A purification method for dimethyl carbonate

Abstract

This invention discloses a purification method for dimethyl carbonate, belonging to the field of dimethyl carbonate processing technology. It addresses the complex technical problem of synthesizing electronic-grade dimethyl carbonate from carbon monoxide and methyl nitrite in existing technologies. The method purifies the bottom material of a degassing tower used in the preparation of dimethyl carbonate from CO and methyl nitrite, comprising the following steps: mixing the bottom material from the degassing tower with activated carbon, and raising the reaction system temperature to 70-80°C. This invention optimizes the distillation process of dimethyl carbonate and uses a prepared adsorption packing to adsorb and remove impurities from the distilled dimethyl carbonate. This not only effectively improves the purity of dimethyl carbonate and reduces the content of impurities such as methanol, water, and metal ions, but also simplifies the post-processing of the resulting electronic-grade dimethyl carbonate product, better meeting production requirements.

Description

Technical Field

[0001] This invention relates to the field of dimethyl carbonate processing technology, and more specifically to a method for purifying dimethyl carbonate. Background Technology

[0002] Dimethyl carbonate (DMC) is an important basic raw material and green solvent in organic chemicals. It has advantages such as low toxicity and biodegradability, and is widely used in polycarbonate synthesis, pharmaceutical intermediates, pesticide adjuvants, and new energy battery electrolytes. With the rapid development of the new energy industry, the demand for high-purity dimethyl carbonate is constantly increasing, especially in the field of lithium-ion battery electrolytes, where extremely strict control requirements are put forward on the content of impurities such as water, methanol, and metal ions in the product.

[0003] The process of catalytically synthesizing dimethyl carbonate (DMC) from carbon monoxide and methyl nitrite is a promising production technology due to its high atom economy, mild reaction conditions, and environmental friendliness. This process typically includes steps such as transesterification, carbonylation, and regeneration. The crude product mainly comes from the bottom of the degassing tower. However, the reaction system of this route is complex, with numerous side reactions. During the reaction, methanol, water, and other byproducts are inevitably generated, resulting in the crude DMC product containing, in addition to the main product DMC, unreacted methanol, water generated from side reactions, trace amounts of catalyst metal ion residues, and colored impurities from heavy components.

[0004] Currently, the process for synthesizing electronic-grade dimethyl carbonate from carbon monoxide and methyl nitrite often employs a combination of vacuum distillation and activated carbon decolorization to remove impurities. However, dimethyl carbonate readily forms an azeotrope with methanol, resulting in a high residual methanol content in the distillation product. Furthermore, due to its hydrophilic nature, dimethyl carbonate readily absorbs moisture during synthesis and separation, leaving residual moisture even after vacuum distillation. Moreover, the catalysts and reaction equipment used in the synthesis process often introduce trace metal ions, which are difficult to completely remove using conventional distillation and activated carbon adsorption processes. To prepare high-purity dimethyl carbonate that meets electronic-grade requirements, multiple distillations are often necessary, making the process complex. Therefore, the process for synthesizing electronic-grade dimethyl carbonate from carbon monoxide and methyl nitrite is inherently complicated. Summary of the Invention

[0005] The purpose of this invention is to provide a purification method for dimethyl carbonate, which solves the technical problem of the complicated process of synthesizing electronic-grade dimethyl carbonate from carbon monoxide and methyl nitrite in the prior art.

[0006] The objective of this invention can be achieved through the following technical solution: a method for purifying dimethyl carbonate, used for purifying the bottom material of a degassing tower in the preparation of dimethyl carbonate from CO and methyl nitrite, comprising the following steps:

[0007] S1. Mix the material from the bottom of the degassing tower with activated carbon, raise the temperature of the reaction system to 70-80℃, keep it warm and stir for 80-100 minutes, and then perform post-treatment to obtain decolorized DMC;

[0008] S2. Decolorized DMC and dimethyl oxalate are fed into a distillation column. The pressure of the distillation column is reduced to 30-40 kPa, and the temperature is gradually increased to 90℃. The column is purified to remove impurities, and the fraction with a temperature of 65-80℃ is collected to obtain distilled DMC.

[0009] S3. The distilled DMC is passed into an adsorption tank filled with adsorption packing material for circulation adsorption to obtain dimethyl carbonate product.

[0010] Furthermore, in step S2, the weight ratio of the decolorized DMC to dimethyl oxalate is 10:2-3; in step S3, the ratio of the amount of distilled DMC to the adsorption packing is 10L:500g, the circulation flow rate of the distilled DMC is 2-3L / min, the circulation adsorption time is 40-60min, and the circulation adsorption temperature is 40-45℃.

