FUTURE BASE FLUIDS- CLASSIFICATION

Prof. M. C. Dwivedi

CONVENER, LAWPSP* SYMPOSIUM

 

20A/ 1004 – 10th FLOOR, MHADA, POWAI, MUMBAI-400076, INDIA

 

 

ABSTRACT

 

API classification of the base oils has been common criteria for quality assessment of petroleum functional fluids base stocks between refiners, traders and manufacturers and blenders of products.  Its applicability is limited to petroleum and at the most synthetic hydrocarbon base stocks. It is approximate and can not assure the quality. With the rising price of petroleum stocks other fluids particularly vegetable oil based stocks and water based fluids will become economically viable. The future will see multiplicity of base stocks. This calls for a broader and compressive classification criteria. The classification proposed in this paper focuses on the molecular structure of the oil constituents.  Viscosity index, iodine value, saponification value, volatility, water content and biodegradability are parameters.  Linearity index is a good indicator of quality, it should be reported (>70) if data is available.   The proposed classification helps to identify the chemical nature, chemical structure, functional and blend characteristics of the stock.  It will provide quality assurance of the base oil and also provided guidance for the selection of additives package for a particular stock and product application.

 

KEY WORDS

Base oil classification. Base stocks grouping, Base oil chemical structure.

FUTURE BASE FLUIDS CLASSIFICATION

 

PROF. M. C. DWIVEDI

CONVENER, LAWPSP* SYMPOSIUM

20A/ 1004 - 10th Floor, MHADA, POWAI, MUMBAI-400076, INDIA

 

 

API classification of base oils (1990) has been a common criterion for procurement of base oils by manufacturers and blenders of lubricant and functional fluid products.  This also severed as a bench mark to the refiners and trade.  However, with the rapid rise in the crude oil prices, and changing refinery process configurations, availability of base oils is reduced and prices increased sharply.  Prices of non petroleum fluids; particularly vegetable oils, remained relatively stable.  This is making many of these fluids cost competitive and viable alternatives.  Superior native tribological properties and eco-compatibility makes these fluids preferable over petroleum based fluids.  The future may therefore see multiple options for base stocks and performance specific products.

 

Non-edible vegetable oils are at lower price than petroleum base stocks and use of these as base stocks for functional fluid formulation makes a strong economic sense.  Several other fluids like water or glycerol etc. may workout economical than petroleum fluids for some applications.  This necessitates a need to consider functional fluid base stocks as ‘Fluids’ rather than ‘Petroleum Based Fluids”  This pressure will get more intense in future as the prices of petroleum base oils increase.  This is likely to happen due to following reasons.  

 

1. Increase in crude oil price

2.   Decreasing production of base oils due to changes in refining strategies and technologies.

3.   GTL processes may provide substantial part of base oils in future, but the prices are likely to be higher than group-I base oils.

4.   Increasing cost of technical services and marketing and low returns from functional fluid business.  

 

On the other hand, prices of vegetable oils are likely to remain stable or even reduce due to following reasons.

 

1.      Increase in acreage of oil seed cultivation in Fareast and African countries.

2.      Introduction of high yield varieties of oil seeds and scientific inputs to agriculture.

3.      Increasing trend of avoiding consumption of oily food.

4.      Increasing availability of used frying pan oils.

 

 

 * Lubricants –Additives- Waxes and Petroleum Specialty Products

 

 
In this situation, functional fluid blending and marketing will gradually get detached from the large refinery companies and independent blending and marketing companies will emerge, offering an  assortment of functional fluid formulations, based on petroleum base oils, water based fluids ,vegetable oils, synthetics and other fluids and their blends, giving superior performance characteristics.

 

Standards and literature developed over five decades to define quality and application practices of functional fluids are mostly by petroleum industry with no consideration for other stocks. Many of these tests are non-scientific and empirical and have relevance only for petroleum products. The need for the future is therefore to develop standards and test protocol, based on tribological requirements and performance characteristics of fluid and eliminate those tests which are biased for petroleum products. The issue is to be considered from the view point of base oil selection, product classification and product characterization.

 

(A)       BASE FLUIDS

Base fluids are classified as follows.

 

1. Hydrocarbon fluids

   (a) Petroleum based fluids– refinery products.

   (b) Synthetic hydrocarbons, including GTL and STL products.

 

2. Vegetable oil based fluids

 

   (a) Native Vegetable Oils (VOs)

   (b) Chemically Modified Vegetable Oils (CMVOs or MVOs)

 

3. Synthetic ester and ether fluids

   (a) Hydrophobic ester fluids

   (b) Hydrophilic ester fluids

 

4. Water based fluids

    (a) Fluids containing less than 95 % water

    (b) Fluids containing more than 95 % water

 

5.      Others

Not classified above like, silicon fluids, organo halogen fluids, etc. and innovative and emerging fluids.

 

1(a)      HYDROCARBON FLUIDS

 

These are common base fluids; products of petroleum refinery which have dominated after 1930s. These are constituted of hydrocarbons, generally of paraffin and naphthene groups. Petroleum based fluids are constituted of thousands of different hydrocarbon molecules over the specified boiling range       (molecular size). The mixtures are complex and random and no two oils are same.

 

These are characterized by physico-chemical characteristics. Chemical compositions are averages and identity of molecule is unimportant. Petroleum fluids have wide and flexible application range and meet 85 to 90% of all industrial, defense and domestic; tribological fluid demand. These are abundantly available at low cost.

 

These have wide viscosity range, moderate viscosity index, moderate low temperature characteristics, excellent thermal and oxidation stability, good water repellency and high hydrolytic stability. These have low to moderate extreme pressure properties and adherence to metal surface. These have low biodegradability(20to30percent) and moderate phytotoxicity and  low eco-compatibility.

 

1(b)      SYNTHETIC HYDROCARBONS

 

Synthetic hydrocarbons are tailor-made hydrocarbon molecules designed to give

superior performance characteristics. These are synthesized by a variety of reactions.

 

1.      Rebuilding the molecules from basic olefins like, propylenes, butylenes

etc. followed by hydrogenation or alkylation to eliminate residual

                  unsaturation.

2.   Olegomerisation, dimerisation, trimerisation of larger olefins followed by

       hydrogenation and /or alkylation.

3.   GTL and STL processes  designed to synthesize hydrocarbon stocks.

 

These fluids have excellent performance characteristics like high VI, high oxidation and thermal stability, high water resistance and hydrolytic stability, low volatility and evaporation losses, excellent surface properties and EP characteristics, and excellent low temperature characteristics. These fluids are designed for specific service conditions have limited additive compatibility requiring specific additives packages. The quality tests and standards as applicable to petroleum base fluids are applicable to these fluids as well. These are compatible to petroleum base fluids. These are predominantly used in IC engine oils, turbine oils and other applications requiring wider temperature range. Like petroleum oils these have low biodegradability, low eco-compatibility and mild to no phytotoxicity.

 

2.         VEGETABLE OIL BASED FLUIDS

 

Vegetable oil based stocks for functional fluids and tribological applications are placed in two categories.

 

(a) Native Vegetable Oils (VOs.)

