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Chemical interesterification of soybean oil and methyl acetate to FAME using CaO as catalyst
Fuel 267 (2020) 117264
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Full Length Article
Chemical interesterification of soybean oil and methyl acetate to FAME using CaO as catalyst A.L.B. Nunes, F. Castilhos
T
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Chemical Engineering Department, Federal University of Santa Maria, Santa Maria, Brazil
A R T I C LE I N FO
A B S T R A C T
Keywords: Methyl ester Heterogeneous catalysis Kinetics Methyl acetate Triacetin
This study evaluated calcium oxide as catalyst from calcium carbonate at different calcination temperatures and the hydration-dehydration technique was used to produce a nanocrystalline catalyst. CaO samples were characterized by XRD, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and nitrogen adsorption/desorption. Interesterification reaction at 275 °C, 1: 40 M ratio (soybean oil: methyl acetate) and 6 wt% catalyst concentration for 120 min was used with Tukey's test to determine the best calcination temperature, 800 °C. Selected catalyst was used in kinetic experiments to evaluate the effect of temperature, catalyst concentration and Oil:MeA molar ratio. The optimum condition was 325 °C, catalyst content of 10 wt%, and 1:40 Oil:MeA molar ratio, with a 62.3 wt% FAME content. Reuse catalyst was tested and the results showed a decreasing catalytic activity. Leaching test and FTIR analyses of the catalyst pointed out to mass loss and adsorbents at the basic sites would be contributing to CaO deactivation.
1. Introduction Industrial process mostly used for the biodiesel production is transesterification reaction between triglycerides (vegetable oils or animal fats) and methanol, using homogeneous alkaline catalysts, generating fatty acid methyl esters (FAMEs) and glycerol [1]. Methanol is commonly used in excess, which generates two immiscible phases, and the need of purification steps to obtain a clean biodiesel, requiring a longer process time. In addition, severe corrosion of the equipment occurs caused by the treatment of wastewater containing acid and base, due to homogeneous catalyst [2]. To overcome these difficulties other biodiesel production technologies have been developed, among them the chemical interesterification route. This process involves the reaction of triglyceride with methyl acetate, generating biodiesel and triacetin, instead of glycerol [3,4]. Triacetin is biodiesel soluble and is considered an additive. Its addition can improve some properties of biodiesel as cloud point, pour point and viscosity, but on the other hand can reduce cetane number and flash point [5]. This reaction has been studied for several raw materials using homogeneous catalysts [6], enzymes [7], supercritical conditions [8,9], and more recently, heterogeneous catalysts for feedstock with a large amount of free fatty acids [10,11]. Heterogeneous chemical interesterification appears as an alternative to reduce operating costs. Heterogeneous catalysts can be easily
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recovered at the end of the reaction, and also used for several reaction cycles without any pretreatment [3]. They are not as corrosive as homogeneous catalysts, nor as expensive as enzymes, and they reduce the high energy costs of supercritical processes [10]. Catalysts most used in biodiesel production are alkaline earth metals in the form of oxides or carbonates. Among them, the most studied one is calcium oxide, pure, modified or supported in various materials [12–15]. Calcium oxide is usually produced by thermal decomposition of calcium carbonate at high temperatures and it comes from minerals such as limestone and calcite, or from natural sources, shells and eggshells [16]. It is also considered to be easy to handle, noncorrosive, low soluble, it has high basicity and can be regenerated and reused. It is one of the most used solid catalysts for transesterification reaction of different raw materials and is highly efficient for the synthesis of biodiesel [17]. However, from the knowledge of these authors, there is no report available in the literature concerning the employment of calcium oxide in interesterification reaction. On the other hand, the use of CaO requires some care, since it is ineffective in reactions with oil raw materials with high FFAs content. This is caused by the inactivation of active sites on the surface of catalyst particles [16,18]. The sites can also be inactivated by the adsorption of CO2 and H2O from the air [19]. Catalytic activity of CaO depends on some factors such as the calcination temperature and its precursor. It requires thermal activation before use, but there is no agreement among researchers on the
Corresponding author. E-mail address: [email protected] (F. Castilhos).
https://doi.org/10.1016/j.fuel.2020.117264 Received 30 October 2019; Received in revised form 29 January 2020; Accepted 30 January 2020 0016-2361/ © 2020 Elsevier Ltd. All rights reserved.
Fuel 267 (2020) 117264
A.L.B. Nunes and F. Castilhos
done as soon as the catalyst sample was withdrawn from the furnace. Nitrogen adsorption/desorption at −196 °C using Micromeritics equipment (Model ASAP 2020) was used to determine textural properties. Samples were degassed under ambient pressure at 200 °C in N2 flow prior to measurements. Specific surface area was determined by Brunauer, Emmett and Teller (BET) method and total pore volume by Barrett-Joyner-Halenda (BJH) method. Mass variation of the catalyst as a function of temperature was evaluated by thermogravimetric analysis, using TGA-50 equipment (Shimadzu). A 10 ± 1 mg sample was inserted into a platinum crucible and degraded in a synthetic air atmosphere with a flow rate of 100 mL/ min. Heating started from room temperature until 1000 °C was reached. Up to 500 °C, a heating rate of 20 °C/min was used. Between 500 °C and 1000 °C, heating rate was 10 °C/min. The results were recorded in TA60WS Collection Monitor software (Shimadzu) and analyzed in TA60 software (Shimadzu). Scanning Electron Microscopy (SEM) analysis was performed to confirm catalyst morphology by VEGA3 scanning electron microscope (Tescan), after metallization with gold. Working sample was analyzed at three different locations to ensure reproducibility. Qualitative analysis of the catalyst was performed by Fourier Transform Infrared Spectrophotometer (IR PRESTIGE-21 model; Shimadzu), operated in the range of 4500–400 cm−1. Samples were prepared by mixing a small amount of KBr and pressing them into discs.
optimum calcination temperature, since many factors can affect it [20–23]. A few researchers have focused their studies on nanocatalysts, since they have a large specific area and high catalytic activity [24]. Nanocatalysts are synthesized in two steps, the first one may involve thermal decomposition, impregnation or agitation and precipitation, and the second is usually the activation by calcination [25–27]. In this context, the aim of this research was to investigate, for the first time, the catalytic activity of calcium oxide for FAME production through the interesterification reaction of soybean oil. This oxide was obtained from commercial calcium carbonate, fully characterized and calcination temperature was evaluated. A nanocrystalline CaO was also prepared for comparison of catalytic activity. Kinetic experiments were carried out under different reaction conditions. In addition, reuse and leaching of the catalyst were also investigated. 2. Materials and methods 2.1. Materials Methyl acetate (ReagentPlus®, 99%) from Sigma-Aldrich and refined soybean oil, purchased on local market, were used without prior treatment. To obtain the calcium oxide catalyst, calcium carbonate (CaCO3, Sigma-Aldrich, A.C.S. Reagent) was purchased. Heptane (99%), methyl heptadecanoate (internal standard), tricaprin (internal standard) and standard references for FAME analysis which include methyl palmitate, methyl oleate, methyl linoleate and methyl linolenate were purchased from Sigma Aldrich, Brazil.
2.5. Experimental procedure and quantification All reactions were carried out in a 500 mL batch reactor made of stainless steel (PARR, model 4575), with temperature controller and pressure and rotation indicators. Initially, the reactor was filled with oil, methyl acetate and catalyst, with an initial reaction volume of approximately 300 mL. Afterwards, it was closed, the stirring rate was adjusted to 600 rpm, the heating was switched on and then the reaction time began to be counted. Samples were collected and the catalyst was separated from liquid phase through centrifugation (Fanem Excelsa Baby 206-R). Liquid phase was filtered using 0.45 μm syringe filters so that all solid particles were discarded. Filtrate was taken into vacuum rota evaporator (Buchi RII) to remove methyl acetate excess at 80 °C for 20 min. In order to compare calcination temperatures of catalyst, reaction experiments were performed with oil to methyl acetate molar ratio of 1:40 with 6% mass of catalyst relative to oil mass at 275 °C for 120 min. A no catalytic reaction was also performed to verify the catalyst activity on interesterification. Statistica software (StatSoftInc) was used to perform Tukey test (p < 0.05), to statistically analyze the conversion results. Through this procedure, the best calcination temperature of the calcium carbonate was determined for the reaction. Kinetic behavior was verified through experiments carried out at temperatures of 250 °C and 325 °C, oil to methyl acetate molar ratio of 1:40 and 1:10 and catalyst content of 6 wt% and 10 wt% for 360 min. Since no previous research on interesterification reaction catalyzed by calcium oxide is available in literature, experimental conditions were defined based on reports concerning transesterification reaction catalyzed by CaO and on supercritical interesterification [29–32]. Samples were collected every 60 min and prepared as already mentioned. Finally, the condition with the highest FAME yield was evaluated in relation to catalyst reuse for four cycles. At each cycle end, the reaction medium was centrifuged and the recovered calcium oxide was fed to a new run, without any washing treatment, with new soybean oil and methyl acetate. The FAME obtained was qualitatively analyzed by Fourier Transform Infrared Spectrophotometer (IR PRESTIGE-21 model; Shimadzu). FAME, triacetin and the reaction intermediates were quantified by chromatographic analysis through internal standard method on the GCMS-QP2010 Shimadzu chromatograph, as reported in a previous work [11].
2.2. Oil characterization Commercial soybean oil was held in a dry place and protected from light. Its acid value was analyzed by titration of the sample with 0.01 M potassium hydroxide solution, according to the methodology of the American Oil Chemists' Society (AOCS) Cd 3d-63. Water content was determined by Karl-Fisher titration. Fatty acid composition was determined according to the method of Hartman and Lago [28], using solution of ammonium chloride and sulfuric acid in methanol as esterifying agent. 2.3. Catalyst preparation Catalyst samples were prepared by thermal decomposition of calcium carbonate, generating the calcium oxide and carbon dioxide. Just before the use, calcium carbonate was calcined in furnace and temperatures tested were 600 °C, 700 °C, 800 °C, 900 °C and 1000 °C. Calcination was performed without airflow, with a heating rate of 15 °C/min to the intended temperature, and remained at this condition for 120 min. Calcium oxide was carefully weighed and added to the reactor to avoid active sites contamination on its surface by the adsorption of CO2 and H2O from the air [19]. Nano CaO was made by the hydration-dehydration method, as suggested by Yoosuk [25]. Calcium carbonate was calcined at 800 °C in the same manner as described above, and thereafter, it was refluxed in water at 60 °C for 360 min, generating calcium hydroxide. After this procedure, the sample was filtered and dried at 100 °C overnight. Subsequently, the product was ground, sieved and passed through dehydration in the furnace at 800 °C for 60 min, to change from hydroxide to oxide form. The product was designated CaOnano. 2.4. Catalysts characterization Powder X-ray diffraction (XRD) patterns were recorded at room temperature in the 5-100° range in the scan mode (0.03°, 1 s) with a Rigaku diffractometer (Miniflex 300) over a 2θ Bragg-Brentano Geometry, using Cu Kα radiation (k = 1.54 Å) and power supply with 30 kV and 10 mA to evaluate crystalline structure. This analysis was 2
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Table 1 Refined soybean oil properties. Property
Measured value
Acid value (mg KOH/g) Water content (wt%) Fatty acid profile (wt%) Palmitic acid (C16:0) Stearic acid (C18:0) Oleic acid (C18:1) Linoleic acid (C18:2) Linolenic acid (C18:3) Others
0.43 0.06 10.66 3.00 22.78 56.06 6.50 1.00
2.6. Evaluation of catalyst leaching To evaluate quantitatively calcium leaching in reaction product, a reaction medium sample was collected after the first use of the catalyst. The sample was centrifuged and the solvent was removed. Three consecutive steps of calcium extraction from the liquid phase were performed by mixing acidic aqueous solution to ensure maximum extraction. A 5% v/v aqueous hydrochloric acid solution was used. At each step, 1 g of sample was stirred for 1 min with 10 mL of acidic solution at room temperature. This step was followed by centrifugation (Fanem Excelsa Baby 206-R), separation of the aqueous phase and further extraction. Then, the collected aqueous phases were analyzed by atomic emission in the flame spectrometer (Agilent 240 AA model) [33,34]. Fig. 1. X-ray diffraction patterns of CaO solids after treating the precursor in different temperatures.
