Modifying the Viscosity of Sulfur ROCCO FANELLI Texas GulfSulphur Company, 75 East 45th St., New York,N. Y .
m e d i u m h a s been s u g temperatures above 160° C. gested (8). Wood, paper, and other porous materials, may be impregnated with molten sulfur (6). Attempts have been made t o use i t to consolidate quickand, etc. (I). Molten sulfur with (4, and without (It?), viscosity-modifying substances, has been proposed for use as a drilling fluid to replace drilling mud and to cement oilzwell casings in the petroleum industry, and also to confine and make fast various types of earth formations (1.3). These uses undoubtedly could be augmented if the viscosity of sulfur at elevated temperatures could be modified.
initiated. A number of substances are known which modify the viscosity of sulfur. The most effective are the halogens, hydrogen sulfide, hydrogen persulfides, and the hydrocarbons. The latter or their derivatives function through the presence of hydrogen sulfide and hydrogen persulfides resulting from their reaction with sulfur. VISCOSITY DETERMmATION
The viscosities were determined in open and closed systems. In the open system (3) volatile matter was allowed to escape. I n the closed system special viscometers of the type shown in Figure 2 were used. After charging, the instrument was placed in an air bath (3)and mounted in a cradle which could be rotated through 360" C. The temperature was shown by an iron-constantan thermocouple fastened t o the narrow end of the viscometer. The viscometer was rotated from the filled position through 180 e C., and the time of emptying the larger bulb noted. The viscometer was calibrated by a water-glycerol mixture of known viscosity. The weight of sulfur in the mixtures was about 35 grams, and the free air space in the sealed viscometer was approximately 50 cc. The materials were sufficiently pure for these determinations. The sulfur was purified according t o a method previously described (8). Chlorine was added in the form of sulfur chloride which was analyzed for its chlorine content. Bromine and iodine were added in elemental form. All mixtures are in terms of weight per cent, and their densities were assumed t o be the same as pure sulfur. I n the closed system experiments, hydrogen sulfide was added to the sulfur as liquid and in the form of hydrogen persulfide. I n the former case the viscometer and sulfur were chilled by dry ice, and a measured volume of liquid hydrogen sulfide was added. During sealing some hydrogen sulfide escapes; hence the indicated concentrations are somewhat high. The addition of hydrogen persulfide to sulfur is a simple m e t h o d of i n c o r p o r a t i n g definite weights of hydrogen sulfide, as it may be analyzed easily and accurately for its Figure 2. V i s hydrogen sulfide content (14). The concometer Used for centrations given indicate the weight the Closed System
i \
15OaC.
180
210
240
270
300
330
Figure 1. Viscosity of Pure Sulfur
The viscosity of pure sulfur (Figure 1) increases sharply with rise in temperature above 160' C., and reaches a maximum of 93,200 centipoises a t 186-188". As the temperature rises still more, the viscosity falls to about 2600 centipoises at 300"C. and t o about 100 centipoises a t the boiling point, 444.6'. These high viscosities often make difficult the handling of molten sulfur. They bar the use of sulfur as a heat transfer medium in an important temperature range. They interfere with the use of elemental sulfur in chemical reactions at high temperatures. They retard penetration or impregnation operations. However, sulfur also has many good qualities. It is cheap and high in punty in all commercial forms. It has a low vapor pressure almost throughout its liquid range. It has interesting
39
INDUSTRIAL AND ENGINEERING CHEMISTRY
40
however, is not so great as was anticipated. The loss of halogens, free and combined, by volatilization from an opeii system is quite slow; Figure 4 shows the change in viscosity of s u l f u r - h a l o pen mixtures with t'ime. T h e m i x t u r e s w e r e m a i n t a i n e d a t 190200" C. for the time indicated, and the viscosity determiuations were made a t 200' C. The curves clearly indicate that, while chlorine is most effective in reducing the viscosity, its volatility in the form of s u l f u r c h l o r i d e is greatest,. With respect to persistency, iodine is much better than chlorine and bromine is better than either. These results are in keeping with t>he following boiling points: sulf u r c h l o r i d e , 138'; iodine, 184"; sulfur bromide, 58" C. a t 0.22 mm.
80 60
4.0
20
0 100 v)
w
2
Vol. 38, No. 1
80
0
a
g60
w V
40 20
EFFECT OF HYDROGEN SULFIDE AND PERSULFIDES
0
30 20
10 -0
I
le0
2 3
220
Figure 3.
"40
I
I
260
280
I
300 320 TEMPERATURE OC.
