Transesterification of castor oil to biodiesel using NaY zeolite-supported La2O3 catalysts

Energy Conversion and Management 173 (2018) 728–734

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Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman

Transesterification of castor oil to biodiesel using NaY zeolite-supported La2O3 catalysts ⁎

Lixiong Dua, Shaoxuan Dingb, Zhuang Lia, Enmin Lva, Jie Luc, , Jincheng Dinga,

T

⁎

a

College of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo, Shandong 255000, China College of Food Science and Engineering, Northwest A&F University, Xianyang, Shanxi 712100, China c Department of Resources and Environmental Engineering, Shandong University of Technology, Zibo, Shandong 255000, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Biodiesel Castor oil Transesterification Zeolite NaY

As the requirements for green and industrial production of biodiesel increase, recyclable mesoporous spherical catalysts need to be developed. To achieve this, La2O3/NaY spherical particle (3–5 mm) heterogeneous catalysts were prepared by a granulating machine for the production of castor oil biodiesel. The effects of calcination temperature on catalytic activity and crushing strength were investigated. The structure, composition and morphology of the La2O3/NaY were characterized by SEM-EDS, XRD and BET analyses. The effects of calcination temperature, catalyst concentration, ethanol/oil molar ratio, reaction temperature and time on the yield of fatty acid ethyl ester (FAEE) were optimized by single-factor analysis. The addition of surfactant has a positive effect on the La2O3 dispersion and pore size of zeolite NaY. The synthesized catalyst shows excellent reusability and crushing strength which are essential for industrial practices. Under the optimization conditions of catalyst concentration 10 wt%, molar ratio of ethanol to oil 15:1, reaction temperature 70 °C for 50 min, the FAEE yield of 84.6% was obtained.

1. Introduction With the continuous development of science and technology, people’s demand for energy is increasing and mineral energy shortage is becoming more and more serious. The energy crisis has gradually become a major challenge facing mankind. Meanwhile, the toxic gases and bituminous coal by refining and burning of traditional petrochemical fuels have caused serious environmental pollution. Therefore, it is urgent to find sustainable and alternative clean energy sources. Biodiesel, a non-toxic, biodegradable and renewable biomass energy, has attracted widespread attention. Meanwhile, biodiesel is regarded as an ideal substitute because of its physical and chemical properties similar to those of traditional petrochemical diesel fuel. Thus, it can be applied to compression-ignition diesel engines with little or no modification [1]. Typically, biodiesel, also known as a mixture of fatty acid methyl esters (FAME), is obtained from either vegetable oils or animal fats [2]. Currently used vegetable materials are sunflowers oil [3,4], rapeseed oil [5,6], soybean oil [7,8], palm oil [9,10], castor oil [11–14], papaya seed oil [15], jatropha seed oil [16,17] and so on. In China, a result of food security [10], the government explicitly prohibits the use of edible

oils for the production of biodiesel. Castor oil is an important non-edible oil with unique properties in nature. Castor has the characteristics of drought, ridge and salt resistance which can be planted in most parts of China. In addition, the castor oil seed contains about 47–49% oil, which is mainly composed of ricinoleic acid [14]. The production capacity of castor oil in China is ranked the second in the world and it is an ideal raw material for biodiesel production [18]. The transesterification is carried out directly with the alkaline catalyst due to the low acid value of refined castor oil. Homogeneous catalysts such as NaOH [19], KOH [20], CH3OK [21], CH3ONa [22] have high catalytic activity for transesterification. However, the usage of homogeneous catalyst has a few disadvantages since it requires more complex processes to wash and purify products and produces large amounts of waste water [23]. In addition, homogeneous catalyst also causes equipment corrosion [24,25] and saponification of the raw materials. Recently, due to growing environmental and economic issues, the green approach of transesterification has stimulated the development of recyclable solid catalysts as a substitute for homogeneous catalysts [26]. The use of heterogeneous catalyst can reduce the problem associated with the homogeneous catalyst because heterogeneous catalyst can be easily separated from the liquid products and can be

⁎ Corresponding authors at: College of Chemistry and Chemical Engineering, Shandong University of Technology, 266 Xincun West Road, Zibo, Shandong 255000, China (J. Ding). Department of Resources and Environmental Engineering, Shandong University of Technology, 266 Xincun West Road, Zibo 255000, China (J. Lu). E-mail addresses: [email protected] (J. Lu), [email protected] (J. Ding).

https://doi.org/10.1016/j.enconman.2018.07.053 Received 25 May 2018; Received in revised form 15 July 2018; Accepted 16 July 2018 Available online 10 August 2018 0196-8904/ © 2018 Published by Elsevier Ltd.

