202
Energy & Fuels 2009, 23, 202–206
Characterization of Biodiesel and Biodiesel Particulate Matter by TG, TG-MS, and FTIR Yi-Chi Chien,*,† Mingming Lu,‡ Ming Chai,‡ and F. James Boreo§ Department of EnVironmental Engineering and Science, Fooyin UniVersity, Kaohsiung County 831, Taiwan, and Department of CiVil and EnVironmental Engineering and Department of Materials Science and Engineering, UniVersity of Cincinnati, Cincinnati, Ohio 45221 ReceiVed May 23, 2008. ReVised Manuscript ReceiVed October 25, 2008
Biodiesel is a potential renewable and carbon-neutral alternative to fossil fuels, and it is environmentally and economically attractive. This paper studies the decomposition kinetics of biodiesel using thermal gravimetric analysis (TGA) in one-stage pyrolysis. Biodiesel can be decomposed at 119-237 °C. The kinetic parameters for biodiesel pyrolysis were obtained from the TGA experiments. The global rate equation for biodiesel pyrolysis can be expressed as dX/dt ) 2.6 × 107 exp(-16.2/8.314 × 10-3T)(1 - X)0.52 (X denotes the reaction conversion). Characteristics of diesel and biodiesel and the associated diesel particulate matter (DPM) emitted from a nonroad diesel generator were also analyzed by Fourier transform infrared (FTIR) spectroscopic methods. The FTIR spectra of biodiesel showed a CdO stretching band of methyl ester at 1743 cm-1 and C-O bands at 1252, 1200, and 1175 cm-1. Furthermore, the FTIR spectra of DPM were similar to those of the fuels, an indication that the chemical structures of DPM are closely related to the fuel and engine oil properties, consistent with our previous study. The temperature series of 11 fragments have been analyzed in nitrogen, which include m/z 29, 31, 44, 74, 87, 105, 143, 263, 294, 296, and 298. The fragments at m/z 294, 296, and 298 represent the methyl ester components of biodiesel, and the fragment at m/z 44 is carbon dioxide, fragments at m/z 29 and 105 represent aldehyde compounds, and fragments at m/z 87 and 143 are shorter chain methyl esters, all of which can be byproducts from biodiesel combustion. The fragments at m/z 57, 67, 95, and 109 represent hydrocarbon components, which may be fragmented from the long carbon chains of methyl esters, and the fragment at m/z 31 is a methoxy group, which may be fragmented from methyl esters. The information of TG-MS as analyzed above can offer a better understanding of the byproduct formation mechanisms of biodiesel combustion.
1. Introduction With the gradual depletion of fossil fuels, the development of renewable energy sources is of increasing importance. Biodiesel is defined as the monoalkyl ester derivatives of long chain fatty acids, produced from oil crops, waste cooking oil, or animal fat via a relative simple transesterification process. The transesterification process is the reaction of a lipid with a short chain alcohol such as methanol to form esters and byproducts.1-3 Biodiesel is a renewable and biodegrable fuel and is becoming environmentally and economically attractive.1 The biodegradability of biodiesel is evidenced by the much shorter half-life comparing with petroleum diesel. As an example, the half-life of approximately 100 ppm B20 in rainwater is 6.8 days.4 Due to its high solubility and biodegrada* To whom correspondence should be addressed. Tel 011-8867-7830542. Fax 011-8867-782-1221. E-mail
[email protected]. † Fooyin University. ‡ Department of Civil and Environmental Engineering, University of Cincinnati. § Department of Materials Science and Engineering, University of Cincinnati. (1) Conceic¸a˜o, M. M.; Fernandes, V. J.; Arau´jo, A. S.; Farias, M. F.; Santos, I. M. G.; Souza, A. G. Energy Fuels 2007, 21, 1522–1527. (2) Hurley, M. D.; Ball, J. C.; Wallington, T. J.; Toft, A.; Nielsen, O. J.; Bertman, S.; Perkovic, M. J. Phys. Chem. A 2007, 111, 2547–2554. (3) Encinar, J. M.; Gonza´lez, J. F.; Rodrı´guez-Reinares, A. Fuel Process. Technol. 2007, 88, 513–522. (4) Prince, R. C.; Haitmanek, C.; Lee, C. C. Chemosphere 2008, 71, 1446–1451.
