【作者】 郑静；

【导师】 张文祥； 贾明君；

【作者基本信息】 吉林大学 ， 物理化学， 2009， 博士

【摘要】 丙二醇(包括1,2-丙二醇和1,3-丙二醇)是一类重要的化工原料,广泛应用于食品、医药和化学工业中。近年来,迅速升温的生物柴油投资热使生产过程中副产的甘油出现过剩,因此为这些甘油寻找有效利用的新途径受到广泛关注。其中,通过催化氢解甘油来生产二元醇被认为是一种具有潜在应用价值的有效方法。本论文主要采用不同方法制备了多种类型铜基催化剂,考察了甘油氢解制1,2-丙二醇的反应性能;另外,结合多种表征手段研究了催化剂的组成、结构、表面酸碱性质及铜物种的状态,并与催化剂的反应性能进行了关联,探讨了催化剂的活性中心性质及催化作用机制等问题。取得的主要结果如下:采用浸渍法制备了具有不同铜负载量的Cu/SiO2催化剂并考察了催化剂的反应性能。结果表明:负载量10 wt.% Cu/SiO2催化剂表现出了较好的催化性能,在优化的反应条件下,甘油的转化率可达99.6%, 1,2-丙二醇的选择性为85.6%;随着反应时间的延长,催化剂的活性有所降低。结合XRD及TPR等表征结果,可以认为催化剂上单质铜粒径的大小是影响催化剂活性的主要因素;催化剂表面铜物种与载体间较弱的相互作用使活性物种易于发生聚集,从而导致活性下降。通过离子交换法制备出了Cu/SiO2、Cu/SBA-15及Cu/TiO2-SiO2等催化剂。结果表明:Cu/SiO2和Cu/SBA-15对甘油氢解制1,2-丙二醇反应表现出很高的活性、选择性和稳定性。Cu/TiO2-SiO2催化剂的反应性能相对较差,这可能是由于载体表面的酸中心数目较多,与活性铜物种产生了较强的相互作用,导致催化活性下降。各种表征结果表明:Cu/SiO2和Cu/SBA-15催化剂表现出高活性的主要原因是由于活性铜物种(Cu0)能够高分散在载体表面;催化剂表面存在的少量Cu+物种(Lewis酸中心)可能也对甘油的活化起到了协同的作用。此外,Cu/SBA-15催化剂表现出相对高稳定性的主要原因是由于SBA-15载体本身的高比表面特征和均匀分布的介孔孔道能够稳定活性铜物种,有效抑制铜物种发生聚集。采用共沉淀法制备了Cu-ZnO和Cu-ZrO2催化剂,并详细考察了各种因素对催化剂反应性能的影响。结果表明Cu-ZnO在相对较低的反应温度下(200℃)就能表现出较高的反应活性。结合各种表征结果,可以看出两种催化剂上的Cu粒径大小和氧化还原性能基本一致,因此催化性能上的差异主要归因于第二组分(ZnO和ZrO2)的性质不同。我们认为Cu-ZnO催化剂表面的酸性特征更适合于甘油脱水过程的进行,从而使Cu-ZnO催化剂表现出了相对高的反应活性。更多还原

【Abstract】 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.更多还原