ASTM D7373-12

Designation: D7373 − 12Standard Test Method forPredicting Biodegradability of Lubricants Using a Bio-kinetic Model1This standard is issued under the fixed designation D7373; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers a procedure for predictingbiodegradability of lubricants using a bio-kinetic model.1.2 The values stated in SI units are to be regarded asstandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2549 Test Method for Separation of Representative Aro-matics and Nonaromatics Fractions of High-Boiling Oilsby Elution ChromatographyD5864 Test Method for Determining Aerobic Aquatic Bio-degradation of Lubricants or Their ComponentsD6300 Practice for Determination of Precision and BiasData for Use in Test Methods for Petroleum Products andLubricantsD6731 Test Method for Determining the Aerobic, AquaticBiodegradability of Lubricants or Lubricant Componentsin a Closed Respirometer3. Terminology3.1 Definitions:3.1.1 aromatics fraction, n—portion of the sample desorbedwith the polar eluants. The aromatics fraction is divided intononpolar and polar based. They may contain aromatics, con-densed naphthenic-aromatics, aromatic olefins, and com-pounds containing sulfur, nitrogen, and oxygen atoms.3.1.2 bio-kinetic model, n—model that can predict the bio-degradability of a lubricant.3.1.3 biodegradability, n—ability of a substance to be bro-ken down into simpler substances by bacteria.3.1.4 effective composition to biodegradation (ECB),n—component of material that can be biodegradable by bacte-ria.3.1.4.1 Discussion—The term ECB is a part of bio-kineticmodel is sum of non-aromatic components in a lubricant.3.1.5 nonaromatics fraction, n—portion of the sampleeluted with n-pentane. The nonaromatics fraction is a mixtureof paraffinic and naphthenic hydrocarbons if sample is astraight-run material. If the sample is a cracked stock, thenonaromatics fraction will also contain aliphatic and cyclicolefins.4. Summary of Test Method4.1 A weighed amount of sample is charged to the top of aglass chromatographic column packed with activated bauxiteand silica gel. To elute the nonaromatics, n-pentane is added tothe column. When all of the nonaromatics are eluted, non-polararomatics fraction is eluted by additions of an equal mixture oftoluene and n-pentane. The ester fraction is eluted by additionsof diethyl ether. Then, the polar-aromatics is eluted by chloro-form and ethyl alcohol.4.2 The solvents are completely removed by evaporation,and the residues are weighed and calculated as thenonaromatics, nonpolar aromatics, ester fractions, and polararomatics of the sample.4.3 ECB is calculated based on the amount of nonaromaticsand ester fractions with their material ECB coefficients. Then,the biodegradability of a lubricant is calculated using thebio-kinetic model.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.12 on Environmental Standards for Lubricants.Current edition approved June 1, 2012. Published October 2012. Originallyapproved in 2007. Last previous edition approved in 2007 as D7373–07ε1. DOI:10.1520/D7373-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 This procedure is able to predict the biodegradability oflubricants within a day without dealing with microorganisms.3Excellent correlation is established between the test results andthe conventional biodegradation tests (see Test Method D5864and Test Method D6731).6. Apparatus6.1 Chromatographic Columns—as shown in Fig. 1 (seeTest Method D2549).6.2 Beakers (100, 250, and 600-mL)—inverted-rim type.6.3 Steam Bath.6.4 Electric Vibrator—for packing column.6.5 Weighing Bottles or Erlenmeyer Flasks—25 and 50 mL.6.6 Graduated Cylinders—50 mL, 100 mL, and 250 mL.7. Reagents and Materials7.1 Purity of Reagents—Reagent grade chemicals shall beused in this test. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available. Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Bauxite, 20- to 60-mesh—Before use, activate the baux-ite by heating at 538°C (1000°F) for 16 h. Transfer theactivated material to an airtight container while still hot andprotect thereafter from atmospheric moisture.7.3 Chloroform—(Warning—Toxic. May be fatal if swal-lowed.)7.4 Cleaning Solution—Chromic-sulfuric acid. (Warning—Causes severe burns.Arecognized carcinogen, strong oxidizer,contact with organic material may cause fire.)7.5 Diethyl Ether—Anhydrous. (Warning—Extremelyflammable.) The ethyl ether used in this test method should befree of peroxides as determined by the procedure in ReagentChemicals, American Chemical Society Specifications.47.6 Ethyl Alcohol, Denatured—Conforming to Formula 2Bof the U.S. Bureau of Internal Revenue. (Warning—Flammable .)3Rhee, In-Sik, “ Development of Bio-kinetic Model for Lubricants,” NLGISpokesman, Volume 69, 2005, pp. 22-29.