Application Note EDXRF3236
Scope
Compliance with ASTM D8252 and performance are demonstrated for the analysis of vanadium (V), nickel (Ni), and iron (Fe) in crude and residual oil in the ultra-low range <50 ppm. The measurement also includes analysis of sulfur (S), in compliance with ASTM D4294.
Background
The quality and grade of crude oil, in part, depend on the metal and sulfur content. Nickel and vanadium are the most critical metals, as is iron in some crudes and residual oils. The metal content is especially important in determining the quality of bunker fuels.
ASTM D8252 addresses the need to measure low levels of nickel and vanadium in crude to meet the NYMEX/CME specifications for light sweet crude oil futures contracts concerning the maximum allowable levels of nickel and vanadium.
To meet industry needs, Rigaku offers the NEX QC II+, a simple, versatile, and portable benchtop EDXRF analyzer for the analysis of metals and sulfur in crude, residual oil, and marine fuels.
International Norms
The Rigaku NEX QC II+ EDXRF analyzer meets ASTM D8252 for the analysis of 2 – 50 ppm vanadium and 2 – 50 ppm nickel in crude and residual oil. Iron and sulfur are also measured for informational purposes. The sulfur measurement can be used for compliance with ASTM D4294.
The units ppm and mg/kg can be used interchangeably.
Calibration
Empirical calibrations were built using a suite of 12 commercially available calibration standards. A summary of the empirical calibrations is shown here.
| Element | Concentration range |
| Ni | 3 – 50 ppm |
| V | 3 – 50 ppm |
| Fe | 3 – 50 ppm |
| S | 0.100 – 5.000 mass% |
Repeatability
| Sample: Std 10 | ||||
| Element | Standard value | Average value | Std. dev | % Relative dev |
| Ni ppm | 51 | 50.4 | 0.4 | 1.1 |
| V ppm | 5.0 | 5.3 | 0.1 | 6.0 |
| Fe ppm | 10.0 | 9.5 | 0.4 | 5.0 |
| S mass% | 4.501 | 4.520 | 0.025 | 1.9 |
| Sample: Std 12 | ||||
| Element | Standard value | Average value | Std. dev | % Relative dev |
| Ni ppm | 30 | 30 | 0.1 | --- |
| V ppm | 50 | 51 | 0.2 | 2.0 |
| Fe ppm | 5.0 | 4.8 | 0.2 | 4.0 |
| S mass% | 0.250 | 0.253 | 0.002 | 1.2 |
| Sample: Std 3 | ||||
| Element | Standard value | Average value | Std. dev | % Relative dev |
| Ni ppm | 5 | 5.1 | 0.1 | 2.0 |
| V ppm | 30 | 29.5 | 0.2 | 1.7 |
| Fe ppm | 40 | 39.7 | 0.3 | 0.8 |
| S mass% | 1.000 | 0.970 | 0.008 | 3.0 |
ASTM D8252-19
In ASTM, little r is called repeatability and represents the precision of the measurement. Little r is 2.77 times the 1σ standard deviation precision of repeat measurements. Comparison of the NEX QC II+ instrument r to the method r of D5282 shows that the NEX QC II+ complies with the ASTM method for the measurement of nickel and vanadium in crude and residual oil.
| Units: mg/kg (ppm) | |||||
| Element | Standard value | Average value | Std. dev 1σ | Instrument r | D8252-19 r |
| Ni | 5.0 | 5.10 | 0.11 | 0.3 | 1.1 |
| V | 5.0 | 5.29 | 0.08 | 0.2 | 1.0 |
Conclusion
The performance shown here demonstrates the ability of the NEX QC II+ to measure metals in crude and residual oil according to ASTM D8252 standards, as well as sulfur content in compliance with D4294. The NEX QC II+ features a simple, user-friendly touchscreen interface and requires minimal maintenance, allowing operators of all skill levels to use and maintain the equipment easily.
