LITERATURE REVIEW

Soap evolved from crude mixtures of alkaline and fatty mixtures. The manufacture of soap dates back to the first century, and by the thirteeth century the soap industry had taken stand to produce sufficient quantities of soap. Pompeii excavations revealed that soap factory dates back to over 2000 years ago.

Chevreul, a French Chemist, showed that soap formation was actually a chemical reaction, while domeier completed his research on the recovery of glycerin from saponification mixtures.

The alkali required for soap formation was obtained by the crude leaching of wood ashes or from the evaporation of naturally occring alkaline waters, e.g. the Nile River, until Lablanc produced cheap sodium carbonate from sodium chloride.

For 2000 years, soap making involved batcherise saponification of oil and fats with alkali and salting out of the resulting soap. Changes have occurred int eh pretreatment of oils and fats, plant procedure, and in the processing of finished products e.g. spray drying. Better raw materials have resulted from solvent crystallization, liquid extraction and hydrolysis hydrogenation of various oils and fats.

Continuous processes cam through Procter and Gamble who installed a high pressure hydrolysis continuous – neutralization process in 1937. Sharples and Lever Brother first developed and installed jointly a continuous – saponification process in 1945. The introduction of synthetic detergents, however, has dwarfed the continuous soap processes. In the seventies, detergent sales reached between $400 and $500 million in United State of America. There is no statistics in the developing countries.

RAW MATERIALS FOR SOAP PRODUCTION

The basic raw material for soap making are:

Alkalis

Fats and oils

Additives like perfumes, colourants, preservatives.

Alkali: The type of alkali used in the production of soap depends on the choice of production. Sodium hydroxide (NaOH) is preferred or rather yield hard soap such as the laundry soap while potassium hydroxide (KoH) gives soft soap of which the toilet soap belongs.

Fats and Oil: Fats and oils are esters-compounds of organic acids with alcohols. These acids are termed fatty acids with glycerol as the alcohol base. Different fatty acids are contained in the fat or oil in varying proportions based on the type and source.

For obvious reasons the type and quantity of fats/oils available to the soap-maker varies.

The naturally occurring fatty acid are monobasic acid in which a hydrocarbon chain is linked at one end to a carbonyl (-CooH) group. The number of carbonations in the molecule is between ten and twenty two, although it can be as high as thirty.

Fatty acids are divided into two.

Saturated fatty acids

Unsaturated fatty acids.

The properties of the resulting soap is determined by the amount and composition of the component fatty acid in the initial fat mixture.

In general, composition of fatty acid suitable for the soap making are restricted to chain length and degree of unsaturation. Chain length of less than 18 carbon atoms are undesirable because their soaps are irritating to the skin. The saturated chain lengths greater than 18 carbon atoms form soaps but insoluble for ready solution.

In summary, fatty acids which are most suitable for soap manufacture comprises.

Mono – unsaturated acids containing a similar number of carbon atons as represented by oleic acid.

Saturated fatty acid containing twelve to eighteen carbon atoms as represnted by lauric acid (C12H24O2) myristic acid (C14H28O2), palmitric acid (C16H32O2)

VEGETABLE OIL FOR SOAP PRODUCTION

They belong to the group of lauric oils and are the most valuable fat raw materials for the soap maker.

They can be saponified by the cold process (vide infra) with very strong caustic solutions. If the hot process (vide infra) is used, lower concentrations of caustic are suitable.

PALM OIL (RED OIL)

In crude form is red and needs to be bleached to a buff shade if a light coloured sopa is required. The bleaching can be heat, steam or chemical treatment or a combination of these as in acid fuller’s earth oil heat treatment to remove coloured impurities. The oil is easily sapornifiable nad may be used in the cold process. It is normal to combine palm oil with lauric oil. The characteristics of soap made from palm oil and tallow are similar. Bleached palm oil can substitute for tallow, but the product will be softer in texture.

SOYA BEAN OIL

It is saponified in crude or refined form. It is blended with other oils, especially coconut to give it necessary form.

