This is Unit 1 : Water Technology and Green Chemistry will be useful for UoP First Year Engineering.

1. c
Engineering
Chemistry
Unit 1 : Water Technology and Green Chemistry
Santosh Damkondwar
For University of Pune
First Year Engineering

2. UNIT 1.
WATER TECHNOLOGY AND GREEN CHEMISTRY
3
PART A. WATER TECHNOLOGY
3
IMPURITIES IN WATER:
3
TYPES OF WATER:
3
1.
SOFT WATER:
3
2.
HARD WATER:
3
HARDNESS OF WATER:
4
UNITS OF HARDNESS:
4
HARDNESS OF WATER BY EDTA METHOD:
4
ALKALINITY OF WATER:
5
ILL EFFECTS OF USING HARD WATER IN BOILERS:
6
1.
SCALE AND SLUDGE FORMATION
6
2.
BOILER CORROSION:
7
3.
PRIMING AND FOAMING:
7
4.
CAUSTIC EMBRITTLEMENT:
7
WATER TREATMENTS:
8
1.
INTERNAL TREATMENT:
8
A.
CALGON CONDITIONING
8
B.
COLLOIDAL CONDITIONING
8
C.
PHOSPHATE CONDITIONING
8
ENGINEERING CHEMISTRY
1

3. 2.
EXTERNAL TREATMENT:
9
A.
ZEOLITE PROCESS (PERMUTIT PROCESS):
9
B.
ION EXCHANGE PROCESS:
10
DESALINATION OF BRACKISH WATER:
11
1.
ELECTRODIALYSIS:
11
2.
REVERSE OSMOSIS:
11
PART B. GREEN CHEMISTRY
12
DEFINITION:
12
PRINCIPLES OF GREEN CHEMISTRY:
12
EFFICIENCY PARAMETERS:
13
TRADITIONAL AND GREEN PATHWAYS OF SYNTHESIS OF:
13
1.
ADIPIC ACID:
13
2.
INDIGO DYE:
14
3.
POLYCARBONATE:
14
ENGINEERING CHEMISTRY
2

4. Unit 1. Water Technology and Green Chemistry
Part A. Water Technology
Impurities in water:
Impurities from
water
Suspended
Impurities
e.g. clay, mud,
organic matter
It can be
removed by
filteration
Dissolved
Impurities
Colloidal
impurities
Biological
Impurities
e.g. Dissolved
gases or salts
e.g. Colloidal
particles of clay,
mud, organic
matter,etc
e.g. algae, fungi,
bacteria, etc
It can be
removed by
softening process
It can be
removed by
Coagulation
(cougulating
agent like potash
alum, sodium
aluminate)
It can be
removed by
Sterlization
(sterlizing agent
like liquid
chlorine, ozone,
UV light)
Types of water:
There are two types depend upon resources:
1.
Soft water:
A water when mixed with soap solution (sodium or potassium salt of higher fatty acids like
oleic, palmitic or stearic) forms lather or foam, is called as soft water.
2.
Hard water:
A water when mixed with soap solution does not form lather or foam, but forms white scum
or precipitate is called as hard water.
ENGINEERING CHEMISTRY
3

5. Hardness of water:
Temporary or Alkaline or Carbonate
Hardness
•It is due to carbonates and bicarbonates of Ca & Mg.
It
•It can be removed by filteration after mere boiling.
It
Permanant or Non-alkaline or Noncarbonate Hardness
•t is due to chlorides, sulphates and nitrates of Ca, Mg,
t
Al, Fe, Mn.
•It can not be removed easily.
Reactions for removal of temporary hardness:
Ca(HCO3) 2
CaCO 3 + CO 2 + H 2O
Mg(HCO 3) 2
Mg(OH) 2 + 2 CO 2
Units of Hardness:
The hardness is calculated in terms of CaCO3 equivalent as:
For bivalent salt:
The units used to express hardness in terms of CaCO3 equivalent are mg/lit [milligram per
liter], ppm [parts per million], ppb [parts per billion], oCl [degree Clark] or oFr [degree French]
Hardness of water by EDTA Me
Method:
EDTA method is a complexometric method of determining hardness of water. As EBT
forms stable complex at pH = 10, this titration is performed at pH = 10. The structure of EDTA is
as follows:
HOOC
CH2
N
HOOC
CH2
CH2
CH2
N
CH2
CH2 COOH
The structure of disodium salt of EDTA is as follows:
HOOC CH2
CH2
N
+
-
Na O OC
ENGINEERING CHEMISTRY
CH2
COOH
CH2
CH2
COOH
N
-
CH2 COO Na
+
4