3. Results and discussion 3.1. Oil characterization Acid value, water content and fatty acid profile of soybean oil are presented in Table 1. As expected the major fatty acid in this oil are linoleic and oleic acid. Acid value is low, since the commercial oil is refined for free fatty acids and other substances removal, that is, the oil is composed almost exclusively of triglycerides, and the water content is also low, which is in accordance to the vast results already presented in the literature [35,36]. 3.2. Catalyst characterization Fig. 1 shows the XRD patterns of the catalyst obtained at different calcination temperatures. The results show that at temperatures below 700 °C CaCO3 is predominant in the composition. CaCO3 diffraction peaks can be observed in 2θ = 23.04°, 29.39°, 31.42°, 35.95°, 39.39°, among others. When the temperature is equal to or greater than 700 °C, CaO peaks at 2θ = 32.12°, 37.26°, 53.71°, 63.97°, 67.18°, 79.41°, 88.24° and 91.16° are present. These results indicate that the crystalline phase of CaO is formed from the calcination temperature of 700 °C, and the increase in the calcination temperature between 700 °C and 1000 °C did not promote structural modifications in the catalyst samples, maintaining the CaO phase. It is possible to verify by the profile of the thermogravimetric analysis for CaCO3, shown in Fig. 2, that is between 600 °C and 760 °C that the main peak of degradation occurs. Fig. 2 also shows the difference thermogravimetry ratio (DTG) profile, where it can be seen that maximum weight loss rate occurred at 740.8 °C. Such weight loss is equivalent to 41%, corresponding to the decomposition of the carbonate into calcium oxide. There is a small previous weight loss, approximately 0.067%, below 600 °C, probably caused by water loss. At temperatures above 760 °C, no significant mass loss was observed, indicating that the total CaCO3 was transformed into CaO at this temperature. The result is in agreement with other works [37,38]. The catalyst morphology was detected by SEM (5000× magnification) and the results are shown in Fig. S1. It is possible to see that
Fig. 2. TGA and DTG profiles of calcium carbonate.
sample calcined at 600 °C (Fig. S1a) presented a typical architecture, aggregate blocks with smooth planes and particles of various sizes (between 20 μm and 2 μm) well defined. When the calcination temperature was 800 °C and 900 °C, as shown in Fig. S1(c) and (d), the particle size became more regular and smaller (most particles of 5 μm) with surfaces more harsh. As calcination temperature increased, the morphologies became similar to each other, and the grains were sintered (Fig. S1e) [39]. Surface area, volume and pore size of the samples, shown in Table 2, are in accordance with the results of the microscopy images. The 600 °C sample has a smaller area, probably due to the non-transformation of carbonate to calcium oxide at this temperature. At 700 °C there is calcium oxide on the surface indicating the area increase. At 800 °C there is complete conversion to calcium oxide. At higher temperatures, sintering process begins, particles edges become smoother with increasing calcination temperature and the surface area of the catalyst decreases [20]. Surfaces areas determined in this work are in 3
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Table 2 Textural properties of CaO catalysts. Calcination temperature (°C)
Surface area (m2/g)
Pore volume (cm3/g)
Pore size (nm)
600 700 800 900 1000 Nano
1.13 9.34 5.58 4.64 4.07 12.15
0.010 0.051 0.026 0.016 0.010 0.078
43.04 21.70 20.35 15.40 11.58 25.31
Table 3 FAME, triacetin and total concentrations for interesterification reactions catalyzed with CaO calcined at different temperatures and nano CaO. Calcination temperature
Concentration (%) FAME
accordance with literature. Sirisomboonchai et al. reported a surface area of 2.16 m2/g for commercial CaO. Yin et al. [20] found a surface area equal to 1.41 m2/g and 2.23 m2/g for CaO calcined at 800 °C and 900 °C, from duck eggshells [22]. On the other hand, Alonso et al. reported a surface area of 26 m2/g for CaO calcined at 785 °C from calcium carbonate [21].
Triacetin
Total
3.59a A ̂ ± (0.14) 4.49a A ̂ ± (0.46)
Without catalyst
3.59
0.00
600 °C
4.49
0.00
700 °C
38.99
0.20
39.19bA ̂ ± (0.58)
800 °C
38.45
0.19
900 °C
38.12
0.18
38.65bA ̂ ± (0.17) 38.30bA ̂ ± (1.22)
1000 °C
38.60
0.20
38.80bA ̂ ± (1.27)
Nano
35.98
0.13
36.11c A ̂ ± (0.25)
Results are average of triplicate analysis, with standard deviations in parentheses. a,b,c Different letters show significant difference according to Tukey test (p < 0.05).
transesterification reaction of waste cooking oil with methanol and catalyst from scallop shell [22]. In this work for the same calcination temperature range, there was no difference of concentration by the statistical test. This may be due to the no great difference in surface areas of these catalysts or in other properties evaluated. It also can be noted low triacetin contents compared to FAME concentrations, not corresponding to reaction stoichiometry. This may be due to that threestep interesterification reaction must be complete to produce one molecule of triacetin, while a molecule of methyl ester is produced at each reaction step. Besides, it is also known that triacetin is susceptible to degradation reactions, which can contribute to reduce its concentration [9]. CaOnano, although presenting twice the area of CaCO3 calcined at 800 °C, showed a little lower catalytic activity in FAME content. Even with the increase of the surface area, it did not show improvement on catalytic activity, not being a good alternative for the studied reaction. According to Tukey test, total concentration is statistically equal for CaO calcined between 700 °C and 1000 °C. Therefore, considering the TGA and DTG profiles (Fig. 2), that indicate a great weight loss occurring at 700 °C and the similar reaction yields of catalysts calcined at 700 °C and 800 °C (Table 3), the temperature of 800 °C was chosen as the most adequate to calcinate CaCO3 for interesterification reaction. This temperature was the minimum temperature that guaranteed all carbonate transformations in CaO without taking into account the dwell time at the set temperature.
3.2.1. Nanocrystalline catalyst characterization Fig. 1 presents X-ray diffractogram of CaOnano, where it can be seen that at this hydration/dehydration process, the formation of a catalyst with a CaO structure occurred. To better characterize CaOnano synthesis and understand this phenomenon, FTIR analysis was performed to compare the hydroxide and oxide generated in hydration/dehydration steps, which is shown in Fig. S2. In FTIR spectrum of the catalyst, a band was observed between 3700 and 3400 cm−1, for calcium hydroxide this band corresponds to the OeH bonds from the hydroxide, already for the CaOnano the less pronounced band is attributed to the bending vibration of HeOeH from water molecules on the external surface of the samples during handling to acquire the spectra [40]. The broad band around 1600–1400 cm−1, as well as a weak band at 873 cm−1 can be assigned to the symmetric and asymmetric stretching vibrations of OeCeO bonds related to carbonation of CaO nanoparticles [41,42]. In the hydroxide this may be related to the hydration process, which was not done in an inert atmosphere, thus allowing the initially calcined CaO to also absorb CO2 molecules from the air. According to SEM images (Fig. S1) after hydration and subsequent calcination at 800 °C (Fig. S1f), the highly textured surface was developed, and the mean particle size was reduced to 100 nm. CaOnano presented a surface area of 12.15 m2/g (Table 2), twice the surface area compared to CaO calcined at 800 °C. This surface area was lower than some values reported in literature. In the work of Yoosuk et al., nano CaO surface area was determined equal to 25.0 m2/g [25]. Zhao et al. reported 22.25 m2/g and 89.52 m2/g surface areas for a commercial nano CaO and a commercial high-surface area nano CaO [43]. As already mentioned the area depends significantly on the precursor used and the catalyst method of preparation.
3.4. Kinetic experiments Fig. 3 presents concentration profiles of compounds in interesterification reaction. The reaction occurs between a triglyceride and three methyl acetate molecules, which is used in excess to displace equilibrium, generating fatty acid methyl esters (FAME) and triacetin (TA), passing through intermediates monoacetyldiglyceride (MADG) and diacetylmonoglyceride (DAMG). Fig. 3a shows the reaction kinetics at 250 °C, 1:40 M ratio (Oil: MeA) and 10 wt% catalyst concentration. It shows the behavior of each intermediate and the generated products. Pressure and temperature profiles measured during the kinetic experiments are shown in Fig. S3. During the reactions the system was pressurized (autogenous pressure), data shown in Fig. S3a, for this condition the pressure reached was close to 4.6 MPa. In 240 min of reaction, there is a 50.4 wt% FAME concentration and 14.9 wt% of triglycerides content in the reaction medium, besides DAMG and MADG. Supercritical methyl acetate is obtained from 234 °C and 4.69 MPa [44], but the critical point of reaction mixture is different from this condition. Brondani et al. calculated the critical properties of the reaction mixture containing soybean oil and methyl acetate, for a 1:40 oil to methyl acetate molar ratio.
3.3. Effect of calcination temperatures on FAME and triacetin contents Table 3 shows contents obtained by chromatographic analysis for the reactions performed with CaO calcined at different temperatures and for CaOnano. According to Tukey's test, total concentration with CaO calcined at 600 °C was equal to no catalyzed reaction and different from all other contents. This great difference confirms that CaO catalyst is active in interesterification reaction, if calcined at temperatures higher than 600 ˚C, and that CaCO3 is not active in this reaction. Statistically similar contents between no catalyzed and with CaO calcined at 600 °C reactions are due to the oxide structure, that was not obtained at this temperature (600 °C), as it could be seen by the characterizations (Figs. 1 and 2). Results in Table 3 also show that total concentration was not different for catalysts calcined between 700 °C and 1000 °C. Sirisomboonchai et al. observed more than a 10% difference in catalytic activity between the calcination temperatures of 700–1000 °C, on the 4
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Fig. 3. Compounds contents profiles (left side: FAME, DAMG, MADG and TG; right side: TA) at different experimental conditions: a) 250 °C, 1:40 oil:MeA molar ratio and 10 wt% catalyst concentration; b) 325 °C, 1:40 oil:MeA molar ratio and 10 wt% catalyst concentration; c) 250 °C, 1:40 oil:MeA molar ratio and 6 wt% catalyst concentration; d) 250 °C, 1:10 oil:MeA molar ratio and 6 wt% catalyst concentration.
model proposed by Brondani et al. that was able to predict that glycerides were thermally degraded through isomerization and polymerization reactions, while triacetin degradation showed to be promoted by catalyst activity [9]. Fig. 3c (250 °C, 4.6 MPa as shown in Fig. S3c) presents compounds profiles in a lower catalyst concentration. Comparing Fig. 3a and c, it can be seen that FAME content reached 52.1 wt% after 300 min with 10 wt% CaO, while only 31.1 wt% FAME content was achieved with 6 wt% CaO (Fig. 3c) at the same time. Additionally, it can be pointed out that a similar effect can be seen in other compounds profiles, as a higher TA content and a higher TG consumption, emphasizing the significant improvement in reaction caused by CaO content increase. With lower catalyst content the reaction stopped in the first step, formation of MADG, not completing the formation of TA and two other molecules of FAME. The same catalyst influence was reported by Zhao et al. in transesterification reaction [43]. Liu et al. evaluated CaO concentration in transesterification reaction, showing the positive influence of the catalyst and a saturation effect at highest catalyst contents [32].
