TRANSESTERIFICATION OF BIODIESEL FROM WASTE COOKING OIL USING ULTRASONIC TECHNIQUE

Abstract

The aim of this research is to explore a new transesterification process from waste cooking oil to biodiesel using ultrasonic technique. The conversion of waste cooking oil with sodium hydroxide as catalyst used ultrasonic type of clamp on tubular reactor at 20 kHz. The reaction time, molar ratio, and biodiesel quality of this process were compared with conventional transesterification. Method analyzed a total glycerol and free glycerol was determined with Gas Chromatography referred to EN 14105 and functional group of fatty acid methyl ester (FAME) used Attenuated Total Reflection Infrared Spectroscopy (ATR-IR) instruments. At the results, with presence of cavitation on the ultrasonic, chemical activity was increased so that the rate of ester formation is significantly enhanced. The ultrasonic technique could reduce the transesterification reaction time to 5 minute compared to 2 hours for mechanical stirring processing. Conversion of triglyceride (TG) to FAME using ultrasonic obtained 95.6929%wt with the methanol to oil molar ratio of 6:1 and 1%wt sodium hydroxide catalyst.

Full text

International Conference on Environment 2010 (ICENV 2010)
TRANSESTERIFICATION OF BIODIESEL FROM WASTE
COOKING OIL USING ULTRASONIC TECHNIQUE
DARWIN SEBAYANG, EGI AGUSTIAN, ACHMAD PRAPTIJANTO
Faculty of Mechanical and Manufacturing Engineering,
Parit Raja – Batu Pahat, Malaysia
Universiti Tun Hussein Onn Malaysia
E-mail: darwin@uthm.edu.my,
egiagustian@yahoo.com
ABSTRACT
The aim of this research is to explore a new transesterification process from waste cooking
oil to biodiesel using ultrasonic technique. The conversion of waste cooking oil with sodium
hydroxide as catalyst used ultrasonic type of clamp on tubular reactor at 20 kHz. The reaction
time, molar ratio, and biodiesel quality of this process were compared with conventional
transesterification. Method analyzed a total glycerol and free glycerol was determined with
Gas Chromatography referred to EN 14105 and functional group of fatty acid methyl ester
(FAME) used Attenuated Total Reflection Infrared Spectroscopy (ATR-IR) instruments. At
the results, with presence of cavitation on the ultrasonic, chemical activity was increased so
that the rate of ester formation is significantly enhanced. The ultrasonic technique could
reduce the transesterification reaction time to 5 minute compared to 2 hours for mechanical
stirring processing. Conversion of triglyceride (TG) to FAME using ultrasonic obtained
95.6929%wt with the methanol to oil molar ratio of 6:1 and 1%wt sodium hydroxide catalyst.
Keywords: Transesterification; Waste cooking oil; Biodiesel; Ultrasonic.
INTRODUCTION
In 2008, Malaysia produced 17.7 million tones of palm oil on 4.5 million hectares of
land, [1] and was the second largest producer of palm oil, is employed more than 570,000
people [2]. Malaysia is the largest exporter of palm oil in the world. About 40% of palm oil
mostly made into cooking oil, margarine, specialty fats and oleochemicals [1]. Most cooking
oil made from palm oil. The local disposal of cooking oil becomes a huge problem because of
the large volumes involved. In the fast food business alone, a single branch which serves
fried food such as fried chicken, french fries and burgers can produce as much as 15 liters of
used cooking oil per day. Considering that there are hundreds of these outlets in Malaysia, the
total amount generated can reach several thousand liters per day. Properties of degraded used
cooking oil after it gets into sewage system are conductive to corrosion of metal and it also
affects installations in waste water treatment plants. Thus, it adds to the cost of treating
effluent or pollutes waterways [2]. Waste cooking oil is one of source alternative for
biodiesel process.
Biodiesel from waste cooking oil (WCO) can reduce the cost of biodiesel production
since the feedstock costs constitutes approximately 70-95% of the overall cost of biodiesel
production [3]. Biodiesel can be produced by the transesterification of triglycerides with
alcohol, commonly methanol, in the presence of a base or acid catalyst into fatty acid methyl
esters (FAME). The TG are converted stepwise to diglycerides (DG), monoglycerides (MG),
and finally glycerol. To complete the production of 3 mol of FAME and 1 mol of glycerin
(GL) needed 1 mol of TG and 3 mol alcohols, as shown in the mechanism that follows [4].
The mechanism overall transeserification reaction has shown in Fig 1. The reaction is
influenced mainly by the type of catalyst, molar ratio of alcohol to TG, mixing, content of
FFA (which are natural degradation products of oils), water content, reaction temperature,
and alcohol used as the reagent [5].

