Biodiesel production from yellow horn (Xanthoceras sorbifolia Bunge.) seed oil using ion exchange resin as heterogeneous catalyst

Bioresource Technology 108 (2012) 112–118

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Biodiesel production from yellow horn (Xanthoceras sorbifolia Bunge.) seed oil using ion exchange resin as heterogeneous catalyst Ji Li, Yu-Jie Fu ⇑, Xue-Jin Qu, Wei Wang, Meng Luo, Chun-Jian Zhao, Yuan-Gang Zu Key Laboratory of Forest Plant Ecology, Ministry of Education, Northeast Forestry University, Harbin 150040, PR China Engineering Research Center of Forest Bio-Preparation, Ministry of Education, Northeast Forestry University, Harbin 150040, PR China

a r t i c l e

i n f o

Article history: Received 11 November 2011 Received in revised form 24 December 2011 Accepted 26 December 2011 Available online 4 January 2012 Keywords: Biodiesel production Ion exchange resin Transesterification process Kinetic model Yellow horn seed oil

a b s t r a c t In this study, biodiesel production from yellow horn (Xanthoceras sorbifolia Bunge.) seed oil using ion exchange resin as heterogeneous catalyst was investigated. After illustration of the mechanisms of transesterification reactions catalyzed by typical ion exchange resins, the factors affecting microwaveassisted transesterification process were studied. A high conversion yield of about 96% was achieved under optimal conditions using high alkaline anion exchange resins as catalyst. Analyzing the FAMEs composition by GC–MS and main physical–chemical properties demonstrated that the biodiesel product prepared from yellow horn seed oil was of high quality. Compared with conventional alkali catalyst, the outstanding characteristics of reusability and operational stability made the resin catalyst more predominant for biodiesel production. In addition, a comprehensive kinetic model was established for analyzing the reaction. The results of present research showed that microwave-assisted transesterification process catalyzed by high alkaline anion exchange resin was a green, effective and economic technology for biodiesel industry. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Nowadays, due to the depletion of energy resources and more environmental problems, biodiesel has received a great deal of attention as the best alternative candidate for conventional fossil fuel (Kosaric and Velikonja, 1995; Lang et al., 2001; Duffy et al., 2009). As a green and renewable bioenergy, biodiesel is reported to be sulfur-free, nontoxic, oxygenated and biodegradable, and these advantages lead to a significant reduction of emissions compared with conventional fuels, especially of unburned hydrocarbons, sulfur dioxide, carbon monoxide and particulate matter (Sendzikiene et al., 2006; Li et al., 2009). Biodiesel is composed of fatty acid methyl esters (FAMEs) and usually produced via the transesterification of plant oils or animal fats with low molecular weight alcohols (McNeff et al., 2008). Commonly, homogeneous alkali catalysts (mainly KOH) are widely used in the current biodiesel industry because of their high activity and low cost. However, removal of these soluble catalysts from biodiesel product is time-consuming and difficult. Moreover, the free fatty acids (FFAs) are readily saponified by the alkali catalysts during the reaction process, leading to a loss of catalysts and increased purification costs (Shu et al., 2007; Liu et al., 2009; Duz et al., 2011). Thus, in order to solve this tough problem, the ⇑ Corresponding author. Tel./fax: +86 451 82190535. E-mail address: [email protected] (Y.-J. Fu). 0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.12.129

development of heterogeneous catalysts for transesterification reaction is crucial to improving efficiency and saving cost for biodiesel production. Based on the previous studies, there are several advantages to using heterogeneous catalysts, which are reusable, noncorrosive and easy to be separated from biodiesel product, rather than the homogeneous ones (Arzamendi et al., 2007; Helwani et al., 2009). Hence, many heterogeneous catalysts, such as Nafion, heteropolyacid, Fe–Zn cyanide, modified CaO and lipase, for biodiesel production from plant oils have been investigated (Narasimharao et al., 2007; Lopez et al., 2007; Tang et al., 2011; Yan et al., 2011). However, these catalysts are still limited by the complicated preparation, high cost or unstable activity (Shibasaki-Kitakawa et al., 2007; Liu et al., 2008). From the viewpoint of environmental friendless and saving cost, ion exchange resin might be predominant to the other heterogeneous catalysts. In general, ion exchange resins are constituted by a cross-linked polymeric matrix on which the active sites for the transesterification reaction are bonded (Özbay et al., 2008). Furthermore, compared with the other heterogeneous catalysts, ion exchange resins are more easily to be separated from the biodiesel product because of the relative larger particle size (0.5–1.5 mm). Until now, biodiesel are most commonly made from soybean oil in the United States and from rapeseed oil in Europe (Halim et al., 2011). However, due to their big requirements in food industry, the utilization of common edible oils for biodiesel production is limited by the finite resources. Thus, it is required to discover