Critical temperature was 244.9 °C and the critical pressure was equal to 4.65 MPa [9]. In this experimental condition the system is on the threshold of critical point; it could have a single supercritical phase composed of interesterification compounds, methyl acetate and catalyst uniform suspension with constant volume and equal to reactor nominal size. At higher temperatures, as profiles shown in Fig. 3b, supercritical state of reaction medium is reached (325 °C and 8.9 MPa, according to Fig. S3b) and is expected that methyl acetate solubilizes all reaction components in a only single phase, mass transfer limitations reduction and increased conversion. As a consequence, in 240 min of reaction, a 62.3 wt% of FAME content is achieved and all triglyceride has already been consumed. This condition also presents greater triacetin content, around 1.0 wt%. Several reports (Dona et al. [29]; Goembira and Saka [8]; Visioli et al. [45], Saka and Isayama [46]) available in literature have related the positive influence of temperature on supercritical interesterification with no catalyst. However after a long reaction time, over 300 min, there may be products decomposition, due to overexposure to elevated temperature, which is in agreement with the 5
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when compared with supercritical methanol due to the production of an unstable intermediate who requires high activation energy [50]. Also according to Table 4, other types of oil have been used in interesterification reaction with methyl acetate, such as macaw and canola oils. Ribeiro et al. obtained 82.46% of conversion efficiency from macaw oil using and γ-alumina catalyst in a batch reactor at 300 °C and autogenous pressure [11]. Visioli et al obtained a 60.24 ester content in a continuous reactor with a packed bed of γ-alumina at 275 °C and 20 MPa [51]. Farobie and Matsumura [50] studied the biodiesel production by using supercritical methyl acetate (SCMA) in a continuous flow reactor from canola oil, reaching reached a 97% yield. Similarly to Doná et al [29] and Campanelli et al. [30] reports, Farobie and Matsumura [50] obtained higher yields than the present work due to higher temperature and pressures.
Comparing Fig. 3c and d (250 °C, 3.0 MPa with profiles in Fig. S3d), which present the results at different oil to methyl acetate molar ratios, it can be seen that FAME content increased with molar ratio. FAME content was 18.8 wt% with 1:10 M ratio and equal to 27.4 wt% with 1:40 M ratio, at 240 min. Again, other content profiles in these figures also corroborate that oil to methyl acetate molar ratio had a significant impact on interesterification reaction. From Fig. S3c and d, it can be seen that the great difference of molar ratios (1:40–1:10) caused different pressures profiles, since pressure was autogenous, that is, it depends on temperature and composition system. Molar ratio increase FAME formation through the higher medium dilution and higher pressure reached, improving system homogenization. Goembira and Saka also investigated the molar ratio effect on ester production through supercritical interesterification and reported a positive effect of the molar ratio on reaction conversion [8]. Sustere, Murnieks and Kampars studied chemical interesterification with four alkyl acetates and confirmed that the FAME concentration increased with alkyl acetate to oil molar ratio [3]. Methyl acetate in excess is required to increase the direct reaction to the products, and it has been shown that are required molar ratios of oil:methyl acetate as high as 1:42 so that high yields are obtained [47]. But studies have shown that increasing the amount of methyl acetate in addition to a ratio of 1:42 does not significantly increase the biodiesel yield [30]. Based on the results presented in Fig. 3, the highest FAME content was 63.2 wt%, obtained at 325 °C, 1:40 oil:MeA molar ratio with 10 wt % of catalyst content at 240 min. Table 4 shows some results available in the literature and from this work regarding interesterification and transesterification reactions using CaO as catalyst or methyl acetate as acyl receptor. It can be seen that only Simões et al. [4] used a heterogeneous catalyst, soybean oil and methyl acetate in FAME production. The yield obtained in the present work is close to reported to these authors and the experimental conditions are similar. Other results reported in literature presented higher yields with no catalysts, but higher temperatures and pressures were applied at supercritical conditions. The works of Doná et al. [29] and Campanelli et al. [30] fall into this case, where higher yields were obtained compared to the present work, mainly due to the higher pressures utilized, that have a known positive effect. The reports of Devaraj et al. [48] and Mohadini et al. [49] used CaO as catalysts with soybean and waste cooking oil, respectively. However, in these reports methanol was used as acyl receptor and FAME was produced through transesterification reaction. Devaraj et al. [48] studied conversion of waste cooking oil to biodiesel in pilot plant using commercial CaO [48], while Mohadesi et al. [49] used in their study calcium oxide from mussel shell in the reaction between soybean oil with methanol, both achieved a yield close to 90%. It can be seen that transesterification reaction required milder conditions to achieve higher yields when compared to interesterification reaction using methyl acetate. This fact was reported by Farobie and Matsumura, who reported that supercritical methyl acetate showed lower reactivity
3.5. Catalyst reusability An important quality of the heterogeneous catalyst is reuse. CaO reuse was tested calcined at 800 °C, in interesterification reaction with oil to methyl acetate ratio of 1:40, catalyst content of 10 wt%, reaction temperature of 325 °C and 240 min. The results of reuse tests are shown in Fig. 4, where it can be seen that FAME content declined after each cycle. FAME concentration was 62 wt% in the first use, followed by 49.65 wt% in second, 48.78 wt% in third cycle and 40.85 wt% in the fourth cycle, corresponding to a 21.15% of catalytic efficiency decay. This decreasing may be associated to catalyst active sites blocked by the reactants, causing activity loss, since it was not washed between the cycles. Another reason for the decrease in content may be the catalyst mass loss in centrifugation step, feed to reactor and also leaching phenomenon between the cycles. CaO is commonly related in literature as a catalyst with catalytic activity decay in reuse tests for transesterification reaction. Yin et al. reported a biodiesel yield decay in all reaction cycles for CaO from duck eggshells [20]. Sirisonboonchai et al. presented a FAME yield decreasing in reuse in transesterification reaction using waste oil and scallop shell catalyst [22]. Zhao et al. also reported a little biodiesel yield decay with commercial nano CaO [43]. Infrared spectroscopy was used to qualitatively determine functional groups in FAME produced and in the catalyst surface in each reuse cycle, in order to better understand catalytic activity decay. Fig. 5 shows infrared spectrum of FAME produced in the first catalyst cycle and catalyst infrared spectra after each reaction cycle. The band in the region of 3455 cm−1 can be observed due to air humidity, since the pressed disc technique was used. The stretching band absorption of C] O present in 1743 cm−1 and the band between 1223 cm−1 and 1171 cm−1 relating to the axial deformation CeO are representative of the ester groups involved in the reaction. The asymmetric and symmetric stretching of the methylene group (CH2), which composes the ester chain, are seen in the 2927 cm−1 and 2854 cm−1 bands respectively; near them is the 3009 cm−1 band (eHC]CHestretching), which
Table 4 FAME production from interesterification and transesterification chemical routes using CaO as catalyst or methyl acetate as acyl receptor. Oil
Soybean Soybean Soybean Soybean Soybean Waste cooking oil Canola Macaw (Acrocomia aculeata) Macaw (Acrocomia aculeata)
Solvent
MeA MeA MeA MeA Methanol Methanol MeA MeA MeA
Reaction condition Reactor type
Temperature [°C]
Oil:solvent molar ratio
Pressure [MPa]
Batch Batch Continuous Batch Batch Batch Continuous Batch Continuous
325 345 350 325 65 80 380 300 275
1:40 1:42 1:60 1:40 1:24 1:6 1:40 1:20 1:2.5 (mass ratio)
8–10 20 20 5–10 ambient ambient 20 – 20
* Based on the oil mass. 6
Catalyst content*
Yield %/time [min]
Ref.
CaO 10 wt% – – Ca-Mg Al 10 wt% CaO 12 wt% CaO 3 wt% – γ-Al2O3 2 wt% γ-Al2O3
63.2/240 106/50 83/45 67/180 88/480 92/120 97/10 82.46/120 60.24/20
This work [30] [29] [4] [49] [48] [50] [11] [51]
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some active species during the interesterification process, which is one of the factors that cause activity reduction. Besides that, this value is lower than some reported in literature in transesterification reaction, as Yoosuk et al. [25] (456 mg calcium/L), Verziu et al. [1] (325 mg calcium/kg) and Zhao et al. [43] (178–875 mg calcium/kg).
4. Conclusion This study evaluated calcium oxide as catalyst in interesterification reaction with methyl acetate from soybean oil. CaO catalyst was obtained from calcium carbonate calcination. Optimum calcination temperature was 800 °C. Nano CaO was also prepared but yielded a lower FAME content. Effect of temperature, oil to methyl acetate molar ratio and catalyst concentration were evaluated through kinetic experiments. FAME content showed to be favored by all these variables. The highest FAME content, equal to 62.3 wt%, was obtained at 325 °C, 10 wt% of catalyst, and 1:40 Oil: MeA molar ratio. Reuse test pointed out to catalytic activity decay, probably due to active sites blocking, mass loss and leaching phenomena.
Fig. 4. Reusability of catalyst.
represents the concentration of unsaturations in the FAME produced. At 1463 cm−1 and 724 cm−1 are the bending vibrations bands of the methylene group. Bands in FAME produced refer to ester molecules and a little humidity and are in agreement with other biodiesel spectra reported in the literature [10,52]. Regarding to catalysts spectra, it can be seen the same bands shown in FAME spectrum. Besides that, catalysts spectra after cycles presented contaminants bands such as H2O (there is an increase of the 3500 cm−1 band) and CO2 due to a strong band between 1540 and 1610 cm−1 relative to the carboxylate anion, once that CO2 can bind to catalyst surface in the form of unidentate carbonate generating this structure [53]. These contaminants may have been adsorbed between cycles or during sample handling for analysis. These results show that catalytic activity decay can be associated to this contaminants adsorption, besides mass loss. Considering that the leaching level of metallic ions of basic oxides in solution is inversely associated with catalyst activity in reuse, atomic emission spectroscopy was used to analyze CaO leaching. In three successive extraction steps, calcium content was equal to 34.04, 15.92 and 7.69 mg calcium/kg FAME, resulting in a total calcium content of 57.66 mg calcium/kg FAME. These results confirm that the catalyst lost
CRediT authorship contribution statement A.L.B. Nunes: Investigation, Methodology, Validation, Writing original draft. F. Castilhos: Conceptualization, Methodology, Resources, Writing - review & editing, Supervision.
Acknowledgments The authors thank to CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) (404675/2013-1) for financial support and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for scholarships.
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.fuel.2020.117264.
