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Energy & Fuels 2006, 20, 2666-2671
Multi-utilization of Chicken Litter as a Biomass Source. Part II. Pyrolysis Nathan Whitely, Riko Ozao,‡ Yan Cao, and Wei-Ping Pan* Institute for Combustion Science and EnVironmental Technology, Western Kentucky UniVersity, Bowling Green, Kentucky 42101 ReceiVed September 24, 2005. ReVised Manuscript ReceiVed July 16, 2006
To determine optimum conditions for producing activated carbon and carbon black from biomass waste (i.e., chicken litter), studies have been performed on the thermal decomposition changes of chicken litter under a nitrogen atmosphere by evolved gas analysis (EGA) including thermogravimetric mass spectrometry (TGMS), TG-fourier transform infrared (TG-FTIR), and pyrolysis-GC/MS. Samples were prepared by milling and sieving the as-collected chicken litter to obtain three kinds of samples differing in particle size distribution (sample A, above 140 mesh; sample B, 140-325 mesh; sample C, below 325 mesh). Samples A and C were found to show the two extremes in volatile matter to ash content ratios of 54/25% and 35/54%. Thus, to obtain carbon byproducts at a higher yield, decomposition of sample A in nitrogen was studied in particular, and it was found that the process can be roughly divided in four stages. The activation energy, E, was also obtained by kinetic analysis for each of the stages: (I) release of absorbed water and ammonia stemming from ammonium salts (25-160 °C), E ) 100.6 kJ mol-1; (II) devolatilization of mainly lignin and hemicellulose, with evolution of sulfur compounds such as H2S (160-290 °C), E ) 52.11 kJ mol-1; (III) devolatilization of mainly cellulose with evolution of N2O (290-390 °C), E ) 193.9 kJ mol-1; and (IV) decomposition of cellulose (390-500 °C), E ) 242.3 kJ mol-1. Activated carbon can be obtained after stage IV. Ammonia evolution in the lowertemperature regions was attributed to the release from ammonium salts, whereas that in upper-temperature regions was attributed to the decomposition of organic nitrogen compounds.
Introduction I,1
As described in detail in Part animal waste such as chicken litter contains a quite high BTU content per unit mass and can be used as a fuel source.2,3 Animal waste also causes serious environmental concern ranging from water and air pollution to methane emissions, which may contribute to global warming. The best way to solve the animal waste issue is to turn this waste into a useful renewable resource for energy1,4 or a chemical byproduct.5 When pyrolyzed in well-designed reactors, chicken waste can provide activated carbon and carbon black which have many applications in pharmaceuticals, waste absorption, and filler technologies in polymers.6 Attempts have been made to produce charcoals from industrial wastes.7-9 Odorless composites can be produced from chicken wastes.10 * To whom correspondence should be addressed. E-mail:
[email protected]. Phone: +1-270-745-2272. Fax: +1-270-745-2221. ‡ Present address: SONY Institute of Higher Education, Atsugi, Kanagawa 243-8501, Japan. (1) Whitely, N.; Ozao, R.; Chen, Z.; Pan, W.-P. Multi-utilization of Chicken Litter as Biomass Source. Part I. Combustion. Energy Fuels 2006, published online July 12, 20, 2660-2665. (2) Plasynski, S. I.; Goldberg, P. M.; Chen, Z.-Y. Using Animal Waste Based Biomass for Power and Heat Production while Reducing Environmental Risks. Presented at the 19th Annual International Pittsburgh Coal Conference, Pittsburgh, PA, September 23-27, 2002. (3) Miller, B. G.; Miller, S. F.; Scaroni, A. W. Utilizing Agricultural By-Products in Industrial Boilers: Penn State’s Experience and Coal’s Role in Providing Security for our Nation’s Food Supply. Presented at the 19th Annual International Pittsburgh Coal Conference, Pittsburgh, PA, September 23-27, 2002. (4) Ozao, R.; Pan, W.-P.; Whitely, N.; Okabe, T. Coal-like Thermal Behavior of a Carbon-Based Environmentally Benign New Material: Woodceramics. Energy Fuels 2004, 18, 638-643. (5) Ozao, R.; Okabe, T.; Nishimoto, Y.; Cao, Y.; Whitely, N.; Pan, W.P. Gas and Mercury Adsorption Properties of Woodceramics Made from Chicken Waste. Energy Fuels 2005, 19, 1729-1734.
