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Indonesian Journal of
Fundamental and Applied Chemistry
Article http://ijfac.unsri.ac.id
DOI: 10.24845/ijfac.v3.i3.77 77
Article Info
Received 14 September 2018
Receive in revised 16 September
2018
Accepted 16 September 2018
Available online 10 October
2018
Biodiesel Production from Waste Cooking Oil
Endang Sri Rahadianti1* , Yerizam 2 and Martha 3
1Applied Master of Renewable Energy Engineering, Politeknik Negeri Sriwijaya, Palembang
2 Chemical Engineering Department, Renewable Energy Engineering, Politeknik Negeri Sriwijaya, Palembang
3 Chemical Engineering Department, Renewable Energy Engineering, Politeknik Negeri Sriwijaya, Palembang
*Corresponding Author: erahadianti@gmail.com
Abstract
Increased energy consumption and the depletion of petroleum reserves have pushed up oil prices globally. The
diminishing petroleum reserves are a problem inherent in this type of fossil energy. One alternative energy
source that has the potential to be developed in Indonesia is biodiesel. Used cooking oil or used cooking oil is a
potential raw material for making biodiesel. In this study biodiesel was made from used cooking oil and
methanol using the transesterification method with KOH catalyst. The production of biodiesel from used cooking
oil begins with mixing raw materials of used cooking oil collected into one. The mixture is then precipitated for
24 hours. The transesterification process was carried out by mixing KOH (1% of oil weight) with methanol (ratio
of methanol: oil 6: 1) at a temperature of 65 oC. After the temperature is reached, the methanol and KOH
solution is added slowly while pumping (stirring), with a variation of time 30, 45, 60.75 and 90 minutes.
Biodiesel purification is done by washing using hot water (temperature 70 C) twice as much washing.
Characteristics of biodiesel based on the best conditions for density 0.886 g / mL, viscosity 5.89 cSt, FFA 0.11%
, acid value 0.256 mgKOH/g and flash point 170.52 oC. The biodiesel products based on these parameters meet
SNI 7182-2015 standards.
Keywords: energy, biodiesel, waste cooking oil, transesterification, free fatty acid (FFA)
Abstrak (Indonesian)
Peningkatan konsumsi energi dan menipisnya cadangan minyak bumi telah
mendorong kenaikan harga minyak secara global. Cadangan minyak bumi yang
semakin berkurang merupakan permasalahan yang melekat pada jenis energi fosil
ini. Salah satu sumber energi alternatif yang berpotensi untuk dikembangkan di
Indonesia adalah biodiesel. Minyak jelantah atau minyak goreng bekas merupakan
bahan baku yang potensial untuk biodiesel. Pada penelitian ini biodiesel dibuat dari
minyak goreng bekas dan metanol dengan metode transesterifikasi menggunakan
katalis KOH. Pembuatan biodiesel bekas dimulai dengan dengan mencampur bahan
baku minyak goreng bekas yang dikumpulkan menjadi satu. Campuran kemudian
diendapkan selama dua kali 24 jam. Proses transesterifikasi dilakukan dengan
mencampurkan KOH (1 % dari bobot minyak) dan metanol (ratio metanol : minyak
6:1) pada temperatur 65 C. Setelah suhu tercapai, metanol dan KOH ditambahkan
secara perlahan sambil dilakukan pemompaan (pengadukan), dengan variasi waktu
30, 45, 60,75 dan 90 menit. Pemurnian dilakukan dengan pencucian menggunakan
air panas (suhu 70 C) sebanyak dua kali pencucian. Karakteristik biodiesel
berdasarkan kondisi terbaik untuk density 0,886 g/mL, viscosity 5,89 cSt, FFA 0,11
% , acid value 0,256 mgKOH/g dan flash point 170,52 0C. Produk biodiesel yang
dihasilkan berdasarkan parameter tersebut memenuhi standar SNI 7182-2015.
Kata Kunci: energi, biodiesel,minyak goreng bekas, transesterifikasi, asam lemak
bebas (FFA)
INTRODUCTION
Increased energy consumption and the depletion
of petroleum reserves have pushed up oil prices
globally. The diminishing petroleum reserve is a
problem that is always attached to this type of fossil
energy [1]. The main reason for finding alternative
Rahadianti et al, Indones. J. Fundam. Appl. Chem., 3(3), 2018, 77-82
DOI: 10.24845/ijfac.v3.i3.77 78
diesel engine fuels is because of the high price of oil
products [2]. To face the challenges in this energy
sector, it is necessary to utilize the potential of new
and renewable energy. One alternative energy source
that has the potential to be developed in Indonesia is
biodiesel.
