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Colloidal Properties of Bio-oils Obtained by Vacuum Pyrolysis of Softwood Bark. Characterization of Water-Soluble and Water-Insoluble Fractions Tuya Ba, Abdelkader Chaala, Manuel Garcia-Perez, Denis Rodrigue, and Christian Roy* De´ partement de Ge´ nie Chimique, Universite´ Laval, Que´ bec, Que´ bec, Canada, G1K 7P4 Received May 7, 2003. Revised Manuscript Received February 10, 2004
Crude bio-oils obtained via the pyrolysis of bark residues are dark, viscous, and sticky materials that visually appear similar to homogeneous liquids. However, microscopic tests revealed the presence of tridimensional compounds (agglomerates) and solid particles that are dispersed in the continuous bio-oil medium. These materials are responsible for the increase in bio-oil viscosity, the non-Newtonian flow behavior, the poor combustion properties, the corrosiveness, and the increase in the plugging frequency of the nozzles. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) tests, and rheology have been used to evaluate the colloidal properties of the bio-oils. The generic composition of the bio-oil, obtained by extracting water-insoluble materials (i.e., the lignin-derivative compounds), has been determined. The extraction produced a yield of lignin-derivative compounds of 29 wt %. The chemical composition of the water-soluble materials, as well as the molecular weight distribution of the water-insoluble components, has also been determined.
1. Introduction Bio-oils produced by a thermal conversion of biomass are complex mixtures composed of oxygenated organic compounds that contain variable amounts of water and carbonaceous materials and structured compounds. The morphology and the chemical composition of bio-oils are strongly dependent on the pyrolysis process and the nature of the feedstock used. It has been shown that bio-oil from softwood bark residues represents a complex colloidal multidispersed system.1 It simultaneously exhibits emulsion and dispersion patterns. Bio-oils can be separated into water-soluble materials (high-polarity compounds) and water-insoluble materials (low-polarity components). The water-insoluble materials are called lignin-derivative compounds, or pyrolytic lignin.2,3 Depending on the dissolving strength of the continuous medium, which consists of water-soluble compounds, the lignin-derivative molecules can be found in a molecular state or in an associate form. It is well-known that, in the presence of a large amount of water, the ligninderivative molecules spontaneously precipitate.4 Study of the generic composition of the bio-oil (coexistence of water-soluble and water-insoluble materials) and its * Author to whom correspondence should be addressed: Phone: (418) 656-7406. Fax: (418) 656-2091. E-mail address:
[email protected]. (1) Chaala, A.; Garcia, M.; Tuya, Ba.; Roy, C. Colloidal Properties of Bio-Oils Obtained by Vacuum Pyrolysis of Softwood Bark Residue. Presented at the 51st Canadian Chemical Engineering Conference, World Trade and Convention Centre, Halifax, Nova Scotia, October 14-17, 2001. (2) Czernik, S.; Johnson, D. K.; Black, S. Biomass Bioenergy 1994, 7, 187-192. (3) Meier, D.; Scholze, B. Fast Pyrolysis Liquid Characteristics. In Biomass Gasification and Pyrolysis; Kaltschmitt, M., Bridgwater, A. V., Eds.; CPL Press: Newbury, U.K., 1997; pp 431-441.