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inedible oil resources which can be used as feedstock or biodiesel industry. According to previous research (Li et al., 2010), yellow horn (Xanthoceras sorbifolia Bunge.) was proved to be an ideal energy crop, which can be widely planted against drought, cold, salt and starvation, because of the advantages associated with its high oil content (55–65%). Moreover, yellow horn seed oil is of high unsaturated fatty acids content (85–93%) and low acid value (0.5– 0.7 mg KOH/g), so that it can be used as high-quality feedstock for biodiesel production. In the published study, transesterification of yellow horn seed oil to biodiesel using heteropolyacid solid catalysts was studied (Zhang et al., 2010). Although the conversion was complete and fast, due to the powder state of heteropolyacids, the separation process of these catalysts from biodiesel product was still complicated. Therefore, in the present study, transesterification of yellow horn seed oil to biodiesel catalyzed by different types of ion exchange resins were performed using a digital microwave-assisted reactor. The main factors affecting the transesterification process, including reaction temperature, molar ratio of methanol/oil, amounts of catalyst and the reusability were investigated. Furthermore, the FAMEs composition and main properties of the biodiesel product were studied. In addition, the kinetic model for the transesterification process was investigated and the Arrhenius plot method was used to analyze the dependence of rate constants on reaction temperature. Those results supported necessary data for the industrial biodiesel production using ion exchange resin as heterogeneous catalyst. 2. Methods 2.1. Materials and chemicals Seeds of yellow horn were collected during autumn in 2010 from Inner Mongolia Autonomous Region, China. The seeds were cracked and the kernels obtained were milled for oil extraction. Yellow horn seed oil was extracted using a HA121-50-01 SFE device. Hexane of analytical grade and methanol were purchased from Kermel Chemical Reagents Corp. (Tianjin, China). Four types of ion exchange resins (Amberlyst-15, Amberlite IRA-900, Amberlite IRC-72 and Amberlite IRC-93) were purchased from Guangfu Chemical Research Institute (Tianjin, China) and their characteristics are shown in Table 1. Before the experimental run, in order to remove foreign matters, the ion exchange resin was washed by ethanol for several times, and was dried for 12 h at 70 °C in an oven so as to remove the residual ethanol. 2.2. Transesterification process catalyzed by ion exchange resin Biodiesel production from plant oil is generally produced by transesterification of triglyceride, but it might also be generated

Fig. 1. The transesterification reactions of triglyceride (1) and free fatty acid (2).

by direct esterification of free fatty acid (FFA) in the feedstock (Marchetti and Errazu, 2010). Both of the reactions can be summarized as (1) and (2) (Fig. 1). The transesterification process was performed in a digital microwave-assisted reactor (Sineo Chemical Equipment Corp., Shanghai, China) equipped with an infrared temperature sensor, a special three necks flask and an electromagnetic stirrer, which allows variations of temperature, duration and irradiation power using the digital control desk. Ten grams of yellow horn seed oil was added into the special 50 mL reaction flask, and mixed with the resin catalyst and methanol of a certain ratio. Then, the mixture was automatically irradiated by microwave with a presetting procedure. When the reaction finished, the excess of methanol in the product was recovered under vacuum at 50 °C using a rotational evaporator. Afterwards, the mixture was centrifuged at 5000 rpm for 10 min to be separated into two layers. The upper layer was the FAMEs (crude biodiesel) with lighter color. The resin catalyst at bottom of the reactor was decanted into a flask for recovering. It could be easily separated and reused by soaking with methanol. Additionally, in order to prove that both resin catalyst and microwave irradiation affected the transesterification process, microwave-assisted reaction without catalyst and resin-catalyzed reactions heated by oil bath were also carried out as comparisons. Otherwise, according to the experimental design, the reaction process included different reaction temperatures, molar ratio of methanol/oil, catalyst amounts and reusability of the catalyst, therefore, these factors were also investigated. 2.3. Transesterification process catalyzed by conventional homogenous catalyst Conventional technology employs a basic homogenous catalyst (mainly KOH) to perform the reaction for plant oil of low acid value (Duz et al., 2011). The transesterification process of yellow horn seed oil catalyzed by KOH was carried out in the microwave-assisted reactor. After optimized, main parameters for the reaction were as follows: 60 °C for 60 min with methanol/oil molar ratio of 8 and a catalyst amount of 5% (w/w of oil). Furthermore, chemical composition of the biodiesel sample produced via this method was also analyzed by GC–MS.