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O
R
O
O
R
O
O
R
O
OMe
R
O
HO
HO
HO
+3 MeOH +
Tri-Glyceride Methanol FAME Glycerol
Catalyst
Figure 1: Mechanism transesterification reaction TG to FAME
Most researchers used base catalyst for transesterification TG such as sodium and
potassium hydroxide [6,7,8]. Using acid catalyst transesterification has been given less
attention because it has a relatively slow reaction rate and also corrodes equipment [9]. The
most useful basic catalysts used in transesterification of fats are sodium or potassium
methoxides. However, sodium or potassium hydroxides were used with very good results
[10]. In the process of transesterification process which methanol and oil are immiscible, the
mixing efficiency is one of the most important factors to adjust in order to improve the yield
of the transesterification [10].
Sonochemistry is one method for chemical reaction using ultrasonic. Ultrasonic is
known to be a useful tool for strengthening the mass transfer of liquid–liquid heterogeneous
systems [11]. With increased liquid–liquid mass transfer, oils and methanol are easily mixed
together. Under ultrasonic irradiation, the transesterification can be carried out at a low
temperature, and smaller amounts of catalyst and methanol are needed. Georgogianni et al
carried out the transesterification from waste oils in the presence of alkaline catalysts and
heterogeneous catalyst using low-frequency ultrasonication (24 kHz) and mechanical stirring
(600 rpm). Their results showed that many advantages of the ultrasonic irradiation, such as
high yields of methyl esters, time saving procedure and so on [12]. Colucci et al. [5]
established that it is feasible to produce biodiesel from soybean oil using ultrasonic mixing,
reporting > 99% conversion to fatty acid methyl esters (FAME) when using ultrasonic energy
(using a probe) for more than 15 min at 40o
The aim of this paper is to explore a new process a parameter study transesterification
using ultrasonic technique from waste cooking oil to biodiesel and to compare with
mechanical stirring method.
C and 1.5% KOH as a catalyst. Other studies on
the transesterification biodiesel has explored to using ultrasonic clamp on reactor with tube
diameter 60 mm was investigated and the process can reduce processing time by almost 80 %
than that of mechanical stirring [13]. D. Sebayang et al reported the process esterification
jatropha oil using clamp on reactor can reduced FFA (free fatty acid) until 3% [14]. The
ASTM D6751-03 for biodiesel fuel requires that the amounts of impurities such as TG, DG
and MG be lower than 0.2, 0.2 and 0.8 %wt, respectively [15]. However, transesterification
of waste cooking oil to biodiesel using ultrasonic clamp on tubular reactor without parameter
temperature has not reported yet. Therefore, this tool is one technique to produce biodiesel
with efficiently and economically.

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MATERIALS AND METHODS
Materials. Waste cooking oil collected from chip cracker potatoes factory in Malaysia and
having the acid value 1.56 mgKOH/mg oil. The chemical reagent used methanol pure
analytic grade (p.a), sodium hydroxide (p.a), potassium hydroxide (p.a), phenolphthalein
indicator (p.a), ethanol (p.a) were purchased from HmbG Chemical Company. Analytical
standards of glycerol, 1-monooleoylglycerol (monoolein), 1,3-dioleoylglycerol (diolein),
1,2,3-trioleoylglycerol (triolein), 1,2,4-Butanetriol (internal standard No.1), 1,2,3-
Tricaproylglycerol (tricaprin) (internal standard No.2) and N-methyl-N-
trimethysilyltrifluoroacetamide (MSTFA) were obtained from Sigma Aldrich.
Apparatus. The schematic representation of the experimental setup based on ultrasonic
technique shown in Fig. 1. The main equipment used ultrasonic type of clamp on tubular
reactor with specification tube tank diameter 21 mm and 60 mm length. Ultrasonic systems
based on unique MMM (Multi-frequency, Multimode, Modulated) technology. The ultrasonic
was used modular ultrasonic generators MSG.1200.IX utilize the MMM Technology. The
specification of generator was 250 mm x 150 mm x 450 mm of dimensions (h x w x d), 17.5
kHz – 28.5 kHz of carrier frequency range (Non-modulated), 1300 W of Max. Input Power,
and 10 kg of weight.
Figure 1. Experimental set-up of ultrasonic clamp on tubular reactor for biodiesel
process
Procedure. WCO was screened to remove food residues and solid precipitate. Then, WCO
dried by heating to 110oC during 10 min. NaOH in the concentration of 1%wt to WCO was
pre-mixed with methanol for each experimental condition. In each experiment, 100 gram of
WCO was fed with mixture methanol-sodium hydroxide to the ultrasonic tubular reactor. The
frequency ultrasonic was used 20 kHz [13] and reaction time were conducted at 3, 5, 10, 15
minute and methanol to WCO molar ratio (12:1, 9:1, 6:1). After completion of the reaction,
the reaction mixture was transferred into a separator tunnel for phase separation. The FAME
mixture formed the upper layer and glycerol form in the lower layer. The traces of catalyst in
FAME layer were washed with warm water and the FAME dried by heating to 110o
Analysis. Attenuated Total Reflection Infrared spectroscopy (ATR-IR) is often used for rapid
analyze of quality control. ATR-IR measurements were performed in a Perkin Elmer
Spectrum 100 and used software spectrum express. The resulting vibrational spectrum
C during
30 minute
Ultrasonic
Generator
Transducers
Acoustical
wave guide
Tube Reactor

