OUTLINE

 Introduction
 Classification of dyes
 Colour fastness
 Manufacturing process of dyes
• Case study: Indigo
• Case study: reactive dyes
 Treatment of waste water from dye industry
• Look around you, at your clothes, the walls, the floor.
Chances are that you see before you a colour riot.
• Humans have been fascinated by colour for thousands
of years and use colours to warn, to seduce and
primarily to decorate.
• So, what about the chemistry behind the decoration?
• What makes one molecule coloured, and another not?
• Why do some clothes fade in the wash?
• Dyes can be said to be coloured, ionizing and aromatic organic
compounds which shows an affinity towards the substrate to
which it is being applied to.
• It is generally applied in a solution that is aqueous.
• Dyes may also require a mordant to better the fastness of the
dye on the material on which it is applied.
• The search for highly coloured, colour fast dyes has fueled major
industry from ancient times right up to the present.
• Nowadays, the chemist with a knowledge of organic chemistry is
at the forefront of new dye development, altering the structures
of known dyes, and inventing new ones.
 CLASSIFICATION OF DYES

• There are several ways for classification of dyes. It

should be noted that each class of dye has a very
unique chemistry, structure and particular way of
bonding.
• Classification based on source of dye
• Chemical classification of dyes
• Industrial classification of dyes
 CLASSIFFICAION BASED ON SOURCE OF DYE

NATURAL DYES

• Some of our most common dyes are derivable from

natural sources, hence the name natural dyes. Some
of this natural dyes and their sources include;
• Natural black (hematein) obtained from the
heartwood of a tree,
• Natural yellow (saffron: a mixture of crotin and
crocetin) obtained from the stigmata of crocus
sativus,
 CLASSIFFICAION BASED ON SOURCE OF DYE

NATURAL DYES
SAFFRON

Figure 1.1. Crocin:

(8,8'-diapocarotene-8,8'-dioic acid bis (6-O-ß-D-glucopyranosyl-D-glucopyranosyl ester)

Figure 1.2. Crocetin (8,8'-diapocarotene-8,8'-dioic acid)

 VAT DYES

• These class of dyes have chemical structures that are complex and
most are derivatives of anthraquinone or Indanthrene.
• To effectively fastening these dyes to fabric, the technique of its
application ensures an oxidation and reduction process which will
be discussed further.
• A very common type in this class is the Indigo.

Figure 1.3. Indigo [ (2E)-2-(3-oxo-1H-indol-2-ylidene)-1H-indol-3-one ]

 REACTIVE
REACTIVE DYES
DYE
• Reactive Dyes: These dyes react to form a covalent link between
the dye and the cellulosic fiber which they are customarily used
to dye.
• Reactive dyes have a very high wash resistance capability. Cotton,
rayon and some nylons are dyed by this type of dye, it is in fact
the newest type to be invented. The general structure of reactive
dyes is given in figure 4. Below.

Figure 1.4. General structure of reactive dyes

 AZO DYES

• “Direct and azoic dyes fall under the “Azo” group of dyes. Azo
compounds are compounds bearing the functional group R–
N=N–R′, in which R and R′ can be either aryl or alkyl.
• IUPAC defines azo compounds as: Derivatives of diazene
(diimide), HN=NH, wherein both hydrogens are substituted by
hydrocarbyl groups. Example is the diphenyldiazene.”

Figure 1.5. Diphenyldiazene

 ACID DYES

 These derive their name from their insolubility in acid

baths.
 They are used for dying protein fibers such as wool, silk
and nylon, also leather and paper (to a lesser extent).
 Usually they are azo, alizarine or anthraquinone
complexes.

