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Journal of Analytical and Applied Pyrolysis 97 (2012) 49–54

Contents lists available at SciVerse ScienceDirect

Journal of Analytical and Applied Pyrolysis

journa l h o me page: www.elsev ier .com/ locate / jaap

haracterization of the water-insoluble pyrolytic cellulose from celluloseyrolysis oil

inlai Weia, Qiang Lub, Xianwei Suia, Zhi Wanga, Ying Zhanga,∗

Anhui Province Key Laboratory for Biomass Clean Energy, University of Science and Technology of China, Hefei 230026, ChinaNational Engineering Laboratory for Biomass Power Generation Equipment, North China Electric Power University, Beijing 102206, China

r t i c l e i n f o

rticle history:eceived 26 November 2011ccepted 2 July 2012vailable online 10 July 2012

eywords:yrolytic celluloseellulose pyrolysisPC

a b s t r a c t

Water-insoluble pyrolytic cellulose with similar appearance to pyrolytic lignin was found in cellulosefast pyrolysis oil. The influence of pyrolysis temperature on pyrolytic cellulose was studied in a temper-ature range of 300–600 ◦C. The yield of the pyrolytic cellulose increased with temperature rising. Thepyrolytic cellulose was characterized by various methods. The molecular weight distribution of pyrolyticcellulose was analyzed by gel permeation chromatography (GPC). Four molecular weight ranges wereobserved, and the Mw of the pyrolytic cellulose varied from 3.4 × 103 to 1.93 × 105 g/mol. According to theelemental analysis (EA), the pyrolytic cellulose possessed higher carbon content and lower oxygen con-tent than cellulose. Thermogravimetric analysis (TGA) indicated that the pyrolytic cellulose underwent

◦

GATIRy-GC/MS

thermo-degradation at 127–800 C and three mass loss peaks were observed. Detected by the pyrolysisgas chromatography–mass spectrometry (Py-GC/MS), the main pyrolysis products of the pyrolytic cel-lulose included saccharides, ketones, acids, furans and others. Fourier transforms infrared spectroscopy(FTIR) also demonstrated that the pyrolytic cellulose had peaks assigned to C O stretching and glyco-sidic bond, which agreed well with the Py-GC/MS results. The pyrolytic cellulose could be a mixture of

their

saccharides, ketones, and

. Introduction

Fast pyrolysis is one of the best ways to convert biomassesources into higher energy density feedstock [1]. It is a techno-ogically and economically viable technique to produce renewableiquid fuels, high-value chemicals, and other derived products [2].

ith the development of global economy, there is an increasingnterest in the research and application of biomass-based pyroly-is oil [3]. However, the pyrolysis bio-oil was not stable [4,5]. It isonsidered that the existence of aldehydes, ketones and pyrolyticignin has detrimental effect on the stability of pyrolysis oil [6–8].

Pyrolytic lignin could be obtained from the pyrolysis oil ofignocelluloses by water precipitation [3,6,9]. It was generally con-idered that pyrolytic lignin was formed from the pyrolysis ofignin. However, we obtained fine powder with similar appearances pyrolytic lignin in cellulose pyrolysis oil by water precipitationethod. We called it pyrolytic cellulose. To our best knowledge,

lthough the water-soluble anhydro-oligosaccharides from cellu-

ose fast pyrolysis have been studied by previous work [10–13],ittle information has been reported on water-insoluble pyrolyticellulose. In this work, pyrolytic cellulose was characterized by

∗ Corresponding author. Tel.: +86 551 360 3463; fax: +86 551 360 6689.E-mail address: zhzhying@ustc.edu.cn (Y. Zhang).

165-2370/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.jaap.2012.07.002

derivatives.© 2012 Elsevier B.V. All rights reserved.

various methods, including GPC, EA, TGA, and FTIR. The pyrolysisof pyrolytic cellulose was performed using Py-GC/MS.

2. Methods

2.1. Fast pyrolysis of cellulose

The fast pyrolysis of cellulose was carried out in a verticalflow reactor under nitrogen flow of 0.5 L/min in a temperaturerange of 300–600 ◦C. The pyrolysis unit consisted of a feeding sys-tem, a pyrolysis system, and a condensation system, as previouslydescribed in Ref. [14].

