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Ultrasonic energy effect on vegetable oil based biodiesel synthetic process
Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Ultrasonic energy effect on vegetable oil based biodiesel synthetic process Seung Bum Lee a, Jae Dong Lee b, In Kwon Hong a,* a b
Department of Chemical Engineering, Dankook University, 448-701, Republic of Korea Division of Energy & Biological Engineering, Kyungwon University, 461-701, Republic of Korea
A R T I C L E I N F O
Article history: Received 8 June 2010 Accepted 23 July 2010 Available online 25 December 2010 Keywords: Ultrasonic energy Biodiesel Transesterification Methyl ester content
A B S T R A C T
The manufacturing process of vegetable oil based biodiesel was introduced in experimental manner. Ultrasonic energy was irradiated to induce the transesterification of the vegetable oil. The ultrasonic irradiation had two effects, those were heating and mixing of the reactants. We performed the experiment under various manufacturing parameters, viz. the ultrasonic irradiation time, sonic power, and irradiation type at constant reaction temperature, 55 8C. The ultrasonic irradiation biodiesel synthetic process reduced the reaction time by 30 min or more comparing to existing processes. The ultrasonic energy densities (Ua) were calculated from the experimental data. The highest yield and methyl ester content were observed at an ultrasonic power of more than 450 W. The reaction conditions were also adjusted to stabilize the reaction media temperature. ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction The development of renewable energy sources that can replace fossil fuels such as oil, coal, and natural gas, can prevent depletion of the available energy resources and environmental pollution. Also, it can contribute to reduce greenhouse gas emissions. Biodiesel (BD) consisting of a mixture of alkylesters resulting from the transesterification reaction of vegetable oil is a source of biodegradable clean energy, and it does not produce carcinogenic aromatic polymer compounds or sulfoxides during its combustion. In addition, the oxygen content of 11–15% in the molecular structure accelerates the combustion process in diesel engines and reduces pollutants such as fine particles, soot, and carbon monoxide when the biodiesel is used as a mixed fuel with petroleum diesel [1–5]. Its larger cetane number and higher lubricity than petroleum diesel in compression ignition engines allow biodiesel to be applied to the compression ignition engine as shown in Table 1. Also, the modification of the engine is not required when biodiesel is mixed with petroleum diesel in small quantities, and it reduces the lubrication properties. However, the poor fuel stability of biodiesel may cause corrosion or damage to the metal engine and, therefore the acid value and moisture content must be controlled in the biodiesel synthetic process. The use of qualified biodiesel prevents the injector of the engine from suffering from clogging and the sedimentation of carbon. In addition to these problems, biodiesel has some defects such as its
high fluidity compared with petroleum diesel and its competition with edible food. However, despite these disadvantages, the production and usage of biodiesel will increase in near future. Vegetable oil as a raw material for biodiesel is usually composed of free fatty acids, phospholipids, sterol, water and other impurities. It cannot be directly used as a fuel because it has high viscosity. Chemical transformation must be performed, including esterification, pyrolysis and emulsification [6,7]. The esterification reaction was first introduced in the form of the alcohol decomposition of castor oil by Rochieder in 1846 and many researchers have studied the production processes of a variety of biodiesels, such as the acid– base catalyst reaction, enzyme esterification, ultrasonic energy method and supercritical fluid media reaction method [8–12]. In this study, the irradiation of ultrasonic energy was used for the esterification of vegetable oils to shorten the reaction time and to increase the product efficiency [13–15]. Ultrasound has a short wavelength, slow transfer rate, and high energy transmittance as the vibrating type energy. The cavitation in the ultrasonic wavelength is the phenomenon of expansion and contraction of the transfer media bubbles. Then, the ultrasonic energy is propagated into the solution by the destruction of the pressurized microbubbles. The energy is used in the biodiesel production process, in which vegetable oil is esterified in a short time to obtain a higher yield. 2. Experimental method 2.1. Biodiesel synthesis using ultrasonic energy
* Corresponding author. Tel.: +82 31 8005 3544; fax: +82 31 8005 3536. E-mail address: [email protected] (I.K. Hong).
Esterification is the process required for the production of environmentally benign fuel from the vegetable oil and it
1226-086X/$ – see front matter ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2010.12.012
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
[()TD$FIG]
Table 1 The properties of biodiesel and petroleum diesel. Properties
Biodiesel
Diesel
Specific gravity Cetane number Cloud point (K) Pour point (K) Flash point (K) Sulfur (wt%) Ash (wt%) Kinematic viscosity at 313 K (cSt) Higher heating value (MJ/kg)
0.87–0.89 46–70 262–289 268–286 408–423 0.0000–0.0024 0.002–0.01 3.7–5.8 39.3–39.8
0.84–0.86 47–55 256–265 237–243 325–350 0.04–0.01 0.06–0.01 1.9–3.8 45.3–46.7
139
performed using methanol and alkaline catalysts. Canola oil, soybean oil, and corn oil were used for the synthesis of biodiesel in this experimental work. Ultrasound was irradiated onto a mixture of vegetable oil and methanol mixture at a mole ratio of 1:6, so that then the vegetable oil was esterified at 55 8C [10]. The reaction temperature was controlled by the pulse time of ultrasonic irradiation. A probe type generator (VCX-600, D = 0.5 in., threaded end, amplitude = 124 nm, Sonics & Material Co., USA) was used for the ultrasonic irradiation. The power range of ultrasound was set from 150 to 750 W and the irradiation time was controlled from 20 to 40 min. The amount of potassium hydroxide (KOH) was 1 wt% of
Fig. 1. GC chromatogram for identification of FAME.
