Separation and emission reduction system, method and application for maleic anhydride production of dialkyl maleate

Abstract

The application discloses a separation and emission reduction system, method and application of maleic anhydride for producing maleic acid dialkyl ester, and relates to the technical field of maleic acid dialkyl ester production. The separation and emission reduction system comprises a reaction product refining tower, a catalyst waste liquid concentration tower and a vacuum unit. The reaction product refining tower can improve the purity of maleic acid dialkyl ester product, greatly reduce the content of maleic acid monoalkyl ester impurities in the product, and effectively prolong the service life of the hydrogenation catalyst in the downstream hydrogenation process for generating BDO. The catalyst waste liquid concentration tower can effectively recover maleic acid dialkyl ester product in the catalyst waste liquid, improve the utilization rate of raw materials, reduce the emission amount of catalyst waste liquid, and reduce the treatment cost of catalyst waste liquid. The vacuum unit is arranged to form a vacuum environment in the reaction product refining tower and the catalyst waste liquid concentration tower, and the operating pressure in the tower is controlled within the vacuum range, so that the operating temperature of the tower kettle is reduced, the catalyst is prevented from being decomposed in the tower kettle, and the selection of the heat source of the tower kettle is facilitated.

Description

Technical Field

[0001] This invention relates to the field of maleic acid dialkyl ester production technology, and more specifically, to a separation and emission reduction system, method, and application for the production of maleic acid dialkyl esters from maleic anhydride. Background Technology

[0002] The most representative dialkyl maleates are dimethyl maleate (DMM), diethyl maleate (DEM), and dipropyl maleate (DPM), with the first two being important raw materials for fine chemicals. The production processes and methods for other dialkyl maleates are basically similar to the former two, and current technologies primarily use DMM and DEM as representatives to describe their process routes and methods. Dimethyl maleate, also known as dimethyl maleate, is a colorless, transparent, oily liquid with a boiling point of 200.4℃, a melting point of -19.0℃, and a relative density of 1.146. Dialkyl maleates can be used as plasticizers in polymer monomers and synthetic resins; they are also used in the manufacture of pesticides, fungicides, rust inhibitors, and organic solvents.

[0003] Dialkyl maleate is also an important organic chemical raw material. In the production process of 1,4-butanediol (BDO) and co-produced tetrahydrofuran (THF) and γ-butyrolactone (GBL) using maleic anhydride as a raw material, the first stage is the esterification reaction of maleic anhydride with low carbon alcohol to produce dialkyl maleate; the second stage is to hydrogenate dialkyl maleate to obtain BDO, THF and GBL.

[0004] Chinese patent CN112961058A discloses a process for preparing dimethyl maleate esters. This patent reveals that traditional methods for producing dimethyl maleate often use maleic anhydride as a raw material, reacting it with methanol under the catalysis of sulfuric acid or p-toluenesulfonic acid. The traditional process is semi-continuous, typically using a reactor and a reactive distillation column. During the reaction, water and excess alcohol are distilled off, yielding a mixture of dimethyl maleate and catalyst. The distilled water and excess alcohol mixture is then distilled to recover valuable methanol. The mixture is subsequently subjected to alkaline washing or water extraction to remove the catalyst, yielding the intermediate product. This traditional production process results in a significant loss of dimethyl maleate during water or alkaline washing, large amounts of catalyst waste, resource waste, and high production costs.

[0005] In addition, during the production of 1,4-butanediol (BDO) and co-production of tetrahydrofuran (THF) and γ-butyrolactone (GBL) using maleic anhydride as a raw material, the dialkyl maleate product contains a large amount of monoalkyl maleate impurities, which adversely affects the activity and life cycle of the hydrogenation catalyst in the downstream dialkyl maleate hydrogenation reaction to BDO, and shortens the hydrogenation catalyst life.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a separation and emission reduction system, method and application for the production of dialkyl maleate from maleic anhydride, which aims to reduce the discharge of catalyst waste liquid and reduce catalyst degradation.

