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Ind. Eng. Chem. Res. 1998, 37, 3806-3811
Thermogravimetric Studies on the Kinetics of Rice Hull Pyrolysis and the Influence of Water Treatment Hsisheng Teng* and Yun-Chou Wei Department of Chemical Engineering, National Cheng Kung University, Tainan 70101, Taiwan
Rice hulls were pyrolyzed in a thermogravimetric analyzer in a helium atmosphere to determine the kinetic parameters of devolatilization reactions. The pyrolysis experiments were conducted by heating rice hulls from room temperature to 1173 K at constant heating rates of 3,10, 30, 60, and 100 K/min. The global mass loss during rice hull pyrolysis was successfully simulated by a combination of four independent parallel reactions, the decompositions of four major components in rice hulls: moisture, hemicellulose, cellulose, and lignin. The activation energy for the decomposition of the nonmoisture components was in the order cellulose > hemicellulose > lignin. It was also found in the present study that the pyrolytic behaviors were significantly influenced by water wash prior to pyrolysis. The water wash elevates the peak temperature and the activation energy for the decomposition of each component of rice hulls. The volatile yields resulting from cellulose and hemicellulose decompositions during rice hull pyrolysis increase due to the water treatment, whereas those from lignin decomposition and the char yield decrease. Introduction Agricultural residues, which remain largely unutilized, present a solid waste disposal problem. Among these residues, rice hulls, which are created as byproducts of the rice milling process, are generated in large amounts every year, especially in the Asian and Pacific region, and landfilling is becoming an unacceptable solution for rice hull disposal. Therefore, there is a tremendous need for converting rice hulls into other forms to bring down the demand for landfill sites. Several technologies have been proposed to solve this problem,1-3 using rice hulls as a source for different industrial processes. Among these technologies, combustion of rice hulls would be the most effective way of solving this disposal problem at present, since the technique for hydrocarbon combustion has been welldeveloped. Because of their high energy content, rice hulls are able to play an important role as an energy source. Apart from combustion, pyrolysis has been widely used for converting solid fossil fuels and biomasses into liquid and gaseous hydrocarbons,4-7 a process which results in a solid char residue. The liquid and gaseous products from rice hull pyrolysis can act as a substitute for fossil fuel and chemical feedstocks. The char residue can be used as a source for the production of activated carbon and silicon-containing compounds.3,8 From an environmental and economic standpoint, pyrolysis is a better solution for rice hull disposal, as compared with the combustion process. The study of pyrolysis is gaining increasing importance, as it is not only an important process but also a first step in the gasification or combustion process.9 The detailed kinetics of rice hull pyrolysis are rarely reported in the open literature. Like all other biomasses, rice hulls are mainly composed of cellulose, hemicellulose, * To whom correspondence should be addressed. Telephone: 886-6-2385371. Fax: 886-6-2344496. E-mail: hteng@ mail.ncku.edu.tw.
and lignin.6,8 Numerous researchers10-13 have extensively investigated cellulose pyrolysis kinetics in the past 2 decades. The current state of knowledge in this aspect has been comprehensively discussed in the work by Antal and Varhegyi,6 in which the pyrolysis kinetics were principally interpreted according to results from thermogravimetric analysis. The well-developed thermogravimetric techniques used in cellulose pyrolysis should be applicable to the pyrolysis of rice hulls. The objectives of this study were to determine the kinetic parameters of the global mass loss during rice hull pyrolysis and to simulate the pyrolytic behaviors using the determined parameters. Global kinetics are of interest in modeling solid hydrocarbon decomposition in many applications in which trying to represent the full complexity of the hydrocarbon degradation process makes no sense.14 Global pyrolysis kinetics applied to rice hulls are generally intended to predict the overall rate of volatiles release (i.e., mass loss) from the solid. Although various volatile products are released during pyrolysis, global kinetics are looked to as offering a clue to the key mechanistic steps in the overall rice hull breakdown process. In the limited number of previous studies on rice hull pyrolysis,1-3,8,15 the kinetic parameters reported were associated either with the overall rice hull decomposition or with the decomposition process at different stages. The kinetic data for the decomposition of each major component in rice hulls have never been reported in the literature, and these data are essential to the design of rice hull gasifiers and pyrolysis reactors. The thermal characteristics of both untreated and water-washed rice hulls were explored by thermogravimetric analysis in the present work. It has been reported that the presence of inorganic impurities can dramatically affect the course of cellulose pyrolysis.6 To comprehend how the inorganic species affect the pyrolytic behavior, a water-wash procedure was implemented to extract a portion of mineral matter out of the rice hulls. Acid wash was not recommended6 and thus
S0888-5885(98)00207-3 CCC: $15.00 © 1998 American Chemical Society Published on Web 09/03/1998
Ind. Eng. Chem. Res., Vol. 37, No. 10, 1998 3807 Table 1. Rice Hull Analysis ultimate (wt %, Dry-Ash-Free Rice Hulls) carbon 45 nitrogen 0.93 hydrogen 5.8 oxygen 48 sulfur 0.20 proximatea (wt %, As-Received Untreated Rice Hulls) moisture 1.9 (1.8) volatile matter 61 (66) fixed carbon 24 (18) ash 13 (8.4) a
The data for the water-washed rice hulls are in parentheses.
