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Preparation, characterization and application of heterogeneous solid base catalyst for biodiesel production from soybean oil
b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
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Preparation, characterization and application of heterogeneous solid base catalyst for biodiesel production from soybean oil Yihuai Li a, Fengxian Qiu a,*, Dongya Yang a, Xiaohua Li b, Ping Sun b a b
School of Chemistry and Chemical Engineering, Jiangsu University, Xuefu Road 301, 212013 Zhenjiang, PR China Jiangsu Provincial Key Laboratory of Power Machinery and Application of Clean Energy, 212013 Zhenjiang, PR China
article info
abstract
Article history:
A solid base catalyst was prepared by neodymium oxide loaded with potassium hydroxide
Received 24 September 2010
and investigated for transesterification of soybean oil with methanol to biodiesel. After
Received in revised form
loading KOH of 30 wt.% on neodymium oxide followed by calcination at 600 C, the catalyst
22 February 2011
gave the highest basicity and the best catalytic activity for this reaction. The obtained
Accepted 4 March 2011
catalyst was characterized by means of X-ray diffraction (XRD), Fourier transform infrared
Available online 24 March 2011
spectroscopy (FTIR), Scanning electron microscopy (SEM), Thermogravimetric analysis
Keywords:
catalyst has longer lifetime and maintained sustained activity after being used for five
Heterogeneous catalyst
times, and were noncorrosive and environmentally benign. The separate effects of the
Transesterification
molar ratio of methanol to oil, reaction temperature, mass ratio of catalyst to oil and
Biodiesel
reaction time were investigated. The experimental results showed that a 14:1 M ratio of
Potassium hydroxide
methanol to oil, addition of 6.0% catalyst, 60 C reaction temperature and 1.5 h reaction
Neodymium oxide
time gave the best results and the biodiesel yield of 92.41% was achieved. The properties of
(TGA), N2 adsorptionedesorption measurements and the Hammett indicator method. The
obtained biodiesel are close to commercial diesel fuel and is rated as a realistic fuel as an alternative to diesel. ª 2011 Elsevier Ltd. All rights reserved.
1.
Introduction
As conventional fuels are diminishing and environmental pollution is aggravating, alternative fuels have gained significant attention [1]. Biodiesel fuel, as a promising alternative diesel fuel to conventional fossil diesel produced by a catalytic transesterification of vegetable oils, animal fats and waste cooking oils with short chain alcohol, is becoming a favorable biofuel in many regions of the world [2,3], Compared to conventional diesel from petroleum, biodiesel is technically and economically more competitive because of its renewability, biodegradability, low emission profiles, high Flash point,
excellent lubricity and superior cetane number [4]. In addition, the use of biodiesel has the potential to reduce both the levels of pollutants and potential or probable carcinogens [5]. Biodiesel can be produced through transesterification of vegetable oils and fats with methanol in the presence of a suitable catalyst. In conventional homogeneous method of fatty acid methyl ester (FAME) synthesis, the removal of catalysts after reaction is unwanted step of biodiesel synthesis, where a large amount of wastewater is produced during neutralization the catalyst (NaOH or KOH) and FAME washing during separation from side products (glycerol, salt). Acidcatalyzed process often uses sulfonic acid and hydrochloric
* Corresponding author. Tel.: þ86 51188791800. E-mail address: [email protected] (F. Qiu). 0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2011.03.009
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acid as catalysts, however, the reaction time is very long (48e96 h) even at reflux of methanol, and a high molar ratio of methanol to oil is needed (30e150:1) [6]. Compared with homogeneous catalysts, heterogeneous catalysts can provide green and recyclable catalytic systems [7,8]. The advantage of heterogeneous catalyst usage is its fast and easy separation from the reaction mixture without requiring the use of neutralization agent. There are many solid heterogeneous acid- and alkali-catalysts for biodiesel synthesis. Tungstated zirconia (WO3/ZrO2) was prepared by method of impregnation was a promising heterogeneous acid catalyst [9]. Various carbohydrate-derived and a carbon-based solid acid catalyst [10,11] have good catalytic activity to high free fatty acid-containing waste oils. Unfortunately, the performances of these acid catalysts are still inferior compared with the base catalysts. For this reason, a wide variety of solid bases have been examined for transesterification reactions for biodiesel synthesis. Example include CaO [12], SrO [13], KNO3 loaded on flyash [14], ZnOeLa2O3 [15] and zinc aluminate [16]. But, these heterogeneous catalysts require a high temperature to achieve the high conversion. Other heterogeneous base catalysts like CaMnO3 [17], KNO3/Al2O3 [18], and MgeAl hydrotalcites [19] have also demonstrated some potential for activity in production of biodiesel. However, these catalysts need more time (more than 3 h) to reach the higher biodiesel yield. The result will increase the production cost due to the requirements for high temperatures and a long time operation. Neodymium oxide (Nd2O3) or rare earth sesquoxides is widely used in various applications such as photonic, luminescent materials, catalyst for automotive industry, UV absorbent, glass-polishing materials, and protective coatings. However, in this work, a new type of catalyst for biodiesel synthesis with KOH as active component on neodymium oxide support was synthesized using the way of impregnation, and reported the activity and selectivity of the basic solids for the transesterification of soybean oil with methanol. A screening of the reaction conditions has been carried out by examining the effect of the concentration of catalyst, the initial methanol/ oil, catalyst/oil molar ratio, reaction temperature and time.
2.
Experimental
2.1.
Materials
Soybean oil was purchased from Jinlongyu Company (Fujian, China). Methanol, zirconium dioxide (ZrO2), titanium dioxide (TiO2), alumina (Al2O3), neodymium oxide (Nd2O3), potassium hydroxide (KOH), potassium iodide (KI), potassium bromate (KBrO3), potassium hydrogen phthalate (C8H5O4K) and potassium nitrate (KNO3) were obtained from Sinopharm Chemical Reagent Co. Ltd., (Shanghai, China). All solvents were AR grade and were used without purification.
2.2.
Preparation of catalyst
All the catalysts were prepared by incipient wetness impregnation of different porous medium supports with solution of potassium compounds. For this purpose, the required amount of aqueous KOH solution was slowly added to the support and
kept 24 h. The catalytic carrier was previously calcined in a muffle for 12 h at 600 C. After impregnation, the catalysts were dried for 12 h at 100 C and then the solid was calcined in a muffle furnace at designed temperature for 12 h before use for the reaction.
2.3.
Characterization of the catalyst
FT-IR spectra of the samples were obtained between 4000 and 400 cm1 on a KBr powder with an FTIR spectrometer (AVATAR 360, Nicolet, Madison, USA). A minimum of 32 scans was signalaveraged with a resolution of 2 cm1 in the 4000e400-cm1 range. Scanning electron microscopy (SEM) images were obtained with 20-kV accelerating voltage with a field emission scanning electron microscope (S-4800, HITACHI Corp., Tokyo, Japan). X-ray diffraction (XRD) patterns of selected samples were obtained were recorded by the reflection scan with nickelfiltered Cu Ka radiation (D8, Bruker-AXS, Germany). The X-ray generator was run at 40 kV and 70 mA. All the XRD measurements were performed at 2q values between 10 and 80 . Thermogravimetric analysis (TGA) was performed on a Netzsch instrument (STA 449C, Netzsch, Seligenstadt, Germany). The programmed heating range was from room temperature to 1300 C, at a heating rate of 10 C/min under a nitrogen atmosphere. The measurement was taken using 6e10 mg samples. The nitrogen adsorption and desorption isotherms were measured at 196 C using a NDVA2000e analytical system made by Quntachrome Corporation (USA). The specific surface area was calculated by Brunauer-Emmett-Teller (BET) method. Pore size distribution and pore volume were calculated by Barrett-Joyner-Halenda (BJH) method. Hammett indicator experiments were conducted to determine the basic strength of each catalyst. The Hammett indicators used were bromothymol blue (pKa ¼ 7.2), phenolphthalein (pKa ¼ 9.8), 2,4-dinitroaniline (pKa ¼ 15), and 4-nitroaniline (pKa ¼ 18.4). Typically, 300 mg of the catalyst was mixed with 1 mL of a solution of Hammett indicators diluted in 10 mL methanol and allowed to sit for at least 2 h. After the equilibration, the color of the catalyst was noted. The basic strength of the catalyst was taken to be higher than the weakest indicator that underwent a color change and lower than the strongest indicator that underwent no color change. To measure the basicity of solid bases, the method of Hammett indicatorbenzene carboxylic acid (0.02 mol/L anhydrous ethanol solution) titration was used.
