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Equilibrio de extracción

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Equilibrium Data for the Extraction of
Coffee and Sunflower Oils with Ethanol
Dados de Equilíbrio para o Processo
de Extração de Óleos de Café e
Girassol Usando Etanol
AUTORES
AUTHORS
Suely Pereira FREITAS
Universidade Federal do Rio de Janeiro
Escola de Química
Ilha do Fundão, Cidade Universitária
Bloco E, Sala 207
CEP: 21949-900
Rio de Janeiro/RJ - Brasil
e-mail: freitasp@eq.ufrj.br
Regina Celi Araujo LAGO
Embrapa Agroindústria de Alimentos
e-mail: lago@ctaa.embrapa.br
SUMMARY
The extraction of vegetable oils using ethanol may be a good solution for countries
where small oil mills are economically feasible. Furthermore, ethanol is environmentally
more attractive than hexane. In this work, experimental solid-liquid equilibrium data
for vegetable oil extraction with ethanol have been investigated as a function of the oil
content in the raw material and the sample to ethanol mass ratio. The maximum solute
concentrations obtained in the micelle were 11.4 and 18.6%, respectively, for coffee and
sunflower oils. These results are inferior to the typical values of between 20 and 30%
obtained with the countercurrent flow processes used in the food industry, with hexane
as the solvent. To estimate the theoretical stages, the tie lines can be ascertained using
the distribution curves and solubility diagrams simultaneously.
RESUMO
A extração de óleos vegetais com etanol pode ser uma solução potencial para
os países onde a operação de usinas comerciais de pequeno porte é economicamente
viável. Além disso, do ponto de vista ambiental, o etanol é um solvente mais atraente
que o hexano. Neste trabalho, os dados de equilíbrio para extração de óleos vegetais
com etanol foram avaliados em função do teor de óleo na matéria-prima e da relação
solvente/substrato. A concentração máxima de soluto na micela foi de 11,4 e 18,6% para
extração dos óleos de café e girassol, respectivamente. Estes resultados são inferiores aos
valores típicos, entre 20 e 30%, alcançados para o processo de extração contínua em
fluxo contra-corrente, usado nas usinas comerciais de extração de óleos vegetais com
hexano. As linhas de amarração, para cálculo do número de estágios teóricos, podem
ser construídas usando-se, simultaneamente, as curvas de distribuição e os diagramas
de solubilidade.
PALAVRAS-CHAVE
KEY WORDS
Solid-liquid extraction; Equilibrium data; Ethanol;
Oleaginous seeds; Coffee oil; Sunflower oil.
Extração sólido-líquido; Dados de equilíbrio;
Etanol; Óleo de café; Óleo de girassol.
Autor Correspondente
Corresponding Author
Braz. J. Food Technol., Campinas, v. 10, n. 3, p. 220-224, jul./set. 2007
220
Recebido/Received: 22/12/2005. Aprovado/Approved: 05/11/2007.
FREITAS, S. P. e LAGO, R. C. A.
1. INTRODUCTION
The vegetable oil processing industry continues to expand.
Today, about thirteen vegetable oils have been used for industrial
food formulations around the world, specially from soybean, palm,
rapeseed, sunflower, cottonseed and peanut. Vegetable oils have
been conventionally obtained combining pressing and organic
solvents extraction. From those hexane-based extractions, it is
possible to achieve oil yields greater than 95% (JOHNSON and
LUSAS, 1983).
In the last years, the authorities have become more and
more aware of the environmental matters concerning the use of
large amounts of toxic organic solvents. As a result, disposal regulations have become very strict and, as a consequence, processing
costs increased. In many countries, most toxic organic solvents
have already been banned in food processing. Thus, in developing
safer processes, the substitution of hexane has been highly recommended (EPA, 2000).
The potential use of ethanol for vegetable oil extraction has
already been investigated (FREITAS et al., 2001; RITTNER, 1991;
RAO et al., 1955). As ethanol is derived from a renewable source it
is regarded as an environmentally cleaner solvent. So, ethanol may
represent a good alternative for countries in which small oils mills
are economically feasible and where ethanol availability turns less
expensive than hexane.
The use of ethanol for green coffee and sunflower oil
extraction has been previously studied on bench scale (KOHL et al.,
2003; FREITAS et al., 2001). In those works, the following independent variables were considered: extraction temperature, sample
to ethanol ratio, moisture present in the seeds and particle size.
