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IN-situ monitoring of hydrogen transfer in carbonization reaction by well resolved high-temperature 1H NMR
ooO8-6223/84 $3.00 + .oO % 1984 Pergamon Press Ltd.
Carbon Vol. 22, No. 2, pp. 169-171, 1984 Pnnted in Great Bntain.
MONITORING OF HYDROGEN TRANSFER IN CARBONIZATION REACTION BY WELL RESOLVED HIGH-TEMPERATURE ‘H NMR
IN-SITU
T. YOKONO,T.
OBARA
and Y.
SANADA
Faculty of Engineering, Hokkaido University, North 13, West 8, Sapporo, Japan
and K. MNAZAWA Technical Research Center, Nippon Kokan K.K., Minami-watarida-cho,
Kawasaki-ku, Kawasaki, Japan
(Receiued 17 February 1983)
Abstract-By means of a well resolved high-temperature ‘H NMR technique, the carbonization process of acenaphthylene as well as the hydrogen transfer from some model compounds and decant oil to anthracene and/or acenaphthylene have been studied. The hydrogen transfer reaction was found to take place in the liquid phase at temperatures above 630 K for the decant oil/anthracene system. 1. INTRODUCTION It has been recognized that chemical stability and viscosity of the intermediate products are very important factors in an understanding of the carbonization process[l]. Especially, the importance of the hydrogen transfer reaction has been stressed by several researchers[2-4] in connection with the stabilization of free radicals formed during pyrolysis; such a stabilization in a coal system was confirmed by high temperature ESR[S]. In addition, as mentioned in the previous papers[&7], high-temperature ‘H NMR is an excellent tool for obtaining in-situ information about chemical reactions during carbonization. On these bases, the present study intends to develop a well resolved high-temperature ‘H NMR method, and further to monitor the hydrogen transfer reaction occurring in some model compounds and pitch during their carbonization processes. 2. EXPERIMENTAL G.R. grade acenaphthylene, anthracene and 1,4_dihydronaphthalene (1 +DHN) were selected as model compounds. The decant oil examined has the following elemental composition: C, 89.3%; H, 9.9%; N, 0.1% ahd S, 0.7%. ‘H NMR spectra were observed in the reaction temperature range from 400 to 680 K by using a Bruker Sxp 4-100 pulse FT NMR spectrometer. The in-situpyrolysis system is as shown in Fig. 1. A 0.3 g weight sample was placed in a 8 mm quartz tube, and sealed off after evacuation to 10e6Torr overnight. In order to improve the resolution of the spectra, a home built shim system was used, and the heater current in the high-temperature probe was cut off during the signal acquisition.
field range, corresponding to aromatic hydrogens and/or those attached to positions 1 and 2 in the acenaphthylene molecule. Assignment of the peaks was done by comparing them with the spectra for various pure model compounds, whereby acenaphthylene was found to exist as a monomer at this temperature[8]. The spectrum becomes broad at 480 K, because of the molecular motion restricted by the polymerization of acenaphthylene, as observed in Fig. 2(b). With a further increase in temperature, a new peak is produced in the r.h.s. Since its position is nearly coincident with that of the aliphatic hydrogen of acenaphthene and its height ratio against the peak in the 1.h.s. is l/3.7 at 660 K, this spectrum can presumably be ascribed to biacenaphthylidene, decacyclene and fluorocyclene. The results are in agreement with those obtained by Fitzer et al. [8]. Such an approach to the thermal reaction gives us insight into the chemical structural changes and molecular motion (related to line width) of model compounds during pyrolysis.
3.
RESULTSAND DISCUSSION Figure 2 shows ‘H NMR spectra for acenaphthylene at various temperatures. At 420 K, there is observed only single absorption in the low magnetic CAR Vol. 22, No. 2-~ E
Fig. 1. High temperature probe and glass reaction tube. 169
170
T. YoKoNoet al. (a) 420K
8
7
6
5
4
3
2
1
6, PPm
Fig. 4. ‘H NMR spectra of pyridine-d, solution from co-carbonization system of l$-dihydronaphthalene/anthracene (mol ratio 2: 1).
500K
2kHz
Fig. 2. High-temperature ‘H NMR spectra of carbonization product of awnaphthylene.
The same method was applied to the hydrogen transfer reaction from 1,4-DHN to anthracene. In a separate series of experiments, we have already reported that 1,4-DHN has a higher ability as a hydrogen donor than that of tetralin[9]. Figure 3 shows the spectra for the 1,4_DHN/anthracene system. With an increase of reaction temperature from 600 to 680 K, a new peak appears at 3.9 ppm owing to hydrogens attached to positions 9 and 10 in 9,10-dihydroanthracene (9,10-DHA). The hydrogen transfer from 1,4-DHN to anthracene was confirmed by the following quenched experiments. Figure 4 shows the usual ‘H NMR spectra of pyridine-d, solutions of the products obtained in the co-carbonization of
680K ..."....... 6QOK
I
I
,
I
1
I
10
8
6
4
2
0
6, wm
Fig. 3. Hip-~m~rature ‘H NMR spectra of cocarbonization system of l,~ihydronap~thalene~anthracene (mol ratio 2: 1).
