Ciência Rural, Santa Maria, v.

55:4,
Correlation e20240100,
between the 2025
heating value and the chemical characteristics ofhttp://doi.org/10.1590/0103-8478cr20240100
Eucalyptus biomass. 1
ISSNe 1678-4596
FORESTRY SCIENCE

Correlation between the heating value and the chemical characteristics

of Eucalyptus biomass
Eraldo Antonio Bonfatti Júnior1* Rudson Silva Oliveira2
Elaine Cristina Lengowski3 Alan Sulato de Andrade2 Dimas Agostinho da Silva2

1
Departamento de Ciência Florestal, Solos e Ambiente, Universidade Estadual Paulista (UNESP), 18610-034, Botucatu, SP, Brasil. E-mail:
bonfattieraldo@gmail.com. *Corresponding author.
2
Departamento de Engenharia e Tecnologia Florestal, Universidade Federal do Paraná (UFPR), Curitiba, PR, Brasil.
3
Faculdade de Engenharia Florestal, Universidade Federal do Mato Grosso (UFMT), Cuiabá, MT, Brasil.

ABSTRACT: The chemical characteristics of lignocellulosic biomass determine its suitability as an energy source, affecting its combustibility,
flame stability, and overall energy efficiency. Therefore, this study assessed the correlation between the chemical characteristics and higher
heating value (HHV) in Eucalyptus biomass components (wood, bark, branches, and leaves) of three species (E. benthamii, E. dunnii, and
E. saligna). The results revealed varying chemical compositions among the components and species, which impacted the HHV differently.
Notably, volatile materials positively influenced the HHV, whereas excessive ash content negatively affected the energy potential. Positive
correlations with HHV were observed for the total extractives content in the bark, total lignin content in the leaves, volatile materials content in
the bark, leaves, and stem, and fixed carbon content in the stem. Conversely, the holocellulose content reduced the bark HHV. Volatile materials,
except in the branches, efficiently increased the HHV. None of the chemical characteristics had a significant impact on the branches HHV.
Key words: wood, bioenergy, biofuel, Pearson correlation.

Correlação entre o poder calorífico e as características químicas da biomassa de Eucalyptus

RESUMO: As características químicas da biomassa lignocelulósica determinam sua adequação como fonte de energia, afetando sua
combustibilidade, estabilidade de chama e eficiência energética geral. Portanto, este estudo avaliou a correlação entre as características
químicas e o poder calorífico superior (PCS) nos componentes da biomassa de eucalipto (madeira, casca, galhos e folhas) de três espécies
(E. benthamii, E. dunnii e E. saligna). Os resultados revelaram composições químicas variadas entre os componentes, o que impactou o
PCS de forma diferente. Notavelmente, os materiais voláteis influenciaram positivamente o PCS, enquanto o teor excessivo de cinzas afetou
negativamente o potencial energético. Correlações positivas com o PCS foram observadas para o teor de extrativos totais na casca, teor de
lignina total nas folhas, teor de materiais voláteis na casca, folhas e caule e teor de carbono fixo no caule. Por outro lado, o teor de holocelulose
reduziu o PCS da casca. Os materiais voláteis, exceto nos galhos, aumentaram eficientemente o PCS. Nenhuma das características químicas
teve impacto significativo no PCS dos galhos.
Palavras-chave: madeira, bioenergia, biocombustível, correlação de Pearson.

The molecular constituents of lignocellulosic Cellulose and hemicelluloses comprise the