[0008] This invention is implemented as follows:

[0009] In a first aspect, the present invention provides a separation and emission reduction system for the production of dialkyl maleate from maleic anhydride, comprising: a reaction product purification tower, a catalyst waste liquid concentration tower, and a vacuum unit;

[0010] The product purification tower is equipped with an inlet for maleic anhydride esterification reaction products, a light component outlet at the top of the product purification tower, a maleic acid dialkyl ester product collection pipe at the top of the product purification tower, and a heavy component outlet at the bottom of the product purification tower. The heavy component outlet is connected to the catalyst waste liquid concentration tower feed pipe and the circulating material pipe, respectively.

[0011] A feed inlet is provided in the middle of the catalyst waste liquid concentration tower, and the feed pipe of the catalyst waste liquid concentration tower is connected to the feed inlet of the catalyst waste liquid concentration tower. A catalyst waste liquid outlet is provided in the bottom of the tower, and a light component outlet is provided at the top of the catalyst waste liquid concentration tower. A high-purity dialkyl maleate ester collection pipe is provided at the top of the catalyst waste liquid concentration tower, and the outlet of the high-purity dialkyl maleate ester collection pipe is connected to the inlet of the maleic anhydride esterification reaction product.

[0012] A discharge pipe is installed at the outlet of the light component of the reaction product purification tower, and the outlet of the light component of the catalyst waste liquid concentration tower is connected to the discharge pipe. A vacuum unit is also installed on the discharge pipe.

[0013] In optional embodiments, a waste liquid buffer tank and a catalyst circulation buffer tank are also included;

[0014] The catalyst waste liquid outlet is connected to the waste liquid buffer tank;

[0015] The outlet of the circulating material pipe is connected to the catalyst circulating buffer tank.

[0016] In an optional embodiment, booster pumps are installed on the feed pipe of the catalyst waste liquid concentration tower, the outlet pipe of the high-purity dialkyl maleate, and the catalyst waste liquid pipeline.

[0017] In an optional embodiment, the reaction product purification tower and the catalyst waste liquid concentration tower are packed towers or plate towers.

[0018] Secondly, the present invention also provides a separation and emission reduction method for the production of dialkyl maleate from maleic anhydride, which utilizes the separation and emission reduction system in any of the above embodiments for treatment, wherein the reflux ratio in the catalyst waste concentration tower is 0.1-3.0, the operating temperature is 100-175℃, and the absolute pressure is 1-10kPa.

[0019] In an optional embodiment, the reflux ratio in the catalyst waste concentration tower is 0.1-0.3, the tower top operating temperature is 90-105℃ and the absolute pressure is 1-3kPa; the tower bottom operating temperature is 150-175℃ and the absolute pressure is 5-10kPa.

[0020] In an optional embodiment, the reflux ratio in the reaction product purification tower is 60-90, the operating temperature is 80-125°C, and the absolute pressure is 1-10 kPa.

[0021] In an optional embodiment, the reflux ratio in the product purification column is 80-90, the column top operating temperature is 80-95℃, and the absolute pressure is 1-3kPa; the column bottom operating temperature is 115-125℃, and the absolute pressure is 5-10kPa.

[0022] In an optional embodiment, the maleic anhydride esterification reaction product entering the reaction product purification tower includes: 94-96% dialkyl maleate, 0.3-0.6% monoalkyl maleate, 2.1-3.0% dialkyl phthalate, 0.8-1.2% catalyst, and 0.8-1.2% other components.

[0023] Thirdly, the present invention provides a system for producing dialkyl maleate from maleic anhydride, including the separation and emission reduction system for producing dialkyl maleate from maleic anhydride according to any one of the foregoing embodiments.

[0024] The present invention has the following beneficial effects:

[0025] This application utilizes a reaction product purification tower to improve the purity of dialkyl maleate products, significantly reduce the content of monoalkyl maleate impurities in the products, and effectively extend the hydrogenation catalyst life of the downstream hydrogenation process to BDO.

[0026] By setting up a catalyst waste liquid concentration tower, maleic acid dialkyl ester products in the catalyst waste liquid can be effectively recovered, improving raw material utilization, reducing the discharge of catalyst waste liquid, lowering catalyst waste liquid treatment costs, and reducing production costs.

