March 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
513
for mixtures of the aliphatic hydrocarbons of comparable volatility is not surprising when the difference in molecular structure of the compounds is considered. ACKNOWLEDGMENT
This work was carried out as part of the activities of a Polymerization Process Corporation Fellowship. Financial support from this source made the study possible. H. H. Reamer supervised the details of the laboratory work and Betty Kendall and Virginia Berry carried out the details of the calculations, LITERATURE CITED
(1) Beattie, Kay, and Kaminsky, J . Am. Chem. Soc., 59, 1589 (1937). ( 2 ) Beattie, Poffenberger, and Hadlock, J . Chem. Phys., 3,96 (1935). (3) Bridgeman, J. Am. Chem. SOC.,49,1174 (1927). (4) Dana, Jenkins, Burdick, and Timm, Refrig. Eng., 12,387 (1926). ( 5 ) Gibson and Kincaid, J . Am. Chem.' SOC.,60, 511 (1938). Figure 4. Ratio of Actual to Raoult's Law Equilibrium Constant (6) Glanville and Sage, IND.ENQ.CHEM.,41, 1272 for Benzene (1949). (7) Reamer,'Sage, and Lacey, Ibid., 41, 482 (1949). (8) Sage and Lacey, Trans. Am. Inst. Mining M e t . Engrs., 136, 136 (1940). the corresponding curve in Figure 4 is dotted for this reason. The !218 (lg3*)*
ratio of the equilibrium constants approaches unity a t the vapor pressure of benzene at each temperature. The greater deviation from Raoult's law in the case of the propane-benzene system than
$;
~
~
~
~
R~~~~~~~ August 22, 1949.
Reaction of Iron with Organic Sulfur Compounds U
LYLE A. H.AMILTON AND W. W. WOODS Socony-Vacuum Oil Company, Inc., Paulsboro, N . J .
BETTER knowledge of the reaction of organic sulfur compounds with iron and other common metals is of interest, particularly in the fields of corrosion and extreme pressure lubrication. Crude petroleum oils contain large amounts of sulfur in various forms and corrosion of equipment through chemical attack by the sulfur is encountered at various stages of processing. Low temperature corrosion from sulfur in reduced forms (at below 100" C.) is generally associated with free sulfur, hydrogen sulfide, or polysulfides. This problem has been dis-
cussed in the literature on pipe-line corrosion and its prevention, and in many reports on corrosion by sulfur, sulfides, and hydrogen sulfide. Corrosion by organic sulfur compounds or by decomposition products of organic sulfur compounds becomes more important in processing operations wherein the sulfur-containing petroleum is in contact with metals a t temperatures above 100O C. When petroleum is cracked a t temperatures of 400" to 500" C. and higher, a large portion of the sulfur is eliminated as hydrogen
I n the temperature range 125" to 275' C., many organic compounds containing bivalent sulfur react with iron. In this reaction a major portion of the sulfur is transferred to the iron as a material which is insoluble in organic liquids and appears to be principally ferrous sulfide. This reaction is common both to corrosion problems in this temperature range and to the action of sulfur compounds as extreme pressure lubricant additives, a problem in controlled corrosion. The extent of the reactions of sulfurized terpene hydrocarbons, sulfurized sperm oil, and n-dodecyl mercaptan with iron is compared over the temperature range 100" to 275" C., and an attempt is
made to establish a sulfur balance throughout the range. Experiments on the reaction of copper with several sulfur compounds are reported. A division of sulfur compounds into two classes, based on extreme pressure lubricant tests, is made. Within one group the rate of reaction with iron appears to correlate with effectiveness in these tests. Compounds in the second group which appear to react with iron a t the same rate are quite ineffective. Two different corrosion processes appear to be involved; both of these terminate in the formation of the same iron sulfide on the iron surface. Chemical differences between the processes are not known but presumably must exist.
