Influence of temperature on the hydrogenation of Australian Loy-Yang brown coal. 2. Structural analysis of the asphaltene fractions

Influence of temperature on the hydrogenation of Australian Loy-Yang brown coal. 2. Structural analysis of the asphaltene fractions John

M. Charlesworth

Department of Chemical Engineering, Australia (Received 26 February 1980)

University

of Melbourne,

Parkviiie,

Victoria 3052,

A study is made of the asphaltene fractions produced by hydroliquefaction of an Australian Lay-Yang brown coal at temperatures ranging from 300 to 500°C. A combination of Fourier-Transform 13C n.m.r. conventional proton n.m.r., i.r. and U.V. spectroscopy is used in conjunction with previously published data to define representative average chemical structures. Results indicate that the asphaltenes increase in aromaticity as the hydrogenation temperature rises, with a rapid change occurring near 450°C. Furthermore, the asphaltenes formed at the highest hydrogenation temperature of 500°C appear to consist of dehydrogenated derivatives of species produced at lower temperatures. Most of the saturated carbon atoms in all fractions occur in condensed cyclic structures with very few sidechains or methylene bridges. Because of this, the commonly assumed value of 0.50 for the saturated carbon to hydrogen atomic ratio used in the Brown-Ladner equation may be in error if applied to systems of this type. Below 450°C the aromatic component of the asphaltenes consists mainly of isolated naphthalenic and mononuclear structures. Below 400°C a small but significant number of carbon atoms are present in alkyl chains at least 8 carbon atoms long.

The term asphaltene is commonly used to describe one of the species which is suggested to be an intermediate in the liquefaction of coal in a hydrogen donor medium’. If asphaltenes are accepted as being true precursors of lower molecular weight oil then an accurate description of their structure needs to be provided to help in understanding the hydrogenation process. Unfortunately, because of the chemical complexity of coal, not only one type of asphaltene molecule, but a distribution of species are produced during the thermal disruption of the coal and subsequent stabilization of free radical fragments2. This presents a problem when attempting to formulate a hypothetical average structure because line broadening in n.m.r. and i.r. spectra, caused by the overlap of a large variety of absorptions, obscures most of the features which normally enable detailed information to be obtained. As a consequence, until recently, most workers familiar with spectroscopic methods have used the techniques to provide a few basic parameters rather than attempting to investigate the problem in great depth3-‘. The established equations developed by Brown and Ladner3 have been used extensively as a means of deriving information from the ‘H n.m.r. data; however, if this approach is adopted then approximations must be made, including fixing the atomic ratio for saturated carbon to hydrogen at an arbitrarily chosen value usually between 0.40 and 0.67. Without supporting evidence this can lead to errors in fundamental properties, including the fraction of carbon atoms present in aromatic rings. 001~2361/80/1208654652.00 @ 1980 IPC Business Press

The advent of quantitative Fourier-Transform (FT) 13C n.m.r. has produced a more theoretically reliable method for determining parameters related to the carbon skeleton of molecules. This technique has been used several times to gather information relevant to coalderived liquids *sgbut, with the exceptions of the work by Whitehurst et ~1.~ and Dereppe et al.“, attempts to deduce a probable average structure for the asphaltene fraction, without resorting to ad hoc assumptions, have been limited. One of the aims of the present paper is to show how quantitative 13C and ‘H n.m.r. measurements can be used in conjunction with other information to provide a unified solution to the structural problem. The work is also a continuation of the study reported in Part 1l1 concerning the effects of temperature on the type and distribution of material formed during the hydrogenation of Loy-Yang brown coal. EXPERIMENTAL Hydrogenations were performed using Loy-Yang brown coal (C, 66.1; H, 4.6; 0,25.5 wt %). The resulting heavy oil was separated into benzene-insolubles (preasphaltenes), benzene-solubles (asphaltenes) and pentane-solubles (maltenes) as described in Part 1ll. Proton n.m.r. data were measured on a JEOL FX-100 instrument at a frequency of 100 MHz in the range G1500 Hz relative to TMS, with integration by machine. Spectra of the asphaltenes and maltenes were recorded in CDCl, solvent in the con-