COTTON SEED OIL

Is refined to a light colour by treatment with caustic soda, and saponified with difficulty to obtain sodium soap, with yellow colour and poor keeping qualities. Thus, blending with other oils is necessary.

TALLOW ANIMAL FATS FOR SOAP PRODUCTION

A fat obtained from the tissues of beef (cattle) and mutton (sheep) by heat treatment, varies in colour from a light shade in edible grade to very dark shade in the lower grades. Tallow is generally blended with other fats. The cheap tallow can be produced in developing countries where modern meat factory exists.

LARD

Is similar to, and obtained in the same way as tallow, from the fat tissues of pigs. The higher grades of lard are valuable raw materials for high grade toilet soaps and have been used in combination coconut oil for this purpose.

GREASES

Such used in soap manufacture are obtained from animal wastes and waste cooking fat from hotels and restaurants, or may be recovered from town refuse. They are used for low grade soaps. They may be split into fatty acids and glycerol, the fatty acids being excellent material for high grade soap.

FISH OIL

In crude form rapidly tends to become rancid. Its fishy odour, brown colour and low detergent powers make it suitable for only low grade soaps. The particularly hydrogenated form may be partially substituted for tallow.

ROSIN & TALL OIL

Are two other organic raw materials which, though neither fats nor oils, have been used in soap production. Rosin is derived from trees of the Pinus species (of Central America and the Caribbean, and now found growing in developing countries). The exude from the tree trunk is a viscous solution of about 75% rosin in turpentine, know as oleoresin. The rosin is obtained by distillation of oleoresin or solvent extraction of the wood. Rosin can be treated as a fatty acid and used to make sodium soaps in combination with other fats. Rosin has been displaced in the soap industry by nut oil with similar properties and lower prices.

Tall oil or liquid rosin is obtained from wood as a by-product of the paper pulp industry using the sulphite process. Pure sodium soaps produced from tall oil alone vary in colour from yellow to dark brown and are soft and tacky. For hard soaps, tall oil normally constitutes not more than 25% of the fat input. Unlike the production of gum and wood rosin which has been stagnant, the production of tall oil rosin has increased with world production of paper by the sulphite process. The only developing countries producing tall oil is Swaziland, although may be produced in others such as Brazil and Chile where paper is being pulped.

GROUNDNUT OIL

In edible and easily saponifiable in crude, refined or hydrogenated (hardened) form. It is combined with other fat to modify consistency.

The blending of soap fatty materials depends on the qualities they impart to the soap as well as economic considerations. Thus, when combined with tallow, coconut oil contribute lathering quality and solubility while the former will contribute mildness and long-lasting lather. Rancidity in crude cotton seed oil soap can be counteracted by tallow and coconut oil. Depending on price and/or availability advantage, palm oil and tallow may substitute each other. Because rosin and coconut oil soap are similar, rosin replaced coconut oil during World War II. When supplies of coconut were sharply reduced.

NON-FATTY MATERIALS

Caustic soda or sodium hydroxide, is the major caustic alkali used in converting fats/oils into sodium soaps. Caustic potash, or potassium hydroxide, is the next caustic alkali which converts fats/oils to potassium soaps. Its is more expensive a chemical.

Each fat/oil has saponification value which enables the soap maker to calculate the amount of alkali needed for completer saponification for a given quantity of oil/fat. The saponification value is the amount in milligram (mg) of potassium hydroxide required to saponify one gram (g) of oil/fat. Thus, the actual amounts of caustic soda required per 100 parts of oil or fat is derived as follows.

Amount of caustic soda = saponification value x M. wt. NaOH x 100

1,000 M. wt. KoH

= Saponification value x 40 x 1

56.1 10

The corrosive nature of caustic dictates that personnel wear protective clothing, gloves and goggles. Besides, it dissolves tin, zinc, dominium, and their alloys. Iron & steal are corroded at high temperatures. Weltered steel plates are used for storage tanks, while black iron pipe can serve for pipelines transporting caustic solutions at low temperatures. Nickel steel should be used for high temperatures. Special lining paints have been used to protect iron and steel.

