A production system for preparing glycolic acid crystals from methyl glycolate

Abstract

The utility model discloses a kind of production systems for preparing glycollic acid crystal from methyl glycolate, in turn including raw material storage tank, hydrolysis reaction kettle, thin film evaporator, flash tank, first crystallization kettle, first solid-liquid separation device, second crystallization kettle and second solid-liquid separation device;Thin film evaporator is connected with the discharge port of hydrolysis reaction kettle, flash tank is connected with the discharge port of thin film evaporator by pressure-reducing valve, first crystallization kettle is connected with the discharge port of flash tank, first solid-liquid separation device is connected with the discharge port of first crystallization kettle, second crystallization kettle is connected with the liquid phase export of first solid-liquid separation device, seed crystal feed port is provided above second crystallization kettle, second solid-liquid separation device is connected with the discharge port of second crystallization kettle.The utility model carries out concentration to glycollic acid aqueous solution in combination with thin film evaporation process and flash process, cooling crystallization is carried out to concentrated solution using two-stage crystallization process, and the yield of glycollic acid crystal is improved.

Description

Technical Field

[0001] This invention belongs to the field of organic chemical synthesis and refining technology, and specifically relates to a production system for preparing glycolic acid crystals from methyl glycolate. Background Technology

[0002] Glycolic acid, also known as glycolic acid, is an important organic compound. Specifically, it is a key monomer in the synthesis of polyglycolic acid (PGA). PGA possesses excellent biodegradability and biocompatibility, and has broad application prospects in packaging materials, agricultural production, medical devices, and oil and gas extraction. Glycolic acid is also a high-value-added chemical, used as an active ingredient in daily skincare products such as toners, masks, and serums; it can be used to prepare electronic-grade chemicals, such as those used in semiconductor cleaning and etching processes; and it can be used to synthesize pharmaceutical intermediates, serving as a key intermediate for certain drugs treating acne and skin diseases.

[0003] The purity of glycolic acid crystals directly affects the performance and quality of the product. The main processes for synthesizing glycolic acid include chloroacetic acid hydrolysis, formaldehyde carbonylation, and methyl glycolate hydrolysis. Among them, methyl glycolate hydrolysis has the advantages of abundant raw material sources (obtained by hydrogenation of dimethyl oxalate, an intermediate product of ethylene glycol production from syngas), mild reaction conditions, few by-products, and green and environmentally friendly process, making it a process route that has been extensively studied in recent years.

[0004] The hydrolysis method for methyl glycolate mainly includes three stages: hydrolysis, concentration, and crystallization. Patent application CN103508878A discloses a method for preparing glycolic acid crystals from methyl glycolate, which involves hydrolyzing methyl glycolate with water to obtain a hydrolysate containing glycolic acid; concentrating the hydrolysate to obtain a high-concentration glycolic acid mother liquor; and cooling and crystallizing the high-concentration glycolic acid mother liquor to obtain glycolic acid crystals. Patent application CN104177250A discloses a process for producing glycolic acid from methyl glycolate, which uses reactive distillation to hydrolyze methyl glycolate, then evaporates and concentrates the glycolic acid aqueous solution, decolorizes it, and crystallizes it to precipitate glycolic acid in crystalline form. The glycolic acid crystals are separated by filtration, washed with solvent, and vacuum dried to obtain glycolic acid crystals.

[0005] In the existing production process, glycolic acid is prone to self-polymerization in the concentration section, generating byproducts such as glycolic acid dimers and glycolic acid tetramers, resulting in a low yield of glycolic acid. It also affects the selection of the crystallization endpoint temperature, which has a key impact on the yield of glycolic acid crystals. Therefore, although the purity of the obtained glycolic acid crystals can reach 99% or even 99.5% or more, the yield is low.

[0006] To further improve the yield of glycolic acid crystals, it is necessary to optimize the production process and equipment. Utility Model Content

[0007] The purpose of this invention is to provide a production system for preparing glycolic acid crystals from methyl glycolate, which can reduce the self-polymerization reaction of glycolic acid and improve the recovery rate of glycolic acid crystals, thereby increasing the yield of glycolic acid crystals.

