This procedure for determining the acidic groups on the surface of the oxidized coal is essentially the same as that
Fi g u r e 3 . Ra t e o f Ox i d a t i o n o f Pi t t s b u r g h Co a l
described by Ubaldini and Siniramed {25) for determining the equivalent weights of naturally occurring “humic acids” . In the Coal Research Laboratory this method has been used in obtaining the equivalent weights of “humic acids” pre
pared by the oxidation of bituminous coals. The procedure is based on the decomposition of calcium acetate by the acid groups and the determination of the resulting acetic acid by the liberation of carbon dioxide from calcium carbonate.
Whether the reaction proceeds in one manner or the other, one mole of carbon dioxide is liberated for each two carboxyl groups. The reaction is carried to completion by refluxing the mixture and sweeping out the carbon dioxide formed with nitrogen. The apparatus used is shown in Figure 5.
Before this method was applied to oxidized coals its re
liability was tested on a number of authentic samples of organic acids. Succinic, benzoic, o-phthalic, o-, in-, and p- hvdroxybenzoic, and gallic acids were employed for this pur
pose. The simple carboxylic acids gave results for equiva
lent weight which were 1 to 2 per cent high— i. e., less than the theoretical amounts of carbon dioxide were evolved dur
ing the reaction. W ith the hydroxy acids the results were all low by about the same amount and cafbon dioxide con
tinued to be evolved slowly if the reaction time was increased.
With the hydroxybenzoic acids the equivalent weights cal
culated on reaction of the carboxyl alone were too low by about 10 per cent when a reaction time of 4 hours was used.
With gallic acid the values were almost exactly half that calculated for reaction of the carboxyl. That this excess evolution of carbon dioxide was due to reaction of the phe
nolic hydroxyls was shown by the fact that the methoxy com
pounds of these acids gave results agreeing with the theoretical values within 1 per cent. Since in a measurement of surface oxidation of coal it is immaterial what type of acidic group reacts, the procedure appeared suitable for the purpose de
sired.
The finely ground sample was placed in flask D, the weight being adjusted to evolve a convenient amount of carbon dioxide:
1 gram of calcium carbonate and 100 ml. of 3 per cent calcium acetate were then added, the flask was attached to the reflux con
denser, C, and the mixture was boiled with a microburner.
Tank nitrogen purified by passage over hot reduced copper was used as a sweeping gas and passed through the sulfuric acid bubble counter, A, and Ascarite tube, B, down through the long tube in the center of the condenser and bubbled through the boiling mixture. The evolved carbon dioxide was swept out through the condenser, sulfuric acid bubble counter, E, and dry
ing tube, F, filled with Anhydrone, into the weighing tube, G, containing Ascarite and Anhydrone. The nitrogen passed out through the guard tube, II, filled with soda lime, the trap, I, and the bubble counter, J , to the atmosphere. Under these condi
tions a manipulative blank of 1 to 2 mg. of carbon dioxide was obtained. This blank could be reduced to 0.2 mg. by a short preliminary refluxing of the reagents before addition of the sam
ple. With slightly oxidized coals difficulty in wetting was ob
served ; part of the sample floated on the surface and was carried up the side of the flask out of contact with the bulk of the re
agents. In such cases addition of 10 ml. of a 1 per cent solution of a wetting agent, such as Aerosol or Nekal B X , was found to im
prove the reproducibility of the procedure. and Figure G. The total acidity has been calculated in terms of carboxyl, since it seems probable that these groups are chicfly responsible for the reaction observed. In calcu
lating carboxyl groups the amount of carbon dioxide evolved from the unoxidized coal was subtracted from the values for the different oxidized samples. The difference, multiplied by two, since each mole of calcium salt reacts with two carboxyl groups, yields the carboxyl groups formed in the oxidation. The amount of carbon dioxide evolved from the unoxidized Pocahontas coal corresponds to the presence of approximately 0.01 per cent of oxygen as carboxyl groups and the corresponding figures for Pittsburgh and Illinois are 0.10 and 0.13 per cent, respectively. In the case of the Pocahontas coal there was a somewhat smaller evolution of carbon dioxide from the sample which had been oxidized at 75° than from the original unoxidized samples. In Figure 6 carboxyl groups, in millimoles per 100 grams of coal, found I N E E R I N G C H E M I S T R Y Vol. 15, No. 9
