Method and system for preparing dimethyl carbonate by decarbonylation of dimethyl oxalate

Abstract

The invention provides a method and system for preparing dimethyl carbonate through dimethyl oxalate decarbonylation, and the method comprises the following steps: dimethyl oxalate is subjected to decarbonylation reaction in a reactor, and a gas phase product and a first liquid phase product are respectively obtained from the decarbonylation reactor: the first liquid phase product enters a dimethyl carbonate product tower; cooling the gas-phase product, carrying out gas-liquid separation to obtain a gas-phase material and a second liquid-phase product, and feeding the gas-phase material and the second liquid-phase product into the carbonate product tower; absorbing by-products containing carbon dioxide and dimethyl ether by the gas-phase material through dimethyl carbonate, and desorbing and removing by-products containing carbon dioxide and dimethyl ether by the discharged liquid-phase absorption material in a desorption tower. According to the method, a separate discharging mode is adopted, condensate of a liquid-phase product and condensate of a gas-phase product are treated at the same time through the dimethyl carbonate product tower, the process is simple, and energy consumption is low; dimethyl carbonate is adopted as an absorbent, carbon dioxide and dimethyl ether in carbon monoxide product gas can be effectively separated, the process is simple, and energy consumption is low.

Description

Technical Field

[0001] The invention relates to a method for producing dimethyl carbonate, and in particular to a method and system for producing dimethyl carbonate by decarbonylation reaction of dimethyl oxalate. Background Art

[0002] Dimethyl carbonate (DMC), because DMC molecules contain active functional groups such as methyl, methoxy and carbonyl, so the chemical properties are active, and it can react with a variety of alcohols, amines, phenols, esters and amino alcohols in a series of chemical reactions. The types of reactions it participates in include carbonyl methoxylation, carbonylation, methylation, etc. At the same time, DMC is also used as an upstream raw material for synthesis to make derivatives. In addition, DMC is also used as a solvent, gasoline additive, electrolyte and other non-chemical reaction uses that have attracted much attention.

[0003] Dimethyl oxalate is an important organic chemical raw material that can be used to produce various dyes, solvents, extractants and various intermediates, and is widely used in fine chemicals. In addition, dimethyl oxalate can be used to prepare ethylene glycol through hydrogenation, which is a new large-scale industrial ethylene glycol synthesis process route.

[0004] In recent years, my country's coal-to-ethylene glycol technology has developed rapidly, with production capacity increasing from 200,000 tons / year in 2010 to 10.83 million tons / year in 2022, accounting for 43.2% of my country's total ethylene glycol production capacity, but the output is only about 4.06 million tons, with a capacity utilization rate of 37.5%. It is expected that the production capacity will increase by 1.8 million tons / year in 2023, and the total capacity will reach 12.63 million tons / year. However, at this stage, the overall price of ethylene glycol is low, and the coal-to-ethylene glycol industry is generally at a loss, so the development of decarbonylation of dimethyl oxalate to produce dimethyl carbonate can not only increase the product chain of the device, but also effectively improve the efficiency of the device.

[0005] Prior art CN201911003422.3 discloses a method for treating a mixed stream containing dimethyl oxalate, a treatment system and an application thereof, which mainly solves the problem of large amount of dimethyl oxalate containing heavy components and difficulty in treatment in the prior art, and adopts a fixed bed reactor for decarbonylation reaction. Methanol is used to purify crude CO, but the introduction of methanol will produce azeotropes of methanol and dimethyl carbonate, thereby increasing separation energy consumption. Summary of the invention

[0006] In order to solve the problems of low purity of CO product and low yield of dimethyl carbonate product in the prior art, the object of the present invention is to provide a new method for preparing dimethyl carbonate by decarbonylating dimethyl oxalate.

[0007] To achieve the aforementioned object, according to a first aspect of the present invention, the present invention provides a method for preparing dimethyl carbonate (OC(OCH3)2) by decarbonylating dimethyl oxalate (CH3OCOCOOCH3), the method comprising:

[0008] 1) subjecting the dimethyl oxalate to a decarbonylation reaction in a decarbonylation reactor to produce dimethyl carbonate, and obtaining a gas phase product and a first liquid phase product from the decarbonylation reactor respectively: the first liquid phase product enters a dimethyl carbonate product tower;

[0009] II) the gas phase product is cooled and then subjected to gas-liquid separation to obtain a gas phase material and a second liquid phase product, and the second liquid phase product enters the carbonate product tower;

[0010] III) the gaseous material is sent to a tail gas purification unit, the tail gas purification unit includes an absorption tower and a desorption tower, wherein the gaseous material absorbs by-products including carbon dioxide and dimethyl ether through the absorbent dimethyl carbonate in the absorption tower, and the liquid absorption material and carbon monoxide flow are discharged from the absorption tower; the liquid absorption material enters the desorption tower for desorption and removal of by-products including carbon dioxide and dimethyl ether to recover the liquid material containing dimethyl carbonate;

[0011] IV) separating and obtaining a dimethyl carbonate product in the dimethyl carbonate product tower.

