An environmental protection device for high-value utilization of new energy electrolyte dimethyl carbonate waste liquid

Abstract

The present application belongs to the cross field of energy saving and environmental protection and advanced manufacturing industry technology, and particularly relates to an environmental protection device for high-value utilization of new energy electrolyte dimethyl carbonate waste liquid. The device is particularly suitable for an industrialized DMC production system using synthesis gas as raw material and palladium chloride as catalyst, can realize efficient reuse of nitric acid components in the waste liquid, effective removal of chloride ions and zero hazardous waste discharge in the whole process, and has significant energy saving, emission reduction and cost reduction advantages. The present application not only solves the problem of high-salinity wastewater treatment in the traditional process, but also realizes the technical leap from "end treatment" to "source control" and "resource recycling" through process reconstruction and equipment innovation, and promotes the transformation and upgrading of the DMC industry to the green and low-carbon direction.

Description

Technical Field

[0001] This invention belongs to the field of dimethyl carbonate (DMC) production technology, specifically relating to an environmentally friendly device for the high-value utilization of waste dimethyl carbonate from new energy electrolytes. Background Technology

[0002] Currently, mainstream 100,000-ton / year dimethyl carbonate (DMC) production plants widely employ oxidative coupling processes based on the syngas route. This process uses a palladium chloride catalyst in the DMC synthesis section, generating the key intermediate methyl nitrite (MN) through a catalytic reaction involving nitric acid. This results in a large volume of complex wastewater containing residual nitric acid, chloride ions, trace amounts of organic acids (such as formic acid and oxalic acid), and other byproducts. This type of wastewater is characterized by high acidity, high salinity, high corrosiveness, and complex composition, making it extremely difficult to treat. Traditional treatment methods typically involve setting up an alkaline washing unit after the nitric acid reduction reactor, using sodium hydroxide (NaOH) solution to neutralize the wastewater and remove acidic components. The wastewater then enters a methanol dehydration tower for methanol recovery, and the bottom wastewater is cooled and sent to a wastewater treatment system. The wastewater treatment system uses two sets of evaporation desalination units. The saline DMC wastewater undergoes pretreatment, triple-effect high-temperature evaporation, and drying to form mixed salts, which are then treated as hazardous waste. The treated wastewater is then sent to a biological treatment system.

[0003] However, this technical approach suffers from a series of insurmountable technical bottlenecks and operational defects, specifically manifested as follows: 1. Significant Environmental Pressure and Hazardous Waste Treatment Challenges: Traditional wastewater treatment methods typically rely on chemical neutralization or physical separation techniques. The salts generated after NaOH neutralization mainly include various inorganic salts such as sodium nitrate, sodium nitrite, sodium chloride (NaCl), sodium formate, sodium oxalate, and sodium carbonate, forming a complex mixture of "mixed salts" that are difficult to separate and purify, classifying them as strictly controlled hazardous waste. On the one hand, if chloride and nitrate ions in chlorinated nitric acid wastewater are discharged directly without proper treatment, they will cause serious damage to aquatic ecosystems and may trigger secondary environmental problems such as soil acidification, posing extremely high environmental risks. On the other hand, the wastewater contains a large amount of salt, and treating this waste salt as hazardous waste is difficult and costly.

[0004] 2. Low resource utilization, resulting in double waste: These methods are not only energy-intensive, but also have a low recovery rate of effective components in the waste liquid, leading to resource waste. In the traditional process, 68% high-concentration HNO3 is used, and the unreacted nitric acid is completely neutralized by 32% NaOH, converting it into nitrate and losing its recovery value. This results in an overall nitric acid utilization rate of less than 80%, leading to serious waste of raw materials. At the same time, in order to complete the neutralization reaction, high-purity NaOH needs to be continuously added, further increasing chemical consumption and operating costs.

[0005] 3. High Energy Consumption and Operation and Maintenance Costs: To treat high-salinity wastewater, production enterprises generally construct multi-stage desalination systems, including membrane concentration pretreatment, triple-effect high-temperature evaporation crystallization, centrifugal dehydration, drying, and packaging storage. The entire system is lengthy, involves numerous types of equipment, occupies a large area, and requires a huge initial investment (up to tens of millions of yuan for a single system). During operation, the triple-effect evaporator consumes a large amount of medium-pressure steam (annual steam consumption can reach tens of thousands of tons), and the centrifuges and circulating pumps consume a lot of electricity. Furthermore, the reverse osmosis membrane is easily fouled and clogged by organic matter and suspended solids in the wastewater, requiring frequent cleaning. The system has a low continuous operation rate, a large maintenance workload, and often requires shutdown for cleaning, seriously affecting the stability of the main unit.

[0006] 4. Severe equipment corrosion restricts system stability: The waste liquid system contains both gaseous and liquid chloride and nitrate ions, which are highly corrosive to stainless steel under high temperatures (near 100°C), leading to a shortened equipment lifespan. Although some companies have attempted to use corrosion-resistant materials such as glass-lined surfaces, carbon fiber reinforced composites, or graphite heat exchangers, existing nitric acid reduction technologies cannot effectively control the localized accumulation of chloride ions, making long-term stable operation difficult and posing risks of leakage, shutdown, and even safety accidents. Especially during intermittent operation or load fluctuations, excessively high local chloride ion concentrations can easily trigger pitting corrosion, crevice corrosion, and other forms of damage.

[0007] Furthermore, while some companies have attempted to add nitric acid concentration and recovery units to reduce subsequent evaporation load, this only reduces the volume of high-salt wastewater and does not fundamentally solve the problem of mixed salt formation. They still need to rely on evaporation desalination systems, and the added equipment brings higher investment and energy consumption burdens, resulting in limited economic viability. At the same time, the concentration process itself also exacerbates equipment corrosion risks, further limiting its widespread application. Summary of the Invention

[0008] This invention aims to overcome the aforementioned deficiencies in existing technologies and provide a device and apparatus for the high-value recycling and utilization of dimethyl carbonate-containing chlorinated nitric acid wastewater that is structurally sound, stable in operation, energy-saving, and environmentally friendly. Its core objective is to eliminate the generation of impurities at the source of the process, achieve closed-loop reuse of nitric acid resources, completely eliminate the alkali neutralization and evaporation desalination processes, reduce energy consumption and hazardous waste disposal costs, and improve the inherent safety and economic benefits of the system. Through process innovation and equipment integration, this invention transforms wastewater treatment from "high energy consumption, high emissions, and high costs" to "low energy consumption, zero emissions, and high recovery," meeting the fundamental needs of modern chemical industry for green and sustainable development.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: An environmentally friendly device for the high-value utilization of waste dimethyl carbonate (DMC) electrolyte from a new energy source is proposed. Based on the DMC synthesis system, a high-efficiency dechlorination tank, a three-phase heat exchanger, and a methyl nitrite reactor are added, while the nitric acid reduction reactor and the entire evaporation and desalination system are eliminated. The specific reaction process is as follows: The circulating gas from the top of the light-duty removal tower has a flow rate of Q: 20,000~120,000 Nm. 3 / h, P: 0.2~0.9MPa, T: 20~70℃, composition: nitrogen (N2): 0~80%, carbon monoxide (CO): 0~20%, methyl nitrite (MN): 0~17%, nitric oxide (NO): 0~17%, methanol (ME): 0~10%, Cl - : 50~3000ppm; First, it is sent to the high-efficiency dechlorination tank, where the operating temperature is controlled at 10~70℃ and the pressure is maintained at 0.1~0.8MPa; After dechlorination treatment, a portion of the circulating gas (Q: 20000~110000Nm) is discharged through a three-way valve. 3 / h is introduced into the MN regeneration tower, and another part of the circulating gas Q: 6000~18000Nm 3 The solution, at a rate of 2000~13000 kg / h, passes through a three-phase heat exchanger and is heated by the purified liquid from the bottom of the methyl nitrite reactor (Q: 2000~13000 kg / h, T: 20~80℃, P: 0.2~0.9 MPa, composition: H2O: 0~90%, methanol (ME): 0~50%, dimethyl carbonate (DMC): 0~1%, dimethyl ether (DME): 0~1%, CO2: 0~1%) and the condensate from the steam drum of the DMC reactor. The heated gas enters the methyl nitrite reactor from the bottom, while the bottom liquid from the MN regeneration tower and the supplementary nitric acid enter the methyl nitrite reactor from the top, coming into countercurrent contact with the gas phase from the bottom of the tower to produce methyl nitrite. The internal temperature of the reactor is controlled at 60-70℃ and the pressure is maintained at 0.1-0.6MPa to promote the rapid progress of the reaction. The purified liquid at the bottom of the methyl nitrite reactor was then sent to the methanol dehydration tower. The wastewater after recovering methanol was cooled and then directly entered the sewage biological treatment pond for treatment. The system uses hot water from the steam drum condenser of the DMC reactor as the heat source.