At first, the �-cellulose (Aladdin, China) was cleaned threetimes to remove organic impurities with dichloromethane, ethanolrespectively, and dried at 105 ◦C for 12 h. During the fast pyrolysisexperiments, 5.0 g of cellulose was fed continually into the reac-tor at a speed of 1.0 g/min, and kept at the preset temperature for15 min. The pyrolysis liquid product was collected in a condensertube bathed in liquid nitrogen. The yield of the liquid and char prod-ucts was calculated by the weight difference of the condenser and

the quartz tubular before and after the experiment. The yield of gaswas calculated by the difference of cellulose and generated pyrol-ysis oil and char. The experiments were conducted at least threetimes to confirm the error was less than 14%.

5 and Applied Pyrolysis 97 (2012) 49–54

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Fig. 1. The mass balance of the cellulose pyrolysis products.

the production of the pyrolytic cellulose.The results of elemental analysis and the HHVs of cellulose and

pyrolytic cellulose at different pyrolysis temperatures are givenin Table 1. With the temperature rising, the carbon content was

Table 1Elemental analysis and HHVs of cellulose and pyrolytic cellulose.

Pyrolysis temperature (◦C) Elemental analysis (wt%) HHVs (MJ kg−1)

C H O

300 65.12 7.94 26.80 28.65

0 X. Wei et al. / Journal of Analytical

.2. Precipitation of pyrolytic cellulose

The pyrolytic cellulose was obtained as follows. First, ethanolas added into pyrolysis oil under vigorous stirring (ethanol to oilass ratio was 5), and then the solution was filtered to remove

nsoluble impurities. Secondly, ethanol was removed by rotaryvaporator at 30 ◦C, and then certain amount of distilled wateras added to the pyrolysis oil under vigorous stirring (water to oilass ratio was 25). The pyrolysis oil mixture was kept overnight

o yield precipitate in the bottom of the flask, the supernatant wasemoved and the precipitate was washed three times with freshistilled water. At last, the precipitate was dried by vacuum freezerying and weighed. The yield of pyrolytic cellulose was based onhe cellulose which was fed into the pyrolysis reactor.

.3. Characterization

The molecular weight distribution of pyrolytic cellulose wasnalyzed by GPC using Waters 1525 (BreezeTM HPLC system). Theemperature of the column oven was 50 ◦C. DMF was used as theluent at a flow rate of 1 mL/min. The pyrolytic cellulose sampleas dissolved in DMF (3 mg/mL) and 100 �L of each sample was

njected. A differential refractometer and a photometer in the ultra-iolet range (280 nm) were used as detectors. Polystyrene witharious molecular weights was used for calibration. The molecu-ar weight was calculated from the experimental data using theoftware Waters Breeze.

The carbon, hydrogen, and nitrogen contents of pyrolytic cel-ulose were measured on an Elementar Vario EL-III analyzer. Thexygen content was estimated by means of percentage difference.he higher heating value (HHV) was calculated by Dulong’s formula15]:

HV =[

338.2 × C + 1442.8 ×(

H − O8

)]× 0.001

HV is in MJ (kg dry basis)−1, and C, H, O as percent on a dry basis.The TGA of pyrolytic cellulose was performed on a Q5000 IR

hermogravimetric Analyzer. The measurement was carried outt the rate of 10 ◦C/min from room temperature to 800 ◦C underitrogen atmosphere.

The pyrolysis of pyrolytic cellulose was performed using a CDS200 HP-R pyrolyzer. In a typical experiment, 0.5 mg of pyrolyticellulose was pyrolyzed. The pyrolysis temperature was set at50 ◦C and held for 20 s, with the heating rate of 20 ◦C/ms. Theyrolysis vapors were analyzed by GC/MS (Perkin Elmer Clarus60). Helium (99.999%) was used as carrier gas to separate theonomeric product on an Elite-35 column (30 m × 0.25 mm, film

hickness 0.25 �m). The temperature of the pyrolysis gas transmis-ion pipe and the injection port were both 300 ◦C. The split ratio was:80, and the oven temperature was set as follows: hold for 3 mint 40 ◦C, ramp to 180 ◦C at 4 ◦C/min, then to 280 ◦C at 10 ◦C/minnd keep for 4 min. Identification of chromatographic peaks waschieved according to the NIST MS library.

