Manufacturing of Soaps

Before the 1950s, soap was manufactured in the saponification process. Soap was prepared in large kettles in which fats, oils, and caustic soda were mixed and heated. After cooling, salt was added to the mixture forming two layers soap and water. The soap was pumped from the top layer to a closed mixing tank where builders, perfumes, and other ingredients were added. Finally, the soap was rolled into flakes, cast, or milled into bars, or spray-dried into soap powder [1, 2]. 

After the 1940s, an important modern process for producing soap is based on the direct hydrolysis of fats by water at high temperatures. The chart of the continuous process is shown in Fig. 5.1. The process involves splitting (or hydrolysis) where fatty acids are neutralized to soap [1, 2, 5]. 

The saponification of triglycerides with an alkali is a bimolecular nucleophilic substitution (SN2). The rate of the reaction depends on the increase of the reaction temperature and on the high mixing during the processing. In the saponification of triglycerides with an alkali, the two reactants are immiscible. The formation of soap as a product affects the emulsification of the two immiscible reactants, which causes an increase in the reaction rate [1, 2, 5]. 

The flow diagram of the continuous process of converting fatty acids into soap (Fig. 5.1) includes an important component—the hydrolyzer— to which the fats and the catalyst were introduced after mixing and preheating in the blend tank. At the same time, deaerated-demineralized hot water is fed to the top contacting section of the hydrolyzer. The fatty acids are discharged from the top of the splitter and the glycerin is 

The resulting crude mixtures of fatty acids may be used, but a separation into more useful components is made. 

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Commercially glycerin is obtained as a byproduct in the manufacture of soap, and by various synthetic routes. Crude glycerin is purified by distillation. The various synthetic routes start with propenc. One proceeds via... 

E. WooUatt, The Manufacture of Soaps, Other Detergents and Glycerin,]ohxi Wiley Sons, Inc., New York, 1985, pp. 296—357. 

The quaHty, ie, level of impurities, of the fats and oils used in the manufacture of soap is important in the production of commercial products. Fats and oils are isolated from various animal and vegetable sources and contain different intrinsic impurities. These impurities may include hydrolysis products of the triglyceride, eg, fatty acid and mono/diglycerides proteinaceous materials and particulate dirt, eg, bone meal and various vitamins, pigments, phosphatides, and sterols, ie, cholesterol and tocopherol as weU as less descript odor and color bodies. These impurities affect the physical properties such as odor and color of the fats and oils and can cause additional degradation of the fats and oils upon storage. For commercial soaps, it is desirable to keep these impurities at the absolute minimum for both storage stabiHty and finished product quaHty considerations. 

Fats and oils are treated as commodities in the open market and are purchased in bulk. As commodities, their prices fluctuate with supply and demand. Furthermore, fats and oils come in different grades that reflect different levels of processing and have industry-standardized specifications such as the American Fats and Oil Association. In the manufacture of soap in the United States, the source of animal fats is domestic whereas the vegetable oils are frequently obtained from Southeast Asia, primarily Malaysia and the Philippines. 

Tallow [61789-97-7] is the fat obtained as a by-product of beef, and to a lesser degree sheep processing, and is the most commonly utilized animal fat in the manufacturing of soaps. The high content of longer chain length fatty acids present in tallow fat necessitates the addition of other oils, such as coconut oil, in order to produce a bar with acceptable performance. 

Coconut oil [8001-31-8] is one of the primary vegetable oils used in the manufacture of soap products. Coconut oil is obtained from the dried fmit (copra) of the coconut palm tree. The fmit is dried either in the sun or over open fires from burning the husks of the fmit, with the oil pressed out of the dried fmit. 

Commercially, soap is most commonly produced through either the direct saponification of fats and oils with caustic or the hydrolysis of fats and oils to fatty acids followed by stoichiometric (equal molar) neutralization with caustic. Both of these approaches yield workable soap in the form of concentrated soap solutions (- 70% soap). This concentration of soap is the target on account of the aqueous-phase properties of soap as well as practical limitations resulting from these properties. Hence, before discussing the commercial manufacturing of soap, it is imperative to understand the phase properties of soap. 

For sodium palmitate, 5-phase is the thermodynamically preferred, or equiUbrium state, at room temperature and up to - 60° C P-phase contains a higher level of hydration and forms at higher temperatures and CO-phase is an anhydrous crystal that forms at temperatures comparable to P-phase. Most soap in the soHd state exists in one or a combination of these three phases. The phase diagram refers to equiUbrium states. In practice, the drying routes and other mechanical manipulation utilized in the formation of soHd soap can result in the formation of nonequilibrium phase stmcture. This point is important when dealing with the manufacturing of soap bars and their performance. 

Direct Saponification. Direct saponification of fats and oils is the traditional process utilized for the manufacturing of soap. Commercially this is done through either a kettle boiling batch process or a continuous process. 

Trade association of manufacturers of soaps, detergents, fatty acids, and glycerine that conducts environmental and human safety research and is a clearinghouse for information on ingredients in soaps and detergents. 

Consider palmitic acid, CUH32O2, a common fatty acid used in the manufacture of soap. A solution of palmitic... 

