Wednesday, April 10, 2013

Relationship between Saponification Value & Molecular weight of vegetable oil

1. Inversely proportional: If a fat has low saponification value, chain length of the fatty acid will be long.

Sap value= mg of KOH/ NaOH required to break ALL the TG in the oil.
The TG gets break into the Sodium Salts of FA (while unreacted NaOH is calculated by neutralizing with HCl).
So basically, the value is just a measurement of the ml of NaOH / KOH.

Triglycerides with long fatty acids have more mass. Also, the long chain fatty acids have a relatively fewer number of carboxylic functional groups per unit mass of the fat and therefore high molecular weight.  As the mass increases, the saponification number decreases (an inverse relationship). So a given mass of a triglyceride will have a larger number of moles at low molecular weight than high, and accordingly consume a larger number of moles KOH.

2. Sap Value = {(3*56.1*1000) / ([Mean MW * 3] + 92.09 - 54)}

Note: The calculated sap value is not applicatble to fats and oils containing high amount of unap matter, FFA's (>0.1%), or mono- and di-glycerides (>0.1%)

3. Approximate Average MW OR Saponification equivalent
Dividing 56100 by the saponification value an approximate measure of the average molecular weight of the acyl chain can be found (this is known as the saponification equivalent). [D]


MANUAL AVG CALCULATION,vol76,no12,p1415-1419.pdf