Study of Kansk-Achinsk lignite liquefaction using deuterated alcohol

Short Communications

7

and Membrane Science’ (Ed. D. A. Cadenhead), Vol. 9, Academic Press, New York, 1975, pp. l-70 Dubinin, M. M. and Stoeckli, H. F. J.

8 9 10

Dubinin, M. M. Carbon 1985, 23, 373 Dubinin, M. M. Carbon 1989, 27, 457 Innes, R. W., Fryer, J. and Stoeckli, H. F.

REFERENCES 1

2 3

4 5 6

Bansal, R. C., Donnet, J. B. and Stoeckli, H. F. ‘Active Carbon’, Marcel Dekker, New York, 1988, pp. 119-162 Stoeckli, H. F. Carbon 1989.27, 962 Stoeckli, H. F. Carbon 1990, 28, 1 Stoeckli, H. F., Rebstein, P. and Ballerini, L. Carbon 1990, 28, 907 Ballerini, L., Huguenin, D., Rebstein, P. and Stoeckli, H. F. J. Chim. Phys. (in press) Dubinin, M. M. ‘Progress in Surface

Study

of Kansk-Achinsk

P. N. Kuznetsov,

N. G. Beregovtsova,

15 16

Dubinin, M. M. and Serpinskii. V. V. Carbon 1981, 19, 402

12

Kraehenbuehl, F., Quellet, C., Schmitter, B. and Stoeckli, H. F. /. Chem. Sot.

17

Faraday Trans. I, 1986, 3439

liquefaction

A. I. Rubaylo,

Technology,

Rodriguez-Reinoso, F. and LinaresSolano, A. ‘Chemistry and Physics of Carbon’ (Ed. P. A. Thrower), Vol. 21, Marcel Dekker, New York, 1989, pp. l-146 Mackay, D. M. and Roberts, P. V. Carbon 1982, 20, 105

Carbon 1989, 27, 71 I1

Dubinin, M. M. and Izotova, T. I. Zh. Fiz. Khim. 1965, 39, 2796

14

Colloid Interface Sci. 1980, 75, 34

lignite

Institute of Chemistry and Chemical (Received 6 September 1990)

13

using deuterated

Siemieniewska, Tomkow, K., Czechowski, F. and Jankowska, A. 1977, 56, 121 Stoeckli, H. F., Ballerini, L. De Bernardini. S. Carbon 1989, 27,

T., Fuel

and 501

alcohol

E. D. Korniyets and N. I. Pavlenko

42 K. Marx

st., Krasnoyarsk,

660049,

USSR

Lignite liquefaction in methanol, ethanol, isopropanol and in their deuterium analogues with different deuterium substitution has been studied. Isotope effect has been estimated at deuterium substitution for

a-hydrogen in ethanol and isopropanol. Deuterium distribution in maltenes, asphaltenes and solid residues has been shown to increase in the order: solid residues>asphaltenes>maltenes. CH,CD,OH had the lowest deuterating activity. In all cases deuterium has been detected mainly in aliphatic structural groups and only a little in the aromatic ring. (Keywords: lignite; liquefaction; deuterium)

Coal liquefaction in solvents is an effective method of liquid fuel production. The efficiency of the process, which is considered to be of a free radical nature’.‘, depends to a great extent on solvent properties. Solvents containing active hydrogen, like tetralin, are widely used. H-donors are considered to prevent recombination of coal radicals into substances difficult to dissolve, ensuring greater coal liquefaction. Since Bartle et u[.~, Ross and Blessing4,’ and Ouchi and co-workers6s7 pioneered work on coal liquefaction in low boiling solvents including alcohols in supercritical conditions, low alcohol solvents have become of interest both for obtaining liquid fuel and for study of coal structure and mechanism of conversion into liquid products4-“. Low rank coals were shown to be the most suitable for liquefaction in alcohol solvents8.“.‘3. Alcohol in coal liquefaction is considered to be determined by H-donor ability4s5 and also by alkylating properties7. Hydrogen transfer from a solvent is a very important stage in the cracking of coal bonds and thorough knowledge of its fundamentals is essential. For investigation of coal liquefaction the method of isotope substitution is effective, giving the 0016-2361/91/040559-05 (1) 1991 Butterworth-Heinemann

