Article pubs.acs.org/EF
Bio-Oil Production from Prosopis juliflora via Microwave Pyrolysis Dadi V. Suriapparao,† N. Pradeep,† and R. Vinu*,†,‡ †
Department of Chemical Engineering and ‡National Centre for Combustion Research and Development, Indian Institute of Technology Madras, Chennai 600036, India S Supporting Information *
ABSTRACT: Microwave pyrolysis is an efficient technique to valorize the abundantly available Prosopis julif lora (PJF) biomass into fuel intermediates. In this study, the effects of microwave power, susceptor, PJF particle size, PJF to susceptor mass ratio, and initial mass of PJF on bio-oil, gas, and char yields, composition of bio-oil, and energy recovery in bio-oil and char were evaluated. Five different susceptors, namely, graphite, char, aluminum, silicon carbide, and fly ash, an industry waste, were utilized. A high bio-oil yield of 40 wt % with a heating value of 26 MJ kg−1 was achieved with fly ash at a microwave power of 560 W, PJF particle size of 2−4 mm, and PJF (50 g)/fly ash composition of 100:1 (wt/wt). The bio-oil contained a mixture of phenolic compounds, aromatic hydrocarbons, cyclopentanones, carboxylic acids, ketones, and furan derivatives. Nearly 51% deoxygenation of PJF was achieved with an atomic O/C ratio of 0.24 in bio-oil. This work demonstrates that the yield and quality of bio-oil are dependent on key parameters such as microwave power, biomass particle size/composition, and type of susceptor.
1. INTRODUCTION Lignocellulosic biomass is one of the potential renewable sources of energy to cater to our sharply increasing energy needs. The valorization of abundantly available biomass is an attractive and viable pathway for energy production through a carbon neutral cycle.1 Pyrolysis is a prominent and costeffective platform for thermochemical conversion of biomass to bio-oil, char, and syngas.2 Among the pyrolysis products, bio-oil can be upgraded to transportation fuels via hydrodeoxygenation. The fast pyrolysis technique is proven to yield high amounts of bio-oil. Fluidized bed reactors are highly suitable to achieve fast pyrolysis conditions due to their ease of operation, shorter particle residence time, and rapid heat transfer.3 Recently, microwave pyrolysis has attracted the attention of the research community due to its selective, rapid, and uniform volumetric heating mechanism.4 Importantly, rapid agitation and size control of biomass particles are not essential unlike fluidized bed pyrolysis. Microwave pyrolysis of various abundantly available biomass feedstocks including douglas fir,5 pine,6,7 oil palm,8,9 rice straw,10−12 wheat straw,13,14 bagasse,15,16 coffee hulls,17 corn stover,6,18 algae,19,20 and sewage sludge21,22 is reported in the literature. Microwave absorbing materials, also known as susceptors, are necessary to convert incident microwave energy into heat energy owing to a low dielectric loss factor of biomasses. Carbonaceous materials such as graphite, activated carbon and biochar,23 ceramics like silicon carbide,6 and metals, metal oxides, and metal hydroxides15 have been reported to act as good susceptors. Besides heat transfer, metal oxides are known to induce catalytic activity and increase reaction rates while simultaneously reducing pyrolysis temperature.15 Production of high yields of bio-oil from biomass via microwave pyrolysis is a challenging task. Owing to the generation of microplasma spots throughout the reaction mixture, very slow or fast heating rates lead to the formation of biochar and gaseous products. Chemical nature, quantity, size and shape of the susceptor are important factors that control heating rate, © 2015 American Chemical Society
pyrolysis temperature, and product distribution. Therefore, a systematic and comprehensive study involving multiple parameters such as biomass to susceptor composition, biomass particle size, microwave power, catalysts, and gas atmospheres are critical to improve the yield of bio-oil via microwave pyrolysis. Borges et al.6 and Lei et al.24 adopted the central composite design of experiments to evaluate the effects of temperature, reaction time, biomass particle size, and loading on volatile yield. However, a comprehensive evaluation of product quality in terms of composition of the bio-oil under different operating conditions is lacking. The current study focuses on upgrading the lignocellulosic biomass variety Prosopis juliflora (P. Julif lora, PJF). It is a highly invasive nitrogen fixing species that can grow in arid and semiarid regions even under harsh environmental conditions such as saline soils. It consumes less water and utilizes relatively higher amounts of CO2 from the atmosphere, which makes it an attractive carbon neutral and energy rich source