~
INDUSTRIAL AND ENGINEERING CHEMISTRY
514
0
Vol. 42, No. 3
sulfide, and this becomes the principal corrosive agent. At lower temperatures, in the range 100' to 400" C., many sulfur compounds appear to react directly with metals to form metal sulfides without prior formation of hydrogen sulfide ( 1 , 5 ) . Reaction of organic sulfur compounds with metals in this temperature range causes harmful corrosion of equipment in some systems, an undesirable effect, but also permits lubricating oils, properly compounded n ith sulfur additives, to carry extreme11 heavy loads without seizure between the lubricated surfaces Most studies in this field have been directed either to preventing the corrosion of equipment or to imparting extreme pressure lubricant properties to oils; only in a few cases has the chemical reaction responsible for both been studied. The data presented in this paper were obtained in a program which had as its objective the development of a relationship between the effectiveness of extreme pressure lubricant additives and chemical structure and reactivity. This objective is reflected in the inclusion of two sulfurized products, in spite of incomplete lcnowledge of their chemical structure ( 8 ) , because they are evtrenie pressure lubricant additives of known effectivrnesq The other conipounds studied were two mercaptans and a disulfide. The reaction between metallic iron and three sulfur conipounds has been examined in a semiquantitative manner over the temperature range 100" to 275" C. A €em qualitative results of reaction between copper metal, copper, iron and lead nnphthenates, and several sulfur compounds are also reported. These results extend Eomewhat those of Prutton, Turnbull, and Dlouhy (6) a h o have repoIted that several mono- and disulfides, when heated at 250" C. in a hydrogen atmosphere with no iron present, decompose very slowly yielding hydrogen sulfide. At the same temperature when iron is present a rapid formation of ferrous sulfide occurs with, in most cases, little accompanying hydrogen sulfide.
TEMPERATURE. OC. Figure 1. Reactivity of Sulfurized Terpene Hydrocarbons 29 grams of iron powder contacted with 100 g r a m s of 1 To sulfur oil blend for 5 minutes
MATERIALS
ID
The sulfur compounds used included: Sulfurized sperm oil, noncorrosive (Oil solutions containing 1% sulfur as the indicated sulfur compound did not darken a polished copper strip immersed for 3 hours a t 100" C.); this W:~S H commercial product and contained 10% sulfur. Sulfurized terpene hydrocarbons, noncorrosive, 32.0% sulfur, this product was prepared according to the directions of Holt ( S ) , except that the final topping temperature was 160" C. Multiple additional washes of a portion of the sample with hot sodium sulfide reduced the sulfur content only to between 29 and 30% sulfur I t is therefore believed that of the 32.0% sulfur content, roughlS 30% is attached to one or two carbon atoms by single linkage8 and 2% is attached only to sulfur (8). n-Dodecyl mercaptan, Connecticut Hard Rubber Company tsrt-Dodecyl mercaptan, Phillips Petroleum Company Dibenzyl disulfide Dibenzyl di- and trisulfides
0.9
0.8
0.6 0
L c1
05
0.4
Metals and metal compounds used included: Iron powder, J. T. Balter, hydrogen reduced; this powder httd ti surface area of approximately 0.7 square meter per gram a~ measured by nitrogen adrorption. Cold rolled steel bars, sawed to size, 10 X 0.125 X 0.75 ulchw and with surface bright Copper powder, precipitated, J. T. Baker Iron naphthenate, 9.577?0 iron Copper naphthenate, 11.0% copper Lead naphthenate, 37.0% lead
03
0.2
0.I
100
125
Figure 2.
150
175 200 225 TEMPERATURE OC.
250
275
Reactivity of Sulfurized Sperm Oil
25 grams of iron powder heated in 100 grams of 1% sulfur blend for 5 minutes
All experiments, except a few noted, were carried out wltb oil blends containing 1.0% added sulfur as a specified compound in an S.A.E. 30-mid-continent solvent-refined motor oil. The oil contained 0.15% sulfur which experiments showed was not removed by any of the conditions used.
March 1950
513
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY ANALYSES
Sulfur in the oil solutions was usually determined by a combustion method having an accuracy of about *o.03y0 ( 2 ) . When the oil contained a metal in solution a Parr bomb method was used. Hydrogen sulfide was determined by two methods. When amounts of 10 mg. or more were involved, the hydrogen sulfide was absorbed in sodium hydroxide and titrated with iodine, using standard methods. When smaller amounts were involved the hydrogen sulfide was slowly flushed with a nitrogen stream, through hydrogen sulfide detector tubes as supplied by the Mines Safety Appliance Company. The tubes are available in two sizes and calibration gave the following values as milligrams of hydrogen sulfide per inch of tube colored: Small tube 0.19 mg. maximum deviation *35% Large tube 0.71 mg. maximum deviation *20% I t is probable that greater accuracy could be attained by carefully packing standard bore tubes with a standard lot of adsorbent of uniform size. Ferrous sulfide was determined by dissolving the sample in 25% sulfuric acid and determining the hydrogen sulfide evolved.
