Fuel Processing Technology, 1 (1977) 21--30
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© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
SOLVOLYSIS EXTRACTION USING QUINOLINE AND PHENOL RESIN AS COAL MODEL
K. OUCHI, A. H I R O T A and H. ITOH
Department of Applied Chemistry, Faculty of Engineering, Hokkaido University, Sapporo (Japan) (Received November 1976)
ABSTRACT Phenol resin as coal model was extracted with quinoline at 420°C for 2 h. The insoluble part was only 2.7%. The soluble part was separated into 7 fractions and their ultimate analysis, molecular weight and NMR spectra were measured. Model structures were proposed for these fractions. The increase of nitrogen content and the identification of the presence of 2,2'-biquinoline in the product are explained by a solvolysis reaction of quinoline with the thermally decomposed radicals of phenol resin. INTRODUCTION
The solvent extraction of coal has been well reviewed by Kiebler [ 1], Dryden [2], Sakabe [3], Wise [4], and others. Above all degrading extraction was practiced in Germany before the war as the Pott--Broche m e t h o d and some experiments on it were and are continued in Japan, United States, England, South Africa, Australia and so on. But the mechanism of extraction is n o t necessarily clear. The total yield of extract and residue often exceeds 100%, which is usually understood as meaning there is solvent remaining in the extract or that polymerization of solvent has occurred. After careful elimination of solvent from the extract an excess yield of extract plus residue is still observed in many cases. Even when a lighter, more volatile solvent which does n o t polymerize at all in blank tests was used, a surplus of the p r o d u c t weight can be seen. We assumed t h a t such surplus of the product weight is due to the weight increase by the combination of solvent molecules with radicals produced from thermal degradation of coal structure, which leads to the stabilization of reduced molecular weight fragments and makes them soluble in the solvent. Thus we attempted to verify or disprove this assumption using phenol resin as a model of coal structure and quinoline as solvent. In this system it was easy to detect the combination of solvent with degraded phenol resin. EXPERIMENTAL
Phenol resin was prepared by condensing 1.5 mole of phenol with 1.5 mole
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of formaldehyde aqueous solution (37%) using 15 ml of aqueous ammonia (28%) as catalyst in a water bath at room temperature for 2 h. After cooling the oil was separated by decantation from the aqueous part and hardened at 170°C for 1 h with stirring. The sample was ground u n d e r - - 1 0 0 (Tyler) mesh and cured further at 180°C for 6 h in a nitrogen atmosphere. The sample of 10 g thus prepared was p u t in an autoclave of 500 ml with 100 g of quinoline. Quinoline was purified by making a complex with phosphoric acid in methanol solution. The precipitated complex was decomposed by adding aqueous caustic soda and separated quinoline was distilled after drying with potassium hydroxide. The autoclave was heated at 3 ° C/min to 420 ° C, then held at this temperature for 2 h with magnetic stirring. After cooling the contents were filtered [insoluble part (Q)] and the solution was distilled under vacuum to eliminate solvent followed by steam distillation. In order to eliminate traces of quinoline the extract was washed thoroughly with 10% hydrochloric acid. The dissolved part of this hydrochloric acid washing was alkalized with excess aqueous potassium hydroxide solution and the precipitate (A) was filtered. The solution was then neutralized by adding hydrochloric acid and the precipitate product (N) was filtered out. The neutralized solution was extracted with methyl ethyl ketone (S). The residue from hydrochloric acid washing was extracted with tetrahydrofuran (THF) by shaking at room temperature. A soluble portion (T) and an insoluble part which was separated into pyridine soluble part (Ps) and insoluble part (PI) resulted from the T H F extraction. Fractions N, A and T were further fractionated by gel permeation chromatography (GPC). A GPC column (1300 cm X 1.5 cm I.D.) filled with Bio-Beads SX-8 was used for fractions N and A (800 mg) using b e n z e n e - m e t h a n o l (9:1) as eluent and a column of 68 cm filled with Bio-Beads SX-4 plus 68 cm with Bio-Beads SX-2 with an I.D. of 1.5 cm was used for fraction T (800 mg) using THF as eluent. The eluted fractions were collected in 5 g each and weighed after evaporation of solvent. IR spectra were taken with a Hitachi EPI-2 apparatus using potassium bromide pellets. NMR spectra were taken in each case by a Hitachi R22 90 MHz apparatus in a [2H] pyridine and [2H] chloroform solution. The molecular weight was measured by vapor pressure o s m o m e t r y using a solution of pyridine and chloroform. RESULTS AND DISCUSSION
The GPC curves of analytical data obtained using Shimadzu T y p e 1A are shown in Fig.1 for fractions N, A and T. Fractions N and A have t w o major peaks and fraction T may be separated into three peaks. The separation curves for fractions N, A and T in preparative GPC are shown in Fig.2. It appears that the separation is much more vague than the separation by analytical GPC. Referring to the results of analytical GPC
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T
--Fraction
if'
x.., 40
35 30 ropc Count no.
