Systematic production and characterization of pyrolysis-oil from date tree wastes for bio-fuel applications

Biomass and Bioenergy 135 (2020) 105523

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Research paper

Systematic production and characterization of pyrolysis-oil from date tree wastes for bio-fuel applications G. Bharath a, Abdul Hai a, K. Rambabu a, Fawzi Banat a, *, Raja Jayaraman b, Hanifa Taher a, Juan-Rodrigo Bastidas-Oyanedel a, c, Muhammad Tahir Ashraf a, c, Jens Ejbye Schmidt c a b c

Department of Chemical Engineering, Khalifa University, 127788, Abu Dhabi, United Arab Emirates Department of Industrial & Systems Engineering, Khalifa University, 127788, Abu Dhabi, United Arab Emirates Department of Chemical Engineering, Biotechnology and Environmental Technology, University of Southern Denmark, 5230, Odense, Denmark

A R T I C L E I N F O

A B S T R A C T

Keywords: Renewable energy Biomass Pyrolysis-oil Biofuels Date palm

The prevailing trends in global energy consumption and the rapid depletion of fossil fuel present an urgent need for alternative fuels, particularly from renewable sources of biomass. In this study, date palm tree mixture wastes (DTM) and date seed (DS) biomass were used as starting materials in the production of bio-oil by pyrolysis. The yields of the pyrolysis oils from DTM and DS were optimized by tuning the experimental parameters. The DS provided a maximum yield of 68 wt% obtained from 30 min of pyrolysis with a biomass loading of 200 g, fluidizing gas flow rate of 10 mL min 1, and at a temperature of 500 � C. In addition, we evaluated the impact of the aging process of the obtained pyrolysis oils. The produced pyrolysis oils (freshly made) were aged for 15 and 30 days at room temperature under closed conditions. All the feedstock biomass were subjected to proximate and ultimate analysis. The TG-DTA results indicated that both biomasses were richer in cellulose and hemicellulose contents than in lignin content. The FT-IR and GC/MS analyses of the fresh and aged oil samples demonstrated the outstanding characteristics of the DS derived bio-oil for use as a bio-fuel. The variation in the chemical composition of the fresh and aged pyrolysis oils are completely described and presented elaborately. This study demonstrates the significance of and a new functionality for the date palm industry to process date palm wastes, particularly the DS as a rich biomass source for the production of bio-fuel.

1. Introduction Biomass is one of the high-potential renewable energy sources aug­ menting fossil fuel production [1,2]. The conversion of biomass into bio-oil provides an environmentally friendly approach to obtaining bio-oils with zero carbon emission [2,3]. Recently, several conversion processes including aqueous phase reforming, fermentation, gasifica­ tion, and thermochemical conversion methods have been made avail­ able for the conversion of biomass into bio-oil [4,5]. Among these, the thermochemical conversion of biomass is considered to be the most viable and emerging technology for the production of biofuels, due to its simplicity, cost-effectiveness, and feedstock flexibility [6]. Thermo­ chemical conversion processes are broadly classified into direct com­ bustion, gasification, and pyrolysis [6,7]. Particularly, pyrolysis is considered to be the most efficient route, by which bio-waste can be thermally degraded at 400–500 � C in the presence of inert gases to produce bio-char (solid), bio-oil (liquid), and gaseous fuel (CO, CH4, and

H2) [7]. The bio-oil produced by the thermochemical decomposition of biomass comprises lignin, hemicellulose, and cellulose. Furthermore, the quantity and quality of the bio-oil depend mainly on the lignocel­ lulosic compositional proportions of lignin, hemicellulose, and cellulose in the biomass [8–10]. Generally, the decomposition of hemicellulosic biomass at 200–300 � C produces mainly acetic acid, acetone, furfural, CO, CO2, and CH4 [11]. The decomposition of cellulosic materials, which usually occurs at 250–400 � C, produces the major macromole­ cules of levoglucosan, glycolaldehyde, hydroxyl acetone, furan, and low-degree oligomers [12]. Meanwhile, volatile matters, char, guaia­ cylglycerol-β-aryl ether, H2, CO, etc. are produced by lignin decompo­ sition at a temperature in the wide range of 200–600 � C [13]. Physico-chemically, the obtained bio-oils are dark brown in color with a smoky odor and an acidic pH of 2–3. These highly viscous oils have a typical composition of 20–30% water, 5–10% hydrogen, 45–47% oxy­ gen, and 45–48% carbon with trace amounts of sulfur and nitrogen [1,4, 7,11]. A low oxygen to carbon (O/C) ratio in the bio-oil ensures that a

* Corresponding author. E-mail address: [email protected] (F. Banat). https://doi.org/10.1016/j.biombioe.2020.105523 Received 6 August 2019; Received in revised form 7 January 2020; Accepted 21 February 2020 Available online 29 February 2020 0961-9534/© 2020 Elsevier Ltd. All rights reserved.

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Fig. 1. Flow diagram of the simplified pyrolysis process.

higher heating value (HHV) and highly stable products are obtained, whereas a high hydrogen to carbon (H/C) ratio ensures the combusti­ bility of bio-oil [14]. Therefore, the quality and composition of bio-oil are quite important for its commercialization and are mainly depen­ dent on the characteristics of the biomass. Conversely, the use of raw bio-oil and its conversion into bio-fuel are limited due to several shortcomings. Mostly, the produced bio-oil is chemically and thermally unstable during the storage stage as it is prone to undergo condensation, polymerization, and oxidation reactions [14]. This increases the viscosity of the bio-oil and results in phase separation upon aging. Typically, several by-products are formed during the aging of bio-oil, which alter the pH, water content, viscosity, molecular weight, degree of phase separation, and coke formation or crystalliza­ tion nature of the bio-oil. Therefore, the aging of bio-oil makes its storage, transport, handling, and conversion to bio-fuel quite difficult. Therefore, the selectivity of biomass with proper proportions of ligno­ cellulosic compounds, and the aging processes of bio-oil are the essential concerns of the fuel industry [5,14]. Recently, researchers are mainly focused on the production of high yield bio-oil from a variety of agri­ cultural biomasses. Additionally, the operating parameters, including the particle size of the biomass, heating rate, pyrolysis temperature, biomass loading rate, inert gas flow rates, and residence time also decide the quality and quantity of the obtained bio-oil. Tsai et al. [15] and Lazzari et al. [16] reported the maximum bio-oil yields of 40% and 38.8% from rice husk and mango seeds at temperatures of 800 and 650 � C, respectively. Isahak et al. [17] identified that at a very high

