Method and system for recovery of mixed wash solution in glycolide preparation process

Abstract

The present application relates to a kind of glycolide preparation process in the recovery method of mixed washing solution and a kind of glycolide preparation process in the recovery system of mixed washing solution.The recovery method provided by the present application is aimed at the recovery separation of the mixed solution of the present application, first proposes the recovery method and system comprising separation-reaction separation-membrane separation, such as rectification technology, azeotropic rectification technology, reaction rectification technology and membrane separation technology, not only can realize the separation recovery of mixed washing solution, but also realize the hydrolysis of glycolic acid oligomer in washing liquid into glycolic acid, can be reused, improve the utilization of glycolic acid.The present application has the advantages of green process, simple process, strong operability, can realize the full recovery and utilization of glycolide washing liquid.

Description

Technical Field

[0001] This invention relates to the recovery process of waste solvents produced during polymer preparation, specifically to a method and system for recovering mixed washing solutions produced during glycolide preparation. Background Technology

[0002] Polyglycolic acid (PEG) is an important biodegradable polyester material. Under the catalysis of enzymes, it can degrade into glycolic acid, participating in human metabolism. Therefore, PEG is widely used in biomedical materials such as surgical sutures, artificial tissues, and controlled drug release. There are two methods for synthesizing PEG. One is direct polycondensation of glycolic acid, also known as the one-step method. This method typically yields polymers with low molecular weight and poor processing strength, making it unsuitable for medical materials. The other method involves first polycondensing glycolic acid to obtain glycolic acid with a low molecular weight, then depolymerizing it to glycolide (C4H4O4), and then polymerizing the glycolide to prepare PEG. This method, also known as the two-step method, can yield high molecular weight PEG. Therefore, the preparation process of glycolide is crucial for producing high molecular weight PEG.

[0003] The preparation of glycolide involves polycondensation, depolymerization, and purification steps. The purpose of purification is to obtain pure glycolide monomers. Methods for purifying crude glycolide include washing and crystallization, which require a large amount of solvent to remove glycolic acid and its oligomers. Acetone, cyclohexane, ethyl acetate, isopropanol, n-propanol, and n-butanol have high solubility for glycolic acid and its oligomers and are several commonly used washing solvents.

[0004] Therefore, the above process generates a large amount of washing waste solvent, which, in addition to the aforementioned possible washing solvents, also contains glycolic acid and its oligomers, as well as a small amount of crude glycolide washed out. Glycolic acid and its oligomers constitute a significant portion of the washing solvent and need to be recovered and hydrolyzed into smaller glycolic acid molecules for reuse in the polycondensation unit to improve the overall utilization rate of glycolic acid. Therefore, research on the recovery of washing waste liquid and the hydrolysis of glycolic acid oligomers during glycolide preparation is of great significance.

[0005] Separating mixed washing solvents is challenging, primarily due to the following reasons: 1. The mixed solvent system is complex. Ethyl acetate-cyclohexane, ethyl acetate-isopropanol, ethyl acetate-acetone, n-butanol-cyclohexane, isopropanol-cyclohexane, and n-propanol-cyclohexane all form azeotropic systems, making separation difficult. 2. During experiments, it was found that conventional distillation methods cannot completely remove the solvent from the system. Even under high vacuum and operating temperatures, a small amount of solvent remains in the glycolic acid and its oligomer reboiler. Furthermore, as the operating temperature or vacuum increases, the amount of washing solvent in the reboiler gradually decreases, leading to decreased product flowability and potential temperature runaway in the reboiler. These issues severely impact distillation operations. The presence of washing solvent in the concentrated glycolic acid and its oligomers significantly increases the separation difficulty after hydrolysis of the concentrated glycolic acid and its oligomers. Therefore, an additional washing solvent removal unit is required after the hydrolysis unit.

[0006] Developing a method for recovering the washing liquid produced during the preparation of glycolide, especially one that can simultaneously meet the requirements for hydrolysis of glycolic acid oligomers, would be of great significance. Summary of the Invention

[0007] The purpose of this invention is to address the problem of difficulty in recovering the washing liquid produced during the preparation and purification of glycolide by providing an efficient, green, and simplified recovery method to achieve the recycling of organic solvents and the reuse of glycolic acid and its oligomers, thereby improving the utilization rate of solvents and glycolic acid.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for recovering a mixed washing solution during the preparation of glycolide, the method comprising:

[0009] (1) The mixed washing solution is sent to the separation unit for separation, and most of the solvent A and solvent B are recovered;

[0010] (2) The remaining material is sent to the reaction separation unit, and solvent C is added as a reaction aid to obtain glycolic acid and its oligomers.

[0011] (3) After the gas phase at the top of the reaction separation unit is liquefied, membrane separation is performed to obtain permeate and concentrate. Optionally, the permeate is condensed and returned to step (2).

[0012] The method of the present invention is aimed at the recovery and separation of the mixed solution of the present invention. For the first time, a recovery method and system including separation-reaction separation and membrane separation, such as distillation technology, azeotropic-reactive distillation technology and membrane separation technology, is proposed. It can not only realize the separation and recovery of mixed washing solvent, but also realize the hydrolysis of glycolic acid oligomers in the washing liquid into glycolic acid, which can be reused and improve the utilization rate of glycolic acid.

[0013] This invention has the advantages of being green, simple, and easy to operate, and can achieve full recovery and utilization of glycolide washing liquid.

[0014] A second aspect of the present invention provides a system for recovering a mixed washing solution in the preparation process of glycolide, the system comprising:

[0015] Along the material flow direction, a separation unit, a reaction separation unit, a membrane separation unit and a condenser are connected in series.