(b) Chemically Modified Vegetable Oils (CMVOs or MVOs)

 

Native vegetable oils or those with little processing have several functional characteristics superior to mineral oils. These include.

 

1. High flash point and fire point

2. Better oiliness, lubricity and EP characteristics

3. Lower volatility

4. High viscosity index

5. Total biodegradability and eco-compatibility

 

VOs have some adverse characteristics.

 

1.      High Pour Point –Some VOs have high concentration of saturated linear chain  

compounds of C16 and C18 carbons, with high pour point. This could be adjusted to product application requirements by dewaxing / deguming, blending and also by use of additives.

 

2.      Limited Kinematic Viscosity Range. - Most of the vegetable oils have viscosities varying in narrow range 30 to 45 cSt. at 40oC, because these are constituted mainly by triglycerides of 7 to 9 fatty acids of C16, C18, and C22 carbon atoms in different structural configurations and ratios. Some oils like jojoba  oil have lower KV ( 23 to 25 cSt.), castor oil has higher KV (256 to 300 cSt). at 40oC. These could be viscosified by blending small quantities of vegetable waxes, animal waxes or oxygenated synthetic polymers like polyglycols. Oxidized VOs particularly waste oil from food processing have higher KV and could also be used for blending. Thus base oil with KVs at 40oC from 25 cSt. to 300, cSt. may be formulated by blending of different native vegetable oils. Chemically modified VOs like alkylated esters, dibasic, tribasic and polyol esters, dimerised, trimerised, polymerised VOs. and estolides etc. cover higher ranges of viscosity      ( up to 4000 cSt. at 40oC). Fatty acid esters have lower KVs (2 to 10 cSt. at 40oC).

 

Thus an assortment of native VOs, and MVOs and their blends can provide

base stocks for the entire range of functional fluid applications.

 

 3.        Unsaturation – Most VOs have substantial unsaturation and are susceptible to oxidation, particularly in high temperature applications. Unsaturation can be kept within limits by blending with saturated stocks. There is not likely to be any difficulty for lower temperature applications as these olefins are thermally stable and resist oxidation. These could also be protected by use of appropriate antioxidant additives.

 

The present oxidation tests are designed for petroleum products and oriented to high temperature applications. High test temperature accelerates oxidation and forms different oxidized compounds than those formed at slow oxidation at lower temperatures. This may misrepresent performance of oils meant for lower temperature applications. There is serious need to revalidate oxidation tests for deferent application temperature ranges. Unsaturation is measured by Iodine Value (IV) or Bromine Number.  Mineral oil base stocks have very little unsaturation ( IV< 2). For VOs unsaturation level is high (IV – 60 to 180). This is equivalent to about 30 percent molecules being monounsaturated.

 

It is essential to include IV in the test protocol to have an idea about the concentration of unsaturated molecules in the product.  This will also indicate chemical nature of the stock.

 

4.         Acidity – Petroleum base stocks are generally neutral and acidity limits are low for most products ( less than 0.2 mgKOH/g). Vegetable oils have up to 3 percent free acids, acidity level may be as high as 1.5mg KOH /g. Presence of acids in products is detrimental as it increases rusting and wear of the metal. Acidity in inorganic form is more corrosive than that in organic form. Organic acids with short organic, chains ( less than C6), are corrosive and reactive to metals. Larger organic acids like those with C16 and above are non-corrosive and do not react to metals at lower temperatures (less than 80oC). Iron salts of fatty acids may form at a very slow pace and when in critical concentration these may act as oxidation catalysts to oxidize the oil, forming more acids. This chain reaction may be terminated by use of additives.

 

Vegetable oils have no inorganic acidity. Acidity is because of presence of free fatty acids (FFA). These are non corrosive at low temperatures. However to be on safer side a limit on FFA for the base stocks will be desirable. A maximum FFA limit of 0.5 percent is suggested. This corresponds to about 1 mg KOH/g. This should work but more rational limits could be fixed after detailed scientific and statistical evaluation of data.

 

5.         Saponification Value (SAP) - SAP value indicates saponifiable material present in the oil. For mineral oils this is small (less than 1) and indicates presence of additives which may hydrolyze and form soaps with alkali (KOH). For synthetic esters SAP value may range from 60 to 120. For most native vegetable oils it is around 80 to 190. SAP value does not indicate any adverse tribological property. It indicates possibility of hydrolysis in presence of moisture particularly at elevated temperatures (more than 120oC). In a situation where multiplicity of lubricants is assumed, it may help in guessing the type of fluid.

 

6.         Environmental and Toxicological Issues - VOs are fully biodegradable and  eco-compatible. Some additives or blending components may have limited biodegradability, this may reduce the biodegradability of product. As these constituents are in small concentrations, more than 90 % biodegradability of product is assured.

 

Toxicity may sometimes be a problem if VOs used are non-edible or used VOs. Oxidized used oils have no toxicity. Non edible VOs are toxic, because of presence of some minor toxic constituents. Toxicity is mild and some of these are being used for soap making and other applications. Toxicity of VOs could be removed or reduced by detoxification processes. However, it would be essential to specify some limits for human and animal toxicity.

 

2(a)   NATIVE VEGETABLE OIL BASE STOCKS

 

Chemical structure of the constituent molecules of VOs has some basic limitations.

 

      1    Presence of unsaturation in some constituents.

      2.   Presence of slightly polar triglyceride ester groups.

      3.   High pour point due to presence of linear saturated chain compounds.

      4.   Presence of hydroxyl ‘OH’ group in some VOs like castor oil.

      5.   Presence of toxic compounds in low concentration.

 

These limitations could be controlled by a variety of process.

Therefore in spite of structural limitation native VOs could be used as base stocks for formulation of all types of tribofluids for low and moderate ( less than 80oC) temperature applications. This constitutes 60 to 70 percent of total functional fluids demand.

 

2(b) CHEMICAL MODIFICATION OF VEGETABLE OILS

 

For extreme pressure, high temperature and cryogenic applications, vegetable oils can be chemically modified to create molecules of desired size and configuration. Constituent molecules of VOs serve as basic blocks to build these molecules. Size or carbon number and structural configuration can be changed.  These fluids may be designed to give.

 

1. Low pour point and low temperature properties.

2. Excellent EP characteristics

3. Wide viscosity range and high VI

4. High thermal and oxidation stability

 

Chemical reactions generally used to modify VO molecules are -

 

1.   Esterification by appropriate organic alcohol to built desired carbon number linear chain of esters. This also reduces polarity of the molecule.

 

2.   Alkylation of unsaturated sites by an appropriate organic group to eliminate double bond and to create side chain to give lower pour point and higher thermal, oxidation and hydrolytic stability. The carbon number can also be changed by proper selection of alkylation groups to get proper KV.

 

3.   Estolide formation or self alkylation and condensation of olefin bonds to form large isoalkyl molecules followed by hydrogenation to saturate the residual unsaturation. Such molecules give excellent EP, high oxidation stability, high VI, and excellent low temperature performance characteristics. Fluids of wide viscosity range (KV-30 to 4000cSt. at 40oC) could be created.

