| Energy is the material foundation of human activity and economic development.However, with the excessive exploitation and use of traditional fossil fuels, more and more environmental issues emerged. Biodiesel, as a kind of biomass fuels, has been put into mass production because of its renewable and environmentally-friendly properties. But large amounts of glycerol were simultaneously generated as a by-product in the production of biodiesel, which led to a sharp drop in its price. In this context, the use of glycerol by transformation into high value chemicals was important to the sustainable development of biodiesel industry. Among the various catalytic processes, one of the promising processes was the selective hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO). In this work, different catalysts (e.g., Cu-,Ni-, Co- and Pd-based catalyst) were applied for the hydrogenolysis of glycerol. The effects of metal-support interaction and multi-metal synergy on glycerol hydrogenolysis were studied in detail. In addition, different supported Ni/Cu catalysts were used for in situ hydrogenolysis of glycerol using 2-propanol as a hydrogen donor,and the reaction pathway of in situ hydrogenolysis was also investigated. The main research contents and results are as follows:(1) The Cu-, Ni-, Co- and Fe-based catalysts prepared by co-precipitation method were applied for the hydrogenolysis of glycerol in a fixed-bed flow reactor. In the case of the Cu-Al, Cu-Mg and Cu-Zn catalysts, the selectivity to 1,2-PDO was higher than 80%, but glycerol conversion was low. In the case of Co-Al and Ni-Al catalysts, high glycerol conversion and low 1,2-PDO selectivity were achieved compared with that of Cu-Al catalyst. The catalytic activity of Fe-Al was poor.(2) In order to improve the catalytic activity and stability of Cu-Al catalyst,different modifiers were used in this work. The experimental results showed that addition of Ce, Nb, Ag and Zr to Cu-Al catalyst enhanced the catalytic performance for glycerol hydrogenolysis, which was related to the increased specific surface area,pore volume, Cu dispersion, metal interaction, acidity and reduction ability. Among the catalysts tested, the Zr-Cu-Al catalyst showed the best catalytic performance with 97.1% glycerol conversion and 95.3% 1,2-PDO selectivity when glycerol hydrogenolysis was performed at 230 ?,3.5 MPa, and using 20 wt% glycerol ethanol solution with 27.8 mL·h-1 of liquid flow rate. The catalytic activity of Zr-Cu-Al catalyst was relatively stable for 100 h, which was likely due to the strong interaction between copper and zirconium species. However, the deactivation of catalyst was observed after 44 h time on stream when using water as a solvent. The sintering of Cu particles was the main factor for the loss of catalytic activity.(3) Incorporation of Ba, Ce, La and Y into Cu-Zn significantly increased the catalytic performance for glycerol, which was related to the presence of large number of base and metal active sites. Among them, the La/Cu-Zn catalyst achieved the best catalytic activity with 87.1% glycerol conversion and 91.8% 1,2-PDO selectivity.Similarly,the introduction of different acid species such as B2O3, CeO2, HSiW,HPW,HPMo and ZrO2 into Co-Al catalyst greatly enhanced the glycerol conversion. This improvement was related to the increase in the acidity on the catalyst surface.However, the etherification activity of glycerol with ethanol increased with the addition of acid species, which led to to the reduction of 1,2-PDO selectivity. When Cu was introduced into Co-Al catalyst, the etherification activity of glycerol with ethanol could be significantly suppressed. In the case of water as a solvent, the HSiW/Co-Al catalyst attained 18.3% 1,3-PDO selectivity and could stabilize to 50 h,which was likely due to the presence of high Br(?)nsted acidity and strong metal interaction on catalyst surface.(4) The effects of process parameters like reaction temperature, operating pressure, glycerol concentration and liquid flow rate on glycerol hydrogenolysis were deeply investigated. The increased reaction temperature was beneficial to the conversion of glycerol, but more by-products would be generated at high reaction temperature, which led to the decrease of the selectivity to 1,2-PDO. High hydrogen pressure was conducive to improving the catalytic performance for glycerol hydrogenolysis, but high opetating pressure increased the equipment cost. Poor catalystic performance for glycerol hydrogenolysis was observed in the case of high glycerol concentration or liquid flow rate.(5) Addition of Ce to Pd-Zr-Al catalyst notably improved the Pd dispersion.Introduction of Nb could significantly increase the acidity on Pd-Zr-Al catalyst surface, which was more advantageous to glycerol hydrogenolysis. The Nb/Pd-Zr-Al catalyst showed the best catalytic activity with 69.2% glycerol conversion and 84.5%1,2-PDO selectivity. Moreover, the catalytic performance for glycerol was almost unchanged over four cycles, which was due to the presence of strong metal interaction.In the case of Nb/Pd-Zr-A1 catalyst, the rate of intermediate acetol hydrogenation to 1,2-PDO exceeded by far its rate of formation via glycerol dehydration, which meant that the dehydration of glycerol was the rate-controlling step. And the 1,2-PDO could further undergo hydrogenolysis reaction and mainly produce 2-propanol in the presence of Nb/Pd-Zr-Al catalyst, but the reaction activity of ethylene glycol was poor.(6) Different supported Ni/Cu catalysts were applied to in situ hydrogenolysis of glycerol. The Ni/Cu/?-Al2O3 and Ni/Cu/ HZSM-5 catalysts showed complete glycerol conversion at 230 ?, 3.5 MPa and using 5 wt% glycerol 2-propanol solution with 27.8 mL·h-1 of liquid flow rate, but only 73.7% and 51.7% 1,2-PDO selectivity were obtainted, respectively. The Ni/Cu/TiO2 catalyst achieved the best performance, up to complete glycerol conversion with 82.2% 1,2-PDO selectivity under the same condition, which was due to the presence of high Ni content and good Cu dispersion.The activity of 1,2-PDO formed by aqueous phase reforming of glycerol was lower than that of 1,2-PDO formed by in situ hydrogenolysis of glycerol using 2-propanol as a hydrogen donor. On one hand, the use of water as a solvent would lead to a great damage to the catalyst; on the other hand, the carbon utilization was low in the case of aqueous phase reforming of glycerol. |
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