[0016] The separation unit is used to feed the mixed washing solution into the separation unit for separation, and recover most of the solvent A and solvent B;

[0017] The reaction separation unit is used to react and separate the residual materials to obtain glycolic acid and its oligomers;

[0018] The membrane separation unit is used to liquefy the gas phase at the top of the reaction separation unit and then separate it using a membrane to obtain permeate and concentrate.

[0019] Preferably, the separation unit includes a first separation unit and a second separation unit connected in series. The mixed washing solution is sequentially fed into the first separation unit and the second separation unit for separation, and most of the solvent A and solvent B are recovered.

[0020] More preferably, the first separation unit and the second separation unit each include at least one packed distillation column and / or one plate distillation column; and / or

[0021] Preferably, the reaction separation unit includes at least one azeotropic-reactive distillation column, and preferably the bottom reboiler of the azeotropic-reactive distillation column is a forced circulation reboiler;

[0022] Preferably, the tube side of the reboiler at the bottom of the reaction separation unit is configured for loading a solid acid catalyst;

[0023] Preferably, the membrane separation unit is located between the top gas phase outlet of the reaction separation unit and the condenser, and a pressurization device is provided between the top gas phase outlet of the reaction separation unit and the membrane separation unit.

[0024] The method and system of the present invention are particularly suitable for the recovery of washing liquid produced in the preparation of glycolide. The preferred embodiment of the present invention adopts a distillation-azeotropic-reactive distillation-membrane separation method, which can simultaneously realize the recovery of mixed washing solvent and the hydrolysis of glycolic acid oligomers, simplifying the process flow and forming a closed loop of washing solvent. Attached Figure Description

[0025] Figure 1 A flowchart illustrating the recovery process of the mixed washing solvent produced during the preparation of glycolide according to an embodiment of the present invention is shown.

[0026] Explanation of reference numerals in the attached figures

[0027] Detailed equipment information:

[0028] ① is the first separation unit, ② is the second separation unit, ③ is the reaction separation unit, ④ is the membrane separation unit, and ⑤ is the pressure pump.

[0029] Specific stock information:

[0030] 1 is the mixed washing solution, 2 is the top product of the first separation unit, 3 is the bottom product of the first separation unit, 4 is the bottom product of the second separation unit, 5 is the top product of the second separation unit, 6 is the top product of the reaction separation unit, 7 is the concentrate, 8 is the permeate after condensation, 9 is the bottom product of the reaction separation unit, and 10 is the fresh solvent C. Detailed Implementation

[0031] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] In this invention, unless otherwise specified, the "bottom" of a container (such as a distillation column, reactor, etc.) refers to the position of the container from top to bottom at 90-100%; the "top" of the container refers to the position of the container from top to bottom at 0-10%; the "upper part" of the container refers to the position of the container from top to bottom at 0-30%; and the "middle part" of the container refers to the position of the container from top to bottom at 30-70%.

[0033] This invention provides a method for recovering a mixed washing solution during the preparation of glycolide, the method comprising:

[0034] (1) The mixed washing solution is sent to the separation unit for separation, and most of the solvent A and solvent B are recovered;

[0035] (2) The remaining material is sent to the reaction separation unit, and solvent C is added as a reaction aid to obtain glycolic acid and its oligomers.

[0036] (3) After the gas phase at the top of the reaction separation unit is liquefied, membrane separation is performed to obtain permeate and concentrate. Optionally, the permeate is condensed and returned to step (2).

[0037] The recovery method described in this invention recovers the washing liquid produced during the preparation of glycolide on the one hand, and hydrolyzes glycolic acid oligomers into glycolic acid through reaction separation, such as the preferred azeotropic-reactive distillation, thereby improving the recovery and utilization rate of glycolic acid. This invention employs a separation-reaction separation-membrane separation method, such as distillation-azeotropic-reactive distillation-membrane separation, to simultaneously achieve the recovery of mixed washing solvents and the hydrolysis of glycolic acid oligomers, simplifying the process flow and creating a closed-loop reuse of the washing solvents.

[0038] In this invention, the separation unit separates solvent A and solvent B based on their different boiling points.

[0039] According to a preferred embodiment of the present invention, in the mixed washing solution, solvent A and solvent B account for 70%-95% of the total mass of the mixed washing solution, and the remainder is glycolic acid and its crude oligomers washed off during the glycolide washing process. Depending on the glycolide washing process, the proportions of solvent A and solvent B used are not entirely the same; under normal conditions, solvent A accounts for 5%-40% of the total detergent usage.

[0040] According to a preferred embodiment of the present invention, solvents A and B are respectively selected from acetone, cyclohexane, ethyl acetate, isopropanol, n-propanol, and n-butanol. Acetone, cyclohexane, ethyl acetate, isopropanol, n-propanol, and n-butanol all have good solubility for glycolic acid and its oligomers, and are commonly used washing solvents. To further improve the washing effect, a mixed solvent is usually used for washing in multiple steps, which can completely wash out glycolic acid and its oligomers from the glycolide product.

[0041] According to a preferred embodiment of the present invention, the separation unit includes a first separation unit and a second separation unit; the mixed washing solution is sequentially introduced into the first separation unit and the second separation unit for separation, and most of the solvent A and solvent B are recovered.

[0042] According to a preferred embodiment of the present invention, the separation unit includes a first separation unit and a second separation unit; the purpose of the first separation unit is to remove components with lower boiling points from the mixed solvent, and the purpose of the second separation unit is to remove and recover components with higher boiling points from the mixed solvent.

[0043] According to a preferred embodiment of the present invention, the first separation unit and the second separation unit are ordinary distillation; ordinary distillation is relative to special distillation such as reactive distillation, and no third component is added as an azeotropic agent or extractant during the process, which is a routine operation in the distillation process.

