Evaluation of direct transesterification of microalgae using microwave irradiation

Evaluation of direct transesterification of microalgae using microwave irradiation

Accepted Manuscript Evaluation of direct transesterification of microalgae using microwave irradiation Chee Loong Teo, Ani Idris PII: DOI: Reference: ...

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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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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

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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

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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

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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

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sustainable renewable fuel. It has all the excellent properties such as highly biodegradable,

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minimal toxicity or non-toxic and environmental friendly. However the production of microalgae

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biodiesel has its share of problems in terms of the high cost involved during harvesting,

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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

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consumed in biodiesel conversion from microalgae biomass (Lardon et al., 2009). Generally,

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biodiesel production from microalgae involves a 2 step extraction–transesterification processes

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where the microalgae was first harvested and dried, and then lipids extracted followed by the

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transesterification process. Therefore efforts were made by several researchers to eliminate

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separate extraction step by introducing one step transesterification, in situ transesterification or

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direct transesterification (DT) and also a sequential 2 stage DT. This technology also eliminates

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the dewatering process and also contributes to the reduction in the amount of extracting solvent

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used (Wahlen et al, 2011).

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Johnson and Wen (2009) revealed that the one step transesterification used on Schizochytrium

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limacinum produced higher yield of biodiesel (63.47%), consumed less time than conventional

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methods and the potential of lipid loss can be avoided during extraction process. Recently, there

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are reported studies on the optimisation of the one step transesterification investigating the

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influence of a variety of parameters such effect of catalyst concentration, amount of methanol,

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reaction temperature and reaction time (Patil et al., 2011; Zhang et al., 2010; Jeong et al., 2009)

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using response surface methodology.

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In addition production of biodiesel from wet marine microalgae is fast becoming the

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solution to dewatering problem. Lee et al. (2010) have reported that microwave irradiation

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allows extraction of 80% crude oil from wet microalgae by chloroform and methanol as

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extracting solvents. The effect of microwave irradiation is very much dependent on the

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intensity/frequency of the microwave irradiation. Reaction rates were enhanced (2 min instead of

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2 h process reaction) upon application of radio frequency microwave energy; therefore offering a

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rapid and simple way to access the biofuel. The field of radio frequencies range from very high

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frequency (VHF) (30 -300 MHz to ultra high frequency (UHF) (300 and 3000 MHz) while the

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term microwave is typically used for frequencies between 3 and 300 GHz (David, 2012).

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In the previous study, the microwave irradiation assisted heating were proven to increase

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the yield of lipid extraction from the marine microalgae in a variety type of extraction techniques

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such as Hara and Radin, Folch, Bligh and Dyer and Chen method (Teo et al, 2014). . This is

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because in conventional heating; heat transfer occurs from the outside to the inside whilst in

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microwave heating solvent extraction, the mass and heat transports occur from the inside of the

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extracted material to the bulk solvent (Virot et al., 2008). While, microwave heating is a non-

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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

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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

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microwave energy and convert it into heat creates pressure gradients causing cavitation to occur

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thus rupturing the cell walls spilling out lipids (Choi et al., 2006; Amarni & Kadi, 2010).The wet

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microalgae and polar solvents when placed under microwaves which consists of oscillating

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electric field were able absorb heat directly causing molecules to vibrate, generates inter and

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intra-molecular friction. The combination of molecular oscillation, friction, collision and

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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

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membranes causing lipids to diffuse out easily and rapidly. (Wahihin et al., 2014) Microwave

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irradiation is an efficient technology because the cost of microwave heating is approximately 67

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percent less than conventional heating. (Wahidin et al., 2014) and it can be scaled up easily thus

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industrial application is viable (Amaro et al., 2011).

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However the potential of applying microwave irradiation in direct transesterification (DT)

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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

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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

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used is clearly described in the methodology section and the yields obtained using this technique

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are compared with the conventional heating OST and the TST process.

