The 11 th International Chemical Engineering Congress & Exhibition (IChEC 2020) Fouman, Iran, 15-17 April, 2020 Influence of auxiliary fuel on the properties of alkaline mixed metal oxide catalyst fabricated by combustion method for biodiesel production H. Nayebzadeh * , B. Rahmanivahid Central Research Laboratory, Esfarayen University of Technology, Esfarayen, North Khorasan, Iran [email protected]Abstract The solution combustion method was utilized for the fabrication of the alkaline mixed metal oxide catalyst containing Ca and Al cations in which the fuel content was assessed by adding the auxiliary fuel, sorbitol, in the mixture. Then, the samples were impregnated by potassium ions to increase their activity in the transesterification reaction. The results revealed that adding an auxiliary fuel increased the combustion reaction temperature and duration such that the crystallinity, external porosity and thermal stability of the sample (KOH/Ca12Al14O33) were enhanced. Moreover, due to the reduction the amorphous structure of the support, the well- bonding between K ions with the surface of support increased, and the activity was increased, consequently. The sample fabricated by the high amount of sorbitol converted more than 91% of canola oil to biodiesel at the conditions of 450 W of microwave power, 12 molar ratio of methanol-to-oil, 4 weight percent of catalyst and 60 min reaction time. The results present that the combustion method is an efficient and fast method for the fabrication of the nanosized catalyst with high activity in which the optimization of the fuel is very important. Moreover, the catalyst can consider as a suitable choice for industrial application Keywords: Alkaline catalyst, Mixed metal oxide, Solution combustion method, Sorbitol, Transesterification, Biodiesel. Introduction Nowadays, heterogeneous biodiesel production was extremely concerned due to simple separation, environmentally friendly process, less amount of wastewater and elimination of some separation and purification steps [1]. Alkaline form of a heterogeneous catalyst containing basic cations such as potassium, sodium, calcium, barium, etc. is suggested because the reaction is fastly performed by using these catalysts against the acid form. Calcium and potassium are the most attractive cations for transesterification reaction, while high leaching of Ca 2+ and K + ions in the reaction mixture is a major drawback that caused to their less reusability [2, 3]. To overcome the problem, alumina, zirconia, ferric oxide, etc. are usually utilized as support that alumina is mostly used due to its simple availability and lower price. Ca and K ions can load on the surface of alumina or incorporated into its lattice. It was mentioned that mixed metal oxide has higher stability compared to supported form. Therefore, Ca/Al to form calcium aluminate can have higher activity than CaO/Al2O3 structure.
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The 11th International Chemical Engineering Congress & Exhibition (IChEC 2020) Fouman, Iran, 15-17 April, 2020
Influence of auxiliary fuel on the properties of alkaline mixed metal oxide catalyst fabricated by combustion method for
biodiesel production
H. Nayebzadeh*, B. Rahmanivahid Central Research Laboratory, Esfarayen University of Technology, Esfarayen, North Khorasan, Iran
Abstract The solution combustion method was utilized for the fabrication of the alkaline mixed metal oxide catalyst containing Ca and Al cations in which the fuel content was assessed by adding the auxiliary fuel, sorbitol, in the mixture. Then, the samples were impregnated by potassium ions to increase their activity in the transesterification reaction. The results revealed that adding an auxiliary fuel increased the combustion reaction temperature and duration such that the crystallinity, external porosity and thermal stability of the sample (KOH/Ca12Al14O33) were enhanced. Moreover, due to the reduction the amorphous structure of the support, the well-bonding between K ions with the surface of support increased, and the activity was increased, consequently. The sample fabricated by the high amount of sorbitol converted more than 91% of canola oil to biodiesel at the conditions of 450 W of microwave power, 12 molar ratio of methanol-to-oil, 4 weight percent of catalyst and 60 min reaction time. The results present that the combustion method is an efficient and fast method for the fabrication of the nanosized catalyst with high activity in which the optimization of the fuel is very important. Moreover, the catalyst can consider as a suitable choice for industrial application Keywords: Alkaline catalyst, Mixed metal oxide, Solution combustion method, Sorbitol, Transesterification, Biodiesel.
