184
Energy & Fuels 2000, 14, 184-189
Analysis of Nitrogen-Containing Species during
Pyrolysis of Coal at Two Different Heating Rates
Koh Kidena, Yoshihisa Hirose, Toshihiro Aibara, Satoru Murata, and
Masakatsu Nomura*
Department of Applied Chemistry, Faculty of Engineering, Osaka University,
2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
Received June 14, 1999. Revised Manuscript Received September 15, 1999
The effect of heating rate on the conversion of nitrogen in coal to nitrogen-containing species
during pyrolysis of coal was investigated. Two pyrolysis apparatuses were employed in this study.
One was an infrared image furnace (IIF) which can heat a sample up to 1100 °C at a heating
rate of 10 K/s. The other apparatus was a Curie-point pyrolyzer (CPP) whose heating rate was
around 3000 K/s. Conversion of nitrogen in coal to HCN from CPP pyrolysis at 1040 °C was
higher than that in the case of IIF pyrolysis at 1000 °C. On the other hand, IIF pyrolysis
experiments at 1000 °C produced large amounts of N2 from low rank coals. The results indicate
that heating rate can be one of the dominant factors affecting the behavior of nitrogen release as
a range of heating rate applied in this study. The pyrolysis of a nitrogen-containing model polymer
showed similar behavior to coal pyrolysis.
Introduction
Many power plants in Japan and other countries are
now using a vast amount of coal as a fuel because they
have reasonable cost performance and there are inherent hazardous problems to construct and operate a
nuclear power plant. However, coal combustion technology has to overcome the severe regulation about NOx
and SOx emissions since coal contains a few percentages
of heteroatoms such as nitrogen and sulfur. NOx and
SOx are, in general, believed to cause both acid rain and
photochemical smog. Recently, regulation of NOx from
power plants or cars is becoming a serious issue and a
lot of attention is paid to the reduction of NOx.1-3 There
are three pathways of NOx evolution during combustion
of nitrogen-containing fuels in the air: fuel-NOx, thermalNOx, and prompt-NOx.4,5 Fuel-NOx originates from
nitrogen atoms in the fuel, thermal-NOx is formed by
the reaction between nitrogen and oxygen in the air at
high temperature, and prompt-NOx is produced by the
reaction of nitrogen in the air with hydrocarbon species.
The suppression of thermal-NOx can be achieved by the
developed combustion technique, the so-called advanced
combustion technology,6 and the amount of prompt-NOx
* Author to whom correspondence should be addressed. Fax: +816-6879-7362. E-mail: [email protected].
(1) Lyngefelt, A.; Leckner, B. Fuel 1993, 72, 1553.
(2) Shimizu, T.; Tachiyama, Y.; Fujita, D.; Kumazawa, K.-i.; Wakayama, O.; Ishizu, K.; Kobayashi, S.; Shikada, S.; Inagaki, M. Energy Fuels
1992, 6, 753.
(3) Shimizu, T.; Inagaki, M. Energy Fuels 1993, 7, 648.
(4) Pershing, D. W.; Wendt, J. O. L. 16th Symposium on Combustion,
1976, p 389.
(5) Chen, S. L.; Heap, M. P.; Pershin, D. W.; Martin, G. B. Fuel 1982,
61, 1218.
(6) Jensen, A.; Johnsson, J. E.; Andries, J.; Laughlin, K.; Read, G.;
Mayer, M.; Baumann, H.; Bonn, B. Fuel 1995, 74, 1555.
is considered to be small.7-9 Therefore, to reduce NOx
emissions from coal combustion, fuel-NOx should be
suppressed, and the investigation of mechanisms of fuelNOx formation from coal is important. The formation
of fuel-NOx is considered to occur in two steps: the first
step includes the conversion of nitrogen species in coal
to NOx precursors such as HCN or NH3, and the
following step is their oxidation under combustion
conditions to form NOx.7-9 To clarify the phenomena of
nitrogen release from coal, numerous coal pyrolysis
experiments have been done in various points of
view,5,10-20 and several reviews including evolution of
nitrogen species from coal were published.21-23 However,
there is no simple relationship between coal nitrogen
content and the amount of NOx emission. Many re(7) Nelson, P. F.; Buckley, A. N.; Kelly, M. D. 24th Symposium on
Combustion, 1992, p 1259.
