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Nov 18, 2013 - A heterogeneous catalyst has been derived from a waste material of fresh water bivalve mollusk (i.e., Margaritifera falcata outer shell...
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Transesterification of Palm Oil Catalyzed by Fresh Water Bivalve Mollusk (Margaritifera falcata) Shell as Heterogeneous Catalyst Rajesh Madhuvilakku, Ramalakshmi Mariappan, Suganya Jeyapal, Sasikala Sundar, and Shakkthivel Piraman* Sustainable Energy and Smart Materials Research Lab, Department of Nanoscience and Technology, Alagappa University, Karaikudi-630 002, Tamilnadu, India ABSTRACT: A heterogeneous catalyst has been derived from a waste material of fresh water bivalve mollusk (i.e., Margaritifera falcata outer shell) for the transesterification of palm oil. The shell was washed, crushed, ground, and calcined at 850 °C to derive active CaO catalyst. The catalyst was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), and differential thermal analysis/ thermogravimetric (DT/TG) analysis. The DT/TG analysis showed the decomposition of calcium carbonate present in the shell at 780 °C. The XRD peaks for calcined shell were observed at 2θ = 32.22°, 53.53°, and 64.03° characteristics of CaO and showed high crystallinity. The textural structure of shell can be observed from the SEM images indicated that the structure of shell changed with calcination temperature. The FTIR absorption bands of the calcined shell were observed at 1471, 1090, and 874 cm−1, which are attributed to the decrease of the reduced mass of the functional group attached to the CO32‑ ions. The waste driven (bivalve mollusk outer shell) catalyzed palm oil transesterification resulted in a high yield (90%) and conversion (98.2%) of biodiesel that was obtained at a 10:1 (methanol to oil) molar ratio and 4 wt % catalyst concentration at 60 °C in 5 h reaction time. The conversion of biodiesel was determined by 1H NMR.

1. INTRODUCTION

have been employed in biodiesel production, for example, MgO, CaO, and hydrotalcites.5−7 CaO closely resembles an environmentally friendly material used as basic oxide catalyst for transesterification reaction, owing to nontoxicity, ease of availability, lower cost, and reusable characteristics. For instance, the mechanochemically synthesized CaO−ZnO catalyst was used for the biodiesel production process8 and also the CaO−CeO2 mixed-oxide catalyst was tried for the biodiesel synthesis.1,9 Graphite oxide was used as an effective host for the CaO nanoparticles,10 and the kinetics of the transesterification catalyzed by CaO−La2O3 and CaO−CeO2 supported catalysts were reported.11 The kinetics and reusability of Zn/CaO catalyst for the transesterification of waste cotton seed oil at high temperature were investigated.12 Allthough there are recent reports on the use of CaO based catalyst for the biodiesel conversion process, synthesis of these catalysts involves several steps that take longer time and are mostly cost intensive. For these reasons, utilization of a waste material as a catalyst is a wise choice to minimize the biodiesel production cost. Waste materials such as egg,13 oyster,14 crab, and cockle shell,15 fly ash,16 and animal bone17 were used for the synthesis of CaO catalyst for the biodiesel synthesis from various vegetable oils. Hence, the objective of this paper is to reveal that the Margaritifera falcata (freshwater bivalve mollusk) outer wall shell has been used as raw material for synthesis of a calcium oxide based heterogeneous catalyst for transesterification of palm oil (PO) to bring down the production cost of biodiesel. Thus, the

Growing demand for energy and depletion of petroleum fuels are driving forces for searching for alternative energy sources. In addition, petroleum fuel is a major contributor to greenhouse gases. As a result, alternative clean environmentally benign fuels are needed.1 Biodiesel has attracted attention in recent years as a renewable sustainable energy source with negligible pollutant emissions.2 Moreover, this fuel can be used directly or mixed with conventional fuel for most diesel engines without extensive engine modifications. Biodiesel (fatty acid alkyl ester) is usually produced from triglycerides, which are naturally derived from vegetable oils and animal fats that are transesterified with shortchain alcohols, such as methanol and ethanol.3 Vegetable oils are mostly used as raw materials for producing biodiesel, because they have practically no sulfur content, offer no storage difficulty, and have excellent lubrication properties as well.4 Generally, the transesterification reaction is carried out using homogeneous base and acid catalysts such as NaOH, KOH, and H2SO4, which are corrosive, sensitive to water, and act as free fatty acids in the reaction system to form soap. Consequently, they reduce both catalytic activity of the catalyst and biodiesel purity. Thus, high amounts of catalysts are required, resulting in increased production cost. In addition, the homogeneous catalysts have to be removed after the reaction and a large amount of wastewater is generated for separation and purification of biodiesel from catalysts and the byproduct (glycerol).5 In order to overcome the drawbacks of homogeneous catalytic transesterification of vegetable oils, recently heterogeneous catalysts have been explored due to their higher catalytic activity, easy separation, and reusability. Several heterogeneous catalysts © 2013 American Chemical Society