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displays the “fingerprints” of functional groups narrowly and intensely in the IR region
(4000-650 cm-1). The formation of FAME group was determined in 1300 to 1060 cm−1
Method analyzed total glycerol and free glycerol referred to EN 14105. Sample was
used after final washing and drying which the composition of TG, DG, MG and glycerol was
analyzed using a Perkin Elmer Gas Chromatography (GC) Model Clarus 500, equipped with
a DB-5 HT capillary column (0.53 mm x 5 m) J&W Scientific. The following condition of
GC are : the column temperature was started at 50°C held for 1 min, programmed 1 with flow
rate at 15°C/min up to 180°C, programmed 2 with flow rate at 7°C/min up to 230°C,
programmed 3 used flow rate at 10°C/min up to 370 °C, final temperature held for 5 min,
detector temperature at 380°C, carrier gas pressure (hydrogen) at 80 kPa, volume injected of
1 ml [17].The conversion of FFA in the WCO into FAME was calculated from the mean of
acid value (Av) of the oil layer by the following equation [18].
spectral region [16].
(1)
where Oil and WCO refers to FAME layer and waste cooking oil, respectively.
RESULTS AND DISCUSSION
ATR-IR analysis was conducted for the preliminary analysis to observe the formation
of functional group desired. In this case, the formation of metoxycarbonyl group substituting
carbonyl group in the oil. At the Fig 2 is the chromatogram of the starting material, namely
CWCO, and the product of FAME was formed, they are WCO1, WCO2, WCO3, WCO4,
respectively. From the result, it is observed in the starting material that there was absorption
at 1099.4 cm-1 peak showing the occurrence of C–CH2–O group in the CWCO spectra.
Meanwhile at the FAME product in WCO1, WCO2, WCO3, WCO4, this absorption was
decreased and showed a new absorption at 1437.3 cm-1 and 1197.3 cm-1 peak, indicating a –
CH3 and O-CH3 group has been formed. The most of important characteristic peak is that of
the O–CH3 (1197.3 cm–1
) initial methyl group that is added. That shows the
transesterification of waste cooking oil has occurred preparing a methyl molecule as the
product. Methyl functional group can also be an indicator of the reaction. This reports that
transesterification process has been successful and FAME was produced.
Figure 2. ATR-IR analysis of CWCO (crude waste cooking oil), WCO1 (1:9, 10 minute),
WCO2 (1:6, 5 minute), WCO3 (9:1, 5 minute) and WCO4 (12:1, 5 minute)
Comparison of ultrasonic technique between mechanical stirring on WCO conversion.
Mechanical stirring transesterification was conducted involving a batch reaction for 120

International Conference on Environment 2010 (ICENV 2010)
minute, 1%wt catalyst, molar ratio methanol to TG (9:1), 70o
Ultrasonic experiments were performed using the same amounts of reactants, catalyst
and molar ratio methanol to TG used in the mechanical stirring transesterification. The high
conversion obtained under ultrasonic conditions could be due to the high speed mixing and
mass transfer between the methanol and TG, as well as the formation of a microemulsion
resulting from the ultrasonic cavitation phenomenon [5] and obtained results shown in Fig 5.
It was observed that ultrasonic results in 94.6214% at 5 min whereas the mechanical stirring
results in much lower extend of conversion 89.3176% at 120 minutes. The indication results
that the reactions under ultrasonic tubular reactor are much faster than those under the
mechanical stirring process.
C temperature reaction followed
by washing and drying. The conversions of FAME were analyzed with acid value (as
palmitic acid) according to AOCS Official Method Ca 5a-40 [19] and calculate the results
used equation 1. The results of the analysis are given in Fig 3
Figure 3. Comparison of conversion between mechanical stirring and ultrasonic
technique.
Effect of reaction time on WCO conversion using ultrasonic technique
Fig 4 reported that relationship between conversions of WCO to FAME products with
reaction time. It can be observed that as reaction time increases, the concentration of TG
decreased from the starting point. At reaction time 3 minute, concentration of TG was found
0% and stable at 10 to 15 minute. This indicated that transesterification has occurred, which
WCO was transformed to FAME. FAME produced drastically during the first 3 minute
conversion about 64.1071%. For the following 5- 15 minute, conversion of FAME increased
and constant at the final time. The phenomena reaction under ultrasonic can be explained as
follows; formation of cavitation bubbles could be stimulated by ultrasonic with sufficient
energy. The symmetric collapse of the cavitation bubbles disrupts the phase boundary to
create micro jets. As a result, oil and methanol form microscale fine emulsions, and they
easily suspend each other [20]. At this point it was observed that FAME product was
successfully produced and equilibrium can be reached in the short reaction. The time reaction
of 5 minute, with molar ratio methanol to TG is 6:1, frequency ultrasonic of 20 kHz and
catalyst NaOH of 1%wt was obtained high conversion of 95.6929%wt.

