- Email: [email protected]
Palm oil transesterification in sub- and supercritical methanol with heterogeneous base catalyst
Chemical Engineering and Processing 72 (2013) 63–67
Contents lists available at ScienceDirect
Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
Palm oil transesterification in sub- and supercritical methanol with heterogeneous base catalyst Nyoman Puspa Asri a , Siti Machmudah b,c , Wahyudiono c , Suprapto a,b , Kusno Budikarjono a,b , Achmad Roesyadi b , Motonobu Goto c,∗ a
Chemical Engineering Department, Faculty of Engineering, WR. Supratman University, Surabaya 6011 Indonesia Chemical Engineering Department, Industrial Technology Faculty, Sepuluh Nopember Institute of Technology, Surabaya 60111 Indonesia c Department of Chemical Engineering, Nagoya University, Nagoya 464-8603, Japan b
a r t i c l e
i n f o
Article history: Received 3 October 2012 Received in revised form 29 May 2013 Accepted 10 July 2013 Available online 20 July 2013 Keywords: Biodiesel Heterogeneous base catalyst Palm oil Sub- and supercritical Transesterification
a b s t r a c t An environmentally benign process for the production of methyl ester using ␥-alumina supported heterogeneous base catalyst in sub- and supercritical methanol has been developed. The production of methyl ester in refluxed methanol conventionally utilized double promoted ␥-alumina heterogeneous base catalyst (CaO/KI/␥-alumina); however, this process requires a large amount of catalyst and a long reaction time to produce a high yield of methyl ester. This study carries out methyl ester production in sub- and supercritical methanol with the introduction of an optimized catalyst used in the previous work for the purpose of improving the process and enhancing efficiency. CaO/KI/␥-Al2 O3 catalyst was prepared by precipitation and impregnation methods. The effects of catalyst amount, reaction temperature, reaction time, and the ratio of oil to methanol on the yield of biodiesel ester were studied. The reaction was carried out in a batch reactor (8.8 ml capacity, stainless steel, AKICO, Japan). Results show that the use of CaO/KI/␥-Al2 O3 catalyst effectively reduces both reaction time and required catalyst amount. The optimum process conditions were at a temperature of 290 ◦ C, ratio of oil to methanol of 1:24, and a catalyst amount of 3% over 60 min of reaction time. The highest yield of biodiesel obtained under these optimum conditions was almost 95%. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Increasing energy demand, depletion of fossil oil reserves, concern over greenhouse emissions and global warming issues have recently led researchers to develop alternative energy from renewable materials using environmentally friendly processes. Biodiesel is one such renewable fuel, developed as a substitute for diesel oil. As an alternative fuel, biodiesel offers many benefits: it is renewable, non-toxic, biodegradable, and contains low SOx and particulate matter content [1–4]. It is also environmentally friendly due to its low carbon monoxide emission [5]. In addition, biodiesel can be used for diesel engines without their requiring modification [6] and can be blended with diesel oil at any proportion [7]. Biodiesel, monoalkyl esters of fatty acids, can be made from vegetable oil, animal oil or recycled cooking oil. Currently, the main feedstock for biodiesel production in Indonesia is palm oil due to its abundant production. Conventionally, biodiesel is produced through a transesterification reaction using a homogeneous catalyst acid/base [8–10]. This conventional process has many
∗ Corresponding author. Tel.: +81 52 789 3992; fax: +81 789 3992. E-mail addresses: [email protected], [email protected] (M. Goto). 0255-2701/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cep.2013.07.003
disadvantages such as the formation of side products in the form of soap [5,11,12] and the complexity of the separation of products from catalyst [8,9]. In addition, alkaline wastes formed in large quantities require an advanced process and large amount of energy to treat, which in turn increases the cost of production [5,13,14]. The drawbacks of the conventional process can be overcome in two ways: by the use of heterogeneous/solid catalysts or by the use of supercritical methanol [5]. Heterogeneous catalyst is a promising alternative to produce biodiesel from vegetable oils. Since heterogeneous catalysts are easily separable and recoverable, they are expected to lead to an effective process with low cost and minimal environmental impact [11,13,14]. Various heterogeneous acid catalysts have been developed to produce biodiesel, including metal–metal hydroxides [15], metal–metal complexes [16], and metal–metal oxides such as zirconium oxide and titanium oxide [14,17]. Acid catalysts require a longer reaction time and relatively higher reaction temperature [14,18]; while, heterogeneous base catalysts such as calcium oxide [19], magnesium oxide [20] and CaO/␥-Al2 O3 [5,21], require shorter reaction time and relatively lower reaction temperature [5]. The study using solid base catalyst of alkali metal with a single promoted CaO/␥-Al2 O3 and a double promoted KI/␥-Al2 O3 have been conducted [21,22]. The study was carried out at atmospheric
64
N.P. Asri et al. / Chemical Engineering and Processing 72 (2013) 63–67
pressure and temperature of 55–65 ◦ C. The results indicated that the activity of the double promoted catalyst was much higher than that of single one, while the yield of biodiesel increased by 30% under the same conditions with 2 h shorter of the reaction time. The highest yield of 95% and 65% were obtain at 65 ◦ C and molar rasio of oil to methanol 1:42 for double promoted catalyst within 5 h of reaction time and single promoted catalyst within 7 h ofreaction time, respectively. However, drawbacks of this process are the lengthy reaction time (5 h) and the high amount of catalyst required (6%). These might be mitigated by employing the supercritical method. Under a supercritical state, methanol dissolves the oil to form a homogeneous phase due to a decrease in dielectric constants [23,24]. Some researchers have used the supercritical method. Kusdiana and Saka [23] examined the transesterification of rapeseed oil in supercritical methanol with molar ratio of 1:24–1:42 at reaction temperatures of 240–350 ◦ C. Without a catalyst, they obtained 95% of biodiesel yield for a short reaction time but at a relatively high operating temperature (350–400 ◦ C). Imahara et al. [25] studied thermal stability of biodiesel in supercritical methanol over a range of conditions between 270 ◦ C/17 MPa and 380 ◦ C/56 MPa. In addition, Petchmala et al. [26] examined transesterification of palm oil with methanol at near-supercritical and supercritical conditions using an acid catalyst (SO4 –ZrO2 ). They reported that 90% of biodiesel yield was achieved at 250 ◦ C in the presence of 0.5% (w/w) SO4 –ZrO2 catalyst [26]. However, it should be noted that Saka and Kusdiana [23] required a relatively high temperature (350 ◦ C), while Petchmala et al. [26] used the transition metal oxide, which is relatively expensive, to promote the catalyst. Therefore, this work focuses on the transesterification of palm oil in sub- and supercritical methanol with double promoted CaO/KI/␥-Al2 O3 catalyst. The effects of the amount of catalyst, reaction temperature, reaction time and molar ratio of oil to methanol were investigated. 2. Experiment 2.1. Material The palm oil used as starting material was purchased from Wako pure chemicals Co., Japan. Analytical grade methanol and hexane and methyl esters standard (methyl palmitate, methyl stearic, methyl linoleic, methyl linolenic and methyl oleic) were supplied by Wako pure chemicals Co., Japan. 2.2. Preparation and characterization of catalyst Double promoted alumina–supported (CaO/KI/␥-alumina) catalyst was prepared via impregnation and precipitation procedure, using optimum conditions as determined from our previous work [22] using the following procedure: 40 g of ␥-Al2 O3 was poured into 50 ml of distilled water, followed by the addition of calcium acetate until 30% (w/w% of ␥-Al2 O3 ) of CaO loading was reached; the solution was then stirred for 3–4 h at room temperature. Calcium acetate was synthesized by reacting stochiometrically of calcium oxide and acetic acid. The formed suspension was impregnated with 35 ml of 35% KI solution (35% weight to alumina). The performed slurry was heated up at 100–105 ◦ C in an oven overnight in order to remove the water content. The synthesized catalyst was milled into powder and then calcinated at 650 ◦ C in a muffle furnace with flowing air for 4 h. The catalyst was kept in a desiccator in the presence of silica gel in order to prevent water and CO2 contacting with the catalyst. By using this preparation procedure of catalyst, the highest yield of biodiesel was obtained [22]. The characterizations of catalysts were performed by X-Ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) and Scanning Electron Microscope (SEM) analysis. XRD gives information on the
