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Contents lists available at ScienceDirect

Journal of Analytical and Applied Pyrolysis

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omparative study of bio-oil production from sugarcane bagasse andalm empty fruit bunch: Yield optimization and bio-oilharacterization

ebastián Vecino Mantilla, Paola Gauthier-Maradei ∗, Pedro Álvarez Gil,indy Tarazona Cárdenas

EIAM, Universidad Industrial de Santander (UIS), Cra 27, Cll 9, Bucaramanga, Colombia

r t i c l e i n f o

rticle history:eceived 3 August 2013ccepted 9 April 2014vailable online xxx

eywords:ntermediate pyrolysisimplex methodologyio-oil maximization

a b s t r a c t

This research focused primarily on the process optimization for bio-oil production in a pilot-scale batchreactor operating in a fixed bed and using two important agricultural residues from Santander Depart-ment in Colombia: sugarcane bagasse (SB) and palm empty fruit bunch (EFB). The Simplex method wasapplied to develop experimental tests in which three main variables were studied: temperature, gas res-idence time and particle size. The choice of such variables was based on literature review suggesting thatthey have a major influence on bio-oil yield. The ranges of the operating conditions were: temperature460–600 ◦C, gas residence time 16–80 s and particle size 0.5–1.4 mm. The analysis of variance (ANOVA)shows the temperature being the most influential variable on the bio-oil yield. The other variables werenot significant for bio-oil production from intermediate pyrolysis. In the case of SB, the best operat-ing conditions (temperature 560 ◦C, gas residence time 77 s and particle size 0.5–0.85 mm) resulted in a

◦
bio-oil yield of 53.4 wt%, whereas in the case of EFB, the best operating conditions (temperature 540 C,gas residence time 31 s and particle size <0.5 mm) resulted in a bio-oil yield of 48.4 wt%. However, thephysical–chemical properties of bio-oil stemming from the two studied biomasses are completely dif-ferent, where the bio-oil from EFB presents the best HHV of 34.91 MJ/kg, the highest pH (3.9) and thelowest density (approximately 958 kg/m3).
© 2014 Elsevier B.V. All rights reserved.

. Introduction

Fossil fuels are the main energy resource; however, their sup-ly is limited and their nature is not renewable. According to the

nternational Energy Agency (IEA), petroleum supply will increaseo 100 Mbpd in 2035, and transportation is the main consumer,ith more than a half of energy consumption in the world [1].n the other hand, the recent environmental changes represent a

hreat to society and require fast actions to reduce the gas emissionsesponsible for greenhouse effects.

This scenario shows the necessity to look for new energy

Please cite this article in press as: S. Vecino Mantilla, et

cane bagasse and palm empty fruit bunch: Yield optimizationhttp://dx.doi.org/10.1016/j.jaap.2014.04.003

esources that can supply the fuel needs of the next decades anditigate the environmental impact of current fuels. There is not

unique solution to this issue, but the use of renewable energies

∗ Corresponding author. Tel.: +57 76 34 4000ext2526.E-mail addresses: [email protected], [email protected]

P. Gauthier-Maradei).

ttp://dx.doi.org/10.1016/j.jaap.2014.04.003165-2370/© 2014 Elsevier B.V. All rights reserved.

has many advantages due to their availabilities and low contribu-tion to pollution. In this context, biomass valorization to energy isshown as an excellent alternative to replace fossil fuels for bothcogeneration and fuels. In the case of fuels, their production couldbe obtained from lignocellulosic materials, such as agro-industrialresidues, a promising option due to their low cost and because theyare not competitive with food.

Recent statistics of oil reserves and fuel production in Colombia,as well as the low rates of new oil well discovery, easily allow pre-dicting an energy emergency in near future. This is the reason whyColombia must develop biofuel production by taking advantage ofits conditions as an agro-industrial country. In fact, the Food andAgricultural Organization (FAO) of the United Nations has classifiedColombia as the 12th largest sugarcane producer and 5th largest oilpalm producer in the world in 2011 [2].

al., Comparative study of bio-oil production from sugar- and bio-oil characterization, J. Anal. Appl. Pyrol. (2014),

In Colombia, as in other sugar producing countries, a stronginterest has emerged for the use of agro-industrial residues stem-ming from harvest as feedstock in energy processes. At a nationallevel, Santander Department (northeast of Colombia) is the 5th

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mailto:[email protected]

dx.doi.org/10.1016/j.jaap.2014.04.003

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argest sugarcane producer and 2nd largest oil palm producer with production of agro-industrial residues of 1276 and 419 kt/year,espectively [3].

One of the promising technologies for biomass valorization tonergy is pyrolysis, with which it is possible to obtain three dif-erent products: bio-oil, biochar and syngas, and such a processs expected to have an important contribution in the short termue to its versatility, efficiency and environmental acceptability4,5]. Pyrolysis allows the thermal decomposition of biomass withr without a very limited quantity of oxygen, at a temperature of00–600 ◦C.

The most appropriate product from pyrolysis is bio-oil becauset is a liquid with a high energy density and is able to substitute con-entional fuels in different applications, such as high power dieselotors, boilers and turbines. Bio-oil is a dark brown liquid with a

moke-like odor; its composition is very different from petroleumerivates. The distribution of compounds in bio-oil depends mainlyn the type of biomass that is used and the severity of the processtemperature, gas residence time, heat rate). The main constituentn bio-oil is water, and the other compounds are mainly hydroxy-aldehydes, hydroxylketones, sugars, carboxylic acids and phenols6].

