Advanced Materials Research Vols. 622-623 (2013) pp 1178-1182 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.622-623. 1178
Shell-Derived Heterogeneous Base Catalyst for Transesterification of Palm Oil Wayu Jindapon1,a, Siyada Jaiyen2, Anurak Winitsorn4, Suchada Butnark4 and Chawalit Ngamcharussrivichai2,3,b 1
Program in Petrochemistry and Polymer Science, Chulalongkorn University, Bangkok 10330, Thailand 2 Fuels Research Center, Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Patumwan, Bangkok 10330, Thailand 3 Center of Excellence for Petrochemical and Materials Technology, Chulalongkorn University, Patumwan, Bangkok 10330, Thailand 4 PTT Research and Technology Institute, PTT Public Company Limited, Wangnoi, Ayutthaya 13170, Thailand a e-mail:
[email protected], be-mail:
[email protected] Keywords: Shell, Calcium oxide, Heterogeneous catalyst, Transesterification
Abstract. In the present work, shell, which is available in abundance, low cost and non-toxicity, was used as a source of calcium for preparation of heterogeneous base catalysts. The catalyst was prepared by dissolution-precipitation method in which a calcined shell was mixed with Zn(NO3)2 and Al2O3 under acidic conditions, followed by calcination at 300-700 °C. ZSA-I was referred to as the catalyst attained under the suitable synthesis conditions. Physicochemical properties of ZSA-I were studied by using X-ray fluorescence spectroscopy (XRF), powder X-ray diffraction (XRD), thermogravimetric/ differential thermal analysis (TG/DTA) and CO2-pulse chemisorption analysis. ZSA-I gave the highest fatty acid methyl ester yield of 99 wt.% in the transesterification of palm oil with methanol and can be reused at least 5 times with a retention of the methyl ester yield higher than 96 wt.%. Introduction Bio-based alternative fuels, such as bio-ethanol and biodiesel, have been in focus for the reasons which are by now well understood. Heavy consumption of fossil resources, effects on global warming and concerns of energy security are main drivers for growth of biodiesel [1]. In this regard, biodiesel (fatty acid alkyl esters) from vegetable oils or animal fats and small alcohols via transesterification (Scheme 1) [2] is regarded as the most viable alternative as a green fuel for diesel engines.
Scheme 1 General equation for alcoholysis of triglyceride presenting in oil and fat. The other advantages of using biodiesel are that it is one of the most renewable fuels available and it is non-toxic and biodegradable [2]. Industrially, the transesterification has been carried out most frequently in the presence of basic catalysts, e.g. sodium or potassium hydroxide, sodium methoxide, mainly due to the fast reaction rate [3]. However, the use of homogeneous catalysts requires extensive conditioning and purification steps for the reaction products, i.e. fatty acid methyl esters (FAME) and glycerol, to separate the soluble catalysts. Heterogeneous catalysts are easily recovered from the products, reducing the amount of wastewater discharged. Moreover, they possess reusability. One of the promising heterogeneous catalysts for the transesterification of vegetable oils is CaO [4]. There are various natural sources that can be used as precursors for the preparation of CaO
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catalyst, such as calcite (CaCO3), dolomite (CaMg(CO3)2), shell and cuttlebone [4-8] all of which are available in abundance, low cost, and non-toxicity. Shell combusted at hight temperature at 1,000 °C is a good catalyst in the production of biodiesel from soybean oil with high purity [1]. In the present work, we prepared the heterogeneous base catalyst from waste shell by dissolution-precipitation method under acidic conditions for the first time. The physicochemical properties of the catalyst attained were studied by various techniques. The transesterification activity, reusability and deactivation of the catalyst were also investigated. Research Methodology Materials & Chemical Reagents. Raw shell was received free of charge from the Thai Dolomite Company Limited in Surat Thani Province, Thailand. It was ground and sieved to < 10 μm before being used. Aluminium oxide (Al2O3) and zinc nitrate (Zn(NO3)2) were