Atmosphere stability of CoMo series catalysts
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To maintain stable activity, sulfided CoMo/Al2O3 hydrogenation catalysts generally require a certain concentration of H2S in the atmosphere. May I ask: (1) In an H2 reduction atmosphere with H2S as the shielding gas, is its protective effect affected by the H2S concentration and reaction temperature? Can reducing the H2S concentration or increasing the reaction temperature still ensure that the catalyst Mo4+ is not reduced to lower oxidation states? (2) If the above problems exist, what is the lower limit for H2S concentration control? What is the maximum temperature the reaction can reach? Thank you! Thank you!
This post was last edited by libingtaoff8 on 2017-2-11 08:56. In a hydrogen reduction atmosphere, the presence of hydrogen sulfide prevents excessive reduction of the catalyst; when the temperature is above 230°C, the concentration of hydrogen sulfide in the recycled hydrogen is generally kept between 500–700 ppm. A temperature below 230°C is not sufficient to achieve the required reduction temperature! There is no requirement for hydrogen sulfide concentration; as for temperature, it just needs to not exceed the design temperature of the catalyst or reactor! Prevent the catalyst from sintering at high temperatures!
1. In an H2 reduction atmosphere, with H2S as the protective gas, its protective effect is influenced by the H2S concentration but not by the reaction temperature. Generally, in hydrogenation units, the hydrogen sulfide concentration in the circulating hydrogen is controlled. Sampling points are usually located in the high-pressure tank or the buffer tank at the inlet of the circulating hydrogen, and the concentration should be maintained between 100 and 300 ppm – it should neither be too high nor too low. A too-high concentration inhibits the desulfurization reaction, while a too-low concentration fails to maintain the sulfided state of the catalyst. The reaction temperature does not affect the hydrogen sulfide concentration, but an excessively high reaction temperature is detrimental to the long-term operation of the catalyst as well as to the equipment; therefore, high reaction temperatures are not recommended. 2. The H2S concentration in the recycled hydrogen should not be lower than 50 ppm ； The temperature at the highest point of the reaction bed should not exceed 400 degrees.
What is the principle behind H2S’s protective effect? ①The presence of H2S inhibits the forward reduction reaction of MoS2. ②Is the sulfidation reaction rate of MoS2-x faster than that of the reduction reaction of MoS2? ① or ②? Thank you for your patient answers! \(≧▽≦)/