Introduction

Soap is an important surface- active agent and it is chemically the alkali metal salts of long-chain fatty acid.  The most commonly used fat and oils for production of soap through saponification  reactions are  animal fallow, coconut oil, and palm oil, palm kernel oil and linoseed oil.  Similarly, potassium and sodium hydroxide are widely used as caustic alkalis  for the purpose [1].  The demand  for these materials for various other domestic and industrial application are high resulting in their high costs.  Consequently, there is a need to explore unconventional  sources of oils and caustic  alkalis for the production of  soap and to determine by means of kinetic approach, the optimum  reacting conditions for efficiency and utilization of the process.  Several workers reported the use of caustic alkalis from ash for soap production and the effects of  a number of factors, notably temperature, ash particle size, etc on the  yield of  caustic alkali [2,3].

The physico-chemical  characteristics of seed oils from plant in the world have been reported [4-6].  One of such oil is obtained from a Treculia africana and has saponification  value of 1960 5-210.  It is found mainly in the south east and south-south zone in the country.  The percentage of seed oil  is significant.  The seed is a rich source of protein,  carbohydrate, vitamins and  also a possible source of raw materials for  the production of vegetable oils, soaps etc [7].

This present study is aimed at determining the appropriate  reacting conditions that will improve the viability of  the saponfication  process of locally sourced alkali  with an unconventional source of oil via kinetic studies.  It will also establish a suitable alternative to the usual palm kernel oil or in special case, coconut oil for use for quality toilet soap production, using raw materials t which  are locally obtained in Nigeria.

Materials and Methods

The breadfruit seed used was obtained from a local market in Onitsha, pulverized with a grinding  machine.  A measured amount of  the pulverized cake was introduced into a thimble  and the solvent (n-hexane) 100m/s was poured into the extractor flash and heat was applied.  It was  allowed for over 20-25 minutes for complete extraction of the oil.  The procedure was repeated severally to obtain much quantity of  the oil.  The miscella was then distilled in an oven at 105⁰c for 2 hours to recover  the solvent and to concentrate  the  oil via distillation process [7].

The alkali use in this study was obtained by dissolving  120g of sieved ash of burnt female palm bunch in a distilled water agitated for 5minutes and allowed to stand for 12 hours.  The material  was decanted and  the brownish filtrate was heated.  The temperature was maintained at 40⁰c  for 10 minutes.  The bleached alkali was separated from the spent earth by filteration using whatman A1 (24cm) filter paper on conical flask to recover the  alkali (KoH) which was then  water-clear.  The concentration of the solution of  local alkali (ngu) produced was determined after bleaching the ngu extract with active  earth to water-clear.  It was further concentrated by boiling and evaporation for some hours.  5mls of  the solution of Ngu extract was titrated against freshly made 0.5m HCL for the kinetic study, three different concentrations of  the  alkali extract was used (1.59mol/L, 2.58Mol/L and 5.08 mol/L).

The fully boiled process of soap production was used in the saponification of  traculie African  oil using local alkaline  extract.  50ml of the oil was measured into a beaker and a steam generator was introduced to raise the  temperature  to about 710⁰C  (This exposes the  free fatty acids present in the oil).  After 2 minutes of heating, the oil was left to cool at 40⁰C.

5g of  the oil dissolved in 20ml of the fat solvent (ethanol)  was introduced into a beaker containing  20ml of 5.08mol/L of the KOH (Ngu) and the mixture was constantly stirred.  An aliquot, 5ml of the broth was taken every 3 minutes into a conical flask that contain 20ml of 10⁰C old distilled water and shaken.  The content was then titrated against  0.5MHCL to a phenolphthalein end paint and the litre values recorded.  The experiment was repeated for different  concentration  of the KOH (Ngu); 2.58mol/L and 1.59/Mol/L respectively.

5ml of  the saponifying  mixture was withdrawn at interval of 3 minutes and titrated  against 0.5MHCL as above to determine the  residual concentration of the KOH in Ngu, until the concentration reduced to a constant  value when the  saponification was complete [5-8]

With the  values appropriate plots were produced (KOH/(KOH) against time) to obtain both the order of reaction, reaction constant  Ko to confirm the  result, the  half life plot was also produced.

Results and Discussion

In the reaction between the treculia Africana (Bread fruit) oil and Ngu (KOH) a local alkali extract, the dominant fatty acid contained in the oil are linoleic and oleic acids.  These fatty acids were hydrolysed according to the following steps.

Splitting the oil

(18H₃₁COO)₃ C₃H₅ + 3H20        (18H₃1COOH + C₃H₅COH)₃

The above equation refers to the splitting of the oil into fatty acid and glycerol

 CkoH₀/CkoHt) versus time (t), produced straight line (fig 1-iv).  This shows that the reaction between the breadfruit oil are Ngu (KOH) was essentially first order and the rate constant (kc) averaged to 0.0696min^-1.  calculating  the half life based on the concentration (K_OH0=2.58mol/L) as in figure II, the result  obtained confirmed a typical first order reaction with t½ = 9.96 minutes [8].

The reaction (saponification process) was observed to increase with initial concentration of the Ngu.  This was why the saponification of breadfruit oil with Ngu took shorter time to go to  completion.  This is thus an evidence to prove that saponification of breadfruit oil and Ngu (KOH) was concentration and time dependent.  Nevertheless, a high quality soap was produced in the process [7,9]

Figure iv show, the effect of changes in concentration of KOH with time at various initial  concentration of KOH.  When C_koH0 = 5.08ml/l, the  saponification reaction between breadfruit and KOH (Ngu), came to completion at a faster rate and it took the total alkali 23 minutes to be consumed in  the reaction [10].  On the other hand, as the relative initial concentrations were reduced by serially diluting the KOH, with distilled water, to obtain lesser concentration of KoH₀ = 2.58ml/L and CkoH₀ = r.59mol/L respectively.  The duration of the reaction was progressively becoming slower with time limit extending to 33 and 39 minutes respectively.  This phenomenon indicates that the reaction is evidently concentration dependent[8].

When a graph of InCKoH₀/CKoHt was plotted against time for each of the concentrations, the curves obtained (figure I-III) were straight lines with postive magnitude.  The calculated concentrations at instant for the reactions  ln(C_KOH/C_KOHt), while the curves for the order of reaction and reaction constant are shown in figure I-II, the half life curve was produced in figure IV. [10].

Conclusion

A first order reaction was obtained in the saponfication of breadfruit oil with Ngu.  The average rate constant was 0.069 min^-1. and the half life value of 9.96 minutes, the reaction rate was a function of the initial  concentration  of local alkali.  The soft soap produced could be modified into a hard soap.  Notwithstanding  the overall cost of production of a high quality, long lasting and wonderful lather  soap using these raw materials makes it economically attractive.  The results of  this work is reliable for use in the design of a hydrolyser for commercial processing.

References

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2. J.C. Eremosale and C. O. Eremosale (1993), studies on the chemical composition and physico-chemical properties of seeds and some wild plant. Plant food.  Human Nutrition 43. 251-258.
3. J. C. Eremosale C. O. Eremosele A. O. Akinonye and T. O. Koralafa (1994); Characterisation of oils and chemical analysis of the seeds of wild plant.  Plant foods.  Human Nut.  461 361-365.
4. A. O. Kuye and C. Okarie (1990), Factors affecting the use of palm bunch, such as ash-a source of alkali for soap production, Ife Technology 2:33.
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6. Nigeria Industrial Standard (1973), Specification for toilet soap. Nigerian Standard Organization UDC 99.
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9. Shrieve R. M. (1977), Chemical Process Industries McGraw-Hill New York.
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