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Used Oil Re-Refining: Two Main Processing Steps
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Used Oil Re-Refining: Two Main Processing Steps

Many years ago, re-refiners had difficulty recycling used oil to produce good-as-new lubricating oil products. But starting in the 1970’s, a series of technical innovations enabled the recycling industry to overcome the challenge, and re-refiners began to produce top quality lubricating products. All of the firms in our industry begin the re-refining process by utilizing a technology that is borrowed from the crude oil refining industry: vacuum distillation. Vacuum distillation is followed by one of two technologies that produce high quality re-refined base oil[1]: a) solvent extraction or b) hydrotreating.



Distillation
is a common processing technology, used not only in petroleum refining, but also to produce grain ethanol – not to mention whiskey and rum. The main idea is that different compounds have different boiling points, and if you boil a liquid you can get different components to separate based on these boiling points. As this is applied to used oil recycling, the lube oil is boiled away from some of the heavier compounds, leaving behind an asphalt residue that is marketed for paving applications. At atmospheric pressure, lube oil has such a high boiling point that it would tend to break down before it vaporized – but if you boil it under a powerful vacuum (similar to the vacuum that astronauts experience in outer space), the boiling point is reached at a lower temperature, preserving the integrity of the lube oil molecules.

The material that emerges from the vacuum distillation process has many of the properties of lube oil, but it still includes some contaminants.

Hydrotreating: The Hydrotreating technology removes contaminants by exposing the oil to hydrogen gas, at very high pressure and temperature, in the presence of a catalyst. The catalyst promotes chemical reactions that remove trace metals and other contaminants from the lube oil.

Solvent Extraction: The solvent extraction process removes contaminants from the distillate by using an environmentally compatible solvent. At the same time, the valuable and reusable components of the oil are retained. The solvent used is also recycled and can be used again as often as necessary.

Most virgin lube refineries use these same processing steps (distillation and hydrotreating or solvent extraction) to make lube oil. It just makes sense that re-refiners that follow these same steps have the capability to produce lube oil that is equivalent to the lube oil made from virgin crude!

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[1] Most re-refiners in the USA use hydrotreating technology. The AVISTA OIL Group uses its exclusive patented technology in its three plants (Germany, Denmark, and USA); Avista technology is based on the Solvent Extraction Concept.

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