be recovered as hydrogen sulfide from the very much larger weight of insoluble material associated with the iron surface. It seems necessary to conclude that either some sulfur is retained in the insoluble material a t the iron surface after treatment with acid, and hence is not iron sulfide, or that some sulfur is lost during the reaction, perhaps as evolved hydrogen sulfide. If the insoluble material, less the iron sulfide, has approximately the same composition as the original sulfurized sperm oil, then the sulfur held in this form represents a large part of the difference between sulfur lost from the oil and sulfur recovered as hydrogen sulfide. I .O
0.9 0.0 0.7
0.6
REACTIONS WITH IRON POWDER
The reactions of oil solutions containing 1.0% added sulfur as ( a ) sulfurized terpene hydrocarbons, ( b ) sulfurized sperm oil, and ( c ) n-dodecyl mercaptan with excess iron powder were studied over the temperature range 100-275' C. The experiments were made as follows: Twenty-five grams of the iron powder were vigorously agitated in 100 grams of oil and rapidly heated to a iven temperature which was maintained for 5 minutes. After t i e 5 minutes, the heat was turned off, agitation was stop ed, the iron was allowed to settle for a minute or two and the oip was decanted through a sintered glass funnel. The iron powder was then washed to constant weight with petroleum ether. On each of the three oil blends (containing 1.0% of added sulfur), values were obtained after 5 minutes at loo", 125', 150°, 175", 200", 225", and in two cases a t 250 O and 275' C. After determining the gross gain in weight of the iron powder the powder was dissolved in acid and the hydrogen sulfide evolved was determined. The original oil and the oil filtrates were analyzed for sulfur. The sulfur removed from the oil was calculated by difference. Data are summarized in Figures 1, 2, and 3. The results were found to be quite reproducible when experiments were carried out by the same operator and with equipment and conditions maintained constant. Changes in stirring rate and ratio of reactants shifted the numerical level but not the relative order of the curves. The data shown are believed to be comparable and points plotted are averages of two or more runs. Sulfur lost from the oil containing sulfurized terpene hydrocarbons could, in large part, be released as hydrogen sulfide from the insoluble material combined on the iron surface by treatment with mineral acid. Since the iron, after solvent washing, had gained in weight by only roughly 20y0 more than the sulfur that could be released as hydrogen sulfide, it can be inferred that this insoluble material combined on the iron surface consisted largely of iron sulfide. At 275" C. the sulfur lost from the oil containing sulfurized sperm oil could be recovered as hydrogen sulfide from the insoluble material associated with the iron surface by treatment with mineral acid. The gain in weight of the iron from material insoluble in organic liquids was very much in excess of the sulfur lost from the oil or recovered from the iron; it is therefore not clearly established from these data that the sulfur associated with the iron surface is combined as iron sulfide, although this would appear most probable. In the temperature range of 175 ' to 225' C. the sulfur lost from the oil containing sulfurized sperm oil exceeded that which could
2Y 0.5 0 0.4
0.3 0.2 01 .
100
Figure 3.
125
150 175 200 225 TEMPERATURE * C .
250
275
Reactivity of Primary Dodecyl Mercaptan
25 grams of iren powder contaoted with 100 grams of 1 % sulfur oil blend for 5 minutes
The sulfur lost from the oil containing dodecyl mercaptan exceeded either the gain in weight of the iron after solvent washing or the sulfur released from the iron as hydrogen sulfide. It is necessary to assume an extra loss of sulfur, perhaps as hydrogen s a d e , during the reaction to achieve a reaction balance. Again the total gain in weight of the iron exceeded the weight of sulfur that could be released with mineral acid. The temperatures at which the reactions observed first become greater than the regarded experimental error are: Approx. Temp.,
c.
150
175 200
1.50
Preliminary data on tertdodecyl mercaptan indicated an appreciable loss of hydrogen sulfide from the oil a t temperatures of 125' C. or higher. Reaction with iron as indicated by gain in weight of the iron exceeded possible error a t about 150" C. In spite of appreciable loss of hydrogen sulfide the curve for gain in weight of the iron was nearly identical with that for sulfurized terpene hydrocarbons until 0.40 gram had been gained.
516
INDUSTRIAL A N D ENGINEERING CHEMISTRY
I
5 IN.
RADIATION SHIELD O I L LEVEL HOT THERMOCOUPLE
AT O I L SURFACE
1/4 IN. BELOW SURFACE
A 29g4C'
238*c. 4 IN.
zoa 'c,
- BLACK
- FLAKY
LACQUER
W I T H CORROSION
8 -GRAY
C
COLORED-SOME
- ALMOST
0 -BROWN
E -BLUE
IJ5 oc.
