Ind. Eng. Chem. Res. 1999, 38, 4507-4512
4507
CORRELATIONS Estimation of Sulfur Content of Petroleum Products and Crude Oils Mohammad R. Riazi,* Nasrin Nasimi, and Yousef A. Roomi Chemical Engineering Department, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait
In this paper simple estimation methods are presented to predict sulfur weight percentage in petroleum fractions and crude oils. Input data needed to use this method are molecular weight, refractive index, and specific gravity (SG). In cases in which molecular weight and refractive index are not available they can be estimated from the boiling point and SG of the fraction using appropriate methods. For crude oils, the C7+ part of the crude mixture was split into several pseudocompounds using the two-parameter distribution model proposed by Riazi (Ind. Eng. Chem. Res. 1997, 36, 4299-4307), and then for each fraction sulfur content was determined. The sulfur content of crude was then determined from its carbon number distribution (or boiling point distribution) and the estimated sulfur content of each pseudocompound. For 132 different fuels and petroleum products with molecular weight ranging from 75 to 1500 and sulfur contents up to 6%, an average deviation of about 0.15% was obtained to estimate sulfur weight percentage from the proposed method. For seven crude oils with sulfur contents up to 2.4%, the proposed methods gave an average deviation of 0.31%. Introduction Sulfur in various fuels and petroleum products promote corrosion of engine parts and contribute to the formation of engine deposits. A high content of sulfur compounds in lubricating oil lower resistance to oxidation and increase the deposition of solids. Knowledge of the amount of sulfur present in a fuel is important in appropriate design and operation of burners and related equipment. In refineries, knowledge of sulfur content of crude oil and its products is important in design and operation of various units. As discussed in detail by Speight,2 most sulfur compounds in a petroleum mixture are in asphaltenes and heavy aromatics. Heavy fractions [low API or high specific gravity (SG)] contain more sulfur than light fractions. In addition, fractions that have higher amounts of asphaltene and resin contain more sulfur compounds. Van Nes and van Westen3 have shown that sulfur weight percentage in a petroleum fraction is related to the percentage of carbon in naphthenic compounds of the fraction. Riazi and Daubert4,5 developed methods for prediction of composition and molecular type analysis of petroleum fractions in terms of molecular weight, refractive index, density, and viscosity. These methods were also included in the American Petroleum Institute (API) Technical Data Book.6 One parameter that well characterizes different types of hydrocarbon compounds is the refractivity intercept (RI), defined as:4
RI ) n - d/2
(1)
where n is the refractive index at 20 °C and d is the liquid density at 20 °C and 1 atm. Highly aromatic * To whom all correspondence should be addressed. Fax: (+965) 4839498; tel: (+965) 4817662; e-mail: riazi@ kuc01.kuniv.edu.kw.
fractions have higher RI values, and those fractions rich in paraffins have lower RI values. For pure hydrocarbons RI varies from 1.03 to 1.07. Another useful characterization parameter is parameter m defined as5
m ) M(n - 1.475)
(2)
where M is the molecular weight. For pure compounds m varies from -10 to 45. Aromatics have positive values of m and paraffins have negative m values. In addition, values of m for benzenes and monoaromatics are much lower than values of m for condensed multicyclic aromatics as shown in Table 1. Other characterization parameters for description of molecular types of petroleum fractions as examined by Riazi and Daubert5 are carbon-to-hydrogen weight ratio (CH), SG, and viscosity gravity constant (VGC). These parameters are the basis for development of a method to estimate sulfur content of a fraction. Characterization techniques for crude oils and reservoir fluids have been discussed in details by Riazi.1,7 In this method a simple distribution model is used to estimate property distributions in crude oils and then the C7+ portion of the crude is split into several (usually three or five) pseudocompounds by using the distribution model and carbon number range chosen for each pseudocompound. The minimum information needed for this technique are molecular weight and SG of the Table 1. Values of Parameter m for Different Types of Hydrocarbons hydrocarbon type
m
paraffins cyclopentanes cyclohexanes benzenes naphthenes condensed tricyclics
-8.79 -5.41 -4.43 2.64 19.5 43.6
10.1021/ie990262d CCC: $18.00 © 1999 American Chemical Society Published on Web 10/08/1999
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Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999
Table 2. Prediction of Sulfur Content of Petroleum Fractions fraction no. of type points light heavy overall
76 56 132
mol. wt. range
sp. gr. range
76-247 0.57-0.86 230-1500 0.80-1.05 76-1500 0.57-1.05
errora sulfur wt % range AAD% MAD% 0.01-1.6 0.07-6.2 0.01-6.2
0.09 0.24 0.15
0.7 1.6 1.6
a AAD% ) abs. average deviation %. MAD% ) max. average deviation %.