Many studies have been made on the pyrolysis of biomass; Daugaard and Brown11 provide the enthalpy of various types of biomass. Modeling and experiments on the pyrolysis of biomass-coal mixtures have also been reported.12-14 However, these studies have been made mainly on plant-based biomass consisting of lignin, hemicellulose, and cellulose, which are nearly free of sulfur (S), nitrogen (N), phosphorus (P), and metallic compounds. However, the chicken litter in this study collected from local Kentucky chicken farms is a mixture of wood-chips and fecal matter,1 it contains about 4 wt % N and, on an oxide basis, about 2 wt % SO3, 5 wt % P2O5, and other mineral matter, such as CaO, Al2O3, K2O, MgO, etc., which should be taken into consideration in the pyrolytic process. (6) Antal, M. J.; Grønli, M. The Art, Science, and Technology of Charcoal Production. Ind. Eng. Chem. Res. 2003, 42, 1619-1640. (7) Rodriguez-Reinoso, F.; Molina-Sabio, M.; Gonzalez, M. T. The Use of Steam and CO2 as Activating Agents in the Preparation of Activated Carbons. Carbon 1995, 33, 15-23. (8) Gonzalez, M. T.; Rodriguez-Reinoso, F.; Garcia, A. N.; Marcilla, A. CO2 Activation of Olive Stones Carbonized under Different Experimental Conditions. Carbon 1997, 35, 159-162. (9) Daud, W. M. A. W.; Ali, W. S. W.; Salaiman, M. Z. The Effect of Carbonization Temperature on Pore Development in Palm-Shell-Based Activated Carbon. Carbon 2000, 38, 1925-1932. (10) Ozao, R.; Okabe, T.; Nishimoto, Y.; Cao, Y.; Whitely, N.; Pan, W.-P. TG-DTA/GC-MS Study of Odorless Woodceramics from Chicken Wastes. J. Therm. Anal. Calorim. 2005, 80, 489-493. (11) Daugaard, D. E.; Brown R. C. Enthalpy for Pyrolysis for Several Types of Biomass. Energy Fuels 2003, 17, 934-939. (12) Vamvuka, D.; Kakaras, E.; Kastanaki, E.; Grammelis, P. Pyrolysis characteristics and kinetics of biomass residuals mixtures with lignite. Fuel 2003, 82, 1949-1960. (13) Vamvuka, D.; Pasadakis, E.; Kastanaki, E. Kinetic Modeling of Coal/ Agricultural By-Product Blends. Energy Fuels 2003, 17, 549-558. (14) Backreedy, R. I.; Jones, J. M.; Pourkashanian, M.; Williams, A. Burn-out of pulverised coal and biomass chars. Fuel 2003, 82, 2097-2105.
10.1021/ef0503111 CCC: $33.50 © 2006 American Chemical Society Published on Web 09/09/2006
Pylrolysis of Chicken Waste
Energy & Fuels, Vol. 20, No. 6, 2006 2667 Table 1. Sample Identification for the Samplesa
Figure 1. TGA curves for all the samples in nitrogen at a heating rate of 20 °C min-1.
