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Reaction mechanism of alkali-alcohol treatment of coal
Fuel Processing Technology, 2 (1979) 131--141 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
131
REACTION MECHANISM OF ALKALI--ALCOHOL TREATMENT OF COAL
MASATAKA MAKABE and KOJI OUCHI Faculty of Engineering, Hokkaido University, Sapporo 060 (Japan) (Received June 30th, 1978}
ABSTRACT Taiheiyo coal was reacted with ethanol--sodium hydroxide at 260--400°C for 1--22 hours. The products dissolved almost completely in pyridine. Structural analysis was carried out for the pyridine soluble part to elucidate the reaction mechanism. The only change @as a reduction in molecular weight. A very slight saturation reaction of aromatic rings also took place, but this did not affect the structural image of the products very much. The main reaction may be splitting of ether linkages resulting in the reduction of molecular weight and at higher temperature dehydration has followed. This somewhat reduced the solubility in pyridine.
INTRODUCTION In a previous paper [ 1 ] the authors showed t h a t t r e a t m e n t o f coals with alcohol--alkali increased th e solubility in pyridine or alcohol, especially in the y o u n g e r coal range. T he reaction conditions were examined. In this reaction, h y d r o g en c o n t e n t increased and oxygen c o n t e n t decreased, resulting in a reduction o f molecular weight. It was estimated t h a t the main reaction was hydrolysis with d e h y d r a t i o n and the addition of h y d r o g e n and et hyl ene p r o d u ced f r o m the reaction o f ethanol and sodium hydroxi de. In this report, the authors desire to elucidate in greater detail the reaction mechanism using structural analysis for the samples obtained under various reaction temperatures or various reaction durations. In using structural analysis, the samples must be dissolved nearly com pl et el y in a proper solvent, since the change of the same part o f sample must be pursued in the measurement, in order to observe t he structural change o f the samples during reaction. Therefore, measurements were made for the products which were almost co mp letely soluble in pyridine. EXPERIMENTS Sample coal was Taiheiyo coal (C, 77.3%; H, 6.8%; N, 1.6%; Odiff, 14.3%; yield o f pyridine ext r a c t o f raw coal was 14.1%).
132 One g of coal crushed under a 100 Tyler mesh, 1 g of sodium hydroxide and 10 g of ethyl alcohol were p u t in a 38 ml small autoclave with magnet: drive stirrer. The atmosphere was replaced with nitrogen, then heated up to 260°C, 300°C, 350°C and 400°C and held at these temperatures for 1 hour. In another series the same mixture was reacted at 260°C for various durations. After the reaction, the product was taken out with water into a beaker and neutralized with dilute hydrochloric acid. The precipitate was separated by centrifugation and filtration, and then dried at 60°C under vacuum. The product thus obtained was extracted by shaking with 10 parts of pyridine at room temperature for 10 hours. 1H-NMR spectra were measured with a Japan Electron Optics Lab., PS-100 t y p e spectrometer, in a solution of d-pyridine with a TMS standard and a 2.5% concentration. IR spectra were taken by the KBr pellet method with special care to eliminate moisture by drying over P2Os. The molecular weight was measured at 90°C by VPO in a 1--4% pyridine solution. The softening point was measured with a micro melting point measurement apparatus. Structural analysis was carried out in the following way: Ha: 6--10 ppm, aromatic hydrogen. Ha : 2--5 ppm, hydrogen attaching to the s-carbon. H~: 1.1--2 ppm, hydrogen attaching to over ~-carbon b u t not to the terminal methyl groups. HT: 0.3--1.1 ppm, terminal methyl hydrogen. First, 60% of the oxygen was assumed to consist of phenolic hydroxyl groups and the other oxygen to be of the ether type. This is a rather arbitrary assumption, but according to Blom et al. [2], Ihnatowicz [3] or Hatami et al. [4] this is fairly reasonable. As phenolic OH was not observed clearly in NMR, the hydrogen number corresponding to 60% of the oxygen (phenolic group) was subtracted from the total number of hydrogens in a molecule and the residual hydrogen number was distributed to each t y p e of hydrogen according to the NMR measurement. Structural indices were obtained from the following equations, of which some have been derived from a modification of the methods of Brown and Ladne r [5], Y o k o y a m a et al. [6], Clutter et al. [7] or Van Krevelen and Chermin [8] and others were derived by the authors. Aromaticity, 1
1
C--~-(Ho~ + H [ 3 ) - 3 H 7 fa =
C
(1) [5]
Atomic hydrogen-to-carbon ratio of the hypothetical unsubstituted aromatic ring system,
133
1
+ 0.60 + 2(0.40 + N)
Ha + ~ H a
Hau
Ca
1
C-
(2) [5]
(Ha +HI3)-~H'r
Degree of aromatic ring substitution, 1 O
Ha + 0.60 + 2 (0.40 + N)
=
1
(3) [5]
Ha + -~ H a + 0.60 + 2 (0.40 + N)
Degree of aromatic ring substitution of aliphatic chain, 1Ha 2
oal =
1
(4)
+ 0.60 + 2(0.40 +N)
Ha + ~ H a
Aromatic carbon number per unit structure, 3 Ca(us)
(5) [6]
-
Hau
1
Ca
2
Polymerization degree, Ca n
=
(6)
Ca (us)
Total carbon number per unit structure, C C(us)
=
(7)
-
12
Aliphatic carbon number per molecule,
(8)
Cal = C - C a
Aliphatic carbon number per unit structure, Cal(us) =
Cal
(9)
n
Aromatic ring number per unit structure, Ra(us) =
Ca (us) - H a u 2
+ 1
(10) [7]
Reaction temp. (°C)
260 260 260 260 260 300 350 400
No.