biomass can be of low molecular mass, extractives carbohydrate fraction with highly hydroxylated chains
and ash, or high molecular mass, carbohydrates, and and affinity for water and are mainly responsible for
lignin. And variations in these constituents directly the hydrophilicity of the biomass (THORESEN et
influence the heating value of lignocellulosic biomass al., 2023) and heat value decrease (BRAND, 2010).
(ESTEVES et al., 2023). Lignin and extractives are the Despite having a lower heating value than lignin
components with the highest heating value (ESTEVES and extractives, carbohydrates constitute the largest
et al., 2023). For energy purposes, forest biomass should fraction of lignocellulosic biomass, up to 70%
have a high lignin content; the higher this content, the (BRAND, 2010).
higher the heating value (ESTEVES et al., 2023). The ash content (AC), volatile material
Some of the extractives are volatile and help maintain content (VMC), and fixed carbon content (FCC)
the flame when directly burning wood; however, the compose the proximate analysis (SINGH et
presence of extractives is not very significant because, al., 2017). The VMC is the fraction of biomass
in addition to naturally having a low extractive content that evaporates upon heating, including water
in biomass, most of them volatilize before being used (SINGH et al., 2017). A higher VMC may indicate
as fuel (BRAND, 2010). rapid ignition, but it also reduces the residence

Received 02.24.24 Approved 08.12.24 Returned by the author 10.22.24

CR-2024-0100.R3 Ciência Rural, v.55, n.4, 2025.
Editors: Alessandro Dal’Col Lúcio Rômulo Trevisan
2 Bonfatti Júnior et al.

time of the fuel inside the thermal machine, subtracting the total extractive and total lignin
consequently lowering energy efficiency (SINGH contents from 100%.
et al., 2017). AC is composed of a heterogeneous The volatile materials, ash, and fixed
set of oxides formed during combustion from carbon contents were determined according to the
inorganic components, and it represents the most standards of the American Society for Testing and
undesirable property, as these components not Materials, ASTM-E872-82 (ASTM, 2019a), ASTM
only fail to generate heat but also induce corrosion D1102-84 (ASTM, 2021), and ASTM E870-82
in thermal machines (BRAND, 2010). The FCC (ASTM, 2019b), respectively. The high heating value
stands inversely proportional to the content of was determined using the standard ASTM D5865-13
volatile materials and ash (VEIGA et al., 2017). It (ASTM, 2013) with an IKAC-5000 automated bomb
represents the mass remaining after the release of calorimeter (IKA, Staufen, Germany).
volatile materials, excluding ash. When considering The experiment was conducted with
the use of wood for energy purposes, a high FCC six randomly selected replicates (trees), and the
is desirable because it prolongs the fuel’s residence data were analyzed using R software version 4.3.2
time in the combustion chamber, thereby enhancing (R CORE TEAM, 2023). Analysis of variance
energy efficiency (BRAND, 2010; SINGH et al., (ANOVA) was performed using Fisher’s test (F)
2017). In addition to the heating value, proximate at 5% significance, and when significant, Tukey’s
analysis provides the primary information for the test at 95% probability was applied to compare
use of biomass as a fuel. means. Pearson’s correlation (r) was performed
In this study, we evaluated whether between higher heating value and the chemical
chemical characteristics (total extractives content, characteristics, followed by a significance test
total lignin content, holocellulose content, volatile (t-test) for the correlation coefficients found.
materials content, ash content, and fixed carbon The results of the chemical composition
content) correlated with the higher heating value and proximate analysis of the tree components of the
of forest lignocellulosic biomass. To this end, the Eucalyptus species are shown in table 1.
biomass of all aboveground arboreal components The leaves and bark had a higher content
(bark, leaves, stems, and branches) of the three of total extractives owing to the intense physiological
Eucalyptus species (Eucalyptus benthamii var. activity of these components (photosynthesis and
benthamii Maiden & Cambage, Eucalyptus dunnii sap conduction) (TAIZ et al., 2014). The total
Maiden, and Eucalyptus saligna var. saligna Sm.) lignin content was similar among leaves, stems, and
were evaluated. branches but lower in the bark, and the holocellulose
The trees were planted in Canoinhas City, content was not just the main compound in the leaves.
Santa Catarina State, Brazil, in 2011 under a 3 m × The volatile materials content was
3 m spacing, totaling 1,111 trees ha-1. Six trees per inversely proportional to the presence of ash and
species were randomly selected. Wood disk samples fixed carbon content (PEREIRA et al., 2012; VEIGA
were taken at 0%, 25%, 50%, 75%, and 100% of et al., 2017). The stems and branches had the highest
the total tree height of the stem, and about 0.5 kg of content of volatile materials, whereas the leaves and
each of the other components was collected. All tree bark were rich in ash and fixed carbon.
components were reduced to sawdust in accordance On average, biomass has a VMC between
with the TECHNICAL ASSOCIATION OF THE 57.2 and 90.6%, FCC between 9.2 and 32.8% and AC
PULP AND PAPER INDUSTRY TAPPI T257 sp- between 0.1 and 2.4% (SHEN et al., 2010). The VMC
21 (TAPPI, 2021a) for analysis, and five wood discs and FCC values found in this study are in line with
sawdust were mixed to create a composite sample what is reported in the literature, however, the AC
for each tree. values for bark and leaves are much higher than what
The acid-insoluble lignin, acid-soluble is expected for lignocellulosic biomass.
lignin, and total extractive contents were determined Leaves had the highest heating value
according to TAPPI T 222 om-21 (TAPPI, 2021b), (Table 2), followed by stems and branches, which
GOLDSCHIMID (1971), according to TAPPI T 204 were not statistically different. Owing to the high ash
cm-17 (TAPPI, 2017), respectively, to determine content and low total lignin content, the bark had the
the chemical composition of the biomass. The lowest heating value. In a study that evaluated the HHV
sum of the acid-insoluble and acid-soluble lignin of 17 different woods, TELMO & LOUSADA (2011)
contents was considered the total lignin content, found variations between 17.63 and 20.81 MJ kg-1, in
and the holocellulose content was obtained by this study the HHV of the bark were below this range.