crystallization structure. Powder XRD patterns were collected in order to investigate diversification peaks after promotion by double promoter. The specific surface area, pore volume and pore diameter of the prepared catalysts were measured using the BET method. SEM (Jeol, JSM-6390LV, Japan) was used to identify the morphology and size of CaO/KI/␥-Al2 O3 catalyst particle. 2.3. Transesterification in sub and supercritical methanol with catalyst Transesterification of palm oil in sub and supercritical methanol was carried out in a batch type reactor (8.8 ml, stainless steel SUS 304, AKICO Co., Japan) with double promoted ␥-Al2 O3 supported catalyst (CaO/KI/␥-Al2 O3 ). The reactor system used consisted of an electric furnace (ISUZU Co, Ltd., model NMF-13AD), a stainless steel SUS 304 reactor (8.8 ml of capacity, 300 ◦ C of maximum temperature, 30 MPa of pressure), and a temperature controller. First, the temperature of the heating furnace was set to the desired temperature (210–290 ◦ C). The reactor was charged with the mixture of palm oil and methanol in a certain molar ratio with various amounts of catalyst from 1 to 4% (w/w of oil), and the reactor was then inserted to the electric furnace. The effect of different operational parameters (amounts of catalyst, reaction temperature, reaction time and molar ratio oil to methanol) on the yield of biodiesel and conversion of palm oil were observed. After reaching the set temperature, the reaction was sustained until the desired reaction time was achieved. The pressure of the reaction was measured between 4 and 12 MPa. Afterwards, the reactor was removed from the electric furnace and immersed in a water bath for cooling in order to stop the reaction. The treated liquid and catalyst were discharged from the reactor into a sampling bottle. An amount of water was added to the solution mixture to dilute the excess methanol. Subsequently, the solution mixture was centrifuged for separation into three phases: the top phase was fatty acid methyl ester (FAME, or biodiesel) and a small amount of un-reacted oil; the middle phase consisted of methanol, water and glycerol, and the bottom phase was solid CaO/KI/␥-alumina catalyst. The biodiesel was analyzed by gas chromatography-flame ionization detector (GC-FID) (Gas Chromatography GC-14B, Shimadzu, Japan) equipped with a HPInnowax capillary column (30 m × 0.250 mm × 0.25 m) The oven temperature was programmed as follows: the initial temperature of 210 ◦ C was held for 9 min, increased to 230 ◦ C at 20 ◦ C/min intervals for 20 min, and then increased to 250 ◦ C at 20 ◦ C/min intervals for 5 min. The injector and detector temperatures were controlled at 250 and 300 ◦ C, respectively. The injection volume was 1 l. The carrier gas was helium, and the makeup gas was hydrogen. Biodiesel analyses can be used to determine the yield % of biodiesel defined as follows: Yield of biodiesel (%) =
W of actual biodiesel × 100% W of oil
where W of the actual biodiesel amount and W of oil are the actual weight of biodiesel from the experiment (mg) and the weight of oil used in the experiment (mg), respectively. 3. Results and discussion 3.1. Catalyst characterization The BET specific surface area, cumulative pore volume, and mean pore diameter of CaO/KI/␥-Al2 O3 catalyst are summarized in Table 1. It can be seen that the specific surface area of the catalyst is 54.55 m2 /g, smaller than that of the single promoted catalyst (83 m2 /g) reported by Asri et al. [21] and Zabeti et al. [5]. This might be due to the double alkaline compound (CaO and KI) anchored to the surface of catalyst causing an increase in active sites, thus
N.P. Asri et al. / Chemical Engineering and Processing 72 (2013) 63–67
65
Table 1 Chractheristic of CaO/KI/␥-Al2 O3 with 30% loading of CaO. Catalyst properties
Value
Techniques
Spesific surface area Pore volume Mean pore size
54.55 (m2 /g) 0.083 (cm3 /g) 38.211 (Å)
BET BET BET
Fig. 3. Biodiesel yield as function of amount of catalyst (wt% to palm oil) at reaction temperature 290 ◦ C, reaction time 30 min, and molar ratio palm oil to methanol 1:24.
3.2. Effect of catalyst amount
Fig. 1. XRD pattern of CaO/KI/␥-Al2 O3 : (a) CaO/KI/␥-Al2 O3 with 30% loading of CaO, (b) ␥-Al2 O3 .
resulting in an increase in catalyst activity. This result was confirmed by X-ray diffraction patterns of CaO/KI/␥-Al2 O3 with 30% of CaO loaded, as shown in Fig. 1a. The XRD pattern has more diffraction peaks appearing at 2. Conversely, XRD patterns for ␥Al2 O3 (Fig. 1b) only registered diffraction peaks at 37.0◦ , 46.0◦ and 66.7◦ , assigned to amorphous Al2 O3 support. A similar pattern was reported by Xie and Li [27]. Moreover, as reported by Ilgen and Akin [11], the activity of the catalyst for transesterification of vegetable oils is not only influenced by the surface area but also by the basicity of the catalyst. Fig. 2 shows SEM images of CaO/KI/␥-Al2 O3 with 30% of CaO loaded. The SEM image shows crystallites of 10 m in size with similar irregular shapes. This line of evidence indicates that the catalyst was a mesoporous structure. According to our previous study, the CaO/KI/␥-Al2 O3 with 30% of CaO loaded was found to be the most active catalyst for transesterification of palm oil with methanol in the reflux condition [22]. Therefore, in our present work, this catalyst was used for transesterification of palm oil under sub- and supercritical methanol.
The effect of catalyst amount (w/w% of oil) on the yield of biodiesel and conversion of palm oil was studied by varying the amount of catalyst from 1 to 4% at a reaction temperature of 290 ◦ C, reaction time of 30 min, and molar ratio of oil to methanol 1:24. The results, shown in Fig. 3, indicate that yield of biodiesel increases significantly by increasing the catalyst amount from 1 to 3%. Without the use of catalyst, the obtained of biodeiesel yield was only 22%. Conversely, biodiesel yield sharply increased from 48 to 81% by using 1 and 3% catalyst, respectively. It is strongly evidenced that the presence of catalyst affected the reaction rate. It can be explained in terms of the transition-state theory, which holds that a catalyst reduces the potential energy barrier over which reactants must pass to form a product [28]. On the contrary, the use of 3.5 to 4% of catalyst led to a decrease in biodiesel yield due to agglomeration occurring on the catalyst, which caused a decrease in the number of active sites and finally reduced the activity of the catalyst. The agglomeration of catalyst could be observed after the reaction. When the mixture of product, rest of reactant and solid catalyst were discharged from the reactor, the solid catalyst was not dispersed in the solution mixture; however, the agglomeration of solid catalyst was observed. Moreover, the solution mixture (oil, methanol and catalyst) became too viscous, leading to a problem of mixing that resulted in the difficulties for diffusion. The same statement also addressed by previous researchers [26,29]. Petchmala et al. [26] confirmed that the conversion of FAME increased considerably from 33 to 90% with an increase in SO4 –ZrO2 catalyst at a proportion of reactants mass from 0 to 0.5%, and slightly decreased for reactant mass above 0.5%. Our present work has found that 3% of catalyst was the optimum condition. Hence, 3% of catalyst was selected for further studies. 3.3. Effect of molar ratio of oil to methanol
Fig. 2. Scanning electron micrographs (SEM) of CaO/KI/␥-Al2 O3 catalyst.
