A separation system and method for a glycolide solid-liquid mixture

Abstract

This invention discloses a separation system and method for a solid-liquid mixture of glycolide. The separation system includes a horizontal screw centrifuge, an intermediate tank, a disc centrifuge, a solvent recovery tank, and a glycolide product tank. This invention utilizes two centrifuges in combination to coarsely separate the solid-liquid mixture of glycolide and solvent into fractions, obtaining purified solid glycolide with low moisture content and liquid solvent with low solid content.

Description

Technical Field

[0001] This invention relates to the field of crude glycolide purification technology, and to a processing system and method for crude glycolide purification. Specifically, it relates to a separation system and method for glycolide solid-liquid mixtures for purifying crude glycolide. The system utilizes two centrifuges in combination to fractionally separate the solid-liquid mixture of glycolide and solvent to obtain purified solid glycolide with low moisture content and liquid solvent with low solid content. Background Technology

[0002] Centrifuges are one of the main pieces of equipment in chemical plants and are also a widely used solid-liquid separation device in the coal chemical industry. The main task of a centrifuge is to separate solid particles and the liquid phase in a conveying liquid through centrifugal force.

[0003] Centrifuges typically process solid-liquid mixtures generated during production. They separate the solid and liquid phases in the production feed, allowing for their respective recovery and reuse. The feed is piped directly to the centrifuge, where the high-speed rotation of the rotor generates strong centrifugal force, accelerating the settling of particles and separating substances with different settling coefficients and buoyant densities. The separated phases are then transported to subsequent production units via different pipelines.

[0004] In actual production, during centrifugal separation, different centrifuges have different separation particle size ranges, and the size and density of solid particles are different, resulting in different centrifugal separation effects. When the particle size is too large, it may increase the load on the centrifuge; when the particle size is too small, the smaller solid particles cannot be separated and are sent to the subsequent equipment in the liquid phase, which may increase the load on the subsequent equipment or cause blockage, resulting in abnormal operation of the equipment and even shortening the service life of the equipment.

[0005] In existing solid-liquid separation solutions, two centrifuges of the same type are often connected in series to centrifuge the liquid in sequence. Since the two centrifuges of the same type have the same separation particle size range, the secondary separation effect is not good. When the solid particles in the liquid have a large particle size range, it is impossible to remove smaller solid particles, which does not achieve the expected effect. This can easily lead to turbid liquid, sedimentation, and blockage of subsequent equipment, affecting the normal operation of production. On the other hand, connecting two centrifuges with a large separation particle size range will cause the centrifuges to be overloaded, affecting the normal operation of the equipment and shortening its service life.

[0006] CN202110960873.7 discloses a method for purifying crude glycolide, including the steps of washing and separating the crude glycolide with solvent A and solvent B respectively, and optionally recrystallizing and separating the washed crude glycolide with solvent B; the solid-liquid separation operation can be carried out in a nitrogen pressure filter, a plate and frame filter, a centrifugal filter or various centrifuges, preferably in a plate and frame filter and a centrifugal filter, but the separation effect is poor. Summary of the Invention

[0007] The purpose of this invention is to provide a separation system and method for a solid-liquid mixture of glycolide, so as to obtain purified solid glycolide with low moisture content and liquid solvent with low solid content.

[0008] To achieve the above-mentioned objectives, the separation system provided by this invention adopts the following technical solution:

[0009] A separation system for a glycolide solid-liquid mixture, the separation system comprising:

[0010] A horizontal screw centrifuge, whose inlet is connected to a mixture feed pipe and a slurry outlet of a disc centrifuge, is used to perform solid-liquid separation on a mixture of coarse glycolide and solvent from the mixture feed pipe and glycolide slurry from the disc centrifuge to obtain a first filtrate and glycolide product.

[0011] An intermediate tank, whose inlet is connected to the filtrate outlet of the horizontal screw centrifuge, is used to receive the first filtrate;

[0012] A disc centrifuge is configured to perform solid-liquid separation on the liquid feed from the intermediate tank to obtain a second filtrate and a glycolide slurry;

[0013] Solvent recovery tank for receiving the second filtrate; and

[0014] A glycolide product tank for receiving the glycolide product.

[0015] According to the separation system of the present invention, preferably, the separation system further includes a transfer pump for feeding the liquid from the intermediate tank into the disc centrifuge.

[0016] According to the separation system of the present invention, preferably, the separation system further includes a plate filter press disposed between the intermediate tank and the horizontal screw centrifuge, for solid-liquid separation of the first filtrate from the horizontal screw centrifuge, and sending the resulting third filtrate into the intermediate tank, while the filter press material enters the horizontal screw centrifuge, either directly or after being mixed with the mixture, thereby reducing the solid content entering the disc centrifuge and ultimately reducing the solid content in the recovered solvent.

