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Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the formation of phenolic compounds
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e1 1
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Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the formation of phenolic compounds lu, Bas‚ak Burcu Uzun, Esin Apaydın-Varol* Elif Sarac¸og Anadolu University, Faculty of Engineering, Dept. of Chemical Engineering, Eskis‚ehir, Turkey
article info
abstract
Article history:
The present study is aimed to investigate the upgrading of beech sawdust pyrolysis bio-oil
Received 15 September 2016
through catalytic cracking of its vapors over Fe-modified ZSM-5 zeolite in a fixed bed
Received in revised form
tubular reactor. The zeolite supported iron catalyst was successfully prepared with varying
30 June 2017
metal loading ratios (1, 5, 10 wt%) via dry impregnation method and further characterized
Accepted 1 July 2017
by BET, XRD, and SEM-EDX techniques. TG/FT-IR/MS analysis was used for the detection of
Available online xxx
biomass thermal degradation. Product yields of non-catalytic and catalytic pyrolysis experiments were determined and the obtained results show that bio-oil yields decreased in
Keywords:
the presence of catalysts. Besides, the bio-oil composition is characterized by GC/MS. It was
Biomass
indicated that the entity of the ZSM-5 and Fe/ZSM-5 catalyst reveal a significant
Catalytic pyrolysis
enhancement quality of the pyrolysis products in comparison with non-catalytic experi-
Upgrading bio-oil
ment. The catalyst increased oxygen removal from the organic phase of bio-oil and further
Fe loaded ZSM-5
developed the production of desirable products such as phenolics and aromatic compounds. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Due to the concerns about the depletion of fossil fuel sources and increasing environmental problems, the attempt to utilize lignocellulosic biomass resources will play a crucial role as an alternative to carbon-based fuels and clean renewable energy in the near future. Biomass is the fourth largest source of energy in the world after conventional fuels and provides about 14% of the world's total energy consumption. Biomass, being the most abundant feedstock, can be converted to valuable products by different technologies [1e4]. Several research has been carried to convert biomass into synthetic fuels such as bio-oil, syngas, and hydrogen via pyrolysis,
steam pyrolysis, catalytic steam gasification and supercritical water gasification [5e8]. Fast pyrolysis of renewable biomass to produce liquid product has attracted attention as the bio-oil is easily transported and stored for further uses such as energy (synthetic fuel or hydrogen) or chemicals (phenolics or aliphatics) production [9e11]. Bio-oils are very complex mixture of oxygenated compounds, totally different from petroleum fuels and containing many valuable chemicals [12]. Bio-oil upgrading refers to minimizing its well-known undesirable properties such as high concentrations of oxygenated molecules, water content, and acidity, low calorific value, high viscosity, and corrosivity. All these downsides become the major obstructions for bio-oil feasibility. Catalytic pyrolysis is carried out to
* Corresponding author. E-mail address: [email protected] (E. Apaydın-Varol). http://dx.doi.org/10.1016/j.ijhydene.2017.07.001 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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overcome most of these problems and to convert oxygenated compounds directly to hydrocarbons which can improve the quality of the final bio-oil properties [2,13]. Moreover, the use of catalysis in the thermochemical processing of biomass is an interesting approach for maximizing product yields and selectivity and also for enhancing the compositions of bio-oil and its physical - chemical properties [14]. Solid acid catalysts such as ZSM-5 zeolite has been investigated as candidate materials for bio-oils upgrading due to its ability to influentially change the composition of the bio-oils by reducing oxygen content via deoxygenation reactions. Besides that, it produces increasing amounts of aromatic species and an organic fraction that can be upgraded to diesel type fuels and valuable chemicals [2,15,16]. Recently, Wang et al. studied the cocracking of distilled fraction obtained from biooil with ethanol over HZSM-5. It was reported that Ga2O3 modified HZSM-5 promoted the aromatization reaction by increasing the yield of oil phase [17,18]. Another catalytic upgrading technology is the hydrogenation of bio-oil. The hydrogen required for this upgrading is supplied by the steam reforming of bio-oil fraction using catalysts including several metals and HZSM-5. Wang et al. reported that HZSM-5 maintained a high catalyst reactivity during the hydrogenation-cracking of bio-oil model compounds while increasing the selectivity of oil phase up to 40% with an aromatic content of around 90% [19]. Although many experimental results related to changes in the bio-oil composition has been carried out, the conversion mechanisms occur on the surface of the catalyst have not been clarified completely. However, it is known that acidic structure of the ZSM-5 zeolite acts as active sites for cracking reactions and then it is estimated that the oxygenated compounds adsorbed in the pores [20]. The synthesis of aromatic compounds and valuable chemicals formed by catalytic cracking and deoxygenation mechanisms are assumed to occur as follows [21]: Cracking :
C6 H8 O4 /C4:5 H8 þ 1:5 CO2 þ H2 O
Decarboxylation :
C6 H8 O4 /C4 H8 þ 2 CO2
(1) (2)
Adjustment of acid sites availability is the most important step in designing solid acid catalysts. The literature data prove that, for biomass pyrolysis, metal modified zeolite materials with reduced acidity can enhance the yield of hydrocarbons and high-value chemicals (e.g. phenols) while producing less coke than commercial ZSM-5 [22]. Also, Sun et al. reported that the addition of metals onto ZSM-5 catalyst demonstrated a better activity in the conversion of oxygenates by promoting the formation of monocyclic aromatic hydrocarbons while decreasing the amount of polycyclic aromatic hydrocarbons [23]. Among the metals, iron is known as quite favorable one in catalytic fields based upon its good activities on hydrogenation and ring opening reactions and also its economical convenience [24]. The effect of Fe, Zr, and Co-modified zeolites on the catalytic upgrading of pine sawdust was investigated by Li et al. It was established that Fe modified HZSM-5 catalyst was the most effective one for the upgrading process via increasing the aromatic hydrocarbons in the generated bio-oil [25]. In the present study, upgrading of pyrolysis bio-oil through catalytic cracking of its vapors over Feþ3-metal loaded ZSM-5
zeolites in a fixed bed tubular reactor is investigated. The aim is to better understand the role of iron loading over ZSM-5 catalyst on the yield and distribution of pyrolysis products. In order to assess the properties of the final upgraded bio-oil as a source for value-added chemicals, the bio-oil is characterized. This paper also focuses on the production of phenolic compounds by catalytic fast pyrolysis and liquid-liquid extraction methods for the recovery of concentrated fractions of phenolics.
Methods Biomass feedstock All the experiments were carried out with beech (Fagus orientalis) sawdust purchased from Eskis‚ehir, Turkey. This sawdust was ground for size reduction and sieved mechanically. Particles having sizes between 1.25 and 0.85 mm were used throughout the experiments. All the ground and sieved samples were kept at the room temperature in a sealed box. The results of proximate and ultimate analyses of beech sawdust are presented in Table 1. Raw material consists of 25.6% hemicellulose, 41.1% cellulose, 25.3% lignin, and 7.9% extractives. For the ultimate analyses C, H, N and O content were determined by elemental analysis using LECO-CHN analyzer (ASTM D 5373). Using elemental analysis results and Du-Long equation calorific value of beech sawdust was calculated to be as 18.55 MJ kg1 [26]. Thermal characteristics and evolved gasses during thermal and catalytic pyrolysis of beech sawdust under N2 atmosphere were investigated using a thermogravimetric analyzer (TGASetaram Labsys Evo) coupled with Fourier transform infrared analysis (FTIR-Thermo Nicolet IZ10). To avoid condensation of the volatiles, the transfer lines from TGA to FTIR was kept at 225 C. FTIR spectra were recorded between 4000 and
Table 1 e Proximate and ultimate analyses of beech sawdust. Proximate Analysis (wt%)
Beech Sawdust
Moisture Ash Volatile Matter Fixed Carbonb Lignin Cellulose Hemicellulose Extractive Ultimate Analysis (wt%) C H N S Ob H/C O/C Molar Formula Calorific Value (MJ kge1)
8.9 0.51 75.6 14.9 25.3 41.1 25.7 7.9 (dafa) 49.9 6.57 0.22 e 43.31 1.58 0.65 CH1.58N0.0038O0.65 18.55
a b
Dry, ash-free basis. By difference.
lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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700 cm1 at a resolution of 4 cm1 with 32 scans. The sample, weighing approximately 10 mg, was heated to 1000 C with a heating rate of 10 C min 1 under nitrogen flowing rate of 20 mL min 1.