Ltd

opportunity to estimate the conversion route of a marked molecule, to determine structural the type of interacting fragments of coal and solvent and to clarify the nature of limiting stages. For this purpose several studies have used tetralin marked with deuterium’4-21, tritium22, naphthalene-14C (Ref. 23), and gaseous deuterium’4,24,25. Isotope effects and isotope distribution in products were studied’4m18.20,25. Various schemes of hydrogen transfer in the coal tetralin gaseous hydrogen system have been suggested’4.22*23,26. In order to study lignite liquefaction in ethanol its perdeuterated and randomly deuterated analogues were used27*28. It has been shown that deuterium introduction into ethanol cr-position resulted in Table 1

considerable isotope effect in liquid product formation. In the present paper results of lignite liquefaction in methanol, ethanol, isopropanol and their different deuterium analogues are presented. Isotope effect and deuterium distribution in products and in different structural positions of maltenes are discussed. EXPERIMENTAL Two lignite samples from the KanskAchinsk basin were used in the experiments. Their composition is shown in Table I. All the solvents, methanol, ethanol, isopropanol and their deuterium analogues as well as hexane and benzene were analytical grade. Liquefaction experiments in ethanol

Composition of lignite samples

Composition (%) Sample

Ash

A

4.5

66.80

4.98

B

5.2

65.70

4.84

C”

H”

S”

N”

Ob

0.13

0.74

27.35

0.14 0.99 -_._. _ .- --~~ _~~

28.33

“Dry ash free b By difference

FUEL,

1991,

Vol 70, April

559

Short Communications Table 2

Influence of deuterium substitution type in ethanol

on the product

Product Experiment numbef

Alcohol

Maltenes

1

CH,CH,OH

2

CH,CH,OD

yields from lignite in the flow reactor

yield (u%)

Isotope

Asphaltenes .__

Total

24.3

16.1

40.4

22.3

14.5

36.8

effect (aHlaD)

Maltenes

Asphaltenes _

_

1.1

1.1

1.1 2.1

Total

3

CH,CD,OH

14.1

4.8

18.9

1.7

3.3

4

CD,CH,OH

22.5

14.1

36.6

1.1

1.1

1.1

5

CD,CD,OH

13.9

2.8

16.7

1.7

5.7

2.4

6

CH,CH,OH

17.0

6.6

23.6

7

CH,CH,OD

14.7

8.3

23.0

1.1

0.8

1.0

8

CH,CD,OH

7.2

4.1

11.3

2.4

1.6

2.1

9

CD,CD,OH

2.8

4.4 _

3.1 _

3.3

1.3

2.7

6.0

1.5

7.5

10

(CH,),CHOH

14.7

2.3

17.0

11

(CD,),CDOH

4.5

1.8

6.3

’ Lignite A was used in experiments

l-5;

lignite B was used in experiments

and isopropanol were carried out in a flow reactor of periodical function. In all experiments, 5 g of lignite was put in the reactor bed. Argon was passed through the lignite bed and after the air removal the reactor was heated. On reaching 25o”C, fresh alcohol was passed continuously by mechanical pump through the lignite bed. It took 15 min to increase the temperature from 20 to 380°C. The reaction conditions were: temperature 380°C; argon flow rate 10 1h- ’ ; alcohol solvent feeding rate 0.2 mol h-i and total pressure 2 MPa. When carrying out experiments with methanol, a rotatory autoclave with 0.25 1 volume was used. Dry lignite loading was 15 g, methanol quantity 20 ml, hydrogen pressure 5 MPa, reaction duration 1 h. Reaction temperature in all cases was 380°C. After experiments in an autoclave or in a flow reactor, the products were extracted first with hexane to obtain maltenes, then with benzene to obtain asphaltenes. The solvents were evaporated, then distilled under vacuum and their yield evaluated. Liquid and solid products were investigated by elemental analysis for the C, H, N and S content and by i.r. spectroscopy. The maltenes were also examined by ‘H n.m.r. spectroscopy (at 50MHz). 1.r. spectra of solid samples (original coal, solid benzene insoluble coal residues and asphaltenes) were obtained from KBr pellets. The spectra of maltenes were recorded from Ccl, solution at equal concentration. Absorbance measurements were made by means of a computer program. ‘H n.m.r. spectra of maltenes were recorded from CDCI, solution. Additional details of experiments and product analysis have been published previously’0~‘2~27. RESULTS

