Universidad de
Guayaquil
Ingeniería Química y Desarrollo
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ISSN – p: 1390 –9428 / ISSN – e: 3028-8533 / INQUIDE / Vol. 06 / Nº 01
Facultad de
Ingeniería Química
Ingeniería Química y Desarrollo
Universidad de Guayaquil | Facultad de Ingeniería Química | Telf. +593 4229 2949 | Guayaquil – Ecuador
https://revistas.ug.edu.ec/index.php/iqd
Email: inquide@ug.edu.ec | francisco.duquea@ug.edu.ec
Pag. 20
Transesterification and epoxidation of coconut oil
Transesterificación y epoxidación del aceite de coco
Eduardo Patricio Gilces Zambrano
1
* ; Karen Estefanía Moreira Mendoza
2
; Segundo Alcides García Muentes
3
;
Ramón Eudoro Cevallos Cedeño
4
Ariana Milena García Bowen
5
Received: 23/07/2023 – Received in revised form: 12/09/2023 – Accepted: 23/12/2023 –
Published: 19/03/2024
Research
Articles
X
Review
Articles
Essay
Articles
* Author for correspondence.
Abstract
Due to the advanced demographic increase in the world, pollution and the gradual increase in the price of oil due to the depletion of natural reserves, it
causes us to think and act immediately in the face of a solution to replace said fuel with profitable, productive and eco-friendly options. planet; as is
biodiesel from animal and vegetable fats through transesterification. Said raw materials are also tested in the epoxidation from which products are obtained
such as: intermediate elements for the production of polyurethanes, lubricants, cosmetics or as PVC stabilizers. This article presents a bibliographical
review of similar studies and demonstration on a laboratory scale, where it was verified that coconut oil complied with most of the parameters of the NTE
INEN 24:1973 standard, except for the percentage of acidity and moisture, making it optimal. for transesterification and epoxidation processes respectively,
also complying with most of the parameters of the NTE INEN 2482:2009 standard, with the exception of the iodine value, which is suitable for the use of
alternative energy. Regarding epoxidation, the values varied considerably, categorizing it in ISO viscosity grade 5 for lubricant.
Keywords: demographic, transesterification, epoxidation, PVC
Resumen
Debido al avanzado incremento demográfico en el mundo, la contaminación y el aumento gradual del precio del petróleo por el agotamiento de las reservas
naturales, provoca pensar y actuar de manera inmediata ante una solución para reemplazar dicho combustible en opciones rentables, productivas y
amigables con el planeta; como lo es el biodiesel a partir de grasas animales y vegetales por medio de la transesterificación. También se prueban dichas
materias primas en la epoxidación de la cual se obtienen productos como: elementos intermediarios para la producción de poliuretanos, lubricantes,
cosméticos o bien como estabilizadores de PVC. Este artículo presenta una revisión bibliográfica ante similares estudios y demostración a escala de
laboratorio, donde se comprobó que el aceite de coco cumplió con la mayoría de los parámetros de la norma NTE INEN 24:1973 a excepción del porcentaje
de acidez y humedad, haciéndolo óptimo para procesos de transesterificación y epoxidación respectivamente, cumpliendo también con la mayoría de los
parámetros de la norma NTE INEN 2482:2009 a excepción del índice de yodo, siendo éste apto para el uso de energía alternativa. En cuanto a la epoxidación
los valores variaron considerablemente categorizándolo en el grado 5 de viscosidad ISO para lubricante.
Palabras claves: demográfico, transesterificación, epoxidación, PVC
1. Introduction
The world population growth causes as an adverse effect the
obligation to increase the demand for energy, which is
produced mostly by traditional non-renewable sources such
as methane, coal and oil, contributing to the increase of CO
x
emissions where this gas, which is caused by man-made
product of the exploitation of these fossil fuels, generates
the greenhouse effect, causing several consequences such as
climate change [1].
Due to these unacceptable consequences and the rapid
industrialization that exploitation entails, it leads to the
depletion of the planet's natural reserves and its
contamination. Therefore, the demand for all this leads
directly to the search for feasible and acceptable alternatives
that are favorable, such as obtaining biodiesel from
vegetable oils, animal fats, waste oils, sludge from sewage
treatment plants, among other sources. [2].