6. The structure of disodium salt of EDTA with Ca/Mg (M) is as follows:
HOOCCH2
CH2 COOH
CH2
N
CH2
N
M
H2C
C
O
CH2
O
C
O
Compound / Complex
EBT (Eriochrome Black T)
M-EBT Complex
M-EDTA Complex
End Point
O
Color
Blue
Wine-red
Colourless
Wine-red to blue
Alkalinity of water:
Alkalinity of water is due to presence of salts or substances of hydroxides, carbonates
and bicarbonates of Ca & Mg.
Total alkalinity can be separately estimated by titration against standard acid using
phenolphthalein and methyl orange indicator.
Indicator
Phenolphthalein
Ions
End point
- and Half Pink to colorless
Complete Neutralization of OH
neutralization of CO3-2
Complete Neutralization of CO3-2 and Yellow to orange
neutralization of HCO3-
Methyl Orange
Following are the only combinations present in water:
1. Only OH4. OH- and CO3-2
2. Only CO3-2
5. CO3-2and HCO3-
3. Only HCO3-
OH- and HCO3-2 cannot be together, so all the ions cannot be together.
Alkalinity
P=0
P=M
P=½M
P>½M
P<½M
ENGINEERING CHEMISTRY
OH0
M
0
2P - M
0
CO3-2
0
0
2P
2 (M - P)
2P
HCO3M
0
0
0
M – 2P
5

7. Ill effects of using hard water in boilers:
Depending upon the operating pressure of the boiler, the feed water should satisfy the
following requirement of hardness.
Types of boiler
Low pressure
Medium pressure
High pressure
Permitted hardness in feed water
40 – 80 ppm
10 – 40 ppm
0 – 10 ppm
If the boiler feed water is not up to the standard limit, it gives rise to
Scale and Sludge formation
1.
a) Scale:
Scales are hard, adherent deposits produced when dissolved salts are thrown
out of boiler feed water as precipitate after saturation point is reached. It forms at hot parts
or region of boiler.
Causes:
2.
3.
4.
1. decomposition of bicarbonates of Ca/Mg
decrease in the solubility of CaCO3
hydrolysis of Mg-salts [to form Mg(OH)2 along with the formation of acid]
presence of silica (to form Ca/Mg-silicates)
Disadvantages:
2.
3.
4.
1. wastage of fuel
lowering of boiler safety
decrease in efficiency
danger of explosion
Prevention: 1. It can be removed with the help of scrapper or piece of wood or wire brush.
2.
It can also be removed by adding chemicals like EDTA which react with scale to
form soluble complex.
3.
It can be removed by giving thermal shocks to boiler, if scales are very hard.
b) Sludge: When boiler is steaming rapidly, dissolved salts from it precipitated out in the form
of loose and slimy precipitate after saturation point is reached, are called as sludge. It forms
at colder portion of the boiler.
Sludges are formed by substances which have greater solubility in hot water than in
cold water. e.g. MgCO3, MgCl2, CaCl2, MgSO4. These are poor conductors of heat, so they
waste a portion of heat generated. They get entrapped with scales.
It can be removed by either using soft water or by blow down operation (by replacing
salt rich water by fresh water) or these can be scrapped off with brush, scrappers.
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8. Boiler Corrosion:
2.
It can be defined as the destruction of boiler metal by a chemical or electrochemical
attack by its environment.
Causes:
O2, CO2 and Mg-salts
Removal: 1. Dissolved oxygen by addition of chemicals like Na2S, Na2SO3 or N2H4.
2.
3.
Mg-salts by using zeolite or ion exchange process.
4.
3.
Dissolved CO2 by adding liquid ammonia (NH4OH).
If acid formed in boiler, by adding alkali externally to neutralize.
Priming and foaming:
A violent or vigorous boiling which lead to the formation of wet steam, is known as
priming and production of persistent foam or bubbles on the surface of water in boilers which
do not break easily is known as foaming.
Priming is mainly occurred due to presence of large amount of dissolved salts, high
steam velocities, improper boiler design or sudden increase in steaming rate. Priming can be
prevented by efficient softening and filtration of boiler feed water, avoiding rapid change in
steaming rate, maintaining low water level or fitting mechanical purifiers.
Foaming is mainly occurred due to presence of substances like oils, soaps (which
reduces surface tension of water). It can be prevented either by adding antifoaming agent
like castor oil or by adding sodium aluminate to remove oil impurities.
4.
Caustic Embrittlement:
It is most likely to take place in boilers which operate under high pressure. It generates
during softening by lime soda process to form caustic soda (NaOH) as soda decomposes to
sodium hydroxide. This causes brittlement of the boiler parts. Thus it is called as caustic
embrittlement.
It can be avoided by using sodium phosphate instead of sodium carbonate while
softening or by treating boiler walls with tannin or lignin which blocks the cracks, thereby
preventing accumulation of caustic soda.
ENGINEERING CHEMISTRY
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9. Water Treatments:
Calgon
Conditioning
Internal
Treatment
Colloidal
Conditioning
Phosphate
Conditioning
Water
Treatments
External
Treatment
1.
Ion Exchange
Process
Internal Treatment:
a.
Zeolite
Process
Calgon Conditioning
It involves the addition of Calgon [sodium hexametaphosphate – (NaPO)6] to boiler
water to form soluble complex compound instead scale and sludge.
b.
Colloidal Conditioning
When boiler feed water is treated with sodium aluminate (NaAlO2), it gets hydrolyzed
forming NaOH and gelatinous precipitate of aluminium hydroxide. And therefore salt formed
due to this can be removed by blow down operation.
c.
Phosphate Conditioning
On the basis of nature of pH of boiler feed water, different phosphates can be used
as:
1.
Trisodium phosphate is used for acidic boiler feed water.
2.
Disodium phosphate is used for weakly alkaline water and
3.
Sodium dihydrogen phosphate is used for highly alkaline boiler feed water.
4.
Sodium pyrophosphate forms disodium hydrogen phosphate on hydrolysis, thereby
can be used in weakly alkaline water.
5.
Sodium metaphosphate when added to water, it forms sodium dihydrogen phosphate.
ENGINEERING CHEMISTRY
8