The molar ratio of oil to methanol is an importance variable influencing the yield of FAME. In transesterification reactions, stochiometrically, three moles of alcohol (preferably methanol) and one mole of triglyceride are required to produce three moles of fatty acid methyl ester (FAME) and one mole of glycerol [5,26]. Theoretically, increasing the molar ratio of oil to methanol can cause the reaction to shift to the right side. In practice, though, an excess of methanol is not favorable due to the high amount of energy needed to recover it, which ultimately increases the total production cost of biodiesel. In this work the effect of molar ratio of oil to methanol was studied at various molar ratios from 1:12 to 1:42 (1:12, 1:18, 1:24, 1:30, 1:36 and 1:42), a constant reaction temperature of 290 ◦ C, a
66
N.P. Asri et al. / Chemical Engineering and Processing 72 (2013) 63–67
Fig. 4. Biodiesel yield as function of molar ratio palm oil to methanol at reaction time 30 min, reaction temperature 290 ◦ C and 3% amount of catalyst.
constant reaction time of 30 min, and 3% (w/w% of oil) of catalyst. Fig. 4 shows the influence of the molar ratio of oil to methanol on the yield of biodiesel. Increasing the molar ratio of oil to methanol resulted in a higher biodiesel yield. By increasing the molar ratio from 1:12 to 1:24, biodiesel yield significantly increased from 51 to 81%, respectively. Beyond the molar ratio of 1:24, the excess added methanol had no significant effect on biodiesel yield. It can be concluded that the yield of biodiesel increased up to a certain molar ratio of oil to methanol, and that the optimum molar ratio of oil to methanol was 1:24. Kusdiana and Saka [23] reported that the highest yield, 95%, was achieved with a molar ratio of rapeseed oil to methanol of 1:42. Meanwhile, with SO4 –ZrO2 catalyst, Petcmala et al. [26] achieved the similar molar ratio (1:24) with 90% yield of biodiesel. 3.4. Effect of reaction temperature To investigate the effect of temperature process, reactions were carried out under sub- and supercritical methanol with solid base CaO/KI/␥-alumina catalyst at temperatures ranging from 210 to 290 ◦ C at 20 ◦ C intervals with a constant reaction time (30 min), molar ratio of oil to methanol (1:24), and amount of catalyst (3%). Fig. 5 shows effects of reaction temperature on biodiesel yield. The reaction temperature significantly influences the transesterification reaction, where the biodiesel yield increased with an increase in reaction temperature. These results are correlated with Arrhenius law, which states that the intrinsic rate constants are a function of reaction temperature [28]. At 210 and 230 ◦ C for 30 min of reaction time, biodiesel yield gradually increased from 64 to 67% due to the subcritical state of methanol; under such a state of, methanol is not completely dissolved to be a homogeneous phase with the
Fig. 5. Biodiesel yield as function of reaction temperature (◦ C) at 30 min time of reaction, 1:24 of molar ratio palm oil to methanol and 3% amount of catalyst.
Fig. 6. Biodiesel yield as function of reaction time (min) at a various of temperature from 210 to 290 ◦ C, 1:24 of molar ratio palm oil to methanol and 3% amount of catalyst.
oil. Yujaroen et al. [30] and Petchmala et al. [26] reported that complete solubility of methanol with oil occurs under the supercritical state. As a comparison with previous work, Kusdiana and Saka [23] obtained 68 and 70% of biodiesel yield at 200 and 230 ◦ C, respectively, following 60 min of treatment without catalyst. At 250 ◦ C, the yield drastically increased up to 74%. The highest yield of biodiesel was 81% achieved at 290 ◦ C and 30 min of reaction. Compared with previous work, Kusdiana and Saka [23] obtained 80% of biodiesel at 300 ◦ C. In fact, theoretically, under the supercritical state, an increase in temperature reduces the polarity of methanol due to weakening of hydrogen bounding; it causes a decrease in the dielectric constant of methanol, eventually increasing the solubility of palm oil in methanol [23,24,30]. Meanwhile, Petchmala et al. [26] reported that the highest yield was 90% achieved at 250 ◦ C for the transesterification of palm oil in near- and supercritical methanol with SO4 –ZrO2 catalyst. 3.5. Effect of reaction time The effect of reaction time on the yield of biodiesel and the conversion of oil was observed by varying the reaction time from 30 to 90 min at 10 min intervals. The reaction was carried out at five different reaction temperatures (210, 230, 250, 270 and 290 ◦ C), a molar ratio of oil to methanol 1:24 and catalyst amount of 3% (w/w). Fig. 6 shows the effect of reaction time on biodiesel yield. As expected, the yield of biodiesel increased with the increasing reaction time at all reaction temperatures. However, the maximum yield was achieved at a certain reaction time; afterward, it decreased slightly due to surface agglomeration and activity reduction of catalyst. At 210 to 250 ◦ C, the highest yield was obtained at 70 min; while at higher temperatures, the maximum one was achieved at 60 min. Biodiesel yield gradually increased with an increase in reaction time at 210 and 230 ◦ C. Moreover, the yield dramatically increased with the increasing reaction time at temperatures from 270 to 290 ◦ C. It can be explained that above 270 ◦ C methanol is in supercritical state. Under this condition, the polarity of methanol is reduced because the degree of hydrogen bonds decreases with increasing temperature [23]. For these conditions, the highest yield was obtained at 60 min of reaction time and a temperature of 290 ◦ C, with the biodiesel yield obtained close to 95% (94.83%). For comparison, previous work achieved the same biodiesel yield (94.94%) over 5 h of treatment [22]; moreover, that experiment was conducted in refluxed methanol with a molar ratio of oil to methanol 1:42 and catalyst amount of 6% (w/w). Whereas if
N.P. Asri et al. / Chemical Engineering and Processing 72 (2013) 63–67
compared with another previous studies which studied the transesterification of palm oil with sub and supercritical methanol without catalyst in the same batch type reactor (data is not shown), the highest yield of 88% was obtained under the same conditions (290 ◦ C and molar ratio of oil methanol 1:24), but the time required is much longer (90 min) than that the present one (60 min). The present results evidence that supercritical methanol with CaO/KI/␥-Al2 O3 catalyst is able to reduce the reaction time, the catalyst amount, and the molar ratio of oil to methanol significantly – 80, 50 and 52%, respectively. Meanwhile, Pethcmala et al. [26] reported that maximum conversion was obtained at 10 min for PPO (purified Palm Oil) and 1 min for PFA (palm fatty acid), with conversions of 90.5 and 74.4%, respectively. It should be noted that the SO4 –ZrO2 catalyst used for their experiment was prepared using a transition metal, which is much more expensive than the alkali metal. 4. Conclusion In this study, transesterification of palm oil was done in sub- and supercritical methanol with solid base alumina supported catalyst (CaO/KI/␥-alumina) at a temperature range of 210–290 ◦ C, a reaction time of 30–70 min, a molar ratio of oil to methanol 1:12–1:42, and a catalyst amount of 1–4%. The measured pressure of the system was between 4 and 12 MPa. The results found that the optimum condition was at 3% amount of catalyst, 290 ◦ C of reaction temperature, 60 min of reaction time and 1:24 of molar ratio of oil to methanol; at the condition, the yield of biodiesel was 95%. In comparison, by using refluxed methanol method, highest yield was 95% obtained at 65 ◦ C, 5 h of reaction time and 6% of catalyst. Therefore, the results lead to the conclusion that the introduction of a solid base catalyst in sub-and supercritical methanol may allow development of an efficient method for transesterification process. Acknowledgements The authors gratefully acknowledged The Directorate General of Higher Education of the ministry of Education Republic of Indonesia for financial support. Special thanks to Applied Chemistry and Biochemistry Department, Engineering Faculty, Kumamoto University for technical assistance, and providing all of the facilities needed for the experiment. References [1] U. Schuchardt, R.M. Secheli, Transesterification of vegetable oil: a review, Journal of the Brazilian Chemical Society 9 (1998) 199–210. [2] S.G. Michael, R.L. McCormic, Combustion of fat and vegetable oil derived fuel in diesel engine, Progress in Energy and Combustion Science 24 (1998) 125–164. [3] F. Maa, M.A. Hanna, Biodiesel production – a review, Bioresources Technology 70 (1999) 1–15. [4] A. Kawashima, K. Matsubara, K. Honda, Development of heterogeneous catalyst for biodiesel production, Bioresources Technology 99 (2008) 3439–3443.
