1、Designation: D7996 15Standard Test Method forMeasuring Visible Spectrum of Asphaltenes in Heavy FuelOils and Crude Oils by Spectroscopy in a MicrofluidicPlatform1This standard is issued under the fixed designation D7996; the number immediately following the designation indicates the year oforiginal
2、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. Scope1.1 This test method covers the measurement, either in thelaboratory or
3、in the field, of visible spectra of asphaltenes andmaltenes in gas oil, diesel fuel, fuel oils, residual fuel oils,lubricating oil, bitumen, and crude oil using microfluidics andspectrographic techniques.21.2 These measurements can be related quantitatively to themass percent of asphaltenes present
4、in the sample.1.3 The test method is limited to asphaltene-containing oilwith asphaltenes content less than 15 % by mass.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of th
5、esafety 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:3D3279 Test Method forn-Hept
6、ane InsolublesD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4175 Terminology Relating to Petroleum, PetroleumProducts, and LubricantsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD6560 Test Method for Determination of Asphaltenes (Hep-tane Insolubles
7、) in Crude Petroleum and Petroleum Prod-uctsE275 Practice for Describing and Measuring Performance ofUltraviolet and Visible Spectrophotometers3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, seeTerminology D4175.3.1.2 absorbance, (A), nthe molecular property of
8、 a sub-stance that determines its ability to take up radiant energy,expressed by:A 5 log101T! 52log10T! (1)where T is the transmittance.3.1.2.1 DiscussionAbsorbance expresses the excess ab-sorption over that of a specified reference or standard. It isimplied that compensation has been affected for r
9、eflectancelosses, solvent absorption losses, and refractive effects, ifpresent, and that attenuation by scattering is small comparedwith attenuation by absorption.3.1.3 asphaltenes (rarely used in the singular), nin petro-leum technology, represent an oil fraction that is soluble in aspecified aroma
10、tic solvent but separates upon addition of anexcess of a specified paraffinic solvent.3.1.3.1 DiscussionIn this test method, the aromatic sol-vent is toluene and the paraffinic solvent is heptane.3.1.4 crude oil, na naturally occurring hydrocarbonmixture, generally in a liquid state, which may also
11、includecompounds of sulfur, nitrogen, oxygen, metals, and otherelements. (Synonymcrude petroleum, crude.)3.1.5 dilution factor (f), nthe proportion of solvent in-crease made to reduce the concentration and thus the absor-bance of a solute, expressed by the ratio of the volume of thediluted solution
12、to the volume of original solution containingthe same quantity of solute as the diluted solution.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.14 on Stability and Cleanliness of
13、 Liquid Fuels.Current edition approved Dec. 1, 2015. Published February 2016. DOI: 10.1520/D7996-15.2This method and the apparatus are covered by US Patent 8,269,961 andCanadian Patent 2,800,879. Interested parties are invited to submit informationregarding the identification of an alternative(s) to
14、 this patented item to ASTMInternational Headquarters. Your comments will receive careful consideration at ameeting of the responsible technical committee,1which you may attend.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. F
15、or Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.6 flocculation, nof asphaltenes from crude oils orheavy fuel oils,
16、 the aggregation of colloidally dispersed as-phaltenes into visibly larger masses that may or may not settle.3.1.7 transmittance, (T), nthe molecular property of asubstance that determines its transportability of radiant power,expressed by:T 5 PPo(2)where:P = the radiant power passing through the sa
17、mple, andPo= the radiant power incident upon the sample.3.2 Definitions of Terms Specific to This Standard:3.2.1 concentration (c), nthe quantity of absorbing sub-stance in a solution in grams per litre.3.2.2 flow cell path length (b), nthe distance inmillimetres, measured in the direction of propag
18、ation of thebeam of radiant energy, between the surface of the specimen onwhich the radiant energy is incident and the surface of thespecimen from which it is emergent.3.2.2.1 DiscussionThis distance does not include thethickness of the cell in which the specimen is contained.3.2.3 maltenes, nthe fr
19、action of an oil after precipitationand subsequent removal of asphaltenes when mixed with aparaffinic solvent such as heptane.3.2.4 microfluidics, nthe science and technology of sys-tems that process or manipulate small amounts of fluids (10-9to 10-18L) using channels with dimensions of tens to hund
