Biodiesel Production from Refined Palm Oil using ... - CORE

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ScienceDirect Energy Procedia 79 (2015) 697 – 703

2015 International Conference on Alternative Energy in Developing Countries and Emerging Economies

Biodiesel Production from Refined Palm Oil using Supercritical Ethyl Acetate in A Microreactor Nanthana Sootchiewcharna, Lalita Attanathob, Prasert Reubroycharoenc,d* a

Department of Petrochemical and Polymer Science, Faculty of Science, Chulalongkorn University, Thailand b Energy Technology Department, Thailand Institute of Scientific and Technological Research, Thailand c Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Thailand d Center of Excellence on Petrochemical and Materials Technology, Chulalongkorn University Research Building, Thailand

Abstract This research investigated the production of Fatty Acid Ethyl Ester (FAEE) from refined palm oil with ethyl acetate at supercritical conditions in a microreactor, which produced triacetin as the by-product instead of glycerol. The experiments were carried out in a microreactor at the reaction temperature in the range of 330°C to 370°C, with a pressure of 200 bar and an oil to ethyl acetate molar ratio of 1:50. Results showed that the residence time and temperature had a positive effect on FAEE and biodiesel yield, with the high FAEE yield of 63.6% and biodiesel yield of 78.3%. © Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ©2015 2015The The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of 2015 AEDCEE. Peer-review under responsibility of the Organizing Committee of 2015 AEDCEE

Keywords: biodiesel; interesterification; microreactor; supercritical ethyl acetate; refined palm oil

* Corresponding author. Tel.: +66-2218-7523; fax: +66-2255-5831. E-mail address: [email protected].

1876-6102 © 2015 The Authors. Published by Elsevier Ltd. 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 the Organizing Committee of 2015 AEDCEE doi:10.1016/j.egypro.2015.11.560

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Nanthana Sootchiewcharn et al. / Energy Procedia 79 (2015) 697 – 703

1. Introduction Biodiesel is an alternative fuel derived from vegetable oil or animal fat by transesterification. During the transesterification, triglyceride reacts with methanol or ethanol to produce ester as a main product and glycerol as a by-product [1-3]. The increase of biodiesel production leads to oversupply of glycerol and subsequently manages as a waste. In order to avoid the glycerol waste elimination problem, the researchers have focused on the glycerol free process for producing biodiesel. Consequently, the interesterification processes of vegetable oil with methyl acetate or ethyl acetate have recently been proposed [4]. As shown in Fig. 1, biodiesel can be produced by interesterification of triglycerides with ethyl acetate. The replacement of ethanol with ethyl acetate produces triacetin as by-product, which has a higher value than glycerol and can also be used as additive in biodiesel fuel [4]. Moreover, the mixture of fatty acid ethyl ester (FAEE) and triacetin can be used together as biodiesel fuel (BDF). CH2

OCOR1

R1COOCH2CH3

CH

OCOR2 + 3 CH3COOCH2CH3

R2COOCH2CH3 + CH

CH2

3

3

R COOCH2CH3

OCOR

Triglycerides

Ethyl acetate

FAEE

CH2

OCOCH3 OCOCH3

CH2

OCOCH3

Triacetin

Fig. 1. Reaction stoichiometry between triglyceride and ethyl acetate to produce FAEE and triacetin.

Currently, there are several methods for producing biodiesel but most of them required the long residence time to achieve the reasonable biodiesel yield. To overcome this problem, the use of microreactor technology is one of the interesting methods. Microreactor is defined as miniaturized reaction systems with the typical channel diameter less than 1 mm [5]. Due to the small dimensions, the high surface area to volume ratio of microreactor is obtained, which provided excellent mass and heat transfer, shorter residence time, short molecular diffusion distance and better process control than macroreactor system. Moreover, the other advantage of microreactor systems is that, the production capacity could be increased by numbering up method by connecting microreactors in series. In comparison, the conventional reactor requires scaling up the size of each reactor unit, which might change the reactor performance. Presently, there are many research works concerning interesterification process of triglyceride with methyl acetate, but there are limited research works that using ethyl acetate as a reactant. As for the feedstock for biodiesel production, Palm oil is the most viable feedstock for biodiesel production in Thailand. Therefore, refined palm oil and ethyl acetate were used as an oil feedstock and reactant in the present study. The objective of this study was to investigate the biodiesel production process from refined palm oil with supercritical ethyl acetate in microreactor at various reaction conditions. 2. Materials and methods 2.1. Materials Refined palm oil from Patum Vegetable Oil Co., Ltd (Thailand) was used as an oil feedstock in this study. Ethyl acetate (99.8% purity) was purchased from RCl labscan. Triolein (99% purity) and ethyl

