Esterification of High FFA Beef Tallow with Microwave Heating
Pongsakorn Suwannapa* and Nakorn Tippayawong
Department of Mechanical Engineering, Faculty of Engineering, Chiang Mai University,
Chiang Mai, Thailand, *Email: p.suwannapa@gmail.com
Abstract
Increasing petroleum price makes biodiesel very attractive. Biodiesel can be produced from animal fats. In this study, laboratory scale
biodiesel production from high FFA beef tallow was carried out via esterification process with microwave oven as a heat source. The
following parameters were investigated: oil to methanol molar ratio (1:3, 1:6, 1:9, 1:12, 1:15), percentage of catalyst used (0.5%, 1%, 1.5%,
2%, 2.5%), and reaction time (10, 20, 30, 40, 50 min). Esterification was found to convert high FFA oil into biodiesel. Maximum yield of
esterified oil were found to be in range of 98%
Keywords: Biodiesel, Beef tallow, Esterification, Microwave heating
I.
INTRODUCTION
Continually increasing diesel oil demand and prices in
Thailand made biodiesel a noticeable solution to solve the
problem [1]. The search for alternatives to diesel fuels is very
important. Triglycerides from vegetable oils and animal fats
are one of the most promising resources. There have been
continuing efforts in research to utilize these biological oils
to power agricultural and automotive engines within
Thailand for the past few decades [2, 3]. It is well known that
there are differences in characteristics of these oils and diesel
fuels, such as heating value, viscosity and chemical
composition. Generally, in short term uses, these oils
performed well. Problems arise only after the engine has
been in operation for long time [4, 5].
Biodiesel is an alternative fuel for compression ignition
engines. It is synthesized from fatty acids, vegetable oils or
animal fats. Biodiesel or fatty acid alkyl ester can be
produced through transesterification of triglycerides or
esterification of free fatty acid (FFA) with alcohol in the
present of a catalyst. Fig 1. shows the esterification reaction.
One mole of FFA and 1 mole of alcohol are esterified to 1
mole of alkyl ester and 1 mole of water. Esterified oils in
form of methyl ester or ethyl ester (known as biodiesel) have
been the predominant triglycerides derived fuels used [6, 7].
Numerous studies on biodiesel production have been
conducted in the past. Most commonly used technology is
based on the use of batch processes with heating from
conventional source like fossil fuel burning. Conventional
heating generally requires high temperatures, long reaction
time, thus high energy consumption. Microwave irradiation
offers an alternative means of heating. Several works on
microwave heated biodiesel production methods have been
reported [8-12]. It was shown that microwave irradiation
accelerated the chemical reaction and high product yields
were achieved within a short time. It was reported that the
reaction was completed in a few minutes
In this study, our research effort was directed to alternative
heat source to convert high FFA beef tallow into biodiesel in
esterification process with lower energy consumption. With
microwave irradiation, it was possible to perform reactions
quickly, efficiently and safely. This work involved design
and modification of a commercially available, domestic
microwave oven to provide heat for the process.
H2SO4
CH2COOH + CH3OH
CH2COOCH3 + H2O
Fig. 1. Esterification reaction
II.
EXPERIMENTAL
A. Materials
In this study, beef tallow (Fig.2) from local slaughterhouse
in Chiang Mai was used as raw starting material. Its
composition is shown in Table I. Laboratory grade methanol
(100%) and sulfuric acid (95% purity) were used without any
purification. They were obtained from a local chemicals
supplier. Before esterification process, neutralized reaction
was proceeded for FFA determination. Beef tallow 100g was
heated to 80oC in a beaker. About 10 drop of phenolphthalein
was put in and stirred for 30 seconds. Sodium hydroxide
solution 0.5 mol/liter was gradually added while stirring until
substance had pH between 8-9. Beef tallow was then washed
with 80oC water for about 3-4 times, then heated to remove
water vapour bubbles. The missing weight from starting
showed the amount of FFA. The result is shown in Table II.
Fig. 2. Beef tallow
Table I
COMPOSITION OF THE FATTY ACID IN BEEF TALLOW AND MOLECULAR WEIGHT [13].
Designation
Acid name
% composition
C14:0
Miristic
2.72
C15:0
Pentadecadonic
0.86
C16:1
Palmitoleic
2.02
C16:0
Palmitic
25.33
C17:0
Heptadecano
1.67
C18:2
Linoleic
0.75
C18:1(cis)
Oleic
29.87
C18:1(trans)
Eladic
1.82
C18:0
Stearic
34.70
C20:0
Arachidic
0.28
mw. of acid in beef tallow
= 273.5 g/mol
mw. of beef tallow
= 858.5 g/mol
mw. of biodiesel
= 287.6 g/mol
mw. of glycerol
= 92.0 g/mol
Table II
FFA AMOUNT OF BEEF TALLOW
No.
1
2
3
Average FFA
%FFA
6.28
6.18
6.8
6.42
B.
