106
Ind. Eng. Chem. Prod. Res. Dev. 1904, 23, 106-111
freely discussing his experiences with thermoset rheometry; Mr. L. L. Earles for his great efforts in making the heat transfer system; and Messrs. S. Stanley and A. Leach for their help at various stages in the experimental program. Literature Cited ANSIlASTM 03123-72 (Reapproved 1978) "Standard Test Method for Spiral Flow of Low-Pressure Thermosetting Molding Compounds". Beck, R. H., Jr.; Golovoy, A. S f f A M E C Tech. Pap. 1072, 78, 87-92. Bird, R. B.; Armstrong, R. C.; Hassager, 0. "Dynamics of Polymerlc Liqulds": Vol. 1; Wiley: New York, 1977. Choi, S. Y. SPE J. 1070, 26, 51-4. Carroll, D. R. M. S. Thesis, Texas A 8 M. University, 1982. Debigs, P.; Alston, W. B.; Vanucci, R. D. NASA TM 79062, 1979. Driscoii, S.; Zlmbone, P.; Dubreull, M.; Egber, R.; Alvarez, R. S E A N E C Tech. Pap. 1075, 2 0 , 99-101.
Dutta, A.; Ryan, M. E. J. Appl. Polym. Sci. 1070, 2 4 , 635-49. Frireile, W. G.; Norfleet, J. S. Sf€ANT€C Tech. Pap. 1071, 77, 397-402. Frirelle, W. G.; Norfleet, J. S. SPE J. 1071, 27, 44-8. Heinle, P. J.; Rodgers, M. A. SPE J. 1080, 25, 56-61. Hess, J. E. Mod. Plast. Nov 1071, 60-1. Maas, T. A. M. M. Po&" f n g . Sci. 1078, 78, 29-31. Macosko, C. M.; Mussatti, F. G. SPEANTEC Tech. Pap. 1072, 78, 73-80. Mussatti, F. 0.; Macosko, C. W. Polym. Eng. Sci. 1073, 73, 236-40. Roller, M. B. Polym. Eng. Scl. 1075, 75, 408-14. SMI, S.; Kamal, M. R. SPf A N E C Tech. Pap. 1080, 26, 86-94, Slysh, R.; Guyler, K. Polym. Eng. Sci. 1078. 78, 607-10. Sundstrom, D. W.; Walters, L. A. S E J. 1071, 27, 58-62. White, R. P. Polym. Eng. Sci. 1074, 74, 50-7. Whoriow, R. W. "Rheologlcai Technlques", Ellis Horwood: Chichester, 1980.
Receiued for review April 27, 1983 Accepted September 19, 1983
Pyrolysis Feedstock Studies: Correlation and Modeling of Hydrogenated Distillates Raymond J. Rennard' and Harold E. Swift Gulf Research & Development Company, Pittsburgh. Pennsylvania 75230
This paper reports the effect of l i i t gas oil hydrogenationon pyrolysis yields. Hydrogenation, in addiin to removing sulfur, Significantly aiters product yields upon pyrotysls. Hydrogenation results in significantly increased olefin, fuel gas, and aromatic yields and drastically reduces fuel oil yields. By implication, this should lead to reduced fouling and longer run lengths. All of the changes in product yields can be predicted on the basis of changes In feedstock composition and physical properties resulting from hydrogenation. By use of these parameters, a model has been developed which accurately predicts all product yields for hydrogenated distillates.
