Reaction between a fat and sodium hydroxide to produce glycerine and soap
Common fats and oils used in soap manufacture
Tallow
Coconut oil
Palm kernel oil
Glycerine
Produced in the saponification reaction, makes soap smoother and softer
Glycerine removal
1. Wet soap is soluble in weak brine, but separates out as electrolyte concentration increases
2. Glycerine is highly soluble in brine
Soap purification
1. Remaining sodium hydroxide is neutralised with a weak acid
2. Two thirds of the remaining water is removed
Finishing
1. Additives such as preservatives, colour and perfume are added and mixed in with the soap
2. Soap is shaped into bars for sale
Detergents are similar in structure and function to soap, and for most uses they are more efficient than soap and so are more commonly used
In addition to the actual 'detergent' molecule, detergents usually incorporate a variety of other ingredients that act as water softeners, free-flowing agents etc.
The first recorded manufacture of soap was in 600BC, when Pliny the Elder described its manufacture by the Phoenicians from goats tallow and ash
Soap was known among the British Celts and throughout the Roman Empire, but was used medicinally, not for cleaning
Soap began to be used for cleaning
Second century AD
Soap began to be commonly used in the Western world
Nineteenth century
The first synthetic detergents were manufactured early this century, and have now taken the place of soap for many applications
Surfactant
The active ingredient in soaps and detergents, an ionic species consisting of a long, linear, non-polar 'tail' with a cationic or anionic 'head' and a counter ion
Wetting agent
The surfactant molecules migrate to align themselves with the solid:water interface, lowering the surface tension so that it penetrates the fabric better
Emulsion
The surfactant molecules surround an oily dirt particle, forming a micelle with a drop of oil in the centre and the ionic heads of the surfactant molecules pointing outwards, keeping the micelle in the polar solution
Saponification reaction
Triglyceride + Caustic soda -> Glycerine + Metal soap
Fatty acids present in oils used in soap manufacture
Lauric acid
Myristic acid
Palmitic acid
Stearic acid
Oleic acid
Linoleic acid
Colgate-Palmolive continuous soap manufacturing process
1. Saponification
2. Lye separation
3. Soap washing
4. Lye separation
5. Neutralisation
6. Drying
Lever Rexona batch soap manufacturing process
1. Oil preparation
2. Saponification
3. Washing
4. Fitting
5. Drying
Laundry or 'hard' soap manufacture
1. Base soap is mixed with colour and preservatives and milled
2. Perfume is added
3. Mixture is plodded then extruded into a continuous bar
4. Bar is cut into billets and stamped out into tablets
Toilet soap manufacture
1. Base soap has extra fatty acids added with preservatives before vacuum drying
2. Perfume, dye and opacifier are added to the dried soap
3. Mixture is milled, plodded and extruded out as a continuous bar, cut into billets and stamped
Detergents use a synthetic surfactant in place of the metal fatty acid salts used in soaps
Detergents are made both in powder and liquid form, and sold as laundry powders, hard surface cleaners, etc.
Toilet soap manufacture
1. Soap has less water and more fatty material (fatty acids and soap) than laundry soap
2. Extra fatty acids added with preservatives before vacuum drying
3. Perfume, dye and opacifier added to dried soap and milled
4. Plodded and extruded into continuous bar, cut into billets and stamped
Detergent powder manufacture
1. Slurry making
2. Spray drying
3. Post dosing
Slurry
Mixture of solid and liquid raw ingredients heated and stirred until homogeneous
Soap is designed as a product to be used once then flushed down the drain, so the environmental implications of its manufacture are not nearly so great as many other chemical processes
The three main components of soap by both cost and volume are oils, caustic and perfumes
All storagetanks are surrounded by bunds to catch the contents of a tank should it rupture or a valve fail
The manufacturing process itself is closely monitored to ensure any losses are kept to a minimum
The sulphonic acid and nonionic detergents used in New Zealand to produce both liquid and powder detergents are fully biodegradable and comply with the relevant Australian standard
Dust present during delivery and transfer of bulk powdered detergent (and powdered raw materials) is a potential problem