Carbon Disulfide from Sulfur Dioxide and Anthracite C . W. SILLER The New Jersey Zinc Company (of Pa.), Palmerton,
A process is described, by which carbon disulfide can be prepared a t good yields from sulfur dioxide and a relatively inexpensive source of carbon, such as anthracite coal. The reaction takes place in steps, each of which can be carried out at the temperature that gives maximum efficiency.
case under discussion, the following combinations must be considered:
c + so2 c + co c + coz c + cos c + csz c + sz so2 + co
T
HE-utilization of the sulfur dioxide obtained as a by-product gas in the roasting of sulfidic ores to the corresponding oxides is a n important problem in chemical economics. At present practically all of this by-product snlfur dioxide is converted into sulfuric acid. This makes the roasting of sulfidic ores rather inflexible from a n economic point of view. For this reason, a large amount of work has been done, aimed at a more profitable utilization of this by-product gas. Lepsoe (8, 9) showed that sulfur dioxi'de can be reduced t o sulfur by passing it over incandescent carbon. Walker (15), Bacon and Boe ( I ) , and Doumani,, Deery, and Bradley (4) have shown that hydrogen sulfide can be prepared by the reaction of sulfur dioxide and methane. Rassow and Hoffman ( l a ) published data concerning the reaction of sulfur dioxide and charcoal which gave mixtures of carbonyl sulfide, sulfur, and carbon disulfide. Dow and Strosacker (5)patented a process for making carbon disulfide by passing mixtures of air or oxygen and sulfur dioxide over heated coke. It is believed that this process did not become commercial because of the low reactivity of coke, andathe consequent low carbon disulfide yields. McElroy (11) described a process for making carbon disulfide in which fuel was passed down a shaft under gas producer conditions; air was introduced at its base and sulfur into the column a t a higher point. It is known t h a t the reaction of sulfur with fuels, other than high grade charcoal, is slow, giving rise t o poor conversions t o carbon disulfide. Carter (5) patented a procedure for making carbon disulfide by passing sulfurous gases (sulfur dioxide, sulfur vapor, and carbonyl sulfide) through a reaction zone containing carbonaceous material at a temperature sufficiently high for the reaction of sulfur and carbon. I n this process it is necessary t o separate and recycle considerable amounts of carbonyl sulfide. As far as is known, none of the methods described above has been used on a commercial basis. The present paper describes a process for preparing carbon disulfide, at good yields, from sulfur dioxide and a relatively inexpensive source of carbon such as anthracite coal. The novel features of this process form the subject matter of a United States patent application.
so2 + coz so2 + cos so2 + csz so2 + sz co + co* co + cos
co + csz
co + sz coz + cos coz + csz coz + sz cos + csz cos + 5 2 cs2 + sz
The reactants listed above are considered t o exist in the presence of excess carbon. The pairs of substances that are underlined will not be given further consideration. The combination CO, C COz, and CO COZare eliminated because in this C investigation only reactions involving sulfur and sulfur compounds are of interest. The combinations C CSz, COS CS2, and CSz SZ will not be considered as such; the decomposition of carbon disulfide and carbonyl sulfide will be treated separately. The pair of substances sulfur dioxide and sulfur is believed t o be stable over the temperature range studied. The reactants sulfur dioxide and carbon dioxide are believed to be stable at low temperatures; at higher temperatures carbon dioxide is converted t o carbon monoxide-this reaction will be considered. Chemical equations can be written for the reactions of the remaining pairs of substances.
+
+
+
+
+
+ 250% = csz+ 4 c o + 2502 = CSZ + 2 c o z 2 c + so2 = cos + co 3c + 2SOz = 2 c o s + coz 4C + 2502 = Sz + 4CO 2 c + 2502 = sz + 2 c o z 6CO + 2SOz = CSz + 5COz 3CO + SO2 = COS + 2 c 0 z 2 c o + so2 = 1/2sz + 2 c o z 2CSz + SO2 = 2COS + 3/2Sz 2COS + SO2 = 3/2& + 2C02 2 c o s + c = csz + 2CO
+
5c 3c
9
c + f%
=
(4) (5)
(6)
(7)
(8) (91 (10)
(11) (12)
cs2
2cos = 2co
+ sz
con + csz = 2 c + sz + 0 2
2cos = 2cos
EQUILIBRIUM CALCULATIONS
When sulfur dioxide is passed over carbon, the following substances can eo-exist: carbon, sulfur, sulfur dioxide, carbon monoxide, carbon dioxide, carbonyl sulfide, and carbon disulfide. Sulfur is written as the diatomic species because Lepsoe (8) has shown that this form predominates at equilibrium over the temperature range investigated. When seven things are grouped in pairs, there are 21 possible combinations, and therefore in the
Pd.
Now that the chemical system of interest has been defined, i t is necessary t o determine whether the reactions proceed s p o n t e neously as written or in the reverse direction. This information can be obtained by calculating the free energy changes that take place from the free energy of formation of the various compounds that appear in the equations; in other words, for the following reactions: 1227
INDUSTRIAL AND ENGINEERING CHEMISTRY
1228
I n these equations, C ( p ) is the symbol for p-graphite commonly used in thermodynamic calculations involving carbon. The standard free energy equations for Reactions 17 to 21, inclusive, are presented in Table I. The standard free energy equations derived from the data listed in Table I are presented in Table 11. The standard free energy changes calculated for the different temperatures are listed in Table 111. Since these calculations were made, Wagman et al. (14) have published some revised data on the free energy of formation of carbon monoxide and carbon dioxide. The differences between the revised data and the data used in this paper were too small to alter the conclusions arrived a t ; consequently, recalculation was not justified. The data presented in Table I11 make it evident that the free energy changes for Reactions 7 to 11, inclusive, are negative a t all temperatures between 600" and 1200' C. This indicates that, from a thermodynamic standpoint, the reactions ran be
TABLE I. STAKDARD FREEENERGY OF FORMATION FOR SULFUR DIOXIDE, CARBOXDISULFIDE,CARBONYL SULFIDE,CARBON MOKOXIDE DIOXIDE,AND CARBOX [General equation:
(AFO
105
Reaction No.
