Apparatus and method for the heterogeneous catalytic production of dimethyl carbonate

Abstract

The application relates to a device and a method for producing dimethyl carbonate by heterogeneous catalysis, and belongs to the field of dimethyl carbonate production processes.The device comprises a reaction rectifying tower, a raw material preheater connected to the upper side of the reaction rectifying tower, a reaction rectifying mixing tank connected to the lower side of the reaction rectifying tower, a methanol preheater connected to the lower side of the reaction rectifying tower, a reaction rectifying tower top condenser connected to the top of the reaction rectifying tower, and a precision filter connected to the bottom of the reaction rectifying tower; a melt crystallizer is connected to the feed preheater at the feed end and connected to the discharge end of the precision filter, and one discharge end is connected to the reaction rectifying mixing tank; an ethylene glycol purification tower is connected to the other discharge end of the melt crystallizer at the middle of the side, and is further connected with an ethylene glycol product cooler at the side, and is connected with an ethylene glycol purification tower top condenser at the top and connected to the reaction rectifying mixing tank.The application has the beneficial effects of short production process, low energy consumption, and low material and energy loss.

Description

Technical Field

[0001] This invention relates to the field of dimethyl carbonate production processes, and particularly to an apparatus and method for heterogeneous catalytic production of dimethyl carbonate. Background Technology

[0002] Dimethyl carbonate (DMC), with the chemical formula CH3OCOOCH3, is a multifunctional chemical product. Due to the presence of functional groups such as methoxy and carbonyl groups in its structure, it can replace halides, dimethyl sulfate, and phosgene as methylating and carbonylating agents. Furthermore, DMC is non-toxic and biodegradable, making it a truly green and pollution-free product. It can be used not only as a solvent for adhesives, lithium battery electrolytes, and gasoline additives, but also as a raw material for the production of developers and polycarbonates. It has wide applications in various fine chemicals such as paints, coatings, pesticides, and electronic chemicals.

[0003] Currently, transesterification is one of the mainstream industrial production routes for dimethyl carbonate. Transesterification uses ethylene carbonate and methanol as raw materials, and alkali metal alkoxides as homogeneous catalysts to react and produce dimethyl carbonate and ethylene glycol. This route has advantages such as high feed conversion rate and mild reaction conditions, making it suitable for large-scale industrial production. However, the homogeneous catalyst is difficult to separate and recover, resulting in significant material waste.

[0004] Furthermore, this route employs reactive distillation technology, where excess methanol reacts with the produced dimethyl carbonate to form a low-boiling-point azeotrope. Separation of the azeotrope is a challenge in this route; industrially, pressure swing distillation is primarily used, but this technology suffers from drawbacks such as high energy consumption, operational complexity, and high equipment investment.

[0005] Patent CN10942264A discloses a method for separating dimethyl carbonate and methanol azeotropes. It employs extractive distillation technology, with main equipment including an extractive distillation column and a solvent recovery column. The extractant is a mixed ionic liquid extractant, one of which is an ionic liquid with a bis(trifluoromethanesulfonyl)imide anion, and the other is one of diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, or tetraethylene glycol dimethyl ether. The resulting dimethyl carbonate has a mass concentration of approximately 99.7%, and the methanol mass is higher than 99.8%. However, because the extractive distillation adds a new substance as an extractant to the system, the purity of the obtained product is not high.

[0006] Patent CN101143803A provides a technology for separating dimethyl carbonate and methanol using a vapor permeation membrane. The saturated vapors of dimethyl carbonate and methanol are separated by passing them through a membrane to obtain dimethyl carbonate with a purity ≥99.5% (wt.). However, the membrane used has drawbacks such as insufficient mechanical strength, low separation efficiency, high cost, and difficulty in replacement.

[0007] Patent CN111704545B uses melt crystallization to separate the azeotrope of dimethyl carbonate and methanol. The crystallization temperature of the azeotrope is between -20 and 40°C, which has disadvantages such as difficulty in crystallizing the azeotrope, high energy consumption, and high operation difficulty.

