1-s2.0-s0165237014000205-main

Journal of Analytical and Applied Pyrolysis 106 (2014) 177186

Contents lists available at ScienceDirect

Journal of Analytical and Applied Pyrolysis

journa l h om epage: www.elsev ier .co

Thermal behavior and kinetics of the pyrolysis ofexplod

Xiaoli Gu Lia

Zhongzha College of Cheb State Key Lab ou 510c Department o

a r t i c l e i n f o

Article history:Received 11 July 2013Accepted 27 January 2014Available onlin

Keywords:Pyrolytic behaSteam explosiPoplar wood s

a b s t r a c t

Steam explosion (SE) pretreatment has been an effective method for the upgrade of biomass, includingpoplar wood sawdust (PWS). The change of PWS components after SE treatment was investigated, e.g.,a signicant increase of extractives and decrease of hemicellulose content, while slight change in cel-

1. Introdu

Currentltrial energypetroleum increasing con sustaina5% of the wothis is proje

CorresponUniversity, Namobile: +86 13

E-mail add

0165-2370/$ http://dx.doi.oe 3 February 2014

vioronawdust

lulose and lignin contents. The pyrolysis characteristics of raw PWS and SE PWS were investigated bythermogravimetric analysis/infrared spectrometry (TG-IR) analytical technology. Pyrolysis of PWS wasperformed on a thermogravimetric analyzer at multiple heating rates of 10, 20, 40, and 80 C/min upto 1000 C to obtain the pyrolysis characteristics of PWS. TG results showed that both raw PWS and SEPWS presented three weight loss stages, respectively. It could be concluded that the pyrolysis processof the two PWS samples has similar characteristics, and the main pyrolysis temperature range of PWS isfrom 200 C to 500 C. The signicant difference between two types of PWS is that the SE pretreated PWSdisplayed a lower volatile content and higher xed carbon content than raw PWS, which could make SEPWS much more favorable in thermochemical application. Derivative thermogravimetric also showedthat one major decomposition reaction took place at a specic heating rate for two PWS feedstocks. Theheating rate mainly inuences the primary pyrolysis stage of the PWS, while the maximum weight lossrate and corresponding temperature change with increasing of heating rate. The evolved gaseous prod-ucts during PWS pyrolysis such as H2O, CO, CO2, CH4 and other volatile compounds were found. Assumingthat the decomposition obeys rst-order kinetics, kinetic parameters of PWS pyrolysis were determinedusing two methods proposed by Kissinger and Ozawa, respectively. Both methods gave analogous val-ues of activation energy for raw PWS and SE PWS samples, ranging from 134 kJ mol1 to 142 kJ mol1.This study gave further conrmation that the steam explosion pretreatment process could transformlignocellulosic biomass into an intermediate feedstock with favorable properties for thermo-chemicalapplications.

2014 Elsevier B.V. All rights reserved.

ction

y, 90% of all transportation energy and 40% of all indus- in the United States are derived from non-renewable[1]. The limited reserve of traditional fossil fuel andoncerns about environment pollution force us to focusble sources for green and renewable fuel. In 2006 onlyrlds primary energy consumption came from biomass,cted to increase to 10% by 2030 [2]. First-generation

ding author at: College of Chemical Engineering, Nanjing Forestrynjing 210037, China. Tel.: +86 25 85427624; fax: +86 25 85418873;951719315.ress: [email protected] (X. Gu).

biofuels, such as ethanol produced from starch, are not an effectiveoption for achieving this goal based upon the availability and cost ofsubstrate [3]. Due to the abundant supply of lignocellulosic biomassthroughout the world, research and development has been widelyfocused on converting lignocellulosic biomass into bio-based fuel,chemicals, and energy. Pyrolysis is the thermochemical decompo-sition of biomass at temperatures between 400 and 650 C in theabsence of O2. As one of the promising thermal approaches, pyroly-sis can be used to convert cheap, local, and abundant lignocellulosicbiomass such as grasses and trees into energy [47]. It playsan important role in the thermochemical conversion of biomassmaterials to bioenergy. Although there are several cost-intensiveways, e.g., esterication [811], hydrogenation [12,13], catalyticreforming [1416], and biological conversion [17], the pyrolysis isstill an effective method to optimize the conversion of biomass,

see front matter 2014 Elsevier B.V. All rights reserved.rg/10.1016/j.jaap.2014.01.018ed poplar wood sawdusta,b,c,, Cheng Liua, Xiangjin Jianga, Xu Maa, Lixianeng Lia

mical Engineering, Nanjing Forestry University, Nanjing 210037, Chinaoratory of Pulp and Paper Engineering, South China University of Technology, Guangzhf Chemistry & Biochemistry, University of Notre Dame, Notre Dame 46656, USAm/locate / jaap

the raw/steam

, Kanghua Chenga,

640, China

178 X. Gu et al. / Journal of Analytical and Applied Pyrolysis 106 (2014) 177186

Table 1Proximate, ultimate and component analysis of the PWS sample.

