The waste shell was utilized as a bioresource of calcium oxide (CaO) in catalyzing a transesterification to produce biodiesel (methyl ester). The economic and environmen-friendly catalysts were prepared by a calcination method at 700–1,000°C for 4 h. The heterogeneous catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and the Brunauer-Emmett-Teller (BET) method. The effects of reaction variables such as reaction time, reaction temperature, methanol/oil molar ratio, and catalyst loading on the yield of biodiesel were investigated. Reusability of waste shell catalyst was also examined. The results indicated that the CaO catalysts derived from waste shell showed good reusability and had high potential to be used as biodiesel production catalysts in transesterification of palm oil with methanol.
Recently, alternative energies have been focused worldwide because of recent energy crisis. Biodiesel is one of the interesting alternative fuels which can be produced from renewable sources [
The catalyst synthesized with the waste shells opens door for renewable catalyst and at the same time recycles the waste generated. Utilization of these waste materials not only reduces the catalyst cost but also promotes environmentally benign process. These shells may also find their utility in other base catalyzed important organic reactions which will add value to the waste generated [
Palm oil was purchased from Morakot Industries Public Company Limited, Thailand. The molecular weight and density of the oil were measured to be 851.06 g/mole and 0.868 g/cm3, respectively. The mussel, cockle, and scallop shells were collected as wastes from university cafeterias. The waste shells were rinsed with water to remove dust and impurities and were then dried in an oven. All chemicals were analytical-grade reagents (Merck, >99% purity) and were used as received.
The catalysts were prepared by a calcination method. The dried waste shells were calcined at 700–1,000°C in air atmosphere with a heating rate of 10°C/min for 4 h [
Preparation of CaO catalyst derived from waste shell (1,000°C).
The X-ray diffraction (XRD) characterization of the waste shell-derived catalyst was performed on a Rigaku (MiniFlex II, England) based generator X-ray diffractometer using CuK
The elemental chemical compositions of the materials were analyzed by X-ray fluorescence spectroscopy (XRF—Oxford, ED-2000, England) under energy dispersive mode for precise measurement of both light and heavy elements.
The microstructures of the calcined waste shells were observed by a scanning electron microscope (SEM). The SEM images of the representative sample were obtained from a Camscan-MX 2000 (England) equipped with an energy dispersive spectroscope (EDS).
To evaluate the surface area, mean pore diameter, and pore volume, adsorption-desorption of nitrogen (N2) at 77 K was carried out by a Quantachrome Instrument (Autosorb-1 Model No. ASIMP.VP4, USA). Before taking adsorption data, degassing at 120°C and a residual pressure of 300
The synthesis of biodiesel from palm oil and methanol was carried out in a 500 mL glass reactor equipped with condenser and mechanical stirrer at atmospheric pressure. The effects of reaction time (2 to 6 h), reaction temperature (50 to 70°C), methanol/oil molar ratio (6 to 18), catalyst loading (5 to 25 wt.%), and reusability of catalyst (1 to 4 times) on the conversion to biodiesel were studied. After a certain period of time, a known amount of sample was taken out from the reactor for analysis. All experiments were repeated 3 times and the standard deviation was never higher than 7% for any point.
Composition of the fatty acid methyl ester (FAME) was analyzed with gas chromatograph-mass spectrometry (GC-MS QP2010 Plus, Shimadzu Corporation, Japan) equipped with a flame ionization detector (FID) and a capillary column 30 m × 0.32 mm × 0.25
where
The XRD patterns of natural and calcined mussel shell are given in Figure
XRD patterns of natural and calcined mussel shell (□: CaCO3, ■: CaO).
XRD patterns of waste mussel, cockle, and scallop shell calcined at 1,000°C (■: CaO).
The chemical compositions of the catalyst are presented in Table
Chemical compositions of waste shell-derived catalyst.
Compound | Concentration (wt.%) | ||
---|---|---|---|
Mussel shell | Cockle shell | Scallop shell | |
CaO | 98.367 | 99.170 | 97.529 |
Na2O | 0.937 | 0.438 | 0.565 |
SO3 | 0.293 | 0.117 | 1.568 |
P2O5 | 0.163 | 0.096 | 0.204 |
SrO | 0.158 | 0.132 | 0.107 |
ZrO2 | 0.046 | — | 0.027 |
Cl | 0.037 | — | — |
Fe2O3 | — | 0.026 | — |
The morphology of waste mussel, cockle, and scallop shell calcined at 1,000°C was examined by SEM (Figure
SEM images of (a) mussel shell, (b) cockle shell, and (c) scallop shell calcined at 1,000°C.