not employed in the present study, since it is very likely that acid wash would alter the degree of polymerization and crystallinity of rice hulls. Experimental Section The proximate and ultimate analyses of the rice hulls used in this study are shown in Table 1. The contents of C, H, N, O, and S elements in the ultimate analysis were determined by an elemental analyzer (Heraeus, CHN-O-RAPID), and the data presented have been normalized to constitute a sum of 100%. As stated in the preceding section, both the untreated and water-washed rice hulls were investigated in the pyrolysis study. The washing process was executed by stirring rice hulls in 353 K hot water for 2 h. After washing, the treated rice hulls were subjected to vacuumdrying at 323 K for 24 h. The proximate analysis in Table 1 displays the data of both the untreated and water-washed rice hulls. It can be clearly observed from the analysis that there is a weight loss, approximately 6% of the untreated rice hulls, due to the water wash. Pyrolysis of rice hulls was performed in a thermogravimetric analyzer (TGA; Perkin-Elmer TGA 7) under a stream of helium with a flow rate of 40 mL/min. The schematic diagram of this type of TGA has been shown elsewhere.8 A sample of rice hulls was loaded in a sample pan in the heated zone of the TGA, and the temperature in the vicinity of the sample was measured by a small thermocouple probe (type K). Pyrolysis was carried out by heating the sample from room temperature to 1173 K at a fixed heating rate. This was then followed by rapid cooling. Several heating rates (3, 10, 30, 60, and 100 K/min) were employed in this study to explore the devolatilization kinetics. The samples used were in the form of small pieces (1-2 mg/piece) to minimize heat-transfer intrusions and the role of secondary, vapor-solid reactions.6 Masstransfer limitations have been determined to be insignificant in the range of devolatilization rates of interest here; this was confirmed by the fact that the pyrolysis behavior was not affected by changing the gas flow rate. Results The chemistry of rice hulls is complicated, but it can be divided by analytical methods into major components: cellulose, hemicellulose, and lignin.6,15 Under this circumstance, the volatile evolution of rice hull pyrolysis is somewhat similar to the combination of those of the components pyrolyzed at the same conditions. It has been reported in the review work of Antal and Varhegyi6 that the thermogravimetric analysis of biomass at low to moderate heating rates usually
Figure 1. Typical volatile evolution rate and char yield curves for untreated rice hulls pyrolyzed at a heating rate of 30 K/min.