Many authors have reported different conditions to perform SBnd EFB pyrolysis with the purpose of improving bio-oil yields.hese operating conditions have been determined using experi-ental design or conventional studies, where the authors have

tudied in a systematic way the behavior and influence of theariables, without any optimization methodology. Recently, Abnisat al. [7] presented the first optimization study applied to bio-oilroduction by pyrolysis from palm shell. In this work, the responseurface methodology was used to study the effects of severalarameters, such as temperature, N2 flow rate, feedstock particleize and reaction time on the pyrolysis efficiency, and to identifyhe optimal conditions for bio-oil production. They obtained a non-inear dependency model that accounts for the influence of theariables on the bio-oil yield with an R2 of 0.93. However, theseesults cannot be used for EFB because the composition of bothesidues is not the same; EFB has 10 db wt% more volatile materialVM) and 6 db wt% less fixed carbon (FC) than palm shell. Sulaimant al. [8] reported an experimental work of pyrolysis using EFB aseedstock. Although their study was focused on the determinationf the conditions that allow maximization of pyrolysis liquids, theanges that have been used to study the effects of particle size andas residence time were small, and it was not possible to identify ifhe variation of the variables had a significant effect on the bio-oilield.

This paper describes an experimental study to optimize bio-oilroduction by intermediate pyrolysis from SB and EFB on a pilotnit of laboratory scale. Optimization was performed using the Sim-lex methodology with the three operating conditions reported in

iterature as having the greatest influence on bio-oil yield: particleize, temperature and gas residence time.

Table 1 shows the different operating conditions used to obtainhe best bio-oil yields, in agreement with literature. Temperature ishe most important variable in the process because it is responsibleor the thermal decomposition of biomass. The highest tempera-ures allow for the cracking of bio-oil, decreasing the bio-oil yieldnd increasing the gaseous products [9]. In addition, the tempera-ure favors the elimination of VM present in the biomass. The bio-oilield is usually maximized between 400 and 550 ◦C. Another impor-ant parameter is the gas residence time in the heating zone becauset determines the final products that can be obtained; longer gas



esidence times allow cracking of the first pyrolysis products, favor-ng syngas yield, whereas shorter gas residence times favor thearrier gas to rapidly remove the VM from the heating zone to avoidecondary reactions [10]. On the other hand, particle size is another

PRESSnd Applied Pyrolysis xxx (2014) xxx–xxx

important variable in the pyrolysis process because bio-oil yield canbe affected by diffusion limitations and temperature fronts presentthe particles. Kim et al. [11] found that small particle sizes favorheat transfer through the bed. Indeed, an increase of the particlesize causes the highest temperature gradients, increasing the solidresidue yield and decreasing the liquid and gaseous yields.

2. Materials and methods

2.1. Feedstock

The SB and EFB residues that were used in this study havebeen supplied by small farms of Santander Department (Colombia).The pretreatment was the same for both types, i.e., each biomasswas dried in an oven at 105 ◦C for one day and was later cut,ground and sifted to obtain particles of different sizes: <0.5 mm,0.5–0.85 mm, 0.85–1 mm and 1–1.4 mm. Proximate analysis wasperformed in agreement with ASTM D7582 using an ATG 2050 (TAInstruments), and ultimate analysis was performed according to XPCEN/TS 15104. The inorganic materials were analyzed using the EN15290–EN 15297 standards.

2.2. Description of the pilot unit

A scheme of the pilot unit is given in Fig. 1. Carrier gas wasfed to the pilot unit at the bottom with a pressure of 100 kPa(relative); this flow was regulated with a flowmeter operatingin the 40–500 N mL/min range. The reactor material was a 316 Lstainless steel tube with 3.5 and 3.9 cm internal and external diam-eters, respectively, and 54-cm length. The reactor was heatedusing an electrical tubular oven (2400 W) generating a heat rate ofapproximately 30 ◦C/min. The volatile and non-condensable gasesproduced by pyrolysis exited the top of the reactor toward a cool-ing zone consisting of two traps made of 316 L stainless steel. Thesetraps used ice and dry ice, respectively, to ensure the condensa-tion of all volatile compounds present in the gas. The gas, freeof volatiles, passed through a mass flowmeter (0–640 NmL/min atNTP) before being evacuated into the atmosphere.

2.3. Experimental development

The application of the Simplex method to the optimization ofbio-oil production was conducted by a factorial space with threedimensions (3D): temperature (T), gas residence time (�) and par-ticle size (Dp). The target variable was the bio-oil yield. The fourinitial lattices are presented in Table 2. The operating conditionsof these initial tests were defined according to literature to maxi-mize the bio-oil yield (see Table 1). The gas flow rate is shown inthe table using normal conditions (T = 293 ◦C, 1 atm) and modifiedusing reaction conditions to calculate the gas residence time.

The four initial lattices correspond to four set operating condi-tions where the temperature was varied from 460 to 520 ◦C, thegas residence time from 65.66 to 33.03 s for the SB and 49.95 to23.50 s for EFB and the particle size between the ranges <0.5 and1.0–1.4 mm.

Once the results of the initial tests were obtained, they wereclassified according to the performance in bio-oil production usingthe following nomenclature: the worst test (W), the next to theworst test (N), prior to the best test (P) and the best test (B). Takinginto account this information, it was possible to calculate the newtest (A) using Eqs. (1)–(3), according to Simplex method [17].

( )


TA = 23

(TB + TP + TN) − TW (1)

�A =(

23

)(�B + �P + �N) − �W (2)

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Table 1Operating conditions to obtain the best bio-oil yield.

Biomass � (s) T (◦C) QN2 (mL/s) P (kPa) Dp (mm) dT/dt (◦C/s) Yield bio-oil (wt%) Refs.

SB – 530 – 12 <0.45 0.20 51.3 [12]2 400–500 – 8 0.45–0.80 0.25–0.40 42.7 [13]

168 450–600 16.67 101 0.45–0.80 0.23–0.46 43.3 [13]– >500 16.67 – <0.50 >3.33 ∼50.0 [14]– 500 3.33 – 0.50–1.00 0.83 66.1 [15]

EFB – 500 0.17 101 0.25 – 30 [16]

Table 2Operating conditions for initial test in the Simplex method.

