【作者】 付庆涛；

【导师】 刘晨光；

【作者基本信息】 中国石油大学 ， 化学工程与技术， 2011， 博士

【摘要】 环己烯作为一种重要的有机化工原料,广泛应用于医药、食品、农用化学品、饲料、聚酯材料及其它精细化工产品的生产,因此苯选择性加氢制备环己烯技术成为一个的重要研究方向。磁稳定床具有传质效率高、床层不易出现沟流、压降低、能控制相间返混、转化率高,易于控制反应时间等优点。本论文探索了纳米氧化铝球和核壳结构磁性纳米氧化铝球的制备过程,制备了三种磁性核壳结构氧化铝微球,评价了复合载体Al₂O₃-ZrO₂的苯选择性加氢性能;制备了兼具磁性和活性的钌基磁性催化剂,并将磁性钌基催化剂应用于磁稳定床中进行苯选择性加氢研究,开发了一种新的磁性催化剂和新的苯选择性加氢工艺。采用溶胶-凝胶法制备了纳米Al₂O₃球和磁性核壳结构纳米Al₂O₃球。在正丙醇的体系中,月桂酸为模板剂,采用一种简单有效的方法合成了纳米氧化铝球。该纳米氧化铝球是借助异丙醇铝水解,缩聚过程以及月桂酸的自组装作用合成的。该微球的粒径分布为80¹20nm,粒径分布均匀,比表面积为550m²/g,孔容为0.8cm³/g,平均孔径为4.9nm。在此基础上,以α-Fe₂O₃为核,硬脂酸为模板剂,通过异丙醇铝水解,缩聚过程以及模板剂自组装合成了一种新型均一核壳结构氧化铁/氧化铝纳米球,然后通过H₂/N₂还原得到磁性氧化铝球。该纳米球具有均一壳层,厚度为30nm,比表面积为140m²/g,孔容为0.22cm³/g,比饱和磁化强度为50.2emu/g。采用油柱成型法制备了三种三重核壳结构磁性氧化铝微球。详细考察了不同磁核制备的氧化铝微球的磁性能。以针状γ-Fe₂O₃为磁核合成的γ-Fe₂O₃/SiO₂/γ-Al₂O₃磁性微球表面光滑,粒径分布为80³00μm,比表面积为200m²/g,平均孔径为16.8nm,孔容为0.77cm³/g,比饱和磁化强度较高（15.1emu/g）,矫顽力和剩磁较低,该微球能够满足磁稳定床的要求。以Fe₃O₄为磁核,氧化硅为中间层,氧化铝为壳层的Fe₃O₄/SiO₂/γ-Al₂O₃磁性微球具有较强的超顺磁性。该磁性微球的比表面积为201.0m²/g,孔容为0.76cm³/g,平均孔径为17.0nm。粒径为80³00μm。分别以球状α-Fe₂O₃和针状α-Fe₂O₃为核制备了α-Fe₂O₃/SiO₂/γ-Al₂O₃微球,通过氢气还原得到了Fe₃O₄/SiO₂/γ-Al₂O₃和Fe/SiO₂/γ-Al₂O₃磁性微球。前者表现为顺磁性,比饱和磁化强度为14.0emu/g,后者表现为铁磁性,比饱和磁化强度为26.0emu/g,矫顽力为430 Oe。该磁性氧化铝微球的磁性能可通过调节还原温度和时间来控制。为了提高环己烯的选择性,对比考察了Al₂O₃和Al₂O₃-ZrO₂负载的Ru-Zn-B催化剂上苯的选择性加氢性能。采用硼氢化钠化学还原法分别制备了Ru-Zn-B/Al₂O₃和Ru-Zn-B/Al₂O₃-ZrO₂催化剂,并对这两种催化剂进行了苯选择性加氢评价研究。结果表明ZrO₂的引入显著提高了环己烯选择性,当Zr/Al原子比为0.1时,环己烯选择性最高。另外发现少量Zn的加入有利于提高Ru-Zn-B/Al₂O₃-ZrO₂催化剂的环己烯选择性。这是因为ZnSO₄水溶液使催化剂表面的亲水性增强,以及Zn²⁺对Ru的稀释作用,提高了环己烯的选择性。设计建造了磁稳定床冷模实验装置,并以细小的铁粉颗粒为固相,氮气为气相,自来水为液相,通过冷模实验研究了液固和气液固三相系统的流动状态,确定了气液固三相之间传质效率高的链式操作状态,获得了磁稳定床的稳定操作区间。在此基础上,设计建造了磁稳定床加氢实验装置,以磁性氧化铝为载体,通过浸渍法制备了均匀型和蛋壳型分布的Ru钌基磁性Ru/γ-Fe₂O₃-γ-Al₂O₃微球催化剂,详细考察了磁性催化剂的制备参数、磁稳定床的操作参数和反应条件对苯选择性加氢的影响。结果表明磁稳定床的链式操作状态和Ru的蛋壳型分布提高了环己烯的选择性,证实了所研制的蛋壳型钌基磁性微球催化剂适用于磁稳定床中苯的选择性加氢工艺,具有较好的应用前景。更多还原