evidences a differential thermogravimetric (DTG) curve resulting from the decompositions of cellulose and hemicellulose. In that study a thermogravimetric experiment combined with a kinetic analysis has been employed to quantitatively determine the amount of volatiles evolved from cellulose and hemicellulose present in a biomass sample. Similar to other previous studies, pyrolysis of rice hulls was conducted in TGA, and examples of the volatile evolution rate and char yield curves for rice hulls pyrolyzed in helium are shown in Figure 1, showing that the pyrolysis process can be approximately described by four distinct devolatilization peaks. The first peak is obviously responsible for the moisture retained in the rice hulls, since its evolution mainly occurs around 373 K. Because rice hulls principally comprise of cellulose, hemicellulose, and lignin, it is likely that the other three peaks can be assigned to the independent decomposition of the three components. Biomass pyrolysis has been successfully modeled by several independent parallel reactions, first-order with respect to the amount of volatile yet to evolve.6 Application of the first-order kinetic model to the present work results in the following expression for the overall reaction:
dV/dt )
∑Vi/dt
(1)
with i ) 1, 2, 3, and 4, and
dVi/dt ) Ai exp(-Ei/RT)(V*i - Vi)
(2)
In the above expressions, Vi is the accumulated amount of evolved volatiles from component i up to time t, V is the sum of Vi, V*i is the ultimate yield of evolution from component i (i.e., at t ) ∞), T is the absolute temperature, R is the universal gas constant, Ai is the preexponential factor, and Ei is the activation energy for the decomposition of component i. If pyrolysis is performed at a constant heating rate, integration of eq 2 gives
∫0T-(Ai/H) exp(-Ei/RT) dT]} and
Vi ) V*i {1 - exp[
volatile yield ) V1 + V2 + V3 + V4 (3) where H is the pyrolysis heating rate. In this approach,
3808 Ind. Eng. Chem. Res., Vol. 37, No. 10, 1998
Figure 2. Deconvolution of the volatile evolution curve for pyrolysis of untreated rice hulls at a heating rate of 30 K/min. The evolution can be divided into four volatile lumps.
Figure 3. Comparison of the volatile evolution rate curves for the untreated (solid line) and the water-washed (dashed line) rice hulls pyrolyzed at a heating rate of 30 K/min.
Table 2. Ultimate Yields of the Volatile Lumps during Rice Hull Pyrolyses at Different Heating Rates
Table 3. Peak Temperatures (Tmax) of the Volatile Lumps during Rice Hull Pyrolyses at Different Heating Rates
heating rate (K/min)
V*1
ultimate volatile yield (wt %, as-received untreated) V*2 V*3 V*4
heating rate (K/min)
3 10 30 60 100
Untreated Rice Hulls 2.1 11 1.9 11 1.9 12 1.6 12 1.7 13
32 31 31 32 30
19 19 18 18 18
3 10 30 60 100
3 10 30 60 100
Water-Washed Rice Hulls 2.0 13 1.8 13 1.8 15 1.8 16 2.2 17
39 39 38 38 35
13 14 14 13 14
3 10 30 60 100
the volatile yield for pyrolysis at 1173 K was used as the total ultimate yield for the model. A nonlinear leastsquares method was used to estimate the first-order kinetic parameters and the ultimate volatile yield for the evolution from each component. Based on the kinetic parameters obtained, the DTG curves were deconvoluted into four independent evolution lumps, and an example of the deconvolution results is shown in Figure 2. The weight fractions of the volatile lumps for the pyrolyses at different heating rates are shown in Table 2, which contains the results for both the untreated and water-washed rice hulls. It can be seen that there is an obvious increase in the yields of lumps 2 and 3 due to the water wash, while the yield of lump 4 decreases. The peak temperature (Tmax) at which the volatile evolution rate reaches a maximum for each lump is shown in Table 3, reflecting that Tmax is a function of the heating rate. The fact that Tmax is affected by the heating rate of pyrolysis has already been reported by many researchers.15,16 Theoretically, if the volatile evolution follows the kinetics shown in eq 2, the value of the peak temperature should increase with an increase in the heating rate, as reflected by the data in Table 3. The influence of water wash on the peak temperature is revealed in Table 3, showing that the peak temperature for each volatile lump generally increases because of the water wash. The comparison
lump1
peak temperature (Tmax, K) lump 2 lump 3 lump 4
Untreated Rice Hulls 319 548 331 570 348 586 363 605 370 617
595 617 635 654 665
644 652 675 703 713
Water-Washed Rice Hulls 316 580 630 327 597 648 355 613 666 369 629 681 375 637 693
651 692 709 729 731
