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Pyrolysis of oil palm mesocarp fiber and palm frond in a slow-heating fixed-bed reactor: A comparative study
Accepted Manuscript Pyrolysis of oil palm mesocarp fiber and palm frond in a slow-heating fixedbed reactor: A comparative study G. Kabir, A.T. Mohd Din, B.H. Hameed PII: DOI: Reference:
S0960-8524(17)30848-9 http://dx.doi.org/10.1016/j.biortech.2017.05.180 BITE 18206
To appear in:
Bioresource Technology
Received Date: Revised Date: Accepted Date:
2 April 2017 26 May 2017 27 May 2017
Please cite this article as: Kabir, G., Mohd Din, A.T., Hameed, B.H., Pyrolysis of oil palm mesocarp fiber and palm frond in a slow-heating fixed-bed reactor: A comparative study, Bioresource Technology (2017), doi: http:// dx.doi.org/10.1016/j.biortech.2017.05.180
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Pyrolysis of oil palm mesocarp fiber and palm frond in a slow-heating fixed-bed reactor: A comparative study
G. Kabir, A. T. Mohd Din, B.H. Hameed* School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia * Corresponding author. Tel.: +6045996422; Fax: +6045941013 E-mail address: [email protected] (B.H. Hameed)
Abstract Oil palm mesocarp fiber (OPMF) and palm frond (PF) were respectively devolatilized by pyrolysis to OPMF-oil and PF-oil bio-oils and biochars, OPMF-char and PF-char in a slowheating fixed-bed reactor. In particular, the OPMF-oil and PF-oil were produced to a maximum yield of 48 wt% and 47 wt% bio-oils at 550 °C and 600 °C, respectively. The high heating values (HHVs) of OPMF-oil and PF-oil were respectively found to be 23 MJ/kg and 21 MJ/kg, whereas 24.84 MJ/kg and 24.15 MJ/kg were for the corresponding biochar. The HHVs of the bio-oils and biochars are associated with low O/C ratios to be higher than those of the corresponding biomass. The Fourier transform infrared spectra and peak area ratios highlighted the effect of pyrolysis temperatures on the bio-oil compositions. The bio-oils are pervaded with numerous oxygenated carbonyl and aromatic compounds as suitable feedstocks for renewable fuels and chemicals. Keywords: Bio-oil; Pyrolysis; Fixed-bed reactor; Palm fond; Oil palm mesocarp fiber
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1.
Introduction Non-food lignocellulosic biomass wastes take a pivotal role in decentralizing the world’s
energy resources away from fossil fuels. The global market demand for palm oil that supports the oil palm industries has led to a rapid increase in generating the lignocellulosic biomass waste. Oil palm mills and plantation activities in Malaysia are among the largest sources of lignocellulosic biomass waste. Approximately 88.74 Mt of waste can be generated in 2020, which can lead to serious waste management problems (Kabir and Hameed, 2016). Annually, the oil palm plantations and mills produces approximately 13 Tg of palm frond and 10 Tg of oil palm mesocarp fiber (Sabil et al., 2013). Therefore, oil palm wastes can be utilized to support energy diversification and reduce the overdependence on fossil fuels for energy (Awalludin et al., 2015). Pyrolysis has been a promising route for converting biomass feedstocks into potent energy and chemical resources in the form of bio-oil, gas, and biochar. Pyrolysis under slow and fast heating has been used in the production of charcoal and bio-oils under the favorable conditions of temperature, heating rate, and vapor residence time (Ly et al., 2015; Yang et al., 2016). The residual pyrolysis oil (bio-oil) from the carbonization of biomass by slow pyrolysis has received significant attention for use as a precursor energy and a valuable chemical. The bio-oils have better energy properties than the corresponding biomass and are useful in the synthesis of valuable chemicals (Salema et al., 2017; Tinwala et al., 2015). Pyrolysis technology has recorded advances in the design and development of novel and effective pyrolysis reactors, such as fixed bed, fluidized bed, and conical-spouted bed reactors, for the production of bio-oils (Amutio et al., 2015; Biswas et al., 2017; Lopez et al., 2017). The reactors facilitate the pyrolytic decomposition of biomass to the primary coproducts, bio-oil, biochar, and gas. Fixed-bed reactors are commonly used for biomass pyrolysis because of their 2
simple design, besides challenges of their scale up and heat transfer limitation (Lopez et al., 2017). The reactors are adequate in biomass pyrolysis processes due to improved bio-oil yields under the reasonable residence time of the pyrolysis vapor. Biomass undergoes pyrolysis in several types of reactors. Beech wood, beech bark pellet, and babool seeds are pyrolyzed in a batch-fluidized reactor and in a fixed-bed reactor. The pyrolysis reactions decreased the oxygen and hydrogen content of the biochar and bio-oils to increase their high heating values (HHVs) (Garg et al., 2016; Morin et al., 2016). Bio-oils contain several families of oxygenated compounds from depolymerization; fragmentation; and cracking of the cellulose, hemicellulose, and the lignin structure of the biomass (Li et al., 2017). Pyrolysis reaction products create a unique composition of bio-oil based on the reactor conditions and the composition of the biomass. The bio-oils have been extensively studied and classified by characterization (Mohammed et al., 2016a; Torri et al., 2016). The characterization presented the inherent chemical composition and physical properties of the bio-oils (Santos et al., 2015). The literature has revealed the features of several bio-oils derived from the pyrolysis of biomass. The oxygenated compounds prevalent in the bio-oils militated against the HHVs of the bio-oils compared with those of the fossil fuels (Alagu et al., 2015; Saikia et al., 2015). PF and OPMF biomass from an oil palm plantation and mill were characterized and underwent pyrolysis in the slow-heating fixed-bed reactor. The effects of reaction temperature on the pyrolysis product distribution and yields were investigated. Moreover, the typical bio-oils and biochar obtained were broadly characterized to establish their potential for renewable energy and other value-added materials.
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2.
Materials and methods
2.1.
Materials
A local oil palm mill in Pinang, Malaysia supplied the OPMF, whereas the PF was obtained from an oil palm plantation at the Engineering campus of the Universiti Sains Malaysia, Nibong Tebal. Nitrogen (99.99% pure) was supplied by Araztech Engineering in Pinang, Malaysia.
2.2.
Methods
2.2.1. Biomass preparation The OPMF and PF biomass samples were open dried for several days and subsequently dried for 24 h in an oven at 105 °C. The samples were ground using a rotary grinding mill. The pulverized biomass was passed through sieves of 125–250 µm mesh and stored in airtight plastic containers for analysis and pyrolysis studies.
2.2.2 Physicochemical characterization of biomass and pyrolysis products The proximate analysis of the biomass, biochar, and bio-oils was examined on a PerkinElmer TGA 7 apparatus according to ASTM D 7582-10. The elemental compositions of the biomass, biochar, and bio-oil were analyzed on an elemental analyzer, Model 2400 Series II CHNO/S analyzer (Perkin–Elmer, USA). The oxygen content of the biomass was calculated by difference. An FTIR spectrometer (Spectrum 400, Perkin–Elmer, USA) examined the functional groups and fingerprints of the biomass, bio-oil, and biochar from the biomass pyrolysis. Pyrolysis products, bio-oil, biochar, and the HHVs of the corresponding biomass were analyzed on a bomb calorimeter (Model: IKA C 200) according to ASTM D2015. The quantity of cellulose, hemicellulose, and lignin in a typical OPMF and PF samples were determined from the procedures 4
reported by (Lopez-Gonzalez et al., 2014). The inorganic elemental compositions of the OPMF and PF biomass and their corresponding biochar (OPMF-char and PF-char) were determined using EDX analysis. The tentative compounds of the bio-oils (OPMF-oil and PF-oil) from the pyrolysis of OPMF and PF were examined using GC/MS techniques on a GC–MS Perkin Elmer Clarus 600/600T with helium as the carrier gas. The compounds were identified using the National Institute of Standards and Technology mass spectrum library. The composition of gas (PM-gas and PF-gas) were analyzed using the gas chromatography (GC) technique (Agilent 7890A) equipped with a thermal conductive detector. Density and viscosity were the major rheological properties examined for the bio-oils under ambient conditions. The density of the bio-oil was determined with a pycnometer. The biooil viscosities were determined on a rotational rheometer (Brookfield viscometer made in the USA, model DV-III, programmable rheometer) equipped with a spindle (SC4-18) and a computer. The pH of the bio-oils was examined with a pH meter (EUTECH pH 1500) at room temperature.
2.2.3 Slow heating pyrolysis of OPMF and PF The pyrolysis of OPMF and PF biomass was performed on a slow-heating fixed-bed reactor (2.2 cm x 35 cm). Approximately 5 g of the biomass was placed on a mesh supported in the reactor, and a cap was used to tightly close the reactor at the top. The reactor was fitted with a K-type thermocouple to monitor the pyrolysis temperature and a gas entry pipe to supply N2 gas into the reactor. The reactor set-up was held within a vertical furnace, and a condenser was connected to the output pipe of the reactor. Nitrogen (99.99% pure) was delivered at 200 mL/min into the reactor, which created an inert condition for the pyrolysis reactions. The furnace heating
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element heated the reactor from the outside up to the pyrolysis reaction temperature at 10 °C/ min and maintained the desired temperature for 15 min. The reactor and furnace temperatures were measured using synchronized temperature PID controllers. The resultant vapors from the biomass decomposition by pyrolysis were condensed to liquid (bio-oil) in a condenser that was maintained at −5 °C, and the non-condensable gasses were vented to the atmosphere. The reactor was cooled to room temperature at the end of 15 min pyrolysis reaction time. The bio-oil and the residual biochar were collected and weighed, whereas the gas was estimated by the difference from mass balance.
3.
Results and discussion
3.1.