HARD WATER

Can still be used for sodium soap making, since the calcium carbonate is absorbed harmlessly into the product, with a small loss of soap, though. Soft water is required for the boiler feed, all the same.

SALT, OR SODIUM CHLORIDE,

The quantity used in soap manufacture must be of high grade, containing not more than 0.5% of magnesium and calcium salt.

PERFUME

This is added to the soap mix, and must be resistant to alkali. It is either synthensized or isolated from essential oils, and includes citronella oil (Ceylon or java type) which contains the alkali resistant alcohol geranial as a major component and many therefore be employed for using in the cold process in plate of the imported isolate or synthetic chemical.

OIL – SOLUBLE DYES (COLOURANTS)

These are recommended for cold process, while ultramarine blue or red clay are suggested for hot process soap (vide infra). Titamin dioxide is a whitening agent.

SODA ASH (SODIUM CARBONATE)

Used to increase bulk, reduce corrosiveness, improve lathering and hardening of soap products. The dense anlydrous grade is recommended for bar/tablet soaps, while the light analydrous grade serves for powder soap or scouring soap powder.

SODIUM SILICATE

Adds body, inhibits corrosion, binds and shines the soap product.

BORAX & GRIC ACID

Serves as fillers and preservative. One of these suffices

MAGNESIUM SULPHATE

Used as a dehydrating agent and it helps to preserve the colour and glossiness of the soap.

BUTYLATED HYDROXY TOLUENE (BHT)

An antioxidant and potential virus inactivator, can stop the problem of colour shedding in coloured soaps.

ALUMINUIM SULPHATE AND HYDROCHLORIC ACID

Very small quantities are required for the ghycerol recovery process.

SOAP MANUFACTURING PROCESSES

Saponification processes described here are simple ones, while mention is merely made of technological complex processes. Three common saponification processes are cold, semi-hot and hot-processes.

COLD PROCESS

This is the simplest process, usually employed in small scale and small batch production. Fat/oil of better quality is required than in the hot process. A higher concentration or strength of caustic solution is used than for the hot process. To the oil (or melted hard fats) in a mixer is added the caustic solution and stirred continuously or up to 2 hours till an intimate mix results. If molter hard fats are to be incorporated, they should be introduced when oil caustic exothermic reaction has progressed to generate heat to keep the hard fat in liquid state and thus prevent settling out of fats. The additives are added at this stage. Colours (if not dissolved previously in fats / oil or caustic or ash solution) and perfumes are next added. The mixture thickens as the process proceeds. When the mix is considered ready, it is transferred into the moulds (frames) usually designed with wood or metal to hold the molten soap during the long process of cooling. The sides are detachable to facilitate the removal of the cooled, solid soap block. There is a temporary rise in temperature prior to the normal cooling in the mould. This heat should be conserved to ensure complete saponification and elimination of free caustic from the final product. Cooling and hardening may continue up to 8 – 12 days after packaging.

SEMI-HOT PROCESS

A modified cold process, semi-hot process, allows fats of higher melting points and rosins to be included in the raw material mix. The liquid fat/oil is raised to the operation temperature of 70 – 800c, as well as the caustic solution. They are then reacted as in cold process. The time required by this process is considerably shorter than in the cold process. The perfume and colourant are added at a later stage to prevent their loss by evaporation. Soap fillers can be more easily incorporated in this process. Heating allows for the correction of inaccurate mixes, and makes for more complete saponification and higher yield. Soap scraps, which arise from the cutting and scabbing of cooled soap and which are wastes in cold process (except when rolled into sellable soap balls) may easily be incorporated into the material feed by first melting them in the mixer before introducing suitable supplementary fat/oils. The extra cost of the extra heating apparatus would have been a disadvantages of this process over the cold process, but the extra yield soon off-set it.

HOT PROCESS

Boiling the sopa reaction mix produces soap of the highest quality. Heating is by steam produced in the boiler plant and passed under pressure to steam coils incorporated in the boiling kettle. The injected steam both heats and agitates the mixture.

Fats/oils are melted from their tanks by means of steam jets, into a storage tank. They are then pumped via meters to the saponification pan. Suitable solutions of caustic and salt are pumped via measuring devices to tanks for introduction later in the process.