Proximate analysisa (wt%) Ultimate analysisb (wt%) Component analysisa (wt%)

Raw PWS SE PWS

Mositure CellAsh HemVolatile mat LignFixed carbon Ext

Car

a On dry basb Ash and mc Average and Estimatede Determinef Determine 58].

especially [18].

Recentlyrecognized order to imethanol proefcient prety of feedsDuring thispressed vapmake the supretreatme1.03 106 Ptages than rlinkage by hmal stabilitreducing thtion of SE indecade duein the lingnbe exploitegetic, and eprocess is bbio-fuels exethanol procrops, and fextent of eness of the echaracteristable for theduring steaduction oristalks [29], or soybean applied in ttent after ppretreatmenocellulosicof structurenation of thdifcult, whreactions. Upretreated

Thermogformed infa useful to[3941], poWith TG-FTevolved pr

rmorremeing bmpleeight

teuld beringwhictionthe ed asancear p

tic reomasood

posit52]. sis viechalso ed

SE Ptreat. Thetive tg rate evofect s thes. Ki

usinedgeteriz9.6 Carbon 45.5 3.7 Hydrogen 6.26

ter 75.54 Nitrogen 1.04 d 11.15 Oxygend 47.2

is.oisture free.d standard deviation of 3 replicates at 95% condence interval.

by difference.d according to the ASTM Standard Test Method E 1690-01.d by high-performance liquid chromatography (HPLC) analyses according to Ref. [

for some certain pretreated lignocellulosic biomass

, the steam explosion (SE) pre-treatment is a well-method to deconstruct the lignocellulosic materials inprove their digestibility during biotransformation forduction [19]. As one of the most cost-effective and

etreatment methods, SE process is suitable for a vari-tocks and benecial to environmental impact [2023].

pretreatment process, biomass is treated in hot com-or, and then the pressure is suddenly decreased, whichbstrate undergo an explosive decomposition. With highnt temperature above 150 C and high pressure abouta, the substrate biomass would take much more advan-aw biomass, e.g., adequate disruption of carbohydrateydrolysis of the hemicellulose [24], enhancing the ther-y of lignin and crystallinity of cellulose [25,26], ande alkali ion content of the samples [27,28]. The applica-

wood treatment has increased considerably in the last to its potential to make chemical and structural changesocellulosic biomass [2932], which means that SE couldd greatly to offer new opportunities in industrial, ener-nvironmental elds [3336]. Besides, SE pretreatmentenecial to improve new strategies about renewabletracted from the biomass. For example, the biomass forduction include lignocellulosic material such as wood,orestry residues. The key factors inuencing the rate andnzymatic hydrolysis of biomass include the effective-nzymes and the chemical, physical, and morphologicalics of the substrates [37]. SE process is especially suit-

latter factor due to autohydrolysis and debrillationm treatment, which are conrmed in bioethanol pro-ginated from different biomass sources, e.g., sunowereel grass [30], wheat straw [31], olive tree pruning [32],hulls [38]. In addition, SE pretreated biomass could behermochemical application due to its higher solid con-yrolysis. For all the reasons above mentioned, the SE

Furthemeasuincludthe sathe wuniformters coconsidsition, applica

On regardabundfor sugpyrolyand bibirch wdecomment [pyrolyysis mwere aperformpared SE pretigatedderivaheatingate thThe efwell asampleminedknowlcharacdate.nt is regarded as an effective tool for improving the lig- material exploitation. However, due to the complexity

and the heterogeneity of components, the determi-e pyrolysis process of SE pretreated biomass is veryich consists of lots of physical changes and chemicalntil now there is rare literatures of the pyrolysis of SEbiomass.ravimetric (TG) analysis coupled with Fourier trans-rared (FTIR) spectroscopy has been proved to beol to investigate the thermal behavior of biomasslymer [4244], even waste thermal degradation [45,46].IR analysis, thermal decomposition characteristics andoducts during pyrolysis could be easily conrmed.

