Weekly Topic 4.17, Issue 23: Reduction of Methanol Synthesis Catalysts – Summary

Hydrogenation is generally divided into two types: one uses coke oven gas with a desulfurization level of below 0.1 ppm as the reducing gas, while the other uses pure hydrogen as the reducing gas. Generally speaking, it is better to use pure hydrogen as the reducing gas, as the temperature is easier to control and it is better for the catalyst; whereas reduction with coke oven gas involves a synthesis reaction, so methanol is present in the water produced. Another point is that, if time is a constraint, hydrogen reduction is better, as it allows for precise desulfurization to be carried out simultaneously with the reduction of the synthesis catalyst.

Is it actually possible to use pure hydrogen for reduction? Where does the hydrogen come from?

Reply to 1# wawjia: Precautions: (1) For system reduction, use high-H2 reduction with qualified purified gas having an H2 content of 65%~70%. Under no circumstances should carbonized feed gas be used, as a high level of CO in the feed gas can cause carbon deposition on the surface of the catalyst, thereby affecting its activity. (2) Control of hot spot temperature: It is necessary to maintain a constant temperature as much as possible, but at 1200°C the temperature should not be kept constant for too long, in order to avoid catalyst reduction throughout the tower and prevent damage to the catalyst due to excessively high temperatures. (3) Pressure control: Generally, 4.0~5.0 MPa is selected, requiring relatively stable system pressure. Due to air leakage from the equipment and venting during water release, the system pressure decreases; therefore, it is necessary to continuously replenish pressure. However, care must be taken to ensure that the process of adding air is slow and steady, i.e., through gradual additions, in order to prevent sudden changes in temperature. (4) Selection of water output rate: The reduction stage can be initiated only after the pure physical water has been removed during the heating phase. Since it is difficult to measure water vapor concentration, the water output rate is used as the main control parameter. It is generally kept below 20 kg/h. The total water output can be calculated only after the catalyst model is provided by the manufacturer. (5) Basic principles of reduction: increase temperature without increasing pressure, and increase pressure without increasing temperature; it is better to allow the temperature to drop than to cause the catalyst to burn, and attention should be paid to maintaining a constant temperature. Strictly implement the principles of “three lows,” “three stabilities,” and “three no’s.” “The “three lows” refer to low-temperature water discharge, low-temperature reduction, and maintaining low-load operation for a certain period after reduction. “The “three stabilities” refer to stable temperature elevation, stable H2 supplementation, and stable water output. “The “three no’s” mean that raising the temperature and increasing H2 levels must not be carried out simultaneously; moisture must not be allowed to enter the synthesis tower, and the duration of high-temperature water output must not be long. (6) The power of the electric furnace should be utilized to the fullest extent possible, the space velocity should be increased as much as feasible, and the axial temperature difference should be reduced. (7) Stop supplying gas when the refined qi level exceeds the limit slightly. (8) When the electric furnace trips, reduction should be stopped; the circulator can continue to operate for a while while allowing appropriate venting to remove the moisture from within the tower. (9) During reduction with high H2 pressure, 800°C is the onset reduction temperature for copper-based catalysts at 5 MPa, and it is the key temperature at which physical water and reduced water are carried away together. The reduction reaction is quite vigorous at this temperature. (10) High-H2 reduction is primarily a low-temperature reduction process; at temperatures of 80–1000°C, the water output can reach around 50%, while at 1200°C it can reach 80%. It is important to maintain stability during operation in this temperature range and to avoid raising the temperature too rapidly. The water outlet speed should be slow, not too rapid, and the water vapor concentration must be kept within the specified range. (11) 140–1600°C is often the second peak for high-H2 reduction; the heating rate should be reduced appropriately depending on the water evolution situation. (13) Ensure the proper water cooling temperature, drain water from the alcohol separator in a timely manner, and strictly prevent the presence of water and alcohol.

Reply to 3# carrier: The hydrogen is purchased from external suppliers, and not a large amount of hydrogen is required; therefore, purchasing it from outside is completely feasible. This is exactly what we do, and many other companies do the same as well

I am here to learn *. . . . . . . .