As the fat/oil and alkali boil in the soap vessel, a vigorous saponification reaction takes place. It may be necessary to boil up a little of the soap from a previous batch with the reaction mix, to ensure adequate mixing between the oily and aqueous phases and allow the reaction to proceed smoothly.

Although saponification time varies with sixe and shape of the vessel as well as with the raw materials, two or four hours may be representative.

When saponification is complete, hot salt solution is passed into the reaction vessel where it is boiled with saturated salt solution (brine). Glycerol dissolves easily in the salt water, but soap only to a limited extend. The mix is allowed to stand for several hours, resulting to two separate layers – top layer of soap and a lower layer, lye a mixture of brine and glycerol. The soap layer may be washed with more brine to remove more glycerol. Counter current washing system is mostly adopted. A lye from a batch of soap in a more advanced stage of the process is used to wash a freshly saponified charge. Although it requires the use of more than one pan, this system has the advantage that the process becomes semi-continous in the production of soap and that the spent lye contains higher concentration of glycerol than when washing were carried out with fresh brine. With careful regulation of the size of the washes, a lye of 8% to 10% glycerol results.

Market for spend lye exists in advance countries, otherwise this waste must be disposed of so as not to cause pollution.

In the next stage, the mixture is allowed to settle for some days to resolve into two layers – top layer of good quality soap curd and a lower layer of lye which is a mixture of dark impure soap and lye. The phases are then separated and more salt and water are added to the soap phase to separate more of the glycerol in a second lye. Next, critical amount of water added to the curd results to the separation of nigre, a thin phase containing coloured impurities and some soap, from neat soap layer containing 30% water. One week is typical of a while cycle of kettle operation. This long production period imposes an constraint on through put. To overcome this delay, large scale manufactures have adopted continuous.

GLYCEROL RECOVERY

The spent lye (about 12% glycerol) is boiled with fatty acids to reduce the excess caustic. On cooling the solid soap is skimmed off and returned to the soap plant. Hydrochloric acid and alum are added to precipitate impurities which are filtered out. Further addition of caustic neutralizes the acid and prevents corrosion in the next pant. The treated lye is concentrated to 80% crude glycerol by evaporation of water in a single or double or triple effect evaporation, depending on the size of operation. The crude (78% glycerol, 0.2% fatty acids, and 22% water) is settled for 48 hours at elevated temperatures, and then distilled at 60 monthly and 2040c. The distillate is condensed in three stages of decreasing temperature, the first stage yielding 99% glycerol. Carbon bleaching followed by filtration in ion exchange give final product.

CENTRIPURE PROCESS

The production of soap from neutral fats can be carried out continuously in three stages. The saponification takes place in a column. Pumps convey fat/oil and caustic to various sections of the column and also circulate soap throughout the column, thereby catalyzing sub-sequent saponification and very quick reaction. Glycerol is removed by counter-current washing with brine. The soap mix is passed to a centrifuge for a quick separation of the soap, as against the three day long separation of kettle process. Continuous quality control is an advantage here.

RETIONALIZED KETTLE PROCESS

This is a combination of certain features of the centripure process with the standard kettle process, to decrease production time and hence increase through put without the heavy capital outlay involved in continuous specification units. Centrifuges and used to take soap from the pans and in the finishing stages, thereby shortening the process time.

PRODUCTION FROM FATTY ACIDS

Raw fats/oils are split using superheated steam to produce fatty acids and sweet water which contains glycerol. The glycerol is removed before the saponification of the fatty acids to yield soap.

1. (C17H35C00)3 C3H5+3H20 Hydrolysis 3C7H35C00H +C3H3(0H)3

Glyceryl Stearate Stearic acid Glycoin

2. (C17H35C00 + Na0H Saponification C17H35C00Na +H20

Stearic acid Caustic Soda Sodium stearate (soap)

THE CHEMISTRY OR SOAP FORMATION

Palm kennel oil reacts with caustic soda (or caustic potash) to form soap.