The pyrolysis process of chicken litter was studied by TGA and kinetic analyses, and the mechanism by which the chicken litter decomposes was thoroughly studied by multiple modes of EGA including TG-MS. Furthermore, TG-FTIR was used particularly to distinguish CH4 (MW ) 16) from water (MW ) 18) or NH3 (MW ) 17) and nitrogen N2 (MW ) 28), CO (MW ) 28), or C2H4 (MW ) 28). Pyrolysis GC/MS experiments were used to understand the initial composition of the chicken litter, as well as the relative thermal stabilities of the components, by pyrolyzing at 200 and 700 °C. Experimental Section Samples. Chicken litter samples were the same as those used in Part I 1. Namely, chicken litter dried at 80 °C for 24 h was milled, and the gross sample was run through a 12.5 mm diameter screen and then through a 4 mm screen. The milled gross sample was run through a hand-riffle 4 times; each time half of the sample was discarded until two 32 oz bottles were filled. One 32 oz bottle was marked as the milled sample. The other 32 oz bottle was run through a series of sieves. From the 32 oz bottle were obtained the following three samples differing in particle size at the indicated ratios: sample A, above 140 mesh (87.5 wt %); sample B, 140-325 mesh (6.25 wt %); and sample C, below 325 mesh (6.25 wt %). Thermogravimetry Analysis (TGA). About15-20 mg portions of the samples were subjected to TGA runs using TA Instruments Hi-resolution TGA 2950 under a dry nitrogen gas flow (Airgas NI ED300 nitrogen, extra dry) at a rate of 50 mL min-1. The results obtained at a heating rate of 20 °C min-1 for all the samples are shown in Figure 1. For kinetic analysis, the samples were run at changing heating rates of 2, 5, 10, and 20 °C min-1. TG-MS. Approximately 10 mg litter samples were analyzed by a TA Instruments 2960 simultaneous differential scanning calorimeter (DSC) thermogravimetric analyzer (TGA) (SDT) interfaced to a Fisons VG Thermolab mass spectrometer (MS) by means of a heated capillary transfer line. The details are the same as in Part I1. Ultrahigh-purity nitrogen was the carrier gas for the MS at a flow rate of 50 mL min-1. Thirty minute purges preceded the heating programs, during which the samples were heated from room temperature to 1000 °C at a rate of 20 °C min-1. TG-FTIR. Approximately 25 mg litter samples were analyzed by a DuPont 951 TGA interfaced to a Perkin-Elmer 1600 series FTIR with a permanent 1 in. silicon transfer line. The details are the same as in Part I. 1 The heating from room temperature to 1000 °C was conducted at a heating rate of 20 °C min-1 in the TGA, under ultrahigh-purity nitrogen at a flow rate of 100 mL min-1. FTIR scans were made in the frequency range of 4500-450 cm-1 at approximately 25 s intervals to obtain the temperature (or time) resolved FTIR spectra. In particular, carbon dioxide CO2(g), methane CH4(g), and ammonia NH3(g) were investigated by
mill 32 oz
A 87.5%
B 6.3%
C 6.3%
moisture ash (750C) volatile matter total
10.59 26.58 54.72 91.89
10.43 25.27 54.43 90.13
11.43 34.62 49.25 95.3
9.44 53.85 34.83 98.12
%C %N %H %S %O
29.09 3.44 5.22 0.8 34.99
30.66 3.35 5.07 0.76 34.9
26.13 4.74 4.69 1.28 28.55
16.75 3.68 3.35 1.24 21.14
BTU/lb
5166
5299
4281
2915
34.33 4.75 2.01 12.99 4.39 5.63 11.67 14.79 0.22 0.02 0.02 6.69
% in ash 27.28 3.86 1.65 16.19 4.57 6.52 12.99 17.14 0.11 0.03 0.02 7.14
33.05 5.25 2.14 12.47 5.42 4.59 10.48 16.49 0.25 0.01 0.02 7.33
57.04 6.64 2.29 6.37 3.62 2.22 6.22 8.66 0.6 0.03 0.01 4.58
SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O P2O5 TiO2 BaO SrO SO3 a
For further details, refer to Part I.1
monitoring the IR absorption bands at 2359 (C-O asymmetrical stretching vibration), 3016 (C-H symmetrical stretching vibration), and 965 cm-1(N-H out-of-plane stretching vibration) of the FTIR spectra, respectively. Pyrolysis GC/MS. Approximately 20 mg of sample A, which has the highest concentration of organic material, was analyzed on a LECO Pegasus II GC/MS system, equipped with a time-of-flight mass spectrometer and high-speed gas chromatograph. The helium carrier gas flows through the sample holder of the Thermex system and through a cryogenic trap before entering the inlet port of the GC. The Thermex system heated the sample to 700 or 200 °C at a rate of 50 °C min-1 and held it isothermal for one minute. During the heating segment, the evolved gases are captured by the cryogenic focusing system at -100 °C, while the GC is held idle at 60 °C. At the end of the thermal method, the cryogen trap is heated rapidly to 300 °C flashing the gases into the GC/MS system for analysis simulating a simultaneous injection. Upon introduction of the sample, the GC was heated to 360 °C at a rate of 60 °C min-1. A 10 m HP-10 column was used to separate the compounds. For the identification, reverse search function (i.e., matching with the internal database) was used on the National Institute of Standards and Technology (NIST) 1998 Mass Spectral Database
Results and Discussions Samples. The samples and the characterization methods are the same as those described in Part I.1 The characteristics of the samples are given in Table 1.1 Similar to the oxidation process in Part I, the most extreme sample compositions were represented by samples A and C. That is, sample A had the highest carbonaceous concentration and sample C had the highest ash content with lowest organic matter concentration. The results show that, by sieving off the small particles (less than 45 µm in size) or, more positively, by collecting particles larger than 150 µm in size, useful samples with higher carbon content can be obtained to produce activated carbon with a higher yield. On the other hand, sample C provides information on the mineral matter contained in the original milled product. TGA. Figure 1 shows the TG curves of the samples obtained at a heating rate of 20 °C min-1 and under 50 mL min-1 flow of gaseous nitrogen. Up to ∼110 °C, sample B, having the highest moisture content, yields the highest mass loss of 6.0%,
2668 Energy & Fuels, Vol. 20, No. 6, 2006
Whitely et al.