of the DTG curves of the untreated and the waterwashed rice hulls is depicted by an example shown in Figure 3. The results demonstrate that the DTG peaks of different components can be more explicitly distinguished by performing the water wash, especially for the second and third peaks. To determine an activation energy suitable for simulating the decomposition reaction carried out at all heating rates of interest, a technique employed by previous workers17-19 was adopted in the present study. The application of this technique was principally based on the assumption that the time derivative of the DTG peaks would be equal to zero at the peak temperature, and thus the correlation between the heating rate and peak temperature was determined to be
ln[H/(Tmax)2] ) ln(AiR/Ei) - Ei/RTmax
(4)
The details for the derivation of eq 4 have been reported elsewhere.20 According to eq 4, the Ei for the first-order decomposition reactions can be determined from the slope of a linear plot of ln[H/(Tmax)2] versus 1/Tmax at various heating rates. As for the values of Ai, they were not determined according to eq 4 in the present study. In a recent TGA study on cellulose pyrolysis by Antal and Varhegyi,21 they reported that the systematic error in temperature
Ind. Eng. Chem. Res., Vol. 37, No. 10, 1998 3809 Table 4. First-Order Kinetic Parameters of the Four-Lump Model for Rice Hull Pyrolysisa lump 1
a
lump 2
lump 3
lump 4
log Ai (min-1) Ei (kJ/mol) V*i (wt %, as-received untreated)
Untreated Rice Hulls 7.3 ( 0.1 13.9 ( 0.1 48 154 1.8 12
16.6 ( 0.1 199 31
1.7 ( 0.6 34 18
log Ai (min-1) Ei (kJ/mol) V*i (wt %, as-received untreated)
Water-Washed Rice Hulls 7.3 ( 0.1 14.2 ( 0.1 49 165 1.9 15
17.7 ( 0.5 216 38
1.6 ( 0.7 36 14
The ultimate volatile yield for each lump (V*i) is the mean of those determined from different heating rates shown in Table 2.
measurement is important at higher heating rates and suggested that “when the thermal lag is almost constant and not too large, the uncertainty in temperature measurement can be represented as an uncertainty in the value of log Ai”. To give the best fit to the weight loss data, their suggestion was employed in the present study to determine the values of log Ai. The resulting kinetic parameters are shown in Table 4, showing a single value of Ei, obtained from eq 4, and values of log Ai ( δ log Ai, where δ log Ai is the standard deviation of the values of log A employed to fit the data for different heating rates.21 Since the Ei determined is not the true value of the activation energy (they should be relatively similar, however), it is not possible to estimate the temperature uncertainty from δ log Ai. Nevertheless, it is expected that the value of δ log Ai is an increasing function of the thermal lag. The volatile yields during pyrolysis in the TGA are compared with the simulated curves obtained from the first-order kinetic model, using eq 3 combined with the kinetic parameters in Table 4. The model predictions and the experimental data are compared in Figure 4, showing that this model successfully predicts the global mass loss process of the rice hull pyrolysis. Discussion Results in Table 4 show that water wash significantly influences the decomposition behavior of rice hull pyrolysis. The first lump (moisture) evolved with an activation energy of about 50 kJ/mol, which is hardly affected by the water wash process. At pyrolysis temperatures higher than that for moisture evolution, the second and third volatile lumps evolved with higher activation energies, and, as the temperature further increased, the activation energy decreased for the evolution of the fourth lump. It has been stated that the chemistry of rice hulls can be divided into major components: cellulose, hemicellulose, and lignin.6,15 The volatile evolution of rice hull pyrolysis is expected to be somewhat similar to the combination of those of the components pyrolyzed at the same conditions. Antal and Varhegyi6 have reported that the volatile evolution during biomass pyrolysis can be analyzed by assuming that the hemicellulose and cellulose components of the whole biomass decompose independently of one another. They have pointed out that the lower temperature peak of the DTG curve for biomass pyrolysis is associated with hemicellulose decomposition and the other is associated with cellulose. As for the third component, lignin, it decomposes slowly over a very broad range of temperature.22,23 Williams and Besler15 have shown that the DTG curve for the decomposition of lignin extracted from rice hulls has a higher peak temperature than those of hemicellulose and cellulose. Therefore, referring to the preceding interpretation on biomass
Figure 4. Volatile yield during pyrolysis of the untreated (a) and the water-washed (b) rice hulls. The symbols are experimental data (9, 100 K/min; ×, 60 K/min; 4, 30 K/min; b, 10 K/min; [, 3 K/min); the solid line curves are predictions from the four-lump model using parameters shown in Table 4.
