Questionnaire on Corrosion Issues in MTBE/Butene Plants

Please provide a detailed description of the solution: 1. The manufacturer and grade of the resin catalyst used. The catalysts that have been used so far mainly come from three manufacturers: Dandong Mingzhu’s D-005Ⅱ type, Hebei Kairui Chemical’s D006/D006Ⅱ types, and the imported Dow Rochem A-35 (on a wet basis). 2. Areas prone to acidic corrosion or those where corrosion has already occurred. Has corrosion occurred in the subsequent butylene refining unit? Detailed introduction; additional Wealth and Haichuan coins are provided with pictures. Since the reactor cylinder and the methanol purifier cylinder are lined with 316 stainless steel, corrosion is virtually non-existent. The areas where corrosion-induced thinning occurred were mainly the outlet pipelines of the methanol purifier and the reactor (one of the elbows in the outlet section of the methanol purifier had a leak), and the corrosion was not severe. Pay special attention to the sewage pipeline network for the normal water washing drainage of the reactor; since wastewater is generated during the catalyst pretreatment washing step, focus on the underground pipelines used for waste discharge. It is advisable to rinse with water after washing. 3. During the current operation of the unit, what accident incidents have occurred due to acidic corrosion, and has it affected the normal operation of the unit? For example, clogging of the filter screens in pumps, pipeline leaks, heat exchanger leaks, and so on. Detailed information is available additionally for Wealth and HaiChuan Coins. It is described in Clause 2: 4. Are the materials of the methanol washing tower and the methanol recovery tower carbon steel or stainless steel? Have anti-corrosion measures been taken on the inner surfaces of the tower walls and pipelines made of carbon steel? Both towers are made of 16MnR, which is low-carbon steel, and no anti-corrosion treatment has been applied. 5. How is the operation of the reactor optimized, and has there been any occurrence of sulfate ions detaching? No sulfonate group loss has occurred. At 80°C, the sulfonate groups begin to detach from the resin catalyst, and at 120°C they detach on a large scale; therefore, operations should avoid excessively high temperatures. The preheating temperature of the feed to the reactor can be lower at the initial stage; as the catalyst gradually becomes deactivated, the temperature of the reaction feed should be increased step by step. When the temperature rise in the reaction bed is severely insufficient, consider replacing the catalyst. In daily operations, pay close attention to the soluble alkalis and alkali metal ions in the butane feed to the reactor, as these substances can cause catalyst deactivation. 6. Operating pressure and temperature of the methanol washing tower and methanol recovery tower. Should the extraction water be desalinated water or steam condensate? The ratio of the extraction water volume to the tetrahydrocarbon feed volume. For the operation of the methanol extraction tower (washing tower), the pressure is 0.7 MPa; for the methanol recovery tower, it is 0.13 MPa. The top temperature is around 82 degrees Celsius. Deionized water is used as the extraction water, and the material-to-water ratio is 5:1 (determined based on the amount of methanol in the butane-methanol mixture). 7. How long did it take to carry out repairs at the areas affected by corrosion? Was a shutdown required for those repairs? Detailed information is available additionally for Wealth and HaiChuan Coins. The corrosion occurred at the elbow at the outlet of the methanol purifier; it has been only 5 years since operations started until the leak was detected. The situation is not serious, and there is no need to shut down operations. 8. Is there a water coalescer? In which process is it used, and what is the effect of its use? Does it have any effect on reducing acidic corrosion? The water coalescer is located before the C4 feed tank, and it currently has little to no dehydration effect. 9. Should deacidification equipment be added? How effective is it? No deacidification equipment was added; in my opinion, this is not necessary. The catalyst is properly pre-treated and washed, and daily operations are carried out without exceeding the optimal temperature to prevent the loss of sulfonate ions. The pH value of the water used in the methanol recovery tower is regularly checked, and when the pH value is below 6, the water in the system is replaced promptly, which helps to avoid the presence of acid and severe corrosion. 10. Other: Your suggestions and opinions regarding the corrosion of this device. The catalyst pretreatment steps must be carried out properly. It is essential to maintain an appropriate pH level in the methanol recovery tower, and to change the water regularly. It is advisable to replace the manual valves at the reactor outlet with those made of 316 stainless steel, as otherwise they may corrode and fail to close properly. It is also recommended to provide additional corrosion resistance for the elbows and related piping at the reactor and methanol purifier outlets, or to upgrade them to 316 stainless steel if possible.