Biomass Test T (◦C) � (s) QN2 (mL/min) at NTP Dp (mm)

SB SB1 500 65.66 150 <0.5SB2 480 33.03 300 0.5–0.85SB3 520 49.95 200 1.0–1.4SB4 460 49.20 250 0.85–1.0

EFB EFB1 500 47.24 150 <0.5EFB2 480 23.50 300 0.5–0.65EFB3 460 49.20 160 0.85–1.0

4

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EFB4 520

pA =(

23

)(DpB + DpP + DpN) − DpW (3)

This calculation allows projecting the operating condition of theorst test through the mean operating conditions of the other three

ests (with the best bio-oil yields) thus obtaining the operating con-itions of a new test to be realized. To reject the worst test and adopthe new test suggested for the method, the system passed from sim-lex 1 (consisting of the initial four tests) to simplex 2 (consisting ofhe 3 best tests and the new test). The stopping criterion accordingo the Simplex method was associated with the bio-oil yield vari-tion. Thus, the experimental work ends when the new test led toorse results than the other tests used in the simplex. In the case

f particle size, which is not a continuous variable, the calculation



as performed using the mean value of each considered particleize range.

The gas residence time was calculated using Eq. (4) and takingnto account the volumetric flow of the carrier gas at operating

Fig. 1. Schema of the py

9.95 155 1.0–1.4

conditions in the reactor (temperature and pressure), as well asthe porosity and volume of the bed.

� = (AT · h/QN2 ) ·(

1 − �bulk

�real

)(4)

where: QN2 : volumetric flow (mL/s) of carrier gas at the tem-perature and pressure of the reactor; AT: cross-sectional area ofthe reactor (cm2); �: gas residence time (s); h: bed length (cm);�bulk/�real: bulk and real density of the biomass particle size (kg/m3,kg/m3).

All tests were performed using nitrogen (4.8 grade) as carriergas at a relative pressure of 100 kPa and a bed height of 25 cm. Theheating rate was approximately 30 ◦C/min.


A total of 16 experimental tests were necessary to optimize thebio-oil yield: seven tests with SB (SB1–SB8) and nine tests with EFB(EFB1–EFB9). Each test was performed twice to guarantee repro-ducibility.

rolysis pilot unit.

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Table 3Physical–chemical and energy properties of SB and EFB.

SB EFB

Moisture (wt%)9.60 8.86

Proximate analysis (wt db%)FC 8.65 12.23VM 90.02 81.01Ash 1.33 6.76

Ultimate analysis (wt db%)H 6.14 6.31Oa 46.46 42.99N 0.30 0.60C 47.10 50.10

Inorganic composition (ppm)K 1642 14,854Ca 435 1084Mg 385 1028P 638 666Si 2568 1588

Bulk density (kg/m3)<0.5 mm 127.4 359.20.5–0.85 mm 165.7 394.00.85–1.0 mm 136.7 371.31.0–1.4 mm 124.5 337.3

Real density (kg/m3)1220.0 1176.5

HHV (MJ/kg)15.08 20.85



.4. Chemical and physical characterization of bio-oil

The bio-oil produced consists of two immiscible phases:queous and organic. The phase separation was obtained byiquid–liquid extraction using dichloromethane (analytical quality)s solvent and a separating funnel. The organic phase was first keptt room temperature during 24 h, and then heated in a water bath at5 ◦C to allow solvent evaporation before storage at 5 ◦C. The aque-us phase, in turn, was stored at the same temperature immediatelyfter separation.

The moisture determination for each phase was performed inriplicate using a Karl Fischer Volumetric Titrator (HI 903, Hannanstruments). The pH of the aqueous phase was measured using aH meter (Schott Instrument); these values can be assumed as theH of bio-oil because the moisture obtained in the organic phaseas lower. Likewise, the density for the two phases was measuredsing a pycnometer of 1 mL. Finally, the high heat value (HHV) ofhe bio-oil was measured for all tests using ASTM D5865 Standardpecification.

A chromatographic analysis of the organic phase of the bio-oilas performed using a GC/MS chromatograph (Agilent Technolo-

ies, HP-5MS column 29.5 m × 250 �m × 0.25 �m). Each sampleas filtered using 0.45 �m filters, and 0.1 g of bio-oil was diluted

n 1 mL of dichloromethane before being injected into the chro-atograph. Helium was used as the carrier gas at a constant flow

f 0.87 mL/min. The GC oven temperature was programmed from0 ◦C (2 min) to 290 ◦C at 5 ◦C/min and held at 290 ◦C for 2 min. Onlyhe 13 peaks of the most important area were taken into accountn each analysis.

. Results and discussion

.1. Biomass characterization

The results of the proximate and ultimate analyses for bothiomasses studied are shown in Table 3 and are in agreementith the literature concerning the same agro-industry residual

iomasses [3,14,18], in which EFB has lower VM than SB and moreC and ash. On the other hand, the ultimate analysis shows that EFBontains more carbon and hydrogen than SB, reflecting the highestVH.

The main inorganic elements are also reported in Table 3 for bothiomasses studied. EFB presents higher ash than SB, with potassium

n the highest concentration, in contrast to SB. These alkali metalshat constitute the ash are used in plants for nutrient transfer androwth [5]. In general, the presence of inorganic materials has annfluence on the conversion and selectivity of the pyrolysis reac-ion. Chiaramonti et al. [19] reported that the water yield in liquidroducts is inversely proportional to the ash amount present in theiomass.

Finally, Table 3 shows the bulk density for each particle size,nd the real density and heating value of both biomasses. Accord-ng to the table, the EFB gives a higher HHV than the SB. The valuesbtained in our study are in agreement with those reported byther authors, such as Sulaiman et al. [8] and Escalante et al. [3]. Onhe other hand, the measured bulk densities show a dependencen particle size. The difference in the bulk density is due to smallarticles that have lower sphericity, which makes the compactionarder; therefore, the fixed bed with smaller diameter particles hasigher porosity [20].