Physicochemical characteristics of OPMF and PF Table 1 shows the physicochemical characteristics of the OPMF and PF biomass
prepared for slow pyrolysis studies. The OPMF and PF contained 40.12 wt% and 45.22 wt% cellulose, 20.12 wt% and 19.22 wt% hemicellulose, and their lignin content are 30.33 wt% and 31.24 wt% lignin respectively. The HHVs of the OPMF and PF biomass were respectively determined to be 17 MJ/kg and 16 MJ/kg, and are significantly lower than that of fossil fuels (42–46 MJ/kg) (Bordoloi et al., 2016). The fractions of the sub-components in the biomass are consistent with the fractions found in other lignocellulosic biomasses reported in the literature (Chang et al., 2016). The sub-components influence the energy density and thermal stability of the biomass and the yield and composition of the biomass pyrolysis products. The ultimate analysis depicts the fractions of C, H, N, S, and O in the biomass, as shown in Table 1. The OPMF and PF biomass contained the total elemental compositions of 45.38 wt% and 41.00 wt% carbon, 10.59 wt% and 6.74 wt% hydrogen, and the oxygen composition were 42.04 wt% and
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51.24 wt% respectively. The oxygen fraction militated against the fuel properties of the biomass and the biomass to have lower HHVs compared with fossil fuels. The fraction of N and S in the biomass are lower than those of fossil fuels and agrees with those fractions inherent in sawdust biomass (Tinwala et al., 2015). Therefore, the thermal decomposition of the biomass by combustion and pyrolysis leads to negligible emissions of gases that are detrimental the human health and environment. The proximate analysis estimated the relative fractions of fixed carbon, volatile matter, and ash of the biomass. The OPMF have fixed carbon content of 27.01 wt%, volatile matter of 66.84 wt%, and the ash contents of 1.40 wt%. Whereas, the fixed carbon, volatile matter and ash content of the PF biomass were found to be 18.97 wt%, 70.33 wt% and 5.87 wt% respectively. The PF has a fraction similar to the moisture of 4.83 wt%, which closely matched that of a mango seed shell (Andrade et al., 2016). On the contrary, the OPMF and PF have a moisture content that is lower than 13.84 wt% of PF (Abnisa et al., 2013) and higher than 2.1 wt% found in kusum seed (Koul et al., 2014). A large amount of moisture in biomass is undesirable and weighs down the fuel properties of the biomass and that of the resulting bio-oils from pyrolysis. The fixed carbon of the OPMF and PF biomass differs from that of Napier grass (17 wt%) (Mohammed et al., 2016b) and Pongamia glabra seed cover (19 wt%) (Bordoloi et al., 2015). The fixed carbon fraction favored the energy value of the biomass as solid fuel and the high yield biochar from pyrolysis. Sorghum bagasse (74 wt%) (Yin et al., 2013) and mango seed shell (94 wt%) (Andrade et al., 2016) have a higher amount of volatile matter compared with the OPMF and PF. The biomass with the high fraction of volatile matters is reactive during pyrolysis, which leads to high yields of bio-oils and gas.
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The elemental compositions of the inorganic elements were analyzed using EDX analysis on the corresponding ash of the biomass, the results are shown in Table 1. Therefore, the OPMF biomass contains 19.17 wt% Si, 6.54 wt% Al, and 24.04 wt% Fe which are higher than 10.63 wt% Si, 1.08 wt% Al, and 7.07wt% Fe determined for PF biomass. However, PF biomass contains 39.81 wt% K and 20.95 wt% Ca which are higher than 13.31 wt% K and 15.54 wt% Ca found in the OPMF biomass. These elements K, Ca, Mg, P, N, and Si are part of plant macronutrients and micronutrients that are precipitated and stored as inorganic minerals in the biomass structure (Nunes et al., 2017). The composition of the inorganic elements of the OPMF and PF biomass differs from those reported for the Karo Bambara shell and the EX-SOKOTO Bambara shell (Mohammed et al., 2016a). The alkali metals catalyze the pyrolysis of biomass and influence the distribution and composition of the bio-oil. The general characteristics of the OPMF and PF are broad within the range of those for the Eucalyptus sp. and Picea abies residues (Torri et al., 2016). Moreover, the OPMF and PF physical and chemical characteristics conformed with those biomass feedstocks used for the synthesis of high-grade bio-oils and chemicals by pyrolysis.
3.2.
Fourier transform infrared (FTIR) of OPMF and PF
Figure S1 presents the FTIR spectra of the OPMF and PF, which highlighted the various functional groups and the fingerprint of the biomass. The spectral exhibited a similar peak of varying intensities, which depicted the extent of the functional groups in the biomass. The absorption bands of the spectra indicated the functional groups that are representative of the basic structural units of the biomass. The absorbance bands at 3408 cm−1 are assigned to stretch
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the vibrations of O-H and conduct the asymmetric and symmetric stretching of the N-H bond. The O-H and N-H stretching vibrations established the presence phenolic alcohols associated with lignin of the biomass basic structural unit and amines from the protein content of the biomass, respectively. The bands at 2920 and 2862 cm−1 correspond to C-H stretching vibrations related to aromatic structural bonds of lignin, and the band at 1379 cm−1 is attributed to the C-H bending corresponds to the bonds of cellulose and hemicellulose. The bands at 1739 and 1627 cm−1 are associated with C=O stretching that corresponds to functional groups associated with lignin and hemicellulose. Moreover, the band at 1239 cm−1 is attributed to the C-O stretching vibration of syringyl ring of lignin. The C-O, C=C and C-O-C stretching vibrations at 1036 cm−1 related to bonds associated with cellulose, hemicellulose and lignin. The spectra indicated that the biomass macro-structural units consist of mostly esters, ketones alkanes and alkyl, ethers, and aromatics groups.
3.3
Thermal pyrolysis of OPMF and PF in a slow heating reactor
3.3.1 Effect of N2 flow rate on product distribution Figure 1 shows the effect of N2 flow on the yield of bio-oils from the pyrolysis of OPMF and PF. The study was conducted at a temperature of 550 °C, a heating rate of 10 °C/min, and an N2 flow rate of 100–300 mL/min. The N2 flows create the inert condition for the pyrolysis reactions in the reactor and evacuate the pyrolysis condensable vapors from the reactor. At 100 mL/min N2 flow rate, the bio-oil from the pyrolysis of the OPMF was 47 wt%, which was lower than 49 wt% bio-oil from the pyrolysis of PF. At the low N2 flow rate (100 mL/min), the condensable vapors from the biomass decomposition accumulate in the reactor, which promotes
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re-condensation, re-polymerization, and cracking reactions. Condensable vapors evacuated ontime from the reactor mitigated the reactions that decreases the bio-oil yield. At 200 and 300 mL/min N2 flow rate, the condensable vapors have short dwelling time in the reactor, which mitigated the vapor condensation, re-polymerization and cracking reactions. The bio-oil yields were maximum at 200 mL/min N2 flow rate, which follows the sufficient dwelling time for the decomposition of the biomass polymeric structure to small hydrocarbons and favors the increased yields of bio-oils. The N2 flow rate remains a critical factor for a proper inert condition for the pyrolysis and mitigating cracking reaction that favors the gas yield. There are similar findings on the effect of the N2 flow rate on the product distribution of the pyrolysis of S. japonica and babool seeds (Garg et al., 2016; Ly et al., 2015).
3.3.2. Effects of pyrolysis temperature on product yields of slow pyrolysis of OPMF and PF The slow pyrolysis of the OPMF and PF biomass was performed in a vertical fixed-bed reactor at pyrolysis temperatures at 400 °C, 500 °C, 550 °C, and 600 °C. The N2 flow rate of 200 mL/min was used in maintaining the required inert condition of the slow heating pyrolysis of the biomass. Figure 2 depicts the distribution and the yields of bio-oil, biochar, and gas from the slow pyrolysis of the OPMF and PF at the different pyrolysis temperatures. The biomass primary structures degrade the three primary products during the pyrolysis reactions by bond cleavage, carboxylation, and cracking reaction. At a low pyrolysis temperature of 400 °C, the pyrolysis of the OPMF and PF respectively produced 41 wt% and 43 wt% bio-oils, 40 wt% and 31 wt% biochar, and 18 wt% and 26 wt% gas. The yields of the bio-oils increased with increasing pyrolysis temperature. Therefore, it is observed that the pyrolysis of the OPMF and PF in the
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temperature range of 500 °C – 600 °C respectively caused high yields of bio-oils ranging from 48–50 wt% and 45–47 wt%. The temperatures expedited the devolatilization of the biomass primary structures, which resulted in the highest yields of the bio-oils. Based on the type of biomass and reactor process, pyrolysis at temperatures above 600 °C would propagates the secondary cracking or reforming of the heavy molecular weight compounds of the pyrolysis vapor. The biochar was decomposed by reduction reaction to CO2 and H2, which results in an increase in gas fraction during the biomass pyrolysis.
3.4.
Characterization of OPMF-oil and PF-oil
Table 2 presents the ultimate analysis and HHVs of the OPMF-oil and PF-oil from the pyrolysis of the PF and OPMF. The OPMF-oil and PF-oil, respectively, have 67.77 wt% and 60.81 wt% C and 19.60 wt% and 28.54 wt% O, which correspond to the bio-oils from the pyrolysis of the eastern red cedar (Yang et al., 2016) and the coppice of poplar (Bartoli et al., 2016). The HHVs of the OPMF-oil and PF-oil were respectively 23 MJ/kg and 21 MJ/kg, which are higher than those of the respective biomass and less than those of the gasoline and diesel fuels. The pyrolysis deoxygenates the biomass, which resulted in bio-oils with low O/C ratio than that of the corresponding biomass. Thus, the pyrolysis alleviated the fuel properties of the bio-oils by improving the HHV of the bio-oils to above that of the corresponding biomass. The resultant O fraction in the bio-oils is relatively high and still affected the HHVs of the bio-oils to less than that of fossil fuels. The N content of the OPMF-oil and PF-oil are determined to be 1.85 wt% and 2.03 wt%, and S in the bio-oils are 0.51 wt% and 0.38 wt% respectively, which agrees with the N and S contents of bio-oil from the pyrolysis of the Ipomoea carnea (Saikia et al., 2015). Therefore, the
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low contents of S and N inferred that the OPMF-oil and PF-oil can be suitable renewable energy feedstock with minimal emissions of SOx and NOx to the environment. The high carbon content and HHV of the bio-oils are coupled with the low values of hydrogen and oxygen fractions. Therefore, the bio-oils can serve as feedstock for renewable fuel.
3.5.