1,4_DHN/anthracene. The peaks at 1.7 and 2.7 ppm correspond to naphthenic hydrogens of tetralin, while those at 3.2 and 5.8 ppm to 1,4- and 2,3-hydrogens of l,CDHN, respectively. Also, the peak at 3.9ppm corresponds to 9, IO-hydrogens of 9,1 O-DHA, and the others are assigned to aromatic hydrogens of both the compounds. The peak intensities at 1.7, 2.7 and 3.9 ppm become larger and those at 3.2 and 5.8 ppm become smaller with increasing temperature, consistent with the results of GC-MS and FI-MS spectroscopic experiments. Based on these observations, the hydrogen transfer reaction and the dispropo~ionation reaction of 1,CDHN may appropriately be expressed as follows:
The monitoring of hydrogen transfer in a similar way was also applied to the decant oil/anthracene system. Figure 5 shows typical examples of resolved ‘H NMR spectra of co-carbonization products at high temperatures. In order to minimize the effect of heater current on observed spectra, the d.c. heater current of the probe was switched off when the R.F. pulse was applied. In this way fine structures due to protons attached to a and (B + y) carbons with reference to the aromatic ring became clearly observabfe at high temperatures. The peak of 3.9 ppm due to 9,lO protons in the 9,10-DHA appears at about 630 K, and the higher the reaction temperature the larger the peak. This indicates that hydrogen transfer occurs from decant oil to anthracene producing 9,10-DHA. It is confident that decant oil abne contributes little to the peak at 3.9 ppm even at 650 K (see Fig. 5 (ii) and (v)). On the other hand, it has recently been found that a~enaphthylene is a better hydrogen acceptor than anthracene[lO]. We therefore then examined the de-
In-situ monitoring
of hydrogen transfer in carbonization
reaction
(a)
10
8
6
4 6,
0
2
PPm
(bj 10
8
4
6 6.
2
0
PW
Fig. 6. Well resolved IH NMR spectra of (a) cocarbonization product from decant oil/acenaphthylene (weight ratio I: I) at 620 K (b) (i) decant oil/a~Mph~yiene (weight ratio 1: 1) at 640 K (ii) decant oil at 650 K. I
10
I
I
I
I
I
8
6
4
2
il
6,
wm
Fig. 5. Well resolved ‘H NMR spectra of (i) co~r~ni~tion product of decant oil/anthra~ne (weight ratio 1: 1) at 630 K; (ii) decant oil at 650 K (h); (iii) decant oil/anthracene (weight ratio 1: 1) at 680 K; (iv) (iii) x 4 and (v) decant oil at 650K.
cant oil/acenaphthylene system whose spectra are as shown in Fig. 6. The peak at 3.3 ppm characteristic of naphthenic hydrogens of acenaphthene and/or biacenaphthyhdene appears at 620 K (Fig. 6a). This result means that hydrogen transfer from decant oil to acenaphthylene and/or the polymerization reaction of acenaphthylene take place at this temperature. Furthermore, in view of the fact that the NMR signal can be obtained, with the liquid state, the hydrogen transfer reaction can be concluded to proceed through the liquid phase.
Acknowledgements-The
authors are most grateful to Messrs. S. Shimokawa and E. Yamada for their assistance in utilizing the Bruker Pulse FT NMR spectrometer in the NMR laboratory. REFERENCB 1. H. Marsh and P. L. Walker, Jr., Chemistry und Physics of Carbon 15, 229 (1979). 2. T. Yokono, H. Marsh and M. Yokono, Fuel 60, 607
(1981). 3. I. Mochida and H. Marsh, Fuel 58, 797 (1979). 4. T. Obara, T. Yokono, K. Miyazawa and Y. Sanada, Carbon 19, 263 (1981). 5. R. F. Sprecher and H. L. Retcofsky, Fuef 62,473 (1983). 6. T. Yokono, K. Miyazawa, Y. Sanada, E. Yamada and S. Shimokawa, Fuel 58, 237 (1979). 7. K. Miyazawa, T. Yokono and Y. Sanada, Carbon 17, 223 (1979).
8. E. Fitzer and K. Muller, Carbon 6, 234 (1968). 9. T. Yokono, T. Obara, H. S~rahama, E. Osawa and Y. Sanada, J. Chem. Sot. Perkin Trans. II@), 979 (1982). 10. T. Obara, T. Yokono and Y. Sanada, Fuel 62, 813 (1983).
