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Pyrolysis and combustion kinetics of date palm biomass using thermogravimetric analysis
Bioresource Technology 118 (2012) 382–389
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Pyrolysis and combustion kinetics of date palm biomass using thermogravimetric analysis Hani H. Sait a,⇑, Ahmad Hussain a, Arshad Adam Salema b, Farid Nasir Ani b a b
Department of Mechanical Engineering, King Abdulaziz University-Rabigh, Saudi Arabia Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, UTM 81310, Johor Bahru, Malaysia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
" First time the detail pyrolysis and
combustion kinetics of date palm biomass was studied. " Date seeds and leaf can become potential feedstock for bio-fuel and bio-char production. " Stem showed low combustion and pyrolysis characteristics since it contains high moisture content. " We assure that kinetic data of date palm biomass could be useful for thermo-chemical technology.
a r t i c l e
i n f o
Article history: Received 21 February 2012 Received in revised form 19 April 2012 Accepted 20 April 2012 Available online 3 May 2012 Keywords: Date palm biomass Thermogravimetric Kinetics Combustion Pyrolysis
a b s t r a c t The present research work is probably the first attempt to focus on the kinetics of pyrolysis and combustion process for date palm biomass wastes like seed, leaf and leaf stem by using Thermogravimetric Analysis (TGA) technique. The physical properties of biomass wastes were also examined. Proximate and ultimate analysis of the date palm biomass was investigated. FT-IR analysis was conducted to determine possible chemical functional groups in the biomass. Results showed that date palm seed and leaf can be characterized as high calorific values and high volatile content biomass materials as compared to the leaf stem. Kinetic analysis of this biomass was also given a particular attention. It is concluded that these biomasses can become useful source of energy, chemicals and bio-char. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Saudi Arabia and its surrounding regions are the home land of the date palm (Phoenix dactylifera) trees. Palm tree is perhaps one of the oldest trees in the world. Recent statistics showed that Saudi Arabia has about 23 millions palm trees, which produce about 780 thousand tons of dates per year (Al-Abdoulhadi et al., 2011). Dates have high nutrition values and provide excellent
⇑ Corresponding author. Tel.: +966 50063264; fax: +966 22564933. E-mail address: [email protected] (H.H. Sait). 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.04.081
health benefits. Each date provides about 20 calories, and is a good source of carbohydrate, fiber, and potassium, with smaller amount of calcium and iron along with other vitamins and minerals. Hence, large amount of dates are consumed as a dietary and its significance is published elsewhere (Ismail et al., 2006). Annually a huge amount of date palm biomass waste is generated while processing date palm fruit. One more feature of the date palm leaf is that it does not fall from the tree even after getting dry. It stays attached to the date palm tree until it is removed manually. This preserves it from getting lost or wasted. However, excess amount of these date palm leaves can cause environmental hazards such as fire, bait for insects and diseases (Ali, 2008).
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Interesting to refer that date seeds represents about one third of the date weight. These excess date seeds are not utilized and hence can serve as a potential source of energy or it can be converted into value-added chemical products. Very recently, Joardder et al. (2012) produced bio-oil and activated carbon from date palm seeds in a fixed bed reactor using pyrolysis technique. Not much information is available regarding utilization of date palm biomass for energy or as fuel. Nevertheless, studies cited in the literature are usually related to farming applications or conversion of date palm biomass into activated carbon for purification purpose or chemical characterization. For instance, Besbes et al. (2004), analyzed two types of date palm seeds in order to investigate its chemical composition. Briones et al. (2011) produced Polyol by chemically modifying date seeds through oxypropylation and liquefaction techniques (using organic solvents in the presence of a catalyst). Recently, production of porous activated carbon from date seed was performed in a tubular furnace with CO2 as activating agent (Reddy et al., 2012). Thermo-chemical process plays an important role in rejuvenation of biomass into energy. Thermogravimetric analysis was used to evaluate kinetic parameters of various biomasses and it has been investigated by numerous researchers (Munir et al., 2009; Ounas et al., 2011; Skreiberg et al., 2011; Syed et al., 2011; Mehrabian et al., 2012; Tiwari and Deo, 2012). Recently, Cai and Chen (2012) determined combustion kinetics of pyrolysis char using iterative linear integral isoconversional method. A TGA study of date seed is available in the literature (Briones et al., 2011), however, little information is available about devolatilization behavior and no kinetic data was provided. The paper was focused on production of polyol from chemical modification of date seeds. Therefore, none has attempted to perform detailed combustion and pyrolysis kinetic analysis of date palm biomass including seed, leaf and leaf stem. Prior knowledge of reaction kinetics is crucial before any attempt to utilize biomass as a feedstock for thermochemical processes. It is worth noted that Saudi Arabia and other surrounding Gulf countries are considered to be major oil producing regions in the world. Therefore, so far none has looked into date palm and other biomass in these regions as potential renewable source of energy. The main objective of this research work was to identify the thermo-chemical characteristics data of date palm biomass. For this, TG analysis was used to investigate the combustion and pyrolysis behavior of date palm biomass such as seeds, leaf and leaf stem. Moreover, Fourier Transform Infrared Spectroscopy (FTIR) was also used to identify the types of chemical functional groups present in the biomass. Proximate and ultimate analysis of the date palm biomass was evaluated. Lastly, the kinetics of pyrolysis and combustion of the date palm biomass is being studied for the first time.
2. Methods 2.1. Material Date palm biomass was obtained locally from Saudi Arabian region. The date seeds were washed with distilled water and dried at room condition. After drying, the seeds were crushed and grinded into powdered form. Date leaves and leaf stem was cleaned to remove any dirt adhered on it and shredded into smaller size. It should be noted that the leaf and leaf stem were dried brownish in colored and not the green colored. In present study no physical or chemical treatment was undertaken. The lignocellulosic components present in the date seed is reported to be; cellulose – 20 wt.%, hemicelluloses – 55 wt.%, lignin – 23 wt.% and ash 1.1 wt.% (Briones et al., 2011). The proximate and ultimate analysis of the date palm biomass has been presented in the Section 3.1.
2.2. Method Bulk density of the samples was tested as mass per unit volume method as mentioned in reference (Obernberger and Thek, 2004). The heating values of the samples were determined using bomb calorimeter model IKA C 2000 according to DIN 51900 method. The proximate analysis of the biomass samples was done according to ASTM D3173 (moisture), ASTM D3174 (ash), and ASTM D3175 (volatile matters) methods. Elemental analyzer was used to determine ultimate analysis of the sample. Combustion and pyrolysis characteristics of the date palm biomass were investigated by thermogravimetric analyzer (TGA) in an air and nitrogen environment respectively. The instrument used for this purpose was METTLER model TGA/SDTA 851E with a fixed heating rate of 20 °C/min. The samples were grounded into powder and sieved to a size of 100 lm. In each test about 5 mg of sample was used. The temperature range was from 25 to 900 °C. During the process of pyrolysis and combustion the initial weight was recorded continuously as a function of temperature and time. The derivative (DTG) curve showed the weight loss of sample per unit time against temperature. The possible chemical functional groups present in the biomass samples were investigated with the help of FT-IR technique (model Perkin Elmer Spectrum 2000 Explorer) in the range of 400– 4000 cm1 wavelength. Biomass sample of about 10 mg was well mixed with 200 mg of potassium bromide (KBr) powder and the mixture was compressed for final analysis.