Introduction Nowadays, heterogeneous biodiesel production was extremely concerned due to simple separation, environmentally friendly process, less amount of wastewater and elimination of some separation and purification steps [1]. Alkaline form of a heterogeneous catalyst containing basic cations such as potassium, sodium, calcium, barium, etc. is suggested because the reaction is fastly performed by using these catalysts against the acid form. Calcium and potassium are the most attractive cations for transesterification reaction, while high leaching of Ca2+ and K+ ions in the reaction mixture is a major drawback that caused to their less reusability [2, 3]. To overcome the problem, alumina, zirconia, ferric oxide, etc. are usually utilized as support that alumina is mostly used due to its simple availability and lower price. Ca and K ions can load on the surface of alumina or incorporated into its lattice. It was mentioned that mixed metal oxide has higher stability compared to supported form. Therefore, Ca/Al to form calcium aluminate can have higher activity than CaO/Al2O3 structure.
The 11th International Chemical Engineering Congress & Exhibition (IChEC 2020) Fouman, Iran, 15-17 April, 2020
High thermal treatment is usually required for the fabrication of mixed metal oxides with well-diffusion of cations into host lattice. Some new methods were reported for the preparation of the catalyst with an appropriate structure with lower energy consumption than the solution combustion synthesis has emerged as an attractive way for the production of homogeneous, high-purity, and crystalline oxide powders at significantly lower temperatures than the conventional synthesis methods [4]. This reaction needs an initial heat source for starting the spontaneous combustion reaction that microwave irradiation can provide uniform heating in a short time. One of the important parameters in the combustion method is the fuel amount. Fuel is a form of soluble carbohydrates that provides the combustion reaction temperature that urea is the traditional fuel. The fuel amount is related to combustion temperature and duration. The stoichiometric amount of fuel is at least required for decomposition most of the reactants [5]. However, although the higher amount of fuel is usually needed for complete combustion, a high amount of urea can eliminate the combustion due to releasing a huge amount of gases from the reaction mixture, which prevents the diffusion of oxygen to a reaction medium for continuous combustion [6]. Therefore, the fuel with high carbon content with less amount can be a suitable choice that had not been reported in any study. In this study, an alkaline heterogeneous mixed metal catalyst containing K, Ca, and Al ions were synthesized by solution combustion method in which the urea was used as fuel and sorbitol in various levels was added to parent solution as an auxiliary fuel. The samples were characterized to assess the effect of auxiliary fuel on the properties of K/Ca-Al mixed oxide. Finally, the fuel influence on the activity of the samples was investigated in the biodiesel production process in which canola oil was converted to esters. Experimental In the solution combustion method, the metal nitrates (Al(NO3)3.9H2O and Ca(NO3)2.6H2O (Ca/Al molar ratio of 12/14)) is mixed with water. Then, urea in the stoichiometric ratio (Ca/Urea ratio of 12/55) was added and sorbitol as auxiliary fuel to improve the combustion reaction in three levels (0, 0.05 and 0.015 molar ratio to urea) was increased. After gelling the mixture by heating at 80 °C, the mixture was transformed into powder form by heating in the domestic microwave oven (Daewoo, 900 watts, 2.45 GHz) after releasing the huge amount of gases and combustion the mixture. The samples were labeled as CA-1-0, CA-1-0.05, and CA-1-0.15. To prepare potassium loaded Ca/Al mixed oxides, 1 gr of each sample was impregnated by 0.1 M KOH aqueous solution (20 wt.%) [7]. The alkaline heterogeneous mixed metal oxide catalyst was obtained by calcination of the mixture at 800 °C for 3 h under (KCA-1-0, KCA-1-0.05, and KCA-1-0.15). The X-ray diffraction (XRD) using UNISANTIS/XMP 300 using Cu Ka radiation was used for crystalline phase determination. The active surface functional groups of the catalysts were analyzed by FTIR in the range of 400-4000 cm-1 using SHIMADZU 4300 (Japan) spectrometer. TGA analysis of the nanocatalysts was performed to evaluate the effect of sorbitol on the quality of the combustion of the metal precursors using the Evolution STA apparatus (SITARAM, France) in atmosphere medium. Field Emission Scanning Electron Microscopy (FESEM) was accomplished using MIRA3 FEG-SEM (TESCAN, Czech republic) to observe the morphology and surface structure of all samples. The activity of the nanocatalysts was examined in the transesterification reaction of canola oil to biodiesel via microwave irradiation. The biodiesel was obtained after reaction of 20 g of canola oil, 14.3 mL methanol, and 0.8 g catalyst, which poured in 100 mL glass reactor
