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MANUFACTURING OF SOAPS
[AN INFORMATIVE REPORT]
INTRODUCTION
• Soap is integral to our society today.
• However, the current widespread use of soap is only a very recent occurrence, despite the fact that it has been made for more than 2500 years.
• Soaps are made from fats and oils, or their fatty acids, by treating them chemically with a strong alkali.
• Soap, from a chemical standpoint, is a water-soluble sodium or potassium salts of fatty acids.
• As with all salts, soap contains a positive ion, usually Na+ or K+, and a negative ion, usually the anions of long-chained carboxylic acids obtained by the hydrolysis of animal or vegetable fats.
HISTORY
• Our forefathers were learning to prepare a type of washing paste by melting fat together with wood ashes.
• An early recipe for soap is recorded on clay tablets from Mesopotamia, which was invented a long time ago in 2500 B.C.
• According to PLINY the elder, who was an ancient natural philosopher, “soap” was prepared both as liquid potassium soap product and in solid form.
• In 385 A.D. THEODOROS PRISCIANUS recommended using soap for the washing of hair. He also provides the first record of the “saponarius” or soapmaker.
• Soaps were very popular in countries like Rome and Germany.
• GALEN, the personal physician of Emperor MARCUS AURELIUS, in the second century A.D. was apparently the first to recognize the value of soap as a washing and cleansing agent.
• In the third century the roman emperor SEPTIMIUS SEVERUS, advised women around him to cleanse their faces with crushed herbs dissolved in oil as a way of making them more attractive to men.
• In 385 A.D. THEODOROS PRISCIANUS recommended using soap for the washing of hair.
• Soapmaking became recognized occupation within the emperial domains in the 18th century, due to emperor CHARLEMAGNE.
• During the ninth century, the Spanish spread the art of soap making into the lands surrounding the Mediterranean, especially in the areas of Marseilles, Venice, Genoa and Alicante.
• As early as the fifteenth century, Portuguese and Spanish missionaries introduced soap into Japan, which apparently, was a huge success.
• The art of soap making reached its high point in the period before the Thirty Years’ War, but the general spread of soap as a commodity occurred only later as it was a luxury product.
• Only after the introduction of large scale soda production and widespread import of fats and oils from the tropics was the foundation laid for the industrial production of soap, permitting it to become a common consumer article.
TYPES OF SOAPS
BAR SOAPS:
DETERGENT SOAPS:
LIQUID SOAPS:
CLEANSING ACTION OF SOAPS
• A soap molecule has two parts: the long chain organic part and the functional group –COO- Na+, i.e., a tail and a head.
• The organic part is water insoluble but is soluble in organic solvents or in oil or grease. The ionic part is soluble in water, as water is a polar solvent.
• When soap is added to water, the organic tail dissolves in the dirt, grime or grease and the ionic head dissolves in water.
• When the clothes are rinsed or agitated, the dirt gets pulled out of the clothes in the water by the soap molecule.
• In this way the soap does its cleaning work on dirty and grimy clothes or hands.
DIAGRAMMATIC REPRESENTATION
RAW MATERIALS
• Soap requires two major raw materials: fat and alkali.
• The alkali most commonly used today is sodium hydroxide.
• Animal fat in the past was obtained directly from a slaughterhouse.
• Modern soapmakers use fat that has been processed into fatty acids.
• Many vegetable fats, including olive oil, palm kernel oil, and coconut oil, are also used in soap making.
• 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).
CHEMICAL PROCESSES INVOLVED
• Bar soap can be manufactured by either using batch or continuous process. Now days, continuous process of soap making are preferred because of their speed, flexibility and cost economy.
• The kettle method of making soap is still used today by small soap manufacturing companies. This process takes from four to eleven days to complete, and the quality of each batch is inconsistent due to the variety of oils used.
• Both the batch kettle boiling as well as continuous soaps making processes produce the soap in liquid form (known as neat soap), and a valuable by-product, glycerine.
BASIC PRINCIPLES IN MANUFACTURING OF SOAPS
Step 1 – SAPONIFICATION
• Saponification of fats and oils is the most widely used soapmaking process.
• This method involves heating fats and oils and reacting them with a liquid alkali to produce soap and water (neat soap) plus glycerine.
• SAPONIFICATION OF FATTY ACID
Step 2 – GLYCERINE REMOVAL
Step 2.1 - Soap removal
• HCl + NaOH → NaCl + H2O
• FeCl2 + 2RCOONa → 2NaCl + (RCOO)2Fe
• 2NaOH + FeCl2 → Fe (OH)2 (s) + 2NaCl
Step 2.2 - Salt removal
• Water is removed from the lye in a vacuum evaporator, causing the salt to crystallize out as the solution becomes supersaturated.
• This is removed in a centrifuge, dissolved in hot water and stored for use as fresh lye.
Step 2.3 - Glycerine purification
• A small amount of caustic soda is added to the crude glycerine and the solution then distilled under vacuum in a heated still.
Step 3 – SOAP PURIFICATION
• Any remaining sodium hydroxide is neutralized with a weak acid such as citric acid and two thirds of the remaining water removed.
• Fats and oils are hydrolyzed (split) with a high-pressure steam to yield crude fatty acids and glycerine.
• The fatty acids are then purified by distillation and neutralized with an alkali to produce soap and water (neat soap).
Step 4 – FINISHING
• Additives such as preservatives, colour and perfume are added and mixed in with the soap.
• The soap is shaped into bars.
• Then it is packed for sale.