Table 2. Kinetic Parameters for Temperature Regions I-IV temp ranges
pre-exponential factor log Z (min-1)
activation energy E (kJ mol-1)
I (RT-160 °C) II (160-290 °C) III (290-390 °C) IV (390-500 °C)
15.22 4.686 17.40 19.46
100.6 52.11 193.9 242.3
suggesting release of adsorbed water (see Table 1). Sample C has the lowest moisture content, but yields a considerably high mass loss of about 5.5% up to ∼110 °C, higher by about 1% than the mass loss of 4.6% for sample A. This is discussed in the later sections for TG-MS and TG-FTIR. For the highertemperature ranges of II-IV, the mass loss for the original sample can be obtained by adding 6.25% each of mass losses for samples B and C to 87.5% of the mass loss for sample A. For kinetic analysis, the pyrolytic process was roughly divided by curve separation as described in Part I1 into five temperature ranges (I-V), namely, (I) 25 to ∼160 °C, (II) 160-290 °C, (III) ∼290-390 °C, (IV) ∼390-500 °C, and (V) temperatures higher than 500 °C. The temperature ranges I-IV of sample A were used for kinetic analysis to obtain activation energy, E (Table 2). At temperatures higher than 500 °C, slight oxidation appears dominant on the samples because nitrogen gas unavoidably contains about 20 ppm O2. In the kinetic modeling of a coal/agricultural mixture using olive kernel and straw reported by Vamvuka et al.,12 the biomass was successfully modeled as a mixture of hemicellulose, cellulose, and lignin (i.e., the pyrolysis as a whole was described by independent and parallel first-order reactions of the components). According to their calculation for the pyrolysis of straw, cellulose decomposition initiates at ∼290 °C and attains maximum rate at ∼340 °C, with an activation energy, E, of 232 kJ mol-1 and a log Z of 20.1 min-1, which are close to the values obtained in the temperature regions III-IV. Likewise, lignin decomposition initiates at temperatures lower than 200 °C but lasts for a longer time, with an activation energy, E, of 31 kJ mol-1 and a log Z of 1.55 min-1; hemicellulose decomposition occurs between approximately 190-320 °C with activation energy, E, of 121 kJ mol-1 and a log Z of 11.1 min-1. Temperature region II might be a mixture of lignin and hemicellulose. Grammelis and Kakaras15 also report kinetic parameters for forest residue: E ) 233.8 kJ mol-1 and log Z ) 18.85 min-1 for cellulose and E ) 34.5 kJ mol-1 and log Z ) 1.674 min-1 for lignin. However, they presume the main reaction zone for lignin decomposition is at temperatures higher than 500 °C, which is different from this study. Thus, since the chicken litter is mainly composed of the wood chips used as the bedding material, the main reactions occurring in temperature regions II and III-IV likely correspond to the decomposition of lignin and hemicellulose and cellulose, respectively. Furthermore, kinetic analysis was performed in the same manner as in Part I1 to the main part of the pyrolysis (i.e., temperature region III), by assuming that the rate of reaction dR/dt (where R is the mass fraction) is described by two separable functions of temperature F(T) and fraction f(R)
dR ) F(T)f(R) dt
(1)
The temperature dependence of the reaction rate function F(T) is generally described by the well-known Arrhenius equation
F(T) ) Z exp
(-E RT )
(2)
Figure 2. Overlay of the derivative weight curve (DTG) with selected MS intensity measurements (m/z 44 and 18) for sample A.