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.FIG. 1 Test ApparatusD7373 − 1227.7 Pressuring Gas—Dry air or nitrogen, delivered to thetop of the column at a regulated gage pressure of 0 to 2 psi(13.8 kPa). (Warning—Compressed gas.)7.8 n-pentane—Commercial grade, aromatic–free. Somesamples of waxy stocks may not dissolve completely inn-pentane, in which case cyclohexane, commercial grade,aromatic-free, may be substituted for n-pentane. (Warning—Extremely flammable liquid.)7.9 Silica Gel—100- to 200-mesh.7.10 Toluene—Reagent grade minimum purity. (Warning—Toluene is flammable. Vapor harmful.)8. Procedure for Composition Analysis8.1 Clean the column with chromic-sulfuric acid (7.4),followed by distilled or demineralized water, acetone, and dryair or nitrogen.8.2 Introduce a small plug of glass wool into column,pressing it firmly into the lower end to prevent the flow of silicagel from the column.8.3 Clamp the column in a vertical position. Add smallincrements of silica gel, while vibrating the column along itslength, until the tightly packed silica gel extends to the lowermark on the chromatographic column.8.4 Continue to vibrate the column and add bauxite until thebauxite layer extends to the upper mark on the chromato-graphic column. Vibrate the column for an additional 3 minafter filling is completed8.5 If the sample is viscous, warm it with intermittentmixing or shaking until it is completely fluid.8.6 Transfer a representative sample (approximately 2 g) toa 25-mL weighing bottle or flask. Determine the weight of thesample to the nearest 1 mg by weighing the flask before andafter sample transfer.8.7 Add 10 mL of n-pentane (7.8) to the flask and dissolvethe sample.8.7.1 If the sample does not dissolve completely in coldn-pentane, warm it in warm water or over a steam bath.8.7.2 If the sample does not dissolve in warm n-pentane,take a fresh sample and substitute cyclohexane for then-pentane.NOTE 1—This procedure is only applicable to liquid-based lubricants.Solid or semisolid lubricants can not be analyzed due to their formations.Therefore, the lubricating grease cannot be analyzed, but its extracted oilcan be analyzed using this procedure.8.8 Add 10 mL of n-pentane to the top of the column toprewet the adsorbent.8.9 When the liquid level reaches the top of the bauxite bed,transfer the sample solution from the weighing flask to the topof the column.8.10 Rinse the flask with three successive 3-mL washes ofn-pentane. Add each wash to the top of the column.8.11 Then rinse the walls of the column bulb with two 3-mLportions of n-pentane, allowing the liquid level to reach the topof the bauxite bed before adding the next portion.8.12 Finally add 35-mL of n-pentane to the column bulb.8.13 Place a 50-mL graduate beneath the column to collectthe eluate. The elution rate should be approximately 1 mL/min.8.14 When the n-pentane level reaches the top of the bauxitebed, add 80 mL of an equal mixture of n-pentane and toluene(50:50 vol %). Connect the pressuring gas to the top of thecolumn and adjust the pressure to maintain an elution rate of 1to 2 mL/min. Collect 50 mL of n-pentane eluate in thegraduate. Rinse the tip of the column with 1 to 2 mL ofn-pentane, adding this to the 50 mL in the graduate. Label the50 mL graduate as n-pentane eluate.8.15 When the 50:50 vol % mixture of toluene and pentanelevel reaches the top of the bauxite bed, release the gaspressure and add 80 mL of diethyl ether (7.5) to the top of thecolumn. Reconnect the gas pressuring system and continue theelution. When 80 mL of elute haven collected in the graduate,rinse the column tip with 1 mL of the 50:50 vol % mixture oftoluene and pentane and add the rinse to the 100 mL graduate.Change the receiver to a 100 mL graduate. Label the 100 mLgraduate as nonpolar aromatic fraction.8.16 When the ether level reaches the top of the bauxite bed,release the gas pressure and add 100 mL of chloroform (7.3)tothe top of the column. Reconnect the gas pressuring system andcontinue the elution. When 80 mL of eluate have beencollected in