Changing the oil in a car every 5,000 kilometers or so seems to be the industry standard (and may well be overkill). But that means a whole lot of pouring and draining motor oil into and out of the U.S. auto fleet: 1.3 billion gallons or so, to be precise.
So what happens to all that used oil—and could it be recycled? After all, reusing that lubricant would not only avoid pumping it out of the ground in the first place, thereby delivering a little energy independence from foreign suppliers, it also might help cut climate-altering greenhouse gas emissions.
ScientificAmerican.com spoke with engineers Joseph Franceschi and James Condela of Universal Lubricants, which just completed a 45.4 million liter refinery in Wichita, Kans., to convert used oil into usable motor oil.
[An edited transcript of the interview follows.]
Can motor oil be recycled—and how?
Franceschi: Yes, oil can be recycled.
In general, you take crude oil and refine it to make a lubricant. This is called base lube stock. Then you have to take that base lube stock and blend it with additives in order to put it into a passenger car. That's what gives it color actually. You're adding an anti-foaming additive, a dispersant and a detergent.
When you put the oil into the engine, it is essentially degraded by heating it, and is also oxidized. As all these additives start to break down, the engine starts to wear more. That puts some heavy metals into the oil. The anti-foaming additive breaks down and you start to get water mixing with the oil and making sludge. The same breakdown happens with the dispersant and the detergent. That's the reason they recommend to change it every X number of miles because of the thermal degradation and oxidation. Oil only has a certain life span.
We clean that used oil by using pretty conventional refinery technologies. One of them is vacuum distillation, which dewaters the oil. Used motor oil comes with somewhere between 5 and 7 percent water in it. The first thing you have to do is get the water out of it.
Then we do wiped-film evaporation. This essentially separates out all the contaminants and additives that are put into passenger car motor oils. Then after that, we go through a hydrotreating process that gets up to 700 degrees Fahrenheit and 1,100 [pounds per square inch]. That infuses hydrogen back into the hydrocarbon molecules and makes it a very high quality re-refined oil.
If you're thinking of it in a very simple way, we're filtering the used oil with very sophisticated technologies and processes.
How much oil is recycled presently?
Franceschi: Most of it is recycled, though small amounts are improperly recycled. The old joke is that if you drive past a quick lube place on Monday mornings, you can see garbage bags full of used oil containers. Things collect back there because people don't want to dump it down a hole or into a sewer.
You're really dealing with a pretty dirty product. It has to be collected properly. We collect 30 million gallons of used oil. … It's one of these industries people don't really know about.
Condela: There's about 1.3 billion gallons of used oil generated in the U.S. each year. Ten percent goes into a re-refining process like ours. The majority of that used oil is collected and sold as a combustible fuel, mainly used in power plants or industrial boilers.
What is re-refined oil used for then?
Franceschi: It's used essentially as a refined crude lubricant. Re-refined oil used to have a bad color associated with it because in the old days they didn't have modern technologies. They did some filtering and poured it over clay. They had these very, sort of, antique technologies. It did not make a high quality oil and it got a very bad reputation.