AH0
17 18 19 20 21
-172,630 5,040 -101,260 93,690 25,780 TABLE
11.
T-1
+ +A IT)] T log T + B
Coefficients A B 3 . 4 3 -0,712 7.67 $1.51 4-2.36 -10.16 1 38 +0.0675 0 . 4 8 +0.775
C
+ -
-
'
AHo
5
+0.168 f1.106 4-1.492 -0.546 -1.054
+ +
STAXDARD
+ A T log T + B T-1 + I T ) ]
AH0
NO.
12 13 14 15 16
+- 64,470 19,790 +- 22,320 9,905 + 69,510 - 14,750
- 146,180 - 74.355
-
49,505
- 4,865 + 195 +- 44,660 5,040 + 49,700 + 2,530 + 101,260
A 9.18 8.34 6.315 -12.21 1.51 0.67 7.08 5.475 0.085 3.465 111.205 3.45 7.67 +ll.lZ 3.87 i.10.16
---
++ ++
B f5.322 +2.357 t2.311 +3,1395 t3.812 +0.847 2.0905 -0.654 - 1.059 -0,304 -1.869 1-0.70 fl.51
-
-0,810
-0,7825 -2.36
TABLE111. STASDARD Reaction NO. 1 2 3 4 5 6 7 8 9
10
11
12 13 14 15 16
I $24.30 +21 68 +25.30 - 5.371 -24.48
X
Source of Data (7)
expected to occur spontaneouslv as written. However, these complex gas phase reactions are believed to have a slow rate compared t o the less complex reactions that occur a t the carbon surface. For this reason it is probable that practically all the sulfur dioxide will react Fith the solid carbon as expressed by Equations 1 to 6, inclusive. Reaction 15 was investigated by Lewis and Lacey (10) and Stock, Sieclie, and Pohland ( 2 3 . From this work it seems that Some carbon disulfide is formed a t low tpmperatures (600' C. and lower) especially in the presence of catalysts. Stock et aE. found that charroal was a good catalyst for this reaction. It is possible that the charcoal was not merely a catalyst but entered into the reaction according to Equation 12. The standard free energy change for Reaction 15 is positive and increases when the temperature is raised; for this reason it is believed that Reaction 15 is of little or no importance in the present investigation. The decomposition of carbonyl sulfidc to the elements (Reaction 16) is accompanied by a large positive free energy change; hence, only negligible amounts of the decomposition products can exist a t equilibrium in the temperature range studied. The remaining reactions (1, 2, 3, 4, 5, 6, 12, 13, and 14) are interrelated, as shown in Table IV. If it is assumed that all the sulfur dioxide reacts, it is evident that the eguilibrium composition of the resulting gas is dependent upon the relative thermal stability of carbonyl sulfide and carbon disulfide (Reactions 13 and 14). I n order to predict the maximum yield of carbon disulfide a t equilibrium, it is necessary to determine the amounts of carbonyl sulfide and carbon disulfide that can exist a t a given temperature. CASE I. T H E R n f i L STABILITY OF CARBOXYLSULFIDE. ASsumed conditions: starting gas, 100% carbonyl sulfide; total pressure, 1 atmosphere. For the reaction:
2COS = 2CO
+ sz
(14)
the equilibrium expression is
(7) (7) (6) (6)
X 10-3 T * -4- C X 105
Letting X equal the fraction of a mole dissociating, the equilibrium expression becomes
Coefficients
Reaction
11
+C
FREEEKERGY EQUATIONS
General equation: ( AFO = AHo
1 2 3 4 5 6 7 8 9 10
X 10-8 T 2
Vol. 40, No. 7
600
-
43,280 - 51,178 - 25,528 - 55,007 38,660 46,560 - 63,028 - 33,428 - 27,230 - 22,400 - 14,835 f 7,778 - 4,618 f 12,396 3,828 +103,292
-
+
700
-
55,446 E4,923 29,643 59,024 50,644 50,121 54,143 29,121 24,801 24,361 16,158 4- 3,840 4,802 8,642 f 4,100 +103,798
---+-
-
-+ + +
I -100.64 - 13.462 - 23.98 - 4.371 -122.22 35.042 f117.306 63.198 26.068 30.01 - 48.192 52.68 21.58 - 74.26 - 9,091 - 25.30
-
++ -
+-
I n the present investigation carbonyl sulfide is in contact with carbon monoxide. In order t o get some idea of the inhibiting action of carbon monoxide on Reaction 14, a n additional calculation was made assuming a starting gas composition of 50% (by volume) carbonyl sulfide and 50y0carbon monoxide; again, the total pressure was assuhed to be 1 atmosphere. Letting X equal the fraction of a mole dissociating, the equilibrium expression becomes
FREEENERGY CHANGES,CALORIES
800 67,539 - 58,659 - 33,740 - 63,031 62,552 - 53,672 - 45,330 - 24,863 - 22,390 26,222 17,464 59 - 4,987 4,928 4,373 104,308
-
C -3.278 -0.154 - 0,392 f0.778 -4.384 -1.260 +4.532 f2.732 + O . 932 -0,804 -2.668 -2 49 +1.106 -3.600 -0,932 -1,492
Temperatures 900 79,548 62,379 - 37,815 67,025 - 74,376 57,207 36,565 - 20,605 - 19,999 - 28,078 - 18,788 - 3,918 - 5,172 1,254 4,644 104,791
-
+ + +
c. 1000
- 91,549 - 66,085 41,869 - 70,999 - 86,196 - 60,732 27,869 - 16,391 - 17,627
-
29,929 20,101 7,811 5,353 - 2,458 4,914 105,271
+ +
1100
- 103,464 69,773 - 45,899 - 74,950 - 97,936 - 64,245
-
19,234 12,206 15,277 31,772 21,416 11,666 5,528 - 6,138 5178 +105:737
+
1200
- 115,292 73,440 - 49,903 - 78,878
-- 109,594 67,742 - 10,661 - 8,050 - 12,945 33,613 - 22,734 - 15,486 - 5,698 +- 9,788 5,440 +106,189
The results obtained from the solution of Equations A and B are presented in Table V and shown on Figures 1 and 2. CASE 11. THERMAL STSBILITY O F CARBON DISULFIDE. Assumed conditions: starting gas, 100% carbon disulfide; total pressure, 1 atmosphere. For the reaction:
I N D U S T R I A L A N D E N G I N E E R I N G C HE MI S T R Y
July 1948
TABLEIV. To Obtain Reaction 1 2 3 4 5 6 12
INTERRELATIONSHIP O F IMPORTANT CHEMICAL REACTIONS Manipulation Add Reactions 5 and 13 Add Reactions 6 and 13 Subtract Reaction 14 from Reaction 5 Subtract the sum of Reactions 14 and 2za from Reaction 6 Add Reactions 3 and 14 Add Reactions 4.14 and 22= Add Reactions 13 and 14 coz (22).
