A separation process and separation device for separating dimethyl oxalate hydrogenation products

Abstract

The present invention belongs to the field of chemical separation technology and provides a separation process and separation device for separating dimethyl oxalate hydrogenation products. The separation process comprises the following steps: first, the dimethyl oxalate hydrogenation product is fed into a methanol removal tower for methanol removal; then, a first mixture from which methanol has been removed is fed into an extractive distillation tower, and an extractant is simultaneously fed into the extractive distillation tower. The extractant and the mixture are in countercurrent contact for extractive distillation, resulting in high-purity methyl glycolate at the top of the tower and a second mixture at the bottom of the tower; finally, the second mixture is fed into a solvent recovery tower, and a high-purity extractant is obtained at the bottom of the tower and circulated to the extractive distillation tower. Using the separation process of the present invention, methyl glycolate with a purity of up to 99.99% can be obtained. The process effectively solves the problem of reduced product purity caused by decreased conversion rate in the dimethyl oxalate hydrogenation stage and increased dimethyl oxalate concentration in the hydrogenation product.

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 be used to produce a variety of chemicals through reactions such as hydrogenolysis, hydrolysis, and oxidation. It can also be used as a polymerization monomer to prepare the biodegradable material polyglycolic acid (PGA). Therefore, it is of great significance in combating white pollution and promoting green and sustainable development. As a polymer precursor for PGA, the purity of MG significantly impacts its quality, generally requiring a purity of 99.9%.

[0003] In recent years, the selective hydrogenation of coal-based syngas to MG via DMO has attracted widespread attention due to its simplicity, high atomic utilization, and ease of low-cost, large-scale production. Furthermore, this process can achieve green, clean, and efficient utilization of coal resources. However, due to the complexity of the hydrogenation process, the hydrogenation reactor outlet stream contains byproducts such as DMO, ethylene glycol, and methanol in addition to the target product MG. Therefore, a rationally designed separation process for the DMO hydrogenation product is essential to obtain high-purity MG.

[0004] The difficulty in the multi-component separation process of hydrogenated products lies in the complete separation of DMO and MG. Estimation of the DMO-MG gas-liquid equilibrium data using Aspen Plus software shows that DMO and MG form a minimum azeotrope at atmospheric pressure, with an azeotropic temperature of 150.61°C and a MG content of 96.36wt% and a DMO content of 3.64wt%. Furthermore, even under reduced pressure to 10kPa, the relative volatility of DMO and MG is very low. Therefore, conventional distillation is used to separate and purify the hydrogenated products. This is not only due to the low relative volatility of the two, resulting in a high number of theoretical distillation plates required to achieve the required separation, and high separation energy consumption, but also due to the formation of the azeotrope, it is difficult to obtain high-purity MG.

[0005] Patent CN117945903A discloses a process for producing MG by hydrogenating DMO. The patent document also addresses the issue of MG product separation and purification: once MG purity reaches 98%, unreacted DMO is difficult to completely separate from the MG. To address this issue, the proposed technical solution connects two reactors in series and precisely controls the reactor temperature to ensure a DMO conversion rate above 99.7%. The DMO content in the hydrogenation reactor outlet product is sufficiently low, with a mass ratio of MG to DMO of 161:1. The products are then separated by conventional distillation. This method, in other words, improves the reaction stage rather than the subsequent separation stage. Therefore, the invention requires extremely strict control of the reactor temperature. Any deviation from the optimal temperature range, or degradation of the catalyst after a period of operation, can result in insufficient DMO conversion or decreased MG selectivity. Furthermore, if the DMO content in the hydrogenation product increases, the patented technology cannot guarantee the production of high-purity MG.

[0006] Patent CN109134258B discloses a product separation process for producing MG from DMO hydrogenation. This invention compares three separation sequences—sequential separation, methanol-preferential separation, and MG-preferential separation—for a hydrogenation reactor outlet composition of 55% MG, 1% water, 2% DMO, 12% ethylene glycol, and 30% methanol. The process optimizes the separation sequence and proposes a superior conventional distillation separation process. However, this technology does not account for the azeotropic effect of MG and DMO, making it difficult to guarantee the purification of MG.