[0008] Existing homogeneous catalysts cannot be recycled, and the separation of dimethyl carbonate and methanol azeotropes is difficult. The production process is long and energy consumption is high. It is necessary to optimize the process and reduce material and energy losses. Therefore, a device and method for heterogeneous catalytic production of dimethyl carbonate are proposed. Summary of the Invention

[0009] The purpose of this invention is to provide an apparatus for heterogeneous catalytic production of dimethyl carbonate, which features a short production process, low energy consumption, and minimal material and energy losses.

[0010] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0011] An apparatus for heterogeneous catalytic production of dimethyl carbonate, comprising:

[0012] The reactive distillation column has a raw material preheater and a reactive distillation mixing tank connected to its upper side, a methanol preheater connected to its lower side, a reactive distillation column top condenser connected to its top, and a precision filter connected to its bottom.

[0013] The melt crystallizer has its feed end connected to the feed preheater and the discharge end of the precision filter, and one of its discharge ends connected to the reactive distillation mixing tank.

[0014] The ethylene glycol purification tower is connected to the other outlet end of the molten crystallizer in the middle of its side. It is also connected to an ethylene glycol product cooler on its side. The top of the tower is connected to the ethylene glycol purification tower top condenser and then to the reactive distillation mixing tank.

[0015] Another objective of this invention is to provide a method for producing dimethyl carbonate using heterogeneous catalysis, which, compared to homogeneous catalysis, features a shorter production process, lower energy consumption, and less material and energy loss.

[0016] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0017] A method for heterogeneous catalytic production of dimethyl carbonate includes the following steps:

[0018] Step 1: Reactive Distillation

[0019] Fresh ethylene carbonate enters the reactive distillation mixing tank and, after preheating, is fed from the top of the reactive distillation column. Fresh methanol, after preheating, enters from the bottom of the reactive distillation column. The reactive distillation column is circulated and heated, and the vaporized methanol comes into countercurrent contact with the ethylene carbonate entering from the top, reacting in the catalyst-filled section of the reactive distillation column. Ethylene carbonate is in excess to ensure complete conversion of methanol into dimethyl carbonate. The low-boiling-point dimethyl carbonate is condensed at the top of the column and collected as the product. The reactive distillation non-condensable gas generated at the top of the reactive distillation column is connected to the tail gas fan to ensure that the reactive distillation is under slight negative pressure or normal pressure. The bottom material mainly contains ethylene carbonate, ethylene glycol, a small amount of dimethyl carbonate, and supported catalyst powder. The catalyst powder is filtered out by a precision filter, and the filtrate enters a melt crystallizer for separation and purification.

[0020] Step 2: Melting and Crystallization

[0021] The filtrate after being filtered through a precision filter enters a melt crystallizer. After undergoing a process of cooling crystallization, sweating, and melting, ethylene carbonate, due to its higher freezing point, crystallizes preferentially. The uncrystallized ethylene glycol and a small amount of dimethyl carbonate are mixed and then sent to an ethylene glycol purification tower for separation. The ethylene carbonate crystals are then heated, sweated, and melted to become a high-purity liquid material, which is returned to the mixing tank of the reactive distillation tower.

[0022] Step 3: Ethylene glycol purification

[0023] The non-crystallizable ethylene glycol and a small amount of dimethyl carbonate separated from the melt crystallizer are fed into the middle of the ethylene glycol purification tower; the low-boiling-point dimethyl carbonate is distilled off from the top of the tower, condensed, and returned to the mixing tank of the reactive distillation tower; the ethylene glycol purification non-condensable gas generated at the top of the ethylene glycol purification tower is connected to a vacuum pump group to ensure that the ethylene glycol purification tower is operating under negative pressure conditions; the high-boiling-point ethylene glycol polymer or other impurities are collected from the bottom of the tower as a waste liquid; the ethylene glycol collected from the side stream of the tower is cooled and collected as a product.