[0010] Furthermore, the outlet pipeline of the high-efficiency dechlorination tank is equipped with an automatic HCl analyzer for real-time monitoring of hydrogen chloride concentration; the bottom outlet pipe of the methyl nitrite reactor is equipped with an automatic pH analyzer for monitoring changes in the acidity of the reaction solution.

[0011] Furthermore, the catalyst in the high-efficiency dechlorination tank is TCl1. The catalyst uses activated carbon as a carrier and is loaded with multiple active metal components such as palladium, titanium, molybdenum, and platinum, as well as trace rare earth elements. The active metal components and rare earth elements work synergistically to form multiple active sites. The catalyst forms a ruby ​​structure after high-temperature activation treatment, and the amount of rare earth elements added is 0.1% of the total mass of the catalyst.

[0012] Furthermore, the process for generating the catalyst TCl1 is as follows: Step 1: Pretreatment of activated carbon carrier Granular activated carbon is acid-washed to remove surface impurities; after acid washing, the activated carbon is washed with deionized water to obtain a pretreated activated carbon carrier, which is then placed in a dry place for later use. Step 2: Preparation of active components and rare earth element solutions Prepare the mixed impregnation solution according to the following steps: ① Prepare single-metal precursor solutions separately: Dissolve palladium chloride (palladium source) and ammonium molybdate (molybdenum source) in deionized water and stir until completely transparent to form a homogeneous aqueous solution; dissolve tetrabutyl titanate (titanium source) and chloroplatinic acid (platinum source) in anhydrous ethanol and stir until completely transparent to form a homogeneous ethanol solution. ② Preparation of rare earth solution: Dissolve rare earth reagents cerium nitrate or lanthanum nitrate in deionized water and stir until homogeneous; ③ Mixing and preparation: Pour the solutions prepared in ① and ② above into volumetric flasks in sequence, add dispersant, dilute to volume with deionized water, and stir to obtain a uniform multi-metal-rare earth mixed impregnation solution; Step 3: Step-by-step soaking Place the activated carbon carrier from step 1 into a constant temperature impregnation tank, pour in the multi-metal-rare earth mixed impregnation solution prepared in step 2, and impregnate multiple times under constant temperature. Step 4: Ultrasonic dispersion The carrier-solution mixture after impregnation in step 3 is transferred to an ultrasonic disperser for ultrasonic dispersion. The ultrasonic vibration breaks up the agglomerates of active components and rare earth elements, so that palladium, titanium, molybdenum, platinum and rare earth elements are uniformly dispersed on the surface of the activated carbon carrier. Step 5: Let it stand for aging The ultrasonically dispersed mixture was transferred to a constant temperature incubator and allowed to age statically, so that the active components, rare earth elements and activated carbon carrier could form a stable adsorption bond. Step 6: Filtering and washing The aged mixture was placed in a vacuum filter and solid-liquid separation was performed using a Buchner funnel. The filter cake was repeatedly washed with deionized water until there were no chloride or nitrate ions in the washing liquid. The filter cake was then filtered until there was no obvious dripping water, thus removing unloaded free active components and impurities to avoid impurities affecting the dechlorination performance and stability of the catalyst. Step 7: Low-temperature drying The washed supported semi-finished catalyst is placed in a low-temperature dryer to remove moisture; Step 8: High-temperature activation and annealing The dried semi-finished catalyst is placed in a programmed temperature reduction tube furnace and activated at high temperature in an H2-Ar2 mixed atmosphere using a programmed temperature rise mode. The high temperature activation causes the catalyst to form stable and reduced metal grains. This structure can effectively prevent the catalyst from pulverizing during use. After activation, the heating of the tube furnace is turned off, and the catalyst is cooled to room temperature under protective gas conditions to obtain catalyst monomer.

[0013] Furthermore, the tank body of the high-efficiency dechlorination tank is made of glass enamel to improve corrosion resistance.

[0014] Furthermore, the three-phase heat exchanger is divided into three independent chambers by a partition; the middle chamber carries circulating gas, while the two side chambers carry hot water and bottom liquid, respectively. The circulating gas inlet is located at the top of the three-phase heat exchanger and enters the flow channel between the heat exchange plates evenly through the distribution plate; after passing through the flow channel, the circulating gas is finally discharged from the bottom outlet. The flow path of the liquid phase is divided into two paths. The hot water inlet is located at the bottom of the three-phase heat exchanger and enters the gap between the plates through the flow guiding structure. The liquid forms a thin layer flow between the plates and is arranged in an alternating manner with the gas flow channel, thereby realizing countercurrent heat exchange between the cold and hot fluids. The liquid in the bottom of the tower enters the heat exchanger through the side inlet, flowing in the same direction as the circulating gas, moving along the flow channel and exchanging heat with the plate surface. The outlet is located on the side of the equipment.

[0015] Furthermore, the heat exchange plate of the three-phase heat exchange is 0.5-1.0 mm thick, the substrate is manufactured by explosive welding process, and a fully welded structure is adopted; the core heat transfer element is a corrugated plate bundle.

[0016] Furthermore, the methyl nitrite reactor adopts a three-chamber vertical series layout, arranged sequentially along the vertical direction. Each reaction chamber is a vertical tube reactor, and the material is transferred step by step through internal channels.

[0017] Furthermore, the pipeline liquid distributor of the methyl nitrite reactor integrates the distribution head and the riser pipe into a single unit, forming a pipeline liquid distributor. The reaction liquid is guided into the riser pipe through small holes to form a uniform liquid film, thereby improving the uniformity of liquid distribution. This solves the problem that traditional liquid distributors, which generally use perforated plates or spray structures, are prone to uneven liquid distribution, especially under high flow rate or low surface tension liquid conditions, making it difficult to form a uniform liquid film, thus enhancing the operational stability of the reactor.

[0018] The improvements and design principles of this invention are as follows: 1. Source Control and Process Restructuring: Instead of being sent to the alkaline washing system, the chlorinated nitric acid wastewater, which originally required neutralization, undergoes absorption and dechlorination (catalytic absorption) to simultaneously capture and fix chloride ions in the system, preventing their toxicity to subsequent equipment and catalysts. This achieves both resource recovery and corrosion control. The wastewater is then directly introduced into the MN regeneration tower and methyl nitrite reactor system, realizing closed-loop reuse of the wastewater and avoiding external discharge of nitric acid.

[0019] 2. Catalytic nitric acid and resource conversion proceed simultaneously: In the methyl nitrite reactor, the supplemented nitric acid reacts with excess methanol and circulating gas to produce methyl nitrite (MN). The complete reaction of nitric acid avoids its corrosive effect on equipment and systems, achieving "two effects in one device"—both resource recovery and corrosion control.

[0020] 3. Precise thermal management ensures safe operation: The endothermic reaction is discharged in real time through a high-efficiency heat exchange unit, maintaining the reaction temperature stable within the optimal window. This ensures the MN product specifications and prevents side reactions or equipment damage. At the same time, the use of hot water from the steam drum of the synthesis system for heating reduces the amount of circulating cold water needed for the steam drum hot water condensate cooler, achieving energy cascade utilization.

