Hydrogenolysis Of Glycerol To Produce 1,2-propanediol Over Cu-Based Catalysts

Hydrogenolysis of glycerol 1,2-Propanediol not only offers a practical route to produce sustainable propylene glycol but also benefits the extent of the value chain of biodiesel as glycerol is a major by-product of biodiesel.Herein,Cu/Cr2O3,Cu/ZrO2 and the modified Cu/ZrO2 catalysts by Cr2O3 and WO3 were prepared with a co-precipitation method and evaluated in the hydrogenolysis of glycerol in terms of activity,selectivity,structural stability and catalyst lifespan.Besides,the influence of solvents such as water and methanol on catalyst stability was also investigated.The main conclusions are listed below.(1)Compared with Cu/Cr2O3 catalysts,Cu/ZrO2 facilitated the dispersion of Cu,resulting in higher activity and stability for the hydrogenolysis of glycerol.However,the Cu/ZrO2 catalysts suffered a rapid deactivation in the steam-rich reaction environment due to the sintering of Cu nanoparticles.The introduction of Cr2O3 to the catalysts didn't improve activity and stability despite the promoted Cu dispersion by Cr2O3.By comparison,the incorporation of WO3 to Cu/ZrO2 catalysts greatly enhanced the Cu dispersion,retarded the aggregation of Cu particles,and prolonged the catalyst lifetime.Under the optimized conditions of temperature at 240?,a H2 pressure at 5 MPa,a molar ratio of H2 to glycerol at 12,and a space velocity of glycerol(50%glycerol in water)at 0.275 h-1,the conversion of glycerol and selectivity of 1,2-propanediol changed slightly during the first 150 h reaction period,remaining at 99.8%and 95.4%,respectively.(2)Substituting water with methanol as the reaction solvent reduced the sintering of Cu catalysts significantly and enhanced their durability for the hydrogenolysis of glycerol.With 50%glycerol in methanol as feedstock,the conversions observed for Cu/ZrO2,Cu/Cr2O3-ZrO2 and Cu/WO3-ZrO2 catalysts were all above 99.5%during the reaction time of 500 h and the selectivities of 1,2-propanediol were 96%,96%and 93%,respectively,under the optimized conditions of 240?,5 MPa H2,0.275 h-1,and a molar ratio of H2 to glycerol at 12.After the long-term reaction,the average Cu particle sizes for Cu/ZrO2,Cu/Cr2O3-ZrO2 and Cu/WO3-ZrO2 catalysts increased from 26.7,14.4 and 14.8 nm to 40.7,19.5 and 20.1 nm,respectively,much better than the Cu sintering in the steam-rich reaction environment.