1229
practical operating conditions which make possible the high carbon disulfide yields (approximately 90%) predicted from the thermodynamic considerations. EXPERIMENTAL
GASES. Commercial tank grade sulfur dioxide, nitrogen, and oxygen were used as received. Several experiments were performed with a gas with a composition like that obtained from a commercial flash roaster. This “roaster” gas was synthesized from commercial tank gases. a 2co = c + COAL. Two anthracite coal samples were used, chosen to represent high and TABLEV. THERMAL STABILITY OF CARBONYL SULFIDEAND CARBON DISULFIDE low grade materials, respectively. The egg coal was crushed and sized. The Equilibrium Gas Composition, Per Cent by Volume dust coal, as received, was nonuniform 2COS = 2CO + Sz (14) C + S2 = CS2 (13) in size and contained a large percentTemp., 50% COS:50% CO 100% cos 100% cs2 Sa CO cos 52 co COS Kp sZ csz age of fines. The dust coal was crushed 0 c. KP 600 0.000786 0.07 50.12 49 81 5.22 10.44 84.34 14.339 6 . 5 93 5 to pass a and then 51.47 47.55 10.92 21.84 67.24 0.011433 0.98 92.3 briquetted; sulfite liquor was used as 700 11.995 7.7 17.62 35.24 4.56 56.84 38.60 47.14 800 0.099057 10.379 8 . 8 91.2 the binder. The resulting briquets were 900 0.58381 9.58 64.37 26 05 23.44 46 88 29.68 8.2043 9 . 8 90.2 89.3 crushed and sized in order more closely 15.97 27.40 2.6433 13.61 70 42 54.80 1000 17.80 8.3052 10.7 1100 9.4927 16.12 74.18 9.70 29.75 59.50 10.75 7.5901 11.6 88.4 to approximate the size characteristics 1200 28.365 17.67 76 48 5.85 31.10 62.20 6.70 7.0102 12.5 87.5 of the crushed egg coal. All the sizing was done on Tyler screens.
c + sz = cs2
(13)
the equilibrium expression is
Letting X equal the fraction of a mole of carbon disulfide dissociating, the equilibrium expression becomes
As there is no volume change involved in Reaction 13, dilution will have no effect upon the stability of carbon disulfide. The results obtained from the solution of Equation C are presented in Table V. These results showthat carbondisulfide isstable a t temperatures from 600 to 1200 C. The maximum possible yield of carbon disulfide a t equilibrium is approximately 90%. The degree of dissociation of carbonyl sulfide into carbon monoxide and sulfur is relatively unimportant because the sulfur is consumed by Reaction 13; this permits Reaction 14 to proceed in the direction of producing more sulfur. O
100
-
80
-
w
x
3 0
> 60 > m I2 w 0
a 40 W
n
20
0 600
800 1000 TEMP. DEG. CENT.
1
Figure 1. Thermal Stability of Carbonyl Sulfide
+
APPARATUS
FURNACES. Two furnaces were employed, one for batch and
2 COS 2CO Sa Initial gas composition, 100% COS
Manuf a c t u r in g procedures are seldom carried out under conditions of true equilibrium. Under these conditions, the actual yield obtained depends not only upon t h e thermodynamic characteristics of the system, but also upon the rates of the various reactions involved. Information concerning the rate of reaction cannot be deduced from thermodynamic data. However, experimentation has shown that the rates of .the controlling reactions in this case are sufficiently rapid to permit setting up 0
the other for continuous operation. The essential features of the furriace designed for batch operation are revealed in Figure 3. The heating units were made by placing Nichrome windings inside 7.5-inch inside diameter Carborundum-clay tubes; this was accomplished with a mandrel. The upper and lower heating units were compensated a t one end. The Carborundum-clay tubes were placed in iron shells fitted with Transite ends and filled with Sil-0-Cel. The reaction chamber was a silica thimble 4 feet long with a 5-inch inside diameter. The open end was fitted with steel flanges which had openings for the sulfur dioxide inlet tube, thermocouple well, and the gas outlet. The reaction tube was gas-tight. After each series of experiments, the reaction tube was removed and emptied. The tube was removed from the furnace by a clamp connected with a steel cable t o a monorail above. The furnace designed for continuoua operation was of simple construction. I t consisted of a 4-inch inside diameter Carbofrax (D-Mix) tube set into a refractory brick heating chamber. The reaction tube was heated externally with Pyrofax gas (approximately 50% butane and 50% propane). The ends of the tube were fitted with steel flanges; the top flange was fabricated t o take a thermocouple well and a port for introducloa ing carbon. A I I I I I hand-operated screw discharge mechanism was connected to the 80 bottom flange. The residue was W discharged into a f gas-tight re60 ceptacle. The sulfur dioxide gas was > m introduced through Ithe bottom flange. 2 W The Carbofrax re0 a 40 action tube was not L entirely gas-tight; according to the manufacturer, it has a porosity of 20 10.67% voids. CARBONDISULFIDE COLLECTION SYSTEM.The gases 0 from the furnaces 600 800 1000 1 ) were led into a large flask which was imTEMP, DEG. CENT. mersed in a salt-ice Figure 2. Thermal Stability of bath. This flask Carbonyl Sulfide served as a dust trap (sulfur) and 2 cos e 2 c o + s , also collected some Initial gas composition, 50% CO, 50% COS
1230
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE VI.
