1、Designation: D8045 16Standard Test Method forAcid Number of Crude Oils and Petroleum Products byCatalytic Thermometric Titration1This standard is issued under the fixed designation D8045; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, 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 determination of acidiccomponents in crude oil and petroleum products inc
3、ludingwaxes, bitumen, base stocks, and asphalts that are soluble inmixtures of xylenes and propan-2-ol. It is applicable for thedetermination of acids whose dissociation constants in waterare larger than 109; extremely weak acids whose dissociationconstants are smaller than 109do not interfere. The
4、valuesobtained by this test method may not be numerically equivalentto other acid value measurements. The range of KOH acidnumbers included in the precision statement is 0.1 mg g to16 mg g.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in
5、thisstandard.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. S
6、ome specifichazards statements are given in Section 7 on Safety Precau-tions.2. Referenced Documents2.1 ASTM Standards:2D664 Test Method for Acid Number of Petroleum Productsby Potentiometric TitrationD974 Test Method for Acid and Base Number by Color-Indicator TitrationD1193 Specification for Reage
7、nt WaterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4175 Terminology Relating to Petroleum Products, LiquidFuels, and LubricantsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD5854 Practice for Mixing and Handling of Liquid Samplesof Petroleum and P
8、etroleum ProductsD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System Performance3. Terminology3.1 For general terminology, refer to Terminology D4175.3.2 Definitions:3.2.1 acid number, nthe quantity of a specified base,exp
9、ressed in milligrams of potassium hydroxide per gram ofsample, required to titrate a sample in a specified solvent to aspecified endpoint using a specified detection system.3.2.2 catalytic thermometric titration, na method to de-termine the end point of a chemical reaction through the use atemperatu
10、re measuring device and the addition of a chemical toenhance the detection of the endpoint.3.2.3 crude oil, na naturally occurring hydrocarbonmixture, generally in a liquid state, which may also includecompounds of sulfur, nitrogen, oxygen, metals, and otherelements.4. Summary of Test Method4.1 The
11、sample and a fixed mass of paraformaldehyde aredissolved in a mixture of xylenes and propan-2-ol. The mixtureis then titrated with potassium hydroxide using a constant rateof titrant addition. A plot of the temperature of the reactionmixture versus the volume of titrant is generated. An exother-mic
12、reaction between the titrant and sample occurs simultane-ously with the endothermic depolymerization of paraformalde-hyde. After all of the acidic material in the sample has reacted,the slope of the plot changes due to the absence of thecompetitive exothermic acid-base reaction. The change inslope i
13、s the inflection point. The depolymerization of para-formaldehyde is catalytically initiated and does not consume asignificant quantity of potassium hydroxide. The net change(positive or negative) in temperature prior to the consumption1This test method is under the jurisdiction of ASTM Committee D0
14、2 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.06 on Analysis of Liquid Fuels and Lubricants.Current edition approved July 1, 2016. Published August 2016. DOI: 10.1520/D8045-16.2For referenced ASTM standards, visit the ASTM website, www.astm.
15、org, orcontact ASTM Customer Service at serviceastm.org. For 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 States1of the acidi
16、c sample will be dependent upon the relativemagnitude of the heats of reaction and environmental influ-ences.5. Significance and Use5.1 Crude oils and oil sands bitumen contain naturallyoccurring acidic species. Acidity of crude oil has been impli-cated in corrosion of distribution and process syste
17、ms. Therelative amount of these materials can be determined bytitrating with bases. The acid number is a measure of thisamount of acidic substance in the oil under the conditions ofthe test.5.2 Acid number of crude and distilled petroleum fractionshas been measured by Test Method D664. Test Method D
18、664was developed for the analysis of lubricants and biodiesel. Thetitration solvent used in Test Method D664 does not properlyaddress dissolving difficult samples such as crude oil, bitumen,and high wax samples addressed in this test method. Refer toAppendix X1.5.3 Test Method D974 is also not appli
