Characterization of Japanese cedar bio-oil produced using a bench-scale auger pyrolyzer
© Kato et al. 2016
Received: 6 November 2015
Accepted: 15 February 2016
Published: 1 April 2016
A bench-scale auger reactor was designed for use as a laboratory-scale fast pyrolyzer for producing bio-oil from Japanese cedar. An analytical pyrolysis method was performed simultaneously to determine the distribution of pyrolysis products. The pyrolysis temperature was found to have the greatest influence on the bio-oil characteristics; bio-oil yields increased as the pyrolysis temperature increased from 450 to 550 °C. The concentration of levoglucosan in the bio-oil, however, decreased significantly with increasing pyrolysis temperature, while it increased following analytical pyrolysis. The same results were obtained for 4-vinylguaiacol and E-isoeugenol, which were the major secondary products produced in the present study. Compared to the yields of these major products obtained via analytical pyrolysis, the yields from the auger reactor were very low, indicating that the auger reactor process had a longer vapor residence time than the analytical pyrolysis process, resulting in the acceleration of secondary reactions of the pyrolysates. The pH values and densities of the bio-oils produced in the auger reactor were similar to those reported by researchers using woody biomass, despite their lower viscosities. From these results, it was concluded that the pyrolysis temperature and residence time of the pyrolysates played a significant role in determining the characteristics of the cedar bio-oil.
KeywordsBench-scale auger reactor Bio-oil Japanese cedar Pyrolysis temperature Secondary reaction Vapor residence time
Bio-oil produced via lignocellulosic biomass pyrolysis is considered to be a substitute for fuel oil and diesel in many static applications, such as boilers, furnaces, engines, and turbines for electricity generation and chemical production (Bridgwater 2003). Bio-oil can be produced from wood, bark, agricultural wastes/residues, nuts and seeds, algae, grasses, forest residues, and cellulose and lignin. The differences in the properties of these feedstocks influence the properties of the obtained bio-oils (Mohan et al. 2006). In addition, several important biomass pyrolysis parameters affect bio-oil production: the heating and heat transfer rate, reaction temperature, residence time of the produced vapor, and cooling rate of the vapor (Bridgwater 2003). Reactors used for bio-oil production mainly consist of bubbling fluidized-bed reactors, circulating fluidized bed and transported bed reactors, vacuum pyrolysis reactors, ablative reactors, and auger reactors (Mohan et al. 2006; Bridgwater 2012). In addition, three processes can be used for biomass pyrolysis: slow pyrolysis, intermediate pyrolysis, and fast pyrolysis. They differ based on the residence time of the generated vapor, which leads to different yields of the liquid pyrolysis products contained in the bio-oil (Bridgwater 2012).
Woody biomass is a key potential feedstock for bio-oil production, and most processes have been performed using wood (Ingram et al. 2008). One of the most important plantation species, Japanese cedar (Cryptomeria japonica), accounts for approximately 60 % of the plantation forests in Japan. Currently there is a growing demand to thin these forests (Baba et al. 2011). However, thinned cedar woods are largely left behind as forest residue and not utilized, which leads to reduced thinning activities. Conversely, the thinned woods are available as feedstock for biomass pyrolysis, and therefore their use in bio-oil production may promote additional forest thinning. Japanese cedar pyrolysis has been studied by several researchers. Asmadi et al. (2010) compared the pyrolysis of cedar (softwood) and Japanese beech wood (hardwood) using a closed small ampoule reactor (nitrogen atmosphere, reaction temperature 600 °C, heating time 40–600 s). They described the secondary char formation, char reactivity, tar formation, and subsequent decomposition for both wood species. Chang et al. (2012) pyrolyzed cedar sawdust in a bubbling fluidized-bed reactor in order to evaluate the effects of condensers (with and without spraying) and different fluidizing gases (pyrolysis gas and nitrogen gas) on product yields. They reported that sawdust pyrolysis at 460 °C in pyrolysis gas with spraying in a condenser led to a maximum bio-oil yield.
