Journal of Analytical and Applied Pyrolysis 139 (2019) 239–249
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Pyrolysis of Millettia (Pongamia) pinnata waste for bio-oil production using a fly ash derived ZSM-5 catalyst
T
Kanit Soongprasita, Viboon Sricharoenchaikulb, Duangduen Atonga,
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a b
National Metal and Materials Technology Center, Thailand Science Park, Klong 1, Klongluang, Pathumthani, 12120, Thailand Department of Environmental Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand
ARTICLE INFO
ABSTRACT
Keywords: Pongamia pinnata Fast pyrolysis ZSM-5 Biomass Bio-oil Py-GCMS Drop-tube pyrolyzer
Fast pyrolysis of Millettia (Pongamia) pinnata waste (PPW) was performed using a scaled-up 180-cm drop-tube pyrolyzer with fly ash (FA)-derived ZSM-5 (FA-ZSM-5) as a deoxygenation and denitrogenation catalyst to upgrade the liquid products. The oil from P. pinnata is typically extracted to produce bio-fuel leaving a large amount of PPW that has some 20% (v/v) oil content. Since the PPW is inedible, due to its toxicity from karanjin and di-ketone pongamol, it represents a potential non-food competing ‘green’ biofuel feedstock. The FA-ZSM-5 catalyst applied in this work was synthesized using alkali hydrothermal treatment of coal FA to yield FA-ZSM-5 with a 329 m2/g surface area and 37.18 Å pore diameter. Pyrolyzer-gas chromatography-mass spectrometry was used to locate the optimal operating window prior to executing a scaled-up reactor operation at 400–700 °C). A maximum bio-oil yield of 43.1% by proportion was obtained at 500 °C, while the solid and gas products were 32.5% and 24.4%, respectively. Oleic acid was a major component in the bio-oil obtained from the non-catalytic condition, while ketones were prominent (79.4%) when FA-ZSM-5 was used, albeit with a low hydrocarbon (HC) selectivity. From the carbon chain length analysis, thermal cracking to smaller molecules was dominant in the presence of the FA-ZSM-5 catalyst, inducing a low HC yield in the liquid product.
1. Introduction
under a H2 environment [14]. Product selectivity of zeolite catalysts is strongly dependent on their acidity and pore diameter [15,16]. The aluminosilicate ZSM-5 catalysts have been applied to the improvement of pyrolytic products from polymeric and biomass feedstocks, and were reported to yield a high hydrocarbon (HC) selectivity of desired straight chain and monocyclic aromatic HCs (MAHs) [17]. Catalytic fast pyrolysis using ZSM-5 as a catalyst has been extensively studied on various biomass feedstocks, such as rice husk [18], pine sawdust [11,19], aspen wood [20], corn stalk [21] and corncob [22]. The ZSM-5 catalysts have three-dimensional pores that include sinusoidal (5.3 × 5.6 Å) and straight (5.2 × 5.7 Å) channels [16]. The catalytic activity of ZSM-5 zeolite has been ascribed to its Brønsted acid sites that result from the substitution of tetravalent silicon by trivalent aluminum, generating a negative charge within the framework. During the reaction, the Brønsted acid site is catalytically active by donating a proton to pyrolytic substrates, such as O- and N- compounds, leading to carbocation formation as intermediates [23]. These intermediate species subsequently undergo a further series of reactions, such as oligomerization, isomerization, hydrogenation and aromatization [19,24,25], which result in the production of favorable linear and aromatic HCs. These reactions mostly
De-oiled biomasses are one of the potential sustainable sources for production of renewable energy. In this work, Millettia (Pongamia) pinnata waste (PPW), a by-product from the oil extraction process for biodiesel production, was converted to bio-fuel products by fast pyrolysis. Utilization of PPW as an animal feedstock is prohibited due to its high toxicity from karanjin and di-ketone pongamol contents. High heating rate pyrolysis is a promising way to produce bio-oil from this otherwise discarded agricultural matter [1–4]. The bio-oil produced from the fast pyrolysis of biomass typically contains a high level of oxygenated compounds (O-compounds), such as carboxylic acids, ketones, alcohols, aldehydes, esters and ethers, and nitrogenated compounds (N-compounds) that result in a high acidity and low heating value [3,5]. Hence, the addition of an effective deoxygenating and denitrogenating catalyst would improve the heating value and stability of the produced bio-oil [5–13]. Zeolite has been reported as promising material for the bio-oil upgrading process, which may be operated under atmospheric pressure without the requirement of a hydrogen (H2) atmosphere. This leads to a low capital investment requirement and low safety concerns compared to the hydrodeoxygenation process
⁎
Corresponding author. E-mail address:
[email protected] (D. Atong).
https://doi.org/10.1016/j.jaap.2019.02.012 Received 1 October 2018; Received in revised form 14 February 2019; Accepted 22 February 2019 Available online 23 February 2019 0165-2370/ © 2019 Elsevier B.V. All rights reserved.