FTIR spectra were obtained on a Bruker EQUINOX55 FT-IR spec-rometer. 2–3 mg of pyrolytic cellulose sample and 300 mg of KBrere used to press pellets for IR analysis. The infrared spectra were

ecorded between 4000 and 400 cm−1.

. Results and discussion

.1. The effect of pyrolysis temperature

In cellulose pyrolysis process, temperature is expected to havehe most significant effect on the yield and chemical compositionsf the products [16]. To investigate the influence of temperature,

Fig. 2. The influence of temperature on the yield of the pyrolytic cellulose.

the yields of the pyrolysis oil, char and gas at different temperatureswere investigated.

The results are shown in Fig. 1. It was observed that the yieldof gas increased from 2.1% to 13.9% with the pyrolysis temper-ature increasing from 300 to 600 ◦C, while the char yield had adeclining trend, which was most likely because of the increasingdecomposition of the cellulose at a higher temperature. The yieldof pyrolysis oil increased from 29.9 to 80.5 wt% with the tempera-ture increasing from 300 to 500 ◦C, and then decreased to 77.4 wt%at 600 ◦C. It demonstrated that temperature could promote cel-lulose decomposition, and higher temperature could promote thesecondary cracking of the pyrolysis vapor to non-condensable gas[17]. As shown in Fig. 2, when the temperature increased from 300to 600 ◦C, the yield of pyrolytic cellulose increased from 0.03 to1.18 wt%. Therefore, it was obvious that the temperature facilitated

400 66.07 7.42 26.38 28.29500 67.09 6.61 26.19 27.50600 71.45 6.20 22.24 29.09Cellulose 43.50 6.35 50.04 14.85

X. Wei et al. / Journal of Analytical and Applied Pyrolysis 97 (2012) 49–54 51

llulos

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urefcFw31Mwt

3

war

cated that the pyrolytic cellulose consisted of different types ofcomponents which displayed different pyrolytic behaviors. It wasconsistent with the GPC result. Compared with pyrolytic lignin,pyrolytic cellulose has lower decomposition temperature [19]. The

Fig. 3. The photograph of pyrolytic ce

ncreased from 65.12 to 71.45 wt%, and the color of pyrolytic cellu-ose changed from light brown to dark brown gradually (Fig. 3). This

ight be due to the fact that the carburization degree of pyrolyticellulose increased with the pyrolysis temperature. The carbon,ydrogen and oxygen contents of cellulose were 6.35% and 50.04%.s shown in Table 1, pyrolytic cellulose had higher carbon contentnd lower oxygen content than cellulose, which led to the higherHV of pyrolytic cellulose than that of cellulose.

.2. Gel permeation chromatography analysis

The mass average (Mw) and the number average (Mn) molec-lar weight of pyrolytic cellulose were measured by GPC. Theesults showed that each pyrolytic cellulose obtained at differ-nt temperatures had similar molecular weight distribution, andour distribution ranges were observed. It indicated that pyrolyticellulose was a mixture with different types of macromolecules.or example, the Mw of the pyrolytic cellulose obtained at 400 ◦Cas around 1.93 × 105 g/mol, 8.2 × 104 g/mol, 1.7 × 104 g/mol,

.4 × 103 g/mol, and the Mn was 1.88 × 105 g/mol, 7.9 × 104 g/mol,

.6 × 104 g/mol, 3.1 × 103 g/mol, respectively. The ratio of Mw andn, which was a measure of the homogeneity of the fragments,as 1.03–1.09 in each distribution range. This demonstrated that

he particle size had monodisperse distribution.

.3. Thermogravimetric analysis

The pyrolysis characteristics of cellulose and pyrolytic celluloseere investigated by TGA. Because the pyrolytic cellulose obtained

t different temperatures had similar pyrolytic behavior, only theesults of cellulose and pyrolytic cellulose obtained at 400 ◦C were

e at different pyrolysis temperatures.

presented in Fig. 4. The pyrolysis temperature of cellulose wasfocused on 280–380 ◦C, and the maximum weight loss rate was2.43 wt%/◦C at 353 ◦C. When the temperature was raised to 500 ◦C,only 12 wt% solid residues were left. A similar phenomenon wasalso reported in other literature [18].