pyrolysis, lumps 2-4 in the DTG curve of rice hull pyrolysis displayed in the present study can be assigned to the decompositions of hemicellulose, cellulose, and lignin, respectively. It has been reported that mineral matter naturally present in biomass would catalyze the devolatilization in an unpredictable variety of ways, resulting in the merging of the evolution peaks.6 Results of proximate analysis in Table 1 show that water wash removes roughly 6% of water-soluble material from the untreated rice hulls. In that, a significant portion of removal resulted from the loss of mineral matter, as indicated
3810 Ind. Eng. Chem. Res., Vol. 37, No. 10, 1998
by the reduction of ash content from 13 to 8.4%. The removed mineral matter might have catalyzed the volatile decomposition if they were present in rice hulls. Previous work6 has displayed the ability of water wash to separate the merged DTG peaks by increasing the temperature of cellulose pyrolysis and sharpening its peak. The comparison of the DTG curves of the untreated and the water-washed rice hulls shown in Figure 3 exhibits the sharpening for the hemicellulose as well as the cellulose peaks due to water wash. The figure also shows that the water wash causes an increase of the peak temperatures for the volatile evolution from the hemicellulose, cellulose, and lignin lumps. The increase in the peak temperatures due to the water wash is quantitatively exhibited in Table 3. The data show that the water wash has little influence on the peak temperature for moisture evolution, whereas the peak temperatures for the other lumps increase significantly because of the water wash. The results strongly indicate that the water-soluble mineral matter present in rice hulls catalyzes the decomposition of hemicellulose, cellulose, and lignin components in rice hulls. It can also be noted that the increase in peak temperature is more significant for the decomposition of cellulose (lump 3) than hemicellulose (lump 2). Therefore, water wash not only elevates the peak temperatures but also diverges the DTG peaks of hemicellulose and cellulose decomposition from rice hulls, which facilitates the deconvolution of DTG curves into independent lumps. These effects of water wash on the shape of DTG curves of rice hull pyrolysis are in agreement with that on other biomass pyrolysis reported by previous researchers.6 The proximate analysis results evidence that some hydrocarbon matter is also removed by the water wash, since the amount of mineral matter removed cannot account for the total weight loss (about 6%) due to the wash process. The analysis also shows that the char yield decreases due to the water wash, whereas the volatile yield increases. Because of the reduction in char yield, the water wash possibly removes some hydrocarbon molecules which are water-soluble and contain functional groups capable of promoting cross-linking reactions between the biomass structures to facilitate char formation. The removed hydrocarbon molecules may contain oxygen functional groups, such as carboxyl and hydroxyl, which are water-soluble and appear to play a role in promoting the cross-linking reactions between coal structures during pyrolysis.24 The results in Table 4 show that the ultimate yields of the hemicellulose and cellulose lumps increase with the water wash, whereas that of lignin decreases. A previous study15 has reported that the cellulose and hemicellulose components are mainly responsible for the volatile portion of the pyrolysis product, whereas lignin is the main contributor to the char. Because of the reduction in both char yield and lignin decomposition, it is very likely that parts of the hydrocarbon molecules removed by the water wash are from the lignin in rice hulls. Table 4 shows that the activation energy for the decomposition of the rice hull components is in the order of cellulose > hemicellulose > lignin. This finding is in agreement with the results reported in the literature.15 It has also been reported that the activation energy for the pyrolysis of cellulose present in filter paper and biomass (sugar cane bagasse and wheat straw) lays