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oleate (98% purity) were purchased from Sigma-Aldrich for using as the GC standards for triglycerides and FAEE analysis. Triacetin (99% purity) was purchased from Applichem. 2.2. Experimental procedure The interesterification process of refined palm oil with ethyl acetate was carried out in 316 L stainless steel microreactor (0.762 mm. internal diameter and 15.14 m long) with the capacity of 6.94 mL. The reactants were mix at oil to solvent molar ratio of 1:50 and then fed into the reaction system by high pressure liquid pump (Series III Pump 10 mL/40 mL Heads, Scientific Systems Inc.). The microreactor was placed in a furnace with controlled temperature and monitored by two thermocouples. The reaction temperature was controlled in the range of 330ºC and 370ºC, pressure of 200 bar and the residence time in the range of 3 and 60 minute. Product samples were collected periodically at the reactor outlet. Then the excess ethyl acetate was removed from biodiesel product by using vacuum rotary evaporator and subsequently the biodiesel sample (FAEE and triacetin) can be obtained. 2.3. Analytical methods The components involved in the biodiesel product were determined by gas chromatography with modified EN14105 method by using a Shimadzu corporation (Japan) model GC-2010 gas chromatograph. The GC column was a DB5-HT column with 15 m long, 0.32 mm internal diameter and 0.10 μm thickness. The column temperature was held at 50°C for 1 min, and then was increased to 100°C at a rate of 10°C min-1, then to 110°C at 5°C min-1, 160°C at 10°C min-1, 280°C at 5°C min-1, and finally to 380°C at 10°C min-1. Helium was used as a carrier gas, with the initial flow and average velocity of 1.59 mL min-1 and 31.0 cm.s-1, respectively. The flame-ionization detector (FID) temperature was set at 380°C.FAEE yield and biodiesel yield at steady state conditions were defined according to the following equations.

FAEE yield (wt%)

Weight of FAEE (g) x 100 Weight of Refined palm oil used (g)

Biodiesel yield (wt%)

¦ Weight of FAEE Triacetin (g) Weight of Refined palm oil used (g)

x 100

(1)

(2)

3. Results and discussion 3.1. Fatty acid composition of Refined palm oil The fatty acid composition of refined palm oil was determined by gas chromatography according to AOAC 991.39 (2005) method and the result was listed in the Table 1.

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Table 1. The fatty acid composition of refined palm oil. Fatty acid

Composition (wt%)

Palmitic acid (C16:0) Stearic acid (C18:0) Oleic acid (C18:1) Linoleic acid (C18:2)

41.3 4.2 41.3 10.6

Refined palm oil used in the present study contained 51.9% of unsaturated fatty acid and 45.5% of saturated fatty acid. Palmitic acid (C16:0) and Oleic acid (C18:1) were the main fatty acid composition in refined palm oil. The approximate molecular weight of refined palm oil was calculated from the fatty acid composition data and found to be 843 g/mol. The acid value of refined palm oil used in this study was measured by titration with 0.1 N KOH and found to be 0.01 mgKOH/g. 3.2. Effect of residence time Fig. 2. shows the effect of reaction time on the composition of liquid biodiesel product in the interesterification of refined palm oil with supercritical ethyl acetate at oil to ethyl acetate molar ratio of 1:50, temperature of 350°C, pressure of 200 bar and residence time of 3-30 min. It can be seen that the composition of liquid product changed as a function of residence time. At residence time of 20 min, the complete triglyceride conversion and FAEE content of 52wt% were obtained. 100

Triglyceride Monoacetindiglyceride Diacetinmonoglyceride FAEE Triacetin FFA

Composition (wt%)

80

60

40

20

0 0

5

10

15 20 25 Residence time (min)

30

35

Fig. 2. Composition of liquid products obtained at oil to ethyl acetate molar ratio of 1:50, 350°C and 200 bar.

The interesterification reaction of triglycerides and ethyl acetate proceeds through three stages, as shown in Fig 3. Firstly, triglyceride reacts with ethyl acetate to generate FAEE and monoacetindiglyceride. In the same manner, FAEE and diacetinmonoglyceride are generated from monoacetindiglyceride and ethyl acetate, and FAEE and triacetin are generated from diacetinmonoglyceride and ethyl acetate. These experimental results demonstrated that the longer residence time, the higher amounts of triglyceride are converted to reaction intermediates and products.

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Triglyceride + Ethyl acetate Monoacetindiglyceride + Ethyl acetate Diacetinmonoglyceride + Ethyl acetate

FAEE + Monoacetindiglyceride FAEE + Diacetinmonoglyceride FAEE + Triacetin

Fig. 3. Interesterification reaction of triglyceride and ethyl acetate in three stages.

