A dimethyl carbonate wastewater treatment process

Abstract

The application provides a dimethyl carbonate wastewater treatment process and relates to the technical field of wastewater treatment. The dimethyl carbonate wastewater treatment process comprises the following steps: S1, collecting wastewater generated in a dimethyl carbonate production process and conveying the wastewater to a conditioning tank for homogeneous and equal quantity treatment, and detecting the COD concentration, methanol concentration, conductivity and pH value of the wastewater through an online monitoring system; S2, performing quality and flow distribution treatment on the wastewater according to the detection results, wherein high-concentration organic wastewater enters a resource recycling unit, and medium and low-concentration wastewater enters a pretreatment unit. By synchronously obtaining multi-dimensional parameter information such as chemical oxygen demand, methanol concentration, conductivity and pH value before the wastewater enters a treatment process, and according to the pollution load difference, targeted flow distribution is implemented, so that wastewater with different properties enters a treatment path matched with the characteristics of the wastewater, and imbalance of treatment strength caused by mixing and dilution of high-concentration organic components and low-concentration wastewater is avoided.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically a dimethyl carbonate wastewater treatment process. Background Technology

[0002] Wastewater treatment technology belongs to the field of environmental engineering and water pollution control technology, specifically involving technologies for the reduction, harmlessness, and resource recovery of industrial wastewater, domestic sewage, and special pollutant wastewater. This technology primarily targets the removal and control of organic pollutants, inorganic salts, suspended solids, ammonia nitrogen, total nitrogen, total phosphorus, and recalcitrant toxic and harmful substances in wastewater. It utilizes physical, chemical, physicochemical, biological, and membrane separation technologies to achieve wastewater purification, pollutant reduction, and water resource recycling. Specifically, the dimethyl carbonate wastewater treatment process refers to a comprehensive treatment process established for wastewater containing dimethyl carbonate, organic carbonate byproducts, methanol, and other organic pollutants generated during the production, storage, transportation, or related chemical production processes of dimethyl carbonate. Its purpose is to reduce the chemical oxygen demand, total organic carbon and other pollutant content in wastewater by separating and recovering organic pollutants, breaking down ester chains, oxidizing and degrading them, performing biochemical treatment and deep purification, improving the biodegradability and treatment efficiency of wastewater, achieving standard discharge or recycling of wastewater, thereby reducing environmental pollution, improving resource utilization, and meeting the needs of green production and circular economy development in the chemical industry.

[0003] In existing dimethyl carbonate (DMC) wastewater treatment processes, most treatment routes focus on overall pollutant reduction. Wastewater is often treated continuously under uniform water quality conditions after entering the treatment stage. However, wastewater of different concentrations and compositions enters subsequent processes in a mixed state, easily leading to significant load fluctuations in some treatment stages. When high-concentration organic components mix with low-concentration wastewater, the pollutant distribution becomes more complex, and some components with recovery value enter the treatment system along with the overall wastewater, increasing resource depletion. Simultaneously, dimethyl carbonate and related organic carbonates possess a certain degree of structural stability and may persist in their original or intermediate stable forms during conventional treatment. Some pollutants have low degradation rates, resulting in a heavy load on subsequent treatment stages. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a dimethyl carbonate wastewater treatment process that solves the problem that in most existing dimethyl carbonate wastewater treatment processes, the treatment routes focus on the overall reduction of pollutants. After the wastewater enters the treatment stage, it is often continuously treated under uniform water quality conditions. Wastewaters of different concentrations and compositions enter the subsequent processes together in a mixed state, which can easily lead to large load fluctuations in some treatment stages.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a dimethyl carbonate wastewater treatment process, comprising the following steps: S1. The wastewater generated during the production of dimethyl carbonate is collected and transported to the equalization tank for homogenization and equalization treatment. The COD concentration, methanol concentration, conductivity and pH value of the wastewater are detected by an online monitoring system. S2. Based on the test results, the wastewater is treated separately according to its quality and flow. High-concentration organic wastewater enters the resource recovery unit, while medium- and low-concentration wastewater enters the pretreatment unit. S3. The resource recovery unit uses distillation separation to recover methanol and unreacted dimethyl carbonate from the wastewater. S4. High-concentration organic wastewater enters the resource recovery unit for distillation treatment. Distillation recovers methanol and unreacted dimethyl carbonate from the wastewater, achieving resource utilization. The distilled wastewater then enters a dedicated dimethyl carbonate esterification and chain-breaking reactor for ester bond breaking. This causes directional hydrolysis and chain-breaking reactions of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and other linear or cyclic organic carbonates in the wastewater, generating low-molecular-weight alcohols and organic acid intermediates. Medium- and low-concentration organic wastewater undergoes homogenization, pH adjustment, and coagulation sedimentation in the pretreatment unit to remove suspended solids, colloids, and some large-molecule organic pollutants and stabilize water quality. The pretreated medium- and low-concentration wastewater is mixed with the high-concentration wastewater treated by the esterification and chain-breaking reactor and then enters an iron-carbon micro-electrolysis reactor for further treatment to promote ring-opening degradation and redox reactions of residual organic matter, improving the wastewater's biodegradability. S5. The effluent from the ester hydrolysis chain breaking reactor enters the iron-carbon micro-electrolysis reactor for further pretreatment to promote the ring-opening degradation and redox reaction of residual organic matter. S6. The micro-electrolysis effluent enters the catalytic oxidation reactor for advanced oxidation treatment, improving the biodegradability of the wastewater; S7. The wastewater after oxidation treatment enters the hydrolysis acidification reactor for acidification degradation. S8. The hydrolyzed and acidified effluent enters the biofilm reactor for the degradation of organic pollutants. S9. The effluent from the biofilm reactor enters the membrane bioreactor for mud-water separation and deep purification. S10. The effluent from the membrane bioreactor enters the reverse osmosis treatment unit for deep desalination. The reverse osmosis permeate is reused in the dimethyl carbonate production system, and the concentrate enters the concentration treatment unit for further treatment.