Fourier transform infrared of OPMF-oil and PF-oil Figure S2 shows the spectra of OPMF-oil and PF-oil obtained from the FTIR analysis
using the conventional KBr technique. The spectra have bands that refer to several compounds with different functionalities in the bio-oils. The bands between 3200 and 3600 cm−1 correspond to the O-H stretching associated with the phenols, alcohols, and water of the bio-oils. The band between 2800 and 3000 cm−1 correspond to C-H stretching, and the band between 1350 and 1480 cm−1 corresponds to the C-H bending associated with the CH3, CH2, and CH aliphatic bonding of heteroatomic compounds. The C-O stretching vibration with an absorption band of 1000–1300 cm−1 refers to ethers. The bands that stretch within 1210–1320 cm−1 and 1715–1800 cm−1, related to C-O and C=O bonds, refer to the esters group. The C=O bond stretching corresponds to the bands between 1650 and1800 cm−1, which refer to the carboxylic acids, aldehydes, esters, and ketones groups in the bio-oils. Moreover, the absorption bands between 690 and 900 cm−1 refer to C-H bending associated with aromatics compounds. The FTIR transmission spectra have several bands of oxygen-based functional groups, which authenticated that the bio-oils are laden by oxygenated compounds. 3.6.
GC-MS compositions of OPMF-oil and PF-oil Figure S3 presents the chromatogram of OPMF-oil and PF-oil, which consist of several
characteristic peaks at various heights aligned with retention times (min). The peaks on the
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chromatograms referred to the wide variety of compounds in the bio-oils, which highlighted the complex mixture of the organic compounds of the bio-oils. The total chromatograms obtained by the GC-MS of bio-oils from the pyrolysis of a palm kernel shell (Chang et al., 2016) and oil palm mesocarp fiber (Khanday et al., 2016) have extensive peaks of various organic compounds similar to Figure S3. Figure 3 shows the relative abundance of the tentative compounds of the bio-oils presented as peak area ratios obtained by GC-MS. Heating at pyrolysis temperatures from 400– 600 °C affected the distribution of organic compounds and their relative abundance in the biooils. The disparities in the peak area ratio of the numerous compounds of bio-oils shown in Figure S3 indicated that the bio-oil chemical compositions are affected by pyrolysis temperature. The temperatures expedite the cracking of the side chains of the benzene derivatives and the furan derivatives to increase the relative abundance of light carbonyl and alcohols compounds. Thus, the relative abundance of the carbonyl compounds of the bio-oils increases with the increasing pyrolysis temperature. The amount of phenol increases with an increasing temperature of up to 600 °C, whereas the relative abundance of the benzene derivatives decreases with increasing temperature. The inhibition in the decomposition of phenol and the reactivity of the benzene derivatives at temperatures from 550–600 °C favored the increasing yield of the phenol. The acid peak area ratios are significantly high, with a maximum value of 550 °C. The bio-oils can be classified as acidic, which is consistent with the high acidity pH value of 3, as shown in Table 2. Table 3 and 4 presents a typical comparative distribution of organic compounds in the OPMF-oil and PF-oil bio-oils from the pyrolysis of PMF and PF at 550 °C respectively. The bio-
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oils consist of complex mixtures of oxygenated compounds detected by the GC-MS. Such compounds are responsible for the low HHVs of the bio-oils (Table 2). Most of the compounds are products of decarbonylation, decarboxylation, cracking, and ring formation reactions that convert the primary oligomers of the biomass to oxygenated light molecules. The lignin of the biomass is devolatilized to pervade the resulting bio-oils with oxygenated aromatic compounds, such as phenols and phenolic derivatives (Chen et al., 2016; Li et al., 2017). The main phenolic compounds detected in the bio-oils include phenols, phenol, 4ethyl-2-methoxy- and phenol, 2,6-dimethoxy-4-(2-propenyl)-. The major benzene derivative compounds of the bio-oils include benzene, 1,4-dimethoxy- and benzene, 1,2,3-trimethoxy-5methyl-. Hemicellulose devolatilized into acidic compounds, such as octanoic acid, dodecanoic acid, n-hexadecanoic acid, 4-guanidinobutyric acid, and oleic acid acetic acid in the bio-oils. Cellulose and hemicellulose decomposed to glucopyranoses (anhydrosugars) and heterocyclic compounds; furan and furan derivatives; acetic acid and propionic acid; and 2-cyclopenten-1one, 2-methyl-, and 1-Hydroxy-2-butanone. The thermal pyrolysis of lignin (Liu et al., 2016; Yang et al., 2016) produced bio-oils that are rich in phenol and phenolic derivatives, consistent with the findings in this report. Thus, the alkali metals of the biomass that contact with the pyrolysis vapor catalyzed the conversion of the levoglucosan to the light organic compounds, such as acetic acid and furfural. The acid compounds are undesirable because they encourage aging and corrosivity, which affect the fuel and chemical properties of the bio-oils (Kabir and Hameed, 2016). The relative abundance of the several families of compounds of the bio-oils revealed that phenol, carbonyls, and benzene derivatives are the dominant group in the bio-oils. The relative abundance of the benzene derivatives in OPMF-oil are more than those of PF-oil, whereas 14
phenols in OPMF-oil are less than those of PF-oil. The bio-oils from the biomass have a significantly high amount of carbonyl compounds, but OPMF-oil has a higher amount of carbonyl than PF-oil (Figure 3). Moreover, acid compounds in the OPMF-oil are more than those in the PF-oil. The amount acid compounds are sufficient to indicate that the bio-oils are highly acidic, which is consistent with the pH of 3, as reported in Table 2. PF-oil has more heterocyclic compounds (furans) than OPMF-oil. A significant amount of alcohol-related compounds is in PF-oil compared with that in the OPMF-oil, whereas the PF-oil and OPMF-oil have the least anhydrous sugar content. The family and distribution of compound found in the OPMF-oil and PF-oil are consistent with those of bio-oils from the slow heating pyrolysis of bocaiuva residues (Cardoso et al., 2016) and licorice (Aysu and Durak, 2015). The aromatic compounds enhance the fuel properties of the bio-oils. Therefore, they are among the most desired components of the bio-oils. Moreover, the aromatics can improve the bio-oil proficiency as a renewable precursor for fuel and valuable chemicals. The octane number of gasoline can be increased from blending with aromatic-laden bio-oil, and several important value- added chemicals and polymers can be derived from the aromatics.
3.7.
Characterization of OPMF-char and PF-char Table 5 shows the proximate analysis of the OPMF-char and PF-char biochars obtained
from the pyrolysis of the corresponding biomass OPMF and PF at a temperature of 550 °C and an N2 flow rate of 200 mL/min. The OPMF-char and PF-char respectively have HHV of 24.84 and 24.15 MJ/kg and fixed carbon of 65.01 and 81.88 wt%. The high carbon contents of the biochars are linked to the high degree of aromaticity during the pyrolysis of the corresponding biomass, which produced the highly carbonized char. The HHVs and fixed carbon of the 15
biochars are higher than that of the corresponding biomass and consistent with those biochars from the pyrolysis of sal seed (Singh et al., 2014). Therefore, the energy densities of the biochars have improved to higher values than those of the corresponding biomass. The OPMF-char and PF-char have ash content of 27.04 wt% and 3.73 wt% and volatile content of 4.89 wt% and 9.97 wt% respectively. The values agree with those of the biochars from Pongamia glabra seed cover (Bordoloi et al., 2015). The biochars inherited some inorganic mineral compounds after the pyrolysis of the corresponding biomass. The mineral becomes an important component of the char. Therefore, the elemental compositions of the mineral contents inherited by the OPMF-char and PF-char from the corresponding biomass were estimated using EDX analysis, as shown in Table 5. The Si, Al and Fe compositions in the OPMF-char are found to be 30.18 wt%, 3.87 wt% and 19.89 wt% respectively and higher than 12.56 wt% Si, 1.08 wt% Al and 3.78 wt% Fe of the PF-char. Whereas, the PF-char have K (46.19 wt%) and Ca (15.57 wt%) higher than 21.99 wt% K and 8.83 wt% Ca found in the OPMF-char. The alkali metals caused the high yield of ash that has a direct effect on the carbon content and the fuel potential of the biochar (Ly et al., 2015). Therefore, the low ash, high HHV, and carbon content improve the biochar energy proficiency more than that of the corresponding biomass feedstocks.
3.8.
Fourier transform infrared analysis on OPMF-char and PF-char biochar Figure S4 shows the FTIR spectra of the OPMF-char and PF-char (biochar) from the
pyrolysis of OPMF and PF. The bands between 3200 and 3600 cm−1 correspond to the hydroxyl stretching attributed to the phenols and the proton vibrations of the water molecule. The intensities of the bands are low compared with those of the bio-oils and biomass, which result
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from the low vibration of the O-H bond due to the dehydration of water and the cracking of volatile matters during the pyrolysis. The decrease in the bands attributed to the stretching vibration due to C=O, C-H, and CH3 (methoxyl group). The peaks between 1030 and 1300 cm−1 bands mostly disappeared compared with those of the biomass. The absence of most bands indicated that the biochars are primarily carbonized. The bands near 1622 and 1384 cm−1 respectively corresponds to the C=C bending and C-H bending vibrations associated with aromatics. Moreover, the volatile matter of the biomass cracked during the pyrolysis, which decreases the CH and alkyl bonds and increases the C2 and CH4 bonds of hydrocarbon gasses. The resultant aliphatic bonds transformed to aromatic bonds, which explains the bands. This result confirmed that aromatics constitute the basic unit of the biochars. 4.
Conclusions Pyrolysis devolatilized OPMF and PF are devolatilized to primarily biochar and bio-oils
with HHVs higher than those of the corresponding biomass. The pyrolysis of the OPMF and PF respectively produces the highest yield of bio-oils of 50 wt% and 47 wt% at 550 °C and 600 °C. The low O/C ratio favored the HHVs of the bio-oils to higher than those of the corresponding biomass. The FTIR spectra and peak area ratios reveled that pyrolysis temperatures influenced the bio-oils compositions. The bio-oils obtained at different pyrolysis temperatures contained oxygenated carbonyls and aromatic compounds suitable for processing high-grade chemicals and fuel. Acknowledgements The authors acknowledge the research grants provided by the Universiti Sains Malaysia, under Research University (RU) grant (Project No: 1001/PJKIMIA/814227) that resulted in this article.
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Figure captions Fig. 1.
Effect of N2 flow rate on the distribution of products from the pyrolysis of (a) OPMF and (b) PF (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 100 − 300 mL/min).
Fig. 2.
Product distributions from the pyrolysis of (a) OPMF and (b) PF (conditions: temperatures of 400 °C to 600 °C, reaction time of 15 min, and N2 flow rate of 200 mL/min).
Fig. 3.