[0027] The light component outlets of the reaction product purification tower and the catalyst waste liquid concentration tower are connected by a discharge pipe. At the same time, a vacuum unit is set up to create a vacuum environment in the reaction product purification tower and the catalyst waste liquid concentration tower, and the operating pressure in the tower is controlled within the vacuum range. This reduces the operating temperature of the tower bottom, avoids catalyst decomposition in the tower bottom, and facilitates the selection of the tower bottom heat source. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A schematic diagram of the separation and emission reduction system for the production of dialkyl maleate from maleic anhydride.

[0030] Illustration: 10 - Reaction product purification tower; 20 - Catalyst waste liquid concentration tower; 30 - Waste liquid buffer tank; 40 - Catalyst circulation buffer tank; 50 - Vacuum unit;

[0031] 101-Refining tower bottom pump; 201-Concentration tower outlet pump; 202-Concentration tower bottom pump; 301-Waste liquid booster pump; 401-Catalyst circulation pump.

[0032] a-Dialkyl maleic acid ester product; b-Catalyst waste liquid in the bottom of the catalyst waste liquid concentration tower; c-Esterification reaction product of maleic anhydride; d-Light component of the reaction product purification tower; e-Heavy component of the reaction product purification tower bottom; f-High-purity dialkyl maleic acid ester; g-Light component of the catalyst waste liquid concentration tower; i-Feed of the catalyst waste liquid concentration tower; j-Circulating material. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0034] This embodiment provides a separation and emission reduction system for the production of dialkyl maleate from maleic anhydride, such as... Figure 1 As shown, it includes: a reaction product purification tower 10, a catalyst waste liquid concentration tower 20, and a vacuum unit 50;

[0035] The reaction product purification tower 10 is equipped with an inlet for maleic anhydride esterification reaction products, a light component outlet at the top, a maleic acid dialkyl ester product collection pipe at the top, and a heavy component outlet at the bottom. The heavy component outlet is connected to the feed pipe and circulating material pipe of the catalyst waste liquid concentration tower 20. The catalyst waste liquid concentration tower 20 has a feed inlet in the middle, and its feed pipe is connected to the [unclear - possibly a specific component or structure]. The feed inlet is connected, the bottom of the tower is equipped with a catalyst waste liquid outlet, the top of the catalyst waste liquid concentration tower 20 is equipped with a light component outlet, and the upper part of the catalyst waste liquid concentration tower 20 is equipped with a high-purity dialkyl maleate collection pipe. The outlet of the high-purity dialkyl maleate collection pipe is connected to the inlet of the maleic anhydride esterification reaction product. The light component outlet of the reaction product purification tower 10 is equipped with a discharge pipe, the light component outlet of the catalyst waste liquid concentration tower 20 is connected to the discharge pipe, and a vacuum unit 50 is also installed on the discharge pipe.

[0036] In the product purification column 10, the maleic anhydride esterification reaction product c enters the lower part of the product purification column 10 through the maleic anhydride esterification reaction product inlet for vacuum distillation. The light component d extracted from the light component outlet at the top of the product purification column 10 contains low-carbon alcohols and dialkyl maleate, which can be used as fuel combustion or further separated and collected as a by-product. The dialkyl maleate product a is extracted from the uppermost dialkyl maleate product collection pipe of the product purification column 10 and sent downstream as an intermediate product for use in the production of BDO. In some embodiments, the dialkyl maleate product a includes 99.8 wt% dialkyl maleate, 0.003 wt% monoalkyl maleate, and 0.197 wt% other components. The reaction product purification tower 10 contains a large amount of dialkyl maleate and a small amount of catalyst. The heavy component e leaves the heavy component outlet and splits into two paths. One path is the catalyst waste liquid concentrate tower feed i, which is sent to the catalyst waste liquid concentrate tower 20 for recovery via the catalyst waste liquid concentrate tower feed pipe. The other path is the circulating material j, which is sent to the catalyst circulating buffer tank 40 via the circulating material pipe.

