These include the alkylation of benzene to produce ethylbenzene and the dehydrogenation of ethylbenzene to produce styrene. The process consists of alkylation, washing, ethylbenzene rectification, dehydrogenation, and styrene rectification.
The brief process is to dry the raw material benzene to a water content of less than 10ppm, blending a cocatalyst with anhydrous hydrogen chloride, and reacting with the ethylene and aluminum trichloride catalyst complex into the alkylation/transalkylation reactor at a temperature of 180 ° C and pressure. The alkylation/transalkylation reaction is carried out at 0.91 MPa.
The reacted material is flashed to recover hydrogen chloride, and then enters a three-stage washing system in series to remove aluminum trichloride and hydrogen chloride. The washed alkylation liquid is sent to a rectification system, and the alkyl liquid is separated into benzene, ethylbenzene, polyethylbenzene, and residual oil. The benzene and polyethylbenzene are returned to the alkylation/transalkylation reactor, and the ethylbenzene product is sent to the storage tank.
The ethylbenzene and primary steam are superheated and mixed with the main steam (steam: ethylbenzene = 1.3:1) into the first stage reactor. The dehydrogenation reaction was carried out at an inlet temperature of 628 ° C, an outlet pressure of 0.0486 MPa and a catalyst, and then dehydrogenation was continued in the second-stage reactor at an inlet temperature of 631 ° C and an outlet pressure of 0.04 MPa to form styrene, and the dehydrogenation mixture was subjected to waste heat. Boiler, superheated steam desuperheater, air conditioner cooling, condensation. The dehydrogenation liquid from the separator enters the rectification system to separate styrene, ethylbenzene, benzene and toluene to obtain a styrene product. Ethylbenzene and benzene are returned for use. The product is toluene to the tank area.
The materials in the production process of the device include ethylbenzene, benzene, styrene, polyethylbenzene, hydrogen, etc., which are flammable, explosive, toxic and harmful, and some have strong corrosive properties such as hydrogen hydride and catalyst complex.
2 key parts
2.1 Alkylation reaction system It is the core part of ethylbenzene production. The reaction temperature and pressure are high, the reaction conditions are harsh, and the material is flammable, explosive and highly corrosive. The reactor is lined with a good performance anti-corrosion insulation lining. Other equipment, valves and pipelines are made of special anti-corrosion materials, but there is still the danger of running, running, dripping and leaking. This type of device has had an accident in which the reactor was corroded and leaked. In addition, once the water enters the reactor, the catalyst complex is poisoned and the equipment and pipeline are blocked. A styrene plant in a plant was forced to stop due to blockage of the reactor discharge port.
2.2 Catalyst Complex Formulation System The system uses benzene, polyethylbenzene, aluminum trichloride, and anhydrous hydrogen chloride to formulate a catalyst complex for alkylation/transalkylation reaction. The material is highly corrosive; if the system enters the water, the catalyst will be deactivated and decomposed to produce a precipitate blocking the pipeline, threatening the entire alkylation reaction. A styrene plant in a factory was forced to stop cleaning due to plugging of the outlet of the system reactor.
2.3 Dehydrogenation reaction system The dehydrogenation reactor is the core part of the dehydrogenation unit. The reactor feeds ethylbenzene and steam at high temperature and under pressure. The water ratio is too low, and frequent parking will shorten the catalyst life. Influent soaking of the catalyst bed will completely destroy the catalyst. Dehydrogenation tail gas contains 80% (molecular ratio) of hydrogen. It is very dangerous if air enters the system. Air enters the reactor to cause hot spots in the catalyst bed, and there is a danger of burning catalyst and equipment. The entry of air into the exhaust system creates an explosive mixture and there is a risk of tempering when the exhaust gas is used as fuel gas. When the exhaust gas compressor fails, the dehydrogenation unit has to be produced under positive pressure and low load, and the exhaust gas is discharged into the atmosphere, which increases the risk. Styrene is included in the entire system material. Styrene is prone to self-polymerization and produces blockages. In severe cases, it is forced to stop to clean up. Steam superheater burner flame and poor furnace temperature control will burn the furnace tube and damage the furnace wall to cause parking. When a styrene plant was started in a factory, a large amount of water in the catalyst bed was forced to replace the new catalyst; the ethylbenzene evaporation system was blocked by a large amount of styrene polymer; the styrene steam superheater flew to cause the entire superheated furnace to burn and other accidents.
2.4 Sulfur-free polymerization inhibitor preparation system This system is used to prepare ethylbenzene and polymerization inhibitors for styrene towers. If the system fails, the content of the polymerization inhibitor in the tower will decrease rapidly, which may cause the self-polymerization of styrene. The preparation material 2,4-dinitrophenol is highly toxic and flammable and explosive when dry. The solvent is made of styrene or ethylbenzene, which is formulated into a 20% solution. When it is lower than 40 °C, it can crystallize and precipitate, block the pipeline, equipment and valves. In a factory, the pipeline of the preparation system has been blocked and forced to stop and the system is set to fire. The polymerization inhibitor accumulated in the ignition insulation layer causes an accident of burns.
