Embed Size (px)
Citation preview
ORIGINAL PAPER
Regeneration of Used Frying Oil
Semra Turan • Arda Yalcuk
Received: 28 August 2012 / Revised: 4 June 2013 / Accepted: 7 August 2013 / Published online: 27 August 2013
� AOCS 2013
Abstract Used frying oils were purified in a packed
column using different amounts of silica gel (SG), alumi-
num oxide (AO), activated charcoal (AC), bentonite (B),
magnesol XL (M), calcium carbonate (CC), zeolite (Z),
bleaching earth (BE) and/or their binary, triple, and qua-
ternary combinations. SG (15 g) improved total polar
material (TPM) by 100 %, conjugated diene (CD) content
by 84 %, and p-anisidine value (AV) by 104 %, while AO
and M improved free fatty acid (FFA) contents by 103 and
105 %, respectively. On the other hand, AC and M
bleached the color by 100 and 90 %, respectively. As the
amount of adsorbent in the column increased, FFA, CD,
AV, and color improved. When the amount of used sun-
flower oil (UO1) loaded in the column containing SL was
increased, FFA, CD, AV and color values increased, while
no change was observed in TPM up to 60 g of UO1.
Loading UO1 at 150 �C in the column caused the absor-
bance values at 460 nm to decrease from 0.740 to 0.240,
while the amount of adsorbed tocopherol increased com-
pared to UO1 at 25 �C. The increasing number of adsor-
bents within the column further improved the
physicochemical properties of UO1 when it was used 30 g.
However, as the amount of different type of used oils
(UO2, UO3 and UO4) was increased to 300 g, improve-
ment ratios of all parameters decreased.
Keywords Used frying oil � Active filtration �Adsorbent � Packed column � Polar material � Free
fatty acid
Introduction
The frying of potato, chicken, turkey, fish, and similar products
generates a significant amount of waste oil in fast-food res-
taurants. As a result of polymerization, hydrolysis and oxida-
tion reactions occurring during the frying process, various
polar compounds and polymers are formed and they adversely
affect human health [1, 2]. The amounts of toxic compounds
increase as the number of frying cycles, the duration of frying
and the temperature increase, and at a certain point the oil
becomes unusable. When the polar content of the oil reaches
25 %, it is no longer possible to use the oil in frying, and the oil
should be discarded as waste oil. If the waste oils are disposed
of into municipal sewage, they cause environmental pollution.
About 75 % of used frying oils are triglycerides and the dis-
posal of these oils causes a significant economic loss [1, 3, 4].
Biodiesel production from used frying oils has been researched
in several studies [5, 6]. However, the yield and quality of
methyl esters were poor when the used oil was utilized directly
without any purification [7]. For these reasons, regeneration of
used frying oil is important.
Several methods have been utilized to purify used frying
oils. These methods are active and passive filtration, mem-
brane processing, and supercritical carbon dioxide extraction
[4, 8]. Among these methods, active filtration is the most
commonly used method in order to remove the thermal
decomposition products from used frying oils. Various
adsorbents are mixed with the oil and then filtered. This
method has advantages such as removing polar compounds
S. Turan (&)
Department of Food Engineering, Faculty of Engineering
and Architecture, Abant Izzet Baysal University,
Bolu 14280, Turkey
e-mail: [email protected]; [email protected]
A. Yalcuk
Department of Environmental Engineering, Faculty of
Engineering and Architecture, Abant Izzet Baysal University,
Bolu 14280, Turkey
123
J Am Oil Chem Soc (2013) 90:1761–1771
DOI 10.1007/s11746-013-2325-x
from the oil, improving the quality of the used oil and
extending the date of expiry, decreasing energy require-
ments, having a short time of processing and possessing the
ability for the adsorbents to be regenerated [3, 8–10].
Several studies have been completed related to the
regeneration of used frying oils when using the active fil-
tration method [3, 10–12]. Different adsorbents (bentonite,
zeolite, active carbon, silica, diatomaceous earth, magne-
sium oxide, aluminum oxide, clay, and celite) or their
combinations have been used for recovering used frying
oils. McNeill et al. [11] improved the quality of used frying
oils by treating them with activated carbon and silica.
Bhattacharya et al. [3] reported that binary and quaternary
adsorbent mixtures were more effective than single
adsorbents for regenerating thermally polymerized frying
oils. Maskan and Bagcı [12] found that a mixture of 2 %
pekmez earth, 3 % bentonite, and 3 % magnesium silicate
was the best adsorbent combination for purifying used
sunflower oil. Some have used adsorbents during deep fat
frying to extend the frying life of oil [13–15]. In addition to
these approaches, a packed column may be prepared using
adsorbents, which are used in active filtration, in order to
adsorb oxidation products and polar compounds. Miyagi
and Nakajima [1] evaluated a column method using silica,
magnesium oxide, activated clay, and aluminum hydroxide
gel to improve the quality of used frying oil. They also
examined the feasibility of recycling used frying oil.
The objective of the present study was to determine the
efficiency of various adsorbents and their combinations for
purifying used frying oil in a packed column. Changes in
total polar material (TPM) content, free fatty acid (FFA)
content, conjugated diene (CD) content, p-anisidine value
(AV), tocopherol content, viscosity, and color of used frying
oil were determined before and after the column adsorbent
treatments to test their effectiveness. In addition, the effects
of adsorbent amounts used in the column, used oil amounts
loaded in the column, used oil temperature and different
types of used oils on adsorption were also examined.
Experimental Methods
Materials
The used sunflower oils (UO1 and UO2) were obtained
from Beypi Inc. (Bolu, Turkey). In this company, sun-
flower oil is used for frying poultry products. Used soybean
oil (UO3) and corn oil (UO4) were prepared after heating
oils at 190 �C for 30 h in a fryer in our laboratory. Used
oils were stored in a freezer at -18 �C until analyzed.
Silica gel 60 (SG, particle size 0.063–0.200 lm), alu-
minum oxide 90 (AO, standardized), activated charcoal
(AC), and calcium carbonate (CC, particle size *14 lm)
were obtained from Merck (Darmstadt, Germany). Zeolite
(Z, particle size \45 lm) was obtained from Sigma-
Aldrich (St. Louis, MO, USA) and bentonite (B) from
AppliChem (Darmstadt, Germany). Magnesol XL (M) was
purchased from The Dallas Group of America, Inc. (Jef-
fersonville, IN, USA). Unilever Margarine Inc. (Tekirdag,
Turkey) provided the bleaching earth (BE) (produced by
double acid activation of bentonite, specific gravity
2.5 g/cm3, loose bulk density 530–560 g/l, compact bulk
density 720–760 g/l). The chemicals that were necessary
for the analyses were purchased from Merck (Darmstadt,
Germany) and Sigma-Aldrich (St. Louis, MO, USA).
Column Adsorbent Treatment
Columns 60 ml in volume (3 9 9 cm) were used. The
columns were packed with different adsorbents or adsor-
bent combinations (15 g). The column was washed twice
with 20 ml of n-hexane in order to settle the filling material
in the column while removing air. The heights of the
adsorbent and flow rates through the column were deter-
mined. Generally, the flow rates ranged between 1 and
1.5 ml/min and adsorbent heights between 1 and 7 cm.
Following column preparation, mixtures of 30 g of oil in
30 ml of n-hexane were fed into the column under vacuum.
The column contents were washed with 60 ml of hexane in
order to reduce the amount of adsorbed oil. The hexane
was removed under vacuum at 40 �C by using a rotary
evaporator. Nitrogen gas was blown over the flask for
15 min to remove any residual solvent. The amount of oil
collected was determined. The oil was placed in a dark
colored bottle and kept at -18 �C until analyzed.
