Page 163 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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3. CHARACTERIZATION OF PETROLEUM FRACTIONS 143
3.7 QUALITY OF PETROLEUM PRODUCTS
Methods presented in this chapter can be used to evaluate % Reduction
the quality of petroleum products from available parameters.
The quality of a petroleum product depends on certain -5
specifications or properties of the fuel to satisfy required
criteria set by the market demand. These characteristics are
specified for best use of a fuel (i.e., highest engine perfor-
mance) or for cleaner environment while the fuel is in use.
These specifications vary from one product to another and -10
from one country to another. For example, for gasoline the
quality is determined by a series of properties such as sulfur
and aromatic contents, octane number, vapor pressure,
hydrogen content, and boiling range. Engine warm-up time
is affected by the percent distilled at 70 C and the ASTM 90% -15
◦
temperature. For the ambient temperature of 26.7 C (80 F)
◦
◦
a gasoline must have ASTM 90% temperature of 188 C and
◦
3% distilled at 70 C to give acceptable warm-up time [63].
◦
Standard organizations such as ASTM give such specifica-
tions for various products. For reformulated gasoline sulfur -20
content of less than 300 ppm (0.03 wt%) is required [63]. HC CO NOx
Amount of particulate emissions is directly related to the FIG. 3.35—Influence of sulfur content in gasoline (from
aromatic and sulfur content of a fuel. Figure 3.35 shows the 500 to 50 ppm) in reduction of pollutant gases. Taken with
influence of sulfur reduction in gasoline from 500 to 50 ppm permission from Ref. [24].
in the reduction of pollutant emissions [24].
Vapor pressure of gasoline of jet fuel determines their ig- produce the required final product. In Example 3.20, it was
nition characteristics. While freezing point is important for shown that to have a product with certain flash point, one can
jet fuels it is not a major characteristic for gas oils. For lubri- determine the volume of various components in the blend.
cating oil properties such as viscosity and viscosity index are The same approach can be extended to any other property. For
important in addition to sulfur and PNA composition. Aniline example, to increase vapor pressure of gasoline n-butane may
point is a useful characteristic to indicate power of solubil- be added during winter season to improve engine starting
ity of solvents as well as aromatic contents of certain fuels. characteristics of the fuel [63]. The amount of required butane
For heavy petroleum products knowledge of properties such to reach a certain vapor pressure value can be determined
as carbon residue, pour point, and cloud point are of inter- through calculation of vapor pressure blending index for the
est. Some important specifications of jet fuels are given in components and the product as discussed in Section 3.6.1.1.
Table 3.30.
One of the techniques used in refining technology to pro-
duce a petroleum product with a certain characteristic is the 3.8 MINIMUM LABORATORY DATA
blending method. Once a certain value for a property (i.e.,
viscosity, octane number, pour point, etc.) of a petroleum As discussed earlier measurement of all properties of various
product is required, the mixture may be blended with a cer- petroleum fractions and products in the laboratory is an
tain component, additive or another petroleum fraction to impossible task due to the required cost and time. However,

TABLE 3.30—Some general characteristics of three fuels [24].
Specifications a
Characteristics Gasoline b Jet fuel Diesel fuel
Max. total sulfur, wt% 0.05 0.2 0.05
Max aromatics content, vol% 20
Max olefins content, vol% 5
Distillation at 10 vol%, C 204
◦
Max final boiling point, C 215 300 370 c
◦
Range of % evaporation at 70 C (E70) 15–47
◦
Min research octane number (RON) 95
Min flash point, C 38 55
◦
Specific gravity range 0.725–0.78 0.775–0.84 0.82–0.86
Min smoke point, C 25
◦
Max freezing point, C −47
◦
Range of Reid vapor pressure, bar 0.35–0.90 d
Min cetane number 49
Taken with permission from Ref. [24].
a European standards in the mid 1990s.
b European unleaded Super 98 premium gasoline.
c At this temperature minimum of 95 vol% should be evaporated.
d Varies with season according to the class of gasoline.

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