of light and heavy phases a t 25°C. Induction time is not represented (about 10 to 20 minutes); zero time corresponds to start of rapid absorption of oxygen. The oxidation of n-hexane was carried out in the presence of an initial concentration of 2 moles per liter of butyric acid. The rate of disappearance of the hydrocarbon was similar to that obtained without initial butyric acid. The kinetic curves for the accumulation of reaction products lead to the same values for k and kd as those found in the oxidation of pure n-hexane (Figure 2 ) . The stability of kd with conversion does not correspond to that observed in the oxidative decarboxylation of capric acid a t 130"C. (Berezin et al., 1958). Berezin observed a decrease of the rate of decarboxylation with the accumulation of acids, and interpreted it as the result of hydrogen-bonded dimerization of the acids. The discrepancy can be interpreted as the result of the approximations made here in the kinetic relationships, or of the decrease a t higher temperature of the equilibrium constant of acid dimerization. When comparing the high value of kd with that of k , it is necessary to take into account the fact that k is the rate constant of the reaction of a peroxy radical with a molecule of n-hexane containing 8 secondary C-H bonds. In liquid-phase oxidation of organic compounds by molecular oxygen, additions of carboxylic acids accelerate the reaction (Chervinskii et al., 1965). The reactivity of the acids demonstrated here explains the effect. However, the inertness of acetic acid toward decarboxylative oxidation and its accelerating effect on the liquid phase oxidation of paraffinic hydrocarbons, show that the acceleration induced by the acids results not only from their own oxidability, but also from other possible effects, such as catalysis of the decomposition of hydroperoxides or of the isomerization of peroxidic radicals.
discussions. The authors gratefully acknowledge the support of the Phillips Petroleum and Petrofina Co., Petrochim, Antwerp, Belgium. Literature Cited
Bell, E. R., Raley, J. H., Rust, F. F., Seubold, F. H., Vaughan, W. E., Discussions Faraday Soc. 1951, No. 10, 242. Berezin, I. V., Makalets, B. I., Zh. Fiz.Khim. 23, 2351 (1959). Berezin, I. V., Makalets, B. I., Chuchukina, L. G., Zh. Obsch. Khim. 28, 2718 (1958). Berezin, I . V., Ramigova, A. M., Zh. Fiz. Khim. 36, 581 (1962). Berezin. I. V.,Ramigova, A. M., Emanuel, K . M., Izu. Akad. Nauk SSSR, Otd. Khim. 1959, 1733. Bulygin, M. G., Blyumberg, E. A., Emanuel, N. M., Neftekhim. 6, 203 (1966). Chervinskii, K. A., Baranova, E . I., Zherebtsova, L. P., Kirichenko, G. S., Zh. Prikl. Khim. 38, 1373 (1965). Elce, A . , Robson, I. K. M., Young, D. P., Brit. Patent 771,991 (April 10, 1957). Kochi, J. K., J . A m . Chem. Soc. 87, 1811 (1965). Makalets, B. I., Khim. Tekhnol. 3 (l), 109 (1960). Mushenko, D. V., Gvozdovskii, G. N., Ignateva, T. F., Tamik, M. I., Khim. i Tekhnol. Topliu i Masel 10 (6), 10 (1965). Paquot, C., De Goursac, F., Bull. SOC.Chim. France 1950, 172. Rouchaud, J., Nietera, P., Ind. Eng. Chem. Process Design Develop. 7, 295 (1968). Wood, H. G., Brown, R . W., Werkman, C. H., J . A m . Chem. SOC. 66, 1812 (1944). Wood, H. G., Werkman, C. H., J . A m . Chem. Soc. 63, 2140 (1941).