[0012] According to a second aspect of the present invention, the present invention provides a system for preparing dimethyl carbonate by decarbonylating dimethyl oxalate, the system comprising:

[0013] The decarbonylation reactor comprises a raw material inlet, a gas phase outlet and a liquid phase outlet, which are preferably respectively arranged at the middle and upper side line position, the top and the bottom position of the decarbonylation reactor;

[0014] A dimethyl carbonate product tower, which is connected to the liquid phase outlet of the decarbonylation reactor, comprises a side line liquid phase inlet, a top outlet, a side line production outlet and a tower bottom outlet;

[0015] A gas-liquid separator, wherein the gas-liquid separator inlet is connected to the gas phase outlet of the decarbonylation reactor, and the liquid phase outlet of the gas phase separator is connected to the side line liquid phase inlet of the dimethyl carbonate product tower;

[0016] A cooler is arranged between the inlet of the gas-liquid separator and the gas phase outlet communicating pipeline of the decarbonylation reactor;

[0017] The tail gas purification unit comprises an absorption tower and a desorption tower connected in series, the feed port of the absorption tower is connected to the gas phase outlet of the gas-liquid separator, the absorption tower comprises a gas phase production outlet and a liquid phase production outlet, the liquid phase production outlet of the absorption tower is connected to the inlet of the desorption tower, and the desorption tower comprises a gas phase production outlet and a liquid phase production outlet.

[0018] The prior art removes all DMC products through the gas phase, which easily evaporates a large amount of unreacted DMO into the gas phase, resulting in high energy consumption. The gas phase product and the liquid phase product of the present invention are discharged simultaneously, which can control part of the DMC product in the liquid phase product and avoid evaporating too much DMO product into the gas phase.

[0019] The present invention utilizes a dimethyl carbonate product tower to simultaneously process the condensate of a liquid phase product and a gas phase product, separates and obtains a DMC product, and simultaneously obtains a small amount of unreacted DMO, which is circulated back to the reactor, has a simple process and low energy consumption.

[0020] The present invention uses its own reaction product dimethyl carbonate as absorbent to effectively separate carbon dioxide and dimethyl ether in carbon monoxide product gas, and uses DMC product as absorption to avoid using methanol as absorption to draw out azeotropic components. The DMC product has high quality and low energy consumption.

[0021] The present invention can further recover dimethyl carbonate and unreacted dimethyl oxalate in the gas phase product in the absorption system, and the yield is high.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The gas phase product and the liquid phase product are discharged separately, and the condensate of the liquid phase product and the gas phase product is treated simultaneously in a dimethyl carbonate product tower, which has a simple process and low energy consumption;

[0024] (2) Using its own reaction product dimethyl carbonate as an absorbent can effectively separate carbon dioxide and dimethyl ether from the carbon monoxide product gas, with a simple process and low energy consumption.

[0025] (3) Dimethyl carbonate and unreacted dimethyl oxalate in the gas phase product are further recovered in the absorption system with high yield.

[0026] (4) In the present invention, the obtained carbon monoxide stream has a low impurity content and can be well recycled to the system for generating the raw material dimethyl oxalate as a raw material. The method of the present invention also includes recycling the carbon monoxide stream to the upstream system for synthesizing the raw material dimethyl oxalate, so that the system for generating dimethyl oxalate has less impurity accumulation, the system operates stably, and the energy consumption is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A process flow chart showing the method of the present invention;

[0028] Figure 2 The process flow of the tail gas treatment system of the present invention is shown.

[0029] Description of Reference Numerals

[0030] 1 is a decarbonylation reactor, 2 is a dimethyl carbonate product tower;

[0031] 3 is a condenser, 4 is a gas-liquid separation tank;

[0032] 5 is the reactor feed, 6 is the gas phase product;

[0033] 7 is the gas phase product after condensation, and 8 is the gas phase material;

[0034] 9 is the second liquid phase product, 10 is the first liquid phase product;

[0035] 11 is a dimethyl carbonate product, and 12 is the top of the dimethyl carbonate product tower;

[0036] 13 is the external discharge material, 14 is the circulating material of the dimethyl carbonate product tower kettle;

[0037] 15 is an exhaust gas treatment system, 16 is a carbon monoxide flow;

[0038] 17 is the tail gas emission flow, and 18 is the liquid phase material containing dimethyl carbonate recovered by the tail gas treatment system.

