Carbon Washing Properties and Practice

A lot of clients ask me if they should apply heat and longer times when carbon washing. In my personal experience I have found that shorter times at ambient temperature works best.
When I perform these experiments, I consider the amount of solvent present, the mass of the oil, the provenance, the starting color, possible contaminants etc.
As you will see in the photo, this oil was very dark to begin with. It was dissolved in a 4:1 ratio of ethanol to winterized oil.
 When one is carbon washing, the aim of the practice is to remove dark colorants such as chlorophyll in particular. However, one may also take up other compounds such as carotenes, sugars, active ingredients, anthocyanins. Some of the compounds that contribute to the color of oil are also antioxidants. If these antioxidants are removed via carbon or bleaching, the oil will start to darken.
It is for this reason that we see the dark line of oxidation on otherwise very clear oil. There is no longer antioxidants present. So, in “water-clear” oil, one may see a dark line of oxidation on the surface. There are primary and secondary oxidation products (peroxide and anisidine value) that can form when using adsorbents.
So, these are the things I take into consideration when answering these questions. A short wash at ambient temperatures is what I have found to work best.
If you are trying this and not seeing the results you want, you can do a few things:
-Increase the percentage of carbon used
-Increase the exposure time for reaction
-Apply heat
Process optimization takes time and one must be patient to achieve desired results. Welcome to science!
I should also point out that the clearest, colorless oil I have made was without carbon at all. If one can extract little pigmenting compounds to begin with, one can avoid this process altogether. I find very cold extraction yield the least colorants. In addition, carbon will always cause some reddening of the oil, and it will be very hard to achieve “water clear” results with those colors present.
My protocol:
1. Mix ethanol and oil together in 4:1 ratio
2. Measure out 5% off the mass of the oil and ethanol combined (yes the entire mass of oil and ethanol combined. Yes, ethanol is a volume. This is irrelevant because this is qualitative not quantitative).
3. Mix carbon into slurry in oil and ethanol and react for 10 minutes.
4. Filter through 5 micron system (I recommend my own system of course!)
5. Repeat as needed.
Specifications for the carbon I use:
Iodine Number, mg/g  900 min 
Moisture (As packaged), wt%  10 maximum
Particle Size Analysis <325 US Mesh [0.045 mm], wt% 65–85 Typical Properties 
Molasses Number: 250 
Apparent Density: g/ml  0.37 min 0.43 max 
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