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Exploration of Green and Environmentally Friendly Operation of MTBE Plants: At present, in China, the production cycle of MTBE plants that use refined liquid hydrocarbons as raw materials is generally 1–2 years. Although the operating pressure of these plants is low (up to 1.5 MPa), they require frequent shutdowns for catalyst replacement, which leads to environmental pollution. To achieve safe, green, and environmentally friendly production in MTBE plants, China National Petroleum Corporation’s Harbin Petrochemical Branch (referred to as Harbin Petrochemical) has carried out explorations and taken effective measures to reduce environmental risks. The MTBE unit at Harbin Petrochemical has a processing capacity of 50 kt/a, and it employs a combined mixed-bed and catalytic distillation process. To be compatible with the downstream A and B units, an isobutane tower has been added to the facility; as a result, more C4 materials are present within the facility’s boundary, increasing the risks to the safety environment. In addition, the saturated hydrocarbons produced by diesel hydrogenation enter the liquid hydrocarbon dewaxing system; the isobutylene content in the feedstock for MTBE plants is below 12%, which is relatively low in the industry. For the above reasons, the MTBE unit at Harbin Petrochemical is characterized by low reaction heat, a high preheating start temperature (the preheating temperature is close to 40°C when the unit starts operating with new catalysts), a high load on the top of the catalytic distillation tower, and high energy consumption. In addition, there are significant fluctuations in the amount of Russian crude oil used as feedstock, the liquid hydrocarbon double-dehydration system operates unstably, and the ammonia nitrogen content in the liquid hydrocarbons after dehydration is high; this reduces the service life of the etherification catalyst. As a result, the catalyst replacement cycle for the plant has been reduced from 2 years to 1 year. Moreover, severe corrosion in the plant requires more frequent shutdowns. Therefore, the current status of the MTBE plant at Harbin Petrochemical results in higher safety and environmental risks compared to similar plants. The environmental risks associated with MTBE plants include shutdown-related environmental risks, operation-related environmental risks, and environmental risks resulting from accidents involving production equipment. Based on years of production experience, the environmental risks associated with Harbin Petrochemical’s MTBE plant have been summarized as follows: ① Rainwater contacting the old etherification catalyst generates acidic wastewater, which pollutes the sewage systems ； ②The methanol recovery system is shut down, resulting in the discharge of wastewater with high COD levels, up to 40,000 mg/L ； ③In the MTBE plant, steam is used for purging the feed materials during shutdowns, while nitrogen is used for purging the reaction system and the catalytic distillation column. Steam is also used for purging the methanol recovery system and the isobutane column. Since two different purging media are used, it is not possible to vent the gases directly to the atmosphere at the same time, which can lead to air pollution ； ④During shutdowns, it is common for the C4 content in the MTBE product to be high (above 5%), which leads to leaks of flammable gases from the internal floating roof tanks ； ⑤During the shutdown of the unit, the material was not completely removed; C4 does not vaporize easily, and its direct discharge on-site poses a safety hazard. Environmental risks during the commissioning of MTBE plants: ① During the plant adjustment phase, substandard MTBE enters the tank area, resulting in the leakage of flammable gases from the internal floating roof tanks ； ②High water injection volume results in high COD in the bottom effluent of the methanol recovery tower ； ③Untimely release of nitrogen from the system causes overpressure in the equipment ； ④Methanol is recovered by soaking the catalyst without reprocessing it, resulting in high COD levels in the wastewater. Environmental risks during the normal operation of the MTBE plant: ① Low temperature at the bottom of the methanol recovery tower, production fluctuations, and direct discharge of methanol-containing extraction water ； ②There is an internal leak in the cooling exchange equipment, resulting in the direct discharge of methanol-containing wastewater. Measures taken: Environmental protection shutdown: ① Do not replace the reagent when it is raining; take proper rain protection measures for the old reagent, and strictly prevent acidic wastewater from coming into contact with rainwater, thereby avoiding improper discharge of wastewater ； ②Measures to reduce COD in wastewater during the shutdown of the methanol recovery system: First, after feeding to the methanol extraction tower is stopped, the system is operated for 1 hour to ensure a reduction in the methanol concentration in the extraction water. Secondly, before shutting down methanol recovery tower C-303, the temperature at the bottom of the tower was brought to the required level; the water level was reduced to its lowest point, and the reflux rate was gradually decreased. The methanol in the reflux tank was recovered and stored in the methanol storage tanks, thereby reducing the amount of wastewater generated at the bottom of the tower during shutdown ； ③Before shutting down the plant, the methanol stored in the low-level storage tanks should be recycled until the storage level reaches zero. During the initial stage of purging the plant, the purge gas must be directed to the flare; direct discharge on-site is strictly prohibited ； ④During the shutdown of the MTBE plant, the flow rate is first reduced, followed by a decrease