2. Experim

2.1. Materi

The popstock, suppand Paper results are l[52]. Prior tfor 3 h, the oof

X. Gu et al. / Journal of Analytical and Applied Pyrolysis 106 (2014) 177186 179

reacto

2.2. TG-FTIR

TG-FTIRwith our fowas used asexperimentavoid therm(1080 C/mWe repeateis about 3results. To Fsignal, so apThe samplethe volume

The quatrometry iAccording tcompound

A = abc

where A is ta is the molof source bsample. Thiare linearlyin a homogquanticatiderivatives,the peak ar

2.3. Steam

The SE ptor capable

10ger, harghai, ork

in Fi eachFig. 1. Sketch of the steam explosion

quantitative analysis

analysis instrument and operational condition are samermer report from Ref. [52]. Nitrogen of purity >99.99%

carrier gas to provide an inert atmosphere. During the the cell of TG is ushed with 100 ml/min nitrogen toal decomposition of the sample. A certain heating rate

of 1.03exchanof disc(Shangand a wshown

For

in) was applied, with a nal temperature of 1000 C.

d three times for each heating rate with the error range% in order to obtain the representative experimentTIR, a weight loss about 10 mg usually gives adequateproximately 15 mg of samples was used in this study.

was loaded into the Al2O3 container for each run with of 70 l.ntitative analysis of each component absorption spec-s based on the BouguerBeerLambert law [54].o this law, the absorbance at any frequency for a singlein a homogenous medium is expressed as:

he measured sample absorbance at the given frequency,ecular absorptivity at the frequency, b is the path lengtheam in the sample, and c is the concentration of thes law implies that the intensities of absorption bands

proportional to the concentration of each componentenous mixture or solution [54]. Therefore, a number ofon parameters, including peak height, peak area, and

could be used in quantitative analysis. In this study,ea was used as the quantication parameter.

explosion pretreatment method

retreatment was performed in a 10 l stainless steel reac- of reaching a temperature of 185 C and a pressure

into water finto the remaintainedSE pretreatmpressure, 9steam explto 5.52 10discharged treatment, at room tem

2.4. Kinetic

Kissingeferential anapplied to at differentusual case oheating ratature and tfollowing d

d

dt= k f (

where =r system.

6 Pa. The reactor was equipped with a tubular heatelectrovalves for steam admission, and a ball valvee. The steam generator was a Yano YN30-0.7-D boilerChina), with a maximum steam production of 43 kg h1

ing pressure of 1.03 106 Pa. A sketch of the reactor isg. 1.

SE pretreatment run, raw PWS sample was immersed

or 12 h at room temperature, and then was introducedactor, and operational conditions were reached and

by charging steam. Common operational conditions toent were: temperature of operation, 180 C; treatment

.65 105 Pa; discharge pressure, 5.52 105 Pa. Afterosion treatment for 10 min, the pressure was reduced5 Pa, and then the sample with steam was suddenlyinto the blowing tank at atmosphere pressure. Afterthe SE sample was thoroughly washed with water, driedperature and stored in vacuum.

models for PWS pyrolysis

r [55] and Ozawa [56] methods were respectively dif-d integral thermal analysis methods which could bedetermine the apparent activation energy of pyrolysis

heating rates. In non-isothermal kinetics, for the mostf a linear heating program corresponded to a constant

e, the dependence of the reaction rate on the temper-he extent of the reaction could be described by theifferential equation (Eq. (1)):

) = k(1 )n (1)

1 m(t) mfm0 mf

, k = A exp(

ERT

)(2)


m(t) was the experimental mass at each monitoring time, mf was thenal mass, and m0 was the initial dry mass. f() was the differentialform kinetic mechanism function and k was the kinetic constantwhich, according to the Arrehenius equation, was a function of thepre-exponential factor (A), apparent activation energy (E), absolutetemperature (T) and constant of ideal gas law (R). n was the reactionorder number and pyrolysis of wood sawdust was largely describedby rst order Arrhenius law [57].

Substitution of Eq. (2) into Eq. (1) yields

d

dt= A exp

( E

RT

)(1 )n (3)

For a linear heating rate, = dT/dt, Eq. (3) becomes

d

dT=(

A

)exp

( E

RT

)(1 )n (4)

The temperaturetime relation was computed from followingexpression (Eq. (5)):

T = T0 + t (5) whose unit was C/min was the constant heating rate, and T0 wasthe initial temperature, Tp was the maximum peaks of DTG curvestemperature.

The function (Eqs. (6) and (7)) was deduced via Eqs. (1)(5), asfollows:

ln

(

T2p

)=

ln() = ln

where g(

Eqs. (6) aactivation eand of Ozawics mechanon the fact with an incran integral heating ratthe heatingin which thculated fromKissinger an

beneted from fast measurement, wide range of temperature andbroad use, were applied in the experiments.

3. Results and discussion

3.1. Lignocellulosic composition of raw and SE PWS

Table 1 shows the lignocellulosic composition of raw and steamexploded PWS samples. As can be observed in Table 1, the SE pro-cess had a clear effect on the chemical composition of the treatedPWS. In detail, there was a clear increase in the percentage ofextractives in the exploded samples (increase of 6.148.54%). Thisincrease could be partly associated with the degradation of lignincaused by the SE pretreatment [37].