Experimental Apparatus
A LG model MS2448ARKB commercially available,
domestic microwave oven was used. It consists of a
continuous focused microwave power delivery system with
an operator selectable power output from 0 to 850 W. A
Digicon model MD400N digital temperature controller was
connected to a 3 mm diameter type K thermocouple inserted
directly into the reaction mixture inside the oven. A stirrer
driven by a low speed motor was also installed from the top
cover of the microwave oven.
Fig 3. shows the experimental setup. Prior to the
experimental runs, the modified microwave oven was tested
and checked that no irradiation leakage occurred.
C.
Experimental Procedure
For commercial microwave ovens, power output is often
less than their indicated power. Actual microwave power
output may be measured. The power output is measured by
heating 250 ml of water in the center of the microwave oven
for 1 min. After running for all power outputs, the difference
between the initial and final temperature was recorded. The
microwave power output and its energy transfer efficiency
may be calculated from (1) & (2).
(1)
(2)
where Pa is the actual microwave power irradiated to the
water, Pi is indicated microwave power (W), mw and cw are
mass and specific heat capacity of the water, ∆T is difference
between the initial and final temperatures of water (oC) and t
is the heating time (s).
Esterification reactions were performed under atmospheric
condition in a 500 ml beaker. A 100g sample of beef tallow
was weighed, melted and poured into the beaker. Solution of
0.5, 1.0, 1.5, 2.0, 2.5g sulfuric acid was first dissolved in
11.2ml, 22.4ml, 33.6ml, 44.8ml, 56ml methanol. This
solution was then mixed with the beef tallow oil, and placed
inside the microwave oven. Shortly afterwards, the oven and
the stirrer were switched on, and the animal oil mixture was
heated up to 40 to 60oC for 10, 20, 30, 40, 50 min.
Temperature profiles were monitored regularly. The heating
and stirring were immediately stopped and the beaker
removed from the microwave oven and allowed to
separation. The yield of esterified oil (y) was calculated from
(3).
(3)
III.
RESULTS AND DISCUSSION
A.
Temperature Evolution
A temperature measurement was possible using a
thermocouple inserted directly into the reaction mixture. The
microwave irradiation was able to attain the set point
temperature at 60oC rapidly, maintaining at the controlled
temperature with very small oscillation.
Fig. 3. Experimental setup of the microwave heated batch reactor
B.
Microwave Power Output
The microwave power output was calculated by measuring
the temperature rise of water. The results are shown in Table
III. Average microwave power output from these
measurements was about 66% of the microwave power input.
Table III
MICROWAVE ENERGY TRANSFER
Microwave power
Input (W)
Starting
temp (oC)
Final
temp (oC)
Heat to
water (W)
ηT (%)
170
340
510
680
850
29
29
29
29
29
35
42
48
56
62
105
227
340
454
576
62
67
67
67
68
C. Esterified Oil
After esterification process, the two conditions that
showed highest yield of esterified oil were highlighted. Fist
condition was 1:9 oil to methanol molar ratio, 1.5% catalyst,
30 min for reaction time. The yield of esterified oil of first
condition was 98.2%. Second condition was 1:15 oil to
methanol molar ratio, 1.5% catalyst, 30 minutes for reaction
time. The yield of esterified oil of second condition was
98.6%.
The composition of fatty acid methyl ester in esterified oil
was analysed by gas chromatography. It was accomplished at
the Science and Technology Service Center, Chiang Mai
University with GC 7890A Agilent Technology.
Fig 4. and Fig 5. show the GC-MS trace of the methyl
ester from this experiment. The composition of fatty acid
methyl ester is summarized in Table IV.
Fig. 4. Chromatograms of #1 sample esterified oil
Fig. 5. Chromatograms of #2 sample esterified oil
Table IV
COMPOSITION OF THE FATTY ACID IN ESTERIFIED OIL
Fatty acid
Myristic
Palmitic
Palmitoleic
Stearic
Heptadecanoic
Oleic
Methyl 9-methyltetradecanoate
Methyl 12-methyltetradecanoate
Methyl n-pentadecanoate
Methyl 14-methylpentadecanoate
Methyl 14-methylhexadecanoate
IV.
Fatty acid composition
Sample #1
Sample #2
2.8
2.7
30.8
30.7
1.7
1.3
30.3
33.3
1.9
1.5
28.0
30.1
0.3
0.3
0.4
0.4
0.6
0.7
0.4
0.4
0.7
0.7
CONCLUSION
A domestic microwave oven was modified to use as a heat
source for esterification of high FFA beef tallow in a batch
system. Microwave heating was found to give fast heating
for the conversion of the animal fat to biodiesel. Although
esterification of animals fats with methanol by acid catalyst
can change into methyl ester, the biodiesel production still
can be improved further by subsequent transesterification.
Un-coverted FFA and triglycerides will be converted more
into ester product.
ACKNOWLEDGEMENTS
Support from Chiang Mai University is appreciated.
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