2.4. Transesterification of soybean oil and chemical analyses The transesterification reactions were performed at 60 C in a 125 ml three-neck reaction flask equipped with a condenser by refluxing 10 mL of methanol (247 mmol) with 15.82 g of soybean oil (commercial edible grade, acid value ¼ 0.976 mg KOH/g, saponification index ¼ 188.6 mg KOH/g, and average molecular weight ¼ 896.88 g/mol) and 0.95 g of catalyst (6 wt.%). The catalyst was activating at 773 K for 12 h before use for the reaction. After the reaction completion, the samples were separated from catalyst and glycerol by centrifuge. The glycerol could be separated because it was insoluble in the esters
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and had a much higher density. Then methanol was removed using rotary evaporation and the obtained product was analyzed by gas chromatography (GC) to determine the biodiesel yield (fatty acid methyl ester, FAME). Reference materials and samples were analyzed by a 7890A gas chromatograph (Agilent Technology Inc. USA), equipped with a flame-ionization detector (FID) and a HP-5 capillary column (30 m 0.32 mm 0.25 mm). Helium was used as the carrier gas. The oven temperature ramp program was 135 C for 10 min, 170 C at 10 C/min, and held for 10 min. 250 C at 25 C/ min, and held 2 min. The flow rate of hydrogen was 30 ml/min and the flow rate of air was about 400 ml/min. Temperatures of the injector and detector were 280 and 300 C. The injection was performed in split mode with a split ratio of 100:1. Biodiesel yield was quantified in the presence of tricaprylin as an internal standard. The analysis of biodiesel for each sample was carried out by dissolving 1 ml of biodiesel sample into 5 ml of n-hexane and injecting 0.5 ml of this solution in GC, in the same condition described as above. The biodiesel yield was calculated from the content of methyl esters analyzed by GC with the following equation: Biodiesel yield ¼
mtricaprylin AB ftricaprylin 100% Atricaprylin ms
(1)
where mtricaprylin ¼ weight of the internal standard, AB ¼ peak area of FAME, ftricaprylin ¼ response factor, Atricaprylin ¼ peak area of the internal standard, and ms ¼ weight of the sample. Determination of sulfur content of biodiesel was measured by Inductively Coupled Plasma Emission Spectrometer (ICP) using Intrepid XP Radial ICP-OES (VISTA-MPX, Varian, USA) with a concentric nebulizer and CCD detectors technology. Flash point was determined by a closed-cup tester (BF-02, Dalian North Analytical Instruments Co., Ltd.), using ASTM D 93.
3.
Results and discussion
3.1.
Screening of catalyst
The catalytic activity screening of Nd2O3 loaded with different potassium compounds (KOH, KI, KBrO3, C8H5O4K or KNO3) in the soybean oil transesterification was performed. The results were summarized Table 1. To make direct comparisons, the same reaction conditions, as shown in Table 1, were employed for each catalyst in all experiments. The reaction conditions were not optimized for the highest reaction yield; however, they provided a way to compare the activities of the catalysts. Obviously, it is observed from Table 1 that pure Nd2O3 and KOH catalyst exhibited no activity and serious saponification phenomenon due to excess KOH amount [20], respectively. However, when potassium compounds were loaded on Nd2O3 and activated at high temperatures, the supported catalysts except KNO3/Nd2O3 showed catalytic activities. Thus, it is essential to support potassium compounds on Nd2O3 to generate the catalytic activities for the transesterification reaction. Among the catalysts tested, Nd2O3 loaded with KOH, KI, KBrO3 or C8H5O4K exhibited comparatively high activities, giving biodiesel yields higher than 80%. Especially, KOH/Nd2O3 demonstrated the superior catalytic activity compared to the
Table 1 e Catalytic activity and base strength of Nd2O3 loaded with different potassium compounds. Basic strength (pKBHþ)
Biodiesel yield (%)
Nd2O3 KOH
<7.2 15e18.4
KOH/Nd2O3 KBrO3/Nd2O3 KI/Nd2O3 C8H5O4K/Nd2O3 KNO3/Nd2O3
9.8e15 7.2e9.8 <7.2 7.2e9.8 <7.2
No reaction Serious saponification phenomenon 89.7 74.06 17.05 32.03 No reaction
Catalyst
Transesterification condition: methanol/oil molar ratio, 12:1; catalyst amount 6 wt.%; reaction time, 3 h; reaction temperature, 60 C. All catalysts were activating at 600 C for 12 h before use for the reaction.
other catalysts. When the transesterification was conducted over the KOH/Nd2O3 catalyst, the highest biodiesel yield of 89.7% was achieved. Over KBrO3/Nd2O3, KI/Nd2O3 and C8H5O4K/Nd2O3 catalysts, however, the lower biodiesel yields in the range of 17.05e74.06% were obtained, attributable to their relatively low catalytic activities. Based on these results, the catalytic activity is in the following order: KOH/Nd2O3 > KBrO3/Nd2O3 > C8H5O4K/ Nd2O3 > KI/Nd2O3 > KNO3/Nd2O3. The base strengths of Nd2O3 modified with different potassium compounds were measured by using Hammett indicators. As evident in Table 1, loading of KBrO3, or C8H5O4K on the surface of Nd2O3 generated the weaker basic sites with pKBHþ in the range of 7.2e9.8. Taking both the base strength and the catalytic activity into account, we can conclude that the observed activities of Nd2O3-supported catalysts seem to be related to their base strengths, i.e. the higher base strengths of the catalysts result in the higher conversions. In particular, the KI/Nd2O3 or KNO3/Nd2O3 sample possessed the weakest base strength in the range of pKBHþ<7.2, consequently exhibiting weak or no catalytic activity. As for the catalytic sites on KOH/ Nd2O3 sample, it can also be proposed that the K2O species, which was possibly formed by dehydroxylation of the OH groups, was at least a part of catalytically active sites. As remarked above, it seems that the transesterification reaction needs strongly basic sites. The effect of supports on the activity of the catalyst was listed in Table 2. Obviously, when KOH was supported on
Table 2 e Catalytic activities and base strengths of KOH supported on the different carriers. Catalyst KOH/TiO2 KOH/ZrO2 KOH/Al2O3 KOH/Nd2O3
Basic strength (pKBHþ) 9.8 < 9.8 < 9.8 < 9.8 <
H H H H
< < < <
15 15 15 15
Biodiesel yield (%) 86.47 85.43 88.87 89.70
Transesterification condition: methanol/oil molar ratio, 12:1; catalyst amount, 6 wt.%; reaction time, 3 h; reaction temperature, 60 C. All catalysts were activating at 600 C for 12 h before use for the reaction.
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Table 3 e The effect of KOH loading amounts on the biodiesel yield. KOH loading amount (%) Basic strength (pKBHþ) Biodiesel yield (%)
14
17
25
30
32
9.8 < H < 15 80.47
9.8 < H < 15 81.52
9.8 < H < 15 85.72
9.8 < H < 15 89.52
9.8 < H < 15 73.45
Transesterification condition: methanol/oil molar ratio, 15:1; catalyst amount, 6 wt.%; reaction time, 3.0 h; reaction temperature, 60 C.
different carriers, the base strengths were almost equality, but the activity of the catalyst was different greatly. KOH/Nd2O3 was the most active catalyst for the transesterification reaction, giving a conversion of 89.70%. Over KOH/ZrO2, KOH/ Al2O3 and KOH/TiO2 catalysts, even though they possessed different centers of a base strength, the high biodiesel yields of 85.43%, 88.87% and 86.47% were also achieved, respectively. Thus, Nd2O3 can be regarded as the best support. From these discussions, KOH/Nd2O3 showed the best catalytic activity. On account of the high activity of the catalysts in the transesterification reaction, KOH/Nd2O3 was, therefore, selected for further investigation and its properties were studied in more detail. A 14 wt.% (KOH to Nd2O3 weight ratio) KOH on Nd2O3 support was prepared by an impregnation method and the following procedure: a solid Nd2O3 support (25 g) was mixed with KOH (3.5 g) in 15 mL of water, and the resulting solid was dried in an oven at 90 C for 24 h. The solid was then crushed and calcined in air at 600 C for 12 h. Similarly, 17, 25, 30 and 32 wt.% KOH loaded Nd2O3 were prepared. The effect of KOH loading amounts on the biodiesel yield was shown in Table 3. It can be seen from Table 3 that when the loading amount of KOH increased from 14 wt.% to 30 wt.%, the biodiesel yield increased from 80.47% to 89.52%. Then, the biodiesel yield decreased with the loading amount of KOH. This is because the base strength of catalyst increases with the loading amount of KOH. On the other hand, the catalytic activity and activity sites also increase with the loading amount of KOH. But, with further increase in the amount of loaded KOH, the basicity may decrease the surface basic sites, which resulted in a drop of the catalytic activity towards the reaction. This is presumably due to the coverage of surface basic sites by the excessive KOH. These sites are inaccessible to incoming reactants when the amount of loaded KOH exceeded 30 wt.%. Therefore, catalytic activity and biodiesel yield decreased. On the basis of the results, the optimum loading amount of KOH was 30 wt.%. Moreover, the biodiesel yield of 30 wt.% KOH/Nd2O3 sample calcined at different temperatures was measured by the same method, and the results are presented in Table 4. From the Table 4, it can be observed that the maximum biodiesel yield, reaching 90.02%, was obtained at a calcination temperature of 600 C. But, a low level of biodiesel yield was observed below
512 and above 700 C. Obviously, the biodiesel yield changes with calcination temperatures parallel the changes in the catalytic activity for the transesterification reaction. Based on these results, the optimal preparation conditions of the catalyst are load KOH, support Nd2O3, loading amount 30% and calcination temperature of 600 C. Therefore, 30 wt.% KOH/Nd2O3 catalyst was selected for further investigation of transesterification of soybean oil.
3.2.