temperature, the bio-oil yield decreases due to the cracking of volatile compounds to afford gaseous products. The yield of bio-oil can also be varied by altering the heating rate of the biomass. Razuan et al. [18] investigated the effect of the heating rate for different agricultural wastes and concluded that the heating rates should be adjusted based on the nature of the biomass. Several reviews [13,36–39] have been pub­ lished presenting a comparative analysis of the production of bio-oil from different agricultural wastes under different operating conditions through pyrolysis [7,19–21]. Among the various agricultural biomass wastes, date palm trees are extensively cultivated globally, particularly in the Gulf region of West Asia. Each year, date palm trees are trimmed to remove dead, old, or broken leaves; fronds foliar; and thorns. The United Arab Emirates (UAE) produces 500,000 Metric tonnes of palm waste annually, including date seeds (DSs) and date tree parts, such as leaves, straws, trunks, and branches, which are landfilled. Recently, few researchers reported the production of bio-oil from these wastes. A maximum bio-oil yield of 50 wt% was obtained from DSs with a viscosity of 6.63 cSt, density of 1042.4 kg m 3, flashpoint of 126 � C, and HHV of 22.39 MJ kg 1 [22]. The obtained DS bio-oil could be a potential source of alternative fuel which is not the case with other available bio-oils from various agricultural wastes [23–25]. However, the production scalability and aging behavior of such a bio-oil are critical parameters to be investigated for the utilization of date palm waste-derived bio-oil as an alternative fuel. The present study highlights the production, characterization, and aging behavior of two different pyrolytic oils obtained from date tree mixture (DTM) wastes and DSs for application as biofuels. A batch py­ rolysis technique was adopted for the production of bio-oil, and the optimization of the oil yield production was achieved by adjusting the process parameters, namely the temperature, time, feedstock loading, and carrier gas flow rate. The physico-chemical properties of the bio-oils were measured based on the aging of the samples for 15 and 30 days at room temperature using analytical techniques, including FTIR, GC/MS, TOC, Karl Fischer titration, and viscometry, along with the basic bio-oil characteristic techniques. The obtained pyrolytic oils from different date palm sources were found to be significantly different in terms of their chemical compositions. Freshly prepared DTM and DS bio-oil samples were denoted as DTM-F and DS-F. The 15 and 30-day aged samples were denoted as DTM-15, DTM-30, DS-15, and DS-30, accordingly. Addi­ tionally, the obtained bio-oil samples were thoroughly investigated using advanced analytical techniques, such as FTIR, GC/MS, TOC, Karl Fischer titration, and viscometry, along with the basic bio-oil charac­ teristic techniques. Moreover, the biomass degradation mechanism and detailed comparative analysis for different components of the produced bio-oil are presented. Additionally, the produced bio-oil could further be enriched into bio-fuel via hydrodeoxygenation, and the biochar could be used as a building block of carbon materials in energy and environ­ mental applications [26–30]. Furthermore, non-condensable bio-gases such as hydrogen, CO, CO2, CH4, and C2H6 would be useful for energy device applications. The obtained bio-wastes were completely converted into value-added products. Fig. 1 illustrates the overall flow diagram of

Table 1 Characteristic analysis of the DTM and DS biomasses. S. No

Biomass feedstock

1

2

3

Date tree mixture waste (DTM)

Date seed (DS)

Proximate analysis (wt. %) Moisture Content Volatile Matter Ash Content Fixed carbon HHV (MJ kg 1)

11.63 72.51 7.543 8.32 12.66

6.02 81.13 5.29 7.55 20.27

Elemental analysis (wt. %) C H N S O O/C H/C

51.88 6.56 – – 41.56 0.80 0.13

70.92 10.45 – – 18.63 0.26 0.15

Component analysis (wt. %) Cellulose Hemicellulose Lignin

30 35 10–20

65 15 5–10

2

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Fig. 2. Schematic diagram of the lab-scale pyrolysis reactor system.

the simplified pyrolysis process.

The obtained DTM and DS biomasses were successfully converted into pyrolytic bio-oil, non-condensable gas, and bio-char using the py­ rolysis reactor. Through this process, a high quantity of high-quality biooils was obtained by altering the experimental parameters. As in a typical pyrolysis, a specific amount of ground biomass was loaded into the silica tube. Subsequently, the reactor was heated up to the desired temperature for a fixed time period. Thereafter, the resulting vapors of condensable and non-condensable gases passed through a condenser. The condensable gases were successfully converted into bio-oil and collected in the water cooling condensers. The yields of pyrolytic-oil and bio-char were determined gravimetrically, and the yield of the noncondensable gases was determined by the difference between the biooil and bio-char. Furthermore, the non-condensable gases were vented to a fume hood. Moreover, different experimental parameters such as the pyrolysis time (10–60 min), temperature (300–600 � C), fluidizing gas flow rate (5–30 mL min 1), and biomass loading (50–350 g) were optimized for the production of quantitative pyrolysis oils. The experi­ ments were carried out under optimized conditions, and the averaged data are presented. The pyrolysis oil and bio-char yields were calculated using Eqs. (1) and (2), respectively. The product yield of the noncondensable gases was estimated using Eq. (3).

2. Materials and methods 2.1. Raw materials The biomasses of the DTM waste (excluding seeds) and DS were used as raw materials in the production of different bio-oils by the pyrolysis method. The feedstock materials were received from local date palm farms in Abu Dhabi, UAE. The DTM waste was obtained from a mixture of different parts of the palm tree, including the fruit punch, leaf, leaf base, trunk, and the sheath fiber from the leaf base. Meanwhile, a large amount of DS was collected from local date fruit industries in Abu Dhabi, UAE. All the samples were washed several times to remove dust, foreign materials, dirt, and fibers, after which they were crushed and sieved to sizes in the range of 50–100 μm. The physical properties of the waste materials including the HHV, proximate and ultimate analysis-based compositions are listed in Table 1. The HHVs of the DTM and DS sam­ ples were determined through oxygen combustion bomb calorimetry (DIN 51900, Parr Instrument Company). The proximate analysis of the feedstock materials was performed in accordance with the ASTM stan­ dards. The ash yields were estimated at 550 � C for 4 h in a muffle furnace. An elemental analyzer (Model EA 1108 with ASTM D3176 standard procedures) was used to determine the elemental composi­ tions (carbon, hydrogen, nitrogen, oxygen, and sulfur) of the feedstock materials. Furthermore, the lignocellulosic composition was assessed through thermogravimetric analysis (TGA) using an SDT Q600 ther­ mogravimetric analyzer at a heating rate of 20 � C min 1 under N2 atmosphere.

mbio oil � 100 mbiomass

Ybio

oil ð%Þ ¼

Ybio

char ð%Þ ¼

Ygas ð%Þ ¼ 100

(1)

mbio char � 100 mbiomass ½Ybio

oil

þ Ybio

(2) char �

(3)

where Ybio oil is the yield of the produced bio-oil from each pyrolysis run; Ybio char is the yield of the bio-char produced; Ygas is the yield of noncondensable gas; mbio oil is the mass of bio-oil produced; mbio char is the mass of biochar, and mbiomass is the amount of biomass subjected to thermochemical conversion.

