Discussion on the service life of alcohols catalysts

A few days ago I visited a synthetic ammonia and alcohol production plant in Shandong. The current operation mode there is as follows: after 12 months of operation, the methanol catalyst remains highly active, being in a period of good activity; therefore, a single-system alcoholization followed by hydrocarbonation process is used, with water cooling and ammonia cooling applied during the hydrocarbonation stage. System gas volume: For the entire system, 2 units of 6M 32 (180 m3/min), 2 units of 4M 20 (73 m3/min), and 4 units of H12 (57 m3/min) are used; in total, this amounts to 8 units with a gas flow rate of 734 m3/min. The ammonia synthesis system requires an additional gas supply of 44,000 m3/h. The daily production is 394 tons of ammonia and 8 tons of crude methanol. The pressure for methanol synthesis is 12 MPa, while the pressure in the ammonia synthesis process is 22.5 MPa. The alcohol synthesis tower in their company has a diameter of φ1000×16m and contains 7m3 of catalyst, while the hydrocarbonation tower also has a diameter of φ1000×16m with 7.9m3 of catalyst. A characteristic of the alkali-catalyzed alcohol hydrocarbonation process is that the levels of CO and CO2 entering the system are low, at around 1%. The heat exchange arrangements and heat transfer area distribution in the alkali-catalyzed alcohol hydrocarbonation towers differ from those in the processes for producing methanol. Based on actual operation results, the temperature differences both axially and laterally within the catalytic bed of the alcohol synthesis tower are very small. The preheater outside the tower has a large heat transfer area, and high-efficiency heat exchangers are used; as a result, the temperature of the hot gas drops to around 50°C after passing through the preheater, indicating a high rate of reaction heat recovery. When the ratio of CO to CO2 in the alcoholization system is only 1%, the alcoholization process can proceed through an exothermic reaction; the electric furnace used for hydrocarbonization requires a current of only 200A to 300A. To minimize the amount of oxides formed during synthesis, in addition to reducing CO+CO2 as much as possible, it is also necessary to reduce the content of H2O. After hydrocarbon cooling, ammonia cooling is applied with the temperature controlled at 5°C, which helps to lower the content of saturated water vapor. The methanol catalyst belongs to the copper-zinc-aluminum series and exhibits excellent activity at medium pressures (10.0 MPa–15.0 MPa) and low temperatures (220°C–280°C), resulting in a high conversion rate of CO+CO2. For XAC hydrocarbonation, the catalyst is of the copper-iron series; it provides very good purification results over a wide pressure range of 3.0 MPa–30 MPa and at temperatures of 210°C–250°C, with trace levels as low as 3 ppm–5 ppm. Its activation temperature is as low as 200°C, while its short-term heat resistance can reach up to 400°C–500°C without any loss of activity. Personal opinions – let’s discuss together. This post was last edited by kaisl1314 on 2008-1-15 at 15:14.]

It will also be two years since we installed our catalyst by June; it’s the same type of catalyst as before. Our reactor tower has a diameter of 2700 mm, and so far there is no noticeable decline in the performance of the catalyst, with a one-pass CO conversion rate of up to 90%. In my opinion, the main reasons are as follows: 1. Strict purification requirements – after desulfurization, the gas is sent to a centrifugal compressor where its pressure is increased to around 7.5 MP before entering the dual-methane process; there are no risks associated with oil, sulfur, chlorine, etc ； 2. The operation is stable; since the plant started operating, no major adjustments have been made to the CO output at the exit or to the CO2 output for decarbonization in response to market changes, and the CO level at the inlet of the methanol tower has always been maintained at around 2%, while the CO2 level has remained around 0.25. The inlet temperature is above 200 degrees, and the drum pressure is adjusted to between 2.5 and 2.6 MP depending on the load; it is currently also kept below 2.6 ； 3. Protective measures for the catalyst during startup, shutdown, and under special operating conditions are timely and appropriate ； 4. During catalytic reduction, indirect hydrogen reduction based on the water output is employed to maintain good catalyst activity. What I would like to ask now is: what are the direct apparent reactions when a catalyst begins to decline? Is this process particularly fast? Is the catalyst lifespan for methanol in China generally short?

LZ, are your two methanol synthesis towers connected in series or in parallel? If they are in parallel, then the conditions in both towers are the same, as is the catalyst used; therefore, there should be no major issues with the catalyst. In that case, it’s possible to check whether there are any problems with the methanol synthesis towers themselves. If they are two separate systems, is the purification efficiency the same in both? If they are connected in series, is it the larger tower that is placed first and the smaller one later? In that case, their service life will definitely differ. It might be worth considering swapping them around, but overall, their lifespan isn’t very long.

I hope the original poster can explain both the question and the conclusion; everyone is looking forward to your answer. Upward, don’t sink!

Director Wang, I have a question: is the 1400 tower now connected to the 1200 tower within the same system, or are they still two separate systems? Which of the two towers has a greater load? If a connection is made in a certain way on a system (in parallel and/or in series)?