Ni-Mo基双金属耐硫甲烷化催化剂研究

发布时间：2018-04-07 16:58

本文选题：甲烷化　切入点：耐硫　出处：《中国矿业大学》2016年硕士论文

【摘要】：中国能源结构的特点是“富煤、贫油、少气”,因此煤制天然气不仅可以实现煤炭资源的清洁高效利用,还能够满足我国对天然气日益增长的需求。煤制天然气一般要经过气化/热解、合成气变换、脱硫脱碳、甲烷化、深加工等工艺过程。Ni基催化剂由于其较高的催化活性和较低的价格而广泛应用于合成气甲烷化过程,但其对原料气中的H2S十分敏感,容易发生硫化而失活,所以在脱硫单元合成气一般要经过精脱硫而使H2S含量低于0.1-0.02 ppm。为了缩短工艺流程,降低运行成本,本论文通过在Ni基催化剂中添加Mo,来提高其耐硫性能。首先,采用沉淀-浸渍法合成了15Ni/Al2O3和15Ni-5Mo/Al2O3催化剂,在常压,反应温度550 oC,原料气n(H2):n(CO):n(N2)=3:1:1,催化剂0.5g,原料气速120 L/(g·h)的条件下,分别对两个催化剂催化活性和稳定性进行了评价。结果表明,Mo的引入使得催化剂的初始活性下降,但由于Ni-Mo复合相态的生成,催化剂15Ni-5Mo/Al2O3的耐硫稳定性明显优于15Ni/Al2O3;通过对反应前后催化剂表征发现,Mo的引入能够增强催化剂耐硫稳定性的主要原因是其能够增强活性组分Ni的分散程度,并形成一定比例的复合型Ni-Mo。考虑到以γ-Al2O3为载体的Ni-Mo双金属催化剂耐硫性能并不十分理想且活性较低,本论文对比了6种载体所合成的15Ni-5Mo双金属催化剂,发现催化剂的耐硫稳定性:Ni-Mo/MCM-41Ni-Mo/KaolinNi-Mo/USYNi-Mo/Al2O3Ni-Mo/NaYNi-Mo/PB(拟薄水铝石Pseudo Bohemite,简称PB),且以MCM-41为载体的催化剂性能最接近商用催化剂(28Ni-5Mo/Al2O3);对比各催化剂的表征结果可以看出以MCM-41为载体的催化剂活性组分Ni分散较均匀且Ni颗粒较小,可以推断出Ni和Mo的相互作用较为充分,因此其耐硫性能和催化稳定性较优,故选择MCM-41为催化剂载体并进行下一步研究。以MCM-41为载体合成一系列不同Ni/Mo比的催化剂,通过对比各催化剂的活性评价结果,发现随着Mo含量的提升,催化剂的耐硫性能和催化稳定性能有显著提升,5%Mo的催化剂在反应过程中,随着与H2S接触时间的增加,CO转化率逐渐下降,而10%Mo的转化率则较为稳定,6.5%Mo的稳定性介于两者之间;通过对比不同催化剂的各项表征结果,Mo的含量越高,Ni分散情况越好,且Ni-Mo复合相态形成的比例越高,这就提高了催化剂的耐硫稳定性;此外,随着Mo含量的提升,Ni的晶粒尺寸也在逐渐降低,表明Mo的引入也有利于提高催化剂的稳定性。最终确定20Ni-10Mo/MCM-41为以分子筛MCM-41为载体的Ni-Mo双金属催化剂的最优配比。
[Abstract]:China's energy structure is characterized by "rich coal, lean oil, less gas", so coal produced natural gas can not only achieve clean and efficient use of coal resources, but also meet the increasing demand for natural gas in China.Generally, the gasification / pyrolysis, syngas conversion, desulphurization and decarbonization, methanation and deep processing of Ni-based catalysts are widely used in the methanation process of syngas due to their high catalytic activity and low price.However, it is very sensitive to H _ 2S in raw gas and is prone to sulfidation and inactivation, so the content of H _ 2S is lower than 0.1-0.02 ppm after refined desulfurization in desulphurization unit.In order to shorten the technological process and reduce the running cost, Mo-based catalysts were added to improve their sulfur tolerance.Firstly, 15Ni/Al2O3 and 15Ni-5Mo/Al2O3 catalysts were synthesized by precipitation-impregnation method. The catalytic activity and stability of the two catalysts were evaluated under the conditions of atmospheric pressure, reaction temperature of 550oC, feedstock gas NH _ 2H _ 2H _ 2O _ 2: n ~ (2): n ~ (2): n ~ (2): 1: 1 / 1, catalyst 0.5 g, feed gas velocity of 120 L / g 路h).The results show that the initial activity of the catalyst decreases due to the introduction of Mo, but due to the formation of Ni-Mo complex phase,The sulfur tolerance stability of the catalyst 15Ni-5Mo/Al2O3 was obviously better than that of 15Ni- / Al _ 2O _ 3, and the main reason that the introduction of Mo could enhance the sulfur tolerance stability of the catalyst was that it could enhance the dispersion of Ni, the active component, before and after the reaction.And a certain proportion of Ni-Mo-composite was formed.Considering that the sulfur tolerance of Ni-Mo bimetallic catalysts supported on 纬 -Al2O3 is not ideal and the activity is low, the 15Ni-5Mo bimetallic catalysts synthesized by six kinds of supports are compared in this paper.The distribution of Ni is more uniform and the Ni particles are smaller.It can be inferred that the interaction between Ni and Mo is more sufficient, so the sulfur tolerance and catalytic stability of Ni and Mo are better. Therefore, MCM-41 is chosen as the catalyst carrier and further research is carried out.A series of catalysts with different Ni/Mo ratios were synthesized with MCM-41 as the support. By comparing the results of the activity evaluation of each catalyst, it was found that with the increase of Mo content,The sulfur tolerance and catalytic stability of the catalyst significantly improved. During the reaction, the CO conversion decreased with the increase of H _ 2S contact time, while the stability of 10%Mo was between 6.5Mo and 6.5Mo.By comparing the characterization results of different catalysts, the higher the content of Mo is, the better the dispersion of Ni is, and the higher the proportion of Ni-Mo complex phase is, the higher the sulfur tolerance stability of the catalyst is.With the increase of Mo content, the grain size of Ni decreases gradually, which indicates that the addition of Mo can also improve the stability of the catalyst.Finally, the optimum ratio of 20Ni-10Mo/MCM-41 as Ni-Mo bimetallic catalyst supported on molecular sieve MCM-41 was determined.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36

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