Introduction While the use of distillate as an olefin feedstock in the United States has fallen far short of earlier projections (Swift et al., 1978), the current crude oil surplus, with its resultant lower crude prices, combined with rising LPG costs has resulted in a renewed interest in cracking liquid feedstocks. Cost effective methods of increasing olefin yields from distillates and utilization of lower cost sour distillates would significantly increase the incentive for light gas oil cracking. Because of their high aromatic and naphthenic content, the cracking of light gas oils results in significantly lower olefin yields and high yields of pyrolysis fuel oil. Since feedstock sulfur is mostly contained in the refractory aromatics fraction, sulfur is concentrated in the fuel oil product during pyrolysis. This environmentally limits the use of all but very low sulfur feedstocks. Over the years a variety of schemes have been investigated for upgrading distillate range olefin feedstocks. By far the most attractive of these schemes is hydrotreating. Hydrotreating allows a wider selection of feedstocks in that gas oils derived from high sulfur crudes can be cracked in conventional plants without violating environmental restrictions. In addition, the reduction in aromatic content and the increase in feedstock hydrogen content should result in increases in olefins yields and significant decreases in pyrolysis fuel oil formation. This has been experimentally verified, and the economic benefits of gas oil hydrogenation have been reported by Rennard and Swift (1981). The present paper summarizes the trends and 0196-4321 18411223-0106$01.50/0
Table I. Pyrolysis Pilot Plant Operating Conditions gas oil feed rate dilution steam rate steam/oil radiant coil inlet coil outlet average P coil outlet temperature transfer line quench RPG range fuel oil
4.5 kg/h 3.375 kg/h 0.75 41 psig 1 5 psig 26 psig 760-805 "C 538 "C C5 's-3 7 5 F 375 "F
Table 11. Hydrogenation Pilot Plant Operating Conditions hydrogen pressure reactor temperature LHSV hydrogen rate aromatic saturation sulfur removal
600-2500 psig 300-374 "C 1-4 h-' 7000-10 000 scf/bbl 17-95% 97-100%
correlations observed in cracking hydrogenated gas oils and discusses the parameters which were found to be significant in developing yield models for cracking both raw and hydrogenated gas oils. Experimental Section All pyrolysis experiments were carried out in a one barrel-per-day,continuous operation pilot plant. This pilot plant was operated for Gulf Oil Chemicals Co. by Gulf Research & Development Co. The pilot unit was designed to simulate a modern naphtha/gas oil cracker in terms of both product yields and operating conditions. Yields ob@ 1984 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23,No. 1, 1984 107 Table 111. Properties of Gas Oils
feed gravity, "API sulfur, wt % hydrogen, wt % carbon, wt %
Coastal B-1 30.4 0.13 12.67 87.00
Coastal B-1 33.8 0.098 13.26 86.46
Forcados Forcados KLGOa 33.1 0.090 12.88 86.04
31.5 0.082 14.04 85.84
KLGO no. 1
KLGO no. 2
42.1 0.001 14.09 86.08
43.2 0.004 14.34 85.95
39.6 0.16 13.68 86.08
West Texas 33.7 1.26 12.99 85.51
West Texas no. 1
West Texas no. 2
36.3 0.009 13.47 86.41
38.2 0.165 13.73 86.07
D-86, "C 10% 5 0% 90%
196 252 301
224 244 212
230 252 304
211 250 301
192 275 329
222 271 322
267 298 324
2 29 270 325
257 292 320
249 288 314
composition, vol % paraffins iS0-
normal cycloparaffins aromatics
16.1 15.7 0.4 48.5 35.4
21.3 20.6 0.6 64.7 13.8
21.2 10.6 16.6 36.9 35.4
35.9 34.8 1.1 61.4 2.8
51.8 31.4 19.9 20.5 27.7
56.3 31.3 19.0 31.1 12.1
58.1 29.8 28.3 40.0 1.4
40.5 17.6 22.9 25.5 34.0
44.8 23.0 21.8 27.1 28.1
47.2 18.3 28.9 33.4 18.8
--
61.0
__
92.2
--
56.3
94.9
--
17.4
44.7
% aromatic saturation a
Kuwait Light Gas Cil.
tained in the pilot plant have been shown to be comparable
to those obtained in Gulfs commercial units at equivalent severities and operating conditions. Standard operating conditions employed in this study are listed in Table I. A more detailed description of the pilot plant and its operation is beyond the scope of this paper. The hydrotreating and hydrogenation of the gas oil feeds used in this study were carried out in a pilot plant at the Gulf Research & Development Co. This pilot unit simulates a commercial hydrotreater employing proprietary Gulf technology and catalysts. The ranges of conditions used for the hydrotreating runs are listed in Table 11. A more detailed description of this unit and its operation is also beyond the scope of this paper.
