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Sains Malaysiana 40(6)(2011): 587594

Biodiesel Production via Transesterication of Palm OilUsin NaOH/Al

2O

3Catalysts

(Pengeluaran Biodiesel Melalui Pengtransesteran Minyak Sawitdengan Menggunakan Mangkin NaOH/Al2O

3)

YUN HIN TAUFIQ-YAP*, NURUL FITRIYAHABDULLAH & MAHIRAN BASRI

ABSTRACT

Due to the increase in price of petroleum and environmental concerns, the search for alternative fuels has gained

importance. In this work, biodiesel production by transesterication of palm oil with methanol has been studied in a

heterogeneous system using sodium hydroxide loaded on alumina (NaOH/Al2O

3). NaOH/Al

2O

3catalyst was prepared by

impregnation of alumina with different amount of an aqueous solution of sodium hydroxide followed by calcination in

air for 3 h. The prepared catalysts were then characterized by using x-ray diffraction (XRD), Fourier transform infraredspectrometer (FT-IR), Brunner-Emmett-Teller surface area measurement (BET), scanning electron microscopy (SEM)

and temperature-programmed desorption of CO2

(CO2-TPD). Moreover, the dependence of the conversion of palm oil

on the reactions variables such as the molar ratio of methanol/oil, the amount of catalysts used, reaction temperatures

and reaction times were performed. The conversion of 99% was achieved under the optimum reaction conditions. The

biodiesel obtained was characterized by FT-IR and the pour point was measured.

Keywords: Biodiesel; heterogeneous catalyst; palm oil; transesterication

ABSTRAK

Disebabkan oleh kenaikan harga minyak mentah dan keperihatinan terhadap alam sekitar, penyelidikan terhadap bahan

bakar alternatif telah menjadi lebih penting. Dalam kajian ini, pengeluaran biodiesel melalui pengtransesteran minyak

sawit dengan metanol telah dikaji dalam sistem heterogen menggunakan natrium hidroksida yang dimuatkan atas alumina(NaOH/Al2O

3). Mangkin NaOH/Al

2O

3telah disediakan dengan proses impregnasi alumina dengan larutan sodium

hidroksida dengan jumlah yang berbeza diikuti dengan pengkalsinan dalam udara selama 3 jam. Mangkin yang telah

disediakan kemudiannya dicirikan dengan menggunakan pembelauan sinar-X (XRD), spektrometer Fourier Transform

infra merah (FT-IR), pengukuran luas permukaan Brunner-Emmett-Teller (BET), imbasan mikroskop elektron (SEM) dan

Penyahjerapan CO2

Suhu Berprogram (CO2-TPD). Selain itu, kebergantungan penukaran minyak sawit kepada hasil

pada pembolehubah tindak balas seperti nisbah molar metanol/minyak, jumlah mangkin yang digunakan, suhu tindak

balas dan masa tindak balas turut dikaji. 99% hasil diperoleh di bawah keadaan tindak balas optimum. Biodiesel yang

diperoleh dicirikan dengan FT-IR dan takat tuang diukur.

Kata kunci: Biodiesel; mangkin heterogen; minyak sawit; pengtransesteran

INTRODUCTION

Biodiesel is a renewable fuel consists of fatty acidmethyl esters (FAME) derived throuh transestericationof veetable oils, animal fat and also recycles oil fromthe food industry with methanol. Biodiesel is reconizedas reen fuel with several advantaes; safe, non-toxicand bioderadable compared to petroleum diesel. It isoxyenated and essentially free of sulfur and aromaticsmakin it a cleaner burnin fuel with reduced emissionof SO

x, CO, unburnt hydrocarbons and particulate matter

(Chai et al. 2007). Moreover, usin biodiesel as a fuel ina car can ive many advantaes such as it is not harmful

to the environment, reduces the environmental effect of awaste product, and enery efcient. But, when comparedwith the cost of diesel obtained from petroleum, the

hih cost is the main drawback in biodiesel production.However, the cost of biodiesel could certainly be loweredby improvin the production process. The rst step in thisdirection could be represented by the use of heteroeneouscatalysts instead of homoeneous ones (Di Serio et al.2007).

