A method and system for preparing electronic grade dimethyl carbonate from dimethyl oxalate

Abstract

The present application relates to a kind of preparation methods and systems of electronic grade dimethyl carbonate prepared from dimethyl oxalate, the method comprises the following steps: dimethyl oxalate is preheated and sent into decarboxylation reactor to carry out decarboxylation reaction, carbon monoxide, dimethyl carbonate and other light components are extracted from the top of decarboxylation reactor, and heavy components are extracted from the bottom of decarboxylation reactor;Carbon monoxide, dimethyl carbonate and other light components extracted are separated after gas-liquid, and liquid phase dimethyl carbonate is sent into rectifying column to carry out rectification purification;Electronic grade dimethyl carbonate product is obtained by crystallization purification in refrigeration crystallization device after rectification, and crystallization mother liquor returns rectifying column;Decarboxylation reactor is three-stage reaction tower, and rectifying section, reaction section, stripping section are sequentially from top to bottom.The present application is completely reacted by the design of three-stage decarboxylation reactor;Heavy components generated are extracted in real time, and catalyst stability is high;Electronic grade DMC is prepared by using rectifying column coupled with crystallization tower, and the yield of DMC is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of electronic-grade dimethyl carbonate production technology, and in particular to a method and system for preparing electronic-grade dimethyl carbonate from dimethyl oxalate. Background Technology

[0002] Dimethyl carbonate (DMC) is a chemically active and physically excellent material that is non-toxic and readily biodegradable. It is a low-pollution, environmentally friendly, and green basic chemical raw material that can be used as a solvent, gasoline additive, lithium-ion battery electrolyte, and carbonylation, methylation, and carbonyl methoxylation reagent. It is widely used in the chemical industry.

[0003] Currently, methods for synthesizing dimethyl carbonate include: phosgene method, transesterification method, gas-phase carbonylation method, methanol oxidative carbonylation method, urea alcoholysis method, and direct synthesis from carbon dioxide (CO2) and methanol. In recent years, domestic coal-to-ethylene glycol technology has become increasingly mature, and the utilization of dimethyl oxalate as an intermediate product has received widespread attention. Research on the decarbonylation of dimethyl oxalate to prepare dimethyl carbonate is increasing.

[0004] CN115894238A discloses a method and apparatus for producing alkyl carbonate from alkyl oxalate. The method employs a batch reactor, where raw materials are fed into the reactor and react upon contact with a catalyst. The products leave the reactor in gaseous form and are then obtained by distillation to obtain DMC. The catalyst is stored in a cylindrical catalyst cage and requires periodic replenishment and recovery. While the apparatus is simple and suitable for industrial application, it suffers from drawbacks such as insufficient purity of the DMC product and high process costs.

[0005] CN115974694A discloses a method for producing dimethyl carbonate from dimethyl oxalate. The method involves feeding dimethyl oxalate, an alkali metal-alkaline earth metal complex organic salt, and methanol into a reactor for a decarbonylation reaction to produce dimethyl carbonate. After washing the gaseous phase of dimethyl carbonate in a scrubbing tower, the product is then separated in a product tower to obtain industrial-grade dimethyl carbonate. This system simplifies the process flow and improves catalyst utilization by incorporating a catalyst recovery process; however, it still suffers from problems such as insufficient purity of the prepared DMC product.

[0006] CN113264833A discloses a method for preparing battery-grade dimethyl carbonate by catalytic reactive dimethyl oxalate distillation. This method improves upon the conventional batch distillation process for dimethyl carbonate from dimethyl oxalate by coupling the pretreatment of raw materials, reactive distillation, and melt crystallization purification of the crude product. However, while this method can produce electronic-grade dimethyl carbonate, the pretreatment process for dimethyl oxalate is relatively complex, requiring a catalyst and involving a long processing time, significantly increasing the cost for industrial application.

[0007] In summary, current technical solutions for preparing dimethyl carbonate from dimethyl oxalate either suffer from insufficient purity of dimethyl carbonate, making it unsuitable for electronic applications, or they involve complex processes, high catalyst costs, and are unsuitable for large-scale industrial applications. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method and system for preparing electronic-grade dimethyl carbonate from dimethyl oxalate. This invention uses reactive distillation and a three-stage decarbonylation reactor to ensure complete reaction; the generated heavy components are collected in real time, and the catalyst has high stability; a distillation column coupled with a crystallization column is used to prepare electronic-grade DMC and improve the yield of electronic-grade DMC.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] The first objective of this invention is to provide a method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate, the method comprising the following steps:

[0011] Dimethyl oxalate is fed into a decarbonylation reactor to carry out the decarbonylation reaction. Carbon monoxide, dimethyl carbonate and other light components are collected from the top of the decarbonylation reactor, while heavy components are collected from the bottom of the decarbonylation reactor.