Results and Discussion The effect of hydrotreating on the cracking yields for different gas oils (middle distillates boiling between 300 and 650 O F ) is reported in this study. The four gas oils are derived from Coastal B-1 Mix (CB-l), West Texas Sour, Nigerian Forcados, and Kuwait crude oils. All except the Kuwait light gas oil (KLGO) are virgin feedstocks. The KLGO was subjected to a mild desulfuration a t a European refinery before shipment to the United States. The aromatic contents of the four gas oils are not tremendously different, ranging from 28.2% for the KLGO to 35.9% for the Forcados oil. However, the paraffm and cycloparaffin content of the four gas oils varies over a considerable range as can be seen from the physical and chemical properties of the feedstocks listed in Table 111. The sulfur content of the four gas oils also varies over a considerable range (0.04% for the Forcados to 1.26% for the West Texas Sour). Hydrogenation of these gas oils was carried out under conditions designed to give widely different levels of aromatic saturation. A summary of the physical and chemical properties of the raw and hydrogenated gas oils studied is shown in Table III. As can be seen, the level of aromatic saturation varied from a low of 17% for the West Texas Sour to a high of 95% for the severely hydrogenated KLGO. It can be seen from Table I11 that hydrogenation results in an increase in API gravity, an increase in both cycloparaffin and paraffin content, and a drastic decrease in sulfur concentration. Hydrogenation also results in a small downward shift in boiling range which is reflected in the slight decrease in the (D-86) 50% boiling point.
Table IV. Pyrolysis of Raw and Hydrogenated CB-1 Light Gas Oil nonhydrogenated "API % paraffins % cycloparaffins % aromatics COT, "C hydrogen methane acetylene ethylene ethane MAPD propylene propane butadiene other C4's RP G fuel oil BTX benzene
175
30.4 16.1 48.5 35.4 785
795
Yields, wt % 0.54 0.57 0.62 8.49 9.30 10.10 0.05 0.06 0.07 10.88 11.61 12.02 3.04 3.15 3.21 0.21 0.26 0.29 9.24 9.51 9.62 0.57 0.59 0.60 2.44 2.54 2.62 5.93 5.58 5.40 15.54 11.25 9.35 30.04 30.55 30.39 13.04 15.03 15.65 4.50 5.53 6.14
-
hydrogenated (61%)
775
33.8 21.3 64.7 13.8 785
0.59 9.70 0.06 13.00 3.15 0.28 10.81 0.58 3.03 6.65 13.96 24.26 13.92 5.53
0.64 10.81 0.08 14.06 3.36 0.36 11.04 0.58 3.12 6.29 9.01 23.93 16.70 6.36
795 0.66 11.11
0.10 14.46 3.15 0.37 10.97 0.60 3.43 6.36 5.93 24.24 18.60 7.80
During hydrogenation, a small amount of the gas oil is converted to a naphtha range material via hydrocracking. The proprietary Gulf catalyst used in these studies is very effective in minimizing this hydrocracking. In achieving 92 % aromatic saturation of the Forcados gas oil, only 4.9 vol % naphtha was formed. At 61% saturation of the CB-1 LGO, the naphtha yield was reduced to 2.1% . In all cases the naphtha range material was separated from the gas oil by distillation and discarded. Table IV shows the yields obtained from the pyrolysis of the raw CB-1LGO and the same gas oil which has been hydrogenated to a 61% aromatics saturation level. It is quite evident from these data that hydrogenation results in a significant increase in olefin yields accompanied by a comparable increase in hydrogen, methane, and aromatics yields. These increases come at the expense of the total fuel oil production which shows a significant decrease after hydrogenation. Similar yield data for ~ r g i nand hydrogcnated Forcados LGO are shown in Table V. Here the gas oil has been hydrogenated to a 92% aromatic saturation level.