[0017] According to the separation system of the present invention, preferably, the separation system further includes a mixing tank for mixing crude ethylene oxide with a solvent, and is connected to the horizontal screw centrifuge via a mixture feed pipe.

[0018] According to the separation system of the present invention, preferably, the intermediate tank is a settling tank, used to settle the received filtrate, and the settled lower layer of liquid is sent to the disc centrifuge, while the upper clear liquid is sent to the mixing tank as part of the solvent. This is beneficial to improving the solid-liquid separation effect of the present invention. On the one hand, sending the clear liquid to the mixing tank is beneficial to the combination of the difficult-to-separate fine particles in the clear liquid with the remaining solid particles, which is convenient for subsequent separation. On the other hand, the relatively reduced amount of liquid going to the disc centrifuge reduces the processing load. In addition, the reduced amount of difficult-to-separate particles, combined with the other two factors, can significantly improve the separation effect.

[0019] According to the separation system of the present invention, preferably, the separation system is further provided with multiple solvent flushing pipes and nitrogen pipes, wherein the solvent flushing pipes are used to introduce solvent to flush the equipment in the separation system, and the nitrogen pipes are used to introduce nitrogen gas for protection into the equipment in the separation system used for solid-liquid separation.

[0020] In another aspect of achieving the above-mentioned objective, the present invention also provides a separation method for solid-liquid separation of a mixture of crude ethylene ester and solvent using the above-mentioned separation system.

[0021] Preferably, the glycolide content in the mixture is 5-40 wt%, such as 10 wt%, 20 wt%, or 35 wt%, more preferably 10-30 wt%.

[0022] Preferably, the solvent is isopropanol.

[0023] In some embodiments, the solvent content in the glycolide product is no more than 15 wt%, preferably no more than 10 wt%; and the glycolide content in the second filtrate is no more than 10 wt%, for example 8 wt%, preferably no more than 5 wt%.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This invention processes crude lactide by using a combination of a decanter and a disc centrifuge. This fully utilizes the advantages of both centrifuges to selectively separate solid particles of different sizes. The feed solution is first sent to the decanter centrifuge to separate the larger particles of crude lactide, reducing its content. The clarified liquid then enters the disc centrifuge for a second separation of the smaller particles, fully recovering the lactide and reducing the solid particle content in the solvent, thus minimizing the impact on subsequent equipment. Simultaneously, the solid phase separated by the disc centrifuge is returned to the decanter centrifuge inlet for further concentration. The entire system has only one outlet for clarified liquid and one outlet for solid phase, achieving effective separation of the solid and liquid phases, improving material recovery rate and production efficiency. Attached Figure Description

[0026] Figure 1 A schematic diagram of one embodiment of the separation system of the present invention is shown;

[0027] Figure 2 A schematic diagram of another embodiment of the separation system of the present invention is shown;

[0028] Figure 3 A schematic diagram of another embodiment of the separation system of the present invention is shown;

[0029] Explanation of reference numerals in the attached figures:

[0030] 1-Intermediate tank; 2-Transfer pump; 3-Horizontal screw centrifuge; 4-Yetide product tank; 5-Disc centrifuge; 6-Solvent recovery tank; 7-Plate and frame filter press; 8-Mixing tank;

[0031] ①-A mixture of crude glycolide and isopropanol solvent; ②-Isopropanol solvent; ③-Nitrogen gas under reduced pressure. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0033] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0034] Figure 1 The diagram illustrates one embodiment of the separation system provided by the present invention. The separation system includes a horizontal screw centrifuge, an intermediate tank, a disc centrifuge, a solvent recovery tank, a glycolide product tank, a feed pump, and a mixing tank. The inlet of the horizontal screw centrifuge is connected to both a mixture feed pipe and the slurry outlet of the disc centrifuge, for solid-liquid separation of the coarse glycolide and solvent mixture from the mixture feed pipe and the glycolide slurry from the disc centrifuge, to obtain a first filtrate and glycolide product. The glycolide product tank is used to receive the glycolide product.

[0035] The mixing tank is used for mixing the crude ethylene oxide with the solvent, and is connected to the horizontal screw centrifuge via the mixture feed pipe. The inlet of the intermediate tank is connected to the filtrate outlet of the horizontal screw centrifuge, and is used to receive the first filtrate. The transfer pump is used to deliver the feed liquid from the intermediate tank into the disc centrifuge.

[0036] The disc centrifuge is configured to perform solid-liquid separation on the liquid feed from the intermediate tank to obtain a second filtrate and a glycolide slurry. The solvent recovery tank is used to receive the second filtrate for subsequent solvent recovery and reuse.

[0037] In addition, the separation system is equipped with multiple solvent flushing pipes and nitrogen pipes. The solvent flushing pipes are used to introduce solvent to flush the equipment in the separation system, and the nitrogen pipes are used to introduce nitrogen gas for protection into the equipment in the separation system used for solid-liquid separation.

