January, 1925
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
21
A Study of the Resins in Western Coal' By H. K. Benson UNIVERSITY OF WASHINGTON, SEATTLE, WASH.
HE presence of resinous matter in coal is quite generally known,2 and it has been of considerable aid in the
DISCUSSION OF REsuLTs-The close agreement between the acid and saponification values indicates that this resin is investigation of the origin of certain coals. Its oc- composed almost entirely of resenes, rather than of acids and currence in some of the western coals3 is so abundant and in esters, the more usual preponderating constituents. The some cases is so readily separated that it seemed desirable to iodine values obtained show the resin to be partly unsaturated, study the properties of the resins with a view to their com- with the unsaturation increasing upon partial decomposition in melting, or more complete in distillation. mercial evaluation. The ultimate analysis indicates that the resin is very high Resins in Newcastle Coal4 in carbon. The empirical formula, Cz4H3502, has been calI n the Newcastle mines in the State of Washington, the culated. As in the resin obtained from Staffordshire there is more hydrogen present than resin-bearing coal occurred in a is equivalent to the oxygen, thus 4*5-ft*bed located On the fourth The resins found in Utah and Washingmaking it intermediate in composilevel and designated s' Bed ton coals can be recovered by mechanical tion to hydrocarbons and carboNo* ** In this Ooal the resin Seam separation or hand picking. Both the reshydrates. Dieterich, has isolated was from Oa5 to inch in thickins studied are free from ester8 and have from amber a substance which he ness' The were picked Out the general characteristics of those usually calls succinosilvic acid, with the by hand and separated from adherclassed as the copal group. formula c&&o4, and from copal ing coal. The analytical constants of the two resa resene called p-resene, C2~H3504. CoNSTANTS-sevins have been determined together with Although the acid value shows the minor modifications were found solubility data. The Washington resin has resin to contain very little acid, yet necessary in determining the a melting point of approximately 400" C. the similaritv in the two formulas constants. As the resin decomindicates the-two substances to be posed on melting, it was necessary to place the powdered resin in a sealed tube. By placing the very closely allied. Hence this resin properly belongs to the tube in a bath of molten sodium nitrate it was possible to liq- group designated by Dieterichs as including those that are uefy the resin without apparent decomposition. Likewise on not esters but contain free resin acid accompanied by inert account of its hardness, its reaction with alcoholic potash was mixtures. In this class are found amber, copal, guaiacum, very slow. The method of Worstal16 was therefore followed. sandarac, and dammar. Elworthye puts the Canadian resins in the same class by B This consisted of placing 1 gram of the powdered resin in a glass-stoppered bottle with 15 cc. benzene, 5 cc. alcohol, and comparison with Prussian amber. The similarity of all these 10 cc. 0.5 N aIcoholic potash. After standing for 18 hours it products is evidenced by Table 11. was titrated in the usual way. The constants are given in TABLE11-COMPARISON OF NEWCASTLE AND OTHERRESINS Table 1. Newcastle Coalmont (Prussian) Amber
T
TABLEI-ANALYTICALCONSTANTS OF NEWCASTLE COAL Color. Light yellow to greenish yellow Light transmission. . . . . . . . . . . . . . . . . Transparent t o translucent Specific gravity (at 22" C.). I .03 Hardness. .Scratched by crystal of copper sulfate Ash .............................. 1 . 0 5 per cent Moisture (110' C. for 3 hours). . . . . . 0.15percent 395O to 402' C. Melting point.. ................... Acid number: 5.3 Original sample. ................. 5.3 Melted sample.. . . . . . . . . . . . . . . 1 4 . 0 to 2 1 . 2 Distilled oil. Saponification number: Original sample.. .............. 8.3 8.3 Melted sample.. . . . . . . . . . . . . . . Iodine number: Original sample. . . . . . . . . . . . . . . . . 281.0 to 312.0 Melted sample.. . . . . . . . . . . . . . . . 01f3.0 Distilled oil.. . . . . . . . . . . . . . . . . . . . 1142.0 Ultimate analysis (ash-free basis), per cent: Carbon. ........................ 79.0 10.36 Hydrogen ....................... Oxygen ........................ 8.94 Nitrogen ....................... Nil Sulfur. ......................... Nil
.........................
........ .........................
....................
1 Presented before the Section of Gas and Fuel Chemistry a t the 67th Meeting of the American Chemical Society, Washington, D. C., April 21 to 20, 1924. 2 Siepmann, 2. Berg. Hutlen Salinenwesen, 84, 26 (1891); White, U.S. Geol. Survey, Professional Paper 85 (1914). 8 Subsequent to the completion of this work, a report of the investigation of a similar resin in the Coalmont, B. C . , mines was published in Mines Branch Investigations, Department of Mines, Canada, 1922. 4 The experimental work was done by Raymond J. Schadt in a chemical engineering thesis under direction of the author. 8 J . A m . Chem. SOL,2S, 861 (1903).