108
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 1, 1984
Table V. Pyrolysis of Raw and Hydrogenated Forcadas Light Gas Oil hydrogenated nonhy drogenated (92%)
Table VII. Pyrolysis of Raw and Hydrogenated Kuwait Light Gas Oil
"MI % paraffins % cycloparaffins % aromatics COT, "C
"MI
775
33.7 27.2 36.9 35.9 785
795
Yields, wt % 0.52 0.57 0.63 7.88 8.80 9.54 0.04 0.06 0.08 13.39 14.46 15.51 3.05 3.20 3.14 0.23 0.27 0.30 10.65 10.58 10.72 0.55 0.54 0.51 3.13 2.92 2.95 6.95 5.95 5.21 15.08 14.01 11.55 28.56 26.33 27.93 9.97 12.30 11.93 3.66 4.09 4.55
hydrogen methane acetylene ethylene ethane MAPD propylene propane butadiene other C4's RP G fuel oil BTX benzene
785
37.5 35.9 61.4 2.8 795
805
0.64 10.88 0.09 16.43 3.80 0.36 12.62 0.66 3.74 7.23 10.47 17.28 15.79 6.94
0.63 11.46 0.11 18.14 3.96 0.40 13.07 0.67 4.06 7.03 10.19 14.60 15.59 7.22
0.69 11.96 0.14 18.59 3.91 0.46 12.73 0.63 4.08 6.27 8.98 15.16 16.40 7.91
% paraffins % cycloparaffins % aromatics
nonhydrogenated
hydrogenated (56%)
39.6 51.8 20.5 27.7 785
775
42.1 56.3 31.1 12.1 785
795
0.40 9.01 0.09 21.37 4.67 0.24 15.69 0.73 4.39 8.41 13.93 12.60 8.47 4.20
0.44 9.90 0.11 22.63 4.91 0.28 15.95 0.74 4.54 7.71 11.31 12.71 8.77 4.65
0.51 10.54 0.14 23.60 4.81 0.34 15.88 0.71 5.02 7.21 8.86 12.44 9.94 5.30
% paraffins % cycloparaffins % aromatics
COT, "C
775
795
Yields, wt % 0.48 0.52 0.57 8.17 9.07 9.52 0.06 0.07 0.09 19.99 20.66 21.27 4.46 4.74 4.81 0.23 0.26 0.31 14.28 14.04 14.84 0.70 0.73 0.74 3.38 3.71 4.14 7.09 7.00 6.82 13.49 11.53 9.74 21.71 21.26 18.94 5.95 6.41 8.21 2.51 2.74 4.02
hydrogen me thane acetylene ethylene ethane MAPD propylene propane butadiene other C4's RPG fuel oil BTX benzene
COT, "C hydrogen methane acetylene ethylene ethane MAPD propylene propane butadiene other C4's RPG fuel oil BTX benzene
39.6 51.8 20.5 27.7 775 785 795 Yields, wt % 0.48 0.52 0.57 8.17 9.07 9.52 0.06 0.07 0.09 19.99 20.66 21.27 4.46 4.74 4.81 0.23 0.26 0.31 14.28 14.04 14.84 0.70 0.73 0.74 3.38 3.71 4.14 7.09 7.00 6.82 13.49 11.53 9.74 21.71 21.26 18.94 5.95 6.41 8.21 2.51 2.74 4.02
775
43.2 58.1 40.0 1.4 785
795
0.50 8.88 0.09 21.48 4.53 0.26 15.47 0.72 4.47 8.62 9.15 16.75 9.08 4.76
0.55 9.79 0.12 23.11 4.80 0.32 16.16 0.74 4.90 8.39 6.22 13.62 11.28 6.03
0.59 10.51 0.14 23.84 4.73 0.36 15.92 0.73 5.14 7.70 5.70 12.84 11.81 6.51
Table VIII. Pyrolysis of Raw and Hydrogenated West Texas Light Gas Oil
Table VI. Pyrolysis of Raw and Hydrogenated Kuwait Light Gas Oil
"MI
hydrogenated (95%)
nonhydrogenated
nonh y drogenated
hydrogenated (17%)
33.7 40.5 25.5 34.0 795
36.3 44.8 27.1 28.1 795
"MI % paraffins % cycloparaffins % aromatics
COT, "C
785
805
Yields, wt % 0.39 0.42 0.46 9.17 9.81 10.51 0.09 0.11 0.14 18.30 18.91 19.45 4.70 4.67 4.73 0.29 0.31 0.37 13.69 13.43 13.18 0.86 0.80 0.77 3.87 3.90 3.94 6.67 5.80 5.29 8.34 6.15 5.69 25.08 26.58 26.06 8.55 9.11 9.42 4.41 4.79 4.80
hydrogen methane acetylene ethylene ethane MAPD propylene propane butadiene other C4's RP G fuel oil BTX benzene I
785 0.42 9.03
805
0.45 0.49 9.64 10.57
0.11 0.13 0.15 20.08 20.34 21.33 4.14 4.17 4.40 0.31 0.34 0.40 14.17 13.76 13.70 0.69 0.66 0.67 4.12 3.96 3.80 6.86 6.08 4.96 13.09 8.58 8.22 19.46 22.58 21.33 7.54 9.26 9.99 3.81 4.75 5.13
HYDROGENATED KLGO ( 8 5 % )
HYDROGENATED KLGO ( 9 5 % ) HYDROGENATED KLGO ( 5 6 % ) KLGO
14
i 0
9
I HYDROGENATED CB-1
:f
18
Y S
CB- 1
E
11
HYDROGENATED CB-1
1
CB-1
I 4 L
775
786
185
805
C O T , *C
4
I 776
I 786
I 706
COT.