[0006] Preferably, the dimethyl carbonate-specific ester dechaining reactor includes a reactor body, a catalytic packing layer, a stirring device, a heating device, and a pH adjustment device, wherein the catalytic packing layer is disposed inside the reactor body.

[0007] Preferably, the catalytic packing layer comprises one or more of a porous ceramic support, an activated carbon support, or a molecular sieve support loaded with metal oxides, wherein the metal oxides comprise at least one of iron oxide, copper oxide, manganese oxide, and cerium oxide.

[0008] Preferably, the reaction temperature in the ester hydrolysis chain-breaking reactor is controlled at 40–90°C, the pH value is 4.0–8.5, and the hydraulic retention time is 20–180 min.

[0009] Preferably, the ester hydrolysis chain-breaking reactor breaks the -O-CO-O- structure in organic carbonates through catalytic hydrolysis, generating methanol, ethanol, bicarbonate and small molecule organic acids.

[0010] Preferably, the online monitoring system includes an online COD analyzer, a TOC analyzer, a conductivity meter, a pH meter, and a data processing module. The data processing module is used to establish a wastewater characteristic parameter database and output process control signals.

[0011] Preferably, the iron-carbon microelectrolysis reactor is filled with iron-carbon composite filler, the iron-carbon mass ratio is 1:(0.8-1.5), and the reaction residence time is 30-180 min.

[0012] Preferably, the catalytic oxidation reactor employs one or more combinations of ozone catalytic oxidation, Fenton oxidation, or ozone-Fenton coupled oxidation processes.

[0013] Preferably, the biofilm reactor is an MBBR reactor with a carrier filling rate of 30% to 70%, and the membrane bioreactor is inoculated with methanol-resistant and ester-degrading bacteria.

[0014] Preferably, the data processing module of the online monitoring system outputs process control signals based on the COD concentration, methanol concentration, conductivity and pH value parameters obtained from online monitoring, and dynamically adjusts the reaction time, reaction temperature and catalyst dosage of the ester decomposition and chain breaking reactor to achieve adaptive treatment for different wastewater qualities.

[0015] This invention provides a process for treating dimethyl carbonate wastewater. It has the following beneficial effects: This invention acquires multi-dimensional parameters such as chemical oxygen demand (COD), methanol concentration, conductivity, and pH before wastewater enters the treatment process. Based on differences in pollution load, it implements targeted flow allocation, ensuring that wastewater with different properties enters the treatment path that matches its characteristics. This avoids the imbalance in treatment intensity caused by mixing and diluting high-concentration organic components with low-concentration wastewater, maintaining high targeting and stability in subsequent treatment processes. It prioritizes the recovery of residual methanol and dimethyl carbonate from wastewater, reducing not only the organic load in the subsequent treatment system but also minimizing the loss of usable substances with wastewater. Addressing the characteristics of organic carbonates—their tendency to form complex structures and slow degradation—it directionally breaks ester bonds and promotes the conversion of linear or cyclic organic carbonates into more easily convertible intermediates. This process significantly reduces the structural complexity of pollutants, lowering mass transfer resistance and reaction difficulty in subsequent reaction stages. Through continuous oxidation-reduction and deep oxidation, some stable organic compounds gradually transform into smaller, more reactive molecular forms, making it easier for subsequent biodegradation processes to form continuous metabolic chains and reducing the long-term accumulation of recalcitrant components. Through acidification, biodegradation, efficient sludge-water separation, and deep desalination, a progressive treatment chain is formed, from pollutant structural reconstruction to resource reuse. This not only addresses both organic matter reduction and salinity control but also promotes improved wastewater quality, making the treatment results more closely aligned with production reuse requirements. Simultaneously, it reduces the risk of concentrated pollutants spreading to subsequent units, improving overall operational stability, resource recycling levels, and unit wastewater treatment efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the main steps of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example:

[0019] like Figure 1 As shown in the figure, an embodiment of the present invention provides a dimethyl carbonate wastewater treatment process, including the following steps: S1. The wastewater generated during the production of dimethyl carbonate is collected and transported to the equalization tank for homogenization and equalization treatment. The COD concentration, methanol concentration, conductivity and pH value of the wastewater are detected by an online monitoring system. Various types of wastewater generated during the transesterification reaction, distillation separation, equipment cleaning, storage and transportation, and auxiliary production processes of the dimethyl carbonate production unit are collected and transported through a pipeline network to an equalization tank for homogenization and equalization treatment. Due to the intermittent discharge, concentration fluctuations, and changes in water volume during the production process, the concentration of organic matter, methanol content, and salt composition in the wastewater varies significantly. Therefore, the equalization tank serves as a buffer to regulate the wastewater volume and quality. The equalization tank is used for homogenization and equalization treatment of the production wastewater, with an effective retention time preferably of 6–24 hours, more preferably 8–12 hours. A mechanical stirring device or a circulation reflux device is installed in the equalization tank to maintain a uniform mixing state of the wastewater. A liquid level control system stabilizes the influent flow rate of subsequent treatment units, thereby reducing the impact of wastewater volume and pollutant concentration fluctuations on subsequent treatment processes and ensuring stable operation of the subsequent treatment units.

[0020] Mechanical stirring or aeration stirring devices are installed in the equalization tank to prevent suspended solids from settling and to maintain uniform mixing of wastewater. Simultaneously, an online monitoring system is installed at the effluent end of the equalization tank to monitor parameters such as chemical oxygen demand (COD), methanol concentration, conductivity, pH value, and temperature of the wastewater in real time. The monitored data is transmitted to the central control system, providing a basis for subsequent wastewater classification and treatment.

[0021] S2. Based on the test results, the wastewater is treated separately according to its quality and flow. High-concentration organic wastewater enters the resource recovery unit, while medium- and low-concentration wastewater enters the pretreatment unit. Based on wastewater quality parameters obtained from the online monitoring system, wastewater is treated separately according to its quality. Wastewater meeting the following criteria is classified as high-concentration organic wastewater and sent to the resource recovery unit for valuable component recovery: COD ≥ 8000–20000 mg / L and / or methanol concentration ≥ 2000–8000 mg / L. Wastewater not meeting these criteria is classified as medium- to low-concentration wastewater and sent to the pretreatment unit. A comprehensive assessment of the wastewater is then conducted based on the pollution load index (PI). When PI ≥ 1, the sample enters the resource recycling unit; otherwise, it enters the preprocessing unit. , α and β are 0.5–0.7 and 0.3–0.5, respectively. For high-concentration organic wastewater with high methanol concentration, high COD value and resource recovery value, it is preferentially transported to the resource recovery unit for recovery of valuable components; for medium- and low-concentration wastewater with relatively low organic matter concentration and limited resource recovery value, it directly enters the pretreatment unit.

[0022] Preferably, different diversion thresholds can be set according to COD concentration, methanol mass fraction, and conductivity to achieve automatic valve switching and improve the system's automation level. By separating and diverting the flow based on the specific gases, the load on subsequent biochemical systems can be reduced, resource utilization can be improved, and overall operating costs can be lowered.

[0023] S3. The resource recovery unit uses distillation to recover methanol and unreacted dimethyl carbonate from the wastewater. High-concentration wastewater entering the resource recovery unit is first preheated to 40–80°C before entering the distillation system. Distillation separation is performed under 20–110 kPa conditions, with the top temperature controlled at 45–75°C and the bottom temperature at 70–120°C, and the reflux ratio at 1:1–5:1. During distillation, methanol and some dimethyl carbonate are recovered as top distillate, refined, and returned to the production system for recycling. The recovery operation ends when the methanol concentration at the top of the column is below 5 wt% for 30 consecutive minutes. After distillation, the methanol recovery rate reaches 80–98%, the dimethyl carbonate recovery rate reaches 60–95%, the methanol concentration in the bottom residue is reduced to below 500 mg / L, and the COD is reduced by 30–70%. The residue is then sent to the pretreatment unit for further processing before entering the distillation separation system. Because the wastewater typically contains high concentrations of methanol, unreacted dimethyl carbonate, and small amounts of low-boiling-point organic matter, atmospheric distillation, vacuum distillation, or multi-effect distillation processes are used for component separation.

[0024] During distillation, methanol and some dimethyl carbonate are recovered as overhead distillate, which is then further refined and returned to the production system for recycling. The bottom residue mainly contains high-boiling-point organic byproducts, some carbonates, and soluble salts. By setting up a resource recovery unit, not only can the concentration of organic pollutants in wastewater be reduced, but the recycling of production raw materials can also be achieved, thereby improving economic efficiency.