[0024] Preferably, the reactive distillation column is a packed column, the packing is metal wire mesh packing, the number of trays is 40 to 80, and the section below the ethylene carbonate inlet is filled with composite packing containing catalyst.

[0025] Preferably, the catalyst includes a combination of imidazole ionic liquids, quaternary ammonium ionic liquids, quaternary phosphonium ionic liquids and alkali metal or alkaline earth metal halide salts.

[0026] Preferably, the reactive distillation column operates at a pressure of -20 to 0 kPa, a top temperature of 70 to 90°C, a bottom temperature of 196 to 226°C, and a reflux ratio of 1 to 2.5:1.

[0027] Preferably, the molar ratio of methanol to ethylene carbonate is 0.5 to 2:1.

[0028] Preferably, the precision filter element is either a metal membrane filter element or an organic material filter element.

[0029] Preferably, the cooling medium used for crystallization is circulating water at 25-30℃, and the heating medium used for sweating and melting is circulating hot water at 60-80℃.

[0030] As a preferred option, the ethylene glycol purification tower is a packed tower with metal wire mesh packing and 30 to 60 trays.

[0031] Preferably, the ethylene glycol purification tower operates at a pressure of -99 to -96 kPa, a top temperature of 120 to 150°C, a bottom temperature of 140 to 160°C, and a reflux ratio of 2 to 10:1.

[0032] In summary, the present invention has the following beneficial effects:

[0033] 1. This invention obtains dimethyl carbonate directly through the complete conversion of methanol, eliminating the separation process of dimethyl carbonate and methanol azeotrope, reducing the energy consumption required for azeotrope separation, and simplifying the process flow.

[0034] 2. This invention uses a heterogeneous supported catalyst, which reduces catalyst consumption and solves the problem of difficult separation and treatment of spent catalysts;

[0035] 3. This invention separates ethylene carbonate by melt crystallization, which has lower energy consumption compared to distillation;

[0036] 4. This invention reduces energy waste caused by feed preheating and top condensation by matching the heat exchange network, thereby further reducing energy consumption. Attached Figure Description

[0037] Figure 1 This is a schematic diagram showing the connection relationship of the various components in this invention.

[0038] In the diagram, 1. Reactive distillation column; 2. Feed preheater; 3. Reactive distillation mixing tank; 4. Methanol preheater; 5. Reactive distillation column top condenser; 6. Precision filter; 7. Melt crystallizer; 8. Feed preheater; 9. Ethylene glycol purification column; 10. Ethylene glycol product cooler; 11. Ethylene glycol purification column top condenser; 12. Reactive distillation non-condensable gas; 13. Bottom material; 14. Ethylene glycol purification non-condensable gas; 15. Liquid material; 16. Mixture; 17. Reactive distillation column bottom reboiler; 18. Ethylene glycol purification column bottom reboiler. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings.

[0040] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

[0041] Example 1:

[0042] An apparatus for heterogeneous catalytic production of dimethyl carbonate

[0043] like Figure 1 As shown, it includes a reactive distillation mixing tank 3, a reactive distillation column 1, a precision filter 6, a melt crystallizer 7, and an ethylene glycol purification column 9.

[0044] The reactive distillation mixing tank 3 is connected to the upper side of the reactive distillation column 1 via the feed preheater 2. The reactive distillation mixing tank 3 has a feed end for ethylene carbonate. A methanol preheater 4 is connected to the side of the reactive distillation column 1 below its ethylene carbonate feed end; the methanol preheater 4 has a feed end for methanol. A reactive distillation column top condenser 5 is connected to the top of the reactive distillation column 1. A precision filter 6 is connected to the bottom of the reactive distillation column 1, and a reactive distillation column reboiler 17 is also provided.

[0045] The feed end of the melt crystallizer 7 is connected to the discharge end of the precision filter 6 via the feed preheater 8. The melt crystallizer 7 has two discharge ends, one of which is connected to the reactive distillation mixing tank 3 and the other is connected to the feed end of the ethylene glycol purification tower 9.