Three principles must be followed when reducing methanol catalysts: 1. Three lows: low-temperature water discharge, low-hydrogen reduction, and a period of low-load operation after reduction. 2. Three stabilities: stable temperature rise, stable hydrogen supply, and stable water output. 3. Three prohibitions: Temperature increase and hydrogen addition must not be carried out simultaneously ； Moisture must not be introduced into the synthesis tower ； Do not allow water to flow at high temperature for a long time. 4. Four controls: Control of the H2 supplementation concentration ； Control the CO2 concentration (because CO2 + ZnO → ZnCO3, and CO2 causes changes in the catalyst’s lattice) ； Although the feed gas may be free of CO2, the reaction that occurs simultaneously during reduction, CO + CuO → Cu + CO2, leads to an increase in the concentration of CO2 ； Hydrogen reduces copper only and not zinc, because zinc is more reactive than hydrogen, while hydrogen is more reactive than copper ； Control the water outlet rate ； Control the heating rate. The reduction method involves adding hydrogen to convert most of the copper oxide into pure elemental copper; the purpose of this reduction is to transform the components of the catalyst into polymers of various active molecules. CuO + H2 = Cu + H2O + Q (80.8 kJ/mol); CuO + CO = Cu + CO2 + Q. The concentrations of H2, CO, and CO2 at the inlet and outlet of the synthesis tower are analyzed every half hour. Throughout the reduction process, it is necessary to maintain a concentration difference of approximately 0.5% between the inlet and outlet of the synthesis tower (for H2+CO) (or H2), with this value not exceeding 1.0% in order to prevent excessive local temperature rise in the catalyst. B. The hot spot temperature in the synthesis tower is controlled by the amount of steam supplied by the steam injector or startup steam, as well as the steam pressure in the drum; the operating pressure can be adjusted using the drum vent valve, and the drum liquid level can be controlled through blowdown ； The (H2+CO) concentration in the gas entering the reactor also directly affects the hot spot temperature in the synthesis reactor. C. Control the CO2 content in the circulating gas to be <5%, and the water vapor concentration to ≤5000 ppm; if the CO2 content exceeds 5%, increase the N2 supply valve to remove the excess CO2 through venting. D. Continuously monitor the temperature inside the synthesis tower; if there is a tendency for a sudden rise in temperature, or if there are issues such as compressor failure or power outages, fresh gas supply should be cut off immediately ； Cut off the hot steam ； Increase the drum blowdown or venting, and add low-temperature boiler water ； Nitrogen filling and replacement system ； Measures such as system pressure relief are taken to prevent the synthesis tower from overheating and to maintain a stable temperature in it.

Reply to 7# TH373637: Because CO2 + ZnO → ZnCO3, and CO2 causes changes in the catalyst’s crystal lattice； Although the feed gas may be free of CO2, the reaction that occurs simultaneously during reduction, CO + CuO → Cu + CO2, leads to an increase in the concentration of CO2. During normal production, with such a high partial pressure of CO2 and even higher temperatures, why doesn’t a reaction occur? So this reaction is impossible; I asked the technical staff from foreign manufacturers, those from Wanfeng. They have no requirements regarding CO2; it’s only because the decomposition of carbonates causes the system pressure to rise that it becomes necessary to vent some gas. However, the CO2 level in the system remained around 15% until the end.

Reply to 8# Shouhou: It depends on what kind of ‘end stage’ is being referred to. What’s being discussed here is the control of catalysts during reduction reactions. CO2 is not produced as a result of reactions involving CO; rather, it is generated from the decomposition of carbonic acid compounds contained in the catalyst additives. It is precisely because of the high partial pressure of CO2 and its toxic effect on catalyst reduction that CO2 needs to be controlled. As for the catalysts produced by Zhejiang Xinhua Wanfeng, I haven’t used them yet; their sales manager’s surname seems to be Zhou

I have reservations regarding the reaction of CO and CuO to produce CO2. When reduction is carried out using hydrogen + nitrogen, a large amount of CO2 is also generated in the system. The control of CO2 content in the catalyst depends on the actual circumstances, with values generally ranging from 3% to 5%.

The previous hydrogen recovery system will suffice; hydrogen is extracted from the syngas using advanced membrane separation technology, and after being compressed by a compressor it is sent to the synthesis tower, thereby achieving the desired result