Discussion on reduction methods for methanol-to-hydrogen catalysts
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Currently, two main reduction methods are employed for copper-based catalysts used in methanol-to-hydrogen conversion. The first is gas reduction, which uses hydrogen/inert gas reduction; hydrogen (H₂) or nitrogen (N₂) is used as the reducing agent to activate the catalyst at specific temperatures. For example, a copper-based catalyst can be reduced by introducing H₂ or N₂ at 220–240°C for 8 hours, converting the active components (such as CuO) into their metallic state. The second method is in-situ reduction using low-concentration methanol-water, in which methanol is passed through a catalyst bed and reduced for 16 hours at 220–250°C with a liquid space velocity of <1. This method uses active hydrogen generated from methanol pyrolysis to reduce the catalyst, without the need for additional reducing gases. Which of these two methods is better? Is there a better way? Feel free to discuss: lol
Currently, the gas reduction method is widely used in industry because it features a mature process, simple control, stable reduction effects, as well as good catalyst activity and lifespan. However, the gas reduction method requires additional hydrogen or inert gas, increasing costs and safety risks. The advantage of the in-situ reduction method using methanol and water is that it requires no additional gas source, is simple to operate, and has low costs. However, this method requires a longer reduction time, and the reduction process is difficult to control, which may lead to uneven catalyst activity and affect the stability of the catalyst’s performance. Currently, other methods have also been proposed, such as liquid-phase reduction, microwave-assisted reduction, or plasma-assisted reduction. These methods may reduce the reduction time and improve catalyst activity, but they are currently still in the laboratory research stage, and further validation is needed for industrial application. Overall, the gas reduction method remains the dominant approach in industrial applications at present, while the in-situ reduction of methanol in water is suitable for use under specific conditions. In the future, it is possible to consider developing new, more efficient and cost-effective reduction techniques, such as microwave or plasma-assisted reduction, in order to further improve the performance and cost-effectiveness of catalysts. .
I’ve only used the first method; I’d like to learn about the second one
The liquid-phase reduction method using a methanol-water mixture is still a recommended approach. After the reduction is complete, the methanol ratio can be increased and normal feeding can resume, thereby significantly reducing the overall startup time. Moreover, no large-scale equipment is required, resulting in notable energy-saving effects
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The several methanol cracking units that I was in charge of debugging 10 years ago did not use hydrogen and nitrogen for reduction; I have seen the process involved, which requires an additional Roots blower to create circulation, and it is used only once every few years. The Roots pump I encountered 14 years ago broke down, and with the owner’s approval, we switched to a reduction method using low-concentration methanol water (with a mass fraction of less than 10%), and the result was excellent; it only took a little over half a day – I think it took just one night. Later, that catalyst seems to have been used until after 2021, which is quite astonishing. Because normally it’s about 3 years. Tips for extending catalyst life: First, start with a low concentration of 5%; increase it to around 10% only when the reduction peak is approaching, as this helps to prolong the reduction time. The reduction process is an exothermic reaction, which causes the temperature at the outlet of the converter to rise. I remember that after the restoration was complete, the temperature required to maintain full control at the beginning was only around 210°C. The second aspect is the control of temperature during normal operation; as long as the residual amount of water on the bed material is not high, it is essential to keep the bed temperature as low as possible (by controlling the temperature of the heat transfer oil), with the temperature being increased gradually over time as use proceeds. Because the higher the temperature, the faster the catalyst ages and loses its effectiveness, resulting in a shorter lifespan.
Yes, it’s also under feed control with a low temperature at present