COLORED
COLD,
HOT
F
- CLEAN
CLEAN
CORROSION
STEEL
TO BLACK
LACQUER
GRAY I N COLOR STEEL
SECTION A I S MOSTLY
ABOVE T H E O I L L E V E L
DURING THE EARLY M I N U T E S OF HEATING
AND I S
GRADUALLY
IMMERSED AS T H E
O I L I S HEATED
Figure 4
Vol. 42, No. 3
I t has been reported ( 5 , 6 )that the reaction is diffusion limited when thick films are involved and that the limiting step is "diffusion of iron ions and electrons outward through the iron sulfide lattice to the surface of the film." Electron diffraction and x-ray diffraction examinations of films formed on the steel bars, both as formed and after stripping on Formvar resin, were made. Electron diffraction patterns, obtained by reflection from the surface of a sample still bearing the corrosion film, showed only the pattern of iron. Attempts to identify the stripped film by electron diffraction were unsuccessful. An x-ray diffraction examination of the stripped film yielded a good powder pattern with strong lines corresponding to the principal spacings of ferrous sulfide and weak lines corresponding to the principal spacings of FeSz (pyrite). KO other lines were observed except those contributed by the supporting resin. Detection of crystalline material in this corrosion film does not prove the absence of amorphous material. Failure to secure an electron diffraction pattern tends to support the opposite conclusion, that a considerable proportion of the corrosion layer is amorphous.
REACTIONS WITH STEEL BARS
REACTIONS WITH COPPER POWDER
In another series of experiments the reaction at the surface of a steel bar was investigated with the oil containing l.OY0 added sulfur as sulfurized terpene hydrocarbons.
A few experiments were made using copper powder in place of iron powder. When an oil blend containing 1.0% of added sulfur as sulfurized sperm oil was heated with copper powder the results were complicated, compared with those with iron powder, by solution of some copper in the oil in addition to the accumulation of the black copper sulfide on the surface of the copper. The experimental conditions were those described for the study with iron powder except for the substitution of 25 grams of copper powder for 25 grams of iron powder. Table I1 illustrates the extent to which copper dissolves in the oil.
In each test a bright cold rolled steel bar 10 X 0.125 X 0.75 inches was immersed to a depth of 4 inches in 75 ml. of test oil in a 100-ml. test tube. Each bar contained a thermocouple 4 inches from the bottom end of the bar, and this was placed a t the oil surface before heating began. A radiation shield was placed 1 inch above the oil surface and the top 5 inches of the bar were heated with a flame. The thermocou le temperature was brought to approximately 371" C. as rap& 8s possible, usually in about 4 minutes, and was held a t this temperature for 30 minutes. As the oil was heated the surface rose about 0.25 inch above the thermocouple. A bar containing several thermocouples was used to construct a curve of temperature against distance from the coolei end of the bar under the conditions given here, and this curve was then used in later tests to calculate the temperature a t various points of the section of the bar immersed. Several bars were heated, as described, in the oil blend used in obtaining the data on reactivity of iron powder with sulfurized terpene hydrocarbons (Figure 1). In these experiments the sulfur concentration in the oil remained relatively constant, dropping only about 5%. The bars, after heating, all had a characteristic appearance. The appearance and the method of sectioning for analysis are shown in Figure 4. In the data which follow, it has been assumed that all the sulfur that is associated with the iron surface as a material insoluble in organic solvents and that can be released as hydrogen sulfide with mineral acid is combined on the surface as ferrous sulfide. The data on the bar sections are shown in Table I. Using the data for the hydrogen sulfide released by mineral acid, the data for the reaction of the oil containing sulfurized terpene hydrocarbons with iron powder have been recalculated to suggest the depth of an iron sulfide film residing on the iron. In Figure 5 the thickness of the ferrous sulfide film formed in each system is plotted against the temperature. 4 bulk density of 4.84 was assumed in each case. The extrapolation of the plot of the iron sulfide film thickness to 100" C. a-here, in actuality, little or no reaction would occur (Figure l), indicates for the iron powder a thickness of ferrous sulfide of about 2 to 8 A,, and for the steel bar a thickness of about 2000 A. The relatively rapid reaction a t 150 O C. must be interpreted to mean that the reaction is quite fast after a critical temperature range is exceeded. The two experiment8 are not directly comparable because of differences in time, stirring, and sulfur concentration-surface area ratios.