Relative abundance and categories of the tentative compounds of (a) OPMF-oil and (b) PF-oil (conditions: temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min).
23
60 OPMF-oil
Bio-oil
Bio-char
Gas
Products yields (wt%)
50
40
30
20
10
0 100
200 N2 flow rate (mL/min)
(a)
24
300 Fig.1
60 Bio-oil
PF-oil
Bio-char
Gas
Products yields (wt%)
50 40 30 20 10 0 100
200 N2 flow rate (mL/min)
Fig.1 (b)
25
300
60
OPMF
Product yields (wt%)
50 40
Biochar
30 20 10 0 400
450
500 Temperature (oC)
550
600
Fig. 2 (a)
60 PF Product yields (wt%)
50 40 30 Gas
20 10 0 400
450
500 Temperature (oC)
Fig. 2 (b).
26
550
600
40 Peak area (%) @ 400 °C
Area peaks (%)
35
OPMF-oil
Peak area (%) @ 450 °C
30
Peak area (%) @ 550 °C
25
Peak area (%) @ 600 °C
20 15 10 5 0
Bio-oils compounds
Fig. 3 (a).
27
50 45 40
Peaks area (%)
35
Peak area (%)@ 400 °C
PF-oil
Peak area (%) @ 450 °C Peak area (%) @ 550 °C Peak area (%) @ 600 °C
30 25 20 15 10 5 0
Bio-oils compounds
Fig. 3 (b).
28
List of Tables Table 1.
Characterization of OPMF and PF biomass.
Property
Biomass type PF
OPMF Proximate analysis (wt%) Moisture
4.75
4.83
Ash
1.40
5.87
Volatile matter
66.84
70.33
Fixed carbon
27.01
18.97
Heating value (MJkg-1)
17.00
16.00
Carbon ( C )
45.38
41.00
Hydrogen (H)
10.59
6.74
Nitrogen (N)
1.32
0.67
Sulphur (S)
0.67
0.35
Oxygen (O)
42.04
51.24
H/C
0.23
0.16
O/C
0.93
1.25
Ultimate analysis (wt %)
Composition analysis (wt %) Cellulose
40.12
45.22
Hemicellulose
20.12
19.22
Lignin
30.33
31.24
Extractives
9.43
4.32
6.54
1.08
Si
19.17
10.63
K
13.31
39.81
Ash analysis (%) (EDX ) Al
29
Ca Mg Fe P S
15.54
20.95
11.19
8.01
24.04
7.07
7.48
9.20
2.73
3.25
30
Table 2.
Characterization of OPM-oil and PF-oil (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min). Bio-oil type
Property OPMF-oil PF-oil Ultimate analysis (wt %) Carbon ( C )
67.77
60.81
Hydrogen (H)
10.27
8.24
Nitrogen (N)
1.85
2.03
Sulphur (S)
0.51
0.38
Oxygen (O)
19.60
28.54
H/C
0.15
0.14
O/C
0.29
0.47
Heating value (MJ/kg)
23.00
21.00
pH
3
3
Density (g/mL)
1.05
1.07
Viscousity (at 30 oC) (cp)
2.55
2.41
31
Table 3.
GC-MS compositions of OPM-oil (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min).
Peak No.
RT (min)
Family/Compounds
%Peak Area
15 32 37 39 41 42
20.736 36.888 43.331 50.254 55.276 55.686
Acids Octanoic Acid Dodecanoic acid Tetradecanoic acid n-Hexadecanoic acid Oleic Acid Octadecanoic acid Total
1.799 2.56 0.977 6.405 4.586 1.531 17.858
22
26.969
Furans 2-Acetyl-2-methyltetrahydrofuran Total
0.334 0.334
9 13 14 16 21 26 30 31 33 34
11.763 18.11 19.686 21.802 26.229 31.091 34.557 35.813 37.714 39.94
Phenols Phenol Phenol, 4-methoxy-3-methylPhenol, 2-ethylPhenol, 4-ethyl-2-methoxyPhenol, 2,6-dimethoxy5-Methyl-2-nitrophenol 4-(Methoxycarbonyl)phenol Phenol, 2,6-dimethoxy-4-(2-propenyl)Phenol, 2,6-dimethoxy-4-(2-propenyl)Phenol, 2,6-dimethoxy-4-(2-propenyl)Total
4.433 0.824 2.002 0.534 9.272 0.325 2.154 0.637 0.788 2.08 23.049
18 19 20 23 24 25 27 28 36 29
23.823 24.513 24.908 28.45 29.22 29.905 31.656 32.757 42.911 33.957
Benzene Derivatives 1,2-Benzenediol, 3-methoxy1,2-Benzenediol 1,2-Benzenediol 1,2-Benzenediol, 4-methyl Vanillin 1,2,3-Trimethoxybenzene 4-Ethyl-1,2-benzenediol Benzene, 1,2,3-trimethoxy-5-methyl2-Pentanone, 1-(2,4,6-trihydroxyphenyl) 2-Propanone, 1-(4-hydroxy-332
2.717 1.756 4.961 0.859 0.461 3.576 0.295 2.276 2.595 1.785
17 10 11 12 47
35
methoxyphenyl)22.63 Decanediamide, N,N'-di-benzoyloxyTotal Ketones 12.368 2-Cyclopenten-1-one, 2-hydroxy-3-methyl13.589 2-Cyclopenten-1-one, 3,5,5-trimethyl 15.834 7-Oxabicyclo[4.1.0]heptan-2-one, 6-methyl3-Penten-2-one, 4-(2,2,6-trimethyl-759.818 oxabicyclo[4.1.0]hept-1-yl)-, (E)Total
40.53
38
46.057
43
56.141
44
56.592
40
51.589
45
57.297
46
58.032
8
8.391
Aldehydes Octanal, 7-hydroxy-3,7-dimethylTotal Esters Pentadecanoic acid, 14-methyl-, methyl ester Icosanoic acid 2-(acetyloxy)-1[(acetyloxy)methyl]ethyl ester Hexadecanoic acid, 1-(hydroxymethyl)-1,2ethanediyl ester 9-Octadecenoic acid (Z)-, methyl ester Hexadecanoic acid, 2,3-bis(acetyloxy)propyl ester 2,4-Dimethylnonanedioic acid dimethyl ester Total Glucopyranoses D-Glucose, 2,3,4-tri-O-methylTotal
33
2.717 23.998 1.085 0.686 2.711 5.049 9.531
1.084 1.084
0.355 1.249 0.914 0.378 2.622 0.632 6.15
0.244 0.244
Table 4.
GC-MS compositions of PF-oil (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min).
Peak RT No. (min)
Family/Compounds
%Peak Area
Acids 10 13
12.073 Pyrazine-2-carboxylic acid, 3-hydroxy12.318 Urocanic acid
0.348 0.968
21
20.426 1H-Imidazole-4-carboxylic acid, 2-ethyl-
1.092
Total 6 15 40
2.408
Alcohols 7.296 3-Pentyn-1-ol 13.404 2,5-Cyclohexadiene-1,4-diol 41.95 7-Octene-2,6-diol, 2,6-dimethylTotal
8 9 28
8.526 12.028 27.589
14 16 20 23 31 36 27 37 39 42
12.568 14.009 18.661 22.257 30.521 36.288 27.214 38.134 40.38 43.756
Furans Furan, 2,4-dimethylVinylfuran Furan Total Phenols Phenol Phenol, 2-methoxyPhenol, 2-methoxy-4-methylPhenol, 4-ethyl-2-methoxyPhenol, 4-methoxy-3-(methoxymethyl)Phenol, 2,6-dimethoxy-4-(2-propenyl)Phenol, 2,6-dimethoxyPhenol, 2,6-dimethoxy-4-(2-propenyl)Phenol, 2,6-dimethoxy-4-(2-propenyl)Desaspidinol Total Benzene Derivatives 34
0.314 7.841 1.266 9.421
0.28 1.953 0.672 2.905 2.74 1.965 3.792 0.482 3.376 2.29 15.03 0.358 2.588 1.487 34.108
24 25 26 30 33 35 41 43
11 17 18 29 34 45
5
44 46 49
23.278 2',6'-Dihydroxyacetophenone 25.168 1,4-Benzenediol, 2-methoxy25.874 1,2-Benzenediol 29.43 1,2-Benzenediol, 3-methyl33.312 5-tert-Butylpyrogallol 35.713 2H-1-Benzopyran-2-one, 3,4-dihydro-6-hydroxy42.571 Ethanone, 1-(4-hydroxy-3,5-dimethoxyphenyl)45.327 Ethanone, 1-(4-hydroxy-3,5-dimethoxyphenyl)Total Ketones 12.118 Ethanone, 1-(1H-pyrrol-2-yl)14.749 3-Hepten-2-one, 4-methyl16.65 2-Cyclopenten-1-one, 3-ethyl-2-hydroxy28.295 2(3H)-Furanone, 5-heptyldihydro34.722 2-Propanone, 1-(4-hydroxy-3-methoxyphenyl)50.594 Neocurdione Total Glucopyranoses 4.325 Levoglucosenone Total
49.654 54.671 60.303
Esters Isopropyl Palmitate 10-Octadecynoic acid, methyl ester Octanedioic acid, 4-isopropyl-, dimethyl ester Total
35
0.907 1.836 1.582 0.498 2.507 1.414 0.643 0.218 9.605 0.594 0.541 3.856 1.118 0.739 0.21 7.058 0.362 0.362
0.809 0.414 2.196 3.419
Table 5.
Characterization of OPM-char and PF-char (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min). Type of biochar
Property OPMF-char
PF-char
Moisture
3.06
4.42
Ash
27.04
3.73
Volatile matter
4.89
9.97
Fixed carbon
65.01
81.88
Heating value (MJ/kg)
24.84
24.15
Proximate analysis (wt%)
Compositions of inorganic elements (%) (EDX ) Al
3.87
1.08
Si
30.18
12.56
K
21.99
46.19
Ca
8.83
15.57
Mg
7.69
6.46
Fe
19.89
3.78
P
4.80
12.28
S
2.75
2.08
36
Highlights •
Pyrolysis devolatilized OPMF and PF to 48 and 47 wt% maximum yield of bio-oil respectively.
•
Maximum yield of bio-oils occurred at 550 oC for OPMF and 600 oC for PF.
•
Compounds of phenols and benzene derivatives pervaded the OPMF-oil and PF-oil.