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Nomenclature PPW FA Py GC MS ZSM-5
HC PAHs MAHs m/z D10% D50% D90%
Pongamia pinnata waste Fly ash Pyrolyzer Gas chromatography Mass spectrometry Zeolite Socony Mobil-5
occur inside the pores and not on the external surface of ZSM-5 [26]. Coal fly ash (FA) is small particulate solid waste from coal-fired power plants and contains silica and alumina, making it a promising starting material for the polymerization reaction to form aluminosilicate structures, such as zeolite. In this work, bio-oil production under catalytic fast pyrolysis of PPW with ZSM-5 synthesized from coal FA (FA-ZSM-5) was investigated. Pyrolyzer-gas chromatography-mass spectrometry (Py-GC/MS) was performed in order to screen the chemical selectivity of FA-ZSM-5 on the pyrolysis vapors. Then, an upscaled drop-tube reactor was used to produce the bio-oil by fast pyrolysis of PPW in the presence of the FA-ZSM-5 catalyst at various biomass: catalyst (B:C) weight ratios and pyrolysis temperatures to evaluate the effects on the product selectivity.
Hydrocarbon Polycyclic aromatic hydrocarbon Monocyclic aromatic hydrocarbon mass-to-charge ratio Particle size at cumulative percentile 10% Particle size at cumulative percentile 50% Particle size at cumulative percentile 90%
bromide (98%, Aldrich) was then added slowly drop by drop as a structure director for ZSM-5 formation and stirred continuously for 3 h. Concentrated H2SO4 was added to control the pH of the mixture at 11. Crystallization of ZSM-5 was then performed out in a polytetrafluoroethylene lined stainless steel autoclave at 160 °C for 72 h. The sodium form of ZSM-5 was filtered and dried for 24 h prior to being ionexchanged with 1 M NH4Cl, dried and calcined at 540 °C for 5 h to yield the protonated FA-ZSM-5. Phase analysis of the synthesized FA-ZSM-5 was performed by X-ray powder diffraction (XRD) analysis using a PANalytical, X’ Pert Pro instrument at 40 kV and 45 mA CuKα radiation. The sample was scanned at a 2θ from 5–60◦ with a step size of 0.02. The microstructure was characterized by scanning electron microscopy (SEM) using a JEOL, JSM-5410 instrument. The particle size and distribution were measured by DLS with a Mastersizer 2000 (Version 5.54 Serial Number: MAL 1021434, Malvern Instrument Ltd). The specific surface area was determined from the nitrogen (N2) adsorption isotherms derived from an Autosorb-1 (Quantachrome instruments) instrument and BrunauerEmmett-Teller (BET) analysis. The acidity of the synthesized HZSM-5 catalysts was determined by ammonia temperature-programmed desorption (NH3-TPD) using a BELCAT instrument. Detailed procedure for the determination of acidity can be found elsewhere [16].
2. Experimental 2.1. Biomass feedstock De-oiled PPW with 20% (v/v) oil residue was supplied as a cake from a local oil extraction plant and was then crushed and sieved through ASTM standard meshes into 125–425 μm sized particles to minimize the thermal gradient between the internal and surface of the biomass upon heating. The chemical composition of the PPW sample was determined by proximate and ultimate analysis using thermogravimetric analysis (TGA) on a METTLER TOLEDO; TGA/SDTA 851e instrument and a CHNS analyzer (LECO; TrueSpec CHN/CHNS), respectively, with the results summarized in Table 1. Overall, PPW was deemed to be suitable as a bio-oil feedstock since it contained a high level (91.8%) of combustible compounds (volatile matter and fixed carbon) and an approximately 52.8% carbon content. A previous TGA study revealed that PPW is completely decomposed at 550 °C [27], which corresponds to the thermal degradation of lignocellulosic compounds. Thus, a pyrolysis temperature in the range of 400–700 °C was applied in this thermal conversion study.
2.3. Analysis of chemical selectivity of the PPW pyrolysis vapors by Py-GC/ MS The analytical Py-GC/MS experiments were conducted using a Pyrolyzer (Frontier; Py-2020iD) with an auto-shot sampler (Frontier; AS-1020E) interfaced to a GC (Shimadzu; GC 2010) with MS (Shimadzu; QP 2010 Plus) to investigate the pyrolysis products formed at 500 °C. In each experimental run, the PPW sample was kept at 0.4 mg while the catalyst quantities were varied to achieve B: C weight ratios of 1:1, 1:5 and 1:10, and placed in the stainless steel crucible covered with a glass wool layer. The details of the experimental set up were as previously reported [27]. National Institute of Standards and Technology (NIST) and Wiley mass spectrum libraries was referred to in order to identify each compound presented in the chromatographic peaks. Detectable pyrolytic products were categorized as O-compound, N-compound, aromatic HC, aliphatic HC and phenol compounds according to
2.2. Synthesis of the FA-ZSM-5 catalyst Coal FA was supplied from local power plant. The chemical composition of the FA sample was characterized by X-ray fluorescence spectrometry (XRF) using a RIGAKU ZSX Primus spectrometer, with the results summarized in Table 2. The FA sample was classified as a Class C FA due to its high CaO content (18.9%). Fe2O3 content was comparable to fly ash data from other countries i.e., Canada (3.1–29.3%), China (0.55–9.9%), India (3.2–5.3%), Italy (3.8–8.8%), Japan (1.1–12%), Spain (6.1–19%), UK (7–15%), and USA (3.5–9.9%) [28]. The particle size and specific surface of FA were determined by dynamic light scattering (DLS) using a particle size analyzer (MALVERN; Mastersizer 2000) and surface area analyzer (Quantachrome Instruments; Autosorb1C), respectively, with the results summarized in Table 3. The FA-ZSM-5 was synthesized using alkali hydrothermal treatment (Fig. 1) followed Vichaphund and co-workers method [6]. For each batch, 3 g of FA was dispersed in 25 ml of 3 M NaOH solution for 3 h to form a mixed silicate and aluminate solution. Sodium metasilicate solution (Na2O3Si • 5H2O, ≥ 97%, Fluka) was added into the FA solution to adjust the initial silica: alumina ratio to 24:1. Tetrapropylammonium
