The oil product you buy starts as a base oil. The base oil makes up about 85% of the oil you buy. The base oil can be refined from crude oil, chemically (synthetically) manufactured, or a blended combination.
Base oils that are refined from crude oil are colorless and pretty much odorless and are sold to the public as mineral oil. The crude oil is a combination of a lot of different chemicals, ranging from light gasoline types of fuels to waxes and tars. When you heat the crude oil, the gasoline and diesel oil boil off pretty early. Unfortunately, the mineral oil, paraffin, wax and tar molecules are all hooked up with each other, and it's not so easy to separate them from each other. Also, the crude oil contains the aforementioned aromatics, which are quite bad in your oil: they are very reactive, and when oxidized they cause all kinds of problems. Refining oil means trying to remove the bad stuff, while leaving the good stuff. The more bad stuff we remove, the better the oil works.
The simplest way to refine oil is to process it with a clay, a material a lot like kitty litter. The clay will soak up much of the aromatics and sulphur and nitrogen compounds. Then, you dilute the oil with solvent like MEK (Methyl-Ethyl-Keytone) and/or Toluene (that's the stuff in model airplane glue that's so popular with teenagers), and freeze the oil. The good stuff will mostly stay liquid, and the waxes will solidify and can then be filtered out. This clay-solvent refining process has been around since about 1930.
Oils refined with the clay-solvent process contain a fair amount of paraffin and wax. These molecules cause several problems in an engine: they sometimes fall out of solution, leading to buildups in your engine that must be cleaned out somehow. Also, as these molecules get hot they thin out quite a bit, much more than mineral oil, so they make the oil's high temperature performance rather poor. Finally, at low temperatures the waxes and paraffins thicken the oil so much that you really couldn't call it a lubricant. If you're curious about this, buy a cheap quart of straight 30wt oil and put it in your refrigerator or freezer over night. You'll be amazed at how thick it becomes. More than half the motor oil sold in N.America in 2004 is made from base oils refined with the clay- solvent process (I like to call it the Kitty-litter and Kerosene refining method), but I don't think this is the type of oil you want to put into an engine you love. These oils are roughly 85% good stuff (oil) and 15% bad stuff (paraffin and wax). To put this in perspective, think of taking a gallon of really excellent oil, and melting a 12" dinner candle into it.
In 1959, Chevron developed a new method of refining base oils called Hydrocracking, where you process the raw oil at high temperatures and pressures with hydrogen and various catalysts. In Hydrocracking, many of the paraffin and wax molecules are broken up into mineral oil molecules, which increases the performance of the base oil dramatically. Also, far more of the aromatics and sulphur and nitrogen compounds are removed from the oil.
Since 1990, Chevron's process has been improved. In 1993, Chevron invented the Hydro-Isomerization process, where wax and paraffin molecules are reshaped into useful lubricants instead of simply being broken up into smaller molecules. By increasing the severity of the hydrocracking process, increasing the temperature and pressure and processing time to process more and more of the unwanted wax and paraffin molecules, the oil's low and high temperature performance and resistance to oxidation can be improved to the point where the distinction between mineral oils and synthetics becomes blurred. Chevron now licenses this process, called Iso- DeWaxing. This process of oil refining is becoming more and more popular, and in 2004 accounts for almost half of all base oils. Iso- DeWaxing not only produces much higher-performance oil, but also allows you to start with lower quality crude oil, making us less dependent on the few countries that happen to produce the purest crude oils.
Jan. 17, 2018