Page 149 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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3. CHARACTERIZATION OF PETROLEUM FRACTIONS 129
Section 2.8. The correlation is specifically developed for jet
fuels with aniline points in the range of 56–77 C. 14:23 10 Venezuelan (5%)
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There are a number of other methods reported in the liter- 8 Middle East (5%)
ature. The Winn nomograph may be used to estimate the CH West African (5%)
ratio and then %H can be estimated from Eq. (3.90). Fein– World Average (5%)
Wilson–Sherman also related %H to aniline point through 6 World Average (2%)
API gravity [60]. The oldest and simplest method was pro- Wt% Sulfur
posed by Bureau of Standards in terms of specific gravity as 4
given in reference [61]:
(3.95) %H = 26 − 15SG 2
The other simple correlation is derived from data on jet fuels
and is in terms of aromatic content (x A ) in the following form 0
[57]: 0 100 200 300 400 500 600
(3.96) %H = 14.9 − 6.38x A Mid Boiling Point, °C
Finally Fig. 3.25 is based on data from Ref. [57]. Analytical FIG. 3.26—Distribution of sulfur in straight-run prod-
correlation is also presented in Fig. 3.25(a), which represents ucts for several crude oils. Numbers in the parentheses
data with an average deviation of 0.5%. Equation (3.96) is pre- indicate sulfur content of crudes.
sented in Fig. 3.25(b). When CH ratio is available, %H can be
determined from Fig. 3.25(a) and then %A can be determined
from Fig. 3.25(b). As boiling point, specific gravity, or aromatic content of
a fraction increases the sulfur content also increases [7].
3.5.2.2 Prediction of Sulfur and Nitrogen Contents Parameters R i , m, and SG have been successfully used to
Sulfur is the most important heteroatom that may be present predict the PNA composition especially aromatic content of
in a crude oil or petroleum products as dissolved free sulfur petroleum fractions as shown in Section 3.5.2.1. On this ba-
and hydrogen sulfide (H 2 S). It may also be present as organic sis the same parameters have been used for the estimation of
compounds such as thiophenes, mercaptanes, alkyl sulfates, sulfur content of petroleum fractions in the following form
sulfides (R S R ), disulfides (R S S R ), or sulfoxides for two ranges of molecular weight.

(R SO R ), where R and R refer to any aliphatic or aromatic

group. Its presence is undesirable for the reasons of corrosion, For fractions with M < 200
catalysts poisoning, bad odor, poor burning, and air pollu-
tion. In addition presence of sulfur in lubricating oils lowers (3.97) %S = 177.448 − 170.946R i + 0.2258m+ 4.054SG
resistance to oxidation and increases solid deposition on en- and for fractions with M ≥ 200
gine parts [62]. New standards and specifications imposed
by governments and environmental authorities in industrial (3.98) %S =−58.02 + 38.463R i − 0.023m+ 22.4SG
countries require very low sulfur content in all petroleum
products. For example, reformulated gasolines (RFG) require For light fractions in which Eq. (3.96) may give very small
sulfur content of less than 300 ppm (<0.03 wt%) [63]. Re- negative values, %S would be considered as zero. Squared cor-
2
cently a federal court has upheld an Environmental Protec- relation coefficients (R ) for these equations are above 0.99.
tion Agency (EPA) rule to cut pollution from tractor-trailers A summary of evaluation of these equations is presented in
and other large trucks and buses. The rule is expected to re- Table 3.25 as given in Ref. [62].
duce tailpipe emissions from tractors, buses, and other trucks In using these equations parameters n 20 , d 20 , M, and SG
up to 90%. The EPA also calls on refineries to reduce the sul- are required. For samples in which any of these parameters --`,```,`,``````,`,````,```,,-`-`,,`,,`,`,,`---
fur content in diesel oils to 15 ppm by 2007 from the current are not known they can be estimated from the methods dis-
level of 500 ppm. The American Lung Association claims that cussed earlier in this chapter. In Chapter 4, it is shown how
low-sulfur fuel will reduce the amount of soot from larger this method can be used to estimate sulfur content of whole
trucks by 90%. This is expected to prevent 8300 premature crudes. The author is not familiar with any other analytical
deaths, 5500 cases of chronic bronchitis, and another 17600 method for estimation of sulfur content of petroleum frac-
cases of acute bronchitis in children as provided by the EPA tions reported in the literature so a comparison with other
[64]. Products with high-sulfur contents have low quality and methods is not presented. Generally amount of sulfur in var-
heating values. Generally, sulfur is associated with heavy and ious products is tabulated for various crudes based on the
aromatic compounds [7]. Therefore, high aromatic content sulfur content of each crude [61].
or high boiling point fractions (i.e., residues and coal liquids) Another heteroatom whose presence has adverse effect on
have naturally higher sulfur contents. Distribution of sulfur in the stability of the finished product and processing catalysts
straight-run products of several crude oils and the world aver- is nitrogen. High nitrogen content fractions require high hy-
age crude with 2 and 5% sulfur contents is shown in Fig. 3.26. drogen consumption in hydro processes. Nitrogen content of
Data used to generate this figure are taken from Ref. [61]. As crudes varies from 0.01 to 0.9 wt%. Most of the compounds
the boiling point of products increases the sulfur content in having nitrogen have boiling points above 400 C(∼750 F)
◦
◦
the products also increases. However, the distribution of sul- and are generally within the aromatic group. Crudes with
fur in products may vary from one crude source to another. higher asphaltene contents have higher nitrogen content as

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