[0007] Patent CN116535315A discloses a vacuum continuous distillation process for a hydrogenation reaction material composed of 82-88 wt% MG, 3-8 wt% methanol, 0.2-0.6 wt% DMO, 3-6 wt% ethylene glycol, and 0.5-1.5 wt% other impurities. The process uses a de-weighting column, a preheater, and a product column to separate the MG. However, for the DMO hydrogenation to MG process, even with a 100% DMO conversion and 100% MG selectivity, the MG content is only 73%. In other words, assuming a 1:1 molar ratio of MG to methanol in the hydrogenation product, assuming no side reactions, the MG content in the hydrogenation product is significantly lower than the 82-88 wt% range specified in the patent. Therefore, the MG content in the hydrogenation reaction material is significantly higher in the patent document than in actual industrial production processes, where it is far lower. Therefore, the patented technology is unlikely to provide a solution for practical industrial separation processes.

[0008] In summary, the existing separation schemes are mostly aimed at hydrogenation reactions with very high conversion rates, close to complete conversion, and very low DMO content in the hydrogenation products. All of them are designed through ordinary distillation separation processes to obtain high-purity MG. However, since the industrial technology for preparing MG by hydrogenation of DMO has just begun the industrialization process, catalyst development is still immature, 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 performance of the catalyst 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 to ensure the development of the subsequent coal-based biodegradable materials industry chain. Summary of the Invention

[0009] In response to the shortcomings of the existing technology, the present invention provides a separation process and separation device for separating DMO hydrogenation products, so as to overcome the problem that incompletely reacted DMO and MG in the DMO to MG reaction form an azeotrope that is difficult to separate, 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 to obtain 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 fed into 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 demethanolation 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 such that, in step (1), the composition of the hydrogenation product, in mass percentage, comprises 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), the mass ratio of MG to DMO in the composition of the hydrogenation product 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 demethanolation 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 an MG discharge port and a second mixture outlet, the extractant feed port and the first mixture feed port are respectively opened at 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 port; the bottom of the solvent recovery tower is provided with an extractant outlet, and the extractant outlet is connected to the extractant feed port.

[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 to perform subsequent separation and purification on the hydrogenation product of DMO hydrogenation to produce MG, thereby obtaining high-purity methyl glycolate with a purity of 99.99%.

[0028] (2) The separation process of the present invention can effectively 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 in an 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 achieves green and sustainable production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the separation device according to the present invention.

[0031] Figure 2 Schematic diagram of the process of conventional separation device in the prior art