FUEL,

1980, Vol 59, December

865

influence

of temperature

on the hydrogenation

b

6

150

200

100

50

0 Chemical

Figure 1 a, 350°C;

of brown

-n._ -1

12.5 shift

10.0

l-5

5.0

2.5

0

Ippml

13C and ‘H n.m.r. spectra of asphaltenes b, 425OC; and c, 500°C

produced

at

centration range 200-400 mg cmW3. Because of the low solubility of the preasphaltenes in chloroform it was found necessary to measure these spectra in d,-pyridine at an approximate concentration of 100 mg cme3. Protonated impurities in the solvent resulted in the production of overlapping peaks in the aromatic region (6 = 5-l 1 ppm). Integration was therefore performed using a planimeter and the extraneous resonances were, as far as possible, excluded from the areas. Carbon-13 n.m.r. spectra of the asphaltenes were recorded using the JEOL FX-100 instrument at 26 MHz in the FT gated decoupling mode; data in the range O6000 Hz relative to TMS were stored. To overcome the problems usually associated with obtaining quantitative ’ 3C n.m.r. measurements, including Nuclear Overhauser Enhancement and long spin-relaxation times compared to pulse repetition rates, the following conditions were chosen as most suitable: 10 ps pulse width, 35” tip angle, 4.68 s pulse delay, 0.68 s aquisition time, 8 192 data points, 1100&12500 accumulations, 400 mg sample, 100 mg Cr(acac),, 1.5 cm3 CDCl, and 10 mm diameter sample tube. The effects of varying many of these parameters have been discussed by other workers” - ’ 6. Infra-red spectra were measured in the range 2W4000 cm-’ using samples pressed into KBr discs at a concentration of approximately 1%. Ultra-violet spectra of the asphaltenes were measured in CH,Cl, solvent at a concentration of 10m3% using a double beam instrument operating in the range 220-600 nm. RESULTS AND DISCUSSION Interpretation

of the n.m.r. spectra

Figure

1 shows examples of ‘H and ’ 3C n.m.r. spectra of asphaltenes prepared at representative hydrogenation

866

FUEL,

1980,

coal (2): J. M. Charlesworth

Vol 59, December

temperatures. For ‘H data it has been previously reported that as many as twelve categories of protons may be quantitatively estimated by dividing the bands appropriately ” . A survey of the tabulated positions of resonances for a variety of compounds reveals that less than half this number of classifications can be made with confidence3,’ 8*19.For this reason and for consistency with other workers in the field, the ‘H spectra were divided into four regions on the 6 scale: (1) H,, protons attached to aromatic rings (l&6.3 ppm in CDCl,, 11-5 ppm in d,pyridine); (2) H,, protons OL to aromatic rings (4.2-2.0 ppm in CDCl,, 5-2.0 ppm in d,-pyridine); (3) H,, protons fl to aromatic rings and protons y and further away in methylene and methine groups. (2.Gl.l ppm in CDCl,, 2.cl.l in d,-pyridine); and (4) H,, protons in methyl groups y to, and further away from, aromatic rings. (l&O in CDCl,, 1.1-O in d,-pyridine). Phenolic protons usually lie in the range 12-5 ppm19 and therefore the true proportion of aromatic protons may be over-estimated by definition (1). However, on the basis of the molecular formulae in Table 1, calculated from the data in Part 1,’ ’ the maximum fraction of the total hydrogen atoms which could possibly be associated with oxygen is approximately 10%. As a significant number of the oxygen atoms are present in ether groups, as shown by the i.r. results (see later discussion) the actual error involved is even smaller. The contribution from these protons will be neglected and the sum of the areas of each region normalized to unity i.e.: H,+H,+H,+H,=l

(1)

Recent studies on the interpretation of the 13C spectra of molecules typically found in coal-derived liquids’ 3*20 have shown that the following three regions can be reliably defined: (1) Co, aromatic carbon atoms attached to oxygen, plus carbon atoms involved in carbonyl functionalities (22&150 ppm); (2) C, aromatic carbon atoms not linked to oxygen (15&100 ppm); and (3) C,, carbon atoms present in saturated structures (7&O ppm). The integrated intensities may again be normalized to unity i.e.: c,+c,+c,=