1 2 3 4 5 6 7 8
1 2 5 10 22 1 1 1
Reaction time (h)
91.0 93.6 95.0 96.4 96.1 95.4 97.5 98.4
Pyridine extraction yield (%)
29.6 44.5 49.6 70.1 73.8 43.0 51.1 72.9
Ethanol extraction yield (%)
Pyridine extraction yield and ultimate analysis of extracts
TABLE 1
76.5 77.6 78.4 78.3 77.6 80.8 81.6 84.9
C 6.8 7.1 7.2 7.7 7.8 8.1 8.3 8.3
H 1.4 1.1 0.9 1.3 1.3 1.3 1.2 1.1
N
15.3 14.2 13.5 12.7 13.3 9.8 8.9 5.7
Odiff
Ultimate analysis of pyridine extracts (%)
1.06 1.09 1.09 1.17 1.20 1.20 1.21 1.17
H/C
1390 1270 1210 1180 980 96O 840 580
Mol. Wt.
315 295 260 260 220 215 155 80
Softening point (°C)
135 Aromatic ring number per molecule, Ra
(11)
-- R a ( u s ) . n
Total ring number per molecule, H
Rt
= C---+ 2
1-
Ca
-2
(12) [8]
Total ring number per unit structure, Rt(us)
Rt = ~
(13)
n
Naphthene and heterocyclic ring number per molecule, Rn
= Rt-
(14)
Ra
Naphthene and heterocyclic ring number per unit structure, Rn Rn(us)
=
(15)
n
Side chain carbon n u m b e r per molecule, Cside = Cal - 4Rn
(16)
Side chain carbon number per unit structure, Cside(us)
Cside = ~
n
(17)
In eqn. 16 the naphthene ring was assumed to attach in a tetralin manner to an aromatic ring. Eqn. 5 is only valid for cata t y p e aromatic rings, b u t the values obtained here are valid since our samples have a ring number smaller than 3 as will be seen later. RESULTS AND DISCUSSION Pyridine and ethanol extraction yield and the analytical data of extracts are shown in Table 1. All the reaction products can dissolve in pyridine in an extraction yield of more than 90%. The ethanol extraction yield increases remarkably with the rise of temperature and with a longer reaction time. As was mentioned, it is absolutely necessary to compare the structure change of the same part of the sample in order to follow the reaction mechanism. More than 90% of the solubility in pyridine is suitable for this purpose. The hydrogen c o n t e n t and ratio of H/C increase and the oxygen content, molecular weight and softening point decrease as the reaction proceeds. This means that a splitting of molecules takes place. There is a very beautiful relationship between the molecular
136
weight and the 0% or softening point as seen in Figs. 1 and 2. The reduction of the molecular weight contributes to the lowering of the softening point.
300
15 E 0 e~
~o E 0 100
/ 500
/
i0 o
5
1600
150(
Molecular weight
5'00 1600 Moleculor weight
1500
Fig. 1. Relation between softening point and molecular weight, o , Time variation; e , temperature variation. Fig. 2. Relation between oxygen percentage and molecular weight, o, Time variation; e , temperature variation.
The decrease of oxygen content also reduces the molecular weight. This suggests that opening and reduction of the ether linkages are the main reason for the reduction of the molecular weight. But a dependency of the ethanol solubility on the molecular weight (Fig. 3) is different in the series of temperature variation from that in another series of time variation. As may be seen
10C . - -
.~
•
o
3
so o b.I
o 5ha
16oo i oo Molecular weight
Fig. 3. Relation between ethanol solubility and molecular weight, o, Time variation; e , temperature variation.
