INTRODUCTION

Soaps are the sodium and potassium salts of long chain fatty acids that are generally made by

saponification (alkaline hydrolysis) of natural fats, such as animal fats or palm oil. Soaps are

precipitated by calcium and magnesium salts in hard water, detergents are not. A soap

molecule consists of a long hydrocarbon chain with a carboxylic acid group on one end

which is ionically bonded to the metal sodium or potassium. The structure of a soap molecule

is represented below:

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CH3-CH2-CH2- CH2-CH2-CH2-CH2- CH2-CH2- CH2-CH2- CH2-CH2- CH2-CH2- C-O− Na+

Detergents, term applied to materials, usually powdery, or liquid in nature. Solutions of

which, aid in the removal of dirt or other foreign matter from contaminated surfaces.

Detergents are synthetic substances whose molecular structures have been tailored with the

essential properties of soaps (Encarta, 2008).

Detergents are structurally similar to soaps, but differ in the water-soluble portion. Examples

of detergents are shown below (Katz, 2000).

A sodium alkyl sulphate

A sodium alkyl benzene sulphonate

HISTORICAL DEVELOPMENT

The earliest recorded evidence of the production of soap like materials dates back to around

2800BC in ancient Babylon. A formula for soap consisting of water, alkali, and cassia oil was

written on a Babylonian clay tablet around 2200BC.

Industrially manufactured bar soaps came into existence in the late eighteenth century as

awareness of the role of hygiene in reducing population of pathogenic microorganisms

spread. The history of detergents is believed to have commenced when Edmund Fremy

prepared sulphonated olive and almond oils by treating them with sulphuric acid in 1831.

Amongst the pioneers of soap manufacturing are William Hesketh Lever and his brother

James who founded what is still one of the largest soap businesses, “Unilever plc”, from a

small soap works in Warrington, 1886 (www.wikipedia.com).

The World War spurred the development of soapless or synthetic detergents, primarily in the

United States. After the war the industrial revolution bore the need for new types of

detergents for automatic washing machines.

In the late 1960s, because of the increasing concern over the pollution of water resources, the

inclusion of harmful chemicals, such as phosphates, in soaps and detergents was actively

discouraged. Instead, biodegradable agents that are easily broken down and digested by

bacteria came into wide use.

SYNTHESIS OF SOAPS AND DETERGENTS

Soaps

There are two variations in small scale soap manufacture, namely; cold process, and hot

process.

Cold process: in this process, the temperature is usually raised to a point sufficient to ensure

complete melting of the fat. Usually the soap is safe to use after approximately 12-48 hours,

but it is not at its peak quality until after several weeks. This process requires exact

measurements of alkali and fat amount, as unreacted excess of either can lead to high pH

value and greasiness of the soap respectively. Most times, a 4-10 % deficit alkali is used.

Hot process: the hydroxide and fat are mixed and heated to 80-100%, a little below boiling

point, until saponification is complete. After saponification, the neat soap is precipitated off,

by addition of common salt, and excess liquid drained off. The hot soft soap is then pumped

into a mould, and the spent alkali solution is processed for glycerine recovery.

PROCESS STEPS

The above illustrations show the kettle process of making soap.

Step 1 - Saponification

A mixture fat/oil is mixed with sodium hydroxide and heated. The soap produced is the salt

of a long chain carboxylic acid.

Step 2 - Glycerine removal

Glycerine is a very valuable by-product, so most of it is removed. Some is left in the soap to

help make it soft and smooth. Soap is not very soluble in salt water, whereas glycerine is, so

salt is added to the wet soap causing it to separate out into soap and glycerine in salt water.

Step 3 - Soap purification

Unreacted sodium hydroxide is neutralized with a weak acid such as citric acid and two-third

of the remaining water removed.

Step 4 - Finishing

Additives such as preservatives, colour and perfume are added and mixed in with the soap

and it is shaped in a mould and packed for sale.

Additives are used to enhance the color, texture, and scent of soap. Fragrances and perfumes

are added to the soap mixture to cover the odor of dirt and to leave behind a fresh-smelling

scent. Abrasives to enhance the texture of soap include talc, silica, and marble pumice

(volcanic ash). Soap made without dye is a dull grey or brown color, but modern

manufacturers color soap to make it more enticing to the consumer.

Detergents

Detergents are made by treating an aromatic, or benzene-type, compound with sulphuric acid,

followed by neutralization with alkali, to convert the product to its sodium salt.

Alkylbenzene + Oleum -----> Alkylbenzene sulphonate + sulfuric acid

Ingredients used in detergent manufacture

Processes of manufacturing detergents

Powder detergents are manufactured using various processes, such as spray drying,

agglomeration, dry mixing or a combination of these. A brief description of these different

processes is given below:

Spray drying

The different stages / operations performed in a spray drying process, are -

Dry and liquid ingredients are first combined into a slurry, or thick suspension, in a

tank known as crutcher.