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atmosphere. To be able to reach steady state conditions for coke removal, samples were kept at 1000 C for 2 h.
Pyrolysis and upgrading of bio-oil via deoxygenation reactions
Catalyst preparation and characterization Iron-modified ZSM-5 zeolite obtained from Zeolyst International (USA) was used as the catalyst for pyrolysis experiments. The acidic zeolite (CBV 8014CBV 8014) having a SiO2/ Al2O3 molar ratio of 80 was chosen for experimental studies. ZSM-5 was promoted with Fe through varying metal loading ratios (1, 5 and 10 wt %) via dry impregnation method. Fe(NO3)3.9H2O was used as a metal source. Dry impregnation was carried out mainly at room temperature by blending iron source with the zeolite gradually. After each blending operation, the sample was dried in an oven (100 C) for 15 min. Then, the impregnated catalysts were heated to 120 C to vaporize all the moisture for 2 h under dry air atmosphere. This moisture removal process was followed by calcination that was carried out at 500 C for 4 h in a bench-scale glass tubular reactor (Protherm, Turkey). Images of Feþ3modified ZSM-5 zeolites are given in Fig. 1. The acidity of H-ZSM 5 and Fe loaded H-ZSM 5 were measured simply to get the pH values of 3.76 and 3.94, respectively. The crystalline structure and metal doping on the catalysts were analyzed by X-ray Diffraction (XRD- Rigaku X-ray Diffractometer). The sample was scanned at 2q from 5 to 60 with a step size of 0.02. Cu-Ka radiation was obtained from a copper X-ray tube operated at 40 kV and 30 mA. XRD patterns were matched to the standards to define crystalline phases by smart lab guidance program. Fe modified ZSM-5 catalysts were analyzed by Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM-EDX) for the identification of their metal ratios and chemical compositions using Zeiss Evo 50 EP/SEM-EDX. The metal loading ratio of catalysts was calculated from the average of at least five different points. Moreover, the surface area (BET method) of the catalysts were characterized by N2 adsorption-desorption experiments. The experiments were conducted at 196 C, using an Automatic Volumetric Sorption Analyzer (Autosorb-1, Quantochrome). The samples were previously outgassed for 3 h at 300 C under vacuum. The formation of cokes and re-generation of the catalyst was studied using a thermogravimetric analyzer (TGA, Setaram-Labsys Evo, France). The mass loss curves were obtained for non-used catalyst and coked catalyst by heating 25 mg of samples from room temperature to 1000 C under N2
The thermal and catalytic fast pyrolysis experiments were conducted under nitrogen atmosphere in a well-swept resistively fixed-bed reactor with a length of 90 cm and an inner diameter of 8 mm, made of 310 stainless steel. Fig. 2 shows the detailed schematic diagram of the experimental set-up. As can be seen, temperature measurements were taken above the bed, with the thermocouple in the middle of the tubular reactor, in order to control the reactor temperature. A-316 stainless steel swage lock needle valve was used for fine control of the nitrogen flow rate before entry into the reactor. All the fast pyrolysis experiments were carried out at 500 C with 500 C mine1 heating rate and a nitrogen gas flow rate of 400 cm3 min1. The reactor tube was successively filled with 5 g biomass (upper zone of the reactor) and 0.50 g catalyst (a lower catalyst layer) for the catalytic upgrading. Thereby, the thermal fast pyrolysis of biomass took place first and then the primary product vapors were upgraded when they passed through the catalyst bed. The obtained pyrolysis vapor was next passed through cold traps in order to collect the liquid product. The liquid phase consisted of aqueous and oil phases, were then separated and weighed. Moreover, the solid products consisted of char and coke-on-the catalyst were weighed to determine the pyrolysis product yields. Experiments were repeated at least three times with a measurement error of less than 0.5%.
Bio-oil characterization Elemental analysis of the bio-oils was carried out to determine the effect of catalyst on the C, H, N and O composition of the bio-oil using LECO CHN analyzer. The elemental compositions and the calorific values of the pyrolysis oils were also determined. The chemical composition of the liquid organic phase was identified by GC/MS (Column:HP-5MS (30 m 0.25 mm ID x 0.25 mm)). An initial oven temperature of 40 C was sustained e1 for 4 min. Then, a heating rate of 3 C min was carried out to reach a final column temperature of 270 C. This condition was held for 20 min. Helium (99.999%) was used as a carrier gas with a constant column flow of 1 mL mine1 and MS was used within 0e300 m/z range. Identification of chromatographic peaks was obtained according to the NIST mass spectrum library.
Fig. 1 e Fe modified ZSM-5 zeolite a. unmodified ZSM-5, b. 1 wt%, c. 5 wt%, d. 10 wt% Fe/ZSM-5. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Fig. 2 e Schematic diagram of the experimental set-up.
Fourier transform infrared (FT-IR) spectrometer (Thermo Fisher Scientific- Nicolet™ IS™ 10 FT-IR Spectrometer) was applied to define chemical functional groups in the beech wood sawdust bio-oil. The wave number scan range was 4000e400 cm1. 1 H-NMR (Proton Nuclear Magnetic Resonance Spectroscopy) spectra of bio-oil and separated phase were recorded using an -Agilent 600 MHz Premium COMPACT- NMR Instrument.
Phenolic phase separation via liquid-liquid extraction method The organic fraction of bio-oil, which has the highest amount of phenolic compounds, was separated into subfractions to enhance the production of phenolics that are very crucial in
the adhesives industry. The liquid-liquid extraction method was carried out for separation by using an acid solution, an alkaline solution, and an organic solvent, as shown in Fig. 3. 5 g of bio-oil was mixed with 2.5 mol Le1 NaOH solution under ultrasonication until the pHy13. At this value, most of the water-insoluble phase which is mainly consisted of ligninderived products such as phenol, guaiacol and syringol [27], was dissolved in the alkaline solution and could then be extracted with 200 mL dichloromethane (organic solvent) to procure neutral fraction. The DCM-insoluble phase was then acidified with 1 mol Le1 HCL solution to obtain phenolic phase. Thereafter, 100 mL of DCM was used again to extract the phenolic phase from HCl solution three times and then DCM was removed from phenolic compounds by using rotary evaporator. The chemical structure of the phenolic phase has also been investigated by using GC/MS and 1H-NMR analyses.
Fig. 3 e Schematic diagram of fractionation steps for the separation of phenolic compounds. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Results and discussion Thermal decomposition behavior of biomass The thermogravimetric analysis (TGA) and differential thermogravimetric analysis (dTG) curves of beech wood sawdust are presented in Fig. 4. According to the TG/dTG curves, except for the first peak that is responsible for the moisture release, beech wood sawdust thermal degradation starts at about 211 C and is completed at 517 C, with a maximum decom position rate at 354 C and a total mass loss about 70 wt%. As stated by the results of pyrolysis behavior of beech wood sawdust, the thermal (non-catalytic) and the ZSM-5 catalyzed fast pyrolysis experiments were carried out at 500 C. The information about functional groups of evolved gasses released during thermal decomposition is detected simultaneously by FTIR. As shown in Fig. 5, 3D FT-IR diagram demonstrates that when the thermal degradation of beech wood sawdust starts around 210 C, related products such as CO2, CO, CH4, H2O, ketones, aldehydes, acids and other hydrocarbons are formed. The band between 2210 and 2400 cm1 is responsible for C]O stretching vibrations related with CO2 and has its maximum at around 350 C whereas CeH stretching vibration band (2840-3061 cm1), assigned to the presence of hydrocarbon gasses mainly CH4, has its maximum absorbance at around 410 C. OeH stretching vibration band between 3100 and 3500 cm1 is attributed to mainly the presence of H2O peaks. Between 1850 and 1690 cm1 carbonyl and C]C stretch vibration bands are seen indicating the release of aldehydes and acids [28].
