Equipment and method for separating and purifying the product of CO esterification to dimethyl carbonate

Abstract

This invention discloses a product separation and purification apparatus and method for dimethyl carbonate (DMC) produced by CO esterification. It includes a pre-separation tower, a DMC separation tower, a methanol absorption tower, an MN desorption tower, a DMM removal tower, an MF distillation tower, a DMM distillation tower, an atmospheric DMC distillation tower, a methanol light component removal tower, a pressurized DMC distillation tower, a wastewater DMC recovery tower, a refined DMC heavy component removal tower, and a DMC purification tower. The DMC product feed line is connected to the inlet of the pre-separation tower, the bottom outlet of the pre-separation tower is connected to the inlet of the wastewater DMC recovery tower, and the top outlet of the pre-separation tower is connected to the bottom inlet of the methanol absorption tower. The upper part of the methanol absorption tower has one or more absorbent inlets. The bottom of the DMM removal tower is connected to the inlet of the atmospheric DMC distillation tower, or connected to both the inlet of the atmospheric DMC distillation tower and the upper absorbent inlet of the methanol absorption tower. This invention can be used for the separation and purification of dimethyl carbonate (DMC) product streams, mainly for the separation and purification of products produced by CO esterification, and features a reasonable process and low energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology. Specifically, it relates to a separation and purification apparatus and method for a reaction product system of CO esterification to produce dimethyl carbonate (DMC). Background Technology

[0002] Dimethyl carbonate (DMC) is a globally recognized green chemical, primarily used in the production of polycarbonate (PC), isocyanate, pharmaceuticals, and pesticides. It is also used as a solvent in lithium-ion battery electrolytes and coatings, and has potential applications as a substitute for methyl tert-butyl ether (MTBE) as a gasoline additive.

[0003] Currently, there are three industrialized dimethyl carbonate synthesis technologies, and one more technology with promising industrialization prospects:

[0004] (1) Phosgene-methanol method: the raw material phosgene is a highly toxic chemical and the by-product HCl is highly corrosive. Therefore, this route has been eliminated.

[0005] (2) Transesterification. Based on the reactants, industrialized process routes include:

[0006] ①Propylene oxide + CO2 + methanol → DMC + propylene glycol

[0007] This method offers mild reaction conditions and high yields. However, the cost of the raw material (propylene oxide) is high, and the separation of the byproduct propylene glycol is difficult. Furthermore, the production process of propylene oxide (chlorohydrin process) is highly polluting, and the market for the byproduct propylene glycol is already in large surplus, making sales difficult.

[0008] ②Urea + 1,2-propanediol → propylene carbonate + liquid ammonia

[0009] Propylene carbonate + methanol → DMC + 1,2-propanediol

[0010] This method has low yield and requires large equipment investment.

[0011] ③ Ethylene oxide + CO2 + methanol → DMC + ethylene glycol

[0012] The Institute of Process Engineering, Chinese Academy of Sciences, has invented a supported ionic liquid catalyst with advantages such as high single-pass conversion rate of ethylene oxide, strong adaptability to raw materials, and no need for catalyst separation. It has also achieved mass production and industrial demonstration applications.

[0013] (3) Liquid-phase methanol oxidative carbonylation method

[0014] 2CH3OH + CO + 0.5O2 → DMC + H2O

[0015] This technical route has several drawbacks: the catalyst CuCl is unstable, has a short lifespan, is highly corrosive, and is difficult to regenerate and recycle; the product contains chlorine, which affects product quality; there are many byproducts; and the CO concentration in oxygen is within the explosive limit range (12.5%–74%), making it prone to explosion.

[0016] (4) CO esterification to dimethyl carbonate. This route uses a supported metal nanocatalyst, which has good space-time yield and selectivity. The reaction conditions are mild, with low pressure (0.2-0.5 MPag) and temperature range of 100-150℃, making it a promising technology for industrialization.

[0017] The reaction principle for the production of dimethyl carbonate by CO esterification is as follows:

[0018] CO + 2CH3ONO → (CH3O)2CO + 2NO

[0019] The raw materials are gaseous CO and methyl nitrite (CH3ONO, abbreviated as MN), the main product is dimethyl carbonate, and the byproducts are dimethyl oxalate (DMO), methyl formate (MF), dimethoxymethane (DMM), and methanol, etc. The stoichiometric equations for the side reactions are as follows:

[0020] 2CO + 2MN → DMO + 2NO

[0021] 4MN→MF+2CH3OH+4NO

[0022] 2MN + MeOH → DMM + H2O

[0023] Dimethyl carbonate has a boiling point of 90°C and a melting point of 2–4°C; it is a liquid at room temperature. Dimethyl oxalate has a boiling point of 174°C and a melting point of 54°C; it is a solid at room temperature.

[0024] Chinese patent (CN103901130B) discloses "an online evaluation device, evaluation method, and production method for the production of dimethyl carbonate catalysts." The evaluation device includes a gas control pipeline system, a fixed-bed reaction system, a product separation and purification system, and an online gas chromatography analysis system. The gas control pipeline system comprises three gas control pipelines, each including a sequentially connected gas delivery pipeline, a pressure regulating valve, a pressure gauge, a flow regulating valve, a mass flow controller, and a switching valve. The three gas pipelines are merged into a single gas pipeline via an equal-diameter four-way connector, and a gas mixing chamber is installed on the merged pipeline. This evaluation device can achieve real-time synchronous analysis of all components of raw materials and products using only one online gas chromatograph, resulting in high analytical efficiency, accurate and reliable data, low capital investment, and efficient production and purification of dimethyl carbonate.

[0025] The aforementioned patents provide a reaction route for CO esterification to produce dimethyl carbonate (also known as methanol carbonylation to produce methyl formate), a catalyst evaluation method, and a separation scheme suitable for laboratory scale and equipment, but do not propose a feasible engineering technology route applicable to industrialization. Summary of the Invention

[0026] The purpose of this invention is to propose a complete and industrially suitable product separation and purification method and system for the CO esterification to dimethyl carbonate reaction system, which features a reasonable process and low energy consumption.

[0027] To achieve the above-mentioned objectives, this invention provides a product separation and purification apparatus and method for the production of dimethyl carbonate via CO esterification, the specific technical solution of which is as follows.