Viscosity of Sulfur Containing
ratio of hydrogen sulfide to the total M eight of the mixture in the closed system. Most of the hydrogen sulfide remains in the gaseous state and only a fraction of it dissolV~5in the liquid sulfur. The hydrogen persulfides dissolve quickly in sulfur a t about 120' C. uith no decomposition; but with increasing temperature, decomposition sets in and liberates hydrogen sulfide. EFFECT OF HALOGENS
Figure 3 presents the variation in viscosity a i t h temperature of sulfur containing various concentrations of halogens. Coinparison of these curves with Figure 1 brings out the enormous modifying effect of these elements on the viscosity of sulfur. Of
the three elements, chlorine is the most effective. Mixtures containing 2y0 chlorine give values mainly under 15 centipoises throughout the entire temperature range. Increasing concentrations give lower viscosities which tend to be independent of temperature, as shown by the 3, 4, and 5% curves. These curves show that the viscosity of pure sulfur can be reduced easily from its maximum of 93,200 centipoises to about 10 centipoises. They also indicate that, with each increment in concentration, the drop in viscosity becomes smaller and tends toward a limiting value. This holds for all knowi substances which modify the viscosity of sulfur. Although iodine is the least effective of the halogens, it substantially reduces the viscosity. Bromine takes a n intermediate position, being considerably more effective than iodine but proportionately less effective than chlorine. As is to be expected for equal concentrations, values given for closed systems are lower than for open systems. The difference,
Hydrogen sulfide (Figure 5 ) is at least as effcctivc as chlorine, if not more so, in reducing the viscosity of SUIfur; but because of its rclaI , tively low solubility in sul340 360 380 400 fur, h i g h h y d r o g e n sulfide p r e s s u r e s are necessary to bring about very low viscosiHalogens ties, Curve 1 shows the viscositv values obtained bv bubbling hydrogen sulfide constantly through sulfur in an open syitcrn. The remaining solid curves are for closed systems in whien the hydrogen sulfide was added in the form of hydrogen persulfide. The broken curves were given by a closed system in which the hydrogen sulfide vvas added as a liquid. EFFECT OF ORGANIC RIATERPAL
A number of hydrocarbons and thcir derivatives have bccn proposed for modifying the viscosity of sulfur abovc 160" C. (4, 5, IO). Their effectiveness has been shown (3)t o bc d u c b to
...
TIME IN HOURS Figure 4.
Viscosity Changes at 200' C. with Time
1. 0.75%ohlorine 2. 1.8 %chlorine
3. 0.2590iodinc 4 . 0.5 %iodine
5. 1.Q %iodine 6. 0.5 '70bromiur
January, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY I
41 I
I
I
400 280 160
40 170
200 250 TEMPERATURE OC. Figure 6. Effect of Traces of Oil on Viscosity of Sulfur
TEMPERATURE
Figure 5.
OC.
Effect of Hydrogen Sulfide on Viscosity of
the presence of hydrogen sulfide and hydrogen persulfides resulting from the action of sulfur on the hydrocarbons. Sulfur, as mined by the Frasch process, is always associated with relatively minute but varying amounts of oil. Hence, its commercial forms are never free of oil. Simply heating this sulfur above 180" C. quickly produces sufficient hydrogen sulfide and hydrogen persulfides t o reduce viscosity greatly. This direct and easy procedure may be made to give sufficiently low viscosities for some purposes.
As an example of this form of heat treatment, the following experiment is cited: A sample of commercial sulfur containing 0.038% oil was heated in an open system from 125" to 260" C. in 1.5 hours and kept a t this temperature for an additional half hour. The viscosities given by the resulting material on cooling to 170" C. are shown by curve 1, Figure 6. Comparison of this eurve with Figure 1 shows how Sulfur effective this treatment can be. Redetermined values with rising temperature are given by eurve 2. The mixture was again cooled to and kept a t 160" C. for 14 hours, and viscosities were determined with rising temperatures (curve 3). This cooling and reheating process was twice repeated, and the respective data are shown by curves 4 and 5. The relative positions of the curves show that prolonged heating in an open system results in a slow loss of hydrogen sulfide and persulfides with resultant increase in viscosities. I n a closed system low viscosities can be maintained indefinitely. Viscosities for temperatures above the boiling point of sulfur may be roughly estimated from Figures 7, 8, and 9 which were
Power Plant of Texas Gulf Sulphur Company at Newgulf, Texas, with Vats of Mined Sulfur a t Upper Right
INDUSTRIAL AND ENGINEERfNG CHEMISTRY
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Vol. 38, No. 1
60 50
30
20
w w
15
2
E W
lo
" 7 6 5
4 3 TEMPERATURE
TEMPERATURE XIOOoc.