3. Results and discussion 3.1. Physical and chemical characteristics Table 1 depicts the bulk density and calorific values of the date palm biomass and was compared with other biomass. This property is important in terms of storage and transportation of the feedstock (McKendry, 2002). Moreover, it also determines the biomass handling system and the sample behavior during thermo-chemical processing. Low bulk density is not attractive, since it shows negative effect on energy density, transportation cost and storage capacity for both producer and end users (Obernberger and Thek, 2004). As a fuel, biomass burning rate was reported to be depended on the bulk density (Ryu et al., 2006). The bulk
Table 1 Density and calorific values of date palm (seed, leaf, and leaf stem) and other biomass. Biomass
Bulk density (kg/m3)
Reference
Seed Leaf Leaf stem Hardwood chip Softwood chips Sawdust Wood House coal Anthracite Wood pellets Pine
560 298 216 230 190 120 500 850 1100 590 285
This study This study This study McKendry (2002) McKendry (2002) McKendry (2002) Biomass energy (2012) Biomass energy (2012) Biomass energy (2012) Obernberger and Thek (2004) Ryu et al. (2006)
CV (MJ/kg) Seed Leaf Leaf stem Bituminous coal Lignite Wood Straw pellets Wood pellets Pine
18.97 17.9 10.9 34 26.8 18.6 18.6 20.3 18.3
This study This study This study McKendry (2002) McKendry (2002) McKendry (2002) Obernberger and Thek (2004) Obernberger and Thek (2004) Ryu et al. (2006)
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density of the date leaf and leaf stem samples was about 298 and 216 kg/m3 respectively, while the values for date seeds were much higher 560 kg/m3. This shows that date seeds can be processed without densification thus reducing major pre-processing cost, which cannot be true for date leaf and leaf stem because of their low bulk density. The bulk density was measured for grinded particles. It was noted that dates seeds showed the highest CV among the date palm biomass. This makes them attractive for energy production option. The CV of date seed was close to wood, straw pellets and pine biomass. Because of high moisture content, date leaf stem showed the lowest CV of 10.9 MJ/kg among the biomass listed in Table 1. Thus, high energy density could be accompanied with high bulk density of date seeds. This collectively with moderate CV makes date seeds an attractive biomass to be used as an alternative fuel. Furthermore, storage and transportation cost of such biomass also becomes cheap and efficient. Table 2 gives the proximate and ultimate analysis of date palm biomass on dry basis and values of coal is given for reference. Date seed and leaf are characterized as high volatile matter and low ash components compared to leaf stem. High volatility makes these biomasses attractive for combustion process (Demirbas, 2004) in addition to bio-oil from pyrolysis process. Absolutely, high moisture content deteriorates the chemical properties of the biomass materials as observed in case of leaf stem. Thus, it would be difficult to ignite or combust leaf stem when used as a fuel. On the other hand, date palm seed and leaf would be good source of energy because of high volatile content. Nevertheless, the volatile matter in date palm biomass was higher than the coal and it was vice versa for fixed carbon as can be inferred from Table 2. The combustible component (volatile matter) in leaf stem was lower than other two date palm biomass samples (seeds and leaf). The ash content of the date palm biomass was found to be higher than coal and other biomasses (McKendry, 2002). This may influence the burning rate during combustion and can even cause fouling and agglomeration behavior (Teixeira et al., in press). In addition to this, biomass with high ash content result in poor combustion behavior, adds disposal cost (Sarenbo, 2009) and other problems such as slagging, handling and processing cost, reduction in energy of fuel, operational problems, and low throughput because of formation of slag (McKendry, 2002). Further, high amount of oxygen and low carbon content in biomass as compared to coal tend to reduce the heating value (see Table 2). On the contrary, high carbon and low oxygen fuels are favorable for combustion applications (Pimenidou and Dupont, 2012). On the other hand, nitrogen and sulfur content in the biomass is usually lower than the coal. The amount of hydrogen content was almost similar for biomass and coal. The FT-IR spectra of date palm biomass revealed intense peak at 3450 cm1 that represents the OAH absorption mainly indicating
the presence of alcohols, phenols, carboxylic acids or water. Another peak at 2900 cm1 indicates the CAH absorption due to CH2 and CH3 asymmetric and symmetric stretching vibrations. These peaks might be because of hemicelluloses, cellulose and lignin (Naik et al., 2010). Existence of carboxylic acids, esters, ethers, alcohols and anhydrides may be attributed due to peak at 1100 cm1 from CAO absorption. Structure of aromatic compounds may also be confirmed from the pattern of the weak peak found at 1800 cm1 for date palm seeds curve. Some additional peaks (1740, 1530, 1455, 1390 cm1) were observed for date seeds compared to leaf and leaf stem. The FT-IR spectrum of date seed from present study and that of previous report (Briones et al., 2011) were almost similar. They also pointed out that the band around 1730 cm1 in date seed is attributed to hemicelluloses due to stretching vibration of C@O. The peaks at 1455 and 1390 cm1 could possibly denote the presence of alkanes (CAH bending). The band that appears at 1530 cm1 is likely due to aromatic ring. 3.2. Pyrolysis and combustion characteristics Typical TG and DTG analysis of date palm biomass (refer to supplement material) was done in a nitrogen environment with flow rate of 50 ml/min. The samples were subjected to constant heating rate of 20 °C/min. The initial loss in weight of the samples from temperature 25 °C to 115 °C was due to evaporation of moisture content, which was about 5 wt.% for date seeds and leaf, and about 17 wt.% in case of leaf stem. Sudden drop in biomass weight after 200 °C was attributed due to release of volatile matter. For instance, the volatile were released in three steps during pyrolysis of seed, while leaf and leaf stem showed two step pyrolysis. Nevertheless, major loss occurred at 308 °C for date seed biomass. This was confirmed from DTG results. It is expected that date palm biomasses can be completely pyrolyzed at 400 °C. After this temperature, there was gradual decrease in weight loss. This was attributed due to burning of remaining solid residue or char, which progressed until 900 °C. The unburned char accounted about 20 wt.% for seed and leaf, and 28 wt.% for leaf stem. The initial devolatization temperature for leaf stem was higher than seed and leaf because of high moisture content. Furthermore, the pyrolysis behavior for leaf stem was different from seed and leaf. The remained char after pyrolysis suggest date palm biomass particularly seed could be good source of bio-char. At moderate temperature of about 500 °C, much higher bio-char yield (40 wt.%) can be obtained from date palm biomass. Nevertheless, the yield of bio-char depends on the temperature and types of pyrolysis (slow or fast) (Kwapinski et al., 2010). The TG and DTG results of date palm biomass under air environment was performed at heating rate of 20 °C/min and air flow rate of 50 ml/min. Apparently, the initial loss in biomass weight of
Table 2 Proximate and ultimate analysis of date palm biomass (wt.%). Biomass
Moisture
Volatile matter
Ash
Fixed carbon
Proximate analysis Seed Leaf Leaf stem Bituminous coal (McKendry, 2002)
4.9 5 17.7 8–12
76.6 78.1 55.3 35
10.8 11.7 19.2 8
7.7 5.2 7.8 57
Biomass
C
H
N
S
O
O/C
H/C
Ultimate analysis Seed Leaf Leaf stem Bituminous coal (McKendry, 2002)
45.3 49.4 36.1 73.1
5.6 5.8 5.2 5.5
1.0 1.2 0.7 1.4
0.8 1.3 0.7 1.7
47.2 42.3 57.2 8.7
1.04 0.86 1.58 0.12
0.12 0.12 0.14 0.07
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decomposition route followed by biomass is given as; extractives, cellulose, hemicelluloses and finally lignin or char. These overlapping reaction mechanisms between lignocelluloses materials increase the complexity of the biomass reactions chemistry. In particular, the chemical composition of lignin varies inherently within the biomass materials and hence its reaction mechanism is still debated in the literature (White et al., 2011). Accordingly, the temperature peaks from DTG curves related to degradation of date palm biomass and the lignocellulosic components is listed in Table 3. The first two peaks during pyrolysis process may be related due to decomposition of cellulose, hemicelluloses and to some extent the lignin component. The degradation of lignin may be attributed due to peak 3 during combustion process. However, the reactions for cellulose, hemicellulose and lignin may superimpose each other during reaction peaks 1, 2 and 3. Naranjo et al. (2012) asserted similar view about decompoistion of lignocellulosic materials. Two DTG peaks were observed for kraft lignin; one initiated around 180 °C and another at 500 °C (Montané et al., 2005). This shows that decomposition of lignin is quite unstable and difficult to predict. The thermograms of pyrolysis and combustion for seed and leaf were relatively similar. However, some difference occurred in peak temperature as shown by DTG curves and depicted in Table 3. This could be due to variance in chemical properties (proximate and ultimate) or lignocelluloses content. The minimum temperature required to pyrolyze and combust the date palm biomass was found to be in range of 180–300 °C. The completion of pyrolysis may vary somewhere in range of 500–600 °C and combustion in range of 600–650 °C. In the later process, the remaining char gets oxidize with the available oxygen in the air, thus further reducing the weight of the biomass. The maximum weight loss for seed (43 wt.%), leaf (57 wt.%) and leaf stem (33 wt.%) occurred in the temperature range of 200–400 °C during pyrolysis. This temperature range was in total agreement with previous literature (Fisher et al., 2002). Furthermore, the DTG results of date seeds obtained by Briones et al. (2011) revealed two weight losses at two temperature range viz. 150–270 and 270–360 °C. Besides this, not much was discussed about TG and DTG analysis of date seeds in their studies. In case of combustion, the maximum weight loss occurred in two steps, firstly, in the temperature range of 200–400 °C and secondly, between 425 and 600 °C. In the air atmosphere, the weight loss was significant as compared to inert atmosphere. This is because of acceleration in reaction activity of the biomass due to availability of oxygen (Grammelis et al., 2009; Munir et al., 2009) in combustion process.