tion, biodiesel has a potential to be used in bioremediation to remove oils or polycyclic aromatic hydrocarbons (PAHs) in contaminated soils.5,6 Biodiesel has an energy density that is slightly less than that of petroleum diesel. It has been proven that it is a technically sufficient alternative diesel fuel in the fuel market. In European countries and the United States, biodiesel has been accepted for use in automobiles, ships, and heating systems.7 Generally, biodiesel can be used either as a direct substitute for fossil fuels or blended with different amounts of petroleum diesel in compression-ignition engines without any modification with environmental and economic advantages.8 In a biodiesel/diesel blend, the greater the percentage of biodiesel present, the greater the reduction of air pollution emission observed, except NOx and carbonyls.9,10 Kulkarni and Dalai also have reported that the biodiesel produced from waste cooking oil gives better engine performance and emits less emission when tested on (5) Taylor, L. T.; Jones, D. M. Chemosphere 2001, 44, 1131–1136. (6) Pereira, G.; Mudge, S. Chemosphere 2004, 54, 297–304. (7) Cetinkaya, M.; Karaosmanoglu, F. Energy Fuels 2005, 19, 645– 652. (8) Conceic¸a˜o, M. M.; Fernandes, V. J.; Bezerra, A. F.; Silva, M. C. D.; Santos, I. M. G.; Silva, F. C.; Souza, A. G. J. Therm. Anal. Calorim. 2007, 87, 865–869. (9) Conceic¸a˜o, M. M.; Candeia, R. A.; Silva, F. C.; Bezerra, A. F.; Fernandes, V. J.; Souza, A. G. Renew. Sust. Energy ReV. 2007, 11, 964– 975. (10) Chai, M.; Lu, M. The Proceedings of the 100th A&WMA Annual Conference and Exhibition; 2007; Paper No. 558.
10.1021/ef800388m CCC: $40.75 2009 American Chemical Society Published on Web 12/05/2008
Characterization of Biodiesel and DPM
commercial diesel engines.11 Furthermore, neat biodiesel is free from sulfur and yields a decrease of 48% CO, 55% hydrocarbon, and 53% particulate matter.12 Wang et al. has performed a study that compared exhaust emissions from nine heavy trucks fueled by petroleum diesel and biodiesel blend without engine modification. They have indicated that the heavy duty trucks fueled with biodiesel blend emitted lower particulate matter, CO, and hydrocarbon than the same trucks fueled with No. 2 diesel.13 In addition, it has been reported that the engine performance is almost unaffected by the use of biodiesel or biodiesel/diesel blend.9 Different vegetable oils, such as corn oil, castor oil, sunflower oil, and soybean oil, have been used to produce biodiesel in Brazil. Some thermal behaviors of the corn biodiesel, babassu biodiesel, castor oil biodiesel, and the soybean biodiesel have been investigated. For example, the evaporation temperature of babassu biodiesel starts around 52 and 60 °C in air and nitrogen, respectively.14 Castor biodiesel presents stability up to 150 °C. Its thermal profile may be altered by the decomposition process due to the formation of intermediate compounds.1 Dantas et al. indicates that the activation energy and pre-exponential constant of the corn biodiesel decomposition in synthetic air atmosphere are 73.94-87.65 kJ · mol-1 and from 8.8 × 104 to 3.2 × 106 s-1, respectively.15 Because of the possibility of increasing use of biodiesel, it is important to quantify the kinetics parameters of biodiesel pyrolysis.1,14-16 However, the kinetics of the biodiesel made from soybean, a main feedstock in the United States, is not well understood. In recent years, thermal analysis tools including thermogravimetry (TG) and differential scanning calorimetry (DSC) are becoming important in providing useful information in terms of kinetic parameters, thermal stability, etc.17 Continuous realtime information regarding the weight loss and gaseous emission can be obtained by coupling mass spectrometry to the thermogravimetry (TG-MS).18 It also gives the advantage of avoiding the multistage sample preparation such as the digestion of sample and can provide more detailed information on the decomposition of biodiesel compounds by identifying fragments ions from the original compounds with temperature changing.19 In addition, characteristics of fresh biodiesel and the diesel particulate matter (DPM) emitted from the nonroad engine were also analyzed using Fourier transform infrared (FTIR) spectroscopy. Thus, the objective of this work is to obtain the pyrolysis kinetics of biodiesel using TG analysis and understand (11) Kulkarni, M. G.; Dalai, A. K. Ind. Eng. Chem. Res. 2006, 45, 2901– 2913. (12) Haas, M. J.; Scott, K. M.; Alleman, T. L.; McCormick, R. L. Energy Fuels 2001, 15, 1207–1212. (13) Wang, W. G.; Lyons, D. W.; Clark, N. N.; Gautam, M.; Norton, P. M. EnViron. Sci. Technol. 