[0012] The carbon monoxide, dimethyl carbonate and other light components collected from the top of the decarbonylation reactor are separated into gas and liquid components. The carbon monoxide is separated as a gaseous product, and the dimethyl carbonate is purified by distillation in the form of a liquid phase in a distillation column to obtain dimethyl carbonate.

[0013] The dimethyl carbonate obtained by distillation is purified by crystallization in a freeze crystallization apparatus to obtain electronic grade dimethyl carbonate product, and the mother liquor from crystallization is returned to the distillation column.

[0014] Furthermore, the decarbonylation reactor is a three-stage reaction tower, consisting of a rectification section, a reaction section, and a stripping section from top to bottom.

[0015] Furthermore, the rectifying section and stripping section of the three-stage reaction tower are filled with packing material; the reaction section of the three-stage reaction tower is filled with catalyst, and the reaction section includes a catalyst bed.

[0016] Furthermore, the height of the packing in the rectification section is one-quarter to one-third of the height of the three-stage reaction tower; the height of the catalyst bed is one-third to one-half of the height of the three-stage reaction tower; and the height of the packing in the stripping section is one-quarter to one-third of the height of the three-stage reaction tower.

[0017] Furthermore, the freeze crystallization apparatus is a melt crystallizer.

[0018] Furthermore, the catalyst is a supported catalyst; the supported catalyst includes a support, an active component, and an auxiliary agent; the support is one or more of activated carbon, silica, and activated alumina; the active component is one or more of alkali metals or alkaline earth metals, and the loading of the active component is 2-10 wt% based on metal content; the auxiliary agent is one or more of phosphorus or boron, and the loading of the auxiliary agent is 0.1-3 wt% based on elemental content.

[0019] Furthermore, the preparation of the catalyst includes the following steps: weighing the active component precursor and the auxiliary agent precursor, dissolving them in water, preparing a solution, impregnating an equal volume onto a support, drying, and then calcining in a tube furnace under a N2 atmosphere to obtain the catalyst.

[0020] Furthermore, the precursor of the active component is an alkali metal salt or an alkaline earth metal salt or a combination thereof, and the precursor of the auxiliary agent is a phosphorus- or boron-containing acid or its salt.

[0021] Further, the method includes the following steps: preheating the raw material dimethyl oxalate (DMO) and feeding it into a decarbonylation reactor, where a decarbonylation reaction occurs on the catalyst of the decarbonylation reactor at 180-250℃ and 1.0-3.0MPa. The top of the decarbonylation reactor yields purified carbon monoxide (CO) and dimethyl carbonate (DMC), while the bottom of the decarbonylation reactor yields a small amount of heavy components. The resulting dimethyl carbonate is purified to 99.9% by distillation in a distillation column, and then crystallized in a freeze crystallization device to obtain electronic-grade dimethyl carbonate. The mother liquor from the crystallization is returned to the distillation column.

[0022] Furthermore, the inlet of the dimethyl oxalate is located between the rectification section and the reaction section of the decarbonylation reactor, flowing downwards through the catalyst bed of the reaction section. The reaction products, carbon monoxide, dimethyl carbonate, and other light components, along with some unreacted dimethyl oxalate, are purified in the rectification section of the decarbonylation reactor in gaseous form. The remaining unreacted dimethyl oxalate and heavy components are separated in the stripping section of the decarbonylation reactor in liquid form. The unreacted dimethyl oxalate obtained from the rectification section is returned to the reaction section in liquid form, and the unreacted dimethyl oxalate obtained from the stripping section is returned in gaseous form for further reaction, thus ensuring that the input dimethyl oxalate... In the complete reaction, carbon monoxide, dimethyl carbonate, and other light components are collected from the top of the decarbonylation reactor. After gas-liquid separation, carbon monoxide is separated as a gaseous product, while dimethyl carbonate and other light components are sent to a distillation column. The heavy components are collected from the bottom of the decarbonylation reactor. During this process, a small amount of unreacted DMO, whether it enters the stripping section in liquid form or the rectification section in gaseous form, will return to the reaction section to continue the reaction, so that the input raw material DMO can be completely reacted. The DMO is sandwiched in the reaction section by the rectification section and the stripping section until it is completely reacted and leaves the three-stage reaction column as a product. There is no additional pipeline for material transportation.

[0023] Other light components are collected from the top of the distillation column as byproducts, while dimethyl carbonate is collected from the side stream and further purified by crystallization to obtain electronic-grade dimethyl carbonate. The bottom material of the distillation column is returned to the decarbonylation reactor.

