Application of Palygorskite in Purification Process of Frying Oil
ARAÚJO, Rian Felipe de Melo ¹,a; FREIRE, Lécia Maria da Silva 1,b;
NUNES, Lívio César Cunha 1,c,
¹Center for Pharmaceutical Technology (NTF), Federal University of Piauí, UFPI,
Teresina, PI, Brazil.
a
rianmelo@hotmail.com, bleciafcs@gmail.com, cliviocesar@hotmail.com
Keywords: palygorskite; frying oil; acid activation
Abstract. The Brazil produces a million tons of waste oils from frying, annually.
Disposal of these usually is done improperly, resulting in serious environmental
problems. In this context, the objective was to develop a method for purification of oils
used in frying, using palygorskite as an cleansing agent. For this, acid activation and
characterization of palygorskite was realized. So, were developed a method for
purification of oil, using 23 factorial design as a tool for process optimization.
Subsequently, was realized the physicochemical characterization of oils by
transesterification followed by GC-MS. The results revealed a significant increase in the
adsorption of the clay after acid activation process, while tests of purification of frying
oil showed effective improvement of their characteristics, highlighting the
disappearance of the smell of rancid oil and bleaching. The results showed that the
purification method used was efficient.
Introduction:
The palygorskite, a great adsorbent material of polar molecules and positive ions, is
classified in the group of special clays being found in large scale only in restricted areas.
The largest producer is in the United States and Brazil, where the main deposits are
located in the city of Guadalupe in the state of Piauí [1].
Acid activation is the usual method used to modify the characteristics of clay
minerals. The activation treatment by inorganic acids increases the surface area of the
clay due to disruption of the structure by elimination of various minerals and impurities
and creating a mesopores. Thus, the creation of these increases the adsorption capacity
of the clay [2].
The vegetable oils used in frying by immersion processes cause risks of
environmental pollution and therefore deserve special attention. These oils are broad
and universally consumed for the preparation of food in industrial and commercial
establishments, as well as in households [3].
A problem found in the use the frying oil is the contamination generated during the
process. Thus is essential your treatment before reuse. The use of palygorskite as
adsorbent of these impurities is due to its chemical properties with cationic
characteristics responsible for its large adsorption capacity. After the immersion frying
process the oils used are waste that may once discarded in nature contaminating the
environment [4].
Thus, the aim of this study was to develop a method of purification of oils subjected
to frying process using palygorskite as adsorbent agent of impurities, besides
characterizing the purified oil in order to prove the effectiveness of the method.
Materials and methods
Palygorskite (Coimbra Mining Company Ltd.) was activated by acid process as the
methodology described by Oliveira (2010) [5]. After activation, palygorskite was
characterized by X-ray diffraction, infrared spectroscopy and surface area analysis
(BET), according to the methodology described by Frini-Srasra (2010) [6]. After
characterization a study was made to determine the best purification process of the
frying oil. For this, were used the factorial design tool 23. The variables used in this
study were the presence or absence of heating and stirring in the process and the
percentage of palygorskite used (5 or 7%). The data chosen to evaluate the importance
of each variable were: acid value; saponification; and moisture content of the sample.
The results showed that the most efficient method of purification is the one that uses
7% palygorskite under magnetic stirring and heating for 3 hours at 90° C.
The oil used in this study was provided by the University Restaurant of Federal
University of Piauí. It was subjected to an only frying process at 190 ° C.
The virgin, frying and the purified oil were characterized organoleptically, by
changes color, odor and homogeneity, as well as by acid value, iodine value,
saponification and gas chromatography according to the methodology described by
Freire (2009), as well as the moisture content by Karl Fische method [7].
Results and discussion
According to the results of the XRD (Figure 1) and the infrared spectra (Figure 2),
were observed no significant changes in their structure after the acid activation
treatment. However, the analyzing of the surface area and pore size (BET) has shown an
increase in adsorption capacity of the clay in increasing the surface area of contact. The
natural palygorskite had an area of 120 m²/g, while the actived showed about 10 times
highe This is due to the elimination of exchangeable cations through dissolution and
increasing porosity, thus the morphology of the clay becomes more open and less
concise [8].
After determining the most effective method of purification by factorial design, were
proceeded the purification of the oil using the chosen methodology. The use of clay
purification promoted by removal of solid waste, impurities and coloring agents
responsible for the color and characteristic odor of rancidity, as shown in Figure 3.
Figure 1: XRD of natural palygorskite (black) and activated (red)
Figure 2: FTIR spectra of natural palygorskite (blue) and activated (black)
Figure 3: CG-MS and visual demonstration of the effectiveness in purification of the
frying oil. Frying oil (left) and purified oil (right)
The amounts of acid, iodine, saponification value and moisture content are
presented in Table 1.
