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INDUSTRIAL AND ENGINEERING CHEMISTRY
(12) Green, Henry, IND.ENG.CSEM.,ANAL.ED.,14, 676 (1942). (13) Green, Henry, J . Applied Phys., 13, 611-22 (1942). (14) Green, Henry, and Weltmann, R. N., to be published. (15) Harkins, W. D., and Gans, D. M., J . Phys. Chem., 36, 86 (1932). (16) Lenher, Samuel, Chem. Industries, 48, 340 (1941). (17) Reiner, Marcus, J . Rheology, 1, 11-20 (1929). (18) Ryan, L. W., Harkins, W. D., and Gans, D. M., IND. ENQ. CHEM.,24, 1288-98 (1932). (19) Scott-Blair, G . W’., “Introduction to Industrial Rheology”, Philadelphia, P.Blakiston’sSon and Co.,” 1938. (20) Shepard, N. A., Street, J. N., and Park, C. R., in Davis and Blake’s “Chemistry and Technology of Rubber”, Chap. XI, New York, Reinhold Pub. Corp., 1937. (21) Sloan, C. K., Am. Ink M U h e T , 15, No. 2, 16-19 (1937). (22) Sluhan, C. A., Paper Trade J., 111, 26-31 (1940).
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(23) Van Antwerpen, F. J., IND.ENG.CHEM.,31, 66-9 (1939); 33, 16-22 (1941); 33,740 (1941); 35, 126-30 (1943). Vogel, M. R., U. S. Patents 2,173,430 (Sept. 19, 1939);2,190,461 (Feb. 13, 1940). (26) Waele, A. de, J. Am. Chem. SOC.,48, 2760--76 (1926). (26) Wiegand, W. B., U. 5. Patent 1,848,213 (March 8, 1932). (27) Wilkes, B. G., and Wickert, J. N., IND.ENQ.CHEM.,29, 1234-9 (1937). (28) Wolfe, H. J. “Printing and Litho Inks”, 3rd ed., New York, McNair Dorland Co., 1941. (29) Wornum, W. E., in “Wetting and Detergency”. pp. 97-105, London, A. Harvey, 1937. (24)
PRESENTED before the Division of Paint, Varnish, and Plastics Chemistry at the 103rd Meeting of the AMERICAN CHEMICAL SOCIETY, Memphis, Tenn.
COAL OXIDATION WALTER FUCHS’, T. S. POLANSKY,
AND A. G . SANDHOFF The Pennsylvania State College, State College, Penna.
By oxidation in three stages, bituminous coal is transformed into furfural-soluble substance with a yield of 90 per cent or better of the coal proper. The furfural solutions may be considered as systems of two completely miscible substances. Methods for the separation of furfural and ash-free carbonaceous material are pointed out, and possible uses are listed.
promoting substances such as vanadates or nitrates. The percentage of acid groupings is further increased by a second step of air oxidation at a lower temperature. Finally, a treatment with a greatly diminished amount of nitric acid is used to give a product which is easily soluble in cold furfural. Furfural-soluble substance is obtained after the air-oxidized preparation has been treated with 1-2 parts of nitric acid. In former work 8-10 parts of nitric acid were necessary to oxidize raw coal to a stage where the product was furfural soluble. Apparatus and Methods
DESCRIBED in a patent (I), bituminous coal in a properly oxidized condition is readily soluble in furfural. The solution of the carbonaceous material in the organic solvent is easily prepared and separated from mineral matter and fusain, and the recovery of both solvent and solute offers no serious problem. The ash-free carbonaceous material thus obtainable appears to lend itself readily to numerous uses in the production of heat, power, and chemical commodities. I n the original work preceding the patent (9, 4), excess nitric acid was used to accomplish the required oxidation within the short period of one hour. For economic reasons i t appeared desirable to accomplish a considerable part and perhaps all of the oxidation work by the use of air. Air oxidation of coal in a “gas-solid” system, resulting in transformation of the coal proper into humic acids, has been reported in the literature as a tedious and time-consuming process. Wheeler and his associates (7) treated pyridineextracted bituminous coal a t 150” C. for several weeks with a current of moist air, and obtained transformation into socalled ulmic acids. Morgan and Jones (6) and Yohe and Harman (8) accomplished essentially the same conversion of coal proper into hydroxycarboxylic acids by exposing, for several weeks, finely ground coal to air in a drying oven kept at 150” C . We have established that acid groupings may be introduced into the coal proper in reasonably short time by the use of air a t elevated temperatures in the presence of small amounts of 1
Present address, 420 Central Park West, New York. N. Y .
