|Abstract Title:||Vapor Pressure Measurement: Recent Advances and an In Depth Study of the Science that Supports It|
|Session Choice:||Alternative approaches to conventional techniques|
|Presenter Name:||Dr Raj Shah|
|Co-authors:||Mr Philip Iaccarino|
Ms Cindy Klager
|Company/Organisation:||Koehler Instrument Company, Inc.|
Abstract Information :
The vapor pressure of a liquid is the pressure exerted by the liquid’s vapor when the vapor and liquid are in equilibrium, and is an indicator of a substance’s volatility. Vapor pressure is important when discussing petroleum products, since a failure to account for vapor pressure can lead to accidents that impact the environment or human health.
Vapor pressure is especially important for automotive and aviation gasolines, since it can affect start-up and warm-up processes, as well as the tendency to vapor lock. Vapor lock occurs when a liquid fuel vaporizes while in the fuel delivery system, and can disrupt the system. Gasoline is more likely to vapor lock with higher temperatures and altitudes. For gasoline, vapor pressure limits are legally regulated in some areas, due to air pollution standards. Gasolines with higher vapor pressures will release larger amounts of volatile vapor into the atmosphere, and can contribute to ground-level ozone, which is associated with numerous health problems.
There are various ASTM methods to test vapor pressure. The Reid method for determining vapor pressure of petroleum products, described in ASTM D323, is the referee method. The result of ASTM D323 is the reid vapor pressure, or RVP. While this method is proven to be reliable, there are some downsides, such as manual test procedures, larger instrumentation, larger sample sizes, and longer test times.
New ASTM methods have been developed that appeal to some of the negative aspects of ASTM D323, and include automated test procedures, small sample sizes, short test times, and improved repeatability and reliability. Instrumentation for the new ASTM methods is smaller and lighter, making it easier to transport and use in the field or at a job site. ASTM D5191 is the mini method for vapor pressure determination. ASTM D5191 measures total pressure, and the results can be converted to the dry vapor pressure equivalent, or DVPE. ASTM D6378 is the triple expansion method for vapor pressure determination. ASTM D6378 determines the true vapor pressure, and results can correlate to the RVPE and DVPE.
This paper will dwell into the theoretical bases for the “mini methods” and will use mathematical models to show their efficacy. It will also discuss experimental results with newly developed instrumentation, as well as statistical variation and equivalence of results of various laboratory vapor pressure techniques.