•
OPMF-oil and PF-oil contained maximum aromatics yield of 43% and 50% peak area respectively.
37
S0960-8524(17)30848-9 http://dx.doi.org/10.1016/j.biortech.2017.05.180 BITE 18206
To appear in:
Bioresource Technology
Received Date: Revised Date: Accepted Date:
2 April 2017 26 May 2017 27 May 2017
Please cite this article as: Kabir, G., Mohd Din, A.T., Hameed, B.H., Pyrolysis of oil palm mesocarp fiber and palm frond in a slow-heating fixed-bed reactor: A comparative study, Bioresource Technology (2017), doi: http:// dx.doi.org/10.1016/j.biortech.2017.05.180
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Pyrolysis of oil palm mesocarp fiber and palm frond in a slow-heating fixed-bed reactor: A comparative study
G. Kabir, A. T. Mohd Din, B.H. Hameed* School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia * Corresponding author. Tel.: +6045996422; Fax: +6045941013 E-mail address: [email protected] (B.H. Hameed)
Abstract Oil palm mesocarp fiber (OPMF) and palm frond (PF) were respectively devolatilized by pyrolysis to OPMF-oil and PF-oil bio-oils and biochars, OPMF-char and PF-char in a slowheating fixed-bed reactor. In particular, the OPMF-oil and PF-oil were produced to a maximum yield of 48 wt% and 47 wt% bio-oils at 550 °C and 600 °C, respectively. The high heating values (HHVs) of OPMF-oil and PF-oil were respectively found to be 23 MJ/kg and 21 MJ/kg, whereas 24.84 MJ/kg and 24.15 MJ/kg were for the corresponding biochar. The HHVs of the bio-oils and biochars are associated with low O/C ratios to be higher than those of the corresponding biomass. The Fourier transform infrared spectra and peak area ratios highlighted the effect of pyrolysis temperatures on the bio-oil compositions. The bio-oils are pervaded with numerous oxygenated carbonyl and aromatic compounds as suitable feedstocks for renewable fuels and chemicals. Keywords: Bio-oil; Pyrolysis; Fixed-bed reactor; Palm fond; Oil palm mesocarp fiber
1
1.
Introduction Non-food lignocellulosic biomass wastes take a pivotal role in decentralizing the world’s
energy resources away from fossil fuels. The global market demand for palm oil that supports the oil palm industries has led to a rapid increase in generating the lignocellulosic biomass waste. Oil palm mills and plantation activities in Malaysia are among the largest sources of lignocellulosic biomass waste. Approximately 88.74 Mt of waste can be generated in 2020, which can lead to serious waste management problems (Kabir and Hameed, 2016). Annually, the oil palm plantations and mills produces approximately 13 Tg of palm frond and 10 Tg of oil palm mesocarp fiber (Sabil et al., 2013). Therefore, oil palm wastes can be utilized to support energy diversification and reduce the overdependence on fossil fuels for energy (Awalludin et al., 2015). Pyrolysis has been a promising route for converting biomass feedstocks into potent energy and chemical resources in the form of bio-oil, gas, and biochar. Pyrolysis under slow and fast heating has been used in the production of charcoal and bio-oils under the favorable conditions of temperature, heating rate, and vapor residence time (Ly et al., 2015; Yang et al., 2016). The residual pyrolysis oil (bio-oil) from the carbonization of biomass by slow pyrolysis has received significant attention for use as a precursor energy and a valuable chemical. The bio-oils have better energy properties than the corresponding biomass and are useful in the synthesis of valuable chemicals (Salema et al., 2017; Tinwala et al., 2015). Pyrolysis technology has recorded advances in the design and development of novel and effective pyrolysis reactors, such as fixed bed, fluidized bed, and conical-spouted bed reactors, for the production of bio-oils (Amutio et al., 2015; Biswas et al., 2017; Lopez et al., 2017). The reactors facilitate the pyrolytic decomposition of biomass to the primary coproducts, bio-oil, biochar, and gas. Fixed-bed reactors are commonly used for biomass pyrolysis because of their 2
simple design, besides challenges of their scale up and heat transfer limitation (Lopez et al., 2017). The reactors are adequate in biomass pyrolysis processes due to improved bio-oil yields under the reasonable residence time of the pyrolysis vapor. Biomass undergoes pyrolysis in several types of reactors. Beech wood, beech bark pellet, and babool seeds are pyrolyzed in a batch-fluidized reactor and in a fixed-bed reactor. The pyrolysis reactions decreased the oxygen and hydrogen content of the biochar and bio-oils to increase their high heating values (HHVs) (Garg et al., 2016; Morin et al., 2016). Bio-oils contain several families of oxygenated compounds from depolymerization; fragmentation; and cracking of the cellulose, hemicellulose, and the lignin structure of the biomass (Li et al., 2017). Pyrolysis reaction products create a unique composition of bio-oil based on the reactor conditions and the composition of the biomass. The bio-oils have been extensively studied and classified by characterization (Mohammed et al., 2016a; Torri et al., 2016). The characterization presented the inherent chemical composition and physical properties of the bio-oils (Santos et al., 2015). The literature has revealed the features of several bio-oils derived from the pyrolysis of biomass. The oxygenated compounds prevalent in the bio-oils militated against the HHVs of the bio-oils compared with those of the fossil fuels (Alagu et al., 2015; Saikia et al., 2015). PF and OPMF biomass from an oil palm plantation and mill were characterized and underwent pyrolysis in the slow-heating fixed-bed reactor. The effects of reaction temperature on the pyrolysis product distribution and yields were investigated. Moreover, the typical bio-oils and biochar obtained were broadly characterized to establish their potential for renewable energy and other value-added materials.
3
2.
Materials and methods
2.1.
Materials
A local oil palm mill in Pinang, Malaysia supplied the OPMF, whereas the PF was obtained from an oil palm plantation at the Engineering campus of the Universiti Sains Malaysia, Nibong Tebal. Nitrogen (99.99% pure) was supplied by Araztech Engineering in Pinang, Malaysia.
2.2.
Methods
2.2.1. Biomass preparation The OPMF and PF biomass samples were open dried for several days and subsequently dried for 24 h in an oven at 105 °C. The samples were ground using a rotary grinding mill. The pulverized biomass was passed through sieves of 125–250 µm mesh and stored in airtight plastic containers for analysis and pyrolysis studies.
2.2.2 Physicochemical characterization of biomass and pyrolysis products The proximate analysis of the biomass, biochar, and bio-oils was examined on a PerkinElmer TGA 7 apparatus according to ASTM D 7582-10. The elemental compositions of the biomass, biochar, and bio-oil were analyzed on an elemental analyzer, Model 2400 Series II CHNO/S analyzer (Perkin–Elmer, USA). The oxygen content of the biomass was calculated by difference. An FTIR spectrometer (Spectrum 400, Perkin–Elmer, USA) examined the functional groups and fingerprints of the biomass, bio-oil, and biochar from the biomass pyrolysis. Pyrolysis products, bio-oil, biochar, and the HHVs of the corresponding biomass were analyzed on a bomb calorimeter (Model: IKA C 200) according to ASTM D2015. The quantity of cellulose, hemicellulose, and lignin in a typical OPMF and PF samples were determined from the procedures 4
reported by (Lopez-Gonzalez et al., 2014). The inorganic elemental compositions of the OPMF and PF biomass and their corresponding biochar (OPMF-char and PF-char) were determined using EDX analysis. The tentative compounds of the bio-oils (OPMF-oil and PF-oil) from the pyrolysis of OPMF and PF were examined using GC/MS techniques on a GC–MS Perkin Elmer Clarus 600/600T with helium as the carrier gas. The compounds were identified using the National Institute of Standards and Technology mass spectrum library. The composition of gas (PM-gas and PF-gas) were analyzed using the gas chromatography (GC) technique (Agilent 7890A) equipped with a thermal conductive detector. Density and viscosity were the major rheological properties examined for the bio-oils under ambient conditions. The density of the bio-oil was determined with a pycnometer. The biooil viscosities were determined on a rotational rheometer (Brookfield viscometer made in the USA, model DV-III, programmable rheometer) equipped with a spindle (SC4-18) and a computer. The pH of the bio-oils was examined with a pH meter (EUTECH pH 1500) at room temperature.
2.2.3 Slow heating pyrolysis of OPMF and PF The pyrolysis of OPMF and PF biomass was performed on a slow-heating fixed-bed reactor (2.2 cm x 35 cm). Approximately 5 g of the biomass was placed on a mesh supported in the reactor, and a cap was used to tightly close the reactor at the top. The reactor was fitted with a K-type thermocouple to monitor the pyrolysis temperature and a gas entry pipe to supply N2 gas into the reactor. The reactor set-up was held within a vertical furnace, and a condenser was connected to the output pipe of the reactor. Nitrogen (99.99% pure) was delivered at 200 mL/min into the reactor, which created an inert condition for the pyrolysis reactions. The furnace heating
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element heated the reactor from the outside up to the pyrolysis reaction temperature at 10 °C/ min and maintained the desired temperature for 15 min. The reactor and furnace temperatures were measured using synchronized temperature PID controllers. The resultant vapors from the biomass decomposition by pyrolysis were condensed to liquid (bio-oil) in a condenser that was maintained at −5 °C, and the non-condensable gasses were vented to the atmosphere. The reactor was cooled to room temperature at the end of 15 min pyrolysis reaction time. The bio-oil and the residual biochar were collected and weighed, whereas the gas was estimated by the difference from mass balance.
3.
Results and discussion
3.1.