.2. Optimization of bio-oil production from SB and EFB pyrolysis

Table 4 presents the bio-oil, aqueous phase, organic phase,iochar and yields obtained in each test for SB and EFB

a Oxygen was calculated by difference.

pyrolysis, respectively. The reported values correspond to the aver-age between two tests made for each point, all standard deviationsbeing lower than 2 wt% in the mass balance closure. Most of themass balance closures exceed 90 wt%. The differences that werefound in the mass balance closures correspond mainly to thedetermination of the gas mass (N2 + syngas) because such flow ismeasured with a mass flowmeter calibrated with nitrogen; there-fore, the mass syngas is corrected using a value of 38 g/mol, suchas the average molecular mass for the syngas according to Garcíaet al. for SB [12], instead of 28 g/mol. The three mass balance clo-sures that were found lower than 90 wt% in the EFB tests correspondto experimental difficulties when the volumetric flow was higherthan the maximum limit of the flowmeter in the outlet line.

For SB pyrolysis, the Simplex method allowed for studying theinfluence of temperature in a range between 460 and 562 ◦C, gasresidence time between 33.03 and 78.72 s and particle size between<0.5 and 1.0–1.4 mm. Optimal conditions were determined forthe SB6 test, where the bio-oil yield was 53.38 wt% (T◦ = 560 ◦C,� = 77.31 s and Dp between 0.5 and 0.85 mm). On the other hand,for EFB pyrolysis, the maximum bio-oil yield was obtained for theEFB5 test with a bio-oil yield of 48.39 wt% (T = 540 ◦C, � = 31.26 s andDp <0.5 mm). In this case, the Simplex method allowed for studyingthe influence of temperature in a range between 460 and 603 ◦C, gasresidence time between 16.40 and 49.95 s and particle size between<0.5 and 1.0–1.4 mm.

Comparing the bio-oil yields from EFB pyrolysis with thoseobtained from SB pyrolysis, the latter gave better results. Indeedthey were even higher values in comparison with other intermedi-ate pyrolysis processes using fixed beds. Abnisa et al. [7] obtaineda maximum of 46.4 wt% for palm shells at a temperature of 500 ◦C,particle size of 1.7–2 mm and N2 flow of 2000 mL/min. Ertas et al.[10] worked with Laurel as feedstock and obtained 21.91 wt% at


500 ◦C, N2 flow of 100 mL/min and particle size of 0.42–0.85 mm,and Demiral et al. [9] obtained a maximum bio-oil yield of 33.18 wt%in soft shells of pistachio pyrolysis using 450 ◦C, 50 mL/min N2 flow

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Table 4The results obtained with the Simplex optimization of bio-oil production.

Test T (◦C) � (s) QN2 (mL/min) at NTP Dp (mm) Yield (wt%) Mass balance closure (wt%)

Bio-oil Aq. phase Org. phase Biochar Syngas

Lattices necessary for Simplex method on SB pyrolysisSB1 500 65.66 150.0 <0.5 48.88 32.57 16.31 29.77 12.41 91.07SB2 480 33.03 300.0 0.5–0.85 47.31 31.72 15.59 31.49 11.79 90.58SB3 520 49.95 200.0 1.0–1.4 52.11 33.37 18.74 31.13 15.84 99.08SB4 460 49.20 250.0 0.85–1 45.20 30.44 14.41 35.30 12.29 92.79SB5 540 49.89 189.9 <0.5 48.55 32.96 15.59 28.48 19.56 96.58SB6 560 77.31 116.0 0.5–0.85 53.38 34.39 18.99 25.31 18.31 96.99SB7 562 71.66 129.0 1.0–1.4 52.39 35.18 17.21 26.10 17.12 95.60

Lattices necessary for Simplex method on EFB pyrolysisEFB1 500 47.24 150.0 <0.5 39.63 24.92 13.33 36.33 15.73 91.69EFB 2 480 23.50 300.0 0.5–0.85 39.88 29.97 9.91 35.86 14.3 90.04EFB 3 520 49.95 160.0 1.0–1.4 41.06 27.78 8.87 31.36 16.97 89.39EFB 4 460 49.20 155.0 0.85–1 36.64 32.27 8.80 37.53 21.23 95.40EFB 5 540 31.26 235.0 <0.5 48.39 30.74 17.66 29.63 17.84 95.86EFB 6 527 22.58 339.8 0.5–0.85 45.68 34.19 11.48 30.6 13.53 89.81EFB 7 578 45.69 157.7 0.85–1 45.72 34.89 10.84 28.42 17.08 91.22EFB 8 577 16.40 422.0 1.0–1.4 46.5 32.24 13.66 29.49 10.99 86.98

32

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EFB 9 603 39.66 171.9 <0.5 46.91

nd particle size of 0.8 mm. This can be explained, according tohiaramonti et al. [19], by the fact that the organic liquid yield

s favored by the highest VM quantity in the biomass. SB is theiomass with the highest VM (90.02 wt db%, Table 3) comparedith EFB VM (81.01 wt db%, Table 3), laurel (76.89 wt db%), soft

hells of pistachio (74.76 wt db%) and palm shells (75.51 wt db%).Comparing the SB4 and EFB4 tests, which are performed in the

ame operating conditions, it can be observed that the bio-oil yields favored for biomass with high VM. The lower amount of bio-il produced using EFB as feedstock (36.64 wt%) compared withB (45.20 wt%) is due mainly to a diminution of the organic phaseield but not for the water production, which in this case is slightlyffected. According to the results of Table 4, the bio-oil that is notroduced during EFB pyrolysis is compensated by a greater gas andhar production, which means that the conversion and selectiv-ty of pyrolysis reactions are affected by the biomass compositionnd therefore, if the VM amount in biomass can partially explain

diminution of conversion, the selectivity cannot be determinedy this property. Recent studies [21] show that there is a catalyticffect of inorganic materials on the pyrolysis reactions. This effects reflected in a decrease of the liquid yield and an increase ofhe gas yield justified for the cracking reactions that are favoredhen any inorganic elements, such as potassium, are present in

he reaction middle. Dupont et al. [21] demonstrated the favorableffect of potassium and the inhibiting effect of silicon on the gasi-cation reaction. EBF presents the highest amount of potassium14,854 ppm) in contrast with SB (1642 ppm), which can explainhe results of the selectivity obtained in the pyrolysis reactions.