Ciência Rural, v.55, n.4, 2025.

 Correlation between the heating value and the chemical characteristics of Eucalyptus biomass. 3

Table 1 - Average values for chemical characteristics per component per species.

Chemical characteristic (%) ------Component------- ------E. benthamii----- --------E. dunnii-------- -------E. saligna-------
Bark 17.98 ± 0.40 aB 16.46 ± 0.55 aB 12.20 ± 0.46 bB
Leavesns 38.47 ± 0.34 A 39.09 ± 0.11 A 39.71 ± 0.24 A
EC
Stemns 3.53 ± 0.29 C 3.58 ± 0.15 C 2.71 ± 0.19 D
Branchesns 5.25 ± 0.21 C 3.61 ± 0.34 C 5.26 ± 0.33 C
Bark 15.57 ± 0.29 bC 20.34 ± 0.21 aB 17.30 ± 0.32 bC
Leaves 23.90 ± 0.38 bB 24.82 ± 0.12 bA 27.54 ± 0.28 aA
LC
Stem 26.41 ± 0.22 aA 22.58 ± 0.18 bAB 26.98 ± 0.20 aA
Branches 22.43 ± 0.50 abB 20.42 ± 0.49 bB 23.87 ± 0.37 aB
Bark 66.45 ± 0.22 bB 63.20 ± 0.36 cB 70.49 ± 0.32 aA
Leaves 37.63 ± 0.37 aC 36.09 ± 0.15 aC 32.76 ± 0.10 bB
HC
Stem 69.70 ± 0.13 bA 73.42 ± 0.10 aA 70.00 ± 0.14 bA
Branches 72.32 ± 0.27 bA 75.97 ± 0.26 aA 70.87 ± 0.16 bA
Bark 74.05 ± 0.07 aC 71.66 ± 0.07 bC 73.23 ± 0.10 aC
Leaves 71.37 ± 0.11 aD 71.33 ± 0.07 aC 68.78 ± 0.15 bD
VMC
Stem 79.85 ± 0.04 cA 82.42 ± 0.06 aA 81.06 ± 0.06 bA
Branchesns 77.25 ± 0.12 B 77.92 ± 0.10 B 77.99 ± 0.15 B
Bark 3.17 ± 0.14 bB 3.63 ± 0.25 aB 3.46 ± 0.12 abB
Leaves 5.04 ± 0.29 aA 4.32 ± 0.03 bA 5.06 ± 0.22 aA
AC
Stemns 0.47 ± 0.06 D 0.42 ± 0.09 D 0.31 ± 0.14 D
Branchesns 1.42 ± 0.40 C 1.22 ± 0.24 C 1.22 ± 0.15 C
Bark 22.78 ± 0.08 bA 24.72 ± 0.17 aA 23.31 ± 0.16 bB
Leaves 23.60 ± 0.15 bA 24.36 ± 0.12 bA 26.16 ± 0.23 aA
FCC Stem 19.68 ± 0.09 aC 17.16 ± 0.12 cC 18.62 ± 0.11 bD
Branchesns 21.33 ± 0.13 B 20.86 ± 0.15 B 20.79 ± 0.26 C