[0037] In the catalyst waste liquid concentration tower 20, the feed i from the bottom of the reaction product purification tower 10 enters the middle of the catalyst waste liquid concentration tower 20 for vacuum distillation, and the light component g is extracted from the light component outlet at the top of the catalyst waste liquid concentration tower 20. High-purity dialkyl maleate f is extracted from the high-purity dialkyl maleate collection pipe at the top of the catalyst waste liquid concentration tower 20, and mixed with the maleic anhydride esterification reaction product c before entering the reaction product purification tower 10 for distillation. The catalyst waste liquid b from the bottom of the catalyst waste liquid concentration tower 20, containing a small amount of dialkyl maleate, is discharged through the catalyst waste liquid pipeline. The catalyst waste liquid b mainly includes organic sulfur, alkyl maleate, and alkyl phthalate.

[0038] In this embodiment, the light component outlet of the reaction product purification tower 10 and the light component outlet of the catalyst waste liquid concentration tower 20 are connected by a discharge pipe. At the same time, by setting up a vacuum unit 50, a vacuum environment is formed in the reaction product purification tower 10 and the catalyst waste liquid concentration tower 20, and the operating pressure in the tower is controlled within the vacuum range, thereby reducing the operating temperature of the tower bottom, avoiding catalyst decomposition in the tower bottom, and facilitating the selection of the tower bottom heat source.

[0039] This application utilizes reaction product purification tower 10 to improve the purity of dialkyl maleate products, significantly reduce the content of monoalkyl maleate impurities in the products, and effectively extend the hydrogenation catalyst life of the downstream hydrogenation process to BDO.

[0040] By setting up a catalyst waste liquid concentration tower 20, the dialkyl maleate product in the catalyst waste liquid can be effectively recovered, improving the raw material utilization rate, reducing the discharge of catalyst waste liquid, reducing the treatment cost of catalyst waste liquid, and reducing production costs.

[0041] In an optional embodiment, it also includes a waste liquid buffer tank 30 and a catalyst circulation buffer tank 40;

[0042] The catalyst waste liquid outlet is connected to the waste liquid buffer tank 30;

[0043] The outlet of the circulating material pipe is connected to the catalyst circulating buffer tank 40.

[0044] The waste liquid b from the bottom of the catalyst waste liquid concentration tower 20 is sent to the waste liquid buffer tank 30 through the catalyst waste liquid pipeline. The material at the bottom of the waste liquid buffer tank 30 is sent to a designated area for treatment as catalyst waste liquid. The catalyst waste liquid is mainly used to discharge catalyst degradation products and avoid the large accumulation of catalyst degradation products in the reaction system.

[0045] The circulating material from the bottom of the catalyst circulating buffer tank 40, after being pressurized by the catalyst circulating pump 401, can be sent back to the reaction unit for reuse.

[0046] In an optional embodiment, booster pumps are installed on the feed pipe of the catalyst waste liquid concentration tower, the outlet pipe of the high-purity dialkyl maleate, and the catalyst waste liquid pipeline.

[0047] In some embodiments, a purification tower bottom pump 101 is installed on the feed pipe of the catalyst waste liquid concentration tower, which facilitates the transfer of the catalyst waste liquid feed to the catalyst waste liquid concentration tower 20 and the catalyst circulation buffer tank 40; a concentration tower outlet pump 201 is installed on the high-purity maleic acid dialkyl ester outlet pipe, which facilitates the transfer of high-purity maleic acid dialkyl ester to the reaction product purification tower 10; and a concentration tower bottom pump 202 is installed on the waste liquid pipeline to facilitate waste liquid discharge.

[0048] In addition, in some embodiments, a waste liquid booster pump 301 is provided on the corresponding discharge pipe to facilitate the discharge of waste liquid in the waste liquid buffer tank 30, and a catalyst circulation pump 401 is provided on the corresponding discharge pipe to facilitate the discharge of catalyst waste liquid in the catalyst circulation buffer tank 40.

[0049] In an optional embodiment, the reaction product purification tower 10 and the catalyst waste liquid concentration tower 20 are packed towers or plate towers, preferably packed towers.