.3. Analysis of variance (ANOVA)

To determine the statistical significance of the different vari-bles studied on the bio-oil yield, an ANOVA analysis waserformed by the General Linear Model (GLM) present in the Stat-raphics Centurion XV software with a confidence level of 95%. Thenalysis was performed by Square Sum Type III allowing measure-ent of the contribution of each variable and eliminating the effects

f the others. The ANOVA analysis results for SB and EFB pyrolysisre shown in Table 5. Temperature is the most significant variable



or both cases studied. In contrast, particle size shows the worst-value, which means that it is not possible to eliminate the nullypothesis, and therefore, this variable has no influence on the bio-il yield. Several authors, such as Ertas et al. [10], Kim et al. [11] and

.51 14.39 30.2 15.07 92.18

Sukiran et al. [33], have observed that the most important variableaffecting bio-oil production is the temperature, followed by the gasflow rate (gas residence time).

In the case of gas residence time, the p-value is higher than0.05 only for the SB pyrolysis tests, indicating that the variable isnot statistically significant with respect to the bio-oil yield in ourtest conditions. However, the gas residence times studied in theEFB pyrolysis (16.40–49.95 s) are shorter than those studied in theSB pyrolysis (33.03–78.72 s). Therefore, it is possible that the vari-able begins to be significant when its value is low, according to theANOVA analysis for EFB pyrolysis, for which the p-value is slightlylower than 0.05. In fact, the study conducted by Abnisa et al. [7],with palm shell as the feedstock in an intermediate pyrolysis reac-tor, shows that the bio-oil yield is strongly influenced at higher N2flow rate (1–5 L/min) and therefore, lower gas residence time. Onthe other hand, Uzon et al. [22] and Ertas et al. [10] used approxi-mately the same flow rate as in our study and concluded that thereis not a significant influence of the gas flow rate (gas residence time)on the bio-oil yield.

A model was proposed to explain the significance of each vari-able on the bio-oil yield using Forward Selection Function of theStatgraphics software. This function allows for adjusting a math-ematic model including only the most significant variables andthe interactions between them. In the case of EFB, the adjustedmodel proposed by Statgraphics software is shown in Eq. (5) andcorresponds to a polynomial equation of the second order. Theparticle size, the interaction between the temperature and par-ticle size and the particle size square are not included becausethey have less influence. The statistical analysis for each parameterand its ANOVA study are presented in Table 6 with a confi-dence level of 95%. The results explain the variability of the datain 98.56%.

Bio-oil YieldEFB (wt%) = −214.124 + 0.734627 · T + 2.94038

·� + 0.054026 · Dp.� − 0.0025607 · T · � − 0.0250646 · �2

+ 0.0054665 · T2 (5)

For the SB pyrolysis, the model was adjusted in agreement with


the model obtained for EFB pyrolysis. Table 7 shows the ANOVAanalysis results with a confidence level of 95% for the adjustedmodel corresponding to Eq. (6). This one variable explains 91.12%of the variability in the data. As with the EFB pyrolysis model, the

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Table 5ANOVA for SB and EFB pyrolysis ( = 0.95).

Variable Sum of squares Free degree Mean square F-test p-Value

Data for SB pyrolysisT 26.3558 1 34.7012 14.37 0.0020Dp 2.4839 1 0.8283 0.34 0.5674� 1.7676 1 2.6050 1.08 0.3166Residual 32.1409 14 2.4150Total (corrected) 118.2380 17

Data for EFB pyrolysisT 157.3110 1 157.3110 38.94 <0.0001Dp 0.0130 1 0.0130 <0.001 0.9560� 21.5960 1 21.5960 5.35 0.0370Residual 56.5620 14 4.0400Total (corrected) 267.015 17

Table 6ANOVA of the model adjusted for the EFB pyrolysis.

Variable Estimated Standard error p-Value

Constant −214.124 25.2565 <0.001T 0.734627 0.0859 <0.001� 2.94038 0.3669 <0.001�*Dp 0.054026 0.0115 0.0007�*� −0.0250646 0.0025 <0.001T2 −0.00054665 7.75E−05 <0.001T*� −0.0025607 0.0004 0.0001

Variable Sum of squares Free degree Mean square F-test p-Value

Adjusted model 263.1630 6 43.8605 125.23 <0.001

ptbrAhysirmm

B

TA

Residual 3.8527 11

Total (corrected) 267.0150 17

article size, the particle size square and the interaction betweenhe temperature and particle size are not taken into accountecause they are found to not be significant in the model, whichesults in a polynomial equation of the second order. In this case,NOVA analysis suggests removing the Dp·� term with a p-valueigher than 0.005 (marked in bold in Table 7). In the EFB pyrol-sis model, this term has the highest p-value, but it remainsignificant in those cases. For the SB pyrolysis model, remov-ng the term Dp·� leads to a degradation of the quality of theegression model, with R2 decreasing to 89.62%. The final adjustedodel, as described by Eq. (6), was thus kept for the SB pyrolysisodel.

io-oil YieldSB (wt%) = −639.54 + 3.37739 · T − 6.5421



·� − 0.024291 · Dp · � + 0.0193014 · T ·� − 0.0298856 · �2 + 0.0043017 · T2 (6)

able 7NOVA of the model adjusted for the SB pyrolysis.

