Separation process and separation device for separating dimethyl oxalate hydrogenation product

Abstract

The invention belongs to the technical field of chemical separation, and provides a separation process and a separation device for separating a dimethyl oxalate hydrogenation product, the separation process comprises the following steps: feeding the dimethyl oxalate hydrogenation product into a methanol removal tower for methanol removal; feeding the first mixture without methanol into an extractive distillation tower, feeding an extracting agent into the extractive distillation tower, and enabling the extracting agent to be in countercurrent contact with the mixture for extractive distillation, so as to obtain high-purity methyl glycolate at the tower top and a second mixture at the tower bottom; and finally feeding the second mixture into a solvent recovery tower to obtain a high-purity extraction agent at the tower bottom, and circulating the high-purity extraction agent to the extractive distillation tower. By adopting the separation process provided by the invention, the methyl glycolate with the purity of 99.99% can be obtained, and the process well solves the problem that the product purity is reduced because the conversion rate in the dimethyl oxalate hydrogenation stage is reduced and the concentration of the dimethyl oxalate in the hydrogenation product is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical separation, and in particular relates to a separation process and a separation device for separating dimethyl oxalate (DMO) hydrogenation products. Background Art

[0002] Methyl glycolate (MG) is an important organic synthesis intermediate. It can generate a variety of chemicals through hydrogenolysis, hydrolysis, oxidation and other reactions. It can also be used as a polymerization monomer to prepare the degradable material polyglycolic acid (PGA). Therefore, it is of great significance to control white pollution and promote green sustainable development. As a polymerization precursor of PGA, the purity of MG has a great influence on the quality of PGA, and the purity is generally required to reach 99.9%.

[0003] In recent years, the process of preparing MG by selective hydrogenation of DMO from coal-based syngas has attracted wide attention due to its simple process, high atomic utilization rate, and easy low-cost large-scale production. This process can achieve green, clean and efficient utilization of coal resources. However, due to the complexity of the hydrogenation reaction process, in addition to the target product MG, the outlet logistics of the hydrogenation reactor also contains by-products such as DMO, ethylene glycol and methanol. Therefore, a reasonable separation process must be designed for the DMO hydrogenation product to obtain high-purity MG.

[0004] The difficulty of the multi-component separation process of hydrogenation products lies in the complete separation of DMO and MG. According to the DMO-MG gas-liquid phase equilibrium data estimated by Aspen plus software, DMO and MG will form a minimum azeotrope at normal pressure, with an azeotropic temperature of 150.61°C, in which the MG content is 96.36wt% and the DMO content is 3.64wt%; at the same time, even under the condition of reduced pressure to 10kPa, the relative volatility of DMO and MG is very small. Therefore, the use of ordinary distillation methods to separate and purify hydrogenation products is not only due to the low relative volatility of the two, the high number of theoretical distillation plates required to achieve certain separation requirements, and the high separation energy consumption, but also due to the formation of azeotropes, it is difficult to obtain high-purity MG.

[0005] Patent CN117945903A discloses a process for preparing MG by hydrogenation of DMO. The patent document also points out the problem of separation and purification of MG products, that is, when the purity of MG reaches 98%, it is difficult to completely separate the unreacted DMO from MG. In response to this problem, the technical solution connects two reactors in series and accurately controls the reactor temperature to ensure that the DMO conversion rate is above 99.7%, the content of DMO in the outlet product of the hydrogenation reactor is low enough, and the mass ratio of MG to DMO is 161:1, and then the products are separated by ordinary distillation. That is, this method is to improve the reaction stage instead of the subsequent separation stage. Therefore, the invention requires extremely strict control of the reactor temperature. Once the temperature deviates from the preferred range, or the catalyst decreases after the reaction device has been running for a period of time, it may lead to insufficient DMO conversion or decreased MG selectivity. When the content of DMO in the hydrogenation product increases, the patented technology is difficult to ensure the acquisition of high-purity MG.

[0006] Patent CN109134258B discloses a product separation process for DMO hydrogenation to MG. The invention compares three separation sequences, namely sequential separation, methanol priority separation and MG priority separation, for the working condition where the outlet composition of the hydrogenation reactor is: MG 55%, water 1%, DMO 2%, ethylene glycol 12% and methanol 30%, optimizes the separation sequence, and proposes a better general distillation separation process. However, the azeotropic phenomenon of MG and DMO is not considered in this technology, so it is difficult to ensure the refining and purification of MG.

