1、Designation: D8045 16D8045 161Standard 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
2、 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 NOTEFootnote 4 was added editorially in December 2016.1. Scope1.1 This test method covers the determin
3、ation of acidic components in crude oil and petroleum products including waxes,bitumen, base stocks, and asphalts that are soluble in mixtures of xylenes and propan-2-ol. It is applicable for the determinationof acids whose dissociation constants in water are larger than 109; extremely weak acids wh
4、ose dissociation constants are smallerthan 109 do not interfere. The values obtained by this test method may not be numerically equivalent to other acid valuemeasurements. The range of KOH acid numbers included in the precision statement is 0.1 mgg to 16 mgg.1.2 The values stated in SI units are to
5、be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices an
6、d determine the applicability of regulatorylimitations prior to use. Some specific hazards statements are given in Section 7 on Safety Precautions.2. Referenced Documents2.1 ASTM Standards:2D664 Test Method for Acid Number of Petroleum Products by Potentiometric TitrationD974 Test Method for Acid an
7、d Base Number by Color-Indicator TitrationD1193 Specification for Reagent WaterD4057 Practice for Manual Sampling of Petroleum and Petroleum ProductsD4175 Terminology Relating to Petroleum Products, Liquid Fuels, and LubricantsD4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
8、D5854 Practice for Mixing and Handling of Liquid Samples of Petroleum and Petroleum ProductsD6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-ment System Performance3. Terminology3.1 For general terminology, refer to Terminology
9、D4175.3.2 Definitions:3.2.1 acid number, nthe quantity of a specified base, expressed in milligrams of potassium hydroxide per gram of sample,required to titrate a sample in a specified solvent to a specified endpoint using a specified detection system.3.2.2 catalytic thermometric titration, na meth
10、od to determine the end point of a chemical reaction through the use atemperature measuring device and the addition of a chemical to enhance the detection of the endpoint.3.2.3 crude oil, na naturally occurring hydrocarbon mixture, generally in a liquid state, which may also include compoundsof sulf
11、ur, nitrogen, oxygen, metals, and other elements.4. Summary of Test Method4.1 The sample and a fixed mass of paraformaldehyde are dissolved in a mixture of xylenes and propan-2-ol. The mixture isthen titrated with potassium hydroxide using a constant rate of titrant addition. A plot of the temperatu
12、re of the reaction mixture1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of SubcommitteeD02.06 on Analysis of Liquid Fuels and Lubricants.Current edition approved July 1, 2016. Published August 20
13、16. DOI: 10.1520/D8045-16.10.1520/D8045-16E01.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document i
14、s not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as approp
15、riate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1versus the volume of titrant is generated. An exothermic reacti
16、on between the titrant and sample occurs simultaneously with theendothermic depolymerization of paraformaldehyde.After all of the acidic material in the sample has reacted, the slope of the plotchanges due to the absence of the competitive exothermic acid-base reaction. The change in slope is the in
17、flection point. Thedepolymerization of paraformaldehyde is catalytically initiated and does not consume a significant quantity of potassiumhydroxide. The net change (positive or negative) in temperature prior to the consumption of the acidic sample will be dependentupon the relative magnitude of the
18、 heats of reaction and environmental influences.5. Significance and Use5.1 Crude oils and oil sands bitumen contain naturally occurring acidic species. Acidity of crude oil has been implicated incorrosion of distribution and process systems. The relative amount of these materials can be determined b
19、y titrating with bases.The acid number is a measure of this amount of acidic substance in the oil under the conditions of the test.5.2 Acid number of crude and distilled petroleum fractions has been measured by Test Method D664. Test Method D664 wasdeveloped for the analysis of lubricants and biodie