[0050] This invention also provides a method for separating and reducing emissions from the production of dialkyl maleic acid esters using the above-mentioned separation and emission reduction system. The reflux ratio in the catalyst waste liquid concentration tower 20 is 0.1-3.0, the operating temperature is 100-175℃, and the absolute pressure is 1-10kPa.

[0051] Specifically, the reflux ratio in the catalyst waste liquid concentration tower 20 can be any value between 0.1, 0.3, 0.5, 1, 1.5, 2, 2.5, 3.0 or 0.1-3.0; the operating temperature of the catalyst waste liquid concentration tower 20 is 100-175℃, specifically any value between 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 175℃ or 100-160℃; the absolute pressure of the catalyst waste liquid concentration tower 20 is 1-10 kPa, specifically any value between 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa or 1-10 kPa, preferably 2-6 kPa.

[0052] In an optional embodiment, the reflux ratio in the catalyst waste concentration tower 20 is 0.1-0.3, the tower top operating temperature is 90-105℃ and the absolute pressure is 1-3kPa; the tower bottom operating temperature is 150-175℃ and the absolute pressure is 5-10kPa, preferably 5-6kPa.

[0053] In an optional embodiment, the reflux ratio in the reaction product purification tower 10 is 60-90, specifically any value between 60, 70, 80, 90, or 60-90; the operating temperature is 80-125°C, specifically any value between 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, or 80-125°C; the absolute pressure is 1-10 kPa, specifically any value between 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa, or 1-10 kPa, preferably 2-6 kPa.

[0054] In an optional embodiment, the reflux ratio in the reaction product purification column 10 is 80-90, the column top operating temperature is 80-95℃, and the absolute pressure is 1-3kPa; the column bottom operating temperature is 115-125℃, and the absolute pressure is 5-10kPa.

[0055] It should be noted that, unless otherwise specified, the pressure in this application refers to absolute pressure.

[0056] In an optional embodiment, the reaction products entering the reaction product purification tower 10 include: 94-96% dialkyl maleate, 0.3-0.6% monoalkyl maleate, 2.1-3.0% dialkyl phthalate, 0.8-1.2% catalyst, and 0.8-1.2% other components. Specifically, the dialkyl maleate can be dimethyl maleate, diethyl maleate, etc. The type of catalyst can be selected from existing technologies; specifically, the catalyst can be benzenesulfonic acid, alkylbenzenesulfonic acid, sulfuric acid, nitric acid, etc. Other components include unreacted raw material low-carbon alcohols and byproducts from the esterification process such as dimethyl ether, wherein the low-carbon alcohols can specifically be methanol corresponding to dimethyl maleate, ethanol corresponding to diethyl maleate, etc.

[0057] This application improves the purity of dialkyl maleate products by using a reaction product purification tower, reducing the content of monoalkyl maleate impurities in the dialkyl maleate products to below 30 ppm, thereby improving product quality and effectively extending the hydrogenation catalyst life of the downstream hydrogenation process to BDO.

[0058] By setting up a catalyst waste liquid concentration tower, maleic acid dialkyl ester products in the catalyst waste liquid can be effectively recovered, improving raw material utilization, reducing the discharge of catalyst waste liquid by more than 85%, reducing catalyst waste liquid treatment costs, and lowering production costs.

[0059] This invention also provides a system for producing dialkyl maleate by maleic anhydride, including the separation and emission reduction system for producing dialkyl maleate by maleic anhydride according to any of the foregoing embodiments, and may also include a reaction apparatus for producing dialkyl maleate by maleic anhydride, etc.

[0060] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0061] Example 1

[0062] This embodiment provides a method for separating and reducing emissions during the production of dialkyl maleate from maleic anhydride, comprising the following steps:

[0063] In step S1, the product c from the esterification reaction of maleic anhydride (40.57 t / h) is fed into the product purification column 10 for vacuum distillation through the middle and lower packed bed. Product c comprises 95% dialkyl maleate, 0.34% monoalkyl maleate, 2.66% dialkyl phthalate, 1% catalyst, and 1% unreacted raw materials and other components. The reflux ratio of the product purification column 10 is controlled at 90, the top operating pressure is 2 kPa(A), the operating temperature is 85℃, the bottom operating pressure is 6 kPa(A), and the bottom operating temperature is 117℃. The light component d, containing methanol and dialkyl maleate, is drawn from the top of the product purification column 10 into the vacuum unit 50; the dialkyl maleate product a is drawn from the top of the product purification column 10 and sent downstream as an intermediate product. The reaction product, containing a large amount of dialkyl maleate and a small amount of catalyst, is purified from the bottom of the purification tower. The heavy component e is pressurized by the bottom pump 101 and then divided into two streams. One stream, the catalyst waste liquid concentrate feed i, is sent to the catalyst waste liquid concentrate tower 20 for concentration, and the other stream, the circulating material j, is sent to the catalyst circulating buffer tank 40.

[0064] S2, the feed i of the catalyst waste liquid concentration tower enters the catalyst waste liquid concentration tower 20 from the middle packing bed for vacuum distillation. The reflux ratio is controlled at 0.3, the top operating pressure is 2 kPa(A), the operating temperature is 95℃, the bottom operating pressure is 5 kPa(A), and the operating temperature is 162℃. The light component g of the catalyst waste liquid concentration tower containing dialkyl maleate is drawn into the vacuum unit 50 from the top of the catalyst waste liquid concentration tower 20. The high-purity dialkyl maleate stream f is drawn from the top of the catalyst waste liquid concentration tower 20, pressurized by the concentration tower outlet pump 201, mixed with the maleic anhydride esterification reaction product c, and then enters the reaction product purification tower 10 for distillation. The bottom waste liquid b of the catalyst waste liquid concentration tower 20 is pressurized by the bottom pump 202 and sent to the waste liquid buffer tank 30. The catalyst waste liquid from the bottom of the waste liquid buffer tank 30 is pressurized by the waste liquid booster pump 301 and sent to the off-site treatment area.

[0065] S3, the circulating material j from the bottom of the catalyst circulation buffer tank 40 is pressurized by the catalyst circulation pump 401 and sent back to the reaction unit for reuse.

[0066] Example 2

[0067] This embodiment provides a method for separating and reducing emissions during the production of dialkyl maleate from maleic anhydride, comprising the following steps:

[0068] S1, the product c from the esterification reaction of maleic anhydride (40.57 t / h) is fed into the product purification column 10 for vacuum distillation through the middle and lower packed bed. Product c contains 95% dialkyl maleate, 0.34% monoalkyl maleate, 2.66% dialkyl phthalate, 1% catalyst, and 1% unreacted raw materials and other components. The reflux ratio of the product purification column 10 is controlled at 80, the top operating pressure is 3 kPa(A), the operating temperature is 92℃, the bottom operating pressure is 6 kPa(A), and the bottom operating temperature is 122℃. The light component d, containing methanol and dialkyl maleate, is drawn from the top of the product purification column 10 into the vacuum unit 50. The dialkyl maleate product a is drawn from the top of the product purification column 10 and sent downstream as an intermediate product. The reaction product, containing a large amount of dialkyl maleate and a small amount of catalyst, is purified from the bottom of the purification tower. The heavy component e is pressurized by the bottom pump 101 and then divided into two streams. One stream, the catalyst waste liquid concentrate feed i, is sent to the catalyst waste liquid concentrate tower 20 for concentration, and the other stream, the circulating material j, is sent to the catalyst circulating buffer tank 40.

[0069] S2, the feed i of the catalyst waste liquid concentration tower enters the catalyst waste liquid concentration tower 20 from the middle packing bed for vacuum distillation. The reflux ratio is controlled at 0.1, the top operating pressure is 3 kPa(A), the operating temperature is 104℃, the bottom operating pressure is 6 kPa(A), and the operating temperature is 172℃. The light component g of the catalyst waste liquid concentration tower containing dialkyl maleate is drawn into the vacuum unit 50 from the top of the catalyst waste liquid concentration tower 20. The high-purity dialkyl maleate stream f is drawn from the top of the catalyst waste liquid concentration tower 20, pressurized by the concentration tower outlet pump 201, mixed with the maleic anhydride esterification reaction product c, and then enters the reaction product purification tower 10 for distillation. The bottom waste liquid b of the catalyst waste liquid concentration tower 20 is pressurized by the bottom pump 202 and sent to the waste liquid buffer tank 30. The catalyst waste liquid from the bottom of the waste liquid buffer tank 30 is pressurized by the waste liquid booster pump 301 and sent to the off-site treatment area.