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zeolite NaY, sodium carboxymethyl cellulose, lanthanum oxide and kaolin were grinded and mixed evenly in the ball grinding mill at a certain proportion (the mass ratio of NaY:Kaolin:La2O3:CMC = 70:20:10:2.5). A small amount of the mixture was placed in a turntable granulator and sprayed in the binder solution to form seed crystals. Then, the mixture was slowly added and continued to spray in the binder solution to form uniform spherical particles (3–5 mm). The obtained spherical particles were dried at 80 °C for 12 h, then placed in a crucible and calcined in a muffle furnace (SXG04123, Shanghai Liangyi Scientific Instruments Co., Ltd., Shanghai, China). The calcination temperature was programmed from room temperature to 600, 800, 1000 °C at the rate of 2 °C·min−1 and then kept constant for 3 h, which were labeled as La2O3/NaY-600, La2O3/ NaY-800 and La2O3/NaY-1000, respectively. Target catalyst was obtained by naturally cooling to room temperature. In addition, a certain amount of surfactants (4 wt%) was added to the mixture and calcined at 800 °C, labeled as S-La2O3/NaY-800.

designed to have higher activity, higher selectivity and longer catalyst lifetimes [27]. Recently, new heterogeneous alkaline catalysts have been used for transesterification to produce biodiesel. Among them, MOFs [28,29], graphene [26,30], ion exchange resin [31,32], zeolite [4,33–36], hydrotalcite [5,37,38] and metal oxides [1,3,39–43] all have good activity in transesterification reaction. There are numerous lanthana supported catalysts that have been used due to their unique alkali catalytic activity. Lee et al. [1] reported that the conversion of biodiesel was 98.76% at 3 wt% CaO-La2O3 catalyst loading, methanol/oil molar ratio of 25:1 and reaction temperature of 160 °C for 3 h. Intensification of alkalinity of lanthana has been done by applying alkali promoters like calcium oxide [1,44], zirconia [45], aluminium oxide [46] and Ni metal [47]. Nizah et al. [48] used jatropha curcas oil with Bi2O3-La2O3 catalyst under reaction conditions of reaction time of 4 h, catalyst loading of 2 wt% (5% Bi2O3 doping amount), methanol/oil molar ratio of 15:1 at 150 °C and the conversion of biodiesel obtained was 93%. Maleki et al. [44] used lithium loaded on CaO-La2O3 mixed oxide for reaction with canola oil and obtained 96.3% FAME conversion using 15:1 methanol/oil molar ratio for 2.5 h with 5 wt% catalyst loading at 65 °C. In addition, the La2O3 as a catalyst for loading has also been reported. Sun et al. [45] reported La2O3/ZrO2 catalysts for sunflower oil transesterification and reported that the FAME conversion was 90% with reaction conditions of 30:1 methanol to oil molar ratio, 21 wt% La2O3/ZrO2 catalyst, at temperature of 200 °C for 5 h. Although they all have high FAME yields, a few people concerned the techniques of catalyst forming. Most of the heterogeneous catalysts reported are used directly in powder form, which caused inconvenience to subsequent processing. For example, powders and oils can easily stick to the reactor wall and are difficult to clean. At the same time, the catalyst powders are too small, difficult to recycle and easy to lose, which is not suitable for direct application to large-scale chemical equipment. The purpose of this work was to synthesize a new type of La2O3/NaY catalyst for transesterification of castor oil. The catalysts were synthesized via a physical mixing method. The uniform spherical catalyst particles of 3–5 mm in diameter were made by the rotation of the granulation machine (LW-83 dB, Zibo Shunyuan Machinery Factory, Zibo, China). The La2O3/NaY catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), N2 adsorption (BET). The optimum reaction parameters such as catalyst concentration, ethanol/oil molar ratio, reaction time and reaction temperature for transesterification were analyzed to determine the stability of catalyst La2O3/NaY. The reusability of the catalyst was also studied.

