Biodiesel Production via Transesterification of Nannochloropsis ...

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Journal of the Japan Institute of Energy , 93, 995-999（2014）

Special Articles: Biomass 特集：バイオマス

Biodiesel Production via Transesterification of Nannochloropsis oculata microalga’s Oil Using Calcium Methoxide as Heterogeneous Catalyst Y. H. TAUFIQ-YAP ※ 1 ※ 2 and S. H. TEO ※ 1 ※ 2 (Received April 22, 2014)

The main challenges facing the commercialization of biodiesel are: profitability, feedstock availability and low cost efficient production process. Although worldwide production of vegetable oil feedstocks is sufficient enough, big area of land needed for cultivating such feedstocks is the major drawback. Algae-biomass (including macroand microalgae) is gaining interest from many current researchers as they have potential to provide sufficient fuel for global consumption. Algae can be produced fast with high lipid content. Moreover, it can provide food avoiding future starving and allow replacing fossil fuels through carbon-neutral biofuels for combustion machines in the transport, industrial and agricultural sectors. In this study, high grade biodiesel was produced from microalgae derived lipids (Nannochloropsis oculata) via transesterification reaction with methanol using calcium methoxide catalyst. The results showed excellent performances with high yield (92 %) of biodiesel at 60 ℃ compared to the highest yield reported at 22 % with using MgZr catalyst. Interestingly, calcium methoxide catalyst could be also successively reused for five times with the maintained biodiesel yield. Biodiesel produced from microalgae oil had high content of polyunsaturated fatty acids, which made it highly suitable as winter grade biodiesel. Key Words Microalga oil, Heterogeneous catalyst, Biodiesel

1.　Introduction

biodegradable than the alternatives, especially biofuel crops

Microalgae, a single-celled alga, has been recognized

such as corn and soy 3). Thus, to deal with the cost issue of

as the most potential candidate to convert solar energy

biodiesel production, utilizing the oils extracted from the

into fuel through photosynthesis, mainly because of their

microalgae as the feedstock has been recognized as one of

potential for reducing the amount of land and water surface

the best solutions.

needed to produce fuels and converting solar energy more

Transesterification process converts triglycerides into

efficiently. In addition to its high biomass productivity, it is reported that microalgae contains abundant lipid (up to 85 % lipids by dry weight), which are considered to be one of the most promising characteristics for biodiesel feedstocks 2). Furthermore, microalgae cells growing in aqueous suspension have more access to water, CO2 and other nutrients. These characteristic make microalgae to be capable for producing 30 times amount of oil per unit land area, compared to terrestrial oil seed crops. Moreover, biodiesel from microalgae lipid is non-toxic and highly ※ 1 ※ 2

Catalysis Science and Technology Research Centre, Faculty of Science, Universiti Putra Malaysia 43400, Serdang, Selangor, Malaysia Department of Chemistry, Faculty of Science, Universiti Putra Malaysia 43400, Serdang, Selangor, Malaysia

This study was partly presented in the 1st Asian Conference on Biomass Science, Jan 14, 2014, Kochi, Japan

J. Jpn. Inst. Energy, Vol. 93, No. 10, 2014

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fatty acid methyl ester (FAME), in the presence of short

　2.2　Catalysis preparation

chain alcohol and a catalyst, with glycerol as by-product.

The catalysts Ca(OCH 3 ) 2 were prepared using

Most of the catalysts used are homogeneous catalysts such

hydrothermal method by heating CaO in an excess

as KOH, NaOH and H 2 SO4 4) 5). However, homogeneously

dehydrated methanol at 65 ℃ at a range of durations of 2

catalyzed reactions generate many environmental and

-12 h with N2 flow (50 mL min-1). The reaction is expressed

corrosion problems. Hence, transesterification reactions

by following eq 1:

catalyzed by heterogeneous catalysts have been ambitious for biodiesel producton. Recently, several studies reported

65 ℃, N2 atmosphere CaO + 2CH3OH

heterogeneous catalysis for biodiesel production 6) ～ 8). Li et al. 6)

Ca (OCH3)2 + H2O (1)

reported Mg-Zr solid base catalyst is suitable for biodiesel

Henceforth, the catalysts were denoted as CMX,

production from Nannochloropsis sp. microalgae with a

where X represents the reflux time of 2, 4, 6, 8, 10 and 12 h,

yield of 22 %. Besides, transesterification of Eustigmatophyte

respectively.