[0011] Furthermore, the adsorption packing is obtained by the following steps:

[0012] A1. Place the molecular sieve in a muffle furnace, raise the temperature of the muffle furnace to 500-600℃, calcine with oxygen for 4-5 hours, and then cool naturally to room temperature to obtain the pretreated molecular sieve.

[0013] A2. Surface treatment of the pretreated molecular sieve was performed using 1,1,3,3-tetramethyl-1,3-divinyldisilazane to prepare an unsaturated modified molecular sieve.

[0014] A3. Mix unsaturated modified molecular sieve, vinylacetic acid, dimethylaminoethyl methacrylate, acrylamide, and toluene. Add emulsion to the reaction system, raise the temperature of the reaction system to 70-80℃, add initiator to the reaction system, keep the reaction at this temperature for 2-3 hours, and then perform post-treatment to obtain amphiphilic molecular sieve.

[0015] The synthesis reaction mechanism of amphiphilic molecular sieves is as follows:

[0016] In the reaction process, unsaturated modified molecular sieve, vinylacetic acid, dimethylaminoethyl methacrylate, acrylamide, and toluene are mixed and then emulsified with an emulsion to form an emulsion coating layer on the outside of the unsaturated modified molecular sieve. Under the action of high temperature and free radical initiator, a copolymer brush layer of polar / nonpolar monomers is formed on the surface of the molecular sieve to obtain an amphiphilic molecular sieve.

[0017] A4. An activated molecular sieve was prepared by modifying the surface of an amphiphilic molecular sieve with triethoxysilane.

[0018] A5. An adsorption packing material is prepared by modifying the surface of an activated molecular sieve with a fluorine-containing polysiloxane coating layer through hydrolysis and polycondensation of siloxane.

[0019] Furthermore, the preparation method of unsaturated modified molecular sieve is as follows: under the protection of an inert gas atmosphere, pretreated molecular sieve, 1,1,3,3-tetramethyl-1,3-divinyldisilazane and toluene are mixed, the temperature of the reaction system is raised to 100-110℃, the reaction is kept at the temperature for 3-4 hours, and then post-treated to obtain unsaturated modified molecular sieve.

[0020] The synthesis reaction mechanism of unsaturated modified molecular sieves is as follows:

[0021] During the reaction, high-temperature aerobic calcination removes the template, impurities, and physically adsorbed water from the molecular sieve, exposing a large number of active reaction sites on the surface of the molecular sieve. 1,1,3,3-Tetramethyl-1,3-divinyldisilazane undergoes an ammonolysis / condensation reaction, introducing vinyl double bonds onto the surface of the pretreated molecular sieve, forming unsaturated reactive sites, thus preparing an unsaturated modified molecular sieve.

[0022] Furthermore, the ratio of the pretreated molecular sieve, 1,1,3,3-tetramethyl-1,3-divinyldisilazane, and toluene is 15g:3-4g:100mL. The post-treatment includes: after the reaction is complete, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed three times with toluene and then transferred to a drying oven at 80-90℃ and dried to constant weight to obtain unsaturated modified molecular sieve.

[0023] Further, in step A3, the ratio of the unsaturated modified molecular sieve, vinylacetic acid, dimethylaminoethyl methacrylate, acrylamide, toluene, emulsion, and initiator is 30g:3-4g:4-5g:2-3g:150mL:250mL:0.3g. The emulsion is composed of deionized water, Tween-80, OP-10, and sodium dodecylbenzenesulfonate in a ratio of 100mL:2g:2g:1g. The initiator is 2,2'-azo(2-methylpropylamidine) dihydrochloride. The post-treatment includes: after the reaction is complete, the reaction system temperature is lowered to room temperature, filtered, the filter cake is washed three times with anhydrous ethanol and then dried, and the filter cake is transferred to a drying oven at a temperature of 70-80℃ and dried to constant weight to obtain the amphiphilic molecular sieve.

[0024] Furthermore, the preparation method of activated molecular sieve is as follows: under the protection of an inert gas atmosphere, amphiphilic molecular sieve, tetrahydrofuran, and propyltriethoxysilane isocyanate are mixed and stirred, the temperature of the reaction system is raised to 50-60℃, the reaction is kept at this temperature for 60-80 min, and then post-processed to obtain activated molecular sieve.

[0025] The synthesis reaction mechanism of activated molecular sieves is as follows:

[0026] During the reaction, the amide group on the amphiphilic molecular sieve undergoes condensation with the isocyanate group on the isocyanate propyltriethoxysilane molecule, and the activated molecular sieve is prepared by modifying the outside of the activated molecular sieve with triethoxysilane.

[0027] Furthermore, the ratio of the amphiphilic molecular sieve, tetrahydrofuran, and propyltriethoxysilane isocyanate is 10g:100mL:1.8-2.3g. The post-treatment includes: after the reaction is complete, the reaction system temperature is lowered to room temperature, filtered, the filter cake is washed three times with tetrahydrofuran and then dried, the filter cake is transferred to a drying oven at 60-70℃ and vacuum dried to constant weight to obtain the activated molecular sieve.