2.3. Characterization of the catalysts The La2O3/NaY catalysts were characterized by X-ray diffraction (XRD) on a Bruker AXS (D8 ADVANCE) with a Cu Kα radiation (wavelength, λ = 0.154 nm, 35 kV, 30 mA) [49]. The La2O3/NaY samples were examined from 10° to 60° (2θ) with a scan rate of 0.048°/s at 40.0 kV. The total surface area of the La2O3/NaY catalysts were obtained using a Brunauer-Emmett-Teller (BET) method with nitrogen adsorption by ASAP 2020 system (Micrometitics USA) at −196.0 °C. In addition, the pore size and pore volume were also analyzed. The surface morphology analysis of the catalysts was studied by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). The NaY and La2O3/NaY were photographed using FEI (SIRION 200) at 10 kV and a magnification of 5000×. The surface elements of the catalysts were analyzed and obtained by EDS (Oxford-instruments INCA Energy). The mechanical strength of the La2O3/NaY catalyst was measured by the particle strength meter (HB-KQD 1705146, Jinan Haibo Laboratory Instrument Co., Ltd. Jinan, China). Each set of catalyst was measured fifty times, and the average value was obtained. The basic strength and basic strength distribution of the catalyst were determined by direct titration with a Hammett indicator. Hammett indicator H0 was used to quantitatively represent the basic strength, which was calculated by Eq. (1) [50].

H0 = PK a + log[B]/[BH+]

(1)

+

[B] and [BH ] represent the concentrations of the indicator and the conjugate acid, and pKa is the logarithm of the dissociation constant of the indicator.

2. Experimental 2.1. Materials

2.4. Alkaline transesterification The zeolite NaY was supplied from Sinopec Catalyst Co., Ltd Qilu Division, Zibo, China. Lanthanum oxide, sodium carboxymethyl cellulose (CMC) and kaolin were purchased from Jining Tianyi New Material Co. Ltd. Refined castor oil was friendly supplied from Zibo Jinxuan Resources and Environmental Technology Development Co., Ltd, Zibo, China and used without additional processing. The fatty acid composition of the castor oil was determined by chromatography (GC) analysis as follows: ricinoleic acid 88.7%, oleic acid 4.7%, palmitic acid 2.8%, stearic acid 2.1%, gaidic acid 0.8%. Ethyl heptadecanoate and a standard FAEE C16-C20 for GC calibration were purchased from Shanghai Klamar (China). Other chemicals that have been applied in this work such as ethanol, n-hexane, nitric acid, and potassium hydroxide were of analytical grade.

The transesterification reaction was carried out in a 250 ml threenecked flask equipped with a condenser at atmospheric pressure. The reactants were stirred in a magnetic whisk and heated in a warmer jacket (SZCL-A, Zhengzhou Great Wall Branch Industry & Trade Co., Ltd. Zhengzhou, China). 30.0 g of castor oil and the required amount of catalyst and ethanol were added in each experiment. The four different reaction parameters were optimized including catalyst concentration (2–12 wt%), molar ratio of ethanol to oil (3:1–18:1), reaction time (20–60 min) and reaction temperature (50–75 °C). After the reaction, the mixture was filtered to remove the catalysts and its volume was measured. The crude biodiesel was refined that excess ethanol was removed under reduced pressure using a rotary evaporator, glycerol and other impurities were removed by washing with water, and finally the product was dried over anhydrous sodium sulfate. The FAEE concentration was measured by an internal standard curve method using ethyl heptadecanoate as the internal standard

