Catalytic Performance of Bulk and Al2O3-Supported Molybdenum Oxide for the Production of Biodiesel from Oil with High Free Fatty Acids Content

Abstract

Non-edible vegetable oils are characterized by high contents of free fatty acids (FFAs) that prevent from using the conventional basic catalysts for the production of biodiesel. In this work, solid acid catalysts are used for the simultaneous esterification and transesterification with methanol of the FFAs and triglycerides contained in sunflower oil acidified with oleic acid. Molybdenum oxide (MoO 3 ), which has been seldom considered as a catalyst for the production of biodiesel, was used in bulk and alumina-supported forms. Results showed that bulk MoO 3 is very active for both transesterification and esterification reactions, but it suffered from severe molybdenum leaching in the reaction medium. When supported on Al 2 O 3 , the MoO 3 performance improved in terms of active phase utilization and stability though molybdenum leaching remained significant. The improvement of catalytic performance was ascribed to the establishment of MoO 3 -Al 2 O 3 interactions that favored the anchorage of molybdenum to the support and the formation of new strong acidic centers, although this effect was offset by a decrease of specific surface area. It is concluded that the development of stable catalysts based on MoO 3 offers an attractive route for the valorization of oils with high FFAs content.Catalysts 2020, 10, 158 2 of 14 of this strategy is obtaining a more sustainable alternative fuel that contributes to reducing the CO 2 emissions to the atmosphere and the dependency of the energy system on petroleum. On the other hand, the basic catalysts usually used in the biodiesel industry (KOH, NaOH, and potassium and sodium methoxides) have important drawbacks [4]. Although they could be replaced by heterogeneous solid catalysts to make their re-utilization possible, some issues concerning those materials such as the lack of the required chemical stability are still not well solved [5][6][7]. Moreover, basic catalysts are not capable of suitably processing virgin, non-edible or waste feedstocks, which are characterized by being relatively rich in free fatty acids (FFAs), because they result deactivated and/or consumed, e.g., by the formation of soaps that also complicate the separation of the products due to their emulsifying properties. In these cases, acid catalysts can be used to perform a pre-esterification of the FFAs followed by base-catalyzed transesterification giving rise to the so-called integrated process for biodiesel production from high FFAs-containing triglyceride feedstocks [1,8]. Nevertheless, this is a multistep process that introduces complexity, thus reducing the competitive advantage of using low-cost feedstocks. It would be more convenient to perform the simultaneous transformation of the triglycerides and FFAs into FAMEs, which can be in fact accomplished using heterogeneous acid catalysts [9][10][11].Heterogeneous acid catalysts considered for biodiesel production comprise a large variety of materials [8][9][10][11][12][13][14][15][16][17][18]. The most representative ones consist on sulfated and tungsta...

Copper molybdate synthesized by sonochemistry route at room temperature as an efficient solid catalyst for esterification of oleic acid

“…This class of catalysts includes, among others, inorganic oxides [19] , enzymes [20] , ion exchange resins [21] and zeolites [22] . However, a high catalytic performance has been exhibited by copper oxide [23] and molybdenum oxide [24] in the transesterification of vegetable oils. Also, they are easily synthesized by conventional and low-cost methods, which reinforces the interest in these compounds [25] , [26] .…”

Effect of Physicochemical Properties of Co and Mo Modified Natural Sourced Hierarchical ZSM-5 Zeolite Catalysts on Vanillin and Phenol Production from Diphenyl Ether

“…The modified Mo catalyst with the weak acid content Moreover, in more detail on the NH3-TPD analysis, apart from the number of catalyst acid sites, the ability of the modified Mo oxide catalyst in adsorbing and desorbing substrate molecules (base species) from the surface greatly supports the performance of heterogeneous catalysts, where the ability of the active site of the catalyst to adsorb-desorb substrates and products is one of the important factors. Furthermore, the Navajas et al also reported that the Molybdenum oxides have interesting activity regarding the active sites as the Lewis acid and the Brönsted acid in the conversion of vegetable oil [52]. Considering the Lewis acidity, the molybdenum species could provide the orbital d and can form the reactive transition state with the substrate and lead the lower energy pathway in the reaction.…”

Hydrodesulfurization of 4,6-Dimethyldibenzothiophene and the Diesel Oil Fraction on NiMo Catalysts Supported over Proton-Exchanged AlMCM-41 and TiMCM-41 Extrudates

“…It is evident that the incorporation of the oxide phases of Ni, Mo and the binder into the HAlMCM-41 material generates a significant increase in the number of acid sites. The electron-deficient species from active-phase components may serve as a kind of newly created Lewis acid site, which recompenses the primary Lewis acidity originating from the parent HAlMCM-41 and being overlapped during impregnation [43,44]. The relatively high Lewis acid site concentrations in the NiMo/HAlMCM-41 can be also ascribed to the presence of the alumina binder (γ-Al 2 O 3 ).…”