A product separation method for preparing methyl glycolate from dimethyl oxalate

Abstract

The present invention provides a product separation method for preparing methyl glycolate from dimethyl oxalate. The method adopts a vacuum continuous distillation method to separate the methyl glycolate product through a deweighting tower, a preheater, and a product tower. Specifically, the method comprises the following steps: step (1) the material flowing out of the dimethyl oxalate hydrogenation reactor enters the deweighting tower, a mixture of methanol and methyl glycolate is obtained at the top of the deweighting tower, and heavy components such as dimethyl oxalate and ethylene glycol are obtained in the bottom of the tower; step (2) the mixture containing methanol and methyl glycolate enters the preheater and is preheated to 90° C., and then is fed into the product tower, a methanol product with a purity of more than 99.9% is obtained at the top of the product tower, and a methyl glycolate product with a purity of more than 98% is obtained in the bottom of the tower.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical production and relates to a product separation method for preparing methyl glycolate from dimethyl oxalate. Background Art

[0002] Methyl glycolate is a colorless, pleasant-smelling liquid that is soluble in water and in alcohols and ethers in all proportions. It is an excellent solvent for many celluloses, resins, and rubbers, and has a wide range of applications in the chemical, pharmaceutical, and dye industries. As an intermediate in organic and pharmaceutical synthesis, methyl glycolate is an important component in the synthesis of isotrichine and its analogs, which have anti-cancer activity. It is also a raw material for the synthesis of anti-carrier additives that improve the compressive and wear resistance of lubricants. As a chemical intermediate, methyl glycolate is commonly used in the following applications: hydrogenation to produce ethylene glycol and hydrolysis to produce glycolic acid. Currently, most methods for producing methyl glycolate are petrochemical, which presents significant corrosion and pollution issues. In response to the oil crisis and in light of my country's energy resources, a method for synthesizing methyl glycolate from synthesis gas via oxalate hydrogenation has been developed, which represents an economical, green, and environmentally friendly production route tailored to my country's national conditions.

[0003] Patent CN101816934A discloses a method for preparing a silver silica catalyst for the hydrogenation of dimethyl oxalate to methyl glycolate and ethylene glycol using a sol-gel method with the addition of polyvinyl pyrrolidone as a protective agent and structure-directing agent. Patent CN102336666A discloses a method for preparing a supported silver catalyst using mesoporous silica as a support for the hydrogenation of dimethyl oxalate to methyl glycolate and ethylene glycol. Although these methods achieve high dimethyl oxalate conversion rates and methyl glycolate selectivity, the methyl glycolate produced using these existing methods still requires subsequent separation and purification steps. Existing published literature primarily focuses on methyl glycolate preparation methods and catalysts, with little coverage of methyl glycolate product separation technologies. The literature "Computers and Applied Chemistry" 2011, Vol. 28, No. 8, pp. 1027-1029 introduced a simulation comparison of product separation schemes for the hydrogenation of dimethyl oxalate to glycolic acid. However, this scheme only simulates the separation of glycolic acid in the methyl glycolate system, and does not separate components such as methanol, dimethyl oxalate, and ethylene glycol.

[0004] The key to hydrogenating dimethyl oxalate to produce methyl glycolate lies in achieving rapid product separation and purification. The effluent from the dimethyl oxalate hydrogenation reactor primarily contains methyl glycolate, methanol, dimethyl oxalate, and ethylene glycol. Because distillation technology does not introduce third impurities, it is often used for separation and purification. However, methyl glycolate is unstable. Under prolonged heating conditions, trace amounts of water can cause methyl glycolate to hydrolyze, producing glycolic acid and methanol. The resulting glycolic acid undergoes a dehydration reaction at high temperatures to form glycolide. Glycolic acid is acidic, which facilitates the hydrolysis of methyl glycolate. Furthermore, the water removed during the glycolide formation process is a reactant in the hydrolysis of methyl glycolate. Simultaneously, distillation allows the light component methanol produced by hydrolysis to be rapidly extracted overhead, breaking the reaction equilibrium constraints of methyl glycolate hydrolysis. The synergistic effects of these various processes result in low methyl glycolate yields during the distillation process for hydrogenating dimethyl oxalate to produce methyl glycolate. To improve the yield of methyl glycolate during the separation process, the key is to reduce the separation temperature and the heating time of the materials. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention aims to solve the problem that methyl glycolate is easily hydrolyzed and polymerized during the product separation process of preparing methyl glycolate from dimethyl oxalate. To achieve this object, the present invention adopts the following technical solutions:

[0006] A method for separating products from dimethyl oxalate to methyl glycolate employs a system comprising a deweighting tower, a preheater, and a product tower. The deweighting tower has a top outlet connected to the preheater inlet, and the preheater outlet communicates with a feed inlet in the middle of the product tower.