[0046] The top of the ethylene glycol purification column 9 is connected to an ethylene glycol purification column top condenser 11, which is also connected to a reactive distillation mixing tank 3. An ethylene glycol product cooler 10 is connected to the middle of the side of the ethylene glycol purification column 9. An ethylene glycol purification column reboiler 18 is installed at the bottom of the ethylene glycol purification column 9.

[0047] How to use:

[0048] Step 1: Reactive Distillation

[0049] Fresh ethylene carbonate enters the reactive distillation mixing tank 3 and, after preheating, is fed from the top of the reactive distillation column 1. Fresh methanol, after preheating, enters from the bottom of the reactive distillation column 1. The reactive distillation column 1 is heated in a circulating manner, and the vaporized methanol comes into countercurrent contact with the ethylene carbonate entering from the top, reacting in the catalyst-filled section of the reactive distillation column 1. Ethylene carbonate is in excess to ensure that methanol is completely converted into dimethyl carbonate. The low-boiling-point dimethyl carbonate is condensed at the top of the column and collected as a product. The reactive distillation non-condensable gas 12 generated at the top of the reactive distillation column 1 is connected to the tail gas fan to ensure that the reactive distillation is under a slightly negative pressure or normal pressure. The bottom material 13 mainly contains ethylene carbonate, ethylene glycol, a small amount of dimethyl carbonate, and supported catalyst powder. The catalyst powder is filtered out by a precision filter 6, and the filtrate enters a melt crystallizer 7 for separation and purification.

[0050] Step 2: Melting and Crystallization

[0051] The filtrate filtered by the precision filter 6 enters the melt crystallizer 7. After cooling, crystallization, sweating, and melting, ethylene carbonate crystallizes preferentially due to its high freezing point (35-38℃). The uncrystallized ethylene glycol and a small amount of dimethyl carbonate mixture 16 enter the ethylene glycol purification tower 9 for separation. The ethylene carbonate crystals are heated, sweated, and melted to become a high-purity liquid material 15, which is returned to the reactive distillation mixing tank 3.

[0052] Step 3: Ethylene glycol purification

[0053] The non-crystallizable ethylene glycol and a small amount of dimethyl carbonate separated from the melt crystallizer 7 are fed into the middle of the ethylene glycol purification tower 9; the low-boiling-point dimethyl carbonate is distilled off from the top of the tower, condensed, and returned to the mixing tank of the reactive distillation tower 1; the ethylene glycol purification non-condensable gas 14 generated at the top of the ethylene glycol purification tower 9 is connected to a vacuum pump group to ensure that the ethylene glycol purification tower 9 is under negative pressure operation conditions; the high-boiling-point ethylene glycol polymer or other impurities are collected from the bottom of the tower as a waste liquid; the ethylene glycol collected from the side stream of the tower is cooled and collected as a product.

[0054] The principle of this embodiment is as follows:

[0055] Theoretically, producing 1 mole of dimethyl carbonate and 1 mole of ethylene glycol as a byproduct requires 1 mole of ethylene carbonate and 2 moles of methanol. To improve the methanol conversion rate, the proportion of ethylene carbonate needs to be increased in the initial stage of production. Excess ethylene carbonate and methanol, after preheating, enter the upper and lower sections of reactive distillation column 1 respectively. The two streams react countercurrently in the reaction section, and the resulting dimethyl carbonate is distilled off the top of the column. After condensation, it is sent off as a high-purity product. The resulting ethylene glycol, unreacted ethylene carbonate, catalyst, and a small amount of dimethyl carbonate are collected from the bottom of the column and enter a precision filter 6 to remove catalyst powder. Then, it enters the melt crystallizer 7, where the separated ethylene carbonate is returned to the reactive distillation mixing tank 3 for recycling as a reaction feedstock. At this point, the proportion of fresh ethylene carbonate in the feed can be appropriately reduced. Unseparated ethylene glycol and dimethyl carbonate enter ethylene glycol purification tower 9. Ethylene glycol and dimethyl carbonate are collected from the top of the tower, high-purity ethylene glycol product is collected from the side stream, and high-boiling-point ethylene glycol polymer is collected from the bottom of the tower and sent to the outside as waste liquid.