67
[5] M. Zabeti, W.H.A.W. Daud, M.K. Aroua, Activity of solid catalysts for biodiesel production: a review, Fuel Processing Technology 90 (2009) 70–77. [6] M.A. Dube, A.Y. Tremblay, J. Liu, Biodiesel production using a membrane reactor, Bioresources Technology 98 (2007) 639–647. [7] J.P. Szybist, J. Song, M. Alam, A.I. Boehman, Biodiesel combustion, emission and emission control, Fuel Processing Technology 88 (2007) 679–691. [8] B. Freedman, R.O. Butterfield, E.H. Pryde, Transesterification kinetics of soybean oil, Journal of American Oil Chemists Society 63 (1986) 1375–1380. [9] M. Canaki, V. Gerpen, Biodiesel production via acid catalyst, Transaction of the American Society of Agricultural Engineers 42 (1999) 1203–1210. [10] M. Kouzu, T. Kasuno, M. Tajika, Y. Sugimoto, S. Yamanaka, J. Hidaka, Calcium oxide as a solid base catalyst for transesterification of soybean oil and it’s application to biodiesel production, Fuel 87 (2008) 2798–2806. [11] O. Ilgen, A.N. Akin, Development of alumina supported alkaline catalyst used for biodiesel production, Journal of Turkey 33 (2009) 281–287. [12] M. Zabeti, W.H.A.W. Daud, M.K. Aroua, Biodiesel production using aluminasupported calcium oxide: an optimization study, Fuel Processing Technology 91 (2010) 243–248. [13] M.D. Serio, R. Tesser, P. Pengmei, E. Santacesaria, Heterogeneous catalysts for biodiesel production, Energy and Fuel 22 (2008) 207–217. [14] S. Furuta, H. Matsuhashi, K. Rata, Biodiesel fuel production with solid amorphous-zirconia catalyst in fixed bed reactor, Journal of Biomass and Bioenergy 30 (2006) 870–873. [15] A.K. Dalai, M.G. Kulkarni, L.C. Meher, Biodiesel production from vegetable oils using heterogeneous catalyst and their application as lubricity additives, in: IEEE EIC Climate Change Technology conference EICCCC, 2006, art 4057358. [16] F.R. Abreu, D.G. Lima, E.H. Hamu, S. Einloft, J.C. Rubim, P.A.Z. Suarez, New metal catalysts for soybean oil transesterification, JAOCS Journal of the American Oil Chemists’ Society 80 (2003) 601–604. [17] J. Jitputti, B. Kitiyanan, P. Rangsunvigit, K. Bunyakiat, L. Attnatho, P. Jenvanipanjakul, Transesterification of kernel oil and crude coconut oil by different solid catalysts, Chemical Engineering Journal 116 (2006) 61–66. [18] J.M. Marchetti, V.U. Miguel, A.F. Errasu, Heterogeneous esterification of oil with high amount of free fatty acids, Fuel 86 (2007) 906–910. [19] M.L. Granados, M.D.Z. Poves, D.M. Alonso, R. Mariscal, F.C. Galisteo, R. MorenoTost, J. Santamaría, J.L.G. Fierro, Biodiesel from sunflower oil by using activated calcium oxide, Applied Catalysis B: Environmental 73 (2007) 317–326. [20] A.R. Yacob, M.K.A. Mustajab, N.S. Samadi, Calcination temperature of nano MgO effect on base transesterification of palm oil, World Academy of Science, Engineering and Technology 56 (2009) 408–412. [21] N.P. Asri, A. Anisa, F. Rizqi, A. Roesyadi, K. Budikaryono, Suprapto, I. Gunardi, Biodiesel production from palm oil using CaO/Al2 O3 as a solid base catalyst, in: Proceeding of the 1st International Seminar on Fundamental & Application of Chemical Engineering, 2010. [22] N.P. Asri, F. Hartanto, R. Ramadhan, S.D. Savitri, I. Gunardi, Suprapto, K. Budikarjono, A. Roesyadi, Transesterification of palm oil to methyl ester using ␥-alumina supported base catalysts, in: Proceeding of Bali International Seminar on Science and Technology (BISSTECH), 2011. [23] D. Kusdiana, S. Saka, Kinetics of transesterification in rapeseed oil to biodiesel fuel as treated in supercritical methanol, Fuel 80 (2001) 693–698. [24] S. Saka, D. Kusdiana, Biodisel fuel from rapeseed oil as prepared in supercritical methanol, Fuel 80 (2001) 225–231. [25] H. Imahara, E. Minami, S. Hari, S. Saka, Thermal stability of biodiesel in supercritical methanol, Fuel 87 (2008) 1–6. [26] A. Petchmala, N. Laosiripojana, B. Jongsomjit, M. Goto, J. Panpranot, O. Mekasuwandumrong, A. Shotipruk, Transesterification of palm oil fatty acid in near – and super-critical methanol with SO4 –ZrO2 catalyst, Fuel 89 (2010) 2387–2392. [27] W. Xie, H. Li, Alumina supported potassium iodide as a heterogeneous catalyst for biodiesel production from soybean oil, Journal of Molecular Catalysis 255 (2006) 1–9. [28] O. Levenspiel, Chemical Reaction Engineering, Wiley International edition, John Wiley and Sons, Inc, Canada, 1999. [29] K. Noiroj, P. Intarapong, A. Luengnaruemitchai, S. Jai-In, A comparative study of KOH/Al2 O3 and KOH/NaY catalyst for biodiesel production via transesterification from palm oil, Renewable Energy 34 (2009) 1145–1150. [30] D. Yujaroen, M. Goto, M. Sasaki, A. Shotipruk, Esterification of palm fatty acid distillate (PFDA) in supercritical methanol: effect of hydrolysis on reaction reactivity, Fuel 88 (2009) 2011–2016.
