Energy Fuels 2010, 24, 6527–6532 Published on Web 11/18/2010
: DOI:10.1021/ef101228f
Heterogeneous Catalysis of Babassu Oil Monitored by Thermogravimetric Analysis Carla Ver^ onica Rodarte de Moura,* Adriano Gomes de Castro, Edmilson Miranda de Moura, Jose Ribeiro dos Santos Jr., and Jose Machado Moita Neto Department of Chemistry, Universidade Federal do Piauı´ (UFPI), Teresina, Piauı´ (PI) CEP 64049-550, Brazil Received July 4, 2010. Revised Manuscript Received October 29, 2010
This paper investigates the transesterification of babassu oil to biodiesel in a fixed-bed reactor using strontium oxide (SrO) as a catalyst. Under room temperature, atmospheric pressure, and 100 g of babassu oil initial feeding, babassu oil conversion reached almost 100% after 3 h using 1.5 g of SrO. This result shows a promising and commercially viable path to produce biodiesel. In terms of technical quality, it was found that the reaction time is a key issue rather than the amount of catalyst in use. In addition, the thermogravimetric analysis (TGA) method was found as accurate as nuclear magnetic resonance (NMR) for measurement of the conversion.
the bed, and not to mention, the catalyst can be reused many times.8,9 The main source of raw material in Brazil for biodiesel production is soybean oil. However, this oil is also consumed in food products. Therefore, it is necessary to diversify supply option raw material for this purpose. Fortunately, Brazil has a great diversity of plants that can be used to manufacture biodiesel. One of them is babassu coconut oil, where northeast Brazil has an area of about 12 million planted hectares, with most concentrated in the states of Maranh~ ao and Piauı´ .10 Monthly, around 140 000 tons of almonds are drawn from this culture, and it is possible to use the entire coconut. For example, the mesocarp can be used in the manufacturing of medium-density fiberboard (MDF) composite; the core material can be used as charcoal.10 With regard to the production of fuel oil, babassu oil has excellent characteristics for biodiesel production because of its composition being predominantly lauric ester.10 This fact facilitates the transesterification reaction, because the lauric ester is composed of short chains that interact more effectively with the alcohol and catalyst to obtain a product with excellent physicochemical characteristics, even though the catalyst is different from NaOH. The literature11 shows that, when using heterogeneous catalysts and babassu oil for synthesis of biodiesel, higher yields are obtained in comparison to other oils. There are many methods for characterization of biodiesel, including gas chromatography (GC),12 high-pressure liquid chromatography,13 nuclear magnetic resonance (NMR) spectroscopy,14,15 and Fourier transform near-infrared (NIR) and infrared (IR) spectroscopy.16 Among such techniques,
Introduction Biodiesel has emerged as a promising alternative to mineral fuels. This renewable characteristic makes it an important source of energy. It can improve air quality because of the reduction in the emission of greenhouse gases and sulfur,1,2 and it can be used in stationary diesel or automotive engines as an additive, without adaptation.3 Industrially, the main catalyst used to produce biodiesel is NaOH, a homogeneous catalyst. However, NaOH can cause some problems in the process, such as the formation of soap or emulsion.4 The heterogeneous catalysts have been widely studied and have advantages in the commercial production of biodiesel, having a positive impact on the economy and the environment.5,6 The literature shows that the alkali metal oxides have been used as catalysts for the transesterification reaction of oils.5 Liu et al.7 have studied the use of strontium oxide (SrO) as the catalyst for the biodiesel production from soybean and achieved conversions exceeding 95%. The researchers say that SrO has an excellent catalytic activity and stability because of its strong basicity and long life and because it is insoluble in methanol.7 The use of a fixed-bed reactor offers advantages for the production of biodiesel, because it can significantly reduce the number of stages of the production process. Requiring limited ancillary equipment, it facilitates adequate contact between fluid phases and the catalyst because of fixation of particles in *To whom correspondence should be addressed. Telephone: 55-86(32155840). Fax: 55-86(32155632). E-mail:
[email protected]. (1) Omer, A. M. Renewable Sustainable Energy Rev. 2008, 12, 1789– 1821. (2) Rashid, U.; Anwar, F. Fuel 2008, 87, 265–273. (3) Pinto, A. C. J. Braz. Chem. Soc. 2005, 16 (6B), 1313–1330. (4) Mohamad, I.; Ali, O. A. Bioresour. Technol. 2002, 85, 253–256. (5) Liu, X.; He, H.; Wang, Y.; Zhu, S.; Piao, X. Fuel 2008, 87, 216–221. (6) Silva, A. R. B.; Neto, A. F. L.; Santos, L. S. S.; Lima, J. R. O.; Chaves, M. H.; Santos, J. R., Jr.; Lima, G. M.; Moura, E. M.; Moura, C. V. R. Bioresour. Technol. 2008, 99, 6793–6798. (7) Liu, X.; He, H.; Wang, Y.; Zhu, S. Catal. Commun. 2007, 8, 1107– 1111. (8) Ramaswamy, R. C.; Ramachandran, P. A.; Dudukovic, M. P. Ind. Eng. Chem. Res. 2007, 46, 8638–8651. (9) Helwani, Z.; Othman, M. R.; Aziz, N.; Fernando, W. J. N.; Kim, J. Fuel Proces. Technol. 2009, 90, 1502–1514. r 2010 American Chemical Society
(10) Lima, J. R. O.; Silva, R. B.; Silva, C. C. M.; Santos, L. S. S.; dos Santos, J. R., Jr.; Moura, E. M.; Moura, C. V. R. Quim. Nova 2007, 30, 600–603. (11) Barros, S. V. Rev. Amazonia 2010, 20, 25. (12) Abreu, F. R.; Lima, D. G.; Hamu, E. H.; Wolf, C.; Suarez, P. A. Z. J. Mol. Catal. A: Chem. 2004, 209, 29–33. (13) Plank, C.; Lorbeer, E. J. Chromatogr., A 1995, 697, 461–468. (14) Holcapek, M.; Jandera, P.; Fischer, J.; Prokes, B. J. Chromatogr., A 1999, 858, 13–31. (15) Neto, P. R. C.; Caro, M. S. B.; Mazzuco, L. M.; Nascimento, M. G. J. Am. Oil Chem. Soc. 2004, 81, 1111–1114. (16) Dube, M. A.; Zheng, S.; McLean, D. D.; Kates, M. J. Am. Oil Chem. Soc. 2004, 81, 599–603.
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Energy Fuels 2010, 24, 6527–6532
: DOI:10.1021/ef101228f
de Moura et al.
NMR and GC have been extensively used and are considered standard techniques for the characterization of substances by many researchers.17 Thermogravimetric analysis (TGA) is a technique to measure the thermal stability of materials, whether pure or mixed, expressing the result as a major change with increasing temperature.18 According to Lima et al.,10 biodiesel is a mixture of alkyl esters that exhibit physical properties similar to pure esters; therefore, it tends to show volatility and a boiling range dependent upon the fatty acid composition, especially with the size of the chain and unsaturation number. Thus, the boiling range of biodiesel will be the average of the boiling points of the fatty esters that comprise the mixture. As described by Goodrum,18 the TGA technique can be used as a screening method for determining the boiling point and monitoring the transesterification reaction because the results are accurate ((5%), there is no evidence that the sample undergoes thermal decomposition when the analysis is performed at 1 atm, and also, the cost of analysis is low. The proposed monitoring of transesterification reactions by TGA does not provide structural information, such as NMR, GC, or IR, based on the properties for use because heating and volatilization of the sample is part of the implementation of fuel. Esters coming into boiling at high temperatures (such as vegetable oils) are good for use and, therefore, are transformed into esters with lower boiling temperature (ethyl or methyl esters). The yield of the transesterification reactions can be advantageously obtained by TGA and compared to established techniques for the same purpose. Therefore, we believe that the biodiesel industry can make use of this technique to control the production of biodiesel, to determine the time of the conversion reaction. Importantly, this technique may be used only to monitor the progress of the transesterification reaction and not to determine the final quality of product.19 Given the facts presented above, the study in question describes the construction of a fixed-bed reactor, where SrO was used as the heterogeneous catalyst and babassu oil was as the feedstock to produce biodiesel. The product was characterized by the techniques of GC-mass spectrometry (MS), 1 H NMR, IR, TGA, and physicochemical characterization. Also described is the possibility of the use of the TGA technique to monitor the yield of biodiesel and compare it to 1 H NMR and GC results.
Figure 1. Schematic view of the process used in this work. Table 1. Optimum Reaction Conditionsa
a
sample
time (h)
catalyst quantity (g)
BD1 BD2 BD3 BD4 BD5 BD6 BD7 BD8 BD9 BD10 BD11 BD12 BD13 BD14 BD15
1 1 1 1 1 2 2 2 2 2 3 3 3 3 3
0.50 1.00 1.50 2.00 2.50 0.50 1.00 1.50 2.00 2.50 0.50 1.00 1.50 2.00 2.50
All of the samples were run at room temperature.