heptane-plus fraction of the crude. However, if true boiling point for a crude is known, more accurate pseudocomponents can be obtained from the distribution model. We use this technique in this work for development of a method for estimation of sulfur content of crude oils and reservoir fluids. The main objective of this work is to propose a method for accurate estimation of the amount of sulfur in a crude oil or various petroleum products and fuels using easily measurable or readily available properties. To the best of our knowledge such methods do not currently exist in the literature. Technical Development As discussed earlier, parameters RI, m, SG, CH, and VGC have the ability to describe molecular type analysis of petroleum fractions. Overall, 132 petroleum fractions with information on the amount of sulfur as well as some general properties such as SG, viscosity at one or two temperatures, and boiling point have been collected using private and open literature sources. Upon extensive analysis of data we found that parameters RI, m, and SG best describe sulfur composition of petroleum fractions, and the following equations were obtained from the data bank. For fractions with M < 250
S% ) 177.4482 - 170.9463RI + 0.2258m + 4.054SG (3) For fractions with M > 200
In using the proposed method the only input data needed are molecular weight, refractive index at 20 °C, liquid density at 20 °C, and SG at 15.5 °C (or API gravity). In cases in which these data are not available they can be predicted from appropriate correlations. For example, molecular weight of heavy fractions can be estimated from viscosity at two temperatures as proposed by Riazi and Daubert.8 If boiling point and SG are known, then methods given by Riazi Daubert9,10 that are also included in the API Technical Data Book6 can be used to estimate parameters M, n, and d needed to calculate RI and m from eqs 1 and 2. For heavy fractions, usually SG and one viscosity data (either at 100 or at 210 °F) are known. The following equations proposed by Riazi and Daubert8 which are also recommended by the API, were used to estimate viscosity at other temperatures and molecular weights: 0.1157 0.1157 SG ) 0.7717 × [ν100 ][ν100 ]
(5)
M ) 223.56 × (-1.245+1.1228SG) (3.4758-3.038SG) ][ν210 ][SG-0.6665] (6) [ν100 in which ν100 and ν210 are kinematic viscosities at 100 and 210 °F (37.8 and 98.9 °C), respectively. Equation 5 can be used to estimate ν100 if ν210 and SG are known and it has accuracy of 1.5%. Then eq 6 can be used to estimate molecular weight M. Equation 6 can estimate molecular weight of petroleum fractions with an average deviation of 2.7% for 158 fractions. Having M and SG, the following equation given by Riazi and Daubert10 can be used to estimate average boiling point (Tb):
Tb ) 3.76587 exp(3.7741 × 10-4M + 2.98404SG 4.252 × 10-3MSG)M0.40167SG-1.58262 (7) where Tb is in K. Accuracy of eq 7 is 1%. Once Tb and SG are known for any fraction the following equations proposed by Riazi and Daubert9 may be used to estimate density (d) and refractive index (n) at 20 °C.
S% ) -58.02 + 38.4628RI - 0.0229m + 22.4SG (4)
d ) 0.98372Tb0.00202SG1.0055
(8)
where RI and m are defined by eqs 1 and 2. For fractions with molecular weights between 200 and 250 both eqs 3 and 4 may be used. In this range of molecular weight, the difference between accuracies of these two equations is within the accuracy of these equations. For light fractions in which eq 3 may give very small negative values, S% would be considered as zero. General information for the fractions used to develop eqs 3 and 4 are given in Table 2. Sulfur weight percentage in the fractions varies from 0.01 to 6.2%. Equation 3 can estimate S% with an average deviation of 0.09%, whereas eq 4 predicts S% with average deviation of 0.24%. Overall average error for all 132 fractions is 0.15%. Values of R2 for these equations were 0.95. As sulfur generally is present more in heavier fractions, eq 4 is more important than eq 3. For example, for the fractions used in this work, sulfur content of fractions with molecular weight less than 200 was usually less than 1%. A detailed evaluation of eq 4 with complete information on various fractions used to evaluate eq 4 are given in Table 3. Generally for heavy fractions, data on API gravity (or SG), sulfur content, and viscosity were available from the literature. Other properties were estimated through appropriate correlations.
