I'm researching about paraffin wax oxidation. We're experiencing a phenomenon of lost of colour in the hydrotreated waxes.
What kind of oxidation phenomena can I have in a hydrotreated paraffin wax?
Has anyone experienced this problem with paraffin waxes?
Answers
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06/10/2009
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keith bowers, B and B Consulting, kebowers47@gmail.com
Color degradation of uninhibited hydrotreated 'waxes' is NORMAL if they ever are exposed to even trace amounts oxygen (air).
If wax (both crystalline and micro-crystalline) are hydrotreated by typical refinery fuels type catalysts and operating conditions to meet US FDA specifications, all the 'natural' oxidation inhibitors (like phenols) are removed but some unstable molecules are usually left in the product. 'Color Stability' and Oxidation Stability are usual Q/A tests to measure those properties of the product wax.
Oxidation is a free radical initiated and perpetuated reaction. Low ppm levels of 'color bodies' are sufficient to degrade the measured color significantly.
If you think about it, liquid waxes (normal paraffins) have extremely high 'cetane numbers', which is a good measure of just how easy it is to start oxidizing (burning) them when in a hot environment. The 'Cetane number measures the 'delay between start of fuel injection and ignition' in a special diesel engine.
It takes only very small amounts of 'free radical scavengers' to stabilize the color. FDA approves use of 'vitamin E' for this purpose. Lower cost additives are used for non-food grade white oils and waxes. 'BHT is one widely used in foods for this purpose.
Often in severe hydrotreating of waxes, it is necessary to employ post hydrotreating processing to achieve color stability due to small amounts of unstable complex molecules remaining. Treating with concentrated sulfuric acid is often used, and is 'clay percolation' with fresh activated 8-14 mesh bauxite at low rates. Both process remove polar and olefinic molecules that cause color degradation on contact with air. Hydrotreating with platinum catalyst and pure hydrogen is also often used in lieu of the two previous processes where spent clay regeneration and ultimately disposal and recovery and regeneration of the sulfuric acid present difficulties.
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06/10/2009
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Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
I suppose, the oil associated with wax may develop color fast. It may do so even during storage.
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