International Conference on Environment 2010 (ICENV 2010)
Figure 4. Reaction profile between reaction time (min) and conversion (%) at molar
ratio methanol to TG (9:1), NaOH 1%wt and frequency ultrasonic 20 kHz.
Effect of molar ratio on WCO conversion using ultrasonic technique
Molar ratio methanol to TG is one parameter important in determining of FAME.
Experiment were conducted with molar ratio of methanol to TG ranging from 6:1, 9:1, 12:1
or 1.356, 2.034, 2.712 at mole ratio. The transesterification reaction stoichiometry requires
three moles of alcohol per mole of triglyceride to yield three moles of FAME and one mole
of glycerin (Fig 1). At Fig 5, it was observed that with an increase in the molar ratio from
1.356 to 2.712, the conversion of WCO to FAME decreased slightly from 95.6929%wt to
71.8487%wt. The conversion of WCO increased rapidly at 1.356 moles at 5 minute. Its mean
ultrasonic tubular reactor of a liquid with two phases is very effective to produce emulsion
with small droplet size. Smaller emulsion droplets will result in increased contact surface area
between the immiscible phases, resulting in higher rate of transesterification reaction [21]. In
contrast, the droplet size of the emulsion is larger when there is a large amount of methanol,
and this result in a slower reaction at the initial stage [20].
Figure 5. Effect of mole ratio of methanol to TG on the conversion of WCO to FAME at
amount of catalyst 1 %wt, ultrasonic frequency of 20 kHz and time reaction of 5
minute.

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Effect of molar ratio on TG, DG, MG using ultrasonic technique
The step reaction transesterification mechanism which DG is the first intermediate
and expected their accumulation in some extend. At the Fig 6 showed that the amount of DG
was low in WCO4 and increased as the WCO3, WCO2, mechanical stirring, respectively.
These mean that under ultrasonic the reaction of DG with amount of methanol is fast enough
to not lead to accumulation or almost completely converted to FAME. Compare with
mechanical stirring of transeseterification, which amount of DG is high because the reaction
was slowly.
During transesterification the amount of MG was larger than of the DG. Sample
WCO4 with molar ratio methanol to TG (12:1) was lower than WCO3, WCO2 and
mechanical stirring. The tendency of molar ratio methanol to TG against DG and MG were
decreased with increased molar ratio methanol to TG. Transesterification reaction with
vigorously agitated by the ultrasonic jet obtained the movement of reactant droplets in the
emulsion [20]. Its mean, DG on the surface of the droplets promptly reacts with methanol to
release MG and FAME, and then MG must be immediately consumed by methanol to form
GL. Compared with mechanical stirring, the concentration of DG and MG mechanical
stirring process showed higher over than ultrasonic process.
Figure 6. Correlation between Concentrations (%wt) TG, MG, DG, Total and Free
Glycerol with Molar Ratio Methanol to TG at frequency ultrasonic 20 kHz, reaction
time 5 minute.
CONCLUSIONS
The process ultrasonic technique obtained conversion WCO to TG about 95.6929%wt
with the methanol to oil molar ratio of 6:1, 1%wt sodium hydroxide as catalyst and 5 minute
reaction time. As results ultrasonic technique a fast time reaction and smaller amount of
methanol obtained a high conversion of methyl ester. Ultrasonic is valuable tool for the
transesterification of waste cooking oil to biodiesel compared to the mechanical stirring
process.
ACKNOLEDGMENTS
The authors would like to thank the Ministry of Higher Education Malaysia and
Universiti Tun Hussein Onn Malaysia (UTHM) through the funding support of Postgraduates
Incentive Research Grant vot 0676 and Centre for Graduate Studies – UTHM.

International Conference on Environment 2010 (ICENV 2010)
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International Conference on Environment 2010 (ICENV 2010)
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