Characteristics of catalytic materials ZSM-5 zeolite catalyst and the catalyst obtained by impregnation of Fe (1, 5 and 10 wt%) were characterized by a number of techniques in order to determine the effect of metal addition on the physicochemical properties of catalysts.
Fig. 5 e 3D infrared spectrum of evolved gasses during thermal degradation of beech wood sawdust.
SEM images and EDX analysis results of metal loaded catalysts reveal the presence of metal particles on ZSM-5 surface (Fig. 6). It is seen from EDX analysis that Fe is accumulated on the catalyst surface. When the metal ratio is increased to 10% from 1%, the accumulations appeared more specifically. EDX analysis results that were achieved from five different regions of the same modified catalyst to determine the average actual loading of Feþ3 represented in Table 2. The consistency between the actual and nominal loading ratios are in good agreement with each other and also with the results of the XRD patterns (discussed below). Phase analysis of the ZSM-5 and Fe/ZSM-5 catalysts was determined by XRD technique as illustrated in Fig. 7. XRD profiles show that all the samples present the typical peaks of MFI type zeolite at ~8 and 23 , evidencing the typical high crystallinity of this structure, regardless of their Si/Al molar ratio, so the framework of ZSM-5 is preserved after Fe impregnation procedure [29]. The specific peak at 2q value of 33.2 as a sign of Fe2O3 is observed from the X-ray diffraction
Fig. 4 e The TG and dTG curves of beech wood sawdust under nitrogen atmosphere. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Fig. 6 e SEM image of catalyst a. ZSM-5, b. 1 wt%, c. 5 wt%, d. 10 wt% Fe/ZSM-5 and their EDX results (EDX analysis was applied to the similar regions as shown in Fig. 6d).
patterns for different loading ratios Fe/ZSM-5 zeolite samples [30,31]. BET surface areas determined by N2 adsorptiondesorption method of ZSM-5 zeolite and Fe-loaded metal
modified ZSM-5 zeolite catalysts are given in Table 3. The surface area of ZSM-5 zeolite was 434.46 m2 ge1, and the surface area of the zeolite samples decreased as the metal loading ratio increased. Feþ3 metal was held on the zeolite
lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Table 2 e Nominal and actual metal loading ratios for Fe modified ZSM-5 catalysts (wt %). Catalyst 1 wt% Fe/ZSM-5 5 wt% Fe/ZSM-5 10 wt% Fe/ZSM-5
Nominal metal loading
Actual metal loading
1 5 10
1.1 5.1 10.2
7
surface, the surface area of the zeolite was reduced by closing the pores of the zeolite. The coke formation on the surface of the catalyst after pyrolysis is the most serious problems since it reduces the surface area by blocking the pores. The observations concerning the coke formation were approved by obtaining mass loss curves using a TGA. Fig. 8 shows typical weight loss curves for the non-used and coked catalysts in relation with temperature. As can be seen, the first mass loss (~2 wt%) for both catalysts that took place between 80 and 175 C is resulting from the volatilization of H2O molecules (moisture) attached on the surface. The fresh Fe loaded HZSM-5 catalyst is then stayed at steady state without losing any weight. On the other hand, used catalyst continued losing weight due to the removal of coke up to around 3.5 wt% until reaching 960 C. During the residence time, no extra weight loss was observed. The difference between the curves of two catalysts demonstrated the coke deposition, and the constant mass loss after 1000 C showed that regeneration of the catalyst was nearly completed.
Effect of Fe loaded ZSM-5 catalyst on the product yields
Fig. 7 e XRD patterns of catalyst a. ZSM-5, b. 1 wt% Fe/ZSM5, c. 5 wt% Fe/ZSM-5, d. 10 wt% Fe/ZSM-5 catalyst.
Table 3 e BET surface area of catalysts. Catalyst ZSM-5 % 1 Fe/ZSM-5 % 5 Fe/ZSM-5 % 10 Fe/ZSM-5
BET Surface area (m2 ge1) 434.46 412.52 393.17 368.59
Yields of bio-oil, char, gas, and water formed from catalytic pyrolysis products are given in Table 4. The same table also illustrates the results from non-catalytic (thermal pyrolysis) run, i.e. under the similar experimental conditions without catalyst bed. Thus, the product yields of beech sawdust catalytic pyrolysis with the modified ZSM-5 can be compared with that of obtained from thermal pyrolysis experiments. The highest bio-oil yield (30.66 wt%) was obtained from the noncatalytic experiments. The presence of Fe/ZSM-5 catalysts decreased bio-oil yields with a simultaneous increase in water and gas yields along with the gradually increase in metal ratios. This behavior is similar to previous studies which investigated the effect of the catalyst on pyrolytic products and it can be clarified that these alterations arise due to the
Fig. 8 e TGA of fresh and coked 10% Fe loaded H-ZSM5 catalysts. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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oxygenated compounds are detected firstly by elemental analysis. The presence of oxygen and its position in the hydrocarbons is known to be the source of the disadvantages of bio-oil. Catalysts can re-arrange the structures of molecules via dehydrogenation, deoxygenation, cracking, and reforming reactions [33]. Table 5 lists the results of the elemental composition and the calorific values of the oils produced via non-catalytic and catalytic pyrolysis. As a result of deoxygenation reactions occurring on the surface of metal loaded catalyst, the oxygen content of bio-oil decreased from 36.5 to 26.36% while carbon content increases. Hydrogen content remains nearly at the same amount as a result of simultaneous decarboxylation and dehydration reactions. Moreover, higher heating values of the bio-oils increase significantly with the increase in C content indicating the higher quality of the oils. Fig. 9 and Table 6 present the main product distribution of the extracted phase and bio-oils obtained by thermal and catalytic pyrolysis. As previously mentioned in the literature, acids (high corrosivity), esters and ethers (reducing heating value), PAHs (carcinogenic) are the undesired products from biomass pyrolysis, whereas phenols, furans, hydrocarbons, and alcohols are highly desirable for valuable chemicals and fuel production [2,9]. Impregnation of Feþ3 metal onto ZSM-5 catalyst induced an influentially increase in the relative area of phenolic compounds. As can be seen in Fig. 8. undesired compounds in bio-oil such as ketones, aldehydes, and esters
Table 4 e Product yield distribution for non-catalytic and catalytic experiments. Catalyst Non-catalytic Fe/ZSM5-1 wt% Fe/ZSM5-5 wt% Fe/ZSM5-10 wt%
Bio-oil Char yield Gas yield Water yield (wt%) (wt%) (wt%) yield (wt%) 30.66 27.71 27.55 25.04
11.74 11.52 11.67 11.45
35.42 38.86 37.13 37.47
22.18 21.91 23.65 26.33
deoxygenation reactions that occur on the catalyst surface. As the primary fast pyrolysis vapors pass through the catalyst bed, highly oxygenated and long chained compounds are converted to lower molecular weight hydrocarbons via catalytic cracking. In this case, more oxygenated compounds in bio-oil are converted into light gas and desirable products for biofuels and valuable chemicals production. Water formation is also encouraged via dehydration and decarboxylation of the oxygenated compounds on the acid sites of zeolite catalysts [2,15,20,22,32]. On the other hand, due to the presence of biomass and catalyst in separate beds, the yield of char is approximately constant for all cases without the formation of extra char and coke on biomass.
Bio-oil characterization Bio-oil is characterized by its highly complex organic chemicals. The amount of oxygen that is related to a number of
Table 5 e Elemental analysis results for non-catalytic and catalytic bio-oils. Bio-oil
Non-catalytic %1 Fe/ZSM-5 %5 Fe/ZSM-5 %10 Fe/ZSM-5 a
Element (wt%)
O/C
Empirical formula
Higher heating value (MJ kge1)
0.48 0.41 0.34 0.30
CH1.37N0.01O0.48 CH1.29N0.03O0.41 CH1.21N0.02O0.34 CH1.25N0.02O0.30
22.05 23.56 26.87 29.78
a
C
H
N
O
56.86 59.89 64.21 66.47
6.52 6.47 6.52 6.97
0.106 0.196 0.145 0.194
36.51 33.44 29.12 26.36
Calculated from difference.