Catalyst characterizations
A series of catalysts were synthesized by incipient wetness impregnation method and calcined at 600 C. In this high temperature, KOH decomposed into K2O. The powder X-ray diffraction patterns of KOH/Nd2O3 samples with various loading amounts of KOH were presented in Fig. 1. As can be seen, when the loading amount of KOH was 14 wt.% (curve a), diffraction peaks (2q ¼ 27.4 , 30.9 , 40.5 , 47.6 and 57.2 ) assigned to the amorphous Nd2O3 support were registered on the XRD patterns, and only a specie such as K2O (2q ¼ 29.6 ) was observed, indicating the good dispersion of K2O on Nd2O3 in the form of a monolayer due to the interaction between K2O and the surface of the support at a low loading of KOH. And when the loading amount of KOH was further increased to 25 wt. % (curve b), the new phase of K2O can be observed at 32.1 and 51.6 . But, when the loading amount of KOH is further increased to over 30 wt. % (curves c and d), a new phase of a compound containing potassium and neodymium elements could be observed at 2q ¼ 25.8 , 38.8 and 41.2 [21]. The phenomena can be a result from the incorporation of Kþ ions into the vacancies in the structure of the neodymium oxide, or Kþ ions may react with hydroxyl groups to form NdeOeK on the surface during heat treatment. The result will confirm by FT-IR spectrum of catalyst. Moreover, the intensi ties of some diffraction peaks (2q ¼ 29.6 , 32.1 , 38.8 , 41.2 and 51.6 ) increased with increase of the loading amount of KOH. On the other hand, the characteristic peaks of Nd2O3 (27.4 , 30.9 , 40.5 , 47.6 and 57.2 ) were almost unchanged on the XRD patterns regardless of the loading amount of KOH. It is noteworthy that the solidestate reaction between the guest compound and the surface of the support in the activation process is favorable for the catalyst to get a high catalytic
Table 4 e The effect of calcination temperature on the biodiesel yield. Calcination temperature ( C) Basic strength (pKBHþ) Biodiesel yield (%)
311
422
512
600
700
790
9.8 < H < 15 78.80
9.8 < H < 15 81.23
9.8 < H < 15 81.00
9.8 < H < 15 90.02
9.8 < H < 15 77.83
9.8 < H < 15 73.50
Transesterification condition: methanol/oil molar ratio, 12:1; catalyst amount, 6 wt.%; reaction time, 3.0 h; reaction temperature, 60 C.
b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
Fig. 1 e XRD patterns of (a) 14 wt.% KOH/Nd2O3, (b) 25 wt.% KOH/Nd2O3, (c) 30 wt.% KOH/Nd2O3, (d) 32 wt.% KOH/Nd2O3.
activity. In the case of KOH/Nd2O3, the Kþ ion of KOH could insert in the vacant sites of Nd2O3, accelerating dissociative dispersion and decomposition of KOH to form basic sites in the activation process. The more potassium compounds are loaded on the Nd2O3, the more free vacancies decrease, which results in the surface enrichment of potassium species that is probably considered to be the active sites for base-catalyzed reactions. When the amount of potassium cations loaded on Nd2O3 was below the saturation uptake of Kþ, it could be well dispersed. As a result, the number of basic sites together with the activities of the catalysts would increase with the potassium contents. However, if Nd2O3 was loaded with too much KOH, the KOH could not be well dispersed and, for this reason, not all but only a part of the loaded KOH could be decomposed. Moreover, as mentioned in the preceding sections, the excess KOH would cover the basic sites on the surface of the catalysts resulting in a lowered catalytic activity (Table 3). SEM images of Nd2O3 and 30 wt.% KOH/Nd2O3 catalyst were shown in Fig. 2. The SEM photographs of Nd2O3 and KOH/
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Nd2O3 samples showed the crystallites of 0.2e1 mm size. Evidently, as shown in Fig. 2, no important difference was observed between Nd2O3 and KOH/Nd2O3 samples, thus suggesting a good dispersion of KOH on the surface of Nd2O3. Based on these results, after loading of KOH, Nd2O3 retained its structure that was important for catalysis and therefore the potassium species was found highly distributed upon the surface of the support. FTIR spectra of Nd2O3 and KOHeNd2O3 catalyst were recorded and shown in Fig. 3. The spectrum of the support shows sharp peak at 1475 cm1. From the spectrum of catalyst, the new peaks at 880 and 706 cm1 are attributed to the KeO and KeOeNd bonds, respectively. Furthermore, the broad band at around 3100e3300 cm1 region could be partly assigned to the stretching vibration of NdeOeK groups [22] which Kþ ions could replace the protons of isolated hydroxy groups to form NdeOeK groups in the activation process and were probably considered to be the active species of this catalyst. This achieves the same results as the XRD analysis. However, this vibration is well overlapped with the broad vibration band of OH groups which is ascribed to OH stretching vibration of the hydroxyl groups attached to the ctalyst surface, in addition to water molecules absorbed from the atmosphere. The BET surface area, pore volume, and pore diameter of Nd2O3 and 30 wt.% KOH/Nd2O3 catalyst were measured. The BET surface area as well as the pore volume decreased with loading potassium hydroxide, and this tendency was more outstanding in the case of potassium. The thermal behavior of 30 wt. % KOH/ Nd2O3 sample was shown in Fig. 4. This figure showed that the first weight loss at lower temperature (<200 C) corresponds to the water loss from internal and external surfaces of the samples. The second weight loss (200e400 C), is due to the decomposition of the KOH and K2CO3. The last weight loss at above 400 C is attributed to the decomposition of the K2O and the residual hydroxyl groups bonded to the oxide lattice. The decomposition products of KOH, probably forming both K2O species and NdeOeK groups in the composite, were possibly the main active sites for the transesterification reaction. In this study, effect of repeated use of KOH/Nd2O3 catalyst on biodiesel yield was investigated in the optimal transesterification reaction conditions. The result in Table 5 indicated that the biodiesel
Fig. 2 e SEM images of (a) Nd2O3 and (b) 30 wt.% KOH/Nd2O3.
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Table 5 e Effect of repeated use of KOH/Nd2O3 catalyst on biodiesel yield. Repeated times
1
2
3
4
5
Biodiesel yield (%)
90.11
90.07
90.06
90.04
90.05
Transesterification condition: methanol/oil molar ratio, 12:1; catalyst amount, 6 wt.%; reaction time, 1.5 h; reaction temperature, 60 C.
Fig. 3 e FT-IR spectra of Nd2O3 and catalyst.
yields had no significant changes and were in excess of 90% during the repeated experiments. It maintained sustained activity even after being used for five times and the biodiesel yield was only slightly decreased from 90.11% to 90.05%. This was because neodymium oxide compounds are dissolvable in methanol.
3.3. Influence of the transesterification reaction conditions The transesterification process consists of a sequence of three consecutive reversible reactions where the triglyceride is successively transformed into diglyceride, monoglyceride, and finally into glycerin and the FAME. The molar ratio of methanol to soybean oil is one of the important factors that affect the conversion to methyl esters. Stoichiometrically, 3 mol of methanol are required for each mole of triglyceride, but in practice a higher molar ratio is employed in order to drive the reaction towards completion and produce more methyl esters
Fig. 4 e Thermogravimetric analysis of 30 wt. % KOH/ Nd2O3.
as products. This is because that the biodiesel yield could be improved by introducing excess amounts of methanol to shift the equilibrium to the right-hand side. As represented in Fig. 5, the biodiesel yields grew as the methanol-loading molar ratio increased, and the biodiesel yield was increased considerably. The maximum biodiesel yield (90.59%) was obtained when the molar ratio was very close to 14:1. In comparison, the biodiesel yield increased from 77.49% to 90.59% when the molar ratio was increased from 6:1 to 14:1. However, beyond the molar ratio of 14:1, the excessively added methanol had no significant effect on the production yield and the biodiesel yield was 90.12% at 16:1. The reason is that the catalyst content decreased with increase of methanol content. Therefore, we could conclude that to elevate the biodiesel production yield an excess methanol feed was effective to a certain extent and the optimum molar ratio of methanol to oil was 14:1. The dependence of the biodiesel yield on the reaction time was investigated. The reaction time was varied in the range 0.5e8 h. Fig. 6 revealed that the transesterification reaction was strongly dependent on reaction time, at the beginning (<0.5 h), the reaction was slow due to the mixing and the dispersion of methanol into oil, and the biodiesel yield was increased very fast in the reaction time range between 0.5 and 1.5 h. Moreover, excess reaction time leaded to a bit reduction in the product yield due to the backward reaction transesterification, resulting in a loss of esters as well as causing more fatty acids to form soaps [23,24]. So the optimum reaction time was obtained at 1.5 h.
Fig. 5 e Effect of different molar of methanol to oil on the biodiesel yield (catalyst amount, 6 wt.%; reaction time, 3.0 h; reaction temperature, 60 C).
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Fig. 6 e Effect of reaction time on the biodiesel yield (methanol/oil molar ratio, 14:1; catalyst amount, 6 wt.%; reaction temperature, 60 C).
In the presence of heterogeneous catalysts, the reaction mixture constitutes a three-phase system, oilemethanol-catalyst, in which the reaction would be slowed down because of the diffusion resistance between different phases. However, the reaction rate can be accelerated at higher reaction temperatures. In this paper, the synthesis of biodiesel from soybean oil was conducted at various temperatures (40 C, 50 C, 60 C, 65 C and 70 C). As shown in Fig. 7, the reaction rate was slow at low temperatures, but the biodiesel yield first increased and then decreased with the increase of the reaction temperature. Generally, a more rapid reaction rate could be obtained at high temperatures, which is due to the endothermic nature of transesterification reaction [25], but at high temperatures, methanol was vaporized and formed a large number of bubbles, which inhibited the reaction on the three-phase interface. The optimum reaction temperature was 60 C and biodiesel yield arrived at 92.41%.
Fig. 8 e Effect of catalyst amount on the biodiesel yield (methanol/oil molar ratio, 14:1; reaction time, 2.0 h; reaction temperature, 60 C).
