener, it is precipitated

as magnesium hydroxide

(Mg(OH)2). These

precipitates are removed by the conventional processes of coagulation/flocculation, sedimentation, and

filtration. Because the precipitates are very slightly soluble, some hardness remains in the water--usually

about 50 to 85 mg/l (as CaCO3). This hardness level is desirable to prevent corrosion problems associated

with water being too soft and having little or no hardness ions.

Reactions:

What are the chemical reactions that happen with lime addition?

Hardness Softening

species chemical Precipitate

CO2. + Ca(OH)

2 -> CaCO3 + H

2O

Ca(HCO3)2

+ Ca(OH)2

-> 2CaCO3 + 2H2O

Mg(HCO3)2

+ Ca(OH)2

-> CaCO3 + MgCO3

+ 2H2O

MgCO3

+ Ca(OH)2

-> CaCO3 + Mg(OH)2

CO2

= carbon dioxide, Ca(OH)2

= calcium hydroxide or hydrated lime, CaCO3

= calcium carbonate,

Ca(HCO3)2 =

calcium bicarbonate, Mg(HCO3)

2 = magnesium bicarbonate, MgCO

3 = magnesium carbonate,

Mg(OH)2

= magnesium hydroxide, MgSO4

= magnesium sulfate, CaSO4 = calcium sulfate, H

2O - water.

What are the chemical reactions with soda ash?

MgSO4

+ Ca(OH)2

-> Mg(OH)2

+CaSO4

CaSO4

+ Na2CO

3 -> CaCO3 + Na

2SO

4

Na2CO

3 = sodium carbonate or soda ash

For each molecule of calcium bicarbonate hardness removed, one molecule of lime is used.

For each molecule of magnesium bicarbonate hardness removed, two molecules of lime are used.

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For each molecule of non-carbonate calcium hardness removed, one molecule of soda ash is used.

Each molecule of non-carbonate magnesium hardness requires one molecule of lime plus one molecule of

soda ash.

Lime soda processes are of two types:

a) Cold lime soda process

b) Hot lime soda process

a. Cold lime soda process: In this process, calculated quantities of lime and soda are mixed with water at

room temperature. The precipitate formed at room temperature is finely divided and does not settle down

easily. They cannot be easily filtered so, it is essential to add a small quantity of coagulant which hydrolysis

to give flocculent and gelatinous precipitate of aluminium hydroxide, thus it entraps the fine precipitate.

There are two kind of softeners used for softening water by this process.

i) Intermittent type softeners, where the softening is done by batch process.

ii) Continuous type softeners.

b. Hot lime soda process: In this process, water is treated with chemicals at a temperature of 94-1000C.

The softeners used are of intermittent type or continuous type.

Advantages of Hot lime soda process:

i) They are more rapid in operation. The time taken for completion is 15 minutes and several hours for hot

and cold lime soda processes respectively.

ii) Elevated temperature accelerates the actual chemical reaction and reduces the viscosity of the water. This

increases the rate of aggregation of the particle. Hence, both the setting rates and filtration rates are

increased. Thus the softening capacity of the hot process is several times higher than the cold process.

iii) The sludge and the precipitate formed settle down rapidly and hence no coagulant is needed.

iv) Quantity of chemical required for softening is low.

v) At the higher temperature, the dissolved gases such as CO2 are driven out of the solution to some extent.

Advantages of Lime-soda Process:

i) It is very economical.

ii) Treated water is alkaline and hence has less corrosion tendencies.

iii) It removes not only hardness causing salt but also minerals.

iv) Due to alkaline nature of treated water, amount of pathogenic bacteria in water is considerably reduced.

v) Iron and manganese are also removed from the water to some extent.

Disadvantages of Lime-soda process:

i) It requires careful operation and skilled supervision for economical and efficient softening.

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ii) Sludge disposal is a problem.

iii) Water softened by this process contains appreciable concentration of soluble salts, such as sodium

sulphate and cannot be used in high pressure boiler.

2. Zeolite process or Permutit process

Permutit is also known as Zeolite. They are capable of exchanging ions reversibly. The chemical formula for

permutit is Na2O, Al2O3SiO2 6H2O. In short it is written as Na2-P or Na2-Z.

For softening of water by this method, hard water is percolated at a specified rate through a bed of zeolite

kept in a cylinder. The hardness causing ions (Ca++ & Mg++) are retained by the permutit as Ca-P & Mg-P.