[()TD$FIG]
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
100
the vegetable oil and used in the form of a mixed solution with methanol. After the esterification processing,the glycerol layer was removed with a separating funnel. The biodiesel was washed with ultrapure water to remove the basic catalyst and unreacted components. Finally, the fatty acid methyl ester (FAME) was analyzed with various analytical instruments to identify its physical characteristics such as the viscosity, heat capacity, and heating value.
98
Methyl Ester Content [%]
96
2.2. Identification of synthetic biodiesel After esterification, the composition of the biodiesel was analyzed by gas chromatography (GC–FID) using a ACME 6100 model (Young-Lin, Korea). The oven temperature was elevated from 140 8C (1 min) to 245 8C at a heating rate of 5 8C/min during the analytical procedure. The temperature of the sample injection port and detection part was kept constant at 250 8C using a HPInnowax column with a column length of 30 m and diameter of 0.32 mm. The mobile phase was high-purity nitrogen, the column flow rate was 3 mL/min, and the split ratio was 10:1.
90 88
Canola Oil Soybean Oil Corn Oil
82 20
30
40
50
60
70
80
o
Temperature [ C] Fig. 2. Variation of ME content with reaction temperature for vegetable oils.
The heat capacity of the vegetable oils was measured by the DSC sapphire method (DSC822e, Mettler Toledo, Switzerland). A 3 mg sample of the vegetable oil was loaded in an aluminum pan with a volume of 20 mL. A three step measurement process was used, consisting of the blank test, sapphire test and sample test. Then samples were heated from 20 to 160 8C, with the heating rate of 10 8C/min. The atmosphere was kept with nitrogen at the rate of 80 mL/min. 3. Results and discussion 3.1. FAME analysis The fatty acid methyl ester (FAME) synthesized by the esterification of vegetable oils was identified by GC–FID analysis and the chromatogram of the FAME produced using ultrasound irradiation is shown in Fig. 1. The FAME derived from the principal component of the vegetable oil contained carbon chains ranging from C16:0 to C18:3 in its chromatogram. From the chromatogram, methyl ester (ME) and linolenic acid methyl ester (LAME) contents were calculated as follows: ½SA AEI C EI V EI 100 AEI m
92
84
2.3. Measuring of heat capacity
ME contentð%Þ ¼
94
86
characteristics for various reaction temperatures and stirring speed ranges. Fig. 2 shows the temperature dependence on the esterification of the vegetable oils. The ME content in the biodiesel was measured at the reaction temperatures of 30–70 8C. The mole ratio between vegetable oil and methanol was 1–6, the stirring speed was 300 rpm, and the reaction time was 1 h. The ME content increased with increasing reaction temperature, but slightly decreased at the temperature higher than 55 8C. This phenomena can be explained as evaporation of methanol due to the boiling temperature of methanol of 64.7 8C, which results in its above 55 8C and decreases the possibility of the vegetable oil molecules coming into contact with it. Due to this reason, the esterification reaction time must be controlled and the reaction temperature kept lower than 55 8C. The ME contents at 55 8C were 97.6, 96.4, and 91.2% for canola oil, soybean oil, and corn oil, respectively. The canola oil showed the highest conversion for biodiesel production among the three vegetable oils. The variation of the ME content of the vegetable oils with the stirring speed rate is presented in Fig. 3. The ME contents of the vegetable oils increased with increasing
[()TD$FIG] 100
(1)
AL LAME contentð%Þ ¼ 100 (2) ½SA AEI P where [ A] is the total peak area of the C14:0 to C24:1 FAME in the chromatogram, also AEI, CEI, and VEI stand for the peak areas of the internal standard, methylheptadecanoate (C17:0), the concentration, and the sample volume (mL), respectively. In addition, AL is the peak area of linolenic acid methyl ester, and m is the amount of biodiesel (mg). EU biodiesel standard (EN 14214) requires ME content and a LAME content, more than 96.5% and less than 12%, respectively, for the BD100.
98 96 94
Methyl Ester Content [%]
140
92 90 88 86
Canola Oil
3.2. Temperature and stirring effect without ultrasound
Soybean Oil 84
A preliminary experiment was conducted to observe the ultrasonic effect on the process in comparison with conventional heating method. The comparison between the conventional heating method and the ultrasonic irradiation procedure was analyzed and was compared with in terms of the esterification
Corn Oil
82 0
100
200
300
400
500
600
700
Stirring Speed [rpm] Fig. 3. Variation of ME content with stirring speed for vegetable oils.
