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Regarding the corrosion and prevention of the methanol recovery system in MTBE plants, Wang Junfeng from Hengli Petrochemical (Dalian) Co., Ltd. analyzed the corrosion issues associated with this system based on the actual production conditions of MTBE plants. We conducted market research on existing MTBE production facilities, including the 500,000-ton/year MTBE plant in Shandong, the 120,000-ton/year MTBE plant in Qingdao, and the 250,000-ton/year MTBE plant owned by Dongying Jiahao Chemical Co., Ltd. Based on the analysis of the operation status of the above three sets of production units, their common issue is that the methanol recovery systems all suffer from corrosion to varying degrees, and the sieve pores in the extractor tower trays are clogged. The possible reasons for corrosion and blockage can be analyzed as follows: First, free acids cause corrosion. The catalysts used in MTBE plants are large-pore, strong-acid cation exchange resins, which are formed from cross-linked styrene beads through sulfonation with sulfuric acid. Before leaving the factory, these catalysts must undergo strict deacidification treatment to remove impurities such as low-molecular-weight benzene sulfonic acid that remain in their pores after the sulfonation reaction. Typical manufacturers subject the catalysts before they leave the factory to strict treatment, and the users also carry out water washing of the catalysts after installation; therefore, this is not the root cause of corrosion in MTBE plants. II. Corrosion caused by metal ions and alkaline substances: The alkali metal ions and alkaline substances present in methanol and C4 replace the H ions in the catalyst, resulting in the loss of hydrogen ions. After passing through the methanol purifier, reactor, and catalytic distillation tower, almost all of these metal ions and alkali metals are adsorbed by the catalyst, while an equivalent amount of H ions is released. These H ions end up in the methanol extraction cycle water, and they are sufficient to make this water acidic, thereby causing corrosion of the equipment. At present, the C4 feedstock used by our company comes from the dehydrogenation unit; the alkali metal content in this feedstock is 0.15 PPm, the alkaline substance content is 1.1 PPm, and the alkaline substance content in methanol is 1 PPm. At the same time, methanol is purified before reacting to remove any small amounts of alkaline substances. Therefore, this type of corrosion will not cause greater corrosion either. III. Corrosion caused by the loss of sulfonic acid groups due to overheating of the reaction bed; the normal temperature for etherification reactions is between 40°C and 75°C. Meanwhile, the probability of desulfonation of the etherification reaction catalyst before 80°C is almost zero. Catalyst sulfonation can only occur when the reaction bed overheats. The factors that cause overheating in the reaction bed include: 1. The methanol pump stops operating suddenly during production, resulting in an excessively low alcohol-to-olefin ratio; this leads to the auto-polymerization of isobutylene, which generates a large amount of heat and causes localized overheating in the reaction bed, thereby leading to catalyst desulfurization. 2. The content of isobutylene in the raw material is unstable, fluctuating between high and low levels, which results in an excessively low alcohol-to-olefin ratio. The self-polymerization of isobutylene causes the reaction bed to overheat, leading to the loss of sulfonate groups. 3. That is, we require the device to operate for long periods of time; in order to achieve the desired conversion rate, we increase the reaction temperature artificially, which leads to desulfurization of the catalyst. In summary, in order for the device to operate over a long period of time, it is necessary to overcome the factors mentioned above, especially to prevent corrosion caused by the detachment of sulfonic acids. First of all, operations must be carried out smoothly, and regular inspections should be intensified to prevent desulfurization from occurring due to overheating of the reaction bed caused by the auto-polymerization of isobutylene resulting from an excessively low alcohol-to-olefin ratio. Second, strictly control the content of alkali metals and alkaline substances in the raw materials to ensure that they are removed in the methanol purifier. Third, the pH value of the circulating extraction water should be measured regularly, and the water should be changed frequently to keep its pH within the range of 6.5–8.0. Fourth, if necessary, add alkali to the circulating extraction water to neutralize it and raise its pH value during operation. Fifth, artificially improve the material quality of the equipment in the circulating extraction water system and add acid-removal equipment in the circulating extraction water pipelines to take precautions against corrosion in advance. April 14, 2015