1

(2)

The prominent peak at 29.7 ppm, which can be seen in the upper two ’ 3C spectra in Figure 1, is normally attributed to CH,, E or further from the end of the chain, and y or further from an aromatic ring in alkyl chains at least 8 carbon atoms long’. The fractional amount of the saturated carbon belonging to this type of unit, N&N,,, is listed in Table 1. The fraction of carbon atoms involved in carbonyl groups appears to be small as the i.r. spectra show only small or negligible absorptions near the carbonyl stretching frequency (see next section). Therefore, the fraction of carbon atoms present in aromatic structures, to a good approximation, becomes the sum of Co and C,. It follows that the average number of aromatic carbon atoms in each unit, N,--, can be written as: Nca = N&o + C,)

(3)

where:N,, is the number of carbon atoms per molecule. The average number of aromatic carbon atoms which are linked to protons, N,H,,is calculated from the ‘H n.m.r.

influence Tab/e

1

Structural parameters

of temperature

on the hydrogenation

of brown

coal (2): J. M. Charlesworth

forasphaltenes C

NCa

T (“C)

NC

~‘4

No

NC

300

61.0

75.0

7.1

350

38.4

r

Rn

0.50

0.53

2.0

0.27

0 i

Ncs

Nsa

Nba

N”c,

NE,

~~~

NI+

hi7

n

0.47

32.2

10.5

4.5

4.7

9.0

9.1

41.2

14.3

7.2

kc+ s

ks

38.4

4.5

0.60

15.3

11.1

3.3

4.9

3.8

5.8

15.0

6.5

4.7

0.56

1.00

3.3

0.14

structure I 41

40

5

0.63

15

11

5

6

4

6

11

6

4.8

0.65

1.61

4

0

375

37.6

35.3

3.7

0.64

13.3

12.0

4.0

4.2

3.8

7.1

10.9

5.3

3.3

0.58

0.96

3.9

0.11

400

35.2

31.0

2.3

0.71

10.3

13.6

5.2

3.2

2.9

8.7

6.5

2.2

2.0

0.60

0.82

4.3

0.07

425

30.7

4.2

2.7

3.3

6.5

5.1

1.0

1.9

0.63

0.80

3:J

0.03

3

4

8

6

0

1.9

0.64

0.91

4

0

25.2

1.9

0.74

7.9

12.6

structure II 31

26

2

0.71

9

114

450

27.8

23.0

1.3

0.79

5.5

11.6

2.8

2.4

5.1

5.8

4.1

1.4

2.0

0.52

0.59

1.7

-co.03

475

30.8

23.0

1.4

0.90

3.1

17.1

1.8

0.7

8.1

3.5

1.8

0.7

1.7

0.52

0.56

1.0


500

30.1

20.5

1.5

0.89

3.2

16.1

1.8

0.9

7.9

1.5

1.4

0.4

1.8

0.75

1.10

2.0


20

2

0.90

3

14

3

3

8

3

2

0

2.0

0.60

0.83

2

structure III 31

0

The average number of naphthenic rings per molecule, R,, is given by:

data using: N;,=NHHa

; 0

R, = rNSC,

at

where: NH, is the number of hydrogen atoms per molecule; and (C/H),,, is the total atomic carbon to hydrogen ratio (data listed in Part 1”). The remaining aromatic carbon atoms can either be joined to saturated groups or bridged to other aromatic carbon atoms. The former type, NC, is given by: N& = N&/n

= NcJn

(9

where: N,$, is the average number of saturated carbon atoms per molecule; and n, is the average number of carbon atoms in each substituent. This latter factor is impossible to calculate unless it is assumed that on average the saturated carbon to hydrogen ratio (C/H), of groups c1to aromatic rings is equal to the same ratio for groups further away. This is the major assumption in the present approach and enables the following expression to be written: n=(l -H,)/H, (6) The average number of aromatic bridge carbon atoms, N& is determined by difference: N;, = Nc, - N$_- NEa- N”,,

(7)

where the average number of aromatic carbon atoms substituted by oxygen, N& is defined as: NE, = N&Z,,

(8)

The value of (C/H), may be calculated from the ‘H and 13C n.m.r. data using the following equation: (9)

(10)

where: I, the average number of naphthenic cycles per substituent, including rings containing oxygen, may be shown to be: r=n+$-n/2

i0

I

(11)

Finally the average numbers of protons in each of the four previously defined categories are simply expressed as

NH,= NH& NH~= NH& (12)