Table 1: Determination of its acidity, iodine, saponification value and moisture
content of virgin, purified and subjected to the process of frying oils.
Oils
Acidity
values
Virgin
Frying
Purified
0.379
0.858
0.535
Iodine
values
(g I2/100g)
5.864
3.114
5.711
Saponification
values
(mg KOH/g)
180.18
186.80
180.90
Moisture
(ppm)
679.1
3275.7
1790.5
Table 1 shows that there was an increase in the acid value of the vegetable oil after
the frying process. This is due to the hydrolysis reactions, which occurred during the
process and increase the amount of free fatty acids [9]. After treatment with
palygorskite, has been observed that the reduction rate is due to the effective adsorption
of free fatty acids present in excess in the frying oil as well as those already present in
the crude oil. Such acids are the products of hydrolytic rancidity, responsible for making
the dark, viscous oil, and unpleasant odor [10].
The iodine values are related to the amount of double bonds present in the sample.
The variation in this index after frying is due to the breakdown of unsaturations, which
occurs mainly because of polymerization reactions, cyclization and oxidation when the
oil is subjected to high temperatures [11]. In Table 1, it is observed that the iodine value
of the purified oil is similar to that of virgin oil.
Further in accordance with Table 1 the saponification index increases after the frying
process. This is because the increase in the amount of free fatty acids, contaminants and
moisture. It is therefore natural that treatment with palygorskite, there is a withdrawal of
excess free fatty acids and contaminants, thereby decreasing the value of the
saponification of the purified oil.
According Corsini (2008), the frying process, lipid oxidation may occur, causing
deterioration in the triacylglycerol and glycerol, which results in the formation of
peroxides, unstable molecules and polar compounds. Non-volatile degradation products,
which remain in the oil promote increased degradation thereof. It is responsible also for
the changes in physical and chemical properties of the oil. The most frequently observed
physical changes are increasing the viscosity, discolouration and foaming [9].
We can also see in Table 1, the residual moisture present in the frying oil was
decreased after treatment with the clay. However, it is still high content favors the
hydrolysis of esters and glycerides present form free fatty acids, which are responsible
for the level of acidity and saponification observed. Therefore, as palygorskite not
completely eliminate the moisture, it is recommended to use an efficient method of
drying.
Table 2 shows the fatty acids composition of virgin oil samples, frying oil and
purified oil.
Table 2: Chromatographic profile of the chemical composition of the fatty acids present
in samples of the virgin, frying oils and purified.
Virgin oil (%)
Frying Oil (%)
Palmitic-16:0
11.03
20.91
22.58
Stearic-18:0
5.32
12.70
8.46
Oleic-18:1
24.15
21.48
28.76
Linoleic-18:2
53.19
29.54
32.55
Linolenic-18:3
6.07
2.62
0.96
Others
0.24
12.75
6.69
Fatty acids
Purified oil (%)
According to Table 2, it can be noted that the profile seen for the oil in the literature
and similar to results obtained for the sample of the virgin soybean oil. Highlighting the
presence of 6.07% of linolenic fatty acid.
The legislation of some countries, such as Chile, France and Belgium, had
restrictions for the content of linolenic acid (C18: 3), for example, vegetable oils with
more than 2% are not allowed in frying because its exposure to high temperature leads
to rapid formation of cyclic monomers which are considered likerisk compounds to the
physiologically view [9].
The formation of these monomers may be evidenced by a reduction of the amount of
linolenic fatty acid present in the frying oil. Is still observed that the amount of palmitic
and stearic fatty acids of the frying oil and purified samples, increase according to crude
oil, which is followed by a decrease of unsaturated fatty acids. This happens due to the
process that the oil passes during the frying process.
Furthermore Table 2 shows that after the purification process, oil with clay had an
even larger decrease in the amount of linolenic fatty acid in relation to the frying oil.
According to France (2002), this event is due to adsorption of long chain fatty acids on
palygorskite. Surface properties, combined with the high levels of specific surface area,
porosity and negative surface charge, makes the activated form of palygorskite one of
the most suitable materials for use as adsorbent of waste from frying oils.[12]
Conclusion:
Frying oils have many impurities arising mainly from food processing. Thus was
carried out the purification using a clay from the Piaui, affording cleaner oil, no
unpleasant odor and lighter color. Thus the product obtained can serve as a potential
raw material for soap production, with better quality than those made from the frying
oil, besides reducing the amount of waste oil in environment.
Acknowledgment: The researchers thank the CAPES, CNPq e FAPEPI
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