PARTIdL
ANALYSES OF
C O A L S USED
Analytical Results, Per Cent b y Weight
I\Iaterial Determined Volatile Carbon Ash Sulfur
TABLE VII.
Egg coal
(B-12-A) 4 98 83 30 11.72 0.65
Dust mal (B-124) 7.17 70.57 26.26 0.54
ANALYSIS O F CARBOS DISULFIDE (EXPERINENT30)
Test Sulfur (mercury test) Boiling range, O C.
csz, 70
Nonvolatile matter, 7G Foreign sulfides, yG Sulfite and sulfate as SO*, %
TABLE VIII.
Result Present 46-47 99.5 0.002 Under 0.001 Under 0.001
GASASALYSISSCHEME of Passes 1 6 1
KO.
Gas
sot cos coz co
Nz (inert)
Absorbent
HI0
SUJOl
KOH (HzOsol.) cutc12 By difference
..6
water. The gas was then led through a series of glass traps immersed in a dry ice-acetone mixture. The volume of the gas determined the number of traps t h a t were necessary for complete condensation of the carbon disulfide. The carbon disulfide collected in the traps usually contained some water carbonyl sulfide, and a little sulfur. The solid and liquid matehals were separated by decantation; the carbonyl sulfide was evolved when the carbon disulfide was warmed t o room temperature. The purity of the carbon disulfide was determined a t intervals by measuring the refractive index. Quantitative analyses were made according to the method of Bell and hgruss ( 2 ) ; the results of a typical analysis are given in Table 1711. EXPERIMENTAL PROCEDURE
FURNACING TECHNIQWE. Batch Operation. The reaction tube, filled with coal, was lowered into the furnace. This was usually done the evening before the experiments were periormed, in order to give ample time for the furnace to reach thermal equilibrium. A measured sulfur dioxide volume 15 as passed through the carbon bed. Temperature surveys were taken at intervals by sliding a Chroniel-hlumel thermocouple through the protection tube. In some cases coal Tras added during a run; it n-as found that this was not necessary because sufficient carbon vias present to perform a large number of experiments. At the conclusion of a series of experiments, the reaction tube was removed, allowed to cool, and emptied. The physical characteristics of the residues were noted. Continuous Operation. The Carbofrax reaction tube was filled with coal. The Pyrofav gas burners were directed in such a way as to cause the flames to strike the middle section of the tube tangentially. When the desired temperature \vas reached, a measured flow df sulfur dioxide was passed upx-ard through the coal charge. Charging and discharging schedules were arrived at through practice. The carbon disulfide condensers were emptied periodically, providing the data necessary for yield calculations. GAS ANALYSISScHmfE. The gases from the furnace contained carbon disulfide, carbonyl sulfide, sulfur dioxide, water, sulfur, carbon monoxide, carbon dioxide, and some inert material. The separation of carbon disulfide and carbonyl sulfide is difficult in the usual gas analysis apparatus. I n order t o keep the gas analysis scheme as simple as possible, i t was decided to analyze the gases after the carbon disulfide had been condensed. The last traces of water and sulfur were retained in the cold traps. For this reason, the scheme yielded only approximate results because some sulfur dioxide, carbonyl sulfide, and probably carbon
Vol. 40, No. 7
dioxide dissolved in the liquid carbon disulfide. After a considerable number of preliminary experiments with synthetic mixtures of known composition, the scheme indicated in Table ST11 was adopted, using a n Orsat apparatus. I t was fully realized t h a t this procedure yielded only semiquantitative results. However, it TT a3 sufficiently accurate to show trends. Samples of the gas were usually taken after the carbon disulfide had been removed by condensation; whenever possible, a sample was obtained of the gas which was evolved from the carbon disulfide when it TTas warmed to room temperature. Whenever the gas contained both carbon disulfide and carbonyl sulfide the carbon disulfide was absorbed in the Nujol along n i t h the carbonyl sulfide. EXPERIJIESTAL RESULTS(BATCH OPERATIOX).During the course of preliminary experiments (data not included in this paper) it \vas observed that when the furnace temperature was uniform throughout its whole length, low carbon disulfide yields and much elemental sulfur were obtained. When the furnace was hot in the middle and cooler a t the ends, the caibon disulfide yields were greater and the quantity of elemental sulfur wa$ reduced. Because these observations were based on only a fev experiments, it x a s decided to repeat the work on a furnace designed to allow careful control of the temperature gradient5 (Figure 3). The results of the experiments designed to investigate the effects of the various operating conditions are presented in Tables I X and X. Furnace Temperature Nearly Uniform (Table I X , experiments 1 t o 5 , inclusive). Low carbon disulfide yields were obtained. SO much elemental sulfur was formed t h a t it was difficult t o prevent the collection system from becoining clogged. -4ccording to Lepsoe (a), raising the temperature of the entire reaction zone nould produce larger amounts of sulfur. Increasing Temperature of Middle Section of Furnace (Table I X , experiments 6 to 19, inclusive). As the temperature of the middle section of the furnace was increased, the carbon disulfide yields increased. Yery little elemental sulfur was detected. Practically all the sulfur dioxide reacted. As the temperature of the middle section was increased, the carbonyl sulfide content of the off gases decreased and the carbon bonoxide content increased. Increasing Sulfur Dioxide Flow Rate (Table IX, experiments 16 to 31, inclusive). The carbon disulfide yields were not substantially affected by increasing the sulfur dioxide rate from 250 to 1500 cc. per minute. Even Figure 3. Fura t the highest sulfur dioxide flo~f, nace for Batch practically all of the gas reacted, Operation showina the sulfur dioxide consuming reaction t o be rapid. QuantiA. Upper heating unit ties of sulfur dioxide greater than 1500 E. i\.liddle h e a t i n gunit cc. per minute mere not used because of Lower heating excessive back pressures and the inD. SO2 inlet ability to maintain the desired temperaE , Thermocouple well F . Gas outlet ture in the middle section of the furnace. G . Silica reaction tube Changing Coal Size (Table I X , experiments 16 to 19 and 32 t o 54, inclusive). The carbon disulfide yield was not seriously affected by increasing the coal size from 100-mesh (agglomerated to -6 20-mesh) to through 2- to 3-mesh, further increase in coal size caused sharp decreases in the yield. Changing Grade of Coal (Table IX, experiments 32 t o 36 and 56 to 58, inclusive). The substitution of a relatively low grade anthracite did not reduce the carbon disulfide yield. This observation indicated t h a t a special grade of anthracite was not needed for carbon disulfide production. Diluting Sulfur Dioxide, Roaster Gas Composition (Table X, experiments 60 t o 78, inclusive). Very high carbon disulfide yields were obtained with a gas approximating the compositiori of roaster gas. The presence of S70 of oxygen seemed to have a
.