bp= NH& N,. = NuH, The values of the parameters calculated from equations (3H12) for each of the eight asphaltene samples are listed in Table 1. The fractions of each category of carbon atoms in average asphaltene molecules are plotted in Figure 2 as a function of hydrogenation temperature. Several points become immediately apparent from the data. Firstly, the fraction of aromatic carbon atoms in each unit increases smoothly up to ~425°C and at the same time there is a decline in the fraction of carbon atoms belonging to saturated substituents. Between 425 and 475°C a more rapid change occurs which sharply reduces the saturated carbon content and further increases the aromaticity. In this temperature range the yield of asphaltenes and preasphaltenes decreases while there is a parallel increase in both the maltenes and gaseous fractions.” Thermal cracking of heavy fragments produced after the initial disruption of the weaker coal cross-linkages may cause this. The two processes, i.e. dehydrogenation and crack-

FUEL, 1980, Vol 59, December

867

influence of temperature on the hydrogenation

of brown coal (2): J. M. Charlesworth

aromaticity is also reflected by the ‘H n.m.r. data for both the maltenes and preasphaltenes listed in Table 2. As ’ 3C spectra were not measured for these materials, one of the Brown-Ladner equations3 must be used to enable the fraction of aromatic carbon atoms to be calculated: ,f 0.L ‘u 0

C E ar ; i( )()

&&=1-(1-H,)

.L c

(13)

s

2

; 0.2 ”

O350

300

Figure 2 asohaltene

Tab/e 2

650

LOO Temperature

500

[*C)

Fractions of each category of carbon atoms in average molecules as a function of hvdrooenation temoerature.

1H n.m.r. data for preasphaltenes

and maltenes

In these calculations, the average value of (C/H), for the asphaltene samples listed in Table 1 (i.e. 0.57) was chosen in preference to the commonly accepted figure of 0.50. Furthermore, to enable a self consistent comparison of the results for all three fractions, the ‘H n.m.r. data for the asphaltenes were used to establish recalculated values of NcJNc. The results are plotted in Figure 3 and although there are deficiencies in this approach it is still evident that the aromaticities lie in the order: preasphaltenes> asphaltenes>maltenes. It is apparent that the maltenes also undergo rapid aromatization near 450°C and by 475°C all three fractions are medominantly composed of aromatic material. I

T (“C)

300 350 400 425 450 475 500

Maltenes

Preasphaltenes Ha

Ho

HP

Hy

Ha

Ho

HP

Hy

0.24 0.41 0.52 0.62 0.64 0.69 -

0.21 0.24 0.26 0.22 0.19 0.15 -

0.40 0.27 0.15 0.11 0.10 0.11 -

0.16 0.09 0.06 0.05 0.07 0.05 -

0.13 0.13 0.26 0.29 0.32 0.61 0.70

0.11 0.14 0.14 0.21 0.19 0.23 0.21

0.52 0.50 0.42 0.41 0.34 0.13 0.09

0.24 0.23 0.18 0.10 0.16 0.04 0.00

ing, are known to commence at ~450°C during petroleum relining by conventional non-catalytic methods2i hence, it is not unexpected to observe the same phenomena for coal-derived liquids. The data in Table 1 indicate a reduction in the average number of carbon atoms per saturated substituent from approximately 7 to 1.8 over the entire range of temperature. Also, the number of naphthenic rings per molecule increases up to 400°C and then begins to decline. At temperatures below 4OO’C,where the conversion of coal is still increasing with increasing temperature”, two simultaneous processes may occur. Firstly, the paraflinic sidechains on already-formed asphaltenes may crack and reform, either by intermolecular polymerization or into give saturated rings. tramolecular cyclization, However, these reactions must compete with hydrogen abstraction from the solvent and a polymerization reaction is even more unlikely, because it has been shown that a continuous reduction in the number average molecular weight of the asphaltenes occurs over the entire temperature range l1 . Secondly, and more probably, the coal fragments initially produced, i.e., at the