Niobium oxide solid catalyst: esterification of fatty acids and modeling for biodiesel production

Abstract

Biodiesel can be obtained from fatty acid raw materials through esterification. The reactivity of lauric, palmitic, stearic, oleic, and linoleic fatty acids with methanol using powdered niobic acid as a heterogeneous catalyst was investigated in this work, both experimentally (in a batch reactor) and theoretically. A 23 experimental design was used, with methanol/fatty acid molar ratio, catalyst concentration, and temperature as main factors. An empirical model demonstrated that temperature is the most important variable. Fourteen heterogeneous and 56 homogeneous‐like kinetic models were tested. A homogeneous‐like model considering zero order for all species and inhibition by water was the most adequate for experiments without catalyst. A homogeneous‐like model considering a second‐order reaction in relation to the fatty acid and no water inhibition was the most adequate for niobic acid catalyzed reaction. Molecular modeling confirmed the experimental results showing that the reactivity is directly related to the increase of unsaturated bonds and the reduction of carbon chain length. The polarity of the fatty acid is determinant in the reactivity. At the molecular level, reaction occurs between the HOMO orbital of methanol and LUMO orbitals of fatty acids and reactivity is higher when the energy difference between these orbitals is lower. Copyright © 2010 John Wiley & Sons, Ltd.

Assessment of niobium phosphate as heterogeneous catalyst in esterification with methyl acetate

“…Catalyst content and MeA:oleic acid molar ratio are less wileyonlinelibrary.com/jctb influential than temperature, but difference in FAME content can be verified comparing experiments 1 and 7 for different molar ratios, and experiments 4 and 7 for different catalyst contents. Similar results were obtained by Gonçalves et al 36 who investigated the methanolic esterification of some fatty acids with alcohol using niobium oxide as catalyst. These authors evaluated the effects of reaction temperature, oil:alcohol molar ratio and catalyst content on the conversion, and concluded that temperature was the factor of greater influence.…”

Nb2O5-catalyzed kinetics of fatty acids esterification for reactive distillation process simulation

“…The niobium (V) oxide that was used as the catalyst was kindly provided by CBMM (Brazil). The catalyst (bulk density = 1370 kg m −3 , bed porosity = 0.70) was provided in the form of cylindrical pellets (diameter = 5 mm and height = 4 mm) and was activated at 200 • C for 1 h before its use (de Araújo Gonç alves et al, 2011). The acid site density of the activated catalyst was evaluated according to the method developed by Lopez et al (2007) and resulted equal to 420 mol g −1 .…”

“…Samples of the reaction mixture were withdrawn at different times and the conversion was evaluated through the variation of the acid fraction of the withdrawn samples after removing the volatile components (water and methanol) by heating each sample at 120 • C for 1 h in a ventilated oven. The acid fraction was measured according to standard acid-base titration procedures recommended in the literature (de Araújo Gonç alves et al, 2011;Rattanaphra et al, 2011;Tesser et al, 2005).…”

A Simple Pseudo-Homogeneous Reversible Kinetic Model for the Esterification of Different Fatty Acids with Methanol in the Presence of Amberlyst-15

“…The use of highly-active heterogeneous catalysts is particularly appealing for the chemical industry to avoid the corrosion and separation problems that were observed in the homogeneous catalysis with strong acids, either organic or inorganic [9]. For these reasons, many heterogeneous catalysts, such as enzymes [10], tungstated zirconia [11], niobium oxide [12], and zeolites [3] have been proposed in the literature. In addition, the use of resin-supported strong solid acids is under continuous development aiming at a more efficient overall production of biodiesel from biomass feedstocks with high FFA content as it has been recently reviewed by Trombettoni and coworkers [13].…”

“…Process simulation and design require the knowledge of appropriate and simple kinetic models. Many works can be found in the literature, which report about kinetic models for fatty acid esterification with different heterogeneous catalysts, such as sulfated zirconia [23,24], Relite CFS [25], silica-supported tungstophosphoric acid [26], niobium oxide [12,27], or Amberlyst-46 [28]. As far as the use of Amberlyst-15 is concerned, simplified or more complex kinetic models can be found to describe the esterification of decanoic acid with methanol [16], nonanoic acid with ethanol [29], or oleic acid with methanol [30,31].…”