[()TD$FIG]
[()TD$FIG]
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
141
(a) Canola oil
110
100
100
98 95
Percent [%]
Temperature [ºC]
90
80
93
BioDiesel Yield Methylester(ME) Content Linolenic acid ME Content
90 88
70 85 10 9 8 7 6
60
Canola Oil
150
300
450
600
750
300
450
600
750
300
450
600
750
Soybean Oil
50
(b) Soybean oil
Corn Oil
100
40 90
120
150
180
210
240
270
300
330
360
98
Ultrasonic Irradiation Time [s] 95
Percent [%]
Fig. 4. Temperature increase as a function of the ultrasonic irradiation time for the vegetable oils.
stirring speed up to 300 rpm and was constant at above 399 rpm of stirring speed.
The ultrasonic energy density was analyzed by the method of Zarzycki et al. [17]. They measured the ultrasonic energy density in the ultrasound induced solvent extraction. According to this reference, the temperature of vegetable oil was measured as a function of the irradiation time in an insulated container. The data of the temperature change with the irradiation time were linearized by the least square method and the real ultrasonic power (Pa) was calculated from the slope of the curve.
(c) Corn oil 100 98 95
(3)
If Pa is constant for the irradiation time and volume of vegetable oil, the ultrasonic energy density as a function of the ultrasonic power and irradiation time can be calculated as following manner: U a ¼ Pa t a ¼ Pa
88
150
Percent [%]
energy time
90
85 8 7 6 5
3.3. Ultrasonic energy density analysis
Pa ¼
93
93 90 88 85 2 1
t V
(4)
0 150
where t is the irradiation time (s) and V is the volume of vegetable oil (mL). In this study, the ultrasonic energy density was calculated using the experimental temperature change under constant vegetable oil volume and temperature. Fig. 4 shows the irradiation time variation on the temperature of the vegetable oil under constant ultrasonic power of 450 W. The ultrasound was irradiated continuously onto a fixed volume of vegetable oil, viz. 100 mL. The reaction temperature increased according to the first order equation with the irradiation time increment from 90 to 360 s. The increasing rates of the vegetable oil temperature were 9.44, 9.33,
Ultrasonic Irradiation Power [W] Fig. 5. Variation of BD properties with ultrasonic irradiation power for vegetable oils.
and 8.67 8C/min for canola, soybean and corn oil, respectively. Canola oil exhibited a largest temperature increase among the vegetable oils. The heat capacity was correlated with the temperature based on the DSC experimental data for each vegetable oil. The mean heat capacity, Cp , was calculated by using the following equation under temperature range from 55 to
Table 2 Energy density of various vegetable oils. Vegetable oil
r (g/cm3)
A
B 103
C 105
Cp
Canola Soybean Corn
0.893 0.888 0.828
4.1047 4.8416 3.7315
10.6 13.4 8.2
1.8836 2.0333 1.4782
2.8055 2.6989 2.7644
(J/g K)
Pa (J/s) 394.35 372.81 330.62
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
142
calculated as follow.
155 8C. C p ¼ A þ BT þ CT 2
(5)
Then, the ultrasonic power (Pa) was calculated from the average density, mean heat capacity of the vegetable oil, and ultrasonic irradiation time (270 s). The results are presented in Table 2. When the ultrasonic power was constant and the reaction time was fixed at 30 min, the ultrasonic energy densities (Ua) irradiated in the experiment were 6337.8, 5959.7, and 4926.5 kJ L1 for canola, soybean and corn oil, respectively. 3.4. Effect of ultrasonic irradiation power Fig. 5 shows the ME content and BD yield for the ultrasound induced vegetable oil esterification process. The BD yield was [()TD$FIG]
(a) Canola oil 100 98
Percent [%]
95 93
amount of methyl ester ðgÞ 100 amount of vegetable oil ðgÞ
(6)
The esterification reaction was performed for 30 min under the conditions of the molar ratio of vegetable oil to methanol of 1–6 and 1 wt% of the alkaline catalyst, KOH. The reaction temperature was constant at 55 8C by using the pulse type irradiation. The BD yield increased with increasing irradiation power from 150 to 450 W. However, the ME content decreased when the irradiation power above 450 W. This phenomenon resulted from the reduction of the real reaction time by the extension of the pulse time used for controlling the reaction temperature when the irradiation power was increased. However, when the reaction temperature was constant, a larger BD yield and ME content were obtained comparing to the case where the pulse interval was reduced or ultrasound was irradiated continuously. The real irradiation time decreased with irradiation strength to keep the constant reaction temperature, 55 8C. Therefore, it can be concluded that the pulse type irradiation at a power of 450 W was the optimum procedure. 3.5. Effect of irradiation time