10. 2.
External Treatment:
a.
Zeolite Process (Permutit Process):
Greek word: Zein – Boiling, lithos– Stone, first used by Cronsted in 1756 and chemical
structure of sodium zeolite may be represented by Na2O.Al2O3.xSiO2.yH2O (abbreviated as
Na2Z)where x = 2 to 10 and y = 2 – 6. Thus zeolite is hydrated sodium alumino silicate,
capable of exchanging their sodium ions by multivalent cations. Sodium pyrophosphate
forms disodium hydrogen phosphate on hydrolysis, thereby can be used in weakly alkaline
water.
Zeolite is classified into two types depends upon their sources:
1. Natural zeolite: These are derived from green sand by washing, heating and treating with
caustic soda. They are non-porous and more durable. e.g. natrolite.
2. Synthetic zeolite: These are prepared by heating together china clay, feldspar and ash
followed by cooling and granulating resultant mass. They are porous and gel like structure.
Process:
In this process, zeolite holds sodium ions and can easily exchange their sodium ions
with other cations like Ca+2, Mg+2, etc. Thus it forms sodium salt when water containing
Ca/Mg-salt passed through it.
Na2Z + CaCl
2
CaZ + 2 NaCl
Na2Z + MgSO
4
MgZ + NaSO4
2
Regeneration:
When zeolite completely converts into Ca/Mg-zeolite, it gets exhausted. At this stage,
the supply of hard water is stopped and exhausted zeolite is reclaimed by treating with
concentrated brine solution (conc. NaCl solution).
CaZ + NaCl
MgZ + Na SO4
2
Na + CaCl
2Z
2
NaZ + MgSO
2
4
Following are the advantages of Zeolite process:
1.
2.
3.
The water of 5-10 ppm is obtained.
Equipment used is compact and occupies less space.
No impurities are precipitated, so there is no danger of sludge formation.
It cannot be used for water having turbidity, suspended matter and acidic or alkaline.
Water containing Fe+2 and Mn+2 cannot be used as their respective zeolite cannot be
regenerated easily with brine solution.
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9

