Analysis of Nitrogen-Containing Species during Pyrolysis of Coal at

Department of Applied Chemistry, Faculty of Engineering, Osaka University, 2-1 ... One was an infrared image furnace (IIF) which can heat a sample up ...
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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) Leppa¨lahti, J. Fuel 1995, 74, 1363. (14) Nelson, P. F.; Li, C.-Z.; Ledesma, E. Energy Fuels 1996, 10, 264. (15) Ha¨ma¨la¨inen, 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) Leppa¨lahti, J.; Koljonen, T. Fuel Process. Technol. 1995, 43, 1. (23) Wo´jtowicz, 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.

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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.

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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 (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. Leppa¨lahti 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

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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