1
Universidad Técnica De Manabí. https://orcid.org/0009-0000-2571-7188 , egilces5229@utm.edu.ec ; Portoviejo; Ecuador.
2
Universidad Técnica De Manabí. https://orcid.org/0000-0002-6516-8336 , kmoreira4312@utm.edu.ec ; Portoviejo; Ecuador.
3
Universidad Técnica De Manabí. https://orcid.org/0000-0002-8152-3406 , segundo.garcia@utm.edu.ec ; Portoviejo; Ecuador.
4
Universidad Técnica De Manabí. https://orcid.org/0000-0002-8583-4674 , ramon.cevallos@utm.edu.ec ; Portoviejo; Ecuador.
5
Universidad Técnica De Manabí. https://orcid.org/0009-0007-8887-9644 , agarcia4908@utm.edu.ec ; Portoviejo; Ecuador.
To obtain biodiesel, the most conventional method used was
transesterification to reduce the viscosity of the fat or oil,
which consisted of combining the triglycerides contained in
the oils and fats with a low molecular weight alcohol
(methanol) to produce a mixture of fatty esters and glycerin
in the presence of a catalyst (sodium hydroxide) [3].
Another method used to give added value to oils and fats is
epoxidation, in which vegetable oils or their corresponding
methyl esters are functionalized through the incorporation
of an oxygen atom in the establishment of the fatty acid
chain. Those obtained from epoxidized FAME (Fatty Acid
Methyl Ester) fatty acid methyl ester have proven to have
better properties for industrial application. This method
allows obtaining a wide range of compounds, since they
function as intermediates for the production of
polyurethanes, lubricants, cosmetics or as PVC stabilizers.
[4].
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Pag. 21
In the present work, coconut oil rich in medium-chain-
length saturated fatty acids was used. Given its low
instauration, it is a very chemically stable fat - 0.1% of its
total weight [5]; 6% monounsaturated oleic acid, 2%
polyunsaturated linoleic acid, 2% saturated stearic acid, 8%
saturated palmitic acid, 7% saturated capric acid, 49%
saturated lauric acid, 18% saturated myristic acid, 8%
saturated caprylic acid [6].
Therefore, the objective was to tansesterify and epoxidize
coconut oil at laboratory scale, characterizing the product,
referring to the NTE INEN 2482:2009 standard for
biodiesel and NTE INEN 24:1973 for coconut fat, for its
subsequent evaluation and categorization as an alternative
for lubricant or alternative energy.
2. Materials and methods
Oil previously obtained from dried coconut copra was used
as raw material. The experimental stages were divided into:
(i) characterization (ii) transesterification (iii) epoxidation
[7].
2.1. Transesterification
Before transformation to their corresponding epoxidized
ester, the vegetable oils were subjected to a
transesterification reaction mechanism where the molecule
went from tri to di and monoglyceride, respectively, giving
as main product three molecules of fatty acid methyl esters
(FAME) and one molecule of glycerol [4].
The technique used was the one described by [8]. The
transesterification reaction was developed in a molar ratio
of alcohol to triglyceride of 3 to 1, reacting in the
methanolysis 1 mole of triglyceride with 3 moles of alcohol,
using an excess of alcohol. However, this could generate
phase separation problems, decreasing the yield and
increasing the production cost.
The optimum molar ratio in basic catalysis is 6:1 (yields >
93%) [9].
According to [10] 27 ml of GR methanol was mixed with 1
g of GR sodium hydroxide (99.9% purity) as catalyst and
100 g of coconut oil was added with constant stirring for 1
hour. Finally, the mixture was allowed to stand for 24 hours
to achieve the splitting of the two phases: one biodiesel
phase and the other glycerol phase.
Figure 1. Typical transesterification of a triglyceride with methanol to
produce fatty acid alkyl esters and glycerol.
Source: [10]
2.2. Epoxidation
Epoxidation is a method that consists of the
functionalization of vegetable oils or their corresponding
methyl esters through the incorporation of an oxygen atom
in the establishment of the fatty acid chain. [4].
As for the experimentation, 150 g of oil was mixed with 17
ml of formic acid in an Erlenmeyer flask; subsequently, 1
ml of sulfuric acid was added until the mixture reached a
yellow to black color. Then, 63 ml of hydrogen peroxide at
30% were added by dripping in a separatory funnel, in a
time of 45 minutes.
