water technology and green chemistry

EngineeringChemistry

Unit 1 : Water Technology and Green Chemistry

Santosh Damkondwar For University of Pune First Year Engineering

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ENGINEERING CHEMISTRY 1

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


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


Unit 1. Water Technology and Green Chemistry

Part A. Water Technology

Impurities in water:

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.

Impurities from water

Suspended Impurities

e.g. clay, mud, organic matter

It can be removed by

filteration

Dissolved Impurities

e.g. Dissolved gases or salts

It can be removed by

softening process

Colloidal impurities

e.g. Colloidal particles of clay,

mud, organic matter,etc

It can be removed by Coagulation (cougulating

agent like potash alum, sodium

aluminate)

Biological Impurities

e.g. algae, fungi, bacteria, etc

It can be removed by Sterlization

(sterlizing agent like liquid

chlorine, ozone, UV light)

ENGINEERING CHEMISTRY

Hardness of water:

Reactions for removal of temporary hardness:

Ca(HCO3)

Mg(HCO

Units of Hardness:The hardness is calculated in terms of CaCO

For bivalent salt:

The units used to express hardness in terms of CaCO

liter], ppm [parts per million], ppb [parts per billion],

Hardness of water by EDTA MeEDTA method is a complexometric method of determining hardness of water.

forms stable complex at pH = 10, this titration is performed at pH = 10.

as follows:HOOC

HOOC

The structure of disodium salt of EDTA is as follows:HOOC

Na+O

-OC

Temporary or Alkaline or Carbonate Hardness

Permanant or Non-alkaline or Non-carbonate Hardness

temporary hardness:

)2 CaCO 3 + CO2 + H2O

Mg(HCO3)2 Mg(OH) 2 + 2 CO2

The hardness is calculated in terms of CaCO3 equivalent as:

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

Hardness of water by EDTA Method:EDTA method is a complexometric method of determining hardness of water.

forms stable complex at pH = 10, this titration is performed at pH = 10. The structure of EDTA is

CH2 CH2 NN

CH2 CH2

CH2CH2

COOH

COOH

The structure of disodium salt of EDTA is as follows:

CH2 CH2 NN

CH2 CH2

CH2CH2

COOH

COO-Na

+

•It is due to carbonates and bicarbonates of Ca & Mg.•It can be removed by filteration after mere boiling.

Temporary or Alkaline or Carbonate

•t is due to chlorides, sulphates and nitrates of Ca, Mg, Al, Fe, Mn.

•It can not be removed easily.-

4

equivalent are mg/lit [milligram per

Cl [degree Clark] or oFr [degree French]

EDTA method is a complexometric method of determining hardness of water. As EBT

The structure of EDTA is

It is due to carbonates and bicarbonates of Ca & Mg.It can be removed by filteration after mere boiling.

t is due to chlorides, sulphates and nitrates of Ca, Mg,


The structure of disodium salt of EDTA with Ca/Mg (M) is as follows:

CH2 CH2NN

CH2CH2

CH2CH2

COOHHOOC

CC

O O

O O

M

Compound / Complex ColorEBT (Eriochrome Black T) BlueM-EBT Complex Wine-redM-EDTA Complex ColourlessEnd Point 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 Ions End pointPhenolphthalein Complete Neutralization of OH- and Half

neutralization of CO3-2Pink to colorless

Methyl Orange Complete Neutralization of CO3-2 and neutralization of HCO3-

Yellow to orange

Following are the only combinations present in water:

1. Only OH- 2. Only CO3-2 3. Only HCO3-

4. OH- and CO3-2 5. CO3-2and HCO3-

OH- and HCO3-2 cannot be together, so all the ions cannot be together.

Alkalinity OH- CO3-2 HCO3-

P = 0 0 0 MP = M M 0 0

P = ½ M 0 2P 0P > ½ M 2P - M 2 (M - P) 0P < ½ M 0 2P M – 2P


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 Permitted hardness in feed waterLow pressure 40 – 80 ppm

Medium pressure 10 – 40 ppmHigh pressure 0 – 10 ppm

If the boiler feed water is not up to the standard limit, it gives rise to

1. Scale and Sludge formationa) 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: 1. decomposition of bicarbonates of Ca/Mg

2. decrease in the solubility of CaCO3

3. hydrolysis of Mg-salts [to form Mg(OH)2 along with the formation of acid]

4. presence of silica (to form Ca/Mg-silicates)

Disadvantages: 1. wastage of fuel

2. lowering of boiler safety

3. decrease in efficiency

4. 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.


