HDXRF VS ICP FOR NICKEL AND VANADIUM IN CRUDE OIL
Technology introduced over the last decade, such as horizontal drilling and hydraulic fracturing, has led to new sources of light tight oil (LTO). LTO has grown in the US from essentially zero in 2010 to about 5 million barrels per day in 2017, exceeding the US production volume of non-tight oil. This trend is expected to continue with projections of 10 million barrels per day in the US by 2025, and signifi cant supply in countries like Russia, China, Canada, Egypt, and Argentina. This is reshaping the landscape of available refi ning feedstock and challenges are arising across the industry. Refi neries in the US Gulf Coast and across the world have invested signifi cantly in processing units to handle much heavier crude oil. The new LTO contains signifi cantly more naphtha than crude from conventional sources. Refi ners are experiencing bottlenecks in the light ends distillation capacity and are having trouble keeping their conversion units, like the FCC, hydrocrackers, and cokers, full.
These changes are also having an impact on the quality of West Texas Intermediate (WTI) traded under the NYMEX Light Sweet Crude Oil (CL) futures contract delivered in Cushing, Oklahoma. The oil delivered is subject to specifi cations such as sulfur and API gravity, and oil blending near to the specifi cation limit is common. Figure 1 plots the sulfur content of WTI delivered at Cushing. The sulfur content is consistently below the specifi ed maximum of 0.42 wt% but never drops below 0.38 wt% as a result of oil blending.
However, this blending creates new processing challenges for refi ners as oils from other sources can introduce changing levels of other contaminants. Figure 2 plots the vanadium content of WTI delivered at Cushing, and depicts a trend toward higher levels over time. This is a result of blending oils from different sources with the WTI prior to delivery in Cushing. These changes in other oil quality parameters due to blending have led to many issues for refi ners processing the crude oil. In response, NYMEX has amended rule 200101 to add fi ve additional quality specifi cations including nickel and vanadium for contracts with delivery in January 2019 and beyond. The maximum concentrations allowed under the amended rule are 8 parts per million in nickel, and 15 parts per million in vanadium.
Petra Source:
crudemonitor.us Figure 2: Vanadium Content of WTI Delivered at Cushing Challenge Source:
crudemonitor.us Figure 1: Sulfur Content of WTI Delivered at Cushing
Nickel and vanadium are naturally occurring in crude oil and become concentrated in the resids and heavier fractions of vacuum gas oils. They are known to rapidly deactivate cracking catalysts and can lead to off-specifi cation coke, resulting in considerable costs to refi ners. While refi ners often look for opportunities to buy lower cost oils to improve profi tability, understanding the content of contaminants like nickel and vanadium is important in order to adequately assess the impact on processing. Nickel and vanadium in crude oil can be tested using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) using ASTM test method D5708B. However, there are drawbacks to this technique. First, it requires a rigorous sample preparation process that involves strong acids, heating with hot plates, furnaces, and consumable gasses in a laboratory setting. Second, it is very time consuming: prep to analysis can take between 8 and 12 hours. Because of these drawbacks, ICP is not an effi cient solution for analysis of nickel and vanadium in crude oil. In response, a faster, easier, and less expensive solution has been developed.
OCTOBER / NOVEMBER •
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MAX™ delivers advanced D4294 sulfur analysis in addition to 12 elements from P to Zn including Ni, V, and Fe. This robust benchtop analyzer complies with ASTM D4294 and ISO 8754 for measuring sulfur in hydrocarbons. Petra MAX is powered by HDXRF, utilizing XOS patented doubly curved crystal optics coupled with a high-performance silicon drift detector and an intense monochromatic excitation beam. This industry-leading technology reduces background noise and increases signal-to-noise output, enabling low detection limits and high precision without the need for consumable helium gas, a vacuum pump, or extensive sample preperation.
Solution
X-ray Fluorescence Spectroscopy (XRF) is an alternative technology to ICP and most commonly used for sulfur analysis in liquid hydrocarbons like crude oil, fuels and lubricants. Utilizing standard methods like ASTM D4294 and ISO 8754, XRF is included in most crude oil specifi cations today. Petra MAX, a new XRF analyzer, delivers ASTM D4294 sulfur compliance with simultaneous measurement of nickel, vanadium, iron, and nine other elements at sub-ppm levels.
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