Simultaneous Maximization of the Char Yield and Volatility of Oil from

Nov 20, 2012 - The recycling of HBO enables the selective production of light bio- ... The HBO recycling increases the char yield from the pyrolysis o...
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Simultaneous Maximization of the Char Yield and Volatility of Oil from Biomass Pyrolysis Yong Huang,† Shinji Kudo,‡ Ondrej Masek,§ Koyo Norinaga,†,∥ and Jun-ichiro Hayashi*,†,‡,∥ †

Interdisciplinary Graduate School of Engineering Sciences, ‡Research and Education Center of Carbon Resources, and ∥Institute for Materials Chemistry and Engineering, Kyushu University, 6-1, Kasuga Koen, Kasuga 816-8580, Japan § UK Biochar Research Centre, School of Geosciences, University of Edinburgh, Kings Buildings, Edinburgh EH9 3JN, United Kingdom ABSTRACT: This study proposes continuous biomass pyrolysis featuring internal recycling of a heavier portion of bio-oil (HBO) that evaporates, leaving solid residue when reheated. The recycling of HBO enables the selective production of light biooil (LBO) that is free from residue after evaporation, and also the maximization of the char yield. The performance of the proposed pyrolysis has been examined experimentally by employing an originally designed simulator of a vapor−solid countercurrent moving bed reactor, which provides the zone for pyrolysis at 120−550 °C (PZ) and the zone for capture of HBO by the parent biomass at 120 °C (CZ) in series. The HBO recycling increases the char yield from the pyrolysis of pine sawdust from 0.25 to 0.36 kg/kg of dry feedstock while producing LBO, in which the organic compounds have carbon numbers no greater than 13. Such a large increase in the char yield is caused by two different events. HBO is captured by the parent biomass in CZ and undergoes self-charring and/or co-carbonization in PZ. The vapor of HBO is decomposed over the surface of pyrolyzing solid (char) in PZ and then converted into a portion of char, LBO, and/or gas.

1. INTRODUCTION Use of biomass has been drawing worldwide attention because of its potential contributions to CO2 mitigation and decreasing the demand of fossil fuels.1−3 Pyrolysis is the simplest method to convert biomass to char and bio-oil, of which the yields are easily controlled by adjusting the heating rate, peak temperature, and other operating variables. In general, a lower heating rate is preferable for the production of more char, while a higher heating rate is beneficial to the production of more bio-oil.4−6 Char is suitable for use as a precursor of activated carbon, soil amendment, reductant in the metallurgical industry, sorbent, and renewable fuel.7−9 In any of these applications, a higher char yield is the most important target of the pyrolysis. It is, unfortunately, difficult to say that the pyrolysis technology for such a purpose has been well-developed.7,10 Some attempts have thus far been made for raising the char yield by modifying the conventional pyrolysis system. Antal et al.11−13 increased the char yield from biomass significantly by elevating the gaseous pressure within the pyrolyzer. Demirbas14 and Katyal et al.15 suggested that a lower peak temperature should be chosen for producing char at a higher yield. However, pressurized pyrolysis implies a higher cost and more difficult operation than atmospheric pyrolysis. Char from low-temperature pyrolysis tends to have high volatile matter content (VMC), which is unfavorable in many applications, e.g., the metallurgical industry and soil amendment (carbon sequestration). There is also a lower limit of temperature for producing smokeless (tar-free) fuel. Bio-oil is another major product of the biomass pyrolysis, and it is produced with the yield even more than 60−70% based on the dry feedstock mass when a heating rate as high as 103 °C/s is applied.16 A comprehensive understanding of properties of biooil and its applications is found elsewhere.2,17−19 A high oxygen content, usually 45−50%,20 is the most significant characteristic © 2012 American Chemical Society

of bio-oil in contrast to petroleum fuels and causes problems in its effective use. Oxygen is present in most of the polar compounds found in bio-oil, such as hydroxyaldehydes, hydroxyketones, sugars, carboxylic acids, and phenols.2 Although the composition of the heavier portion of bio-oil has not been fully clarified, it usually includes polymeric or oligomeric sugars and phenols.2,18 It is reported that most of the phenolic compounds are present with a molecular mass ranging from several hundred to 5000 or even more,2,18 resulting in the formation of substantial amounts of nonvolatile material upon reheating. It is moreover believed that some reactive components of sugar and phenols have propensities to undergo polymerization during the reheating. Consequently, 35−50 wt % of the starting bio-oil is often left as solid residue, termed coke or char, after heating to 400 °C or higher temperatures.2,18,21 In most potential applications of the bio-oil as a diesel or turbine fuel18 or a feedstock for steam reforming,22 the presence of the coke-/ char-forming portion of bio-oil is undesirable because it causes operational problems in such applications. Biomass is generally a good sorbent of liquids because of its macroporous nature that provides space for condensation and retention of them. In addition to this, the polymeric structure of biomass can sorb (i.e., absorb and/or adsorb) polar liquids. It is thus expected that biomass, if in contact with vaporous or liquid bio-oil, captures and retains its heavier portion within the macropores or dense matrix and, therefore, that the parent biomass (feedstock for pyrolysis) is able to preferentially separate such a portion of the bio-oil from the lighter portion. Reheating of the bio-oil retained by parent biomass will result in its Received: August 16, 2012 Revised: November 19, 2012 Published: November 20, 2012 247