+
s
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1948
1231
CONDITIONS A N D RESULTS (BATCHOPERATION) TABLE IX. EXPERIMENTAL Experiment NO.
1 2 3 4 5
B-12-A B-12-A B-12-A B-12-A B-12-A
-6f20 -6f20 -6+20 -6f20 -6+20
1000 1000 500 500 500
6 7
B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A
-6f20
500 500 500 500 500 500 500 500 500 500 500 500 500
8 9 11 12 13 14 15 16 17 18 19 20 21
22
23 24 25 26
27 28 29 30 31
.
Rate of soz, Elapsed Time, cc./ Hours Min.
Kind of Coal
01
B-12-A B-12-A B-12-A B-12-4 B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A B-12-A B-124
Mesh
-6f20 -6f20 -6f20 -6f20 -6f20
-6f20 -6f20
-6f20 -6+20 -6f20 -6f20 -6+20
250 250 250 250 250 1000 1000 1000 1000 1500 1500 1500
-6+20 -6+20
-6+20
-6+20
-6+20 -6f20
-6f20 -6f20
-6f20 -6f20
-6f20 -6f20
- 100a
32 33 34 35 36 41 42 43 44 45 46 47 48 49 50 51 52 53 54
B-12-A B-12-A B-12 A B-12 A B-12 A B-12 A B-12-A B-12 A B-12-A B-12-4 B-12-.4 B-12-A B-12-A B-12-A B-12-.1 B-12-A B-12-A B-12-A B-12-A
-3+6 -3+6 -3+6 -3f6 -2+3 -2f3 -2+3 -1+2 -1+2 -1f2 1 to 2 1 to 2 1 to 2 1 to 2
56 57 58
B-12-C B-12-C B-124
100a lOOQ 100a
-loom
- 100a - 100a - 100a
inch inch inch inch
3 7 12 17 22
Temperature Survey, O C. Inches from Bottom of Reaction Tube 0 5 10 15 20 25 Furnace Temperature Nearly Uniform 1000 1050 1000 980 1000 975 800 875 900 880 940 850 872 885 890 900 900 912 870 890 920 925 890 920 870 900 910 850 900 900
Increasing Temperature of Middle Section 5 700 780 890 970 700 780 930 1000 10 940 1010 625 775 16 950 1020 630 775 22 970 1060 6 660 790 950 1060 12 665 780 950 1080 680 800 18 665 790 950 1080 24 665 790 950 1075 30 5 980 1125 590 770 11 675 820 1020 1175 650 800 1050 1150 17 770 1020 1170 670 23 6 12 18 24 30
6 12 18 24 6 12 18
640 695 680 670 665 680 685 700 690 750 780 850
500 500 500 500 500 500 500 500 500 500 500 500 500 500 500 500 500 500 500
6 12 18 24 30 6 12 18 24 6 12 18 6 12 18 6 12 18 24
650 760 800 750 750 700 750 750 750 670 815 780 740 790 790 715 780 780 780
500 500 500
6 12 18
730 770 780
Increasing 785 800 790 770 775 775 760 785 785 850 830 970
SO1 Flow R a t e 1150 1060 1080 1190 1175 1060 1070 1170 1060 1170 1015 1150 1000 1160 1075 1200 1025 1180 1000 1160 960 1130 1125 1190
Changing Coal Size 800 1000 1150 830 1060 1190 920 1090 1190 ... 1150 1150 800 1025 1135 830 1030 1180. 840 1070 1185 845 1040 1170 750 935 1150 1245 870 1075 850 1030 1195 995 1150 810 850 1040 1180 860 1050 ll?O 780 1010 1100 850 990 1140 1140 850 1010 855 1010 1150
...
,... ....
Changing Grade of Coal 760 940 1160 800 1050 1200 840 1030 1200
of Furnace 875 890 890 920 890 920 885 925 1000 940 1000 930 1020 990 1030 975 1030 980 1040 950 1075 990 1060 970 1020 1076
Gas Composition,
% by Volume (after CSz Condensed)
30
so2 cos coz co
.. .. .. *. ..
1000 940 890 880 890
..
.. .. ..
.. .. *. ..
..