Contents lists available at ScienceDirect
Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
Palm oil transesterification in sub- and supercritical methanol with heterogeneous base catalyst Nyoman Puspa Asri a , Siti Machmudah b,c , Wahyudiono c , Suprapto a,b , Kusno Budikarjono a,b , Achmad Roesyadi b , Motonobu Goto c,∗ a
Chemical Engineering Department, Faculty of Engineering, WR. Supratman University, Surabaya 6011 Indonesia Chemical Engineering Department, Industrial Technology Faculty, Sepuluh Nopember Institute of Technology, Surabaya 60111 Indonesia c Department of Chemical Engineering, Nagoya University, Nagoya 464-8603, Japan b
a r t i c l e
i n f o
Article history: Received 3 October 2012 Received in revised form 29 May 2013 Accepted 10 July 2013 Available online 20 July 2013 Keywords: Biodiesel Heterogeneous base catalyst Palm oil Sub- and supercritical Transesterification
a b s t r a c t An environmentally benign process for the production of methyl ester using ␥-alumina supported heterogeneous base catalyst in sub- and supercritical methanol has been developed. The production of methyl ester in refluxed methanol conventionally utilized double promoted ␥-alumina heterogeneous base catalyst (CaO/KI/␥-alumina); however, this process requires a large amount of catalyst and a long reaction time to produce a high yield of methyl ester. This study carries out methyl ester production in sub- and supercritical methanol with the introduction of an optimized catalyst used in the previous work for the purpose of improving the process and enhancing efficiency. CaO/KI/␥-Al2 O3 catalyst was prepared by precipitation and impregnation methods. The effects of catalyst amount, reaction temperature, reaction time, and the ratio of oil to methanol on the yield of biodiesel ester were studied. The reaction was carried out in a batch reactor (8.8 ml capacity, stainless steel, AKICO, Japan). Results show that the use of CaO/KI/␥-Al2 O3 catalyst effectively reduces both reaction time and required catalyst amount. The optimum process conditions were at a temperature of 290 ◦ C, ratio of oil to methanol of 1:24, and a catalyst amount of 3% over 60 min of reaction time. The highest yield of biodiesel obtained under these optimum conditions was almost 95%. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Increasing energy demand, depletion of fossil oil reserves, concern over greenhouse emissions and global warming issues have recently led researchers to develop alternative energy from renewable materials using environmentally friendly processes. Biodiesel is one such renewable fuel, developed as a substitute for diesel oil. As an alternative fuel, biodiesel offers many benefits: it is renewable, non-toxic, biodegradable, and contains low SOx and particulate matter content [1–4]. It is also environmentally friendly due to its low carbon monoxide emission [5]. In addition, biodiesel can be used for diesel engines without their requiring modification [6] and can be blended with diesel oil at any proportion [7]. Biodiesel, monoalkyl esters of fatty acids, can be made from vegetable oil, animal oil or recycled cooking oil. Currently, the main feedstock for biodiesel production in Indonesia is palm oil due to its abundant production. Conventionally, biodiesel is produced through a transesterification reaction using a homogeneous catalyst acid/base [8–10]. This conventional process has many
∗ Corresponding author. Tel.: +81 52 789 3992; fax: +81 789 3992. E-mail addresses: [email protected], [email protected] (M. Goto). 0255-2701/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cep.2013.07.003
disadvantages such as the formation of side products in the form of soap [5,11,12] and the complexity of the separation of products from catalyst [8,9]. In addition, alkaline wastes formed in large quantities require an advanced process and large amount of energy to treat, which in turn increases the cost of production [5,13,14]. The drawbacks of the conventional process can be overcome in two ways: by the use of heterogeneous/solid catalysts or by the use of supercritical methanol [5]. Heterogeneous catalyst is a promising alternative to produce biodiesel from vegetable oils. Since heterogeneous catalysts are easily separable and recoverable, they are expected to lead to an effective process with low cost and minimal environmental impact [11,13,14]. Various heterogeneous acid catalysts have been developed to produce biodiesel, including metal–metal hydroxides [15], metal–metal complexes [16], and metal–metal oxides such as zirconium oxide and titanium oxide [14,17]. Acid catalysts require a longer reaction time and relatively higher reaction temperature [14,18]; while, heterogeneous base catalysts such as calcium oxide [19], magnesium oxide [20] and CaO/␥-Al2 O3 [5,21], require shorter reaction time and relatively lower reaction temperature [5]. The study using solid base catalyst of alkali metal with a single promoted CaO/␥-Al2 O3 and a double promoted KI/␥-Al2 O3 have been conducted [21,22]. The study was carried out at atmospheric
64
N.P. Asri et al. / Chemical Engineering and Processing 72 (2013) 63–67
pressure and temperature of 55–65 ◦ C. The results indicated that the activity of the double promoted catalyst was much higher than that of single one, while the yield of biodiesel increased by 30% under the same conditions with 2 h shorter of the reaction time. The highest yield of 95% and 65% were obtain at 65 ◦ C and molar rasio of oil to methanol 1:42 for double promoted catalyst within 5 h of reaction time and single promoted catalyst within 7 h ofreaction time, respectively. However, drawbacks of this process are the lengthy reaction time (5 h) and the high amount of catalyst required (6%). These might be mitigated by employing the supercritical method. Under a supercritical state, methanol dissolves the oil to form a homogeneous phase due to a decrease in dielectric constants [23,24]. Some researchers have used the supercritical method. Kusdiana and Saka [23] examined the transesterification of rapeseed oil in supercritical methanol with molar ratio of 1:24–1:42 at reaction temperatures of 240–350 ◦ C. Without a catalyst, they obtained 95% of biodiesel yield for a short reaction time but at a relatively high operating temperature (350–400 ◦ C). Imahara et al. [25] studied thermal stability of biodiesel in supercritical methanol over a range of conditions between 270 ◦ C/17 MPa and 380 ◦ C/56 MPa. In addition, Petchmala et al. [26] examined transesterification of palm oil with methanol at near-supercritical and supercritical conditions using an acid catalyst (SO4 –ZrO2 ). They reported that 90% of biodiesel yield was achieved at 250 ◦ C in the presence of 0.5% (w/w) SO4 –ZrO2 catalyst [26]. However, it should be noted that Saka and Kusdiana [23] required a relatively high temperature (350 ◦ C), while Petchmala et al. [26] used the transition metal oxide, which is relatively expensive, to promote the catalyst. Therefore, this work focuses on the transesterification of palm oil in sub- and supercritical methanol with double promoted CaO/KI/␥-Al2 O3 catalyst. The effects of the amount of catalyst, reaction temperature, reaction time and molar ratio of oil to methanol were investigated. 2. Experiment 2.1. Material The palm oil used as starting material was purchased from Wako pure chemicals Co., Japan. Analytical grade methanol and hexane and methyl esters standard (methyl palmitate, methyl stearic, methyl linoleic, methyl linolenic and methyl oleic) were supplied by Wako pure chemicals Co., Japan. 2.2. Preparation and characterization of catalyst Double promoted alumina–supported (CaO/KI/␥-alumina) catalyst was prepared via impregnation and precipitation procedure, using optimum conditions as determined from our previous work [22] using the following procedure: 40 g of ␥-Al2 O3 was poured into 50 ml of distilled water, followed by the addition of calcium acetate until 30% (w/w% of ␥-Al2 O3 ) of CaO loading was reached; the solution was then stirred for 3–4 h at room temperature. Calcium acetate was synthesized by reacting stochiometrically of calcium oxide and acetic acid. The formed suspension was impregnated with 35 ml of 35% KI solution (35% weight to alumina). The performed slurry was heated up at 100–105 ◦ C in an oven overnight in order to remove the water content. The synthesized catalyst was milled into powder and then calcinated at 650 ◦ C in a muffle furnace with flowing air for 4 h. The catalyst was kept in a desiccator in the presence of silica gel in order to prevent water and CO2 contacting with the catalyst. By using this preparation procedure of catalyst, the highest yield of biodiesel was obtained [22]. The characterizations of catalysts were performed by X-Ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) and Scanning Electron Microscope (SEM) analysis. XRD gives information on the