[0007] Patent CN116535315A discloses a vacuum continuous distillation process for hydrogenation reaction materials composed of MG 82-88wt%, methanol 3-8wt%, DMO 0.2-0.6wt%, ethylene glycol 3-6wt%, and other impurities 0.5-1.5wt%, using a deweighting tower, a preheater and a product tower to separate MG. However, for the DMO hydrogenation to MG reaction process, even if the DMO conversion rate is 100% and the MG selectivity is 100%, the MG content is only 73%; that is, according to the molar ratio of MG and methanol generated in the hydrogenation product of 1:1 without any side reaction, the MG content in the hydrogenation product material is significantly less than the given range of 82-88wt% in the patent; therefore, the MG content in the hydrogenation reaction material in the application document is significantly higher, and in the actual industrial production process, the MG content is much lower than this content. Therefore, it is difficult for this patent technology to provide a solution for the actual industrial separation process.

[0008] In summary, the existing separation schemes are mostly aimed at very high hydrogenation reaction conversion rates, close to complete conversion, and very low DMO content in the hydrogenation products, and all of them are designed through ordinary distillation separation processes to obtain high-purity MG. However, since the industrial technology of DMO hydrogenation to prepare MG has just begun the industrialization process, catalyst development is not yet mature, and there are still problems such as low stability, short life, and easy deactivation in industrial applications. As the operation of the device increases, the catalyst performance gradually decreases, and the DMO content in the hydrogenation product at the outlet of the hydrogenation reactor continues to rise. Due to the azeotropic phenomenon of MG and DMO, conventional distillation separation technology cannot effectively achieve complete separation of the two, resulting in the inability to obtain high-purity MG to meet the subsequent application requirements as a polyester monomer. Therefore, it is urgent to propose an effective separation method for hydrogenation products containing a certain amount of DMO to ensure the acquisition of high-purity MG products and the development of the subsequent coal-based biodegradable materials industry chain. Summary of the invention

[0009] In view of the deficiencies of the prior art, the present invention provides a separation process and a separation device for separating DMO hydrogenation products, so as to overcome the difficulty of separating the azeotropic mixture formed by the incompletely reacted DMO and MG in the DMO to MG reaction, and obtain high-purity MG.

[0010] To achieve the above object, the technical solution of the present invention is as follows:

[0011] A separation process for separating DMO hydrogenation products comprises the following steps:

[0012] (1) The hydrogenation product of DMO to prepare MG is first sent to a methanol removal tower to remove methanol, thereby obtaining a first mixture from which methanol has been removed;

[0013] (2) feeding the first mixture into an extractive distillation tower, and simultaneously feeding an extractant into the extractive distillation tower, the extractant and the mixture are in countercurrent contact, and extractive distillation is performed, high-purity MG is obtained at the top of the tower, and a second mixture is obtained at the bottom of the tower;

[0014] (3) The second mixture is sent to a solvent recovery tower, and a high-purity extractant is obtained at the bottom of the tower and circulated to the extractive distillation tower.

[0015] The present invention is further configured such that, in step (1), the number of theoretical plates of the methanol removal tower is 12-20, the reflux ratio is 0.05-3.0, and the operating pressure is 0.2-0.3 bar.

[0016] The present invention is further configured such that, in step (2), the number of theoretical plates of the extractive distillation tower is 20-60, the reflux ratio is 1.0-3.0, and the operating pressure is 0.1-0.3 bar.

[0017] The present invention is further configured such that, in step (2), the extractant is selected from di(2-ethylhexyl) phthalate and / or dihexyl phthalate.

[0018] The present invention is further configured such that, in step (2), the molar ratio of the extractant to the MG-DMO azeotrope in the first mixture is (0.4-1.2): 1. The molar amount of the MG-DMO azeotrope is the sum of the molar amounts of MG and DMO.

[0019] The present invention is further configured such that, in step (2), the molar ratio of the extractant to the MG-DMO azeotrope is (0.6-1.14):1.

[0020] The present invention is further configured that, in step (1), the composition of the hydrogenation product, in terms of mass percentage, includes the following components: MG 12.0-51.0%, DMO 0.2-3.9%, ethylene glycol 2.0-4.0%, and methanol 41.0-85.7%.

[0021] The present invention is further configured such that, in step (1), in the composition of the hydrogenation product, the mass ratio of MG to DMO is (13-60):1.

[0022] The present invention is further configured such that, in step (3), the number of theoretical plates of the solvent recovery tower is 5-25, the reflux ratio is 0.05-0.5, and the operating pressure is 0.1-0.3 bar.