Extraction kinetics showed that the highest yields have resulted
with incubation time of 20 and 40 min, respectively to green
coffee and sunflower oils. Time increasing up to 60 min had small
influence on extraction yield. The optimized conditions for these
processes for coffee beans and sunflower seeds, respectively, have
been determined: temperature of 75 and 70 °C, particle size inferior to 1.0 and 1.7 mm, sample to ethanol ratio 1:3 and moisture
of the seed inferior to 3%. Under these conditions, the amount of
solute obtained was higher than the lipids fraction extracted with
petroleum-ether. According to the authors, extraction temperatures
above 70 °C have probably favored wax removal by ethanol.
The extraction mechanism is a combination of diffusion and
mixing of soluble material in the solvent. The distribution relationship in solid-liquid extraction depends mainly on the temperature
and the chemical nature of the species involved. At about 85 °C,
above the boiling point of ethanol at atmospheric pressure (78 °C),
vegetable oils are totally miscible with ethanol. As a consequence,
the solubility of oil in ethanol at temperatures below 78 °C becomes
the limiting extraction parameter, requiring greater solvent to sample
ratio than the hexane-based process, which seems to be controlled
by diffusion. According to Rittner (1991), ethanol as a solvent is
compatible with the equipment currently used in vegetable oils
industries and would require minor changes in operating conditions
and plant layout to be implemented on a large scale. To enhance oil
solubility, the extractor can be operated at pressures slightly superior
to atmospheric (20 to 30 psig) and temperature about 85 °C.
The equilibrium condition between the cake (raffinate
phase) and miscella (solvent phase) is a very important aspect
of vegetable oil extraction. Solid-liquid equilibrium data is necessary for both design and process simulation of extractors used in
Braz. J. Food Technol., Campinas, v. 10, n. 3, p. 220-224, jul./set. 2007
Equilibrium Data for the Extraction of
Coffee and Sunflower Oils with Ethanol
food industry. Until now, no expressive data are available in the
literature concerning ethanol-based vegetable oil extractions. In
this work, solid-liquid equilibrium results for coffee and sunflower
oils extraction with ethanol 99.2% are presented. In order to obtain
equilibrium data, the effects of sample to ethanol mass ratio were
evaluated.
2. MATERIAL AND METHODS
Commercial Robusta coffee beans, commercial sunflower
seeds and ethanol 99.2% were used.
Oil content in the samples was determined using petroleum
ether 30-60 °C, after 16 h of reflux, in a Butt type extractor (AOCS,
1996). Proximate composition was determined according to AOAC
methods (AOAC, 1995).
Ethanol extracts obtained were filtered and fatty acid
composition was determined by gas chromatography of methyl
esters prepared according to Hartman and Lago (1973). The fatty
acid analysis of oils was performed on a HP5890 gas chromatography equipped with a fused silica capillary column SP2340
(60 m x 0.32 mm x 0.25 µm). The temperature program was 150 up
to 200 °C at a rate of 1.3 °C/min. Sample dilution was 2%, the volume
injected was 1 µL and the carrier gas was H2 at 2.5 mL/min.
The samples were ground in a pilot hammer mill. Green
coffee beans and sunflower seeds with size particle ranges of
0.5 mm < d < 1.0 mm and 0.85 mm < d < 1.70 mm, respectively, were selected. Due to high oil content in the sunflower seed
(about 45%) particle size reduction below 0.85 mm led to oil loss
in the milling.
In order to enhance the efficiency of the ethanol extraction
process, the initial moisture of all samples was reduced to 3% in a
tray dryer with hot air flow at 60 °C.
2.1 Extraction experiments and
concentrations at equilibrium
The sample and ethanol were placed in an erlenmayer flask
and maintained in a temperature-controlled bath under continuous
stirring to homogenize the mixture. The mixture, after 16 h, was
filtered under vacuum through filter paper and both fractions,
miscella and cake, were weighed. The ethanol in the miscella
was removed in a rotary evaporator while the solvent retained in
the cake was removed at 60 °C in an oven with hot air flow. The
yield of lipid extraction and solute concentration in both phases at
equilibrium was correlated, at 70 and 75 °C, with mass ratios of
sample to solvent. The maximum amount of solute (Mo), present
in both samples, was determined using ethanol at infinite dilution
(solvent to sample mass ratio as 20:1). The equilibrium data were
recorded by macroscopic mass balance of the solute in the cake
and miscella phases.
