A recovery treatment method and system for refining waste liquid of cyclic ester, and application thereof

Abstract

The application discloses a recovery treatment method and system of refined cyclic ester waste liquid and application, the waste liquid contains cyclic ester oligomer and solvent, the method comprises the following steps: mixing the waste liquid with water and / or water vapor, then removing the solvent, and finally hydrolyzing to obtain a cyclic ester precursor. The recovery treatment system comprises a mixing unit, a solvent recovery unit and a hydrolysis unit. According to the method, the cyclic ester precursor can be recycled through the hydrolysis process under the precursor for recycling of the solvent.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of waste liquid recycling, and particularly relates to a recovery treatment method and system of refined cyclic ester waste liquid and application. BACKGROUND

[0002] Polylactic acid, polyglycolic acid and the like are obtained by polymerization of cyclic ester and are a new type of biodegradable material. Such materials have biocompatibility and are widely used in medical, food and clothing industries.

[0003] The production processes of polylactic acid and polyglycolic acid are similar, and the current industrial production mode adopts ring-opening polymerization as follows: lactic acid / glycolic acid is reacted in a pre-polymerization kettle to generate lactic acid oligomer / glycolic acid oligomer, then the oligomer is depolymerized to obtain crude lactide / ethylene glycol, which is subjected to ring-opening polymerization to obtain high molecular polylactic acid / polyglycolic acid.

[0004] The monomer refining unit is usually realized by recrystallization, and a large amount of crude solvent containing oligomers and / or cyclic esters is generated in the process, and direct recycling will cause accumulation of oligomers and / or cyclic esters in the system, so that the purity of cyclic ester cannot meet the requirements of ring-opening polymerization. In addition, oligomers can undergo hydrolysis under certain conditions to obtain cyclic ester precursors. SUMMARY

[0005] In order to overcome the problems in the prior art, the present application provides a recovery treatment method and system of refined cyclic ester waste liquid and application, which realizes the recycling of cyclic ester precursors through hydrolysis and the like while purifying the crude solvent.

[0006] One of the purposes of the present application is to provide a recovery treatment method of refined cyclic ester waste liquid, the waste liquid containing cyclic ester oligomers and solvent, the method comprising: mixing the waste liquid with water and / or water vapor, then removing the solvent, and finally hydrolyzing to obtain cyclic ester precursors.

[0007] In the present application, the cyclic ester precursor refers to a raw material for preparing cyclic ester, i.e. an organic acid. For example, when the cyclic ester is ethylene glycol, the cyclic ester precursor is glycolic acid; when the cyclic ester is lactide, the cyclic ester is lactic acid; and when the cyclic ester is caprolactone, the cyclic ester is 6-hydroxyhexanoic acid.

[0008] In a preferred embodiment, the waste liquid comes from the cyclic ester refining process, preferably from the cyclic ester recrystallization process.

[0009] In a preferred embodiment, the cyclic ester is at least one selected from ethylene glycol, lactide, caprolactone.

[0010] In a preferred embodiment, the oligomer is selected from at least one of dimers to eicosamers of cyclic esters.

[0011] In a preferred embodiment, the solvent is selected from at least one of alcoholic solvents, C2-C7 ester solvents, and ether solvents.

[0012] In a further preferred embodiment, the solvent is selected from at least one of ethanol, n-propanol, isopropanol, n-butanol, and n-octanol.

[0013] In a preferred embodiment, the weight ratio of the waste liquid to the water and / or water vapor is (0.1-20): 1.

[0014] In a further preferred embodiment, the weight ratio of the waste liquid to the water and / or water vapor is (1-10): 1.

[0015] For example, the weight ratio of the solvent to the water and / or water vapor is 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 12:1, 15:1, 16:1, 18:1, or 20:1.

[0016] In the present application, water and / or water vapor is mixed with the waste liquid, and water will azeotrope with the solvent in the waste liquid in the subsequent solvent recovery, thereby facilitating the recovery of the solvent. The inventors have found through a large number of experiments that the effect of using water vapor is better than that of using water.

[0017] In a preferred embodiment, the solvent removal is performed in a solvent recovery column.

[0018] In a further preferred embodiment, the gas phase fraction of the solvent recovery column feed is 0-0.9, preferably 0.1-0.9; and / or, the column bottom temperature is 40-100°C; and / or, the operating pressure is 10-100 kPa(a); and / or, the number of theoretical plates is 5-40.