[0044] As mentioned above, the first and second separation units in this invention can be general distillation apparatuses, consisting of a distillation column, condenser, reflux tank, and reboiler, etc. Distillation columns are mainly divided into packed distillation columns and plate distillation columns. This invention does not have special requirements for the first and second distillation columns used in the first and second separation units. Preferably, both the first and second distillation columns are ordinary column equipment, which can be packed distillation columns or plate distillation columns. For this invention, using ordinary packed distillation columns or plate distillation columns can achieve the above-mentioned objectives.

[0045] According to a preferred embodiment of the present invention, the equipment used in the first separation unit and the second separation unit respectively includes at least one packed distillation column and / or a plate distillation column. A distillation column is a tower-type gas-liquid contact device used for distillation, utilizing the different volatility of the components in the mixture to achieve separation. Distillation columns are mainly divided into two categories: packed distillation columns and plate distillation columns.

[0046] According to a preferred embodiment of the present invention, the operating conditions of the first separation unit include: a pressure of 0.5-1 atm and a reflux ratio of 0.5-5. The purpose of the first separation unit is to completely remove solvent A. Solvent B may form an azeotrope with solvent A, resulting in some solvent B being carried out during the removal of solvent A. The resulting mixed solvent can still be used as a mixed washing liquid. To ensure the operating temperature of the first separation unit and prevent the condensation of glycolic acid, it needs to be carried out under negative pressure, with a preferred operating range of 0.5-1 atm. A lower operating temperature would reduce the required condensation temperature at the top of the column, requiring a colder medium, while a higher operating temperature would result in a higher temperature at the bottom of the column, leading to the condensation reaction of glycolic acid. The reflux ratio of the first separation unit is preferably in the range of 0.5-5. A lower reflux ratio would result in a small amount of solvent B being distilled from the top of the column in addition to the azeotropic composition of solvent A and solvent B, while a higher reflux ratio would significantly increase the energy consumption of the distillation process.

[0047] According to a preferred embodiment of the present invention, the operating conditions of the second separation unit include: a pressure of 0.5-1 atm and a reflux ratio of 0.2-5. The purpose of the second separation unit is to remove and recover solvent B. During the distillation process, to ensure the fluidity of the product in the reboiler and a low operating temperature in the reboiler, it is necessary to maintain a 5%-10% solvent B residue in the reboiler product. The second distillation needs to be carried out at a low temperature to ensure that glycolic acid does not undergo or reduces the occurrence of a condensation reaction in the reboiler product. The preferred operating pressure range is 0.5-1 atm. Lower pressures would reduce the required condensation temperature at the top of the column, requiring a colder medium, while higher pressures would result in a higher reboiler temperature, leading to a condensation reaction of glycolic acid. The preferred reflux ratio of the second separation unit is in the range of 0.2-5. Lower pressures would result in some glycolic acid and its oligomers distilling off from the top of the column during distillation, causing losses, while higher pressures would significantly increase the energy consumption of the distillation process.

[0048] According to a preferred embodiment of the present invention, the solvent C is water. Water can form an azeotropic system well with most washing solvents, which helps to completely remove solvent B that was not completely removed in the separation unit in the reaction separation unit. Furthermore, water facilitates the hydrolysis of glycolic acid oligomers into monomeric glycolic acid, making it convenient to recycle the washed glycolic acid.

[0049] According to a preferred embodiment of the present invention, the reaction separation unit is an azeotropic-reactive distillation unit. The purpose of the reaction separation unit is twofold: to remove solvent B that was not completely removed in the separation unit via azeotropic distillation, and to degrade the glycolic acid oligomer into glycolic acid through reactive hydrolysis, facilitating its recycling.

[0050] According to a preferred embodiment of the present invention, the mass flow rate of solvent C is 0.2-5 times the mass flow rate of the raw materials in the reaction separation unit; the purpose of the reaction separation unit is to remove residual solvent B and achieve the hydrolysis of glycolic acid oligomers. Experiments have shown that within the above-mentioned ratio range, solvent B can be completely removed, and the degree of hydrolysis of glycolic acid in the reaction separation unit is relatively high.

[0051] According to a preferred embodiment of the present invention, the operating conditions of the reaction separation unit include: a pressure of 0.2-1 atm and a reflux ratio of 0.5-5. To effectively remove residual solvent B, the operating pressure of the reaction separation unit needs to be controlled within a certain range. A lower pressure will cause the temperature of the reboiler to be too low, which is not conducive to the hydrolysis reaction, while a higher pressure will increase the difficulty of separating solvent B. Therefore, the preferred operating pressure is 0.2-1 atm. Simultaneously, to completely remove residual solvent B and reduce the loss of glycolic acid in this process, the reflux ratio needs to be controlled within a certain range, preferably between 0.5 and 5.

[0052] According to a preferred embodiment of the present invention, the equipment used in the reaction separation unit includes at least one azeotropic-reactive distillation column; preferably, the bottom reboiler of the azeotropic-reactive distillation column is a forced circulation reboiler; more preferably, the tube side of the reboiler is filled with a solid acid catalyst to improve the hydrolysis effect of glycolic acid oligomers.

