This document summarizes an article about severe hydrocracked oils that can potentially allow for longer intervals between oil changes. It discusses how hydrocracking improves upon traditional solvent refining by using hydrogen to convert petroleum crude into base stocks while removing impurities. Severe hydrocracking produces Group II and Group III base stocks that have benefits like improved oxidation resistance, cleaner burning, and better low-temperature properties compared to conventional oils. However, hydrocracked oils may require modifications to existing machinery due to differences in properties from traditional oils.

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2. Fluid power
Edited by Lawrence Kren
Automobiles that never need oil changes? How about doubling,
even tripling, the time between service for turbines, rotary
compressors, gear units, and other high-speed machinery?
Severe-hydrocracked lubricating oils could make all this possible
— at about half the cost of synthetic oils.
The push toward
lifetime lubes
E. R. Booser
Consulting Engineer
Niskayuna, N.Y.
M
akers
of most
Euro-
pean
cars to-
day
suggest changing oil
every 6,500 to 9,500
miles. Volkswagen and
Peugeot plan to extend
that figure to 18,000
miles or 24 months for
its passenger cars, and
Daimler-Benz may de- Conoco’s recent $500 million hydrocracking plant turns petroleum
but a “fill-for-life” vehi- crude into Group II and Group III lube oil base stocks.
cle by 2010.
Key to the success of
such initiatives is better quality motor oils. process largely unchanged since the early
Current synthetic oils let automobiles run 1900s. Here, distillation separates hydro-
25,000 miles between oil changes or about carbon molecules by boiling point and their
five times longer than most conventional respective molecular size and viscosity.
types. Despite the advantage, their rela- Added solvents selectively extract aromat-
tively high cost has limited market share ics and other impurities such as sulfur, ni-
to about 3%. But emerging severe hydroc- trogen, and oxygen compounds. These ex-
racked oils cost about half as much as syn- tracts are an environmental concern and
thetics and last just as long. This has ma- are often burned as fuel.
jor oil companies scurrying to supply the Hydrocracking instead treats base oils
expected boon. What’s in it for them: with hydrogen rather than solvents. It
greater efficiencies and a more environ- yields more useful products while elimi-
mentally friendly, adaptable process. nating the environmental problems. More-
Traditional refineries distill petroleum over, hydrocrackers can use less-expensive
crude into mineral lubricating oils using a petroleum crude which helps refineries re-
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3. Fluid power
Flow diagrams for solvent refining and hydrocracking. A catalytic dewaxing step follows hydrocracking to convert
waxy, straight-chain paraffins to branched-chain paraffins with lower pour points.
(1) Remove sulfur, nitrogen, and oxygen
impurities from crude oil. (2) Convert aromatic
hydrocarbons to cycloparaffins that remain in
Group II base stocks. (3) Open ring structure
to paraffinic chains in Group III base stocks.
Only the carbon atom skeletons are shown —
the rest of the four valence bonds of each
carbon atom are filled with hydrogen atoms.
coup installation costs. Production can modern hydrocracker — a small 1,000 bar-
readily shift from lubricants to automotive rel-per-day unit — was activated by Stan-
and diesel fuels that meet more demand- dard Oil of Calif. in 1959 to produce im-
ing emissions regulations. And by-prod- proved transportation fuels. By 1972, Gulf
ucts from lube-oil production serve as Oil had built three severe hydrocrackers
high-end fuels for transportation vehicles. for lubricant production, but further instal-
Although hydrocracking may seem re- lations by Gulf and others got sidetracked
cent, it dates back to the 1930s. The first as production focused on environmentally
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4. Fluid power
Characteristics of hydrocarbon types
PARAFFIN CHAIN CYCLOPARAFFIN AROMATIC
No deposits Very little deposits, some varnish Black sludge
Clear, colorless Slight color Dark color
High viscosity index (VI) Intermediate VI Lower VI
Branched chain: low pour point Low pour point Poor at low temperatures
Straight chain: wax Intermediate additive solvency Good additive solvency
Poor additive solvency Higher viscosity for same volatility Higher viscosity
Low viscosity and volatility Some medicinal and cosmetic uses Aromatic portion is carcinogenic
Nontoxic
improved gasolines and diesel fuels. most conventional additives. Group III base
More recently, Chevron has become a stocks undergo even more severe hydroc-
major developer and operator of high-pres- racking, nearly completing the conversion
sure hydroprocessors and has licensed the to branched-chain paraffins. Group III oils
technology to Petro-Canada and Conoco. provides longer service life and a viscosity
These large-scale installations cost about a less sensitive to temperature changes as in-
half-billion dollars each and pose daunting dicated by a very high viscosity index
engineering challenges. For example, cat- (VHVI – above 120).
