Accepted Manuscript Evaluation of direct transesterification of microalgae using microwave irradiation Chee Loong Teo, Ani Idris PII: DOI: Reference:
S0960-8524(14)01456-4 http://dx.doi.org/10.1016/j.biortech.2014.10.035 BITE 14078
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Bioresource Technology
Received Date: Revised Date: Accepted Date:
13 September 2014 7 October 2014 8 October 2014
Please cite this article as: Teo, C.L., Idris, A., Evaluation of direct transesterification of microalgae using microwave irradiation, Bioresource Technology (2014), doi: http://dx.doi.org/10.1016/j.biortech.2014.10.035
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1 1
Title
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Evaluation of direct transesterification of microalgae using microwave irradiation
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Author names and affiliations
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Chee Loong Teo1, Ani Idris1*
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1
Department of Bioprocess Engineering, Faculty of Chemical Engineering, c/o Institute of
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Bioproduct Development (IBD), Universiti Teknologi Malaysia, 81310, UTM Johor Bahru,
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Johor, Malaysia
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*Corresponding author. Address: Department of Bioprocess Engineering, Faculty of Chemical
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Engineering, c/o Institute of Bioproduct Development (IBD), Universiti Teknologi Malaysia,
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81310 UTM Johor Bahru, Johor, Malaysia. Tel.: +6 075535603, Fax: +607 5588166,
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E-mail address:
[email protected] (Ani Idris)
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Abstract
25
Nannochloropsis sp. wet biomass was directly transesterified (DT) under microwave
26
(MW) irradiation in the presence of methanol and various alkali and acid catalyst. Two different
27
types of direct transesterification (DT) were used; one step and two step transesterification. The
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biodiesel yield obtained from the MWDT was compared with that obtained using conventional
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method (lipid extraction followed by transesterification) and water bath heating DT method.
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Findings revealed that MWDT efficiencies were higher compared to water bath heating DT by at
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least 14.34% and can achieve a maximum of 43.37% with proper selection of catalysts. The use
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of combined catalyst (NaOH and H2SO4) increased the yield obtained by 2.3 folds (water bath
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heating DT) and 2.87 folds (MWDT) compared with the one step single alkaline catalyst
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respectively. The property of biodiesel produced by MWDT has high lubricating property, good
35
cetane number and short carbon chain FAME’s compared with water bath heating DT.
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Keywords: Biodiesel, direct transesterifiation, microwave irradiation, microalgae, catalyst
37 38
1. Introduction
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Biodiesel from microalgae, the oil for our future generation is recognized as an alternative
41
sustainable renewable fuel. It has all the excellent properties such as highly biodegradable,
42
minimal toxicity or non-toxic and environmental friendly. However the production of microalgae
43
biodiesel has its share of problems in terms of the high cost involved during harvesting,
44
dewatering, lipid extraction and prior to the conversion into biodiesel (Owen et al., 2010, Teo et
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al., 2014, Wahidin et al., 2014). It was reported that lipid extraction accounts for 90% of energy
46
consumed in biodiesel conversion from microalgae biomass (Lardon et al., 2009). Generally,
3 47
biodiesel production from microalgae involves a 2 step extraction–transesterification processes
48
where the microalgae was first harvested and dried, and then lipids extracted followed by the
49
transesterification process. Therefore efforts were made by several researchers to eliminate
50
separate extraction step by introducing one step transesterification, in situ transesterification or
51
direct transesterification (DT) and also a sequential 2 stage DT. This technology also eliminates
52
the dewatering process and also contributes to the reduction in the amount of extracting solvent
53
used (Wahlen et al, 2011).
54
Johnson and Wen (2009) revealed that the one step transesterification used on Schizochytrium
55
limacinum produced higher yield of biodiesel (63.47%), consumed less time than conventional
56
methods and the potential of lipid loss can be avoided during extraction process. Recently, there
57
are reported studies on the optimisation of the one step transesterification investigating the
58
influence of a variety of parameters such effect of catalyst concentration, amount of methanol,
59
reaction temperature and reaction time (Patil et al., 2011; Zhang et al., 2010; Jeong et al., 2009)
60
using response surface methodology.
61
In addition production of biodiesel from wet marine microalgae is fast becoming the
62
solution to dewatering problem. Lee et al. (2010) have reported that microwave irradiation
63
allows extraction of 80% crude oil from wet microalgae by chloroform and methanol as
64
extracting solvents. The effect of microwave irradiation is very much dependent on the
65
intensity/frequency of the microwave irradiation. Reaction rates were enhanced (2 min instead of
66
2 h process reaction) upon application of radio frequency microwave energy; therefore offering a
67
rapid and simple way to access the biofuel. The field of radio frequencies range from very high
68
frequency (VHF) (30 -300 MHz to ultra high frequency (UHF) (300 and 3000 MHz) while the
69
term microwave is typically used for frequencies between 3 and 300 GHz (David, 2012).