11. b.
Ion Exchange Process:
It is also called as demineralization or deionization process. Ion exchange resins are
insoluble, cross linked, long chain organic polymers (made from styrene—divinyl benzene)
with micro-porous structure and the functional groups attached to the chain are responsible
for the ion-exchanging properties.
Resins containing acidic functional groups like -COOH, -SO3H, etc are capable of
exchanging their H+ ions with other cations. These can be represented as RH2. e.g. Amberlite
IR 120, Dowex 50, Nalcite-HCR.
Resins containing basic functional groups like –NH2, -OH, etc are capable of
exchanging their anions with other anions. These are represented as R’(OH)2. e.g. Amberlite
400, Dowex 3, Zeolite FF.
Process:
When hard water passed through cation exchanger which removes all cations
like Ca+2, Mg+2, etc from it and equivalent amount of H+ ions are released from this
exchanger to water. Thus, water received from cation exchanger is acidic in nature.
RH2 + CaCl2
RH2 + MgSO
4
RCa + 2 HCl
RMg + H SO4
2
Acidic water is the passed through anion exchanger which removes all the anions like
SO4-2, Cl-, NO3-, etc present in water and release amount of OH- from this exchanger to water.
R'(OH)2 + 2 HCl
R'Cl + 2 H2O
2
R'(OH)2 + H2SO4
R'SO + 2 H2O
4
Regeneration: Exhausted cation exchanger is regenerated by using dil. HCl
RCa + 2 HCl
RH + CaCl2
2
RMg + 2 HCl
RH + MgCl2
2
and exhausted anion exchanger is regenerated by using dil. NaOH.
R'Cl2 + 2 NaOH
R'SO4 + 2 NaOH
R'(OH) + 2 NaCl
2
R'(OH) + Na2SO4
2
Following are the advantages of Ion exchange process:
1. Process can be used for highly alkaline or acidic water sample.
2. It produces water with 0-2 ppm hardness
It cannot be used directly for turbid water and equipment & chemicals are costly.
ENGINEERING CHEMISTRY
10

12. Desalination of Brackish Water:
The process of removing dissolved salts from sea water to make it potable for drinking
and suitable for agriculture purpose is called as desalination.
Desalination of
Brackish Water
Electrodialysis
Reverse Osmosis
1. Electrodialysis:
The process of removing dissolved ionic impurities (salt, organic dyes) from water by
using membranes and electric field is known as electrodialysis.
An electrodialysis cell consists of a large number of paired sets of plastic membranes.
The membranes are ion-selective.
The cation selective membrane will allow only cations to pass through it, as it consist of
functional groups like –COO-, -SO3--, etc (which repel and do not allow anion to pass through
it). The anion selective membrane will allow only anions to pass through it, as it consists of
functional groups like –NR3+ (which repel and do not allow cation to pass through it).
It can be applicable for removing ionic pollutant, salts from sea water. The drinking
water can be obtained by this technique. But it does not remove dissolved organic matter,
colloidal impurities and it is expensive.
2. Reverse Osmosis:
The reversal of solvent flow, from higher concentration solution to lower concentration
solution through a semi-permeable membrane, by applying an external pressure slightly
greater than osmotic pressure of higher concentration solution, is known as reverse osmosis.
When a pressure of 200 psi is applied on it to force the solvent to pass through the
semi-permeable membrane which consist of polymeric material film made of proper porosity
(from materials like acrylics, polyamides, aramids, etc), it produces the water which can be
used for drinking purpose.
RO removes all types of impurities. It costs low and simple to operate.
ENGINEERING CHEMISTRY
11

13. Part B.
Green Chemistry
Definition:
Green chemistry (Clean Chemistry) is the design of chemical products or processes
that reduces or eliminates the use and/or generation of hazardous products.
Principles of Green Chemistry:
Paul Anastus and John Warner have suggested twelve principles of Green Chemistry
and are well accepted by chemists all over the world.
1. Prevention of Waste: It is better to prevent the waste than to treat or clean up after it is
formed.
2. High Atom Economy: Synthetic methods should be designed to maximize the
incorporation of all materials used in the process into the final products.
3. Less Hazardous Chemical Synthesis: Wherever applicable, synthetic methods should be
designed to use and generate substances that possess little or no toxicity to people or the
environment.
4. Designing Safer Chemicals: Chemical products should be designed to effect their desired
function while minimizing the toxicity.
5. Use of Safer Solvent and Auxiliaries: The use of auxiliary substances (e.g. solvents or
separating agents) should be made unnecessary whenever possible and innocuous when
used.
6. Design for Energy Efficiency: Energy requirements of chemical processes should be
recognized for their environment and economic impacts should be minimized.
7. Use of Renewable Feedstock: A raw material or feedstock should be renewable rather
than depleting whenever technically and economically practicable.
8. Reduce Derivatives: Unnecessary derivatization should be minimized or avoided if possible,
because such steps requires additional reagents and can generate waste.
9. Catalysis: Catalysts are used wherever required which are superior to stoichiometric
reagents.
10. Designing of Degrading Products: Chemical products should be designed in such a way
that at the end of their function they break down into innocuous degradation products
and do not persist in the environment.
11. New Analytical Method or Real Time Analysis for Population Growth: Analytical
methodologies need to be further improved to allow for real time, in process monitoring
and control prior to the formation of hazardous substances.
12. Safer Chemicals for Accidental Prevention: The chemicals should be chosen to minimize
the potential for chemical accidents including releases, explosions and fires.
ENGINEERING CHEMISTRY
12