2000, 34, 933–939. (14) Santos, N. A.; Tavares, M. L. A.; Rosenhaim, R.; Silva, F. C.; Fernandes, V. J.; Santos, I. M. G.; Souza, A. G. J. Therm. Anal. Calorim. 2007, 87, 649–652. (15) Dantas, M. B.; Conceic¸a˜o, M. M.; Fernandes, V. J.; Santos, N. A.; Rosenhaim, R.; Marques, A. L. B.; Santos, I. M. G.; Souza, A. G. J. Therm. Anal. Calorim. 2007, 87, 835–839. (16) Candeia, R. A.; Freitas, J. C. O.; Souza, M. A. F.; Conceic¸a˜o, M. M.; Santos, I. M. G.; Soledade, L. E. B.; Souza, A. G. J. Therm. Anal. Calorim. 2007, 87, 653–656. (17) Chien, Y. C.; Shih, P. H.; Hsien, I. H. EnViron. Eng. Sci. 2005, 22, 601–607. (18) Otero, M.; Dı´ez, C.; Calvo, L. F.; Garcı´a, A. I.; Mora´n, A. Biomass Bioenerg. 2002, 22, 319–329. (19) E´hen, Z.; Nova´k, C.; Sztatisz, J.; Bene, O. J. Therm. Anal. Calorim. 2004, 78, 427–440.
Energy & Fuels, Vol. 23, 2009 203 Table 1. Typical Biodiesel Composition and Energy Content element
analysis (wt %)
carbon hydrogen oxygen nitrogen sulfur chlorine
79.01 12.90 8.04 (balanced) 0.02 not detected 0.03
high heating value
39 594 kJ · kg-1 (17 038 Btu · lb-1)
the fragmentation patterns of biodiesel, which can be used to help interpret byproduct formation in biodiesel combustion studies. 2. Experimental Methods The sample of soybean biodiesel (BD-100, Nexsol biodiesel) used in this study was purchased from Peter Cremer Co. The sample was used as received for TG and was blended with diesel fuel for use in the nonroad diesel engine. Ultimate analysis of the biodiesel sample was determined by OKI Analytical, a commercial laboratory in Cincinnati, OH. Preliminary pyrolysis kinetics of biodiesel was determined using TG (TA Instrument 5100/Dynamic TGA 2950, with the capability of determining weight loss and temperature difference simultaneously). Approximately 4-6 mg of the biodiesel sample was heated from room temperature to 400 °C at heating rates of 3, 5, 8, and 10 °C · min-1, respectively, in 100 mL min-1 high purity nitrogen. When the experiment was finished, the furnace power was turned off but the carrier gas was kept flowing until the furnace was cooled down to room temperature. Aluminum oxide was used as a reference in all TG experiments. The TG-MS experiments were performed simultaneously using a thermogravimeter (STA 409 CD, Netzsch Instruments, Inc.) and a quadrupole mass spectrometer (QMA 400, Balzers Instruments, Inc.). A Skimmer coupling system (Netzsch Instruments, Inc.) is equipped to combine these two instruments together. About 2-8 mg biodiesel was decomposed with TG and the gas products were introduced to the mass spectrometry for obtaining evolution curves. The sample was heated up to 400 °C at a heating rate of 5 °C min-1 in 100 mL min-1 of high purity nitrogen. In addition, the functional groups of biodiesel and DPM were investigated by using FTIR spectroscopy (Nicolet Nexus 870 FTIR, Thermo Electron Corp.). The DPM was collected from a nonroad Generac diesel generator (1992, Model SD080, model No. 92A-03040-S), which operated at 0, 50, and 75 kW for idle, lowload, and high-load modes, respectively. Detailed procedures of DPM collection have been published elsewhere and are briefly described here.20 DPM samples were collected by a high volume sampler at a flow rate of approximately 300 L min-1 with a sampling time of approximately 30 min. Approximately 15 mg of DPM was dissolved in dichloromethane (DCM) solution with sonic vibration for 30 min. Then the solution was concentrated to about 1 mL from which three drops were placed onto a potassium bromide (KBr) pellet for the FTIR analysis. In addition, a droplet of the diesel or biodiesel sample was placed onto a KBr pellet and measured by FTIR spectroscopy. For all spectra reported, a 64 scan data accumulation was conducted at a resolution of 4 cm-1.
