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Waste biomass to liquids: Low temperature conversion

of sugarcane bagasse to bio-oil. The effect of combined

hydrolysis treatments

Josilaine A. Cunha a, Marcelo M. Pereira a, Ligia M.M. Valente a,Pilar Ramrez de la Piscina b, Narcs Homs b,c,*, Margareth Rose L. Santos a,**aUniversidade Federal do Rio de Janeiro, Centro de Tecnologia, Instituto de Qumica, Departamento de Qumica Inorganica, Cidade

Universitaria, Rio de Janeiro, 21949-900 RJ, Brazilb Departament de Qumica Inorganica and Institut de Nanociencia i Nanotecnologia, Universitat de Barcelona, C/Mart i Franques 1-11,

08028 Barcelona, SpaincCatalonia Institute for Energy Research (IREC), C/Jardins de les Dones de Negre 1, 08930 Barcelona, Spain

a r t i c l e i n f o

Article history:

Received 10 March 2010

Received in revised form

9 February 2011

Accepted 10 February 2011

Keywords:

Biomass

Sugarcane bagasse

Pyrolysis

Bio-oil

LTC-pyrolysis

Biofuels

a b s t r a c t

This article describes the influence of different sugarcane bagasse hydrolysis pretreatments

on modifications to biomass feedstock and the characteristics of the resultant pyrolysis

products. Sugarcane bagasse was pretreated with acid, alkaline or sequential acid/alkaline

solutions and pretreated samples were then subjected to a low temperature conversion (LTC)

process under He or O2/He atmospheres at 350e450 C. Both pretreated samples and

sugarcane bagassein naturawere analyzed by determination of their chemical composition

and by thermogravimetric, FTIR and SEM analyses. The gases yielded during LTC were

monitored on-line by quadrupole mass spectrometry, and the liquid fractions obtained were

characterized by FTIR and 1H and 13C NMR. Irrespective of the sugarcane bagasse pretreat-

ment applied, the main bio-oil component obtained was levoglucosan. However, the LTC

yield of bio-oil depended on the hydrolysis treatment of the biomass and decreased in the

presence of O2. The acid hydrolysis pretreatment increased the LTC bio-oil yield notably.

2011 Elsevier Ltd. All rights reserved.

1. Introduction

The demand for energy is growing at a rapid rate due to an

increase in both world population and industrialization. There

is a recognized need, therefore, to move toward sustainable

energy production in order to reduce greenhouse gas emis-

sions and fossil fuel dependence[1e3].

In this context, biomass has been shown to be a potential

source of renewable energy. Thus, both developing and

industrialized countries are now seeking new technologies

which can efficiently transform biomass resources intoalternative fuels [4]. The use of agricultural waste or agri-

cultural residues for these purposes, in principle, does not

add carbon dioxide to the atmosphere, in contrast to the use

of fossil fuels [5e7]. Moreover, second-generation biofuels

will not compete with food crops, since the raw material

they use is the crop wastes that would otherwise be dis-

carded[8e10].

* Corresponding author. Dep artament de Qumica Inorganica and Institut de Nanociencia i Nanotecnologia, Universitat de Barcelona,C/Mart i Franques 1-11, 08028 Barcelona, Spain.** Corresponding author.

E-mail addresses:[email protected](N. Homs),[email protected](M.R.L. Santos).

A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m

h t t p : / / w w w . e l s e v i e r . c o m / l o c a t e / b i o m b i o e

b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 1 0 6 e2 1 1 6

0961-9534/$ esee front matter 2011 Elsevier Ltd. All rights reserved.

doi:10.1016/j.biombioe.2011.02.019
mailto:[email protected]:[email protected]://www.sciencedirect.com/http://www.elsevier.com/locate/biombioehttp://dx.doi.org/10.1016/j.biombioe.2011.02.019http://dx.doi.org/10.1016/j.biombioe.2011.02.019http://dx.doi.org/10.1016/j.biombioe.2011.02.019http://dx.doi.org/10.1016/j.biombioe.2011.02.019http://dx.doi.org/10.1016/j.biombioe.2011.02.019http://dx.doi.org/10.1016/j.biombioe.2011.02.019http://www.elsevier.com/locate/biombioehttp://www.sciencedirect.com/mailto:[email protected]:[email protected]

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Biomass can be transformed using biochemical methods

(such as alcoholic fermentation) and thermochemical

methods (such as direct combustion, pyrolysis or gasification)

[11,12]. Pyrolysis of biomass has been employed to produce

organic intermediates (methane and acetic acid), charcoal and

fuel gas[13]. Many studies devoted to the thermal decompo-

sition of lignocellulosic materials have been reported in the

last two decades, due to the production of activated carbonsfrom solid char derived from agricultural waste pyrolysis

[14,15]. Nowadays, pyrolytic processes can be refined to obtain

char, oil and/or gas, depending on the temperature and reac-

tion time [16e18]. In this context, the Low Temperature

Conversion (LTC) process, initially developed by Bayer et al.