where R is the universal gas constant, E is the activation energy, and Z is the preexponential factor. In TGA, the runs were made under a constant heating rate of dT/dt ) β. Thus, eqs 1 and 2 can be rewritten and combined to give
dR Z -E f(R) ) exp dT β RT
( )
(3)
TGA runs with different heating rates (i.e., with different β values) were obtained to determine the kinetic parameters Z and E from the linearized transformation of eq 3 to predict percent conversion at various temperatures
ln
-E Z dR/dT + ) ln β RT f(R)
()
(4)
It has been calculated using TA Instruments software that the reaction in temperature region III completes within 1.5 min at 400 °C. This is in good agreement with Nussbaumer,16 who reported that the devolatilization of 100 mg of beech wood takes about 1 min when heated at a rate of 100 °C min-1. Grammelis and Kakaras15 calculated pyrolysis to last 0.77 s; however, it cannot be compared directly because the calculation is done at a gas temperature of 900 °C. TG-MS and FTIR. Figure 2 shows the overlay of the DTG curve with MS intensities for m/z 44 and 18 for sample A. Figure 3 shows equivalent FT-IR data for sample A. Because the mass spectra for CH4 and NH3 yield the principal peaks at m/z values of 16 and 17, respectively, they cannot be clearly distinguished from the fractions of H2O (m/z 18). From Figure 3, it can be understood that sample A evolves H2O in two stages: the first evolution occurring at temperatures lower than 200 °C is attributed to adsorbed water and loosely bound OH groups; the second one occurs as a result of devolatilization of cellulose and lignin, which covers a broad temperature range to attain peak maximum at ∼350 °C, and it gradually decreases at higher temperatures. Furthermore, from a combination of Figures 2 and 3, it can be understood that gaseous CO2 is evolved in two stages. The first evolution initiates at 200 °C, with a maximum at ∼350 °C, which is concurrent with devolatilization (i.e., decomposition of cellulose and lignin), as stated above, but slightly preceding the H2O evolution as confirmed by the two peaks in DTG (Figure 3), and the second is concurrent to the third broad weight loss. However, the peak intensity for m/z 44 (15) Grammelis, P.; Kakaras, E. Biomass Combustion Modeling in Fluidized Beds. Energy Fuels 2005, 19, 292-297. (16) Nussbaumer, T. Combustion and Co-combustion of Biomass: Fundamentals, Technologies, and Primary Measured for Emission Reduction. Energy Fuels 2003, 17, 1510-1521.
Pylrolysis of Chicken Waste
Figure 3. Change in absorbance for bands at 2359 (CO2), 3016 (CH4), and 965 cm-1 (NH3) of the FTIR spectra obtained for the gas evolved while heating sample A.
Figure 4. Overlay of the derivative weight curve (DTG) with selected MS intensity measurements (m/z 44 and 18) for sample C.
at the higher temperatures does not coincide with the intensity profile observed by FTIR. Propane, C3H8, also has a mass number of 44, but if propane should be present, an increase in methane, CH4, should have been observed by FTIR. It is therefore unlikely to assign m/z 44 to propane. Since N2O also yields an intense peak at m/z 44, it is presumed that N2O is evolved in this temperature range together with CO2. The presence of NO, which yields m/z 30, is difficult to identify because nitrogen used as the carrier gas has m/z 28 near the m/z 30 signal. In Figure 3, NH3 evolution is found to occur in two stages, below 200 °C and between 200 and 400 °C, after which the peak for m/z 44 is observed to increase. Nitrous oxide is often observed in this temperature range for coal pyrolysis,17 and although not clarified yet, NH3 in biomass is believed to contribute to the formation of NOx. Chicken litter contains higher N than wood-based biomass, and as is shown in the GCMS results, amides and nitrogen-containing heterocycles can provide nitrogen sources. It is therefore postulated that NH3 and other N-containing compounds are converted into N2O during pyrolysis, and N2O can be evolved at 400 °C or higher. Figures 4 and 5 show the DTG-MS and FTIR for sample C. In Figure 4, the original MS signals for m/z 44 and 18 are multiplied by 1000× and 70× for clarity. The water evolutions in sample C show a reverse trend in that the initial water evolution is greater than the second. However, the CO2 evolution profiles as observed in the MS spectrum and in FTIR are in good agreement. Thus, in sample C, an intense carbon dioxide (17) Gani, A.; Morishita, K.; Nishikawa, K.; Naruse, I. Characteristics of Co-combustion of Low-Rank Coal with Biomass. Energy Fuels 2005, 19, 1652-1659.