[0024] Furthermore, the method includes the following steps:

[0025] Dimethyl oxalate, the raw material, is discharged from the raw material buffer tank and preheated before being fed into the upper section of the decarbonylation reactor. The material flows from top to bottom through the catalyst bed in the reaction section of the decarbonylation reactor and reacts. The resulting reaction products are CO, DMC, and a small amount of gaseous unreacted DMO. The vapor is purified by passing upward in the rectification section at the top of the decarbonylation reactor in gas phase. CO, DMC, and a small amount of light components are collected from the top of the decarbonylation reactor. A small amount of unreacted DMO is returned to the reaction section of the decarbonylation reactor to continue the reaction. A small amount of liquid unreacted DMO and heavy components are separated in the stripping section of the decarbonylation reactor. The heavy components are collected from the bottom of the decarbonylation reactor, and the unreacted DMO is returned to the reaction section of the decarbonylation reactor to continue the reaction.

[0026] The DMC and CO obtained from the top of the decarbonylation reactor undergo gas-liquid separation in the gas-liquid separator. The gaseous CO is taken as the product, and the liquid DMC enters the distillation column for separation. A small amount of light components are collected from the top of the distillation column as a by-product light component. 99.9% pure DMC is collected from the side stream of the distillation column, and the bottom material of the distillation column is returned to the decarbonylation reactor.

[0027] After distillation, the DMC enters the cryogenic crystallization unit via an intermediate DMC buffer tank. After crystallization and purification, electronic-grade DMC is obtained. The mother liquor is returned to the distillation column via a mother liquor buffer tank to recover DMC.

[0028] Furthermore, the dimethyl oxalate needs to be preheated before being fed into the system, and the preheating temperature is 180-240℃; the feed mass hourly space velocity (WHSV) of the dimethyl oxalate is 0.1-10 h⁻¹. -1 .

[0029] More preferably, the feed mass hourly space velocity (WHSV) of the dimethyl oxalate is 1-5 h⁻¹. -1 .

[0030] Furthermore, a liquid distributor is installed after the dimethyl oxalate inlet, between the rectification section and the reaction section of the decarbonylation reactor; the location where the bottom material of the rectification column returns to the decarbonylation reactor is between the reaction section and the stripping section, and a liquid distributor is installed at this location.

[0031] Furthermore, the operating conditions of the three-stage reaction tower are: top temperature 30-150℃, bottom temperature 180-250℃, pressure 1.0-3.0MPa, and reflux ratio 0.5-5.

[0032] Furthermore, the operating conditions of the distillation column are: top temperature 30-100℃, bottom temperature 90-150℃, pressure 0.1-0.5MPa, and reflux ratio 0.5-5.

[0033] Furthermore, the crystallization method is melt crystallization, and the operating parameters are as follows: Dimethyl carbonate obtained from 99.9% purity distillation is fed into a melt crystallizer and subjected to freezing and holding at a rate of 0.5-2℃ / min to cool the material to -5 to 0℃, holding for 60-120 min. Uncrystallized mother liquor is filtered out and returned to the distillation column. After freezing and holding, the temperature is increased to 2℃ at a rate of 0.2℃-2.0℃ / min, followed by a stepwise increase of 1℃ after every 30-60 min of holding. When the temperature reaches 4-5℃, the sweating ends, and the sweated liquid is returned to the bottom of the distillation column. Then, the temperature is further increased at a rate of 1-5℃ / min to 25-40℃ to completely melt the crystalline dimethyl carbonate in the melt crystallizer. This melt is electronic-grade dimethyl carbonate.

[0034] Furthermore, the purity of the electronic-grade dimethyl carbonate can reach 99.99%.

[0035] A second object of the present invention is to provide a system for the preparation method of electronic-grade dimethyl carbonate from dimethyl oxalate described above, the system comprising:

[0036] A decarbonylation reactor is used to realize the decarbonylation reaction of dimethyl oxalate;

[0037] A distillation column, connected to a decarbonylation reactor, is used for the distillation purification of dimethyl carbonate generated after decarbonylation;

[0038] A freeze crystallization apparatus is connected to a distillation column. The freeze crystallization apparatus is used to crystallize dimethyl carbonate after distillation purification to obtain electronic-grade dimethyl carbonate product.

[0039] Furthermore, the decarbonylation reactor is a three-stage reaction tower.

[0040] Furthermore, the freeze crystallization apparatus is a melt crystallizer.

[0041] Furthermore, the system also includes a raw material buffer tank and a raw material preheater, the raw material buffer tank and the raw material preheater being connected, and the raw material preheater being connected to the decarbonylation reactor.

[0042] Furthermore, the system also includes a DMC buffer tank, the distillation column is connected to the DMC buffer tank, and the DMC buffer tank is connected to a freeze crystallization device.

[0043] Furthermore, the system also includes a mother liquor buffer tank, the freeze crystallization device is connected to the mother liquor buffer tank, and the mother liquor buffer tank is connected to a distillation column.