alytic reactors and some support hardware
run at temperatures to 900°F and pres- Oil’s worst enemy
sures to 3,000 psi. Steady improvements to Over time, oil reacts with dissolved at-
piston pumps, catalysts, and other compo- mospheric oxygen and breaks down or oxi-
nents exposed to the severe conditions help dizes. Oxidation starts a chain reaction
make the operations more reliable. that first forms hydroperoxides then pro-
gresses to other oxidation products, all of
The hydrocracking process which increase acidity, viscosity, darken
Mineral oils derived from petroleum have color, and leave surface deposits. Internal
three basic hydrocarbon structures: paraf- combustion engines that leak combustion
fins, cycloparaffins, and aromatics. Most de- gases into the oil (blow-by) accelerate the
sirable are paraffins in which hydrogen process. Oxidation-inhibiting additives
atoms completely saturate carbon-atom slow the deterioration over a hundred-fold
chains. These hydrogen-saturated paraffin by eliminating the initial hydroperoxides
chains can also form ring structures or cy- and by interrupting the chain sequence.
cloparaffins. The third type has a six-mem- Useful life continues through an induc-
ber aromatic ring structure with an unsatu- tion period as the oxidation inhibitor is
rated carbon-atom skeleton. slowly consumed. Oxidation depends
The high temperatures and pressures of strongly on temperature as life generally
the hydrocracking process destabilize hy- halves for every 10°C (18°F) above normal
drocarbon structures in crude petroleum. operating temperatures. Although addi-
This leads first to hydrogen saturation of tional inhibitor delays life-ending oil
aromatic rings to form cy-
cloparaffins, and finally to New refineries producing both API Group II
opening of cycloparaffin rings
to give chain-structured hy-
and Group III hydrocracked base stocks
drocarbons. Start-up year: 1997 1998 2000
So-called Group II base Petro-Canada Chevron Equilon (Texaco-Shell)
stocks are processed only to Conoco-Pennzoil Ergon
where most aromatic hydro- Modrica (Yugoslavia) ExxonMobil
carbons are eliminated along Imperial Oil (Canada)
with sulfur, nitrogen, and Motiva (Aramco)
oxygen impurities. The re-
Sunoco
maining cycloparaffins pro-
vide sufficient solubility for
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5. Fluid power
American Petroleum Institute (API) base oil categories
Group Saturates,% Aromatics,% Sulfur,% Viscosity index Capacity, barrels/day
I. Solvent-refined mineral oil <90 >10 >0.03 80 to <120 96,000
II. Hydroprocessed >90 <10 <0.03 80 to <120 86,000
III. Hydrocracked (VHVI) >90 <10 <0.03 120+ 7000
IV. PAO polyalphaolefins (100) (0) (0) 3000
(such as Mobil 1)
V. All other synthetics such as esters for jet engine oils and for compounding some automotive and industrial oils.
Lubricant production and relative costs
last about three times longer than tradi-
% of total Relative
production cost
tional solvent-refined oils at a given operat-
ing temperature. One reason is the absence
Mineral oil 97 1 of aromatics. While traditional solvent-re-
SYNTHETIC OILS fined base stocks contain up to 35% aro-
PAO synthetic hydrocarbons 1.4 3 matic hydrocarbons, severely hydrocracked
Glycols 0.7 4 oils are often clear and colorless with less
Polyol esters 0.5 7 than 0.5% aromatics. This helps minimize
Diesters 0.2 5 varnish, dark deposits, insoluble sludge,
Phosphate esters 0.15 8 and other problems that shorten oil life. The
composition works in a variety of applica-
tions including premium turbine oils (used
breakdown, slow accumulation of oxida- in gas and steam turbines, electric motors,
tion products and contaminants such as compressors, and a wide variety of rotating
wear particles and soot eventually signal machinery), high-pressure hydraulic oils,
an oil change. and extreme-pressure gear oils.
