E
5
R
FLOW CONTROL VALVE
ALUMINUM BLOCK NICHROME WINDING
1
SUPEREX INSULATION
HE RM O W E L L
CATALYST TUBE ALUM IN UM BLOCK NIC HROME WINDING
TO
GAS HOLDER
I HYDROGEN ER
i
HIGH-PRESSU
LOW-PRESSU -CRACKED
ICE
LIQUID PRODUCT
Figure 1.
Flow diagram of hydrofining unit
Hydrofining Thermally Cracked Shale=Oil Naphtha L. G. MAYFIELD5 R. E. KELLERB, AND W. P. Sfation, U. S. Bureau o f Mines, Lararnie, Wyo.
P. L. COTTINGHAM, J. C. ANTWEILER', Petroleum and Oil-Shale Experiment
M
ATERIALS in the gasoline boiling range can be produced
in good yields from shale oils by thermal cracking. but these thermally cracked naphthas contain approximately lOOj0 sulfur, nitrogen, and oxygen compounds (W)in addition to quantities of other constituents such as diolefins which contribute to gum formation and poor stability characteristics. Bny of several recently described (6-10) petroleum-hydrogenation processes operating in the temperature range 700" to 800' F. a t pressures of 400 t o 1000 pounds per square inch probably would remove most of these undesirable materials, but these processes have in I 2
4
Present Present Present Present
1146
address, address, address, address,
Geological Survey, Denver, Colo. Montana State College, Boseman, hlont.
Bay Petroleum Co., Denver, Colo. Dow Chemlcal Co., Freeport, Tzx.
COKER
common the disadvantage of hydrogenat'ing t,he monoolpfins in the charge stock d h attendant octane loss. Hydrogenating rav- shale naphtha at temperatures below 800" F., with pressure kept below 200 pounds per square inch t o avoid saturation of monoolefins, in a manner similar t o that described by Cassglandt: and others (5), has been unsuccessful in removing the gum-forming materials. Likewise, fixed-bed hydroforming a t this low pressure with more elevated temperatures has failed t o improve stability t o the extent desired but has improved octane characteristics. Studies have therefore been made of hydrogenating or "hj-drofining" raw shale-oil naphthas a t pressures of 400 t o 800 pounds per square inch to eliminate most of the objectionable ma.terials but with temperatures in the reforming-temperature range of
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 48, No. 7
SYNTHETIC FUELS AND CHEMICALS
Table I.
Properties of Naphthas from Thermal Cracking o f N-T-U Crude Raw Naphtha
Light Naphtha'
Heavy Naphtha
100.0 51.9
47.6 68.5
52.4 38.7
99 167 288 375 400 0.71 0.99 1.2 7.2 1499 0.3
96 135 186 233 261 0.26 0.17
265 315 340 391 417 1.06 1.64 1.8 8.7 5034 0.25
Raw naphtha, vol. yo API gravity, 60' F. ASTM distn., O F. at 760 mm. I.B.P. 10% rec. 50% rec. 90% rec. E.P. Sulfur, wt. yo Nitrogen, wt. yo Tar acids, vol. yo Tar bases, vol. % Gum, Cu dish, mg./100 ml." Induction period, hoursC
0. 6b
2.2 10 8.0
Hydrocarbons, vol. % of neutral oil Paraffins Naphthenes Olefins Aromatics
29 6 47 18
34 8 52 6
29 6
Octane numbers F-2, clear F-2, 3 ml. TEL F-1, clear F-1, 3 ml. TEL
65 73 75 81
70 77 79 88
66 72 73 79
+ +
a
37 28
Washed with equal volume of 10% $odium hydroxide solution.
* Tar acids determined on raw sample.
Inhibited with 0.01 wt. % of U.O.P. No. 5 .
900' t o 1050' F.,in order t h a t the loss in olefins may be partly counteracted b y formation of aromatics. Results of hydrofining raw naphthas of full boiling range and heavy naphthas from thermally cracked shale oil are presented in this paper.