Fig. 9 e Chemical composition of thermal and catalytic pyrolysis bio-oils and phenolic phase (Data adapted from GC-MS results). lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Table 6 e Phenolic compounds distribution of the bio-oils and phenolic phase (adopted from GC-MS data, % relative area). Compound
Formula
Relative area (%) Thermal Pyrolysis
Phenol Phenol, 2-methylPhenol, 3-methylPhenol, 2,6- dimethylPhenol, 2,3- dimethylPhenol, 2,4- dimethylPhenol, 3,5- dimethylGuaiacol Syringol Methylsyringol Phenol, 2-(1-methylethyl)Phenol, 2-methoxy-4-(1propenyl)4-methylguaiacol (cresol) 4-ethylguaiacol 2-methoxy-4 vinylphenol Phenol, 2-methoxy-3-(2propenyl)Phenol, 2-methoxy-4-propyl Phenol, 2,6- dimethoxy-4-(2propenyl) 2-Hydroxy-4-methylphenol Maltol 4-Hydroxy-3,5-dimethoxybenzaldehyde 2-Hydroxyphenol (catechol) 3-Methoxy catechol Other phenolics Total Phenolics
1 wt% Fe/ ZSM-5
5 wt% Fe/ ZSM-5
10 wt% Fe/ ZSM-5
Phenolic Phase
C6H6O C7H8O C7H8O C8H10O C8H10O C8H10O C8H10O C7H802 C8H10O3 C9H12O3 C10H14O C8H8O2
0.49 0.84 1.02 0.17 e 0.67 0.35 2.27 6.14 e e 0.52
0.92 0.87 1.35 0.28 e 1.03 e 2.49 7.98 e e 0.50
1.52 1.25 1.78 0.35 e 1.58 0.40 2.52 7.68 e e 0.61
1.77 1.30 1.96 0.42 e 1.41 e 2.60 8.63 e e 0.57
1.94 2.50 3.02 0.40 2.75 0.43 1.00 5.06 15.56 11.35 1.78 0.87
C8H10O2 C9H12O2 C9H12O2 C10H12O2
1.97 1.20 2.32 0,55
1.97 1.21 1.80 0,60
2.00 1.14 1.39 0,75
1.48 2.14 1.68 0,57
4.17 2.77 2.66 e
C10H14O2 C11H14O3
0.36 4.50
0.86 7.35
0.19 8.10
0.85 8.33
0.41 8.52
C7H8O2 C6H6O3 C9H10O4
1.78 0.23 1.37
1.89 0.22 2.81
2.22 0.40 1.70
2.82 0.32 2.07
1.26 0.50 4.52
C6H6O2 C7H8O3 C8H10O3, C8H10O, C7H8O etc.
1.61 e 0.60 28.61
2.56 e 5.11 41.80
2.77 e 6.75 44.36
3.04 e 7.33 49.27
0.74 1.62 12.59 86.42
Fig. 10 e FTIR spectrum of bio-oil obtained from catalytic pyrolysis (10 wt% Fe/ZSM-5). lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Table 7 e Results of 1H-NMR for the catalytic pyrolysis bio-oil and its phenolic phase. Type of hydrogen
Chemical shift d (ppm)
Aldehyde (ReCHO) and/or carboxylic acid (ReCOOH) Aromatic (AreH) and phenolic (AreOH) Phenolic (AreOH) or olefinic protons Ring-joined methylene (AreCH2eAr) and methoxy CH3, CH2, and CH a to one aromatic ring (benzylic) CH3 g, b-CH3, CH2, and CH g or further from an aromatic ring
decrease prominently in the presence of 10 wt% Fe loaded ZSM-5 when compared with bio-oil obtained from thermal pyrolysis of beech sawdust. Using 10 wt% Fe-ZSM-5 catalyst is furthermore effective to formation of the highest amount of phenols (49.27 wt%) and aromatics (21 wt%) and that could be attributed to a possible improved dehydrogenation and deoxygenation reactions on the catalyst. Among all bio oil chemicals, phenolic compounds are important industrial ones and could be used to produce solvents or phenolic-based adhesives i.e. novolac and resole resins [32,34]. This study also investigated the recovery of concentrated fractions of phenolics via extraction method. Bio-oil that has the highest amount of phenol (49.3%) is separated into two fractions: phenolics and others. This extracted phenolic phase is determined to contain 86.42% phenolic compounds and particularly guaiacol, syringol methyl syringol and phenol, 2,6-dimethoxy-4- (2-propenyl) are the main products that have significant increments when compared with bio-oil. The FTIR spectrum of the bio-oil obtained from 10 wt% Fe/ ZSM-5 catalyst is given in Fig. 10. The OeH stretching vibrations between 3200 and 3400 cm1 indicate the presence of phenols and alcohols. The CeH stretching vibrations between 2800 and 3000 cm1 and CeH deformation vibrations between 1350 and 1475 cm1 indicate the presence of alkanes. The C]O stretching vibrations with absorbance between 1650 and 1750 cm1 indicate the presence of ketones or aldehydes. The absorbance peaks between 1575 and 1675 cm1 representing C] C stretching vibrations are indicative of alkenes and aromatics [35]. These functional groups are observed for all bio-oil samples. 1 H-NMR spectroscopy is applied to the bio-oil obtained from catalytic pyrolysis (10 wt% Fe/ZSM-5) and its extracted fraction (phenolic phase). Organic groups with respect to their chemical shifts are given in Table 7. The percentage of phenolics (AreOH) increased strongly for the extracted phase, whereas other functional groups decreased. Chemical shift region between 4.5 and 3.3 increased significantly for the extracted phase when compared with the bio-oil obtained by an entity of 10 wt% Fe/ZMS-5 catalyst. The main reason for this increase can be explained by the presence of phenolic groups bonded with hydroxyl, methyl, methoxy and ether groups [36]. Thus, the results from 1H-NMR are consistent with the GCeMS analysis.
Conclusions The effect of different loading ratios (1, 5, 10 wt%) of Fe modified ZSM-5 catalysts on the product yields and
Bio-oil (%) 10 wt% Fe/ZSM-5
Phenolic phase
0.6 16.3 2.3 18.1 39.6 23.1
0.3 26.8 5.3 29.1 21.6 16.9
12.0e9.0 8.5e6.5 6.5e5 4.5e3.3 3.3e2.0 2.0e0.5
compositions of bio-oil obtained from the fast pyrolysis of beech wood sawdust were investigated. The presence of a catalyst bed decreased the bio-oil yield while increasing water formation and gas product yield as a result of deoxygenation ability of the catalyst. On the other hand, compared to noncatalytic pyrolysis, the existence of catalysts altered significantly the quality of the bio-oil. It was demonstrated that an impregnation of 10 wt% Fe to ZSM-5 resulted in a considerable increase in the amount of phenolic compounds, aromatic and aliphatic hydrocarbons present in the bio-oils. GC-MS data revealed that about 29% of thermal bio-oil was composed of phenolics. In comparison, within the presence of Fe/ZSM-5 catalyst, phenolic compound formation was enhanced and bio-oil constituted approximately 50% of phenolics that can be further separated by extraction. The increase in phenolic phase was attributed to the cracking, dehydrogenation and deoxygenation reactions. The results showed that using a Fe/ ZSM-5 catalyst bed for upgrading is an efficient method to minimize oxygenated compounds while increasing carbon content as well as keeping the hydrogen content steady in the bio-oil.