Table 1 Characteristics of the ion exchange resins.

Character Structure Matrix Functional group Temperature (oC) pH range (a) mmol/g (dry) (b) mmol/g (wet) Bead size (%) Moisture content (%) True (g/ml) Apparent (g/ml)

Amberlyst-15

Amberlite IRA-900

Amberlite IRC-72

Amberlite IRC-93

Cation (high acidic) Macroporous Styrene-DVB SO 3 Max. 120 1–14 P4.2 P1.4 (0.40–1.25 mm)P95 50–55 1.20–1.30 0.70–0.80

Anion (high alkaline) Macroporous Styrene-DVB –N+(CH3)3 Max. 80 1–14 P3.6 P1.1 (0.40–1.25 mm)P95 50–60 1.06–1.11 0.65–0.75

Cation (weak acidic) Macroporous Acrylic-DVB –COOH Max. 100 5–14 P9.5 P3.0 (0.40–1.25 mm)P95 60–72 1.05–1.15 0.70–0.75

Anion (weak alkaline) Macroporous Styrene-DVB –N(CH3)2 Max. 80 1–9 P4.4 P1.2 (0.40–1.25 mm)P95 50–60 1.05–1.12 0.66–0.71

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2.4. GC–MS analysis of FAMEs The FAMEs composition of biodiesel product was analyzed by Varian 450-GC/240-MS gas chromatography/mass spectrometer (Varian, Santa Clara, CA, USA) equipped with an HP-5 silica capillary column (30 m  0.32 mm i.d.; film thickness 0.2 lm). The column temperature was initially 60 °C (held for 2 min) and then increased to 200 °C at 20 °C/min, held for 2 min, and finally increased to 230 °C at 10 °C/min. The mass spectrometer was operated in positive ion mode with ionization energy of 70 eV. Injector and detector temperatures were 280 and 290 °C, respectively, and the ion source temperature was 230 °C. Helium was used as carrier gas and the split ratio was 1:40. Mass units were monitored from m/z 35 to 425. The chemical components were identified on the basis of comparing their retention indices and mass spectra with publish data and computer matching with National Institute of Standards and Technology (NIST, 3.0) libraries provided with computer controlling the GC–MS system. 2.5. Properties evaluation of biodiesel product The main properties of biodiesel product were determined using standard test methods according to ASTM (American Society for Testing and Materials) standard methods. Additionally, the obtained results were compared with the reported properties of common biodiesels. 2.6. Statistical analysis The experimental results were expressed as mean ± SD of three parallel measurements and the calculations were carried out with the help of the statistical package Statgraphics Plus for Windows V6.0. 3. Results and discussion 3.1. Mechanisms of microwave-assisted transesterification process catalyzed by ion exchange resins In order to test the catalytic actions, four typical ion exchange resins were investigated. As shown in Table 2, the conversion yield (96.3%) of transesterification process catalyzed by high alkaline anion exchange resin (Amberlite IRA-900) was obviously the highest among the four different types of resin catalysts. Hence, it was proved to be the proper resin catalyst for biodiesel production from yellow horn seed oil. The results showed that the high acidic cation

Table 2 Comparison of different transesterification processes. Catalyst

Transesterification process heated by microwave irradiation Temperature (oC)