and NaCl window) and attenuated total reflection cell, with ATR with ZnSe crystal in the spectral range from 4000 to 400 cm-1. The GC-MS analysis was performed in a chromatograph Varian CP-3380 column BP 20, 12 m 0.25 mm (SGE), with Carbowax 20M (polyethylene glycol) as the stationary phase, with a flame ionization detector (FID). Conditions: initial column temperature, 200 °C; increasing the temperature at a rate of 10 °C/min to 240 °C; injector temperature, 250 °C; splitting ratio, 1:100; and detector temperature, 260 °C. The specific surface area was performed from adsorption-desorption Brunauer-Emmett-Teller (BET) method isotherms of nitrogen measured at 77 K in an ASAP2010 apparatus (Micromeritics, Norcross, GA). The samples were run in an atmosphere of N2 and degassed at 250 °C for 20 h before analysis. The 1H NMR spectra were obtained using a Bruker Avance DPX 250 apparatus, at 250 MHz, and a Varian 500, at 500 MHz, with CDCl3 as the solvent, which served as the internal standard. The viscosity, density, sulfur, flash point, cold filter plugging point, free and total glycerol, mono-, di-, and triglyceride, and determination of oxidation stability (accelerated oxidation test) were determined in accordance with methods described in ANP resolution 07/2008.20 The neutralization number, saponification number, and acidity index were determined by analytical norms of the Adolfo Lutz Institute.21 Catalyst Preparation. SrO was prepared from calcinations of SrCO3 in a muffle furnace at 1200 °C for 5 h, as described by Liu et al.,7 and it was characterized by IR and BET analysis. Fixed-Bed Reactor Construction. The fixed-bed reactor (Figure 1) consists of a catalyst-packed hollow glass tube, a beaker (600 mL), silicone hoses (fluid flow), and an immersion pump, with a discharge flow rate of 360 L/h. The beaker used
Experimental Section Reagents and Equipments. All reagents used in this work were analytical-grade, purchased from Synth, Vetec, and Sigma-Aldrich, and used without prior purification. The refined babassu oil was a donation from Oleos Nilo, an oil company located in Teresina, Piauı´ (PI), Brazil. TGA was executed using a differential thermal analysis (DTA)/thermogravimetry (TG) analyzer (SDT 2960, TA Instruments) in nitrogen, with a heating rate of 3 °C/min, using an aluminum pan of 20 μL with a hole of approximately 0.5 mm in diameter in the lid. All of the analyses were performed in triplicate. IR spectra were obtained using a Fourier transform infrared (FTIR) spectrometer Bomer MB series B 100 and an attenuated total reflectance (ATR) cell with ZnSe crystal and angle of 45°. It was a technique of transmission (KBr pellet
(20) Ag^encia Nacional de Petr oleo, Gas Natural e Biocombustı´ veis (ANP). Resoluc-a~o 07/2008; http://anp.gov.br (acessed on July 2010). (21) Instituto Adolfo Lutz. Normas Analı´ticas do Instituto Adolfo Lutz, 3rd ed.; Instituto Adolfo Lutz: Sao Paulo, Brazil, 1985; Vol. 1: Metodos Químicos e Físicos para Analise de Alimentos, pp 245-250.
(17) Knothe, G. J. Am. Oil Chem. Soc. 2000, 77, 489–493. (18) Goodrum, J. W. J. Am. Oil Chem. Soc. 1997, 74, 947–950. (19) Chand, P.; Reddy, V. Ch.; Verkade, J. G.; Wang, T.; Grewell, D. Energy Fuels 2009, 23, 989–992.
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Energy Fuels 2010, 24, 6527–6532
: DOI:10.1021/ef101228f
de Moura et al.
Figure 2. IR spectra of SrCO3 and SrO. Table 2. TGA and Viscometer Results TGA
samples
time (h)
catalyst (wt %)
OB
Figure 3. Viscosity reaction time.
range temperature (°C)
weight loss (%)
315.61-476.10
P98.73 98.73 49.38 P49.76 99.14 51.68 P48.08 99.76 52.71 P47.11 99.82 61.30 P38.52 99.82 61.67 P38.15 99.82 62.43 P37.39 99.82 63.75 P36.07 99.82 63.86 P35.96 99.82 63.92 P35.90 99.82 64.35 P35.47 99.82 64.32 P34.68 99.00 76.78 P22.98 99.76 91.37 P 7.38 99.15 89.58 P 9.41 98.99 90.12 P 8.89 99.01
BD1
1
0.5
135.90-330.20 330.20-489.60
BD2
1
1.0
154.20-319.00 319.00-483.80
BD3
1
1.5
183.60-323.80 323.8-482.00
BD4
1
2.0
182.70-315.80 315.8-482.45
BD5
1
2.5
182.50-314.76 314.76-476.78
BD6
2
0.5
176.70-311.80 311.8-474.48
BD7
2
1.0
178.70-319.80 319.8-476.67
BD8
2
1.5
185.60-311.54 311.54-476.45
BD9
2
2.0
181.70-314.56 314.56-477.25
BD10
2
2.5
182.76-319.23 319.23-473.45
BD11
3
0.5
150.50-323.40 323.40-475.80
BD12
3
1.0
164.20-323.00 323.00-482.80
BD13
3
1.5
131.93-340.93 340.93-430.29
BD14
3
2.0
182.68-364.80 364.8-437.56
BD15
3
2.5
178.70-385.69 365.69-439.45
viscosity at 40 °C (mm2/s)
outer diameter, 1.5 cm in inner diameter, and 3.5 cm long. A cotton-cloth filter was used as a bed to pack the catalyst, and this filter covered the entire area of the reactor, forming an inner shirt. The filter was filled with varying amounts of catalyst, because this amount has been optimized for this study, as described in Biodiesel Production, and methanol was percolated to package it and avoid the formation of bubbles along the bed. Biodiesel Production. In Table 1, the reaction conditions investigated and adjusted parameters used in this study are described. The amount of catalyst varied from 0.5 to 2.5% based on the mass of vegetable oil. The time ranged from 1 to 3 h, and the reactions occurred at room temperature (approximately 25 °C). In all of the experiments, 100 g of babassu oil, 20 g of methanol, and catalyst (0.5-2.5%) were used. The oil and methanol were mixed in advance in the beaker, and the catalyst was packed directly into the reactor. The mixture (oil/methanol) was suctioned by the pump to soak up the reactor (where the catalyst was located) and then place it in the beaker, running a cycle. After the reaction time, the mixture was transferred to a decanter funnel, where it settled. Glycerin was drained (heavy phase, higher density), and biodiesel (light phase) was separated and washed 3 times with warm water (30 mL). Afterward, biodiesel was filtered through anhydrous sodium sulfate.