[0053] The bottom of the reaction separation unit contains concentrated glycolic acid and its oligomers, resulting in relatively poor fluidity. Therefore, a forced-circulation reboiler is required to reduce scaling caused by poor fluidity during reboiling. The forced-circulation reboiler carries the bottom product on the tube side and the heating medium on the shell side. Simultaneously, a solid acid catalyst needs to be packed in the tube side through which the bottom product flows. The catalyst catalyzes the hydrolysis of glycolic acid oligomers, converting them into glycolic acid and its dimers or trimers. The addition of a solid acid catalyst to the tube side also increases the resistance to bottom product flow, which is why a forced-circulation reboiler is preferred. Experimental results show that solid acid catalysts require higher temperatures to achieve better hydrolysis efficiency. The reboiler in the bottom of the column has the highest temperature and the highest concentration of glycolic acid oligomers, making it the optimal location for the hydrolysis reaction. Combined with solvent C, most glycolic acid oligomers can be hydrolyzed, significantly improving the recovery rate of glycolic acid.

[0054] According to a preferred embodiment of the present invention, the solid acid catalyst is an ion exchange resin, preferably one or more of Amberlyst 15, Amberlyst 35, Amberlyst 36, Amberlyst 45, Amberlyst 21, and Amberlyst 26. Ion exchange resins are a type of solid acid catalyst, and when participating in liquid-phase hydrolysis reactions, they have the advantages of good separation and no acid residue. For the hydrolysis reaction of glycolic acid oligomers, using one or more of Amberlyst 15, Amberlyst 35, Amberlyst 36, Amberlyst 45, Amberlyst 21, and Amberlyst 26 can achieve a very good hydrolysis effect, capable of hydrolyzing most glycolic acid oligomers into glycolic acid and glycolic acid dimers or trimers, thus meeting the requirements of the present invention.

[0055] According to the present invention, the gas phase at the top of the reaction separation unit is liquefied and then separated by membrane separation. According to one embodiment of the present invention, the product distilled from the reaction separation unit is liquefied after compression and enters the membrane separation device. The product is liquefied by providing pressure through compression, which pushes the product at the top of the column into the membrane separation device.

[0056] According to a preferred embodiment of the present invention, the membrane separation method is pervaporation.

[0057] According to a preferred embodiment of the present invention, the membrane separation employs a molecular sieve membrane, and the membrane separation method is pervaporation. The top product of the reaction separation unit is a mixture of water and solvent B. Since solvent B and water exhibit azeotropic properties, traditional distillation processes struggle to completely separate them. Membrane separation is required for deep separation of water from solvent B. Molecular sieve membranes are thin films prepared from molecular sieves with a thickness on the micrometer scale, enabling molecular separation. Due to the extremely small pore size of molecular sieves, they exhibit very strong water separation characteristics and are commonly used inorganic membrane materials for dehydration. Pervaporation refers to the conventional operation method of membrane separation, where the feed liquid enters the membrane module, flows across the membrane surface, and a low pressure is maintained on the back side of the membrane. The components in the feed liquid permeate through the membrane to the back side. Because the back side of the membrane is under low pressure, the components vaporize into vapor upon passing through the membrane. The vapor is removed by a vacuum pump or by purging with an inert gas, allowing the permeation process to continue. Commonly used molecular sieve membranes can be used in this invention, and will not be described in detail here.

[0058] According to a preferred embodiment of the present invention, the membrane separation unit is positioned between the gas phase outlet at the top of the reaction separation unit and the condenser. Pervaporation requires preheating the feedstock at the feed inlet to achieve a superheated state. The above design fully utilizes the high-grade vapor phase exiting the top of the column, achieving full utilization of thermal energy and reducing the overall energy consumption for recovery.

[0059] According to a preferred embodiment of the present invention, a pressurizing device is provided between the vapor phase outlet at the top of the azeotropic distillation column and the membrane separation unit. Since pervaporation requires a certain pressure as a driving force to propel water molecules through the membrane side into the permeate side, it is preferable to add a pressurizing device at the upstream end of the membrane separation unit to pressurize the vapor phase product exiting the top of the azeotropic reactive distillation column.

[0060] According to a preferred embodiment of the present invention, the membrane separation unit is located between the top gas phase outlet of the reaction separation unit and the condenser, and a pressurization device is provided between the top gas phase outlet of the reaction separation unit and the membrane separation unit.

[0061] According to a preferred embodiment of the present invention, the permeate from the membrane separation and solvent C are combined and enter the reaction separation unit. The permeate from the membrane separation is solvent C, and this portion of solvent C, along with the added solvent C, enters from the upper middle part of the reaction separation unit. Compared to the amount of solvent B entering the reaction separation unit, solvent C, in addition to forming an azeotrope with solvent B, can also undergo a hydrolysis reaction with the oligomers of glycolic acid, ensuring the fluidity of the column bottom. Therefore, it is preferred that the addition of solvent C is in excess.

[0062] According to a second aspect of the present invention, the present invention provides a system for recovering a mixed washing solution in the preparation process of glycolide, the system comprising:

[0063] Along the material flow direction, a separation unit, a reaction separation unit, a membrane separation unit and a condenser are connected in series.

[0064] The separation unit is used to feed the mixed washing solution into the separation unit for separation, and recover most of the solvent A and solvent B;

[0065] The reaction separation unit is used to react and separate the residual materials to obtain glycolic acid and its oligomers;

[0066] The membrane separation unit is used to liquefy the gas phase at the top of the reaction separation unit and then separate it using a membrane to obtain permeate and concentrate.

[0067] According to a preferred embodiment of the present invention, preferably, the separation unit includes a first separation unit and a second separation unit connected in series, wherein the mixed washing solution is sequentially introduced into the first separation unit and the second separation unit for separation, and most of the solvent A and solvent B are recovered.

[0068] According to a preferred embodiment of the present invention, more preferably, the first separation unit and the second separation unit each include at least one packed distillation column and / or a plate distillation column.

