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Estimation of the content of fatty acid methyl esters (FAME) in biodiesel samples from dynamic viscosity measurements
Fuel Processing Technology 92 (2011) 597–599
Contents lists available at ScienceDirect
Fuel Processing Technology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / f u p r o c
Estimation of the content of fatty acid methyl esters (FAME) in biodiesel samples from dynamic viscosity measurements M.E. Borges a,⁎, L. Díaz a, J. Gavín b, A. Brito a a b
Chemical Engineering Department, University of La Laguna; Avda. Astrofísico Fco. Sánchez s/n, La Laguna, Tenerife, Canary Island, 38200, Spain Organic Chemistry Department, University of La Laguna; Avda. Astrofísico Fco. Sánchez s/n, La Laguna, Tenerife, Canary Island, 38200, Spain
a r t i c l e
i n f o
Article history: Received 22 July 2010 Accepted 16 November 2010 Available online 28 December 2010 Keywords: Biodiesel FAME NMR Viscosity
a b s t r a c t In order for biodiesel to be commercialized as pure biofuel or blending stock for diesel fuels, it must meet a set of requirements defined in standard specifications for a safe and satisfactory engine operation, one of these specifications is the content of fatty acid methyl esters (FAME). Besides, this parameter indicates the performance of the transesterification reaction for biofuel production from vegetable oils. There are several methods to determinate FAME content in biodiesel samples (chromatography, nuclear magnetic resonance spectroscopy and FTIR spectroscopy); however, they take long times and high cost for FAME content determination. From a practical point of view, in industrial biodiesel production is usually necessary to estimate the FAME value quickly. This paper presents correlations experimentally obtained from different oil feedstocks in order to estimate the biodiesel FAME content from the biodiesel dynamic viscosity, a fast determination parameter. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Rapid diminishing of energy reserves and fluctuating petroleum prices has intensified the search for renewable energy sources [1]. Biodiesel is an alternative diesel fuel consisting of fatty acid alkyl esters obtained from vegetable oil or animal fats. It has been the focus of a considerable amount of recent research because it is renewable, reduces the emission of some pollutants, and is also readily biodegradable in the environment [2,3]. Biodiesel can be produced through transesterification of vegetable oil or by esterification of free fatty acids with light alcohols [4,5] in presence of a suitable catalyst. The reaction requires acid or alkali catalysts. Homogeneous base catalysts, such as NaOH and KOH, are prefered instead of acid catalysts due to the high reaction rates obtained for low reaction temperatures [6]. However, these alkali compounds have some drawbacks. They must be neutralized giving rise to wastewaters, they cannot be reutilized, they favour the formation of stable emulsions making the methyl esters (biodiesel) separation difficult, glycerol is obtained as an aqueous solution of relatively low purity and the reaction becomes very sensitive to the presence of water and free fatty acids [7,8]. Heterogeneous solid base catalysts can solvent these problems: they can be easily separated from the reaction mixture without the use of water as solvent, they
⁎ Corresponding author. E-mail address: [email protected] (M.E. Borges). 0378-3820/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2010.11.016
can be regenerated and have a less corrosive character, leading to safer, cheaper and more environment-friendly operations [6,9]. The conversion of vegetable oil to its FAME results in an important reduction in its viscosity, usually from 25-40 cSt to 4-5 cSt, depending on the type of oil used as feedstock. Derived from our studies on the use of several solids as catalyst for the transesterification of vegetal oils with methanol, we developed a reliable and fast method to monitor the transesterification reaction development. The usual way to determine the reaction yield is to analyse the FAME content of the biodiesel reaction product. Analytic methods used, mainly gas chromatography, require previous sample treatment or tedious calibrations. Recently, less complicated analytic methods (RMN, IR) have been developed [10–14] but they require costly equipment and analysis. In a biodiesel production industry, it is important to monitor quickly the reaction extent achieved in the process or the methyl esters content in a biodiesel sample. In this work, we decide to investigate a cheap and fast method to quantify directly the FAME content in the reaction mixture and then the transesterification reaction yield. Biodiesel viscosity is a very important parameter to fit with for its use in diesel engines. Because biodiesel is a mixture of several FAMEs with each component contributing to the overall viscosity, it could be possible to find the relation between viscosity and the fatty acid methyl esters content of the biodiesel. Dynamic viscosity value can be determinate by a fast, cheap and no destructive analysis with low cost equipment. Therefore, the aim of this work is to develop a correlation in order to determine the methyl esters content in biodiesel from its dynamic viscosity value.