the graduate, rinse the column tip with 1 mL ofether and add the rinse to the 100 mL graduate. Change thereceiver to a 250 mL graduate. Label the 100 mL graduate asether-eluted fraction.8.17 When the chloroform level reaches the top of thebauxite bed, release the gas pressure and add 75 mL of ethylalcohol (7.6). Reconnect the gas pressuring system and con-tinue the elution until the alcohol level reaches the top of thebauxite bed. Release the gas pressure. Rinse the column tipwith 1 mL of chloroform adding this to the graduate. Label the250 mL graduate as chloroform-alcohol-eluted fraction.8.18 Weigh a 100 mL inverted-rim beaker to the nearest1 mg. Quantitatively transfers the n-pentane eluate to thisbeaker and allows the n-pentane to evaporate at room tempera-ture. Cyclohexane, if used as the elution solvent, is evaporatedon a steam bath. Evaporation is accelerated in both cases bydirecting a controlled steam of dry nitrogen downward onto thesurface of the liquid.8.19 When all the solvent appears to be evaporated, stop thenitrogen flow, allow the beaker to come to room temperature,and dry the outside of the beaker to remove any condensedmoisture. Reweigh the beaker to the nearest 1 mg.8.20 Repeat the evaporation step for 5-min periods until theweight loss between successive evaporations is less than 20mg. Heat from a stream bath is generally required during thefinal evaporation steps to remove completely the elutionsolvent. The weight of the residue in the beaker is the quantityof the nonaromatics friction.8.21 Weigh a 250 mL inverted-rim beaker to the nearest 1mg. Quantitatively transfer the chloroform-alcohol-eluted frac-tion to this beaker and evaporate on a stream bath with aD7373 − 123controlled stream of dry nitrogen directed downward onto thesurface of the liquid. When the solvent is evaporated, removethe beaker from the steam bath, cool to room temperature, andadd quantitatively the ether-eluted fraction. Evaporate the etherat room temperature as described in 8.18 – 8.20. Determine theweight of the residue (ester fraction) to the nearest 1 mg.8.22 The weight of aromatics (polar and nonpolar), esterfraction plus the nonaromatics fraction recovered must equal atleast 95% of the sample charged. If 95% recovery is notobtained, repeat the test. Recoveries greater than 100% indicateincomplete removal of solvent or the condensation of moisturein the beakers.8.23 Transfer all sample fractions into suitable size ofsample vials for storage pending further analysis.9. Calculation9.1 Calculate the percentage of the nonpolar aromatics andpolar aromatics fraction, nonaromatics and ester fraction asfollows:Nonaromatics, wt % 5 @a/~total recovered!# 3100 (1)Nonpolar aromatic, wt % 5 @b/~total recovered!# 3100 (2)Ester fraction, wt % 5 @c/~total recovered!# 3100 (3)Polar aromatics, wt % 5 @d/~total recovered!# 3100 (4)where:a = weight of nonaromatics recovered byn-pentane,b = weight of nonpolar aromatics recoveredby 50:50 mixture of toluene andn-pentane,c = weight of ester fraction recovered by di-ethyl ether,d = weight of polar aromatics recovered bychloroform and ethyl alcohol, andTotal recovered = a + b + c + d.9.2 Calculate ECB value of sample as follows:ECB 5(ac~ηaCa1 ηcCc(5)where:η = ECB coefficient listed in Table 1,Ca= Fraction of nonaromatics (n-pentane), andCc= Fraction of ester (diethyl ether).9.3 Calculate the biodegradability of a lubricant usingbio-kinetic model as follows:B~t! 5 B~1!10.49ln~6.8 3ECB22.38!lnt (6)where:t = time, days (i.e., 28),B(t) = Biodegradability of a lubricant with time, andB(1) = 0.01.10. Report10.1 The value calculated in 9.3 is reported as the biode-gradability of a lubricant.11. Precision and Bias11.1 Precision—The precision of this test method as deter-mined by statistical examination of interlaboratory results inaccordance with Practice D6300 is as follows:11.1.1 Repeatability—Two test results obtained within onelaboratory obtained by the same operator using the sameequipment on the same day in the same laboratory shall bejudged not equivalent if they differ by more than the “r” valuefor that material; “r” is the interval representing the criticaldifference between two test results for the same material.Repeatability (r)=1%11.1.2 Reproducibility—Two test results obtained by differ-ent operators using different equipment in different laboratoriesshall be judged not equivalent if they differ by more than the“R” v