The 11th International Chemical Engineering Congress & Exhibition (IChEC 2020) Fouman, Iran, 15-17 April, 2020
connected with a condenser. The reaction was performed for 60 min under microwave power of 450 W [8]. After the reaction, the top layer containing biodiesel was separated by the settling method for 1 h and heated to remove excess methanol. The fatty acid methyl ester (FAME) content of produced biodiesel was determined according to the EN14214 method using a gas chromatograph (GC, Tief Gostar Faraz co., Iran) equipped with FID detector and SUPRAWAX-280 capillary column (30 m×0.25 mm×0.25 µm). Results and discussion The effect of adding excess fuel during the combustion method on the crystalline structure and morphology of synthesized samples is illustrated in Figure 1. All the samples show the calcium aluminate structure (mayenite, Ca12Al14O33, as called CA) (JCPDS No. 78-0910). In the car and Al2O3 system, mayenite forms as the first structure of calcium aluminate [9]. The intensity of these phases was increased by loading sorbitol as an auxiliary fuel for complete combustion. It can conclude to increase the combustion temperature and duration and transformation a higher amount of precursors or amorphous to crystalline structure and then diffusing the Ca ions in alumina lattice. In addition, the K2O (JCPDS No. 47-1701) and KO2 (JCPDS No. 10-0235) phases can detect that are related to the bonding of potassium ions on the surface of the support. By increasing the crystallinity of the support, the bonding of the potassium components with the surface was increased, and the intensity of these structures was enhanced [10].
Figure 1. (a) XRD and (b) FESEM images of a synthesized alkaline catalyst via combustion method with
additive fuel The FESEM images show that by increasing a low amount of sorbitol, the combustion reaction was firstly performed incomplete such that the agglomerated particles observe. It can be due to the high proportion of C/H in sorbitol molecules. On the other hand, the porosity of the catalyst as an important parameter for the samples used in the transesterification reaction
The 11th International Chemical Engineering Congress & Exhibition (IChEC 2020) Fouman, Iran, 15-17 April, 2020
was significantly increased [9]. However, at a higher amount, the urea makes the initial flame and the combustion was performed by continuous combustion of carbon molecules of sorbitol. Therefore, the growth of rod-like nanosized calcium aluminate can be detectable. The FTIR spectra and TGA plots of the nanocatalysts are illustrated in Figure 2. The Ca–O bond is observed around 470 cm-1 [2]. The stretching vibrations for tetrahedral (AlO4) and octahedral (AlO6) of Al–O are respectively observed in the 700-850 cm-1 and 500-700 cm-1
that was reduced these peaks intensity due to more diffusion of Ca ion in alumina lattice [8]. Bonding of the potassium component on the support surface to form Ca/Al–O–K is also observed at 1470, 1395, 1020, and 935 cm-1 [4]. A bond between 3200-3400 cm-1 is related to the O-H stretching vibration of an absorbed water molecule on the surface of the nanocatalysts as well as a bending bond of OH 1670 cm-1 [11]. TG plots of the support (without potassium loading) prepared by different sorbitol amounts are also depicted in Figure 2. Three regions can mention for weight loss of the samples which totally explain the level of completing the combustion reaction. Evaporation of moisture of the samples was occurred below 200 °C. The sample prepared without using sorbitol presented the highest wight loss that confirms low decomposition of precursores during combustion due to insuffient temperature of the medium [12]. The second reduction in weight in the range of 200-500°C is owing to pyrolysis of organic groups and/or nitrate precursors, which exhibit incomplete combustion reaction [54]. High weight loss of CA-1-0 can prove its lower crystalinity compared to other sample which observed in the XRD patterns [12]. Diffison of Ca ion in alumina lattice is occurred in high temperature such that CA-1-0.15 shows the lowest weight loss that can prove almost complete diffusion of Ca ions in alumina in the sample due to increase of reaction temperature and duration [13].
