Analysis of Nitrogen-Containing Species duringPyrolysis of Coal at Two Different Heating Rates

Koh Kidena, Yoshihisa Hirose, Toshihiro Aibara, Satoru Murata, andMasakatsu 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 speciesduring 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 heatingrate of 10 K/s. The other apparatus was a Curie-point pyrolyzer (CPP) whose heating rate wasaround 3000 K/s. Conversion of nitrogen in coal to HCN from CPP pyrolysis at 1040 °C washigher than that in the case of IIF pyrolysis at 1000 °C. On the other hand, IIF pyrolysisexperiments at 1000 °C produced large amounts of N2 from low rank coals. The results indicatethat heating rate can be one of the dominant factors affecting the behavior of nitrogen release asa range of heating rate applied in this study. The pyrolysis of a nitrogen-containing model polymershowed similar behavior to coal pyrolysis.

Introduction

Many power plants in Japan and other countries arenow using a vast amount of coal as a fuel because theyhave reasonable cost performance and there are inher-ent hazardous problems to construct and operate anuclear power plant. However, coal combustion technol-ogy has to overcome the severe regulation about NOxand SOx emissions since coal contains a few percentagesof heteroatoms such as nitrogen and sulfur. NOx andSOx are, in general, believed to cause both acid rain andphotochemical smog. Recently, regulation of NOx frompower plants or cars is becoming a serious issue and alot of attention is paid to the reduction of NOx.1-3 Thereare three pathways of NOx evolution during combustionof nitrogen-containing fuels in the air: fuel-NOx, thermal-NOx, and prompt-NOx.4,5 Fuel-NOx originates fromnitrogen atoms in the fuel, thermal-NOx is formed bythe reaction between nitrogen and oxygen in the air athigh temperature, and prompt-NOx is produced by thereaction of nitrogen in the air with hydrocarbon species.The suppression of thermal-NOx can be achieved by thedeveloped combustion technique, the so-called advancedcombustion technology,6 and the amount of prompt-NOx

is considered to be small.7-9 Therefore, to reduce NOxemissions from coal combustion, fuel-NOx should besuppressed, and the investigation of mechanisms of fuel-NOx formation from coal is important. The formationof fuel-NOx is considered to occur in two steps: the firststep includes the conversion of nitrogen species in coalto NOx precursors such as HCN or NH3, and thefollowing step is their oxidation under combustionconditions to form NOx.7-9 To clarify the phenomena ofnitrogen release from coal, numerous coal pyrolysisexperiments have been done in various points ofview,5,10-20 and several reviews including evolution ofnitrogen species from coal were published.21-23 However,there is no simple relationship between coal nitrogencontent and the amount of NOx emission. Many re-

* Author to whom correspondence should be addressed. Fax: +81-6-6879-7362. E-mail: nomura@ap.chem.eng.osaka-u.ac.jp.

(1) Lyngefelt, A.; Leckner, B. Fuel 1993, 72, 1553.(2) Shimizu, T.; Tachiyama, Y.; Fujita, D.; Kumazawa, K.-i.; Wakaya-

ma, O.; Ishizu, K.; Kobayashi, S.; Shikada, S.; Inagaki, M. Energy Fuels1992, 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,

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Mayer, M.; Baumann, H.; Bonn, B. Fuel 1995, 74, 1555.

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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) Leppalahti, J. Fuel 1995, 74, 1363.(14) Nelson, P. F.; Li, C.-Z.; Ledesma, E. Energy Fuels 1996, 10,

264.(15) Hamalainen, 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) Leppalahti, J.; Koljonen, T. Fuel Process. Technol. 1995, 43, 1.(23) Wojtowicz, M. A.; Pels, J. R.; Moulijn, J. A. Fuel Process.

Technol. 1993, 34, 1.