【Abstract】 Cyclohexene is an important raw material, which can be widely used in production of medicine, pesticide, dye, washes, dynamite, feedstuff, polyester, and other fine chemicals. Selective hydrogenation of benzene to cyclohexene is becoming an important chemical process for production of cyclohexene. A magnetically stabilized bed （MSB） has many advantages of high mass-transfer efficiency, low pressure drop, high conversion, and easy to avoid channeling flow, interphase backmixing and residence time over conventional fixed bed and fluidized bed, since the magnetic catalyst particles are dispersed in a uniform and stable arrangement by the magnetic field. The preparation process of alumina nanospheres and the magnetic core-shell alumina nanospheres were explored in this paper. Selective hydrogenation of benzene on the Ru and Ru-Zn-B catalysts supported on Al₂O₃-ZrO₂ composite was investigated. Three kinds of magnetic core-shell alumina microspheres were prepared, which have both suitable magnetism and high activity for hydrogenation, therefore it is capable of applying to the MSB. The final goal of this paer is to develop novel magnetic catalysts and MSB technology for selective hydrogenation of benzene.Alumina nanospheres and magnetic core-shell alumina nanospheres were synthesized by sol-gel method. It presents a simple and efficient approach to synthesize alumina nanospheres, which can be produced using lauric acid as template in 1-propanol system. A novel and uniform alumina nanospheres with a size of 80–120 nm has been successfully prepared by lauric acid via combination of the sol-gel process with the surfactant self-assembly approach. The alumina nanospheres possess average pore diameter 4.9 nm, a large pore volume 0.8 cm³/g, and a high specific surface area 550 m²/g. On the basis of above method, well-structured nanospheres with a magnetic core/alumina shell （MFeCA） structure were obtained by self-assembly of stearic acid/alumina species complex in 1-propanol system. The thickness of alumina shell is very uniform （30nm）. The surface area, pore volume and average pore size of the sample is 140m²/g, 0.22 cm³/g and 5.2 nm, respectively. The saturation magnetization values of the sample is as high as 50.2 emu/g.Magnetic alumina composite microspheres withγ-Fe₂O₃ core/Al₂O₃ shell structure were prepared by the oil column method. The results show that the specific surface area and pore volume of theγ-Fe₂O₃/SiO₂/Al₂O₃ composite microspheres calcined at 500℃were 200 m²/g and 0.77cm³/g, respectively. The saturation magnetization is 15.1emu/g. Magnetic alumina composite microspheres consisting of Fe₃O₄ core, an intermediate layer of SiO₂ and Al₂O₃ shell structure were also prepared by the oil column method. The sample is of uniform particle size and a strong superparamagnetic. The specific surface area, pore volume and average pore diameter of the microsphere were 201m²/g, 0.76cm³/g, 17nm, respectivly. The particle size distribution of the sample is 80³00μm. In addition,α-Fe₂O₃/SiO₂/γ-Al₂O₃ microspheres composed of the sphericalα-Fe₂O₃ or the needle type ofα-Fe₂O₃ were prepared by oil column method. Magnetic Fe₃O₄/SiO₂/γ-Al₂O₃ and Fe/SiO₂/γ-Al₂O₃ microspheres were obtained by hydrogen reduction. The former represents paramagnetic magnetization 14.0emu/g, while the latter shows the ferromagnetic saturation magnetization 26.0emu/g, coercivity 430 Oe. Therefore, it is easy to get different magnetic alumina carrier by controlling the reduction temperature and time.Ru-Zn-B/Al₂O₃-ZrO₂ and Ru-Zn-B/Al₂O₃ catalyst were prapared by chemical reduction method using sodium borohydride as chemical reductant. The performance of two catalysts was characterized using selective hydrogenation of benzene in autoclave reactor. The results show that ZrO₂ is favorable to increase the selectivity of cyclohexene on Ru-Zn-B/Al₂O₃ catalyst obviously, the highest selectivity of cyclohexene occurs when the Zr/Al atomic ratio is 0.1. Ru catalyst containing a small amount of zinc is in favor of improving selectivity of cyclohexene. The reason may be that ZnSO₄ solution enhances the hydrophily of the surface of the catalyst obviously, and Zn²⁺ dilutes Ru to increase the dispersion of Ru nanoparticles, therefore improves the selectivity for cyclohexene.A model MSB unit was designed and constructed, and was used to investigate the flow state with Fe fine particles as model catalyst, nitrogen as gas and water as liquid. The results indicated that the high mass-transfer efficiency is obtained when the magnetically stabilized bed is in the state of chain operation. On the basis, Ru-based magnetic microspheres （Ru/γ-Fe₂O₃-SiO₂-γ-Al₂O₃） catalysts with uniform and egg-type distribution of Ru on catalyst pellets were prepared by impregnation method, respectively. A MSB unit for hydrogenation was designed and constructed, and used to characterize the selective hydrogenation of benzene. The effects of catalyst preparation parameters and reaction conditions on the selective hydrogenation of benzene were investigated in detail. The results show that the state of chain operation in MSB and the egg-type distribution of Ru on catalyst pellets increase the selectivity for cyclohexene obviously, this verify that the magnetic ruthenium-based catalysts and magnetically stabilized bed have a good prospect of industrial applications.更多还原