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2. Materials and Methods

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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

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(9000rpm, 6minutes). The supernatant consisting of the culture medium was removed and the

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concentrated microalgae which contain less than 20% water (from 20 litres culture) were

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collected.

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2.4 Direct transesterification (DT)

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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

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mixture was then heated to 90 oC for 40 min. The transesterification was performed in the water

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bath with constant shaking at 120 rpm.

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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

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methanol and the first catalyst (NaOH) was poured into a round bottom type flask containing

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concentrated microalgae. The mixture was heated at 90 oC in a water bath with constant shaking

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at 120 rpm. After 20 min., the mixture of methanol and HCl was added and the solution was

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continuously heated in the water bath with constant shaking at 120 rpm for another 20 min. The

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process was repeated using 3 other catalysts listed as follows:

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i)

Methanol plus HCl (90 oC, 20 min), then methanol plus NaOH (90 oC, 20 min)

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ii)

Methanol plus NaOH (90 oC, 20 min), then methanol plus H2SO4 (90 oC, 20 min)

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iii)

Methanol plus H2SO4 (90 oC, 20 min), then methanol plus NaOH (90 oC, 20 min)

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2.4.3 Enhancing the OST and TST via microwave irradiation heating

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The transesterification processes in section 2.4.1 and 2.4.2 were repeated. However, the

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flask was placed in the cavity of the microwave. During the transesterification process, a

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condenser was used in order to prevent loss of solvent due to vaporization. The temperature of

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condenser was maintained between 15-16 oC via chiller (Julabo, 32-ME) during the whole

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process. The experiments were performed in MAS-II microwave synthesis workstation (Sineo

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Microwave Technology Co. Ltd, 1000W) with an operational frequency of 2450 MHz).

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Temperature of reaction mixture was measured directly by using infrared (IR) thermocouple and

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maintained at 65°C and 800watt. The homogeneity of mixture was ensured using a magnetic

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stirrer with speed maintained at 400rpm. The reaction period in the MWTST took 5 minutes for

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each single step while in the MWOST the reaction time was kept to 10 minutes for the whole

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process

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2.5 Conventional Process

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The results of the MWOST, MWTST, OST and TST were compared with the normal

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conventional method of biodiesel extraction which involved the step by step process of lipid

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extraction followed by transesterification process which is detailed out in the following section.

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2.5.1 Lipid extraction

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Wet microalgal biomass (200 ml) was mixed with methanol-chloroform (1:2 v/v) for

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lipid extraction according to Bligh and Dyer method (Bligh EG and Dyer WJ, 1959). The

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mixture was heated in the oven at 100oC for 2 hours. The mixture was then left to cool to room

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temperature. After the lipid extraction the methanol-chloroform phase that contains the extracted

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lipids was centrifuged at 4000 rpm for 5 minutes and then separated using separating funnel.

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Then, the solvent containing lipid extracted was evaporated by a rotary evaporator.

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2.5.2

Alkali-based Transesterification

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Methanol was mixed with 0.5g of NaOH and stirred for 20 minutes at 400 rpm at

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approximately 65°C. The ratio of methanol to oil in the mixture was kept to 6:1. The mixture of

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catalyst and methanol was then poured into the conical flask containing the algae oil so as to

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initiate the transesterification process. The conical flask was stirred continuously for 3 hours at

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300 rpm and allowed to settle for 16 hours in order to obtain 2 separate layers; the supernatant

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layer (glycerol) and sediment layers (biodiesel). The biodiesel was separated carefully from the

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sediment layer by a flask separator and washed using 5 % water until the entire methanol is

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removed. The biodiesel was dried using dryer and kept under running fan for 12 hours. The

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percentage of efficiency was calculated according to equation (1) (Zayed and Jehad, 2014)

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Produced biodiesel

Eficiency % Initial crude oil weight

(1)