Compared with cellulose, pyrolytic cellulose had a significantlydifferent pyrolytic behavior. It began to decompose at 127 ◦C, andthree DTG peaks were found at 258 ◦C, 345 ◦C and 416 ◦C. It indi-

Fig. 4. TG and DTG thermograms of cellulose (black line) and pyrolytic cellulose (redline). (For interpretation of the references to color in this figure legend, the readeris referred to the web version of the article.)

52 X. Wei et al. / Journal of Analytical and Applied Pyrolysis 97 (2012) 49–54

vapor

marc

3

ayrpypsph

ptwsm(i

Fc

Fig. 5. GC/MS traces of the pyrolysis

aximum weight loss rate (0.39 wt%/◦C) was obtained at 258 ◦Cnd 28 wt% solid residues were left at 500 ◦C. The high solidesidue may be related to the high carbon content of pyrolyticellulose.

.4. Pyrolysis-gas chromatography/mass spectrometry analysis

The pyrolysis products of cellulose and pyrolytic cellulose werenalyzed by Py-GC/MS. According to the TGA data above, the pyrol-sis temperature of Py-GC/MS was set at 350 ◦C, 400 ◦C and 450 ◦C,espectively. As shown in Fig. 5, the pyrolysis result showed that theyrolysis products at 350 ◦C were very limited at the same pyrol-sis time. It could be due to that the temperature was too low toyrolyze the pyrolytic cellulose. The pyrolysis result at 450 ◦C wasimilar to that at 400 ◦C. The pyrolytic product distribution of theyrolytic cellulose which were obtained at different temperaturesad no big difference.

Peak identification for the main products of cellulose andyrolytic cellulose obtained at 400 ◦C is given in Table 2, in whichhe contaminations were removed and the pyrolysis temperatureas 450 ◦C. The main pyrolysis products of cellulose included

accharides (51.3%), furans (12.6%), and aldehydes (3.8%) and theain pyrolysis products of pyrolytic cellulose included saccharides

42.9%), ketones (7.4%), acids (9.2%), and furans (3.7%) (as shownn Fig. 6). It was noted that levoglucosan was the primary product

ig. 6. Comparison of main pyrolysis compounds between pyrolytic cellulose andellulose.

of cellulose and pyrolytic cellulose.

accounting for 40.1% of the total pyrolysis products of pyrolyticcellulose, which might be formed by the sequential cleavage ofthe two �-(1→4)-glycosidic bonds of the pyrolytic cellulose andthe intermolecular rearrangement. The levoglucosan was foundin the pyrolysate of pyrolytic lignin [20] which proved that theso-called pyrolytic lignin probably included pyrolytic cellulose.Ketones and acids could be derived from the cracking of pyranring [21]. Surprisingly, many kinds of benzenes were producedin the pyrolysis products of pyrolytic cellulose, however, theywere not observed during the cellulose pyrolysis. This may beattributed to the fact that the carbon chains of pyrolytic cellulosewere recombined at high temperature [22–24].

3.5. Fourier transform infrared spectroscopy analysis

The chemical structure of pyrolytic cellulose and cellulose wasanalyzed using FTIR. The results demonstrated that each pyrolyticcellulose obtained at different temperatures had similar infraredspectra. The infrared spectra of the pure cellulose and the pyrolyticcellulose obtained at 400 ◦C are presented in Fig. 7. The broad IRband centered around 3200–3500 cm−1 indicated O H stretch-

ing vibration of hydroxyls and water. For cellulose, the peak at2902 cm−1 resulted from the stretching vibration of C H bond. TheO H bending vibration frequencies at 1640 cm−1 demonstrated

Fig. 7. FTIR spectra of cellulose (blue line) and pyrolytic cellulose (red line). (Forinterpretation of the references to color in this figure legend, the reader is referredto the web version of the article.)

X. Wei et al. / Journal of Analytical and Applied Pyrolysis 97 (2012) 49–54 53

Table 2Major pyrolysis products of pyrolytic cellulose(obtained at 400 ◦C) and cellulose analyzed with Py-GC/MS at 450 ◦C.