I 03
IO2
10
- BAR
L X
STEEL
- 30 MINUTES
0- POWDERED I RON
-
5 MINUTES (DENSITY OF FeS = 4.84)
'C,I 100
150
200
212
302
392
OF.
250
300
350
400
482 572 662 TEMPERATURE
752
Figure 5. Ferrous Sulfide Thickness Produced by 1% Sulfur Oil Blend of Sulfurized Terpene Hydrocarbons
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1950
.a0 TABLE I. REACTION OF STEELBARWITH SULFURIZED TERPENE HYDROCARBONS (1% added sulfur in petroleum oil") Depth of F& Film Cm. x 4'01 (A. X 104) 4 38
Fe8, Mg.b*c Area, AV./ Total sq. em. Sq. Inches 5.3 2.12 A 366 0.328 5.0 A 374 0.437 B 282-366 0.766 4.7 1.38 2 85 B 299-374 0.766 6.1 0.437 5.5 B 310-382 0.985 2.4 0.42 0.87 C 230-282 232-299 0.656 2.0 C 238-310 0 766 2.1 0.766 1.1 0.34 0.70 D 191-232 0.437 1.3 D 202-238 1.533 1.6 0.19 0.39 E 135-191 1.313 1.6 E 143-191 2.079 2.9 E 152-202 a 75 ml. of oil containing 1.0% sulfur (656 mg. added sulfur). 7 square !nches (45 square om.) of iron surface. Less than 5% sulfur reacted with iron. b Each bar immersed to thermocouple (4 inches) in oil then heated to 371O C. (thermocouple) and held at this temperature for 3'0 minutes: bars then sectioned and analyzed for FeS. 0 Probable error is approximately 10%. Section
Temp.,
c.
TABLE11. SOLUTION OF COPPERIN OIL CONTAINING
0
Oil alone, no added sulfur compound
Oil containing 1% added sulfur aulfurized sperm oil a
c.0"
200 225
as
200 225 Reaction temperature waa maintained for 5 minutes.
Copper Found in Oil after Filtering, Wt. % Nil Nil
I
(0
2
8
.70
u
rr'
a"
.60
3
2E
.50
w
a a
8 A0 LL
0
+ -30 I
Yw
3
.20
z 2
.IO
z
0
100
SULFURIZED SPERMOIL Temp
517
125
150 175 200 225 TEMPERATURE, OC.
250
Figure 6. Reaction of Copper and Sulfurized Terpene Hydrocarbons 25 grams of copper powder contacted with 108 grams of 1 % sulfur oil blend for 5 minutes
0.06 0.11
Since the oil did not dissolve copper in the absence of the sulfurized sperm oil it seems probable that the soluble copper is held in solution as a soluble derivative of the sulfurized sperm oil. Oils containing sulfurized terpene hydrocarbons or dibenayl disulfide did not dissolve much copper. The removal of sulfur by copper from a number of sulfur compounds which did not cause solution of copper in the oil is shown in Table 111. All conditions were the same as those used for the iron powder experiments, except for initial concentration of added sulfur.
TABLE 111. REMOVAL OF SULFUR FROM OIL BLENDS BY COPPER POWDER % sulfur Removed at Indicated Sulfur Added to Oil Blend, Temp." Sulfur Compound Wt. % 95OC. 150OC. 175OC. 225O C. None Nil 0 0 0 0 72 100 100 100 Sulfur, flowers 100 100 100 100 Dibenzyl disulfide 0.57 0 2 9 80 Dibenzyl tri- and tetrasulfide 0.95 57 67 57 93 Sulfurized terpene 0.57 hydrocarbons 0 60 99 0 a Reaction temperature was maintained for 5 minutes.