[0008] To achieve the above objectives, the process design concept of this utility model is as follows:

[0009] A production system for preparing glycolic acid crystals from methyl glycolate is provided, the production system comprising: Raw material storage tanks are used to store methyl glycolate; A hydrolysis reactor is connected to the raw material storage tank, and a water inlet and a catalyst inlet are respectively provided above the hydrolysis reactor; A thin-film evaporator is connected to the outlet of the hydrolysis reactor. A first condensation assembly is provided above the thin-film evaporator. The first condensation assembly includes a first condenser and a first mixed liquid receiving tank. A flash tank is connected to the outlet of the thin-film evaporator via a pressure reducing valve. A second condensation assembly is provided above the flash tank. The second condensation assembly includes a second condenser, a second mixed liquid receiving tank, and a second vacuum pump connected in sequence. The first crystallization vessel is connected to the outlet of the flash tank; The first solid-liquid separation device is connected to the outlet of the first crystallization vessel; The second crystallization vessel is connected to the liquid phase outlet of the first solid-liquid separation device, and a seed crystal inlet is provided above the second crystallization vessel; The second solid-liquid separation device is connected to the outlet of the second crystallization vessel.

[0010] In one embodiment, a reflux condenser is provided above the hydrolysis reactor. The reflux condenser has a gas phase inlet, a condensate outlet and a gas phase outlet. The gas phase inlet and the condensate outlet of the reflux condenser are both connected to the hydrolysis reactor. The gas outlet of the reflux condenser is connected in sequence to an alcohol collection tank and a first vacuum pump.

[0011] As a further improvement, the hydrolysis reactor includes a first hydrolysis reactor and a second hydrolysis reactor, with the water inlet and the catalyst inlet located above the first hydrolysis reactor, and the condenser reflux device located above the second hydrolysis reactor. The first hydrolysis reactor is connected to the raw material storage tank, and the thin-film evaporator is connected to the outlet of the second hydrolysis reactor.

[0012] Optionally, the first hydrolysis reactor and the second hydrolysis reactor are installed with a height difference, wherein the height of the discharge port of the first hydrolysis reactor is higher than the height of the feed port of the second hydrolysis reactor.

[0013] In one embodiment, the first hydrolysis reactor is connected to the raw material storage tank via a feed pump, and a preheater is provided between the feed pump and the first hydrolysis reactor.

[0014] As a further improvement, a buffer tank, a circulation pipeline, and a circulation pump installed on the circulation pipeline are provided between the thin-film evaporator and the flash tank. One end of the circulation pipeline is connected to the thin-film evaporator, and the other end of the circulation pipeline is connected to the feed end of the flash tank through the pressure reducing valve.

[0015] Optionally, the thin-film evaporator is a scraped film evaporator or a falling film evaporator.

[0016] In one embodiment, the first solid-liquid separation device is selected from a centrifuge; The second solid-liquid separation device is selected from a pressure filtration device with a filtration pore size of 100μm~500μm.

[0017] In one embodiment, a loss-in-weight scale is provided at the catalyst inlet; A weight loss scale is installed at the seed crystal inlet.

[0018] As a further improvement, the liquid phase outlet of the second solid-liquid separation device is connected to the water inlet of the hydrolysis reactor via a delivery pump and a delivery pipeline, and a three-way valve is installed on the delivery pipeline.

[0019] The production system for preparing glycolic acid crystals from methyl glycolate provided in this embodiment of the invention uses a thin-film evaporator to initially concentrate the glycolic acid aqueous solution, and a flash tank to further concentrate the material after the initial concentration by the thin-film evaporator to obtain a concentrated solution. This shortens the concentration time of the glycolic acid aqueous solution and reduces the self-polymerization reaction of glycolic acid. A two-stage crystallization process is used to cool and crystallize the concentrated solution, which improves the recovery rate of glycolic acid crystals. Through the above methods, this embodiment of the invention can improve the yield of glycolic acid crystals. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1This is a schematic diagram of the structure of a production system for preparing glycolic acid crystals from methyl glycolate according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a production system for preparing glycolic acid crystals from methyl glycolate according to another embodiment of the present invention. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0023] Those skilled in the art should understand that, in the disclosure of this utility model, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limitations on this utility model.

