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Certifying sulphur in automotive fuels and monitoring chlorine for corrosion mitigation

With the high volatility in crude prices leading to uncertainty in budgets, refiners are seeking new, innovative ways to respond to the industry’s dynamic landscape.

Kyle Kuwitzky
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Article Summary
Refineries are facing many new challenges, including complying with new regulations, protecting against chlorine-induced corrosion, and the costs associated with both.

• Globally, adoption of regulations like Euro VI and Tier 3 continue to lower the required sulphur level in automotive fuels. With these changes come challenges, and it is more important than ever to seek out the most precise and reliable solution to produce the best data.

• Refinery corrosion is a critical and very expensive problem. Leading refiners have found that by lowering the chloride content of desalted crude oil and process streams, they can significantly extend turnaround times, lower the costs of corrosion, and decrease related safety hazards. In order to do so, they must implement a process to monitor chlorine levels.

Introducing Sindie +Cl
Sindie +Cl utilises a technique known as Monochromatic Wavelength Dispersive X-ray Fluorescence (MWDXRF) – delivering exceptional reproducibility. It delivers both sulphur and chlorine trace analysis with one push of a button and zero hassle. Samples are measured directly, which means it can analyse even the heaviest of hydrocarbons like crude oil or coker residuals, without the hassle of boats, injectors, furnaces, or changing detectors.

Method Compliance
•    ASTM D2622, D7039, D7536
•    SH / T 0842

Application Study
1. Certifying Sulfur in Automotive Fuels

MWDXRF has long been used  in the petroleum industry for certification of sulphur levels in diesel and gasoline blends. To study the performance of Sindie +Cl, 10 repeat measurements were performed on commercially-available diesel and gasoline standards with 10 ppm and 9 ppm sulphur respectively. Ten separate aliquots of each of the diesel and gasoline samples were measured for five minutes each using ASTM D7039 methodology. The result of 10 measurements on a 10 ppm sulphur in diesel standard was an average value of 9.59 ppm sulphur, with a standard deviation of 0.44 ppm, and a relative standard deviation (RSD) of 4.62%. The results of the ten measurements on the 9 ppm sulphur in gasoline standard was an average of 8.62 ppm, 0.41 ppm standard deviation, and 4.71% RSD. Additionally, as outlined in the ASTM D7039 method, if the repeats are paired (i.e. 1 and 2, 3 and 4, etc.), each paired repeat is within the method’s repeatability standard. The measurement data for this study can be seen in Table 1.

2. Monitoring Chlorine for Corrosion Mitigation
In an effort to mitigate the multi-billion dollar costs of corrosion in global refineries, the regular monitoring of chlorine in desalted crude oil is becoming more critical. To assess the performance of Sindie +Cl for this application, ten repeat measurements were performed on a commercially available 10 ppm chlorine in crude oil standard. The sulphur content of this standard was unknown. Ten separate aliquots of the crude oil were measured simultaneously for chlorine and sulphur using a five-minute measurement time. A modified D7536 procedure was used for chlorine measurements, which included a 0-500 ppm chlorine in mineral oil calibration for the measurement of crude oil. Results of the ten chlorine measurements averaged 10.13 ppm chlorine, with a standard deviation of 0.30 ppm, and a 2.95% RSD. Despite the modified chlorine procedure, if the repeats are paired (i.e. 1 and 2, 3 and 4, etc.), each paired repeat is within D7536 repeatability. For the sulphur values, results averaged 443.33 ppm, with a standard deviation of 1.42 ppm, and an RSD of 0.32%. Paired repeat measurements exhibit precision within ASTM D2622 repeatability. The measurement data for this study can be seen in Table 2.
3. Automatic Sulfur Correction
Many heavy samples, like crude oil, VGO or coker residual, may have percent-level sulphur present while chlorine may be as low as a few parts per million. High sulphur levels will typically depress the chlorine measurement result during XRF analysis. Sindie +Cl can measure the sulphur and chlorine concentrations simultaneously and then automatically correct the chlorine measurement. To illustrate this issue, a coker residual sample was first analysed for chlorine and sulphur with the automatic sulphur correction disabled, and then the sample was reanalysed with the automatic sulphur correction enabled to demonstrate this capability. This comparison can be seen in Table 3, where the use of automatic sulphur correction will assist in the prevention of reporting falsely low measurement results.

The results of this application study demonstrate that Sindie +Cl is an ideal solution for multiple applications where precision, ease-of-use, and flexibility is needed. Get Sindie +Cl to certify low sulphur level fuels for regulatory purposes, and monitor chlorine in desalted crudes and other process streams to identify potential sources of corrosion.

Sindie +Cl delivers the precision, hassle-free operation, and flexibility needed to meet the application needs of the industry’s dynamic landscape.
Monochromatic Wavelength Dispersive X-ray Fluorescence
Sindie +Cl is powered by Monochromatic Wavelength Dispersive X-ray Fluorescence (MWDXRF), an XOS technology consisting of a low power X-ray tube, a point-to-point focusing optic for excitation, a sample cell, additional focusing optics for collection and two X-ray detectors (Figure 1). The first focusing optic captures a narrow bandwidth of X-rays from the source and focuses this intense monochromatic beam to a small spot on the sample. The monochromatic primary beam excites the sample and secondary characteristic fluorescence X-rays are emitted. Collection optics collect only the characteristic X-rays for sulphur and chlorine. These characteristic X-rays are then focused onto the detectors, eliminating the scattered background peak caused by the X-ray tube which improves the signal-to-background ratio (S/B) by a factor of 10 compared to conventional WDXRF technology.

XOS has delivered sulphur and chlorine analysis solutions using MWDXRF since 2005, and has installed over 2,000 MWDXRF analysers worldwide for certification of sulphur in finished products and chlorine monitoring for corrosion mitigation. Our newest product, Sindie +Cl, is an ideal solution for multiple applications: certify low sulphur level fuels for regulatory purposes, and monitor chlorine in desalted crudes and other process streams to identify potential sources of corrosion.

Using MWDXRF to Identify Chlorides in Crude
A major US refiner identified chlorides in crude feedstocks as a major problem leading to irreversible corrosion in critical piping systems and equipment. This caused serious problems like unplanned rate cuts, unit shutdowns, and loss of containment at refineries. Traditional salt in crude testing units are unable to detect the presence of corrosion causing species such as organic and non-extractable inorganic chlorides. Organic chloride species are not typically naturally occurring but instead are introduced through contamination. Non-extractable inorganic chlorides are salts that become encapsulated by asphaltenes, paraffin, or solids. Because they are encapsulated and not able to be removed during desalting, they can also not be detected by routine salt in crude testing. Using XOS instruments powered by MWDXRF technology, the refinery implemented a comprehensive total chloride-monitoring program and ultimately lowered chlorides to an acceptable level.
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