Ta b l e II. Di s t r i b u t i o n o f Ox y g e n i n Ox i d i z e d Co a l s
Temperature Time O: Used HaO O O CO Fixed
Millimoles per
0 C. Hours 100 g. % % % %
Pocahontas Nio. 3 Coal
75 240 10.86 30.85 11.05 1.66 56.43
75 306 11.40 29.20 J1.31 1.58 57.90
100 261 39.40 31.60 12.80 2.04 53.50
100 312 40.90 32.16 12.84 1.81 53.13
125 90 86.40 29.85 13.19 2.08 54.85
125 215 143.0 27.62 14.75 2.38 55.25
Pittsburgh Coal
75 223 36.49 18.82 14.44 1.70 65.03
75 319 48.38 21.19 9.06 1 .59 68.15
100 240 104.8 27.77 12.50 2.10 57.63
100 52 45.7 19.04 10.06 1.53 69.35
125 43 139.4 17.93 15.06 2.01 65.00
125 212 316.0 27.17 18.77 2.47 51.62
Illinois No. 6 Coal
75 246.5 49.35 18.27 13.31 2.09 66.32
75 323.0 68.27 20.21 12.15 1.96 65.36
100 260 189.8 33.14 18.07 2.53 46.26
100 62 106.9 24.50 13.84 2.06 59.60
125 46 275.4 34.77 16.22 3.59 15.38
125 148 327.4 29.9 19.16 2.23 48.71
September 15, 1943 A N A L Y T I C A L E D I T I O N by this method, are plotted as a function of
the amount of oxygen known to have been fixed in preparing the sample. 'Itfjs evident that only a fraction of the total oxygen fixed reacts like a carboxyl group and that this fraction varies greatly with the coal, ranging from a few per cent for the Pocahontas up to 40 per cent for the Illinois. There is, however, for each coal a general linear relation between the oxygen found as carboxyls and the total fixed. The method is obviously less sensitive for high-rank coals. W ith a Pitts
burgh seam coal, samples prepared containing 1.0 per cent by weight of “fixed” oxygen evolve approximately 1 mg. of carbon dioxide per gram of sample.
T h e r m a l D e c o m p o s itio n o f th e S u rfa c e C o m p le x
I t is known that the gaseous products obtained from the thermal decomposition of partly oxidized coals contain larger propor
tions of the oxides of carbon than do those from virgin coals.
T a b l e III . De t e r m in a t io n o p Ac id Gr o u p s o n Ox i d i z e d Co a l s
Oxidation Time O2 Fixed COi Carboxyl
° C. Hours . Millimoles per 100 grams -Pocahontas No. 3 Coal
0 0.36
75 240 6.13 0.31
75 306 6.60 0.29
100 261 21.1 0.52 0.32
100 312 21.8 0.61 0.50
125 99 47.4 0.66 0.60
125 215 79.0 0.95 1.18
Pittsburgh Coal
0 3.14
75 223 23.75
75 319 32.98
100 168 66.1 5^71 5Ü4
100 240 60.4 5.07 3.86
100 52 31.7 4.43 2.58
125 43 90.6 5.09 3.90
125 212 163.1 7.46 8.64
30 £07 3.64 1.00
Illinois No. 6 Coal
0 4.28
7 i 246.5 32.73 11.02 13.58
75 323.0 44.83 , .
100 260 87.8 12.56 16.56
100 62 63.7 8.95 9.34
125 46 125.0 14.98 21.40
125 148 159.6 15.32 22.08
The results are shown in Table IV and Figure 8. It is evident that this is a more sensitive procedure for determin
ing surface oxidation of coal, since a much larger fraction of the oxygen appears as a measurable product, in this case oxides of carbon, than was the case in the carboxyl group determination. The particular experimental arrangements used did not permit the determination of water vapor. Modi
fication of the analytical procedure to permit determination of the water evolved might increase the sensitivity consider
ably, since it seems probable that, as in the oxidation step itself, the larger fraction of the oxygen appearing as volatile products will be as water. Carbon monoxide appeared in all samples in small amounts.
S u m m a r y
A number of possible methods for determining the extent of surface oxidation of bituminous coals have been examined qualitatively. These were sorption of electrolytes; pH of aqueous suspensions; sorption of basic organic compounds;
carboxyl group determination; oxidation-reduction potential;
rate of oxidation; rate of drying; thermal decomposition of the surface complex. Of these, only two—carboxyl group determination and thermal decomposition of surface complex—showed sufficient promise to justify detailed
In order to collect the gaseous products quantitatively, ap
proximately 10 grams of the coal sample were placed in the bot
tom of a small molecular still, such as that shown in Figure 7.
The still was evacuated through a small multiple-stage mercury diffusion pump which was in turn backed by a Toepler. The discharge tube of the Toepler delivered the evolved gases into a mercury-filled gas sampling tube. The collected gas was meas
ured and analyzed in an Orsat apparatus and the volumes were calculated to standard conditions. It was found convenient to cover the coal sample with a 200-mesh nickel screen to prevent spurting when gas evolution became rapid. The condenser of the still was kept filled with a dry ice-ethylene chloride mixture to freeze out water and hydrocarbon vapors. Heat was applied to the still by means of an electrically heated aluminum block.