[0023] The present invention also provides a separation device for implementing the above separation process, comprising a methanol removal tower, an extractive distillation tower and a solvent recovery tower connected in sequence; wherein:

[0024] The top and bottom of the demethanolating tower are respectively provided with a methanol outlet and a first mixture outlet, the top and bottom of the extractive distillation tower are respectively provided with a MG outlet and a second mixture outlet, the extractant feed inlet and the first mixture feed inlet are respectively opened in the upper part and the middle and lower part of the extractive distillation tower, and the first mixture outlet pipeline is connected to the first mixture feed inlet; the bottom of the solvent recovery tower is provided with an extractant outlet, and the extractant outlet is connected to the extractant feed inlet.

[0025] The present invention is further configured such that the methanol removal tower, the extractive distillation tower and the solvent recovery tower are all selected from plate towers or packed towers.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The separation process provided by the present invention is used for subsequent separation and purification of the hydrogenation product of DMO hydrogenation to prepare MG, thereby obtaining high-purity methyl glycolate with a purity of 99.99%.

[0028] (2) The separation process of the present invention can well solve the problem of decreased product purity due to decreased conversion rate in the DMO hydrogenation stage and increased DMO concentration at the reactor outlet. The separation process and device of the present invention can still achieve efficient separation of the target product and obtain high-purity MG.

[0029] (3) The separation process and separation device of the present invention separate high-purity MG by the extractive distillation tower, and the remaining extractant does not form an azeotrope with DMO and ethylene glycol, and can be recovered and recycled by conventional distillation, which significantly simplifies the process flow, reduces environmental impact, reduces costs, and realizes green and sustainable production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the separation device described in the present invention.

[0031] Figure 2 A schematic diagram of a conventional separation device in the prior art

[0032] Among them, 10, methanol removal tower, 11, methanol outlet, 12, first mixture outlet, 20, extractive distillation tower, 21, methyl glycolate outlet, 22, second mixture outlet, 23, extractant feed inlet, 24, first mixture feed inlet, 30, solvent recovery tower, 31, extractant outlet, 40, ordinary distillation tower, 41, methyl glycolate outlet of ordinary distillation tower, 42, bottom outlet of ordinary distillation tower. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0034] A separation process for separating DMO hydrogenation products comprises the following steps:

[0035] (1) The hydrogenation product of DMO to prepare MG is first sent to a methanol removal tower to remove methanol, thereby obtaining a first mixture from which methanol has been removed;

[0036] (2) feeding the first mixture into an extractive distillation tower, and simultaneously feeding an extractant into the extractive distillation tower, the extractant and the mixture are in countercurrent contact, and extractive distillation is performed, high-purity MG is obtained at the top of the tower, and a second mixture is obtained at the bottom of the tower;

[0037] (3) The second mixture is sent to a solvent recovery tower, and a high-purity extractant is obtained at the bottom of the tower and circulated to the extractive distillation tower.

[0038] In one embodiment of the present invention, in step (1), the number of theoretical plates of the demethanolation tower is 12-20, the reflux ratio is 0.05-3.0, and the operating pressure is 0.2-0.3 bar.

[0039] In one embodiment of the present invention, in step (2), the number of theoretical plates of the extractive distillation tower is 20-60, the reflux ratio is 1.0-3.0, and the operating pressure is 0.1-0.3 bar.

[0040] In one embodiment of the present invention, in step (2), the extractant is selected from di(2-ethylhexyl) phthalate and / or dihexyl phthalate.

[0041] In one embodiment of the present invention, in step (2), the molar ratio of the extractant to the MG-DMO azeotrope in the first mixture is 0.4-1.2:1; preferably, the molar ratio of the extractant to the MG-DMO azeotrope in the first mixture is 0.6-1.14:1, for example, the molar ratio is 0.6:1, 0.64:1, 0.68:1, 0.75:1, 0.80:1, 0.85:1, 0.9:1 or 1:1.

[0042] In one embodiment of the present invention, the extractant enters the extractive distillation tower through 1 / 10 to 1 / 5 theoretical plates of the total number of plates of the extractive distillation tower.

[0043] In one embodiment of the present invention, in step (1), the composition of the DMO hydrogenation product, in terms of mass percentage, includes the following components: MG 12.0-51.0%, DMO 0.2-3.9%, ethylene glycol 2.0-4.0%, and methanol 41.0-85.7%.

[0044] In one embodiment of the present invention, in step (1), the mass ratio of MG to DMO in the composition of the DMO hydrogenation product is (13-60):1.

