Heterogeneous base catalysts for edible palm and non-edible Jatropha-based biodiesel production
© Lee et al.; licensee Chemistry Central Ltd. 2014
Received: 27 January 2014
Accepted: 23 April 2014
Published: 3 May 2014
Transesterification catalyzed by solid base catalyst is a brilliant technology for the noble process featuring the fast reaction under mild reacting condition in biodiesel production. Heterogeneous base catalysts are generally more reactive than solid acid catalysts which require extreme operating condition for high conversion and biodiesel yield. In the present study, synthesis of biodiesel was studied by using edible (palm) or non-edible (Jatropha) feedstock catalyzed by heterogeneous base catalysts such as supported alkali metal (NaOH/Al2O3), alkaline-earth metal oxide (MgO, CaO and SrO) and mixed metal oxides catalysts (CaMgO and CaZnO).
The chemical characteristic, textural properties, basicity profile and leaching test of synthesized catalysts were studied by using X-ray diffraction, BET measurement, TPD-CO2 and ICP-AES analysis, respectively. Transesterification activity of solid base catalysts showed that > 90% of palm biodiesel and > 80% of Jatropha biodiesel yield under 3 wt.% of catalyst, 3 h reaction time, methanol to oil ratio of 15:1 under 65°C. This indicated that other than physicochemical characteristic of catalysts; different types of natural oil greatly influence the catalytic reaction due to the presence of free fatty acids (FFAs).
Among the solid base catalysts, calcium based mixed metal oxides catalysts with binary metal system (CaMgO and CaZnO) showed capability to maintain the transesterification activity for 3 continuous runs at ~ 80% yield. These catalysts render high durability characteristic in transesterification with low active metal leaching for several cycles.
KeywordsTransesterification Palm oil Jatropha oil Solid base catalyst Alkaline-earth metal oxide Mixed metal oxides
Industrialization processes continue to grow globally in par with human population which leads to the growing worldwide demand for energy as well as for petrochemical resources, coal and natural gases. This phenomenon has caused the depletion rate of fossil energy resources to increase exponentially and caused alarming environmental problems to the society. Recently, many fuel developers have showed interests in alternative renewable fuels to substitute or blend with petroleum-based fuels. An alternative fuel shall be easily available, environment friendly and techno-economically competitive [1, 2].
Biodiesel plays a major role in energy sector due to its similar combustion properties with petroleum. Furthermore, biodiesel is sometimes more superior than petroleum diesel with improved physical and chemical properties, such as higher flash point, higher cetane number, ultralow sulfur content, better lubricity, improved biodegradability, and smaller carbon footprint [3–5]. Chemically, biodiesel is a mixture of methyl esters with long-chain fatty acids and is typically made from transesterification reaction of biological triglyceride sources such as vegetable oil and animal fats with alcohol in the presence of catalyst. This process reduces the viscosity to a value comparable to that of diesel and hence improves combustion .
According to Meng et al. (2009), biological feedstock supply for biodiesel production covers more than 75% of the overall production cost . The favorable properties in selecting the best biodiesel feedstock include lowest oil price, high oil content, favorable fatty acid composition (saturated or unsaturated acid), low cultivation maintenance and costs, controllable growth and harvesting season, consistent seeds maturity rates and potential market for agricultural by-products .
In general, biodiesel feedstock can be divided into 4 main categories which are: (a) edible vegetable oil, (b) non-edible vegetable oil, (c) waste or recycled oil and (d) animal fats . The most common feedstock employed in biodiesel production is edible and inedible oil from oleaginous plants grown in different regions. Soybean oil, sunflower oil, rapeseed oil and palm oil have been used as edible feedstock in biodiesel synthesis . In Malaysia, biodiesel production is synonymous to palm oil as oil palm plantations possesses higher productivity per hectare of oil palm with lowest oil production cost per unit as compared to other vegetable oils like rapeseed and soybean [11, 12]. A hectare of oil-palm plantation produces approximately 3.62 tonnes/ha/year of oil, 5–9 times higher than other oil producing crops like soybean, sunflower and rapeseed, which produces 0.4, 0.46 and 0.68 tonnes/ha/year, respectively . This keeps the price of palm-based biodiesel competitive enough to meet the demand of commodity market [9, 14].
