Wet Processing –I

(Pretreatment)

Prepared by

ABDULLAH NUR UDDIN RONY & KHURSHEDUL ALAM

BTEC, 2ND

BATCH

1

2. WATER

Q. Define water. Ans:

Water is a complex compound. It is very important compound in textile wet processing. The total

amount of water in the world is about 75%. Natural water is obtained in 3 steps. They are solid,

liquid & vapour. Water has a uncompareable power to dissolve other compound. It is very

difficult to obtain pure water in nature. Water is consists of two part Hydrogen & one part

Oxygen. Its chemical formula is H2O. Water is converted to ice at 0°C & converted to vapour at

100°C the concentration of water is highest at 4°C.

Q. Classify water on the basis of hardness.

Ans:

DESCRIPTION TOTAL HARDNESS (degree)

Very soft 0 - 4°

Soft 5 - 8°

Mild 9 - 14°

Fairly mild 15 - 18°

Hard 19 - 30°

Very hard >30°

Q. Classify water on the basis of source.

Or, discuss different source of water. Dhaka textile - '06, '04.

Ans: On the basis of source water may be classified into followings-

1) RAIN WATER:

Rain, collected immediately after precitation, is the purest of all natural water.

It may contain traces of gases dissolved out of the atmosphere & possibly an

almost infinitely small amount of finely divided solid matter derived from the air.

It also contain dissolved or Sulfur di-oxide or Sulfuric acid, CO2, NH3, NO2 &

other by products of industrialization.

Suspended impurities present in it, can be filtered by using sand bed.

Suitable for boiling, washing & dyeing process.

2) SURFACE WATER:

Surface water may consists of rain water which has collected from streams, rivers

or lakes.

This type of water contains organic & inorganic matters which are dissolved in it

& also contain suspended impurities.

Then the nutrifying bacteria will in time convert the organic substances into

nitrates which are not objectionable in dyeing & printing.

Wet Processing –I

(Pretreatment)

Prepared by

ABDULLAH NUR UDDIN RONY & KHURSHEDUL ALAM

BTEC, 2ND

BATCH

2

Surface waters may receive considerable additions of dissolved mineral salts from

shallow springs which feed the streams.

It contains Chloride, Sulfate, Carbonate, Bicarbonate of Na, P, Ca & Fe.

Not suitable for dyeing & finishing.

3) SUBSOIL WATER:

This type of water is collected from shallow springs & wells which are about 50 ft

(15 m) or so deep.

It is usually free from suspended impurities because it has been filtered by its

passage through the soil. It'll however contain dissolve organic water.

Subsoil water is often rich in dissolved Carbon di oxide, a gas abundantly present

in the skin of the soil.

Subsoil waters are very variable with regard to the impurities which they contain.

Not suitable for dyeing & finishing.

4) DEEP WELL WATER:

This type of water is obtained from 500 m below the surface. It is free from

organic matters.

The soluble impurities in water may be composed of a variety of substances.

Soluble organic compounds, ammonium salts, Nitrates & Nitrites of animal; or

vegetable origin may be found. If they are present in considerable quantities, the

sewage contamination is undesirable for many textile purposes.

The presence of salts of Ca or Mg in solution can be most undesirable in many

finishing process.

Q. Why water is called universal solvent?

Ans: Water is called universal solvent, because the solvency power of water is very high & most

of the solute of this world is easily dissolved in the water.

Q. what do you mean by water hardness? Dhaka textile- '06, '05, '04, '03. Noakhali textile- '08, '09.

Ans: Hardness is a term applied to water denoting a measurement of its pH & metal

salt content. The presence of Ca & Mg salt i.e. Bi-Carbonates, Sulfates,

Chlorides in water is called causes of hardness of water. The water which

contains these salt is called hard water. Hard water does not easily form lather

with soap as the salt of Ca & Mg react with soap to form insoluble organic salts.

CaSO4 + 2 RCOONa → (RCOO)2Ca ↓ + Na2SO4.

MgSO4 + 2 RCOONa → (RCOO)2Mg ↓ + Na2SO4.

Q. State different types of water hardness. Dhaka textile- '07.

Ans: Water hardness may be classified into following two types-

Wet Processing –I

(Pretreatment)

Prepared by

ABDULLAH NUR UDDIN RONY & KHURSHEDUL ALAM

BTEC, 2ND

BATCH

3

1) TEMPORARY HARDNESS:

Temporary hardness is due to the presence of Bi-Carbonates of Ca & Mg. this type

of hardness is called temporary hardness, because, it can be removed by easy

means like boiling. When temporary hard water is boiled, the Carbonates

decompose with liberation of CO2 & precipitation of the insoluble Carbonates

which are reformed.

Ca(HCO3)2 ∆→ CaCO3↓ + CO2 + H2O

Mg(HCO3)2 ∆→ MgCO3 ↓ + CO2 + H2O

2) PERMANENT HARDNESS:

It is due to the presence of Sulfates, Chlorides of Ca & Mg. this type of hard

water is called permanent hardness. These salts do not decomposes on boiling. So,

permanent hardness can not be removed.