[0045] In one embodiment of the present invention, in step (3), the number of theoretical plates of the solvent recovery tower is 5-25, the reflux ratio is 0.05-0.5, and the operating pressure is 0.1-0.3 bar.

[0046] In one embodiment of the present invention, the top temperature of the methanol removal tower is 25-40°C, and the bottom temperature is 100-120°C; the top temperature of the extractive distillation tower is 80-115°C, and the bottom temperature is 150-185°C; the top temperature of the solvent recovery tower is 115-155°C, and the bottom temperature is 280-340°C.

[0047] The present invention also provides a separation device for implementing the above separation process, such as Figure 1 As shown, it includes a methanol removal tower 10, an extractive distillation tower 20 and a solvent recovery tower 30 connected in sequence; wherein,

[0048] The top and bottom of the demethanolation tower 10 are respectively provided with a methanol outlet 11 and a first mixture outlet 12 after demethanolation; the extractive distillation tower 20 is used to separate and obtain high-purity MG; the top and bottom of the extractive distillation tower 20 are respectively provided with a MG discharge port 21 and a second mixture outlet 22; an extractant feed port 23 and a first mixture feed port 24 are respectively opened in the upper part and the middle and lower part of the extractive distillation tower 20; the first mixture outlet 12 is connected to the first mixture feed port 24 through a pipeline; the bottom of the solvent recovery tower 30 is provided with an extractant outlet 31, and the extractant outlet 31 is connected to the extractant feed port 23.

[0049] The present invention is further configured such that the methanol removal tower 10, the extractive distillation tower 20 and the solvent recovery tower 30 are all selected from plate towers or packed towers.

[0050] The technology of the present invention is further described in detail below in conjunction with specific examples. The methanol removal tower, extractive distillation tower and solvent recovery tower described in the following specific examples are all plate towers.

[0051] Example 1

[0052] A separation process for separating DMO hydrogenation products, using Figure 1 The separation device shown comprises the following steps:

[0053] (1) A DMO hydrogenation product, a dimethyl oxalate-methyl glycolate-ethylene glycol-methanol mixed liquid, with a feed temperature of 25°C, a flow rate of 1000 kg / h, and a pressure of 1 bar, is transported from the 10th theoretical plate to a de-methanolation tower 10. The mass percentage of each component in the mixed liquid is: 85.7% methanol, 12.0% methyl glycolate, 2.1% ethylene glycol, 0.2% DMO, and a mass ratio of MG to DMO of 60:1. The number of theoretical plates of the de-methanolation tower 10 is 20, the operating pressure is 0.3 bar, the reflux ratio is 0.05, 99.9% methanol is obtained at the top of the tower, the output is 857 kg / h, and the temperature is 36°C; a first mixture of dimethyl oxalate-methyl glycolate-ethylene glycol mixture is obtained at the bottom of the tower, the output is 143 kg / h, and the temperature is 118°C.

[0054] (2) The dimethyl oxalate-methyl glycolate-ethylene glycol mixture obtained at the bottom of the demethanol tower 10 in step (1) is continuously fed into the extractive distillation tower 20 via the 10th theoretical plate, the extractive distillation tower 20 has 20 theoretical plates, an operating pressure of 0.1 bar, and a reflux ratio of 3.0; the extractant di(2-ethylhexyl) phthalate with a flow rate of 600 kg / h enters the extractive distillation tower 20 from the second theoretical plate, the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 1.14:1, the tower top temperature is 84° C., MG with a purity of 99.996% is obtained at the tower top, the DMO content is ≤0.01%, and the recovery rate is 119 kg / h; a second mixture of dimethyl oxalate-ethylene glycol and extractant is obtained at the bottom of the tower, and the temperature is 154° C.

[0055] (3) The dimethyl oxalate-ethylene glycol and extractant mixture obtained at the bottom of the extractive distillation tower 20 is continuously fed to the solvent recovery tower 30 from the 6th theoretical plate. The number of theoretical plates of the solvent recovery tower 30 is 10, the operating pressure is 0.1 bar, and the reflux ratio is 0.1. The dimethyl oxalate-ethylene glycol mixture is obtained at the top of the solvent recovery tower 30, and the temperature is 128°C; the extractant di(2-ethylhexyl) phthalate with a purity of more than 99.99% is extracted from the bottom of the tower, the extraction amount is 599kg / h, and the temperature is 296°C. The bottom outlet pipe of the solvent recovery tower 30 is connected to the extractant feed port 23 of the extractive distillation tower 20, and the high-purity extractant recovered by the solvent recovery tower 30 is recycled. The feed composition of the de-methanol tower 10 and the material composition at the top of the extractive distillation tower 20 and the recovery rate of MG in this embodiment are recorded in Table 1.