BioDiesel Yield Methylester(ME) Content Linolenic acid ME Content
90 88 85 10 9 8 7 6 15
20
25
30
35
40
45
(b) Soybean oil 100 98 95
Percent [%]
BD yield ð%Þ ¼
93 90 88 85 8 7 6 5 15
Fig. 6 shows the variation of the ME content and BD yield with the ultrasonic irradiation time for the esterification of the vegetable oil. The other variables, viz. the ultrasound power, reaction temperature, vegetable oil/methanol molar ratio, and the amount of KOH, were kept constant. The ultrasound power, reaction temperature, vegetable oil/methanol molar ratio, and amount of KOH were 450 W, 55 8C, 1–6, and 1 wt%, respectively. The BD yield and ME content were both 95% at the reaction time of 30 min for the three vegetable oils. The canola oil showed largest BD yield (97.4%) and ME content (97.5%) among three types of oils at the reaction time of 30 min. The temperature increasing effect was small for canola oil because of the large heat capacity. Then the ultrasound irradiation pulse interval must be reduced. This ultrasound irradiation method shortened the reaction time more than 30 min comparing to the conventional heating method and showed an excellent conversion rate [16–18]. 4. Conclusion
20
25
30
35
40
45
(c) Corn oil 100 98
Ultrasonic energy was irradiated onto the vegetable oil during biodiesel synthetic process. The ultrasonic irradiation had alternating mixing and heating effect comparing to conventional biodiesel synthetic process. The ultrasound irradiation reduced reaction time and improved biodiesel properties without any additional mixing step in the vegetable oil esterification process. The results can be summarized as follows:
Percent [%]
95 93 90 88 85 2 1 0 15
20
25
30
35
40
45
Ultrasonic Irradiation Time [min] Fig. 6. Variation of BD properties with ultrasonic irradiation time for vegetable oils.
1. The BD yield increased with increasing ultrasonic power from 150 to 450 W, but the ME content decreased at ultrasonic powers over 450 W. This is due to the decrease of the real irradiation time caused by the increase in the pulse interval required for tuning the temperature due to the extension of the irradiation power. 2. The BD yield and ME content were both 95% at the reaction time of 30 min for all of the three vegetable oils. The canola oil exhibited best biodiesel properties of other two oils. This improvement phenomenon can be explained and was considered to be due to the larger ultrasonic energy density, Ua of 6337.8 kJ L1, compared to the other two vegetable oils at an ultrasound irradiation time of 30 min.
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
3. The ultrasound irradiation method enabled to reduce the reaction time by 30 min or more comparing to conventional heating method. Also this method improved conversion rate.
References [1] [2] [3] [4] [5] [6] [7]
Y.K. Hong, W.H. Hong, Korean Chem. Eng. Res. 45 (5) (2007) 424. S.S. Kim, K.H. Kim, S.C. Shin, E.S. Yim, J. Korean Ind. Eng. Chem. 18 (5) (2007) 401. J. Janaun, N. Ellis, Renew. Sustain. Energy Rev. 14 (2010) 1312. C.S. Wassell Jr., T.P. Dittmer, Energy Policy 34 (2006) 33993. A. Demirbas, Energy Convers. Manage. 14 (2009) 50. Y.K. Lim, S.C. Shin, E.S. Yim, H.O. Song, J. Korean Ind. Eng. Chem. 19 (2008) 137. C.T. Hou, J.F. Shaw, Biocatalysis and Bioenergy, John Wiley & Sons, NY, 2008.
143
[8] H.D. Hanh, N.T. Dong, K. Okitsu, R. Nishimura, Y. Maeda, Renew. Energy 34 (2009) 766. [9] D. Yu, L. Tian, H. Wu, S. Wang, Y. Wang, D. Ma, X. Fang, Process Biochem. 45 (2010) 519. [10] C. Stavarache, M. Vinatoru, Y. Maeda, Ultrason. Sonochem. 14 (2007) 380. [11] C. Stavarache, M. Vinatoru, R. Nishimura, Y. Maeda, Ultrason. Sonochem. 12 (2005) 367. [12] J.Z. Yin, M. Xiao, J.B. Song, Energy Convers. Manage. 49 (2008) 908. [13] T.J. Mason, Chemistry with Ultrasound, Elsevier Science, NY, 1990. [14] L.T. Thanh, K. Okitsu, Y. Sadanaga, N. Takenaka, Y. Maeda, H. Bandow, Bioresour. Technol. 101 (2010) 639. [15] T.J. Mason, J.P. Lorimer, Sonochemistry, John Wiley & Sons, NY, 1998. [16] S.B. Lee, K.H. Han, J.D. Lee, I.K. Hong, J. Ind. Eng. Chem. 16 (6) (2010) 1006. [17] M. Ramirez-del-Solar, N. de la Rosa-Fox, L. Esquivias, J. Zarzycki, J. Non-Cryst. Solids 121 (1990) 40. [18] H.J. Kim, M.H. Chi, I.K. Hong, J. Ind. Eng. Chem. 13 (6) (2009) 919.