3. Results and Discussion 3.1. Ultimate Analysis. Ultimate analysis of the commercial biodiesel sample is shown in Table 1. Note that the biodiesel contains approximately 8% oxygen, which is not present in petroleum diesel. In addition, there was no sulfur detected. The high heating value of the biodiesel is 39 594 kJ kg-1 (17 038 Btu lb-1). (20) Liang, F.; Lu, M.; Keener, T. C.; Liu, Z.; Khang, S. J. J. EnViron. Monit. 2005, 7, 983–988.
204 Energy & Fuels, Vol. 23, 2009
Figure 1. Typical FTIR spectra of the (a) B50, (b) diesel, and (c) biodiesel sample.
Chien et al.
1a,c. The absorbance at 3010 cm-1 indicated the HCdCH bond association, while absorbance at 1376 cm-1 indicated the -CH3 bond. 3.3. Thermogravimetric Analysis. In order to have a better understanding of the biodiesel decomposition, the thermal degradation behavior of the biodiesel molecules was investigated. Typical TG curves of the biodiesel decomposition obtained in this study are shown in the top of Figure 2. Experimentally, the thermal decomposition of biodiesel at heating rates of 3, 5, 8, and 10 °C min-1, respectively, are in a single step that describe the evaporation and decomposition of biodiesel. It is consistent with that of corn-oil biodiesel (produced by the ethanol routes) pyrolysis. However, the decomposition begins at 119-125 °C and is completed at 212-237 °C with no residue left that is lower than that of cornoil biodiesel pyrolysis.15 The heating rate is a crucial factor affecting the decomposition results. The higher heating rate may decrease the distribution of the heat in the biodiesel molecules and make the decomposition start at higher temperature. Thus, the shape of the TG curves, the initial decomposition temperature, and the temperature for a given weight loss are increasing with the increasing heating rates (shown in Figure 2, top). In the bottom of Figure 2, DTG curves of biodiesel decomposition presented one transition in the peak temperature of 183-219 °C. The peak temperature was also increased with the higher heating rate. 3.4. Kinetics Calculation. The kinetic parameters for the pyrolysis of biodiesel molecules were calculated on the basis of weight loss data at different heating rates (from room temperature to 400 °C at 3, 5, 8, and 10 °C min-1). The calculation was based on the classical law of kinetics and the overall rate equation is expressed in the Arrhenius equation
( )
Ea dX ) A exp (1 - X)n dt RT w0 - w X) w0 - wf
( )
Ea RT where t ) time (min), A ) pre-exponential factor (min-1), Ea ) activation energy (kcal mol-1), T ) reaction temperature (K), R ) gas constant, w ) mass of the biodiesel sample at time t, w0 ) initial mass of the samples, wf ) final mass of the samples, X ) conversion, n ) reaction order for the unreacted sample, and k ) rate constant (min-1). The kinetic analysis indicates that the activation energy and pre-exponential constant of the biodiesel sample are 68.75 kJ mol-1 (16.2 kcal mol-1) and 2.6 × 107 min-1, respectively. The activation energy is slightly lower than that of the methanolbased biodiesel (71.51-88.66 kJ mol-1) and ethanol-based biodiesel (80.71-92.84 kJ · mol-1), as reported by an oxidative TG study in Brazil.8 The lower activation energy may be associated with better combustion properties and also as a result of a different feed stock. In addition, the reaction order of the decomposition of biodiesel sample is 0.52. The decomposition of biodiesel molecules can be satisfactorily described by the following rate equation: k ) A exp -
Figure 2. TG curves (top) and DTG curves (bottom) of biodiesel decomposition at heating rates of (a) 3 °C min-1, (b) 5 °C min-1, (c) 8 °C min-1, and (d) 10 °C min-1 in nitrogen.
3.2. Infrared Analysis of Fuels. The FTIR spectra of B50 biodiesel (50% biodiesel and 50% diesel blend), diesel, and B100 biodiesel (100% biodiesel) are shown in spectra a, b, and c of Figure 1, respectively. The main components of diesel are aliphatic hydrocarcons, whose chemical structures are similar to long carbon sides chain of the main components of biodiesel. The aliphatic hydrogen at 2928 and 2856 cm-1 are indicated in Figure 1. The observation of an absorption peak at 727 cm-1 suggested the CH2 out-of-plane bending. In addition, since the biodiesel is mainly monoalkyl ester, the intense CdO stretching band of methyl ester appears at 1743 cm-1. The medium C-O bands at 1252, 1200, and 1175 cm-1 are also expected in Figure
(
)
dX 16.2 ) 2.6 × 107 × exp (1 - X)0.52 dt 8.314 × 10-3T The conversion and reaction time are the important information related to optimize the engine operation conditions. On the other hand, the decomposition temperature is the key factor that affects the exhaust gas distribution.