4 70
In the previous study, the microwave irradiation assisted heating were proven to increase
71
the yield of lipid extraction from the marine microalgae in a variety type of extraction techniques
72
such as Hara and Radin, Folch, Bligh and Dyer and Chen method (Teo et al, 2014). . This is
73
because in conventional heating; heat transfer occurs from the outside to the inside whilst in
74
microwave heating solvent extraction, the mass and heat transports occur from the inside of the
75
extracted material to the bulk solvent (Virot et al., 2008). While, microwave heating is a non-
76
contact heat source, which heats the overall target reactants simultaneously as compared to
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conductive heating. Many studies also revealed that microwave assisted method is better than
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other synthetic method and microwave irradiation system was proven to enhance the product
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yield, product purity and rate of reaction (Suppalakpanya et al., 2010; Koberg et al., 2011). In
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another recent study (Wahidin et al., 2014) performed an alternative method of lipid extraction
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from wet microalgae biomass using water bath-assisted and microwave irradiation solvent
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extraction and the results demonstrated that the lipid yield from microwave irradiation was much
83
higher compared to the water bath-assisted extraction due to the significantly higher cell
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disruption occurring in the microwave setup. The ability of the materials to rapidly absorb
85
microwave energy and convert it into heat creates pressure gradients causing cavitation to occur
86
thus rupturing the cell walls spilling out lipids (Choi et al., 2006; Amarni & Kadi, 2010).The wet
87
microalgae and polar solvents when placed under microwaves which consists of oscillating
88
electric field were able absorb heat directly causing molecules to vibrate, generates inter and
89
intra-molecular friction. The combination of molecular oscillation, friction, collision and
90
movement of large amounts of charged ions generates high heating rates (within seconds) within
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the algae cells, simultaneously develops pressurized effects which ruptures the cell wall
92
membranes causing lipids to diffuse out easily and rapidly. (Wahihin et al., 2014) Microwave
5 93
irradiation is an efficient technology because the cost of microwave heating is approximately 67
94
percent less than conventional heating. (Wahidin et al., 2014) and it can be scaled up easily thus
95
industrial application is viable (Amaro et al., 2011).
96 97
However the potential of applying microwave irradiation in direct transesterification (DT)
98
or in situ transesterification has not been extensively explored yet. Thus the objective of this
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study is to investigate the influence of the microwave irradiation heating on the quality and
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quantity of biodiesel obtained using the one step transesterification (OST) and two step
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transesterification (TST). In the OST only one particular catalyst is used throughout the biodiesel
102
production process while in the TST process, two catalysts were used, the first catalyst was used
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in the 1st part of the process followed by the 2nd catalyst after a certain period of time. Other
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critical parameters influencing the DT such as type of catalysts, catalysts combination were also
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investigated. Marine microalgae Nannochloropsis sp. was chosen because it has high lipid
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content (20-35% crude oil) (Rodolfi et al., 2009; Chisti, 2007) and can be cultivated easily.
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Marine microalgae were harvested upon reaching the maximum growth phase (10 days),
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centrifuged and the wet biomass were used for the DT (Teo et al., 2014). The MWOST method
109
used is clearly described in the methodology section and the yields obtained using this technique
110
are compared with the conventional heating OST and the TST process.
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2. Materials and Methods
113 114
2.1 Microalgal cultures
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The strains of Nannochloropsis sp. originally obtained from the culture collection of
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Borneo Marine Research institute (BMRI), Universiti Malaysia Sabah, Malaysia, were
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maintained in Walne’s medium agar which contained 15% agar (1 L Walne’s medium mix with
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15g agar powder).
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2.2 Cultivation of Marine microalgae under Walne medium
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Nannochloropsis sp. was cultivated in Walne medium with 10% starting inoculum taken
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from stock culture. The marine microalgae were cultivated in LED photobioreactor at 21oC ±0.5
123 124
o
C, pH 7.8±0.2 and under a light intensity of 200 µmol m-2s-1 with a 16:8 light-dark cycle with
aeration condition as the control growth environment.
125 126
2.3 Harvesting
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The 20 L marine microalgae after 10 days cultivation was dewatered by centrifugation
128
(9000rpm, 6minutes). The supernatant consisting of the culture medium was removed and the
129
concentrated microalgae which contain less than 20% water (from 20 litres culture) were
130
collected.
