INDUSTRIAL AND ENGINEERING CHEMISTRY
1268
to the formation in alkaline solution of the second form of ~ o l l a g e n 'and ~ was in accord with the work of Miss Lloyd'4 on the action of alkaline solutions on gelatin. It was for this reason that in the final work the hide pieces were brought to a p H of 2, as from the results of Wilson and KernI6 such treatment should restore the collagen to its initial condition. It proved, however, to have little influence on the plumping of the pieces. Even keeping in a buffer solution at a p H of 8, at a temperature of 40" C., had little influence on the plumping. Nevertheless, bating a t 40" C. for 6 hours in a solution containing 5 grams of a commercial bate, buffered a t p H 8, restored the hide kept in alkaline solution for 1 week practically to its initial condition, as shown in the table. Hide kept a t p H 12.5 for the longer period, however, did not fall so completely. The results obtained would indicate that disintegration products of the collagen are a t least partially responsible for the incomplete falling of the hide pieces. The finding la 14 1s
Wilson, "Chemistry of Leather Manufacture," p. 109. Biochem. J . , 14, 147 (1920). Wilson, "Chemistry of Leather Manufacture." p. 111.
Vol. 19, No. 11
is fully in accord with the conclusion of MarriottI6 that removal of disintegrated cQllagen is an important function of the bating process and offers a convenient method of measuring this activity of bating preparations. It is significant that in the depression of hide plumped a t p H 11, the plumping (1.27) produced by a 4-normal solution of sodium chloride corresponds closely with the figure (1.24) obtained when hide plumped a t p H 12.5 is brought back to a p H of 8. Probably, therefore, the small influence of sodium chloride on the reduction of the plumping of hide produced by alkaline solutions is connected with the presence of partially disintegrated collagen rather than with the existence of the collagen in another form. Whereas G u ~ t a v s o n 'has ~ offered evidence of the importance to be attached to the previous history of the hide, as influencing its behavior towards tanning agents, this investigation stresses the important effect of that history on its physical properties. 18
J. Inst. SOC.Leather Trades Chem., 10, 132 (1926).
17
THIS JOURNAL, 19, 243 (1927).
Origin and Decomposition of Carbon Disulfide in Gas-Making' The Carbon-Sulfur Complex By Wilbert J. Huff and John C. Holtz DZPARTMZNT OF GAS ERGIREERING, THE JOHNS HOPKINSUSIVERSITY, BALTIXORB, MD.
T
HIS paper describes an extension of the experimental inquiry into the origin of carbon disulfide previously reported by one of the writers.2 I n the initial work it was shown that coal undergoing carbonization gave no carbon disulfide when the rate of change of temperature was very low, while coal undergoing a very rapid change in temperature gave important quantities of carbon disulfide. Under the experimental conditions of that inquiry no carbon disulfide was formed when coal gas containing hydrogen sulfide was passed over heated coke, and the carbon disulfide contained in that coal gas was partially decomposed. It was suggested that this carbon disulfide was formed in local high-sulfur regions which when heated suddenly became chemically active in the presence of a deficiency of carbon and hydrogen, thus forming carbon disulfide which was swept rapidly out of the retort by the gas stream; whereas, when heated slowly, with the aid of diffusion, the sulfur might combine to form hydrogen sulfide and non-volatile solid carbon-sulfur complexes rather than carbon disulfide. The need of additional inquiry into any explanation of the formation of carbon disulfide was stressed a t that time. Production of Carbon Disulfide during Cracking of Oil
I n such an investigation the formation of carbon disulfide during the cracking of oil is of interest, because the sulfur compounds of the oil are probably uniformly dissolved in the remaining oil constituents, thus affording an experimental condition quite unlike that prevailing in coal, whose heterogeneous make-up is recognized. OIL USED-For the qualitative preliminary experiments Presented before the Ninth Annual Con1 Received July 30, 1927. vention of the American Gas Association, Chicago, Ill., October 10 to 14, 1927. 1 Huff, THIS JOURNAL, 18, 357 (1926).