[0056] Example 2:

[0057] A method for heterogeneous catalytic production of dimethyl carbonate

[0058] Raw material feed rates: Ethylene carbonate = 1 kg / h, Methanol = 0.64 kg / h.

[0059] Methanol enters from the bottom of reactive distillation column 1. The reboiler 17 in the bottom of the column is heated by steam circulation, causing the methanol to vaporize. Ethylene carbonate enters from the top of reactive distillation column 1 via reactive mixing tank 3, reacting counter-currently with the methanol vapor in the reaction section. The resulting dimethyl carbonate vapor is condensed by the top condenser 5 of the reactive distillation column, establishing reflux and collection, with the reflux ratio controlled at 1. Reactive distillation column 1 is a packed column with wire mesh packing and 40 trays. The section below the ethylene carbonate inlet is filled with composite packing containing catalyst. The catalyst includes imidazole ionic liquids, quaternary ammonium ionic liquids, quaternary phosphonium ionic liquids, and alkali metal composites. The top temperature of reactive distillation column 1 is 70°C. The molar ratio of methanol to ethylene carbonate is 0.5:1. The precision filter 6 uses a metal membrane filter element. The pressure at the top of the column is controlled at -20 kPa, and the dimethyl carbonate product collected at the top of the column is 0.88 kg / h with a purity of 99.92% (wt.). The temperature of the bottom of the column is 196℃. The catalyst powder in the bottom discharge is removed by a precision filter 6, and then heat-exchanged in the feed preheater 8, where the temperature is reduced to 85℃ before entering the melting and crystallization section. First, it is cooled by circulating water at 28℃ to form ethylene carbonate crystals. The remaining uncrystallized material, containing most of ethylene glycol and a small amount of dimethyl carbonate, enters the ethylene glycol purification column 9. The ethylene carbonate crystals are heated by circulating hot water at 80℃ and then melted, forming high-purity ethylene carbonate liquid, which is returned to the reactive distillation mixing tank 3. The ethylene glycol purification column 9 is a packed column with metal wire mesh packing and 30 trays. The top temperature of the ethylene glycol purification column 9 is 120℃. The pressure in ethylene glycol purification column 9 is controlled at -96 kPa, the reflux ratio is controlled at 1, and a side stream of 0.59 kg / h of ethylene glycol product with a purity of 98.1% (wt.) is collected. The top composition of the column is a mixture of 94.6% (wt.) ethylene glycol and 5.4% (wt.) dimethyl carbonate, which is returned to the reactive distillation mixing tank 3 for recycling. The bottom temperature of the column is controlled below 155℃, and the product consists of high-boiling-point substances such as ethylene glycol polymers.

[0060] Example 3:

[0061] A method for heterogeneous catalytic production of dimethyl carbonate

[0062] Raw material feed rates: Ethylene carbonate = 1.5 kg / h, Methanol = 0.64 kg / h.