[0025] S4. High-concentration organic wastewater enters the resource recovery unit for distillation treatment. Distillation recovers methanol and unreacted dimethyl carbonate from the wastewater, achieving resource utilization. The distilled wastewater then enters a dedicated dimethyl carbonate esterification and chain-breaking reactor for ester bond breaking. This causes directional hydrolysis and chain-breaking reactions of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and other linear or cyclic organic carbonates in the wastewater, generating low-molecular-weight alcohols and organic acid intermediates. Medium- and low-concentration organic wastewater undergoes homogenization, pH adjustment, and coagulation sedimentation in the pretreatment unit to remove suspended solids, colloids, and some large-molecule organic pollutants and stabilize water quality. The pretreated medium- and low-concentration wastewater is mixed with the high-concentration wastewater treated by the esterification and chain-breaking reactor and then enters an iron-carbon micro-electrolysis reactor for further treatment to promote ring-opening degradation and redox reactions of residual organic matter, improving the wastewater's biodegradability. The distillation-treated wastewater enters a dedicated dimethyl carbonate chain-breaking reactor. Because the wastewater from dimethyl carbonate production contains a large amount of structurally stable organic carbonate compounds, including dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and other linear or cyclic organic carbonates, these substances exhibit strong resistance to biodegradation. Direct entry into the biological system would lead to reduced treatment efficiency.

[0026] In the esterolysis chain-breaking reactor, by controlling the reaction temperature, pH value, and catalyst dosage, the ester bonds in organic carbonate molecules undergo a directional breaking reaction. Carbonates are then progressively hydrolyzed to generate low-molecular-weight alcohols such as methanol and ethanol, as well as small-molecular-weight organic acid intermediates such as formate and acetate, thereby reducing molecular structural complexity and improving the biodegradability of wastewater.

[0027] This step specifically degrades carbonate pollutants, effectively solving the problem of difficult degradation of organic carbonates in traditional processes and creating favorable conditions for subsequent oxidation and biological treatment.

[0028] S5. The effluent from the ester hydrolysis chain breaking reactor enters the iron-carbon micro-electrolysis reactor for further pretreatment to promote the ring-opening degradation and redox reaction of residual organic matter. The effluent from the esterification chain-breaking reactor enters the iron-carbon micro-electrolysis reactor. The reactor is filled with iron filings and carbonaceous materials, which form a large number of micro-galvanic cells in the wastewater electrolyte environment.

[0029] Iron is continuously released as the anode. The carbon material acts as the cathode, receiving electrons and generating a continuous redox reaction. This process promotes chain scission, ring opening, and decolorization of residual organic pollutants, while also reducing the molecular weight of some recalcitrant organic compounds. Furthermore, the active ferrous ions generated in the reaction can synergistically enhance subsequent oxidation processes, improving the efficiency of advanced oxidation.

[0030] Iron-carbon micro-electrolysis treatment can effectively improve the biodegradability of wastewater and remove some colloidal substances and suspended particles. S6. The micro-electrolysis effluent enters the catalytic oxidation reactor for advanced oxidation treatment, improving the biodegradability of the wastewater; The water from micro-electrolysis enters a catalytic oxidation reactor for advanced oxidation treatment. The reactor contains a catalyst system and an oxidant, which generates hydroxyl radicals through catalytic action. superoxide radicals Highly reactive oxide species.

[0031] These active free radicals have extremely high oxidizing power, which can attack the residual recalcitrant organic matter in wastewater, destroy its aromatic ring structure, ester structure and long-chain organic molecule structure, and further oxidize it into small molecule organic acids, alcohols and carbon dioxide that are easily biodegradable.

[0032] After catalytic oxidation treatment, the B / C ratio of the wastewater is significantly improved, and COD is effectively reduced, providing good influent conditions for subsequent biological treatment.

[0033] S7. The wastewater after oxidation treatment enters the hydrolysis acidification reactor for acidification degradation. The wastewater after catalytic oxidation treatment enters the hydrolysis acidification reactor. Under anaerobic conditions, the hydrolysis acidification bacteria further decompose the macromolecular organic matter in the wastewater into volatile fatty acids (VFA), acetic acid, propionic acid, and other small molecule organic acids.

[0034] This process can further reduce the molecular weight of organic matter and increase the content of available carbon sources in wastewater, providing sufficient substrate for subsequent aerobic biological treatment. At the same time, the acidification process can buffer fluctuations in influent water quality and improve the operational stability of the entire biological treatment system.

[0035] S8. The hydrolyzed and acidified effluent enters the biofilm reactor for the degradation of organic pollutants. The hydrolyzed and acidified effluent enters the biofilm reactor. The reactor is equipped with high specific surface area packing material, where a large number of microorganisms attach and grow to form a stable biofilm.

[0036] Under aerated conditions, aerobic microorganisms in the biofilm utilize organic pollutants in wastewater as carbon and energy sources for metabolic activities, gradually degrading the organic pollutants into carbon dioxide, water, and microbial cell matter. Because biofilm systems have high biomass and strong shock resistance, they are particularly suitable for treating chemical wastewater containing complex organic components.

[0037] After treatment by a biofilm reactor, most of the biodegradable organic matter is effectively removed.