[0007] The separation process is as follows: The effluent from the dimethyl oxalate hydrogenation reactor is fed through the feed port into a de-weighting column. Methanol and methyl glycolate are obtained at the top of the de-weighting column, while heavy components such as dimethyl oxalate and ethylene glycol are obtained at the bottom. The overhead stream from the de-weighting column is pumped to a preheater for preheating before being fed to the product column. After the preheated liquid is fed to the product column, methanol is obtained at the top of the product column, while the target product, methyl glycolate, is obtained at the bottom.

[0008] Furthermore, the effluent of the dimethyl oxalate hydrogenation reactor includes the following components and their mass percentages: 82-88% of methyl glycolate, 3-8% of methanol, 0.2-0.6% of dimethyl oxalate, 3-6% of ethylene glycol, and 0.5-1.5% of other impurities.

[0009] Furthermore, the deweighting tower adopts reduced pressure operation, with an operating pressure of 5 to 40 KPa, a reflux ratio R=1 to 5, a top temperature of 34 to 84°C, and a kettle temperature of 120 to 166°C.

[0010] Furthermore, the outlet temperature of the preheater is 90°C.

[0011] Furthermore, the product tower adopts reduced pressure operation, with an operating pressure of 5 to 15 KPa, a reflux ratio R=1 to 5, a top temperature of 3 to 23°C, and a kettle temperature of 72 to 94°C.

[0012] Furthermore, the number of theoretical plates of the deweighting tower is 20 to 45, and a feed port is provided in the middle.

[0013] Furthermore, the deweighting tower is a plate separation tower or a packed separation tower, the overhead stream of the deweighting tower contains methanol and methyl glycolate, and the bottom stream contains dimethyl oxalate, ethylene glycol and methyl glycolate, etc.

[0014] Furthermore, the product tower has 20 to 40 theoretical plates, a feed port is provided in the middle, and a heat exchanger is built into the lower part of the product tower.

[0015] Furthermore, the product tower is a plate separation tower or a packed separation tower, the overhead stream of the product tower is methanol, and the bottom stream is the target product methyl glycolate.

[0016] Furthermore, the product tower is provided with a rectifying section, a stripping section, a built-in reboiler and a tower kettle from top to bottom.

[0017] Furthermore, the built-in reboiler is composed of upper and lower circular tube plates and a plurality of heat exchange tubes. The upper and lower tube plates are evenly and symmetrically provided with a plurality of holes, and the heat exchange tubes are welded between the upper and lower symmetrical holes.

[0018] Furthermore, the spacing between the upper and lower tubesheets of the built-in reboiler matches the length of the heat exchange tubes, and the diameter of the upper and lower circular tubesheets matches the inner diameter of the product column. The enclosed space formed by the upper and lower tubesheets, the outer wall of the product column, and the heat exchange tubes constitutes the shell of the built-in reboiler. Heating steam is fed into the upper portion of the shell, and condensate is discharged from the lower portion. The upper and lower tubesheets separate the stripping section from the column bottom and are connected by heat exchange tubes. The material exchanges heat and vaporizes on the inner walls of the heat exchange tubes.

[0019] Compared with the prior art, the present invention has the following advantages: 1. The yield of methyl glycolate separated and purified by intermittent distillation is only about 30%, while the degassing tower and the product tower of the present invention adopt continuous decompression operation to ensure that the distillation section of the degassing tower and the bottom temperature of the product tower are both below 90°C, which greatly reduces the possibility of hydrolysis or polymerization of methyl glycolate, and the product yield can be increased to about 80%.

[0020] 2. Use a preheater to preheat the mixture entering the product tower. The methanol vapor entering the distillation tower from the middle feed port goes directly to the top of the tower, reducing the load of the product tower and helping to reduce the heating time of the material in the reboiler.

