Mild oxidation of reductively ethylated solid fuels

Mild oxidation of reductively ethylated solid fuels Rezzan Doiru*,

Alec Gainest,

Aral Olcayz

and Taner Tu@ul$

“Hacettepe University, Chemistry Faculty, Ankara, Turkey TCukurova University, Faculty of Basic Science, Adana, Turkey SAnkara University, Department of Industrial and Applied Chemistry, Ankara, Turkey (Received 12 February 1979)

A reductively ethylated lignite and a reductively ethylated coking coal have been oxidized by alkaline nitrobenzene. The products of the oxidation were separated into fractions by extraction with organic solvents, and the compounds present in the resulting solutions were characterized by a combination of gas chromatography and mass spectrometry. These compounds had molecular weights less than 300 and the oxidation, though mild, had fragmented the reductively ethylated fuels. Many problems remain, but the method appears to lead to an understanding of the structures of reductively ethylated solid fuels. The structures of the oxidation products are listed and discussed; in general they confirm the interpretation of the n.m.r. spectra of reductively ethylated solid fuels*.

The improved solubilization of reductively ethylated solid fuels suggests the possibility of determining their structure and from this structure determining that of the parent fuels. As part of an attempt to achieve this, two reductively ethylated solid fuels have been mildly oxidized with alkaline nitrobenzene, and the products obtained have been characterized by a mass spectrometer coupled to a gas chromatograph. Infrared, ultra violet and especially n.m.r. spectra of reductively ethylated fuels have been reported previously*. EXPERIMENTAL The two fuels used in this investigation, a lignite and a coking coal, were crushed to minus 80 mesh B.S. and extracted with a 50: 50 mixture of ethanol/benzene. The ultimate analyses of the residues used are given in Table 1. Reductive ethylation was achieved by the method of Stemberg er al. ‘. After discarding material soluble in aqueous alcohol the products were separated according to their solubility in chloroform, ether, tetrahydrofuran, methylalcohol and pyridine, these solvents being used consecutively; and each solution was oxidized by alkaline nitrobenzene according to the method adopted by Olcay et al.3. The solutions remaining after steam distillation of the oxidation products were completely extracted with the same series of organic solvents as used above, and a portion of each solution was then injected into a gas chromatograph. Stationary phase 5% SE30 and 3% OV-101 both on GCQ (a diatomaceous earth after standard treatment) were used in the columns with nitrogen as carrier gas. The temperature of the column was generally raised from 80 to 250°C at lO”C/min, though this programme was sometimes varied. Compounds leaving the column entered a Finnigan 3000E quadrupole mass spectrometer through a glass jet separator. Ionization was carried out at 1.33 mPa pressure with 70 eV electrons. The total ion current monitored by the mass spectrometer formed the gas chromatogram, and mass spectra were obtained of all resolvable peaks.

0016-2361179/110823-0482.00 0 1979 IPC Business Press

RESULTS AND DISCUSSION The mild oxidation of lignites by alkaline nitrobenzene3 gave products which were difficult to characterize by gas chromatography. In contrast, after mild oxidation, the material from the reductively ethylated solid fuels investigated here gave gas chromatograms. The compounds issuing from the gas chromatograph and identified by mass spectrometry are listed in Tables 2 and 3. Compounds formed by the reduction of nitrobenzene or present as impurities in the organic solvents have not been included in the Tables. Tables 2 and 3 result from observations of a few hundred gas chromatogram peaks, but of course one can not be certain that these peaks accounted for all the oxidized products; some high boiling material may not have left the columns or may not have given resolvable peaks. Whereas similar compounds were always obtained when the reductive ethylation-mild oxidation was repeated, we have yet to define our procedures sufficiently precisely to be able to reproduce our results exactly. Consequently no attempt has yet been made to determine the yields of each product. None of the peaks observed in the gas chromatogram seemed overwhelmingly important compared with the others. Some compounds, for example benzaldehyde, were observed amongst the oxidation products of many of the different fractions of the reductively ethylated fuels. The mass spectra of many of the compounds postulated in Tables 2 and 3 were not listed in reference tabulations available to us. Such compounds were identified by the application of general principles, and a few identifications may be incorrect.