[0038] S9. The effluent from the biofilm reactor enters the membrane bioreactor for mud-water separation and deep purification. The effluent from the biofilm reactor enters the membrane bioreactor for sludge-water separation and advanced treatment. The membrane bioreactor employs a submerged ultrafiltration membrane or an external membrane module. The effluent from the biofilm reactor enters the membrane bioreactor, where activated sludge and treated water are efficiently separated through membrane separation. The membrane bioreactor uses a submerged ultrafiltration membrane or an external membrane module with a pore size of 0.01–0.1 μm and a membrane flux of 10–30 L / (m²). 2 •h); During operation, the sludge concentration is controlled at 6000–15000 mg / L, the hydraulic retention time is 4–12 h, the submerged membrane suction negative pressure is -5 to -50 kPa or the external operating pressure is 0.05–0.3 MPa; an aeration system is also installed, with an aeration intensity of 5–15 m 3 / (m 2•h) to reduce membrane fouling and maintain dissolved oxygen; during membrane module operation, periodic backwashing or chemical cleaning is adopted, with a backwashing cycle of 10 to 60 minutes; after treatment by the membrane bioreactor, the effluent COD is reduced to 50 to 200 mg / L and ammonia nitrogen is reduced to 5 to 20 mg / L, achieving deep purification of wastewater.

[0039] Membrane modules effectively retain microorganisms, suspended particles, and large organic molecules, maintaining a high sludge concentration and long sludge age within the reactor, thus improving the system's ability to remove recalcitrant organic matter. Simultaneously, they produce high-quality effluent with extremely low turbidity and suspended solids content.

[0040] After treatment by a membrane bioreactor, the COD, ammonia nitrogen, and suspended solids in the wastewater are further reduced, meeting the requirements for advanced treatment.

[0041] S10. The effluent from the membrane bioreactor enters the reverse osmosis treatment unit for deep desalination. The reverse osmosis permeate is reused in the dimethyl carbonate production system, and the concentrate enters the concentration treatment unit for further treatment.

[0042] The effluent from the membrane bioreactor enters the reverse osmosis treatment unit for deep desalination. The reverse osmosis system uses a semi-permeable membrane to selectively separate water molecules and dissolved salts, achieving wastewater desalination and purification under high pressure.

[0043] Reverse osmosis permeate has low conductivity and high water quality, and can be directly reused as circulating cooling water, process water, or equipment cleaning water in the dimethyl carbonate production system, thus realizing the recycling of water resources.

[0044] The concentrate produced by reverse osmosis enters the concentration treatment unit, where it undergoes further treatment through evaporation concentration, crystallization and salt separation, or other volume reduction processes to reduce the final discharge volume. If necessary, valuable salts in the concentrate can be recovered and reused, achieving the goals of resource recovery and volume reduction in the wastewater treatment process.

[0045] Furthermore, the dimethyl carbonate-specific ester decomposition and chain breaking reactor includes a reactor body, a catalytic packing layer, a stirring device, a heating device, and a pH adjustment device, with the catalytic packing layer located inside the reactor body.

[0046] The dimethyl carbonate (DMC)-specific esterolysis and chain-breaking reactor mainly comprises key components such as the reactor body, catalytic packing layer, stirring device, heating device, and pH adjustment device. The reactor body can be made of corrosion-resistant metal or polymer composite material to ensure it is not corroded by organic carbonates and acidic / alkaline media during long-term operation. The catalytic packing layer, located inside the reactor body, plays a crucial role in catalyzing hydrolysis and chain-breaking reactions. The stirring device maintains uniform mixing of the reaction solution, preventing localized overheating or underconcentration, thereby improving reaction efficiency. The heating device enables precise temperature control, ensuring the esterolysis and chain-breaking reaction proceeds under optimal conditions. The pH adjustment device adjusts the pH of the reaction system according to reaction requirements, ensuring efficient and stable operation of the esterolysis process.

[0047] The catalytic packing layer includes one or more of a porous ceramic support, an activated carbon support, or a molecular sieve support loaded with metal oxides, and the metal oxides include at least one of iron oxide, copper oxide, manganese oxide, and cerium oxide.

[0048] The catalytic packing layer comprises one or more of the following: porous ceramic supports loaded with metal oxides, activated carbon supports, or molecular sieve supports. These supports possess large specific surface areas and controllable pore structures, which facilitates sufficient contact between reactant molecules and the catalyst surface, thereby improving catalytic efficiency. The metal oxides include at least one of iron oxide, copper oxide, manganese oxide, and cerium oxide. During catalysis, metal oxides promote the breaking of -O-CO-O- bonds through surface active sites, thus accelerating the hydrolysis reaction of organic carbonates. By rationally combining the types of supports and metal oxides, highly selective esterification and chain-breaking reactions can be achieved for different types of organic carbonates.

[0049] The reaction temperature in the ester hydrolysis chain-breaking reactor was controlled at 40–90℃, the pH value at 4.0–8.5, and the hydraulic retention time at 20–180 min.