[0044] Further, the system specifically includes: a raw material buffer tank, a raw material preheater, a three-stage reaction tower, a three-stage reaction tower top condenser, a three-stage reaction tower top gas-liquid separator (reflux tank), a distillation tower, a DMC buffer tank, a melt crystallizer, and a crystallization mother liquor buffer tank; the raw material is fed into the raw material buffer tank, which is connected to the raw material preheater, and the raw material preheater is connected to the three-stage reaction tower; the top of the three-stage reaction tower is connected to the three-stage reaction tower top condenser, and the three-stage reaction tower top condenser is connected to the three-stage reaction tower... The top gas-liquid separator is connected to collect CO product. The top gas-liquid separator of the three-stage reaction tower is connected to the three-stage reaction tower for reflux. The top gas-liquid separator of the three-stage reaction tower is connected to the middle section of the distillation tower so that liquid DMC enters the distillation tower for separation. The bottom of the distillation tower is connected to the three-stage reaction tower. The side stream of the distillation tower is connected to the DMC buffer tank. The DMC buffer tank is connected to the melt crystallizer. The melt crystallizer is connected to the crystallization mother liquor buffer tank. The crystallization mother liquor buffer tank is connected to the distillation tower.

[0045] Furthermore, the heavy components are extracted from the bottom of the three-stage reaction tower.

[0046] Furthermore, the CO product is extracted from the top gas-liquid separator of the three-stage reaction tower, and the CO product is gaseous CO.

[0047] Furthermore, a light component byproduct is collected from the top of the distillation column.

[0048] Furthermore, the side stream of the distillation column yields 99.9% DMC.

[0049] Furthermore, 99.99% electronic grade dimethyl carbonate (DMC) is obtained through the melt crystallizer, which is the electronic grade DMC product.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] 1) This invention uses a three-stage reaction tower. Compared with a reaction vessel, the small amount of heavy components produced are collected in real time and will not stay or accumulate in the reaction tower. The composition in the reactor is more stable and there is no need to update the catalyst in real time. Compared with a fixed bed, the heavy components will not be adsorbed or carbonized on the catalyst surface, avoiding the reduction in activity and regeneration process caused by carbonization of heavy components.

[0052] 2) This invention uses a three-stage reaction tower. A small amount of unreacted DMO in the reaction stage, whether it enters the stripping stage in liquid form or the rectification stage in gaseous form, will return to the reaction stage to continue the reaction, so that the input raw material DMO can be completely reacted. The three-stage reaction tower can make the input raw material DMO completely react, reducing the energy consumption of DMO recovery tower equipment and DMO recycling.

[0053] 3) This invention couples the DMC crystallizer with the distillation column, which improves the purity of electronic-grade DMC products. The crystallization mother liquor containing relatively more impurities in the DMC crystallizer can be returned to the distillation column for secondary purification. The light components (byproducts) are separated from the top of the distillation column as byproducts, while the heavy components are returned to the bottom of the distillation column and separated from the bottom of the three-stage reaction column as heavy components, thereby improving the yield of electronic-grade DMC. Attached Figure Description

[0054] Figure 1 This is a flowchart of the method for preparing electronic-grade dimethyl carbonate (DMC) from dimethyl oxalate (DMO) by decarbonylation according to the present invention.

[0055] in:

[0056] 1. Raw material buffer tank; 2. Raw material preheater; 3. Three-stage reaction tower; 4. Three-stage reaction tower top condenser; 5. Three-stage reaction tower top gas-liquid separator; 6. Distillation tower; 7. DMC buffer tank; 8. Melt crystallizer; 9. Crystallization mother liquor buffer tank; 10. Raw material; 11. CO product; 12. Light component by-product; 13. Heavy component; 14. Electronic grade DMC product. Detailed Implementation

[0057] The present invention will now be described in detail with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Component models, material names, connection structures, control methods, and other features not explicitly stated in this technical solution are considered to be common technical features disclosed in the prior art.

[0058] This invention discloses a method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate, comprising the following steps:

[0059] The raw material, dimethyl oxalate, is preheated and fed into a three-stage decarbonylation reactor 3. Under conditions of 180-250℃ and 1.0-3.0MPa, a decarbonylation reaction occurs on the catalyst in the three-stage reactor 3. The top of the decarbonylation reactor yields purified CO and DMC, while the bottom yields a small amount of heavy component 13. The dimethyl carbonate generated after decarbonylation is purified to 99.9% in a distillation column 6 and then crystallized in a freeze crystallization unit to obtain an electronic grade product. The mother liquor is returned to distillation column 6.

[0060] This invention can completely convert dimethyl oxalate, and the generated heavy components leave the reaction zone in a timely manner, with good catalyst stability; the cooling crystallization kettle is coupled with the distillation column, and the impurities enriched in the crystallization section are returned to the distillation column with the crystallization mother liquor, which improves the yield of electronic grade DMC.