[0021] 4. Clean emissions and resource output: After the reaction is completed, the product is separated into gas and liquid phases. The MN gas is sent back to the main process line for DMC synthesis, realizing a closed-loop resource system. The liquid phase product is mainly composed of water and trace organic matter, with extremely low salt content (total dissolved solids <50mg / L) and chemical oxygen demand (COD) <20 mg / L. It can be directly introduced into the wastewater biological treatment system without the need for evaporation and desalination.

[0022] 5. Cost-saving and performance guarantee: The existing equipment layout is very compact, with no more space for additional equipment. The existing nitric acid reduction reactor and its surrounding area are utilized as much as possible for layout, eliminating the gas booster and liquid booster pump. The system's own pressure difference is used as much as possible to optimize the number of equipment and process flow. At the same time, the system pressure drop is guaranteed to meet the requirements for gas and liquid output. This not only saves investment and speeds up the construction progress, but also reduces operating costs, while ensuring that all indicators meet the standards.

[0023] The beneficial effects of this invention are as follows: 1. Eliminate hazardous waste emissions The unreacted nitric acid from the nitric acid reduction reactor of the 100,000-ton DMC unit is directly neutralized with sodium hydroxide, resulting in wastewater containing a large amount of salt (4,000 tons / year). Approximately 12 tons of mixed salt are produced daily. Current operational problems include: 1) The supporting wastewater evaporation unit is severely inefficient due to the high boiling point organic matter and high salt content in the wastewater, with evaporation only reaching 60%–70% of the design load, wasting a large amount of steam; 2) High maintenance difficulty: frequent pipe blockage due to salt buildup requires frequent shutdowns for maintenance; 3) The fine particles of crystalline salt prevent the centrifuge from operating normally, forcing manual salt removal, which is labor-intensive, wasteful, and creates a poor working environment with safety hazards; 4) High cost: the mixed salt contains organic matter, making it difficult to dispose of as ordinary solid waste. Treatment as hazardous solid waste is expensive. Based on an annual production of approximately 4,000 tons of hazardous waste mixed salt, the outsourced disposal cost alone reaches 3,600 yuan / ton, with annual expenditures approaching 14 million yuan, not including the increased steam and electricity consumption due to inefficiency. 5) Inventory backlog: Due to its extremely large production volume, it is difficult for general hazardous waste disposal centers to handle it. Hazardous waste disposal channels are limited, and the storage space for miscellaneous salts is also limited. Once the storage space is full, it will cause the DMC system to shut down, which will seriously affect the continuity of production.

[0024] This case fundamentally optimizes the process route: by optimizing the treatment of nitric acid involved in the reaction, a distillation separation unit is added to distill, purify, and reuse it, significantly reducing the amount of nitric acid used. The elimination of the alkali neutralization step fundamentally blocks the formation pathway of sodium nitrate, sodium nitrite, and other miscellaneous salts. The resulting wastewater can be directly sent to the biological treatment tank. The system no longer generates hazardous waste requiring outsourced disposal, saving steam, electricity, and treatment costs associated with miscellaneous salt treatment. This not only solves the environmental problem of miscellaneous salts but also saves a significant amount of steam and electricity. It not only alleviates the long-standing environmental compliance pressures and social responsibility risks that have plagued production but also significantly improves the company's economic benefits through resource recycling, achieving "zero hazardous waste" emissions. This is of great strategic significance for ensuring the long-term stable operation of the DMC unit.

[0025] 2. Effectively extend the service life of key equipment By leveraging dechlorination catalysts and precise temperature control technology, the long-standing problems of localized chloride ion enrichment and high-temperature corrosion that have plagued the industry have been successfully solved. This extends the service life of the reactor and related pipelines and valves by more than two times, reduces the number of unplanned shutdowns, and extends the operating cycle of the equipment to more than two years.

[0026] 3. Significantly saves resources and operating costs From an economic perspective, this device outperforms the original device in terms of engineering investment, raw material savings, energy consumption reduction, and labor and maintenance cost reduction.

[0027] 4. Environmental benefits By introducing this equipment and device, the treatment efficiency of chlorinated nitric acid waste liquid has been significantly improved, while the amount of pollutant emissions has been greatly reduced, resulting in positive environmental benefits.

[0028] 5. The technology is highly replicable and has a wide range of applications. This invention is not only applicable to the synthesis of DMC from syngas, but can also be extended to other chemical processes involving chlorine-containing nitric acid systems, such as the synthesis of nitro compounds and the production of pharmaceutical intermediates, and has broad prospects for industrialization. Attached Figure Description

[0029] Figure 1 This is the original dimethyl carbonate production process flow chart; Figure 2 This is a flow chart of the dimethyl carbonate production process of the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: like Figure 1 As shown, the original equipment flow chart for the DMC process is as follows: DMC gas removal tower top gas phase (Q: 20000~120000Nm) 3 / h, P: 0.2~0.9MPa, T: 20~70℃, composition: nitrogen (N2): 0~80%, carbon monoxide (CO): 0~20%, methyl nitrite (MN): 0~17%, nitric oxide (NO): 0~17%, methanol (ME): 0~10%, Cl - (50~3000ppm) Partial (Q: 20000~110000Nm) 3 The solution ( / h) is sent to the MN regeneration tower. The bottom liquid of the MN regeneration tower (Q: 4000~10000Kg / h, P: 0.4~0.7MPa, T: 20~60℃, composition ME: 0~69%, HNO3: 0~12%, DMC: 0~15%, H2O: 0~50%, CO2: 0~2.5%, Cl) is also supplied. - (50~3000ppm) is sent to the nitric acid reduction reactor. The gas from the top gas phase outlet pipeline of the MN regeneration tower is sent to the DMC circulating gas compressor.

[0031] A portion of the recycle gas from the top of the DMC gas removal tower (Q: 6000~18000Nm) 3 The solution ( / h) is sent to four nitric acid reduction reactors, where it enters the liquid phase bubbling stage. The bottom liquid pumped from the MN regeneration tower and the supplementary HNO3 react together in the nitric acid reduction reactor under stirring to generate MN. The resulting MN-containing gas (Q: 7000~19000 Nm³) 3 / h, P: 0.2~0.6MPa, T: 30~80℃, composition N2: 0~60%, CO: 0~18%, NO: 0~12%, MN: 0~12%, CO2: 0~6%, H2O: 0~5%, dimethyl ether (DME): 0~3%, H2: 0~2%, Cl - (50~3000ppm) enters the middle of the MN regeneration tower. The liquid from the nitric acid reduction reactor is sent to an alkali treatment tank where HNO3 is neutralized with NaOH solution. The liquid in the alkali treatment tank (Q: 3000~16000Kg / h, T: 40~70℃, P: 0~0.2MPa, composition: H2O: 0~80%, ME: 0~50%, DMC: 0~10%, NaCO3: 0~3%, NaNO3: 0~3%, NaCl 10~100ppm, DME: 0~3%, CO2: 0~2%) is sent to a methanol dehydration tower. Methanol is recovered at the top of the tower. The bottom liquid of the methanol dehydration tower (Q: 4000~20000Kg / h, T: 20~60℃, composition: H2O: 0~98%, NaCO3: 0~5%, NaNO3: 0~5%, HCOONa: 0~2%, NaNO2: 0~1.5%, (COONa)2: 0~800ppm, NaCl) 10~100ppm, ME: 0~500ppm, COD 1000~20000, BOD 5300~1200, TN 200~2000, TDS 300~15000) sent to wastewater treatment.

[0032] The bottom liquid from the methanol dehydration tower enters the acidification tank, where nitric acid is added to control the pH at around 1, and the mixture is stirred before being fed into the resin adsorption unit. This special resin can adsorb organic matter under high salinity conditions. The adsorbed effluent is neutralized in a neutralization tank with 32% NaOH to control the pH at around 7 before entering a triple-effect evaporator. The wastewater is concentrated, and the evaporation condensate is sent to the biochemical tank. The concentrated evaporate containing crystalline salts is directly sent to a centrifuge for separation. The separated and dried crystalline salts are directly packaged and treated as solid waste.