[0028] This invention provides a product separation and purification apparatus for CO esterification to dimethyl carbonate, characterized in that: the CO esterification to dimethyl carbonate product separation and purification apparatus includes a pre-separation tower, a DMC separation tower, a methanol absorption tower, an MN desorption tower, a DMM removal tower, an MF distillation tower, a DMM distillation tower, an atmospheric pressure DMC distillation tower, a methanol light removal tower, a pressurized DMC distillation tower, and a wastewater DMC recovery tower, and the DMC product feed pipeline is connected to the inlet of the pre-separation tower;

[0029] The bottom outlet of the pre-separation tower is connected to the inlet of the wastewater DMC recovery tower, the bottom outlet of the wastewater DMC recovery tower is connected to the wastewater extraction pipeline, the top outlet of the wastewater DMC recovery tower is connected to the DMC product extraction pipeline, the pre-separation tower is provided with a side outlet, the side outlet of the pre-separation tower is connected to the inlet of the DMC separation tower, the bottom outlet of the DMC separation tower is connected to the DMC product extraction pipeline, the top outlet of the DMC separation tower is connected to the inlet of the MN desorption tower, and the top outlet of the pre-separation tower is connected to the bottom feed inlet of the methanol absorption tower.

[0030] The methanol absorption tower is equipped with one or more absorbent inlets at its upper part; the top outlet of the methanol absorption tower is connected to the circulating gas extraction pipeline, the bottom outlet of the methanol absorption tower is connected to the inlet of the MN desorption tower, the top outlet of the MN desorption tower is connected to the circulating gas extraction pipeline, the bottom outlet of the MN desorption tower is connected to the inlet of the DMM stripping tower, the top outlet of the DMM stripping tower is connected to the feed inlet of the MF distillation tower, and the bottom outlet of the DMM stripping tower is connected to the feed inlet of the atmospheric DMC distillation tower, or connected to the feed inlet of the atmospheric DMC distillation tower and the absorbent inlet at the top of the methanol absorption tower respectively; the top outlet of the MF distillation tower is connected to the MF product extraction pipeline, the bottom outlet of the MF distillation tower is connected to the feed inlet of the DMM distillation tower, the top outlet of the DMM distillation tower is connected to the DMM product extraction pipeline, and the bottom outlet of the DMM distillation tower is connected to the recovered methanol outlet pipeline;

[0031] The top outlet of the atmospheric DMC distillation column is connected to the feed inlet of the methanol light product removal column, and the bottom outlet of the atmospheric DMC distillation column is connected to the methanol product outlet pipeline. The top outlet of the methanol light product removal column is connected to the light product extraction pipeline, and the bottom outlet of the methanol light product removal column is connected to the feed inlet of the pressurized DMC distillation column. The top outlet of the pressurized DMC distillation column is connected to the inlet of the atmospheric DMC distillation column, and the bottom outlet of the pressurized DMC distillation column is connected to the DMC product extraction pipeline. The DMC product extraction pipeline is connected to the primary DMC extraction pipeline, or to the primary DMC extraction pipeline and the feed inlet of the refined DMC heavy product removal column, respectively.

[0032] In this invention, the preferred DMC product extraction pipeline is connected to both the primary DMC extraction pipeline and the feed inlet of the refined DMC deweighting tower. In this case, the CO esterification to dimethyl carbonate product separation and purification apparatus of this invention further includes a refined DMC deweighting tower and a DMC purification tower. The DMC product extraction pipeline is divided into two lines: one connected to the primary DMC extraction pipeline, and the other connected to the feed inlet of the refined DMC deweighting tower. The top outlet of the refined DMC deweighting tower is connected to the feed inlet of the DMC purification tower, the bottom outlet of the refined DMC deweighting tower is connected to the DMO stream outlet pipeline, the top outlet of the DMC purification tower is connected to the feed inlet of the atmospheric DMC distillation tower, and the bottom outlet of the DMC purification tower is connected to the electronic-grade DMC stream outlet pipeline.

[0033] In this invention, the bottom of the DMM removal tower is preferably connected to the feed inlet of the atmospheric DMC distillation tower and the absorbent inlet at the top of the methanol absorption tower, respectively.

[0034] Preferably, the methanol absorption tower of the present invention has three absorbent inlets arranged sequentially from top to bottom at the top, which are preferably fresh methanol absorbent inlet, recovered methanol absorbent inlet and methanol absorbent from the bottom of the DMM removal tower.

[0035] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention preferably has 90 to 150 theoretical plates in the separation tower, and the side stream sampling position is located 10 to 30 theoretical plates away from the top of the tower, preferably 15 to 25 theoretical plates.

[0036] The CO esterification to dimethyl carbonate product separation and purification device of the present invention includes a methanol absorption tower with 10 to 40 theoretical plates, preferably 20 to 30 theoretical plates.

[0037] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention has a DMM removal tower with 35 to 65 theoretical plates, preferably 45 to 55 theoretical plates.

[0038] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention includes an MN desorption tower with 30 to 75 theoretical plates, preferably 50 to 60 theoretical plates.

[0039] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention has a DMC separation tower with 30 to 50 theoretical plates, preferably 35 to 45 theoretical plates.

[0040] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention has an MF distillation column with 40 to 70 theoretical plates, preferably 50 to 65 theoretical plates.

[0041] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention includes a DMM distillation column with 40 to 70 theoretical plates, preferably 50 to 65 theoretical plates.

[0042] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention includes an atmospheric pressure DMC distillation column with 60 to 90 theoretical plates, preferably 65 to 80 theoretical plates.

[0043] The product separation and purification apparatus for CO esterification to dimethyl carbonate of the present invention has a methanol light removal tower with 20 to 40 theoretical plates, preferably 25 to 35 theoretical plates.

[0044] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention includes a pressurized DMC distillation column with 60 to 100 theoretical plates, preferably 75 to 85 theoretical plates.

[0045] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention has a DMC deweighting tower with 60 to 100 theoretical plates, preferably 75 to 85 theoretical plates.

[0046] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention includes a DMC purification tower with 30 to 50 theoretical plates, preferably 35 to 45 theoretical plates.

[0047] This invention provides a method for separating and purifying dimethyl carbonate produced by CO esterification, characterized by comprising the following steps:

[0048] 1) The product stream of CO esterification to produce dimethyl carbonate is cooled and condensed and then enters the pre-separation tower for pre-separation. The separated gas phase is sent to the bottom of the methanol absorption tower, and the separated bottom heavy phase is sent to the wastewater DMC recovery tower. After the wastewater is removed, first-grade DMC product is obtained. The separated liquid phase is collected as a side stream and sent to the feed inlet of the DMC separation tower. The pressure at the top of the pre-separation tower is 0.3 MPa, the temperature at the top of the tower is 30-60℃, and the temperature at the bottom of the tower is 120-170℃.

