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合成气加压流化床等温甲烷化催化剂研究
Alternative TitleStudy on Catalyst for Syngas Methanation in Pressurized Fluidized bed Reactor
刘姣
Subtype博士
Thesis Advisor许光文
2013-05-01
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword甲烷化   替代天然气   流化床   固定床   耐磨
Abstract以煤为原料通过气化、甲烷化反应生产合成天然气,不但符合煤炭清洁高效利用的发展方向,同时通过管道输送并经调压配气后进行工业和民用可以有效利用新疆、内蒙古等边远地区丰富的煤炭资源。目前甲烷化技术的开发与应用以多段绝热固定床反应器及其催化剂为主,但该工艺在操作灵活性与传热性能方面不利于强放热的快速甲烷化过程。本论文以利用具有较好传热传质性能的流化床反应器为前提,对合成气制甲烷流化床催化剂进行研究,旨在探索一种适用于流化床甲烷化生产合成天然气的高活性、耐高温、高耐磨的催化剂的制备方法。为了提高整个工艺的能效,要求流化床甲烷化反应温度不低于823 K以获得高价值蒸汽,所以耐高温、耐磨催化剂是实现流化床甲烷化过程的关键。本论文研究分四部分进行:耐高温甲烷化催化剂的研制,耐磨流化床甲烷化催化剂的成型,流化床甲烷化工艺条件的优化以及中试技术方案的工艺设计。1. 耐高温高活性甲烷化催化剂的制备。采用20Ni-10Mg/Al2O3体系,研究制备方法对催化剂结构及合成气甲烷化反应活性的影响,以筛选出同时具有低温、高温甲烷化活性和稳定性的催化剂的制备方法。实验结果表明:(1) 分别以碳酸钠(CP-1)、氨水(CP-2)、氢氧化钠(CP-3)为沉淀剂通过共沉淀法制备的催化剂,在不同反应温度下的催化剂活性均是CP-3 > CP-1 > CP-2,尤其是CP-2样品,其CH4选择性一直在60%以下,因为CP-2催化剂中Ni晶粒分散在无定形的Al2O3载体上,载体比表面积较小,在还原过程中容易发生团聚使得Ni晶粒变大,加速催化剂表面碳的沉积,常压下积碳速率高达5.27 wt.%?h-1。(2) 采用双水解和尿素基水热均匀沉淀法制备的催化剂(分别记为ABP和HP)通过与CP-3催化剂的活性比较发现,当反应温度低于780 K时,三个催化剂上的CO转化率有明显的差别,其中HP > ABP > CP-3,但当温度继续升高时,三者之间选择性的差距变得不明显,而且不论是在常压还是高压下连续反应,三个催化剂均具有较好的稳定性和抗积碳能力。(3) 通过H2-TPR表征发现活性组分与载体之间的相互作用对催化剂活性有较大的影响。这种相互作用有利于催化剂中金属Ni的分散,抑制高温下Ni晶粒的团聚和烧结,进而影响催化剂的稳定性。2. 流化床甲烷化催化剂的成型。通过向催化剂前驱体中引入一定量的粘结剂并采用喷雾干燥法成型可以制备出具有一定粒度分布的球形催化剂颗粒。粘结剂的添加会降低加压流化床甲烷化反应过程中的CO转化率和CH4选择性,但可明显提高催化剂的耐磨性,向催化剂中加入5 wt.%硅溶胶,CO转化率从97%降低到93%,CH4选择性从87%降至86%,而同时磨损率也从6.74% h-1降低至1.55% h-1。粘结剂的种类对催化剂活性影响的程度不同,添加量同样是8 wt.%,铝溶胶对催化剂催化性能的影响明显弱于硅溶胶,这与过量的硅溶胶削弱催化剂中活性组分与载体之间的相互作用有关。焙烧温度对催化剂耐磨性影响不大,但823 K焙烧催化剂的稳定性较差,反应10 h就发生明显的失活,这主要是由Cγ沉积在催化剂表面引起的。所以含5 wt.%硅溶胶的Ni-Mg/Al2O3催化剂经873 K焙烧后耐磨性好,在加压流化床甲烷合成反应中表现出较高的催化活性和稳定性。3. 催化剂同时应用于流化床与固定床的甲烷化性能比较以及流化床甲烷化工艺条件的优化。结果表明:无论是在自制Ni-Mg/Al2O3还是商业N112催化剂的催化作用下,流化床反应器中甲烷化活性均高于固定床,尤其是CO转化率,同时TPO表征发现固定床反应后Ni-Mg/Al2O3催化剂表面的主要积碳类型是最不具活性的Cγ物种,而流化床中主要是Cβ,且积碳量不到固定床的一半。通过在不同反应温度、空速、表观气速、压力等条件下分别比较固定床和流化床甲烷化反应性能,进一步证实了流化床甲烷化技术的优越性,产生这种结果的原因主要是流化床反应器中床层空隙率大,能够参与反应的催化剂活性表面比颗粒堆积的固定床多,反应气体与催化剂表面有效接触面积增加,同时固定床反应器中存在的温度梯度和热点温度不利于强放热的甲烷化反应发生。进一步考察温度、H2/CO比、CO2、水蒸汽等因素对流化床甲烷化反应活性和催化剂稳定性的影响,从长时间的稳定性和热力学方面考虑,甲烷化需要在823 K以下进行反应;H2/CO比增大,CO转化率和CH4选择性均增加,解离后的CO加氢是甲烷化反应的速率控制步骤。自制Ni-Mg/Al2O3催化剂表现出了良好的抗水稳定性。4. 5000 m3?h-1甲烷中试技术方案的工艺设计。基于上述实验数据,本论文还开展了流化床-固定床两段甲烷化工艺的中试技术方案设计。首先借助Aspen Plus模拟优化了流化床-固定床两段甲烷合成工艺,流化床进口温度533 K,CO转化率达95%时,固定床进口温度在473-503 K之间,均可保证固定床出口温度低于623 K,产生的合成天然气满足天然气国家标准中一类天然气的要求。然后分别采用Levenspiel鼓泡床模型和一维拟均相模型对流化床与固定床反应器的主要结构参数进行了初步计算,完成了5000 m3?h-1甲烷中试技术方案的工艺设计。关键词:甲烷化,合成气,替代天然气,流化床,催化剂,固定床,耐磨
