A fixed bed process and apparatus for the decarboxylation of dimethyl oxalate to dimethyl carbonate

Abstract

The application provides a fixed bed process and device for preparing dimethyl carbonate by decarboxylation of dimethyl oxalate, and the process comprises the following steps: feeding dimethyl oxalate and an additive into a fixed bed reactor from the bottom of the fixed bed reactor, and performing decarboxylation reaction in a liquid flow direction from bottom to top; feeding the obtained product into a primary flash tank to perform flash separation, so as to obtain a liquid phase component and a gas phase component; feeding the gas phase component into a light component removal tower to perform primary rectification, so as to obtain a light component and a heavy component; feeding the heavy component into a heavy component removal tower to perform secondary rectification, so as to obtain purified dimethyl carbonate. Through the synergistic innovation design of the feeding mode, material circulation, reactor structure, temperature control and tail gas treatment, the application realizes stable and controllable reaction process, effectively improves the purity and yield of dimethyl carbonate, reduces catalyst consumption and production cost, improves process safety and environmental protection, is suitable for different scale industrial production, and fills the technical blank of the existing fixed bed decarboxylation process.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, and in particular to a fixed-bed process and apparatus for the decarbonylation of dimethyl oxalate to dimethyl carbonate. Background Technology

[0002] Dimethyl carbonate (DMC) is a non-toxic, environmentally friendly green chemical raw material with excellent chemical properties. It is widely used in solvents, coatings, pharmaceutical intermediates, lithium battery electrolytes, and other fields, and market demand is increasing daily. Currently, the main methods for preparing dimethyl carbonate include the phosgene method, transesterification method, and carbonylation method. Among these, the phosgene method suffers from severe toxicity and pollution and has been gradually phased out. The transesterification method has high raw material costs and limited product yield, making it difficult to achieve large-scale profitability. Although the gas-phase oxidative carbonylation method developed by Ube Industries in Japan has a raw material cost advantage, it suffers from huge equipment investment, harsh reaction conditions (high pressure, mixing of flammable, explosive, and toxic gases), difficulties in environmental treatment, and high requirements for equipment materials. It is only suitable for large-scale chemical enterprises and is difficult to adapt to small and medium-sized industrial production.

[0003] The decarbonylation of dimethyl oxalate (DMO) to dimethyl carbonate is a novel and green preparation process with advantages such as wide availability of raw materials, simple reaction steps, and no pollution, making it highly promising for industrial application. However, current research on the decarbonylation of DMO to DMC technology faces the following technical bottlenecks: 1. Core bottleneck of the catalyst system: (1) Active components are easily lost: mainstream alkali metal carbonate (Cs2CO3, Rb2CO3) supported catalysts are prone to desorption and loss of active components during the reaction process, resulting in rapid decay of catalyst activity; (2) Weak resistance to carbon buildup: Carbon buildup is easily generated during the reaction process, covering the active sites of the catalyst, resulting in a catalyst life of only tens or hundreds of hours. Frequent regeneration significantly increases production costs and reduces the operating rate of the equipment. (3) It is difficult to balance activity and selectivity: When the reaction temperature is increased to improve the conversion rate of DMO, side reactions such as DMC decomposition and methanol generation are easily triggered, which leads to a decrease in the selectivity of the target product and restricts the product yield. (4) High catalyst cost: Cesium, rubidium and other precious metal components are expensive, and the loss and regeneration of active components further increase the catalyst consumption and reduce technical economy.

[0004] 2. Core bottlenecks in reaction engineering: (1) Contradictions in reactor selection: Liquid phase reactor process is complicated to operate, catalyst is easily broken, active components are easily lost, catalyst cost is high, reaction residence time is long and temperature is high, resulting in many side reactions and high energy consumption. At the same time, the scale of equipment is limited. (2) Significant engineering scale-up effect: Laboratory pilot data is difficult to be directly scaled up to industrial scale. Engineering challenges such as bed temperature control, material uniform distribution, and catalyst loading optimization are prominent, and there is a lack of experience in operating large-scale equipment. (3) Poor adaptability to reaction conditions: The alkaline reaction system and high temperature conditions place high demands on the materials of core equipment such as reactors and heat exchangers, which can easily lead to equipment corrosion and increase equipment investment costs.

[0005] 3. Separation and energy consumption bottlenecks: (1) Difficulty in product separation: The high temperature of the liquid phase reactor process leads to many side reactions and complex reaction liquid components, making separation difficult; (2) High energy consumption for separation: The liquid phase batch process produces a lot of by-products, requiring complex separation processes such as multi-tower distillation, side-stream extraction, and vacuum operation. The consumption of steam and cooling water is large, which significantly increases the overall energy consumption of the unit.