Energy & Fuels, Vol. 20, No. 6, 2006 2669
Figure 5. Change in absorbance for bands at 2359 (CO2), 3016 (CH4), and 965 cm-1 (NH3) of the FTIR spectra obtained for the gas evolved while heating sample C.
Figure 6. Overlay of the derivative weight curve (DTG) with selected MS intensity measurements (m/z 34, 64, and 60) for sample C.
evolution is noted at the onset of devolatilization as in the case of sample A, and several other evolutions occur in the temperature range of 400-1000 °C corresponding to peaks seen within the DTG. These numerous high-temperature mass losses with the release of CO2 are indicative of the decomposition of mineral carbonates contained in soil. Figure 6 shows additional masses present in the pyrolysis of sample C not detected in other experiments. The signal for m/z 34 is representative of hydrogen sulfide (H2S), which may stem from the decomposition of some organic sulfur materials that can be rationalized by the evolution range occurring concurrently with the organic matrix decomposition. Carbonyl sulfide (COS), whose molecular mass is 60, is also taken into consideration; it yields a spectrum at m/z 34 with 60% intensity of the peak at m/z 60. Since the peak intensities are not synchronized, the signal for m/z 34, having a peak in 200-300 °C, indicates the evolution of H2S. Furthermore, the evolution of sulfur dioxide (SO2), which yields peaks at m/z 64 (intensity ) 100) and m/z 48 (intensity ) 47) is also suggested during the decomposition in the same temperature range. The reason signals for m/z 34, 64, 60 were not detected in sample A might be because of the weaker signal intensities as compared with those of m/z 44, 18, etc.. Figure 7 summarizes the temperature range at which the gases were detected. Under pyrolytic conditions, it can be seen that the methane evolution occurs at a higher temperature and over a much broader temperature range, as compared with combustion, and the methane emission appears to be unrelated to carbon dioxide evolution. Thus, in the absence oxygen, the char disproportionates at higher temperatures to release thermody-
2670 Energy & Fuels, Vol. 20, No. 6, 2006
Figure 7. Temperature ranges of gas evolution. The numbers in the parentheses denote the number of peaks, and italic letters, ff, f, m, and w, each denote the intensity from very strong, strong, medium, and weak peaks, respectively.
namically stable methane and leaves hydrogen-depleted char behind. The ammonia emissions are slightly lower in intensity and occur over two broad regions instead of the four pronounced peaks seen in oxidation for sample A. The absence of the very intense evolution of ammonia at approximately 500 °C in combustion1 suggests that the reaction mechanism is different in pyrolysis (i.e., ammonia is released from the decomposition of the organic matrix). A comparison of samples A and C shows that the N content is approximately the same (i.e., 3.35 and 3.68% for A and C, respectively), which is considerably high, compared with woodbased biomass, such as sawdust generally containing about 0.2%
Whitely et al.