(8) Nelson, P. F.; Kelly, M. D.; Wornat, M. J. Fuel 1991, 70, 403.
(9) Kelly, M. D.; Buckley, A. N.; Nelson, P. F. Proceedings of ICCS
1991, Newcastle, UK, 1991, p 356.
(10) Kambara, S.; Takarada, T.; Yamamoto, Y.; Kato, K. Energy
Fuels 1993, 7, 1013.
(11) Ohtsuka, Y.; Mori, H.; Watanabe, T.; Asami, K. Fuel 1994, 73,
1093.
(12) Kambara, S.; Takarada, T.; Toyoshima, M.; Kato, K. Fuel 1995,
74, 1247.
(13) Leppälahti, J. Fuel 1995, 74, 1363.
(14) Nelson, P. F.; Li, C.-Z.; Ledesma, E. Energy Fuels 1996, 10,
264.
(15) Hämäläinen, J. P.; Aho, M. J. Fuel 1996, 75, 1377.
(16) Wu, Z.; Ohtsuka, Y. Energy Fuels 1997, 11, 477.
(17) Li, C.-Z.; Buckley, A. N.; Nelson, P. F. Fuel 1998, 77, 157.
(18) Bassilakis, R.; Zhao, Y.; Solomon, P. R.; Serio, M. A. Energy
Fuels 1993, 7, 710.
(19) Bartle, K. D.; Taylor, J. M.; Williams, A. Fuel 1992, 71, 714.
(20) Stanczyk, K.; Boudou, J. P. Fuel 1994, 73, 940.
(21) Johnsson, J. E. Fuel 1994, 73, 1398.
(22) Leppälahti, J.; Koljonen, T. Fuel Process. Technol. 1995, 43, 1.
(23) Wójtowicz, M. A.; Pels, J. R.; Moulijn, J. A. Fuel Process.
Technol. 1993, 34, 1.
10.1021/ef9901241 CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/20/1999
Analysis of Nitrogen-Containing Species in Pyrolysis
searchers focused their interest on the functionality of
nitrogen in coal. XPS (X-ray photoelectron spectroscopy)
is a common technique to investigate nitrogen-containing species in coal.24-27 15N NMR (nuclear magnetic
resonance) spectroscopy28,29 and XANES (X-ray adsorption near-edge structure)30 have also been used to
investigate nitrogen functionality in coal. By using these
analytical techniques, the relationship between the
behavior of nitrogen release from coal and the functional
form of nitrogen in coal was reported. Nelson et al.7
concluded that thermal stability of nitrogen species in
the tars obeyed the following order: pyrrolic < pyridinic
< cyanoaromatic. Kelemen et al.25 employed XPS measurement to identify and quantify the changes in
organically bound nitrogen forms which are present in
the tars and chars after pyrolysis. They found that
pyrrolic nitrogen decreased and nitrogen in graphitic
type increased in the char as the temperature increased.
However, there are no logical viewpoints to discuss
nitrogen release from coal.
The distribution of nitrogen-containing gaseous products was significantly different among experiments as
summarized in the papers,18,21-23 this being partly due
to the different pyrolysis conditions. Ohtsuka et al.11
reported results from pyrolysis in a fixed-bed quartz
reactor, showing that the major nitrogen-containing
gaseous product was N2. Stanczyk also detected the
predominant formation of N2 by mass spectroscopy
during slow heating of coal.20 On the other hand,
Takarada et al.10,12 found that HCN was the main
nitrogen-containing gaseous product in pyrolysis experiments by using a pyroprobe. Nelson et al.7 observed
HCN and NH3 as nitrogen-containing gaseous products
at a high heating rate in a fluidized-bed reactor. In the
paper above metioned, the differences of experimental
results may be caused by the variation of coal sample
and pyrolysis conditions including different heat-treatment temperature and heating rate. Although the
comparison of data from the pyrolysis at different
heating rates was done in several papers and reviews,18,21-23 only a few coals were used as objects of
the studies, or the difference of heating rate was too
large to discuss the effect of heating rate on the pyrolysis
products. In the present study, the analysis of nitrogencontaining species during pyrolysis of coal at two
different heating rates by using a series of the coal
samples was performed in order to investigate the effect
of pyrolysis conditions on the pyrolysates. The pyrolysis
of a model polymer was also examined with these two
pyrolysis techniques.