20.62 19.81 19.12 16.40 16.45 15.75 15.35 15.16
Results and Discussion Catalyst Results. Figure 2 shows the IR spectra of strontium carbonate (SrCO3) and SrO compounds. It may be noted in the spectrum of SrO decreased the bands in 1473, 856, and 700 cm-1 relating to stretching and deformation of CO bonds. We also observed the appearance of a band at 592 cm-1, which was attributed to the stretching of the Sr-O bond. The surface areas found for SrO and SrCO3 were 2.94 and 2.02 m2/g, respectively. With regard to the size of the pores found for SrO between 20 and 500 A˚, they were considered as mesopores. Biodiesel Results. To match the parameters, such as the reaction time and amount of catalyst, we used measures of viscosity and thermal analysis (Table 2). Statistical analysis of biodiesel viscosity measurements showed that the time variation (increase) of the reaction led to a decrease in the viscosity (Figure 3); however, when it increased the amount of catalyst, no significant change is observed in the results. According to ANP resolution 07/2008, biodiesel is considered within the standard if the present viscosity is between
15.15 11.30 11.34 8.12 4.74 4.81 5.10
had no lock; the pressure of the reactor was the same of the fluid caused by the pump. The hollow glass tube measured 2 cm in 6529
Energy Fuels 2010, 24, 6527–6532
: DOI:10.1021/ef101228f
de Moura et al.
Figure 4. TGA curve of babassu oil (BO) and BD13.
3 and 6 mm2/s, thereby only samples BD13, BD14, and BD15 were considered suitable. The samples of TGA curves showed the same profile, as seen in the example shown in Figure 4. In all cases, two thermal events were observed: the first assigned to biodiesel and the second attributed to the fresh oil. Using the results of the temperature on sets, which were calculated by the software equipment of TGA, we found the average boiling point of biodiesel. On average, the value was 261.91 °C (biodiesel) and 400.69 °C (oil). According to Helwan et al.,9 the conversion degree of the product is the most important factor in reactor building. The key variables that dictate the conversion and selectivity are temperature, pressure, reaction time, and degree of mixing. In transesterification, the selectivity of the reaction is not adversely affected by the increase in the temperature. The pressure in the reactor should be maintained at a sufficient level that keeps the alcohol in the liquid phase. The conversion rate can be improved by increasing the reaction time. Another important parameter in the reactor design is the degree of mixing, and for bath reactors, this parameter is directly related to the amount of energy introduced through the impeller.22 In this study, according to the results obtained, the degree of mixing was controlled by the rotor of the pump and was efficient. The methods used for multiple comparisons are contained in the general category of analysis of variance (ANOVA). These methods use a single test to determine whether there are differences between the means of populations rather than paired comparisons, which are made with the t test. After the ANOVA indicates a potential difference, multiple comparison procedures can be employed to identify which specific means differ from other populations.23 This study evaluated the influence of two factors in the conversion of the reaction:
Table 3. Conversion (%) of Biodiesel Found by TGA, NMR, and GC
TGA RMN CG
BD11
BD12
BD13
BD14
BD15
64.32 64.75 64.68
76.78 77.45 76.78
91.37 98.32 98.54
88.60 97.87 97.92
88.87 97.25 96.87
reaction time and amount of catalyst. The values used for statistical calculation were the percentage of weight loss found for the first event shown in the TGA curves. The results showed that the probability of occurrence of the null hypothesis