I ) 0.3773Tb-0.02269SG0.9182
(9)
where Tb is in K, d is liquid density at 20 °C in g/cm3, and n can be calculated from the following equation.
n)
(11+-2II )
1/2
(10)
Average errors for eqs 8 and 9 are 0.03% and 0.5%, respectively. For light fractions in which Tb is known from distillation data, M can be estimated from the following equation given by Riazi and Daubert.9
M ) 1.6607 × 10-4Tb2.1962SG-1.0164
(11)
where Tb is in K. Accuracy of this equation is about 2.5%. However, for fractions with molecular weights greater than 300, the following equations may be used to estimate I and M as recommended by Riazi and Daubert.10
I ) 1.8429 × 10-2 exp(1.16352 × 10-3Tb + 5.1445G - 5.9202 × 10-4TbSG)Tb-0.407SG-3.333 (12)
Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999 4509 Table 3. Evaluation of Eq 4 for Estimation of Sulfur Content of Heavy Fractions with Estimated Properties no.
fraction
SGa
T b, K
M
d20
n20
RI
m
1 2 3 4 5 6 7 8 9
Kuwait crude cut # 1 Kuwait crude cut # 2 Kuwait crude cut # 3 Kuwait crude cut # 4 Kuwait crude cut # 5 Kuwait crude cut # 6 Kuwait crude cut # 7 Kuwait crude cut # 8 vacuum gas oil crude assay 94 vacuum gas oil crude assay 91 atmospheric residue crude assay 94 atmospheric residue crude assay 91 atmospheric residue crude assay 84 kerosene 31 API # 1 kerosene 31 API # 2 kerosene 31 API # 3 kerosene 31 API # 4 gasoline 31 API # 1 gasoline 31 API # 2 vacuum gas oil 31 API # 1 vacuum gas oil 31 API # 2 vacuum gas oil 31 API # 3 residue 31 API # 1 residue 31 API # 2 marine diesel oil T-093-96 marine diesel oil T-075-96 diesel oil T-106-96 diesel oil T-097-96 marine diesel oil (avg.) D-1 diesel oil (avg.) petroleum cut # 1 petroleum cut # 2 petroleum cut # 3 petroleum cut # 4 petroleum cut # 5 deasphalting unit feed deasphalting unit DAO C4 deasphalting unit DAO C5 deasphalting unit feed lube oil deasphalting unit DAO (lube oil) F. C. C. heavy gas oil M. C. hydroc. VGO hydroc. Feed VGO FCC H. G.O cut M. C. Deasphalting unit feed DAO C4 DAO C5 D. A. feed lube oil D. A. feed crack stock DAO L.O Kuwait vacuum Buzurgan Cambimas vacuum Arabian light atmosphere Saudi Arabia vacuum Boscan tar sand triangle Athambasaca Cold Lake Jobo TIA Juan vacuum
0.8370 0.8425 0.8477 0.8528 0.8577 0.8624 0.8712 0.8753 0.9189
-
543a 553a 563a 573a 583a 593a 613a 623a 662a
202 209 216 223 230 238 253 261 337
0.8331 0.8386 0.8438 0.8490 0.8539 0.8586 0.8675 0.8716 0.9154
1.4676 1.4707 1.4735 1.4764 1.4791 1.4817 1.4866 1.4888 1.5028
1.0511 1.0514 1.0516 1.0519 1.0522 1.0524 1.0528 1.0530 1.0451
-1.4849 -0.9012 -0.3133 0.3165 0.9479 1.5925 2.930 3.606 9.375
1.03 1.21 1.37 1.50 1.60 1.67 1.86 2.05 2.81
1.19 1.31 1.42 1.54 1.64 1.74 1.92 2.05 2.55
0.16 0.10 0.05 0.04 0.04 0.07 0.06 0.0 0.26
0.9240
-
676a
360 0.9206 1.5068 1.0465
11.4436
2.70
2.67
0.03
0.9710
50.9
748
573 0.9679 1.5516 1.0677
43.8892
4.20
3.79
0.41
0.9800
81.8
752
628 0.9769 1.5629 1.0745
55.2273
4.20
3.99
0.21
0.9760
68.2
752
609 0.9729 1.5580 1.0716
50.5717
4.20
3.90
0.30
1.0459 -10.4499 1.0467 -7.1641 1.0469 -6.3171 1.0471 -5.7596 1.0481 -3.0794 1.0491 -0.0706 1.0432 6.3146 1.0510 18.3263 1.0456 10.1811 1.0973 96.8158 1.1356 174.2679 1.0474 -4.4575 1.0475 -4.2444 1.0470 -5.8533 1.0469 -5.9681 1.0475 -5.9681 1.0470 -4.3821 1.0462 -5.7997 1.0460 -8.8412 1.0494 -1.2398 1.0489 -1.2173 1.0484 -0.9005 1.0983 99.0491 1.0652 44.8482 1.0744 59.7173 1.1289 160.0637