Tab/e 7 Ultimate

Coal Lignite

analyses of extracted

fuels (wt %, daf)

Carbon

Hydrogen

89.0 71.9

5.0 4.85

FUEL, 1979, Vol 58, November

823

Mild oxidation of reductively eth ylated solid fuels: I?. Dogru et al. Table Za Compounds identified after mild oxidation of a reductively ethylated coal: aliphatic and aromatic compounds not containing oxygen C”H2n+2

C,H20 R2

9zzns.13

sgn<12

c,< R< c,, R,=C,

L C,"

R< C

L H=C,

R=C

1

2

R.C

R=C7

R=CI

, C,+C3

3

R=C,

R=C

2

R=C

6

R=C

6

n=3

All the compounds identified have molecular weights of less than 300. This should be compared with the average molecular weight of a few thousand of reductively ethylated fuels. Although oxidation by alkaline nitrobenzene was indeed mild it was successful in fragmenting the structures of the reductively ethylated fuels. Tables 2a and 3a list compounds which contained no oxygen atoms and which therefore appear to have escaped oxidation - or where oxidation caused dehydrogenation. These Tables show the presence of naphthalene, acenaphthene, anthracene and perylene (the last, only in the lignite) in the parent fuels. Similarly, Tables 2c and .?c include compounds containing ether linkages which have not been attacked by potassium/naphthalene/tetrahydrofuran and therefore provide direct evidence of these linkages in the parent fuels. Both aromatic-0-aliphatic and ahphatic-Oaliphatic linkages occurred. Obviously the naphthalene present in Tables 2c and 3c could have arisen from that used as an electron transfer catalyst in the reductive ethylation. J. W. Larsen (private communication 1978) using naphthalene and tetrahydrofuran labelled with 14C, has shown that small but significant amounts of these compounds were incorporated into a sample of Bruceton coal during its reductive ethylation, and some naphthalene compounds and some of those containing tetrahydrofuran and furan nuclei may have originated in the same way. However, studies on the mechanism of reductive ethylation which we are carrying out to complement the present work have so far revealed no compounds in which naphthalene nuclei or tetrahydrofuran moieties are linked to themselves or to other organic groups.

824

FUEL, 1979, Vol 58, November

N.m.r. spectra of reductively ethylated fuels’ indicated the presence of benzene rings substituted by long branched and unbranched paraffin chains. Such material was identified in the present work and is listed in Tables 2a and 3a. The presence of alkylated benzenes is also suggested by some of the structures in Tables 2b and 3b if it be assumed that carbonyl groups were formed by oxidation at points of branching. The identification of simple paraffins (Tables 2a and 3a), despite the fact that fuels were first extracted with benzene/alcohol, suggests that paraffins were released when the fuel structure was loosened during reaction. N.m.r. spectra’ suggested that many of the benzene rings present in reductively ethylated fuels were lightly substituted, a contention which is supported by the large numbers of singly and doubly substituted structures listed in Tables 2 and 3. Indeed, it is surprising that so few polysubstituted aromatics could be identified. Comparison of Table 1 and 2 shows, in agreement with the n.m.r. spectra*, that the compounds isolated from the coal were rather more substituted than those isolated from lignite. Carbon atoms LYto aromatic rings gave few sharp peaks in the 13C n.m.r. spectra of reductively ethylated fuels*, and this suggested that such carbon atoms were comparatively rigid. Tables Zb and 2b reveal many structures in which a carbonyl group is cr to an aromatic ring. This may indicate a predominance of branching at this position in reductively ethylated fuels - and perhaps therefore in the parent fuels - which might have

Table 26 ethylated

Compounds identified after mild oxidation of a reductively coal: aromatic compounds with carbonyl groups

C,
L

L_

R.C,

L

R-C,

R :C!

fl=S

y

/

R< c 1 5

2<0<8

R=C3”.3

Rz~

0

I..

R=C 1125

R=C

n=:

R =C,

R-C R=C 15’21

R=C2

n=2

CsR
L

R= c,

n.?

R=C

Mild oxidation of reductively ethylated solid fuels: R. &jru Tab/e 2c Compounds identified after mild oxidation of a reductively ethylated coal: aromatic compounds with ether linkages or hydroxyl groups but no carbonyl groups

C?R
CONCLUSION In general the structure of the compounds confnrns the interpretation of the n.m.r. spectra of reductively ethylated solid fuels*. Naphthalene, acenaphthene, anthracene and

RX5

9

i

et al.