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Ultrasonic energy effect on vegetable oil based biodiesel synthetic process Seung Bum Lee a, Jae Dong Lee b, In Kwon Hong a,* a b
Department of Chemical Engineering, Dankook University, 448-701, Republic of Korea Division of Energy & Biological Engineering, Kyungwon University, 461-701, Republic of Korea
A R T I C L E I N F O
Article history: Received 8 June 2010 Accepted 23 July 2010 Available online 25 December 2010 Keywords: Ultrasonic energy Biodiesel Transesterification Methyl ester content
A B S T R A C T
The manufacturing process of vegetable oil based biodiesel was introduced in experimental manner. Ultrasonic energy was irradiated to induce the transesterification of the vegetable oil. The ultrasonic irradiation had two effects, those were heating and mixing of the reactants. We performed the experiment under various manufacturing parameters, viz. the ultrasonic irradiation time, sonic power, and irradiation type at constant reaction temperature, 55 8C. The ultrasonic irradiation biodiesel synthetic process reduced the reaction time by 30 min or more comparing to existing processes. The ultrasonic energy densities (Ua) were calculated from the experimental data. The highest yield and methyl ester content were observed at an ultrasonic power of more than 450 W. The reaction conditions were also adjusted to stabilize the reaction media temperature. ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction The development of renewable energy sources that can replace fossil fuels such as oil, coal, and natural gas, can prevent depletion of the available energy resources and environmental pollution. Also, it can contribute to reduce greenhouse gas emissions. Biodiesel (BD) consisting of a mixture of alkylesters resulting from the transesterification reaction of vegetable oil is a source of biodegradable clean energy, and it does not produce carcinogenic aromatic polymer compounds or sulfoxides during its combustion. In addition, the oxygen content of 11–15% in the molecular structure accelerates the combustion process in diesel engines and reduces pollutants such as fine particles, soot, and carbon monoxide when the biodiesel is used as a mixed fuel with petroleum diesel [1–5]. Its larger cetane number and higher lubricity than petroleum diesel in compression ignition engines allow biodiesel to be applied to the compression ignition engine as shown in Table 1. Also, the modification of the engine is not required when biodiesel is mixed with petroleum diesel in small quantities, and it reduces the lubrication properties. However, the poor fuel stability of biodiesel may cause corrosion or damage to the metal engine and, therefore the acid value and moisture content must be controlled in the biodiesel synthetic process. The use of qualified biodiesel prevents the injector of the engine from suffering from clogging and the sedimentation of carbon. In addition to these problems, biodiesel has some defects such as its
high fluidity compared with petroleum diesel and its competition with edible food. However, despite these disadvantages, the production and usage of biodiesel will increase in near future. Vegetable oil as a raw material for biodiesel is usually composed of free fatty acids, phospholipids, sterol, water and other impurities. It cannot be directly used as a fuel because it has high viscosity. Chemical transformation must be performed, including esterification, pyrolysis and emulsification [6,7]. The esterification reaction was first introduced in the form of the alcohol decomposition of castor oil by Rochieder in 1846 and many researchers have studied the production processes of a variety of biodiesels, such as the acid– base catalyst reaction, enzyme esterification, ultrasonic energy method and supercritical fluid media reaction method [8–12]. In this study, the irradiation of ultrasonic energy was used for the esterification of vegetable oils to shorten the reaction time and to increase the product efficiency [13–15]. Ultrasound has a short wavelength, slow transfer rate, and high energy transmittance as the vibrating type energy. The cavitation in the ultrasonic wavelength is the phenomenon of expansion and contraction of the transfer media bubbles. Then, the ultrasonic energy is propagated into the solution by the destruction of the pressurized microbubbles. The energy is used in the biodiesel production process, in which vegetable oil is esterified in a short time to obtain a higher yield. 2. Experimental method 2.1. Biodiesel synthesis using ultrasonic energy
* Corresponding author. Tel.: +82 31 8005 3544; fax: +82 31 8005 3536. E-mail address: [email protected] (I.K. Hong).
Esterification is the process required for the production of environmentally benign fuel from the vegetable oil and it
1226-086X/$ – see front matter ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2010.12.012
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
[()TD$FIG]
Table 1 The properties of biodiesel and petroleum diesel. Properties
Biodiesel
Diesel
Specific gravity Cetane number Cloud point (K) Pour point (K) Flash point (K) Sulfur (wt%) Ash (wt%) Kinematic viscosity at 313 K (cSt) Higher heating value (MJ/kg)
0.87–0.89 46–70 262–289 268–286 408–423 0.0000–0.0024 0.002–0.01 3.7–5.8 39.3–39.8
0.84–0.86 47–55 256–265 237–243 325–350 0.04–0.01 0.06–0.01 1.9–3.8 45.3–46.7
139
performed using methanol and alkaline catalysts. Canola oil, soybean oil, and corn oil were used for the synthesis of biodiesel in this experimental work. Ultrasound was irradiated onto a mixture of vegetable oil and methanol mixture at a mole ratio of 1:6, so that then the vegetable oil was esterified at 55 8C [10]. The reaction temperature was controlled by the pulse time of ultrasonic irradiation. A probe type generator (VCX-600, D = 0.5 in., threaded end, amplitude = 124 nm, Sonics & Material Co., USA) was used for the ultrasonic irradiation. The power range of ultrasound was set from 150 to 750 W and the irradiation time was controlled from 20 to 40 min. The amount of potassium hydroxide (KOH) was 1 wt% of
Fig. 1. GC chromatogram for identification of FAME.