between 203 and 237 kJ/mol,6 which is analogous to the pyrolysis of the cellulose component in rice hulls found in the present study. An activation energy of 124 kJ/ mol for hemicellulose decomposition in the temperature range 500-630 K was reported.25 The difference between our data and the reported data in the activation energy for hemicellulose decomposition may result from the difference in pyrolysis temperatures. Another study15 found that the activation energy varied in a range 125259 kJ/mol, with the temperature range and heating rate in pyrolysis similar to those employed in the present work. The results are in agreement with the findings from the present study for the hemicellulose decomposition. As for the decomposition of lignin, the activation energy was found to be 82 kJ/mol in one study,26 and the value was reported to vary within 5693 kJ/mol in another.15 Our data for lignin decomposition are lower than those reported by the previous studies. The inconsistency may be attributed to the presence of mineral matter in rice hulls, which catalyzes the lignin decomposition by lowering the activation energy of the process. Table 4 also reflects that the activation energy for the decomposition of each component of rice hulls was elevated by the wash process, indicating again that the mineral matter removed by water wash is capable of catalyzing the pyrolytic decompositions. The first-order kinetic parameters shown in Table 4 give an excellent simulation of the experimental data for rice hull pyrolysis, as revealed by Figure 4. The determination of activation energies and preexponential factors from eq 4 and the method suggested by Antal and Varhegyi21 displays an application of the simplest model that would both work and give fundamentally correct magnitudes. The proposed independent firstorder reaction model is a compromise between oversimplification (e.g., a single-reaction first-order approach) and unnecessary complexity (e.g., a model with distributed kinetic parameters). The relative simplicity gives this model the potential for applications in the design of industrial biomass-pyrolysis facilities. Furthermore, the final product distribution for gasification or pyrolysis of biomass is principally dictated by the devolatilization, and thus it is essential to know the products as well as the extent of devolatilization at a given temperature. Consequently, the kinetic data presented in the present work, for the pyrolysis of both untreated and waterwashed rice hulls, will provide a basic knowledge of kinetic data on the decomposition, which is essentially required in the design and development of a modern process for rice hull gasification and pyrolysis. Conclusions It has been demonstrated on the basis of this study that the volatiles in rice hull pyrolysis can be divided into four noninteracting lumps which evolve by four independent parallel first-order reactions. The four lumps are assigned to the decompositions of moisture, hemicellulose, cellulose, and lignin, in the order of increasing peak temperature. The pyrolytic behaviors were significantly influenced by water treatment prior to pyrolysis. The peak temperatures and the activation energies of the volatile lumps were elevated due to water wash, indicating that the water wash removed mineral species which are capable of catalyzing the pyrolytic reactions. The volatile yield of rice hull pyrolysis increases due to the
Ind. Eng. Chem. Res., Vol. 37, No. 10, 1998 3811