[0021] 3. The lower portion of the product tower is equipped with an integrated built-in reboiler. The liquid descending from the stripping section primarily contains methyl glycolate and a small amount of methanol. After being heated on the inner wall of the reboiler's heat exchange tubes, the material vaporizes to form steam (primarily methanol and a small amount of methyl glycolate), which rises toward the top of the tower. The unvaporized methyl glycolate passes through the heat exchange tubes and falls directly into the tower bottom. Because the tower bottom is not equipped with a heat source, this effectively reduces the heating time of methyl glycolate in the product tower, reduces the possibility of methyl glycolate decomposition, and increases the product yield by approximately 10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below with reference to the accompanying drawings.

[0023] Figure 1 The present invention provides a flow chart of a product separation method for preparing methyl glycolate from dimethyl oxalate.

[0024] Figure 2 Schematic diagram of a built-in reboiler in the product tower of the present invention.

[0025] Figure 3 for Figure 2 A top view of a cross section of a reboiler;

[0026] Markings in the figure: 1-deweight removal tower; 2-preheater; 3-product tower; 4-built-in reboiler, 5-tower wall, 6-upper circular tube sheet, 7-lower circular tube sheet, 8-heat exchange tube, 9-steam inlet, 10-steam condensate outlet. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0028] Example 1

[0029] The effluent from the dimethyl oxalate hydrogenation reactor contains the following components and their weight percentages: 87% methyl glycolate, 6% methanol, 0.5% dimethyl oxalate, 5.4% ethylene glycol, and 1.1% other impurities. The effluent to be separated is fed through the feed port to a de-weighting column. The de-weighting column has 20 theoretical stages, with feed starting on the 10th stage. The de-weighting column operates under reduced pressure at 5 kPa, a reflux ratio of 5, a top temperature of 34.3°C, and a bottom temperature of 120.0°C. Methanol and methyl glycolate are withdrawn when a stable flow appears at the top of the column. The resulting methanol concentration at the top is 6.4% by weight, and the methyl glycolate concentration is 93.3% by weight. The methanol and methyl glycolate taken out from the top of the tower enter the preheater with an outlet temperature of 90°C. The preheated solution enters the product tower from the middle feed port. The product tower has 40 theoretical plates, and the feed is made on the 20th plate. The product tower adopts reduced pressure operation with an operating pressure of 5 kPa, a reflux ratio of 1, a top temperature of 3.7°C, and a bottom temperature of 72.5°C. The mass fraction of methanol obtained at the top of the tower is 99.9%, and the mass fraction of methyl glycolate obtained in the bottom of the tower is 99.2%.

[0030] Example 2

[0031] The effluent from the dimethyl oxalate hydrogenation reactor contains the following components and their weight percentages: 87% methyl glycolate, 6% methanol, 0.5% dimethyl oxalate, 5.4% ethylene glycol, and 1.1% other impurities. The effluent to be separated is fed through the feed port to a de-weighting column. The de-weighting column has 26 theoretical stages, with feed starting on the 13th stage. The de-weighting column operates under reduced pressure at 5 kPa, a reflux ratio of 5, a top temperature of 34.4°C, and a bottom temperature of 120.2°C. Methanol and methyl glycolate are withdrawn when a stable flow appears at the top of the column. The resulting methanol concentration at the top is 6.4% by weight, and the methyl glycolate concentration is 93.4% by weight. The methanol and methyl glycolate taken out from the top of the tower enter the preheater with an outlet temperature of 90°C. The preheated solution enters the product tower from the middle feed port. The product tower has 36 theoretical plates, and the feed is made on the 18th plate. The product tower adopts reduced pressure operation with an operating pressure of 5 kPa, a reflux ratio of 1, a top temperature of 3.7°C, and a bottom temperature of 72.5°C. The mass fraction of methanol obtained at the top of the tower is 99.9%, and the mass fraction of methyl glycolate obtained in the bottom of the tower is 99.3%.

[0032] Example 3

[0033] The effluent from the dimethyl oxalate hydrogenation reactor contains the following components and their weight percentages: 87% methyl glycolate, 6% methanol, 0.5% dimethyl oxalate, 5.4% ethylene glycol, and 1.1% other impurities. The effluent to be separated is fed through the feed port to a de-weighting column. The de-weighting column has 30 theoretical stages, with feed starting on the 15th stage. The de-weighting column operates under reduced pressure at 10 kPa, a reflux ratio of 4, a top temperature of 49.0°C, and a bottom temperature of 132.8°C. Methanol and methyl glycolate are withdrawn when a stable flow appears at the top of the column. The resulting methanol concentration at the top is 6.4% by weight, and the methyl glycolate concentration is 93.3% by weight. The methanol and methyl glycolate taken out from the top of the tower enter the preheater with an outlet temperature of 90°C. The preheated solution enters the product tower from the middle feed port. The product tower has 34 theoretical plates, and the feed is made on the 17th plate. The product tower adopts reduced pressure operation with an operating pressure of 10 kPa, a reflux ratio of 2, a top temperature of 15.4°C, and a bottom temperature of 85.2°C. The mass fraction of methanol obtained at the top of the tower is 99.9%, and the mass fraction of methyl glycolate obtained in the bottom of the tower is 99.3%.

