58

Researches on the Chemistry of CoalPart VII—An Investigation of German Brown Coals

and Irish Peat

By William A. Bone, D.Sc., F.R.S., and Louis J. Tei, B.Sc.

{Received July 7, 1934)

In continuance of investigations in the Fuel Research Laboratories of the Imperial College, London, on the chemical constitution and maturing of coals, it was thought advisable to examine some representative German brown coals in the hope of obtaining further light upon the origin of those constituents of bituminous coals which are mainly responsible for their coking propensities. The present paper summarizes the results thereof which are supplemented by some observations on a typical Irish peat.

It may be recalled how in previous papers of the series* it has been shown in regard to the dry organic substance of brown coals ( ., Morwellbrown coal, Italian and Canadian brown lignites) :—(i) that on being raised to a certain temperature, varying between 300 and 400° in different cases, it underwent an “ internal condensation ” characterized by the simultaneous elimination of oxides of carbon (but chiefly the dioxide) and steam without any appearance of oil, hydrogen, or more than a negligible amount of gaseous hydrocarbon ; (ii) that on further raising the temperature there followed another range (up to circa 500°) in which methane and heavy hydrocarbons also appeared, as though alkyl side- chains were being eliminated ; but (iii) that hydrogen was not evolved until the temperature exceeded 500°. Moreover, it was shown that on being extracted with benzene under pressure it yielded neutral oils, phenols ( plus acidic bodies) and phenolic esters plus a “ residue ” (con­stituting upwards of 80% of the whole coal substance) which was largely benzenoid in character.

The present investigation was undertaken to ascertain (i) whether typical German brown coals—which in some other respects differ from those previously examined—would behave similarly when subjected to the said treatments, and (ii) how far previous conclusions, that the main “ coking constituent ” of bituminous coals probably originated in the

* ‘ Proc. Roy. Soc.,’ A, vol. 99, p. 236 (1921), and vol. 120, p. 523 (1928).

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Researches on the Chemistry o f Coal 59

phenols and phenolic esters of brown coals, would be borne out or need modifying.

A—General D escription and Proximate A nalysis of the Coals

The four brown coals selected for the investigation, procured for us from Germany by the Fuel Research Board, were as follows :—

Nos. 1 and 2—From the Rheinische Braunkohlen Syndikat of Cologne, being of tertiary origin from an open-working in which the seam had a total thickness of 50 metres with an “ overburden ” of 12 to 15 metres. No. 1 was an average sample of the coal between 20 and 25 metres, while No. 2 was an average of that between 30 and 50 metres, down the seam.

No. 3—From the open “ Siegfried ” mine near the village of Deuben (“ Weissenfels-Zeitrer Bezirk ”), about 30 kilometres S.S.E. of Halle, where the seam is 12 metres thick with an “ overburden ” of 20 metres.

No. 4—From the “ Walters-Hoffnung ” mine near the village of Stetden (“ Oberoblingen Bezirk ”), 15 kilometres W. of Halle, where the seam is 18 metres thick under an “ overburden ” of 50 metres. Deposits of potash occur in this district and the coal-ash contains it.

A Proximate Analyses—As received the two Rhenish coals were nearly in their natural state and contained 57*6 and 59-1%, respectively, of moisture. The two Saxon coals, however, had been partly dried (down to about 15% moisture-content) before being despatched to us. The ash contents of the dry coals were as follows :—

Rhenish Saxon

No. 1 No. 2 No. 3 No. 47*6% 5-2% 11-2% 110%

The “ volatiles ” yielded by the dry-ashless coal substance at 900° were as follows :—

Rhenish Saxon

No. 1 No. 2 No. 3 No. 4Volatiles 55*9 54-6 60-3 60*1

B Montan-Wax Content—These German coals contained notably larger proportions of “ montax wax ” than did either the Australian or Canadian brown coals previously examined in our laboratories. Such wax—which in our specimens was readily extracted from the dry coal by boiling benzene at atmospheric pressure, and melted between 80 and 85°

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—has usually been considered a mixture of higher fatty acids and theiresters together with (may be) higher hydrocarbons. Thus, after hydro­lysing it, Tropsch and Dilthey isolated myricyl alcohol C3oH620 2 (m.p. 88°) “ bituminol ” C32H660, carbocerinic and montanic acids (C27H540 2, m p 81-5 to 82°, and C29H580 2, m.p. 86-5°) ; while Pschorr and Pfaff similarly isolated tetracosanol (C24H50O, m.p. 83°), as well as the fore­going substances from it. Recently Holde and Bleiberg have isolated noctocosanic acid (C2sH660 2, m.p. 89 ).

