Ultrasonics Sonochemistry 21 (2014) 1752–1762
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Biodiesel production from non-edible Silybum marianum oil using heterogeneous solid base catalyst under ultrasonication Mohammed Takase a, Yao Chen b, Hongyang Liu b, Ting Zhao a, Liuqing Yang a,⇑, Xiangyang Wu b,⇑ a b
School of Chemistry and Chemical Engineering, Jiangsu University, 301 Xuefu Rd., 212013 Zhenjiang, Jiangsu, China School of the Environment, Jiangsu University, 301 Xuefu Rd., 212013 Zhenjiang, Jiangsu, China
a r t i c l e
i n f o
Article history: Received 9 March 2014 Received in revised form 5 April 2014 Accepted 6 April 2014 Available online 16 April 2014 Keywords: Biodiesel Heterogeneous catalyst Transesterification Titanium Silybum marianum
a b s t r a c t The aim of this study is to investigate modified TiO2 doped with C4H4O6HK as heterogeneous solid base catalyst for transesterification of non-edible, Silybum marianum oil to biodiesel using methanol under ultrasonication. Upon screening the catalytic performance of modified TiO2 doped with different K-compounds, 0.7 C4H4O6HK doped on TiO2 was selected. The preparation of the catalyst was done using incipient wetness impregnation method. Having doped modified TiO2 with C4H4O6HK, followed by impregnation, drying and calcination at 600 °C for 6 h, the catalyst was characterized by XRD, FTIR, SEM, BET, TGA, UV and the Hammett indicators. The yield of the biodiesel was proportional to the catalyst basicity. The catalyst had granular and porous structures with high basicity and superior performance. Combined conditions of 16:1 molar ratio of methanol to oil, 5 wt.% catalyst amount, 60 °C reaction temperature and 30 min reaction time was enough for maximum yield of 90.1%. The catalyst maintained sustained activity after five cycles of use. The oxidative stability which was the main problem of the biodiesel was improved from 2.0 h to 3.2 h after 30 days using ascorbic acid as antioxidant. The other properties including the flash point, cetane number and the cold flow ones were however, comparable to international standards. The study indicated that Ti-0.7-600-6 is an efficient, economical and environmentally, friendly catalyst under ultrasonication for producing biodiesel from S. marianum oil with a substantial yield. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The continuing rise in global prices of crude oil coupled with the dwindling reserve of conventional energy resources and their associated environmental problems have increased the awareness of other alternative renewable and sustainable resources for fuel industry [1]. Biodiesel, mono-alkyl esters of long chain fatty acids produced from vegetable oils are the most suitable alternate to diesel fuel. Globally, biodiesel is becoming the preferable biofuel [2,3]. Compared with conventional diesel, biodiesel has a lot of advantages which include renewable, biodegradable, low emissions, high flash point and excellent lubricity [4,5]. Biodiesel also reduce the levels of pollutants and can be blended with diesel or used in pure form [6]. Vegetable oils are normally transesterificated using bases, acids and enzymes as catalysts [7,8]. Base catalysts are grouped into ⇑ Corresponding authors. Tel./fax: +86 511 88791800 (L. Yang), +86 511 88791200 (X. Wu). E-mail addresses: [email protected] (L. Yang), [email protected] (X. Wu). http://dx.doi.org/10.1016/j.ultsonch.2014.04.003 1350-4177/Ó 2014 Elsevier B.V. All rights reserved.