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conversion to coke/char at an extent equivalent with or even more than that achieved by reheating of the same bio-oil alone. Furthermore, a chemical interaction between the bio-oil and the pyrolyzing biomass during the reheating may also promote conversion of the bio-oil to char, lighter bio-oil, and/or gases. The present authors21 studied the pyrolysis of a woody biomass, chipped Japanese cedar, in a screw conveyer reactor with experimental simulation of recycling of bio-oil. In this process, a portion of bio-oil was captured by the feedstock packed in an external vessel (sorber) and then reintroduced (recycled) into the pyrolyzer. It was found that the pyrolysis at 500 °C reached a steady state, while the bio-oil was recycled at a rate of about 40% of the biomass feed rate on a mass basis. This recycling increased the char yield, and more importantly, the biooil recovered in the downstream of the sorber left very little solid residue upon reheating. It is believed that countercurrent moving bed reactor (i.e., updraft reactor) is an excellent candidate for the pyrolysis with internal bio-oil recycling because of the following reasons: First, the upper part of the bed, if its temperature is sufficiently low to allow for condensation and/or sorption of a heavier portion of the bio-oil into/onto the parent biomass, plays a role as a bio-oil sorber. Second, it is expected in the lower part of the bed that biooil vapor undergoes a chemical interaction with the pyrolyzing solid and is thereby converted into char/coke, lighter bio-oil, and/or gases. It is known that in situ contact of bio-oil vapor with the pyrolyzing parent biomass, in particular, cellulose, causes deposition of the vapor onto the solid to a substantial degree.23,24 Effectiveness of a moving bed pyrolyzer in promotion of tar conversion to char/coke and increasing the content of light aromatics in the tar for coal pyrolysis were reported by Miura et al.25 The present study proposes a simple system for atmospheric and continuous biomass pyrolysis with internal bio-oil recycling. As shown in Figure 1, the pyrolysis system consists of two zones playing different roles: bio-oil capturing zone (CZ) and pyrolysis zone (PZ), below CZ. In a usual updraft pyrolyzer, temperatures at the bottom of PZ and the top of CZ are the highest and lowest, respectively, and a temperature gradient is formed between them. The temperature at the top of CZ is maintained high enough to avoid the condensation of water. PZ and CZ are not clearly distinguished from each other because of continuity of the temperature. The vapor of bio-oil formed together with light gases goes upward through PZ and then CZ, while a portion of the bio-oil is converted into char, light bio-oil (LBO), and/or light gases over the pyrolyzing solid that moves downward in PZ and also sorbed in/on the parent biomass in CZ. Thus, the biooil, probably its heavier portion, is continuously and automatically recycled between PZ and CZ, being carried by the parent biomass as a reactive medium. The noncondensable gases are burned with air, and the hot flue gas is supplied to the pyrolyzer from its bottom. The temperature of the flue gas at PZ bottom is optimized, so that requirements, such as the VMC and yield of the char, are satisfied. In this study, an original reactor was developed for simulating the proposed pyrolysis system with a main purpose to examine its effectiveness on simultaneous maximization of the yield of char and volatility of the bio-oil.

Figure 1. Conceptual illustration of a moving bed pyrolysis system that consists of the zones for pyrolysis (lower) and capture of bio-oil (upper). fractions with particle sizes in the range of 0.5−1.0 or 1.0−4.0 mm. The fractions were dried in air at 80 °C to reduce the moisture content to about 2 wt % before use for the pyrolysis. Rice husk was neither pulverized nor sieved (major/minor axes of ca. 6.3/2.4 mm) but just dried in the same way as the other samples. Detailed characteristics of the pyrolysis were investigated for pine, while the pyrolysis of the other samples was performed under selected conditions. The elemental analyses and ash contents of the samples are shown in Table 1.