[0070] S3, the circulating material j from the bottom of the catalyst circulation buffer tank 40 is pressurized by the catalyst circulation pump 401 and sent back to the reaction unit for reuse.

[0071] Comparative Example 1

[0072] This comparative example provides a method for separating and reducing emissions from maleic anhydride in the production of dialkyl maleate. The only difference from Example 1 is that in the product purification tower 10, the reflux ratio is controlled at 48, the tower top operating pressure is 15 kPa (A), the operating temperature is 134°C, the tower bottom operating pressure is 25 kPa (A), and the tower bottom operating temperature is 175°C.

[0073] Comparative Example 2

[0074] This comparative example provides a method for separating and reducing emissions from maleic anhydride in the production of dialkyl maleate. The only difference from Example 1 is that in the catalyst waste liquid concentration tower 20, the reflux ratio is controlled at 0.1, the tower top operating pressure is 15 kPa (A), the operating temperature is 143°C, and the tower bottom operating pressure is 25 kPa (A) and the operating temperature is 219°C.

[0075] Comparative Example 3

[0076] This comparative example provides a method for separating and reducing emissions from the production of dialkyl maleate from maleic anhydride. The only difference from Example 1 is that: no catalyst waste liquid concentration tower is set up. The dilute catalyst stream containing a large amount of dialkyl maleate and a small amount of catalyst in the bottom of the purification tower 10 is pressurized by the bottom pump 101 of the purification tower and divided into two streams. One stream, the feed i of the catalyst waste liquid concentration tower, is sent as waste liquid (equivalent to the bottom waste liquid b of the catalyst waste liquid concentration tower) to be treated outside the boundary. The other stream, the circulating stream j, is sent back to the reaction unit for reuse.

[0077] The composition of dialkyl maleate product a, catalyst waste liquid concentrate tower bottom waste liquid b, and high-purity dialkyl maleate f in the above examples and comparative examples, as well as the flow rate of the corresponding material per ton of reactants, were recorded. The results are shown in the table below.

[0078]

[0079] As can be seen from the above examples and comparative examples, compared with Example 1 and Comparative Example 1, by setting up a reaction product purification tower, the purity of maleic acid dialkyl ester product a in Example 1 reaches 99.83742%, which is higher than the purity of maleic acid dialkyl ester product a in Comparative Example 1 (99.65114%). Furthermore, the content of maleic acid monoalkyl ester impurities in maleic acid dialkyl ester product a in Example 1 is 0.00025%, and the content of catalyst degradation products is 0.00881%, both significantly lower than in Comparative Example 1. Maleic acid monoalkyl esters easily poison and deactivate the catalyst in the downstream hydrogenation of maleic acid dialkyl ester to 1,4-butanediol. This method, by reducing the content of maleic acid monoalkyl ester impurities in the maleic acid dialkyl ester product to less than 30 ppm, greatly extends the hydrogenation catalyst life.

[0080] Compared to Comparative Example 2, by adjusting the conditions of the catalyst waste liquid concentration tower, the concentration of dialkyl maleate discharged from the bottom waste liquid b of the catalyst waste liquid concentration tower can be effectively reduced, which is beneficial to improving the yield of dialkyl maleate. Furthermore, the reduced concentration of monoalkyl maleate in high-purity dialkyl maleate f and the increased concentration of monoalkyl maleate in the bottom waste liquid b of the catalyst waste liquid concentration tower are beneficial to reducing the accumulation of monoalkyl maleate in the system and, after long-term circulation, reducing the concentration of monoalkyl maleate in product a.