Characterization of Biodiesel and DPM
Energy & Fuels, Vol. 23, 2009 205
Figure 4. TG-MS plots of selected ions of biodiesel and TG curve.
Figure 3. FTIR spectra of DPM emitted from the (top) diesel and (bottom) biodiesel used in the nonroad diesel engine in the load of (a) 50 kW, (b) 0 kW, and (c) 75 kW.
3.5. Infrared Analysis of DPM. The chemical structure of DPM emitted from the petroleum diesel and biodiesel used in a nonroad diesel engine operated in different loads was also investigated by FTIR spectroscopy (shown in Figure 3, top). In a previous study, we indicated that the chemical composition of DPM emitted from the same diesel engine may be a combination of fuel evaporation and engine oil generated by combustion and is mostly alkanes, PAHs, and carboxylic acids.20 Therefore, the FTIR spectra of DPM bear some resemblance to that of diesel fuel (shown in Figure 3, top and Figure 1), with the exception of the absorbance at 1747 cm-1, which indicated a carboxylic functional group found only in the DPM FTIR spectra. This is consistent with our previous studies that the engine oil contains carboxylic and benzoic acids not present in diesel.20 Furthermore, there was a small peak at 1577 cm-1 that is due to a functional group containing a nitrogen atom. Overall, operation at different loads has not significantly altered the DPM composition, as the FTIR spectra of DPM at different loads appear similar. However, the distributions of individual composition at each load required further study, as FTIR is unable to provide this information. Interestingly, the spectra of DPM emitted from the B50 used in the nonroad engine also bore close resemblance to that of the B50 fuel (shown in Figure 3 bottom). The spectra also showed the same trend in the different operation loads. It is noted that the absorbances at 1648 and 1558 cm-1 were not found in the spectra of B50. It may be due to the monosubstituted amides in the solid state, which may be due to the minor nitrogen composition in the biodiesel fuel.
3.6. Thermogravimetry-Mass Spectrometry (TG-MS) Analysis. The following m/z ratio (mass-to-charge ratio) analyses were obtained from TG-MS to better understand the decomposition mechanisms of biodiesel: 29, 31, 44, 74, 87, 105, 143, 263, 294, 296, and 298. The temperature series of selected MS fragments are shown in Figure 4. It suggests that the decomposition of biodiesel occurs at approximately 120 °C, which is consistent with the previous TG result. The m/z 294, 296, and 298 fragments are considered molecular weight ions of biodiesel components C18:0, C18:1, and C18:2, respectively. The intensities of these three molecular peaks are lower than those of other fragments peaks, which is consistent with MS spectra reference.21 Between 140 and 250 °C, m/z 74 has the highest ion current, followed by m/z 87. The other peaks follow the same trend: increasing under low temperature, showing a peak between 150 and 240 °C, and slightly decreasing under high temperature. The m/z ratios not plotted in Figure 4 include m/z 57 (C4H9+), which may be fragment of alkanes; m/z 41 (C3H5+) and 55 (C4H7+), which may be fragments of alkenes; and m/z 67 (C5H7+), 95 (C7H11+), and 109 (C8H13+), which may be fragments of dienes. Those fragments are from C-C bond cleavage of the long carbon chain of methyl esters, depending on the numbers and locations of the CdC double bonds of the original esters.22 Peaks at m/z 87 (C2H4COOCH3+) and 143 (C6H12COOCH3+) are shorter chain methyl esters, which are also from C-C bond cleavage of the carbon chain of methyl esters. These compounds may be expected from the byproducts of biodiesel decomposition, as the shorter chain esters have been reported.23 A well-known McLafferty rearrangement could occur during the MS analysis due to a six-member ring structure of an intermediate, which will form the ion with m/z 74.24 The mechanism of this rearrangement is shown in Figure 5. The R1 group in the figure could be C12H25, C14H29, C14H27, or C14H25, representing the major fractions of biodiesel composition, such as C16:0, C18:0, C18:1, and C18:2. (21) Mass Spectrometry Data Centre. Eight Peak Index of Mass Spectra; The Royal Society of Chemistry. Nottingham, UK, 1983. (22) Silverstein, R. M.; Webster, F. X.; Kiemle, D. Spectrometric Identification of Organic Compounds; John Wiley & Sons: Hoboken, NJ, 2005. (23) Archambault, D.; Billaud, F. J. Chim. Phys. Phys.-Chim. Biol. 1999, 96, 778–796. (24) McLafferty, F. W. Interpretation of Mass Spectra; University Science Books: Mill Valley, CA, 1980.