While the outgoing water contains sodium salts.

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2. Alkaline Electrolyte Fuel Cell (AFC)

Alkaline fuel cells (AFCs) were one of the first fuel cell technologies developed, and they were the first type

widely used in the U.S. space program to produce electrical energy and water onboard spacecraft. These fuel

cells use a solution of potassium hydroxide in water as the

electrolyte and can use a variety of non-precious metals as a

catalyst at the anode and cathode. High-temperature AFCs

operate at temperatures between 100°C and 250°C (212°F and

482°F). However, newer AFC designs operate at lower

temperatures of roughly 23°C to 70°C (74°F to 158°F)

Reactions

The electrolyte employed in AFC is potassium hydroxide and

unlike the acid electrolyte fuel cell where H+ is conducted

from the anode to the cathode in the AFC OH- is conducted

from the cathode to the anode. The reaction at the anode and

cathode is shown below:

Water is produced twice as fast as is been consumed hence the need to remove excess water to avoid dilution

of the electrolyte. The main limitation of AFC for terrestrial application is the degradation the KOH

electrolyte by CO2 poisoning as shown below, therefore pure H2-O2 must be used.

Advantages

1. Advantages offered by AFC include improved cathode performance, non-precious metal such as nickel

can be used as catalyst and extremely inexpensive electrolyte.

2. AFCs' high performance is due to the rate at which chemical reactions take place in the cell. They have

also demonstrated efficiencies near 60 percent in space applications.

Disadvantages

1. The disadvantage of this fuel cell type is that it is easily poisoned by carbon dioxide (CO2 ). In fact, even

the small amount of CO2 in the air can affect this cell's operation, making it necessary to purify both the

hydrogen and oxygen used in the cell. This purification process is costly. Susceptibility to poisoning also

affects the cell's lifetime (the amount of time before it must be replaced), further adding to cost.

2. Cost is less of a factor for remote locations such as space or under the sea. However, to effectively

compete in most mainstream commercial markets, these fuel cells will have to become more cost-

effective. AFC stacks have been shown to maintain sufficiently stable operation for more than 8,000

operating hours. To be economically viable in large-scale utility applications, these fuel cells need to

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reach operating times exceeding 40,000 hours, something that has not yet been achieved due to material

durability issues. This is possibly the most significant obstacle in commercializing this fuel cell

technology.

3. Phosphoric Acid Fuel Cell (PAFC)

Phosphoric acid fuel cells use liquid phosphoric acid as an electrolyte—the acid is contained in a Teflon-

bonded silicon carbide matrix—and porous carbon electrodes

containing a platinum catalyst. The chemical reactions that take place in

the cell are shown in the diagram to the right.

Reactions

Phosphorous acid fuel cell uses liquid H3PO4 as electrolyte. The

electrolyte is embedded in SiC matrix between two porous graphite

electrodes coated with a platinum catalyst. The half reaction is as

follows:

PAFC will operate optimally in the temperature range of about 180- 210

0C with electrical efficiency of about 40% but could be as high as 70%

when used in a combined heat and power application. The technology of PAFC is relatively matured but

current research interest is how to make it cost competitive with conventional power technologies.

Advantages

The phosphoric acid fuel cell (PAFC) is considered the "first generation" of modern fuel cells. It is one of the

most mature cell types and the first to be used commercially, with over 200 units currently in use. This type

of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large

vehicles such as city buses.

PAFCs are more tolerant of impurities in fossil fuels that have been reformed into hydrogen than PEM cells,

which are easily "poisoned" by carbon monoxide—carbon monoxide binds to the platinum catalyst at the

anode, decreasing the fuel cell's efficiency. They are 85 percent efficient when used for the co-generation of

electricity and heat, but less efficient at generating electricity alone (37 to 42 percent). This is only slightly

more efficient than combustion-based power plants, which typically operate at 33 to 35 percent efficiency.

Disadvantages

PAFCs are also less powerful than other fuel cells, given the same weight and volume. As a result, these fuel

cells are typically large and heavy. PAFCs are also expensive. Like PEM fuel cells, PAFCs require an

expensive platinum catalyst, which raises the cost of the fuel cell. A typical phosphoric acid fuel cell costs

between $4,000 and $4,500 per kilowatt to operate.