[0006] Furthermore, there is currently no stable operating experience of a commercially available fixed-bed DMO decarbonylation to DMC unit in China, and the process package and core equipment are insufficient. The purity and impurities (oxalic acid, water, etc.) of the raw material DMO significantly affect catalyst life, hindering the deep integration of the technology with the coal chemical industry chain. It is precisely because many bottlenecks in the DMO decarbonylation process have not yet been overcome that its industrial-scale promotion is further limited. Summary of the Invention

[0007] Based on the technical problems existing in the background art, this invention proposes a fixed-bed process and apparatus for the decarbonylation of dimethyl oxalate to dimethyl carbonate. Addressing the limitations of existing DMO decarbonylation processes, such as the limited scale of batch reactors, easy loss of active components from alkali metal catalysts, weak resistance to carbon deposition, high energy consumption, poor safety, and difficulty in product separation, this invention achieves stable and controllable reaction process through synergistic innovative design of feeding mode, material circulation, reactor structure, and temperature control. This effectively improves the purity and yield of dimethyl carbonate, reduces catalyst consumption and production costs, enhances process safety and environmental friendliness, and is adaptable to industrial production of different scales, filling the technological gap in existing fixed-bed decarbonylation processes.

[0008] The present invention proposes a fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate, comprising the following steps: S1. Dimethyl oxalate and additives are fed into the DMO heater and heated. Then, they are introduced into the fixed-bed reactor from the bottom and flow through the non-metallic decarbonylation catalyst filled in the tubes of the fixed-bed reactor in a bottom-in, top-out liquid flow manner to carry out the decarbonylation reaction, and obtain decarbonylation products including dimethyl carbonate, as well as residual raw materials and by-products. S2. After the above decarbonylation products, as well as the residual raw materials and by-products, are discharged from the fixed bed reactor, they are fed into a primary flash tank for flash separation to obtain gaseous and liquid components. The liquid component contains residual dimethyl oxalate and auxiliary raw materials, as well as some decarbonylation products of dimethyl carbonate. The liquid component is returned to the fixed bed reactor. S3. After the above gaseous components are discharged from the primary flash tank, they are fed into the light component removal tower for primary distillation to obtain light components and heavy components. The light components are cooled by the condenser and returned to the light component removal tower, while the heavy components are fed into the heavy component removal tower for secondary distillation to obtain purified dimethyl carbonate.

[0009] In this invention, the raw material dimethyl oxalate can be stored in a DMO feed tank before feeding. An auxiliary agent tank is set up next to the fixed-bed reactor to store the auxiliary agent. During feeding, the liquid dimethyl oxalate in the DMO feed tank is mixed with the auxiliary agent in the auxiliary agent tank in a certain proportion. The mixed material is used as the raw material for the reaction. The auxiliary agent can be continuously mixed with dimethyl oxalate in a quantitative manner to ensure that the feed components are uniform and stable, laying the foundation for the subsequent decarbonylation reaction. This co-feeding mode is not used in the existing DMO decarbonylation process. Meanwhile, the mixed raw materials enter the fixed-bed reactor from the bottom inlet, adopting a "bottom-in, top-out" flow pattern. Its core innovation lies in: by precisely controlling the feed flow rate and the liquid level in the reactor, ensuring that the catalyst is completely submerged in liquid dimethyl oxalate, forming a "liquid-phase full-tank" reaction system. This design achieves full contact between the material and the catalyst, with no catalyst dry zone or reaction dead zone, significantly improving the utilization rate of active sites. Moreover, compared with the liquid-phase batch reaction process, it significantly reduces catalyst wear, extends catalyst life, and makes bed temperature control easier. After the decarbonylation reaction is completed, the material needs to be separated by flash evaporation to achieve gas-liquid separation, in preparation for subsequent distillation purification. In order to obtain high-purity dimethyl carbonate product and solve the problems of unstable product purity, raw material waste and high energy consumption in the existing distillation process, this process adopts a distillation system that combines light removal tower and heavy removal tower for staged separation and purification.

[0010] Preferably, in step S1, the auxiliary agent is a low surface energy polar organic solvent, and the non-metallic decarbonylation catalyst is a polymer catalyst with solid base properties. The mass ratio of dimethyl oxalate to the adjuvant is 100:1-5:1, preferably 50:1-20:1.

[0011] The low surface energy polar organic solvent can be specifically selected from at least one of tetrafluoropropanol, hexafluoroisopropanol or trifluoroethanol. The low surface energy polar organic solvent of the present invention can, on the one hand, improve the reactivity and stability of polymer catalysts with solid base properties, ensuring efficient decarbonylation reaction, and on the other hand, reduce the surface tension of liquid dimethyl oxalate, ensuring that the surface of polymer catalysts with solid base properties is fully wetted by raw materials, preventing the formation of dry zones in the catalyst, and extending the service life of the catalyst. The solid base polymer catalyst can be selected as a melamine-grafted chlorosphere-based decarbonylation catalyst or a transition metal anion complex-modified organic amine-grafted chlorosphere-based decarbonylation catalyst. In this invention, dimethyl oxalate undergoes a decarbonylation reaction in a liquid phase environment within a temperature range of 120-170℃ under the synergistic effect of a polymer catalyst with solid alkaline properties and an auxiliary agent, generating dimethyl carbonate and gaseous byproducts (mainly carbon monoxide). The reaction equation is as follows: (CH3OOC)2 → (CH3O)2CO + CO↑. Compared with existing processes, this synergistic reaction system has a lower reaction temperature, significantly reduced side reactions, and greatly improved product purity.