The good news is, oils with a paraffinic
molecular structure stave off oxidation. Hy- Measuring oil life
drocracked oils have such a structure and Laboratory bench tests are the tradi-
tional method to evaluate oxidation
Expected oil life life. For example, the Turbine Oil
Stability Test (TOST - ASTM D943)
Year 1990 2010
bubbles oxygen through an oil sam-
Automobile engines 3,000 to 4,000 mile 20,000 to 40,000 mile ple raised to 95°C and in contact
Railroad diesels 3 month 1 yr with water and metal catalysts. But
Steam turbines 10 yr 25 yr TOSTs can take several thousand
Gas turbines 5 yr 10 yr hours to complete because of better
Electric motors 2 yr 5 yr base oils and additives. A more ag-
Gear sets, EP oil 0.5 yr 1 yr gressive Rotary Bomb Oxidation
Test (RBOT - ASTM D2272) boosts
pressure to 100 psi and tempera-
tures to 150°C. Both tests
Typical test life measure the initial induc-
tion period involving only
Solvent refined Hydrocracked slow oxidation. This in-
TURBINE OIL duction period typically
precedes much more
TOST life, hr 4,000 18,000 rapid oxidation as meas-
RBOT life, min 500 1800 ured by elevated oil acid-
HYDRAULIC OIL ity (TOST) or drop in oxy-
TOST life, hr 2,000 6,000 gen pressure (RBOT).
Turbine Oil Stability Test (TOST - ASTM D943). Rotary Bomb Oxidation Test (RBOT - ASTM In addition to these
D2272). These are typical results for premium turbine grade and hydraulic mineral oils tests, automotive engine
commonly used in steam and gas turbines, compressors, electric motors and generators, and a oils are put through accel-
wide range of industrial applications. erated wear and life eval-
uations in test engines.
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6. Fluid power
Key benefits of hydrocracked lubricants
• Improves action of antioxidant additives.
• Lets some applications run at higher temperatures.
• Less carbon formation and fewer deposits.
• Improved low temperature fluidity.
• Separates water and releases foam more efficiently.
• Lower oil volatility for reduced emissions.
• Biodegrades faster.
• Lower impurities and toxicity make them suitable for use in some
cosmetics and pharmaceuticals.
From here come standards including the Paraffinic-hydrocracked oils also have
new GF-3 motor oil classification. GF-3 is different solvent properties that may com-
scheduled for adoption by the International promise some gaskets, seals, and non-
Lubricant Standardization and Approval metallic components. For instance, such
Committee, and then by the API as Service oils can displace plasticizers in elastomers
Classification SL. Oils meeting the new and plastic parts, possibly changing their
standard (Group II hydrocracked oils for dimensions and mechanical properties.
instance) are less volatile which helps cut Although compatible replacements are
airborne components. They also have a rel- typically available for new designs, exist-
atively lower viscosity to improve gas ing diesel engines, automotive compo-
mileage and cold-weather starting. Best of nents, gear units, and other machines can
all, Group II oils extend time between oil encounter problems. The new oils also sep-
changes and reduce wear of engine valve arate water more rapidly which may re-
train and piston ring surfaces. Diesel en- quire modified lubrication systems. Im-
gines get the new PC-9 classification which proved filtration may also be needed to
also relies heavily on hydrocracked base avoid build-up of contaminants and wear
stocks. particles between longer oil-change inter-
Several lubricant suppliers in North vals. All these issues need addressing if
America and Europe are marketing “syn- hydrocracked oils are to deliver on their
thetic” engine oils compounded with even promise of longer life at a lower cost. s
more severely hydrocracked Group III base
stocks. These oils are said to be equivalent Background information for this article
to polyalphaolefin synthetics such as Mobil comes from Conoco, ExxonMobil, General
1. VHVI oils should make major inroads as Electric, and Petro-Canada. A source of
automakers push for reduced maintenance further information on lubricant properties
and longer oil-change intervals. and performance in bearings is a new book
by M. M. Khonsari and E. R. Booser,
Limitations and fixes Applied Tribology: Bearing Design and
The new Group II and Group III oils Lubrication, John Wiley & Sons, New York.
aren’t without problems, however. One It’s available at www.amazon.com
drawback is a lower solubility to additives.
Automotive engine oils are particularly
challenging because they contain a rela-
tively large amount of oxidation inhibitors,
antiwear additives, and detergents.
Additive separation can be a problem in
some high-speed compressors. Centrifug-
ing action in bearings slings additives out- We want your feedback.
ward, likely because of incomplete solubil- Did you find this material interesting? Circle 785
ity in the base oil. One way to boost addi-
Do you want more information of this type? Circle 786
tive solubility is to blend Group III base
stocks with synthetic ester fluid. Similar Comment via e-mail to mdeditor@penton.com
results are possible by adding Group I sol- What related topics would you like to see covered? What additional
vent-refined oils to Group II hydrocracked information on this topic would you find useful?
base stocks, but at the expense of potential
longer life.
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