Reasons for removing the method for determining thiol sulfur content from the thiol specifications for automotive gasoline in GB 17930-2016
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As stated in the title, the GB 17930-2016 National VI gasoline standard has been released. Compared to GB 17930-2013, the technical specifications and testing methods for mercaptans have been revised. The requirement for thiols has been changed to passing the Drabek test, and the testing method for thiol sulfur content has been removed. It has been changed from \"Passing the Drab test or a thiol sulfur content (by mass) of not more than 0.001%; compliance with either of these two criteria is sufficient to deem it qualified\" to \"Passing the Drab test\". I would like to ask all the teachers: what is the reason for abolishing the experimental method for determining mercaptan sulfur content? Personal opinion: The Drabek test is not suitable for detecting gasoline containing amounts of phenols above trace levels. What should be done in such cases? Previously, the sulfur mercaptan content could be used as a method for detection; but now, if phenols are still present and prevent the use of the Drabek test, the sample should be deemed Unqualified outright. Or perhaps the addition of phenols to gasoline is no longer allowed. Have you all encountered the same problem? At the same time, the Doctor test is a qualitative analysis, while the determination of thiol sulfur content is a quantitative analysis. Personally, I think qualitative analysis should be more accurate. PS: Since I only work with oil additives, my knowledge of oils themselves is limited; please feel free to provide more explanations! Thank you!
Personal understanding: 1. Given that the total sulfur content is currently controlled to be no more than 10, the thiolic sulfur content cannot exceed 10 either; therefore, quantitative analysis is no longer necessary； 2. The sensitivity of Dr. is related to the type of oil as well as to different thiol compounds; relevant studies have shown that Dr. is more sensitive to large molecular thiols, and a concentration of 1 ppm may already be sufficient to cause failure in testing ； Olefins affect the sensitivity of the Drucker test; when the olefin content is high, the sensitivity decreases, while it increases otherwise. 3. Using the potentiometric method to determine thiolic sulfur is meaningless when it is below 3 ppm; therefore, the Drabek test actually sets higher requirements for gasoline quality. 4. Phenols were detected, rendering the Drabek test invalid; it should be considered unqualified. Increasing the induction period may not be possible by adding phenolic antioxidants. 5. The new standards set stricter requirements for gasoline quality, encouraging a reduction in total sulfur, thiols, and olefins.
Thank you very much. As you mentioned, there are large-molecule thiols; even 1 ppm of them can cause the test to fail. In the past, it was possible to measure the sulfur content of thiols in order to determine whether they met the requirements. Previously, the sulfur content in National V gasoline was also required to be below 10 ppm; therefore, as long as the sulfur content meets the specified standard, the mercaptan sulfur content should also be within acceptable limits. Therefore, the indicators for thiol should also be satisfactory. So, in your view, the requirements for thiols in previous National V gasoline were relatively lenient; now, after the method adjustments, it’s possible for the sulfur content to be very low yet still fail the Drabek test, resulting in non-compliance with the thiol standards. Indeed, the quality requirements for oil products have been raised, imposing greater demands on refineries as well.
It is not clear whether, prior to the introduction of the new standards in 2016, refining companies or oil depots measured both the mercaptan index using the Drabek test and the mercaptan sulfur content, or chose one of these methods, or used only the Drabek test for testing； Now that the new standard has been introduced, only the doctoral testing method can be used; has this led to instability in quality? Welcome everyone to discuss :)