[0050] Within the esterolysis chain-breaking reactor, the reaction temperature is controlled within the range of 40–90°C to balance reaction rate and energy consumption requirements, avoiding side reactions or decreased catalyst activity caused by high temperatures. The pH value of the reaction system is controlled between 4.0 and 8.5 to ensure the catalytic activity of the metal oxide and the smooth progress of the esterolysis reaction, while reducing the formation of by-products. The hydraulic retention time is 20–180 minutes, which can be flexibly adjusted according to wastewater concentration, ester content, and catalyst activity to achieve optimal degradation efficiency. The above-mentioned control of reaction conditions ensures that the esterolysis chain-breaking process operates efficiently in a mild and controllable environment.

[0051] The ester hydrolysis chain-breaking reactor breaks the -O-CO-O- structure in organic carbonates through catalytic hydrolysis, generating methanol, ethanol, bicarbonate, and small molecule organic acids.

[0052] The esterolysis chain-breaking reactor breaks down the -O-CO-O- structures in organic carbonates through catalytic hydrolysis. This chain-breaking reaction is mainly achieved through the interaction of water molecules with active sites on the surface of metal oxides, generating small molecule products, including methanol, ethanol, bicarbonates, and small organic acids. These products have good biodegradability, facilitating subsequent wastewater treatment or resource recycling. The reactor is designed to ensure maximum reaction completion and minimize unreacted or partially degraded organic carbonate residues, thereby achieving the goal of efficient and environmentally friendly wastewater treatment.

[0053] The online monitoring system includes an online COD analyzer, a TOC analyzer, a conductivity meter, a pH meter, and a data processing module. The data processing module is used to establish a database of wastewater characteristic parameters and output process control signals.

[0054] The online monitoring system includes an online COD analyzer, a TOC analyzer, a conductivity meter, a pH meter, and a data processing module. Methanol concentration is detected using an online gas chromatograph, and model calibration is performed using TOC and conductivity data to improve detection accuracy. By monitoring parameters such as total organic matter, dissolved carbon content, conductivity, and pH in the wastewater in real time, the reactor's operating status can be monitored immediately. The data processing module is used to establish a database of wastewater characteristic parameters. Through analysis of historical and real-time data, process parameters can be optimized, and control signals can be automatically output to adjust temperature, pH, and stirring speed. The data processing module connects to a PLC or DCS control system to output standard control signals of 4-20 mA or 0-10 V. When the reaction temperature is lower than the set value, the control module adjusts the output power of the heating device; when the temperature is too high, it controls the cooling system to operate, achieving automatic temperature regulation. When the pH deviates from the set range, the control module drives the acid metering pump or alkali metering pump respectively to achieve automatic pH adjustment. The stirring speed is adjusted through a frequency converter, and the control module outputs control signals based on changes in dissolved oxygen or reaction rate to achieve dynamic adjustment of stirring intensity, thereby realizing intelligent operation of the reactor. This monitoring system not only improves operational safety but also effectively reduces operating costs, enabling a continuous, efficient, and stable ester hydrolysis and chain scission process.

[0055] The iron-carbon microelectrolysis reactor is filled with iron-carbon composite filler, with an iron-carbon mass ratio of 1:(0.8-1.5), and the reaction residence time is 30-180 min.

[0056] The iron-carbon microelectrolysis reactor is filled with an iron-carbon composite packing material. The iron component in the iron-carbon composite packing material can be one or more of cast iron filings, sponge iron, reduced iron powder, and sintered iron particles, while the carbon component can be one or more of activated carbon, coke, graphite particles, and biochar. The iron-carbon mass ratio is controlled at 1:(0.8–1.5), preferably 1:(1.0–1.2), to ensure the formation of a stable and efficient microelectrolysis reaction environment in the system.

[0057] As wastewater flows through the iron-carbon packing layer, numerous micro-galvanic cell structures are formed between the iron and carbon components, with iron acting as the anode and undergoing an oxidation reaction to release iron. Carbon acts as the cathode, promoting electron transfer and reduction reactions. Through micro-electrolysis, the structure of recalcitrant intermediates formed during the degradation of organic carbonates in wastewater can be effectively destroyed, improving the biodegradability of the wastewater. Simultaneously, the nascent hydrogen and active iron ions generated during micro-electrolysis can reduce and flocculate some organic pollutants, thereby reducing wastewater color and some COD load.

[0058] The residence time in the iron-carbon microelectrolysis reactor is controlled to be 30–180 min, preferably 60–120 min. A shorter residence time can be used under lower organic load conditions, while for high-concentration organic carbonate wastewater, the residence time should be appropriately extended to improve pollutant conversion efficiency. By rationally controlling the iron-carbon ratio and residence time, ring-opening, chain-breaking, and pre-oxidation treatment of organic pollutants can be achieved. The iron-carbon microelectrolysis unit mainly promotes the structural transformation and pre-degradation of organic pollutants through micro-galvanic cell reactions, nascent hydrogen reduction, and iron ion flocculation. The subsequent advanced oxidation unit utilizes the generated by microelectrolysis... As a catalyst, it further generates hydroxyl radicals to achieve deep oxidative degradation, creating favorable conditions for subsequent advanced oxidation and biological treatment.

[0059] In addition, to prevent packing caking and passivation, the packing activity can be restored periodically by aeration flushing, backwashing, or weak acid regeneration, thereby extending the service life of the reactor and maintaining stable treatment results.