Variable Estimated Standar

Constant −639.54 −140.05T 3.37739 0.70� −6.5421 1.61Dp*� −0.024291 0.00T*� 0.0193014 0.00T2 −0.0043017 0.01�2 −0.0298856 0.00

Variable Sum of squares Free degree

Adjusted model 117.8790 6

Residual 11.4864 11

Total (corrected) 129.3660 17

0.3502

3.4. Influence of the temperature and gas residence time on thebio-oil yield

The results obtained with ANOVA are useful to examine theinfluence of different variables on the bio-oil yield; accordingto these results, only the temperature and gas residence timewere analyzed. The results obtained during the Simplex optimiza-tion were used to generate the response surfaces by a physicalinterpolating method (Thin Plate Spline, TPS) on the OriginPro8®

software. Fig. 2 shows the influence of the temperature and gasresidence time on the bio-oil yield in the case of EFB and SBpyrolysis.

Fig. 2 confirms the results obtained with ANOVA, in which thegas residence time has less influence on the bio-oil yield in contrast


with the temperature, which it is the most important variable. Nev-ertheless, it is worth noting that the gas residence time influenceis apparently more important at higher temperatures.

d error p-Value

70 0.000525 0.000558 0.001948 0.200509 0.002278 0.000780 0.0032

Mean square F-test p-Value

19.6466 18.81 <0.0011.0442

dx.doi.org/10.1016/j.jaap.2014.04.003



time

imsytfl

3o

partmttmhtpt

Fig. 2. Influence of the temperature and gas residence

In all cases, the low influence of the gas residence time observedn this work is interesting at an industrial scale because even though

any studies [23,24] report that it is necessary to work with thehortest gas residence time (∼1 s) to guarantee the highest bio-oilield, the gas residence time may not be as relevant as previouslyhought and would in contrast involve the use of highest volumetricows of carrier gas, i.e., elevated costs.

.5. Influence of the temperature and gas residence time on therganic and aqueous phase yields

Figs. 3 and 4 represent the behavior of the organic and aqueoushase yields (wt% on a bio-oil basis) as a function of the temper-ture and gas residence time of bio-oil from EFB and SB pyrolysis,espectively. Both EFB and SB pyrolysis show the same behavior;he organic phase yield is favored by temperature until a maxi-

um, after which the yield slightly decreases for gas residenceimes lower than 30 s and more strongly for longer gas residenceimes. The gas residence time corresponds to the most important

aximal temperature obtained with both biomasses. On the other



and, the aqueous phase yield presents the opposite behavior tohat observed with the organic phase. In this case, the aqueoushase yield decreases with temperature until a minimum. Beyondhis temperature, the aqueous phase yield begins to increase and is

Fig. 3. Influence of the temperature and gas residence time on the (a) organic

on the bio-oil yield from (a) EFB and (b) SB pyrolysis.

greater for gas residence times longer than 50 s. The minimal tem-perature is observed in this gas residence time and corresponds to500–520 ◦C, approximately. A particular behavior is observed forthe SB biomass, for which the gas residence time is high, muchlonger than used in the EFB test. In these conditions (beyond 65 s),the organic phase yield tends to increase and the aqueous phaseyield to decrease. However, the change that is observed in theaqueous and organic phase yields is only 2 wt%, the same orderof magnitude as the standard deviation calculated using the exper-imental data.

It is possible to observe that the distribution between the phaseschanges with the gas residence time as a result of different reactionsthat occur consecutively or in parallel do not have the same kineticreaction rate. Miller and Bellan [25] propose a chemical reactionscheme of biomass degradation taking into account the three maincompounds (cellulose, hemicellulose and lignin). The first proposedstep implies the activation of the virgin biomass component that, inthe second step, is transformed into products (Tar, Char and Gas).The kinetic parameters proposed by the authors suggest that thekinetic rate of the first step for the cellulose is the fastest, followed


by hemicellulose and finally by lignin (much lower than the others).On the other hand, in the second step, specifically for the tar pro-duction, the kinetic rate for hemicellulose is the fastest, followed bycellulose, which is slightly lower, and by lignin, which is two times

and (b) aqueous phase yields (wt% on bio-oil basis) from EFB pyrolysis.

dx.doi.org/10.1016/j.jaap.2014.04.003


8 S. Vecino Mantilla et al. / Journal of Analytical and Applied Pyrolysis xxx (2014) xxx–xxx

rganic

sadlcBvzobtfidncipsr

bthc[

Fig. 4. Influence of the temperature and gas residence time on the (a) o

lower than the others. Therefore, the bell behavior observed for thequeous phase can be explained according to the vapors produceduring pyrolysis due to the degradations of cellulose, hemicellu-

ose and lignin that in the first step transform to “active” biomassomponents and in the last step react to produce the vapor phase.ecause the kinetic rates of those reactions are not the same, theapor phase must depend on the gas residence time in the reactionone. If the gas residence time is lower, only the fast reactions canccur, i.e., the tar formation from cellulose degradation constitutedy light compounds, such as formic and acetic acids and others, orhe tar formation from hemicellulose degradation constituted byurfural, furan and formic and acetic acids [26]. On the other hand,f the gas residence time increases, the tar formation from ligninegradation is present in the reactor, producing, for example, phe-ols (phenol, o-, m- and p-cresol, syringaldehyde) and other organicompounds [26], mostly present in the organic phase, that begin toncrease with gas residence time. The condition for which thesehenomena begin to present an opposed behavior is 30 s, whichuggests that the kinetic rate of cracking reactions is important,esulting in a decrease of the organic phase and bio-oil yields.

The behavior observed in Figs. 3 and 4 for gas residence timeselow 65 s can be explained by secondary reactions occurring in



he reactor, which are more important when the temperature isigher and the gas residence time is longer, producing more lightompounds, such as H2O, CO2, CO, H2 and C1–C4 hydrocarbons11]. The increase of the aqueous phase is favored by a second

Fig. 5. Organic phase (�), syngas (�) and char yields (�) as a func

and (b) aqueous phase yields (wt% on bio-oil basis) from SB pyrolysis.

degradation of products from that of the first degradation ofbiomass. This second degradation is the result of many reactions,such as repolymerization, recondensation and thermal crackingcatalyzed by the ash that is present in the biomass [9]; there-fore, the presence of inorganic material produces high amounts ofwater, gas and char [27]. Abdullah et al. [28] suggested that potas-sium is the best catalyst for secondary reactions, explaining whythe aqueous phase yield from EFB pyrolysis is higher than what isobtained with SB, as shown by comparing the B4 and R4 tests (seeTable 4).