Amberlyst-15 Amberlite IRA-900 Amberlite IRC-72 Amberlite IRC-93 Alkali (KOH) None Amberlyst-15 Amberlite IRA-900

Duration (min)

Amount (%, of oil)

Conversion yield (%)

60 60

90 90

5 5

83.5 ± 3.6 96.3 ± 3.2

60

90

5

55.7 ± 4.5

60

90

5

57.4 ± 5.3

60 60 5 60 90 0 Transesterification process heated by oil bath 60 180 5 60 180 5

97.5 ± 3.8 58.2 ± 3.5 23.6 ± 4.1 25.8 ± 5.7

exchange resin (Amberlyst-15) was also effective for the transesterification process. However, its catalytic action was still weaker than the Amberlite IRA-900 resin. In addition, from the results, it was also concluded that the weak acidic cation exchange resin (Amberlite IRC-72) and weak alkaline anion exchange resin (Amberlite IRC-93) were not efficient for catalyzing the reaction. This phenomenon could be explained that the weak acidity or alkalinity of the both ion exchange resins were not benefit for catalyzing reactions and the cations or anions were hardly librated in the reaction system. Furthermore, the limited range of pH value also restricted their utilization. Therefore, the weak acidic and alkaline ion exchange resins may not be proper catalysts for transesterification reactions. In order to clarify the transesterification process in the present study, Fig. 2 was used to illustrate the catalytic mechanisms of different ion exchange resins. The mechanism of the transesterification reaction catalyzed by high alkaline anion exchange resin was shown in Fig. 2A, for FFA and triglyceride. However, it was also applied for mono- and di-glyceride. The reaction of the catalyst with molecule of methanol produced the methoxyl and protonated catalyst. After the nucleophilic attack of the methoxyl, a tetrahedral intermediate was generated, which deprotonated the catalyst to regenerate the active species, and formed the FAME. In reaction (II), the generated diglyceride was able to react with methanol, starting another catalytic cycle. The mechanism of the transesterification reaction catalyzed by high acidic cation exchange resin was shown in Fig. 2B. The protonation of the carbonyl group leads to the carbocation, and after the nucleophilic attack of the methanol molecule, a tetrahedral intermediate was generated, which formed the FAME, and to regenerate the catalyst. The diglyceride generated in reaction (IV) was able to react with methanol, starting another catalytic cycle. According to previous researches, the catalytic activity of ion exchange resins mainly depends on their swelling properties which controls reactants accessibility to the active sites and, therefore, affects their overall reactivity (Lotero et al., 2005; Tesser et al., 2010). Moreover, the resins which show a high tendency to incorporate alcohol would be subjected to a remarkable swelling phenomenon. In the present transesterification process, once the reaction started, ion exchange resins would firstly adsorb molecules in the system. Mazzotti et al. (1997) reported that the adsorption strength of alcohol on anion exchange resin was high. On the opposite, the cation exchange resin was more prone to adsorb FFAs or glycerides. Thus, the different adsorptive actions made different catalytic mechanisms of the two kinds of ion exchange resins, and this was why the anion exchange resins showed a higher catalytic activity than that of the cation exchange resin. On the basis of above mechanism, as an agent, high alkaline anion exchange resin would activate the absorbed molecules (mostly methanol molecule) during the reaction. Hence, transesterification process could be easily facilitated by the resin catalyst. Microwave-assisted transesterification process catalyzed by high alkaline anion exchange resin was proved to be an efficient method for biodiesel production. A high conversion yield (96.3%), which was much higher than that (25.8%) of the transesterification process heated by oil bath, was obtained in a short duration (90 min) using this emerging technology (Table 2). Compared with conventional method for heating, microwave irradiation generated an electromagnetic field to accelerate the movements of molecules during the reaction (Eskilsson and Björklund, 2000). Oliveira and Franca (2002) also reported that microwave energy could produce a volumetrically distributed heat source in the system, and the highly localized temperature thus generated would cause furious impact between oil and methanol at more rapid rates. Therefore, microwave irradiation was an alternative heating technology for assisting transesterification process to produce biodiesel.

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Fig. 2. The mechanisms of the transesterification reaction catalyzed by high alkaline anion exchange resin (A) and high acidic cation exchange resin (B).