[0039] 19 is an absorption tower and 20 is a desorption tower. DETAILED DESCRIPTION

[0040] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0041] In the present invention, unless otherwise specified, directional words such as "upper, lower, left, right" generally refer to the upper, lower, left, and right shown in the accompanying drawings; "inner and outer" refer to the inner and outer relative to the outline of each component itself.

[0042] In the present invention, unless otherwise specified, directional words such as "up, down, top, bottom" are usually used with reference to the directions shown in the drawings or are used to describe the relative positional relationships of components in the vertical, perpendicular or gravity direction.

[0043] “Vertical direction” refers to the up-and-down direction of the paper as shown in the diagram; “lateral direction” refers to the left-and-right direction of the roughly horizontal paper as shown in the diagram; “inside and outside” usually refer to the inside and outside of the chamber relative to the chamber or the radial inside and outside relative to the center of a circle.

[0044] The present invention provides a method for preparing dimethyl carbonate by decarbonylating dimethyl oxalate, the method comprising:

[0045] 1) subjecting the dimethyl oxalate to a decarbonylation reaction in a decarbonylation reactor to produce dimethyl carbonate, and obtaining a gas phase product and a first liquid phase product from the decarbonylation reactor respectively: the first liquid phase product enters a dimethyl carbonate product tower;

[0046] II) the gas phase product is cooled and then subjected to gas-liquid separation to obtain a gas phase material and a second liquid phase product, and the second liquid phase product enters the dimethyl carbonate product tower;

[0047] III) the gaseous material is sent to a tail gas purification unit, the tail gas purification unit includes an absorption tower and a desorption tower, wherein the gaseous material absorbs by-products including carbon dioxide and dimethyl ether through the absorbent dimethyl carbonate in the absorption tower, and the liquid absorption material and carbon monoxide flow are discharged from the absorption tower; the liquid absorption material enters the desorption tower for desorption and removal of by-products including carbon dioxide and dimethyl ether to recover the liquid material containing dimethyl carbonate;

[0048] IV) separating and obtaining a dimethyl carbonate product in the dimethyl carbonate product tower.

[0049] In the present invention, the first liquid phase product in step I) contains dimethyl carbonate DMC, preferably based on the total amount of dimethyl carbonate DMC produced, the dimethyl carbonate DMC in the first liquid phase product accounts for more than 5wt%, preferably 5-80wt%. The prior art removes all DMC products through the gas phase, which easily evaporates a large amount of unreacted DMO into the gas phase, resulting in high energy consumption. The gas phase product and the liquid phase product of the present invention are discharged simultaneously, and part of the DMC product can be controlled in the liquid phase product to avoid excessive DMO product evaporating into the gas phase.

[0050] In the present invention, the obtained carbon monoxide stream 16 has a low impurity content and can be well recycled to the system for generating the raw material dimethyl oxalate as a raw material. The method of the present invention also includes recycling the carbon monoxide stream to the upstream system for synthesizing the raw material dimethyl oxalate, so that the system for generating dimethyl oxalate has less impurity accumulation, the system operates stably, and the energy consumption is low.

[0051] In the present invention, in step I), the operating conditions of the decarbonylation reactor can be selected in a wide range, and commonly used operating conditions can achieve the purpose of the present invention. The present invention has no special requirements for this. The following exemplary description is given for the present invention, but the scope of the present invention is not limited thereto. Preferably, in step I), the operating conditions of the decarbonylation reactor include: an operating pressure of 0.3-2.0 MPaG, preferably 0.5-1.5 MPaG, and / or an operating temperature of 120-250° C., preferably 150-200° C.; and / or a liquid phase residence time of 0.1-20 hours, preferably 0.3-5h, more preferably 1-2h.

[0052] In the present invention, there is no special requirement for the amount of catalyst used in the decarbonylation reactor. It is illustrated for exemplary purposes but does not limit the scope of the present invention. For example, the concentration in the liquid phase is 0.1-20wt%. The catalyst is a special requirement and can be a commonly used catalyst in the art, such as one or more alkaline compounds, such as potassium carbonate.

[0053] In the present invention, by controlling the operating conditions of the decarbonylation reactor, the dimethyl oxalate can be decarbonylated in the decarbonylation reactor to produce dimethyl carbonate, and a gas phase product and a first liquid phase product are obtained from the decarbonylation reactor, respectively. In the prior art, all DMC products are removed through the gas phase, thereby easily evaporating a large amount of unreacted DMO into the gas phase, which has high energy consumption. The present invention discharges the gas phase product and the liquid phase product at the same time, controls the appropriate reaction temperature and pressure, controls part of the DMC product in the liquid phase product, and avoids evaporating too much DMO product into the gas phase.