The active ingredient in the oil for this reaction is lauric acid, C11H23 OOH. This acid exists in the oil in its triester form called trilaurin,.

CH2COO11H23

CH00C11H23

CH2C00C11H23

The triester reacts with caustic to form soap as expressed in the equation below.

CH2COO11H23

CH00C11H23 + 3NaOH CH2OH

Caustic soda CHOH

CH2C00C11H23 3C11H23COONa CH20H

Sodium laureate (soap) Glycerol

PROCESSES AND STEPS INVOLVED IN PRODUCTION OF SOAP

The process of soap production starts from the blending mixing of the oil, bleaching of the oil and boiling of the soap prope manufacture of soap.

BLENDING / MIXING OF OIL

In a bid to produce quality soap (soap with high detergency and foamability only one brand of oil is not preferable in producing a high quality soap, so the oils have to be blended to get the desired result.

Also for many other purposes, including conventional toilet soaps and household soaps made by the modern vacuum chilling/extrusion processes, a blend of about 15 – 25% lauric oil (coconut or palm kernel) and 75 – 86% hard fat usually tallow or palm oil and it gives a soap base with an excellent combination of properties.

The hard fat gives a firm texture and good detergency at high washing temperatives, the lauric oil also gives a firm soaps, but improves the rate of solution and freedom of lather.

TYPES OF OIL/FAT AND ITS PROPERTIES

OIL/FAT

PROPERTIES OF SOAP FORMED

1.

Palm oil

Moderate foaming and less soluble

2.

P.K.O

Excellent foaming but highly soluble

3.

Coconut oil

Excellent foaming hut highly soluble

4.

Soya bean oil

Moderate foaming and less soluble

5.

Tallow (MUTEN)

Moderate foaming and less soluble

6.

Tallow (BEEF)

Moderate foaming and less soluble

In this section, for toilet soap we blended palm kernel oil (P.K.O) and animal fat (Tallow) in the ratio of 85:15 for toilet soap and 95:5 for laundry soap respectively.

REASONS FOR OIL/FAT BLENDING

To achieve a soap that is neither too lard nor too soft. With soft fat p.o.k) alone, one will obtain a high soluble soap though with high lathering ability. but with the combination of p.o.k and tallow, you obtain a soap with high detergency (high soil removal).

To achieve a soap with high stain removal and lathering ability N/B the longer the carbon chain length of the voil/fat the harder the soap e.g. vegetable oil (palm oil), animal fat (tallow) while the shorter the carbon chain length of the oil the softer the soap it produces e.g. p.o.k and coconut oil etc.

BLEACHING

In this section oil/fat are drawn from the blending tank to the bleaching tank. Oil/fat contain inaugurates, moisture, colour, odour, due to caroten and some gums (phosphatides) etc. so in other to produce a quality house lokd soap there are need for the oil to be bleached using bleaching earth (fullers earth) and vacuum. H2SO4 acid in the case of palm oil, CaCO3.

Methods used to bleach oils and fats can be divided into adsorption bleaching used for both edible and soap making fats, and chemical bleaching used only for soap making fats.

ADSORPTION BLEACHING

The molten fat, or oil is brought into contact with a powedered solid adsorbent, which can be natural fullers earth, or clay, or to a limited extents, activated carbon used in conjunction with activated earth. Activated earths are made by the action of mineral acids on suitable mineral substances, such as bentonite or montuorillonite. The adsorbent removes colouring malted from the oil which is then separated by filtration. Sulpharic acid markedly improves the performance of natural fullers earth and may also be useful with activated earths. And addition to the bleaching vessel of about 10% of the weight of natural earth used is often found suitable for soap making oils.

Bat wise bleaching in single vessels which is usual for soap making oils can be carried out in open vessels, filted with alosed steam coils And with an agitator to keep the earth in suspension in the oil and to promote heat transfer without local over heating, but closed vessels working under vacuum (50 – 70 mm Hg absolute preserve) and usually used and are usually used and are better because

Moisture is removed more effectively

There is less risk of undesirable oxidation of the oil by air, partiality if steps are taven to deacrate the oil as much as possible before it reacted bleaching temperature.

