Reduction of synthetic catalysts
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What are the requirements for the CO and CO2 content in the reducing gas for synthetic catalyst reduction? Why can’t the levels of CO and CO2 be too high?
High carbon monoxide content, rapid reduction reactions, and difficult temperature control； When the carbon dioxide concentration reaches a certain level, it can cause the catalyst to oxidize.
If pure hydrogen is available, it is the best choice. My personal opinion is to prevent CO and CO2 from reacting with H2.
Both should be kept as low as possible. Although CO is also a reducing gas, it undergoes the hydrogenation reaction to produce methanol at temperatures above the catalyst’s activation temperature. Firstly, the reaction releases a large amount of heat, making it difficult to control the reduction temperature; secondly, the excessive production of methanol affects the accuracy of measuring the amount of water produced during reduction, thereby making it hard to determine the degree of reduction. Excessively high CO2 levels cause the catalyst to undergo repeated oxidation and reduction, leading to the growth of copper crystals in the reduced state, a reduction in the active surface area, and a decrease in the catalyst’s activity.
To reduce the occurrence of side reactions and improve the activation rate.
Because at relatively low catalyst temperatures, carbon dioxide can react with zinc oxide in the catalyst to form zinc carbonate, which may weaken the catalyst, the concentration of CO2 should be kept low
During reduction, the temperature in the synthesis tower needs to be raised to 230° (not higher than this value); this temperature falls within the active range of the synthesis catalyst. If its content is too high, it will affect the effluent flow rate, and it will also raise the temperature inside the tower, thereby affecting the catalyst’s lifespan. Ensure that the CO and CO2 concentrations at the outlet of the synthesis tower are controlled at 10%.
Reduction of quality indicators: O2 content < 1000 mg/kg; total sulfides < 0.1 mg/m3 (standard conditions); CO2 content < 2.0%； NH3 content < 200 mg/kg; free of oil mist, unsaturated hydrocarbons, chlorides, and heavy metals.
A high carbon monoxide content results in large heat release during the reaction, making it difficult to control the temperature； A high carbon dioxide content results in large size of the reducing agent particles and few active intergranular areas, which affects catalytic activity ； At the same time, the carbon dioxide produced by the high-reactivity reduction of carbon monoxide is also high.