Kinetic studies on the synthesis of fuel additives from glycerol using CeO2–ZrO2 metal oxide catalyst

Rajeswari M Kulkarni,Deeksha Anand,Pradima J Britto,Archna Narula,R Nidhi Herle,C Bhagyalakshmi,Syed Saqline

doi:10.18331/brj2020.7.1.2

Abstract

Highly stable and active CeO2-ZrO2 metal oxide catalyst was synthesized via the combustion method and was further functionalized with sulphate (SO42-) groups. The morphology, surface functionalities, and composition of the metal oxide catalyst were determined by scanning electron microscopy, N2 adsorption and desorption measurement, X-ray diffraction, and Fourier transform infrared spectroscopy. The synthesized catalyst was used for esterification of glycerol with acetic acid. Effects of the process parameters including acetic acid to glycerol molar ratios (3-20), catalyst loadings (1-9 wt.%) and reaction temperatures (70–110°C) on the glycerol conversion and glycerol acetates selectivity were studied. Excellent catalytic activity was observed by using the sulphated metal oxide catalyst resulting in a glycerol conversion as high as 99.12%. The selectivity towards the di and triacetin (fuel additive) formed stood at 57.28% and 21.26% respectively. The reaction rate constants and activation energies were also estimated using a Quasi-Newton algorithm, namely Broyden’s method and Arrhenius equations at 80-110℃. The calculated values were in accordance with the experimental values which confirmed the model. Finally, the developed catalyst could be reused for three consecutive cycle without major loss of its activity. Overall, the findings presented here could be instrumental to drive future research and commercialization efforts directed toward biodiesel glycerol valorisation into fuel additives.

Highlights

The dearth of fossil fuel reserves, energy security and increasing greenhouse gas emissions have fuelled the search for green and clean energy alternatives (Reddy et al, 2010)
Among the unsulphated and sulphated mixed oxide catalysts, the catalyst containing a higher amount of acid sites (SO42–/CeO2-ZrO2) resulted in the maximum glycerol conversion and was selected for further studies
It was observed that sulphated CeO2–ZrO2 mixed oxide catalyst exhibited a favourable performance in comparison with the unsulphated catalyst

Summary

Introduction

The dearth of fossil fuel reserves, energy security and increasing greenhouse gas emissions have fuelled the search for green and clean energy alternatives (Reddy et al, 2010). Animal fat, microalgal oil, etc., have been utilized to produce biodiesel through the transesterification process (Pradima et al, 2017). The transesterification of the afore-mentioned oil feedstocks through catalytic routes produces biodiesel as the main product (90 wt.%) and glycerol as by-product (10 wt.%) (Budzaki et al, 2018). The rapid expansion of the biodiesel industry has, in turn, increased the production of glycerol which is low-cost bio-feed available for value addition (Ishak et al, 2016; Sun et al, 2016). Glycerol (glycerine/1,2,3-propanetriol) contains three hydroxyl groups that can be functionalized through a catalytic process. It can be valorised into value-added products such as chemicals, solvents, polyesters, oxygenated fuel additives, etc. The catalytic conversion of glycerol can contribute to the economic viability of the biodiesel industry

Methods

Results

Conclusion