0.07 0.30 0.36 0.41 0.93 1.54 2.56 3.10 2.81 4.80 5.20 0.69 0.75 0.54 0.52 0.73 0.55 0.20 0.41 1.16 1.35 1.50 4.05 3.30 3.65 4.9
0.0 0.33 0.46 0.55 0.99 1.49 2.26 2.97 2.55 4.42 4.70 0.77 0.81 0.56 0.54 0.79 0.57 0.19 0.34 1.28 1.30 1.36 4.42 3.40 3.75 4.68
0.07 0.03 0.10 0.14 0.06 0.05 0.3 0.13 0.26 0.38 0.50 0.09 0.05 0.02 0.02 0.05 0.02 0.01 0.07 0.12 0.05 0.14 0.37 0.10 0.10 0.22
27.3183
2.7
2.76
0.06
20.9175 11.9166 13.0997 20.9175 99.0491 44.8482 59.7173 160.0637 169.3553 27.3183 164.1416 175.1727 282.1741 30.1384 179.7868 87.2318 66.2079 68.0595 57.8722 113.7255 289.2786
3.1 2.5 3 3.1 4.05 3.3 3.65 4.9 3 2.7 5.45 6.2 3.26 3 5.2 5.6 4.38 4.9 4.4 3.9 2.6
3.38 2.67 2.69 3.38 4.42 3.40 3.75 4.68 4.61 2.76 5.00 5.73 3.09 3.38 5.01 4.34 4.32 5.62 4.64 4.55 2.87
0.28 0.17 0.31 0.28 0.37 0.10 0.10 0.22 1.61 0.06 0.45 0.47 0.17 0.38 0.19 1.26 0.06 0.72 0.24 0.65 0.27
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61
0.7772 0.8001 0.8066 0.8110 0.8316 0.8551 0.9065 0.9367 0.9189 1.0025 1.0285 0.8217 0.8232 0.8114 0.8104 0.8222 0.8118 0.7930 0.8010 0.8440 0.8460 0.8500 1.0030 0.9590 0.9740 1.0246
ν210Fa (cst)
0.95 (100) 1.43 (100) 1.63 (100) 1.79 (100) 2.71 (100) 4.79 (100) 25.4 (100) 13.04 49.4 (100) 324 2134 2.306 (100) 2.361 (100) 1.898 (100) 1.849 (100) 2.32 (100) 1.913 (100) 1.49 (100) 2.00 (100) 2.90 (100) 3.70 (100) 4.80 (100) 345 631 105 1565
0.9321
35.4
585 574 573 573 572 583 651 713 677 740 681 576 576 578 578 576 578 576 578 447 475 508 525 548 772 693
246 237 236 237 236 244 321 429 359 793 1006 239 239 241 241 239 241 257 269 221 238 253 804 658 704 972
804
0.9529 12 0.9242 0.9250 9 0.9529 12 1.0030 345 0.9590 63 0.9740 105 1.0246 1565 1.0254 1870 0.9321 35.4 1.0328 1900 1.0513 3355 1.0231 7800 0.9541 27 1.0366 2700 0.9979 20000 (100) 0.9923 7000 (100) 1.0298 110 1.0000 79.0 1.0100 515.4 1.0209 7959
688 683 697 688 739 781 772 693 687 804 682 661 622 740 670 746 743 697 722 728 620
0.7734 0.7962 0.8027 0.8072 0.8278 0.8513 0.9030 0.9334 0.9155 0.9994 1.0253 0.8179 0.8194 0.8076 0.8066 0.8184 0.8080 0.7887 0.7968 0.8400 0.8420 0.8461 0.9999 0.9559 0.9709 1.0214
1.4326 1.4448 1.4483 1.4507 1.4619 1.4747 1.4947 1.5177 1.5034 1.5970 1.6483 1.4564 1.4572 1.4507 1.4502 1.4567 1.4510 1.4406 1.4444 1.4694 1.4699 1.4714 1.5982 1.5431 1.5599 1.6396
633 0.9291 1.5181 1.0536 390 370b 393 390 804 658 704 972 1006 633 939 881 1439 510 977 762 649 509 553 844 1484
0.9495 0.9208 0.9216 0.9495 0.9999 0.9559 0.9709 1.0214 1.0222 0.9291 1.0297 1.0481 1.0198 0.9510 1.0334 0.9948 0.9892 1.0267 0.9969 1.0069 1.0175
1.5286 1.5072 1.5083 1.5286 1.5982 1.5431 1.5599 1.6396 1.6433 1.5181 1.6498 1.6737 1.6711 1.5341 1.6590 1.5895 1.5770 1.6088 1.5796 1.6098 1.6699
1.0539 1.0468 1.0475 1.0539 1.0983 1.0652 1.0744 1.1289 1.1322 1.0536 1.1349 1.1497 1.1613 1.0586 1.1423 1.0921 1.0824 1.0954 1.0812 1.1063 1.1611
S%, exp S%, pred abs. dev. %
a Properties are measured values (such as SG, ν, and some values of T ). Viscosity data (ν b 210) are given at 210 °F (98.9 °C); for kinematic viscosity data at 100 °F (37.8 °C), values of temperature (100 °F) are specified in the parentheses. b For this fraction the aniline point was 180 °F. Using API method,6 M was estimated from aniline point and SG. References: Fractions 1-24, private communication, industrial source, Kuwait;13 fractions 25-30, private communication, industrial source, Saudi Arabia;14 fractions 31-35, Jones;15 fractions 36-43, Refining Handbook;16 fractions 44-50, Refining Processes;17 fractions 51-61, Speight.2