Acknowledgements € ll Stiftung The authors would like to thank Heinrich Bo (Turkey) and Anadolu University Scientific Research Council (Project Number: 1601F028) for the financial support of this work.
references
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lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the formation of phenolic compounds lu, Bas‚ak Burcu Uzun, Esin Apaydın-Varol* Elif Sarac¸og Anadolu University, Faculty of Engineering, Dept. of Chemical Engineering, Eskis‚ehir, Turkey
article info
abstract
Article history:
The present study is aimed to investigate the upgrading of beech sawdust pyrolysis bio-oil
Received 15 September 2016
through catalytic cracking of its vapors over Fe-modified ZSM-5 zeolite in a fixed bed
Received in revised form
tubular reactor. The zeolite supported iron catalyst was successfully prepared with varying
30 June 2017
metal loading ratios (1, 5, 10 wt%) via dry impregnation method and further characterized
Accepted 1 July 2017
by BET, XRD, and SEM-EDX techniques. TG/FT-IR/MS analysis was used for the detection of
Available online xxx
biomass thermal degradation. Product yields of non-catalytic and catalytic pyrolysis experiments were determined and the obtained results show that bio-oil yields decreased in
Keywords:
the presence of catalysts. Besides, the bio-oil composition is characterized by GC/MS. It was
Biomass
indicated that the entity of the ZSM-5 and Fe/ZSM-5 catalyst reveal a significant
Catalytic pyrolysis
enhancement quality of the pyrolysis products in comparison with non-catalytic experi-
Upgrading bio-oil
ment. The catalyst increased oxygen removal from the organic phase of bio-oil and further
Fe loaded ZSM-5
developed the production of desirable products such as phenolics and aromatic compounds. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Due to the concerns about the depletion of fossil fuel sources and increasing environmental problems, the attempt to utilize lignocellulosic biomass resources will play a crucial role as an alternative to carbon-based fuels and clean renewable energy in the near future. Biomass is the fourth largest source of energy in the world after conventional fuels and provides about 14% of the world's total energy consumption. Biomass, being the most abundant feedstock, can be converted to valuable products by different technologies [1e4]. Several research has been carried to convert biomass into synthetic fuels such as bio-oil, syngas, and hydrogen via pyrolysis,
steam pyrolysis, catalytic steam gasification and supercritical water gasification [5e8]. Fast pyrolysis of renewable biomass to produce liquid product has attracted attention as the bio-oil is easily transported and stored for further uses such as energy (synthetic fuel or hydrogen) or chemicals (phenolics or aliphatics) production [9e11]. Bio-oils are very complex mixture of oxygenated compounds, totally different from petroleum fuels and containing many valuable chemicals [12]. Bio-oil upgrading refers to minimizing its well-known undesirable properties such as high concentrations of oxygenated molecules, water content, and acidity, low calorific value, high viscosity, and corrosivity. All these downsides become the major obstructions for bio-oil feasibility. Catalytic pyrolysis is carried out to
* Corresponding author. E-mail address: [email protected] (E. Apaydın-Varol). http://dx.doi.org/10.1016/j.ijhydene.2017.07.001 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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overcome most of these problems and to convert oxygenated compounds directly to hydrocarbons which can improve the quality of the final bio-oil properties [2,13]. Moreover, the use of catalysis in the thermochemical processing of biomass is an interesting approach for maximizing product yields and selectivity and also for enhancing the compositions of bio-oil and its physical - chemical properties [14]. Solid acid catalysts such as ZSM-5 zeolite has been investigated as candidate materials for bio-oils upgrading due to its ability to influentially change the composition of the bio-oils by reducing oxygen content via deoxygenation reactions. Besides that, it produces increasing amounts of aromatic species and an organic fraction that can be upgraded to diesel type fuels and valuable chemicals [2,15,16]. Recently, Wang et al. studied the cocracking of distilled fraction obtained from biooil with ethanol over HZSM-5. It was reported that Ga2O3 modified HZSM-5 promoted the aromatization reaction by increasing the yield of oil phase [17,18]. Another catalytic upgrading technology is the hydrogenation of bio-oil. The hydrogen required for this upgrading is supplied by the steam reforming of bio-oil fraction using catalysts including several metals and HZSM-5. Wang et al. reported that HZSM-5 maintained a high catalyst reactivity during the hydrogenation-cracking of bio-oil model compounds while increasing the selectivity of oil phase up to 40% with an aromatic content of around 90% [19]. Although many experimental results related to changes in the bio-oil composition has been carried out, the conversion mechanisms occur on the surface of the catalyst have not been clarified completely. However, it is known that acidic structure of the ZSM-5 zeolite acts as active sites for cracking reactions and then it is estimated that the oxygenated compounds adsorbed in the pores [20]. The synthesis of aromatic compounds and valuable chemicals formed by catalytic cracking and deoxygenation mechanisms are assumed to occur as follows [21]: Cracking :
C6 H8 O4 /C4:5 H8 þ 1:5 CO2 þ H2 O
Decarboxylation :
C6 H8 O4 /C4 H8 þ 2 CO2
(1) (2)
Adjustment of acid sites availability is the most important step in designing solid acid catalysts. The literature data prove that, for biomass pyrolysis, metal modified zeolite materials with reduced acidity can enhance the yield of hydrocarbons and high-value chemicals (e.g. phenols) while producing less coke than commercial ZSM-5 [22]. Also, Sun et al. reported that the addition of metals onto ZSM-5 catalyst demonstrated a better activity in the conversion of oxygenates by promoting the formation of monocyclic aromatic hydrocarbons while decreasing the amount of polycyclic aromatic hydrocarbons [23]. Among the metals, iron is known as quite favorable one in catalytic fields based upon its good activities on hydrogenation and ring opening reactions and also its economical convenience [24]. The effect of Fe, Zr, and Co-modified zeolites on the catalytic upgrading of pine sawdust was investigated by Li et al. It was established that Fe modified HZSM-5 catalyst was the most effective one for the upgrading process via increasing the aromatic hydrocarbons in the generated bio-oil [25]. In the present study, upgrading of pyrolysis bio-oil through catalytic cracking of its vapors over Feþ3-metal loaded ZSM-5
zeolites in a fixed bed tubular reactor is investigated. The aim is to better understand the role of iron loading over ZSM-5 catalyst on the yield and distribution of pyrolysis products. In order to assess the properties of the final upgraded bio-oil as a source for value-added chemicals, the bio-oil is characterized. This paper also focuses on the production of phenolic compounds by catalytic fast pyrolysis and liquid-liquid extraction methods for the recovery of concentrated fractions of phenolics.
Methods Biomass feedstock All the experiments were carried out with beech (Fagus orientalis) sawdust purchased from Eskis‚ehir, Turkey. This sawdust was ground for size reduction and sieved mechanically. Particles having sizes between 1.25 and 0.85 mm were used throughout the experiments. All the ground and sieved samples were kept at the room temperature in a sealed box. The results of proximate and ultimate analyses of beech sawdust are presented in Table 1. Raw material consists of 25.6% hemicellulose, 41.1% cellulose, 25.3% lignin, and 7.9% extractives. For the ultimate analyses C, H, N and O content were determined by elemental analysis using LECO-CHN analyzer (ASTM D 5373). Using elemental analysis results and Du-Long equation calorific value of beech sawdust was calculated to be as 18.55 MJ kg1 [26]. Thermal characteristics and evolved gasses during thermal and catalytic pyrolysis of beech sawdust under N2 atmosphere were investigated using a thermogravimetric analyzer (TGASetaram Labsys Evo) coupled with Fourier transform infrared analysis (FTIR-Thermo Nicolet IZ10). To avoid condensation of the volatiles, the transfer lines from TGA to FTIR was kept at 225 C. FTIR spectra were recorded between 4000 and
Table 1 e Proximate and ultimate analyses of beech sawdust. Proximate Analysis (wt%)
Beech Sawdust
Moisture Ash Volatile Matter Fixed Carbonb Lignin Cellulose Hemicellulose Extractive Ultimate Analysis (wt%) C H N S Ob H/C O/C Molar Formula Calorific Value (MJ kge1)
8.9 0.51 75.6 14.9 25.3 41.1 25.7 7.9 (dafa) 49.9 6.57 0.22 e 43.31 1.58 0.65 CH1.58N0.0038O0.65 18.55
a b
Dry, ash-free basis. By difference.
lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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700 cm1 at a resolution of 4 cm1 with 32 scans. The sample, weighing approximately 10 mg, was heated to 1000 C with a heating rate of 10 C min 1 under nitrogen flowing rate of 20 mL min 1.
