1、Designation: D8045 171Standard 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 revi
2、sion, 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.1NOTESubsections 16.1.1 and 16.1.2 were corrected editorially in July 2018.1. Scope*1.1 This test method covers
3、the determination of acidiccomponents in crude oil and petroleum products includingwaxes, 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
4、 acids whose dissociationconstants are smaller than 109do not interfere. The 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
5、are to be regarded asstandard. No other units of measurement are included in 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, health, and envir
6、onmental practices and deter-mine the applicability of regulatory limitations prior to use.Some specific hazards statements are given in Section 7 onSafety Precautions.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization establis
7、hed in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D664 Test Method for Acid Number of Petroleum Productsby Potentiom
8、etric TitrationD974 Test Method for Acid and Base Number by Color-Indicator TitrationD1193 Specification for Reagent WaterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4175 Terminology Relating to Petroleum Products, LiquidFuels, and LubricantsD4177 Practice for Automatic Sam
9、pling of Petroleum andPetroleum ProductsD5854 Practice for Mixing and Handling of Liquid Samplesof Petroleum and Petroleum ProductsD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System Performance3. Terminology3.1 For genera
10、l terminology, refer to Terminology D4175.3.2 Definitions:3.2.1 acid number, nthe quantity of a specified base,expressed 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 catalyt
11、ic thermometric titration, na method to de-termine the end point of a chemical reaction through the use atemperature 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
12、may also includecompounds of sulfur, nitrogen, oxygen, metals, and otherelements.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.06 on Analysis of Liquid Fuels and Lubricants.Curr
13、ent edition approved July 1, 2017. Published July 2017. Originally approvedin 2016. Last previous edition approved in 2016 as D8045 161. DOI: 10.1520/D8045-17E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book
14、of ASTMStandards volume information, refer to the standards 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 StatesThis international st
15、andard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14.
16、Summary of Test Method4.1 The 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
17、 is generated. An exother-mic 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
18、reaction. The change inslope is 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 consumptionof the acidic sample will be depen
19、dent 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 systems. Therelative amount
20、 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 D664was developed for t
21、he 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 applicable to measuringacid
22、ity 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 acidic material in thes
23、ample. 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 salts of polybasic acids.
24、7. Safety Precautions7.1 Wear chemical resistant gloves. Avoid excessive inha-lation of organic vapors and paraformaldehyde (flammablesolid) by working in a fume hood when possible. Pre-weighedparaformaldehyde packets should be substituted, if possible, tominimize potential exposures when preparing
25、titration slurrysolutions. The titrant solution is corrosive and paraformalde-hyde releases small quantities of formaldehyde during depo-lymerization.7.2 Consult Safety Data Sheets (SDS) for chemicals listedin this test method for further information.8. Apparatus8.1 Automatic Titrator, capable of pr
26、oviding 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 thetitration 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
27、.8.4 Burette, typically less than 20 mL capacity with a guardtube containing adsorbent to retard the rate of titrant reactionwith atmospheric carbon dioxide.8.5 Constant or Variable Speed Propeller Stirrer, sufficientto ensure adequate mixing of the sample and titrant.8.6 Titration Beaker, with suff
28、icient volume and made of amaterial that does not interact with the sample, titrant ortitration solvent.8.7 Volumetric Dispenser, capable of consistently deliveringdesired volume of titration solvent.9. Reagents9.1 Potassium Hydroxide Solution, Standard Alcoholic,(0.1 M)Add 6 g of potassium hydroxid
29、e (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 thesupernatant liquid through a fine sintered-glass funnel. Storethe solution in a chemically resistant bottle. Dispense in amanner such that the solution is prot
30、ected from atmosphericcarbon dioxide (CO2) by means of a guard tube containingsoda lime or soda non-fibrous silicate absorbents and such thatit does not come into contact with cork, rubber, or saponifiablestopcock grease. Commercially prepared reagent is also suit-able. Standardize frequently enough
31、 to detect concentrationchanges of 0.0005 mol L by standard industry practices or bythermometric titration of known quantities of benzoic acidsolution 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(War
32、ningFlammable.) A technicalgrade of hydrocarbon that includes predominantly o-xylene,m-xylene, p-xylene and lesser quantities of ethyl benzene. 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.
33、Larger quantities of titration solvent can be prepared usingvolumetric ratios (25:75) of the same proportions. Commer-cially prepared reagent is also suitable.9.5 Toluene, pre-dissolution solvent (99 % purity).9.6 Paraformaldehyde (polyoxymethylene)(WarningFlammable solid. Harmful if inhaled. Irrita
34、nt.) Terminated withhydroxyl end groups and in fine-powder form. Fine powdermesh is critical to successful and rapid analysis of the material.Too large mesh reacts slowly, resulting in erroneous results. AD8045 1712sample of paraformaldehyde with greater than 80 % by masshaving a mesh size between 1
35、00 and 200 was found suitable.Avoid moist, aged, or oxidized reagent.9.7 Benzoic acid (99.9 % purity).9.8 n-heptane (99 % purity).9.9 WaterType 1 deionized, or higher, as defined bySpecification D1193.9.10 Titration Slurry with Indicator17 g 6 0.5 g of para-formaldehyde are added to one liter of tit
36、ration 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 sample into a containerfor analysis by a laboratory or test facility. Sampling practicesare covered in Practices D405
37、7 and D4177.10.2 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 temperature.Manual mixing and warming may be required for more viscoussamples.10.3 For samples that contain more than 10 % ent
38、rainedwater, 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 for the solventdilution in the hydrocarbon sample weight before analysis.11. Preparation of Apparatus11.1 If the burette has n
39、ot 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, stirrer, titrant tubing, thermistor, and soforth) that are to be immersed in the titration solvent are cleanand free of acidic or
40、 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 tested. Control charts shall be established andmaintained according to generally accepted guidelines. Prac-tice D6299 can be us
41、ed 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 valuecan be verified. The blank value is determined indirectly. Astable sample with a known acid number is measured usingthree or
42、 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 allsample masses.13.1.3 The sample volume in milliliters (y-axis) is plottedversus the sample mass in grams (x-axis). Using th
43、e 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. See example in Fig. 1.13.1.4 If the blank value exceeds 0.1 mL, prepare freshtitration solvent, confirm the titrant concentrati
44、on 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 13.2).13.2 Sample Analysis:13.2.1 Samples that are very viscous or solid at roomtemperature (that is, asphalt) shall be heated
45、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-dissolve the sample after weighing byNOTE 1The above example shows a blank calculation for a sample of crude oil with a KOH acid nu
46、mber 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 OilD8045 1713adding
47、 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 number value. This amount usedmay be adjus
48、ted 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. Titrant volume 0.15 mL indicates thataddition
49、al 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, then 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 (withpre-dissolution solvent) may be heated (65 C) to ensure fullsolubi
