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Apr-2019

The next generation of elemental analysis

With tightening sulphur regulations across the globe, petroleum professionals have the unique challenge of certifying their products as efficiently as possible.

Joseph Iaia
XOS
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Article Summary
In addition, there is an increasing need to test critical elements in various matrices to protect valuable equipment and avoid downtime. Petra MAX delivers D4294 sulphur analysis in addition to 12 elements in matrices like hydrocarbon, water and catalysts. Petra MAX is also available with a new autosampler design, delivering continuous sample loading and sample tracking capabilities. This analyser was designed to save time for refineries, terminals, and third-party labs. Throughout this paper, we will review some of the features that make Petra MAX so unique compared to its counterparts in the market.

D4294 sulfur analysis 
Petra MAX complies with ASTM D4294 and ISO 8754 for sulphur analysis in various hydrocarbon matrices, delivering an LOD as low as 5.7 ppm. To demonstrate the precision of Petra MAX, various hydrocarbon samples, including heating oil, kerosene, jet A, vacuum gas oil (VGO), and crude oil were analysed. The analyses were performed at separate laboratories with unique instruments and users. The results shown in Table 1 (see page 2) demonstrate that Petra MAX delivers precise measurements across a wide range of hydrocarbon sample types. In addition, Petra MAX is a valuable tool to monitor trends and identify materials that simply do not meet specification.
 
Elemental analysis of NI, V, AND FE   
The blending of crude oils from different sources has become more commonplace within the industry to meet specifications for the classification of sweet crude oil. The introduction of new crudes brings new challenges, like higher concentrations of metals such as nickel (Ni), vanadium (V), and iron (Fe). Ni and V are known to rapidly deactivate process catalysts in the  catalytic  cracker (FCC) and hydrotreaters. In response, many refiners have incorporated Ni and V analysis into their routine crude assay, and pipelines have set specifications for Ni and V in their common stream sweet crude. Fe is introduced into crude oil from corrosion byproducts during transportation and can lead to pump and exchanger fouling, and off- specification coke.

Each refinery or pipeline location has their own specifications for specific elements like S, V, Ni and Fe. The desired level or limit for each heavy metal may vary depending on the detriment its presence causes to the equipment, process, or finished product. But in the case of V, Ni, and Fe, current methods can take a significant amount of time to prepare (including hours for ashing), analyse, and if outsourced, can be quite costly. Table A outlines common pipeline feed specifications.

To study the precision of Petra MAX for simultaneous measurement of S, Ni, V, and Fe, ten repeat measurements were performed on two different crude  oil samples containing these elements. The results shown in Tables 2 and 3 demonstrate that Petra MAX delivers precise measurement results well below desired specifications, and therefore is a valuable tool for monitoring trends as well as identifying materials that do not meet specification. Please see Table 4 for Petra MAX’s dynamic range, LODs, and applications.
 
Eliminate the need to centrifuge     
The X-ray fluorescence (XRF)  testing method is known to have interferences. A common matrix effect interference involves particulates settling to the bottom of the sample cup and absorbing the X-ray signal. This matrix effect will ultimately influence the total sulphur measurement and lead to a biased result. Refineries and third-party certification companies using XRF for high-particulate samples have relied on centrifuging samples to ensure an accurate sulphur measurement – which involves a time-consuming sample preparation process.

Many D4294 analysers are designed with the X-ray detector focused on the bottom of a sample cup where settling occurs, as depicted in Diagram 1. Since particulate solids and water settle over time, it is difficult to obtain accurate sulphur measurements due to the changing concentration of interferences. To combat the effects of settling in crude oil, Petra MAX delivers a new, innovative sample chamber that rotates the sample on its side, providing a clear measurement window for more accurate results. See Diagram 2.

To study the effects of particulate solids on sulphur measurements, a crude oil sample was analysed using a traditional XRF analyser and Petra MAX. The following sample analysis procedure was performed using both methods:

1. A particulate-free certified reference standard of 2 wt% S in mineral oil sample was measured for 100-seconds to check instrument accuracy.

2. One-litre bottles of crude oil containing a high- level of particulates were shaken vigorously, and samples were prepared and measured immediately for 100-seconds.

3. Measurements were repeated 5 times  with a 5-second pause in-between. The data was collected and compiled to evaluate the effect of particulate settling on sulphur analysis.

The results are shown in Graph 1. While the traditional XRF results show a rapid drift in sulphur concentration  due to particulate settling, the results from Petra MAX remain stable for each repeat measurement. This demonstrates that, even with high levels of particulates, Petra MAX delivers accurate and precise sulphur measurements in crude oil for ASTM D4294 and ISO 8754 methodology.
 
Precision compare between HDXRF VS. ICP FOR NI, FE, AND V     
As petroleum professionals continue to refine their production processes, products such as crude oil can contain higher concentrations of problematic metals like nickel (Ni), iron (Fe), and vanadium (V). In the face of tightening regulations and increased demand for sweeter crudes, refiners are looking to buy lower cost oils that contain these metals, with the intent of assessing their concentration levels throughout the refining process. To compound the challenge of attaining a sweet crude and mitigating risk of damages from metals, refineries and other petroleum certification sites, such as terminals and third-party labs, must adhere to regulations that require them to utilise D5708B methodology, which specifies ICP analysis. There is, however, an option for users to screen samples before ICP using XRF analysis.

High Definition X-ray Fluorescence (HDXRF®), XOS’ patented technology, is an improved version of the XRF technique, and a cost-effective alternative to ICP. While some may utilise an in-house ICP setup, many professionals, such as those working at pipelines, must send samples out. This is yet another necessary burden these professionals must deal with as the costs and downtime will ramp up significantly when products come back from ICP analysis out of spec. By testing in-house and getting results in less than five minutes, refineries, terminals, and labs will be able to make real-time decisions when products are off-spec and can improve their overall processes when products are within spec.
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