When increasing the amount of loading catalyst, the slurry (mixture of catalyst and reactants) was become too viscous giving rise to a problem of mixing and a demand of higher power consumption for adequate stirring. On the other hand, when the catalyst loading amount was not enough, maximum biodiesel yield could not be reached. To avoid this kind of problem, an optimum amount of catalyst loading had to be investigated. The influence of the catalyst amounts was studied at a 14:1 M ratio of methanol to soybean oil at reflux of methanol for 2 h. The catalyst amount was varied in the range of 1.0% and 9.0%. These percentages were weight fractions of the oil supplied for this reaction. The reaction profile of Fig. 8 indicated that the transesterification reaction was strongly dependent upon the catalyst applied. As is evident from Fig. 8, when the catalyst amount increased from 1.0% to 6.0%, the biodiesel production yield was increased. However, with further increase in the catalyst amount the biodiesel yield was
Table 6 e The various absorption peaks of biodiesel. Group Wavenumber attribution (cm1)
Fig. 7 e Effect of reaction temperature on the biodiesel yield (methanol/oil molar ratio, 14:1; catalyst amount, 6 wt.%; reaction time, 1.5 h).
3462.27 3008.91 2925.76
eOH ¼ CeH eCH2
2855.00
eCH2
1743.54 1461.48 1360.75 1017.78
eC]O eCH2 eCH3 CeOeC
1171.41
CeOeC
722.75
eCH2
Vibration type Stretching Stretching Asymmetric stretching vibration Symmetric stretching vibration Stretching Shear-type vibration Bending vibration Anti-symmetric stretching vibration Symmetric stretching vibration Plane rocking vibration
Absorption intensity Weak Strong Strong Strong Strong Middling Middling Weak Middling Weak
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Table 7 e The properties of ICP-OES spectrometer. Type
Intrepid XP Radial ICP-OES
Nebulizer RF-generator Power Reflected power Observation high Optical system Grating Focal length Optical range Resolution Detector Emission lines used For the S analysis
Concentric, with a cyclonic spray chamber 40.68 MHz crystal-controlled 1200 W 20 W 6 mm above the coil Czerny-Turner vacuum-monochromator Holographic, 1800 groves/mm 0.75m 160e800 nm 1st order: 0.018 nm Photomultiplier l1 ¼ 180.731 nm l2 ¼ 181.970 nm
decreased, which was possibly due to a mixing problem involving reactants, products and solid catalyst. The optimum catalyst loading amount was found to be 6.0% in this system and the maximum biodiesel yield reached to 92.40%. From the above results, the reaction does not require too much time to dispose of the products, for example, neutralization, washing and drying. If the catalyst can be used commercially, filtration is a possible way to recycle the catalyst and decrease the cost. As a heterogeneous solid base catalyst, the prepared KOH/Nd2O3 catalyst has a longer catalyst lifetime and better stability than current homogeneous catalysts. It is noncorrosive and environmentally benign. It can be applied to produce biodiesel commercially.
3.4.
Characterization and properties of biodiesel
FT-IR spectrum of the obtained biodiesel was listed in Table 6. From the analysis of the Table 6, we could get the sample including all groups which we needed. At the same time, it proved that the compound was the kind of structures having long-chain fatty acid esters. The content of sulfur and its proper determination play an important role regarding fuels and products of petrochemical industry. The problem of appropriate determination of sulfur is important both from environmental and analytical aspects,
because some specifications order to the compulsion decrease of the concentration of sulfur (e.g. from 2005 their maximum concentration is 50 mg/kg in fuels in the countries of European Union). Over the past few decades, there are numerous spectroscopic techniques to analyze the qualitative and quantitative elemental composition of fuels. For example, inductively coupled plasma atomic emission spectroscopy (ICPeAES), inductively coupled plasma mass spectroscopy (ICPeMS) and flame or graphic furnace atomic absorption spectroscopy (AAS) were adopted. Each technique has advantageous properties in terms of analytical figures of merit. The atomic absorption and emission techniques are typically used for analysis of the products of hydrocarbon industry. The ICP technique is a fast analytical method, but needs preliminary sample preparation (e.g. digestion). In this work, the sulfur content of biodiesel was carried out by Inductively Coupled Plasma Emission Spectrometer (ICP) using Intrepid XP Radial ICP-OES (VISTA-MPX, Varian, USA) with a concentric nebulizer and CCD detectors technology. After performing the background equivalent concentration experiment to test the instrument sensitivity, the ICP operating conditions applied are presented in Table 7. In order to determine the sulfur content, the biodiesel was carried out by nitrification firstly. A certain amount of biodiesel was added to concentrated hydrochloric acid (8 mL) and concentrated nitric acid (2 mL), and placed overnight. Subsequently, the mixture was gently filtered and got clear liquid, then the clear liquid was evaporated in the fuming cupboard about 20 min. Calibration standards were made up from some standard solutions of sulfur. The ranges of the calibration curves (5 points) were selected to match the expected different concentrations standard solution for the sulfur element of the sample investigated. Linearity was checked in the range of 0e40 mg/g. From the calibration curve, the sulfur content of biodiesel was obtained. The sulfur content of the obtained biodiesel was listed in Table 8. The properties of biodiesel, density, cetane number, flash point, cold filter plugging point, acid number, water content, ash content and total glycerol content, were determined and listed in the Table 8. Table 8 also showed comparisons of the obtained biodiesel and the standards of biodiesel in china, Europe and the United States. The properties of the obtained biodiesel, in general, show many similarities, and therefore,
Table 8 e Comparison of properties of the obtained biodiesel and the standards of biodiesel in china, Europe and the United States. Item
Obtained biodiesel 1
China GB/T 20828e2007
USA ASTM D 6751e03
Density (kg L ) Flash point ( C) Cold filter plugging point ( C)
0.896 (20 C) 168 5.0
0.82e0.90 (20 C) 130 e
0.82e0.90 (20 C) ＞130 e
Sulfur content (w/w,%) Cetane value Acid value (KOH) (mg g1) Water content (w/w,%) Ash content (w/w,%) Total glycerol content (w/w,%)
0.0065 56 0.6 0.04 0.018 0.020
0.05 49 0.8 0.05 0.05 0.024
0.0015 47 ＜0.8 0.05 0.02 0.024
Europe EN 14214 0.86e0.90 (15 C) ＞120 Spring:0 Summer:10 Autumn:20 ＜0.001 ＞51 ＜0.5 0.05 0.02 0.025
b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
the properties of obtained biodiesel from the soybean oil is rated as a realistic fuel as an alternative to diesel.
4.
Conclusions
Nd2O3 loaded with KOH, which was prepared by impregnation of powdered Nd2O3 with an aqueous solution of KOH followed by calcination at a high temperature, showed high catalytic activities for the transesterification reaction. Both the K2O species formed by the thermal decomposition of loaded KOH, and the surface KeOeNd groups formed by saltesupport interactions, were probably the main reasons for the catalytic activity towards the reaction. The activities of the heterogeneous base catalysts correlated with their corresponding basic properties. The catalyst with 30 wt.% KOH loading on Nd2O3 and calcined at 600 C for 12 h was found to be the optimum catalyst, which gave the best catalytic activity. When the reaction was carried out at reflux of methanol, with a molar ratio of methanol to oil of 14:1, a reaction time 1.5 h, a reaction temperature 60 C and a catalyst amount 6.0%, the highest biodiesel yield reached 92.41%. The properties of obtained biodiesel from soybean oil are close to commercial diesel fuel and is rated as a realistic fuel as an alternative to diesel.
Acknowledgment This project was supported by the Natural Science of Jiangsu Province (BK2008247), Jiangsu Provincial Key Laboratory of Power Machinery and Application of Clean Energy Foundation (QK08007).
references
[1] Fukuda H, Kondo A, Noda H. Biodiesel fuel production by transesterification of oils. J Biosci Bioeng 2001;92:405e16. [2] Marchetti JM, Miguel VU, Errazu AF. Possible methods for biodiesel production. Renew Sust Energ Rev 2007;11:1300e11. [3] Qiu FX, Li YH, Yang DY, Li XH, Sun P. Biodiesel production from mixed soybean oil and rapeseed oil. Appl Energ 2011;88:2050e5. [4] Meher LC, Kulkarni MG, Dalai AK, Naik SN. Transesterification of karanja (Pongamia pinnata) oil by solid basic catalysts. Eur J Lipid Sci Tech 2006;108:389e97. [5] Singh SP, Singh D. Biodiesel production through the use of different sources and characterization of oils and their esters as the substitute of diesel: a review. Renew Sust Energ Rev 2010;14:200e16. [6] Lotero E, Liu Y, Lopez DE, Suwannakarn K, Bruce DA, Goodwin Jr JG. Synthesis of biodiesel via acid catalysis. Ind Eng Chem Res 2005;44:5353e63. [7] Qiu FX, Li YH, Yang DY, Li XH, Sun P. Heterogeneous solid base nanocatalyst: preparation, characterization and application in biodiesel production. Bioresour Technol 2011; 102:4150e6.