Nannochloropsis sp. biomass using microwave and ultrasonic radiation with the aid of an SrO catalyst resulted in 18 %

　2.3　Catalysis characterization

and 37 % biodiesel yield, respectively 7). Furthermore,

Thermogravimetric and differential thermal analyses

Umdu et al. also found a high biodiesel yield (97.5 %) from

(TG/DTA) of Ca(OCH 3) 2 catalysts were performed using

Nannochloropsis oculata microalga’s lipid by using Al 2O3

the Mettler Toledo thermogravimetric analyzer. Structures

8)

supported CaO catalyst.

of the Ca(OCH3)2 was investigated by using X-ray diffraction

In this work, biodiesel was produced from yellow

(XRD) with a Shimadzu XRD-6000 diffractometer. Surface

green microalgae, Nannochloropsis oculata (N. oculata),

functional groups of the catalyst were determined using

catalyzed by a hydrothermal synthesized Ca(OCH3) 2 solid

infrared spectra analysed by attenuated total reflection-

catalyst. Ca(OCH 3) 2 catalyst can be easily prepared as a

Fourier transform-infrared spectroscopy (ATR-FTIR)

superior base catalyst and can be separated from biodiesel.

(PerkinElmer (PC) Spectrum 100 FTIR spectrometer). The

Ca(OCH 3) 2 catalyst was previously studied to produce

total surface area (S BET), total pore volume (cm3 g-1) and

.

average pore size (nm) of the catalyst were determined

biodiesel from soybean, rapeseed and vegetable oil

9) ～ 11)

We reported for the first time the conversion of microalgae

using Brunauer - Emmett - Teller (BET) method. The

oil to biodiesel with Ca(OCH3) 2 catalyst. The effect of the

morphology observations of the catalyst were performed

catalyst dosage, methanol to oil molar ratio and reaction

using a field emission scanning electron microscopy

time were investigated by carrying out experiments at

(FESEM, JOEL JSM6700F) and a Transmission Electron

varying reaction conditions. The efficiency and reusability of

Microscopy (TEM, Hitachi, H7100).

the catalyst in biodiesel production will also be discussed. 　2.4 Transesterification reaction and FAME yield 2.　Experimental section 　2.1　Biomass preparation

analysis Transesterification of microalgae lipid was performed

The microalgae N. oculata was purchased from

in a micro-reactor at 60 ℃ with different parameters such

AlgaeTech Sdn. Bhd., (Klang, Malaysia). Photoautotrophic

as volumes of methanol, varied concentrations of powder

cultivation of N. oculata was initially carried in an

catalysts and different reaction times. The methyl

Erlenmeyer flask containing (1000 mL) modified F/2 medium,

ester yield was calculated from data analyzed by gas

at 24-28 ℃ with air flowing (flow rate: 20 cm3 min-1) under

chromatography (GC) (Agilent technologies 7890A)

16 h on and 8 h off artificial light cycle (light intensity: 60 W

with a flame ionization detector (FID) and a fused silica

m-2). The strain must be constantly agitated during growth

capillary HP-88 column (300 m x 0.25 mm i.d., 0.20 μm

to avoid sediment build-up which hinders growth. The

film thickness) (Agilent, USA). The transesterified oil was

culture suspension having been flocculated, the microalgal

injected at 140 ℃ (held for 5 min) with the split ratio of 1:30.

cells were then washed with distilled water to remove

FAME was separated from the transesterified oil in the

coagulants. The cells were then dried at 70 ℃ for 24 h and

column heated at 240 ℃ with the heating rate at 4 ℃ min-1

triturated to create dry microalgae powder for experiment.

and held for 15 min. The sample size injected was 1 μL;

The lipid extraction was performed using modified Bligh

with helium as the carrier gas flowing at the rate of

and Dyer method .