598
M.E. Borges et al. / Fuel Processing Technology 92 (2011) 597–599
2. Experimental 2.1. Materials The biodiesel studied was produced by transesterification of three types of oils: sunflower oil, fried oil and Jatropha Curcas oil. The first one was commercial edible-grade sunflower oil purchased from the market and used without further purification; the second one was waste oil from frying in a canteen and it was previously filtered to remove suspended solids; the third one was Jatropha oil, which was extracted from its seeds. The main properties of these oils are shown in Table 1. Methanol used was analytical grade obtained from Scharlau. 2.2. Biodiesel synthesis and analysis Heterogeneous and homogeneous transesterification reactions were performed in a 250 ml jacketed glass reactor, equipped with a reflux condenser and agitation, using several catalysts. In order to obtain biodiesel reaction products with a broad range of reaction yields, several transesterification reactions were carried out at different temperatures (from 50 to 60 °C), reaction times (from 30 min to 240 min), methanol/oil molar ratios (6:1– 24:1) and catalyst amounts (4-20 wt.%). Different solids as heterogeneous catalysts were used for heterogeneous reactions and KOH was used as catalyst for homogeneous reactions. In all cases, the catalyst was separated from the reaction mixture after reaction and the liquid product obtained was evaporated to remove methanol excess, and then the upper phase containing fatty acid methyl esters (biodiesel phase) and the lower phase containing glycerol were separated in a decantation funnel. The biodiesel product from each reaction was collected and its dynamic viscosity was measured using a rotational viscometer VISCO STAR Plus L. Moreover, the same biodiesel sample was analyzed by 1H Nuclear Magnetic Resonance (NMR) spectrometry (Bruker Avance 400) in order to estimate the fatty acid methyl ester yield using following formula [12]: Yield ð%Þ =
2A1 d100 3A2
where A1 and A2 are the areas of the methoxy and the methylene protons, respectively. This relevant signals chosen for integration are those of methoxy groups in the methyls esters at 3.7 ppm (singlet) and of the α-carbonyl methylene groups present in all fatty ester derivatives at 2.3 ppm (triplet). Previously, biodiesel samples were dried with anhydrous Na2SO4 and, then submitted to NMR analysis in deuterated chloroform (CDCl3) using tetramethylsilanen (TMS) as internal standard. 3. Results and discussion Fig. 1 shows as an example 1H-NMR spectra of samples containing several FAME content. It can be seen that the only significant change in the spectra is the appearance of a new singlet peak at 3.7 ppm when fatty acid methyl esters are produced. All other peaks related to aliphatic and olefinic hydrogens of the alkyl chain remain in the Table 1 Properties of feedstock oils for biodiesel samples production. Property
Sunflower oil
Waste oil
Jatropha Curcas oil
Density at 15 °C (g/cm3) Kinematic viscosity at 40 °C (cSt) Acid value (mg KOH/g) Iodine index (g Iodine/100 g sample) Turbidity (NTU)
0.924 29.4 0.17 138.8 2.24
0.930 34.5 2.02 122.3 9.99
0.923 27.6 2.95 121.0 3.59
Fig. 1. 1H-NMR spectra: (a) sunflower oil, (b) biodiesel sample with 39.7% FAME, (c) biodiesel sample with 95.6% FAME.
M.E. Borges et al. / Fuel Processing Technology 92 (2011) 597–599
100
measures in biodiesel samples. This method is suitable for the determination of methyl ester contents considering different sources of vegetable oils.
Sunflower and Jatropha oil
90
599
Waste oil
FAME yield (%)
80 70
Acknowledgements
60
The authors acknowledge a research grant support by Programa de FPU del Ministerio de Educación, Spain.