Table 1 Proximate and ultimate analysis of the 125–425 μm sized PPW particles used as a biomass feedstock in this study. Composition Proximate analysis Moisture Volatile matter Fixed carbon Ash Ultimate analysis Carbon Hydrogen Nitrogen Sulfur Oxygen (by difference)
240
%Weight 5.33 74.73 17.10 2.84 52.79 6.26 3.88 0.06 37.01
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of 60 min to ensure a uniform temperature profile. To initiate the experiment, 30 g (at 1 g/min) of dried PPW was fed into the pyrolyzer with a N2 flush and purge system. During the pyrolysis process, PPW was decomposed to gas and solid, with the later being collected at the bottom of reactor. The produced gas was subsequently directed through the catalytic unit, which contained 3 g of FAZSM-5 mixed with 80 g of silicon carbide. Soot and small particulates were separated in the cyclone and moisture was trapped with water cooled condenser. For HCs, such as bio-oil and other condensate products, three liquid N2 cooled condensers in series were used to ensure efficient collection. Non-condensable products (permanent gas) were then passed through a gas clean up unit to eliminate any remaining particulate residue prior to volume measurement using a flowmeter. The composition of the gas, including carbon dioxide, carbon monoxide, H2 and methane, were measured using an online-gas analyzer equipped with nondispersive infrared and flame ionization detectors. The experiment was performed for 30 min to ensure steady state operation.
Table 2 Chemical composition of the power plant coal FA used in this study for the FA-ZSM-5 synthesis. Compound
%Weight
SiO2 Al2O3 CaO Fe2O3 SO3 K2O MgO Na2O TiO2 P2O3 MnO ZrO2 Loss on ignition
34.14 19.13 18.93 14.57 5.47 2.42 2.08 1.13 0.50 0.23 0.11 0.04 0.64
Table 3 Particle size and specific surface area of the obtained coal FA. Particle size (μm)
Coal FA
Mean diameter [d(4,3)]
D10% [d (v,0.1)]
D50% [d (v,0.5)]
D90% [d (v,0.9)]
29.01
2.58
13.60
76.01
2.5. Characterization of the bio-oil
Surface area (m2/g)
The bio-oil obtained from the fast pyrolysis of PPW was characterized using GC/MS in order to study the activity and selectivity of the synthesized FA-ZSM-5 catalyst. The as-formed bio-oil was evaporated at room temperature for 48 h to remove moisture. The bio-oil was diluted to 5% (v/v) with acetone and filtered prior to injecting into the GC/MS. The injected sample was separated using a DB-1701 column starting at 50 °C for 1 min and then heating at 4 °C/min to 280 °C and held at this temperature for 10 min. Identification of each chemical species was executed at a mass-tocharge ratio (m/z) value of 200–800 at a 70 eV ionization energy and a 625 amu/s scan speed. The NIST and Wiley mass spectrum libraries were correlated with each peak.
1.28
the criteria shown in Table 4. The relative peak area was calculated to define the selectivity for the compounds in the pyrolysis vapor. 2.4. Drop-tube pyrolyzer In this work a 316 l stainless steel drop-tube pyrolyzer with a 7.62 cm diameter and 180 cm height was used as the main reactor vessel for the fast pyrolysis of PPW. The experimental set up with an auxiliary system is displayed schematically in Fig. 2. Full description of this pyrolyzer system can be found in the work by Vichaphund and coworkers [16]. Prior to each run, the reaction zone temperature was raised to the desired set point (400–700 °C) followed by a soaking time
3. Results and discussion 3.1. Characteristics of the synthesized FA-ZSM-5 catalyst The XRD pattern of synthesized FA-ZSM-5 sample showed peaks
Fig. 1. Outline of the synthesis of FA-ZSM-5 by alkali hydrothermal treatment. 241
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Table 4 Criteria used to identify categories of compounds obtained from the Py-GC/MS analysis [27]. Category
Compounds
Example
N-compound Aromatic HC Aliphatic HC O-compound
Amine, amide and other with eNe in their structure Aromatic ring in the HC structure Linear and cyclic HC structure Alcohol, aldehyde, carboxylic acid, ester, ether, furan, ketone and sugar Phenol and phenol-derivative
eNHe, eNH2, eNe C6H6 (benzene), eC6H6e (derivative) C12H24 (linear), C12H22 (cyclic) eOH, eCOeH, eCOeOH, eCOeOe, eOe, C4H10O (furan), eCOe, eCnH2nOne derivative C6H6O derivative
Phenol
corresponding to the ZSM-5 and Wairakite (Fig. 3). The appearance of the certain peaks at a 2θ of around 7–9 and 23–25 indicated the ZSM-5 structure (JCPDS 44-0003) [29], and confirmed that the alkali concentration was sufficient to dissolve the silicon and aluminum in the coal FA to free ions prior to preparing the aluminosilicate structure by polymerization. The Wairakite structure (from JCPDS 89-0276), which is an aluminosilicate structure containing calcium ions, resulted from the high-calcium content of the FA raw material (ASTM Class C) used in this work. The average particle size of the synthesized FA-ZSM-5 was 16.23 μm with a BET specific surface area of 329 m2/g. The pore diameter and total pore volume of FA-ZSM-5 was 37.18 Å and 0.193 cm3/ g, respectively. The SEM analysis revealed that the FA-ZSM-5 consisted of agglomerated particles of a shape close to a cube or rectangular cube (Fig. 4), which is similar to those reported previously [30]. Fig. 3. Representative XRD diffractogram of the synthesized FA-ZSM-5.
