Biodiesel Synthesis from Pongamia pinnata oil over Modified CeO2 Catalysts

378 ArticleJ. Mex. Chem. Soc. 2014, 58(4) J. Mex. Chem. Soc. 2014, 58(4), 378-385 Venkatesh et al. © 2014, Sociedad Química de México ISSN 1870-249X Biodiesel Synthesis from Pongamia pinnata oil over Modified CeO2 Catalysts Venkatesh,1,2 Sathgatta Zaheeruddin Mohamed Shamshuddin,*1,2 Manjunatha Shyamsundar,1,2 Vanagoor Thammannigowda Vasanth1 1 Chemistry Research Laboratory, HMS Institute of Technology, NH4, Kyathsandra, Tumkur, Karnataka, India. Research and Development Center, Bharathiar University, Coimbatore, India. * . 2 Received March 24th, 2014; Accepted May 19th, 2014 Abstract. This study investigates the use of CeO2, ZrO2, MgO and CeO2-ZrO2, CeO2-MgO, CeO2-ZrO2-MgO mixed oxides as solid base catalysts for the transesterification of Pongamia pinnata oil with methanol to produce biodiesel. SO42-/CeO2 and SO42-/CeO2-ZrO2 were also prepared and used as solid acid catalysts for esterification of Pongamia pinnata oil (P-oil) to reduce the % of free fatty acid (FFA) in P-oil. These oxide catalysts were prepared by an incipient wetness impregnation method and characterized by techniques such as NH3TPD for surface acidity, CO2-TPD for surface basicity and powder X-ray diffraction for crystalinity. The effect of nature of the catalyst, methanol to P-oil molar ratio and reaction time in esterification as well as in transesterification was investigated. The catalytic materials were reactivated & reused for five reaction cycles and the results showed that the ceria based catalysts have reasonably good reusability both in esterification and transesterification reaction. The test results also revealed that the CeO2-ZrO2 modified with MgO could have potential for use in the large scale biodiesel production. Keywords: Biodiesel, Transesterification, Pongamia pinnata oil, modified CeO2, CeO2-ZrO2, MgO. Resumen. En este trabajo se investiga el uso de los óxidos mixtos CeO2, ZrO2, MgO and CeO2-ZrO2, CeO2-MgO, CeO2-ZrO2-MgO como catalizadores básicos sólidos en la transesterificación con metanol de aceite de Pongamia pinnata (aceite-P) para producir biodiesel.  También se prepararon  SO42-/CeO2 and SO42-/CeO2-ZrO2 y se usaron como catalizadores ácidos para la esterificación del aceite-P y reducir el % de ácidos grasos libres (FFA).  Los óxidos se sintetizaron por un método de impregnación a mojado incipiente y se caracterizaron por técnicas como NH3-TPD, para medir la acidez superficial, CO2-TPD para la basicidad de la superficie y difracción de rayos X para obtener la cristalinidad.  Se investigaron el efecto de la naturaleza del catalizador, la razón molar entre metanol y aceite-P y el tiempo de reacción, tanto para la transesterificación como para la esterificación.  Los catalizadores se reactivaron y reusaron por cinco ciclos de reacción y los resultados mostraron que los catalizadores a base de ceria pueden reusarse razonablemente bien para ambas reacciones. Asimismo se mostró que el óxido CeO2-ZrO2 modificado con MgO tiene potencial para su uso en producción de biodiesel a gran escala. Palabras clave: Biodiesel, Transesterificación, aceite de Pongamia pinnata,  CeO2, CeO2-ZrO2 modificada, MgO. Introduction used in redox catalysis and as an effective antioxidant. Despite the considerable interest on CeO2 catalytic systems, CeO2 has not been studied yet as a solid acid or solid base catalyst [8]. It has reported that the incorporation of CeO2 into ZrO2 increases the acidity, which is evidenced by low Homax values. Ceria-zirconia mixed oxides showed enhanced redox as well as acid-base properties [9]. Biodiesel can be synthesized by using vegetable oils such as palm oil, rapeseed oil, jatropha oil, rubber seed oil, etc. Since, Pongamia pinnata trees are grown extensively in southern parts of India (especially in Karnataka State) and abundant availability of the seeds, Pongamia pinnata oil (P-oil) was selected for the present study to synthesize biodiesel. Further, P-oil is less expensive compared to other vegetable oils, which makes the production of biodiesel from P-oil much more economical. Biodiesel has been synthesized from P-oil by using base catalysts such as KOH, NaOH, MgO-ZrO2, MgO, etc [10-12] and acid catalysts such as sulfuric acid [13]. Further, it has been reported that the biodiesel obtained from P-oil shows no corrosion on piston metal and piston liner when compared to biodiesel obtained for other oil seeds [14]. In this article focus is made on the synthesis and characterization of ceria (C) & its modified forms such as its solid acid forms like sulfated ceria (SC), ceria-zirconia (CZ), sul- The rapid depletion of fossil fuel reservoirs has made biodiesel as an alternative fuel in recent years due to its similar characteristics to diesel fossil fuel. Moreover, biodiesel is ecofriendly since it produces exhaust gas free from sulphur & aromatic compounds and it is biodegradable & non-toxic [1-4]. Biodiesel is produced by the transesterification of triglycerides of oils and fats with low molecular mass alcohols, like methanol in presence of catalysts. The conventional catalysts for the transesterification reaction are homogeneous strong bases (e.g. alkali hydroxides and methoxides) or homogeneous strong acids (e.g. H2SO4, HCl, H3PO4) [5]. Commonly, bases are preferred over acid catalysts due to their fast reaction rates and less corrosive properties. But the removal of the base after the reaction is difficult, because of the formation of soap and emulsion which makes separation of ester difficult [6]. Efforts have been made in recent years towards to the development of heterogeneous catalysts to produce biodiesel in which separation or purification of the reaction products is much easier [7]. Cerium dioxide (CeO2) is a multifunctional inorganic compound holding a great promise for a wide range of technological applications, including heterogeneous catalysis. CeO2 is widely 379 Biodiesel Synthesis from Pongamia pinnata oil over Modified CeO2 Catalysts fated ceria-zirconia (SCZ), as acid catalysts for esterification to reduce the % FFA and its solid base forms such as CeO2MgO (CM), CeO2-ZrO2-MgO (CZM), as base catalysts for the transesterification to produce biodiesel from Pongamia pinnata oil (P-oil). Pure metal oxides such as ceria (C), zirconia (Z) and MgO (M) were also used as either solid acid or solid base catalysts. The effect of nature of the catalyst, methanol: P-oil molar ratio, reaction time in both esterification and transesterification was investigated. Reusability & reactivation studies of these catalysts was also taken-up. Results and discussion Catalyst characterization Total surface acidity (TSA) The total surface acidity (TSA) and total surface basicity (TSB) values of solid catalysts used in the present study are given in Table 1. TSA values of the solid acids used in the present study followed the order: SCZ > SC > CZ > Z > C Pure ceria and pure zirconia were found to consist of both acidic & basic sites (Table 1). However, over pur (...truncated)