[0049] 2) In the methanol absorption tower, the bottom stream of the methanol absorption tower comes into countercurrent contact with the absorbent entering from the top of the methanol absorption tower to carry out the absorption process. DMC, MF, DMM, DMO and other components in the product stream of CO esterification to dimethyl carbonate are absorbed into the methanol. The gas coming out of the top of the methanol absorption tower is mixed and used as the circulating gas. The rich absorbent at the bottom of the methanol absorption tower is sent to the middle of the MN desorption tower for desorption. The light components are then used as the circulating gas. The bottom of the MN desorption tower contains heavy components, mainly including DMC, methanol, MF and DMM. These are then sent to the DMM removal tower for separation. The top stream of the DMM removal tower is distilled to obtain MF product, DMM product and recovered methanol. The recovered methanol can be used as the absorbent in the methanol absorption tower. The bottom stream of the DMM removal tower can be sent to the feed inlet of the atmospheric pressure DMC distillation tower, or part of it can be returned to the methanol absorption tower as supplementary absorbent and the other part can be sent to the feed inlet of the atmospheric pressure DMC distillation tower.

[0050] 3) In the DMC separation tower, the stream entering through the DMC separation tower inlet is separated into light components and first-grade DMC product. The light components enter the upper part of the MN desorption tower.

[0051] 4) In the atmospheric DMC distillation column, the bottom product of the atmospheric DMC distillation column is methanol, which can be recovered and reused in the unit. The vapor product at the top of the column is sent to the methanol light component removal column. The top of the methanol light component removal column is a small amount of light component, which is sent to the storage tank as waste liquid. The bottom product is a DMC-methanol mixture, which is sent to the feed inlet of the pressurized DMC distillation column. The top product is a DMC-methanol azeotrope under pressurized conditions, which is returned to the atmospheric DMC distillation column. The bottom product is grade I DMC product.

[0052] 5) The first-grade DMC product obtained from the wastewater DMC recovery tower, the first-grade DMC product obtained from the DMC separation tower, and the first-grade DMC product obtained from the pressurized DMC distillation tower can be exported as products, or part of them can be exported as products and the other part can be sent to the DMC de-weighting tower. DMO product is obtained at the bottom of the tower, and the top stream is sent to the DMC distillation tower. Electronic-grade DMC product is obtained at the bottom of the tower, and the top stream is returned to the atmospheric pressure DMC distillation tower.

[0053] The present invention discloses a method for separating and purifying products from CO esterification to dimethyl carbonate. In a preferred embodiment, the DMC-methanol mixture from the bottom product stream of the DMM removal column and the top product stream of the pressurized DMC distillation column enters different positions of the atmospheric pressure DMC distillation column according to its DMC concentration.

[0054] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top pressure of the atmospheric pressure DMC distillation column is 0.16-0.2 MPa, the top temperature is 65-85℃, preferably 70-80℃, and the bottom temperature is 70-95℃, preferably 75-90℃.

[0055] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification. The methanol light component removal tower has a top pressure of 0.16–0.2 MPa and a top temperature of 40–70°C, preferably 50–60°C. The bottom temperature is 70–95°C, preferably 75–90°C.

[0056] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the pressure of the pressurized DMC distillation column is 1.2-1.5 MPa, the top temperature is 130-160°C, preferably 140-150°C, and the bottom temperature is 170-210°C, preferably 185-195°C.

[0057] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top pressure of the DMC removal column is 0.16-0.2 MPa, the top temperature is 95-115°C, preferably 100-110°C, and the bottom temperature is 105-135°C, preferably 115-125°C.

[0058] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top pressure of the DMC purification column is 1.2-1.5 MPa, the top temperature is 130-160°C, preferably 140-150°C, and the bottom temperature is 170-210°C, preferably 185-195°C.

[0059] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification. Preferably, the methanol absorption tower has three streams as absorbents. From top to bottom along the methanol absorption tower, the streams are fresh methanol, recovered methanol from within the unit, and a mixture containing methanol and DMC from the bottom of the DMM removal tower.

[0060] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top temperature of the MN desorption column is 0–25°C, preferably 10–20°C, and the bottom temperature is 100–130°C, preferably 105–120°C.

[0061] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top temperature of the de-DMM removal column is 35–60°C, preferably 40–55°C, and the bottom temperature is 75–95°C, preferably 80–90°C.

[0062] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification. The top gas-phase cooling temperature of the DMC separation column is 90–120°C, preferably 100–115°C. The bottom temperature is 145–170°C, preferably 150–165°C.

[0063] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top vapor phase cooling temperature of the MF distillation column is 35-50°C, preferably 40-45°C; and the bottom temperature is 55-75°C, preferably 60-70°C.

[0064] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top vapor phase cooling temperature of the DMM distillation column is 35-50°C, preferably 40-45°C; and the bottom temperature is 55-75°C, preferably 60-70°C.

[0065] This invention can be used for the separation and purification of dimethyl carbonate product streams, and is mainly used for the separation and purification of dimethyl carbonate produced by CO esterification.

[0066] Compared with existing technologies, the product separation and purification apparatus and method for CO esterification to dimethyl carbonate described in this invention have the following advantages:

[0067] (1) This invention proposes a complete product separation and purification method and system suitable for industrial application for the reaction system of CO esterification to produce dimethyl carbonate, which has the characteristics of reasonable process and low energy consumption.

[0068] (2) This invention sets up a pre-separation tower and a DMC separation tower, which can pre-separate 70-90% of the DMC production, reducing the amount of DMC to be processed in subsequent processes. In particular, the DMC-methanol separation system (which contains azeotropes) has extremely high energy consumption, thus significantly saving energy. The bottom product of the pre-separation tower is processed by the wastewater DMC recovery tower to remove heavy components, yielding Grade I DMC. In addition, the bottom product of the DMC separation tower is also Grade I DMC. The two products combined yield Grade I DMC, which accounts for approximately 80-95% of the total.

[0069] (3) In this invention, a portion of the DMC-methanol mixture at the bottom of the DMM stripping tower can be returned to the upper part of the methanol absorption tower as an absorbent, thereby reducing the amount of fresh methanol used and thus reducing the amount of methanol to be separated in subsequent processes, saving energy. In addition, using the recycled DMC-methanol mixture as an absorbent increases the DMC concentration in the DMC methanol solution at the bottom of the DMM stripping tower (DMC concentration), reducing the separation difficulty and energy consumption of the subsequent atmospheric pressure DMC distillation tower.