137
later, the OH content in both series is also different and a series of time variation always has a larger OH content than the series of temperature variation. Probably, when the reaction temperature rises, OH groups may be eliminated more rapidly b y thermal dehydration or through hydrogenation. This may be the reason that the series of time variation has a larger molecular weight for the same ethanol solubility. The changes in optical densities in the IR spectra of the pyridine soluble part are shown in Fig. 4. OH absorption at 3300 cm -~ increases at the early stage of the reaction and then decreases. The first increase may be ascribed to the opening of ether linkages and the later decrease may come from the thermal dehydration or dehydration by hydrogenation with the hydrogen produced from the reaction between ethanol and sodium hydroxide. Aliphatic C--H absorption at 2920 and 1450 cm -1 and methyl absorption at 1380 cm -1 increase. One reason may be the partial saturation of aromatic rings as proved later by NMR. CO absorption at 1700 cm -~ also increases at the first stage, b u t later decreases slightly. One origin of this absorption may be the oxidation of --CH2OH in coal to --COOH as in the case of alcohol and alkali reaction. Here it is seen that the content of OH groups in the series of time variation is always larger than in the series of temperature variation. 0
0.05 ~ j"
o
1380 ~
1380
"
d o.2
~0.II 0
300 400 Temperature,'C (1hr)
[
~
10 20 Time, hr (260"C)
16oo L 2920
0.7
&o.5
f
0
0.3 // 300 400 Temperature,'C(lhr)
10 20 Time, hr (260°C)
Fig. 4. Variation of optical density with time or temperature.
138
Structural indices of the pyridine soluble part in the series of temperature variation are given in Table 2 and Figs. 5 and 6. In the series of temperature variation, fa, n and Ous decrease and other indices increase with a rise in the reaction temperature, but the molecular weight per unit structure, Mol. Wt./n, also increases with a rise in the temperature, meaning that a condensation reaction takes place between the unit structures. There is the possibility that this increase in molecular weight per unit structure causes an increase in the structural indices. Thus in order to TABLE 2 Structural indices Values in parentheses are corrected values for the same Mol. Wt./n as sample 1. 1
Ha Ha H~ H~
fa Hau/Ca a
aal Ca Cal Rt Ra Rn Cside
2 21.8 21.7 31.8 10.6 0.66 0.93 0.54 0.20
3 16.1 25.0 32.4 9.2 0.61 0.92 0.61 0.27
4 12.5 27.1 32.0 8.6 0.59 0.90 0.67 0.32
5 13.9 29.3 32.5 8.7 0.56 0.97 0.66 0.35
6 9.7 24.4 29.5 7.4 0.54 1.04 0.67 0.35
7 8.7 23.6 27.6 6.8 0.52 0.97 0.65 0.40
8 8.3 19.5 25.7 8.1 0.52 0.92 0.62 0.38
6.9 13.3 17.4 4.9 0.55 0.83 0.55 0.39
58.3 30.3 13.5 10.4 3.1 21.0
50.3 31.8 13.2 9.0 4.1 19.3
46.6 32.4 13.5 8.6 4.9 17.6
43.2 33.8 11.3 7.4 3.9 22.2
33.9 29.4 9.5 5.4 4.0 17.4
30.7 27.9 9.2 5.3 4.0 16.0
27.7 25.3 8.0 5.0 3.0 16.2
20.5 17.0 6.4 4.0 2.4 9.7
n
8.3
7.1
6.2
6.8
6.1
4.8 (5.5)
3.9 (4.9)
2.3 (3.4)
Ca(us)
7.0
7.1
7.5
6.4
5.6
Cal(us)
3.6
4.5
5.2
5.0
4.9
Rt(us)
1.6
1.9
2.2
1.7
1.6
Ra(us)
1.3
1.3
1.4
1.1
0.9
Rn(us)
0.4
0.6
0.8
0.6
0.7
Cside(us)
2.5
2.7
2.8
3.3
2.9
167 1.6
179 2.0
195 2.2
174 1.9
162 2.2
Mol. Wt./n O/n
6.4
7.1
9.0
(5.6)
(5.6)
(6.9)
5.9 (5.1) 1.9 (1.7) 1.1 (1.8) 0.8 (O.7) 3.4 (2.9)
6.5 (5.2) 2.1 (1.6) 1.3 (1.0) 0.8 (O.6) 4.2 (3.3)
7.4 (5.7) 2.8 (2.2) 1.8 (1.3) 1.1 (O.8) 4.3 (3.3)
183 1.1
(1.0)
201 1.1
(0.9)
232 0.8 (O.6)
139
...RaCu~) n-"
......
I
._.