Physicochemical characteristics of OPMF and PF Table 1 shows the physicochemical characteristics of the OPMF and PF biomass
prepared for slow pyrolysis studies. The OPMF and PF contained 40.12 wt% and 45.22 wt% cellulose, 20.12 wt% and 19.22 wt% hemicellulose, and their lignin content are 30.33 wt% and 31.24 wt% lignin respectively. The HHVs of the OPMF and PF biomass were respectively determined to be 17 MJ/kg and 16 MJ/kg, and are significantly lower than that of fossil fuels (42–46 MJ/kg) (Bordoloi et al., 2016). The fractions of the sub-components in the biomass are consistent with the fractions found in other lignocellulosic biomasses reported in the literature (Chang et al., 2016). The sub-components influence the energy density and thermal stability of the biomass and the yield and composition of the biomass pyrolysis products. The ultimate analysis depicts the fractions of C, H, N, S, and O in the biomass, as shown in Table 1. The OPMF and PF biomass contained the total elemental compositions of 45.38 wt% and 41.00 wt% carbon, 10.59 wt% and 6.74 wt% hydrogen, and the oxygen composition were 42.04 wt% and
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51.24 wt% respectively. The oxygen fraction militated against the fuel properties of the biomass and the biomass to have lower HHVs compared with fossil fuels. The fraction of N and S in the biomass are lower than those of fossil fuels and agrees with those fractions inherent in sawdust biomass (Tinwala et al., 2015). Therefore, the thermal decomposition of the biomass by combustion and pyrolysis leads to negligible emissions of gases that are detrimental the human health and environment. The proximate analysis estimated the relative fractions of fixed carbon, volatile matter, and ash of the biomass. The OPMF have fixed carbon content of 27.01 wt%, volatile matter of 66.84 wt%, and the ash contents of 1.40 wt%. Whereas, the fixed carbon, volatile matter and ash content of the PF biomass were found to be 18.97 wt%, 70.33 wt% and 5.87 wt% respectively. The PF has a fraction similar to the moisture of 4.83 wt%, which closely matched that of a mango seed shell (Andrade et al., 2016). On the contrary, the OPMF and PF have a moisture content that is lower than 13.84 wt% of PF (Abnisa et al., 2013) and higher than 2.1 wt% found in kusum seed (Koul et al., 2014). A large amount of moisture in biomass is undesirable and weighs down the fuel properties of the biomass and that of the resulting bio-oils from pyrolysis. The fixed carbon of the OPMF and PF biomass differs from that of Napier grass (17 wt%) (Mohammed et al., 2016b) and Pongamia glabra seed cover (19 wt%) (Bordoloi et al., 2015). The fixed carbon fraction favored the energy value of the biomass as solid fuel and the high yield biochar from pyrolysis. Sorghum bagasse (74 wt%) (Yin et al., 2013) and mango seed shell (94 wt%) (Andrade et al., 2016) have a higher amount of volatile matter compared with the OPMF and PF. The biomass with the high fraction of volatile matters is reactive during pyrolysis, which leads to high yields of bio-oils and gas.
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The elemental compositions of the inorganic elements were analyzed using EDX analysis on the corresponding ash of the biomass, the results are shown in Table 1. Therefore, the OPMF biomass contains 19.17 wt% Si, 6.54 wt% Al, and 24.04 wt% Fe which are higher than 10.63 wt% Si, 1.08 wt% Al, and 7.07wt% Fe determined for PF biomass. However, PF biomass contains 39.81 wt% K and 20.95 wt% Ca which are higher than 13.31 wt% K and 15.54 wt% Ca found in the OPMF biomass. These elements K, Ca, Mg, P, N, and Si are part of plant macronutrients and micronutrients that are precipitated and stored as inorganic minerals in the biomass structure (Nunes et al., 2017). The composition of the inorganic elements of the OPMF and PF biomass differs from those reported for the Karo Bambara shell and the EX-SOKOTO Bambara shell (Mohammed et al., 2016a). The alkali metals catalyze the pyrolysis of biomass and influence the distribution and composition of the bio-oil. The general characteristics of the OPMF and PF are broad within the range of those for the Eucalyptus sp. and Picea abies residues (Torri et al., 2016). Moreover, the OPMF and PF physical and chemical characteristics conformed with those biomass feedstocks used for the synthesis of high-grade bio-oils and chemicals by pyrolysis.
3.2.
Fourier transform infrared (FTIR) of OPMF and PF
Figure S1 presents the FTIR spectra of the OPMF and PF, which highlighted the various functional groups and the fingerprint of the biomass. The spectral exhibited a similar peak of varying intensities, which depicted the extent of the functional groups in the biomass. The absorption bands of the spectra indicated the functional groups that are representative of the basic structural units of the biomass. The absorbance bands at 3408 cm−1 are assigned to stretch
8
the vibrations of O-H and conduct the asymmetric and symmetric stretching of the N-H bond. The O-H and N-H stretching vibrations established the presence phenolic alcohols associated with lignin of the biomass basic structural unit and amines from the protein content of the biomass, respectively. The bands at 2920 and 2862 cm−1 correspond to C-H stretching vibrations related to aromatic structural bonds of lignin, and the band at 1379 cm−1 is attributed to the C-H bending corresponds to the bonds of cellulose and hemicellulose. The bands at 1739 and 1627 cm−1 are associated with C=O stretching that corresponds to functional groups associated with lignin and hemicellulose. Moreover, the band at 1239 cm−1 is attributed to the C-O stretching vibration of syringyl ring of lignin. The C-O, C=C and C-O-C stretching vibrations at 1036 cm−1 related to bonds associated with cellulose, hemicellulose and lignin. The spectra indicated that the biomass macro-structural units consist of mostly esters, ketones alkanes and alkyl, ethers, and aromatics groups.
3.3
Thermal pyrolysis of OPMF and PF in a slow heating reactor
3.3.1 Effect of N2 flow rate on product distribution Figure 1 shows the effect of N2 flow on the yield of bio-oils from the pyrolysis of OPMF and PF. The study was conducted at a temperature of 550 °C, a heating rate of 10 °C/min, and an N2 flow rate of 100–300 mL/min. The N2 flows create the inert condition for the pyrolysis reactions in the reactor and evacuate the pyrolysis condensable vapors from the reactor. At 100 mL/min N2 flow rate, the bio-oil from the pyrolysis of the OPMF was 47 wt%, which was lower than 49 wt% bio-oil from the pyrolysis of PF. At the low N2 flow rate (100 mL/min), the condensable vapors from the biomass decomposition accumulate in the reactor, which promotes
9
re-condensation, re-polymerization, and cracking reactions. Condensable vapors evacuated ontime from the reactor mitigated the reactions that decreases the bio-oil yield. At 200 and 300 mL/min N2 flow rate, the condensable vapors have short dwelling time in the reactor, which mitigated the vapor condensation, re-polymerization and cracking reactions. The bio-oil yields were maximum at 200 mL/min N2 flow rate, which follows the sufficient dwelling time for the decomposition of the biomass polymeric structure to small hydrocarbons and favors the increased yields of bio-oils. The N2 flow rate remains a critical factor for a proper inert condition for the pyrolysis and mitigating cracking reaction that favors the gas yield. There are similar findings on the effect of the N2 flow rate on the product distribution of the pyrolysis of S. japonica and babool seeds (Garg et al., 2016; Ly et al., 2015).
3.3.2. Effects of pyrolysis temperature on product yields of slow pyrolysis of OPMF and PF The slow pyrolysis of the OPMF and PF biomass was performed in a vertical fixed-bed reactor at pyrolysis temperatures at 400 °C, 500 °C, 550 °C, and 600 °C. The N2 flow rate of 200 mL/min was used in maintaining the required inert condition of the slow heating pyrolysis of the biomass. Figure 2 depicts the distribution and the yields of bio-oil, biochar, and gas from the slow pyrolysis of the OPMF and PF at the different pyrolysis temperatures. The biomass primary structures degrade the three primary products during the pyrolysis reactions by bond cleavage, carboxylation, and cracking reaction. At a low pyrolysis temperature of 400 °C, the pyrolysis of the OPMF and PF respectively produced 41 wt% and 43 wt% bio-oils, 40 wt% and 31 wt% biochar, and 18 wt% and 26 wt% gas. The yields of the bio-oils increased with increasing pyrolysis temperature. Therefore, it is observed that the pyrolysis of the OPMF and PF in the
10
temperature range of 500 °C – 600 °C respectively caused high yields of bio-oils ranging from 48–50 wt% and 45–47 wt%. The temperatures expedited the devolatilization of the biomass primary structures, which resulted in the highest yields of the bio-oils. Based on the type of biomass and reactor process, pyrolysis at temperatures above 600 °C would propagates the secondary cracking or reforming of the heavy molecular weight compounds of the pyrolysis vapor. The biochar was decomposed by reduction reaction to CO2 and H2, which results in an increase in gas fraction during the biomass pyrolysis.
3.4.
Characterization of OPMF-oil and PF-oil
Table 2 presents the ultimate analysis and HHVs of the OPMF-oil and PF-oil from the pyrolysis of the PF and OPMF. The OPMF-oil and PF-oil, respectively, have 67.77 wt% and 60.81 wt% C and 19.60 wt% and 28.54 wt% O, which correspond to the bio-oils from the pyrolysis of the eastern red cedar (Yang et al., 2016) and the coppice of poplar (Bartoli et al., 2016). The HHVs of the OPMF-oil and PF-oil were respectively 23 MJ/kg and 21 MJ/kg, which are higher than those of the respective biomass and less than those of the gasoline and diesel fuels. The pyrolysis deoxygenates the biomass, which resulted in bio-oils with low O/C ratio than that of the corresponding biomass. Thus, the pyrolysis alleviated the fuel properties of the bio-oils by improving the HHV of the bio-oils to above that of the corresponding biomass. The resultant O fraction in the bio-oils is relatively high and still affected the HHVs of the bio-oils to less than that of fossil fuels. The N content of the OPMF-oil and PF-oil are determined to be 1.85 wt% and 2.03 wt%, and S in the bio-oils are 0.51 wt% and 0.38 wt% respectively, which agrees with the N and S contents of bio-oil from the pyrolysis of the Ipomoea carnea (Saikia et al., 2015). Therefore, the
11
low contents of S and N inferred that the OPMF-oil and PF-oil can be suitable renewable energy feedstock with minimal emissions of SOx and NOx to the environment. The high carbon content and HHV of the bio-oils are coupled with the low values of hydrogen and oxygen fractions. Therefore, the bio-oils can serve as feedstock for renewable fuel.
3.5.
Fourier transform infrared of OPMF-oil and PF-oil Figure S2 shows the spectra of OPMF-oil and PF-oil obtained from the FTIR analysis
using the conventional KBr technique. The spectra have bands that refer to several compounds with different functionalities in the bio-oils. The bands between 3200 and 3600 cm−1 correspond to the O-H stretching associated with the phenols, alcohols, and water of the bio-oils. The band between 2800 and 3000 cm−1 correspond to C-H stretching, and the band between 1350 and 1480 cm−1 corresponds to the C-H bending associated with the CH3, CH2, and CH aliphatic bonding of heteroatomic compounds. The C-O stretching vibration with an absorption band of 1000–1300 cm−1 refers to ethers. The bands that stretch within 1210–1320 cm−1 and 1715–1800 cm−1, related to C-O and C=O bonds, refer to the esters group. The C=O bond stretching corresponds to the bands between 1650 and1800 cm−1, which refer to the carboxylic acids, aldehydes, esters, and ketones groups in the bio-oils. Moreover, the absorption bands between 690 and 900 cm−1 refer to C-H bending associated with aromatics compounds. The FTIR transmission spectra have several bands of oxygen-based functional groups, which authenticated that the bio-oils are laden by oxygenated compounds. 3.6.