Recently, biodiesel is mostly produced by atransesterication reaction of oil with an alcohol in thepresence of a catalyst, to yield mono-alkyl esters andlycerol, which are then separated, and puried (Akn& can 2007). Transesterication or alcoholysis is thedisplacement of alcohol from an ester by another in a

process similar to hydrolysis, except than alcohol is usedinstead of water (Meher et al. 2004). The reaction isrepresented by the eneral equation below:


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RCOOR1 +R2OH RCOOR2 + R1OHEster Alcohol Ester Alcohol

.

Transesterication is one of the reversible reactionsand proceeds essentially by mixin the reactants. However,the presence of a catalyst accelerates the conversion oftrilycerides to biodiesel (Meher et al. 2004).

Current technoloy processes for biodieselmanufacturin employ transesterication of trilycerideswith methanol usin homoeneous acid or base catalysts.The homoeneous acid-catalyzed process often useshydrochloric acid and sulfonic acid as a catalyst. Theproblem with this process is the costly separation of thecatalyst, corrosive to equipment and toxic (Chai et al. 2007;Kiss et al. 2006). Moreover, the reaction time is very lonand a hih molar ratio of methanol to oil is needed (30-150:1 mol %) (Xie et al. 2006). Potassium hydroxide andsodium hydroxide are usually used as a homoeneous base-

catalyst. These base catalysts show hiher performancefor obtainin biodiesel but, they also react with free fattyacids (FFA) to form unwanted soap by-products in whichan expensive separation is required (Chai et al. 2007; Kisset al. 2006). Since the homoeneous catalysts can causemany problems and increased the production cost, they canbe replaced by environmentally friendly heteroeneouscatalysts because of environmental constraints andsimplifications in the existin processes. Moreover,heteroeneous catalysts can be more easily separated andive place to hiher quality of ester products and lycerolby product. In this case, pure hih rade lycerol can be

obtained without expensive renin operations (Di Serioet al. 2007). Most heteroeneous catalysts employed fortransesterication are solid bases. Solid base catalystshave a hiher activity and faster reaction rate as comparedto solid acid catalysts. If the oil has a hih free fattyacid and water content, solid acid catalysts is enerallyused (Boz & Kara 2009). However, solid acid catalystsneed hih reaction temperature to complete the reaction.Nevertheless, one of the major problems associated withheteroeneous catalysts is the formation of three phaseswith alcohol and oil which leads to diffusions limitationsthus lowerin the rate of reaction (Mbaraka & Shanks2006). One way of overcomin mass transfer problemin heteroeneous catalysts is usin structure promotersor catalysts supports which can provide more specicsurface area and pores for active species where they cananchor and react with lare trilycerides molecules (Zabetiet al. 2009). Alumina has been widely used as a supportin catalysis processes owin to its extremely thermal andmechanical stability, hih specic surface area, lare poresize and pore volume.

Kim et al. (2004) reported on Na/NaOH/-Al2O

3for

the production of biodiesel from soybean oil. The biodieselyields reached 83% when methanol to oil loadin ratio 9:1

was used with the presence ofn-hexane as the co-solvent.Arzamendi et al. (2007) have studied the performance ofNaOH/Al

2O

3as a solid base catalyst for transesterication

of sunower oil to biodiesel. They found that, the asprepared catalyst is better than that of the calcined catalysts.For calcined catalysts, the oil conversion achieved about86% after 24 hours of reaction at 12:1 molar methanol/oil ratio. However, for the non calcined catalysts withthe reaction parameters same as the calcined catalysts,the conversion increased up to 99%. In another work,Xie and Li (2006) developed KI/ Al

2O

3to catalyze the

transesterication of soybean oil to biodiesel. The catalystwith 35 wt.% KI loaded on Al

2O

3and calcined at 773 K

for 3 h was found to be the optimum catalyst. The hihestconversion 96% reached when the reaction was carried outfor 8 hours, 2.5% catalyst amount and 15:1 methanol tosoybean oil molar ratio. Boz and Kara (2009) found thatKF/ Al

2O

3are the active catalyst in the transesterication of

canola oil with methanol and ive hihest yield of 99.6%at the end of 8 hours at 60C with methanol/oil molar ratioof 15:1 and catalyst amount of 3 wt.%.