When AC used alone in the column, the oil-hexane
mixture taken from the column was filtered by double filter
paper in order to remove any AC residue from the oil. This
filtration difficulty was also mentioned by Maskan and
Bagcı [12] when working with AC.
Effects of Adsorbent Amount on Oil Properties
Column adsorption processes were conducted by using
different amounts of adsorbents such as SG (3.75, 7.5, 15,
and 22.5 g), AO (3.75, 7.5, and 15 g) and AC (3.75, 7.5,
and 15 g). About 30 g of UO1 was fed into the column in
n-hexane under vacuum.
Effects of Oil Amount Fed to the Column on Oil Properties
Column adsorption process was conducted using 15 g of
SG and the amounts of UO1 were 30, 40, 50, 60, 150 and
300 g. In addition, 60, 150 and 300 g of UO3 and UO4
were fed into the column in n-hexane under vacuum.
1762 J Am Oil Chem Soc (2013) 90:1761–1771
123
Effects of Used Oil Temperature on Oil Properties
A column with 15 g SG was fed with 60 g of UO1 at 25,
50, 100 or 150 �C under vacuum and no solvent was used
during this process. Hot oil flowed through the column
more rapidly than a colder one. In total, 55–57 g of oil was
eluted from the column under vacuum and the remainder
was adsorbed by SG. This oil can be recovered by washing
the column with n-hexane.
Effects of Different Type of Used Oils on Adsorption
The column adsorption process was conducted using 15 g
of SG ? AO ? BE (7.5 ? 3.75 ? 3.75 g) or SG ? AO
? BE ? B (7.5 ? 3.75 ? 3.75 ? 3.75 g) and the amounts
of UO2, UO3 and UO4 were 150 and 300 g.
Analyses
FFA, CD and AV were determined using AOCS [16]
methods Ca 5a-40, Ti 1a-64, and Cd 18-90, respectively.
The tocopherol contents of fresh, used, and treated oils
were determined according to Wong et al. [17] by using a
Shimadzu UV 1700 UV spectrophotometer (Kyoto, Japan).
Viscosity measurements were performed by using an And
SV-10 Vibro viscometer (AND Co., Japan). Colors of the
samples were determined according to Miyagi and Nakaj-
ima [1] at 460 nm in a spectrophotometer against methy-
lene chloride.
TPM content was measured using a Miroil-Optifry Oil
Tester (Miroil Division of Oil Process Systems, Inc.,
Allentown, PA, USA) at room temperature (25 �C). This
apparatus measures any variations in levels of polar com-
pounds in oil, compared with a measurement and setting
from fresh oil. TPM content of fresh oil was considered to
be zero and fresh sunflower oil (FO1) was used to calibrate
the equipment. The polar material contents of fresh, used,
and treated oils were also determined by using the chro-
matographical method of AOCS (Official method Cd
20–91) [16] in order to test the reliability of the measure-
ments. Taking the TPM content of fresh oil into consid-
eration, both methods yielded similar results.
Evaluation of Efficiency of Adsorption Process
The efficiency of the column adsorption process was
reported in terms of percentage improvement (PI), which is
an index for comparing the quality of treated oil with that
of fresh oil, according to Miyagi and Nakajima [1]. The PI
for each parameter was calculated by using the following
equation:
PI ¼ 100 Cu � Ctð Þ= Cu � Cfð Þ ð1Þ
where, Cu, Cf, and Ct are the contents or property of each
parameter in the used, fresh and adsorbent treated oil.
Statistical Analysis
The SPSS 11.5 software package was used for statistical
evaluation of the data. The differences in the means were
determined by using one-way analysis of variance
(ANOVA) and the results were evaluated at the 0.05 sig-
nificance level. The differences between the runs were
determined by the Duncan test. While FFA, CD, AV, color
and tocopherol contents were determined in duplicates,
TPM and viscosity values were determined as three or four
replicates.
Results and Discussion
Characteristics of Fresh and Used Frying Oils
The physical and chemical characteristics of fresh and used
frying oils are presented in Table 1. The fresh oils (FO1,
FO2, FO3, FO4) had lower values of FFA, TPM, CD, AV,
viscosity, and absorbance at 460 nm than those of used oils
(UO1, UO2, UO3, UO4). These parameters increased due
Table 1 Physical and chemical characteristics of fresh and used oils
Properties Sunflower oil 1 Sunflower oil 2 Soybean oil Corn oil
FO1 UO1 FO2 UO2 FO3 UO3 FO4 UO4
FFA (%) 0.14 ± 0.00 0.94 ± 0.03 0.20 ± 0.05 2.20 ± 0.01 0.14 ± 0.00 0.42 ± 0.03 0.21 ± 0.02 0.41 ± 0.02
TPM (%) 0.0 ± 0.0 8.7 ± 0.0 0.0 ± 0.0 16.4 ± 0.3 1.6 ± 0.2 29.8 ± 0.3 2.6 ± 0.2 19.6 ± 0.2
CD (%) 0.27 ± 0.01 0.59 ± 0.05 0.23 ± 0.01 1.36 ± 0.01 0.46 ± 0.03 2.29 ± 0.09 0.23 ± 0.02 1.65 ± 0.06
AV 6.9 ± 0.0 35.0 ± 2.1 6.7 ± 0.1 58.2 ± 0.1 2.7 ± 0.5 175.6 ± 2.3 5.1 ± 0.1 112.4 ± 0.5
Viscosity (mPa�s, 30 �C) 48.9 ± 0.02 57.0 ± 1.17 42.6 ± 0.1 61.9 ± 0.2 47.7 ± 0.0 80.2 ± 0.1 48.5 ± 0.1 68.2 ± 0.1
Color (460 nm) 0.071 ± 0.000 0.740 ± 0.001 0.087 ± 0.000 1.223 ± 0.001 0.105 ± 0.000 0.316 ± 0.001 0.121 ± 0.000 0.371 ± 0.000
Tocopherol (mg/kg oil) 478.9 ± 0.5 444.7 ± 3.4 558.1 ± 3.2 278.2 ± 8.3 592.0 ± 1.4 99.5 ± 4.1 879.9 ± 10.5 229.8 ± 7.6
Results are given as means ± SD
FO1 and FO2 fresh sunflower oils, FO3 fresh soybean oil, FO4 fresh corn oil, UO1 and UO2 used sunflower oil, UO3 used soybean oil, UO4 used corn oil, FFA free fatty acid,TPM change in total polar material, CD conjugated diene, AV P-anisidine value
J Am Oil Chem Soc (2013) 90:1761–1771 1763
123
to thermal oxidation during frying. Bhattacharya et al. [3]
reported that thermally polymerized palm oil had higher
FFA, CD, AV, viscosity, TPM, and color values than did
fresh oil, indicating oxidative deterioration of oils. Lin
et al. [18] found that used oil had greater FFA, TPM, PV,
polymers and lower oxidative stability index values than
fresh oil. Among the used oils, UO3 had the highest TPM,
CD, AV and viscosity values.
Effects of Adsorbent Amount on the Physical
and Chemical Characteristics of Used Oil
Following column packing with varying amounts of
adsorbents, UO1 was passed through the column. Oil
analyses are presented in Table 2. Increasing the amount of
adsorbent improved the chemical and physical character-
istics of the oil. The most effective adsorbents for treating
oil were SG and AC.
The FFA results from hydrolysis of triacylglycerol and it
is the most significant indicator of frying oil deterioration.
Many countries use FFA content as an index in regulating
frying oil. Although it is included in the decomposition
products, measurement of FFA is especially important
when it is produced in large amounts [1, 15, 19].
Increasing the amount of SG from 3.75 to 22.5 g
reduced the FFA content of the oil from 0.94 to 0.16 %,
reaching a value that was very similar to that of fresh oil. PI
was as high as 98 %.
