Re: synth vs. dino Manufacture Techniques

[Richard Beels <beels@technologist.com>]

Well, let's bring it back on-topic then (and I wanted to actually work this
AM, right?).  And I even changed the subject since we all know about
Chinese manufacturing techniques (and if you don't get the pun.....).  :-)

First, the six primary lubrication requirement areas for an engine
lubricant are (remember these):
1.  Lubrication.  Keeping metal away from metal via oil film.  Synthetics
have a greater film strength than a mineral, thus lubricate better.
2.  Cool.  As a result of doing number 1 better, we are creating less heat.
Then what heat that is created is dissipated faster as synthetics dissipate
heat faster than mineral based oils.
3. Detergency.  Synthetics (esters) have a slightly higher level of natural
detergency than mineral based oils.
4. Dispercency.  Synthetics generally have a lower level of natural
dispersency than mineral based oils.
5. Cushion:  Since synthetic lubricants have inherently higher natural VI
(or resistance to thinning with elevated temperatures) the oil film remains
thicker and with increased film strength provides much *better* cushioning
than mineral based oils.
6. Corrosion protection/prevention:  Synthetics have a higher natural
affinity for metals and provide better corrosion protection than mineral
based oils. This also relates to oil film for start-up, shut down.

Full synthetic oils are based on synthesized organic chemicals (more on
that later) as opposed to refined crude oil, and the additives are
generally of better quality and/or higher doses. Crude oil is a mixture of
literally thousands of different molecules, some being excellent lubricant
bases (isoparaffins) and some quite undesirable (volatiles, asphalts,
sulfur compounds, unsaturated species, waxes, metals, etc.). Conventional
mineral oils basestocks are derived from crude by distilling off the light
volatile components and asphalts, hydrotreating out the sulfur, nitrogen,
and unsaturated compounds, and solvent extracting or isomerizing the waxes.
 Unfortunately, the process cannot economically remove ALL of the
undesirable components, and the remaining undesirable "weak links" limit
the life and effectiveness of the basestock.  Hence, mineral oil stocks are
economic compromises which provide quite satisfactory performance in
conventional motor oils, but are not up to the performance capabilities of
the more expensive synthetics.    

Synthetic basestocks are made by deciding which molecules would be best for
the job, and then building those specific molecules from pure basic
chemical building blocks.  The result is a mixture of pure, similar
molecules with no undesirable weak links to remove because they weren't in
there to begin with. The ability to pick which molecules you want in the
basestock allows you to select the strongest, most stable species with
better low temperature flow and lubricity characteristics.  Combined with
the right additives one can build a better oil.  The primary difference is
the chemistry of the basestock, which affects several of the oils
properties.  An incidental difference is the quality of the additives.  

The most common types of synthetic basestocks are PAOs and esters.  PAOs
are mixtures of pure synthetic isoparaffins which have excellent thermal
and oxidative stability (no unsaturates), great low temperature fluidity
(no waxes), and a high viscosity index (no aromatics or naphthenics).  On
the downside, they have poor detergency and dispersency characteristics,
low additive solubility, and tend to shrink and harden some seals. Esters
are similar to PAOs except that the molecules have some oxygen atoms in
them which gives them polarity. This gives esters some advantages over PAOs
like lower volatility, better lubricity, higher oxidative stability,
excellent additive solubility, and good detergency and dispersency.  The
downsides of esters are higher price and a tendency to swell and soften
some seals.

Since the differences between PAOs and esters compliment each other, most
synthetic motor oil formulations contain mixtures of both, mostly the
lower-cost PAO with about 10 to 20% ester to balance off their downsides.
The original synthetic motor oils of 25 years ago were based on 100% ester
(as are all jet engine oils today), but PAOs became more popular in the
late 70s due to their much lower cost.  Today the market is trending toward
severely hydrocracked mineral oils which are even cheaper than mineral oils
- and they are being called "synthetic".

As an aside, polarity provides four important properties:
1.   Polar molecules are attracted to each other, therefore requiring more
energy (heat) to break into the vapor phase. This translates to lower vapor
pressure, lower volatility, and higher flash point.
2.   Polar molecules are attracted to metal surfaces and line up on the
surfaces forming a protective film.  This translates into improved
lubricity and fuel efficiency, and to a lesser degree some wear protection.
3.   Polar molecules are good solvents (detergents) and are attracted to
solid particles, helping to disperse them.  This makes them much cleaner
with respect to varnish and sludge.
4.   The polar oxygen groups provide a site for microbe attack making the
molecules biodegradable.

Synthetic basestocks offer some significant benefits to motor oils.  The
higher thermal and oxidative stability allows longer life at high
temperatures; the lack of waxes and the high VI offer much better flow at
low temperatures; the lower volatility offers less oil consumption; and the
combination of these properties offers better fuel efficiency and some
reduced wear (mainly on cold starts).  They do not, however, change your
tires or wash your windows... <g>

Additives do the rest of the job, providing oxidation control, rust
prevention, acid neutralization, sludge and varnish control, corrosion
protection, and most of the wear protection.  The additives do the same job
in mineral oils, but synthetic formulas usually have a more robust additive
package.  The reason is simple - additives cost 5 to 10 times as much as
mineral basestocks but only a little more than synthetic basestocks.  Since
convention oils are low profit commodities, there is a strong economic
driver to minimize the expensive additives so as to barely pass the
required specifications.  Very often if a test result is "too good", it's
interpreted as an opportunity to cut back the additives!  Synthetic oils,
however, are designed to be the best the company can make (in theory) and
will sell for a much higher price and profit.  Since the expensive
additives are replacing expensive basestocks, the net treat cost is much
lower and the driver becomes higher performance.

Now, to manufacturing.  It's a really simple chemical process. Let's take
polyalphaolefins (PAOs). First, olefins: Linear olefins are straight-chain
hydrocarbon molecules, having from 4 to 30+ carbons, with a double bond
between two of the carbon atoms.  Alpha olefins are molecules with a double
bond at the end of the chain (the alpha position), while internal olefins
have the double bond within the chain. Alpha olefins are easier and cheaper
to make. Olefins are manufactured from ethylene (the plant usually has a
pipeline directly feeding the process) and are done so with a wide variety
of single carbon numbers and blends - each with their own variety of
applications.  PAO is produced by the oligomerization of the olefin,
followed by hydrogenation of the product oligomer.  The physical properties
of the PAO, such as volatility and viscosity, depend primarily on the
molecular weight of the starting olefin and the degree of oligomerization.

Hope this all answers your questions.


Cheers,
	Richard
	88 90Q - <insert pithy witticism here>
	88 Golf GTi - PRO Rally