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4. Molten Carbonate Fuel Cell (MCFC)

Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power

plants for electrical utility, industrial, and military applications. MCFCs are high-temperature fuel cells that

use an electrolyte composed of a molten carbonate salt

mixture suspended in a porous, chemically inert ceramic

lithium aluminum oxide (LiAlO2) matrix. Since they

operate at extremely high temperatures of 650°C (roughly

1,200°F) and above, non-precious metals can be used as

catalysts at the anode and cathode, reducing costs.

Reactions

In MCFC the electrolyte is a molten mixture of Li2CO3

and K2CO3 sustained by LiOAlO2 matrix. The mobile

charge carrier is carbonate ion, CO32- and the reaction at

the anode and cathode is as follows:

There is the need for recirculation of CO2 because the

CO2 is produced at the anode to be consumed at the cathode. It does not suffer from CO poisoning like most

other fuel cell, the CO is actually a fuel. The anode electrode is usually nickel/chromium alloy while the

cathode is made of lithiated nickel oxide hence the advantages of using non-precious catalyst. It enjoys fuel

flexibility as hydrogen, methane and simple alcohol could be used as fuel.

Advantages

One of its advantage is the corrosive nature of the molten electrolyte. MCFC is most suitable for stationary,

continuous power application.

Improved efficiency is another reason MCFCs offer significant cost reductions over phosphoric acid fuel cells

(PAFCs). Molten carbonate fuel cells can reach efficiencies approaching 60 percent, considerably higher than

the 37-42 percent efficiencies of a phosphoric acid fuel cell plant. When the waste heat is captured and used,

overall fuel efficiencies can be as high as 85 percent.

Unlike alkaline, phosphoric acid, and polymer electrolyte membrane fuel cells, MCFCs don't require an

external reformer to convert more energy-dense fuels to hydrogen. Due to the high temperatures at which

MCFCs operate, these fuels are converted to hydrogen within the fuel cell itself by a process called internal

reforming, which also reduces cost.

Disadvantages

Molten carbonate fuel cells are not prone to carbon monoxide or carbon dioxide "poisoning" —they can even

use carbon oxides as fuel—making them more attractive for fueling with gases made from coal. Because they

are more resistant to impurities than other fuel cell types, scientists believe that they could even be capable

[© 2012-13 Onwards: TMC Textbook on EC] Page 18

of internal reforming of coal, assuming they can be made resistant to impurities such as sulfur and

particulates that result from converting coal, a dirtier fossil fuel source than many others, into hydrogen.

The primary disadvantage of current MCFC technology is durability. The high temperatures at which these

cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing

cell life. Scientists are currently exploring corrosion-resistant materials for components as well as fuel cell

designs that increase cell life without decreasing performance.

5. Solid Oxide Fuel Cell (SOFC)

Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic compound as the electrolyte. Since the

electrolyte is a solid, the cells do not have to be constructed in the plate-like configuration typical of other

fuel cell types. SOFCs are expected to be around 50-60 percent efficient at converting fuel to electricity. In

applications designed to capture and utilize the system's waste heat

(co-generation), overall fuel use efficiencies could top 80-85 percent.

Reactions

SOFC is made of solid oxide ceramic electrolyte sandwiched

between two porous electrodes. The common electrolyte material is

yttria-stabilised Zirconia (YSZ). The anode is usually made of

Ni/8YSZ material while typical cathode material is strontium doped

LaMnO3 (LSM). In SOFC O2- is the mobile ion conductor and the

reactions at the anode and cathode are

Water is produced at the anode unlike PEMFC, AFC and PAFC in

which water is produced at the cathode. The operating temperature is between 600 and 10000C. Although the

high operating temperature could lead to low open circuit voltage but at the same time it increases its

performance with the possibility of inwardly processing hydrocarbon.

Solid oxide fuel cells operate at very high temperatures—around 1,000°C (1,830°F). High temperature

operation removes the need for precious-metal catalyst, thereby reducing cost. It also allows SOFCs to

reform fuels internally, which enables the use of a variety of fuels and reduces the cost associated with

adding a reformer to the system.

Advantages

SOFCs are also the most sulfur-resistant fuel cell type; they can tolerate several orders of magnitude more

sulfur than other cell types. In addition, they are not poisoned by carbon monoxide (CO), which can even be

used as fuel. This allows SOFCs to use gases made from coal.

[© 2012-13 Onwards: TMC Textbook on EC] Page 19

Disadvantages

1. High-temperature operation has disadvantages. It results in a slow startup and requires significant

thermal shielding to retain heat and protect personnel, which may be acceptable for utility applications

but not for transportation and small portable applications. The high operating temperatures also place

stringent durability requirements on materials. The development of low-cost materials with high

durability at cell operating temperatures is the key technical challenge facing this technology.