20、redsof micrometres.43.3 Abbreviations:3.3.1 AUabsorbance unit3.3.2 CVcoefficient of variability3.3.3 PTFEpolytetrafluoroethylene4. Summary of Test Method4.1 This test describes a method for measuring the visiblespectrum of asphaltenes in crude oil and petroleum products,such as fuel oils, diesel fue
21、l oils, gas turbine fuel oils, heavyfuel oils, residual fuel oils, and lubricating oils. The oil sampleis mixed with heptane to induce precipitation of asphaltenes.The precipitated asphaltenes are removed using a porous filter.The change in visible spectrum of the sample before and afterprecipitatio
22、n is due to the removal of asphaltenes. The visiblespectrum of asphaltenes obtained using this technique isproportional to the concentration of the precipitated as-phaltenes.4.2 In the first step, the visible spectrum of the dilutedsample is measured by mixing the sample with toluene at 1 +40 v/v ra
23、tio (1 part sample in 40 parts solvent) using anautomated metering system. The two streams of sample andtoluene are mixed in a microfluidic mixer for effective masstransfer. The visible spectrum of the mixture is measureddownstream of the membrane. The absorbance is recordedonce a plateau is reached
24、.4.3 In the second step, the spectrum of the maltenes ismeasured. The second portion of the sample is mixed withheptane at1+40v/vratio (1 part sample in 40 parts solvent).The asphaltenes precipitate as the sample comes in contactwith heptane in the microfluidic mixer. As the mixtures passesthrough t
25、he membrane, the asphaltenes fraction is retainedwhile the maltenes permeate through. The visible spectrum ofthe maltenes is measured downstream of the membrane.4.4 The difference between the spectra of the diluted oilsample and maltenes are calculated and correlated to concen-tration of asphaltenes
26、.5. Significance and Use5.1 This procedure describes a rapid and sensitive methodfor measuring the visible spectrum of asphaltenes in crude oilsand petroleum products containing residual material using amicrofluidic technique.5.2 The method is sensitive to small changes in concentra-tion of asphalte
27、nes. Therefore, it can be used as a qualitycontrol and chain-of-custody check for fuel or crude oilsamples.5.3 The visible spectrum of asphaltenes obtained using thistechnique is correlated to the mass concentration of asphaltenesusing conventional gravimetric techniques (see X1.3.3).5.4 This test m
28、ethod can be used by refiners as well asupstream laboratories. The test is intended for samples withasphaltenes content less than 15 % by mass.6. Apparatus56.1 SpectrometerEquipped to handle liquid samples in acell having optical path length of 3 mm and capable ofmeasuring absorbance in the spectral
29、 region from 500 nm to900 nm with a spectral resolution of 2 nm or less. Wavelengthmeasurement shall be repeatable and known to be accuratewithin 60.2 nm or less as measured by the argon emission lineat 706.722 nm.6.1.1 The performance of the spectrophotometer can bemeasured using Practice E275.6.2
30、Syringe PumpsThree syringe pumps with 4000 stepsper centimeter. The accuracy and precision of the pumps haveto be at least 0.10 % CV and 0.03 % CV respectively.6.3 Syringes5 mL syringe for heptane, 5 mL syringe fortoluene, and a 250 L syringe for toluene.6.4 Flow Cell3 mm optical path length.6.4.1 A
31、 flow cell with minimal dead volume.6.5 Microfluidic MixerAny type of microfluidic mixersmay be used. However, since the asphaltenes precipitate in themixer and eventually clog the mixer if run for too long, amultichannel design is preferred.4Whitesides, G. M. “The Origins and Future of Microfluidic
32、s,” Nature, Vol. 442,No. 7101, 2006, p. 368373.5The sole source of supply of the microfluidic asphaltenes content apparatusknown to the committee at this time is Schlumberger Canada Limited, 9450 17thAve., Edmonton, AB, T6N 1M9, Canada, or 14910 Airline Rd., Rosharon, TX77583, U.S., http:/. If you a
33、re aware of alternative suppliers, pleaseprovide this information to ASTM International Headquarters. Your comments willreceive careful consideration at a meeting of the responsible technical committee,1which you may attend.D7996 1526.6 Microfluidic Membrane Filtration Unit200 nm PTFEmembrane.6.7 Sa
34、mple Loop200 L stainless steel, PTFE, or chemi-cally compatible sample loop.7. Reagents and Materials7.1 Purity of ReagentsReagents of HPLC grade are re-quired for this test.7.2 Heptane. CAS 142-82-5 (WarningFlammable. Vaporharmful. Vapor may cause flash fire.)7.3 Toluene. CAS 108-88-33 (WarningFlam