Temperatures were controlled to =*=5° C. The whole system was thoroughly evacuated at room temperature, 10-3 mm. of mer
cury, raised to 350° in 45 minutes, and maintained at that tem
perature for 3 hours with continuous evacuation. Fi g u r e 6. Carbo xt t l Gr o u p s o n Co a j, a s a Fu n c t io n o f De g r e e o f Ox id a t i o n
570 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 15, No. 9 coals—Pocahontas No. 3, Pitts
burgh, and Illinois No. 6—were oxi
dized at 75°, 100°, and 125° C. for varying periods and under such conditions that the extent of oxidation was definitely known.
Carboxyl group determinations showed that only a frac
tion of the total oxygen fixed reacts like a carboxyl group,
Examination of the gaseous products obtained by thermal decomposition of these oxidized coals in vacuum at 350° C.
also showed a linear relation between oxygen fixed and that evolved as oxides of carbon, and since a larger fraction of the
Ta b l e IV. Ca r b o n Ox i d e s Ev o l v e d i n Va c u u m De c o m p o s i
Hours Millimoles per 100 grains Pocahontas No. 3 Coal
100 312 21.S 11.61 5.66 0.27 3.27
125 99 47.4 10. G8 9.20 6.87
125 215 79.0 22.33 13.58 1.2$ 11.19
Pittsburgh Coal
0 11.93 4.92 0.24
75 223 23.73 16.11 8.71 0.13 3.79
75 319 32.98 17.43 10.84 5.92
100 16S 60.1 27.17 15.24 0.77 10.32
100 240 60.4 25.57 15.19 10.27
125 43 90.6 27.69 17.14 0.84 12.22
125 212 163.1 40.30 26.16 2.09 21.24
Illinois No. 0 Coal
0 24.75 13.72 0.47
75 247 32.73 41.20 24.92 0.89 11.20
75 323 44.83 45. OS 20.78 3.79 13.06
100 260 87.8 61.00 38.43 1.90 24.71
100 62 63.7 42.72 24.96 0.06 11.24
125 46 125.0 65.70 40.8S 4.96 27.16
125 148 159.6 75.73 47.90 6.12 34.18
L ite r a tu r e C ite d
(6) Graham, J. I., Trans. Inst. M inina Engrs., 48, 521-34 (1914-15);
49,35-43 (1914-15). Tverdogo Topliva, 5, 510-25 (1934).
(11) Kucherenko, N. A., Coke and Chem. (17. S. S. It.), 1933, No. 12, . 63-5.
(12) Lefcbvre, Henri, and Faivre, R., Compt. rend., 203, 8S1-3 (1936).
(13) Michaelis, P., Glückauf, 71, 413-23 (1935).
(14) Pentegov, B. P., and Nyankovskil, R. N., Pub. Far Eastern Stale Univ. (Vladivostok), Ser. 7, No. 6 (1927).
(15) Peters, Kurt, and Cremer, Werner, Angcw. Chem., 47, 529-36 (1934).
(16) Purdon, A. O., Chimic & industrie, 44, 3-10 (1940).
(17) Rees, O. W., and Wagner, W . F., Ind. Eng. Chem., 35, 346-S
Tverdogo Topliva, 5, 5S1-90 (1934).
(21) Stansfield, E., Lang, W. A., and Gilbart, K. C., Fuel, 15, 12-14 (1936).
(22) Syskov, IC. I., Khim. Tverdogo Topliva, 7, 759-67 (1936).
(23) Syskov, K. I., and Ushakova, A. A., Ibid., 8, 692-702 (1937).
(26) Voitova, E. V., Khim. Tverdogo Topliva, 8, 611-17 (1937).
(27) Vologdin, M. V., Ibid., 8, 844-52 (1937).
(28) Vologdin, M. V., and Kamendrovskaya, E. A., Ibid., 7, 22-31 (1936).
(29) Winmill, T. F., Trans. Inst. M ining Engrs., 46, 563-7S (1913-14); 48, 503-20, 535—19 (1914-15); 51,493-9,510-47 (1915- 16).
(30) Yohe, G. R., and Harman, C. A., J . Am. Chem. Soc., 63, 555-6 (1941).
Ab s t r a c t e d from a thesis by John A . Radspinner presented to the Gradu
ate Faculty of the Carnegie Institute of Technology in partial fulfillment of the requirements for the D.Sc. degree, March, 1042.