[0070] (4) When the methanol absorption tower of the present invention uses three absorbents, the methanol absorption tower from top to bottom is ① methanol, ② methanol recovered by the device, and ③ DMC methanol mixture at the bottom of the DMM removal tower. This reduces the amount of fresh methanol used, saves the raw materials of the device, reduces the amount of methanol processed in the subsequent process, and thus saves energy.

[0071] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but this does not limit the scope of the invention. Attached Figure Description

[0072] Figure 1 This is a schematic diagram of a product separation and purification apparatus for the CO esterification of methyl formate according to the present invention.

[0073] The reference numerals in the figure are:

[0074] 1-DMC product feed pipeline, 2-Pre-separation tower, 3-DMC separation tower, 4-Methanol absorption tower, 5-MN desorption tower, 6-DMM removal tower, 7-MF distillation tower, 8-Ambient pressure DMC distillation tower, 9-Methanol light component removal tower, 10-Pressurized DMC distillation tower, 11-Wastewater DMC recovery tower, 12-Refined DMC heavy component removal tower, 13-DMC refining tower, 14-DMM distillation tower, 15-Wastewater extraction pipeline, 16-DMC product extraction pipeline, 17-Circulating gas extraction pipeline, 18-MF product extraction pipeline, 19-DMM product extraction pipeline, 20-Recovered methanol outlet pipeline, 21-Methanol product outlet pipeline, 22-Grade 1 DMC pipeline, 23-DMO logistics outlet pipeline, 24-Electronic grade DMC logistics outlet pipeline.

[0075] like Figure 1 As shown, this invention discloses a product separation and purification apparatus for CO esterification to dimethyl carbonate, comprising a pre-separation tower 2, a DMC separation tower 3, a methanol absorption tower 4, an MN desorption tower 5, a DMM removal tower 6, an MF distillation tower 7, a DMM distillation tower 14, an atmospheric pressure DMC distillation tower 8, a methanol light component removal tower 9, a pressurized DMC distillation tower 10, a wastewater DMC recovery tower 11, a refined DMC heavy component removal tower 12, and a DMC purification tower 13. The DMC product feed pipeline 1 is connected to the inlet of the pre-separation tower 2. The bottom outlet of the separation tower is connected to the inlet of the wastewater DMC recovery tower 11. The bottom of the wastewater DMC recovery tower 11 is connected to the wastewater extraction pipeline 15. The top of the wastewater DMC recovery tower 11 is connected to the DMC product extraction pipeline 16. The side outlet of the pre-separation tower 2 is connected to the inlet of the DMC separation tower 3. The bottom of the DMC separation tower 3 is connected to the DMC product extraction pipeline 16. The top of the DMC separation tower 3 is connected to the inlet of the MN desorption tower 5. The top of the pre-separation tower 2 is connected to the bottom feed inlet of the methanol absorption tower 4.

[0076] The upper part of the methanol absorption tower 4 is provided with one or more absorbent inlets. Figure 1(Three are shown in the figure); the top outlet of the methanol absorption tower is connected to the circulating gas extraction pipeline 17, the bottom outlet of the methanol absorption tower is connected to the inlet of the MN desorption tower 5, the top outlet of the MN desorption tower is connected to the circulating gas extraction pipeline 17, the bottom outlet of the MN desorption tower is connected to the inlet of the DMM stripping tower 6, the top outlet of the DMM stripping tower is connected to the feed inlet of the MF distillation tower 7, and the bottom of the DMM stripping tower is connected to the feed inlet of the atmospheric DMC distillation tower 8, or connected to the feed inlet of the atmospheric DMC distillation tower 8 and the upper absorbent inlet of the methanol absorption tower 4 respectively (the figure shows the latter case, that is, the bottom of the DMM stripping tower is connected to the feed inlet of the atmospheric DMC distillation tower 8 and the upper absorbent inlet of the methanol absorption tower 4 respectively); the top of the MF distillation tower is connected to the MF product extraction pipeline 18, the bottom of the MF distillation tower is connected to the feed inlet of the DMM distillation tower 14, the top of the DMM distillation tower is connected to the DMM product extraction pipeline 19, and the bottom of the DMM distillation tower is connected to the recovered methanol outlet pipeline 20.

[0077] The top outlet of the atmospheric DMC distillation column 8 is connected to the feed line of the methanol light product removal column 9, and the bottom of the atmospheric DMC distillation column is connected to the methanol product outlet line 21. The top of the methanol light product removal column is connected to the light product extraction line 22, and the bottom outlet of the methanol light product removal column is connected to the feed inlet of the pressurized DMC distillation column 10. The top outlet of the pressurized DMC distillation column is connected to the inlet of the atmospheric DMC distillation column 8, and the bottom of the pressurized DMC distillation column is connected to the DMC product extraction line 16. The DMC product extraction line 16 is connected to the first-grade DMC extraction line 22, or to the first-grade DMC extraction line 22 and the feed inlet of the refined DMC heavy product removal column 12, respectively.

[0078] Preferably, the DMC product extraction line 16 of this invention is connected to the primary DMC extraction line 22 and the inlet of the refined DMC de-weighting tower 12 respectively (e.g., Figure 1 As shown), at this time, the top of the DMC deweighting tower 12 is connected to the feed inlet of the DMC refining tower 13, the bottom of the DMC deweighting tower 12 is connected to the DMO logistics outlet pipeline 23, the top of the DMC refining tower 13 is connected to the feed inlet of the atmospheric pressure DMC distillation tower 8, and the bottom of the DMC refining tower is connected to the electronic grade DMC logistics outlet pipeline 24.

[0079] In this invention, the methanol absorption tower preferably has three absorbent inlets arranged sequentially from top to bottom at the top. The figure shows the preferred configuration, with the fresh methanol inlet, the recovered methanol inlet, and the methanol stream inlet from the bottom of the DMM removal tower arranged sequentially from top to bottom along the top of the methanol absorption tower 4.

[0080] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention preferably has 90 to 150 theoretical plates in the pre-separation tower 2, and the side stream sampling position is located 10 to 30 theoretical plates away from the top of the tower, preferably 15 to 25 theoretical plates.

[0081] The CO esterification to dimethyl carbonate product separation and purification device of the present invention has a methanol absorption tower 4 equipped with 10 to 40 theoretical plates, preferably 20 to 30 theoretical plates.