Fig. 5. FTIR analysis of biodiesel and of catalyst after cycles. 7
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References [27]
[1] Verziu M, Coman SM, Richards R, Parvulescu VI. Transesterification of vegetable oils over CaO catalysts. Catal Today 2011;167:64–70. https://doi.org/10.1016/j. cattod.2010.12.031. [2] Calero J, Luna D, Sancho ED, Luna C, Bautista FM, Romero AA, et al. An overview on glycerol-free processes for the production of renewable liquid biofuels, applicable in diesel engines. Renew Sustain Energy Rev 2015;42:1437–52. https://doi. org/10.1016/j.rser.2014.11.007. [3] Sustere Z, Murnieks R, Kampars V. Chemical interesterification of rapeseed oil with methyl, ethyl, propyl and isopropyl acetates and fuel properties of obtained mixtures. Fuel Process Technol 2016;149:320–5. https://doi.org/10.1016/j.fuproc. 2016.04.033. [4] Simões SS, Ribeiro JS, Celante D, Brondani LN, Castilhos F. Heterogeneous catalyst screening for fatty acid methyl esters production through interesterification reaction. Renew Energy 2020;146:719–26. https://doi.org/10.1016/j.renene.2019.07. 023. [5] Casas A, Ruiz JR, Ramos MJ, Pérez A. Effects of triacetin on biodiesel quality. Energy Fuels 2010;24:4481–9. https://doi.org/10.1021/ef100406b. [6] Casas A, Ramos MJ, Pérez Á. New trends in biodiesel production: chemical interesterification of sunflower oil with methyl acetate. Biomass Bioenergy 2011;35:1702–9. https://doi.org/10.1016/j.biombioe.2011.01.003. [7] Xu Y, Du W, Liu D. Study on the kinetics of enzymatic interesterification of triglycerides for biodiesel production with methyl acetate as the acyl acceptor. J Mol Catal B Enzym 2005;32:241–5. https://doi.org/10.1016/j.molcatb.2004.12.013. [8] Goembira F, Saka S. Optimization of biodiesel production by supercritical methyl acetate. Bioresour Technol 2013;131:47–52. https://doi.org/10.1016/j.biortech. 2012.12.130. [9] Brondani LN, Simões SS, Celante D, Castilhos F. Kinetic modeling of supercritical interesterification with heterogeneous catalyst to produce methyl esters considering degradation effects. Ind Eng Chem Res 2019;58:816–27. https://doi.org/10.1021/ acs.iecr.8b04715. [10] dos Santos Ribeiro J, Celante D, Simões SS, Bassaco MM, da Silva C, de Castilhos F. Efficiency of heterogeneous catalysts in interesterification reaction from macaw oil (Acrocomia aculeata) and methyl acetate. Fuel 2017;200:499–505. https://doi.org/ 10.1016/j.fuel.2017.04.003. [11] Ribeiro JS, Celante D, Brondani LN, Trojahn DO, da Silva C, de Castilhos F. Synthesis of methyl esters and triacetin from macaw oil (Acrocomia aculeata) and methyl acetate over γ-alumina. Ind Crops Prod 2018;124:84–90. https://doi.org/ 10.1016/j.indcrop.2018.07.062. [12] Di Serio M, Tesser R, Pengmei L, Santacesaria E. Heterogeneous catalysts for biodiesel production. Energy Fuels 2008;22:207–17. https://doi.org/10.1021/ ie070663q. [13] Semwal S, Arora AK, Badoni RP, Tuli DK. Biodiesel production using heterogeneous catalysts. Bioresour Technol 2011;102:2151–61. https://doi.org/10.1016/j. biortech.2010.10.080. [14] Tang Y, Liu H, Ren H, Cheng Q, Cui Y, Zhang J. Development KCl/CaO as a catalyst for biodiesel production by tri-component coupling Transesterification. Environ Prog Sustain Energy 2018:1–7. https://doi.org/10.1002/ep.12977. [15] Tang Y, Li L, Wang S, Cheng Q, Zhang J. Tricomponent coupling biodiesel production catalyzed by surface modified calcium oxide. Environ Prog Sustain Energy 2016;35:257–62. https://doi.org/10.1002/ep.12194. [16] Marinković DM, Stanković MV, Veličković AV, Avramović JM, Miladinović MR, Stamenković OO, et al. Calcium oxide as a promising heterogeneous catalyst for biodiesel production: current state and perspectives. Renew Sustain Energy Rev 2016;56:1387–408. https://doi.org/10.1016/j.rser.2015.12.007. [17] Kesic Z, Lukic I, Zdujic M, Mojovic L, Skala D. Calcium oxide based catalysts for biodiesel production: a review. Chem Ind Chem Eng Q 2016;22:391–408. https:// doi.org/10.2298/CICEQ160203010K. [18] Soares Dias AP, Puna J, Neiva Correia MJ, Nogueira I, Gomes J, Bordado J. Effect of the oil acidity on the methanolysis performances of lime catalyst biodiesel from waste frying oils (WFO). Fuel Process Technol 2013;116:94–100. https://doi.org/ 10.1016/j.fuproc.2013.05.002. [19] Granados ML, Poves MDZ, Alonso DM, Mariscal R, Galisteo FC, Moreno-Tost R, et al. Biodiesel from sunflower oil by using activated calcium oxide. Appl Catal B Environ 2007;73:317–26. https://doi.org/10.1016/j.apcatb.2006.12.017. [20] Yin X, Duan X, You Q, Dai C, Tan Z, Zhu X. Biodiesel production from soybean oil deodorizer distillate usingcalcined duck eggshell as catalyst. Energy Convers Manage 2016;112:199–207. https://doi.org/10.1016/j.enconman.2016.01.026. [21] Alonso DM, Vila F, Mariscal R, Ojeda M, Granados ML, Santamaría-González J. Relevance of the physicochemical properties of CaO catalysts for the methanolysis of triglycerides to obtain biodiesel. Catal Today 2010;158:114–20. https://doi.org/ 10.1016/j.cattod.2010.05.003. [22] Sirisomboonchai S, Abuduwayiti M, Guan G, Samart C, Abliz S, Hao X, et al. Biodiesel production from waste cooking oil using calcined scallop shell as catalyst. Energy Convers Manage 2015;95:242–7. https://doi.org/10.1016/j.enconman. 2015.02.044. [23] Anjana PA, Niju S, Meera Sheriffa Begum KM, Anantharaman N. Utilization of limestone derived calcium oxide for biodiesel production from non-edible pongamia oil. Environ Prog Sustain Energy 2016;35:1758–64. https://doi.org/10. 1002/ep.12384. [24] Banković-Ilić IB, Miladinović MR, Stamenković OS, Veljković VB. Application of nano CaO–based catalysts in biodiesel synthesis. Renew Sustain Energy Rev 2017;72:746–60. https://doi.org/10.1016/j.rser.2017.01.076. [25] Yoosuk B, Udomsap P, Puttasawat B, Krasae P. Modification of calcite by hydrationdehydration method for heterogeneous biodiesel production process: the effects of water on properties and activity. Chem Eng J 2010;162:135–41. https://doi.org/10. 1016/j.cej.2010.05.013. [26] Bai H, Shen X, Liu X, Liu S. Synthesis of porous CaO microsphere and its application
[28] [29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[49]
[50]
[51]
[52]
[53]
8
in catalyzing transesterification reaction for biodiesel. Trans Nonferrous Met Soc China 2009;19:s674–7. https://doi.org/10.1016/S1003-6326(10)60130-6. Reddy C, Reddy V, Oshel R, Verkade JG. Room-temperature conversion of soybean oil and poultry fat to biodiesel catalyzed by nanocrystalline calcium oxides. Energy Fuels 2006;20:1310–4. https://doi.org/10.1021/ef050435d. Hartman L, Lago RC. Rapid preparation of fatty acid methyl esters from lipids. Lab Pract 1973;22. 475–6 passim. Doná G, Cardozo-Filho L, Silva C, Castilhos F. Biodiesel production using supercritical methyl acetate in a tubular packed bed reactor. Fuel Process Technol 2013;106:605–10. https://doi.org/10.1016/j.fuproc.2012.09.047. Campanelli P, Banchero M, Manna L. Synthesis of biodiesel from edible, non-edible and waste cooking oils via supercritical methyl acetate transesterification. Fuel 2010;89:3675–82. https://doi.org/10.1016/j.fuel.2010.07.033. Calero J, Luna D, Sancho ED, Luna C, Bautista FM, Romero AA, et al. Development of a new biodiesel that integrates glycerol, by using CaO as heterogeneous catalyst, in the partial methanolysis of sunflower oil. Fuel 2014;122:94–102. https://doi. org/10.1016/j.fuel.2014.01.033. Liu X, He H, Wang Y, Zhu S, Piao X. Transesterification of soybean oil to biodiesel using CaO as a solid base catalyst. Fuel 2008;87:216–21. https://doi.org/10.1016/j. fuel.2007.04.013. Kouzu M, Yamanaka S, Hidaka J, Tsunomori M. Heterogeneous catalysis of calcium oxide used for transesterification of soybean oil with refluxing methanol. Appl Catal A Gen 2009;355:94–9. https://doi.org/10.1016/j.apcata.2008.12.003. Celante D, Schenkel JVD, de Castilhos F. Biodiesel production from soybean oil and dimethyl carbonate catalyzed by potassium methoxide. Fuel 2018;212:101–7. https://doi.org/10.1016/j.fuel.2017.10.040. Aransiola EF, Ojumu TV, Oyekola OO, Madzimbamuto TF, Ikhu-Omoregbe DIO. A review of current technology for biodiesel production: state of the art. Biomass Bioenergy 2014;61:276–97. https://doi.org/10.1016/j.biombioe.2013.11.014. Prados CP, Rezende DR, Batista LR, Alves MIR, Antoniosi Filho NR. Simultaneous gas chromatographic analysis of total esters, mono-, di- and triacylglycerides and free and total glycerol in methyl or ethyl biodiesel. Fuel 2012;96:476–81. https:// doi.org/10.1016/j.fuel.2011.11.060. Cho YB, Seo G, Chang DR. Transesterification of tributyrin with methanol over calcium oxide catalysts prepared from various precursors. Fuel Process Technol 2009;90:1252–8. https://doi.org/10.1016/j.fuproc.2009.06.007. Yang J, Kaewpanha M, Karnjanakom S, Guan G, Hao X, Abudula A. Steam reforming of biomass tar over calcined egg shell supported catalysts for hydrogen production. Int J Hydrogen Energy 2016;41:6699–705. https://doi.org/10.1016/j. ijhydene.2016.03.056. Zhu H, Wu Z, Chen Y, Zhang P, Duan S, Liu X, et al. Preparation of biodiesel catalyzed by solid super base of calcium oxide and its refining process. Chin J Catal 2006;27:391–6. https://doi.org/10.1016/S1872-2067(06)60024-7. Ghiasi M, Malekzadeh A. Synthesis of CaCO3 nanoparticles via citrate method and sequential preparation of CaO and Ca(OH)2 nanoparticles. Cryst Res Technol 2012;47:471–8. https://doi.org/10.1002/crat.201100240. Correia LM, de Sousa Campelo N, Novaes DS, Cavalcante CL, Cecilia JA, RodríguezCastellón E, et al. Characterization and application of dolomite as catalytic precursor for canola and sunflower oils for biodiesel production. Chem Eng J 2015;269:35–43. https://doi.org/10.1016/j.cej.2015.01.097. Niju S, Anushya C, Balajii M. Process optimization for biodiesel production from Moringa oleifera oil using conch shells as heterogeneous catalyst. Environ Prog Sustain Energy 2018:1–12. https://doi.org/10.1002/ep.13015. Zhao L, Qiu Z, Stagg-Williams SM. Transesterification of canola oil catalyzed by nanopowder calcium oxide. Fuel Process Technol 2013;114:154–62. https://doi. org/10.1016/j.fuproc.2013.03.027. 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. Bioresour Technol 2010;101:965–9. https://doi.org/10.1016/j. biortech.2009.09.004. Visioli LJ, Trentini CP, de Castilhos F, da Silva C. Esters production in continuous reactor from macauba pulp oil using methyl acetate in pressurized conditions. J Supercrit Fluids 2018;140:238–47. https://doi.org/10.1016/j.supflu.2018.06.018. Saka S, Isayama Y. A new process for catalyst-free production of biodiesel using supercritical methyl acetate. Fuel 2009;88:1307–13. https://doi.org/10.1016/j. fuel.2008.12.028. Marx S. Glycerol-free biodiesel production through transesterification: a review. Fuel Process Technol 2016;151:139–47. https://doi.org/10.1016/j.fuproc.2016.05. 033. Devaraj K, Veerasamy M, Aathika S, Mani Y, Thanarasu A, Dhanasekaran A, et al. Study on effectiveness of activated calcium oxide in pilot plant biodiesel production. J Clean Prod 2019;225:18–26. https://doi.org/10.1016/j.jclepro.2019.03. 244. Mohadesi M, Moradi G, Davvodbeygi Y, Hosseini S. Soybean oil transesterification reactions in the presence of mussel shell: Pseudo-first order kinetics. Iran J Chem Chem Eng 2018;37:43–51. Farobie O, Matsumura Y. Continuous production of biodiesel under supercritical methyl acetate conditions: experimental investigation and kinetic model. Bioresour Technol 2017;241:720–5. https://doi.org/10.1016/j.biortech.2017.05.210. Visioli LJ, de Castilhos F, da Silva C. Use of heterogeneous acid catalyst combined with pressurized conditions for esters production from macauba pulp oil and methyl acetate. J Supercrit Fluids 2019;150:65–74. https://doi.org/10.1016/j.supflu.2019. 03.023. Chakraborty R, Bepari S, Banerjee A. Transesterification of soybean oil catalyzed by fly ash and egg shell derived solid catalysts. Chem Eng J 2010;165:798–805. https://doi.org/10.1016/j.cej.2010.10.019. Philipp R, Fujimoto K. FTIR spectroscopic study of carbon dioxide adsorption/ desorption on magnesia/calcium oxide catalysts. J Phys Chem 1992;96:9035–8. https://doi.org/10.1021/j100201a063.