analytical reagent grade purchased from Ajax Finechem. Nitric acid (HNO3, 50-70%) was purchased from JT Baker. Catalyst Preparation. A shell-derived catalyst was prepared by dissolution-precipitation method. Firstly, the raw shell was calcined at 600 °C, and then it was mixed with Zn(NO3)2 solution under acidic conditions using HNO3 for pH adjustment. The slurry was vigorously stirred at ambient temperature to which Al2O3 was added. Secondly, the resulting mixture was sonicated until dry. Finally, the catalyst paste was further dried in an oven at 100 °C for 24 h, crushed into powder and calcined in a muffle furnace at 300-700 °C for 2 h at heating rate of 3 °C min-1. Catalyst Characterization. Elemental analysis was performed on a JEOL ED-2000 energy dispersive X-ray fluorescence spectrometer. Crystalline structure of shell and ZSA-I was determined by means of powder X-ray diffraction (XRD) using a Rigaku DMAX 2200/ Ultima+ diffractometer equipped with Cu Kα radiation. Thermal decomposition of spent catalyst was carried out on a Perkin Elmer Diamond thermogravimetry with a temperature ramp rate of 8 °C min-1 under nitrogen flow. Total basicity of shell and ZSA-I was determined by CO2-pulse chemisorption analysis using an AutoChem II 2920 chemisorption analyzer. Transesterification Procedure. Refined bleached deodorized (RBD) palm oil was received from the Chumporn Palm Oil Industry Public Company Limited. A 100-mL round bottom flask equipped with a water-cooled condenser and a magnetic stirrer was used as a batch reactor for transesterification of palm oil with methanol. To a typical reaction, the following conditions were applied; methanol/oil molar ratio of 30, amount of catalyst of 10 wt.%, reaction temperature of 60 °C, reaction time of 3 h [5]. After the reaction, the solid was recovered by centrifuge and then the excess methanol was removed by evaporation, resulting in a two-layer separation of liquid products. The upper layer consisting of fatty acid methyl esters (FAME) was subsequently washed with deionized water and dried with Na2SO4. Determination of FAME. Composition of FAME was analyzed with a Shimadzu 14B gas chromatograph (GC) equipped with a flame ionization detector (FID) and a 30-m DB-Wax capillary column. The quantity of FAME produced was determined following the standard method EN 14103 using methyl heptadecanoate (99.5%, Fluka) as the reference standard. Results and Discussion Catalyst Characterization. Table 1 shows the elemental composition of shell and ZSA-I catalysts analyzed by XRF technique. Shell was mainly composed of Ca, whereas Ca, Al and Zn were found in ZSA-I. As evidenced by the XRD results, the calcined shell had CaO and Ca(OH)2 phases. CaO was generated from CaCO3 that originally presenting in raw shell via decarbonation at temperatures higher than 800 ºC, according to Eq. (1) [5]. However, CaO was transformed to Ca(OH)2 upon exposure with atmospheric moisture during the XRD analysis (Eq. (2)). In the case of calcined ZSA-I, it composed of various metal hydroxides and oxides, including CaO, Ca(OH)2, ZnO, Ca12Al14O33 and ZnAl2O4 with a small amount of Ca(NO3)2 and CaCO3 remaining. Due to its too low crystallinity, Al2O3 was not detected but it was supposed to exist in this catalyst. The characterization by the
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CO2-pulse chemisorption indicated that ZSA-I (53 μmol g-1) had higher basicity than the calcined shell (35 μmol g-1), although the Ca content of the former (47.0%) was lower than that of the latter (68.0%). This result suggested that using the dissolution-precipitation method can enhance the amount of basic sites of the natural Ca source. Table 1 Physicochemical properties of shell and ZSA-I catalysts Catalyst
Calcination temperature (°C)
Elemental compositiona (wt.%)
Metal phaseb
Basicityc (μmol g-1)
Shell
800
CaO, 68.6; MgO, 0.5; Al2O3, 0.2; SiO2, 0.8
C, CO
35
ZSA-I
500
CaO, 47.0; Al2O3, 26.0; ZnO, 8.0
C, CO, CC, Z, CA, CN, ZA
53
a
b
Elemental composition was determined by XRF technique. Metal phase was determined by XRD technique: C = CaO, CO = Ca(OH)2, CC = CaCO3, Z = ZnO, CA = Ca12Al14O33, ZA = ZnAl2O4, and CN = Ca(NO)3. c Basicity was determined by CO2-pulse chemisorption analysis.