[0028] Furthermore, the preparation method of the adsorption packing is as follows: Activated molecular sieve, anhydrous ethanol, tetraethyl orthosilicate, aminomethyltriethoxysilane, and nonafluorohexyltriethoxysilane are mixed, the temperature of the reaction system is raised to 50-60℃, a catalyst is added to the reaction system, the reaction is kept at the temperature for 40-60 min, and the mixture is allowed to stand for aging for 20-22 h. After post-treatment, the adsorption packing is obtained.

[0029] The synthesis reaction mechanism of the adsorption filler is as follows:

[0030] During the reaction, under the catalytic action of the catalyst, the siloxane bonds on the activated molecular sieve, tetraethyl orthosilicate, aminomethyltriethoxysilane, and nonafluorohexyltriethoxysilane molecules hydrolyze to form silanols. Then, the silanols undergo dehydration condensation to form Si-O-Si bonds. The amino group on the aminomethyltriethoxysilane molecule and the nonafluorohexyl group on the nonafluorohexyltriethoxysilane molecule modify the polysilane network, forming a polysiloxane coating on the outside of the activated molecular sieve, thus preparing the adsorption filler.

[0031] Furthermore, the ratio of the activated molecular sieve, anhydrous ethanol, tetraethyl orthosilicate, aminomethyltriethoxysilane, nonafluorohexyltriethoxysilane, and catalyst is 10g:100mL:2g:1.5-1.8g:0.9-1.3g:10mL, and the catalyst is a 3-5mol / L hydrochloric acid solution. The post-treatment includes: after the reaction is complete, the reaction system temperature is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral, dried, and the filter cake is transferred to a drying oven at 85-90℃ and dried to constant weight to obtain the adsorption packing.

[0032] The present invention has the following beneficial effects:

[0033] 1. This invention utilizes activated carbon to heat-treat materials from the bottom of a degassing tower. Activated carbon, with its large specific surface area and well-developed pore structure, effectively removes colored impurities and some organic impurities through physical adsorption, laying a good foundation for subsequent distillation and adsorption steps. This prevents these impurities from contaminating the distillation tower and adsorption packing. During distillation, high-boiling-point dimethyl oxalate preferentially forms a new azeotrope with methanol. By eliminating the front fraction (below 65°C) and not collecting the back fraction (above 80°C), the content of methanol and other impurities in the distilled DMC is effectively reduced. The remaining impurities in the distilled DMC are then adsorbed through the adsorption packing, further increasing the dimethyl carbonate content to meet electronic grade requirements while simplifying the post-processing flow and better meeting production needs.

[0034] 2. This invention utilizes molecular sieves as a base material, which undergoes aerobic high-temperature calcination to modify its surface with unsaturated double bonds. Then, in-situ polymerization is carried out in an emulsified environment to modify the surface of the molecular sieve with an amphiphilic molecular sieve. Finally, polysiloxane is applied to the outside of the amphiphilic molecular sieve to prepare an adsorption packing. The amphiphilic modification layer in the adsorption packing contains both hydrophilic groups such as carboxyl and amide groups, and side alkane branches on the polymer backbone. Methanol in distilled DMC is a polar small molecule. The amide and carboxyl groups in the amphiphilic layer are strong hydrogen bond donors and acceptors, forming strong hydrogen bonds with the hydroxyl groups of methanol, thus firmly adsorbing methanol molecules onto the polymer chain and reducing the methanol content. Similarly, water molecules are strongly polar molecules, and the hydrophilic groups in the amphiphilic layer have an affinity for water molecules, forming water transfer channels that facilitate the migration of water molecules into the molecular sieve, reducing the water content in dimethyl carbonate. Furthermore, the carboxyl groups in the amphiphilic layer can undergo ion exchange with metal cations, adsorbing trace metal elements in dimethyl carbonate and reducing the metal ion content in dimethyl carbonate.

[0035] 3. This invention utilizes a sol-gel method to promote the co-hydrolysis and condensation of tetraethyl orthosilicate, aminosilane, and fluorosilane on the exterior of an amphiphilic molecular sieve, forming a polysiloxane coating. After hydrolysis, tetraethyl orthosilicate forms a SiO2 network rich in silanol groups. The strong hydrophilicity of silanol groups results in extremely high adsorption efficiency and capacity for water molecules. Combined with the amphiphilic modification layer, this enhances the dehydration performance of the adsorption packing. The aminomethyltriethoxysilane introduces an amino group, which also possesses excellent hydrogen bonding ability with methanol molecules, further capturing trace amounts of methanol penetrating the amphiphilic layer. Combined with the amphiphilic modification layer, this ensures that the methanol content in the product is reduced to a minimum. The nonafluorohexyltriethoxysilane introduces a long-chain perfluorinated group. The strong electronegativity of fluorine atoms and their powerful electron-withdrawing effect make the fluorocarbon chain a strong Lewis base, exhibiting a strong complexing and capturing ability for metal cations belonging to Lewis acids. Combined with the amphiphilic modification layer, this deeply removes metal ions, reducing the metal ion content in the product. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In this invention, the molecular sieve is a 3A molecular sieve with a bulk density of 99 g / mL, a particle size of 2 mm, and an effective ingredient content of 99%.