25
Fig.1. Analytical GPC separation curves of Fractions T, A and N.
(a)
140
(c)
(b)
120
100
8O
=~ 6o
i
I
k
I
I-A
I I-B
t l-C
I
l I
5
lO
I II 15
20
I 5
25 Fraction
I I0
15
5
10
15
number
Fig.2. Preparative GPC curves of Fractions T, A and N. (a) Fraction T (THF soluble). Gel: Bio-Beads SX-4, SX-2. Solvent: THF. (b) Fraction A (alkali precipitate). Gel: BioBeads SX-8. Solvent: benzene--methanol (9:1). (c) Fraction N (neutralized precipitate). Gel: Bio-Beads SX-8. Solvent: benzene--methanol (9:1).
the separated fractions in preparative GPC were collected into t w o parts for fractions N and A and into three parts for fraction T. Each of the c u t points is shown in Fig.2. Fraction No. 12 of fraction A showed the existence of crystals. After recrystallization with n-hexane, these crystals were assigned to be 2,2 '-biquinoline by melting point (198 ° C, r e f , 5 : 1 9 6 ° C), IR and mass spectra.
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Phenol resin P
iQu no ne,420°C, 2h, f i l t e r
I insoluble (Q)
soluble
2.7%
Vacuum d i s t i l l a t i o n , steam d i s t i l l a t i o n and dry
H I [ washing
q soluble
I insoluble
I THF extract 1
C
I
extraction
pyridine
I insoluble
(PI) 11,7%
-i
soluble (Ps) 25,6%
15~f separation
[GPC separation r - -
high mol.wt, (I-A) 21.3%
i KOH, excess adding ! soluble
i ppt (A)
soluble (T)
insoluble
~
LHC[, neutralization
?
low mol.wt. (I-B) 14.94
2~2'-
Alkaline
2:2'-
biquinoline 12.2:
pF,t. (]i-A) 49.4
biquinoline 80.0];
ppt.(N)
soluble
GPC separation i
•
neutralization ppt.(III-A) 7.5%
q
2~2'biquinoline l.l ~
methyl ethyl ketone extrac extract (S) 0.4!~
Fig.3. Separation process of quinoline extract.
Calibration curves for 2,2'-biquinoline for analytical GPC were obtained using purified samples and the c o n t e n t of 2,2'-biquinoline in fractions N, A and T was determined from this calibration curve. The separation process and the yield of each fraction are given in Fig.3. The total yield (except for biquinoline) was 130.8%. The excess a m o u n t of product (over 100%} can be ascribed to the addition of quinoline to phenol resin. The definite evidence of this solvolytic addition of quinoline to the resin is the increase of nitrogen c o n t e n t o f each fraction (Table 1). The original resin already contained nitrogen which was generally understood to be the addition of ammonia as the tertiary bonded nitrogen between methylene bridges. IR spectra are s h o w n in Fig.4. PI, Ps, I-A and I-B have spectra quite similar to that of the original sample, but the spectrum of IIA is different except for
TABLE 1 The ultimate analysis of fractions Fraction
C (%)
H (%)
N (%)
0 (diff.) (%)
Phenol resin Q PI Ps I-A I-B II-A III-A
75.1 71.8 83.7 85.2 80.6 82.2 80.3 75.1
5.9 3.1 3.5 4.3 5.6 5.9 5.8 5.3
2.0 2.6 2.9 2.7 2.6 4.3 6.6 5.4
16.9 22.6 10.6 7.9 11.2 7.7 7.3 14.2
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PYRIDINE INSOLUBLE~
P Y R I D I N ~
ALKALI PPT,,GPC-IIA
NEUTRALIZEDRPT,,GPC-IIIA
4000
3000
2000
1800
1600
1400
1200
i000
800
600
WAVE NUMBER (cm -t)
Fig.4. IR spectra of each fraction.