Of the various pyrolysis reactors used for bio-oil production, auger pyrolysis reactors have a compact design, a lower carrier gas flow, and lower process temperatures (Mohan et al. 2006). Some studies of bio-oil production from woody biomass using auger pyrolysis reactors have been conducted. Ingram et al. (2008) pyrolyzed pine wood, pine bark, oak wood, and oak bark at 450 °C and characterized the physical and chemical properties of the produced bio-oils. Puy et al. (2011) examined the pyrolytic characteristics of pine woodchips from forest residues of two different species at different reaction temperatures, different solid residence times, and different biomass flows, evaluating the process performance, the chemical properties, and the composition of the pyrolysis products. Brown and Brown (2012) pyrolyzed red oak wood and investigated various process parameters, including the heat carrier inlet temperature and mass flow rate, the rotational speed of the screws in the reactor, and the volumetric flow rate of the sweep gas for system optimization. Kim et al. (2014) pyrolyzed pine wood at 500–550 °C using a semi-pilot scale reactor equipped with multistage condensers and characterized the bio-oil generated from each condenser. In these studies, two types of auger reactors were used: single-screw (Ingram et al. 2008; Puy et al. 2011; Kim et al. 2014) and twin-screw (Brown and Brown 2012). The former has a simpler design than the latter, which requires a heat carrier for heat transfer to the feedstock (Brown and Brown 2012). In the present study, a single-screw reactor with a simpler design and no need for a heat carrier was used in the first step of bio-oil production.
Typical fast pyrolysis processes involve short vapor residence times of less than 2 s (Bridgwater 2012). Long vapor residence times cause secondary reactions of the pyrolysis products, which provide products similar to those obtained via fragmentation reaction at high pyrolysis temperatures (Collard and Blin 2014). These fragmentation and secondary reactions of cellulose and hemicellulose during pyrolysis produce low-molecular-weight products, such as formaldehyde, methanol, acetaldehyde, acetone, glycolaldehyde, and acetol (Shen and Gu 2009; Asmadi et al. 2010; Shen et al. 2010; Branca et al. 2013). Lignin pyrolysis at high temperatures affords phenols and catechols via secondary reactions (Asmadi et al. 2010). These reactions can also increase the yield of non-condensable gases, such as CO, CO2, H2, and CH4 (Shen and Gu 2009; Asmadi et al. 2010; Patwardhan et al. 2011). Enhanced CO formation during cellulose and hemicellulose pyrolysis at elevated temperatures has been reported (Shen and Gu 2009; Shen et al. 2010; Qu et al. 2011). Conversely, the formation of CO2 decreased at elevated temperatures during cellulose pyrolysis (Qu et al. 2011). The release rates for CH4 and H2 were observed to reach a maximum at 500–600 °C and ~600 °C, respectively, during lignocellulose pyrolysis (Yang et al. 2007). Furthermore, the gas yield from wood pyrolysis was observed to increase at longer vapor residence times (Asmadi et al. 2010). The formation of CO was also promoted at longer vapor residence times during cellulose pyrolysis (Shen and Gu 2009). The suppression of secondary reactions is also important for bio-oil production via fast pyrolysis (Mohan et al. 2006).
The objective of the present study was to evaluate the effects of pyrolysis temperature on the properties of bio-oil obtained from Japanese cedar. In addition, the pyrolysis reactions for cedar bio-oil production using a bench-scale auger reactor were compared to those of an analytical fast pyrolysis process.
Results and discussion
Properties of the Japanese cedar feedstock
Proximate and ultimate analysis of Japanese cedar woodchip prepared from whole trunk
Proximate analysis (wt%)
Ultimate analysis (wt%)
The results of the ultimate analysis performed in the present study are similar to those for Japanese cedar wood meal reported by Phuphuakrat et al. (2010).
Effect of pyrolysis temperature on the yields of char, gas, and bio-oil
Yield of char, gas, and bio-oil produced from cedar using auger reactor at various pyrolysis temperatures
Pyrolysis temperature (°C)
Yield (wt% of dry feedstock)
Cedar bio-oils produced in the auger reactor were collected directly from the bottoms (without ethanol washing) of two cyclones cooled at different temperatures (see Fig. 1). After each cedar bio-oil production run, greater than 90 % of the total bio-oil yield was obtained from Cyclone-1. Therefore, the bio-oils collected from the bottom of Cyclone-1 were used to determine their physical and chemical properties. Kim et al. (2014) produced pine bio-oil using an auger reactor combined with three condensers; the first and second condensers were equipped with heat exchangers, and third condenser was cooled to ~25 °C. They reported that the total bio-oil yield from the three condensers reached 59.8 wt% of the feedstock.
Effect of pyrolysis temperature on the physical properties of the bio-oil
Physical properties of cedar bio-oils produced at various pyrolysis temperatures
Pyrolysis temperaturea (°C)
Moisture content (wt%)
Viscosity (mPa s)
The physical characteristics of typical wood bio-oils (at 40 °C and 25 % water) are as follows: density, 1.20 kg/L; pH, 2.5; and viscosity, 40–100 mPa s (Bridgwater 2003). The cedar bio-oils collected in the present study had density and pH values similar to those for typical bio-oils, but lower viscosities, which were influenced by their higher moisture contents. This result is in agreement with those of Lou et al. (2004), who produced bio-oils from four different types of plant biomass and found that bio-oil with high moisture, which was produced from rice straw, contents had lower kinetic viscosity values.