3.2. Fast pyrolysis of PPW by Py-GCMS
yield, fast pyrolysis was performed with the synthesized FA-ZSM-5 catalyst at three different catalyst contents (B:C weight ratio of 1:1. 1:5 and 1:10). At a B:C weight ratio of 1:1, carboxylic acids and N-compounds were still detected, which might be due to an insufficient number of acid sites in the FA-ZSM-5 catalyst relative to the amount of pyrolysis vapor for the deoxygenation and denitrogenation reactions. The distribution of the chemical compositions of the pyrolysis vapors clearly changed, especially for compounds with a RT of 2–20 min, at higher catalyst contents (B:C weight ratio of 1:5 and 1:10), where the higher intensities and clear peaks indicated a greater level of formed HCs, while the intensity of carboxylic acids and N-compounds was
The fast pyrolysis of 125–425 μm sized PPW particles with the FAZSM-5 catalytic upgrading of the pyrolysis vapors was performed using a Py-GC/MS instrument. The main objective was to study the distribution of the chemical composition of pyrolysis vapors and to evaluate the effect of the FA-ZSM-5 catalyst on the yield of HCs. A typical chromatogram from the GC/MS analysis is illustrated in Fig. 5A. Without the catalyst, an outstanding signal was clearly observed at a retention time (RT) of 37.25 min, which was identified as oleic acid. In addition, N-compounds were detected at a RT of 5.84, 39.61 and 42.2 min, while a small amount of aromatic and aliphatic HCs were formed. In an effort to remove the O-compounds and increase the HC
Fig. 2. Schematic representation of the drop-tube pyrolyzer used in this work. (a) Carrier gas (N2) supply, (b) totameter, (c) stainless steel reactor with gas preheater, (d) cyclone, (e) water-cooled condenser, (f) liquid N2 condenser, (g) gas washer, (h) flow meter and (i) online-gas analyzer. 242
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decreased. At a B:C weight ratio of 1:10, the carboxylic acid signal disappeared, which suggested that the deoxygenation reaction was dominant. Fig. 5B shows chemical compositions of pyrolysis vapors, which were categorized by the reaction stage, including depolymerization/ dehydration products, secondary products and acid catalyzed products, as suggested by Mochizuki and co-workers [5]. Dehydration/ depolymerization products are directly produced from the degradation of lignin and cellulose structures, such as phenol, sugar and furan, while the secondary products are obtained from further decomposition of the aforementioned compounds to O- and N-compounds. Acid catalyzed products are mainly composed of aromatic and aliphatic HCs, which require the presence of a high level of selective acid sites under the catalytic condition. As mentioned earlier, carboxylic acids are a major component of the PPW pyrolysis vapor from low acid catalyzed products. The carboxylic acid content was decreased under the catalysis of FA-ZSM-5 from 58.3% (no catalyst) to 24.0% with the FA-ZSM-5 catalyst at a B: C weight ratio of 1:5 and was not detected when the B:C weight ratio was increased to 1:10. In addition the level of N-compounds was also drastically reduced
Fig. 4. Representative SEM image (10,000 x magnification) of the synthesized FA-ZSM-5 catalyst. Image shown is representative of those seen from at least 3 fields of view per sample and 3 samples.
Fig. 5. (A) Representative chromatogram of the pyrolysis vapors and (B) chemical compounds obtained from the fast pyrolysis of PPW at 500 °C without (thermal) or with the FA-ZSM-5 catalyst at various B:C weight ratios.