[0012] Preferably, in step S1, before feeding dimethyl oxalate and the additive into the DMO heater, the process further includes feeding them into an inlet / outlet heat exchanger to exchange heat with the gaseous products generated from the decarbonylation reaction in the fixed-bed reactor.

[0013] In this invention, dimethyl oxalate and additives pass through a feed heat exchanger before being fed into the DMO heater. The high-temperature gaseous products and dimethyl carbonate gas from the fixed-bed reactor are used to heat the raw materials, thereby increasing the feed temperature. The raw materials are heated to the reaction temperature through the heat exchanger before being introduced into the fixed-bed reactor, which can effectively improve energy utilization.

[0014] Preferably, the fixed-bed reactor has multiple staggered reaction tubes filled with non-metallic decarbonylation catalysts inside, and the outside of the reaction tubes is a shell space where heating medium flows. Preferably, during the decarbonylation reaction, saturated steam at 1.5-2.0 MPa is introduced into the shell space to stabilize the reaction temperature in the fixed-bed reactor at 120-170°C. The feed flow rate is controlled so that the non-metallic decarbonylation catalyst is completely submerged in dimethyl oxalate. The decarbonylation products, including dimethyl carbonate, carbon monoxide, and carbon dioxide, are discharged from the top, while unreacted dimethyl oxalate and residual raw materials of the additives overflow from the upper side outlet of the fixed-bed reactor.

[0015] In this invention, a tubular fixed-bed reactor is employed. Unlike the uniformly distributed tube design of conventional tubular reactors, the tubes in this invention are arranged in a staggered manner. A non-metallic decarbonylation catalyst is packed inside the tubes. The non-metallic decarbonylation catalyst, used in conjunction with the aforementioned auxiliary agents, forms a synergistic effect, resulting in advantages such as low loss and long lifespan. The reactor shell space serves as a heat exchange channel for introducing a heat source. The staggered arrangement of the tubes achieves strong heat exchange between the heat source steam and the tubes, resulting in more uniform heat exchange and precise control of the reaction temperature. This avoids localized excessively high or low temperatures that could affect the reaction effect. At the same time, an insulation jacket is provided in the shell to reduce heat loss and lower energy consumption.

[0016] In this invention, since the catalyst used has a reaction temperature range of 120-170℃, 1.5-2.0MPa saturated steam can be introduced into the shell of the fixed-bed reactor as a heat source for the decarbonylation reaction. The core innovation lies in the fact that, through a closed-loop steam flow regulation system, the reaction temperature deviation in the reactor can be stably controlled within ±1℃, precisely matching the optimal reaction temperature range of non-metallic catalysts. This solves the problems of large reaction temperature fluctuations (above ±5℃) and low reaction selectivity in existing liquid-phase batch processes. At the same time, the use of 1.5-2.0MPa saturated steam reduces energy consumption by 15%-20% compared to the commonly used steam above 2.0MPa in existing processes.

[0017] In this invention, a side inlet (overflow port) is provided at the top of the fixed-bed reactor, and a gas outlet is provided at the top. Its core innovation lies in the fact that unreacted liquid dimethyl oxalate and additives overflow into the first-stage flash tank through the side inlet, while the dimethyl carbonate vapor and gaseous byproducts generated by the reaction escape from the top gas outlet and simultaneously enter the top of the first-stage flash tank. This achieves simultaneous collection and entry of gas and liquid materials into the flash tank, avoiding the problems of material retention and incomplete reaction caused by the stepwise extraction of gas and liquid in the existing process, and improving the utilization rate of raw materials.

[0018] Preferably, in step S2, the first-stage flash tank is equipped with a baffle plate inside; During the flash evaporation process, the operating temperature of the primary flash tank is controlled to be consistent with that of the fixed-bed reactor. By using a baffle plate to reduce gas-liquid entrainment, the gas phase components, including dimethyl oxalate and residual raw materials of the additives, are discharged from the top of the primary flash tank. The liquid phase components settle at the bottom of the primary flash tank and are returned to the bottom of the fixed-bed reactor via a reaction circulation pump. The conversion rate of DMO raw materials participating in the reaction reaches more than 95%.

[0019] In this invention, to reduce energy consumption, the operating temperature of the primary flash tank is kept consistent with the reaction temperature of the fixed-bed reactor. No additional heating or cooling is required. Efficient gas-liquid separation can be achieved by utilizing only the temperature and pressure difference of the material itself. Compared with the existing flash evaporation process, energy consumption is reduced by more than 30%. At the same time, the flash tank is equipped with a baffle plate to reduce gas-liquid entrainment and improve the separation effect.

[0020] In this invention, after flash separation, the gaseous products (carbon monoxide and carbon dioxide) and dimethyl carbonate vapor are discharged from the top of the primary flash tank and enter the subsequent distillation system for purification. The unreacted liquid dimethyl oxalate, additives, and a small amount of dimethyl carbonate settle at the bottom of the primary flash tank and are returned to the bottom feed inlet of the fixed-bed reactor by a reaction circulation pump installed at the bottom of the primary flash tank. This achieves a closed-loop material circulation reaction between the fixed-bed reactor, the primary flash tank, and the reaction circulation pump. The core innovation lies in the fact that the circulation pipeline is equipped with a flow regulating valve and a purity detection interface, which can adjust the circulation flow rate in real time according to the DMO conversion rate to ensure that the unreacted dimethyl oxalate reacts fully and reduce raw material waste.