[0081] Compared with Example 1 and Comparative Example 3, by setting up a catalyst waste liquid concentration tower, the dialkyl maleate and a small amount of catalyst in the high-purity dialkyl maleate f in Example 1 can be effectively recovered, with a recovery rate of 226 kg / h. In addition, the waste catalyst discharge rate is also reduced from 263 kg / h of the feed i of the catalyst waste liquid concentration tower in Comparative Example 3 to 37 kg / h of the bottom waste b of the catalyst waste liquid concentration tower in Example 1, with the waste catalyst discharge rate reduced by more than 85%, thereby significantly reducing the cost of catalyst waste liquid treatment.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A separation and emission reduction system for the production of dialkyl maleate from maleic anhydride, characterized in that, include: Reaction product purification tower, catalyst waste liquid concentration tower and vacuum unit; The reaction product purification tower is provided with an inlet for maleic anhydride esterification reaction products, a light component outlet is provided at the top of the reaction product purification tower, a maleic acid dialkyl ester product collection pipe is provided at the top of the reaction product purification tower, and a heavy component outlet is provided at the bottom of the reaction product purification tower. The heavy component outlet is connected to a catalyst waste liquid concentration tower feed pipe and a circulating material pipe, respectively. The catalyst waste liquid concentration tower is provided with a feed inlet in the middle, and the feed pipe of the catalyst waste liquid concentration tower is connected to the feed inlet of the catalyst waste liquid concentration tower. The bottom of the tower is provided with a catalyst waste liquid outlet, and the top of the catalyst waste liquid concentration tower is provided with a light component outlet. The upper part of the catalyst waste liquid concentration tower is provided with a high-purity dialkyl maleate collection pipe, and the outlet of the high-purity dialkyl maleate collection pipe is connected to the inlet of the maleic anhydride esterification reaction product. A discharge pipe is provided at the light component outlet of the reaction product purification tower, and the light component outlet of the catalyst waste liquid concentration tower is connected to the discharge pipe. A vacuum unit is also provided on the discharge pipe.

2. The separation and emission reduction system according to claim 1, characterized in that, It also includes waste liquid buffer tanks and catalyst circulation buffer tanks; The catalyst waste liquid outlet is connected to the waste liquid buffer tank; The outlet of the circulating material pipe is connected to the catalyst circulating buffer tank.

3. The separation and emission reduction system according to claim 1, characterized in that, Booster pumps are installed on the feed pipe of the catalyst waste liquid concentration tower, the outlet pipe of the high-purity dialkyl maleate, and the catalyst waste liquid pipeline.

4. The separation and emission reduction system according to claim 1, characterized in that, The reaction product purification tower and catalyst waste liquid concentration tower are packed towers or plate towers.

5. A method for separation and emission reduction in the production of dialkyl maleate from maleic anhydride, characterized in that: The catalyst waste liquid is treated using the separation and emission reduction system according to any one of claims 1-4, wherein the reflux ratio in the catalyst waste liquid concentration tower is 0.1-3.0, the operating temperature is 100-175℃, and the absolute pressure is 1-10kPa.

6. The separation and emission reduction method according to claim 5, characterized in that, The reflux ratio in the catalyst waste liquid concentration tower is 0.1-0.3, the tower top operating temperature is 90-105℃ and the absolute pressure is 1-3kPa; the tower bottom operating temperature is 150-175℃ and the absolute pressure is 5-10kPa.

7. The separation and emission reduction method according to claim 5, characterized in that, The reflux ratio in the product purification tower is 60-90, the operating temperature is 80-125℃, and the absolute pressure is 1-10kPa.

8. The separation and emission reduction method according to claim 7, characterized in that, The reflux ratio in the purification tower of the reaction product is 80-90, the operating temperature at the top of the tower is 80-95℃, and the absolute pressure is 1-3kPa; the operating temperature at the bottom of the tower is 115-125℃, and the absolute pressure is 5-10kPa.

9. The separation and emission reduction method according to claim 5, characterized in that, The maleic anhydride esterification reaction products entering the inlet of the reaction product purification tower include: 94-96% dialkyl maleate, 0.3-0.6% monoalkyl maleate, 2.1-3.0% dialkyl phthalate, 0.8-1.2% catalyst, and 0.8-1.2% other components.

10. A system for producing dialkyl maleate esters via the maleic anhydride process, characterized in that, Includes the separation and emission reduction system as described in any one of claims 1-4.

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