Ni基催化剂上丙酮加氢制备异丙醇的工艺研究

发布时间：2018-09-14 16:40

【摘要】：异丙醇是一种具有重大工业应用价值的化工产品,广泛应用于油墨、涂料、药品和电子工业等许多领域。丙酮加氢法是异丙醇制备技术中能耗极低,流程简单以及对设备腐蚀很轻的一种方法,工业发展前景极大。其核心技术是要开发一种催化性能好、经济性高以及制备简单的催化剂。本论文采用等体积浸渍法将具有良好加氢活性且价格较为低廉的Ni负载于ZSM-5载体上,制得加氢性能较为优越的Ni/ZSM-5催化剂,并添加Cu、 Zn、Fe、Co、Mg、Mn、Ca、K作为活性助剂对其改性,探究了不同的制备条件以及不同反应工艺条件对Ni基催化剂丙酮加氢制备异丙醇反应性能的影响,使用X射线衍射(XRD)、X射线光电子能谱分析(XPS)、扫描电镜(SEM)、N2吸附／脱附以及NH3-TPD等表征手段探讨了部分条件的变化给催化剂的微观结构、酸性、孔隙组成以及负载元素存在形式等带来的影响。首先,本文采取等体积浸渍法制得一系列Ni/ZSM-5催化剂,探究了不同的催化剂制备条件以及反应条件对催化剂丙酮加氢性能的影响。结果表明,催化剂制备最佳浸渍温度为40℃,最佳浸渍时间是3 h,活性组分Ni的最佳负载量为12 wt.%。最佳的反应工艺条件为：催化剂氢气还原温度450℃,还原时间4 h,反应温度130℃,反应压力3.5 MPa,氢酮进料摩尔比5：1,且催化剂稳定性较好。然后加入不同的活性助剂,采取等体积浸渍法制得一系列Ni-M/ZSM-5 (M= Zn、Fe、Cu、Mg、Co、Mn、Ca、K)催化剂,考察了不同活性助剂对催化性能的影响。结果表明,添加Ca活性助剂,催化剂展现出最佳的加氢性能。通过进一步优化Ca的负载量并考察添加Ca助剂后催化剂的结构、酸性、表面元素存在形式以及孔隙结构等的变化得到的结果表明,Ca助剂的最优负载量为9 wt.%。与Ni/ZSM-5催化剂相比：XRD表明,助剂Ca的加入提高了Ni在ZSM-5载体表层的分散度并且大大缩小了Ni微粒的尺寸；XPS表明,Ni的存在方式为NiO,Ca的存在方式为CaO,助剂Ca的引入使得催化剂中镍的电子云密度增加,镍与氢原子之间的作用力减小,氢气在催化剂上的脱附变得更为容易,有利于加氢反应的进行,抑制了Ni与载体之间的相互作用,即NiAl2O4物种的生成,对Ni2+的还原十分有利；N2吸附／脱附表明,引入Ca助剂以后,催化剂的孔径减小,较小的孔径有利于主反应的发生；NH3-TPD表明,Ca的添加减小了催化剂的酸性,进而修饰了ZSM-5载体的孔道结构,提高了活性组分Ni在载体上的分散度,调节了Ni/ZSM-5催化剂存在的化学环境,增强了催化剂的还原性及加氢活性。最后在不同的焙烧温度下,采取等体积浸渍法制得一系列Ni-Ca/ZSM-5催化剂,探究了焙烧温度对Ni-Ca/ZSM-5催化剂丙酮加氢性能以及形貌、分散度、孔隙结构等的影响。结果表明,最佳的催化剂焙烧温度为450℃。SEM表明,450℃焙烧的催化剂表面较为粗糙杂乱,颗粒分布更为分散,晶粒的不规则度较大,活性组分分布均匀,催化性能高；700℃焙烧条件下制得的催化剂颗粒表面光滑,结构规整,颗粒排布较为密集,不利于活性组分的均匀分布,因此导致催化剂的性能急剧下降。N2吸附／脱附结果表明,450℃焙烧的Ni-Ca/ZSM-5催化剂其比表面积比空白ZSM-5载体有所增加；催化剂的比表面积随着焙烧温度的提高而减小,过高的焙烧温度会导致催化剂孔结构的坍塌,平均孔径变大,比表面积减小。XRD结果表明,700℃焙烧的催化剂中NiO晶粒结构变得更加规整,晶化程度变大,结晶趋于完善,过高的焙烧温度对催化剂性能产生不利的影响。
[Abstract]:Isopropanol is a kind of chemical product with great industrial application value, which is widely used in ink, paint, medicine and electronic industry. Acetone hydrogenation is a method of preparing isopropanol with low energy consumption, simple process and light corrosion to equipment. Its core technology is to develop a kind of method. In this paper, Ni/ZSM-5 catalysts with good hydrogenation activity and low cost were prepared by immersing Ni on ZSM-5 carrier with equal volume method, and Cu, Zn, Fe, Co, Mg, Mn, Ca and K were added as active promoters to modify Ni/ZSM-5 catalysts. The effects of preparation conditions and different reaction conditions on the performance of Ni-based catalyst for acetone hydrogenation to isopropanol were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), N2 adsorption/desorption and NH3-TPD. Firstly, a series of Ni/ZSM-5 catalysts were prepared by isovolumetric impregnation method, and the effects of preparation conditions and reaction conditions on the performance of the catalysts for acetone hydrogenation were investigated. The optimum reaction conditions are as follows: hydrogen reduction temperature 450, reduction time 4 h, reaction temperature 130, reaction pressure 3.5 MPa, molar ratio of hydrogen