[0061] refer to Figure 1 This invention provides a preparation system for a method of producing electronic-grade dimethyl carbonate from dimethyl oxalate, the system comprising:

[0062] The system comprises: a raw material buffer tank 1, a raw material preheater 2, a three-stage reaction tower 3, a three-stage reaction tower top condenser 4, a three-stage reaction tower top gas-liquid separator 5 (reflux tank), a distillation column 6, a DMC buffer tank 7, a melt crystallizer 8, and a crystallization mother liquor buffer tank 9. The raw material buffer tank 1 is connected to the raw material preheater 2, and the raw material preheater 2 is connected to the three-stage reaction tower 3. The top of the three-stage reaction tower 3 is connected to the three-stage reaction tower top condenser, and the three-stage reaction tower top condenser is connected to the three-stage reaction tower top gas-liquid separator to collect CO. Product 11, wherein the top gas-liquid separator of the three-stage reaction tower 3 is connected to the three-stage reaction tower 3 for reflux, the top gas-liquid separator of the three-stage reaction tower 3 is connected to the middle part of the distillation tower 6 so that liquid DMC enters the distillation tower 6 for separation; the bottom of the distillation tower 6 is connected to the three-stage reaction tower 3, the side stream of the distillation tower 6 is connected to the DMC buffer tank 7, the DMC buffer tank 7 is connected to the melt crystallizer 8, the melt crystallizer 8 is connected to the crystallization mother liquor buffer tank 9, and the crystallization mother liquor buffer tank 9 is connected to the distillation tower 6.

[0063] In this system, the components are mainly connected by pipelines.

[0064] Raw material 10 is fed into raw material buffer tank 1. Heavy component 13 is collected from the bottom of the three-stage reaction tower 3. CO product 11, which is gaseous CO, is collected from the top gas-liquid separator of the three-stage reaction tower 3. Light component by-product 12 is collected from the top of the distillation tower 6. 99.9% DMC is obtained from the side stream of the distillation tower 6. 99.99% electronic grade dimethyl carbonate (DMC) is obtained through the melt crystallizer 8.

[0065] Unless otherwise specified in this embodiment, all raw materials used in the embodiments of this application are purchased through commercial channels.

[0066] In the following examples, activated carbon and activated alumina are both commercially available products.

[0067] Example 1:

[0068] Decarbonylation catalyst: Weigh 14.15g of potassium carbonate and 5.72g of boric acid, dissolve them in water, and impregnate them with an equal volume of 100g of active alumina support. Dry them in an oven at 120℃ for 8h, and then calcine them in a tube furnace at 400℃ for 4h under N2 atmosphere to obtain 8K1B / Al2O3 catalyst.

[0069] An apparatus for preparing carbonates by decarbonylation of oxalate esters, such as Figure 1 As shown, the lower section of the three-stage reaction tower is filled with packing material that is one-quarter the height of the tower (stripping section), the middle section is filled with decarbonylation catalyst that is half the height of the tower (reaction section), and the upper section is filled with packing material that is one-quarter the height of the tower (rectification section).

[0070] This embodiment provides a method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate:

[0071] The feedstock DMO (feedstock 10) enters the feedstock buffer tank 1, is preheated to 210°C by the feedstock preheater 2, and then introduced into the three-stage reaction tower 3. The feedstock DMO is fed between the rectification section and the catalyst section of the three-stage reaction tower 3, where a liquid distributor is installed. The feed mass hourly space velocity (WHSV) of dimethyl oxalate (DMO) is 5 h⁻¹. -1The three-stage reaction tower 3 operates at a pressure of 2.0 MPa, with a bottom temperature of 235°C and a top temperature of 45°C. The catalyst section temperature is 210-220°C. CO product 11 is collected from the top of the tower via the three-stage reaction tower top condenser 4 and the three-stage reaction tower top gas-liquid separator 5. The reflux ratio of the three-stage reaction tower 3 is 3. Heavy component 13 is collected from the bottom, mainly including oxalate oligomers and coking products. After gas-liquid separation, CO is collected as the product (i.e., CO product 11), while the liquid crude DMC enters the distillation tower 6 for atmospheric distillation at a top temperature of 35°C. Light component by-product 12 is collected from the top, mainly including dimethyl ether and methanol. The bottom temperature of the distillation tower is 115°C, and DMC with a purity greater than 99.9% is collected via a side stream. The bottom liquid of the distillation tower 6 is returned to the three-stage reaction tower 3, located between the reaction section and the stripping section. The liquid distributor is located at this position, and the reflux ratio of distillation column 6 is 3. DMC with a purity greater than 99.9% enters the DMC melt crystallizer 8 via the DMC buffer tank 7. The material is cooled to -2℃ at a rate of 0.5℃ / min and held at this temperature for 120 minutes, removing the uncrystallized mother liquor. After the freezing and holding period, the temperature is increased to 2℃ at a rate of 0.5℃ / min, followed by a stepwise increase of 1℃ after every 60 minutes of holding. The temperature increases to 5℃, at which point the sweating process ends, and the sweated liquid is returned to the bottom of distillation column 6 via the crystallization mother liquor buffer tank 9. The material in the melt crystallizer 8 is then further heated to 35℃ at a rate of 5℃ / min to completely melt the crystalline dimethyl carbonate, yielding electronic-grade DMC product 14, which is 99.99% electronic-grade dimethyl carbonate. The crystallization mother liquor is returned to distillation column 6 for further distillation. After 800 hours of continuous operation, the catalyst performance showed no significant decrease.

