Catalysts For Preparation Of Valued-added Glycerol Derivates:Synthesis And Their Catalytic Performance

With the rapid development of biodiesel industry,a large amount of glycerol as the main by-product was accumulated in the recent year.Therefore,synthesis of high value added derivates are of great importance to lessen the surplus of glycerol.CeO2-NiO samples were prepared and applied to synthesis of glycerol carbonate(GC)with the raw of glycerol(GL)and diethyl carbonate(DEC).The microstructural and physicochemical properties of the catalysts were determined by XRD,XPS,SEM,EDX,CO2-TPD,N2-adsorption,FT-IR,and TG-DTG.A statistic result exhibited that the particle size(100-300 nm)of CeO2-NiO was smaller than that of fresh NiO(500-800 nm),which signified addation of Ce during sample synthesis could promote NiO particles dispersion.CeO2-NiO with Ce/Ni atomic ratio of 0.2 and annealed at 400 ℃ was found with the highest catalyst activity.94.14%of glycerol conversion and 90.95%of GC selectivity were obtained over this catalyst under the optimum conditions(5 wt.%catalyst of glycerol,85°C,8 h,1GL:3DEC).This catalyst can be reused up to three cycles with a minimal decrease in its catalytic activity.It was found the highly dispersed NiO particles and the strong basic sites derived from the substitution of Ce4+ by Ni2+ in the CeO2 lattices synergistically promoted the glycerol conversion.The thermodynamic and kinetics parameters of this reaction for synthesis of glycerol carbonate were studied.The reaction equilibrium constants were investigated experimentally in the temperature region of 338-358 k,and the standard molar properties(at 298 k)were obtained(AH0 = 115.71KJ·mol-1,△G0＝13.523KJ·mol-1,△S0 =0.343KJ·mol-1).Effects of the different reaction conditions such as stirring speed,reaction temperature,catalyst amount,reactant mole ratio on the reaction kinetics were also studied.Different order kinetic equations were used to simulate law of the transesterifiaction process.The result shows a three order equation of glycerol(two orders)and DEC(one order)was more appropriate to interpret the law of glycerol transesterification with diethyl carbonate.Additionally,activation energy was also calculated(87.90 kJ·mol"1).A co-precipitation method was employed in synthesis of Ce1-xCdxO samples which were adopted for glycerol carbonate synthesis and characterized by various technologies.SEM result demonstrated the spherical particles of CdO were uniformly dispersed on the surface of lamellar CeO2.The results from XRD,XPS and CO2-TPD demonstrateed that Ce4+ doped into CdO lattice could promote more oxygen atom adsorbed on the bimetal sample surface,which was favor of generation of moderate basic sites.The Ce0.7Cd0.3O sample annealed at 500℃ was observed with the highest catalytic activity.When the reaction conditions were fixed at 5 wt.%catalyst of glycerol at 90℃ for 3h with the reactants ratio of 1GL:3DEC,the best result was achieved with 96.84%of glycerol conversion and 100%of GC selectivity,respectively.Besides,it was found that conversion of glycerol was synergistically accelerated by the moderate and strong basic sites.