 

4.   Epoxidation of double bond gives molecules with high thermal, oxidation and hydrolytic stability. These will also have excellent corrosion protection and rust prevention. However epoxy molecules are known to be incompatible to other oil constituents and may not give physically stable formulations. Special additives system will be required for such fluids.

 

In addition, there are other chemical reactions which may be used to suitably alter structure of VOs constituents. Such functionally oriented molecules derived from VOs can give functional fluids to meet all extreme conditions of application.

 

Thus VOs, MVOs and their blends can give functional fluids for all types of tribological applications.

 

3. SYNTHETIC FLUIDS

 

Synthetic fluids were developed during the war in 1940s to meet extreme military requirements. Later these found acceptance in aerospace, power generation heavy construction and earth moving machinery. These perform under extreme conditions of temperature and load where petroleum based fluids fail. However, over the last fifty years; their market share has not exceeded ten percent because of high costs. These fluids are synthesized from basic hydrocarbons, petrochemicals, or natural raw materials. These are classified based on chemical structure. The general nature of these molecules is ‘Linear’.

 

3.1 SYNTHETIC HYDROCARBONS

 

These are hydrocarbons with appropriate chemical structure and linearity to give desired performance characteristics. These constitute major part (60-70 percent) of synthetic lubricants in automotive sector.  These have been discussed in (1b).

 

3.2 ESTER AND ETHER FLUIDS

 

Esters, ether and such derivatives constitute about 20-30 percent of synthetic fluid demand. These are of mono, di, or tribasic esters. Esters of diols, triols and polyols also form molecules of similar structure. The esterification groups are selected based on requirements of KV and VI of the fluid and desired performance properties. Number of carbon atoms and polarity could be changed by appropriate selection of esterification group. Corresponding ethers also have similar tribological characteristics. These are high performance fluids recommended for high load, and extreme conditions of temperature. These have high temperature oxidation resistance and stability, good low temperature viscosity. In most cases hydrolytic stability is low particularly as the acidity increases during application.

 

      Biodegradability of these is from 40 to 70 percent. Eco-compatibility and toxicity vary widely.

 

These are expensive fluids used for critical applications like, aviation, high temperature gas turbine lubrication for power generation, heavy metallurgical machines etc. Some of the derivative esters like; organic phosphate esters are used as fire retardant power transmission fluids in aircraft and metallurgical operations.

 

 Synthetics differ from CMVOs as these are pure compounds with narrow range of properties, while CMVOs are complex mixtures of several such esters over a wider carbon number range.

 

Organo-esters from glycols, diols, triols, polyols, ethylene oxide and propylene oxide condensed alkylene glycols, particularly those with short organic chains are hydrophilic. These are used in tribological applications such as fire resistant fluids, metal working fluids etc. In some power transmission fluids applications, these are used in pure form. These fluids can be formulated in desired viscosity range, and have high density, fire resistance, high heat capacity, high thermal and oxidation resistance. Some of these have high linearity and high VI. Biodegradability is medium 30 to 60 percent) and eco-compatibility may vary widely.

 

4. WATER BASED FLUIDS

 

Water based fluids are used in several functional applications over moderate range of temperatures (4 to 60oC). These are, low cost, in desired viscosity range, high VI, highest heat capacity and eco-friendly fluids. A group of these are not true solutions and are emulsions, suspensions / dispersions of hydrophilic polymers in water. These are shear sensitive and breakdown at high shear rates. These are classified in two groups.

 

4.1 ORGANIC AQUEOUS SOLUTIONS

 

These are true solution of polyhydric organic alcohols, like glycols, glycerols etc. in water at various concentrations covering the whole range of viscosity from 1 to 16000 cSt. at 40oC.

 

There are two types of these fluids.

 

1. More Than 95 % Organic Constituent

 

These are aqueous organic solutions of polyhydric alcohols, amides and amino derivatives. The cost is high because of substantial concentration of organic component. Application temperatures are extended below + 4oC and above 60oC depending on concentration of organic component. Glycols, glycerol; PVA solutions have freezing temperature well below ─15oC and boiling point well above 130oC. Water sugar solutions also give high viscosities and may be used for some applications. These have high eco-compatibility, high fire resistance, high heat capacity, high oxidation and thermal stability, high VI. These are widely used as fire retardant fluids, cutting and metal working fluids etc.

 

2.  Less Than 5 Percent Organic Constituents

 

These are less expensive, moderate viscosity, high heat capacity and highly eco-compatible formulations. The application temperature range is narrow                 (4 to 60oC). This covers more than 70 percent industrial applications at atmospheric conditions, like metal cutting, metal working, quenching, grinding etc. These can also be used as fire retardant hydraulic fluids.

 

Water mineral oil emulsions are used in applications like metal cutting, grinding, rolling, stone cutting and grinding. Some of these have more than 5 % mineral oil    ( 10-30 %) while others have less than 5% mineral oil ( 3 to 0.5%).

 

4.2       WATER POLYMER SUSPENSIONS AND GELS

 

A small amount of water soluble polymer can give a solution with viscosity as high as 16,000 cSt. For example 0.1 percent polyacrylamide can viscosify water to about 200 cSt. and give a gel with KV 16,000 cSt. at 40oC, at 2 percent concentration. These are not true solutions and are shear sensitive and breakdown at high shear rate. These are also temperature sensitive and cream out at temperature above 80oC. These are eco-compatible and have highest heat capacity. Many of these have been used for atmospheric applications as cutting fluids, hydraulic fluids, gear oils, etc.

 

(B)    BASE OIL CLASSIFICATION

 

B.1   API CLASSIFICATION OF BASE OILS

 

Performance of a functional fluid depends on base oil composition as the base oil constitutes more than 95 % of the product. All rheological, and physico-chemical characteristics of fluid are attributes of the chemical structure of the constituent molecules of base oil. It is the base oil that performs and carries out the intended mechanical function. Additives provide marginal enhancement to specific characteristics. The molecules constituting the base oil are subjected to physical stresses and chemical severity. Their chemical or morphological breakdown means breakdown of the fluid. Therefore base oil quality is primary requirement of oil formulations. Base oils are bulk products and a general quality index is required to assess suitability for a particular application. The common criteria for petroleum and hydrocarbon base oil quality are “API Classification”. This grades base oils in five groups based on three characteristics    (Table-1).

 

1. Sulfur content,

2. Saturates content,

3. Viscosity Index

 

1.   SULFUR CONTENT

 

Sulfur is a minor constituent and does not influence bulk rheological or physicochemical properties of the fluid. Sulfur compounds are also incorporated as additives. Some sulfur compounds present in base oil may be corrosive; these could be taken care by use of appropriate additives, while others impart lubricity and EP characteristics.  In all the functions where the fluid remains in liquid form; little sulfur (0.3%) present in the oil cannot be a potential environmental or health hazard. In IC engine oils, a part of lubricating oil may burn or evaporate with fuel, but the quantity as compared to fuel is so small that it cannot contribute any significant sulfur concentration in the exhaust gases. Special significance attached to sulfur, in API classification appears to be out of place.