[19], involves pyrolysis at around 400 C. The aim of this

process is to maximize the yield of liquid products having

high-heating power (bio-oil) [20]. The pyrolysis treatment at

temperature higher than 400 C can modify the bio-oil

composition leading to undesirable products as polycyclic

aromatic hydrocarbons[21].

On the other hand, the distribution of pyrolysis products

can be modified by the presence of catalysts and/or by thechemical pretreatment of the biomass[21,22]. It is now well

recognized that the chemical pretreatment of lignocellulosic

materials can remove extractives, hemicellulose, and lignin,

reduce the crystallinity of cellulose, and increase the porosity

of material[23,24]. Thus, the yield and composition of ulterior

bio-oil obtained by pyrolysis could be modified[25].

Sugarcane has historically played an important role in the

Brazilian economy [26,27]. In recent years, special Brazilian

governmental programs have led to a significant increase in

the crop areas devotedto sugarcane and to an improvement in

the sugarcane yield per hectare in order to meet the demand

for ethanol as fuel. According to the Brazilian Institute of

Geography and Statistic, this rise in sugarcane productiongenerated about 160 million tonsof bagasse in 2008 [28]. Inthis

respect,sugarcane bagasse constitutesa typical example of an

agricultural byproduct that is abundantly available worldwide

[29e31]. Sugarcane bagasse typically has a cellulose:hemi-

cellulose:lignin ratio of around 40:35:15. This lignocellulosic

content can be hydrolyzed to liberate the lignin and depoly-

merize the polysaccharides [32,33]. Polysaccharides and lignin

are bound through reactive ether and ester links[34,35]which

may be hydrolyzed at mild temperatures in the presence of

acids or bases. All these processes involve complex carbohy-

drate and lignin reactions[36].

We report here the influence of the acidic or alkaline

nature of the sugarcane bagasse hydrolysis pretreatment onsolid residue composition and on that of the bio-oil yielded

after the LTC-pyrolysis process carried out at 350e450 C. We

focused on the characteristics of the bio-oil liquid fraction due

to its potential future interest for second-generation bio-fuel

production.

2. Materials and experimental procedures

Sugarcane bagassein naturawas sundried, ground and sieved.

Only particles in the 20e80 mesh range were retained for

analysis and experiments; the corresponding samples of

bagasse in natura used were labeled BC. For comparative

purposes, a sample of BC was washed with water at room

temperature and then dried at 105 C until constant weight;

the resulting sample was labeled BCW.

Chemical composition of samples (C, H, N, %wt/wt) was

determined using a Perkin Elmer 2400 CHN model and the

oxygen content (%wt/wt) was then calculated by subtraction.

Thermogravimetric and derivative thermogravimetric

analysis (TG/DTG) data were recorded using a Universal TA2060 apparatus. A heating rate of 20 C min1 and a N2flow of

100 mL min1 were used.

The infrared spectra were obtained with a Nicolet Magna

760 spectrometer at 4 cm1 of resolution.

A HitachiH-2300BSE microscope was usedfor the scanning

electron microscopy study of the materials.1H NMR and 13C NMR were recorded using a Bruker 300

spectrometer (300 MHz for 1H and 75MHz for 13C) and a Bruker

200 (200 MHz for 1H). Spectra were recorded at 25 C using

acetone-d6, dH 2.04 ppm and dC 206.58 ppm as solvent

signals references.

2.1. The hydrolysis experiments

BC hydrolysis was carried out under acidic, basic or sequential

acid/base treatments at 25 Cor122 C at ambient pressure for

1 h.