Received: Revised: Accepted: Published: 17407

August 8, 2013 October 11, 2013 November 18, 2013 November 18, 2013 dx.doi.org/10.1021/ie4025903 | Ind. Eng. Chem. Res. 2013, 52, 17407−17413

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present work attempts to develop CaO nanocatalyst from natural waste of bivalve mollusk shell and to exploit its catalytic activity toward the transesterification process for the fist time. The effect of various process parameters such as weight percent of catalyst loading, reaction temperature, reaction time, and methanol to oil ratio on the fatty acid methyl ester (FAME) were also investigated.

2. MATERIALS AND METHODS 2.1. Materials and Catalyst Preparation. Palm Oil (PO) was purchased from a local market. Fresh water bivalve mollusks were collected from local ponds. Methanol (>99% purity) and orthophosphoric acid (H3PO4) were procured from E-Merck, India. All the other chemicals used were of reagent grade. The waste M. falcata exterior shells were collected from a local pond and washed with water followed by double distilled water to remove impurities and sands deposited on the shell surface. Subsequently, the shells were treated in a hot air oven at 105 °C for 24 h to remove water from shell surfaces.16 The dried shells were ground to get fine powder and calcined at 850 °C based on the decomposition temperature of calcium carbonate (i.e., 800 °C) in a muffle furnace for 2.5 h.18 2.2. Catalyst Characterization. The powders of bivalve shells were analyzed through a thermogravimetric/differential thermal analyzer (TG/DTA Mettler Toledo,Switzerland) under air flow conditions with a ramping rate of 10 °C min−1 to determine thermal transition of the sample. X-ray powder diffraction (XRD, 6000SH1MADZU) coupled with Cu Kα radiation was used to study the structure of the catalysts on calcination. The functional groups present in the catalyst were obtained from Varian 1000 FTIR instrument in the range of 400−4000 cm−1. Scanning electron microscopy (SEM) coupled with electron dispersive X-ray (EDX) were obtained using A Leo Supra 50Vp field emission SEM system with 5 kV accelerating voltage to study the morphology, size, and elemental composition present in the produced catalyst. 2.3. Biodiesel Synthesis. PO and methanol were taken in appropriate molar ratios (10:1 molar ratio) with 4 wt % catalyst at constant temperature at 60 °C. The reaction was carried out using a three-necked round-bottom flask immersed in the constant temperature water bath placed on the plate of the magnetic stirrer fitted with a condenser in the middle neck and thermometer in the side neck. Initially, refined PO was preheated at 80 °C to remove impurities and moisture. The freshly prepared CaO nanocatalyst was mixed with methanol, the mixture was transferred to the preheated oil, and the transesterification of PO was conducted for 5 h at required reaction temperature (40−70 °C). Upon the reaction completion confirmed by TLC test, the products were allowed to settle overnight, producing three distinct phases (i.e., methyl ester on top, glycerol in the middle, and catalyst phase at the bottom). After separation of the methyl ester from the glycerol and catalyst phases, 1.0 mL of H3PO4 was added with biodiesel to neutralize the product. The obtained product was characterized by 1H NMR to determine the conversion of methyl ester.

Figure 1. TGA/DTA curves of uncalcined bivalve mollusk shell powder.

(freshwater bivalve mollusk). From TGA, a three stage weight loss was observed. The weight loss observed at 0−347 °C is due to loss of surface water present in the grind shell powder. Another slight weight loss (about 3.3%) at 347−629 °C is attributed to loss of inorganic impurities present in the shell. The complete decomposition temperature indicates that the escape of carbon dioxide from calcium carbonate started at 536 °C and continued until 780 °C . The first derivative, DTA at 380 °C, also confirms the decomposition of CaCO3. Another derivative at 500 °C is attributed to the loss of inorganic impurities present in the shell.2 The complete decomposition (accounting for weight loss 42.34%) was observed at 800 °C. Above 800 °C, the weight loss remained constant. However, the bivalve shells which combusted at 850 °C were selected in this study. XRD Analysis. Figure 2a and b depicts the XRD patterns of uncalcined and calcined bivalve mollusk shell powder catalyst, respectively. The crushed shell was calcined at 850 °C for 2.5 h in a tubular muffler furnace similar to the case of Agrawal et al.18 The eggshell and mollusk shell are generally known to contain CaCO3 as a main Ca based component.13 CaCO3 is mainly

