TO GAS HOLDER
K
w
tW I 2
8 4 9 7"
1
t CYCLE TIMER
30 :I
METER
DRAIN
WATER
FRESH OIL
1
TO NT
v
7
J
A
5:
v)
LIC l l D PRODUCT
L. P. SEPARATOR
RAW PRODUCT RECYCLE OIL
r
The recycle hydrogenation unit
I
P. L. COTTINGHAM, E. R. WHITE', and C. M. FROST' Petroleum and Oil-Shale Experiment Station, Bureau of Mines, Laramie, Wyo.
Hydrogenating Shale Oil to Catalytic Reforming Stock b
Motor gasoline from ordinary shale oil
b
High temperatures combined with high pressures in hydrogenation produce higher yields of promising quality
UNLESS
SUBJECTEDto thermal cracking during retorting, Colorado shale oils contain little or no gasoline fraction. They have high pour points and viscosities compared with good petroleum crudes, gravities in the range of about 17" to 22' API, sulfur and nitrogen content of nearly 1 and 2010, respectively, and carbon-hydrogen weight ratios of
1 Present address, Bureau of Mines, Grand Forks, N. D.
about 7.0 to 7.5. Their properties when prepared by conventional retorting processes have been reported ( 7 , 4-6, 70-73, 75). Poor yields are obtained in catalytic cracking an< thermal cracking produces gasoline fractions having low octane numbers, high sulfur and nitrogen contents; naphthene contents of less than 10% make them unsatisfactory as charge stocks for new catalytic reforming processes (2, 3, 79). Hydrogenation of Colorado shale oil
produced in the Nevada-Texas-Utah retort has been studied (7, 7 7 , 72) in order to produce synthetic crude oils for refining by ordinary crude oil refining methods. The gasoline fractions obtained had low octane numbers. I n one experiment, a high yield of gasoline having low octane numbers ( 4 ) was obtained by hydrogenating gas-combustion shale oil; this was the only article describing types of hydrocarbons in the gasoline. I n these laboratories, the effect of VOL. 49, NO. 4
APRIL 1957
679
r THERMOWELL
hydrogenation temperature has been investigated a t higher ranges than those used by previous workers. The charge stock was crude shale oil prepared from Colorado shale (Table I) in the gascombustion retort and the catalyst, cobalt molybdate.
I
Apparatus and Operating Procedure Hydrogen from standard shipping cylinders was compressed to 3000 pounds per square inch in two flow-hydrogen storage cylinders and to about 5000 pounds per square inch in hydrogen accumulators. At the beginning of each run, the reaction system was purged with inert gas and filled with hydrogen from the accumulators to a pressure of 3000 pounds per square inch. After oil feed was started, metered water containing sodium chromate corrosion inhibitor was pumped into one of the flow-hydrogen cylinders to displace hydrogen into the reaction system at a known rate. When one cylinder was filled with water, hydrogen was displaced from the second in a similar manner while the first was being drained of water and repressurized from the accumulator vessel. Products from the reactor passed through a cooler-condenser kept at 55” F., into one of two high pressure separatorg placed on stream for alternate 2-hour periods and drained to a low pressure separator at the end of each period. The emptied high pressure separators were repressurized with gas from the accumulator before they were replaced on stream in order to eliminate pressure fluctuations and resultant effects on space velocity. Gas was withdrawn from the high pressure separator a t a rate to keep
Table I. Properties of Colorado Shale Oil Prepared in Gas-Combustion Retort Specific gravity, 60/60 F. API gravity, 60’ F. Pour point, F. Viscosity, S.S.U.at loo3 F. Analysis, wt. % Sulfur Nitrogen Carbon Hydrogen C / H wt. ratio Ash ASTM dist. cor. to 760 mm., O F. I.B.P. Recovery, ’% 5 10 20 50 90
E.P. Total recovery, vol. % Loss, vol. %
680
0.9393 19.2 79 311
ALUNDUM
CATALYST
Figure 1.