:-
0 w
0
i
i
4 0
11
0.6 0.5
0
--o
cl 0,¢ o 5"15 o
Y
J i
i
1.0
O O.3 ~o
Q
02 400 T e m p e r o t u r e °C(1 hr) 300
38o 4bo Temperature°C (,1 hr)
Fig. 5. Change of fa, Hau/Ca and oal with temperature (1 h). Fig. 6. Change of Ra(us), Rn(us), Cside(us), Mol. Wt./n, and Ous with temperature (1 h). o , Corrected values for constant molecular weight per unit structure.
understand the real reaction mechanism, it is reasonable to compare the structural indices at the same molecular weight per unit structure as the first one, that is the one of 260°C/1 h. These corrected structural indices are shown in black circles. Ra(us) shows nearly constant values or a very slight decrease and Rn (us) or Cside(us) increases, fa also decreases. These tendencies mean slight saturation of aromatic rings. Ra (us) to be approximately 1 means benzene nuclei. That one benzene nucleus in five (one unit structure in five unit structures) is saturated by hydrogenation, is sufficient to explain the change of these structural indices. But this change is very small and affects only very slightly the average structural image of the sample. For example, Ra changes from 1.3 to 1.0 and this does not alter the conclusion that this sample has benzene nuclei as its unit structure in average. Ous also decreases to nearly one third. This perhaps is caused by the elimination of ether or hydroxyl oxygens. The former makes a reduction in the molecular weight and polymerization degree. As shown by studies of carbonization of phenol resin [ 9--11], dehydration from hydroxyl groups easily occurs at a temperature higher than 300°C. The
140
increase in molecular weight per unit structure may be caused by a type of condensation reaction such as
The results for the series of time variation are shown in Figs. 7 and 8.
~ c r ~
Ra(u s)
"~ 1.0
o 0.6
Rn(us)
0
rr 0.5
___.----o-
O 1.0 0
"1" QO
'~ o.3 b 0.2
o-
Y
v3 30 ® '1o ~n 0-o ('=) 2 0
2O--O m 0 :3 Q
1'0
0
o
o-
o
o
1.0
2hO
Time hr (260°C)
0
~b Time
2'o hr
(260"C)
Fig. 7. Change of fa, Hau/Ca and aal with time (260°C). Fig. 8. Change of Ra(us), Rn(us), Cside(us) and Ous with time (260°C).
Here also fa, Ra(us) and n decrease with reaction duration and other indices increase. The decrease of aromatic ring per unit structure Ra(us) means that a slight saturation of aromatic rings takes place, but this is only to the same degree as in the case of temperature variation. The slight increase of naphthenic ring per unit structure Rn(us) and of a al or slight decrease of [a correspond to this change. In this case, Ous does not change. Therefore, only the splitting of ether linkages bonding unit structures takes place with the reduction of molecular weight, but a dehydration reaction does not appreciably occur. This probably contributed to the solubility in pyridine at a higher molecular weight than in the case of temperature variation. CONCLUSION
Under the reaction condition of 260°C/1 h, coal can react with alcohol--
141 sodium hydroxide and the reaction product dissolves almost completely in pyridine. The structure changes of the reaction products obtained when the temperature or reaction time was varied, were examined by a structural analytical method. The average structure of a unit structure does n o t change or changes with only a slight saturation of aromatic rings. In the series of temperature variation, some condensation reaction takes place resulting in an increase in molecular weight per unit structure. The splitting of ether linkages is the main reason for the reduction of molecular weight and of the high solubility into pyridine. At a higher temperature, dehydration also takes place, reducing the oxygen c o n t e n t per unit structure. ACKNOWLEDGEMENTS The authors express their sincere thanks to Mr. T. Yoshida at the Government Industrial Development Laboratory, Hokkaido, for his aid in the measurement of NMR spectra. The financial support by the Iwatani Naoji Foundation's Research Grant is greatly appreciated.
REFERENCES 1 2 3 4 5 6 7 8 9 10 11
Makabe, M. and Ouchi, K., 1978. Fuel, 57: 289.
Blom, L., Edelhaysen, L. and Van Krevelen, D.W., 1957. Fuel, 36: 135. Ihnatowicz, A., 1952. Glownego Institute Gonictwa Komunikat, No. 125, Katowice. Hatami, M., Osawa, S. and Sugimura, H., 1967. Nenryo Kyokai-shi, 46: 819. Brown, J.K. and Ladner, W.R., 1960. Fuel, 39: 87. Yokoyama, S., Onishi, N. and Takeya, G., 1975. Nippon Kagaku Kaishi, 10: 1963. Clutter, D.R., Petrakis, L., Stenger, R.L. and Jensen, R.K., 1972. Anal. Chem., 44: 1395. Van Krevelen, D.W. and Chermin, H.A.G., 1954. Fuel, 33: 79. Ouchi, K. and Honda, H., 1959. Fuel, 38: 429. Ouchi, K., 1966. Carbon, 4: 59. Yamashita, Y. and Ouchi, K., 1974. Nenryo Kyokai-shi, 53: 1064.
