108 CHAPTER 5 TWO-STEP ACID ALKALI CATALYZED TRANSESTERIFICATION OF C. pentandra SEED OIL FOR BIODIESEL PRODUCTION 5.1 INTRODUCTION Environmental concerns of fossil fuel depletion and fluctuating oil price has intensified the search for alternate fuel from renewable resources. Vegetable oil and animal fats are found to be the best alternate energy source that can be used directly in the existing engine. Their direct use is limited due to two main reasons, that is high viscosity and low volatility (Knothe and Steidley 2005). Transesterification technique has been widely used to reduce the viscosity of oils and fats. Transesterification is nothing but displacement of alcohol from an ester by another alcohol (Srivastava and Prasad 2000). The advantages of biodiesel as diesel fuel is its portability, ready availability, renewability, higher combustion efficiency, lower sulfur and aromatic content, higher cetane number and higher biodegradability (Demirbas 2009a). The use of edible vegetable oils and animal fats for biodiesel production has received great concern because they compete with food materials (Kalam et al 2008). The demand for vegetable oils for food has increased tremendously in recent years. It is impossible to justify the use of these oils for fuel purposes such as biodiesel production. Moreover, these oils could be more expensive to use as fuel (Demirbas 2009b). The uses of non-edible plant oil sources are keeping competition with food edible oil for biodiesel feed stock. Hence, the contribution of non-edible oil from C. pentandra will be significant source for biodiesel production.
21
Embed
CHAPTER 5 TWO-STEP ACID ALKALI CATALYZED ...shodhganga.inflibnet.ac.in/bitstream/10603/24546/10/10_chapter5.pdf · The use of edible vegetable oils and animal fats for biodiesel production
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
108
CHAPTER 5
TWO-STEP ACID ALKALI CATALYZED TRANSESTERIFICATION OF
C. pentandra SEED OIL FOR BIODIESEL PRODUCTION
5.1 INTRODUCTION
Environmental concerns of fossil fuel depletion and fluctuating oil price has
intensified the search for alternate fuel from renewable resources. Vegetable oil and
animal fats are found to be the best alternate energy source that can be used directly
in the existing engine. Their direct use is limited due to two main reasons, that is
high viscosity and low volatility (Knothe and Steidley 2005). Transesterification
technique has been widely used to reduce the viscosity of oils and fats.
Transesterification is nothing but displacement of alcohol from an ester by another
alcohol (Srivastava and Prasad 2000). The advantages of biodiesel as diesel fuel is
its portability, ready availability, renewability, higher combustion efficiency, lower
sulfur and aromatic content, higher cetane number and higher biodegradability
(Demirbas 2009a).
The use of edible vegetable oils and animal fats for biodiesel production has
received great concern because they compete with food materials (Kalam et al
2008). The demand for vegetable oils for food has increased tremendously in recent
years. It is impossible to justify the use of these oils for fuel purposes such as
biodiesel production. Moreover, these oils could be more expensive to use as fuel
(Demirbas 2009b). The uses of non-edible plant oil sources are keeping competition
with food edible oil for biodiesel feed stock. Hence, the contribution of non-edible
oil from C. pentandra will be significant source for biodiesel production.
109
5.1.1 Description of the Plant
C. pentandra is a tall, deciduous tree bearing short, sharp prickles all along
the trunk, branches and supported by pronounced buttresses at the base. It has a
light crown and is leafless for a long period. Leaves are alternate with slender green
petioles. There are usually 5 leaflets in a mature form. Great quantities of flowers
are in lateral clusters near the ends of the twigs. Fruit is leathery, ellipsoid,
pendulous capsule, 10-30 cm long and usually tapering at both ends. White, pale
yellow or grey floss originates from the inside wall of the fruit. Seed capsules split
open along 5 lines. Each capsule releases 120-175 seeds rounded black seeds
embedded in a mass of grey woolly hairs. Seeds are in dark brown color. The
generic name comes from a local South American word. The specific name,
‘pentandra’, is Latin for ‘five-stemmed’ from the Greek word ‘penta’ (five) and
‘andron’ (male).
5.1.2 Economic Benefits
The pressed cake is cattle feed containing about 26% protein. Sheep, goats
and cattle relish the foliage. The fiber from the inner wall of the fruit is unique in
that it combines springiness and resilience to make it ideal for stuffing pillows,
mattresses and cushions, life jackets and lifeboats. It is an excellent material for
insulating iceboxes, refrigerators, cold-storage plants, offices, theatres and
aeroplanes.
C. pentandra seed contains 20 to 25% non-drying oil, and is used as a
lubricant, in soap manufacturing and in cooking. Medicine: Compressed fresh
leaves are used against dizziness, decoction of the boiled roots is used to treat
oedema, gum is eaten to relieve stomach upset, tender shoot decoction is a
contraceptive and leaf infusion is taken orally against cough and hoarse throat.
