crude oil, a mineral oil, and a refinery fraction were analyzed. The results are shown in Table 3, Table 4, and Table 5 on the next page. ASTM D8045 demonstrates excellent method pre- cision for low TAN values.
40 Analytical Instrumentation Conclusion
The new thermometric standard, D8045, offers the highest accuracy for the analysis of the total acid content in crudes and refi nery fractions. By solving sample solubility and measuring accuracy issues, ASTM D8045 offers increased precision between buyers and sellers of petroleum products and is a recommended standard to add to these agreements. By using 75% less solvent and reducing the analysis time, the new solvent system also considerably lowers the cost of testing.
Table 6 provides on overview of the new D8045’s most important improvements for the analyst compared to ASTM D664.
From crude feedstock to refi nery fractions, extensive testing and method development using the Metrohm Titrotherm for acid number determination by D8045 proves to be simple and precise. With improved measurement, refi ners can better adjust their plant operation to control and mitigate corrosion risk from naphthenic acid while ensuring fair trade and commerce throughout the industry.
References
[1] Derungs, W. A. Naphthenic Acid Corrosion – An Old Enemy of the Petroleum Industry. Corr. 1956, 12, pp. 617–622.
[2] Turnbull, A.; Slavcheva, E.; Shone, B. Factors Controlling Naphtenic Acid Corrosion. Corr. 1998, 54 (11), pp. 922–930.
[3] Slavcheva, E.; Shone, B.; Turnbull, A. Review of naphtenic acid corrosion in oil refi ning. Br. Corr. J. 1999, 34 (2), pp. 125–131.
[4] Babaian-Kibala, E.; Craig H. L.; Rusk, G. L.; Quinter R. C.; Summers M. A. Naphthenic Acid Corrosion in Refi nery Settings. Mater. Perform. 1993, pp. 50–55.
05
[5] Bota, G. M.; Qu, D., Nesic, S.; Wolf, H. A. Naphthenic Acid Corrosion of Mild Steel in the Presence of Sulfi de Scales Formed in Crude Oil Fractions at High Temperature. NACE 2010 Paper # 1035377
[6] Gutzeit, J. Naphthenic Acid Corrosion in Oil Refi neries. Mater. Perform. 1977, 16 (10), pp. 24–35.
[7] Murray, D. TAN Thermometric Method Evaluation. Canadian Crude Quality Technical Association Technical Report. April 2014.
Table 2. Thermometric titration method correlated to the ASTM D664 Method
Mean thermometric TAN [mg KOH/g]
Metrohm White Paper Metrohm White Paper Metrohm White Paper
Vacuum Light Gas Oil Vacuum Heavy Gas Oil Atmsp. Heavy Gas Oil 650 Endpoint Gas Oil
0.76 0.73 1.23 1.25 1.15 0.73
Sample ID Sample ID
Crude oilCrude oil Crude oilCrude oilCrude oil Crude oilCrude oilCrude oil Crude oilCrude oilCrude oil Crude oilCrude oilCrude oil Crude oilCrude oilCrude oil Crude oilCrude oilCrude oil Crude oilCrude oilCrude oil Crude oilCrude oilCrude oil Crude oilCrude oilCrude oil
Crude oil
Run # Run #
10
99 9
88 8
77 7
66 6
55 5
44 4
33 3
22 2
11 1
Sample weight [g]
10 10
5.1924 5.1623 5.0474 5.0192 5.0100 5.0643 5.0858 5.0956 5.0278 5.1419
5.1419 5.1419
5.0278 5.0278
5.0956 5.0956
5.0858 5.0858
5.0643 5.0643
5.0100 5.0100
5.0192 5.0192
5.0474 5.0474
5.1623 5.1623
5.1924 5.1924
Sample weight [g]
Sample weight [g]
1.1% 0%
0.8% 1.2% 1.1%
Titration rate [mL/min]
22 2
22 2
22 2
22 2
22 2
22 2
22 2
22 2
22 2
22 2
Titration rate [mL/min]
Titration rate [mL/min]
30 30 30 30 30 30 30 30 30 30
30 30 30 30 30 30 30 30 30 30
Table 2. Thermometric titration method correlated to the ASTM D664 Method Sample
Desalted Crude Raw Crude
RSD (n=8) 2.1%
Potentiometric TAN result [mg KOH/g]
0.73 0.67 1.20 1.23 1.10 0.69
Table 3. Repeatability of the acid number determination in crude oil by thermometric titration Table 3. Repeatability of the acid number determination in crude oil by thermometric titration Run #
Solvent volume [mL]
Solvent volume [mL]
Solvent volume [mL] 30 30 30 30 30 30 30 30 30 30
Table 3. Repeatability of the acid number determination in crude oil by thermometric titration Table 3. Repeatability of the acid number determination in crude oil by thermometric titration Sample ID
Difference 4.0%
8.6% 2.5% 1.6% 4.4% 5.6%
End point [mL] 0.1367
0.1333 0.1400 0.1400 0.1333 0.1333 0.1400 0.1333 0.1467 0.1367 mean SD