Carbon Vol. 22, No. 2, pp. 169-171, 1984 Pnnted in Great Bntain.
MONITORING OF HYDROGEN TRANSFER IN CARBONIZATION REACTION BY WELL RESOLVED HIGH-TEMPERATURE ‘H NMR
IN-SITU
T. YOKONO,T.
OBARA
and Y.
SANADA
Faculty of Engineering, Hokkaido University, North 13, West 8, Sapporo, Japan
and K. MNAZAWA Technical Research Center, Nippon Kokan K.K., Minami-watarida-cho,
Kawasaki-ku, Kawasaki, Japan
(Receiued 17 February 1983)
Abstract-By means of a well resolved high-temperature ‘H NMR technique, the carbonization process of acenaphthylene as well as the hydrogen transfer from some model compounds and decant oil to anthracene and/or acenaphthylene have been studied. The hydrogen transfer reaction was found to take place in the liquid phase at temperatures above 630 K for the decant oil/anthracene system. 1. INTRODUCTION It has been recognized that chemical stability and viscosity of the intermediate products are very important factors in an understanding of the carbonization process[l]. Especially, the importance of the hydrogen transfer reaction has been stressed by several researchers[2-4] in connection with the stabilization of free radicals formed during pyrolysis; such a stabilization in a coal system was confirmed by high temperature ESR[S]. In addition, as mentioned in the previous papers[&7], high-temperature ‘H NMR is an excellent tool for obtaining in-situ information about chemical reactions during carbonization. On these bases, the present study intends to develop a well resolved high-temperature ‘H NMR method, and further to monitor the hydrogen transfer reaction occurring in some model compounds and pitch during their carbonization processes. 2. EXPERIMENTAL G.R. grade acenaphthylene, anthracene and 1,4_dihydronaphthalene (1 +DHN) were selected as model compounds. The decant oil examined has the following elemental composition: C, 89.3%; H, 9.9%; N, 0.1% ahd S, 0.7%. ‘H NMR spectra were observed in the reaction temperature range from 400 to 680 K by using a Bruker Sxp 4-100 pulse FT NMR spectrometer. The in-situpyrolysis system is as shown in Fig. 1. A 0.3 g weight sample was placed in a 8 mm quartz tube, and sealed off after evacuation to 10e6Torr overnight. In order to improve the resolution of the spectra, a home built shim system was used, and the heater current in the high-temperature probe was cut off during the signal acquisition.
field range, corresponding to aromatic hydrogens and/or those attached to positions 1 and 2 in the acenaphthylene molecule. Assignment of the peaks was done by comparing them with the spectra for various pure model compounds, whereby acenaphthylene was found to exist as a monomer at this temperature[8]. The spectrum becomes broad at 480 K, because of the molecular motion restricted by the polymerization of acenaphthylene, as observed in Fig. 2(b). With a further increase in temperature, a new peak is produced in the r.h.s. Since its position is nearly coincident with that of the aliphatic hydrogen of acenaphthene and its height ratio against the peak in the 1.h.s. is l/3.7 at 660 K, this spectrum can presumably be ascribed to biacenaphthylidene, decacyclene and fluorocyclene. The results are in agreement with those obtained by Fitzer et al. [8]. Such an approach to the thermal reaction gives us insight into the chemical structural changes and molecular motion (related to line width) of model compounds during pyrolysis.
3.
RESULTSAND DISCUSSION Figure 2 shows ‘H NMR spectra for acenaphthylene at various temperatures. At 420 K, there is observed only single absorption in the low magnetic CAR Vol. 22, No. 2-~ E
Fig. 1. High temperature probe and glass reaction tube. 169
170
T. YoKoNoet al. (a) 420K
8
7
6
5
4
3
2
1
6, PPm
Fig. 4. ‘H NMR spectra of pyridine-d, solution from co-carbonization system of l$-dihydronaphthalene/anthracene (mol ratio 2: 1).
500K
2kHz
Fig. 2. High-temperature ‘H NMR spectra of carbonization product of awnaphthylene.
The same method was applied to the hydrogen transfer reaction from 1,4-DHN to anthracene. In a separate series of experiments, we have already reported that 1,4-DHN has a higher ability as a hydrogen donor than that of tetralin[9]. Figure 3 shows the spectra for the 1,4_DHN/anthracene system. With an increase of reaction temperature from 600 to 680 K, a new peak appears at 3.9 ppm owing to hydrogens attached to positions 9 and 10 in 9,10-dihydroanthracene (9,10-DHA). The hydrogen transfer from 1,4-DHN to anthracene was confirmed by the following quenched experiments. Figure 4 shows the usual ‘H NMR spectra of pyridine-d, solutions of the products obtained in the co-carbonization of
680K ..."....... 6QOK
I
I
,
I
1
I
10
8
6
4
2
0
6, wm
Fig. 3. Hip-~m~rature ‘H NMR spectra of cocarbonization system of l,~ihydronap~thalene~anthracene (mol ratio 2: 1).