[0038] Example 1

[0039] This embodiment provides a method for preparing an adsorption packing material for the purification of dimethyl carbonate, comprising the following steps:

[0040] Step 1: Preparation of pretreated molecular sieves

[0041] The molecular sieve was placed in a muffle furnace, the temperature of which was raised to 500°C and calcined with oxygen for 4 hours. It was then allowed to cool naturally to room temperature to obtain the pretreated molecular sieve.

[0042] Step 2: Preparation of unsaturated modified molecular sieves

[0043] Weigh out 600g of pretreated molecular sieve, 120g of 1,1,3,3-tetramethyl-1,3-divinyldisilazane, and 4000mL of toluene and add them to an argon-protected reactor. Stir the mixture and raise the reactor temperature to 100℃. Maintain the temperature for 3 hours. Lower the reactor temperature to room temperature, filter the mixture, wash the filter cake three times with toluene, and transfer it to a drying oven at 80℃. Dry the cake to constant weight to obtain unsaturated modified molecular sieve.

[0044] Step 3: Preparation of amphiphilic molecular sieves

[0045] Deionized water, Tween-80, OP-10 and sodium dodecylbenzenesulfonate were mixed evenly at a ratio of 100 mL: 2 g: 2 g: 1 g to obtain an emulsion.

[0046] Weigh out 600g of unsaturated modified molecular sieve, 60g of vinylacetic acid, 80g of dimethylaminoethyl methacrylate, 40g of acrylamide, and 3000mL of toluene and add them to a reaction vessel. Stir the mixture and add 5000mL of emulsion to the reaction vessel. Raise the temperature of the reaction vessel to 70℃ and add 6g of 2,2'-azo(2-methylpropylamidine) dihydrochloride to the reaction vessel. Keep the reaction vessel at this temperature for 2 hours. Lower the temperature of the reaction vessel to room temperature, filter the mixture, wash the filter cake three times with anhydrous ethanol, and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain the amphiphilic molecular sieve.

[0047] Step 4: Preparation of activated molecular sieves

[0048] Weigh out 600g of amphiphilic molecular sieve, 6000mL of tetrahydrofuran, and 108g of propyltriethoxysilane isocyanate and add them to an argon-protected reactor. Stir the mixture and raise the reactor temperature to 50℃. Maintain the temperature for 60min. Lower the reactor temperature to room temperature and filter the mixture. Wash the filter cake three times with tetrahydrofuran and dry it under vacuum. Transfer the filter cake to a drying oven at 60℃ and dry it under vacuum until constant weight to obtain the activated molecular sieve.

[0049] Step 5: Preparation of adsorption packing material

[0050] Weigh out 500g of activated molecular sieve, 5000mL of anhydrous ethanol, 100g of tetraethyl orthosilicate, 75g of aminomethyltriethoxysilane, and 45g of nonafluorohexyltriethoxysilane, and add them to a reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 50℃. Add 500mL of 3mol / L hydrochloric acid solution to the reaction vessel and keep it at this temperature for 40min. Allow it to stand and age for 20h. Lower the temperature of the reaction vessel to room temperature, filter the mixture, wash the filter cake with purified water until neutral, and then dry it. Transfer the filter cake to a drying oven at 85℃ and dry it to constant weight to obtain the adsorption packing.

[0051] Example 2

[0052] This embodiment provides a method for preparing an adsorption packing material for the purification of dimethyl carbonate, comprising the following steps:

[0053] Step 1: Preparation of pretreated molecular sieves

[0054] The molecular sieve was placed in a muffle furnace, the temperature of which was raised to 550°C and calcined with oxygen for 4.5 hours. It was then allowed to cool naturally to room temperature to obtain the pretreated molecular sieve.

[0055] Step 2: Preparation of unsaturated modified molecular sieves

[0056] Weigh out 600g of pretreated molecular sieve, 140g of 1,1,3,3-tetramethyl-1,3-divinyldisilazane, and 4000mL of toluene and add them to an argon-protected reactor. Stir the mixture and raise the reactor temperature to 105℃. Maintain the temperature for 3.5h. Then lower the reactor temperature to room temperature, filter the mixture, wash the filter cake three times with toluene, and transfer it to a drying oven at 85℃. Dry the cake to constant weight to obtain unsaturated modified molecular sieve.