Apparatus and Procedure As shown by a simplified diagram in Figure 1, the reactor was the fixed-bed type, equipped for downward flow, with an internal diameter of 1.25 inches and a length of 47.5 inches. Total volume was 950 cc., but a catalyst charge of only 200 cc. was used, the catalyst being centered in the reactor and the space above and below it filled with Alundum grain. Catalyst crushed t o 4t o &mesh size was measured in a graduate that was tapped by hand t o ensure uniform packing and was weighed before it was charged t o the reactor. Oil and hydrogen were preheated in a downflow chamber packed with l/l-inch Alundum grain mounted above the reactor. The preheater, reactor, condenser, receiver system, and automatic back-pressure regulator were constructed of stainless steel, and stainless steel tubing was used t o make all connections. At the start of a run the system was pressurized three times with helium t o approximately 100 pounds per square inch and vented t o the atmosphere t o purge it of air, after which it was brought t o operating pressure with hydrogen. Naphtha feed was transferred from a water-cooled charge tank to a buret for metering before being pumped by a piston-type pump t o the preheater, where it was mixed with hydrogen obtained from standard shipping cylinders and metered through a rotameter. Product oil was continuously drained from the unit t o maintain a nearly constant low level in the high-pressure receiver and prevent changes in the fluid velocity in the reactor. Outlet gases were reduced t o atmospheric pressure, metered through a July 1956
positive-displacement dry meter, and stored in a gas holder from which samples were taken for mass-spectrometer analyses. Hydrogen consumption was calculated from gas-volume measurements, and catalyst deposits were determined from the gain in weight of the used catalyst, which was removed from the unit and cooled in a closed container before being weighed. Processing periods were usually 4 t o 8 hours long. Over 15 volumes of naphtha per volume of catalyst were processed in each run, but runs of 24 hours or longer were made a t those conditions t h a t appeared t o be most favorable.
Feed Stocks and Catalyst Several naphthas prepared by recycle thermal cracking of N-T-U shale oil were used in the catalytic hydrofining work described in this paper. Although differences in conditions under which the naphthas were produced caused some small differences in properties, the raw naphtha described in Table I is typical. I t s low volatility is shown by the 50% boiling point of 288' F., which compares with a national average of 221" F. for premium-grade gasolines and 230' F. for regular-grade gasolines sold during the summer of 1954 ( 3 ) . The sulfur content, higher than desirable in motor gasolines, consists largely of thiophenic-type compounds. I n such high percentage it causes a serious loss in tetraethyllead susceptibility, even though thiophenic compounds are not as harmful to this property as most other sulfur compounds. Nitrogen compounds, present largely as tar bases, contribute t o the high gum content, which in this instance amounts t o 1.5 grams per 100 ml. of naphtha by the copper-dish method. The very poor stability is shown by the induction period of only 0.3 hour. Analyses of 5% fractions from the distillation of raw thermally cracked shale-oil naphtha, such as t h a t described in Table I, show t h a t the fractions boiling below 260" F. (approximately 40 t o 50 volume yo of the naphtha) contain relatively little sulfur and nitrogen and have low gum contents and good octane ratings; being highly olefinic, they have good sensitivity. This portion of the naphtha can be separated and treated b y washing with dilute caustic solution t o produce doctor-sweet, stable blending stock, leaving only the high-boiling fraction for hydrofining. Properties of a light naphtha prepared from this low-boiling fraction by treating with 10% sodium hydroxide solution in five washes, each equivalent t o 20% by volume of the light naphtha, are shown in Table I. Also shown are properties of the corresponding heavy naphtha in which the content of sulfur, nitrogen, and gum is much greater than that of the whole naphtha. I n this fraction the copper-dish gum content has increased, partly as the result of thermal treatment during distillation, to over 5 grams per 100 ml. of heavy naphtha. I n addition to the hydrofining experiments with raw naphtha, a number of experiments were made with heavy naphtha as feed stock to prepare hydrofined naphtha suitable for blending with the light naphtha to make finished gasoline. Although several catalysts were investigated for use in hydrofining shale-oil naphtha, results given in this paper are those obtained with coprecipitated cobalt molybdate catalyst of the general type studied by Byrnes, Bradley, and Lee ( 4 ) .
Variables of Hydrofining Temperature. Previous experiments in the hydrogenation of shale-oil fractions over cobalt molybdate catalyst showed that, at temperatures below 900" F. with pressures of 500 t o 1000 pounds per square inch and space velocities of 2 or less, lowsulfur, stable products could be produced ( 1 ) . Gasolines obtained under these conditions, however, contained a predominance of normal paraffinic hydrocarbons, few olefins, and only a small percentage of aromatics and had low octane ratings and poor sensitivities.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1147
-
Results of studies of hydrofinmg raw shale-oil naphtha a t temperatures above 900' F. to improve octane number and stability and to reduce sulfur content are shown in Table 11, which includes for comparison the results from a run a t 836" F. The yield of 400' F. end point gasoline decreased from 95.4 volume yo a t 836" F. to 84.37, a t 1001" F., and the total liquid yield also decreased, showing the influence of higher temperature in causing greater gas formation. Polymer yield, which varied only from 1.9 t o 2.47,, apparently was not affected by operating temperature. Sulfur removal was good a t all temperatures93 t o 99% of the sulfur being eliminated in these runs-but 27 to 357, of the nitrogen was left in the gasoline. Oxidation stability appeared to be very good for all products, iis ehonn by the induction periods of over 24 hours, but copper-dish gum content increased with increase in operating temperature, indicating less hydrogenation a t the higher temperatures. The change in the character of the predominating reaction mechanisms between 836' and 1001" F. is evident from the decrease in content of saturated hydrocarbons in the products from the higher operating temperatures and the increase in aromatic content.
