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Utilization of waste cockle shell (Anadara granosa) in biodiesel production from palm olein: Optimization using response surface methodology
Fuel 90 (2011) 2353–2358
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Fuel journal homepage: www.elsevier.com/locate/fuel
Utilization of waste cockle shell (Anadara granosa) in biodiesel production from palm olein: Optimization using response surface methodology Peng-Lim Boey a, Gaanty Pragas Maniam a,⇑, Shafida Abd Hamid b, Dafaalla Mohamed Hag Ali a,c a
School of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia Kulliyyah of Science, International Islamic University Malaysia, Jalan Sultan Ahmad Shah, Bandar Indera Mahkota, 25200 Kuantan, Pahang, Malaysia c Chemistry Department, Sudan University of Science and Technology, P.O. Box 407 Khartoum, Sudan b
a r t i c l e
i n f o
Article history: Received 30 November 2009 Received in revised form 1 March 2011 Accepted 1 March 2011 Available online 29 March 2011 Keywords: Biodiesel Methyl ester Transesterification Cockle shell Palm olein
a b s t r a c t The cockle shell, which is available in abundance, has no any eminent use and is commonly regarded as a waste, was utilized as a source of calcium oxide in catalyzing a transesterification reaction to produce biodiesel (methyl esters). A central composite design (CCD) was used to optimize the two major influential reaction variables: catalyst and methanol amount towards purity and yield of methyl esters. The analysis of variance (ANOVA) indicated that the catalyst has a positive influence on purity but negative on the yield. Meanwhile, the methanol/oil mass ratio showed a positive effect on both purity and yield. Using CCD, the optimum reaction conditions were found to be 4.9 wt.% of catalyst and 0.54:1 methanol/ oil mass ratio. The prepared catalyst was capable of being reused under the suggested optimal conditions. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Biodiesel has been in the limelight recently not only as an alternate or extender but also as a sustainable fuel. It is renewable, biodegradable, with low exhaust emission, nontoxic, higher flash point, excellent lubricity, carbon neutral, and environmentally acceptable as a fuel for diesel engines [1,2]. Triglycerides for biodiesel production come from various sources; edible oil, inedible oil, fats, waste oil and recently from algae [3–6]. Glycerol, the coproduct of the reaction, is mainly used in the food, pharmaceutical and cosmetics industries. Interestingly, a recent US patent revealed that methanol, one of the reactants in this reaction, could be produced from the glycerol itself, thus, opening up an avenue to produce raw material from the by-product of the reaction itself [7]. Production of biodiesel by transesterification is catalyzed by both homogeneous and heterogeneous catalysts. Although noncatalytic transesterification is possible, via supercritical methanol, catalytic transesterification is commonly accepted as an industrial process due to its lower operational cost [8]. Typically, homogeneous catalysts, including sodium or potassium hydroxide or their corresponding alkoxides, have been employed for their faster kinetics. Under this type of catalyst, reactions can be completed in less than one hour with remarkable purity and yield. However, unlike heterogeneous catalysts, homogeneous catalysts cannot ⇑ Corresponding author. Tel.: +60 16 4110236; fax: +60 4 6574854. E-mail address: [email protected] (G.P. Maniam). 0016-2361/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2011.03.002
tolerate the presence of moisture and free fatty acids (FFA). Both impurities lead to hydrolysis, ester being converted to acids (Fig. 1a), and saponification, a soap formation reaction (Fig. 1b), which results in lower yield and tedious product separation [9]. Among the heterogeneous catalysts that are being used in transesterification reaction, CaO has a promising place, and many reports have been published on CaO-catalyzed transeserification using laboratory grade CaO [10–12]. However, the utilization of waste materials as heterogeneous catalysts has been of recent interest in the search for a sustainable process. Oyster and chicken egg shells have been successfully used as effective catalysts in converting triglycerides to methyl esters [13,14]. In addition to these wastes, we have reported the use of crab shell as well as mixed crab/cockle shell as a catalyst in producing methyl esters [6,15,16]. On the other hand, cockles (Anadara granosa), which live predominantly on intertidal mudflats, are an important protein source in the South East Asian region [17]. In Malaysia, the retail value of cockles alone in 2007 was estimated at over 32 million US dollars [18]. As a result, the generation of waste shells is abundant, and the plentiful supply makes it feasible for the shell to be used or co-used as a catalyst in the biodiesel industry and, to our best knowledge, no one has reported the use of cockle shells as catalyst in palm olein transesterification. Optimization of process variables in biodiesel production has been worked by many [19–21]. However, most of the studies present either purity or yield as a response. Little attention has been given to both the purity and yield as the responses and the relation
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Fig. 1. (a) Hydrolysis of fatty acid methyl esters in presence of moitsure and (b) saponification of fatty acids.
between them. As such, the present paper explores the utilization of the abundantly available and under-utilized waste cockle shell in the production of biodiesel using palm olein and methanol and to study the influence of reaction variables on purity and yield of the product. To assess and understand the effect of the selected variables, statistical analysis was performed using central composite design. A reusability study of the catalyst was also conducted.
mixture of calcined catalyst (900 °C, 2 h) and methanol. The contents were refluxed under magnetic stirring. Two most influential reaction parameters (catalyst amount and methanol/oil mass ratio) were studied to find the optimum reaction conditions. After completion, the reaction mixture was allowed to cool, causing the glycerol to separate by gravity. A centrifuge was used to further separate the layers (methyl ester, glycerol and catalyst) and the residual methanol in methyl ester layer was evaporated out using a rotary evaporator at 80 °C to obtain a pure methyl ester. Biodiesel purity (methyl ester content in the top methyl ester layer) was determined by GC as stipulated in EN 14103 and the yield was quantified as follows: Yield ð%Þ ¼
methyl ester purity ð%Þ weight of obtained methyl ester ðgÞ weight of oil used ðgÞ
2. Experimental
2.4. Gas chromatography analysis
2.1. Materials
Standard materials and samples were analyzed by a gas chromatography (Perkin Elmer, Clarus 500) fitted with a flame ionization detector (FID). The FAME content (purity) was determined by following the European regulation procedure EN 14103 with a polar capillary column (Supelco Wax, 30 m 0.25 mm i.d. 0.25 lm) using methyl heptadecanoate as an internal standard. Peaks of methyl esters were identified by comparing them with their respective authentic standards.