50 40
References
30
[1] M.K. Lam, K.T. Lee, A.R. Mohamed, Sulfated tin oxide as solid superacid catalyst for transesterification of waste cooking oil: An optimization study, Applied Catalysis B: Environmental 93 (2009) 134–139. [2] A. Bouaid, M. Martinez, J. Aracil, Long storage stability of biodiesel from vegetable and used frying oils, Fuel 86 (16) (2007) 2596–2602. [3] N. Seshu Babu, R. Sree, P.S. Sai Prasad, N. Lingaiah, Room-Temperature transesterificación of edible and non-edible oils using a heterogeneous Strong Basic Mg/La catalyst, Energy and Fuels 22 (2008) 1965–1971. [4] A. Banerjee, R. Chakraborty, Parametric sensitivity in transesterification of waste cooking oil for biodiesel production—A review, Resources, Conservation and Recycling 53 (9) (2009) 490–497. [5] F. Ma, M.A. Hanna, Biodiesel production: a review, Bioresource Technology 70 (1) (1999) 1–15. [6] W. Xie, Z. Yang, Ba-ZnO catalyst for soybean oil transesterification, Catalysis Letters 117 (2007) 159–165. [7] G. Arzamendi, I. Campo, E. Arguiñarena, M. Sánchez, M. Montes, L.M. Gandía, Synthesis of biodiesel with heterogeneous NaOH/alumina catalysts: comparison with homogeneous NaOH, Chemical Engineering Journal 134 (2007) 123–130. [8] Z. Wen, X. Yu, S. Tu, J. Yan, E. Dahlquist, Synthesis of biodiesel from vegetable oil with methanol catalyzed by Li-doped magnesium oxide catalysts, Applied Energy 87 (2010) 743–748. [9] K.G. Georgogianni, A.K. Katsoulidis, P.J. Pomonis, M.G. Kontominas, Transesterification of rapeseed oil for the production of biodiesel using homogeneous and heterogeneous catalysis, Fuel Processing Technology 90 (2009) 1016–1022. [10] J.S. Oliveira, R. Montalvão, L. Daher, P.A.Z. Suarez, J.C. Rubim, Determination of methyl ester contents in biodiesel blends by FTIR-ATR and FTNIR spectroscopies, Talanta 69 (5) (2006) 1278–1284. [11] M.R. Monteiro, A.R.P. Ambrozin, L.M. Lião, A.G. Ferreira, Determination of biodiesel blend levels in different diesel samples by 1H NMR, Fuel 88 (4) (2009) 691–696. [12] G. Gelbard, O. Brès, R.M. Vargas, F. Vielfaure, U.F. Schuchardt, 1H Nuclear Magnetic Resonance determination of the yield of the transesterification of rapeseed oil with methanol, Journal of the American Oil Chemist's Society 72 (10) (1995) 1239–1241. [13] F. Jin, K. Kawasaki, H. Kishida, K. Tohji, T. Moriya, H. Enomoto, NMR spectroscopic study on methanolysis reaction of vegetable oil, Fuel 86 (2007) 1201–1207. [14] M. Morgenstern, J. Cline, S. Meyer, S. Cataldo, Determination of the kinetics of biodiesel production using proton nuclear magnetic resonance spectroscopy (1H NMR), Energy and Fuels 20 (2006) 1350–1353.
20 10 0 0
5
10
15
20
25
30
35
40
Dynamic viscosity (cp) Fig. 2. Fatty acid methyl esters content vs biodiesel samples dynamic viscosity.
