CARBON
ISULFIDE PR
Effect of Catalysts on Reaction of Methane with Sulfur CARLISLE M. THACKER AND ELMER MILLER The Pure Oil Company, Chicago, Ill. High yields of carbon disulfide can be obtained by the reaction of methane with sulfur at 700' C. and below when the reaction is carried out in the presence of a suitable catalyst. Catalysts of the activated clay types give much higher yields under given conditions than do other types of catalysts, such as metallic oxides, metallic sulfides, activated charcoal, etc. Catalysts particularly suitable for carbon disulfide production from methane include silica gel, activated alumina or promoted activated alumina, and Florite. With activated alumina containing a small amount of chromium oxide, a conversion to carbon disulfide of over 90% of the charged methane can be effected below 700' C.
I
mine equilibrium conversions for six reactions of methane with sulfur which appeared most likely to occur under the conditions of the investigation. Calculations were also made to determine the equilibrium for the reaction of hydrogen sulfide with methane to produce carbon disulfide. The seven reactions considered were as follows:
The free energies of these reactions are given in Table I. The theoretical conversions a t equilibrium are shown in Figure 1. With the exception of curve 7, the figure defines onlv the limits of equilibrium conversions possible, since a t least three reactions are taking place simultaneously due to the presence of the three molecular species of sulfur. Figure 1 shows practically complete conversion of methane to carbon disulfide and hydrogen sulfide in the range 500' to 700" C. Below 700" C. the equilibrium is not so favorable for conversion to carbon disulfide and hydrogen. The equilibrium is even less favorable for carbon disulfide production a t 700' C. from methane and hydrogen sulfide.
N 1736 Lampadius first synthesized carbon disulfide by
heating sulfur with charcoal. The manufacture of carbon disulfide by this reaction is now a well established industry. Two methods are now in use in this country-the retort and the electrothermal. In the first, reaction takes place in directfired retorts of cast iron or refractory firebrick. The electrothermal process involves internal heating by an electric current passing through the bed of charcoal. T o obtain a sufficiently high reaction rate, temperatures of 800" to 1000' C. are required; rapid deterioration of equipment results in the retort process, and high consumption of electrical energy in the electrothermal process. Both methods require specially prepared charcoal which materially adds to the cost of manufacture. Methane and many other hydrocarbons offer possibilities as cheap raw materials for carbon disulfide manufacture. A number of patents have been issued on proposed processes utilizing methane or other hydrocarbons. De Simo ( 7 ) recently patented a catalytic process for converting methane with sulfur vapors into carbon disulfide at 800' to 1000' C. It has also been proposed to produce carbon disulfide by the reaction of methane with hydrogen sulfide ( 6 , 10). Such methods require temperatures of 800" to 1000" C. for successful conversions of saturated hydrocarbons. The use of acetylene and other unsaturates (4, 5 ) permits low-reaction temperatures, but these raw materials have not been used in commercial operations, probably because side reactions result in a low efficiency of conversion to carbon disulfide. This article is based on investigations to develop catalysts that would cause high rates of reaction a t or below 700" C., a temperature range much lower than had previously proved feasible for reactions of methane with sulfur. The more favorable catalysts to be discussed were disclosed in a recent patent (8).
MATERIALS AND CATALYSTS
The methane was 92% grade, obtained from Carbide and Carbon Chemicals Corporation. Specifications require the following: Not less than 92% methane by volume, not more than 4.5% air, not more than 2% ethane, and not more than 2% nitrogen. Prior to use, this methane was passed a t 300' C. over freshly reduced copper turnings to remove oxygen. I n earlier work, commercial sulfur flowers was used; later, sublimed sulfur was employed to reduce fouling of check valves in the sulfur pump. There was no detectable difference in the reaction with the two grades of sulfur. All catalysts were in granular form of 8 t o 14 mesh size, as follows: 1. Manganese dioxide (25% by weight) on kieselguhr. Prepared from manganous chloride by chlorine oxidation in the presence of sodium hydroxide, followed by water washing until free of chlorides. 2 . Alumina-manganese, approximately 20 to 1. Prepared from manganese nitrate and Alorco, grade A, by addition of ammonium sulfide. 3. Alumina-vanadium, approximately 20 to 1. Prepared by impre nating Alorco, grade A, with ammonium metavanadate. 4. Surified. silica gel. Prepared by extracting silica gel, commercial grade, with hydrochloric acid, followed by washing with water. 5. Alumina-chromium ap roxiniately 20 to 1. Prepared by impregnating Alorco, grade with chromic acid.
