CHARACTERIZATION OF OLIVE RESIDUES FOR POWER

CHARACTERIZATION OF OLIVE RESIDUES FOR POWER GENERATION BY NEARINFRARED
SPECTROSCOPY
Jesús Mata Sáncheza, José Antonio Pérez Jiménez*a, Manuel Jesús Díaz Villanuevaa, Antonio Serranob, Nieves Núñezb,
Jesús López Giménezc
a
Department of Biomass, CTAER Andalucía Foundation, Scientific and Technology Park, GEOLIT, Jaén (Spain)
b
NIR Soluciones, S.L., Rabanales 21 Science and Technology Park, Córdoba, Spain.
c
Department of Rural Engineering, Faculty of Agricultural and Forestry Engineering, University of Córdoba.
*Corresponding e-mail: [email protected]
ABSTRACT: The main objective of this work is to evaluate the viability of NIR technology as an efficient method
for biomass characterization generated by olive residues. Solid biofuels quality parameters are determined by official
methods established by the European Standard Technology Committee. Nevertheless, their implementation in the
bioenergetic industry is scarce because these methods are expensive, tedious and time-consuming. Therefore, a faster,
more reliable and cheaper analytical technique is mandatory in order to increase the quality control of these products
in the bioenergetic industry. NIR spectroscopy is an eligible technique due to its high response speed, low cost per
sample, absence of sample preparation, and versatility for the analysis of many different products and parameters. In
this work, several biomass samples from olive industry such as olive stone, olive tree pruning (leaves, branches and a
mixture of them) and dry solid olive waste (orujillo) have been analyzed in reflectance mode by using different NIR
instruments without sample manipulation or only after a grinding up to 0.25 mm. The spectra showed a good
absorbance in the representative NIRS regions; consequently, a great amount of information can be obtained.
Keyword: Olive tree, quality standards, biomass, residues, NIR
1
INTRODUCTION
Solid biofuels are a real option for thermic and
electrical generation as alternative to the traditional
generation from fossil fuels. Energy policy established by
the European Union, Spain and Andalusia (Southern
Spanish region) aimed at promoting renewable energy
use and production. Due to its vast forest areas and
mainly agricultural land use, Andalusia has a high
potential for biomass generation. Within this context,
olive industry is one of the main generators of solid
biofuels both from residues generated in olive tree
plantations and those generated by the olive oil industry.
Only in Andalusia, the olive tree cultivated ground is
over 1.400.000 Ha and the production of olive oil is over
800.000 t/year. In addition, residues generated by both
agricultural activities represent a large bulk. For example,
olive stones generated are over 450.000 t/year, olive
pruning is over 2.000.000 t/year and orujillo residue is
over 684.000 t/year (Economy, Innovation and Science
Department of Andalucia Governement, 2011).
From the point of view of energy stability and
sustainable development, the energetic use of forest
residues, agricultural and/or industrial by-products leads
to a key strategic position for the future. The
characterization of biomass is a substantial improvement
in the valorization of these resources, allowing a rational
and controlled use of its energy potential. Based on its
quality parameters, solid biofuels could be managed to
obtain a most efficient energetic valorization. Currently,
solid biofuels quality parameters are determined by
official methods established by the European Standard
Technology Committee. However, their implementation
in the bioenergetic industry is scarce because these
methods are expensive, tedious and time-consuming.
In this way, a faster, more reliable and cheaper
analytical technique is required in order to increase the
quality control of these products in the bioenergetic
industry. NIR spectroscopy is, therefore, an eligible
technique due to its high response speed, low cost per
sample, absence of sample preparation, and versatility for
the analysis of many different products and parameters.
Near infrared radiation (NIR) covers the range of the
electromagnetic spectrum between 780 nm and 2500 nm
and it was discovered by Friedrich Wilhelm Herschel in
1800 (Davies, 2000). In NIR spectroscopy, the product is
irradiated with NIR radiation, and the reflected or
transmitted radiation is measured. While the radiation
penetrates the product, its spectral characteristics change
through wavelength dependent scattering and absorption
processes. This change depends on the chemical
composition of the product, as well as on its light
scattering properties which are related to the
microstructure. Understanding this phenomenon, it is
possible to know the chemical constitution and physical
parameters of the sample. Advanced multivariate
statistical techniques are required to extract the required
information from the usually convoluted spectra.
Furthermore, NIRS technology is fully implemented in
the agrifood industry for the determination of parameters
such as moisture, protein, fiber, fat or sugar in a large
number of products (Shenk et al., 2001; Muller and
Steinhart, 2007)
NIR radiation interacts with organic molecules and
especially with structural groups O-H as in water, C-H,
C-O, C-O-H and C=C bonds. These bonds are frequently
found in biomass and they are related with important
quality parameters like moisture, carbon content or
energetic power.
The main objective of this research is to evaluate the
viability of NIR technology as an efficient method to
analyze solid biofuels obtained from olive residues, in
comparison with official methods.
2
MATERIALS AND METHODS.
2.1 Raw materials and sample preparation
A sampling plan of olive residues such as olive
stones, leaves, branches and orujillo were collected from
different Andalusian industries. These samples have been
b)
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Absorbance (Log 1/R)
analyzed by NIR technology and by official methods
established by the European Standard Technology
Committee. Near infrared spectroscopy analysis has been
carried out without sample manipulation or after a
grinding up to 0.25 mm.
In this research, it has been analyzed 71 samples of
olive stones, 20 samples of olive tree pruning and 16
samples of dry solid olive waste.