Oxidations were carried out either in an ordinary electric drying oven or in an electrically heated rotary furnace. The rotary furnace was equipped with an automatic feeding device and a temperature control unit. Auxiliary apparatus to regulate the composition, the moisture content, and the rate of flow of the oxidizing gas were also provided. The setup is shown in Figure 1. T o ascertain the effect of oxidation, three analytical methods were used: 1. ALKALIDIGESTION. A 0.5-gram sample was placed into a 250-cc. Erlenmeyer flask equipped with reflux condenser, and 1cc. alcohol and 25 cc. 0.1 N sodium hydroxide solution were added. The mixture was boiled for 30 minutes and filtered and the filtrate was titrated with 0.1 N hydrochloric acid solution, phenolphthalein being used as indicator. 2. MODIFIEDALKALIDIGESTION.In cases of extensive oxidation, the alkaline filtrates became too dark for convenient titration. In these cases 25 cc. of a 0.1 N calcium chloride solution were added just before filtration. This reagent causes preoipitation of insoluble Ca humate according to the equation:
Hum. Naz,,
+ nCaClz = Hum. Ca, + 2nNaC1
The other conditions of procedure 1 remain unchanged. 3. C ~ L C I UACETATE M DECOMPOSITION. A 0.5-gram sample and 25 cc. of a 0.1 N calcium acetate solution were placed into a 250-cc. Erlenmeyer flask equipped with reflux condenser; the mixture was refluxed for 30 minutes, cooled, and filtered. The residue was carefully washed with water, and the filtrate containing acetic acid was titrated with 0.1 N sodium hydroxide solution, phenolphthalein being the indicator. The reaction as indicated in the equation, Hum. Ha,
+ nCa(CH8COO)9 =
Hum. Ca,
+
2nCHaCOOH
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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proceeds to an equilibrium which depends upon the acid strength of the particular hydroxycarboxylic acid used in the test. Thus, while procedures 1 and 2 Provide estimates of the Percentage acid groupings that have been introduced by oxidation, method is indicative of acid strength. Under the conditions of these determinations, furfural-soluble preparations were found to combine with 40 cc. or more of 0.1 N sodium hydroxide solution per gram and to decompose 30 cc. or more of the acetate solution.
approximately 5-7 minutes; simultaneously a countercurrent of air (or of a n air-oxygen mixture) was sent through the oven. I n these experiments temperatures between 1500 and 350" C., air and air-oxygen mixtures of varying moisture content and a t various rates O f flow, and a number of potential catalysts or Promoters (Various vanadates, sulfates, and nitrates) were tested. On the basis of these tests ammonium
FIGURE1. ROTARY FURKACE WITH AUXILIARYEQUIPMENT
Oxidation Procedures PROCEDURE 1. Twenty-gram samples of powdered coal were placed in shallow pans and kept in the drying oven a t 150" C. for a number of weeks. The progress of oxidation is illustrated in Table I. The coal used in these experiments was a Central Pennsylvania coal, Upper Freeport seam, 0.9 per cent moisture, 30.1 per cent volatile matter, 6.1 per cent ash, 62.9 per cent fixed carbon. The coal was ground to pass a 50-mesh sieve.
TABLE I. OXIDATIONOF COALIN A DRYING OVENAT 150' C. Oxidation period, weeks 0.1 N NaOH, cc./g. 0.1 N Ca(Ac)a, cc./g.
0 1.0
1 2 3 4 5 6 8.7 11.4 19.0 22.3 44.0 44.6 3.7 5.8 8.0 11.2 14.4
... ...
By ascribing definite equivalent weights to the various intermediate products of the oxidation, the figures of Table I assume a clearer meaning. Computation shows that the equivalent weights of the various hypothetical coal acids dropped from 10,000 to 225 during 6 weeks. Weathered coals and coal samples that had received a brief oxidizing treatment in the rotary furnace attained an equivalent weight of 250 or less in 3 to 4 weeks. In experiments extended to 10 weeks, no further essential decrease of equivalent weight was noted, b u t the acetate figures improved to 20 cc. per gram or better. In these cases furfural-soluble substance was shown to be present by the following procedure: The oxidized preparations were extracted with alkali, the alkaline solutions were precipitated with acid, and the precipitate was treated with furfural. PROCEDURE 2. In a considerable number of experiments powdered coal was passed through the rotary furnace a t a rate of 160 grams per hour, corresponding to a contact time of
nitrate was found to be the most effective and convenient. It wm established in the early phases of this work that air at 350' C. was just as effective an oxidizing agent as an airoxygen mixture at lo\ver temperatures. I n most experiments the coal was passed through the oven repeatedly because the length of the oven permitted only a short period of contact. After each pass the progress of oxidation was ascertained. Results are presented in Table 11; the rate of air flow waa 1500 cc. per minute, and the yield 160 grams per hour. The smaller the particle size, the more quickly the effect of air oxidation is noted. I n large scale operations the use of a Raymond bowl mill or similar equipment would make i t possible to introduce coal sprayed with suitable substances at temperatures up to 350' C. and to obtain a -200 mesh oxidized product at some suitable lower temperature-e. g., 100" c. TABLE 11. AIR OXIDATION OF COALIN 350' C.
A
ROTARY FURNACE AT
Pass No. 1 2 3 4 0.1 N NaOH, cc./gram Test 1 3.3 4.8 5.9 10.85 Test 2 6.4" 10.2' 11.8 5 5 grama ammonium nitrate per 1000 grams of coal added.
...
5
12.0'
...
By increasing the number of passes, .preparations of a n equivalent weight of 500 or less were obtained. At this stage they were easily 'further oxidized at a lower temperature, giving rise to products of the desired percentage of acid groupings though not of the desired acid strength. PROCEDURE 3. This second stage of air oxidation was carried out as follows: 500 grams of coal preoxidized at 350" C. were placed in a porcelain dish, 100 cc. of a 25 per cent ammonium nitrate solution were added, and with constant stirring the mixture was brought to dryness by heating
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INDUSTRIAL AND ENGINEERING CHEMISTRY
gradually on an electric hot plate to about 150’ C. Agitation a t this temperature was continued until white fumes were no longer visible. The time to complete the operation varied from 30 to 75 minutes. The results of a number of runs are compiled in Table 111. OF COALPR~PARATIONS AT 150’ C. TABLE111. OXIDATION
PRESENCE OF 5 PERCENTAMMONIUM NITRATE
Experiment
No.
0.1 N NaOH, cc.
Before treatment After treatment
IN
1
2
3
4
5
1.8 11.6
10.2 25.0
20.5 38.6
20.5 37.4
20.5
39.2
Experiment 1 refers to original coal. The results were essentially the same when 10 per cent of ammonium nitrate had been added. During the operation, ammonia combined with the hydroxycarboxylic acids, while a considerable quantity of nitrogen oxides, together with excess ammonium salt, escaped. PROCEDURB 4. Preparations that had been passed five to ten times through the rotary furnace a t 350’ C. and subsequently were treated with 5 per cent ammonium nitrate, as indicated in section 3, showed an alkali consumption of 3040 cc. 0.1 N sodium hydroxide and an acetate number of 3-7. I n order to increase the acid strength t o the point where acetate numbers of 25 or better are obtained, a treatment with nitric acid still offers the most convenient and quickest procedure. In order to ascertain the minimum amount of nitric acid necessary to give, in each case, the maximum yield of furfuralsoluble substance, 50-gram samples of the air-oxidized preparations were treated for 1-2 hours with increasing amounts of nitric acid, and the yield of furfural-soluble substance was determined. The alkali number of the samples was 24.0 cc. 0.1 N sodium hydroxide per gram; the acetate number was 2.7 cc. 0.1 N calcium acetate per gram. The following table is illustrative of the results: Cc. oono. HNOi
Furfural-sol. substance, %
50 QO
150
>90