For the hydrolysis treatments, BC samples (2.0 g) were

treated with2 M HCl (25 mL) or0.5M NaOH(25mL)solutionsat

25 C (samples BCA1 and BCB1 respectively), 122 C (BCA2 and

BCB2 samples respectively) or under ultrasonic irradiation

(BCA3 and BCB3 samples). In the sequential acid/base treat-

ment, BC samples were first hydrolyzed under acidic condi-

tions and then treated with the alkaline solution; the

corresponding samples treated at 25 C, 122 C or under

ultrasonic irradiation at 25 C were BCS1, BCS2, and BCS3,respectively.

In all cases, the resulting samples were filtered off and

washed with distilled water until the wash-water remained

neutral. The samples were oven dried at 105 C until constant

weight, their chemical composition was then determined and

finally, they were analyzed by FTIR, TG/DTG and SEM.

2.2. The pyrolysis experiments

The LTC-pyrolysis experiments were performed in an appa-

ratus designed for this purpose using about 0.1 g of BC or

hydrolyzed samples. The main element of this device was

a tubular reactor inserted vertically into an electrically heatedtubular furnace; the temperature was controlled inside the

sample bed by a NieCr thermocouple. In all cases, gaseous,

liquid and solid fractions were formed. The gases produced

were analyzed on-line by a mass spectrometer (MS) with

a quadrupole analyzer MKS model e-vision. The liquid frac-

tion was condensed at the reactor outlet, extracted with

acetone and then the solvent was removed at low pressure

and the residue analyzed by FTIR, 1H and 13C NMR.

The LTC-pyrolysis experiments were carried out in three

series; in all cases the samples were heated at a rate of

10 C min1 and the final pyrolysis temperature was main-

tained for 15 min. All experiments were performed in dupli-

cate. The first series of experiments was carried out to

b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 1 0 6e2 1 1 6 2107
http://dx.doi.org/10.1016/j.biombioe.2011.02.019http://dx.doi.org/10.1016/j.biombioe.2011.02.019http://dx.doi.org/10.1016/j.biombioe.2011.02.019http://dx.doi.org/10.1016/j.biombioe.2011.02.019

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determine the effect of the final pyrolysis temperature on the

yield of gas, liquid and solid fractions. In this series, LTC-

pyrolysis of BC samples was carried out under an inert

atmosphere (He, 150 mL min1) with pyrolysis temperatures

of 350, 400 or 450 C.

The second group of experiments was performed to

establish the effect of the bagasse hydrolysis pretreatment on

LTC-pyrolysis yields, and this series of experiments wascarried out under inert atmosphere (He, 150 mL min1) at

350 C.

The last group of experiments was performed to establish

the effect of the use of an oxidant atmosphere (5% O2/He,

150 mL min1) on LTC-pyrolysis yields; a final temperature of

350 C was used.

3. Results and discussion

3.1. Effect of different treatments on sugarcane bagasse

characteristics

As stated above, BC samples were hydrolyzed with acidic,

alkaline or sequential acidic/alkaline treatments at 25 C,

122 C or under ultrasonic irradiation. All treated samples

were studied by chemical analysis, FTIR, DT/DTG and SEM. For

each treatment, acidic, alkaline or sequential acidic/alkaline,

the sample treated at 122 C showed the highest degree of

modification when compared with the original bagasse in

natura; consequently, throughout the rest of the paper, the

results of characterization of pretreated samples will refer

exclusively to those samples treated at 122 C. The subsequent

LTC experiments were carried out using BCA2, BCB2 and BCS2

samples.Table 1shows the chemical composition of the BC and the

modified sugarcane bagasse following the different hydrolysis

treatments at 122 C. Although no significant differences in

the chemical composition were observed after the hydrolysis

treatments, a slight reduction in oxygen content was noted

following acidic treatment, which could be related to the

removal of oxygen-rich compounds by the acid treatment.

As stated in the experimental section, for comparative

purposes we prepared a blank sample (BCW) by washing in

water and subsequently drying (105 C) a BC sample. Fig. 1

shows FTIR spectra of both BC and BCW samples. No signifi-

cant differences can be distinguished related to the simple

removal of extractives when BC was treated with water to give

BCW. The spectra are complex but the presence of differentfunctional groups corresponding to the expected composition

based on cellulose, hemicellulose and lignin structures can be

deduced[37]. A broad band above 3000 cm1 was observed,

corresponding to the y(OeH) of hydroxyl groups, such as those

of alcoholic and phenolic components. y(CeH) absorptions in

the 2800e3000 cm1 region were also clearly observed. Below

1800cm1, the spectrafingerprint enabledthe presenceof C]O,

CeOeC and C]C linkages, among others, to be determined.