The catalyst bed
pressure constant, and was regulated manually by means of a 30 to 1 geared needle valve. Gases dissolved in the oil were separated a t approximately atmospheric pressure and temperature in the low pressure separator from which they were piped to the gas meter. Product oil from each single-pass run was distilled in a batch still. During recycle runs, oil from the separators went to a small continuous still, where the gasoline fraction was removed as the final product. Oil heavier than gasoline was considered as recycle stock in all runs. Arrangement of the catalyst and thermocouples in the reactor is shown in Figure 1. The vessel had an internal
diameter of 1 inch and was 30 inches long, Its top 18 inches were filled with ‘/e-inch Alundum grain and served as a preheater: the lower 12 inches contained 6- to 8-mesh catalyst. Temperatures were measured by thermocouples placed in a stainless steel tube running dorvn the center of the reactor. Additional thermocouples, placed along the outer wall of the reactor, were used hith an automatic controller to regulate current to electric heating elements surrounding the reactor. Figure 2 shows a typical temperature profile for the catalyst bed during a hydrogenation run of the type described previously as “quasi-isothermal” ( 9 ) . The temperature record for each thermo-
920 1
0.67 2.10 84.90 11.32 7.5 0.03
I
273 369 427 548 695
...
I-
+07860 8 0
2
4
6
8
733
DEPTH OF BED, INCHES
70 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 2.
Temperature profile of catalyst
IO
12
H Y D R O G E N I N THE PETROLEUM I N D U S T R Y Table II. Material Balanues and Liquid Product Properties (Single-pass hydrogenation of raw gas-combustion shale oil over cobalt molybdate catalyst: 3000 lb./sq. inch; 1.0 Vo/Vc/hr.; 6000 cu. ft./bbl. Hn feed) Catalyst temp., Av. Max,
O
F. 759 771
784 786
842 845
842 843
889 890
890 892
901 903
979 980
933 934
1010 1012
Recovery, wt. % of feed Synthetic crude Gasoline Recycle oil Gas Catalyst deposit
95.4 15.7 79.7 3.0 0.7
90.9 18.4 72.5 6.1 1.5
93.0 26.2 66.8 4.0 1.0
87.9 26.2 61.7 9.4 1.3
85.8 37.2 48.6 11.7 0.6
84.9 38.3 46.6 12.2 1.1
86.6 39.4 47.2 10.7 0.8
76.3 47.9 28.4 20.9 0.9
62.7 49.4 13.3 34.1 1.1
45.0 38.6 6.4 52.3 1.2
Recovery, vol. % of feed Synthetic crude Gasoline Recycle oil
102.2 19.3 82.9
100.4 22.7 77.7
105.0 32.5 72.5
99.9 32.6 67.3
100.8 46.9 53.9
100.6 48.4 52.2
101.9 49.8 52.1
92.1 61.0 31.1
77.3 63.1 14.2
54.9 48.7 6.2
Properties of liquid product Sp. gr., 60/60° F. Analysis, wt. % Sulfur Nitrogen Hydrogen Carbon C/H ratio
0.8768
0.8467
0.02 0.40 13.51 86.07 6.37
Gasoline properties Sp. gr., 60/60 O F. Sulfur, wt. % Nitrogen, wt. %
0.01 0.25 13.38 86.36 6.45
0.7667 0.02 0.13
0.7612 0.01 0.07
0.8287 0.01 0.13 13.46 86.38 6.42 0.7560 0.01 0.03
0.8266 0.02 0.20 13.64 86.12 6.31 0.7530 0.02 0.03
0.7996 0.02 0.04 13.81 86.13 6.24 0.7458 0.02 0.01
0.7955 0.03 0.02 13.72 86.23 6.29 0.7432 0.02 0.01
0.7986 0.02 0.04 13.84 86.10 6.22 0.7563 0.02 0.01
0.7782 0.02 0.03 13.55 86.40 6.38 0.7465 0.01 0.005
0.7623 0.02 0.04 13.57 86.36 6.36
0.7696 0.03 0.03 13.64 86.30 6.33 0.7465 0.02 0.005
0.7354 0.01 0.005
Hydrocarbons, vol. % Paratiins Naphthenes Olefins Aromatics
55 27 3 15
62 23 2 13
60 21 1 18
62 23 1 14
61 21 1 17
60 25 1 14
59 22 1 18
58 19 1 22
58 16 1 25
55 7 1 37
Octanes Research clear Research 3 ml. TEL
49.8 72.9
47 72
50 74
48 71
51 74
50 74
48 73
55 78
70 84
79 92
123
120
107
111
102
112
102
88
84
189 306 371 393 97.5 1.1 1.4
172 289 367 399 96.8 1 .o 2.2
174 295 375 397 94.2 1.2 4.6
163 279 369 384 94.5 1.0 4.5
158 276 383 394 94.6 1 .o 4.4
176 277 359 387 98.2 1.1 0.7
154 257 361 393 96.2 0.8 3.0
125 222 377 391 91.0 1.2 7.8
127 205
0.8761 0.01 0.30 158" 53a
0.8643 0.01 0.16 15ga 540
0.8568 0.02 0.27 155 52
0.8477 0.02 0.06 168 59
0.8530 0.03 0.03 169 58
0.8472 0.02 0.07 163 58
+
ASTM dist., O F. at 760 mm. I.B.P. 150 Recovery, % 10 50 90
E.P. Rec., vol. % Res., vol. % Loss, vol. %
215 315 380 402 97.5 1 .o 1.5
Recycle-oil properties Sp. gr., 60/60 O F. Sulfur, wt. yo Nitrogen, wt. Aniline point, F. Diesel index (I
0.9026 0.02 0.45
... ...
