Trace levels 0. Petroleum products like gasoline, diesel and fuel oil, may include many organic sulfur compounds. These can be classified as acidic and non-acidic. Acidic sulfur compounds are the thiols mercaptans. Thiophene, sulfides, and disulfides are examples of non-acidic sulfur.
|Published (Last):||12 April 2007|
|PDF File Size:||4.37 Mb|
|ePub File Size:||6.41 Mb|
|Price:||Free* [*Free Regsitration Required]|
These challenges are made more difficult by the variety of regulations and specifications, and the implications they present for their refining process. Regulators across the globe are moving to even more restrictive regulations on sulfur content in a variety of fuels with many countries now requiring maximum sulfur concentration in automotive fuels of 10 to 15 parts per million ppm. These regulations have furthered the need for refineries to maximize the precision of their sulfur analysis methodology.
Desulfurization processes are expensive utilizing catalyst, hydrogen, and heat. By using a more precise sulfur measurement technique, refiners can produce product closer to the specification maximums, reducing giveaway and saving money. This savings is illustrated in Figure 1. In addition to production efficiencies, refiners can avoid inaccurate reporting which can lead to regulatory missteps and contract disputes by using a test method with better precision.
With several different methodology options for sulfur analysis available, refineries, terminals, and test inspection certification companies must take care to select a method that produces the least amount of variability in their measurements. Each participating laboratory performs analyses following ASTM methods for various test parameters, including sulfur, using the samples provided. First, an understanding of the test methods is critical to interpreting the data presented. Rather than using filters or traditional crystals that are flat or singly curved, MWDXRF incorporates doubly curved crystal DCC optics to provide a focused, monochromatic excitation X-ray beam to excite the sample.
A second DCC optic is used to collect the sulfur signal and focus it onto the detector. Upon exposure, fluorescent X-rays are emitted from the sample at energy levels that are unique to each element. Additionally, the background signal, an energy region not characteristic of sulfur or other interfering elements, is collected and subtracted from the sulfur signal to improve precision and LOD.
To isolate the sulfur signal and to reduce noise, WDXRF utilizes a filter and a collection crystal before the sulfur signal reaches the detector. The sample is combusted in the tube, and sulfur is oxidized to sulfur dioxide SO2 in the oxygen-rich atmosphere.
Water produced during the sample combustion is removed by a membrane dryer and the sample combustion gasses are exposed to ultraviolet UV light. The resulting signal is a measure of the sulfur contained in the sample. The data shown represents sulfur data collected throughout the study from January to December Understanding the Data Mean Concentration and Reproducibility Both graphs and tables shown below track average sample concentration and reproducibility R.
Reproducibility is the difference between two single and independent results obtained by different operators applying the same test method in different laboratories using different apparatus on identical test material.
A lower reproducibility value correlates to a better level of precision which can minimize risks from inaccurate reporting such as regulatory fines and contract disputes. The data presented is filtered to show all samples whose average concentration ranged between 5 and 15 ppm. These values were chosen based on the most common regulatory requirements for sulfur content in automotive fuel in Europe, United States, China, and others around the world. It is critical for an analyzer to have low reproducibility values better precision when measuring these types of samples.
Each column cluster in the graphs represents reproducibility for one sample measured by multiple laboratories each using D, D, or D Within each column cluster, each color-coded bar corresponds to reproducibility for one test method. D is in orange, D is in gray, and D is in blue. For many test methods, precision is often dependent on concentration. For context, the monthly average sulfur concentration is graphed as a red dot and its value is shown on the right axis of the graphs.
Both tables are color-coded to indicate relative monthly performance; green represents the best method reproducibility, yellow represents the second best reproducibility, and red represents the poorest reproducibility. The average R value across the 3 years of study data is the key performance indicator shown in both graphs and tables.
NSure: Nitrogen & Sulfur
5453RD – Custom Range Sulfur in Diesel (2 ml)