ASTM: Gasoline Today and Tomorrow – An Executive Report

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Octane Week | ASTM: Gasoline Today and Tomorrow - An Executive Report (from p5) of the cold finger is a glass hook from which is suspended a glass cradle that holds the silver strip. The silver coupon is 0.50 in. by 0.10 in. by 0.71 in. Samples are tested at 50°C for four hours. ʻWhen trying to address a real-world issue by developing a new scientific method, we try to replicate as many of the issues as possible,” Fenwick explained. “The method IP227 seems to control more similar variables than some of the other proposed methods. We are concerned that the ratio of gasoline to silver might have an impact upon the results. “As with a carʼs fuel tank, at any given time there are usually several gallons of gasoline to react with the small amount of silver within the fuel sensor unit. IP227 has this greater ratio than do the other proposed methods. “Our other concern stems from the use of open containers within some of the other proposed methods. A carʼs fuel tank is a closed system. The apparatus used in IP227 is also a closed system that contains any volatile vapors that may contribute to increased corrosion.” While it is still unclear what levels and types of sulfur produce the greatest effects, Fenwick said that there are some synergistic effects at relatively low levels. “We are looking forward to increased studies to help determine what might be the best predictor to help prevent future situations,” he said. Petro-Canadaʼs Method to be Included The Silver Corrosion Task Force has also agreed to include Petro-Canadaʼs silver wool method fin the round-robin. The Canadian oil company has generated a lot of interest in its rapid ultrasonic silver wool method, PCM 1005-03, and now that issues pertaining to its deployment have been resolved, the method will go forward for testing. “Petro-Canada agreed to make the method public, but we will retain the copyright on our original method,” explained David Surette, Petro-Canadaʼs manager-Quality Strategies and Systems. “The method is available for the ILS, and if it is chosen as a method to develop, it will be available at no cost.” Petro-Canada has had more than two years experience with the method and data on thousands of actual gasoline samples. It is a step out from the IP227, Surette told us. The modified test exposes a small amount of fresh silver wool to 180 mL of fuel sample in a pre-cleaned disposable glass test cell for one hour at 50°C in an ultrasonic bath. After the test, the silver wool is removed from the sample, rinsed with wash solvent and dried. The wool is then pressed into a disk slightly smaller than a dime and rated according to a color scale. The rating scale is expanded beyond the five classifications in the IP227 test method. The silver wool disk produces so many color variations that it is possible to distinguish 16 distinct classifications. The elimination of cleaning glassware or preparing the silver strip inherently produced a superior, more robust test method with no sample-to-sample contamination to worry about, Surette explained. “The use of the ultrasonic bath reduces the analysis time considerably while ensuring a high degree of agitation, such that the reaction is not diffusion-limited and the corrosion is uniform.” Petro-Canadaʼs PCM 1005-03 method offers many advantages over the use of silver strips, Surette continued. “Firstly, the silver wool has an extremely uniform surface as compared with the cleaned silver strip and that leads to uniform corrosion and the resolution of the individual colors, the expanded rating scale. Secondly the wool is only used once, reducing any chance of sample to sample contamination. Thirdly the small amount of wool used makes the test economically attractive.” PCM 1005-03 gains additional robustness and precision from the use of inexpensive pre-cleaned test cells that are used only once. This eliminates all contamination from cleaning agents or residual solvents or the cross contamination from sample to sample if the cleaning is not well done. ”This is important if some samples contain silver corrosion inhibitors since these additives have been found difficult to remove completely from glass surfaces,” he advised. The ultrasonic bath reduces the test time from four hours to one hour. “In addition, it provides a high degree of agitation such that the reaction is not diffusionlimited,” he emphasized. It also eliminates completely the “streaking” effect found in the IP227 method and leads to uniform corrosion rates at the silver surface which yield the resolution of the various “corrosion colors.” – Carol Cole 6 February 2007