3.2. Parameters of the transesterification process In order to investigate the effect of different reaction temperatures on conversion yield, the transesterification processes were carried out at 40, 45, 50, 55 and 60 °C with 5% (w/w of oil) resin catalyst and a methanol/oil molar ratio of 8 for 90 min. In general, the increase in temperature would accelerate the reaction rate for such endothermic reaction (Feng et al., 2010). Fig. 3A showed that increasing temperature had a positive effect on the conversion of transesterification. However, the reactions became very violent over 60 °C in microwave-assisted reactor, and there would also be a loss of methanol at high temperature (Ramadhas et al., 2005). Taking conversion rate, stability and safety into account, a reaction temperature of 60 °C was chosen for subsequent tests. The molar ratio of methanol/oil was an important factor affecting the conversion yield. As known, transesterification process could be accelerated by increasing the amounts of methanol, so that high methanol/oil molar ratio could enhance the conversion yield. Although the required methanol/oil molar ratio for this reaction was 3, due to the continual generation of methanol vapor during the reaction, the molar ratio used in practical process had to be higher than the theoretical value. In the current study, the methanol/oil molar ratio was in a range of 5–9. It was found that the conversion yield was nearly 96% when the methanol/oil molar ratio of 8, and the conversion almost kept stable with further increase in the molar ratio (Fig. 3B). Therefore, a methanol/oil molar ratio of 8 was used for the current transesterification process. The amount of resin catalyst was also optimized. Experiments were carried out by varying the catalyst amounts between 1% and 5% (w/w of oil) and keeping a methanol/oil molar ratio of 8 for 90 min at 60 °C. As shown in Fig. 3C, the conversion yield increased considerably with an increase in the amount of catalyst. When the catalyst amount was 3% of oil, the conversion yield was about 96% and hardly increased with an increase in catalyst

amount. Thus, in the current study, a catalyst amount of 3% (w/w of oil) was used for biodiesel preparation. 3.3. Kinetics of the transesterification process In the present study, kinetics of the transesterification process was measured as a function of temperatures in the range between 40 and 60 °C (Fig. 4). For the limited experimental data, an exponential equation was fitted using Eq. (1) to represent the entire reaction behavior during the reaction time, by applying BoxLucas1 model.

Conversion yieldð%Þ ¼ a½1  expðbtÞ

ð1Þ

where a, b were constants and t was the reaction time. As shown in Table 3, the constant values of different temperatures were given, and the correlation coefficient (R > 0.99) of ANOVA statistics showed that the model was well fitted for the experimental data. Therefore, the equation allows the regeneration of as many data points as required for evaluating all the reaction parameters. According to previous researches, Darnoko and Cheryan (2000) asserted that alkali catalyzed transesterification process occurs in a second order reaction, while Freedman et al. (1986) found that acid catalyzed transesterification process was a first order reaction. In order to calculate the exact rate constant, a decision of the reaction type for a transesterification process should be carried out. Based on the evaluation method of physical chemistry, if the process was a first order reaction, the logarithm of CA (the concentration of substrate) would be linearly depended on the value of 1000/T (the reaction temperature in Kelvin); and, if the process was a second order reaction, the inverse CA would be linearly depended on the value of 1000/T. As shown in Fig. 5, our results suggested that the transesterification catalyzed by high alkaline anion exchange resin occurred in a first order reaction, since all kinetic data curves

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Fig. 4. Kinetics of the transesterification process at different temperatures: 40 °C (green curve), 50 °C (blue curve) and 60 °C (red curve). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Table 3 Constant values of the kinetic equation. Reaction temperature (°C)

Constant values of the kinetic model a

b

40 50 60

84.56 93.66 99.54

0.016 0.026 0.045

Correlation coefficient (R)

0.9943 0.9973 0.9968

Due to the considerable effect of reaction temperature on rate constant, the correlation between them was represented using the Arrhenius plot in the current study, which correlates the natural logarithm of the rate constant [ln(k)] with the inverse of temperature (1/T). Meanwhile, the activation energy (Ea) of transesterification reaction could also be calculated using the Arrhenius equation:

lnðkÞ ¼ Ea =RT þ lnðAÞ

ð3Þ

where R is the ideal gas constant and A is the pre-exponential factor. The Arrhenius plot of transesterification process catalyzed by the resin catalyst was performed at temperatures of 40, 50 and 60 °C. On the basis of fitting Eq. (4), it is possible to confirm that ln(k) appeared to change linearly with 1/T in the studied temperature range as expected for a single rate-limited thermally activated process.