2.2. Catalyst preparation The La2O3/NaY catalyst was obtained by physical mixing. The 729

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oxide has a large degree of dispersion on zeolite NaY or presents in an amorphous form [46]. Meanwhile, the XRD pattern of the S-La2O3/ NaY-800 is the same as La2O3/NaY-800.

solution. A GC2010 equipped with a HP-19091 column (30 mm × 0.32 mm × 0.25 mm) and a flame ionisation detector was used in the determination of FAEE concentration (wt%). The chromatographic conditions for the subsequent detection of fatty acid ethyl ester were applied: detector temperature = 280 °C, inlet temperature = 280 °C, injection volume = 0.4 μL, split ratio = 30:1, Nitrogen as carrier gas. The following temperature program was applied: initial temperature = 100 °C, ramp rate of 5 °C·min−1 to 200 °C, holding 5 min, then ramp rate of 2 °C·min−1 to 240 °C and holding 10 min. The FAEE concentration was calculated according to Eq. (2):

The FAEE concentration =

3.1.2. Scanning electron microscopy with energy dispersive X-ray spectroscopy The surface morphology of the catalyst and the distribution of La elements were detected by SEM-EDS, as shown in Fig. 2. Fig. 2b and d shows that the La2O3/NaY-600 and La2O3/NaY-800 are composed of elliptical and irregular particles, and there are a lot of gaps between the particles, which is similar to the structure of the original NaY powder (Fig. 2a). From Fig. 2f, it can be observed that the distribution of catalyst particles is more uniform and the particle spacing is larger, which means larger pore size and more active sites. Meanwhile, from the EDS surface distribution of the lanthanum element, it can also be clearly seen that the distribution in the S-La2O3/NaY-800 is more uniform (Fig. 2c, e and g). It also indicated that the addition of surfactants could effectively avoid the formation of massive structures during the nucleation and through the aggregation. However, when the calcination temperature rises to 1000 °C, the structure is obviously different from the structure of La2O3/NaY-600 and La2O3/NaY-800, because of the high temperature which destroyed the original structure of zeolite NaY (Fig. 2h). This can also be confirmed by BET and XRD analyses.

n

∑i=1 (A s + A 0b)C0 V/kA 0m × 100%

(2)

where As and A0 are the average peak area of the fatty acid ethyl ester and ethyl heptadecanoate, respectively. C0 is the concentration of the ethyl heptadecanoate, V is the total volume after reaction, and m is the mass of castor oil. k and b are the slope and intercept of standard curve, respectively. Using the same method, each sample was tested three times in a short time interval and the average value was obtained. The absolute difference between the results of three independent tests should not exceed 3.0% of the mean value. 3. Results and discussion

3.1.3. Specific surface area and porosity analysis The BET specific surface area, average pore diameter and pore volumes of the samples are shown in Table 1. The BET specific surface area of La2O3/NaY-1000 catalyst is only 2.7377 m2/g, far less than the specific surface areas of La2O3/NaY-600 (369.7630 m2/g) and La2O3/ NaY-800 (249.5518 m2/g). The pore diameters of La2O3/NaY-600 and La2O3/NaY-800 are similar, while La2O3/NaY-1000 has much larger aperture than La2O3/NaY-600. The pores volume data shows that the pore of La2O3/NaY-600 and La2O3/NaY-800 are smaller and numerous, while the La2O3/NaY-1000 pores are larger and less, which also confirms that the NaY molecular sieve structure is destroyed by high temperature. The specific surface area, average pore diameter and pore volume of S-La2O3/NaY-800 are better than La2O3/NaY-800, which may be related to better dispersion. It can be perfectly verified with the SEM image and XRD pattern too.

