Page 159 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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3. CHARACTERIZATION OF PETROLEUM FRACTIONS 139
by ASTM D 908 and MON is measured by ASTM D 357 test
ethers (oxygenates).
methods. Generally there are three kinds of gasolines: regu- TABLE 3.28—Octane numbers of some alcohols and
lar, intermediate, and premium with PON of 87, 90, and 93, Compound RON MON
respectively. In France the minimum required RON for su- Methanol 125–135 100–105
95–101
113–117
MTBE
perplus gasoline is 98 [24]. Required RON of gasolines vary Ethanol 120–130 98–103
with parameters such as air temperature, altitude, humidity, ETBE 118–122 100–102
engine speed, and coolant temperature. Generally for every TBA 105–110 95–100
300 m altitude RON required decreases by 3 points and for TAME 110–114 96–100
every 11 C rise in temperature RON required increases by 1.5 MTBE: methyl-tertiary-butyl ether; ETBE: ethyl-tertiary-butyl ether;
◦
TBA: tertiary-butyl alcohol; TAME: tertiary-amyl-methyl ether.
points [63]. Improving the octane number of fuel would result Source: Ref. [24].
in reducing power loss of the engine, improving fuel economy,
and a reduction in environmental pollutants and engine dam-
age. For these reasons, octane number is one of the important after addition of an additive. ON ox is the corresponding octane
properties related to the quality of gasolines. There are a num- number of oxygenate, which can be taken as the average val-
ber of additives that can improve octane number of gasoline ues for the ranges of RON and MON as given in Table 3.28. For
or jet fuels. These additives are tetra-ethyl lead (TEL), alco- example for MTBE, the range of RON ox is 113–117; therefore,
hols, and ethers such as ethanol, methyl-tertiary-butyl ether for this oxygenate the value of RON ox for use in Eq. (3.136)
(MTBE), ethyl-tertiary-butyl ether (ETBE), or tertiary-amyl is 115. Similarly the value MON ox for this oxygenate is are
methyl ether (TAME). Use of lead in fuels is prohibited in 98. Equation (3.136) represents a simple linear relation for
nearly all industrialized countries due to its hazardous nature octane number blending without considering the interaction
in the environment, but is still being used in many third world between the components. This relation is valid for addition
and underdeveloped countries. For a fuel with octane number of additives in small quantities (low values of x ox , i.e., < 0.15).
(ON) of 100, increase in the ON depends on the concentra- However, when large quantities of two components are added
tion of TEL added. The following correlations are developed (i.e., two types of gasolines on 25:75 volume basis), linear mix-
based on the data provided by Speight [7]: ing rule as given by Eq. (3.136) is not valid and the interac-
tion between components should be taken into account [61].
2
ON ON Du Pont has introduced interaction parameters between two

TEL =−871.05 + 2507.81 − 2415.94
100 100 or three components for blending indexes of octane number
3 which are presented in graphical forms [89]. Several other
ON

(3.134) + 779.12 blending approaches are provided in the literature [61]. The
100 simplest form of their tabulated blending indexes have been
ON = 100.35 + 11.06(TEL) − 3.406(TEL) 2 converted into the following analytical relations: --`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
3
(3.135) + 0.577(TEL) − 0.038(TEL) 4 BI RON =
36.01 + 38.33X − 99.8X + 341.3X − 507.2X + 268.64X 11 ≤ RON<76
⎧ 2 3 4 5
where ON is the octane number and TEL is milliliter TEL ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ −299.5 + 1272X − 1552.9X + 651X
2 3 76 ≤ RON ≤ 103
added to one U.S. gallon of fuel. These relations nearly repro- 2206.3 − 4313.64X + 2178.57X 2 103 ≤ RON ≤ 106
duce the exact data given by Speight and valid for ON above ⎪ ⎪ ⎪ ⎪ ⎪ ⎩ X = RON/100
100. In these equations when clear octane number (without
TEL) is 100, TEL concentration is zero. By subtracting the cal- (3.137)
culated ON from 100, the increase in the octane number due
to the addition of TEL can be estimated, which may be used where BI RON is the blending index for RON and should be used
to calculate the increase in ON of fuels with clear ON different together with Eq. (3.117) to calculate RON of a blend. Equa-
from 100. Equation (3.134) is useful to calculate amount of tion (3.137) reproduce the tabulated values of RON blending
TEL required for a certain ON while Eq. (3.135) gives ON of indexes with AAD of 0.06%.
fuel after a certain amount of TEL is added. For example, if Estimation of octane number of a fuel from its bulk proper-
0.3 mL of TEL is added to each U.S. gallon of a gasoline with ties is a challenging task, since ON very much depends on the
RON of 95, Eq. (3.135) gives ON of 104.4, which indicates an chemical structure of components of the mixture. Figure 3.32
increase of 4.4 in the ON. This increase is based on the refer- shows variation of RON with boiling point of pure hydrocar-
ence ON of 100 which can be used for ON different from 100. bons from different families as produced from data given in
Therefore, the ON of gasoline in this example will be 95 + 4.4 Table 2.2. If PIONA composition of a fuel is known, RON of a
or 99.4. Different relations for octane number of various fuels fuel may be estimated from the pseudocomponent techniques
(naphthas, gasolines, and reformates) in terms of TEL con- in the following form:
centration are given elsewhere [88].
RON = x NP (RON) NP + x IP (RON) IP + x O (RON) O
Octane numbers of some oxygenates (alcohols and ethers) (3.138)
are given in Table 3.28 [24]. Once these oxygenates are added + x N (RON) N + x A (RON) A
to a fuel with volume fraction of x ox the octane number of where x is the volume fraction of different hydrocarbon
product blend is [24] families i.e., n-paraffins (NP), isoparaffins (IP), olefins (O),
naphthenes (N), and aromatics (A). RON NP , RON IP , RON o ,
(3.136) ON = x ox (ON) ox + (1 − x ox )(ON) clear
RON N , and RON A are the values of RON of pseudocompo-
where ON clear is the clear octane number (RON or MON) of nents from n-paraffin, isoparaffins, olefins, naphthenes, and
a fuel and ON is the corresponding octane number of blend aromatics families whose boiling points are the same as the

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