2. Boiler Corrosion: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. Dissolved CO2 by adding liquid ammonia (NH4OH).

3. Mg-salts by using zeolite or ion exchange process.

4. If acid formed in boiler, by adding alkali externally to neutralize.

3. 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.


Water Treatments:

1. Internal Treatment:

a. Calgon ConditioningIt involves the addition of Calgon [sodium hexametaphosphate – (NaPO)6] to boiler

water to form soluble complex compound instead scale and sludge.

b. Colloidal ConditioningWhen 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 ConditioningOn 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.

Water

Treatments

Internal Treatment

Calgon Conditioning

Colloidal Conditioning

Phosphate Conditioning

External Treatment

Zeolite Process

Ion Exchange Process


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 + CaCl2 CaZ + 2 NaCl

Na2Z + MgSO4 MgZ + Na2SO4

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 Na2Z + CaCl2

MgZ + Na2SO4 Na2Z + MgSO4

Following are the advantages of Zeolite process:

1. The water of 5-10 ppm is obtained.

2. Equipment used is compact and occupies less space.

3. 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.


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 RCa + 2 HCl

RH2 + MgSO4 RMg + H2SO4

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'Cl2 + 2 H2O

R'(OH)2 + H2SO4 R'SO4 + 2 H2O

Regeneration: Exhausted cation exchanger is regenerated by using dil. HCl

RCa + 2 HCl RH2 + CaCl2

RMg + 2 HCl RH2 + MgCl2

and exhausted anion exchanger is regenerated by using dil. NaOH.

R'Cl2 + 2 NaOH R'(OH)2 + 2 NaCl

R'SO4 + 2 NaOH R'(OH)2 + Na2SO4

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.


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.

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.

Desalination of Brackish Water

Electrodialysis Reverse Osmosis


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.


Efficiency Parameters:Following parameters are considered to measure efficiency of chemical processes.

1. Atom Economy: The formula for atom economy was given by Trost.

Atom Economy = Molecular weight of desired productMolecular weight of all product × 100

2. Conversion:

Conversion = Amount of reactant taken− Amount of reactant unconsumedAmount of reactant taken × 100

Conversion = Amount of reactant reactedAmount of reactant taken × 100

3. Reaction Yield:

Reaction Yield = Amount of product formedExpected amount of product × 100

4. Reaction Selectivity:

Reaction Selctivity = Amount of desired product formedExpected amount of product formed× 100

5. Environmental Load Factor:

E = Total mass of ef luent generated Mass of desired product

6. Mass Intensity:

MI = mass of reactant usedAmount 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.

Ni, Al2O3

370 - 800 psi

Co, O2

120 - 140 psi

O

Benzene

Adipic acid

Cyclohexanone

HNO3

Cu, NH4VO3

HOOC

COOHCyclohexane

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.


b. Green Pathway:

O

OH

OH

OH

OH

OH

COOH

O

OH

OH

Adipic acid3 - dehydroxyshikimate Cis, Cis - muconic acid

HOOC

COOH

D - glucose

E-coli

E-coli

HOOC

COOH

Pt, H2

50 psi

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

ClCH2COOH

N

H

COOH

Aniline

NaNH2NH

OH

AirNH

NH

O

O

Indigo dye

The problems of traditional route are: Non-renewable, toxic (aniline) feedstock.

b. Green Pathway:

TryptophanaseL - tryptophan

NH

Air NH

NH

O

O

Indigo dye

NH

OH

OH

Naphthalene

dioxygenase


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).

C

CH3

CH3

OH OHNaOH / H2O

Bisphenol - A

+ COCl2CH2Cl2

Interfacial Polymerization

C

CH3

CH3

O OA C A

O

n

Polycarbonate



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:

C

CH3

CH3

OH OH

Bisphenol - A

+

Diphenyl carbonate

Solid state Polymerization

C

CH3

CH3

O OA C A

O

n

Polycarbonate

O C O

O


1. Does not require solvent, reaction carried out in molten state.

2. Avoids use of poisonous starting material.

water technology and green chemistry

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