Solid acid as catalyst for biodiesel production via simultaneous esterification and transesterification of macaw palm oil
Graphical abstract
Introduction
As traditional fossil fuels are not renewable and their depletion is in the offing, probably in the next several decades, the search for alternative fuels is becoming increasingly attractive (Fu et al., 2013). In this context, biodiesel stands out as an alternative fuel which produces low aromatic gases and CO2 emissions. Moreover, it is also renewable, biodegradable, non-flammable, non-toxic, and sulfur-free (Syazwani et al., 2015). Biodiesel consists of a mixture of fatty acid alkyl esters, derived from renewable lipid feedstocks, such as vegetable oils and animal fats, which are basically triacylglycerols (Banković-Ilić et al., 2014).
Alcoholysis is the process that most frequently takes place, which is an established method for the transformation of vegetable oils into biodiesel. The transesterification reaction can occur in the presence of homogeneous or heterogeneous catalysts (acids or bases) or enzyme (mostly lipases) with alcohol (methanol and ethanol) (Avhad and Marchetti, 2015, Banković-Ilić et al., 2014).
Biodiesel production from non-edible oils has drawn the attention of researchers due to its high biodiesel yield and easy processing. However, edible oils for producing biodiesel is the subject of debate on its use as fuel or as food, thus these factors have negatively affected its production from edible oils. Therefore, non-edible vegetable oils have become more attractive for biodiesel production (Ong et al., 2013). Hence, many resources have been analyzed in order to explore non-edible feedstocks for biodiesel production, such as Jatropha oil (Jatropha curcas L.) (Nizah et al., 2014), Karanja oil (Pongamia pinnata L.) (Thiruvengadaravi et al., 2012), Sea Mango oil (Cerbera odollam Gaertn.) (Kansedo and Lee, 2013), Rubber seed oil (Hevea brasiliensis Muell. Arg) (Reshad et al., 2015), Moringa oil (Moringa oleifera Lam.) (Fernandes et al., 2015), Kusum oil (Schleichera oleosa L.) (Silitonga et al., 2015), Andiroba oil (Carapa guianensis Aubl.), Castanhola oil (Terminalia catappa L.) (Iha et al., 2014), Mahua oil (Madhuca indica J.F. Gmel) and Simarouba oil (Simarouba glauca DC) (Jena et al., 2010).
Macaw palm (Acrocomia aculeata (Jacq.) Lodd ex Mart.), commonly known in Brazil as Macaúba, is a native oleaginous palm tree which grows abundantly in the Brazilian cerrado, located mainly in the center of the country, but adapted from cooler subtropical scenarios to drier semiarid ecosystems, and widely spread across Mexico, Antilles, Argentina, Uruguay and Paraguay (Moura et al., 2009). This palm tree can reach 15–20 m in height, with 20–30 cm of trunk diameter and covered by dark thorns that are usually 10 cm in length (César et al., 2015). Its fruits are spherical, with 2.5–5.0 cm in diameter. A single plant has 2–6 clusters, with a total number of fruits ranging from 260 to 1270 per palm tree, producing estimated yields of 4000 kg of oil/ha (Ciconini et al., 2013).
However, its oil presents high acidity and cannot be used as feedstock for biodiesel production by a conventional alkaline route (Aguieiras et al., 2014). In this case, the biodiesel synthesis should be carried out via simultaneous esterification and transesterification process using acid catalysts, which enables the use of low-quality raw materials with high concentrations of free fatty acids (FFA).
The major focus of recent advances is on the rational development of recyclable solid acids catalysts. These catalysts have been established as being other alternatives to the heterogeneous alkaline, unrecyclable-homogeneous acid and alkaline catalysts. Several encouraging results described in literature have highlighted the potentials of solid acid catalyzed-biodiesel production (Sani et al., 2014). Among the most studied solid acids are mixed oxides (Liu et al., 2015, Amani et al., 2014), ion-exchange resin (Fu et al., 2015, Shibasaki-Kitakawa et al., 2015), heteropolyacid (Narkhede et al., 2014, Gong et al., 2014), sulfated zirconia (Patel et al., 2013, Saravanan et al., 2015) and zeolite (Vieira et al., 2015, Sun et al., 2015).
The aim of the present work is to optimize the performance of sulfated niobium (Nb2O5/SO4) as a heterogeneous catalyst in a simultaneous esterification and transesterification for biodiesel production using macaw palm oil with high free fatty acid content and ethanol as acylant agent. Ethanol has some advantages when used in a process for biodiesel production. It has a superior dissolving power in vegetable oils and the ethyl esters (FAEE) show lower smoke opacity, lower exhaust temperature and lower pour point (Yusoff et al., 2014). The evaluation of exhaust gas emissions (including nitrogen oxides, CO2 and smoke density) shows that FAEE has a less negative environmental effect in comparison to methyl esters (FAME) (Brunschwig et al., 2012, Stamenkovic et al., 2011). Additionally, unlike methanol (which is generally derived from fossil sources), ethanol is produced mainly from renewable sources via fermentation processes, and because its large scale production as a substitute fuel for gasoline already exists, the supply of bioethanol for the industrial production of biodiesel can be easily achieved (Brunschwig et al., 2012).
Section snippets
Materials
Macaw palm oil with high free fatty acid content was supplied by Association of Small Farmers D’Antas (Minas Gerais, Brazil). Hydrated niobium oxide HY340 (amorphous) with high surface area (BET ∼170 m2/g) containing 80% Nb2O5 was supplied by Companhia Brasileira de Metalurgia e Mineração—CBMM and calcined at 500 °C for 5 h before use. Sulfuric acid (98.0%) and anhydrous ethanol (98.0%) were purchased from VETEC® Sigma-Aldrich. Anhydrous sodium sulfate, ethyl acetate (99.5%) and hexane (65.0%)
Properties of macaw palm oil
The fatty acid composition and physico-chemical characterization of the macaw palm oil are shown in Table 1.
Macaw palm oil contains a large amount of unsaturated fatty acids (78.5%) primarily, oleic acid (53.4%), and a lower amount of saturated acid (21.5%), typically palmitic (18.7%). Its acidity and moisture content was 39.0 mg KOH/g and 1.25%, respectively, which was a determining factor in the choice of an acid catalyst because the use of alkaline catalysts are recommended when the oil has
Conclusion
In this study, by optimizing the reaction parameters, macaw palm biodiesel was produced with ester content of over 99% and viscosity level which is below 5.0 mm2/s. These values were obtained with the following reaction conditions: molar ratio of 120:1, reaction temperature of 250 °C, reaction time of 4 h and 30% catalyst concentration. There are few reports in literature regarding the use of Nb2O5/SO4 as catalyst for biodiesel production. Based on the obtained experimental results, it can be
Acknowledgements
The authors gratefully acknowledge the financial support of CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico-Process Number 404812/2013-9). Leyvison Rafael V. da Conceição would especially like to thank the support of Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).
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