[0032] Among them, 10, demethanolation tower, 11, methanol outlet, 12, first mixture outlet, 20, extractive distillation tower, 21, methyl glycolate outlet, 22, second mixture outlet, 23, extractant feed port, 24, first mixture feed port, 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 will be further described below with reference to the accompanying drawings and examples. The following examples 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 to obtain 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 fed into 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 extractive distillation tower has a theoretical plate number of 20-60, a reflux ratio of 1.0-3.0, and an operating pressure of 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 to 1.2:1; preferably, the molar ratio of the extractant to the MG-DMO azeotrope in the first mixture is 0.6 to 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 from 1 / 10 to 1 / 5 theoretical plates of the total number of plates in 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, comprises 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 demethanolation 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 an MG discharge port 21 and a second mixture outlet 22. The extractant feed port 23 and the first mixture feed port 24 are respectively opened at 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 by 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 with reference to specific examples. In the following specific examples, the methanol removal tower, extractive distillation tower and solvent recovery tower 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 mixture, having 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 percentages of the components in the mixture are: 85.7% methanol, 12.0% methyl glycolate, 2.1% ethylene glycol, and 0.2% DMO, with a mass ratio of MG to DMO of 60:1. The de-methanolation tower 10 has 20 theoretical plates, an operating pressure of 0.3 bar, a reflux ratio of 0.05, and a methanol content of 99.9% at the top of the tower, with an output of 857 kg / h and a temperature of 36°C. A first mixture of dimethyl oxalate-methyl glycolate-ethylene glycol is obtained at the bottom of the tower, with an output of 143 kg / h and a temperature of 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 the 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 into 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 at a temperature of 128°C; the extractant di(2-ethylhexyl) phthalate with a purity of more than 99.99% is extracted from the bottom of the tower at a rate of 599 kg / h at a temperature of 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 demethanolation tower 10 and the material composition at the top of the extractive distillation tower 20 as well as 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 mixture having 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 percentages of the components in the mixture are: methanol 71.4%, MG 24.1%, ethylene glycol 3.7%, and DMO 0.8%, with a mass ratio of MG to DMO of 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 a methanol output of 99.9% 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 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 demethanolation tower 10 is continuously fed to the extractive distillation tower 20 via the 15th theoretical plate. The extractive distillation tower 20 has 30 theoretical plates, an operating pressure of 0.3 bar, and a reflux ratio of 2.0. The extractive distillation tower 20 is fed with an extractant, di(2-ethylhexyl) phthalate, at a flow rate of 800 kg / h, into the extractive distillation tower 20 via the 4th theoretical plate. 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 at a temperature of 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, with an extraction rate of 799 kg / h and a temperature of 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 of 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 mixture 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 percentages of the components in the mixture are: 56.4% methanol, 37.8% methyl glycolate, 3.5% ethylene glycol, and 2.3% DMO. The mass ratio of MG to DMO is 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 demethanol 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 into the solvent recovery tower 30 from the 10th theoretical plate. The solvent recovery tower has 15 theoretical plates, an operating pressure of 0.2 bar, and a reflux ratio of 0.3. The dimethyl oxalate-ethylene glycol mixture is obtained at the top of the solvent recovery tower at a temperature of 136°C; dihexyl phthalate with a purity of more than 99.99% is extracted from the bottom of the tower at an extraction rate of 999 kg / h at a temperature of 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 demethanolation 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 mixture 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 the de-methanolation tower 10. The mass percentage of each component in the mixture is: methanol 41.5%, methyl glycolate 50.7%, ethylene glycol 3.9%, DMO 3.9%, and the mass ratio of MG to DMO is 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. 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 114°C.

[0069] (2) The dimethyl oxalate-methyl glycolate-ethylene glycol mixture obtained at the bottom of the demethanol 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. 99.999% MG is obtained at the top of the tower, the DMO content is ≤0.01%, the recovery rate is 506 kg / h, and the temperature is 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 into the solvent recovery tower 30 from the 12th theoretical plate. The solvent recovery tower has 25 theoretical plates, an operating pressure of 0.1 bar, and a reflux ratio of 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 at an extraction rate of 1199 kg / h at a temperature of 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 demethanol 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 demethanolation tower 10 and a conventional distillation tower 40 connected in sequence. The top of the conventional distillation tower is an MG discharge port 41, and the bottom outlet 42 is used to extract the mixture after the MG is separated. Compared with the extractive distillation tower, no extractant is added to the conventional 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 conventional distillation tower 40 is used in step (2). Compared to the extractive distillation tower 20, the conventional distillation tower 40 does not contain an extractant and does not have a solvent recovery tower. Other operating parameters are the same as in Example 1. The methyl glycolate outlet 41 at the top of the conventional distillation tower has a production rate of 119 kg / h, a top temperature of 84°C, a MG purity of 98.38%, and a DMO content of 1.62%. The feed composition of the demethanolation tower, the material composition at the top of the conventional distillation tower, and the MG recovery rate in this comparative example are recorded in Table 1.

[0075] Comparative Example 2

[0076] Refer to Example 2. The difference from Example 2 is that, unlike extractive distillation column 20, conventional distillation column 40 does not incorporate an extractant and does not have a solvent recovery column. Other operating parameters were the same as in Example 2. The overhead output was 240 kg / h, the top temperature was 112°C, the MG purity was 96.76%, and the DMO content was 3.24%. The feed composition for the demethanolation column, the composition of the material at the top of the conventional distillation column, and the MG recovery rate in this comparative example are reported in Table 1.

