Biodiesel Production over Niobium-Containing Catalysts: A Review

Daniel Carreira Batalha,Márcio José Da Silva

doi:10.3390/en14175506

Abstract

Nowadays, the synthesis of biofuels from renewable raw materials is very popular. Among the various challenges involved in improving these processes, environmentally benign catalysts compatible with an inexpensive feedstock have become more important. Herein, we report the recent advances achieved in the development of Niobium-containing heterogeneous catalysts as well as their use in routes to produce biodiesel. The efficiency of different Niobium catalysts in esterification and transesterification reactions of lipids and oleaginous raw materials was evaluated, considering the effect of main reaction parameters such as temperature, time, catalyst load, and oil:alcohol molar ratio on the biodiesel yield. The catalytic performance of Niobium compounds was discussed considering the characterization data obtained by different techniques, including NH3-TPD, BET, and Pyr-FT-IR analysis. The high catalytic activity is attributed to its inherent properties, such as the active sites distribution over a high specific surface area, strength of acidity, nature, amount of acidic sites, and inherent mesoporosity. On top of this, recycling experiments have proven that most Niobium catalysts are stable and can be repeatedly used with consistent catalytic activity.

Highlights

IntroductionThe inevitable depletion of fossil fuels and the environmental problems resulting from huge emission of greenhouse gases generated in their burning have motivated the search for energy sources that are renewable and of low cost [1,2]
Biodiesel: Main CatalystsThe inevitable depletion of fossil fuels and the environmental problems resulting from huge emission of greenhouse gases generated in their burning have motivated the search for energy sources that are renewable and of low cost [1,2].In this sense, the conversion of biomass resources to biofuels has risen as a potential alternative to reduce the dependence on petrol derivatives [3,4]
The results showed that the Niobium oxide was an efficient catalyst to esterify palmitic acid with ethyl alcohol to produce biodiesel, achieving conversion higher than 80% in 60 min (Figure 13)

Summary

Introduction

The inevitable depletion of fossil fuels and the environmental problems resulting from huge emission of greenhouse gases generated in their burning have motivated the search for energy sources that are renewable and of low cost [1,2]. The great advantage of use of Niobium catalysts is the possibility of easy recovery and reuse This contributes to reducing the waste generation and the cost of the process, being the industrial procedure more economically and environmentally viable [24,25]. The production of biodiesel can be performed through esterification reactions of FFAs and transesterification of triglycerides, performed in conditions of homogeneous or heterogeneous catalysis Within these two great classes of reactions, the catalysts can be subdivided in acidic and alkaline catalysts. The application of Nb-containing compounds in biodiesel production routes still needs extensive research, since they have already presented a huge potential to convert triglycerides and FFAs. Brønsted and Lewis acidic sites, good thermal stability, versatility, and easy recovery and reuse are inherent properties of Niobium catalysts. The use of affordable commercially available Niobium catalysts (i.e., phosphate and oxide) avoids laborious synthesis and the problems of leaching of solid-supported or sulfated catalysts

Niobium Catalysts

Characteristic of the Niobium Compounds

Niobium-Catalyzed Processes of Biofuel Production

Sulfated Niobium Oxide

Niobium Oxide and Niobium Phosphate

Niobium as Catalytic Support and as a Dopant

Others

Findings

Conclusions