homogeneous and heterogeneous. On commercial scale, homogeneous base catalysts are used. There are however, drawbacks in using the homogeneous base catalysts. These include corrosion of equipment and the need to deal with the waste from the neutralization of acids. Acid catalyzed process also consume much time with the consequent consumption of energy. Comparing the homogeneous to heterogeneous, heterogeneous catalysts can provide green and recyclable catalytic activities [9]. For example, studies by Kulkarni et al. [10] and Laosiripojana et al. [11] on heteropolyacid impregnated on different supports (silica, zirconia, alumina, and activated carbon), SO4-ZrO2 and WO3-ZrO2 indicate realistic heterogeneous solid acid catalysts for canola oil biodiesel. However, the concerns of heterogeneous solid acid catalyst have to do with longer reaction time and higher temperatures. Current studies on new methods such as incipient wetness impregnation of loading CaO [12], SrO [13] and KNO3 on flyash [14], ZnO-La2O3 [15] and zinc aluminate [16] respectively, have shown promising for heterogeneous solid base catalyst for biodiesel. Much of the heterogeneous solid base catalysts are currently applied to edible oils [9,17–19] which is worsening the current increment in the global food demand [20]. Other heterogeneous base catalysts are
1753
M. Takase et al. / Ultrasonics Sonochemistry 21 (2014) 1752–1762
very expensive and also complicated in preparation, hence the continuous need for new and efficient catalyst. Various methods such as non-catalytic supercritical, conventional, microwave and ultrasound-assisted are used in producing biodiesel [21–24]. Among the methods, ultrasonication is one of the much preferred and studied using different feedstocks [21]. This is because ultrasonication can increase the interaction between the phases due to the collapse of cavitation bubbles and the ultrasonic jet which causes impingement of one liquid to another which consequently enhances the reaction. It also offers potentially shorter reaction times [21]. In this study, Silybum marianum oil, non-edible feedstock was used. This is because the plant is commonly grown in Guangdong, Hubei, Shanxi and Qinghai (China) and mild climatic regions of different parts of Asia [25,26]. Even though it has received attention for it medicinal and pharmaceutical importance [27,28], studies, indicated that the seeds of the plant contains a lot of oil [29,30]. Our previous studies indicate that the seeds contain a lot of oil [31,32]. The oil is also abundant in silymarin industrial oil production as by-product. This study was therefore undertaken to investigate biodiesel production from S. marianum oil using efficient, economical and environmentally friendly heterogeneous solid base catalyst prepared from modified TiO2 doped with C4H4O6HK under ultrasonication. In our preliminary study, it was found that the catalyst (prepared from potassium bitartrate as active component on modified titanium) could give relatively high yield of biodiesel with reduced time from the oil. The process variables focused on the biodiesel production in the study include methanol to oil ratio, amount of catalyst, reaction temperature, and reaction time. The reaction mechanism of the catalyst is shown in Fig. 1a (supplementary materials). The mechanism of the reaction involves proton abstraction which occurs from the methanol by Ti-0.7-600-6 thereby generating methoxide ion (ROA). The methoxide ion then attacks carbonyl carbon of the triglyceride molecule from S. marianum oil, which forms a tetrahedral intermediate ion. The tetrahedral intermediate ion is then rearranged to generate a diglyceride ion and methyl ester molecule. The diglyceride ion then reacts with the protonated base catalyst leading to the generation of diglyceride molecule and restoring the base catalyst to its original form. The resulting diglyceride molecule finally reacts with another methanol molecule which then continues the catalytic cycle [33].
2.2. Oil extraction The extraction process was a slight modification of our previous works [31,32]. Briefly, the seeds of S. marianum were dried at 110 °C for about 8 h in oven in order to remove the excess moisture before the extraction process. The dried seeds were then crushed and weighed. The extraction process was carried out using soxhlet extractor with petroleum ether (60–90 °C) for 7 h. About 6 L of petroleum ether per kilogram of S. marianum seeds was used. The oil extracted was recovered with rotary evaporator and its amount was then determined using Li et al. [30] method. 2.3. Preparation of pure TiO2 support 0.2 mol of titanium dioxide was first added to 250 ml of distilled water at room temperature (30 °C) for 10 min under mechanical stirring. This was followed by addition of ammonium hydroxide slowly at constant mechanical stirring till pH of the solution which ranged between 10 and 12 was reached. The solution was then kept at constant temperature of 30 °C for 24 h. The resultant precipitate (white) was then separated through filtration and washed three times with distilled water, then followed by drying at 110 °C for 10 h. The solid (TiO2) was then calcined at 530 °C for 5 h to obtain the modified TiO2 [23]. 2.4. Preparation of catalyst All the catalysts used in the study were doped with porous medium supports using solution of potassium compounds by incipient wetness impregnation method [9]. After doping the modified titanium dioxide with potassium bitartrate and allowed for 24 h impregnation period, the catalyst was dried at 110 °C for 10 h and the solid was then calcined in muffle furnace at various loading ratios, temperatures and times (Table 3a–c). The solid base catalyst (Ti-0.7-600-6) was obtained typically by doping 0.7 potassium bitartrate (KHC4H4O6) to modified titanium dioxide (TiO2) in 30 ml distilled water, allowed for 24 h to impregnate, then dried at 110 °C for 10 h and finally calcined at 600 °C for 6 h. A summary of the synthesis scheme of the prepared Ti-0.7-600-6 is illustrated in Fig. 1b (supplementary materials). 2.5. Characterization of the catalysts Fourier transformation infrared (FT-IR) spectra of the samples were obtained between 500 and 4000 cm 1 on KBr powder with FTIR spectrometer (AVATAR 360, Nicolet, Madison, USA). A minimum of 32 scans were performed. The resolution of 2 cm 1 was in the range of 500–4000 cm 1. X-ray diffraction (XRD) patterns of the samples were examined using a reflection scan with nickel-filtered Cu Ka radiation (D8, Bruker-AXS, Germany). The X-ray generator was ran at 40 kV and 70 mA. The measurements were performed at 2h° between 20 and 80°. Scanning electron microscopy (SEM) images were obtained with 20-kV accelerating voltage using field emission scanning electron microscope (S-4800, HITACHI Corp., Tokyo, Japan).