about 5 wt.% in temperature range of 25–150 °C for date seed and leaf was recorded due to moisture evaporation. Interestingly, leaf stem showed highest drop in weight at this temperature range indicating high moisture content of about 30 wt.%. The weight loss was about 12 wt.% higher than pyrolysis process. The combustion of date palm biomass progressed in different stages as observed by the DTG result. The initial degradation temperature for date seed and leaf was similar i.e. around 200 °C. But it was delayed for leaf stem biomass to about 250 °C. This could be due to high moisture content in leaf stem biomass. At temperature of about 600 °C almost all the volatile matter was combusted from date seed and leaf and the weight loss was stabilized. However, for leaf stem the combustion was observed to complete little earlier than seed and leaf at temperature of about 550 °C. This may be because of lower volatile matter in leaf stem compared to seed and leaf (see Table 3). The total residue remained at the end of the experiment was about 12 wt.%, 14 wt.% and 20 wt.% for seed, leaf and leaf stem respectively. This was lower than pyrolysis process due to accessibility of oxygen in combustion process. Hence, at such high temperature (>800 °C) the char is assumed to convert into ash by reacting with oxygen present in the air. From the above results, it was evident that leaf stem is characterized as high moisture content biomass. Therefore, it cannot be used as fuel directly in thermo-chemical processes such as pyrolysis, combustion and gasification, except that it has to be dried to a desired moisture value. Whereas the moisture content of date seed and leaf were well below the threshold value required to combust the fuel. In case of pyrolysis process, the moisture content in the feedstock should be lower than 10 wt.% to gain product quality (Bridgwater, 2012). The type of conversion technology or process also depends on the amount of moisture content in the biomass (McKendry, 2002). Even though high moisture content (50 wt.%) biomass can be treated in thermo-chemical process system but with expense of overall energy balance. Presence of any moisture will certainly reduce the CV of the biomass (see Table 1). It was interesting to know that the moisture content in date seed and leaf biomass (5 wt.%) was also much lower than other biomasses reported in reference (McKendry, 2002). Because of low moisture content, the pyrolysis and combustion characteristic of date seed and leaf was much better than leaf stem biomass. In particular, the initial degradation temperature or the ignition temperature was low in case of seed and leaf. The initial ignition temperature, peak temperature and burning rate are greatly depended on the chemical composition of the biomass (Demirbas, 2004). Even the burning environment (nitrogen and air) defines the initial ignition temperature of the biomass fuel as observed in this study. Thus, the ignition temperature for date biomass (seed and leaf) in air was less than 200 °C. For leaf stem it was about 300 °C in air atmosphere. It seems that leaf stem has the lowest combustible property. The rapid degradation rates of seed and leaf biomass as seen from the thermograms was due to the high volatile content and low ash content in the biomass samples, which was in agreement with Munir et al. (2009). Cellulose and hemicelluloses (250–350 °C) are highly reactive and burns at low temperature compared to lignin, which has quite broad burning range for temperature (250–700 °C) (Beall and Eickner, 1970; Fisher et al., 2002). Typically, the thermo-chemical
3.3. Conversion rate The degree of conversion for date palm biomass (X), in the pyrolysis reaction can be obtained by the following equation:
X ¼ ðW 0 WÞ=ðW 0 W 1 Þ
ð1Þ
where W0, W, and W1 refer to initial, instantaneous and final masses respectively. Fig. 1 presents the degree of conversion against temperature for date palm biomass at a heating rate of 20 °C/min in a nitrogen environment.
Table 3 Peak temperature related to decomposition of date palm biomass (C – cellulose; H – hemicellulose; L – lignin). Biomass
Seed Leaf Stem
Pyrolysis temperature (°C)
Combustion temperature (°C)
Peak 1
Peak 2
Peak 3
Peak 1
Peak 2
Peak 3
215 (C + L) 290 (C + L) 300 (C + L)
305 (C + H + L) 340 (C + H + L) 350 (C + H + L)
– – –
215 (C + L) 310 (C + L) 285 (C + L)
295 (C + H + L) 490 (H + L) 350 (C + H + L)
500 (L) – 475 (L)
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The conversion rate was influenced by the temperature. For each date palm biomass, three principle stages of reaction were found as shown in Fig. 1. The degree of conversion was within 10% when the temperature was increased to 250 °C for seeds and leaf. Leaf stem showed 25% degree of conversion until 250 °C. The second stage with a degree of conversion up to 70% was observed in temperature range of 250–450 °C for seeds and leaf, and between 250 and 375 °C for leaf stem. This constitutes the major conversion reaction mainly due to decomposition of the organic constituents into volatiles and char. The remaining conversion in which there was gradual breakdown of lignin into char and gases was found within temperature range of 450 and 850 °C for seeds and leaf and 375–850 °C for leaf stem. Finally, it can be concluded that the degree of conversion keeps on changing with the rise in pyrolysis temperature. Similarly, sugarcane bagasse was reported to undergo conversion by three steps (Ramajo-Escalera et al., 2006). The maximum conversion rate in leaf stem and leaf proposes the production of liquid via pyrolysis process. 3.4. Kinetic parameters Thermogravimetric data was used to characterize the biomass samples as well as to investigate the kinetics of the reaction that results from thermal degradation. Chemical kinetics of biomass pyrolysis and combustion coupled with the description of transport phenomena could provide useful information for the design and optimization of thermo-chemical systems. Currently several methods are available in the literature that can be used to calculate kinetic parameters (Guo and Lua, 2001; White et al., 2011). However, fundamentally every kinetic model obeys the famous Arrhenius equation and the rate of reaction is given by
E kðTÞ ¼ A exp RT da ¼ AeE=RT ð1 aÞn dt
ð2Þ
ð3Þ
where A is the frequency or pre-exponential factor, E is the activation energy of the reaction, R is the universal gas constant, T is the absolute temperature, n is the order of reaction, t is the time, and a is the fraction of reactant decomposed at time t (min). The extent of reaction, a is defined in terms of mass change in the biomass sample or the mass of volatile generated
w w a¼ 0 w0 wf
ð4Þ
where w0, w, wf are the initial, actual and final weights of the sample respectively. For constant heating rate, b, following equation can be expressed:
b¼
da da dt ¼ dT dt dT
ð5Þ
The term da/dT is the non-isothermal reaction rate and substituting Eq. (5) into Eq. (2) will result as follow:
da A E=RT ð1 aÞn ¼ e dT b
ð6Þ
Rearranging and integrating Eq. (6), the following expression can be obtained:
Z
1 ð1 aÞ1n A ¼ b 1n
T
eE=RT dT
ð7Þ
0
R Since eE=RT dT has no exact integral, eE/RT can be expressed as an asymptotic series and its integration with ignoring the higher–order terms gives:
1 ð1 aÞ1n ART 2 2RT E=RT e ¼ 1 E 1n bE
ð8Þ
Expressing Eq. (8) in logarithmic form result in following equation:
" ln
1 ð1 aÞ1n
# ¼ ln
T 2 ð1 nÞ
AR 2RT E 1 ðfor n–1Þ bE E RT
ð9Þ
If assuming that 2RT/E 1 than Eq. (9) becomes:
" ln
1 ð1 aÞ1n
#
T 2 ð1 nÞ
¼ ln
AR E ðfor n–1Þ bE RT
ð10Þ
In order to simplify the calculations, the order of the reaction, n is assumed to be unity, and hence Eq. (10) can be presented as follow:
lnð1 aÞ AR E ¼ ln ln bE RT T2
ð11Þ
Above Eq. (11) will result in a straight line with slope E/R and an intercept of ln [AR/bE]. This was done by plotting graph between following:
" ln
1 ð1 aÞ T 2 ð1 nÞ
# ¼ versus
1 ðfor n–1Þ T
ð12Þ
or
lnð1 aÞ 1 versus ðfor n ¼ 1Þ ln T T2
ð13Þ
The values of a and T would be obtained from the TG analysis. The criterion used for the acceptable values of E and A is that the final value of n should yield the values of E whose linear correlation coefficient are best fitted. Table 4 presents the overall kinetic values of date palm biomass in air and nitrogen environment. The TG and DTG results of date palm biomass under nitrogen and air environment suggest peak temperature related to decomposition of date palm biomass components comprising of cellulose; hemicelluloses and lignin both in the nitrogen and air Table 4 Kinetic parameters for the components of date palm biomass. Biomass
Fig. 1. Conversion rate for date palm biomass during pyrolysis process.
Leaf Stem Seed
A (s1)
E (kJ/mole) In N2
In Air
In N2
In Air
25.85 12.03 20.24
29.00 13.45 27.15
3930 413 1646
11,434 1012 9139
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387
Fig. 2. Kinetic plots for date (A) seed, (B) leaf and (C) leaf stem at 20 °C/min.
environment. These peak temperatures are tabulated in Table 3 which basically represents the decomposition and combustion reaction. As the various date palm biomass components, comprising of seed, leaf and leaf stem biomass, exhibits different peak temperatures during pyrolysis and combustion so the kinetic parameters were determined separately for each biomass component in the pyrolysis and combustion phase. The thermal degradation characteristics and the kinetic parameters (activation energy and pre-exponential factor) of date biomass were determined for
the different peaks. Regression analysis was performed for the scattered data as shown in Fig. 2, which gave high correlation coefficients ranged 81–99 % for seed, leaf stem and leaf. However, the combustion and pyrolysis kinetic correlation for leaf stem and leaf can be taken with confident since they show variation less than 5% (Naranjo et al., 2012). Thermo-chemical conversion of biomass results from a strong interaction between chemical and physical processes at the levels of both the single particle and the reaction environment. Hence,
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Table 5 Kinetic parameters for date palm biomass in nitrogen atmosphere. Biomass
Activation energy, E (kJ/mol)
Reaction order (n)
Peak 1 Leaf Stem Seed
22.1 9.7 12.7
1.9 1.9 2.0
Peak 2 Leaf Stem Seed
43.6 32.8 30.7
1.00 1.00 0.90
Frequency factor, A (s1)
R2
1192 207 178
0.93 0.81 0.81
191,634 26,326 13,485
0.99 0.99 0.95
Table 6 Kinetic parameters for date palm biomass in air atmosphere. Frequency factor, A (s1)
R2
Biomass
Activation energy, E (kJ/mol)
Reaction order (n)
Peak 1 Leaf Stem Seed
21.94 9.04 14.94
1.0 1.0 0.9
1469 101 136
Peak 2 Leaf Stem Seed
24.46 20.53 30.95
1.0 1.0 1.0
4557 3613 12,177
0.98 0.98 0.95
Peak 3 Leaf Stem Seed
– 10.26 28.02
– 1.0 1.0
–
– 0.90 0.98
the kinetic studies of biomass lignocelluloses materials are very useful for the prediction of reaction performance. Present kinetic data cannot be supported by the literature since there was total lack of detailed kinetic study of date palm biomass in air and nitrogen environment. The results of thermal degradation of seed, leaf and leaf stem in the pyrolysis first reaction zones for peak 1 and peak 2 are summarized in Table 5. From the kinetic plots, the degradation reactions of date biomass were found to depend on Arrhenius equation. The variation in activation energy (E) for various date palm biomasses indicates the different chemical reaction regimes of thermal degradation. For the first peak, the activation energy of leaf, leaf stem and seed was 22.1, 9.7, and 12.7 kJ/mol respectively. For the second peak, the activation energy of leaf, leaf stem and seed was 43.6, 32.8 and 30.7 kJ/mol respectively. The kinetic parameters for all the date biomass in the peak 2 were higher than in the first peak zone. It is observed that the activation energy is proportional to the pre-exponential factor as governed by the Arrhenius equation. In the air atmosphere, the kinetic parameters for the leaf, leaf stem and seeds corresponding to peaks 1, 2 and 3 are shown in Table 6. Kinetic parameters of date palm biomass showed activation energy in range of 9.7–43.6 kJ/mole in N2 atmosphere, while in air it was in range of 9.04–30.95 kJ/mole. The highest value of activation energy was for the seed material which denotes the high temperature sensitivity reaction in air. Leaf stem biomass showed lowest activation energy as considerable amount of energy might be consumed in order to vaporize the moisture out of the biomass due to high moisture content in the leaf stem. Furthermore, from kinetics it could be evident that the thermal degradation of date palm biomass under oxygen atmosphere might be influenced by thermal and mass transfer limits. Apparently, activation energy in air was higher than nitrogen atmosphere which agreed well with results of Munir et al. (2009).