lower temperatures, are those which contain either the smallest proportion of naphthenic cycles or the greatest number of thermally unstable naphthenic cycles. Any instability is likely to be due to naphthenic rings with relatively long parafinic side-chains because these are known to become more susceptible to thermal destruction as the molecular weight of the chains increases2i. At 2475°C the data in Table 1 show that many of the naphthenic rings have dehydrogenated to produce condensed aromatic structures which appear to be sufficiently stable to resist any further change. This general increase in

868

FUEL,

1980,

Vol 59, December

INTERPRETATION SPECTRA

OF

THE

I.R.

AND

U.V.

The i.r. spectra of the asphaltenes formed at hydrogenation temperatures of 350,425 and 500°C are shown in Figure 4. All three spectra show large hydroxyl absorptions (3400 cm-‘), almost certainly due to the presence of phenolic groups, and aromatic C-H stretching bands (3050 cm-‘) which increases in intensity as the hydrcgenation temperature increases. The aliphatic C-H stretching absorptions (methyl at 2962 cm-‘, methylene at 2962 and 2853 cm - ‘) also appear in each spectrum and decrease in magnitude as the temperature is increased. The carbonyl absorption (1700 cm-‘) which normally possesses a large extinction coellicient22 is either weak or absent, and, as expected, all spectra show strong aromatic C-C stretching absorptions (1600 and 1450 cm-‘). The low intensity of the C-H bending absorption of methyl groups (1375 cm- ‘) and the weakness of the band at 2962 cm-’ indicate that only a small proportion of methyl groups occur in the molecules. The broad absorption between 1100 and 13OOcm-’ indicates that aryl ethers are

0.2

300

350

400 Temperature

L50

500

r ‘Cl

Fraction of carbon atoms in aromatic rings (BrownFigure 3 Ladner method) as a function of hydrogenation temperature. 0, Preasphaltenes; A, asphaltenes; and n, maltenes

influence of temperature on the hydrogenation

of brown coal (2): J. M. Charlesworth

type units were chosen for structure I in preference to combinations of mono and fused triaromatic ring systems because the n.m.r. spectra of phenanthrene and anthracene both exhibit resonances for at least two protons above 8.2 ppmz4,“. The ‘H n.m.r. spectrum of the 350°C asphaltenes sample, Figure 1, shows no indication of any resonances above 8.0 ppm. For the 425°C sample, an average structure with a maximum of two condensed rings also appears probable owing to the large number of aromatic carbon atoms bonded to hydrogen, compared to those bonded to other aromatic carbon atoms.

._I_p_t 3500

2500

ei--+~1800 Wovenumber

Figure 4 I.r. spectra of asphaltenes and C, 5CJO’C

1400

1000

600

I cm-‘) produced

at A, 350°C;

El, 425°C;

*

present, and the bands between 700 and 900 cm-’ are characteristic of the out-of-plane C-H bending of polynuclear aromatic hydrocarbons. The position and intensity of these latter absorptions indicates the substitution pattern of the rings. Colthup et ~1.‘~ have summarized similar data for a variety of compounds. From this information it is possible to conclude that the band at 750 cm-’ is due to 4 adjacent hydrogens, the band at 810 cm-’ is due to 2 and possibly 3 adjacent hydrogens, and the band at 870 cm-’ is caused by an isolated hydrogen atom. Based on these assignments the spectra indicate fewer condensed aromatic rings in the asphaltenes formed at 350 and 425°C and show a change from molecules with mainly 2 and 3 adjacent hydrogens to those containing more polynuclear structures, some of which have 4 adjacent hydrogen atoms. The U.V.spectra (Figure 5) of the same samples confirm that the aromaticity increases with rising hydrogenation temperature because both the maximum absorptivity and the absorptivity at longer wavelengths increase in a parallel fashion. This behaviour at longer wavelengths also supports the assertion that the number of condensed aromatic rings per unit mass increases with temperature as it is established that a bathochromic shift follows a rise in the level of conjugation. DETAILED MOLECULAR ASPHALTENES