3. RESULTS AND DISCUSSION 3.1. Characterization of the Catalyst. TGA/DTA Studies. The decomposition temperature of calcium carbonate (CaCO3) of bivalve shells was determined by differential thermal and thermogravimetric (TGA/DTA) analysis. Figure 1 depicts the decomposition temperature of crushed shells of M. falcata

Figure 2. XRD patterns of (a) uncalcined bivalve mollusk shell powder catalyst and (b) 850 °C calcined bivalve mollusk shell powder catalyst. 17408

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present in the form of orthorhombic aragonite in uncalcined bivalve shell powder catalyst. Furthermore, XRD patterns of uncalcined bivalve shell powder catalyst characteristic peaks corresponding to CaCO3 crystalline phase are observed at 2θ = 33.142°, 26.229°, 27.222°, 45.870°, and 52.447°. The XRD spectra were compared with JCPDS file. These spectra were fully matched with JCPDS file no. 75-2230. The average particle size of the uncalcined shell powder orthorhombic particles is 78 nm. After the calcination at 850 °C, most of the diffraction peaks of carbonates disappeared. These results indicate that CaCO3 transformed into CaO. Whereas the characteristic peaks corresponding to CaO crystalline phase are observed at 2θ = 37.26°, 32.22°, 53.63°, and 64.03°, the XRD spectra were compared with the JCPDS file. These spectra were fully matched with JCPDS file no. 48-1467. The average particle size of the calcined shell powder cubic particles is 67 nm. Narrow and high intensity peaks of the calcined catalyst define the well crystallized structure of the catalyst. FTIR Spectra. FTIR analyses were made for uncalcined bivalve shell powder and bivalve shell calcined at 850 °C for 2.5 h (Figure 3). In the uncalcined shell powder, the major absorption bands

Figure 4. SEM images of (a) uncalcined bivalve mollusk shell powder catalyst and (b) 850 °C calcined bivalve mollusk shell powder catalyst.

powder had aggregated cubic structure with a mean size of ±117 nm. The change of the structure of the shells may be a result of the change of composition.19 3.2. Characterization of the Oil. The viscosity of the palm oil was determined using a Rheotek TCB-7 viscometer at different temperatures, and the results are presented in Table 1. A marginal decrease of viscosity when increasing the temperature was obtained as 64.00 cSt at 30 °C, while at 50 °C it was 29 cSt.

Figure 3. FTIR spectra of (a) uncalcined bivalve mollusk shell powder catalyst and (b) 850 °C calcined bivalve mollusk shell powder catalyst.

occurred at 1443, 869, and 712 cm−1, attributed to the asymmetric stretch, out-of-plane band, and in-plane bend vibration modes, respectively, for CO32‑ molecules. After the calcination, bivalve shells lost carbonate ions and absorption bands of CO32‑ shift to higher energy (i.e., 1471, 1090, 874 cm−1). This has been attributed to the decrease of the reduced mass of the functional group attached to the CO32‑ ions. After the calcinations process, a new peak appears at 3642 cm−1 indicating the presence of Ca(OH)2, formed from exposure of CaO with atmospheric air.19 SEM Images. The heterogeneous catalyst was prepared by calcining waste shells at high temperature. The morphology of ground shells and calcined shells can be observed from the SEM images (Figure 4). Naturally ground shells had aggregated macropore structure. The average size of the particles is ±128 nm. However, the shells calcined at 850 °C showed a decrease in the size of particles due to removal of CO2 from CaCO3 molecules. The SEM image indicates that the structure of the shells changed with calcination temperature. Calcined shell

Table 1. Fatty Acid Composition of Palm Oil fatty acid

symbol

saturated acid lauric C12:0 myristic C14:0 palmitic C16:0 steric C18:0 arachidic C20:0 monounsaturated acids palmitoleic C16 oleic C18 polyunsaturated acids linoleic C18:2 linolenic C18:3 17409

mean

range

0.2 1.1 44.7 4.2 0.4

0.1−0.3 1.0−1.3 43.9−46.0 3.9−4.4 0.3−0.7

0.1 39.2

0−0.1 38.0−40.6

10.0 0.3

9.2−10.5 0.3−0.6

temperature (°C)

viscosity (cSt)

30 40 50

64 44 29

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Scheme 1. Transesterification Mechanism of Triglyceride to Methyl Ester over Bivalve Mollusk Shell Derived CaO Catalyst