crystallization structure. Powder XRD patterns were collected in order to investigate diversification peaks after promotion by double promoter. The specific surface area, pore volume and pore diameter of the prepared catalysts were measured using the BET method. SEM (Jeol, JSM-6390LV, Japan) was used to identify the morphology and size of CaO/KI/␥-Al2 O3 catalyst particle. 2.3. Transesterification in sub and supercritical methanol with catalyst Transesterification of palm oil in sub and supercritical methanol was carried out in a batch type reactor (8.8 ml, stainless steel SUS 304, AKICO Co., Japan) with double promoted ␥-Al2 O3 supported catalyst (CaO/KI/␥-Al2 O3 ). The reactor system used consisted of an electric furnace (ISUZU Co, Ltd., model NMF-13AD), a stainless steel SUS 304 reactor (8.8 ml of capacity, 300 ◦ C of maximum temperature, 30 MPa of pressure), and a temperature controller. First, the temperature of the heating furnace was set to the desired temperature (210–290 ◦ C). The reactor was charged with the mixture of palm oil and methanol in a certain molar ratio with various amounts of catalyst from 1 to 4% (w/w of oil), and the reactor was then inserted to the electric furnace. The effect of different operational parameters (amounts of catalyst, reaction temperature, reaction time and molar ratio oil to methanol) on the yield of biodiesel and conversion of palm oil were observed. After reaching the set temperature, the reaction was sustained until the desired reaction time was achieved. The pressure of the reaction was measured between 4 and 12 MPa. Afterwards, the reactor was removed from the electric furnace and immersed in a water bath for cooling in order to stop the reaction. The treated liquid and catalyst were discharged from the reactor into a sampling bottle. An amount of water was added to the solution mixture to dilute the excess methanol. Subsequently, the solution mixture was centrifuged for separation into three phases: the top phase was fatty acid methyl ester (FAME, or biodiesel) and a small amount of un-reacted oil; the middle phase consisted of methanol, water and glycerol, and the bottom phase was solid CaO/KI/␥-alumina catalyst. The biodiesel was analyzed by gas chromatography-flame ionization detector (GC-FID) (Gas Chromatography GC-14B, Shimadzu, Japan) equipped with a HPInnowax capillary column (30 m × 0.250 mm × 0.25 m) The oven temperature was programmed as follows: the initial temperature of 210 ◦ C was held for 9 min, increased to 230 ◦ C at 20 ◦ C/min intervals for 20 min, and then increased to 250 ◦ C at 20 ◦ C/min intervals for 5 min. The injector and detector temperatures were controlled at 250 and 300 ◦ C, respectively. The injection volume was 1 l. The carrier gas was helium, and the makeup gas was hydrogen. Biodiesel analyses can be used to determine the yield % of biodiesel defined as follows: Yield of biodiesel (%) =
W of actual biodiesel × 100% W of oil
where W of the actual biodiesel amount and W of oil are the actual weight of biodiesel from the experiment (mg) and the weight of oil used in the experiment (mg), respectively. 3. Results and discussion 3.1. Catalyst characterization The BET specific surface area, cumulative pore volume, and mean pore diameter of CaO/KI/␥-Al2 O3 catalyst are summarized in Table 1. It can be seen that the specific surface area of the catalyst is 54.55 m2 /g, smaller than that of the single promoted catalyst (83 m2 /g) reported by Asri et al. [21] and Zabeti et al. [5]. This might be due to the double alkaline compound (CaO and KI) anchored to the surface of catalyst causing an increase in active sites, thus
N.P. Asri et al. / Chemical Engineering and Processing 72 (2013) 63–67
65
Table 1 Chractheristic of CaO/KI/␥-Al2 O3 with 30% loading of CaO. Catalyst properties
Value
Techniques
Spesific surface area Pore volume Mean pore size
54.55 (m2 /g) 0.083 (cm3 /g) 38.211 (Å)
BET BET BET
Fig. 3. Biodiesel yield as function of amount of catalyst (wt% to palm oil) at reaction temperature 290 ◦ C, reaction time 30 min, and molar ratio palm oil to methanol 1:24.
3.2. Effect of catalyst amount
Fig. 1. XRD pattern of CaO/KI/␥-Al2 O3 : (a) CaO/KI/␥-Al2 O3 with 30% loading of CaO, (b) ␥-Al2 O3 .
resulting in an increase in catalyst activity. This result was confirmed by X-ray diffraction patterns of CaO/KI/␥-Al2 O3 with 30% of CaO loaded, as shown in Fig. 1a. The XRD pattern has more diffraction peaks appearing at 2. Conversely, XRD patterns for ␥Al2 O3 (Fig. 1b) only registered diffraction peaks at 37.0◦ , 46.0◦ and 66.7◦ , assigned to amorphous Al2 O3 support. A similar pattern was reported by Xie and Li [27]. Moreover, as reported by Ilgen and Akin [11], the activity of the catalyst for transesterification of vegetable oils is not only influenced by the surface area but also by the basicity of the catalyst. Fig. 2 shows SEM images of CaO/KI/␥-Al2 O3 with 30% of CaO loaded. The SEM image shows crystallites of 10 m in size with similar irregular shapes. This line of evidence indicates that the catalyst was a mesoporous structure. According to our previous study, the CaO/KI/␥-Al2 O3 with 30% of CaO loaded was found to be the most active catalyst for transesterification of palm oil with methanol in the reflux condition [22]. Therefore, in our present work, this catalyst was used for transesterification of palm oil under sub- and supercritical methanol.
The effect of catalyst amount (w/w% of oil) on the yield of biodiesel and conversion of palm oil was studied by varying the amount of catalyst from 1 to 4% at a reaction temperature of 290 ◦ C, reaction time of 30 min, and molar ratio of oil to methanol 1:24. The results, shown in Fig. 3, indicate that yield of biodiesel increases significantly by increasing the catalyst amount from 1 to 3%. Without the use of catalyst, the obtained of biodeiesel yield was only 22%. Conversely, biodiesel yield sharply increased from 48 to 81% by using 1 and 3% catalyst, respectively. It is strongly evidenced that the presence of catalyst affected the reaction rate. It can be explained in terms of the transition-state theory, which holds that a catalyst reduces the potential energy barrier over which reactants must pass to form a product [28]. On the contrary, the use of 3.5 to 4% of catalyst led to a decrease in biodiesel yield due to agglomeration occurring on the catalyst, which caused a decrease in the number of active sites and finally reduced the activity of the catalyst. The agglomeration of catalyst could be observed after the reaction. When the mixture of product, rest of reactant and solid catalyst were discharged from the reactor, the solid catalyst was not dispersed in the solution mixture; however, the agglomeration of solid catalyst was observed. Moreover, the solution mixture (oil, methanol and catalyst) became too viscous, leading to a problem of mixing that resulted in the difficulties for diffusion. The same statement also addressed by previous researchers [26,29]. Petchmala et al. [26] confirmed that the conversion of FAME increased considerably from 33 to 90% with an increase in SO4 –ZrO2 catalyst at a proportion of reactants mass from 0 to 0.5%, and slightly decreased for reactant mass above 0.5%. Our present work has found that 3% of catalyst was the optimum condition. Hence, 3% of catalyst was selected for further studies. 3.3. Effect of molar ratio of oil to methanol
Fig. 2. Scanning electron micrographs (SEM) of CaO/KI/␥-Al2 O3 catalyst.
