Wednesday, June 1, 2011

OXIDATION HISTORY

A slow oxidation over a long period will produce the same alterations as a rapid oxidation over a short period. The first attack by oxygen upon an oil results in peroxide formation peroxides then decompose into either free fatty acid petrol insoluble acids or the original unsaturated compound or aldehyde. Analysis for any of the decomposition products determines the amount of oxidation which has taken place but this knowledge is far less important than knowledge of the speed at which oxidation is liable to take place.
    Oxidation acids are not removed by most commercial refining processes and their amount is a safe indication of the extent of past oxidation but not of its cause nor of the likelihood of future oxidation .
    Considerable amounts of oxy-acids indicate the existence in time past of a considerable swing of the catalyst anti oxidant balance in favour of oxidation . If the reasons for the presence of oxy acids in an oil have been dealt with the presence of less than 2 % in a vegetable oil is not objectionable.
   The peroxide content of an oil has repeatedly been proposed as a criterion of suitability but it gives no indication whatever of future oxidation tendencies a given value may be due to slow formation over a long period in which case it is harmless or to a quick formation over a short period in which case it is a pointer to danger.