131 132
2.4 Direct transesterification (DT)
133 134
2.4.1 One step transesterification (OST)
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In the one step transesterification, methanol with three different catalyst; i) methanol plus
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NaOH ii) methanol plus HCl iii) methanol plus H2SO4 were used. Each of these combination was
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then poured into a round bottom type flask containing concentrated microalgae (10 mL). The
7 138
mixture was then heated to 90 oC for 40 min. The transesterification was performed in the water
139
bath with constant shaking at 120 rpm.
140 141
2.4.2 Two step transesterification
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In the TST, methanol was used with different catalysts. During the first part of reaction
143
methanol and the first catalyst (NaOH) was poured into a round bottom type flask containing
144
concentrated microalgae. The mixture was heated at 90 oC in a water bath with constant shaking
145
at 120 rpm. After 20 min., the mixture of methanol and HCl was added and the solution was
146
continuously heated in the water bath with constant shaking at 120 rpm for another 20 min. The
147
process was repeated using 3 other catalysts listed as follows:
148
i)
Methanol plus HCl (90 oC, 20 min), then methanol plus NaOH (90 oC, 20 min)
149
ii)
Methanol plus NaOH (90 oC, 20 min), then methanol plus H2SO4 (90 oC, 20 min)
150
iii)
Methanol plus H2SO4 (90 oC, 20 min), then methanol plus NaOH (90 oC, 20 min)
151 152
2.4.3 Enhancing the OST and TST via microwave irradiation heating
153
The transesterification processes in section 2.4.1 and 2.4.2 were repeated. However, the
154
flask was placed in the cavity of the microwave. During the transesterification process, a
155
condenser was used in order to prevent loss of solvent due to vaporization. The temperature of
156
condenser was maintained between 15-16 oC via chiller (Julabo, 32-ME) during the whole
157
process. The experiments were performed in MAS-II microwave synthesis workstation (Sineo
158
Microwave Technology Co. Ltd, 1000W) with an operational frequency of 2450 MHz).
159
Temperature of reaction mixture was measured directly by using infrared (IR) thermocouple and
160
maintained at 65°C and 800watt. The homogeneity of mixture was ensured using a magnetic
8 161
stirrer with speed maintained at 400rpm. The reaction period in the MWTST took 5 minutes for
162
each single step while in the MWOST the reaction time was kept to 10 minutes for the whole
163
process
164 165
2.5 Conventional Process
166
The results of the MWOST, MWTST, OST and TST were compared with the normal
167
conventional method of biodiesel extraction which involved the step by step process of lipid
168
extraction followed by transesterification process which is detailed out in the following section.
169 170
2.5.1 Lipid extraction
171
Wet microalgal biomass (200 ml) was mixed with methanol-chloroform (1:2 v/v) for
172
lipid extraction according to Bligh and Dyer method (Bligh EG and Dyer WJ, 1959). The
173
mixture was heated in the oven at 100oC for 2 hours. The mixture was then left to cool to room
174
temperature. After the lipid extraction the methanol-chloroform phase that contains the extracted
175
lipids was centrifuged at 4000 rpm for 5 minutes and then separated using separating funnel.
176
Then, the solvent containing lipid extracted was evaporated by a rotary evaporator.
177 178
2.5.2
Alkali-based Transesterification
179
Methanol was mixed with 0.5g of NaOH and stirred for 20 minutes at 400 rpm at
180
approximately 65°C. The ratio of methanol to oil in the mixture was kept to 6:1. The mixture of
181
catalyst and methanol was then poured into the conical flask containing the algae oil so as to
182
initiate the transesterification process. The conical flask was stirred continuously for 3 hours at
183
300 rpm and allowed to settle for 16 hours in order to obtain 2 separate layers; the supernatant
9 184
layer (glycerol) and sediment layers (biodiesel). The biodiesel was separated carefully from the
185
sediment layer by a flask separator and washed using 5 % water until the entire methanol is
186
removed. The biodiesel was dried using dryer and kept under running fan for 12 hours. The
187
percentage of efficiency was calculated according to equation (1) (Zayed and Jehad, 2014)
188 189
Produced biodiesel
Eficiency % Initial crude oil weight
(1)
190 191
2.6
Gas Chromatography (GC) analysis of fatty acid methyl esters (FAME)
192
Separation and identification of FAME were performed and analyzed using gas
193
chromatography (GC) (Agilent Technologies, 7820A) and HP-88 capillary column (60 m x 0.25
194
mm x 0.2µm) using hydrogen as the carrier gas at 40 ml/minutes. The column temperature was
195
set at 220 ºC as maximum temperature. Both of the injector and flame ionization detector (FID)
196
temperature were set at 220ºC. The back inlet was set at splitless mode and 220ºC as initial
197
temperature. The column initial temperature was set at 80oC during the initial 2 minutes; the
198
thermal gradient was 220 ºC at a rate of 13 ºC per minutes, the post temperature at 50 ºC in 2
199
minutes (Teo et al., 2014).