Cockle shells (A. granosa) were obtained from the local market. Refined palm olein (Elaeis guineensis) of Tenera hybrid was purchased from Delima Oil Products, Malaysia. The fatty acids composition of the oil was found as: myristic acid 0.8%, palmitic acid 41.3%, stearic acid 3.6%, oleic acid 44.0%, linoleic acid 9.8%, and traces of other acids. Fatty acid methyl ester (FAME) standards and internal standards were obtained from Sigma–Aldrich (Switzerland) and of chromatographic grade. Analytical grade methanol (MeOH) and n-hexane were purchased from ChemAR. 2.2. Catalyst preparation and characterization The shells were cleaned by washing thoroughly with warm water several times. Then they were dried overnight in an oven at 105 °C. Crushed and powdered shells were then sieved (<1 mm) before being subjected to heat treatment in a furnace. The basic strength of the catalyst was tested using Hammett indicators. The following Hammett indicators were used: phenolphthalein (H_ = 8.2), 2,4-dinitroaniline (H_ = 15) and 4-nitroaniline (H_ = 18.4). About 25 mg of the sample was shaken with 1 m3 of a solution of Hammett indicator diluted in methanol and left to equilibrate for 2 h [22]. Surface analysis of the catalyst was examined using Micromeritics ASAP 2000. The sample was degassed at 105 °C prior to analysis and the adsorption of N2 was measured at 196 °C. The surface area was calculated using BET equation over the pressure range P/P0 = 0.01–0.30, where a linear relationship was maintained. The catalyst was examined by thermogravimetric analysis (TGA) using the Mettler Toledo TGA/SDTA 851e instrument, from 30 to 900 °C with 20 °C /min heating rate, under N2 environment; scanning electron microscopy coupled with electron dispersive X-ray (SEM-EDX) were obtained using the Leo Supra 50VP Field Emission SEM system with 15 kV accelerating voltage; X-ray diffraction (XRD) on Siemens Diffractometer D5000 using Cu Ka radiation, 2h ranged from 25° to 125° with a step size of 0.1°, at a scanning speed of 1° min1.
2.5. Statistical analysis Statistical analysis was performed using Design-ExpertÒ 7.1 (Stat-Ease, Inc., Minneapolis, USA). 3. Results and discussion 3.1. Catalyst characterization The catalyst changed both the colour of phenolphthalein (H_ = 8.2) from colourless to pink and the colour of 2,4-dinitroaniline (H_ = 15) from yellow to mauve but failed to change the colour of 4-nitroaniline (H_ = 18.4). As such, the catalyst basic strength was designated as 15 < H_ < 18.4, and considered as a strong base for transesterification reaction. The TGA result (Fig. 2) exhibits one major decomposition of 42%, ranged 575–800 °C, with centered temperature around 750 °C. The decomposition can be attributed to the evolvement of CO2 and the weight loss matched to the stoichiometrical weight loss of 44% when CaCO3 transforms to CaO.
2.3. Reaction Transesterification reactions were performed in a 25 mL 2-neck glass reactor with a condenser, immersed in a water bath. The studied methanol/oil mass ratio was in the range of 0.12–0.68 g/ g whereas catalyst amount was in the range of 2.2 to 7.8 wt.%. A central composite design under response surface methodology was used to assess the experimental outputs statistically. In a typical reaction, 10.0 g of oil was added in a thin stream onto the
Fig. 2. TGA profile of the catalyst.
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Fig. 3. SEM images of: (a) uncalcined and (b) calcined catalyst at 900 °C, 2 h.
As explained by Fig. 3, SEM micrographs of calcined catalyst demonstrated the presence of morphologies relatively smaller and similar to each other increases the surface area of the catalyst. In contrast, at equal magnifications of 3000, uncalcined catalyst showed a bulky substance. This observation is in line with the results obtained from N2 physisorption measurement, in which much higher surface area (15 m2 g1) and higher pore volume (0.10 cm3 g1) were observed for the calcined catalyst as compared to 3 m2 g1 and 0.01 cm3 g1 for the uncalcined catalyst, respectively. As depicted by Fig. 4, XRD results revealed that the composition of uncalcined cockle shell mainly consists of CaCO3 with the absence of CaO peak. However, with the increase in activation temperature, CaCO3 completely transforms to CaO by evolving the CO2. The composition of calcined catalyst at and above 700 °C mainly consists of the active ingredient, CaO (lime). Narrow and high intense peaks of the calcined catalyst define the well-crystallized structure of the catalyst. In addition, from the EDX results, the uncalcined sample exhibits oxygen as the major component, and calcium is the chief element in the calcined catalyst. Stoichiometrically, these were true; as in CaCO3, oxygen is the major content (48%) and in CaO, Ca is the chief constituent (71%).
3.2. Statistical analysis As depicted in Table 1, small central composite design (CCD) was used with four factorial points (entry 1–4), four axial (star) points with alpha value 1.414 (entry 5–8), and two centre points (entry 9 and 10). The recommended CCD alpha value is the distance that the axial points are from the centre of the design space.