1,
THEORETICAL CON SIDERATIONS
I n the temperature range 500" to 700" C. calculations are complicated by the various modifications of sulfur that are present in the vapors. Although no appreciable amounts of monatomic sulfur are present in this range, a t 500" C. sulfur vapors contain three molecular species, Sa,Se,and SZ. As the temperature rises, the concentrations of the heavier modifications decrease, and the result is a gas that is almost free of Sa and Ss at 700' C., a t or below atmospheric pressures. From free energy data (3, 9) calculations were made to deter-
TABLE I. FREEENERGIES OF REACTIONS PRODCCING CARBON DISULFIDE FROM METHANE Temp. OK.
700 800 900 1000
182
-
1 -27,780 -28,170 -28,580 -28,990
2 -17,900 -23,290 -28,740 -34,190
Reaction Number 3 4 6 6 7 -17,820 -1120 3,860 3,860 25,450 -23,890 -3790 -1.650 20,510 -1,360 -30,060 -6520 -6,600 -7,260 15,450 -36,230 -9290 -11,890 -12,910 10,310
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1944
6. Florite (activated bauxite). commercial grade. from Floridin Company. 7. Purified Florite. Prepared by extracting No. 6 with hydrochloric acid, followed by washing with water. 8. Alorco (activated alumina), grade A, obtained from Aluminum Company of America. . I
-
I
100
183
with sodium hydroxide, followed by washing with water until neutral to litmus. After drying and screening, the general procedure followed
was to heat the catalyst in nitrogen a t reaction temperature for several hours before use. APPARATUS AND PROCEDURE
0
TMERATURE,
0
C.
Figure 1. Equilibrium Conversions of Methane to Carbon Disulfide
The reaction was carried out in an electrically heated 18-8 stainless tube furnace, with a heatin section 18 inches long. Methane was fed into the bottom of t f e furnace and preheated as it passed up to the top, where it met sulfur vapors preheated to reaction temperature. The mixed vapors then passed down through an inner tube containing the catalyst. The outside tube serving as a preheater for methane was 2 inches inside diameter with a 3/le-inch wall; the inner tube containing the catalyst was 11/2 inches inside diameter with a 1/8-inch wall. I n most cases about 100 cc. of catalyst were used. The temperature of the furnace was held constant to 1 3 " C. by a Micromax regulator. Temperatures were determined by a chromel-alumel thermocouple in a stainless steel tube passing through the catalyst bed. At the higher temperature there was considerable corrosion of the 18-8 reactors. I n later experiments (not reported here) a 25-20 alloy withstood the corrosive gases much better than the original equipment. Figure 2 gives a flowsheet of the experimental unit. Molten sulfur, a t about 130" C., was pumped from a reservoir t o a heated coil where it was vaporized and preheated to reaction temperature. The rate of sulfur feed was determined by calibrating the pump before and after each run. Because of the peculiar viscosity characteristics of liquid sulfur, care was exercised in maintaining the temperature of the sulfur reservoir and transfer lines t o the pump within specified limits. As the temperature is raised above the melting point, the viscosity of liquid sulfur ( I ) slow:y decreases with increasing temperatureuntil about 160' C. isreached. Between 160' and 188' C. the viscosity rapidly increases and reaches a maximum of 93,200 centipoises a t 186-188" C. Further increase in temperature decreases the viscosity. Operation of the sulfur reservoir and transfer lines a t about 130' C. was satisfactory, since this temperature is sufficiently above the melting point of sulfur and below the high viscosity range t o prevent trouble by small temperature gradients in the system. The vaporized sulfur met the stream of preheated methane and passed through the catalyst bed to a condenser held a t 130' C. to remove unreacted sulfur. A t high flows a small portion of the sulfur passed through the sulfur condenser as a dust and settled out in the lines. On leaving the sulfur condenser, the the gases were passed through a trap cooled with dry ice and methanol where the carbon disulfide and some hydrogen sulfide were condensed. Hydrogen sulfide remaining in the gas was re-