20、sel. The titration solvent used in Test Method D664 does not properly addressdissolving difficult samples such as crude oil, bitumen, and high wax samples addressed in this test method. Refer to AppendixX1.5.3 Test Method D974 is also not applicable to measuring acidity of crudes and highly colored
21、samples because the indicatoris not visible or it is difficult to discern a color change to detect the end point of the titration.6. Interferences6.1 Any material that reacts with potassium hydroxide will interfere and overestimate the amount of acidic material in thesample. In crude oils, bitumens,
22、 synthetic crude oils, and subsequent fractions, the constituents that may be considered to haveacidic characteristics include inorganic and organic acids, particularly naphthenic acids, phenolic compounds, resins, salts of heavymetals, and acid salts of polybasic acids.7. Safety Precautions7.1 Wear
23、 chemical resistant gloves and avoid excessive inhalation of organic vapors by working in a fume hood when possible.The titrant solution is corrosive and paraformaldehyde (flammable solid) releases small quantities of formaldehyde duringdepolymerization.7.2 Consult Safety Data Sheets (SDS) for chemi
24、cals listed in this test method for further information.8. Apparatus8.1 Automatic Titrator, capable of providing a dose rate of 2 mLmin.8.2 Thermistor, a device capable of measuring the temperature to 0.001 C. The device should be immersed in the titrationsolvent to a depth recommended by the manufa
25、cturer and 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 guard tube containing adsorbent to retard the rate of titrant reaction withatmospheric carbon dioxide.8.5 Constant or Variable Speed Propel
26、ler Stirrer, sufficient to ensure adequate mixing of the sample and titrant.8.6 Titration Beaker, with sufficient volume and made of a material that does not interact with the sample, titrant or titrationsolvent.8.7 Volumetric Dispenser, capable of consistently delivering desired volume of titration
27、 solvent.9. Reagents9.1 Potassium Hydroxide Solution, Standard Alcoholic, (0.1 M)Add 6 g of potassium hydroxide (KOH) to approximately 1 Lof propan-2-ol. Boil gently for 10 min to dissolve. Allow the solution to stand for two days and then filter the supernatant liquidthrough a fine sintered-glass f
28、unnel. Store the solution in a chemically resistant bottle. Dispense in a manner such that the solutionis protected from atmospheric carbon dioxide (CO2) by means of a guard tube containing soda lime or soda non-fibrous silicateabsorbents and such that it does not come into contact with cork, rubber
29、, or saponifiable stopcock grease. Commercially preparedreagent is also suitable. Standardize frequently enough to detect concentration changes of 0.0005 molL by standard industrypractices or by thermometric titration of known quantities of benzoic acid solution dissolved in n-heptane. See Appendix
30、fordetails.9.2 Propan-2-ol (anhydrous, also referred to as isopropyl alcohol, 99 % purity).9.3 Mixed Xylenes(WarningFlammable.) A technical grade of hydrocarbon that includes predominantly o-xylene,m-xylene, p-xylene and lesser quantities of ethyl benzene. The boiling point range is typically 136 C
31、to 140 C.D8045 16129.4 Titration SolventAdd 250 mL 6 10 mL of anhydrous isopropyl alcohol to 750 mL 6 10 mL of mixed xylenes. Largerquantities of titration solvent can be prepared using volumetric ratios (25:75) of the same proportions. Commercially preparedreagent is also suitable.9.5 Toluene, pre-
32、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 successful and rapid analysis of the material. Too large mesh reacts slowly,resulting in erroneous results.As
33、ample of paraformaldehyde with greater than 80 % by mass having a mesh size between 100 and200 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 by Specification D1193.9.10 Titratio
34、n Slurry with Indicator17 g 6 0.5 g of paraformaldehyde are added to one liter of titration solvent.10. Sampling10.1 Sampling is defined as all of the steps required to obtain an aliquot representative of the contents of any pipe, tank, or othersystem and to place the sample into a container for ana
35、lysis by a laboratory or test facility. Sampling practices are covered inPractices D4057 and D4177.10.2 The sample should be well homogenized prior to taking an aliquot for testing. Power mixing per Practice D5854 is advisedfor crude oils that are fluid at room temperature. Manual mixing and warming