Meltinp Doint. O C. Ultimaie analysis, per cent: Carbon Hydrogen Oxygen
(Wash.) 395
(B. C.) 270 to 297
79.60 10.30 8.94
79.80
10.11 9.13
350 to 37510 78.82 10.23 10.95
SOLUBILITY EXPERIMENT-A sample of the coal containing the resin closely adherent and distributed was used for extraction purposes. The proximate analysis on this sample was as follows: Moisture Volatile combustible matter Fixed carbon Ash
Per cent 2.98 54.36 23.78 18.88
The sample was finely ground, 48 per cent passing 200 mesh and 68 per cent, 100 mesh. The extractions were carried out in the ordinary Soxhlet extracting apparatus using 5 to 7 grams in each determination. Table I11 gives the results. The effect of preheating the coal-free resin was ascertained by heating it in an open dish by an oil bath a t a constant temperature of 150" C. for half an hour and then extracting with turpentine. The residue was next heated successively in increments of 25" C . until the extractions decreased. The results are given in Table IV. Wheelerand Wigginton, Fuel. 1, 12 (1922). "Analysis of Resins, Balsams, and Gum Resins;' p. 111. 8 Ibid., p. 7. * Report on Mines Branch Investigations for 1922, p. 56. 10 Thorpe, Dictionary of Applied Chemistry., Vol. 1, leal, p. ,183.
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Upon melting the resin a marked increase in solubility occurred. For this experiment the resin was placed in a distillation flask connected with a condenser. A molten bath of sodium nitrate was used for heating. At 350’ C. the first drop of oil appeared in the receiver. At 400’ C. the contents was entirely liquid and about 3 cc. of a light yellow oil had distilled over. The molten resin was poured out of the flask, cooled, and powdered. I n this state it was completely soluble in turpentine. TABLE111-sOLUBILITY COLOR OF
No. 1 2 3 4 5 6 7 8 9 10
SOLVENT Turpentine Cumene Cymene Toluene Ether Benzene Carbon tetrachloride Acetone Petroleum ether Carbon disulfide
OF
NEWCASTLE RESIN
HARDNESS OF
EXTRACTEDEXTRACTEDPer cent RESIN
Per cent extracted, ash-free basis 26.60 38.50 10.63 16.20 6.38 11.67
Medium brown Very dark Medium brown Dark brown Light brown
RESIN extracted Medium 21.60 Medium 31.20 Medium 8.64 Hard 13.14 Medium hard 5.18 9.46
Dark brown Dark brown
Hard Soft
2.00 2.14
2.47 2.64
Medium brown
Sticky
3.21
3.96
Muddy brown
Crystalline
4.91
6.05
....
....
DISCUSSION OF SOLUBILITY RESULTS-In addition to the solvents already noted, chloroform, glycerol, furfural, rosemary, and cajeput oil were used, but the solubilities were so slight as not to warrant quantitative determinations. It appears that cumene, turpentine, toluene, benzene, and cymene are the best solvents. Inasmuch as the extracted resin is darker in color and softer than in the original state, it may be assumed that these solvents extracted a portion of the soluble matter of coal or that oxidation and condensation products were formed upon the prolonged heating of the solvents which were not removed by heating to 110’ C . under a vacuum of 29 inches. TABLE IV--EFFECT OM PREHEATING ON SOLUBILITY Temperature
c.
150 175 200 225 250
,
Per cent extracted 24.4 37.8 38.2 57.7 31.8
From Table I1 it appears that if the resin is preheated to 225’ C. in air it reaches its maximum solubility but still leaves a residue of 42.3 per cent, while if melted in the absence of air it is completely soluble in turpentine. At 175” C. the resin begins to darken and vapor is given off. Examination of the heated residues showed disparity in color among the particles, suggesting unequal heating. Prolonged heating a t lower temperatures might therefore prove effective in increasing the solubility in turpentine. The resin seems very similar to fossil resins such as amber and copal with respect to solubility and the formation of resin oil. COMMERCIAL ASPECTS OF THE RESIN-According to the superintendent of the mine, resin seams are encountered from which the resin can be picked off by hand, while in other cases it occurs in combination with coal but. as the major portion. Its production in the pure state and in the extracted condition involves no unusual difficulty. I t s use in varnish manufacture is involved in the intricacies of the industry. Varnishes made up in the usual way dried to a very hard finish but tended to darken the objects to which it was applied. Resins in Utah Coalll
The sample of resin-bearing coal was obtained from the Clearcreek Mine in the Pleasant Valley Coal Field of Utah. The resin in this coal occurs in thin sheets (sometimes ?/IS 11 The experimental work was done by W. C. McIndoe in a master’s thesis as du Pont Fellow in 1921-22, under the direction of the author.