[0056] Example 2

[0057] A separation process for separating DMO hydrogenation products, using Figure 1 The separation device shown comprises the following steps:

[0058] (1) A dimethyl oxalate-methyl glycolate-ethylene glycol-methanol mixed liquid with a feed temperature of 25°C, a flow rate of 1000 kg / h, and a pressure of 1 bar is transported from the fourth theoretical plate to a de-methanolation tower 10. The mass percentage of each component in the mixed liquid is: methanol 71.4%, MG 24.1%, ethylene glycol 3.7%, DMO 0.8%, and the mass ratio of MG to DMO is 30:1. The de-methanolation tower 10 has 12 theoretical plates, an operating pressure of 0.2 bar, a reflux ratio of 3.0, and 99.9% methanol is obtained at the top of the tower, with an output of 714 kg / h and a temperature of 28°C; a first mixture of dimethyl oxalate / methyl glycolate-ethylene glycol mixture is obtained at the bottom of the tower at a temperature of 106°C.

[0059] (2) The dimethyl oxalate-methyl glycolate-ethylene glycol mixture obtained at the bottom of the de-methanol tower 10 is continuously fed to the extractive distillation tower 20 via the 15th theoretical plate, wherein the extractive distillation tower 20 has 30 theoretical plates, an operating pressure of 0.3 bar, and a reflux ratio of 2.0; the extractant di(2-ethylhexyl) phthalate with a flow rate of 800 kg / h enters the extractive distillation tower 20 from the 4th theoretical plate, and the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 0.75:1. MG of 99.991% is obtained at the top of the extractive distillation tower 20, with a DMO content of ≤0.01%, an output of 240 kg / h, and a temperature of 112° C.; a mixture of dimethyl oxalate-ethylene glycol and the extractant is obtained at the bottom of the tower, and the temperature is 180° C.

[0060] (3) The dimethyl oxalate-ethylene glycol and extractant mixture obtained at the bottom of the extractive distillation tower in step (2) is continuously fed to the solvent recovery tower 30 from the second theoretical plate. The number of theoretical plates of the solvent recovery tower is 5, the operating pressure is 0.3 bar, and the reflux ratio is 0.5. The dimethyl oxalate-ethylene glycol mixture is obtained at the top of the solvent recovery tower 30 at a temperature of 153° C. The extractant di(2-ethylhexyl) phthalate with a purity of more than 99.99% is extracted from the bottom of the tower, the extraction amount is 799 kg / h, and the temperature is 333° C. The bottom outlet pipe of the solvent recovery tower 30 is connected to the extractant feed port 23 of the extractive distillation tower 20, and the high-purity extractant recovered by the solvent recovery tower 30 is recycled. The feed composition of the demethanol tower 10 and the material composition at the top of the extractive distillation tower 20 and the recovery rate of MG in this embodiment are recorded in Table 1.

[0061] Example 3

[0062] A separation process for separating DMO hydrogenation products, using Figure 1 The separation device shown comprises the following steps:

[0063] (1) A dimethyl oxalate-methyl glycolate-ethylene glycol-methanol mixed liquid with a feed temperature of 25° C., a flow rate of 1000 kg / h, and a pressure of 1 bar is transported from the seventh theoretical plate to a de-methanolation tower 10. The mass percentage of each component in the mixed liquid is: 56.4% methanol, 37.8% methyl glycolate, 3.5% ethylene glycol, 2.3% DMO, and a mass ratio of MG to DMO of 16:1. The number of theoretical plates of the de-methanolation tower 10 is 15, the operating pressure is 0.3 bar, the reflux ratio is 2.0, 99.9% methanol is obtained at the top of the tower, the output is 564 kg / h, and the temperature is 36° C. A dimethyl oxalate / methyl glycolate-ethylene glycol mixture is obtained at the bottom of the tower at a temperature of 115° C.

[0064] (2) The dimethyl oxalate-methyl glycolate-ethylene glycol mixture obtained at the bottom of the de-methanol tower in step (1) is continuously fed into an extractive distillation tower 20 via the 20th theoretical plate, wherein the extractive distillation tower has 40 theoretical plates, an operating pressure of 0.2 bar, and a reflux ratio of 1.5; dihexyl phthalate, an extractant, with a flow rate of 1000 kg / h, enters the extractive distillation tower from the 8th theoretical plate, and the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 0.68:1; 99.992% MG is obtained at the top of the tower, the DMO content is ≤0.01%, the recovery rate is 377 kg / h, the temperature is 101° C., and a mixture of dimethyl oxalate-ethylene glycol and the extractant is obtained at the bottom of the tower, and the temperature is 168° C.