TPM content is another important criterion for frying
applications. TPM is a ‘‘chemical index’’ used to determine
the extent of cumulative degradation of oil and is a good
indicator of frying oil quality. TPM is included in the non-
triacylglycerol part of oil, which is commonly categorized
as polymerized and decomposed products in terms of
molecular weight and polarity [3, 20].
The TPM content dropped to 1.3 % when 3.75 g of SG
was used, achieving 85 % PI. Increasing SG content to
7.5 g resulted in adsorbing all polar material. In terms of
TPM content, 7.5 g of SG was sufficient for processing
30 g of oil. There was no need for using excess SG.
Clinically harmful effects might be caused by oxidation
products including peroxides, aldehydes, ketones, hydro-
peroxides, polymers, and oxidized monomers [19]. While
CD content indicates primary oxidation products, AV
measures secondary oxidation products. A 100 % PI was
achieved in terms of CD when the amount of SG was
22.5 g and 104 % PI was achieved in removing aldehydes,
the secondary products of oxidation, when 15 g of SG was
used. The effectiveness of SG in improving TPM was in
agreement with Bhattacharya et al. [3] and Miyagi and
Nakajima [1].
The degradation products (dimers, trimers, polymers,
epoxides, alcohols and hydrocarbons) which are formed
during frying are primary causes of altered oil viscosity
[19, 21]. Decreasing viscosity is an indicator of reduced
polymer contents in oil, which account for the high
molecular weight fraction of degradation products [1]. The
viscosity decreased by 58 % by using 22.5 g of SG.
The SG was also effective in lightening the color, with
22.5 g SG reducing the absorbance at 460 nm to 0.091.
Table 2 Effects of adsorbent amount on the physical and the chemical characteristics of used oil
Amountofadsorbent(g)
Amountof oil (g)
FFA (%) TPM (%) CD (%) AV (mmol/kg oil) Viscosity (mPa�s,30 �C)
Absorbance, 460 nm Tocopherol(mg/kg)
Value PI Value PI Value PI Value PI Value PI Value PI Value
SG, 3.75 UO1, 30 0.73 ± 0.01a 26 1.3 ± 0.2a 85 0.47 ± 0.03a 38 21.1 ± 0.9a 49 56.1 ± 0.1a 12 0.391 ± 0.001a 52 382.9 ± 0.8b
SG, 7.5 UO1, 30 0.62 ± 0.01b 40 0.0 ± 0.0b 100 0.39 ± 0.01b 63 10.7 ± 0.4b 86 55.5 ± 0.1b 19 0.222 ± 0.001c 77 389.6 ± 5.8b
SG, 15 UO1, 30 0.27 ± 0.05c 84 0.0 ± 0.0b 100 0.32 ± 0.03c 84 5.8 ± 0.3c 104 54.6 ± 0.1c 30 0.262 ± 0.001b 71 391.9 ± 4.7a
SG, 22.5 UO1, 30 0.16 ± 0.02d 98 0.0 ± 0.0b 100 0.27 ± 0.00c 100 2.2 ± 0.5d 117 52.3 ± 0.0d 58 0.091 ± 0.000d 97 386.6 ± 4.4b
AO, 3.75 UO1, 30 0.59 ± 0.03a 44 3.9 ± 0.2a 55 0.59 ± 0.01a 0 34.0 ± 0.3a 4 54.4 ± 0.1b 32 0.689 ± 0.001a 8 408.5 ± 2.0a
AO, 7.5 UO1, 30 0.18 ± 0.02b 95 1.7 ± 0.3b 80 0.49 ± 0.01b 31 27.7 ± 0.9b 26 55.0 ± 0.1a 25 0.453 ± 0.001b 43 395.3 ± 2.2b
AO, 15 g UO1, 30 0.12 ± 0.02b 103 0.6 ± 0.0c 93 0.46 ± 0.00c 41 23.1 ± 0.5c 42 54.8 ± 0.3a 27 0.340 ± 0.001c 60 400.8 ± 0.8b
AC, 3.75 UO1, 30 0.60 ± 0.03a 43 3.0 ± 0.2a 66 0.57 ± 0.00a 6 20.9 ± 0.1a 50 54.2 ± 0.1a 34 0.399 ± 0.001a 51 324.7 ± 5.1a
AC, 7.5 UO1, 30 0.20 ± 0.04b 93 0.0 ± 0.0b 100 0.54 ± 0.02b 16 6.0 ± 0.3b 103 54.3 ± 0.1a 33 0.095 ± 0.000b 96 236.6 ± 6.4b
AC, 15 UO1, 30 0.16 ± 0.02b 98 0.0 ± 0.0b 100 0.36 ± 0.01c 72 3.2 ± 0.9c 113 54.3 ± 0.0a 34 0.069 ± 0.000c 100 8.6 ± 0.6c
B, 15 UO1, 30 0.75 ± 0.03b 24 1.6 ± 0.2d 82 0.52 ± 0.01bc 22 24.1 ± 0.2b 39 53.2 ± 0.0c 47 0.363 ± 0.001d 56 331.3 ± 4.8c
Z, 15 UO1, 30 0.81 ± 0.05ab 16 7.3 ± 0.2a 16 0.54 ± 0.01b 16 34.6 ± 1.3a 1 57.1 ± 0.1a -1 0.725 ± 0.001a 2 402.9 ± 0.2b
BE, 15 UO1, 30 0.79 ± 0.05ab 19 2.7 ± 0.4c 100 0.50 ± 0.01bc 28 20.8 ± 6.2b 51 55.3 ± 0.1b 21 0.452 ± 0.001c 43 313.5 ± 2.5d
M, 15 UO1, 30 0.10 ± 0.02c 105 0.0 ± 0.0e 100 0.46 ± 0.03c 41 8.6 ± 0.1c 94 53.2 ± 0.1c 47 0.141 ± 0.001e 90 409.4 ± 0.4b
CC, 15 UO1, 30 0.86 ± 0.00a 10 6.6 ± 0.5b 24 0.6 ± 0.03a -3 35.0 ± 0.3a 0 57.2 ± 0.1a -2 0.691 ± 0.001b 7 425.7 ± 5.4a
Results are given as means ± SD
UO1 used sunflower oil, SG silica gel, AO aluminum oxide, AC activated charcoal, B bentonite, Z zeolite, BE bleaching earth, M Magnesol XL, CC calcium carbonate, FFA freefatty acid, TPM change in total polar material, CD conjugated diene, AV P-anisidine value, PI percentage improvementa–e Means followed by different superscripts in the same column indicatedifferent superscripts (P \ 0.05)
1764 J Am Oil Chem Soc (2013) 90:1761–1771
123
Absorbance at 460 nm was employed as the color index
similar to Miyagi and Nakajima [1]. It has been reported
that color is the primary parameter used for determining the
replacement time of frying oil [21, 22].
Despite these favorable changes, SG also caused a
decrease in the tocopherol levels, which delayed oil oxi-
dation, by 50–60 mg/kg. However, the change in the
tocopherol levels was not proportional to SG content.
AO was more effective in reducing the FFA content than
SG and 95 % PI was attained when 7.5 g of AO was used.
TPM content was reduced to 0.6 % when 15 g of adsorbent
was used; however, 100 % removal could not be achieved.
CDs and aldehydes, which are oxidation products, were
adsorbed by 41 and 42 %, respectively, using the same
amount of adsorbent. Similarly, increasing the AO content
resulted in a lighter oil color; however, it was not as
effective as SG in reducing color. Increasing AO content
was not effective in reducing viscosity. On the other hand,
AO reduced the tocopherol content less than did SG.
Therefore, increasing AO content improved the parameters.
AC was sufficiently effective in removing free fatty
acids, polar materials, aldehydes, and color constituents,
causing an improvement of 93, 100, 103, and 96 %,
respectively, when 7.5 g was used for packing; however, it
also caused absorption of the tocopherols, reducing the
tocopherol content to 8.6 mg/kg (P \ 0.05). Increasing AC
content caused a sharper decrease in tocopherol levels.