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Fig. 6. Compounds in the pyrolysis vapors categorized by the criteria in Table 4. Table 5 Acid site of FA-ZSM-5 carried out by NH3 temperature programmed desorption (TPD) technique. Catalysts
FA-ZSM5
Acid site (mmol NH3/g) / Temperature (°C) Weak acid
Strong acid
Total
0.451 / 175
0.186 / 660
0.634
from 24.8% (no catalyst) to 8.30% with FA-ZSM-5 at a B: C weight ratio of 1:10. The addition of FA-ZSM-5 increased the yield of HCs and at a B: C weight ratio of 1:10 gave the highest yield of aromatic HCs (82.7%) with an additional 7.9% aliphatic HCs. High loading of FA-ZSM-5 directly gave high amount of acid sites which promoted deoxygenation and denitrogenation reactions at the acid site of zeolite [23]. From our previous study on pyrolysis of PPW with Zeolite Y as catalysts [27], significant improvement on aromatic HC yield (98.3%) was obtained when biomass to catalyst ratio was increased to 1:5. Thus, higher catalyst loading is crucial operating parameter to facilitate sites for pyrolysis vapors to undergo de-oxygenation and de-nitrogenation reactions to form value added products such aromatic and aliphatic hydrocarbons. This result was also agreeable with Vichaphund and coworkers [6],who reported positive effect of increasing catalyst content on enhancing aromatic hydrocarbon content (above 93%) in pyrolysis of jatropha as well as decreasing of oxygenated and nitrogenated compounds. The significant increase in the proportion of aromatic HCs corresponded well with the reduction in the level of O- and N-compounds (Fig. 6). A remarkable reduction in the level of O-compounds was observed at high catalyst contents (B: C weight ratio of 1:5 and 1:10), which indicated that the decarboxylation and decarbonylation reactions were promoted at high acid site contents (0.634 mmol NH3/g) as shown in Table 5. Weak acid sites were found at desorption temperature ˜ 175 °C (0.451 mmol NH3/g) corresponded to non-framework Lewis acid sites while strong acid sites was at ˜ 660 °C (0.186 mmol NH3/g) associated with Brønsted acid sites. However, phenol, a starting material for chemical synthesis, was not observed under these catalytic conditions. The absent of phenol, categorized as depolymerization/dehydration product, was possibly due to its conversion into secondary products. Shadangi and Mohanty [8] studied bio-oil production from fresh karanja seed (Pongamia pinnata seed prior to oil extraction) and reported low phenol (3% of peak area)
Fig. 7. (A) Chemical composition (as categories) of the HC products and (B) carbon chain length of the chemical compounds of the pyrolysis vapors from PPW.
for thermal conversion and 1.9%, 0.8%, and not detected when adding Al2O3, CaO, and Kaolin, respectively, for feed to catalyst ratio of 8:1. Mullen and co-workers suggested that light organic molecules such as phenol and oxygenated compounds could be cracked to olefin and aromatized to aromatic compounds over HZSM-5 catalysts [31]. Murata and co-worker [32] stated that phenol was converted to aromatics via hydrodeoxygenation and dehydroaromatization over large size pore structure catalysts. Moreover, deactivation of the FA-ZSM-5 catalyst was not clearly noted under high catalyst contents as noticed by continue increase of hydrocarbon products at these conditions. In general, coke formation is usually found on microporous zeolite leading to pore blocking, and results from the polymerization of intermediates and condensation of HCs during the reaction [30,33,34]. Formation of coke on the catalyst surface limits transportation of intermediate species to the acid sites and results in lower aromatic HC yields [35]. In contrast, bio-oil production under particular metal oxide catalysts favored secondary reactions at high catalyst contents and so results in tar formation on the catalyst’s surface and poor bio-oil quality and yields. Lu and co-workers studied the pyrolysis of poplar wood and reported that bio-oil yield, as total peak area, was greatly decreased by approximately 44% when using CaO catalyst [36]. Asikin-Mijan and co-
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workers reported deactivation of CaO catalyst due to the reaction with carboxylic acid which resulted in an inactive CaCO3 [37]. In addition, Vichaphund and co-workers also reported the presence of cyclic ketones (14.28%), typically unstable compounds, in bio-oil from catalytic pyrolysis of Jatropha using Co-CaO and led to poor bio-oil quality such as lower heating value and short shelf life [16]. The HC compounds were categorized as linear, cyclic, MAHs and polycyclic aromatic HCs (PAHs), as shown in Fig. 7A. Linear and cyclic HC yields were slightly changed in the presence of the FA-ZSM-5 catalyst in the pyrolysis process, where the FA-ZSM-5 catalyst showed a selective production of MAHs, such as benzene and benzene derivatives, rather than PAHs. In accord, a high selectivity for aromatic products was also reported in the fast pyrolysis of jatropha waste with a synthesized [15] and commercial [32] ZSM-5 catalyst using Py-GC/MS. The aromatic selectivity of bio-oil is controlled by mass transfer and transition state effects, which were dependent on the pore opening and internal void space, respectively, in the zeolite framework [23]. This suggested that the synthesized FA-ZSM-5 catalyst in this study may have an appropriate pore structure that favors monocyclic aromatic hydrocarbon production. The internal pore structure including an
Fig. 8. Product distribution from the fast pyrolysis of PPW at different temperatures using a drop-tube pyrolyzer (a) without (thermal) or (b) with the FAZSM-5 catalyst addition.
Fig. 9. (A) Representative chromatogram and (B) chemical compounds in the bio-oil obtained from the non-catalytic (thermal) fast pyrolysis of PPW in a drop-tube pyrolyzer. 245
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Fig. 10. (A) Representative chromatogram of the bio-oil and (B) chemical compounds obtained from the catalytic fast pyrolysis of PPW with FA-ZSM-5 at different pyrolysis temperatures in a drop-tube pyrolyzer.
average pore size of 37.18 Å with the micropore size determined by NLDFT of 6.00 Å, and total pore volume (0.193 cm3/g) of FA-ZSM-5 catalyst allow the oxygenated species to easily diffuse into zeolite framework consequently undergo a series of deoxygenation (decarbonylation, decarboxylation, dehydration) and aromatization at active sites to attain more MAH [24,26]. In contrast, in the pyrolysis of lignin to bio-oil using the ZSM-5 catalyst, phenol and phenol derivative compounds were reported as the main composition, while MAHs and PAHs were quite low [32,38]. Thus, the composition of the biomass feedstock can likely affect the chemical composition of the obtained bio-oil. Carbon chain length was categorized into C5–12 (gasoline), C13–20 (diesel) and C > 20 [39], as illustrated in Fig. 7B. The FA-ZSM-5 catalyst promoted fragmentation of the HC chains and so resulted in an enhanced proportion of C5–12 up to 60% and 90.3% at a B: C weight ratio of 1:5 and 1:10, respectively. Overall, the FA-ZSM-5 catalyst showed a high selectivity towards aromatic HC products (82.7%) via decarbonylation and decarboxylation of O-compounds and denitrogenation of N-compounds. Moreover, fragmentation of the alkyl group from Oand N-compounds was evident by the presence of shortened chain length products.