19、cable to measuringacidity of crudes and highly colored samples because theindicator is not visible or it is difficult to discern a color changeto detect the end point of the titration.6. Interferences6.1 Any material that reacts with potassium hydroxide willinterfere and overestimate the amount of a
20、cidic material in thesample. In crude oils, bitumens, synthetic crude oils, andsubsequent fractions, the constituents that may be consideredto have acidic characteristics include inorganic and organicacids, particularly naphthenic acids, phenolic compounds,resins, salts of heavy metals, and acid sal
21、ts of polybasic acids.7. Safety Precautions7.1 Wear chemical resistant gloves and avoid excessiveinhalation of organic vapors by working in a fume hood whenpossible. The titrant solution is corrosive and paraformalde-hyde (flammable solid) releases small quantities of formalde-hyde during depolymeri
22、zation.7.2 Consult Safety Data Sheets (SDS) for chemicals listedin this test method for further information.8. Apparatus8.1 Automatic Titrator, capable of providing a dose rate of2 mL min.8.2 Thermistor, a device capable of measuring the tempera-ture to 0.001 C. The device should be immersed in thet
23、itration solvent to a depth recommended by the manufacturerand have a response time of less than 0.3 s.8.3 Analytical Balance, capable of weighing to 60.1 mg.8.4 Burette, typically less than 20 mL capacity with a guardtube containing adsorbent to retard the rate of titrant reactionwith atmospheric c
24、arbon dioxide.8.5 Constant or Variable Speed Propeller Stirrer, sufficientto ensure adequate mixing of the sample and titrant.8.6 Titration Beaker, with sufficient volume and made of amaterial that does not interact with the sample, titrant ortitration solvent.8.7 Volumetric Dispenser, capable of co
25、nsistently deliveringdesired volume of titration solvent.9. Reagents9.1 Potassium Hydroxide Solution, Standard Alcoholic,(0.1 M)Add 6 g of potassium hydroxide (KOH) to approxi-mately 1 L of propan-2-ol. Boil gently for 10 min to dissolve.Allow the solution to stand for two days and then filter thesu
26、pernatant liquid through a fine sintered-glass funnel. Storethe solution in a chemically resistant bottle. Dispense in amanner such that the solution is protected from atmosphericcarbon dioxide (CO2) by means of a guard tube containingsoda lime or soda non-fibrous silicate absorbents and such thatit
27、 does not come into contact with cork, rubber, or saponifiablestopcock grease. Commercially prepared reagent is also suit-able. Standardize frequently enough to detect concentrationchanges of 0.0005 mol L by standard industry practices or bythermometric titration of known quantities of benzoic acids
28、olution dissolved in n-heptane. See Appendix for details.9.2 Propan-2-ol (anhydrous, also referred to as isopropylalcohol, 99 % purity).9.3 Mixed Xylenes(WarningFlammable.) A technicalgrade of hydrocarbon that includes predominantly o-xylene,m-xylene, p-xylene and lesser quantities of ethyl benzene.
29、 Theboiling point range is typically 136 C to 140 C.9.4 Titration SolventAdd 250 mL 6 10 mL of anhydrousisopropyl alcohol to 750 mL 6 10 mL of mixed xylenes.Larger quantities of titration solvent can be prepared usingvolumetric ratios (25:75) of the same proportions. Commer-cially prepared reagent i
30、s also suitable.9.5 Toluene, pre-dissolution solvent (99 % purity).9.6 Paraformaldehyde (polyoxymethylene)(WarningFlammable solid.) Terminated with hydroxyl end groups and infine-powder form. Fine powder mesh is critical to successfuland rapid analysis of the material. Too large mesh reactsslowly, r
31、esulting in erroneous results. A sample of paraform-aldehyde with greater than 80 % by mass having a mesh sizebetween 100 and 200 was found suitable.Avoid moist, aged, oroxidized reagent.9.7 Benzoic acid (99.9 % purity).9.8 n-heptane (99 % purity).9.9 WaterType 1 deionized, or higher, as defined byS
32、pecification D1193.9.10 Titration Slurry with Indicator17 g 6 0.5 g of para-formaldehyde are added to one liter of titration solvent.10. Sampling10.1 Sampling is defined as all of the steps required toobtain an aliquot representative of the contents of any pipe,tank, or other system and to place the
33、 sample into a containerfor analysis by a laboratory or test facility. Sampling practicesare covered in Practices D4057 and D4177.D8045 16210.2 The sample should be well homogenized prior totaking an aliquot for testing. Power mixing per Practice D5854is advised for crude oils that are fluid at room
34、 temperature.Manual mixing and warming may be required for more viscoussamples.10.3 For samples that contain more than 10 % entrainedwater, it is advised to remove the water prior to testing usingindustry accepted methods. If adding toluene or other solventto aid in water removal, be sure to correct