The four coals in question yielded (when “ dry ”) the following per­centages of the*wax :—

No. 1 No. 2 No. 3 No. 42-5 2-8 7-5 6-0,

as compared with the 1 • 3% yielded by the Morwell and the 0 • 4% by the Canadian brown coals previously examined. And if a small per­centage of sulphur be disregarded, the ultimate compositions of the wax- contents (videTable V) all closely approximated to the empirical formula CnH2w0 2 (with n = 27 to 32) requiring C = 79 0 to 80-0, H = 13 15 to 13-35, and O = 7-85 to 6-65.

C Ultimate Compositions o f the Coal The ultimate com­positions of the dry-ashless coal substances, both (a) before and (b) after

6 0 W. A. Bone and L. J. Tei

being “ dewaxed ” in each case, were as follows ::—

Table ICoal No. 1

____ L

2JL

3l___

4

(a) 0b) (a) (b) id) ib) («) ib)C 64-30 65-85 66-50 66-35 68-45 68-95 69-50 70-05H 5-85 4-70 5-65 4-85 6-40 5-30 5-95 5-45N 0-50 0-55 0-85 0-70 0-55 0-55 0-55 0-55S 0-40 0-30 0-30 0-30 3-80 4-20 3-90 4-70o 28-95 28-60 26-70 27-80 20-80 21-00 20-10 19-25

C/H ratio.. 11*0 14-0 11-75 13-7 10-7 13-0 11-7 12-85

If, as seems reasonable, the montan-wax in the original coal be regarded as an incidental rather than a basal constituent, the figures under ( ) rather than those under (a) would represent the composition of the true coal substance. And although the two Rhenish have higher C/H ratios, their lower carbon and higher oxygen contents show them to be less mature than the two Saxon coals. Also, the much higher sulphur con­tents of the last named should be noted.

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Researches on the Chemistry o f Coal 61

D The Action o f Heat upon the Dry and Dewaxed Coal Substance—A quantitative study was made of the gases evolved during the fractional carbonization of the dry de-waxed coal-substance in successive tempera­ture-ranges up to 800° when thermal decomposition had been almost completed. The results, while agreeing generally with those previously obtained with other brown coals, are of sufficient interest in themselves to warrant detailed consideration. Seeing, however, that there was a close similarity between the results from the two Rhenish coals as well as between those from the two Saxon coals, it will suffice for us to detail those of one from each area, and therefore we have selected the maturer of the two coals in each case, namely, Rhenish No. 2 and Saxon No. 4. The temperature at which oils first appeared was 300° with the former and 275° with the latter ; accordingly the results are tabulated (Tables III and IV) so as to show, in each case, the amounts and compositions of the gas evolved (i) up to such “ oil point,” and (ii) over selected tempera­ture-ranges thereafter until thermal decomposition had been completed within each range.

Attention may be directed to the fact that with each of the four coals, practically all that happened up to its “ oil point ” was an expulsion of carbon dioxide and steam* in molecular ratios between 1 :1*7 and 1:2-6 , the mean being remarkably near the corresponding 1 :2-25 ratio previously found with Morwell brown coal on undergoing much the same “ internal condensation ” up to its “ oil point ” of 375°. Thus for the present coals we obtained the results shown in Table II.

Coal“ Oil

point ”

T able IIWeight evolved per

100 gm of dry dewaxed coal substance

%C02 in gas

h 2oc o 2

No. 1 ........... 260°Gas4-9

Steam5 0 93-2 2-6

No. 2 .......... 300° 6-1 4 0 91*4 1 -7No. 3 .......... 288° 4-6 3-5 90-9 2-0No. 4 .......... 275° 3-9 3-8 92-9 2-5

A detailed investigation of the stage-wise carbonization of No. 2 up to 480° showed that its “ oil point ” synchronized with the first appearance of paraffin hydrocarbons (principally methane, ethane, and propane) among the gaseous products ; hydrogen first appeared between 400°

* There was also relatively little carbon monoxide expelled ( Tables III and IV), but no other oxygenated product.

