Newsgroups: sci.chem
Subject: Re: used motor oil
From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Date: Thu, 12 Jun 1997 17:50:12 GMT

kinch@ns1.evcom.net (Richard Kinch) wrote:

>Tom Monson (monson@sr.hp.com) wrote:
>: Can anyone point me to a reference, or is anyone familiar with common
>: methods of re-refining used motor oil?  Filtration?  Distillation?
>It's not just contaminated, it's structurally degraded.  You can clean it
>and mix in fresh additives, but it is still inherently inferior as a
>lubricant.

This is demonstrably not true. In fact the rerefined base grades have
a superior viscosity index than the base grades of the original oil.
The viscosity index is a measure of the reduction of viscosity between
40C and 100C, and rerefined oils don't reduce viscosity with temperature
as much as the original oil. I've never seen an explanation, but I
suspect it is because some of the hydrocarbon components with poor VI
are broken down during use, and thus disappear from the rerefined base
grade.

The process of making rerefined oil can, and does, remove most of the
degradation products along with accumulated fuel residues, contaminants
and wear metals. The quality of the product oil is defined by the
quality of the additive package, and in most cases, the rerefined oil
price niche is below the premium grade oils, so a cheaper additive
package is used. If the premium package was used, the rerefined oil
would cost more than the premium grade, and consumers would probably
buy the virgin oil because of the common perception that "rerefined"
is inferior.

To the original poster, from memory, McKetta ( Encyclopedia of Chemical
Processing and Design ) has a reasonable monograph about lubricant
rerefining processes. There was an article about one process in the
Oil & Gas Journal ( 19 Aug 1991 p60 ). There have been concerns about
some contaminants, and a couple of articles appeared in Environmental
Science & Technology ( v.29 p.81-86, v.29 p.87-91 (1995)) demonstrating
that the product was OK. Alternatively, any large rerefining company
should have somebody who could answer polite questions.

      Bruce Hamilton

From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Newsgroups: sci.chem
Subject: Re: used motor oil
Date: Mon, 16 Jun 1997 09:35:41 GMT

Peter Butler  <pbutler1@@ix.netcom.com> wrote:

[ on rerefined oils...]
>After reading the above and 5 more followups I have a question: Why not
>just inject used motor oil into the crude oil refining process?
>Perhaps with a small cleanup first?

Crude oil is currently $0.42/US gallon. Used oil can contain a real
mixture of additives and contaminants that refineries don't usually
encounter in feeds...
1. Extreme pressure additives, usually organometallics - bad for refineries
2. Detergent/dispersant - will hold up water in HC stream
3. Dirt and particulate wear metals - bad for pumps and process plant
4. Soluble corrosion products and wear metals - bad for refinery processes.
5. Carbon and acidic combustion byproducts - undesirable.
6. Viscosity Index improvers - usually polymeric - degrade during processing
7. Bases to neutralise acidic combustion products.
8. Gycols from coolant leaks
etc. etc.

They would have to be removed prior to blending, and most would increase
the refinery's solid waste disposal costs, and the rest would probably
end up in the low $ value residual fuel oil products, as only a few
refineries have the ability to make the more valuable lubricant base
grades - most just crack the heavy fraction ( above components don't do
nice things to cracking catalyst beds ) or blend into residual fuel oils.
Far better to clean up the product into a more valuable rerefined
lubricant base grade than risk the danger of adding a variable feedstock
to a refinery process.

        Bruce Hamilton