2.2. Pyrolysis oil production The pyrolysis process was performed in a bench-scale pyrolysis unit, consisting of a fluidized bed reactor, feeding system, gas mass flow controller, quenching system with cooling condensers, and a char sep­ aration system, as shown in Fig. 2. A silica tube was used for the fluid­ ized bed reactor material with an internal diameter and length of approximately 12 cm and 90 cm, respectively. Nitrogen was used as the fluidizing gas, and the flow rate was controlled using a mass flow controller (Porter 200 Series MFC). A quenching system equipped with a cooling condenser was used to condense the pyrolyzed gas for lique­ faction. The pyrolysis time, temperature, fluidizing gas flow, and loading of different biomass feedstocks were selected as the experi­ mental parameters and were optimized for the optimum production of pyrolytic bio-oil.

2.3. Characterization of the pyrolysis oils from the DTM and DS wastes The pyrolysis oils, obtained in a maximum yield, under the best experimental conditions of time, temperature, fluidizing gas flow, and biomass loading, were subjected to aging along with various charac­ terizations. The obtained samples were stored, and the produced oils (freshly made) were aged at room temperature over two different pe­ riods: 15 and 30 days. The characterizations carried out were Fourier transform infrared spectroscopy (FTIR), Karl Fischer titration (H2O), pyrolysis-gas chromatography–mass spectrometry (GC/MS), viscom­ etry, and elemental analysis using an elemental analyzer (EA1110, CE 3

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Fig. 3. TG-DTA studies of (a) DTM and (b) DS feedstock samples.

instruments). The HHVs of the obtained bio-oils were determined using an oxygen combustion bomb calorimeter (DIN 51900, Parr Instrument Company). The GC/MS analysis for various oil samples was performed to gain a better understanding of the aging process and the associated compositional changes in the pyrolysis oil samples obtained from the date palm biomasses. The analysis was performed using an Agilent GC/ MS system (Agilent 7890B GC & 5977A MSD) equipped with a DB-1 ms ultra-inert column (122-0132UI) with a length of 30 m, internal diam­ eter of 0.25 mm, and a film thickness of 0.25 μm. Helium was used as the carrier gas at a flow rate of 1.2 mL min 1. The split ratio was set as 1:200, and the oven temperature was increased from 100 to 250 � C at a ramping rate of 10 � C min 1. The system was interfaced with an Agilent OpenLAB CDS EZChrome Software, and the various components for the obtained peaks were identified using the NIST 14 mass spectral library.

respectively. In this thermal pyrolysis process, the hemicellulose was readily decomposed compared to the cases of lignin and cellulose. Meanwhile, a broad temperature range of 200–500 � C was observed for the decomposition of the lignocellulosic components in the DS sample. Therefore, it is difficult to differentiate between hemicellulose and cellulose decomposition zones. However, the lignocellulosic composition of a biomass could be inferred indirectly by analyzing the products from the thermal decomposition of the biomass [24–26]. Specifically, hemicellulose is a complex polysaccharide ((C5H8O4)m) that widely exists in woody biomass. The pyrolysis of hemicellulose would produce main products, including water, 2-furfuraldehyde, anhydroxylopyranose, dianhydroxylopyranose, propionic acids, 2-methylfuran, hydroxyl-1-butanone, hydroxyl-1-propanone, methanol, formic, and acetic acid [31]. Similarly, the pyrolysis of cellulose would produce some main compounds, including levoglucosan, glyco­ laldehyde, hydroxyl acetone, furan, and low-degree oligomers. Levo­ glucosan can further decompose to afford anhydro-monosaccharides, pyrans, and light oxygenates [32,33]. The low-degree oligomers can be further decomposed into light oxygenates, furan, char, and permanent gases. Furthermore, lignin is mainly present in woody species. During the pyrolysis process, lignin decomposes into the major macromolecules of guaiacylglycerol-β-aryl ether (40–60%), diarylpropane (5–10%), diphenyl ether (5%), phenyl coumarone (10%), pinoresinol (5% or less), and biphenyl (5–10%). These intermediate macromolecules are con­ verted into several byproducts, including guaiacol, trimethox­ yacetophenone (TMAP), dimethoxyphenol, dimethoxyacetophenone (DMAP), and 4-alkylguaiacol at different pyrolysis temperatures in the range of 200–500 � C [34]. Notably, the proportions of the lignocellulosic compounds play a significant role in the composition of the pyrolysis oil. From the TGA results, it was observed that the DTM samples mainly contained 30 wt% hemicellulose, 35 wt% cellulose, and approximately 5–10 wt% lignin. Conversely, the DS biomass indicated less moisture and the loss of some volatile compounds at 50–170 � C compared to the case with the DTM biomass. A sharp DTA curve observed at 280–350 � C confirmed that the DS biomass contained around 65 wt% cellulose, 20 wt% hemicellulose, and ~15 wt% lignin. A slow and steady weight loss was observed above 400 � C and 600 � C for the DTM and DS samples, respectively, which can be related to the decomposition of lignin. Furthermore, the bio-char yield was estimated to be 35 wt% for DTM and 5–10 wt% for DS based on the TG-DTA curves given in Fig. 3(a) and (b). This study proves that the DS biomass may afford a higher pyrolysis oil yield with different chemical compounds compared to the DTM biomass. Although the feedstock analysis indicated that the DTM biomass may produce a higher bio-char yield during the pyrolytic pro­ cess, the actual yields of pyrolysis oil, bio-char, and non-condensable