[0033] The hot water temperature in the steam drum of the DMC reactor is 90~120℃. Because the hot water absorbs the heat generated by the reaction, some of it vaporizes into steam, so hot water needs to be replenished into the steam drum. After entering the steam drum condenser, the hot water mixes with hot water from outside the boundary and then enters the hot water storage tank. The hot water from the outlet of the storage tank is pressurized by the hot water feed pump and then cooled by a hot water cooler to maintain its temperature at 80℃ before being sent to the DMC reactor steam drum.

[0034] like Figure 2 As shown, the process of the present invention is as follows: To achieve high-value recycling of dimethyl carbonate (DMC) chlorinated nitric acid waste liquid, this design adds a high-efficiency dechlorination tank, a three-phase heat exchanger, and a methyl nitrite reactor to the existing DMC synthesis system, while eliminating the nitric acid reduction reactor and the entire evaporation and desalination system. Specifically, the circulating gas from the top of the light-light carbon removal tower (Q: 20000~120000 Nm³) 3 / h, P: 0.2~0.9MPa, T: 20~70℃, composition: nitrogen (N2): 0~80%, carbon monoxide (CO): 0~20%, methyl nitrite (MN): 0~17%, nitric oxide (NO): 0~17%, methanol (ME): 0~10%, Cl - The hydrogen chloride (50~3000ppm) is first fed into the newly added high-efficiency dechlorination tank, which is made of glass-lined material to ensure good corrosion resistance. An automatic HCl analyzer is installed on the outlet pipeline for real-time monitoring of the hydrogen chloride concentration. Based on actual operating data, the operating temperature of the high-efficiency dechlorination tank is controlled between 10 and 70℃, and the pressure is maintained within the range of 0 to 0.8MPa to ensure the smooth progress of the reaction. Subsequently, the dechlorinated circulating gas is partially discharged through a three-way valve (Q: 20000~110000Nm³). 3 / h) is introduced into the MN regeneration tower, and another part (Q: 6000~18000Nm) 3 The gas (Q: 2000~13000Kg / h, T: 20~80℃, P: 0.2~0.9MPa, composition H2O: 0~90%, methanol ME: 0~50%, dimethyl carbonate DMC: 0~1%, dimethyl ether DME: 0~1%, CO2: 0~1%) and the condensate from the steam drum of the DMC reactor are heated by a three-phase heat exchanger. This equipment is made of 316L stainless steel, which has good high-temperature resistance and corrosion resistance. The heated gas enters the methyl nitrite reactor from the bottom. Due to the presence of nitric acid, 304L stainless steel is selected to ensure corrosion resistance under high-temperature conditions. At the same time, the bottom liquid from the MN regeneration tower and the supplementary nitric acid enter the methyl nitrite reactor from the top, and come into countercurrent contact with the gas phase from the bottom of the tower, causing the reaction of nitric acid to generate methyl nitrite. The internal temperature of the reactor is controlled at 10~70℃ and the pressure is maintained at 0.1~0.6MPa to promote the rapid progress of the reaction. An automatic pH analyzer is installed at the bottom outlet pipe of this reactor to monitor changes in the acidity of the reaction solution, thereby controlling the amount of nitric acid added and the reaction conditions. The purified liquid from the bottom of the methyl nitrite reactor is then sent to a methanol dehydration tower. The wastewater after methanol recovery is cooled and directly enters the wastewater biological treatment pond for further treatment. Hot water from the steam drum condenser of the DMC reactor is used as the heat source. The operating parameters of the entire system are monitored and adjusted in real time through a distributed control system (DCS), ensuring the coordinated operation of each device and the stability of the overall process.

[0035] Design principle of this invention: 1. The equipment has a very small voltage drop, relying solely on the system's own voltage drop, saving energy without the need for booster equipment: The system pressure drop is no greater than 30 kPa, and the circulating gas can return to the system without pressurization. The pressure drop of the high-efficiency dechlorination tank is approximately 2 kPa, the three-phase heat exchanger approximately 5 kPa, and the methyl nitrite reactor approximately 10 kPa. Therefore, no additional booster pump or reflux booster pump is needed. This saves investment and ensures that the circulating gas can be directly returned to the synthesis system after the MN reaction. The booster pump, as a rotating device, has high power consumption and a certain failure rate. Without a backup unit, a failure will lead to a plant shutdown.

[0036] 2. No steam consumption The hot water temperature in the steam drum of the DMC reactor is about 100℃, which needs to be cooled down to 80℃ by a cooler for recycling. This system uses this hot water as its heat source, which saves electricity for the air cooler and eliminates the need to consume low-pressure steam, thus greatly reducing costs.

[0037] 3. High-efficiency dechlorination tank The high-efficiency dechlorination tank is one of the core devices in this design for removing chlorine from waste gas and waste liquid. The main reason for choosing a glass-lined tank is that the chloride ion content in the circulating gas is high, exceeding 2000 ppm. When chloride ions coexist, the oxidizing power of nitric acid is further enhanced, leading to accelerated corrosion of the equipment materials. Chloride ions, with their high polarization and coordination ability, easily form complexes with metal ions, thus accelerating the corrosion process of metal materials. Due to the presence of chloride ions, the equipment and internal components can only be made of special materials such as glass-lined tanks, carbon fiber, graphite, PETG, ceramics, and PI, while nitric acid can only be made of 304 or 304L stainless steel. Glass-lined tanks have excellent corrosion resistance and chemical stability, effectively resisting the erosion of the equipment by acidic components in the waste liquid. Furthermore, the smooth surface of glass-lined tanks does not easily attract impurities, facilitating cleaning and maintenance, thereby extending the service life of the equipment.

[0038] This dechlorination catalyst, TCl1, is a key material specifically designed to remove chlorine or chloride impurities, preventing environmental pollution and catalyst poisoning. It primarily removes hydrogen chloride (HCl) and other chlorine-containing impurities from gaseous or liquid states through a combination of physical adsorption and chemical reaction. The main reaction for dechlorination is... HCl + CH3OH → CH3Cl + H2O This reaction efficiently removes chlorine by reacting hydrogen chloride (HCl) in the circulating gas with methanol to produce chloromethane (CH3Cl) and water. Experimental studies show that under suitable temperature and pressure conditions, the chlorine removal rate of this reaction can reach over 98%, significantly reducing the risk of corrosion to downstream equipment from the waste gas and liquid.

[0039] The preparation method of the dechlorination catalyst TCl1 is as follows: support pretreatment → preparation of active component and rare earth element solution → stepwise impregnation (multi-metal + rare earth) → ultrasonic dispersion → static aging → filtration and washing → low temperature drying → high temperature activation → sieving → finished catalyst.

[0040] (1) Raw material preparation The raw materials used are categorized by function into carrier-related raw materials, active component precursors, rare earth element raw materials, and auxiliary raw materials, as detailed below: Carrier-related raw materials: granular activated carbon (preferably coconut shell activated carbon, particle size 2-5mm, specific surface area 800-1200m² / g), 10% hydrochloric acid (HCl), and deionized water. Hydrochloric acid is used to remove impurities from the carrier, and deionized water is used for washing and solution preparation to avoid impurities affecting catalyst performance. Active component precursors: palladium source (palladium chloride, purity ≥99.5%), titanium source (tetrabutyl titanate, purity ≥99%), molybdenum source (ammonium molybdate, purity ≥99%), and platinum source (chloroplatinic acid, purity ≥99.9%). High-purity precursors are selected to ensure the purity and catalytic activity of the active components. Rare earth element raw material: cerium nitrate (purity ≥99%), added at 0.1% of the total catalyst mass; even a trace amount can achieve synergistic effects with multiple metals. Auxiliary raw materials: polyethylene glycol, deionized water, and anhydrous ethanol. Polyethylene glycol is used as a dispersant to prevent the aggregation of active components, while anhydrous ethanol is used to dissolve precursors such as titanium and platinum sources that are difficult to dissolve in water, ensuring a homogeneous solution.

