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EP-4037809-B1 - ELEMENTAL SULFUR ANALYSIS IN FLUIDS

EP4037809B1EP 4037809 B1EP4037809 B1EP 4037809B1EP-4037809-B1

Inventors

  • LOCKLEAR, JAY
  • CROWE, Clinton

Dates

Publication Date
20260506
Application Date
20201002

Claims (16)

  1. A method of determining the amount of elemental sulfur in an unrefined or refined hydrocarbon fluid, comprising: a) obtaining a sample of an unrefined or refined hydrocarbon fluid containing elemental sulfur; b) adding a caustic solution to said sample and reacting said caustic solution with said elemental sulfur to yield reaction products, wherein the reaction products are colored; c) comparing the absorbance of the reaction products with the absorbance of a series of standard solutions of known elemental sulfur concentration prepared using the same method as in step b); and, d) determining the concentration of said elemental sulfur in said sample based on said absorbance comparison in step c).
  2. The method of claim 1, wherein said comparing step comprises using an Ultraviolet-visible (UV-VIS) spectrometer to obtain the absorbances.
  3. The method of claim 2, wherein said UV-VIS spectrometer scans from 300-700 nm.
  4. The method of any of claims 1-3, wherein said caustic solution is a mixture of a caustic chemical, an alcohol and a hydrocarbon solvent.
  5. The method of claim 4, wherein said caustic solution comprises tetrabutylammonium hydroxide 30-hydrate in an organic solvent.
  6. The method of claim 5, wherein the concentration of said tetrabutylammonium hydroxide 30-hydrate in the caustic solution is between about 0.01 and 0.1M.
  7. The method of any of claims 1-6, wherein the volume ratio of said caustic solution to said sample is 5:1.
  8. The method of any of claims 1-6, wherein 10 mL of a caustic solution is added to about 0.5 mL of said sample.
  9. The method of any of claims 1-8, wherein the unrefined or refined hydrocarbon fluid is selected from a group consisting of gasoline, jet fuel, waxes, kerosene, condensates, black oils, solid hydrocarbons that are solubilized in liquid hydrocarbons, and combinations thereof.
  10. The method of any of claims 1-9, wherein the unrefined or refined hydrocarbon fluid is a gas produced from a reservoir.
  11. The method of any of claims 1-10, further comprising the step of treating said unrefined or refined hydrocarbon fluid to convert said elemental sulfur to insoluble sulfur products and removing said insoluble sulfur products from said fluid.
  12. The method of any of claims 1-10, further comprising the step of treating equipment surfaces in contact with said unrefined or refined hydrocarbon fluid to prevent corrosive damage from said elemental sulfur.
  13. The method of any of claims 1-12, wherein said fluid is translucent.
  14. A test kit for determining an amount of elemental sulfur in an unrefined or refined hydrocarbon fluid, said test kit comprising a storage container comprising: a) a first container having a known amount of a caustic chemical; b) a second container having a known amount of a hydrocarbon solvent; c) said first container or a third container having a known amount of an alcohol; d) a fourth container having elemental sulfur at a known concentration; and e) a set of instructions for using said test kit to perform the method of claim 4.
  15. The test kit of claim 14, said storage container further comprising a plurality of cuvettes and a plurality of pipettes for transferring solutions into the plurality of cuvettes, wherein each said cuvette has a cap such that it can be used for mixing at least two of said caustic chemical, said hydrocarbon solvent, said alcohol, and said elemental sulfur.
  16. The test kit of claim 14 or 15, wherein said hydrocarbon solvent is selected from a group consisting of gasoline, diesel, kerosene, hexane, benzene, toluene, xylene, heavy aromatic naphtha, mixtures of naphtha and naphthalene, and naphthalene, or said alcohol is selected from a group consisting of methanol, ethanol, isopropanol, and butanol, or said caustic chemical is selected from the group consisting of tetrabutylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, lithium hydroxide, cesium hydroxide, magnesium hydroxide, lithium methoxide, sodium methoxide, potassium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, lithium propoxide, sodium propoxide, and potassium propoxide.