131
REACTION MECHANISM OF ALKALI--ALCOHOL TREATMENT OF COAL
MASATAKA MAKABE and KOJI OUCHI Faculty of Engineering, Hokkaido University, Sapporo 060 (Japan) (Received June 30th, 1978}
ABSTRACT Taiheiyo coal was reacted with ethanol--sodium hydroxide at 260--400°C for 1--22 hours. The products dissolved almost completely in pyridine. Structural analysis was carried out for the pyridine soluble part to elucidate the reaction mechanism. The only change @as a reduction in molecular weight. A very slight saturation reaction of aromatic rings also took place, but this did not affect the structural image of the products very much. The main reaction may be splitting of ether linkages resulting in the reduction of molecular weight and at higher temperature dehydration has followed. This somewhat reduced the solubility in pyridine.
INTRODUCTION In a previous paper [ 1 ] the authors showed t h a t t r e a t m e n t o f coals with alcohol--alkali increased th e solubility in pyridine or alcohol, especially in the y o u n g e r coal range. T he reaction conditions were examined. In this reaction, h y d r o g en c o n t e n t increased and oxygen c o n t e n t decreased, resulting in a reduction o f molecular weight. It was estimated t h a t the main reaction was hydrolysis with d e h y d r a t i o n and the addition of h y d r o g e n and et hyl ene p r o d u ced f r o m the reaction o f ethanol and sodium hydroxi de. In this report, the authors desire to elucidate in greater detail the reaction mechanism using structural analysis for the samples obtained under various reaction temperatures or various reaction durations. In using structural analysis, the samples must be dissolved nearly com pl et el y in a proper solvent, since the change of the same part o f sample must be pursued in the measurement, in order to observe t he structural change o f the samples during reaction. Therefore, measurements were made for the products which were almost co mp letely soluble in pyridine. EXPERIMENTS Sample coal was Taiheiyo coal (C, 77.3%; H, 6.8%; N, 1.6%; Odiff, 14.3%; yield o f pyridine ext r a c t o f raw coal was 14.1%).
132 One g of coal crushed under a 100 Tyler mesh, 1 g of sodium hydroxide and 10 g of ethyl alcohol were p u t in a 38 ml small autoclave with magnet: drive stirrer. The atmosphere was replaced with nitrogen, then heated up to 260°C, 300°C, 350°C and 400°C and held at these temperatures for 1 hour. In another series the same mixture was reacted at 260°C for various durations. After the reaction, the product was taken out with water into a beaker and neutralized with dilute hydrochloric acid. The precipitate was separated by centrifugation and filtration, and then dried at 60°C under vacuum. The product thus obtained was extracted by shaking with 10 parts of pyridine at room temperature for 10 hours. 1H-NMR spectra were measured with a Japan Electron Optics Lab., PS-100 t y p e spectrometer, in a solution of d-pyridine with a TMS standard and a 2.5% concentration. IR spectra were taken by the KBr pellet method with special care to eliminate moisture by drying over P2Os. The molecular weight was measured at 90°C by VPO in a 1--4% pyridine solution. The softening point was measured with a micro melting point measurement apparatus. Structural analysis was carried out in the following way: Ha: 6--10 ppm, aromatic hydrogen. Ha : 2--5 ppm, hydrogen attaching to the s-carbon. H~: 1.1--2 ppm, hydrogen attaching to over ~-carbon b u t not to the terminal methyl groups. HT: 0.3--1.1 ppm, terminal methyl hydrogen. First, 60% of the oxygen was assumed to consist of phenolic hydroxyl groups and the other oxygen to be of the ether type. This is a rather arbitrary assumption, but according to Blom et al. [2], Ihnatowicz [3] or Hatami et al. [4] this is fairly reasonable. As phenolic OH was not observed clearly in NMR, the hydrogen number corresponding to 60% of the oxygen (phenolic group) was subtracted from the total number of hydrogens in a molecule and the residual hydrogen number was distributed to each t y p e of hydrogen according to the NMR measurement. Structural indices were obtained from the following equations, of which some have been derived from a modification of the methods of Brown and Ladne r [5], Y o k o y a m a et al. [6], Clutter et al. [7] or Van Krevelen and Chermin [8] and others were derived by the authors. Aromaticity, 1
1
C--~-(Ho~ + H [ 3 ) - 3 H 7 fa =
C
(1) [5]
Atomic hydrogen-to-carbon ratio of the hypothetical unsubstituted aromatic ring system,
133
1
+ 0.60 + 2(0.40 + N)
Ha + ~ H a
Hau
Ca
1
C-
(2) [5]
(Ha +HI3)-~H'r
Degree of aromatic ring substitution, 1 O
Ha + 0.60 + 2 (0.40 + N)
=
1
(3) [5]
Ha + -~ H a + 0.60 + 2 (0.40 + N)
Degree of aromatic ring substitution of aliphatic chain, 1Ha 2
oal =
1
(4)
+ 0.60 + 2(0.40 +N)
Ha + ~ H a
Aromatic carbon number per unit structure, 3 Ca(us)
(5) [6]
-
Hau
1
Ca
2
Polymerization degree, Ca n
=
(6)
Ca (us)
Total carbon number per unit structure, C C(us)
=
(7)
-
12
Aliphatic carbon number per molecule,
(8)
Cal = C - C a
Aliphatic carbon number per unit structure, Cal(us) =
Cal
(9)
n
Aromatic ring number per unit structure, Ra(us) =
Ca (us) - H a u 2
+ 1
(10) [7]
Reaction temp. (°C)
260 260 260 260 260 300 350 400
No.