0.8582 0.02 0.06
... ...
...
387 89.6 1.4 9.0
0.8922 0.07 0.15 132 39
0.9804 0.07 0.13
...
.*.
Determined on 400° to 700° F. gas oil
Table 111. Run temp., F. Analysis, vol. % Methane Ethane Propane Butanes Pentanes Ethylene Propylene Carbon dioxide Carbon monoxide
Gas Analyses from Single-Pass Hydrogenation
759
784
842
842
889
890
901
933
979
1010
33 25 17 8
47 20 7 13 7
54 23 14 5
54 21 13 8 9 .
53 19 11 4 4 6
57 22 12 7
9 .
48 20 13 7 2 2
52 20 16 6 5 1
56 23 10 5 1 1
49 25 17 6 1 1 1
....* . 8 8
.... 6
..
.... 4 e .
4
....
..
.... 8
.*
..3
.. .. .... 2
.... ..
VOL. 49, NO. 4
*.
..4 APRIL 1957
....
681
coupIe in the catalyst section was averaged and then plotted to produce this profile. The area under the resultant curve then was measured with a planimeter and the calculated average temperature was used as the temperature for the run. Experimental
NAPHTHENES
F-1,+3 ML. T E L
r i
I
I
'
I
NITROGEN
i .oo IO0
90
fl 80 W
f
70
-J
9
60
d -I 50 W
7 40 30 20 I O
750
800
850
cATA LY sT Figure 3.
682
900
950
TEMPE R ATU RE,"E
Effects of hydrogenation temperature
INDUSTRIAL AND ENGINEERING CHEMISTRY
1000
T o determine the effect of temperature on yields and types of gasolines that can be prepared, several single-pass hydrogenation runs were made with raiv gas-combustion shale oil over the temperature range of 760" to 1010" F. (Tables I1 and 111). The flow pattern was as shown on page 679, except that no oil was recycled to the reactor. Gasoline fractions of 400" F. end point were separated and their properties were determined. Oil boiling above 400' F. was reported as recycle stock. At temperatures from 760" to about 900" F., composition of the gasoline was fairly constant-in volume per cent about 60% paraffins, 23% naphthenes, 15% aromatics, and 1 or 2% olefins (Figure 3 A ) . !Vhen higher reaction temperatures were used, paraffin content decreased slightly, and naphthene to a greater extent. Aromatic content increased and reached 37% for the gasoline fraction produced at 1010" F. Changes in hydrocarbon types are reflected in the Research octane numbers of the gasolines shown in Figure 3R. Changes in reaction temperature below 900' F. had little effect: the clear octane numbers were in the range 47 to 50, and the octane level with 3 ml. of tetraethyllead per gallon, about 72 to 74. Both increased greatlv when reaction temperatures above 900" F. were used. Research octane numbers of 79.0 clear and 92.4 with 3 ml. of tetraethyllead per gallon were obtained at 1010" F. This leaded octane rating wouId be satisfactory for many automobiles. The greatly increased octane numbers produced at higher temperatures correspond to increased quantities of aromatic hydrocarbons contained in these gasolines. Aromatics are formed in lieu of naphthenes that otherwise would be present in the gasoline (Figure 3A). Although reactions producing these aromatics do not necessarily involve naphthenes as a n intermediate step, undoubtedly a portion of them are formed from naphthenes by reforming-type reactions. This suggests that reforming gasolines produced a t lower temperatures would result in much improved octane ratings. The influence of hydrogenation temperature on sulfur and nitrogen content of the gasoline is shown in Figure 3C. Sulfur content was low-about 0.01 to Os0270 for all gasolines-but nitrogen content was highest (0.1 3y0)in the sample produced a t 760" F. I t decreased,
HYDROGEN IN THE PETROLEUM INDUSTRY Table IV. Conditions and Material Balance for Recycle Hydrogenation to Produce Reforming Stock Operating conditions Catalyst temp,, F. Av.