Table 1. Elemental Analyses (wt %, dafa) and Ash Contents (wt %) of the Samples sample

C

H

N

Ob

ash content

cherry pinec mallee rice husk

50.0 49.9 52.0 47.7

5.8 6.0 5.3 6.0

0.1 99.9995 vol %) through the containers at a rate of 20, 100, 200, or 500 mL/min (at 20 °C). In the case of a flow rate of 200 mL/min, the pressure drop between the inlet and outlet of the reactor train (22 containers) was as small as 58.8 Pa. The feedstock was dried completely in this pre-pyrolysis period. Then, the container train was pulled up at a constant rate of 6.85 mm/min, while the temperature inside each container changed in the same manner as indicated in Figure 3. In this figure, the times of 0 and 69.3 min correspond to those when the top surface of a container reaches the bottom of furnace 4 and when its bottom surface reaches the top of furnace 1, respectively. As also seen in the figure, the peak temperature was 550 °C. In the downstream of the container train, the aerosol filter (at 200 °C), the first condenser (at 0 °C), the second condenser (at −70 °C), and the gasbag were connected in series. A commercial thimble filter made of pure silica fiber (No. 88R, Advantec Co., Ltd.) was used as the filter material for capturing the heavier portion of bio-oil. The second condenser was packed with glass beads (2 mm in diameter) for enhancing heat transfer and condensing water and organic compounds completely, except for C1−C4 hydrocarbons. The Teflon-made tube between the bottom container and the 249

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Figure 4. Illustration of the arrangement of the container train through the sequence of R1−R3. 1701; 60 m × 0.25 mm, with a film thickness of 0.25 μm) was employed for separation of compounds with the following temperature history: temperature holding at 40 °C for 5 min, heating to 280 °C at a rate of 4 °C/min, and temperature holding at 280 °C for 20 min. The interpretation of the mass spectra was mainly based on an automatic library search (NIST08, version 2.0f). Volatilities of LBO1-O and LBO1-W from R3 were examined with a thermogravimetric analyzer (TGA; Seiko Instruments, Inc., EXSTAR TG/DTA 7200) at a heating rate of 10 °C/min from 25 to 900 °C under atmospheric flow of N2 (200 N mL min−1). The water content of LBO1 from R3 was determined by a Karl Fischer titrimetry.

3. RESULTS AND DISCUSSION 3.1. Solid Product. Figure 5 shows solid yields for the individual containers/runs. The containers of nc = 1−10, 11−20, and 21−30 had passed through PZ before the end of R1, R2, and R3, respectively. The solid yields for those containers, i.e., char yields, are also shown in a different manner in Figure 6. The char

Figure 6. Char yield as a function of the container number for R1−R3.

yield increased from 0.25 to 0.36 kg/kg of dry feedstock with nc from 1 to 9, and it became steady at around 0.36 when nc ≥ 10. This trend demonstrated that the pyrolysis was operated at a steady state in R2−R3. The containers of nc = 11−18, 21−28, and 31−38 were in PZ at the ends of R1, R2, and R3, respectively. The solid yields for the containers in the lower part of PZ (nc of 16−18, 26−28, and 36−38 and temperature of 123−220 °C) were 1.2−1.4. Such large yields resulted from sorption of HBO as well as progress of the pyrolysis to little extent. Lower solid yields were given in the containers that were in CZ (nc of 19−22, 29− 32, and 39−42) at the end of the three runs, but the yields were greater than 1.0 because of sorption of HBO. The char yield at nc = 1, i.e., 0.25, was the lowest among those at nc = 1−30. This was attributed to no exposure of the pyrolyzing solid to HBO/LBO vapor coming down from other containers and also no sorption of HBO. The increase with nc of the char yield from 0.25 to 0.36 was thus caused by the chemical interaction between the pyrolyzing solid and HBO/LBO vapor23,24 and/or the conversion of the sorbed HBO into a part of char by self-charring or co-carbonization with the parent

Figure 5. Solid yield as a function of the container number for R1−R3. 250

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feedstock.21 It was important to distinguish one of these two different chemical events from the other. It was, however, difficult to do it by analyzing only the data from R1−R3 because all of the char yields for nc ≥ 2 could be contributed by those two events. The solids in the containers of nc = 36−42 were heated in R3 up to the temperature of 123−220 °C where the pyrolysis, if any, took place to a small degree, while HBO vapor was sorbed into/ onto the solids. An additional pyrolysis run, R4, was performed, setting the containers of nc = 36−42 at the top part of the train that consisted of 22 containers. The char yields for nc = 36−42 are shown in Table 2. The char yield at nc = 36 was 0.30 kg/kg of