[()TD$FIG]
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
100
the vegetable oil and used in the form of a mixed solution with methanol. After the esterification processing,the glycerol layer was removed with a separating funnel. The biodiesel was washed with ultrapure water to remove the basic catalyst and unreacted components. Finally, the fatty acid methyl ester (FAME) was analyzed with various analytical instruments to identify its physical characteristics such as the viscosity, heat capacity, and heating value.
98
Methyl Ester Content [%]
96
2.2. Identification of synthetic biodiesel After esterification, the composition of the biodiesel was analyzed by gas chromatography (GC–FID) using a ACME 6100 model (Young-Lin, Korea). The oven temperature was elevated from 140 8C (1 min) to 245 8C at a heating rate of 5 8C/min during the analytical procedure. The temperature of the sample injection port and detection part was kept constant at 250 8C using a HPInnowax column with a column length of 30 m and diameter of 0.32 mm. The mobile phase was high-purity nitrogen, the column flow rate was 3 mL/min, and the split ratio was 10:1.
90 88
Canola Oil Soybean Oil Corn Oil
82 20
30
40
50
60
70
80
o
Temperature [ C] Fig. 2. Variation of ME content with reaction temperature for vegetable oils.
The heat capacity of the vegetable oils was measured by the DSC sapphire method (DSC822e, Mettler Toledo, Switzerland). A 3 mg sample of the vegetable oil was loaded in an aluminum pan with a volume of 20 mL. A three step measurement process was used, consisting of the blank test, sapphire test and sample test. Then samples were heated from 20 to 160 8C, with the heating rate of 10 8C/min. The atmosphere was kept with nitrogen at the rate of 80 mL/min. 3. Results and discussion 3.1. FAME analysis The fatty acid methyl ester (FAME) synthesized by the esterification of vegetable oils was identified by GC–FID analysis and the chromatogram of the FAME produced using ultrasound irradiation is shown in Fig. 1. The FAME derived from the principal component of the vegetable oil contained carbon chains ranging from C16:0 to C18:3 in its chromatogram. From the chromatogram, methyl ester (ME) and linolenic acid methyl ester (LAME) contents were calculated as follows: ½SA AEI C EI V EI 100 AEI m
92
84
2.3. Measuring of heat capacity
ME contentð%Þ ¼
94
86
characteristics for various reaction temperatures and stirring speed ranges. Fig. 2 shows the temperature dependence on the esterification of the vegetable oils. The ME content in the biodiesel was measured at the reaction temperatures of 30–70 8C. The mole ratio between vegetable oil and methanol was 1–6, the stirring speed was 300 rpm, and the reaction time was 1 h. The ME content increased with increasing reaction temperature, but slightly decreased at the temperature higher than 55 8C. This phenomena can be explained as evaporation of methanol due to the boiling temperature of methanol of 64.7 8C, which results in its above 55 8C and decreases the possibility of the vegetable oil molecules coming into contact with it. Due to this reason, the esterification reaction time must be controlled and the reaction temperature kept lower than 55 8C. The ME contents at 55 8C were 97.6, 96.4, and 91.2% for canola oil, soybean oil, and corn oil, respectively. The canola oil showed the highest conversion for biodiesel production among the three vegetable oils. The variation of the ME content of the vegetable oils with the stirring speed rate is presented in Fig. 3. The ME contents of the vegetable oils increased with increasing
[()TD$FIG] 100
(1)
AL LAME contentð%Þ ¼ 100 (2) ½SA AEI P where [ A] is the total peak area of the C14:0 to C24:1 FAME in the chromatogram, also AEI, CEI, and VEI stand for the peak areas of the internal standard, methylheptadecanoate (C17:0), the concentration, and the sample volume (mL), respectively. In addition, AL is the peak area of linolenic acid methyl ester, and m is the amount of biodiesel (mg). EU biodiesel standard (EN 14214) requires ME content and a LAME content, more than 96.5% and less than 12%, respectively, for the BD100.
98 96 94
Methyl Ester Content [%]
140
92 90 88 86
Canola Oil
3.2. Temperature and stirring effect without ultrasound
Soybean Oil 84
A preliminary experiment was conducted to observe the ultrasonic effect on the process in comparison with conventional heating method. The comparison between the conventional heating method and the ultrasonic irradiation procedure was analyzed and was compared with in terms of the esterification
Corn Oil
82 0
100
200
300
400
500
600
700
Stirring Speed [rpm] Fig. 3. Variation of ME content with stirring speed for vegetable oils.