Q. Write down the name of mineral metallic salts which is responsible for

water hardness.

Ans: The name of mineral metallic salts which is responsible for water hardness-

1. Ca(OH)2; 2. Mg(HCO3)2; 3. Al(HCO3)2;

4. Fe(HCO3)2; 5. CaSO4; 6. MgSO4;

7. Al2(SO4)3; 8. FeSO4; 9. CaCl2;

10. MgCl2; 11. AlCl2; 12. FeCl2.

Q. Why soap does not create foam easily with hard water? Explain with

reaction.

Ans: Soap does not create foam easily with hard water as the salt of Ca & Mg react with

soap to form insoluble organic salts.

CaSO4 + 2 RCOONa → (RCOO)2Ca ↓ + Na2SO4.

MgSO4 + 2 RCOONa → (RCOO)2Mg ↓ + Na2SO4.

Q. How water hardness is expressed? Dhaka textile- '06.

Ans: the hardness of water is expressed by the amount of Ca present in water. In this

methods, Bi-Carbonates, Sulfates, Chlorides of Ca & Mg & also carbonates of Mg

are not taken into consideration.

Hardness is expressed by-

1. PPM: The number of grains of CaCO3 which is present in one million grains of water is

called PPM. 1 grains of CaCO3 present in 1 million grains water.

2. IN DEGREES: The number of grains of CaCO3 which is present in 70,000 grains of

water.

The relation is DEGREE = PPM * 0.07 .

Wet Processing –I

(Pretreatment)

Prepared by

ABDULLAH NUR UDDIN RONY & KHURSHEDUL ALAM

BTEC, 2ND

BATCH

4

Q. What do you mean by 7.14 PPM?

Ans: 7.14 PPM means 7.14 mg CaCO3 is present in one million part of water.

Q. Establish a relation between PPM & DEGREE of hardness.

Ans: We know that,

1000000 grains hard water contain = x grain CaCO3

1 grains hard water contain = (x ÷ 1000000) grain CaCO3

700000 grains hard water contain = (700000x ÷ 1000000) grain CaCO3

= 0.07 grain CaCO3

so, Degree of hardness = 0.07 * PPM.

Q. Write down the scales of hardness.

Ans:

DESCRIPTION DEFINITION

1° dH (German) Hardness 10 mg CaO in 1 L of water.

1° fH (French) Hardness 10 mg CaCO3 in 1 L of water

1° eH (English) Hardness 10 mg CaCO3 in 0.7 L of water

1° aH (American) Hardness 10 mg CaCO3 in 1 L of water

Q. State the properties of hard water.

Or, describe the effects of hard water in textile wet processing.

Or, State the disadvantages of hard water.

Or, state the problem occurred by using hard water in textile industry. Noakhali textile- '08. Dhaka textile- ' 05.

Ans: 1) SCALE FORMATION:

If hard water is used in boiler, then a layer is formed on the inner surface of the vessel or

in the inner side of tube. This layer is very hard just like as stone which is not removed

without hammer or chesser or tessel. This is called scale.

In boiler, temporary hard water produce CaCO3 & Mg (OH)2. the combination of

CaCO3 & Mg(OH)2 is called scale.

Ca(H CO3)2 ∆→ CaCO3 ↓ + CO2 ↑ + H2O

Mg(H CO3)2 ∆→ Mg CO3 ↓ + CO2↑ + H2O

Mg CO3 + H2O ∆→ Mg(OH)2 + CO2↑

CaCO3 + Mg(OH)2 → Scale.

As a result, in boiler more heat will be needed &for that, more fuel will be required. For scale

formation, equally heat transformation in boiler tube is not possible very often. As a result,

for excess heat of a particular part of the tube, the tube may burst.

Wet Processing –I

(Pretreatment)

Prepared by

ABDULLAH NUR UDDIN RONY & KHURSHEDUL ALAM

BTEC, 2ND

BATCH

5

Heat loss of tube up to 40% according to the diameter of the tube. Heat loss by pipe scaling

up to 40% for 20 mm scale.

SCALE THICKNESS HEAT LOSS

1 mm → approximately 10%

3 mm → „ 17%

5 mm → „ 22%

10 mm → „ 30%

20 mm → „ 43%

2) REACTION WITH SOAP:

Soap is the Na & K salt of higher fatty acid (C17H35COONa). The Hard water does not easily

form lather by reacting with soap. The Ca & Mg salt of hard water react with soap 7 produce

insoluble organic salts which becomes the wastage of soap.

CaSO4 + 2 C17H35COONa → (C17H35COO)2Ca + Na2SO4

Insoluble organic salt

If we use hard water in wet processing, then they produce insoluble salt.

3) DEPOSOTION OF INSOLUBLE SALT ON THE SURFACE OF FABRIC / TEXTILE

GOOD DURING SCOURING:

Insoluble salt that is produced by reaction of soap & hard water is deposited with the fabric

during scouring. As a result, the surface of scoured fabric become harsh, hard & non-flexible

which creates problem in the next process.