[0021] Preferably, in step S3, the light-weight removal tower is equipped with a high-efficiency mass transfer tray. In a single distillation process, light components including carbon monoxide, carbon dioxide, methanol, and dimethyl ether are removed, with a light component removal rate of 99%. The light components are discharged from the top of the light component removal tower, while the heavy components settle in the bottom of the light component removal tower and are then fed into the heavy component removal tower via the light component removal tower circulation pump.

[0022] In this invention, the gaseous products (carbon monoxide and carbon dioxide) discharged from the top of the primary flash tank, along with dimethyl carbonate vapor, are fed into a light component removal tower after passing through an inlet / outlet heat exchanger. The light component removal tower employs a "high-efficiency mass transfer tray," the core innovation of which lies in: by optimizing the tray structure, the separation efficiency between light components and gaseous products is improved. The top of the light component removal tower precisely discharges gaseous products (carbon monoxide and carbon dioxide) and light component impurities (methanol, dimethyl ether, methyl formate, etc.), while the bottom of the tower yields liquid materials (unreacted dimethyl oxalate and the decarbonylation product dimethyl carbonate). A reboiler is arranged in the bottom of the light component removal tower, and the bottom temperature of the light component removal tower is reasonably controlled to ensure that all light components can be separated, achieving a light component removal rate of over 99%, thus preventing light components from entering subsequent processes and affecting product purity.

[0023] Preferably, in step S3, the deweight removal tower is equipped with a reflux ratio adjustment system; During the secondary distillation process, the temperature of the bottom of the de-reduction column is controlled at 160-170℃, and the reflux ratio is adjusted by the reflux ratio adjustment system. Dimethyl carbonate with a purity of not less than 99.9% is discharged from the top of the de-reduction column, condensed by the de-reduction column condenser, and then enters the de-reduction column reflux tank. When the purity of the product in the de-reduction column reflux tank reaches the preset purity, it enters the purified DMC collection tank for collection. Unreacted dimethyl oxalate is then discharged from the bottom of the column and returned to the DMO feed tank by the de-reduction column bottom pump to participate in the reaction again, thereby reducing the loss of DMO raw materials.

[0024] In this invention, the liquid material from the bottom of the light-light removal tower is pumped into the heavy-weight removal tower via a light-light removal tower bottom pump. The operating temperature of the heavy-weight removal tower bottom is controlled at around 165°C to accommodate the boiling point difference between dimethyl carbonate and dimethyl oxalate. Its core innovation lies in the following: a reflux condensation adjustment system is installed at the top of the heavy-weight removal tower, which can adjust the reflux ratio in real time according to the product purity to ensure that the dimethyl carbonate product discharged from the top of the tower has a purity of ≥99.9%. At the same time, the unreacted dimethyl oxalate discharged from the bottom of the tower is returned to the dimethyl oxalate storage tank via a circulation pump to participate in the reaction again, achieving full recovery of raw materials and increasing the raw material utilization rate to over 98%. In addition, an insulation layer is installed at the bottom of the heavy-weight removal tower to reduce heat loss and reduce distillation energy consumption.

[0025] Preferably, in step S3, the light components discharged from the top of the light component removal tower are controlled at a top temperature of around 60°C. The gaseous products are cooled by a two-stage condenser, wherein the first-stage condenser uses circulating water for cooling and the second-stage condenser uses a refrigerant at around -20°C for cooling. The resulting liquid light components are collected as by-products and enter the reflux tank of the light component removal tower, and then return to the light component removal tower. The uncondensed carbon monoxide and carbon dioxide gases are connected to the flare system. Similarly, the non-condensable gases discharged from the condenser of the heavy component removal tower are also connected to the flare system.

[0026] Preferably, in step S2, the online / offline purity detection of the liquid phase component returned to the bottom of the fixed bed reactor via the reaction circulation pump, when the purity of dimethyl oxalate is detected to be less than 70%, the liquid phase component is discharged into the waste heavy component collection tank via the reaction circulation pump, and new dimethyl oxalate and additives are added into the reaction system.

[0027] The gaseous products and light components discharged from the top of the light component removal tower are condensed and cooled by a two-stage heat exchanger. The core innovation lies in the "series-type high-efficiency condensation" design of the two-stage heat exchanger. The first-stage cooler uses circulating water cooling to remove most of the light components; the second-stage cooler uses refrigerant at around -20°C to achieve deep condensation of the light components. The condensed liquid light components (methanol, dimethyl ether, methyl formate, etc.) are collected and can be recycled as by-products. At the same time, it can be used as a reflux regulation system, which can adjust the reflux ratio in real time according to the condensation of light components, so that the recovery rate of light components reaches more than 99%, achieving efficient utilization of resources.