compared to other lignocellulosic biomasses. Traditionally harvested as a fuel plant for domestic use, it is now widely used as a fuel for small scale electricity generation by cofiring with coal in the state of Tamil Nadu, India.25 P. julif lora is also known to invade millions of hectares of rangeland in South Africa, East Africa, Australia, South America, and other parts of Asia.26 Better recovery of energy and resources from P. julif lora is possible via microwave pyrolysis rather than direct combustion. To the best of our knowledge, this is the first study to report bio-oil production from P. julif lora via microwave pyrolysis. In this study, microwave pyrolysis of P. julif lora is conducted under a wide range of reaction conditions to maximize the biooil yield and improve its quality. The effects of various parameters such as (i) microwave power (280−700 W), (ii) PJF particle size ( 1.38 (420 W) > 1.06 (280 W), whereas the yield ratio (wt/wt) of gas to char varies in the order: 1.64 (700 W) > 1.52 (420 W)
3. RESULTS AND DISCUSSION A thorough investigation of the effects of different operating parameters such as microwave power, susceptor type, PJF particle size, PJF/susceptor ratio, and initial mass of PJF on product yields and characteristics was carried out. Table 2 depicts the various experimental conditions and the corresponding char, bio-oil and noncondensable gas yields, and heating values of char and bio-oil. Tables S1 and S2 (in Supporting Information) provide the yields and selectivities of the product groups in bio-oil obtained at different conditions, respectively. Tables S3−S21 (in Supporting Information) depict the composition of the bio-oils in terms of the yield of individual organic compounds. The compounds obtained from bio-oil were classified into seven main categories, viz. guaiacols, syringols, simple phenolics, aromatic hydrocarbons, C2−C5 ketones, acids and alcohols, furan derivatives, and cyclopentanones. The yields and selectivities of the above product groups were evaluated, and the variation was correlated with operating conditions. Phenolic compounds originate from lignin in PJF, while the formation of carboxylic acids, ketones 2574
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position of carbonyl compounds and carboxylic acids. The variation in yields of cyclopentanones and furan derivatives with microwave power is not significant, which means that most of cellulose and hemicellulose fractions are being converted into gaseous compounds even at low powers without much variation in condensable compounds present in bio-oil. 3.2. Effect of Juliflora Particle Size. It is evident from proximate and elemental analysis data (Table 1) that different particle sizes have different chemical composition especially in terms of ash content due to a difference in the grindability index of compounds present in PJF. The smaller size fractions contain high ash content thereby giving a low heating value. Particle size also affects the surface area available for chemical interaction and heat transfer rates. Therefore, it is reasonable to expect that biomass particle size controls product yields and distribution in a significant manner. In order to obtain a comprehensive understanding about the effect of particle size, pyrolysis of PJF of five different particle sizes in the range of 52.56 (2−4 mm) > 37.52 (1.4−2 mm) ≈ 35.2 ( (1.4−2 mm) > 0.97 ( 1.48 (280 W) > 1.44 (560 W). Clearly, high microwave power of 700 W favors biomass conversion to oil and noncondensable gases. The absolute yields of bio-oil are similar at 420, 560, and 700 W (c.a. 35.93 ± 0.7 wt %). A similar observation is also reported in the case of microwave pyrolysis of wheat straw wherein the bio-oil yield was ca. 31 wt % from 400 to 600 W.37 High yield of bio-oil is not the only marker to qualify a particular microwave power as optimum. The qualities of biooil in terms of heating value and composition are also important. The energy recovered in bio-oil follows the order: 55.27% (560 W) > 51.44% (700 W) > 47.34% (420 W) > 40.53% (280 W), while that recovered in char follows the trend: 46.44% (280 W) > 41.78% (560 W) > 40.84% (420 W) > 38.64% (700 W). Huang et al.12 also observed a decreasing trend of energy recovered in char with increasing microwave power. At low microwave powers, most of the energy is recovered in char, and at high powers most of the energy is recovered in noncondensable gases. Optimum energy recovery in bio-oil occurs at an intermediate microwave power of 560 W. Figure 4 depicts the variation of selectivities of major compounds in bio-oil and noncondensable gases with micro-
Figure 4. Variation of selectivities of key components in bio-oil and gaseous fractions with microwave power.
