碱金属蒸气对整体式镍基催化剂重整性能的影响

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	碱金属蒸气对整体式镍基催化剂重整性能的影响
其他题名	The Effects of alkali vapor over Ni-based monolithic catalyst for biomass fuel gas reforming
	高妍
导师	王铁军
	2008-06-04
学位授予单位	中国科学院广州能源研究所
学位授予地点	广州能源研究所
学位名称	硕士
关键词	生物质合成气催化重整整体式催化剂碱金属蒸气
摘要	生物质气化产生的合成气作为一种清洁可再生燃料被广泛应用于各种领域，例如液体燃料的合成以及燃料电池的应用等。但由于气化得到的粗燃气存在H2含量低，H2/CO值过低等问题，合成气不能直接达到后续合成甲醇、二甲醚等液体燃料所需合成气的要求。另外气化过程难免伴随焦油以及其他无机污染物的产生，这些污染物不仅对气化过程造成不良影响，气化粗燃气的应用也受到限制。气化粗燃气中焦油的存在不仅堵塞管道，使气化设备难以运行，还会引起催化剂严重失活。同样地，无机物的存在也影响到了气化炉的操作以及下游设备的运行。生物质本身固有的碱金属会在生物质的热转化过程中形成化合物，如KCl, K2SO4, NaCl等，与气化炉中的床料反应生成低熔点的共晶化合物引起颗粒团聚，降低床内流化质量，一部分则以蒸汽的形式挥发析出，掺杂在气化产生的粗燃气中，造成下游设备腐蚀，甚至催化剂的失活。因此，生物质气化粗燃气的深度净化处理成为研究者关注的热点。目前，应用于燃气净化的商业镍基催化剂存在积碳严重、活性组分易烧结、流失等问题。而蜂窝状整体式催化剂由于床层压降小，轴温度梯度小，适合强吸/放热反应，在一定程度上催化剂大量积碳等问题。本文采用分步浸渍法制备以堇青石为载体的Ni-MgO/γ-Al2O3整体式催化剂，以模拟生物质气的重整为评价反应，对催化剂的活性和稳定性进行研究，并筛选出合适Ni/Mg的催化剂以研究碱金属对重整催化剂的影响。得到的结论如下： 1．自制的整体式催化剂具有较高的活性和较好的稳定性，在750℃时，反应60 h后，催化剂上出口气各成分随时间变化不明显，镍的表面分散度保持较高水平，其抗积碳性能良好，氧烧碳实验表明催化剂具有良好的抗积碳性能。 2．用分步浸渍法制备的不同的Ni/Mg 比的整体式催化剂，当Ni/Mg =1时，催化剂上的CH4转化率最高达到95%以上，H2/CO保持在1.2左右。 3．采用碱金属盐在反应器中直接蒸发，并沉积在催化剂表面的方法模拟工业应用中混杂在燃气中的飞灰对催化剂性能的影响。实验中碱金属在燃气中的含量达到6.5-7.8mg/L，条件较工业实践中苛刻。 4．通过对不同钾盐沉积效果的研究发现，碱金属的沉积引起催化剂的活性和稳定性的降低。而碱金属盐熔点的高低与催化剂失活的程度没有必然联系。经过沉积后的催化剂表面由于碱金属的覆盖，活性中心数目减小，催化剂比表面积降低，催化剂的活性随之受到影响，但Ni的平均粒径基本没有变化。由XPS和SEM表征结果推测，钾在催化剂表面上可能的存在形式为K σ+ (Naσ+)，其中0≤σ≦0.5
其他摘要	As one of the most promising renewable energy, biomass fuel gas from gasification has been applied in various areas, such as liquid fuel synthesis and solid oxide fuel cell. However, the fuel gas could not be utilized directly in synthesis of liquid fuel because of its low content of H2 and low ratio of H2/CO. In addition, biomass gasification is inevitably accompanied by the formation of tar and inorganic impurities, which possesses negative influence on gasification process and utilization of product gas as well. It has been well-known that tar causes such serious problems as tube blocking and deactivation of catalyst. Similarly, some alkali elements, which are generally used as the nutrient for plants and abundant in the biomass feedstock e.g. potassium, are apt to vaporize and form alkali compounds, such as KCl, K2SO4, NaCl, leading to the elemental deposition inside the equipments and corruption of devices downstream by aerosol, even the catalyst deactivation ultimately. Until recently, studies have been focused on cleanup of biomass raw fuel gas. Previously, commercial Ni-based catalyst faced challenges like carbon deposition, agglomeration and loss of active phases. Whereas, honeycomb monolithic catalysts, characterized as low pressure drop and low axial temperature gradient, mitigate these problems. In this paper, NiMgO/-Al2O3 monolithic catalyst was prepared by two-step impregnation. Its performance in biomass fuel gas reforming was investigated. By screening out the optimal ratio of Ni/Mg from different catalysts, the effects of alkali vapor on NiMgO/-Al2O3 monolithic catalyst was studied in the reaction of dry reforming of biomass fuel gas. The experimental results are listed below: 1 The self-made monolithic catalyst showed high activity and stability. After 60 h reaction at 750℃, the outlet gas composition almost maintained the same. From the results of catalyst characterization, high dispersion of Ni prevent agglomeration and no obvious carbon deposition was observed. 2 By comparing different catalysts in biomass fuel gas reforming, the catalyst( Ni/Mg=1) showed high CH4 conversion and optimal H2/CO. 3 The effects of fly ash on the catalyst performance in practical biomass fuel gas reforming was modeled, the concentration of alkali in fuel gas was much higher than that under practical condition. 4 Catalyst activity decreased with the coverage of alkali on the surface of catalyst. It showed no necessary connection between the catalyst deactivation and melting point. Additionally, deposition of alkali had influence on the BET area and pore structure. No sintering of Ni was observed by XRD characterization.
页数	67
语种	中文
文献类型	学位论文
条目标识符	http://ir.giec.ac.cn/handle/344007/5798
专题	中国科学院广州能源研究所
推荐引用方式 GB/T 7714	高妍. 碱金属蒸气对整体式镍基催化剂重整性能的影响[D]. 广州能源研究所. 中国科学院广州能源研究所,2008.

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