AND DISCUSSION

Isotope effect Data for the yield of liquid products

560

FUEL, 1991, Vol 70, April

G&---=1

3000

Figure 1 1.r. spectra by lignite liquefaction ethanols

6-l

I

Clll

of asphaltenes obtained in different deuterated

from two lignite samples undergoing liquefaction in periodical flow reactor in ethanol and isopropanol, with different deuterium substitution, are summarized in Table 2. Lignite samples differ noticeably in reaction ability, which is probably connected with their composition peculiarities. The table shows that protium substitution by deuterium in alcohol methyl and hydroxyl groups has little influence on maltene and asphaltene yields. Deuterium introduction into a-position is accompanied by considerable isotope effect. Thus, in experiment 3, introduction of deuterium into ethanol methylene group results in a decrease in maltene yield from 24.3% to 14.1% and a decrease in asphaltene yield from 16.1% to 4.8%. Maximum isotope effect is reached at full deuteration of alkyl chain and makes up for ethanol 3.1 and 2.4 for lignite samples B and A, respectively. The last value according to Ref. 28 corresponds to the kinetic isotope effect of 2.8. Similar changes in product yields were observed by Scowronski et LZ~.‘~-‘~and Cronauer et ~1.‘~ in coal liquefaction in deuterated tetralin. The results obtained show that alcohols manifest hydrogen donor properties in lignite liquefaction, cleavage

of a-atoms being a limiting stage of liquid product formation. Liquid and solid products obtained from lignite liquefaction in alcohols were studied by i.r. spectroscopy in the regions characteristic of C-H and C-D aliphatic bond stretching vibrations. In Figure 1 i.r. spectra of asphaltenes obtained by lignite liquefaction in different deuterated ethanols are shown as an example. It can be seen that in the spectra of products obtained by lignite liquefaction in deuterated alcohols, besides 286&2930 cm- ’ bands, absorption in the 2000-2280 cm-’ region is observed, indicating the presence of C-D aliphatic groups. As the recording conditions of samples were similar, the intensities obtained can be used to determine relative C-H and C-D content of aliphatic groups. When calculating it was assumed that the C-H bond absorption integral intensity is twice that of C-D. The data on relative total content of C-H and C-D aliphatic groups are presented in Table 3. Solid (benzene insoluble) coal residues are seen to have a higher (almost four times) content of aliphatic groups than the original lignite. Earlier it was shown10,29 that the observed enrichment by aliphatic fragments was conditioned by alcohol alkylation of aromatic lignite rings. This conclusion is also confirmed by the fact that change in spectra in the regions of C-H and C-D vibration of aliphatic groups corresponds to the type of deuterium substitution in the initial alcohol. For asphaltenes this is seen from the spectra in Figure I. The total content of aliphatic groups in the products obtained in different deuterium analogues of ethanol differs only slightly. Hence, either the alkylation process does not include C-H and O-H bond breakdown in alcohol or such a breakdown does not limit alkylation. Table 4 shows data on elemental composition of maltenes, obtained in different deuterium analogues of ethanol.

Short Communications Table 3 and C-D

Influence of deuterium substitution type in ethanol groups in products obtained by lignite liquefaction Content

on the content

(relative

of aliphatic

C-H

unit)

Maltenes

Asphaltenes

Solid residues”

CH,CH,OH CH,CD,OH CD,CD,OH CD,CH,OH CH,CH,OD

75 71 61 66 55

35 41 46 51 35

25 21 26 25 25

of aliphatic

groups

Table 4 Elemental composition analogues of ethanol

in the original

ofmaltenes

lignite made up 6 relative

obtained

by lignite liquefaction

Elemental

composition

units

in different deuterium

(wt%)

H

O+S+N

H/C

CH,CH,OH CH,CD,OH CD,CD,OH CD,CH,OH CH,CH,OD

80.4 80.0 78.0 76.0 80.8

8.8 8.5 8.7 8.7 8.6

10.8 11.5 13.3 15.3 10.6

1.31 1.28 1.34 1.37 1.28

content

makes

up

K-8.8%,

Deuterium

distribution

in the products of

[ignite conversion From i.r. spectra analysis it follows that C-H and C-D group ratio in aliphatic fragments depends on the type substitution. Separate of deuterium determination of intensities in the region of stretching vibrations of C-H and C-D aliphatic bonds makes it possible to estimate deuteration degree of aliphatic fragments X,,:

X,1=

2A(C-D) A(C-H) + 2A(C-D)