400P.S.I., 5.0 L.H.S.V.,
.
I V
375 IOOC 1025 REACTION TEMPERATURE,'F.
925
I050
950
Figure 2.
Effect of temperature on yield in hydrofining heavy naphtha
Table II.
Effect of Temperature in Hydrofining Raw ShaleOil Naphtha Pressure, lb./sq. inch Space velocity, Vo/V,/hr. HZrate, cu. feet/bbl.
P. Feed H1 consumed, cu. f e e t / bbl. 400' F. gasoline yield, vol. 70 Polymer, vol. yo Gasoline properties Sulfur, wt. % 0.71 Nitrogen, wt. yo 0.99 Gum, Cu dish, mg./ 100 ml." 1499 Induction period (raw), hours 0.3 Hydrocarbons, vol. 7o of neutral oil Paraffins 29' Temperature,
IO0
CT w m I
90
=3
z w z I4 -
u
80
0
:H
70
I
300 r-z w L
2000 SCF/BBL. H2
925 Figure 3.
1148
1-
400 F! S.I,, 5.0 L.H.S.V.,
950 975 1000 REACTION TEMPERATURE,
1025
"E
Effect of temperature on properties in hydrofining heavy naphtha
1050
Naphthenes Olefins Aromatics Octane n u m b e r s F-2, clear F-2, 3 ml. T E L F-1, clear F-1, 3 ml. T E L
+ +
a
400 5.0 2000 836
95.4 2.0
90.8 2.3
0.04
...
0.03 0.27
...
6.4
24+
1
75J
18
17
65
52 68 55 73
81
979
780
6 j 47
73 75
949
8
24+
86.7
1.9 0.01 0.35
1001 890 84.3 2.4 0.02 0.35
23.8
57.4
24+
24+
65
56
0
79 1 20
6 29
2 7 35
64 78
65
68
81
82
65 82
70
75
86
89
Inhibited with 0.01 wt. yo of U.O.P. No. 5.
Decreasing the sulfur content and changing the hydrocarbon composition improved the tetraethyllead suceptibility of all four products. Thus, the 836" F. product, in which most of the olefins have been converted t o saturates with little change in aromatic content, has poorer octane ratings and sensitivity but better tetraethyllead susceptibility than the raw feed stock; but the 1001" F. product, in which both saturated-hydrocarbon and aromatic contents have been increased, has not only higher octane ratings and better tetraethyllead susceptibility than the feed but also sensitivity about equal to that of the feed. The effects of temperature in hydrofining heavy naphtha were investigated over the range 930' t o 1045" F. a t 400 pounds per square inch and 5.0 L.H.S.V., and results meie similar to those obtained with the whole naphtha. Liquid-product yield, shown in Figure 2, waF slightly better than for the whole naphtha, but
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 48, No. 7
SYNTHETIC FUELS AND CHEMICALS it decreased rapidly with increase in reaction temperature through the range studied. Motor- and research-method octane ratings, with 3 ml. of tetraethyllead per gallon, shown in Figure 3, were better than those of the feed throughout the temperature range studied, and sensitivity of the leaded fuel increased with increasing temperature. Gum content, determined by the copper-dish method, was higher for the hydrofined heavy naphthas than for hydrofined whole naphthas prepared under similar conditions and, as shown by Figure 3, increased from 33 mg. per 100 ml. in the sample hydrofined a t 930' F. to 350 mg. per 100 ml. in the sample hydrofined a t 1045" F. Pressure. Table I11 shows results from hydrofining raw shale-oil naphtha a t pressures of 200, 400, and 800 pounds per square inch and illustrates the changes in degree of hydrogenation reactions that are obtained by use of different pressures. Liquid yield did not show any appreciable change with increase of pressure, but hydrogen consumption and oxidation stability of the product increased and sulfur, nitrogen, tar-acid and tar-base content, and copper-dish gum content of the product decreased. Hydrocarbon composition and octane numbers also show the effect of greater hydrogenation a t the higher pressures. Although the gasoline prepared a t 800 pounds per square inch was the most stable of the three, that prepared by hydrofining at 400 pounds per square inch was stable enough to be acceptable for most motor-fuel purposes.