[0072] Example 2:

[0073] Decarbonylation catalyst: 6.13g of cesium carbonate and 2.13g of diammonium hydrogen phosphate ((NH4)2HPO4) were weighed and dissolved in water. The same volume was impregnated onto an activated carbon support, dried in an oven at 120℃ for 12h, and then placed in a tube furnace and calcined at 350℃ for 4h under N2 atmosphere to obtain 5Cs0.5P / AC catalyst.

[0074] An apparatus for preparing carbonates by decarbonylation of oxalate esters, such as Figure 1 As shown, the lower section of the three-stage reaction tower is filled with packing material that is one-third the height of the tower, the middle section is filled with decarbonylation catalyst that is one-third the height of the tower, and the upper section is filled with packing material that is one-third the height of the tower.

[0075] This embodiment provides a method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate:

[0076] The feedstock DMO (feedstock 10) enters the feedstock buffer tank 1, is preheated to 200°C by the feedstock preheater 2, and then introduced into the three-stage reaction tower 3. The feedstock DMO is fed between the rectification section and the catalyst section of the three-stage reaction tower 3, where a liquid distributor is installed. The feed mass hourly space velocity (WHSV) of dimethyl oxalate (DMO) is 0.1 h⁻¹. -1 The catalyst section temperature is 180-190℃, the three-stage reaction tower operates at a pressure of 1.5MPa, the bottom temperature is 225℃, and the top temperature is 45℃. CO product 11 is collected from the top of the three-stage reaction tower via the top condenser 4 and the top gas-liquid separator 5. The reflux ratio of the three-stage reaction tower 3 is 0.5, and heavy component 13 is collected from the bottom, mainly including oxalate oligomers and coking products. After gas-liquid separation, CO is collected as the product (i.e., CO product 11) from the top of the three-stage reaction tower 3. The liquid crude DMC enters the distillation tower 6 for atmospheric distillation at a top temperature of 35℃. Light component by-product 12 is collected from the top, mainly including dimethyl ether and methanol. The bottom temperature is 120℃, and DMC with a purity greater than 99.9% is collected via a side stream. The liquid from the bottom of the distillation tower 6 is returned to the three-stage reaction tower 3, returning to the reaction section. Between the distillation section and the stripping section, a liquid distributor is installed at this location, and the reflux ratio of distillation column 6 is 0.5. The DMC enters the DMC melt crystallizer 8 via the DMC buffer tank 7, where it is cooled to -2°C at a rate of 1°C / min and held at that temperature for 90 minutes, removing the uncrystallized mother liquor. After the freezing and holding period, the temperature is increased to 2°C at a rate of 2°C / min, followed by a stepwise increase of 1°C after every 60 minutes of holding. When the temperature reaches 4°C, the sweating ends, and the sweated liquid is returned to the bottom of distillation column 6 via the crystallization mother liquor buffer tank 9. Then, the material in the melt crystallizer 8 continues to be heated to 35°C at a rate of 5°C / min to completely melt the crystalline dimethyl carbonate, yielding electronic-grade DMC product 14, which is 99.99% pure electronic-grade dimethyl carbonate. The crystallization mother liquor is returned to distillation column 6 for further distillation. After 800 hours of continuous operation, the catalyst performance showed no significant decrease.

[0077] Example 3:

[0078] Decarbonylation catalyst: Weigh 9.45g of rubidium carbonate and 7.35g of potassium hydrogen phosphate (K2HPO4), dissolve them in water, and impregnate them with an equal volume of active SiO2 support. Dry them in an oven at 120℃ for 12h, and then calcine them in a tube furnace at 350℃ for 4h under N2 atmosphere to obtain 7Rb1P / SiO2 catalyst.

[0079] An apparatus for preparing carbonates by decarbonylation of oxalate esters, such as Figure 1 As shown, the lower section of the three-stage reaction tower is filled with packing material that is one-third the height of the tower, the middle section is filled with decarbonylation catalyst that is one-third the height of the tower, and the upper section is filled with packing material that is one-third the height of the tower.