The molar ratio of oil to methanol is an importance variable influencing the yield of FAME. In transesterification reactions, stochiometrically, three moles of alcohol (preferably methanol) and one mole of triglyceride are required to produce three moles of fatty acid methyl ester (FAME) and one mole of glycerol [5,26]. Theoretically, increasing the molar ratio of oil to methanol can cause the reaction to shift to the right side. In practice, though, an excess of methanol is not favorable due to the high amount of energy needed to recover it, which ultimately increases the total production cost of biodiesel. In this work the effect of molar ratio of oil to methanol was studied at various molar ratios from 1:12 to 1:42 (1:12, 1:18, 1:24, 1:30, 1:36 and 1:42), a constant reaction temperature of 290 ◦ C, a
66
N.P. Asri et al. / Chemical Engineering and Processing 72 (2013) 63–67
Fig. 4. Biodiesel yield as function of molar ratio palm oil to methanol at reaction time 30 min, reaction temperature 290 ◦ C and 3% amount of catalyst.
constant reaction time of 30 min, and 3% (w/w% of oil) of catalyst. Fig. 4 shows the influence of the molar ratio of oil to methanol on the yield of biodiesel. Increasing the molar ratio of oil to methanol resulted in a higher biodiesel yield. By increasing the molar ratio from 1:12 to 1:24, biodiesel yield significantly increased from 51 to 81%, respectively. Beyond the molar ratio of 1:24, the excess added methanol had no significant effect on biodiesel yield. It can be concluded that the yield of biodiesel increased up to a certain molar ratio of oil to methanol, and that the optimum molar ratio of oil to methanol was 1:24. Kusdiana and Saka [23] reported that the highest yield, 95%, was achieved with a molar ratio of rapeseed oil to methanol of 1:42. Meanwhile, with SO4 –ZrO2 catalyst, Petcmala et al. [26] achieved the similar molar ratio (1:24) with 90% yield of biodiesel. 3.4. Effect of reaction temperature To investigate the effect of temperature process, reactions were carried out under sub- and supercritical methanol with solid base CaO/KI/␥-alumina catalyst at temperatures ranging from 210 to 290 ◦ C at 20 ◦ C intervals with a constant reaction time (30 min), molar ratio of oil to methanol (1:24), and amount of catalyst (3%). Fig. 5 shows effects of reaction temperature on biodiesel yield. The reaction temperature significantly influences the transesterification reaction, where the biodiesel yield increased with an increase in reaction temperature. These results are correlated with Arrhenius law, which states that the intrinsic rate constants are a function of reaction temperature [28]. At 210 and 230 ◦ C for 30 min of reaction time, biodiesel yield gradually increased from 64 to 67% due to the subcritical state of methanol; under such a state of, methanol is not completely dissolved to be a homogeneous phase with the
Fig. 5. Biodiesel yield as function of reaction temperature (◦ C) at 30 min time of reaction, 1:24 of molar ratio palm oil to methanol and 3% amount of catalyst.
Fig. 6. Biodiesel yield as function of reaction time (min) at a various of temperature from 210 to 290 ◦ C, 1:24 of molar ratio palm oil to methanol and 3% amount of catalyst.
oil. Yujaroen et al. [30] and Petchmala et al. [26] reported that complete solubility of methanol with oil occurs under the supercritical state. As a comparison with previous work, Kusdiana and Saka [23] obtained 68 and 70% of biodiesel yield at 200 and 230 ◦ C, respectively, following 60 min of treatment without catalyst. At 250 ◦ C, the yield drastically increased up to 74%. The highest yield of biodiesel was 81% achieved at 290 ◦ C and 30 min of reaction. Compared with previous work, Kusdiana and Saka [23] obtained 80% of biodiesel at 300 ◦ C. In fact, theoretically, under the supercritical state, an increase in temperature reduces the polarity of methanol due to weakening of hydrogen bounding; it causes a decrease in the dielectric constant of methanol, eventually increasing the solubility of palm oil in methanol [23,24,30]. Meanwhile, Petchmala et al. [26] reported that the highest yield was 90% achieved at 250 ◦ C for the transesterification of palm oil in near- and supercritical methanol with SO4 –ZrO2 catalyst. 3.5. Effect of reaction time The effect of reaction time on the yield of biodiesel and the conversion of oil was observed by varying the reaction time from 30 to 90 min at 10 min intervals. The reaction was carried out at five different reaction temperatures (210, 230, 250, 270 and 290 ◦ C), a molar ratio of oil to methanol 1:24 and catalyst amount of 3% (w/w). Fig. 6 shows the effect of reaction time on biodiesel yield. As expected, the yield of biodiesel increased with the increasing reaction time at all reaction temperatures. However, the maximum yield was achieved at a certain reaction time; afterward, it decreased slightly due to surface agglomeration and activity reduction of catalyst. At 210 to 250 ◦ C, the highest yield was obtained at 70 min; while at higher temperatures, the maximum one was achieved at 60 min. Biodiesel yield gradually increased with an increase in reaction time at 210 and 230 ◦ C. Moreover, the yield dramatically increased with the increasing reaction time at temperatures from 270 to 290 ◦ C. It can be explained that above 270 ◦ C methanol is in supercritical state. Under this condition, the polarity of methanol is reduced because the degree of hydrogen bonds decreases with increasing temperature [23]. For these conditions, the highest yield was obtained at 60 min of reaction time and a temperature of 290 ◦ C, with the biodiesel yield obtained close to 95% (94.83%). For comparison, previous work achieved the same biodiesel yield (94.94%) over 5 h of treatment [22]; moreover, that experiment was conducted in refluxed methanol with a molar ratio of oil to methanol 1:42 and catalyst amount of 6% (w/w). Whereas if
N.P. Asri et al. / Chemical Engineering and Processing 72 (2013) 63–67
compared with another previous studies which studied the transesterification of palm oil with sub and supercritical methanol without catalyst in the same batch type reactor (data is not shown), the highest yield of 88% was obtained under the same conditions (290 ◦ C and molar ratio of oil methanol 1:24), but the time required is much longer (90 min) than that the present one (60 min). The present results evidence that supercritical methanol with CaO/KI/␥-Al2 O3 catalyst is able to reduce the reaction time, the catalyst amount, and the molar ratio of oil to methanol significantly – 80, 50 and 52%, respectively. Meanwhile, Pethcmala et al. [26] reported that maximum conversion was obtained at 10 min for PPO (purified Palm Oil) and 1 min for PFA (palm fatty acid), with conversions of 90.5 and 74.4%, respectively. It should be noted that the SO4 –ZrO2 catalyst used for their experiment was prepared using a transition metal, which is much more expensive than the alkali metal. 4. Conclusion In this study, transesterification of palm oil was done in sub- and supercritical methanol with solid base alumina supported catalyst (CaO/KI/␥-alumina) at a temperature range of 210–290 ◦ C, a reaction time of 30–70 min, a molar ratio of oil to methanol 1:12–1:42, and a catalyst amount of 1–4%. The measured pressure of the system was between 4 and 12 MPa. The results found that the optimum condition was at 3% amount of catalyst, 290 ◦ C of reaction temperature, 60 min of reaction time and 1:24 of molar ratio of oil to methanol; at the condition, the yield of biodiesel was 95%. In comparison, by using refluxed methanol method, highest yield was 95% obtained at 65 ◦ C, 5 h of reaction time and 6% of catalyst. Therefore, the results lead to the conclusion that the introduction of a solid base catalyst in sub-and supercritical methanol may allow development of an efficient method for transesterification process. Acknowledgements The authors gratefully acknowledged The Directorate General of Higher Education of the ministry of Education Republic of Indonesia for financial support. Special thanks to Applied Chemistry and Biochemistry Department, Engineering Faculty, Kumamoto University for technical assistance, and providing all of the facilities needed for the experiment. References [1] U. Schuchardt, R.M. Secheli, Transesterification of vegetable oil: a review, Journal of the Brazilian Chemical Society 9 (1998) 199–210. [2] S.G. Michael, R.L. McCormic, Combustion of fat and vegetable oil derived fuel in diesel engine, Progress in Energy and Combustion Science 24 (1998) 125–164. [3] F. Maa, M.A. Hanna, Biodiesel production – a review, Bioresources Technology 70 (1999) 1–15. [4] A. Kawashima, K. Matsubara, K. Honda, Development of heterogeneous catalyst for biodiesel production, Bioresources Technology 99 (2008) 3439–3443.