M ) 42.965[exp(2.097 × 10-4Tb - 7.78712SG + -3
2.0848 × 10 TbSG)]Tb
1.26007
SG
4.98308
(13)
where Tb is in K and SG is the specific gravity at 60 °F (15.5 °C). Equations 12 and 13 give average errors of about 0.5% and 2%, respectively. To further evaluate the proposed method, four different petroleum products (naphtha, kerosene, diesel oil,
and gas oil) were obtained from Shuaiba Refinery of Kuwait National Petroleum Company (KNPC). Measured values of boiling point, SG, refractive index, and sulfur content as well as estimated properties needed for eqs 3 and 4 and predicted sulfur content are all given in Table 4. These data were not used in development of eqs 3 and 4, yet estimated sulfur contents are very close to measured values. These equations can be also evalu-
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Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999
Table 4. Estimation of Sulfur Content of Four Kuwaiti Petroleum Productsa petroleum product
Tb,a K
SGa
n2Oa
M
n2O pred.
dZO
RI
m
Sa %, exp
S%, pred.
abs. dev. %
naphtha kerosene diesel oil gas oil
373 468 583 707
0.715 0.791 0.860 0.928
1.405 1.441 1.480 1.526
104 154.4 229.8 324.8
1.400 1.442 1.480 1.510
0.710 0.787 0.856 0.925
1.045 1.049 1.052 1.048
-7.801 -5.086 1.264 11.307
0.001 0.001 1.3 2.4
0 0.17 1.3 2.8
0 0.17 0 0.4
a Values have been measured in laboratory. These data were not used in development of eqs 3 and 4. Samples were obtained from Kuwait National Petroleum Company, Shuaiba Refinery.
ated indirectly through estimation of sulfur contents of crude oils as outlined below. Estimation of Sulfur Content of Crude Oils. Data analyzed by Gary and Handwerk11 and Speight2 on sulfur content of crude oils indicate that the amount of sulfur in various distillates from a crude increases with increase in carbon number (or molecular weight or boiling point). Analysis of crude by gas chromatography gives weight fractions of pure hydrocarbons up to n-pentane, hexanes (C6 fraction), and heptane-plus fraction (C7+). The C7+ portion of the crude can be presented by a distribution model proposed by Riazi,7 and then using a technique proposed by Riazi,1 it can be presented by a number of defined pseudocompounds. The distribution model is presented by the probability density function F(P*) given as:
F(P*) )
2
B B P*B-1 exp - P*B A A
(
)
P - Po Po
(15)
in which P is a property such as M, Tb, SG, or I. Parameters A, B, and Po can be determined from properties of C7+ as described by Riazi.7 Once these parameters are known, the gaussian quadrature technique can be used to estimate weight percentage, molecular weight, boiling point, and SG of various pseudocomponents. Using boiling point and SG, refractive index and density at 20 °C can be estimated from methods previously discussed. After calculation of RI and m from eqs 1 and 2 for each pseudocomponent, eqs 3 and 4 can be used to estimate sulfur content of each pseudocomponent. Sulfur content of the whole crude then is calculated from the following equation:
sulfur wt % of crude )
∑i Xwi (sulfur wt %)i
cut
wt %
mol. wt.