[0024] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0025] This invention provides a production system for preparing glycolic acid crystals from methyl glycolate, such as... Figure 1 As shown, the production system includes, in sequence, a raw material storage tank 1, a hydrolysis reactor 2, a thin film evaporator 3, a flash tank 4, a first crystallization reactor 5, a first solid-liquid separation device 6, a second crystallization reactor 7, and a second solid-liquid separation device 8.

[0026] Raw material storage tank 1 is used to store methyl glycolate; hydrolysis reactor 2 is connected to raw material storage tank 1 via a feed pump. A water inlet, a catalyst inlet, and a reflux condenser 21 are respectively provided above the hydrolysis reactor 2. Preferably, a loss-in-weight scale 24 is provided at the catalyst inlet. The reflux condenser 21 has a gas phase inlet, a condensate outlet, and a gas phase outlet. Both the gas phase inlet and the condensate outlet of the reflux condenser 21 are connected to the hydrolysis reactor 2, used to condense the gas phase material from the hydrolysis reactor 2 and reflux it back into the hydrolysis reactor 2 for circulation. The gas outlet of the reflux condenser 21 is connected in sequence to an alcohol collection tank 22 and a first vacuum pump 23.

[0027] The thin-film evaporator 3 is connected to the outlet of the hydrolysis reactor 2 via a discharge pump. A first condensation assembly is installed above the thin-film evaporator 3, which includes a first condenser 31 and a first mixed liquid receiving tank 32. The thin-film evaporator 3 is used for the preliminary concentration of the glycolic acid aqueous solution. Low-boiling-point organic matter and water are separated from the glycolic acid aqueous solution and enter the first condenser 31. The condensate obtained after condensation by the first condenser 31 enters the first mixed liquid receiving tank 32.

[0028] The flash tank 4 is connected to the outlet of the thin-film evaporator 3 via a pressure reducing valve. A second condensation assembly is installed above the flash tank 4. The second condensation assembly includes a second condenser 41, a second mixed liquid receiving tank 42, and a second vacuum pump 43 connected in sequence. The flash tank 4 is used to further concentrate the material after preliminary concentration by the thin-film evaporator 3 to obtain a concentrated liquid. The separated low-boiling-point organic matter and water enter the second condenser 41. The condensate obtained after condensation by the second condenser 41 enters the second mixed liquid receiving tank 42. The second vacuum pump 43 is used to maintain a stable vacuum level inside the flash tank 4.

[0029] The first crystallization vessel 5 is connected to the outlet of the flash tank 4 and is used to cool and crystallize the concentrate; the first solid-liquid separation device 6 is connected to the first crystallization vessel 5 and is used to separate the crystal slurry discharged from the first crystallization vessel 5 to obtain glycolic acid crystals and primary crystallization mother liquor.

[0030] The second crystallization vessel 7 is connected to the liquid phase outlet of the first solid-liquid separation device 6 and is used to cool and crystallize the primary crystallization mother liquor. A seed inlet is provided above the second crystallization vessel 7. Preferably, a weight loss scale 71 is provided at the seed inlet. The second solid-liquid separation device 8 is connected to the second crystallization vessel 7 and is used to perform solid-liquid separation on the crystal slurry discharged from the second crystallization vessel 7 to obtain glycolic acid crystals and secondary crystallization mother liquor.

[0031] In one embodiment, a preheater 11 is provided between the feed pump and the hydrolysis reactor 2 to heat the methyl glycolate entering the hydrolysis reactor 2.