Table 3a ethylated

Compounds identified after mild oxidation of a reductively lignite; aliphatic and aromatic compounds not containing

oxygen

L

1 L

C,Hzn+2

R=C,

2
l&-t<:13

@f$RG$o-i-H

@(CH2),-O-R OH

O-R R=C,

i\

R=C,

R=C5

0-(CH2)nO-H

QcH2-OH

QROH

(7~0,

O-R

@R

0”

m”

m

QCH2GR

R y&C9

C,SR”C2

C,
R = C,

2

OH

RX7

n =3

&JR,

~oH@CH2-oH

Q O-R2

O-R RX,

C,G R
n=2

2

R=C 14

R=C 21

R=C,

R=C,

1
R eon C,< R
RX,

<3.

R-“eoH

R=C,

RzC,

3

Tab/e 2d Compounds identified after mild oxidation of a reductively ethylated coal: aliphatic compounds containing oxygen 0 R-O-C

R:C

”

H

CHn

2n-1

2n+,-OH

R-0-(CH2$-OH

R=C

5

L

R=C

Tab/e 36 ethylated

R-6-H

Compounds identified after mild oxidation lignite; aromatic compounds with carbonyl @e-R

o&-H 5

C4Gw

2

@a

Of-O-R

of a reductively groups Q!-R

6 $-OH

s&7<

2~0~3

4
8

R= C

c

“1” R=G ‘

R,-O-C-R2

R-0-KHZ),-C-H

1

R,=C5

R=C

1

R=C 2

i?

R,-O-fCH2)n-O-R2

R=C

R=C

0 1

n.2

5

n=2

15

23

R,-t-O-R2

R=C O-R

R

C
L

R=C

0”’

5

?

C-H 3

R= C

R=C,

2

RI-i-R2 R,. C,

R2=C3

L caused the rigidity of the carbon atoms. Some carbonyl groups occurred fl and further from the aromatic ring, indicating that a variety of linking and branching occurred. This point may be expanded. Tables 2 and 3 list diverse compounds - none of which were formed in relatively large quantities - which one can easily imagine bonded together to form the many different structures which taken as a whole comprised the reductively ethylated lignite and the reductively ethylated coal.

l<-n<3

R=C

1

“~2

R=C

1

R

R2

2 R=C

I 2

RzC 2

1

FUEL, 1979, Vol 58, November

825

Mild oxidation of reductively ethylated solid fuels: R. Dojru et al. Tab/e 3c Compounds ethylated hydroxyl

identified

after mild oxidation

of a reductively

lignite; aromatic compounds with ether linkages or groups but no carbonyl groups

Tab/e 3d

Compounds

ethylated

lignite; aliphatic

0 $-OH

8 C,,H23-C-CH

identified

after mild oxidation

compounds

containing

of a reductively

oxygen

H C8 H17-+

3

-CH20H CL H9

J_@-OH 3

R=C 2

mKH21n-

n =2

n=3

R=C,

R=C

R=C 2 3

OH

CO-OR

R=C

I, Ho+$;

-H

R=C,

R .C,

n=8

QR

L

perylene have been identified. In many compounds carbonyl groups were (Yto an aromatic ring, suggesting that the reductively ethylated fuels were branched at this position. Among the many products of oxidation identified, no compounds predominated, and the structures of the reductively ethylated fuels were branched and linked together in many different ways.

_OR 2

REFERENCES 1

@cH~-o-(CH~I~-OH

2 OH

CL” RCC

826

9

3

R,= C ,

L

C7H15C

6

n=3

FUEL, 1979, Vol 58, November

3

Sternberg, H. W., Delle Donne, C. L., Pantages, P., Moroni, E. C. and Markby, R. E. Fuel 1971,50,432; Sternberg, H. W. and Delle Donne, C. L. Fuel 1974,53,172; Bimer, J., Coke and Gus 1974, 19,68; Ignasiak, B. S. and Gawlak, M. Fuel 1977,56,216 Do&u, R., Erbatur, G., Gaines, A. F., Yurnm, Y., Igli, S. and Wirthlin, T. Fuel 1978, 57, 399 Olcay, A., Evliya, H., Gaines, A. F. and Homer, J. Fuel 1973, 52,20