[0082] The CO esterification to dimethyl carbonate product separation and purification device of the present invention has a DMM removal tower 6 with 35 to 65 theoretical plates, preferably 45 to 55 theoretical plates.

[0083] The CO esterification to dimethyl carbonate product separation and purification device of the present invention has MN desorption tower 5 equipped with 30 to 75 theoretical plates, preferably 50 to 60 theoretical plates.

[0084] The CO esterification to dimethyl carbonate product separation and purification device of the present invention has 30 to 50 theoretical plates in the DMC separation tower 3, preferably 35 to 45 theoretical plates.

[0085] The product separation and purification apparatus for CO esterification to dimethyl carbonate described in this invention has an MF distillation column 7 equipped with 40 to 70 theoretical plates, preferably 50 to 65 theoretical plates.

[0086] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention has a DMM distillation column 14 with 40 to 70 theoretical plates, preferably 50 to 65 theoretical plates.

[0087] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention has an atmospheric pressure DMC distillation column 8 equipped with 60 to 90 theoretical plates, preferably 65 to 80 theoretical plates.

[0088] The CO esterification to dimethyl carbonate product separation and purification device of the present invention has a methanol light removal tower 9 with 20 to 40 theoretical plates, preferably 25 to 35 theoretical plates.

[0089] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention has a pressurized DMC distillation column 10 with 60 to 100 theoretical plates, preferably 75 to 85 theoretical plates.

[0090] The CO esterification to dimethyl carbonate product separation and purification device of the present invention has a DMC deweighting tower 12 with 60 to 100 theoretical plates, preferably 75 to 85 theoretical plates.

[0091] The CO esterification to dimethyl carbonate product separation and purification apparatus of the present invention has a DMC purification tower 13 with 30 to 50 theoretical plates, preferably 35 to 45 theoretical plates.

[0092] Unless otherwise specified, the distillation column in the apparatus of this invention refers to the distillation column system, including the distillation column body and auxiliary equipment such as the bottom reboiler, the bottom product transfer pump, the top condenser, the top reflux tank, and the top reflux and product transfer pump.

[0093] CO esterification to synthesize dimethyl carbonate.

[0094] Under conditions of 110–150 °C and 0.1–0.6 MPa, the following reaction occurs in the presence of a catalyst:

[0095] CO+2CH3ONO(MN)→C3H6O3(DMC)+2NO

[0096] 2CO+2CH3ONO(MN)→C4H6O4(DMO)+2NO

[0097] 2CO+H2+2CH3ONO(MN)→2HCOOCH3(MF)+2NO

[0098] 2MN + MeOH → DMM + H2O + 2NO

[0099] 4MN→MF+2CH3OH+4NO

[0100] This invention does not limit the catalyst used in the synthesis of dimethyl carbonate by CO esterification, but preferably uses the catalyst and evaluation method disclosed in Chinese Patent CN103901130B.

[0101] Based on the preferred catalyst and evaluation method, the composition of the reactor outlet gas phase is as follows:

[0102] DMC: 12-20%, MF: 1-3%, DMM: 1-4%, DMO: 0.01-0.1%, MeOH: 1-3%, MN+NO: 20-32%, CO: 1-3%, N2 and other components: 40-60%.

[0103] like Figure 1 As shown, the operation method of the product separation and purification device for CO esterification to dimethyl carbonate described in this invention is as follows:

[0104] 1) The product stream of CO esterification to produce dimethyl carbonate is cooled and condensed and then enters the pre-separation tower 2 for pre-separation. The separated gas phase is sent to the bottom of the methanol absorption tower 4. The separated bottom heavy phase is sent to the wastewater DMC recovery tower 11. After the wastewater is removed, first-grade DMC product is obtained. The separated liquid phase is sent to the feed port of the DMC separation tower 3 by side stream. The top pressure of the pre-separation tower 2 is 0.3 MPa, the top temperature is 30-60℃, and the bottom temperature is 120-170℃.

[0105] 2) In methanol absorption tower 4, the bottom stream of methanol absorption tower is countercurrently contacted with the absorbent entering from the top of methanol absorption tower for absorption process. DMC, MF, DMM, DMO and other components in the product stream of CO esterification to dimethyl carbonate are absorbed into methanol. The gas coming out of the top of methanol absorption tower is mixed and used as circulating gas. The rich absorbent at the bottom of methanol absorption tower is sent to the middle of MN desorption tower 5 for desorption. The light components are then used as circulating gas. The bottom of MN desorption tower 5 contains heavy components, mainly including DMC, methanol, MF and DMM. It is then sent to DMM removal tower 6 for separation. The top stream of DMM removal tower is distilled to obtain MF product, DMM product and recovered methanol. The recovered methanol can be used as the absorbent in methanol absorption tower 4. Part of the bottom stream of DMM removal tower is returned to methanol absorption tower 4 as supplementary absorbent, and the other part is sent to the feed port of atmospheric pressure DMC distillation tower 8.

[0106] 3) In DMC separation tower 3, the stream entering through the feed inlet of DMC separation tower 3 is separated into light components and first-grade DMC product. The light components enter the upper part of MN desorption tower 5.

[0107] 4) The DMC-methanol mixture from the bottom product stream of the DMM stripping column and the top product stream of the pressurized DMC distillation column enters different positions of the atmospheric DMC distillation column 8. The bottom product of the atmospheric DMC distillation column is methanol, which can be recovered and reused in the unit. The vapor product at the top of the column is sent to the methanol light phase stripping column 9. The top of the methanol light phase stripping column contains a small amount of light components, which are sent to the storage tank as waste liquid. The bottom product is a DMC-methanol mixture, which is sent to the feed inlet of the pressurized DMC distillation column 10. The top product is a DMC-methanol azeotrope under pressurized conditions, which is returned to the atmospheric DMC distillation column 8. The bottom product is grade I DMC product.

[0108] 5) The first-grade DMC product obtained from the wastewater DMC recovery tower 11, the first-grade DMC product obtained from the DMC separation tower 3, and the first-grade DMC product obtained from the pressurized DMC distillation tower 10 are partially exported as products, and the other part is sent to the DMC de-weighting tower 12, where DMO product is obtained at the bottom of the tower, and the top stream is sent to the DMC distillation tower 13, where electronic-grade DMC product is obtained at the bottom of the tower, and the top stream is returned to the atmospheric pressure DMC distillation tower 8.