CaCO3(s)
CaO(s) + CO2(g)
(1)
CaO(s) + H2O(g)
Ca(OH)2(s)
(2)
Effects of Calcination Temperature of Shell and ZSA-I Catalysts. Table 2 shows the FAME yield from the methanolysis of palm oil over shell and ZSA-I calcined at various temperatures. The FAME formed over shells increased from 92.9 to 99.1 wt.% when the calcination temperature was increased from 600 to 800 °C. Since the conversion of CaCO3 to CaO occurrs preferentially at high temperatures, the higher FAME yield was obtained when the reaction was catalyzed by shell calcined at 800 °C [5]. The highest initial rate of reaction was achieved over ZSA-I calcined at 300 °C but decreased from 5.74 to 1.23 gFAME g-1cat. h-1 when the calcination temperature was extended to 700 °C. It should be due to the transformation of the active phases to Ca12Al14O33 (Eq. (3)), which it is less active in the transesterification [9]. The highest FAME yield was attained when ZSA-I was calcined at 500 °C. 12CaO (s) + 7Al2O3 (s)
Ca12Al14O33(s)
(3)
Table 2 FAME yield and initial rate of reaction attained from the transesterificationa of palm oil with methanol over shell and ZSA-I calcined at various temperatures Calcination temperature (°C) Catalyst
Raw shell
Final
Initial rate of reaction, determined at 1 h (gFAME g-1cat. h-1)
FAME yield (wt.%)
600 n.d.b 92.2 800 4.39 99.1 600 300 5.74 95.8 600 500 3.99 99.9 ZSA-I 600 700 1.23 89.9 a Reaction conditions: catalyst amount, 10 wt.%; methanol/oil molar ratio, 30; temperature, 60 ºC; time, 3 h. b n.d. means not determined. Shell
Reusability of Shell and ZSA-I Catalysts. In this study, the reusability of shell and ZSA-I catalysts was investigated. Shell and ZSA-I catalysts were calcined at 800 ºC and 500 ºC, respectively, for 2 h before being used at the first run. After the reaction, the catalysts were recovered by centrifuge and thoroughly washed with methanol. As shown in Fig. 1, it was found that ZSA-I can be repeatedly used more than five repetitions with the retention of the FAME yield higher than 96 wt.%. However,
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shell exhibited a faster drop of the activity by which the FAME yield was reduced to 80 wt.% at the fifth repetition. These results suggested that the calcined shell was deactivated more easily than ZSA-I.