[0038] During operation, the mixture of crude lactide and solvent is sent to a horizontal screw centrifuge 3 for centrifugation. The separated slurry, as the lactide product, is sent to a lactide dissolving tank 4, and the first filtrate is sent to an intermediate tank 1. The liquid in the intermediate tank 1 is sent to a disc centrifuge 5 via a transfer pump 2 for centrifugation. The second filtrate is sent to a solvent recovery tank 6, and the separated lactide slurry is returned to the horizontal screw centrifuge 3 for further centrifugation. Additionally, the horizontal screw centrifuge 3, disc centrifuge 5, and transfer pump 2 should be intermittently flushed with isopropanol solvent, or during shutdowns, to reduce the deposition of solid materials in the equipment and pipelines, ensuring normal equipment operation. Furthermore, during operation, reduced-pressure nitrogen is used to protect the operation of the horizontal screw centrifuge 3 and disc centrifuge 5 to prevent air leakage into the system and the formation of an explosive mixture with the gaseous solvent. Nitrogen is also used for the mechanical seal protection of the centrifuges.

[0039] Figure 2 A schematic diagram of another embodiment of the separation system provided by the present invention is shown. The separation system includes a horizontal screw centrifuge, an intermediate tank, a disc centrifuge, a solvent recovery tank, a glycolide product tank, a feed pump, a mixing tank, and a plate and frame filter press. The inlet of the horizontal screw centrifuge is connected to both a mixture feed pipe and the slurry outlet of the disc centrifuge, for solid-liquid separation of the mixture of coarse glycolide and solvent from the mixture feed pipe and the glycolide slurry from the disc centrifuge, to obtain a first filtrate and glycolide product. The glycolide product tank is used to receive the glycolide product.

[0040] The mixing tank is used for mixing crude ethylene oxide with solvent, and is connected to the horizontal screw centrifuge through the mixture feed pipe.

[0041] A plate filter press is located between the intermediate tank and the horizontal screw centrifuge. It is used to perform solid-liquid separation on the first filtrate from the horizontal screw centrifuge, and send the resulting third filtrate into the intermediate tank, while the filter material enters the horizontal screw centrifuge.

[0042] The inlet of the intermediate tank is connected to the filtrate outlet of the plate and frame filter press, and is used to receive the third filtrate. The transfer pump is used to deliver the feed liquid from the intermediate tank into the disc centrifuge.

[0043] The disc centrifuge is configured to perform solid-liquid separation on the liquid feed from the intermediate tank to obtain a second filtrate and a glycolide slurry. The solvent recovery tank is used to receive the second filtrate for subsequent solvent recovery and reuse.

[0044] Figure 3The diagram illustrates one embodiment of the separation system provided by the present invention. The separation system includes a horizontal screw centrifuge, an intermediate tank, a disc centrifuge, a solvent recovery tank, a glycolide product tank, a feed pump, and a mixing tank. The inlet of the horizontal screw centrifuge is connected to both a mixture feed pipe and the slurry outlet of the disc centrifuge, for solid-liquid separation of the coarse glycolide and solvent mixture from the mixture feed pipe and the glycolide slurry from the disc centrifuge, to obtain a first filtrate and glycolide product. The glycolide product tank is used to receive the glycolide product.

[0045] The mixing tank is used for mixing crude ethylene oxide with solvent, and is connected to the horizontal screw centrifuge through the mixture feed pipe.

[0046] The intermediate tank is a settling tank, with its inlet connected to the filtrate outlet of the horizontal screw centrifuge. It is used to settle the received filtrate and to pump the settled lower layer of liquid into the disc centrifuge using a transfer pump. The upper clear liquid is sent into the mixing tank as part of the solvent (i.e., replacing part of the original solvent).

[0047] The disc centrifuge is configured to perform solid-liquid separation on the liquid feed from the intermediate tank to obtain a second filtrate and a glycolide slurry. The solvent recovery tank is used to receive the second filtrate for subsequent solvent recovery and reuse.

[0048] The present invention will be further described below with reference to embodiments:

[0049] Example 1

[0050] use Figure 1 The separation system separates a mixture of crude glycolide and isopropanol solvent (glycolide content 25 wt%) at room temperature.

[0051] The mixture is first sent to a horizontal screw centrifuge 3 for centrifugation. The separated slurry, as the glycolide product, is sent to a glycolide dissolving tank 4, and the first filtrate is sent to an intermediate tank 1. The liquid in the intermediate tank 1 is sent to a disc centrifuge 5 via a transfer pump 2 for centrifugation. The second filtrate is sent to a solvent recovery tank 6, and the separated glycolide slurry is returned to the horizontal screw centrifuge 3 for further centrifugation.

