PARTⅣ BIOMASS DEGRADATIONTHERMAL BEHAVIOUR/TREATMENT OF SOMEVEGETABLE RESIDUES.IV. THERMAL DECOMPOSITION
OF THE EUCALYPTUS WOOD
Cornelia Vasile*1, Carmen-Mihaela Popescu1, Maria-Cristina Popescu1, Mihai Brebu1,Dimitris S. Argyropoulos2, Stefan Willför3
1“P.Poni” Institute of Macromolecular Chemistry,
41A Gr. Ghica Voda Alley, Iasi 700487 , Romania
2
Forest Biomaterials Laboratory College of Natural Resources
North Carolina State University, USA
3
Abo Akademi University, FinlandE-mail: cvasile@icmpp.ro
Abstract: In our previous papers, thermogravimetric analysis (TGA), differential scanningcalorimetry (DSC) and pyrolysis coupled with gas chromatography-mass spectroscopy(Py-GC-MS) techniques were used to investigate the thermochemical conversion of theagricultural biomass, namely the of oilseed rape (Brassica napus L.) and of the Spanish
broom (Spartium junceum) fibres.
1. Introduction
The widespread availability of biomass, the third among primary energy resources after
coal and oil, which is also renewable and potentially neutral in relation to global warming
motivated the extensive research undertaken in the past decade for the industrial developmentof thermochemical conversion plants. [1,2] Despite the abundance of the Eucalyptus species
only recently has a start been made towards its full utilization. [3] In the Iberian region of theEuropean Union, Eucalyptus globulus, occupies an increasingly large part of the surface area,[4] being over one million hectares which produces more than seven million m3/year of roundwood, mainly for pulp manufacturing [5]. Only few papers are known about thermal
characterization of the Eucalyptus wood.[6] This paper deals with thermogravimetric study of
the Eucalyptus wood, in order to elucidate the dependence of the thermal characteristics andkinetic parameters of each thermogravimetric step on different parameters and also toestablish the differences found between samples after various treatments.
2. Materials and methods
The unfractionated samples of wood chips of Eucalyptus globulus from the same batchas the pulp, unbleached Kraft pulp brown stock of Eucalyptus globulus (sampled after- 193 -The 5th ISFR (October 11-14, 2009, Chengdu, China)washing stages) were provided by Abö Akademi University, Laboratory of Wood and Paper
Chemistry, Turku, Finland. All samples are from the COST E41 joint analysis effort. The
selected samples for study have very different content in extractives, carbohydrates andlignins (average composition presented in Tab.1). Eucalyptus BSP has ~ 20 wt% morecarbohydrates, while lignin content is very small of 1-1.7 wt%.[7]Tab. 1 Average content of total extractives, carbohydrates and ligninin Eucalyptus globulus chips and pulp samples.
Samples

Moisture(%)

Extractives(%)

Carbohydrates (%)

Lignin (%)

Ash(%)

Eucalyptus chips

7.03

1.06–2.98

57.1–70.6

24.5–27.6

0.53

Eucalyptus BSP

5.9

0.14–2.16

88.7–99.2

1.0–1.7

1.32

TG/DTG curves were recorded on a Shimadzu Thermogravimetric Analyser under thefollowing operational conditions: heating rates of: 1, 2.5, 5 and 10 ºC/min, temperature rangeof 25-600 ºC, sample mass of about 20 mg, platinum crucible, nitrogen flow of 100 cm3/min.
3. Results and discussions
Kinetic of wood pyrolysis is needed for the design of chemical reactors applied forrecovering energy and chemicals. The kinetic analysis is complicated by the composite natureof wood, constituted by a mixture of hemicellulose, cellulose, lignin and extractives, withproportion, chemistry, and reactivity affected by variety. Widely different kinetic parameters
have been published in the literature because of the greatly different experimental conditions,various experimental problems and the occasional use of unsuitable evaluation methods. The
related kinetic mechanisms, usually obtained by the use of a single experiment (heating rate),are based either on a one step reaction or on several parallel reactions. [8] These mechanisms,
properly coupled with the description of transport phenomena, have been applied for
fixed-bed reactors, where the coarse particles and/or the significant external heat transfer
limitations establish slow heating rates and low conversion temperatures (slow conventionalpyrolysis). As a constant ratio between the yields of char and volatiles is assumed, only theconversion time can be predicted. Results of kinetic modeling of wood pyrolysis obtained forfast heating rates or isothermal conditions are needed for the development of fast pyrolysis
technologies and, in some cases, for the devolatilization stage of gasifiers and combustors.
Furthermore, the kinetic constants, estimated by means of different literature sources and usedby Chan et al.[9] to model large particle pyrolysis, are also of interest being capable ofpredicting at least qualitatively the correct behavior of wood pyrolysis. The present study isfocused on the influence of the heating rate and conversion degree on kinetics ofdecomposition of Eucalyptus wood samples.
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TG/DTG curves of the Eucalyptus wood samples at different heating rates – Fig. 1 – areshifted to higher temperatures with increasing heating rate; the composition of thedecomposition products depend on heating conditions, as can be observed from the residue
quantity which decreases with increasing the heating rate -Tab. 2.