In the following paragraphs, we will analyze the more

relevant features observed in the infrared spectra of the BCW

and those of the different pretreated samples at 122 C(Fig. 2).

The bands in the region 1700e1760 cm1 are characteristic

of y(C]O) (Fig. 2A). The spectrum corresponding to the BCWsample showed a broad band with maximum at 1732 cm1.

Absorptions at ca. 1735e1740 cm1 are associated with y(C]O)

of carbohydrate structures; and a band at 1740 cm1 has been

assigned to the acetyl, uronic, and feluric ester groups of

hemicellulose [38]. On the other hand, a component of the

carbonyl band appearing at a lower wavenumber is related to

the conjunction of a carbonyl group with an aromatic ring, as

occurs with carbohydrate linked with lignin components [39].

Following acidic hydrolysis, it was mainly the component at

ca. 1702 cm1 which remained, although a shoulder at ca.

1735 cm1 was still present. No bands in the 1700e1735 cm1

region were observed for the samples BCB2 and BCS2. y(C]O)

bands usually disappear with high-temperature treatments ofcellulose, hemicellulose and lignin structures due to forma-

tion of CeOeC bonds between rings [40]. However, in our

study, the intensity of the bands at ca. 1250 cm1 and

1050 cm1 characteristic of CeOeC and CeO bonds respec-

tively, diminished following acid or basic treatment.

On the other hand, when the FTIR spectra of BCB2 and

BCS2 samples were compared with those of BCW and BCA2

(Fig. 2A), a high reduction in the intensity of the bands located

ca. 1515 cm1, 1605 cm1 and 834 cm1 in the spectra of the

samples BCB2 and BCS2 with respect to those of BCW and

BCA2 was clearly noted. These bands are associated with the

presence of lignin; 1515 cm1 and 1605 cm1 (aromatic ring

vibrations) and 834 cm1 (CeH in plane bending)[38,41].

Table 1eChemical compositionof the sugarcane bagassein naturaand that of the samples obtained afterhydrolysis treatments at 122 C.

(%wt/wt) BC BCA2 BCB2 BCS2

C 43.89 48.62 42.48 44.69

H 7.05 6.90 7.37 7.43

N 0.32 0.08 0.15 0.16

Oa 48.74 44.40 50.00 47.72

a Calculated by subtraction.

Fig. 1 eFTIR spectra of a) sugarcane bagasse in natura(BC)

and b) water washed sugarcane bagasse (BCW).


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Besides the reduction in the y(C]O) absorption intensity,

the extraction of carbohydrates would produce a higherreduction in y(OeH) absorption intensity (band centered at

3400e3450 cm1) with respect to thatofy(CeH) (band centered

at ca. 2900 cm1); this can be observed clearly inFig. 2B, if the

spectra of BCA2, BCB2 or BCS2 are compared with that of BCW.

The spectral changes of the BCB2 and BCS2 with respect

BCW agree with the extraction of hemicellulose and the

partial release or degradation of lignin; the partial release of

both hemicellulose and lignin has already been reported as

taking place at 55 C under alkaline conditions[38].

The thermogravimetric behavior of samples was analyzed

and TG (%wt/wt) and DTG (%wt/wt/C) curves were obtained

up to 1000 C. Fig. 3 shows the curves corresponding to

the bagasse in natura (BC) and those corresponding to thesample washed with water (BCW) (Fig. 3A and B respectively).

Fig. 4 displays the thermogravimetric curves of pretreated

samples. The DTG curve of BC shows three well-defined peaks

with maximum at 225 C,320 Cand370 C (Fig.3A),whilst that

of BCW shows peaks at 320 C and 370 C.The peakat 225 C in

the DTG curve of BC (Fig. 3A) was related to the extractive

residues present in this sample, which were removed after

washing with water (see the DTG curve of BCW inFig. 3B).

The two peaks in the DTG curve of BC and BCW, with

maxima at 320 C and 370 C, can be assigned primarily to the

decomposition of hemicellulose and cellulose respectively

[42,43]. Hemicellulose is formed of short branched polymer

chains of several C6 (mainly glucose, mannose and galactose)and C5 (xylose and arabinose) sugars. The side chains and the

axial hydroxyl groups of the sugars prevent hemicellulose

from forming semi crystalline domains; around 200 sugar

units comprise the hemicellulose chain. Cellulose is a polymer

of glucose units (ca. 10000) without any branches. The

hydroxyl groups in equatorialposition permitstrong hydrogen

bonds, giving semi crystalline polymer chains of glucose.

