My wife and I take a vacation every year to the East Coast to celebrate the 4th of July in Washington, D.C. We then head north to Boston, and this year we went on to Maine. We visited some good friends who work as volunteers in the National Park Service and were based at Acadia National Park.
For those of you who may not know, Acadia was donated to the National Park Service by none other than John D. Rockefeller, who made his fortune in oil refining and marketing after Colonel Drake successfully drilled for oil near Titusville, Pennsylvania, in 1859. Originally, the product of most interest was kerosene. It fueled the lamps that provided light to homes and businesses and replaced whale oil. At the time, the residual material left from the distillation of kerosene was used for road paving. As time went on, the crude was further fractionated into the myriad products we use today.
As a simple point of interest, heres one breakdown of what comes from a barrel of crude, courtesy of the California Energy Commission:
Finished motor gasoline (51.4%)
Distillate fuel oil (15.3%)
Jet fuel (12.3%)
Still gas (5.4%)
Marketable coke (5.0%)
Residual fuel oil (3.3%)
Liquid refinery gas (2.8%)
Asphalt and road oil (1.7%)
Other refined products (1.5%)
The standard measure of crude oil, the barrel, is 42 gallons. This measurement is based on the volume of a wine tierce, which was defined in the 15th century by Richard III, then king of England. According to the American Oil and Gas Historical Society, a 42-gallon barrel weighed more than 300 pounds-about as much as a man could reasonably wrestle. Twenty would fit on a typical barge or railroad flatcar.
Given that the crude was Pennsylvania grade, it was very paraffinic and required only minimal refining. It could be fractionated through vacuum distillation and dewaxed using a cold press. Bright stock, which is derived from the residual of the base oil fractionation process, would be treated with propane to remove resinous materials and minimally dewaxed. As more crude sources were discovered and developed, new processes were introduced to produce acceptable base stocks.
Before we go any further with this discussion, there are some definitions that need to be clarified. The terms base oil and base stock get used interchangeably, but they are different. The American Petroleum Institutes Engine Oil Licensing and Certification System (API 1509) defines them as follows:
A base stock is a lubricant component that is produced by a single manufacturer to the same specifications (independent of feed source or manufacturers location); that meets the same manufacturers specification; and that is identified by a unique formula, product identification number or both. Base stocks may be manufactured using a variety of different processes including but not limited to distillation, solvent refining, hydrogen processing, oligomerization, esterification and rerefining. Rerefined stock shall be substantially free from materials introduced through manufacturing, contamination or previous use.
A base stock slate is a product line of base stocks that have different viscosities but are in the same base stock grouping and from the same manufacturer.
A base oil is the base stock or blend of base stocks used in an API-licensed oil.
One of the early discoveries related to engine oil formulations was that different crude sources created base stocks of different quality and performance. Before 1993, each base oil slate required a different additive combination to create a satisfactory finished product. When the API Engine Oil Licensing and Certification System was being developed, one of the major drivers for product development was a means of minimizing engine testing, which is costly and time consuming.
A group was formed to develop a system of base oil identification that would allow formulators to read test data from one base stock to another. One of the principals from that group, Ernie Henderson, has shared a lot of background information on the groups deliberations. Much of what follows comes from Ernies notes.
Ernie stated that prior to 1993, base oils were simply called paraffinic or naphthenic based on crude type. Before then, solvent processing was the primary technology and had been in use for decades. In addition, finished lubricant formulators blended paraffinic base oils from different manufacturers, and substitutions and interchanges were common. The main mechanism to support substitutions was crude oil interchanges.
The original version of the API base oil categories included Group I (less than 90 percent saturates or greater than 0.03 percent sulfur) and Group II (greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulfur). Group III encompassed all other base stocks, including synthetics and naphthenics.
Ernie noted that the API base oil categories were created in 1993, following the introduction of hydroprocessing in the 1980s. This created new and different types of paraffinic base oils. In addition to the classic Group I (solvent or separation processing), it brought into focus the new processing as Group II (hydroprocessing or conversion technology). Several refiners, including Chevron, Petro-Canada and Sun Yabucoa, among others, had introduced Group II base stocks.
Viscosity index was not an issue, as saturates and sulfur were set based on an industry survey of refinery capabilities, which assessed both virgin and rerefined base stocks. The technical association of the European lubricants industry (ATIEL) concurred with the descriptions developed by Ernie and his group.
Today, base oil classifications have added viscosity index into the mix for mineral oils: between 80 and 120 for Group I, between 90 and 120 for Group II. Group III now includes oils with the same sulfur and saturates requirements as Group II but with a V.I. of 120 or higher. Group IV was added for polyalphaolefins, and Group V is now the catch-all category for base stocks that dont fit in the first four groups.
These designations and descriptions are the current working information from which base oil interchange and viscosity grade read-across determinations are made. Without these classifications and what they represent, the cost of engine testing and therefore engine oils would be much higher.
Even though we are still using these definitions, things have not been stagnant. Ernie pointed out that there are continuing innovations in base oil refining. The past decade has created significant innovations and changes within the industry. These include:
Producing and marketing Group IA oils with higher amounts of saturates and Group IB oils with fewer saturates, and Group I+ oils with viscosity index closer to 120;
Group II+ oils with high V.I., typically 112 to 119, created by hydroprocessing or dual solvent and hydroprocessing;
Developing oils marketed as Group III+ (V.I. at 130 or higher), Group III3.5 (V.I. of 130-140) and Group III synthetics, which most closely resemble Group IV oils;
Group IV PAOs made from C8 or C12 feeds, and Group IV+ with V.I. 5 to 15 higher than conventional PAO;
ATIELs debut of Group VI in 2004. These are poly-internal-olefins, which are similar to PAOs but with higher V.I.
These subsets within API groups have been identified to meet new performance demands, take advantage of base oil interchange rules and differentiate products in the marketplace. As an industry, weve seen the use of terms like Group II+ and Group III+ to describe some improvements in performance properties. However, these are not recognized by API and are simply considered to be Group II and Group III, respectively.
Alongside these innovations, some interesting challenges have begun to surface. For instance, General Motors engineers raised a question at the ASTM meeting in Denver in June. They are concerned that similar engine oils containing different Group III base oils may be giving different results in engine tests. Another issue is volatility, which has become an important property. Are there other factors to be considered, like low-temperature cold-cranking simulator viscosity or a more detailed comparison of compositional properties?
Given all of the above issues, as well as the advanced state of base stock refining and the introduction of new materials such as gas-to-liquid base oils, it may be time to expand the table of API Groups. Ive never shied away from taking things to the next level. My take on the base stock table is above (with apologies to Ernie and others).
As best I can decipher it, base oils are moving toward better oxidation resistance, lower volatility and viscosities suitable for new lower-viscosity engine oils. Its going to be a lot of fun for refiners and formulators, but the end result will be much better engine oils.
Industry consultant Steve Swedberg has over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at firstname.lastname@example.org.