4. Conclusions The kinetic data obtained from this study would be useful to model, design and develop thermo-chemical system for Saudi Ara-
482 9666
0.94 0.92 0.822
bian date palm biomass. Among the date palm biomass, seed and leaf showed almost similar pyrolysis and combustion characteristics. On the other hand, the leaf stem was characterized by high moisture content and low volatile matter, thus making them unattractive for thermo-chemical process. The highest degree of reaction and conversion was found within the temperature range of 200–450 °C. Overall, date palm biomass has the potential either to be converted into bio-fuels or used as fuel for energy. Acknowledgements This paper was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under Grant No. 1-829D1432. The authors, therefore, acknowledge with thanks DSR technical and financial support. The first two authors would like to thank UTM and team members of Sustainable Energy Research Group (SURE) under Energy Research Alliance, UTM for their support and conducting the above research work. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.biortech.2012.04. 081. References Al-Abdoulhadi, I.A., Dinar, H.A., Ebert, G., Buttner, C., 2011. Effect of salinity on leaf growth, leaf injury and biomass production in date palm cultivators. Indian J. Sci. Technol. 4 (11), 1542–1546. Ali, Y.S.S., 2008. Use of date palm leaves compost as a substitution to peatmoss. Am. J. Plant Physiol. 3 (4), 131–136. Beall, F.C., Eickner, H.W., 1970. Thermal degradation of wood components: a review of the literature. In: USDA Forest Service Research Paper FPL 130, Forest Products Laboratory, US Forest Service, US Department of Agriculture, Madison, WI. Besbes, S., Blecker, C., Deroanne, C., Drira, N.E., Attia, H., 2004. Date seeds: chemical composition and characteristic profiles of the lipid fraction. Food Chem. 84 (4), 577–584. Biomass energy, 2012.. (accessed 06.02.12).
H.H. Sait et al. / Bioresource Technology 118 (2012) 382–389 Bridgwater, A.V., 2012. Review of fast pyrolysis of biomass and product upgrading. Biomass Bioenergy 38, 68–94. Briones, R., Serrano, L., Younes, R.B., Mondragon, I., Labidi, J., 2011. Polyol production by chemical modification of date seeds. Ind. Crop. Prod. 34 (1), 1035–1040. Cai, J., Chen, Y., 2012. Iterative linear integral isoconversional method: Theory and application. Bioresour. Technol. 103 (1), 309–312. Demirbas, A., 2004. Combustion characteristics of different biomass fuels. Prog. Energy Combust. 30, 219–230. Fisher, T., Hajaligol, M., Waymack, B., Kellogg, D., 2002. Pyrolysis behavior and kinetics of biomass derived materials. J. Anal. Appl. Pyrol. 62, 331–349. Grammelis, P., Basinas, P., Malliopoulou, A., Sakellaropoulos, G., 2009. Pyrolysis kinetics and combustion characteristics of waste recovered fuels. Fuel 88 (1), 195–205. Guo, J., Lua, A.C., 2001. Kinetic study on pyrolytic process of oil palm solid waste using two step consecutive reaction model. Biomass Bioenergy 20, 223–233. Ismail, B., Henry, J., Haffar, I., Baalbaki, R., 2006. Date consumption and dietary significance in the United Arab Emirates. J. Sci. Food Agric. 86, 1196–1201. Joardder, M.U.H., Shazib Uddin, M., Islam, M.N., 2012. The utilization of waste date seed as bio-oil and activated carbon by pyrolysis process. Adv. Mech. Eng. Art. ID 316806, 1–6. Kwapinski, W., Byrne, C., Kryachko, E., Wolfram, P., Adley, C., Leahy, J., Novotny, E., Hayes, M., 2010. Biochar from biomass and waste. Waste Biomass Valor. 1 (2), 177–189. McKendry, P., 2002. Energy production from biomass (part 1): overview of biomass. Bioresour. Technol. 83 (1), 37–46. Mehrabian, R., Scharler, R., Obernberger, I., 2012. Effects of pyrolysis conditions on the heating rate in biomass particles and applicability of TGA kinetic parameters in particle thermal conversion modeling. Fuel 93, 567–575. Montané, D., Torné-Fernández, V., Fierro, V., 2005. Activated carbons from lignin: kinetic modeling of the pyrolysis of Kraft lignin activated with phosphoric acid. Chem. Eng. J. 106, 1–12. Munir, S., Daood, S.S., Nimmo, W., Cunliffe, A.M., Gibbs, B.M., 2009. Thermal analysis and devolatilization kinetics of cotton stalk, sugar cane bagasse and shea meal under nitrogen and air atmospheres. Bioresour. Technol. 100 (3), 1413–1418. Naik, S., Goud, V.V., Rout, P.K., Jacobson, K., Dalai, A.K., 2010. Characterization of Canadian biomass for alternative renewable biofuel. Renew. Energy 35 (8), 1624–1631.
389
Naranjo, R.A., Conesa, J.A., Pedretti, E.F., Romero, O.R., 2012. Kinetic analysis: simultaneous modelling of pyrolysis and combustion processes of dichrostachys cinerea. Biomass Bioenergy 36, 170–175. Obernberger, I., Thek, G., 2004. Physical characterisation and chemical composition of densified biomass fuels with regard to their combustion behaviour. Biomass Bioenergy 27 (6), 653–669. Ounas, A., Aboulkas, A., El harfi, K., Bacaoui, A., Yaacoubi, A., 2011. Pyrolysis of olive residue and sugar cane bagasse: non-isothermal thermogravimetric kinetic analysis. Bioresour. Technol. 102, 11234–11238. Pimenidou, P., Dupont, V., 2012. Characterisation of palm empty fruit bunch (PEFB) and pinewood bio-oils and kinetics of their thermal degradation. Bioresour. Technol. 109, 198–205. Ramajo-Escalera, B., Espina, A., García, J.R., Sosa-Arnao, J.H., Nebra, S.A., 2006. Model-free kinetics applied to sugarcane bagasse combustion. Thermochim. Acta 448, 111–116. Reddy, K.S.K., Al Shoaibi, A., Srinivasakannan, C., 2012. Activated carbon from date palm seed: process optimization using response surface methodology. Waste Biomass Valorization 3 (2), 149–156. Ryu, C., Yang, Y.B., Khor, A., Yates, N.E., Sharifi, V.N., Swithenbank, J., 2006. Effect of fuel properties on biomass combustion: part I. Experiments—fuel type, equivalence ratio and particle size. Fuel 85 (7–8), 1039–1046. Sarenbo, S., 2009. Wood ash dilemma-reduced quality due to poor combustion performance. Biomass Bioenergy 33 (9), 1212–1220. Skreiberg, A., Skreiberg, Ø., Sandquist, J., Sørum, L., 2011. TGA and macro-TGA characterisation of biomass fuels and fuel mixtures. Fuel 90, 2182–2197. Syed, S., Qudaih, R., Talab, I., Janajreh, I., 2011. Kinetics of pyrolysis and combustion of oil shale sample from thermogravimetric data. Fuel 90, 1631–1637. Teixeira, P., Lopes, H., Gulyurtlu, I., Lapa, N., in press. Use of chemical fractionation to understand partitioning of biomass ash constituents during co-firing in fluidized bed combustion. Fuel. Tiwari, P., Deo, M., 2012. Compositional and kinetic analysis of oil shale pyrolysis using TGA–MS. Fuel 94, 333–341. White, J.E., Catallo, W.J., Legendre, B.L., 2011. Biomass pyrolysis kinetics: a comparative critical review with relevant agricultural residue case studies. J. Anal. Appl. Pyrol. 91, 1–33.