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W. A. Bone and L. J. Tei

and 420°. The C/A ratios obtained in explosion analyses of the residual gases after removal of H2S, COa, CTOH2n, and CO were 1 -6 at 315°, 1 -75 at 420° (when propane, ethane, methane, and hydrogen were all present) and 2-2 at 450°, by which temperature the paraffin-constituent had become practically all methane. At 480° the C/A ratio had risen to 2*4, the residual gas consisting of methane and hydrogen only.

62

Table III—Gases evolved from Rhenish Coal No. 2 ; cc at N.T.P. per 100 gm of dry dewaxed coal substance

Temperaturerange

Totalgas HaS c o 2 CO CwH2to

CH4and h 2 n 2

°CUp to 300 3196 Nil 2920 247 10

CjtUji+ 2

Nil Nil 19300 to 420 6190 18 4272 860 235 767 Nil 38420 to 500 5114 10 1978 583 133 1890 496 24500 to 600 4500 3 1104 850 41 1395 1000 107600 to 700 7367 Nil 567 1739 44 1606 3160 251700 to 800 5272 Nil 179 1108 5 691 3000 289

Totals . . . . 31639 31 11020 5387 468 6349 7656 728

Table IV—Gases evolved from Saxon Coal No. 4 ; cc at N.T.P. from 100 gm of dry dewaxed coal substance

Temperaturerange

Totalgas h 2s c o 2 CO c wh 2w

c h 4*and h 2 n 2

°CUp to 275 2024 28 1874 85 4

CnHi2«+26 Nil 27

275 to 400 6305 960 4388 543 98 299 Nil 17400 to 500 6322 481 2584 668 357 2121 Nil 111500 to 600 5750 93 1386 934 78 1933 1109 217600 to 700 7807 14 995 2071 24 1461 3068 174700 to 800 5281 Nil 221 1368 9 787 2730 166

Totals . . . . 33489 1576 11448 5669 570 6607 6909 712* Mainly CH4.

The results obtained with coals Nos. 2 and 4 over their complete carbonization ranges (Tables III and IV) showed that whereas 90% of the total H2S, and 80% of the total yields of COa and unsaturated CnH2n hydrocarbons, had been evolved below 500°, and about 80% of the total yield of paraffins (almost all methane) between 400 and 700°, 80% of the hydrogen and 60% of the total yield of carbonic oxide were not evolved until the temperature exceeded 600°.

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Researches on the Chemistry o f Coal 63

Of the total sulphur in the coal the proportion eliminated as sul­phuretted hydrogen up to 800° was only 15% in the case of No. 2 Rhenish, but as much as 48% in the case of the No. 4 Saxon coal. The question of the sulphur-distribution among the various carbonization products in the case of the last-named coal is, however, reserved for a future communication.

The Benzene Pressure-Extraction of the D ry D ewaxed Coal

The Extraction Process—Each coal, having been thoroughly dried in vacuo at 105°, ground so as to pass through a 20- but not a 40-mesh screen, and suitably “ dewaxed,” was extracted Soxhlet-wise by boiling benzene in successive stages, namely, at 250, 500, and 700-750 lbs per sq inch (*.e., at circa 210°, 260°, and 285°) according to our usual pro­cedure. There was always some elimination of water and gas evolution (mainly COa), more particularly at the 250 lbs stage, indicative of some “ internal condensation ” of the coal substance having set in, but pre­sumably such would not involve any breakdown of its essential chemical structure.

