SOAP AND DETERGENT

• Soap manufacturing

  1. Saponification

  2. Glycerine removal

  3. Soap purification

  4. Finishing
• Saponification


  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
• Base powder


  Powder produced by spray drying the slurry
• Ingredients in detergent base powder

  • Sodium tripolyphosphate (water softener, pH buffer)
  • Sodium sulphate (bulking and free-flowing agent)
  • Soap noodles (causes rapid foam collapse)
  • Zeolite (water softener, granulating agent)
  • Sodium carboxymethyl cellulose (increases negative charge on fibres)
• Liquid ingredients in detergent base powder

  • Linear alkylbenzene sulphonic acid (surfactant)
  • Caustic soda solution (neutralises LAS)
  • Coconut diethanolamide or fatty alcohol ethoxylate (nonionic detergent and foam former)
  • Fluorescer (absorbs UV, emits blue light)
  • Water (dissolves and mixes ingredients)
• Liquid detergent manufacture

  1. Soap premix manufacture

  2. Ingredient mixing

  3. Enzyme addition
• Typical post dosing ingredients

  • Soda ash (pH buffer, water softener)
  • Bleach (sodium perborate)
  • Bleach activator (e.g. tetraacetylethylenediamine)
  • Enzymes (e.g. alkaline protease)
  • Colour and perfume
• Glycerine recovery


  1. Soap removal

  2. Salt removal

  3. Glycerine purification
• 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 storage tanks 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