Contents lists available at SciVerse ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Pyrolysis and combustion kinetics of date palm biomass using thermogravimetric analysis Hani H. Sait a,⇑, Ahmad Hussain a, Arshad Adam Salema b, Farid Nasir Ani b a b
Department of Mechanical Engineering, King Abdulaziz University-Rabigh, Saudi Arabia Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, UTM 81310, Johor Bahru, Malaysia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
" First time the detail pyrolysis and
combustion kinetics of date palm biomass was studied. " Date seeds and leaf can become potential feedstock for bio-fuel and bio-char production. " Stem showed low combustion and pyrolysis characteristics since it contains high moisture content. " We assure that kinetic data of date palm biomass could be useful for thermo-chemical technology.
a r t i c l e
i n f o
Article history: Received 21 February 2012 Received in revised form 19 April 2012 Accepted 20 April 2012 Available online 3 May 2012 Keywords: Date palm biomass Thermogravimetric Kinetics Combustion Pyrolysis
a b s t r a c t The present research work is probably the first attempt to focus on the kinetics of pyrolysis and combustion process for date palm biomass wastes like seed, leaf and leaf stem by using Thermogravimetric Analysis (TGA) technique. The physical properties of biomass wastes were also examined. Proximate and ultimate analysis of the date palm biomass was investigated. FT-IR analysis was conducted to determine possible chemical functional groups in the biomass. Results showed that date palm seed and leaf can be characterized as high calorific values and high volatile content biomass materials as compared to the leaf stem. Kinetic analysis of this biomass was also given a particular attention. It is concluded that these biomasses can become useful source of energy, chemicals and bio-char. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Saudi Arabia and its surrounding regions are the home land of the date palm (Phoenix dactylifera) trees. Palm tree is perhaps one of the oldest trees in the world. Recent statistics showed that Saudi Arabia has about 23 millions palm trees, which produce about 780 thousand tons of dates per year (Al-Abdoulhadi et al., 2011). Dates have high nutrition values and provide excellent
⇑ Corresponding author. Tel.: +966 50063264; fax: +966 22564933. E-mail address: [email protected] (H.H. Sait). 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.04.081
health benefits. Each date provides about 20 calories, and is a good source of carbohydrate, fiber, and potassium, with smaller amount of calcium and iron along with other vitamins and minerals. Hence, large amount of dates are consumed as a dietary and its significance is published elsewhere (Ismail et al., 2006). Annually a huge amount of date palm biomass waste is generated while processing date palm fruit. One more feature of the date palm leaf is that it does not fall from the tree even after getting dry. It stays attached to the date palm tree until it is removed manually. This preserves it from getting lost or wasted. However, excess amount of these date palm leaves can cause environmental hazards such as fire, bait for insects and diseases (Ali, 2008).
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Interesting to refer that date seeds represents about one third of the date weight. These excess date seeds are not utilized and hence can serve as a potential source of energy or it can be converted into value-added chemical products. Very recently, Joardder et al. (2012) produced bio-oil and activated carbon from date palm seeds in a fixed bed reactor using pyrolysis technique. Not much information is available regarding utilization of date palm biomass for energy or as fuel. Nevertheless, studies cited in the literature are usually related to farming applications or conversion of date palm biomass into activated carbon for purification purpose or chemical characterization. For instance, Besbes et al. (2004), analyzed two types of date palm seeds in order to investigate its chemical composition. Briones et al. (2011) produced Polyol by chemically modifying date seeds through oxypropylation and liquefaction techniques (using organic solvents in the presence of a catalyst). Recently, production of porous activated carbon from date seed was performed in a tubular furnace with CO2 as activating agent (Reddy et al., 2012). Thermo-chemical process plays an important role in rejuvenation of biomass into energy. Thermogravimetric analysis was used to evaluate kinetic parameters of various biomasses and it has been investigated by numerous researchers (Munir et al., 2009; Ounas et al., 2011; Skreiberg et al., 2011; Syed et al., 2011; Mehrabian et al., 2012; Tiwari and Deo, 2012). Recently, Cai and Chen (2012) determined combustion kinetics of pyrolysis char using iterative linear integral isoconversional method. A TGA study of date seed is available in the literature (Briones et al., 2011), however, little information is available about devolatilization behavior and no kinetic data was provided. The paper was focused on production of polyol from chemical modification of date seeds. Therefore, none has attempted to perform detailed combustion and pyrolysis kinetic analysis of date palm biomass including seed, leaf and leaf stem. Prior knowledge of reaction kinetics is crucial before any attempt to utilize biomass as a feedstock for thermochemical processes. It is worth noted that Saudi Arabia and other surrounding Gulf countries are considered to be major oil producing regions in the world. Therefore, so far none has looked into date palm and other biomass in these regions as potential renewable source of energy. The main objective of this research work was to identify the thermo-chemical characteristics data of date palm biomass. For this, TG analysis was used to investigate the combustion and pyrolysis behavior of date palm biomass such as seeds, leaf and leaf stem. Moreover, Fourier Transform Infrared Spectroscopy (FTIR) was also used to identify the types of chemical functional groups present in the biomass. Proximate and ultimate analysis of the date palm biomass was evaluated. Lastly, the kinetics of pyrolysis and combustion of the date palm biomass is being studied for the first time.
2. Methods 2.1. Material Date palm biomass was obtained locally from Saudi Arabian region. The date seeds were washed with distilled water and dried at room condition. After drying, the seeds were crushed and grinded into powdered form. Date leaves and leaf stem was cleaned to remove any dirt adhered on it and shredded into smaller size. It should be noted that the leaf and leaf stem were dried brownish in colored and not the green colored. In present study no physical or chemical treatment was undertaken. The lignocellulosic components present in the date seed is reported to be; cellulose – 20 wt.%, hemicelluloses – 55 wt.%, lignin – 23 wt.% and ash 1.1 wt.% (Briones et al., 2011). The proximate and ultimate analysis of the date palm biomass has been presented in the Section 3.1.
2.2. Method Bulk density of the samples was tested as mass per unit volume method as mentioned in reference (Obernberger and Thek, 2004). The heating values of the samples were determined using bomb calorimeter model IKA C 2000 according to DIN 51900 method. The proximate analysis of the biomass samples was done according to ASTM D3173 (moisture), ASTM D3174 (ash), and ASTM D3175 (volatile matters) methods. Elemental analyzer was used to determine ultimate analysis of the sample. Combustion and pyrolysis characteristics of the date palm biomass were investigated by thermogravimetric analyzer (TGA) in an air and nitrogen environment respectively. The instrument used for this purpose was METTLER model TGA/SDTA 851E with a fixed heating rate of 20 °C/min. The samples were grounded into powder and sieved to a size of 100 lm. In each test about 5 mg of sample was used. The temperature range was from 25 to 900 °C. During the process of pyrolysis and combustion the initial weight was recorded continuously as a function of temperature and time. The derivative (DTG) curve showed the weight loss of sample per unit time against temperature. The possible chemical functional groups present in the biomass samples were investigated with the help of FT-IR technique (model Perkin Elmer Spectrum 2000 Explorer) in the range of 400– 4000 cm1 wavelength. Biomass sample of about 10 mg was well mixed with 200 mg of potassium bromide (KBr) powder and the mixture was compressed for final analysis.