3. Results and discussion 3.1. Feedstock material analysis The proximate and ultimate analysis results of the feedstock bio­ masses of both DTM and DS are presented in Table 1. The DS biomass had a considerably lower moisture content (6.02 wt%), higher content of volatile compounds (81.3 wt%), and a HHV of 20.27 MJ kg 1 compared to those of the DTM biomass. The elemental analysis presented O/C ratios of 0.80 and 0.26 for DTM and DS, respectively. Meanwhile, the H/ C ratios of DTM and DS were estimated as 0.13 and 0.15 wt%, respec­ tively. Generally, a low O/C ratio results in the elimination of water and acidic components, whereas a high H/C ratio ensures the combustibility of biomass [12]. In addition, the TG-DTA was used to understand the pyrolysis behaviors and lignocellulosic compositions of the obtained raw biomasses of DTM and DS. Fig. 3 shows the TGA curves for both of the samples tested at a heating rate of 20 � C min 1 under a nitrogen at­ mosphere. The TG-DTA curves of both samples exhibit three decompo­ sition regions: 50–170 � C, 180–550 � C, and 450–900 � C, which correspond to the moisture and loss of volatile materials, active pyrolysis-oil production, and the bio-char and gases production, respectively. Specifically, the DTM sample lost a higher percentage of moisture and volatile compounds than the DS sample at a temperature range of 50–170 � C. A sudden weight loss was observed between 180 and 550 � C due to the decomposition of the lignocellulosic components in the DTM biomass. The DTM samples showed the explicit decompo­ sition of the lignocellulosic compounds, which were mainly composed of hemicellulose, cellulose, and lignin [23]. The DTA curves of the DTM biomass exhibited differential weight losses at 220–280 � C and 300–380 � C, corresponding to the decompositions of hemicellulose and cellulose, 4

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Fig. 4. Time-dependent non-condensable gases (CO, CH4, N2, CO2, and H2) versus pyrolysis temperature (30–500 � C) under N2 atmosphere. A Teledyne continuous emission monitoring system (CEMS) equipped with IR and TCD used for continuous monitoring of gase products.

Fig. 5. Effect of the pyrolysis experimental parameters: (a) residence time, (b) temperature, (c) biomass loading, and (d) nitrogen gas flowrate, on the bio-oil yields from the DTM and DS samples. 5

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Table 2 Analysis of the pyrolysis-oil samples derived from the DTM and DS feedstock. Test Type

Biofuel Date Tree Mixture

Density (kg⋅m 3) Viscosity @ 25 � C (cP) pH Moisture Content (ppm) Total Organic Carbon (ppm) HHV (MJ⋅kg 1)

Date Seeds

Fresh

After 15 Days

After 30 Days

Fresh

After 15 Days

After 30 Days

1011.24 1.3676 2.0–4.0 290,967 41,565 24.35

1018.35 1.3725 2.0–3.0 278,145 41,353 23.08

1019.11 1.4158 2.0–3.0 275,368 41,104 21.46

1020.15 1.4179 2.0–4.0 140,297 42,570 29.06

1028.72 1.4284 2.0–3.0 137,683 42,147 28.22

1031.37 1.4301 2.0–3.0 135,429 42,021 26.95

gases mainly depend on the experimental parameters of the pyrolytic process.

optimum temperature of 500 � C is used for the thermochemical con­ version of biomass to pyrolysis oil. A similar temperature effect was found for the pyrolysis of pomegranate seeds under a nitrogen atmo­ sphere [35]. Furthermore, the biomass loading and flow rate of the fluidizing gas significantly affected the bio-oil production. Fig. 5(c) shows the yield of pyrolysis oil at a temperature of 500 � C, nitrogen flow rate of 10 mL min 1, and an operating time of 30 min with different biomass loadings. It is observed that at 200 g of feedstock loading, the highest yield of pyrolysis oil was obtained for both the DTM and DS samples; 68% of bio-oil was produced from the DS sample. A feedstock loading of >200 g resulted in decreased oil yield due to the agglomer­ ation and charring effect. Fig. 5(d) shows the variation of oil yields with respect to the changes in the flow rate of nitrogen gas from 5 to 30 mL min 1 at 500 � C for 30 min, with 50 g of the sample. As can be clearly seen, increasing the flow rate from 5 to 10 mL min 1 increased the production yield from 14 to 29.8 wt% for the DTM sample and from 40 to 66 wt% for the DS sample. This significant increase in the yield was expected and is mainly attributed to the effect of the gas flow rate in removing the volatiles from the pyrolysis environment. This minimizes the occurrence of side-reactions, such as cracking and polymerization. The experimental results confirmed that the maximum pyrolysis-oil yield was obtained under the optimum condition with the following experimental parameters: operating temperature of 500 � C, operating time of 30 min, feedstock biomass loading of 200 g, and flow rate of the fluidizing gas being 10 mL min 1. Importantly, the same preparatory condition was applied to the preparation of pyrolysis oils from the DTM and DS biomasses for further analysis.

3.2. Optimization of the operational parameters The pyrolysis-oil yield (wt.%) was maximized by tuning the experi­ mental parameters, including time, temperature, feedstock material loading, and the flow rate of the fluidizing gas. The highest pyrolysis yields of bio-oil (66.5 wt%), bio-char (27.3 wt%), and non-condensable gases (6.2 wt%) were obtained from the DS sample, compared to only 30.1% from the DTM sample, under identical experimental conditions. Fig. 4 shows the time-dependent observations for the production of noncondensable gases (mol %) including CO, CH4, N2, CO2, and H2 versus pyrolysis temperature under the nitrogen atmosphere. Specifically, the DS sample produced a significant amount of CO2 and H2 during the pyrolysis. This is mainly because the DS sample contains a larger volatile matter fraction and lower moisture content, which is also indicated by the larger HHV determined for the DS samples. The effect of increasing the pyrolysis time from 10 to 60 min on the bio-oil yield is illustrated in Fig. 5(a) for both the DTM and DS samples at 500 � C, 50 g of the samples, and a nitrogen gas flow rate of 10 mL min 1. The results demonstrate that the yield of pyrolysis oil increased with the time up to 30 min, for both DTM and DS; further increase resulted in a steady-state where no more bio-oil was produced. Fig. 5(b) shows the effect of varying the temperature on the yield of pyrolysis oil after 30 min of pyrolysis of 50 g of the samples with a ni­ trogen gas flow rate of 10 mL min 1. When the temperature was increased from 300 to 600 � C, the yield of pyrolysis oil increased initially up to 500 � C and then slightly decreased up to 600 � C, for both the DTM and DS samples. This is mainly due to the decomposition of some oil compound vapors into non-condensable gases. It appears that the