(I)

where A is the absorption intensity in the vibration region of C-H and C-D groups. Results obtained from i.r. spectra determining deuteration degree of products in the presence of deuterium analogues of methanol, ethanol and isopropanol are presented in Table5. Deuteration degree X,, is seen to decrease in the order: solid residues> asphaltenes > maltenes, which coincides with that obtained for coal hydrogenation in tetralin in the presence of gaseous deuterium14.15 or tritiumz6. The deuterating activity of different deuterium analogues calculated per deuterium atom changes in the sequence CH,CH,OD > CD,CH,OH > CD,CD,OH > CH,CD,OH. Possessing H-donor properties, the alcohol methylene group is thus a very weak deuterating agent. The highest deuteration degree is

Edi x=

i

(4)

xdi+xh; I I

C

Hydrogen

(3)

ChP It is evident that CH, = CHt = 1. Similar equations can be written for deuterium distribution. Deuteration degree of products, not accounting for distribution in different structural groups, is determined by the ratio:

Alcohol

carbon content 78-80%, H/C ratio 1.28-1.33, which demonstrates that the composition of maltenes does not depend on the type of deuterium substitution in alcohol, conforming with i.r. spectra data.

observed in CH,CH,OD, probably due to heteromolecular H-D exchange. The analysis of proton distribution in ethanol after reaction has shown that considerable exchange of deuterium took place from CD, groups to hydroxyl groups. This type of exchange in the presence of catalyst was noted recently3’; this is why the CD, group is the active deuterating agent. A highly significant observation was that when being an H-donor, the methylene group failed to take part in the exchange reaction. Let us examine protium and deuterium distribution in the different structural non-equivalent positions in maltenes, depending on the type of deuterium substitution in the initial alcohol. For this purpose a method31 has been developed based on the combination of data obtained from i.r. and ‘H n.m.r. spectra. In the ‘H n.m.r. spectra, signals of the following proton-containing structural groups can be singled out3*: the region of 6.0-8.0 ppm corresponds to protons in aromatic rings, H,,; 4.5-6.0 ppm to protons in hydroxyl groups, Ho,; 1.94.5 ppm to protons in aliphatic fragments in site c[ to aromatic ring, H,; OS-l.9 ppm to protons in other aliphatic groups, H,,. In ‘H n.m.r. spectrum integrals from proton signals are proportional to the quantity of these protons:

where hf and di are proton and deuterium content respectively, in different structural positions. Deuteration degree Xi of i-structural position is determined as: Xi-

di _XDi h:‘+d, Hi

where Di and Hi represent distribution of deuterium and protons respectively and are determined by equations of type (2) and (3). On the condition that product composition at deuteration does not change, the following relationship must be fulfilled : Hi=XDi+(l

-X)H;

(6)

In the process under assumption indicated realized, and follows elemental composition spectra. From Equation for Di can be written:

consideration the is supposed to be from the data on (Table 4) and i.r. (6) the expression

D,=Hi-(l-XWP L

I Thus for determining deuterium distribution in liquids it is necessary to estimate either X or Xi parameters or their combination. For this purpose X,, values, obtained from i.r. spectra (Equation (1)) have been used. As in i.r. spectra, bands from C-H and C-D groups in different positions (c(, 8, y and so on) do not separate. X,, corresponds to the relationship:

=d,+d,Y

x

h,+h,,

From Equations x=,=1-(l-Xx)L

i-structural total proton Analogously

position

of and

protons xhi

is

in the

quantity in de sample. the equation for proton

(7) into (5) we obtain:

X,=1-(1-X)$

Chi hi is quantity

(7)

X

Placing expression

a’

where

sample can be

Hf=hp

Alcohol

“The content

distribution in deuterated written (d-index):

(8) and (9) we can write: H* + H& (10) H,+Hg,

which after regrouping x=1-(1-x,,)------

can be written as:

H,+HoY H: + H&

FUEL, 1991, Vol 70, April

(11)

