April 4, 2013

Re-refined Engine Oil
by Edward Eckert, CLS, OMA
Diagnostics Manager

I have always performed oil changes on my vehicles. Once the corner of the garage was full with jugs of used oil, it was on to the recycling center or auto parts store for disposal. The EPA estimates that if all American do- it- yourselfers recycled their oil, it would be enough oil for greater than fifty-million cars a year. 1.3 billion gallons of used motor oil is produced by drivers in the U.S. annually. Unfortunately, the EPA also estimates that 200 million gallons of oil are disposed of improperly or illegally. It takes the amount of used oil from only one oil change to pollute one-million gallons of fresh water. When engine oil is disposed of properly, it’s recycled for many different applications; making marine fuels, fuel for industrial/utility furnaces and boilers, and mixing with asphalt for road paving.  The engine oil is recycled but in a form that is not “renewable” but it can be a renewable resource by re-refining it.

Engine oil is a complex mixture of approximately 85% base stock, and 15% additives. Base stock is refined to different viscosities. Based on the viscosity grade and type of engine oil, the proper base stock is selected then blended with various additives. Viscosity improvers, anti-foaming agents, dispersants, detergents, and corrosion inhibitors are all additives to name a few. When new oil is put into service, it undergoes another complex chemical change due to thermal stress, contaminants, acidic by-products from combustion, and mechanical stress. Engine oil additives do deplete, but the base stock maintains its physical properties and lubricity. Oil does not “wear out” it just gets dirty. Re-refining engine oil removes all the remaining additives, impurities, and contaminants, and the final product (base stock) is as good as virgin base stock refined from crude oil. In fact, out of a 42 gallon barrel of crude oil, only 3 - 6 % is refined for base stock in lubricants. When re-refining used engine oil, 1 gallon produces 2.5 quarts of final product. 10-15% of used motor oil recycled is re-refined in the U.S.

The processes today of re-refining used engine oil has greatly advanced with the use of modern technologies. The recycled product is run through vacuum distillation to remove water and other contaminants. After vacuum distillation it’s run through a wiped film evaporator (WFE) to remove any remaining contaminants and additives. The WFE is used in many industrial applications that process pharmaceuticals, foods, and chemicals. It then goes through the hydrofinishing process using hydrotreating reactors up to three times, to infuse hydrogen back into the hydrocarbon molecules. The finished product is a highly refined and high quality base sock, ready to be blended with additives and used again. Rerefined oils go through the same strict refining, blending, and performance standards applied to virgin crude oil. Re-refined base stock is not only used for motor oils, but also transmission fluids, hydraulic oils and gear oils.

API-licensed re-refined oils must undergo rigorous testing (cold-start, pumpability, rust-corrosion, engine-wear, and high-temperature high shear viscosity tests) just like virgin crude oils.  The API ensures all engine oils that display the sunburst symbol with the API classification, consistently meet performance specifications. In used oil analysis, the test data for oils that use re-refined base stock versus virgin crude oil base stock are no different. Routine oil analysis testing cannot tell whether oil is re-refined or not.

Oil has the potential to be re-refined again and again. Rerefining is an energy-efficient and environmentally beneficial method of managing used oil. Again, lubricating oil does not wear out, it just gets dirty.


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