Biodiesel can be used as a substitute for fossil
fuels such as diesel oil. Used cooking oil or used
cooking oil is a potential raw material for making
biodiesel. Its abundant availability can be estimated
from an increase in the rate of growth of oil palm in
2004-2014 at around 11.09% per year [3]. The
projected consumption of CPO (crude palm oil) in
2015 for the production of cooking oil and margarine
is around 5.9 million tons or 54.63% of the total CPO
production [4].
Used cooking oil or Jelantah can be converted to
biodiesel because the chemical composition contains
free fatty acids (FFA) and when reacted with alcohol
and using simple technology will become biodiesel
[5]. Biodiesel is derived from fats and oils either by
chemical means [6]. There are at least four ways in
which oils and fats can be converted into biodiesel,
namely, transesterification, blending, micro emulsions
and pyrolisis. Among these, transesterification is the
most commonly used methods as it reduces the
viscosity of oil [7]. Biodiesel production by
transesterification reaction can be catalyzed with
alkali, acidic or enzymatic catalyst. Alkali and acid
transesterification processes require less reaction time
with reduced processing costs as compared to the
enzyme catalyst process [8,9].
Several studies on biodiesel synthesis from used
cooking oil have been carried out. The study [10] has
synthesized biodiesel from used cooking oil with the
trans-esterification process. Research [11] has
synthesized biodiesel using a two-stage catalyst
process, namely the esterification process with ferry
sulfate catalyst and potassium hydroxide base
catalyst. The biodiesel processing process that uses
two stages, namely esterification and
transesterification requires double consumption of
methanol. The addition of catalyst can increase
conversion percentage of biodiesel produced [12].
In this study biodiesel was made from used
cooking oil and methanol using the transesterification
method using KOH catalyst. As for the selection of
used cooking oil as a raw material for making
biodiesel, in addition to being easy to obtain and the
price is low also to utilize used cooking oil which is
usually disposed of to be a useful product [13].
MATERIALS AND METHOD
Materials
Waste cooking oil (WCO) used in the research
was obtained from street sellers in Palembang City,
Indonesia. Samples was taken from Bukit Besar,
Palembang, South Sumatera. The chemical and
reagent for synthesize include methanol, palmitat acid
and KOH were purchase form Merck. The distillated
water wa used to make reagents. The characteristic of
waste cooking oil is summarized in Table 1. Methanol
was used as alcohol for the transesterification
reaction. KOH was used as base catalyst.
Synthesis of Methyl Ester
The production of biodiesel from used cooking
oil begins with mixing raw materials of used cooking
oil collected into one. The mixture is then precipitated
for 24 hours. After pretreatment, a preliminary
analysis of used cooking oil was carried out, namely
FFA level test (max.5%). The trasesterification
process was carried out by mixing KOH (1% of oil
weight) with methanol (ratio of methanol: oil 6: 1).
Used cooking oil is then heated to 65oC. After the
temperature is reached, the methanol and KOH
solution is added slowly while pumping (stirring).
Heating and stirring are evenly carried out at 65oC
with a variation of 30, 45, 60, 75 and 90 minutes.
After the heating process, the mixture is allowed to
stand for + 1 hour. After the precipitate the separation
process is done by taking the bottom first (glycerol),
then the upper liquid (biodiesel). Biodiesel
purification is done by washing using hot water
(temperature 70 oC) twice as much washing. Ratio
between volume of biodiesel and water for washing
are 1: 1. Biodiesel is then heated at 110 oC for 10
minutes using a hot plate to remove moisture. The
qualitative analysis of biodiesel characteristics refers
to SNI 7182-2015.
RESULTS AND DISCUSSION
Analyses of raw material
Used cooking oil before being reacted with
methanol is precipitated for 2 times 24 hours, and
then an initial analysis of used cooking oil is carried
out. The waste cooking oil was illustrated in Figure 1.
Based on the analyses that have done, the
characteristic of raw material can be seen in Table 1.