Table 1 Factorial design, star points, and centre points with their corresponding responses. Standard order
Catalyst (wt.%)
MeOH/oil mass ratio (g/g)
Purity (P) (wt.%)
Yield (Y) (wt.%)
1 2 3 4 5 6 7 8 9 10
3 7 3 7 2.2 7.8 5 5 5 5
0.2 0.2 0.6 0.6 0.4 0.4 0.12 0.68 0.4 0.4
64.7 70.1 61.1 98.1 56.5 90.7 65.6 98.5 98.6 99.3
61.1 63.4 85.2 60.6 70.7 63.9 55.7 69.8 97.1 96.8
The reported purity and yield was obtained as an average of duplicate determinations after 3 h of reaction duration. The statistical Model Fit Summary (which consists of sequential model sum of squares and lack of fit tests) suggests that the quadratic model is the best fit-model for both purity and yield. Furthermore, from the Analysis of Variance (ANOVA) (Tables 2a and 2b), the ‘‘Prob > F’’ value for the quadratic model was significant (<0.01) for both purity and the yield. Values of less than 0.1000 indicate model terms are significant. The F value for both responses were quite high, denotes more of the variance being explained by the model. In addition, the p-values of the studied variables for purity (Table 2a) as well as for the yield (Table 2b) were found to be less than 0.05, implying their significant effects on the responses. Regression analysis generated the following models for purity (P) and the yield (Y):
P ¼ 98:95 þ 11:35X C þ 8:87X M þ 7:90X C X M 13:76X 2C 9:53X 2M ð1Þ Y ¼ 96:95 3:99X C þ 5:16X M 6:72X C X M 14:19X 2C 16:46X 2M ð2Þ The models indicate that the catalyst amount is the most important positive factor in determining the purity, while for the biodiesel yield, the methanol amount is the major positive contributor. In the case of biodiesel yield, the catalyst amount exhibits a negative influence, hence, any increase in catalyst amount beyond the optimal value will result in a drop in product yield. The methanol amount influences both purity and yield positively; with a much larger impact on purity. 3.3. Influence of individual effect (main effect) Fig. 4. Powder XRD patterns of uncalcined, and calcined catalyst at different activation temperatures. d, CaCO3; j, CaO.
The Perturbation plot (Fig. 5) compares the effect of the individual variable across the studied range towards response in the design
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Table 2a ANOVA table for purity.
Table 3 The preset criteria for process optimization.
Source
Sum of squares
df
Mean square
F value
p-value (Prob > F)
Factor/response
Goal
Lower limit
Upper limit
Model C M CM C2 M2 Residual
2847.39 1029.81 628.84 249.64 865.07 415.29 103.31
5 1 1 1 1 1 4
569.48 1029.81 628.84 249.64 865.07 415.29 25.83
22.05 39.87 24.35 9.67 33.49 16.08
0.0052 0.0032 0.0078 0.0359 0.0044 0.0160
Catalyst amount (wt.%) MeOH/oil mass ratio Purity (wt.%) Yield (wt.%)
In range In range Target Target
3 0.2 56.5 55.7
7 0.6 99.3 97.1
Table 4 Suggested optimum values (by software) and the corresponding experimental values.
C, catalyst amount; M, MeOH/oil mass ratio.
Table 2b ANOVA table for yield. Source
Sum of squares
df
Mean square
F value
p-value (Prob > F)
Model C M CM C2 M2 Residual
2044.61 127.33 212.60 180.90 920.16 1238.92 33.39
5 1 1 1 1 1 4
408.92 127.33 212.60 180.90 920.16 1238.92 8.35
48.99 15.25 25.47 21.67 110.23 148.42
0.0011 0.0175 0.0072 0.0096 0.0005 0.0003
C, catalyst amount; M, MeOH/oil mass ratio.
space, without any interaction effect. A steep slope or curvature in a factor shows that the response is sensitive to that factor. In contrast, a fairly flat line shows that the response is insensitive to the change in that particular factor. The perturbation plot could also be used to find those factors that most affect the response. As such, the catalyst amount has more influence on the purity of the product, as depicted by Fig. 5a. The influence difference between the factors was very predominant at their lowest levels (1) compared to the highest levels (1), while they exhibited an insignificant trend in the range of 0–0.75. Both factors have equal influences towards yield of the product (Fig. 5b). Unlike in the case of purity, both factors have a different impact on the yield at both the lowest and the highest levels. At the lowest level (1), the catalyst amount recorded a higher yield than methanol and at the other extreme level (1), the opposite trend was observed. Their similar effects were only seen in a very narrow range around the centre point (0). By observing Fig. 5, it can be deduced that both studied factors were more sensitive towards the yield than to the purity. Hence, any deviation of the studied factors from the optimal values will have more impact on the biodiesel yield.
Response
Suggested value
Experimental value
Purity (wt.%) Yield (wt.%)
99.49 97.59
99.36 ± 0.21 97.48 ± 0.24
Reaction conditions: as per suggested by software (catalyst amount, 4.9 wt.%; MeOH/oil mass ratio, 0.54:1), reaction time, 3 h.