3.3. Physico-chemical properties of the pyrolysis oil Due to the instability of bio-oils during their storage and

Fig. 6. FTIR spectra of (a) DTM and (b) DS pyrolysis oils. 6

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transportation. Evaluating the changes in the bio-oil properties upon storage is quite important to understand their instability. Therefore, fresh and aged bio-oils produced from 50-g samples at 500 � C, a 10-mL min 1 nitrogen flow rate, and 30-min residence time were subjected to various physio-chemical property analyses, including density, viscosity, HHV, moisture content, and total organic carbon (TOC). The test results for both the DTM and DS samples are illustrated in Table 2. As can be seen from the results, the aging process considerably affected the bio-oil properties. The density and viscosity of the bio-oils slightly increased with aging for both DTM and DS, due to the forma­ tion of new by-products by oil oxidation. However, the moisture TOC contents decreased with the aging, which is attributed to the formation of stable anti-oxidant products that inhibited the moisture absorption and organic carbon reduction. Notably, the HHV also decreased (for more than 10% its original value) with aging in-spite of the lowered moisture content, which could be attributed to the decrease in the concentration of the aromatic compounds due to the ring-opening re­ actions and formation of stable oxidation products. The comparison of the properties between the DTM and DS derived bio-oils showed a large HHV for the DS oil with increased oil stability. The HHV of the DTM biooil decreased by 11.8%, while that of the DS bio-oil decreased only by 7.2% for a 30-day aging period. Furthermore, the moisture content for the DS-derived pyrolysis oil was nearly 50% less than that for the DTMderived pyrolysis oil at all times of the aging study; this accounts for the HHV associated with the DS-derived bio-oil.

Table 3 GC/MS analyses and their compositions for the DTM-derived pyrolysis oil samples. S. No

Compounds names

1

Oxygenated compounds (including acids) i. Acetic acid ii. Phosphonic acid iii. 2-Furanmethanol iv. 14-Oxa-1,11diazatetracyclo v. 2-Methyl-2cyclopentene-1-one vi. Furan, 2-ethyl-5methylvii. 2-Cyclopenten-1-one, 2-hydroxy viii. Butanoic acid, 4hydroxy ix. 2(5H)-Furanone x. Maltol xi. Actinobolin xii. 1,4:3,6-Dianhydro-. alpha.-D- glucopyranose xiii. 2-Vinyl-9-[3-deoxy-. beta.-D-ribofuranosyl] hypoxanthine xiv. 5Hydroxymethylfurfural xv. D-Glucose (Allose) xvi. 1,2-Benzenediol, 3methoxy xvii. 3-Dodecanoylaminobenzoic acid

3.4. Aging effect studies on the pyrolysis oil 3.4.1. FTIR analysis The FTIR analysis was conducted to identify the changes in the specific functional groups in the fresh and aged samples. The spectra of the bio-oil obtained from the DTM and DS samples are shown in Fig. 6(a) and (b), respectively. Specifically, the changes in the concentrations of the functional groups are determined from the percentage variation of the transmittance intensities in the obtained FTIR spectra. Each figure presents the spectra obtained for the fresh bio-oil, 15-day aged sample, and 30-day aged sample. The spectra of the DTM bio-oils consisted of high-intensity bands of hydroxyl, carbonyl, and methoxy groups. The DTM-F sample exhibited a broad band at 3000–3320 cm 1 associated with the stretching vibration of the O–H bond. This indicated the pres­ ence of large amounts of water/acid/alcohol/phenols in the samples [36]. Moreover, the intense bands observed at 1705, 1636, 1391, 1266, and 596 cm 1 corresponded to the spectral stretch of the carboxylic – O) groups, aromatic (C– – C) stretching vibration, C–H bending vi­ (C– bration of aldehyde, C–O stretching band of aromatic ester, and C–H out of plane bending vibrations, respectively [11,14]. In the case of the aged pyrolysis oils of DTM-15 and DTM-30, the spectra showed additional sharp intense peaks at 2850–2968, 1679, 1512, and 1459 cm 1 attrib­ – O) uted to the C–H stretching vibrations, stretching band of the (C– carboxylic acid and esters group, stretching vibration of the nitro com­ pound (N–O), and the strong C–H bending vibration of the methylene group, respectively [14]. The results indicated that the freshly prepared pyrolysis oils are not stable and are susceptible to oxidation to afford many by-products. Particularly, new by-products of the ester and ether groups are formed during the aging process. Moreover, the intensity of – O) increased with the aging days, due to the the carbonyl band (C– continuous oxidation of the pyrolysis oil [37]. Importantly, the addi­ tional band at 1459 cm 1 for the 15 and 30-day aged DTM-based py­ rolysis oil indicated the presence of a long-chain linear aliphatic – C band at structure due to the oil oxidation [37]. Meanwhile, the C– 1636 cm 1 disappeared for DTM-15 and DTM-30, indicating the for­ mation of additional chemical by-products of carbonyl and C–H groups. Fig. 6(b) shows the FTIR spectra of the DS-F, DS-15, and DS-30 samples; the obtained FTIR spectra specified the chemical composition changes due to the aging of the pyrolysis oil. The DS-F sample exhibited a broad intense peak at 3016–3703 cm 1 corresponding to the stretching

2

Hydrocarbons i. 1,7-Diaminoheptane

3

Phenols i. Phenol, 2,6-dimethoxyii. 1,2-Benzenediol, 3methyliii. Catechol iv. Hydroquinone v. 1,2-Benzenediol, 4methylvi. Phenol, 3-methyl vii. 2-methylphenol viii. 4-methylphenol ix. Tetrahydrofurfuryl alcohol

4

Aldehydes and Ketones i. 2-Furaldehyde ii. 2,3-Butanedione iii. 2-Furancarboxalde­ hyde, 5-methyl iv. 1,3-Propanedione, 1,3bis(4-bromophenyl) v. 2-Cyclopenten-1-one, 3methyl vi. 2-Cyclopenten-1-one, 2-methyl vii. 2-Cyclopenten-1-one, 3-ethyl viii. 1-(2,4,6Trihydroxyphenyl)-2pentanone