67
[5] M. Zabeti, W.H.A.W. Daud, M.K. Aroua, Activity of solid catalysts for biodiesel production: a review, Fuel Processing Technology 90 (2009) 70–77. [6] M.A. Dube, A.Y. Tremblay, J. Liu, Biodiesel production using a membrane reactor, Bioresources Technology 98 (2007) 639–647. [7] J.P. Szybist, J. Song, M. Alam, A.I. Boehman, Biodiesel combustion, emission and emission control, Fuel Processing Technology 88 (2007) 679–691. [8] B. Freedman, R.O. Butterfield, E.H. Pryde, Transesterification kinetics of soybean oil, Journal of American Oil Chemists Society 63 (1986) 1375–1380. [9] M. Canaki, V. Gerpen, Biodiesel production via acid catalyst, Transaction of the American Society of Agricultural Engineers 42 (1999) 1203–1210. [10] M. Kouzu, T. Kasuno, M. Tajika, Y. Sugimoto, S. Yamanaka, J. Hidaka, Calcium oxide as a solid base catalyst for transesterification of soybean oil and it’s application to biodiesel production, Fuel 87 (2008) 2798–2806. [11] O. Ilgen, A.N. Akin, Development of alumina supported alkaline catalyst used for biodiesel production, Journal of Turkey 33 (2009) 281–287. [12] M. Zabeti, W.H.A.W. Daud, M.K. Aroua, Biodiesel production using aluminasupported calcium oxide: an optimization study, Fuel Processing Technology 91 (2010) 243–248. [13] M.D. Serio, R. Tesser, P. Pengmei, E. Santacesaria, Heterogeneous catalysts for biodiesel production, Energy and Fuel 22 (2008) 207–217. [14] S. Furuta, H. Matsuhashi, K. Rata, Biodiesel fuel production with solid amorphous-zirconia catalyst in fixed bed reactor, Journal of Biomass and Bioenergy 30 (2006) 870–873. [15] A.K. Dalai, M.G. Kulkarni, L.C. Meher, Biodiesel production from vegetable oils using heterogeneous catalyst and their application as lubricity additives, in: IEEE EIC Climate Change Technology conference EICCCC, 2006, art 4057358. [16] F.R. Abreu, D.G. Lima, E.H. Hamu, S. Einloft, J.C. Rubim, P.A.Z. Suarez, New metal catalysts for soybean oil transesterification, JAOCS Journal of the American Oil Chemists’ Society 80 (2003) 601–604. [17] J. Jitputti, B. Kitiyanan, P. Rangsunvigit, K. Bunyakiat, L. Attnatho, P. Jenvanipanjakul, Transesterification of kernel oil and crude coconut oil by different solid catalysts, Chemical Engineering Journal 116 (2006) 61–66. [18] J.M. Marchetti, V.U. Miguel, A.F. Errasu, Heterogeneous esterification of oil with high amount of free fatty acids, Fuel 86 (2007) 906–910. [19] M.L. Granados, M.D.Z. Poves, D.M. Alonso, R. Mariscal, F.C. Galisteo, R. MorenoTost, J. Santamaría, J.L.G. Fierro, Biodiesel from sunflower oil by using activated calcium oxide, Applied Catalysis B: Environmental 73 (2007) 317–326. [20] A.R. Yacob, M.K.A. Mustajab, N.S. Samadi, Calcination temperature of nano MgO effect on base transesterification of palm oil, World Academy of Science, Engineering and Technology 56 (2009) 408–412. [21] N.P. Asri, A. Anisa, F. Rizqi, A. Roesyadi, K. Budikaryono, Suprapto, I. Gunardi, Biodiesel production from palm oil using CaO/Al2 O3 as a solid base catalyst, in: Proceeding of the 1st International Seminar on Fundamental & Application of Chemical Engineering, 2010. [22] N.P. Asri, F. Hartanto, R. Ramadhan, S.D. Savitri, I. Gunardi, Suprapto, K. Budikarjono, A. Roesyadi, Transesterification of palm oil to methyl ester using ␥-alumina supported base catalysts, in: Proceeding of Bali International Seminar on Science and Technology (BISSTECH), 2011. [23] D. Kusdiana, S. Saka, Kinetics of transesterification in rapeseed oil to biodiesel fuel as treated in supercritical methanol, Fuel 80 (2001) 693–698. [24] S. Saka, D. Kusdiana, Biodisel fuel from rapeseed oil as prepared in supercritical methanol, Fuel 80 (2001) 225–231. [25] H. Imahara, E. Minami, S. Hari, S. Saka, Thermal stability of biodiesel in supercritical methanol, Fuel 87 (2008) 1–6. [26] A. Petchmala, N. Laosiripojana, B. Jongsomjit, M. Goto, J. Panpranot, O. Mekasuwandumrong, A. Shotipruk, Transesterification of palm oil fatty acid in near – and super-critical methanol with SO4 –ZrO2 catalyst, Fuel 89 (2010) 2387–2392. [27] W. Xie, H. Li, Alumina supported potassium iodide as a heterogeneous catalyst for biodiesel production from soybean oil, Journal of Molecular Catalysis 255 (2006) 1–9. [28] O. Levenspiel, Chemical Reaction Engineering, Wiley International edition, John Wiley and Sons, Inc, Canada, 1999. [29] K. Noiroj, P. Intarapong, A. Luengnaruemitchai, S. Jai-In, A comparative study of KOH/Al2 O3 and KOH/NaY catalyst for biodiesel production via transesterification from palm oil, Renewable Energy 34 (2009) 1145–1150. [30] D. Yujaroen, M. Goto, M. Sasaki, A. Shotipruk, Esterification of palm fatty acid distillate (PFDA) in supercritical methanol: effect of hydrolysis on reaction reactivity, Fuel 88 (2009) 2011–2016.