561

Short Communications Using Equation (11) we can calculate the total degree of deuteration X. Knowing X and using Equations (7) and (8), deuterium distribution to different structural groups Di and Xi can be evaluated. ‘H n.m.r. and i.r. spectra experimental results and calculated data on deuterium distribution for different maltenes are presented in ‘Table 6. It can be seen that the main deuterium part in maltenes (67-98%) is in aliphatic structures and only an insignificant part (not more than 23%) is in aromatic rings. Thus when using methanol-d,, deuterium distribution is mainly to aliphatic fragments (86%), of which 64% is in the a-position (D, = 0.64) which agrees with the earlier conclusion”~‘* about methylation pro22% of deuterium ceeding. Also, distributes to &positions of aliphatic fragments, and 14% to aromatic rings which is probably conditioned by H-D exchange. In diRerent ethanol maltene samples differences in deuterium distribution to aliphatic structural positions are less significant. Nevertheless it is important to note that there is a likeness in deuterium distribution in maltenes and in the initial alcohol. Thus, in the case of CH,CD,OH, the majority of deuterium is in the a-position to the aromatic ring (D,=0.54) and less in the fly-position (Dp,,,=0.49); in CD,CH,OH the distribution is reversed and for CD,CD,OH distribution is almost equal. In isopropanol products the prevailing deuterium content is also in aliphatic structures, mainly in a-position. For these samples it is characteristic to find increased deuterium content in aromatic rings (D,,=0.23) as compared to methanol and ethanol samples (D,, is not more than 0.15). Deuterium distribution described here differs considerably from that observed by previous authors14~17~24.25 for coal liquefaction in deuterated tetralin or in the presence of gaseous deuterium. According to their data the main deuterium fraction was in aromatic rings (about 40-50%) and in aiiphatic groups in cr-positions to aromatic ring (about

Table 6

Distribution

of protons

and deuterium

Table 5 deuterium

Deuteration degree of aliphatic groups substitution

type in different

of lignite liquefaction

Deuteration Alcohol

Maltenes

CD,OD

0.25 (0.06)

CH,CD,OH

products

dependent

on

alcohols degree” (%)

Asphaltenes

Solid residues

0.09 (0.05)

0.12 (0.06)

0.16 (0.08)

CD,CH,OH

0.42 (0.14)

0.44 (0.15)

0.55 (0.18)

CD,CD,OH

0.42 (0.08)

0.59 (0.12)

0.60 (0.12)

CH,CH,OD

0.20 (0.20)

0.25 (0.25)

0.30 (0.30)

(CD,),CDOH

0.24 (0.03)

0.0

0.0

(CD,),CDOD

0.34 (0.04)

0.22 (0.03)

0.71 (0.09)

u Values in brackets

are calculated

_

on a basis of one alcohol

30-40%). The smaller fraction (not more than 20%) is found in bi and other aliphatic positions. Deuterium distribution depended little on coal species. Apparently the differences in deuterium distribution in tetralin and alcohol coal products are connected with peculiarities of the introduction mechanism. For coal liquefaction in deuterated tetralin or gaseous deuterium, the label introduction into products occurs through hydrogenation and exchange’4~‘7~22~23. For coal liquefaction in alcohols, the greater contribution is apparently made by alkylation. The fact that for the samples obtained in CH,CD,OH and CD,CH,OH, no considerable differences in deuterium distribution to t( and /$-positions are observed, is difficult to explain by both H-D exchange and hydrogenation. In reactions of H-D exchange which are known3’ to take place in coal liquefaction, mainly benzyl hydrogen atoms participate, and possibly also aromatic atoms. Hydrogen exchange in other aliphatic coal fragments is unlikely. The explanations of deuterium distribution in different deuterium ethanol samples can be related to alcohol CD,-OH exchange observed and also to the alkylation mechanism of aromatic rings. Earlier” we supposed that alcohol alkylation of lignite occurs via radicals. If in the process ethyl radical is formed, it

in maltenes,

‘H n.m.r. data

obtained

by lignite liquefaction

ACKNOWLEDGEMENT The contribution of G. D. Holopova and T. T. Sokolova to the analytical ‘H n.m.r. and i.r. data is acknowledged. REFERENCES 1

