Kigadal The test method can also be applied in online applications which can not perfom air saturation procedures prior to the measurement. The marking live crude oil is used for crude oils in pressurized systems that will result in actual boiling of the sample when brought to normal atmospheric pressure at room temperature. This expansion method is used for automated vapor pressure instruments to determine the vapor pressure exerted in vacuum of crude oils. Crude Ast Vapor Pressure: Testing Evaluating how your products and services meet and exceed quality, safety, sustainability and performance standards.
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Christoph Wagner on behalf of Eralytics Free to read Download Regulatory changes and increasing safety concerns in recent years led to extensive adjustments in process and laboratory vapour pressure testing.
However, due to the sample preparation required by this standard, process analysers were never able to comply with it, but can only offer correlating measuring methods. Additionally, with ASTM D it is not possible to address the actual situation during transport of live crude oils. Developments for crude oil measurements according to the advanced standard ASTM D as well as recent Tier 3 regulatory changes for vapour pressure testing of gasoline lead to changes that for the first time allow using the same measurement principle for process as well as laboratory measurements.
Introduction Vapour pressure is one of the key parameters measured in the gasoline blending process. While most process vapour pressure testers, which use their own methods, can be correlated to RVP ASTM D , it is nearly impossible to perform process measurements exactly to this standard. With the piston based ASTM D it is possible to perform high quality measurements according to the standard, but again the sample preparation as described in the standard cannot be done correctly.
In between the multiple saturation steps it is required to let the sample cool again for approximately 2 minutes. These steps are necessary for reproducible measurements. During the measurement a single expansion is performed, thus just the total vapour pressure a combination of the partial pressure of the dissolved air and the vapour pressure of the liquid is accessible. This can lead to uncontrollable deviations caused by the user when the sample preparation is not performed as requested by the standard.
However, this standard is based on a triple expansion step, which allows calculating the absolute vapor pressure of the liquid, as well as the partial pressure of the dissolved air. Cooling or air saturation is not necessary, thus making it the ideal solution for process measurements. For the reproducibility this value even increases to 92 kPa. This covers a large area of gasolines which have a common vapour pressure range of 48 kPa to kPa .
When dealing with the vapour pressure of crude oils recent incidents showed that the currently used measurement methods are not sufficiently reflecting the conditions that occur during transportation or storage. The temperature will be kept at The piston is used to introduce the sample into the measurement cell. It incorporates a pressure sensor and is used to create the vacuum above the sample to determine the vapour pressure. This eliminates the need of a vacuum pump before or during the measurement.
This allows to measure at realistic conditions e. The spectrum is shown in figure 2 and some properties and parameters based on this spectrum are listed in table 1. For comparison a sample was taken every hour during daytime and measured with eralytics laboratory vapour pressure tester ERAVAP figure 4. The online and laboratory vapour pressure measurements of gasoline were performed at A triple expansion was used as mentioned in ASTM D to measure the vapour pressure of the sample, the partial pressure caused by dissolved air and the total pressure.
The crude oil measurements were performed with a Zarzaitine crude oil density: 0. Typical compositions for crude oils of this region can be found in the literature  .
Due to transport and storage some of the light ends possibly were lost before the measurement, thus lowering the resulting vapour pressure, compared to literature values. When measuring the vapour pressure, the measurement cell was moved by a shaker as required by ASTM D Vapour Pressure Testing of Gasoline During the measurement campaign with the process analyser the recorded vapour pressure remained in a stable region around When comparing these results with the laboratory measurements an offset of 0.
When performing reference measurements using pentane, this effect was not visible. This shows that a small loss of volatile content happened during sampling.
However, this offset was significantly lower than the reproducibility or even repeatability of ASTM D and D, as indicated in figure 4. This proofs an easy and direct comparison between the process and laboratory vapour pressure tester. The process monitoring of the vapour pressure during blending is capable of performing trustfully measurements without the need of ongoing sampling for laboratory measurement.
Additionally the triple expansion of ASTM D eliminates the influence caused by different air saturation levels of gasoline during the process measurements. For simplicity, just 2 states are indicated in the line plots showing the correlation between vapour pressure and. When blending crudes of high viscosity with e. Dealing with light crude oil containing high amounts of dissolved volatile hydrocarbons will increase the vapour pressure even further.
For the first time the methods required by authorities, as well as the methods available for process and laboratory instruments are the same, allowing an easy comparison between laboratory and online measurements. This reduces the need for manual control measurements and allows higher automation for processes where vapour pressure is a key parameter.
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ASTM D6377 (R)
US EPA Confirms ASTM D6377 as an Alternative Test Method For Measuring Vapor Pressure of Crude Oils