MS.
Pressure, lb./sq. in. H2 rate, cu. ft./bbl. total feed4 HZ consumed, cu. ft./bbl. fresh feeda Throughput, Vo/Vc Space velocity, Vo/Ve/hr. Recycle/fresh feed ratio
Recovery, yo of fresh feed Gasoline Recycle oil Gas Catalyst deposit C4 plus CS from gas C4-plus gasoline
902 908 3000 6000
2200 547 1.48 0.99
Vol.
Wt.
%
%
90.8 4.0
72.4 3.7 21.9 0.02 5.2 77.6
... ... 8.3
99.1
At 60° F. and 760 mm.
as operating temperature was increased, to O.Olyo in the gasoline obtained a t 890' .F. and remained below this percentage in the higher temperature products. Yields of total liquid product and 400" F. end point gasoline are shown in Figure 30. Maximum liquid yield was obtained at about 840" F., but little change occurred over operating temperatures of 760" to 900" F. where yield of total liquid exceeded 100% by volume. When operating temperatures were raised above 900" F., however, liquid yields decreased rapidly as the result of the greatly increased extent of cracking to gas. Quantity of gasoline produced increased with increased cracking to a maximum of 65y0 a t a temperature of about 960' F. At higher temperatures, gasoline yield decreased. The data plotted in Figure 3 0 include only the liquid product and its gasoline fraction that were recovered in the hydrogenation receiver with a water-cooled condenser operated a t 55 F. T h e addition of C4 and C S material from the gas would increase the yields shown about 0.5 to 470 in the range of 760" to 900" F., and to a greater extent a t higher temperatures. Some of this material could be blended into gasolines obtained below 900" F., but volatility of the gasolines from the higher temperature runs was such that this could not be done without exceeding vapor pressure requirements. T h e results of these single-pass experiments show that gasoline with low sulfur and nitrogen content and with good octane number can be obtained by hydrogenation a t very high
temperature. The yield of gasoline a t 1010' F. was approximately 49% by volume-about the same as the best yields reported for recycle thermal cracking of crude shale oil (79). However, the 92.4 leaded Research octane number and the negligible sulfur and nitrogen content of the hydrogenated gasoline are much better than those reported (87.3 octane, 0.72% sulfur, and 1.10% nitrogen) for the thermally cracked gasoline. Gasoline obtained a t the maximum yield for single-pass hydrogenation of 65% by volume would have a leaded Research octane rating of about 82 (Figures 3B and 0). Although gasoline produced by high temperature hydrogenation is of good quality, better yields are desirable. Although hydrocarbon analyses of gasolines from lower temperature runs indicate that their octane numbers may be improved by reforming, low nitrogen content is preferable in gasoline for catalytic reforming. Considering nitrogen content and total liquid recovery, it appears that gasoline used as reforming stock is best prepared a t a temperature of about 900" F. Singlepass gasoline yield a t this temperature was not maximum, but recycle hydrogenation offers a means for converting the liquid product entirely into gasoline. Hydrogenated gasoline for laboratory reforming studies was prepared by hydrogenating gas-combustion crude in a recycle run at 902' F. and 3000 pounds per square inch (Figure 2 and Table IV). At the start of this run, the initial portion of fresh feed was mixed with a n equal quantity of recycle stock from a preceding single-pass run made at similar conditions. This stock was replaced with recycle oil from the recycle run as soon as it became available. Oil boiling above the gasoline range was used as recycle stock, and the recycle ratio of 1 to 1 used a t the start of the run permitted consumption of nearly all this stock as rapidly as it was separated from the gasoline in the still. The final material balance showed an average recycle ratio of 0.99 to 1 and an accumulation of only 4.0'% by volume of the fresh feed as recycle stock. This remaining recycle oil could have been converted to gasoline by a different adjustment of the recycle ratio. T o decrease the operating time required for producing sufficient hydrogenated gasoline for laboratory purposes, space velocity was increased from 1.0 volume of oil per volume of catalyst per hour, used for the single-pass runs, to 1.48 for the recycle run. Total operating time was 370 hours, and total throughput was 547 volumes of oil per volume of catalyst. Carbon deposit on the catalyst was only 0.02% by weight
