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Technical InformationHydrocracked Base Oils What Are They?

Base Oil Manufacture

Before describing the Hydrocracking process and comparing it to the Solvent Refiningprocess, we will first review the general principles of lubricant base oil manufacture.Lubricant base oils are produced in a series of steps, which are designed to enhancecertain desirable properties. These include viscosity index, oxidation resistance,thermal stability and low temperature fluidity.

Starting from petroleum crude oil, the typical process for making a lubricant base oil isas follows:

Separation of lighter boiling materials, such as gasoline, diesel, etcDistillation to give desired base oil viscosity gradesSelective removal of impurities, such as aromatics and polar compoundsHydrodewaxing to improve low temperature fluidityFinishing to improve oxidation resistance and heat stability

Generally both Solvent Refined and Hydrocracked base oils are manufactured thisway, but differ in the methods employed

Solvent Refining Process

Developed over seventy years ago, this process attempts to remove the undesirablecomponents from the feed, by solvent extraction. Initially, light oils such as gasoline,diesel, etc are separated from crude petroleum by atmospheric distillation. Theresulting material is charged to a vacuum distillation tower, where lubricant fractionsof specific viscosity ranges are taken off. These fractions are then treated individuallyin a solvent extraction tower. A solvent, e.g., furfural, is mixed with them and extractsabout 80% of the aromatic material present. After reducing the aromatic content, thesolvent extracted lube fraction is dewaxed by chilling to a low temperature, whichremoves much of the wax and so improves the low temperature fluidity of the product.Finally, the dewaxed lube fractions are sometimes finished to improve their colour andstability, depending on the application requirements. One common method offinishing is mild hydrofinishing. This step should not be confused with Hydrocrackingprocess, as conditions of temperature and pressure in hydrofinishing are mild and lesseffective.

Hydrocracking Process

In the Hydrocracking process, the elimination of aromatics and polar compounds isachieved by chemically reacting the feedstock with hydrogen, in the presence of acatalyst, at high temperatures and pressures.

Several different reactions occur in this process, the principal ones being:

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Several different reactions occur in this process, the principal ones being:

Removal of polar compounds, containing sulphur, nitrogen and oxygenConversion of aromatic hydrocarbons to saturated cyclic hydrocarbonsBreaking up of heavy polycyclo-paraffins to lighter saturated hydrocarbons

These reactions take place at temperatures as high as 400°C, pressures around 3000psi and in the presence of a catalyst. The hydrocarbon molecules that are formed arevery stable and this makes them ideal for use as lubricant base oils.

There are three stages in the Hydrocracking process. The first one removes unwantedpolar compounds and converts the aromatic components to saturated hydrocarbons.After separation into desired viscosity grades by vacuum distillation, batches of waxylube base oil are hydrodewaxed. These are then passed through another hydrocrackerfor additional saturation. This final step maximizes base oil stability, by removing thelast traces of aromatic and polar molecules and is called hydrofinishing.

Hydrocracking results in base oils having the following attractive features:

Very High Viscosity Index (100 to 130)Low VolatilitySuperior Oxidation ResistanceHigh Thermal StabilityExcellent Low Temperature FluidityLow Toxicity

These features give performance characteristics in finished lubricants very similar tosynthetics, such as poly-alpha-olefins (PAO).

Comparison of the Products of Hydrocracking and Solvent RefiningBase Oils

There are significant differences in certain characteristics between Hydrocracked andSolvent Refined base oils. The main reason for the difference lies in the virtualelimination of aromatic molecules (less than 0.5%) in Hydrocracking process.Hydrocracked base oils are termed “99.5+% Pure”. In comparison, the aromaticscontent of Solvent Refined base oils is somewhere around 20%; so Solvent Refinedbase oils are considered only “80% Pure”.

Characteristic Significant Difference

COLOUR Hydrocracked base oils are clear andcolourless

VISCOSITY INDEXHydrocracked base oils have higher VIs sothey ‘thin-out’ less at high temperaturesthan Solvent Refined oils.

OXIDATION RESISTANCE

Hydrocracked base oils respond very wellto anti-oxidants and so have superiorresistance to oxidation and a longerlubricant life.

THERMAL STABILITYHydrocracked base oils have considerablybetter resistance to heat than SolventRefined oils.

CARBON RESIDUE Hydrocracked base oils produce lowerresidues than Solvent Refined oils.

DEMULSIBILITY Hydrocracked oils separate easier fromwater than Solvent Refined oils

LOW TOXICITY Hydrocracked base oils have low toxicity,due to a virtual absence of impurities.Hydrocracked base oils biodegrade faster

BIODEGRADABILITYHydrocracked base oils biodegrade fasterthan Solvent Refined oils - 60% vs 30%, asmeasured by the CEC-L33-A-93 test.

Lubricating Base Oils Groups.

American Petroleum Institute (API) designates several types of lubricant base oilidentified as:

Group I - Saturates < 90% and/or Sulfur >0.03% and Viscosity Index >= 80 to<120

- Manufactured by solvent extraction, solvent or catalytic dewaxing. Common Group Ibase oil are 150SN (solvent neutral), 500SN, and 150BS (brightstok)

Group II – Saturates >= 90% and Sulfur <=0.03% and Viscosity Index >= 80 to<120

- Manufactured by hydrocracking and solvent or catalytic dewaxing and hydro-finishing processes. Group II base oil has superior anti-oxidation properties sincevirtually all hydrocarbon molecules are saturated. It has water-white color.

Group III – Saturates >= 90% Sulfur <=0.03% and Viscosity Index >= 120

- Manufactured by special processes such as isohydromerization. Can be manufacturedfrom base oil or slax wax from dewaxing process.