Figure 1.6. Alizarine (1,2-dihydroxy-9,10-anthracenedione)

 BASIC DYES

• Basic Dyes: Basic dyes are mostly amino and

substitute amino compounds soluble in acids and
made insoluble in basic solution.
• They can be used to dye wool or cotton in the
presence of a mordant, but are usually used for
duplicator inks, carbon paper, and typewriter
ribbons.
• In solvent other than water, the form writing and
printing inks. Figure 7. Below is triarylmethane, an
example of basic dyes.
 BASIC DYES

Figure 1.7. Triarylmethane: an example of basic dyes

 DISPERSE DYES

• Disperse Dyes: Modern synthetics (cellulose, acetate, plastics,

polyesters) are difficult to dye.
• Disperse dyes are applied as a very finely divided material which
are absorbed onto the fiber with which they from a solid solution.
• Insoluble anthraquinone dyes are best and most commonly used
because of its ability to penetrate the fiber.

Figure 1.8. Anthraquinone [anthracene-9,10-dione]

 MORDANT DYES

• Mordant Dyes: Mordant dyes combine with metallic

salts to form highly insoluble coloured materials
called lakes.
• These materials are usually used as pigments. If cloth
made of cotton, wool or protein fiber is impregnated
with salt and then contacted with a lake forming dye,
metallic precipitate forms in the fiber and the
resultant colours becomes very resistant to washing
and sunlight.
 MORDANT DYES

Figure 1.9. Structure of Mordant Black 1.

[4-Amino-3-hydroxy-7-nitronaphthalene-1-sulfonic acid]
 SULFUR DYES

• Sulfur Dyes: Sulfur dyes are low-cost dyes that

possess good fastness to sunlight, washing and acids,
their downside is that the produce dull colours and
are sensitive to chlorine and hypochlorites.
• This class is the most locally used type because of its
price. The most important member of the class is
Sulfur Black 1. It is produced by the reaction of 2,4-
dinitrophenol and sodium sulfide in hot water.
 SULFUR DYES

Figure 1.10. Sulfur black 1 [2,4-Dinitrophenol]

 A basis for colour resistance to fadeness

 Colour fastness is a term used in the dying of Textile materials

(and other dyed materials), to describe the resistance of the
material colour to fading.
 when a fabric does not shed its colour when subjected to certain
conditions such as sunlight, laundering, and perspiration,
the fabric is said to be colour fast.
 It is important to note that the type of material to be dyed will
determine the type of dye to be used on it, and in extension the
fastness of the colour of the resultant dyed material.
 Thus it is important to know the factors that influence the
production of dyes.
MANUFACTURE OF DYES
 PROCESS DIAGRAM FOR THE DYE INDUSTRY

Process Diagram for the Dye Industry

INDUSTRIAL MANUFACTURE OF INDIGO

 Indigo is probably the oldest dye known to man,

It is one of the most important members of this
group.
 Natural indigo extracted from the plant
'Indigofera tinctorie' was used by the Egyptians
in 200 BC.
 The first synthetic indigo was introduced to the
textile trade in 1897 & had the effect of
completely replacing the natural product.
INDUSTRIAL MANUFACTURE OF INDIGO

 Indigo can be synthesize using the Baeyer-

Drewson reaction, which is an Aldor
Condensation reaction.

Ethanoic acid

(2E)-2-(3-oxo-1H-indol-2-ylidene)-1H-indol-3-one

Figure 2.1 Shows the Baeyer-Drewson reaction of

2-nitrobenzaldehyde with acetone to produce synthetic indigo
INDUSTRIAL MANUFACTURE OF INDIGO

Natural extraction
The raw materials used in the natural production of
indigo are leaves from a variety of plant species
including:
 Indigo
 woad,
 polygonum.
Only the leaves are used since they contain the greatest
concentration of dye molecules. In the synthetic
process, a number of chemicals are employed as
described below.
INDUSTRIAL MANUFACTURE OF INDIGO

First year leaves of woad.