Other AbstractComplete methanation of syngas from coal for the production of substitute natural gas (SNG) is considered to be an efficient way for the use of coal resource in remote areas because the produced SNG can be transported with the existing nature gas pipelines. The conversion of coal to SNG provides as well a guarantee for the secure supply of natural gas fuel in China, while its relatively simple process, high energy conversion efficiency and low water consumption make it further attractive in comparison with many other coal conversion technologies like coal-to-liquid and coal to DME. The adiabatic fixed bed methanation process is well developed and paid much attention. However, the process itself is complicated, difficult to control and low tolerance to process variation in, for example, the load (feed) and composition of syngas. By comparison, the fluidized bed reactor is inherently isothermal and suitable for the highly exothermic reactions. Therefore, this study is based on fluidized bed syngas methanation and devoted to developing the highly active, attrition-resistant and thermostable catalyst for fluidized bed methanation. To raise the efficiency of the exothermic heat utilization, it is suggested that methanation in fluidized bed reactor should not be below 823 K. This study covers the following four major research contents.1. Preparation of the highly active and thermostable methanation catalyst. The catalysts were based on 20Ni-10Mg/Al2O3 and prepared with different methods including co-precipitation, homogeneous precipitation and acid-base pairing. The catalyst evaluation was by syngas methanation at 623-923 K in a fixed bed reactor. (1) The activity of the Ni-Mg/Al2O3 prepared by co-precipitation using respectively NH4OH (CP-1), Na2CO3 (CP-2) and NaOH (CP-3) as the precipitants followed an order of CP-3 > CP-1 > CP-2 at all tested reaction temperatures. For CP-2, the selectivity to CH4 was always lower than 60%. Its Ni-crystallites existed possibly on the amorphous-like support so that this catalyst had lower surface area, and the agglomeration and sintering of Ni particles were easier which would accelerate the carbon deposition on the the surface of this catalyst. The average carbon deposition rate was 5.27 wt.%?h-1 for the spent CP-2. (2) The methanation performances of the catalysts made by the homogeneous precipitation (HP) and acid-base pairing (ABP) methods were comparable to that of CP-3 co-precipitated with NaOH at temperatures higher than 780 K. At temperatures lower than 780 K, the CO conversion followed the order of HP > ABP > CP-3.
Pages138
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8287
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
刘姣. 合成气加压流化床等温甲烷化催化剂研究[D]. 中国科学院研究生院,2013.
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