Thus, amount of AC in column should be limited.
The highest PI values were obtained with 22.5 g of SG,
15 g of AO and AC. Optimum amount of SG can be
assumed as 15 g for 30 g of oil. However, 1:2 adsorbent/oil
ratio may be high in practical applications.
The most effective adsorbent among B, Z, BE, M, and
CC was M in treating used oil when 15 g was used. M
reduced the FFA content to 0.1 % and the TPM content to
undetectable, lower values than for fresh oil. Additionally,
the aldehydes and color constituents were reduced by 94
and 90 %, respectively. BE was not as effective in
removing FFA as was M, whereas it was effective in
completely removing polar materials, and 51 and 43 % of
the aldehydes and color constituents, respectively. Using
15 g of Z resulted in 16 % decreases in the FFA, TPM
content and CD. Using 15 g of CC was not effective in
reducing any of the stated constituents. Generally, adsor-
bents that were used in different ratios affected FFA con-
tent, TPM content, CD content, AV, spectrophotometric
color value and viscosity of UO1 (P \ 0.05).
Miyagi and Nakajima [1] reported that increasing the
amount of SG in a funnel from 5 to 15 g increased the PI of
TPM from 32.7 to 81.3 % and the PI of FFA from 35.1 to
85.1 % when 35 g of used oil was utilized. Viscosity and
color values decreased proportionally to the SG content.
They also investigated the adsorption ability of SG, mag-
nesium oxide, activated clay, and aluminum hydroxide gel
(10 g of adsorbent and 25 g of used oil). SG was effective
in removing TPM (70.1 %) and reducing the AV (81.6 %)
of the used oil. Aluminum hydroxide was effective in
removing FFA (89.2 %) and reducing the viscosity
(50.0 %), and active clay was the most effective in the
reducing the absorbance at 460 nm (76.8 %).
Effects of Oil Feed Amount on Used Oil Characteristics
The physical and chemical properties of the treated oils are
shown in Table 3. FFA content decreased from 0.94 to
0.27 % when 40 g of used oil was used, whereas it only
dropped to 0.73 % when 300 g of used oil was applied.
Increasing the oil content decreased the PI of FFA. Even
15 g of SG removed all polar materials in 60 g of oil. TPM
increased to 4.7 %, as 300 g of UO1 was loaded onto
column. Increasing the amount of oil adversely affected
CD, AV, viscosity and color values, and the PI values were
detected at lower values. The lowest viscosity and the
lightest color was attained with 40 g of oil. The absorbance
at 460 nm increased from 0.131 to 0.529 when the amount
of oil fed into the column was increased from 40 to 300 g.
The tocopherol levels of the treated oil samples varied from
391.9 to 425.8 mg/kg. Optimum amount of oil in feed can
be assumed as 40 g, because the PI values were the highest
for FFA, TPM, AV and color value. However, even at
300 g oil load, PI values of FFA, TPM, AV and color value
were 27, 54, 46 and 31 %, respectively.
Effects of different type of used oils on adsorption were
also studied. When the amount of UO3 increased from 60
to 300 g, FFA increased from 0.15 to 0.25 % and PI of
FFA was 60 % at 300 g oil load. TPMs of UO3 were 16.5,
20.6 and 22.4 % at 60, 150 or 300 g oil applied, respec-
tively. On the other hand, color and viscosity improve-
ments were 56 and 36 % at 300 g of UO3.
Similar to other used oils, loading a larger amount of
UO4 caused a decrease in PI values of all parameters. PI
values of FFA, TPM, viscosity and color were 45, 52, 50
and 38 %, respectively, at 300 g of oil applied to column.
However, removal of oxidation products was low; in both
cases when 300 g of UO3 and UO4 were used.
Miyagi and Nakajima [1] also reported reduced
improvements when increasing the amount of oil loaded
into SG-packed columns. PI for TPM content was 97.2 %
for the initial 10 g of oil fed into the column whereas this
ratio decreased to 13.1 % when 75 g of oil was fed into the
column. Using more oil than 75 g increased the polar
material content further.
J Am Oil Chem Soc (2013) 90:1761–1771 1765
123
Ta
ble
3E
ffec
tso
fth
eam
ou
nt
of
use
do
ilfe
din
toth
ep
ack
edco
lum
nco
nta
inin
gS
Go
nth
ep
hy
sica
lan
dth
ech
emic
alch
arac
teri
stic
so
fu
sed
oil
Am
ou
nt
of
adso
rben
t
(g)
Am
ou
nt
of
oil
(g)
FF
A(%
)T
PM
(%)
CD
(%)
AV
(mm
ol/
kg
oil
)V
isco
sity
(mP
a�s,
30
�C)
Ab
sorb
ance
,
46
0n
m
To
cop
her
ol
(mg
/
kg
)
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
SG
,1
5U
O1
,3
00
.27
±0
.05
d8
40
.0±
0.0
c1
00
0.3
2±
0.0
3c
84
5.8
±0
.3e
10
45
4.6
±0
.1c
30
0.2
62
±0
.00
1c
71
39
1.9
±4
.7d
SG
,1
5U
O1
,4
00
.27
±0
.02
d8
40
.0±
0.0
c1
00
0.3
8±
0.0
3b
66
5.1
±0
.0e
10
65
2.6
±0
.1f
54
0.1
31
±0
.00
1f
91
41
6.1
±8
.8ab
SG
,1
5U
O1
,5
00
.40
±0
.00
c6
80
.0±
0.0
c1
00
0.4
0±
0.0
0b
59
7.9
±0
.5d
96
53
.5±
0.2
e4
30
.17
8±
0.0
01
e8
44
06
.2±
3.0
bc
SG
,1
5U
O1
,6
00
.51
±0
.00
b5
40
.0±
0.0
c1
00
0.4
0±
0.0
1b
59
11
.7±
0.2
c8
35
3.9
±0
.0d
38
0.2
16
±0
.00
1d
78
39
8.4
±0
.1cd
SG
,1
5U
O1
,1
50
0.7
4±
0.0
2a
25
3.5
±0
.1b
65
0.4
8±
0.0
4a
34
19
.1±
0.4
b5
75
5.3
±0
.0b
24
0.4
34
±0
.01
b4
63
95
.9±
7.3
cd
SG
,1
5U
O1
,3
00
0.7
3±
0.0
4a
27
4.7
±0
.1a
54
0.5
2±
0.0
0a
21
22
.0±
0.2
a4
65
6.3
±0
.1a
13
0.5
29
±0
.01
a3
14
25
.8±
4.9
a
SG
,1
5U
O3
,6
00
.15
±0
.02
b9
81
6.5
±0
.2c
47
2.0
4±
0.0
5a
13
10
1.9
±5
.1c
43
66
.5±
0.1
5c
42
0.1
41
±0
.00
1c
83
51
.1±
5.1
a
SG
,1
5U
O3
,1
50
0.2
0±
0.0
2a
77
20
.6±
0.2
b3
32
.11
±0
.10
a1
01
36
.6±
1.5
b2
36
9.4
±0
.10
a3
30
.18
5±
0.0
00
b6
25
2.2
±0
.2a
SG
,1
5U
O3
,3
00
0.2
5±
0.0
0a
60
22
.4±
0.2
a2
62
.17
±0
.05
a6
15
2.5
±3
.6a
13
68
.6±
0.0
5b
36
0.1
98
±0
.00
1a
56
54
.7±
1.4
a
SG
,1
5U
O4
,6
00
.24
±0
.02
b8
68
.7±
0.2
c6
41
.54
±0
.05
a8
52
.9±
0.9
c5
55
9.3
±0
.46
a4
10
.19
6±
0.0
01
c5
71
37
.9±
3.2
a
SG
,1
5U
O4
,1
50
0.2
8±
0.0
1b
67
10
.0±
0.2
b5
61
.54
±0
.09
a8
82
.2±
1.2
b2
85
8.2
±0
.04
b4
70
.20
3±
0.0
00
b5
41
41
.1±
0.7
a
SG
,1
5U
O4
,3
00
0.3
2±
0.0
2a
45
10
.8±
0.3
a5
21
.53
±0
.06
a9
99
.5±
0.5
a1
25
7.5
±0
.05
c5
00
.23
6±
0.0
01
a3
81
38
.7±
3.3
a
Res
ult
sar
eg
iven
asm
ean
s±
SD
UO
1u
sed
sun
flo
wer
oil
,U
O3
use
dso
yb
ean
oil
,U
O4
use
dco
rno
il,
SG
sili
cag
el,
FF
Afr
eefa
tty
acid
,T
PM
chan
ge
into
tal
po
lar
mat
eria
l,C
Dco
nju
gat
edd
ien
e,A
VP
-an
isid
ine
val
ue,
PI
per
cen
tag
eim
pro
vem
ent
a–f
Mea
ns
foll
ow
edb
yd
iffe
ren
tsu
per
scri
pts
inth
esa
me
colu
mn
ind
icat
edif
fere
nt
sup
ersc
rip
ts(P
\0
.05
)
1766 J Am Oil Chem Soc (2013) 90:1761–1771
123
Effects of Oil Feed Temperature on Used Oil Chemical
Characteristics
Table 4 presents the physical and the chemical character-
istics of the oil collected from the column packed with 15 g
of SG, which was fed with UO1 at 25, 50, 100 and 150 �C.