3. RESULTS AND DISCUSSION
The proximate composition of commercial Robusta green
coffee beans and sunflower seeds, given in Table 1, was similar to
the values reported in the literature (FOLSTAR, 1985; MACRAE,
1993; HARTMAN et al., 1999).
The fatty acids composition of coffee extracts consisted
of saturated and unsaturated acids while fatty acids of sunflower
extracts were predominantly unsaturated acids (Table 2). The results
221
FREITAS, S. P. e LAGO, R. C. A.
Equilibrium Data for the Extraction of
Coffee and Sunflower Oils with Ethanol
TABLE 1. Proximate composition of Robusta coffee and sunflower seeds [g.100 g–1].
Oil
Protein
Moisture
Total ash
Starch
Crude fibre
Carbohydrates**
Commercial Robusta coffee*
10.50 ± 0.15
13.53 ± 0.04
11.40 ± 0.17
3.63 ± 0.08
3.14 ± 0.04
14.49 ± 0.60
-
Literature data1
9.00 to 12.60
11.00 to 15.60
10.20 to 11.00
4.20
18.50
-
Sunflower seeds*
44.34 ± 0.62
23.04 ± 0.28
5.40 ± 0.001
3.75 ± 0.35
nd
nd
23.47
Literature data2
47.83 to 54.80
18.34 to 22.16
4.41 to 5.87
3.06 to 3.69
1.97 to 2.32
15.47 to 19.83
Sunflower oil*
5.25 ± 0.19
3.79 ± 0.49
33.57 ± 0.51
56.11 ± 1.47
traces
traces
1.00 ± 0.02
Literature data2
4.88 to 5.41
2.97 to 4.41
32.55 to 41.67
46.54 to 56.11
0.11 to 0.20
0.27 to 0.39
0.82 to 0.99
1
Trugo (2001) and Folstar (1985); 2 Hartman (1999). nd - no determined
*Average of three replicates ± standard deviation. **by difference.
TABLE 2. Fatty acids composition of coffee and sunflower oils (%).
Fatty acids
C16:0
C18:0
C18:1
C18:2
C18:3
C20:0
C22:0
Coffee oil*
32.26 ± 2.15
7.76 ± 0.40
11.21 ± 0.89
42.69 ± 2.43
1.17 ± 0.14
2.92 ± 0.32
traces
Literature data1
32.1 to 33.2
7.5 to 8.2
8.2 to 12.5
42.6 to 46,2
0.9 to 1.4
2.6 to 3.3
-
*Average of three replicates ± standard deviation; 1Folstar (1985); 2Hartman et al. (1999).
obtained are in agreement with the literature data for coffee and
sunflower oils extracted with petroleum-ether (FOLSTAR, 1985;
HARTMAN et al., 1999).
Figure 1 presents extraction yields (M/Mo) of coffee and
sunflower oils as a function of sample to ethanol mass ratio. M is
the amount of solute extracted at equilibrium and Mo is the amount
of solute present in the raw material. At the same sample to solvent
mass ratio, the coffee oil yield is higher than that of sunflower oil.
That fact is due to higher oil content present in the sunflower seeds
(44.3%) than in the coffee beans (10.5%) promoting the faster
ethanol saturation in the first case.
M/Mo (%)
The equilibrium diagrams are presented in Figures 2 and 3
for the system: solute (a) + inert (b) + solvent (c). Equilibrium is
reached when the maximum amount of solute is transferred to the
solvent phase. The concentration in the two phases expressed as
mass ratio (X for the raffinate phase and Y for the solvent phase) is
defined on an inert free basis (GEANKOPLIS, 2003):
 ma 
 mb 
Xa = 
Xb = 


m
+
m
 a
 m a +mc  cake
c  cake
100
90
 ma 
 mb 
Ya = 
Yb = 


 ma + mc  miscella
 ma + mc  miscella
80
70
60
50
As expected, the equilibrium yield M/Mo decreases if the
sample to solvent mass ratio increases. On the order hand, the
miscella retained in the cake increases as the sample to solvent
mass ratio increases and higher is the oil loss remaining with in the
cake (Figure 2 and 3). The results shown are in accordance with the
findings of Dibert et al. (1989).