{::%
These data illustrate the well-known fact that free sulfur and sulfur bonded only to other sulfur atoms, as the third and fourth sulfur atoms in tri- and tetrasulfides, are removed completely by reaction with copper metal a t 100' C. The sulfurized terpene hydrocarbons seem to be slightly more reactive than dibenzyl disulfide. The gain in weight of 25 grams of copper powder after reaction for 5 minutes with 100 grams of oil containing 1% of added sulfur as the sulfurized terpene hydrocarbons is shown in Figure 6. Comparison with Figure 1 shows the temperature a t which
reaction exceeds experimental error to be essentially the same for both iron and copper. Thus, it appears to be primarily a characteristic of the sulfur compound. REACTION
OF METAL NAPHTHENATES WITH BLENDS O F SULFUR COMPOUNDS
Preliminary investigation indicated that the extent of reaction of the sulfur compounds with metal as naphthenate was much more difficult to determine quantitatively than was the case with metal as powder. To 100-gram samples of oil blends containing 1.0% of addedsulfur as sulfurized terpene hydrocarbons were added two molar equivalents, based on the sulfur, of copper, of lead, and of iron naphthenates. The solutions were then heated for 5 minutes to temperatures of 100' 125" 150" 175", and 200" C. The l a d solutions were filtered throdgh wlighed Gooch crucibles m t h asbestos fiber pads. The copper and iron samples clogged the filters and attempts to separate the insoluble portions were unsuccessful. Similar ex eriments were made with oil blends containing 1.0% of added su&r as sulfuriaed sperm oil. The lead precipitates were washed to constant weight with petroleum ether and their weighta were determined. Results are shown in Figure 7,plotting 13.4% of the total weight of insolubles as sulfur. These data indicate orders of magnitude only, as small and variable particle size complicates filtration and leaves considerable doubt as to the completeness of removal of solid material. EXTREME PRESSURE LUBRICANT T E S T S
One of the functional effects associated with some sulfur compounds is the ability to impart extreme pressure lubricant properties to mineral oils. Such extreme pressure lubricant properties are commonly measured by determining the load an oil will carry under certain standard test conditions. Two such tests are the .4lmen Pin test (9) and the S.A.E. test ( 7 ) . Data obtained on oils containing sulfur compounds in these two tests are presented in Table IV. The oil blends are those used in the preceding chemical tests and contain 1.0% of added sulfur. An oil, in the Almen test, characteristically either fails at from 2 to 5 weights or carries a considerably higher load when sulfur compounds are used. It does not show a linear relation with
INDUSTRIAL AND ENGINEERING CHEMISTRY
518
sulfur concentration for materials such as the sulfurized terpene hydrocarbons. The S.A.E. test does show more nearly a linear relation with sulfur concentration, with materials which are used as extreme pressure lubricant additives. Bearing in mind these test characteristics, the data in Table IV indicate that the sulfide and disulfide materials become less effective in the S.A.E. test as their reactivity decreases, as measured in the iron powder study. The two mercaptans, however, were quite ineffective as extreme pressure lubricant agents although their reactivity with iron is of the same order of magnitude as the sulfides.
I
G
4
I
0.5
I4
c
C 0.4 V
w
a 0 b:
0.3
II. 3
J
3
0.2
SULFURIZED SPERM OIL 100
125
150
175
200
225
T E MP ER ATU RE OC
250
reaction steps for the chemical basis causing the functional differences. As a preliminary to study of alternate intermediate reaction steps with different types of sulfur compounds, a detailed study of the over-all reaction with a given sulfur compound is appropriate. It is not yet possible to write a chemical equation for the over-all reaction of a sulfur-containing organic compound with iron since this requires a knowledge of both the reactants and the products formed. Some knowledge of the sulfur-containing reactant and of the sulfur-containing reaction product is available in several specific cases, but h o d e d g e is lacking as to the nature of the sulfur-free organic reaction products, and there is some doubt as to the exact form of the iron reactant. Prutton indicates that ferrous sulfide film growth under hydrogen sulfide attack (51, and probably under attack by sulfurcontaining oils ( 6 ) , involves: ( a ) diffusion of iron ions and electrons outward through the iron sulfide lattice to the surface of the film; and ( b ) chemical reaction of iron a t the outer surface of the film either with the sulfur compound or elementary sulfur formed by the dissociation of the compound. If this view is correct, the iron reactant must be iron ions and electrons, or the electrical equivalent, iron atoms, and the reaction must be a t the surface and between these and the organic sulfur compound or its dissociation fragments. It therefore appears that the over-all reaction of an aliphatic disulfide can best be represented as:
RSSR 275
I
Figure 7. Sulfur Precipitated by Heating 100 Grams of Oil Containing Lead Naphthenate and 1% Sulfur for 5 Minutes DISCUSSIOR
The formation of iron sulfide a t the rubbing surface, where it acts as the lubricant, has been suggested as the basis of the action of sulfur compounds as extreme pressure lubricant assistants ( 6 ) , and as metal cutting assistants (4). Present data on sulfide and disulfide materials might be construed to support this view, but the data on mercaptans make it seem necessary to conclude that the extent of formation of iron sulfide at a given temperature may not be the only factor. Greenhill ( 1 ) has shoTn that the coefficient of friction of an iron sulfide film decreases with thickness up to 2 X 1 0 + em. and remains constant Kith increased thickness thereafter. Such a film therefore does act as a lubricant. However, he interprets further lubrication studies as indicating that metal-sulfur-organic films are formed under mild conditions and have lower coefficients of friction. Sulfide materials are grouped as an ineffective class in these studies, whereas mercaptans and other -SH compounds are effective. The present data and other published and unpublished data group sulfides and disulfides as effective compounds in tests as extreme pressure lubricants and mercaptans as ineffective compounds. Thus two independent sets of data, based on different types of functional tests, agree in grouping sulfide and disulfide materials as one class and mercaptans and other active -SH compounds as a different class but differ in indicating which group is effective. The amount of oil-insoluble material, presumably ferrous sulfide, formed by reaction with iron powder does not indicate a basis for division of these materials into these two classes but rather indicates that properly chosen members from each group should be equivalent. Since no basic difference is apparent in the over-all chemical reaction as measured, either in product or in gross rate, it appears necessary to look to the intermediate
Vol. 42, No. 3
+ 2Fe (or 2Fe+++ 4e) +2FeS + hydrocrtrbon(It,Ti?)