2. Scientists are currently exploring the potential for developing lower-temperature SOFCs operating at or

below 800°C that have fewer durability problems and cost less. Lower-temperature SOFCs produce less

electrical power, however, and stack materials that will function in this lower temperature range have

not been identified.

[© 2012-13 Onwards: TMC Textbook on EC] Page 20

Fuel Cell Comparison Chart

Fuel Cell

Type

Common Electrolyte Operating

Temperature

Applications Advantages Disadvantages

Polymer

Electrolyte

Membrane

(PEM)

Solid organic polymer

poly-perfluorosulfonic

acid

50 - 100°C

122 - 212°F

Backup power

Portable power

Small

distributed

generation

Transportation

Solid electrolyte

reduces corrosion

& electrolyte

management

problems

Low temperature

Quick start-up

Requires expensive

catalysts

High sensitivity to

fuel impurities

Low temperature

waste heat

Waste heat

temperature not

suitable for combined

heat and power

(CHP)

Alkaline

(AFC)

Aqueous solution of

potassium hydroxide

soaked in a matrix

90 - 100°C

194 - 212°F

Military

Space

Cathode reaction

faster in alkaline

electrolyte, higher

performance

Expensive removal of

CO2 from fuel and air

streams required

(CO2 degrades the

electrolyte)

Phosphoric

Acid (PAFC)

Liquid phosphoric acid

soaked in a matrix

150 - 200°C

302 - 392°F

Distributed

generation

Higher overall

efficiency with

CHP

Increased

tolerance to

impurities in

hydrogen

Requires expensive

platinum catalysts

Low current and

power

Large size/weight

Molten

Carbonate

(MCFC)

Liquid solution of

lithium, sodium,

and/or potassium

carbonates soaked in a

matrix

600 - 700°C

1112 - 1292°F

Electric utility

Large

distributed

generation

High efficiency

Fuel flexibility

Can use a variety

of catalysts

Suitable for CHP

High temperature

speeds corrosion and

breakdown of cell

components

Complex electrolyte

management

Slow start-up

Solid Oxide

(SOFC)

Solid zirconium oxide

to which a small

amount of Yttria is

added

650 - 1000°C

1202 - 1832°F

Auxiliary

power

Electric utility

Large

distributed

generation

High efficiency

Fuel flexibility

Can use a variety

of catalysts

Solid electrolyte

reduces

electrolyte

management

problems

Suitable for CHP

High temperature

enhances corrosion

and breakdown of

cell components

Slow start-up

Brittleness of ceramic

electrolyte with

thermal cycling

[© 2012-13 Onwards: TMC Textbook on EC] Page 21

4) Reserve Batteries

A fourth battery category is commonly referred to as the reserve cell. Also called deferred-action batteries,

reserve batteries are special purpose primary batteries usually designed for emergency use. The electrolyte

is usually stored separately from the electrodes which remain in a dry inactive state. The battery is only

activated when it is actually needed by introducing the electrolyte into the active cell area. This has the

double benefit of avoiding deterioration of the active materials during storage and at the same time it

eliminates the loss of capacity due to self discharge until the battery is called into use. They can thus be

stored for 10 years or more yet provide full power in an instant when it is required.

Definitions

A reserve battery, also called stand-by battery, is a primary battery where part is isolated until the battery

needs to be used. When long storage is required, reserve batteries are often used, since the active

chemicals of the cell are segregated until needed, thus reducing self-discharge.

A reserve battery is distinguished from a backup battery, in that a reserve battery is inert until it is activated,

while a backup battery is already functional, even if it is not delivering current.

Reserve batteries have been designed using a number of different electrochemical systems to take advantage

of the long unactivated shelf life achieved by this type of battery design. Relatively few of these have

achieved wide usage because of the lower capacity of the reserve structure (compared with a standard

battery of the same system), poorer shelf life after activation, higher cost, and generally acceptable shelf life

of active primary batteries for most applications. For the special applications that prompted their

development, nevertheless, the reserve structure offers the needed advantageous characteristics. In recent

years, however, the use of reserve batteries has declined because of the improved storability of active

primary batteries and the limited number of applications requiring extended storage. Most of these

applications are for special military weapon systems. The reserve batteries are usually designed for specific

applications, each design optimized to meet the requirements of the application.