lnðkÞ ¼ 3:25ð1=TÞ þ 2:555ðR2 ¼ 0:9937Þ Fig. 3. Effects of factors on conversion yield of transesterification process: (A) temperature; (B) molar ratio of methanol/oil; (C) catalyst amount.

fitted the equation with a high correlation (R2 = 0.9808). A second order reaction equation was also tried to fit the data, but the regression results did not correlate so well (R2 = 0.9148). Thus, we concluded that the transesterification process catalyzed by the resin in this study was a first order reaction and the rate constant (k) could be calculated using Eq. (2).

lnðC A0 =C A Þ ¼ kt

ð2Þ

where CA0 is the original concentration of substrate and CA is the real-time concentration of substrate.

ð4Þ

As shown in Table 4, the rate constant values of different temperatures were given. Furthermore, based on the results, the reaction temperature was proved to be a positive factor which was closely relative with the conversion efficiency of transesterification reaction. 3.4. Compared with conventional technology The selection of a technology for biodiesel production would mainly depend on the advantages and disadvantages such as conversion efficiency, complexity, total cost, environmental friendliness and safety. According to previous researches, the esterification reactions, which were heated using conventional reactors such as

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warmer and oil bath, were time-consuming (Ferrão-Gonzales et al., 2011). In order to reduce the reaction duration, microwave-assisted reactor, which was proved to be an alternative and effective heating system for chemical reactions, was introduced into the present study (Hsiao et al., 2011). Afterwards, the evaluation of conventional alkali catalyst and high alkaline anion exchange resin were carried out under same conditions. As comparison, even though the reaction duration required for the resin catalyst (75–80 min) was a little longer than that of using alkali catalyst (60 min), the conversion yields of both the microwave-assisted transesterification processes were similar. Moreover, there were no differences in the FAMEs composition of biodiesel products (Table 5). Nevertheless, the reusability and operational stability of resin catalyst were outstanding advantages which were different from conventional alkali catalyst. Furthermore, the resin was more easily to be separated from the biodiesel product, and large cost for removing the soluble alkali catalyst from the biodiesel product could be saved. Therefore, catalyzed transesterification process using high alkaline anion exchange resin was predominant to that using conventional alkali catalyst. 3.5. FAMEs analysis and properties evaluation of biodiesel product The chemical compositions of biodiesel product were determined by GC–MS, and the results were listed in Table 5. It was found that the product sample mainly contained six constituents: hexadecanoic acid methyl ester (1), octadecadienoic acid methyl ester (2), octadecenoic acid methyl ester (3), octadecanoic acid methyl ester (4), eicosenoic acid methyl ester (5) and docosenoic acid methyl ester (6). Furthermore, the predominant contents of biodiesel product from yellow horn seed oil were octadecenoic acid methyl ester (42.12%) and octadecadienoic acid methyl ester (30.40%). In order to evaluate the quality of biodiesel product prepared using resin catalyst, its main properties were determined against the relevant specification of biodiesel ASTM D-6751 standard. The results summarized in Table 6 showed that all of the measured values were in the range of test limit. Compared with the reported data, biodiesel produced from yellow horn seed oil was better in the properties of flash point (165 °C), acid value (0.06 mg KOH/g) and sulfated ash (0.003%). Therefore, the biodiesel produced from

Fig. 5. Kinetic data curves of transesterification process catalyzed by high alkaline anion exchange resin: (A) first order reaction; (B) second order reaction.

Table 4 Rate constants of the transesterification process. Reaction temperature (°C)

Rate constant (s1)

40 50 60

2.22  104 4.01  104 7.75  104

Table 5 FAME profiles and relative contents of biodiesel samples prepared using different catalysts. No.