[0034] Example 4

[0035] The effluent from the dimethyl oxalate hydrogenation reactor contains the following components and their weight percentages: 87% methyl glycolate, 6% methanol, 0.5% dimethyl oxalate, 5.4% ethylene glycol, and 1.1% other impurities. The effluent to be separated is fed through the feed port to a de-weighting column. The de-weighting column has 34 theoretical stages, with feed starting on the 17th stage. The de-weighting column operates under reduced pressure at 15 kPa, a reflux ratio of 4, a top temperature of 58.2°C, and a bottom temperature of 141.4°C. Methanol and methyl glycolate are withdrawn after a stable flow appears at the top of the column. The resulting methanol concentration at the top is 6.4% by weight, and the methyl glycolate concentration is 93.3% by weight. The methanol and methyl glycolate taken out from the top of the tower enter the preheater, and the outlet temperature of the preheater is 90°C. The preheated solution enters the product tower from the middle feed port. The product tower has 30 theoretical plates, and the feed is made on the 15th plate. The product tower adopts reduced pressure operation with an operating pressure of 10KPa, a reflux ratio of 3, a top temperature of 15.4°C, and a bottom temperature of 85.2°C. The mass fraction of methanol obtained at the top of the tower is 99.9%, and the mass fraction of methyl glycolate obtained in the bottom of the tower is 99.3%.

[0036] Example 5

[0037] The effluent from the dimethyl oxalate hydrogenation reactor contains the following components and their weight percentages: 87% methyl glycolate, 6% methanol, 0.5% dimethyl oxalate, 5.4% ethylene glycol, and 1.1% other impurities. The effluent to be separated is fed through the feed port to a de-weighting column. The de-weighting column has 38 theoretical stages, with feed starting on the 19th stage. The de-weighting column operates under reduced pressure at 20 kPa, a reflux ratio of 3, a top temperature of 65.2°C, and a bottom temperature of 148.1°C. Methanol and methyl glycolate are withdrawn after a stable flow appears at the top of the column. The resulting methanol concentration at the top is 6.4% by weight, and the methyl glycolate concentration is 93.3% by weight. The methanol and methyl glycolate taken out from the top of the tower enter the preheater, and the outlet temperature of the preheater is 90°C. The preheated solution enters the product tower from the middle feed port. The product tower has 28 theoretical plates, and the feed is made on the 14th plate. The product tower adopts reduced pressure operation with an operating pressure of 15 kPa, a reflux ratio of 4, a top temperature of 22.8°C, and a bottom temperature of 94.0°C. The mass fraction of methanol obtained at the top of the tower is 99.9%, and the mass fraction of methyl glycolate obtained in the bottom of the tower is 99.3%.

[0038] Example 6

[0039] The effluent from the dimethyl oxalate hydrogenation reactor contains the following components and their weight percentages: 87% methyl glycolate, 6% methanol, 0.5% dimethyl oxalate, 5.4% ethylene glycol, and 1.1% other impurities. The effluent to be separated is fed through the feed port to a de-weighting column. The de-weighting column has 40 theoretical stages, with feed starting at the 20th stage. The de-weighting column operates under reduced pressure at 30 kPa, a reflux ratio of 2, a top temperature of 75.5°C, and a bottom temperature of 158.3°C. Methanol and methyl glycolate are withdrawn when a stable flow appears at the top of the column. The resulting methanol concentration at the top is 6.4% by weight, and the methyl glycolate concentration is 93.3% by weight. The methanol and methyl glycolate taken out from the top of the tower enter the preheater, and the outlet temperature of the preheater is 90°C. The preheated solution enters the product tower from the middle feed port. The product tower has 24 theoretical plates, and the feed is made on the 12th plate. The product tower adopts reduced pressure operation with an operating pressure of 15 kPa, a reflux ratio of 5, a top temperature of 22.8°C, and a bottom temperature of 94.0°C. The mass fraction of methanol obtained at the top of the tower is 99.9%, and the mass fraction of methyl glycolate obtained in the bottom of the tower is 99.3%.