Molecular formulas

Relative content (wt.%) DTM-F

DTM15

DTM30

45.972

65.38

68.398

CH3COOH H3PO3 C5H6O2 C14H16N2O

– 14.694 4.088 –

27.814 12.478 3.149 2.956

38.473 5.269 1.534 3.464

C6H8O

1.123

0.786

1.599

C7H10O

0.894

0.685

1.775

C5H6O2

2.357

0.967

1.227

C4H8O3

1.744

0.967

0.696

C4H4O2 C6H6O3 C13H20N2O6 C6H8O4

1.206 – 3.463 –

1.048 – 2.473 –

0.953 0.95 1.229 1.756

C12H14N4O5

11.732

6.834

2.8

C6H6O3

1.524

2.469

3.067

C6H12O6 C7H8O3

– 3.15

– 2.754

0.889 1.444

C19H29NO3

–

–

0.992

C7H18N2

0.879 0.879

0.628 0.628

1.069 1.069

C7H8O C8H10O3

18.003 3.416 1.148

14.408 2.843 1.057

11.783 1.056 1.048

C6H6O2 C6H6O2 C7H8O2

6.76 1.036 3.179

5.167 0.951 2.613

4.862 0.656 2.293

C7H8O C7H8O C7H8O C5H10O2

1.347 0.60 – 0.517

– 0.457 0.815 0.505

– 0.323 1.107 0.438

C5H4O2 C4H6O2 C6H6O2

35.146 22.712 2.88 2.253

19.584 11.386 2.057 1.786

18.75 13.211 1.471 1.347

C15H10Br2O2

2.295

2.001

–

C6H8O

1.874

1.568

1.191

C6H8O

1.123

0.786

0.599

C7H10O

0.745

–

–

C11H14O4

1.264

–

0.931

vibration of the O–H bond. This band confirmed the presence of large amounts of water, acid, alcohol, and phenols in the freshly produced pyrolysis oil from the DS [37]. Moreover, the spectrum of the DS-F sample exhibited many peaks indicative of the C–H stretching and bending vibrations that occur in the unsaturated, saturated, and aro­ matic compounds present in the pyrolysis oil. The characteristic bands of 7

G. Bharath et al.

Biomass and Bioenergy 135 (2020) 105523

Fig. 7. (a) Pyrolysis-oil (Py-oil) components (wt.%) of DTM-F, DTM-15 and DTM-30, and (b) Pyrolysis-oil (Py-oil) components (wt.%) of DS-F, DS-15 and DS-30.

the saturated aliphatic species in the sample were observed at 2780–3000 cm 1, and they were associated with the C–H stretching vibrations [38,39]. Particularly, the intense peaks at 2930 and 2857 cm 1 corresponded to the asymmetric C–H stretch and symmetric C–H vibrations of the methylene groups, respectively. The intensity of the asymmetric C–H stretch is slightly higher than that of the symmetric vibrations of C–H due to the large number of saturated aliphatic com­ pounds present in the produced pyrolysis oil. The small intense char­ – O) peak at 1710 cm 1 indicated the acteristic carbonyl band (C– presence of carboxylic acids, ester, aldehydes, and ketones in the DS-F sample. Moreover, the spectrum of the freshly prepared DS-derived pyrolysis oil exhibited a high intense peak at 1636 cm 1 associated – C [39]. In addition, the with the stretching vibration of alkenyl C– samples recorded intense peaks at 1465, 1254, and 604 cm 1, which corresponded to the bending vibration of C–H, stretching vibration of aromatic amine (C–N), and strong stretching of a halo compound (C–I), respectively [40]. The spectral analysis of the freshly prepared DS-derived pyrolysis oil indicated that the sample contained both stretching and bending vibrations of C–H and C–C. Moreover, the – C–C were highly predictable stretching and bending vibrations of C– due to the alkene and alkyne groups of the unsaturated C–C multiple bonding present in the sample. Therefore, the large number of aliphatic and aromatic structures is the molecular backbone of the hydrocarbons present in the freshly prepared pyrolysis oil from DS. Conversely, the DS-15 and DS-30 samples displayed some additional peaks at 1160 and 604 cm 1 corresponding to the stretches of carbonyl (C–O), and the C–I stretch of aliphatic iodo compounds, respectively [40]. Importantly, the – O) band increased as the number of days intensity of the carboxylic (C– of aging of the DS-derived pyrolysis oil increased. The relatively highly – O bands at 1710 cm 1 for DS-15 and DS-30 are mostly intense C– related to the formation of carbonyl groups via the continuous oxidation of pyrolysis oil. The DS-15 and DS-30 samples showed intense bands at – C for 1610 and 1517 cm 1 corresponding to the stretching bands of C– α, β-unsaturated ketone, and aromatic skeletal vibrations, respectively [36,40]. These spectral data confirmed the formation of conjugated –C bonds with carbonyl groups resulting in the disappearance of a C– peak in the DS-15 and DS-30 sample spectra. The results of these in­ vestigations confirmed that the produced oil quality and their chemical compositions are mainly dependent on the aging of the pyrolysis oil. Moreover, the DS-derived pyrolysis oils were more significant for biofuel production than the oil produced from the DTM wastes.

and DTM-30 oil samples matched with the NIST 14 mass spectral library. The relative wt.% values of the compounds were calculated based on the curve area obtained for the peak of each component and are presented in Table 3 and Fig. 7(a). A variety of oxygenated compounds, and hydro­ carbons was identified in the oil composition, which consisted of satu­ rated and unsaturated, straight-chain and cyclic organic compounds. Comparing the chromatogram of the fresh DTM oil sample (Fig. S1(a)) with that of the aged samples (Figs. S1(b) and (c)), it was evident that the number of specific hydrocarbons increased with time, clearly indi­ cating the bio-oil oxidation and hydrolysis owing to the aging of the oil, giving rise to new by-products. A comparison of the constituent com­ positions of DTM-F, DTM-15, and DTM-30 showed the oxidation of unsaturated compounds to saturated compounds in the following aging hierarchy: alcohols→aldehydes→acids. For instance, the concentration of catechol, an unsaturated benzenediol, decreased to 5.167 wt% in DTM-15 from its initial 6.76 wt% in DTM-F. Further aging decreased the concentration of catechol to 4.862 wt% in DTM-30. A similar trend was – C compounds, including 3-methylobserved for other unsaturated C– 1,2-benzenediol and 2-furanone. The reduction of the composition of these benzene compounds signified the opening of the resonance sta­ – C bond due to the oxidation effects favored under ambient bilized C– conditions through hydrolysis [14]. The resulting oxidation products contributed either to the increased wt.% values of the existing simple saturated hydrocarbons or the appearance of new products in the chromatogram. In the same way, the aging phenomena resulted in increased acid formation due to the oxidation of the native alcohols and aldehydes present in the bio-oil. Illustratively, the wt.% values of 2-fur­ anmethanol (alcohol) and 2-furaldehyde (aldehyde) decreased from 4.088 wt% and 22.712 wt% to 3.149 wt% and 13.211 wt%, respectively, for the 15-day aging period. This was attributed to the 22.9% and 41.8% reductions in the alcohol and aldehyde compositions, respectively. Further aging reduced the respective compositions of alcohol and aldehyde to 1.534 wt% and 11.386 wt% accounting for the total re­ ductions of 51.3% and 62.5%, respectively. A similar trend was observed for other alcohols and aldehyde-containing compounds, including 2-methylphenol, 2,3-butanedione and 5-methyl, and 2-furancarboxalde­ hyde. The chain-cracking oxidation of these components resulted in small-chain carbon acids, such as acetic acid, whose concentration increased with the aging process and were recorded as 27.814 wt% in DTM-15 and 38.473 wt% in DTM-3. From the obtained results, it was very clear that the aging process was associated with an incremental degree of saturation coupled with the functional oxidation for breaking long carbon chains to short ones. These observations were in line with the inferences made from the FTIR analysis of DTM, particularly for the – O and intensity reduction/disappearance of the bands indicative of C– – C, as well as the appearance of new bands for the C–H stretch [7,39]. C–