[0054] According to a preferred embodiment of the present invention, in step I), based on the total amount of dimethyl carbonate produced, the proportion of dimethyl carbonate in the first liquid phase product is 5-80wt%, preferably 6-70wt%, thereby preventing too much DMO product from evaporating into the gas phase.

[0055] In the present invention, as long as the decarbonylation reactor can achieve the purpose of obtaining a gas phase product and a first liquid phase product respectively from the decarbonylation reactor, there is no special requirement for their respective discharge positions. According to the present invention, preferably in step I), the decarbonylation reactor comprises a raw material inlet, a gas phase outlet and a liquid phase outlet, which are respectively arranged at the middle and upper side line position of the decarbonylation reactor, the upper part of the reactor, and the lower part of the reactor; preferably, they are respectively arranged at the middle and upper side line position, the top and the bottom of the decarbonylation reactor.

[0056] In the present invention, there is no special requirement for the cooling conditions in step II), and generally steam, hot water, or circulating water can be used as the cooling medium. The operating conditions generally include: a cooling temperature of 30 to 150°C, preferably 40 to 120°C.

[0057] In the present invention, in step II), the technology of gas-liquid separation is a well-known technology in the art, and the present invention has no special requirements for this. It is an exemplary description, but it does not limit the scope of the present invention. The operating conditions are generally the same as the cooling conditions in step II).

[0058] In the present invention, there are no special requirements for the operating conditions of the absorption tower. The following exemplary description is not intended to limit the scope of the present invention. According to a preferred embodiment of the present invention, in step III), the operating conditions of the absorption tower include: an operating pressure of 0.1-2.0 MPaG, an absorbent temperature of 10-60°C, preferably 20-40°C; a weight ratio of the absorbent to the tail gas of 1-50, preferably 5-30, more preferably 8-25; preferably, the dimethyl carbonate product is used as the absorbent to absorb dimethyl ether and carbon dioxide byproducts in the absorption tower, and dimethyl ether and carbon dioxide are removed in the desorption tower. Compared with the prior art of using methanol as an absorbent to treat gas phase products, using dimethyl carbonate as an absorbent avoids the formation of an azeotrope of methanol and dimethyl carbonate, and greatly reduces energy consumption.

[0059] In the present invention, there is no special requirement for the operating conditions of the desorption tower. The following exemplary description is given, but the scope of the present invention is not limited thereto. In step III), the operating conditions of the desorption tower include: an operating pressure of -0.01-1.0 MPaG, a portion of the desorbed tower bottom product is recycled back to the absorption tower as an absorbent, and a portion is returned as a product to the dimethyl carbonate product tower to recover dimethyl carbonate and dimethyl oxalate, and the diversion is carried out according to specific needs.

[0060] In the present invention, the dimethyl carbonate product tower is used to separate and obtain the dimethyl carbonate product, and there is no special requirement for its operating conditions. The following exemplary description is not intended to limit the scope of the present invention. For the present invention, preferably in step IV), the operating conditions of the dimethyl carbonate product tower include: an operating pressure of -0.08MPaG to 0.2MPaG, and / or a tower bottom operating temperature of 110-200° C. Compared with the operating pressure of 0-50kpag in the prior art, the present invention includes vacuum operation to reduce the tower bottom temperature, thereby reducing the decomposition of the tower bottom material.

[0061] According to a preferred embodiment of the present invention, part of the material extracted from the bottom of the dimethyl carbonate product tower is recycled back to the decarbonylation reactor, and part is extracted as a heavy component; the split is carried out according to the specific needs. Compared with the prior art that only recovers the condensate of the gas phase product for separation, the product tower of the present invention processes the condensate of the liquid phase product and the gas phase product at the same time, and the bottom material is recycled back to the reactor, which greatly improves the utilization rate of the raw materials.

[0062] According to a preferred embodiment of the present invention, the method comprises recycling the carbon monoxide stream back to an upstream system for synthesizing dimethyl oxalate as a raw material.

[0063] like Figure 1 and Figure 2 As shown, the present invention provides a system for preparing dimethyl carbonate by decarbonylating dimethyl oxalate, the system comprising:

[0064] The decarbonylation reactor comprises a raw material inlet, a gas phase outlet and a liquid phase outlet, which are preferably respectively arranged at the middle and upper side line position, the top and the bottom position of the decarbonylation reactor;

[0065] A dimethyl carbonate product tower, which is connected to the liquid phase outlet of the decarbonylation reactor, comprises a side line liquid phase inlet, a top outlet, a side line production outlet and a tower bottom outlet;

[0066] A gas-liquid separator, wherein the gas-liquid separator inlet is connected to the gas phase outlet of the decarbonylation reactor, and the liquid phase outlet of the gas phase separator is connected to the side line liquid phase inlet of the dimethyl carbonate product tower;

[0067] A cooler is arranged between the inlet of the gas-liquid separator and the gas phase outlet communicating pipeline of the decarbonylation reactor;

[0068] The tail gas purification unit comprises an absorption tower and a desorption tower connected in series, the feed port of the absorption tower is connected to the gas phase outlet of the gas-liquid separator, the absorption tower comprises a gas phase production outlet and a liquid phase production outlet, the liquid phase production outlet of the absorption tower is connected to the inlet of the desorption tower, and the desorption tower comprises a gas phase production outlet and a liquid phase production outlet.

