Biodiesel Production from Used Cooking Oil Using Calcined Sodium Silicate Catalyst

M.O. Daramola*, D. Nkazi, K. Mtshali

School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Wits 2050, Johannesburg, South Africa

*Corresponding author; E-mail: Michael.daramola@wits.ac.za; +27117177536

Abstract

The recent oil crises and growing public awareness of global warming and greenhouse emissions are creating major technological, as well as social and political challenges worldwide. These challenges are related closely to energy generation and exploitation. The aforementioned problems have prompted the consideration of alternative and renewable types of energy. One of the expected key technologies for building sustainable societies and thus mitigating global warming due to CO₂emission is the production of renewable fuels and chemicals from the conversion of biomass [1]. An alternative type of energy source that is highly favoured from an environmental perspective is biofuel of which biodiesel is a member.

Homogeneous acid and base catalysts have been extensively studied for the production of biodiesel [2,3]. But homogeneous catalysts cannot be reused or regenerated, because the catalysts are partly consumed in the reaction (during saponification). Also, separation of the catalyst from products is difficult and requires additional equipment which could result in higher production costs [4]. In addition, the process is not environmentally friendly because a large amount of wastewater is produced in the separation step [5]. Developing new solid catalysts seems to be an appropriate solution to overcome problems associated with the use of homogeneous catalysts for biodiesel production. Against this background, this study investigated  biodiesel production from used cooking oil (UCO) using heterogeneous sodium silicate catalyst. The conversion of UCO to biodiesel exploited the potential of the catalyst to convert high free fatty acid (FFA) content feedstock to biodiesel directly, thereby by-passing the esterification state whereby FFA content of the feedstock is reduced prior to transesterification reaction.

The transesterification reaction was conducted in a batch reactor with 2.51 g of the catalysts and at UCO to methanol ratio of 1:6. In addition, the reaction temperature was varied between 25^oC to 63^oC, and the reaction time was varied from 0 to 180 minutes at a 30 minute step increase to understand their effects on the activity of the catalyst during transesterification of UCO to biodiesel. The fatty acid methyl ester (FAME) yield increased with reaction time and reaction temperature and the highest FAME yield of   ̴30% was obtained at 63^oC after 180 minutes.  Furthermore, results of this study compare favourably with literature. However, further studies are required for in-depth understanding of the activity and kinetics of the catalyst for biodiesel production from UCO. As far as could be ascertained, this is the first open report on the conversion of UCO to biodiesel over a calcined heterogeneous solid sodium silicate catalyst. However, a more in-depth study on the activity of the catalyst and the kinetics in transforming UCO to biodiesel is required. At the same time, improvement of the synthesis protocol of the catalyst via optimization study is required. Evaluation of performance stability and optimization of the transesterification operating conditions are essential.

Keywords: Used cooking oil, Biodiesel, Heterogeneous catalysis, Transesterification 

References

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