colloidal behavior may help to determine appropriate methods to produce, handle, store, process, and burn this type of oil. No information on the colloidal properties of bio-oils and only a few data on the chemical composition of lignin-derivative compounds are reported in the literature.5-7 Recently, Oasmaa and co-workers pyrolyzed forestry residues in a fast pyrolysis reactor.8-10 The bio-oil obtained was similar to that obtained via the vacuum pyrolysis of softwood bark residues, in terms of physicochemical and colloidal properties.8 This is due to the presence of bark and resinous needles in the forestry residues. This bio-oil is rich in alkali metals, not stable, and easily separated into bottom and upper layers.9 The influence of the lignin-derivative compounds on bio-oil aging has been put into perspective.10 Refining bio-oils obtained via the vacuum pyrolysis of softwood bark residues is an important issue. Several processing problems seem to be associated with the lignin derivatives (water insolubles). By analogy with asphaltenes, lignin derivatives are assumed to be solvated in the system by the water-soluble molecules, (4) Radlein, D. The Production of Chemicals from Fast Pyrolysis BioOils. In Fast Pyrolysis of Biomass: A Handbook; Bridgewater, A., Czernic, S., Diebold, J. et al., Eds.; CPL Press: Newbury, U.K., 1999; Vol. 1, pp 164-188. (5) Sipila¨, K.; Kuoppala, E.; Fagerna¨s, L.; Oasmaa, A. Biomass Bioenergy 1998, 14, 103-113. (6) Scholze, B.; Meier, D. J. Anal. Appl. Pyrolysis 2001, 60, 41-54. (7) Scholze, B.; Hanser, C.; Meier, D. J. Anal. Appl. Pyrolysis 2001, 58-59, 387-400. (8) Oasmaa, A.; Kuoppala, E.; Gust, S.; Solantausta, Y. Energy Fuels 2003, 17, 1-12. (9) Oasmaa, A.; Kuoppala, E.; Solantausta, Y. Energy Fuels 2003, 17, 433-443. (10) Oasmaa, A.; Kuoppala, E. Energy Fuels 2003, 17, 1075-1084.
10.1021/ef030118b CCC: $27.50 © 2004 American Chemical Society Published on Web 04/27/2004
Bio-oils from Vacuum Pyrolysis of Softwood Bark
where they agglomerate and form micelles. Because the water solubles peptize the lignin-derivative molecules, it seems appropriate to refer to the “macromalecular model” that was suggested by Pfeiffer and Saal.11 Scholze et al.6 indicated that the lignin-derivative compounds have an average molecular weight of 10005000 g/mol. The tendency of softwood to yield lignin derivatives with large molecular weights is greater than that of hardwood. The content of methanol-insoluble materials (MIMs) in softwood-bark-derived bio-oils represents not only solid materials such as charcoal particles, but also waxy materials, including a large percentage of fatty acids. Waxy materials may self-associate in the oil to form micelle-like structures (flocks). These flocks agglomerate, and, because their density is lower than that of the remaining constituent of the oil, they move to the oil/ air interface. There is evidence of the disrupted existence of these flocks at 50-60 °C.1 A rheological study showed that bio-oils have viscoelastic behavior.12 The non-Newtonian character of the bio-oils at low temperature is due to the presence of the flocks, water, and charcoal particles. At high temperature, the flocks dissolve or melt, causing changes in the viscosity of the bio-oil. 2. Experimental Section 2.1. Bio-oil Production. The feedstock used was air-dry softwood bark residues that were obtained from a wood shredding plant (Energex, Lac Me´gantic, Que´bec, Canada). It was composed of ∼31 vol % balsam fir (Abies balsamea), 55 vol % white spruce (Picea glauca), and 14 vol % black spruce (Picea mariana). The average moisture content of the air-dry feedstock at the reactor inlet was 10 wt %. The softwood bark residues were pyrolyzed in a continuousfeed pilot-plant unit (50 kg/h) that was operated by Pyrovac Institute (Que´bec City, Canada). The process is well-documented and has been described in detail elsewhere.13-15 Approximately one ton of the feedstock was fed under vacuum into a 3-m long and 0.6-m-diameter reactor. Inside the reactor, the bark residues are pyrolyzed on two horizontal heating plates. The heating plates are made of tubes in which molten salts circulate and serve as a heating medium. The reactor temperature was set at ∼530 °C, and the average total pressure in the reactor was maintained at 40 kPa (run number H67). During the pyrolysis process, the bark residues are