Hemicellulose presents an easier hydrolysis and thermal

decomposition than cellulose, due to its amorphous structure.

Although the highest weight loss took place up to ca.

400 C, in all cases a continuous loss of weight above this

temperature, and up to the final temperature of the experi-

ment, was observed; this loss did not produce significant

peaks in the DTG curves. The degradation of lignin has been

reported to occur preferably above 300 C, with a very lowmass loss rate. Lignin is a tri-dimensional polymer which

comprises phenyl-propane units highly cross-linked and

consequently it is difficult to decompose [44e46].

Fig. 4shows the thermogravimetric analysis of sugarcane

bagasse after acid (Fig. 4A), alkaline (Fig. 4B) and sequential

acid/alkaline treatments (Fig. 4C)at 122 C. Several differences

can be observed if the DTG profiles of pretreated samples are

compared with that of BCW (Fig. 3B). Samples pretreated with

alkaline (BCB2) or sequential acid/alkaline (BCS2) solutions

showed only one wide DTG peak, which started at 250 C and

reached maximum at ca. 350 C(Fig. 4B and C); this is mainly

attributed to the superimposed thermal decomposition of

cellulose and lignin. Although the peak is asymmetric, thedisappearance of the maximum at 320 C indicates degrada-

tion of hemicellulose produced by the alkaline hydrolysis, in

agreement with FTIR analysis of these samples. On the other

hand, the main DTG peak for BCB2 and BCS2 appeared at

a lower temperature (350 C) than that of BCW, and this could

be related to a partial modification of the cellulose and/or

lignin structure, agreeing with FTIR results, which indicated

that the basic treatment produced partial degradation of

lignin structures.

On the other hand, a wide peak at 300e400 C with two

maxima at 320 C and 370 C was still noted in the DTG profile

of the sample pretreated with acid (sample BCA2Fig. 4A); in

this case, the intensity of the first maximum was slightlylower than that of BCW (compare Figs. 4A and 3B), which

would agree with the partial removal of hemicellulose by an

acid treatment as was shown by FTIR. The easy hydrolysis of

hemicellulose can once again be related to its amorphous

random branched structure, whereas the crystalline structure

of cellulose and the cross-linked phenolic units present in

lignin structure are more resistant to hydrolysis. The ther-

mogravimetric results indicate that hydrolysis treatment

affects the composition of sugarcane bagasse, and are in good

agreement with the observed infrared features of the pre-

treated samples previously discussed. Both TG/DTG and FTIR

results enable us to conclude that a basic hydrolysis treatment

produces a more effective extraction of hemicellulose.

Fig. 2 e FTIR spectra, A) 1800-600 cmL1 region and B) 4000-2500 cmL1 region, of several treated sugarcane bagasse samples;

a) BCW, b) BCA2, c) BCB2 and d) BCS2.


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Fig. 5comprises micrographs corresponding to the sugar-

cane bagasse in natura (BC) and those corresponding to the

samples treated at 122 C with acidic, alkaline or sequential

acidic/alkaline treatments, BCA2, BCB2 and BCS2 respectively.Several differences can be observed when comparing the

micrographs of the samples treated at 122 C with different

hydrolysis media.

The BC micrographs show the presence of sugar crystal-

lites on the surface of the material, which correspond to the

residual extractives in this sample. The micrographs of the

pretreated samples do not show the sugar crystallites, due to

the easy removal of extractives. In the BCA2 sample,

substantial disorganization can be observed in the fibers,

compared to the BC sample. As stated above, it was deduced

that acid treatment led to partial removal of hemicellulose.

Basic or sequential acid/basic hydrolysis treatments resulted

in materialsconsisting of skeletal structureswithout apparent

amorphous surface morphology. This effect was more notable

in the BCS2 sample. These results indicate that extraction of

hemicellulose by an alkali or sequential treatment is more

efficient than that achieved by acidic hydrolysis, and are ingood agreement with FTIR and thermogravimetric analyses.

3.2. LTC-pyrolysis results

The effect of the pyrolysis process temperature (350 C, 400 C,

450 C) was firstly investigated in sugarcane bagasse in natura.

Table 2 shows the liquid (bio-oil) and solid fraction yield

obtained as a function of the temperature used in the pyrol-

ysis experiments under inert atmosphere. An increase in bio-

oil yield was obtained when the pyrolysis temperature

decreased from 450 C to 350 C, with abio-oil fraction of 18 (%

wt/wt) at 350 C. Since the highest bio-oil yield was observed

at the lowest LTC temperature (350 C), this was the

Fig. 3 eTG and DTG curves of A) BC and B) BCW samples.


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Fig. 4 eTG and DTG curves of several treated sugarcane bagasse samples; A) BCA2, B) BCB2 and C) BCS2.


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temperature selected for the subsequent pyrolysis experi-

ments of modified sugarcane bagasse.

As stated above, LTC-pyrolysis of BC, BCA2, BCB2 and BCS2

samples was carried out and the effect of inert (He) and

oxidant (5% v/v O2/He) atmospheres was explored. As

described in the experimental section, the formed gases were

analyzed by MS; in all cases, CO2, CO, C2H6, CH4and H2O, were

detected.Fig. 6shows the amount of liquid and solid fractions

(%wt/wt) obtained from LTC experiments of BC and pretreated

Fig. 5 eScanning electron microscopy of BC and several treated sugarcane bagasse samples.

Table 2 eDistribution of products obtained after LTCunder inert atmosphere of sugarcane bagasse in natura atdifferent temperatures.

T (C) Oil (%wt/wt) Solid (%wt/wt)

350 18.0 11.0

400 16.0 16.5

450 12.5 15.0


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samples. The yields of liquid and solid fractions depended on

both the hydrolysis pretreatment and the LTC atmosphereused. In all cases, an LTC oxidant atmosphere led to the

formation of a higher amount of solid fraction, whereas the

liquid fraction was lower. However, the LTC atmosphere had

less influence on the liquid yield than on the solid yield. On

the other hand, when results of LTC of the pretreated samples

were compared to those of sugarcane bagasse in natura,

several differences in the amount of liquid and solid fractions

obtained could be appreciated. The amount of solid fraction

obtained was always higher for pretreated samples, being in

the order BC< BCA2< BCB2< BCS2. The LTCof BCB2 and BCS2led to a lower amount of bio-oil than that of the original BC

sample. However, when the LTC products of BCA2 and BC

were compared, a higher amount of bio-oil in the case of BCA2

was observed. Under inert atmosphere, the LTC of BCA2

sample gave a bio-oil yield (31 %wt/wt) 72% higher than that

obtained from the BC sample (18 %wt/wt). These results

indicate that LTC of extractives does not significantly

contribute to bio-oil formation. Moreover, as stated above, the

acid treatment produced structural modification, fiber disor-

ganization and the partial extraction of hemicellulose. Thus,

the relative amount of cellulose in the acid-treated sample

increased when it was compared with BC sample, and this

may be related with the higher bio-oil yield produced by theLTC process of the former. On the other hand, alkaline or

sequential treatments, besides a more effective extraction of

Fig. 6 eYield of liquid (>, A) and solid (,, -) fractions

(% wt/wt) obtained after the LTC process of BC and several

treated sugarcane bagasse samples. LTC process was

carried out at 350 C under He (filled symbols) or 5% O2/He

(empty symbols) atmosphere.

Fig. 7 e 1H NMR spectra, corresponding to the bio-oil obtained by LTC of BC sample at 350 C under different atmospheres;

A) under He (spectrum registered at 200 MHz), B) under 5% O2/He (spectrum registered at 300 MHz).


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hemicellulose than acid treatment produced the partial

degradation of lignin. Under LTC conditions unprotected

cellulose may suffer dehydration and oxidation reactions

producing the diminution of bio-oil yield[25].

The obtained bio-oil was analyzed by NMR and FTIR

spectroscopy.Fig. 7shows the 1H NMR spectra of the bio-oil

obtained by LTC of sugarcane bagasse in naturain inert (He)

(Fig. 7A) and in oxidant atmosphere (5% O2/He) (Fig. 7B). Both1H NMR spectra showed prominent signals at d9.54, s; 7.32, d,

J 3.3 Hz; 6.53, d, J 3.3 Hz and 4.60, s characteristic of

5-hydroxymethylfurfural. The singlet at d w5.2 is related to

levoglucosan [47]; signals at d 3.30e4.50 are ascribed to

carbohydrate moiety (carbinolic protons). The signal at ca.