3
atmosphere. To be able to reach steady state conditions for coke removal, samples were kept at 1000 C for 2 h.
Pyrolysis and upgrading of bio-oil via deoxygenation reactions
Catalyst preparation and characterization Iron-modified ZSM-5 zeolite obtained from Zeolyst International (USA) was used as the catalyst for pyrolysis experiments. The acidic zeolite (CBV 8014CBV 8014) having a SiO2/ Al2O3 molar ratio of 80 was chosen for experimental studies. ZSM-5 was promoted with Fe through varying metal loading ratios (1, 5 and 10 wt %) via dry impregnation method. Fe(NO3)3.9H2O was used as a metal source. Dry impregnation was carried out mainly at room temperature by blending iron source with the zeolite gradually. After each blending operation, the sample was dried in an oven (100 C) for 15 min. Then, the impregnated catalysts were heated to 120 C to vaporize all the moisture for 2 h under dry air atmosphere. This moisture removal process was followed by calcination that was carried out at 500 C for 4 h in a bench-scale glass tubular reactor (Protherm, Turkey). Images of Feþ3modified ZSM-5 zeolites are given in Fig. 1. The acidity of H-ZSM 5 and Fe loaded H-ZSM 5 were measured simply to get the pH values of 3.76 and 3.94, respectively. The crystalline structure and metal doping on the catalysts were analyzed by X-ray Diffraction (XRD- Rigaku X-ray Diffractometer). The sample was scanned at 2q from 5 to 60 with a step size of 0.02. Cu-Ka radiation was obtained from a copper X-ray tube operated at 40 kV and 30 mA. XRD patterns were matched to the standards to define crystalline phases by smart lab guidance program. Fe modified ZSM-5 catalysts were analyzed by Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM-EDX) for the identification of their metal ratios and chemical compositions using Zeiss Evo 50 EP/SEM-EDX. The metal loading ratio of catalysts was calculated from the average of at least five different points. Moreover, the surface area (BET method) of the catalysts were characterized by N2 adsorption-desorption experiments. The experiments were conducted at 196 C, using an Automatic Volumetric Sorption Analyzer (Autosorb-1, Quantochrome). The samples were previously outgassed for 3 h at 300 C under vacuum. The formation of cokes and re-generation of the catalyst was studied using a thermogravimetric analyzer (TGA, Setaram-Labsys Evo, France). The mass loss curves were obtained for non-used catalyst and coked catalyst by heating 25 mg of samples from room temperature to 1000 C under N2
The thermal and catalytic fast pyrolysis experiments were conducted under nitrogen atmosphere in a well-swept resistively fixed-bed reactor with a length of 90 cm and an inner diameter of 8 mm, made of 310 stainless steel. Fig. 2 shows the detailed schematic diagram of the experimental set-up. As can be seen, temperature measurements were taken above the bed, with the thermocouple in the middle of the tubular reactor, in order to control the reactor temperature. A-316 stainless steel swage lock needle valve was used for fine control of the nitrogen flow rate before entry into the reactor. All the fast pyrolysis experiments were carried out at 500 C with 500 C mine1 heating rate and a nitrogen gas flow rate of 400 cm3 min1. The reactor tube was successively filled with 5 g biomass (upper zone of the reactor) and 0.50 g catalyst (a lower catalyst layer) for the catalytic upgrading. Thereby, the thermal fast pyrolysis of biomass took place first and then the primary product vapors were upgraded when they passed through the catalyst bed. The obtained pyrolysis vapor was next passed through cold traps in order to collect the liquid product. The liquid phase consisted of aqueous and oil phases, were then separated and weighed. Moreover, the solid products consisted of char and coke-on-the catalyst were weighed to determine the pyrolysis product yields. Experiments were repeated at least three times with a measurement error of less than 0.5%.
Bio-oil characterization Elemental analysis of the bio-oils was carried out to determine the effect of catalyst on the C, H, N and O composition of the bio-oil using LECO CHN analyzer. The elemental compositions and the calorific values of the pyrolysis oils were also determined. The chemical composition of the liquid organic phase was identified by GC/MS (Column:HP-5MS (30 m 0.25 mm ID x 0.25 mm)). An initial oven temperature of 40 C was sustained e1 for 4 min. Then, a heating rate of 3 C min was carried out to reach a final column temperature of 270 C. This condition was held for 20 min. Helium (99.999%) was used as a carrier gas with a constant column flow of 1 mL mine1 and MS was used within 0e300 m/z range. Identification of chromatographic peaks was obtained according to the NIST mass spectrum library.
Fig. 1 e Fe modified ZSM-5 zeolite a. unmodified ZSM-5, b. 1 wt%, c. 5 wt%, d. 10 wt% Fe/ZSM-5. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Fig. 2 e Schematic diagram of the experimental set-up.
Fourier transform infrared (FT-IR) spectrometer (Thermo Fisher Scientific- Nicolet™ IS™ 10 FT-IR Spectrometer) was applied to define chemical functional groups in the beech wood sawdust bio-oil. The wave number scan range was 4000e400 cm1. 1 H-NMR (Proton Nuclear Magnetic Resonance Spectroscopy) spectra of bio-oil and separated phase were recorded using an -Agilent 600 MHz Premium COMPACT- NMR Instrument.
Phenolic phase separation via liquid-liquid extraction method The organic fraction of bio-oil, which has the highest amount of phenolic compounds, was separated into subfractions to enhance the production of phenolics that are very crucial in
the adhesives industry. The liquid-liquid extraction method was carried out for separation by using an acid solution, an alkaline solution, and an organic solvent, as shown in Fig. 3. 5 g of bio-oil was mixed with 2.5 mol Le1 NaOH solution under ultrasonication until the pHy13. At this value, most of the water-insoluble phase which is mainly consisted of ligninderived products such as phenol, guaiacol and syringol [27], was dissolved in the alkaline solution and could then be extracted with 200 mL dichloromethane (organic solvent) to procure neutral fraction. The DCM-insoluble phase was then acidified with 1 mol Le1 HCL solution to obtain phenolic phase. Thereafter, 100 mL of DCM was used again to extract the phenolic phase from HCl solution three times and then DCM was removed from phenolic compounds by using rotary evaporator. The chemical structure of the phenolic phase has also been investigated by using GC/MS and 1H-NMR analyses.
Fig. 3 e Schematic diagram of fractionation steps for the separation of phenolic compounds. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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5
Results and discussion Thermal decomposition behavior of biomass The thermogravimetric analysis (TGA) and differential thermogravimetric analysis (dTG) curves of beech wood sawdust are presented in Fig. 4. According to the TG/dTG curves, except for the first peak that is responsible for the moisture release, beech wood sawdust thermal degradation starts at about 211 C and is completed at 517 C, with a maximum decom position rate at 354 C and a total mass loss about 70 wt%. As stated by the results of pyrolysis behavior of beech wood sawdust, the thermal (non-catalytic) and the ZSM-5 catalyzed fast pyrolysis experiments were carried out at 500 C. The information about functional groups of evolved gasses released during thermal decomposition is detected simultaneously by FTIR. As shown in Fig. 5, 3D FT-IR diagram demonstrates that when the thermal degradation of beech wood sawdust starts around 210 C, related products such as CO2, CO, CH4, H2O, ketones, aldehydes, acids and other hydrocarbons are formed. The band between 2210 and 2400 cm1 is responsible for C]O stretching vibrations related with CO2 and has its maximum at around 350 C whereas CeH stretching vibration band (2840-3061 cm1), assigned to the presence of hydrocarbon gasses mainly CH4, has its maximum absorbance at around 410 C. OeH stretching vibration band between 3100 and 3500 cm1 is attributed to mainly the presence of H2O peaks. Between 1850 and 1690 cm1 carbonyl and C]C stretch vibration bands are seen indicating the release of aldehydes and acids [28].