[0069] In the present invention, switch valves can be set at each raw material inlet and outlet to flexibly control opening or closing, and each raw material inlet or outlet can be connected through a pipeline according to production needs, for example, the outlet of the desorption tower kettle is connected with the feed inlet of the absorption tower through a pipeline, for example, the outlet of the desorption tower kettle is connected with the side line liquid phase inlet of the dimethyl carbonate product tower through a pipeline, for example, the outlet of the dimethyl carbonate product tower kettle is connected with the raw material inlet of the decarbonylation reactor through a pipeline.

[0070] According to a preferred embodiment of the present invention, Figure 1The process shown in the figure is carried out, the dimethyl oxalate reactor raw material 5 and the dimethyl carbonate product tower kettle circulating material 14 are mixed and then enter the decarbonylation reactor 1, and a catalytic decarbonylation reaction occurs in the decarbonylation reactor 1 to generate dimethyl carbonate, wherein the catalyst can be an alkaline earth metal compound; a gas phase product 6 and a first liquid phase product 10 are respectively obtained from the decarbonylation reactor: the first liquid phase product 10 enters the dimethyl carbonate product tower 2; the gas phase product 6 is cooled by the condenser 3 to obtain a condensed gas phase product 7, and then enters the gas-liquid separation tank 4 to separate and obtain a gas phase material 8 and a second liquid phase product 9, and the second liquid phase product 9 enters the carbonate product tower 2, and the carbon is taken out from the side line. The dimethyl carbonate product 11 is obtained, and the top of the tower is the top extraction 12 of the dimethyl carbonate product tower; the bottom material is divided into two parts, one part is used as the external discharge material 13, and the other part is used as the bottom circulating material 14 of the dimethyl carbonate product tower; the gaseous material 8 is removed from the by-product substances such as carbon dioxide and dimethyl ether by the tail gas treatment system 15 to obtain the tail gas emission flow 17, the carbon monoxide flow 16 and the tail gas treatment system to recover the liquid phase material 18 containing dimethyl carbonate, wherein the tail gas treatment system recovers the liquid phase material 18 containing dimethyl carbonate and is recycled to the dimethyl carbonate product tower 2 to further recover dimethyl carbonate and dimethyl oxalate, and the tail gas treatment system 15 includes an absorption tower and a desorption tower.

[0071] like Figure 2 As shown, the tail gas treatment system 15 includes an absorption tower 19 and a desorption tower 20 connected in series, the gaseous material 8 enters the absorption tower 19, and the carbon monoxide flow 16 is discharged from the top of the absorption tower. The liquid phase material of the absorption tower enters the desorption tower 20, and the tail gas emission flow 17 is discharged from the top of the desorption tower. A part of the discharge from the bottom of the desorption tower 20 returns to the absorption tower for reabsorption, and the other part of the tail gas treatment system recovers the liquid phase material 18 containing dimethyl carbonate and enters the carbonate product tower 2.

[0072] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0073] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0074] The following examples are as follows Figure 1 He Ru Figure 2The process shown in the figure is carried out, the dimethyl oxalate reactor raw material 5 and the dimethyl carbonate product tower kettle circulating material 14 are mixed and then enter the decarbonylation reactor 1, and a catalytic decarbonylation reaction occurs in the decarbonylation reactor 1 to generate dimethyl carbonate, wherein the catalyst is an alkaline earth metal compound potassium carbonate, and the concentration of the catalyst in the liquid phase is 2wt%; a gas phase product 6 and a first liquid phase product 10 are respectively obtained from the decarbonylation reactor: the first liquid phase product 10 enters the dimethyl carbonate product tower 2; the gas phase product 6 is passed through a condenser 3 (operating conditions include: condensation temperature After cooling at 40°C, a condensed gas product 7 is obtained, which then enters a gas-liquid separation tank 4 (operating conditions include: an operating temperature of 40°C), and is separated to obtain a gas material 8 and a second liquid product 9. The second liquid product 9 enters the carbonate product tower 2, and a dimethyl carbonate product 11 is produced from the side line, and the top of the tower is the dimethyl carbonate product tower top production 12; a part of the tower bottom material is used as an external discharge material 13, accounting for 0.5%, and the other part is used as a dimethyl carbonate product tower bottom circulating material 14; the gas phase material 8 is passed through an exhaust gas treatment system 15 (such as Figure 2 The tail gas treatment system 15 includes an absorption tower 19 and a desorption tower 20 connected in series, a gaseous material 8 enters the absorption tower 19, a carbon monoxide stream 16 is discharged from the top of the absorption tower, a liquid phase material of the absorption tower enters the desorption tower 20 (operating conditions include: an operating pressure of 0.05 MPaG), a tail gas emission stream 17 is discharged from the top of the desorption tower, most of the discharge from the bottom of the desorption tower 20 is returned to the absorption tower for reabsorption, and another 0.5% of the tail gas treatment system recovers a liquid phase material 18 containing dimethyl carbonate and enters the carbonate product tower 2.

