June 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
CHBMICALS CONSUMPTION.The quantities of potassium hydroxide and methanol consumed in the extraction process were also studied during pilot plant operations. Potassium left the system only via the by-product cresylate stream as cresylates and mercaptides; none was detected in either the mercaptan stream or the oil product. Caustic consumption was directly proportional to the volume of the cresylate stream, which consistently contained the equivalent of 22 % potassium hydroxide. With stripping-steam rates between 2 and 5 pounds, caustic usage was approximately 0.15 pound per barrel of oil treated. Because of difficulty in controlling mechanical losses in the pilot plant, less information was obtained on methanol consumption. Methanol addition during a long period of continuous operation averaged 0.0770by volume of the oil treated. Infrared spectrographic analyses of the treated oil indicated a methanol content of 0.02 to 0.05% by volume. MamRIALs OF CONSTRUCTION. The effects of corrosion were investigated in the pilot plant equipment itself and on other materials by inserting test strips in the pilot plant. Carbon steel proved satisfactory for use throughout the plant except in the primary fractionator and hot-caustic transfer lines where the temperature exceeded 140" F. For hot-caustic service, Monel showed excellent resistance to corrosion.
1489
CONCLUSION
The present investigation has led to a feasible commercial process for removal of mercaptans from light distillate fuels without degradation in color. No specific operating conditions have been defined or recommended, as they would vary with the commercial application t o be made of the process. Consideration would have t o be given t o the stock t o be treated, the level of mercaptan removal desired, other sweetening processes available in the refinery scheme, and the economics of these and other factors. ACKNOWLEDGMENT
The authors wish t o express appreciation t o their many associates who participated in this development, and especially t o J. A. Brooks, T. E. Earle, and J. D. Lewis, who assisted in the laboratory investigations. LITERATURE CITED
(1) Bent, R. D., and McCullough, J. H., OiZGnsJ., 47, No. 19,95-103
(1948). (2) Brandt, P. L., and Hougen, J. O., Ibid., 37,No. 46, 98-103 (1939). (3) Tamele, M. W., and Ryland, L. B., IND.ENG.CHEM.,ANAL.ED., 8, 16-9 (1936). RECEIVED for review June 15, 1950. ACCEPTED March 13, 1952. Preaented before the Division of Petroleum Chemistry a t the 117th Meeting of the AMERICAN CHEMICAL SOCIETY, Houston, Tex., March 1950.
Engrnyring
Vacuum Retorting of Oil Shale in a Fluidized Bed
Process deveIo pment I
JOHN W. PRINGLE', PAUL L. BARRICK, AND HENRY F. WIGTON DEPARTMENT OF CHEMICAL ENGINEERING, UNIVERSITY OF COLORADO, BOULDER, COLO.
THE
1 use of vacuum in oil shale retorting was reported by McKee and Goodwin ( I ) , who indicated that a waxy, brown semisolid material was produced by heating shale a t 10 t o 15 mm. absolute pressure. The use of a fluidized system in conjunction with vacuum has apparently not been previously investigated. Studies have shown ( 2 , 3, 6) t h a t fluidized systems possess many desirable features, the most important being uniform temperature distribution throughout the bed, high heat transfer coefficients, high reaction rates, smooth and efficient mechanical operation, and very high throughput for the system. A fluidized system was employed in the present investigation principally because of the uniform temperature throughout the bed. The oil shale retorts in present operation generally employ temperatures in excess of 450" C . (6, 7 ) . The oil produced boils over a wide temperature range and contains materials of varied and complex structure (8). The complexity of the products obtained has added considerably to the difficulty of chemical classification of the shale oil and identification of the parent organic material as it occurs in the shale. The authors originally considered t h a t the use of vacuum in shale retorting might result in less degradation of the organic material and yield a product which, provided it could be chemically classified, would point to the structure of the organic material
Present addreas, Dow Chemical Co.. Denver. Colo
in the shale. A preliminary study of the effects of pressure and temperature on the retorting of shale under vacuum is presented here. APPARATUS AND PROCEDURE
The apparatus employed consisted of a borosilicate glass retort approximately 24 inches high and 1 inch in inside diameter, wound externally with two sections of Nichrome heating wire. The lower section provided the heat for heating the fluidized bed and retortin the shale, while the upper section was heated t o prevent confensation of the oil in the section provided for detachment of all solids from the gas stream. The oil-condensing system consisted of three separate condensers. The first was air-cooled, attached directly t o the retort, the second was water-cooled, and the third was a trap cooled by a dry ice and acetone solution. Separate receivers were provided for all condensers. A &lasswool filter was used t o prevent any entrained oil from entering the vacuum system, and a solid sodium hydroxide tower was added to prevent the discharge of objectionable acidic gases into the laboratory by the vacuum pump. A diagram of the retorting and condensing system is shown in Figure 1, and Figure 2 is a photograph of the apparatus. The system was fluidized by a stream of nitrogen entering the bottom of the retort. Raw shale was fed in a t the side arm in the middle of the retort and discharged through a large-bore stopcock a t the bottom of the retort. H e s t transfer through the glass walls of the retort was too slow t o allow continuous operation except at a very slow rate. Subsequently all runs were
1490
INDUSTRIAL AND ENGINEERING CHEMISTRY
VoI. 44, No. 6
composition occurs under the conditions employed. Per cent of organic removed wm calculated from the ignition loss of t i e retorted shale and checked by the actual loss in weight of the shale during retorting. The data reported as total time in Table I included the time for heating and cooling the bed, and the retort time is the time during which the bed was at the retort. temperature indicated.