1 2 3 4 5 6 7 8
1 2 5 10 22 1 1 1
Reaction time (h)
91.0 93.6 95.0 96.4 96.1 95.4 97.5 98.4
Pyridine extraction yield (%)
29.6 44.5 49.6 70.1 73.8 43.0 51.1 72.9
Ethanol extraction yield (%)
Pyridine extraction yield and ultimate analysis of extracts
TABLE 1
76.5 77.6 78.4 78.3 77.6 80.8 81.6 84.9
C 6.8 7.1 7.2 7.7 7.8 8.1 8.3 8.3
H 1.4 1.1 0.9 1.3 1.3 1.3 1.2 1.1
N
15.3 14.2 13.5 12.7 13.3 9.8 8.9 5.7
Odiff
Ultimate analysis of pyridine extracts (%)
1.06 1.09 1.09 1.17 1.20 1.20 1.21 1.17
H/C
1390 1270 1210 1180 980 96O 840 580
Mol. Wt.
315 295 260 260 220 215 155 80
Softening point (°C)
135 Aromatic ring number per molecule, Ra
(11)
-- R a ( u s ) . n
Total ring number per molecule, H
Rt
= C---+ 2
1-
Ca
-2
(12) [8]
Total ring number per unit structure, Rt(us)
Rt = ~
(13)
n
Naphthene and heterocyclic ring number per molecule, Rn
= Rt-
(14)
Ra
Naphthene and heterocyclic ring number per unit structure, Rn Rn(us)
=
(15)
n
Side chain carbon n u m b e r per molecule, Cside = Cal - 4Rn
(16)
Side chain carbon number per unit structure, Cside(us)
Cside = ~
n
(17)
In eqn. 16 the naphthene ring was assumed to attach in a tetralin manner to an aromatic ring. Eqn. 5 is only valid for cata t y p e aromatic rings, b u t the values obtained here are valid since our samples have a ring number smaller than 3 as will be seen later. RESULTS AND DISCUSSION Pyridine and ethanol extraction yield and the analytical data of extracts are shown in Table 1. All the reaction products can dissolve in pyridine in an extraction yield of more than 90%. The ethanol extraction yield increases remarkably with the rise of temperature and with a longer reaction time. As was mentioned, it is absolutely necessary to compare the structure change of the same part of the sample in order to follow the reaction mechanism. More than 90% of the solubility in pyridine is suitable for this purpose. The hydrogen c o n t e n t and ratio of H/C increase and the oxygen content, molecular weight and softening point decrease as the reaction proceeds. This means that a splitting of molecules takes place. There is a very beautiful relationship between the molecular
136
weight and the 0% or softening point as seen in Figs. 1 and 2. The reduction of the molecular weight contributes to the lowering of the softening point.
300
15 E 0 e~
~o E 0 100
/ 500
/
i0 o
5
1600
150(
Molecular weight
5'00 1600 Moleculor weight
1500
Fig. 1. Relation between softening point and molecular weight, o , Time variation; e , temperature variation. Fig. 2. Relation between oxygen percentage and molecular weight, o, Time variation; e , temperature variation.
The decrease of oxygen content also reduces the molecular weight. This suggests that opening and reduction of the ether linkages are the main reason for the reduction of the molecular weight. But a dependency of the ethanol solubility on the molecular weight (Fig. 3) is different in the series of temperature variation from that in another series of time variation. As may be seen
10C . - -
.~
•
o
3
so o b.I
o 5ha
16oo i oo Molecular weight
Fig. 3. Relation between ethanol solubility and molecular weight, o, Time variation; e , temperature variation.