[0028] The top of the deweighting tower is designed with a condenser reflux tank to collect dimethyl carbonate vapor, reduce product loss, and improve product yield. The small amount of gas discharged from the top of the condenser reflux tank is also connected to the flare system, reducing equipment investment and environmental costs. In addition, CO gas can be recovered by setting up a gas separation system (the gas products are mainly CO and CO2) for other uses.

[0029] Furthermore, to ensure the long-term stable operation of the entire production system and address issues such as the inability to monitor catalyst activity in real time, complex catalyst replacement processes, and long downtime in existing processes, this invention incorporates targeted innovations: Regularly monitoring the purity of dimethyl oxalate at the outlet of the reaction circulation pump and setting a reasonable purity threshold. The core innovation lies in employing an online / offline purity detection device to monitor dimethyl oxalate purity in real time and determine catalyst activity. When the dimethyl oxalate purity is detected to be below the threshold, it indicates a decrease in catalyst activity, with multi-carbon products generated during the reaction occupying active sites, thus affecting the reaction conversion rate and failing to meet production requirements. In this case, the material is pumped into a waste heavy component collection tank via the reaction circulation pump, while fresh DMO and additives are simultaneously introduced into the fixed-bed reactor. The fresh additives clean the adsorption and desorption at the catalyst active site interfaces within the tube reactor, restoring the normal reaction process. The catalyst replacement cycle can reach more than one year, thereby ensuring long-term stable system operation and improving production efficiency.

[0030] The present invention also proposes a fixed-bed apparatus for the decarbonylation of dimethyl oxalate to dimethyl carbonate, comprising: a DMO heater, a fixed-bed reactor, a primary flash tank, a light-weight removal tower, and a heavy-weight removal tower; The DMO heater includes an inlet and an outlet for feeding dimethyl oxalate and additives, with the outlet connected to the bottom inlet of the fixed-bed reactor. The fixed-bed reactor is filled with a non-metallic decarbonylation catalyst for the decarbonylation reaction. It includes an outlet for the decarbonylation product and an outlet for the residual raw material, both of which are connected to the upper feed inlet of the primary flash tank. The primary flash tank includes a gas phase component outlet and a liquid phase component outlet. The liquid phase component outlet is connected to the bottom inlet of the fixed bed reactor, and the gas phase component outlet is connected to the inlet of the light component removal tower through an inlet and outlet heat exchanger. The light component removal tower includes a light component outlet and a heavy component outlet. The light component outlet is connected to a condenser, a light component removal tower reflux tank, and a light component removal tower reboiler that are matched with the light component removal tower. The outlet of the light component removal tower reflux tank is connected to the top reflux port of the light component removal tower, and the heavy component outlet is connected to the inlet of the heavy component removal tower. The de-heavy component tower also includes a light component outlet and a heavy component outlet. The light component outlet is connected to the de-heavy component tower condenser, the de-heavy component tower reflux tank, and the de-heavy component tower reboiler that are matched with the de-heavy component tower. The outlet of the de-heavy component tower reflux tank is connected to the refined DMC collection tank, and the heavy component outlet is connected to the DMO feed tank.

[0031] Compared with existing liquid-phase batch reactor technology, this invention has the following significant features and innovative advantages, all of which are directly brought about by the innovative design of this invention: (1) Innovative advantages of reactor and feed: The fixed bed reactor with "liquid phase full tank + staggered tube" is adopted and "bottom in and top out" feed mode is used to completely solve the pain points of the batch reactor, such as the difficulty in scale-up, easy wear of catalyst and easy loss of active components; the catalyst is completely submerged in liquid raw materials, with no dry area and no dead zone of reaction, the active sites are fully utilized and the catalyst loss is reduced. At the same time, the 1.5-2.0MPa saturated steam closed-loop temperature control keeps the temperature fluctuation within ±1℃. The lower reaction temperature reduces side reactions and greatly improves reaction selectivity.

[0032] (2) Material circulation and energy consumption innovation advantages: synchronous gas-liquid split flash evaporation, closed-loop circulation without additional energy consumption, and collaborative design reduce energy consumption by 15%-30% compared with existing processes; the raw material full recovery design greatly reduces raw material waste and lowers raw material costs; at the same time, no high-pressure steam is required, resulting in significant energy consumption advantages.

[0033] (3) Innovative advantages in product purity and resource utilization: High-efficiency mass transfer dual-tower distillation + real-time adjustment of reflux ratio can obtain dimethyl carbonate products with a purity of ≥99.9%; deep condensation and recovery of light components with a recovery rate of over 99% breaks through the bottleneck of existing processes where "environmental protection and energy saving cannot be taken into account".

[0034] (4) Cost and safety innovation advantages: online / offline monitoring of catalyst activity + rapid catalyst replacement design improves production efficiency; catalyst loss is reduced, energy consumption is reduced, and raw material utilization is improved. The overall production cost is reduced by more than 20% compared with the existing liquid phase batch reaction process. At the same time, the liquid phase reaction system has no high pressure, flammable, explosive and toxic gas mixing, which greatly improves safety and is suitable for small and medium-sized industrial production, filling the gap in the adaptability of existing processes.