[0080] This embodiment provides a method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate:

[0081] The feedstock DMO (feedstock 10) enters the feedstock buffer tank 1, is preheated to 200°C by the feedstock preheater 2, and then introduced into the three-stage reaction tower 3. The feedstock DMO is fed between the rectification section and the catalyst section of the three-stage reaction tower 3, where a liquid distributor is built-in. The feed mass hourly space velocity (WHSV) of dimethyl oxalate (DMO) is 10 h⁻¹. -1 The catalyst section temperature is 230-240℃. The operating pressure of the three-stage reaction tower 3 is 2.0MPa, the bottom temperature is 245℃, and the top temperature is 50℃. CO product 11 is collected from the top of the three-stage reaction tower via the top condenser 4 and the top gas-liquid separator 5. The reflux ratio of the three-stage reaction tower 3 is 5. Heavy component 13 is collected from the bottom of the tower. Heavy component 13 mainly includes: After gas-liquid separation, CO is collected as a product (i.e., CO product 11) from the top of the three-stage reaction tower 3. The liquid crude DMC enters the distillation tower 6 at a pressure of 0.5MPa and a top temperature of 55℃. Light component by-product 12 is collected from the top of the tower. Light component by-product 12 mainly includes: The bottom temperature is 150℃. DMC with a purity greater than 99.9% is collected from the side stream. The bottom liquid of the distillation tower 6 is returned to the three-stage reaction tower 3. The return position is between the reaction section and the stripping section. This position is built-in. The liquid distributor and the reflux ratio of distillation column 6 are 5. DMC with a purity greater than 99.9% enters the DMC melt crystallizer 8 via the DMC buffer tank 7. The material is cooled to -5℃ at a rate of 0.5℃ / min and held at this temperature for 60 minutes, removing the uncrystallized mother liquor. After the freezing and holding period, the temperature is increased to 2℃ at a rate of 0.2℃ / min, followed by a stepwise increase of 1℃ after every 60 minutes of holding. The temperature increases to 4℃, at which point the sweating process ends, and the sweated liquid is returned to the bottom of distillation column 6 via the crystallization mother liquor buffer tank 9. The material in the melt crystallizer 8 is then further heated to 40℃ at a rate of 3℃ / min to completely melt the crystalline dimethyl carbonate, yielding electronic-grade DMC product 14, which is 99.99% electronic-grade dimethyl carbonate. The crystallization mother liquor is returned to distillation column 6 for further distillation. After 800 hours of continuous operation, the catalyst performance showed no significant decrease.

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing dimethyl carbonate from dimethyl oxalate. The steps in this comparative example are basically the same as those in Example 1, except that the three-stage reaction tower 3 is replaced with a fixed-bed reactor. The reactor is filled with the same catalyst as in Example 1. The oxalate feedstock is preheated and enters from the top of the reactor, while the product exits from the bottom and enters the carbonate distillation tower to obtain dimethyl carbonate. The single-pass conversion rate of oxalate is 94%. After 300 hours of continuous operation, the reactor becomes clogged due to coking.

[0084] Comparative Example 2

[0085] This comparative example provides a method for preparing dimethyl carbonate from dimethyl oxalate. The difference between this comparative example and Example 1 is that in this comparative example, the three-stage reaction tower 3 is replaced with a batch reactor. The same catalyst as in Example 1 is loaded into the batch reactor. Oxalate ester is preheated and enters from the top of the reactor. A bottom-insertion tube is installed inside the reactor, through which the product is filtered and collected. The single-pass conversion rate of oxalate ester is 85%, with some oxalate ester leaving the reactor unreacted. The decarbonylation product requires two towers to separate and recover DMC and DMO respectively, adding one tower compared to the example and increasing the energy consumption for DMO recycling.

[0086] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate, characterized in that, The method includes the following steps: Dimethyl oxalate is fed into a decarbonylation reactor to carry out the decarbonylation reaction. Carbon monoxide, dimethyl carbonate and other light components are collected from the top of the decarbonylation reactor, while heavy components are collected from the bottom of the decarbonylation reactor. The carbon monoxide, dimethyl carbonate and other light components collected from the top of the decarbonylation reactor are separated by gas-liquid separation. The carbon monoxide is separated as a gaseous product, and the dimethyl carbonate is purified by distillation in the form of liquid in the distillation column (6) to obtain dimethyl carbonate. The dimethyl carbonate obtained by distillation is purified by crystallization in a freeze crystallization device to obtain electronic grade dimethyl carbonate product, and the crystallization mother liquor is returned to the distillation column (6); The decarbonylation reactor is a three-stage reaction tower (3), consisting of a rectification section, a reaction section, and a stripping section from top to bottom.

2. The method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate according to claim 1, characterized in that, The rectifying and stripping sections of the three-stage reaction tower (3) are filled with packing material; The reaction section of the three-stage reaction tower (3) is filled with a catalyst, and the reaction section includes a catalyst bed.