110
5.1.3 Origin of Plant
It is believed that this tree originated in Central America. It has been
cultivated for a long time and can be found pantropically between 16 degrees north
and 16 degrees south.
It is native to India, Indonesia and United States of America. In Australia,
Cambodia, Eritrea, Ethiopia, Gambia, Ghana, Kenya, South Africa, Tanzania,
Thailand, Uganda and Zanziba are the region where it grows exotically In India, it
is found usually in southern parts of India. C. pentandra is grown around villages
and temples in Tamil Nadu, India, as an ornamental tree.
At present the C. pentandra oil has only limited application and the natural
production of seeds remain under utilized. Literature shows that no work has been
established so far on the production of biodiesel using C. pentandra oil. In this
present investigation, C. pentandra oil has been used as a potential source for
biodiesel production. The reaction conditions have been investigated to optimize the
process variables that lead to higher yield of biodiesel and to develop a simple
kinetic model for extraction process.
5.2 METHODOLOGY
Pods of C. pentandra were collected from local villages near Chennai, Tamil
Nadu, India during the month of July. Sample was identified as C. pentandra and
authenticated at Centre for Advanced Studies in Botany, University of Madras,
Chennai, Tamil Nadu, India.
5.2.1 Extraction
The C. pentandra pods were disrupted and seeds were removed manually
from the fiber. The collected seeds were dried under sun, ground to powder, passed
through 60 mesh and then the seed powder was dried at 105 C until a constant
111
weight was obtained. The C. pentandra seed powder was mixed with one forth
weight of diatomaceous earth for better solvent flow through sample. The mixture
was packed inside a thimble and extracted as prescribed in Chapter 3. The oil yields
obtained was expressed in terms of weight percentage of the samples.
5.2.2 Oil Characterization
The acid, saponification and iodine values were determined by titrimetry
(Sadasivam and Manickam 2004). Water content was determined using a KF
titrator. The unsaponifiable fractions of the extracted oils were analyed in duplicate
and the results are presented as mean values (Leon-Camacho et al 2004).
5.2.3 Biodiesel Production and Characterization
The transesterification reaction was carried out in a system as described in
Chapter 3. The effect of different parameters like catalyst concentration, methanol
to oil molar ratio, reaction temperature and reaction time were optimized. The
stirring rate of 600 rpm was kept constant throughout the process to get sufficient
mixing.
5.2.3.1 Acid catalyzed pre-esterification process
The alkali catalyzed reaction is reported to be very sensitive to the content of
FFAs, which should not exceed a certain limit to avoid deactivation of catalyst by
formation of soaps and emulsion (Van Gerpen 2005). Therefore, FFAs were first
converted to respective esters in a pretreatment process with methanol using an acid
catalyst (H2SO4). It was reviewed from the literature and found that the product
having acid value < 2 mg KOH g-1 is used for alkali catalyzed reaction (Sharma et
al 2008).
The acid catalyzed esterification is a pretreatment process employed to
decrease the acid value of the feedstock below 2 mg KOH g-1. Based on the results
112
of Chongkhong and Tongurai (2007) esterification reaction was performed by
employing methanol to oil ratio as 8:1 at 65°C with 1.834 wt% H2SO4 as a catalyst.
The FFA level of the mixture was checked at different time intervals. When the
required FFA level was reached, the mixture was cooled to room temperature and
transferred to a separating funnel without agitation, leading to separation of two
phases. Finally the acid value of the product separated at the bottom was
determined.
5.2.3.2 Alkali-catalyzed transesterification process
Alkali-catalyzed transesterification is the most effective in the
transesterification processes and is used in the commercial production of biodiesel.
Even at ambient temperature, the alkali-catalyzed reaction proceeds rapidly usually
reaching 95% conversion. It is noted that the parameters like catalyst concentration,
methanol to oil molar ratio, reaction temperature and reaction time play an
important role in production of biodiesel (Pilar et al 2004). The effect on varying
these parameters such as catalyst concentration (0.25, 0.50, 0.75, 1.0 and 1.25
wt%), methanol to oil molar ratio (3:1, 6:1, 9:1 and 12:1), reaction temperature (45,
50, 55, 60 and 65°C), reaction time (15, 30, 45 and 60 min) on the biodiesel yield
was studied.
The H1NMR spectra of bio-diesel were recorded. as per Knothe and Kenar
(2004), Gelbard et al (1995). Error bars shown in the figures represent the standard
deviations of experiments that had been done in triplicates.