EC: total extractive content; LC: total lignin content; HC: holocellulose content; VMC: volatile materials content; AC: ash content; FCC:
fixed carbon content; ns: non-significant for the species factor within the component factor at 95% probability for the Fisher's test; equal
lowercase letters in the line do not differ among species and equal uppercase letters in the column do not differ among components at 95%
probability by Tukey’s test.

The chemical characteristics that showed The volatile materials content efficiently
significant positive correlations with higher heating increased the higher heating value, with branches
values were the extractives content of the bark, being the only exception. The ash content was
total lignin content of the leaves, content of volatile significantly harmful to the energy use of the
materials in the bark, leaves, and steam, and fixed forest biomass when very high. Volatile materials
carbon content of the steam (Table 3). However, the were mainly formed by compounds with high
holocellulose content reduced the heating value of the heating values. However, ash did not participate
bark, and the presence of ash negatively affected the in combustion; and therefore, did not release heat
biomass of the leaves and bark (Table 3). (SINGH et al., 2017; ESTEVES et al., 2023).

Table 2 - Average values for higher heating value per component per species.

Energy characteristic ------Component------ -----E. benthamii------ -------E. dunnii------- -------E. saligna-------

Bark 16.79 ± 0.03 aC 16.11 ± 0.11 bC 15.97 ± 0.14 bC
Leaves 20.66 ± 0.11 aA 20.76 ± 0.03 aA 20.12 ± 0.08 bA
HHV (MJ kg-1)
Stem 18.32 ± 0.09 aB 17.79 ± 0.06 bB 17.95 ± 0.04 abB
Branchesns 18.17 ± 0.04 B 17.99 ± 0.33 B 18.11 ± 0.07 B

HHV: higher heating value; ns: non-significant for the species factor within the component factor at 95% probability for the Fisher's test;
equal lowercase letters in the line do not differ among species and equal uppercase letters in the column do not differ among components
at 95% probability by Tukey’s test.

Ciência Rural, v.55, n.4, 2025.

4 Bonfatti Júnior et al.

Table 3 - Correlation between the higher heating value and the chemical characteristics of the different components of Eucalyptus trees.

Chemical characteristic (%) -----------Bark----------- ----------Leaves--------- -----------Stem----------- ---------Branches--------

0.575 -0.144 0.241 0.024
EC
(0.01)* (0.57)ns (0.33)ns (0.92)ns
-0.360 0.564 0.324 0.168
LC
(0.14)ns (0.01)* (0.19)ns (0.50)ns
-0.233 -0.556 -0.422 -0.153
HC
(0.35)ns (0.02)* (0.08)ns (0.55)ns
0.497 0.694 0.602 0.037
VMC
(0.04)* (0.00)* (0.01)* (0.89)ns
-0.496 -0.775 0.442 0.130
AC
(0.04)* (0.00)* (0.07)ns (0.61)ns
-0.369 -0.449 0.577 -0.099
FCC
(0.13)ns (0.06)ns (0.01)* (0.70)ns

EC: total extractive content; LC: total lignin content; HC: holocellulose content; VMC: volatile materials content; AC: ash content;
FCC: fixed carbon content; in parentheses is the p-value result;
*
is significant and ns is non-significant at 95% probability by t-test, respectively.

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