3.4. Optimization Before proceeding to the optimization process, the goal for each reaction variable, as well as response, was set (Table 3). Numerical optimization was used and a total of 22 solution were suggested by the software. Among them, a set of solutions, catalyst amount 4.9 wt.% and MeOH/oil mass ratio of 0.54:1, was selected that gave maximum responses, as tabulated in Table 4, together with experimental values. The close similarity between suggested and experimental values of purity and yield proves the validity of the chosen model of this study. The optimal catalyst amount, 4.9 wt.%, below the centre point of 5 wt.% makes sense, as any increase in the factor results in a decrease in the yield, as indicated by the negative sign in the yield model (2). Similar works with waste CaO have been carried out previously and the reported optimal conditions were 25 wt.% catalyst concentration under 6:1 MeOH/oil molar ratio [13] and in another related work 3 wt.% catalyst and 9:1 MeOH/ oil molar ratio were used [14]. 3.5. Reusability of the prepared catalyst Under the optimized conditions (4.9 wt.% catalyst and 0.54:1 MeOH/oil mass ratio), the prepared catalyst was able to be reused at least for three times, with a purity above 96.5% (Fig. 6); the minimum requirement of methyl ester content under EN 14214:2003, and a yield above 97%. Before reuse, the spent catalyst was washed
Fig. 5. Influence of main effect on biodiesel (a) purity (P) and (b) yield (Y). C, catalyst amount; M, MeOH/oil mass ratio.
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Fig. 6. Methyl ester purity under optimal reaction conditions using calcined (900 °C, 2 h) spent catalyst for three reuses.
Property
Unit
Specification
Results
Test method
Ester content Density (at 15 °C) Viscosity (at 40 °C) Cloud point Pour point Monoglyceride content Diglyceride content Triglyceride content
% (m/m) kg/m3
96.5 Min. 860–900
99.1 887
EN 14103 EN ISO 3675
mm2/s
3.5–5.0
4.4
EN ISO 3104
°C °C % (m/m)
Report Report 0.80 Max.
15 12 0.22
ASTM D2500 ASTM D97 EN 14105
% (m/m)
0.20 Max.
0.03
EN 14105
% (m/m)
0.20 Max.
Not detected
EN 14105
the structure of catalyst has changed to CaO, the active species that catalyzed the reaction, and traces of Ca(OH)2 as shown in Fig. 8. 3.6. Properties of the prepared biodiesel The product was found to meet with the selected important physical and chemical key properties of biodiesel, as tabulated in Table 5. The cloud and cold point results indicate that the biofuel is suitable to be used in tropical countries. These parameters are the critical factors in cold weather continents and in order to use the fuel in these cold climate countries, cold flow additives can be added. 4. Conclusions
Fig. 7. Powder XRD patterns of spent catalyst: (a) first cycle, (b) second cycle and (c) third cycle. d, calcium diglyceroxide; j, Ca(OH)2.
Thermally activated waste cockle shell at 900 °C for 2 h has been successfully utilized as a heterogeneous catalyst in the transesterification of palm olein into biodiesel. The prepared catalyst, without much deterioration in the activity, was capable of being reused for at least three times under the suggested optimal conditions of 4.9 wt.% catalyst and 0.54:1 MeOH/oil mass ratio, thus creating another low cost catalyst source for biodiesel production. Statistical analysis has proved that the studied variables (catalyst amount and MeOH/oil mass ratio) recorded p-values less than 0.05, hence proving their significants towards both the responses. It was found from the perturbation plot that both the studied factors were more sensitive towards the yield rather than the purity of the product. Acknowledgements Financial support by Universiti Sains Malaysia (USM) under USM-RU-PRGS Grant (1001/PKIMIA/841005), and the award of USM Fellowship are gratefully acknowledged. The authors would also like to thank Stat-Ease, Inc., Minneapolis (USA) for their support in providing the statistics software. References
Fig. 8. Powder XRD patterns of calcined (900 °C, 2 h) spent catalyst: (a) first cycle, (b) second cycle and (c) third cycle. d, Ca(OH)2; j, CaO.
with methanol and n-hexane to remove the adsorbed materials and calcined at 900 °C for 2 h. As depicted by Fig. 7, the washed uncalcined spent catalyst was consist of Ca(OH)2 and traces of calcium diglyceroxides. However, upon calcination at 900 °C for 2 h,
[1] Wedel RV. Emissions reductions with biodiesel. In: Wedel RV, editor. Technical handbook for marine biodiesel in recreational boats, 2nd ed. National Renewable Energy Laboratory, US Department of Energy; 1999.. [2] Knothe G. Introduction. In: Knothe G, Gerpen JV, Krahl J, editors. The biodiesel handbook. Urbana (Il): AOCS Press; 2005. p. 1–3. [3] Haas MJ, Foglia TA. Alternate feedstocks and technologies for biodiesel production. In: Knothe G, Gerpen JV, Krahl J, editors. The biodiesel handbook. Urbana (Il): AOCS Press; 2005. p. 42–61. [4] Lim BP, Maniam GP, Hamid SA. Biodiesel from adsorbed waste oil on spent bleaching clay using CaO as a heterogeneous catalyst. Eur J Sci Res 2009;33:347–57.
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[5] Meng X, Yang J, Xu X, Zhang L, Nie Q, Xian M. Biodiesel production from oleaginous microorganisms. Renew Energy 2009;34:1–5. [6] Boey P-L, Maniam GP, Hamid SA, Ali DMH. Crab and cockle shells as catalysts for the preparation of methyl esters from low free fatty acid chicken fat. J Am Oil Chem Soc 2011;88:283–8. [7] Goetsch D, Machay IS, White LR. Production of methanol from the crude glycerol by-product of producing biodiesel. United States Patent, Patent No.: US 7,388,034 B1; 2008. [8] Warabi Y, Kusdiana D, Saka S. Reactivity of triglycerides and fatty acids of rapeseed oil in supercritical alcohols. Bioresour Technol 2004;91:283–7. [9] Wright HJ, Segur JB, Clark HV, Coburn SK, Langdon EE, DuPuis RN. A report on ester interchange. Oil Soap 1944;21:145–8. [10] Gryglewicz S. Rapeseed oil methyl esters preparation using heterogeneous catalysts. Bioresour Technol 1999;70:249–53. [11] 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. [12] Kawashima A, Matsubara K, Honda K. Acceleration of catalytic activity of calcium oxide for biodiesel production. Bioresour Technol 2009;100:696–700. [13] Nakatani N, Takamori H, Takeda K, Sakugawa H. Transesterification of soybean oil using combusted oyster shell waste as a catalyst. Bioresour Technol 2009;100:1510–3. [14] Wei Z, Xu C, Li B. Application of waste eggshell as low-cost solid catalyst for biodiesel production. Bioresour Technol 2009;100:2883–5.