200 201
3. Results and Discussions
202
3.1 Comparison of conventional, two step and one step transesterification
203
Figure 1:
204 205
Figure 1 shows that the transesterification efficiency for the DT using
206
conventional heating OST and TST and the conventional process (defined as control; C). The
10 207
OS1 (NaOH) biodiesel production method gave the lowest efficiency (13.46%) followed by the
208
second lowest OS2 (HCl) method. This is probably due to the insufficient extraction and
209
transesterification was performed on limited lipids extracted in the OST method. The low
210
extraction yield was probably contributed by the insufficient extraction using water bath heating.
211
The findings revealed that a single catalyst on its own in conventional heating OST could not
212
achieve high efficiency. Similar results were obtained by Laurens et al.(2012) who reported that
213
CH2ONA when used alone as a catalyst in the OST did not produce any biodiesel and suggested
214
TST using combined catalysts (CH3ONa/BF3) for higher biodiesel yields (Laurens et al., 2012).
215
Although, the cost of NaOH as the catalyst is cheaper than acid catalyst but it is highly
216
hygroscopic and tend to absorb moisture from air during storage and forms water when react in
217
the alcohol which ultimately influenced the yield (Leung and Guo, 2006). In addition, the
218
hydrolysis and saponification which occurred when alkali catalyzed transesterification was used
219
tend to reduce the yield of biodiesel (Mardina et al., 2013). When H2SO4 (OS3) was used as the
220
catalyst the biodiesel yield was slightly improved when compared with HCl (OS2).
221
However the higher biodiesel yields were obtained when TST was used using TS3 catalysts
222
(NaOH + H2SO4) and TS1 catalyst (NaOH + HCl) achieving 28.85% and 30.85 % respectively.
223
These catalysts combination in TST tend to have a synergistic effect; increase the hydrolysis rate
224
of cell by using NaOH and promotes transesterification of lipids to biodiesel via H2SO4 in the
225
second stage previously explained by Griffiths et al., (2010). When acid catalyst was used in
226
biodiesel transesterification, the fatty acids are protonated by the acid and become tetrahedral
227
intermediates with methanol which are then easily converted to biodiesel. If the water is present
228
in the reaction, it will combine with acid catalyst leading to a reversible acid catalyst deactivation
229
thus forming proton clusters (Lotero et al., 2005). Griffiths et al., (2010) reported that when
11 230
using direct transesterification method, the alkaline catalyst hydrolysis of microalgae in the
231
initial stage lead to higher biodiesel yield. Upon comparing OS1 and TS4, it was observed that
232
the biodiesel yield efficiency increased by 2.3 folds.
233 234 235
3.2 Comparison of conventional, MWTST and MWOST
236 237
Figure 2:
238 239
Figure 2 depicts the biodiesel yield efficiency for MWOST and MWTST and the control. In most
240
cases it was observed that the microwave irradiation has enhanced the one step and two step
241
transesterification. A similar trend was observed for the different catalyst and the TST was
242
observed to be better. However the use of microwave heating has increased the efficiency yields
243
by many folds (5%-43.37%). The application of microwave irradiation heating allows heat to be
244
directly transferred to the microalgae and the rapid oscillations of the molecules tend to disrupt
245
the cell walls of microalgae (Wahidin et al., 2014) thus releasing lipids. The microwave
246
irradiations also promote the implosion of cavitated bubbles inside and outside the marine
247
microalgae causing more crude oil to be extracted out during the reaction (Teo et al., 2014).
248
Cavitation can be defined as the generation, subsequent growth and collapse of the cavity by
249
releasing large amounts of energy on a small location due to high energy densities (Parag R.