Because of FFA less than 5 %, the feedstock can be
transesterified with an alkali catalyst.
Used cooking oil has various characteristics
depending on many factors, including the type of oil
source commodity, duration of use, fried food
Rahadianti et al, Indones. J. Fundam. Appl. Chem., 3(3), 2018, 77-82
DOI: 10.24845/ijfac.v3.i3.77 79
ingredients and frying temperature. The main
characteristics of used cooking oil are the relatively
high levels of free fatty acids, density and viscosity.
Figure 1. Waste Cooking Oil
Table 1. The characteristics of waste cooking oil
T
y
pe of Anal
y
ses Value Uni
t
Method
Densit
y
(400C) 0,9104
g
/mL Measuremen
t
Viscosit
y
8,8843 cS
t
Measuremen
t
F
r
ee Fatt
y
Aci
d
2,9572 % Titration
Acid Value 6,1721 m
g
KOH/
g
Titration
In Table 1 the characteristics of used cooking oil
used in this study are within the range of
characteristics of the results of the study [14] namely
acid numbers ranging from 1.78 to 17.85 mg/KOH/g,
density 0.9183 - 0.9273 and viscosity 39.81 - 51.44
cSt.
Synthesis of Biodiesel
Biodiesel synthesis is done using heating at a
temperature of 65oC which is the optimum
temperature for the Trans esterification process that
has been done before, where temperature variations
are made between the ranges of 45-65oC. The
temperature at 65oC was selected based on the
pleminary study result. The research was done in oil
to metanol volume ratio 6:1, catalyst concentration 1
wt % KOH, and temperature at 65oC. The biodiesel
product is shown in Figure 2.
Figure 2. Biodiesel product
The Effect of reaction time to the density
Biodiesel density testing aims to determine the
level of fuel feasibility in the engine (in this case
diesel engine). The density values were measured at
40 oC and space pressure. The density values were
measured at 40 C and space pressure. From Figure 3
it can be seen that the density at various reaction
times has decreased in density. The longer the
reaction time, the biodiesel density decreases. The
density range obtained from the analysis results is
0.886-0.889 g/mL. The optimum condition at 90
minutes reaction time obtained a density value of
0.886 g/mL. Different results from previous research
which obtained biodiesel density from used cooking
oil were 0, 852 g/mL [15], 852 kg/m3 [16] and 0.874
g/mL [17]. This is in line with the statement [18],
where the density biodiesel obtained from the
transesterification with conventional heat treatment
ranges from 0.85 to 0.86 g/mL. The effect of the
reaction time on density is shown in Figures 3.
Figure 3. The effect of reaction time to the density of
product
Density is the mass of biodiesel per unit volume
at a certain temperature. From this statement it can be
seen that the lower the density value the better the
biodiesel. There are several factors that influence the
results of biodiesel density analysis, namely, the first
factor is the possibility that there are still a number of
used biodiesel washing water, where the water density
is 0.99 g/mL which will certainly affect the
measurement of biodiesel density. The second factor
is that there are still triglyceride molecules that have
not been converted into methyl esters (biodiesel).
Based on the results of the analysis, it can be
seen that the biodiesel density obtained meets SNI
7182-2015 which is in the range 0.886-0.888 gr / ml.
According to [19], the density values within the SNI
limit can produce perfect combustion. Biodiesel with
a density that exceeds the standard will cause
0.85
0.875
0.9
0 20406080100
Density(gr/ml)
Time(minute)
Rahadianti et al, Indones. J. Fundam. Appl. Chem., 3(3), 2018, 77-82
DOI: 10.24845/ijfac.v3.i3.77 80
incomplete combustion reactions that can increase
engine emissions and wear. This will be happen if the
density is low in the ability of high oil fuels [20]. It
can be optimized at a temperature of 65oC with a
mixing time of 90 minutes with a density of 0.886
g/mL.
The Effect of reaction time to the viscosity
Viscosity is a number that states the amount of
resistance of a liquid material to flow or the size of
the amount of shear resistance of a liquid material.
Wahyuni found that the higher of the viscosity, the
thicker and more difficult liquid material to flow [21].
From Figure 4 it can be seen that at 90 minutes
reaction time an increase in viscosity occurs, due to
incomplete biodiesel manufacturing process because
the boiling point of methanol is 64.70C, then methanol
will quickly evaporate before the perfect biodiesel
process occurs. The optimum mixing time for
viscosity is 75 minutes, with viscosity of 5.89 cSt.