water treatment, whereas the char yield decreases, reflecting that water wash removes some hydrocarbon molecules which contain functional groups capable of promoting cross-linking reactions facilitating char formation during pyrolysis. It is also demonstrated in the present study that the DTG peaks for hemicellulose and cellulose decompositions during rice hull pyrolysis are sharpened and diverged due to the water wash. Acknowledgment This research was supported by the National Science Council in Taiwan, through Project NSC 87-2214-E-003038. Literature Cited (1) Boateng, A. A.; Fan, L. T.; Walawender, W. P.; Chee, C. S. Morphological Development of Rice-Hull-Derived Charcoal in a Fluidized-Bed Reactor. Fuel 1991, 70, 995. (2) Boateng, A. A.; Fan, L. T.; Walawender, W. P.; Chee, C. S.; Chern, S. M. Kinetics of Rice Hull Char Burnout in a Bench-Scale Fluidized-Bed Reactor. Chem. Eng. Commun. 1992, 113, 117. (3) Vempati, R. K.; Musthyala, S. C.; Mollah, M. Y. A.; Cocke, D. L. Surface Analyses of Pyrolyzed Rice Husk Using Scanning Force Microscopy. Fuel 1995, 74, 1722. (4) Howard, J. B. Fundamentals of Coal Pyrolysis and Hydropyrolysis. In Chemistry of Coal Utilization, Second Supplementary Volume; Elliott, M. A., Ed.; John Wiley and Sons: New York, 1981; Chapter 12, pp 665-784. (5) Solomon, P. R.; Serio, M. A.; Suuberg, E. M. Coal Pyrolysis: Experiments, Kinetic Rates and Mechanisms. Prog. Energy Combust. Sci. 1992, 18, 133. (6) Antal, M. J.; Varhegyi, G. Cellulose Pyrolysis Kinetics: The Current State of Knowledge. Ind. Eng. Chem. Res. 1995, 34, 703. (7) Agblevor, F. A.; Besler, S.; Wiselogel, A. E. Fast Pyrolysis of Stored Biomass Feedstocks. Energy Fuels 1995, 9, 635. (8) Liou, T.-H.; Chang, F.-W.; Lo, J.-J. Pyrolysis Kinetics of Acid-Leached Rice Husk. Ind. Eng. Chem. Res. 1997, 36, 568. (9) Srivastava, V. K.; Jalan, R. K. Predictions of Concentration in the Pyrolysis of Biomass MaterialssI. Energy Convers. Manage. 1994, 35, 1031. (10) Broido, A.; Nelson, M. A. Char Yield on Pyrolysis of Cellulose. Combust. Flame 1975, 24, 263. (11) Bradbury, A. G. W.; Sakai, Y.; Shafizadeh, F. A Kinetic Model for Pyrolysis of Cellulose. J. Appl. Polym. Sci. 1979, 23, 3271. (12) Varhegyi, G.; Antal, M. J.; Szekely, T.; Szabo, P. Kinetics of the Thermal Decomposition of Cellulose, Hemicellulose, and Sugar Cane Bagasse. Energy Fuels 1989, 3, 329.
(13) Varhegyi, G.; Jakab, E.; Antal, M. J. Is the BroidoShafizadeh Model for Cellulose Pyrolysis True? Energy Fuels 1994, 8, 1345. (14) Milosavljevic, I.; Suuberg, E. M. Cellulose Thermal Decomposition Kinetics: Global Mass Loss Kinetics. Ind. Eng. Chem. Res. 1995, 34, 1081. (15) Williams, P. T.; Besler, S. The Pyrolysis of Rice Husks in a Thermogravimetric Analyzer and Static Batch Reactor. Fuel 1993, 72, 151. (16) Raman, P.; Walawender, W. P.; Fan, L. T.; Howell, J. A. Thermogravimetric Analysis of Biomass. Devolatilization Studies on Feedlot Manure. Ind. Eng. Chem. Process Des. Dev. 1981, 20, 630. (17) Kissinger, H. E. Reaction Kinetics in Differential Thermal Analysis. Anal. Chem. 1957, 29, 1702. (18) Reich, L. A Rapid Estimation of Activation Energy from Thermogravimetric Traces. Polym. Lett. 1964, 2, 621. (19) Sˇ esta´k, J.; Sˇ atava, V.; Wendlandt, W. W. The Study of Heterogeneous Processes by Thermal Analysis. Thermochim. Acta 1973, 7, 333. (20) Teng, H.; Lin, H.-C.; Ho, J.-A. Thermogravimetric Analysis on Global Mass Loss Kinetics of Rice Hull Pyrolysis. Ind. Eng. Chem. Res. 1997, 36, 3974. (21) Antal, M. J., Jr.; Varhegyi, G. Impact of Systematic Errors on the Determination of Cellulose Pyrolysis Kinetics. Energy Fuels 1997, 11, 1309. (22) Evans, R. J.; Milne, T. A. Molecular Characterization of the Pyrolysis of Biomass. 1. Fundamentals. Energy Fuels 1987, 1, 123. (23) Evans, R. J.; Milne, T. A. Molecular Characterization of the Pyrolysis of Biomass. 2. Applications. Energy Fuels 1987, 1, 311. (24) Teng, H.; Ho, J.-A.; Hsu, Y.-F.; Hsieh, C.-T. Preparation of Activated Carbons from Bituminous Coals with CO2 Activation. 1. Effects of Oxygen Content in Raw Coals. Ind. Eng. Chem. Res. 1996, 35, 4043. (25) Chornet, E.; Roy, C. Compensation Effect in the Thermal Decomposition of Cellulosic Materials. Thermochim. Acta 1980, 35, 389. (26) Nunn, T. R.; Howard, J. B.; Longwell, J. P.; Peters, W. A. Product Compositions and Kinetics in the Rapid Pyrolysis of Milled Wood Lignin. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 844.
Received for review April 2, 1998 Revised manuscript received June 29, 1998 Accepted July 9, 1998 IE980207P