[()TD$FIG]
[()TD$FIG]
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
141
(a) Canola oil
110
100
100
98 95
Percent [%]
Temperature [ºC]
90
80
93
BioDiesel Yield Methylester(ME) Content Linolenic acid ME Content
90 88
70 85 10 9 8 7 6
60
Canola Oil
150
300
450
600
750
300
450
600
750
300
450
600
750
Soybean Oil
50
(b) Soybean oil
Corn Oil
100
40 90
120
150
180
210
240
270
300
330
360
98
Ultrasonic Irradiation Time [s] 95
Percent [%]
Fig. 4. Temperature increase as a function of the ultrasonic irradiation time for the vegetable oils.
stirring speed up to 300 rpm and was constant at above 399 rpm of stirring speed.
The ultrasonic energy density was analyzed by the method of Zarzycki et al. [17]. They measured the ultrasonic energy density in the ultrasound induced solvent extraction. According to this reference, the temperature of vegetable oil was measured as a function of the irradiation time in an insulated container. The data of the temperature change with the irradiation time were linearized by the least square method and the real ultrasonic power (Pa) was calculated from the slope of the curve.
(c) Corn oil 100 98 95
(3)
If Pa is constant for the irradiation time and volume of vegetable oil, the ultrasonic energy density as a function of the ultrasonic power and irradiation time can be calculated as following manner: U a ¼ Pa t a ¼ Pa
88
150
Percent [%]
energy time
90
85 8 7 6 5
3.3. Ultrasonic energy density analysis
Pa ¼
93
93 90 88 85 2 1
t V
(4)
0 150
where t is the irradiation time (s) and V is the volume of vegetable oil (mL). In this study, the ultrasonic energy density was calculated using the experimental temperature change under constant vegetable oil volume and temperature. Fig. 4 shows the irradiation time variation on the temperature of the vegetable oil under constant ultrasonic power of 450 W. The ultrasound was irradiated continuously onto a fixed volume of vegetable oil, viz. 100 mL. The reaction temperature increased according to the first order equation with the irradiation time increment from 90 to 360 s. The increasing rates of the vegetable oil temperature were 9.44, 9.33,
Ultrasonic Irradiation Power [W] Fig. 5. Variation of BD properties with ultrasonic irradiation power for vegetable oils.
and 8.67 8C/min for canola, soybean and corn oil, respectively. Canola oil exhibited a largest temperature increase among the vegetable oils. The heat capacity was correlated with the temperature based on the DSC experimental data for each vegetable oil. The mean heat capacity, Cp , was calculated by using the following equation under temperature range from 55 to
Table 2 Energy density of various vegetable oils. Vegetable oil
r (g/cm3)
A
B 103
C 105
Cp
Canola Soybean Corn
0.893 0.888 0.828
4.1047 4.8416 3.7315
10.6 13.4 8.2
1.8836 2.0333 1.4782
2.8055 2.6989 2.7644
(J/g K)
Pa (J/s) 394.35 372.81 330.62
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
142
calculated as follow.
155 8C. C p ¼ A þ BT þ CT 2
(5)
Then, the ultrasonic power (Pa) was calculated from the average density, mean heat capacity of the vegetable oil, and ultrasonic irradiation time (270 s). The results are presented in Table 2. When the ultrasonic power was constant and the reaction time was fixed at 30 min, the ultrasonic energy densities (Ua) irradiated in the experiment were 6337.8, 5959.7, and 4926.5 kJ L1 for canola, soybean and corn oil, respectively. 3.4. Effect of ultrasonic irradiation power Fig. 5 shows the ME content and BD yield for the ultrasound induced vegetable oil esterification process. The BD yield was [()TD$FIG]
(a) Canola oil 100 98
Percent [%]
95 93
amount of methyl ester ðgÞ 100 amount of vegetable oil ðgÞ
(6)
The esterification reaction was performed for 30 min under the conditions of the molar ratio of vegetable oil to methanol of 1–6 and 1 wt% of the alkaline catalyst, KOH. The reaction temperature was constant at 55 8C by using the pulse type irradiation. The BD yield increased with increasing irradiation power from 150 to 450 W. However, the ME content decreased when the irradiation power above 450 W. This phenomenon resulted from the reduction of the real reaction time by the extension of the pulse time used for controlling the reaction temperature when the irradiation power was increased. However, when the reaction temperature was constant, a larger BD yield and ME content were obtained comparing to the case where the pulse interval was reduced or ultrasound was irradiated continuously. The real irradiation time decreased with irradiation strength to keep the constant reaction temperature, 55 8C. Therefore, it can be concluded that the pulse type irradiation at a power of 450 W was the optimum procedure. 3.5. Effect of irradiation time