The longer reaction time allowed the reaction to achieve completion and higher FAEE and biodiesel (FAEE+Triacetin) yield in the product were obtained as shown in Fig. 4. The generation of triacetin was observed after residence time of 3 min. At residence time of 20 min, 63.6% and 78.3% of FAEE yield and biodiesel yield were obtained. These results are in accordance with the literature reported by Tan K.T. et al. [6] which studied the interesterification of purified palm oil with supercritical methyl acetate to produce fatty acid methyl ester and triacetin in batch type tube reactor at 340-420°C and 150-250 bar. It was observed that the longer duration of reaction time allowed the reaction to achieve completion, which resulted in the higher biodiesel yield. At temperature of 400°C and oil to methyl acetate molar ratio of 1:30, biodiesel yield of 40% and 55% were observed at reaction time of 15 and 30 min, respectively. 100

FAEE Biodiesel

Yield (%)

80

60

40

20

0 0

5

10

15 20 Residence time (min)

25

30

35

Fig. 4. Effect of reaction time on FAEE and biodiesel yield at oil to ethyl acetate molar ratio of 1:50, 350°C and 200 bar.

3.3. Effect of temperature The effect of temperature on triglyceride conversion was investigated at oil to ethyl acetate molar ratio of 1:50, pressure of 200 bar, residence time in the range of 0-60 min, at the reaction temperature at 330, 350 and 370°C and the results are shown in Fig 5. It can be seen that the increasing of temperature led to a faster initial reaction rate. At residence time of 10 min, triglyceride conversion was 41.6%, 92.4% and 100% at the temperature of 330, 350 and 370°C, respectively. Triglyceride conversions higher than 95% were observed after 30 min at all of temperature used in this study. Moreover, the complete triglyceride conversions were achieved at 10 and 20 min of residence time at 370 and 350°C, respectively. The experimental results in terms of FAEE and biodiesel yield are shown in Fig. 6. It can be seen that temperature directly influent the reaction rate and enhance FAEE and biodiesel yield. At the temperature

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of 350°C and 20 min of residence time, the highest FAEE yield of 63.6% and biodiesel yield of 78.3% were observed. However, a different behaviour was observed at 370°C, where the yield increased with the increasing of residence time up to 10 min. Prolonging the residence time further to 20 min led to the lower yield. This observation can be explained by the thermal decomposition as reported by Imahara et al. [7]. The thermal stability of fatty acid methyl ester model compounds and biodiesel prepared from various plant oils were studied at supercritical methanol condition at 270°C/170 bar and 380°C/560 bar. It was found that all fatty acid methyl esters including poly-unsaturated ones were stable at 270°C/170 bar, but at 350°C/430 bar, they were partly decomposed which led to the decreasing of FAME yield. 100

TG conversion (%)

80

330 350 370

60

40

20

0 0

10

20 30 40 50 60 Residence time (min) Fig. 5. Effect of temperature on triglyceride conversion at oil: ethyl acetate molar ratio of 1:50, 200 bar, at 330°C, 350°C and 370°C 100

330 350 370

_____ FAEE

----- Biodiesel

Yield (%)

80

60

40

20

0

0

10

20

30

40

50

60

Residence time (min) Fig. 6. Effect of temperature on FAEE and biodiesel yield at oil:ethyl acetate molar ratio of 1:50, 200 bar, at 330°C, 350°C and

370°C


4. Conclusion This study investigated the biodiesel production by glycerol-free process from refined palm oil with supercritical ethyl acetate in microreactor. The influence of residence time and temperature was presented. Results showed that the residence time and temperature had positive effect on FAEE and biodiesel yield. The high FAEE yield of 63.6% and biodiesel yield of 78.3% were obtained at oil to ethyl acetate molar ratio of 1:50, the temperature of 350°C, and 20 min of residence time. However, the high temperature led to thermal decomposition, which reduced the product yield.

Acknowledgements The authors would like to acknowledge Thailand Institute of Scientific and Technological ResearchMinistry of Science and Technology, the Ratchadaphiseksomphot Endowment Fund 2014 of Chulalongkorn University (CU-57-045-EN), and Thailand Research Fund (IRG5780001) for the financial support. References [1] Silva CD, Castilhos FD, Oliveira JV, Filho LC. Continuous production of soybean biodiesel with compressed ethanol in a microtue reactor. Fuel Processing Technology 2010;91:1274-1281. [2] Tan KT, Lee KT, Mohamed AR. Production of FAME by palm oil transesterification via supercritical methanol technology. Biomass And Bioenery 2009;33:1096-1099. [3] Imahara H, Xin J, Saka S. Effect of CO2/N2 addition to supercritical methanol on reactiveties and fuel qualities in biodiesel production. Fuel 2009;88:1329-1332. [4] Tan KT, Lee KT, Mohamed AR. A glycerol-free process to produce biodiesel by supercritical methyl acetate technology: An optimization study via Response Surface Methodology. Bioresource Technologyt 2010;101:965-969. [5] Hejda S, Drhova M, Kristal J, Buzek D, Krystynik P, Kluson P. Microreactor as efficient tool for light induced oxidation reactions. Chemical Engineering Journal 2014;255:178-184. [6] Tan KT, Lee KT, Mohamed AR. Prospects of non-catalytic supercritical methyl acetate process in biodiesel production. Fuel Processing Technology 2011;92:1905-1909. [7] Imahara H, Minami E, Hari S, Saka S. Thermal stability of biodiesel in supercritical methanol. Fuel 2008;87:1-6.

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