Molecular weight distribution of cedar bio-oils produced at various pyrolysis temperatures
Pyrolysis temperaturea (°C)
Identification of the pyrolysis products in the cedar bio-oil
Major pyrolysis products identified in chromatograms of cedar bio-oil produced at 500 °C and analytical cedar pyrolysis at 500 °C
Effect of pyrolysis temperature on the gas composition
Chemical compositions of gases yielded by cedar pyrolysis at various pyrolysis temperatures
Pyrolysis with auger reactor (°C)
Gas composition (vol%)a
Analytical pyrolysis (°C)
Effect of pyrolysis temperature on the chemical properties of the bio-oil
An increased pyrolysis temperature from 450 to 550 °C decreased the area percentages for the major pyrolysis products in the bio-oil, except for acetaldehyde, methanol, acetol, acetic acid, and phenol (Fig. 3a–d). The concentrations of the first four products increased when the temperature increased from 450 to 500 °C (Fig. 3c), while that of phenol increased when the temperature was raised from 450 to 550 °C (Fig. 3d). These pyrolysates are produced via fragmentation and/or secondary reactions (Shen and Gu 2009; Asmadi et al. 2010; Branca et al. 2013). It should be noted that the effect of the pyrolysis temperature on the yields of pyrolysates was different for the analytical cedar pyrolysis and cedar bio-oil production processes. The yield of levoglucosan increased during analytical cedar pyrolysis when the temperature was raised from 450 to 550 °C (Fig. 3e). Furthermore, the yields of acetol and acetic acid were lower following analytical pyrolysis (Fig. 3f, g) than were observed in the cedar bio-oil (Fig. 3b, c). The auger reactor had a longer vapor residence time than that of the micro-pyrolyzer used for analytical pyrolysis, which may have promoted secondary reactions of the pyrolysates in the vapor phase in the former. Notably, levoglucosan produced via cellulose pyrolysis is thermally decomposed in the vapor phase by secondary reactions (Hosoya et al. 2008; Ronsse et al. 2012). These results indicate that the different effects of the pyrolysis temperature on the yields of pyrolysates were due to fragmentation and secondary reactions. Conversely, the guaiacol yields in the cedar bio-oil were lower than those for analytical cedar pyrolysis (Fig. 3d, h), which may be affected by the collectability of the bio-oil from the auger reactor because the bio-oil has to be analyzed after the collection from condensers while in analytical pyrolysis, pyrolysates can be directly analyzed without the collection.
Japanese cedar pyrolysis at 450–550 °C using a bench-scale auger reactor was conducted to determine the effects of pyrolysis temperature on bio-oil production. The obtained cedar bio-oil had a lower viscosity than typical bio-oils, likely due to its high moisture content and low molecular weight distribution. In the cedar bio-oil, the yield of levoglucosan (derived from cellulose) decreased at elevated temperatures, while it increased following analytical cedar pyrolysis. Furthermore, the yields of 4-vinylguaiacol and E-isoeugenol derived from lignin were lower in the bio-oil than in the pyrolysates obtained following analytical pyrolysis. The auger reactor used for cedar bio-oil production had a longer vapor residence time than the micro-pyrolyzer used for the analytical pyrolysis, which likely promoted secondary reactions of the pyrolysates in the vapor phase. Therefore, it can be concluded that the properties of the cedar bio-oil were influenced by both the pyrolysis temperature and the vapor residence time.
Woodchips prepared from a Japanese cedar (C. japonica) trunk were provided by Azuma–Sansho Co., Ltd, Akita, Japan. After air-drying, the woodchips were milled using a hammer mill with a 3-mm screen (Sansho Industry Co., Ltd). The milled chips were sieved to particle sizes below 0.71 mm (analytical fast pyrolysis) and from 0.71 to 2 mm (bio-oil production). The properties of the sieved cedar feedstock were determined as follows: the proximate analysis was performed according to Japanese industrial standard methods and the ultimate analysis was provided by Shimadzu techno-research.