Oils at these temperatures were equally affected by the
packed column treatment achieving similar values for FFA
content (0.30–0.39 %), TPM content (0.0–2.6 %), oxida-
tion products (0.44–0.50 % for CD and 8.6–8.9 mmol/kg
oil for AV), color values (0.240-0.322 absorbance at
460 nm), and viscosity (52.3–54.4 mPa�s). Feeding hot oil
into the column increased the amount of tocopherol
adsorbed by SG. On the other hand, the lowest TPM was
obtained at 150 and 25 �C. Moreover, the highest PI of AV,
color value and viscosity were attained with oil at 150 �C.
Therefore, this temperature was the optimum for the
adsorption process.
Effects of Adsorbent Combinations on Used Oil
Characteristics
Table 5 shows the physical and the chemical characteris-
tics of used oil when using equal amounts of two adsor-
bents in the packed column. The adsorbent pairs for
reducing FFA content the most were SG ? AC, SG ? AO,
AO ? M, and SG ? M combinations. PI values were
[98 %. On the other hand, the SG ? B, SG ? Z and
SG ? BE could only provide 50–60 % improvement. This
value was still[40 % PI when 7.5 g of SG was used alone.
All binary adsorbent pairs reduced the TPM content to
the value for fresh oil. The fact that TPM content of the oil
treated in a column packed with 7.5 g of SG was also
similar confirmed these results. In other words, 7.5 g of SG
alone was sufficient to remove all the TPM from the used
oil.
Binary adsorbent pairs excluding AO ? M and
SG ? AO achieved PI values [ 69 % in removing CDs.
The lowest AV was attained with SG ? AC followed by
SG ? B, SG ? BE, SG ? M, and SG ? AO. On the other
hand, AO ? M was only effective in reducing AV by
46 %.
SG ? BE, SG ? AC and SG ? Z improved viscosity in
the range of 89-93 %. The viscosity of the oils treated by
these adsorbent pairs was very close to 48.9 mPa�s, which
was the same as for fresh oil.
The most effective binary adsorbent combinations in
attaining a lighter oil color were SG ? M and SG ? AC.
Table 4 Effects of the temperature of used oil fed into the packed column containing SG on the physical and the chemical characteristics of used
oil
Amount ofadsorbent
Temperatureof oil (oC)
FFA (%) TPM (%) CD (%) AV (mmol/kgoil)
Viscosity (mPa�s,30 �C)
Absorbance, 460 nm Tocopherol(mg/kg)
Value PI Value PI Value PI Value PI Value PI Value PI Value
SG, 15 25 0.36 ± 0.02ab 73 0.0 ± 0.0c 100 0.44 ± 0.00b 47 8.6 ± 0.3a 94 53.0 ± 0.1c 49 0.292 ± 0.001c 67 403.9 ± 4.2a
SG, 15 50 0.30 ± 0.00c 80 1.5 ± 0.1b 80 0.49 ± 0.00a 32 8.9 ± 0.1a 93 53.4 ± 0.1b 46 0.322 ± 0.001a 62 397.8 ± 5.2ab
SG, 15 100 0.39 ± 0.00a 69 2.6 ± 0.2a 66 0.50 ± 0.01a 28 8.8 ± 0.6a 93 54.4 ± 0.1a 35 0.319 ± 0.001b 63 386.5 ± 5.4b
SG, 15 150 0.33 ± 0.02bc 76 0.0 ± 0.0c 100 0.45 ± 0.00b 44 7.8 ± 0.2a 97 52.3 ± 0.1d 58 0.240 ± 0.001d 75 386.6 ± 0.5b
Results are given as means ± SD. 60 g of UO1 was used in the trials
SG silica gel, FFA free fatty acid, TPM change in total polar material, CD conjugated diene, AV P-anisidine value, PI percentage improvementa–d Means followed by different superscripts in the same column indicate statistical differences (P \ 0.05)
Table 5 Physical and the chemical characteristics of used oil treated in a column packed with two types of adsorbents
Adsorbentcombination
Amount ofadsorbent(g)
FFA (%) TPM (%) CD (%) AV (mmol/kg oil) Viscosity (mPa�s,30 �C)
Absorbance, 460 nm Tocopherol(mg/kg)
Value PI Value PI Value PI Value PI Value PI Value PI Value
SG ? AO 7.5 ? 7.5 0.14 ± 0.04b 100 0.0 ± 0.0 100 0.47 ± 0.01a 38 7.0 ± 0.8c 100 54.5 ± 0.1a 31 0.198 ± 0.001d 81 391.1 ± 5.3b
SG ? B 7.5 ? 7.5 0.47 ± 0.04a 59 0.0 ± 0.0 100 0.37 ± 0.00b 69 5.0 ± 0.4d 107 53.8 ± 0.1b 39 0.203 ± 0.001c 80 396.1 ± 2.6b
SG ? Z 7.5 ? 7.5 0.53 ± 0.05 51 0.0 ± 0.0 100 0.37 ± 0.02b 69 10.2 ± 0.4b 88 49.6 ± 0.2f 91 0.279 ± 0.001b 69 398.3 ± 4.0b
SG ? BE 7.5 ? 7.5 0.45 ± 0.01a 61 0.0 ± 0.0 100 0.32 ± 0.00b 84 5.1 ± 0.2d 106 49.5 ± 0.1f 93 0.151 ± 0.001e 88 314.2 ± 7.1c
SG ? AC 7.5 ? 7.5 0.11 ± 0.00b 104 0.0 ± 0.0 100 0.36 ± 0.01b 72 2.2 ± 0.1e 117 49.8 ± 0.1e 89 0.136 ± 0.001f 90 170.9 ± 3.8d
SG ? M 7.5 ? 7.5 0.16 ± 0.02b 98 0.0 ± 0.0 100 0.37 ± 0.01b 69 6.4 ± 0.0c 102 53.5 ± 0.1c 43 0.123 ± 0.001g 92 420.5 ± 5.3a
AO ? M 7.5 ? 7.5 0.11 ± 0.00b 104 0.0 ± 0.0 100 0.49 ± 0.01a 31 22.1 ± 0.8a 46 52.8 ± 0.0d 52 0.304 ± 0.001a 65 412.3 ± 1.1a
Results are given as means ± SD. 30 g of UO1 was used in trials
SG silica gel, AO aluminum oxide, AC activated charcoal, B bentonite, Z zeolite, BE bleaching earth, M magnesol XL, CC calcium carbonate, FFA free fatty acid, TPM changein total polar material, CD conjugated diene, AV P-anisidine value, PI percentage improvementa–g Means followed by different superscripts in the same column indicate statistical differences (P \ 0.05)
J Am Oil Chem Soc (2013) 90:1761–1771 1767
123
Ta
ble
6P
hy
sica
lan
dth
ech
emic
alch
arac
teri
stic
so
fu
sed
oil
trea
ted
ina
colu
mn
pac
ked
wit
hth
ree
typ
eso
fad
sorb
ents
Ad
sorb
ent
com
bin
atio
n
Am
ou
nt
of
adso
rben
t(g
)
FF
A(%
)T
PM
(%)
CD
(%)
AV
(mm
ol/
kg
oil
)V
isco
sity
(mP
a�s,
30
�C)
Ab
sorb
ance
,4
60
nm
To
cop
her
ol
(mg
/kg
)
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
SG
?A
O?