400
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out-of-plane vibration. This shows the existence of CO and ether linkage. The spectrum of IIIA has a different feature in the 2500--3500 cm -~ region, but in other respects is quite similar to those of PI, Ps, I-A and I-B which have the same features as the original resin. NMR spectra are shown in Fig.5. The band at 4--4.5 ppm may be assigned to the methylene bridges between benzene nuclei. The molecular weight, number of each atom in a molecule and hydrogen distribution are tabulated in Table 2. Structural parameters were calculated by the following modified Brown-Ladner equations putting x and y values to be 2. The results are given in Table 3. Carbon aromaticity fa =
c - - ( H a / x + H0/y) + N
(1)
C+N
Ring condensation index H a + Ha/X + 0 + N Hau/Ca C - (H a/x + H0/y)
(2)
I~)~.._,,,L~ ~PYRD IN IE~O I LUBLE THFSOLUBLE, GPC-IA THFSOLUBLE, GPC-IB ~
ALKALI PPT., GPC-IIA "
I
~-..., t
I
A
J
or'--" TMS
NEUTRALIZED
1
6 5 4 3 2 1 C Chel:liCal shift fr'om TtlS (pl)ll) Fig.5. NMR spectra of each fraction. *, Solvent impurity in Cs2HsN; **, solvent impurity in C2HC13 ; ***, water. 10
9
8
7
PPT,,~PC-[II~ _ ~
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TABLE 2 M o l e c u l a r weight, n u m b e r o f e a c h a t o m , a n d h y d r o g e n d i s t r i b u t i o n Fraction
Ps I-A I-B II-A III-A
Mol.wt.
Number of atoms
1710 540 510 455 305
Hydrogen distribution
C
H
N
O
Ha
Ha
H0
121.4 38.0 35.9 30.5 19.1
73.5 31.3 30.1 26.5 16.2
3.2 1.4 1.9 2.1 1.2
8.4 2.1 1.4 2.1 2.7
57.3 23.0 17.1 17.1 14.6
7.0 5.7 9.5 2.3 1.2
9.3 2.6 3.0 7.0 0.4
Substitution index
Ha/x 0
+ 0
(3)
=
H a + H a/x + 0 + N
where C, N and O are the numbers of carbon, nitrogen and oxygen atoms in a molecule, respectively; H a is the number of aromatic hydrogen atoms in a molecule (6--9 ppm); H a is the number of aliphatic hydrogen atoms attached at a-position carbon atoms in a molecule (2--4.5 ppm); H0 is the n u m b e r of aliphatic hydrogen atoms attached at over-~-position carbon atoms in a molecule (0.5 --2 ppm). The model structures are proposed in Fig.6 referring to the structural param eters, ultimate analysis and original structure of phenol resin. Ether bonding between benzene nuclei was assumed from the fact t h a t water was evolved TABLE3 U l t i m a t e analysis, m o l e c u l a r weight, a n d s t r u c t u r a l p a r a m e t e r s U l t i m a t e analysis
Ps exp. model I-A exp. model I-B exp. model II-A exp. model III-A exp. model
Mol. wt.
C (%)
H (%)
N (%)
0 (%)
85.2 83.8 84.4 85.2 84.5 82.4 80.3 80.9 75.1 75.2
4.3 5.2 5.8 6.0 5.9 6.1 5.8 6.1 5.3 6.3
2.7 3.3 3.6 2.7 5.3 5.3 6.6 6.1 5.4 4.2
7.9 7.6 6.3 6.1 4.3 6.1 7.3 7.0 14.2 14.3
1710 1676 540 521 510 524 455 459 305 319
Structural parameter fa
Hau/Ca
a
0.93 0.93 0.89 0.87 0.84 0.84 0.86 0.88 0.96 0.86
0.62 0.75 0.84 0.85 0.79 0.78 0.80 0.79 0.98 1.00
0.16 0.13 0.17 0.21 0.25 0.28 0.15 0.18 0.17 0.33
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CH3 I
THF soluble~ G P C - I A
OH
OH
CH CH 3
CH3
THF soluble, G P C - I . B
OH
OH
ON
CH2-- N~CH3
Alkali
N
CH2
ppt.~ GPC ITA
Neutrallzed ppt.~ G P C - 1 T r A
O
O OH
Pyridine
N OH
O
OH
soluble Ps
Fig.6. Model structures of each fraction.