[0019] In a still further preferred embodiment, the gas phase fraction of the solvent recovery column feed is 0.3-0.6; and / or, the column bottom temperature is 60-95°C; and / or, the operating pressure is 30-80 kPa(a); and / or, the number of theoretical plates is 10-25.

[0020] For example, the solvent recovery column is fed with a gas phase fraction of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9; and / or, the column bottom temperature is 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C; and / or, the operating pressure is 10 kPa(a), 20 kPa(a), 30 kPa(a), 40 kPa(a), 50 kPa(a), 60 kPa(a), 70 kPa(a), 80 kPa(a), 90 kPa(a) or 100 kPa(a); and / or, the number of theoretical plates is 5, 10, 15, 20, 25, 30, 35 or 40.

[0021] In a preferred embodiment, the solvent recovery column is a plate column or a packed column, preferably a packed column.

[0022] In the present application, since water and / or steam is first mixed with the waste liquid, the solvent recovery is avoided under high temperature conditions, and can be achieved below 100°C. That is, the disadvantages caused by high temperature are avoided, such as the column bottom temperature is higher than 100°C, the oligomers are polymerized to form high polymers in the column bottom, and the pipelines are blocked, etc.

[0023] In a preferred embodiment, the mixture of solvent and part of water in the waste liquid is removed from the solvent recovery column, and after the solvent is removed (to obtain the material to be dehydrated), a dehydration treatment is performed to obtain the recovered solvent.

[0024] In a further embodiment, the dehydration treatment is performed by one or more combinations of azeotropic distillation, extractive distillation, membrane separation, and adsorption.

[0025] In a preferred embodiment, when azeotropic distillation is used for dehydration, azeotropic distillation is performed in an azeotropic distillation column with an azeotropic agent and the material to be dehydrated, wherein the azeotropic agent is selected from a solvent that can form a ternary azeotrope with water and solvent.

[0026] In a further preferred embodiment, the azeotropic agent is selected from at least one of benzene, toluene, ethyl acetate, and chloroform.

[0027] In a further preferred embodiment, the mass ratio of the azeotropic agent to the material to be dehydrated (i.e., the water-containing solvent) is 0.1-2, preferably 0.1-1, the operating pressure of the azeotropic distillation column is 110-800 kPa, preferably 110-300 kPa, the column bottom temperature is 78-200°C, preferably 78-150°C, and the number of theoretical plates is 10-30.

[0028] For example, the mass ratio of the azeotropic agent to the material to be dehydrated (i.e., the aqueous solvent) is 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, or 2; the operating pressure of the azeotropic distillation column is 110 kPa, 120 kPa, 130 kPa, 140 kPa, 150 kPa, 200 kPa, 300 kPa, 400 kPa, 500 kPa, 600 kPa, 700 kPa, or 800 kPa; the bottom temperature is 78℃, 90℃, 100℃, 120℃, 140℃, 160℃, 180℃, or 200℃; and the theoretical number of plates is 10, 15, 20, 25, or 30.

[0029] In a preferred embodiment, when extractive distillation is used, the extractant and the material to be dehydrated are dehydrated in an extraction tower, wherein the extractant is selected from at least one of alcohol solvents, ionic liquids, and ester solvents.

[0030] The alcohol solvent is preferably an alcohol solvent with a boiling point higher than that of the solvent in the cyclic ester waste liquid, and more preferably an alcohol with C4 or more.

[0031] In a further preferred embodiment, the mass ratio of the extractant to the material to be dehydrated (i.e., the aqueous solvent) is 0.2 to 2, preferably 1 to 2; the operating pressure of the extraction tower is 150 to 800 kPa, preferably 150 to 300 kPa; the top temperature of the tower is 78 to 200°C, preferably 78 to 150°C; and the number of theoretical plates is 10 to 30.

[0032] For example, the mass ratio of the extractant to the material to be dehydrated (i.e., the aqueous solvent) is 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, or 2; the operating pressure of the extraction tower is 150 kPa, 200 kPa, 300 kPa, 400 kPa, 500 kPa, 600 kPa, 700 kPa, or 800 kPa; the top temperature of the tower is 78°C, 90°C, 100°C, 120°C, 140°C, 160°C, 180°C, or 200°C; and the theoretical number of plates is 10, 15, 20, 25, or 30.

[0033] In a preferred embodiment, when membrane separation dehydration is employed, a pervaporation membrane is used.

[0034] Any pervaporation membrane available on the market that can be used for dehydration of organic solvents will work.