Meanwhile, there was a signicant decrease in the hemicel-lulose content after SE treatment, which could be explained thathigher temperature and pressure promoted to reach a constantdegree of hemicellulose solubilization or degradation, causing anincrease in extractives, as already described. Removal of hemicel-lulose with SE pretreatment has been well reported. Hendriks andZeeman [59] have described the degradation of isolated hemicel-lulose with steam and the formation of acids that could catalyzefurther hydrolysis (autohydrolysis). Ruiz et al. [29] have alsoreported the degradation of cellulose and mainly hemicellulosesof sunower stalks. Other authors have found a loss of 30% of

(theE [60lso

[61].or cetme

biomass

mpeadind ceot shgh Sllulocomr detdecoas

E prepolym

O

O

Schem f cellu ERTp

+ ln(

AR

E

)(6)

AE

Rg() 5.331 1.052 E

RTp(7)

) = ln(1 ) when n = 1.0 (8)nd (7) provided the formula for calculating the apparentnergy (E) and the pre-exponential factor (A) of Kissingera, respectively. g() was the integral form of the kinet-

ism function in Eq. (7). Kissingers method was basedthat the reaction rate d/dt rose to a maximum valueease in reaction temperature [55]. Ozawas method wastechnique which expressed straight lines at differentes according to relationship between the logarithm of

rate and reciprocal temperature at constant mass loss,e apparent activation energy of degradation was cal-

the slope of linear relationships [56]. The methods ofd Ozawa, as two sorts of non-isothermal kinetics which

xylosewith Swere areport

As fpretreation ofof biomhigh telose, leof woodoes nAlthouhemicemal deFurthelulose

It wafter Sand re

O

OH

OH

CH2OH

*

O

OH

OH

CH2OH

O

O*

n

O

OH

OH

CH2OH

OH

SE

Hyd rolysis

Cellul oseGluco se

O

OH

OH*

O

OH

OHO

O*

n

O

OH

OH

OH

SE

Hydrolysis

Hemicellulo se

(Xylan)

Xylose

e 1. Reaction sequence for consecutive decomposition and degradation reaction o major component of hemicellulose) in bamboo treated]. A removal of about 50% of xylan or hemicellulose

found after SE of Eucalyptus globulus in a previous

llulose content, it showed slightly change during the SEnt. Previous studies showed that cellulose decomposi-ass was related to alkali metal content and crystallinity[62,63]. Yamashiki and coworkers [64] explained thatrature water penetrated to the amorphous part of cellu-g to recrystallination by releasing free water moleculell during SE treatment. However, increased crytallinityow any dependency on cellulose decomposition [26].E pretreatment played signicant roles in alteration ofses, the effect of SE might be independent on the ther-position of cellulose under the examined conditions.ailed research is required to explain this nature of cel-mposition of pretreated biomass.also indicated that lignin content slightly increasedtreatment, which might be attributed to condensationerization reaction between decomposition product of

HO CHOHOH2C

SE

Degradation

Hydroxymethylfufural (HMF)

H

O CHO

SE

Degradation

Furfural

lose and hemicellulose (xylan) during steam explosion (SE).


Table 2Weight loss of raw PWS and SE PWS at different stages (%).

Sample Temperature range (C) Total

500

Raw PWS SE PWS

hemicelluloat similar rfrom hemicfraction of aseverely molignin [25].

3.2. Therma

In ordertics of raw were conduing rate of species are be divided released garelease whebiomass [66the temperasharply witPWS and ing to the mis nearly thgas species which indicstage (detaicontinues iamount of gple, comparis apparentcarbohydration of polycleavage ofof carbohydmonomericfurfural, thuScheme 1) [

It can alsraw PWS anture divisioII, the tempepyrolysis rastages is shraw PWS isvolatiles ocwhich mayvolatiles weexplosion tr

3.3. Effect o

Fig. 3a aPWS at the iments werPWS startetion continuyield dropprate as the t

20

40

60

80

100

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Deriv

. Weig

ht (%

/min

)

(321 ,-17.5)

I II III

(a)

0 200 40 0 600 80 0

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Temp erature (oC)

CO2

CH4

CO

H2O

0

20

40

60

80

00

(31 7,-15.9)

IIIIII

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Deriv

. Weig

ht (%

/min

)

0 200 40 0 60 0 80 0

00

05

10

15

20

Temperature (oC)