to ketone 5:1, and the stability of the catalyst is good. A series of Ni-M/ZSM-5 (M=Zn, Fe, Cu, Mg, Co, Mn, Ca, K) catalysts were used to investigate the effects of different active promoters on the catalytic performance. Compared with Ni/ZSM-5 catalyst, XRD showed that the addition of Ca increased the dispersion of Ni in the surface layer of ZSM-5 support and greatly reduced the size of Ni particles; XPS showed that the existence of Ni was NiO, the existence of Ca was CaO, and the addition of Ca was CaO. The electron cloud density of nickel in the catalyst increases, the interaction force between nickel and hydrogen atoms decreases, the desorption of hydrogen on the catalyst becomes easier, which is conducive to the hydrogenation reaction, and inhibits the interaction between nickel and the support, i.e. the formation of NiAl2O4 species, which is favorable to the reduction of Ni2 +. NH3-TPD showed that the addition of Ca reduced the acidity of the catalyst, thus modifying the pore structure of ZSM-5 support, improving the dispersion of active component Ni on the support, adjusting the chemical environment of Ni/ZSM-5 catalyst and enhancing the catalyst return. Finally, a series of Ni-Ca/ZSM-5 catalysts were prepared by isovolumetric impregnation method at different calcination temperatures. The effects of calcination temperature on the performance, morphology, dispersion and pore structure of Ni-Ca/ZSM-5 catalysts for acetone hydrogenation were investigated. The results showed that the optimum calcination temperature was 450 C. SEM showed that the calcination temperature was 450 C. The surface of the catalyst is rough and disordered, the particle distribution is more dispersed, the grain irregularity is larger, the active component distribution is uniform, and the catalytic performance is high; the catalyst particles prepared under the condition of 700 C calcination have smooth surface, regular structure and dense particle arrangement, which is not conducive to the uniform distribution of the active component, thus leading to the performance of the catalyst. N2 adsorption/desorption results show that the specific surface area of Ni-Ca/ZSM-5 catalyst calcined at 450 C is larger than that of blank ZSM-5 carrier, and the specific surface area of the catalyst decreases with the increase of calcination temperature. Excessive calcination temperature will lead to the collapse of pore structure, the average pore size and the specific surface area of the catalyst decrease. The results show that the crystalline structure of NiO in the catalyst calcined at 700 C becomes more regular, the crystallization degree becomes larger and the crystallization tends to be perfect.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36;TQ223.123

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