Figure 2. (a) FTIR and (b) TGA plots of a synthesized alkaline catalyst via combustion method with
additive fuel
The activity of the nanocatalysts in the biodiesel production process from canola oil is shown in Figure 3. As expected from the results, the KCA-1-0.015 showed the highest activity due to its higher crystallinity, higher Ca ion diffusion into Al2O3 lattice to form Ca12Al14O33, better active phases bonding (potassium component) with the support surface, and higher thermal stability of the support. Moreover, the sample converted a suitable amount of oil to biodiesel that can reach higher conversion after optimizing the reaction which can be evaluated in our future works. Wavenumber (cm-1)4000 3500 3000 2500 2000 1500 1000 500
The 11th International Chemical Engineering Congress & Exhibition (IChEC 2020) Fouman, Iran, 15-17 April, 2020
Figure 3. Performance of synthesized alkaline catalyst via combustion method with additive fuel in the
biodiesel production process The stability of the optimum nanocatalyst (KCA-1.0.15) in the transesterification reaction was assessed by several using the sample after each use. After each reaction, the used catalyst was washed with the methanol-hexane solution and calcined at 800 °C for 1 h to eliminate all of remained reactants and products into properties and on the surface of the catalyst. The activity of the sample was reduced to 83.8% after 5 uses (around 8.5% reduction in the activity) that prove to increase the activity of the sample by doping the Ca ions into alumina lattice as compared to the results reported for supported catalysts (CaO/Al2O3) [14, 15]. Conclusions The alkaline metal oxide is a highly active catalyst for the production of biodiesel that presented low stability in most studies due to solubility in the reaction medium. In this study, doped metal oxide of Ca and Al ions to form calcium aluminate was fabricated by solution combustion method. For improving the combustion temperature for obtaining the powder with the appropriate properties, an auxiliary fuel with high carbon content (sorbitol) was used. The results presented that urea/sorbitol at the molar ratio of 1/0.15 can result in the doped metal oxide nanocatalyst with high crystallinity and stability under reaction temperature. The KCA-1-0.15 nanocatalyst also showed sufficient bonding of potassium components with the surface of the support. The sample converted 91.6% of triglycerides of canola oil to FAME. Moreover, the sample preserved its activity at least 5 times that can confirm the positive effect of the combustion method for the fabrication of doped structure nanocatalyst with sufficient incorporation of dopant ions into host lattice. References [1] B. Sajjadi, A. A. A. Raman, H. Arandiyan, "A comprehensive review on properties of edible and non-edible vegetable oil-based biodiesel: Composition, specifications and prediction models. Renewable and Sustainable Energy Reviews", 63, pp. 62-92, (2016). [2] M. Hojjat, H. Nayebzadeh, M. Khadangi-Mahrood, B. Rahmani-Vahid, "Optimization of process conditions for biodiesel production over CaO–Al2O3/ZrO2 catalyst using response surface methodology. Chemical Papers", 71(3), pp. 689-698, (2016).