[0041] (2) Equipment preparation Carrier pretreatment equipment: glass reactor, constant temperature water bath, vacuum filter, deionized water generator, used for impurity removal, washing and separation of the carrier; Solution preparation equipment: electronic balance (accuracy 0.001g), volumetric flask, pipette, magnetic stirrer, used for accurate weighing of raw materials and preparation of uniform mixed impregnation solution; Impregnation and dispersion equipment: ultrasonic disperser (power 200-500W), constant temperature impregnation tank, used for uniform loading and dispersion of active components to avoid agglomeration; Drying and activation equipment: forced air drying oven, programmed temperature rise tube reduction furnace (maximum temperature ≥1000℃, precise temperature control), used for catalyst drying and high-temperature activation and annealing steps; Post-processing equipment: standard inspection sieve (2-5mm aperture), sealing packaging machine, used for catalyst screening and storage to ensure that the catalyst particle size meets the requirements of the high-efficiency dechlorination tank and avoid moisture contamination.

[0042] (3) Detailed preparation steps Step 1: Pretreatment of activated carbon carrier Granular activated carbon was added to a glass reactor, and a 10% hydrochloric acid solution was poured in, controlling the solid-liquid ratio at 1:5 (mass-volume ratio). A constant temperature water bath was turned on, and the temperature was controlled at 40℃. The mixture was stirred for 2 hours. Through the acid washing action of hydrochloric acid, impurities, ash, and metal oxides on the surface of the activated carbon carrier were removed. At the same time, the carrier surface was activated, increasing the specific surface area and adsorption performance of the carrier, laying the foundation for subsequent loading of active components. After acid washing, the activated carbon was repeatedly washed with deionized water until the washing solution was neutral (pH=6.5-7.5). The solution was then filtered through a vacuum filter to obtain the pretreated activated carbon carrier, which was then placed in a dry place for later use.

[0043] Step 2: Preparation of active components and rare earth element solutions The raw materials were accurately weighed using an electronic balance, and the mixed impregnation solution was prepared according to the following steps: ① Prepare single-metal precursor solutions separately: Dissolve palladium source (palladium chloride) and molybdenum source (ammonium molybdate) in deionized water and stir until completely transparent to form a homogeneous aqueous solution; dissolve titanium source (tetrabutyl titanate) and platinum source (chloroplatinic acid) in anhydrous ethanol and stir until completely transparent to form a homogeneous ethanol solution; ② Prepare rare earth solution: Dissolve rare earth reagent (cerium nitrate or lanthanum nitrate) in deionized water and stir until homogeneous; ③ Mix and adjust: Pour the above single-metal aqueous solution, single-metal ethanol solution and rare earth solution into volumetric flasks in sequence, add a small amount of polyethylene glycol as a dispersant, dilute to volume with deionized water, turn on the magnetic stirrer and stir for 30 minutes to obtain a homogeneous multi-metal-rare earth mixed impregnation solution, in which the total concentration of active components is 2%-5% and the concentration of rare earth is 0.01%-0.05%, ensuring that the active components and rare earth elements are uniformly dispersed.

[0044] Step 3: Step-by-step soaking The pretreated activated carbon carrier was placed in a constant temperature impregnation tank, and the prepared multi-metal-rare earth mixed impregnation solution was poured in, controlling the liquid-solid ratio to be 1:3 (mass-volume ratio). The temperature of the constant temperature impregnation tank was controlled at 50℃. The carrier was first stirred and impregnated for 1 hour, and then allowed to stand for 1 hour. This operation was repeated twice. Stepwise impregnation ensures that the active components and rare earth elements fully penetrate into the pores of the activated carbon carrier, avoiding the problem of uneven loading caused by single impregnation. After the last impregnation, the carrier was stirred for another 30 minutes to further ensure that the multi-metal and rare earth elements were uniformly adsorbed on the surface and in the pores of the carrier, laying the foundation for the formation of multiple active sites.

[0045] Step 4: Ultrasonic dispersion The impregnated carrier-solution mixture was transferred to an ultrasonic disperser, and the ultrasonic power was adjusted to 300W. The mixture was ultrasonically dispersed for 20-30 minutes. The ultrasonic vibration broke up the agglomerates of active components and rare earth elements, so that palladium, titanium, molybdenum, platinum and rare earth elements were uniformly dispersed on the surface of the activated carbon carrier. This avoided the reduction of active sites caused by agglomeration, further enhanced the dispersibility of multiple active sites and improved the dechlorination activity of the catalyst.

[0046] Step 5: Let it stand for aging The ultrasonically dispersed mixture was transferred to a constant temperature incubator and kept at 25°C for 4-6 hours to allow the active components, rare earth elements and activated carbon support to form a stable adsorption bond, reduce the shedding of active components in subsequent steps and improve the stability of the catalyst.

[0047] Step 6: Filtering and washing The aged mixture is placed in a vacuum filter and solid-liquid separation is performed using a Buchner funnel. The filter cake (i.e., the supported semi-finished catalyst) is repeatedly washed with deionized water until there are no chloride ions or nitrate ions in the washing liquid (this can be tested with silver nitrate solution; the absence of white precipitate indicates it is qualified). The filter cake is then filtered until there is no obvious dripping water, removing unloaded free active components and impurities to avoid impurities affecting the dechlorination performance and stability of the catalyst.

[0048] Step 7: Low-temperature drying The washed supported semi-finished catalyst is placed in a forced-air drying oven and dried at 110℃ for 8-10 hours to slowly remove free water from the catalyst, retain the bond between the active components and the support, avoid direct high-temperature drying which could cause cracking of the activated carbon support, and ensure the integrity of the catalyst.

[0049] Step 8: High-temperature activation and annealing (core step) The dried semi-finished catalyst was placed in a temperature-programmed reduction tube furnace and activated at high temperature in an H2-Ar2 mixed atmosphere (H2 / Ar2 volume ratio 95:5). The specific heating process was as follows: the temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 hour to remove the water of crystallization from the catalyst; then the temperature was increased to 500℃ at a rate of 10℃ / min and held for 2 hours to decompose the metal precursor into metal oxides and form the active phase; finally, the temperature was increased to 800-900℃ at a rate of 8℃ / min and held for 3 hours to form stable and reduced metal grains in the catalyst through high-temperature activation. This structure can effectively prevent the catalyst from pulverizing during use and further improve the stability and durability of the catalyst. After activation, the heating of the tube furnace was turned off, and the catalyst was cooled to room temperature under protective gas conditions to obtain the catalyst monomer.

[0050] Step 9: Screening and Finished Product The cooled catalyst monomers are sieved using a standard inspection sieve with a pore size of 2-5 mm to remove broken particles and powder, resulting in catalyst particles with uniform particle size. This ensures that the catalyst particle size meets the usage specifications of the high-efficiency dechlorination tank. After sieving, the catalyst is sealed and packaged using a sealing packaging machine to prevent it from getting damp or contaminated. The finished TCl1 catalyst can then be directly loaded into the high-efficiency dechlorination tank for use.

[0051] Compared with the prior art, the present invention has the following significant advantages: The catalyst of this invention uses activated carbon as a carrier and loads multiple metals such as palladium, titanium, molybdenum, and platinum, as well as trace rare earth elements. Through the synergistic effect of multiple metals and rare earths, multiple active sites are formed. Compared with existing single metal or bimetallic catalysts, it significantly improves the adsorption and conversion capacity of chloride ions, with a chloride ion removal rate of not less than 98% and a significant improvement in chloride removal efficiency.

[0052] The catalyst undergoes high-temperature activation treatment to form a stable structure, effectively avoiding pulverization during use. It also enhances the catalyst's adaptability to a wide temperature range (200-500℃) and different pressure conditions, exhibiting excellent stability and durability. Its service life is extended by 2-3 times, reducing the frequency of catalyst replacement and lowering production costs and maintenance difficulty.