C2 C3 iC4 nC4 iC5 nC5 C6 C7+(1) C7+(2) C7+(3) C7+(4) C7+(5) total
0.03 0.39 0.62 1.08 0.77 1.31 1.93 9.1 15.2 26.4 18.5 24.8 100
30.1 44.1 58.1 58.1 72.2 72.2 82 112.0 169.1 267.1 405.8 660.9
sp. gr.
0.690 0.753 0.810 0.864 0.904 0.943
Tb, °C
64 123 216 333 438 527
predicted sulfur wt. % 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.1 0.7 1.9 2.9 3.8 2.1
a Measured C 7+ properties: mol. wt. ) 266.6, sp. gr. ) 0.891, wt % in the crude ) 93.9.
(14)
where P* is defined by:
P* )
Table 5. Prediction of Sulfur Content of Kuwaiti Crude for Exporta
(16)
in which Xwi is the weight fraction of pseudocomponent i in the crude. The method can be best explained by an example with Kuwaiti crude for export. The crude has API gravity of 31 and sulfur content of 2.4%. The C7+ portion of the crude has 93.9 wt % with molecular weight of 266.6 and specific gravity of 0.891. The C7+ fraction was split into five pseudocomponents with known molecular weight, boiling point, and SG according to the method outlined by Riazi.1 The refractive index and density for each pseudocomponent were calculated by correlations of Riazi and Daubert9 given by eqs 8 and 9 (or 12). Parameters RI and m were calculated through eqs 1 and 2 and then sulfur content of each pseudocomponent was determined using eqs 3 and 4. Sulfur content of the whole crude was then calculated from eq 16. Details of
calculations are given in Table 5. Estimated sulfur weight percentage for the crude is 2.1%, which differs by 0.3% from the experimental value. As can be seen from Table 5, sulfur content of C6 fraction is very low and sulfur compounds are mainly in the C7+ part of the crude. For pure hydrocarbons up to C5, no sulfur compound is present. Therefore, if only information on C7+ part of a crude is available, its sulfur content can be estimated through the proposed method. In many cases analysis of a crude is given by boiling point and SG of various cuts. Such data for Kuwaiti crude for export are given in Table 6. Actually this is the same crude that was presented in Table 5. Usually in boiling point distribution of crudes or heavy fractions, boiling point of the residue is not known. This boiling point can be determined through the distribution model presented by eq 14. On the basis of data available for boiling point versus cumulative weight fraction, parameters A, B, and To (for Po) in eq 14 were determined as A ) 1.989, B ) 1.5, and To ) 333 K. Then the average boiling point is calculated by the following equation as given by Riazi:7
Tavg ) To(1 + 0.689AT2/3)
(17)
where both To and Tavg are in K. This equation gives an average boiling point of 696 °C. Knowing the average boiling point of whole crude and boiling points of various cuts with their weight percentage, one can determine the boiling point of the residue. For the crude in Table 6, the boiling point of residue was determined to be 628.5 °C. Having boiling point and SG of different cuts, various properties and sulfur content of each cut can be estimated as discussed earlier. Sulfur content of the whole crude is calculated from eq 16. As shown in Table 6, estimated sulfur content of crude is within 0.02% of measured value. This method is more accurate than the method shown in Table 5, because more detailed data
Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999 4511 Table 6. Boiling Point Distribution and Sulfur Content of Kuwaiti Crude for Export Tb, °C
mass %
wt %
SG
20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00 75.00 80.00 85.00 90.00 95.00 100.00 105.00 110.00 115.00 120.00 125.00 130.00 135.00 140.00 145.00 150.00 155.00 160.00 165.00 170.00 175.00 180.00 185.00 190.00 195.00 200.00 210.00 220.00 230.00 240.00 250.00 260.00 270.00 280.00 290.00 300.00 310.00 320.00 330.00 340.00 350.00 360.00 449.00 628.46
1.70 1.96 2.25 2.56 2.89 3.26 3.64 4.06 4.50 4.97 5.46 5.98 6.53 7.11 7.71 8.34 9.00 9.40 9.92 10.51 11.17 11.88 12.61 13.37 14.13 14.90 15.66 16.41 17.16 17.90 18.63 19.35 20.06 20.77 21.48 22.19 22.90 24.35 25.82 27.33 28.89 30.47 32.07 33.66 35.22 36.71 38.13 39.45 40.68 41.86 43.04 44.33 45.89 71.89 100.09
1.70 0.26 0.29 0.31 0.33 0.37 0.38 0.42 0.44 0.47 0.49 0.52 0.55 0.58 0.60 0.63 0.66 0.40 0.52 0.59 0.66 0.71 0.73 0.76 0.76 0.77 0.76 0.75 0.75 0.74 0.73 0.72 0.71 0.71 0.71 0.71 0.71 1.45 1.47 1.51 1.56 1.58 1.60 1.59 1.56 1.49 1.42 1.32 0.23 1.18 1.18 1.29 1.56 26.00 28.20
0.57 0.58 0.60 0.61 0.62 0.63 0.64 0.65 0.66 0.67 0.68 0.69 0.70 0.70 0.71 0.71 0.72 0.72 0.73 0.73 0.74 0.74 0.75 0.75 0.75 0.76 0.76 0.76 0.77 0.77 0.77 0.78 0.78 0.78 0.79 0.79 0.79 0.80 0.80 0.81 0.82 0.82 0.83 0.83 0.84 0.84 0.85 0.85 0.86 0.86 0.87 0.87 0.88 0.92 1.0285
S%, exp
S%, pred
abs. dev.
0.006 0.000 0.006 0.006 0.000 0.006 0.006 0.000 0.006 0.006 0.000 0.006 0.006 0.000 0.006 0.007 0.000 0.007 0.007 0.000 0.007 0.007 0.002 0.005 0.007 0.008 0.001 0.008 0.013 0.005 0.008 0.017 0.009 0.008 0.021 0.013 0.008 0.025 0.017 0.008 0.028 0.020 0.009 0.032 0.023 0.009 0.036 0.027 0.009 0.040 0.031 0.01 0.015 0.035 0.011 0.050 0.039 0.016 0.055 0.039 0.019 0.062 0.043 0.022 0.068 0.046 0.026 0.076 0.050 0.031 0.085 0.051 0.036 0.094 0.058 0.041 0.104 0.063 0.047 0.115 0.068 0.054 0.128 0.074 0.061 0.141 0.080 0.068 0.155 0.087 0.077 0.171 0.091 0.086 0.188 0.102 0.095 0.206 0.111 0.106 0.227 0.121 0.117 0.249 0.132 0.129 0.272 0.143 0.142 0.296 0.154 0.17 0.350 0.180 0.201 0.411 0.210 0.31 0.481 0.171 0.46 0.556 0.096 0.64 0.639 0.001 0.83 0.730 0.100 1.03 1.191 0.161 1.21 1.311 0.101 1.37 1.424 0.054 1.5 1.535 0.035 1.6 1.639 0.039 1.67 1.738 0.068 1.75 1.831 0.081 1.86 1.922 0.062 2.05 2.005 0.045 2.4 2.00 0.40 2.81 2.86 0.05 5.2 4.80 0.40 total predicted S ) % dev. )
(S%) × wt % 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.02 0.02 0.00 0.02 0.02 0.03 0.03 0.74 1.35 2.38 0.02
Figure 1. Sulfur distribution of Kuwaiti crude for export from Table 6. Table 7. Results of Estimation of Sulfur Contents of Kuwaiti Crude Oilsa crude
API gravity
S%, exp
S%, pred.