CO2

CH4

CO

H2O5.03 67.76 5.81 78.602.12 60.37 0.06 62.55

se and lignin [26]. According to Chau and Wayman [65],eaction condition with SE, some reactive componentsellulose, e.g., furfural, may react with lignin and increasecid insoluble lignin. In addition, lignin structure can bedied, which could also increase the apparent yield of

l behavior analysis

to compare the difference of the pyrolysis characteris-PWS and SE PWS, pyrolysis of these two PWS samplescted by TG-FTIR under a nitrogen atmosphere at a heat-20 C/min. The weight loss of PWS and released gasshown in Fig. 2. The pyrolysis of the PWS substrate couldinto three stages according to the weight loss rate ands species. The initial decrease in weight is due to waterre temperature is below 200 C, which occurs in most]. The second stage is the primary pyrolysis of PWS, asture increases from 200 to 500 C, the weight decreasesh the maximum weight loss rate of 17.5%/min for raw15.9%/min for SE PWS. The temperature correspond-aximum weight loss rate of these two PWS samples

e same with the value about 320 C. A large amount ofsuch as CO2, CO, CH4 and H2O are released in this stage,ate that they mainly come from this primary pyrolysisled discussion seen in Section 3.4). As the temperaturencreasing, the weight variation is very small and lessas species are released, especially for SE PWS. For exam-ed with raw PWS, CO2 emission from SE PWS pyrolysisly decreased, which could be explained by the loss oftes during the SE pretreatment. Actually, depolymeriza-saccharides, originated from SE pre-treatment through

glucosidic linkages, could be desirable for conversionrates through steam permeation processes. Besides,

carbohydrates might be further degraded into HMF ands a true component loss of carbohydrate occurs (see67].o be seen from Fig. 2a and b that the pyrolysis process ofd SE PWS has similar characteristics, such as tempera-n at three pyrolysis stages, gas species emission at stagerature of start pyrolysis, nish pyrolysis, and maximumte. The weight loss of these two PWS at three differentown in Table 2, which shows that the total weight loss

higher than SE PWS. This means that the evolution ofcurs more easily during the pyrolysis of raw biomass,

be interpreted by the fact that the substances causingre partially converted into aqueous chemicals in steameatment.

f heating rate on thermal raw PWS and SE PWS

nd b shows the mass loss curves of raw PWS and SExed heating rates from the TG experiments. TG exper-e carried out at the heating rates of 1080 C/min. Raw

Weig

ht (%

)R

ela

tive Inte

nsity

1

Weig

ht (%

)

(b)

0.

0.

0.

0.

0.

Rela

tive Inte

nsityd to decompose at 200 C and signicant decomposi-ed until the temperature reached 500 C, where mass

ed to 2530%. After that, pyrolysis progressed at sloweremperature increased to 1000 C, where the nal yield

Fig. 2. Weight loss and released gas species of the PWS at a heating rate of 20 C/min:(a) raw PWS and (b) SE PWS.


20

40

60

80

100

80oC/min

We

igh

t (%

)

(a)

20

40

60

80

100

We

ight (%

)

(b)

Fig. 3.

reached abopared with occurred inmass yield ilarly, decommass yield

Fig. 3 alsyield in ththat the nand SE PW1080 C/mthe fact thasolid resistament. The rof ash. The 0.35 g/g SE-at 500 C, xfeedstock dyields wereOn the mas

50

40

30

20

10

0(a)

0100 20 0 300 40 0 50 0 60 0 700 800 900 10 00

40oC/min

20oC/min

10oC/min

Temperature (oC)

o

-

-

-

-

-

Deriv. W

eig

ht (%

/min

)

(b)100 200 300 400 500 600 700 80 0 900 1000

80 C/min

40oC/min

20oC/min

10oC/min

Tem pera ture (oC)

Curve of TG (a) and DTG (b) for PWS at different heating rates.

ut 20% (see Fig. 3a). SE PWS performed differently com-raw PWS in TG experiments. Signicant decomposition

a narrower temperature range (200400 C) and thedropped less dramatically, only from 90% to 40%. Sim-

position continued at slower rates until the ultimatereached about 35% (see Fig. 3b).o indicated that there was nearly no changes of masse temperature range of 5001000 C. It was shownal weight is about 1525% and 3040% for raw PWSS, respectively. In the measured heating rate range ofin, the weight loss change of substrate PWS is due tot the increased cellulose crystallinity made the PWSnt to the thermal decomposition during SE pretreat-esidue left was mostly xed carbon and a trace amountxed carbon yields were about 0.20 g/g raw PWS andPWS. On the basis of the mass yield of SE pretreatmented carbon yield increased by about 70% per 1 g biomassue to steam exploded effect. On the other hand, volatile

80% for raw PWS and 65% for steam exploded PWS.s yield, SE treatment reduced the volatile yield by 23%.