 

2.   SATURATES CONTENT

 

Saturates content in group I base oils is below 90 percent and for other groups it is more than 90 percent. Saturates mean n-paraffins, i-paraffins, and cycloparaffins or naphthenes.  Normal paraffins have high pour point, high viscosity index, and also high emulsibility. I-paraffins have moderate to low, VI, low pour point, high oxidation stability and low emulsifiability. Naphthenics have low VI, low pour point, high oxidation and hydrolytic stability. Some characteristics oppose each other, therefore an appropriate combination of saturates will result in an optimum performance and quality of base oil.

 

Aromatics, have to be less than 10 percent in all the base oils except for those of group-I. Aromatics are characterized by low VI, low pour point, low oxidation stability and low emulsifiability. These also have higher carbon formation tendency. Therefore while aromatics are undesirable for IC engine lubrication where oil is exposed to high temperatures and is likely to decompose, these are desirable in gear oils and hydraulic oils where oiliness is important. Even though, aromatics are undesirable their presences in the range 8 to 12 percent enhances overall oxidation stability. Appropriate level of aromatics can enhance the oil performance.

 

Diaromatics is another group of hydrocarbons found in distillate stocks in small concentration (up to 2%). These are more reactive and have poor oxidation stability and high carbon forming tendency. At low concentration (up to 2 %) these may offer better EP characteristics in gear oils, particularly for low temperature high load applications.

 

The API base oil classification is not comprehensive and does not identify these differences within ‘Saturates’ or functions of ‘Aromatic’ constituents. This may lead to inaccuracy in selection of proper quality of base oil.

 

3.   VISCOSITY INDEX (VI)

 

Viscosity index is another parameter of API base oil classification. VI is high    (90 to100) for normal paraffins and low (80-95) for i-paraffins and naphthenics. Aromatics have lower VI ( 70-80). Not all-i-parrafins have low VIs; it dependent on the linearity of the molecule. If a free linear chain is more than 8 carbon atoms VI will be 90 or higher.

 

Lube oil base stocks have carbon number from C26 to C40. Therefore most iso-paraffins with one side chain will have free linear chains of more than 8 carbon atoms and VI higher than 90. Iso- paraffin with two or more short iso-chains will have rigid molecules with lower VIs. Thus VI is not an independent property; it is derivative of ‘Saturates’ concentration and chemical structure of saturate constituents. Range of VI indicated in API classification (80-120) is too wide to be index of quality. Range of VI for mineral base oils is from 80-95, except for some synthetic oils of group III.  VI range of 80-120 appears to be absurd for group I and II oils. Such a range makes it impossible to make a distinction between good or bad quality base oils.

 

Selection of base oil depends on viscosity and these are designated accordingly (150N, 300N, 500N, etc.).  Viscosity grade oils are prepared by blending high and low viscosity oils. Viscosity can also be modified by using small quantity (1-2 %) of polymers as viscosifier. Such blended stocks have poor shear stability and do not give as good performance as distillates of the same viscosity range. Viscosity of the stock is required to be specified with API group to correctly specify the base oil.

 

            API grouping does not address to performance and composition factors and cannot provide performance or quality assurance. This can be made comprehensive and more accurate by incorporating additional parameters and information to give better quality reflection.

 

B.2      Standard Guide For Characteristics of Hydrocarbon Lubricants Base Oil ASTM D-6074.

 

This has larger spectrum of properties, but does not quantify (Table-2). It is unnecessarily loaded with extra concern for presence of minor constituents; like nitrogen, metals etc. Specifications are preoccupied with the base oils from re-refining. This is a futile exercise as, for a user it does not matter whether the base oil is virgin or re-refined. There is no way how two types of oils could be distinguished.

 

In absence of any quantitative limits for the base oils of different viscosity ranges, ASTM D- 6074 is of no use. Specification limits of contaminants are also meaningless as base oil is not the end product. The end product is formulated from base oil by blending appropriate additives package. Pollution potential of end product for a particular application should be considered for environmental impact. How and in what form the product is used and what is rejected in the environment, is important; which should have rational limits.  There is no logic in applying contamination limits on base oil or intermediate products.

 

Limits on concentration of each contaminant in a product should be decided based on detailed evaluation of environmental impact.

 

B.3      MODIFIED BASE OIL CLASSIFICATION

 

In an earlier paper, a more comprehensive classification of hydrocarbon base oils    (Table-3) in line with the API has been suggested. This includes two additional parameters (1) Kinematic viscosity at 40oC (KV) and (2) Linearity Index (LI) that take care of chemical structure of molecules constituting the oil. API designation requires KV at 40oC to be specified with any group, like “150N Group I”. In the suggested classification each group is divided into five sub-groups of common KV values as follows.

 

Sub group       Kinematic viscosity at 40oC.

    (a)                13 cSt. (70SUS) and lower

    (b)                32 cSt. (150 SUS)

    (c)                65 cSt. (300 SUS)

    (d)                110 cSt. (500 SUS)

    (e)                150 cSt. (750 SUS) and above

 

Group I, II and III are essentially those in API classification, except that there is special mention of GTL and STL products and group II+. Group IV also includes all other synthetic hydrocarbons besides PAOs.  Even though better than API, for hydrocarbon stocks, this classification does not take care of other base stocks. A more comprehensive product identity and quality is desirable to meet the challenges of the future.

 

PERFORMANCE CHARACTERISTICS AND MOLECULAR STRUCTURE OFBASE OIL CONSTITUENTS.

 

Physical, physico-chemical and performance characteristics of base oil are attributes ofthe chemical structure and nature of the constituent molecules. Influence of these molecular parameters are discussed as follows.

 

1.     MOLECULAR SIZE

Blending of close viscosity oils gives better products rather than blending of dissimilar oils. Viscosity should be natural molecular viscosity and not the made up blend viscosity. The oil should have least variation of molecular size or carbon number. This is controlled by “Boling Range”. Oils of narrow boiling range have less variation in molecular weight and size and are better base oils. These also have lower volatility losses. Viscosity, density and other bulk properties depend on molecular weight.

 

2.     MOLECULAR STRUCTURE

Intensive characteristics like, VI, pour point etc. depend on the type of molecule  i.e. paraffins, i-paraffins, naphthenes, aromatics, diaromatics etc. Chemical characteristics like thermal decomposition, oxidation stability, EP characteristics etc. also depend on molecular structure. No single group of hydrocarbons has all the desirable characteristics of a functional fluid. Therefore an optimum combination is to be formulated for a particular application.

 

A large number of studies have been reported on influence of oil constituents on performance. Low temperature studies are confined to effect of oil constituents on VI, and EP characteristics. EP effect is often not clear because of presence of sulfur or additives. High temperature studies mainly cover ­oxidation stability or carbon and varnish formation in IC engines. Interfacial properties like foaming, air release, demulsification, etc. are sensitive to contaminations. It is not possible to make generalizations as contaminants are not definite.

 

In general, influence of molecular size and structure on fluids characteristics is summarized as follows.

 

1.      Functional fluids have carbon numbers from C24 to C40.

2.      Each ring compound group has 6 carbon atoms, (sometimes five). Higher and

lower carbon rings are not present. Fused ring components and diaromatics are

less than 2 percent.