temperature for the pyrolysis was a factor determining the elemental composition and other properties, such as VMC.26−28 3.2. Analysis of Product Distribution. For the pyrolysis under the present conditions, determination of the overall product distribution from a single run, in which only the top 10 containers passed through the furnaces, did not make sense. Then, the data for R1−R3 were further analyzed to estimate the yields of char, LBO (including water), and noncondensable gases at steady state. Table 3 shows the material balances for R1−R3. The mass of the solid remaining in the PZ and CZ seemed to be steady in R2−R3, in other words, no or a negligible accumulation of the material inside the pyrolysis system. The masses of the char, LBO, and gases were also steady in R2−R3. It was thus estimated that the pyrolysis system was operated at a steady or nearly steady state in R2−R3. Assuming that R3 was performed at a steady state, the product yields were given by the following equations:

Table 2. Char Yields of nc = 36−42 in R4 nc

solid yield in R3 (kg/kg of dry feedstock)

char yield in R4 (kg/kg of dry feedstock)

36 37 38 39 40 41 42

1.22 1.38 1.25 1.08 1.04 1.04 1.05

0.30 0.33 0.36 0.35 0.35 0.36 0.36

char yield = (mass of char/mass of newly charged biomass) /(total mass of products/mass of newly charged biomass) = 0.36 kg/kg of dry feedstock

dry feedstock. It was clearly higher than the char yield at nc = 1, i.e., 0.25, but also lower than the steady-state char yield, 0.36. Thus, the self-pyrolysis and/or co-carbonization of the sorbed HBO induced an increase in the char yield by 0.05 kg/kg of dry feedstock, while the HBO/LBO deposition onto the pyrolyzing solid caused a char yield increase by 0.06. The results shown in Figures 4−6 and Table 2 provided evidence that both of the two different chemical events contributed to the increase in the char yield. Char samples were subjected to VMC measurements. In Figure 7, VMCs of the chars are plotted against nc. VMC was

LBO yield = (mass of LBO/mass of newly charged biomass)/(total mass of products /mass of newly charged biomass) = 0.47 kg/kg of dry feedstock

gas yield = (mass of gas/mass of newly charged biomass) /(total mass of products/mass of newly charged biomass) = 0.17 kg/kg of dry feedstock

The steady-state char yield, 0.36 kg/kg of dry feedstock, was in good agreement with the char yields for the containers of nc = 13−30, which are shown in Figure 6. The water content of LBO from R3 was 66 wt % of LBO. The water yield and total yield of the organic compounds of LBO were thus estimated as 0.31 and 0.16 kg/kg of dry feedstock, respectively. 3.3. Liquid Product. The compounds detected in the entire portion of LBO from R3 are listed in Table 4. Among 120 organic compounds detected and identified by GC/MS, 99 compounds were oxygen-containing compounds. Detection of the organic compounds with a carbon number (number of carbon atoms per molecule) no greater than 13 strongly suggested high volatility of LBO, which was then examined by subjecting LBO1 to the TGA. Figure 8 draws mass release profiles of LBO1-O and LBO1-W, the evaporations of which were almost completed at 220 and 170 °C, respectively. Moreover, no residue was left after the

Figure 7. VMC as a function of the container number for R1−R3.

stable at around 0.16 kg/kg of dry char over the range of nc = 1− 30. The char yield increased significantly with n c , as demonstrated in Figure 6, but its quality was maintained. This trend was reasonably explained by the fact that the peak Table 3. Material Balance for the Pyrolysis of Pine in R1−R3 mass of solid charged to the pyrolyzer (g)

mass of product (g)

run ID

newly charged biomass

reheated solid

char

LBO

gas

solids remaining in PZ/CZ

R1 R2 R3

154.4 (nc = 1−22) 70.2 (nc = 23−32) 70.4 (nc = 33−42)

0 74.0 (nc = 11−22) 75.0 (nc = 21−32)

22.6 (nc = 1−10) 24.7 (nc = 11−20) 25.3 (nc = 21−30)

42.1 32.7 32.7

15.6 11.8 11.7

74.0 (nc = 11−22) 75.0 (nc = 21−32) 75.7 (nc = 31−42)