-40

-30

-20

-10

Deriv. W

eig

ht (%

/min

)

Fig. 4. DTG

These couldapplication

Fig. 4 ssponding toSE PWS, therates; (2) a narrow temheating ratthan that foof PWS subof other bio

In additindicated abiomass asthat the pyis much infrom the d500 C (corheating ratFor raw PW100 200 300 40 0 500 600 700 800 900 100 0

80oC/min

40oC/min

20oC/min

10oC/min

Temperature (oC)Temperature (oC)

100 20 0 300 40 0 500 60 0 70 0 800 900 100 0

80K/min

40K/min

20K/min

10K/min

curves for raw PWS (a) and SE PWS (b) at different heating rates.

make SE PWS much more favorable in thermochemical because of its higher solid content after pyrolysis.hows the derivative thermogravimetry (DTG) corre-

mass loss data shown in Fig. 3. For both raw PWS andre were common trends: (1) four peaks for four heatinglarger peak at higher heating rates; (3) peak located in aperature range; (4) a higher peak temperature at higheres; (5) larger absolute DTG values (%/min) for raw PWSr SE PWS. These thermogravimetric curves of pyrolysisstrate were found comparable to similar pyrolysis studymass reported in the literature [49,68].ion, studies conducted on the inuence of heating raten increase in thermal lag occurs on the pyrolysis of

the heating rate increases [69]. It is obviously shownrolysis process of PWS with increase of temperatureuenced by heating rate, and differences can be seenetails of the primary pyrolysis ranging from 200 C toresponding to stage II in Fig. 1), which indicate thate mainly inuences on the primary pyrolysis stage.S and SE PWS, the curves of weight loss and weight


Fig. 5. 3D infrared spectrum of evolution gases during raw PWS (a) and SE PWS (b) pyrolysis at the heating rate of 20 C/min.

loss rate versus temperature shift toward the right as the heatingrate increases. The DTG curves for different heating rates (Fig. 4)showed that the rate of decomposition shifted to a higher mag-nitude and the main peak became broader as the heating rateincreased. For example, the maximum mass loss rate (%/min) occursat about 30

at 80 C/miattributed ttion effectswill have eto take placrate there wlel and serie[70].

3.4. Three-dimensional FTIR spectra analysis

In order to obtain information about the evolution with the tem-perature of the composition of the gases evolved from TG furnace,the 3D FTIR spectrum of the evolved gases and volatile compounds

PWSancecan b

30 ts wrdan

obteous

mon

Fig. 6. FTIR sp(iii) 400 C, (iv1.6 C at a heating rate of 10 C/min, whereas, thatn occurs at about 344.6 C for SE PWS. This could beo heat ux and initiation of secondary cracking reac-. The reason for these changes is that PWS particlesnough time to heat uniformly and for slow reactionse at lower temperatures. However, at very high heatingill be enough heat to initiate multiple complex paral-s reactions for hydrocarbon evolution from the sample

of raw absorbure, it 10 andproducIn accospectraing gascarbonectrum for pyrolysis products evolving from raw PWS (a) and SE PWS (b) with different) 500 C. and SE PWS pyrolysis including information on infrared, wave number and time are shown in Fig. 5. In this g-e concluded that most of the gas was evolved betweenmin. Several FTIR spectra of all the pyrolysis volatileere selected for primary analysis at different times.ce with the TG data in Fig. 3, the characteristics ofained at 200500 C are shown in Fig. 6. The follow-

species were qualied by the spectra: carbon dioxide,oxide, methane, water, etc. temperatures at the heating rate of 20 C/min: (i) 200 C, (ii) 300 C,


1.60

-10.5

-10.0

-9.5

-9.0

-8.5

ln(B

/T2)

raw PWS experiment

SE PWS experiment

raw PWS fitting curve

SE PWS fitting curve

As seen ysis were In the initin wave nwhile, non40003400pyrolysis temetric stre11311077pounds, e.gthe region obonyls (incltemperaturrelated to C(IR) absorbatemperaturwas decrea

Accordina specic w[54]. Thus tcess reectcarbon dioxucts such ahydrocarbogases evoluthe releasewere in agrFig. 2a and and other oimum valuee.g., 321 C other produimum prodmore energOCH3 an

group CHtion producbridges of l

Table 3Activation ene

Biomass

Raw PWS SE PWS

a R2, correla

1.60

3.0

3.5

4.0

4.5 raw PWS experiment

SE PWS experiment

raw PWS fitting curve

SE PWS fitting curve

lnB

ndar0 C,

wate. Wickinyrolyrs 23e in . As tper

00 C400n of com

cokinill beiew S py2002 w

c speehydizati

netic

h thergy

and 1.62 1.64 1.66 1.68 1.70 1.72 1.74 1.76

1/T (1/K)