3. Results and discussion 3.1. Physical and chemical characteristics Table 1 depicts the bulk density and calorific values of the date palm biomass and was compared with other biomass. This property is important in terms of storage and transportation of the feedstock (McKendry, 2002). Moreover, it also determines the biomass handling system and the sample behavior during thermo-chemical processing. Low bulk density is not attractive, since it shows negative effect on energy density, transportation cost and storage capacity for both producer and end users (Obernberger and Thek, 2004). As a fuel, biomass burning rate was reported to be depended on the bulk density (Ryu et al., 2006). The bulk
Table 1 Density and calorific values of date palm (seed, leaf, and leaf stem) and other biomass. Biomass
Bulk density (kg/m3)
Reference
Seed Leaf Leaf stem Hardwood chip Softwood chips Sawdust Wood House coal Anthracite Wood pellets Pine
560 298 216 230 190 120 500 850 1100 590 285
This study This study This study McKendry (2002) McKendry (2002) McKendry (2002) Biomass energy (2012) Biomass energy (2012) Biomass energy (2012) Obernberger and Thek (2004) Ryu et al. (2006)
CV (MJ/kg) Seed Leaf Leaf stem Bituminous coal Lignite Wood Straw pellets Wood pellets Pine
18.97 17.9 10.9 34 26.8 18.6 18.6 20.3 18.3
This study This study This study McKendry (2002) McKendry (2002) McKendry (2002) Obernberger and Thek (2004) Obernberger and Thek (2004) Ryu et al. (2006)
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density of the date leaf and leaf stem samples was about 298 and 216 kg/m3 respectively, while the values for date seeds were much higher 560 kg/m3. This shows that date seeds can be processed without densification thus reducing major pre-processing cost, which cannot be true for date leaf and leaf stem because of their low bulk density. The bulk density was measured for grinded particles. It was noted that dates seeds showed the highest CV among the date palm biomass. This makes them attractive for energy production option. The CV of date seed was close to wood, straw pellets and pine biomass. Because of high moisture content, date leaf stem showed the lowest CV of 10.9 MJ/kg among the biomass listed in Table 1. Thus, high energy density could be accompanied with high bulk density of date seeds. This collectively with moderate CV makes date seeds an attractive biomass to be used as an alternative fuel. Furthermore, storage and transportation cost of such biomass also becomes cheap and efficient. Table 2 gives the proximate and ultimate analysis of date palm biomass on dry basis and values of coal is given for reference. Date seed and leaf are characterized as high volatile matter and low ash components compared to leaf stem. High volatility makes these biomasses attractive for combustion process (Demirbas, 2004) in addition to bio-oil from pyrolysis process. Absolutely, high moisture content deteriorates the chemical properties of the biomass materials as observed in case of leaf stem. Thus, it would be difficult to ignite or combust leaf stem when used as a fuel. On the other hand, date palm seed and leaf would be good source of energy because of high volatile content. Nevertheless, the volatile matter in date palm biomass was higher than the coal and it was vice versa for fixed carbon as can be inferred from Table 2. The combustible component (volatile matter) in leaf stem was lower than other two date palm biomass samples (seeds and leaf). The ash content of the date palm biomass was found to be higher than coal and other biomasses (McKendry, 2002). This may influence the burning rate during combustion and can even cause fouling and agglomeration behavior (Teixeira et al., in press). In addition to this, biomass with high ash content result in poor combustion behavior, adds disposal cost (Sarenbo, 2009) and other problems such as slagging, handling and processing cost, reduction in energy of fuel, operational problems, and low throughput because of formation of slag (McKendry, 2002). Further, high amount of oxygen and low carbon content in biomass as compared to coal tend to reduce the heating value (see Table 2). On the contrary, high carbon and low oxygen fuels are favorable for combustion applications (Pimenidou and Dupont, 2012). On the other hand, nitrogen and sulfur content in the biomass is usually lower than the coal. The amount of hydrogen content was almost similar for biomass and coal. The FT-IR spectra of date palm biomass revealed intense peak at 3450 cm1 that represents the OAH absorption mainly indicating
the presence of alcohols, phenols, carboxylic acids or water. Another peak at 2900 cm1 indicates the CAH absorption due to CH2 and CH3 asymmetric and symmetric stretching vibrations. These peaks might be because of hemicelluloses, cellulose and lignin (Naik et al., 2010). Existence of carboxylic acids, esters, ethers, alcohols and anhydrides may be attributed due to peak at 1100 cm1 from CAO absorption. Structure of aromatic compounds may also be confirmed from the pattern of the weak peak found at 1800 cm1 for date palm seeds curve. Some additional peaks (1740, 1530, 1455, 1390 cm1) were observed for date seeds compared to leaf and leaf stem. The FT-IR spectrum of date seed from present study and that of previous report (Briones et al., 2011) were almost similar. They also pointed out that the band around 1730 cm1 in date seed is attributed to hemicelluloses due to stretching vibration of C@O. The peaks at 1455 and 1390 cm1 could possibly denote the presence of alkanes (CAH bending). The band that appears at 1530 cm1 is likely due to aromatic ring. 3.2. Pyrolysis and combustion characteristics Typical TG and DTG analysis of date palm biomass (refer to supplement material) was done in a nitrogen environment with flow rate of 50 ml/min. The samples were subjected to constant heating rate of 20 °C/min. The initial loss in weight of the samples from temperature 25 °C to 115 °C was due to evaporation of moisture content, which was about 5 wt.% for date seeds and leaf, and about 17 wt.% in case of leaf stem. Sudden drop in biomass weight after 200 °C was attributed due to release of volatile matter. For instance, the volatile were released in three steps during pyrolysis of seed, while leaf and leaf stem showed two step pyrolysis. Nevertheless, major loss occurred at 308 °C for date seed biomass. This was confirmed from DTG results. It is expected that date palm biomasses can be completely pyrolyzed at 400 °C. After this temperature, there was gradual decrease in weight loss. This was attributed due to burning of remaining solid residue or char, which progressed until 900 °C. The unburned char accounted about 20 wt.% for seed and leaf, and 28 wt.% for leaf stem. The initial devolatization temperature for leaf stem was higher than seed and leaf because of high moisture content. Furthermore, the pyrolysis behavior for leaf stem was different from seed and leaf. The remained char after pyrolysis suggest date palm biomass particularly seed could be good source of bio-char. At moderate temperature of about 500 °C, much higher bio-char yield (40 wt.%) can be obtained from date palm biomass. Nevertheless, the yield of bio-char depends on the temperature and types of pyrolysis (slow or fast) (Kwapinski et al., 2010). The TG and DTG results of date palm biomass under air environment was performed at heating rate of 20 °C/min and air flow rate of 50 ml/min. Apparently, the initial loss in biomass weight of
Table 2 Proximate and ultimate analysis of date palm biomass (wt.%). Biomass
Moisture
Volatile matter
Ash
Fixed carbon
Proximate analysis Seed Leaf Leaf stem Bituminous coal (McKendry, 2002)
4.9 5 17.7 8–12
76.6 78.1 55.3 35
10.8 11.7 19.2 8
7.7 5.2 7.8 57
Biomass
C
H
N
S
O
O/C
H/C
Ultimate analysis Seed Leaf Leaf stem Bituminous coal (McKendry, 2002)
45.3 49.4 36.1 73.1
5.6 5.8 5.2 5.5
1.0 1.2 0.7 1.4
0.8 1.3 0.7 1.7
47.2 42.3 57.2 8.7
1.04 0.86 1.58 0.12
0.12 0.12 0.14 0.07
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decomposition route followed by biomass is given as; extractives, cellulose, hemicelluloses and finally lignin or char. These overlapping reaction mechanisms between lignocelluloses materials increase the complexity of the biomass reactions chemistry. In particular, the chemical composition of lignin varies inherently within the biomass materials and hence its reaction mechanism is still debated in the literature (White et al., 2011). Accordingly, the temperature peaks from DTG curves related to degradation of date palm biomass and the lignocellulosic components is listed in Table 3. The first two peaks during pyrolysis process may be related due to decomposition of cellulose, hemicelluloses and to some extent the lignin component. The degradation of lignin may be attributed due to peak 3 during combustion process. However, the reactions for cellulose, hemicellulose and lignin may superimpose each other during reaction peaks 1, 2 and 3. Naranjo et al. (2012) asserted similar view about decompoistion of lignocellulosic materials. Two DTG peaks were observed for kraft lignin; one initiated around 180 °C and another at 500 °C (Montané et al., 2005). This shows that decomposition of lignin is quite unstable and difficult to predict. The thermograms of pyrolysis and combustion for seed and leaf were relatively similar. However, some difference occurred in peak temperature as shown by DTG curves and depicted in Table 3. This could be due to variance in chemical properties (proximate and ultimate) or lignocelluloses content. The minimum temperature required to pyrolyze and combust the date palm biomass was found to be in range of 180–300 °C. The completion of pyrolysis may vary somewhere in range of 500–600 °C and combustion in range of 600–650 °C. In the later process, the remaining char gets oxidize with the available oxygen in the air, thus further reducing the weight of the biomass. The maximum weight loss for seed (43 wt.%), leaf (57 wt.%) and leaf stem (33 wt.%) occurred in the temperature range of 200–400 °C during pyrolysis. This temperature range was in total agreement with previous literature (Fisher et al., 2002). Furthermore, the DTG results of date seeds obtained by Briones et al. (2011) revealed two weight losses at two temperature range viz. 150–270 and 270–360 °C. Besides this, not much was discussed about TG and DTG analysis of date seeds in their studies. In case of combustion, the maximum weight loss occurred in two steps, firstly, in the temperature range of 200–400 °C and secondly, between 425 and 600 °C. In the air atmosphere, the weight loss was significant as compared to inert atmosphere. This is because of acceleration in reaction activity of the biomass due to availability of oxygen (Grammelis et al., 2009; Munir et al., 2009) in combustion process.