W
U
ll
Figure 1. Fluidized Vacuum R e t o r t i n g S y s t e m 1. 2. 3.
4. 5. 6. 7. 8. 9. 10. 11.
12.
Vacuum gage Retort Upper heater Lower heater Receivers Air-cooled condenser Water-cooled condenser Dry ice trap Glass wool filter Sodium hydroxide Vacuum line Nitrogen inlet
batch, in which the charge of shale was heated rapidly t o the desired temperature and maintained at this temperature for a given time. A charge of 73 grams of 28- t o 32-mesh Colorado shale from the Green River formation was used. A maximum temperature limit of 425' C. was imposed t o prevent t,he deformation of the glass apparatus when under vacuum. DATA AND RESULTS
The primary data taken were material balances for each run conbased on the weights of the ran, shale, spentshale, and densed in the various receivers, S e l e c t 4 samples were for sulfur, carbon, and hydrogen; and melting points, densities, molecular weights, and iodine equivalent were taken, The primary data are shown in Table 1. The data reported as per cent condensed oil and per cent organic removed are based on an organic content of 20.5% for the raw shale, The organic contents of the original shale and of retorted shale were determined from a total ignition loss minus mineral carbon dioxide. Loss in weight of the shale due t o decomposition of inorganic carbonates, if such occurs a t the temperatures employed, was not considered in determining the per cent of organic removed, However, it is thought that little or no Ininera1 carbonate de-
Figure 2.
Yacuurn R e t o r t i n g Apparatus
Samples Of spent shale mere extracted for 8 hours in a Soshlct extractor t o determine the soluble material produced by the heating. These data were combined with data on per cent. of the organic material condensed as O i l and per cent Of the organic material removed from the shale t o give a material balance. Data for these material balances are shown in Table 11. Methyl ethyl ketone was the solvent used. The per cent loss includes gas and entrained oil which passed through the system uncondensed, and was determined b' difference. A separat,e series of runs \vas made to determine the effect of temperature and Pressure on the soluble material in the heated shale. The data for 5- and BOO-mm. absolute pressure during retorting a t various t'emperatures are shown in Table 111. -4 comparison between the per cents of organic material removed is also shown in this table. From the data in Tables I and I11 it may h e seen that the lower retorting pressures effect a TABLE I. EFFECTS OF TELIPERATURE A N D PRESSURE OS RETORTING OF OIL SHALEU N D E R VACCUM higher degree of removal of the organic material PresRetort Total Condensed Organic from the shale and result in a higher yield of consure, Time, Time, Tzmp., Oil, Removed, densed oil, other retorting conditions being the Run Mm. Min. Min. C. 70 % 1 5 30 50 330 43.4 51.7 same. This effect is clearly shown by a graph2 5 30 45 350 70.8 80 0 ical representation of the data in Figures 3 and 4. 3 5 15 26 370 71.0 74.2 4 5 30 40 390 83.2 92 4 The data in Table I11 show t h a t the soluble 5 5 5 20 410 88.0 98 5 material in t'he shale decreases to a minimum as 6 5 15 30 330 37.6 42,7 7 5 15 40 350 59.4 68.4 the shale is heated to 300" t o 330" C., and then 8 5 30 45 370 75.2 83.6 Q 25 30 35 330 31.4 44.0 increases for a short interval before again de10 25 30 35 360 56.0 (6.3 creasing a t higher temperatures. The minimum 11 25 30 40 380 69.3 86.0 12 25 30 40 400 73.4 93.3 point appears to occur at a lower temperature a t 13 . 100 30 35 330 22.7 26.5 14 100 30 35 350 35.0 40.0 5-mm. pressure than a t 600-mm. 15 100 30 35 370 53.4 72.2 The oil produced by the vacuum retorting proc16 100 30 40 390 68.0 86.8 17 100 30 40 410 70.0 Q5,G ess was found t o condense in two fractions. A 18 500 30 35 350 30.0 Not determined lQ 500 30 35 370 40.9 N o t determined semisolid mat'erial with a rather sharp melting 20 500 30 40 410 67.5 sot point of 85" to 90" F. was collected in the air21 GOO 30 35 325 Xot determjned 21.7 22 600 30 35 350 Not determined 33.5 cooled condenser, while a light fluid material 23 600 30 40 375 Not determined 61.2 24 600 30 40 400 X o t determined 84.0 and some water were condensed in the dry ice trap. Only a trace of oil condensed in the water-
June 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE11. MATERIALBALANCESBASEDO N TOTALORGANIC CONTENT OF SHALE
Temp.,
Pressure, Mm. 5 5 5 5 5 25 25 100 100
c.