of the fresh feed or 7.1'% of the fresh catalyst weight. There was no noticeable loss in catalyst activity during the run and the operation could have been continued much longer before a shutdown for regeneration would have been necessary. Hydrogen consumption was high (2200 cubic feet per barrel), as expected during destructive hydrogenation to gasoline. Yields per pass based on total feed were 45.7% by volume gasoline and 51.7% recycle oil for a total liquid yield of 97.470-not greatly different from the yields for the single-pass operation with fresh feed at 1.0 space velocity and 900" F. shown in Figure 3 0 . Gasoline yield on the fresh-feed basis was 90.870 by volume. Addition of Cb - Cg fractions from the gas would increase this to 99.1% and total yield including accumulated recycle oil, to 103.1%. Properties of the gasoline and recycle oil are given in Table v. For comparison, properties of a typical gasoline produced by recycle thermal cracking of crude shale oil at 920" F. are shown also. The hydrogenated gasoline was intentionally cut to a high end point to permit greater flexibility in future reforming studies; but other properties show even more striking differences from the thermally cracked gasoline. Sulfur content of the hydrogenated gasoline is low, and nitrogen was almost eliminated. Gum content, which relates to certain types of nitrogen compounds (74,76-78) and would be an important factor in a catalytic reforming stock, also is low. Octane numbers of the hydrogenated gasoline are lower than those of the thermally cracked gasoline. The types of hydrocarbons in the two gasolines are considerably different. I n the hydrogenated sample, most of the olefins are eliminated and paraffins and naphthenes are formed ; naphthene content, more than five times as great as that of the thermally cracked gasoline, would be of considerable advantage for reforming purposes. Catalytic reforming studies are being conducted to determine whether hydrogenated stock can be upgraded satisfactorily for use as motor fuel. Gas analysis for the hydrogenation run is shown in Table V I . Two thirds of the gas consists of methane and ethane, with methane predominating. Most of the Cd - Cg fraction consists of butane.
Summary
'\
Gasolines having higher octane numbers than any previously reported from ordinary Colorado shale oil were obtained using high temperatures during hydrogenation of gas-combustion crude a t 3000 VOL. 49, NO. 4
APRIL 1957
683
Table V.
Properties of Products from Processing to Reforming Stock HydroThermally Recycle Cracked genated Gasoline Gasoline Oil
Sp. gr., 60/60" F. API gravity, 60" F. Aniline point, ' F. Diesel index Sulfur, wt. % Nitrogen, wt. 70 Gum,ASTM, mg./100 ml. Reid vapor pressure, lb./sq. in. Hydrocarbons in neutral oil, vol. % ' Paraffins Naphthenes Olefins Aromatics Octane number F-2 clear F-1 clear F-1 3 ml. TEL ASTM dist. cor. to 760 mm., ' F. I.B.P. Recovery, % 5 10 20 50 90 E.P. Total, vol. yo Loss, vol. %
0.7468 58.0
... ...
0.06 0.01 2.0 9.6
49 22 6 23 51 54 76
+
pounds pressure. Single-pass hydrogenation at 1010" F. produced gasoline in yields approximating the best reported for recycle thermal cracking of crude shale oil; the hydrogenated gasoline had better octane numbers and low sulfur and nitrogen content. The influence of hydrogenation temperature on yields and properties for single-pass operation in the range of 7 6 0 " to 1010" F. was studied. Temperature changes below 900" F., ordinarily used for high pressure hydrogenation, have little effect on octane numbers and hydrocarbon types; above 900" F., however, higher reaction temperature produces higher octane gasoline. Classes of hydrocarbons contained in the gasoline were determined for the entire temperature range; the relatively high octanes obtained in this work are attributed to the increased percentages of aromatics formed in place of naphthenes at high temperatures. Sulfur content was low for all gasolines, but nitrogen content was highest in the gasoline produced a t the lowest tem-
Table VI.
a
Methane Ethane Propane Butane Pentane Ethylene Pentene Carbon dioxide At 60' F. and 760 mm.
684
0.8669 31.7 136 42.9 0.06 0.08
...
... ... ... ... . . I
... I..
..
t
0.7732 51.5
..*
...
0.61 0.86 60 8.6 32 4 45 19 68 76 84
115
402
107
135 158 195 278 410 446 93.2 5.7
428 436 456 519 Foaming
140 157 198 277 370 405 96.0 3.0
...