in the pressure and reflux in the catalytic distillation tower; then feeding is stopped. It is necessary to maintain the temperature at the bottom of the tower at the appropriate level, so that qualified product can be stored in the MTBE storage tanks. This prevents C4 from leaking out of the tanks, as the C4 components evaporate from the top of the tower ； ⑤When shutting down the MTBE unit for material withdrawal, the reflux rate should be gradually reduced to ensure complete withdrawal of the material. Steam tape is used at the blind ends of various components to vaporize the medium; in particular, it is necessary to ensure that the medium is vaporized at the lowest points of the reboiler and the reflux line, in order to prevent direct discharge onto site. Environmentally friendly startup: During the startup of the @MTBE unit, especially when the product from the bottom of the catalytic distillation column is of satisfactory quality, the liquid level at the bottom of the column is lowered to a minimum before feeding begins. Wait until the reactor pressure is equal to the pressure in the catalytic distillation column before opening the reactor to the column feed valve. At the start of operation of the unit, the feed rate is set at 2/3 of the design value; it is then increased to the normal level once stable operation is achieved. These measures are taken to reduce the time required for product adjustment, thereby preventing the production of substandard MTBE products from entering the floating roof tank and causing leaks of flammable gases ； ② The methanol recovery system started up as scheduled and is operating normally; the methanol extraction tower feeds at the lower liquid level limit. Water is not discharged from tower C-303 when its bottom temperature is not within the specified range, in order to prevent high COD levels in the wastewater ； ③During the commissioning of the unit, with the tower pressure remaining constant, nitrogen is discharged from the catalytic distillation tower and the isobutane tower based on the reflux temperature; it is strictly prohibited to allow excessive nitrogen pressure due to low bottom temperatures, in order to ensure product quality and optimal operating conditions of the equipment ； ④The methanol recovered from the soaked catalyst is stored in a methanol storage tank at low levels, and it is reprocessed once the plant resumes normal operation. Risk avoidance: Controlling the quality of the extraction water at the bottom of the methanol recovery tower during normal production is key to managing the COD level in the wastewater. ①First, strengthen the monitoring of the bottom temperature of the methanol recovery tower, ensuring it remains above 102°C ； Second, stabilize production to reduce water discharge ； Third, introduce cationic absorption resins for water extraction to reduce the amount of water that needs to be replaced and minimize equipment corrosion and leakage ； Fourth, strengthen the analysis of abnormalities in system water discharge and replenishment to detect leaks in reboilers or coolers in a timely manner, and focus on improving the corrosion resistance of the equipment itself, such as by using coated cores and upgrading the material used in the equipment, to ensure the long-term operation of heat exchange equipment ； ②Avoid raw material with C4. When the raw material contains C4, the temperature at the sensitive point of the catalytic distillation tower is strictly controlled; if the C4 content exceeds 2%, the feed is stopped to ensure that the C4 content in the MTBE product does not exceed the specified limits, thereby preventing leaks from the internal floating roof tank ； ③A two-level inspection system for water content in raw materials is implemented at the workshop and team levels; once water is detected in the raw materials, the pipeline is shut down promptly, and the upstream unit is contacted for handling, thereby reducing the amount of water removed from the MTBE unit ； ④In the liquid hydrocarbon double-dehydration system, it is important to control the amount of water and its quality used in the washing process; demineralized water should be used for washing, and the pH value of the wastewater from washing must be regulated to ensure that the ammonia nitrogen ion content in the liquid hydrocarbon after dehydration is within acceptable limits. If the liquid hydrocarbon deep desulfurization system can be shut down, it will reduce the loss of basic ions ； If enhanced dehydration is necessary, it is important to prevent water from soaking the catalyst and causing the loss of basic ammonia nitrogen ions. Implementation effect: Production practice has shown that by taking appropriate measures, the filter replacement cycle of the device can be extended from 1 year to 2 years. In other words, the environmental risks associated with starting up and shutting down the facility are reduced by one time every 2 years. For a 50 kt/a MTBE facility, this means that 57 tons of solid waste catalyst (on a wet basis) and 35 tons of wastewater with high COD levels can be avoided per 2 years, resulting in a 50% reduction in risks. Therefore, taking measures to extend the device replacement cycle can effectively reduce environmental risks. Green and environmentally friendly production at Harbin Petrochemical’s MTBE plant is achievable. Based on the device’s many years of operational experience, the most common environmental risks are high COD levels in the wastewater and leaks from the MTBE storage tanks. To reduce the environmental risks associated with MTBE plants, corresponding measures can be taken during the three phases of shutdown, startup, and normal operation. In summary, preventing etherification catalyst poisoning and extending the catalyst replacement cycle in the plant can effectively reduce environmental risks.