Fig. 1. Reusability test for shell calcined at 800 ºC and ZSA-I calcined at 500 ºC in the transesterification of palm oil with methanol (Symbol: ■ = shell, ▲ = ZSA-I). Reaction conditions: see Table 2. Deactivation of Shell and ZSM-I Catalysts. The TGA technique was applied to the deactivation study of shell and ZSA-I catalysts. Figure 2A shows that the spent shell exhibited two-step weight loss upto 300 °C. The weight losses at 220 and 275 °C corresponded to the decomposition of glycerol and glyceride derivatives, such as monoglycerides and diglycerides, respectively. It was supposed that CaO active sites of shell were transformed into calcium methoxide (Ca(OCH3)2) (Eq. (4)) and calcium glyceroxides (Ca(C3H7O3)2) (Eq. (5)) during the reaction [7,10]. Calcium methoxide itself is a good heterogeneous catalyst for the methanolysis of vegetable oil due to a high basicity and low solubility in methanol. Therefore, the deactivation of shell should be related to the formation of calcium glyceroxides, since it resulted in a viscous catalyst paste, which is difficult to wash and recover. CaO(s) + 2CH3OH(l)
Ca(OCH3)2(s) + H2O(l)
(4)
CaO(s) + 2C3H8O3(l)
Ca(C3H7O3)2(s) + H2O(l)
(5)
Fig. 2. Weight loss and DTG curves for spent shell (A) and spent ZSA-I (B). In the case of spent ZSA-I, the amount of the organic phase found within this temperature range (200-300 °C) was significantly smaller (Fig. 2B). The weight losses related to glycerol and glyceride derivatives were reduced to 1.0 wt.%. The presence of mixed metal hydroxides and oxides in ZSA-I
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may be helpful to reduce the amount of calcium glyceroxides [6]. In addition, the weight losses found at around 400 and 729 ºC in both spent catalysts should be attributed to Ca(OH)2 and CaCO3 that were in situ formed during the combustion of organics deposit. Conclusions In the present study, we demonstrated that our developed dissolution-precipitation method is a good procedure for the preparation of the heterogeneous base catalyst from shell. The catalyst attained (ZSA-I) composed of various metal hydroxide and oxide phases, including CaO, Ca(OH)2, CaCO3, ZnO, Ca(NO3)2, Ca12Al14O33 and ZnAl2O4, and had higher basicity than the original shell. ZSA-I calcined at 500 ºC gave the FAME yield as high as 99.9 wt.% in the transesterification of palm oil with methanol at 60 ºC and ambient pressure. The ZSA-I catalyst can be reused at least 5 times with the retention of the FAME yield higher than 96 wt.%. Interestingly, the presence of mixed metal phase reduced the amount of organics deposit and the deactivation of CaO active sites. Acknowledgements The authors are grateful to the Chumporn Palm Oil Industry Public Company Limited and the Thai Dolomite Company Limited for donating the palm oil and shell samples, respectively. The financial supports from the PTT Public Company Limited and the Center of Excellence for Petrochemical and Materials Technology, Chulalongkorn University are acknowledged. References [1] N. Nakatani, H. Takamori, K. Takeda, V. Sakugawa, Bioresource Technol. Vol. 100 (2009), p. 1510-1513. [2] S. Yan, M. Kim, S. Mohan, S. Salley, Ng.Simon, Appl. Catal. Gen-A, Vol. 93-95 (2009), p. 281-290. [3] T. Ebiura, T. Echizen, A. Ishikawa, K. Murai, T. Baba, Appl. Catal. Gen-A, Vol. 283 (2005), p. 111–116. [4] C. Ngamcharussrivichai, P. Nunthasanti, S.Tanachai, K. Bunyakiat, Fuel Process Technol, Vol. 91(2010), p. 1409–1415 [5] C. Ngamcharussrivichai,W. Wiwatnimit, S. Wangnoi, J. Mol. Catal. A-Chem, Vol. 276 (2007), p. 24–33. [6] C. Ngamcharussrivichai, P. Totarat, K. Bunyakiat, Appl. Catal. Gen-A, Vol. 341(2008), p.77-85. [7] M. Kouzu, T. Kasuno, M. Tajika, Y. Sugimoto, S. Yamanaka, J. Hidaka, Fuel, Vol. 87 (2008), p. 2798–2806. [8] A. Zieba, A. Pacula, E.M. Serwicka, A. Drelinkiewicz, Fuel, Vol. 89 (2010), p. 1961-1972. [9] S.F. Wu and M.Z. Jiang, Ind. Eng. Chem. Res. Vol 49 (2010), p. 12269–12275. [10] M. López, Granados, D. Martín Alonso, I. Sádaba, R. Mariscal, P. Ocón, Appl. Catal. Gen-B, Vol. 89 (2009), p. 265-272.