[0075] In the present invention, the obtained carbon monoxide flow 16 has a low impurity content and can be well recycled back to the system for generating raw material dimethyl oxalate as raw material.

[0076] In the present invention, pressure refers to the gauge pressure, and the heating load of the decarbonylation reactor refers to the heat required to maintain the temperature of the decarbonylation reactor, which may be steam heating, jacket heating or coil heating.

[0077] In the present invention, the purity is detected by gas chromatography.

[0078] In the present invention, gas phase purity refers to molar purity, and liquid phase purity refers to weight purity.

[0079] Example 1

[0080] 10t / h of dimethyl oxalate flow enters the decarbonylation reactor, the reactor temperature is 170°C, the reaction pressure is 0.9MPAG, the material residence time is 1.5h, and based on the total amount of dimethyl carbonate produced, the proportion of dimethyl carbonate in the first liquid phase product is 17wt%; the temperature of gas phase product cooling and gas-liquid separation is 40°C;

[0081] The operating pressure of the dimethyl carbonate product tower is -0.08 MPaG, the operating temperature of the tower bottom is 118°C, and 7226 kg / h of product with a purity of 99.99 wt% is obtained from the dimethyl carbonate product tower;

[0082] The temperature of the absorbent in the tail gas treatment system is 40°C, the pressure of the absorption tower is 0.8MPaG, the weight ratio of the absorbent to the tail gas is 21, and 2214kg / h of CO product is obtained, with a purity of 99.4mol%, containing 0.6% dimethyl carbonate, and the contents of CO2 and dimethyl ether are both less than 0.01mol%, which can be well recycled back to the system for generating dimethyl oxalate as raw materials. The tail gas system only needs to supplement the absorbent dimethyl carbonate at the initial start-up, and no longer needs to supplement the absorbent after the operation is stable, and 35kg / h of dimethyl carbonate-containing materials are recovered from the desorption tower kettle, among which the DMC purity is 98.6%, the DMO content is 1.4%, and the heating load of the decarbonylation reactor is 2.0MW.

[0083] Example 2

[0084] 10t / h of dimethyl oxalate flow enters the decarbonylation reactor, the reactor temperature is 170°C, the reaction pressure is 0.7MPAG, the material residence time is 1.4h, and based on the total amount of dimethyl carbonate produced, the proportion of dimethyl carbonate in the first liquid phase product is 6.2wt%; the temperature for cooling the gas phase product and gas-liquid separation is 40°C;

[0085] The operating pressure of the dimethyl carbonate product tower is 0 MPaG, the operating temperature of the tower bottom is 164°C, and 7209 kg / h of product with a purity of 99.99% wt is obtained from the dimethyl carbonate product tower;

[0086] The temperature of the tail gas treatment system absorbent is 40°C, the pressure of the absorption tower is 0.6MPaG, the weight ratio of absorbent to tail gas is 21, and 2287kg / h of CO product is obtained, with a purity of 99.15mol%, containing 0.81% dimethyl carbonate, CO2 content of 0.04%, and dimethyl ether content of less than 0.01mol%, which can be well recycled to the system for generating dimethyl oxalate as raw materials. And the tail gas system only needs to supplement the absorbent dimethyl carbonate at the initial start-up, and no longer needs to supplement the absorbent after stable operation, and 42kg / h of dimethyl carbonate-containing materials are recovered from the desorption tower kettle, wherein the purity of DMC is 97.2%, the content of DMO is 2.8%, and the heating load of the decarbonylation reactor is 2.1MW.

