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 the metals mentioned above, 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. In addition to this, regulations for sweet crude will tighten in January 2019 to lower the allowable limit to 8ppm and 15ppm for nickel and vanadium, respectively. 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 utilize D5708B methodology, which specifies ICP analysis. There is, however, an option for users to screen samples before ICP using XRF analysis.
As mentioned, there are two well-known methods for elemental analysis: X-ray fluorescence (XRF), and inductively coupled plasma (ICP). In ICP measurements in compliance with method D5708B, also known as Inductively Coupled Plasma Optical Emission Spectroscopy (ICP – OES), samples must be digested with sulfuric acid, constantly stirred under gentle heat, then burned off in a muffle furnace to remove the carbon. After this, the sample must be reconstituted with nitric acid before finally being analyzed. ICP analysis is a highly precise form of elemental quantification, however, it involves exhaustive sample preparation and lengthy wait times for results – usually between 6 to 12 hours.
XRF analysis involves exposing the sample to X-rays to produce an emission at an energy level that is characteristic of the element of interest. This method involves minimal sample preparation and provides results in minutes. High Definition X-ray Fluorescence (HDXRF®), XOS’ patented technology, is an improved version of the XRF technique. HDXRF applies state-of-the-art monochromating and focusing optics enabling a dramatically higher signal-to-background ratio. This technique also reduces background noise delivering lower limits of detection and significantly better precision.