14. Efficiency Parameters:
Following parameters are considered to measure efficiency of chemical processes.
1.
2.
Atom Economy: The formula for atom economy was given by Trost.
Molecular weight of desired product
Atom Economy =
× 100
Molecular weight of all product
Conversion:
Amount of reactant taken − Amount of reactant unconsumed
Conversion =
× 100
Amount of reactant taken
Conversion =
Amount of reactant reacted
× 100
Amount of reactant taken
Reaction Yield =
3.
Reaction Yield:
4.
Reaction Selectivity:
5.
Environmental Load Factor:
6.
Mass Intensity:
Reaction Selctivity =
E=
Amount of product formed
× 100
Expected amount of product
Amount of desired product formed
× 100
Expected amount of product formed
Total mass of ef luent generated
Mass of desired product
MI =
mass of reactant used
Amount of reactant taken
It is related to environmental factor as E = MI – 1.
Traditional and Green Pathways of Synthesis of:
1.
Adipic acid:
Adipic acid is required for the manufacture of Nylon-66.
a.
Traditional Pathway: The traditional process is modified by Frost.
O
Ni, Al 2O 3
370 - 800 psi
Benzene
HOOC
Cu, NH4VO 3
Co, O2
120 - 140 psi
Cyclohexane
HNO3
Cyclohexanone
COOH
Adipic acid
The problems of traditional route are:
1. Non-renewable, carcinogenic feedstock
2. Energy consuming and more steps are requires.
3. Higher temperature and pressure is required.
ENGINEERING CHEMISTRY
13

15. b.
Green Pathway:
OH
COOH
OH
E-coli
O
OH
OH
E-coli
O
OH
OH
D - glucose
HOOC
Pt, H2
50 psi
HOOC
COOH
COOH
OH
3 - dehydroxyshikimate
Cis, Cis - muconic acid
Adipic acid
The following are the benefits of green route are:
1. It uses cheap and renewable feedstock.
2. It requires safer for lower temperature and pressure.
3. It requires fewer steps and derivatives.
2.
Indigo Dye:
a.
Traditional Pathway:
NH2
OH
ClCH2COOH
COOH
H
N
Air
NaNH2
N
H
N
Aniline
O
N
H
O
H
Indigo dye
The problems of traditional route are: Non-renewable, toxic (aniline) feedstock.
b.
Green Pathway:
OH
O
Naphthalene
Tryptophanase
L - tryptophan
Air
H
N
OH
dioxygenase
N
H
N
H
N
H
O
Indigo dye
The following are the benefits of green route are:
1.
Renewable plant origin starting material and it requires less steps for synthesis.
2.
Eco-friendly process and no waste matter is formed.
3.
Polycarbonate:
c.
Traditional Pathway: The method is modified by Komiya Et al (Asahi chemicals).
CH3
HO
C
CH3
Bisphenol - A
ENGINEERING CHEMISTRY
OH
+ COCl2
CH2Cl2
O
CH3
NaOH / H2O
A
Interfacial Polymerization
O
C
CH3
O
C
A
n
Polycarbonate
14

16. The following are the benefits of green route are:
1. It uses poisonous material phosgene (COCl2).
2. It uses non-renewable CH2Cl2 solvent (poisonous) which is difficult to separate from
product.
d.
Green Pathway:
O
CH3
HO
OH
C
+
C
O
CH3
Bisphenol - A
O
Diphenyl carbonate
Solid state Polymerization
O
CH3
A
O
C
CH3
O
C
A
n
Polycarbonate
The following are the benefits of green route are:
1.
Does not require solvent, reaction carried out in molten state.
2.
Avoids use of poisonous starting material.
ENGINEERING CHEMISTRY
15