Study Of Glycerol/CO₂ Synthesis Of Glycerol Carbonate

Recently,the problems of accelerating the change of energy structure and the development of new energy have been gradually place on the research agenda,due to the reduce of fossil fuel reserves and its impact on global warming.Compared with traditional fossil fuels,biodiesel has the advantages of good combustion performance,abundant sources and reproducibility,which makes biodiesel a hot alternative energy source for fossil fuels.However,excess glycerin as the by-product of biodiesel,will emerge after a large amount of biodiesel production.So how to convert excess glycerin into higher value-added products becomes particularly important.On the other hand,as CO₂ is the main greenhouse gas and the richest C1 resource,it is of great practical significance to take effective emission reduction measures and reasonable chemical transformation.Glycerol is used to react with CO₂ to prepare high value-added chemical product glycerol carbonate（GC）,which can not only effectively alleviate the excess glycerol and CO₂ emissions,but also increase their added-value.In this paper,the thermodynamic calculation of the reaction between glycerol and CO₂ to synthesize GC is firstly carried out.It is found that the reaction is thermodynamically constrained,which is difficult to proceed spontaneously.Then,the coupling agent epoxide was added into the system to change reaction pathway.The thermodynamical calculation results showed that the addition of epoxide could reduce the change of Gibbs free energy of the reaction.The change of Gibbs free energy is negative and the reaction could proceed spontaneously.This paper examines the influence of preparation conditions of KI/CeO₂ and reaction process conditions on GC synthesis,and the structure of the KI/CeO₂ catalysts was characterized.The main research content were as follows:（1）KI/CeO₂ was an efficient catalyst that can catalyze the GC synthesis from glycerol and CO₂.The influence of preparation conditions of KI/CeO₂ on the GC synthesis was studied.It was shown that the catalytic efficiency of KI/CeO₂ was the highest at the conditions that the loading of KI was 20%,the calcination temperature was 500℃ and the calcination time was 6h.（2）The effect of reaction process conditions on the GC synthesis from glycerol and CO₂ was investigated using the of KI/CeO₂ catalyst under the optimal preparation conditions.It ws found that the activity of the KI/CeO₂ catalyst is the highest at the conditions that the reaction time was 2h,the reaction temperature was 130 ℃,the initial pressure of CO₂ was 5MPa,and the amount of KI/CeO₂ catalyst was 2%of the reactant mass,the molar ratio of propylene oxide and glycerol was 3:1.At this time,the conversion of glycerol was 69.8%,the selectivity of GC was 87.1%,and the yield of GC was 60.7%.（3）In the catalyst preparation,KI could interacte with CeO₂.The results of XRD and FT-IR showed that KI and KIO3 were the main active components of the KI/CeO₂ catalyst,which could effectively promote the reaction.It was educed from the CO₂-TPD technique that the stronge basity of KI/CeO₂ catalyst could facilitate the conversion of glycerol and also result in the decomposition of GC to reduce the GC selectivity.N2-physical adsorption analysis revealed that the KI loading and calcination temperature not only affect the basity strength of the KI/CeO₂ catalyst and the content of active basic sites,but also the catalyst microscopic pore structure,which determined catalyst activity.