[0060] The catalytic oxidation reactor employs one or more combinations of ozone catalytic oxidation, Fenton oxidation, or ozone-Fenton coupled oxidation processes.

[0061] The catalytic oxidation reactor employs one or more combinations of ozone catalytic oxidation, Fenton oxidation, or ozone-Fenton coupled oxidation processes to further degrade the recalcitrant organic matter and intermediate metabolites remaining after iron-carbon microelectrolysis.

[0062] When using ozone catalytic oxidation, ozone gas is continuously added to the reactor through an ozone generator, promoting the decomposition of ozone on the catalyst surface to generate hydroxyl radicals (·OH). Hydroxyl radicals have extremely high redox potentials and can rapidly attack carbon-oxygen bonds, carbon-carbon double bonds, and aromatic ring structures in organic molecules, thereby converting complex organic compounds into small-molecule organic acids, alcohols, and carbon dioxide.

[0063] When using the Fenton oxidation process, hydrogen peroxide and ferrous ions are added to the reaction system to generate a large number of hydroxyl radicals under acidic conditions, achieving deep oxidative degradation of organic pollutants. The Fenton reaction is characterized by its fast reaction rate and strong oxidizing power, making it particularly suitable for the pretreatment and advanced treatment of high-COD wastewater.

[0064] When using an ozone-Fenton coupled oxidation process, the synergistic effect of ozone oxidation and Fenton oxidation significantly improves free radical yield and oxidation efficiency, further enhancing the removal capacity of organic carbonate degradation products and recalcitrant organic compounds. Process coupling reduces oxidant dosage, lowers operating costs, and improves the overall stability and adaptability of the treatment system.

[0065] The above-mentioned catalytic oxidation treatment can effectively reduce the residual COD concentration in wastewater, improve the biodegradability of wastewater, and provide good influent conditions for subsequent biological treatment units.

[0066] The biofilm reactor uses an MBBR reactor with a carrier filling rate of 30%–70%. The reactor is inoculated with methanol-resistant and ester-degrading bacteria, preferably 40%–60%. The total inoculation volume of the methanol-resistant and ester-degrading bacteria is 5%–20% of the effective reactor volume, preferably 10%–15%. The volume ratio of methanol-resistant to ester-degrading bacteria is (2–8):1, preferably (3–5):1. During the start-up phase, dissolved oxygen is controlled at 2–4 mg / L. After 7–30 days of biofilm formation, a stable biofilm is established for the efficient degradation of methanol, residual esters, and their chain-segmented products.

[0067] The biofilm reactor adopts a moving bed biofilm reactor (MBBR) structure, with a high specific surface area biological carrier installed inside the reactor. The carrier filling rate is 30% to 70%, preferably 40% to 60%. The carrier material can be made of polyethylene, polypropylene, polyurethane, or composite polymer materials, and has the characteristics of moderate density, good biocompatibility, and wear resistance.

[0068] During operation, the carrier is fluidized through an aeration system or mechanical stirring system, allowing a large number of microorganisms to attach and grow on the carrier surface, forming a stable biofilm. Compared with traditional activated sludge processes, the MBBR system has advantages such as high biomass, strong resistance to shock loads, low sludge production, and high operational stability.

[0069] The biofilm reactor was inoculated with methanol-resistant and ester-degrading bacterial communities. The methanol-resistant communities efficiently utilize methanol generated during ester chain scission as a carbon and energy source for metabolism; the ester-degrading communities further decompose residual esters and their hydrolysis products. These two types of functional bacteria form a synergistic degradation system, significantly improving the removal efficiency of organic pollutants.

[0070] As the system operates, the biofilm gradually forms a multi-layered structure that combines aerobic, anoxic, and microanaerobic zones, enabling the simultaneous degradation of organic matter, nitrification, and partial denitrification, thereby improving the overall treatment capacity of the system and the stability of the effluent quality.

[0071] The data processing module of the online monitoring system outputs process control signals based on the COD concentration, methanol concentration, conductivity and pH value parameters obtained from online monitoring. It dynamically adjusts the reaction time, reaction temperature and catalyst dosage of the ester decomposition and chain breaking reactor to achieve adaptive treatment for different wastewater qualities.

[0072] The intelligent control system is connected to the online monitoring system. Based on parameters such as methanol concentration, organic carbonate concentration, COD concentration and conductivity obtained from online monitoring, the system performs real-time analysis and dynamic adjustment of the operating status of each processing unit.

[0073] The intelligent control system includes a data acquisition module, a data analysis module, a control decision module, and an execution module. The data acquisition module is responsible for receiving real-time operating data transmitted from various online monitoring devices; the data analysis module analyzes and predicts the changing trends of wastewater composition by establishing a wastewater characteristic database and process model; the control decision module generates optimized control commands based on the analysis results; and the execution module automatically adjusts the relevant equipment.