%:2 verted to
cs*
15 5 10 11 9
850 840 820 810 850 870 950 930 940 840 870 850 920
4 3 2 2 3 4 2 2 2
12 5 10 14 14 6 6 6 7
5 9 5 5 5 5 3 4 2
75 72 75 71 70 70 82 75 80
5
67 71 83 85 87 80 80 80 82 78 78
32 49 71 75 77 60 64 70 67 75 76 71
80 78 81 84 83 56 80 81 80
32 41 60 72 74 4
..
..
..
28 47 40 39 34 47 49 48 45 43 64 66 67
1030 1090 1080 1090 1080 1080 1080 1130 1085 1075 1050 1130
960 1010 1040 1045 1050 1010 1015 1070 1040 940 920 1020
825 910 960 970 970 915 930 970 950 820 825 825
2 2 2 2 2 2 2 1 1 2 2 1
5 6 5 5 5 6 7 7 7 8 10 15
5 4 2 2 2 .3 2 2 3 2 . 2
1050 1110 1175
975 1010 1060
1040 1095 1085 1075 1080 1180 1130 1070 1100 1105 1050 1075 1090 1110
970 1030 1000 985 930 1050 1025 950 990 995 970 995 990 1000
850 910 950 950 950 900 945 910 900 840 960 940 850 885 895 920 870 870 875
2 2 2 2 1 2 2 1 1 2 2 1 2 2 2 3 2 2 2
6 7 6 6 6 5 6 7 8 5 7 8 6 7 8 8 11 13 14
3 5 3 2 2 5 3 2 2 5 3 2 5 3 3 5 4 3 3
69 78 81 69 75 80 69 72 72 71
69 69 47 67 70 48 65 66 37 42 43 40
1120 1170 1180
1020 1080 1090
940 990 1000
2 2 1
7 7 7
5 3 2
64 81 84
3 45 75
.... ....
.... *...
so
64
During experiments 1 t o 5, inclusive, a considerable amount of sulfur was produced. The sulfur clogged the exhaust line and caused difficulty in obtaining reproducible results. During the remainder of the experiments, no trouble was encountered: only a very small amount of sulfur was obrerved. a Coal samples prepared b y grinding material through 100 mesh, briquetting with sulfite liquor binder, and crushing briquets through 6 and on 20 mesh.
slightly adverse effect on the yield. The capacity of the furnace for producing carbon disulfide was greatly reduced when sulfur dioxide gas was diluted and the consumption of carbon per unit of carbon disulfide produced increased because of the oxygen content of the simulated roaster gas. Effect of Heat-Treating Coal (Table X, experiments 66 t o 78, inclusive). I n all the experiments described above, the yields obtained for the first 5 or 6 hours were low and increased as the reaction was continued; the initial yields were not very reproducible. The ultimate yields were reproducible t o within about 5%. The irregularity in the initial yields was believed t o be due, at least in part, t o the heat treatment of the coal before i t reacted with sulfur dioxide. I n t h e usual course of the work, the carbonizing time varied from 16 t o 72 hours, depending on whether the coal sample was charged on the last day of the week or prior t o a holiday. I n order to investigate this effect more carefully; a series of exp r i m e n t s (66 t o 70) was performed with a coal sample t h a t had een heated at 900 " C. for 69 hours while the coal used in experiments 72 to 78 was heated at 900" 6. for 21 hours. A comparison
of the results for these two series of experiments makes it clcar t h a t the coal with the more severe heat treatment gave the higher initial carbon disulfide yield; however, the heat treatment had no effect upon the ultimate yield. I n spite of the long heat treatment of the coal u s e d i n experiments 66 to 70, the initial yield was low compared t o the ultimate yield. This increase in yield as the reaction proceeded was attributed to the activration of the anthracite by the various chemical reactions t h a t took place. Miscellaneous Experiments. The results of two experiments are sufficiently interesting to be recorded. I n one experiment, the coal was removed from the top section of the reaction tube. Under these conditions, the carbon disulfide yield was almost halved, showing t h a t the u per section of the coal charge was needed t o give high carbon $sulfide yields. I n another experiment, the temperature of the upper section of the coal bed was increased from about 900" to 1000" C. T h a t this change did not cause a significant change in the carbon disulfide yield, indicated t h a t close temperature control on the top heating unit was not necessary.
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S-TR Y
1232
Vol. 40,
No. 7
TABLE X. EFFECTOF DILUTIKO SO2 UPON YIELDOF CS2
25
60 61 62 63 64 65 72
100 100
75 76 77 78
8 8 8 8 8 8 8.7 8.7 8.7 8.7 8.7 8.7 8.7
84 84 84 84 84 84 91.3 91.3 91.3 91.3 91.3 91.3 91.3
0 0 0 0
66 67 68 69 70
8.7 8.7 8.7 8.7 8.7
91.3 91.3 91.3 91.3 91.3
0 0 0 0 0
73 74 ..
100 100 100 100 100
1250 1250 1250 1150 1150 1150 1150 1150 1150 1150
13-124 -64-20 B-12-A -6+20 n-12-A - 6 f 2 0 B-12-A - 6 f 2 0 B-12-A - 6 + 2 0 B-12-A - 6 f 2 0 B-12-A -6+20 B-12-A -6+20 ~ 3 - 1 2 -~6 f 2 0 B-12-A -6+20 B-12-A - 6 f 2 0 B-12-A -6+20 B-IZ-A -6+20
100 100 100 100 100
1150 1150 1150 1150 1150
B-12-4 - 6 + 2 0 B-12-A - 6 i - 2 0 B-12-A -6+20 B-12-A -6i-20 B-12-A -61-20
100 100 100 100 100
0
io0
1250 1250 1250
750 740 765 765 760 755 630 670 680 680 680 670 670
6 12 18 24 30 36 6 12 18 24 30 36 42
MECHANISM O F PROCESS
The results of the experimental work sufficiently supplement those of the equilibrium calculations to make it possible to indicate the over-all chemical process for preparing carbon disulfide from anthracite coal and sulfur dioxide. It is rather evident that the process proceeded in steps; therefore, for the sake of simplicity it will be considered as such.