Present experiments and those of Prutton (6) have both demonstrated that in the absence of iron, at temperatures of 150" to 250" C., decomposition products of the sulfur compounds are observed only in minor amounts, if a t all. I t therefore appears justifiable to conclude that if decomposition products are present under these conditions they must be of a transient t-ype which recombines to form the original sulfur compound, and an equilibrium must exist between the original compound and the tlecomposition fragments.
PRESSURE LUBRICAXT Tmw TABLE IV. EXTREME Almen Pin Test Torque a t Weights a t highest weight Additive occurred carried Bulfurized terpene 30 swaged 61 hydrocarbons 30 65 8 8 Dibenzyl disulfide 3 7 30 swaged 66 Sulfurized sperm oil 3O-t 70 2 7 n-Dodecyl mercaptan 3 8 tert-Dodecyl mercaptan 2 10 e Failed during two break-in periods.
which failure
+
S.A.E. Teat (1000 R.P.AI.1, Pounds Failed 174 150
100 20n, 10 sec.
20a, 10 sec
The most probable dissociation fragments which nicet this equilibrium requirement are those which would be formed if thermal dissociation of single bonds in the molecule of the sulfur compound occurred. This process would lead to formation of pairs of free radicals or of pairs of ions. The extensive literature on the action of mercaptans and disulfides as modifiers in polymer formation, where it seems well established that the intermediates are free radicals of the type RS.,encourages the belief that free radicals are the most probable fragments in these nonpolar systems. In all organic sulfur compounds which have been discussed, the sulfur atom is held between two other atoms by two separate chemical bonds which, in most cases, differ considerably in strength. It thus seems probable that these will be broken bv
March 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
reaction, at different rates. If only one bond breaks, a free radical or an ion will result which could react with iron to form an iron mercaptide. The iron mercaptide could then decompose to ferrous sulfide and an organic product. If the reaction does not involve dissociation fragments it may be a bimolecular reaction between the iron atom (or ion electrons) and the sulfur containing molecule, and the intermediate complex may decompose to ferrous sulfide or to iron mercaptide, Speculations as to the course and mechanisms of the reaction illustrate lack of knowledge of the actual reaction steps. Investigation of the changes through which the organic portions of a number of organic sulfur compounds pass on reaction with iron will probably be necessary before the functional differences cited can be explained on a logical chemical basis.
+
519
LITERATURE CITED
(1) Greenhill, E. B., J.Inst. PetroEeum, 34,659 (1948). (2) Hagerman, D. B.,Anal. Chem., 19,381 (1947) (3) Holt, L. C.,U. S. Patent 2,443,823,Example 1 (June 22,1948). (4) Merchant, M. E., preprint, American Society of Lubrication Eneineers. Annual Meetinn. Buffalo. N. Y. (1948). (5) Prutton, C. F., Turnbull, D.,and Dlouhy, G., IND. ENG.CHEM., 37,1092(1945). (6) Prutton, C.F.,Turnbull, D., and Dlouhy, G . , J . Inst. Petroleum, 32,90 (1946)., (7) 8.A.E. Journal, 39,23-4 (1936). (8) Westlake, H.E., Chem. Rev., 39,219 (1946);Farmer, H.E.,and Shipley, F. W., J. Polymer Sci., 1,293(1946). (9) Wolf, H. R.,and Mougey, H. C., Proc. Am. Petroleum Inst., 1932, pp. 118-30. RECEIVED April 7, 1949. Presented as a part of the Symposium on Organic Sulfur Compounds before the Division of Petroleum Chemistry at the 115th SOCIETY,San Francisco, Calif. Meeting of the AMERICAN CHPJMICAL
Fermentation of Cigar-Type Tobacco C. 0. JENSEN' AND H. B. PARMELE, P. LoriZZard Company, Jersey City, N . J .