Fractionation o f the Primary Benzene Pressure-Extract—A preliminary examination of the benzene solution of the combined pressure-extract in each case having shown it to be a complex mixture of phenolic sub­stances and the like with hydrolysable esters, neutral oils and minute quantities of basic bodies, it was successively extracted with ( ) 10% HC1 aq, and (b) a series of three 10% aqueous alkaline (NaHC03, Na2C 0 3, and NaOH) solutions which effectively removed all basic, phenolic, and acidic constituents. Afterwards the neutral esters and non-hydrolysable oils were recovered from it for subsequent examination. During each of the extractions of the benzene solution referred to, some emulsified “ tarry ” matter was precipitated and could be removed by filtration only with great difficulty. The precipitate from (a) was entirely insoluble in ether ; that from (b) was soluble in water, and after reprecipitation with hydrochloric acid it was resolved into ether-soluble and ether- insoluble portions.

The quantitative results of the benzene pressure extraction and subse­quent fractionation of the resulting primary extracts are summarized in Tables V and VI ; and the general properties of the various fractions were briefly as follows :—

(a) The HC1 -solubleConstituents, which were present in very small amounts, were organic bases.

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(b) The Alkali-soluble Constituents—These contained, besides p. cresol and catechol, certain other complex acidic bodies which ‘‘ coupled” with diazotized bases and were presumably also mainly phenolic, although it is possible that some were not. This fraction will, therefore, be referred to as the “ phenolic ” constituents. And since they now (as it were) appeared in place of the characteristic fraction IV (i.e., the main coking constituents) of the benzene pressure-extract obtained from bituminous coals, they may also be conveniently designated as the IV fraction.

(c) The Tarry Constituents—There was some evidence (though not conclusive) of these having been formed by polymerization or resinifica-

Table V—Percentage Yields from Benzene Pressure-Extractions referred to theDry-ashless Coals

Fractions from benzene pressure-extraction

5 4 W. A. Bone and L. J. Tei

,------------------------------ ----------------------- s,Montan Tarry constituents* D r y *

Coal wax x____ residueBasic IA IB II III' IV' Soluble Insoluble recovered

in inether ether

Rhenish No. 1 2-5 Trace 0-7 2-5 0*6 0*4 1*4 2*3 2*2 71*5 1„ No. 2 2-8 015 1 0 2*5 0-8 2 0 3*2 5*3 3*9 63*4 ■■

Saxon No. 3 .. 7-5 01 0 11 4-4 1*8 1*8 2*6 5*5 3*4 60*8 !„ No. 4 .. 6 0 Trace 0-4 3-3 2*3 Trace 1*5 1*8 3*5 70*4

IA and B and II — neutral, non-hydrolysable oils ; III' = phenolic esters ; IV' = phenolic bodies. * Polymerized bodies precipitated during fractionation.t C 02 and HaO were also eliminated and there was some mechanical loss during each extraction.

tion from the alkaline solution of ( b). They were further divided into ether-soluble and -insoluble portions, of which the former could be further resolved by our standard treatment (#.v.) into four fractions simulating the familiar fractions I to IV of the benzene pressure- extracts from bituminous coals. Albeit those now obtained were all acidic, instead of being mainly neutral, in reaction ; and (like fractions III and IV from bituminous coals) they exhibited binding power when strongly heated in admixture with excess of finely divided coke. The ether-insoluble portion had no such binding power.

(d) The Neutral Constituents—After removal of fraction IA by steam distillation, these were first of all resolved into hydrolysable phenolic- esters and non-hydrolysable viscous oils. Since the former appeared in place of fraction III of the extract from bituminous coals it may

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VOL. CXLVII

Tabl

e V

I—U

ltim

ate

Com

posit

ions

of M

onta

n W

axes

; Be

nzen

e Pr

essu

re-E

xtra

cts

IA a

nd B

and

II;

and

Resid

ues.

Mon

tan

wax

IAIB

IIR

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ue

Coal

No.

:1

23

41

23

4..

12

34

12

34

12

34

C78

-680

0

79 1

79 0

83-2

79-7

800

78-6

83-0

82-0

82

-181

*180

-778

-6

79-8

78-4

71-8

73-0

72-5

72-9

H11

-612

-8

12-3

12*8

9-6

9-3

101

10*8

101

10-7

10

-610

*58

010

-2

100

10-2

4-3

40

4-3

4-7

NN

ilN

ilTr

.N

ilN

ilN

ilN

ilN

ilN

ilN

il'N

ilN

ilN

ilTr

.N

ilN

il0-

61*

310

0-9

S0-

201

0-7

1-6

Tr.