3.      VI is high for hydrocarbons with more than 8 carbon free chain length.

4.      Oxidation stability is low, for free linear chain larger than 16 carbons.

5.      Aromatics give better EP characteristics, oxidation protection and additives compatibility.

 

Based on the above factors a model lubricant molecule could be conceptualized as;         An isolinear compound with C8 to C11 free chains with alkane linkage with 8 to 11 carbon atoms. If the side linkage is constituted by an aromatic or naphthenic ring, the molecule will become thermally stronger but will have 8 to 11 carbons in non-liner configuration that will reduce flexibility of molecule and lead to lower VI. Table -4 gives some of these assumed liner molecules of API group III oils. Same number of carbon atoms could be arranged to give low linearity and low VIs. Petroleum oils are mixtures of a variety of hydrocarbons some with high and other with low VIs.

 

LINEARITY INDEX

 

Constituent molecules of base oil could be compared with the ‘Ideal Base Fluids’ structure in terms of Linearity Index (LI). This is defined as the percent of carbon atoms associated with ‘Flexible’ linear chains. That means free liner chains of 8 to 12 carbon atoms, giving high VI and high oxidation stability. Compact chemical structure of ring compounds and those of short linear chains (less than 8 carbon atoms) are considered ‘Rigid’. Long linear chains (more than 12 carbon atoms) are considered ‘Weak’ as these have low thermal and oxidation stability. Carbon atoms linked to a double bond or a polar group are considered ‘Rigid’.

 

Linearity of molecule is quantified as linearity Index (LI) defined as the percent of carbon atoms in flexible linear chains (C8 to C12) out of total carbon atoms. LI of a normal paraffin of 8 to 12 carbon atoms will be 100 and that of aromatics like benzene, toluene, xylene etc. and naphthenics like cyclohexane etc. zero. This is estimated by

 

LI =

 

CT – Total number of carbon atoms in the molecule.

CR-Number of ‘Rigid’ and ‘Weak’ carbon atoms in the molecule.

 

Additional ‘rigid’ carbon atoms should also be counted in CR as follows.

 

1.   Carbon atoms in alkyl chains of aromatic and naphthenic rings, if these chains are

smaller than C7. For larger chains one carbon atoms attached to ring should be counted as ‘rigid’.

2.   A double bond should be considered as hindrance and two carbon atoms attached

to it should be taken as ‘rigid’, provided the chain associated to it has between C7

to C12 carbon atoms.

3.   Carbon atoms attached to polar groups like oxygen, phosphorous. Sulfur, hydroxyl, amine, amide etc. should be considered ‘rigid’.

 

In Table -4, linear hydrocarbon with 24 to 34 carbon, ideal lubricant structure, with optimal side chain placement for linear and with one aromatic or naphthenic ring are listed. LI is calculated and corresponding VI ranges are reported.   LI can incorporate both saturation and VI characteristics as well as oxidation stability and may be taken as a parameter for deciding the quality of base oils. This makes reporting ‘Saturates’ as in API classification redundant.

 

Values of LI over different ranges could be specified as quality index. This eliminates the risk of mixing of wide viscosity difference oils. Table -3 gives base oil classification based on this concept. It is applicable to only hydrocarbon stocks of API group I, II, III and IV, and is likely to give more accurate quality assessment of the base oil.

 

LI should be 65 - 85 to for high VI and high oxidation stability of base stocks.

 

CARBON DISTRIBUTION IN MOLECULES

 

Common methods to determine carbon atoms in various structural configurations in hydrocarbon and petroleum base oils are as follows. These could be used for experimental determination of CT and CR in petroleum and hydrocarbon stocks.

 

1.   ASTM D – 3238

Carbon distribution and structural group analysis of petroleum oils by the n-d-m method.

 

2.   ASTM D -6352

Boiling range distribution of petroleum distillates- 170 to 700oC by gas chromatography

 

3.   ASTM D - 2549

Separation of representative aromatic and monoaromatic, fraction of high boiling oils by elution chromatography.

 

4.   ASTM D - 1319

Hydrocarbon types in liquid petroleum products by fluorescent adsorption.

 

5.   G.C. M.S. based analysis.

 

6.   Urea adducible.

 

Linearity index for non-hydrocarbon fluids may also be calculated on the basis of these

guidelines, based on the chemical structure of the compound. For mixtures like VOs and

CMVOs, LI for each constituent may be calculated and LI of the product may be proportionally averaged. In Table-5 estimated linearity index of some fatty acids, vegetable oils and CMVOs are reported. Values for fatty acids are generally low, those for VOs (triglycerides ) are moderate ( 50-80), and for CMVOs high ( 70-95).

 

Linearity Index for synthetic fluids may also be similarly calculated from the chemicaltructure. LI for some synthetic fluids; diester, pthalates, trimallitates, polyol esters andphosphate esters are reported in Table-6. Phosphate esters, particularly those with shortalkyl chains or aryl group substitutions have lower LIs. These are generally not preferredas functional fluids and are chosen for some specialized applications for fire resistanceand superior EP properties.

BLENDED BASE STOCKS

Refineries produce a limited number of base stocks (mostly three to five) in common viscosity grades; because of processing limitations.  Manufacturers of synthetic or VOs stocks also have such limitations. Viscosity grade requirements of blenders are much larger.   ASTM D 2422 has 20 viscosity grades; from KV (at 40oC); 2 cSt. to 3200 cSt.     (ISO VG 2 to ISO VG 3200).  Intermediate grades are prepared by blending two or more oils of adjustment lower and higher viscosity grades.  Available base stocks are four to five and all the intermediate grades are to be prepared by blending these.  This causes wider distribution of molecules in the oil with widely differing boiling points and volatilities in the product.  

During application lighter constituents vaporize more as a result the oil ‘thickens’ as KV increases.  In practice, for petroleum and hydrocarbon stock normally 15 % change in KV is considered detrimental to performance requiring oil change.  This corresponds to 5 to 10% loss of lighter low KV component in blend.  Therefore a maximum evaporation loss or volatility value of 5 % could be fixed for a good quality stock.  A better assessment of the blend could be done by GLC based tests like ASTM D 6417 or ASTM D 5480.  These tests may not be easily available. Volatility loss limit of 5 percent is fixed for petroleum and hydrocarbon base stocks.  This is about 2 percent for synthetics and VO stocks as these have narrow distribution of molecular weight.  Volatility test has no meaning for water based fluids as the test (ASTM D 972) is conducted at 100oC. Also WBFs are recommended at atmospheric conditions.Sometimes KV of a light fraction is made up by blending polymer ‘viscosifiers’ to meet the KV specifications of required base oil.  Such oils are sensitive to shear stress and break down at high shear applications.   These may also cream out at higher temperature (more then 90oC). 

API classification does not provide any safe guard for such blended stocks.  Inclusion of volatility or evaporation loss limits (ASTM D 972) appears to be essential in base oil classification for quality assurance.