+
STEPI. It is believed that the chief product of the SO2 C reaction in the lower portion of the furnace (500" t o 700" C.) was carbonyl sulfide. This reaction is expressed by the following equation:
+ 2soz = 2cos + coz
980 1160 1080 980 1170 1140 980 1190 1150 1025 1200 1160 970 1160 1140 470 1180 1160 920 1130 1100 950 1150 1120 950 1165 1140 945 1165 1135 930 1170 1140 945 1170 1140 945 1170 1135
Effect of Heat-Treating Coal 6 690 770 930 1190 12 690 770 910 1170 18 695 760 915 1180 24 680 750 895 1150 30 690 755 910 1180
EXPERIXENTAL RESULTS(COXTISUOUSOPERATIOX).The furnace used in these experiments was designed with two objectives in mind. The Pyrofax heating system made it possible to employ higher temperatures than could be attained with Nichrome windings and the use of a Carbofrax reaction tube made it possible to observe the behavior of this material under actual conditions. When the middle portion of the furnace was operated at 1250" C. and the sulfur dioxide rate was 2000 cc. per minute, conversions up to about 85% were obtained. At higher gas rates, the yields diminished (45% a t 4000 cc. per minute). At these high gas rates all of the sulfur dioxide reacted, but sulfur was lost as carbonyl sulfide not as elemental sulfur. Either there was insufficient heat transfer t o dissociate all the carbonyl sulfide or the carbonyl sulfide dissociated too rapidly for the sulfur to be consumed by the carbon disulfide-forming reaction and back reaction to carbonyl sulfide occurred in the cooler top portion of the coal bed. It was found that when the middle section of the furnace was 1250' C. the capacity of the reaction tube was 1.27 pounds of carbon disulfide per hour per cubic foot of reaction chamber volume. iifter 118 hours of operation, the reaction tube was removed and broken to observe its physical condition. The portion of the tube that attained the highest temperatures (approximately 1260" C.) was glazed on the outside wall. There were only slight evidences of attack on the inside of the tube; the mold marks were clearly visible. Some pitting had occurred where the temperature gradient was steep. There was no indication that the tube had suffered a loss in strength.
3c
790 795 816 825 810 800 710 750 750 760 750 740 745
(4)
Because even a t high sulfur dioxide f l o rates ~ all the sulfur dioxide reacted, it is evident t h a t Reaction 4 was rapid. As the carbon dioxide passed to the hotter portions of the coal column it was converted to carbon monoxide according t o the following reaction:
1180 1180 1180 1165 1190
30
970
860
1025 1060 1015 1040 990 1010 1030 1025 1030 1025 1023
920 930 915 940 885 920 930 935 930 930 935
1010 890
COS
COz
CO
CSz L"
0.4 0.5
1.4 1.4 1.4 1.4 1.4 1.3 1. o
1.3 1.0 0.4 0.5 0.4 0.3 1.0 1.3 0.9 0.8 0.6 0.6 0.6
7.0 10 27 22 25 24 15 15 17 17 17 17 17
5 39 56 74 83 82 5 34 50 67 83 88 93
1.0 1.1 1.0 1.0 1.0
19 20 19 18 17
0.6 0.4 0.4 0.4 0.5 0.5 0.4 0.5
1035 940 1040
SO1
940
1045 940 1030 920 1040 930
1.6
1.3 1.0
1.o
0.3 0.3 0.3
1.o 1.0
0.4 0.4
1.4 1.5
0.5 0.4 0.4
1.0 1.0 1.0
+
coz d = 2 c o By adding Equations 4 and 23, Reaction 3 is obtained.
+
27
56
74 85 93
(23)
+
2c so2 = cos co (3) STEP11. It is believed that when the carbonyl sulfide reached the hot middle portion of the coal column it dissociated according to the following reaction: 2cos =
2co
+ 2s
(14)
This view is strongly supported by the experimental observation t h a t the carbon disulfide yields were increased by increasing the temperature of the middle portion of the coal column. STEP111. I t is believed that the atomic sulfur that was formed in Step 11, in the presence of hot coal, was highly reactive and reacted with the coal according to the following reaction:
c 3. 2s = csz
(13) It cannot be decided whether Reaction 13 occurred in the hottest portion or the cooler top section of the coal column. It is possible that the top section functioned only as a prolongation of the middle zone in respect to the carbon-sulfur reaction. OVER-ALL PROCESS.The equation that expresses the over-all chemical process can be obtained as follows:
4c
+ 2soz
5C
+ 2S02
2cos c + 25
= = =
+22s c o + cs,
2cos 2co
= CSz
+ 4CO
(3) (14)
(~ 13) ~ - ,
(1)
It is important to know that Reaction 1 takes place in steps, because each step can be carried out individually at the temperature that gives maximum efficiency. The sulfur dioxide-carbon system is complex, in that there are a large number of possible reactions. Because of the difficulties in obtaining precise analytical results on the products of the reactions, it is practically impossible rigidly to prove a mechanism. However, the mechanism presented above seems to be consistent with both the results of the experimental work and the equilibrium calculations. The results of further experimentation may alter the picture. INDICATION OF AUTOGENOUS PROCESS
If it is agreed that Reaction 1 represents the over-all chemical process, then it becomes evident that 4 moles of carbon monoxide are formed for every mole of carbon disulfide. Reaction 1 is endothermic and requires 62,980 calories of heat t o produce 1 Of The heat derived from burning moles of carbon monoxide is 270,480 calories or 4.3 times the amount neccssarp to form I mole of carbon disulfide. This
July 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
makes it possible to consider carrying out the process autogenously by using the by-product, carbon monoxide, as fuel for heating the reaction tube. This would not be the case if roaster gas were used directly as a source of sulfur dioxide because of the low calorific value of the by-product, gas, resulting from dilution by nitrogen. DISCUSSION L
+