wave power. It is clear that the selectivities of total phenolics, i.e., guaiacols + syringols + simple phenols, and aromatic compounds increase with microwave power. This is accompanied by a concomitant decrease in the production of C3−C5 acids/ketones/alcohols, furan derivatives, and cyclopentanones. Importantly, the yields of acetic acid and furfural decrease with microwave power. As the average heating rate of the sample increases with microwave power proportionately, the described variations can also be correlated with heating rate. This suggests that high microwave powers favor more efficient cracking of lignin into phenolic derivatives, which gets further converted to aromatic compounds via liberation of noncondensable gases from the propyl subunits of lignin. This can be verified by the increase in production of C1−C3 hydrocarbons like methane, ethane, ethylene, propane and propylene, and hydrogen. It is known that the yields of noncondensable gases comprising CO, H2, and light hydrocarbons increase with microwave power, which is consistent with our study.12,37,38 The evolution of these gases and CO2 can be related to secondary decom2575
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also supports the variation of HHV of bio-oil with particle size. The selectivity of cyclopentanones increased by 30%, while that of furans was doubled in moving from smallest ( aluminum (60.53) > fly ash (52.56) > graphite (30.32). It is also evident that raw PJF biomass without any susceptor absorbs microwaves owing to the presence of fixed carbon and ash. However, because of the absence of susceptors the final temperature attained at the end of 15 min is only 270 °C. This emphasizes the importance of even minute quantities of susceptors to initiate the pyrolysis reactions and sustain them. Moreover, this also shows the possibility of altering the heating rates using susceptors. Because of the formation of localized microplasma spots, the region around microplasma on the surface of the susceptor shoots up to very high temperatures.9 This leads to more energy efficient flash pyrolysis conditions. The formation of microplasma spots was observed in an independent experiment with bare graphite and activated carbon subjected to microwaves. Menendez et al.39 observed two types of microplasma, viz. ball lightning plasma and arc discharge plasma during microwave heating of carbonaceous materials. Importantly, the tiny micro flashes were observed just after 1−2 s of microwave irradiation.39 The early evolution of gases such as CO and CH4 at low bulk temperatures ( 26.61 (1.4−2 mm) ≈ 26.16 (2−4 mm) > 19.82 (0.5−1.4 mm), while the HHV (MJ kg1−) of char follows an opposite trend: 28.00 (2−4 mm) > 26.99 (1.4−2 mm) ≈ 26.92 (0.5−1.4 mm) > 24.77 (0.25−0.5 mm) > 21.45 ( 40.05% (0.5−1.4 mm) > 37.49% (1.4−2 mm) ≈ 36.74% ( 52.36% ( 51.36% (1.4−2 mm) > 45.32% (0.25−0.5 mm) > 28.09% (0.5−1.4 mm). Both bio-oil and char obtained with 2−4 mm size range possess highest energy recovery, and therefore, lowest energy recovered in the form of noncondensable gases. This also implies low grinding costs if the process were to be scaled up. In order to understand the observed trends in energy recovery and the effect of particle size, the selectivities and yields of major products were investigated (Figure 5). It is clear
Figure 5. Variation of (a) selectivities of different product groups in bio-oil, (b) total phenolics yield, and (c) selectivities of noncondensable gases, with average particle size of PJF.