N or coal (1-2%). As described above, sample A evolves N2O as the organic matter decomposes, and sample C evolves a large amount of NH3 at lower temperatures, which was also observed in combustion.1 Such ammonia emissions at low temperatures suggest the presence of ammonia salts. Pyrolysis GC/MS. The relatively large number of volatile components contained in the sample required elaborating the spectra, and as described in the Experimental Section, searches were made against the NIST library. Thus, an attempt was made to simplify the pyrolysis GC/MS by extracting the sample using methylene chloride. The compounds identified from methylene chloride extraction GC/MS included hydrocarbons such as pentadecane, undecane, hexadecane; benzene derivatives such as dibutyl phthalate; fatty acids such as dedecanoic acid, tetradecanoic acid, hexanioinic acid, undecanoic acid; and steroids. When the results of the extraction GC/MS are taken into account, Table 3 shows the most abundant compounds identified as possible compounds or classes of compounds from the pyrolysis GC/MS obtained by heating sample A up to 200 and to 700 °C. The major compounds thus detected at 200 °C are not a subset of those found at 700 °C because the rapid heating in pyrolysis GC/MS results in decomposition and recombination of the compounds. However, N-, S-, and Pcontaining compounds are found by pyrolysis GC/MS heating to 700 °C. Nitrogen sources such as 4-amino-1-pentanol and the heterocyclic compounds containing N (e.g., 4-methylpyrimidine, 1H-pyrrole-2-carboxaldehyde, and 2-methyliminoperhydro-1,3-oxazine) were found by heating to 200 °C. These decompose at lower temperatures to provide the sources for NH3 and H2O; on the other hand, acetamide has a boiling point of 221 °C and may remain to higher temperatures. Sulfur source such as H2S and methane thiol (CH3SH), both of which are sources of strong odor, were found by heating to 200 °C. H2S has a strong odor, and methane thiol is known to form during the demethylation of lignin. This also suggests lignin decomposition occurs at temperatures lower than 200 °C. On the other hand, dimethyl sulfone (CH3)2SO2 has a boiling point of 236 °C and is thus found at higher temperatures. Phosphonic
Table 3. Compounds Identified from Pyrolysis GC/MS of Sample A up to 200°C and 700°C heated to 200 °C
heated to 700 °C
water N-containing compounds S-containing compounds
acetamide 4-amino-1-pentanol methane thiol hydrogen sulfide
N-containing compounds
acetamide N-butyl tert-butylamine carbamic
S-containing compounds
dimethyl sulfone
P-containing compounds
phosphonic acid
heterocyclic N-containing
4-methyl-pyrimidine 1H-pyrrole-2-carboxaldehyde 2-methyliminoperhydro-1,3-oxazine
heterocyclic N-containing
heterocyclic O-containing
2-furanmethanol furfural 2(5H)-furanone
heterocyclic O-containing
phenols
2-methoxy-phenol
phenols
2-methyl phenol dimethylated phenols 2,4,6 trimethyl phenol 2-methoxy-4-vinyl-phenol
carboxylic acids
acetic acid 3-methyl butanoic acid hexanoic acid
steroids
cholesterol derivative
others
benzene derivatives, fatty acids
2-methoxy-4-vinylphenol hydroxy-aldehydes
glycidol
carboxylic acids
acetic acid
others
1,2-ethanediol diacetate
2-furanmethanol furfural indole
Pylrolysis of Chicken Waste
acid (H3PO3) was the only P-containing compound identified which is not stable at higher temperatures because it undergoes decomposition at 200 °C. Difficulties were found in identifying P by MS. That is, it may be in the form of a mono-, di-, or tribasic acid, or it may be in the form of mineral apatite, (Ca5(PO4)3F; this requires looking for all the possible m/z values in the range of 95, 79, 63, 48, 32, etc., or m/z 124 for P4, yellow phosphorus, which may be generated by the pyrolysis of apatite at high temperatures. Further studies for phosphorus compounds are yet to be done. Conclusions The thermal decomposition behavior of chicken litter under a nitrogen atmosphere was examined by thermogravimetry analyses combined with evolved gas analysis using mass spectrometry (MS) and Fourier transform infrared spectroscopy (FTIR). Furthermore, the pyrolysis GC/MS was used to identify discrete compounds that evolve from the sample as it decomposes. Since classification of the original biomass produces products with different volatile matter-to-ash ratios, sample A, which has a volatile matter-to-ash ratio of approximately 2, and sample C, which has a ratio of approximately 0.6, were used for the study.
Energy & Fuels, Vol. 20, No. 6, 2006 2671
Chicken litter decomposition process in nitrogen was roughly divided into the following four stages to obtain activation energy, E, by kinetic analysis: (I) release of absorbed water and ammonia stemming from ammonium salts (room temperature-160 °C), E ) 100.6 kJ mol-1, (II) devolatilization of mainly lignin and hemicellulose, with evolution of sulfur compounds such as H2S (160-290 °C), E ) 52.11 kJ mol-1, (III) devolatilization of mainly cellulose with evolution of N2O (290-390 °C), E ) 193.9 kJ mol-1, and (IV) decomposition of cellulose (390-500 °C), E ) 242.3 kJ mol-1. The ammonia evolution in lower temperature regions was attributed to the release from ammonium salts, whereas that in upper temperature regions was attributed to the decomposition of organic nitrogen compounds. Phosphorus was detected by pyrolysis GC/MS, but the source and the decomposition behavior is yet to be clarified. Acknowledgment. This work is supported by the USDA-ARS project 6406-12630-002-02S. EF0503111
