Bentonite and Its Modified Forms as Solid Catalyst for Biodiesel Production
Suryadi Ismadji*, Felycia Edi Soetaredjo, Stevie Harsono, and Michael Theodorus Leonardo Department of Chemical Engineering
Widya Mandala Surabaya Catholic University, Kalijudan 37, Surabaya 60114, Indonesia
*Corresponding Author’s E-mail: [email protected] Keywords: Bentonite; Solid Catalyst; Biodiesel.
Abstract
Bentonite has potential application as raw material for solid catalys in the biodiesel production.
The bentonite used in this study was obtained from a bentonite mining locate in Ponorogo, East Java, Indonesia. The catalyst was prepared by the impregnation of bentonite from Pacitan with potassium hydroxide. The ratio between KOH and bentonite was 1:20, 1:10, 1:5, 1:4, 1:3, and 1:2. The characterization of raw bentonite and its modified forms were conducted using several methods such as nitrogen sorption, X-Ray diffraction (XRD) analysis, and Fourrier Transform Infrared Spectroscophy (FTIR) method.
Transesterification process of palm oil was carried out at 60oC with amount of catalyst 3% and methanol to oil ratio was 6. The reaction time was varied from 1 to 6 hours. It was found that the optimum condition for biodiesel production using modified bentonite as catalyst was: KOH/bentonite ratio 1:4 and reaction time 3 hours. Raw bentonite could not be used as catalyst for biodiesel preparation.
1. Introduction
With increasing price of crude oil due to the depletion of fossil fuels resources and the environmental concern in last decades has attracted attetion of researchers to find new, environmental friendly, and renewable energy resources. One of the renewable energy resources is biodiesel. The production of biodiesel is catalytically performed either through transeaterification of triglycerides in the presence of catalyst or the deoxygenative ecofining of triglycerides in non-alcohol environment.
The use of homogeneous acid or base catalyst such as sulphuric acid or sodium hydroxide for the production of biodiesel causes difficulties in recovery after the reaction and produces toxic wastewater. Solid catalysts have been studied as substitutes for homogeneous catalysts, and have the advantages of being easy to recover and reuse, also being compatible with environment considerations (Dhainaut et al., 2010; Gao et al., 2010; Liu et al., 2010; Wen et al., 2010).
Different types of solid catalysts such as metal oxides have been employed in the biodiesel production. Also, in order to minimize the mass transfer limitation for heterogeneous catalysts in liquid phase reaction, different kind of catalyst supports have also been explored for this purpose (Zabeti et al., 2009). In the present work, we studied the transesterification of palm oil with methanol using bentonite and its modified form as catalysts. Effects of KOH/bentonite loading and reaction time on the yield of biodiesel were investigated. Several important fuel properties of biodiesel produced from this experiment were compared with the standard range of diesel fuel or biodiesel specification (Indonesia National Standard).
2. Experimental
Bentonite used in this study was obtained from Ponorogo, East Java, Indonesia. The elemental analysis composition of the bentonite are as follow: Al2O3 30.71%, SiO2 48.22%, FeO 3.14%, CaO 3.76%, MgO 0.56%, K2O 0.17%, Na2O 1.42%, MnO 0.4%. The following pretreatments of the bentonite were conducted: removal of organic impurities using hydrogen peroxide solution, drying until its moisture content 10%, and size reduction to obtain powder bentonite with particle size 80/100 mesh.
Refined palm oil from a commercial brand in Indonesia market was used as raw materials for biodiesel production. This oil was directly used without any further purification. Methanol and potassium hydroxide were obtained from Sigma Aldrich as analytical grade. Methyl heptadecanoate and standard reference for FAME analysis (methyl palmitate, methyl myristate, methyl oleate, methyl stearate and methyl linoleate) were purchased from Kurniajaya Mukti Santosa Pty ltd (Fluka brand).