3 Safety points
3.1 alkylation reaction system
3.1.1 The temperature and pressure of the reactor should be strictly monitored. The water content of the feed benzene and polyethylbenzene should be less than 10 ppm. The reactor should be shut down and the opening and cooling speed should be strictly controlled; the interlock of the reactor system must be put into normal use, and the interlock should be verified regularly and recorded.
3.1.2 During the inspection of the post, the monitoring of the reactor should be strengthened. Regular use of a special infrared thermometer to determine the presence or absence of hot spots in the reactor, it is found that the hot spots must be urgently treated immediately; the spray water used for cooling the reactor must be kept ready for use, at least once a month.
3.1.3 The airtight test and drying of the reactor before driving shall be strictly checked.
3.1.4 Corrosion of equipment, pipelines, valves and instruments that are susceptible to corrosion should be checked frequently. Wall thickness of anti-corrosion linings, equipment and pipelines. Find problems and repair or replace them in time.
3.1.5 When the acid material leaks, it should be neutralized with alkali and then put into waste oil. When working in underground wastewater tanks and accident tanks, wear appropriate protective equipment. The accident tank should always be kept liquid-free or low-liquid.
3.2 Catalyst Complex Preparation System
3.2.1 The water content of polyethylbenzene and benzene should be less than 10ppm, and the water content of hydrogen chloride should be less than 50PPppm.
3.2.2 Ammonia-decomposed agglomerated aluminum chloride is prohibited from being reused for production.
3.2.3 Catalyst Preparation When driving, the exhaust gas absorption system should maintain normal driving.
3.3 dehydrogenation reaction system
3.3.1 Strictly control the reactor inlet temperature. Feed steam: Ethylbenzene should not be lower than 1.3:1. The content of diethylbenzene in ethylbenzene is less than 10ppm, and the number of opening and stopping is minimized to prevent catalyst breakage. When the reactor is initially driven, it should first be heated by nitrogen gas, and the bed temperature can reach above 200 °C before steam can be introduced. The inlet pressure of the exhaust compressor should be maintained at 0.0276 MPa. The interlock system of the reactor, steam superheater and exhaust compressor must be used normally and periodically checked and recorded.
3.3.2 The safety valve shall be pressed once a year, and the explosion-proof membrane shall be inspected once a year, and the problem shall be replaced or repaired in time.
3.3.3 Exhaust system Three online oxygen analyzers should be used normally. When two indication values ​​exceed 1%, the interlock should act to raise the system to positive pressure operation. The exhaust gas needs to be discharged into the flare system during negative pressure operation and is not allowed to be discharged into the atmosphere.
3.3.4 When the hot spot is found in the reactor bed, the cause should be found immediately, and if necessary, stop the treatment.
3.3.5 The steam superheater should be prevented from overheating. Always adjust the flame to the furnace of the superheater, do not directly contact the furnace tube and the furnace wall. The reaction system should be slowly changed from positive pressure to negative pressure to prevent the load from suddenly increasing, and the superheated furnace tube is quenched and damaged.
3.3.6 The interface of the water and dehydrogenation mixture separator should be strictly controlled at 70% to prevent the dehydrogenation solution from carrying water or dehydrogenation solution in the water.
3.3.7 Ethylbenzene evaporator should stop circulating Ethylbenzene feed and increase sewage discharge 2 hours before stopping. Immediately after parking, the system should be washed with ethylbenzene to prevent styrene self-polymer blocking system.
3.3.8 The expansion joint should be inspected regularly, and the nitrogen of the expansion joint should be unblocked.
3.4 Sulfur-free polymerization inhibitor preparation system
3.4.1 Winter should ensure the normal operation of the system's insulation and heat tracing system. The ethylbenzene/styrene tower feed line should be purged for long-term parking.
3.4.2 Appropriate protective equipment should be worn during the operation, and a special warehouse should be set up in the barrel. The operator takes a shower immediately after the work is completed. Showers and eyewashes should be kept for years and checked frequently.
3.5 other parts
3.5.1 The pressure swing adsorption unit should be sealed with nitrogen at a pressure of 0.147 MPa. Always check the electrostatic grounding and hydrogen leaks of the hydrogen refining unit.
3.5.2 The top production line of the styrene distillation column should be inspected, and the polymerization inhibitor should be added on time, the addition amount is 5-15ppm, the styrene temperature of the storage tank is 5°C; the ethylbenzene is washed during parking to prevent styrene. Self-polymerization.
3.5.3 When the ethylbenzene/styrene tower is opened, prevent the humid air from entering, and seal the nitrogen after the repair. Drive to do the airtight and vacuum test.
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