In this work, a series of solid base catalyst consistinof NaOH supported on commercial alumina wereprepared for the transesterication of palm oil withmethanol in order to nd a proper support which can workbetter compared to homoeneous catalyst. Durin catalystpreparation, different amount of sodium compounds wereimprenated into alumina. A screenin of the reactioncondition has been carried out by examinin the effectof methanol/oil molar ratio, catalyst amount, reactiontemperatures and reaction times.

EXPERIMENTAL DETAILS

PREPARATION OF THE CATALYST

All the catalysts were prepared by imprenation of aluminawith an aqueous solution of sodium hydroxide. Aluminawas imprenated with 15 ml of different amounts sodiumhydroxide (45 and 50 wt.%) solutions. This imprenate wasdried overniht in oven. The catalysts were then calcined inair for 3 hours. The obtained catalysts were denoted as 45Na and 50 Na (before calcine) 45 NaC, and 50 NaC (aftercalcined). Finally, the prepared catalysts were characterizedby XRD, FT-IR, BET, SEM, and CO

2-TPD.

CATALYSTS CHARACTERIZATIONS

X-ray diffraction (XRD) analysis of all the synthesizedcatalysts was carried out usin a Shidmadzu diffractometermodel XRD 6000 employin CuK

radiation to generated

diffraction patterns at ambient temperature. The UniversalAttenuated Total Reflection method was applied fordeterminin IR spectra of the samples. Spectra wererecorded on Perkin Elmer model 100 Series instrumentwith scannin rane from 280 to 4000 cm-1. The BETsurface area of the catalysts was measured by performinnitroen absorption at 77 K. The experiment was done by

usin Thermo Finnian Sorptomatic Instrument model1990. Surface structure and morpholoy of the catalystswas observed under a scannin electron microscope


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589

(SEM) using LEO 1455 VP electron microscope operated atacceleratin voltaes of 30 kV. Microraphs were recordedat various manications. Finally, the basic strenth ofthe catalysts was evaluated by temperature-prorammeddesorption of CO

2(CO

2-TPD) was performed by usin the

Thermo Finnian TPD/R/O 1100 series instrument.

TRANSESTERIFICATION REACTION

The typical reaction was carried out in a 250 mL round-bottom ask, with a thermometer, mechanical stirrin,and coil condenser. The system was preheated to 60C,and then the desired amount of palm oil was added. Molarratio of methanol to palm oil used was 15:1. When thesystem reached the desired temperature aain, methanoland 3 wt.% catalyst were added while stirrin at 1200rpm in order to keep the system uniform in temperatureand suspension. The reaction was performin for 3 h.

Samples were taken out and catalyst were separatedfrom the reaction product by centrifuation. The reactionproduct was then poured into a separation funnel andwas left overniht for settlement. In this process, the twolayers were formed, whereby the upper layer was thebiodiesel and lycerin would settle down at the bottomof the separation funnel. The synthesized biodiesel wascharacterized by FT-IR and the pour point was measuredaccording to ASTM D97 standard methods.

RESULTS AND DISCUSSION

CATALYST CHARACTERIZATIONS

XRD analyses have been performed to obtain moreinformation about the catalyst structure. Fiure 1 showsthe XRD patterns of NaOH/Al

2O

3catalyst (before and

after calcination) with different loadin amounts ofNaOH. XRD patterns shows that 45Na catalyst had formas semi amorphous and almost identical to the support,Al

2O

3unless that the intensity of the peak was decreased

indicatin the ood dispersion of NaOH on alumina. Forthe other catalysts, several diffractions peaks clearly visibleshowin the presence of NaOH and sodium aluminate(NaAlO

2). These indicate that NaOH has reacted with the

support, Al2O

3ivin rise to the formation of aluminates

that oriinated the stroner basic sites of the catalysts(Arzamendi et al. 2007; Kim et al. 2004).

To further understand the correlation between thecatalysts composition and calcination temperature,characterization by FT-IR was carried out. From the FT-IRspectra shown in Fiure 2, all the catalysts showed a veryintense broad band at 3300 to 3700 cm-1 that correspondinto O-H stretchin vibration of the hydroxyl roupsattached to Al

2O

3. However, the bands become weaker

after calcination. Additionally, there was another band at1450 cm-1 which were probably attributed to carbonate(Wan et al. 2009). But when the catalysts were calcined,the intensity of this band was radually decreased.