Experimental Section
Samples. Seven kinds of sample coals were employed in
this study. These samples were provided by Argonne National
(24) Burchill, P.; Welch, L. S. Fuel 1989, 68, 100.
(25) Kelemen, S. R.; Gorbaty, M. L.; Kwiatek, P. J. Energy Fuels
1994, 8, 896.
(26) Buckley, A. N. Fuel Process. Technol. 1994, 38, 165.
(27) Sawada, Y.; Ninomiya, Y. Proceedings of 9th ICCS, Essen,
Germany, 1997, p 433.
(28) Knicker, H.; Hatcher, P. G.; Scaroni, A. W. Energy Fuels 1995,
9, 999.
(29) Solum, M. S.; Pugmire, R. J.; Grant, D. M.; Kelemen, S. R.;
Gorbaty, M. L.; Wind, R. A. Energy Fuels 1997, 11, 491.
(30) Kirtley, S. M.; Mullins, O. C.; Elp, J.; Cramer, A. P. Fuel 1993,
72, 133.
Energy & Fuels, Vol. 14, No. 1, 2000 185
Table 1. Properties of the Sample Coals
coal
Pocahontas No.3
Upper Freeport
Pittsburgh No.8
Miike
Taiheiyo
South Banko
Yallourn
PC
UF
PT
MK
TH
SB
YL
C%(daf)
N%(daf)
ash%(db)
91.1
85.5
83.2
79.9
78.7
72.3
65.9
1.33
1.55
1.64
1.20
1.17
1.36
0.63
4.8
13.2
9.3
16.0
12.6
2.7
1.6
Laboratory, Center for Coal Utilization, Japan, and Nippon
Brown Coal Liquefaction Co. Ltd., Japan. Their analytical data
are shown in Table 1. The samples were pulverized under 100
mesh, and dried at 60 °C in vacuo prior to use.
Pyrolysis of Coal with IIF and Analysis of Products.
In the experiments using an infrared image furnace (IIF,
Shinku-Riko Co. Ltd., QHC-P610CP), about 0.5 g of dried coal
sample was put on the quartz plate at the center of the furnace.
The temperautre was monitored by a thermocouple positioned
at the center of the furnace and close to the coal particles. By
monitoring temperature, infrared output was controlled to
keep the programmed temperature. All runs were carried out
under He flow (99.99%, 200 mL/min) after the interior of the
furnace was purged with He for more than 2 h. The nitrogen
level after purging was checked by using GC (vide infra)
connected directly to the furnace, and we observed a small and
constant amount of nitrogen after purging. Then, the sample
was heated to the determined temperature at a heating rate
of 10 K/s followed by a 10 s holding time at that temperature.
The char fraction that remained on the quartz plate and
the tar fraction that deposited on the inner surface of the
furnace were collected and weighed to calculate the yield of
each fraction. The yield of volatile fraction was obtained by
subtracting the weight of char and tar fractions from the
weight of initial sample. Nitrogen content of these fractions
was determined by the elemental analysis of each fraction. All
gaseous products were collected into an aluminum gas bag
which was placed at the exit of the pyrolysis furnace by flowing
helium for 2 h from the beginning of the pyrolysis. Amounts
of HCN and NH3 collected in the gas bag were quantified by
a gas detector tube (Gastec Co. Ltd.). Yields of N2 were
estimated by on-line GC-TCD (Shimadzu GC-8A) equipped
with Molecular sieve-5A (2 m) stainless steel column under
the following conditions: column temperature ) 70 °C, injection and detector temperature ) 100 °C, and TCD current )
180 mA. The nitrogen level in GC analysis increased by a
factor of 100 (in maximum) against the level of background
nitrogen. Observed background nitrogen may come from a He
bomb or air, but we confirmed that it was constant before
pyrolysis. The amount of nitrogen from pyrolysate was estimated by subtracting the area of backgound N2 from the
observed N2 area. Furthermore, the nitrogen level after
pyrolysis decreased exponentially, and it dropped into backgound level after 2 h. Therefore, the amount of N2 could be
calculated by integrating the peak area during 2 h of analysis.