IO0 00
95OL96O%, 50 LHS.V., 2000 SCF/flBL. H2
c--
O t
I
Table 111.
Temperature, F. Space velocity, Ti,/ Vc/hr. HZrate, cu. feet/bbl. Pressure, lb./sq. inch Temperature, O F. HS consumed, cu. feet/bbl. 400' F. gasoline yield, vol. % Polymer, vol. % Gasoline properties Sulfur, wt. % Nitrogen, wt. % Tar acids, vol. % Tar bases, vol. % Gum, Cu dish, mg./100 ml.= Induction period (raw), hours Hydrocarbons, vol. % of neutral oil Para5ns Naphthenes Olefins Aromatics Octane numbers F-2, clear F-2, + 3 ml. TEL F-1, clear F-1, + 3 ml. TEL
200
400
800
945 320 88.8 2.6
96 1 760 89.7 2.6
958 910 87.0 4.1
0.04 0.54 0.8 5.8 53.8 2b
0.02 0.38 1.0 4.6 25.5 24 f
0.01 0.27 0.1 3.3 16.8 24
55 8 11 26
64 8 25
71 2 5 22
63 '78 70 84
62 78 68 84
60 80 65 83
3
I
I
800
Effect of pressure on properties in hydrofining heavy naphtha
Figure 4.
945-960 5.0 2000
I
I
400 600 PRESSURE, !? S.I.
200
Effect of Pressure in Hydrofining Raw Shale-Oil Naphtha
+
2o
Inhibited with 0.01 wt. % of U.O.P. No. 5. Increased to 8 hours with 0.01 wt. % of U.O.P. No. 5.
t
970'-985' F. 400 F! S.I,., 2000 S ~ F / B B L .H, I
-
200 Hydrofining heavy shale-oil naphtha at pressures of 200, 400, 600, and 800 pounds per square inch produced results that accorded with those obtained in hydrofining whole naphtha. Figure 4,which presents some of these results, shows the increased elimination of sulfur and nitrogen and the decreased copper-dish gum content of the heavy naphtha obtained through using higher pressure. Space Velocity. Space velocities from 2.5 t o 15.0 volumes of oil per volume of catalyst per hour were studied with heavy July 1956
~~~
IO0 OO
COPPER-DISH GUM
-
-
2
4
6
8
IO
12
14
16
SPACE VELOCITY, Vo /Vc /HOUR Figure
5.
Effect of space velocity on properties in hydrofining heavy naphtha
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
1149
1 I
cn-
54 zz
+40
I
970'985'F;,
I
I
I
1
1
1-1 Table
40OFS.l., 2 0 0 0 S C F / BBL. H2
IV.
Final Products from Hydrofining Whole Naphtha and Heavy Naphtha Heavy Naphtha Whole Hydrofined Blend Naphtha
Operating conditions Temperature, O F. Pressure, lb./sq. inch H2 rate, cu. feet/bbl. reactor charge H 2 consumed, cu. feet/bbl. whole naphtha Space velocity, V,/V,/hr. Yields Gasoline, vol. 70 10-lb. R.v.p. gasoline, vol. 70 C4+ in gas, vol. % ' Polymer, vol. % Gas, wt. % Cat. deposit, wt. of reactor feed Gasoline properties A P I gravity, 60' F. Sulfur, wt. yo Nitrogen, wt. 7' Gum, Cu dish, mg./100 mLc Induction period, hoursc ASTM distn., O F . at 760 mm. I.B.P. 1 0 ~rec. c SOYo rec. 90% rec.
E.P.
\
Hydrocarbons, vol. Paraffins Naphthenes Olefins Aromatics
t5
-5
Figure 6.