From the results shown in Table 1, the BET surface areaof the synthesized catalysts was found to be lower thanthe pure alumina. From a qualitative point of view, thiswas an expected result since in heteroeneous catalysis;the reduction of the specic surface area of the supportis a well documented consequence when a catalyst waspromoted with alkali metals (Mross 1983; Perrichan& Durrupty 1988; Szczepaska & Malinowski 1969).These results are not surprisin since surface and poresof alumina were covered by sodium compounds durinthe imprenation step (Arzamendi et al. 2007; Boz &Kara 2009). However, after calcination, there is a slihtlyincreased in the BET surface area of the catalysts. From

2 (Deree)

Intensity(a.u

.)

FIgURE 1. XRD patterns for support, Al2O

3and the prepared catalysts before

(45 Na, 50 Na) and after calcined (45 NaC, 50 NaC)


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590

The results from BET surface area were furtherconrmed by SEM imaes. From the SEM imaes in Fiure3, it clearly showed that before calcined, the catalysts (45Na and 50 Na) were still in bulky form. However, a plate-like form of catalysts was observed after calcination (45NaC and 50 NaC). The result suested that the shape ofa catalyst can affect the surface area.

The CO2-TPD proles for all the tested catalysts are

displayed in Fiure 4. From the CO2-TPD analysis, a very

broad desorption band can be observed extendin from450 to 630C that could be assined to stroner basic sites(Albuquerque et al. 2008; Di Serio et al. 2006). However,amon the four catalysts that have been presented in

Wavenumber (cm-1)

Transmitance(a.u.

)

FIgURE 2. FT-IR spectra for all synthesize catalysts

TABLE 1. BET surface areas of both non-calcinedand calcined catalysts

Catalyst BET Surface Area(m2/)

Al2O

3

45 Na

50 Na

45 NaC

50 NaC

136

37

45

44

51

here, it can be concluded that calcination has a positiveeffect on the prepared catalysts.

FIgURE 3. SEM imaes of before and after calcined catalysts

50 NaC

45 NaC

50 Na

45 Na


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591

this Fiure, 50 NaC ave the stronest basic sites. Thisconclusion has been made due to the CO

2desorption

peak occurred at hiher temperature and lare area ofCO

2desorption peak which suested that 50 NaC has the

hihest basic concentration from the other catalysts.

TRANSESTERIFICATION REACTION

The FT-IR result shows the quality of the biodiesel (Fiure5). The palm oil and the biodiesel were analyzed usin FT-IR. In the transesterication of palm oil, the FT-IR spectraof palm oil and biodiesel are very similar because of hihchemical similarities that exist amon trilycerides andmethyl ester. However, small different are observed in

this three reion (C=O ester, CH3and C-O ester) because

biodiesel had a different compound bonded compared tothe palm oil. The stron ester peaks at 1750 cm -1 (C=Oester) and at 1170-1200 cm-1 (C-O ester) are clearlypresent in the spectra. Outside these two reions, anothercharacteristic peak that indicates the presence of CH

3roup

in the mixtures of methyl ester can be observed at 1445cm-1 (Siatis et al. 2006).

METHANOL/OIL MOLAR RATIO

The stoichiometric ratio for transesterication requires 3moles of methanol for each mole of to yield 3 moles offatty acid methyl ester and 1 mole of lycerol. Since the

Temperature (C)

Intensity(a.u.)

FIgURE 4. Temperature-Prorammed Desorption of Carbon Dioxide (CO2-TPD)

proles of all synthesized catalysts and support

Wavenumber (cm-1

)

Transmittance(a.u.

)

FIgURE 5. FT-IR spectra for palm oil and synthesized biodieselfrom various prepared catalysts


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transesterication reaction is reversible reaction, excessmethanol is required to drive the reaction towards product.As represented by Fiure 6, when methanol/oil molar ratiowas increased, conversion was increased considerably. Themaximum conversion was obtained when the methanol/oil ratio reach 15:1. There is evident that to elevate theconversion, an excess methanol feed was effective onlyto a certain extent (Kim et al. 2004; Wan et al. 2009; Xieet al. 2006; Xie & Li 2006).