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Bacteria were found to be the agents which initiate the H E present study deals same as those which function with the fermentation in bulk fermentation (4, 6, fermentation process in bullcs of cigar leaf tobacco. Enor sweating of leaf tobacco IO), although a similar result zymes of the tobacco plant, fungi, and chemical reactions preparatory to the manufacmay be accomplished. Forced unaided by microorganisms are discussed as possible causature of cigars and of scrap tive agents. Actively fermenting bulks were found to sweating at 50" or above (1, 1.9, 21) may also be an enchewing tobacco. It aims to have 700 million bacteria per gram at some stages. The explain the primary reaction rise in temperature of bulks followed an increase of bactirely different process. which takes place when such terial numbers. Seven species of bacteria were isolated Invariably heat, carbon leaf is piled in bulks of about from fermenting Wisconsin cigar leaf tobacco. Four of dioxide, and ammonia are these species produced heat when grown on sterilized to2000 to 40,000 pounds (1000 g e n e r a t e d in f e r m e n t i n g to 20,000 kg.) at 30 to 40% bacco; -threedid not. tobacco (IO, l 7 , 1 8 ) . Aloss of moisture. dry matter takes place; this The procedure followed in includes nicotine and other the bulk sweating of tobacco has remained essentially unnitrogen compounds, crude fiber, and ether-soluble and waterchanged for many- vears. In preparation for bulk sweating soluble subst&es (6-9,13). Frankenburg has shown that there enough water is added to the dry bales to prevent breakage is an increase in the protein nitrogen fraction (6) and an increase in nonalkaloid pyridine compounds during the process ( 7 ) . of the leayes when bands of the latter are removed. The hands of filler tobacco, which includes all tobacco except that Reviews of previous work have been made by Johnson (IO), used for cigar binders and wrappers, are usually untied and, in Reid, McKinstry, and Haley ( I @ , and others (4, 1.9,l a ) . Sevsome cases, the midribs are removed from the leaves before fereral theories have been advanced to explain tobacco fermentamentation. In any event the whole leavw, stemmed strips, or tion. This process has been said to be caused by the enzymes of hands are adjusted to the necessary moisture content and placed the leaf, by bacteria, by fungi, and by chemical changes occurin piles. Bulks of cigar wrappers may contain 4000 pounds ring without the aid of either microorganisms or enzymes. Most (2000 kg.) of tobacco or less, 28 to 32% water, and be allowed to published studies have supported either the enzyme or microorganism theories of fermentation as applied to the preparation of ferment until a temperature of 50' C. is reached. For binders and fillers the bulks may contain from 20,000 to 40,000 pounds (10,000 leaf for cigar-making purposes. The work of Johnson (10) lends to 20,000 kg.) of tobacco, 32 to 40% water, and be allowed to support to both of these theories, with particular emphasis on the reach a temperature of 55' to 70' C. High moisture contents and probable importance of fungi. Reid, McKinstry, and Haley (16, high temperatures are permitted when dark leaf is not objection16) support the bacterial hypothesis. It is the purpose of the able, whereas low moisture contents and low temperatures are work described in this paper to indicate more definitely the fundaemployed when light colored leaf is desired, as is the case with mental cause of cigar leaf fermentation. high grade cigar wrappers. Sour wine or vinegar is sometimes CHEMICAL THEORY OF FERMENTATION added along with the necessary water before the leaf is bulked. Such treatment is said to assist in the development of an atThe rate and extent of fermentation can be measured by protractive odor or aroma. duction of carbon dioxide and ammonia, changes in pH, and rise The process of bulk fermentation is often designated as rein temperature. Changes in odor, taste, and burning qualities sweating, when the tobacco subjected to it has been stored for a can also be used as criteria of fermentation. By using any or all year or more, and allowed to age or undergo natural seasonal of these indexes, it can be shown that sterilized tobacco, adjusted sweating in bales or cases. The agenh which initiate aging procto the optimum moisture content with sterilized water, remains esses in cigar leaf and in cigaret tobacco are not necessarily the entirely inactive. The agents required in fermentation are destroyed by heating, which means that the process is biological and 1 Present address, The Pennsylvania State College, State College, Pa.