Fig. 7. Kissinger method for raw PWS and SE PWS.

in Fig. 6, the evolved gases of raw or SE PWS pyrol-both indentied by their characteristic absorbance.ial pyrolysis stage (at 200 C), CO2 was presentedumbers 24002250 cm1 and 780600 cm1. Mean--conspicuous peak was shown in the wavenumbers

cm1, which means very little H2O evolved. Withmperature increased to 300 C, very little C O asym-tching absorbance wave appeared in the wave of

cm1, indicating the existence of hydroxyls com-., alcohols [71]. The C O stretching absorbance peaks inf 19001650 cm1 were representative of furans or car-uding aldehyde or ketone compounds). As the pyrolysise reached 400 C, adsorption wave in 30002700 cm1,

H asymmetric stretching for CH4. The similar infrarednce of raw PWS and SE PWS was both observed at thee of 500 C, and the absorbance wave mentioned abovesed to some extent with the temperature increases.g to the LambertBeer law, the adsorption spectrum atave number is linearly dependent on gas concentrationhe variation of absorbance in the whole pyrolysis pro-s the concentration trend of the gas species. Except foride appears two conspicuous peaks, other volatile prod-s CH4, CO, H2O, esters, carbonyl groups and aromaticns show one distinct peak. It was shown in Fig. 6 that thetion was mainly concentrated between 200 and 500 C,

of CO, CH4, H2O, and hydroxyl/carbonyl compoundseement with weight loss thermogravimetric data (seeb). In detail, it is observed that visible peaks of CO, H2O,rganic volatiles evolution emerges and reaches the max-s during the sharp mass loss stage at around 300 C,

2.0

2.5

in secoand 50boundsamplethe craPWS pnumbeincreas300 Cthe temuntil 8below reactiocess acend ofCO2 w

In vSE PWbelow and COorganiand aldcarbon

3.5. Ki

Wittion enslope for raw PWS and 317 C for SE PWS. Compared withcts, the evolution of CH4 is delayed and reaches its max-uction at the higher temperature, due to the fact thaty is required to crack a weakly bonded methoxy groupd the break of having higher bond energy of methylene2 [72]. Carbon monoxide was one of the decomposi-ts of ether groups, which may originate from the etherignin subunits connection and/or the ether compounds

rgy and Arrhenius constants obtained using Kissingers method.

E (kJ mol1) A (min1) R2 a

138.65 1.704 1012 0.936134.79 8.846 1011 0.973

tion coefcient.

seen from 134.79 kJ mOzawas mewere obtain(Fig. 8). Taband 137.54

Kinetic pture range Kisssingers

Table 4Activation ene

Biomass

Raw PWS SE PWS

a R2, correla1.62 1.64 1.66 1.68 1.70 1.72 1.74 1.76

1/T (1/K)

Fig. 8. Ozawa method for raw PWS and SE PWS.

y cracking of volatiles. In the temperatures between 200 H2O released mainly from the evolution of bulk water,r and crystallization water in mineral substance in PWSth the temperature increases, the water produced fromg or reaction of oxygen functional groups occurred insis. A different trend of the carbon dioxide (at wave58 cm1) was observed that the content increases withtemperature and reached the maximum peak at abouthe temperature exceeded 400 C, the decreased CO2 inature of 300400 C, remained a certain concentration. This is due to the CO2 releases from volatile matter

C. As the temperature increases, the polymerizationcoking in solid phase is primary reaction, and this pro-panies the emission of low concentration CO2. At theg polymerization reaction, the absorbance intensity of

decreased.of the above FTIR spectra analysis, both raw PWS androlysis process were subdivided into three steps: (1)C, some gaseous compounds, such as H2O, CH4, COere detected; (2) between 200 C and 500 C, volatilecies besides gases, including furans, phenols, ketoneses, etc., were evolved; (3) at temperature above 500 C,

on and char formation occurred.

parameters of PWS pyrolysis

e operative equation of Kissingers method, activa- and pre-exponential factor were calculated from theintercept of the tting linear line (Fig. 7). It can be

Table 3 that the activation energies were 138.65 andol1 for raw PWS and SE PWS, respectively. Usingthod, the activation energy and pre-exponential factored from the slope and intercept of the tting linear linele 4 showed that the activation energies were 141.25

kJ mol1 for raw PWS and SE PWS, respectively.arameters were determined for the specic tempera-

instead of the whole temperature range. For example, and Ozawas methods use the peak temperature for

rgy and Arrhenius constants obtained using Ozawas method.

E (kJ mol1) A (min1) R2 a

141.25 1.677 1012 0.944137.54 7.152 1011 0.977

tion coefcient.


each heating rate. Using both approaches, the activation energieswere very analogous (138.65 kJ mol1 vs. 141.25 kJ mol1 for rawPWS, 134.79 kJ mol1 vs. 137.54 kJ mol1 for SE PWS).