Tr.

Tr.

Tr.

0-3

0-3

1-3

1-4

0-7

0-6

1*7

2-6

0-4

0-6

0-9

3-7

0 (d

iff.)

9-6

7-1

7-9

6-6

7-2

110

9-9

10*6

6-6

7-0

617-

010

-610

*68-

58-

822

-921

121

-317

-8

C/H

rat

io

......

.\6-

86*

26-

46-

28-

68-

61-

97-

38-

27-

67*

87*

810

17-

78

07*

716

*718

*217

015

-7%

ONResearches on the Chemistry o f Coal

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66 W. A. Bone and L. J. Tei

conveniently be designated III'. The latter were further resolved into fractions soluble and insoluble in light petroleum (b.p. 40 to 60°) corre­sponding closely with the fractions I and II of the extract from bituminous coals, except that (as might be expected) their oxygen contents were higher than those of the last named. Moreover, although fractions IA and B and II were always non-nitrogenous (or practically so), IB and II always contained sulphur. Their ultimate compositions {vide Table YI) closely approximated to those of the corresponding fractions from the Morwell and Canadian brown coals previously examined*; and their low C/H ratios (with one exception all between 7-3 and 8-6) indicated a non-benzenoid constitution.

(e) The Residues—The C/H ratios (15-7 to 18-2) for the “ residues”were all notably higher than those for the original dry dewaxed coals (q.v.), though below the 19*0 to 19*6 previously obtained for the corre­sponding “ residues ” from the Morwell and Canadian brown coals ; and, as will be shown in a subsequent paper, like the latter, they were largely benzenoid in character.

The Benzene Pressure-Extraction of a Turraun Irish Peat

In view of the results obtained with brown coals, it was thought advisable to carry out a similar benzene pressure-extraction of a typical peat, and for this purpose a well-rotted sample of Irish peat, supplied to us through the Fuel Research Board by the Turraun Peat Company, was selected.

The sample reached us in an air-dried condition (HaO = 13%), but after the completion of its drying in vacuo at 105°, and deduction of its ash content (about 3%), the anhydrous and ashless peat substance contained :—

C = 57*4, H = 5-3, N = 1 -1, S = 0-9, and O (diff.) = 35• 3%.

It contained also 3-1% of wax (C = 74*3, H = 10-2, 0 =15 -5 % ) extractable by boiling benzene at atmospheric pressure. On further benzene pressure-extraction up to 750 lbs per sq in, during which some water and carbon dioxide were eliminated, the “ dewaxed ” peat substance yielded nearly 19% of total extract of much the same character as the extracts similarly obtained from brown coals ; and like them it could be resolved, by the procedure already described, into fractions closely resembling the corresponding ones for brown coals. There was, in

* ‘ Proc. Roy. Soc.,’ A, vol. 120, p. 537 (1928).

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Researches on the Chemistry o f Coal 67

fact, little difference between the peat and brown coal fractions. The percentage yields on the dry peat substance are shown in Table VII.

T able VIIFractions of the benzene pressure-extract

Tarry substancesMontan IIP

wax Bases IA IB II and Soluble InsolubleIV' in in

ether ether3 1 0-5 3-6 2-5 1-7 4-4 1 0 4-5

Fractions III' and IV' (like the corresponding fractions from brown coal) were composed of complex phenolic bodies, and the “ tarry substances” formed during their extractions from benzene solution by means of aqueous alkaline solution also closely resembled the corre­sponding substances obtained from the brown coals.

The ashless residue after the benzene pressure-extraction contained :—

C = 69-6, H = 4-0, N = 1-8, S = 1 -4, and O = 23-2%.Ratio C/H = 17-4,

and it was also largely benzenoid in character.The investigation as a whole thus supports the view that fractions III

and IV of the benzene pressure extracts of bituminous coals have prob­ably originated in the phenolic bodies comprising fractions III' and IV' of the benzene pressure-extract for peats and brown coals. The develop­ment of the benzenoid structure of the main organic substance throughout the lignin-peat-coal series will be discussed in a subsequent paper.

In conclusion, we desire to thank the Fuel Research Board of the Department of Scientific and Industrial Research for grants which have enabled the investigations to be carried out.

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