(a)Fig. 1 The TG/DTG curves of the Eucalyptus chips (a) and Eucalyptus BSP (b).

(b)

The first thermogravimetric step corresponding mainly to the loss of the physicallyabsorbed water and some of low molecular weight compounds is evident only at high heating
rates of 5 – 10 oC.
Tab. 2 Temperature interval (Ti-Tm-Tf) and mass loss (wt %)of the second thermogravimetric step
Heating rate

Eucalyptus chips

Eucalyptus BSP(°C/min)Ti (oC)

Tm(oC)Tf (oC)wt (%)Ti (oC)

Tm(oC)Tf (oC)wt (%)

1

227.1

354.5

405.7

63

229.4

337.3

417.2

79

2.5

228.4

363.5

421.3

73

236.0

346.5

419.4

865

230.4

391.3

447.1

78

238.4

363.7

436.4

80

10233.2

390.4

449.0

75

268.3

372.0

441.1

77

The differences between Eucalyptus samples appear in the second thermogravimetricstep. All characteristic temperatures increase at high heating rates. The onset temperatures arelower for Eucalyptus chips, while the Tm are higher than those of the Eucalyptus BSP. Mass- 195 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
losses are higher for Eucalyptus BSP. Decomposition is a complex process both because thestudied samples have many components and each of them decomposes in several stages andbecause the thermal behavior is determined by operational conditions especially heating rate,
final temperature of heating, heat transfer, degradation/decomposition occurs by competitive
and/or consecutive reactions.
The kinetic parameters evaluation was done with a commercial program which giveoverall kinetic parameters values by using at least 7 intergral [10-12] and differential [13-16]
methods – Fig. 2,3. The Reich – Levi method was also employed in evaluation of variation of
the kinetic parameters with conversion degree. The global kinetic parameter values, used forcomparative purposes, have been evaluated in the same conditions for all studied samples.
The obtained values for all kinetic parameters lay in the limits found for other wood species,
but of course the Eucalyptus samples have some particularities related to the variation of thekinetic parameters with samples characteristics and operational parameters. Some discrepancy
was found in respect with values of cellulose decomposition for the second thermogravimetricstep and this can be justified from the possible interference of the lignin decomposition.
200E u c a lyp tu s ch ip sE u c a lyp tu s B S P

180

E (kJ/mole)160
140120100800246810o

H eating rate ( C /m in)

Fig. 2 Variation of the global activation energy vs. heating rate evaluatedby Coats- Redfern method(a)(b)
Fig. 3 Reich Levi graphs for variation of the activation energy with conversion degree for
Eucalyptus chips (a) and Eucalyptus BSP (b) samples- 196 -

PARTⅣ BIOMASS DEGRADATION
At low heating rates the values of the activation energy E of both Eucalyptus samples arealmost similar. At medium heating rate of 4 - 6 oC/min a minimum is observed in the case of
Eucalyptus chips and then the activation energy increases, while that of Eucalyptus BSP
increases with increasing heating rate. The same variation of the activation energy withheating rate is observed from the Reich-Levi graphs for the whole range of the conversion
degree studied (a < 0.6). Pre-exponential factor A shows the same variation with heating rate
as activation energy. The reaction order n takes values between 0.9 and 1.5 for Eucalyptus
chips and varies between 1.0 and 1.8 for Eucalyptus BSP indicating that the reaction
mechanism for cellulose decomposition is controlled by a reaction order law. Concerning thevariation of the activation energy with conversion degree – Fig.3 – it is seems that a small
decrease appears at low conversion degree (a < 0.15) and than the values are almost constantfor a certain heating rate. The Flynn-Wall graphs (not shown) are much complicated for
Eucalyptus chips than for Eucalyptus BSP. The discontinuities of the lines for the entire
conversion degree region are a proof for a complex reaction mechanism. Decomposition of
Eucalyptus BSP sample seems to be much simpler in the conversion degree interval 0.33 < a< 0.74 where the line are almost parallel.

(a)(b)
Fig. 4 The dependence of the activation energy on the heating rate and conversion degree for
Eucalyptus chips (a) and Eucalyptus BSP (b) samples
It can be concluded that both heating rate, temperature interval or conversion degree
significantly influence the kinetic parameters values, therefore the complex dependence of theactivation energy both on heating rate and conversion degree should be known – Fig. 4.

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