converted to pyrolysis oil, wood charcoal, reaction water, and noncondensable gas. Charcoal was removed from the reactor by a water-cooled screw conveyor system. Pyrolytic vapors and gases were withdrawn from the reactor and sucked toward a (11) Pfeiffer, J. P.; Saal, R. J. Phys. Chem. 1940, 44, 139. (12) Chaala, A.; Garcia, M.; Roy, C. Co-pyrolysis under Vacuum of Bagasse and Petroleum Residue. In Progress in Thermochemical Biomass Conversion; Bridgwater, A. V., Ed.; Blackwell Science, Ltd.: Oxford, U.K., 2001; pp 1349-1363. (13) Roy, C.; Blanchette, D.; Korving, L.; Yang, J.; De Caumia, B. Development of a Novel Vacuum Pyrolysis Reactor with Improved Heat Transfer Potential. In Developments in Thermochemical Biomass Conversion; Bridgwater, A. V., Boocock, D. G. B., Eds.; Blackie Academic and Professional: London, U.K., 1997; pp 351-367. (14) Roy, C.; Morin, D.; Dube´, F. The Biomass PyrocyclingTM Process. In Biomass Gasification and Pyrolysis: State of the Art and Future Prospects; Kaltschmitt, M., Bridgwater, A. V., Eds.; CPL Press: Newbury, U.K., 1997; pp 307-315. (15) Roy, C.; Blanchette, D.; de Caumia, B.; Dube´, F.; Pinault, J.; Be´langer, E.; Laprise, P. In Industrial Scale Demonstration of the PyrocyclingTM Process for the Conversion of Biomass to Biofuels and Chemicals, First World Conference and Exhibition on Biomass for Energy and Industry (Sevilla, Spain, June 5-9, 2000); pp 1032-1035.
Energy & Fuels, Vol. 18, No. 3, 2004 705 two-stage (packed-tower) condensation system, where the heavy bio-oil was condensed in the first tower while a mixture of light bio-oil and pyrolytic water was condensed in the second tower. The bio-oil from the second tower was separated by decantation and then mixed together with the bio-oil from the first tower. The noncondensable gas was burned. 2.2. Bio-oil Filtration. The bio-oil produced contained an average of 2 wt % of solid residue, which was mainly composed of charcoal fines. These fines must be removed because they can wear and plug the fuel injection system. A filtration process was performed batchwise with Whatman filter paper No. 3 (retention size of 6 µm). To accommodate the filtration, the bio-oil was heated at a temperature of 50 °C. 2.3. Bio-oil Characterization. 2.3.1. Physico-Chemical Properties. Physicochemical properties of the samples were measured according to ASTM methods: for density, ASTM D 369; for kinematic viscosity, ASTM D 445-88; for flash point, ASTM D 3828-93; for gross calorific value, ASTM D4809; for water content, ASTM D 1744; and for ash content, ASTM D 482. The apparent viscosity was measured using a Brookfield model LVDV III+ viscometer. The content in MIMs was determined according to the method that was described by Oasmaa et al.16 Conradson carbon residue (CCR) was measured according to ASTM standard test method D 189, and the ash content was determined following ASTM standard test method D 482. The pH values were determined using a Fischer Scientific model Accumet AB15 pH meter. A LECO model CHN-600 elemental analyzer for macroscopic samples (system 785-600) was used for the determination of the carbon, hydrogen, and nitrogen contents of the samples. A LECO model S-144DR elemental analyzer was used for sulfur content determination. Oxygen was calculated by difference. 2.3.2. Molecular Weight Distribution. The molecular weight distribution (MWD) was measured by gel permeation chromatography (GPC), using a Waters model 510 pump with a model 410 refractive index detector. The separation was performed using four Shordex columns in series: AD-802/S, KD-802, AD-802.5/S, and KD-803, with exclusion limits of 5 × 103, 5 × 103, 2 × 104, and 7 × 104, respectively. The columns AD-802/S and AD-802.5/S were 250 mm long, and the columns KD-802 and KD-803 were 300 mm long. All the columns had an internal diameter (i.d.) of 8 mm. The samples were dissolved in N,N-dimethyl formamide (DMF) with 0.04% of lithium bromide and 0.5% of trichloroacetate at a concentration of 10 mg/mL. The samples were filtered (using CHROMSPEC syringe filters that were made of polytetrafluoroethylene (PTFE), with a pore size of 0.45 µm) to avoid plugging of the columns. The analysis was performed at room temperature and a volume of 20 µL was injected for each sample. The same aforementioned DMF solvent was used as the eluent, with a flow rate of 1 mL/min. A series of poly(ethylene glycol)s with molecular weights of 106, 600, 960, 1470, 4250, 7100, and 12600 g/mol was used to calibrate this analysis. The average molecular weights (such as the number-average molecular weight (Mn) and the weight-average molecular weight (Mw)) were calculated automatically, using the GPC “Millennium” software version 3.05 from Waters. 