Characteristics of catalytic materials ZSM-5 zeolite catalyst and the catalyst obtained by impregnation of Fe (1, 5 and 10 wt%) were characterized by a number of techniques in order to determine the effect of metal addition on the physicochemical properties of catalysts.
Fig. 5 e 3D infrared spectrum of evolved gasses during thermal degradation of beech wood sawdust.
SEM images and EDX analysis results of metal loaded catalysts reveal the presence of metal particles on ZSM-5 surface (Fig. 6). It is seen from EDX analysis that Fe is accumulated on the catalyst surface. When the metal ratio is increased to 10% from 1%, the accumulations appeared more specifically. EDX analysis results that were achieved from five different regions of the same modified catalyst to determine the average actual loading of Feþ3 represented in Table 2. The consistency between the actual and nominal loading ratios are in good agreement with each other and also with the results of the XRD patterns (discussed below). Phase analysis of the ZSM-5 and Fe/ZSM-5 catalysts was determined by XRD technique as illustrated in Fig. 7. XRD profiles show that all the samples present the typical peaks of MFI type zeolite at ~8 and 23 , evidencing the typical high crystallinity of this structure, regardless of their Si/Al molar ratio, so the framework of ZSM-5 is preserved after Fe impregnation procedure [29]. The specific peak at 2q value of 33.2 as a sign of Fe2O3 is observed from the X-ray diffraction
Fig. 4 e The TG and dTG curves of beech wood sawdust under nitrogen atmosphere. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Fig. 6 e SEM image of catalyst a. ZSM-5, b. 1 wt%, c. 5 wt%, d. 10 wt% Fe/ZSM-5 and their EDX results (EDX analysis was applied to the similar regions as shown in Fig. 6d).
patterns for different loading ratios Fe/ZSM-5 zeolite samples [30,31]. BET surface areas determined by N2 adsorptiondesorption method of ZSM-5 zeolite and Fe-loaded metal
modified ZSM-5 zeolite catalysts are given in Table 3. The surface area of ZSM-5 zeolite was 434.46 m2 ge1, and the surface area of the zeolite samples decreased as the metal loading ratio increased. Feþ3 metal was held on the zeolite
lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Table 2 e Nominal and actual metal loading ratios for Fe modified ZSM-5 catalysts (wt %). Catalyst 1 wt% Fe/ZSM-5 5 wt% Fe/ZSM-5 10 wt% Fe/ZSM-5
Nominal metal loading
Actual metal loading
1 5 10
1.1 5.1 10.2
7
surface, the surface area of the zeolite was reduced by closing the pores of the zeolite. The coke formation on the surface of the catalyst after pyrolysis is the most serious problems since it reduces the surface area by blocking the pores. The observations concerning the coke formation were approved by obtaining mass loss curves using a TGA. Fig. 8 shows typical weight loss curves for the non-used and coked catalysts in relation with temperature. As can be seen, the first mass loss (~2 wt%) for both catalysts that took place between 80 and 175 C is resulting from the volatilization of H2O molecules (moisture) attached on the surface. The fresh Fe loaded HZSM-5 catalyst is then stayed at steady state without losing any weight. On the other hand, used catalyst continued losing weight due to the removal of coke up to around 3.5 wt% until reaching 960 C. During the residence time, no extra weight loss was observed. The difference between the curves of two catalysts demonstrated the coke deposition, and the constant mass loss after 1000 C showed that regeneration of the catalyst was nearly completed.
Effect of Fe loaded ZSM-5 catalyst on the product yields
Fig. 7 e XRD patterns of catalyst a. ZSM-5, b. 1 wt% Fe/ZSM5, c. 5 wt% Fe/ZSM-5, d. 10 wt% Fe/ZSM-5 catalyst.
Table 3 e BET surface area of catalysts. Catalyst ZSM-5 % 1 Fe/ZSM-5 % 5 Fe/ZSM-5 % 10 Fe/ZSM-5
BET Surface area (m2 ge1) 434.46 412.52 393.17 368.59
Yields of bio-oil, char, gas, and water formed from catalytic pyrolysis products are given in Table 4. The same table also illustrates the results from non-catalytic (thermal pyrolysis) run, i.e. under the similar experimental conditions without catalyst bed. Thus, the product yields of beech sawdust catalytic pyrolysis with the modified ZSM-5 can be compared with that of obtained from thermal pyrolysis experiments. The highest bio-oil yield (30.66 wt%) was obtained from the noncatalytic experiments. The presence of Fe/ZSM-5 catalysts decreased bio-oil yields with a simultaneous increase in water and gas yields along with the gradually increase in metal ratios. This behavior is similar to previous studies which investigated the effect of the catalyst on pyrolytic products and it can be clarified that these alterations arise due to the
Fig. 8 e TGA of fresh and coked 10% Fe loaded H-ZSM5 catalysts. lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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oxygenated compounds are detected firstly by elemental analysis. The presence of oxygen and its position in the hydrocarbons is known to be the source of the disadvantages of bio-oil. Catalysts can re-arrange the structures of molecules via dehydrogenation, deoxygenation, cracking, and reforming reactions [33]. Table 5 lists the results of the elemental composition and the calorific values of the oils produced via non-catalytic and catalytic pyrolysis. As a result of deoxygenation reactions occurring on the surface of metal loaded catalyst, the oxygen content of bio-oil decreased from 36.5 to 26.36% while carbon content increases. Hydrogen content remains nearly at the same amount as a result of simultaneous decarboxylation and dehydration reactions. Moreover, higher heating values of the bio-oils increase significantly with the increase in C content indicating the higher quality of the oils. Fig. 9 and Table 6 present the main product distribution of the extracted phase and bio-oils obtained by thermal and catalytic pyrolysis. As previously mentioned in the literature, acids (high corrosivity), esters and ethers (reducing heating value), PAHs (carcinogenic) are the undesired products from biomass pyrolysis, whereas phenols, furans, hydrocarbons, and alcohols are highly desirable for valuable chemicals and fuel production [2,9]. Impregnation of Feþ3 metal onto ZSM-5 catalyst induced an influentially increase in the relative area of phenolic compounds. As can be seen in Fig. 8. undesired compounds in bio-oil such as ketones, aldehydes, and esters
Table 4 e Product yield distribution for non-catalytic and catalytic experiments. Catalyst Non-catalytic Fe/ZSM5-1 wt% Fe/ZSM5-5 wt% Fe/ZSM5-10 wt%
Bio-oil Char yield Gas yield Water yield (wt%) (wt%) (wt%) yield (wt%) 30.66 27.71 27.55 25.04
11.74 11.52 11.67 11.45
35.42 38.86 37.13 37.47
22.18 21.91 23.65 26.33
deoxygenation reactions that occur on the catalyst surface. As the primary fast pyrolysis vapors pass through the catalyst bed, highly oxygenated and long chained compounds are converted to lower molecular weight hydrocarbons via catalytic cracking. In this case, more oxygenated compounds in bio-oil are converted into light gas and desirable products for biofuels and valuable chemicals production. Water formation is also encouraged via dehydration and decarboxylation of the oxygenated compounds on the acid sites of zeolite catalysts [2,15,20,22,32]. On the other hand, due to the presence of biomass and catalyst in separate beds, the yield of char is approximately constant for all cases without the formation of extra char and coke on biomass.
Bio-oil characterization Bio-oil is characterized by its highly complex organic chemicals. The amount of oxygen that is related to a number of
Table 5 e Elemental analysis results for non-catalytic and catalytic bio-oils. Bio-oil
Non-catalytic %1 Fe/ZSM-5 %5 Fe/ZSM-5 %10 Fe/ZSM-5 a
Element (wt%)
O/C
Empirical formula
Higher heating value (MJ kge1)
0.48 0.41 0.34 0.30
CH1.37N0.01O0.48 CH1.29N0.03O0.41 CH1.21N0.02O0.34 CH1.25N0.02O0.30
22.05 23.56 26.87 29.78
a
C
H
N
O
56.86 59.89 64.21 66.47
6.52 6.47 6.52 6.97
0.106 0.196 0.145 0.194
36.51 33.44 29.12 26.36
Calculated from difference.