[0053] The preparation process of this invention is simple, highly operable, and controllable. It employs stepwise impregnation and ultrasonic dispersion processes to ensure uniform loading of active components and avoid agglomeration. The preparation process does not require complex equipment, is easy to scale up for industrial production, and can achieve batch preparation to meet the needs of large-scale use of high-efficiency dechlorination tanks.

[0054] The catalyst is made from high-purity raw materials, and the preparation process produces no harmful pollutants, making it green and environmentally friendly. The catalyst has uniform performance and is suitable for use in various high-efficiency dechlorination tanks. It can be widely used in chemical, environmental protection, water treatment and other fields, with broad application prospects. The catalytic performance indicators are shown in Table 1.

[0055] Table 1 - Catalyst Performance Indicators 4. Three-phase heat exchanger This high-efficiency heat exchange equipment uses a three-phase heat exchanger to achieve simultaneous indirect heat exchange between three fluids: circulating gas, hot water from the steam drum of the DMC reactor, and liquid from the bottom of the methyl nitrite reactor. The core of this equipment is to allow the three media to complete heat transfer and distribution simultaneously through a special flow channel structure, replacing two two-phase heat exchangers and achieving system integration and energy efficiency improvement.

[0056] In this three-phase heat exchanger, the interior is divided into three independent chambers by partitions. The middle chamber carries circulating gas, while the two side chambers carry hot water and the bottom liquid, respectively. The circulating gas inlet is located at the top of the heat exchanger and enters the flow channels between the heat exchange plates evenly through a distribution plate. As the gas flows downwards along the channels, its velocity distribution gradually becomes uniform, eventually exiting from the bottom outlet. The liquid phase flows in two separate paths: the hot water flows in the opposite direction, with its inlet located at the bottom of the heat exchanger and entering the gaps between the plates through a guide structure. The liquid forms a thin layer of flow between the plates, interspersed with the gas flow channels, thus achieving countercurrent heat exchange between the hot and cold fluids. The bottom liquid enters the heat exchanger through a dedicated inlet, flowing in a direction opposite to the circulating gas, moving along a specifically designed flow channel while exchanging heat with the plate surfaces. The outlet is located on the side of the equipment. This flow path design not only improves the heat transfer efficiency of the fluids but also significantly reduces pressure drop, ensuring stable operation under complex conditions. Heat transfer between the three phase fluids is not entirely independent, but rather interconnected through the thermal conductivity of the plate materials, forming a complex coupled heat transfer system. The heat exchanger can effectively regulate the temperature distribution of each phase fluid, avoiding side reactions caused by localized overheating or undercooling, thereby improving the system's energy utilization and reaction selectivity. Compared to traditional heat exchange equipment, this three-phase heat exchanger exhibits significant performance advantages in terms of heat exchange efficiency, pressure loss, and floor space.

[0057] This three-phase heat exchanger, as a highly efficient and compact heat exchange device, employs explosive welding technology for the manufacture of its heat exchange plates. The heat exchange plates are one of the core components of the three-phase heat exchanger, and their design parameters significantly impact the overall performance of the equipment. Its basic structure consists of multiple layers of stacked metal plates, with a plate thickness of 0.5-1.0 mm, ensuring good thermal conductivity and mechanical strength. Its core heat transfer element is a corrugated plate bundle. When the fluid flows within the flat flow channels, the corrugated structure generates a strong "static stirring" effect, creating turbulence even at low Reynolds numbers, greatly improving the surface heat transfer coefficient. The hot and cold fluids flow in a pure counter-current manner within the plate channels and outside the plate space, resulting in a large average temperature difference, high heat utilization, and a terminal temperature difference as low as 1℃. The flow channel dimensions are optimized according to specific operating conditions, typically with a width ranging from 0.5-6 mm and a depth ranging from 0.5-6 mm, ensuring uniform and continuous distribution and avoiding localized overheating or flow dead zones.

[0058] The corrugated plate bundle has a herringbone pattern, oblique corrugations, or a combination of corrugations. The fluid forms a thin flow layer of 0.5-1.0 mm thickness and a velocity of 0.5-2.0 m / s between the plates, effectively disrupting the boundary layer and improving the heat transfer coefficient. The heat exchanger of this invention has an overall heat transfer coefficient more than five times that of a shell-and-tube heat exchanger, a heat transfer coefficient greater than 2500 W / (m²・K), a large average temperature difference, and a terminal temperature difference as low as 1°C. It is lightweight and has a small footprint, significantly reducing equipment investment and operating costs. The heat exchanger is made of 316L material, which has excellent high-temperature resistance and corrosion resistance, making it suitable for handling gaseous media containing acidic components.

[0059] The three-phase heat exchanger of this invention has the following characteristics: Low pressure drop: Adjustable plate spacing and height achieve low pressure drop across the fluid on both sides. The pressure drop can be as low as 0.05 kPa, effectively reducing energy consumption.

[0060] High pressure resistance: The equipment has high structural stability, can withstand a pressure difference of more than 100 bar on both sides, and can adapt to negative pressure-vacuum conditions.

[0061] The structure is very compact, saving up to 45% of steel compared to traditional shell and tube heat exchangers, and has a small footprint, making it easier to install, transport and lay out pipelines.

[0062] 5. Methyl nitrite reactor Limitations of traditional reaction equipment 1) Low nitric acid recovery rate: Traditional equipment has difficulty in achieving a nitric acid recovery rate of over 80%. For example, traditional reaction equipment such as bubble reactors dominated early applications, and the utilization rate of nitric acid was only 75% when two units were connected in parallel. Currently, the nitric acid recovery rate of four parallel single-stage stirred nitric acid reduction reactors is difficult to exceed 80%, resulting in serious waste of resources.

[0063] 2) Large equipment footprint: To ensure pressure drop, the equipment is connected in parallel. The two bubble reactors are huge, and the four nitric acid reduction reactors not only occupy a large space, but also have complex piping.

[0064] 3) High operating costs: Traditional processes have high energy consumption, including high steam consumption and high electricity consumption, as well as high maintenance costs.

[0065] 4) Poor control precision: It is difficult to achieve precise temperature control and material ratio. The nitric acid reduction reaction is usually accompanied by complex side reactions, such as the formation of methyl nitrate, which leads to the harm of methanol dehydration tower treatment in the downstream system.

[0066] 5) Safety hazards: The problem of gas-liquid phase retention is common. Once the corroded MN leaks, there will be an explosion hazard.

[0067] Although current research has made some progress in nitric acid reaction equipment and MN synthesis processes, significant research gaps remain in achieving low pressure drop, complete reaction, no gas-liquid phase retention, precise temperature control, and high nitric acid utilization. First, due to limitations in structural design, traditional reaction equipment often struggles to achieve complete reaction under low pressure conditions, resulting in low nitric acid utilization. Second, gas-liquid phase retention is a common problem in existing equipment, which not only affects reaction efficiency but can also lead to equipment corrosion and safety hazards. Furthermore, the temperature control systems in existing equipment are externally jacketed, making precise temperature control difficult and thus limiting further improvements in reaction selectivity and conversion rate.

[0068] To address the aforementioned issues, the combined methyl nitrite reactor, through its multi-chamber vertical series layout, multi-stage reaction design, and advanced temperature control technology, successfully fills this research gap, demonstrating significant technological innovation and application potential. The methyl nitrite reactor is another core piece of equipment in this design used to achieve the reaction of nitric acid to methyl nitrite. It is made of 304L stainless steel, which has excellent resistance to nitric acid corrosion and mechanical strength. The reactor is directly connected to the circulating gas from the DMC synthesis section, and reacts with the supplemented 68% nitric acid solution and methanol from the MN regeneration tower bottom liquid under mild conditions to produce methyl nitrite (MN). Through multi-stage reactions, the reaction efficiency is improved, ensuring that the MN concentration in the outlet gas is increased to ~17%, and the nitric acid content in the waste liquid is reduced to below 1 ppm, achieving the resource reuse of nitric acid.