3.1. Catalyst characterization 3.1.1. X-ray diffraction analysis The XRD patterns of the La2O3/NaY catalyst calcined at different temperatures are shown in Fig. 1. A typical pattern belonging to zeolite NaY appears at the identical 2θ angles of 6.3°, 15.6°, 23.7°, 27.2°, 31.5° (Fig. 1a). This pattern was observed in the XRD patterns of NaY zeolite powder calcined at 600 °C (Fig. 1b). The figure shows that the characteristic peak of the catalyst La2O3/NaY-600 and La2O3/NaY-800 is basically the same as the zeolite NaY powder, which means that the incorporation of La2O3 does not change the original structure of zeolite NaY and has little effect on the zeolite NaY crystal (Fig. 1b and c). With the increase of La2O3 incorporation, the characteristic peak intensity of NaY decreased slightly, which may be related to the decrease of crystallinity of zeolite NaY. When the calcination temperature is increased to 1000 °C, it can be seen that the peak shape is completely different from the La2O3/NaY-600 and La2O3/NaY-800, and the characteristic peak of zeolite NaY is not found (Fig. 1e). This also indicates that the high temperature destroys the structure of the zeolite NaY, which can be confirmed with the SEM and BET analyses. In addition, the absence of La2O3 diffraction peak in the XRD pattern indicates that lanthanum

3.1.4. Crushing strength of the catalyst In addition, the crushing strength of the catalysts calcined at different temperatures was also measured. The data are listed in Table 1. As can be seen, the crushing strength of La2O3/NaY-1000 is the highest, reaching 267 N, but the SEM and BET data indicate that the zeolite NaY structure has been destroyed and does not have any catalytic activity. On the contrary, the La2O3/NaY-600 has a bad crushing strength and is easily broken by stirrer. It is not conducive to recycling and not suitable for applications in large-scale chemical equipment (such as fluidized bed reactor), although its specific surface area and catalytic activity are excellent. The La2O3/NaY-800 has a lower crushing strength than La2O3/NaY-1000, but it can maintain the shape of spherical particles after agitation. In fact, its crushing strength (126 N) meets most industrial requirements. Meanwhile, the S-La2O3/NaY-800 also has a large BET surface area and shows excellent catalytic activity. 3.1.5. Basic strength and basic strength distribution In fact, the basic site on the heterogeneous catalyst is the active center for transesterification reaction. Therefore, the influence of basic strength and basic strength distribution of the catalyst on the transesterification is crucial. As indicated in Table 2, S-La2O3/NaY-800 shows the highest value in base strength (9.3 < H0 < 15.0). Moreover, the total basicity of each catalysts is ranked as: La2O3/NaY-600 > SLa2O3/NaY-800 > La2O3/NaY-800 > La2O3/NaY-1000. As mentioned before, S-La2O3/NaY-800 exhibits the best transesterification catalytic activity in this series of catalysts.

Fig. 1. The XRD patterns of (a) zeolite NaY (b) La2O3/NaY-600 (c) La2O3/NaY800 (d) S-La2O3/NaY-800 (e) La2O3/NaY-1000. 730

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Fig. 2. (a) The SEM patterns of zeolite NaY, (b and c) The SEM and EDS patterns of La2O3/NaY-600, (d and e) The SEM and EDS patterns of La2O3/NaY-800, (f and g) The SEM and EDS patterns of S-La2O3/NaY-800, (h) The SEM patterns of La2O3/NaY-1000. Table 1 The BET specific surface area, average pore diameter, pore volumes and crushing strength of the catalysts. Sample

BET surface area (m2/g)

Pore diameter (nm)

Pore volume (cm3/g)

Crushing strength (N)

La2O3/NaY600 La2O3/NaY800 S-La2O3/ NaY-800 La2O3/NaY1000

369.7630

7.0145

0.035975

< 10

249.5518

7.4482

0.033892

126

276.0386

8.5960

0.040109

114

2.7377

16.6770

0.000387

267

Table 2 The basic strength and basic strength distribution of catalysts. Sample

La2O3/NaY600 La2O3/NaY800 S-La2O3/ NaY800 La2O3/NaY1000

Basicity (mmol/g) 4.8 < H- < 7.1

7.2 < H- < 9.3

9.3 < H- < 15

Total basicity (mmol/g)

1.3

8.8

2.6

12.7

1.2

8.3

2.4

11.9

1.4

8.5

2.7

12.6

0.8

6.7

0

7.5

Fig. 3. Effect of molar ratio of ethanol to oil on FAEE yield (catalyst concentration = 10 wt%, temperature = 70 °C, time = 50 min).