I
0
I I I 'I I 1 2 4 6 8 10 12 14 SPACE VELOCITY, Vo/Vc/ HOUR I
I 16
Effect of space velocity on properties in hydrofining heavy naphtha
shale-oil naphtha feed stock a t a pressure of 400 pounds per square inch and temperatures in the range 970' to 955' F. Figure 5 shows the effects of different space velocities on percentages of original sulfur and nitrogen eliminated and on the copper-dish gum content of the hydrofined heavy naphtha; it illustrates the desirability of opprating at spare velorities in the lower part of the range studied to obtain low sulfur and gum content in the pi oduc ts. Changes in the types of hydrocarbons and in octane ratings resulting from different space velocities are shown in Figure 6. The heavy naphtha feed stock for these experiments contained 4370 olefins, and a t a space velocity of 2 5 nearly all of these were converted to eaturates and aromatics. At higher space velocities, less change in types of hydrocarbons occurred. Very little change in clear motor-method or research-method octane numbers occurred a t the conditions used for the spacevelocity study, but examination of the data on effects of temperatures shoms that a different choice of operating temperatures for this study would have produced different results because of greater aromatization a t higher temperatures or greater hydrogenation of olefins a t lower temperatures. Increases in leaded octane ratings, showing increased tetraethyllead susceptibility, are greatest a t the lomer space velocities, at which the largest increases in saturated hydiocai bons and best d f u i elimination occurred. 1150
Octane numbers F-2, clear F-2, 3 ml. TEL F-1, clear F-1, 3 ml, TEL 10-lb. R.v,p., F-2 10-lb. R.v.p., F-l
+ +
a
70of
957 800 3000
969 800 3000
690 7.5 88.7 2.1 4.1
8.6 0.1 51.5 0.02 0.56 16.4 24+
930 7.5 I
b
93.0 93.9 1.3 2.5 5.7 0.1
86.2 91.7 5.2 2.8 11.0 0.1
60.6 0.10 0.35 22.4 24+
55.7 0.03 0.24 11.0 244-
117 199 289 354 379
108 138 223 338 374
117 164 263 358 383
62 3 5 30
46 7 28 19
76 0 3 21
61 77 67 83
67 77 75 86 78 87
61 80 66
neutral oil
+ 3 ml. TEL + 3 ml. TEL
85 83 87
Yields expressed a s 7cof heavy naphtha charge to reactor. a s % of original whole naphtha. Inhibited with 0.01 wt. % of U.O.P. No. 5.
* Yields expressed c
lOOO[
100 -
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 48, No. 7
Figure 7 shows the variation in hydrogen consumption with change in space velocity and substantiates the results of Figures 5 and 6, which indicate that the greatest degree of hydrogenation occurs at the lowest space velocity investigated. Hydrogen Rate. Because hydrogen flow rates of 2000 cubic feet per barrel were found to produce stable gasolines with low gum content, the other variables were investigated with this hydrogen rate. However, higher hydrogen rates, in the range of 3000 to 4000 cubic feet per barrel, were found to be advantageous in reducing the gum content of the products and catalyst deposits during long runs a t the lower space velocities. At space velocities of 10 and more, hydrogen rates exceeding 3000 cubic feet per barrel produced no added improvement but caused the products to be less stable than those obtained a t low hydrogen rates, probably because of high velocity in the reactor. Physical limitations of the apparatus prevented a satisfactory study of high hydrogen rates a t these higher space velocities.
Preparation of Gasolines Table I V compares the yields and properties of gasoline obtained by hydrofining raw whole shale-oil naphtha with those of gasoline prepared by hydrofining heavy naphtha and blending the hydrofined heavy product with caystic-washed light naphtha. Operating conditions for each run were 800 pounds per square inch, 7.5 L.H.S.V., and 3000 standard cubic feet of hydrogen per bbl., but the temperature of the run with whole naphtha was 969' F. compared with 957' F. for the run with heavy naphtha. This difference, however, is not considered to be great enough to affect the results significantly. The heavy-naphtha feed and the light-naphtha blending stock were separated by distillation of a 400" F. end-point naphtha in the refinery of the Bureau of Mines Oil-Shale Experiment Station a t Rifle, Colo. The light naphtha (38 volume yo of the original naphtha) was washed with 10% caustic solution in a continuous treating unit a t the refinery. Properties of the fractions were similar to those given in Table I. The hydrofined heavy naphtha and the treated light naphtha were combined in proportions corresponding to the percentages in the original naphtha in order to make the final blend shown in Table IV. Hydrogen consumption for hydrofining the heavy naphtha, when expressed on the basis of original whole naphtha, was only about three fourths that required for hydrofining the whole naphtha; but product yield on the basis of charge to the