[0109] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top pressure of the atmospheric pressure DMC distillation column 8 is 0.16-0.2 MPa, the top temperature is 65-85℃, preferably 70-80℃, and the bottom temperature is 70-95℃, preferably 75-90℃.

[0110] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification. The methanol light residue removal tower 9 has a top pressure of 0.16–0.2 MPa and a top temperature of 40–70°C, preferably 50–60°C. The bottom temperature is 70–95°C, preferably 75–90°C.

[0111] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the pressure at the top of the pressurized DMC distillation column 10 is 1.2-1.5 MPa, the temperature at the top of the column is 130-160°C, preferably 140-150°C, and the temperature at the bottom of the column is 170-210°C, preferably 185-195°C.

[0112] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top pressure of the DMC removal column 12 is 0.16-0.2 MPa, the top temperature is 95-115℃, preferably 100-110℃, and the bottom temperature is 105-135℃, preferably 115-125℃.

[0113] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification. The top pressure of the DMC purification column 13 is 1.2-1.5 MPa, the top temperature is 130-160℃, preferably 140-150℃, and the bottom temperature is 170-210℃, preferably 185-195℃.

[0114] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification. Preferably, the methanol absorption tower 4 has three streams as absorbents. From top to bottom along the methanol absorption tower, the absorbents are fresh methanol, recovered methanol from within the unit, and a mixture containing methanol and DMC from the bottom of the DMM removal tower.

[0115] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top temperature of the MN desorption tower 5 is 0-25°C, preferably 10-20°C, and the bottom temperature is 100-130°C, preferably 105-120°C.

[0116] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top temperature of the DMM removal column 6 is 35–60°C, preferably 40–55°C, and the bottom temperature is 75–95°C, preferably 80–90°C.

[0117] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification. The top temperature of the DMC separation column 3 is 90–120°C, preferably 100–115°C. The bottom temperature is 145–170°C, preferably 150–165°C.

[0118] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top temperature of the MF distillation column 7 is 35-50°C, preferably 40-45°C; and the bottom temperature is 55-75°C, preferably 60-70°C.

[0119] The present invention discloses a method for separating and purifying dimethyl carbonate produced by CO esterification, wherein the top temperature of the DMM distillation column 14 is 35-50°C, preferably 40-45°C, and the bottom temperature is 55-75°C, preferably 60-70°C.

[0120] The product stream of CO esterification to dimethyl carbonate described in this invention is cooled and condensed to 55-80°C before entering the pre-separation tower 2 for pre-separation. The cooling and condensation is preferably carried out by a heat exchanger, which exchanges heat with a suitable stream (e.g., the stream entering the reactor).

[0121] The main function of pre-separation column 2 is to separate heavy components (DMC, H2O, DMO, etc.) from the bulk gaseous reactants, and to collect a high-concentration mixture of DMC and methanol via a side stream. The pre-separation column is a distillation column with a side stream, typically equipped with a bottom reboiler, a liquid side stream collector, a top condenser, and a reflux tank.

[0122] The function of methanol absorption tower 4 is to absorb reaction products such as DMC, MF, DMM, and DMO in the circulating gas into methanol using methanol absorbent.

[0123] The vapor phase from the top reflux tank of pre-separation tower 2 enters the lower feed inlet of methanol absorption tower 4, with three streams serving as absorbents: fresh methanol, recovered methanol from within the unit, and a methanol-DMC mixture from the bottom of DMM removal tower 6. The vapor phase from the top of methanol absorption tower 4 is used as recirculated gas and pressurized by the compressor, while the bottom absorbent-rich liquid is sent to the middle feed inlet of MN desorption tower 5. Methanol absorption tower 4 preferably has 1-3 intercoolers to ensure absorption efficiency. The temperature range for each absorbent and the intercooler in the absorption tower is 0-40℃, with a preferred range of 5-20℃.

[0124] The main function of MN desorption tower 5 is to separate the rich absorbent from the bottom of methanol absorption tower 4 into light components, which are then returned to the circulating gas system. The bottom of the tower contains heavy components, including DMC, methanol, MF, and DMM. MN desorption tower 5 is a distillation tower, equipped with a reboiler at the bottom and a cooler and condenser at the top.

[0125] The main function of DMM removal column 6 is to separate the reaction products. The main components at the top of the column are MF and DMM, while the main components at the bottom are DMC and methanol. DMM removal column 6 is a distillation column, equipped with a reboiler at the bottom and a condenser and reflux tank at the top.

[0126] The main function of DMC separation column 3 is to separate the liquid phase outflow from pre-separation column 2 into light components and grade I DMC product. DMC separation column 3 is a distillation column, equipped with a reboiler at the bottom and a condenser and reflux tank at the top. The liquid phase outflow from pre-separation column 2 enters DMC separation column 3. The top product is DMC, methanol, and other light components, while the bottom product is mainly grade I DMC (≥99.5%), which can be exported as a product or sent to the electronic-grade DMC refining section for final export as electronic-grade DMC.

[0127] The main function of MF distillation column 7 is to separate the feed into MF product at the top and a mixture of DMM and methanol at the bottom. MF distillation column 7 is a distillation column, equipped with a reboiler at the bottom and a condenser and reflux tank at the top.

[0128] The top product from the DMM removal column 6 enters the MF distillation column 7. The top product is MF premium grade (≥96%), which can be used directly as a product or sent to the hydrolysis unit. The bottom product is a mixture of DMM and methanol, which is sent to the feed inlet of the DMM distillation column 14.

[0129] The main function of DMM distillation column 14 is to separate the feed into DMM product at the top and methanol at the bottom. DMM distillation column 14 is a distillation column, with a reboiler at the bottom and a condenser and reflux tank at the top.

[0130] The top product of the DMM distillation column 14 is DMM (divided into three product specifications according to concentrations of 85%, 90%, and 99%), which is directly exported as a product; the bottom product is methanol stream, which can be recycled.

[0131] The main function of the DMC-methanol separation section is to separate DMC and methanol. It can employ techniques such as pressure swing distillation, extractive distillation, and azeotropic distillation. This invention preferably uses pressure swing distillation. The DMC-methanol separation section includes an atmospheric pressure DMC distillation column 8, a methanol light-light-removal column 9, and a pressurized DMC distillation column 10.

[0132] Atmospheric DMC distillation column 8, methanol light removal column 9, and pressurized DMC distillation column 10 are all distillation columns, each equipped with a reboiler, a top condenser, and a reflux tank.