The slurry is heated and then pumped to the top of a tower where it is sprayed through

nozzles (under high pressure) to create small droplets. The droplets fall through a

current of hot air, thereby forming hollow granules as they dry.

Collected from the bottom of the spray tower, the dried granules are screened to

obtain a relatively standard size.

After the granules have been cooled, heat sensitive ingredients, which are not

compatible with the spray drying temperatures (like bleach, enzymes and fragrance)

are added.

Agglomeration

Agglomeration is detergent powder manufacturing chemical technique that results in high-

density powders. The process involves blending of dry raw materials with liquid ingredients.

The technique involves machines, such as a liquid binder, rolling or shear mixing that causes

the ingredients to collide and adhere to each other, producing larger particles.

Dry Mixing

Dry mixing is a detergent powder manufacturing technique, which is used to blend dry raw

materials. The technique may also involve the addition of small quantities of a liquid.

UNIT OPERATIONS

Soap Industry

Saponification reactor

Filtration unit

Evaporator

Detergents

Sulphonation vessel

Dehumidifier

Melting of sulphur

Burning of sulphur

Heater, for pre-heating before conversion

Catalytic conversion

Heat exchange

Separator

Multi-tube film reactor

Sulphonic acid-gas separation

Stabilization

Electrostatic precipitation

Scrubbing

Neutralization

Spray drying

Crystallization

Sieving

Packaging

USES OF SOAPS AND DETERGENTS

i. Used as surfactants for washing and cleaning.

ii. Soaps are important components of lubricants

iii. Soaps are also used in textile spinning

iv. Detergents are used as fuel additives to prevent fouling

v. Detergents are used as biological reagent for the isolation and purification of integral

membrane proteins.

CLEANING ACTION

Soaps and detergents have a molecular structure that acts as a link between water and the dirt

particles, loosening the particles from the underlying fibres or other surfaces to be cleaned.

The molecule can perform this function because one end is hydrophilic (attracted to water)

and the other is hydrophobic (attracted to substances that are not water soluble). The

hydrophilic end is similar in structure to water-soluble salts. The hydrophobic part of the

molecule frequently consists of a hydrocarbon chain that is similar to the structure of grease,

oil, and many fats. The net result of this peculiar structure permits soap to reduce the surface

tension of water (by increasing wetting) and to adhere to and make soluble substances

otherwise insoluble in water (emulsification) (Encarta, 2008).

The washing or cleaning action of soaps and detergents can thus be summarized into two

stages.

i. Wetting action

ii. Emulsification

TYPES OF SOAP AND DETERGENTS

Soaps can be categorized as hard and soft, or based on their usage; i.e. laundry, medicated,

multipurpose, etc.

Hard soaps are made from oils and fats that contain a high percentage of saturated acids,

which are saponified with sodium hydroxide. Soft soaps are semifluid soaps made from

linseed oil, cotton-seed oil, and fish oils, which are saponified with potassium hydroxide

(Encarta, 2008).

Detergents are chemically classified into three broad groups, depending on the electrical

charge of the surfactants. They are; anionic, cationic, and non-ionic or zwitterionic detergents

(www.wikipedia.com).

ENVIRONMENTAL IMPLICATIONS

Detergent powder manufacturing has some specific environmental issues that are not

associated with any other industry. These issues include dust control and volatile organic

emissions. Dust present during the process of delivery and transfer of bulk powdered

detergent is a potential problem. In order to filter out most of the dust, dry and wet cyclones

are used, and all the emissions are monitored.

If the dust level in these does exceeds the acceptable limits, appropriate remedial action must

be taken. The permissible dust levels in emissions are under below 50-mg m -3. The spray-

drying tower also releases volatile organics, which can be minimized by having tight

specifications specifying what can be added as a primary detergent active material. Spot

checks must be made on the total hydrocarbon content of the exhaust gases using a flame

ionization detector.

Other environmental pollution problems in soap and detergent manufacturing are:

Odour from waste streams

Noise from operational equipment

Solid waste from its poorly disposed packaging

Effluent waste and harmful gas emissions like SO2

WAYS OF MINIMISING ENVIRONMENTAL HAZARDS

Use of biodegradable materials in packaging

Wearing gas masks and safety clothing when in the processing area.

Citing the industry away from human settlements.

ECONOMIC CONSIDERATION OF SOAP AND DETERGENT INDUSTRIES

Since soap consumers cut across every class in society, and is used in virtually every

household, it is evident that the demand for it, is high, therefore it’s a very viable enterprise.

Also, its raw materials can be sourced locally.