Used Oil Cleaning and Reusing

RRedistillation?

Many years ago I supplied pumps to a company that recycled used oil. Their process:

Add 1% Sulphuric Acid.

Add 10% Fullers Earth.

Recirculate through a heater to about 350 deg C.

Pump through filters.

I'm not sure how easy or practical this would be for you, but it worked for them (though it didn't do the pumps much good!).

Your process will probably benefit from steps to remove water and other substances that have different density than the oil that the filters are missing.

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If you have time, settling tanks will help.

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Heated settling tanks would be better.

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Centrifugal oil purifier would be faster and can be very effective.

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Vacuum de-watering systems can be very effective and fast at removing water and volatiles, but they are not cheap.

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Centrifugal oil purifier would be the first thing I would want to add to the process.

Where the oil is used makes a big difference. Trying to recycle used motor oil is a lot different than say recycling lubrication oil (which I take Metamol 68 oil as being used for?).

You seem to be on the right track, but what is the oil you are trying to recycle being used in? This may give us an idea of what the dull colour is being caused by (chemical state change, unwanted molecular bonding (clumping) byproducts, unfiltered impurity's, etc).

Not really my field but the additional information may help someone else here with your question.

You might try going to a 5 micron mess. Caution thou, below 5 micron you can begin to remove some additives from the oil. You need to check with the manufacture of the product your using and check the specification on their additive package before proceeding.