[0032] As a further improvement, a buffer tank 33, a circulation pipeline 34, and a circulation pump 35 are provided between the thin-film evaporator 3 and the flash tank 4. One end of the circulation pipeline 34 is connected to the thin-film evaporator 3, and the other end is connected to the feed end of the flash tank 4 through a pressure reducing valve. After one concentration in the thin-film evaporator 3, if the water content of the glycolic acid aqueous solution is too high, it can be re-entered into the thin-film evaporator 3 through the circulation loop for further concentration.

[0033] Preferably, the thin-film evaporator 3 is a scraped film evaporator or a falling film evaporator. It is sufficient to use a conventional scraped film evaporator or a falling film evaporator available on the market, without the need for special structural modifications.

[0034] In one embodiment, the first solid-liquid separation device 6 is selected from a centrifuge, and the second solid-liquid separation device 7 is selected from a pressure filtration device with a filtration pore size of 100μm~500μm.

[0035] As a further improvement, the liquid phase outlet of the second solid-liquid separation device 8 is connected to the water inlet of the hydrolysis reactor 2 via a transfer pump 9 and a transfer pipeline. A three-way valve 91 is installed on the transfer pipeline. Specifically, the inlet of the three-way valve 91 is connected to the outlet of the transfer pump 9, one outlet of the three-way valve 91 is connected to the water inlet of the hydrolysis reactor 2, and the other outlet is connected to an external mother liquor collection tank or waste liquid collection tank. The secondary crystallization mother liquor separated by the second solid-liquid separation device 8 can be returned to the hydrolysis reactor 2 for circulation via the transfer pipeline. When the circulation cycle exceeds a certain number of times, the impurity concentration in the secondary crystallization mother liquor increases, and the three-way valve 91 is switched to discharge the secondary crystallization mother liquor to the outside.

[0036] Please see Figure 2 This invention provides another production system for preparing glycolic acid crystals from methyl glycolate, which is similar to... Figure 1 The difference in the production system shown is that the hydrolysis reactor includes a first hydrolysis reactor 2A and a second hydrolysis reactor 2B. The water inlet and catalyst inlet are located above the first hydrolysis reactor 2A, and the reflux condenser 21 is located above the second hydrolysis reactor 2B. The first hydrolysis reactor 2A is connected to the raw material storage tank 1 via a feed pump, and the thin-film evaporator 3 is connected to the outlet of the second hydrolysis reactor 2B. Methyl glycolate undergoes a normal or slightly positive pressure hydrolysis reaction in the first hydrolysis reactor 2A, and a negative pressure hydrolysis reaction in the second hydrolysis reactor 2B, which can shorten the reaction cycle and improve production efficiency.

[0037] Preferably, the first hydrolysis reactor 2A and the second hydrolysis reactor 2B are installed with a height difference, and the height of the discharge port of the first hydrolysis reactor 2A is higher than the height of the feed port of the second hydrolysis reactor 2B.

[0038] The glycolic acid crystal production system provided in this embodiment of the invention has the following process: Add a certain amount of water and glycolic acid crystals (purity above 99.5%) as a catalyst to the first hydrolysis reactor 2A, start stirring and heat to 50~95℃; turn on the feed pump and add methyl glycolate to the first hydrolysis reactor 2A. The methyl glycolate is preheated by a preheater. The mass ratio of water to methyl glycolate is (1~20):1. The amount of glycolic acid crystals added is 1wt%~2wt% of the total feed amount. The pressure of the first hydrolysis reactor is atmospheric pressure or slightly positive pressure, and the hydrolysis reaction time is 2~8 hours.

[0039] The first vacuum pump 23 is turned on in advance to maintain the pressure in the second hydrolysis reactor 2B at 50kPa~90kPa and the temperature at the same level as the first hydrolysis reactor 2A. The temperature of the reflux condenser 21 is set at 50~70℃ and the temperature of the alcohol collection tank 22 is set at 0~20℃. The valve is opened to introduce the material in the first hydrolysis reactor 2A into the second hydrolysis reactor 2B. The material continues to undergo hydrolysis in the second hydrolysis reactor 2B for 3~8 hours to obtain the hydrolysis product, namely, an aqueous solution of glycolic acid, in which the mass fraction of glycolic acid is 30%~50%.