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[8] Sakai T, Kawashima A, Koshikawa T. Economic assessment of batch biodiesel production processes using homogeneous and heterogeneous alkali catalysts. Bioresour Technol 2009; 100:3268e76. [9] Park YM, Lee JY, Chung SH, Park IS, Lee SY, Kim DK, et al. Esterification of used vegetable oils using the heterogeneous WO3/ZrO2 catalyst for production of biodiesel. Bioresour Technol 2010;101:S59e61. [10] Lou WY, Zong MH, Duan ZQ. Efficient production of biodiesel from high free fatty acid-containing waste oils using various carbohydrate-derived solid acid catalysts. Bioresour Technol 2008;99:8752e8. [11] Shu Q, Gao J, Nawaz Z, Liao Y, Wang D, Wang J. Synthesis of biodiesel from waste vegetable oil with large amounts of free fatty acids using a carbon-based solid acid catalyst. Appl Energ 2010;87:2589e96. [12] Liu X, He H, Wang Y, Zhu S, Piao X. Transesterification of soybean oil to biodiesel using CaO as a solid base catalyst. Fuel 2008;87:216e21. [13] Liu X, He H, Wang Y, Zhu S. Transesterification of soybean oil to biodiesel using SrO as a solid base catalyst. Catal Commun 2007;8:1107e11. [14] Kotwal MS, Niphadkar PS, Deshpande SS, Bokade VV, Joshi PN. Transesterification of sunflower oil catalyzed by flyash-based solid catalysts. Fuel 2009;88:1773e8. [15] Yan S, Salley SO, Ng KYS. Simultaneous transesterification and esterification of unrefined or waste oils over ZnO-La2O3 catalysts. Appl Catal A-Gen 2009;353:203e12. [16] Bournay L, Casanave D, Delfort B, Hillion G, Chodorge JA. New heterogeneous process for biodiesel production: a way to improve the quality and the value of the crude glycerin produced by biodiesel plants. Catal Today 2005;106:190e2. [17] Kawashima A, Matsubara K, Honda K. Development of heterogeneous base catalysts for biodiesel production. Bioresour Technol 2008;99:3439e43. [18] Xie W, Peng H, Chen L. Transesterification of soybean oil catalyzed by potassium loaded on alumina as a solid-base catalyst. Appl Catal A-Gen 2006;300:67e74. [19] Xie W, Peng H, Chen L. Calcined MgeAl hydrotalcites as solid base catalysts for methanolysis of soybean oil. J Molecul Catal A-Chem 2006;246:24e32. [20] Helwani Z, Othman MR, Aziz N, Fernando WJN, Kim J. Technologies for production of biodiesel focusing on green catalytic techniques: a review. Fuel Process Technol 2009;90: 1502e14. [21] Noiroj K, Intarapong P, Luengnaruemitchai A, Jai-In S. A comparative study of KOH/Al2O3 and KOH/NaY catalysts for biodiesel production via transesterification from palm oil. Renew Energ 2009;34:1145e50. [22] Krupay BW, Amenomiya Y. Al-kali-promoted alumina catalysts: I. Chemisorption and oxygen exchange of carbon monoxide and carbon diox-ide on potassium-promoted alumina catalysts. J Catal 1981;67:362e70. [23] Eevera T, Rajendran K, Saradha S. Biodiesel production process optimization and characterization to assess the suitability of the product for varied environmental conditions. Renew Energ 2009;34:762e5. [24] Ma F, Clement LD, Hanna MA. The effects of catalyst, free fatty acids, and water on transesterification of beef tallow. Trans Am Soc Agric Eng 1998;41:1261e4. [25] Wen ZZ, Yu XH, Tu ST, Yan JY, Dahlquist E. Biodiesel production from waste cooking oil catalyzed by TiO2eMgO mixed oxides. Bioresour Technol 2010;101:9570e6.
Available at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
Preparation, characterization and application of heterogeneous solid base catalyst for biodiesel production from soybean oil Yihuai Li a, Fengxian Qiu a,*, Dongya Yang a, Xiaohua Li b, Ping Sun b a b
School of Chemistry and Chemical Engineering, Jiangsu University, Xuefu Road 301, 212013 Zhenjiang, PR China Jiangsu Provincial Key Laboratory of Power Machinery and Application of Clean Energy, 212013 Zhenjiang, PR China
article info
abstract
Article history:
A solid base catalyst was prepared by neodymium oxide loaded with potassium hydroxide
Received 24 September 2010
and investigated for transesterification of soybean oil with methanol to biodiesel. After
Received in revised form
loading KOH of 30 wt.% on neodymium oxide followed by calcination at 600 C, the catalyst
22 February 2011
gave the highest basicity and the best catalytic activity for this reaction. The obtained
Accepted 4 March 2011
catalyst was characterized by means of X-ray diffraction (XRD), Fourier transform infrared
Available online 24 March 2011
spectroscopy (FTIR), Scanning electron microscopy (SEM), Thermogravimetric analysis
Keywords:
catalyst has longer lifetime and maintained sustained activity after being used for five
Heterogeneous catalyst
times, and were noncorrosive and environmentally benign. The separate effects of the
Transesterification
molar ratio of methanol to oil, reaction temperature, mass ratio of catalyst to oil and
Biodiesel
reaction time were investigated. The experimental results showed that a 14:1 M ratio of
Potassium hydroxide
methanol to oil, addition of 6.0% catalyst, 60 C reaction temperature and 1.5 h reaction
Neodymium oxide
time gave the best results and the biodiesel yield of 92.41% was achieved. The properties of
(TGA), N2 adsorptionedesorption measurements and the Hammett indicator method. The
obtained biodiesel are close to commercial diesel fuel and is rated as a realistic fuel as an alternative to diesel. ª 2011 Elsevier Ltd. All rights reserved.
1.
Introduction
As conventional fuels are diminishing and environmental pollution is aggravating, alternative fuels have gained significant attention [1]. Biodiesel fuel, as a promising alternative diesel fuel to conventional fossil diesel produced by a catalytic transesterification of vegetable oils, animal fats and waste cooking oils with short chain alcohol, is becoming a favorable biofuel in many regions of the world [2,3], Compared to conventional diesel from petroleum, biodiesel is technically and economically more competitive because of its renewability, biodegradability, low emission profiles, high Flash point,
excellent lubricity and superior cetane number [4]. In addition, the use of biodiesel has the potential to reduce both the levels of pollutants and potential or probable carcinogens [5]. Biodiesel can be produced through transesterification of vegetable oils and fats with methanol in the presence of a suitable catalyst. In conventional homogeneous method of fatty acid methyl ester (FAME) synthesis, the removal of catalysts after reaction is unwanted step of biodiesel synthesis, where a large amount of wastewater is produced during neutralization the catalyst (NaOH or KOH) and FAME washing during separation from side products (glycerol, salt). Acidcatalyzed process often uses sulfonic acid and hydrochloric
* Corresponding author. Tel.: þ86 51188791800. E-mail address: [email protected] (F. Qiu). 0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2011.03.009
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acid as catalysts, however, the reaction time is very long (48e96 h) even at reflux of methanol, and a high molar ratio of methanol to oil is needed (30e150:1) [6]. Compared with homogeneous catalysts, heterogeneous catalysts can provide green and recyclable catalytic systems [7,8]. The advantage of heterogeneous catalyst usage is its fast and easy separation from the reaction mixture without requiring the use of neutralization agent. There are many solid heterogeneous acid- and alkali-catalysts for biodiesel synthesis. Tungstated zirconia (WO3/ZrO2) was prepared by method of impregnation was a promising heterogeneous acid catalyst [9]. Various carbohydrate-derived and a carbon-based solid acid catalyst [10,11] have good catalytic activity to high free fatty acid-containing waste oils. Unfortunately, the performances of these acid catalysts are still inferior compared with the base catalysts. For this reason, a wide variety of solid bases have been examined for transesterification reactions for biodiesel synthesis. Example include CaO [12], SrO [13], KNO3 loaded on flyash [14], ZnOeLa2O3 [15] and zinc aluminate [16]. But, these heterogeneous catalysts require a high temperature to achieve the high conversion. Other heterogeneous base catalysts like CaMnO3 [17], KNO3/Al2O3 [18], and MgeAl hydrotalcites [19] have also demonstrated some potential for activity in production of biodiesel. However, these catalysts need more time (more than 3 h) to reach the higher biodiesel yield. The result will increase the production cost due to the requirements for high temperatures and a long time operation. Neodymium oxide (Nd2O3) or rare earth sesquoxides is widely used in various applications such as photonic, luminescent materials, catalyst for automotive industry, UV absorbent, glass-polishing materials, and protective coatings. However, in this work, a new type of catalyst for biodiesel synthesis with KOH as active component on neodymium oxide support was synthesized using the way of impregnation, and reported the activity and selectivity of the basic solids for the transesterification of soybean oil with methanol. A screening of the reaction conditions has been carried out by examining the effect of the concentration of catalyst, the initial methanol/ oil, catalyst/oil molar ratio, reaction temperature and time.
2.
Experimental
2.1.
Materials
Soybean oil was purchased from Jinlongyu Company (Fujian, China). Methanol, zirconium dioxide (ZrO2), titanium dioxide (TiO2), alumina (Al2O3), neodymium oxide (Nd2O3), potassium hydroxide (KOH), potassium iodide (KI), potassium bromate (KBrO3), potassium hydrogen phthalate (C8H5O4K) and potassium nitrate (KNO3) were obtained from Sinopharm Chemical Reagent Co. Ltd., (Shanghai, China). All solvents were AR grade and were used without purification.
2.2.
Preparation of catalyst
All the catalysts were prepared by incipient wetness impregnation of different porous medium supports with solution of potassium compounds. For this purpose, the required amount of aqueous KOH solution was slowly added to the support and
kept 24 h. The catalytic carrier was previously calcined in a muffle for 12 h at 600 C. After impregnation, the catalysts were dried for 12 h at 100 C and then the solid was calcined in a muffle furnace at designed temperature for 12 h before use for the reaction.
2.3.