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The 11th International Chemical Engineering Congress & Exhibition (IChEC 2020) Fouman, Iran, 15-17 April, 2020
[3] Marinkovic Milos M., S. N. I., Vasic Marija B., Ljupkovic Radomir B., Rancic Sofija M., Spalovic Boban R., et al., "Synthesis of biodiesel from sunflower oil over potassium loaded alumina as heterogeneous catalyst: The effect of process parameters. Hemijska industrija", 70(1-10), pp., (2016). [4] M. Hashemzehi, N. Saghatoleslami, H. Nayebzadeh, "A study on the structure and catalytic performance of ZnxCu1−xAl2O4 catalysts synthesized by the solution combustion method for the esterification reaction. Comptes Rendus Chimie", 19(8), pp. 955-962, (2016). [5] S. Alaei, M. Haghighi, J. Toghiani, B. Rahmani Vahid, "Magnetic and reusable MgO/MgFe2O4 nanocatalyst for biodiesel production from sunflower oil: Influence of fuel ratio in combustion synthesis on catalytic properties and performance. Industrial Crops and Products", 117, pp. 322-332, (2018). [6] A.-H. Azmoon, A. Ahmadpour, H. Nayebzadeh, N. Saghatoleslami, A. Heydari, "Fabrication of nanosized SO42−/Co–Al mixed oxide via solution combustion method used in esterification reaction: effect of urea-nitrate ratio on the properties and performance. Journal of Nanostructure in Chemistry", pp., (2019). [7] H. Nayebzadeh, N. Saghatoleslami, M. Haghighi, M. Tabasizadeh, E. Binaeian, "Comparative assessment of the ability of a microwave absorber nanocatalyst in the microwave-assisted biodiesel production process. Comptes Rendus Chimie", 21(7), pp. 676-683, (2018). [8] H. Nayebzadeh, N. Saghatoleslami, M. Haghighi, M. Tabasizadeh, "Catalytic Activity of KOH–CaO–Al2O3 Nanocomposites in Biodiesel Production: Impact of Preparation Method. International Journal of Self-Propagating High-Temperature Synthesis", 28(1), pp. 18-27, (2019). [9] N. Avci, K. Korthout, M. A. Newton, P. F. Smet, D. Poelman, "Valence states of europium in CaAl2O4:Eu phosphors Optical Materials Express", 2(3), pp. 321-330, (2012). [10] A. Rezayan, M. Taghizadeh, "Synthesis of magnetic mesoporous nanocrystalline KOH/ZSM-5-Fe3O4 for biodiesel production: Process optimization and kinetics study. Process Safety and Environmental Protection", 117, pp. 711-721, (2018). [11] F. Naderi, H. Nayebzadeh, "Performance and stability assessment of Mg-Al-Fe nanocatalyst in the transesterification of sunflower oil: Effect of Al/Fe molar ratio. Industrial Crops and Products", 141, pp. 111814, (2019). [12] B. Rahmani Vahid, M. Haghighi, "Urea-nitrate combustion synthesis of MgO/MgAl2O4 nanocatalyst used in biodiesel production from sunflower oil: Influence of fuel ratio on catalytic properties and performance. Energy Conversion and Management", 126, pp. 362-372, (2016). [13] J. Chen, L. Jia, X. Guo, L. Xiang, S. Lou, "Production of novel biodiesel from transesterification over KF-modified Ca-Al hydrotalcite catalyst. RSC Advances", 4(104), pp. 60025-60033, (2014).
The 11th International Chemical Engineering Congress & Exhibition (IChEC 2020) Fouman, Iran, 15-17 April, 2020
[14] V. Narula, M. F. Khan, A. Negi, S. Kalra, A. Thakur, S. Jain, "Low temperature optimization of biodiesel production from algal oil using CaO and CaO/Al2O3 as catalyst by the application of response surface methodology. Energy", 140, pp. 879-884, (2017). [15] M. Zabeti, W. M. A. W. Daud, M. K. Aroua, "Optimization of the activity of CaO/Al2O3 catalyst for biodiesel production using response surface methodology. Applied Catalysis A: General", 366(1), pp. 154-159, (2009).