[0069] According to a preferred embodiment of the present invention, preferably, the reaction separation unit includes at least one azeotropic-reactive distillation column, and preferably the bottom reboiler of the azeotropic-reactive distillation column is a forced circulation reboiler.

[0070] According to a preferred embodiment of the present invention, preferably, the tube side of the reboiler at the bottom of the reaction separation unit is configured for loading a solid acid catalyst.

[0071] According to a preferred embodiment of the present invention, preferably, the membrane separation unit is located between the top gas phase outlet of the reaction separation unit and the condenser, and a pressurization device is provided between the top gas phase outlet of the reaction separation unit and the membrane separation unit.

[0072] According to a preferred embodiment of the present invention, a first separation reaction unit, a second separation reaction unit, a reaction separation unit, and a membrane separation unit and a condenser disposed at the top gas phase outlet of the reaction separation unit are connected in series along the material flow direction; the tube side of the reboiler at the bottom of the third separation reaction is used to pack a solid acid catalyst.

[0073] The first separation unit is used to perform a first distillation on the mixed washing solution to completely remove solvent A from the first separation unit;

[0074] The second separation unit is used to perform the second distillation, from which most of the solvent B is separated;

[0075] The reaction separation unit is used to carry out a third azeotropic reactive distillation in the presence of solvent C, and to completely separate solvent B and the mixture containing glycolic acid and its oligomers from the reaction separation unit.

[0076] The membrane separation unit is used to separate the gas phase from the top of the reaction separation unit through the pressurization device to obtain permeate and a concentrate mainly composed of solvent B. Optionally, the permeate can be condensed and returned to the reaction separation unit via the top condenser.

[0077] According to a preferred embodiment of the present invention, the first separation unit includes a feed inlet, a top gas phase outlet, a bottom outlet, a condensate reflux inlet on the upper side wall, a top condenser, a bottom reboiler, and a reboiler circulation inlet on the lower side wall.

[0078] According to a preferred embodiment of the present invention, the second separation unit includes a feed inlet, a top gas phase outlet, a bottom outlet, a condensate reflux inlet on the upper side wall, a top condenser, a bottom reboiler, and a reboiler circulation inlet on the lower side wall.

[0079] According to a preferred embodiment of the present invention, the reaction separation unit includes a feed inlet, a gas phase outlet at the top of the column, a bottom outlet, a condensate reflux and azeotropic agent inlet on the upper side wall, a top condenser, a bottom reboiler, and a reboiler circulation inlet on the lower side wall.

[0080] According to a preferred embodiment of the present invention, the following embodiments employ the following... Figure 1 The process is as shown. The method of this invention is used to recover the mixed washing solution 1 in the glycolide preparation process. The mixed washing solution 1 enters from the middle of the first separation unit ①. The top product 2 of the first separation unit is a solution containing solvent A, which can be directly returned to the washing unit for glycolide preparation. The bottom product 3 of the first separation unit is the bottom product after removing solvent A. The bottom product 3 of the first distillation column enters from the middle of the second separation unit ②. The top product 5 of the second distillation column is solvent B. The bottom product 4 of the second separation unit is a concentrated solution of glycolic acid and its oligomers, which contains a small amount of residual solvent B. It enters the reaction separation unit ③. The top product 6 of the reaction separation unit is a gas phase product that enters the membrane separation unit ④ directly through the pressurized pump ⑤. The concentrated solution 7 of the membrane separation is mainly solvent B, which can be combined with the top product 5 of the second separation unit and returned to the washing unit for glycolide preparation. The condensed permeate 8 of the membrane separation, mainly solvent C, and the added fresh solvent C10 enter the reaction separation unit ③ together. The bottom product 9 of the reaction separation unit mainly consists of glycolic acid and its dimers and trimers. The following examples use... Figure 1 The process shown is used for recycling.

[0081] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0082] The reagents and raw materials used in this invention are all commercially available.

[0083] In this invention, the purity or concentration of the products in all embodiments was detected by GC or HPLC, and the moisture content was determined by Karl Fischer titration.

[0084] In this embodiment of the invention, the molecular sieve membrane used is a molecular sieve membrane from Jiangsu Jiutian High-Tech Co., Ltd.

[0085] Example 1

[0086] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 70% of the total mass, and cyclohexane accounts for 40% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 0.5 atm and a reflux ratio of 1. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 78.8% and 21.2%, respectively. The recovery rate of cyclohexane is 98.4%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 0.5 atm and a reflux ratio of 2. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.88%. The bottom product is a concentrate of glycolic acid and its oligomers, in which n-propanol accounts for 7.2% of the total mass. The obtained bottom product then enters the reaction separation unit for further recovery processing.

[0087] Example 2

[0088] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 80% of the total mass, and cyclohexane accounts for 30% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 0.75 atm and a reflux ratio of 1. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 79.0% and 21.0%, respectively. The recovery rate of cyclohexane is 98.6%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 0.5 atm and a reflux ratio of 2. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.86%. The bottom product is a concentrate of glycolic acid and its oligomers, in which n-propanol accounts for 7.3% of the total mass. The obtained bottom product then enters the reaction separation unit for further recovery processing.

[0089] Example 3

[0090] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 95% of the total mass, and cyclohexane accounts for 5% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 1 atm and a reflux ratio of 1. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 77.5% and 22.5%, respectively. The recovery rate of cyclohexane is 99.0%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 0.5 atm and a reflux ratio of 2. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.90%. The bottom product is a concentrate of glycolic acid and its oligomers, with n-propanol accounting for 7.2% of the total mass. This bottom product then enters the reaction separation unit for further recovery processing.