that the selectivity of aromatic hydrocarbons decreased with an increase in average particle size from 27.47% for graphite (1.08) > SiC (1.03), suggesting that aluminum and fly ash are good susceptors to obtain high bio-oil yield while minimizing char yields. On the other hand, the product yield ratios (wt/wt) of gas to char are in the order of SiC (1.87) > char (1.73) > aluminum ∼ fly ash (1.44) > graphite (1.37), which is similar to the trend observed for average heating rates. This shows that the production of gaseous products can be correlated with average heating rate, while the bio-oil formation is linked to various parameters such as particle size, microwave power, and susceptor type, and parameter optimization is essential. The heating values of bio-oil with different susceptors varied in the range of 22−29 MJ kg−1. The highest value was achieved with SiC followed by aluminum, fly ash, char, and graphite. The percent energy recovered in bio-oil follows the trend: aluminum (57.86%) ≈ fly ash (55.27%) > char (46.36%) ≈ SiC (44.30%) > graphite (39.16%). Energy recovered in char is in the range of 41.76−48.26%; the highest value was noticed with graphite followed by aluminum (44.76%) and char, SiC, and fly ash (all 42%). Even though a slightly higher energy recovery in bio-oil was obtained with aluminum, fly ash was chosen to be the best susceptor for obtaining a high yield of quality bio-oil by merit of being an easily available industrial waste. The high activity obtained with fly ash can be attributed to the presence of oxides like SiO2, Al2O3, Fe2O3, CaO, and MgO that are known to catalyze the cracking of biomass and hydrocarbons. For example, alumina imparts acidity and acts as a solid acid catalyst in cracking reactions. The formation of alumina via reaction of aluminum with traces of oxygen entrapped in the reaction mixture is possible at high temperatures,40 which justifies the high activity of aluminum powder as a susceptor for bio-oil formation. Moreover, aluminum powder reflects microwaves, and hence, causes homogeneous cracking of the reaction mixture. Susceptors have a significant effect on the selectivity of different organic products found in bio-oil. The chemical composition of bio-oils obtained with different susceptors is shown in Figure 6. The absolute yield of total phenolics is unaffected by the choice of susceptors (15.91 ± 0.91 wt %); however, the trend in selectivity is different: SiC (55.44%) > graphite (52.45%) > char (46.47%) ≈ aluminum (45.58%) ≈ fly ash (44.7%). The use of SiC was found to result in high selectivity of phenolic compounds (c.a. 57.76% for corn stover and 61.5% for saw dust) in an earlier study.6 Fly ash selectively favors the formation of acetic acid (3.18 wt %) and furfural (2.76 wt %), whereas SiC gives low yields of these low molecular weight organics (0.23 and 0.87 wt %). The selectivity of linear ketones, acids, and alcohols is in the range of 7.36− 23.5% with maximum selectivity attained using fly ash followed by aluminum powder and char. Similarly, high selectivity of furan derivatives is attained with fly ash (ca. 16%). Importantly, very low yield (1.24 wt %) and selectivity (3.38%) of aromatics observed with fly ash suggest that compared to other susceptors, the secondary cracking and condensation reactions are minimized by using fly ash. The selectivity of cyclopentanones is independent of the type of susceptor used, suggesting that the hemicellulose component in PJF readily undergoes cracking irrespective of susceptor used, and the chemical nature of the susceptor has a negligible effect on such
Figure 6. Composition of bio-oil obtained with different susceptors (PJF mass = 20 g, PJF to susceptor ratio (wt/wt) = 100:1, PJF particle size = 2−4 mm, microwave power = 560 W).
reactions. The selectivities of light gases for different susceptors are depicted in Figure 7. It is clear that the evolution of
Figure 7. Selectivity of light gases with susceptors at 560 W and PJF (20 g)/susceptor ratio of 100:1 (wt/wt). Other gases include C4, C5 hydrocarbons, and unidentified oxygenates.
