铁基费托合成催化剂的化学磨损研究

费托(Fischer-Tropsch，F-T)合成技术可以将CO和H2转化为长链烃分子，是煤炭、天然气以及生物质转化制取清洁液体燃料的重要途径。相对于钴基催化剂，铁基费托合成催化剂由于其价格低廉、活性高、目标产物选择性高等优点而被大规模工业化应用。浆态床反应器由于其反应热易扩散、床层压降小和催化剂易装卸等优点，被广泛应用于工业生产。但是，浆态床反应器对催化剂耐磨损强度有很高要求，一方面浆态床反应器中催化剂磨损会导致催化剂的流失，是催化剂失活的重要原因之一；另一方面，催化剂的磨损会导致过滤器堵塞，影响催化剂与蜡产物的在线分离。因此，抗磨损铁基费托合成催化剂的研究与开发就成了一个重要的课题。随着反应的进行，催化剂的物相和性质发生了一系列变化，催化剂的强度也随之改变，我们称之为化学磨损。催化剂的抗化学磨损强度很大程度决定了反应过程中催化剂的磨损程度。本论文研究了不同预处理条件对催化剂强度的影响。并采用多种表征手段揭示预处理条件对催化剂物相结构和织构性质等的影响规律。在此基础上，找出影响催化剂化学磨损的内在原因，为工业催化剂组成和预处理优化、反应工艺优化提供基础支持。论文主要工作及相关结论如下：在高强度铁基费托合成催化剂的研究中，在低温低空速下，随着预处理时间的增加，催化剂碳化和积碳程度增加，催化剂宏观尺寸收缩，强度增加；提高预处理温度，催化剂碳化和积碳程度增加，宏观尺寸收缩程度增加，强度增加。在低强度铁基费托合成催化剂的研究中，同时提高了空速和预处理时间，催化剂碳化程度在增加到一定水平后将保持稳定，其积碳程度一直在增加，催化剂宏观尺寸先收缩后膨胀，催化剂强度先增加后降低。综合上述，催化剂在预处理初期，碳化过程占主导，催化剂体积收缩，粒度降低，强度增加；在预处理后期，积碳过程占主导，催化剂体积膨胀，粒度增加，强度降低。;Fisher-Tropsch synthesis, by which CO and H2 can be transformed into long chain hydrocarbon and value-added chemicals, was considered as an important way for coal, natural gas and biomass utilization. Iron-based Fischer-Tropsch catalysts have been found widely industry application due to their lower cost, higher activity, moderate operating temperature and flexible products spectrum compared to cobalt catalysts. The slurry-bed reactor has long been used in industry owing to its efficient reaction heat removal, low pressure drop and convenient online catalyst replacement. However, the catalysts used in the Slurry-bed Reactor should be highly attrition resistive since the attrition of catalyst would lead to the loss of catalyst, reduce the catalyst activity and stability, and enhance the selectivity of low carbon hydrocarbon. Besides, the attrition of catalyst would lead to the blockage of filter, which would make the online separation of catalyst and wax more difficult. Therefore, research and development of high attrition resistance iron-based catalysts are vital for efficient Fischer-Tropsch synthesis process.The attrition behavior of iron-based catalysts during reaction was mainly determined by the chemical attrition which was generally referred to the strength variation caused by structural evolution. The effect of different pretreatment protocols on the attrition resistance of the catalyst was extensively studied in present thesis. Specifically, the effect of the pretreatment conditions on the phase structure and texture properties of the catalysts was examined by a combination of characterization methods. Then, the intrinsic cause of chemical attrition of catalysts was proposed, which would help the development of new generation iron-based catalysts with higher attrition resistance and also optimized catalytic performance.The main work of this thesis and related conclusions were summarized below.In the case of fresh model samples with high attrition resistance, the carburization rate and carbon deposition rate increased with the increase of carburization time when low temperature and low space velocity were employed, while the macro size of catalysts decreased. One can find the attrition resistance of catalysts increased. Similarly, the increase of carburization temperature led to the increased carbide content and carbon deposition content, meanwhile, the macro size of catalysts decreased and attrition resistance increased.In the case of fresh model samples with low attrition resistance, the increase of space velocity and reaction time made the carbide content increased to a certain level and then kept constant, while the degree of carbon deposition and catalyst particle size kept increasing. One can also find the attrition resistance of catalyst increased first and then decreased.Based on the results obtained in present study, the picture of attrition resistance variation caused by pretreatment could be tentatively drawn. In the initial stage of pretreatment，the carburization process of catalysts lead to the volume shrinkage, catalyst particle size decreasing and finally the attrition resistance increasing. While in the late stage of pretreatment, where carbon deposition process dominated, the catalyst volume expansion, particle size increasing could be observed, which caused the attrition resistance decreasing.&nbsp;</p