What differentiates the reserve cell from primary and secondary cells in the fact that a key component of

the cell is separated from the remaining components, until just prior to activation. The component most

often isolated is the electrolyte. This battery structure is commonly observed in thermal batteries, whereby

the electrolyte remains inactive in a solid state until the melting point of the electrolyte is reached, allowing

for ionic conduction, thus activating the battery. Reserve batteries effectively eliminate the possibility of self-

discharge and minimize chemical deterioration. Most reserve batteries are used only once and then

discarded. Reserve batteries are used in timing, temperature and pressure sensitive detonation devices in

missiles, torpedoes, and other weapon systems.

[© 2012-13 Onwards: TMC Textbook on EC] Page 22

Types and Activation

The reserve batteries can be classified by the type of activating medium or mechanism that is involved in

the activation:

1. Water-activated batteries: Activation by fresh- or seawater.

Activation of the reserve battery is accomplished by adding the missing component just prior to use. In the

simplest designs, this is done by manually pouring or adding the electrolyte into the cell or placing the

battery in the electrolyte (as in the case of sea water activated batteries).

2. Electrolyte-activated batteries: Activation by the complete electrolyte or with the electrolyte

solvent. The electrolyte solute is contained in or formed in the cell.

In more sophisticated applications the electrolyte storage and the activation mechanism are contained within

the overall battery structure, and the electrolyte is brought automatically to the active electrochemical

components by remotely activating the activation mechanism. The trigger for activation can be a mechanical

or electrical impulse, the shock and spin accompanying the firing of a shell or missile, and so on. Activation

can be completed very rapidly if required, usually in less than one second. The penalty for automatic

activation is a substantial reduction in the specific energy and/or energy density of the battery due to the

volume and weight of the activating mechanism. It is therefore not general practice to rate these batteries in

terms of specific energy or energy density.

3. Gas-activated batteries: Activation by introducing a gas into the cell. The gas can be either the

active cathode material or part of the electrolyte.

The gas-activated batteries are a class of reserve batteries which are activated by introduction of a gas into

the battery system. There are two types of gas-activated batteries: those in which the gas serves as the

cathodic active material and those in which the gas serves to form the electrolyte. The gas-activated batteries

were attractive because they offered the potential of a simple and positive means of activation. In addition,

because the gas is nonconductive, it can be distributed through a multicell assembly without the danger of

short-circuiting the battery through the distribution system. Gas-activated batteries are no longer in

production, however, because of the more advantageous characteristics of other systems.

4. Heat-activated batteries: A solid salt electrolyte is heated to the molten condition and

becomes ionically conductive, thus activating the cell. These are known as thermal batteries.

The thermal or heat-activated battery is another class of reserve battery. It employs a salt electrolyte, which is

solid and, hence, nonconductive at the normal storage temperatures when the battery must be inactive. The

battery is activated by heating it to a temperature sufficiently high to melt the electrolyte, thus making it

ionically conductive and permitting the flow of current. The heat source and activating mechanism, which

can be set off by electrical or mechanical means, can be built into the battery in a compact configuration to

give very rapid activation. In the inactive stage the thermal battery can be stored for periods of 10 years or

more.

[© 2012-13 Onwards: TMC Textbook on EC] Page 23

Review Questions

1. What is a battery? How does it differ from a cell?

2. What are the important requirement of a battery?

3. What is a primary battery? Give an example. Or What are primary cells?

4. What are secondary cells? What are the advantages of alkaline battery over dry battery?

5. Write the cell representation of lead storage cell?

6. Describe lithium battery. What are the advantages of Li-S battery?

7. Lithium battery is the cell of future, why?

8. What is a primary battery? Give an example.

9. Write a note on Ni – Cd battery.

10. Explain the construction and working of lead – acid storage battery.

11. What is reversible battery? Describe the construction and working of a lead storage battery with the

reaction occurring during charging and discharging.

12. What is lithium battery? Give the reactions involved.

13. How NICAD battery constructed. Explain with cell reaction .

14. Give the description of lead storage battery and explain its functioning during discharging and

recharging.