250
Gogate, 2007). Therefore in this case, cavitation phenomena occurs on the microalgae cell
251
surfaces due to the generation of high temperature and pressure gradients generated by
252
microwave irradiation thus rupturing the cell walls. The high amounts of lipids released allowed
253
transesterification process to occur more efficiently thus further enhanced the biodiesel yield. An
12 254
increment of 2.87 folds was observed when comparing MOS1(NaOH) and MTS3(NaOH +
255
H2SO4)
256 257
3.3 Comparison efficiency in between microwave irradiation and without microwave irradiation
258 259
Figure 3:
260 261
Figure 3 clearly demonstrates the potential effect of microwave irradiation heating to
262
direct transesterification including OST and TST methods. The use of microwave has improved
263
the efficiency yields in all the methods but the correct combination of alkaline-acid catalyst plus
264
the microwave irradiation can promote the transesterification process leading to high biodiesel
265
yields. The direct heating of microwave irradiation ruptures cell walls allowing almost all the
266
lipids to spill out and thus more lipids are available to be transesterified to biodiesel. The lipid
267
production is proportional to biodiesel production. From the figure 3, the increment in efficiency
268
can be calculated by Equation 2.
269 270
! " # $$## %
&' ())*+*(,+-. '/0(1 2/03 3(/0*,4 ())*+*(,+ '/0(1 2/03 3(/0*,4 ())*+*(,+-
5 100
(2)
271 272
From the calculation, the increment in efficiency of the various MWDT’s are as follows: O1
273
(14.34%), O2 (18.20%), O3 (14.30%), T1 (27.11%), T2 (5%), T3 (43.37%) and T4 (25%).
274
Highest increment yield was obtained in the MWTST using a combination of (NaOH + H2SO4)
275
(T3) where an increment of 43.37% was achieved. The application of microwave irradiation has
276
provided both the simultaneous disruption of microalgae cell walls at the same time promotes the
13 277
transesterification of extracted lipids to biodiesel. Thus, the rate of collision between methanol
278
and crude oil molecule was increased and the rate of transesterification efficiency was increased
279
(Teo et al., 2014). Previous studies (Baghurst and Mingos, 1992, Idris et al., 2012) have shown
280
that microwave has the tendency to speed up reactions and play a critical role in organic
281
synthesis. Microwave irradiation is not simply dielectric heating rather a specific activation
282
effect of microwave was involved in the chemical reaction (Idris et al., 2012) and interaction
283
between solvents and catalyst with microwave need to be considered.
284 285
3.4 Fatty acid methyl ester composition analysis via GC, Cetane number and Iodine value
286 287
Table 2 shows the composition of biodiesel found in conventional, water bath heating and
288
microwave irradiation. Those methods produced biodiesel consisting of C16-C18 fatty acid
289
methyl ester. However conventional and water bath heating were observed to produce higher
290
carbon chain methyl ester such C18:3, C20:4 and conventional method also produce C22. While
291
microwave irradiation method tends to produce shorter carbon chains such as C14 and C18:1n9t
292
which were not present in conventional and water bath heating method. According to Cheng et
293
al.,(2013) microwave irradiation produced shorter carbon chain because the longer carbon chains
294
tend to be polarized and thus they become unstable leading to the formation of shorter carbon.
295 296
Table 2:
297 298 299
The physical quality of biofuel is very much dependent on the lipid composition. The degree of unsaturation (DU) is very much influenced by the amount of saturated,
14 300
monounsaturated and polyunsaturated fatty acid’s present and can be determined using Equation
301
3 (Ramos et al, 2009):
302
DU = wt % of monounsaturated fatty acid + 2(wt % of polyunsaturated fatty acid)
303
Table 3 depicts the amount of saturated, monounsaturated and polyunsaturated fatty acid and the
304
calculated DU values. These values obtained are significant as they can be used to predict the
305
iodine value (IV) and cetane number (CN). CN for biodiesels is predicted using Eq. (4):
(3)
306
89 : 5&( ;". % . 89&( 4 307
where XMe is the weight percentage of each methyl ester and CNMe is the cetane number of each
308
individual methyl ester.
309
The iodine value (IV) of biodiesel is very much dependent on the molecular weight of the
310
fatty compound (MWf). The IV of a pure compound can be computed by Equation (5),
311
> 100 ×
312
where db is the number of double bonds and 253.81 is the atomic weight of two iodine atoms
313
that are theoretically added to one double bond. Subsequently, the IV of a mixture of fatty
314
compounds can be calculated by Equation 6,
315
>G*H0I1( ∑ 100 ×
316
where Af is the amount in (%) of a fatty compound in a mixture. Equations 4 and 5 assume full
317
iodination.