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Table 4. List of Compounds Detected in LBO from R3 number

compound/formula

PFa (%)

number

compound/formula

PF (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2-methoxy-4-methylphenol/C8H10O2 2-methoxyphenol/C7H8O2 furfural/C5H4O2 4-ethyl-2-methoxyphenol/C9H12O2 3-methylcyclopentane-1,2-dione/C6H8O2 5-methylfuran-2-carbaldehyde/C6H6O2 acetic acid/C2H4O2 o-cresol/C7H8O p-cresol/C7H8O (E)-2-methoxy-4-(prop-1-enyl)phenol/C10H12O2 phenol/C6H6O 2,4-dimethylphenol/C8H10O furan-2(5H)-one/C4H4O2 m-cresol/C7H8O 2-methylfuran/C5H6O 1-(furan-2-yl)ethanone/C6H6O2 3-penten-2-one/C5H8O maltol/C6H6O3 methyl acetate/C3H6O2 propionic acid/C3H6O2 eugenol/C10H12O2 2-methoxy-4-propylphenol/C10H14O2 4-methyl-1H-imidazole/C4H6N2 3,4-dimethoxytoluene/C9H12O2 2-oxobutyl acetate/C6H10O3 2,5-dimethylfuran/C6H8O 1-hydroxybutan-2-one/C4H8O2 3-methylcyclopent-2-enone/C6H8O toluene/C7H8 4-methoxy-3-methylphenol/C8H10O2 2-butanone/C4H8O 2-methylcyclopent-2-enone/C6H8O (Z)-2-methoxy-4-(prop-1-enyl)phenol/C10H12O2 2,5-dimethoxytetrahydrofuran/C6H12O3 vinyl acrylate/C5H6O2 3-furaldehyde/C5H4O2 2-methyliminoperhydro-1,3-oxazine/C5H10N2O vinyl acetate/C4H6O2 5-methylfuran-2(5H)-one/C5H6O2 3,5-dimethylphenol/C8H10O 1,2-cyclopentanedione/C5H6O2 2-methylbenzofuran/C9H8O 2-oxopropyl acetate/C5H8O3 2-(1H-imidazol-4-yl)acetic acid/C5H6N2O2 6-methylpyrimidin-4(1H)-one/C5H6N2O p-xylene/C8H10 1-(4-hydroxybenzylidene)acetone/C10H10O2 furan-2,5-dione/C4H2O3 1,2-cyclohexanediol/C6H12O2 4,7-dimethylbenzofuran/C10H10O 1-(2-hydroxy-4-methoxyphenyl)ethanone/C9H10O3 2,5-hexanedione/C6H10O2 butyric acid/C4H8O2 4-ethylphenol/C8H10O 3-ethylphenol/C8H10O butanal/C4H8O 2-furanmethanol/C5H6O2 2-methoxybenzofuran-3-carbaldehyde/C10H8O3 4-ethyl-3-methylphenol/C9H12O ethylbenzene/C8H10

12.38 9.14 7.53 5.31 5.11 4.87 2.91 2.38 2.32 2.27 2.14 1.83 1.81 1.67 1.66 1.54 1.47 1.45 1.45 1.35 1.30 1.28 1.25 1.16 1.16 0.98 0.87 0.86 0.77 0.73 0.67 0.60 0.60 0.53 0.52 0.51 0.49 0.49 0.48 0.41 0.40 0.39 0.39 0.39 0.38 0.38 0.38 0.37 0.37 0.36 0.35 0.35 0.35 0.31 0.30 0.30 0.30 0.29 0.26 0.25

61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120

2,3-dimethoxytoluene/C9H12O2 3,4-dimethylphenol/C8H10O but-3-en-2-one/C4H6O 2,3,6-trimethylphenol/C9H12O dicyclopropylmethanone/C7H10O cyclopentanone/C5H8O benzene/C6H6 naphthalene/C10H8 2-ethylfuran/C6H8O 1,2,4-trimethylbenzene/C9H12 1-(2-hydroxy-6-methoxyphenyl)ethanone/C9H10O3 vinylfuran/C6H6O methyl propionate/C4H8O2 acrylic acid/C3H4O2 3-hexanone/C6H12O 2-ethyl-5-methylfuran/C7H10O 1-(2-hydroxy-5-methoxyphenyl)ethanone/C9H10O3 1,2-dimethoxy-4-propylbenzene/C11H16O2 2-methoxy-4-vinylphenol/C9H10O2 3,4-dimethylcyclopent-2-enone/C7H10O 5-methylcyclopenta-1,3-diene/C6H8 2,3-pentanedione/C5H8O2 2,5-dimethylanisole/C9H12O 5-methylfuran-2(3H)-one/C5H6O2 2-methylnaphthalene/C11H10 2-acetyl-5-methylfuran/C7H8O2 1,7-dimethylnaphthalene/C12H12 styrene/C8H8 2,6-dimethylnaphthalene/C12H12 2,3-dimethylcyclopent-2-enone/C7H10O 2-acetyl-5-norbornene/C9H12O 1,1-dimethoxypropane/C5H12O2 2-methylene-7-oxabicyclo[2.2.1]hept-5-ene/C7H8O 3-methylfuran/C5H6O dibenzofuran/C12H8O 1,3-dioxol-2-one/C3H2O3 5-norbornane-2-carboxaldehyde/C8H10O 7-methoxy-2,2-dimethyl-2H-chromene/C12H14O2 m-xylene/C8H10 2,3,5-trimethylfuran/C7H10O methyl 2-hydroxyacetate/C3H6O3 2-propen-1-ol/C3H6O 1-(furan-2-yl)propan-1-one/C7H8O2 2-methylpenta-1,4-diene/C6H10 1-ethyl-3-methylbenzene/C9H12 fluorene/C13H10 1,4-dimethoxybuta-1,3-diene/C6H10O2 2-(furan-2-yl)-2-methoxyethanol/C7H10O3 2,4-dihydroxy-2,5-dimethylfuran-3(2H)-one/C6H8O4 benzofuran/C8H6O pent-2-enal/C5H8O indene/C9H8 9H-xanthene/C13H10O 2,4-dimethylfuran/C6H8O 4-methoxy-1-naphthaldehyde/C12H10O2 mesitylene/C9H12 2-methoxy-5-methylphenol/C8H10O2 1,3,8-p-menthatriene/C10H14 limonene/C10H16 1-ethylidene-1H-indene/C11H10