[0133] The main function of the electronic-grade DMC refining section is to refine primary DMC (≥99.5%) to electronic-grade DMC (≥99.99%). Common technical routes include crystallization and distillation, and this invention preferably uses distillation.

[0134] The electronic-grade DMC refining section includes a DMC de-weighting tower 12 and a DMC refining tower 13, both of which are distillation towers. Each tower is equipped with a reboiler, a top condenser, and a reflux tank.

Claims

1. A product separation and purification apparatus for carbon dioxide esterification for dimethyl carbonate production, characterized by: The product separation and purification device for preparing dimethyl carbonate by CO esterification comprises a pre-separation tower, a DMC separation tower, a methanol absorption tower, an MN desorption tower, a DMM removal tower, an MF rectification tower, a DMM rectification tower, an atmospheric DMC rectification tower, a methanol light component removal tower, a pressurized DMC rectification tower and a wastewater DMC recovery tower, and a DMC product feeding pipeline is connected with the inlet of the pre-separation tower; The bottom outlet of the pre-separation tower is connected with the inlet of the wastewater DMC recovery tower, the bottom of the wastewater DMC recovery tower is connected with a wastewater extraction pipeline, the top of the wastewater DMC recovery tower is connected with a DMC product extraction pipeline, the pre-separation tower is provided with a side outlet, the side outlet of the pre-separation tower is connected with the inlet of the DMC separation tower, the bottom of the DMC separation tower is connected with a DMC product extraction pipeline, the top of the DMC separation tower is connected with the inlet of the MN desorption tower, and the top of the pre-separation tower is connected with the bottom feeding port of the methanol absorption tower; The upper part of the methanol absorption tower is provided with one or more absorption agent inlets, the top outlet of the methanol absorption tower is connected with a circulating gas extraction pipeline, the bottom outlet of the methanol absorption tower is connected with the inlet of the MN desorption tower, the top outlet of the MN desorption tower is connected with a circulating gas extraction pipeline, the bottom outlet of the MN desorption tower is connected with the inlet of the DMM removal tower, the top outlet of the DMM removal tower is connected with the feeding port of the MF rectification tower, the bottom of the DMM removal tower is connected with the feeding port of the atmospheric DMC rectification tower or the feeding port of the atmospheric DMC rectification tower and the upper absorption agent inlet of the methanol absorption tower respectively, the top of the MF rectification tower is connected with an MF product extraction pipeline, the bottom of the MF rectification tower is connected with the feeding port of the DMM rectification tower, the top of the DMM rectification tower is connected with a DMM product extraction pipeline, and the bottom of the DMM rectification tower is connected with a recovered methanol outlet pipeline; The top outlet of the atmospheric DMC rectification tower is connected with the feeding port of the methanol light component removal tower, the bottom outlet of the atmospheric DMC rectification tower is connected with a methanol product outlet pipeline, the top outlet of the methanol light component removal tower is connected with a light product extraction pipeline, the bottom outlet of the methanol light component removal tower is connected with the feeding port of the pressurized DMC rectification tower, the top outlet of the pressurized DMC rectification tower is connected with the inlet of the atmospheric DMC rectification tower, the bottom outlet of the pressurized DMC rectification tower is connected with a DMC product extraction pipeline, the DMC product extraction pipeline is connected with a primary product DMC extraction pipeline or the primary product DMC extraction pipeline and the feeding port of a refined DMC heavy component removal tower respectively, the top outlet of the refined DMC heavy component removal tower is connected with the feeding port of a DMC purification tower, the bottom outlet of the refined DMC heavy component removal tower is connected with a DMO stream outlet pipeline, the top outlet of the DMC purification tower is connected with the feeding port of the atmospheric DMC rectification tower, and the bottom outlet of the DMC purification tower is connected with an electronic grade DMC stream outlet pipeline.

2. The product separation and purification apparatus for the production of dimethyl carbonate by CO esterification according to claim 1, characterized by: The DMC product extraction pipeline is connected with the primary product DMC extraction pipeline and the feeding port of the refined DMC heavy component removal tower respectively.

3. The product separation and purification apparatus for the production of dimethyl carbonate by CO esterification according to claim 1, characterized in that: The bottom outlet of the DMM removal tower is connected with the feeding port of the atmospheric DMC rectification tower and the upper absorption agent inlet of the methanol absorption tower respectively.

4. The product separation and purification apparatus for the production of dimethyl carbonate by CO esterification according to claim 1, characterized in that: Three absorption agent inlets are sequentially arranged from top to bottom in the upper part of the methanol absorption tower.

5. The product separation and purification apparatus for the production of dimethyl carbonate by CO esterification according to claim 1, characterized in that: The pre-separation tower is provided with 90-150 theoretical plates, the side line extraction position is located at 10-30 theoretical plates from the top of the pre-separation tower, the methanol absorption tower is provided with 10-40 theoretical plates, the DMM removal tower is provided with 35-65 theoretical plates, the MN desorption tower is provided with 30-75 theoretical plates, the DMC separation tower is provided with 30-50 theoretical plates, the MF rectification tower is provided with 40-70 theoretical plates, the DMM rectification tower is provided with 40-70 theoretical plates, the atmospheric DMC rectification tower is provided with 60-90 theoretical plates, the methanol light component removal tower is provided with 20-40 theoretical plates, the pressurized DMC rectification tower is provided with 60-100 theoretical plates, the refined DMC heavy component removal tower is provided with 60-100 theoretical plates, and the DMC refining tower is provided with 30-50 theoretical plates.

6. The product separation and purification apparatus for the production of dimethyl carbonate by CO esterification according to claim 1 or 5, characterized by: The pre-separation tower is provided with 90-150 theoretical plates, the side line extraction position is located at 10-30 theoretical plates from the top of the pre-separation tower, the methanol absorption tower is provided with 10-40 theoretical plates, the DMM removal tower is provided with 35-65 theoretical plates, the MN desorption tower is provided with 30-75 theoretical plates, the DMC separation tower is provided with 30-50 theoretical plates, the MF rectification tower is provided with 40-70 theoretical plates, the DMM rectification tower is provided with 40-70 theoretical plates, the atmospheric DMC rectification tower is provided with 60-90 theoretical plates, the methanol light component removal tower is provided with 20-40 theoretical plates, the pressurized DMC rectification tower is provided with 60-100 theoretical plates, the refined DMC heavy component removal tower is provided with 60-100 theoretical plates, and the DMC refining tower is provided with 30-50 theoretical plates.

