International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 12, December 2013
ISSN 2319 - 4847
ESTERIFICATION OF HIGH FREE FATTY
ACID CRUDE PALM KERNEL OIL AS
FEEDSTOCK FOR BASE-CATALYZED
TRANSESTERIFICATION REACTION
Viele, E. L*, Chukwuma, F.O. and Uyigue, L.
Dept. of Chemical Engineering
University of Port Harcourt, Choba, Port Harcourt, Nigeria.
*Corresponding Author
ABSTRACT
This paper is focusing on the need to use high free fatty acid (FFA) vegetable fats and oils in base-catalyzed transesterification
reaction for the production of bio-diesel instead of the favored high-cost refined vegetable oils. In this work, gas chromatographic
and titrimetric analyses were carried out to determine the average molecular weight of the fatty acids in the crude palm kernel oil
(PKO) and the volume of base used to neutralize the FFA in the oil respectively. These parameters were used to calculate the
percentage FFA content of the crude and esterified PKO. Esterification reaction was then carried out between the FFA and
ethanol (99.5%v/v) in the presence of concentrated H 2SO4 as catalyst at 75oC within one hour reaction time. In a two-step
esterification, the FFA content of the crude PKO was reduced from 7.2297% to 0.4806%, thereby meeting the required 1%
maximum FFA content for vegetable fats and oils to be used in a base-catalyzed transesterification reaction. Thus, acid
esterification is recommended as a method for treating oils with high FFA content, prior to base-catalyzed transesterification for
the production of bio-diesel.
Keywords: Palm kernel oil, free fatty acids, estrification, transesterification
1. INTRODUCTION
Bio-diesel have been recognized world-wide as a renewable fuel which can be used as an alternative to petroleum-based
diesel fuel due to its advantages. Bio-diesel is biodegradable, renewable, nontoxic, and have excellent lubricity [1]. Biodiesel is very similar to the petroleum diesel fuel in terms of physical properties and functionality and therefore can be
used as 100% replacement or used at any concentration with petroleum diesel in existing diesel compression-ignition
engines with little or no engine modifications [2]. Moreover, the use of pure bio-diesel in the transport sector lowers the
soot emissions by 60%, carbon monoxide and hydrocarbons by 50% and carbon dioxide by 80%, respectively [3].
Bio-diesel is defined as mono-alkyl esters of long chain fatty acids derived from plant and animal oils and fats that fulfill
most of the requirements of petroleum diesel. It is produced in a transesterification process by reacting vegetable oils or
animal fats with excess short-chain alcohol (methanol or ethanol) in the presence of a catalyst [4], [5]. The catalyst can
either be an acid, a base or an enzyme to improve the reaction rate and yield. The use of enzyme catalyst in
transesterification reaction makes the process too expensive while acid catalyzed transesterirification is a very slow
process requiring a duration of 6 hours and above for completion of reaction. The base-catalyzed transesterification
process stands out to be the most preferred method because the reaction rate is faster, the process is economical and can
be carried out at moderate temperatures resulting to a conversion of 98% to bio-diesel with no intermediate compounds
[6]. However, this transesterification method is sensitive to both moisture and FFA contents of the feedstock oil. The
standard bio-diesel production suffers from the presence of moisture and free fatty acids in the feedstock [7]. On one
hand, the presence of water above a limit of 0.5% favors the formation of FFA during the hydrolysis of triglycerides to
diglycerides [8] as shown in eq. 1
CH2-COO-R1
│
CH-COOR2
│
CH2-COOR3
Triglyceride
+
H2O
Water
→
CH2-OH
│
CH-COOR2
│
CH2-COOR3
Diglyceride
+
O
│
HO-C-R1
(1)
Free Fatty Acid
On the other hand, the presence of FFA above a threshold value of 1.0% [9] favors saponification reaction against the
preferred transesterification reaction thereby leading to the formation of soap, reduction in the bio-diesel yield, catalyst
Volume 2, Issue 12, December 2013
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 12, December 2013
ISSN 2319 - 4847
inefficiency, increase in viscosity and making the separation of glycerol difficult [10]. Free fatty acids consist of the long
carbon chains that are disconnected from the glycerol backbone due to moisture. If an oil or fat containing a free fatty
acid of more than 1.0% (unrefined vegetable oils and animal fats or waste vegetable oils) such as oleic acid is used to
produce bio-diesel through a based-catalyzed transesterification process, the alkali catalyst will react with the free fatty
acid to form soap as shown in eq. 2.
O
║
HO-C-(CH2)7 CH=CH(CH2)7 CH3
Oleic Acid
+
KOH →
Potassium
Hydroxide
O
║
K+ˉO-C-(CH2)7CH=CH(CH2)7CH3
Potassium
Oleate (soap)
+
H2 O
Water
(2)
This reaction is undesirable because it binds the catalyst into a form that does not contribute to accelerating the reaction.