[0087] Example 3

[0088] 10t / h of dimethyl oxalate flow enters the decarbonylation reactor, the reactor temperature is 200°C, the reaction pressure is 1.5MPAG, the material residence time is 1.0h, and based on the total amount of dimethyl carbonate produced, the proportion of dimethyl carbonate in the first liquid phase product is 7.7wt%; the temperature for cooling the gas phase product and gas-liquid separation is 40°C;

[0089] The operating pressure of the dimethyl carbonate product tower is 0.1 MPaG, the operating temperature of the tower bottom is 189°C, and 7251 kg / h of product with a purity of 99.95% wt is obtained from the dimethyl carbonate product tower;

[0090] The temperature of the absorbent in the tail gas treatment system is 40°C, the pressure in the absorption tower is 1.4MPaG, the weight ratio of the absorbent to the tail gas is 21, and 2099kg / h of CO product is obtained, with a purity of 99.63mol%, containing 0.37% dimethyl carbonate, CO2 content less than 0.01%, and dimethyl ether content less than 0.01mol%, which can be well recycled to the system for generating dimethyl oxalate as raw materials. The tail gas system only needs to supplement the absorbent dimethyl carbonate at the initial start-up, and no longer needs to supplement the absorbent after the operation is stable, and 8kg / h of dimethyl carbonate-containing materials are recovered from the desorption tower kettle, wherein the purity of DMC is 98.7%, the content of DMO is 1.3%, and the heating load of the decarbonylation reactor is 2.2MW.

[0091] Example 4

[0092] 10t / h of dimethyl oxalate flow enters the decarbonylation reactor, the reactor temperature is 150°C, the reaction pressure is 1.5MPAG, the material residence time is 5.0h, and based on the total amount of dimethyl carbonate produced, the proportion of dimethyl carbonate in the first liquid phase product is 67wt%; the temperature of gas phase product cooling and gas-liquid separation is 120°C;

[0093] The operating pressure of the dimethyl carbonate product tower is 0.1 MPaG, the operating temperature of the tower bottom is 189°C, and 7275 kg / h of product with a purity of 99.99% wt is obtained from the dimethyl carbonate product tower;

[0094] The temperature of the tail gas treatment system absorbent is 20°C, the pressure of the absorption tower is 1.4MPaG, the weight ratio of the absorbent to the tail gas is 11, and 2229kg / h of CO product is obtained, with a purity of 99.63mol%, containing 0.37% dimethyl carbonate, CO2 content less than 0.01%, and dimethyl ether content less than 0.01mol%, which can be well recycled to the system for generating dimethyl oxalate as raw materials. The tail gas system only needs to supplement the absorbent dimethyl carbonate at the initial start-up, and no longer needs to supplement the absorbent after stable operation, and 1247kg / h of dimethyl carbonate-containing materials can be recovered from the desorption tower, wherein the purity of DMC is 98.9%, the content of DMO is 1.1%, and the heating load of the decarbonylation reactor is 1.7MW.

[0095] Comparative Example 1

[0096] The process of Example 1 was repeated, except that the gaseous product did not pass through the tail gas treatment system, and the CO2 and dimethyl ether in the CO were directly recycled back to the system for generating dimethyl oxalate as raw materials, wherein the CO purity in the gas phase discharged from the gas-liquid separator was 94 mol%, the CO2 content was 3%, and the dimethyl ether content was 2%, which would cause the impurities to accumulate in the system for generating dimethyl oxalate and be difficult to discharge, affecting the stable operation of the raw material dimethyl oxalate production system, and the energy consumption was high.

[0097] Comparative Example 2

[0098] The process of Example 1 is repeated, except that: the tail gas treatment system uses methanol as the absorbent. Due to the carryover of the tail gas, the tail gas system needs to be supplemented with 151 kg / h of methanol, and 200 kg / h of material containing methanol and DMC is discharged, wherein the methanol content is 49%, the DMC content is 50%, and the DMO content is 0.3%. This material flow is not suitable for direct recovery in the product tower, otherwise it will lead to a decrease in the purity of the DMC product.

[0099] Example 5

[0100] The process of Example 1 was repeated, except that: the pressure of the decarbonylation reactor was reduced to 0.6 MPaG, the proportion of dimethyl carbonate in the first liquid phase product was reduced to 1.2 wt %, and the heating load required for the decarbonylation reactor was increased from 2.0 MW to 2.3 MW, an increase of 15%. At the same time, a larger amount of dimethyl oxalate was evaporated to the gas phase, which further increased the gas phase cooling load and separation energy consumption.

