Lube Notes: Petroleum Oil Production and Oil vs Synthetic

Volume 1 Issue 3 - Lubrication

Lube NotesComparing Synthetic Oil vs Conventional Oil

If you read the first two installments of Lube Notes, you have probably come to realize that I am gradually equipping you to evaluate lubricating products including a comparison between synthetic oil vs conventional oil. I am convinced that understanding some basic principles of lubrication can free us from believing everything that we read or hear. In this issue, I will briefly explain how petroleum oils are refined, introduce synthetic base oils and explain motor oil’s classification system used to assign quality levels to finished base stocks.

Petroleum Oil

Oil refinery products from a 42 gallon barrel - click to enlarge

Crude oil, truly today’s black gold, comes from nature as a dirty blend of hydrocarbons and contaminants of every kind. The job of the refinery (see figures one (page 17) and two (page 18)) is to clean this mixture and then crack it into various fractions for specific use. Crude oil typically comes with inorganic salt crystals and water mixed into the oil. It is necessary to remove this salt and water. This removal is accomplished by adding even more water and then allowing the crude mixture to settle. The oil is then heated by a large furnace until it becomes part semi-fluid and part vapor. This mixture then proceeds to the atmospheric tower, the heart of the refinery. The semi-fluids become asphalt and other derivatives while the vapors condense at various levels in the tower depending upon molecular weight. The portion of the vapor with lower molecular weight separates immediately, including kerosene and diesel. While diesel is derived from the first stage of the refining process, today’s ultra low sulfur diesel requires an extra step to remove sulfur (this step seems to be an excuse to raise the price). Vapors with higher molecular weight must go through an additional process to further crack – or separate – the oil into a greater variety of components or fractions as they are called. Lubricating oils – the fractions with which we are particularly concerned – are made from these latter, heavier fractions of the crude remaining after the gas oils have been removed. (Of note, recently refineries have developed methods to effectively use the heavier lubricating oil fractions for making gasoline. This competition for the portion of crude oil that previously was only usable for lubricating oils is one of the reasons for the rapid rise in the cost of petroleum lubricating oils.)

Crude oils from different regions of the world can be different with some being naphthenic and paraffinic. The paraffinic are much better feed stock for lubricating oils. Naphthenic oils contain no wax and are superior in cold flow applications. All crude oils contain roughly the same mix of hydrogen and carbon: 83 to 87 percent carbon and 11 to 14 percent hydrogen. Oxygen, nitrogen and sulfur round out the elements, with various metallic compounds also trapped in the oil. When dealing with lubrication qualities, it is important to consider the variation of molecular structure – from one molecule to the next – within the same sample of crude. Paraffinic molecules come in various carbon and hydrogen combinations to be sure, but to grasp the near-infinite molecular arrangements, consider a typical oil molecule of 25 carbon and 52 hydrogen atoms: this compound can occur naturally in any of 37,000,000 different molecular arrangements.



maxxTORQUE in Print

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