Pyrolysis of Coal with CPP and Analysis of Products.
In the experiments using a Curie-point pyrolyzer (CPP, Japan
Analytical Industry Co. Ltd., JHP-3), about 1.0-1.5 mg of dried
coal sample was used. The detailed procedure of the pyrolysis
is described elsewhere.31 CPP can heat up the sample to the
determined temperature in 0.3 s. Therefore, the heating rate
in CPP experiments was calculated to be 2000-3300 K/s. The
yields of char and tar fractions were obtained by weighing
them, the remainder (weight of coal sample - weights of char
and tar fractions) being the volatile fraction. Only HCN could
be analyzed by GC (Shimadzu GC-14B, with flame thermoionic
detector, FTD) with a fused silica capillary column, Pora PLOT
Q (0.53 mm × 25 m). FTD can detect only nitrogen and
(31) Murata, S.; Mori, T.; Murakami, A.; Nomura, M. Energy Fuels
1995, 9, 119.
186
Energy & Fuels, Vol. 14, No. 1, 2000
Kidena et al.
Figure 1. The yield of IIF pyrolysis of the coals at 1000 °C
for 10 s.
Figure 2. Nitrogen balance of each product after IIF pyrolysis
of coal.
phosphorus-containing organic compounds in higher sensitivity than the TCD by a factor of 106. Gaseous HCN was
synthesized from potassium cyanide (5 mg) and sulfuric acid
(0.18 mol/L, 0.2 mL) at 40 °C and used as the standard sample
in order to determine the concentration of HCN from GC
analysis. Helium carrier and TCD should be used for the
analyses of N2 and NH3; however, they were not successful
because of a trace amount of these products and the detectable
limitation. On the other hand, since the use of N2 (instead of
He) was appropriate enough to analyze HCN, we determined
to use N2 as a carrier in the CPP experiments. The observed
area of HCN is higher than the limit of detection by a factor
of 105.
Results and Discussion
Pyrolysis of Coal with IIF. Pyrolysis of seven kinds
of coals was conducted at 1000 °C with IIF. The yields
of char, tar, and volatile are shown in Figure 1. We
employed coal samples with a wide range of carbon
content, from C 65.9% for YL coal to C 91.1% for PC
coal. Nitrogen content ranged from 0.6% to 1.6%. In
higher rank coals such as PC and UF, the yields of char
were high, and lower rank coals, YL and SB, yielded
larger amounts of volatile. Such tendency was observed
in the proximate analyses (volatile matter) data of coal.
The resulting char, tar, and gaseous products such as
HCN, NH3, and N2 were found to contain nitrogen.
Figure 2 presents the nitrogen balance from pyrolysis
of coal with IIF. N conversion to each product was
calculated on the basis of nitrogen content in original
coal and above products as shown in eqs 1-5:
HCN )
NH3 )
N2 )
HCN(mol)
(1)
[wt of sample (g)] × %N,raw(db)/100/14
NH3(mol)
[wt of sample (g)] × %N,raw(db)/100/14
N2(mol) × 2
[wt of sample (g)] × %N,raw(db)/100/14
char-N )
tar-N )
char yield (wt%, db) × %N,char(db)
%N,raw(db)
tar yield (wt%, daf) × %N,tar(daf)
%N,raw(daf)
(2)
(3)
(4)
(5)
For example, coal-N conversion to char-N was defined
as the ratio of the amount of nitrogen in char to that in
the original coal. Figure 2 shows that coal-N conversion
to char-N was high with high rank coals, while that to
Figure 3. Plots of coal-nitrogen conversion to nitrogencontaining gaseous products from IIF pyrolysis at 1000 °C: 4,
N2; ], HCN; 0, NH3.
volatile-N was high with low rank coals. However, YL
pyrolysis resulted in higher char-N than SB and TH.