2.3.3. Gas Chromatography-Mass Spectroscopy Analysis. The bio-oil and the water-soluble fraction (WSF) were analyzed via GC (Hewlett-Packard, model 5890). The separation was made using a 30 m × 0.25 mm i.d. HP5-MS fused silica capillary column with a film thickness of 0.25 µm. The GC oven temperature was held at 50 °C for 2 min and then programmed to attain a temperature of 290 °C at 5 °C/min. The injector temperature was 290 °C with split mode. Helium (16) Oasmaa, A.; Leppa¨ma¨ki, E.; Koponen, P.; Levander, J.; Tapola, E. Physical Characterization of Biomass-Based Pyrolysis Liquids. Applications of Standard Fuel Oil Analyses; VTT Publications 306; VTT Energy, Espoo, Finland, 1997; 46 pp + app. 30 pp.
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Ba et al. Table 1. Product Yieldsa (from Run No. H-67) product
yield (wt %)
bio-oilb
26.1 18.9 27.4 27.6
pyrolysis water gas charcoal total a
100
On an anhydrous feedstock basis. b Water-free basis.
Table 2. Methanol-Insoluble Material (MIM) and Solid Contents of the Unfiltered and Filtered Whole Bio-oil
MIM content (wt %) solid content (wt %)
Figure 1. Schematic diagram of the water-insoluble fraction (WIF) extraction. was the carrier gas. The end of the column was directly introduced into the ion source of a Hewlett-Packard model 5970 series mass selective detector (MSD) that was operated in an electron impact ionization mode. Typical mass spectrometry (MS) operating conditions were as follows: temperature of transfer line, 270 °C; temperature of ion source, 250 °C; and electron energy, 70 eV. Data acquisition was performed with personal-computer (PC)-based G1034C Chemstation software and an NBS mass spectra laboratory database. Computerized matches were manually evaluated by comparing mass spectra and retention time with standard compounds, to ensure identification quality. 2.3.4. Generic Composition. Bio-oil was separated into two main products: a water-insoluble fraction (WIF) and a watersoluble fraction (WSF). The experiment was performed according to the method that was described by Scholze et al.6 Three grams of bio-oil was added to 300 mL ice-cooled distilled water drop by drop under strong stirring (5000 rpm). A schematic diagram of the experimental setup is shown in Figure 1. During slow addition of the bio-oil to chilled water, the water-insoluble materials precipitate. The bio-oil/water mixture was continuously stirred for 2 h to precipitate all lignin derivatives. Subsequently, the mixture was filtrated through a Bu¨chner funnel (glass fiber filter, 47 mm in diameter, with a pore size of 0.2 µm), and the substrate was resuspended in water and stirred again for ∼14 h, to further wash out the WSF. Finally, the suspension was filtered and the substrate (WIF) was carefully dried under vacuum at room temperature before weighing. The filtrate (WSF) was later evaporated in a rotary evaporator at 40 °C, to remove water. The WIF and the WSF were analyzed. 2.3.5. Thermogravimetric Analysis. Thermogravimetric analysis (TGA) was performed on a thermogravimetry/differential thermal analysis (TG/DTA) system that was controlled by a microprocessor (Seiko model 220). This system was connected to a data station (Seiko model SSC/5200). Samples of 7-8 mg were heated from room temperature to 600 °C at a constant heating rate of 10 °C/min under nitrogen and air consecutively, with a flow rate of 200 mL/min. 2.3.6. Microscopic Analysis. The samples were analyzed using an optical microscope (Karl Zeiss) that was coupled to a solid-state camera (COHU). The morphology of the samples and the structure dissolution temperature were determined. A drop of sample was placed on a glass slide between adhesive-tape spacers with a cover glass on the top. The sample normal thickness was ∼50 µm (one layer of tape). The microscope was equipped with a 40× magnifying objective with a numerical aperture of 0.65 and binocular eyepieces with 10× magnification. Temperature regulation was provided by an
unfiltered bio-oil
filtered bio-oil
difference