 INDUSTRIAL MANUFACTURE OF INDIGO

Natural extraction

By product (CO2)

Fresh Thick indigo

Leaves broth indigotin paste
Fermentation vessel Oxidation Heating

Air

 The first tank is a fermentation vessel into which the freshly cut plants are placed.
 An enzyme known as indimulsin is added to hydrolyze, or break down, the indican
into indoxyl and glucose.
 During this process carbon dioxide is given off and the broth in the tank turns a
murky yellow.
 INDUSTRIAL MANUFACTURE
INDUSTRIAL OF INDIGOOF INDIGO
MANUFACTURE

Natural extraction
By product (CO2)

Fresh Thick indigo

Leaves broth indigotin paste
Fermentation vessel Oxidation Heating

Air

 In the second tank, the indoxyl-rich mixture is stirred with paddles to mix it with air.
 This allows the air to oxidize the indoxyl to indigotin, which settles to the bottom of
the tank.
 The upper layer of liquid is siphoned away and the settled pigment is transferred
to a third tank where it is heated to stop the fermentation process.
 The resultant mixture is filtered to remove impurities and dried to form a thick paste.
 INDUSTRIAL MANUFACTURE
INDUSTRIAL OF INDIGOOF INDIGO
MANUFACTURE

Insolubility of Indigo

 Indigo is not soluble in water, so to dye cloth the indigo needs to be

made into a water-soluble form.
 The insoluble indigo dye is synthesized and then reduced with
sodium hydrosulfite (sodium dithionite), as shown in Figure 3.2, to
the water soluble leucoindigo (sometimes called indigo white).
 When the clear yellow leucoindigo solution comes into contact with
air it oxidizes back to the insoluble blue indigo compound.
 INDUSTRIAL MANUFACTURE
INDUSTRIAL OF INDIGOOF INDIGO
MANUFACTURE

Insolubility of Indigo

Indigo white
3,3′-dioxo-2,2′-bisindolyden-5,5′-disulfonic acid
disodium salt

Figure 2.3 The conversion of the insoluble blue indigo dye to the
clear yellow, water soluble leucoindigo or indigo white

“When the yellow leucoindigo oxidises back to the insoluble blue indigo
compound, it becomes insoluble to water. Hence, when this material
(containing the indigo) is being washed, the indigo will not be washed
off.”
INDUSTRIAL MANUFACTURE OF INDIGO
Reactive dyes react chemically with the fibre being dyed and
If correctly applied, cannot be removed by washing or boiling.
They mostly used for dyeing cellulosic fibres.

Properties of Reactive Dyes

o They are cationic dyes used for dyeing cellulose, protein and polyamide fibres
o They are found in powdered, liquid, and print paste form
o They form covalent bond with fibre polymer and become an integral part of the
fibre
o Reactive dyes are soluble in water
o They have very good light fastness
o They have a very stable electron arrangement and can protect the degrading
effect of ultra-violent ray.
 Chemistry Behind Reactive Dyeing

The general structure of reactive dyes is D—B—G—X,

where
D= the dye part or chromophoric group (colour producing part),
this may be direct, acid, disperse dye etc.
B= bridging group that links reactive system to chromophore.
G= reactive group enabling dye to react with hydroxy group of
cellulose.
X= bonds between reactive group.
 Chemistry Behind Reactive Dyeing

NH (Bridging part)

N N

Cl C C NH
N
N N

Figure 1.4. General structure of reactive dyes

Figure 2.4 General structure of reactive dyes

 Dying Mechanism of Reactive Dye

• Reactive dyeing principle is based on fibre reactivity and involves

reaction of a functional group of dyestuff with a site on fibre to
form a covalent link between dye molecule and a material.

• The main feature of the dyestuff is its low affinity to cellulose;

therefore large amounts of salt are required to force its deposition
on the fabric.

• After this has been achieved, addition of alkali causes the

deposited dyes to react with the fibre.

• Only a successfully concluded reaction guarantees a fast dyeing.