same position being in good agreement with the values published in bibliography [13,14]. In Fig. 2, the viscosity value is plotted against the FAME yield of each biodiesel sample. As can be seen, the same correlation has been obtained for both vegetal oils studied; however, biodiesel samples obtained from waste oil fits another curve. For practical purposes, equation 1 is applicable for predicting biodiesel FAME yields from its viscosity, Eq. 2 must be used when biodiesel proceeds of waste oil feedstock where μ is the dynamic viscosity measured at 40 °C in centipoises. −μ FAME yield ð%Þ = 158; 5 eð 6;8Þ
ð1Þ
− μ FAME yield ð%Þ = 135;1eð 10;1Þ
ð2Þ
4. Conclusions In summary, we have demonstrated that it is possible to develop a fast fatty acid methyl esters content estimation from viscosity
Contents lists available at ScienceDirect
Fuel Processing Technology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / f u p r o c
Estimation of the content of fatty acid methyl esters (FAME) in biodiesel samples from dynamic viscosity measurements M.E. Borges a,⁎, L. Díaz a, J. Gavín b, A. Brito a a b
Chemical Engineering Department, University of La Laguna; Avda. Astrofísico Fco. Sánchez s/n, La Laguna, Tenerife, Canary Island, 38200, Spain Organic Chemistry Department, University of La Laguna; Avda. Astrofísico Fco. Sánchez s/n, La Laguna, Tenerife, Canary Island, 38200, Spain
a r t i c l e
i n f o
Article history: Received 22 July 2010 Accepted 16 November 2010 Available online 28 December 2010 Keywords: Biodiesel FAME NMR Viscosity
a b s t r a c t In order for biodiesel to be commercialized as pure biofuel or blending stock for diesel fuels, it must meet a set of requirements defined in standard specifications for a safe and satisfactory engine operation, one of these specifications is the content of fatty acid methyl esters (FAME). Besides, this parameter indicates the performance of the transesterification reaction for biofuel production from vegetable oils. There are several methods to determinate FAME content in biodiesel samples (chromatography, nuclear magnetic resonance spectroscopy and FTIR spectroscopy); however, they take long times and high cost for FAME content determination. From a practical point of view, in industrial biodiesel production is usually necessary to estimate the FAME value quickly. This paper presents correlations experimentally obtained from different oil feedstocks in order to estimate the biodiesel FAME content from the biodiesel dynamic viscosity, a fast determination parameter. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Rapid diminishing of energy reserves and fluctuating petroleum prices has intensified the search for renewable energy sources [1]. Biodiesel is an alternative diesel fuel consisting of fatty acid alkyl esters obtained from vegetable oil or animal fats. It has been the focus of a considerable amount of recent research because it is renewable, reduces the emission of some pollutants, and is also readily biodegradable in the environment [2,3]. Biodiesel can be produced through transesterification of vegetable oil or by esterification of free fatty acids with light alcohols [4,5] in presence of a suitable catalyst. The reaction requires acid or alkali catalysts. Homogeneous base catalysts, such as NaOH and KOH, are prefered instead of acid catalysts due to the high reaction rates obtained for low reaction temperatures [6]. However, these alkali compounds have some drawbacks. They must be neutralized giving rise to wastewaters, they cannot be reutilized, they favour the formation of stable emulsions making the methyl esters (biodiesel) separation difficult, glycerol is obtained as an aqueous solution of relatively low purity and the reaction becomes very sensitive to the presence of water and free fatty acids [7,8]. Heterogeneous solid base catalysts can solvent these problems: they can be easily separated from the reaction mixture without the use of water as solvent, they
⁎ Corresponding author. E-mail address: [email protected] (M.E. Borges). 0378-3820/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2010.11.016
can be regenerated and have a less corrosive character, leading to safer, cheaper and more environment-friendly operations [6,9]. The conversion of vegetable oil to its FAME results in an important reduction in its viscosity, usually from 25-40 cSt to 4-5 cSt, depending on the type of oil used as feedstock. Derived from our studies on the use of several solids as catalyst for the transesterification of vegetal oils with methanol, we developed a reliable and fast method to monitor the transesterification reaction development. The usual way to determine the reaction yield is to analyse the FAME content of the biodiesel reaction product. Analytic methods used, mainly gas chromatography, require previous sample treatment or tedious calibrations. Recently, less complicated analytic methods (RMN, IR) have been developed [10–14] but they require costly equipment and analysis. In a biodiesel production industry, it is important to monitor quickly the reaction extent achieved in the process or the methyl esters content in a biodiesel sample. In this work, we decide to investigate a cheap and fast method to quantify directly the FAME content in the reaction mixture and then the transesterification reaction yield. Biodiesel viscosity is a very important parameter to fit with for its use in diesel engines. Because biodiesel is a mixture of several FAMEs with each component contributing to the overall viscosity, it could be possible to find the relation between viscosity and the fatty acid methyl esters content of the biodiesel. Dynamic viscosity value can be determinate by a fast, cheap and no destructive analysis with low cost equipment. Therefore, the aim of this work is to develop a correlation in order to determine the methyl esters content in biodiesel from its dynamic viscosity value.