[0040] The hydrolysis products from the second hydrolysis reactor 2B enter the thin-film evaporator 3 for preliminary concentration. The temperature of the thin-film evaporator 3 is set at 80~95℃, and the temperature of the first condenser 31 is set at 10~40℃. The material forms a thin liquid film in the thin-film evaporator, and under negative pressure, the material's own temperature, and heating, the water evaporates rapidly, concentrating the mass fraction of glycolic acid to over 60%.

[0041] The pressure inside the flash tank 4 is maintained at 50Pa~2kPa, and the temperature of the second condenser 41 is set at -20~10℃. After the material is initially concentrated by the thin film evaporator 3, it enters the flash tank 4 through the pressure reducing valve. The pressure drops sharply, and at the same time, it achieves rapid flash evaporation by using its own heat. The mass fraction of glycolic acid can be concentrated to more than 75%, and the temperature of the concentrate drops.

[0042] The concentrate enters the first crystallization vessel 5, where the temperature is maintained at 0~15℃ and the crystallization time is 0.5~1 hour. The resulting crystal slurry is introduced into the first solid-liquid separator 6. After solid-liquid separation, glycolic acid crystals and primary crystallization mother liquor are obtained. The primary crystallization mother liquor enters the second crystallization vessel 7, where the temperature is maintained at -20~-5℃. Glycolic acid crystals (purity above 99.5%) are added to the second crystallization vessel 7 as seed crystals. The amount of glycolic acid crystals added is 0.5wt%~1wt% of the primary crystallization mother liquor. The crystallization time is 1~1.5 hours. The resulting crystal slurry is introduced into the second solid-liquid separator 8. After solid-liquid separation, glycolic acid crystals and secondary crystallization mother liquor are obtained.

[0043] The glycolic acid crystals obtained from the two crystallizations are vacuum dried to obtain the finished glycolic acid crystals. The mother liquor from the secondary crystallization is returned to the first hydrolysis reactor 2A or discharged through the transfer pump 9.

[0044] The present invention has the following beneficial effects: 1. The thin film evaporator 3 is connected to the outlet of the hydrolysis reactor 2, and the flash tank 4 is connected to the outlet of the thin film evaporator 3 through a pressure reducing valve. The thin film evaporator 3 is used to initially concentrate the glycolic acid aqueous solution, and the flash tank 4 is used to further concentrate the material after the initial concentration by the thin film evaporator 3 to obtain a concentrated liquid. This shortens the concentration time of the glycolic acid aqueous solution and reduces the self-polymerization reaction of glycolic acid. 2. A two-stage crystallization process is used to cool and crystallize the concentrate. The crystallization endpoint temperature of the second stage is lower than that of the first stage. Seed crystals are added during the second stage crystallization process to improve the recovery rate of glycolic acid crystals. 3. The aqueous solution of glycolic acid enters the thin film evaporator 3 from the hydrolysis reactor 2. It can use its own negative pressure and heat energy to evaporate part of the water in the thin film evaporator 3. After the material is initially concentrated in the thin film evaporator 3, it enters the flash tank 4 for flash evaporation. The temperature of the concentrated liquid is greatly reduced, which is beneficial to the subsequent crystallization and saves system energy consumption. It is understandable that the components connected in the above production system are connected by pipelines. Conventional heat tracing can be configured on the pipelines connecting the reactor / device as needed to ensure that the material being transported is in a relatively stable temperature state. Conventional valves and pumps can be configured on the pipelines connecting the reactor / device as needed to ensure the material is transported. In addition, heat exchange units can be configured on the reactor / device as needed to maintain the reactor / device at the set temperature. For example, an electric heating jacket can be installed on the outside of the shell of the thin film evaporator 3.