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Full Length Article
Chemical interesterification of soybean oil and methyl acetate to FAME using CaO as catalyst A.L.B. Nunes, F. Castilhos
T
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Chemical Engineering Department, Federal University of Santa Maria, Santa Maria, Brazil
A R T I C LE I N FO
A B S T R A C T
Keywords: Methyl ester Heterogeneous catalysis Kinetics Methyl acetate Triacetin
This study evaluated calcium oxide as catalyst from calcium carbonate at different calcination temperatures and the hydration-dehydration technique was used to produce a nanocrystalline catalyst. CaO samples were characterized by XRD, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and nitrogen adsorption/desorption. Interesterification reaction at 275 °C, 1: 40 M ratio (soybean oil: methyl acetate) and 6 wt% catalyst concentration for 120 min was used with Tukey's test to determine the best calcination temperature, 800 °C. Selected catalyst was used in kinetic experiments to evaluate the effect of temperature, catalyst concentration and Oil:MeA molar ratio. The optimum condition was 325 °C, catalyst content of 10 wt%, and 1:40 Oil:MeA molar ratio, with a 62.3 wt% FAME content. Reuse catalyst was tested and the results showed a decreasing catalytic activity. Leaching test and FTIR analyses of the catalyst pointed out to mass loss and adsorbents at the basic sites would be contributing to CaO deactivation.
1. Introduction Industrial process mostly used for the biodiesel production is transesterification reaction between triglycerides (vegetable oils or animal fats) and methanol, using homogeneous alkaline catalysts, generating fatty acid methyl esters (FAMEs) and glycerol [1]. Methanol is commonly used in excess, which generates two immiscible phases, and the need of purification steps to obtain a clean biodiesel, requiring a longer process time. In addition, severe corrosion of the equipment occurs caused by the treatment of wastewater containing acid and base, due to homogeneous catalyst [2]. To overcome these difficulties other biodiesel production technologies have been developed, among them the chemical interesterification route. This process involves the reaction of triglyceride with methyl acetate, generating biodiesel and triacetin, instead of glycerol [3,4]. Triacetin is biodiesel soluble and is considered an additive. Its addition can improve some properties of biodiesel as cloud point, pour point and viscosity, but on the other hand can reduce cetane number and flash point [5]. This reaction has been studied for several raw materials using homogeneous catalysts [6], enzymes [7], supercritical conditions [8,9], and more recently, heterogeneous catalysts for feedstock with a large amount of free fatty acids [10,11]. Heterogeneous chemical interesterification appears as an alternative to reduce operating costs. Heterogeneous catalysts can be easily
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recovered at the end of the reaction, and also used for several reaction cycles without any pretreatment [3]. They are not as corrosive as homogeneous catalysts, nor as expensive as enzymes, and they reduce the high energy costs of supercritical processes [10]. Catalysts most used in biodiesel production are alkaline earth metals in the form of oxides or carbonates. Among them, the most studied one is calcium oxide, pure, modified or supported in various materials [12–15]. Calcium oxide is usually produced by thermal decomposition of calcium carbonate at high temperatures and it comes from minerals such as limestone and calcite, or from natural sources, shells and eggshells [16]. It is also considered to be easy to handle, noncorrosive, low soluble, it has high basicity and can be regenerated and reused. It is one of the most used solid catalysts for transesterification reaction of different raw materials and is highly efficient for the synthesis of biodiesel [17]. However, from the knowledge of these authors, there is no report available in the literature concerning the employment of calcium oxide in interesterification reaction. On the other hand, the use of CaO requires some care, since it is ineffective in reactions with oil raw materials with high FFAs content. This is caused by the inactivation of active sites on the surface of catalyst particles [16,18]. The sites can also be inactivated by the adsorption of CO2 and H2O from the air [19]. Catalytic activity of CaO depends on some factors such as the calcination temperature and its precursor. It requires thermal activation before use, but there is no agreement among researchers on the
Corresponding author. E-mail address: [email protected] (F. Castilhos).
https://doi.org/10.1016/j.fuel.2020.117264 Received 30 October 2019; Received in revised form 29 January 2020; Accepted 30 January 2020 0016-2361/ © 2020 Elsevier Ltd. All rights reserved.
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done as soon as the catalyst sample was withdrawn from the furnace. Nitrogen adsorption/desorption at −196 °C using Micromeritics equipment (Model ASAP 2020) was used to determine textural properties. Samples were degassed under ambient pressure at 200 °C in N2 flow prior to measurements. Specific surface area was determined by Brunauer, Emmett and Teller (BET) method and total pore volume by Barrett-Joyner-Halenda (BJH) method. Mass variation of the catalyst as a function of temperature was evaluated by thermogravimetric analysis, using TGA-50 equipment (Shimadzu). A 10 ± 1 mg sample was inserted into a platinum crucible and degraded in a synthetic air atmosphere with a flow rate of 100 mL/ min. Heating started from room temperature until 1000 °C was reached. Up to 500 °C, a heating rate of 20 °C/min was used. Between 500 °C and 1000 °C, heating rate was 10 °C/min. The results were recorded in TA60WS Collection Monitor software (Shimadzu) and analyzed in TA60 software (Shimadzu). Scanning Electron Microscopy (SEM) analysis was performed to confirm catalyst morphology by VEGA3 scanning electron microscope (Tescan), after metallization with gold. Working sample was analyzed at three different locations to ensure reproducibility. Qualitative analysis of the catalyst was performed by Fourier Transform Infrared Spectrophotometer (IR PRESTIGE-21 model; Shimadzu), operated in the range of 4500–400 cm−1. Samples were prepared by mixing a small amount of KBr and pressing them into discs.
optimum calcination temperature, since many factors can affect it [20–23]. A few researchers have focused their studies on nanocatalysts, since they have a large specific area and high catalytic activity [24]. Nanocatalysts are synthesized in two steps, the first one may involve thermal decomposition, impregnation or agitation and precipitation, and the second is usually the activation by calcination [25–27]. In this context, the aim of this research was to investigate, for the first time, the catalytic activity of calcium oxide for FAME production through the interesterification reaction of soybean oil. This oxide was obtained from commercial calcium carbonate, fully characterized and calcination temperature was evaluated. A nanocrystalline CaO was also prepared for comparison of catalytic activity. Kinetic experiments were carried out under different reaction conditions. In addition, reuse and leaching of the catalyst were also investigated. 2. Materials and methods 2.1. Materials Methyl acetate (ReagentPlus®, 99%) from Sigma-Aldrich and refined soybean oil, purchased on local market, were used without prior treatment. To obtain the calcium oxide catalyst, calcium carbonate (CaCO3, Sigma-Aldrich, A.C.S. Reagent) was purchased. Heptane (99%), methyl heptadecanoate (internal standard), tricaprin (internal standard) and standard references for FAME analysis which include methyl palmitate, methyl oleate, methyl linoleate and methyl linolenate were purchased from Sigma Aldrich, Brazil.
2.5. Experimental procedure and quantification All reactions were carried out in a 500 mL batch reactor made of stainless steel (PARR, model 4575), with temperature controller and pressure and rotation indicators. Initially, the reactor was filled with oil, methyl acetate and catalyst, with an initial reaction volume of approximately 300 mL. Afterwards, it was closed, the stirring rate was adjusted to 600 rpm, the heating was switched on and then the reaction time began to be counted. Samples were collected and the catalyst was separated from liquid phase through centrifugation (Fanem Excelsa Baby 206-R). Liquid phase was filtered using 0.45 μm syringe filters so that all solid particles were discarded. Filtrate was taken into vacuum rota evaporator (Buchi RII) to remove methyl acetate excess at 80 °C for 20 min. In order to compare calcination temperatures of catalyst, reaction experiments were performed with oil to methyl acetate molar ratio of 1:40 with 6% mass of catalyst relative to oil mass at 275 °C for 120 min. A no catalytic reaction was also performed to verify the catalyst activity on interesterification. Statistica software (StatSoftInc) was used to perform Tukey test (p < 0.05), to statistically analyze the conversion results. Through this procedure, the best calcination temperature of the calcium carbonate was determined for the reaction. Kinetic behavior was verified through experiments carried out at temperatures of 250 °C and 325 °C, oil to methyl acetate molar ratio of 1:40 and 1:10 and catalyst content of 6 wt% and 10 wt% for 360 min. Since no previous research on interesterification reaction catalyzed by calcium oxide is available in literature, experimental conditions were defined based on reports concerning transesterification reaction catalyzed by CaO and on supercritical interesterification [29–32]. Samples were collected every 60 min and prepared as already mentioned. Finally, the condition with the highest FAME yield was evaluated in relation to catalyst reuse for four cycles. At each cycle end, the reaction medium was centrifuged and the recovered calcium oxide was fed to a new run, without any washing treatment, with new soybean oil and methyl acetate. The FAME obtained was qualitatively analyzed by Fourier Transform Infrared Spectrophotometer (IR PRESTIGE-21 model; Shimadzu). FAME, triacetin and the reaction intermediates were quantified by chromatographic analysis through internal standard method on the GCMS-QP2010 Shimadzu chromatograph, as reported in a previous work [11].
2.2. Oil characterization Commercial soybean oil was held in a dry place and protected from light. Its acid value was analyzed by titration of the sample with 0.01 M potassium hydroxide solution, according to the methodology of the American Oil Chemists' Society (AOCS) Cd 3d-63. Water content was determined by Karl-Fisher titration. Fatty acid composition was determined according to the method of Hartman and Lago [28], using solution of ammonium chloride and sulfuric acid in methanol as esterifying agent. 2.3. Catalyst preparation Catalyst samples were prepared by thermal decomposition of calcium carbonate, generating the calcium oxide and carbon dioxide. Just before the use, calcium carbonate was calcined in furnace and temperatures tested were 600 °C, 700 °C, 800 °C, 900 °C and 1000 °C. Calcination was performed without airflow, with a heating rate of 15 °C/min to the intended temperature, and remained at this condition for 120 min. Calcium oxide was carefully weighed and added to the reactor to avoid active sites contamination on its surface by the adsorption of CO2 and H2O from the air [19]. Nano CaO was made by the hydration-dehydration method, as suggested by Yoosuk [25]. Calcium carbonate was calcined at 800 °C in the same manner as described above, and thereafter, it was refluxed in water at 60 °C for 360 min, generating calcium hydroxide. After this procedure, the sample was filtered and dried at 100 °C overnight. Subsequently, the product was ground, sieved and passed through dehydration in the furnace at 800 °C for 60 min, to change from hydroxide to oxide form. The product was designated CaOnano. 2.4. Catalysts characterization Powder X-ray diffraction (XRD) patterns were recorded at room temperature in the 5-100° range in the scan mode (0.03°, 1 s) with a Rigaku diffractometer (Miniflex 300) over a 2θ Bragg-Brentano Geometry, using Cu Kα radiation (k = 1.54 Å) and power supply with 30 kV and 10 mA to evaluate crystalline structure. This analysis was 2
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Table 1 Refined soybean oil properties. Property
Measured value
Acid value (mg KOH/g) Water content (wt%) Fatty acid profile (wt%) Palmitic acid (C16:0) Stearic acid (C18:0) Oleic acid (C18:1) Linoleic acid (C18:2) Linolenic acid (C18:3) Others
0.43 0.06 10.66 3.00 22.78 56.06 6.50 1.00
2.6. Evaluation of catalyst leaching To evaluate quantitatively calcium leaching in reaction product, a reaction medium sample was collected after the first use of the catalyst. The sample was centrifuged and the solvent was removed. Three consecutive steps of calcium extraction from the liquid phase were performed by mixing acidic aqueous solution to ensure maximum extraction. A 5% v/v aqueous hydrochloric acid solution was used. At each step, 1 g of sample was stirred for 1 min with 10 mL of acidic solution at room temperature. This step was followed by centrifugation (Fanem Excelsa Baby 206-R), separation of the aqueous phase and further extraction. Then, the collected aqueous phases were analyzed by atomic emission in the flame spectrometer (Agilent 240 AA model) [33,34]. Fig. 1. X-ray diffraction patterns of CaO solids after treating the precursor in different temperatures.