1,4_DHN/anthracene. The peaks at 1.7 and 2.7 ppm correspond to naphthenic hydrogens of tetralin, while those at 3.2 and 5.8 ppm to 1,4- and 2,3-hydrogens of l,CDHN, respectively. Also, the peak at 3.9ppm corresponds to 9, IO-hydrogens of 9,1 O-DHA, and the others are assigned to aromatic hydrogens of both the compounds. The peak intensities at 1.7, 2.7 and 3.9 ppm become larger and those at 3.2 and 5.8 ppm become smaller with increasing temperature, consistent with the results of GC-MS and FI-MS spectroscopic experiments. Based on these observations, the hydrogen transfer reaction and the dispropo~ionation reaction of 1,CDHN may appropriately be expressed as follows:
The monitoring of hydrogen transfer in a similar way was also applied to the decant oil/anthracene system. Figure 5 shows typical examples of resolved ‘H NMR spectra of co-carbonization products at high temperatures. In order to minimize the effect of heater current on observed spectra, the d.c. heater current of the probe was switched off when the R.F. pulse was applied. In this way fine structures due to protons attached to a and (B + y) carbons with reference to the aromatic ring became clearly observabfe at high temperatures. The peak of 3.9 ppm due to 9,lO protons in the 9,10-DHA appears at about 630 K, and the higher the reaction temperature the larger the peak. This indicates that hydrogen transfer occurs from decant oil to anthracene producing 9,10-DHA. It is confident that decant oil abne contributes little to the peak at 3.9 ppm even at 650 K (see Fig. 5 (ii) and (v)). On the other hand, it has recently been found that a~enaphthylene is a better hydrogen acceptor than anthracene[lO]. We therefore then examined the de-
In-situ monitoring
of hydrogen transfer in carbonization
reaction
(a)
10
8
6
4 6,
0
2
PPm
(bj 10
8
4
6 6.
2
0
PW
Fig. 6. Well resolved IH NMR spectra of (a) cocarbonization product from decant oil/acenaphthylene (weight ratio I: I) at 620 K (b) (i) decant oil/a~Mph~yiene (weight ratio 1: 1) at 640 K (ii) decant oil at 650 K. I
10
I
I
I
I
I
8
6
4
2
il
6,
wm
Fig. 5. Well resolved ‘H NMR spectra of (i) co~r~ni~tion product of decant oil/anthra~ne (weight ratio 1: 1) at 630 K; (ii) decant oil at 650 K (h); (iii) decant oil/anthracene (weight ratio 1: 1) at 680 K; (iv) (iii) x 4 and (v) decant oil at 650K.
cant oil/acenaphthylene system whose spectra are as shown in Fig. 6. The peak at 3.3 ppm characteristic of naphthenic hydrogens of acenaphthene and/or biacenaphthyhdene appears at 620 K (Fig. 6a). This result means that hydrogen transfer from decant oil to acenaphthylene and/or the polymerization reaction of acenaphthylene take place at this temperature. Furthermore, in view of the fact that the NMR signal can be obtained, with the liquid state, the hydrogen transfer reaction can be concluded to proceed through the liquid phase.
Acknowledgements-The
authors are most grateful to Messrs. S. Shimokawa and E. Yamada for their assistance in utilizing the Bruker Pulse FT NMR spectrometer in the NMR laboratory. REFERENCB 1. H. Marsh and P. L. Walker, Jr., Chemistry und Physics of Carbon 15, 229 (1979). 2. T. Yokono, H. Marsh and M. Yokono, Fuel 60, 607
(1981). 3. I. Mochida and H. Marsh, Fuel 58, 797 (1979). 4. T. Obara, T. Yokono, K. Miyazawa and Y. Sanada, Carbon 19, 263 (1981). 5. R. F. Sprecher and H. L. Retcofsky, Fuef 62,473 (1983). 6. T. Yokono, K. Miyazawa, Y. Sanada, E. Yamada and S. Shimokawa, Fuel 58, 237 (1979). 7. K. Miyazawa, T. Yokono and Y. Sanada, Carbon 17, 223 (1979).
8. E. Fitzer and K. Muller, Carbon 6, 234 (1968). 9. T. Yokono, T. Obara, H. S~rahama, E. Osawa and Y. Sanada, J. Chem. Sot. Perkin Trans. II@), 979 (1982). 10. T. Obara, T. Yokono and Y. Sanada, Fuel 62, 813 (1983).