[15] Boey P-L, Maniam GP, Hamid SA. Biodiesel production via transesterification of palm olein using waste mud crab (Scylla serrata) shell as a heterogeneous catalyst. Bioresour Technol 2009;100:6362–8. [16] Boey P-L, Maniam GP, Hamid SA. Utilization of waste crab shell (Scylla serrata) as a catalyst in palm olein transesterification. J Oleo Sci 2009;58:499–502. [17] Awang-Hazmi AJ, Zuki ABZ, Noordin MM, Jalia A, Norimah Y. Mineral composition of the cockle (Anadara granosa) shells of west coast of Peninsular Malaysia and it’s potential as biomaterial for use in bone repair. Anim Vet Adv 2007;6:591–4. [18] Department of Fisheries Malaysia; 2008.. [19] Ferella F, Di Celso GM, De Michelis I, Stanisci V, Vegliò F. Optimization of the transesterification reaction in biodiesel production. Fuel 2010;89:36–42. [20] Cavalcante KSB, Penha MNC, Mendonça KKM, Louzeiro HC, Vasconcelos ACS, Maciel AP, et al. Optimization of transesterification of castor oil with ethanol using a central composite rotatable design (CCRD). Fuel 2010;89:1172–6. [21] Jeong G-T, Yang H-S, Park D-H. Optimization of transesterification of animal fat ester using response surface methodology. Bioresour Technol 2009;100:25–30. [22] Watkins RS, Lee AF, Wilson K. Li–CaO catalysed tri-glyceride transesterification for biodiesel applications. Green Chem 2004;6:335–40.
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Utilization of waste cockle shell (Anadara granosa) in biodiesel production from palm olein: Optimization using response surface methodology Peng-Lim Boey a, Gaanty Pragas Maniam a,⇑, Shafida Abd Hamid b, Dafaalla Mohamed Hag Ali a,c a
School of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia Kulliyyah of Science, International Islamic University Malaysia, Jalan Sultan Ahmad Shah, Bandar Indera Mahkota, 25200 Kuantan, Pahang, Malaysia c Chemistry Department, Sudan University of Science and Technology, P.O. Box 407 Khartoum, Sudan b
a r t i c l e
i n f o
Article history: Received 30 November 2009 Received in revised form 1 March 2011 Accepted 1 March 2011 Available online 29 March 2011 Keywords: Biodiesel Methyl ester Transesterification Cockle shell Palm olein
a b s t r a c t The cockle shell, which is available in abundance, has no any eminent use and is commonly regarded as a waste, was utilized as a source of calcium oxide in catalyzing a transesterification reaction to produce biodiesel (methyl esters). A central composite design (CCD) was used to optimize the two major influential reaction variables: catalyst and methanol amount towards purity and yield of methyl esters. The analysis of variance (ANOVA) indicated that the catalyst has a positive influence on purity but negative on the yield. Meanwhile, the methanol/oil mass ratio showed a positive effect on both purity and yield. Using CCD, the optimum reaction conditions were found to be 4.9 wt.% of catalyst and 0.54:1 methanol/ oil mass ratio. The prepared catalyst was capable of being reused under the suggested optimal conditions. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Biodiesel has been in the limelight recently not only as an alternate or extender but also as a sustainable fuel. It is renewable, biodegradable, with low exhaust emission, nontoxic, higher flash point, excellent lubricity, carbon neutral, and environmentally acceptable as a fuel for diesel engines [1,2]. Triglycerides for biodiesel production come from various sources; edible oil, inedible oil, fats, waste oil and recently from algae [3–6]. Glycerol, the coproduct of the reaction, is mainly used in the food, pharmaceutical and cosmetics industries. Interestingly, a recent US patent revealed that methanol, one of the reactants in this reaction, could be produced from the glycerol itself, thus, opening up an avenue to produce raw material from the by-product of the reaction itself [7]. Production of biodiesel by transesterification is catalyzed by both homogeneous and heterogeneous catalysts. Although noncatalytic transesterification is possible, via supercritical methanol, catalytic transesterification is commonly accepted as an industrial process due to its lower operational cost [8]. Typically, homogeneous catalysts, including sodium or potassium hydroxide or their corresponding alkoxides, have been employed for their faster kinetics. Under this type of catalyst, reactions can be completed in less than one hour with remarkable purity and yield. However, unlike heterogeneous catalysts, homogeneous catalysts cannot ⇑ Corresponding author. Tel.: +60 16 4110236; fax: +60 4 6574854. E-mail address: [email protected] (G.P. Maniam). 0016-2361/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2011.03.002
tolerate the presence of moisture and free fatty acids (FFA). Both impurities lead to hydrolysis, ester being converted to acids (Fig. 1a), and saponification, a soap formation reaction (Fig. 1b), which results in lower yield and tedious product separation [9]. Among the heterogeneous catalysts that are being used in transesterification reaction, CaO has a promising place, and many reports have been published on CaO-catalyzed transeserification using laboratory grade CaO [10–12]. However, the utilization of waste materials as heterogeneous catalysts has been of recent interest in the search for a sustainable process. Oyster and chicken egg shells have been successfully used as effective catalysts in converting triglycerides to methyl esters [13,14]. In addition to these wastes, we have reported the use of crab shell as well as mixed crab/cockle shell as a catalyst in producing methyl esters [6,15,16]. On the other hand, cockles (Anadara granosa), which live predominantly on intertidal mudflats, are an important protein source in the South East Asian region [17]. In Malaysia, the retail value of cockles alone in 2007 was estimated at over 32 million US dollars [18]. As a result, the generation of waste shells is abundant, and the plentiful supply makes it feasible for the shell to be used or co-used as a catalyst in the biodiesel industry and, to our best knowledge, no one has reported the use of cockle shells as catalyst in palm olein transesterification. Optimization of process variables in biodiesel production has been worked by many [19–21]. However, most of the studies present either purity or yield as a response. Little attention has been given to both the purity and yield as the responses and the relation
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P.-L. Boey et al. / Fuel 90 (2011) 2353–2358
Fig. 1. (a) Hydrolysis of fatty acid methyl esters in presence of moitsure and (b) saponification of fatty acids.