3. Results and discussion 3.1. Oil characterization Acid value, water content and fatty acid profile of soybean oil are presented in Table 1. As expected the major fatty acid in this oil are linoleic and oleic acid. Acid value is low, since the commercial oil is refined for free fatty acids and other substances removal, that is, the oil is composed almost exclusively of triglycerides, and the water content is also low, which is in accordance to the vast results already presented in the literature [35,36]. 3.2. Catalyst characterization Fig. 1 shows the XRD patterns of the catalyst obtained at different calcination temperatures. The results show that at temperatures below 700 °C CaCO3 is predominant in the composition. CaCO3 diffraction peaks can be observed in 2θ = 23.04°, 29.39°, 31.42°, 35.95°, 39.39°, among others. When the temperature is equal to or greater than 700 °C, CaO peaks at 2θ = 32.12°, 37.26°, 53.71°, 63.97°, 67.18°, 79.41°, 88.24° and 91.16° are present. These results indicate that the crystalline phase of CaO is formed from the calcination temperature of 700 °C, and the increase in the calcination temperature between 700 °C and 1000 °C did not promote structural modifications in the catalyst samples, maintaining the CaO phase. It is possible to verify by the profile of the thermogravimetric analysis for CaCO3, shown in Fig. 2, that is between 600 °C and 760 °C that the main peak of degradation occurs. Fig. 2 also shows the difference thermogravimetry ratio (DTG) profile, where it can be seen that maximum weight loss rate occurred at 740.8 °C. Such weight loss is equivalent to 41%, corresponding to the decomposition of the carbonate into calcium oxide. There is a small previous weight loss, approximately 0.067%, below 600 °C, probably caused by water loss. At temperatures above 760 °C, no significant mass loss was observed, indicating that the total CaCO3 was transformed into CaO at this temperature. The result is in agreement with other works [37,38]. The catalyst morphology was detected by SEM (5000× magnification) and the results are shown in Fig. S1. It is possible to see that
Fig. 2. TGA and DTG profiles of calcium carbonate.
sample calcined at 600 °C (Fig. S1a) presented a typical architecture, aggregate blocks with smooth planes and particles of various sizes (between 20 μm and 2 μm) well defined. When the calcination temperature was 800 °C and 900 °C, as shown in Fig. S1(c) and (d), the particle size became more regular and smaller (most particles of 5 μm) with surfaces more harsh. As calcination temperature increased, the morphologies became similar to each other, and the grains were sintered (Fig. S1e) [39]. Surface area, volume and pore size of the samples, shown in Table 2, are in accordance with the results of the microscopy images. The 600 °C sample has a smaller area, probably due to the non-transformation of carbonate to calcium oxide at this temperature. At 700 °C there is calcium oxide on the surface indicating the area increase. At 800 °C there is complete conversion to calcium oxide. At higher temperatures, sintering process begins, particles edges become smoother with increasing calcination temperature and the surface area of the catalyst decreases [20]. Surfaces areas determined in this work are in 3
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Table 2 Textural properties of CaO catalysts. Calcination temperature (°C)
Surface area (m2/g)
Pore volume (cm3/g)
Pore size (nm)
600 700 800 900 1000 Nano
1.13 9.34 5.58 4.64 4.07 12.15
0.010 0.051 0.026 0.016 0.010 0.078
43.04 21.70 20.35 15.40 11.58 25.31
Table 3 FAME, triacetin and total concentrations for interesterification reactions catalyzed with CaO calcined at different temperatures and nano CaO. Calcination temperature
Concentration (%) FAME
accordance with literature. Sirisomboonchai et al. reported a surface area of 2.16 m2/g for commercial CaO. Yin et al. [20] found a surface area equal to 1.41 m2/g and 2.23 m2/g for CaO calcined at 800 °C and 900 °C, from duck eggshells [22]. On the other hand, Alonso et al. reported a surface area of 26 m2/g for CaO calcined at 785 °C from calcium carbonate [21].
Triacetin
Total
3.59a A ̂ ± (0.14) 4.49a A ̂ ± (0.46)
Without catalyst
3.59
0.00
600 °C
4.49
0.00
700 °C
38.99
0.20
39.19bA ̂ ± (0.58)
800 °C
38.45
0.19
900 °C
38.12
0.18
38.65bA ̂ ± (0.17) 38.30bA ̂ ± (1.22)
1000 °C
38.60
0.20
38.80bA ̂ ± (1.27)
Nano
35.98
0.13
36.11c A ̂ ± (0.25)
Results are average of triplicate analysis, with standard deviations in parentheses. a,b,c Different letters show significant difference according to Tukey test (p < 0.05).
transesterification reaction of waste cooking oil with methanol and catalyst from scallop shell [22]. In this work for the same calcination temperature range, there was no difference of concentration by the statistical test. This may be due to the no great difference in surface areas of these catalysts or in other properties evaluated. It also can be noted low triacetin contents compared to FAME concentrations, not corresponding to reaction stoichiometry. This may be due to that threestep interesterification reaction must be complete to produce one molecule of triacetin, while a molecule of methyl ester is produced at each reaction step. Besides, it is also known that triacetin is susceptible to degradation reactions, which can contribute to reduce its concentration [9]. CaOnano, although presenting twice the area of CaCO3 calcined at 800 °C, showed a little lower catalytic activity in FAME content. Even with the increase of the surface area, it did not show improvement on catalytic activity, not being a good alternative for the studied reaction. According to Tukey test, total concentration is statistically equal for CaO calcined between 700 °C and 1000 °C. Therefore, considering the TGA and DTG profiles (Fig. 2), that indicate a great weight loss occurring at 700 °C and the similar reaction yields of catalysts calcined at 700 °C and 800 °C (Table 3), the temperature of 800 °C was chosen as the most adequate to calcinate CaCO3 for interesterification reaction. This temperature was the minimum temperature that guaranteed all carbonate transformations in CaO without taking into account the dwell time at the set temperature.
3.2.1. Nanocrystalline catalyst characterization Fig. 1 presents X-ray diffractogram of CaOnano, where it can be seen that at this hydration/dehydration process, the formation of a catalyst with a CaO structure occurred. To better characterize CaOnano synthesis and understand this phenomenon, FTIR analysis was performed to compare the hydroxide and oxide generated in hydration/dehydration steps, which is shown in Fig. S2. In FTIR spectrum of the catalyst, a band was observed between 3700 and 3400 cm−1, for calcium hydroxide this band corresponds to the OeH bonds from the hydroxide, already for the CaOnano the less pronounced band is attributed to the bending vibration of HeOeH from water molecules on the external surface of the samples during handling to acquire the spectra [40]. The broad band around 1600–1400 cm−1, as well as a weak band at 873 cm−1 can be assigned to the symmetric and asymmetric stretching vibrations of OeCeO bonds related to carbonation of CaO nanoparticles [41,42]. In the hydroxide this may be related to the hydration process, which was not done in an inert atmosphere, thus allowing the initially calcined CaO to also absorb CO2 molecules from the air. According to SEM images (Fig. S1) after hydration and subsequent calcination at 800 °C (Fig. S1f), the highly textured surface was developed, and the mean particle size was reduced to 100 nm. CaOnano presented a surface area of 12.15 m2/g (Table 2), twice the surface area compared to CaO calcined at 800 °C. This surface area was lower than some values reported in literature. In the work of Yoosuk et al., nano CaO surface area was determined equal to 25.0 m2/g [25]. Zhao et al. reported 22.25 m2/g and 89.52 m2/g surface areas for a commercial nano CaO and a commercial high-surface area nano CaO [43]. As already mentioned the area depends significantly on the precursor used and the catalyst method of preparation.
3.4. Kinetic experiments Fig. 3 presents concentration profiles of compounds in interesterification reaction. The reaction occurs between a triglyceride and three methyl acetate molecules, which is used in excess to displace equilibrium, generating fatty acid methyl esters (FAME) and triacetin (TA), passing through intermediates monoacetyldiglyceride (MADG) and diacetylmonoglyceride (DAMG). Fig. 3a shows the reaction kinetics at 250 °C, 1:40 M ratio (Oil: MeA) and 10 wt% catalyst concentration. It shows the behavior of each intermediate and the generated products. Pressure and temperature profiles measured during the kinetic experiments are shown in Fig. S3. During the reactions the system was pressurized (autogenous pressure), data shown in Fig. S3a, for this condition the pressure reached was close to 4.6 MPa. In 240 min of reaction, there is a 50.4 wt% FAME concentration and 14.9 wt% of triglycerides content in the reaction medium, besides DAMG and MADG. Supercritical methyl acetate is obtained from 234 °C and 4.69 MPa [44], but the critical point of reaction mixture is different from this condition. Brondani et al. calculated the critical properties of the reaction mixture containing soybean oil and methyl acetate, for a 1:40 oil to methyl acetate molar ratio.
3.3. Effect of calcination temperatures on FAME and triacetin contents Table 3 shows contents obtained by chromatographic analysis for the reactions performed with CaO calcined at different temperatures and for CaOnano. According to Tukey's test, total concentration with CaO calcined at 600 °C was equal to no catalyzed reaction and different from all other contents. This great difference confirms that CaO catalyst is active in interesterification reaction, if calcined at temperatures higher than 600 ˚C, and that CaCO3 is not active in this reaction. Statistically similar contents between no catalyzed and with CaO calcined at 600 °C reactions are due to the oxide structure, that was not obtained at this temperature (600 °C), as it could be seen by the characterizations (Figs. 1 and 2). Results in Table 3 also show that total concentration was not different for catalysts calcined between 700 °C and 1000 °C. Sirisomboonchai et al. observed more than a 10% difference in catalytic activity between the calcination temperatures of 700–1000 °C, on the 4
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Fig. 3. Compounds contents profiles (left side: FAME, DAMG, MADG and TG; right side: TA) at different experimental conditions: a) 250 °C, 1:40 oil:MeA molar ratio and 10 wt% catalyst concentration; b) 325 °C, 1:40 oil:MeA molar ratio and 10 wt% catalyst concentration; c) 250 °C, 1:40 oil:MeA molar ratio and 6 wt% catalyst concentration; d) 250 °C, 1:10 oil:MeA molar ratio and 6 wt% catalyst concentration.
model proposed by Brondani et al. that was able to predict that glycerides were thermally degraded through isomerization and polymerization reactions, while triacetin degradation showed to be promoted by catalyst activity [9]. Fig. 3c (250 °C, 4.6 MPa as shown in Fig. S3c) presents compounds profiles in a lower catalyst concentration. Comparing Fig. 3a and c, it can be seen that FAME content reached 52.1 wt% after 300 min with 10 wt% CaO, while only 31.1 wt% FAME content was achieved with 6 wt% CaO (Fig. 3c) at the same time. Additionally, it can be pointed out that a similar effect can be seen in other compounds profiles, as a higher TA content and a higher TG consumption, emphasizing the significant improvement in reaction caused by CaO content increase. With lower catalyst content the reaction stopped in the first step, formation of MADG, not completing the formation of TA and two other molecules of FAME. The same catalyst influence was reported by Zhao et al. in transesterification reaction [43]. Liu et al. evaluated CaO concentration in transesterification reaction, showing the positive influence of the catalyst and a saturation effect at highest catalyst contents [32].