3. The method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate according to claim 2, characterized in that, The height of the packing in the rectification section is one-quarter to one-third of the height of the three-stage reaction tower (3); The height of the catalyst bed is one-third to one-half the height of the three-stage reaction tower (3); The height of the packing material in the stripping section is one-quarter to one-third of the height of the three-stage reaction tower (3).

4. The method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate according to claim 2, characterized in that, The catalyst is a supported catalyst; The supported catalyst includes a support, an active component, and an additive; The carrier is one or more of activated carbon, silicon dioxide, and activated alumina; The active component is one or more of alkali metals or alkaline earth metals, and the loading of the active component is 2-10 wt% based on the metal content. The additive is one or more of phosphorus or boron, and the loading of the additive is 0.1-3 wt% by element.

5. The method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate according to claim 2, characterized in that, The inlet of dimethyl oxalate is located between the rectification section and the reaction section of the decarbonylation reactor. It flows downward through the catalyst bed of the reaction section. The reaction products carbon monoxide, dimethyl carbonate and other light components, along with some unreacted dimethyl oxalate, are purified in the rectification section of the decarbonylation reactor in gaseous form. Some unreacted dimethyl oxalate and heavy components are separated in the stripping section of the decarbonylation reactor in liquid form. The unreacted dimethyl oxalate separated in the rectification section and stripping section is returned to the reaction section for further reaction, so that the input dimethyl oxalate is completely reacted. The carbon monoxide, dimethyl carbonate and other light components are collected from the top of the decarbonylation reactor. After gas-liquid separation, the carbon monoxide is separated as a gaseous product, and the dimethyl carbonate and other light components are sent to the rectification column (6). The heavy components are collected from the bottom of the decarbonylation reactor. Other light components are collected from the top of the distillation column (6) as by-products, and dimethyl carbonate is collected from the side stream for further crystallization and purification to obtain electronic grade dimethyl carbonate product. The bottom material of the distillation column (6) is returned to the decarbonylation reactor.

6. The method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate according to claim 5, characterized in that, The dimethyl oxalate needs to be preheated before being fed into the feed at a temperature of 180-240°C; the feed mass hourly space velocity (WHSV) of the dimethyl oxalate is 0.1-10 h⁻¹. -1 .

7. The method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate according to claim 5, characterized in that, A liquid distributor is installed at the location between the distillation section and the reaction section of the decarbonylation reactor, after the dimethyl oxalate inlet. The location where the bottom material of the distillation column (6) is returned to the decarbonylation reactor is between the reaction section and the stripping section, and a liquid distributor is built into this location.

8. The method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate according to claim 1, characterized in that, The operating conditions of the three-stage reaction tower (3) are: top temperature 30-150℃, bottom temperature 180-250℃, pressure 1.0-3.0MPa, and reflux ratio 0.5-5; And / or, the operating conditions of the distillation column (6) are: top temperature 30-100℃, bottom temperature 90-150℃, pressure 0.1-0.5MPa, and reflux ratio 0.5-5.

9. The method for preparing electronic-grade dimethyl carbonate from dimethyl oxalate according to claim 1, characterized in that, The crystallization method is melt crystallization; The crystallization method includes sending the dimethyl carbonate collected from the top side stream of the distillation column (6) into a freezing crystallization device, cooling the dimethyl carbonate to -5 to 0℃ at a cooling rate of 0.5-2℃ / min, and holding it at that temperature for 60-120min. The uncrystallized dimethyl carbonate is filtered out and returned to the distillation column (6); then the freeze crystallization device containing crystalline dimethyl carbonate is heated to induce sweating. First, the temperature is increased to 2℃ at a rate of 0.2-2.0℃ / min, and then the temperature is increased stepwise. After holding at the temperature for 30-60 minutes, the temperature is increased by 1℃. When the temperature reaches 4-5℃, the sweating ends and the sweating liquid is returned to the bottom of the distillation column (6); then the temperature is increased to 25-40℃ to melt all the crystalline dimethyl carbonate in the freeze crystallization device. The resulting molten liquid is electronic grade dimethyl carbonate.

10. A system for preparing electronic-grade dimethyl carbonate from dimethyl oxalate as described in any one of claims 1-9, characterized in that, The system includes: A decarbonylation reactor is used to realize the decarbonylation reaction of dimethyl oxalate; A distillation column (6) is connected to a decarbonylation reactor and is used for the distillation purification of dimethyl carbonate generated after decarbonylation. A freezing crystallization device is connected to a distillation column (6). The freezing crystallization device is used to crystallize dimethyl carbonate after distillation and purification to obtain electronic grade dimethyl carbonate product. Preferably, a raw material preheater is provided before the decarbonylation reactor for preheating dimethyl oxalate; Both the decarbonylation reactor and the top of the distillation column are equipped with gas-liquid separators for the purification of the product.

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