[0063] Methanol enters from the bottom of reactive distillation column 1. The reboiler 17 in the bottom of the column is heated by steam circulation, causing the methanol to vaporize. Ethylene carbonate enters from the top of reactive distillation column 1 via reactive mixing tank 3, where it reacts counter-currently with the methanol vapor in the reaction section. The resulting dimethyl carbonate vapor is condensed in the top condenser of reactive distillation column 1, establishing reflux and collection, with a reflux ratio controlled at 2.5. Reactive distillation column 1 is a packed column with wire mesh packing and 50 trays. The section below the ethylene carbonate inlet is filled with composite packing containing catalyst. The catalyst includes imidazole ionic liquids, quaternary ammonium ionic liquids, quaternary phosphorus ionic liquids, and alkali metal composites. The top temperature of the reactive distillation column is 80°C. The molar ratio of methanol to ethylene carbonate is 1:1. The precision filter 6 uses a metal membrane filter element. The pressure at the top of the column is controlled at -20 kPa, and the dimethyl carbonate product collected at the top of the column is 0.82 kg / h with a purity of 99.99% (wt.). The temperature of the bottom of the column is 203℃. The catalyst powder in the bottom discharge is removed by a precision filter 6, and then heat-exchanged in the feed preheater 8, where the temperature is reduced to 98℃ before entering the melting and crystallization section. First, it is cooled by circulating water at 28℃ to form ethylene carbonate crystals. The remaining uncrystallized material, containing most of ethylene glycol and a small amount of dimethyl carbonate, enters the ethylene glycol purification column 9. The ethylene carbonate crystals are heated by circulating hot water at 80℃ and then melted, forming high-purity ethylene carbonate liquid, which is returned to the reactive distillation mixing tank 3. The ethylene glycol purification column 9 is a packed column with metal wire mesh packing and 40 trays. The top temperature of the ethylene glycol purification column 9 is 130℃. The pressure in ethylene glycol purification column 9 is controlled at -99 kPa, the reflux ratio is controlled at 5, and 0.59 kg / h of ethylene glycol product with a purity of 99.9% (wt.) is collected from the side stream. The composition at the top of the column is a mixture of 92.5% (wt.) ethylene glycol and 7.5% (wt.) dimethyl carbonate, which is returned to the reactive distillation mixing tank 3 for recycling. The temperature of the column bottom is controlled below 155℃, and the product is high-boiling-point substances such as ethylene glycol polymers.

[0064] Example 4:

[0065] A method for heterogeneous catalytic production of dimethyl carbonate

[0066] Raw material feed rates: Ethylene carbonate = 2 kg / h, Methanol = 0.64 kg / h.

[0067] Methanol enters from the bottom of reactive distillation column 1. The reboiler 17 in the bottom of the column is heated by steam circulation, causing the methanol to vaporize. Ethylene carbonate enters from the top of reactive distillation column 1 via reactive mixing tank 3, reacting counter-currently with the methanol vapor in the reaction section. The resulting dimethyl carbonate vapor is condensed by the top condenser 5 of the reactive distillation column, establishing reflux and collection, with the reflux ratio controlled at 2.5. Reactive distillation column 1 is a packed column with wire mesh packing and 70 trays. The section below the ethylene carbonate inlet is filled with composite packing containing catalyst. The catalyst includes a combination of imidazole ionic liquid, quaternary ammonium ionic liquid, quaternary phosphonium ionic liquid, and alkaline earth metal halide salts. The top temperature of reactive distillation column 1 is 90°C. The molar ratio of methanol to ethylene carbonate is 1.5:1. The precision filter 6 uses organic material filter elements. The pressure at the top of the column is controlled at 0 kPa, and the dimethyl carbonate product collected at the top of the column is 0.83 kg / h with a purity of 99.95% (wt.). The temperature of the bottom of the column is 226℃. The catalyst powder in the bottom discharge is removed by a precision filter 6, and then heat-exchanged in the feed preheater 8, where the temperature is reduced to 116℃ before entering the melting and crystallization section. First, it is cooled by circulating water at 28℃ to form ethylene carbonate crystals. The remaining uncrystallized material, containing most of ethylene glycol and a small amount of dimethyl carbonate, enters the ethylene glycol purification column 9. The ethylene carbonate crystals are heated by circulating hot water at 80℃ and then melted, forming high-purity ethylene carbonate liquid, which is returned to the reactive distillation mixing tank 3. The ethylene glycol purification column 9 is a packed column with metal wire mesh packing and 50 trays. The top temperature of the ethylene glycol purification column 9 is 140℃. The pressure in ethylene glycol purification column 9 is controlled at -96 kPa, the reflux ratio is controlled at 10, and 0.62 kg / h of ethylene glycol product with a purity of 99.9% (wt.) is collected from the side stream. The composition at the top of the column is a mixture of 93.7% (wt.) ethylene glycol and 6.3% (wt.) dimethyl carbonate, which is returned to the reactive distillation mixing tank 3 for recycling. The temperature of the column bottom is controlled below 160℃, and the product is high-boiling-point substances such as ethylene glycol polymers.