The modification of bentonite as catalyst for biodiesel production was conducted using the following procedure: A series of KOH/bentonite catalyst were prepared by the impregnation of bentonite from Ponorogo with potassium hydroxide. The ratio between KOH and bentonite were 1:20, 1:10, 1:5, 1:4, 1:3, and 1:2. The preparation of catalyst was conducted in three-neck round bottom flask (500 mL) equipped with a reflux condenser, temperature indicator, and mechanical stirrer. The impregnation of bentonite with KOH was conducted at temperature of 60oC for 24 h under continuous stirring. After the impregnation completed, the slurry was dried in oven at 110oC for 24 h to remove water. The catalyst was then calcined in a tubular muffle furnace at a temperature of 300oC for 5 h.
The characterization of raw bentonite and its modified forms were conducted using several methods such as nitrogen sorption, X-Ray diffraction (XRD) analysis, and Fourrier Transform Infrared Spectroscophy (FTIR) method. The nitrogen sorption analysis was conducted on an Quadrasorb SI. Before the nitrogen sorption measurement, the samples were degassed under vacuum condition at 150oC for at least 24 h. The BET surface area was calculated using standard BET equation in the relative pressure (p/po) range of 0.06 to 0.3. The XRD analysis was carried out using a Rigaku Miniflex Goniometer. The XRD patterns of the bentonite and its modified forms were obtained at 30 kV and 15 mA, using Cu Kα radiation at a step size of 0.01o. While the Qualitative analysis of bentonite and the catalysts was conducted by FTIR method using KBr technique. FTIR analysis was carried out on Shimadzu 8400S FTIR instrument in wavenumber range of 4000-500 cm-
1.
Transesterification process of palm oil was carried out in three-neck round bottom flask (500 mL) equipped with a reflux condenser, temperature indicator, and mechanical stirrer. The reactor was placed in a controlled water bath heater. A known amount of catalyst was added to a known volume of methanol. The mixture then heated at a desired temperature in a controlled water bath heater.
Subsequently, palm oil was added into the mixture under vigorous stirring. The molar ratio between methanol to oil used in this study was 6 and the transesterification reaction was carried out for 1-6 hours. After the reaction completed, the catalyst was removed from the mixture by centrifuge, the glycerin phase was separated and the biodiesel phase was washed with water, decanted and heated to remove water and methanol.
The compositions of the biodiesel produced from transesterification of palm oil and methanol using bentonite as solid catalyst were determined by gas chromatography method. GC-17A equipped with DB-Wax capillary column and FID (flame ionization detector) was used for this purpose. Helium was used as the carrier gas. Methyl heptadecanoate was used as internal standard. Peaks of methyl esters were identified by comparing them with the reference standards. The injector and detector temperatures were 240oC and 280oC, respectively. The initial oven temperature was 80oC with equilibration time of 3 min. After isothermal period, the column oven was heated at heating rate of 10oC/min to 270oC and held for 20 min. The yield of biodiesel was determined by the following equation
where FAME is fatty acid methyl esters.
3. Results and Discussion
The surface areas of bentonite and its modified forms were determined by nitrogen adsorption and the results are summarized in Table 1.
Table 1. The BET surface area and pore volume of bentonite and KOH/bentonite catalysts Catalyst BET surface area, m2/g Pore Volume cm3/g
Raw bentonite 118 0.48
KOH/bentonite 1:20 102 0.31
KOH/bentonite 1:10 72 0.22
KOH/bentonite 1:5 48 0.12
KOH/bentonite 1:4 32 0.06
KOH/bentonite 1:3 15 0.04
KOH/bentonite 1:2 12 0.01
The BET surface area of catalyst decrease with the increase of KOH loading. During the impregnation, the KOH molecules filled the available pores in the bentonite, leading to the decrease of the surface area and pore volume of the catalyst.