184 Energy & Fuels 2000, 14, 184-189

10.1021/ef9901241 CCC: $19.00 © 2000 American Chemical SocietyPublished on Web 11/20/1999

searchers focused their interest on the functionality ofnitrogen in coal. XPS (X-ray photoelectron spectroscopy)is a common technique to investigate nitrogen-contain-ing species in coal.24-27 15N NMR (nuclear magneticresonance) spectroscopy28,29 and XANES (X-ray adsorp-tion near-edge structure)30 have also been used toinvestigate nitrogen functionality in coal. By using theseanalytical techniques, the relationship between thebehavior of nitrogen release from coal and the functionalform of nitrogen in coal was reported. Nelson et al.7concluded that thermal stability of nitrogen species inthe tars obeyed the following order: pyrrolic < pyridinic< cyanoaromatic. Kelemen et al.25 employed XPS mea-surement to identify and quantify the changes inorganically bound nitrogen forms which are present inthe tars and chars after pyrolysis. They found thatpyrrolic nitrogen decreased and nitrogen in graphitictype increased in the char as the temperature increased.However, there are no logical viewpoints to discussnitrogen release from coal.

The distribution of nitrogen-containing gaseous prod-ucts was significantly different among experiments assummarized in the papers,18,21-23 this being partly dueto the different pyrolysis conditions. Ohtsuka et al.11

reported results from pyrolysis in a fixed-bed quartzreactor, showing that the major nitrogen-containinggaseous product was N2. Stanczyk also detected thepredominant formation of N2 by mass spectroscopyduring slow heating of coal.20 On the other hand,Takarada et al.10,12 found that HCN was the mainnitrogen-containing gaseous product in pyrolysis experi-ments by using a pyroprobe. Nelson et al.7 observedHCN and NH3 as nitrogen-containing gaseous productsat a high heating rate in a fluidized-bed reactor. In thepaper above metioned, the differences of experimentalresults may be caused by the variation of coal sampleand pyrolysis conditions including different heat-treat-ment temperature and heating rate. Although thecomparison of data from the pyrolysis at differentheating rates was done in several papers and re-views,18,21-23 only a few coals were used as objects ofthe studies, or the difference of heating rate was toolarge to discuss the effect of heating rate on the pyrolysisproducts. In the present study, the analysis of nitrogen-containing species during pyrolysis of coal at twodifferent heating rates by using a series of the coalsamples was performed in order to investigate the effectof pyrolysis conditions on the pyrolysates. The pyrolysisof a model polymer was also examined with these twopyrolysis techniques.

Experimental Section

Samples. Seven kinds of sample coals were employed inthis study. These samples were provided by Argonne National

Laboratory, Center for Coal Utilization, Japan, and NipponBrown Coal Liquefaction Co. Ltd., Japan. Their analytical dataare shown in Table 1. The samples were pulverized under 100mesh, 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 coalsample was put on the quartz plate at the center of the furnace.The temperautre was monitored by a thermocouple positionedat the center of the furnace and close to the coal particles. Bymonitoring temperature, infrared output was controlled tokeep the programmed temperature. All runs were carried outunder He flow (99.99%, 200 mL/min) after the interior of thefurnace was purged with He for more than 2 h. The nitrogenlevel after purging was checked by using GC (vide infra)connected directly to the furnace, and we observed a small andconstant amount of nitrogen after purging. Then, the samplewas heated to the determined temperature at a heating rateof 10 K/s followed by a 10 s holding time at that temperature.