This value is greater than the viscosity reported by
[15], which is 4.7 cSt. Decreased cooking oil
viscosity indicates a certain amount of triglyceride
molecules have been successfully converted into
shorter or simpler molecules, namely methyl esters.
The effect of the viscosity is shown in Figures 4.
Figure 4. The effect of reaction time to the viscosity
of product
Based on the results of the analysis, it can be
seen that almost all of the biodiesel viscosity obtained
meets SNI 7182-2015 which is in the range of 5.89 -
6.25 cSt. High viscosity can affect the atomization of
combustion during injection and other flow losses in
the combustion channel. So that it affects the quality
of biodiesel [22].
The Effect of reaction time to the acid value
Acid numbers are a measure of the amount of
free fatty acids and are calculated based on the
molecular weight of fatty acids or a mixture of fatty
acids [23]. The number of acids is the number of
milligrams of KOH needed to neutralize free acids in
one gram of biodiesel [24].
A high acid level indicates the formation of large
free fatty acids from oil hydrolysis. The higher the
acid number, the lower the oil quality [25]. According
to [23] oil or fat will be converted into free fatty acids
and glycerol in a hydrolysis reaction. Hydrolysis
reactions can occur because of the presence of a
number of water in oil or fat that can cause damage to
oil or fat. In Figure 5, the acid number shows that
for each time the value has met the SNI standard.
The decrease in acid numbers indicates that a
number of free fatty acids contained in used
cooking oil have been converted into biodiesel.
The effect of the acid value of the biodiesel product is
shown in Figures 5.
Figure 5. The effect of reaction time to the acid
value of product
A high acid value indicates that there is still free
fatty acid in biodiesel, where biodiesel will be
corrosive to the engine when used. The amount of
methanol is intentionally given excess in addition to
pushing the reaction towards the product is also
intended so that the water formed from the reaction of
free fatty acids with methanol can be absorbed by
methanol so as not to block the course of the reaction
of free fatty acid conversion into methyl esters. This
is because the reaction of free fatty acids with
methanol which forms methyl esters and water is
reversible so that the water formed can react again
with methyl esters (biodiesel) under certain operating
conditions. Therefore, the lower the acid number, the
better the quality of biodiesel [26]. The optimum acid
number occurs at a reaction time of 75 minutes with a
temperature of 650C which is 0.2589 mg-KOH/g.
5.75
5.8
5.85
5.9
5.95
0 20406080100
Viscosity(cSt)
Time(minute)
0
0.1
0.2
0.3
0.4
0.5
0 20406080100
AcidValue
Time(minute)
Rahadianti et al, Indones. J. Fundam. Appl. Chem., 3(3), 2018, 77-82
DOI: 10.24845/ijfac.v3.i3.77 81
Comparison of Product Quality with SNI Standard
No. 7182 – 2015
Biodiesel produced from the best conditions
based on the criteria of density, viscosity, acid value
and FFA content is shown in Table2.
Table 2. Comparison of Product Biodiesel dengan
SNI
Standard 7182 - 2015
T
y
pe of Anal
y
ses Result Uni
t
SNI
Densit
y
(400C) 0,886
g
/mL 0,856
–
0,890
Viscosit
y
5,89 cS
t
2,3
–
6,0
F
r
ee Fatt
y
Acid(FFA) 0,11 % Max 5
Acid Value 0,256 m
g
KOH/
g
Max. 0,5
Biodiesel FFA levels meet SNI requirements,
with a value of 0.11%. This decrease in FFA levels
from used cooking oil shows that a number of free
fatty acids contained in used cooking oil have been
converted to biodiesel. The characteristics of
biodiesel from the reaction with 1% KOH catalyst,
temperature of 650C with a variation of reaction time
at 30 to 90 with 15 minute intervals, generally have
the required quality of SNI 7182-2015.
CONCLUSION
1. Used cooking oil as raw material with a FFA
value of 2.9572% can be converted into biodiesel
using the transesterification method directly
without going through the esterification process.
2. Characteristics of the physical properties of
biodiesel in general have met the standards of
SNI 7182-2015 based on parameters of quality
density, viscosity, acid numbers and FFA.
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