The behavior of syngas, char and organic phase yields as a func-tion of the aqueous phase yield is presented in Fig. 5. The increaseof the organic phase yield is mainly the result of the decrease ofthe char yield, a phenomenon that is more important when SB isused as a feedstock for the pyrolysis. On the other hand, the syngasand organic phase yields increase with the aqueous phase yield,especially in the case of the SB tests. This can be explained basedon EFB composition, which presents more CF than SB, favoringchar formation and decreasing the volatile formation (gases andvapors). According to Fig. 5, the effect of secondary reactions ismore important for biomasses with lesser amounts of FC, favor-ing higher amounts of vapors. In other words, because SB pyrolysis


tends to produce more volatiles than EFB pyrolysis, it is possible toaffirm that the effect of secondary reactions in the reactor will begreater and, therefore, the production of vapors (including organicand aqueous phases of bio-oil and syngas components).

tion of the aqueous phase yield for (a) SB and (b) EFB tests.

dx.doi.org/10.1016/j.jaap.2014.04.003



Table 8Amount of moisture in the different phase of the bio-oil from SB and EFB pyrolysis.

Moisture (wt%) � (wt%) Moisture (wt%) � (wt%)

AqueousSB1 70.9956 0.8921 EFB1 71.1186 0.4705SB2 71.2531 1.1535 EFB2 69.7470 0.9453SB3 72.0381 0.8476 EFB3 71.3565 0.8329SB4 72.9849 0.7982 EFB4 76.7749 1.1196SB5 71.5789 0.6174 EFB5 72.2720 0.7062SB6 66.3308 0.6396 EFB6 69.7259 0.5027SB7 71.2256 0.7655 EFB7 70.6751 0.8629

EFB8 71.0732 0.4671EFB9 71.3163 1.0145

OrganicSB1 4.2707 0.4468 EFB1 2.0562 0.0045SB2 5.2421 0.4737 EFB2 2.4337 0.4112SB3 6.2059 0.4842 EFB3 2.6709 0.0499SB4 5.6519 0.4790 EFB4 2.7568 0.1636SB5 5.3821 0.4217 EFB5 1.6097 0.0298SB6 4.4251 0.4942 EFB6 2.5649 0.0223SB7 4.3058 0.3050 EFB7 2.3476 0.1481

EFB8 1.5925 0.1135EFB9 1.8303 0.0816

Table 9pH, density and high heat value for bio-oil produced from SB and EFB pyrolysis.

Physical properties of bio-oil from SB pyrolysis Physical properties of bio-oil from EFB pyrolysis

Test pH Density [kg/m3] HHV (MJ/kg) Test pH Density [kg/m3] HHV (MJ/kg)

Aqueous phase Organic phase Aqueous phase Organic phase

SB1 2.71 1028.45 1072.20 25.52 EFB1 3.84 975.80 914.40 28.62SB2 2.35 1036.70 1073.50 24.67 EFB2 3.58 975.40 948.10 30.93SB3 2.28 1036.35 1075.40 23.74 EFB3 3.55 975.60 957.70 30.67SB4 2.40 1033.96 1071.80 24.37 EFB4 3.58 976.50 952.50 33.15SB5 2.26 1032.06 1078.40 24.48 EFB5 3.94 972.05 958.15 34.91SB6 2.38 1037.08 1083.90 25.22 EFB6 3.44 978.30 956.54 29.02SB7 2.22 1035.20 1101.00 24.77 EFB7 3.59 985.90 966.50 32.23

3

datfb

ThmtahwmtafftwiEasTi

The organic phase composition can also explain the differencethat is observed in the bio-oil density values (see Table 9). Themost important compound present in the organic phase of bio-oil

Table 10Chemical composition of the organic phase in bio-oils.

Compound[

A/∑

Ai

]× 100 EFB4 SB4

Acetic acid 1.77 15.30Phenol 6.23 5.012-Methoxyphenol (guaiacol) 1.50 4.44Phenol, 2-methyl-(o-cresol) 0.48 2.55Phenol, 2-methyl-(cresol) – 2.64Phenol, 2,6-dimethoxy-(syringol) 2.89 5.35Pentadecane 0.77 –Hexadecanoic acid (methyl-ester)* 6.90 –Hexadecanoic acid* 14.19 –9-Octadecenoic acid, methyl ester * 57.76 –Octadecanoic acid, methyl ester 0.85 –9-Octadecenoic acid (z)-decyl ester* 6.12 –Octadecanoic acid 0.00 –Phenol, 2,6-dimethoxy-4-(2-propenyl) 0.51 –2-Propanone, 1-hydroxy – 3.802-Furancarboxaldehyde (furfural) – 32.272-Cyclopenten-1-one – 1.05

.6. Physical and chemical characterization of bio-oil

Table 8 shows the amount of moisture in each phase of the pro-uced bio-oil. In the aqueous phase, the moisture varies between 66nd 76 wt% depending on the operating conditions and the biomasshat is used for pyrolysis, much higher than in the organic phase,or which the amount of moisture is low, varying approximatelyetween 4 and 6 wt% for SB tests and 1 and 3 wt% for EFB tests.

