Study Of Hydrogenolysis Of Glycerol Over Cu-based Catalysts

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 (denoted as 1, 2-PDO) is believed a sustainable process with renewable potential application.There are many patents and literature reports that different catalytic systems, such as various supported Rh, Ni, Ru, Pt, Pt-Ru and Cu catalysts, are active for the hydrogenolysis of glycerol to 1, 2-PDO. It was known that Cu-based catalysts have shown unusual ability for breaking C-O bonds by H2 rather than attacking C-C bonds in the glycerol molecule during the reaction, thus might become suitable catalyst system for the title reaction. Montassier et al. reported that the hydrogenolysis of glycerol could be carried out over Raney Cu, Cu/C, and Cu-Pt and Cu-Ru bimetallic catalysts under 1.0-4.0 MPa hydrogen pressure. They found that the Cu/C catalyst exhibits good catalytic properties, and 40% conversion of glycerol with 84.5% selectivity of 1,2-propanediol could be achieved at 533 K under 4.0 MPa H2 by using a dynamic fixed-bed flow reactor. H. C. Liu et al. reported that Cu-ZnO catalysts could catalyze hydrogenolysis of glycerol to 1, 2-PDO with very high selectivity of 94% at 22.5% conversion at 473 K and under 4.2 MPa. Very recently, L. Huang et al. investigated several Cu-based catalysts for the hydrogenolysis of glycerol, and found that Cu/ZnO/Al2O3 catalyst is the most effective catalyst (96% conversion of glycerol with 92% selectivity of 1, 2-PDO, at 463 K, 0.64 MPa and 0.08 h-1 in a fix-bed reactor). In the same work, they also mentioned that Cu/SiO2 catalyst prepared by incipient-wetness technique is active for the reaction. However, the catalytic activity of such catalyst is quite low compared with other Cu-based catalysts, the Cu/SiO2 catalyst with very high loading of copper (i.e. 10 wt.% Cu) just could give a 5.9% conversion of glycerol with 57.5% selectivity of 1, 2-PDO under 5 MPa hydrogen pressure at 473 K by using an autoclave reactor.The main research work is as follows:1. We have prepared Cu/SiO2 catalyst by impregnation (IM) method and researched their catalytic performance over the hydrogenolysis glycerol to 1,2-PDO. By the study about the effect of support, prepare method, loading amount, we found that the 10%Cu/SiO2 catalysts which prepared by impregnation method performed good activity. We also amply studied the influence of the reaction conditions (including temperature, hydrogen pressure, water content, M H2/Mglycerol and LHSV) on the catalytic performance. The temperature was 250℃and the pressure was maintained at 4MPa, Cu/SiO2 exhibited high activity (99.6%) and selectivity (85.6%). In order to study its resistance to deactivation, the stability of the Cu/SiO2 catalyst was examined at 250℃for 120h. From the results of XRD, we could conform that during the reaction the active site was sintered.2. The catalytic property of supported copper silica prepared by ion-exchanged method (denoted as Cu/SiO2-IE) was investigated for the hydrogenolysis of glycerol in a fixed-bed tubular reactor. Compared with the Cu/SiO2 catalyst prepared by wet impregnation and sol-gel methods, Cu/SiO2-IE shows very high activity (99.6% conversion of glycerol) and selectivity (86.4% to 1, 2-propanediol) at 523 K and under hydrogen pressure of 4.0 MPa. The main reason for its good performance in the title reaction may be assigned to the co-existence of two types of active centers, which are the highly dispersed metallic copper and copper ions, on the Cu/SiO2-IE catalysts.3. Cu-Zn0 was selected as the catalyst for glycerol hydrogenolysis. The effect of different preparation methods and conditions of catalysts on its activity had been widely investigated, and it was followed by investigating the affection of reaction condition on the results of glycerol hydrogenolysis. Compare with the Cu-ZrO2 catalyst, Cu-Zn0 performed more activity at low reaction temperature (200℃), it may caused by the acidic ZnO surfaces.4. In order to study about the effect of the acid of support on the glycerol hudrogenolysis, we prepared the catalyst with the support of titania-silica materials with different ratio, it could be found that with the increasing of acid of support, the activity decreaseing.