Characterization of the catalyst
FT-IR spectra of the samples were obtained between 4000 and 400 cm1 on a KBr powder with an FTIR spectrometer (AVATAR 360, Nicolet, Madison, USA). A minimum of 32 scans was signalaveraged with a resolution of 2 cm1 in the 4000e400-cm1 range. Scanning electron microscopy (SEM) images were obtained with 20-kV accelerating voltage with a field emission scanning electron microscope (S-4800, HITACHI Corp., Tokyo, Japan). X-ray diffraction (XRD) patterns of selected samples were obtained were recorded by the reflection scan with nickelfiltered Cu Ka radiation (D8, Bruker-AXS, Germany). The X-ray generator was run at 40 kV and 70 mA. All the XRD measurements were performed at 2q values between 10 and 80 . Thermogravimetric analysis (TGA) was performed on a Netzsch instrument (STA 449C, Netzsch, Seligenstadt, Germany). The programmed heating range was from room temperature to 1300 C, at a heating rate of 10 C/min under a nitrogen atmosphere. The measurement was taken using 6e10 mg samples. The nitrogen adsorption and desorption isotherms were measured at 196 C using a NDVA2000e analytical system made by Quntachrome Corporation (USA). The specific surface area was calculated by Brunauer-Emmett-Teller (BET) method. Pore size distribution and pore volume were calculated by Barrett-Joyner-Halenda (BJH) method. Hammett indicator experiments were conducted to determine the basic strength of each catalyst. The Hammett indicators used were bromothymol blue (pKa ¼ 7.2), phenolphthalein (pKa ¼ 9.8), 2,4-dinitroaniline (pKa ¼ 15), and 4-nitroaniline (pKa ¼ 18.4). Typically, 300 mg of the catalyst was mixed with 1 mL of a solution of Hammett indicators diluted in 10 mL methanol and allowed to sit for at least 2 h. After the equilibration, the color of the catalyst was noted. The basic strength of the catalyst was taken to be higher than the weakest indicator that underwent a color change and lower than the strongest indicator that underwent no color change. To measure the basicity of solid bases, the method of Hammett indicatorbenzene carboxylic acid (0.02 mol/L anhydrous ethanol solution) titration was used.
2.4. Transesterification of soybean oil and chemical analyses The transesterification reactions were performed at 60 C in a 125 ml three-neck reaction flask equipped with a condenser by refluxing 10 mL of methanol (247 mmol) with 15.82 g of soybean oil (commercial edible grade, acid value ¼ 0.976 mg KOH/g, saponification index ¼ 188.6 mg KOH/g, and average molecular weight ¼ 896.88 g/mol) and 0.95 g of catalyst (6 wt.%). The catalyst was activating at 773 K for 12 h before use for the reaction. After the reaction completion, the samples were separated from catalyst and glycerol by centrifuge. The glycerol could be separated because it was insoluble in the esters
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and had a much higher density. Then methanol was removed using rotary evaporation and the obtained product was analyzed by gas chromatography (GC) to determine the biodiesel yield (fatty acid methyl ester, FAME). Reference materials and samples were analyzed by a 7890A gas chromatograph (Agilent Technology Inc. USA), equipped with a flame-ionization detector (FID) and a HP-5 capillary column (30 m 0.32 mm 0.25 mm). Helium was used as the carrier gas. The oven temperature ramp program was 135 C for 10 min, 170 C at 10 C/min, and held for 10 min. 250 C at 25 C/ min, and held 2 min. The flow rate of hydrogen was 30 ml/min and the flow rate of air was about 400 ml/min. Temperatures of the injector and detector were 280 and 300 C. The injection was performed in split mode with a split ratio of 100:1. Biodiesel yield was quantified in the presence of tricaprylin as an internal standard. The analysis of biodiesel for each sample was carried out by dissolving 1 ml of biodiesel sample into 5 ml of n-hexane and injecting 0.5 ml of this solution in GC, in the same condition described as above. The biodiesel yield was calculated from the content of methyl esters analyzed by GC with the following equation: Biodiesel yield ¼
mtricaprylin AB ftricaprylin 100% Atricaprylin ms
(1)
where mtricaprylin ¼ weight of the internal standard, AB ¼ peak area of FAME, ftricaprylin ¼ response factor, Atricaprylin ¼ peak area of the internal standard, and ms ¼ weight of the sample. Determination of sulfur content of biodiesel was measured by Inductively Coupled Plasma Emission Spectrometer (ICP) using Intrepid XP Radial ICP-OES (VISTA-MPX, Varian, USA) with a concentric nebulizer and CCD detectors technology. Flash point was determined by a closed-cup tester (BF-02, Dalian North Analytical Instruments Co., Ltd.), using ASTM D 93.
3.
Results and discussion
3.1.
Screening of catalyst
The catalytic activity screening of Nd2O3 loaded with different potassium compounds (KOH, KI, KBrO3, C8H5O4K or KNO3) in the soybean oil transesterification was performed. The results were summarized Table 1. To make direct comparisons, the same reaction conditions, as shown in Table 1, were employed for each catalyst in all experiments. The reaction conditions were not optimized for the highest reaction yield; however, they provided a way to compare the activities of the catalysts. Obviously, it is observed from Table 1 that pure Nd2O3 and KOH catalyst exhibited no activity and serious saponification phenomenon due to excess KOH amount [20], respectively. However, when potassium compounds were loaded on Nd2O3 and activated at high temperatures, the supported catalysts except KNO3/Nd2O3 showed catalytic activities. Thus, it is essential to support potassium compounds on Nd2O3 to generate the catalytic activities for the transesterification reaction. Among the catalysts tested, Nd2O3 loaded with KOH, KI, KBrO3 or C8H5O4K exhibited comparatively high activities, giving biodiesel yields higher than 80%. Especially, KOH/Nd2O3 demonstrated the superior catalytic activity compared to the
Table 1 e Catalytic activity and base strength of Nd2O3 loaded with different potassium compounds. Basic strength (pKBHþ)
Biodiesel yield (%)
Nd2O3 KOH
<7.2 15e18.4
KOH/Nd2O3 KBrO3/Nd2O3 KI/Nd2O3 C8H5O4K/Nd2O3 KNO3/Nd2O3
9.8e15 7.2e9.8 <7.2 7.2e9.8 <7.2
No reaction Serious saponification phenomenon 89.7 74.06 17.05 32.03 No reaction
Catalyst
Transesterification condition: methanol/oil molar ratio, 12:1; catalyst amount 6 wt.%; reaction time, 3 h; reaction temperature, 60 C. All catalysts were activating at 600 C for 12 h before use for the reaction.
other catalysts. When the transesterification was conducted over the KOH/Nd2O3 catalyst, the highest biodiesel yield of 89.7% was achieved. Over KBrO3/Nd2O3, KI/Nd2O3 and C8H5O4K/Nd2O3 catalysts, however, the lower biodiesel yields in the range of 17.05e74.06% were obtained, attributable to their relatively low catalytic activities. Based on these results, the catalytic activity is in the following order: KOH/Nd2O3 > KBrO3/Nd2O3 > C8H5O4K/ Nd2O3 > KI/Nd2O3 > KNO3/Nd2O3. The base strengths of Nd2O3 modified with different potassium compounds were measured by using Hammett indicators. As evident in Table 1, loading of KBrO3, or C8H5O4K on the surface of Nd2O3 generated the weaker basic sites with pKBHþ in the range of 7.2e9.8. Taking both the base strength and the catalytic activity into account, we can conclude that the observed activities of Nd2O3-supported catalysts seem to be related to their base strengths, i.e. the higher base strengths of the catalysts result in the higher conversions. In particular, the KI/Nd2O3 or KNO3/Nd2O3 sample possessed the weakest base strength in the range of pKBHþ<7.2, consequently exhibiting weak or no catalytic activity. As for the catalytic sites on KOH/ Nd2O3 sample, it can also be proposed that the K2O species, which was possibly formed by dehydroxylation of the OH groups, was at least a part of catalytically active sites. As remarked above, it seems that the transesterification reaction needs strongly basic sites. The effect of supports on the activity of the catalyst was listed in Table 2. Obviously, when KOH was supported on
Table 2 e Catalytic activities and base strengths of KOH supported on the different carriers. Catalyst KOH/TiO2 KOH/ZrO2 KOH/Al2O3 KOH/Nd2O3
Basic strength (pKBHþ) 9.8 < 9.8 < 9.8 < 9.8 <
H H H H
< < < <
15 15 15 15
Biodiesel yield (%) 86.47 85.43 88.87 89.70
Transesterification condition: methanol/oil molar ratio, 12:1; catalyst amount, 6 wt.%; reaction time, 3 h; reaction temperature, 60 C. All catalysts were activating at 600 C for 12 h before use for the reaction.
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Table 3 e The effect of KOH loading amounts on the biodiesel yield. KOH loading amount (%) Basic strength (pKBHþ) Biodiesel yield (%)
14
17
25
30
32
9.8 < H < 15 80.47
9.8 < H < 15 81.52
9.8 < H < 15 85.72
9.8 < H < 15 89.52
9.8 < H < 15 73.45
Transesterification condition: methanol/oil molar ratio, 15:1; catalyst amount, 6 wt.%; reaction time, 3.0 h; reaction temperature, 60 C.