Run 1 2 8 4 5 9 11 13 15
330 350 370 390 410 330 380 330 370
Oil,
Soluble,
Residue,
Loue.
43.3 70.6 75.2 83.2 88.0 31.4 69.3 22.7 53.4
11.2 7.0 5.9 2.5 0.6 10.8 6.0 10.5 7.9
37.1 13.0 10.5 5.1 0.9 45.2 10.0 54.0 19.7
8.3 9.2 8.4 9.2 10.5 12.6 14.7 13.8 20.0
%
%
%
MATERIALI N SHALEA N D REMOVAL OF ORGANIC MATERIAL FROM SHALE Temp.
c.
100
600 Mm., % Removal Soluble Trace 10 9 5 7 2.5 8.3 1.9 1.2 15.0 16.0 Trace 22.0 Nil 34.0 2.8 52.0 5,7 71.5 Trace 87.0 Trace
rapidly with the evolution of gas and the formation of light oil. Crude shale oils produced by other known processes generally yield more than 40% distillate up t o 300" C. a t 40 mm.
%
TABLE 111. EFFECT OF TEMPERATURE AND PRESSURE O N SOLUBLE
1491
10:2
1.5 Trace 11.2 7.0 5,9 2,5 0.6
W
a
w
5 Mm., % Removal Soluble 5.2 6 0
25:4 51.7 80.0 83.6 92.4 98.5
60
c
40
..
3 30
350
370
390
410
RETORT T E M P - D E G
cooled condenser. The heavy oil was found t o have a n average density of 0.94 at 80" F. and a molecular weight of about 400, determined by the freezing point depression in benzene. Based on this molecular weight, the oil was found to absorb 1.2 moles of iodine per mole of oil. Chemical analysis of the oil showed it t o be about 81% carbon, 11% hydrogen, and 0.5% sulfur. This compares very closely with a n analysis of kerogen (organic matter) in Colorado oil shale by the U. S. Bureau of Mines (4)carbon 78.4%, hydrogen 10.4010,sulfur 1.2%,
Figure 4.
C.
Effects of Temperature and Pressure on Oil Produced from Shale
From the iodine absorption and the carbon-hydrogen ratio it is concluded that the heavy oil produced by vacuum retorting at low temperatures is of olefinic and cyclic character. The high initial boiling point may indicate that this oil represents larger fragments of the parent organic material in the oil shale than those obtained by other retorting methods. The cracking and further chemical analysis of this oil will be the subject of further investigations. ACKNOWLEDGMENT
The authors sincerely thank t h e Koppers Co., Pittsburgh,
0
;
>
Pa., for the financial aid that helped make this project possible. The aid of the U. S. Bureau of Mines in providing samples of
80
L
c
oil shale and shale oil is also deeply appreciated.
w 0 L
2
60
LITERATURE CITED
(1) McKee, R. H., and Goodwin, R. T., Colo. School Mines Quart., 18 (No. l ) ,Suppl. A (1923). (2) Nicholson, E. W., Moise, J. E., and Hardy, R. L., IND. ENQ. CHEM.,40,2033-9 (1948). (3) Parent, J. D., et al., Chem. Eng. Progress, 43, 429 (1947). (4) U. S. Bur. Mines, Bull. 415 (1938). (5) U. S. Bur. Mines, Rept. Invest. 4457 (1949). (6) Ibid., 4652 (1950). (7) Ibid., 4744 (1950). (8) Ibid., 4771 (1951).
40
20
RECEIVED for review September 10, 1951.
I 320
340
360
380
400
RETORT T E M P - D E G
C
Figure 3. Effects of Pressure and Temperature on Removal of Organic Material from Oil Shale nitrogen 2.6%, oxygen 6.4%, and ash 1.0%. The oil was soluble in hydrocarbons, alcohols, acetone, ether, methyl ethyl ketone, and benzene. A hard, microcrystalline wax was obtained by crystallization from ether and acetone. The oil was soluble in concentrated sulfuric and phosphoric acids, and was polymerized by dilute acids. Attempts t o fractionate the heavy oil a t 5- t o 10-mm. pressure showed only a trace of distillate at pot temperatures up to 350" to 375" C., and a t this point the oil decomposed
ACCEPTED March 3, 1952.