Octane Week | ASTM: Gasoline Today and Tomorrow - An Executive Report ASTM Task Force Wrestles with Hydrogen Sulfide in Sample Quality Control Issue This story appeared on July 31, 2006. Because of sample stability concerns, the ASTMʼs Silver Corrosion Task Force will delay a round robin of silver corrosion test methods and instead conduct a ruggedness study to see if a small sample set can be blended, shipped and tested. That decision, announced at the July 2006 D02.05.C Subcommittee meeting in Toronto, Ontario, Canada, might answer some critical questions but it sets back the timetable for finalizing a test method and adding it to D4814, a process subcommittee D02.A members had hoped to complete by the upcoming ASTM meeting in December. The decision to conduct a small ruggedness study stemmed from growing evidence that sample stability could not be controlled during the course of the round robin. That suspicion first emerged at the D02.05.C Subcommittee meeting last December, when round robin designers noted that some of the gasoline samples would contain hydrogen sulfide, which would oxidize over time, making it difficult, if not impossible to ensure that participating labs were sampling and testing the “same” material. Since then, Silver Corrosion Task Force Chairman Kevin Bly has probed the issue of hydrogen sulfide oxidation. “The problem is keeping the sample stable long enough to ensure all labs receive the same material in the Inter Laboratory Study,” Bly told the recent meeting. “How long can samples containing hydrogen sulfide be expected to be stable after preparation?” Knowing that, ILS designers could determine whether it would be possible to blend, package and ship samples, as well as have labs perform tests, within that timeframe. Blyʼs group considered an alternative strategy – excluding hydrogen sulfide as a blending component and replacing it with other active components that yield corrosion – but that was discounted. “We decided to keep hydrogen sulfide because thatʼs representative of whatʼs out there in the real world,” said Bly. Hydrogen sulfide is critical to the round robin, a task force member told Octane Week. “The species of interest is elemental sulfur, and hydrogen sulfide is the catalyst. Elemental sulfur on its own is not corrosive. There have been samples with very high levels of elemental sulfur, 20-30 ppm, and they still pass the test. Elemental sulfur needs to be activated.” Another alternative would be to prepare samples with varying levels of elemental sulfur and ship them to labs, where operators would add a fixed amount of hydrogen sulfide just prior to testing. This suggestion was appealing to the members at the meeting as a means to address the hydrogen sulfide stability issue, provided the appropriate guidance and procedure could be given to the labs to safely dose each sample with a fixed quantity of hydrogen sulfide. David Surette, Bob Falkiner and Weldon Cappel agreed to work as a separate Action Team to develop such a procedure that could subsequently be tested by several labs to determine suitability and address potential safety concerns involving the proper handling of hydrogen sulfide. To assess the stability of hydrogen sulfide in gasoline, the laboratory at Lyondell-Citgo prepared a blend of light cat cracked gasoline mixed with an untreated naphtha stream containing 30.8 ppm of hydrogen sulfide in liquid to yield a sample containing 5.9 ppm of hydrogen sulfide. The material was split and stored in three separate quart bottles for analysis over a three week period. Samples were tightly closed and stored in a cold room. Each week for three weeks, a sample was tested along with the previous weekʼs sample to determine the corresponding hydrogen sulfide concentration. During that time, hydrogen sulfide levels dropped to 0. 8 ppm relative to the 5.9 ppm concentration in the original blend. In short, the conclusion was that maintaining a stable solution of hydrogen sulfide in a gasoline matrix would be difficult for more than a short period of time, less than one week. The decline in hydrogen sulfide was believed to be due to two main reasons. First, hydrogen sulfide might simply have escaped when the sample bottle was opened. Second, hydrogen sulfide can change chemically over time through polymerization to polysulfides, which tends to be more corrosive than hydrogen sulfide. Unfortunately, the hydrogen sulfide study did not include a sulfur (continued on p8) February 2007 7
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