Analytical pyrolysis of cedar wood meal was performed using two pyrolysis–gas chromatography (Py-GC) systems: a Py-GC/flame ionization detector (Py-GC/FID) consisting of a micro-pyrolyzer (EGA/PY-3030D, Frontier lab) and a GC-2010 Plus (Shimadzu), and a Py-GC/mass spectrometer (Py-GC/MS) consisting of a micro-pyrolyzer (JCI-22, JAi) and a JMS T-100GCV GC-TOFMS instrument (JEOL). Samples (0.5 mg) were pyrolyzed at 450, 500, 550, and 600 °C using the Py-GC/FID and at 590 °C using the Py-GC/MS. For both Py-GC analyses, the GC was equipped with an Rtx-Wax capillary column (60 m × 0.25 mm i.d.; 0.25 µm film thickness, RESTEK). The injector temperature was maintained at 250 °C, and split injection was used with a 1:100 split rate. The column oven temperature was held at 40 °C for 5 min and then raised to 250 °C at a rate of 4 °C/min. The temperature was then maintained for 60 min. For the Py-GC/MS analysis, a NIST mass spectral library was employed to identify each peak. After identification, each peak of the chromatograms resulting from Py-GC/FID analysis was identified based on the retention times of authentic samples (methane (GL Science), methanol, acetic acid, guaiacol, phenol, eugenol, 5-hydroxymethylfurfural, coniferylalcohol, levoglucosan (Wako), 4-methylguaiacol, furfural (TCI), and 2(5H)furanone (Aldrich)) and the results obtained via Py-GC/MS analysis.
Bio-oil production using a bench-scale auger reactor
Bio-oils were produced from cedar wood meal at 450, 480, 500, and 550 °C using the bench-scale auger reactor shown in Fig. 1. The wood meal was fed at 5.23–6.35 g/min for 90 min along with 2 L/min nitrogen into the cylindrical reactor (inside diameter: 40 mm, length: 789 mm) with an internal auger lying along the reactor’s axis. The distance between the screws of the auger was approximately 28 mm, and the auger speed was 20 rpm. The heating zone for pyrolysis was 305 mm long along the reactor axis. In the heating zone, N2 velocity calculated from the reactor inside diameter and N2 flow is more than 2.65 cm/s, which indicates that the vapor residence time in that zone can be shorter than 11.5 s. After pyrolysis, the char was moved to a vapor-char separation zone and dropped into a char collector. The vapor-char separation zone was lower than the chip supply zone in the reactor, which was inclined at an angle of 11°. To separate the non-condensable gases and bio-oil, two cyclones (Cyclone-1 and Cyclone-2) were cooled with two water cooling circulation systems at 20 and 4 °C, respectively. The non-condensable gases were washed with a wet scrubber and collected in gas bags at 5 L/min. The collected gas was analyzed using a GC/thermal conductivity detector (TCD) GC-7000 (J-science lab) as previously reported (Kojima et al. 2014). Ultimate analysis of the char was provided by Shimadzu techno-research.
Determination of the physical and chemical properties of the generated bio-oils
The water content of the obtained bio-oils was determined via Karl Fischer titration. The pH of the samples was measured using a HM-30V pH meter (Toa) at room temperature. Dynamic viscosities of the bio-oils were determined using a VM-10A-L viscometer (Sekonic) at 40 °C.
The product distributions of the bio-oils were analyzed via GC/MS and GC/FID. Prior to each analysis, the bio-oil was diluted to approximately 60–70 wt% with ethanol. The analytical conditions were the same as those described above for the analytical pyrolysis.
The molecular distributions of the bio-oils were determined using gel permeation chromatography (GPC). GPC was performed using an LC-2000 HPLC system (JASCO) with a photodiode array (PDA) detector (frequency from 200 to 400 nm). GPC KF-802 and KF-801 columns (Shodex) were used with tetrahydrofuran (THF) containing 10 mM phosphate as the mobile phase flowing at 0.6 ml/min. Samples for GPC were prepared by dissolving the bio-oil in THF at approximately 10 wt%. Each bio-oil solution in THF was filtered using a 0.45-μm filter prior to GPC analysis. The GPC column was standardized using polystyrene molecular weight standards in the range from 108 to 197,000 g/mol. Therefore, the molecular weights of the bio-oils as determined by GPC were polystyrene equivalent molecular weights.
- C. japonica :
flame ionization detector
gel permeation chromatography
number-average molecular weights
weight-average molecular weights
thermal conductivity detector
YK participated in the analytical pyrolysis, the cedar bio-oil production, and analyses of the physical and chemical properties of the bio-oil and drafted the manuscript. RE participated in the analytical pyrolysis, the cedar bio-oil production, and analyses of the physical and chemical properties of the bio-oil and carried out the proximate analysis. MA participated in the analytical pyrolysis and helped to draft the manuscript. YK conceived of the study, carried out of its design and coordination, and finalized the manuscript. All authors read and approved the final manuscript.
This work was supported by a Grant from the Bio-oriented Technology Research Advancement Institution (BRAIN) of Japan.
The authors declare that they have no competing interests.
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