between them. As such, the present paper explores the utilization of the abundantly available and under-utilized waste cockle shell in the production of biodiesel using palm olein and methanol and to study the influence of reaction variables on purity and yield of the product. To assess and understand the effect of the selected variables, statistical analysis was performed using central composite design. A reusability study of the catalyst was also conducted.
mixture of calcined catalyst (900 °C, 2 h) and methanol. The contents were refluxed under magnetic stirring. Two most influential reaction parameters (catalyst amount and methanol/oil mass ratio) were studied to find the optimum reaction conditions. After completion, the reaction mixture was allowed to cool, causing the glycerol to separate by gravity. A centrifuge was used to further separate the layers (methyl ester, glycerol and catalyst) and the residual methanol in methyl ester layer was evaporated out using a rotary evaporator at 80 °C to obtain a pure methyl ester. Biodiesel purity (methyl ester content in the top methyl ester layer) was determined by GC as stipulated in EN 14103 and the yield was quantified as follows: Yield ð%Þ ¼
methyl ester purity ð%Þ weight of obtained methyl ester ðgÞ weight of oil used ðgÞ
2. Experimental
2.4. Gas chromatography analysis
2.1. Materials
Standard materials and samples were analyzed by a gas chromatography (Perkin Elmer, Clarus 500) fitted with a flame ionization detector (FID). The FAME content (purity) was determined by following the European regulation procedure EN 14103 with a polar capillary column (Supelco Wax, 30 m 0.25 mm i.d. 0.25 lm) using methyl heptadecanoate as an internal standard. Peaks of methyl esters were identified by comparing them with their respective authentic standards.
Cockle shells (A. granosa) were obtained from the local market. Refined palm olein (Elaeis guineensis) of Tenera hybrid was purchased from Delima Oil Products, Malaysia. The fatty acids composition of the oil was found as: myristic acid 0.8%, palmitic acid 41.3%, stearic acid 3.6%, oleic acid 44.0%, linoleic acid 9.8%, and traces of other acids. Fatty acid methyl ester (FAME) standards and internal standards were obtained from Sigma–Aldrich (Switzerland) and of chromatographic grade. Analytical grade methanol (MeOH) and n-hexane were purchased from ChemAR. 2.2. Catalyst preparation and characterization The shells were cleaned by washing thoroughly with warm water several times. Then they were dried overnight in an oven at 105 °C. Crushed and powdered shells were then sieved (<1 mm) before being subjected to heat treatment in a furnace. The basic strength of the catalyst was tested using Hammett indicators. The following Hammett indicators were used: phenolphthalein (H_ = 8.2), 2,4-dinitroaniline (H_ = 15) and 4-nitroaniline (H_ = 18.4). About 25 mg of the sample was shaken with 1 m3 of a solution of Hammett indicator diluted in methanol and left to equilibrate for 2 h [22]. Surface analysis of the catalyst was examined using Micromeritics ASAP 2000. The sample was degassed at 105 °C prior to analysis and the adsorption of N2 was measured at 196 °C. The surface area was calculated using BET equation over the pressure range P/P0 = 0.01–0.30, where a linear relationship was maintained. The catalyst was examined by thermogravimetric analysis (TGA) using the Mettler Toledo TGA/SDTA 851e instrument, from 30 to 900 °C with 20 °C /min heating rate, under N2 environment; scanning electron microscopy coupled with electron dispersive X-ray (SEM-EDX) were obtained using the Leo Supra 50VP Field Emission SEM system with 15 kV accelerating voltage; X-ray diffraction (XRD) on Siemens Diffractometer D5000 using Cu Ka radiation, 2h ranged from 25° to 125° with a step size of 0.1°, at a scanning speed of 1° min1.
2.5. Statistical analysis Statistical analysis was performed using Design-ExpertÒ 7.1 (Stat-Ease, Inc., Minneapolis, USA). 3. Results and discussion 3.1. Catalyst characterization The catalyst changed both the colour of phenolphthalein (H_ = 8.2) from colourless to pink and the colour of 2,4-dinitroaniline (H_ = 15) from yellow to mauve but failed to change the colour of 4-nitroaniline (H_ = 18.4). As such, the catalyst basic strength was designated as 15 < H_ < 18.4, and considered as a strong base for transesterification reaction. The TGA result (Fig. 2) exhibits one major decomposition of 42%, ranged 575–800 °C, with centered temperature around 750 °C. The decomposition can be attributed to the evolvement of CO2 and the weight loss matched to the stoichiometrical weight loss of 44% when CaCO3 transforms to CaO.