which we report herewith, a gas oil having the following properties was used (unless otherwise noted) : Dala on Original Oil Color Black Viscosity 2 . 7 7 a t 77OF. ( 2 5 ' C . ) Water Trace Sulfur 3 . 6 1 7 , by wt. Specific gravity 0.9123 220' F. (104' C.) Flash point 245' F. (118' C.) Burning point Remarks: Gas Chemists' Handbook Method, 3 cc. per minute
Distillation Data PER CENTOFF By By SPECIFIC TEXPERATURE volume weight GRAVITY F. c. ann -1 A 4 300-3% 149-i?? 376-400 191-204 0.4 0.3 0.769 2.8 2.5 0.817 400-450 204-232 450-500 232-260 9.5 8.8 0.839 500-550 260-288 15.2 14.7 0.869 550-600 600-650 650-700 700-722 Coke TOTAL
288-316 316-343 343-371 371-383
16.6 17.0 17,6 18.7
16.4 17.0 17.8 19.1 1.12
-
-
97.8
97.72
0.892 0.904 0.916 0.920
DESCRIPTION OF
FRACTION
Colorless Colorless Colorless Very light yellowish green Light yellowish green Yellowish green Dark yellowish green Reddish brown
APPARATUSA S D PROCEDURE-The apparatus possessed no novel features. The cracking tube was an inclined quartz tube about 36 inches (91 cm.) long, 7/8 inches (22 mm.) internal diameter, wall thickness about 1/8 inch (3 mm.). An electric furnace heating about 12 inches (30 cm.) of tube for an interval from about 6 to about 18 inches (15 to 45 cm.) from the upper end was used. The furnace temperatures were measured by means of base-metal couples placed a t the center of the furnace between the furnace wall and the quartz tube. The upper end of the quartz tube was equipped with a suitable device for feeding the oil a t various controllable rates, and the lower end was attached to a suitable tar trap,
November, 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1269
cotton tar filter tube, and gasometer. The oil rate was about the loss of sulfur to products other than carbon disulfide. 2 cc. in 5 minutes. The gas obtained was examined for car- Since a carbonaceous deposit always appeared in the crackbon disulfide by the method developed by one of the writer^.^ ing tube, it was not possible to decide whether the appearance RESULTS-cracking experiments upon this high-sulfur of the carbon disulfide was due to interaction with this cargas oil, using no added atmosphere of gas other than that bon or to the addition of sulfur by the cracked oil products produced by the cracking, showed that a furnace temperature followed by subsequent scission. of 1200" F. (649' C.) gave so small a quantity of carbon Further Study of Interaction between Carbon and disulfide that the cupric xanthate precipitate could not be Hydrogen Sulfide obtained from 2-liter gas samples. From gas samples produced a t 1350" F. (732" C.) a definite precipitate was formed To further examine the interaction between carbon und hyand from gas a t furnace temperatures of 1800" F. (982" C.) drogen sulfide a cartridge of sugar charcoal about 2 inches very heavy precipitates were obtained. (5 cm.) long was inserted into the cracking tube a t the cenThese experiments indicated that carbon disulfide might ter of the furnace. Nitrogen (containing 0.2 per cent oxygen be produced from a gas-making material that was initially as an impurity) provided the bulk of the gas stream. To homogeneous, and emphasized the importance of temper- this was added hydrogen sulfide sufficient to give 200 grains per 100 cubicfeet (4.6 grams atureeffects in this producper cubic meter) using the tion. No information was method of Gollmar.6 Suitavailable t o indicate To investigate the origin of carbon disulfide in the able provision was made to whether this carbon disuldecomposition of a homogeneous gas-making material, remove spray from the gas fide was produced by scisa high-sulfur gas oil was cracked at various temperastream before this entered sion in the degeneration of tures. Over the range studied, increasing temperathe quartz tube. The furcomplex organic sulfur comtures gave increasing amounts of carbon disulfide. nace temperature was mainpounds or by synthesis from Heterogeneous conditions were recognized in the protained a t about 1550" F. carbon and sulfur. duction of retort carbon. To determine the part (843" C.) No hydrogen played by this, and by the hydrogen sulfide, a number Scission or Synthesis? sulfide was observed on the of experiments were made using a medicinal oil and stain paper test when apTo throw some light upon hydrogen sulfide, and also sugar charcoal and hydrogen plied to the gas first passing this question of scission or sulfide. A large amount of hydrogen sulfide disover the char, but a distinct synthesis, several liters of appeared without producing a corresponding amount odor of sulfur dioxide was sulfur-free oil gas were preof carbon disulfide. In the experiments with sugar observed for a short time, pared by cracking a mechars an extended delay occurred before carbon diwhich was possibly due to dicinal oil a t 1500-1600" E'. sulfide was produced in sufficient quantities to be dethe occlusion of oxygen by (816-871" C . ) . 