reactor was better for the heavy naphtha than for the whole naphtha, and yield data are obviously even more favorable for the heavy naphtha run when calculated for the blended gasoline. The volumetric advantage of the blend was not as great when results were calculated to the 10-pound R.v.p. basis because of the greater volatility and higher vapor pressure of the blend gasoline, which required less butane for vapor-pressure adjustment than did the hydrofined whole naphtha. The quantity of C4+ material in the gas from each run was sufficient t o permit blending the gasolines to 10-pound R.v.P. without the use of butane from extrrnal sources. The hydrofined whole naphtha had lower sulfur and gum content than the blend, because the content of these materials in the light-naphtha blending stock was greater than in the hydrofined naphthas. The light naphtha used here had a copper-dish gum content of 32.3 mg. per 100 ml., part of which may be attributed to the use of the treating equipment on an intermittent basis with a variety of stocks; operation of this type of equipment on a continuous basis with a single feed stock should produce lower gum content. All naphthas had good oxidation stability, shown by the induction periods of over 24 hours. The paraffinic hydrocarbon content of the blend is much lower
and the olefin content greater than that of the hydrofined whole naphtha; this difference, as well as the greater sulfur content of the blend gasoline, is reflected in the octane ratings. Clear motor and research ratings of the blend were higher, and sensitivity was better, but tetraethyllead susceptibility was lower than for the hydrofined whole naphtha. Motor-method octane numbers of either 10-pound R.v.p. gasoline, with 3 ml. of tetraethyllead, equaled or were better than the average octane numbers of regular-grade gasoline sold in the western mountain states and Pacific coast area of the United States during 1954 (S), and research-method octane numbers were much better than the average. Gasolines of higher octane number could be made with sacrifice of yield by raising the operating temperatures.
Conclusions Specification gasolines have been produced a t pressures from 400 to 800 pounds per square inch, from both raw whole shaleoil naphtha and heavy naphtha (blended with light naphtha after hydrofining), but the higher pressure produces lower catalyst deposits and contributes to longer catalyst life. The higher pressures also greatly improve the gum content of the product but have relatively little effect on octane numbers. Octane numbers increase rapidly as operating temperatures are raised above 950" F., but the gum content increases rapidly as the temperature is raised above 1000' F.; temperatures between 950' and 1000' F. therefore appear desirable to obtain best product properties. Hydrofining the raw naphtha boiling between 260' and 400' F. and blending with the caustic-treated light naphtha appear more desirable than hydrofining the raw whole 400' F. end-point naphtha and offer the advantages of lower hydrogen consumption, better gasoline yield, less feed to the reactor, and more volatile gasoline than is obtained in hydrofining the whole naphtha,
Acknowledgment This project was part of the Synthetic Liquid Fuels Program of the Bureau of Mines and was performed a t the Petroleum and Oil-Shale Experiment Station under the general direction of H. P. Rue and H. M. Thorne and the immediate supervision of W. I. R. Murphy. Special thanks are due various members of the personnel of the station for their valuable assistance in carrying out this project. The work was done under a cooperative agreement between the University of Wyoming and the U. S. Department of the Interior, Bureau of Mines.
Literature Cited Antweiler, J. C., Mayfield, L. G., Cottingham, P. L., Murphy, W. I. R., XIIth International Congress of Pure and Applied Chemistry, New York, Sept. 10 t o 13, 1951. (2) Ball, J. S., Dinneen, G. U., Smith, J. R., Bailey, C. W., Van Meter, R., IND.ENG.CHEM.41, 581-7 (1949). (3) Blade, 0. C., U. S. Bur. Mines, Rept. Invest. 5111 (January 1955). (4) Byrnes, A. C., Bradley, W. E., Lee, M. W., IND.ENG.CHEM. 35, 1160-7 (1943). ( 5 ) Casagrande, R. M., Meerbott, W. K., Sartor, A. F., Trainer, (1)
R . P., Ibid., 47, 744-8 (1955).
(6) Cole, R. M., Davidson, D. D., I b i d . , 41, 2711-15 (1949). (7) Grote, H. W., Watkins, C. H., Poll, H. F., Hendricks, G. W., Oil Cas J . 52, 211-16 (April 19, 1954). (8) Hoog, H., Klinkert, H. G., Schaafsma, A., Ibid., 52, 92-6 (June 8,1953). (9) Voorhies, A., Jr., Smith, W. M., IND.ENG.CHEM.41, 2708-10 (1949).
(10) Zahnstecher, L. W., Petrarca, C. A., Oil Cas J . 53, 78--81 (Dec. 20, 1954). RECEIVED for review November 7, 1955.
ACCEPTED February 20, 1956.
END OF SYMPOSIUM July 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
1151