It can be seen that activation energy of volatile evolution fromSE PWS is lolution of voPWS, whereimplies thaings. The dpretreated ysis.

4. Conclus

Applicatcomponentpyrolysis chpretreated nology. Kincharacteristobtained co

(1) A clear contentture anddegradaslightlyconditio

(2) The pyracteristto the wysis temthe primtion, thof the Sto its hipyrolysless aggcant decslower r

(3) Heatingand botversus tincreasedo not tive thethermoinvestig

(4) Kinetic two meBoth massumpThe valuthe twoenergy raw PW134 kJ mmethodsion coumay be

Acknowled

A projecment of Jia

grateful to Natural Science Fund in Jiangsu Province of China(BK20130963), the opening funding of State Key Laboratory of Pulpand Paper Engineering in South China University of Technology(201209), National College Students Practice and Innovation Train-

ojectnovaangs

Teacfor P

nces

. Energ4(201rnatio. Enerartmohan

ical re. Vispudity fe

(201. Panherm41.u, Z.F.

vapo10) 18ng, P.uperc. Xio

-oil usan, C

od lign008) hao, Yversiotion 4. Ellio(2007ang, Qrotrey Rese. Gayuate conols, . Gayution oldehy(2004. Nilstion oalytic

Meso.C. Chtion, I. Bridmass, assnetmenatar, Jductioam-ex939i, G. H

its crrce Te

Zhu, X: tech

(201umarocellul & En. Negrarioulosion

Ramoterials. Bisw

struccessinwer than that from raw PWS. This means that the evo-latiles occurs more easily during the pyrolysis of SEas for the pyrolysis of raw PWS, high activation energyt the reaction needs more energy from the surround-etails of the reaction mechanism for steam explosionPWS will be a future topic of interest in the PWS pyrol-

ions

ion of steam explosion (SE) signicantly inuenced thes and thermal decomposition behavior of PWS. Thearacteristics of the raw PWS and the steam explosionPWS were investigated by TG-FTIR analytical tech-etic measurement and calculation showed differentics of steam exploded lignocellulosic biomass. Thenclusions are as follows:

increase of extractives and decrease of hemicellulose was investigated due to the fact that higher tempera-

pressure promoted hemicellulose solubilization andtion during SE pretreatment. Meanwhile, it showed

change about cellulose and lignin contents under SEn.olysis process of raw PWS and SE PWS has similar char-ics which could be divided into three stages accordingeight loss rate and released gas species. The main pyrol-perature range of the PWS is from 200 C to 800 C withary pyrolysis occurs from 200 C to 500 C. In addi-

e total weight loss of the raw PWS is higher than thatE PWS, which make SE PWS more advantageous duegher solid content after pyrolysis. Within this primaryis temperature range, pyrolysis of SE PWS progressedressively than that of raw PWS. After this initial signi-omposition, the pyrolysis reactions continued at muchates with temperature increasing to 800 C.

rate mainly inuences the primary pyrolysis stage,h of the curves of weight loss and weight loss rateemperature shift toward the right as the heating rates, while the nal weight are all about 2040%, whichchange much with heating rate. The resulting deriva-rmogravimetry also veried that SE PWS was morechemical favorable than raw PWS in the conditionsated.parameters of PWS pyrolysis were determined usingthods proposed by Kissinger or Ozawa, respectively.ethods were applicable in this study, based upon thetion that the decomposition obeys rst-order kinetics.es for activation energy were quite comparable using

methods, and both methods showed the activationof volatile evolution of SE PWS was lower than that ofS. In detail, the apparent activation energy ranges fromol1 to 142 kJ mol1 with both Kissingers and Ozawass. All above results further conrmed that steam explo-ld turn lignocellulosic biomass into a solid fuel, whicha favorable feedstock for thermochemical application.

gements

t funded by the Priority Academic Program Develop-ngsu Higher Education Institutions. The authors are

ing Prand Infrom JiYoungFunds

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Thermal behavior and kinetics of the pyrolysis of the raw/steam exploded poplar wood sawdust1 Introduction2 Experimental2.1 Materials2.2 TG-FTIR quantitative analysis2.3 Steam explosion pretreatment method2.4 Kinetic models for PWS pyrolysis

3 Results and discussion3.1 Lignocellulosic composition of raw and SE PWS3.2 Thermal behavior analysis3.3 Effect of heating rate on thermal raw PWS and SE PWS3.4 Three-dimensional FTIR spectra analysis3.5 Kinetic parameters of PWS pyrolysis

4 ConclusionsAcknowledgementsReferences

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