4 T h e tected. This delay was increased with an increase in the char. This odor soon cracked products contained the heated carbon surface. It is believed that this disappeared but for a short no hydrogen sulfide, but delay is due to the formation of a carbon-sulfur comtime longer no hydrogen for the first experiment suffiplex, which probably plays an important, if not an sulfide was detected on the cient of this compound was exclusive, part in the origin and decomposition of stain paper. Following this added to give a concentracarbon disulfide under gas-making conditions. A interval hydrogen sulfide tion of 400 grains per 100 discussion of this complex is given. appeared, but the tests for cubic feet (9.2 grams per carbon disulfide still recubic meter) of the oil gas mained negative until about mixture. This was allowed to stand to permit mixing by diffusion and then passed 20 liters of gas had passed over the char, when traces of through the clean cracking tube while additional medicinal carbon disulfide were observed in the gas samples. This oil was cracked therein a t a furnace temperature of 1500- compound was found in all the gas subsequently tested. 1600" F. The test for carbon disulfide failed to show a For a short time after it appeared qualitative tests showed precipitate. The disappearance of an important amount of evidence of some increase in its concentration, after which hydrogen sulfide was observed. Allowing for the dilution time no further increase was noted qualitatively. An analyeffects due to the cracking of the added medicinal oil, a con- sis of the char, which was sulfur-free a t the beginning of centration of 140 grains of hydrogen sulfide per 100 cubic the experiment, showed that it had absorbed 2.8 per cent feet (3.2 grams per cubic meter) was calculated upon the sulfur. assumption of no sulfur loss to retort carbon or tar, or volatile The experiment was repeated in substantially the same organic sulfur compounds other than carbon disulfide, whereas manner except that the sugar char was broken into much only 70 grains per 100 cubic feet (1.6 grams per cubic meter) smaller pieces, thereby presenting a more extensive surface remained in the finished gas, showing an important loss of to the gas stream. Carbon disulfide did not appear until sulfur to one or more of these products. 32 liters of gas had been passed over the char, and the char The experiment was repeated, save that a very high con- upon analysis showed 5.5 per cent sulfur. centration of hydrogen sulfide (over 3000 grains per 100 cubic Previous experimental work2 had shown that under cerfeet or 69 grams per cubic meter) was admixed. A heavy tain conditions hydrogen sulfide in coal gas failed to give precipitate was obtained in the carbon disulfide test, and carbon disulfide when passed over heated coke, and the caran important loss in hydrogen sulfide was again noted in the bon disulfide present already was partially decomposed. finished gas. The present information therefore suggests that carbon surThe experiments therefore showed that sulfur associated faces, when exposed to sulfur-containing gases a t temperawith hydrogen in the form of hydrogen sulfide might be con- tures encountered in gas-making, possess for a time the propverted to carbon disulfide under some conditions of cracking. erty of absorbing sulfur from those gases, thereby assisting However, this conversion, under the conditions tested, favored in the decomposition of the sulfur compounds. This ability 8 Huff, J . A m . Chem. Sac.. 48, 81 (1926). to absorb sulfur probably diminishes as the exposed carbon
4 Nul01 as supplied by the Standard Oil Company of New Jersey. showed no stain test with bright metallic copper after 72 hours.
This
5
An:. Gas Assocn. Monthly, 8, 461 (1926).
1270
INDUSTRIAL AND ENGINEERING CHEMISTRY
surface attains saturation, and carbon disulfide is ultimately given off from such surfaces. Other Investigations of Carbon-Sulfur Complex The carbon-sulfur complex formed has been studied by a number of investigators. From a phase-rule study Powell6 deduced that the sulfur is held in two forms-(a) as adsorbed free sulfur, and (b) as sulfur in solid solution in the carbon or held upon the surface in such a manner that it is impossible to differentiate it from solid solution by the means employed. However, Powell did not observe the formation of carbon disulfide, which apparently persists only after the carbon-sulfur surface has attained a certain favorable concentration of sulfur. Solution and adsorption are generally held to be physical phenomena, but the evidence herewith presented indicates that some chemical forces, or forces of a like magnitude, may also come into play to bond part of the sulfur and carbon together. Wibaut' made an extensive study of the carbon-sulfur complex and showed the great resistance to decomposition by heat and vacuum which this complex attains under certain conditions. Although he passed sulfur vapors over charcoal he did not detect the formation of carbon disulfide, Other investigations dealing with complexes between carbon and sulfur have been made by Mixter,8 Stock and Praetorius,g and Arctowiski.lo The production of carbon disulfide by the action of hydrogen sulfide on heated charcoal has been patented.l* Evidence for Existence of Carbon-Sulfur Complex The tendency for heated surfaces, such as those of certain refractories, to decompose sulfur compounds in gas is n d l known. After a time these surfaces lose this property. This loss in decomposing power is generally attributed to the accumulation of carbon, and in accordance therewith it is found that the decomposing properties are restored by burning off the carbonaceous deposit. In such experiment in this laboratory the carbonaceous deposits have always contained sulfur, which was, of course, also removed by the burning-off process. It is