35、mable. Vaporharmful. Vapor may cause flash fire.)8. Sampling and Test Specimens8.1 Obtain the sample in accordance with the procedures ofPractices D4057 or D4177.8.2 When working with the oil sample in the laboratory, theoil shall be stirred either manually or mechanically until themixture is homoge
36、nous and representative for the wholesample before withdrawing an aliquot for testing.8.3 It is recommended to heat the sample in a vial in an ovenat 60 C for no more than 60 min. The sample vial should thenbe agitated using a sonicator for 30 s prior to sub-samplingusing a syringe.8.3.1 Perform hea
37、ting in a closed container such as a glassbottle to minimize oxidative degradation. Loosen the cap of thebottle to avoid building pressure in the container due toevaporation of light ends.8.4 Use a 500 L syringe to subsample from the bottle rightafter sonication of the sample. Inject the sample into
38、 thesample loop immediately after subsampling.9. Procedure9.1 First, load the sample into the 200 L sample loop. Halfof the sample will be used for spectroscopy of the diluted oilsample and the other half will be used for spectroscopy of themaltenes.9.2 Prime the system and the flow cells with tolue
39、ne andacquire light and dark reference spectra.9.3 Check the integrity of the membrane and ensure thereare no defects in the membrane. Any ruptures in the membranecould cause the asphaltenes pass through the membrane. Theintegrity of the membrane may be tested by monitoring thepressure differential
40、across it when a known flow rate isinjected into the system.9.3.1 The temperature of the microfluidic section should bekept at 30 C.9.4 Dilute the test sample with toluene at1+40v/v(1volume of crude oil sample in 40 volumes of solvent) using themicrofluidic mixer. Half of the sample loop volume (100
41、 L)should be used for this step. The spectrum of the diluted oil isrecorded as the fluid passes through the flow cell.9.4.1 Maintain a flow rate of 10 L min for the sample and400 L min for toluene.9.4.2 Use a dilution ratio of1+80v/viftheabsorbancesignal saturates or exceeds the linear range of the
42、spectrometerNOTE 1The schematic on the top shows the oil run and the one at the bottom shows that of the maltenes run.FIG. 1 Schematic Diagram of the SystemD7996 153at1+40v/v.Insuch a case, ensure that the extra dilution isconsidered in the final calculations (see Eq 5 in 10.1.3.1).9.4.3 Record the
43、spectrum at a rate of at least once everysecond.9.4.4 Plot the absorbance at 590 nm and 780 nm (Aoil(=590 nm)and Aoil(=780 nm), respectively) as a function of time.Agraph suchas Fig. 2(a) is expected for each wavelength. The measurementcontinues until the sample injection is complete.9.4.5 At 590 nm
44、, standard deviation of the plateau regionshould be 60.02 AU or lower for an average absorbance of 1or less and 60.05 AU or lower for an average absorbancelarger than 1. This criterion can be used to ensure that the heartof the plug (stable region) is used for analysis.9.5 Prime the system with hept
45、ane and acquire light anddark reference spectra.9.6 Check the integrity of the membrane according to 9.3.9.7 Mix the second portion of the sample (100 L) withheptane at1+40v/vratio to precipitate asphaltenes. Thespectrum of the maltenes is recorded as the fluid passes throughthe flow cell. Record th
46、e spectrum as a function of time.9.7.1 A flow rate of 10 L min for the sample and400 L min for heptane is recommended.9.7.2 Record the spectrum at a rate of at least once everysecond.9.7.3 Plot the absorbance at 590 nm and 780 nm (Amalt(=590 nm)and Amalt(=780 nm), respectively) as a function of time
47、. A graphsuch as Fig. 2(b) is expected for each wavelength. Continue themeasurement until the sample injection is complete.9.8 When the measurement is complete, flush the systemand microchips with toluene to remove the remaining oil andasphaltenes residues.9.9 When the measurements are finished, rem
48、ove the dis-posable membrane, and dispose of it in an environmentallysafe way.10. Calculation10.1 Calculation of Results:10.1.1 The following calculations may be run automaticallyor the data may be exported to another piece of software formanual analysis.10.1.2 Time-averaged spectrum of the sample a
49、nd maltenesare calculated using the following equation:W51n(t5t1t2Wt(3)where W, Wt, and n represent time-averaged spectrum,spectrum at time t, and number of spectra from t1to t2,respectively.NOTE 1In this test method, W represents the visible spectrum,whereas Adenotes the absorbance at a specific wavelength of .10.1.3 The spectrum of asphaltenes is calculated using thefollowing equation:Wasp5 Woil2 Wmalt(4)where Wasp, Woil, and Wmaltdenote time-averaged spectrumof asphaltenes, oil, and maltenes, respectively