[0045] The above description is merely a preferred embodiment of this utility model and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of this utility model is not limited to the specific combination of the above-described technical features, but should also cover other technical solutions formed by any combination of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this utility model.

Claims

1. A production system for preparing glycolic acid crystals from methyl glycolate, characterized in that, The production system includes: Raw material storage tank (1) is used to store methyl glycolate; A hydrolysis reactor (2) is connected to the raw material storage tank (1), and a water inlet and a catalyst inlet are respectively provided above the hydrolysis reactor (2); A thin film evaporator (3) is connected to the outlet of the hydrolysis reactor (2). A first condensation assembly is provided above the thin film evaporator (3). The first condensation assembly includes a first condenser (31) and a first mixed liquid receiving tank (32). The flash tank (4) is connected to the outlet of the thin film evaporator (3) through a pressure reducing valve. A second condensing assembly is provided above the flash tank (4). The second condensing assembly includes a second condenser (41), a second mixed liquid receiving tank (42), and a second vacuum pump (43) connected in sequence. The first crystallization vessel (5) is connected to the outlet of the flash tank (4); The first solid-liquid separation device (6) is connected to the outlet of the first crystallizing vessel (5); The second crystallization vessel (7) is connected to the liquid phase outlet of the first solid-liquid separation device (6), and a seed inlet is provided above the second crystallization vessel (7); The second solid-liquid separation device (8) is connected to the outlet of the second crystallization vessel (7).

2. The production system according to claim 1, characterized in that, A reflux condenser (21) is also provided above the hydrolysis reactor (2). The reflux condenser (21) is provided with a gas phase inlet, a condensate outlet and a gas phase outlet. The gas phase inlet and the condensate outlet of the reflux condenser (21) are both connected to the hydrolysis reactor (2). The gas outlet of the reflux condenser (21) is connected in sequence to the alcohol collection tank (22) and the first vacuum pump (23).

3. The production system according to claim 2, characterized in that, The hydrolysis reactor (2) includes a first hydrolysis reactor (2A) and a second hydrolysis reactor (2B). The water inlet and the catalyst inlet are located above the first hydrolysis reactor (2A), and the condenser reflux device (21) is located above the second hydrolysis reactor (2B). The first hydrolysis reactor (2A) is connected to the raw material storage tank (1), and the thin film evaporator (3) is connected to the outlet of the second hydrolysis reactor (2B).

4. The production system according to claim 3, characterized in that, The first hydrolysis reactor (2A) and the second hydrolysis reactor (2B) are installed with a height difference, and the height of the discharge port of the first hydrolysis reactor (2A) is higher than the height of the feed port of the second hydrolysis reactor (2B).

5. The production system according to claim 3, characterized in that, The first hydrolysis reactor (2A) is connected to the raw material storage tank (1) via a feed pump, and a preheater (11) is provided between the feed pump and the first hydrolysis reactor (2A).

6. The production system according to any one of claims 1 to 5, characterized in that, A buffer tank (33), a circulation pipeline (34), and a circulation pump (35) are provided between the thin film evaporator (3) and the flash tank (4). One end of the circulation pipeline (34) is connected to the thin film evaporator (3), and the other end of the circulation pipeline (34) is connected to the feed end of the flash tank (4) through the pressure reducing valve.

7. The production system according to claim 6, characterized in that, The thin-film evaporator (3) is a scraped film evaporator or a falling film evaporator.

8. The production system according to claim 1, characterized in that, The first solid-liquid separation device (6) is selected from a centrifuge; The second solid-liquid separation device (8) is selected from a pressure filtration device with a filtration pore size of 100μm~500μm.

9. The production system according to claim 1, characterized in that, A loss scale (24) is installed at the catalyst inlet. A weight loss scale (71) is provided at the seed crystal inlet.

10. The production system according to any one of claims 1 to 5, characterized in that, The liquid phase outlet of the second solid-liquid separation device (8) is connected to the water inlet of the hydrolysis reactor (2) through a delivery pump (9) and a delivery pipeline. A three-way valve (91) is installed on the delivery pipeline.

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