[0065] (3) The dimethyl oxalate-ethylene glycol and extractant mixture obtained at the bottom of the extractive distillation tower in step (2) is continuously fed to the solvent recovery tower 30 from the 10th theoretical plate. The number of theoretical plates of the solvent recovery tower is 15, the operating pressure is 0.2 bar, and the reflux ratio is 0.3. The dimethyl oxalate-ethylene glycol mixture is obtained at the top of the solvent recovery tower at a temperature of 136° C.; the extractant dihexyl phthalate with a purity of more than 99.99% is extracted from the bottom of the tower, the extraction amount is 999 kg / h, and the temperature is 303° C. The bottom outlet pipe of the solvent recovery tower 30 is connected to the extractant feed port 23 of the extractive distillation tower 20, and the high-purity extractant recovered by the solvent recovery tower 30 is recycled. The feed composition of the de-methanol tower 10 and the material composition of the top of the extractive distillation tower 20 and the recovery rate of MG in this embodiment are recorded in Table 1.

[0066] Example 4

[0067] A separation process for separating DMO hydrogenation products, using Figure 1 The separation device shown comprises the following steps:

[0068] (1) A dimethyl oxalate-methyl glycolate-ethylene glycol-methanol mixed liquid with a feed temperature of 25°C, a flow rate of 1000 kg / h and a pressure of 1 bar is transported from the 12th theoretical plate to a de-methanolation tower 10. The mass percentage of each component in the mixed liquid is: 41.5% methanol, 50.7% methyl glycolate, 3.9% ethylene glycol, 3.9% DMO, and a mass ratio of MG to DMO of 13:1. The number of theoretical plates of the de-methanolation tower 10 is 17, the operating pressure is 0.3 bar, the reflux ratio is 1.0, and 99.9% methanol is obtained at the top of the tower, with an output of 415 kg / h, and a temperature of 36°C. A dimethyl oxalate-methyl glycolate-ethylene glycol mixture is obtained at the bottom of the tower at a temperature of 114°C.

[0069] (2) The dimethyl oxalate-methyl glycolate-ethylene glycol mixture obtained at the bottom of the de-methanol tower in step (1) is continuously fed into an extractive distillation tower 20 via the 40th theoretical plate, wherein the extractive distillation tower has 60 theoretical plates, an operating pressure of 0.1 bar, and a reflux ratio of 1.0; dihexyl phthalate, an extractant, with a flow rate of 1200 kg / h, enters the extractive distillation tower from the 10th theoretical plate, and the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 0.64:1, and 99.999% MG is obtained at the top of the tower, with a DMO content of ≤0.01%, an output of 506 kg / h, and a temperature of 101° C.; a mixture of dimethyl oxalate-ethylene glycol and the extractant is obtained at the bottom of the tower, and the temperature is 165° C.

[0070] (3) The dimethyl oxalate-ethylene glycol and extractant mixture obtained at the bottom of the extractive distillation tower in step (2) is continuously fed to the solvent recovery tower 30 from the 12th theoretical plate. The number of theoretical plates of the solvent recovery tower is 25, the operating pressure is 0.1 bar, and the reflux ratio is 0.05. The dimethyl oxalate-ethylene glycol mixture is obtained at the top of the solvent recovery tower at a temperature of 116°C; the extractant dihexyl phthalate with a purity of more than 99.99% is extracted from the bottom of the tower, the extraction amount is 1199 kg / h, and the temperature is 280°C. The bottom outlet pipe of the solvent recovery tower 30 is connected to the extractant feed port 23 of the extractive distillation tower 20, and the high-purity extractant recovered by the solvent recovery tower 30 is recycled. The feed composition of the de-methanol tower 10 and the material composition of the top of the extractive distillation tower 20 and the recovery rate of MG in this embodiment are recorded in Table 1.

[0071] Comparative Examples 1 to 4

[0072] Use Figure 2 The separation device of the prior art shown includes a de-methanolation tower 10 and a common distillation tower 40 connected in sequence. The top of the common distillation tower is a MG discharge port 41, and the bottom outlet 42 is used to extract the mixture after MG is separated. Compared with the extractive distillation tower, no extractant is added to the common distillation tower, and there is no solvent recovery tower.