The FTIR spectrum of the bentonite as indicated in Table 2 reveals the presence of functional groups such as Al(Mg)-O-H stretching (3614 cm-1), H-O-H stretching (3360 cm-1), H-O-H bending (1670 cm-1), Si-O-Si stretching (1061 cm-1), OH bending bounded Fe3+ and Al3+ (921 cm-1), and Si-O stretching (789 cm-1). A shift of absorption band of Al(Mg)-O-H stretching group from 3614 cm-1 to higher wavenumbers indicates the presence of new functional group in the investigates catalysts (Al- O-K group or compound). Band at about 3433 cm-1 indicates the presence of the stretching vibration
Table 2. FTIR spectra for bentonite and KOH/bentonite 1:4 Functional group Wavenumber, cm-1
Bentonite
Wavenumber, cm-1 KOH/bentonite 1:4
Al(Mg)-O-H stretching 3614 3692
H-O-H stretching 3360 3362
H-O-H bending 1670 1685
Si-O-Si stretching 1061 1058
OH bending bounded Fe3+ and Al3+
921 920
Si-O stretching 789 792
stretching vibration of Al-O-K - 3433
The XRD patterns of raw bentonite and KOH/bentonite (1:4) are given in Figure 1. During calcinations, potassium hydroxide was converted to K2O as indicated in XRD pattern. Peaks observed around 2θ = 31o, 39o, 51o, 55o and 62o are belong to K2O phase
Figure 1. The XRD pattern for (a) raw bentonite and (b) KOH/bentonite 1:4 (a)
(b)
Figure 2 depicts the percentage of the biodiesel yield as the function of KOH/bentonite loading.
Figure 2. The effect of KOH/bentonite loading on the yield of biodiesel
Figure 2 shows that the ratio of KOH gave significant effect on the amount of biodiesel produced. The highest yield (88 %) was obtained at KOH/bentonite 1:4 loading. Increasing ratio of KOH/bentonite also increased the number of active sites K2O which has high catalytic activity and basicity. The active site K2O is responsible for the transesterification reaction between triglycerides and methanol to form biodiesel. Until a certain loading, the KOH molecules were converted to K2O during the calcination process. However, with further increase of KOH loading, the interactions between KOH with internal layer of bentonite (Al-O-H stretching groups) were excessive and during the calcinations, a new phase of Al-O-K compound was formed. This new phase compound (Al-O-K) has lower catalytic activity and basicity than the K2O phase (Noiroj et al., 2009). With the presence of excess amount of Al-O-K compound, the activity of catalyst become lower leading to decrease the amount of biodiesel produced.
The variation of the biodiesel yield with reaction time is given in Figure 3. From this it can be seen that the optimum reaction time for the biodiesel production is 3 hours. During the first three hours the yield of biodiesel increases with the increase of reaction time. After three hours, the yield of biodiesel almost constant as the consequence of the equilibrium conversion has been reached.
The physical properties of biodiesel obtained in this study was also compared with the standard of biodiesel issued by Indonesia National Standard (SNI). The measurements of physical properties of biodiesel produced in this study were conducted according to ASTM standards, and the results are
Table 2. Comparison the properties of biodiesel produced in this experiment with the standard issued by Indonesia National Standard (SNI)
Properties Biodiesel produced SNI Kinematic viscosity at 40oC
(cSt)
4.0 1.9-6.0
Specific gravity (15oC) 0.87 0.86-0.90
Cetane index 60 >45
Flash point (oC) 173 Min 65
Pour point (oC) 16 Max 18
Heating value (Mj/kg) 37.6 -
4. Conclusion
A new solid catalyst from bentonite for biodiesel preparation was obtained in this study. The catalysts were prepared by the impregnation of bentonite from Ponorogo with potassium hydroxide.
The ratio between KOH and bentonite were 1:20, 1:10, 1:5, 1:4, 1:3, and 1:2. The optimum ratio of KOH/bentonite for the biodiesel production was 1:4 with the maximum yield of biodiesel was 88%.
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