4) REACTION WITH DYESTUFF:

If hard water is used in dyeing, then it react with dye molecules & reduce the tinctorial power of

dyestuff. As a result, uneven shade (depth of dyeing0 of colour is produced. Sometimes, dyestuff

are precipited & spoil.

5) CORROSION OF BOILER:

Corrosion can be serious problem in boiler, if hard water is used in it. Dissolved O2 in the

presence of CO2 is the common cause of corrosion. Fe present in hard water reacts with CO2 to

form Fe CO3, which is the main process of corrosion. This Fe CO3 is hydrolised & produce

Fe(OH)2. this agents / components damage the boiler.

Fe + H2O + CO2 → Fe CO3 + H2O

Fe CO3 + H2O → Fe(OH)2 + CO2

Q. Write the ideal quality of feed water for textile wet processing industries. Dhaka textile- ' 04.

Ans: Standard for textile dye house water supply / Specification for process water:

pH should be in the range of 7 – 8.

Water should be odorless & colorless.

Water hardness → maximum 5° dH.

Solid content: < 50 mg/L.

Dissolved solids : < 1 mg/L.

Wet Processing –I

(Pretreatment)

Prepared by

ABDULLAH NUR UDDIN RONY & KHURSHEDUL ALAM

BTEC, 2ND

BATCH

6

Inorganic salts: < 500 mg/L.

Organic salts: < 20 mg/L.

Iron (Fe): < 0.1 mg/L.

Mn : < 0.02 mg/L.

Cu: < 0.005 mg/L.

Nitrate: < 50 mg/L.

Nitrite: < 5 mg/L.

Q. What are the potential problem caused by acid & alkali in textile wet

processing? Dhaka textile- ' 07, ' 03.

Ans:

PROCESS Problem

1. desizing De-active enzymes & insolubilize size mtls, such as starch,

PVA etc.

2. Scouring Combine with soap, precipitate metal organic acids. Produce

yellowing or off-white shades, reduce cleaning efficiency &

reduce water absorption.

3.Bleaching Decompose bleach bath.

H2O2 → H2O + [O]

4. Mercerizing Form insoluble metal acids, reduce absorbency & lusture.

5. Dyeing. Combine with dyes, changing their shades, insolubilize dyes,

cause tippy dyeing & reduce dye diffusion.

6. Printing Break emulsion, change thickness, efficiency & viscosity,

Combine with dyes, changing their shades, insolubilize dyes,

cause tippy dyeing & reduce dye diffusion.

7. Finishing Interfere with catalysts, cause resins & other additives to

become non-reactive break emulsion & de-actives soap.

Q Define soft water.

Ans: the water which does not contain H CO3-, Cl

-, SO4

2- salt of Ca

2+, Mg

2+, Fe

2+,

Al3+

& form foam easily by reacting with soap is called soft water e.g. Rain water.

Q What is water softening? State the name of method of water softening. Dhaka textile- ' 04.

Ans: WATER SOFTENING: To remove the impurities of hard water by some desirable

process is called water softening.

WATER SOFTENING PLANT / METHODS OF WATER SOFTENING:

1. soda lime process.

2. Base exchange process (permutit).

3. Demineralisation.

Wet Processing –I

(Pretreatment)

Prepared by

ABDULLAH NUR UDDIN RONY & KHURSHEDUL ALAM

BTEC, 2ND

BATCH

7

4. Soda alum.

5. Aeration.

6. Chelation on sequestration.

7. Calgon process.

Q. Describe the base exchange process for softening hard water. Noakhali textile- '08. Dhaka textile- ' 06, ' 04.

Ans: This method depends upon the use of zeolite or base exchange complexes.

The zeolites are hydrated silicates of Na & Al with a generated formula-

(Na2O)x (Al2O3)y (SiO2)z (H2O)n

When zeolites or base exchange complexes are brought in contact with hard

water, following reaction

For temporary hardness-

Ca(HCO3)2 + Na2O.Z → CaO.Z + Na2CO3 + H2O

Mg(HCO3)2 + Na2O.Z → MgO.Z + Na2CO3 + H2O

For permanent hardness-

CaSO4+ Na2O.Z → CaO.Z + NaSO4.

MgSO4+ Na2O.Z → MgO.Z + NaSO4.

In water Z is an abbreviation for the Al2O3.SiO2.H2O part of zeolite. The soft

water obtained from this base exchange process is of 0 – 20° hardness or

levelness. After a long time the whole of the Na in base exchange substance is

replaced by Ca or Mg. it is said to be exhausted because it will not soften any

hard water more. Then it has to be generated.

Regeneration: CaO.Z + 2NaCl → Na2O.Z + CaCl2

The CaCl2 & residual NaCl are washed away & the regenerated Na2O.Z can be

used to soften the hard water again.

PROCESS: