I
EDGAR L. PIRET, R. F. HEIN', E: D. BESSER2, and R. G. WHITE University of Minnesota, Minneapolis, Minn.
Oxidation of Peat to Organic Acids Peat can now be oxidized to produce
with alkaline permanganate
b
water-soluble polycarboxylic acids with nitric acid or air humic acids
PEAT
4
-
b
is available in many parts of the world in large quantities and its economic potentialities have attracted considerable interest. Almost 14 billion short tons of air-dried peat are estimated as the U. S. reserve, of which some 7 billion tons of good quality peat are located in the State of Minnesota (7, 37). Its possibilities are therefore particularly important to this State. The object of this investigation was to study in a preliminary manner some of the potentialities of peat as a source of chemical products. I n this work a sample of Minnesota peat was subjected to oxidation by three oxidative techniques previously used on coal-i.e., alkaline permanganate solution, dilute nitric acid, and prolonged exposure to air a t 150' C. The effects of the oxidations were measured by the method of carbon balances (4) or by solubility of the oxidized peat in an acetone-water mixture (37, 39). While much work on the oxidation of coal has been reported (2, 22), the literature on the controlled oxidation of peat
1 Present address, E. I. du Pont de Nemours & Go., Inc., Wilmington, Del. Present address, U. S. Naval Ordnance Testing Station, Inyokern, Calif.
-
is limited (4, 27, 22, 36). Howard and associates (24) have shown that watersoluble aromatic acids can be obtained by the alkaline oxidation of coal. Pilot plant studies of this process have been made (73, 74). Some of the benzenoid acids thus produced have potentia1 value as constituents of modified alkyd resins, plasticizers (Z),drilling muds (74),and lubricants (33), and may have other uses awaiting development. Naturally occurring humic acids are already present as an important fraction of peat, and the peat bogs, which are often very large, represent a fairly concentrated source of these complex acids. Feat, as compared to coal or lignite, is physically and chemically much less homogeneous ; the molecular arrangements are generally less condensed; and it probably contains a greater variety of compounds including aliphatic, heterocyclic, and carbocyclic structures. These characteristics should correspond to a higher reactivity for peat. The composition of peat deposits varies widely and the various strata in the same bog show large differences in analysis. Since the humic acid conient (as determined by alkali extraction) may be 10% in one stratum and 40% in another stratum of the same bog, there should also be ample opportunity to control, by proper selection of the peat,
the yields and products obtainable by chemical action. The promise shown by coal oxidation work, the probable higher reactivity of peat, and the enormous supplies of this undeveloped resource have prompted the present investigation. The following literature is pertinent to the oxidation methods used in this work. Controlled oxidation of suspensions of bituminous coal in aqueous alkali by oxygen gas, at elevated temperatures and pressure, has afforded mixed water-soluble aromatic acids in yields u p to 60% based on the weight of coal (73). Bone and others ( 4 ) made a quantitative study of the oxidation products from cellulose, lignin, peat, lignite, bituminous, and anthracite coal treated with alkaline permanganate. With peat, 10 tq 25% of the carbon appeared chiefly as benzenoid acids. Use of alkaline permanganate in studies of the constitution of coal has been made by Kent (28), Bailey and coworkers ( I ) , and Bone ( 5 ) . The relative effects of alkaline and acidic permanganate have also been compared (77). Mild oxidation methods on coal have yielded so-called regenerated humic acids of a condensed cyclic structure with a n average molecular weight between 300 and 1350 (22). Orlov (35)digested peat with alkali and oxidized the humic VOL. 49, NO. 4
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Table 1.
Standard Tyler Screen Analysis for Peat Screen Mesh Peat Retained, % ’
Figure 1. Apparatus for permanganate oxidation of
10 20 28 35 48 65 100 200
Fines Total
0.00 0.06 6.73 16.40 7.07 11.33 8.37 14.22 35.82
100.00
Table [I,
acids thus extracted with alkaline permanganate. The products obtained were oxalic acid with a small amount of benzoic and terephthalic acids; no mellitic acid was found. The use of nitric acid to produce regenerated humic acids and watersoluble acids from coal has had much study (3, 6, 8-77, 78, 79, 23, 29, 30, 32, 38, 43, 46). Juettner (25) oxidized coal successively with nitric acid and alkaline permanganate. The yield of mellitic acid was much higher than with either alone. Schulz and Howard (42) found a correlation between the carbonhydrogen ratio of special coal fractions and the yield of mellitic acid. Juettner (25)reports similar results. The consumption of nitric acid can be greatly reduced when the ’oxidation is conducted in the presence of air or oxygen (26, 47). Fuchs, Polansky, and Sandhoff (76) used several procedures for the preoxidation of coal with air, and after nitric acid treatment obtained a 90% yield of furfural-soluble material. Kinney and Polansky (37, 39) used the same oxidizing techniques to prepare humic acidlike products, the extracta-
bility of which they tested with various solvents, including water-acetone mixtures. Material Used
The peat used in this work was taken from the sedge-grass peat bog 12 miles north of Minneapolis in Anoka County (44). I n preparing a master sample, 250 pounds of this sedge peat, containing 56% moisture, were dried to approximately 10% moisture in a forced circulation, hot-air drier. This air-dried sample was then thoroughly mixed by the ASTM procedure used in coal sampling and ground to -20 mesh. The master sample was then stored in sealed containers. The screen analysis of this sample, which is important particularly as it may affect air oxidation, is given in Table I and its ultimate and proximate chemical analysis in Table 11. Its heating value is 8050 B.t.u. per pound on a moisture-free basis. Using an analytical method of Souci (45) which is based on the hydrolysis of the organic constituents the following
h
+TO ASPIRATOR
A A
500ml.3-’NECKED FLASK Figure 2.
73 8
Chemical Analysis of Master Sample Ultimate Proximate AnalysisQ,% Analysis? % Carbon 59.2 Volatile matter 63.8 Hydrogen 4.55 Ash 13.5 Nitrogen 2.95 Fixed carbon _22.7 Total 100.0 Sulfur 1.9 Moisture 13.5 Oxygen 31.4 Total 100.0 Dry and ash-free basis. Dry basis.
Apparatus for analytical determinations
INDUSTRIAL AND ENGINEERING CHEMISTRY
values, on a moisture- and ash-free basis, were found-cellulose, 8.7%; hemicellulose, 28.170; pectin, 5.470; and bitumen, 3.37,. This analysis indicates the peat to be of a low rank. Permanganate Oxidation
The alkaline permanganate method of oxidation was used first because of its convenience and in order to establish the yields of aromatic polycarboxylic acids possible with the peat used. The method of Bone and others (4) was followed in which 5-gram samples of peat were suspended in 500 ml. of carbon dioxide-free distilled water containing 8 grams of potassium hydroxide. The apparatus for these experiments is shown in Figure 1. With the mixture refluxing continuously, a 3.570 aqueous potassium permanganate solution was added in small increments, time being allowed after each addition for fading of the purple color. The volumes of permanganate solution were chosen to give permanganate-to-peat ratios of 4.0, 4.33, 4.67, 5.0, 5.28, or 5.33. At the end of each reaction period, the mixture was cooled and filtered to remove the precipitated manganese dioxide and any insolubles. The filtrate was then analyzed for four types of carbon compounds-carbonate carbon, volatile acids, oxalic acid, and higher acids. Analytical Procedure. The analytical methods, based on a carbon balance, are modifications of standard procedures suggested by Howard (4, 24, 26). The apparatus used in this work is illustrated in Figure 2. Carbonate carbon was determined by collecting the carbon dioxide evolved from an acidified sample. Volatile
ORGANIC ACIDS FROM P E A T
too
polycarboxylic acids is from 20 to 13% and the change in carbonate is from 46 to 53%, both a difference of 7%. The percentage carbon as oxalate and volatile acids remains about the same. This indicates that in this range a component in the polycarboxylic acids is oxidized in preference to the oxalate. The yields of polycarboxylic acids obtained, calculated from the ratio of the carbon in the polycarboxylic acids to the total carbon present in the product, compare well with those of Bone on Irish peats (4) in which 10 to 25% yields (depending upon the peat) were found.
90
!E 8 0 z
70
a 60
8 50
*0 4 0
I-
2 - 30
E-
n
20
IO 0
(26, 27). The mixture was separated into the following groups : Group I.
Ammonium salts insoluble in concentrated ammonia solution. Group 11. Barium salts insoluble in water, glacial acetic acid, and formic acid. Group 111. Barium salts insoluble in water and glacial acetic acid, but soluble in formic acid. Group IV. Barium salts insoluble in water, but soluble in glacial acetic acid. Group V. Barium salts soluble in water.
Partial Analysis of Acids 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5 4
WEIGHT RATIO OF K M n 0 4 TO PEAT Figure 3. Effect of potassium permanganate-peat ratio on carbon distribution
acids, calculated as acetic acid, were determined by distilling an aliquot acidified with dilute sulfuric acid followed by titration of the distillate. Oxalate carbon was precipitated as calcium oxalate, which was dissolved in hot dilute sulfuric acid and titrated at 65' to 75' C. with standard permanganate. Total carbon was measured as carbon dioxide after the complete oxidation of a n aliquot by a mixture of chromic and sulfuric acids. Finally, the yield of higher acids was estimated from the difference between total carbon and the sum of the other three types of carbon. The results in Figure 3 show that as the permanganate-to-peat ratio is increased from 4.0 to 5.33 the carbon present in the polycarboxylic acid fraction seems to decrease from 22.7% to a constant value of about 12.5 or 1301,. This value is obtained at a ratio slightly less than 5.0 grams of permanganate per gram of peat. The color characteristics of the solutions after the complete reduction of the permanganate indicate the extent of the oxidation. When the ratio of grams of permanganate to grams of peat is 4.0, the solution is extremely dark in appearance; this color changes to brown, to dark orange, to orange, and finally to yellow as the peat-topermanganate ratio is raised to 5.0. The curve indicating the percentage carbon as oxalate is unique in that it falls from 30 to 0% between the permanganate-peat ratios of 4.7 and 5.4. The amount of carbon oxidized to carbonate rises almost 30% from 52.5 to 82%, indicating that nearly all oxidation taking place over this range is that of the oxidation of oxalate to carbonate. The amount of volatile acids remains constant. Between ratios of 4.3 and 4.7 the change in the percentage carbon as
A sample of the polycarboxylic acids, prepared by using a 5 to 1 permanganateto-peat ratio, was subjected to various analyses. A methyl ethyl ketone extraction procedure similar to that of Franke and Kiebler (73) was used to isolate the material. The product was a tancolored, water-soluble, and somewhat hygroscopic powder. This acid mixture proved soluble 1 to 10 in water, which probably indicates that only small amounts of tereohthalic acid wkre oresent. The solubility of pure terephthalic acid is 1 to 62,000 in cold water and that of isophthalic acid is 1 to 7700 a t 25' C. (20). Sodium fusion of the acid product showed the presence of a small amount of nitrogen and a trace of sulfur. With phenylhydrazine, a yellow crystalline phenylhydrazone was rapidly formed (m:p. 265' to 270' C. decomposes). This probably shows the presence of carbonyl groups in the mixture. The nature of the oxidation by which these acids were obtained precludes the possibility of aldehyde groups. The neutral equivalent for the acid mixture was found to be 75.7. Assuming the acids belong to the benzene series, this would average two to three carboxyl groups per molecule. I t is probable that molecules larger than the benzene series are present (9, 24, 26, 27). A partial fractionation of the acid mixture was made by a method similar to that of Juettner, Smith, and Howard
~
The acids of Groups 11, 111, IV, and V were recovered from the salts by precipitating the barium with sulfuric acid and filtering. These were converted to the lead salts by adding lead acetate and by treating with hydrogen sulfide to form the acids and lead sulfide. The results of this separation (Table 111) were obtained from a 6-gram sample of the acid mixture. The analvsis for Grouo I corresponds closelv , to that of ammonium mellitate (carbon, 32.41%, and hydrogen, 5.44%). Further separation of the constituents of each group, necessary for identifying individual acids, has not yet been accomplished. Recent analytical investigations of related acids have involved chromatographic fractionation (34), spectrographic studies of the methyl esters (34, decarboxylation (72, 3 4 , hydrogenolysis (72), and solvent fractionation (40).
Nitric Acid Oxidation The nitric acid treatment of coal to give regenerated humic acids has had considerable study. Nitric acid, or the oxides of nitrogen, appear to be the least expensive reagents other than air for the oxidation of peat. Nitric acid treatment leads to the formation of the humic acids which are intermediate products in the controlled oxidation of coal to benzenoid acids. Nitric acid, however, is not the best reagent for the second
Table 111.
Partial Analysis of Polycarboxylic Acids Acid Recovered Analysis Group G. % Carbon, yo Hydrogen, Yo
I I1 111
1v V
a
1.0 0.1 1.6 0.06 0.8
Unrecovered 2.4 Total 6.0 Determined on ammonium salt. Not determined.
17
31.28@
2
b
27
41.61
1 13
40.40
40 100
b
VOL. 49, NO. 4
5 * 54Q b
2.78 b
3.44
APRIL 1957
739
The difference may be due to oxidation products such as carbon dioxide. For longer reaction times, however, the amounts of extractable humic acids obtained by the oxidative action of the nitric acid are not significantly greater than those obtained by the action of the hydrochloric.
Air Oxidation
step to polycarboxylic acids as shown by Gauzelin and Crussard (77). Virtually no work has been reported on the controlled oxidation of peat using nitric acid. Ten-gram samples of air-dried peat were refluxed for various periods of time in a 1-liter round-bottomed flask with attached condenser using 200, 400, or 800 ml. of a 570 nitric acid solution. Each refluxed mixture was filtered through a weighed, sintered-glass crucible of medium porosity, and the residue was washed, dried a t 110' C., and weighed. The crucible was then transferred to a weighed Soxhlet thimble and extracted for 4 days with a wateracetone mixture to remove the humic acids. By using 150 ml. of a 40% acetone-in-water solution, the acetone concentration in the condensate corresponded to that of the solution found by Kinney and Polansky ( 3 7 , 3 8 ) to be an excellent solvent for regenerated humic acids. The thimble was dried and weighed. The material soluble in the nitric acid and the extractable humic acids were then calculated separately on a dry, ash-free basis. Results are presented in Figure 4. The nitric acid solubles include the carbon dioxide lost. There is little residue after extraction. Two additional series were run on 10gram samples of peat using 200 ml. of 2.5 and 1.25y0 nitric acid solutions, respectively. The 200-ml. series gave results similar to greater amounts so that 400 and 800 ml. of acid solution were not
740
used in these series. The results, along with those of the previous series using 200 ml. of 570 nitric acid, are presented in Figure 5. A sixth series using 0.81iV hydrochloric acid (same normality as 570 nitric acid) was run to determine the role of the hydrogen ion, and these results are also shown in Figure 5. In Figures 4 and 5, the highest yield of extractable humic acids resulting from the nitric acid treatment occurs after 1 to 2 hours, and amounts to 14 to 2070 of the dry, ash-free weight of the peat. In the same time, the yield of acid-soluble and volatile products is approximately 59y0\vith 570nitric acid. The yield of humic acids diminishes with further treatment, while the soluble and volatile materials increase. In each case the yield of acid-soluble and volatile products approached a constant value; the greater the concentration or volume of acid the higher was this value. The yield of humic acids is considerably lower, and that of the soluble and volatile products considerably greater, than those reported for coal (6, 23, 26). The amount of peat converted to soluble and volatile products by hydrochloric acid was at no time as great as that by nitric acid (Figure 5). The yield of soluble and volatile products obtained with hydrochloric acid reaches a maximum of 59Y0. Approximately 2570 more of the peat is rendered acidsoluble by the .5Y0 nitric acid than by the equivalent hydrochloric acid treatment.
INDUSTRIAL AND ENGINEERING CHEMISTRY
One of the most successful prepararive methods for regenerated humic acids is the air oxidation of coal followed by alkaline extraction and acidification (75, 76, 3 7 , 39). Apparently no similar work has been done on peat. In rhe present work an air oxidation method described by Fuchs, Polansky, and Sandhoff (76) was used, and the humic acid content of the product was derermined by Soxhlet extraction with the above acetone-water mixture. For these experiments, 100-gram portions of peat were placed in shallow pans and heated in an oven at 150' C. Each portion was mixed thoroughly daily and a 10-gram sample was removed from each pan a t weekly intervals. The weighed samples were extracted with the acetone-water mixture. Difficulty was experienced during the extraction because of occasional Icss'of peat from the thimble so that occasional data points are missing. The results of these air oxidation runs are shown in Figure 6. Less than lO7c, based on the dry sample, was initially extractable. The extractables rise to a maximum of 32 to 3670 after 2 to 5 weeks. A decline to between 13 and 22Y0 follows in 6 to 10 weeks. Two samples of these extracted products were analyzed. Sample I
Carbon Hydrogen Nitrogen Ash
52.76 5.28 4.15 1.60
Sample
11
54.72 6.23 3.07 1.89
These experiments show that of the three oxidation methods tried, mild oxidation by air is the only one giving an important yield of humic acids and a low rate of further oxidation. Obviously optimum temperatures and conditions should be found. An alternative hydrolysis and air oxidation method was also tried. In this case a 100-gram peat sample was refluxed for 24 hours in 2000 ml. of 0.82s hydrochloric acid to prevent carbohydrate contamination in the extraction operation. The portion of the peat sample insoluble in hydrochloric acid weighed 53.8 grams after being filtered and dried. From this, 6.25 grams of material was extracted with the acetone-water mixture. The residue was then reground and exposed to air at 150" C. for 2 weeks, the sampIe being
O R G A N I C ACIDS F R O M P E A T (16) Fuchs, W., Polansky, T. S., Sandhoff, A. G., Ibid., 35, 343 (1943). (17) . . Gauzelin. M., Crussard. L., Fuel 17. 19,36 (1938). (18) Grosskinsky, O., Gluckauf 88, 376-9 (1952). (19) Guignet, E., Comfit. Rend. 88, 590 (1879). (20) “Handbook of Chemistry and Physics,” C. D. Hodgman, editor, 31st ed., Chemical Rubber Publ. Co., Cleveland, Ohio, 1949. (21) Hoss, E. (to Gesellschaft fur Kohlentechnik m. b. H.), Ger. Patent 721,000 (April 23, 1942). (22) Howard, H. C., in “Chemistry of Coal Utilization” (H. H. Lowry, editor), chap. 9, Wiley, New York, ,
TREATMENT WITH 200 mL OF 4812 N HCI (EQUIVALENT c
ob Figure acid
5.
I
I
I
20
30
40
I
I
50 TIME ( H O U R S ) Distribution of products from peat treated with nitric or hydrochloric
IO
mixed daily. O n extracting this material with the acetone-water mixture, an additional 4.3 grams was obtained. The total yield, therefore, of humic acids from the hydrolysis and one air oxidation pass was 10.5 grams-that is, 10.5% of the original sample. Thus the humic acids obtained come in part from the primary material and in part from the air oxidation. Acknowledgment
This work was supported by a grant of the Graduate School of the University
of Minnesota’ and by The Iron Range Resources and Rehabilitation Commission of the State of Minnesota. The authors also wish to acknowledge gratefully the assistance of W. P. Armstrong, H. C. Howard, and Alfred Gillet, University of Liege, Belgium. literature Cited
(1) Bailey, A. E. W., others, Fuel 33, 209-21 (1954); Ibid., 34, 37-49 11955). (2) Ba‘slick,’ M., Bull. sac. chim. France 1954, pp. 1239-46. (3) Benning, A., Brennstoff-Chem. 36, 38 (1955). (4) Bone, W. A., Groocock, C. M., Parsons, L. G. B., Sapiro, R. H., Proc. Roy. SOG.(London) 148 A, 492-522 (1935). (5) Bone, W. A., Horton, L., Ward, S. G., Zbid., 127 A, 480-510 (1930). (6) Charmbury, H. B., Eckerd, J. W., La Torre, J. S., Kinney, C. R., J . Am. Chem. SOC. 67, 625 (1945). (7) Corgan, J. A., U. S. Bur. Mines, Minerals Yearbook 1940, pp. 92932 (publ. 1941). (8) Dickson. G.. Easterfield. T. H.. J. Chem.’Soc. ’1898, p. 163. ( 9 ) Dimroth, O., Kerkovius, B., Ann. 399, 120 (1913). (IO) Donath, E., Braunlich, F., Chem. Ztg. 28, 180, 953 (1904). I1 B. L. van. J . S. African Chem. . 1 , Duuren. Inst. 6. 31-5 (1953). ’ (12) Entel, J.; J. Am. Chem. Sac. 76, 3646 (1954); Zbid., 77, 611 (1955). (13) Franke, N. W., Kiebler, M. W., Chem. Ind. 58, 580 (1946). (14) Franke, N. W., Kiebler, M. W., Ruof. C. H.. Savich. T. R.,Howard. H. d..IND.‘ENG.CHEM. 44. 278492 (1952). (15) Friedman, L. D., Kinney, C. R., Zbid., 42, 2525 (1950). \
TIME (WEEKS) Figure 6.
150” C.
Air oxidation of peat at
r
I
1945
(23) Hiwa;d, H. C., IND. ENG. CHEW 35, 156 (1943). (24)‘ Howard. H. C.. Smith. R. C.. Tomarelli, R. C., ‘J. Am.‘Chem. ’Soc. 61, 2398 (1939). (25) Juettner, B., Zbid., 59, 208 (1937). (26) Juettner, B., Smith, R. C., Howard, H. C.. Ibid., 57, 2322 (1935). (27) Ibid., 59; 236-41 (1937): (28) Kent, C. R., Fuel 19, 119-25 (1940). (29) Kinney, C. R., Kerschner, P. M., Zbid., 31, 414-17 (1952). (30) Kinney, C. R., Ockert, K. F., IND. ENG.CHEM.48, 327-32 (1956). (31) Kinney, C . R., Polansky, T. S., Gauger, A. W., Penn State Coll., Mineral Inds. Expt. Sta., Bull. 44, 68 pp. 1946. (32) Mever, H., Monatsh. 35. 163 (1914). (33) Montgomery, C. W., Gilbert, W. I., Kline. R. E. (to Gulf Research & Development Go.), U. S. Patent 2,568,965 (Sept. 25,1951). (34) . . Montgomerv, R. S., others, Fuel 35, 49,?16, 60‘(1956). . (35) Orlov. N. A,. Tishchenko, V. V., Tar‘asenkava, E. M., J. A@@. Chem. (U.S.S.R.) 8, 501-4 (1935). (36) Piret, Edgar L., Armstrong, W. P., Pmc. Minn. Acad. Sci. 15, 128-31 (1947). (37) Plummer, C. E., “Report of Progress in Peat Development,” Iron Range Resources and Rehabilitation Commission, State Office Bldg., St. Paul, Minn., 1949. (38) Polansky, T. S., Kinney, C. R., Fuel 31. 409-13 (1952). (39) Polahky, T. S., Kinney, C. R., IND. ENG.CHEM.39, 925 (1947). (40) Roy, A. N., Howard, H. C., J. A m . Chem. SOC. 74, 3239-42 (1952). (41) Savich, T. R., Howard, H. C., IND. END.CHEW44, 1409-11 (1952). (42) Schulz, G., Howard, H. C., J . Am. Chem. Sac. 68, 994 (1946). (43) Shotts, R. Q., Trans. Am. Inst. Mining Met. Engrs. 187, Tech. Pub. No. 2867-F (in Mining Eng. 187, No. 8, 889-97) (1950); Ibid., 196, Tech. Pub. No. 3526-F (in Mining Eng. 5 , NO. 5, 522-6) (1953); Ibid., 202, Tech. Pub. No. 4040-F (in Mining Eng. 7, No. 6, 563-9) (1955). (44) Soper, E. K., “The Peat Deposits of Minnesota,” Minn. Geol. Survey, Bull. 16, pp. 33, 76-81 (1919). (45) Souci, S. W., Kolloid-2. 82, 87-99 (1938). (46) Tropsch, H., Schellenberg, A., Ges Abhandl. Kenntnis Kohle 6, 214 (1923).
. ,
RECEIVED for review October 20, 1956 ACCEPTED January 17, 1957 VOL. 49, NO. 4
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