The raw materials for the manufacture of soap, the alkali salts of saturated and unsaturated C10-C20 carboxylic acids, are natural fats and fatty oils, especially tallow oil and other animal fats (lard), coconut oil, palm kernel oil, peanut oil, and even olive oil. In addition, the tall oil fatty acids, which are obtained in the kraft pulping process, are used for soap production. A typical formulation of fats for the manufacture of soap contains 80-90% tallow oil and 10-20% coconut oil [2]. For the manufacture of soft soaps, the potassium salts of fatty acids are used, as are linseed oil, soybean oil, and cottonseed oil acids. High-quality soap can only be produced by high-quality fats, independent of the soap being produced by saponification of the natural fat with caustic soda solution or by neutralization of distilled fatty acids, obtained by hydrolysis of fats, with soda or caustic soda solutions. Fatty acids produced by paraffin wax oxidation are of inferior quality due to a high content of unwanted byproducts. Therefore in industrially developed countries these fatty acids are not used for the manufacture of soap. This now seems to be true as well for the developing countries. 

Further important auxiliary agents for the manufacture of soap are caustic soda solution, calcined soda, sodium chloride, and (for the manufacture of soft soap) caustic pottash solution, potassium carbonate, and potassium chloride. 

Ethylene glycol is the principal ingredient in automobile antifreeze and is also used to make polyester textile hbers such as Dacron. Glycerine is recovered as a by-product in the manufacture of soap and is used in cosmetics. Both glycerine and pentaerythritol are also used in the manufacture of paint and explosives. 

Grave wax" is a term for a crumbly, waxy substance called adipocere. Adipocere starts to form on the human body about a month after it is buried. It forms easily on the fatty parts of the body such as the cheeks, abdomen, and buttocks. The waxy adipocere protects the body from further decomposition and has even been found on 10O-year-old exhumed corpses. This buildup occurs when a body is buried in highly basic (alkaline) soil. The waxy substance is produced by a chemical reaction between the basic soil and fats in the body in a process called saponification. Saponification is also the process used in the manufacture of soap. 

Base liner, in landfills, 25 877 Base manufacture, of soap, 22 736-741 Base metal catalysts, 10 47 Base metal oxide catalysts, 10 100 Base-metal thermocouples, 24 461 Base oils, 15 215 Base plate dental wax, 3 298 specification, 8 300t Bases. See also Alkalis Basic entries cellulose as, 11 266... 

Alcohols are also widely produced from fats and oils, and in some cases one of the oldest techniques utilised in the manufacture of soap, fat splitting, is also used as part of the process. Vegetable oils as well as animal fats are all triglycerides and consequently a key step of the various technologies used in the alcohol manufacture involves the separation of glycerine. Oleochemical alcohols are produced using two... 

Sodium hydroxide (NaOH) is one of the most useful industrial sodium compounds. It is also known as lye or caustic soda and is one of the strongest base alkahs (high pH value) on the household market. It is used as a drain and oven cleaner, and it saponifies fats in the manufacture of soap. It must be used with care because it is also capable of producing serious skin burns. 

Calcium acetate [CalCH COOl H O] is used as a food additive and a mordant to flx dyes in the textile industry. It is used as an alkali (base) in the manufacture of soaps, to improve some lubricants, and as an antimold to preserve baked goods for a longer shelf life. 

Strontium nitrate [Sr(NOj)j], when burned, produces a bright red flame, and it is used in fireworks. During mihtary combat, it is used to make tracer bullets so that their paths can be tracked at night. Strontium is also used in making specialty metals when alloyed with other metals and in the manufacture of soaps, greases, and similar materials that are resistant to extreme high or low temperatures. 

Strontium hydroxide [Sr(OH)j] is used to extract sugar from sugar beet molasses. It is also used in the manufacture of soaps, adhesives, plastics, glass, and lubricants that can be used in very high or low temperature environments. 

Barium hydroxide (hydrate) [Ba(OH)2] exists in several forms and has many uses in oil and grease additives, water treatment, vulcanization of rubber, and the manufacture of soaps, beet sugar, glass, and steel. 

Sodium silicate (Na SiO ), better known as water glass, is one of the few silicon compounds that dissolves in water. Produced at high temperatures (SiO + 2NaOH + heat—> H O + Na SiOjj, it is used in the manufacture of soaps, adhesives, and food preservatives. 

Hexanedioic acid is used in the manufacture of nylon-6, 6. Esters of benzoic acid are used in perfumery. Sodium benzoate is used as a food preservative. Higher fatty acids are used for the manufacture of soaps and detergents. 

Uses. Solvent for oils, resins, ethyl cellulose manufacture of soap, plastics... 

Uses. Manufacture of pharmaceuticals stabilizer in gasoline in production of insecticides and fungicides in manufacture of soaps and surfactants... 

Triglycerides. Triglycerides can be hydrolyzed to give fatty acids and glycerol (Scheme 2). The fatty acids obtained have many industrial uses, mostly for the manufacture of soap. Glycerol is currently viewed as a by-product from... 

The Hungarian soda has been known from the time of the Roman dominion as a product of the efflorescence of the soil. The crude soda or szekso is collected by scraping, and sold to the refiners, who lixiviate it with water evaporate the soln. to dryness and fuse the mass. When cold, the product is broken up and marketed. It is used locally at Szegedin in the manufacture of soap. J. Moser has published an analysis of the raw material, and S. Sehapringer, two analyses of the Hungarian soda. The former s analysis is ... 

Near the end of the eighteenth century the difference between the two fixed alkalies—potassium and sodium carbonates—was known sodium carbonate barilla was largely made from the ashes of sea plants, and potash from the ashes of land plants. The Arabs also had brought some natural soda into Europe, via Spain. These sources were not sufficient to cope with the demand for alkali for the manufacture of soap, glass, etc. Potash was at that time the cheaper and dominant alkali. With the steadily increasing demands for alkali and the very limited sources of supply presented by the incineration of wood, many attempts were naturally made to substitute the base of common salt, because that with a suitable method of extraction nature has provided inexhaustible, abundant, and cheap... 

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