Kinetic Study on Esterification of Oleic Acid with Ultrasound Assisted

Available online at www.sciencedirect.com

ScienceDirect Procedia Environmental Sciences 23 (2015) 78 – 85

International Conference on Tropical and Coastal Region Eco-Development 2014(ICTCRED 2014)

Kinetic Study on Esterification of Oleic Acid with Ultrasound Assisted Dianita Dini Suprarukmi, Bagus Agang Sudrajat, Widayat* Department of Chemical Engineering, Faculty of Engineering,Diponegoro University Jl. Prof. H. Soedharto,SH, Tembalang, Semarang 50275, Indonesia

Abstract As the limitation of nonrenewable energy resourcesand for covering energy demand in future, it is important to search and apply the renewable energy resources which is effective, efficient and sustainable. The literatures of kinetic reaction of biodiesel from oleic acid arerare and most literatures used conventional method. The objective of this research isto examine kinetic reaction of oleic acid esterification which is assisted by ultrasonic wave. Variables that used in this research are catalyst concentration and reaction temperature. Oleic acid and methanol are reacted inside three neck flask and assisted by ultrasonic wave. Gas Chromatography is used to identify contain of FAMEin biodiesel. The highestconversion for the temperature variable is 86.67% at 70 oC, and the highest conversion for the catalyst variable is 87% at 1.4% wt. Model of kinetic reaction is reversible second order reaction with R2 0.986 for temperature variable and 0.975 for catalyst variable. Crown © 2015 PublishedbybyElsevier ElsevierB.V. B.V. This is an open access article under the CC BY-NC-ND license © 2014Copyright The Authors.Published (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of scientific committee of the ICTCRED 2014. Peer-review under responsibility of scientific committee of the ICTCRED 2014 Keywords:energy; biodiesel; oleic acid; ultrasonic wave; reaction kinetic

1. Introduction Non-renewable energy such as fossil fuel is used to fulfil energy demand. With the limitation of non-renewable energy resources, to fulfil energy demand in future, it is important to search and apply renewableenergy which is efficient, effective, sustainable and environmental-friendly. One of that solution is biodiesel. Biodiesel is one of the potential alternative fuel to replace diesel oil because it contains mono-alkyl esters of long chain fatty acids that is derived from vegetable oil or animal fat [1]. Biodiesel can be produced by triglycerides with based catalyst or also

* Widayat. Tel.: +6224-7460058; fax: +6224-764-80675. E-mail address:[email protected]

1878-0296 Crown Copyright © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of scientific committee of the ICTCRED 2014 doi:10.1016/j.proenv.2015.01.012

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can be produced by free fatty acid by using acid catalyst [2]. Biodiesel production processes that have been researched were homogenous catalyst trans-esterification and esterification [3], heterogeneous base-catalyst [4], enzymatic trans-esterification [5], non-catalyst supercritical transesterification[6], microwave-assisted trans-esterification [7], and ultrasound-assisted [8]. Base-catalyst transesterification has deficiencies in catalyst separation so that need large energy demand. Saponification reaction also occur in base-catalyst process if there is no pretreatment of the raw material. Acid-catalyst trans-esterification has low reaction rate. Enzymatic trans-esterification has high cost. Non-catalyst supercritical trans-esterification has difficult condition and high cost. Yield and reaction time of microwave-assisted trans-esterification are lower than ultrasound assisted production. Ultrasound-assisted production is an efficient method and haveshort reaction time than conventional method. With this method, high conversion (92%) is obtained in 70 second whereas for 91% conversion needs 1 hour reaction time on conventional method [9]. Generally, biodiesel production needs reactor as a place to convert materials to the biodiesel and for biodiesel production which is assisted by ultrasound. To make and design reactor, it is important to know the kinetic model of reaction, and after that volume of the reactor can be calculated. Research about reaction kinetic of esterification oleic acid and methanol has been done by Cardoso [10]. He used SnCl and H2SO4 as a catalyst in a batch reactor for 2 hours reaction time, and the yield was 90 %. Reaction model that he got was first order reaction. Aulia [11]studied about trans-esterification of cooking oil with KOH as catalyst, obtained reaction model which fit with second order reversible reaction, and the yield was 89%. The objectives of this research are to know the type of the reaction is it reversible or irreversible, is first order or second order, and also made the equation of kinetic reaction model from acid-catalyst esterification reaction of oleic acid and methanol assisted by ultrasound. 2. Materials and Methods First,three-neck flaskarranged withcondenser andput inan ultrasoniccleaner. The research used oleic acid as raw material for biodiesel production and reacted with methanol. Before oleic acid and methanol were reacted, 1.2% wt. H2SO4 was added to oleic acid, and both of raw materials were heated according to variable temperature on separated place. After oleic acid and methanol reach the temperature variable, both of them put into three neck flask for esterification process and then assisted by ultrasound. Reaction time began after materials were pouredintothreeneck flaskandevery 9 minutes 10mlsamples were takenforanalysis ofresidualfattyacid and stopped after 45 minutes. The temperature which gave highest conversion from experiment of temperature variable was used as fix temperature for catalyst loading variable. GasChromatography was used to analyze FAME content in biodiesel. Theresidualfattyacid that would be usedforcalculatingk value was calculated by titrimetric analysis. Sample was taken 10 ml and thenaddedneutralethanol and after that, the mixtures were cooledat room temperaturein order tostopthe reaction. Add3drops ofindicatorPPandthe solutionswere titratedbyKOHforFFA contentanalysis.Normality of oleic acid calculated by:

VOleic u N Oleic

VKOH u N KOH

(1)

Normality of residual oleic acid calculated by this equation:

VSample u N Sample VKOH u N KOH

(2)

Methyl ester conversion calculated by:

X

N Oleic - N Sample N Oleic

(3)

FAME was calculated from oleic acid because FAME was formed from oleic acid and methanol. With assumption

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that all of methanol reacted with oleic acid, so the amount of FAMEis similar to amount of the oleic that reactedandit can be calculated by:

N Fame

N InitialOleic - N Re sidualOleic

(4)

To analyse the kineticreaction for this study, the result data of methyl ester conversion was being calculated based on the chosen model. After made a graph from the model, will be obtained k value from the slope of the graph.

Fig 1. Main instruments for esterification process 3. Results and Discussion The kinetic reaction model of esterification was tested by R2value in four types of kinetic reaction rate model. Models that tested in the experiment are for first or second order irreversible and reversible reaction. Based on experiment results and model that being tested, data of methyl ester conversion can be calculated to make a graph, time vs conversion.After that, for choosing model and test the quality of themodel, we can use R2 value. Chosen model of reaction order is a model that has R2 value nearest 1. Table 1. R2 value in various model. R2 value

R2 value

T variable

Catalyst Variable

0.9038

0.8822

2 Order irreversible

0.9082

0.8874

1st Order reversible

0.9859

0.9654

2nd Order reversible

0.9860

0.9752

Assumption 1st Order irreversible nd

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Based on the calculation of R2 value, the model which has R2 value nearest 1 is second order reversible reaction with R2 value 0.986 for temperature variable and 0.9752 for catalyst loading variable. So, the model that being used is reversible model. 3.1. Temperature effect to reaction rate Figure 2 showed that higher temperature also gave higher conversion. The maximum conversion for this variable is 86.67% at temperature 70 0C. This trend is same as in the literature. In Mandake observation [12], trend with increased temperature, followed by increasing of conversion. Cardoso [10] made oleic acid esterification with SnCl2 as catalyst and also get the same trend. Table 2 showed, based on arrhenius equation, increased temperature followed by increaseof k value. With increased k value, the reaction rate become faster and the conversion that obtained was increased [13]. That phenomenon is appropriate with Arrhenius equation

k

Ae

§ Ea · ¨ ¸ © RT ¹

(5)

Wherek = kinetic reaction value (t-1), Ea = activation energy (kJ/mol), T = absolute temperature (K), A = frequency factor (t-1)

Fig 2. Effect of temperature Table 2.k value at various temperature T(oC )

k1 (min-1)

k2 (lt/mol.min)

30

38 x 10-3

1.66 x 10-3

40

49 x 10

-3

1.68 x 10-3

50

67 x 10-3

60 70

2 x 10-3

112 x 10

-3

3.2 x 10

215 x 10

-3

5 x 10-3

Mean R2

0.9860 -3

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3.2. Effect of catalyst loading The effect of catalyst loading is shown in figures 3. The catalyst loading was varied from 0.8 to 1.6 % wt for esterification reaction with keeping the temperature at 70 0C. The maximum conversion for this variable is 87% at catalyst loading 1.4% wt.