This may be caused by the low content of nitrogen in
YL, the relatively large error being involved in calculation of N conversion to each product. The cumulative
conversion of nitrogen in the products, nitrogen recovery
was excellent, ranging from 92 to 105%. Therefore, the
contribution of other nitrogen-containing volatile products such as nitriles, amines, amides, or pyridine should
be small, even if they are present as gaseous products.
The plots of coal-N conversion to N-containing gaseous
products against carbon content of coal are shown in
Figure 3. This figure clearly indicates that coal-N
conversion to N2 for low rank coals, YL, SB, and TH,
was very high. Although N conversion to HCN was
slightly higher than that to NH3, its rank dependence
was not observed; the coal-N conversions to HCN and
NH3 were 3-10% and 2-6%, respectively. In the review
papers18,21-23 comparing the results from low and high
heating rates, NH3 yield is higher than HCN yield at
low heating rates. The results in this study were
different from their results. Ohtsuka et al.16 observed
N2 in the pyrolysis of low rank coals, and the heating
rate of their experimental conditions was comparable
to our conditions; therefore, we can confirm that low
rank coals generate N2 at a certain heating rate.
To investigate the effect of pyrolysis temperature on
the product distribution and coal-N conversion, IIF
pyrolysis experiments of TH coal at 700-1100 °C were
performed. Both fraction yields and coal-N conversion
to gaseous nitrogen-containing products were plotted
against pyrolysis temperature as shown in Figure 4.
Analysis of Nitrogen-Containing Species in Pyrolysis
Energy & Fuels, Vol. 14, No. 1, 2000 187
Figure 4. (a) Pyrolysis yields and (b) nitrogen conversion to gaseous products from IIF pyrolysis of TH coal at various temperatures.
Figure 5. The yields of CPP pyrolysis of the sample coals.
Nitrogen balances for each pyrolysis temperature are
not shown here, but they ranged from 93 to 105%, these
being satisfied within the experimental error. As the
pyrolysis temperature increased from 700 to 1100 °C,
the yield of the volatile fraction slightly increased, and
coal-N conversion to N2 doubled. Coal-N conversion to
HCN also increased with pyrolysis temperature. Those
results were not contrary to the reported ones: not only
volatile fractions but also nitrogen species in coal can
release more easily during pyrolysis at higher temperatures. However, coal-N conversion to NH3 did not
change in the temperature range examined here.
Pyrolysis of Coal with CPP. At first, the pyrolysis
of TH coal with CPP was conducted at 670, 764, 920,
and 1040 °C because we could not choose the pyrolysis
temperature arbitrarily due to the limited number of
pyrofoils commercially available in CPP experiments.
The yield of volatile fraction from pyrolysis with CPP
increased with temperature and the yield at 1040 °C
was similar to the volatile yield from IIF pyrolysis at
1000 °C. The pyrolysis experiments with CPP were
conducted at 1040 °C using seven kinds of sample coals.
The yields of char, tar, and volatile fractions are given
in Figure 5. The yield of each fraction changed depending on coal rank in a fashion similar to IIF pyrolysis.
High rank coals showed higher yields of char, while low
rank coals yielded large amounts of volatiles.
We next carried out analysis of HCN in the CPP
experiments. Coal-N conversion to HCN is shown in
Figure 6. It ranged from 11 to 23%, and decreased with
an increase in coal rank. It is noted that coal-N
Figure 6. N conversion to HCN obtained from the pyrolysis
with CPP at 1040 °C.