[0074] When an increase in organic carbonate concentration is detected, the system automatically extends the residence time of the ester decomposition reactor and increases the catalyst load to ensure that the chain-breaking reaction proceeds fully. When a high methanol concentration is detected, the aeration intensity and microbial activity of the subsequent biological treatment unit can be appropriately increased to promote the rapid degradation of methanol. When the COD load fluctuates significantly, the system can automatically adjust the oxidant dosage and advanced oxidation reaction time to maintain a stable treatment effect.

[0075] Furthermore, the intelligent control system can continuously refine the control model based on long-term operating data, enabling adaptive regulation of wastewater from different sources, with varying concentrations and compositions. By dynamically optimizing key parameters such as reaction temperature, reaction time, catalyst load, oxidant dosage, and aeration intensity, energy and chemical consumption can be reduced while ensuring treatment effectiveness, thereby improving the automation level and economy of the entire wastewater treatment system.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dimethyl carbonate wastewater treatment process, characterized in that, Includes the following steps: S1. The wastewater generated during the production of dimethyl carbonate is collected and transported to the equalization tank for homogenization and equalization treatment. The COD concentration, methanol concentration, conductivity and pH value of the wastewater are detected by an online monitoring system. S2. Based on the detection results of the online monitoring system, the wastewater is treated separately according to its quality, wherein high-concentration organic wastewater enters the resource recovery unit and medium- and low-concentration organic wastewater enters the pretreatment unit. S3. High-concentration organic wastewater enters the resource recovery unit for distillation treatment to recover methanol and unreacted dimethyl carbonate from the wastewater. S4. The high-concentration organic wastewater after distillation enters the dimethyl carbonate-specific ester decomposition and chain breaking reactor for ester bond breaking treatment. The dimethyl carbonate-specific ester decomposition and chain breaking reactor includes a reactor body, a catalytic packing layer, a stirring device, a heating device, and a pH adjustment device. The catalytic packing layer is disposed inside the reactor body. The catalytic packing layer includes one or more of a porous ceramic support, an activated carbon support, or a molecular sieve support loaded with metal oxides, and the metal oxides include at least one of iron oxide, copper oxide, manganese oxide, and cerium oxide. The reaction temperature in the ester hydrolysis chain-breaking reactor is controlled at 40–90°C, the pH value is controlled at 4.0–8.5, and the hydraulic retention time is controlled at 20–180 minutes. Catalytic hydrolysis breaks the -O-CO-O- structure in dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and other organic carbonates, generating methanol, ethanol, bicarbonate and small molecule organic acids. Low- to medium-concentration organic wastewater enters the pretreatment unit for homogenization, pH adjustment, and coagulation and sedimentation to remove suspended solids, colloids, and some large molecular organic pollutants. S5. The pretreated low-to-medium concentration organic wastewater is mixed with the high-concentration organic wastewater treated by the ester hydrolysis chain-breaking reactor and then fed into the iron-carbon micro-electrolysis reactor for further treatment to promote chain breaking, ring opening and redox reactions of residual organic matter. S6. The effluent from the iron-carbon micro-electrolysis enters the catalytic oxidation reactor for advanced oxidation treatment to improve the biodegradability of the wastewater. S7. Wastewater treated by catalytic oxidation enters the hydrolysis acidification reactor for acidification degradation. S8. The hydrolyzed and acidified effluent enters the biofilm reactor for the degradation of organic pollutants. S9. The effluent from the biofilm reactor enters the membrane bioreactor for mud-water separation and deep purification. S10. The effluent from the membrane bioreactor enters the reverse osmosis treatment unit for deep desalination. The reverse osmosis permeate is reused in the dimethyl carbonate production system, and the reverse osmosis concentrate enters the concentration treatment unit for further treatment.

2. The dimethyl carbonate wastewater treatment process according to claim 1, characterized in that: The online monitoring system includes an online COD analyzer, a TOC analyzer, a conductivity meter, a pH meter, and a data processing module. The data processing module is used to establish a database of wastewater characteristic parameters and output process control signals.

3. The dimethyl carbonate wastewater treatment process according to claim 1, characterized in that: The iron-carbon microelectrolysis reactor is filled with iron-carbon composite filler, with an iron-carbon mass ratio of 1:(0.8-1.5), and a reaction residence time of 30-180 min.

4. The dimethyl carbonate wastewater treatment process according to claim 1, characterized in that: The catalytic oxidation reactor employs one or more of the following methods in combination: ozone catalytic oxidation, Fenton oxidation, or ozone-Fenton coupled oxidation.

5. The dimethyl carbonate wastewater treatment process according to claim 1, characterized in that: The biofilm reactor is an MBBR reactor with a carrier filling rate of 30% to 70%. The biofilm reactor is inoculated with methanol-resistant and ester-degrading bacteria.

6. The dimethyl carbonate wastewater treatment process according to claim 2, characterized in that: The data processing module of the online monitoring system outputs process control signals based on the COD concentration, methanol concentration, conductivity and pH value parameters obtained from online monitoring. It dynamically adjusts the reaction time, reaction temperature and catalyst dosage of the ester decomposition and chain breaking reactor to achieve adaptive treatment for different wastewater qualities.

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