COMPREHENSIVE BASE OIL CLASSIFICATION

 The future appears to be for multiplicity of base oils. Formulators will select a variety of

base stocks depending on performance requirements and economics. A comprehensive

base oil classification therefore should take into consideration all these options. It should

also provide information about the chemical nature of the stock. This will help in selection of additives.

 

The comprehensive base oil classification is given in table-7. This includes all the features and groups of API classification and further includes native vegetable oils, chemically modified vegetable oils, synthetic esters and ether fluids, polyalkylene glycols and water based fluids.

 

The properties listed are, Viscosity Index (VI), Iodine Value (IV), Saponification value (SAP), Water content, and biodegradability. This also has KV at 40oC. Each group is divided into five sub groups according to KV at 40oC. Therefore separate mention of viscosity along with the group as in API is not required. Group I, II, II+, III and IV are same as those for API, except that re-refined stocks are included. ‘Sulfur Content’ and ‘Saturates’ as in API classification are not included as ‘Sulfur’ is considered ‘Superfluous’ and ‘Saturates’ are adequately represented in VI, and IV.

 

Group V includes native vegetable oils as these are complex mixtures of triglycerides.

These are identified by high IV (more than 80), and high SAP value.

 

Group VI, includes esters and non-hydrocarbons as in group V of API classification. These are saturated esters and would be identified by low IV (less than 5) and high SAP

(more than 60).

 

Chemically modified vegetable oils (CMVOs) are included in group VII. These are characterized by high VI (>140), lower IV (less than 20) and high SAP (more than 80). Group VIII has hydrophobic esters of polyhydric alcohol glycols and polyols. These are

characterized by high VI, high SAP and low IV and also low to moderate water content

(less than 1 %).

 

Hydrophilic glycol esters and polyakylene esters and their water solutions are placed in

group IX. These are characterized by low IV, high SAP and low water content (2 – 30

percent).

 

Water based fluids; emulsions of different fluids in water or viscosified water with polymer dispersions, are included in group X. These are characterized by physical appearance, low SAP, low IV and moderate to high (30 to 99 percent) water content.

 

An additional group XI is also included to take care of other fluids, like silicons, halo-organics, organosilicons, and innovative fluids. These are not well defined and will be identified by individual fluid properties.

 

Linearity index has not been included in the final format, even though it gives important information about the structure of molecules, which may be useful in selection of additive package.  This is because of following reasons.

 

1.      Methods available for determination of distribution and form of association of carbon atoms are not so accurate, particularly for mixtures.  These are not commonly available in laboratories and need experienced operators and expensive equipment.

 

2.      LI varies from a low to high value for all types of base fluids.  Therefore fluid type cannot be identified by LI.  For a fluid to be a good stock for formulation of functional fluids, LI has to be higher than 70.

 

3.      Parameters as included in Table -7 can give all the required information about stock.  Also, these could be determined in a common laboratory.

 

If the viscosity grade (a) to (e) is not fixed, and KV of stock at 40oC is to be specified as in API classification, the table -7 can be presented in compact form (Table-8).  LI should be greater than 70 if the carbon distribution data is available.

 

The final classification is given in Table -8.  Properties required to be reported for characterization of a base stock are given in table – 9. with typical methods.  The classification provides information about viscosity grade, chemical nature and characteristics of base fluids for an intended application. This provides guidance for selection of additive system. It also has information about biodegradability and environmental issues.

 

REFERENCES

 

1. Shubkin R. L., Synthetic Lubricants And High-Performance Functional

    Fluids, Marcel Dekkar (1993)

 

2. Gunderson R.C. and Hart A.W.; Synthetic Lubricants, Reinhold Publishing Co.

    (1962).

 

3. Bailey’s Industrial oil & Fat. Vol. 1 to Vol. 6, 5th Edn. Wiley Interscience (1996)

 

4. Dwivedi M. C., Hydrocarbon Composition Based, Base Oil Classification,

    LAWPSP Publication Vol. 14, BS.03, (2004)

 

5. Dwivedi M.C. , Standardization of Vegetable Oil Based Functional Fluids,

    LAWPSP Publication Vol. 15, SL.02, (2006. )

TABLE -1

 

API BASE OIL CLASSIFICATION

 

GROUP

 

TYPE

SULFUR

(WT. %)

SATURATES

(VOL. %)

VI

I

Mineral oil

Re-refined oil

>0.03  and / or

<90

80 to 119

II

Mineral oil

Re-refined oil

<0.03  and

>90

80 to 119

II+*

Mineral oil

Re-refined oil

<0.03  and

>90

110 to 119

III

Mineral oil –Chemically

Processed and hydrofinished

GTL and STL products

<0.03  and

>90

>120

IV

Synthesized Hydrocarbons

Synthetic hydrocarbons, PAOs, Polymers,

Alkylates etc.

V

Esters and non-hydrocarbons

All products not in Group I-IV

 

Notes -

1.   Group II+ is not an official API category but often used in industry.

 

2.      Re-refined mineral oil stocks are not specifically indicated in API.

 

3.      GTL and STL product are not includes in API classification.


TABLE – 2

SUGGESTED PHYSICAL AND COMPOSITIONAL PROPERTIES AND TEST METHODS FOR LUBRICANT BASE OILS

(ASTM D-6074-99)

PROPERTY

TYPICAL LEVEL

TEST METHOD

A.  PHYSICAL PROPERTIES

1.       Appearance

Clear

Free of suspended particles - visual

2.       Color

 

D-1500

3.       Density at 15oC                            (kg/m3)

 

D-1298, D-4052

4.       Flash Point                                      (oC)

 

D-92

5.       Kinematic  Viscosity                     (Cst)

            at 40oC

           at 100oC

 

D-445

6.       Pour Point                                      (oC)

 

D-97

7.       Viscosity Index

 

D-2270

8.       Volatility Loss                                (%)

 

D-2887, D-5480

NOACK (CEC L-40-A-93 or JPI-5S-41-93)

9.       Demulsibility 30 mins.                 (ml)

 

D-1401

B.  COMPOSITIONAL PROPERTIES

 10.  Carbon Residue                          (% mass)

 

D-524, D-189, D-4530

 11.  Nitrogen                                      (mg/kg)

 

D-4629

 12.  Precipitation number                

 

D-91

 13.  Saturates                                      (Wt. %)

 

D-2007

 14.  Sulfur                                           (Wt. %)

 

D-2622, D-4294, D-3120

C. CHEMICAL PROPERTIES

15.  Acid Number                              ( mgKOH/g)

£ 0.10

D-974, D-664

16.  Base Number                              ( mgKOH/g)

£ 0.30

D-4739, D-2896

17  Total Chlorine                                   ( mg/kg)

£ 50

D-4929

18.  Copper Corrosion  3hrs., 100oC

≤1

D-130

19.  Elemental Analysis                           ( mg/kg)

    Mg, Na, Ba, Cu, B, Pb, Mn, Ni, Si

    Al, As, Cd, Ca, Fe, P, Zn, Cr, Sn

    Total of all above

 

 

 

