Precision Comparison Case Study — HDXRF® vs ICP (IP 501 & IP 621)
As petroleum professionals continue to refine their production processes, products such as crude oil, residual fuel oils, and VGO can contain higher concentrations of problematic metals like nickel (Ni), iron (Fe), and vanadium (V).
Satbir Nayar and Julian Doug van Berkum
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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.
The reason these metals need to be continually monitored is due to their problematic effects on refining processes. For example, nickel and iron rapidly deactivate process catalysts used in hydrotreaters and FCC units, which leads to off- specification coke and increased, unplanned costs to refiners. To compound the challenge of attaining a sweet crude and mitigating the risk of damage from metals, refineries, and other petroleum certification sites, such as terminals and third- party labs, must adhere to regulations that might require them to utilise IP 501 and IP 621 methodology. There is, however, an option for users to screen samples before ICP using XRF (X-ray fluorescence) analysis or to supplement their wet chemistry procedures with the use of XRF to further improve their processes.
As mentioned, there are two well-known technologies for elemental analysis: X-ray fluorescence (XRF in various methods and forms such as energy-dispersive XRF (EDXRF) or wavelength-dispersive XRF (WDXRF)) and wet chemistry (ICP and AAS), which includes methods such as IP 501 and IP 621. With IP 501 and IP 621, samples must first go through a time-consuming and sensitive sample preparation process which involves breaking down the sample, mixing it with other materials, digesting it in acid, and then diluting it in water. Only after this lengthy and complicated process is the sample then measured with either ICP OES (IP 501) or ICP-OES/AAS (IP 621). Both methods are considered highly precise, however, not only do they typically take 4-10 hours to complete, but due to the multiple complex steps, they require specially trained operators. In addition, the multiple steps may increase the likelihood for variability within the process and negatively impact precision.
While professionals in the petroleum industry might be more familiar with IP 501 and IP 621 or feel they need to adhere to these methods in particular, those looking to reduce downtime during the process may consider a cost-effective, faster, in-house alternative. Some labs may have the luxury of running these wet chemistry methods in- house, but many professionals, such as those working at terminals, pipelines, and smaller labs, may have to send samples out for testing. This not only results in higher costs, but more importantly, significant turnaround time for the data—which can occasionally result in increased downtime when products come back from IP 501/621 analysis as being 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 based on the faster availability of that data.
Petra MAX, powered by HDXRF®, can be used as a cost-effective screening tool, enabling users to pre-screen their samples before sending them out for wet chemistry testing and make critical decisions faster. Likewise, even those with access to in-house ICP/AAS processes can save hours of sample preparation time by first screening the samples with Petra MAX, then running off-spec or near off-spec with wet chemistry.
Recently, a large European refinery was interested in testing the performance of Petra MAX as a potential addition to their in-house testing process, as they saw great value in obtaining Ni, V, and Fe results in under five minutes. This refinery performed an elemental analysis study comparing the precision performance between Petra MAX (HDXRF®) and ICP (IP 501 and IP 621) with VGO and fuel oils. In this paper, we will review the study performed and discuss the data provided by the refinery.
The refinery prepared and measured 10 different VGO samples both on Petra MAX and with IP 621 for Ni, V, and Fe. A second set of 10 fuel oil samples were also run on Petra MAX as well as with IP 501 for Ni and V, in addition to a single sample for Fe. The samples run on Petra MAX were measured for a five-minute measurement time, with sample preparation limited to pouring 7-8 ml into a sample cup and applying the sample film.
As shown in Tables 1, 2 and 3 for VGO, and Tables 4, 5, and 6 for fuel oil, the results of Petra MAX compare quite favourably to that of the ICP methods (IP 501 and IP 621) between the two different sample types and across multiple element concentrations and measurements. The differences between the Petra MAX results and the IP 501 and IP 621 results are all well within reproducibility for those methods and in almost all cases, even with repeatability, are great indicators of comparable accuracy. Given its minimal sample preparation, rapid five-minute results and ease of use, Petra MAX is a valuable tool for industry professionals to determine Ni, V, and Fe concentrations in VGO and fuel oils.
Petra MAX, powered by HDXRF, delivers comparable results to IP 501 and IP 621 in five minutes or less. In addition, users have minimal sample preparation and can achieve results with the push of a button. Those looking to save time and money in elemental quantification by screening samples before ICP analysis can achieve comparable results with Petra MAX.
This study resulted in the refinery purchasing Petra MAX—a decision that has since saved them significant sample preparation and testing time while simultaneously reducing turnaround time for metal and sulphur analyses.
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