7. The process for separating and purifying the product of the production of dimethyl carbonate by the CO esterification of claim 1, characterized by The method comprises the following steps: 1) The product stream of dimethyl carbonate prepared by CO esterification is cooled and condensed, and then enters a pre-separation tower for pre-separation; the gas phase after separation is sent to the bottom of a methanol absorption tower; the heavy components after separation are sent to a waste water DMC recovery tower, and after removal of waste water, a primary product DMC is obtained; the liquid phase after separation is extracted from a side line and sent to the feed inlet of a DMC separation tower; the pre-separation tower has a top pressure of 0.3 MPag, a top temperature of 30-60 DEG C, and a bottom temperature of 120-170 DEG C; 2) In the methanol absorption tower, the stream entering the bottom of the methanol absorption tower is countercurrently contacted with the absorbent entering the upper part of the methanol absorption tower to perform an absorption process; the gas mixture from the top of the methanol absorption tower is used as a circulating gas; the rich absorbent from the bottom of the methanol absorption tower is sent to an MN desorption tower for desorption, and then the light components are used as a circulating gas; the heavy components from the bottom of the MN desorption tower are sent to a DMM removal tower for separation; the top stream of the DMM removal tower is rectified to obtain MF products, DMM products and recovered methanol; the bottom stream of the DMM removal tower is sent to the feed inlet of an atmospheric DMC rectification tower, or part of the bottom stream is returned to the methanol absorption tower as a supplementary absorbent, and the other part is sent to the feed inlet of the atmospheric DMC rectification tower; 3) In the DMC separation tower, the stream entering the feed inlet of the DMC separation tower is separated into light components and primary product DMC; the light components enter the MN desorption tower; 4) in the normal pressure DMC rectifying tower, the normal pressure DMC rectifying tower bottom is methanol product, which comes out through the methanol product outlet pipeline, the normal pressure DMC rectifying tower top gas phase product is sent to the methanol light component removal tower, the methanol light component removal tower top is light component, the tower bottom is DMC-methanol mixture, the DMC-methanol mixture is sent to the pressurized DMC rectifying tower feed inlet, the pressurized DMC rectifying tower top product stream returns to the normal pressure DMC rectifying tower, and the tower bottom stream is the first grade DMC product; 5) the first grade DMC product obtained from the waste water DMC recovery tower, the first grade DMC product obtained from the DMC separation tower and the first grade DMC product obtained from the pressurized DMC rectifying tower are exported as products, or part of them is exported as products, and the other part is sent to the refined DMC heavy component removal tower, the DMO product is obtained from the refined DMC heavy component removal tower bottom, the refined DMC heavy component removal tower top stream is sent to the DMC rectifying tower, the electronic grade DMC product is obtained from the DMC rectifying tower bottom, and the DMC rectifying tower top stream returns to the normal pressure DMC rectifying tower.

8. The method of claim 7, wherein: The normal pressure DMC rectifying tower top pressure is 0.16-0.2 MPa, the normal pressure DMC rectifying tower top temperature is 65-85℃, the normal pressure DMC rectifying tower bottom temperature is 70-95℃; the methanol light component removal tower top pressure is 0.16-0.2 MPa, the methanol light component removal tower top temperature is 40-70℃, the methanol light component removal tower bottom temperature is 70-95℃; the pressurized DMC rectifying tower top pressure is 1.2-1.5 MPa, the pressurized DMC rectifying tower top temperature is 130-160℃, the pressurized DMC rectifying tower bottom temperature is 170-210℃; the refined DMC heavy component removal tower top pressure is 0.16-0.2 MPa, the refined DMC heavy component removal tower top temperature is 95-115℃, the refined DMC heavy component removal tower bottom temperature is 105-135℃; the DMC refining tower top pressure is 1.2-1.5 MPa, the DMC refining tower top temperature is 130-160℃, the DMC refining tower bottom temperature is 170-210℃; the MN desorption tower top temperature is 0-25℃, the MN desorption tower bottom temperature is 100-130℃; the DMM removal tower top temperature is 35-60℃, the DMM removal tower bottom temperature is 75-95℃; the DMC separation tower top temperature is 90-120℃, the DMC separation tower bottom temperature is 145-170℃; the MF rectifying tower top temperature is 35-50℃, the MF rectifying tower bottom temperature is 55-75℃; the DMM rectifying tower top temperature is 35-50℃, the DMM rectifying tower bottom temperature is 55-75℃.

9. The method according to claim 7 or 8, characterized in that: The normal pressure DMC rectifying tower top temperature is 70-80℃, the normal pressure DMC rectifying tower bottom temperature is 75-90℃; the methanol light component removal tower top temperature is 50-60℃, the methanol light component removal tower bottom temperature is 75-90℃, the pressurized DMC rectifying tower top temperature is 140-150℃, the pressurized DMC rectifying tower bottom temperature is 185-195℃; the refined DMC heavy component removal tower top temperature is 100-110℃, the refined DMC heavy component removal tower bottom temperature is 115-125℃; the DMC refining tower top temperature is 140-150℃, the DMC refining tower bottom temperature is 185-195℃; the MN desorption tower top temperature is 10-20℃, the MN desorption tower bottom temperature is 105-120℃; the DMM removal tower top temperature is 40-55℃, the DMM removal tower bottom temperature is 80-90℃; the DMC separation tower top temperature is 100-115℃, the DMC separation tower bottom temperature is 150-165℃; the MF rectifying tower top temperature is 40-45℃, the MF rectifying tower bottom temperature is 60-70℃; the DMM rectifying tower top temperature is 40-45℃, the DMM rectifying tower bottom temperature is 60-70℃.

10. The method of claim 7, wherein: The methanol absorption tower has three streams as absorbents, which are fresh methanol, recovered methanol from the product separation and refining device for preparing dimethyl carbonate by esterification of CO, and mixed liquid containing methanol and DMC from the bottom of the DMM removal tower.

11. The method of claim 7, wherein: The bottom stream of the DMM removal tower is partly returned to the methanol absorption tower as supplementary absorbent, and the other part is sent to the feed inlet of the atmospheric DMC rectification tower.

12. The method of claim 7, wherein: The first-grade DMC product obtained from the wastewater DMC recovery tower, the first-grade DMC product obtained from the DMC separation tower, and the first-grade DMC product obtained from the pressurized DMC rectification tower are partly exported as products, and the other part is sent to the heavy component removal tower for refined DMC.

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