1 mL min-1. Methyl heptadecanoate and hexane was used

12)

as an internal standard and solvent, respectively. The gas chromatogram of the biodiesel product is shown in


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Fig. 1　Gas chromatogram of N. oculata derived biodiesel using Ca(OCH 3) 2

Fig. 1. The FAME content was determined in agreement with the European regulated procedure EN 14103 13). All values reported were the average of three measurements. 3.　Results and Discussion 　3.1 Lipid extraction and fatty acid constituent of N.

oculata The Bligh and Dyer method was used to extract the highest lipid content. As shown in Fig. 2, the presence of unsaturated (54.38 %) and saturated (45.62 %) fatty acids indicates more unsaturated fatty acid content. The result clearly shows that the raw material contains 36.16 % of monounsaturated, 5.22 % of diunsaturated, and 25.21 % of polyunsaturated fatty acids. The molecular weight (MWoil) of microalgae oil was calcilated to be 831.62 g mol-1 from eq 2. MWoil = [(3 x MWfatty acid) + MWglycerol] - 3 x MWwater

(2)

　3.2　Catalyst characterization Fig. 3(a) corresponds to the TG/ DTA thermogram of the synthesized Ca(OCH 3) 2 catalyst under air flow condition. The thermogravimetry analysis suggested that

Fig. 3 TG/DTA spectrum (a) of Ca(OCH 3 ) 2 catalyst, X-ray diffraction patterns of CaO and Ca(OCH 3) 2 (b) catalysts

the synthesized Ca(OCH3)2 catalyst is stable below 400 ℃ . The X-ray diffraction patterns of all catalysts are shown

2θ of 32.1° and 37.2° (JPDS File No. 00-037-1497). The

in Fig. 3(b). CaO gave very appreciable broad peaks at

characteristic peak of Ca(OCH3)2 (CM2 - CM12) was clearly observed at 2θ of 10.8° 14). FTIR spectra (Fig. 4) of the Ca(OCH 3) 2 catalysts indicated the important functional groups i.e. -C-O stretching vibration of primary alcohol (1070 cm-1), -OH stretching vibration of primary alcohol (3650 cm-1), CH 3 stretching vibrations (2800-3000 cm-1) and -C-H alkene bending (1465 cm-1). The BET isotherm of Ca(OCH3)2 (CM2 - CM12) and CaO catalysts showed Type IV-like isotherms. The catalysts with surface area were arranged in the sequence of: CaO

Fig. 2　Fatty acid methyl ester profile of N. oculata

< CM2 < CM4 < CM6 < CM12 < CM10 < CM8. It showed


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Fig. 4　FTIR spectra of Ca(OCH 3) 2 catalysts

Fig. 6 Influence of methanol/oil molar ratio (a), catalyst loading (b) and reaction time (c) on the FAME yield of crude microalgae lipid by CM8 catalyst

could accelerate the transesterification reaction rate and produce more biodiesel 16). 　3.3.2 Influence of catalyst concentration of CM8 catalyst on FAME yield The results indicated that a high concentration of the Fig. 5 SEM and TEM micrographs of CaO (a & c) and Ca(OCH 3) 2 (b & d) catalysts

catalyst facilitates the increase in total number of available active catalytic sites for the reaction. The yield of FAME increased with the loading of the catalyst, and reached a

that CM8 catalyst possessed the highest surface area of

maximum of 92.0 % when 12 wt. % of catalyst was used (Fig.

31 m2 g-1, with a total pore volume of 0.21 cm3 g-1 and an

6(b)). However, when the loading further increased to 15

average pore diameter of 31.97 nm.

wt. %, the biodiesel yield started to decrease to 61.6 %.

Fig. 5 shows the morphology of Ca(OCH3)2 (CM8) and CaO catalysts. As shown in Fig. 5(a), the CaO catalyst was found to be compact forming an irregular shape. The CM8

　3.3.3 Effect of reaction time on FAME yield using Ca(OCH 3) 2 , CaO and NaOH catalysts Fig. 6(c) shows the comparison of FAME yield

catalyst (Fig. 5(b)) seems to be a flower-like cluster structure

using two solid catalysts (Ca(OCH 3) 2 and CaO) and one

which was similar to that reported by Kouzu et al. 15). From

homogeneous catalyst (NaOH). The NaOH catalyst reacts

the TEM images (Fig. 5(c)) the CaO catalyst was seen to

significantly faster compared to the heterogeneous catalysts.

be cubic in shape which is consistent with results reported

For the heterogeneous catalyst system, the results revealed

by one of us 13). The TEM images pictured that the crystal

that the reaction rate is very slow and maximum FAME

sizes of CM8 (Fig. 5(d)), catalyst is significantly smaller than

yield of 80 % is achieved after 3 h which is due to the

untreated CaO catalyst.

heterogeneous mass transfer systems between the solid catalyst and the liquid reactant. The catalyst showed higher

　3.3　Transesterification of N. oculata lipid

conversion rate and achieved 92 % FAME yield compared

　3.3.1 Influence of molar ratio of methanol to oil on

to 80 % of CaO over the same duration.

