Acidic corrosion problem in the methanol recovery system of MTBE plants
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Since the new plant came online in May, the pH of the extraction water from the methanol washing tower has consistently been around 5. At present, the plant can only maintain a pH level above 6 by periodically replacing the extraction water using desalinated water and by discharging wastewater. Note: The wastewater discharge from my methanol recovery system is intermittent; currently, it is discharged only during replacement processes. Could you all help me analyze this? Do your devices also have such a problem? The catalyst used in my device is of type D500-II
We’re using D-006; it works well and is quite durable
There was a problem with the catalyst; the sulfonic acid groups came off, causing the extraction water to become acidic and thus corroding the equipment
1. Water is present in the raw material; under conditions of water and high temperature, the sulfonic acid groups in the catalyst are removed. 2. Formic acid is contained in the methanol used as raw material; it is recommended to conduct tests for this. 3. The metal cations (sodium, calcium, iron), sulfides, and alkaline substances present in the raw materials displace the hydrogen ions in the catalyst, resulting in the loss of H+. It is recommended to use an acid-removing catalyst
Agree with the person above. But it is considered that the third point is the main reason. It is best to choose an acid scavenger; they are still available on the market today and have become more widely used recently.
The catalyst sulfonate groups are removed; the moisture content of the raw materials must be strictly controlled, and the catalyst should be soaked in methanol for a sufficient amount of time at the beginning of operation
Our company’s 70,000-ton MTBE plant utilizes the mixed-bed catalytic distillation technology provided by Hebei Kairui. The methanol recovery tower makes use of a purifying agent to clean the extraction water, which effectively prevents corrosion in this tower; the purifying agent is replaced every six months. Generally, the pH level should be kept above 7, and there is no need to change the water frequently.
Is the reaction temperature too high, causing the sulfonate groups to detach?
Corrosion is also severe here; regarding the extraction system, the pumps have been replaced. The old design used carbon steel pipelines, while today’s designs mostly use stainless steel. Whether sulfate ions are present or not, methanol will cause corrosion to the pipelines when there is water present and the temperature is relatively high.
In which year did you start? Was it that version with the two towers built separately?
It is possible that the poor stability of the new catalyst is causing some of the sulfonic acids to detach. The key at present is to stabilize the process in the etherification unit in order to avoid overheating; over time, the phenomenon of sulfonate detachment may slow down. It is also advisable to carry out continuous replacement of the water wash tower at this time.