[0069] The technical solution of the methyl nitrite reactor of the present invention This design employs a three-chamber vertical series layout, arranged sequentially along the vertical direction. Each reaction chamber is a vertical tube reactor, with material transfer achieved through internal channels. Without catalysts or packing materials, this layout effectively reduces system pressure drop while providing ample space for gas-liquid contact and reaction. Within each reaction chamber, the residence time of materials is precisely controlled, ensuring the sufficiency and stability of the reaction process. Furthermore, the multi-chamber vertical series design reduces gas-liquid phase stagnation, avoiding side reactions or equipment corrosion caused by localized accumulation. By optimizing the pressure distribution and material flow paths between the reaction chambers, the three stages are seamlessly connected through a precise material transfer and control system, forming a highly efficient and stable reaction system. This design significantly improves overall reaction efficiency while reducing energy consumption and operational complexity. Results show that the reactor's structural design effectively controls the accumulation of trace chloride ions, preventing corrosion of downstream equipment, and achieves precise temperature control, thereby enhancing the overall process stability and safety.

[0070] The liquid distributor head is a core component of the liquid distributor, responsible for uniformly distributing the liquid entering the reactor into hundreds or thousands of risers. Traditional liquid distributors generally employ perforated plates or spray structures, which easily lead to uneven liquid distribution, especially under high flow rate or low surface tension liquid conditions, making it difficult to form a uniform liquid film. Secondly, some liquid distributors are prone to clogging due to their small orifice diameter, especially when processing liquids containing solid particles. Furthermore, the structure of existing liquid distributors is often overly complex, increasing manufacturing costs and the difficulty of installation and maintenance. This invention solves many problems of existing reactor liquid distributors through an innovative design of a novel pipeline liquid distributor, thereby significantly improving the reactor's operating efficiency and economy. Specifically, the distributor head is welded to the riser pipe to form a highly efficient pipeline liquid distribution system, achieving uniform liquid distribution through a precisely designed perforation layout. This design not only effectively avoids the problems of high manufacturing costs and difficult maintenance caused by the complex structure of traditional distributors, but also significantly improves the uniformity of liquid distribution, thereby enhancing the mass and heat transfer efficiency within the tower. Furthermore, the application of new liquid distributors is expected to reduce equipment failure rates and extend equipment lifespan. The primary task of the distributor head is to ensure the formation of a uniform liquid film within the pipe. After the reaction liquid enters the reactor, it must form a uniformly thick liquid film along the pipe wall. Only in this way can the counter-current gas efficiently contact the liquid for reaction. Preventing flow deviation: Without a distributor head or with uneven distribution, the liquid velocity and flow rate within the pipe will be inconsistent (some pipes will have more flow, some less), which will lead to a significant decrease in reaction efficiency and even equipment corrosion. The distributor head is welded to the riser pipe, together forming the pipeline liquid distributor. A socket connection is used between the distributor head and the riser pipe. Microstructure: Related research shows that a reasonable orifice layout is crucial for improving the performance of the liquid distributor. The orifice layout on the distributor head is carefully designed to ensure uniform liquid distribution within the riser pipe. Specifically, each dispensing head typically has nine small holes, each approximately 2 mm in diameter. These holes are arranged in three layers, spaced about 20 mm apart. Each layer of holes is evenly distributed at 120° intervals, and the layers are staggered by 30°. The reaction liquid is guided into the riser through these holes. This layered design ensures that the liquid forms a multi-layered flow structure during the dispensing process, thereby improving the uniformity of liquid distribution. For example, the second layer of holes is rotated 30° relative to the first layer, and the third layer is rotated another 30° relative to the second layer. The advantage of this staggered layout is that it avoids local concentration of liquid during the dispensing process, thus forming a more uniform liquid film. Fluid dynamics simulation analysis shows that this layout can significantly improve the uniformity coefficient of liquid distribution and reduce the non-uniformity index of liquid distribution.It acts like a "precise nozzle," distributing the reaction liquid (a mixture of nitric acid and methanol) flowing down from above evenly into each riser through nine small holes. This ensures the liquid forms a uniformly thick film along the pipe wall. The descending velocity of this film is typically between 0.1 and 0.2 m / s. Too high a velocity results in a short residence time, hindering the reaction; too low a velocity prevents the formation of a continuous film, leading to dry pipe walls, which can cause localized overheating and severe corrosion. Gas flows upward through the gaps in the pipe. To ensure sufficient turbulence and prevent flooding, the operating gas velocity is controlled between 0.5 and 1.5 m / s, allowing the gas to effectively penetrate the liquid film for mass transfer. This ensures sufficient contact and complete reaction between the gas and liquid phases within a short time, achieving deep absorption and conversion.

[0071] 6. Heat source system In terms of heat source selection, hot water is used as the heating medium. Its main advantage is that it can quickly remove the large amount of reaction heat released by the MN synthesis reaction, accurately control the reaction temperature within the safe range of 60~70℃, avoid the temperature-sensitive zone of 90~100℃ that is prone to pitting corrosion of stainless steel, and has low operating costs.

[0072] To address the potential risks posed by the high temperature and high MN content in the methyl nitrite reactor, corresponding control measures and safety interlock protections were implemented. An automatic pH analyzer installed at the bottom outlet pipe of the reactor can monitor the acidity changes of the reaction solution in real time, thus providing data support for optimizing reaction conditions.

[0073] 7. On-site feedback after the actual operation of this system Significantly saves resources and operating costs From an economic perspective, this new unit outperforms the original unit in terms of engineering investment, raw material savings, energy consumption reduction, and lower labor and maintenance costs. Specific calculations are as follows: 1) Investment savings: The original investment in the four nitric acid reduction reactors plus supporting equipment was approximately 4 million yuan; the investment in wastewater pretreatment was approximately 5 million yuan; the investment in triple-effect evaporation was approximately 19 million yuan; and the investment in equipment upgrades was approximately 8.9 million yuan (based on a 10-year depreciation of 890,000 yuan per year). The investment can be reduced as follows: 400+500+1900-890=19.1 million yuan 2) Raw material savings and reduced operating costs: (Steam at 150 yuan / t, electricity consumption at 0.65 yuan / t, 68% nitric acid at 1600 yuan / t, 32% caustic soda at 800 yuan / t) a. Significantly reduces the cost of raw materials nitric acid and sodium hydroxide for the DMC unit, with the consumption of 68% nitric acid decreasing from 48 kg / t to 5 kg / t; and the consumption of 32% sodium hydroxide decreasing from 8.9 kg / t to 0 kg / t.

[0074] (48-5)×1.6 yuan / kg + (8.9-0)×0.8 yuan / kg = 7,592,000 yuan / year b. Saves operating costs for 4 nitric acid reduction reactors: 4 × 135 kWh / unit × 0.65 yuan / kWh × 8000h = 2,808,000 yuan / year c. Saves on nitric acid costs in the acidification unit: Reaction with sodium carbonate: 17.1 kg pH adjustment: 0.63 kg of acid is needed to achieve pH=2. 17.73 / 68%×1600=41.72 yuan / t d. Save on caustic soda costs in the neutralization unit: 32% caustic soda: pH=7, requires 0.4 kg of alkali. 0.4 / 32%×800=1 yuan / t e. Saves on resin adsorption unit costs: Electricity consumption: (200.4 kWh × 0.65 yuan / kWh) / 360m 3 =0.36 yuan / t Steam: (37.5t × 150 yuan / t) / 360m 3 =15.63 yuan / t Specialty resin loss: 30 × 5 × 15% / 8000 = 28.125 yuan / h = 28.13 / 15 = 1.88 yuan / t Total operating cost: 0.36 + 15.63 + 1.88 = 17.86 yuan / t f. Saves on triple-effect evaporation costs: Steam consumption per ton: 500 kg / t = 0.5 × 150 = 75 yuan / t g. Saves centrifuge power consumption: Electricity consumption: 18 kWh / t 18 × 0.65 = 11.7 yuan / t h. Save on packaging costs: The unit has a capacity of 9 people, with manual unloading and bagging of materials. The processing cost is 22 yuan / t. Total savings of 15t / h in wastewater salt treatment operating costs: (41.72 + 1 + 17.86 + 75 + 11.7 + 22) × 15 × 8000 = 2031.35 million yuan / year i. Hot water from the DMC steam drum is used for heat exchange in the new unit, saving electricity consumption compared to two DMC steam drum air coolers: 22kW × 2 units × 0.65 yuan × 8000 hours = 229,000 yuan / year g. Saves on hazardous waste treatment costs for mixed salts; the treatment cost for 4000t / h of mixed salts is 3600 yuan / t. 4000 × 3600 = 14.4 million / year k. Operating costs of the new unit: This device is placed within the DMC boundary area, eliminating the need for additional labor costs; Utilizing the system pressure difference, no additional transmission equipment is added, resulting in zero power consumption; The heat exchange requirements can be met using DMC steam drum condensate, with no steam consumption; High-efficiency dechlorination tank catalyst 2m 3 The price is approximately 400,000 yuan, and it needs to be replaced every two years, which is 200,000 yuan per year.

