Methanol section: One question per day. How is the catalyst protected during normal operation? 2016.03.30

Answer: ① When using a catalyst, careful operation is necessary to minimize fluctuations in temperature at various points and avoid overheating. It is also important to maintain the purity of the feed gas by removing all kinds of toxic substances; if these toxins are present in excessive amounts, it is necessary to reduce the load or shut down production. Try to avoid introducing liquids or lubricants into the catalyst. ② When starting and stopping, increasing or decreasing quantities, raising or lowering temperatures, and increasing or decreasing pressures, it is necessary to avoid sharp fluctuations in operating conditions. The pressure rise and fall rate should be less than 0.2 MPa per minute, while the temperature rise and fall rate should be kept within 20–30°C per hour. ③ During the maintenance of the synthesis system, if the synthesis tower does not require maintenance, it is important to protect the catalyst; this is generally achieved by filling the tower with nitrogen (≥99.9%) to maintain a slight positive pressure, thereby preventing air from entering the tower and damaging the catalyst.

How to protect the catalyst during normal production? Answer: First, when using a catalyst, careful operation is necessary to minimize fluctuations in temperature at various points and to avoid overheating. It is also important to maintain the purity of the feed gas by removing all kinds of contaminants; if the level of these contaminants exceeds acceptable limits, it is necessary to reduce the load or even stop production. Try to avoid introducing liquids or lubricants into the catalyst. II. When starting and stopping, increasing or decreasing quantities, raising or lowering temperatures, and increasing or decreasing pressures, it is necessary to avoid sharp fluctuations in operating conditions. The pressure rise and fall rate should be less than 0.2 MPa per minute, while the temperature rise and fall rate should be kept within 20–30°C per hour. Three. During the maintenance of the synthesis system, if the synthesis tower does not require maintenance, it is important to protect the catalyst; this is generally achieved by filling the tower with nitrogen (≥99.9%) to maintain a slight positive pressure, thereby preventing air from entering the tower and damaging the catalyst.

1. When using catalysts, careful operation is necessary to minimize fluctuations in temperature at various points and to avoid overheating. It is also important to maintain the purity of the feed gas by removing all types of contaminants; if the level of these contaminants exceeds acceptable limits, it is necessary to reduce the load or even stop production. Try to avoid introducing liquids or lubricants into the catalyst. 2. When starting or stopping the operation, adjusting the volume or amount, raising or lowering the temperature, or increasing or decreasing the pressure, it is necessary to avoid sharp fluctuations in the operating conditions. The pressure rise and fall rate should be less than 0.2 MPa per minute, while the temperature rise and fall rate should be kept within 20–30°C per hour. 3. During the maintenance of the synthesis system, if the synthesis tower does not need to be serviced, it is important to protect the catalyst; this is generally achieved by filling the tower with nitrogen (≥99.9%) to maintain a slight positive pressure, thereby preventing air from entering the tower and damaging the catalyst.

The main reasons for the reduced lifespan of catalysts include poisoning, thermal aging, decreased strength, and frequent start-up and shutdown cycles. 1. Measures to prevent poisoning are as follows: The preventive measures are listed below. a) Install precision desulfurization and dechlorination units before the feed gas enters the methanol system. Operate with care to ensure that the total sulfur content in the gas fed into the methanol synthesis system is less than 0.1×10-6, and the chlorine content is less than 0.1×10-6. b) Improve the oil separation efficiency and strive to reduce the oil content in the gas entering the tower. 2. Measures to prevent thermal aging include: a) During reduction and start-up/shutdown processes, operate strictly in accordance with predetermined parameters to prevent overheating. b) While ensuring production volume and stable operation, the operating temperature should be reduced as much as possible. Any increase in the hotspot temperature should be done carefully, with the increase amount not being too large; 5°C is generally a suitable value. c) Improve the structure of the internals in the synthesis tower to reduce axial and radial temperature differences. d) Reasonably control the CO2 content in the fresh gas. 3. Measures to prevent a decrease in catalyst strength include: a) During operation, strive to avoid unnecessary shutdowns in order to maintain stable production over long periods of time. b) When parking is necessary, the feed gas in the synthesis tower should be replaced with purified gas or pure nitrogen.

During start-up and shutdown, the temperature and pressure should be increased or decreased slowly; during normal operation, the fluctuations in composition should be minimal. In the initial stage, a high hydrogen-to-carbon ratio and high flow rate are required. Pipeline purging and chemical cleaning are necessary to prevent the entry of iron particles and dust, as well as to avoid catalyst poisoning caused by excessive sulfur levels in the process gas.