Two decades ago, it would have been incomprehensible to imagine base oil viscosity index requirements for some applications at 120 or above. Additives were used to increase V.I. for engine oils, and base oils didnt need to be higher than 95 to 100 V.I. for almost any applications. In fact, when the API Engine Oil Licensing and Certification System defined the base oil Groups I through V in early 1993, no Group III base oils (120 V.I. or greater) had been commercialized.
Yet here we are today, looking at the possible need for 125 V.I. to 130 V.I. or even higher – before additives are incorporated – to meet future requirements for low viscosity SAE J300 engine oils. What will this mean for base oil refiners and for global base oil supply volumes?
These potentially very high V.I. requirements do not affect all base oils, all engine oils or even all passenger car engine oils. Heavier base oils can be used to formulate historical grades such as SAE 10W-30 and 10W-40, and the Noack volatility limits can be easily met using a 5 centiStoke or 6 centiStoke base oil. The need for higher V.I. base oils specifically applies to low viscosity engine oils such as SAE 5W-20, 0W-20, etc., where a 15 percent Noack volatility is required on a light base oil (about 4 cSt) to meet ILSAC GF-5 specifications.
What does this have to do with V.I.? Everything.
The V.I. of a base oil is a great quality surrogate to indicate a base oils oxidation stability and volatility. The higher the V.I., the better the oxidation stability and the better (lower) the volatility for a given viscosity base oil. The reason for this correlation has to do with isoparaffin molecules, which are more stable under heat and pressure and are less volatile relative to other molecules. Figure 1 (page 32), shows the relationship between volatility and V.I. for base oils in the 3.8 to 4.0 cSt range.
The gold bars represent the range of Noack volatilities measured in various 4 cSt samples across the industry. As V.I. increases, the volatility improves (decreases). This graph shows that 115 to 120 V.I. is required to reliably meet a 15 percent Noack volatility on a 4 cSt base oil. This sets the stage for using API Group II+ (115 to 118 V.I.) and Group III oils for blending todays low viscosity engine oils.
What about the next generation of passenger car engine oils, ILSAC GF-6? Or GF-7? At this stage in development, it is unclear whether a 3.8 to 4.0 cSt base oil will be required to have 15 percent, 13 percent or even 11 percent Noack. If a 13 percent Noack was required, Figure 1 shows that a 125 to 130 V.I. range would be necessary to reliably produce on-spec base oil.
Using the assumption that a 13 percent Noack may be required in future passenger car engine oil categories, My Energy developed a model to predict the refinery yield impact of going to higher V.I. levels. The Group II base oil plants in the U.S. are not producing Group III viscosity index levels, due to the combination of crudes being run and the refining processes used here. The resulting low base oil yields would render it economically unattractive to operate at higher V.I. levels.
Instead, it is more economical to import Group III material from Asia or the Middle East, where a full diet of local and/or imported, waxier crudes render the fuels hydrocracker bottoms more easily upgraded to 120 V.I. When the need arises for higher V.I. material to meet lower Noack limits, the likely plants to rise to the challenge are existing base oil plants already at the 120 V.I. level. Figure 2 shows the estimated capacity of existing Group III base oil plants by region that are most likely to raise V.I. level.
Three base oil producers already make Group III+ (an informal designation understood to mean higher than 130 V.I.) and are represented in Figure 2. Petronas (Melaka, Malaysia), Pertamina-SK (Dumai, Indonesia) and Shell-Qatar Petroleum (Ras Laffan, Qatar) already produce 130 to 135 V.I. material through hydro-isomerization of their high-wax feedstocks. It is assumed that the output from these plants would remain unchanged when next-generation engine oils require a lower Noack, since they already achieve 13 percent Noack or lower on their 4 cSt offerings.
The most economically viable operations for increasing V.I. to meet lower Noack requirements make up the Group III capacity shown in Figure 2. Increased operating intensity, by virtue of higher temperatures and higher hydrogen consumption, will result in higher V.I. product. However, this will come at the expense of lower base oil yields, higher operating costs and shorter catalyst life. Each Group III plant was evaluated, taking into account current crude slates, to assess the yield penalty for increasing from their current V.I. levels to a 128 to 130 V.I. range in order to meet a 13 percent Noack limit on their 4 cSt material.
The results of this evaluation are shown in Figure 3 for each region, assuming the existing Group III operations move to Group III+ viscosity index levels.
The base oil yield impact from raising V.I. to meet a 13 percent Noack target on the 4 cSt stream is significant. Output is reduced by almost half in Western Europe and Asia, and by about one-third in the Middle East. For Group III production in Western Europe, the model assumed that crudes run in refineries producing Group III base oil were primarily North African, Urals blends, select North Sea crudes, or Arab Light. The model used Arab Light crude for the current Group III base oil plants in Asia, since this crude represents the majority of current crude imports to these fuels refineries. For the Middle East model, it was assumed that current crude feed could be economically supplemented with one of the higher wax crudes segregated from the Abqaiq, Berri, Shaybah or Khurais fields in Saudi Arabia, or with waxier United Arab Emirates crudes such as those from Murban. Improved feed helped mitigate the yield loss in the Middle East when V.I. was raised.
This is a screening quality exercise meant to show the base oil yield impact of a decision to move from current 15 percent Noack to 13 percent Noack volatility for low viscosity engine oils. Additional base oils in the 3 cSt range, as well as additional diesel, will be produced – at the expense of base oils in the 4 cSt to 8 cSt range. More detailed studies are required to fully assess the impact on each refinery based on its configuration, current feedstocks and potentially waxier feedstocks, should they be economically available and transportable to the refinery site.
The global base oil refining industry has become specialized in terms of market sectors, whereby Group I and II refineries produce base oils used in all demand segments, with the exception of the lowest viscosity passenger car engine oils. Group II+ and Group III base oil refineries are providing the 4 cSt material required to meet todays 15 percent Noack volatility specification for low viscosity ILSAC GF-5 passenger car engine oils.
As engine oil specifications continue to become more stringent to meet emissions and fuel economy standards, base oil refiners will have tough decisions to make regarding trade-offs in yield and quality to meet even lower Noack standards in the future.
Based in Hummelstown, Pa., Amy Claxton, P.E. is a registered professional chemical engineer and owner of My Energy Consulting and Training. With over 30 years in the refining industry, her expertise includes raw materials selection, manufacturing processes and economics, global supply and demand, and intellectual property analysis and support. Email: aaclaxt@yahoo.com. Web: www.myenergyinc.com