FAME yield by CM8 catalyst Increasing methanol:lipid ratio from 10:1 to 60:1

　3.4　Catalyst stability and reusability

significantly increased the biodiesel yield from 6.9 to 85.4 %

In order to test the catalyst reusability, CM8

(Fig. 6(a)). Due to reversible reaction, the enhancing FAME

catalyst was recycled. The results (Fig. 7(a)) showed that

yield indicated that the increasing amount of methanol

CM8 can be reused up to five times with biodiesel yield of


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to be inexpensive, feasible, effective and potential method of producing high quality biodiesel from phototropic microalgae N. oculata. References 1） Patil, P. D.; Gude, V. G.; Camacho, L. M.; Deng, S., Energ Fuel, 24, 1298-304 (2010) 2） Huang, G. H,; Chen, F., Wei, D., Zhang, X. W.; Chen, G., Appl Energy, 87, 78-46 (2010) 3） Schenk, M.; Thomas-Hall, S. R.; Stephens, E.; Marx, U. C.; Mussgnug, J. H.; Posten, C. et al., Bioenergy Resources, 1, 20-43 (2008) 4） Xu, R. Y.; Mi, Y. L., J Am Soc, 88, 91-9 (2011) 5） Xu, H.; Miao, X. L.; Wu, Q. Y., J Biotechnol, 126, 499-507 (2006) 6） Li, Y. S.; Lian, S.; Tong, D.; Song, R. L.; Yang, W. Y.; Fan, Y.; Qing, R. W., Appl Energ, 88(10), 3313-7 (2011) 7） Koberg, M.; Cohen, M.; Amotz, A. B.; Gedanken, A., Bioresource Technol, 102, 4265-9(2001) 8） Umdu, E. S.; Tuncer, M.; Seker, E., Bioresource Technol, Fig. 7 Reusability test (a) and XRD pattern and SEM (b) micrograph of deactivated Ca(OCH 3) 2 catalyst

100, 2828-31(2009) 9） Liu, X. J.; Piao, X. L. Wang, Y. J.; Zhu, S. L.; He, H. Y., Fuel, 87, 1076-82 (2008) 10） Gryglewicz, S., Bioresource Technol, 70, 249-53 (1999)

～ 92.7 - 96.0 %. The deactivation of the catalyst is due to

11） Deshmane, V. G.; Adewuyi, Y. G., Fuel, 107, 474-82 (2013)

the impurities that come from microalgae lipid, such as

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phospholipids and moisture, which can observed from the SEM image and XRD profile shown in Fig. 7(b).

405-16(2001) 13） Taufiq-Yap, Y. H.; Lee, H. V.; Yunus, R.; Juan, J. C., J Chem Eng, 178, 342-7(2011)

4.　Conclusions In summary, Nannochloropsis microalgae oil was obtained using soxhlet extraction method. Transesterification of microalgae oil gave a high FAME yield in the presence of Ca(OCH3)2 solid catalyst. The catalyst could be reused at least five times and excess methanol is needed to achieve 92.0 % FAME yield. The results suggested that this process

14） Hassan, M.; Robiah, Y.; Thomas, S. Y. C.; Rashid, U.; Taufiq Yap, Y. H., Appl Catal A: Gen, 425-426, 18490(2012) 15） Kouzu, M.; Kasuno, T.; Tajika, M.; Yamanaka, S.; Hidaka, J., Appl Catal A: Gen, 334: 357-65(2008) 16） Islam, A.; Taufiq-Yap, Y. H.; Chu, C. H.; Ravindra, P.; Chan, E. S., Renew Energ, 59, 23-9(2013)