0.24 0.23 0.23 0.23 0.22 0.21 0.21 0.20 0.19 0.19 0.19 0.18 0.17 0.17 0.17 0.17 0.16 0.16 0.15 0.15 0.14 0.14 0.14 0.14 0.14 0.14 0.12 0.12 0.11 0.11 0.11 0.10 0.09 0.09 0.09 0.09 0.09 0.08 0.08 0.08 0.08 0.07 0.07 0.07 0.07 0.06 0.06 0.05 0.04 0.04 0.04 0.03 0.03 0.03 0.03 0.02 0.02 0.01 0.01 0.01

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Table 4. continued a

PF = peak-area-based fraction.

for the pyrolysis of pine. Table 5 summarizes the results. It is noted that only the samples charged in the top six containers experienced the peak temperature (i.e., only nc = 1−6 passed through furnace 1) in R7−R13 and the char yields of nc = 6 did not reach the maximum values that could be reached at nc ≥ 10. The char yields were compared between R5 and R6 with different N2 flow rates, which gave char yields for nc = 6 and 10 very similar to each other. There was thus no or, if any, very little effect of the flow rate on the char yield. It was initially suspected that the gas flow rate, in other words, the residence time and concentration of HBO vapor in PZ, influenced the char yield to a certain degree. However, it was not the case under the present conditions. The same conclusion was drawn from the comparison between R8 and R10. The equivalent char yields for R8 with those for R9 also suggested no or little effect of the particle size. The effect of the peak temperature was revealed from the results of R6, R7, and R8, as expected. The differences in the char yield between nc = 1 and 6 at 550, 580, and 600 °C were all in the range of 0.07−0.08 kg/kg of dry feedstock. R11, R12, and R13 were carried out to investigate the applicability of the present pyrolysis system to different types of biomass. The char yields of nc = 6 were higher than those of nc = 1 by 0.07, 0.06, and 0.04 kg/kg of dry mallee, cherry, and rice husk, respectively. It was believed that the char yields of nc = 6 would be lower than the maximum yields that could be attained if more containers (e.g., nc = 10) passed through furnace 1. It was, however, confirmed that the present pyrolysis system increased the char yields of those samples. In comparison to the char yields of nc = 1 and 6 in Table 5, a similar increase in the char yields was found for the woody biomasses (pine, mallee, and cherry), whose cellulose contents accounted for 40−50 wt %,29 while a less char yield growth took place to rice husk with a cellulose content of around 30 wt %.30 Most of the top 25 compounds listed in Table 4 seemed to be formed from lignin or hemicellulose, which indicated that the components produced from cellulose were preferentially converted to char, LBO, and/or gases.23,24 It was thus suggested that the cellulose content of the parent feedstock was an important factor to influence the increase in the char yield because of bio-oil recycling. In addition to this, the inorganic species, such as potassium and calcium species, in the biomass, which favored the char-forming reactions,31 possibly influenced the increase in the char yield to a more or less extent.