hydrogen follows the trend: graphite, char (41.86 ± 0.83%) > fly ash, aluminum (34.21%) > SiC (25.81%). In an earlier study, hydrogen evolution was found to be low with SiC.6 The selectivity of C1−C3 hydrocarbons with different susceptors also follows a similar trend. High production of CO2, C2, and C3 hydrocarbons with fly ash suggests that decarboxylation of linear low molecular weight acids is a plausible pathway. 3.4. Effect of Juliflora to Fly Ash Ratio. The composition of PJF to fly ash can affect both microwave energy utilization and catalytic activity. The efficiency of cracking depends on the density of tiny microplasma spots, which in turn depends on the number of fly ash particles present in unit volume of the reaction mixture. In order to assess the effect of susceptor quantity on product yields and composition, experiments were performed at four different PJF to fly ash ratios (wt/wt), viz. 5:1, 100:1, 400:1, and 1000:1 at 560 W with 20 g of 2−4 mm PJF particles. It can be observed from Figure 2c that the ratio of 2577
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a negligible effect on pyrolysis; it mainly controls the heating rate, and hence, affects the relative yields of char, bio-oil, and noncondensable gases. 3.5. Effect of Initial Mass of Juliflora. In order to evaluate the feasibility of scale-up of microwave pyrolysis process, PJF pyrolysis was conducted at different initial masses of feed starting from 5 to 50 g at the established optimal conditions of 560 W power and PJF (2−4 mm) to a fly ash ratio of 100:1 (wt/wt). The bio-oil, char, and gas yields and corresponding average heating rates are reported in Table 2 (E3, E12−E15), and the overall product yields are depicted in Figure S8 (see Supporting Information). It is evident from the temperature profiles depicted in Figure 2e that the average heating rate varied from 68.3 °C min−1 at 5 g to 52.8 °C min−1 at 50 g. Even though there is an increase in quantity of both biomass and susceptor at a constant ratio of 100:1, the effect of increase in mass on oil yield is significant in the range of small masses (5, 10, and 20 g), while for initial masses greater than 20 g, the oil yield tends to saturate at ca. 40 wt % at 50 g (Figure 9). This corresponds to a steady increase
PJF/fly ash affects the temperature profiles, and hence, the average heating rates. The bio-oil, char, and gas yields with average heating rates are reported in Table 2 (E3, E5−E7). The overall product yields are depicted in Figure S7 (see Supporting Information). It is evident from the bio-oil yields that low quantity of susceptor is sufficient to promote and sustain pyrolysis. This can be justified by the role of susceptor as only an initiator of microwave energy conversion to heat, which is then sustained by the formation of char and decomposition of lignin intrinsically present in biomass. A high yield ratio (wt/wt) of bio-oil to char was observed with 400:1 composition (1.65), followed by 1.42 for 100:1 composition. Nevertheless, the heating value of bio-oil obtained with 100:1 composition was higher than that obtained with 400:1 composition. On the contrary, a low PJF to fly ash ratio of 5:1 favored a high yield of noncondensable gases due to a greater extent of cracking of primary volatiles by the char formed and the susceptors themselves. The energy recovered in bio-oil followed the order: 55.27% (100:1) > 50.15% (400:1) > 46.75% (1000:1) > 42.00% (5:1). The HHV and energy recovered in char were similar for all PJF/fly ash compositions. The yields of various bio-oil components obtained with different PJF/flyash ratios are shown in Figure 8. The selectivity
Figure 9. Variation of wt % yields of different product groups in bio-oil with initial mass of PJF. Other conditions include PJF to fly ash ratio (wt/wt) of 100:1, microwave power of 560 W, and PJF particle size of 2−4 mm.
in the yield ratio (wt/wt) of bio-oil to char from 0.36 to 1.62. The yield ratio (wt/wt) of gas to char varies in the range of 2.39 at 5 g to 1.40 at 50 g. Therefore, the high initial mass of PJF favors bio-oil generation with low gas yields. The above observations indicate that the number of microplasma spots generated per unit volume may be a critical factor influencing the heating rates achieved and the product yields. With a bulk density of 0.366 g cc−1 for 2−4 mm PJF particles, the volume occupied by 5 and 50 g of biomass are 13.66 cc and 136.6 cc, respectively. This shows that in the case of low initial mass of the sample, more microplasma spots per unit volume could be generated, which eventually lead to excessive cracking of biomass, and hence, high gas yields. On the other hand, with a high initial mass of sample, lesser number of microplasma spots will be generated per unit volume of the sample, which results in controlled cracking. Therefore, an optimal generation of microplasma spots is the key to control the severity of pyrolysis during microwave processing.
Figure 8. Composition of bio-oil obtained at different PJF to fly ash ratios (wt/wt) (PJF mass = 20 g, PJF particle size = 2−4 mm, microwave power = 560 W).