598
M.E. Borges et al. / Fuel Processing Technology 92 (2011) 597–599
2. Experimental 2.1. Materials The biodiesel studied was produced by transesterification of three types of oils: sunflower oil, fried oil and Jatropha Curcas oil. The first one was commercial edible-grade sunflower oil purchased from the market and used without further purification; the second one was waste oil from frying in a canteen and it was previously filtered to remove suspended solids; the third one was Jatropha oil, which was extracted from its seeds. The main properties of these oils are shown in Table 1. Methanol used was analytical grade obtained from Scharlau. 2.2. Biodiesel synthesis and analysis Heterogeneous and homogeneous transesterification reactions were performed in a 250 ml jacketed glass reactor, equipped with a reflux condenser and agitation, using several catalysts. In order to obtain biodiesel reaction products with a broad range of reaction yields, several transesterification reactions were carried out at different temperatures (from 50 to 60 °C), reaction times (from 30 min to 240 min), methanol/oil molar ratios (6:1– 24:1) and catalyst amounts (4-20 wt.%). Different solids as heterogeneous catalysts were used for heterogeneous reactions and KOH was used as catalyst for homogeneous reactions. In all cases, the catalyst was separated from the reaction mixture after reaction and the liquid product obtained was evaporated to remove methanol excess, and then the upper phase containing fatty acid methyl esters (biodiesel phase) and the lower phase containing glycerol were separated in a decantation funnel. The biodiesel product from each reaction was collected and its dynamic viscosity was measured using a rotational viscometer VISCO STAR Plus L. Moreover, the same biodiesel sample was analyzed by 1H Nuclear Magnetic Resonance (NMR) spectrometry (Bruker Avance 400) in order to estimate the fatty acid methyl ester yield using following formula [12]: Yield ð%Þ =
2A1 d100 3A2
where A1 and A2 are the areas of the methoxy and the methylene protons, respectively. This relevant signals chosen for integration are those of methoxy groups in the methyls esters at 3.7 ppm (singlet) and of the α-carbonyl methylene groups present in all fatty ester derivatives at 2.3 ppm (triplet). Previously, biodiesel samples were dried with anhydrous Na2SO4 and, then submitted to NMR analysis in deuterated chloroform (CDCl3) using tetramethylsilanen (TMS) as internal standard. 3. Results and discussion Fig. 1 shows as an example 1H-NMR spectra of samples containing several FAME content. It can be seen that the only significant change in the spectra is the appearance of a new singlet peak at 3.7 ppm when fatty acid methyl esters are produced. All other peaks related to aliphatic and olefinic hydrogens of the alkyl chain remain in the Table 1 Properties of feedstock oils for biodiesel samples production. Property
Sunflower oil
Waste oil
Jatropha Curcas oil
Density at 15 °C (g/cm3) Kinematic viscosity at 40 °C (cSt) Acid value (mg KOH/g) Iodine index (g Iodine/100 g sample) Turbidity (NTU)
0.924 29.4 0.17 138.8 2.24
0.930 34.5 2.02 122.3 9.99
0.923 27.6 2.95 121.0 3.59
Fig. 1. 1H-NMR spectra: (a) sunflower oil, (b) biodiesel sample with 39.7% FAME, (c) biodiesel sample with 95.6% FAME.
M.E. Borges et al. / Fuel Processing Technology 92 (2011) 597–599
100
measures in biodiesel samples. This method is suitable for the determination of methyl ester contents considering different sources of vegetable oils.
Sunflower and Jatropha oil
90
599
Waste oil
FAME yield (%)
80 70
Acknowledgements
60
The authors acknowledge a research grant support by Programa de FPU del Ministerio de Educación, Spain.
