Preliminary plant design and economics for the processing of mafura oil soap and castor oil soap from mafura nuts and castor beans.

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University of Dar es Salaam
The perliminary design of a plant for processing mafura oil soap and castor oil soap from mafura nuts and castor beans has been undertaken. The economic evaluation of the venture using standard methods of profitability measures has also been carried out after which useful recommendations have been given. Qual amounts of mafura nuts and castor beans totalling 3,000 metric tons for use in 300 working days per year have been considered. All of this amount is produced in Tanzania. Reducing the oilseeds to thin flakes before passing them to the hydraulically operated cage press is considered worthwhile, however, flaked mafura nuts are cooked subsequent to pressing whereas flaked castor beans are pressed at room temperature so as to get a clear oil not obtainable at elevated temperatures. Datchwise hydraulic pressing is deemed advisable in view of the small quantities of oilseeds processed per day, The oil cakes of mafura and castor seeds obtained after pressing the flakes have been left out in the plant economics calculations but these products may be used directly as fertilizer or as animal feed after being specially treated. An attention is drawn to some features of design peculiar to the handling of castor oil. Due to the fact that castor oil contains a hydroxy triglyceride of ricinoleic <as its main component, it has <acid been found reasonable to dehydroxyllate it using 90w% phosphoric acid. Diatomaceous earth is used as a carrier for the acid and a bleaching agent for the oil. The dehydrated castor oil so obtained is then subjected to the process of selective hydrogenation using nickel as a catalyst. The hydrogenated oil, with an iodine number in the neighbourhood of 20 and the saponification number of about 190, is considered suitable for soap-making. Degumming of the oils has been done by means of water and the resulting oils are neutralized using 4W% sodium hydroxide solution. The soap stock obtained on separation may be processed for inferior soap-making or for fatty acids (obtained by fatty- splitting) used to make good quality soap or sold to other industries for other uses. The value of soap-stock has not been considered in the economics of the plant. Since the oils are not for edible purposes, washing need not be done. In saponifying the oils 20W sodium hydroxide solution is used. Additives, mainly sodium silicates are included in the process, Making of soap by a semi-boiled process has been used although several methods have been surveyed. Framing of the soap-mass and then manually cutting it into bars of standard sizes of 43.5 x 4.0 x 3.3 cm, has been advised. The project has been shown to be viable. The total capital investment for the project is T.Shs.12.6 million and the total product cost is T.Shs.17.1 million. The project has a payout period of 2.2 years and the rates of return on investment before and after tax are 56,0% and 29.£3 respectively. At full capacity utilization, the plant has break-even and shut-down points of 66.7 and 25,0% of plant capacity respectively and the discounted cash flow rate of return is 34.0. The cost of production per bar of soap is T.Shs.6.00, thus, an ex-factory price of T,Shs.7,50 is recommended.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF TS177.R5)
Production engineering, Mafura Nuts, Manufacturing processes
Risasi, R. R. (1982). Preliminary plant design and economics for the processing of mafura oil soap and castor oil soap from mafura nuts and castor beans. Master dissertation, University of Dar es Salaam.