Critical temperature was 244.9 °C and the critical pressure was equal to 4.65 MPa [9]. In this experimental condition the system is on the threshold of critical point; it could have a single supercritical phase composed of interesterification compounds, methyl acetate and catalyst uniform suspension with constant volume and equal to reactor nominal size. At higher temperatures, as profiles shown in Fig. 3b, supercritical state of reaction medium is reached (325 °C and 8.9 MPa, according to Fig. S3b) and is expected that methyl acetate solubilizes all reaction components in a only single phase, mass transfer limitations reduction and increased conversion. As a consequence, in 240 min of reaction, a 62.3 wt% of FAME content is achieved and all triglyceride has already been consumed. This condition also presents greater triacetin content, around 1.0 wt%. Several reports (Dona et al. [29]; Goembira and Saka [8]; Visioli et al. [45], Saka and Isayama [46]) available in literature have related the positive influence of temperature on supercritical interesterification with no catalyst. However after a long reaction time, over 300 min, there may be products decomposition, due to overexposure to elevated temperature, which is in agreement with the 5
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when compared with supercritical methanol due to the production of an unstable intermediate who requires high activation energy [50]. Also according to Table 4, other types of oil have been used in interesterification reaction with methyl acetate, such as macaw and canola oils. Ribeiro et al. obtained 82.46% of conversion efficiency from macaw oil using and γ-alumina catalyst in a batch reactor at 300 °C and autogenous pressure [11]. Visioli et al obtained a 60.24 ester content in a continuous reactor with a packed bed of γ-alumina at 275 °C and 20 MPa [51]. Farobie and Matsumura [50] studied the biodiesel production by using supercritical methyl acetate (SCMA) in a continuous flow reactor from canola oil, reaching reached a 97% yield. Similarly to Doná et al [29] and Campanelli et al. [30] reports, Farobie and Matsumura [50] obtained higher yields than the present work due to higher temperature and pressures.
Comparing Fig. 3c and d (250 °C, 3.0 MPa with profiles in Fig. S3d), which present the results at different oil to methyl acetate molar ratios, it can be seen that FAME content increased with molar ratio. FAME content was 18.8 wt% with 1:10 M ratio and equal to 27.4 wt% with 1:40 M ratio, at 240 min. Again, other content profiles in these figures also corroborate that oil to methyl acetate molar ratio had a significant impact on interesterification reaction. From Fig. S3c and d, it can be seen that the great difference of molar ratios (1:40–1:10) caused different pressures profiles, since pressure was autogenous, that is, it depends on temperature and composition system. Molar ratio increase FAME formation through the higher medium dilution and higher pressure reached, improving system homogenization. Goembira and Saka also investigated the molar ratio effect on ester production through supercritical interesterification and reported a positive effect of the molar ratio on reaction conversion [8]. Sustere, Murnieks and Kampars studied chemical interesterification with four alkyl acetates and confirmed that the FAME concentration increased with alkyl acetate to oil molar ratio [3]. Methyl acetate in excess is required to increase the direct reaction to the products, and it has been shown that are required molar ratios of oil:methyl acetate as high as 1:42 so that high yields are obtained [47]. But studies have shown that increasing the amount of methyl acetate in addition to a ratio of 1:42 does not significantly increase the biodiesel yield [30]. Based on the results presented in Fig. 3, the highest FAME content was 63.2 wt%, obtained at 325 °C, 1:40 oil:MeA molar ratio with 10 wt % of catalyst content at 240 min. Table 4 shows some results available in the literature and from this work regarding interesterification and transesterification reactions using CaO as catalyst or methyl acetate as acyl receptor. It can be seen that only Simões et al. [4] used a heterogeneous catalyst, soybean oil and methyl acetate in FAME production. The yield obtained in the present work is close to reported to these authors and the experimental conditions are similar. Other results reported in literature presented higher yields with no catalysts, but higher temperatures and pressures were applied at supercritical conditions. The works of Doná et al. [29] and Campanelli et al. [30] fall into this case, where higher yields were obtained compared to the present work, mainly due to the higher pressures utilized, that have a known positive effect. The reports of Devaraj et al. [48] and Mohadini et al. [49] used CaO as catalysts with soybean and waste cooking oil, respectively. However, in these reports methanol was used as acyl receptor and FAME was produced through transesterification reaction. Devaraj et al. [48] studied conversion of waste cooking oil to biodiesel in pilot plant using commercial CaO [48], while Mohadesi et al. [49] used in their study calcium oxide from mussel shell in the reaction between soybean oil with methanol, both achieved a yield close to 90%. It can be seen that transesterification reaction required milder conditions to achieve higher yields when compared to interesterification reaction using methyl acetate. This fact was reported by Farobie and Matsumura, who reported that supercritical methyl acetate showed lower reactivity
3.5. Catalyst reusability An important quality of the heterogeneous catalyst is reuse. CaO reuse was tested calcined at 800 °C, in interesterification reaction with oil to methyl acetate ratio of 1:40, catalyst content of 10 wt%, reaction temperature of 325 °C and 240 min. The results of reuse tests are shown in Fig. 4, where it can be seen that FAME content declined after each cycle. FAME concentration was 62 wt% in the first use, followed by 49.65 wt% in second, 48.78 wt% in third cycle and 40.85 wt% in the fourth cycle, corresponding to a 21.15% of catalytic efficiency decay. This decreasing may be associated to catalyst active sites blocked by the reactants, causing activity loss, since it was not washed between the cycles. Another reason for the decrease in content may be the catalyst mass loss in centrifugation step, feed to reactor and also leaching phenomenon between the cycles. CaO is commonly related in literature as a catalyst with catalytic activity decay in reuse tests for transesterification reaction. Yin et al. reported a biodiesel yield decay in all reaction cycles for CaO from duck eggshells [20]. Sirisonboonchai et al. presented a FAME yield decreasing in reuse in transesterification reaction using waste oil and scallop shell catalyst [22]. Zhao et al. also reported a little biodiesel yield decay with commercial nano CaO [43]. Infrared spectroscopy was used to qualitatively determine functional groups in FAME produced and in the catalyst surface in each reuse cycle, in order to better understand catalytic activity decay. Fig. 5 shows infrared spectrum of FAME produced in the first catalyst cycle and catalyst infrared spectra after each reaction cycle. The band in the region of 3455 cm−1 can be observed due to air humidity, since the pressed disc technique was used. The stretching band absorption of C] O present in 1743 cm−1 and the band between 1223 cm−1 and 1171 cm−1 relating to the axial deformation CeO are representative of the ester groups involved in the reaction. The asymmetric and symmetric stretching of the methylene group (CH2), which composes the ester chain, are seen in the 2927 cm−1 and 2854 cm−1 bands respectively; near them is the 3009 cm−1 band (eHC]CHestretching), which
Table 4 FAME production from interesterification and transesterification chemical routes using CaO as catalyst or methyl acetate as acyl receptor. Oil
Soybean Soybean Soybean Soybean Soybean Waste cooking oil Canola Macaw (Acrocomia aculeata) Macaw (Acrocomia aculeata)
Solvent
MeA MeA MeA MeA Methanol Methanol MeA MeA MeA
Reaction condition Reactor type
Temperature [°C]
Oil:solvent molar ratio
Pressure [MPa]
Batch Batch Continuous Batch Batch Batch Continuous Batch Continuous
325 345 350 325 65 80 380 300 275
1:40 1:42 1:60 1:40 1:24 1:6 1:40 1:20 1:2.5 (mass ratio)
8–10 20 20 5–10 ambient ambient 20 – 20
* Based on the oil mass. 6
Catalyst content*
Yield %/time [min]
Ref.
CaO 10 wt% – – Ca-Mg Al 10 wt% CaO 12 wt% CaO 3 wt% – γ-Al2O3 2 wt% γ-Al2O3
63.2/240 106/50 83/45 67/180 88/480 92/120 97/10 82.46/120 60.24/20
This work [30] [29] [4] [49] [48] [50] [11] [51]
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some active species during the interesterification process, which is one of the factors that cause activity reduction. Besides that, this value is lower than some reported in literature in transesterification reaction, as Yoosuk et al. [25] (456 mg calcium/L), Verziu et al. [1] (325 mg calcium/kg) and Zhao et al. [43] (178–875 mg calcium/kg).
4. Conclusion This study evaluated calcium oxide as catalyst in interesterification reaction with methyl acetate from soybean oil. CaO catalyst was obtained from calcium carbonate calcination. Optimum calcination temperature was 800 °C. Nano CaO was also prepared but yielded a lower FAME content. Effect of temperature, oil to methyl acetate molar ratio and catalyst concentration were evaluated through kinetic experiments. FAME content showed to be favored by all these variables. The highest FAME content, equal to 62.3 wt%, was obtained at 325 °C, 10 wt% of catalyst, and 1:40 Oil: MeA molar ratio. Reuse test pointed out to catalytic activity decay, probably due to active sites blocking, mass loss and leaching phenomena.
Fig. 4. Reusability of catalyst.
represents the concentration of unsaturations in the FAME produced. At 1463 cm−1 and 724 cm−1 are the bending vibrations bands of the methylene group. Bands in FAME produced refer to ester molecules and a little humidity and are in agreement with other biodiesel spectra reported in the literature [10,52]. Regarding to catalysts spectra, it can be seen the same bands shown in FAME spectrum. Besides that, catalysts spectra after cycles presented contaminants bands such as H2O (there is an increase of the 3500 cm−1 band) and CO2 due to a strong band between 1540 and 1610 cm−1 relative to the carboxylate anion, once that CO2 can bind to catalyst surface in the form of unidentate carbonate generating this structure [53]. These contaminants may have been adsorbed between cycles or during sample handling for analysis. These results show that catalytic activity decay can be associated to this contaminants adsorption, besides mass loss. Considering that the leaching level of metallic ions of basic oxides in solution is inversely associated with catalyst activity in reuse, atomic emission spectroscopy was used to analyze CaO leaching. In three successive extraction steps, calcium content was equal to 34.04, 15.92 and 7.69 mg calcium/kg FAME, resulting in a total calcium content of 57.66 mg calcium/kg FAME. These results confirm that the catalyst lost
CRediT authorship contribution statement A.L.B. Nunes: Investigation, Methodology, Validation, Writing original draft. F. Castilhos: Conceptualization, Methodology, Resources, Writing - review & editing, Supervision.
Acknowledgments The authors thank to CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) (404675/2013-1) for financial support and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for scholarships.
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.fuel.2020.117264.