@AB.CD× E2
(5)
&'F
KF × @AB.CD × E2 &'F
(6)
318
Generally, CN is related to the combustion quality and ignition delay, where higher CN
319
values reflect better ignition property and lower IV values reflects better lubricating properties
15 320
Meher et al.(2006). IV value is a predication of total unsaturation of a biodiesel and is
321
proportional to DU: higher DU represents higher IV (Knothe, 2002; Knothe et al.,1997;
322
Kyriakidis and Katsiloulis, 2000).
323 324
Table 3:
325 326
Table 3 shows that the degree of unsaturation, saturation, cetane number and iodine value in
327
conventional, water bath heating method and microwave irradiation method. Biodiesel produced
328
from microwave irradiation method produces a high cetane number as good as the conventional
329
and water bath method. The iodine value for FAMEs obtained from the microwave irradiation
330
has a lower value compared to water bath heating and conventional method. This means that the
331
microwave irradiation method’s lubricating property of biodiesel was better than water bath
332
heating and conventional method. Ultimately, the biodiesel property will influence the efficiency
333
of engine.
334 335
4. Conclusion
336
MW was proven to increase the efficiency of all DT methods especially for the combined
337
catalyst (NaOH and H2SO4) in the TST where the highest efficiency increment of 43.7% was
338
achieved. Besides C16 –C18 carbon chains; shorter carbon chains FAMEs (C14 and C18:1n9t)
339
were also produced by MWDT due to polarization of the longer carbon chains under MW. The
340
conventional and water bath heating were observed to produce higher carbon chain FAMEs such
341
as C18:3, C20:4 and conventional method also produced C22. Biodiesel produced from MWDT
342
has good ignition and lubricating property indicated by CN (67.8) and IV (44.2).
16 343 344
ACKNOWLEDGEMENTS
345
Financial support from Universiti Teknologi Malaysia (Research University Grant 06H40) for
346
this research is gratefully acknowledged.
347 348
References
349
1.
350
from oil cake using hexane: comparison with the conventional extraction. Innov Food Sci Emerg
351
Technol. 11, 322–7.
Amarni, F., Kadi, H., 2010. Kinetics study of microwave-assisted solvent extraction of oil
352 353
2.
Amaro, H.M., Guedes, A.C., Malcata, F.X., 2011. Advances and perspectives in using
354
microalgae to produce biodiesel. Appl Energy. 88, 3402–10.
355 356
3.
Baghurst, D. R. and Mingos D. M. P.,1992. Superheating effects associated with
357
microwave dielectric heating, J. Chem. Soc. Chem. Commu. 674-677.
358 359
4.
Bligh, E.G., Dyer, W.J., 1959. A rapid method of total lipid extraction and purification,
360
Can. J. Biochem. Physiol. 37, 911–917.
361 362
5.
363
microstructures and fractal characterization of cell wall disruption for microwave irradiation-
364
assisted lipid extraction from wet microalgae. Bioresour Technol. 150, 67–72.
365
Cheng, J., Sun, J., Huang, J., Feng, J., Zhou, JH., Kefa Cen, 2013. Dynamic
17
6.
Chisti, Y.,2007. Biodiesel from microalgae. Biotechnology Advanced. 25, 294-306.
368
7.
Choi, I., Choi, S.J., Chun, J.K., Moon, T.W., 2006. Extraction yield of soluble protein
369
and microstructure of soybean affected by microwave heating. Food Process Preserv. 30,407–19.
366 367
370 371
8.
David M. Pozar, 2012 Microwave Engineering Fourth Edition JohnWiley & Sons, Inc.
372 373
9.
Griffiths,
M.J.,
Hille-van,
R.P., Harrison,
S.T.L.
2010.
Selection of direct
374
transesterification as the preferred method for assay of fatty acid content of microalgae. Lipids.
375
45,1053-60.
376 377
10.
Idris A, Attaullah B, Noordin MY, Tan KG. 2012. A Simultaneous cooling and dielectric
378
heating: An advanced technology to improve the yield of lactides. Progress in electromagnetic
379
research symposium. 141 -145
380 381
11.
Jeong, G.T., Yang, H.S., Park, D.H. 2009. Optimization of transesterification of animal
382
fat ester using response surface methodology. Bioresour Technol. 100,25 -30.
383 384
12.
385
Schizochytrium limacinum by direct transesterification of algal biomass. Energy Fuels. 23,5179-
386
83.
387
Johnson, M.B., Wen, Z.Y. 2009. Production of biodiesel fuel from the microalga
18 388
13.
Knothe, G., Dunn, R.O., Bagby, M.O., 1997. Biodiesel: The use of vegetable oils and
389
their derivatives as alternative diesel fuels. In: Saha B.C., Woodward, J. (Eds.), Fuels and
390
Chemicals from Biomass, ACS symposium series 666, Washington, DC (Chapter 10).