[0057] Step 3: Preparation of amphiphilic molecular sieves

[0058] Deionized water, Tween-80, OP-10 and sodium dodecylbenzenesulfonate were mixed evenly at a ratio of 100 mL: 2 g: 2 g: 1 g to obtain an emulsion.

[0059] Weigh out 600g of unsaturated modified molecular sieve, 70g of vinylacetic acid, 90g of dimethylaminoethyl methacrylate, 50g of acrylamide, and 3000mL of toluene and add them to a reaction vessel. Stir the mixture and add 5000mL of emulsion to the reaction vessel. Raise the temperature of the reaction vessel to 75℃ and add 6g of 2,2'-azo(2-methylpropylamidine) dihydrochloride to the reaction vessel. Keep the reaction vessel at this temperature for 2.5h. Lower the temperature of the reaction vessel to room temperature, filter the mixture, wash the filter cake three times with anhydrous ethanol, and then dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight to obtain the amphiphilic molecular sieve.

[0060] Step 4: Preparation of activated molecular sieves

[0061] Weigh out 600g of amphiphilic molecular sieve, 6000mL of tetrahydrofuran, and 123g of propyltriethoxysilane isocyanate and add them to an argon-protected reactor. Stir the mixture and raise the reactor temperature to 55℃. Maintain the temperature for 70min. Lower the reactor temperature to room temperature and filter the mixture. Wash the filter cake three times with tetrahydrofuran and dry it under vacuum. Transfer the filter cake to a drying oven at 65℃ and dry it under vacuum until constant weight to obtain the activated molecular sieve.

[0062] Step 5: Preparation of adsorption packing material

[0063] Weigh out 500g of activated molecular sieve, 5000mL of anhydrous ethanol, 100g of tetraethyl orthosilicate, 83g of aminomethyltriethoxysilane, and 55g of nonafluorohexyltriethoxysilane, and add them to a reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 55℃. Add 500mL of 4mol / L hydrochloric acid solution to the reaction vessel and keep it at this temperature for 50min. Allow it to stand and age for 21h. Lower the temperature of the reaction vessel to room temperature, filter the mixture, wash the filter cake with purified water until neutral, and then dry it. Transfer the filter cake to a drying oven at 87℃ and dry it to constant weight to obtain the adsorption packing.

[0064] Example 3

[0065] This embodiment provides a method for preparing an adsorption packing material for the purification of dimethyl carbonate, comprising the following steps:

[0066] Step 1: Preparation of pretreated molecular sieves

[0067] The molecular sieve was placed in a muffle furnace, the temperature of which was raised to 600℃ and calcined with oxygen for 5 hours. It was then allowed to cool naturally to room temperature to obtain the pretreated molecular sieve.

[0068] Step 2: Preparation of unsaturated modified molecular sieves

[0069] Weigh out 600g of pretreated molecular sieve, 160g of 1,1,3,3-tetramethyl-1,3-divinyldisilazane, and 4000mL of toluene and add them to an argon-protected reactor. Stir the mixture and raise the reactor temperature to 110℃. Maintain the temperature for 4 hours. Then lower the reactor temperature to room temperature, filter the mixture, wash the filter cake three times with toluene, and transfer it to a drying oven at 90℃. Dry the cake to constant weight to obtain unsaturated modified molecular sieve.

[0070] Step 3: Preparation of amphiphilic molecular sieves

[0071] Deionized water, Tween-80, OP-10 and sodium dodecylbenzenesulfonate were mixed evenly at a ratio of 100 mL: 2 g: 2 g: 1 g to obtain an emulsion.

[0072] Weigh out 600g of unsaturated modified molecular sieve, 80g of vinylacetic acid, 100g of dimethylaminoethyl methacrylate, 60g of acrylamide, and 3000mL of toluene and add them to a reaction vessel. Stir the mixture and add 5000mL of emulsion to the reaction vessel. Raise the temperature of the reaction vessel to 80℃ and add 6g of 2,2'-azo(2-methylpropylamidine) dihydrochloride to the reaction vessel. Keep the reaction vessel at this temperature for 3 hours. Lower the temperature of the reaction vessel to room temperature, filter the mixture, wash the filter cake three times with anhydrous ethanol, and then dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight to obtain the amphiphilic molecular sieve.

[0073] Step 4: Preparation of activated molecular sieves

[0074] Weigh out 600g of amphiphilic molecular sieve, 6000mL of tetrahydrofuran, and 138g of propyltriethoxysilane isocyanate and add them to an argon-protected reactor. Stir the mixture and raise the reactor temperature to 60℃. Maintain the temperature for 80min. Lower the reactor temperature to room temperature and filter the mixture. Wash the filter cake three times with tetrahydrofuran and dry it under vacuum. Transfer the filter cake to a drying oven at 70℃ and dry it under vacuum to constant weight to obtain the activated molecular sieve.

