Page 151 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

T1: IML
QC: IML/FFX
P2: IML/FFX
P1: IML/FFX
AT029-Manual-v7.cls
June 22, 2007
14:23
AT029-Manual
AT029-03
3. CHARACTERIZATION OF PETROLEUM FRACTIONS 131
consideration or storage and transportation of products. One
of the most important properties of petroleum products re- part, methods of prediction of vapor pressure, fuel vapor liq-
uid (V/L) ratio, fuel volatility index, and flash points are pre-
lated to volatility after the boiling point is vapor pressure. sented.
For petroleum fractions, vapor pressure is measured by the
method of Reid. Methods of prediction of true vapor pressure 3.6.1.1 Reid Vapor Pressure
of petroleum fractions are discussed in Chapter 7. However, Reid vapor pressure is the absolute pressure exerted by a mix-
Reid vapor pressure and other properties related to volatility ture at 37.8 C (311 K or 100 F) at a vapor-to-liquid volume
◦
◦
are discussed in this section. The specific characteristics of ratio of 4 [4]. The RVP is one of the important properties of
petroleum products that are considered in this part are flash, gasolines and jet fuels and it is used as a criterion for blend-
pour, cloud, freezing, aniline, and smoke points as well as car- ing of products. RVP is also a useful parameter for estimation
bon residue and octane number. Not all these properties apply of losses from storage tanks during filling or draining. For
to every petroleum fraction or product. For example, octane example, according to Nelson method losses can be approxi-
number applies to gasoline and engine type fuels, while car- mately calculated as follows: losses in vol% = (14.5 RVP −1)/6,
bon residue is a characteristic of heavy fractions, residues, where RVP is in bar [24, 66]. The apparatus and procedures
and crude oils. Freezing, cloud, and pour points are related for standard measurement of RVP are specified in ASTM
to the presence of heavy hydrocarbons and are characteristics D 323 or IP 402 test methods (see Fig. 3.27). In general, true
of heavy products. They are also important properties under vapor pressure is higher than RVP because of light gases dis-
very cold conditions. Predictive methods for some of these solved in liquid fuel. Prediction of true vapor pressure of pure
properties are rare and scatter. Some of these methods are hydrocarbons and mixtures is discussed in detail in Chapter 7
developed based on a limited data and should be used with (Section 7.3). The RVP and boiling range of gasoline governs
care and caution. ease of starting, engine warm-up, mileage economy, and ten-
dency toward vapor lock [63]. Vapor lock tendency is directly
3.6.1 Properties Related to Volatility related to RVP and at ambient temperature of 21 C (70 F)
◦
◦
the maximum allowable RVP is 75.8 kPa (11 psia), while this
Properties that are related to volatility of petroleum fraction limit at 32 C (90 F) reduces to 55.2 kPa (8 psia) [63]. RVP
◦
◦
are boiling point range, density, Reid vapor pressure, and flash can also be used to estimate true vapor pressure of petroleum
--`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
point. Prediction of boiling point and density of petroleum fractions at various temperatures as shown in Section 7.3.
fractions have been discussed earlier in this chapter. In this True vapor pressure is important in the calculations related
to losses and rate of evaporation of liquid petroleum prod-
ucts. Because RVP does not represent true vapor pressure,
the current tendency is to substitute RVP with more modern
and meaningful techniques [24]. The more sophisticated in-
struments for measurement of TVP at various temperatures
are discussed in ASTM D 4953 test method. This method
can be used to measure RVP of gasolines with oxygenates
and measured values are closer to actual vapor pressures
[4, 24].
As will be discussed in Chapters 6 and 7, accurate calcu-
lation of true vapor pressure requires rigorous vapor liquid
equilibrium (VLE) calculations through equations of state.
The API-TDB [2] method for calculation of RVP requires a
tedious procedure with a series of flash calculations through
Soave cubic equation of state. Simple relations for estima-
tion of RVP have been proposed by Jenkins and White and
are given in Ref. [61]. These relations are in terms of tem-
peratures along ASTM D 86 distillation curve. An example of
these relations in terms of temperatures at 5, 10, 30, and 50
vol% distilled is given below:
RVP = 3.3922 − 0.02537(T 5 ) − 0.070739(T 10 ) + 0.00917(T 30 )
−4
− 0.0393(T 50 ) + 6.8257 × 10 (T 10 ) 2
(3.100)
where all temperatures are in C and RVP is in bar. The diffi-
◦
culty with this equation is that it requires distillation data up
to 50% point and frequently large errors with negative RVP
values for heavier fuels have been observed. Another method
FIG. 3.27—Apparatus to measure RVP of for prediction of RVP was proposed by Bird and Kimball [61].
petroleum products by ASTM D 323 test method In this method the gasoline is divided into a number (i.e.,
(courtesy of KISR). 28) of cuts characterized by their average boiling points. A

Copyright ASTM International
Provided by IHS Markit under license with ASTM Licensee=International Dealers Demo/2222333001, User=Anggiansah, Erick
No reproduction or networking permitted without license from IHS Not for Resale, 08/26/2021 21:56:35 MDT