1 806
*c
Figure 1. Propylene yields as a function of temperature for hydrogenated and nonhydrogenated gas oils.
Figure 2. Ethylene yields as a function of temperature for hydrogenated and nonhydrogenated gas oils.
The hydrogenation of KLGO to 56 and 95% saturation and West Texas Sour LGO to 17 and 45% aromatic sat-
uration shows similar yield effects as can be seen in Tables VI-IX.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 1, 1984 109
Table X. Trends in Product Yields and Feedstock Properties for the Hydrogenation of Light Gas Oils
Table IX. Pyrolysis of Raw and Hydrogenated West Texas Light Gas Oil
hydrogenated nonhydrogenated
(17%)
33.7 40.5 25.5 34.0 795
38.2 47.2 33.4 18.8 795
"API % paraffins % cycloparaffins % aromatics
COT, "C
785
805
Yields, wt
785
hydrogen methane
805
methane acetylene ethylene ethane MAPD propylene pro pan e butadiene other C4's RPG fuel oil BTX benzene
-FUEL OIL -_ B E N Z E N E CB-1
HYDROGENATED CB-1
' "1
P
201
KLGO
d
12
KLGO ( 9 5 % )
-0:NATED HYDROGENATED KLGO (58%)
___----
H Y D R O G E N A T E D CB-1
/ - -
___-___
KLGO (95%) CE-1 HYDROGENATED KLGO (SEX)
-------
I 7S6
acetylene ethylene ethane MAPD
%
0.39 0.42 0.46 0.42 0.47 0.46 9.17 9.81 10.51 9.84 10.44 10.90 0.09 0.11 0.14 0.11 0.12 0.16 18.30 18.91 19.45 20.48 20.75 21.49 4.70 4.67 4.73 4.57 4.72 4.46 0.29 0.31 0.37 0.32 0.34 0.41 13.69 13.43 13.18 14.96 14.32 13.94 0.86 0.80 0.77 0.79 0.78 0.70 3.87 3.90 3.94 4.31 4.24 4.31 6.67 5.80 5.29 7.20 6.34 5.74 8.34 6.15 5.69 10.31 7.95 5.77 25.08 26.58 26.06 16.45 19.51 20.42 8.55 9.11 9.42 10.25 10.03 11.24 4.41 4.79 4.80 4.82 5.38 5.93
hydrogen
component
KLGO
I 796
I 8D6
C0T.W
Figure 3. Benzene and fuel oil yields as a function of temperature for hydrogenated and nonhydrogenated gae oils.