BE
5?
5?
50
.25
±0
.04
a8
60
.0±
0.0
10
00
.39
±0
.01
abc
63
14
.3±
0.8
b7
45
0.7
±0
.1h
78
0.1
16
±0
.00
1e
93
35
1.5
±1
0.8
e
SG
?A
O?
AC
5?
5?
50
.07
±0
.02
d1
09
0.0
±0
.01
00
0.3
7±
0.0
1bcd
69
1.6
±0
.1h
11
95
2.7
±0
.1de
53
0.0
33
±0
.00
0e
10
61
10
.3±
4.4
g
SG
?A
O?
B5
?5
?5
0.1
1±
0.0
0cd
10
40
.0±
0.0
10
00
.44
±0
.03
a4
71
0.9
±0
.2c
86
52
.8±
0.0
cd
52
0.1
24
±0
.00
1d
92
40
2.2
±1
.7b
SG
?A
O?
Z5
?5
?5
0.1
3±
0.0
2cd
10
20
.0±
0.0
10
00
.41
±0
.00
ab
56
15
.4±
0.1
a7
05
1.8
±0
.1g
65
0.2
13
±0
.00
1b
79
41
8.4
±4
.7b
SG
?A
O?
BE
7.5
?3
.75
?3
.75
0.1
1±
0.0
0cd
10
40
.0±
0.0
10
00
.31
±0
.02
e8
83
.4±
0.0
g1
12
52
.1±
0.1
f6
10
.06
8±
0.0
00
e1
00
39
2.8
±7
.0cd
SG
?A
O?
AC
7.5
?3
.75
?3
.75
0.1
0±
0.0
2cd
10
50
.0±
0.0
10
00
.32
±0
.01
de
84
2.2
±0
.1h
11
75
2.9
±0
.0c
51
0.0
51
±0
.00
0e
10
31
52
.7±
5.9
f
SG
?A
O?
B7
.5?
3.7
5?
3.7
50
.07
±0
.02
d1
09
0.0
±0
.01
00
0.3
4±
0.0
0cde
78
4.5
±0
.8f
10
95
2.8
±0
.1a
52
0.2
13
±0
.00
1b
79
44
7.7
±1
5.6
a
SG
?A
O?
Z7
.5?
3.7
5?
3.7
50
.20
±0
.00
b9
30
.0±
0.0
10
00
.35
±0
.00
bcde
75
6.9
±0
.2e
10
05
3.7
±0
.2b
41
0.2
89
±0
.00
1a
67
41
7.5
±2
2.6
b
SG
?A
O?
M5
?5
?5
0.1
3±
0.0
2cd
10
10
.0±
0.0
10
00
.39
±0
.02
abc
63
7.7
±0
.1d
97
52
.6±
0.1
e5
40
.18
2±
0.0
01
bc
83
37
4.4
±4
.7d
SG
?A
O?
M7
.5?
3.7
5?
3.7
50
.15
±0
.04
b9
90
.0±
0.0
10
00
.38
±0
.07
abc
66
4.0
±0
.1fg
11
04
9.2
±0
.1ı
97
0.1
37
±0
.00
1cd
90
38
0.5
±0
.5cd
Res
ult
sar
eg
iven
asm
ean
s±
SD
.3
0g
of
UO
1w
asu
sed
intr
ials
SG
sili
cag
el,
AO
alu
min
um
ox
ide,
AC
acti
vat
edch
arco
al,
Bb
ento
nit
e,Z
zeo
lite
,B
Eb
leac
hin
gea
rth
,M
mag
nes
ol
XL
,C
Cca
lciu
mca
rbo
nat
e,F
FA
free
fatt
yac
id,
TP
Mch
ang
ein
tota
lp
ola
r
mat
eria
l,C
Dco
nju
gat
edd
ien
e,A
VP
-an
isid
ine
val
ue,
PI
per
cen
tag
eim
pro
vem
ent
a-ı
Mea
ns
foll
ow
edb
yd
iffe
ren
tsu
per
scri
pts
inth
esa
me
colu
mn
ind
icat
est
atis
tica
ld
iffe
ren
ces
(P\
0.0
5)
Ta
ble
7P
hy
sica
lan
dth
ech
emic
alch
arac
teri
stic
so
fu
sed
oil
trea
ted
ina
colu
mn
pac
ked
wit
hfo
ur
typ
eso
fad
sorb
ent
Ad
sorb
ent
com
bin
atio
n
Am
ou
nt
of
adso
rben
t(g
)F
FA
(%)
TP
M(%
)C
D(%
)A
V(m
mo
l/k
go
il)
Vis
cosi
ty(m
Pa�
s,
30
�C)
Ab
sorb
ance
,
46
0n
m
To
cop
her
ol
(mg
/kg
)
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
SG
?A
O?
BE
?B
3.7
5?
3.7
5?
3.7
5?
3.7
50
.11
±0
.04
a1
04
0.0
±0
.01
00
0.4
0±
0.0
0b
59
10
.9±
0.3
d8
64
8.2
±0
.1d
10
90
.13
6±
0.0
01
a9
03
10
.8±
3.2
c
SG
?A
O?
AC
?B
3.7
5?
3.7
5?
3.7
5?
3.7
50
.13
±0
.02
a1
01
0.0
±0
.01
00
0.4
5±
0.0
1a
44
4.3
±1
.3d
10
94
8.2
±0
.2d
10
80
.08
1±
0.0
00
a9
91
80
.5±
3.0
e
SG
?A
O?
BE
?Z
3.7
5?
3.7
5?
3.7
5?
3.7
50
.11
±0
.00
a1
04
0.0
±0
.01
00
0.4
2±
0.0
0ab
53
15
.7±
2.6
c6
94
9.6
±0
.1c
91
0.1
10
±0
.00
1a
94
35
4.1
±2
.4b
SG
?A
O?
AC
?Z
3.7
5?
3.7
5?
3.7
5?
3.7
50
.11
±0
.00
a1
04
0.0
±0
.01
00
0.4
3±
0.0
1ab
50
5.2
±0
.2a
10
65
2.3
±0
.0b
58
0.1
09
±0
.00
1a
94
24
5.4
±5
.7d
SG
?A
O?
B?
