Determination of the total base number of engine oils using potentiometric titration

A brief review of the methods for determining the total base number of engine oils (TBN) is presented. This integral indicator characterizes the total content of basic impurities (additives) in terms of the amount of potassium hydroxides in one gram of engine oil (mg KOH/g). Used engine oils are usually titrated with hydrochloric acid in a non-aqueous medium, the potential of the indicator electrode being under control. The same technique can be successfully used in analysis of commercial (fresh) oils. Titration curves are recorded with an indicator glass electrode. TBN of fresh and used engine oils are determined with approximately the same convergence (S_r < 2 %). To check the compatibility of redetermined TBN values, the repeatability and reproducibility limits specified in GOST 11362–96 were used. Using the M-10G2 oil as an example, different variants of potentiometric titration are compared, the corresponding metrological characteristics were determined, and recommendations for testing laboratories were developed. Titration of oil to a certain fixed potential recommended in GOST 11362–96 results in underestimated TBN values compared to other options used for identification of the equivalence point and worsens the reproducibility of the results when using samples of different weights. We recommend to determine TBN values for fresh or used engine oils by direct potentiometric titration using three-tangent method. The accuracy of the obtained results is checked by the standard method of additives (spike recovery test); the error of determination being less than 15 % rel. It is shown using Shewhart maps, that the metrological characteristics of the repeatability and reproducibility are stable, but the results of analysis of control samples often go beyond the warning limits, especially for the samples of used oil. Promising directions of future studies are proposed.

1. Novikov E. A., Kiryukhin M. V. Used Oil Analysis. An Uncharted Territory / Analitika. 2015. N 3(22). P. 36 – 47 [in Russian].

2. Myalo O. V., Myalo V. V., Keruchenko L. S. The results of an experimental study of the diagnosis of high-alkaline motor oils by the way of «drop sample» / Vestn. Omsk. Agrar. Univ. 2018. N 4(32). P. 66 – 76 [in Russian].

3. Rozbakh O. V. Quality control efficiency in oil analysis / Omsk. Nauch. Vestn. 2006. N 1. P. 119 – 120 [in Russian].

4. Vereshchagin V. I., Runda M. M., Koval’skii B. I., Bezborodov Yu. N. Control methods and the results of motor oil analysis for long-term storage and operation of internal-combustion engines. — Krasnoyarsk: SFU, 2016. — 188 p. [in Russian].

5. Fitch J., Troyer D. Oil Analysis Basics. 2nd Edition. — Tulsa: Noria Corporation, 2010. — 183 p.

6. ISO 6618:1997. Petroleum products and lubricating oils. Neutralization number. Colour indicator titration method. Confirmed in 2017. — 11 p.

7. Laushkin A. V., Khaziev A. A. Theoretical aspects of changing TBN of motor oil during the automobile transport exploitation / Transport. Transport. Sooruzh. Ékol. 2014. N 1. P. 88 – 94 [in Russian].

8. ISO 3771:2011. Petroleum products. Total base number. Perchloric acid potentiometric titration method. Confirmed in 2016. — 8 p.

9. Interstate Standard GOST 11362–96. Petroleum products and lubricants. Neutralization number. Potentiometric titration method. — Minsk, 2006. — 17 p. [in Russian].

10. ASTM D 4739–17. Standard test method for base number determination by potentiometric hydrochloric acid titration. — West Conshohocken: ASTM Int., 2017. — 8 p. DOI: 10.1520/D4739–17.

11. Determination of Total Base Number (TBN) according to ASTM D2896/ISO 3771 / Xylem Inc. Publication 44760119. 2019. https://www.ysi.com (accessed July 14, 2020).

12. Determination of the total base number in petroleum products / Metrohm. Application Bulletin AB-405-1-EN. 2017. https://metrohm-russia.ru/specials/thermometric/1360597_AB-405_1_EN.pdf (accessed July 12, 2020).

13. Fox M. V., Pawlak Z., Picken D. J. Acid-base determination of lubricating oils / Tribology Int. 1991. Vol. 24. N 6. P. 335 – 340. DOI: 10.1016/0301-679X(91)90003-R.

14. Dong J., Van De Voort F. R., Yaylayan V., et al. Determination of total base number (TBN) in lubricating oils by mid-FTIR spectroscopy / Lubr. Eng. 2001. Vol. 57. N 11. P. 24 – 30.

15. Martalov A. S., Bratkov A. A., Samoshenkov D. V. Determination of basic number of mineral engine oils with IR-spectroscopy using / Neftepererab. Neftekhim. 2007. N 7. P. 49 – 50 [in Russian].

16. Vershinin V. I. Group formation and choice of standard substances in the determination of total concentrations of similar compounds as total indices / J. Anal. Chem. 2017. Vol. 72. N 9. P. 947 – 956. DOI: 10.1134/s1061934817090131.

17. RF State Standard GOST 8581–78. Motor oils for motor and tractor diesel engines. — Moscow, 2011. — 6 p. [in Russian].

18. ISO 7870-2:2013. Control charts. Part 2: Shewhart control charts. Confirmed in 2019. — 44 p.

19. Harvey D. Modern Analytical Chemistry. Textbook. Ch. 9. — NY: McGraw-Hill Higher Education, 2000. — 798 p.

20. ISO 6619:1988. Petroleum products and lubricants. Neutralization number. Potentiometric titration method. Confirmed in 2018. — 8 p.

21. Vershinin V. I. Total indices as a tool to estimate sum content of similar analytes. Review / Talanta. 2015. Vol. 131. N 1. P. 293 – 300. DOI: 10.1016/j.talanta.2014.07.102.

22. Vershinin V. I. Determination of similar substances summary content (theory of total indices). — Omsk: OmGU, 2016. — 287 p. [in Russian].