Diffusion, Based On The Hydrotalcite Layer Spacing Of The Catalyst Carrier Controlled Glycerol Hydrogenolysis Within

Recently, more attention has been drawn on finding of new applications of glycerol, owing to the large surplus of this agent formed as a by-product during the production of biodiesel. Among them, hydrogenolysis of glycerol to 1,2-propanediol is believed a sustainable process with renewable potential application. The metal Cu was loaded on the hydrotaclite-derived mixed oxides to prepare Cu/mixed-oxide catalysts, and the Cu/mixed-oxide catalysts were used in glycerol hydrogenolysis. The obtained catalyst was characterized by using techniques of XRD, BET, EDS, CO2-TPD.The effect of hydrotalcite support was investigated. It was found that Cu/Mg-Al mixed-oxide catalysts had the highest catalytic activity. The effect of reaction variables was also studied. Under optimum conditions,3.6 wt% of Cu/Mg-Al mixed-oxide catalyst, pure glycerol solution, reaction temperature (210℃), hydrogen pressure (9 MPa), reaction time 24 h,99% conversion of glycerol with 89% yield of 1,2-propanediol could be achieved.Information on mass transport is crucial for understanding glycerol hydrogenolysis. The basal spacing of Cu/Mg-Al mixed-oxide catalysts before and after reaction were analysed by XRD analysis. It was found that the basal spacing of hydrotalcite could work as an effective probe, reflecting if the glycerol hydrogenolysis is limited by mass transport. Using the basal spacing of hydrotalcite as probe, effect of internal diffusion on the glycerol hydrogenolysis was elucidated. The mass-transfer limitations show little influence on the reaction conversion profile. However, the yield with respect to 1,2-propanediol is affected by the diffusion limitation in the Mg(Al)O supported Cu catalyst. The relationship between internal diffusion and reaction conditions was also investigated. In the case of glycerol hydrogenolysis with high concentration, and low reaction pressure and temperature, the mass transfer is more easily limited in the interlayer space of hydrotalcite, forming the structure of hydrotalcite with enhanced basal spacing; however, in the reverse reaction condition, it is less easily limited, forming the structure of common hydrotalcite.