2.30 2.00
0.71 0.55
1.59 1.45
Instec hot stage that was coupled to an Instec model RTC1 control unit. The sample was heated at a rate of 0.5 °C/min from room temperature to 70 °C. After 10 min at 70 °C, the sample was then cooled to room temperature at a rate of 0.5 °C/min. The structure dissolution temperature was reported when the last rodlike structure dissolved. Each experiment was repeated three times. 2.3.7. Differential Scanning Calorimetry Test. A differential scanning calorimetry (DSC) test was performed using a Seiko model Exstar 6000s thermoanalyzer that was interfaced with a computer for data storage and processing. The DSC experiments were conducted with ∼15 mg of sample under a flow of dry nitrogen (50 mL/min). Samples cooled to -30 °C with liquid nitrogen were maintained at this temperature for 10 min and subsequently heated at a linear heating rate of 10 °C/min until 100 °C. The structure dissolution temperature range was measured, and the experiments were repeated three times to obtain the average value. The enthalpy of melting was calculated using the system software. 2.3.8. Rheological Analysis. The rheological tests were performed on the bio-oil in dynamic mode. The dynamic measurements were performed on an ARES rheometer (controlled-strain) from Rheometric Scientific, using a cone with angle of 0.0401 rad and a plate with a diameter of 50 mm. The temperature varied from 30 °C. to 80 °C. A strain sweep has been performed on a large deformation range (10-3-10+2) at a frequency of 3 Hz.
3. Results and Discussion 3.1. Pyrolysis Yields. The vacuum pyrolysis product yields are given in Table 1. The process generated 26.1 wt % bio-oil, 27.6 wt % charcoal, and 27.4 wt % gas. An amount of pyrolytic water (18.9 wt %) that was loaded with 7 wt % soluble organics was also produced. For this test, the lack of mass balance closure was 2.8 wt %. 3.2. Bio-oil Filtration. The effect of the filtration was evaluated by the content in MIMs that were contained in the bio-oil. These materials contained, in addition to the actual charcoal particles, heavy organic waxylike materials. To determine the solid content, the MIM was washed with dichloromethane. The particles that remained on the Millipore glass fiber filter (0.2 µm) after dichloromethane washings represented the solid content. The results of the extraction tests are presented in Table 2. The MIM and solid contents in the bio-oil were reduced by 69% and 72%, respectively, after the filtration. However, bio-oil still contained 0.55 wt % charcoal fines. This content is higher than the limit specified (traces) for gas turbine systems that use conventional fuels as feed. To remove as much fines as possible from
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Table 3. Physicochemical Properties of the Whole Bio-oil property
value
water content density @ 28 °C kinematic viscosity at 50 °C at 80 °C gross calorific value (dry basis) MIM content solid content (CH2Cl2 insolubles) Conradson carbon residue (CCR) pH acidity elemental analysis (anhydrous basis) C H N S ash O (by difference)
13.0 wt % 1188 kg/m3 62 cSt 15 cSt 27.9 MJ/kg 0.71 wt % 0.55 wt % 20.5 wt % 3.00 4.77 g NaOH/100 g oil 62.6 wt % 7.0 wt % 1.1 wt % 350 °C, the residual products of decomposition start to burn. In the first step, the devolatilization, the decomposition, and the oxidation of the major portion of hemicellulose and cellulose-derivatives occurred, which led to the formation of residual tarry products. These products, together with the WIF, then decompose, yielding carbonaceous solid materials. The devolatilization of these solids occurs until the combustion temperature is reached. The DTG showed that the combustion of the carbonaceous solid materials occurred in two steps: the first step at 420 °C, which probably concerns the reactive charcoal, and the second step at 480 °C, which corresponds to the less-reactive charcoal. The TG curves under nitrogen and air intercept at 260 °C. After this temperature, the thermogravimetry under oxygen is higher than that under nitrogen. This may be due to the contribution of the oxygen during the decomposition. In contact with air, the surface of the oil droplet reacts with oxygen and forms a plastic core that prevents the vapor from evolving. The droplet (19) Garcia-Perez, M.; Chaala, A.; Roy, C. J. Anal. Appl. Pyrolysis 2002, 65, 111-136.