1.2 ppm is due to water impurity.

Interestingly, the NMR characterization of the bio-oil

produced by LTC of modified sugarcane (BCA2, BCB2, BCS2)

indicated in all cases that levoglucosan was the main

component. As an example,Fig. 8shows 1H(Fig. 8A) and 13C

NMR (Fig. 8B) spectra corresponding to the bio-oil produced

after the LTC under He atmosphere of BCA2. Characteristic

signals of levoglucosan can be distinguished; 1H NMR signals

at d 5.24, s (H-1); 4.43, m (H-5); 4.09, bd, J 7.0 Hz (H-6a); 3.58,

dd,J 5.9 and 7.0 Hz (H-6b); 3.51 bs (H-4) and 3.37, bs (H-2) and

those from the 13C NMR spectrum at d 103.22, 77.57, 74.53,

72.54, 72.25 and 65.83.

FTIR spectra of the bio-oil produced by LTC of different

samples arepresented in Fig.9. The broad absorbance bands ofy(OeH) stretching vibration between 3200 and 3600 cm1 indi-

cated the presence of highly polymeric hydroxyl groups and

water impurities in the oil. The absorptions at 2800e3000 cm1

region and those around 1460 cm1 are characteristic ofy(CeH)

and d(CeH) vibrations of eCH3 and/or eCH2-groups. Other

absorptionsbetween1630and1760cm1werealso observed. As

stated above, this is a characteristic spectral region ofy(C]O)

andcould indicatethe presenceof ketones,aldehydes and acids

or esters. Specifically, 5-hydroxymethylfurfural shows a char-

acteristic and intense absorption at 1666 cm1. The FTIR spec-

trum of the bio-oil obtained from sugarcane bagassein natura

Fig. 8 e NMR spectra of the bio-oil obtained from the BCA2 sample after LTC at 350 C under He atmosphere. A) 1H NMR (300

MHz); B) 13C NMR (75 MHz).


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(BC) (Fig. 9, spectrum a)shows a band at 1668 cm1 which could

be assigned to the presence of 5-hydroxymethylfurfural, in

agreement with NMR results. The intensity of this band

decreased strongly in the spectrum corresponding to bio-oil of

BCA2 (Fig. 9spectrum b), and it was no longer present in the

spectra of the bio-oil obtained from BCB2 and BCS2 samples

(Fig. 9, spectra c and d). The residual extractives of BC sample

may produce 5-hydroxymethylfurfural under the LTC condi-

tions applied in this study.

4. Conclusions

Sugarcane bagasse was modified by acid, alkaline and

sequential acid/alkaline hydrolysis. SEM, TG-DTG and FTIR

analysis showed that the hydrolysis treatments determined

the composition and fiber organization of the sugarcane

bagasse. Acid treatment removed extractives and hemi-

cellulose and led to amorphous, highly disordered fibers.

Alkaline hydrolysis removed more effectively hemicellulose,

degraded lignin and left highly ordered residual fibers.

With the goal of producing bio-oil, low temperature

pyrolysis of modified biomass was carried out under inert or

oxidant atmospheres. Bio-oil yielded by LTC of modified

samples did not differ qualitatively in composition, and lev-oglucosan comprised its main component. The acid

pretreatment increased the bio-oil yield of the LTC process,

whereas the basic treatment produced the opposite effect

when compared to that of the in natura sugarcane bagasse.

The yield of bio-oil increased by 72% when the LTC process of

BCA2 was carried out under He, and by 53% when it was

carried out under oxidant atmosphere. The LTC bio-oil yield

correlated with the fiber organization and composition of

pretreated samples. The higher bio-oil production in LTC

process from BCA2 sample with respect to BC sample is

related to the relative amount of cellulose, which is higher in

the acid-treated material because this treatment mainly

removes extractives and hemicellulose.

The degradation of lignin after the basic and sequential

treatments may leave cellulose unprotected and favor dehy-

dration and oxidation reactions under LTC conditions, thus

leading to a decrease in bio-oil yield.

Acknowledgments

The authors are grateful to ANP/CENPES-Brazil, and the

Spanish and Catalan governments (Consolider Ingenio 2010,

Multicat CSD2009-00050, MAT2008-02561 and 2009SGR-0674

projects) for the financial support and to CAPES-Brazil, for

a scholarship.

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