 Dying Mechanism of Reactive Dye

• The dyeing mechanism of material with reactive dye

takes place in 3 stages:-
1. Dye absorption:
• When fibre is immersed in dye liquor, an electrolyte is
added to assist the exhaustion of dye.
• Here NaCl is used as the electrolyte. This electrolyte
neutralize the negative charge formed in the fibre
surface and puts extra energy to increase dye absorption.
• When the textile material is introduces to dye liquor the
dye is exhausted on to the fibre.
 Dying Mechanism of Reactive Dye

• The dyeing mechanism of material with reactive

dye takes place in 3 stages:-
2. Fixation:
• Fixation of dye means the reaction of reactive group
of dye with terminal –OH or-NH2 group of fibre and
thus forming strong covalent bond with the fibre.
• This is an important phase, which is controlled by
maintaining proper pH by adding alkali.
• The alkali used for this purpose depends on brand of
dye and dyeing temperature.
• Reactions taking place in the stage are shown in the
next slide
 Dying Mechanism of Reactive Dye

alkali
1 D-SO2-CH2-CH2-OSO3Na + OH-Cell D-SO2-CH2-CH2-O-Cell + NaHSO3
pH= 10-12.5

alkali
2. D-SO2-CH2-CH2-OSO3Na + OH-Wool D-SO2-CH2-CH2-O-Wool + NaHSO3
pH= 10-12.5

Reactive red 2 dye [3,6-dichloro-N-phenyl-1,2,4,5-tetrazin-3-amine]

Figure 2.5. Fixation of reactive dyes

Dying Mechanism of Reactive Dye
 Dying Mechanism of Reactive Dye

• The dyeing mechanism of material with reactive

dye takes place in 3 stages:-
3. Wash-off:

• As the dyeing is completed, a good wash must be applied

to the material to remove extra and unfixed dyes from
material surface.
• This is necessary for level dyeing and good wash-fastness.
It is done by a series of hot wash, cold wash and soap
solution wash.
 Examples of Reactive Dye and Country of Origin

Trade name Manufacturer Country

Procion I.C.I U.K
Cibacron Ciba Switzerland
Remazol Hoechst Germany
Levafix Bayer Germany
Reactone Geigy Switzerland
Primazin BASF Germany
Drimarine Sandoz Switzerland
TREATMENT OF WASTEWATER FROM THE DYE INDUSTRY
 TREATMENT OF WASTEWATER FROM THE DYE
INDUSTRY

• Textile dyeing industry is one of the most water

consuming industries after thermal, engineering pulp and
paper industries.
• As the textile industry is one of the most water consuming
industries, water treatment systems play an important role
here. Water treatment can be carried out using reverse
osmosis, ultrafiltration, nanofiltration, microfiltration, etc
• Biological oxidation process is widely used and
recommended due to its positive results, lower sludge
generation and low running costs.
 TREATMENT OF WASTEWATER FROM THE DYE
INDUSTRY

• Textile dyeing industry is one of the most water

consuming industries after thermal, engineering
pulp and paper industries.
• As the textile industry is one of the most water
consuming industries, water treatment systems
play an important role here. Water treatment can
be carried out using reverse osmosis,
ultrafiltration, nanofiltration, microfiltration, etc
• Biological oxidation process is widely used and
recommended due to its positive results, lower
sludge generation and low running costs.
 TREATMENT OF WASTEWATER FROM THE DYE
INDUSTRY

Aerobic biological treatment

• A common example of the aerobic biological
treatment of wastewater is the sequencing Batch
Reactor Activated Sludge Process (SBR Process) a
reform process from
• activated sludge, which is a new operating mode. Its
operation is mainly composed of five
• processes:
• inflow
• reaction
• sedimentation
• outflow
• standby.
 TREATMENT OF WASTEWATER FROM THE DYE
INDUSTRY

SBR treatment process not only has a high removal rate of Colour,
but also has a high removal efficiency of color. It can only be used to
remove low concentration of wastewater.
 TREATMENT OF WASTEWATER FROM THE DYE
INDUSTRY

Anaerobic biological treatment

• Anaerobic biological treatment process is a method

that make use of the anaerobic bacteria to decompose
organic matter in anaerobic conditions.
• Currently, the hydrolysis acidification process is the
main anaerobic treatment process, which can increase
the biodegradability of the sewage to facilitate the
following biological treatment process.