[0091] Example 4

[0092] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 90% of the total mass, and cyclohexane accounts for 20% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 0.75 atm and a reflux ratio of 0.5. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 78.0% and 22.0%, respectively. The recovery rate of cyclohexane is 99.1%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 0.5 atm and a reflux ratio of 2. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.89%. The bottom product is a concentrated solution of glycolic acid and its oligomers, in which n-propanol accounts for 7.3% of the total mass. The obtained bottom product then enters the reaction separation unit for further recovery processing.

[0093] Example 5

[0094] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 90% of the total mass, and cyclohexane accounts for 20% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 0.75 atm and a reflux ratio of 3. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 79.6% and 20.4%, respectively. The recovery rate of cyclohexane is 98.6%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 0.5 atm and a reflux ratio of 2. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.85%. The bottom product is a concentrate of glycolic acid and its oligomers, with n-propanol accounting for 7.4% of the total mass. This bottom product then enters the reaction separation unit for further recovery processing.

[0095] Example 6

[0096] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 90% of the total mass, and cyclohexane accounts for 20% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 0.75 atm and a reflux ratio of 5. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 79.5% and 20.5%, respectively. The recovery rate of cyclohexane is 98.3%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 0.5 atm and a reflux ratio of 2. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.87%. The bottom product is a concentrate of glycolic acid and its oligomers, in which n-propanol accounts for 7.2% of the total mass. The obtained bottom product then enters the reaction separation unit for further recovery processing.

[0097] Example 7

[0098] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 90% of the total mass, and cyclohexane accounts for 20% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 0.75 atm and a reflux ratio of 1. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 78.2% and 21.4%, respectively. The recovery rate of cyclohexane is 98.8%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 0.75 atm and a reflux ratio of 2. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.88%. The bottom product is a concentrate of glycolic acid and its oligomers, containing a small amount of residual n-propanol, which is determined to account for 7.5% of the total mass. The obtained bottom product then enters the reaction separation unit for further recovery processing.

[0099] Example 8

[0100] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 90% of the total mass, and cyclohexane accounts for 20% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 0.75 atm and a reflux ratio of 1. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 78.3% and 21.4%, respectively. The recovery rate of cyclohexane is 98.7%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 1 atm and a reflux ratio of 2. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.86%. The bottom product is a concentrate of glycolic acid and its oligomers, in which n-propanol accounts for 7.8% of the total mass. The obtained bottom product then enters the reaction separation unit for further recovery processing.

[0101] Example 9

[0102] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 90% of the total mass, and cyclohexane accounts for 20% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 0.75 atm and a reflux ratio of 1. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 78.1% and 21.6%, respectively. The recovery rate of cyclohexane is 98.8%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 0.5 atm and a reflux ratio of 0.2. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.58%. The bottom product is a concentrate of glycolic acid and its oligomers, in which n-propanol accounts for 7.0% of the total mass. The obtained bottom product then enters the reaction separation unit for further recovery processing.

[0103] Example 10

[0104] A batch of washing liquid from the preparation of glycolide, wherein cyclohexane and n-propanol solvents account for 90% of the total mass, and cyclohexane accounts for 20% of the total mass of cyclohexane and n-propanol. This washing liquid first enters the first separation unit. The first separation unit operates at a pressure of 0.75 atm and a reflux ratio of 1. A mixture of cyclohexane and n-propanol is obtained at the top of the column, with concentrations of 78.1% and 21.5%, respectively. The recovery rate of cyclohexane is 98.8%. The bottom product from the first separation unit then enters the second separation unit, which operates at a pressure of 0.5 atm and a reflux ratio of 5. n-Propanol solvent is obtained at the top of the second separation unit, with a concentration of 99.92%. The bottom product is a concentrated solution of glycolic acid and its oligomers, in which n-propanol accounts for 8.0% of the total mass. The obtained bottom product then enters the reaction separation unit for further recovery processing.

[0105] Example 11

[0106] The concentrated glycolic acid and its oligomers obtained from the first and second separation units in Example 7 contained a small amount of n-propanol, accounting for 7.5% of the total mass. Glycolic acid and its dimers and trimers accounted for 7.8% of the total glycolic acid and its oligomers. This concentrated solution entered the reaction separation unit, with water added at 0.2 times the feed flow rate. The forced circulation reboiler was packed with Amberlyst 15 solid acid catalyst. The operating pressure of the reaction separation unit was 0.2 atm, and the reflux ratio was 0.5. The gaseous product obtained at the top of the reaction separation unit was pressurized and then entered a membrane separation unit. The concentrated product was n-propanol, which was measured to contain 562 ppm of water and 99.90% n-propanol. The overall recovery rate of n-propanol (including the operation of the first and second separation units) was 98.2%. The permeate, consisting of water, was returned to the distillation column after passing through a condenser. The main product of the reaction separation unit is glycolic acid and its oligomers. After solid acid catalytic hydrolysis, the proportion of glycolic acid and its dimers and trimers reaches 48.2%, which plays a good role in azeotropic-reactive distillation.

[0107] Example 12

[0108] The concentrated glycolic acid and its oligomers obtained from the first and second separation units in Example 7 contained a small amount of n-propanol, accounting for 7.5% of the total mass. Glycolic acid and its dimers and trimers accounted for 7.8% of the total glycolic acid and its oligomers. This concentrated solution entered the reaction separation unit, with water added at 1 times the feed flow rate. The forced circulation reboiler was packed with Amberlyst 35 solid acid catalyst. The operating pressure of the reaction separation unit was 0.2 atm, and the reflux ratio was 1. The gaseous product obtained at the top of the reaction separation unit was compressed and then entered a membrane separation unit. The concentrated product was n-propanol, which was measured to contain 602 ppm of water and 99.92% n-propanol. The overall recovery rate of n-propanol (including the operation of the first and second separation units) was 97.8%. The permeate, consisting of water, was returned to the distillation column after passing through a condenser. The main product of the bottom column of the reaction separation unit is glycolic acid and its oligomers. After solid acid catalytic hydrolysis, the proportion of glycolic acid and its dimers and trimers reaches 56.5%, which plays a good role in azeotropic-reactive distillation.