3.3. Drop-tube pyrolysis of PPW The distribution of products obtained from the fast pyrolysis of PPW using the drop-tube pyrolyzer is summarized in Fig. 8. For the thermal (non-catalytic) operation, the highest bio-oil production of 43.1% was found at 500 °C, while char and gas products were 32.5% and 24.4%, respectively. A somewhat high char yield of 60.9% at 400 °C indicated that PPW was only partially decomposed at this relatively low reaction temperature. At 700 °C, the gas fraction was abruptly increased to 54.6%, due to the appreciable level of thermal cracking of bio-oil and other condensates to gas products at the high temperature. The catalytic fast pyrolysis exhibited a product distribution in broadly the same fashion as the non-catalytic results, but to a different extent. The catalytic bio-oil products were found at 26.7–39.2%, with the highest yield being obtained at 600 °C. The gas fractions obtained at 400–600 °C slightly increased with increasing temperature up to 600 °C and markedly at 700 °C, while the proportion of bio-oil also increased up to 600 °C (but decreased at 700 °C), which was at the expense of char reduction. The high pyrolysis temperature of 700 °C obviously enhanced the thermal cracking of bio-oil to gas products, as clearly 246
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10. For the non-catalytic (thermal) fast pyrolysis, carboxylic acid, assigned as oleic acid, appeared at a RT of 54.59 min for pyrolysis at 400 °C and 500 °C, but was not observed at 600 °C or 700 °C, while Ncompounds were noticeable as major products at a RT of 25 min (Fig. 9A). Secondary products, especially carboxylic acids and N-compounds, were found in the non-catalytic pyrolysis of PPW (Fig. 9B). The highest selectivity for aliphatic HC formation (29.2%) was attained at 600 °C, although the lowest level of N-compounds (20%) was obtained at the lower temperature of 500 °C. A relatively low level of depolymerization/dehydration products (less than 20%) was found at all temperatures tested. With respect to the bio-oil obtained from the catalytic (FA-ZSM-5) fast pyrolysis of PPW, a representative chromatograph is displayed in Fig. 10A. The peak intensity at a RT of about 5 min was prominent at all reaction temperatures and was identified as a ketone. N-compounds were found at a RT of 23, 64 and 75 min, and represent products from secondary reactions, while sugar and pyran were observed at a RT of 48 min and 76 min, respectively. A higher intensity and stronger signals were detected at a pyrolysis temperature of 700 °C, especially for compounds with a RT of 25–50 min. Most of these peaks represented Ncompounds, along with some acid catalyzed products, such as aromatic HCs. Ketone and N-compounds were formed during the catalytic FAZSM-5 trials at around 56.9–77.5% and 7.2–16.2%, respectively, as displayed in Fig. 10B. Acid catalyzed products were found in low contents, with a maximum aromatic HC content of 6.12%. Data from thermal degradation of PPW using drop tube reactor indicated high selectivity on carboxylic acid, mostly oleic acid (C18-1) along with more unfavorable nitrogenated compounds and favorable aliphatic hydrocarbons. Addition of ZSM-5 catalyst resulted in lower bio-oil yield with more selective content on ketone compound rather than targeted aliphatic hydrocarbons. Steric hindrance of pyrolysis vapors could possibly explain this lower hydrocarbon selectivity. Borah and coworkers [40] studied the diffusion of pentane isomer (n-pentane, isopentane, and neopentane) in zeolite NaY. They reported self-diffusivity and activation energy of pentane isomer which related to its structure. Branched structures (isopentane and neopentane) display superior diffusivity with lower activation energy than linear structure (n-pentane). In the other words, molecular diameter and structure related with pore diameter of zeolite, levitation effect, plays an important role on diffusion of pyrolysis products through the micropore structure. As a result, produced carboxylic acid and N-compound from drop-tube pyrolyzer may have low diffusivity through micropore structure of ZSM-5 (6.0 Å diameter) and a series of reactions such as cracking and deoxygenation (dehydration, decarbonylation and decarboxylation) of large oxygenates [26] are mostly occurred on the external surface. Hence, smaller oxygenated compounds, particularly ketones, were found in higher content than hydrocarbons, which can be produced at acid site inside pore structure via aromatization reaction. Low aromatic yield from catalytic pyrolysis of pongamia pinnata seed was also reported by Shadangi and Mohanty [8] who used semibatch reactor for bio-oil production. They reported 18.1% of oleonitrile in liquid product obtained from thermal conditions. Addition of CaO, Al2O3, and kaolin as catalysts resulted in esters as major products which were converted from carboxylic acid while ketone compounds were possibly produced from ketonization or ketonic decarboxylation which is a reaction of two carboxylic molecules (Eq 1). This reaction plays a crucial role on elimination of oxygen atom during biomass conversion [40 > 41]. Significantly high ketone is correspond to the reduction of carboxylic acid with catalyst addition, especially at 700 °C.
