论文标题:钌基氨合成催化剂的成型及机械强度研究
Study of Forming and Mechanical Strength of Ruthenium Based Catalysts for Ammonia Synthesis
论文作者 胡晓敏
论文导师 刘化章,论文学位 硕士,论文专业 工业催化
论文单位 浙江工业大学,点击次数 88,论文页数 83页File Size4095k
2005-05-01论文网 http://www.lw23.com/lunwen_55929097/ 活性炭;钌催化剂;正交设计;成型;机械强度;可靠性
active carbon; supported ruthenium catalyst; orthogonal design; forming; mechanical strength; reliability
催化剂的机械强度是固体催化剂的一项重要的性能指标。一种成功的工业催化剂,除具有足够的活性、选择性和耐热性外,还必须具有足够的机械强度,以便抵抗在使用过程中的各种应力。催化剂机械强度对于工业装置的正常运转具有十分重要的地位。而催化剂的成型不仅是催化剂制备过程的重要步骤,也是影响催化剂机械强度的主要因素。因此,对一种工业催化剂而言,选择适当的成型方法与工艺条件,并进行机械强度的标准化测定,这是使其具备足够的机械强度,满足工业正常运行的保证。 本论文从钌基氨合成催化剂载体活性炭的成型以及机械强度研究入手,运用磨损强度和堆积压碎强度两种测定方法,对钌基催化剂的机械强度进行了较详细的考察,为实现钌催化剂的工业化提供借鉴。研究中得到以下主要结果: (1) 粉末活性炭不能直接成型。以粒度为100-200目椰壳活性炭粉末为原料,在添加粘结剂(15%羧甲基纤维素)以及40MPa压力的条件下,可以得到一定形状和强度的成型活性炭。但由该活性炭为载体制备的催化剂活性下降。 (2) 讨论了成型压力、成型时间、酸处理、粘结剂以及水粉比等成型条件对成型活性炭强度的影响。无论选择什么添加剂,活性炭的强度都随着成型压力的增大而增大。活性炭的强度随着成型时间的增加有一定的增大。添加粘结剂后,活性炭的强度都有所增加,在选择的几种粘结剂中,羧甲基纤维素的使用效果最好。水分含量对活性炭成型也有影响,水粉比约为0.6时比较适宜。活性炭经硝酸处理,强度降低。 (3) 测定了原粒度活性炭的堆积压碎强度和磨耗强度。不同种类的商业活性炭堆积压碎强度和磨耗强度显著不同。其中,产地为海南和上海的活性炭的堆积压碎强度和磨耗强度较高。 (4) 研究了钌催化剂机械强度与载体活性炭的关系,探讨了催化剂制备过程中,载体活性炭的预处理对钌催化剂机械强度的影响。活性炭预处理包括硝酸处理、氢气处理、高温石墨化处理等。其中,硝酸处理使活性炭的堆积压碎
Mechanical strength is one of the key parameters for industrial application of a solid catalyst. A successful technical catalyst is required not only to have high activity, selectivity and heat-resistance, but also enough high mechanical strength in order to resist some mechanical stresses. Therefore, the whole manipulation of catalyst bed could be well done in the case that the catalyst has enough high mechanical strength. Forming of catalysts is an important step during the process of preparation, and also it has a strong influence on the mechanical strength of catalyst. Therefore, as for a technical catalyst, it is important to select the appropriate forming method and technical condition and to determine the strength scientifically for the industrial equipment in order working.Our group has successfully developed Ruthenium-based catalyst supported on active carbon, which has high catalyst activity at low pressure and low temperature. At present, pilot and commercial scale researches have been carrying on. The determination methods of abrasion and bulk crushing strength (BCS) are applied in this thesis. The forming methods and mechanical-strength researches of activated carbon are firstly started with. Then the forming and the mechanical strength of Ruthenium-based catalyst have been investigated, which gives some references for the commercial practice of Ruthenium-based catalyst. The main results are as the following:1. The formed activated carbon cannot be directly prepared form activated carbon powder. Activated carbon derived from coal is better than activated carbon derived from coconut shell as raw material of preparing formed activated carbon, butit is not appropriate for the carrier of ammonia synthesis catalysts. The formed activated carbons derived from coconut shell are prepared through orthogonal test design under the pressure 40 MPa, which are cylindrical tablets with the diameter of 20 mm and the thickness of 6-8 mm, and have high radial mechanical strength. However, the Ru-based catalyst prepared from formed activated carbon has low activity.2. The influences of forming conditions are investigated. It is found that the mechanical strength of formed activated carbon increased mixing with binder; Carboxyl methyl cellulose (CMC) is the best one of three binders. And formed activated carbon has high strength increasing with the forming pressure, whatever binder is selected. The content of water also has strong influence on the strength, and the appropriate ratio between water and powder is 0.6. The formed activated carbon has low strength, which is prepared from activated carbon modified with nitric acid.3. The bulk crushing strength and abrasion strength of activated carbon are determined. The bulk crushing strength and Abrasion strength are evidently different with the category of activated carbon.4. The influences on mechanical strength of activated carbon after pretreatment are studied. The fine particle percentage and abrasion loss declined markedly under nitric acid treatment. After high temperature treatment, bulk crushing strength was increased. But it was depressed with the increasing of treatment temperature.5. The influences of infusing and drying methods during the preparation process are investigated. The bulk crushing strength and abrasion strength were depressed after infusing. The infrared drying had less influence on the mechanical strength among the three drying methods.6. The bulk crushing strength and abrasion strength of Ruthenium-based catalyst are determined. Under the pressure of 2 MPa, the fine particle percentage of Ru-based catalyst with granularity of 1.0-1.4 mm is 2.5%. Its abrasion strength is 3.5%. The bulk crushing strength and abrasion strength of Ru-based catalyst are increased to some degree with granularity.7. The mechanical reliability of the catalyst is investigated. It is found that the
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