[0109] Example 13

[0110] The concentrated glycolic acid and its oligomers obtained from the first and second separation units in Example 7 contained a small amount of n-propanol, accounting for 7.5% of the total mass. Glycolic acid and its dimers and trimers accounted for 7.8% of the total glycolic acid and its oligomers. This concentrated solution entered the reaction separation unit, with water added at three times the feed flow rate. The forced circulation reboiler was packed with Amberlyst 36 solid acid catalyst. The operating pressure of the reaction separation unit was 0.2 atm, and the reflux ratio was 2. The gaseous product obtained at the top of the reaction separation unit was compressed and then entered a membrane separation unit. The concentrated product was n-propanol, which was measured to contain 593 ppm of water and 99.94% n-propanol. The overall recovery rate of n-propanol (including the operations of the first and second separation units) was 97.6%. The permeate, consisting of water, was returned to the distillation column after passing through a condenser. The main product of the reaction separation unit is glycolic acid and its oligomers. After solid acid catalytic hydrolysis, the proportion of glycolic acid and its dimers and trimers reaches 67.4%, which plays a good role in azeotropic-reactive distillation.

[0111] Example 14

[0112] The concentrated glycolic acid and its oligomers obtained from the first and second separation units in Example 7 contained a small amount of n-propanol, accounting for 7.5% of the total mass. Glycolic acid and its dimers and trimers accounted for 7.8% of the total glycolic acid and its oligomers. This concentrated solution entered the reaction separation unit, with water added at five times the feed flow rate. The forced circulation reboiler was packed with Amberlyst 45 solid acid catalyst. The operating pressure of the reaction separation unit was 0.2 atm, and the reflux ratio was 5. The gaseous product obtained at the top of the reaction separation unit was compressed and then entered a membrane separation unit. The concentrated product was n-propanol, which was measured to contain 541 ppm of water and 99.96% n-propanol. The overall recovery rate of n-propanol (including the operation of the first and second separation units) was 97.1%. The permeate, consisting of water, was returned to the distillation column after passing through a condenser. The main product of the reaction separation unit is glycolic acid and its oligomers. After solid acid catalytic hydrolysis, the proportion of glycolic acid and its dimers and trimers reaches 69.1%, which plays a good role in azeotropic-reactive distillation.

[0113] Example 15

[0114] The concentrated glycolic acid and its oligomers obtained from the first and second separation units in Example 7 contained a small amount of n-propanol, accounting for 7.5% of the total mass. Glycolic acid and its dimers and trimers accounted for 7.8% of the total glycolic acid and its oligomers. This concentrated solution entered the reaction separation unit, with water added at three times the feed flow rate. The forced circulation reboiler was packed with Amberlyst 21 solid acid catalyst. The operating pressure of the reaction separation unit was 0.2 atm, and the reflux ratio was 2. The gaseous product obtained at the top of the reaction separation unit was compressed and then entered a membrane separation unit. The concentrated product was n-propanol, which was measured to contain 584 ppm of water and 99.95% n-propanol. The overall recovery rate of n-propanol (including the operation of the first and second separation units) was 97.7%. The permeate, consisting of water, was returned to the distillation column after passing through a condenser. The main product of the reaction separation unit is glycolic acid and its oligomers. After solid acid catalytic hydrolysis, the proportion of glycolic acid and its dimers and trimers reaches 66.9%, which plays a good role in azeotropic-reactive distillation.

[0115] Example 16

[0116] The concentrated glycolic acid and its oligomers obtained from the first and second separation units in Example 7 contained a small amount of n-propanol, accounting for 7.5% of the total mass. Glycolic acid and its dimers and trimers accounted for 7.8% of the total glycolic acid and its oligomers. This concentrated solution entered the reaction separation unit, with water added at three times the feed flow rate. The forced circulation reboiler was packed with Amberlyst 26 solid acid catalyst. The operating pressure of the reaction separation unit was 0.5 atm, and the reflux ratio was 2. The gaseous product obtained at the top of the reaction separation unit was compressed and then entered a membrane separation unit. The concentrated product was n-propanol, which was measured to contain 573 ppm of water and 99.94% n-propanol. The overall recovery rate of n-propanol (including the operation of the first and second separation units) was 97.5%. The permeate, consisting of water, was returned to the distillation column after passing through a condenser. The main product of the reaction separation unit is glycolic acid and its oligomers. After solid acid catalytic hydrolysis, the proportion of glycolic acid and its dimers and trimers reaches 72.2%, which plays a good role in azeotropic-reactive distillation.

[0117] Example 17

[0118] The concentrated glycolic acid and its oligomers obtained from the first and second separation units in Example 7 contained a small amount of n-propanol, accounting for 7.5% of the total mass. Glycolic acid and its dimers and trimers accounted for 7.8% of the total glycolic acid and its oligomers. This concentrated solution entered the reaction separation unit, with water added at three times the feed flow rate. The forced circulation reboiler was packed with Amberlyst 15 solid acid catalyst. The operating pressure of the reaction separation unit was 0.75 atm, and the reflux ratio was 2. The gaseous product obtained at the top of the reaction separation unit was compressed and then entered a membrane separation unit. The concentrated product was n-propanol, which was measured to contain 566 ppm of water and 99.94% n-propanol. The overall recovery rate of n-propanol (including the operations of the first and second separation units) was 97.6%. The permeate, consisting of water, was returned to the distillation column after passing through a condenser. The main product of the reaction separation unit is glycolic acid and its oligomers. After solid acid catalytic hydrolysis, the proportion of glycolic acid and its dimers and trimers reaches 78.5%, which plays a good role in azeotropic-reactive distillation.