Excessive soap in the products can inhibit later processing of the bio-diesel, including water washing. Moreover, this
technique converts the free fatty acids into soap when they could be converted to bio-diesel, thus resulting in low yield of
the bio-diesel product [11].
Therefore, the development of low-cost bio-diesel production processes requires the use of feedstock with low FFA (< 1%)
which will be very efficient in promoting the base-catalyzed transesterification. Thus, highly refined oil containing very
low FFA (<0.2%) and about 0.05% moisture is the most preferred raw material [12]. However, the use of this type of oil
in transesterification makes the process very expensive due to extra cost of refining. Crude vegetable oils or waste cooking
oils are therefore recommended. The approach is to convert the FFA to its ester by acid esterification process and
ensuring that the FFA content of the esterified oil is less than 1.0%, followed by transesterification with a base catalyst.
Esterification is the central reaction to reduce the levels of FFA in the low-cost feedstocks to an acceptable range.
Esterification is a reversible reaction between carboxylic acids and an alcohol in the presence of a strong catalyst,
resulting in the formation of water and at least one ester product [13]. The process is described in eq. 3
O
║
R- C-OH + R-OH
Free Fatty Alcohol
Acid
catalyst
↔
O
║
R-C-OR + H2O
Ester
Water
(3)
In this work, the free fatty acids (FFAs) in crude palm kernel oil (PKO) was determined and converted to its ester by
repeated direct esterification reactions with ethanol (99.5%v/v) using concentrated sulphuric acid as the catalyst. The
objective is to reduce the FFA content of the PKO to the desired level (< 1.0%) suitable for use as feedstock in basecatalyzed transesterification reaction for the production of bio-diesel.
2. Experimental Procedure
2.1 Materials
The main material used for this study is crude palm kernel oil (PKO) obtained from Rivers Vegetable Oil Company
limited, Rivers State, Nigeria. Other materials and equipment used in this work will be mentioned at the appropriate
section.
2.2 Methods
The methods adopted for this work includes gas chromatographic analysis, titrimetric analysis and esterification.
2.2.1 Gas chromatographic analysis of the crude PKO
The chemical composition of the fatty acids in the crude PKO was determined using a gas chromatograph equipped with
flame ionization detector (GC-FID). The GC-FID (version 6.2 and varian-CP 3800) was initially calibrated with fatty acid
standards before the PKO sample was injected. The injection technique was the micro-syringe type with an injection
volume of 5.0 µL. The operating temperatures of injection and that of the FID were respectively 250 and 300 o C. Other
conditions of the measurement include an oven temperature of 70 oC (at 1min hold) with a programming rate of 1oC/min.
and 250 oC (at 40 mins. hold). The carrier gas was nitrogen at flow rate of 1.4 ml/min. Actual concentrations of the fatty
acids in the crude PKO sample was detected as the displayed peaks of the chromatogram. The molecular weight of the
FFA was calculated from the result of the composition from the chromatogram.
2.2.2 Percentage free fatty acid content of the crude PKO
The percentage FFA content of the crude PKO was determined using the standard analytical methods for fats and oils by
the American Oil Chemists Society [14].
10g of the crude PKO was measured into a 250 ml conical flask and 20g of absolute ethanol (99.5%v/v) was also
measured and added. The mixture was slightly heated to dissolve the oil. Three drops of phenolphthalein indicator was
added and titration was done with 0.1M NaOH. The percentage FFA value was calculated from the equation 4.
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Volume 2, Issue 12, December 2013
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A
V  M W
 100
(4)
m
Where, A is the %FFA
V is the volume of NaOH used, (ml)
M is the molarity of the NaOH used, (mol/1000ml)
W is the average molecular weight of the fatty acid component in the PKO, g/mol
m is the mass of the PKO sample, g.
2.2.3 Esterification (acid pretreatment) of the PKO
The pretreatment of the crude PKO (esterification) was carried out by applying the procedure described by [11]. 100g of
PKO (containing 7.2297g of FFA) was measured into a conical flask and heated to 75o C. 22.77g of ethanol (99.5%v/v)
was measured into another conical flask and 0.51g of concentrated H2SO4 was added and agitated for proper mixing. The
ethanol-acid mixture was slowly added to the oil and stirred at the same temperature for one hour. The resultant mixture
was allowed to settle for another one hour. The top layer was removed while the bottom layer was heated to 110oC and
maintained for 30 minutes to evaporate the water before it was allowed to cool to room temperature. The percentage FFA
content of the esterified oil was measured using the same titration method above.
The above esterification reaction procedure was repeated on the esterified oil to further convert the remaining FFA to its
ester. The percentage FFA content was also measured. The entire procedure was repeated until the percentage FFA
content of the oil was measured to be less than 1.0%.