different carriers, the base strengths were almost equality, but the activity of the catalyst was different greatly. KOH/Nd2O3 was the most active catalyst for the transesterification reaction, giving a conversion of 89.70%. Over KOH/ZrO2, KOH/ Al2O3 and KOH/TiO2 catalysts, even though they possessed different centers of a base strength, the high biodiesel yields of 85.43%, 88.87% and 86.47% were also achieved, respectively. Thus, Nd2O3 can be regarded as the best support. From these discussions, KOH/Nd2O3 showed the best catalytic activity. On account of the high activity of the catalysts in the transesterification reaction, KOH/Nd2O3 was, therefore, selected for further investigation and its properties were studied in more detail. A 14 wt.% (KOH to Nd2O3 weight ratio) KOH on Nd2O3 support was prepared by an impregnation method and the following procedure: a solid Nd2O3 support (25 g) was mixed with KOH (3.5 g) in 15 mL of water, and the resulting solid was dried in an oven at 90 C for 24 h. The solid was then crushed and calcined in air at 600 C for 12 h. Similarly, 17, 25, 30 and 32 wt.% KOH loaded Nd2O3 were prepared. The effect of KOH loading amounts on the biodiesel yield was shown in Table 3. It can be seen from Table 3 that when the loading amount of KOH increased from 14 wt.% to 30 wt.%, the biodiesel yield increased from 80.47% to 89.52%. Then, the biodiesel yield decreased with the loading amount of KOH. This is because the base strength of catalyst increases with the loading amount of KOH. On the other hand, the catalytic activity and activity sites also increase with the loading amount of KOH. But, with further increase in the amount of loaded KOH, the basicity may decrease the surface basic sites, which resulted in a drop of the catalytic activity towards the reaction. This is presumably due to the coverage of surface basic sites by the excessive KOH. These sites are inaccessible to incoming reactants when the amount of loaded KOH exceeded 30 wt.%. Therefore, catalytic activity and biodiesel yield decreased. On the basis of the results, the optimum loading amount of KOH was 30 wt.%. Moreover, the biodiesel yield of 30 wt.% KOH/Nd2O3 sample calcined at different temperatures was measured by the same method, and the results are presented in Table 4. From the Table 4, it can be observed that the maximum biodiesel yield, reaching 90.02%, was obtained at a calcination temperature of 600 C. But, a low level of biodiesel yield was observed below
512 and above 700 C. Obviously, the biodiesel yield changes with calcination temperatures parallel the changes in the catalytic activity for the transesterification reaction. Based on these results, the optimal preparation conditions of the catalyst are load KOH, support Nd2O3, loading amount 30% and calcination temperature of 600 C. Therefore, 30 wt.% KOH/Nd2O3 catalyst was selected for further investigation of transesterification of soybean oil.
3.2.
Catalyst characterizations
A series of catalysts were synthesized by incipient wetness impregnation method and calcined at 600 C. In this high temperature, KOH decomposed into K2O. The powder X-ray diffraction patterns of KOH/Nd2O3 samples with various loading amounts of KOH were presented in Fig. 1. As can be seen, when the loading amount of KOH was 14 wt.% (curve a), diffraction peaks (2q ¼ 27.4 , 30.9 , 40.5 , 47.6 and 57.2 ) assigned to the amorphous Nd2O3 support were registered on the XRD patterns, and only a specie such as K2O (2q ¼ 29.6 ) was observed, indicating the good dispersion of K2O on Nd2O3 in the form of a monolayer due to the interaction between K2O and the surface of the support at a low loading of KOH. And when the loading amount of KOH was further increased to 25 wt. % (curve b), the new phase of K2O can be observed at 32.1 and 51.6 . But, when the loading amount of KOH is further increased to over 30 wt. % (curves c and d), a new phase of a compound containing potassium and neodymium elements could be observed at 2q ¼ 25.8 , 38.8 and 41.2 [21]. The phenomena can be a result from the incorporation of Kþ ions into the vacancies in the structure of the neodymium oxide, or Kþ ions may react with hydroxyl groups to form NdeOeK on the surface during heat treatment. The result will confirm by FT-IR spectrum of catalyst. Moreover, the intensi ties of some diffraction peaks (2q ¼ 29.6 , 32.1 , 38.8 , 41.2 and 51.6 ) increased with increase of the loading amount of KOH. On the other hand, the characteristic peaks of Nd2O3 (27.4 , 30.9 , 40.5 , 47.6 and 57.2 ) were almost unchanged on the XRD patterns regardless of the loading amount of KOH. It is noteworthy that the solidestate reaction between the guest compound and the surface of the support in the activation process is favorable for the catalyst to get a high catalytic
Table 4 e The effect of calcination temperature on the biodiesel yield. Calcination temperature ( C) Basic strength (pKBHþ) Biodiesel yield (%)
311
422
512
600
700
790
9.8 < H < 15 78.80
9.8 < H < 15 81.23
9.8 < H < 15 81.00
9.8 < H < 15 90.02
9.8 < H < 15 77.83
9.8 < H < 15 73.50
Transesterification condition: methanol/oil molar ratio, 12:1; catalyst amount, 6 wt.%; reaction time, 3.0 h; reaction temperature, 60 C.
b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
Fig. 1 e XRD patterns of (a) 14 wt.% KOH/Nd2O3, (b) 25 wt.% KOH/Nd2O3, (c) 30 wt.% KOH/Nd2O3, (d) 32 wt.% KOH/Nd2O3.
activity. In the case of KOH/Nd2O3, the Kþ ion of KOH could insert in the vacant sites of Nd2O3, accelerating dissociative dispersion and decomposition of KOH to form basic sites in the activation process. The more potassium compounds are loaded on the Nd2O3, the more free vacancies decrease, which results in the surface enrichment of potassium species that is probably considered to be the active sites for base-catalyzed reactions. When the amount of potassium cations loaded on Nd2O3 was below the saturation uptake of Kþ, it could be well dispersed. As a result, the number of basic sites together with the activities of the catalysts would increase with the potassium contents. However, if Nd2O3 was loaded with too much KOH, the KOH could not be well dispersed and, for this reason, not all but only a part of the loaded KOH could be decomposed. Moreover, as mentioned in the preceding sections, the excess KOH would cover the basic sites on the surface of the catalysts resulting in a lowered catalytic activity (Table 3). SEM images of Nd2O3 and 30 wt.% KOH/Nd2O3 catalyst were shown in Fig. 2. The SEM photographs of Nd2O3 and KOH/
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Nd2O3 samples showed the crystallites of 0.2e1 mm size. Evidently, as shown in Fig. 2, no important difference was observed between Nd2O3 and KOH/Nd2O3 samples, thus suggesting a good dispersion of KOH on the surface of Nd2O3. Based on these results, after loading of KOH, Nd2O3 retained its structure that was important for catalysis and therefore the potassium species was found highly distributed upon the surface of the support. FTIR spectra of Nd2O3 and KOHeNd2O3 catalyst were recorded and shown in Fig. 3. The spectrum of the support shows sharp peak at 1475 cm1. From the spectrum of catalyst, the new peaks at 880 and 706 cm1 are attributed to the KeO and KeOeNd bonds, respectively. Furthermore, the broad band at around 3100e3300 cm1 region could be partly assigned to the stretching vibration of NdeOeK groups [22] which Kþ ions could replace the protons of isolated hydroxy groups to form NdeOeK groups in the activation process and were probably considered to be the active species of this catalyst. This achieves the same results as the XRD analysis. However, this vibration is well overlapped with the broad vibration band of OH groups which is ascribed to OH stretching vibration of the hydroxyl groups attached to the ctalyst surface, in addition to water molecules absorbed from the atmosphere. The BET surface area, pore volume, and pore diameter of Nd2O3 and 30 wt.% KOH/Nd2O3 catalyst were measured. The BET surface area as well as the pore volume decreased with loading potassium hydroxide, and this tendency was more outstanding in the case of potassium. The thermal behavior of 30 wt. % KOH/ Nd2O3 sample was shown in Fig. 4. This figure showed that the first weight loss at lower temperature (<200 C) corresponds to the water loss from internal and external surfaces of the samples. The second weight loss (200e400 C), is due to the decomposition of the KOH and K2CO3. The last weight loss at above 400 C is attributed to the decomposition of the K2O and the residual hydroxyl groups bonded to the oxide lattice. The decomposition products of KOH, probably forming both K2O species and NdeOeK groups in the composite, were possibly the main active sites for the transesterification reaction. In this study, effect of repeated use of KOH/Nd2O3 catalyst on biodiesel yield was investigated in the optimal transesterification reaction conditions. The result in Table 5 indicated that the biodiesel
Fig. 2 e SEM images of (a) Nd2O3 and (b) 30 wt.% KOH/Nd2O3.
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b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
Table 5 e Effect of repeated use of KOH/Nd2O3 catalyst on biodiesel yield. Repeated times
1
2
3
4
5
Biodiesel yield (%)
90.11
90.07
90.06
90.04
90.05
Transesterification condition: methanol/oil molar ratio, 12:1; catalyst amount, 6 wt.%; reaction time, 1.5 h; reaction temperature, 60 C.
Fig. 3 e FT-IR spectra of Nd2O3 and catalyst.
yields had no significant changes and were in excess of 90% during the repeated experiments. It maintained sustained activity even after being used for five times and the biodiesel yield was only slightly decreased from 90.11% to 90.05%. This was because neodymium oxide compounds are dissolvable in methanol.
3.3. Influence of the transesterification reaction conditions The transesterification process consists of a sequence of three consecutive reversible reactions where the triglyceride is successively transformed into diglyceride, monoglyceride, and finally into glycerin and the FAME. The molar ratio of methanol to soybean oil is one of the important factors that affect the conversion to methyl esters. Stoichiometrically, 3 mol of methanol are required for each mole of triglyceride, but in practice a higher molar ratio is employed in order to drive the reaction towards completion and produce more methyl esters
Fig. 4 e Thermogravimetric analysis of 30 wt. % KOH/ Nd2O3.
as products. This is because that the biodiesel yield could be improved by introducing excess amounts of methanol to shift the equilibrium to the right-hand side. As represented in Fig. 5, the biodiesel yields grew as the methanol-loading molar ratio increased, and the biodiesel yield was increased considerably. The maximum biodiesel yield (90.59%) was obtained when the molar ratio was very close to 14:1. In comparison, the biodiesel yield increased from 77.49% to 90.59% when the molar ratio was increased from 6:1 to 14:1. However, beyond the molar ratio of 14:1, the excessively added methanol had no significant effect on the production yield and the biodiesel yield was 90.12% at 16:1. The reason is that the catalyst content decreased with increase of methanol content. Therefore, we could conclude that to elevate the biodiesel production yield an excess methanol feed was effective to a certain extent and the optimum molar ratio of methanol to oil was 14:1. The dependence of the biodiesel yield on the reaction time was investigated. The reaction time was varied in the range 0.5e8 h. Fig. 6 revealed that the transesterification reaction was strongly dependent on reaction time, at the beginning (<0.5 h), the reaction was slow due to the mixing and the dispersion of methanol into oil, and the biodiesel yield was increased very fast in the reaction time range between 0.5 and 1.5 h. Moreover, excess reaction time leaded to a bit reduction in the product yield due to the backward reaction transesterification, resulting in a loss of esters as well as causing more fatty acids to form soaps [23,24]. So the optimum reaction time was obtained at 1.5 h.
