From Homogeneous to Heterogeneous Catalysts in Biodiesel Production

Abstract

The production of biodiesel as a fuel in diesel engines greatly increased in recent years and is expected to grow more and more in the near future. Increasing biodiesel consumption requires optimized production processes allowing high production capacities, simplified operations, high yields, and the use of more economic feedstocks such as waste oils and fats. However, the latter often contain large amounts of free fatty acids and cannot be processed with the commonly practiced technology based on the use of alkaline catalysts in the homogeneous phase that requires the use of highly refined oil as raw materials. Therefore, the development of processes for low-cost biodiesel production requires the individuation of heterogeneous catalysts that are very efficient in promoting the transesterification reaction also in the presence of free fatty acids and water, allowing the prompt separation of pure glycerol and not requiring expensive purification of this byproduct. In the present contribution, the performances of different heterogeneous catalysts are compared both in the absence and in the presence of free fatty acids. In some cases, the resistance of the catalysts to the presence of water and the eventual deactivating effects after the first use have also been tested. The catalysts considered are both basic and acidic in nature, such as hydrotalcite, MgO, TiO 2 grafted on silica, vanadyl phosphate, and different metals-substituted vanadyl phosphate of the type Me(H 2 O) x VO 1-x PO 4 ‚2H 2 O, where Me is a trivalent cation such as Al, Ga, Fe, and Cr and where x ) 0.18-0.20. Finally, the understanding of the kinetic behavior of the most stable catalyst TiO 2 /SiO 2 has been deepened.

Biodiesel Production from Castor Oil under Subcritical Methanol Conditions

“…As much heterogeneous catalyst as lipase catalyst can be more easily separated than homogeneous catalyst but they tend to lose their catalytic activity after several reuse and they have high cost [11]- [14].…”

Ultrasonic enhancement of the acidity, surface area and free fatty acids esterification catalytic activity of sulphated ZrO 2 –TiO 2 systems

“…biodiesel, as represented in the Scheme 1. The esterification reaction can be performed using both homogeneous [11,12] and heterogeneous catalysis [13,14]. For liquid phase reactions, the latter approach is preferred as it brings benefits such as the easier separation of the catalyst from the products, thus facilitating catalyst recovery and re-use.…”

Kinetic Modeling Studies of Heterogeneously Catalyzed Biodiesel Synthesis Reactions

“…Heterogeneously catalysed transesterification reactions 3,4 that include alkali oxides 5,6 , alkaline earth oxides [7][8][9] , zeolites 10,11 , and hydrotalcites [12][13][14][15] , are preferred over homogeneous reactions, due to various reasons, including soap formation, catalyst loss and involvement of significantly more number of separation steps in the latter case. Dossin et al 2,16 introduced the kinetic studies of MgO catalyzed transesterification of alkyl esters with methanol using ER type mechanism.…”