50 40
References
30
[1] M.K. Lam, K.T. Lee, A.R. Mohamed, Sulfated tin oxide as solid superacid catalyst for transesterification of waste cooking oil: An optimization study, Applied Catalysis B: Environmental 93 (2009) 134–139. [2] A. Bouaid, M. Martinez, J. Aracil, Long storage stability of biodiesel from vegetable and used frying oils, Fuel 86 (16) (2007) 2596–2602. [3] N. Seshu Babu, R. Sree, P.S. Sai Prasad, N. Lingaiah, Room-Temperature transesterificación of edible and non-edible oils using a heterogeneous Strong Basic Mg/La catalyst, Energy and Fuels 22 (2008) 1965–1971. [4] A. Banerjee, R. Chakraborty, Parametric sensitivity in transesterification of waste cooking oil for biodiesel production—A review, Resources, Conservation and Recycling 53 (9) (2009) 490–497. [5] F. Ma, M.A. Hanna, Biodiesel production: a review, Bioresource Technology 70 (1) (1999) 1–15. [6] W. Xie, Z. Yang, Ba-ZnO catalyst for soybean oil transesterification, Catalysis Letters 117 (2007) 159–165. [7] G. Arzamendi, I. Campo, E. Arguiñarena, M. Sánchez, M. Montes, L.M. Gandía, Synthesis of biodiesel with heterogeneous NaOH/alumina catalysts: comparison with homogeneous NaOH, Chemical Engineering Journal 134 (2007) 123–130. [8] Z. Wen, X. Yu, S. Tu, J. Yan, E. Dahlquist, Synthesis of biodiesel from vegetable oil with methanol catalyzed by Li-doped magnesium oxide catalysts, Applied Energy 87 (2010) 743–748. [9] K.G. Georgogianni, A.K. Katsoulidis, P.J. Pomonis, M.G. Kontominas, Transesterification of rapeseed oil for the production of biodiesel using homogeneous and heterogeneous catalysis, Fuel Processing Technology 90 (2009) 1016–1022. [10] J.S. Oliveira, R. Montalvão, L. Daher, P.A.Z. Suarez, J.C. Rubim, Determination of methyl ester contents in biodiesel blends by FTIR-ATR and FTNIR spectroscopies, Talanta 69 (5) (2006) 1278–1284. [11] M.R. Monteiro, A.R.P. Ambrozin, L.M. Lião, A.G. Ferreira, Determination of biodiesel blend levels in different diesel samples by 1H NMR, Fuel 88 (4) (2009) 691–696. [12] G. Gelbard, O. Brès, R.M. Vargas, F. Vielfaure, U.F. Schuchardt, 1H Nuclear Magnetic Resonance determination of the yield of the transesterification of rapeseed oil with methanol, Journal of the American Oil Chemist's Society 72 (10) (1995) 1239–1241. [13] F. Jin, K. Kawasaki, H. Kishida, K. Tohji, T. Moriya, H. Enomoto, NMR spectroscopic study on methanolysis reaction of vegetable oil, Fuel 86 (2007) 1201–1207. [14] M. Morgenstern, J. Cline, S. Meyer, S. Cataldo, Determination of the kinetics of biodiesel production using proton nuclear magnetic resonance spectroscopy (1H NMR), Energy and Fuels 20 (2006) 1350–1353.
20 10 0 0
5
10
15
20
25
30
35
40
Dynamic viscosity (cp) Fig. 2. Fatty acid methyl esters content vs biodiesel samples dynamic viscosity.
same position being in good agreement with the values published in bibliography [13,14]. In Fig. 2, the viscosity value is plotted against the FAME yield of each biodiesel sample. As can be seen, the same correlation has been obtained for both vegetal oils studied; however, biodiesel samples obtained from waste oil fits another curve. For practical purposes, equation 1 is applicable for predicting biodiesel FAME yields from its viscosity, Eq. 2 must be used when biodiesel proceeds of waste oil feedstock where μ is the dynamic viscosity measured at 40 °C in centipoises. −μ FAME yield ð%Þ = 158; 5 eð 6;8Þ
ð1Þ
− μ FAME yield ð%Þ = 135;1eð 10;1Þ
ð2Þ
4. Conclusions In summary, we have demonstrated that it is possible to develop a fast fatty acid methyl esters content estimation from viscosity