137
later, the OH content in both series is also different and a series of time variation always has a larger OH content than the series of temperature variation. Probably, when the reaction temperature rises, OH groups may be eliminated more rapidly b y thermal dehydration or through hydrogenation. This may be the reason that the series of time variation has a larger molecular weight for the same ethanol solubility. The changes in optical densities in the IR spectra of the pyridine soluble part are shown in Fig. 4. OH absorption at 3300 cm -~ increases at the early stage of the reaction and then decreases. The first increase may be ascribed to the opening of ether linkages and the later decrease may come from the thermal dehydration or dehydration by hydrogenation with the hydrogen produced from the reaction between ethanol and sodium hydroxide. Aliphatic C--H absorption at 2920 and 1450 cm -1 and methyl absorption at 1380 cm -1 increase. One reason may be the partial saturation of aromatic rings as proved later by NMR. CO absorption at 1700 cm -~ also increases at the first stage, b u t later decreases slightly. One origin of this absorption may be the oxidation of --CH2OH in coal to --COOH as in the case of alcohol and alkali reaction. Here it is seen that the content of OH groups in the series of time variation is always larger than in the series of temperature variation. 0
0.05 ~ j"
o
1380 ~
1380
"
d o.2
~0.II 0
300 400 Temperature,'C (1hr)
[
~
10 20 Time, hr (260"C)
16oo L 2920
0.7
&o.5
f
0
0.3 // 300 400 Temperature,'C(lhr)
10 20 Time, hr (260°C)
Fig. 4. Variation of optical density with time or temperature.
138
Structural indices of the pyridine soluble part in the series of temperature variation are given in Table 2 and Figs. 5 and 6. In the series of temperature variation, fa, n and Ous decrease and other indices increase with a rise in the reaction temperature, but the molecular weight per unit structure, Mol. Wt./n, also increases with a rise in the temperature, meaning that a condensation reaction takes place between the unit structures. There is the possibility that this increase in molecular weight per unit structure causes an increase in the structural indices. Thus in order to TABLE 2 Structural indices Values in parentheses are corrected values for the same Mol. Wt./n as sample 1. 1
Ha Ha H~ H~
fa Hau/Ca a
aal Ca Cal Rt Ra Rn Cside
2 21.8 21.7 31.8 10.6 0.66 0.93 0.54 0.20
3 16.1 25.0 32.4 9.2 0.61 0.92 0.61 0.27
4 12.5 27.1 32.0 8.6 0.59 0.90 0.67 0.32
5 13.9 29.3 32.5 8.7 0.56 0.97 0.66 0.35
6 9.7 24.4 29.5 7.4 0.54 1.04 0.67 0.35
7 8.7 23.6 27.6 6.8 0.52 0.97 0.65 0.40
8 8.3 19.5 25.7 8.1 0.52 0.92 0.62 0.38
6.9 13.3 17.4 4.9 0.55 0.83 0.55 0.39
58.3 30.3 13.5 10.4 3.1 21.0
50.3 31.8 13.2 9.0 4.1 19.3
46.6 32.4 13.5 8.6 4.9 17.6
43.2 33.8 11.3 7.4 3.9 22.2
33.9 29.4 9.5 5.4 4.0 17.4
30.7 27.9 9.2 5.3 4.0 16.0
27.7 25.3 8.0 5.0 3.0 16.2
20.5 17.0 6.4 4.0 2.4 9.7
n
8.3
7.1
6.2
6.8
6.1
4.8 (5.5)
3.9 (4.9)
2.3 (3.4)
Ca(us)
7.0
7.1
7.5
6.4
5.6
Cal(us)
3.6
4.5
5.2
5.0
4.9
Rt(us)
1.6
1.9
2.2
1.7
1.6
Ra(us)
1.3
1.3
1.4
1.1
0.9
Rn(us)
0.4
0.6
0.8
0.6
0.7
Cside(us)
2.5
2.7
2.8
3.3
2.9
167 1.6
179 2.0
195 2.2
174 1.9
162 2.2
Mol. Wt./n O/n
6.4
7.1
9.0
(5.6)
(5.6)
(6.9)
5.9 (5.1) 1.9 (1.7) 1.1 (1.8) 0.8 (O.7) 3.4 (2.9)
6.5 (5.2) 2.1 (1.6) 1.3 (1.0) 0.8 (O.6) 4.2 (3.3)
7.4 (5.7) 2.8 (2.2) 1.8 (1.3) 1.1 (O.8) 4.3 (3.3)
183 1.1
(1.0)
201 1.1
(0.9)
232 0.8 (O.6)
139
...RaCu~) n-"
......
I
._.