71.0
0.0
perature. Nitrogen content decreased with increased reaction temperature up to 900" F., and it remained below 0.01% at higher temperatures. As operating temperature was raised, gasoline yield increased to a maximum of about 65% a t 960' F. At higher temperatures, it decreased. Yield of total liquid product exceeded 1OOyo by volume below 900' F., but decreased rapidly a t higher temperatures. High octane numbers of the aromatic gasolines suggest that conversion of naphthenes to aromatics by reforming the gasolines produced at low temperatures may be advantageous. It is concluded that a hydrogenation temperature of about 900" F. would give the best balance of liquid yield and gasoline properties for producing a reformer feed stock. Laboratory supplies of such stock were made by hydrogenating crude shale oil a t that temperature and 3000 pounds pressure. Recycle operation was used to convert the liquid product to gasoline as the chief product, and a
G a s Analysis for Recycle Hydrogenation Fresh Fresh Mole Feed, Feed, % Vol. % Wt. 7 0 43.8 23.7
1.1 0.9 1.1
INDUSTRIAL AND ENGINEERING CHEMISTRY
.. .. . I
0.7
..
5.1 5.1 5.9
3.7 1.0 0.2 0.5 0.4
Fresh Feed, SCF/BbLa 396 2 14 167 81 18 10 8 10
yield of 99% by volume of C4-plus gasoline was obtained. Sulfur and nitrogen content were low and naphthene content was several times as great as that of thermally cracked gasoline. Coke yield was low, and long operating periods between catalyst regenerations are probable.
Acknowledgment This project, part of the synthetic liquid fuels program of the Bureau of Mines, was performed at the Petroleum and Oil-Shale Experiment Station, Laramie, Wyo., under the general direction of H. P. Rue and H. M. Thorne and the immediate supervision of W. I. R . Murphy. The valuable assistance of H. C. Carpenter, C.B. Hopkins, and G. C. Freeman, also of the bureau, is acknowledged.
Literature Cited (1) Ball, J. S., Industry-Bureau of Mines Oil-Shale Conference, Univ. of Wyoming Science Camp, Laramie. Wyo., August 1954; minutes of conference, Bur. Mines Admin, Publ., p. 47. ( 2 ) Ball, J. S., Dinneen, G. U., Smith, J. R., Bailey, C. W., Van Meter, R., IND. ENG. CHEY. 41, 581 ( 1 949). ( 3 ) Cottingham, P. L., Antweiler, J. C., Mayfield, L. E., Kelley, R . E., Coker, W. P., Ibid., 48, 1146 ( 1 956). ( 4 ) Crecelius, R. L., Kindschy, E. O., White, E. R.? Cottingham, P. L., Murphy, W. I. R.: Petroleum Re,finer 35, 90.6, 171 (1956). ( 5 ) Dinneen. G. U.: Petroleum Rejner 33, No. 2, 113 (1954). ( 6 ) Dinneen. G. U.: Ball, J. S., Thorne, H. M., IND.ENG.CHEM.44, 2632 (1952). ( 7 ) Hoog? H., Koome, J., Weeda, K. A., "Oil Shale and Cannel Coal," vol. 2 , p. 562, Institute of Petroleum, London. 1951. ( 8 ) Lankford,'J. D.? Ellis, C. F., IND. ENG.CHEM.43, 27 (1951). ( 9 ) Malloy, J. B., Seelig, H. S., A.2.Ch.E. J. 1, 528 (1955). ( 1 0 ) Murphy, W. I. R., Industry-Bureau of Mines Oil-Shale Conference. Univ. of Wyoming Science Camp, Laramie, Wyo., August 1954; minutes of conference, Bur. Mines Admin. Publ., p. 111. Pelipetz, M. G., Wolfson, M. L., Ginsberg, H., Clark, E. L., Chem. Eng. Progr. 48, 353 (1952). Smith, W. M., Landrum, T. C., Phillips, G. E., IND.ENG. CHEM. 44, 586 (1952). Stanfield, K. E., Thorne, H. M., Ibid.,43, 16 (1951). Thompson, R. B., Chenicek, J. A., Druge, L. W., Symon, Ted, Ibid., 43, 935 (1951). Thorne, H . M., Murphy, W. I. R., Ball, J. S.. Stanfield, K. E., Horne, J. W.. Zbid.,43, 20 (1951). U. S. Bur. Mines Rept. Invest. 4457, pp. 49-50, 1948. Ibid., 4652, p. 63, 1949. Ibid.,4771, p. 81. 1950. Ibid., 4866, pp. 31, 68, 1951.
RECEIVED for review July 28, 1956 ACCEPTED February 18, 1957