Figure 8. TGA curves of LBO1-W and LBO1-O for R3.

evaporation. Selective production of LBO with no or a negligible residue after evaporation by the internal recycling of HBO was thus demonstrated. HBO, most of which was unamenable to GC/MS analysis because of the high boiling point and high molecular weight, was converted completely by internal recycling. The peak-area-based fraction (PF) was thus calculated for the individual compounds with an assumption that the 120 GC/MS-detected compounds represented the organic compounds contained in LBO. Although the response factor depended upon the compound type, PF indicated the abundances of the individual compounds in LBO semi-quantitatively. As exhibited in Table 4, 2-methoxy-4methylphenol and 2-methoxyphenol had the highest PFs in the LBO, 12 and 9%, respectively. The PFs of the top 20 and 50 compounds accounted for more than 70 and 90% of the total PF, respectively. 3.4. Gaseous Product. The noncondensable gases consisted mainly of CO, CO2, CH4, and H2, while minor compounds, such as C2H4, C2H6, C2H4O, C3H6, C3H8, C4H8, C4H10, and C4H4O, were detected and quantified. As exhibited in Figure 9, no

4. CONCLUSION The biomass pyrolysis with the internal recycling of bio-oil was studied with the originally developed experimental simulator of an updraft moving bed pyrolyzer, which consisted of PZ and CZ. In the pyrolysis of the pine with a peak temperature of 550 °C, a steady state was reached with stable char, liquid, and gas yields of 0.36, 0.47, and 0.17 kg/kg of the dry feedstock, respectively. A heavier portion of the bio-oil was sorbed to the parent biomass in the lower part of PZ and CZ, recycled into the middle and then upper parts of PZ, and converted there into the char and other products. In PZ, a portion of the bio-oil vapor was deposited into the pyrolyzing solid. These events caused the char yield to increase from 0.25 to 0.36 kg/kg of the dry feedstock. The resulting liquid comprised organic compounds with a carbon number of 2−13 and water and contained a negligible mass

Figure 9. Composition of noncondensable gases for R1−R3.

significant change in the gas composition was detected through R1−R3. Molar concentrations of CO2, CO, and CH4 were within narrow ranges of 41−43, 36−37, and 15−16%, respectively, on a N2-free basis. Concentrations of H2 and others were as low as 3− 4 and about 3%, respectively. The lower heating values of the gases from R1, R2, and R3 were calculated from the data of each component as 12.4, 13.0, and 13.1 MJ N−1 m−3 on a N2/ moisture-free basis, respectively. 3.5. Effects of Pyrolysis Conditions on the Extent of Increase in the Char Yield. Experimental conditions, such as peak temperature, flow rate of N2, and particle size, were varied 253

dx.doi.org/10.1021/ef301366x | Energy Fuels 2013, 27, 247−254

Energy & Fuels

Article

Table 5. Effects of Biomass Type, Particle Size, N2 Flow Rate, and Peak Temperature for the Pyrolysis on the Char Yields of 1st and 6th or 10th Containers char yield (kg/kg of dry feedstock)

a

run ID

sample

particle size (mm)

N2 flow rate [mL (STP)/min]

peak temperature (°C)