2
Figure 8. Viscosity of Sulfur at Elevated Temperatures Figure 7. Viscosity at Elevated Temperatures of Sulfur Contairiing Hydrogen Sulfide
-+
1. Sulfur HIS a t atmospheric pressure 2. Pure sulfur
obtained by plotting the appropriate values given by the above systems on log-log paper. T h e effect of pressure on sulfur is t o increase the viscosity (11). This tendency is reflected in the extrapolated values of Figures 7 and 9 for closed systems as compared with those from Figure 8 based on values given by an open system. CORROSION BY HALOGEN MIXTURES
These halogen mixtures would be expected to be highly corrosive, but preliminary experiments with a number of metals indicate strong resistance to disintegration. The tests were carried
TABLE I. CORROSION RESISTANCE OF METALS TO SULFUR AND SULFUR-HALOGEN MIXTURES
Temp., OC. 210 410
Pure sulfur S%ine+
1%
-Av.
Penetration", Inches/Month18-8 steel Hastelloy +3 Mo C None 0.13%gain in wt.6
Aluminum 18-8 steel None 0.000002 None 0.00008
.... ....
210 410
Sulfur 0.7% bromne
0.000003 0.00001 0.000005 l . J % gain 0.,1%' 'gain In wt.b in wt.6
210
Sulfur 1.7% chlorine
410
0.000009 0.00047
0.000004 0.00019
0.00002 0.00029
210
0.001
0.000012 0.0004
o.oboi6
+
+
a !ea6
410
0.001
....
.. . . 0.000007
0.00005
.... ....
U. 8. Steel Research Lsb. specifications: fully resistant, penetration
than 0.00035 inch per month. natiafactorily resistant, 0.00035-0.0035 inch; fairly reshtant, 0.0035-O.Olb inch. b Metal Bound, no swelhng.
XIOO°C.
Figure 9. Viscosity at Elevated Temperatures of Sulfur Containing Halogens 1 2:
2 ochlorine I.$ a chlorine
3. 4.
670iodine
3 yo iodine
out in sealed glass tubes. Test pieces were completely immersed in the mixture a t 210" and 410" C. for 30 to 40 days. Some of the results are shown in Table I. The sulfur-chlorine mixtures are particularly destructive toward aluminum. At the end of the experiments the aluminum was coated with a thick, adherent, protective film. This film \=,-as a mixed aluminum chloride and sulfide. At 410" C. the sulfur-bromine mixture deposited the same type of coating on the aluminum. The iodine-sulfur mixtures appear to be the least corrosive. The easy hydrolysis of the sulfur halides makes it imperative that water in any form be rigorously excluded. These values are given merely to indicate that a number of common metals under these conditions satisfactorily resist thc action of these sulfur-halogen mixtures. So many factors enter the corrosion picture that one cannot predict with certainty the behavior of a metal under another set of conditions. Recent advances in the fabrication of highly resistant metals to heat, pressure, and corrosion indicate that all adverse conditions can be met successfully. DISCUSSION
Substances which reduce the viscosity of sulfur above 160' C. do so through chemical reaction with the sulfur. The similarity in the shape of the curves for the various substances indicates the same underlying mechanism. In the temperature range below 160' C. the molecular complexity and structure of the liquid is relatively simple, consisting mainly of eight-membered puckered rings. I n this region the viscosity ranges from about 12 centipoises at 120" C. through a minimum of about 7 centipoises a t 157" and back again to 12 centipoises a t lBQo, and these values remain essentially unchanged by the addition of viscosity-modifying substances. Above 160 C. these rings rupture to form long chains which increase in length up to 187". O
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1946
This polymerization of sulfur into long chains brings about the increase in viscosity with rising temperature (3, 7). Increase in temperature beyond 187" results in a shortening of the chains and, consequently, a falling off in the viscosity as shown in Figure 1. Reduction in the viscosity by the halogens, hydrogen sulfide, and hydrogen persulfides must be due to a reaction which shortens the chains. This scission is believe8 to take place with the halogen atoms taking terminal positions of the segments. Thus for chlorine we would have: ClSS-S
a
.
*
S-S-C1
or C1-S-S-S
*
S-S-S
I n the same manner hydrogen sulfide and persulfides shorten the chains with hydrogen as the terminal atoms of the segments. Such a mechanism would also explain why these substances persist so tenaciously in the liquid sulfur even when the mixture is kept far above their boiling points. There appears to be a great deal of uncertainty as to the direct combination of sulfur with iodine (9). While sulfur iodides may be made by indirect methods, the direct addition of iodine t o sulfur seems to have failed to produce them. The quick and tremendous reduction in the viscosity of sulfur above 160" C.
43
by minute amounts of iodine must indicate that some form of chemical combination does take place, and that it is rapid and quite persistent through a wide range in temperature, if the above mechanism for the reduckion of viscosity is sound. LITERATURE CITED
Ackley, C. S.,U. S.Patent 2,232,898 (Feb. 25, 1941). Bacon, R. F., and Fanelli, R., IND.ENQ.CHEM.,34,1043 (1942). Bacon, R. F., rand Fanelli, R., J . Am. Chem. Soc., 65, 639 (1943). Cain, G. A,, and Chatelain, J. B., U.6 . Patent 2,161,245 (June 6, 1939).