15. Define Fuel cell. Explain alkaline fuel Cell. Give its merits and demerits.

16. Define green chemistry.

17. Which of the Twelve Principles of Green Chemistry deals with atom economy?

[© 2012-13 Onwards: TMC Textbook on EC] Page 24

Bibliography and Further Readings

1. A Text book of Engineering Chemistry: Shashi Chawla; Dhanpat Rai & Sons, New Delhi.

2. Applied Chemistry by N. Krishnamurthy:P. Vallinavagam. And K. Jeysubramanian TMH

3. Applied Chemistry for Engineers: T.S. Gyngell.

4. Applied Chemistry: A.V. Bharati and Walekar, Tech Max Publications, Pune.

5. Bateman, John H., Materials of Construction Publishing Corporation, London.

6. Chemistry of Advanced Materials: CNR Rao, Rsc Publication.

7. Chemistry of Engineering Materials: Robert B Leighou Mc Graw – Hill Book Company, Inc New York

8. Engineering Chemistry: Arty Dixit Dr. Kirtiwardhan Dixit, Harivansh Prakashan, Chandrapur.

9. Engineering Materials: Kenneth G Budinski (Prentice – Hall of India)

10. Fundamentals of Corrosion: Michael Henthorne, Chemical Engineering.

11. Fundamentals of Engineering Chemistry (Theory and Practice) :S. K. Singh (New Age Materials

12. G Nagendrappa, Resonance, Vol.7, No.1, pp.64–76; No.10, pp.59–68;

13. http://en.wikipedia. org/wiki/Green, chemistry

14. http://www.epa.gov/greenchemistry/pubs/whats_gc.html

15. IS : 2547 (Part 1) 1967, Specification for Gypsum Building Plasters,

16. IS : 7i2-1973, Specification For Building Limes.

17. Larminie, J., Dicks, A. and Knovel, ( 2003), Fuel cell systems explained, 2nd ed., J. Wiley, Chichester, West Sussex.

18. Leena Rao, Resonance, Vol.12, No.8, pp.65–75; No.10, pp.30–36, 2007.

19. Makuch G. (2004), Micro Fuel Cells Strive for Commercialization

20. Materials Science and Engineering an Introduction, William D. Callister, (Jr. Wiley publisher).

21. Neville, A.M. Properties of Concrete, Pitnian Publishing, London.

22. Sammes, N.M. and SpringerLink, ( 2006), Fuel cell technology, Springer, London

23. Shetty, M.S., Concrete Technology, Chand &L Company Ltd., New Delhi.

24. Text Book of Engineering Chemistry: S.S. Dara, S. Chand and Company Ltd. New Delhi.

25. Textbook of Engineering Chemistry: P.C. Jain and Monica Jain, Dhanpat Rai and Sons, New Delhi.

26. Textbook of Engineering Chemistry: S.N. Narkhede, R.T. Jadhav, AB. Bhake, A.U. Zadgaonkar, Das Ganu

Prakashan, Nagpur.

27. VKAhluwalia andMKidwai, NewTrends inGreenChemistry, Anamaya Publishers, New Delhi, 2004.

28. Water Treatment : F. I. Bilane, Mir publisher

29. Winterbone, D.E., (1997), Advanced Thermodynamics for Engineers, Elsevier.

30. Zhang J. (2008), PEM Fuel Cell Electrocatalysis, Institute for Fuel Cell Innovation, National Research Council

Canada.

`

[© 2012-13 Onwards: TMC Textbook on EC] Page 25

Modal Question Paper for

Winter 2012

First Semester of

Bachelor of Engineering (BE) Examination

Engineering Chemistry

Time: Two Hours] [Max. Marks: 40

NB:-

1) All the Five Questions are compulsory.

2) All questions carry equal marks.

Q1. (a) Compare Lime-Soda process and Zeolite

process for Softening of water.

or

(b) What is the importance of Waste water

treatment? Give a brief idea about tertiary

treatment methods.

Q2. What is the significance of Corrosion Science?

Enlist causes and Consequence of corrosion.

or

(b) Explain any three types of corrosions based on

the reactions and physical states.

Q3. (a) Enlist the Proportion and role of

microscopic constituents of cement? How is

cement manufactured by Dry process?

or

(b) Can Fly ash be used as cementing material?

Elaborate its advantages, limitations &

applications.

Q4. (a) What is Green Chemistry? Explain twelve

principles of green chemistry

or

(b) What are three major types of chemical

batteries? Mention their advantages and

disadvantages?

Q5. Write short notes on (Any Two):

(a) Reverse osmosis processes

(b) Pilling Bed worth rule

(c) Ready Mix Concrete

(d) Concept of carbon credits