2. Materials and methods 2.1. Materials The S. marianum seeds were obtained from Zhongxing Pharmaceutical Co., Ltd. (Zhenjiang, Jiangsu, China). Methanol, potassium bitartrate (KHC4H4O6), ammonium hydroxide, titanium dioxide (TiO2), alumina (Al2O3), potassium iodide (KI), potassium bromate (KBrO3), and potassium nitrate (KNO3) were all obtained from Sinopharm Chemical Reagent Co. Ltd., (Shanghai, China). All solvents were AR grade.
Table 1 Activity of catalyst and base strength of TiO2 load on different potassium compounds. Catalyst
Modified TiO2
KI/TiO2
K2CO3/TiO2
KBrO3/TiO2
C8H5O4K/TiO2
C4H4O6KNa.4H2O/TiO2
KHC4H4O6/TiO2
Basic strength Biodiesel yield (%)
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Biodiesel production from non-edible Silybum marianum oil using heterogeneous solid base catalyst under ultrasonication Mohammed Takase a, Yao Chen b, Hongyang Liu b, Ting Zhao a, Liuqing Yang a,⇑, Xiangyang Wu b,⇑ a b
School of Chemistry and Chemical Engineering, Jiangsu University, 301 Xuefu Rd., 212013 Zhenjiang, Jiangsu, China School of the Environment, Jiangsu University, 301 Xuefu Rd., 212013 Zhenjiang, Jiangsu, China
a r t i c l e
i n f o
Article history: Received 9 March 2014 Received in revised form 5 April 2014 Accepted 6 April 2014 Available online 16 April 2014 Keywords: Biodiesel Heterogeneous catalyst Transesterification Titanium Silybum marianum
a b s t r a c t The aim of this study is to investigate modified TiO2 doped with C4H4O6HK as heterogeneous solid base catalyst for transesterification of non-edible, Silybum marianum oil to biodiesel using methanol under ultrasonication. Upon screening the catalytic performance of modified TiO2 doped with different K-compounds, 0.7 C4H4O6HK doped on TiO2 was selected. The preparation of the catalyst was done using incipient wetness impregnation method. Having doped modified TiO2 with C4H4O6HK, followed by impregnation, drying and calcination at 600 °C for 6 h, the catalyst was characterized by XRD, FTIR, SEM, BET, TGA, UV and the Hammett indicators. The yield of the biodiesel was proportional to the catalyst basicity. The catalyst had granular and porous structures with high basicity and superior performance. Combined conditions of 16:1 molar ratio of methanol to oil, 5 wt.% catalyst amount, 60 °C reaction temperature and 30 min reaction time was enough for maximum yield of 90.1%. The catalyst maintained sustained activity after five cycles of use. The oxidative stability which was the main problem of the biodiesel was improved from 2.0 h to 3.2 h after 30 days using ascorbic acid as antioxidant. The other properties including the flash point, cetane number and the cold flow ones were however, comparable to international standards. The study indicated that Ti-0.7-600-6 is an efficient, economical and environmentally, friendly catalyst under ultrasonication for producing biodiesel from S. marianum oil with a substantial yield. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The continuing rise in global prices of crude oil coupled with the dwindling reserve of conventional energy resources and their associated environmental problems have increased the awareness of other alternative renewable and sustainable resources for fuel industry [1]. Biodiesel, mono-alkyl esters of long chain fatty acids produced from vegetable oils are the most suitable alternate to diesel fuel. Globally, biodiesel is becoming the preferable biofuel [2,3]. Compared with conventional diesel, biodiesel has a lot of advantages which include renewable, biodegradable, low emissions, high flash point and excellent lubricity [4,5]. Biodiesel also reduce the levels of pollutants and can be blended with diesel or used in pure form [6]. Vegetable oils are normally transesterificated using bases, acids and enzymes as catalysts [7,8]. Base catalysts are grouped into ⇑ Corresponding authors. Tel./fax: +86 511 88791800 (L. Yang), +86 511 88791200 (X. Wu). E-mail addresses: [email protected] (L. Yang), [email protected] (X. Wu). http://dx.doi.org/10.1016/j.ultsonch.2014.04.003 1350-4177/Ó 2014 Elsevier B.V. All rights reserved.
