Gasoline true vapor pressure

Vapor Pressure—Equilibrium pressure exerted by vapors over a liquid at a given temperature [2.1, 2.3]. The Reid vapor pressure (RVP) is typically used to describe the vapor pressure of petroleum fuels without oxygenates at 100°F (ASTM Test Method D 323, Test Method for Vapor Pressure of Petroleum Products) [2.5]. The term true vapor pressure is often used to distinguish between vapor pressure and Reid vapor pressure. The Reid vapor pressure test involves saturating the fuel with water before testing and cannot be used for gasoline-alcohol blends or neat alcohol fuels a new procedure has been developed which does not use water and is called Dry Vapor Pressure Equivalent, or DVPE (see ASTM D 4814-95c under Additional Information section). 

Abstdute Bias—Since there is no accepted reference material suitable for determining the bias for the procedures in this test method for measuring vapor pressure of gasoline or gasoline-oxygenate blends, bias cannot be determined. The amount of bias between this test vapor pressure and true vapor pressure is unknown. 

Evaporation losses are a function of so many variables such as. (1) liquid or surface temperature, (2) variation in atmospheric temperature, (3) true vapor pressure of liquid, (4) volume of vapor space (how full), (5) color or reflectiveness of surface, (6) frequency of filling, (7) construction of tank, (8) degree of saturation attained in gas space, etc., that only the gross approximation indicated in Table 8-1 for a 10 R.v.p. gasoline... 

The final gasoline, a debutanized total of 41.7 -1- 7.33 or 49.0 per cent, will have a vapor pressure of only about 5 psia. Butane will be added to produce a total gasoline of 10 R.v.p. Most approximately the amount of mixed butanes required will be a little more than the difference in vapor pressures, namely, 5 to 6 per cent, but more specifically, using the true vapor pressures of Table 4-12, and a mole basis ... 

Experimental Vaporization Curves. When such complex materials as gasoline and petroleum fractions are dealt with, the application of the aforementioned equilibrium laws is cumbersome. Furthermore, the component analyses of these heavy oils cannot be easily obtained and even if such analyses are-availalUe, accurate vapor-pressure or equilibrium data for the compounds or fractions contained in them are not always available. At present most equilibrium relations are obtained by determining experimental flash-vaporization curves or by computing such curves from the empirical relationships discussed in Chap. 4. Empirical flash curves can be estimated from true-boiling-point or ASTM curves, and with less accuracy from Hempel or Saybolt distillation curves. 

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