2.3. Reaction Transesterification reactions were performed in a 25 mL 2-neck glass reactor with a condenser, immersed in a water bath. The studied methanol/oil mass ratio was in the range of 0.12–0.68 g/ g whereas catalyst amount was in the range of 2.2 to 7.8 wt.%. A central composite design under response surface methodology was used to assess the experimental outputs statistically. In a typical reaction, 10.0 g of oil was added in a thin stream onto the
Fig. 2. TGA profile of the catalyst.
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Fig. 3. SEM images of: (a) uncalcined and (b) calcined catalyst at 900 °C, 2 h.
As explained by Fig. 3, SEM micrographs of calcined catalyst demonstrated the presence of morphologies relatively smaller and similar to each other increases the surface area of the catalyst. In contrast, at equal magnifications of 3000, uncalcined catalyst showed a bulky substance. This observation is in line with the results obtained from N2 physisorption measurement, in which much higher surface area (15 m2 g1) and higher pore volume (0.10 cm3 g1) were observed for the calcined catalyst as compared to 3 m2 g1 and 0.01 cm3 g1 for the uncalcined catalyst, respectively. As depicted by Fig. 4, XRD results revealed that the composition of uncalcined cockle shell mainly consists of CaCO3 with the absence of CaO peak. However, with the increase in activation temperature, CaCO3 completely transforms to CaO by evolving the CO2. The composition of calcined catalyst at and above 700 °C mainly consists of the active ingredient, CaO (lime). Narrow and high intense peaks of the calcined catalyst define the well-crystallized structure of the catalyst. In addition, from the EDX results, the uncalcined sample exhibits oxygen as the major component, and calcium is the chief element in the calcined catalyst. Stoichiometrically, these were true; as in CaCO3, oxygen is the major content (48%) and in CaO, Ca is the chief constituent (71%).
3.2. Statistical analysis As depicted in Table 1, small central composite design (CCD) was used with four factorial points (entry 1–4), four axial (star) points with alpha value 1.414 (entry 5–8), and two centre points (entry 9 and 10). The recommended CCD alpha value is the distance that the axial points are from the centre of the design space.
Table 1 Factorial design, star points, and centre points with their corresponding responses. Standard order
Catalyst (wt.%)
MeOH/oil mass ratio (g/g)
Purity (P) (wt.%)
Yield (Y) (wt.%)
1 2 3 4 5 6 7 8 9 10
3 7 3 7 2.2 7.8 5 5 5 5
0.2 0.2 0.6 0.6 0.4 0.4 0.12 0.68 0.4 0.4
64.7 70.1 61.1 98.1 56.5 90.7 65.6 98.5 98.6 99.3
61.1 63.4 85.2 60.6 70.7 63.9 55.7 69.8 97.1 96.8
The reported purity and yield was obtained as an average of duplicate determinations after 3 h of reaction duration. The statistical Model Fit Summary (which consists of sequential model sum of squares and lack of fit tests) suggests that the quadratic model is the best fit-model for both purity and yield. Furthermore, from the Analysis of Variance (ANOVA) (Tables 2a and 2b), the ‘‘Prob > F’’ value for the quadratic model was significant (<0.01) for both purity and the yield. Values of less than 0.1000 indicate model terms are significant. The F value for both responses were quite high, denotes more of the variance being explained by the model. In addition, the p-values of the studied variables for purity (Table 2a) as well as for the yield (Table 2b) were found to be less than 0.05, implying their significant effects on the responses. Regression analysis generated the following models for purity (P) and the yield (Y):
P ¼ 98:95 þ 11:35X C þ 8:87X M þ 7:90X C X M 13:76X 2C 9:53X 2M ð1Þ Y ¼ 96:95 3:99X C þ 5:16X M 6:72X C X M 14:19X 2C 16:46X 2M ð2Þ The models indicate that the catalyst amount is the most important positive factor in determining the purity, while for the biodiesel yield, the methanol amount is the major positive contributor. In the case of biodiesel yield, the catalyst amount exhibits a negative influence, hence, any increase in catalyst amount beyond the optimal value will result in a drop in product yield. The methanol amount influences both purity and yield positively; with a much larger impact on purity. 3.3. Influence of individual effect (main effect) Fig. 4. Powder XRD patterns of uncalcined, and calcined catalyst at different activation temperatures. d, CaCO3; j, CaO.
The Perturbation plot (Fig. 5) compares the effect of the individual variable across the studied range towards response in the design
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Table 2a ANOVA table for purity.
Table 3 The preset criteria for process optimization.
Source
Sum of squares
df
Mean square
F value
p-value (Prob > F)
Factor/response
Goal
Lower limit
Upper limit
Model C M CM C2 M2 Residual
2847.39 1029.81 628.84 249.64 865.07 415.29 103.31
5 1 1 1 1 1 4
569.48 1029.81 628.84 249.64 865.07 415.29 25.83
22.05 39.87 24.35 9.67 33.49 16.08
0.0052 0.0032 0.0078 0.0359 0.0044 0.0160
Catalyst amount (wt.%) MeOH/oil mass ratio Purity (wt.%) Yield (wt.%)
In range In range Target Target
3 0.2 56.5 55.7
7 0.6 99.3 97.1
Table 4 Suggested optimum values (by software) and the corresponding experimental values.
C, catalyst amount; M, MeOH/oil mass ratio.