Group IV – Poly Alpha Olefins (PAO)

Group V – All others not included above such as naphthenics, PAG and esters.

What is Oil Oxidation?

Over time, oil tends to break down by reacting with dissolved atmospheric oxygen.This oxidation starts a chain reaction that first forms hydro peroxides and thenprogresses to other oxidation products - all of which increase acidity and viscosity,darken colour, and leave surface deposits and varnish. By eliminating the initial hydroperoxides and by interrupting the chain sequence, oxidation-inhibiting additives slowthis deterioration rate by more than a hundredfold.

Useful life continues through an induction period as the oxidation inhibitor supply isslowly depleted.

Deterioration rate depends strongly on temperature. Although adding an inhibitordelays life-ending breakdown, slow accumulation of oxidation products andcontaminants such as wear particles and soot in engine oils eventually signal a needfor an oil change.

The good news is that life expectancy is extended with the paraffinic structure of newhydrocracked Group II and Group III oils. Absence of aromatic hydrocarbons givesmore effective oxidation inhibitor action, minimizes sludge and varnish deposits, andgenerally avoids related machinery problems.

Laboratory bench tests are traditionally used to evaluate oxidation life. For example,the turbine oil stability test (TOST-ASTM D943) bubbles oxygen through an oilsample in contact with water and metal catalysts at 95ºC. Because TOST time takesseveral thousand hours with better base oils and additives, the more aggressiverotating pressure vessel oxidation test (RPVOT) raises pressure to 90 psi at 150ºC.Both tests measure the length of an initial induction period involving only slowoxidation. This induction period typically precedes much more rapid oxidation asmeasured by increased oil acidity (TOST) or a drop in oxygen pressure (RPVOT).

Typical test lives in the table below indicate there is an approximate threefold increasewith hydrocracked Group II base stocks compared to Group I for premium turbinegrade and hydraulic mineral oils used in turbines, compressors, electric motors andgenerators, and a wide range of industrial applications.

Typical Test Life Solvent-refined HydrocrackedTurbine OilTOST life, hours 4000 18000RPVOT life, min 500 1800Hydraulic oilTOST life, hours 2000 6000

Oxidation Test Life with Solvent-refined Group I and Hydrocracked Group II Oils

Commonly Asked Questions on Hydrocracked Base Oils

1. What are hydrocracking and hydrodewaxing?

Hydrocracking and hydrodewaxing are refining processes that use catalyst andhydrogen at high pressure to make high-quality lubricant base oils. Hydrocracking isused to improve VI (Viscosity Index) and remove impurities, while hydrodewaxingconverts wax molecules into high quality lubricant components.

2. What do Group I, II, and III mean, and what’s so great about Group II andGroup III?

Groups I, II, and III are broad categories of base stocks developed by the AmericanPetroleum Institute (API) for the purpose of creating guidelines for licensing engineoils. Typically, solvent-refined base oils fall into Group I, while hydro processed basestocks fall into Group II. Unconventional Base Oils (UCBOs) or Very-High VI stocksare normally categorized as Group III.

Group I oils contain high levels of sulphur and aromatics, which are compounds thatcan diminish performance. Group II & III oils have lower levels of these impurities,which result in enhanced oxidation performance for fully-formulated lubricants. Withhydrodewaxing technology, Group II and III base oils have low-wax composition,which delivers improved low-temperature performance compared to conventionalGroup I base oils.

Due to their high level of purity, Group II & III base oils provide additional benefits incrankcase applications. For example, in heavy-duty engines, motor oils made withGroup II & III base oils have demonstrated a soot dispersancy markedly higher thanthose made with conventional base oils. They have also demonstrated potential forgreater fuel economy in passenger car engine oils.

3. What makes Group II & III base oils more resistant to oxidation?

Group II & III base oils contain lower levels of reactive compounds compared tosolvent-refined Group I base oils. These “impurities,” which include aromatics andsulphur compounds, are much more susceptible to oxidative attack. Once thesecompounds begin to oxidize, a complex chain of reactions occurs that ultimatelycauses both the base oil and the additive to degrade. The virtual absence of theseimpurities means Group II & III base oils deliver exceptional resistance to oxidation.

4. Are Group II & III Base Oils synthetic?

A recent ruling from a respected advertising self-regulatory body decided a case on theuse of the term synthetic. It found that synthetic base stocks are not limited to PAOs.The decision said that the key requirement for calling a base stock synthetic is that itbe the result of conversion or processing of one complex mixture. Group II & III baseoils clearly meet the test.

oils clearly meet the test.

5. Are Group II & III base oils better for the environment?

Yes. Group II & III base oils have low toxicity as measured by eye and skin irritation,inhalation, and oral and dermal toxicity tests. They are neither mutagenic norcarcinogenic, as indicated by their performance in the modified Ames test and IP346polycyclic aromatic test. In fact, these base oils are so pure, they meet therequirements of FDA-approved mineral oils (21CFR 178.3620(c)). This means thatGroup II & III base oils can be used in or used to manufacture a variety of non-foodarticles intended for incidental contact with food.

6. Why should I use Hydrocracked base oils?

Hydrocracked base oils offer superior product performance, resulting in greateroxidation and thermal stability, soot dispersancy in Heavy Duty Motor Oils, and lowtemperature performance. In addition to these benefits, hydrocracked base oils alsohave high VI and low volatility.

Hydrocracked base oils can be formulated with a wide variety of additives either toachieve the latest industry specifications or simply to produce premium performancelubricants.

Hydrocracked base oils can help to meet challenging future lubricant specificationscost-effectively, whereas Group I oils often cannot. Hydrocracked base oils areespecially valuable where they can replace traditional synthetic base oils to achievesynthetic performance.

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