[0119] Example 18

[0120] The concentrated glycolic acid and its oligomers obtained from the first and second separation units in Example 7 contained a small amount of n-propanol, accounting for 7.5% of the total mass. Glycolic acid and its dimers and trimers accounted for 7.8% of the total glycolic acid and its oligomers. This concentrated solution entered the reaction separation unit, with water added at three times the feed flow rate. The forced circulation reboiler was packed with Amberlyst 15 solid acid catalyst. The operating pressure of the reaction separation unit was 1 atm, and the reflux ratio was 2. The gaseous product obtained at the top of the reaction separation unit was compressed and then entered a membrane separation unit. The concentrated product was n-propanol, which was measured to contain 574 ppm of water and 99.95% n-propanol. The overall recovery rate of n-propanol (including the operations of the first and second separation units) was 97.7%. The permeate, consisting of water, was returned to the distillation column after passing through a condenser. The main product of the reaction separation unit is glycolic acid and its oligomers. After solid acid catalytic hydrolysis, the proportion of glycolic acid and its dimers and trimers reaches 81.2%, which plays a good role in azeotropic-reactive distillation.

[0121] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0122] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for recovering a mixed washing solution during the preparation of glycolide, characterized in that, The method includes: (1) The mixed washing solution is sent to the separation unit for separation, and most of the solvent A and solvent B are recovered; (2) The remaining material is sent to the reaction separation unit, and solvent C is added as a reaction aid to obtain glycolic acid and its oligomers; (3) The gas phase at the top of the reaction separation unit is liquefied and then separated by membrane to obtain permeate and concentrate; In step (1), the separation unit includes a first separation unit and a second separation unit; the mixed washing solution is sequentially introduced into the first separation unit and the second separation unit for separation; the separation method of the first separation unit and the second separation unit is ordinary distillation; the solvent A and solvent B are each one of acetone, cyclohexane, ethyl acetate, isopropanol, n-propanol and n-butanol; In step (2), the solvent C is water, the reaction separation unit is an azeotropic-reactive distillation unit, and the equipment used in the reaction separation unit includes at least one azeotropic-reactive distillation column. The bottom reboiler of the azeotropic-reactive distillation column is a forced circulation reboiler, and the tube side of the bottom reboiler of the azeotropic-reactive distillation column is filled with a solid acid catalyst for the hydrolysis of glycolic acid oligomers. The solid acid catalyst is an ion exchange resin. In step (3), the membrane separation method is pervaporation, and the membrane separation uses a molecular sieve membrane.

2. The recycling method according to claim 1, wherein, In step (3), the method further includes the step of condensing the permeate and returning it to step (2).

3. The recycling method according to claim 1 or 2, wherein, In step (1), Based on the total mass of the mixed washing solution, solvent A and solvent B account for 70%-95% of the total mass, and the remainder is crude glycolic acid and its oligomers washed off during the washing process of crude glycolide.

4. The recycling method according to claim 1, wherein, In step (1), The operating conditions of the first separation unit include: a pressure of 0.5-1 atm, a reflux ratio of 0.5-5; and / or The operating conditions of the second separation unit include: pressure of 0.5-1 atm and reflux ratio of 0.2-5.

5. The recycling method according to claim 4, wherein, In step (1), The equipment used in the first separation unit and the second separation unit each includes at least one packed distillation column and / or a plate distillation column.

6. The recycling method according to claim 1 or 2, wherein, The mass flow rate of solvent C is 0.2-5 times the mass flow rate of the feedstock in the reaction separation unit; and / or The operating conditions of the reaction separation unit include: pressure of 0.2-1 atm and reflux ratio of 0.5-5.

7. The recycling method according to claim 1, wherein, In step (2), The ion exchange resin is one or more of amberlyst 15, amberlyst 35, amberlyst 36, amberlyst 45, amberlyst 21, and amberlyst 26.

8. A system for recovering a mixed washing solution in the glycolide preparation process for use in the recovery method according to any one of claims 1-7, characterized in that, The system includes: Along the material flow direction, a separation unit, a reaction separation unit, a membrane separation unit and a condenser are connected in series. The separation unit includes a first separation unit and a second separation unit connected in series. The mixed washing solution is sequentially fed into the first separation unit and the second separation unit for separation, and most of the solvent A and solvent B are recovered. Solvent A and solvent B are each one of acetone, cyclohexane, ethyl acetate, isopropanol, n-propanol and n-butanol. The reaction separation unit is used to react and separate the residual materials to obtain glycolic acid and its oligomers; The membrane separation unit is used to liquefy the gas phase at the top of the reaction separation unit and then separate it using a membrane to obtain permeate and concentrate. The reaction separation unit includes at least one azeotropic-reactive distillation column, the bottom reboiler of the azeotropic-reactive distillation column is a forced circulation reboiler, and the tube side of the bottom reboiler of the reaction separation unit is configured for loading solid acid catalyst.

9. The recycling system according to claim 8, wherein, The membrane separation unit is located between the top gas phase outlet of the reaction separation unit and the condenser, and a pressurization device is provided between the top gas phase outlet of the reaction separation unit and the membrane separation unit.

10. The recycling system according to claim 8, wherein, The first separation unit and the second separation unit each include at least one packed distillation column and / or a plate distillation column.

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