9. Molybdenum-chromium, approximately 3 to 1, on pumice. Prepared by impregnating purified pumice with ammonium molybdate and chromic acid. Pumice was purified by extracting the commercial grade with hydrochloric acid, followed by washing with water. 10. Alumina-manganese, approximately 20 t o 1. Prepared by impregnating Alorco, grade A, with manganous chloride. The material was then chlorinated in an alkaline solution, followed by water washing until free of chlorides. 11. Manganese dioxide-potassium carbonate on kieselguhr. Prepared by adding 1% by weight of potassium carbonate to catalyst 1. 12. Alumina-iron, approximately 20 to 1. Prepared by impregnating Alorco, grade A, with ferric nitrate. 13. Iron sulfide. Made from the material commonly used for generating hydrogen sulfide in the laboratory. After breaking and screening, it was heated a t 600" C. for 18 hours in hydrogen prior to use. 14. Cobalt-tungsten, approximately 1 to 10 on purified pumice. Prepared by impregnating purified pumice with cobalt nitrate and a m m o n i u m tungstate. Pumice was % Calibration Point purified as outlined for -w- Valves catalyst 9. 15. Silica gel, commercial grade. 16. Alfrax. commercial grade. 17. Super F i l t r o l , commercial grade. An activated clay used as received. 18. Activated charcoal obtained from Carbide and Carbon Chemicals Corporation. 19. Cobalt-tungsten, approximately 3 to 1 on purified pumice. Prepared as described for catalyst 14. 20. Thorium nickel, approximately 3 to 1. Prepared from thorium nitrate and nickel nitrate by precipitating Figure 2. Flow Sheet of Laboratory Unit for Reaction of Methane with Sulfur ~
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INDUSTRIAL AND ENGINEERING CHEMISTRY
184
other catalysts investigated; these catalysts belong to the general class of activated clays. Results in Table I1 as well as miscellaneous results in Table I11 are typical of all data obtained in this study of many catalysts. They show clearly that the activated clay types are excellent catalysts for the reaction of methane with sulfur to produce carbon disulfide. Alfrax, metallic oxides or sulfides supported on pumice, nickel sulfide on thoria, activated charcoal, etc., are inferior to the clay-type catslysts reported.
00 N u1 0
R
Vol. 36, No. 2
Bo
8 f3 40
TABLE111.
*
W X
w.
20 Catalyst NO.
C, SILICA G a
4
0
2 8
500
550
600
TEMPWXTJRS,
700
650 0
C.
1.3 16
Figure 3. Effect of Temperature on Methane Conversion to Carbon Disulfide
moved by scrubbing with a dilute solution of sodium carbonate. The unabsorbed gas, mainly methane, was metered and a sample taken for analysis. ANALYTICAL METHODS. The condensate from the dry icemethanol trap was carefully stabilized in a low-temperature apparatus to remove most of the hydrogen sulfide. A portion of the residue was weighed and then diluted with thiophene-free benzene. This mixture was analyzed by the method of Bell and Agruss ( 2 ) for the following constituents: carbon disulfide, hydrogen sulfide, mercaptan sulfur, sulfide sulfur, disulfide sulfur, and sulfur (nonvolatile material a t 110' C.). The gases obtained were analyzed by the usual absorption and combustion technique. No analyses Tere made on the sulfur recovered.. On solidifying, there was a slight darkening which indicated only small traces of tarlike materials associated with recovered sulfur. YIELDS WITH VARIOUS CATALYSTS
Table IIA gives results with a number of catalysts when operating a t a space velocity of 825 and a methane-sulfur ratio of 0.5. Space velocity is defined here as the total volume of gases at 0" C. and 760 mm. passed through a unit volume of catalyst space per hour. I n calculating the total gas volume, i t is assumed that all sulfur present is in the diatomic form. Results in Table IIB were obtained under similar conditions but additional catalysts are included. Under the conditions employed, silica gel, activated alumina, promoted activated alumina, and Florite are superior to the
TABLE 11. EFFECT OF
CaTALYSTS O N Y I E L D O F C A R B O N
DISULFIDE Mole
A.
E.