GC-MS compositions of OPMF-oil and PF-oil Figure S3 presents the chromatogram of OPMF-oil and PF-oil, which consist of several
characteristic peaks at various heights aligned with retention times (min). The peaks on the
12
chromatograms referred to the wide variety of compounds in the bio-oils, which highlighted the complex mixture of the organic compounds of the bio-oils. The total chromatograms obtained by the GC-MS of bio-oils from the pyrolysis of a palm kernel shell (Chang et al., 2016) and oil palm mesocarp fiber (Khanday et al., 2016) have extensive peaks of various organic compounds similar to Figure S3. Figure 3 shows the relative abundance of the tentative compounds of the bio-oils presented as peak area ratios obtained by GC-MS. Heating at pyrolysis temperatures from 400– 600 °C affected the distribution of organic compounds and their relative abundance in the biooils. The disparities in the peak area ratio of the numerous compounds of bio-oils shown in Figure S3 indicated that the bio-oil chemical compositions are affected by pyrolysis temperature. The temperatures expedite the cracking of the side chains of the benzene derivatives and the furan derivatives to increase the relative abundance of light carbonyl and alcohols compounds. Thus, the relative abundance of the carbonyl compounds of the bio-oils increases with the increasing pyrolysis temperature. The amount of phenol increases with an increasing temperature of up to 600 °C, whereas the relative abundance of the benzene derivatives decreases with increasing temperature. The inhibition in the decomposition of phenol and the reactivity of the benzene derivatives at temperatures from 550–600 °C favored the increasing yield of the phenol. The acid peak area ratios are significantly high, with a maximum value of 550 °C. The bio-oils can be classified as acidic, which is consistent with the high acidity pH value of 3, as shown in Table 2. Table 3 and 4 presents a typical comparative distribution of organic compounds in the OPMF-oil and PF-oil bio-oils from the pyrolysis of PMF and PF at 550 °C respectively. The bio-
13
oils consist of complex mixtures of oxygenated compounds detected by the GC-MS. Such compounds are responsible for the low HHVs of the bio-oils (Table 2). Most of the compounds are products of decarbonylation, decarboxylation, cracking, and ring formation reactions that convert the primary oligomers of the biomass to oxygenated light molecules. The lignin of the biomass is devolatilized to pervade the resulting bio-oils with oxygenated aromatic compounds, such as phenols and phenolic derivatives (Chen et al., 2016; Li et al., 2017). The main phenolic compounds detected in the bio-oils include phenols, phenol, 4ethyl-2-methoxy- and phenol, 2,6-dimethoxy-4-(2-propenyl)-. The major benzene derivative compounds of the bio-oils include benzene, 1,4-dimethoxy- and benzene, 1,2,3-trimethoxy-5methyl-. Hemicellulose devolatilized into acidic compounds, such as octanoic acid, dodecanoic acid, n-hexadecanoic acid, 4-guanidinobutyric acid, and oleic acid acetic acid in the bio-oils. Cellulose and hemicellulose decomposed to glucopyranoses (anhydrosugars) and heterocyclic compounds; furan and furan derivatives; acetic acid and propionic acid; and 2-cyclopenten-1one, 2-methyl-, and 1-Hydroxy-2-butanone. The thermal pyrolysis of lignin (Liu et al., 2016; Yang et al., 2016) produced bio-oils that are rich in phenol and phenolic derivatives, consistent with the findings in this report. Thus, the alkali metals of the biomass that contact with the pyrolysis vapor catalyzed the conversion of the levoglucosan to the light organic compounds, such as acetic acid and furfural. The acid compounds are undesirable because they encourage aging and corrosivity, which affect the fuel and chemical properties of the bio-oils (Kabir and Hameed, 2016). The relative abundance of the several families of compounds of the bio-oils revealed that phenol, carbonyls, and benzene derivatives are the dominant group in the bio-oils. The relative abundance of the benzene derivatives in OPMF-oil are more than those of PF-oil, whereas 14
phenols in OPMF-oil are less than those of PF-oil. The bio-oils from the biomass have a significantly high amount of carbonyl compounds, but OPMF-oil has a higher amount of carbonyl than PF-oil (Figure 3). Moreover, acid compounds in the OPMF-oil are more than those in the PF-oil. The amount acid compounds are sufficient to indicate that the bio-oils are highly acidic, which is consistent with the pH of 3, as reported in Table 2. PF-oil has more heterocyclic compounds (furans) than OPMF-oil. A significant amount of alcohol-related compounds is in PF-oil compared with that in the OPMF-oil, whereas the PF-oil and OPMF-oil have the least anhydrous sugar content. The family and distribution of compound found in the OPMF-oil and PF-oil are consistent with those of bio-oils from the slow heating pyrolysis of bocaiuva residues (Cardoso et al., 2016) and licorice (Aysu and Durak, 2015). The aromatic compounds enhance the fuel properties of the bio-oils. Therefore, they are among the most desired components of the bio-oils. Moreover, the aromatics can improve the bio-oil proficiency as a renewable precursor for fuel and valuable chemicals. The octane number of gasoline can be increased from blending with aromatic-laden bio-oil, and several important value- added chemicals and polymers can be derived from the aromatics.
3.7.
Characterization of OPMF-char and PF-char Table 5 shows the proximate analysis of the OPMF-char and PF-char biochars obtained
from the pyrolysis of the corresponding biomass OPMF and PF at a temperature of 550 °C and an N2 flow rate of 200 mL/min. The OPMF-char and PF-char respectively have HHV of 24.84 and 24.15 MJ/kg and fixed carbon of 65.01 and 81.88 wt%. The high carbon contents of the biochars are linked to the high degree of aromaticity during the pyrolysis of the corresponding biomass, which produced the highly carbonized char. The HHVs and fixed carbon of the 15
biochars are higher than that of the corresponding biomass and consistent with those biochars from the pyrolysis of sal seed (Singh et al., 2014). Therefore, the energy densities of the biochars have improved to higher values than those of the corresponding biomass. The OPMF-char and PF-char have ash content of 27.04 wt% and 3.73 wt% and volatile content of 4.89 wt% and 9.97 wt% respectively. The values agree with those of the biochars from Pongamia glabra seed cover (Bordoloi et al., 2015). The biochars inherited some inorganic mineral compounds after the pyrolysis of the corresponding biomass. The mineral becomes an important component of the char. Therefore, the elemental compositions of the mineral contents inherited by the OPMF-char and PF-char from the corresponding biomass were estimated using EDX analysis, as shown in Table 5. The Si, Al and Fe compositions in the OPMF-char are found to be 30.18 wt%, 3.87 wt% and 19.89 wt% respectively and higher than 12.56 wt% Si, 1.08 wt% Al and 3.78 wt% Fe of the PF-char. Whereas, the PF-char have K (46.19 wt%) and Ca (15.57 wt%) higher than 21.99 wt% K and 8.83 wt% Ca found in the OPMF-char. The alkali metals caused the high yield of ash that has a direct effect on the carbon content and the fuel potential of the biochar (Ly et al., 2015). Therefore, the low ash, high HHV, and carbon content improve the biochar energy proficiency more than that of the corresponding biomass feedstocks.
3.8.
Fourier transform infrared analysis on OPMF-char and PF-char biochar Figure S4 shows the FTIR spectra of the OPMF-char and PF-char (biochar) from the
pyrolysis of OPMF and PF. The bands between 3200 and 3600 cm−1 correspond to the hydroxyl stretching attributed to the phenols and the proton vibrations of the water molecule. The intensities of the bands are low compared with those of the bio-oils and biomass, which result
16
from the low vibration of the O-H bond due to the dehydration of water and the cracking of volatile matters during the pyrolysis. The decrease in the bands attributed to the stretching vibration due to C=O, C-H, and CH3 (methoxyl group). The peaks between 1030 and 1300 cm−1 bands mostly disappeared compared with those of the biomass. The absence of most bands indicated that the biochars are primarily carbonized. The bands near 1622 and 1384 cm−1 respectively corresponds to the C=C bending and C-H bending vibrations associated with aromatics. Moreover, the volatile matter of the biomass cracked during the pyrolysis, which decreases the CH and alkyl bonds and increases the C2 and CH4 bonds of hydrocarbon gasses. The resultant aliphatic bonds transformed to aromatic bonds, which explains the bands. This result confirmed that aromatics constitute the basic unit of the biochars. 4.
Conclusions Pyrolysis devolatilized OPMF and PF are devolatilized to primarily biochar and bio-oils
with HHVs higher than those of the corresponding biomass. The pyrolysis of the OPMF and PF respectively produces the highest yield of bio-oils of 50 wt% and 47 wt% at 550 °C and 600 °C. The low O/C ratio favored the HHVs of the bio-oils to higher than those of the corresponding biomass. The FTIR spectra and peak area ratios reveled that pyrolysis temperatures influenced the bio-oils compositions. The bio-oils obtained at different pyrolysis temperatures contained oxygenated carbonyls and aromatic compounds suitable for processing high-grade chemicals and fuel. Acknowledgements The authors acknowledge the research grants provided by the Universiti Sains Malaysia, under Research University (RU) grant (Project No: 1001/PJKIMIA/814227) that resulted in this article.
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Figure captions Fig. 1.
Effect of N2 flow rate on the distribution of products from the pyrolysis of (a) OPMF and (b) PF (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 100 − 300 mL/min).
Fig. 2.
Product distributions from the pyrolysis of (a) OPMF and (b) PF (conditions: temperatures of 400 °C to 600 °C, reaction time of 15 min, and N2 flow rate of 200 mL/min).
Fig. 3.
Relative abundance and categories of the tentative compounds of (a) OPMF-oil and (b) PF-oil (conditions: temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min).