[0035] (5) Industrial feasibility and innovative advantages: The entire process is continuous and stable. Although the equipment is conventional chemical equipment, the performance has been significantly improved through innovative design of structure and process. The operating parameters are easy to control and the system is easy to maintain. It can achieve large-scale industrial continuous production according to production needs. At the same time, it is suitable for small and medium-sized enterprises and has good industrial application prospects and promotion value. It completely solves the core technical bottleneck of the existing DMO decarbonylation process and forms a significant differentiated innovation from the existing process. Attached Figure Description

[0036] Figure 1 This is a flowchart of the fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to the present invention; The diagram is labeled as follows: 1-Additive feed tank, 2-DMO feed tank, 3-Additive feed pump, 4-DMO feed pump, 5-Inlet / outlet heat exchanger, 6-DMO heater, 7-Fixed bed reactor, 8-First stage flash tank, 9-Reaction circulation pump, 10-Waste heavy component collection tank, 11-Light component removal tower, 12-First stage cooler, 13-Second stage cooler, 14-Light component removal tower reflux tank, 15-Light component removal tower reflux pump, 16-Light component collection tank, 17-Light component removal tower reboiler, 18-Light component removal tower kettle pump, 19-Heavy component removal tower, 20-Heavy component removal tower condenser, 21-Heavy component removal tower reflux tank, 22-Heavy component removal tower reflux pump, 23-Heavy component removal tower reboiler, 24-Heavy component removal tower kettle pump, 25-Refined DMC collection tank. Detailed Implementation

[0037] The following detailed description of the process flow and advantages of the present invention, with reference to specific embodiments, is provided. These embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0038] Example 1 Reference Figure 1 This embodiment proposes a fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate, specifically including: (1) The additive and dimethyl oxalate are stored in the additive tank 1 and the DMO feed tank 2, respectively, and are fed into the feed heat exchanger 5 via the additive feed pump 3 and the DMO feed pump 4 for heat exchange. The additive is a low surface energy polar organic solvent, specifically tetrafluoropropanol, and the mass ratio of the two is 3:100. With the help of the additive, the surface of the subsequent non-metallic decarbonylation catalyst is fully wetted by the raw material. In the feed heat exchanger 5, the additive and dimethyl oxalate exchange heat with the high temperature product gas from the outlet of the subsequent first-stage flash tank 8. After heat exchange, the additive and dimethyl oxalate are then fed into the DMO heater 6 and heated to the set reaction temperature. (2) The additives and dimethyl oxalate that have reached the reaction temperature enter the fixed-bed reactor 7 for decarbonylation reaction. The fixed-bed reactor 7 is a tubular fixed-bed reactor, which has multiple staggered reaction tubes filled with non-metallic decarbonylation catalysts. The non-metallic decarbonylation catalysts are polymer catalysts with solid alkaline properties, specifically melamine-grafted chlorosphere-based decarbonylation catalysts, which can be prepared according to the method described in Example 1 of the published patent CN121715217A. The outside of the reaction tubes is a shell space where the heating medium flows. In the fixed-bed reactor 7, 1.7M is introduced from the shell space. The saturated steam of Pa is used to stabilize the reaction temperature of the fixed-bed reactor 7 at 170℃ (closed-loop temperature control ±1℃) through a closed-loop regulation system. The mixture of additives and dimethyl oxalate is fed into the bottom inlet of the fixed-bed reactor 7. The feed flow rate is controlled to ensure that the aforementioned non-metallic decarbonylation catalyst is completely submerged in liquid dimethyl oxalate. The mixture flows through the catalyst bed in the reaction tube in a bottom-in, top-out liquid flow manner. Under the synergistic effect of the non-metallic decarbonylation catalyst and the additives, dimethyl oxalate undergoes a decarbonylation reaction to produce dimethyl carbonate and carbon monoxide, along with a small amount of byproducts. (3) The products of dimethyl carbonate and carbon monoxide are drawn out from the top outlet of the fixed bed reactor 7 and fed into the first-stage flash tank 8 for flash separation. At the same time, unreacted dimethyl oxalate and additives overflow from the upper side outlet of the fixed bed reactor 7 and are simultaneously fed into the first-stage flash tank 8 for flash separation. The first-stage flash tank 8 is equipped with a guide plate, and its operating temperature is consistent with that of the fixed bed reactor 7, that is, the operating temperature is synchronously 170℃. With the help of the guide plate, gas-liquid entrainment is reduced, and gas phase material and liquid phase material are obtained. Among them, the gas phase material is discharged from the top of the first-stage flash tank 8, and the liquid phase material dimethyl oxalate settles at the bottom and returns to the bottom of the fixed bed reactor 7 through the reaction circulation pump (with flow regulating valve) 9 to achieve closed-loop circulation. The conversion rate of dimethyl oxalate reaches more than 95%. (4) The separated gaseous material is drawn from the top of the primary flash tank 8 and fed into the light component removal tower 11 for primary distillation. The light component removal tower 11 is equipped with high-efficiency mass transfer trays, and the light component removal rate reaches 99%. The bottom of the light component removal tower 11 is also equipped with a light component removal tower reboiler 17 to regulate the bottom temperature and achieve effective separation of light components. Carbon monoxide and light components (methanol, dimethyl ether, methyl formate) are discharged from the top of the tower, and the liquid material (dimethyl oxalate + dimethyl carbonate) discharged from the bottom of the tower is sent to the heavy component removal tower 19 via the light component removal tower circulation pump 18. The bottom of the heavy component removal tower 19 is also equipped with a heavy component removal tower reboiler 2. 3. Used to regulate the bottom temperature of the column. The bottom temperature of the de-reacting column 19 is controlled at 168℃. The de-reacting column 19 is also equipped with a reflux ratio adjustment system. Specifically, the reflux is adjusted by the de-reacting column reflux pump 22. By adjusting the reflux ratio, the dimethyl carbonate with a purity of 99.9% discharged from the top of the column passes through the de-reacting column condenser 20 and the de-reacting column reflux tank 21 in sequence, and then enters the purified DMC collection tank 25 for collection by the de-reacting column reflux pump 22. The unreacted dimethyl oxalate in the bottom of the column is returned to the DMO feed tank 2 by the de-reacting column bottom pump 24 to participate in the reaction again. The raw material utilization rate reaches 98.2%. (5) The light components discharged from the top of the light component removal tower 11 are cooled by the primary cooler 12 and the secondary cooler 13. The primary cooler uses circulating water for cooling and the secondary cooler uses a refrigerant at around -20°C. The condensed liquid light components (methanol, dimethyl ether, etc.) are collected as by-products with a recovery rate of 99%. They enter the light component removal tower reflux tank 14 and are then returned to the light component removal tower 11 by the light component removal tower reflux pump 15. The uncondensed carbon monoxide and carbon dioxide gases are introduced into the flare system. The non-condensable gases in the heavy component removal tower condenser 20 are also introduced into the flare system. (6) The purity of dimethyl oxalate at the outlet of reaction circulation pump 9 is detected online / offline. The purity threshold is set to 70%. When the purity is detected to be lower than 70%, the feeding is stopped and all materials are discharged into the waste heavy component collection tank 10 through reaction circulation pump 9. Then, fresh DMO and fresh additives are added back to the reaction system to resume feeding and reaction operation.

[0039] In this embodiment, the conversion rate of dimethyl oxalate is over 95%, the yield of dimethyl carbonate is over 95%, the product purity is 99.9%, and the system can operate continuously and stably for more than one year.

[0040] Example 2 This embodiment also proposes a fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate, specifically referring to Embodiment 1. In addition to the reaction temperature of the fixed-bed reactor 7 being stabilized at 160℃ (closed-loop temperature control ±1℃), the operating temperature of the first-stage flash tank 8 is also synchronously set at 160℃.

[0041] In this embodiment, the conversion rate of dimethyl oxalate is 91%, the yield of dimethyl carbonate is 89%, the product purity is 99.9%, and the system can operate continuously and stably for more than one year.

[0042] The above results indicate that the reaction conversion rate and product yield can be further adjusted by modifying the process parameters, demonstrating strong adaptability.

[0043] Comparative Example 1 This comparative example presents a fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate, specifically following the steps described in Example 1, except that the use of additives is omitted.

[0044] In this comparative example, the conversion rate of dimethyl oxalate was 93%, the yield of dimethyl carbonate was 91%, the product purity was 98.2%, and the system's continuous stable operation time was only 800 hours.

[0045] Comparative Example 2 This comparative example presents a fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate, specifically referring to Example 1, except that the auxiliary agent used is a low-surface-energy nonpolar organic solvent, specifically n-hexane.

[0046] In this comparative example, the conversion rate of dimethyl oxalate was 87%, the yield of dimethyl carbonate was 73%, the product purity was 98.7%, and the system's continuous stable operation time was only 1200 hours.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate, characterized in that, Includes the following steps: S1. Dimethyl oxalate and additives are fed into a DMO heater and heated. Then, they are introduced into the fixed-bed reactor from the bottom and flow through the non-metallic decarbonylation catalyst packed in the fixed-bed reactor in a bottom-in, top-out liquid flow manner to carry out the decarbonylation reaction, and obtain decarbonylation products including dimethyl carbonate, as well as residual raw materials and by-products. S2. After the above decarbonylation products, as well as the residual raw materials and by-products, are discharged from the fixed bed reactor, they are fed into a primary flash tank for flash separation to obtain liquid phase components and gas phase components including the residual raw materials. The liquid phase components are returned to the fixed bed reactor. S3. After the above gaseous components are discharged from the primary flash tank, they are fed into the light component removal tower for primary distillation to obtain light components and heavy components. The light components are cooled by the condenser and returned to the light component removal tower, while the heavy components are fed into the heavy component removal tower for secondary distillation to obtain purified dimethyl carbonate.

2. The fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 1, characterized in that, In step S1, the auxiliary agent is a low surface energy polar organic solvent, and the non-metallic decarbonylation catalyst is a polymer catalyst with solid basic properties. The mass ratio of dimethyl oxalate to the adjuvant is 100:1-5:

1.

3. The fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 1 or 2, characterized in that, In step S1, before feeding dimethyl oxalate and the additives into the DMO heater, the process also includes feeding them into the feed heat exchanger to exchange heat with the gaseous products generated by the decarbonylation reaction in the fixed-bed reactor.