about 5 wt.% in temperature range of 25–150 °C for date seed and leaf was recorded due to moisture evaporation. Interestingly, leaf stem showed highest drop in weight at this temperature range indicating high moisture content of about 30 wt.%. The weight loss was about 12 wt.% higher than pyrolysis process. The combustion of date palm biomass progressed in different stages as observed by the DTG result. The initial degradation temperature for date seed and leaf was similar i.e. around 200 °C. But it was delayed for leaf stem biomass to about 250 °C. This could be due to high moisture content in leaf stem biomass. At temperature of about 600 °C almost all the volatile matter was combusted from date seed and leaf and the weight loss was stabilized. However, for leaf stem the combustion was observed to complete little earlier than seed and leaf at temperature of about 550 °C. This may be because of lower volatile matter in leaf stem compared to seed and leaf (see Table 3). The total residue remained at the end of the experiment was about 12 wt.%, 14 wt.% and 20 wt.% for seed, leaf and leaf stem respectively. This was lower than pyrolysis process due to accessibility of oxygen in combustion process. Hence, at such high temperature (>800 °C) the char is assumed to convert into ash by reacting with oxygen present in the air. From the above results, it was evident that leaf stem is characterized as high moisture content biomass. Therefore, it cannot be used as fuel directly in thermo-chemical processes such as pyrolysis, combustion and gasification, except that it has to be dried to a desired moisture value. Whereas the moisture content of date seed and leaf were well below the threshold value required to combust the fuel. In case of pyrolysis process, the moisture content in the feedstock should be lower than 10 wt.% to gain product quality (Bridgwater, 2012). The type of conversion technology or process also depends on the amount of moisture content in the biomass (McKendry, 2002). Even though high moisture content (50 wt.%) biomass can be treated in thermo-chemical process system but with expense of overall energy balance. Presence of any moisture will certainly reduce the CV of the biomass (see Table 1). It was interesting to know that the moisture content in date seed and leaf biomass (5 wt.%) was also much lower than other biomasses reported in reference (McKendry, 2002). Because of low moisture content, the pyrolysis and combustion characteristic of date seed and leaf was much better than leaf stem biomass. In particular, the initial degradation temperature or the ignition temperature was low in case of seed and leaf. The initial ignition temperature, peak temperature and burning rate are greatly depended on the chemical composition of the biomass (Demirbas, 2004). Even the burning environment (nitrogen and air) defines the initial ignition temperature of the biomass fuel as observed in this study. Thus, the ignition temperature for date biomass (seed and leaf) in air was less than 200 °C. For leaf stem it was about 300 °C in air atmosphere. It seems that leaf stem has the lowest combustible property. The rapid degradation rates of seed and leaf biomass as seen from the thermograms was due to the high volatile content and low ash content in the biomass samples, which was in agreement with Munir et al. (2009). Cellulose and hemicelluloses (250–350 °C) are highly reactive and burns at low temperature compared to lignin, which has quite broad burning range for temperature (250–700 °C) (Beall and Eickner, 1970; Fisher et al., 2002). Typically, the thermo-chemical
3.3. Conversion rate The degree of conversion for date palm biomass (X), in the pyrolysis reaction can be obtained by the following equation:
X ¼ ðW 0 WÞ=ðW 0 W 1 Þ
ð1Þ
where W0, W, and W1 refer to initial, instantaneous and final masses respectively. Fig. 1 presents the degree of conversion against temperature for date palm biomass at a heating rate of 20 °C/min in a nitrogen environment.
Table 3 Peak temperature related to decomposition of date palm biomass (C – cellulose; H – hemicellulose; L – lignin). Biomass
Seed Leaf Stem
Pyrolysis temperature (°C)
Combustion temperature (°C)
Peak 1
Peak 2
Peak 3
Peak 1
Peak 2
Peak 3
215 (C + L) 290 (C + L) 300 (C + L)
305 (C + H + L) 340 (C + H + L) 350 (C + H + L)
– – –
215 (C + L) 310 (C + L) 285 (C + L)
295 (C + H + L) 490 (H + L) 350 (C + H + L)
500 (L) – 475 (L)
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The conversion rate was influenced by the temperature. For each date palm biomass, three principle stages of reaction were found as shown in Fig. 1. The degree of conversion was within 10% when the temperature was increased to 250 °C for seeds and leaf. Leaf stem showed 25% degree of conversion until 250 °C. The second stage with a degree of conversion up to 70% was observed in temperature range of 250–450 °C for seeds and leaf, and between 250 and 375 °C for leaf stem. This constitutes the major conversion reaction mainly due to decomposition of the organic constituents into volatiles and char. The remaining conversion in which there was gradual breakdown of lignin into char and gases was found within temperature range of 450 and 850 °C for seeds and leaf and 375–850 °C for leaf stem. Finally, it can be concluded that the degree of conversion keeps on changing with the rise in pyrolysis temperature. Similarly, sugarcane bagasse was reported to undergo conversion by three steps (Ramajo-Escalera et al., 2006). The maximum conversion rate in leaf stem and leaf proposes the production of liquid via pyrolysis process. 3.4. Kinetic parameters Thermogravimetric data was used to characterize the biomass samples as well as to investigate the kinetics of the reaction that results from thermal degradation. Chemical kinetics of biomass pyrolysis and combustion coupled with the description of transport phenomena could provide useful information for the design and optimization of thermo-chemical systems. Currently several methods are available in the literature that can be used to calculate kinetic parameters (Guo and Lua, 2001; White et al., 2011). However, fundamentally every kinetic model obeys the famous Arrhenius equation and the rate of reaction is given by
E kðTÞ ¼ A exp RT da ¼ AeE=RT ð1 aÞn dt
ð2Þ
ð3Þ
where A is the frequency or pre-exponential factor, E is the activation energy of the reaction, R is the universal gas constant, T is the absolute temperature, n is the order of reaction, t is the time, and a is the fraction of reactant decomposed at time t (min). The extent of reaction, a is defined in terms of mass change in the biomass sample or the mass of volatile generated
w w a¼ 0 w0 wf
ð4Þ
where w0, w, wf are the initial, actual and final weights of the sample respectively. For constant heating rate, b, following equation can be expressed:
b¼
da da dt ¼ dT dt dT
ð5Þ
The term da/dT is the non-isothermal reaction rate and substituting Eq. (5) into Eq. (2) will result as follow:
da A E=RT ð1 aÞn ¼ e dT b
ð6Þ
Rearranging and integrating Eq. (6), the following expression can be obtained:
Z
1 ð1 aÞ1n A ¼ b 1n
T
eE=RT dT
ð7Þ
0
R Since eE=RT dT has no exact integral, eE/RT can be expressed as an asymptotic series and its integration with ignoring the higher–order terms gives:
1 ð1 aÞ1n ART 2 2RT E=RT e ¼ 1 E 1n bE
ð8Þ
Expressing Eq. (8) in logarithmic form result in following equation:
" ln
1 ð1 aÞ1n
# ¼ ln
T 2 ð1 nÞ
AR 2RT E 1 ðfor n–1Þ bE E RT
ð9Þ
If assuming that 2RT/E 1 than Eq. (9) becomes:
" ln
1 ð1 aÞ1n
#
T 2 ð1 nÞ
¼ ln
AR E ðfor n–1Þ bE RT
ð10Þ
In order to simplify the calculations, the order of the reaction, n is assumed to be unity, and hence Eq. (10) can be presented as follow:
lnð1 aÞ AR E ¼ ln ln bE RT T2
ð11Þ
Above Eq. (11) will result in a straight line with slope E/R and an intercept of ln [AR/bE]. This was done by plotting graph between following:
" ln
1 ð1 aÞ T 2 ð1 nÞ
# ¼ versus
1 ðfor n–1Þ T
ð12Þ
or
lnð1 aÞ 1 versus ðfor n ¼ 1Þ ln T T2
ð13Þ
The values of a and T would be obtained from the TG analysis. The criterion used for the acceptable values of E and A is that the final value of n should yield the values of E whose linear correlation coefficient are best fitted. Table 4 presents the overall kinetic values of date palm biomass in air and nitrogen environment. The TG and DTG results of date palm biomass under nitrogen and air environment suggest peak temperature related to decomposition of date palm biomass components comprising of cellulose; hemicelluloses and lignin both in the nitrogen and air Table 4 Kinetic parameters for the components of date palm biomass. Biomass
Fig. 1. Conversion rate for date palm biomass during pyrolysis process.
Leaf Stem Seed
A (s1)
E (kJ/mole) In N2
In Air
In N2
In Air
25.85 12.03 20.24
29.00 13.45 27.15
3930 413 1646
11,434 1012 9139
H.H. Sait et al. / Bioresource Technology 118 (2012) 382–389
387
Fig. 2. Kinetic plots for date (A) seed, (B) leaf and (C) leaf stem at 20 °C/min.
environment. These peak temperatures are tabulated in Table 3 which basically represents the decomposition and combustion reaction. As the various date palm biomass components, comprising of seed, leaf and leaf stem biomass, exhibits different peak temperatures during pyrolysis and combustion so the kinetic parameters were determined separately for each biomass component in the pyrolysis and combustion phase. The thermal degradation characteristics and the kinetic parameters (activation energy and pre-exponential factor) of date biomass were determined for
the different peaks. Regression analysis was performed for the scattered data as shown in Fig. 2, which gave high correlation coefficients ranged 81–99 % for seed, leaf stem and leaf. However, the combustion and pyrolysis kinetic correlation for leaf stem and leaf can be taken with confident since they show variation less than 5% (Naranjo et al., 2012). Thermo-chemical conversion of biomass results from a strong interaction between chemical and physical processes at the levels of both the single particle and the reaction environment. Hence,
388
H.H. Sait et al. / Bioresource Technology 118 (2012) 382–389
Table 5 Kinetic parameters for date palm biomass in nitrogen atmosphere. Biomass
Activation energy, E (kJ/mol)
Reaction order (n)
Peak 1 Leaf Stem Seed
22.1 9.7 12.7
1.9 1.9 2.0
Peak 2 Leaf Stem Seed
43.6 32.8 30.7
1.00 1.00 0.90
Frequency factor, A (s1)
R2
1192 207 178
0.93 0.81 0.81
191,634 26,326 13,485
0.99 0.99 0.95
Table 6 Kinetic parameters for date palm biomass in air atmosphere. Frequency factor, A (s1)
R2
Biomass
Activation energy, E (kJ/mol)
Reaction order (n)
Peak 1 Leaf Stem Seed
21.94 9.04 14.94
1.0 1.0 0.9
1469 101 136
Peak 2 Leaf Stem Seed
24.46 20.53 30.95
1.0 1.0 1.0
4557 3613 12,177
0.98 0.98 0.95
Peak 3 Leaf Stem Seed
– 10.26 28.02
– 1.0 1.0
–
– 0.90 0.98
the kinetic studies of biomass lignocelluloses materials are very useful for the prediction of reaction performance. Present kinetic data cannot be supported by the literature since there was total lack of detailed kinetic study of date palm biomass in air and nitrogen environment. The results of thermal degradation of seed, leaf and leaf stem in the pyrolysis first reaction zones for peak 1 and peak 2 are summarized in Table 5. From the kinetic plots, the degradation reactions of date biomass were found to depend on Arrhenius equation. The variation in activation energy (E) for various date palm biomasses indicates the different chemical reaction regimes of thermal degradation. For the first peak, the activation energy of leaf, leaf stem and seed was 22.1, 9.7, and 12.7 kJ/mol respectively. For the second peak, the activation energy of leaf, leaf stem and seed was 43.6, 32.8 and 30.7 kJ/mol respectively. The kinetic parameters for all the date biomass in the peak 2 were higher than in the first peak zone. It is observed that the activation energy is proportional to the pre-exponential factor as governed by the Arrhenius equation. In the air atmosphere, the kinetic parameters for the leaf, leaf stem and seeds corresponding to peaks 1, 2 and 3 are shown in Table 6. Kinetic parameters of date palm biomass showed activation energy in range of 9.7–43.6 kJ/mole in N2 atmosphere, while in air it was in range of 9.04–30.95 kJ/mole. The highest value of activation energy was for the seed material which denotes the high temperature sensitivity reaction in air. Leaf stem biomass showed lowest activation energy as considerable amount of energy might be consumed in order to vaporize the moisture out of the biomass due to high moisture content in the leaf stem. Furthermore, from kinetics it could be evident that the thermal degradation of date palm biomass under oxygen atmosphere might be influenced by thermal and mass transfer limits. Apparently, activation energy in air was higher than nitrogen atmosphere which agreed well with results of Munir et al. (2009).