conversion to HCN in CPP pyrolysis was higher than
that in IIF pyrolysis for all the coals studied. Thus, the
behavior of nitrogen release during pyrolysis of coal can
be considered to be different depending on the heating
rate of pyrolysis experiments. Furthermore, the discrepancy observed in the distribution of nitrogencontaining gaseous products among the previous reports
by other researchers5,7,8,10-20 seemed to be related to the
difference of pyrolysis conditions, especially heating
rate. Therefore, when we discuss the nitrogen release
from coal, we should pay attention to the pyrolysis
conditions, especially to the heating rate. The heating
rate in CPP experiments is close to that in pyroprobe
by Kambara et al.10,12 Although we could not analyze
nitrogen-containing gaseous products other than HCN,
the amount of NH3 and N2 are considered to be small
according to the results using pyroprobe. In a recent
paper, Takagi et al. found only a small amount of N2 in
CPP experiments.32
Influence of the Heating Rate on the Distribution of Pyrolysis Products. The volatile yields were
different from coal to coal, therefore, it is not clear
whether the amount of nitrogen-containing gaseous
products is proportional to the amount of volatile
fraction or not. To estimate the distribution of N(32) Takagi, H.; Isoda, T.; Kusakabe, K.; Morooka, S. Energy Fuels
1999, 13, 934.
188
Energy & Fuels, Vol. 14, No. 1, 2000
Kidena et al.
Table 2. N Conversion to N-Containing Gaseous
Products in the Pyrolysis of N-Containing Polymer
pyrolysis system N-containing
(conditions)
gases
IIF
(1000 °C, 10 s)
CPP
(1040 °C, 3 s)
HCN
NH3
N2
HCN
N conversion (%, coal-N basis)
PVPa
PVP + HClb
-c
0.3
5.5
2.7
4.0
a Poly(4-vinylpyridine). b 10% HCl(aq)-treated PVP. c Less than
detectable limitation (<0.1%).
Figure 7. The plots of the selectivity of nitrogen in gaseous
products to whole nitrogen in volatile fraction during the
pyrolysis with IIF (open symbols) or CPP (filled symbols): 4,
IIF-N2; ], IIF-HCN; 0, IIF-NH3; [, CPP-HCN.
containing gaseous products in the volatile fraction,
selectivity of each N-containing gaseous product toward
whole amounts of volatile materials was estimated
according to the following assumption: nitrogen atoms
were distributed uniformly among each pyrolysis fraction. The plots of the selectivity of nitrogen-containing
compounds in gaseous products against carbon content
of coal are shown in Figure 7. Hydrogen cyanide
selectivity in CPP pyrolysis reached 50-100%. This
supports that HCN is the main product among nitrogencontaining gases. Although the coal-N conversion to
HCN decreased with an increasing carbon content of
coal as shown in Figure 6, HCN selectivity was high
for the high rank coal. Therefore, products other than
HCN should be considered as the gaseous species in low
rank coals. On the other hand, in IIF experiments,
nitrogen in the volatile fraction is distributed to N2,
HCN, and NH3. The sum of the selectivity of three gases
did not reach 1.0 as shown in Figure 7. This indicates
the assumption for the determination of the selectivity
is not correct. Char-N/char-yield was >1.0 in almost all
cases examined. Therefore, nitrogen atoms tend to be
concentrated in char fraction with this pyrolysis, especially at lower heating rates. However, we can apply this
assumption in order to discuss the volatility of each
gaseous product in the pyrolysis experiments. In high
rank coals, HCN seems to be volatilized easily in both
pyrolysis systems, and N2 selectivity became high for
three low rank coals at low heating rate. Although we
could not analyze N2 and NH3 in CPP experiments,
there is significant influence of the heating rate on the
distribution of gaseous products. High selectivity of N2
in IIF pyrolysis of low rank coal agrees well with the
results reported by Ohtsuka et al.16 Their pyrolysis
conditions were similar to our conditions, and they also
employed low rank coals. The heating rate of our IIF
experiments and Ohtsuka’s experiments were relatively
lower than that of CPP experiments. It may bring about
a secondary reaction of other species to N2 during
pyrolysis. Leppälahti et al.22 also discussed the effect
of heating rate on the distribution of pyrolysate in the
reaction system. At low heating rate, residence time
becomes relatively long, and the pyrolysates have
chances to react with other fractions. In the present
study, since the selectivity of HCN was high in the CPP
experiment and low in the IIF experiment, the following
idea could be proposed: HCN was released from coal
as a primary gaseous product, and then it reacted with
char-N or tar-N to generate other species, N2, especially
in low rank coals.