[0075] Step 5: Preparation of adsorption packing material

[0076] Weigh out 500g of activated molecular sieve, 5000mL of anhydrous ethanol, 100g of tetraethyl orthosilicate, 90g of aminomethyltriethoxysilane, and 65g of nonafluorohexyltriethoxysilane. Add them to a reaction vessel and stir. Raise the temperature of the reaction vessel to 60℃, add 500mL of 5mol / L hydrochloric acid solution to the reaction vessel, keep the reaction at this temperature for 60min, let it stand and age for 22h, lower the temperature of the reaction vessel to room temperature, filter, wash the filter cake with purified water until neutral, and then dry it. Transfer the filter cake to a drying oven at 90℃ and dry it to constant weight to obtain the adsorption packing.

[0077] Example 4

[0078] This embodiment provides a purification method for dimethyl carbonate, used for purifying the bottom material of a degassing tower in the preparation of dimethyl carbonate from CO and methyl nitrite, comprising the following steps:

[0079] Step 1: Preparation of decolorized DMC

[0080] Weigh 10 kg of material from the bottom of the degassing tower and 200 g of activated carbon and add them to the reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 70°C. Keep the mixture warm and stir for 80 min. Then lower the temperature of the reaction vessel to room temperature and filter the mixture to obtain decolorized DMC.

[0081] Step 2: Preparation of Distilled DMC

[0082] Decolorized DMC and dimethyl oxalate were added to a distillation column at a weight ratio of 10:2. The pressure of the distillation column was reduced to 30 kPa, and the temperature was gradually increased to remove the fraction below 65°C. The fraction in the 65-80°C range was collected to obtain distilled DMC.

[0083] Step 3: Preparation of dimethyl carbonate product

[0084] Weigh out 500g of the adsorption packing material prepared in Example 1 and place it into the adsorption tank. Then, 10L of distilled DMC is fed into the adsorption tank at a flow rate of 2L / min. The temperature of the adsorption tank is raised to 40℃, and the adsorption is circulated for 40min. The product is then discharged to obtain dimethyl carbonate.

[0085] Example 5

[0086] This embodiment provides a purification method for dimethyl carbonate, used for purifying the bottom material of a degassing tower in the preparation of dimethyl carbonate from CO and methyl nitrite, comprising the following steps:

[0087] Step 1: Preparation of decolorized DMC

[0088] Weigh 10 kg of material from the bottom of the degassing tower and 200 g of activated carbon and add them to the reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 75°C. Keep the mixture warm and stir for 90 min. Then lower the temperature of the reaction vessel to room temperature and filter the mixture to obtain decolorized DMC.

[0089] Step 2: Preparation of Distilled DMC

[0090] Decolorized DMC and dimethyl oxalate were added to a distillation column at a weight ratio of 10:2.5. The pressure of the distillation column was reduced to 35 kPa, and the temperature was gradually increased to remove the fraction below 65°C. The fraction in the 65-80°C range was collected to obtain distilled DMC.

[0091] Step 3: Preparation of dimethyl carbonate product

[0092] Weigh out 500g of the adsorption packing material prepared in Example 2 and place it into the adsorption tank. Then, 10L of distilled DMC is fed into the adsorption tank at a flow rate of 2.5L / min. The temperature of the adsorption tank is raised to 43℃, and the adsorption is circulated for 50min. The product is then discharged to obtain dimethyl carbonate.

[0093] Example 6

[0094] This embodiment provides a purification method for dimethyl carbonate, used for purifying the bottom material of a degassing tower in the preparation of dimethyl carbonate from CO and methyl nitrite, comprising the following steps:

[0095] Step 1: Preparation of decolorized DMC

[0096] Weigh 10 kg of material from the bottom of the degassing tower and 200 g of activated carbon and add them to the reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 80°C. Keep the mixture at this temperature and stir for 100 min. Then lower the temperature of the reaction vessel to room temperature and filter the mixture to obtain decolorized DMC.

[0097] Step 2: Preparation of Distilled DMC

[0098] Decolorized DMC and dimethyl oxalate were added to a distillation column at a weight ratio of 10:3. The pressure of the distillation column was reduced to 40 kPa, and the temperature was gradually increased to remove the fraction below 65°C. The fraction in the 65-80°C range was collected to obtain distilled DMC.

[0099] Step 3: Preparation of dimethyl carbonate product

[0100] Weigh out 500g of the adsorption packing material prepared in Example 3 and place it into the adsorption tank. Then, 10L of distilled DMC is fed into the adsorption tank at a flow rate of 3L / min. The temperature of the adsorption tank is raised to 45℃, and the adsorption is circulated for 60min. The product is then discharged to obtain dimethyl carbonate.