CATALYST AMOUNT

The inuence of catalyst amount on the conversion ofbiodiesel was investiated. The catalyst amount wasvaried in the rane of 1-5 wt.%. As shown in Fiure7, the conversion was increased with the increased ofcatalyst amount from 1 to 3 wt.%. However, with furtherincreased in the catalyst amount the conversion was slihtly

decreased. This was probably because the slurry (mixtureof catalyst and reactants) become too viscous ivin riseto a problem of mixin and demand of hiher power

consumption for adequate stirrin (Kim et al. 2004; Wanet al. 2009; Xie et al. 2006; Xie & Li 2006).

REACTION TIME

The inuences of reaction time on palm oil conversion

are illustrated in Fiure 8. The reaction time was variedin the rane 1-7 hours. As can be seen, the conversion wasincreased steadily in the rst 3 hours and reached 99%conversion. The conversion thereafter remained nearlyconstant after 3 hours of reaction time.

REACTION TEMPERATURE

Transesterication can occur at different temperaturesdependin on the types of catalyst and alcohol used.The inuenced of reaction temperature on conversion ofpalm oil to boidiesel was investiated with four differenttemperature. From the result shown in Fiure 9, theconversion increased as the reaction temperature increasedand ive the hihest conversion of 99% at 60C. However,

Methanol/oil molar ratio (mol/mol)

Conversion(%)

FIgURE 6. Inuence of methanol/oil molar ratio on the conversion. Reaction condition:catalyst amount 3 wt.%, reaction time 3 hours, reaction temperature 60C

Catalyst amount (wt.%)

Conversion(%)

FIgURE 7. Inuence of catalyst amount on the conversion. Reaction condition: methanol/oil molar ratio 15:1, reaction time 3 hours, reaction temperature 60C


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when the temperature reaches to the boilin point ofmethanol, a lot of methanols bubbles were formed henceinhibit the mass transfer on the phase interface thus lowerthe conversion (Zabeti et al. 2009).

POUR POINT

The prepared palm oil methyl ester was evaluated for theirpotential as diesel fuel based on pour point characteristic.Pour point is dened as the lowest temperature that theproduct still can be poured by ravity (May et al. 2005).From this study, the pour point of methyl ester of palm oilprepared is 10C. The pour point of this methyl ester wasfound to be comparable with Malaysian petroleum dieseland it also was found to be in reasonable areement withthe ASTM biodiesel standard.

CONCLUSION

Amon all the synthesized catalysts in this work, thecatalyst with 50 wt.% sodium hydroxide loaded on

alumina and calcined in air for 3 h was found to be theoptimum catalyst which ave the best catalytic activity.Formation of sodium aluminate by loadin sodiumhydroxide on alumina oriinated the active basic sites ofthe catalysts. The hihest conversion 99% reached whenthe reaction was carried out at 60C with molar ratio of

methanol/oil 15:1, reaction time 3 h and catalyst amount3 wt.%. Moreover, the biodiesel synthesized also has apour point that in reasonable areement with the ASTMbiodiesel standard.

ACKNOWLEDgEMENT

Financial support from Universiti Putra Malaysia throuhgraduate Research Fellowship (for A.N. Fitriyah) isratefully acknowleded.

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Reaction time (h)

Conversion(%)

FIgURE 8. Inuence of reaction time on conversion. Reaction condition: molarratio methanol/oil 15:1, catalyst amount 3 wt.%, reaction temperature 60C

Temperature (C)

Conversion(%)

FIgURE 9. Inuence of reaction temperature on conversion. Reaction condition:methanol/oil molar ratio 15:1, catalyst amount 3 wt%, reaction time 3 hours


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Tauq Yap Yun Hin* & Nurul Fitriyah binti AbdullahCentre of Excellence for Catalysis Science and Technoloy andDepartment of Chemistry, Faculty of ScienceUniversiti Putra Malaysia

43400 UPM Serdan, SelanorMalaysia

Mahiran BasriDepartment of ChemistryFaculty of Science, Universiti Putra Malaysia43400 UPM Serdan, Selanor,Malaysia

*Correspondin author; email: [email protected]

Received: 15 April 2010Accepted: 25 October 2010

08 yun hin taufiq

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