homogeneous and heterogeneous. On commercial scale, homogeneous base catalysts are used. There are however, drawbacks in using the homogeneous base catalysts. These include corrosion of equipment and the need to deal with the waste from the neutralization of acids. Acid catalyzed process also consume much time with the consequent consumption of energy. Comparing the homogeneous to heterogeneous, heterogeneous catalysts can provide green and recyclable catalytic activities [9]. For example, studies by Kulkarni et al. [10] and Laosiripojana et al. [11] on heteropolyacid impregnated on different supports (silica, zirconia, alumina, and activated carbon), SO4-ZrO2 and WO3-ZrO2 indicate realistic heterogeneous solid acid catalysts for canola oil biodiesel. However, the concerns of heterogeneous solid acid catalyst have to do with longer reaction time and higher temperatures. Current studies on new methods such as incipient wetness impregnation of loading CaO [12], SrO [13] and KNO3 on flyash [14], ZnO-La2O3 [15] and zinc aluminate [16] respectively, have shown promising for heterogeneous solid base catalyst for biodiesel. Much of the heterogeneous solid base catalysts are currently applied to edible oils [9,17–19] which is worsening the current increment in the global food demand [20]. Other heterogeneous base catalysts are
1753
M. Takase et al. / Ultrasonics Sonochemistry 21 (2014) 1752–1762
very expensive and also complicated in preparation, hence the continuous need for new and efficient catalyst. Various methods such as non-catalytic supercritical, conventional, microwave and ultrasound-assisted are used in producing biodiesel [21–24]. Among the methods, ultrasonication is one of the much preferred and studied using different feedstocks [21]. This is because ultrasonication can increase the interaction between the phases due to the collapse of cavitation bubbles and the ultrasonic jet which causes impingement of one liquid to another which consequently enhances the reaction. It also offers potentially shorter reaction times [21]. In this study, Silybum marianum oil, non-edible feedstock was used. This is because the plant is commonly grown in Guangdong, Hubei, Shanxi and Qinghai (China) and mild climatic regions of different parts of Asia [25,26]. Even though it has received attention for it medicinal and pharmaceutical importance [27,28], studies, indicated that the seeds of the plant contains a lot of oil [29,30]. Our previous studies indicate that the seeds contain a lot of oil [31,32]. The oil is also abundant in silymarin industrial oil production as by-product. This study was therefore undertaken to investigate biodiesel production from S. marianum oil using efficient, economical and environmentally friendly heterogeneous solid base catalyst prepared from modified TiO2 doped with C4H4O6HK under ultrasonication. In our preliminary study, it was found that the catalyst (prepared from potassium bitartrate as active component on modified titanium) could give relatively high yield of biodiesel with reduced time from the oil. The process variables focused on the biodiesel production in the study include methanol to oil ratio, amount of catalyst, reaction temperature, and reaction time. The reaction mechanism of the catalyst is shown in Fig. 1a (supplementary materials). The mechanism of the reaction involves proton abstraction which occurs from the methanol by Ti-0.7-600-6 thereby generating methoxide ion (ROA). The methoxide ion then attacks carbonyl carbon of the triglyceride molecule from S. marianum oil, which forms a tetrahedral intermediate ion. The tetrahedral intermediate ion is then rearranged to generate a diglyceride ion and methyl ester molecule. The diglyceride ion then reacts with the protonated base catalyst leading to the generation of diglyceride molecule and restoring the base catalyst to its original form. The resulting diglyceride molecule finally reacts with another methanol molecule which then continues the catalytic cycle [33].