M3
.75
?3
.75
?3
.75
?3
.75
0.1
5±
0.0
0a
99
0.0
±0
.01
00
0.4
5±
0.0
3a
44
11
.9±
0.2
b8
25
3.3
±0
.2a
46
0.1
97
±0
.00
1a
81
41
2.9
±6
.7a
Res
ult
sar
eg
iven
asm
ean
s±
SD
.3
0g
of
UO
1w
asu
sed
intr
ials
SG
sili
cag
el,
AO
alu
min
um
ox
ide,
AC
acti
vat
edch
arco
al,
Bb
ento
nit
e,Z
zeo
lite
,B
Eb
leac
hin
gea
rth
,M
mag
nes
ol
XL
,C
Cca
lciu
mca
rbo
nat
e,F
FA
free
fatt
yac
id,
TP
Mch
ang
ein
tota
lp
ola
r
mat
eria
l,C
Dco
nju
gat
edd
ien
e,A
VP
-an
isid
ine
val
ue,
PI
per
cen
tag
eim
pro
vem
ent
a–e
Mea
ns
foll
ow
edb
yd
iffe
ren
tsu
per
scri
pts
inth
esa
me
colu
mn
ind
icat
edif
fere
nt
sup
ersc
rip
ts(P
\0
.05
)
1768 J Am Oil Chem Soc (2013) 90:1761–1771
123
The effects of SG and M were most effective in reducing
color. Increasing the AC or SG ratio of the adsorbent pairs
reduced the tocopherol content. The SG ? AC reduced the
tocopherol contents the most. The tocopherol levels of the
oils from this treatment were lower by 50–60 % than the
values obtained with other columns. Using two adsorbents
together in the column changed the measured parameters
except for TPM content (P \ 0.05).
Effects of Using Three Adsorbents on Used Oil
Characteristics
Table 6 shows the physical and the chemical characteristics
of used oil when using three adsorbents in the packed col-
umn. The FFA contents of all triple adsorbent combinations
were improved by 86–109 %, TPM content by 100 %, AV
by 70–119 %, and color removal by 67–106 %. PI val-
ues [ 100 % indicated that in some cases the values for the
treated used oil were lower than the values for fresh oil.
The triple adsorbent combinations reducing FFA content
the most were SG ? AO ? AC (5 ? 5?5 g) and
SG ? AO ? B (7.5 ? 3.75 ? 3.75 g) with AO having a
substantial contribution. AO was previously shown to be
effective in reducing FFA when used either alone or in bi-
adsorbent pairs.
TPM content of the treated used oil was the same as that of
fresh oil when either one of the adsorbent combinations was
utilized. The lowest CD content was achieved when the oil
was treated with SG ? AO ? BE (7.5 ? 3.75 ? 3.75 g).
SG ? AO ? AC (5 ? 5 ? 5 g) achieved the greatest
removal of AV from used oil. The SG ? AO ? AC
(5 ? 5 ? 5 g), SG ? AO ? BE (7.5 ? 3.75 ? 3.75 g)
and SG ? AO ? AC (7.5 ? 3.75 ? 3.75 g) triple adsor-
bent combinations achieved lighter color with[100 % or PI
in terms of the absorbance values at 460 nm.
All adsorbent mixtures reduced viscosity. The triple
adsorbent combination reducing the viscosity the most was
SG ? AO ? M (7.5 ? 3.75 ? 3.75 g) reducing the vis-
cosity from 57.0 to 49.2 mPa�s resulting in 97 % PI.
The AC present in SG ? AO ? AC (5 ? 5?5 g) and
SG ? AO ? AC (7.5 ? 3.75 ? 3.75 g) absorbed more
effectively the tocopherols from the used oil than without
AC. Increasing the amount of AC lowered the tocopherol
levels even further. Using three adsorbents together in the
column caused changes in the measured parameters of the
treated used oil except for TPM content (P \ 0.05).
Effects of Using Four Adsorbents on Used Oil
Characteristics
Table 7 shows the physical and the chemical characteris-
tics of used oil using four adsorbents together in the packed
column. FFA of the used oil decreased to 0.13 %, AV to Ta
ble
8P
hy
sica
lan
dth
ech
emic
alch
arac
teri
stic
so
fd
iffe
ren
tu
sed
oil
str
eate
din
aco
lum
np
ack
edw
ith
thre
eo
rfo
ur
typ
eso
fad
sorb
ents
Adso
rben
tA
mount
of
adso
rben
t(g
)A
mount
of
oil
(g)
FF
A(%
)T
PM
(%)
CD
(%)
AV
(mm
ol/
kg
oil
)V
isco
sity
(mP
a�s,
30
�C)
Abso
rban
ce,
460
nm
Toco
pher
ol
(mg/k
g)
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
PI
Val
ue
SG
?A
O?
BE
7.5
?3.7
5?
3.7
5U
O2,
300
1.6
1±
0.0
2b
30
13.3
±0.0
b19
0.9
6±
0.0
0a
37
43.9
±0.6
a28
57.3
±0.1
a35
0.7
99
±0.0
b37
254.2
±6.4
a
SG
?A
O?
BE
?B
3.7
5?
3.7
5?
3.7
5?
3.7
5U
O2,
300
1.7
6±
0.0
5a
22
14.3
±0.0
a13
1.0
0±
0.0
9a
28
45.9
±1.2
a24
55.7
±0.1
b48
0.9
18
±0.0
a26
197.0
±4.3
b
SG
?A
O?
BE
?B
3.7
5?
3.7
5?
3.7
5?
3.7
5U
O2,
150
1.6
9±
0.0
3ab
25
11.7
±0.0
c29
0.9
5±
0.0
2a
38
43.3
±1.5
a29
55.3
±0.1
b51
0.7
83
±0.0
c38
194.4
±8.1
b
SG
?A
O?
BE
7.5
?3.7
5?
3.7
5U
O3,
300
0.2
8±
0.0
4a
52
26.1
±0.3
b13
1.5
2±
0.3
7a
42
137.0
±1.6
a16
74.8
±2.1
b17
0.2
44
±0.0
b34
76.7
±0.9
a
SG
?A
O?
BE
?B
3.7
5?
3.7
5?
3.7
5?
3.7
5U
O3,
300
0.2
5±
0.0
1a
62
27.2
±0.0
a9
1.9
0±
0.0
5a
21
138.6
±1.6
a15
76.2
±0.0
a12
0.2
50
±0.0
a31
69.3
±0.8
a
SG
?A
O?
BE
?B
3.7
5?
3.7
5?
3.7
5?
3.7
5U
O3,
150
0.2
0±
0.0
0a
80
25.7
±0.0
c15
1.8
4±
0.1
2a
25
114.5
±4.8
b30
71.3
±0.1
c27
0.2
28
±0.0
0c
42
71.0
±1.7
a
SG
?A
O?
BE
7.5
?3.7
5?
3.7
5U
O4,
300
0.2
2±
0.0
3a
94
16.7
±0.0
b17
1.3
2±
0.0
9a
23
89.2
±1.4
a17
62.5
±0.3
c27
0.2
50
±0.0
0c
48
167.8
±1.3
b
SG
?A
O?
BE
?B
3.7
5?
3.7
5?
3.7
5?
3.7
5U
O4,
300
0.2
6±
0.0
2a
77
17.7
±0.2
a11
1.3
5±
0.0
8a
21
93.8
±0.9
a13
64.4
±0.1
a18
0.3
02
±0.0
a28
186.5
±1.4
a
SG
?A
O?
BE
?B
3.7
5?
3.7
5?
3.7
5?