35、 for the solventdilution in the hydrocarbon sample weight before analysis.11. Preparation of Apparatus11.1 If the burette has not been used within the last 12 hdispense sufficient titrant through the burette to remove airbubbles from the delivery tubing. Ensure that all of thecomponents (that is, st
36、irrer, titrant tubing, thermistor, and soforth) that are to be immersed in the titration solvent are cleanand free of acidic or basic contamination.12. Quality Control12.1 Measure a quality control sample each day a sample(s)is tested. The quality control sample should be of similarmatrix to sample
37、tested. Control charts shall be established andmaintained according to generally accepted guidelines. Prac-tice D6299 can be used for this purpose.13. Procedure13.1 Blank Determination:13.1.1 The blank value must be 0.1 mL. This is generallythe case when high purity propan-2-ol is used. The blank va
38、luecan be verified. The blank value is determined indirectly. Astable sample with a known acid number is measured usingthree or more different sample masses. The largest sample sizemust not use a volume of titrant greater than the volume of theburette.13.1.2 The volume of titrant must be 0.15 mL for
39、 allsample masses.13.1.3 The sample volume in milliliters (y-axis) is plottedversus the sample mass in grams (x-axis). Using the linearequation for the best fit line (R2value must be 0.98 or greater),extrapolate to determine the volume of titration solvent thatcorresponds to a sample size of 0.0 g.
40、See example in Fig. 1.13.1.4 If the blank value exceeds 0.1 mL, prepare freshtitration solvent, confirm the titrant concentration and repeatthe analysis. If the blank is below 0.1 mL, it is not necessary toapply a blank correction factor provided that the sample massesshown in Table 1 are used (see
41、13.2).13.2 Sample Analysis:13.2.1 Samples that are very viscous or solid at roomtemperature (that is, asphalt) shall be heated in an oven(120 C) until the material flows and sample can be stirred tohomogenize.13.2.2 For samples that do not readily dissolve in the slurry,it is permissible to pre-diss
42、olve the sample after weighing byadding in up to 10 mL of toluene or xylenes. In this case,solvent conditions shall be matched if determining the blankvalue.13.2.3 Weigh the appropriate amount of sample into thetitration beaker. Table 1 shows recommended initial samplesize based on expected acid num
43、ber value. This amount usedmay be adjusted to accommodate for solubility limitations andto conduct the blank determination. For unknowns, it is advisedto start with a 5 g sample size, and adjust sample size as neededfor subsequent measurements. The volume of titrant consumedhas to be 0.15 mL. Titran
44、t volume 0.15 mL indicates thatadditional sample is required, and 5.0 mL of titrant suggestsless sample is needed.13.2.4 When using less than the sample masses recom-mended in Table 1, due to solubility issues (that is, for asphalt,wax, and bitumen) and/or unavailability of necessary samplevolume, t
45、hen the blank value shall be determined for thesample and applied to the calculation of the acid number value.13.2.5 For samples that have been heated in an oven, thebeaker containing the sample and titration solvent (withNOTE 1The above example shows a blank calculation for a sample of crude oil wi
46、th a KOH acid number of approximately 0.9 mg g. The blank valueis equal to the value of y when x is set to a value of zero (0.039 mL in this particular example). The software can be configured to calculate the equationand slope automatically.FIG. 1 Example Blank Calculation for a Sample of Crude Oil
47、D8045 163pre-dissolution solvent) may be heated (65 C) to ensure fullsolubility of the sample prior to the start of the titration. It isadvised to cool the sample to room temperature before testing,provided the sample remains in solution. Analysis at slightlyelevated temperatures is allowable but th
48、e rate of coolingshould be minimized. Conditions shall be matched if determin-ing the blank value. This approach can affect the precision andaccuracy of the method and is not recommended for samplesthat can be successfully analyzed without heating.13.2.6 Add titration solvent, typically 30 mL, to th
49、e titrationbeaker and place the thermistor and titrant delivery line into thesample. Stir the contents for a minimum of 30 s as rapidly aspossible without exposing the thermistor to a vortex andcausing sample or solvent loss. The sample shall be fullydissolved before titrating. Increase mixing time as needed tocompletely dissolve the sample. Samples shall stay in solutionthroughout the titration.13.2.7 Manual Paraformaldehyde AdditionAdd 0.50 g 60.10 g of paraformaldehyde per 30 mL of titration solvent tothe beaker and start the titration. It is perm