Figures 1 and 2 show plots of single pass yields for ethylene and propylene as a function of coil outlet temperature for nonhydrogenated and hydrogenated Kuwait and CB-1gas oils. Here the effects of hydrogenation in increasing ethylene and propylene yields are quite obvious. Similar plots of benzene and fuel oil yields for these same feedstocks are shown in Figure 3. Here again the effect of hydrogenation is apparent. The data shown in the above plots are representative of the results observed for all of the gas oils. It is interesting to note that the spread in ethylene yields between hydrogenated and nonhydrogenated gas oils falls within a fairly narrow range for each feedstock a t each severity; i.e., the differences in ethylene yields fall between 1.5 and 2.7% for all cases. The incremental increases in observed ethylene yields seem to decrease as the level of feedstock aromatic saturation increases. The spread in propylene yields, while somewhat larger than that in the
propylene propane butadiene other C4's
increase decrease n o trend
Product Yields X X X X X X X X X X
total RPD fuel oil aromatics
X X X
Feedstock Properties gravity, API X X boiling range % hydrogen X % paraffins X % cycloparaffins X X % aromatics
case of ethylene, still falls within a relatively narrow range and shows the same trend as ethylene with respect to increasing levels of hydrogenation. Variations in aromatic and fuel oil yields between hydrogenated and nonhydrogenated gas oils are significantly larger than the variations observed for olefii yields, and in general appear to change in proportion to the extent of hydrogenation. In general, there is an increase in the light product yields (hydrogen through C4's) upon hydrogenation. The increase in light products appears to be made at the expense of fuel oil yields, which decrease in all cases. No significant trends in gasoline production could be discerned upon hydrogenation of the various gas oils. The general trends observed upon hydrogenation are summarized in Table X both with respect to product yields and feedstock properties. Obviously, hydrogenation results in a decrease in feedstock aromatic content and a corresponding increase in cycloparaffin content. These changes are qualitatively proportional to the severity of hydrogenation. What is surprising is that in every case hydrogenation resulted in an increase in feedstock paraffin content, indicating ring opening during hydrogenation. These changes and the slight decrease in boiliig range are reflected in the observed API gravity. Needless to say, the hydrogen content of the feedstocks mirrors the extent of the hydrogenation. All of the observed changes in product yields are qualitatively predictable from the observed changes in the properties of the hydrogenated gas oils. Quantifying the effects, however, is another matter. Straightforward correlations between observed changes in product yields and simple feedstock parameters do not exist. Changes in hydrogen content, gravity, etc., while they qualitatively follow the trends in product yields, cannot be used t o quantitatively predict yield changes. One parameter which might be expected to correlate quantitatively with changes in product yields is the feedstock carbon/hydrogen ratio. However, this proved not to be the case. Figure 4 shows a plot of weight percent ethylene yield as a function of reduced carbon/hydrogen ratio for all the gas oils in this study at a coil outlet temperature of 785 "C. Similar plots for other products and severities show the same lack of fit. Attempts to directly
110
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 1, 1984 FUEL OIL
0 BENZENE
-
20 8
D 15-
0
w
>
"
I
Figure 4. Ethylene yields vs. carbon/hydrogen ratio for hydrogenated and nonhydrogenatedgas oils.
20
28
32
R
Figure 6. Benzene and fuel oil yields as a function of R for hydrogenated and nonhydrogenated gas oils. 20
-
/
ETHYLENE
30
r
. 0-
> L.-
c
BUTADIENE
i---_--i-~ 22 23 24 26
I 21
I 27
1 28
21
1 30
, 31
_I_.
32
Figure 5. Olefin yields as a function of R for hydrogenated and nonhydrogenated gas oils.
/
i x
3 NON-HYDROGENATED X HYDROGENATED
correlate product yields with carbon/hydrogen ratios using equations of the form
Y = f(C/H,BR)
(1) 25
where Y is the product yield and C/H and BR are the reduced carbon/hydrogen ratio and feedstock D-86 50% boiling point, respectively, improved the fit for most products, but it was still far from quantitative. Attempts to correlate the individual product yields with feedstock gravity and boiling range, with equations of the form
Figure 7. Paraffin/cycloparaffin ratio as a function of R for hydrogenated and nonhydrogenated gas oils. FUEL OIL
0 BENZENE
Y = f(C0T) + Al(API*BR") + A2(API*BR") (2) where Y is the individual product yield, API is the feedstock gravity in degrees API, and BR and BR are the feedstock D-86 50% boiling point raised to the m and n power, respectively, were more successful. Figure 5 shows plots of olefin yields vs. this function (R) for all the feedstocks in this study at a COT of 795 "C. Similar plots were obtained at the other severities. Using equations of this form it was possible to quantitatively correlate all yields with the exception of methane, BTX, and fuel oil. Figure 6 shows plots of benzene and fuel oil yields as a function of R at a COT of 795 "C. The lack of fit is obvious. For methane the fit is slightly better, but deviations between observed and predicted yields still fall outside of acceptable limits. This same function, however, has been successfully used to correlate all product yields (including methane, BTX, and fuel oil) with feedstock gravity and boiling range for 26 nonhydrogenated gas oils. Obviously, with respect to methane, BTX, and fuel oil, hydrogenation results in changes in the gas oils that are not adequately defiied by gravity and boiling range alone. This is evident from the data in Figure 7 which shows paraffin/cycloparaffin ratios plotted against R for a series of nonhydrogenated and hydrogenated gas oils. Since cycloparaffins
35
30 R
so
QY
4
t
1 1 5 1
10
\ 15
30
R
Figure 8. Observed yields for benzene and fuel oil as a function of R.
