【作者】 孙辉；

【导师】 楼辉；

【作者基本信息】 浙江大学 ， 化学， 2012， 博士

【摘要】 生物柴油是一种清洁的可再生生物质能源,其使用能有效降低尾气中碳、硫的排放,因此具有替代化石柴油的潜力。生物柴油通常由植物油和甲醇在催化剂的作用下通过酯交换反应制得。由于传统工业应用中该方法主要在均相酸碱催化剂催化下发生,会造成比较严重的环境污染,因此二十多年来,科学家们一直致力于开发可重复利用的非均相催化剂以及制备生物柴油的新方法。和酸性催化剂以及酶催化剂相比,碱性催化剂一般具有更高的反应活性,因此近年来相比其他类型催化剂得到了更广泛的研究。本论文的研究工作将稀土氧化物固体碱催化剂以及有序介孔固体碱催化剂应用于生物柴油的制备中,详细分析了几类催化剂的物理化学性质,考察了各类固体碱催化剂在植物油和甲醇酯交换制备生物柴油反应中的催化活性,并且提出了催化剂活性中心的形成机理。得到以下主要结论：1)稀土氧化物负载的KF固体碱催化剂是一类具有很高活性的生物柴油转化催化剂。研究发现,催化剂的催化活性和催化剂的碱性相关联。通过表征,提出稀土氧化物上负载KF后形成的碱中心是由于F-离子和稀土氧化物表面的协同作用所引起的。此类催化剂虽然具有很高的催化活性,但是催化剂在一次使用后便已经失活。再生催化剂时需要重新加入活性组分KF,因此其催化效果同均相催化剂类似,是一类不经济、不环保的固体碱催化剂。2)ZrO2上负载La2O3的固体碱催化剂对葵花籽油制备生物柴油的反应有良好的催化活性。研究发现,载体ZrO2的晶粒随着La2O3的负载而逐渐减小,这可能和催化剂焙烧过程中La2O3-ZrO2固溶体的形成有关。在催化活性方面,发现经过600℃焙烧后的21%La2O3/ZrO2催化剂在酯交换反应中表现出了最好的催化活性。虽然该催化剂具有一定的活性,但其稳定性依然不够理想,5次反应后其生物柴油的产率只有28.8%。而这结果可能和负载型La2O3/ZrO2催化剂表面活性La2O3物种的流失有关。3)通过一锅法合成了介孔Ca/SBA-15催化剂。当Ca/Si摩尔比达到0.5：1的时候SBA-15的有序介孔结构也得到了很好的保持。和浸渍法制备的Ca/SBA-15样品相比,一锅法制备的Ca/SBA-15不但可以使钙物种得到更好的分散,而且具有更高的比表面积和更多的中强碱中心。另外,一锅法制备的Ca/SBA-15还可以减少原料和能源的使用。这类催化剂在葵花籽油和甲醇的酯交换反应中表现出了比普通浸渍法制备的Ca/SBA-15更好的稳定性,5次反应后几乎不失活。另外,原料油中5%的水含量和/或者3%的游离脂肪酸含量并不会影响其在酯交换反应中的活性。4)通过水热合成法制备了棒状的CaxSiO2+x固体碱催化剂。该类催化剂可以成功地应用于大豆油和甲醇酯交换法制备生物柴油的研究中。在适当的反应条件下,550。C焙烧的Ca4SiO6催化剂上生物柴油的产率高达95%。另外,该类催化剂还能在室温下催化制备生物柴油的反应,这可大大降低生产过程中的能量消耗。该催化剂虽然具有很好的活性,但其重复利用的效果依然不够理想,5次使用后就存在较严重的失活,而这与催化剂上活性组分的流失有关。更多还原

【Abstract】 Petrochemical sources, such as coal and natural gases are supplying the majority of the energy needs of the world, but all of these sources are finite and will be consumed shortly. Therefore, research is now being directed towards the use of alternative renewable fuels. Biodiesel, a mixture of alkyl esters obtained from vegetable or animal oils, is a promising nontoxic and biodegradable fuel arising from biomass. Biodiesel is usually produced by the transesterification of triglycerides with short-chain alcohols (generally methanol and ethanol) in the presence of a catalyst. Although both acids, bases, enzymes can be used for the transesterification reaction, alkaline catalysts are more widely investigated because the rate of transesterification reaction by alkaline catalysts is much faster than that by acid catalysts and enzymes.Conventionally, homogeneous basic catalysts, such as sodium or potassium hydroxide dissolved in methanol, are used for the transesterification reaction. These traditional homogeneous catalysts have certain advantages including high activity and mild reaction conditions. The removal of these catalysts is however technically difficult, and a large amount of wastewater was produced during biodiesel separating and cleaning. In order to circumvent the difficulties with homogeneous catalysts, heterogeneous basic catalysts have been widely studied in the past decades. They have some outstanding advantages, such as simplifying of separation and no toxicity, no corrosion, or no environmental pollutionIn this thesis, several kinds of solid base have been used in transesterification of vegetable oils with methanol to biodiesel production. The catalyst was characterized by TG-DTA, XRD, FTIR, SEM, TEM and CO2-TPD, and the mechanism for the formation of basic sites was discussed. Results were as follows,1) KF loaded Rare Earth Metal Oxides (Re2O3, Re=Y, La, Sm, Eu) were prepared by incipitation impregnation method and were applied in the transesterification reaction of rapeseed oil with methanol. The mechnism for the formation of basic sites and the phase change of the KF-loaded Re2O3catalyst with different calcination temperatures is proposed.2) La2O3supported on ZrO2catalysts was prepared by impregnation method. and used in the transesterification of sunflower oil with methanol. This catalyst possess better stability than KF/Re2O3. however, leaching still occurred on this catalyst. 3) SBA-15supported CaO was prepared by one-pot synthesis method, and applied in the transesterification of different vegetable oils with methanol. This kind of catalyst showed good stability not only in transesterification reaction, but also in reactions with low contents of free fatty acids (FFA) and water.4) Rod-like CaxSiOx+2catalysts were synthesized by using one-pot hydrothermal method. Catalysts calcined at550℃were used in the transesterification reaction of soybean oil with methanol. Under methanol reflux condition, FAME yields of82%and95%were achieved on Ca4SiO6in a reaction time of1and2h, separately. Besides, a FAME yield of ca.80%can be achieved under room temperature over Ca4SiO6catalyst.更多还原