Component

1 2 3 4 5 6

Relative content (%)

Palmitic acid methyl ester Linoleic acid methyl ester Oleic acid methyl ester Stearic acid methyl ester Eicosenoic acid methyl ester Docosenoic acid methyl ester

Anion exchange resin (Amberlite IRA-900)

Alkali (KOH)

5.27 42.12 30.40 2.03 10.09 3.49

5.94 41.27 29.04 3.12 9.78 3.67

Table 6 Main properties of yellow horn seed oil methyl esters against ASTM D-6751 standard and common biodiesel samples. Property 2

Viscocity at 40 °C (mm /s) Flash point (oC) Acid value (mg KOH/g) Cetane number Sulfated ash (% mass) Residues carbon (% mass) *

Reported by Rakesh et al. (2010). YHME is yellow horn seed oil methyl ester. b RSME is rapeseed oil methyl ester. c SBME is soybean oil methyl ester. a

Test method

Test limit

YHMEa

RSMEb,*

SBMEc,*

ASTM ASTM ASTM ASTM ASTM ASTM

1.9–6.0 Min. 130 Max. 0.80 Min. 47 Max. 0.015 Max. 0.50

4.4 165 0.06 56.1 0.003 0.02

4.4 150 0.10 57.3 0.010 0.02

4.5 160 0.15 55.8 0.008 0.02

D-445 D-93 D-664 D-613 D-874 D-524

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yellow horn seed oil using the presented technology was of high quality and could be exploited as an ideal substitution for the biodiesels produced from common edible oils. 3.6. Reusability of resin catalyst In the viewpoint of saving cost, the reusability of resin catalyst was investigated. In our experiments, it was found that the conversion kept stable at the first 7 runs. However, the conversion started to decrease gradually after the 7th run. This phenomenon was mainly relative to the fragmentation and loss during the process of reaction and reusing the catalyst. Nevertheless, a conversion yield of 70% could be still obtained even when transesterification process of the 10th run was finished. Hence, the advantage of biodiesel production using high alkaline anion exchange resin as heterogeneous catalyst was obvious. Nevertheless, in order to keep high conversion, it is necessary to add new resins regularly during transesterification process. 4. Conclusion In the present study, microwave-assisted transesterification process catalyzed by high alkaline anion exchange resin was proved to be a high-performance technology for biodiesel production. The catalytic mechanisms of typical ion exchange resins were clarified. From the viewpoints of environmental friendless and saving cost, the reusability and operational stability of the resin catalyst made it predominant to conventional alkali catalyst. Additionally, a comprehensive kinetic model for the transesterification process was established. In conclusion, this research formed a necessary basis for studies on the improvement of industrial biodiesel production using ion exchange resin as heterogeneous catalyst. Acknowledgements The authors gratefully acknowledge the financial supports by Special Fund of Forestry Industrial Research for Public Welfare of China (201004040), Agricultural Science and Technology Achievements Transformation Fund Program (2009GB23600514), Heilongjiang Province Science Foundation for Excellent Youths (JC200704), Project for Distinguished Teacher Abroad, Chinese Ministry of Education (MS2010DBLY031) and the Key Program for Science and Technology Development of Harbin (2009AA3BS083). References Arzamendi, G., Campoa, I., Arguinarena, E., Sanchez, M., Montes, M., Gandia, L.M., 2007. Synthesis of biodiesel with heterogeneous NaOH/alumina catalysts: comparison with homogeneous NaOH. Chem. Eng. J. 134, 123–130. Darnoko, D., Cheryan, M., 2000. Kinetics of palm oil transesterification in a batch reactor. J. Am. Oil Chem. Soc. 77, 1263–1267. Duffy, J.E., Canuel, E.A., Adey, W., Swaddle, J.P., 2009. Biofuels: algae. Science 326, 1345. Duz, M.Z., Saydut, A., Ozturk, G., 2011. Alkali catalyzed transesterification of safflower seed oil assisted by microwave irradiation. Fuel Process. Technol. 92, 308–313. Eskilsson, C.S., Björklund, E., 2000. Analytical-scale microwave-assisted extraction. J. Chromatogr. A 902 (1), 227–250. Feng, Y.H., He, B.Q., Cao, Y.H., Li, J.X., Liu, M., Yan, F., Liang, X.P., 2010. Biodiesel production using cation-exchange resin as heterogeneous catalyst. Bioresour. Technol. 101, 1518–1521.

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