[0068] Example 5:

[0069] A method for heterogeneous catalytic production of dimethyl carbonate

[0070] Raw material feed rates: ethylene carbonate = 3.52 kg / h, methanol = 0.64 kg / h.

[0071] Methanol enters from the bottom of reactive distillation column 1. The reboiler 17 in the bottom of the column is heated by steam circulation, causing the methanol to vaporize. Ethylene carbonate enters from the top of reactive distillation column 1 via reactive mixing tank 3, reacting counter-currently with the methanol vapor in the reaction section. The resulting dimethyl carbonate vapor is condensed by the top condenser 5 of the reactive distillation column, establishing reflux and collection, with the reflux ratio controlled at 2.5. Reactive distillation column 1 is a packed column with wire mesh packing and 80 trays. The section below the ethylene carbonate inlet is filled with composite packing containing catalyst. The catalyst includes a combination of imidazole ionic liquid, quaternary ammonium ionic liquid, quaternary phosphonium ionic liquid, and alkaline earth metal halide salts. The top temperature of reactive distillation column 1 is 90°C. The molar ratio of methanol to ethylene carbonate is 2:1. The precision filter 6 uses organic material filter elements. The pressure at the top of the column is controlled at -20 kPa, and the dimethyl carbonate product collected at the top of the column is 0.88 kg / h with a purity of 99.99% (wt.). The temperature of the bottom of the column is 210℃. The catalyst powder in the bottom discharge is removed by a precision filter 6, and then heat-exchanged in the feed preheater 8, where the temperature is reduced to 105℃ before entering the melting and crystallization section. First, it is cooled by circulating water at 28℃ to form ethylene carbonate crystals. The remaining uncrystallized material, containing most of ethylene glycol and a small amount of dimethyl carbonate, enters the ethylene glycol purification column 9. The ethylene carbonate crystals are heated by circulating hot water at 80℃ and then melted, forming high-purity ethylene carbonate liquid, which is returned to the reactive distillation mixing tank 3. The ethylene glycol purification column 9 is a packed column with metal wire mesh packing and 60 trays. The top temperature of the ethylene glycol purification column 9 is 150℃. The pressure in ethylene glycol purification column 9 is controlled at -96 kPa, the reflux ratio is controlled at 1, and a side stream of 0.66 kg / h of ethylene glycol product with a purity of 98.3% (wt.) is collected. The top composition of the column is a mixture of 96.7% (wt.) ethylene glycol and 3.3% (wt.) dimethyl carbonate, which is returned to the reactive distillation mixing tank 3 for recycling. The bottom temperature of the column is controlled below 160℃, and the product is high-boiling-point substances such as ethylene glycol polymers.

Claims

1. An apparatus for heterogeneous catalytic production of dimethyl carbonate, characterized in that, include: The reactive distillation column has a raw material preheater and a reactive distillation mixing tank connected to its upper side, a methanol preheater connected to its lower side, a reactive distillation column top condenser connected to its top, and a precision filter connected to its bottom. The melt crystallizer has its feed end connected to the feed preheater and the discharge end of the precision filter, and one of its discharge ends connected to the reactive distillation mixing tank. The ethylene glycol purification tower is connected to the other outlet end of the molten crystallizer in the middle of its side. It is also connected to an ethylene glycol product cooler on its side. The top of the tower is connected to the ethylene glycol purification tower top condenser and then to the reactive distillation mixing tank. The reactive distillation column is a packed column with metal wire mesh packing and 40 to 80 trays. The section below the ethylene carbonate inlet is filled with composite packing containing catalyst. Catalysts include complexes of imidazole ionic liquids, quaternary ammonium ionic liquids, quaternary phosphorus ionic liquids and alkali metal or alkaline earth metal halide salts; The filter element of a precision filter is either a metal membrane filter element or an organic material filter element. The ethylene glycol purification tower is a packed tower, with metal wire mesh packing and 30 to 60 trays.