Finally, the mixture was heated to a temperature of 60 °C
and left to react for 3 hours, producing an exothermic
reaction; the yellow color gradually disappeared until a
white product was obtained.
Once the reaction was neutralized, the water was discarded
and consequently the pH was measured, which was 7
(neutral). Finally, the oily phase was washed with distilled
water at 60°C until the water was clear.
Figure 2. General reaction scheme for the process of obtaining epoxidized
FAMEs (a) Transesterification of vegetable oils (b) Epoxidation.
Source:[4]
2.3. Physical-chemical tests
The physicochemical properties were determined by
laboratory tests based on established methodologies. The
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Pag. 22
specifications and experiments are detailed below, based on
the standards set out in Table 1, to carry out the respective
quality control of the oil, biodiesel and epoxidized biodiesel
oil (lubricant). It is worth mentioning that the tests for each
of the physical-chemical parameters were carried out in
triplicate.
Table N° 1. Standardized test methods
PROPERTIES
Test Method
IODINE CONTENT
NTE INEN 37
KINEMATIC VISCOSITY 40°C
ASTM D 445-09
RELATIVE DENSITY,25/25°C
NTE INEN 35
ACIDITY (AS LAURIC ACID)
NTE INEN 38
SAPONIFICATION INDEX
NTE INEN 40
HUMIDITY
NTE INEN 39
Source:[11]; [12]
2.3.1. Iodine Index
Approximately 0.08 g of the samples were placed in an
Erlenmeyer flask. Next, 10 ml of chloroform were added to
dissolve the fat and 7.5 ml of Wijs' reagent were added,
covered and the content was shaken in the dark.
Subsequently, the mixture was kept in the absence of light
for 1 hour to avoid photo degradation. Then, 10 ml of a
potassium iodide solution and 25 ml of water were added.
Finally, a titration with the sodium thiosulfate solution was
carried out until the total absence of the yellow color
produced by the iodine was observed, resulting in the
presence of a faint yellow color. Finally, a pinch of starch
was added and continued until the exact moment of the
color change.
The formula to be used was as follows:
Where:
= iodine value of the sample, in g/g.
V = arithmetic means of the volumes of sodium thiosulfate
solution used in the titration of the test (blank), cm
3
= volume of sodium thiosulfate solution used in the
titration of the sample, cm
3
N = normality of the sodium thiosulfate solution.
m = mass of the sample analyzed, in g.
2.3.2. Density
A 25 ml pycnometer was used to measure the density of the
samples.
The relative density will be:
Where:
= relative density at 25/25C.
m = mass of the empty pycnometer, in g.
= mass of the pycnometer with distilled water, in g.
= mass of the pycnometer with sample, in g.
2.3.3. Kinematic viscosity
The Oswalt Viscometer was used to measure the viscosity
of the samples at 40°C. Its operation was based on the
measurement of the time where the fluid traveled a distance
between a given space.
The kinematic viscosity is given by the following
expression:
The values of water viscosity for various temperatures are
shown below. [13].
Where:
= kinematic viscosity in mSt
= dynamic viscosity of water in mSt
= sample density
= water density
sample drop time
water fall time
2.3.4. pH
It is important to maintain a regulated pH to neutralize the
mixture in the transesterification and epoxidation of the
methyl esters. For this, litmus paper strips were used.
2.3.5. Humidity
For moisture determination, the crucibles were washed and
placed in the oven for 90 minutes at a temperature of
100_°C. Once dried, the crucibles were weighed on the
balance and the sample was added. Next, it was weighed
again with the sample and taken to the oven for 2 hours at a
temperature of 100_°C. Finally, the crucible with the
sample was removed from the oven and placed in the
desiccator for 30 minutes. Finally, the crucibles were
weighed, and the corresponding data were taken.
La fórmula empleada fue la siguiente:
Where:
B = mass of crucible with sample before heating, in g.
C = mass of crucible with the sample after heating, in g.
A = mass of empty crucible, in g.