Fig. 5. FTIR analysis of biodiesel and of catalyst after cycles. 7
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References [27]
[1] Verziu M, Coman SM, Richards R, Parvulescu VI. Transesterification of vegetable oils over CaO catalysts. Catal Today 2011;167:64–70. https://doi.org/10.1016/j. cattod.2010.12.031. [2] Calero J, Luna D, Sancho ED, Luna C, Bautista FM, Romero AA, et al. An overview on glycerol-free processes for the production of renewable liquid biofuels, applicable in diesel engines. Renew Sustain Energy Rev 2015;42:1437–52. https://doi. org/10.1016/j.rser.2014.11.007. [3] Sustere Z, Murnieks R, Kampars V. Chemical interesterification of rapeseed oil with methyl, ethyl, propyl and isopropyl acetates and fuel properties of obtained mixtures. Fuel Process Technol 2016;149:320–5. https://doi.org/10.1016/j.fuproc. 2016.04.033. [4] Simões SS, Ribeiro JS, Celante D, Brondani LN, Castilhos F. Heterogeneous catalyst screening for fatty acid methyl esters production through interesterification reaction. Renew Energy 2020;146:719–26. https://doi.org/10.1016/j.renene.2019.07. 023. [5] Casas A, Ruiz JR, Ramos MJ, Pérez A. Effects of triacetin on biodiesel quality. Energy Fuels 2010;24:4481–9. https://doi.org/10.1021/ef100406b. [6] Casas A, Ramos MJ, Pérez Á. New trends in biodiesel production: chemical interesterification of sunflower oil with methyl acetate. Biomass Bioenergy 2011;35:1702–9. https://doi.org/10.1016/j.biombioe.2011.01.003. [7] Xu Y, Du W, Liu D. Study on the kinetics of enzymatic interesterification of triglycerides for biodiesel production with methyl acetate as the acyl acceptor. J Mol Catal B Enzym 2005;32:241–5. https://doi.org/10.1016/j.molcatb.2004.12.013. [8] Goembira F, Saka S. Optimization of biodiesel production by supercritical methyl acetate. Bioresour Technol 2013;131:47–52. https://doi.org/10.1016/j.biortech. 2012.12.130. [9] Brondani LN, Simões SS, Celante D, Castilhos F. Kinetic modeling of supercritical interesterification with heterogeneous catalyst to produce methyl esters considering degradation effects. Ind Eng Chem Res 2019;58:816–27. https://doi.org/10.1021/ acs.iecr.8b04715. [10] dos Santos Ribeiro J, Celante D, Simões SS, Bassaco MM, da Silva C, de Castilhos F. Efficiency of heterogeneous catalysts in interesterification reaction from macaw oil (Acrocomia aculeata) and methyl acetate. Fuel 2017;200:499–505. https://doi.org/ 10.1016/j.fuel.2017.04.003. [11] Ribeiro JS, Celante D, Brondani LN, Trojahn DO, da Silva C, de Castilhos F. Synthesis of methyl esters and triacetin from macaw oil (Acrocomia aculeata) and methyl acetate over γ-alumina. Ind Crops Prod 2018;124:84–90. https://doi.org/ 10.1016/j.indcrop.2018.07.062. [12] Di Serio M, Tesser R, Pengmei L, Santacesaria E. Heterogeneous catalysts for biodiesel production. Energy Fuels 2008;22:207–17. https://doi.org/10.1021/ ie070663q. [13] Semwal S, Arora AK, Badoni RP, Tuli DK. Biodiesel production using heterogeneous catalysts. Bioresour Technol 2011;102:2151–61. https://doi.org/10.1016/j. biortech.2010.10.080. [14] Tang Y, Liu H, Ren H, Cheng Q, Cui Y, Zhang J. Development KCl/CaO as a catalyst for biodiesel production by tri-component coupling Transesterification. Environ Prog Sustain Energy 2018:1–7. https://doi.org/10.1002/ep.12977. [15] Tang Y, Li L, Wang S, Cheng Q, Zhang J. Tricomponent coupling biodiesel production catalyzed by surface modified calcium oxide. Environ Prog Sustain Energy 2016;35:257–62. https://doi.org/10.1002/ep.12194. [16] Marinković DM, Stanković MV, Veličković AV, Avramović JM, Miladinović MR, Stamenković OO, et al. Calcium oxide as a promising heterogeneous catalyst for biodiesel production: current state and perspectives. Renew Sustain Energy Rev 2016;56:1387–408. https://doi.org/10.1016/j.rser.2015.12.007. [17] Kesic Z, Lukic I, Zdujic M, Mojovic L, Skala D. Calcium oxide based catalysts for biodiesel production: a review. Chem Ind Chem Eng Q 2016;22:391–408. https:// doi.org/10.2298/CICEQ160203010K. [18] Soares Dias AP, Puna J, Neiva Correia MJ, Nogueira I, Gomes J, Bordado J. Effect of the oil acidity on the methanolysis performances of lime catalyst biodiesel from waste frying oils (WFO). Fuel Process Technol 2013;116:94–100. https://doi.org/ 10.1016/j.fuproc.2013.05.002. [19] Granados ML, Poves MDZ, Alonso DM, Mariscal R, Galisteo FC, Moreno-Tost R, et al. Biodiesel from sunflower oil by using activated calcium oxide. Appl Catal B Environ 2007;73:317–26. https://doi.org/10.1016/j.apcatb.2006.12.017. [20] Yin X, Duan X, You Q, Dai C, Tan Z, Zhu X. Biodiesel production from soybean oil deodorizer distillate usingcalcined duck eggshell as catalyst. Energy Convers Manage 2016;112:199–207. https://doi.org/10.1016/j.enconman.2016.01.026. [21] Alonso DM, Vila F, Mariscal R, Ojeda M, Granados ML, Santamaría-González J. Relevance of the physicochemical properties of CaO catalysts for the methanolysis of triglycerides to obtain biodiesel. Catal Today 2010;158:114–20. https://doi.org/ 10.1016/j.cattod.2010.05.003. [22] Sirisomboonchai S, Abuduwayiti M, Guan G, Samart C, Abliz S, Hao X, et al. Biodiesel production from waste cooking oil using calcined scallop shell as catalyst. Energy Convers Manage 2015;95:242–7. https://doi.org/10.1016/j.enconman. 2015.02.044. [23] Anjana PA, Niju S, Meera Sheriffa Begum KM, Anantharaman N. Utilization of limestone derived calcium oxide for biodiesel production from non-edible pongamia oil. Environ Prog Sustain Energy 2016;35:1758–64. https://doi.org/10. 1002/ep.12384. [24] Banković-Ilić IB, Miladinović MR, Stamenković OS, Veljković VB. Application of nano CaO–based catalysts in biodiesel synthesis. Renew Sustain Energy Rev 2017;72:746–60. https://doi.org/10.1016/j.rser.2017.01.076. [25] Yoosuk B, Udomsap P, Puttasawat B, Krasae P. Modification of calcite by hydrationdehydration method for heterogeneous biodiesel production process: the effects of water on properties and activity. Chem Eng J 2010;162:135–41. https://doi.org/10. 1016/j.cej.2010.05.013. [26] Bai H, Shen X, Liu X, Liu S. Synthesis of porous CaO microsphere and its application
[28] [29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[49]
[50]
[51]
[52]
[53]
8
in catalyzing transesterification reaction for biodiesel. Trans Nonferrous Met Soc China 2009;19:s674–7. https://doi.org/10.1016/S1003-6326(10)60130-6. Reddy C, Reddy V, Oshel R, Verkade JG. Room-temperature conversion of soybean oil and poultry fat to biodiesel catalyzed by nanocrystalline calcium oxides. Energy Fuels 2006;20:1310–4. https://doi.org/10.1021/ef050435d. Hartman L, Lago RC. Rapid preparation of fatty acid methyl esters from lipids. Lab Pract 1973;22. 475–6 passim. Doná G, Cardozo-Filho L, Silva C, Castilhos F. Biodiesel production using supercritical methyl acetate in a tubular packed bed reactor. Fuel Process Technol 2013;106:605–10. https://doi.org/10.1016/j.fuproc.2012.09.047. Campanelli P, Banchero M, Manna L. Synthesis of biodiesel from edible, non-edible and waste cooking oils via supercritical methyl acetate transesterification. Fuel 2010;89:3675–82. https://doi.org/10.1016/j.fuel.2010.07.033. Calero J, Luna D, Sancho ED, Luna C, Bautista FM, Romero AA, et al. Development of a new biodiesel that integrates glycerol, by using CaO as heterogeneous catalyst, in the partial methanolysis of sunflower oil. Fuel 2014;122:94–102. https://doi. org/10.1016/j.fuel.2014.01.033. Liu X, He H, Wang Y, Zhu S, Piao X. Transesterification of soybean oil to biodiesel using CaO as a solid base catalyst. Fuel 2008;87:216–21. https://doi.org/10.1016/j. fuel.2007.04.013. Kouzu M, Yamanaka S, Hidaka J, Tsunomori M. Heterogeneous catalysis of calcium oxide used for transesterification of soybean oil with refluxing methanol. Appl Catal A Gen 2009;355:94–9. https://doi.org/10.1016/j.apcata.2008.12.003. Celante D, Schenkel JVD, de Castilhos F. Biodiesel production from soybean oil and dimethyl carbonate catalyzed by potassium methoxide. Fuel 2018;212:101–7. https://doi.org/10.1016/j.fuel.2017.10.040. Aransiola EF, Ojumu TV, Oyekola OO, Madzimbamuto TF, Ikhu-Omoregbe DIO. A review of current technology for biodiesel production: state of the art. Biomass Bioenergy 2014;61:276–97. https://doi.org/10.1016/j.biombioe.2013.11.014. Prados CP, Rezende DR, Batista LR, Alves MIR, Antoniosi Filho NR. Simultaneous gas chromatographic analysis of total esters, mono-, di- and triacylglycerides and free and total glycerol in methyl or ethyl biodiesel. Fuel 2012;96:476–81. https:// doi.org/10.1016/j.fuel.2011.11.060. Cho YB, Seo G, Chang DR. Transesterification of tributyrin with methanol over calcium oxide catalysts prepared from various precursors. Fuel Process Technol 2009;90:1252–8. https://doi.org/10.1016/j.fuproc.2009.06.007. Yang J, Kaewpanha M, Karnjanakom S, Guan G, Hao X, Abudula A. Steam reforming of biomass tar over calcined egg shell supported catalysts for hydrogen production. Int J Hydrogen Energy 2016;41:6699–705. https://doi.org/10.1016/j. ijhydene.2016.03.056. Zhu H, Wu Z, Chen Y, Zhang P, Duan S, Liu X, et al. Preparation of biodiesel catalyzed by solid super base of calcium oxide and its refining process. Chin J Catal 2006;27:391–6. https://doi.org/10.1016/S1872-2067(06)60024-7. Ghiasi M, Malekzadeh A. Synthesis of CaCO3 nanoparticles via citrate method and sequential preparation of CaO and Ca(OH)2 nanoparticles. Cryst Res Technol 2012;47:471–8. https://doi.org/10.1002/crat.201100240. Correia LM, de Sousa Campelo N, Novaes DS, Cavalcante CL, Cecilia JA, RodríguezCastellón E, et al. Characterization and application of dolomite as catalytic precursor for canola and sunflower oils for biodiesel production. Chem Eng J 2015;269:35–43. https://doi.org/10.1016/j.cej.2015.01.097. Niju S, Anushya C, Balajii M. Process optimization for biodiesel production from Moringa oleifera oil using conch shells as heterogeneous catalyst. Environ Prog Sustain Energy 2018:1–12. https://doi.org/10.1002/ep.13015. Zhao L, Qiu Z, Stagg-Williams SM. Transesterification of canola oil catalyzed by nanopowder calcium oxide. Fuel Process Technol 2013;114:154–62. https://doi. org/10.1016/j.fuproc.2013.03.027. 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. Bioresour Technol 2010;101:965–9. https://doi.org/10.1016/j. biortech.2009.09.004. Visioli LJ, Trentini CP, de Castilhos F, da Silva C. Esters production in continuous reactor from macauba pulp oil using methyl acetate in pressurized conditions. J Supercrit Fluids 2018;140:238–47. https://doi.org/10.1016/j.supflu.2018.06.018. Saka S, Isayama Y. A new process for catalyst-free production of biodiesel using supercritical methyl acetate. Fuel 2009;88:1307–13. https://doi.org/10.1016/j. fuel.2008.12.028. Marx S. Glycerol-free biodiesel production through transesterification: a review. Fuel Process Technol 2016;151:139–47. https://doi.org/10.1016/j.fuproc.2016.05. 033. Devaraj K, Veerasamy M, Aathika S, Mani Y, Thanarasu A, Dhanasekaran A, et al. Study on effectiveness of activated calcium oxide in pilot plant biodiesel production. J Clean Prod 2019;225:18–26. https://doi.org/10.1016/j.jclepro.2019.03. 244. Mohadesi M, Moradi G, Davvodbeygi Y, Hosseini S. Soybean oil transesterification reactions in the presence of mussel shell: Pseudo-first order kinetics. Iran J Chem Chem Eng 2018;37:43–51. Farobie O, Matsumura Y. Continuous production of biodiesel under supercritical methyl acetate conditions: experimental investigation and kinetic model. Bioresour Technol 2017;241:720–5. https://doi.org/10.1016/j.biortech.2017.05.210. Visioli LJ, de Castilhos F, da Silva C. Use of heterogeneous acid catalyst combined with pressurized conditions for esters production from macauba pulp oil and methyl acetate. J Supercrit Fluids 2019;150:65–74. https://doi.org/10.1016/j.supflu.2019. 03.023. Chakraborty R, Bepari S, Banerjee A. Transesterification of soybean oil catalyzed by fly ash and egg shell derived solid catalysts. Chem Eng J 2010;165:798–805. https://doi.org/10.1016/j.cej.2010.10.019. Philipp R, Fujimoto K. FTIR spectroscopic study of carbon dioxide adsorption/ desorption on magnesia/calcium oxide catalysts. J Phys Chem 1992;96:9035–8. https://doi.org/10.1021/j100201a063.