甲烷催化裂解制氢催化剂的制备与再生性能研究

发布时间：2018-04-20 18:07

本文选题：催化剂 + 甲烷　；参考：《中国石油大学(华东)》2015年硕士论文

【摘要】：伴随着世界性能源危机的日益加剧,原油的重质化和劣质化问题日益凸显,并且对环境保护的要求也日趋严格,寻找可再生的替代能源并提高对重劣质原油的加工能力,已成为当务之急。氢气作为一种高效清洁的能源,不仅可以直接使用,而且是作为炼厂重质、劣质原料加工重要手段的加氢过程的基础原料。因此,如何稳定高效的制取氢气便成为亟待解决的问题。本论文基于一种两步法甲烷裂解制氢过程,采用镍作为活性金属,考察常规载体氧化铝担载的氧化镍催化剂的反应活性,对引入镁和镧元素对催化剂活性的影响进行了探究,并对催化剂的反应-再生循环性能进行了考察。同时,采用水热合成的方法制备了一种以分子筛为载体的镍基催化剂,对其催化甲烷裂解性能进行了评价,并与采用浸渍法制备的分子筛催化剂进行了反应活性对比。采用溶胶凝胶法制备了不同负载量的NiO/Al2O3催化剂,氧化镍负载量的不同会导致镍物种在催化剂上的存在状态不同,随着氧化镍负载量的增加,甲烷转化率逐渐增加,而氢气选择性逐渐降低,当氧化镍负载量为40wt%时可以获得较好的甲烷转化率和氢气选择性。镁和稀土元素铈、镧、锆的引入可以提高催化剂的甲烷转化率,镁的加入与Al2O3载体形成MgAl2O4,从而抑制NiAl2O4的形成,减弱活性组分与载体之间的相互作用,使得催化剂中镍物种更易被还原。但是过量氧化镁会与镍形成NiMgO2结构,使得氧化镍的还原变难。适量镧的引入不仅可以减弱催化剂与载体的相互作用,同时有利于提高活性组分镍在催化剂表面的分散程度。实验发现氧化镁、氧化镧添加量分别为5wt%、3wt%时可以获得最高的甲烷转化率。采用水热合成的方法制备了一种镍基ZSM-5分子筛催化剂。氧化镍加入量不大于10wt%时可以形成较好的ZSM-5分子筛晶相,通过紫外可见近红外光谱仪表征发现,部分镍物种以骨架镍原子的形式存在于分子筛的骨架当中。与浸渍法制备的催化剂相比,镍物种在催化剂表面可以得到更好的分散。水热合成分子筛催化剂的甲烷转化率高于采用浸渍法制备具有相同氧化镍负载量的催化剂。对制备的40wt%NiO-5wt%MgO-3wt%La2O3/Al2O3催化剂进行了反再循环实验。再生时间延长使催化剂的甲烷转化率升高,而氢气选择性降低。催化剂经历部分再生后,表面仍将残留一部分积碳,这部分积碳具有还原性,将消耗表面晶格氧,从而提高氢气选择性,但甲烷转化率逐渐降低。提高再生温度有利于积碳的燃烧,使得催化剂的甲烷转化率升高,但是氢气选择性降低。
[Abstract]:With the worsening of the world energy crisis, the problem of heavy and inferior crude oil is becoming more and more serious, and the requirement of environmental protection is becoming more and more strict, so as to find renewable alternative energy and improve the processing capacity of heavy and poor crude oil. It has become a top priority. As a kind of efficient and clean energy, hydrogen is not only used directly, but also as the basic raw material of hydrogenation process, which is an important means of processing heavy and inferior raw materials in refineries. Therefore, how to produce hydrogen stably and efficiently becomes an urgent problem. In this paper, based on a two-step process of methane pyrolysis to produce hydrogen, nickel was used as active metal to investigate the reaction activity of nickel oxide catalyst supported on conventional support alumina, and the effect of introducing magnesium and lanthanum elements on catalyst activity was investigated. The reaction-regeneration cycle performance of the catalyst was also investigated. At the same time, a nickel based catalyst supported on molecular sieve was prepared by hydrothermal synthesis. The catalytic activity of the catalyst was evaluated and compared with that prepared by impregnation method. NiO/Al2O3 catalysts with different loading amounts were prepared by sol-gel method. The different supported amounts of nickel oxide lead to the different states of nickel species on the catalyst. With the increase of the amount of nickel oxide loading, methane conversion increases gradually. The hydrogen selectivity decreases gradually and the methane conversion and hydrogen selectivity can be obtained when the amount of nickel oxide is 40 wt%. The addition of magnesium and rare earth elements cerium, lanthanum and zirconium can increase the methane conversion of the catalyst, and the addition of magnesium can form MgAl _ 2O _ 4 with the support of Al2O3, which inhibits the formation of NiAl2O4 and weakens the interaction between the active components and the support. The nickel species in the catalyst can be reduced more easily. However, excessive magnesium oxide can form NiMgO2 structure with nickel, which makes the reduction of nickel oxide difficult. The addition of proper amount of lanthanum not only weakens the interaction between the catalyst and the support, but also improves the dispersion of nickel on the surface of the catalyst. It is found that the highest methane conversion can be obtained when the addition amount of magnesium oxide and lanthanum oxide is 5 wtwt% and 3 wt% respectively. A nickel-based ZSM-5 molecular sieve catalyst was prepared by hydrothermal synthesis. A good crystalline phase of ZSM-5 molecular sieve can be formed when the amount of nickel oxide is less than 10 wt%. It is found by UV-Vis near infrared spectrometer that some nickel species exist in the framework of molecular sieve in the form of skeleton nickel atom. Compared with the catalyst prepared by impregnation, nickel species can be dispersed better on the surface of the catalyst. The methane conversion of hydrothermal molecular sieve catalyst is higher than that of catalyst with the same amount of nickel oxide supported by impregnation method. The reverse recirculation experiment of the prepared 40wt%NiO-5wt%MgO-3wt%La2O3/Al2O3 catalyst was carried out. The longer the regeneration time, the higher the methane conversion and the lower the hydrogen selectivity. After partial regeneration of the catalyst, a part of carbon will remain on the surface, which is reductive, which will consume lattice oxygen on the surface and improve the selectivity of hydrogen, but the conversion rate of methane will decrease gradually. The increase of regeneration temperature is beneficial to the combustion of carbon deposition, which increases the methane conversion of the catalyst, but decreases the selectivity of hydrogen.
【学位授予单位】：中国石油大学(华东)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;TQ116.2

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