3.4.2. Compositional profile The chromatograms obtained for the various DTM and DS bio-oils are presented in Fig. S1 and Fig. S2, respectively. Table 3 elaborates the various compounds with the obtained peaks of the DTM-F, DTM-15, 8

G. Bharath et al.

Biomass and Bioenergy 135 (2020) 105523

aldehyde components on the aldehydes/ketones and acids without any cracking effects. For the DS samples, the results of the GC/MS analysis are highlighted in Fig. S2, and the relative wt.% values of the various analytes of the DS oil samples are presented in Table 4 and Fig. 7(b). The analyte identities of the DS oil were almost the same as compared to the DTM constituents. The oxidation trend was also similar to the tendency of saturation for the – C and C– – C compounds associated with the break-down effect of the C– – long-chain carbon atoms to short chains. Notably, the presence of oxalic acid monoamide indicated the enriched oil content of the seeds, which could have been presented as long-chain saturated and unsaturated fatty acids (Fig. S2 (a)). These fatty acids were thermally cracked through a high-temperature pyrolysis to yield the dioic acid product. Various lit­ eratures have reported the augmented oil content of different types of DSs [7,18]. Furthermore, the substantial amount of 2-furanmethanol present in the DS-F sample highlighted the transformed oil capacity of the DSs. Remarkably, the oxidation effects of this 2-furanmethanol were lower and relatively weaker in the aged samples of the DS oils (Figs. S2 (b) & (c)). The DS-15 and DS-30 samples reported 13.211 wt% and 13.017 wt% of 2-furanmethanol, respectively, which accounted for the loss values of 37.1% and 38.1%. The total loss value of 2-furanmethanol was comparatively less than the 51.3% loss observed in the DTM bio-oil aging studies. The acidification process of 2-furanmethanol was greatly stalled by the inherent anti-oxidant components present in the DS oils. These compounds include 2-methylphenol, hydroquinone, D-allose, and other phenolic derivatives. In a similar way, the other oxidation prone products also exhibited weak oxidation effects toward their concentra­ tion losses with aging. The compound, 2-furaldehyde, experienced an oxidation loss of only 5.7% in the first 15 days accounting for an overall loss of 32% at the end of a 30-day aging period. Catechol, the ortho isomeric form of benzenediols, also experienced an initial oxidation loss of 19.7% and a final loss of 29.6% for the DS-15 and DS-30 samples. The results confirmed the excellent oil stability of the DS bio-oil due to the considerable anti-oxidant nature of the phenolic components present in the DS pyrolysis oil. The presence of acetic acid in the DS-30 bio-oil sample confirmed the persistence of the oxidation effects during the aging period, and these observations were in accordance with the FTIR analysis of the DS samples. The saturation tendency of the DS oxidation without major carbon chain cracking was in support of the disappear­ – C peak in the FTIR spectra of the DS-15 and DS-30 ance of the C– – O could be ascribed samples. The mild increase in the intensity of C– to the acid formation due to the carbon chain opening of the ring structured compounds and oxidation attacks [41,42].

Table 4 GC/MS analyses and their compositions for the DS-derived pyrolysis oil samples. S. No

Compounds names

1

Oxygenated compounds (including acids) i. Acetic acid ii. Phosphonic acid iii. 2-Furanmethanol iv. 14-Oxa-1,11 diazatetracyclo v. 2-Methyl-2cyclopentene-1-one vi. Furan, 2-ethyl-5methylvii. 2-Cyclopenten-1-one, 2-hydroxy viii. Butanoic acid, 4hydroxy ix. 2(5H)-Furanone x. Maltol xi. Actinobolin xii. 1,4:3,6-Dianhydro-. alpha.-D- glucopyranose xiii. 2-Vinyl-9-[3-deoxy-. beta.-D-ribofuranosyl] hypoxanthine xiv. 5Hydroxymethylfurfural xv. D-Glucose (Allose) xvi. 1,2-Benzenediol, 3methoxy xvii. (2Z)-2-Amino-2hydrazono-Nphenylethanamide

2

Hydrocarbons i. Cyclopropane-pentyl

3

Phenols i. Phenol, 2,6-dimethoxyii. 1,2-Benzenediol, 3methyliii. Catechol iv. Hydroquinone v. 1,2-Benzenediol, 4methylvi. 2-methylphenol vii. 4-methylphenol

4

Aldehydes and Ketones i. 2-Furaldehyde ii. 2,3-Butanedione iii. 2-Furancarboxalde­ hyde, 5-methyl iv. 2-Cyclopenten-1-one, 3-methyl v. 2-Cyclopenten-1-one, 2methyl vi. 2-Cyclopenten-1-one, 3-ethyl vii. 2-Butanone, 1(acetyloxy) viii. 2(5H)-Furanone, 3methyl