Acknowledgment
The authors owe much to L. Sajus and I. Seree de Roch, Institut FranCais du Petrole, France, for interesting
RECEIVED for review April 5 , 1968 ACCEPTED August 5, 1968
DELAYED COKING OF LOW-TEMPERATURE LIGNITE PITCH J O H N S . B E R B E R , R I C H A R D 1. R I C E , A N D R O B E R T 1. L Y N C H Morgantown Coal Research Center, Bureau of Mines, U. S . Department of the Interior, Morgantown, W . V a . 26505
LOW-TEMPERATURE tar pitch
has been processed by delayed coking in what is believed to be the first effort to extend the technique to this material. Petroleum residuals have been processed by delayed coking commercially for a number of years (Martin et al., 1959). Pilot-plant studies have also been carried out on coke oven pitch (Martin et al., 1959) and a low-temperature tar topped to a temperature of 425" F. (Dell, 1959). This is believed to be the first time, however, that low-temperature tar pitch has been subjected to delayed coking. Previous publications on the upgrading and utilization of low-temperature tar fractions give details on the preparation of biodegrad270
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
able detergents from the olefin fraction (Berber et al., 1965), phthalic and maleic anhydrides from the neutral oil (Berber et al., 1967b), and carbon electrode binders from the thermal cracking of the pitch (Berber et al., 1967a). Material, Equipment, and Process
The tar was produced by the Texas Power & Light Co. from a Texas lignite carboniied a t 950" F. in a fluidized bed. The pitch was obtained by distilling the crude tar under vacuum to an atmospheric boiling point of 630" F. and amounted to 45% of the tar. Chemical and physical properties of the pitch are given in Table I.
A Texas lignite pitch was subjected to delayed coking at 800'
to 12OO0F., yields of coke, gas, and oil determined, and the effect of coking temperature established. As expected, a n increase in coking temperature increased the coke and gas yields and decreased the oil yield. Yields a t 800' and 1200' F., respectively, were cake, 25 and 45, oil, 4 3 and 17, and gas, 17 and 3 9 weight %. The coke appears suitable as a n aggregate for metallurgical electrode manufacture or low-sulfur fuel far power generation, the oil a s a source of electrode binder and phthalic and maleic anhydrides, and the gas as a substitute for natural gas or source of hydrogen via steam reforming. Table 1. Properties of Lignite Pitch AS
Ultimate annlysis
Receiued, %
Carbon Hydrogen
84.12 8.53 0.81
Nitrogen Oxygen
4.62 0.90 0.01 0.00 510 90 105 0 1.128 0.35 0.00
Sulfur Chlorine Moisture Flash point, F. Softening paint (r&h)glycerol, e C. Softening point (cuhe in glycerol), C. Penetration at 77" F., 100 grams, 5 seconds Specific gravity, 25"C./2P C. Ash Water
Ductility, cm. at 77" F. Bitumen. soluble in CS, Free carbon Distillation
late fraction is used to flush the pump t o prevent solidification of the pitch. Figure 2 shows the major units of the system. The oil from the separator is vacuum-distilled to ahout 750" F. to produce an aromatic-rich distillate and a residue. The distillate can be catalytically oxidized to phthalic and maleic anhydrides, while the residue, pitch, is potenPitch I
r-' Gas
t
7
water
0
78.80 20.85
To 300" C. Softening point of residue (r&h)," C.
6.40
,*,....
20.81
Figure ^C I I K uarayt.u W U L ~ a p p a ~ a ~ ucwsists a V I a11 UCLLLLCL~LY heated (15.6 kw. max.) steel drum (C, Figure 1) fabricated from a 5-foot length of 8-inch carbon steel pipe. The drum is flanged a t the top and bottom ends to facilitate coke removal and cleaning of the vessel. Coke removal is further facilitated by use of a tilting drum. The pitch feed tank ( A ) consists of a 15-inch length of 8-inch diameter carbon steel pipe with open top and a cone welded to the bottom. A %inch coupling is fitted to the outlet. The pitch tank is electrically heated by a 1.8-kw. heater. The pitch to he coked is ground, liquified in the pitch feed tank (by heating to 400" F,), and pumped by a small gear unit ( B ) driven by an electric motor and hydraulic speed control ( J ) through the preheater ( F ) which raises the temperature to about 485°F. The hot pitch is then fed a t ahout 2 pounds per hour to the delayed coking drum (C) which is maintained at the desired coking temperature. About 5 pounds are introduced per hour. Rates of 2 to 6 pounds per ,hour had no noticeable effect on the results, although a higher rate might have had an influence. Residence time in the drum had a much greater effect than feed rate. The pitch remains in the coking drum for several hours during which time the volatile matter is driven off. Vapors from the drum are then condensed (D)and oil collects in the bottom of the separator ( E ) . The gases are water scrubbed ( H ) , metered (G), and vented. A small tank ( K ) containing crude tar distil^-
veiaycu
Gas and Oil sepai
Figure 2. Delayed coking apparatus VOL. 7 NO, 4 DECEMBER 1 9 6 8
271
tially useful as a hinder for carbon electrodes, road paving, roofing, or piping material, depending on its specifications, such as softening point, carbon-hydrogen ratio, hydrogen content, and coking value. Coke Yields and Quality
The pitch was coked a t 800" to 1200" F. and atmospheric pressure. Coke yields ranged from 25% a t 800°F. to 45% a t 1200°F. (Figure 3), the increased yield resulting from greater degradation of the pitch a t the higher temperature.