3. RESULTS AND DISCUSSION
3.1 Gas chromatographic analysis
The result obtained from the gas chromatographic analysis (figure 1) showed the fatty acid peak values present in the
crude PKO. The values are representative amount (concentration) of the fatty acid compounds present in the crude PKO.
This result was used to calculate the average molecular weight of the free fatty acid in the crude PKO. Table 1 showed the
percentage composition of the fatty acid in the crude PKO. The average molecular weight of the free fatty acids was
calculated to be 208.9507.
Figure 1: Gas Chromatogram (GC-FID) for composition
of fatty acids in the crude PKO
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Components
Table 1: Composition of the fatty acids in PKO
Composition
Composition (%)
Molecular
weight*
Percentage
weight
Caproic acid, C6:0
1.1137
1.2835
116.2
1.4914
Caprylic acid, C8:0
3.5487
4.0898
144.2
5.8975
Capric acid, C10:0
4.1675
4.8030
172.3
8.2756
Lauric acid, C12:0
42.4581
49.5279
200.3
99.2044
Myristic acid, C14:0
14.8625
17.1289
228.4
39.1224
Palmitic acid, C16:0
10.4482
12.0415
256.4
30.8744
Stearic acid, C18:0
6.5025
7.4941
184.5
13.8266
Oleic acid, C18:1
3.1508
3.6313
282.5
10.2584
86.2520
100
Total
*values obtained [15]
by
208.9507
3.2 Percentage of free fatty acid content
The result of the titration (endpoint) to determine the volume of base used to neutralize the acid content of the crude and
esterified PKO for the calculation of the percentage FFA content is shown in table 2. The average volume of base used to
neutralize the FFA in the crude PKO is 34.6ml. This value resulted in a calculated FFA content of 7.2297% in the crude
PKO. After the first esterification step, the volume of base used is 11.63ml with a calculated FFA content of 2.4308%.
This value is greater than the acceptable value of 1.0%. A second esterification was carried out and the volume of base
used to neutralize the acid content became 2.3ml and a calculated FFA of 0.4806%.
Table 2: Endpoint volume and FFA content
Endpoint
1 Endpoint
2 Endpoint
3
(ml)
(ml)
(ml)
Average
endpoint (ml)
FFA (%)
Crude PKO
34.8
34.6
34.4
34.6
7.2297
1st step esterification
11.8
11.6
11.5
11.6333
2.4308
2nd step esterification
2.4
2.3
2.2
2.3
0.4806
The titration experiment is a neutralization reaction between the FFA in the PKO and the base (NaOH). The volume of
base required to neutralize the acid in the PKO is an indication of the amount of FFA in the oil. From the experiment, it
was observed that at a constant weight of 10g of PKO for each step of esterification, there was continuous reduction in
volume of the NaOH used, indicating that the amount of FFA in each of the PKO samples was continuously reduced. That
is, the FFA had been converted to its ester.
Furthermore, since esterification is the reaction of a carboxylic acid and an alcohol to produce an ester and water in the
presence of a catalyst such as concentrated sulphuric acid [13], the drop in the FFA level of the PKO is an indication that
the FFA was consumed in the esterification reaction between the free fatty acids in the oil and the acidified ethanol. The
formation of two distinct layers as observed in the experimentation indicated that water was formed as a by-product of the
process which also indicated that an ester was produced based on equation 3. In this work, a two-step esterification
reaction was used to reduce the FFA content of the crude PKO from 7.2297% to 0.4806%. This value is in agreement
with the report of [9] where in the maximum acceptable FFA level for base-catalyzed transesterification reaction is 1.0
wt.%. Also, the two-step esterification achieved in this work corroborates the works of [16] and [17], wherein, a two-step
esterification was used to reduce the FFA content of waste oil to 1wt% within one hour. The final PKO of 0.4806% FFA
(< 1%) stands out to be a suitable feedstock for base-catalyzed transesterification reaction.
4. CONCLUSION
Based on the results obtained from the gas chromatographic and titrimetric analyses, and the subsequent percentage FFA
values, it can be confirmed that esterification is a suitable pretreatment method capable of reducing the FFA content of
vegetable fats and oils to an acceptable value. The FFA values obtained were also observed to improve considerably after
Volume 2, Issue 12, December 2013
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 2, Issue 12, December 2013
ISSN 2319 - 4847
each step of pretreatment in relation to the original FFA value of the crude PKO. The final PKO with FFA value of
0.4806% obtained at the end of the second step of the two-step esterification process is within the acceptable limit (<
1.0%) and therefore is recommended as a suitable feedstock for base-catalyzed transesterification reaction for the
production of bio-diesel. Thus, esterification is recommended as a pretreatment method for treating high FFA vegetable
fats and oils for the production of bio-diesel.
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