Pyrolytic cellulose Cellulose

No. Main compounds No. Main compounds

1 Acetic acid 1 Hydroxyacetaldehyde2 Methyl furan 2 3-Methyl-2-pentanone3 2,3-Hexanediol 3 5-Methyl-2(3H)-furanone4 2,5-Dimethyl-furan 4 Furfural5 1-(Methylenecyclopropyl)-ethanone 5 4-Hydroxydihydro-2(3H)-furanone6 2-Hydroxypropanoic acid 6 3-Ethyl-2-hydroxy-2-cyclopenten-1-one7 Furfural 7 3-Methyl-1,2-cyclopentanedione8 2-Cyclopentene-1,4-dione 8 3-Dimethyl-cyclohexane9 2-Hydroxy-2-cyclopenten-1-one 9 4H-Pyran-4-one

10 5-Methyl-2-furancarboxaldehyde 10 2,5-Dimethyl-4-hydroxy-3(2H)-furanone11 Dihydro-3-methylene-2,5-furandione 11 Levoglucosenone12 3-Methyl-3-cyclohexen-1-one 12 3,5-Dihydroxy-2-methyl-4H-pyran-4-one13 3-Methyl-1,2-cyclopentannedione 13 1,4:3,6-dianhydro-a-D-glucopyranose14 2-Methyl-benzofuran 14 5-Hydroxymethyl-furfural15 4-(5-Methyl-2-furanyl)-2-butanone 15 2,3-Anhydro-D-mannose16 4,7-Dimethyl-benzofuran 16 5-Methyl-1,3-cyclohexanedione17 1,4:3,6-Dianhydro-�-d-glucopyranose 17 3,4-Altrosan18 5-(Hydroxymethyl)-2-furancarboxylic acid 18 1,6-Anhydro-�-d-glucofuranose19 2,4,6-Trimethyl-benzaldehyde 19 1,6-Anhydro-�-d-galactofuranose20 1,6-Anhydro-�-d-glucopyranose21 5-(5-Methyl-2-furfurylideno)-furan-2(5H)-one22 1,6-Anhydro-3,4-o-isopropyliden-�-D-galactopyranose

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hat the sample combined micro amount of water. The strongbsorption peak at 1059 cm−1 should be the stretching vibrationf C O bond in cellulose, as well as the C O bond in hemiacetalf pyranose [25,26]. The peak at 897 cm−1 corresponded to �-d-lucoside bond.

As for the pyrolytic cellulose, the broad peaks at849–2962 cm−1 were assigned to the stretching vibration ofethyl and methylene. The characteristic peak of �-d-glucoside

ond (897 cm−1) was weak, the �-mannoside bond (803 cm−1) andther glycosidic bond (923 cm−1, 890 cm−1) were relatively strong.he peak at 1261 cm−1 corresponded to the C O C stretchingibration. The peaks at 1705 and 1621 cm−1 were C O and C Ctretching, respectively, which resulted from the removal of waterrom cellulose by pyrolysis.

. Conclusions

In pyrolysis experiments, the yield of pyrolytic cellulosencreased with the rising of temperature. The high temperatureould facilitate production of the pyrolytic cellulose. The carbonontent of pyrolytic cellulose also increased with temperature,hich led to the color of the pyrolytic cellulose darken gradu-

lly. The molecular weight of pyrolytic cellulose had four distinctistribution ranges.

Pyrolytic cellulose displayed different decomposition behaviorsrom cellulose. The main pyrolysis products of the pyrolytic cel-ulose included saccharides, ketones, acids and furans. Based onTIR, pyrolytic cellulose had peaks assigned to C O stretching,hich agreed well with the Py-GC/MS results that contained a large

mount of ketones. According to the various analysis results above,yrolytic cellulose could be a mixture mainly containing saccha-ides, ketones, and their derivatives. More work will be done toiscover the detailed structure of the pyrolytic cellulose.

cknowledgments

We gratefully acknowledge the financial support provided byhe Fundamental Research Funds for the Central Universities,ational High-tech R&D Program of China (SS2012AA051803), and

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Key Program of National Natural Science Foundation of China(50930006).

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