The physical properties of each bio-oil are presented in Table 9.he pH was measured only in the aqueous phase, according to theumidity results presented in Table 8. The pH shows a high acidity,ainly for bio-oil from SB pyrolysis. The difference between the

wo bio-oils must be linked to their chemical compositions. Thequeous phase is rich in acids, sugars and other compounds withigh polarity [8], favoring low pH values. Typically, bio-oil fromood pyrolysis has a pH of approximately 2.5 [29], which is theost common value used to represent the mean pH of bio-oil. In

he case of SB, for García et al. [12], the bio-oil produced presented pH of 2.7, and according to Abnisa et al. [7], for bio-oil producedrom palm shell, the pH was 2.5. The values obtained in our studyor bio-oil from SB pyrolysis are close to those observed in litera-ure, in contrast to the pH of bio-oil produced from EFB pyrolysis,hich is higher. This result can be explained by the bio-oil chem-

cal composition and supposing that the bio-oil produced fromFB pyrolysis contains fewer carboxyl acids, e.g., acetic or formic



cid, according to Mohan [29] and more compounds with high pH,uch as phenols. This is in agreement with what is observed inable 10, which presents the most important compounds containedn the organic phase of each bio-oil produced by both SB and EFB

EFB8 3.65 975.60 971.00 32.45EFB9 3.88 988.00 982.00 28.22

pyrolysis. In this table, only EFB4 and SB4 are compared becausethose tests were performed at the same operating conditions(T = 520 ◦C, � = 49.95 s, 1 < Dp < 1.4 mm).


2-Furancarboxaldehyde, 5-methyl – 7.822-Cyclopenten-1-one, hydroxy-3methyl – 5.362-Cyclopenten-1-one, 2-hydroxy-3-ethyl – 1.25Benzeneethanol, 2-methoxy – 3.50

dx.doi.org/10.1016/j.jaap.2014.04.003

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roduced by EFB pyrolysis is 9-octadecenoic acid methyl ester oris-oleic acid methyl ester, which has a lower density than water870 kg/m3 at 20 ◦C [30]). In contrast, in the bio-oil from SB pyrol-sis, the main components are 2-furancarboxaldehyde or furfural,hich has a density of 1160 kg/m3 at 20 ◦C, and acetic acid with

050 kg/m3 [32]. On the other hand, for both biomasses, the den-ities observed for the two phases are similar but not the same,xplaining why the organic phase of bio-oil from SB tends to remainelow the aqueous phase, in contrast with what happens in the casef EFB.

Compared with standard specifications proposed in ASTM7544-12 for liquid biofuels from pyrolysis, the density require-ent for pyrolysis liquids as biofuels for use in industrial burners

anges between 1100 and 1300 kg/m3. However, although the den-ity of bio-oil produced by SB pyrolysis is slightly below the lowerimit value, the density of bio-oil from EFB pyrolysis is far fromhis range; nevertheless, it is worth noting that it almost fulfills theequirements for fossil fuel densities specified in ASTM D975-12amaximum density of 876 kg/m3).

For both biomasses, the higher HHV is obtained mainly for theaximum bio-oil yield (in bold in Table 9), the best value corre-

ponding to the bio-oil produced from EFB pyrolysis (34.91 MJ/kg).ccording to Table 9, the HHV value determined for EFB bio-oil pre-ented more dispersion in the range of the operating conditions ofur study, in contrast to SB bio-oil, which always showed similaralue of approximately 25 MJ/kg.

The maximum HHV observed for EFB bio-oil agrees with thatbserved by Abdullah et al. [26] and is higher than what wasbserved for other biomasses, such as SB (25.22 MJ/kg, in thistudy), corncob (26.22 MJ/kg [31]) and laurel (31.04 MJ/kg [10]).igh HHV values, as obtained with EFB, are very interesting andre similar to heavy fuel oil (approximately 42 MJ/kg [32]), whicheans that 1.2 kg of bio-oil produced from biomass can generate

he same quantity of energy than 1 kg of heavy fuel oil. Accord-ng to Table 10, the presence of organic compounds, such asentadecane, hexadecanoic acid methyl ester, hexadecanoic acid,-octadecenoic acid methyl ester, octadecanoic acid methyl esternd 9-octadecenoic acid (z)-decyl ester, advantageously promotesigh HHV values for the bio-oil produced from EFB pyrolysis. Thoserganic compounds stem from the vegetable oil that remains inhe EFB after the extraction step during the biodiesel process, andhey were not thermally degraded in the reactor. To confirm thisypothesis, the ethanol-toluene extractives (3.34 wt%) were ana-

yzed using the same GC/MS method proposed for the bio-oil. Theompounds that were identified by chromatography are showny an asterisk in Table 10 and confirm that the bio-oil from EFBontains the same organic compounds. This means that the liquidroduct obtained by EFB pyrolysis is a mixture of pyrolyzed com-ounds (resulting from the thermal degradation of lignocellulosiciomass) and volatile molecules (organic compounds of vegetableil).

. Conclusions

According to the experimental results of the Simplex method,he maximal bio-oil yield was obtained with SB as biomass; nev-rtheless, the bio-oil that presents the best physical–chemicalharacteristics was obtained using EFB at a temperature of 540 ◦C,as residence time of 31 s and particle size <0.5 mm. This workound a correlation model to mathematically describe the pyrol-sis process of SB and EFB. In both cases, this model corresponds



o a polynomial equation of the second order where temperatures the most significant variable, which agrees with the ANOVA, andan explain 91.12 and 98.56% of the variability in the data, respec-ively. The temperature is the most influential factor in the pyrolysis

[

[

PRESSnd Applied Pyrolysis xxx (2014) xxx–xxx

process, in contrast with gas residence time, i.e., it is not neces-sary to reach the lowest gas residence times to obtain the highestbio-oil yield; a gas residence time of 30 s is proposed to maximizethe organic phase yield. The bio-oil that can be obtained at theoptimal operating conditions of EFB pyrolysis presents an HHV of34.91 MJ/kg, a pH of 3.9 and a density of 958 kg/m3. The high HHV,high pH and low density values are attributed to the bio-oil chem-ical composition, which mainly consists of phenols and long chainFAME (fatty acid methyl ester), whereas carboxyl acids and furfuralare negligible.

Acknowledgements

The authors wish to thank the Universidad Industrial deSantander, Vicerrectoría de Investigación y Extensión, which finan-cially supported this study (projects no. 5445 and 5451).

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comparative study of bio-oil production from sugarcane bagasse and palm empty fruit bunch: yield...

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