Molecular formulas

Relative content (%) DS-F

DS-15

DS-30

64.004

66.281

64.685

CH3COOH H3PO3 C5H6O2 C14H16N2O

– 2.182 21.026 1.838

– 1.637 13.211 4.054

17.926 1.422 1.728 3.464

C6H8O

–

0.327

–

C7H10O

0.951

0.692

0.508

C5H6O2

4.008

3.44

2.287

C4H8O3

2.745

2.264

0.696

C4H4O2 C6H6O3 C13H20N2O6 C6H8O4

1.833 – – 2.687

1.638 1.96 2.023 2.166

0.953 0.95 1.229 3.063

C12H14N4O5

–

–

2.8

C6H6O3

4.515

9.363

3.067

C6H12O6 C18H22O6

19.612 1.22

23.506 –

23.148 1.444

C8H10N4O

1.387

–

–

C8H16

6.838 6.838

5.723 5.723

–

C8H10O3 C7H8O2

13.374 – 0.717

12.573 – 1.326

13.625 1.056 1.048

C6H6O2 C6H6O2 C7H8O2

7.933 0.888 3.589

6.371 0.888 3.599

5.588 0.656 –

C7H8O C7H8O

0.247 –

0.569 –

4.17 1.107

C5H4O2 C4H6O2 C6H6O2

15.784 5.102 3.192 2.787

15.423 4.811 4.095 2.694

21.69 15.017 3.471 1.347

C6H8O

1.68

2.247

1.256

C6H8O

0.572

–

0.599

C7H10O

0.358

–

–

C6H10O3

1.806

1.576

–

C5H6O2

0.287

–

–

3.5. Prospective application of the produced bio-oils A qualitative analysis of the GC/MS results of the DTM and DS oil samples highlighted the various valuable products associated with the obtained bio-oils. Specifically, 2-furanmethanol, otherwise known as Furfuryl alcohol, is the hydroxymethylated furan product, which is a potential hypergolic rocket fuel. The product was obtained by the thermal cracking of the cellulose portion of the date products. The presence of significant levels of 2-furanmethanol, particularly in the DS pyrolysis oil (21.02 wt% in DS-F), confirms the promising significance of this pyrolysis product. The large amount of cellulose content available in the DS produced substantial amounts of 2-furanmethanol. Catechol, a dihydroxyenated benzene product obtained from cellulose was identi­ fied in the DS-F sample with a relative composition of 7.9 wt%. This component has an economic value as a natural pesticide and as a pre­ cursor for many perfumes and pharmaceutical products. Another useful product identified in the pyrolysis-oil is D-allose, which is a rare form of monosaccharides. This product is obtained from the breakdown/diges­ tion of hemicellulose and can be used as an antibiotic for ischemiareperfusion injury. Furthermore, it was available inherently in the DS sample and in the aged DTM sample. A considerable amount of pentyl cyclopropane was also identified in the DS sample, and this component

Additionally, the oxidation effects were well pronounced in the initial stages of aging, which was inferred from the considerable weight losses of the components in DTM-15. The aging period, from 15 days to 30 days, was associated with a reduced oxidation rate due to the reduced driving potential for oxidation and formation of various stable by-products, such as D-allose (antioxidant), which inhibited the further oxidation effects of the alcohol and aldehyde groups. The formation of new functional by-products with relatively large carbon chains, such as 3-lauramidobenzoic acid, hydroquinone, and 1-(2,4,6-trihyd)-2-penta­ none was ascribed to the selective oxidation effects of the alcohol and 9

Biomass and Bioenergy 135 (2020) 105523

G. Bharath et al.

is an important starting material for the synthesis of 1-methyl-1,2-dicy­ clopropylcyclopropane (Syntin), which is a commercial rocket fuel [42]. Thus, the pyrolysis oils obtained from the DS and DTM materials contain significant levels of valuable products, which ensure their market po­ tential. Moreover, this finding provides a reason for further research on the selective separation of these valuable components based on specific applications. Conversely, the obtained DS and DTM-based bio-char can be converted into highly mesoporous activated carbon for energy and environmental applications [28,43–46]. A quick comparison of the GC/MS results of the oil products of DTM and DS revealed that the components of the DS-derived oil samples had a considerably higher economic value. Analytes such as 2-furanmethanol, D-allose, and catechol were present in considerable levels in the DS sample. However, the high lignin composition of DTM resulted in high amounts of 2-furaldehyde and actinobolin products. In addition, the increased phenolic content and presence of other antioxidant compo­ nents in the DS pyrolysis-oil streams reduced the oxidation and hydro­ lysis effect for the bio-oil components ensuring enhanced durability and chemical stability of the DS derived bio-oil.

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4. Conclusions A high quantity of pyrolysis oils was produced from the DTM and DS biomasses through a lab-scale pyrolysis technique at 500 � C for 30 min with a feedstock loading of 200 g and fluidizing gas flow rate of 10 mL min 1. The proximate, ultimate, and TG analyses were used to charac­ terize the physico-chemical properties of the raw feedstock biomasses of DTM and DS. Under the optimized operating conditions, the DS pro­ duced a higher yield of pyrolysis-oil (68 wt%) than DTM (38 wt%). The physico-chemical properties of the obtained pyrolysis oil such as the water content, HHV, pH, viscosity, chemical composition, and byproduct formation were efficiently studied. The aging effects on the stability and chemical composition of the as-derived oil samples were further studied through FTIR and GC/MS techniques. The GC/MS analysis of the fresh and aged pyrolysis-oil samples clearly indicated the change in the chemical properties due to the continuous oxidation and polymerizations of the chemically reactive components, including ole­ fins, aldehydes, and alcohols. The carbonyl, water, and acid contents, as well as the viscosity increased during the aging process. The aging dependent major chemical changes were investigated through an indepth GC/MS analysis. The HHV of the DS-derived pyrolysis-oil was found to be 29.06 MJ kg 1, which is higher than those of the other biomass-derived pyrolysis oils. Studies and detailed investigations showed that the obtained DS derived pyrolysis-oil used as a potential feedstock for producing alternative fuels is both chemically and ther­ mally stable, and it contains some value-added chemicals. Acknowledgments This publication is based upon work supported by the Khalifa Uni­ versity of Science and Technology under Award No. CIRA-2018- 27. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.biombioe.2020.105523. References [1] H. Goyal, D. Seal, R. Saxena, Bio-fuels from thermochemical conversion of renewable resources: a review, Renew. Sustain. Energy Rev. 12 (2) (2008) 504–517. [2] M. Balat, M. Balat, E. Kırtay, H. Balat, Main routes for the thermo-conversion of biomass into fuels and chemicals. Part 1: pyrolysis systems, Energy Convers. Manag. 50 (12) (2009) 3147–3157. [3] M. Naushad, Surfactant assisted nano-composite cation exchanger: development, characterization and applications for the removal of toxic Pb2þ from aqueous medium, Chem. Eng. J. 235 (2014) 100–108.

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