[0101] Comparative Example 1

[0102] The difference between this comparative example and Example 6 is that dimethyl oxalate was not added in step two.

[0103] Comparative Example 2

[0104] The difference between this comparative example and Example 6 is that, in the preparation of the adsorption packing material, step 1 is omitted, and the molecular sieve in step 1 is used instead of the pretreated molecular sieve in step 2.

[0105] Comparative Example 3

[0106] The difference between this comparative example and Example 6 is that, in the preparation of the adsorption packing material, vinylacetic acid was not added in step 3.

[0107] Comparative Example 4

[0108] The difference between this comparative example and Example 6 is that, in the preparation of the adsorption packing material, step 5 is omitted, and the activated molecular sieve prepared in step 4 is used as the adsorption packing material to participate in the preparation of dimethyl carbonate product.

[0109] Performance testing:

[0110] The purity, methanol content, water content, and metal ion content of the distilled DMC and dimethyl carbonate products in Examples 4-6 and Comparative Examples 1-4 were determined according to the standard GB / T 33107-2016 "Dimethyl Carbonate for Industrial Use". The metal ion content is the total content of sodium, potassium, copper, iron, lead, zinc, chromium, and nickel in the sample. The specific measurement data are shown in Table 1-2 below.

[0111] Table 1 - Performance Test Data of Distillation DMC

[0112]

[0113] Table 2 - Performance Test Data of Dimethyl Carbonate Products

[0114]

[0115] Data Analysis:

[0116] Comparative analysis of the data in Tables 1-2 shows that the dimethyl carbonate content in the distilled DMC prepared by this invention reaches 99.96%, the methanol content is reduced to 16.6 ppm, the water content is reduced to 10.1 ppm, and the metal ion content is reduced to 6.1 μg / mL. After cyclic adsorption by the adsorption packing material, the dimethyl carbonate content in the product reaches 99.995%, the methanol content is reduced to 1.2 ppm, the water content is reduced to 1.8 ppm, and the metal ion content is reduced to 1.01 μg / mL. The prepared dimethyl carbonate product meets the standard requirements for electronic grade dimethyl carbonate.

[0117] In Comparative Example 1, no dimethyl oxalate was added during the distillation step. During distillation, it could form a new azeotrope with methanol, thereby effectively reducing the methanol residue in the distilled DMC. The high methanol residue and water content weakened the methanol removal effect of distillation, making it difficult for subsequent adsorption to completely compensate.

[0118] Comparative Example 2 directly used the original molecular sieve in the preparation of the adsorption packing without high-temperature calcination to remove impurities and introduce active sites. As a result, there were insufficient reaction sites on the surface of the molecular sieve, the modification efficiency was reduced, the adsorption packing activity was poor, and the dehydration and metal ion removal capabilities were reduced, ultimately leading to water and metal impurity residues.

[0119] In Comparative Example 3, vinylacetic acid was not introduced during the preparation of the amphiphilic molecular sieve. Vinylacetic acid is an important polar monomer for amphiphilic modification, which can provide carboxyl groups and enhance the interaction with methanol, water and metal ions. The absence of vinylacetic acid weakens the polar functional groups of the adsorption layer, reduces the ability to adsorb methanol and water, and also weakens the metal capture ability.

[0120] In Comparative Example 4, step 5 was omitted in the preparation of the adsorption packing material, and only activated molecular sieves were used. The SiO2 network enhanced the dehydration ability, the amino group enhanced the methanol adsorption, the fluorine-containing group enhanced the metal ion complexation and capture, and the polysiloxane coating was missing. As a result, the adsorbent's triple capture ability for methanol, water and metal ions was significantly reduced, and the performance was obviously degraded.

[0121] This invention optimizes the distillation process of dimethyl carbonate and prepares an adsorption packing material by modifying the surface of a molecular sieve with an amphiphilic molecular sieve at high temperature and then coating it with polysiloxane. This material adsorbs and removes impurities from the distilled dimethyl carbonate, effectively improving the purity of dimethyl carbonate and reducing the content of impurities such as methanol, water, and metal ions, thus producing an electronic-grade dimethyl carbonate product.