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Energy & Fuels, Vol. 18, No. 3, 2004 711
Figure 7. Figure 7. Elastic modulus (G′), viscous modulus (G′′), and complex viscosity (η*) versus strain for the whole bio-oil at different temperatures.
grows under the vapor pressure effect while keeping its spherical form. From time to time, vapors escape from the droplet, disrupting the rigid core, which gets harder and harder. As a result, a rather macroporous carbonaceous residue is formed. At a certain temperature, this residue starts to burn. The combustion occurred in two steps: first, the residue becomes red, catches fire, and stops burning. A fraction of a second later, the residue catches fire again. The residue obtained at the end, which represents the ash content, exhibits the same morphology (spherical form) as the carbonaceous residue. 3.3.7. Microscopic Analysis of the Bio-oil. Microscopic analysis of the whole oil was performed in the temper-
ature range of 25-70 °C by heating and cooling at a rate of 0.5 °C/min. A microphotograph of the whole oil at room temperature is presented in Figure 5a. The bio-oil obtained from softwood bark residues is a multiphase and viscous colloidal system in which the distinction between the continuous medium and the dispersed phase is not obvious. The hollocellulosederived compounds, water, charcoal particles, droplets, and waxy materials form a pastelike structured material (see Figure 5a). Heating of the whole oil has clearly proven the existence of phase separation (see Figure 5b). This is due to the Brownian motion of the droplets. During heating, the droplet motion becomes free, causing
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coalescence, which leads to phase separation. Some droplets solubilize in the matrix after 60 °C. It is important to observe that the charcoal particles have a tendency to move toward the interphase. These particles are concentrated at the interface between the dispersed phase and the matrix (Figure 5b). The measured structure dissolution temperature, the structure precipitation temperature, and the droplet disappearance temperature are listed in Table 8. The structure dissolution temperature represents the temperature at which the final rodlike structure melts. The structure precipitation temperature indicates the temperature at which the first rodlike structure is observed. 3.3.8. Differential Scanning Calorimetry Analysis of the Bio-oil. The DSC curve of the bio-oil is shown in Figure 6. One clear endothermic peak has been observed in the temperature region of 30-60 °C. The endothermic effect is due to the dissolution of the waxy materials, including the fatty acids. These data are in good agreement with the microscopic analysis results. The temperature that corresponds to the endothermic peak (Tp), the melting enthalpy of the three-dimensional structures (∆H), and the structure dissolution temperature (SDT) are reported in Table 9. Three parallel experiments were conducted, to obtain an average value. The SDT measured under the microscope lies in the same range. The glass-transition temperature (Tg) was not observed in this range of temperatures. This may be attributed to the specific nature of the bio-oil components. 3.3.9. Rheological Properties of the Bio-oil. Experimental curves that represent the evolution of elastic modulus (G′), viscous modulus (G′′), and complex viscosity (η*) versus the deformation in the temperature range of 30 °C to 80 °C are reported in Figure 7. The data cannot be recorded in the investigated strain range for all the temperatures used, because of the limited torque range of the rheometer. Figure 7 shows that the bio-oil exhibits a loss-modulus (G′)-dominant behavior, which confirms the presence of three-dimensional structures. The G′(ω) curve at 30 °C contains four regions, including two plateaus. The first region (1 × 10-3-4 × 10-3) presents a plateau, where the