£ 25

D-5185, D-4628

D-4925, D4951

20.  Glycol                                                 (mg/kg)

£ 5

D – 4291

21.  PCB content                                       (mg/kg)

£ 2

D-4059

22.  Total Volatile Organic  Halogens       (mg/kg)

£ 5

EPA-8120

23.  Water                                                  (mg/kg)

£ 150

D-1744

D.  TOXICOLOGICAL PROPERTIES

24.  Mutagenicity Index

Pass

E-1687

25.  DMSO Extractable                         (wt. %)

Pass

IP-346

26.  Chronic Animal Bioassay Analysis, Number   

       Tumor Bearing Animals / Test Group (%)

Pass

No method prescribed

 

TABLE – 3

CLASSIFICATION OF PETROLEUM AND HYDROCARBON BASE OILS

GROUP AND TYPE

CARBON NUMBER

SATURATES (WT %)

SULFUR

(WT %)

VI

LI

MINERAL OIL

I (a)     70N

 

20-24

 

< 90

 

> 0.03

 

80-95

 

85-90

I (b)     150N

22-28

< 90

> 0.03

80-90

80-85

I (c)     300N

24-32

< 90

> 0.03

80-90

75-80

I (d)     500N

26-34

< 90

> 0.03

80-85

70-75

I (e)     750N

32-44

< 90

> 0.03

75-80

65-70

II (a)    70N

20-24

> 90

< 0.03

90-100

85-90

II (b)   150N

22-28

> 90

< 0.03

90-95

80-85

II(c)     300N

24-32

> 90

< 0.03

85-90

75-80

II (d)    500N

26-34

> 90

< 0.03

80-90

70-75

II (e)    750N

32-44

> 90

< 0.03

80-85

65-70

III (a)   70N

20-24

> 90

< 0.03

90-120

90-95

III (b)  150N

22-28

> 90

< 0.03

90-110

85-90

III (c)   300N

24-32

> 90

< 0.03

90-100

80-85

III (d)   500N

26-34

> 90

< 0.03

85-95

75-80

III (e)   750N

32-44

> 90

< 0.03

85-90

70-75

IV

-

> 90

< 0.03

120-160

-

V

-

-

< 0.03

> 160

-

 Above numbers are suggestive comprehensive experimental verification is required to fix right limits.

TABLE – 4

LINEARITY INDEX OF HYDROCARBON MOLECULES STRUCTURED AS IDEAL FLUIDS WITHOUT AND WITH ONE  C6 RING, ONE ISOCHAIN OPTIMALLY PLACED.

CARBON  NUMBER

LINEARITY

INDEX

EXPECTED

VI RANGE

OXIDATION

STABILITY

24 – Linear

- One Ring

100

75

110-120

90-100

High

High

25 – Linear

- One Ring

100

76

100-120

90-100

High

High

26 – Linear

- One Ring

100

77

100-120

90-100

High

High

27 – Linear

- One Ring

100

78

110-120

90-100

High

High

28 – Linear

- One Ring

100

79

110-120

90-100

High

High

29 – Linear

- One Ring

100

69

110-120

85-95

High

High

30 – Linear

- One Ring

100

69

110-120

85-95

Medium

High

31– Linear

- One Ring

100

68

110-120

85-95

Medium

High

32 – Linear

- One Ring

100

69

110-120

85-95

Medium

Medium

33 – Linear

- One Ring

100

68

100-110

85-95

Medium

Medium

34 – Linear

- One Ring

100

65

100-110

85-95

Medium

Medium

 TABLE – 5

LINEARITY INDEX OF SOME FATTY ACIDS, VOs, AND CMVOs.

 

FATTY ACID/VO

CHEMICAL CONSTITUTION

CT

CA

LI

A.  FATTY ACIDS AND VEGETABLE OILS (VOs)

1.  Lauric Acid

C12:0

12

1

92

2.  Mysristic acid

C14:0

14

13

8

3. Palmitic acid

C16:0

16

15

6

4.  Plamitaleic acid

C16:1

16

3

81

5.  Stearic Acid

C18:0

18

17

6

6. Oleic Acid

C18:1

18

3

83

7. Linoleic Acid

C18:2

(9, 12 Octadecodienoic)

18

7

61

8. Linoleic Acid

C18:3

(9,12, 15,Octadecatrienoic)

18

10

44

9. Ground Nut Oil

 

16-18

-

76

10.  Coconut Oil

 

12-18

-

57

11.  Palm Oil

 

14-18

-

53

12. Soybean Oil

 

16-18

-

77

13. Neem Oil

 

14-18

-

65

14. Cotton Seed Oil

 

14-18

-

71

15. Karanja Oil

 

16-18

-

79

B. CHEMICALLY MODIFIED VEGETABLE OILS ( CMVOs)

16.  9, 2, nolylbenzene,

      alkyl hexyl oleate

C6, H5. C9 H19. C18 H34. C6H13O

39

6

87

17.  9 Toluene alkyl

       -2 EH oleate

C7H5.CH2.C18H3.C8H17O

33

7

79

18.  9 Butyl alkyl 2 EH 

        oleate

C4 H9C18 H34. C8H17O

30

4

87

19.   9 Methyl alkyl  

        -2 EH oleate

CH3C18 H3. C8H17O

27

1

96

20.  Dimmer methyl

       oleate

(C18 H3 CH3 O)2

38

2

95

21.  Palm oil alkyl ester

Methyl alkyl palm oil 2 EH ester

-

-

83

22.   Soybean oil

       toluene alkyl ester

Toluene alkyl 2 EH ester

-

-

78

23.  Nonyl alkyl

       karanja oil

Nonene–karanja 2 EH ester

-

-

84

 

LI for MVOs calculated from VO composition

LI of native VOs calculated from fatty acid composition and rounded to nearest digit.

 

TABLE-6

 

LINEARITY INDEX OF  SOME ORGANO-ESTER FLUIDS

 

ORGANIC ESTER FLUID

CHEMICAL CONSTITUTION

 

CT

CA

LI (%)

(A) Dieseters

1.  2 EH Adipate

(CH2)4, (COO C8 H17)2

22

6

73

2.  Oleic Adipate

(CH2)4. (COO C16 H30)2

38

6

84

3. 2EH Azelate

(CH2)7. (COO C8 H17)2

25

2

92

4. Oleic Azelate

(CH2)7. (COO C16 H30)2

41

2

95

5.  2 EH Dodecanedioate

(CH2)10. (COO C8 H17)2

28

2

92

6. Oleic Dodecanedioate

(CH2)10. (COO C16 H30)2

44

2

95

(B)  Phthalates

 

 

 

 

1.  2EH Phthalate

(C6H4). (COO C8 H17)2

24

8

67

2.  Oleic Phthalate

C6H4. (COO C16 H30)2

40

8

80

(C ) Trimellitates

 

 

 

 

1.  2 EH Trimellitates

C6H3. (COO C8 H17)3

33

9

73

2.  Oleic Trimellitates

C6H3. (COO C16 H30)3

57

9

84

(D) Polyol Esters

 

 

 

 