[0122] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for purifying dimethyl carbonate, used for purifying the bottom feed of a degassing tower in the preparation of dimethyl carbonate from CO and methyl nitrite, characterized in that, Includes the following steps: S1. Mix the material from the bottom of the degassing tower with activated carbon, raise the temperature of the reaction system to 70-80℃, keep it warm and stir for 80-100 minutes, and then perform post-treatment to obtain decolorized DMC; S2. Decolorized DMC and dimethyl oxalate are fed into a distillation column. The pressure of the distillation column is reduced to 30-40 kPa, and the temperature is gradually increased to 90℃. The column is purified to remove impurities, and the fraction with a temperature of 65-80℃ is collected to obtain distilled DMC. S3. The distilled DMC is passed into an adsorption tank filled with adsorption packing material for circulation adsorption to obtain dimethyl carbonate product. The adsorption packing material is obtained by the following steps: A1. Place the molecular sieve in a muffle furnace, raise the temperature of the muffle furnace to 500-600℃, calcine with oxygen for 4-5 hours, and then cool naturally to room temperature to obtain the pretreated molecular sieve. A2. Under an inert gas atmosphere, pretreated molecular sieve, 1,1,3,3-tetramethyl-1,3-divinyldisilazane, and toluene are mixed. The reaction system temperature is raised to 100-110℃ and kept at this temperature for 3-4 hours. After post-treatment, unsaturated modified molecular sieve is obtained. The ratio of the amount of pretreated molecular sieve, 1,1,3,3-tetramethyl-1,3-divinyldisilazane, and toluene is 15g:3-4g:100mL. A3. Mix unsaturated modified molecular sieve, vinylacetic acid, dimethylaminoethyl methacrylate, acrylamide, and toluene. Add an emulsion to the reaction system, raise the temperature of the reaction system to 70-80℃, add an initiator, and keep the reaction at this temperature for 2-3 hours. After post-treatment, obtain an amphiphilic molecular sieve. The ratio of the unsaturated modified molecular sieve, vinylacetic acid, dimethylaminoethyl methacrylate, acrylamide, toluene, emulsion, and initiator is 30g:3-4g:4-5g:2-3g:150mL:250mL:0.3g. The emulsion is composed of deionized water, Tween-80, OP-10, and sodium dodecylbenzenesulfonate in a ratio of 100mL:2g:2g:1g. The initiator is 2,2'-azo(2-methylpropylamidine) dihydrochloride. A4. Under an inert gas atmosphere, the amphiphilic molecular sieve, tetrahydrofuran, and propyltriethoxysilane are mixed and stirred. The temperature of the reaction system is raised to 50-60℃ and the reaction is maintained for 60-80 min. After post-treatment, activated molecular sieve is obtained. The ratio of the amount of the amphiphilic molecular sieve, tetrahydrofuran, and propyltriethoxysilane is 10g:100mL:1.8-2.3g. A5. Mix activated molecular sieve, anhydrous ethanol, tetraethyl orthosilicate, aminomethyltriethoxysilane, and nonafluorohexyltriethoxysilane. Raise the temperature of the reaction system to 50-60℃, add the catalyst to the reaction system, keep the reaction at this temperature for 40-60 min, allow it to stand and age for 20-22 h, and then perform post-treatment to obtain the adsorption packing. The ratio of the activated molecular sieve, anhydrous ethanol, tetraethyl orthosilicate, aminomethyltriethoxysilane, nonafluorohexyltriethoxysilane, and catalyst is 10g:100mL:2g:1.5-1.8g:0.9-1.3g:10mL. The catalyst is a 3-5mol / L hydrochloric acid solution.

2. The method for purifying dimethyl carbonate according to claim 1, characterized in that, In step S2, the weight ratio of the decolorized DMC to dimethyl oxalate is 10:2-3; in step S3, the ratio of distilled DMC to adsorption packing is 10L:500g, the circulation flow rate of the distilled DMC is 2-3L / min, the circulation adsorption time is 40-60min, and the circulation adsorption temperature is 40-45℃.

3. The purification method for dimethyl carbonate according to claim 1, characterized in that, In step A2, the post-processing includes: after the reaction is complete, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed three times with toluene and then transferred to a drying oven at a temperature of 80-90℃ and dried to constant weight to obtain unsaturated modified molecular sieve.

4. The purification method for dimethyl carbonate according to claim 1, characterized in that, In step A3, the post-processing includes: after the reaction is complete, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed three times with anhydrous ethanol and then dried, the filter cake is transferred to a drying oven at a temperature of 70-80℃ and dried to constant weight to obtain amphiphilic molecular sieve.

5. The method for purifying dimethyl carbonate according to claim 1, characterized in that, In step A4, the post-processing includes: after the reaction is complete, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed three times with tetrahydrofuran and then dried, the filter cake is transferred to a drying oven at a temperature of 60-70℃ and vacuum dried to constant weight to obtain activated molecular sieve.

6. The purification method for dimethyl carbonate according to claim 1, characterized in that, In step A5, the post-processing includes: after the reaction is complete, the temperature of the reaction system is reduced to room temperature, the mixture is filtered, the filter cake is washed with purified water until neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 85-90℃ and dried to constant weight to obtain the adsorption packing.

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