of total phenolic compounds lies in the range 45−55% with the maximum occurring for PJF to fly ash ratio (wt/wt) of 400:1 and a minimum value for 100:1 ratio. Contrastingly, the selectivities of acids/ketones/alcohols and furans are maximum at 100:1 and having values of 23.5% and 15.8%, respectively. The production of aromatic compounds is maximum at a 5:1 PJF/fly ash ratio with 14% selectivity, suggesting that a large amount of susceptor only leads to inter- and intramolecular condensation of low molecular weight organics. The composition of bio-oil does not show significant variation suggesting that at such low ratios, the PJF to susceptor ratio has 2578
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Energy & Fuels The bio-oil yield obtained in microwave pyrolysis is comparable with that of conventional pyrolysis in fluidized bed and free-fall fast pyrolysis reactors. In the literature, 30−60 wt % of bio-oil production is reported via catalytic fast pyrolysis of different types of biomass feedstocks at different operating conditions such as temperature, particle size, and type of catalyst.41−45 Zhang et al.42 obtained nearly 50 wt % of bio-oil from corn cob biomass in a fluidized bed reactor with FCC catalysts. Pattiya and co-workers43,44 observed ca. 50 and 60 wt % of bio-oil production from sugar cane tops and cassava stalks in free fall and fluidized bed reactors, respectively. Therefore, the obtained bio-oil yields from PJF via microwave pyrolysis are comparable with the literature. Nevertheless, huge potential exists in improving the bio-oil yields by making suitable process modifications. A significant increase in energy recovery in bio-oil is observed with the initial mass of PJF. The trend can be described as follows: 58.72% (50 g) > 55.27% (20 g) > 50.16% (30 g) > 39.14% (10 g) > 15.57% (5 g). No significant change in energy recovery in char can be observed (39.94 ± 1.36%). The variations in composition of bio-oil components with different initial masses are shown in Figure 9. An increase in yield of guaiacols, simple phenols, syringols, and hence, the total phenolics with initial mass of PJF is evident. The selectivity of total phenolics is also high (64%) for 50 g of initial PJF. The yield and selectivity of linear acids/ketones/alcohols and furans initially increased with mass up to 20 g and then decreased. The selectivities of aromatics, furans, and cyclopentanones got stabilized at 7.7%, 9.7%, and 7.4%, respectively, for large initial masses of PJF. These observations strongly suggest that scaling up of the process is possible to obtain high yield of bio-oil with high energy recovery. In order to obtain an overall understanding of the competing reactions during microwave pyrolysis, the selectivities of acids/ ketones/alcohols and furans + cyclopentanones are plotted against the selectivity of total phenolics + aromatics, as depicted in Figure 10. The portrayed data are inclusive of all the experimental conditions reported in this study. Phenolics and aromatics are produced via lignin decomposition, and an increase in selectivity of this group correlates well with a decrease in selectivity of furans + cyclopentanones and acids/ ketones/alcohols. As furans and cyclopentanones are predominantly derived as primary pyrolysates from carbohydrates, the observed correlation suggests that under microwave heating, the decomposition of lignin promotes the secondary cracking of furans and cyclopentanones to form noncondensable gases. C2−C4 organics like acetic acid, propionic acid, and propanone are formed via pyrolysis of both carbohydrates and lignin. Importantly, acetic acid is a major pyrolysate obtained from lignin and produced only in minor quantities from hemicellulose and cellulose pyrolysis.46−48 The observed trends suggest that under mild microwave heating conditions, such as low power levels, C2−C3 oxygenates are preferentially liberated from lignin without the cleavage of interlinking covalent bonds (like α-O-4, β-O-4, β-5, 4-O-5, and 5-5) in lignin, while at all other conditions, the primary oxygenates liberated from lignin are further decomposed to light gases. An overall assessment of yields and heating values of biochars reveals that char production is insensitive to reaction conditions with an average yield of 25.5 ± 1.78 wt % and heating value of 27.7 ± 1.87 MJ kg−1. Therefore, the effect of microwave operating conditions is only to alter the relative yields of bio-oil and gaseous fractions. In order to understand the extent of
Figure 10. Variation of selectivities of acids/ketones/alcohols and furans + cyclopentanones versus total phenolics + aromatics. The data correspond to all the microwave pyrolysis experiments reported in this study.
valorization and deoxygenation of raw PJF into bio-oil and char, C, H, and O content in bio-oils and char are evaluated. Table S22 (in Supporting Information) depicts the C, H, and O content in bio-oils calculated using GC/MS composition data. The O/C and H/C ratios of bio-oils lie in the range of 0.17− 0.33 and 1.18−1.29, respectively. The atomic H/C and atomic O/C ratios of raw PJF, char, and bio-oil are depicted in the form of van Krevelen diagram in Figure 11 and compared with
Figure 11. Van Krevelen diagram for coals, petroleum-derived liquid fuels, P. juliflora, P. julif lora-derived bio-oil and biochar.
coals of different ranks, ethanol, diesel, kerosene, and gasoline. At optimal conditions, the percentage oxygen removal achieved for the conversion of raw PJF into char and bio-oil were 55% and 51%, respectively. Interestingly, the oxygen removal was as high as 65% for PJF particles of smallest size (