To study the fuel properties, two 200 mL batches of biodiesel were produced
at optimized condition. The obtained dried methyl ester was properly stored in an
airtight brown glass container for characterization studies. Biodiesel fuel properties
were determined by ASTM test methods (ASTM 1998) and compared with ASTM
D6751 standards.
113
5.3 RESULTS AND DISCUSSION
5.3.1 Effect of Different Solvents on Extraction of Oil
The selection of the solvent system for oil extraction from C. pentandra seed
is an important factor. Solvent selection for extraction of oil at the initial step would
allow cost-effective for fuel production without further expense required for the
purification of the product. The solvent chosen should have good extraction
capacity and low viscosity to enhance the free circulation. An efficient extraction
requires the penetration of solvent into the seed and to match the polarity of the
targeted compounds. An organic solvent has a higher solubility with oil, this solvent
system was used further to degrade the cell walls of the seed and to dissolve the oil
to enhance the oil yield.
The percent oil yield values for the different solvents at 60°C are shown in
Table 5.1 for oil extraction. The solvent required for extraction was selected on the
basis of oil yield and umsaponifiable matter content. Higher amount of
unsaponifiable matter requires intensified pre-treatment for oil to be used for
biodiesel production. The oil yields peaked for THF at 27.2 wt% with 3.56 wt%.
This higher amount of unsaponifiable matter was undesirable. Methanol extract
yields was poor due high polar in nature and having high percentage of
unsaponifiable matter. Solvent hexane yields high oil (26.4 wt%) with less amount
of unsaponifiable matter (1.98 wt%). Hence, it was chosen for as a solvent for
extraction.
114
Table 5.1 Effect of different solvents on extraction of C. pentandra oil
Solvents Yield (wt%) Unsaponifiable matter wt%
Hexane 26.4 1.98
Petroleum ether 27 2.81
Tetra hydro furan 27.2 3.56
Methanol 14 5
Chloroform 20.4 2.9
5.3.2 Effect of Solvent Ratios on Oil Extraction
The effect of seed to hexane weight ratios on the oil extraction is shown in Figure
5.1. The experiments were studied under batch condition at 250 rpm, 65°C for 2 h
in a temperature controlled shaker. The influence of seed to hexane ratio from 1:4 to
1:12 on oil extraction was studied. As the seed to solvent ratio increased from 1:4 to
1:10, the oil yield was found to be increased from 11.9 wt% to 26.1 wt%. The trend
was continued with increase in seed to hexane ratio up to 1:10. Further increase
above 1:10 did not show much improvement in the oil extraction. Therefore the
ratio of 1:10 was found to be an optimum ratio for the further study.
0
5
10
15
20
25
30
1:4 1:6 1:8 1:10 1:12 Seed to Hexane weight ratio
Figure 5.1 Effect of oil yield on weight of seed to solvent different ratio
115
5.3.3 Kinetic and Thermodynamic Studies on Oil Extraction
Extraction was performed in batch mode at different time intervals 20, 40, 60
80 and 100 min. The percentage oil yields at various temperatures are given in
Table 5.2. From the analysis of the data, the oil yield was found to be increased
with increase in extraction time. The yield was also analyzed with respect to the
extraction time at constant temperature ranging from 30 to 60°C.
Table 5.2 Percent oil yield at various extraction temperature
Temperature (°C) Time (min) 30 40 50 60
20 8.92 10.62 12.43 14.6
40 9.58 11.49 13.52 15.92
60 10.29 12.46 14.72 17.39
80 11.06 13.46 15.97 18.97
100 11.89 14.6 17.4 20.7
Using the values in Table 5.2 and applying the differential method, plots of
ln Y versus ln (dY/dt) at different temperatures with optimum conditions were
established. A first-order kinetic model was fitted well with average regression
coefficient (R2) value obtained as 0.936 (Figure 5.2). The reaction rate constants
and the order of the reaction were determined using the intercept and slope of the
liner plot (Table 5.3).
116
Figure 5.2 Plot of ln (dY/dt) versus ln Y at different temperatures ranged from 30
to 60°C for extraction of oil
Table 5.3 Values of the reaction rate constants at different temperature
Temperature (°C) k min-1 R2 value
30 2.9557*10-3 0.9996
40 3.284*10-3 0.9575
50 3.7975*10-3 0.9646
60 4.0533*10-3 0.9949
117
5.3.3.1 Calculation of activation energy
The rate constant k increases with increasing temperature, and this trend is
shown in Table 4.3. The changes can be described by the Arrhenius equation
(Levenspiel 2003). A plot of ln k versus 1/T (Figure 5.3) gives a straight line whose
slope represents the activation energy of extraction ( Ea/R) and whose intercept is
the Arrhenius constant (ln A). Thus, the activation energy and the Arrhenius
constant were calculated as Ea= 9.1803 kJ mol-1 and A =0.147 s-1, respectively.