10
20
30
40
50
Sample/ethanol ratio (% w/w)
60
green coffee (0.5 mm <d<1 mm)
sunflower (0.8 mm <d <1.7 mm)
FIGURE 1. Coffee and sunflower oil yield as a function of sample/
ethanol mass ratio at equilibrium. M - amount of solute extracted
at equilibrium; Mo - amount of solute in the sample.
Braz. J. Food Technol., Campinas, v. 10, n. 3, p. 220-224, jul./set. 2007
where mi represents the mass of component i in equilibrium (DIBERT
et al., 1989). For both samples, the distribution curve, Xa= f(Ya), has
shown that the cake (a porous media) has a higher concentration
of solute than the solvent phase (miscella), due to the low solubility
of solutes in ethanol at 70 and 75 °C and also to the adsorption of
solute on the solid matrix.
For both samples, complete oil extraction was reached for
sample to ethanol mass ratio of up to 0.05. In this case, on an inert
free basis, the miscella has the same solute concentration than the
cake, (Ya = Xa) as can be observed in Figures 3 and 4. As sample to
ethanol mass ratio increases, the cake presents a higher concentration of solute component than the miscella due to low oil yield.
As a consequence, the experimental data in the distribution curve
deviate from the diagonal line (X = Y). The auxiliary lines, shown in
222
FREITAS, S. P. e LAGO, R. C. A.
Solubility diagram: coffe oil in ethanol
at 75 °C; 0.5 < dp < 1 mm
3.50
1.00
3.00
0.80
2.50
Xb
Xb
1.20
Solubility diagram of sunflower oil in ethanol
at 70 °C; 0.85 < dp < 1.7 mm
0.60
2.00
1.50
0.40
1.00
0.20
0.00
0.00
0.50
0.05
0.10
0.15 0.20
Xa or Ya
0.25
0.30
0.35
0.00
0.00
0.40
0.05
0.08
Xa or Ya
0.10
0.13
0.15
0.40
0.40
0.35
0.30
0.30
0.25
Xa
0.35
0.25
Xa
0.03
Distribution curve: coffe oil in cake (Xa) and miscella (Ya)
at 75 °C; 0.5 < dp < 1 mm
Distribution curve: sunflower oil in cake (Xa) and miscella (Ya)
at 70 °C; 0.85 < dp < 1.7 mm
0.20
0.20
0.15
0.15
0.10
0.05
0.10
0.00
0.00
0.05
0.00
0.00
Equilibrium Data for the Extraction of
Coffee and Sunflower Oils with Ethanol
0.05
0.10
0.15
0.20
Ya
0.25
0.30
0.35
0.40
FIGURE 2. Equilibrium data for sunflower oil extraction with
ethanol. The diagonal line (dashed line) representing equilibrium
diagram where solute is infinitely soluble in solvent.
Figures 2 and 3, illustrate the graphical procedure to obtain pairs
of points representing the two phases in equilibrium.
The maximum solute concentrations in the miscella have
been found as 11.4 and 18.6%, respectively to coffee and sunflower
oils. The higher value achieved in the last case is due to a higher
oil content in the sunflower raw material. These values are greater
than the ones reported by Dibert et al. (1989).
According to Figures 2 and 3, the inert concentration in the
cake, on an inert free basis, depends on the oil content in the raw
material. It can be observed that solvent drains better from the coffee
beans than from the sunflower seeds, which can be explained by
the occurrence of a higher amount of residual oil in the sunflower
cake and its smaller porosity.
4. CONCLUSIONS
The experimental equilibrium curves presented in this work
could be useful in determining the number of theoretical stages on
the design of a continuous extraction column. The maximum solute
Braz. J. Food Technol., Campinas, v. 10, n. 3, p. 220-224, jul./set. 2007
0.03
0.05
0.08
0.10
0.13
0.15
Ya
FIGURE 3. Equilibrium data for coffee oil extraction with ethanol.
The diagonal line (dashed line) representing equilibrium diagram
where solute is infinitely soluble in solvent.
concentrations in the miscella were 11.4 and 18.6%, respectively to
coffee and sunflower oils. These results are inferior to typical values
(between 20 and 30%) reached from countercurrent flow processes,
used in the food industry, having hexane as solvent. As expected,
the poor solubility of vegetable oil in ethanol in the temperature
range from 70 to 75 °C is the limiting extraction factor.
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Equilibrium Data for the Extraction of
Coffee and Sunflower Oils with Ethanol
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