1.  2EH Pentaerythritol Esters

C.(CH2.COO C8H17)4

41

9

78

2.  Oleic Pentaerythritol Ester

C.(CH2.COO C16H30)4

73

9

88

3. 2 EH – Trimethylol Propane Ester

CH3.CH2 .C.( CH2 .COOC8H17)3

33

9

73

4.  Oleic Trimethylol Propane Ester

CH3.CH2 .C.( CH2 COOC16H30)3

57

9

84

5.  2 EH Neopentylglycol Ester

( CH3 )2.C.(CH2CO.C8H17)

23

7

74

6.  Oleic Neopentyglycol Ester

( CH3 )2.C.(CH2CO.C16H30)

39

7

82

(E) Phosphate   Esters

 

 

 

 

1.  Tri n-Octyl Phosphate Ester

PO4 .( C8 H17)43

24

3

88

2.  Di-2 EH Phenyl Phospahte Ester

PO4. (C8H17)2 .( C6 H5)

22

9

59

3. Iso-propy Phenyl Phosphate Ester

    ( IPPP)

PO4 .( C6H5.C3H7)2 .( C6H5)

24

24

0

4. Tri-oleic Phosphate Ester

PO4 .( C16 H30)3

48

3

94

 

 

TABLE – 7

 

COMPREHENSIVE - BASE FLUID CLASSIFICATION

 

GROUP

Viscosity at 40oC

cSt. (SUS)

 

 

VI

 

IV

 

SAP

 

Water

(ppm)

 

volatility

(%)

Biodegrad-

ability

(%)

 

Type

I(a)

13 (70)

>85

 

 

 

<2

 

 

 

<0.2

 

 

 

<100

 

 

 

<5

 

 

 

30–50

 

Mineral oil- solvent extracted

neutral, Re-refined stocks

I(b)

32 ( 150)

>85

I( c )

65 (300)

>85

I (d)

110(500)

>80

I ( e)

150(750)

>80

II (a)

13 (70)

>90

 

 

<2

 

 

<0.2

 

 

<100

 

 

<5

 

 

30–50

Mineral oil –hydrofinished,,

deep extracted neutral.

Re-refined stocks

II (b)

32 (150)

>90

II (c )

65(300)

>90

II (d )

110(500)

>85

II (e)

150(750)

>85

III (a )

13(70)

>95

 

 

<2

 

 

<0.2

 

 

<100

 

 

<5

 

 

30–60

Mineral oils – hydroprocessed.,

GTL and STL products.

III (b )

32(150)

>95

III (c )

65(300)

>95

III (d )

110(500)

>90

III (e )

150(750)

>90

IV (a)

13(70)

>120

 

 

<2

 

 

<0.2

 

 

<100

 

 

<2

 

 

60–80

Synthetic hydrocarbons –

alkaylation, polymerization

hydrofinished hydrocarbons stocks

IV (b)

32(150)

>120

IV (c)

65(300)

>120

IV (d)

110(500)

>120

IV (e)

150(750)

>120

V (a)

13 (70

>100

 

 

 

>80

 

 

 

>90

 

 

 

<1000

 

 

 

<2

 

 

 

95–100

Processed and blended vegetable oils

V(b)

32 (150)

>100

V(c )

65 (300)

>100

V( d)

110 ( 500)

>100

V (e)

150(750)

>100

VI (a)

13 (70)

>120

 

 

<5

 

 

>60

 

 

<200

 

 

<2

 

 

50 – 80

Saturated synthetic esters and

ethers

VI(b)

32 (150)

>120

VI(c )

65(300)

>120

VI( d)

110(500)

>120

VI (e)

150(750)

>120

VII (a)

13 (70)

>140

 

 

 

<20

 

 

 

>90

 

 

 

<200

 

 

 

<2

 

 

90–95

Modified VOs; - alkylated esters, polymerized esters, estolides, etc.

VII(b)

32 (150)

>140

VII(c )

65(300)

>140

VII( d)

110(500)

>140

VII (e)

150(750)

>140

VIII (a)

13 (70)

>140

 

 

<5

 

 

>90

 

 

<1000

 

 

<2

 

 

50–80

Hydrophobic esters of glycols, diols, triols and polyols

VIII(b)

32 (150)

>140

VIII(c )

65(300)

>140

VIII( d)

110(500)

>140

VIII (e)

150(750)

>140

IX( a)

13 (70)

>140

 

 

 

<5

 

 

 

>90

 

 

 

<30(%)

 

 

 

NA

 

 

 

NA

(>90)

Hydrophilic esters, ethers and their water solutions

IX( b)

32 (150)

>140

IX(c)

65(300)

>140

IX( d)

110(500)

>140

IX( e)

150(750)

>140

X( a)

13 (70)

>140

 

 

<1

 

 

<1

 

 

>90(%)

 

 

NA

 

 

NA

(>90)

Water based emulsions suspensions and polymer dispersions

X( b)

32 (150)

>160

X(c)

65(300)

>160

X( d)

110(500)

>160

X( e)

150(750)

>160

XI ( a to e)

 

 

 

 

 

 

 

Fluids not included in group I to X

 

TABLE – 8

 

BASE FLUID CLASSIFICATION

 

GROUP

VI

IV

SAP

Water

( ppm)

Volatility

(%)

Biodegrad

ability

(%)

Type

I

80 –85

<2

<0.2

<100

<5

<40

Mineral oil- solvent extracted

neutral, Re-refined stocks

II

85–90

<2

<0.2

<100

<5

<40

Mineral oil –hydrofinished,,

deep extracted neutral.

Re-refined stocks

III

90–95

<2

<0.2

<100

<5

<60

Mineral oils – hydroprocessed.,

GTL and STL products.

IV

>120

<2

<0.2

<100

<2

<80

Synthetic hydrocarbons –

alkaylation, polymerization

 hydrofinished hydrocarbons stocks

V

>100

>80

>90

<1000

<2

95-100

Processed and blended

 vegetable oils

VI

>120

<5

>60

<200

<2

<80

Saturated synthetic esters and

 ethers

VII

>140

<20

>90

<500

<2

90-95

Modified VOs;- alkylated

esters, polymerized esters,

estolides, etc. 

VIII

>140

<5

>90

<1000

<2

<80

Hydrophobic esters of glycols,

 diols, triols and polyols

IX

>140

<5

>90

<30(%)

NA

NA

>90

Hydrophilic esters, ethers and

 their water solutions

X

>140

<1

<1

<90(%)

NA

NA

>90

Water based emulsions

 suspensions and polymer

 dispersions

XI

 

 

 

 

 

 

Fluids not included in group I

 to X

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TABLE – 9

BASE OIL CLASSIFICATION

PROPERTIES AND TEST METHODS

PROPERTY

TYPICAL TEST METHODS

 

1.  Kinematic Viscosity at 40oC        ( cSt.)

ASTM D 446

2.  Viscosity Index ( VI)

ASTM D2270

3. Iodine Number (IV) Bromine number

ASTMD 1159

4. Saponification value ( SAP)    (mgKOH/g)

ASTM D 94

5.  Evaporation loss / volatility           ( %)

ASTM D 972

6. Water content                             (ppm/ %)

ASTM D -1744, ASTM D 95

7. Biodegradability                           (%)

ASTM D 5864