Coke produced a t 800°F. was like char, being darker and smoother than the product a t 1200°F. At 1200"F., the coke was silver-grey in color, typical of coke (Figures 4 and 5). The ash content of the coke was virtually the same over the entire range of coking temperatures (Figure 6 ) . Iron content of the coke (Figure 7) also remained constant a t all temperatures as expected. The sulfur content of the coke decreased slightly with increasing temperature (Figure 8) indicating that, a t higher temperatures, there was less sulfur per unit weight of coke produced, even though less of the original sulfur was being passed off with the gas and oil. At 800"F., 0.0068 pounds of sulfur per pound of pitch fed was removed with the gas and oil, whereas a t 1200"F., only 0.0054 pounds of
reportedly is usable as fuel for generating electric power (Donnelly and Barbour, 1966). The relatively low sulfur content of the coke, 0.80%,makes it potentially attractive as a fuel in view of present air pollution standards. Other properties of the coke, while important for certain applications, were not determined because the coke was calcined and used to make electrodes. The coke, following calcination, is also of possible value as aggregate in the production of metallurgical electrodes, although the ash concentration is slightly higher than in petroleum coke currently in use. The ash content should be less than 0.5%. The coke loses a maximum of up to 15% by weight when calcined to 2000°F. No ash was lost during calcination.
0 I-
< C
z W (2
0 rx
n
>
+ W
z a X
kW
5
800
-
10
I
I
"
1
"
"
I
I
-
1,000
1,100
1,200
COKING TEMPERATURE, "F
I
"
Figure 1 1 . Effect of temperature on methane-hydrogen ratio
a
.o
900
I -
Table II. Gas Composition, Coking Temperature 950' F.
800
1,000
900
1,100
1,200
Component
COKING TEMPERATURE, "F
CO? CO H? CH, C,Hr, C?HA
Figure 8. Coking temperature v s . sulfur content of coke
c
iH8
(2-
Vol. ' c
0.74 4.91 5.67 43.83 13.97 9.94 13.54 .5.40
Oil Yields
1
90 800
I
I 900
I
I 1,000
I
I 1,100
I
1,200
COKING TEMPERATURE, "F
Figure
9. Effect of temperature on specific gravity
of oil
The oil yield was a function of coking temperature and varied from 43% of the feed pitch a t 800" F . to 17' a t 1200°F. (Figure 3 ) . Specific gravity of the oil was about 0.95 a t 800°F. and 1.18 a t 1200°F. (Figure 9). Distilled to 720" F., the oil gave a distillate containing 15 to 25'; combined acids and bases, the remainder consisting of a neutral oil. Fluorescence indicator adsorption (F.I.A.) analysis o f a typical neutral oil showed 89.2' aromatics, 6 . 9 5 olefins, and 3.9% paraffins. Vapor-phase catalytic oxidation of the neutral oil yielded better than 30% phthalic and maleic anhydrides, a good yield considering it is based on a mixture of hydrocarbons as feed. Distillation residue from the oil shows promise as a binder for metallurgical electrodes. Evaluation of the coke and residue is still in progress.