2

in different

x,,

x

Curran, G. P., Struck, R. T. and Gorin, E. Ind. Eng. Chem. Proc. Des. Dev. 1976, 6, 166 Whitehurst, D. D., Mitchell, T. 0. and Farcasiu, M. ‘Coal Liquefaction’, Academic Press, New York, 1980, p. 255 Bartle, K. D., Martin, D. F. and Williams, D. F. Fuel 1975, 54, 226 Ross, D. S. and Blessing, J. E. Fuel 1979, 58,433 Ross, D. S. and Blessing, J. E. Fuel 1979, 58,438 Makabe, M., Hirano, Y. and Ouchi, K. K. Fuel 1978, 57, 289 Mondragon, F., Itoh, H. and Ouchi, K. K. Fuel 1982, 61, I131 Bimer, J. and Salbut, D. K&s. Smalu. Gas. 1986, 31, 23 Luyk, H. E. and Klesment, 1. R. OilShale 1986,3, 319 Kuznetsov, P. N., Sharypov, v. I.,

deuterium

Deuterium

Ha,

H OH

H*

HP,

CH,OH

0.155

0.035

0.465

0.345

CD,OD

0.160

0.045

0.410

0.385

0.14

0.130

0.044

0.368

0.462

0.25 _

0.24

CH,CH,OH

0.00 _

CH,CD,OH

0.140

0.046

0.354

0.460

0.09

0.07

0.01

Dar

Do,,

atom

can easily be isomerized and therefore join an aromatic ring by any carbon atom. In isopropanol, as well as hydrogenation, alkylation, exchange and isomerization of isopropyl group and its destruction can take place, greatly complicating product composition.

11. data

Alcohol

deuterium

Da

alcohols

distribution

D,,

X,,

_

_

0.64 _

0.22 _

0.00

0.54

_

X,,,

X,

XP, _

0.22 _

0.00

0.33 _

0.15

0.49

0.01

0.00

0.11

0.08

_

CD,CH,OH

0.125

0.059

0.354

0.462

0.42

0.41

0.15

0.01

0.39

0.45

0.46

0.14

0.44

0.40

CD,CD,OH

0.137

0.037

0.326

0.500

0.42

0.41

0.12

0.05

0.43

0.41

0.38

0.45

0.48

0.36

CH,CH,OD

0.138

0.047

0.350

0.464

0.13

0.01

0.070

0.360

0.370

0.44 _

0.42 _

0.18 _

0.05

0.200

0.20 _

0.19

(CH,),CHOH

0.23 _

0.18 _

(CD,),CDOH

0.190

0.060

0.320

0.440

0.24

0.26

0.23

0.10

0.47

0.20

0.30

0.37

0.34

0.14

562

FUEL, 1991, Vol 70, April

Short

I1

12

13 14

15 16

17

Rubaylo, A. I. and Korniyets, E. D. Fuel 1988.67, 1685 P. N., Belskaya, T. A., Kuznetsov, Tomilova, T. A., Beregovtsiva, N. G. and Sharypov, V. I. Fuel 1989,68, 1580 Kuznetsov, P. N., Ivanchenko, N. M. and Beregovtsova, N. G. et al. Fuel 1990, 69,985 Ozaki, V., Mondragon, F., Makabe, M., Itoh, H. and Ouchi, K. Fuel 1985,64,767 Skovronski, R. P., Ratto, S. S. and L. A. Proceedings of a Heredy, Conference on Atomic, Nuclear and Fossil Energy Research, I-4 December 1980, American Nuclear Society, York, p. 207 Skovronski, R. P. and Heredy, L. A. Fuel 1984,63,440 Cronauer, D. C., McNeil, R. I., Young, D. C. and Ruberto, R. G. Fuel 1982,, 61, 610 Cronauer, D. C., McNeil, R. I.,

On the nitrogen

Maximilian

containing

18 19 20 21

22 23 24 25

Young, D. C. and Ruberto, R. G. Proceedings of Am. Nucl. Sot., Am. Chem. Sot. Meeting, Mayaques, Puerto Rico, l--I December 1980, p. 365 Franz, J. A. and Camaioni, D. M. Fuel 1984,63, 990 Brower, K. R. J. Org. Chem. 1982, 47, 1989 Brower, K. R. and Pajak, J. J. Org. Cljem. 1984, 49, 3970 Chernetskaja, N. V., Gajke, R., Polubentseva, M. F. and Lipovich, V. G.