[0077] Comparative Example 3

[0078] Referring to Example 3, the difference from Example 3 is that a conventional distillation tower was used in step (2), i.e., no extractant was added to the extractive distillation tower 20, and no solvent recovery tower was used. Other operating parameters were the same as in Example 3. The overhead output was 377 kg / h, the tower top temperature was 101°C, the MG purity was 96.14%, and the DMO content was 3.86%. The feed composition of the demethanolation tower, the composition of the material at the top of the conventional 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 conventional distillation tower was used in step (2), i.e., no extractant was added to the extractive distillation tower 20, and no solvent recovery tower was used. Other operating parameters were the same as in Example 4. The overhead output was 506 kg / h, the tower top temperature was 101°C, the MG purity was 94.88%, and the DMO content was 5.12%. The feed composition of the demethanolation tower, the material composition of the extractive distillation tower overhead, and the MG recovery rate in this comparative example are recorded in Table 1.

[0081] Comparative Example 5

[0082] Reference is made to Example 2, which differs from Example 2 in that: the extractant added in step (2) is N-methylpyrrolidone, the flow rate is 203 kg / 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 240 kg / h, and the temperature is 112°C. The extractant N-methylpyrrolidone is recovered in step (3). The feed composition of the demethanolation 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.

[0083] Comparative Example 6

[0084] Reference Example 2 differs from Example 2 in 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 rate is 240 kg / h, and the temperature is 112°C. The extractant benzyl alcohol is recovered in step (3). The feed composition of the demethanolation tower, the material composition of the extractive distillation tower top, and the MG recovery rate in this comparative example are recorded in Table 1.

[0085] Comparative Example 7

[0086] Reference Example 2 differs from Example 2 in that: the extractant added in step (2) is sulfolane, the flow rate is 246 kg / 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 rate is 240 kg / h, and the temperature is 112°C. The extractant sulfolane is recovered in step (3). The feed composition of the demethanolation tower and the material composition of the extractive distillation tower top, as well as the MG recovery rate in this comparative example, are recorded in Table 1.

[0087] Comparative Example 8

[0088] Reference Example 2 differs from Example 2 in that the extractant added in step (2) is dimethyl phthalate, the flow rate is 397 kg / h, the molar ratio of the extractant to the MG-DMO azeotrope in the feed is 0.75:1, 98.26% MG is obtained at the top of the tower, the DMO content is 1.74%, the extraction rate is 240 kg / h, and the temperature is 112°C. The extractant dimethyl phthalate is recovered in step (3). The feed composition of the demethanoling tower, 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, except that the extractant di(2-ethylhexyl) phthalate was added in the second step at a rate of 300 kg / h, the molar ratio of the extractant to the MG-DMO azeotrope in the feed was 0.3:1, and 99.80% MG was obtained at the top of the tower with a DMO content of 0.20% at a temperature of 112°C. In the third step, the solvent recovery tower bottom circulation rate was 299 kg / h and the temperature was 333°C. The feed composition, the material composition of the extractive distillation tower top, and the MG recovery rate 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] The results in Table 1 demonstrate that the separation process provided by the present invention demonstrates excellent separation efficiency for the azeotropic system of MG and DMO. Through optimized separation process conditions, high-purity MG with a purity of ≥99.99% was obtained, while the DMO content in the MG product was reduced to ≤0.01%. Furthermore, this separation process is applicable to a wider range of DMO hydrogenation reactor outlet material compositions and has lower requirements for hydrogenation reaction conditions. It effectively addresses the issue of reduced product purity caused by decreased conversion rate in the DMO hydrogenation stage and increased DMO concentration in the hydrogenated product.

[0094] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A separation process for separating dimethyl oxalate hydrogenation products, characterized in that: The steps include: (1) The hydrogenation product of dimethyl oxalate to prepare methyl glycolate is first fed into 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 to obtain high-purity methyl glycolate at the top of the tower and the second mixture at the bottom of the tower; (3) sending the second mixture into a solvent recovery tower, obtaining a high-purity extractant at the bottom of the tower, and circulating it to the extractive distillation tower; In step (2), the extractant is selected from di(2-ethylhexyl) phthalate and / or dihexyl phthalate, and the molar ratio of the extractant to the methyl glycolate-dimethyl oxalate azeotrope in the first mixture is (0.4~1.2):

1.

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 (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.

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

1.

6. The separation process for separating dimethyl oxalate hydrogenation products according to claim 1, wherein: 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.

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