Description

PRIOR RELATED APPLICATIONS This invention claims priority to US Application No. 62/910,501, filed on October 4, 2019. FIELD OF THE DISCLOSURE The disclosure relates generally to methods of determining the concentration of elemental sulfur in hydrocarbons. BACKGROUND OF THE DISCLOSURE Hydrocarbon fluids and gases often contain a variety of sulfur compounds, including elemental sulfur. When sulfur is present in concentrations of 1 percent or more by weight, the hydrocarbon is characterized as "sour" and concentrations of 0.5 percent or less are "sweet" hydrocarbons. It is well known that elemental sulfur and other sulfur compounds contained in hydrocarbon streams are corrosive and damaging to metal equipment, particularly copper and copper alloys. The sulfur has a particularly corrosive effect on equipment such as brass valves, gauges and in-tank fuel pump copper commutators. Even after processing, sulfur and sulfur compounds may be present in a hydrocarbon stream in varying concentrations, and additional contamination may take place as a consequence of transporting the hydrocarbon stream through pipelines containing residual sulfur contaminants from previous transportation of sour hydrocarbon streams. This is problematic because it increases sulfur dioxide (SO2) emissions when fossil fuels are combusted, and poisons catalysts utilized in the refining process. To monitor the amount of elemental sulfur present in crude, intermediates and final products, the fluids are analyzed in a lab setting by gas or liquid chromatographic methods with various detectors or x-ray fluorescence (XRF), or in the field through various 'portable' methods involving toxic chemicals. For the chromatographic methods, the elemental sulfur is separated from other molecules based on interactions with a stationary phase in the separation column, before being analyzed with a detector. While the detection limit for these instruments is in the ppm to ppb range, the portability of these methods is extremely low and the capital cost for the chromatographic instruments are high. XRF relies on the emission of characteristic "secondary" (or fluorescent) x-rays from sulfur in fluid that has been excited by bombarding with high-energy X-rays or gamma rays. XRF analysis has higher concentration detection limits than chromatographic methods and is not specific to elemental sulfur, meaning it will detect all sulfur material as one species. Additional disadvantages of XRF include requirements of special permits because of the radiation, high capital costs, and limited portability. Similar spectroscopy-based tests include ASTM D2622, which determines Wavelength Dispersive X-ray Fluorescence Spectrometry, and ASTM D4294 - 16e1, which uses Energy Dispersive X-ray Fluorescence Spectrometry. In each case, the equipment is expensive and not portable. Another test is ASTM D5453-93. In this method, a measured quantity of the hydrocarbon sample is injected into a pyrotube and oxidized in a rich pure oxygen stream in the combustion zone at approximately 1000°C where it is converted into CO2, SO2 and H2O. Once the gases exit the combustion zone, they are passed through a semipermeable Nafion® membrane where the water is quantitatively removed. The gases enter the sulfur reaction chamber where they are exposed to an UV light. The SO2 molecules absorb the radiation to become excited, and the relaxation releases a secondary energy that is captured by a Photo Multiplier Tube, amplified, processed and recorded. The signal obtained is proportional to the total sulfur content of the original sample and is not specific to elemental sulfur. However, this method requires complex, expensive equipment and is not suitable for well pad or field use. Yet another test is a Gas Chromatography (GC) chemiluminescence test, described in ASTM D5623, which uses GC combined with a Pulsed Flame Photometric Detector (PFPD). This method is used to identify organic sulfur compounds in some of the lighter feedstocks with a boiling point of 230°C or lower at atmospheric pressure. Again, this type of sophisticated equipment is expensive and not well suited for field use. Another ASTM test for sulfur is ASTM D129-18. This is a bomb test method for determination of the amount of sulfur in petroleum products with low volatilities and entails oxidizing samples by combustion and determining the amount of sulfur is by gravimetry. Portable methods do exist to allow for elemental sulfur detection in the field. While portable, these methods use highly toxic chemicals, which adds additional steps to the analysis process and presents significant hazards to workers. For example, a polarographic technique use a mercury electrode for detecting the elemental sulfur in the presence of cyanide. There is also a turbidimetric technique using barium chloride to form a barium sulfate white precipitate. The amount of precipitate so formed, either measured with a turbidity meter or a colorimeter, generally ranges