Vol. 17, No, f
inch in thickness) in the beds and pockets of the coal aa well as permeating the whole mass of the coal. The coal bed from which these samples were obtained is 13.5 feet thick. EXTRACTION-Inasmuch as the resin could not be separated by hand-picking, it was necessary to determine the choice of solvent and the method of extraction. The coal was ground fine enough to pass a 10-mesh sieve and rolled to obtain a homogeneous and representative sample. The extraction was made in an electrically heated Soxhlet apparatus. The results are given in Table V. TABLE V-RESIN SOLVSNT Benzene Ether Ethyl alcohol Carbon disulfide Petroleum ether Carbon tetrachloride Cymene Acetone
FROM UTAHCOAG Grams from 10 grams Pounds coal Per cent per ton 0.3251 3.25 65.0 0.3177 3.17 63.5 0.0340 0.34 6:8 Discont~nued-coalsubstance also dissolved 0.7719 7.72 154.2 0.3261 3.26 65.2 1.0866 10.86 217.3 0.8422 8.42 168.4
Cymene appeared to be the best solvent, but it was difficult to recover the resin from the solution, even in uucuo, and a poor quality of resin was produced. This also applies t o acetone, and leaves petroleum ether as the solvent that is both effective in quantity and quality of resin extracted. Furthermore, the commercial brand known as Oronite was found suitable for use in such extraction. With this solvent and by means of centrifugal filtration a 20-gram sample of the resin was prepared for use in the determination of the analytical constants, TABLE VI-ANALYTICAL
CONSTANTS O F UTAH RESIN Color.. Light brown Light transmission. Transparent Hardness. Powders easily Specific gravity (22’ ‘2.). 0.9887 Melting point., .................... 98Oto 101‘ C. Acid nimber.. ..................... 156 t o 160 Saponification number. . . . . . . . . . . . . . . 163 to 173 Iodine number., .................... 60 Ultimate analysis, per cent: Carbon 80.4 Hydrogen. ....................... 9.4 Oxygen.. 10.2 Nitrogen ......................... Nil Sulfur.. ......................... Nil
............................ ................. ......................... ............ .......................... ........................
COMPOSITION-Using Tschirch’s method for precipitation of resinic acids, 1 gram of resin was dissolved in ether and agitated successively with solution of ammonium carbonate, sodium carbonate, and potassium hydroxide. Upon acidifying with hydrochloric acid a precipitate of resinic acids was obtained. After steam distillation the ethereal solution yielded a residue weighing 0.119 gram, or about 12 per cent of the original sample. Upon saponifying this residue with 0.5 N alcoholic potash and treating with acetic anhydride, no effect was observed. It is concluded, therefore, that the resin consists of approximately 88 per cent resin acids and 12 per cent of inert material or resenes. With the close agreement between acid and saponification values, this resin may be classed as belonging to those “which are not esters but contain only free resin acids occasionally accompanied by inert admixtures.”* From Zanzibar copal, trachyolic acid, Ca&ssOs, has been isolated as the main constituent, and it also is free from esters. It contains also a resene, C&&804. From the ultimate analysis the simplest empirical formula is Cl&I1hO, or in a mixture of resin acid and resene its polymer might reasonably be assigned as C5&1700s. Like the copals, the resin is insoluble in ammonia and alcohol and soluble in sulfuric acid, chloroform, benzene, and, after melting, in linseed oil and turpentine. COMMERCIAL METHODO F EXTRACTION-Inasmuch as the specific gravity of the resin is less than 1.0 and that of coal is 1.4,it was suggested by the U. S. Mines Experiment Station, Seattle, Wash., that a “float and sink” method of extraction
January, 1925
INDUSTRIAL A N D ENGINEERING CHEMISTRY
might be used. The resin-bearing coal was ground in a ball mill with a brine solution of 1.2 specific gravity, and upon settling the resin was found floating on the surface of the brine, but quantitative separations were not undertaken. COMM~RCIAL ASPECTSOB THE Rmm-Being insoluble in
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alcohol, the resin cannot be made into “spirit varnishes,” but a concentrated petroleum ether solution acts in a similar way, producing a hard, smooth, transparent, yellow coating, which is somewhat brittle. By melting the resin it dissolves in linseed oil and gives a fairly hard, transparent surface.