Other wet oxidation experiments with this same sample of preoxidized coal, but conducted with dilute nitric acid, indicated that the same results may be achieved if the time is materially increased. Experiments of this type established the fact that the higher the alkali and acetate numbers, the less nitric acid is needed to accomplish the desired results. Two examples of procedure are added: One hundred grams of a preparation with an alkali value of 39 and an acetate value of 7 were placed in an Erlenmeyer flask immersed in cold water, and 100 cc. of concentrated nitric acid were added in four portions. After the first violent reaction subsided, the mixture was heated in a boiling water bath for 1-2 hours, diluted with water, filtered through a Buchner funnel, washed free from nitric acid, and air-dried. I n another case 100 grams of a preparation with an alkali value of 29 and acetate number of 3 were placed in a %liter round-bottom flask and cooled with ice, and 250 cc. of concentrated nitric acid were added. The remaining procedure was essentially the same as described above. I n either case, 100 grams of oxidized coal gave approximately 120 grams of washed air-dried product. I n addition, a certain amount of soluble substance appeared in the dark colored filtrates and wash water. In both cases the isolated product was soluble in furfural to 90 per cent or better. Fusain and mineral matter are insoluble. Preparation and Properties of Furfural Solutions One thousand cubic centimeters of furfural were placed in a %liter beaker equipped with a stirrer, and 250 grams of
345
product were gradually introduced. Stirring was continued for 30 minutes, the whole operation taking approximately one hour. The mixture was then centrifuged, and the resulting solution of approximately 22 per cent strength was poured through a paper filter. The filtered solutions were concentrated under vacuum to approximately 40 per cent strength. To separate furfural and coal substance, several methods were found to be efficient; precipitation with isopropyl ether, precipitation by pouring into excess water, or steam distillation and, undoubtedly, spray evaporation or the use of drum dryers would serve the same purpose on a plant scale. It was noted that a small fraction of the product is soluble in water and isopropyl ether. As previously shown (4), the solutions of oxidized coal in furfural do not exhibit the Tyndall phenomenon and cannot be classified as colloidal systems. I n the present investigation we have established that the solubility of the oxidized coal substance (hydroxycarboxylic acids) has no limiting value. By mixing the components a t room temperature and atmospheric pressure, solutions up to 30 per cent strength have been prepared. These solutions were easily filterable in the absence of suspended particles; their specific gravities were measured and found to be represented by the expression
+
(1.154% 1.600y)/100 where 5 = percentage furfural y = percentage oxidized coal
By concentration m vacuo, solutions of much greater strength were prepared. Finally it was observed that the addition of a small amount of furfural to an excess of the oxidized coal gave a system that assumed the consistency of an asphalt on standing. I n view of these facts any system composed of coal, oxidized to the proper stage, and furfural may be classified as a binary system comprising two completely miscible liquids. It has been recognized that amorphous, nonuniform substances may be considered as liquids (9). Past experiences and tentative experimental work have disclosed the following possible uses of this new material. The ash-free carbonaceous substance recovered from the furfural solution may be used as an ash-free powdered fuel, either as such or in the possible preparation of a colloidal fuel; as a starting material for the production of active carbon, carbon black, various plastics, paints and varnishes, tanning agents, and insecticides (6). It may be used in the staining of wood and in the purification of water (3). It may be of value in soil beneficiation, it is amenable to hydrogenation, and finally, in mixture with strongly swelling coals, it will give blends of greatly diminished coking pressure and coke of improved quality and smaller ash content. Acknowledgment The aid and assistance of Frieda Fuchs is gratefully acknowledged. Literature Cited (1) Fuchs, W.,U. S. Patent 2,242,822(May, 1941). (2) Fuchs, W., and Horn, O,,Brsnnstof-Chm., 12, 65 (1931). (3) Ibid., 12, 67 (1931). (4) Fuchs, W.. and Sandhoff, A. G., Fuel, 19, 45,69 (1940). (5) Morgan, G. T., and Jones, J. I., J . SOC.C h m . I d . , 57, T290 (1938). (6) Ullmann, F., “Encykloptidie der technischen Chemie”, 2nd ed., Vol. 4,p. 479, Vol. 6,p. 205 (1928-32). (7) Wheeler, R, V., et d.,reviewed in Fuchs’ “Die Chemie der Kohle”, pp. 294 and ff. (1931). (8) Yohe, G. R., and Harman, C. A., Trans.Illinois Shta Acad. Sci., 32, 134 (1939). (9) Zsigmondy, R.,“Kolloidchemie”, 6th ed., Leipzig, Akademisohe Verlagsgesellschaft, 1927. PBBSF~NTBD before the Division of Gas and Fuel Chemistry at the 104th Meeting of the AMBRIOAN CHIIMICAL SOCIBTY, Buffalo, N. Y.