Fig. 5 e Effect of different molar of methanol to oil on the biodiesel yield (catalyst amount, 6 wt.%; reaction time, 3.0 h; reaction temperature, 60 C).
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b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
Fig. 6 e Effect of reaction time on the biodiesel yield (methanol/oil molar ratio, 14:1; catalyst amount, 6 wt.%; reaction temperature, 60 C).
In the presence of heterogeneous catalysts, the reaction mixture constitutes a three-phase system, oilemethanol-catalyst, in which the reaction would be slowed down because of the diffusion resistance between different phases. However, the reaction rate can be accelerated at higher reaction temperatures. In this paper, the synthesis of biodiesel from soybean oil was conducted at various temperatures (40 C, 50 C, 60 C, 65 C and 70 C). As shown in Fig. 7, the reaction rate was slow at low temperatures, but the biodiesel yield first increased and then decreased with the increase of the reaction temperature. Generally, a more rapid reaction rate could be obtained at high temperatures, which is due to the endothermic nature of transesterification reaction [25], but at high temperatures, methanol was vaporized and formed a large number of bubbles, which inhibited the reaction on the three-phase interface. The optimum reaction temperature was 60 C and biodiesel yield arrived at 92.41%.
Fig. 8 e Effect of catalyst amount on the biodiesel yield (methanol/oil molar ratio, 14:1; reaction time, 2.0 h; reaction temperature, 60 C).
When increasing the amount of loading catalyst, the slurry (mixture of catalyst and reactants) was become too viscous giving rise to a problem of mixing and a demand of higher power consumption for adequate stirring. On the other hand, when the catalyst loading amount was not enough, maximum biodiesel yield could not be reached. To avoid this kind of problem, an optimum amount of catalyst loading had to be investigated. The influence of the catalyst amounts was studied at a 14:1 M ratio of methanol to soybean oil at reflux of methanol for 2 h. The catalyst amount was varied in the range of 1.0% and 9.0%. These percentages were weight fractions of the oil supplied for this reaction. The reaction profile of Fig. 8 indicated that the transesterification reaction was strongly dependent upon the catalyst applied. As is evident from Fig. 8, when the catalyst amount increased from 1.0% to 6.0%, the biodiesel production yield was increased. However, with further increase in the catalyst amount the biodiesel yield was
Table 6 e The various absorption peaks of biodiesel. Group Wavenumber attribution (cm1)
Fig. 7 e Effect of reaction temperature on the biodiesel yield (methanol/oil molar ratio, 14:1; catalyst amount, 6 wt.%; reaction time, 1.5 h).
3462.27 3008.91 2925.76
eOH ¼ CeH eCH2
2855.00
eCH2
1743.54 1461.48 1360.75 1017.78
eC]O eCH2 eCH3 CeOeC
1171.41
CeOeC
722.75
eCH2
Vibration type Stretching Stretching Asymmetric stretching vibration Symmetric stretching vibration Stretching Shear-type vibration Bending vibration Anti-symmetric stretching vibration Symmetric stretching vibration Plane rocking vibration
Absorption intensity Weak Strong Strong Strong Strong Middling Middling Weak Middling Weak
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b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
Table 7 e The properties of ICP-OES spectrometer. Type
Intrepid XP Radial ICP-OES
Nebulizer RF-generator Power Reflected power Observation high Optical system Grating Focal length Optical range Resolution Detector Emission lines used For the S analysis
Concentric, with a cyclonic spray chamber 40.68 MHz crystal-controlled 1200 W 20 W 6 mm above the coil Czerny-Turner vacuum-monochromator Holographic, 1800 groves/mm 0.75m 160e800 nm 1st order: 0.018 nm Photomultiplier l1 ¼ 180.731 nm l2 ¼ 181.970 nm
decreased, which was possibly due to a mixing problem involving reactants, products and solid catalyst. The optimum catalyst loading amount was found to be 6.0% in this system and the maximum biodiesel yield reached to 92.40%. From the above results, the reaction does not require too much time to dispose of the products, for example, neutralization, washing and drying. If the catalyst can be used commercially, filtration is a possible way to recycle the catalyst and decrease the cost. As a heterogeneous solid base catalyst, the prepared KOH/Nd2O3 catalyst has a longer catalyst lifetime and better stability than current homogeneous catalysts. It is noncorrosive and environmentally benign. It can be applied to produce biodiesel commercially.
3.4.
Characterization and properties of biodiesel
FT-IR spectrum of the obtained biodiesel was listed in Table 6. From the analysis of the Table 6, we could get the sample including all groups which we needed. At the same time, it proved that the compound was the kind of structures having long-chain fatty acid esters. The content of sulfur and its proper determination play an important role regarding fuels and products of petrochemical industry. The problem of appropriate determination of sulfur is important both from environmental and analytical aspects,
because some specifications order to the compulsion decrease of the concentration of sulfur (e.g. from 2005 their maximum concentration is 50 mg/kg in fuels in the countries of European Union). Over the past few decades, there are numerous spectroscopic techniques to analyze the qualitative and quantitative elemental composition of fuels. For example, inductively coupled plasma atomic emission spectroscopy (ICPeAES), inductively coupled plasma mass spectroscopy (ICPeMS) and flame or graphic furnace atomic absorption spectroscopy (AAS) were adopted. Each technique has advantageous properties in terms of analytical figures of merit. The atomic absorption and emission techniques are typically used for analysis of the products of hydrocarbon industry. The ICP technique is a fast analytical method, but needs preliminary sample preparation (e.g. digestion). In this work, the sulfur content of biodiesel was carried out by Inductively Coupled Plasma Emission Spectrometer (ICP) using Intrepid XP Radial ICP-OES (VISTA-MPX, Varian, USA) with a concentric nebulizer and CCD detectors technology. After performing the background equivalent concentration experiment to test the instrument sensitivity, the ICP operating conditions applied are presented in Table 7. In order to determine the sulfur content, the biodiesel was carried out by nitrification firstly. A certain amount of biodiesel was added to concentrated hydrochloric acid (8 mL) and concentrated nitric acid (2 mL), and placed overnight. Subsequently, the mixture was gently filtered and got clear liquid, then the clear liquid was evaporated in the fuming cupboard about 20 min. Calibration standards were made up from some standard solutions of sulfur. The ranges of the calibration curves (5 points) were selected to match the expected different concentrations standard solution for the sulfur element of the sample investigated. Linearity was checked in the range of 0e40 mg/g. From the calibration curve, the sulfur content of biodiesel was obtained. The sulfur content of the obtained biodiesel was listed in Table 8. The properties of biodiesel, density, cetane number, flash point, cold filter plugging point, acid number, water content, ash content and total glycerol content, were determined and listed in the Table 8. Table 8 also showed comparisons of the obtained biodiesel and the standards of biodiesel in china, Europe and the United States. The properties of the obtained biodiesel, in general, show many similarities, and therefore,
Table 8 e Comparison of properties of the obtained biodiesel and the standards of biodiesel in china, Europe and the United States. Item
Obtained biodiesel 1
China GB/T 20828e2007
USA ASTM D 6751e03
Density (kg L ) Flash point ( C) Cold filter plugging point ( C)
0.896 (20 C) 168 5.0
0.82e0.90 (20 C) 130 e
0.82e0.90 (20 C) ＞130 e
Sulfur content (w/w,%) Cetane value Acid value (KOH) (mg g1) Water content (w/w,%) Ash content (w/w,%) Total glycerol content (w/w,%)
0.0065 56 0.6 0.04 0.018 0.020
0.05 49 0.8 0.05 0.05 0.024
0.0015 47 ＜0.8 0.05 0.02 0.024
Europe EN 14214 0.86e0.90 (15 C) ＞120 Spring:0 Summer:10 Autumn:20 ＜0.001 ＞51 ＜0.5 0.05 0.02 0.025
b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 7 8 7 e2 7 9 5
the properties of obtained biodiesel from the soybean oil is rated as a realistic fuel as an alternative to diesel.
4.
Conclusions
Nd2O3 loaded with KOH, which was prepared by impregnation of powdered Nd2O3 with an aqueous solution of KOH followed by calcination at a high temperature, showed high catalytic activities for the transesterification reaction. Both the K2O species formed by the thermal decomposition of loaded KOH, and the surface KeOeNd groups formed by saltesupport interactions, were probably the main reasons for the catalytic activity towards the reaction. The activities of the heterogeneous base catalysts correlated with their corresponding basic properties. The catalyst with 30 wt.% KOH loading on Nd2O3 and calcined at 600 C for 12 h was found to be the optimum catalyst, which gave the best catalytic activity. When the reaction was carried out at reflux of methanol, with a molar ratio of methanol to oil of 14:1, a reaction time 1.5 h, a reaction temperature 60 C and a catalyst amount 6.0%, the highest biodiesel yield reached 92.41%. The properties of obtained biodiesel from soybean oil are close to commercial diesel fuel and is rated as a realistic fuel as an alternative to diesel.
Acknowledgment This project was supported by the Natural Science of Jiangsu Province (BK2008247), Jiangsu Provincial Key Laboratory of Power Machinery and Application of Clean Energy Foundation (QK08007).
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