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Pag. 23
2.3.6. Saponification Index
In an Erlenmeyer flask of 250 ml, 2 g of the sample were
weighed, where 40 ml NaOH to 0.081 N were added; later,
the sample was heated to 60_ºC, and it was shaken at 240
rpm for one hour until saponification. A similar blank assay
was performed in all aspects. Once the sample was
saponified, it was titrated by adding 4 drops of
phenolphthalein indicator.
The formula used was as follows:
Where:
i = saponification index of the product, in mg/g.
40 = chemical equivalent of NaOH.
V
2
= volume of hydrochloric or sulfuric acid solution used
in the titration of the sample, in cm
3
.
V
1
= volume of hydrochloric or sulfuric acid solution used
in the titration of the blank, in cm
3
.
N = standardization of the hydrochloric or sulfuric acid
solution.
m = mass of the sample analyzed, in g.
2.3.7. Percentage of Acidity
For the determination of the percentage of acidity, it was
made by titration or titration; 2 g of the sample was added
in an Erlenmeyer flask with 10 mL of ethanol; later, 3 drops
of phenolphthalein were added. The mixture was stirred
constantly until homogenized, and by titration 0.081 N
NaOH was added dropwise until a pink color was obtained.
The formula used was the following:
Where:
%A = acidity of the product, in mass percentage.
M = molecular mass of acid used to express the result (200).
V = volume of the sodium or potassium hydroxide solution
used in the titration, in
N = normality of the sodium or potassium hydroxide
solution.
m = mass of the sample analyzed, in g.
2.3.8. Acidity Index
The formula used was as follows:
Where:
AI = acid number of the product, in mg/g.
56.1 = molar mass of potassium hydroxide.
V = volume of the sodium or potassium hydroxide solution
used in the titration, in cm
3
.
N = normality of the sodium or potassium hydroxide
solution.
m = mass of the sample analyzed, in g.
3. Results
As shown in Table 2, it is observed that most of the
parameters are within the permissible range according to the
standard established for coconut fat. However, the acidity
percentage is not within the range of the standard, but its
acidity index to be used as a base material for vegetable oils,
as mentioned by [14], which must have an acidity index
lower than 2 mg KOH/g of fat, which represents an optimal
acidity for the subsequent stages of the process.
As for the percentage of moisture, there was a slight
increase in the maximum allowed by the standard, which
does not vary much in the transesterification process, since,
according to [17], it is very feasible to have values slightly
higher than the maximum of the standard, since the
probability of saponification decreases, which was verified
with the saponification index, which indicates a high purity
of the fat.
Table Nº3. Characterization of biodiesel.
Chemical
physical
parameters
Unit
Experi
mental
part
Referen
ce
Specificati
on
Percentage
of acidity
%
0.486
0 – 0.5
ASTM
D664
pH
-
6
-
-
Density at
15ºC
kg/m
3
703.2
880
máx.
ASTM
D1298
Kinematic
viscosity at
40ºC
mm
2
/s
1.97
1.9- 6
ASTM
D445
Table Nº 2. Characterization of coconut oil.
Chemical
physical
parameters
Unit
Experimental
part
Reference
Specification
Percentage of
acidity
%
0.405
0 – 0.2
NTE INEN 38
Acidity index
mg
KOH/g
of fat
1.14
2 máx
[14]
pH
-
6
-
-
Relative
density
25/25ºC
-
0.9104
0.907 -
0.919
NTE INEN 35
Kinematic
viscosity at 40
ºC
mm
2
/s
22.69
21.84 -
27.23
[15]
[16]
Humidity
%
0.07
0.05
NTE INEN 39
Saponification
index
g
NaOH/
of fat
255
250-264
NTE INEN 40
Iodine index
2
/100g
m
7.875
7.5 – 10.5
NTE INEN 37
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Pag. 24
Humidity
%
0.048
0-0.05
ASTM
D6751
Saponifica
tion index
g
NaOH/
of fat
257
370
máx.
ASTM
D5558-95
Iodine
index
2
/100
7.25
120
máx.