The Common Occurrence of Corrosion by Electrolyte Concentration Cells’ By Robert J. McKay THEINTERNATIONAL NICKEL Co.,NEWYORK,N . Y
M AN earlier paper2 at-
It should be noted that The results of recent corrosion study in the writer’s this definition of electrolyte tention was directed to laboratory, and in others, indicate widespread corrosive concentration cells takes in the accelerated corroaction by electrolyte concentration cells. Consideration a greater range than the sion of copper-bearing alloys of these cells shows, for instance, how pitting may occur concentration cells comby electrolytic cells whose on the most homogeneous metals, and that, contrary to monly used in the demone. m. f. is due only to differwidely accepted views, the theoretical considerations stration laboratory. In the ences in the concentration would lead one to expect pitting, rather than uniform corlatter the osmotic pressure of the copper ion in the rosion, under a broad range of common, well-defined concorrodingsolution. At that of attainable concentrations ditions. Pits should be expected in all cases where any time no reference could be is large in comparison with solid or colloidal product can remain as a film or mass in found in the literature on the solution pressure of the close proximity to the metal. Their location is detercorrosion to the action of electrode, the electrode is mined by conditions in the solution, rather than in the such cells, and therefore the same as the ion whose metal. For the explanation of the phenomena, the reathe theoretical discussion concentration is varied, and soning of electrochemistry is necessary, but the original was confined to this particthe measurablee. m. f. agrees concept of the “electrolytic theory of corrosion” is insufular case, though qualitawith that calculated by ficient. tive tests indicated widethe Newst formula. These simde t m e s are selected smead distribution. The purpose of the present paper is to demonstrate that for demonstration purposes. In practice; ‘we must ordinacorrosion by such concentration cells is of common occur- rily consider, not these simple cells, but combinations in rence, rather than of the limited application shown in the which are salts of different elements from the electrodes and former paper. I n fact, it is pow believed that a great many, wherein the absolute value of the e. m. f. therefore depends on possibly all, of the so-called paradoxes and anomalies of cor- more complicated reactions. Such cells, of course, include rosion are readily and simply explainable by consideration the important class of “oxidation-reduction” cells. The of these cells. Many of the present inaccuracies in the e. m. f. of these cells is a function of the difference in concensolution of corrosion problems will be avoided only when tration4and disappears when the concentrations are equalized. it is generally understood that such cells are as common and The concept which is considered new is that of corrosion by cells caused by differences in concentration of solution as as important as the galvanic or voltaic cell. Electrolytic corrosion, as generally understood by engi- distinct from differences in the metal. The great changes in the single potential of electrodes of neers, is corrosion due primarily to an e. m. f . set up between two electrodes of different materials in the same electrolyte. the same metal immersed in different solutions were pointed ~ data show that the single potentials in This was the concept of the “electrolytic theory” of corrosion3 out by B a ~ e r . His and there is abundance of proof that corrosion is caused by salt solutions containing oxygen are much more valuable for such galvanic cells. However, the attempt to explain all the predicting corrosion than the potential as usually determined phenomena of various types of corrosion on this basis has against a normal solution of the salt. But, in his interesting data on the localization of corrosion by contact between two been unsuccessful. Electrolyte concentration cells may be defined as cells different metals, he failed to note the relatively great effect of whose e. m. f. is set up by two electrodes of the same material contact of the same metal with two concentrations of solution. Probably the most active. and widespread corroding agent in different electrolytes. Lewis4 defines a concentration cell as “two similar electrodes dipping into solutions of the same is oxygen and no corrosion test should be made, or practical salt, the solutions being at different concentrations of the corrosion problem answered, without the most careful considsalt. The source of e. m. f . is to be found in the tendency of eration and thorough knowledge of the oxygen content of the two solutions to equalize their concentrations.” This the corroding solution and its supply to the corroded surface.61’ latter type of cell is at least as prevalent as the former, and Usually, oxygen in aqueous solution is peculiarly adapted to as powerful. Theoretically, then, it should be as active in the setting up of concentration cells, owing to its low maxiproducing corrosion, and recent experiments in the writer’s mum concentration under atmospheric pressure and the laborattory, and published results by others, have shown this resulting high percentage concentration changes with slight to be true. corrosion. The author has measured the e. m. f. of monel
I
1
a 8 4
Received Auaust 9, 1924. McKay, Trans. A m . Electrochem. SOC.,41,201(1922). Whitney, J . A m . Chcm. SOC.,26, 294 (1903). “A System of Physical Chemistry,” 1916. Longmans, Green & Co.
6 0. Bauer, Mitt. kgl. Matmial-pr&fununssamt,36, 114 (1918); 2. Mdadlkunde, 10, 124 (1919). 0 Thompson and McKay, THIS JOURNAL, 16,1114(1923). 1 Whitman, Russell, Welling, and Cochrane, Ibid., 15,672 (1923).