[0052] Testing revealed that the solvent content of the glycolide product was approximately 12 wt%; the glycolide content of the second filtrate was 9 wt%.

[0053] Example 2

[0054] use Figure 2 The separation system separates a mixture of crude glycolide and isopropanol solvent (glycolide content 25 wt%) at room temperature.

[0055] The mixture is first sent to a horizontal screw centrifuge 3 for centrifugation. The separated slurry, as the glycolide product, is sent to a glycolide dissolving tank 4. The first filtrate is sent to a plate filter press for solid-liquid separation. The third filtrate is sent to an intermediate tank 1, while the filter press material enters the horizontal screw centrifuge. The liquid in the intermediate tank 1 is sent to a disc centrifuge 5 via a transfer pump 2 for centrifugation. The second filtrate is sent to a solvent recovery tank 6, and the separated glycolide slurry is returned to the horizontal screw centrifuge 3 for further centrifugation.

[0056] The solvent content of the glycolide product was found to be approximately 12 wt%; the glycolide content of the second filtrate was approximately 8 wt%.

[0057] Example 3

[0058] use Figure 3 The separation system separates a mixture of crude glycolide and isopropanol solvent (glycolide content 25 wt%) at room temperature.

[0059] The mixture is first sent to a horizontal screw centrifuge 3 for centrifugation. The separated slurry, as the glycolide product, is sent to a glycolide dissolving tank 4, and the first filtrate is sent to a settling tank, which serves as an intermediate tank 1. The lower layer of liquid settled in the settling tank is pumped into the disc centrifuge, and the upper clear liquid is sent to a mixing tank. The second filtrate, after separation by the disc centrifuge 5, is sent to a solvent recovery tank 6, and the separated glycolide slurry is returned to the horizontal screw centrifuge 3 for further centrifugation.

[0060] The solvent content of the glycolide product was found to be approximately 11 wt%; the glycolide content of the second filtrate was approximately 5 wt%.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the horizontal screw centrifuge is replaced with a plate and frame filter press, otherwise the same.

[0063] Testing revealed that the solvent content of the glycolide product exceeded 20 wt%; the glycolide content of the second filtrate exceeded 10 wt%.

[0064] As can be seen from the comparison of Examples 1-3 and Comparative Example 1, the separation system of the present invention, through the combination of a horizontal screw centrifuge and a disc centrifuge, can effectively separate glycolide from the solvent. Furthermore, the separation effect was further significantly improved in Example 3 by using a settling tank, and the glycolide yield was also significantly higher than in Examples 1 and 2.

[0065] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are within the spirit and scope of the present invention.

Claims

1. A separation system for a glycolide solid-liquid mixture, characterized in that, The separation system includes: A horizontal screw centrifuge, whose inlet is connected to a mixture feed pipe and a slurry outlet of a disc centrifuge, is used to perform solid-liquid separation on a mixture of crude glycolide and solvent from the mixture feed pipe and glycolide slurry from the disc centrifuge to obtain a first filtrate and glycolide product. An intermediate tank, whose inlet is connected to the filtrate outlet of the horizontal screw centrifuge, is used to receive the first filtrate; A disc centrifuge is configured to perform solid-liquid separation on the liquid feed from the intermediate tank to obtain a second filtrate and a glycolide slurry; Solvent recovery tank for receiving the second filtrate; and A glycolide product tank for receiving the glycolide product; The separation system also includes a mixing tank for mixing crude glycolide with solvent, which is connected to the horizontal screw centrifuge via a mixture feed pipe; the intermediate tank is a settling tank for settling the received filtrate, and the settled lower layer of liquid is sent to the disc centrifuge, while the upper clear liquid is sent to the mixing tank as part of the solvent.

2. The separation system according to claim 1, characterized in that, The separation system also includes a transfer pump for feeding the liquid from the intermediate tank into the disc centrifuge.

3. The separation system according to claim 2, characterized in that, The separation system is also equipped with multiple solvent flushing pipes and nitrogen pipes. The solvent flushing pipes are used to introduce solvent to flush the equipment in the separation system, and the nitrogen pipes are used to introduce nitrogen gas for protection into the equipment in the separation system used for solid-liquid separation.

4. A separation method for solid-liquid separation of a mixture of crude glycolide and solvent using the separation system according to any one of claims 1-3.

5. The method according to claim 4, characterized in that, The mixture contains 5-40 wt% glycolide.

6. The method according to claim 4, characterized in that, The mixture contains 10-30 wt% glycolide.

7. The method according to any one of claims 4-6, characterized in that, The solvent is isopropanol.

8. The method according to claim 6, characterized in that, The solvent content in the glycolide product does not exceed 15 wt%; the glycolide content in the second filtrate does not exceed 10 wt%.

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