23
60 OPMF-oil
Bio-oil
Bio-char
Gas
Products yields (wt%)
50
40
30
20
10
0 100
200 N2 flow rate (mL/min)
(a)
24
300 Fig.1
60 Bio-oil
PF-oil
Bio-char
Gas
Products yields (wt%)
50 40 30 20 10 0 100
200 N2 flow rate (mL/min)
Fig.1 (b)
25
300
60
OPMF
Product yields (wt%)
50 40
Biochar
30 20 10 0 400
450
500 Temperature (oC)
550
600
Fig. 2 (a)
60 PF Product yields (wt%)
50 40 30 Gas
20 10 0 400
450
500 Temperature (oC)
Fig. 2 (b).
26
550
600
40 Peak area (%) @ 400 °C
Area peaks (%)
35
OPMF-oil
Peak area (%) @ 450 °C
30
Peak area (%) @ 550 °C
25
Peak area (%) @ 600 °C
20 15 10 5 0
Bio-oils compounds
Fig. 3 (a).
27
50 45 40
Peaks area (%)
35
Peak area (%)@ 400 °C
PF-oil
Peak area (%) @ 450 °C Peak area (%) @ 550 °C Peak area (%) @ 600 °C
30 25 20 15 10 5 0
Bio-oils compounds
Fig. 3 (b).
28
List of Tables Table 1.
Characterization of OPMF and PF biomass.
Property
Biomass type PF
OPMF Proximate analysis (wt%) Moisture
4.75
4.83
Ash
1.40
5.87
Volatile matter
66.84
70.33
Fixed carbon
27.01
18.97
Heating value (MJkg-1)
17.00
16.00
Carbon ( C )
45.38
41.00
Hydrogen (H)
10.59
6.74
Nitrogen (N)
1.32
0.67
Sulphur (S)
0.67
0.35
Oxygen (O)
42.04
51.24
H/C
0.23
0.16
O/C
0.93
1.25
Ultimate analysis (wt %)
Composition analysis (wt %) Cellulose
40.12
45.22
Hemicellulose
20.12
19.22
Lignin
30.33
31.24
Extractives
9.43
4.32
6.54
1.08
Si
19.17
10.63
K
13.31
39.81
Ash analysis (%) (EDX ) Al
29
Ca Mg Fe P S
15.54
20.95
11.19
8.01
24.04
7.07
7.48
9.20
2.73
3.25
30
Table 2.
Characterization of OPM-oil and PF-oil (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min). Bio-oil type
Property OPMF-oil PF-oil Ultimate analysis (wt %) Carbon ( C )
67.77
60.81
Hydrogen (H)
10.27
8.24
Nitrogen (N)
1.85
2.03
Sulphur (S)
0.51
0.38
Oxygen (O)
19.60
28.54
H/C
0.15
0.14
O/C
0.29
0.47
Heating value (MJ/kg)
23.00
21.00
pH
3
3
Density (g/mL)
1.05
1.07
Viscousity (at 30 oC) (cp)
2.55
2.41
31
Table 3.
GC-MS compositions of OPM-oil (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min).
Peak No.
RT (min)
Family/Compounds
%Peak Area
15 32 37 39 41 42
20.736 36.888 43.331 50.254 55.276 55.686
Acids Octanoic Acid Dodecanoic acid Tetradecanoic acid n-Hexadecanoic acid Oleic Acid Octadecanoic acid Total
1.799 2.56 0.977 6.405 4.586 1.531 17.858
22
26.969
Furans 2-Acetyl-2-methyltetrahydrofuran Total
0.334 0.334
9 13 14 16 21 26 30 31 33 34
11.763 18.11 19.686 21.802 26.229 31.091 34.557 35.813 37.714 39.94
Phenols Phenol Phenol, 4-methoxy-3-methylPhenol, 2-ethylPhenol, 4-ethyl-2-methoxyPhenol, 2,6-dimethoxy5-Methyl-2-nitrophenol 4-(Methoxycarbonyl)phenol Phenol, 2,6-dimethoxy-4-(2-propenyl)Phenol, 2,6-dimethoxy-4-(2-propenyl)Phenol, 2,6-dimethoxy-4-(2-propenyl)Total
4.433 0.824 2.002 0.534 9.272 0.325 2.154 0.637 0.788 2.08 23.049
18 19 20 23 24 25 27 28 36 29
23.823 24.513 24.908 28.45 29.22 29.905 31.656 32.757 42.911 33.957
Benzene Derivatives 1,2-Benzenediol, 3-methoxy1,2-Benzenediol 1,2-Benzenediol 1,2-Benzenediol, 4-methyl Vanillin 1,2,3-Trimethoxybenzene 4-Ethyl-1,2-benzenediol Benzene, 1,2,3-trimethoxy-5-methyl2-Pentanone, 1-(2,4,6-trihydroxyphenyl) 2-Propanone, 1-(4-hydroxy-332
2.717 1.756 4.961 0.859 0.461 3.576 0.295 2.276 2.595 1.785
17 10 11 12 47
35
methoxyphenyl)22.63 Decanediamide, N,N'-di-benzoyloxyTotal Ketones 12.368 2-Cyclopenten-1-one, 2-hydroxy-3-methyl13.589 2-Cyclopenten-1-one, 3,5,5-trimethyl 15.834 7-Oxabicyclo[4.1.0]heptan-2-one, 6-methyl3-Penten-2-one, 4-(2,2,6-trimethyl-759.818 oxabicyclo[4.1.0]hept-1-yl)-, (E)Total
40.53
38
46.057
43
56.141
44
56.592
40
51.589
45
57.297
46
58.032
8
8.391
Aldehydes Octanal, 7-hydroxy-3,7-dimethylTotal Esters Pentadecanoic acid, 14-methyl-, methyl ester Icosanoic acid 2-(acetyloxy)-1[(acetyloxy)methyl]ethyl ester Hexadecanoic acid, 1-(hydroxymethyl)-1,2ethanediyl ester 9-Octadecenoic acid (Z)-, methyl ester Hexadecanoic acid, 2,3-bis(acetyloxy)propyl ester 2,4-Dimethylnonanedioic acid dimethyl ester Total Glucopyranoses D-Glucose, 2,3,4-tri-O-methylTotal
33
2.717 23.998 1.085 0.686 2.711 5.049 9.531
1.084 1.084
0.355 1.249 0.914 0.378 2.622 0.632 6.15
0.244 0.244
Table 4.
GC-MS compositions of PF-oil (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min).
Peak RT No. (min)
Family/Compounds
%Peak Area
Acids 10 13
12.073 Pyrazine-2-carboxylic acid, 3-hydroxy12.318 Urocanic acid
0.348 0.968
21
20.426 1H-Imidazole-4-carboxylic acid, 2-ethyl-
1.092
Total 6 15 40
2.408
Alcohols 7.296 3-Pentyn-1-ol 13.404 2,5-Cyclohexadiene-1,4-diol 41.95 7-Octene-2,6-diol, 2,6-dimethylTotal
8 9 28
8.526 12.028 27.589
14 16 20 23 31 36 27 37 39 42
12.568 14.009 18.661 22.257 30.521 36.288 27.214 38.134 40.38 43.756
Furans Furan, 2,4-dimethylVinylfuran Furan Total Phenols Phenol Phenol, 2-methoxyPhenol, 2-methoxy-4-methylPhenol, 4-ethyl-2-methoxyPhenol, 4-methoxy-3-(methoxymethyl)Phenol, 2,6-dimethoxy-4-(2-propenyl)Phenol, 2,6-dimethoxyPhenol, 2,6-dimethoxy-4-(2-propenyl)Phenol, 2,6-dimethoxy-4-(2-propenyl)Desaspidinol Total Benzene Derivatives 34
0.314 7.841 1.266 9.421
0.28 1.953 0.672 2.905 2.74 1.965 3.792 0.482 3.376 2.29 15.03 0.358 2.588 1.487 34.108
24 25 26 30 33 35 41 43
11 17 18 29 34 45
5
44 46 49
23.278 2',6'-Dihydroxyacetophenone 25.168 1,4-Benzenediol, 2-methoxy25.874 1,2-Benzenediol 29.43 1,2-Benzenediol, 3-methyl33.312 5-tert-Butylpyrogallol 35.713 2H-1-Benzopyran-2-one, 3,4-dihydro-6-hydroxy42.571 Ethanone, 1-(4-hydroxy-3,5-dimethoxyphenyl)45.327 Ethanone, 1-(4-hydroxy-3,5-dimethoxyphenyl)Total Ketones 12.118 Ethanone, 1-(1H-pyrrol-2-yl)14.749 3-Hepten-2-one, 4-methyl16.65 2-Cyclopenten-1-one, 3-ethyl-2-hydroxy28.295 2(3H)-Furanone, 5-heptyldihydro34.722 2-Propanone, 1-(4-hydroxy-3-methoxyphenyl)50.594 Neocurdione Total Glucopyranoses 4.325 Levoglucosenone Total
49.654 54.671 60.303
Esters Isopropyl Palmitate 10-Octadecynoic acid, methyl ester Octanedioic acid, 4-isopropyl-, dimethyl ester Total
35
0.907 1.836 1.582 0.498 2.507 1.414 0.643 0.218 9.605 0.594 0.541 3.856 1.118 0.739 0.21 7.058 0.362 0.362
0.809 0.414 2.196 3.419
Table 5.
Characterization of OPM-char and PF-char (temperature = 550 °C, heating rate = 10 °C/min, and N2 flow rate = 200 mL/min). Type of biochar
Property OPMF-char
PF-char
Moisture
3.06
4.42
Ash
27.04
3.73
Volatile matter
4.89
9.97
Fixed carbon
65.01
81.88
Heating value (MJ/kg)
24.84
24.15
Proximate analysis (wt%)
Compositions of inorganic elements (%) (EDX ) Al
3.87
1.08
Si
30.18
12.56
K
21.99
46.19
Ca
8.83
15.57
Mg
7.69
6.46
Fe
19.89
3.78
P
4.80
12.28
S
2.75
2.08
36
Highlights •
Pyrolysis devolatilized OPMF and PF to 48 and 47 wt% maximum yield of bio-oil respectively.
•
Maximum yield of bio-oils occurred at 550 oC for OPMF and 600 oC for PF.
•
Compounds of phenols and benzene derivatives pervaded the OPMF-oil and PF-oil.
•
OPMF-oil and PF-oil contained maximum aromatics yield of 43% and 50% peak area respectively.
37