The fatty acid composition of palm oil is presented in Table 1. The palm oil comprises mainly palmitic acid (44.7%), followed by oleic acid (39.2%), whereas a trace amount of palmitoleic acid is present. 3.3. CaO Catalyst Assisted Transesterification Mechanism. The CaO powder (bivalve shells) derived at 850 °C shows the presence of hydroxide which was formed on the CaO surface when exposed to air (observed by FTIR). However, a slight increase of biodiesel yield was reported. The formation of Ca(OH)2 is not detrimental to the CaO as catalyst.2,20 Usually, CaO is soluble to some extent (0.035 wt %), and the dissolution is as follows. CaO ↔ Ca 2 + + O2 − Ca(OH)2 ↔ Ca 2 + + 2OH−

Transesterification reaction starts with dissociation of CaO and Ca(OH)2 into O2‑ and OH−, respectively, which are responsible for the formation methoxide anion. The methoxide anion later attacks the carbonyl carbon of the triglyceride to form a tetrahedral intermediate, and further the intermediate molecules rearrange to form a mole of methyl ester and diglyceride. The methoxide attacks the second and third carbonyl carbon atom in the diglyceride step-by-step, forming three moles of methyl ester and a mole of glycerol (Scheme 1).15 Characterization of Biodiesel by 1H NMR. The conversion of oil to fatty acid methyl ester (Biodiesel) was analyzed by 1H NMR. Figure 5 depicts the conversion of the palm oil to methyl

Figure 5. 1H NMR spectrum of biodiesel obtained from bivalve mollusk shell powder catalyst 4 wt %, 10:1 methanol to oil molar ratio, 5 h reaction time, and 60 °C reaction temperature.

esters was determined by the ratio of the signals at 3.68 ppm (methoxy groups of the methyl esters) and 2.30 ppm (α-carbon CH2 groups of all fatty acid derivatives) as described by Gelbard 17410

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Figure 6. (a) Effect of catalyst concentration on the yield (%) of biodiesel [methanol to oil ratio, 10:1; temperature, 60 °C; reaction time, 5 h]. (b) Effect of methanol/oil molar ratio on yield (%) of biodiesel [catalyst amount, 4 wt %; reaction temperature, 60 °C; reaction time, 5 h]. (c) Effect of temperature on yield (%) of biodiesel [methanol to oil ratio, 10:1; catalyst amount, 4 wt %; reaction time, 5 h]. (d) Effect of reaction time on the yield (%) of biodiesel [methanol to oil ratio, 10:1; catalyst amount, 4 wt %; reaction temperature, 60 °C].

et al.21 Knoth and Kenar22 derived an equation for the determination of biodiesel (eq1) C = 100 × (2AME /3A CH2 )

bivalve mollusk shells on the transesterification of the palm oil was investigated by varying its concentration from 0.3 to 5 wt % (based on the molecular weight of oil used). The reaction was carried out at 60 °C for 5 h with 6:1 methanol to oil ratio, and the results are depicted in Figure 6a. When the catalyst amount was increased from 0.3 to 4 wt %, the yield gradually increased and attained a maximum yield of 92.2%. Beyond 4 wt % catalyst concentration, the yield of the biodiesel production dropped from 92.2% to 75.5% (at 5 wt %). A 4 wt % value is quite less than that used by Obadiah et al.,17 where 20 wt % of the catalyst (waste animal bone) was found to be optimum. The reason for the decrease of yield at higher catalyst in our case may be due to the reaction mixture becoming more viscous, which could resist the mass transfer in the liquid−liquid−solid system for the transesterification process.12 From the result, 4 wt % catalyst is adopted for further reaction variable optimization. Effect of Methanol to Oil Ratio. The effect of methanol/oil molar ratio on the yield of FAME over bivalve mollusk shell derived catalyst (calcined for 2.5 h) was investigated. Chemically, the transesterification reaction of palm oil consists of three consecutive and reversible reactions. In the reaction sequence,

(1)

C denotes the conversion (%) of triglycerides to fatty acid methyl esters; AME is the integration value of the protons of methyl ester, and ACH2 is the integration value of the methyl protons. The factors 2 and 3 in the numerator and denominator are ascribed to the number of protons (2) on methylene and number of protons (3) on methyl ester. The yields were calculated using eq2 given by Leung and Guo.23 production yield (%) = weight of product/weight of raw oil × 100

(2)

Obviously, the M. falcata shell derived catalyst was identified as an effective catalyst for transesterification of palm oil. The yield of FAME (fatty acid methyl ester) was attained to be 92.2%. 3.4. Optimization of Reaction Variables. Effect of Catalyst Concentration. The effect of catalyst obtained from 17411