3.7
5U
O4,
150
0.2
4±
0.0
4a
87
15.5
±0.4
c24
1.3
8±
0.0
6a
19
83.5
±0.4
b23
63.8
±0.1
b21
0.2
72
±0.0
b40
181.8
±8.1
ab
Res
ult
sar
egiv
enas
mea
ns
±S
D
UO
2use
dsu
nfl
ow
eroil
,U
O3
use
dso
ybea
noil
,U
O4
use
dco
rnoil
,SG
sili
cagel
,A
Oal
um
inum
oxid
e,A
Cac
tivat
edch
arco
al,
Bben
tonit
e,Z
zeoli
te,
BE
ble
achin
gea
rth,
Mm
agnes
ol
XL
,C
Cca
lciu
mca
rbonat
e,F
FA
free
fatt
yac
id,
TP
Mch
ange
into
tal
pola
rm
ater
ial,
CD
conju
gat
eddie
ne,
AV
P-a
nis
idin
eval
ue,
PI
per
centa
ge
impro
vem
ent
a–
cM
eans
foll
ow
edby
dif
fere
nt
super
scri
pts
inth
esa
me
colu
mn
indic
ate
stat
isti
cal
dif
fere
nce
s(P
\0.0
5)
J Am Oil Chem Soc (2013) 90:1761–1771 1769
123
4.3, viscosity to 48.2 mPa�s, and the absorbance at 460 nm
to 0.081 when the treatment column was packed with equal
amounts of the four adsorbents in the SG ? AO
? AC ? B combination. The quaternary adsorbents were
effective in reducing CD by 44–59 %. Using four adsor-
bents rather than two or three was more effective in
reducing the FFA content, removing the aldehydes, low-
ering the viscosity, and lightening the color.
As in other trials, the adsorbent combinations containing
AC; SG ? AO ? AC ? B (3.75 ? 3.75 ? 3.75 ? 3.75
g) resulted in the lowest tocopherol level (181 mg/kg). All
adsorbents in the quaternary adsorbent combinations,
especially AC, removed tocopherols.
Bhattacharya et al. [3] evaluated a quaternary adsorbent
combination consisting of 3.75 % M, 1.25 % SG, 3.75 %
AC and 1.25 % aluminum hydroxide in a packed column
for treating used palm oil. The treatment of hot oil (150 �C)
improved the FFA content by 40.1–48.0 %, AV by
53.2–58.9 %, CD content by 70.1–75.9 %, TPM content by
41.7–55.8 %, viscosity by 15.1–18.4 %, and lovibond red
color value by 68.0–76.4 %, and yellow color value by
63.2–81.9 % when adsorbents were used at 10 % based on
the weight of oil.
Effects of Different Type of Used Oils on Adsorption
Some physical and the chemical properties of different
types of used oils treated in a column packed with adsor-
bent combinations are shown in Table 8. While the highest
PI of FFA (77–94 %) was determined for UO4, the highest
TPM reduction (13–29 %) was obtained for UO2. Triple or
quaternary adsorbent combinations caused similar changes
in used oil parameters. However, oils obtained with a triple
adsorbent combination had lower TPM, CD, AV, color
values than those obtained with quaternary adsorbent
combinations. Generally, 15 g of adsorbent combinations
was not sufficient for the regeneration of 300 g of used oils.
Loading 150 g of used oils onto the columns resulted in
better PI values than with 300 g of oils.
Conclusions
SG was especially suitable for improving oil quality due to
its reducing both FFA and TPM contents as well as
adsorbing primary and secondary oxidation products. To
obtain a better PI, the optimum SG amount was 15 g, and
the optimum amount of used oil was 40 g. In the absence
of solvent, the optimum temperature of the used oil was
150 �C. SG can be used alone or with other adsorbents.
Increasing the number of adsorbents in the column resulted
in lower FFA, CD, and AV, lower viscosity, and a lighter
color in used oil. However, the lowest adsorption efficiency
was attained when 5 % (w/w) of the used oil was applied to
the column. Therefore, the column adsorption process can
be used with other purifying methods (e.g., membrane fil-
tration) in the regeneration of the used oils.
Acknowledgments The present study was supported by Abant Izzet
Baysal University, Scientific Research Projects (Project No.
2010.09.01.338).
References
1. Miyagi A, Nakajima M (2003) Regeneration of used frying
oils using adsorption processing. J Am Oil Chem Soc 80:91–96
2. Romero A, Bastida S, Sanchez-Muniz FJ (2006) Cyclic fatty acid
monomer formation in domestic frying of frozen foods in sun-
flower oil and high oleic sunflower oil without replenishment.
Food and Chem Toxicol 44:1674–1681
3. Bhattacharya AB, Sajilata MG, Tiwari SR, Singhal RS (2008)
Regeneration of thermally polymerized frying oils with adsor-
bents. Food Chem 110:562–570
4. Yoon J, Han BS, Kang YC, Kim KH, Jung MY, Kwon YA (2000)
Purification of used frying oil by supercritical carbon dioxide
extraction. Food Chem 71:275–279
5. Zheng S, Kates M, Dube MA, McLean DD (2006) Acid-cata-
lyzed production of biodiesel from waste frying oil. Biomass
Bioenergy 30:267–272
6. Birla A, Singh B, Upadhyay SN, Sharma YC (2012) Kinetics
studies of synthesis of biodiesel from waste frying oil using a
heterogeneous catalyst derived from snail shell. Biosource
Technol 106:95–100
7. Kheang LS, May CY, Foon CS, Ngan MA (2006) Recovery and
conversion of palm olein-derived used frying oil to methyl esters
for biodiesel. J. Oil Palm Res 18:247–252
8. Miyagi A, Subramanian R, Nakajima M (2003) Membrane and
additional adsorption process for quality improvement of used
frying oils. J Am Oil Chem Soc 80:927–932
9. Subramanian R, Nandini KE, Sheila PM, Gopalakrishna AG,
Raghavarao KSMS, Nakajima M, Kimura T, Maekawa T (2000)
Membrane processing of used frying oils. J Am Oil Chem Soc
77:323–328
10. Yates RA, Caldwell JD (1993) Regeneration of oils used for deep
frying: a comparison of active filter aids. J Am Oil Chem Soc
70:507–511
11. McNeill J, Kakuda Y, Kamel B (1986) Improving the quality of
used frying oils by treatment with activated carbon and silica.
J Am Oil Chem Soc 63:1564–1567
12. Maskan M, Bagcı HI (2003) Effect of different adsorbents on
purification of used sunflower seed oil utilized for frying. Eur
Food Res Technol 217:215–218
13. Lin S, Akoh CC, Reynolds AE (2001) Recovery of used frying
oils with adsorbent combinations: refrying and frequent oil
replenishment. Food Res Int 34:159–166
14. Mancini-Filho J, Smith LM, Creveling RK, Al-Shaikh HF (1986)
Effects of selected chemical treatments on quality of fats used for
deep frying. J Am Oil Chem Soc 63:1452–1456
15. Maskan M, Bagcı HI (2003) The recovery of used sunflower seed
oil utilized in repeated deep-fat frying process. Eur Food Res
Technol 218:26–31
16. AOCS (1997) Official and recommended methods of the Amer-
ican Oil Chemist’s Society. American Oil Chemist’s Society
Press, Champaign
17. Wong ML, Timms RE, Goh EM (1988) Calorimetric determi-
nation of total tocopherols in palm oil, olein and stearin. J Am Oil
Chem Soc 65:258–261
1770 J Am Oil Chem Soc (2013) 90:1761–1771
123
18. Lin S, Akoh CC, Reynolds AE (1998) The recovery of used
frying oils with various adsorbents. J Food Lipids 5:1–16
19. Paul S, Mittal GS (1997) Regulating the use of degraded oil/fat in
deep-fat/oil food frying. Crit Rev Food Sci Nutr 37:635–662
20. Blumenthal MM (1996) Frying technology. In: Hui YH (ed)
Bailey’s Industrial Oils and Fats Products, 5th edn. John Wiley
and Sons Inc, New York, pp 429–479
21. Maskan M (2003) Change in colour and rheological behaviour of
sunflower seed oil during frying and after adsorbent treatment of
used oil. Eur Food Res Technol 218:20–25
22. Kajimoto G (1994) Effective utilization of waste edible oil.
J Japan Oil Chem Soc 43:305–313
J Am Oil Chem Soc (2013) 90:1761–1771 1771
123