Instead of edible palm oil, non-edible feedstock is getting interest as a biodiesel feedstock in biodiesel production. Amongst the varieties of non-edible plant oil, Jatropha is the most favorable for biodiesel production as they meet the major requirement of biodiesel standards of USA, Germany and European Standard Organization. Jatropha crops can be well adapted to arid and semiarid conditions like non-cropped marginal lands and waste lands with harsh environments. Hence, the cultivation cost is lower as these crops can still sustain reasonably high yield without intensive care. Besides, Jatropha oil possesses similar composition as other vegetable oil, which favors biodiesel production. In addition, Jatropha oil contains of toxic phorbol ester which is unsuitable for human consumption and thus reduces the competitive with food supply market [15, 16].
A new type of heterogeneous catalysis technology has been developed to adapt the natural characteristics of biodiesel feedstock and existing transesterification technology. Utilization of heterogeneous catalyst for biodiesel production has offered some relief to biodiesel producers by improving their ability to process alternative and cheaper feedstock with simplified processes and cheaper manufacturing processes with prolonged catalyst lifetime. The three factors namely catalytic activity, catalyst life and oil flexibility have tremendous impact on the cost of biodiesel [3, 17]. According to some research studies, the heterogeneous catalysts used for palm-based and Jatropha-based biodiesel productions are mainly from solid base catalysts e.g. alkali metal supported catalyst, hydrotalcite, alkaline-earth metal oxides, mixed metal oxides and natural waste shell, which render high transesterification activity with > 80% of biodiesel yield. It was realized that the main criteria to catalyze transesterification of these biodiesel feedstock with base catalysts is low FFA <3 wt.% and moisture 1 wt.% in the feedstock to avoid from unfavorable side reaction such as oil hydrolysis and saponification [18–27]. The formation of soap was observed in base catalyzed transesterification of high acid oil with low biodiesel yield.
By drawing on this, an attempt has been made in the present work to produce biodiesel from edible (palm) and non-edible (Jatropha) oils using heterogeneous base catalysts: (a) supported alkali metal catalysts– sodium hydroxide supported with alumina (NaOH/Al2O3), (b) alkaline-earth metal oxides– magnesium oxide (MgO), calcium oxide (CaO) and strontium oxide (SrO) and (c) calcium-based mixed metal oxides– (CaMgO and CaZnO). This study was aimed to investigate the versatility of solid base catalysts with different chemical characteristic for transesterification of edible and non-edible biodiesel feedstock. The physicochemical properties (chemical composition, textural properties and basicity) of synthesized solid base catalysts produced thru wet impregnation and co-precipitation techniques were investigated. Furthermore, effects of the catalyst loading and reaction time towards catalyst activity were investigated in order to optimize transesterification conditions. The reusability of the solid catalysts was evaluated by batch experiment and the reasons for the deactivation of the catalyst were also discussed by performed the catalyst leaching test.
Results and discussion
Surface area profile of synthesized base catalysts
Calcination temperature (°C)
BET area (m2/g)
Pore volume (cm3/g)
Pore diameter (Å)
Alkali supported alumina
Alkaline-earth metal oxide
Calcium-based mixed metal oxides
TPD-CO 2 profile of synthesized base catalysts
Amount of basic site (μ mol of CO2/g)
(μ mol of CO2/g)
Alkali supported alumina
Alkaline-earth metal oxide
Calcium-based mixed oxide
Transesterification of edible palm and non-edible Jatropha oils
The transesterification of edible (palm) and non-edible (Jatropha) oils in the presence of different solid base catalysts (NaOH/Al2O3, MgO, CaO, SrO, CaMgO and CaZnO) were studied thoroughly by varying the transesterification conditions. The transesterification reaction was performed at different reaction time (2–6 h) and catalyst amount (1–5 wt.%) under constant reflux temperature (65°C) and methanol to oil ratio of 15:1.
Other than oil characteristics, the rate of transesterification is greatly depending on catalyst’s basicity. Among the solid base catalysts, the catalytic activity of MgO for both palm and Jatropha-based transesterification are low, which is 52% and 5%, respectively. The results suggested that, under reflux condition, the optimum content of biodiesel synthesis using edible and non-edible oil greatly depend on the type of the solid base catalyst used. According to Di Serio and his co-researcher , basicity of catalyst is directly proportional to the biodiesel yield. MgO catalyst with lower amount of basicity is less active than other catalysts by producing less yield of biodiesel under mild condition. This fact has been proven by the correlation effect between transesterification activities and basicity of different catalysts (Figure 5).
