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THE SYNTHESIS OF GLYCEROL CARBONATE FROM GLYCEROL AND CARBON DIOXIDE OVER HETEROGENEOUS CATALYSTS

Razali, N A (2018) THE SYNTHESIS OF GLYCEROL CARBONATE FROM GLYCEROL AND CARBON DIOXIDE OVER HETEROGENEOUS CATALYSTS. PhD thesis, University of Sheffield.

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Abstract

The aim of this work is to synthesise glycerol carbonate from carbon dioxide (CO2) and glycerol. Two key challenges that were investigated in this work including: (1) thermodynamic limitation of this work and (2) desirability of using crude glycerol as a feedstock. In this work, carboxylation of glycerol is carried out over La2O3 (commercial) and La2O2CO3 catalysts prepared via co-precipitation, sol-gel and hydrothermal methods. These catalysts are characterised using BET, ATR-FTIR, SEM, XRD, TPD-CO2 and TPD-NH3. The carboxylation reaction is thermodynamically limited, therefore a range of dehydrating agents were introduced to improve the glycerol conversion by shifting the reaction equilibrium to the product side. The impact of dehydrating agents on glycerol conversion and glycerol carbonate formation were therefore studied. Reaction conditions were as follows: 6 wt.% La2O3, relative to glycerol, glycerol to dehydrating agent ratio of 22.5:50 mmol, 160 °C and reaction pressure, 45 bar CO2 and reaction time, 18 hours. High selectivity to glycerol carbonate is observed upon the introduction of adiponitrile (17%), followed by benzonitrile (5%), acetonitrile (4%), and no glycerol carbonate was detected upon the introduction of acetic anhydride. Additionally this work demonstrated for the first time the efficacy of lanthanum-based catalysts to synthesise glycerol carbonate via the direct carboxylation of crude glycerol. Crude glycerol employed herein comprises 74% glycerol, 20% of fatty acid methyl esters, 5 wt.% water, 1% methanol, and 7 g/L of sodium methoxide. It was analysed by GG-MS, ICP-MS and Karl Fisher titration technique. The impact of single and multiple impurities are the aspects investigated in this work. The addition of 10 wt.% water inhibited the formation of glycerol carbonate while blending of glycerol and methanol (80:20 mol%) increased the selectivity to glycerol carbonate to 22%. Only 4% selectivity to glycerol carbonate over La2O3-C was observed in the presence of multiple impurities including methanol, fatty acid methyl ester and sodium methoxide. As a result, modification of La2O3-C catalyst is crucial. Introduction of ZrO2/La2O2CO3/Ga2O3 greatly improved the selectivity to glycerol carbonate (21%); while a selectivity of 5% to glycerol carbonate observed for the direct carboxylation of crude glycerol

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Chemical and Biological Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.736566
Depositing User: Miss N A Razali
Date Deposited: 13 Mar 2018 11:24
Last Modified: 25 Sep 2019 20:03
URI: http://etheses.whiterose.ac.uk/id/eprint/19350

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