Laundry soap production regarding to this project is batch system. Soap making or the saponification process is done by reacting fatty acids with a caustic alkali, the properties of the resulting soap depending on the mixture of fats used, the kind of caustic alkali and the actual process employed. Caustic soda is most often used but caustic potash, or a mixture of the two, are also suitable. Potash produces a finer product. Sophisticated items such as perfumed bath preparations require prior bleaching and deodorization of the fats to achieve the color, odor and performance features desired in the finished bar.
i) Oil slowly heated in an open pan; concentrated caustic soda solution added, slowly in small quantities at a time, boiling over a period of several hours. The mixture must be boiled under controlled conditions, to ensure completion of the saponification process without over-boiling.
ii) A moderate heat is maintained and each addition of caustic soda solution is allowed to react fully with the oils, before the next addition. Hasty addition of caustic soda solution will result in undesirable graining. If the mass shows signs of separating or graining, further water is added to bring the oil charge to a homogeneous state.
iii) After as much as 5 hours boiling, a fatty layer emerges on top of the mixture. This is mostly half-spent caustic, some of which should be added to the next batch in the pan to speed emulsification. Eventually the soap separates as a loose curd leaving more ½ spent caustic. The mass thickens, gets increasingly transparent and finally assumes a peculiar shiny translucent surface free from froth. If colors are to be added to the soap these should be incorporated before closing the boiling operation.
iv) On settling and cooling, which may take up to 4 days, the soap separates into 3 layers, pure neat soap uppermost, next an impure nigre soap and at the bottom a nigre lye. The pure soap is skimmed off for further processing the nigre soap goes to be re-worked and the lye gets returned to a next boiling batch. Perfumes, if any, may be added after the soap charge in the pan has become cooled a little.
v) Builders and fillers are added and thoroughly crunched in; the soap is then transferred to frames for subsequent cooling and cutting.
A valuable by-product of this process is glycerin, which is usually recovered by chemical treatment, followed by evaporation and refining. (Refined glycerin is an important industrial material used in foods, cosmetics, drugs and many other products.)
If the producer requires alternative technology one can employ Semi-Boiled or Cold processes which are economical and simple ways of making soft or potash soaps, requiring low-cost investment in equipment and no sophisticated skills. In addition to the above two alternatives, continuous processes with automated and compact equipment are widely employed to save installation space, consumption of steam and electric power and labor.