Durability of catalyst
Leaching tests profile of CaMgO and CaZnO
17.9 ± 0.5
36.2 ± 0.3
10.0 ± 0.4
74.3 ± 0.7
3rd run b
15.6 ± 0.7
29.8 ± 0.2
8.6 ± 0.3
67.4 ± 0.6
Preparation of solid base catalysts
Supported alkaline metal catalysts: NaOH/Al2O3
The catalyst was prepared by incipient wetness impregnation of γ-Al2O3 powder with an aqueous solution of NaOH compounds. Al2O3 support was impregnated with 15 ml sodium hydroxide (50 wt.%) solution. The impregnate was dried in oven at 100°C overnight and undergone thermal treatment at 500°C.
Alkaline-earth metal oxide: MgO, CaO and SrO
MgO, CaO and SrO were obtained after calcination of pulverized magnesium carbonate (MgCO3), lime stone (CaCO3) and strontium carbonate (SrCO3).
Mixed metal oxide: CaMgO and CaZnO
The mixed metal oxide catalysts were prepared by using co-precipitation method, and subsequent calcinations of the precursors. These catalysts were obtained by slowly adding a 2 M aqueous solution of the corresponding metal nitrates to an aqueous solution containing Na2CO3 and NaOH. The precipitation was performed under vigorous stirring at 65°C, for 1 day. Finally, the solids were filtered, washed with deionized water and dried at 100°C. The synthesized precursors were then undergone thermal treatment (800°C) in the air to produce mixed metal oxides.
The crystalline phases of synthesized catalysts were analyzed by powder X-ray diffraction analysis using a Shimadzu diffractometer model XRD 6000 with employing Cu-Kα radiation to generate diffraction patterns from powder crystalline samples at ambient temperature. Specific surface area of the catalysts was obtained by the BET (Brunauer-Emmer-Teller) method using Thermo Finnigan Sorptomatic 1900 series nitrogen adsorption/desorption analyzer. The total basicity and basic strength of the catalysts were measured by temperature programmed desorption of carbon dioxide (CO2-TPD) using a Thermo Finnigan TPDRO 1100 apparatus provided with a thermal conductivity detector. The elemental composition of fresh and used catalysts was determined by using inductively coupled plasma-atomic emission spectrometer (ICP-AES) analysis that conducted by using Perkin Elmer Emission Spectrometer Model Plasma 1000.
Physicochemical properties and characteristic of palm oil and Jatropha oil
Specific gravity (gcm−3)
Viscosity at 40°C (cSt)
Sulphated Ash (% mass)
Flash point (°C)
Cloud point (°C)
Saponification number (mg g−1)
Free Fatty acids% (Kg Kg−1 × 100)
Fatty acid composition (%)
Palmitic acid (16:0)
Stearic acid (18:0)
Oleic acid (18:1)
Linoleic acid (18:2)
Heterogeneous base catalysts (NaOH/Al2O3, MgO, CaO, SrO, CaMgO and CaZnO) were used as catalysts for the production of biodiesel from edible palm and non-edible Jatropha oils. All the base catalysts showed the presence of strong basic strength on the active site except for MgO which contained dominant amount of medium basic sites. The transesterification activity of the heterogeneous base catalysts are correlated with basicity and basic strengths of the catalysts. The optimum conditions for solid base catalysts to achieve >90% of palm biodiesel is 3 wt.% of catalyst, 15:1 of methanol to oil molar ratio within 3 h. Jatropha biodiesel yield required higher amount of catalyst (4 wt.%) and longer reaction time (4 h) under reflux temperature to achieve yield > 80%. It is reasonable to conclude that the type of feedstock oil and chemical characteristic of solid base catalyst strongly affects the yield of biodiesel. Despite of good transesterification activity for solid base catalyst, a good candidate of basic catalyst should be able to tolerate free fatty acids and moisture content in feedstock oil. High catalyst’s reusability without leaching of active component is another desirable characteristic in good candidate catalyst. Calcium-based mixed metal oxides catalysts (CaMgO and CaZnO) render high durability characteristic in transesterification with low active metal leaching for several cycles. The strong interactions between active metals provide a superior synergism of high basicity and stability effect for transesterification reaction.
First Author: Hwei Voon Lee.
Co-Authors: Joon Ching Juan, Nurul Fitriyah binti Abdullah, Rabiah Nizah MF, Yun Hin Taufiq-Yap.
The authors acknowledge the financial support of the Graduate Research Fellowship (GRF) from the Universiti Putra Malaysia and the financial support from Ministry of Higher Education Malaysia for Fundamental Research Grant Scheme (FRGS, Project Number: FP056-2013B).
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