4. Conclusions The kinetic data obtained from this study would be useful to model, design and develop thermo-chemical system for Saudi Ara-
482 9666
0.94 0.92 0.822
bian date palm biomass. Among the date palm biomass, seed and leaf showed almost similar pyrolysis and combustion characteristics. On the other hand, the leaf stem was characterized by high moisture content and low volatile matter, thus making them unattractive for thermo-chemical process. The highest degree of reaction and conversion was found within the temperature range of 200–450 °C. Overall, date palm biomass has the potential either to be converted into bio-fuels or used as fuel for energy. Acknowledgements This paper was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, under Grant No. 1-829D1432. The authors, therefore, acknowledge with thanks DSR technical and financial support. The first two authors would like to thank UTM and team members of Sustainable Energy Research Group (SURE) under Energy Research Alliance, UTM for their support and conducting the above research work. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.biortech.2012.04. 081. References Al-Abdoulhadi, I.A., Dinar, H.A., Ebert, G., Buttner, C., 2011. Effect of salinity on leaf growth, leaf injury and biomass production in date palm cultivators. Indian J. Sci. Technol. 4 (11), 1542–1546. Ali, Y.S.S., 2008. Use of date palm leaves compost as a substitution to peatmoss. Am. J. Plant Physiol. 3 (4), 131–136. Beall, F.C., Eickner, H.W., 1970. Thermal degradation of wood components: a review of the literature. In: USDA Forest Service Research Paper FPL 130, Forest Products Laboratory, US Forest Service, US Department of Agriculture, Madison, WI. Besbes, S., Blecker, C., Deroanne, C., Drira, N.E., Attia, H., 2004. Date seeds: chemical composition and characteristic profiles of the lipid fraction. Food Chem. 84 (4), 577–584. Biomass energy, 2012.
H.H. Sait et al. / Bioresource Technology 118 (2012) 382–389 Bridgwater, A.V., 2012. Review of fast pyrolysis of biomass and product upgrading. Biomass Bioenergy 38, 68–94. Briones, R., Serrano, L., Younes, R.B., Mondragon, I., Labidi, J., 2011. Polyol production by chemical modification of date seeds. Ind. Crop. Prod. 34 (1), 1035–1040. Cai, J., Chen, Y., 2012. Iterative linear integral isoconversional method: Theory and application. Bioresour. Technol. 103 (1), 309–312. Demirbas, A., 2004. Combustion characteristics of different biomass fuels. Prog. Energy Combust. 30, 219–230. Fisher, T., Hajaligol, M., Waymack, B., Kellogg, D., 2002. Pyrolysis behavior and kinetics of biomass derived materials. J. Anal. Appl. Pyrol. 62, 331–349. Grammelis, P., Basinas, P., Malliopoulou, A., Sakellaropoulos, G., 2009. Pyrolysis kinetics and combustion characteristics of waste recovered fuels. Fuel 88 (1), 195–205. Guo, J., Lua, A.C., 2001. Kinetic study on pyrolytic process of oil palm solid waste using two step consecutive reaction model. Biomass Bioenergy 20, 223–233. Ismail, B., Henry, J., Haffar, I., Baalbaki, R., 2006. Date consumption and dietary significance in the United Arab Emirates. J. Sci. Food Agric. 86, 1196–1201. Joardder, M.U.H., Shazib Uddin, M., Islam, M.N., 2012. The utilization of waste date seed as bio-oil and activated carbon by pyrolysis process. Adv. Mech. Eng. Art. ID 316806, 1–6. Kwapinski, W., Byrne, C., Kryachko, E., Wolfram, P., Adley, C., Leahy, J., Novotny, E., Hayes, M., 2010. Biochar from biomass and waste. Waste Biomass Valor. 1 (2), 177–189. McKendry, P., 2002. Energy production from biomass (part 1): overview of biomass. Bioresour. Technol. 83 (1), 37–46. Mehrabian, R., Scharler, R., Obernberger, I., 2012. Effects of pyrolysis conditions on the heating rate in biomass particles and applicability of TGA kinetic parameters in particle thermal conversion modeling. Fuel 93, 567–575. Montané, D., Torné-Fernández, V., Fierro, V., 2005. Activated carbons from lignin: kinetic modeling of the pyrolysis of Kraft lignin activated with phosphoric acid. Chem. Eng. J. 106, 1–12. Munir, S., Daood, S.S., Nimmo, W., Cunliffe, A.M., Gibbs, B.M., 2009. Thermal analysis and devolatilization kinetics of cotton stalk, sugar cane bagasse and shea meal under nitrogen and air atmospheres. Bioresour. Technol. 100 (3), 1413–1418. Naik, S., Goud, V.V., Rout, P.K., Jacobson, K., Dalai, A.K., 2010. Characterization of Canadian biomass for alternative renewable biofuel. Renew. Energy 35 (8), 1624–1631.
389
Naranjo, R.A., Conesa, J.A., Pedretti, E.F., Romero, O.R., 2012. Kinetic analysis: simultaneous modelling of pyrolysis and combustion processes of dichrostachys cinerea. Biomass Bioenergy 36, 170–175. Obernberger, I., Thek, G., 2004. Physical characterisation and chemical composition of densified biomass fuels with regard to their combustion behaviour. Biomass Bioenergy 27 (6), 653–669. Ounas, A., Aboulkas, A., El harfi, K., Bacaoui, A., Yaacoubi, A., 2011. Pyrolysis of olive residue and sugar cane bagasse: non-isothermal thermogravimetric kinetic analysis. Bioresour. Technol. 102, 11234–11238. Pimenidou, P., Dupont, V., 2012. Characterisation of palm empty fruit bunch (PEFB) and pinewood bio-oils and kinetics of their thermal degradation. Bioresour. Technol. 109, 198–205. Ramajo-Escalera, B., Espina, A., García, J.R., Sosa-Arnao, J.H., Nebra, S.A., 2006. Model-free kinetics applied to sugarcane bagasse combustion. Thermochim. Acta 448, 111–116. Reddy, K.S.K., Al Shoaibi, A., Srinivasakannan, C., 2012. Activated carbon from date palm seed: process optimization using response surface methodology. Waste Biomass Valorization 3 (2), 149–156. Ryu, C., Yang, Y.B., Khor, A., Yates, N.E., Sharifi, V.N., Swithenbank, J., 2006. Effect of fuel properties on biomass combustion: part I. Experiments—fuel type, equivalence ratio and particle size. Fuel 85 (7–8), 1039–1046. Sarenbo, S., 2009. Wood ash dilemma-reduced quality due to poor combustion performance. Biomass Bioenergy 33 (9), 1212–1220. Skreiberg, A., Skreiberg, Ø., Sandquist, J., Sørum, L., 2011. TGA and macro-TGA characterisation of biomass fuels and fuel mixtures. Fuel 90, 2182–2197. Syed, S., Qudaih, R., Talab, I., Janajreh, I., 2011. Kinetics of pyrolysis and combustion of oil shale sample from thermogravimetric data. Fuel 90, 1631–1637. Teixeira, P., Lopes, H., Gulyurtlu, I., Lapa, N., in press. Use of chemical fractionation to understand partitioning of biomass ash constituents during co-firing in fluidized bed combustion. Fuel. Tiwari, P., Deo, M., 2012. Compositional and kinetic analysis of oil shale pyrolysis using TGA–MS. Fuel 94, 333–341. White, J.E., Catallo, W.J., Legendre, B.L., 2011. Biomass pyrolysis kinetics: a comparative critical review with relevant agricultural residue case studies. J. Anal. Appl. Pyrol. 91, 1–33.