STRUCTURE

OF THE

In attempting to describe the detailed structure of asphaltenes it will not be possible to design a molecule which fits the data exactly, because, apart from experimental errors, most of the average parameters are non-integer quantities. Some discretion must therefore be applied when interpreting the measurements and structures postulated which provide close approximations to the empirical results. The three structures described later, tit reasonably closely the experimental data for the 350,425, and 500°C asphaltenes, respectively. The structural parameters for these molecules are given in Table 1. Arbitrary assumptions must be made for the positions of aromatic ring substituents (indicated by *) particularly for structure 1; however, it is not possible to draw other markedly dissimilar carbon skeletons which give parameters a good deal closer to those listed in Table 1. Two naphthalenic

(35O’C

OH

1

structure

* OH

Asphoitene

)

*OH

Structure

I L25.C

II Asphaltene

00 33 Structure

(

5OO’C

III Aspholtene) * Arbitrartly

posItIoned

group

These structures illustrate that in the hypothetically typical species most of the saturated carbon atoms appear in the form of condensed rings rather than acyclic methylene bridges or polymethylene side-chains, which in turn explains why the values of (C/H), are higher than the widely accepted figure of 0.50. The apparent absence of methylene linkages is not unexpected for model com-

Fiwre 5 B, 425’C;

UN. spectra of asphaltenes produced and C. 350°C

FUEL,

1980,

at A, 5OO’C;

Vol 59, December

869

Influence of temperature on the hydrogenation

of brown coal (2):

pounds containing benzene rings bridged by a sequence of two or more methylene groups are known to be among the most labile molecules under hydrogenation conditions similar to those used in this study26-2s. A signiticant number of long-chains are present in the asphaltenes prepared below 4OO”C, as shown by the values of N,< +/Nc listed in Table 1, however, the proportion of this type of carbon atom decreases as the hydrogenation temperature rises, and becomes of minor importance above 400°C. As was proposed earlier, the asphaltenes initially formed may contain most of the paraffinic sidechains which are then diluted at higher hydrogenation temperatures by more condensed species. It also seems probable that these long-chains may crack to produce some of the free paraffinic material which is known to be present in the pentane-soluble portion of the heavy oi129. The similarities between the carbon skeletons of the three structures leads to speculation that the high aromatic content at 500°C is due to dehydrogenation of saturated six membered cycles in asphaltenes produced earlier in the reaction. Like the dehydrogenation reaction which tetralin undergoes, the increased aromaticity may be caused by transfer of hydrogen to other species in the mixture either by direct abstraction or via a shuttling mechanism of the type described by Whitehurst et al.‘. That the asphaltenes formed at 350 and 425°C have only isolated units of two condensed aromatic rings may reflect a property of the original coal. Examination of the hydrogenation products from higher-rank coals using polargraphic reduction as a means of defining the number of condensed rings has shown that mono-aromatics and naphthalenic systems are the most abundant types2. ACKNOWLEDGEMENTS The author is grateful to the Australian Research Grants Committee for providing financial support for the work and to Mr R. S. Yost and Professor S. R. Siemon for useful discussions. REFERENCES 1 2