suggested, therefore, that the loss in decomposing power is due not merely to the presence of carbon upon the surface but rather to the gradual formation of a carbon-sulfur complex. The writers have cracked the high-sulfur gas oil previously mentioned both in the open tube and in the tube containing a 4-inch (lo-cm.) cartridge of clean pumice (8 to 20 mesh). With the fresh cartridge in place it was possible to elevate the cracking temperature from 1200Oto 1350" F. (649 to 732" C.) without producing sufficient carbon disulfide t o be detected in the test. This absence of carbon disulfide is attributed to terminal surfaces upon which there had not yet been built the requisite carbon-sulfur complex. That carbon-containing surfaces free from this complex sulfur condition possess a property similar to that of the clean pumice was shown by using a coke cartridge, purged with hydrogen a t a high temperature, in place of the pumice. Again no carbon disulfide was found a t 1350" F. (732" (3.). With continued use, however, this carbon-sulfur complex may be expected to form, and continuation of the last experiment showed carbon disulfide ultimately appearing in the exit gas, as predicted. J . A m . Chem. Soc., 46, 1 (1923). Rec. tyav. chim., 41, 153 (1922). 8 A m . J . Sci., [3]46, 363 (1893),especially p. 373. 9 Bcr., 45, 3568; C. A . , 1, 2525 (1913);Gas World, 68, 665; C. A., 7, 2022 (1913). 102. anorg. Chem., 8 , 314 (1895). 11 Walter, U. S. Patent 1,193,210 (August 1, 1916); C. A., 10, 2393 (lQl6). 8
7
Vol. 19, N o . 11
This delay in the formation of carbon disulfide over cracking surfaces has been noted in the operation of carbureted water-gas plants. Klein12in discussing the formation of carbon disulfide from high-sulfur, high-coke oils in commercial practice says: When using a high-coke oil, a large part of the coke is deposited on the checker brick. During the run in which it is deposited the coke is too cool to react with the hydrogen sulfide. If permitted to remain, however, it becomes incandescent during the succeeding blow, and on the following run is active in the formation of carbon disulfide. Granting that the formation of carbon disulfide may be accelerated by increased temperatures on the reacting surfaces, the delay in its formation encountered in our experiments could not be explained by the assumption of external temperature changes. It is therefore suggested that the delayed formation of the appropriate carbon-sulfur complex may explain, in part a t least, the delay noted by Klein. With increasing temperatures of cracking, the dissociation of hydrogen sulfide and other compounds containing sulfur increases and the deposition of carbon also increases. At certain higher temperatures encountered in gas-making practice, therefore, it may be expected that the formation of this carbon-sulfur complex may quickly occur, Thus it may be possible to explain the very rapid production of carbon disulfide from a quickly formed complex when a sulfurcontaining oil or coal is suddenly thrown upon a very hot surface. Until the matter is studied further, however, it does not seem possible to state whether the carbon disulfide of gas-making processes is derived in part from the scission of original organic sulfur compounds or whether it is derived exclusively from the decomposition of a carbon-sulfur comp!ex which first forms upon the cracking surface. The present presumptive evidence, however, indicates that such a complex plays an important, if not an exclusive, part in the formation of carbon disulfide. Conditions which favor the fixation of high local-sulfur as sudden heating with diminished concentrations-such diffusion, and reduction of exposed surfaces-together with the rapid removal of formed carbon disulfide may be expected to favor the presence of carbon disulfide. These conditions are obtained in the rapid heating of coal, as previously pointed out.* Any process or device which will allow the gas to make extended contact with active heated surfaces sufficiently low in or completely free from sulfur, whether or not they are initially carbon surfaces, will diminish the concentration of carbon disulfide in the gas, and may yield a gas completely free from this compound. There is a t present no evidence to show that carbon disulfide is produced by a simple reaction between hydrogen sulfide and carbon. Analogy with Carbon-Oxygen Complex in Combustion of Carbon The evidence in favor of the existence of a solid complex of carbon and sulfur in the process of forming carbon disulfide presents an analogy with the formation of a somewhat similar complex of carbon and oxygen in the combustion of carbon, as pointed out by Rhead and Wheeler.13 Their conception of what takes place during combustion is somewhat as follows : Each oxygen molecule that comes into collision with the carbon becomes "fixed,"* * for the present it is sufficient to assume that several carbon molecules hold one oxygen molecule, in bond as it were, and do not allow it to escape in conjunction with one of their atoms. A considerable evolution of heat takes place during this attachment of oxygen molecules, SO much so that some of them eventually acquire sufficient energy 11 18
A m . Gus Assocn. Monthly, 5, 183 (1923). J . Chem. SOC.(London), lOlT, 846 (1912);103T, 461 (1913).
Kovemher, 1X27
IlVDU8TIZIAL A M D &A\'GI:INE&RIKC CHBiWISTItY
1271
Problems for Further Study
to seize Iml