[0101] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various specific technical features in any suitable manner. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations. However, these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing dimethyl carbonate by decarbonylating dimethyl oxalate, characterized in that: The method includes: 1) subjecting the dimethyl oxalate to a decarbonylation reaction in a decarbonylation reactor to produce dimethyl carbonate, and obtaining a gas phase product and a first liquid phase product from the decarbonylation reactor respectively: the first liquid phase product enters a dimethyl carbonate product tower; II) the gas phase product is cooled and then subjected to gas-liquid separation to obtain a gas phase material and a second liquid phase product, and the second liquid phase product enters the dimethyl carbonate product tower; III) the gaseous material is sent to a tail gas purification unit, the tail gas purification unit includes an absorption tower and a desorption tower, wherein the gaseous material absorbs by-products including carbon dioxide and dimethyl ether through the absorbent dimethyl carbonate in the absorption tower, and the liquid absorption material and carbon monoxide flow are discharged from the absorption tower; the liquid absorption material enters the desorption tower for desorption and removal of by-products including carbon dioxide and dimethyl ether to recover the liquid material containing dimethyl carbonate; IV) separating and obtaining a dimethyl carbonate product in the dimethyl carbonate product tower.

2. The method according to claim 1, wherein: In step I), based on the total amount of dimethyl carbonate produced in step I), the proportion of dimethyl carbonate in the first liquid phase product is 5-80wt%, preferably 6-70wt%.

3. The method according to claim 1 or 2, wherein: In step I), the operating conditions of the decarbonylation reactor include: an operating pressure of 0.3-2.0 MPaG, preferably 0.5-1.5 MPaG; and / or an operating temperature of 120-250° C., preferably 150-200° C.; and / or a liquid phase residence time of 0.1-20 hours, preferably 0.3-5 hours; a catalyst concentration in the liquid phase of 0.1-20 wt%, the catalyst being one or more of the alkaline compounds.

4. The method according to any one of claims 1 to 3, wherein: In step I), the decarbonylation reactor comprises a raw material inlet, a gas phase outlet and a liquid phase outlet, which are respectively arranged at the middle and upper side line position of the decarbonylation reactor, the upper part of the reactor, and the lower part of the reactor; preferably, they are respectively arranged at the middle and upper side line position, the top and the bottom of the decarbonylation reactor.

5. The method according to any one of claims 1 to 4, wherein: In step II), The cooling conditions include: the cooling temperature is 30 to 150°C, preferably 40 to 120°C.

6. The method according to any one of claims 1 to 5, wherein: In step III), the operating conditions of the absorption tower include: an operating pressure of 0.1-2.0 MPaG, an absorbent temperature of 10-60°C, preferably 20-40°C; a weight ratio of the absorbent to the tail gas of 1-50, preferably 5-30, more preferably 8-25; preferably, the dimethyl carbonate product is used as the absorbent.

7. The method according to any one of claims 1 to 6, wherein: In step III), the operating conditions of the desorption tower include: an operating pressure of -0.01 MPaG to 1.0 MPaG, part of the desorption tower bottom product is recycled back to the absorption tower as an absorbent, and part is returned to the dimethyl carbonate product tower as a product to recover dimethyl carbonate.

8. The method according to any one of claims 1 to 7, wherein: In step IV), the operating conditions of the dimethyl carbonate product tower include: an operating pressure of -0.08 MPaG to 0.2 MPaG, and / or a tower bottom operating temperature of 110-200°C.

9. The method according to any one of claims 1 to 8, wherein: The material extracted from the bottom of the dimethyl carbonate product tower is partially recycled back to the decarbonylation reactor, and partially extracted as a heavy component; and / or The method includes recycling the carbon monoxide stream back to an upstream system for synthesizing raw material dimethyl oxalate.

10. A system for preparing dimethyl carbonate by decarbonylating dimethyl oxalate, characterized in that: The system includes: The decarbonylation reactor comprises a raw material inlet, a gas phase outlet and a liquid phase outlet, which are preferably respectively arranged at the middle and upper side line position, the top and the bottom position of the decarbonylation reactor; A dimethyl carbonate product tower is connected to the liquid phase outlet of the decarbonylation reactor, and includes a side line liquid phase inlet, a top outlet, a side line production outlet, and a tower bottom outlet; A gas-liquid separator, wherein the gas-liquid separator inlet is connected to the gas phase outlet of the decarbonylation reactor, and the gas phase separator liquid phase outlet is connected to the side line liquid phase inlet of the dimethyl carbonate product tower; A cooler is arranged between the inlet of the gas-liquid separator and the gas phase outlet communicating pipeline of the decarbonylation reactor; The tail gas purification unit comprises an absorption tower and a desorption tower connected in series, the feed port of the absorption tower is connected to the gas phase outlet of the gas-liquid separator, the absorption tower comprises a gas phase production outlet and a liquid phase production outlet, the liquid phase production outlet of the absorption tower is connected to the inlet of the desorption tower, and the desorption tower comprises a gas phase production outlet and a liquid phase production outlet.

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