[0075] 3) Direct benefits: 759.20 + 280.80 + 2031.35 + 22.9 + 1440 - 20 = 4514.25 million yuan / year 4) Indirect benefits: Reduced operation and maintenance costs: Simplified process flow, reduction of more than 30% in operating positions, 50% decrease in equipment failure rate, and significant improvement in overall operation and maintenance efficiency.

[0076] Taking into account all the above benefits, after the project is put into operation, it can generate direct economic benefits of approximately RMB 45.1425 million for the enterprise annually, with an investment payback period of less than one year, fully demonstrating its economic feasibility and promotional value.

[0077] 8. Environmental benefits Specifically, the application of the high-efficiency dechlorination tank reduced the hydrogen chloride concentration in the wastewater from an initial 2000 mg / L to below 1 mg / L, achieving a removal rate exceeding 99.99%, effectively mitigating the impact of chloride ions on subsequent wastewater treatment systems. Furthermore, the reaction in the methyl nitrite reactor to generate methyl nitrite from nitric acid converts nitrate ions in the wastewater into reusable methyl nitrite, further reducing the chemical oxygen demand (COD) and total nitrogen (TN) content of the wastewater. According to actual monitoring data, the COD concentration of the treated wastewater decreased from 14000 mg / L to below 50 mg / L, and the TN concentration decreased from 2000 mg / L to below 10 mg / L, both meeting relevant emission standards and significantly reducing the risk of water pollution. Simultaneously, the efficient conversion of chloride ions prevents secondary pollution of the atmosphere and soil by chlorides. It effectively suppresses side reactions, reduces the emission of nitrogenous pollutants, and complies with current environmental protection policies. This not only achieves high-value reuse of nitric acid resources in the wastewater but also avoids high hazardous waste treatment costs (saving tens of millions of yuan annually), demonstrating promising prospects for widespread application.

Claims

1. An environmentally friendly device for the high-value utilization of waste dimethyl carbonate electrolyte in new energy sources, characterized in that, Based on the DMC synthesis system, a high-efficiency dechlorination tank, a three-phase heat exchanger, and a methyl nitrite reactor were added, while the nitric acid reduction reactor and the entire evaporation and desalination system were eliminated. The specific reaction process is as follows: The circulating gas from the top of the light-duty removal tower has a flow rate of Q: 20,000~120,000 Nm. 3 / h, P: 0.2~0.9MPa, T: 20~70℃, circulating gas composition: nitrogen N2: 0~80%, carbon monoxide CO: 0~20%, methyl nitrite MN: 0~17%, nitric oxide NO: 0~17%, methanol ME: 0~10%, Cl - The concentration of each component in the circulating gas is 50~3000ppm and is not zero. It is first sent to a high-efficiency dechlorination tank, which is equipped with a dechlorination catalyst. The operating temperature of the high-efficiency dechlorination tank is controlled at 10~70℃ and the pressure is maintained at 0.1~0.8MPa. After dechlorination treatment, a portion of the circulating gas (Q: 20000~110000Nm) is discharged through a three-way valve. 3 / h is introduced into the MN regeneration tower, and another part of the circulating gas Q: 6000~18000Nm 3 The water flow rate is 2000~13000Kg / h, T:20~80℃, P:0.2~0.9MPa, and the composition is: H2O:0~90%, methanol ME:0~50%, dimethyl carbonate DMC:0~1%, dimethyl ether DME:0~1%, CO2:0~1%, and hot water from the steam drum condenser of the DMC reactor. The heated gas enters the methyl nitrite reactor from the bottom, while the bottom liquid from the MN regeneration tower and the supplementary nitric acid enter the methyl nitrite reactor from the top, coming into countercurrent contact with the gas phase from the bottom of the methyl nitrite reactor to produce methyl nitrite. The internal temperature of the reactor is controlled at 60-70℃ and the pressure is maintained at 0.1-0.6MPa to promote the rapid progress of the reaction. The purified liquid at the bottom of the methyl nitrite reactor was then sent to the methanol dehydration tower. The wastewater after recovering methanol was cooled and then directly entered the sewage biological treatment pond for treatment. The system uses hot water from the steam drum condenser of the DMC reactor as the heat source.

2. The environmental protection device for high-value utilization of dimethyl carbonate waste liquid from new energy electrolytes according to claim 1, characterized in that, The outlet pipeline of the high-efficiency dechlorination tank is equipped with an automatic HCl analyzer for real-time monitoring of hydrogen chloride concentration; the bottom outlet pipe of the methyl nitrite reactor is equipped with an automatic pH analyzer for monitoring changes in the acidity of the reaction solution.

3. The environmental protection device for high-value utilization of dimethyl carbonate waste liquid from new energy electrolytes according to claim 1, characterized in that, The high-efficiency dechlorination tank is made of glass-lined tank to improve corrosion resistance.

4. The environmental protection device for high-value utilization of dimethyl carbonate waste liquid from new energy electrolytes according to claim 1, characterized in that, The three-phase heat exchanger is divided into three independent chambers by a partition; the middle chamber carries circulating gas, while the two side chambers carry hot water and purified liquid from the bottom of the methyl nitrite reactor, respectively. The circulating gas inlet is located at the top of the three-phase heat exchanger and enters the flow channel between the heat exchange plates evenly through the distribution plate; after passing through the flow channel, the circulating gas is finally discharged from the bottom outlet. The flow path of the liquid phase is divided into two paths. The hot water inlet is located at the bottom of the three-phase heat exchanger and enters the gap between the plates through the flow guiding structure. The liquid forms a thin layer flow between the plates and is arranged in an alternating manner with the gas flow channel, thereby realizing countercurrent heat exchange between the cold and hot fluids. The purified liquid at the bottom of the methyl nitrite reactor enters the heat exchanger through the side inlet, flowing in a parallel direction with the circulating gas. It moves along the flow channel and exchanges heat with the plate surface. The outlet is located on the side of the equipment.

5. The environmental protection device for high-value utilization of dimethyl carbonate waste liquid from new energy electrolytes according to claim 4, characterized in that, The heat exchange plate of the three-phase heat exchanger is 0.5-1.0 mm thick, the substrate is manufactured by explosive welding process, and the structure is fully welded; the core heat transfer element is a corrugated plate bundle.

6. The environmental protection device for high-value utilization of dimethyl carbonate waste liquid from new energy electrolytes according to claim 1, characterized in that, The methyl nitrite reactor adopts a three-chamber vertical series layout, arranged sequentially along the vertical direction. Each reaction chamber is a vertical tube reactor, and the material is transferred step by step through internal channels.

7. The environmental protection device for high-value utilization of dimethyl carbonate waste liquid from new energy electrolytes according to claim 6, characterized in that, The liquid distributor of the methyl nitrite reactor includes a distribution head and a riser pipe, and the distribution head and the riser pipe are welded together. The reaction liquid is guided into the vertical tube reactor through a small hole to form a uniform liquid film, thereby improving the uniformity of liquid distribution.

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