:-
0 w
0
i
i
4 0
11
0.6 0.5
0
--o
cl 0,¢ o 5"15 o
Y
J i
i
1.0
O O.3 ~o
Q
02 400 T e m p e r o t u r e °C(1 hr) 300
38o 4bo Temperature°C (,1 hr)
Fig. 5. Change of fa, Hau/Ca and oal with temperature (1 h). Fig. 6. Change of Ra(us), Rn(us), Cside(us), Mol. Wt./n, and Ous with temperature (1 h). o , Corrected values for constant molecular weight per unit structure.
understand the real reaction mechanism, it is reasonable to compare the structural indices at the same molecular weight per unit structure as the first one, that is the one of 260°C/1 h. These corrected structural indices are shown in black circles. Ra(us) shows nearly constant values or a very slight decrease and Rn (us) or Cside(us) increases, fa also decreases. These tendencies mean slight saturation of aromatic rings. Ra (us) to be approximately 1 means benzene nuclei. That one benzene nucleus in five (one unit structure in five unit structures) is saturated by hydrogenation, is sufficient to explain the change of these structural indices. But this change is very small and affects only very slightly the average structural image of the sample. For example, Ra changes from 1.3 to 1.0 and this does not alter the conclusion that this sample has benzene nuclei as its unit structure in average. Ous also decreases to nearly one third. This perhaps is caused by the elimination of ether or hydroxyl oxygens. The former makes a reduction in the molecular weight and polymerization degree. As shown by studies of carbonization of phenol resin [ 9--11], dehydration from hydroxyl groups easily occurs at a temperature higher than 300°C. The
140
increase in molecular weight per unit structure may be caused by a type of condensation reaction such as
The results for the series of time variation are shown in Figs. 7 and 8.
~ c r ~
Ra(u s)
"~ 1.0
o 0.6
Rn(us)
0
rr 0.5
___.----o-
O 1.0 0
"1" QO
'~ o.3 b 0.2
o-
Y
v3 30 ® '1o ~n 0-o ('=) 2 0
2O--O m 0 :3 Q
1'0
0
o
o-
o
o
1.0
2hO
Time hr (260°C)
0
~b Time
2'o hr
(260"C)
Fig. 7. Change of fa, Hau/Ca and aal with time (260°C). Fig. 8. Change of Ra(us), Rn(us), Cside(us) and Ous with time (260°C).
Here also fa, Ra(us) and n decrease with reaction duration and other indices increase. The decrease of aromatic ring per unit structure Ra(us) means that a slight saturation of aromatic rings takes place, but this is only to the same degree as in the case of temperature variation. The slight increase of naphthenic ring per unit structure Rn(us) and of a al or slight decrease of [a correspond to this change. In this case, Ous does not change. Therefore, only the splitting of ether linkages bonding unit structures takes place with the reduction of molecular weight, but a dehydration reaction does not appreciably occur. This probably contributed to the solubility in pyridine at a higher molecular weight than in the case of temperature variation. CONCLUSION
Under the reaction condition of 260°C/1 h, coal can react with alcohol--
141 sodium hydroxide and the reaction product dissolves almost completely in pyridine. The structure changes of the reaction products obtained when the temperature or reaction time was varied, were examined by a structural analytical method. The average structure of a unit structure does n o t change or changes with only a slight saturation of aromatic rings. In the series of temperature variation, some condensation reaction takes place resulting in an increase in molecular weight per unit structure. The splitting of ether linkages is the main reason for the reduction of molecular weight and of the high solubility into pyridine. At a higher temperature, dehydration also takes place, reducing the oxygen c o n t e n t per unit structure. ACKNOWLEDGEMENTS The authors express their sincere thanks to Mr. T. Yoshida at the Government Industrial Development Laboratory, Hokkaido, for his aid in the measurement of NMR spectra. The financial support by the Iwatani Naoji Foundation's Research Grant is greatly appreciated.
REFERENCES 1 2 3 4 5 6 7 8 9 10 11
Makabe, M. and Ouchi, K., 1978. Fuel, 57: 289.
Blom, L., Edelhaysen, L. and Van Krevelen, D.W., 1957. Fuel, 36: 135. Ihnatowicz, A., 1952. Glownego Institute Gonictwa Komunikat, No. 125, Katowice. Hatami, M., Osawa, S. and Sugimura, H., 1967. Nenryo Kyokai-shi, 46: 819. Brown, J.K. and Ladner, W.R., 1960. Fuel, 39: 87. Yokoyama, S., Onishi, N. and Takeya, G., 1975. Nippon Kagaku Kaishi, 10: 1963. Clutter, D.R., Petrakis, L., Stenger, R.L. and Jensen, R.K., 1972. Anal. Chem., 44: 1395. Van Krevelen, D.W. and Chermin, H.A.G., 1954. Fuel, 33: 79. Ouchi, K. and Honda, H., 1959. Fuel, 38: 429. Ouchi, K., 1966. Carbon, 4: 59. Yamashita, Y. and Ouchi, K., 1974. Nenryo Kyokai-shi, 53: 1064.