One comprehensive experimental study of the SO2 C system has been reported in the literature. Rassow and Hoffman (12) caused carefully purified beech charcoal to react with dried sulfur dioxide a t temperatures ranging from 700" t o 1000° C. in 50" steps. As no mention was made of temperature gradients, it is assumed that the temperature was constant throughout the carbon charge. The maximum carbon disulfide yield was 357&, obtained a t temperatures of 850' t o 900" C. Large quantities of sulfur and carbonyl sulfide were obtained a t all temperatures. It is believed that the failure of Rassow and Hoffman to obtain high carbon disulfide yields was due to the uniformity of the temperature of the carbon bed. Similar results were obtained in the present investigation when the temperature of the coal column was uniform a t 900" and 1000" C. It seems that sulfur generated by the dissociation of carbonyl sulfide is more reactive toward coal than that obtained by other reactions. The discrepancy between the results of Rassow and Hoffman and those of the present investigation emphasizes the importance of considering the process in steps and carrying out each step under optimum temperature conditions. The size of the experimental equipment used in this investigation did not allow an accurate determination of the carbon efficiency of the process. The condition of the furnace residues indicated that high carbon efficiencies were possible. Quantitative data on this point must await the results of operations on a pilot plant scale. The type of carbon used in the process was important. When metallurgical coke was substituted for the anthracite coal, very little carbon disulfide was formed. The low chemical reactivity of metallurgical coke is well known. I n addition to having a greater initial reactivity than coke, the anthracite coal was con-
1233
tinually activated by the chemical reactions t h a t took place. It is practically4mpossible to activate graphitic carbon. The results of the experiments indicated that the reactions involved in Steps I and I11 took place a t high rates. The slowest step in the process seemed to be the dissociation of carbonyl sulfide. The rate of this reaction really depended upon the rate at which the energy necessary for dissociation could be supplied. For this reason, the efficiency of a furnace for making carbon disulfide will depend chiefly upon the length and temperature of the middle hot zone and the thermal conductivity of the materials of construction. ACKNOWLEDGMENT
The author gratefully acknowledges the indispensable assistance of D. L. Gamble, H. M. Cyr, and G. W. Bisbing. LITERATURE CITED (1)
Bacon, R. F., and Boe, E. S., IND.ENG.CHEM.,37, 469-74 (1945).
Bell, R. T . , and Agruss, M. S., IND. ENG.CHEM.,ANAL.ED., 13, 297-9 (1941), Method 111. (3) Carter, B. M., U. S. Patent 2!141,740 (Dee. 27, 1938). (4) Doumani. T. F., Deery, R. F., and Bradley, W. E., IND.EKG. CHEM.,36,329-32 (1944). (5) Dow, H., and Strosacker, C. J., U. S. Patent 1,350,858 (Aug. 24, (2)
1920). (6) Kelley, K. K., U. S. Bur. Mines, Bull. 384 (1935). (7) Ibid., Bull. 406 (1937). ENG.CHEM.,30,92-100 (1938). (8) Lepsoe, R., IND. (9) Ibid., 32, 910-18 (1940). (10) Lewis, G. N., and Lacey, W. N., J . Am. Chem. Soc., 37, 1976-83 (1915), (11) McElroy, K. P., U. S. Patent 1,369,825 (March 1, 1921). (12) Rassow, B., and Hoffman, K., J . p r a k t . Chem., 104, 207-40 (1922). (13) Stock, A., Siecke, W., and Pohland, E., Ber., 57B, 719-35 (1924). (14) Wagman, D. D., Kilpatrick, J. E., Taylor, W. J., Pitzer, K. S., and Rossini, F. D., J . Research Natl. Bur. S t a n d a r d s , 34,14361 (1945). ENG.CHEM.,38,906-12 (1946). (15) Walker, 8. W., IND. December 1, 1947. Presented before the Divpion of Industrial RECEIVED and Engineering Chemistry a t the 113th Meeting of the AMERICAN CHEMICAL SOCIETY, Chicago, Ill.
DIPHASE METAL CLEANERS Preferential Wetting by the Two Phases IRVING REICH AND FOSTER DEE SNELL Foster D. Snell, Inc., 29 W e s t 15th Street, New York 11, N . Y.
D
IPHASE metal cleaners, which involve the simultaneous contacting of the surface to be cleaned with a free unemulsified solvent phase and a n aqueous phase, present many aspects of theoretical interest. I n the course of a n investigation of such cleaners, a n attempt was made to explore the basic mechanism of their detergent action. Certain results obtained appear anomalous in the light of experience with textile cleaning by aqueous solutions of soap or synthetic detergents; however, they are explicable in the light of fundamental concepts. The diphase solvent cleaner (2, 4 ) used in these experiments had the following formula (in milliliters) : mineral spirits 56, triethanolamine 2, oleic acid 4,butyl Cellosolve 1, and pine oil 15. Pine oil and butyl Cellosolve were added to permit the formation of a homogeneous solution of triethanolamine oleate in the mineral spirits, and for other reasons. The interfacial contact angles of droplets of water on steel un-
der baths of solvent were measured as follows. The steel was grounded with a fine Alundum. paste, rinsed several times with distilled water, wiped dry with filter paper, and then placed in a glass cuvette containing mineral spirits. Droplets of water averaging about 1 mm. in diameter were placed on the steel surface under the mineral spirits through a capillary tube. Contact angles were determined by measuring heights and widths of droplets with a microscope having a micrometer eyepiece. The contact angle is specified by the formula, tan8/2
=
2H/D
where H i s the height and D the base width of the drop. Angles on glass were measured similarly. The glass consisted of microscope slides cleaned by rinsing with acetone, wiped with filter paper, rinsed under distilled water, and finally wiped dry. The materials were not specially purified; hence effects due t o