[0073] Comparative Example 1

[0074] Referring to Example 1, the difference from Example 1 is that a common distillation tower 40 is used in step (2). Compared with the extractive distillation tower 20, the common distillation tower 40 does not have the addition of an extractant and a solvent recovery tower, and the other operating parameters are the same as those of Example 1. The output of the methyl glycolate outlet 41 at the top of the common distillation tower is 119 kg / h, the top temperature is 84° C., the MG purity is 98.38%, and the DMO content is 1.62%. The feed composition of the demethanol tower, the material composition at the top of the common distillation tower, and the MG recovery rate in this comparative example are recorded in Table 1.

[0075] Comparative Example 2

[0076] Referring to Example 2, the difference from Example 2 is that: the common distillation tower 40, compared with the extractive distillation tower 20, does not have the addition of an extractant, and does not have a solvent recovery tower, and other operating parameters are the same as in Example 2. The top extraction rate is 240 kg / h, the top temperature is 112°C, the MG purity is 96.76%, and the DMO content is 3.24%. The feed composition of the demethanol tower and the material composition of the top of the common distillation tower and the MG recovery rate in this comparative example are recorded in Table 1.

[0077] Comparative Example 3

[0078] Referring to Example 3, the difference from Example 3 is that a common distillation tower is used in step (2), that is, no extractant is added to the extractive distillation tower 20, and no solvent recovery tower is used, and other operating parameters are the same as those in Example 3. The top extraction rate is 377 kg / h, the top temperature is 101° C., the MG purity is 96.14%, and the DMO content is 3.86%. The feed composition of the demethanolation tower and the material composition of the top of the common distillation tower and the MG recovery rate in this comparative example are recorded in Table 1.

[0079] Comparative Example 4

[0080] Referring to Example 4, the difference from Example 4 is that a common distillation tower is used in step (2), that is, no extractant is added to the extractive distillation tower 20, and no solvent recovery tower is used, and other operating parameters are the same as those of Example 4. The top extraction rate is 506 kg / h, the top temperature is 101° C., the MG purity is 94.88%, and the DMO content is 5.12%. The feed composition of the demethanol tower, the material composition of the top of the extractive distillation tower, and the MG recovery rate in this comparative example are recorded in Table 1.

[0081] Comparative Example 5

[0082] Referring to Example 2, the difference from Example 2 is that the extractant added in step (2) is N-methylpyrrolidone, the flow rate is 203kg / h, the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 0.75:1, 94.76% MG is obtained at the top of the tower, the DMO content is 3.33%, the recovery rate is 240kg / h, and the temperature is 112°C. In step (3), the extractant N-methylpyrrolidone is recovered. The feed composition of the demethanol tower and the material composition of the top of the extractive distillation tower and the recovery rate of MG in this comparative example are recorded in Table 1.

[0083] Comparative Example 6

[0084] Referring to Example 2, the difference from Example 2 is that the extractant added in step (2) is benzyl alcohol, the flow rate is 221 kg / h, the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 0.75:1, 97.09% MG is obtained at the top of the tower, the DMO content is 2.91%, the extraction amount is 240 kg / h, and the temperature is 112°C. In step (3), the extractant benzyl alcohol is recovered. The feed composition of the de-methanol tower, the material composition of the top of the extractive distillation tower, and the recovery rate of MG in this comparative example are recorded in Table 1.

[0085] Comparative Example 7

[0086] Referring to Example 2, the difference from Example 2 is that the extractant added in step (2) is sulfolane, the flow rate is 246kg / h, the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 0.75:1, 97.10% MG is obtained at the top of the tower, the DMO content is 2.90%, the extraction amount is 240kg / h, and the temperature is 112°C. In step (3), the extractant sulfolane is recovered. The feed composition of the demethanol tower and the material composition of the top of the extractive distillation tower and the recovery rate of MG in this comparative example are recorded in Table 1.

[0087] Comparative Example 8

[0088] With reference to Example 2, the difference from Example 2 is that the extractant added in step (2) is dimethyl phthalate, the flow rate is 397kg / h, the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 0.75:1, 98.26% of MG is obtained at the top of the tower, the DMO content is 1.74%, the extraction amount is 240kg / h, and the temperature is 112°C. In step (3), the extractant dimethyl phthalate is recovered. The feed composition of the demethanol tower and the material composition of the extractive distillation tower top and the recovery rate of MG in this comparative example are recorded in Table 1.