Table 2b ANOVA table for yield. Source
Sum of squares
df
Mean square
F value
p-value (Prob > F)
Model C M CM C2 M2 Residual
2044.61 127.33 212.60 180.90 920.16 1238.92 33.39
5 1 1 1 1 1 4
408.92 127.33 212.60 180.90 920.16 1238.92 8.35
48.99 15.25 25.47 21.67 110.23 148.42
0.0011 0.0175 0.0072 0.0096 0.0005 0.0003
C, catalyst amount; M, MeOH/oil mass ratio.
space, without any interaction effect. A steep slope or curvature in a factor shows that the response is sensitive to that factor. In contrast, a fairly flat line shows that the response is insensitive to the change in that particular factor. The perturbation plot could also be used to find those factors that most affect the response. As such, the catalyst amount has more influence on the purity of the product, as depicted by Fig. 5a. The influence difference between the factors was very predominant at their lowest levels (1) compared to the highest levels (1), while they exhibited an insignificant trend in the range of 0–0.75. Both factors have equal influences towards yield of the product (Fig. 5b). Unlike in the case of purity, both factors have a different impact on the yield at both the lowest and the highest levels. At the lowest level (1), the catalyst amount recorded a higher yield than methanol and at the other extreme level (1), the opposite trend was observed. Their similar effects were only seen in a very narrow range around the centre point (0). By observing Fig. 5, it can be deduced that both studied factors were more sensitive towards the yield than to the purity. Hence, any deviation of the studied factors from the optimal values will have more impact on the biodiesel yield.
Response
Suggested value
Experimental value
Purity (wt.%) Yield (wt.%)
99.49 97.59
99.36 ± 0.21 97.48 ± 0.24
Reaction conditions: as per suggested by software (catalyst amount, 4.9 wt.%; MeOH/oil mass ratio, 0.54:1), reaction time, 3 h.
3.4. Optimization Before proceeding to the optimization process, the goal for each reaction variable, as well as response, was set (Table 3). Numerical optimization was used and a total of 22 solution were suggested by the software. Among them, a set of solutions, catalyst amount 4.9 wt.% and MeOH/oil mass ratio of 0.54:1, was selected that gave maximum responses, as tabulated in Table 4, together with experimental values. The close similarity between suggested and experimental values of purity and yield proves the validity of the chosen model of this study. The optimal catalyst amount, 4.9 wt.%, below the centre point of 5 wt.% makes sense, as any increase in the factor results in a decrease in the yield, as indicated by the negative sign in the yield model (2). Similar works with waste CaO have been carried out previously and the reported optimal conditions were 25 wt.% catalyst concentration under 6:1 MeOH/oil molar ratio [13] and in another related work 3 wt.% catalyst and 9:1 MeOH/ oil molar ratio were used [14]. 3.5. Reusability of the prepared catalyst Under the optimized conditions (4.9 wt.% catalyst and 0.54:1 MeOH/oil mass ratio), the prepared catalyst was able to be reused at least for three times, with a purity above 96.5% (Fig. 6); the minimum requirement of methyl ester content under EN 14214:2003, and a yield above 97%. Before reuse, the spent catalyst was washed
Fig. 5. Influence of main effect on biodiesel (a) purity (P) and (b) yield (Y). C, catalyst amount; M, MeOH/oil mass ratio.
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Fig. 6. Methyl ester purity under optimal reaction conditions using calcined (900 °C, 2 h) spent catalyst for three reuses.
Property
Unit
Specification
Results
Test method
Ester content Density (at 15 °C) Viscosity (at 40 °C) Cloud point Pour point Monoglyceride content Diglyceride content Triglyceride content
% (m/m) kg/m3
96.5 Min. 860–900
99.1 887
EN 14103 EN ISO 3675
mm2/s
3.5–5.0
4.4
EN ISO 3104
°C °C % (m/m)
Report Report 0.80 Max.
15 12 0.22
ASTM D2500 ASTM D97 EN 14105
% (m/m)
0.20 Max.
0.03
EN 14105
% (m/m)
0.20 Max.
Not detected
EN 14105
the structure of catalyst has changed to CaO, the active species that catalyzed the reaction, and traces of Ca(OH)2 as shown in Fig. 8. 3.6. Properties of the prepared biodiesel The product was found to meet with the selected important physical and chemical key properties of biodiesel, as tabulated in Table 5. The cloud and cold point results indicate that the biofuel is suitable to be used in tropical countries. These parameters are the critical factors in cold weather continents and in order to use the fuel in these cold climate countries, cold flow additives can be added. 4. Conclusions
Fig. 7. Powder XRD patterns of spent catalyst: (a) first cycle, (b) second cycle and (c) third cycle. d, calcium diglyceroxide; j, Ca(OH)2.
Thermally activated waste cockle shell at 900 °C for 2 h has been successfully utilized as a heterogeneous catalyst in the transesterification of palm olein into biodiesel. The prepared catalyst, without much deterioration in the activity, was capable of being reused for at least three times under the suggested optimal conditions of 4.9 wt.% catalyst and 0.54:1 MeOH/oil mass ratio, thus creating another low cost catalyst source for biodiesel production. Statistical analysis has proved that the studied variables (catalyst amount and MeOH/oil mass ratio) recorded p-values less than 0.05, hence proving their significants towards both the responses. It was found from the perturbation plot that both the studied factors were more sensitive towards the yield rather than the purity of the product. Acknowledgements Financial support by Universiti Sains Malaysia (USM) under USM-RU-PRGS Grant (1001/PKIMIA/841005), and the award of USM Fellowship are gratefully acknowledged. The authors would also like to thank Stat-Ease, Inc., Minneapolis (USA) for their support in providing the statistics software. References
Fig. 8. Powder XRD patterns of calcined (900 °C, 2 h) spent catalyst: (a) first cycle, (b) second cycle and (c) third cycle. d, Ca(OH)2; j, CaO.
with methanol and n-hexane to remove the adsorbed materials and calcined at 900 °C for 2 h. As depicted by Fig. 7, the washed uncalcined spent catalyst was consist of Ca(OH)2 and traces of calcium diglyceroxides. However, upon calcination at 900 °C for 2 h,
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