EN 14111
According to the values obtained in Table 3, the only
relatively low value was the iodine index compared to the
maximum acceptable value of 120 mgI2/g for fuels to be
used in internal combustion engines. A low iodine value
will result in very low carbon deposits in the internal parts
of the engine and the tendency to block the injector orifices,
so it is not recommended to be used as an engine fuel, but
as a base fuel to be used as alternative energy in subsequent
purification and refining processes to increase its autonomy
and make it suitable for further use; However, this is also
due to the structure of the oil in which 92% are saturated
fatty acids, with lauric acid being the predominant one, at
49%, which agrees with the theory that the higher the
percentage of unsaturated fatty acids in the sample, the more
iodine will react with these double bonds, which ultimately
results in a higher iodine content; This is proven by the
structure of coconut oil, which has a higher percentage of
saturated fatty acids, which is why the iodine value is low,
since the remaining 8% is unsaturated fatty acids.
In addition, this characteristic makes it attractive for
obtaining biodiesel, since the lower the iodine content in the
starting oil, the better the fuel in terms of oxidative stability
and increased engine lubrication, which concludes that it is
suitable for a lubricant in its subsequent epoxidation
process.
Table Nº4. Characterization of the epoxidized oil.
Chemical
physical
parameters
Unit
Experime
ntal part
Referen
ce
Specifica
tion
Percentage
of acidity
%
0.702
0 – 0.5
ASTM
D664
pH
-
3
-
-
Relative
density 15
ºC
-
0.94
-
NTE
INEN 35
Density at
15 ºC
kg/m
3
940
880 máx.
ASTM
D1298
Relative
density 40
ºC
-
0.88
-
NTE
INEN 35
Density at
40 ºC
kg/m
3
880
-
-
Kinematic
viscosity at
40 ºC
cSt
4.69
1.98-3520
[18]
Iodine
index
2
/100
3.15
120 máx.
EN 14111
As shown in Table 4, the percentage of acidity increased
compared to the transesterified oil, which in turn exceeds
the limit of the standard; one of the causes that provokes this
is the oxidation of the oil because in the epoxidation process
it incorporates an oxygen atom in the establishment of the
fatty acid, where, this degradation by oxidation increased
and in turn also increased the acidity percentage. Due to this
addition of oxygen in the epoxidation process, its density at
15ºC increased considerably surpassing the limit of the
norm; it is worth mentioning that the characterization of the
density at 40ºC was also carried out to obtain a kinematic
viscosity at that temperature, where it is shown that the
density reduced by the action of the temperature and that in
turn it adjusts to the maximum value of the norm of the
density at 15ºC. It is also shown that the kinematic viscosity
at 40ºC was within the reference while the iodine index was
below the norm.
3.1. Discussion
The study was conducted to test the theory of epoxidation
in which it incorporates an oxygen atom through the
unsaturated chain (double bonds) and it was decided to work
with coconut oil or fat, which is very rich in lauric acid
(saturated) and this theory was affirmed, since the oil or fat
did epoxidize because the lowest percentage of this oil
(10%) is formed by unsaturated acids, that is to say that 10%
of this oil epoxidized correctly and it could be categorized
as an ISO grade 5 lubricant.
As for transesterification, according to the results, it serves
as a base to be used as biofuel, since due to its low iodine
index it cannot be used directly as biodiesel.
4. Conclusions
Biodiesel was obtained from coconut vegetable fat in one
stage by using sodium hydroxide as a catalyst, presenting
relatively low values required by the standard as: the iodine
index, which shows that this biodiesel cannot be used as fuel
in combustion engines but it does serve as a raw material
for this, and as for the epoxidation it is affirmed with the
theory that due to the low percentage of unsaturated fatty
acids that the coconut fat has, feasible values were not
obtained for this process, but this does serve as raw material
for a grade 5 lubricant according to the kinematic viscosity
of the ISO.
The oil, biodiesel and epoxy obtained from coconut fat meet
most of the parameters established in the standards NTE
INEN 2482:2009 for biodiesel and NTE INEN 24:1973 for
coconut fat, and its quality depends on these standards.
The optimum time at a temperature of 60 ºC for the
transesterification was defined that 60 min was the best
because it had more combustion time in a test of igniting
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Pag. 25
pieces of paper with the biodiesel and that in the other times
of 35 and 45 min it did not have a good combustion stability.
According to its kinematic viscosity of epoxy, it is
categorized into ISO viscosity grade 5, which its limits
range from 4.14 to 5.06 cSt [18] and where this type of high
fluidity and superior quality lubricating oil is specially
formulated to work in high speed and precision systems
[19].
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