[0089] Comparative Example 9

[0090] Refer to Example 2, the difference is that the flow rate of adding the extractant di(2-ethylhexyl)phthalate in the second step is 300kg / h, the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 0.3:1, 99.80% MG is obtained at the top of the tower, the DMO content is 0.20%, and the temperature is 112°C. In the third step, the solvent recovery tower bottom circulation flow rate is 299kg / h, and the temperature is 333°C. The feed composition and the material composition of the extractive distillation tower top and the recovery rate of MG in this comparative example are recorded in Table 1.

[0091] Table 1 Feed composition, distillation tower top composition and MG recovery rate of each embodiment and comparative example

[0092]

[0093] It can be seen from the results in Table 1 that the separation process provided by the present invention exhibits excellent separation effect for the azeotropic system of MG and DMO; by designing the conditions for the separation process, high-purity MG with a purity of ≥99.99% is obtained, and the DMO content in the MG product is reduced to ≤0.01%. In addition, the separation process is applicable to a wider range of composition of the outlet material of the DMO hydrogenation reactor, and has lower requirements for the hydrogenation reaction conditions, which can well solve the problem of decreased product purity due to decreased conversion rate in the DMO hydrogenation stage and increased DMO concentration in the hydrogenation product.

[0094] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A separation process for separating dimethyl oxalate hydrogenation products, characterized in that: The steps include: (1) sending the hydrogenation product of dimethyl oxalate to prepare methyl glycolate to a methanol removal tower to remove methanol, thereby obtaining a first mixture from which methanol has been removed; (2) feeding the first mixture into an extractive distillation tower, and simultaneously feeding an extractant into the extractive distillation tower, the extractant and the mixture are in countercurrent contact, and extractive distillation is performed, high-purity methyl glycolate is obtained at the top of the tower, and a second mixture is obtained at the bottom of the tower; (3) The second mixture is sent to a solvent recovery tower, and a high-purity extractant is obtained at the bottom of the tower and circulated to the extractive distillation tower.

2. A separation process for separating dimethyl oxalate hydrogenation products according to claim 1, characterized in that: In step (1), the number of theoretical plates of the demethanol tower is 12-20, the reflux ratio is 0.05-3.0, and the operating pressure is 0.2-0.3 bar.

3. A separation process for separating dimethyl oxalate hydrogenation products according to claim 1, characterized in that: In step (2), the number of theoretical plates of the extractive distillation tower is 20-60, the reflux ratio is 1.0-3.0, and the operating pressure is 0.1-0.3 bar.

4. A separation process for separating dimethyl oxalate hydrogenation products according to claim 1, characterized in that: In step (2), the extractant is selected from di(2-ethylhexyl) phthalate and / or dihexyl phthalate.

5. A separation process for separating dimethyl oxalate hydrogenation products according to claim 1, characterized in that: In step (2), the molar ratio of the extractant to the methyl glycolate-dimethyl oxalate azeotrope in the first mixture is (0.4-1.2):

1.

6. A separation process for separating dimethyl oxalate hydrogenation products according to claim 1, characterized in that: In step (1), the composition of the hydrogenation product, in terms of mass percentage, includes the following components: 12.0-51.0% of methyl glycolate, 0.2-3.9% of dimethyl oxalate, 2.0-4.0% of ethylene glycol, and 41.0-85.7% of methanol.

7. A separation process for separating dimethyl oxalate hydrogenation products according to claim 1, characterized in that: In step (1), in the composition of the hydrogenation product, the mass ratio of methyl glycolate to dimethyl oxalate is (13-60):

1.

8. A separation process for separating dimethyl oxalate hydrogenation products according to claim 1, characterized in that: In step (3), the number of theoretical plates of the solvent recovery tower is 5-25, the reflux ratio is 0.05-0.5, and the operating pressure is 0.1-0.3 bar.

9. A separation device for implementing the separation process according to any one of claims 1 to 8, characterized in that: It includes a methanol removal tower, an extractive distillation tower and a solvent recovery tower connected in sequence; wherein, The top and bottom of the demethanol tower are respectively provided with a methanol outlet and a first mixture outlet, the top and bottom of the extractive distillation tower are respectively provided with a methyl glycolate outlet and a second mixture outlet, the extractant feed inlet and the first mixture feed inlet are respectively opened in the upper part and the middle and lower part of the extractive distillation tower, and the first mixture outlet pipeline is connected to the first mixture feed inlet; the bottom of the solvent recovery tower is provided with an extractant outlet, and the extractant outlet is connected to the extractant feed inlet.

10. The separation device according to claim 9, characterized in that The methanol removal tower, the extractive distillation tower and the solvent recovery tower are all selected from plate towers or packed towers.

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