391 392
14.
Knothe, G., 2002. Structure indices in FA chemistry. How relevant is the iodine value? J.
393
Am. Oil Chem. Soc. 9, 847–853.
394 395
15.
Koberg, M., Abu-Much, R., Gedanken, A. 2011. Optimization of bio-diesel production
396
from soybean and wastes of cooked oil: combining dielectric microwave irradiation and a SrO
397
catalyst. Bioresour Technol. 102,1073–8.
398 399
16.
Kyriakidis, N.B., Katsiloulis, T., 2000. Calculation of iodine value from measurements of
400
fatty acid methyl esters of some oils: comparison with the relevant American oil chemists society
401
method. J. Am. Chem. Soc. 77, 1235–1238.
402 403
17.
Lardon, L., Helias, A., Sialve, B., Steyer, J. 2009. Bernard O. Life-cycle assessment of
404
biodiesel production from microalgae. Environ Sci Technol. 43,6475–81.
405 406
18.
407
Accurate and reliable quantification of total microalgal fuel potential as fatty acid methyl esters
408
by in situ transesterification. Anal Bioanal Chem. 403, 167-78.
409
Laurens, L.M.L., Quinn, M., Van Wychen, S., Templeton, D.W., Wolfrum, E.J. 2012.
19 410
19.
Lee, J.Y., Yoo, C., Jun, S.Y., Ahn, C.Y., Oh, H.M., 2010. Comparison of several
411
methods for effective lipid extraction from microalgae, Bioresour Technol. 101, S75–S77.
412 413
20.
Leung, D.Y.C., Guo, Y. 2006. Transesterification of neat and used frying oil:
414
optimization for biodiesel production. Fuel Process Technol. 87,883–90.
415 416
21.
Lotero, E., Liu, Y., Lopez, D. E., Suwannakarn, K., Bruce, D. A., & Goodwin Jr., J. G.
417
2005. Synthesis of biodiesel via acid catalysis. Industrial & Engineering Chemistry Research,
418
44(14),5353-5363.
419 420
22.
Mardina, P., Yong, C. S., Young, H. C., 2013. Effect of alkali catalyst on biodiesel
421
production in South Korea from mixtures of fresh soybean oil and waste cooking oil. J Mater
422
Cycles Waste Manag. 15,223–228
423 424
23.
Owen, N.A., Inderwildi, O.R., King, D.A. 2010. The status of conventional world oil
425
reserves-hype or cause for concern. Energy Policy. 38,4743–9.
426 427
24.
Patil, P.D., Gude, V.G., Mannarswamy, A., Cooke, P., Munson-McGee, S.,
428
Nirmalakhandan, N. 2011. Optimization of microwave-assisted transesterification of dry algal
429
biomass using response surface methodology. Bioresour Technol. 102,1399-405.
430 431
25.
Parag, R. G, 2008. Cavitational reactors for process intensification of chemical
432
processing applications: A critical review. Chemical Engineering and Processing 47, 515–527.
20 433 434
26.
Ramos, M.J., Fernández, C.M., Casas, A., Rodríguez, L., Pérez, Á., 2009. Influence of
435
fatty acid composition of raw materials on biodiesel properties. Bioresour. Technol. 100 (1),
436
261–268.
437 438
27.
Rodolfi, L., Chini Zittelli, G., Bassi, N., Padovani, G., Biondi, N., Bonini, G., Tredici,
439
M.R., 2009. Microalgae for oil: strain selection, induction of lipid synthesis and outdoor mass
440
cultivation in a low-cost photobioreactor. Biotechnology Bioengineering. 102, 100–112.
441 442
28.
Suppalakpanya, K., Ratanawilai, S.B., Tongurai, C. 2010. Production of ethyl ester from
443
crude palm oil by two-step reaction with a microwave system. Fuel. 89,2140–4.
444 445
29.
Teo, C.L., Idris, A., 2014. Enhancing the various solvent extraction method via
446
microwave irradiation for extraction of lipids from marine microalgae in biodiesel production
447
Bioresour Technol. 171, 477-481
448 449
30.
Teo, C.L., Madiha, A., Attaullah, B., Mohamad, T., Afendi, M.Y. Idris, A.,
450
2014. Enhancing growth and lipid production of marine microalgae for biodiesel production via
451
the use of different LED wavelengths Bioresour Technol. 162, 38-44.
452 453
31.
454
integrated extraction of total fats and oils. J. of Chromatography A. 1196–1197, 57–64.