2.2. Oil extraction The extraction process was a slight modification of our previous works [31,32]. Briefly, the seeds of S. marianum were dried at 110 °C for about 8 h in oven in order to remove the excess moisture before the extraction process. The dried seeds were then crushed and weighed. The extraction process was carried out using soxhlet extractor with petroleum ether (60–90 °C) for 7 h. About 6 L of petroleum ether per kilogram of S. marianum seeds was used. The oil extracted was recovered with rotary evaporator and its amount was then determined using Li et al. [30] method. 2.3. Preparation of pure TiO2 support 0.2 mol of titanium dioxide was first added to 250 ml of distilled water at room temperature (30 °C) for 10 min under mechanical stirring. This was followed by addition of ammonium hydroxide slowly at constant mechanical stirring till pH of the solution which ranged between 10 and 12 was reached. The solution was then kept at constant temperature of 30 °C for 24 h. The resultant precipitate (white) was then separated through filtration and washed three times with distilled water, then followed by drying at 110 °C for 10 h. The solid (TiO2) was then calcined at 530 °C for 5 h to obtain the modified TiO2 [23]. 2.4. Preparation of catalyst All the catalysts used in the study were doped with porous medium supports using solution of potassium compounds by incipient wetness impregnation method [9]. After doping the modified titanium dioxide with potassium bitartrate and allowed for 24 h impregnation period, the catalyst was dried at 110 °C for 10 h and the solid was then calcined in muffle furnace at various loading ratios, temperatures and times (Table 3a–c). The solid base catalyst (Ti-0.7-600-6) was obtained typically by doping 0.7 potassium bitartrate (KHC4H4O6) to modified titanium dioxide (TiO2) in 30 ml distilled water, allowed for 24 h to impregnate, then dried at 110 °C for 10 h and finally calcined at 600 °C for 6 h. A summary of the synthesis scheme of the prepared Ti-0.7-600-6 is illustrated in Fig. 1b (supplementary materials). 2.5. Characterization of the catalysts Fourier transformation infrared (FT-IR) spectra of the samples were obtained between 500 and 4000 cm 1 on KBr powder with FTIR spectrometer (AVATAR 360, Nicolet, Madison, USA). A minimum of 32 scans were performed. The resolution of 2 cm 1 was in the range of 500–4000 cm 1. X-ray diffraction (XRD) patterns of the samples were examined using a reflection scan with nickel-filtered Cu Ka radiation (D8, Bruker-AXS, Germany). The X-ray generator was ran at 40 kV and 70 mA. The measurements were performed at 2h° between 20 and 80°. Scanning electron microscopy (SEM) images were obtained with 20-kV accelerating voltage using field emission scanning electron microscope (S-4800, HITACHI Corp., Tokyo, Japan).
2. Materials and methods 2.1. Materials The S. marianum seeds were obtained from Zhongxing Pharmaceutical Co., Ltd. (Zhenjiang, Jiangsu, China). Methanol, potassium bitartrate (KHC4H4O6), ammonium hydroxide, titanium dioxide (TiO2), alumina (Al2O3), potassium iodide (KI), potassium bromate (KBrO3), and potassium nitrate (KNO3) were all obtained from Sinopharm Chemical Reagent Co. Ltd., (Shanghai, China). All solvents were AR grade.
Table 1 Activity of catalyst and base strength of TiO2 load on different potassium compounds. Catalyst
Modified TiO2
KI/TiO2
K2CO3/TiO2
KBrO3/TiO2
C8H5O4K/TiO2
C4H4O6KNa.4H2O/TiO2
KHC4H4O6/TiO2
Basic strength Biodiesel yield (%)