4. The fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 1 or 2, characterized in that, In step S1, the fixed-bed reactor is equipped with multiple staggered reaction tubes filled with non-metallic decarbonylation catalysts, and the outside of the reaction tubes is a shell space in which heating medium flows. During the decarbonylation reaction, saturated steam at 1.5-2.0 MPa is introduced into the shell space to stabilize the reaction temperature in the fixed-bed reactor at 120-170℃. The feed flow rate is controlled so that the non-metallic decarbonylation catalyst is completely submerged in dimethyl oxalate. The decarbonylation products, including dimethyl carbonate, carbon monoxide, and carbon dioxide, are discharged from the top, while the residual raw materials, including dimethyl oxalate and additives, overflow from the upper side outlet of the fixed-bed reactor.

5. The fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 1 or 2, characterized in that, In step S2, a baffle plate is installed inside the primary flash tank; During the flash evaporation process, the operating temperature of the primary flash tank is controlled to be consistent with that of the fixed bed reactor. By using a baffle plate to reduce gas-liquid entrainment, the gas phase components are discharged from the top of the primary flash tank, while the liquid phase components, including the residual raw materials, settle at the bottom of the primary flash tank and are returned to the bottom of the fixed bed reactor via a reaction circulation pump.

6. The fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 1, characterized in that, In step S3, the light-weight removal tower is equipped with a high-efficiency mass transfer tray. In a single distillation process, light components including carbon monoxide, carbon dioxide, methanol, and dimethyl ether are removed, with a light component removal rate of 99%. The light components are discharged from the top of the light component removal tower, while the heavy components settle in the bottom of the light component removal tower and are then fed into the heavy component removal tower via the light component removal tower circulation pump.

7. The fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 1, characterized in that, In step S3, the deweight removal tower is equipped with a reflux ratio adjustment system; During the secondary distillation process, the bottom temperature of the de-reduction column is controlled at 160-170℃. The reflux ratio is adjusted by the reflux ratio adjustment system. Dimethyl carbonate with a purity of not less than 99.9% is discharged from the top of the de-reduction column. After being condensed by the de-reduction column condenser, it enters the de-reduction column reflux tank. When the purity of the product in the de-reduction reflux tank reaches the preset purity, it enters the purified DMC collection tank for collection. Unreacted dimethyl oxalate is then discharged from the bottom of the column and returned to the DMO feed tank by the de-reduction column bottom pump to participate in the reaction again.

8. The fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 6 or 7, characterized in that, In step S3, the temperature at the top of the light component removal tower is controlled at 60°C. The light component discharged from the top of the light component removal tower is cooled by two-stage condensation. The first-stage condenser uses circulating water for cooling, and the second-stage condenser uses -20°C refrigerant for cooling. The resulting liquid light component is collected as a byproduct and enters the light component removal tower reflux tank, and then returns to the light component removal tower. Uncondensed carbon monoxide and carbon dioxide gases are connected to the flare system. Similarly, the non-condensable gases discharged from the heavy component removal tower condenser are also connected to the flare system.

9. The fixed-bed process for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 1, characterized in that, In step S2, the online / offline purity detection of the liquid phase component returned to the bottom of the fixed bed reactor via the reaction circulation pump is performed. When the purity of dimethyl oxalate is detected to be less than 70%, the liquid phase component is discharged into the waste heavy component collection tank via the reaction circulation pump, and new dimethyl oxalate and additives are added into the reaction system.

10. A fixed-bed apparatus for the decarbonylation of dimethyl oxalate to dimethyl carbonate, characterized in that, include: DMO heater, fixed-bed reactor, primary flash tank, light-weight removal tower and heavy-weight removal tower; The DMO heater includes an inlet and an outlet for feeding dimethyl oxalate and additives, with the outlet connected to the bottom inlet of the fixed-bed reactor. The fixed-bed reactor is filled with a non-metallic decarbonylation catalyst for the decarbonylation reaction. It includes an outlet for the decarbonylation product and an outlet for the residual raw material, both of which are connected to the upper feed inlet of the primary flash tank. The primary flash tank includes a gas phase component outlet and a liquid phase component outlet. The liquid phase component outlet is connected to the bottom inlet of the fixed bed reactor, and the gas phase component outlet is connected to the inlet of the light component removal tower through an inlet and outlet heat exchanger. The light component removal tower includes a light component outlet and a heavy component outlet. The light component outlet is connected to a condenser, a light component removal tower reflux tank, and a light component removal tower reboiler that are matched with the light component removal tower. The outlet of the light component removal tower reflux tank is connected to the top reflux port of the light component removal tower, and the heavy component outlet is connected to the inlet of the heavy component removal tower. The de-heavy component tower also includes a light component outlet and a heavy component outlet. The light component outlet is connected to the de-heavy component tower condenser, the de-heavy component tower reflux tank, and the de-heavy component tower reboiler that are matched with the de-heavy component tower. The outlet of the de-heavy component tower reflux tank is connected to the refined DMC collection tank, and the heavy component outlet is connected to the DMO feed tank.

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