50 min). When the molar ratio of ethanol to oil increased from 3:1 to 15:1, the yield of FAEE increased from 47.4% to 84.6%, because an excessive amount of ethanol provides more effective collisions for the reactive molecules [51]. However, when the molar ratio of ethanol to oil was further increased, there was no significant increase in FAEE yield. The reason may be that excessive ethanol molecules occupy or dilute the active sites on the surface of the catalyst [52]. Therefore, the molar ratio of ethanol to oil of 15:1 was found to be optimal in this study.

In general, although La2O3/NaY-600 has high basic strength and specific surface area, its crushing strength is too low to meet the requirements. The La2O3/NaY-1000 is the opposite. Only S-La2O3/NaY800 shows relatively high specific surface area, crushing strength and basic strength. In addition, the addition of surfactants made the dispersion of La2O3 more uniform.

3.2.2. Effect of catalyst concentration The effect of the catalyst concentration (as referred to the starting oil weight) on the yield of FAEE is shown in Fig. 4. At the fixed molar ratio of ethanol to oil of 15:1, the reaction temperature of 70 °C and the reaction time of 50 min, the concentration of the catalyst varied in the range of 2–12%. The low levels of catalyst concentration resulted in low FAEE yields which could be attributed to the less accessible active sites for reactant. When the catalyst concentration was increased from 2% to 10%, the yield of FAEE increased from 12.2% to 84.5%. However, when the catalyst concentration exceeds 10%, the increase of the FAEE yield is no longer significant. Excessive catalyst will increase the viscosity of the reaction system and have an adverse effect on the mass transfer between the reactants. Therefore, the optimum catalyst concentration of the transesterification reaction is 10 wt%.

3.2. Influence of reaction conditions on the transesterification 3.2.1. Effect of ethanol/oil molar ratio The molar ratio of ethanol to oil is also an important factor affecting the yield of FAEE. From a stoichiometric point of view, 1 mol of castor oil would be completely reacted with 3 mol of ethanol to produce biodiesel. However, since the transesterification reaction is a reversible reaction, it is usually necessary to add an excessive amount of ethanol to make it react in the positive direction. Fig. 3 shows the effect of the different molar ratios of ethanol to oil on FAEE yield (catalyst concentration of 10 wt%, reaction temperature of 70 °C, reaction time of 731

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Fig. 4. Effect of catalyst concentration on FAEE yield (ethanol:oil molar ratio = 15:1, temperature = 70 °C, time = 50 min).

Fig. 6. Effect of reaction time on FAEE yield (ethanol:oil molar ratio = 15:1, catalyst concentration = 10 wt%, temperature = 70 °C).

3.2.3. Effect of reaction temperature Temperature is one of the most important factors affecting the yield of FAEE. The effect of reaction temperature on the yield of FAEE was shown in Fig. 5 (the molar ratio of ethanol to oil 15:1, reaction time 50 min, and catalyst concentration 10%). When the reaction temperature increased from 50 to 70 °C, the yield of FAEE increased from 24.6 to 84.7%. On the one hand, higher temperature is beneficial to the endothermic reaction. On the other hand, the increase of temperature could reduce the viscosity of castor oil, which would significantly accelerate the motion speed and mass transfer rate of molecules and improve the mass transfer limit between the reactants [31]. When the temperature was over 70 °C, the FAEE yield increase was no longer significant. When the temperature exceeded the boiling point of the ethanol, the ethanol began to vaporize, which would reduce the concentration of ethanol in the reaction system and have a negative effect. Therefore, the optimum reaction temperature should be set at 70 °C.

low FAEE yields. With the reaction time exceeding 30 min, the FAEE yield increased rapidly and the maximum yield was 84.6% at 50 min of reaction. With the further extension of time, the FAEE yield slightly decreased. Therefore, the optimal reaction time is 50 min. 3.3. Catalyst stability

