Green biodiesel production from waste cooking oil using an environmentally benign acid catalyst
Graphical abstract
Introduction
The production of second-generation biofuel from nonfood and waste feedstock such as Jatropha curcas, Sterculia foetida, Ceiba pentandra, and Cerbera manghas, as well as used cooking oil has been become the solution of energy scarcity, in order to prevent any reduction in the supply of feedstock to the food industry (Naik et al., 2010). Biodiesel is a one of promising biofuel because it is highly biodegradable, low toxicity and directly use in boiler and internal combustion engine. However, the biodiesel has presented several drawbacks including low oxidation stability, low cold flow properties, and low energy content (Atabani et al., 2012). The improvement of oxidation stability and cold flow properties has been proposed with different techniques such as adding the additive compounds, blending of biodiesel, and blending with diesel (up to B80). All techniques presented acceptable induction period under European standard and improved cold flow properties (Sarin et al., 2010, Jane and Sharma, 2011, Joshi et al., 2011, Zuleta et al., 2012). For 2nd generation biodiesel, nonedible oil and waste cooking oil contain large amount of free fatty acids (FFA), which induce saponification in the products obtained by conventional alkali-catalyzed transesterification. Therefore, alkali homogeneous catalysis systems are not suitable for the production of second-generation biodiesel (Martinez-Guerra and Gude, 2014, Bhuiya et al., 2016).
An acid catalyst was introduced to remove FFA produced during sequential acid esterification and alkali transesterification, which increased the biodiesel yield to nearly 97% (Fadhil et al., 2016). Heteropoly acid as heteropoly tungstate was studied for use in biodiesel production from high-acid value oil. A conversion of 90% was obtained by leaching active species during the reaction (Sheikh et al., 2013). Tungstosilicic acid functionalized on various types of mesoporous silica were used in biodiesel production from oil containing large amounts of free fatty acids (Narkhede et al., 2014, Bala et al., 2015). 12-Tungstosilicic acid functionalized on SBA-15 yielded 85% conversion of waste cooking oil to biodiesel under reaction temperature 60 °C and atmospheric pressure (Narkhede et al., 2014). Meanwhile, tungstosilicic acid functionalized on KIT-6 yielded over 99% conversion of free fatty acid and the biodiesel yield was 93% (Bala et al., 2015); however, tungstosilicic acid presented low reusability.
Ion-exchange resins have also been used as catalysts in biodiesel production from high free fatty acid oil. Over 95% conversion of free fatty acids was obtained; however, physical damage to the catalyst was also observed (Fu et al., 2015). Because of the leaching of the active site and reduction in the stability of these catalysts, it is necessary to develop functionalized materials for fabricating highly efficient catalysts. Methyl propyl sulfonic acid was used to catalyze the simultaneous esterification and transesterification of rubber seed oil. The biodiesel yield was high, up to 95%, and the catalyst displayed good reusability without any reduction in the biodiesel yield through four reaction cycles (Karnjanakom et al., 2016). Although the sulfonic acid functionalized on silica displayed excellent catalytic activity, the catalyst preparation was a complex process.
Carbon-based catalysts were used for biodiesel production owing to their high stability, facile preparation, and low toxicity. In addition, the carbon material could be derived from biomass waste, thereby promoting the waste utilization concept. 4-sufophenyl activated carbon containing high acid density up to 0.72 mmol H+/g displayed the catalytic activity in rapeseed free fatty acid conversion similar with amberlyst-15 (Malins et al., 2015).
Polyethylene terephthalate waste-derived activated carbon and Resorcinol and formaldehyde sulfonated mesoporous carbon was sulfonated and performed high catalytic performance in esterification of high free fatty acid oil to obtain biodiesel (Fadhil et al., 2016, Chang et al., 2015).
Normally, the rate of acid heterogeneous catalysis is not only dependent on the acidic properties but also on the diffusion of reactants and products (Konwar et al., 2016); therefore, the morphology of the catalyst should be controlled. Carbon spheres display a good morphology for this purpose owing to controllable interparticle pore size. Several papers have reported the application of carbon sphere catalysts (Song et al., 2015, Zhao et al., 2015).
In this work, a carbon microsphere catalyst was prepared by sequential hydrothermal carbonization and sulfonation of xylose and was used as a catalyst for biodiesel production from waste cooking oil, in line with the principles of green carbon science (He et al., 2013). The concept is shown diagrammatically in Scheme 1.
Section snippets
Catalyst preparation and characterization
The sulfonated carbon microsphere (CM-SO3H) was prepared by sequential hydrothermal carbonization and sulfonation of xylose.
First, 25.0 g xylose was dissolved in 50.0 mL distilled water and placed in an autoclave. The mixture was heated to 190 °C for 24 h under autogenous pressure. After hydrothermal carbonization, the carbon solid was collected by centrifugation at 4000 rpm for 15 min and then washed with distilled water. The carbon solid product was dried at 90 °C for 4 h.
Next, the carbon solid was
Catalyst characterization
The morphology and particle size distribution of hydrothermal carbon, CM-SO3H, and reused CM-SO3H are shown in a scanning electron micrograph (Fig. 1). Both hydrothermal carbon and CM-SO3H displayed spherical shape, with particle diameters of 1 and 2 μm, respectively. The particle size distribution of hydrothermal carbon was uniform, whereas the sulfonated carbon microsphere showed particle size distribution in the range of 1–4 μm. The nonuniformity of particle size caused the growth of carbon
Conclusions
Sulfonated carbon microspheres were successfully used as catalysts for biodiesel production from waste cooking oil. The catalyst demonstrated good catalytic activity with 96.5% and 89.6% yield at a reaction temperature of 110 °C, reaction time of 2 h, and catalyst loading of 10 wt% for with and without treatment waste cooking oil, respectively. Meanwhile, the catalytic stability needs to be improved due to the leaching of sulfonic acid; however, the sulfonated carbon microsphere catalyst is still
Acknowledgements
The authors gratefully acknowledge the financial support provided by The Thailand Research Fund and National University project, Thammasat University. The catalyst characterization was supported by the Central Scientific Instrument Center, Faculty of Science and Technology, Thammasat University. We would like to acknowledge the AEC Scholarship awarded by the Faculty of Science and Technology, Thammasat University for supporting T.T.T. Vi. The authors would like to thank Dr. Narong Chanlek from
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