SD SD
Table 4. Repeatability of the acid number determination in a refinery fraction by thermometric titration Sample ID
Table 4. Repeatability of the acid number determination in a refinery fraction by thermometric titration Table 4. Repeatability of the acid number determination in a refinery fraction by thermometric titration Sample ID Sample ID
Table 4. Repeatability of the acid number determination in a refi nery fraction by thermometric titration
Refinery stream Refinery streamRefinery streamRefinery stream Refinery streamRefinery streamRefinery stream Refinery streamRefinery streamRefinery stream Refinery streamRefinery streamRefinery stream Refinery streamRefinery streamRefinery stream Refinery streamRefinery streamRefinery stream Refinery streamRefinery streamRefinery stream Refinery streamRefinery streamRefinery stream Refinery streamRefinery streamRefinery stream Precision
Refinery stream Refinery stream
Run # 11
Metrohm White Paper 10
99 9
88 8
77 7
66 6
55 5
44 4
33 3
22 2
1 10 10
19.9484 20.0509 20.2944 19.3136 20.1019 20.1044 20.2357 20.1517 20.3568
20.3568 20.3568
20.1517 20.1517
20.2357 20.2357
20.1044 20.1044
20.1019 20.1019
19.3136 19.3136
20.2944 20.2944
20.0509 20.0509
19.9484 19.9484
20.152 20.152
22
Author Details G. Bryce McGarvey1
Bert Thakkar1 , ,
Colette E. McGarvey1 Larry Tucker2 Lori Carey2
, and Stephanie Kappes3
Imperial Oil – Sarnia Technology Applications and Research; 2
Affi liations: 1
Metrohm USA,
Metrohm Headquarters, Herisau Contact:
3
Alyson Lanciki, Email:
alyson.lanciki@
metrohm.com
Web:
www.metrohm.com 06
06 06
,
Table 5. Repeatability of the acid number determination in mineral oil by thermometric titration Sample ID
,
Table 5. Repeatability of the acid number determination in mineral oil by thermometric titration Sample ID Mineral oil
Table 5. Repeatability of the acid number determination in mineral oil by thermometric titration Sample ID Mineral oilMineral oil
Table 5. Repeatability of the acid number determination in mineral oil by thermometric titration
The single-laboratory precision as well as the precision be- tween multiple laboratories have been studied in the devel- opment of the ASTM D8045 thermometric acid number stan- dard. This was done in a ten-laboratory study of twelve crudes and refinery fractions. Both the single-laboratory precision, or repeatability, and the precision between multiple laborato- ries, or reproducibility, proved to be much better than that of method D664 when measuring crudes and refinery fractions. These improvements are attributed to an improved solvent system that makes the sample fully accessible for reaction to the titrant as well as the use of a precise, enthalpy-detecting sensor that is unaffected by difficult samples or harsh solvents.
Run # 11
Mineral oilMineral oil Mineral oil
Mineral oilMineral oil Mineral oil
Mineral oilMineral oil Mineral oil
Mineral oilMineral oil Mineral oil
Mineral oilMineral oil Mineral oil
Mineral oilMineral oil Mineral oil
Mineral oilMineral oil Mineral oil
Mineral oilMineral oil Mineral oil
Mineral oilMineral oil Mineral oil
22 2
1
33 3
44 4
66 6
77 7
88 8
10
99 9
10 10
55 5
Run # Run #
Sample weight [g]
10.2058 10.1955 10.3425 10.1028 10.307
10.1955 10.1955
10.3425 10.3425
10.1028 10.1028
10.0383 10.0328 10.0974 10.0852 10.1142
10.0383 10.0383
10.307 10.307
10.0328 10.0328
10.0974 10.0974
10.0852 10.0852
10.1142 10.1142
10.2058 10.2058
Sample weight [g]
Sample weight [g]
Titration rate [mL/min]
22 2
22 2
22 2
22 2
22 2
22 2
22 2
22 2
22 2
Table 6. Method parameters of ASTM D8045 and ASTM D664 Solvent system
Reagent cost per titration Titration time
Sample size for expected TAN of 0.05–1.0 mg KOH/g
22 2
Titration rate [mL/min]
Titration rate [mL/min]
Solvent volume [mL]
From crude feedstock to refinery fractions, extensive testing and method development using the Metrohm Titrotherm for acid number determination by D8045 proves to be simple and precise. With improved measurement, refiners can better ad- just their plant operation to control and mitigate corrosion risk from naphthenic acid while ensuring fair trade and commerce throughout the industry.