费托合成搅拌釜气含率的冷模实验与cfd模拟

为解决费托合成实验室气-液搅拌釜相分散的问题,冷模实验以轻柴油-空气为工作介质模拟费托合成工况。采用化学刻蚀法制备的光纤探针,考察不同表观气速、搅拌转速及气体分布器结构的搅拌釜内气含率分布。同时,采用双流体模型和标准k-ε湍流模型,对搅拌釜流场进行数值模拟。结果表明:局部气含率随表观气速增大而增大、随搅拌转速增大而增大;改进入口气体分布器对气体均匀分布的作用明显;改变釜体结构可以有效地改善釜底物相分散

费托合成搅拌釜气含率的冷模实验与CFD模拟

为解决费托合成实验室气-液搅拌釜相分散的问题,冷模实验以轻柴油-空气为工作介质模拟费托合成工况。采用化学刻蚀法制备的光纤探针,考察不同表观气速、搅拌转速及气体分布器结构的搅拌釜内气含率分布。同时,采用双流体模型和标准k-ε湍流模型,对搅拌釜流场进行数值模拟。结果表明:局部气含率随表观气速增大而增大、随搅拌转速增大而增大;改进入口气体分布器对气体均匀分布的作用明显;改变釜体结构可以有效地改善釜底物相分散

费托合成搅拌釜气含率的冷模实验与cfd模拟

为解决费托合成实验室气-液搅拌釜相分散的问题,冷模实验以轻柴油-空气为工作介质模拟费托合成工况。采用化学刻蚀法制备的光纤探针,考察不同表观气速、搅拌转速及气体分布器结构的搅拌釜内气含率分布。同时,采用双流体模型和标准k-ε湍流模型,对搅拌釜流场进行数值模拟。结果表明:局部气含率随表观气速增大而增大、随搅拌转速增大而增大;改进入口气体分布器对气体均匀分布的作用明显;改变釜体结构可以有效地改善釜底物相分散

炭化过程对铁基费托合成催化剂强度和结构的影响

以模型费托合成Fe基催化剂为研究对象,在纯CO气氛中对催化剂进行不同时间的预处理,采用多种手段对预处理后催化剂的物理化学性质和抗磨损能力进行了表征。结果表明,在预处理初期,随着预处理时间的延长,催化剂的炭化程度显著提高,伴随着催化剂比表面积的降低和颗粒粒径的减小,而催化剂的抗磨损能力逐渐提高。当预处理时间超过72 h后,继续延长预处理时间,催化剂的炭化程度不再增加,而积炭程度逐渐增加,伴随着催化剂比表面积和颗粒粒径的增加,催化剂的质量也同时增加,并导致催化剂的抗磨损能力逐渐降低

炭化过程对铁基费托合成催化剂强度和结构的影响

以模型费托合成Fe基催化剂为研究对象,在纯CO气氛中对催化剂进行不同时间的预处理,采用多种手段对预处理后催化剂的物理化学性质和抗磨损能力进行了表征。结果表明,在预处理初期,随着预处理时间的延长,催化剂的炭化程度显著提高,伴随着催化剂比表面积的降低和颗粒粒径的减小,而催化剂的抗磨损能力逐渐提高。当预处理时间超过72 h后,继续延长预处理时间,催化剂的炭化程度不再增加,而积炭程度逐渐增加,伴随着催化剂比表面积和颗粒粒径的增加,催化剂的质量也同时增加,并导致催化剂的抗磨损能力逐渐降低。</p