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the catalyst was recovered by centrifuge and thoroughly washed with methanol and subsequently calcined to remove hydroxide ion to get CaO catalyst. The regeneration of CaO catalyst will be used as heterogeneous catalyst for transesterification of palm oil.

triglycerides are converted stepwise to diglyceride, monoglyceride, and finally to glycerol, and a fatty acid ester is liberated. Stoichiometrically, the transesterification reaction requires three moles of methanol for each mole of triglyceride. However, in practice, the methanol loading needs to be high enough to shift the equilibrium favorably toward the right side of the reaction.24 The FAME content increased significantly by increasing the methanol/oil from 6:1 to 10:1. This higher amount of methanol would promote the formation of methoxy species on the CaO surface and also shift the reaction equilibrium to the forward direction,13 thus increasing the rate of yield up to 92.2%. The use of higher molar ratio of methanol/oil (10:1) was found to improve the methyl ester yield because excess alcohol not only promotes the transesterification rate but removes product molecules from the catalyst surface and regenerates the catalytic sites.12 However, further increase in methanol/oil ratio up to 15:1 did not promote the reaction but rather instantly decreased it. It was considered that the glycerol would largely dissolve in excessive methanol and subsequently inhibit the reaction of methanol to the reactants and catalyst, thus interfering with the separation of glycerin and leading to lowering of the conversion by shifting the equilibrium in the reverse direction.25 However, it was found that the 10:1 methanol/oil ratio was the optimum ratio for high yield of biodiesel (Figure 6b). Effect of Reaction Temperature. Transesterification reaction temperature is an important parameter in the biodiesel conversion which has to be optimized for better conversion. The molar ratio of methanol to oil 10:1, catalyst dosage 4 wt %, and reaction time 5 h were kept constant, and the reaction temperature was varied from 40 to 70 °C. The yields of biodiesel at different reaction temperatures are shown in Figure 6c. The yield of biodiesel increases with the temperature up to 60 °C (92.2% yield) and then tends to decrease. This behavior may be due to the lessening of interaction between reactants on the active sites of the catalyst surface.26 At low temperatures (40−50 °C), the reaction did not fully complete and showed low yield of FAME. On the other hand, at higher temperature, methanol would vaporize and form bubbles, which leads inhibition of reaction on the three-phase (catalyst/methanol/oil) interface and thus to the low yield.27 Hence, in the present case, a low temperature of 60 °C is considered to be the best suited for the biodiesel yield. This value is relatively same as that used by Agrawal et al.18 and Omraei et al.28 where 60 °C was found to be optimum for high yield of biodiesel. Effect of Reaction Time. Figure 6d graphically illustrates the change of the yield as a function of reaction time with the reaction conditions of 60 °C, 4 wt % catalyst concentration, and 10:1 methanol to oil molar ratio. As can be seen from the graph, the reaction could not properly take place at 3 and 4 h intervals, showing low yield of 70.8% and 82.6%, respectively. On the other hand, the reaction attained equilibrium at 5 h, and thereafter, biodiesel yield was slightly reduced. Because the catalyst may react with the fatty acids, causing additional saponification reaction at the longer time intervals.29 The optimum reaction time for the maximum yield of biodiesel may vary with the type of catalyst.18,30 In the present case, with respect to the obtained results, the optimum reaction time for the high yield of biodiesel is considered to be 5 h. 3.5. Biodiesel Production Activity. Bivalve mollusk shell derived catalyst illustrates a potential source of heterogeneous catalyst with high catalytic activity and conversion (98.2%) of biodiesel being obtained at 10:1 methanol to oil molar ratio, 4 wt % catalyst at 60 °C in 5 h. After the transesterification reaction,

4. CONCLUSIONS The CaO catalyst derived from M. falcata (bivalve mollusk) shell was elucidated to become active in heterogeneous transesterification for biodiesel production. The sample was calcined at 850 °C for 2.5 h for the conversion of CaCO3 to CaO, which leads to better catalytic activity and yield of biodiesel production. This highly efficient and low-cost catalyst could make the process of biodiesel production economically and ecologically friendly. The ecologically friendly and economic process could effectively reduce the processing cost of biodiesel, making it competitive with petroleum diesel. The conversion of biodiesel was found of be 98.2% using 4 wt % catalyst with 10:1 molar ratio of methanol to oil.



AUTHOR INFORMATION

Corresponding Author

*.E-mail:[email protected]. Tel: 04565- 238100, extn. 372. Fax: 04565- 225202, 225525. Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS Authors are grateful to the UGC, DST New Delhi, India for their financial support and Department of Physics, Alagappa University for providing XRD facility.



REFERENCES

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