36、 may be required for more viscous samples.10.3 For samples that contain more than 10 % entrained water, it is advised to remove the water prior to testing using industryaccepted methods. If adding toluene or other solvent to aid in water removal, be sure to correct for the solvent dilution in thehyd
37、rocarbon sample weight before analysis.11. Preparation of Apparatus11.1 If the burette has not been used within the last 12 h dispense sufficient titrant through the burette to remove air bubblesfrom the delivery tubing. Ensure that all of the components (that is, stirrer, titrant tubing, thermistor
38、, and so forth) that are to beimmersed in the titration solvent are clean and 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 similar matrixto sample tested. Control charts shall be
39、 established and maintained according to generally accepted guidelines. Practice D6299can be used for this purpose.13. Procedure13.1 Blank Determination:13.1.1 The blank value must be 0.1 mL. This is generally the case when high purity propan-2-ol is used. The blank value canbe verified. The blank v
40、alue is determined indirectly. A stable sample with a known acid number is measured using three or moredifferent sample masses. The largest sample size must not use a volume of titrant greater than the volume of the burette.13.1.2 The volume of titrant must be 0.15 mL for all sample masses.13.1.3 Th
41、e sample volume in milliliters (y-axis) is plotted versus the sample mass in grams (x-axis). Using the linear equationfor the best fit line (R2 value must be 0.98 or greater), extrapolate to determine the volume of titration solvent that correspondsto a sample size of 0.0 g. See example in Fig. 1.13
42、.1.4 If the blank value exceeds 0.1 mL, prepare fresh titration solvent, confirm the titrant concentration and repeat theanalysis. If the blank is below 0.1 mL, it is not necessary to apply a blank correction factor provided that the sample masses shownin Table 1 are used (see 13.2).13.2 Sample Anal
43、ysis:13.2.1 Samples that are very viscous or solid at room temperature (that is, asphalt) shall be heated in an oven (120 C) untilthe material flows and sample can be stirred to homogenize.13.2.2 For samples that do not readily dissolve in the slurry, it is permissible to pre-dissolve the sample aft
44、er weighing by addingin up to 10 mL of toluene or xylenes. In this case, solvent conditions shall be matched if determining the blank value.13.2.3 Weigh the appropriate amount of sample into the titration beaker. Table 1 shows recommended initial sample size basedon expected acid number value. This
45、amount used may be adjusted to accommodate for solubility limitations and to conduct theblank determination. For unknowns, it is advised to start with a 5 g sample size, and adjust sample size as needed for subsequentmeasurements. The volume of titrant consumed has to be 0.15 mL. Titrant volume 0.15
46、 mL indicates that additional sample isrequired, and 5.0 mL of titrant suggests less sample is needed.D8045 161313.2.4 When using less than the sample masses recommended in Table 1, due to solubility issues (that is, for asphalt, wax, andbitumen) and/or unavailability of necessary sample volume, the
47、n the blank value shall be determined for the sample and appliedto the calculation of the acid number value.13.2.5 For samples that have been heated in an oven, the beaker containing the sample and titration solvent (with pre-dissolutionsolvent) may be heated (65 C) to ensure full solubility of the
48、sample prior to the start of the titration. It is advised to cool thesample to room temperature before testing, provided the sample remains in solution. Analysis at slightly elevated temperatures isallowable but the rate of cooling should be minimized. Conditions shall be matched if determining the
49、blank value. This approachcan affect the precision and accuracy of the method and is not recommended for samples that can be successfully analyzed withoutheating.13.2.6 Add titration solvent, typically 30 mL, to the titration beaker and place the thermistor and titrant delivery line into thesample. Stir the contents for a minimum of 30 s as rapidly as possible without exposing the thermistor to a vortex and causingsample or solvent loss. The sample shall be fully dissolved before titrating. Increase mixing time as needed to completely dissolvethe