Solvent volume [mL]
30 30 30 30 30 30 30 30 30 30
30 30 30 30 30 30 30 30 30 30
Solvent volume [mL] 30 30 30 30 30 30 30 30 30 30
0.1300 0.1267 0.1167 0.1167 0.1200 0.1200 0.1200 0.1167 0.1333 mean SD
SD
Table 6. Method parameters of ASTM D8045 and ASTM D664 ASTM D664
Toluene/IPA/H2O (120 mL) $ 4.09/sample ~ 220 s
20 g ± 2.0 g Sensor maintenance procedure
1. Solvent rinse 2. Two minute rehydration 3. IPA dip Fill with electrolyte fill solution. The probe must not dry out during storage.
SD ASTM D8045
Xylene/IPA (30 mL) $ 1.07/sample ~ 60 s
~ 10 g
1. Solvent rinse No rehydration No fill solution Store dry.
0.1267 0.1267
0.1300 0.1300
0.1267 0.1267
0.1167 0.1167
0.1200 0.1200
0.1200 0.1200
0.1200 0.1200
0.1167 0.1167
0.1333 0.1333
mean mean
0.1167 0.1167
[mg KOH/g] [mg KOH/g]
0.07 0.07
0.07 0.07
0.07 0.07
0.06 0.06
0.07 0.07
0.07 0.07
0.07 0.07
0.06 0.06
0.0670 0.0048
0.0670 0.0670
0.07 0.07
0.0048 0.0048
0.06 0.06
[mg KOH/g]TAN 0.07 0.07 0.07 0.06 0.06 0.07 0.07 0.07 0.06 0.07
22 2
22 2
22 2
22 2
22 2
22 2
22 2
22 2
22 2
2 Conclusion
30 30 30 30 30 30 30 30 30 30
30 30 30 30 30 30 30 30 30 30
Run # Run #
Sample weight [g]
20.152
Sample weight [g]
Sample weight [g]
Titration rate [mL/min]
Titration rate [mL/min]
Titration rate [mL/min]
Solvent volume [mL]
Solvent volume [mL]
Solvent volume [mL] 30 30 30 30 30 30 30 30 30 30
End point [mL] 0.1733
The new thermometric standard, D8045, offers the highest accuracy for the analysis of the total acid content in crudes and refinery fractions. By solving sample solubility and mea- suring accuracy issues, ASTM D8045 offers increased preci- sion between buyers and sellers of petroleum products and is a recommended standard to add to these agreements. By us- ing 75% less solvent and reducing the analysis time, the new solvent system also considerably lowers the cost of testing. Table 6 provides on overview of the new D8045’s most impor- tant improvements for the analyst compared to ASTM D664.
0.1633 0.1600 0.1533 0.1467 0.1567 0.1467 0.1533 0.1533 0.1567 mean SD
SD SD
End point [mL] 0.1267
End point [mL] End point [mL]
mean mean
0.0420 0.0042
0.0420 0.0420
0.04 0.04
0.0042 0.0042
TAN TAN
0.1567 0.1567
0.1533 0.1533
0.1533 0.1533
0.1467 0.1467
0.1567 0.1567
0.1467 0.1467
0.1533 0.1533
0.1600 0.1600
0.1633 0.1633
0.1733 0.1733
End point [mL] End point [mL]
TAN TAN
[mg KOH/g] [mg KOH/g]
0.04 0.04
0.04 0.04
0.04 0.04
0.04 0.04
0.04 0.04
0.04 0.04
0.04 0.04
0.05 0.05
0.05 0.05
[mg KOH/g]TAN 0.05 0.05 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04
0.1367 0.1367
mean mean
0.1467 0.1467
0.1333 0.1333
0.1400 0.1400
0.1333 0.1333
0.1333 0.1333
0.1400 0.1400
0.1400 0.1400
0.1333 0.1333
0.1367 0.1367
End point [mL] End point [mL]
TAN TAN
[mg KOH/g] [mg KOH/g]
0.1520 0.0063
0.1520 0.1520
0.15 0.15
0.0063 0.0063
0.16 0.16
0.15 0.15
0.15 0.15
0.15 0.15
0.15 0.15
0.16 0.16
0.16 0.16
0.14 0.14
0.15 0.15
[mg KOH/g]TAN 0.15 0.14 0.16 0.16 0.15 0.15 0.15 0.15 0.16 0.15
Figure 4. Correlation of the results of the thermometric TAN determination and the potentiometric TAN determination ac- cording to ASTM D664
PIN April / May 2022
40
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