M n0a on kieselguhr 7.1 Al2Os:Mn = 2 0 : l AlqOa: V = 20: 1 Silica gel 42.1 A1aOs:Cr = 2 0 : l 26.4 Florite 23.8 Purified Florite Alorco 27.4 Space Velocity 775; Molal Ratio, CHI:&
1 2 3 4 5 6 7 8 9 10
12 13 14
70CHI Converted
to CSa Composition 550' C. 60OrC. Space Velocity 825 : Molal Ratio, CHI: Sz = 0.5
Catalyst No.
11
L t h C E L L . 4 N E O U S DATAOK P R O D T C T I O K O F C A R B O N D I S U L F I D E FROM LIETHANE
12.9 55.3 51.8 69.6 65.7 63.9 59.4
.... .... ....
hlo: Cr = 3 :1, on pumice Al208:h,ln = 2O:l 25% hfnOz-l% KzCOa o n kieselguhr A1zOa:Fe = 2O:l Iron sulfide C o : W = l O : l , on pumice
1.0
-
....
0.6
5.7 57.8 7.5 50.6 4.8 6.7
17 18 7 19 20
TABLE IJ'.
T:mp., Composition C. Silica gel, purified 500 Alz03:lIn = 20: 1 500 Alorco 550 600 Silica gel 550 Alfrax 550 682 Super Filtro 560 596 Activated charcoal 600 Purified Florite 600 Co:W = 1 : 3 , o n p u m i c e 645 Th:Ni = 3 : l 648
Space Velocity 845 810 690 690 690 715 875 965 I050 915 800 1030 985
Ratio, CHI:
hIole 70 CHa Converted to
S1
cs2
0.5 0.5 0.5 0.7 0.5 0.5 0.4 0.4 0.4 0.4 0.5 0.4 0.4
16 5 8 5 26 5 54.0 44.8 0.8 27.D 24.5 44.0 36.7 59.4 20.4 25.8
EFFECTO F TEMPERATURE ON R E A C T I O N CATALYST 5
(Space velocity 870, ratio, C H I : & = 0.5) Run No. 1 2 3 Temperature, O C. 548 667 604 Mole % CH4 converted to CSz 25.2 66.4 75.5 Stabilized liquid, % sulfur as gas 1.45 0.81 0.74 Trace 0 0 0.03 0.02 0.03 0.18 0.10 0.25 0 0.60 0.10 82.5 82.8 82.7
USING
4 680
93.5 0.87 0 0.04 0.12 0.30 83.1
Table IV illustrates the effect of temperature when using B chromium oxide-activated alumina catalyst (No. 5 ) . EXects of temperature when using this and other catalysts are shown in Figure 3. Table IV also gives analyses of the liquid products obtained in the four runs with catalyst 5 ; they are typical of analyses obtained on liquid products from all runs outlined i n this article. Wide ranges of space velocities, with other conditions held constant, are not reported here because difficulties were encountered in adjusting the sulfur pump to give the desired feed ratios at low flows. Sufficient data are presented, however, to show a n increase in conversion with decrease in space velocity. As would be expected, increase in temperature increases the conversion to carbon disulfide decidedly. Analysis of the data shows that the reaction of sulfur with methane under the conditions described Droceeds without appreciable side reaction according to the equation: CH, -I- 45 = CSz 2HzS.
+
LITERATURE CITED
Bacon and Fanelli, J . Am. Chem. SOC.,65, 639-48 (1943). Bell and Agruss, IND. ENG.CHEM.,A N ~ LED., . 13, 297-9 (1941). Kelley, U. S. Bur. Mines, Bull. 406 (1937). Komlos, Komlos, and Engelke, Brit. Patent 265,994 (Oot. 27, 1927); German Patent 469,839 (Dec. 29, 1928). (5) Maihle, Chinzie & industrie, 31, 255-61 (1934). (6) Rakovski and Kamnava. J. Applied Chem. (U.S.S.R.), 13,
(1) (2) (3) (4)
1436-41 (1940). (7) Simo, de (to Shell Development Co.), U. S. Patent 2,187,393 (Jan. 16, 1940). (8) Thaoker (to Pure Oil Co.), U. S. Patent 2,330,934 (Oot. 5, 1943). (9) Thacker, Folkins, and Miller, IND.ENO.CHDM.,33, 584-90 (1941). (10) Waterman and Vlodrop, J . SOC.Chem. Ind., 58, 1Q9-10 (1939).