must be considered as precursors for methane, BTX, and fuel oil, it is not surprising that a model based on gravity-boiling range alone will not accurately predict these products for hydrogenated feedstocks. From the above, it is evident that any model used to predict product yields for both hydrogenated and nonhydrogenated feedstocks must contain compositional as well
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 1, 1984 111 Table XI. Observed and Predicted Yields for Hydrogenated Kuwait Light Gas Oil
“MI
39.6 527 51.8 20.5 27.7
50%, “F % paraffins % cycloparaffins 7% aromatics % hydrogenation
43.2 518 58.1 40.0 1.4 93.0
0.0
yields, wt % hydrogen methane acetylene ethylene ethane
MAPD propylene propane butadiene other C4’s RP G fuel oil BTX benzene
obsd
pred
obsd
pred
0.57 9.5 0.09 21.3 4.8 0.31 14.8 0.74 4.1
0.47 9.6 0.11 22.1 4.6 0.32 14.8 0.71 4.2 6.5 9.0 19.6
0.59 10.5 0.14 23.8 4.7 0.36 15.9 0.73 5.1 7.7 5.7 12.8 11.8 6.5
0.52 10.7 0.14 24.1 4.8 0.34 16.0 0.74 4.9 7.5 7.5 11.6 11.2 5.8
6.8
9.8 18.9 8.2 4.0
8.0
3.8
as gravity-boiling range terms. Such a model was developed employing yield equations of the form Y = f(C0T) + A1(API*BRm)+ A2(API*BRn) + A3(PAR) A4(CYCLO) (3) where Y, HCOT), API,and BR are defined as before, and PAR and CYCLO are the weight percent feedstock paraffin and cycloparaffin content, respectively, and A l , A2, and A3 are the correlation coefficients. Multiple regression analysis was used to generate the coefficients for the yield equations from a larger data base consisting of 32 different hydrogenated and nonhydrogenated distillate feedstocks. In this model gravity-boii range terms are still required,
+
since paraffin-cycloparaffin content alone does not adequately define a distillate range feedstock. Figure 8 shows plots of observed yields for benzene and fuel oil as a function of R” = f(API*BR) f(composition) for the ten feedstocks in this study of a COT of 795 OC. These plots are representative of those obtained for all products at all severities. The model generated from this function can be used to predict yields from both virgin and processed feedstocks. For virgin gas oils, this model gives results comparable to the gravity-boiling range model. For processed or hydrogenated feedstocks, only the model containing the compositional terms will accurately predict all product yields. An example of this model is shown in Table XI, which shows observed and predicted yields for a Kuwait gas oil at zero and 95% aromatic saturation. As can be seen, the model accurately predicts the significant changes in observed yields (including methane, BTX, and fuel oil) resulting from hydrogenation. In summary, hydrogenation of light gas oil feedstocks, in addition to removing sulfur, significantly alters the product yields obtained by thermal coil cracking. Hydrogenation results in a significant increase in olefin, fuel gas, and BTX yields and drasticaly reduces fuel oil yields. By implication, this should lead to reduced fouling and increased run lengths. All of the changes in product yields can be predicted on the basis of changes in feedstock composition and physical properties resulting from hydrogenation.
+
Registry No. Hydrogen, 1333-74-0;methane, 7482-8; ethylene, 7485-1; propylene, 11547-1;benzene, 71-43-2; butadiene, 106-99-0.
Literature Cited Rennard, R. J.; Swm, H. E. Chem. Eng. Rog. Doc 1001, 77, 69. Swlft, H. E.; Hanls, G. A,; Rennard, R. J.; Beuther, H. “PetrodremicalFeedstock Values and Supplles-bCracklng and Upgradlng of Feedstocks for Olefin Productkn”; Chemlcal Marketlng Research Assoclatlon Meetlng, New Orleans. Nov 1970.
Received for review April 15, 1983 Accepted September 12, 1983