The char fraction that remained on the quartz plate andthe tar fraction that deposited on the inner surface of thefurnace were collected and weighed to calculate the yield ofeach fraction. The yield of volatile fraction was obtained bysubtracting the weight of char and tar fractions from theweight of initial sample. Nitrogen content of these fractionswas determined by the elemental analysis of each fraction. Allgaseous products were collected into an aluminum gas bagwhich was placed at the exit of the pyrolysis furnace by flowinghelium for 2 h from the beginning of the pyrolysis. Amountsof HCN and NH3 collected in the gas bag were quantified bya gas detector tube (Gastec Co. Ltd.). Yields of N2 wereestimated by on-line GC-TCD (Shimadzu GC-8A) equippedwith Molecular sieve-5A (2 m) stainless steel column underthe following conditions: column temperature ) 70 °C, injec-tion and detector temperature ) 100 °C, and TCD current )180 mA. The nitrogen level in GC analysis increased by afactor of 100 (in maximum) against the level of backgroundnitrogen. Observed background nitrogen may come from a Hebomb or air, but we confirmed that it was constant beforepyrolysis. The amount of nitrogen from pyrolysate was esti-mated by subtracting the area of backgound N2 from theobserved N2 area. Furthermore, the nitrogen level afterpyrolysis decreased exponentially, and it dropped into back-gound level after 2 h. Therefore, the amount of N2 could becalculated 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, JapanAnalytical Industry Co. Ltd., JHP-3), about 1.0-1.5 mg of driedcoal sample was used. The detailed procedure of the pyrolysisis described elsewhere.31 CPP can heat up the sample to thedetermined temperature in 0.3 s. Therefore, the heating ratein CPP experiments was calculated to be 2000-3300 K/s. Theyields of char and tar fractions were obtained by weighingthem, the remainder (weight of coal sample - weights of charand tar fractions) being the volatile fraction. Only HCN couldbe analyzed by GC (Shimadzu GC-14B, with flame thermoionicdetector, FTD) with a fused silica capillary column, Pora PLOTQ (0.53 mm × 25 m). FTD can detect only nitrogen and

(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.(31) Murata, S.; Mori, T.; Murakami, A.; Nomura, M. Energy Fuels

1995, 9, 119.

Table 1. Properties of the Sample Coals

coal C%(daf) N%(daf) ash%(db)

Pocahontas No.3 PC 91.1 1.33 4.8Upper Freeport UF 85.5 1.55 13.2Pittsburgh No.8 PT 83.2 1.64 9.3Miike MK 79.9 1.20 16.0Taiheiyo TH 78.7 1.17 12.6South Banko SB 72.3 1.36 2.7Yallourn YL 65.9 0.63 1.6

Analysis of Nitrogen-Containing Species in Pyrolysis Energy & Fuels, Vol. 14, No. 1, 2000 185

phosphorus-containing organic compounds in higher sensitiv-ity than the TCD by a factor of 106. Gaseous HCN wassynthesized from potassium cyanide (5 mg) and sulfuric acid(0.18 mol/L, 0.2 mL) at 40 °C and used as the standard samplein order to determine the concentration of HCN from GCanalysis. Helium carrier and TCD should be used for theanalyses of N2 and NH3; however, they were not successfulbecause of a trace amount of these products and the detectablelimitation. On the other hand, since the use of N2 (instead ofHe) was appropriate enough to analyze HCN, we determinedto use N2 as a carrier in the CPP experiments. The observedarea of HCN is higher than the limit of detection by a factorof 105.

Results and Discussion

Pyrolysis of Coal with IIF. Pyrolysis of seven kindsof coals was conducted at 1000 °C with IIF. The yieldsof char, tar, and volatile are shown in Figure 1. Weemployed coal samples with a wide range of carboncontent, from C 65.9% for YL coal to C 91.1% for PCcoal. Nitrogen content ranged from 0.6% to 1.6%. Inhigher rank coals such as PC and UF, the yields of charwere high, and lower rank coals, YL and SB, yieldedlarger amounts of volatile. Such tendency was observedin the proximate analyses (volatile matter) data of coal.The resulting char, tar, and gaseous products such asHCN, NH3, and N2 were found to contain nitrogen.Figure 2 presents the nitrogen balance from pyrolysisof coal with IIF. N conversion to each product wascalculated on the basis of nitrogen content in originalcoal and above products as shown in eqs 1-5:

For example, coal-N conversion to char-N was definedas the ratio of the amount of nitrogen in char to that inthe original coal. Figure 2 shows that coal-N conversionto char-N was high with high rank coals, while that to

volatile-N was high with low rank coals. However, YLpyrolysis resulted in higher char-N than SB and TH.This may be caused by the low content of nitrogen inYL, the relatively large error being involved in calcula-tion of N conversion to each product. The cumulativeconversion of nitrogen in the products, nitrogen recoverywas excellent, ranging from 92 to 105%. Therefore, thecontribution of other nitrogen-containing volatile prod-ucts such as nitriles, amines, amides, or pyridine shouldbe small, even if they are present as gaseous products.The plots of coal-N conversion to N-containing gaseousproducts against carbon content of coal are shown inFigure 3. This figure clearly indicates that coal-Nconversion to N2 for low rank coals, YL, SB, and TH,was very high. Although N conversion to HCN wasslightly higher than that to NH3, its rank dependencewas not observed; the coal-N conversions to HCN andNH3 were 3-10% and 2-6%, respectively. In the reviewpapers18,21-23 comparing the results from low and highheating rates, NH3 yield is higher than HCN yield atlow heating rates. The results in this study weredifferent from their results. Ohtsuka et al.16 observedN2 in the pyrolysis of low rank coals, and the heatingrate of their experimental conditions was comparableto our conditions; therefore, we can confirm that lowrank coals generate N2 at a certain heating rate.

To investigate the effect of pyrolysis temperature onthe product distribution and coal-N conversion, IIFpyrolysis experiments of TH coal at 700-1100 °C wereperformed. Both fraction yields and coal-N conversionto gaseous nitrogen-containing products were plottedagainst pyrolysis temperature as shown in Figure 4.

Figure 1. The yield of IIF pyrolysis of the coals at 1000 °Cfor 10 s.

Figure 2. Nitrogen balance of each product after IIF pyrolysisof coal.

Figure 3. Plots of coal-nitrogen conversion to nitrogen-containing gaseous products from IIF pyrolysis at 1000 °C: 4,N2; ], HCN; 0, NH3.

HCN )HCN(mol)

[wt of sample (g)] × %N,raw(db)/100/14(1)

NH3 )NH3(mol)

[wt of sample (g)] × %N,raw(db)/100/14(2)

N2 )N2(mol) × 2

[wt of sample (g)] × %N,raw(db)/100/14(3)

char-N )char yield (wt%, db) × %N,char(db)

%N,raw(db)(4)

tar-N )tar yield (wt%, daf) × %N,tar(daf)

%N,raw(daf)(5)

186 Energy & Fuels, Vol. 14, No. 1, 2000 Kidena et al.

Nitrogen balances for each pyrolysis temperature arenot shown here, but they ranged from 93 to 105%, thesebeing satisfied within the experimental error. As thepyrolysis temperature increased from 700 to 1100 °C,the yield of the volatile fraction slightly increased, andcoal-N conversion to N2 doubled. Coal-N conversion toHCN also increased with pyrolysis temperature. Thoseresults were not contrary to the reported ones: not onlyvolatile fractions but also nitrogen species in coal canrelease more easily during pyrolysis at higher temper-atures. However, coal-N conversion to NH3 did notchange in the temperature range examined here.

Pyrolysis of Coal with CPP. At first, the pyrolysisof TH coal with CPP was conducted at 670, 764, 920,and 1040 °C because we could not choose the pyrolysistemperature arbitrarily due to the limited number ofpyrofoils commercially available in CPP experiments.The yield of volatile fraction from pyrolysis with CPPincreased with temperature and the yield at 1040 °Cwas similar to the volatile yield from IIF pyrolysis at1000 °C. The pyrolysis experiments with CPP wereconducted at 1040 °C using seven kinds of sample coals.The yields of char, tar, and volatile fractions are givenin Figure 5. The yield of each fraction changed depend-ing on coal rank in a fashion similar to IIF pyrolysis.High rank coals showed higher yields of char, while lowrank coals yielded large amounts of volatiles.