190 191

2.6

Gas Chromatography (GC) analysis of fatty acid methyl esters (FAME)

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Separation and identification of FAME were performed and analyzed using gas

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chromatography (GC) (Agilent Technologies, 7820A) and HP-88 capillary column (60 m x 0.25

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mm x 0.2µm) using hydrogen as the carrier gas at 40 ml/minutes. The column temperature was

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set at 220 ºC as maximum temperature. Both of the injector and flame ionization detector (FID)

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temperature were set at 220ºC. The back inlet was set at splitless mode and 220ºC as initial

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temperature. The column initial temperature was set at 80oC during the initial 2 minutes; the

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thermal gradient was 220 ºC at a rate of 13 ºC per minutes, the post temperature at 50 ºC in 2

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minutes (Teo et al., 2014).

200 201

3. Results and Discussions

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3.1 Comparison of conventional, two step and one step transesterification

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Figure 1:

204 205

Figure 1 shows that the transesterification efficiency for the DT using

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conventional heating OST and TST and the conventional process (defined as control; C). The

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OS1 (NaOH) biodiesel production method gave the lowest efficiency (13.46%) followed by the

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second lowest OS2 (HCl) method. This is probably due to the insufficient extraction and

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transesterification was performed on limited lipids extracted in the OST method. The low

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extraction yield was probably contributed by the insufficient extraction using water bath heating.

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The findings revealed that a single catalyst on its own in conventional heating OST could not

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achieve high efficiency. Similar results were obtained by Laurens et al.(2012) who reported that

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CH2ONA when used alone as a catalyst in the OST did not produce any biodiesel and suggested

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TST using combined catalysts (CH3ONa/BF3) for higher biodiesel yields (Laurens et al., 2012).

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Although, the cost of NaOH as the catalyst is cheaper than acid catalyst but it is highly

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hygroscopic and tend to absorb moisture from air during storage and forms water when react in

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the alcohol which ultimately influenced the yield (Leung and Guo, 2006). In addition, the

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hydrolysis and saponification which occurred when alkali catalyzed transesterification was used

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tend to reduce the yield of biodiesel (Mardina et al., 2013). When H2SO4 (OS3) was used as the

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catalyst the biodiesel yield was slightly improved when compared with HCl (OS2).

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However the higher biodiesel yields were obtained when TST was used using TS3 catalysts

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(NaOH + H2SO4) and TS1 catalyst (NaOH + HCl) achieving 28.85% and 30.85 % respectively.

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These catalysts combination in TST tend to have a synergistic effect; increase the hydrolysis rate

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of cell by using NaOH and promotes transesterification of lipids to biodiesel via H2SO4 in the

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second stage previously explained by Griffiths et al., (2010). When acid catalyst was used in

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biodiesel transesterification, the fatty acids are protonated by the acid and become tetrahedral

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intermediates with methanol which are then easily converted to biodiesel. If the water is present

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in the reaction, it will combine with acid catalyst leading to a reversible acid catalyst deactivation

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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

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initial stage lead to higher biodiesel yield. Upon comparing OS1 and TS4, it was observed that

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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

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cases it was observed that the microwave irradiation has enhanced the one step and two step

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transesterification. A similar trend was observed for the different catalyst and the TST was

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observed to be better. However the use of microwave heating has increased the efficiency yields

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by many folds (5%-43.37%). The application of microwave irradiation heating allows heat to be

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directly transferred to the microalgae and the rapid oscillations of the molecules tend to disrupt

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the cell walls of microalgae (Wahidin et al., 2014) thus releasing lipids. The microwave

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irradiations also promote the implosion of cavitated bubbles inside and outside the marine

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microalgae causing more crude oil to be extracted out during the reaction (Teo et al., 2014).

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Cavitation can be defined as the generation, subsequent growth and collapse of the cavity by

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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

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microwave irradiation thus rupturing the cell walls. The high amounts of lipids released allowed

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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

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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

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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

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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