Fig. 9 e Chemical composition of thermal and catalytic pyrolysis bio-oils and phenolic phase (Data adapted from GC-MS results). lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Table 6 e Phenolic compounds distribution of the bio-oils and phenolic phase (adopted from GC-MS data, % relative area). Compound
Formula
Relative area (%) Thermal Pyrolysis
Phenol Phenol, 2-methylPhenol, 3-methylPhenol, 2,6- dimethylPhenol, 2,3- dimethylPhenol, 2,4- dimethylPhenol, 3,5- dimethylGuaiacol Syringol Methylsyringol Phenol, 2-(1-methylethyl)Phenol, 2-methoxy-4-(1propenyl)4-methylguaiacol (cresol) 4-ethylguaiacol 2-methoxy-4 vinylphenol Phenol, 2-methoxy-3-(2propenyl)Phenol, 2-methoxy-4-propyl Phenol, 2,6- dimethoxy-4-(2propenyl) 2-Hydroxy-4-methylphenol Maltol 4-Hydroxy-3,5-dimethoxybenzaldehyde 2-Hydroxyphenol (catechol) 3-Methoxy catechol Other phenolics Total Phenolics
1 wt% Fe/ ZSM-5
5 wt% Fe/ ZSM-5
10 wt% Fe/ ZSM-5
Phenolic Phase
C6H6O C7H8O C7H8O C8H10O C8H10O C8H10O C8H10O C7H802 C8H10O3 C9H12O3 C10H14O C8H8O2
0.49 0.84 1.02 0.17 e 0.67 0.35 2.27 6.14 e e 0.52
0.92 0.87 1.35 0.28 e 1.03 e 2.49 7.98 e e 0.50
1.52 1.25 1.78 0.35 e 1.58 0.40 2.52 7.68 e e 0.61
1.77 1.30 1.96 0.42 e 1.41 e 2.60 8.63 e e 0.57
1.94 2.50 3.02 0.40 2.75 0.43 1.00 5.06 15.56 11.35 1.78 0.87
C8H10O2 C9H12O2 C9H12O2 C10H12O2
1.97 1.20 2.32 0,55
1.97 1.21 1.80 0,60
2.00 1.14 1.39 0,75
1.48 2.14 1.68 0,57
4.17 2.77 2.66 e
C10H14O2 C11H14O3
0.36 4.50
0.86 7.35
0.19 8.10
0.85 8.33
0.41 8.52
C7H8O2 C6H6O3 C9H10O4
1.78 0.23 1.37
1.89 0.22 2.81
2.22 0.40 1.70
2.82 0.32 2.07
1.26 0.50 4.52
C6H6O2 C7H8O3 C8H10O3, C8H10O, C7H8O etc.
1.61 e 0.60 28.61
2.56 e 5.11 41.80
2.77 e 6.75 44.36
3.04 e 7.33 49.27
0.74 1.62 12.59 86.42
Fig. 10 e FTIR spectrum of bio-oil obtained from catalytic pyrolysis (10 wt% Fe/ZSM-5). lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001
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Table 7 e Results of 1H-NMR for the catalytic pyrolysis bio-oil and its phenolic phase. Type of hydrogen
Chemical shift d (ppm)
Aldehyde (ReCHO) and/or carboxylic acid (ReCOOH) Aromatic (AreH) and phenolic (AreOH) Phenolic (AreOH) or olefinic protons Ring-joined methylene (AreCH2eAr) and methoxy CH3, CH2, and CH a to one aromatic ring (benzylic) CH3 g, b-CH3, CH2, and CH g or further from an aromatic ring
decrease prominently in the presence of 10 wt% Fe loaded ZSM-5 when compared with bio-oil obtained from thermal pyrolysis of beech sawdust. Using 10 wt% Fe-ZSM-5 catalyst is furthermore effective to formation of the highest amount of phenols (49.27 wt%) and aromatics (21 wt%) and that could be attributed to a possible improved dehydrogenation and deoxygenation reactions on the catalyst. Among all bio oil chemicals, phenolic compounds are important industrial ones and could be used to produce solvents or phenolic-based adhesives i.e. novolac and resole resins [32,34]. This study also investigated the recovery of concentrated fractions of phenolics via extraction method. Bio-oil that has the highest amount of phenol (49.3%) is separated into two fractions: phenolics and others. This extracted phenolic phase is determined to contain 86.42% phenolic compounds and particularly guaiacol, syringol methyl syringol and phenol, 2,6-dimethoxy-4- (2-propenyl) are the main products that have significant increments when compared with bio-oil. The FTIR spectrum of the bio-oil obtained from 10 wt% Fe/ ZSM-5 catalyst is given in Fig. 10. The OeH stretching vibrations between 3200 and 3400 cm1 indicate the presence of phenols and alcohols. The CeH stretching vibrations between 2800 and 3000 cm1 and CeH deformation vibrations between 1350 and 1475 cm1 indicate the presence of alkanes. The C]O stretching vibrations with absorbance between 1650 and 1750 cm1 indicate the presence of ketones or aldehydes. The absorbance peaks between 1575 and 1675 cm1 representing C] C stretching vibrations are indicative of alkenes and aromatics [35]. These functional groups are observed for all bio-oil samples. 1 H-NMR spectroscopy is applied to the bio-oil obtained from catalytic pyrolysis (10 wt% Fe/ZSM-5) and its extracted fraction (phenolic phase). Organic groups with respect to their chemical shifts are given in Table 7. The percentage of phenolics (AreOH) increased strongly for the extracted phase, whereas other functional groups decreased. Chemical shift region between 4.5 and 3.3 increased significantly for the extracted phase when compared with the bio-oil obtained by an entity of 10 wt% Fe/ZMS-5 catalyst. The main reason for this increase can be explained by the presence of phenolic groups bonded with hydroxyl, methyl, methoxy and ether groups [36]. Thus, the results from 1H-NMR are consistent with the GCeMS analysis.
Conclusions The effect of different loading ratios (1, 5, 10 wt%) of Fe modified ZSM-5 catalysts on the product yields and
Bio-oil (%) 10 wt% Fe/ZSM-5
Phenolic phase
0.6 16.3 2.3 18.1 39.6 23.1
0.3 26.8 5.3 29.1 21.6 16.9
12.0e9.0 8.5e6.5 6.5e5 4.5e3.3 3.3e2.0 2.0e0.5
compositions of bio-oil obtained from the fast pyrolysis of beech wood sawdust were investigated. The presence of a catalyst bed decreased the bio-oil yield while increasing water formation and gas product yield as a result of deoxygenation ability of the catalyst. On the other hand, compared to noncatalytic pyrolysis, the existence of catalysts altered significantly the quality of the bio-oil. It was demonstrated that an impregnation of 10 wt% Fe to ZSM-5 resulted in a considerable increase in the amount of phenolic compounds, aromatic and aliphatic hydrocarbons present in the bio-oils. GC-MS data revealed that about 29% of thermal bio-oil was composed of phenolics. In comparison, within the presence of Fe/ZSM-5 catalyst, phenolic compound formation was enhanced and bio-oil constituted approximately 50% of phenolics that can be further separated by extraction. The increase in phenolic phase was attributed to the cracking, dehydrogenation and deoxygenation reactions. The results showed that using a Fe/ ZSM-5 catalyst bed for upgrading is an efficient method to minimize oxygenated compounds while increasing carbon content as well as keeping the hydrogen content steady in the bio-oil.
Acknowledgements € ll Stiftung The authors would like to thank Heinrich Bo (Turkey) and Anadolu University Scientific Research Council (Project Number: 1601F028) for the financial support of this work.
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lu E, et al., Upgrading of fast pyrolysis bio-oil over Fe modified ZSM-5 catalyst to enhance the Please cite this article in press as: Sarac¸og formation of phenolic compounds, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.001