Fig. 11. Compounds of bio-oil, categorized by (A) the criteria in Table 4 and (B) carbon chain length, obtained without (thermal) or with FA-ZSM-5 pyrolysis of PPW at different temperatures.
Fig. 12. HC products (as categories) in the bio-oil obtained without (thermal) or with FA-ZSM-5 pyrolysis of PPW at different temperatures.
R1-COOH + R2-COOH → R1COR2 + CO2 + H2O
indicated by the significant increase in the gas fraction to 57.0%. Vichaphund et al. [16] also reported slight decrease of bio-oil yield from 47.2% to 29.4–32.2% via fast pyrolysis of Jatropha waste with ZSM-5 catalyst using a fixed bed reactor. Identification of the chemical composition in the bio-oil products was performed by GC/MS analysis, with the results shown in Figs. 9 and
(1)
Moreover, these intermediate ketones can further undergo aldol reaction, resulting in gasoline/diesel molecular range and larger products [41]. Wan and co-workers [42] studied catalytic treatment of liquid products from pyrolysis of oak and switchgrass using Ru/TiO2 as 247
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catalysts. They reported that sharpen increasing of ketone compound are directly corresponded with lower carboxylic acid which confirmed ketonization reaction under catalytic pyrolysis at 400 °C. Wang and coworkers [43] proposed reaction pathways of propionic conversion to aromatic over ZSM-5 catalysts. First, propionic acid were converted to ketone via ketonization reaction and followed by aldol condensation to larger carbon chain with ketone as functional group. Subsequent cyclization, aromatization, and dealkylation reactions of ketone leads to the formation of favorable aromatic compounds. It appeared that aromatic formation by these reactions was not appreciably realized in this work when catalysts were added, resulted in high ketone in bio-oil products. In this work, the lower selectivity for aromatic HCs than expected when compared with the Py-GC/MS results may due to short reaction time of pyrolyzed gas within the catalytic zone. However, the high ketone content is a promising indicator that FA-ZSM-5 synthesized from fly ash could possibly promote more aromatic formation if contact time can be prolonged. O-compounds were produced in the range of 74.1–90.6%, which was significantly enhanced compared to the non-catalytic (thermal) conditions, although the level of N-compounds was reduced to 7.2–16.2% (Fig. 11A). Majority of O-compound species are ketones as indicated in Fig. 10 which are main products from ketonization reaction of carboxylic acid, Eq. 1, as mentioned earlier. However, subsequent favorable reactions such cracking, cyclization, acylation and aromatization to aromatic structure could not appreciably achieved due to restricted timeframe between these reactants and acid sites on the FA-ZSM-5 surface during the conversion process. Aho and co-workers [19] also reported greater 1.55 times more ketones than thermal conversion process when HZSM-5 was used during pyrolysis of woody biomass while PAHs were slightly increased from 0% (thermal) to 3.1%. The reduction of nitrogenated compounds from 64% (thermal) to 27% and less than 18% of hydrocarbon compounds by addition of ZSM-5 catalysts were also reported by Vichaphund and co-worker [16] who pyrolyzed Jatropha using drop tube reactor. In contrast, using ZSM-5 as catalysts for fast pyrolysis of palm kernel shell wastes resulted in substantially higher N-compounds from 11.3% (thermal) to 42.6% with slight increase of aromatic compounds from 2.4% (thermal) to 3.4% as reported by Kim and co-workers [44]. Biomass conversion under thermal and catalytic pyrolysis clearly led to a difference in the carbon change length in the bio-oil (Fig. 11B). For the thermal pyrolysis, C13–20 were the main products at 79.5% and 75.4% at a pyrolysis temperature of 400 °C and 500 °C, respectively, and continued to decrease as the temperature increased to 600 °C (50.7%) and 700 °C (28.2%). Small molecules (C5–12) were the main products (75.6–91.85%) in the catalytic pyrolysis, with a maximum proportion at 500 °C. It may be suggested from this finding that FAZSM-5 catalysts also enhanced the thermal cracking of the produced HC compounds under pyrolysis in the drop tube pyrolyzer. In other words, thermal cracking to small molecular products is dominate and results in the production of small HCs. Linear HCs were the dominant HC form at moderate reaction temperatures, while PAHs become more prominent at the higher temperature of 700 °C (Fig. 12). High linear hydrocarbon also found as main composition of bio-oil from pyrolysis of Pongamia pinnata seed materials which were reported by Shadangi and Mohanty [8]. From their results, 22.1% of linear hydrocarbon is appeared with total hydrocarbon yield at 24.8%. This confirms characteristic of Pongamia pinnata on production of hydrocarbon with linear structure under thermal condition. Moreover, their addition of metal oxide catalysts also resulted in similar kinds of compound products as thermal process cases with a little variation. Yield of bio-oil was not significantly changed under catalytic condition. In the drop tube pyrolyzer runs, it is apparent that most of the hydrocarbon-based products from catalytic experiments are in the form of ketones which are intermediate products, as seen on Fig. 10. This led to lower bio-oil and other hydrocarbons as noticed in catalytic trials. The effect of these catalysts on promoting the formation of these secondary
