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Posted by D Sherman [24.32.202.83] on Monday, April 26, 2010 at 12:12:27 :
In Reply to: After Reading Mr Joes Question On Oil posted by copey [206.80.245.135] on Monday, April 26, 2010 at 05:28:40 :
Wikipedia has an excellent article about synthetic lubricating oils. It's rather technical, but it has to be. The gist of it is that there are several fairly different synthetic bases used in different brands of synthetic oil, but they're all made by starting with simple, pure organic molecules like esters and olefins and building them up into larger molecules that are suitable for lube oil. The starting molecules are still usually derived from petroleum. With regular lube oil, the manufacturing is more a matter of fractionating the crude oil and removing the parts that are too light or too heavy for lubricating purposes, which still leaves you with a complicated soup of different kinds of molecules.
So, I think the main difference is the purity of the base. With synthetic oil, the chemists can get precisely what they want, whereas with ordinary mineral oil, they have to work around a range of molecules, some of which they'd rather not have. In both cases the additive package comes later, and in both cases the ultimate source is still fossil hydrocarbons.
As for the old claim about Pennsylvania oil being better, I noticed a long time ago that "Quaker State" oil was only advertising that it was made from "pure Pennsylvania-grade crude oil". That's sort of the difference between "chocolate cookies" and "chocolatly-flavored cookies", in marketing lingo. As I understand it, crude oils everywhere are classified as either "asphalt base" or "paraffin base". Paraffin-base crude makes the best lube oil, whereas asphalt-base crude is the easiest to make gasoline from. The oil they used to get out of Pennsylvania was paraffin base, and so it developed an early reputation as a superior lube oil, especially when refining was fairly primitive. I've read of the oil from shallow wells being used directly to lubricate wagon axles without any refining at all. I'm pretty sure the West Texas and California crudes are asphalt base, and they were the main cheaper competition for Pennsylvania oil in the early days.
The synthetic oil Germany used during the war was made from coal by reacting it wish steam at high temperature and pressure in what's called the Fischer-Tropsch process. I'm not sure what kind of lube oil they can get out of that system. I do know that part of the reason Germany focused so much research on jet turbines late in the war was that it was very hard to get decent av-gas out of their Fischer-Tropsch process, but turbine fuel was easy to make.