Gas Yield + 4 C
W
Z 4
I
L W
z 1 W >
I W +
.o I 800
I
I
900
I
I 1,000
I
I 1,100
I
1,200
COKING TEMPERATURE, "F
Figure 10. Ethylene-ethane ratio as function of temperature
The gas yield was 17% a t 800°F. and increased to 39% a t 1200°F. (Figure 3). The effect of coking temperature on the ethylene-ethane ratio is shown in Figure 10. Greater dehydrogenation and thermal cracking probably resulted from the higher temperature. In addition, an increase in coking temperature is accompanied by a decrease in the methane-hydrogen ratio (Figure 111, which drops from 8 to 1 a t 800°F. to about 2 to 1 at, 1150°F. Typical analysis of gas obtained a t 950°F. is given in Table 11. Discrepancies in total yields are due t o handling losses. Also a small amount ofunreacted pitch remained a t 800" F. No water solubles were detected. VOL. 7 N O . 4 DECEMBER 1968
273
Conclusions
Delayed coking appears promising as a method of increasing the commercial value of lignite pitch. The technique yields three products: coke, oil, and gas. The coke is potentially valuable as an aggregate for metallurgical electrodes, other graphite products, and a low-sulfur fuel. The oil, upon distillation, is a valuable chemical intermediate. Gas resulting from the coking of the pitch, following stripping to remove the CB compounds, is a possible substitute for natural gas or a source of hydrogen by the steam-reforming process. Ethylene could also be recovered from the gas stream and used as a raw material.
Berber, J. S. Rice, R. L., Fortney, D. R., IND. ENG. CHEM.PROD. RES. DEVELOP. 6,197 (1967a). Berber, J. S., Rice, R. L., Hiser, A. L., Wainwright, H. W., Bur. Mines. Rept. Invest. 6916, 17 pp., 1967b. Dell, M. B., Ind. Eng. Chem. 51, 1297 (1959). Donnelly, F. J., Barbour, L. T., Hydrocarbon Process. Petrol. Refiner. 4 5 , 2 2 1 (1966). Martin, S.W., Wills, L. E., in “Advances in Petroleum Chemistry and Refining,” Vol. 11, J. J. McKetta, Jr., and K. A. Kobe, Eds., pp. 367-87, Interscience., Xew York, 1959. RECEIVED for review April 1, 1968 ACCEPTED August 13,1968
Literature Cited
Berber, J. S., Rahfuse, R. V., Wainwright, H. W., IND. ENG.CHEM.PROD. RES. DEVELOP. 4 , 2 4 2 (1965).
Division of Fuel Chemistry, 155th Meeting, ACS, San Francisco, Calif., April 1968.
REFINING OF PYROLYTIC SHALE OIL D.
P .
MONTGOMERY
Phillips Petroleum Company, Bartlesuille, Okla. 74003
A pyrolytic shale oil was refined into marketable products to determine the severity of hydrodenitrogenation needed for sustained refining and the yields and qualities 6f the refined products. The refining steps were: delayed coking, with recycle of heavy coker distillate; hydrodenitrogenation of coker distillate, followed by fractionation; further hydrodenitrogenation of naphtha; reforming of nitrogen-free naphtha; catalytic cracking of gas oil from the hydrodenitrogenated coker distillate. Temperature and pressure maximums of 950’ F. and 1500 p.s.i.g. were well within the scope of current refinery practice. Nitrogen content of the reformer feedstock was 1.5 p.p.m., and that of the cracking stock was 100 p.p.m. (basic); thus, both were adequately free of nitrogen to ensure long catalyst life. Reformates and catalytic gasolines of 98 octane number were produced. The hydrodenitrogenated coker distillate yielded a large volume of specification grade diesel fuel. Yields and product distributions for each refining step were determined, along with properties of the finished liquids.
BECAUSE of revived interest by both industry and government in the production of petroleum products from oil shale, a pilot-scale study of the refining of pyrolytic shale oil was made by Phillips Petroleum Co. This study used current refining techniques and incorporated no novel or unproved refining steps. Only commercially available catalysts were employed. The question to be answered was not whether shale oil can be refined to a synthetic crude and then to finished products, but what refining severity is required to reduce 274
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
the nitrogen to a satisfactory level for continuous processing in a conventional refinery, and what yields and qualities of the products result. Domestic oil shale locations and the problems associated with recovering oil from these shales have been presented (Oil Gas J , 1964), and recent refining developments were discussed (Chem Eng Progr., 1966). Pyrolytic shale oils are characteristically high in concentrations of nitrogen, sulfur, and oxygen; concentrations are typically 2, 1, and 1%,respectively. Because nitrogen is a potent poison for