Heating in vacuum bleachers is usually by internal steam coils, but in case of very large bleaching vessels, external circulation through a tubular or similar heater is sometimes used, and is preperable. Coolers may be fitted cool the oil before it is filtered. With soap making tallows and grease it is primarily to remove polythene, for which purpose the oil should be filtered at below about 700c. Bleaching temperature is not very critical, typically, good quality tallows and fats are bleached at 90 – 950c, power qualities at about 1100c, and palm oil at 120 – 1300c. About 15 minutes is said to be sufficient for equilibrium to be reached, but the complete bleaching cycle takes several hours.

The role of water is important. Complete drying of the bleaching earth will destroy its efficiency, and water in the oil changed to the bleacher does not harm as regards final quality. It has been reported that addition of water can improve the performance of activated earths when bleaching tallow, other experience shows that sufficient water is important when palm oil is being bleached with activated earth, or with natural earth plus 10% and, if necessary, water is added to bring the level to about 2%. On the other hand, it is usually found necessary to adjust temperature, pressure and time, so that the oil is substantially dry before the bleaching stage is completed in order to achieve proper adsorption of colouring matter.

CHEMICAL BLEACHING

This usually involves the oxidation of colouring matter in the oil or fat. The result varies preatly with the kind of fat, and palm oil, and by products containing palm oil residues, are particularly responsive to oxidation bleaching. In some cases, an undesirable odour develops, and chemical bleaching is not used with edible fats, or usually, with fats to be made into the better quality toilet soaps.

The oxidation can be carried out with air (or oxygen, with alkali dichromate plus acid) with sources of available chlorine, or of chlorine dioxide, or with other reagents. Air can be blown through hot palm oil to produce air bleached palm oil. Soap made from this oil has a slight brownish shade and a characteristic odour. These qualities limit its use, but it has been employed in orange/red carbolic toilet soaps. The oil is agitated with air for several hours after addition of sodium dictroniate, salt, and hydro chloric acid. After the mix has settled, the aqueous layer is run to waste and the oil is washed several times with water. More recently, most chemical bleaching processes have used chlorine compounds.

The bleached fat should be saponified as soon, as possible. Soaps made from chemically bleached fats tend to deteriorate more than those made from adsorption bleached materials.

BOILING/PROPER MANUFACTURE OF SOAP

INGREDIENTS:

The primary materials used in the manufacture of bar soaps are natural fats and oils.

But for better quality soaps, blend of top – quality animal tallow and coconut oil. These basic materials are eventually converted to their neutral salts by the use of some alkaline material, such as sodium hydroxide. Additional minor ingredient are added, eg. Sodium silicate or magnesium sulphate, to control alkalinity, odor, and aging stability.

SOAP MAKING PROCESS:

The basic process simply are that of splilting the fat stocks into falty acid and glycerin, followed by separation and neutralization of the resulting fatty acids with alkali. Two systems are in common use, the kettle method and the continous hydrolyser.

KETTLE METHOD

The kettle is first charge with fat and a sodium hydroxide solution. Then follows by a sequence of heating, separating, and washing to convert the raw materials to finished base soap and separate the impurities and by products. The process normally takes several days for any single kettle. Although there have been improvement improvements in handling and purification, such as continuous centrifugation, the basic process of saponifying fats directly with caustic remains unchanged.

HYDROLYSER PROCESS

The development of continous hydrolysis is the most important basic improvement in the processing of fats into soap since the early days of soap making. There are several advantages over the kettle process

Better quality soap can be made from darver fats

glycerin recovering is simplified because no salt is added and the resulting finished glycerin is of greater quality

a single hydrolyser unit produces about the same quality of soap as 10 kettle thus effecting savings in manufacturing space a reducting of in-process inventory, and

high of flexibility is possible in controlling the chemical and physical properties of the finished products.

The hydrolyzing process consists essentially of hydrolysis

falty acid distrillation,

post hardening (optional)

neutralization and

glycerin recovery.

The basic hydrolyser process is shown in the figure below