Darrin, M., IND.ENQ.CHEM.,20, 801 (1928). Duecker, W. W., Chem. & Met. Eng., 41, 583 (1934). Kauzmann, W., and Eyring, H., J . A m . Chem. SOC.,62, 3113 (1940).
Kobb6, W. H., Chem. & Met. Eng., 34, 163 (1927). Mellor, 5. W., "Comprehensive Treatise on Inorganic and Theoretical Chemistry", Vol. X, p. 653 (1930). Petty, G. M., Univ. of Pittsburgh, Bull. 30, 2 (Nov. 15, 1935). Powell, R. E., and Eyring, H., J . A m . Chem. SOC.,6 5 , 6 4 8 (1943). Read, H. L., U. S.Patent 2,341,572 (Feb. 4 , 1944). Ibid., 2,341,573 (Feb. 15, 1944). Walton, J. H., and Parsons, L. B., J . A m . Chem. SOC.,43, 2539 (1921).
New Catalvsts for Friedel-Crafts Type Reactions J
A. N. SACHANEN AND P. D. CAESAR Socony-Vacuum Laboratories, Paulsboro, N . J . Various typical reactions, catalyzed by Friedel-Crafts catalysts or strong acids, may be carried out in the presence of heterogeneous catalysts of the silica-alumina type or homogeneous catalysts such as hydrogen halides or organic halides. The syntheses of anthraquinone and benzophenone are described as new examples of the application of such catalysts to conventional reactions of the Friedel-Crafts type. I
F
RIEDEL-Crafts chemistry was founded in 1877 when Friedel and Crafts discovered the condensation of aromatic hydrocarbons and alkyl or acyl halides with aluminum chloride. Since then, halides of aluminum, tin, zinc, iron, and other metals, and acids such as sulfuric, phosphoric, and anhydrous hydrofluoric have been found to catalyze a wide variety of condensation reactions. The scope of the condensation reactions has been greatly expanded in the last twenty-five years. The alkylation of paraffins and naphthenes, particularly of isoparaffins, is a recent development commercialized on a large scale in the production of high-octane hydrocarbons and fuels. These same catalysts have been applied to other types of reactions such as isomerization, transfer of radicals, and cracking. The application of silica-alumina and certain homogeneous catalysts t o reactions of these types presents new fields of scientific endeavor. SILICA-ALUMINA CATALYSTS
Active heterogeneous catalysts containing silica and alumina are produced either by activation of some natural clays or by synthesis. Silica gel, notwithstanding its enormous surface, does not catalyze the reactions described in the present paper. A small proportion of alumina, of the order of 1% by weight of the silica,
is sufficient to produce an active catalyst. Commercial cracking catalysts contain approximately 10% alumina. Oxides such as thoria or zirconia can be substituted for the alumina. Silicaalumina catalysts were first developed for the catalytic cracking of petroleum oils. Approximately 1,000,000 barrels of oil are now cracked daily over these catalysts. The alkylation of aromatic hydrocarbons with olefins, long established in Friedel-Crafts and strong acid syntheses, was the first application of silica-alumina to condensations of the FriedelCrafts type. Michel (11) described the condensation of naphthalene with propylene under pressure over fuller's earth to proSchollkopf (19) alkylated duce tetraisopropylnaphthalene. naphthalene with ethylene a t 230" C. under 20-40 atmospheres pressure over an activated hydrosilicate catalyst. Sachanen and O'Kelly (17) described the alkylation of benzene with propylene, butylenes, and amylenes over silica-alumina a t 450" C. and 100 atmospheres. Under these conditions the alkylation proceeded smoothly but was accompanied by partial cracking of the paraffinic side chains. As a result, toluene, ethylbenzene, and xylenes were produced in substantial yields. Destructive alkylation reactions Catalyzed by aluminum chloride, as observed by Ipatieff and co-workers (7), were carried out over silica-alumina catalysts by Sachanen and Davis (16). These investigators reacted benzene with pentanes over an activated clay for 45 minutes a t 480" C. and 1050 pounds per square inch. Twenty-eight per cent (by weight' of benzene charged) of alkylbenzenes boiling from 105-210" C. was produced. The application of silica-alumina to reactions formerly catalyzed by FriedelCrafts and strong acid catalysts was increased in scope by Hansford, Myers, and Sachanen (4) and by Thomas, Hoekstra, and Pinkston (8.9). These investigators dealkylated alkylaromatic hydrocarbons in the presence of silica-alumina at 450-550 C. An example of these reactions was the conversion of ethylbenzene to benzene and ethylene. O
