Study Of Forming And Mechanical Strength Of Ruthenium Based Catalysts For Ammonia Synthesis

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...