oxygenated products should be further investigated. 4. Conclusion Bio-oil production from PPW was investigated with and without the synthesized FA-ZSM-5 catalyst. Py-GC/MS experiments were performed to evaluate the catalytic performance and chemical selectivity of the FA-ZSM-5 on the pyrolysis vapor at 500 °C. The up-scaled bio-oil production was studied using a drop-tube pyrolyzer at a 1 g/min PPW feed rate. The synthesized FA-ZSM-5 catalyst exhibited a ZSM-5 structure with Wairakite as a secondary compound and consisted of agglomerated particles shaped close to a cube or rectangular cube with a 37.18 Å pore diameter. Pyrolysis of PPW by Py-GC/MS revealed that FA-ZSM-5 promoted deoxygenation and denitrogenation reactions, resulting in a high selectivity for aromatic (82.7%) and aliphatic (7.9%) HCs at a B: C weight ratio of 1:10. The proportion of O- and N-compounds was decreased to 1.13% and 8.30%, respectively. Up-scaled bio-oil production by the drop-tube pyrolyzer yielded a maximum bio-oil fraction of 43.1% at 500 °C without a catalyst. Introduction of the FA-ZSM-5 catalyst then reduced the bio-oil yield to 39.2% while increasing the gas and solid fraction to 33.2% and 27.7%, respectively, at 600 °C. Oleic acid was the major compound in the bio-oil formed by the non-catalytic (thermal) process. Ketone was a key compound (79.4%) when FA-ZSM5 was used, with a low HC selectivity suggesting that thermal cracking to smaller molecules may dominate in the presence of the catalyst and so result in low HC yields. Acknowledgements This research was supported by National Metal and Materials Technology Center, Thailand [Project No.MT-B-58-CER-07-308-I]. References [1] P. Basu, Biomass Gasification and Pyrolysis: Practical Design and Theory, Elsevier, Massachusetts, 2010. [2] A.V. Bridgwater, Principles and practice of biomass fast pyrolysis process for liquids, J. Anal. Appl. Pyrol. 51 (1999) 3–22. [3] S. Czernik, A.V. Bridgwater, Overview of application of biomass fast pyrolysis oil, Energy Fuel 18 (2004) 590–598. [4] A. Demirbas, Effects of temperature and particle size on bio-char yield from pyrolysis of agricultural residues, J. Anal. Appl. Pyrol. 72 (2004) 243–248. [5] T. Mochizuki, S.Y. Chen, M. Toba, Y. Yoshimura, Pyrolyzer-GC/MS system-based analysis of the effects of zeolite catalysts on the fast pyrolysis of jatropha husk, Appl. Catal. A:-Gen. 456 (2013) 174–181. [6] S. Vichaphund, D. Aht-Ong, V. Sricharoenchaikul, D. Atong, Characteristic of fly ash derived zeolite and its catalytic performance for fast pyrolysis of Jatropha waste, Environ. Technol. 35 (2014) 2254–2261. [7] N.K. Nayan, S. Kumar, R.K. Singh, Characterization of the liquid product obtained by pyrolysis of karanja seed, Bioresour. Technol. 124 (2012) 186–189. [8] K.P. Shadangi, K. Mohanty, Thermal and catalytic pyrolysis of karanja seed to produce liquid fuel, Fuel 115 (2014) 434–442. [9] L. Prasad, P.M.V. Subbarao, J.P. Subrahmanyam, Pyrolysis and gasification characteristics of pongamia residue (de-oil cake) using thermogravimetry and downdraft gasifier, Appl. Therm. Eng. 63 (2014) 379–386. [10] N. Mukta, Y. Sreevalli, Propagation techniques evaluation and improvement of the biodiesel plant, Pongamia pinnata (L.) Pierre-a review, Ind. Crop. Prod. 31 (2010) 1–12. [11] C. Torri, M. Reinikainen, C. Linfors, D. Fabbri, A. Oasmaa, E. Kuoppala, Investigation on catalytic pyrolysis of pine sawdust: catalysts screening by Py-GCMIP-AED, J. Anal. Appl. Pyrol. 88 (2010) 7–13. [12] Q. Lu, Z. Zhang, X. Wang, C. Dong, Y. Liu, Catalytic upgrading of biomass fast pyrolysis vapors using mesoporous ZrO2, TiO2 and SiO2, Energy Procedia 61 (2014) 1937–1941. [13] A. Pattiya, J.O. Titiloye, A.V. Bridgewater, Fast pyrolysis of cassava rhizome in the presence of catalysts, J. Anal. Appl. Pyrol. 81 (2008) 72–79. [14] P.M. Mortensen, J.D. Grunwaldt, P.A. Jensen, K.G. Knuden, A.D. Jensen, A review of catalytic upgrading of bio-oil to engine fuels, Appl. Catal. A: Gen. 407 (2011) 1–19. [15] S. Vichaphund, D. Aht-Ong, V. Sricharoenchaikul, D. Atong, Production of aromatic compounds from catalytic fast pyrolysis of Jatropha residues using metal/HZSM-5 prepared by ion-exchange and impregnation methods, Renew. Energ. 79 (2015) 28–37. [16] S. Vichaphund, V. Sricharoenchaikul, D. Atong, Utilization of fly ash-derived HZSM5: catalytic pyrolysis of Jatropha wastes in a fixed-bed reactor, Environ. Technol. 38
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