abs. dev.%
1 2 3 4 5 6 7 total
31 40.2 37.2 36.3 32.7 36.4 32.7 31-40.2
2.4 1.08 1.74 1.9 2.14 1.8 2.2 1.1-2.4
2.1 1.58 1.7 1.57 1.71 1.67 1.76 -
0.3 0.5 0.04 0.33 0.43 0.13 0.44 0.31
a
Data obtained from local industrial source.13
Using this technique, sulfur contents of seven different Kuwaiti crudes were estimated. Experimental data for these crudes were received from a local industrial source,13 and summary of estimated and experimental data are given in Table 7. As shown in this table, estimated values are within 0.3% of experimental values. Conclusions In this work a method is presented to estimate sulfur weight percentage of various petroleum fractions and products using molecular weight, refractive index, and density as input parameters. Minimum information needed for a fraction is its SG and boiling point or viscosity. A method is also outlined to estimate sulfur content of crude oils. The only information needed for the crude is its distillation data or weight percentage of C7+ fraction with molecular weight and SG at 15.5 °C. Acknowledgment
were available for the crude. A graphical presentation of estimated and experimental sulfur distribution versus boiling point for the crude of Table 6 is shown in Figure 1. In cases in which only boiling point for various cuts of crudes are known, SG of each cut can be calculated using the relations given by Riazi and Al-Sahhaf.12
M ) [355.395 - 50.9165 ln(1080 - Tb)]1.5 (18) SG ) 1.07 - exp(3.56073 - 2.93886M0.1) (19) For each cut, M can be estimated from eq 18 using the given boiling point, and SG can be estimated from eq 19. Therefore, for each cut Tb and SG are known.
This paper was presented at the Division of Petroleum Chemistry of the American Chemical Society (ACS) Annual Meeting, Boston, August 23-27, 1998. The authors are grateful to KNPC for providing data and the petroleum samples. Nomenclature d ) liquid density of fraction at 20 °C and 1 atm, g/cm3 I ) refractive index parameter M ) molecular weight of the fraction m ) parameter defined by eq 2 n ) refractive index of fraction at 20 °C and 1 atm P ) parameter such as M, Tb, or SG
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Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999
RI ) refractivity intercept defined by eq 1 Tb ) normal boiling point, K S% ) sulfur weight percentage of the fraction SG ) specific gravity of the fraction at 15.5 °C Xwi ) weight fraction of pseudocomponent i in a crude oil ν ) kinematic viscosity at 100 or 210 °F, cSt
Literature Cited (1) Riazi, M. R. A Distribution Model for C7+ Fractions Characterization of Petroleum Fluids. Ind. Eng. Chem. Res. 1997, 36, 4299-4307. (2) Speight, J. G. The Chemistry and Technology of Petroleum, 2nd ed.; Marcel Dekker: New York, 1991. (3) Van Nes, K.; Van Westen, H. A. Aspects of the Constitution of Mineral Oils; Elsevier: New York, 1951. (4) Riazi, M. R.; Daubert, T. E. Prediction of the Composition of Petroleum Fractions. Ind. Eng. Chem. Process Des. Dev. 1980, 19, 289-294. (5) Riazi, M. R.; Daubert, T. E. Prediction of Molecular Type Analysis of Petroleum Fractions and Coal Liquids. Ind. Eng. Chem. Process Des. Dev. 1986, 25, 1009-1015. (6) API Technical Data Book - Petroleum Refining, 5th ed.; Daubert, T. E., Danner, R. P., Eds., American Petroleum Institute: Washington, DC, 1989; Chapter 2, pp 15-30. (7) Riazi, M. R. Distribution Model for Properties of HydrocarbonPlus Fractions. Ind. Eng. Chem. Res. 1989, 28, 1831-1735.
(8) Riazi, M. R.; Daubert, T. E. Molecular Weight of Heavy Fractions from Viscosity. Oil Gas J. 1987, 58, 110-113. (9) Riazi, M. R.; Daubert, T. E. Simplify Property Predictions. Hydrocarbon Process. 1980, 59, 115-116. (10) Riazi, M. R.; Daubert, T. E. Characterization Parameters for Petroleum Fractions. Ind. Eng. Chem. Res. 1987, 26, 755-759. (11) Gary, J. H., Handwerk, G. E. Petroleum Refinings Technology and Economics, 3rd ed.; Marcel Dekker: New York, 1994. (12) Riazi, M. R.; Al-Sahhaf, T. A. Physical Properties of Heavy Petroleum Fractions and Crude Oils. Fluid Phase Equilib. 1996, 117, 217-224. (13) Industrial Source, Private Communication, Kuwait, 1997. (14) Industrial Source, Private Communication, Saudi Arabia, 1997. (15) Jones, D. S. J. Elements of Petroleum Processing; Wiley: New York, 1995. (16) Refining Handbook ’90, A Special Report. Hydrocarbon Process. 1990, 69, 83. (17) Refining Processes ’94, A Special Report. Hydrocarbon Process. 1994, 73, 87.
Received for review April 13, 1999 Revised manuscript received July 12, 1999 Accepted August 18, 1999 IE990262D