3 4 5 6 7 8 9 10 11

12 13 14 15 16 17 18 19

870

Weller, S., Pelipetz, M. G. and Friedman, S. lnd. Eng. Chem. 1951, 43, 1572 Whitehurst, D. D., Farcasiu, M., Mitchel. T. 0. and Dickert, J. J. ‘The Nature and Origin of Asphaltenes in Processed Coals’, EPRI AF-480, Project 410-1, Annual Report July 1977 Brown, J. K. and Ladner, W. R. Fuel 1961,39, 87 Ramsay, J. W., McDonald, F. R. and Petersen, J. C. Ind. Eng. Chem. Prod. Res. Den. 1967, 6, 127 Dickson,F. EDavis, 3. E. and Wirkkaia, R. A. Anal. Chem. 1969, 41, 1335 Clutter, D. F., Petrakis, L., Stenger, R. L. and Jensen, R. K. Anal. Chem. 1969, 41, 21 Haley, G. A. Anal. Chem. 1972, 44, 580 Retcofsky, H. L. and Friedel, R. A. ‘Spectrometry of Fuel’, Plenum Press, Chapter 8, 1970 Yokoyama, S., Bodily, D. M. and Wiser, W. H. Fuel 1979,58,162 Dereppe, J. N., Moreaux, C. and Castex, H. Fuel 197857, 435 Charlesworth, J. M. Fuel 1980, 59, 000 Bartle, K. D., Martin,T. G. and Williams, D. F. Fuel 1975,54,226 Ladner, W. R. and Snape, C. E. Fuel 1978, 57, 658 Thiault, B. and Merssman, H. Org. Mug. Resonance 19757,575 Wehrli, F. W. and Wirthlin, T. ‘Interpretation of 13C N.M.R. Spectra’, Heyden, London, 1976 Dorn, H. C. and Wooton, D. L. Anal. Chem. 1976, 48, 2146 Hooper, R. J. and Evans, D. G. Am. Chem. Sot. Div. Fuel Gem., Preprints 1979, L4 (l), I3 1 Bartle, K. D. and Smith, J. A. S. Fuel 1967, 46, 29 Chamberlain, N. F. ‘The Practice of N.M.R. Spectroscopy’, Plenum Press, London, 1974

FUEL,

1980,Vol 59,

December

20 21

22 23

24 25 26 27 28 29

J. M. Charlesworth

Knight, S. A. Chem. Ind. 1967, 1920 Knight, W. N. N. and Peniston-Bird, M. L. ‘Modern Petroleum Technology’ (Eds. G. D. Hobson and W. Pohl) Applied Science, Chapter 9, 1975 Bellamy, L. J. ‘The Infrared Spectra of Complex Molecules’, Wiley, New York, 1966 Colthup, N. B., Daly, L. H. and Wiberley, S. E. ‘Introduction to Infrared and Raman Spectroscopy’, Academic Press, New York, 1964 Bovey, F. A. ‘N.M.R. Spectroscopy’, New York, Academic Press, 1969 Williams, D. H. and Fleming, M. A. ‘Spectroscopic Methods in Organic Chemistry’, McGraw-Hill, London, 1973 Benjamin, B. M., Raaen, V. F., Maupin, P. H., Brown, L. L. and Collins, C. J. Fuel 1979, 57, 269 Cronauer, D. C., Jewell, D. M., Shah, Y. T. and Keuser, K. A. lnd. Eng. Chem. Fundam. 1978, 17, 291 Cronauer, D. C., Jewel], D. M., Shah, Y. T. and Modi, R. J. Ind. Eng. Chem. Fundam. 1979, 18, 153 Charlesworth, J. M. results to be published in Fuel

APPENDIX Nomenclature number of carbon atoms per molecule number of hydrogen atoms per molecule number of oxygen atoms per molecule number of aromatic carbon atoms per molecule number of saturated carbon atoms per molecule number of aromatic carbon atoms substituted by hydrogen number of aromatic carbon atoms substituted by saturated carbon atoms number of aromatic carbon atoms substituted by oxygen number of aromatic carbon atoms attached directly to other aromatic carbon atoms number of hydrogen atoms in the a position relative to an aromatic carbon atom number of hydrogen atoms in the p position relative to an aromatic carbon and hydrogen atoms y and further away in methylene and methine groups number of hydrogen atoms in methyl groups in the y position, and further away from aromatic carbon atoms number of saturated carbon atoms per substituent atomic carbon to hydrogen ratio for saturated substituents number of naphthenic rings per saturated substituent number of naphthenic rings per molecule Fractional amount of saturated carbon atoms belonging to carbon atoms E to, or further away from, paraffinic chain ends protons attached to aromatic rings protons c1to aromatic rings protons /I to aromatic rings and protons y and further away in methylene and methine groups protons in methyl groups y to, and further away from, aromatic rings