Pyrolysis of Model Compounds. To investigate the
decomposition behavior of pyridinic and quaternary
nitrogen with the two pyrolyzers, we employed model
compounds such as poly(4-vinylpyridine) (PVP) which
represents pyridinic type compounds. Pyrolysis of PVP
and acid-treated PVP were conducted. Acid treatment
of the polymer was conducted by stirring the mixture
of 10% HCl(aq) and polymer at room temperature for 2
h. The conversion of pyridinic nitrogen in PVP to
quaternary (protonated) form was estimated as 85% on
the basis of the atomic ratio of chlorine to nitrogen in
the treated PVP. Table 2 shows the polymer-N conversion to nitrogen-containing gaseous products in IIF and
CPP pyrolysis experiments. In both pyrolysis experiments, polymers pyrolyzed almost completely; char yield
was approximately zero, and N conversion to gaseous
product was low. The remainder should be tar fraction.
When we analyzed the tar fraction collected, pyridine
and its oligomer were observed. Therefore, in the
pyrolysis of the model polymer, degradation of the
polymer chain occurred along with the decomposition
of the heteroaromatic ring. Influences of heating rate
were also observed in the pyrolysis of the model
polymer. From Table 2, the N conversion to HCN was
higher in CPP pyrolysis than in IIF pyrolysis, this being
similar to the results from coal pyrolysis. The results
indicate that the decomposition of the heteroaromatic
ring is easy in the rapid heating. In this case, IIF
pyrolysis degraded the polymer to oligomer preferably.
However, a detectable difference between the pyrolysis
of PVP and that of acid-treated PVP was observed: N
conversion to HCN in the IIF pyrolysis of PVP was less
than the detectable range, while acid-treated PVP
generated a detectable amount of HCN in IIF pyrolysis.
Therefore, decomposition of the heteroaromatic ring
occurred in IIF pyrolysis. However, acid-treatment
affected N conversion to HCN in different way for the
two pyrolysis systems. In the present study, although
we can mention the discrepancy of pyrolytic behavior
in two different pyrolysis systems, we could not discuss
the relationship between the nitrogen form in the
polymer and the product distribution.
Conclusions
By using two different pyrolysis furnaces, an infrared
image furnace (IIF), and a Curie-point pyrolyzer (CPP),
the pyrolysis experiments of seven coal samples were
performed. In the IIF pyrolysis, we succeeded in analyzing gaseous products such as HCN, NH3, and N2
Analysis of Nitrogen-Containing Species in Pyrolysis
quantitatively. On the other hand, only the amount of
HCN was determined by GC in the CPP pyrolysis of
coal. We obtained good nitrogen balance in the IIF
pyrolysis. Coal-N conversion to N2 was high in the IIF
pyrolysis of low rank coals. On the other hand, coal-N
conversion to HCN in CPP pyrolysis was relatively
higher than that in IIF pyrolysis. To compare the
volatility of nitrogen-containing gaseous products under
two different pyrolysis conditions, we calculated the
selectivity of each product according to an assumption
in which nitrogen atoms were distributed uniformly
among each pyrolysis fraction. The selectivity of HCN
is rather high in CPP pyrolysis; on the other hand, in
the case of IIF pyrolysis, selectivity of N2 is large for
low rank coal. Therefore, it is considered that rapid
Energy & Fuels, Vol. 14, No. 1, 2000 189
pyrolysis induced the emission of HCN and the secondary reaction occurred to form N2 in the pyrolysis at
lower heating rates. Finally, the pyrolysis of the model
polymer was performed. It also indicated the influence
of heating rate on the behavior of nitrogen release. Acid
treatment can affect the N conversion to HCN in both
pyrolysis systems in different ways.
Acknowledgment. This work was performed as an
international research grant sponsored by the New
Energy and Industrial Technology Development Organization (NEDO), Japan.
EF9901241