The physical properties of the CaO catalyst are summarized in Table
The physical properties of waste shell-derived catalyst.
Physical property | Derived catalyst | ||
---|---|---|---|
Mussel shell | Cockle shell | Scallop shell | |
Surface area (m2/g) | 89.91 | 59.87 | 74.96 |
Pore volume (cm3/g) | 0.130 | 0.087 | 0.097 |
Mean pore diameter (Å) | 34.55 | 25.53 | 30.55 |
The yield of biodiesel was affected by reaction variables, such as reaction time, reaction temperature, methanol/oil molar ratio, catalyst loading, and reusability of catalyst. The reaction variables were associated with the type of catalysts used [
The effect of reaction time on the conversion of palm oil to biodiesel was investigated. Reaction time is one of the key parameters during the transesterification carried out in glass reactor. Figure
Effect of reaction time on % yield of biodiesel.
In general, the reaction temperature can influence the reaction rate and yield of biodiesel. The transesterification of triglyceride (TG) with methanol to methyl ester was carried out over the catalysts of CaO at reaction temperature 50–70°C. The % yields of biodiesel after 3 h of reaction time are shown as a function of temperature in Figure
Effect of reaction temperature on % yield of biodiesel.
The excess of methanol is necessary because it can increase the rate of methanolysis. Normally, stoichiometric molar ratio of methanol to TG is near 6 : 1 when the alkali-catalyzed process is used. However, it increases to 30 : 1, even 50 : 1, in the acid-catalyzed one to ensure high conversion [
Effect of methanol/oil molar ratio on % yield of biodiesel.
Figure
Effect of catalyst loading on % yield of biodiesel.
The reusability of catalyst is examined by carrying out reaction cycles. When transesterification reaction finished, the catalyst is separated from the mixture and used again without any subsequent treatment in a second reaction under the same conditions as before. It is found that the prepared catalyst is active for 3 reaction cycles, with yield above 90%. After 3 reaction cycles, the biodiesel yield lowers to 90% (Figure
Effect of reusability of catalyst on % yield of biodiesel.
The fuel properties of methyl ester obtained in this work are summarized in Table
The fuel properties of biodiesel.
Fuel property | Derived catalyst | ||
---|---|---|---|
Mussel shell | Cockle shell | Scallop shell | |
Kinematic viscosity (mm2/s) at 40°C | 4.4 | 4.6 | 4.5 |
Density (g/cm3) at 80°C | 0.877 | 0.878 | 0.878 |
Flash point (°C) | 164 | 165 | 164 |
Cloud point (°C) | 11 | 12 | 11 |
Pour point (°C) | 7 | 8 | 8 |
Acid value (mg KOH/g oil) | 0.47 | 0.67 | 0.55 |
Water content (%) | 0.02 | 0.03 | 0.02 |
Using cost-effective and environment-friendly catalysts is particularly useful for the production of biodiesel. The waste shells are used as the catalyst for this process. This catalyst contains CaCO3 which is converted to CaO after calcination at temperatures 1,000°C for 4 h. The optimum conditions, which yielded a conversion of palm oil of nearly 95% for all waste shell-derived catalysts, were reaction time 3 h, reaction temperature 65°C, methanol/oil molar ratio 9, and catalyst loading 10 wt.% with pressure 1 atm in glass reactor. The experimental results show that CaO catalyst had excellent activity and stability during transesterification. The catalyst was used for 4 cycles and apparent low activity loss was observed. The fuel properties of the biodiesel so obtained meet all biodiesel standards. As a solid catalyst, CaO can decrease the cost of biodiesel and the steps of purification. It has potential for industrial application in the transesterification of palm oil to methyl ester.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors acknowledge sincerely the Department of Materials Science and Engineering (MATSE), Faculty of Engineering and Industrial Technology, Silpakorn University, (SU), and National Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials (PPAM), Chulalongkorn University (CU) for supporting and encouraging this investigation.