[0040] Example 7

[0041] The effluent from the dimethyl oxalate hydrogenation reactor contains the following components and their weight percentages: 87% methyl glycolate, 6% methanol, 0.5% dimethyl oxalate, 5.4% ethylene glycol, and 1.1% other impurities. The effluent to be separated is fed through the feed port to a de-weighting column. The de-weighting column has 44 theoretical stages, with feed starting at the 22nd stage. The de-weighting column operates under reduced pressure at 40 kPa, a reflux ratio of 1, a top temperature of 83.2°C, and a bottom temperature of 165.9°C. Methanol and methyl glycolate are withdrawn when a stable flow appears at the top of the column. The resulting methanol concentration at the top is 6.4% by weight, and the methyl glycolate concentration is 93.3% by weight. The methanol and methyl glycolate taken out from the top of the tower enter the preheater, and the outlet temperature of the preheater is 90°C. The preheated solution enters the product tower from the middle feed port. The product tower has 20 theoretical plates, and the feed is made on the 10th plate. The product tower adopts reduced pressure operation with an operating pressure of 15 kPa, a reflux ratio of 5, a top temperature of 22.8°C, and a bottom temperature of 94.0°C. The mass fraction of methanol obtained at the top of the tower is 99.9%, and the mass fraction of methyl glycolate obtained in the bottom of the tower is 99.2%.

[0042] The above content is merely an example of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the present invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for separating products from dimethyl oxalate to methyl glycolate, characterized in that , including the following steps: (1) De-weighting: The material flowing out of the dimethyl oxalate hydrogenation reactor is fed into a de-weighting tower. The theoretical number of the de-weighting tower is 20 to 45, and a feed port is provided in the middle. The operating pressure of the de-weighting tower is 5 to 40 kPa, the reflux ratio R=1 to 5, the top temperature is 34 to 84 °C, and the kettle temperature is 120 to 166 °C. A mixture of methanol and methyl glycolate is obtained at the top of the de-weighting tower, and dimethyl oxalate and ethylene glycol are obtained at the bottom of the tower. (2) Preheating: The material extracted from the top of the deweighting tower is sent to the preheater for preheating, and then sent to the product tower; (3) Product purification: The preheated methanol and methyl glycolate solution are fed into the product tower for separation; the operating pressure of the product tower is 5-15 kPa, the reflux ratio R=1-5, the top temperature is 3-23 °C, and the kettle temperature is 72-94 °C; methanol is obtained at the top of the product tower, and the target product methyl glycolate is obtained at the bottom of the tower; The material flowing out of the dimethyl oxalate hydrogenation reactor includes the following components and their mass percentages: 82-88% of methyl glycolate, 3-8% of methanol, 0.2-0.6% of dimethyl oxalate, 3-6% of ethylene glycol, and 0.5-1.5% of other impurities; The product tower adopts an integrated built-in reboiler. The tower is divided into a distillation section, a stripping section, a built-in reboiler and a tower kettle from top to bottom.

2. The method for separating products from dimethyl oxalate to methyl glycolate according to claim 1, wherein: In step (2), the preheater outlet temperature is 90°C.

3. The method for separating products from dimethyl oxalate to methyl glycolate according to claim 1, wherein: In step (3), the product tower has 20 to 40 theoretical plates, with a feed port in the middle.

4. The method for separating products of dimethyl oxalate to methyl glycolate according to claim 1, characterized in that: The integrated built-in reboiler consists of upper and lower circular tube sheets and multiple heat exchange tubes. Several holes are evenly and symmetrically opened on the upper and lower tube sheets, and heat exchange tubes are welded between the upper and lower symmetrical holes. The spacing between the upper and lower tube sheets is consistent with the length of the heat exchange tubes. The diameter of the upper and lower circular tube sheets is consistent with the inner diameter of the product tower. The enclosed space formed by the upper and lower tube sheets, the outer wall of the product tower and the heat exchange tubes constitutes the shell of the built-in reboiler. The heating steam is fed from the upper part of the shell, and the steam condensate is discharged from the lower part of the shell. The upper and lower tube sheets separate the distillation section and the tower kettle, and are connected through the heat exchange tubes. The material exchanges heat and vaporizes on the inner wall of the heat exchange tube.

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