We next carried out analysis of HCN in the CPPexperiments. Coal-N conversion to HCN is shown inFigure 6. It ranged from 11 to 23%, and decreased withan increase in coal rank. It is noted that coal-N

conversion to HCN in CPP pyrolysis was higher thanthat in IIF pyrolysis for all the coals studied. Thus, thebehavior of nitrogen release during pyrolysis of coal canbe considered to be different depending on the heatingrate of pyrolysis experiments. Furthermore, the dis-crepancy observed in the distribution of nitrogen-containing gaseous products among the previous reportsby other researchers5,7,8,10-20 seemed to be related to thedifference of pyrolysis conditions, especially heatingrate. Therefore, when we discuss the nitrogen releasefrom coal, we should pay attention to the pyrolysisconditions, especially to the heating rate. The heatingrate in CPP experiments is close to that in pyroprobeby Kambara et al.10,12 Although we could not analyzenitrogen-containing gaseous products other than HCN,the amount of NH3 and N2 are considered to be smallaccording to the results using pyroprobe. In a recentpaper, Takagi et al. found only a small amount of N2 inCPP experiments.32

Influence of the Heating Rate on the Distribu-tion of Pyrolysis Products. The volatile yields weredifferent from coal to coal, therefore, it is not clearwhether the amount of nitrogen-containing gaseousproducts is proportional to the amount of volatilefraction or not. To estimate the distribution of N-

(32) Takagi, H.; Isoda, T.; Kusakabe, K.; Morooka, S. Energy Fuels1999, 13, 934.

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.

Figure 6. N conversion to HCN obtained from the pyrolysiswith CPP at 1040 °C.

Analysis of Nitrogen-Containing Species in Pyrolysis Energy & Fuels, Vol. 14, No. 1, 2000 187

containing gaseous products in the volatile fraction,selectivity of each N-containing gaseous product towardwhole amounts of volatile materials was estimatedaccording to the following assumption: nitrogen atomswere distributed uniformly among each pyrolysis frac-tion. The plots of the selectivity of nitrogen-containingcompounds in gaseous products against carbon contentof coal are shown in Figure 7. Hydrogen cyanideselectivity in CPP pyrolysis reached 50-100%. Thissupports that HCN is the main product among nitrogen-containing gases. Although the coal-N conversion toHCN decreased with an increasing carbon content ofcoal as shown in Figure 6, HCN selectivity was highfor the high rank coal. Therefore, products other thanHCN should be considered as the gaseous species in lowrank 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 gasesdid not reach 1.0 as shown in Figure 7. This indicatesthe assumption for the determination of the selectivityis not correct. Char-N/char-yield was >1.0 in almost allcases examined. Therefore, nitrogen atoms tend to beconcentrated in char fraction with this pyrolysis, espe-cially at lower heating rates. However, we can apply thisassumption in order to discuss the volatility of eachgaseous product in the pyrolysis experiments. In highrank coals, HCN seems to be volatilized easily in bothpyrolysis systems, and N2 selectivity became high forthree low rank coals at low heating rate. Although wecould not analyze N2 and NH3 in CPP experiments,there is significant influence of the heating rate on thedistribution of gaseous products. High selectivity of N2in IIF pyrolysis of low rank coal agrees well with theresults reported by Ohtsuka et al.16 Their pyrolysisconditions were similar to our conditions, and they alsoemployed low rank coals. The heating rate of our IIFexperiments and Ohtsuka’s experiments were relativelylower than that of CPP experiments. It may bring abouta secondary reaction of other species to N2 duringpyrolysis. Leppalahti et al.22 also discussed the effectof heating rate on the distribution of pyrolysate in thereaction system. At low heating rate, residence timebecomes relatively long, and the pyrolysates havechances to react with other fractions. In the presentstudy, since the selectivity of HCN was high in the CPPexperiment and low in the IIF experiment, the following

idea could be proposed: HCN was released from coalas a primary gaseous product, and then it reacted withchar-N or tar-N to generate other species, N2, especiallyin low rank coals.