206 Energy & Fuels, Vol. 23, 2009
Chien et al.
of oxygenated fuels. Therefore, the TG-MS information may be helpful in understanding the decomposition mechanisms of biodiesel compounds and the potential byproducts formed. Figure 5. Mechanism of McLafferty rearrangement.
Figure 6. Selected TG-MS ions and TG curve.
Peaks at m/z 31 (methoxy, CH3O+) and 263 (C17H31CO+) may be fragments of C-O bond cleavage of C18:2 methyl ester (shown in Figure 6 with other selected MS ions). The pyrolysis of an oxygen-containing compound can result in formaldehyde and similar fragments.25 The m/z 29 fragment represents formaldehyde ion and m/z )105 represents benzalaldehyde ion.26 This is an indication that aldehydes can be formed in biodiesel decomposition and is consistent with observations from engine tests.10,27 In addition to hydrocarbon fragments, the temperature series of CO2 (m/z 44) is also shown in Figure 6 (under nitrogen environment, however, we were not able to track the m/z ratio of CO). CO2 has been reported from pyrolysis of vegetable oil (triglycerides), which have similar structures as methyl esters (biodiesel).28,29 CO2 can be a unique byproduct in the pyrolysis (25) Lu¨ftl, S.; Archodoulaki, V. M.; Seidler, S. Polym. Degrad. Stab. 2006, 91, 464–471. (26) McLafferty, F. W.; Stauffer, D. B. The Wiley/NBS Registry of Mass Spectral Data; John Wiley & Sons: New York, 1989. (27) Krahl, J.; Baum, K.; Hackbarth, U.; Jeberien, H. E.; Munack, A.; Schutt, C.; Schroder, O.; Walter, N.; Bunger, J.; Muller, M. M.; Weigel, A. ASAE Meeting Paper No. 996136, 1999. (28) Idem, R. O.; Katikaneni, S. P. R.; Bakhshi, N. N. Energy Fuels 1996, 10, 1150–1162.
4. Conclusions The chemical functional groups of biodiesel and associated particulate emissions from a nonroad diesel engine have been determined by FTIR spectroscopy. The FTIR spectra of biodiesel showed an CdO stretching band of methyl ester at 1743 cm-1 and C-O bands at 1252, 1200, and 1175 cm-1, respectively. The FTIR spectra of its particulate emissions were largely similar to that of the fuel used. However, compared with diesel fuel, the FTIR spectra of the particulate emissions show the OdC-O functional group at 1747 cm-1 that may be due to the n-alkanoic acids. The absorbances at 1648 and 1558 cm-1 were not found in the spectra of B50 that may be due to the monosubstituted amides formed in solid state in the thermal decomposition process. The thermal behavior of biodiesel decomposition was also investigated in this paper with TG and TG-MS. The activation energy, pre-exponential constant, and reaction order of the pyrolysis of biodiesel sample are 67.75 kJ mol-1 (16.2 kcal mol-1), 2.6 × 107 min-1, and 0.52, respectively. The global rate equation for pyrolysis of the biodiesel can be expressed as dX/dt ) 2.6 × 107 × exp(-16.2/8.314 × 10-3T)(1 - X)0.52 (X denotes the reaction conversion). The temperature series of 11 m/z fragments have been analyzed by means of TG-MS. On the basis of the analysis above, it is expected that smaller esters, CO2, and aldehydes may be found as byproducts of biodiesel pyrolysis. The methoxy group may be fragmented from the methyl ester of biodiesel components, and many hydrocarbon fragments may be expected from the carbon chain of biodiesel components. TG-MS can offer more information on the expected byproducts from biodiesel decomposition in a quicker and simpler way than the actual pyrolytic experiments and may be helpful in understanding the reaction mechanisms of byproduct formation. Acknowledgment. The financial support of the Taiwan National Science Council is gratefully acknowledged. We are also grateful for the help provided by Mr. Michael Starr, University of Cincinnati, with the FTIR analysis and Prof. Soofin Cheng and Mr. ChungShen Kao, Taiwan University, with the TG-MS analysis. EF800388M (29) Adebanjo, A. O.; Dalai, A. K.; Bakhshi, N. N. Energy Fuels 2005, 19, 1735–1741.