response of the material to the deformation is not dependent on the imposed deformation. At these sinusoidal deformations, the three-dimensional structures disassociate/associate in a relatively rapid manner in the formation of networks. In the second region (4 × 10-3-2.5 × 10-1), the curve is very sensitive to the magnitude of the imposed strain history. This is one of the characteristics of weak-link gels, where the yields principally occur through links between flocks.20 The sensitivity to the strain decreases in the third region (2.5 × 10-1-1.3 × 100) which represents the second plateau. In that region, the test introduces minimal modification of the sample morphology. The response to the imposed strain may be affected by the links between flocks and links internal to flocks. In the fourth section, the curves decrease again with a slope lower than that of the second section. The con(20) Shih, W. H.; Shih, W. Y.; Kim, S. I.; Liu, J.; Aksay, I. A. Phys. Rev. A 1990, 42, 4772-4779.
Ba et al.
tinuous shearing may cause the deformation of the droplets, their destruction, and the dispersion of the new droplets that have formed. The viscous modulus (G′′) and the complex viscosity of the bio-oil (η) have the same tendency as the elastic modulus G′. However, at high temperature and high strain, the curves of G′′(ω) and η(ω) present plateaus and have a tendency to converge at higher strains. 4. Conclusion The objective of this work was to study the structural properties of bio-oils that are obtained during the vacuum pyrolysis of softwood bark residues, to provide fundamental background information on the behavior of the bio-oil during processing, storage, and combustion. Bio-oil obtained via the vacuum pyrolysis of softwood bark residues is a multiphase viscous colloidal system that is composed of water-soluble and water-insoluble materials. The elemental composition and the gas chromatography-mass spectroscopy (GC-MS) analysis indicate that the major portion of the polar compounds contained in the whole bio-oil is concentrated in the water-soluble fraction (WSF). The microscopic analysis of the bio-oil reveals the presence of solid particles, structured materials, and droplets, which form a complex colloidal system. Thermogravimetric analysis (TGA) indicated that the water-soluble compounds decompose at a relatively higher temperature than the whole bio-oil and the WSF. This analysis may allow prediction of the generic composition of the bio-oil. Actually, at 292 °C, the residual fraction was 30 wt %. This is in agreement with the content of compounds that are extracted from biooil as the water-insoluble fraction (WIF). The decomposed portion of the bio-oil (70 wt %) is represented by water, hemicellulose, and cellulose-derived compounds, which constitute the WSF. The complete decomposition of the bio-oil yielded a carbonaceous residue of ∼16 wt %. This value is comparable to the Conradson carbon residue value. Additional measurements with different bio-oils are required, however, to achieve a reliable prediction of bio-oil generic composition by the thermogravimetry method. The rheological study is indicative of the fluid regime of the bio-oil and revealed the transformations that occur during frequency or temperature changes. The existence of microstructures revealed by microscopy, differential scanning calorimetry (DSC), and rheology are partly responsible for the non-Newtonian behavior observed at temperatures lower than 40 °C. This behavior changes when the three-dimensional structures that are contained in the bio-oil melt. Acknowledgment. This project has been supported by NSERC. The authors wish to thank the Pyrovac pilotplant team for the pyrolysis test, as well as Mrs. Micheline Gingras and Mrs. Joanne Lagace´ for the laboratory analyses. Thanks are also due to Dr. X. Lu (for the DSC analysis), Dr. J. Yang (for the TGA tests), and Dr. H. Pakdel (for the GC/MS analysis). EF030118B