2. The method for heterogeneous catalytic production of dimethyl carbonate according to claim 1, characterized in that, Includes the following steps: Step 1: Reactive Distillation Fresh ethylene carbonate enters the reactive distillation mixing tank and, after preheating, is fed from the top of the reactive distillation column. Fresh methanol, after preheating, enters from the bottom of the reactive distillation column. The reactive distillation column is circulated and heated, and the vaporized methanol comes into countercurrent contact with the ethylene carbonate entering from the top, reacting in the catalyst-filled section of the reactive distillation column. Ethylene carbonate is in excess to ensure complete conversion of methanol into dimethyl carbonate. The low-boiling-point dimethyl carbonate is condensed at the top of the column and collected as the product. The reactive distillation non-condensable gas generated at the top of the reactive distillation column is connected to the tail gas fan to ensure that the reactive distillation is under slight negative pressure or normal pressure. The bottom material mainly contains ethylene carbonate, ethylene glycol, a small amount of dimethyl carbonate, and supported catalyst powder. The catalyst powder is filtered out by a precision filter, and the filtrate enters a melt crystallizer for separation and purification. Step 2: Melting and Crystallization The filtrate after being filtered through a precision filter enters a melt crystallizer. After undergoing a process of cooling crystallization, sweating, and melting, ethylene carbonate, due to its higher freezing point, crystallizes preferentially. The uncrystallized ethylene glycol and a small amount of dimethyl carbonate are mixed and then sent to an ethylene glycol purification tower for separation. The ethylene carbonate crystals are then heated, sweated, and melted to become a high-purity liquid material, which is returned to the mixing tank of the reactive distillation tower. Step 3: Ethylene glycol purification The non-crystallizable ethylene glycol and a small amount of dimethyl carbonate separated from the melt crystallizer are fed into the middle of the ethylene glycol purification tower; the low-boiling-point dimethyl carbonate is distilled off from the top of the tower, condensed, and returned to the mixing tank of the reactive distillation tower; the non-condensable ethylene glycol purified gas generated at the top of the ethylene glycol purification tower is connected to a vacuum pump unit to ensure that the ethylene glycol purification tower is operating under negative pressure; the high-boiling-point ethylene glycol polymer or other impurities are collected from the bottom of the tower as waste liquid; the ethylene glycol collected from the side stream of the tower is cooled and collected as product. The reactive distillation column operates at a pressure of -20 to 0 kPa, a top temperature of 70 to 90°C, a bottom temperature of 196 to 226°C, and a reflux ratio of 1 to 2.5:

1. The molar ratio of methanol to ethylene carbonate is 0.5~2:1; The cooling medium used for crystallization is 28℃ circulating water, and the heating medium used for sweating and melting is 80℃ circulating hot water; The ethylene glycol purification tower operates at a pressure of -99 to -96 kPa, a top temperature of 120 to 150°C, a bottom temperature of 140 to 160°C, and a reflux ratio of 2 to 10:

1.

3. The method for heterogeneous catalytic production of dimethyl carbonate according to claim 2, characterized in that, The reactive distillation column is a packed column with metal wire mesh packing and 40 to 80 trays. The section below the ethylene carbonate inlet is filled with composite packing containing catalyst.

4. The method for heterogeneous catalytic production of dimethyl carbonate according to claim 3, characterized in that, Catalysts include complexes of imidazole ionic liquids, quaternary ammonium ionic liquids, quaternary phosphonium ionic liquids and alkali metal or alkaline earth metal halide salts.

5. The method for heterogeneous catalytic production of dimethyl carbonate according to claim 2, characterized in that, Precision filter elements are either metal membrane filter elements or organic material filter elements.

6. The method for heterogeneous catalytic production of dimethyl carbonate according to claim 2, characterized in that, The ethylene glycol purification tower is a packed tower, with metal wire mesh packing and 30 to 60 trays.

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