3.2.4. Effect of reaction time The reaction time is also one of the factors affecting the FAEE yield. In this experiment, the reaction time changed from 20 to 60 min and the FAEE yield was illustrated in Fig. 6 (the molar ratio of ethanol to oil 15:1, reaction temperature 70 °C, catalyst concentration 10%). During the first 20 min of reaction, the reaction rate is slow, which resulted in

Reusability of catalyst is an essential property to evaluate the quality of heterogeneous catalysts. The transesterification reaction was repeated 5 times under optimized conditions to verify the reusability of the catalysts. After each experiment, the catalyst was recovered by filtration. The catalyst was washed with ethanol and distilled water 3 times, then dried in the oven at 120 °C for 6 h and subsequently calcined at 600 °C for 3 h to activate the catalyst. In fact, the ethanol and water absorbed inside the molecular sieve can be removed by heating [53]. The reusability of catalyst is shown in Fig. 7. It was observed that a high FAEE yield of above 75% was obtained after 5 runs. The decrease in FAEE yield may be due to the deposition of organics in the interior of the molecular sieve resulting in the reduction of active sites and the leaching of the active ingredient (La2O3). Further, the concentration of lanthanum in the mixed solution after separating the catalyst was measured by Atomic Absorption Spectroscopy (AAS) to evaluate the leaching property of lanthanum. The detection result was 23 ppm,

Fig. 5. Effect of temperature on FAEE yield (ethanol:oil molar ratio = 15:1, catalyst concentration = 10 wt%, time = 50 min).

Fig. 7. Catalyst reusability of S-La2O3/NaY-800 (ethanol:oil molar ratio = 15:1, catalyst concentration = 10 wt%, temperature = 70 °C, time = 50 min). 732

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Table 3 Physiochemical properties of the castor oil biodiesel. [8] Specification

Density Viscosity Flash point Calorific value Water content Cetane number Acid value Methyl ester content

Unit

3

kg/m mm2/s o C MJ/kg wt % – mg KOH/ g wt %

GB 251992017

EN 14,214

Castor oil biodiesel

820–900 1.9–6.0 > 130 – < 0.05 > 49.0 < 0.50

860–900 3.5–5.0 > 120 – < 0.05 > 51.0 < 0.50

915 11.2 168 38 0.031 58 0.3077

> 96.5

> 96.5

99.7

[9]

[10]

[11]

[12] [13]

[14]

which indicated that the leaching of lanthanum is negligible. [15]

3.4. Biodiesel characterization [16]

The physicochemical properties of biodiesel are the main basis for determining whether it can be used directly in diesel engines. Properties of the castor oil biodiesel were tested and evaluated according to GB standard test methods and are listed in Table 3. The results showed that it fulfilled the requirements of EN 14,214 and GB 25199-2017 standards, except for the viscosity. In general, the viscosity can be reduced by mixing with petrochemical diesel.

[17]

[18]

[19] [20]

4. Conclusions Transesterification of non-edible castor oil with ethanol was catalyzed by the formed spherical (3–5 mm) S-La2O3/NaY-800. The SLa2O3/NaY-800 catalyst has excellent crushing strength (114 N) and high catalytic activity. The optimized FAEE yield of 84.6% was obtained at optimum reaction conditions (catalyst concentration of 10 wt %, ethanol to oil molar ratio of 15:1, reaction temperature of 70 °C for 50 min). The high catalytic activity of S-La2O3/NaY-800 is related to the good dispersion and large pore size of La2O3 in zeolite NaY. In addition, catalyst durability tests showed that the S-La2O3/NaY-800 catalyst could maintain higher than 75% FAEE yield after 5 cycles of operation.

[21] [22]

[23] [24] [25] [26]

[27]

Acknowledgments

[28]

• The authors acknowledge the support from the Natural Science

Foundation of Shandong Province, China (ZR2015EL044), the Research Excellence Award of Shandong University of Technology (SDUT) and SDUT & Zibo City Integration Development Project (Grant No. 2016ZBXC116). The authors also wish to express their thanks to Zibo Jinxuan Resources and Environmental Technology Development Co. Ltd. for their sincere help during this work.

[29] [30] [31]

[32]

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