BioDiesel Yield Methylester(ME) Content Linolenic acid ME Content
90 88 85 10 9 8 7 6 15
20
25
30
35
40
45
(b) Soybean oil 100 98 95
Percent [%]
BD yield ð%Þ ¼
93 90 88 85 8 7 6 5 15
Fig. 6 shows the variation of the ME content and BD yield with the ultrasonic irradiation time for the esterification of the vegetable oil. The other variables, viz. the ultrasound power, reaction temperature, vegetable oil/methanol molar ratio, and the amount of KOH, were kept constant. The ultrasound power, reaction temperature, vegetable oil/methanol molar ratio, and amount of KOH were 450 W, 55 8C, 1–6, and 1 wt%, respectively. The BD yield and ME content were both 95% at the reaction time of 30 min for the three vegetable oils. The canola oil showed largest BD yield (97.4%) and ME content (97.5%) among three types of oils at the reaction time of 30 min. The temperature increasing effect was small for canola oil because of the large heat capacity. Then the ultrasound irradiation pulse interval must be reduced. This ultrasound irradiation method shortened the reaction time more than 30 min comparing to the conventional heating method and showed an excellent conversion rate [16–18]. 4. Conclusion
20
25
30
35
40
45
(c) Corn oil 100 98
Ultrasonic energy was irradiated onto the vegetable oil during biodiesel synthetic process. The ultrasonic irradiation had alternating mixing and heating effect comparing to conventional biodiesel synthetic process. The ultrasound irradiation reduced reaction time and improved biodiesel properties without any additional mixing step in the vegetable oil esterification process. The results can be summarized as follows:
Percent [%]
95 93 90 88 85 2 1 0 15
20
25
30
35
40
45
Ultrasonic Irradiation Time [min] Fig. 6. Variation of BD properties with ultrasonic irradiation time for vegetable oils.
1. The BD yield increased with increasing ultrasonic power from 150 to 450 W, but the ME content decreased at ultrasonic powers over 450 W. This is due to the decrease of the real irradiation time caused by the increase in the pulse interval required for tuning the temperature due to the extension of the irradiation power. 2. The BD yield and ME content were both 95% at the reaction time of 30 min for all of the three vegetable oils. The canola oil exhibited best biodiesel properties of other two oils. This improvement phenomenon can be explained and was considered to be due to the larger ultrasonic energy density, Ua of 6337.8 kJ L1, compared to the other two vegetable oils at an ultrasound irradiation time of 30 min.
S.B. Lee et al. / Journal of Industrial and Engineering Chemistry 17 (2011) 138–143
3. The ultrasound irradiation method enabled to reduce the reaction time by 30 min or more comparing to conventional heating method. Also this method improved conversion rate.
References [1] [2] [3] [4] [5] [6] [7]
Y.K. Hong, W.H. Hong, Korean Chem. Eng. Res. 45 (5) (2007) 424. S.S. Kim, K.H. Kim, S.C. Shin, E.S. Yim, J. Korean Ind. Eng. Chem. 18 (5) (2007) 401. J. Janaun, N. Ellis, Renew. Sustain. Energy Rev. 14 (2010) 1312. C.S. Wassell Jr., T.P. Dittmer, Energy Policy 34 (2006) 33993. A. Demirbas, Energy Convers. Manage. 14 (2009) 50. Y.K. Lim, S.C. Shin, E.S. Yim, H.O. Song, J. Korean Ind. Eng. Chem. 19 (2008) 137. C.T. Hou, J.F. Shaw, Biocatalysis and Bioenergy, John Wiley & Sons, NY, 2008.
143
[8] H.D. Hanh, N.T. Dong, K. Okitsu, R. Nishimura, Y. Maeda, Renew. Energy 34 (2009) 766. [9] D. Yu, L. Tian, H. Wu, S. Wang, Y. Wang, D. Ma, X. Fang, Process Biochem. 45 (2010) 519. [10] C. Stavarache, M. Vinatoru, Y. Maeda, Ultrason. Sonochem. 14 (2007) 380. [11] C. Stavarache, M. Vinatoru, R. Nishimura, Y. Maeda, Ultrason. Sonochem. 12 (2005) 367. [12] J.Z. Yin, M. Xiao, J.B. Song, Energy Convers. Manage. 49 (2008) 908. [13] T.J. Mason, Chemistry with Ultrasound, Elsevier Science, NY, 1990. [14] L.T. Thanh, K. Okitsu, Y. Sadanaga, N. Takenaka, Y. Maeda, H. Bandow, Bioresour. Technol. 101 (2010) 639. [15] T.J. Mason, J.P. Lorimer, Sonochemistry, John Wiley & Sons, NY, 1998. [16] S.B. Lee, K.H. Han, J.D. Lee, I.K. Hong, J. Ind. Eng. Chem. 16 (6) (2010) 1006. [17] M. Ramirez-del-Solar, N. de la Rosa-Fox, L. Esquivias, J. Zarzycki, J. Non-Cryst. Solids 121 (1990) 40. [18] H.J. Kim, M.H. Chi, I.K. Hong, J. Ind. Eng. Chem. 13 (6) (2009) 919.