as the first d e c om pos i t i on gas at 300°C [6, 7]. It was also assumed t hat there existed tertiary bonded nitrogen atoms in the original resin as the result of ammonia addition used as catalyst. Of course the proposition of these model structures does n o t mean the real existence of these structure in the product. The structural parameters and ultimate analytical values based on these model structures are also given in Table 3. In the calculation o f structural parameters by Brown--Ladner equations there is a potential assumption t hat ether and m o n o m e t h y l e n e bridges between aromatic nuclei and direct linkages o f aromatic nuclei are n o t contained. So the structural parameters of models were calculated with a modification on this assumption. The accordance o f experimental and model values is almost identical. The increase o f nitrogen c o n t e n t definitely means the addition of quinoline to the resin structure. Fr om this and the proposed model structures, the mechanism of the extraction reaction of phenol resin with quinoline is proposed as in Fig.7. First m e t h y l e n e bridges break o f f thermally, producing radicals. These radi-
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OH
OH
OH
OH
"CH 2
OH
~.
OH
+ , ~ . N ~ . C H 2 J - . . ~ CH2.. OH
CH2~
OH
OH
2}2'-biquinoline
I OH
~ICH2~
OH
CH2-CH3_~~v~CH2--
Fig.7. Mechanism of solvolysis reaction.
cals combine with quinoline molecules directly or through methylene bridges. The latter split again and the produced quinoline radicals combine with other quinoline radicals producing 2,2'-biquinoline. The split methylene radicals sometimes combine with other methylene radicals producing ethylene bridges. Sometimes these ethylene bridges split again giving ethyl side chains. Otherwise t w o phenol nuclei combine together through ether bridges with the evolving water molecules. In brief this reaction is a kind of solvolysis reaction. Although quinoline was used in this study in order to detect solvent addition easily, generally speak ing such t y p e of solvolysis reaction must take place in the wide field of extraction treatment of coal, and as a consequence the total yield of extraction products, that is to say the sum of the yields of extract and residue, exceeds 100%. Under the high-pressure hydrogen atmosphere the thermally split radicals may be stabilized by hydrogen molecules, b u t in an inert atmosphere the produced radicals may be stabilized by the solvent molecules which surround the radicals and the molecular weight of coal is being reduced to dissolve into the solvent. CONCLUSION
Phenol resin was taken as coal model in order to elucidate the extraction mechanism with quinoline. After the extraction the nitrogen c o n t e n t increases markedly in every fraction and structural analysis shows the addition of quinoline molecules to fractured phenol resin. A mechanism of solvolytic addition of quinoline molecules to the thermally split phenol resin radicals was proposed. This results in a reduction of molecular weight.
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REFERENCES 1 Kiebler, M.W., 1945. In: H.H. Lowry (Editor), Chemistry of Coal Utilization, Vol.1, Wiley, New York, 715 pp. 2 I:lTden, I.G.C., 1963. In: H.H. Lowry (Editor), Chemistry of Coal Utilization, Supplementary Volume, Wiley, New York, 237 pp. 3 Sakabe, T., 1956. In: A. Baba (Editor), Advance of Coal Science, Vol. 2, Hakua Shobo, Tokyo, 327 pp. 4 Wise, W.S., 1971. Solvent Treatment of Coal, Mills and Boon, London. 5 Beilsteins Handbuch der Organischen Chemie, Zweite Erg~nzungs Werk, 1954, Vol. 23, Springer-Verlag, Berlin, p. 267. 6 0 u c h i , K. and Honda, H., 1959. Thermal cracking of phenol-formaldehyde resins taken as coal models. Fuel, 38: 429. 7 Yamashita, Y. and Ouchi, K., 1975. Carbonization reaction of phenol resin and Tempoku coal. Nenryo Kyokaishi (J. Fuel Soc. of Japan), 53: 1064.