Proceedings of Symposium ‘Problemy kinetiki i katalisa’. 21-27 Mav 1990. Donetsk, 1990, p. 24 Kabe, T. J. Jap. Petrol. Inst. 1986,29,345 Kabe, T., Nitoh, O., Funatsu, E. and Yamamoto, K. Fuel 1987,66, 1321 Vassalo, A. M., Fredericks, P. M. and Wilson, M.A. Org. Geochem. 1983,5,75 Kershaw. J. R. and Barras. G. Fue/ 1977, 56,455

constituents

of coal-tar

26 27

28

29

30 31

32

33

Communications

Kabe, T., Nitoh, O., Fukatsu, E. and Yamamoto, K. Fuel 1987, 66, 1326 Kuznetsov, P.N., Sharypov, V. I. and Beregovtsova, N. G. React. Kinet. Catal. Lett. 1989, 40, 59 Kuznetsov, P. N., Sharypov, V. I., Bereeovtsova, N. G.. Rubavlo, A. I. and KorGyets, E. D. F& 1990: 69. 911 Kuznetsov, P. N., Sharypov, V. I., Rubaylo, A. I., Korniyets, E. D. Claim. tverd. topl. 1988. 2, 102 Nugent, W. A. and Zubyk, R. M. J. Inorg. Chem. 1986, 25, 4604 Rubaylo, A. I., Korniyets, E. D. and Kuznetsov, P. N. Chim. tverd. top/. 1988, 2, 92 Bartle, K. D. and Jones, D. W. ‘Analytical Methods for Coal and Coal Products’ Vol. 2, Academic Press, London, 1978, p. 103 King, H. H. and Stock, L. M. Fuel 1982, 61, 257

pitch

Zander

Riitgerswerke AG, Kekul&tra@e 30, D-4620 (Received 16 November 7990)

Castrop-Rauxel,

Germany

Experimental evidence for a statistical distribution of the nitrogen present in coal-tar pitch among pitch constituents is presented. It is shown that the concentration of basic nitrogen compounds in pitch fractions increases with increasing molecular weight of the fractions. The general suggestion is derived that the high-molecular weight portion of coal-tar pitch is probably not predominantly a mixture of polycyclic aromatic hydrocarbons but rather a mixture of heterocyclic systems. Ion exchange chromatography, charge-transfer fractionation using picric acid as the complexing agent as well as precipitation of hydrochlorides with gaseous HCI have been used for isolation of basic pitch constituents. (Keywords: pitch; nitrogen compounds; separation techniques)

The atomic N/C ratio of fractions obtained from a typical coal-tar pitch by preparative size exclusion chromatography (s.e.c.) was found to be practically constant over the entire molecular weight range studied (20& 2500 Dalton, 16 fractions) and to come close to the N/C ratio of the entire pitch material’. This observation supports the earlier theory that the nitrogen present in pitch (ca. lo/,) is statistically distributed among pitch constituents*. With regard to a statistical distribution of nitrogen among pitch constituents two boundary cases have to be distinguished which both are consistent with the observed independence of the N/C ratio of pitch fractions from their molecular weight. In boundary case A it is assumed that the concentration of nitrogen compounds in pitch fractions is constant over the entire molecular weight range of pitch while the average number of nitrogen atoms per nitrogen containing increases increasing molecule with molecular weight of pitch fraction.

00162361/91/04056343 0 1991 Butterworth-Heinemann

Ltd.

Conversely in boundary case B the average number of nitrogen atoms per nitrogen containing molecule is assumed to be constant over the entire molecular weight range of pitch while the concentration of nitrogen compounds in pitch fractions increases with increasing molecular weight of pitch fraction3. Of course, these two boundary cases must apply to both basic and neutral nitrogen compounds present in pitches. In this note the problem is studied with regard to the basic nitrogen containing pitch constituents. Some more general conclusions regarding the molecular structure of coal-tar pitch are also derived.

EXPERIMENTAL Materials

The investigation was performed on two typical high-temperature coal-tar pitches. Characteristics of pitch A are given in Ref. 1, and of pitch B in Ref. 4.

Methods For the isolation of the basic nitrogen containing constituents of the toluene soluble part (TS fraction) of an entire coal-tar pitch or pitch fractions obtained by preparative s.e.c. three methods have been applied: charge-transfer fractionation (c.t.f.) using picric acid as an electron acceptor compound; precipitation of the hydrochlorides of bases with dry gaseous HCl (HCI method); and ion exchange chromatography. Experimental details of both c.t.f. and the HCl method have been given in reference 4. Ion exchange chromatography was performed on the acid form of the cation resin Amberlyst 15 (Rohm & Haas, analytical grade, mesh size 2&50) using toluene as the solvent. The toluene solution of the pitch material was prepared by heating 1 g pitch material in 250 ml toluene for 30 min at boiling temperature. The toluene insoluble portion was removed by filtration and its weight determined after careful drying.

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