Biodiesel Processing Using Sodium and Potassium Geopolymer Powders as Heterogeneous Catalysts.

Renata F Botti,Murilo F Mello,Giorgia Franchin,Leticia K Santos,Paolo Colombo,Murilo D.M Innocentini,Danilo L Flumignan,Thais A Faleiros

doi:10.3390/molecules25122839

Abstract

This work investigates the catalytic activity of geopolymers produced using two different alkali components (sodium or potassium) and four treatment temperatures (110 to 700 °C) for the methyl transesterification of soybean oil. The geopolymers were prepared with metakaolin as an aluminosilicate source and alkaline activating solutions containing either sodium or potassium in the same molar oxide proportions. The potassium-based formulation displayed a higher specific surface area and lower average pore size (28.64–62.54 m²/g; 9 nm) than the sodium formulation (6.34–32.62 m²/g; 17 nm). The reduction in specific surface area (SSA) after the heat treatment was more severe for the sodium formulation due to the higher thermal shrinkage. The catalytic activity of the geopolymer powders was compared under the same reactional conditions (70–75 °C, 150% methanol excess, 4 h reaction) and same weight amounts (3% to oil). The differences in performance were attributed to the influences of sodium and potassium on the geopolymerization process and to the accessibility of the reactants to the catalytic sites. The Na-based geopolymers performed better, with FAME contents in the biodiesel phase of 85.1% and 89.9% for samples treated at 500 and 300 °C, respectively. These results are competitive in comparison with most heterogeneous base catalysts reported in the literature, considering the very mild conditions of temperature, excess methanol and catalyst amount and the short time spent in reactions.

Highlights

The continuous depletion of global petroleum reserves and the growing health and environmental concerns about burning fossil fuels have stimulated the research of alternative energy resources
Sodium and potassium-based geopolymer powders were tested as heterogeneous catalysts for the methyl transesterification of soybean oil in order to produce fatty acid methyl esters (FAME)
The increase in the heat treatment temperature caused a reduction in the specific surface area (SSA) for both formulations, but this was more severe for the sodium formulation due to its higher thermal shrinkage

Summary

Introduction

The continuous depletion of global petroleum reserves and the growing health and environmental concerns about burning fossil fuels have stimulated the research of alternative energy resources. In the case of diesel engines, the progressive adoption of more stringent exhaust emission standards and the pressure of the market have forced countries to find renewable fuel substitutes with similar or improved performance but with lower prices and a lower impact on the environment. The large variety of sources from which biodiesel can be produced has encouraged countries to find their own large-scale feedstock; for instance, rapeseed in Europe, soybean and lard in Brazil and the USA and palm and jathropa in Asia [4]. There are two common industrial methods for purifying biodiesel: wet and dry washing. Both methods have many disadvantages, including increased processing time and cost because of the use of additional chemicals (water, ion-exchange resins, adsorbents, etc.) and the wastewater treatment

Methods

Results

Conclusion