Pyrolysis of Model Compounds. To investigate thedecomposition behavior of pyridinic and quaternarynitrogen with the two pyrolyzers, we employed modelcompounds such as poly(4-vinylpyridine) (PVP) whichrepresents pyridinic type compounds. Pyrolysis of PVPand acid-treated PVP were conducted. Acid treatmentof the polymer was conducted by stirring the mixtureof 10% HCl(aq) and polymer at room temperature for 2h. The conversion of pyridinic nitrogen in PVP toquaternary (protonated) form was estimated as 85% onthe basis of the atomic ratio of chlorine to nitrogen inthe treated PVP. Table 2 shows the polymer-N conver-sion to nitrogen-containing gaseous products in IIF andCPP pyrolysis experiments. In both pyrolysis experi-ments, polymers pyrolyzed almost completely; char yieldwas approximately zero, and N conversion to gaseousproduct was low. The remainder should be tar fraction.When we analyzed the tar fraction collected, pyridineand its oligomer were observed. Therefore, in thepyrolysis of the model polymer, degradation of thepolymer chain occurred along with the decompositionof the heteroaromatic ring. Influences of heating ratewere also observed in the pyrolysis of the modelpolymer. From Table 2, the N conversion to HCN washigher in CPP pyrolysis than in IIF pyrolysis, this beingsimilar to the results from coal pyrolysis. The resultsindicate that the decomposition of the heteroaromaticring is easy in the rapid heating. In this case, IIFpyrolysis degraded the polymer to oligomer preferably.However, a detectable difference between the pyrolysisof PVP and that of acid-treated PVP was observed: Nconversion to HCN in the IIF pyrolysis of PVP was lessthan the detectable range, while acid-treated PVPgenerated a detectable amount of HCN in IIF pyrolysis.Therefore, decomposition of the heteroaromatic ringoccurred in IIF pyrolysis. However, acid-treatmentaffected N conversion to HCN in different way for thetwo pyrolysis systems. In the present study, althoughwe can mention the discrepancy of pyrolytic behaviorin two different pyrolysis systems, we could not discussthe relationship between the nitrogen form in thepolymer and the product distribution.

Conclusions

By using two different pyrolysis furnaces, an infraredimage furnace (IIF), and a Curie-point pyrolyzer (CPP),the pyrolysis experiments of seven coal samples wereperformed. In the IIF pyrolysis, we succeeded in analyz-ing gaseous products such as HCN, NH3, and N2

Figure 7. The plots of the selectivity of nitrogen in gaseousproducts to whole nitrogen in volatile fraction during thepyrolysis with IIF (open symbols) or CPP (filled symbols): 4,IIF-N2; ], IIF-HCN; 0, IIF-NH3; [, CPP-HCN.

Table 2. N Conversion to N-Containing GaseousProducts in the Pyrolysis of N-Containing Polymer

N conversion (%, coal-N basis)pyrolysis system(conditions)

N-containinggases PVPa PVP + HClb

IIF HCN -c 2.7(1000 °C, 10 s) NH3 0.3 -

N2 - -CPP HCN 5.5 4.0(1040 °C, 3 s)

a Poly(4-vinylpyridine). b 10% HCl(aq)-treated PVP. c Less thandetectable limitation (<0.1%).

188 Energy & Fuels, Vol. 14, No. 1, 2000 Kidena et al.

quantitatively. On the other hand, only the amount ofHCN was determined by GC in the CPP pyrolysis ofcoal. We obtained good nitrogen balance in the IIFpyrolysis. Coal-N conversion to N2 was high in the IIFpyrolysis of low rank coals. On the other hand, coal-Nconversion to HCN in CPP pyrolysis was relativelyhigher than that in IIF pyrolysis. To compare thevolatility of nitrogen-containing gaseous products undertwo different pyrolysis conditions, we calculated theselectivity of each product according to an assumptionin which nitrogen atoms were distributed uniformlyamong each pyrolysis fraction. The selectivity of HCNis rather high in CPP pyrolysis; on the other hand, inthe case of IIF pyrolysis, selectivity of N2 is large forlow rank coal. Therefore, it is considered that rapid

pyrolysis induced the emission of HCN and the second-ary reaction occurred to form N2 in the pyrolysis atlower heating rates. Finally, the pyrolysis of the modelpolymer was performed. It also indicated the influenceof heating rate on the behavior of nitrogen release. Acidtreatment can affect the N conversion to HCN in bothpyrolysis systems in different ways.

Acknowledgment. This work was performed as aninternational research grant sponsored by the NewEnergy and Industrial Technology Development Orga-nization (NEDO), Japan.

EF9901241

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