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3. RESULTS AND DISCUSSION
An example of duplicate NIR spectra corresponding
to two representative samples of intact and ground olive
stone, obtained by the instruments described above are
shown in Figure 1.
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0
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Wavelength (nm)
c)
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Absorbance (Log 1/R)
2.2 Near-infrared spectroscopy
In this study, spectral response for different types of
intact and ground biomass has been obtained by different
NIRS instruments. These instruments can be classified
into three groups according to optic system and spectral
region:
a) NIRS instruments with monochromator and
continuous spectrum, with a spectral region
from 400 to 2500 nm collecting data every 2
nm. Sealed rectangular sample containers were
used with a vertical transport module obtaining
spectra all over the surface of the sample
container. Each analysis takes 2 to 3 minutes.
NIRS instruments such as FOSS or UNITY
commercial firms are included in this group.
b) Fourier transform near-infrared instrument with
continuous spectrum and a spectral region from
12000 cm-1 (800 nm) to 4000 cm-1 (2500 nm)
collecting data every 16 cm-1. Open round
sample containers were used with a rotation
system obtaining spectra all over the surface of
the sample. Each analysis takes 20 seconds
approximately. Commercial NIRS instruments
from firms like BRUKER, BÜCHI or PERKINELMER are included in this group.
c) Diode array NIRS instruments with a spectral
region from 380 nm to 1690 nm collecting data
every 3 nm. Open round sample containers were
used. Each analysis takes less than one second.
NIRS instruments like CORONA or PERTEN
commercial firms are included in this group.
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Wavelength (nm)
Figure 1. Sample spectra of intact (red) and ground
(blue) olive stones obtained by duplicate analysis by
instruments a), b), and c)
As it is shown in Figure 1, differences between
ground samples spectra are slighter than those obtained
from intact sample spectra, being the duplicate spectra of
the ground samples almost equal. Instruments type c)
were discarded due to the absence of interesting bands in
their spectral region (380-1690 nm), only the water band
(1430 nm) could give information of interest. In the other
hand, the most significant spectral region corresponds to
the range between 1100 to 2500 nm, where characteristic
absorption bands can be seen in the spectra obtained by
instrument a) and b) at 1450 nm and 1930 nm
corresponding to O-H bonds, at 1720 nm and 2300 nm
corresponding to C-H bonds, or at 2100 nm
corresponding to C-O bonds.
1.4
a)
Olive tree pruning
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Dry solid olive waste
Olive stone
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Absorbance (Log 1/R)
Absorbance (log 1/R)
Olive wood pellet
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Wavelength (nm)
Wavelength (nm)
Figure 2. Intact sample spectra of different solid biomass
from olive industry.
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In addition, spectra corresponding to olive stones,
leaves, pruning, branches, olive tree firewood, and
orujillo, are shown in Figure 2. As can be seen, spectra
are very similar while significant differences are found in
spectral region corresponding to the fat content (1720 nm
and 2300 nm), being this effect more marked in olive
stone and olive tree pruning.
On the other hand, a spectral study of the solid
biofuels samples has been carried out in order to detect
similarities and differences among them and to establish
different set of samples in the subsequent calibration
model. Figure 3 shows the graphic representation of three
first principal components of the solid biofuel spectra. A
clear difference between solid biofuel spectra is found,
being olive tree residues the solid biofuel most different.
Despite of the possibility of developing a global
chemometric model, it would be better to develop a
specific calibration model for each kind of residue in
order to obtain the best results and detect easily outliers.
Figure 3. Graphic representation of spectral population
of olive stone, olive tree pruning and orujillo.
When a feasibility study of an NIRS application is
performed, it is important to study the spectral
repeatability in our samples. This study can be done with
the statistical parameter called RMS (root mean squared).
This parameter gives information about the spectral
difference between a sub-sample and the spectral mean of
some sub-samples of one sample. In this study it has been
the spectral mean with 20 intact sub-samples for each
type of sample.
Solid biofuel
RMS (A)
RMS (B)
Olive tree pruning
8000
10000
Olive stone
11500
14000
Dry solid olive waste
13500
12000
Table 2. RMS value of different products studied with
instruments a) and b)
These RMS values indicate that uniformity of
samples is satisfactory for the use of NIRS technology. It
is remarkable that olive tree pruning presents the lowest
values of this parameter in spite of its heterogeneity.
4. CONCLUSION
Based on the results NIRS technology could be used
as a sustainable method to analyze solid biofuels from the
official method data by using the spectral region between
1100 and 2500 nm. NIRS spectra information could be
used to predict quality parameters such as moisture,
carbon content , nitrogen content or net calorific value.
NIRS method allows increasing the quality control of
products in the bioenergetic industry and enables
comprehensive traceability of raw materials and
processes in order to a better use of resources.
5. REFERENCES
Muller, A.; Steinhart, H. 2007. Recent developments
in instrumental analysis for food quality. Food Chem.
102, 436-444.
Shenk J.S., Workman J.J., Jr. and Westerhaus M.O.
2001. Application of NIR Spectroscopy to Agricultural
Products. Handbook of Near Infrared Analysis. Second
Edition. Burns D.A. and Ciurzack E. W. (eds). Practical
Spectroscopy Series, Vol. 27. Marcel Dekker, USA.
Davies, A.M.C., 2000. William Herschel and the
discovery of near infrared.Spectrosc. Eur. 12, 10–16