Fig 3. Effect of catalyst loading Generally, with increasingcatalyst concentration, the maximumconversionalso increasedaccording to theresearch conductedbyShakoor [13]andMandake[12]. It was found that with an increasing in catalyst loading the conversion of acid increases with the increase in the active sites. At higher catalysts loading the rate of mass transfer is high and therefore there is no significant increase in the rate of reaction [13] as shown in table 3. However,at a concentration catalyst of1.6 %, the conversionis smallerthantheaddition of1.4%. The same resulthappened inthe research of esterification of oleicacid and ethanol whichhas beenconducted bySetyawardhani[14]. ResearchersusetheH2SO4 as catalyst with concentration of0.09 to 0.9% by weight. Table 3.k value for various catalystloading Catalyst loading (% wt.)

k1 (min-1)

k2 (lt/mol.min)

0.8

164 x 10-3

4.5 x 10-3

1

142 x 10-3

3.6 x 10-3

214 x 10

-3

5.1 x 10-3

134 x 10

-3

3 x 10

153 x 10

-3

4.2 x 10-3

1.2 1.4 1.6

Mean R2

0.9752

-3

3.3 General form of kinetic modelling In 1889, Arrhenius suggested an empirical equation which describes temperature effect to the constantareaction rate. From Arrhenius equation, there were two factors, A and Ea, and both known as Arrhenius parameter. Plot from log k to 1/T is linear for some reaction and for normal temperature [15] The equation analogue to linear equation, which often symbolize with y = mx + c, then the relation between activation energy, temperature, and reaction rate can be analysed in graph form ln k vs 1/T with –(Ea/RT) as the

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gradient and ln A as the intercept [15].Calculation of data experiment, obtained graph which is shown on figure 4.

Fig4. Relation between k and 1/T From graph slope can be calculated Ea value using this equation:

Slope

Ea Ea Ea Ea



Ea R

(6)

 slope u R (4405) u 8.314 36623.17 J mol 36.623 J mol

(7)

For A value can be determined from intercept of graph above [15]

ln A 11.12 A 67507.9 Then model relation between equation and reaction rate constant to temperature is:

 rA

dX A  dt

C Ao 67507.9 u e

2 2 2 2 36.623ª 1 X A  X Ae   X A 1 X Ae º » « 2 RT «¬ X Ae »¼

(8)

3.4 Qualitative analysis of methyl ester using Gas Chromatography This analysis is to identify FAME contain in biodiesel from experiment result. FAME from temperature variable has retention time 1.71:2.1:9.8 and 10.98. For catalyst concentration variable has retention time 1.66:2.06:9.77 and 10.94. Beside two picture from GC analysis result, from quantitative analysis sample which been analysed in

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instrument chemistry laboratory of Chemical Engineering Faculty MalangPolytechnic, there is Methyl Ester contain in sample of temperature variable about 83.83% and for the catalyst loading variable is 86.9%.

Fig5. GC Analysis of Methyl Ester for T=700C, 1.2 % wt. catalyst

Fig 6. GC Analysis of Methyl Ester for T=700C, 1,4 % wt. catalyst

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4. Conclusion Kinetic reaction model in this experiment uses reversible order 2 reaction with R2 value 0.986 for temperature variable and 0.9752 for catalyst loading variable. With increased reaction temperature then the maximum conversion which obtained is higher, and also obtained maximum conversion 0.86. With increased catalyst concentration, the maximum conversion which obtained is higher, and also obtained maximum conversion 0.87. Equation model between reaction rate constant to temperature is shown in equation 8.

Acknowledgements

The support from Department of Chemical Engineering Diponegoro University, and C-BioreLaboratory where this research was taken place are gratefully acknowledged

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