nc = 1

nc = 6

nc = 10

R5 R6 R7 R8 R9 R10 R11 R12 R13

pinea pinea pineb pineb pineb pineb malleeb cherryb rice huskb

0.5−1.0 0.5−1.0 0.5−1.0 0.5−1.0 1.0−4.0 0.5−1.0 0.5−1.0 0.5−1.0 not sizedc

20 200 200 200 200 500 200 200 200

550 550 580 600 600 600 540 600 550

0.27 0.25 0.24 0.23 0.23 0.21 0.35 0.26 0.42

0.34 0.33 0.32 0.31 0.31 0.30 0.42 0.32 0.46

0.36 0.36

nc = 1−10 passed through furnace 1. bnc = 1−6 passed through furnace 1. cAs-received material was used (major/minor axes of ca. 6.3/2.4 mm). (12) Antal, M. J.; Croiset, E.; Dai, X.; DeAlmeida, C.; Mok, W. S.-L.; Norberg, N.; Richard, J.-R.; Majthoub, M. A. Energy Fuels 1996, 10, 652−658. (13) Antal, M. J.; Allen, S. G.; Dai, X.; Shimizu, B.; Tam, M. S.; Grønli, M. Ind. Eng. Chem. Res. 2000, 39, 4024−4031. (14) Demirbas, A. J. Anal. Appl. Pyrolysis 2004, 72, 243−248. (15) Katyal, S.; Thambimuthu, K.; Valix, M. Renewable Energy 2003, 28, 713−725. (16) Bridgwater, A. V.; Peacocke, G. V. C. Renewable Sustainable Energy Rev 2000, 4, 1−73. (17) Diebold, J. P. A review of the chemical and physical mechanisms of the storage stability of fast pyrolysis bio-oils. In Fast Pyrolysis of Biomass a Handbook; Bridgwater, A. V., Ed.; CPL Press: Newbury, U.K., 2008; Vol. 2, pp 243−292. (18) Czernik, S.; Bridgwater, A. V. Energy Fuels 2004, 18, 590−598. (19) Salehi, E.; Abedi, J.; Harding, T. Energy Fuels 2011, 25, 4145− 4154. (20) Oasmaa, A.; Czernik, S. Energy Fuels 1999, 13, 914−921. (21) Huang, Y.; Kudo, S.; Norinaga, K.; Amaike, M.; Hayashi, J.-i. Energy Fuels 2012, 26, 256−264. (22) Wang, D.; Czernik, S.; Montane, D.; Mann, M.; Chornet, E. Ind. Eng. Chem. Res. 1997, 36, 1507−1518. (23) Sonoyama, N.; Hayashi, J.-i. Fuel 2012, DOI: 10.1016/ j.fuel.2012.04.023. (24) Antal, M. J.; Varhegyi, G. Ind. Eng. Chem. Res. 1995, 34, 703−717. (25) Miura, K.; Hayashi, J.-i.; Sano, N.; Hashimoto, K.; Iwakiri, H. J. Fuel Soc. Jpn. 1992, 71, 1184−1192. (26) Imam, T.; Capareda, S. J. Anal. Appl. Pyrolysis 2012, 93, 170−177. (27) Wang, X.; Kersten, S. R. A.; Prins, W.; Swaaij, W. P. M. Ind. Eng. Chem. Res. 2005, 44, 8786−8795. (28) Garcia-Perez, M.; Wang, X. S.; Shen, J.; Rhodes, M. J.; Tian, F.; Lee, W.-J.; Wu, H.; Li, C.-Z. Ind. Eng. Chem. Res. 2008, 47, 1846−1854. (29) Pettersen, R. C. The chemical composition of wood. In The Chemistry of Solid Wood; Rowell, R., Ed.; American Chemical Society (ACS): Washington, D.C., 1984; Advances in Chemistry, Vol. 207, Chapter 2, pp 57−126. (30) Abdelwahab, O.; Nemr, A. E.; Sikaily, A. E.; Khaled, A. Egypt. J. Aquat. Res. 2005, 31, 1−11. (31) Agblevor, F. A.; Besler, S. Energy Fuels 1996, 10, 293−298.

fraction of evaporation residue. The increase in the char yield by such internal recycling of bio-oil was confirmed under a variety of conditions with different peak temperatures, carrier gas flow rates, particle sizes, and types of feedstock.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: +81-92-583-7796. Fax: +81-92-583-7793. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS A part of this work was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan. The authors are grateful to the Strategic Funds for the Promotion of Science and Technology that was operated by the Japan Science and Technology Agency (JST) and the Funding Program for Next Generation World-Leading Researchers (NEXT Program) established by the Japan Society for the Promotion of Science (JSPS). Yong Huang also thanks the China Scholarship Council [Grant (2010) 3006] for financial support.

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REFERENCES

(1) Lucia, L. A.; Argyropoulos, D. S.; Adamopoulos, L.; Gaspar, A. R. Chemicals, materials, and energy from biomass: A review. In Materials, Chemicals, and Energy from Forest Biomass; Argyropoulos, D. S., Ed.; American Chemical Society (ACS): Washington, D.C., 2007; ACS Symposium Series, Vol. 954, Chapter 1, pp 2−30. (2) Mohan, D.; Pittman, C. U., Jr.; Steele, P. H. Energy Fuels 2006, 20, 848−889. (3) Mathews, J. A. Energy Policy 2008, 36, 940−945. (4) Scott, D. S.; Piskorz, J.; Radlein, D. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 581−588. (5) Ma, L.; Wang, T.; Liu, Q.; Zhang, X.; Ma, W.; Zhang, Q. Biotechnol. Adv. 2012, 30, 859−873. (6) Dall’Ora, M.; Jensen, P. A.; Jensen, A. D. Energy Fuels 2008, 22, 2955−2962. (7) Antal, M. J.; Grønli, M. Ind. Eng. Chem. Res. 2003, 42, 1619−1640. (8) Sohi, S. P.; Lopez-Capel, E.; Bol, R.; Krull, E. Adv. Agron. 2010, 105, 47−82. (9) MacPhee, J. A.; Gransden, J. F.; Giroux, L.; Price, J. T. Fuel Process. Technol. 2009, 90, 16−20. (10) Wang, L.; Trninic, M.; Skreiberg, Ø.; Gronli, M.; Considine, R.; Antal, M. J. Energy Fuels 2011, 25, 3251−3265. (11) Antal, M. J.; Mok, W. S. L.; Varhegyi, G.; Szekely, T. Energy Fuels 1990, 4, 221−225. 254

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