455
Virot, M., Tomaoa, V., Giniesa, C., Visinonib, F., Chemata, F., 2008. Microwave-
21 456
32.
Wahidin, S., Idris, A., Siti, R. M. S. 2014. Rapid biodiesel production using wet
457
microalgae via microwave Irradiation Energy Convers Manage. 84, 227–233.
458 459
33.
Wahlen, B.D., Willis, R.M., Seefeldt, L.C. 2011. Biodiesel production by simultaneous
460
extraction and conversion of total lipids from microalgae, cyanobacteria, andwild mixed-cultures.
461
Bioresour Technol. 102,2724-30.
462 463
34.
Zayed, A.H., Jehad, Y., 2014. Parametric study of the alkali catalyzed transesterification
464
of waste frying oil for Biodiesel production. Energy Convers Manage. 79, 246–254.
465 466
35.
467
assisted transesterification of yellow horn oil to biodiesel using a heteropolyacid solid catalyst.
468
Bioresour Technol. 101,931-6.
469
Zhang, S., Zu, Y.G., Fu, Y.J., Luo, M., Zhang, D.Y., Efferth, T. 2010. Rapid microwave-
22 470 471
Figure 1: Comparison of transesterification efficiency for 8 types of methods. C (control), One
472
step DT; OS1 (NaOH), OS2 (HCl), OS3(H2SO4), Two step;TS1( NaOH + HCl ), TS2(HCl +
473
NaOH), TS3 (NaOH + H2SO4) and TS4 (H2SO4 + NaOH)
474 475
Figure 2: Comparison of transesterification efficiency for 8 types of methods. C (control),
476
Microwave one step; MOS1 (NaOH), MOS2 (HCl), MOS3 (H2SO4), Microwave two step;
477
MTS1 (NaOH + HCl ), MTS2(HCl + NaOH), MTS3 (NaOH + H2SO4) and MTS4 (H2SO4 +
478
NaOH). All the methods except control apply microwave irradiation assisted.
479 480
Figure 3: Comparison variety of transesterfication method between without microwave
481
irradiation and microwave irradiation. O1 (NaOH), O2 (HCl), O3(H2SO4), T1( NaOH + HCl ),
482
T2(HCl + NaOH), T3 (NaOH + H2SO4) and T4 (H2SO4 + NaOH)
483 484
23 485
Table 1:
486
Fatty acid methyl ester (FAME) composition analysis
487 488 489 490 491 492 493 494 495 496 497 498
Type of method
Conventional
Water bath heating
Microwave irradiation
Methyl ester
wt.%
wt.%
wt.%
C14:0
-
-
12
C16:0
50
21.43
17
C18:0
2
11.86
31
C18:1n9t
-
-
11
C18:1n9c
14
5.93
9
C18:2n6t
6
10.47
10
C18:2n6c
6
10.47
10
C18:3
1
24.38
-
C20:4
5
15.46
-
C22:0
16
-
-
24 499
Table 2:
500
Degree of unsaturation, saturation, cetane number and iodine value FAME component (%)
501 502 503
Conventional
Water bath Heating
Microwave Irradiation
Saturated
68
33.29
60
Monounsaturated
14
5.93
20
Polyunsaturated
18
60.78
20
Degree of unsaturation
50
127.49
60
Cetane number (CN)
67.73
60.78
67.8
Iodine value (IV)
53.7
161.45
44.28
25
35 Efficiency
30
Efficiency (%)
25 20 15 10 5 0 C
504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519
Figure 1:
OS1
OS2 TS1 TS2 Types ofOS3 Transesterification
TS3
TS4
26
50 45
Efficiency
Efficiency (%)
40 35 30 25 20 15 10 5 0 C
520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535
Figure 2:
MOS1
MOS2 MOS3 MTS1 MTS2 Type of transesterification
MTS3
MTS4
27
Efficiency (%)
50 45
without microwave irradiation
40
microwave irradiation
35 30 25 20 15 10 5 0
O1
536 537 538 539 540 541
Figure 3:
O2
O3 T1 T2 Type of transesterification
T3
T4
28 542
Microwave irradiation direct transesterification of wet marine microalgae to FAMEs
543
Two types of direct transesterification (DT) were used; one step and two step
544
The DT was performed in presence of methanol and various alkali and acid catalyst.
545
Microwave irradiation enhanced the biodiesel yields with short carbon chain FAME’s
546
Microwave irradiated two step DT with NaOH and H2SO4 exhibits the highest efficiency
547 548 549
29
550 551