[0035] In a further preferred embodiment, the pervaporation membrane uses a molecular sieve as the membrane material with a pore size of 4.1 Å, which can be purchased from the market.

[0036] In a preferred embodiment, when using adsorption dehydration, molecular sieve adsorption can be employed and carried out in an adsorption bed.

[0037] The molecular sieve in question is a molecular sieve disclosed in the prior art that can be used to adsorb water.

[0038] Preferably, when azeotropic distillation is used for dehydration, the obtained water is treated to remove the azeotropic agent and then optionally recycled to a process of mixing waste liquid with water and / or water vapor, and the recovered solvent is used in the cyclic ester refining process; and / or, when extractive distillation is used for dehydration, the obtained water is treated to remove the extractant and then optionally recycled to a process of mixing waste liquid with water and / or water vapor, and the recovered solvent is used in the cyclic ester refining process; and / or, when membrane separation is used for dehydration, the obtained water is optionally directly recycled to a process of mixing waste liquid with water and / or water vapor, and the recovered solvent is used in the cyclic ester refining process.

[0039] The methods for removing the extractant and the azeotropic agent can be those disclosed in the prior art, such as, but not limited to, separation, rotary evaporation, and distillation.

[0040] Therefore, no waste liquid is generated in this invention, and the separated water and solvent can be reused.

[0041] In a preferred embodiment, the distillate from the bottom of the solvent recovery tower is subjected to the hydrolysis treatment.

[0042] In a further preferred embodiment, the solvent content in the distillate from the bottom of the column is below 500 ppm, preferably below 100 ppm.

[0043] The purpose of solvent removal is to remove all the solvent, but not all the water; some water is left in the reboiler. This not only lowers the reboiler temperature but also facilitates subsequent hydrolysis.

[0044] In a preferred embodiment, the material after solvent removal is subjected to hydrolysis treatment, wherein the weight ratio of water to oligomers in the material after solvent removal (i.e., the distillate from the bottom of the solvent recovery tower) is 1 to 20, preferably 3 to 10.

[0045] For example, in the hydrolysis, the weight ratio of water to oligomers in the solvent-removed material (i.e., the distillate from the solvent recovery tower) is 1, 2, 5, 8, 10, 12, 15, 18, or 20. The amount of water includes water in the distillate from the tower bottom and optionally added water.

[0046] Liquid chromatography can be used to detect the weight of oligomers in the distillate from the bottom of the column.

[0047] In a preferred embodiment, the hydrolysis temperature is 60–150°C, and / or the pressure is 120–600 kPa(a), and / or the time is 0.5–5 h.

[0048] In a further preferred embodiment, the hydrolysis temperature is 80–120°C, and / or the pressure is 150–400 kPa(a), and / or the time is 1–3 h.

[0049] For example, the hydrolysis temperature is 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C, and / or the pressure is 120 kPa(a), 150 kPa(a), 200 kPa(a), 250 kPa(a), 300 kPa(a), 350 kPa(a), 400 kPa(a), 450 kPa(a), 500 kPa(a), 550 kPa(a), or 600 kPa(a), and / or the time is 0.5 h, 1 h, 2 h, 3 h, 4 h, or 5 h.

[0050] In a preferred embodiment, the hydrolysis is carried out under a protective atmosphere.

[0051] In a further preferred embodiment, the protective atmosphere is selected from at least one of nitrogen, argon, and helium.

[0052] Preferably, the hydrolysis is carried out in a hydrolysis reactor.

[0053] In a preferred embodiment, the cyclic ester precursor is purified after the hydrolysis.

[0054] In a further preferred embodiment, the purification process is carried out using one or more combinations of membrane separation and extraction separation.

[0055] In a preferred embodiment, when membrane separation and purification are employed, the membrane is a pervaporation membrane.

[0056] Any pervaporation membrane available on the market that can be used to separate cyclic ester precursors from water is acceptable.

[0057] In a further preferred embodiment, the pervaporation membrane uses molecular sieves as the membrane material, with a pore size of 3.0 to 4.1 Å (e.g., 4 Å or 4.1 Å), which can be purchased from the market.

[0058] In a preferred embodiment, when extraction separation and purification is used, the extractant and the material to be purified are processed in an extraction tower, wherein the extractant is selected from at least one of alcohol solvents, ionic liquids, and ether solvents.

[0059] The alcohol solvent is preferably an alcohol solvent with a boiling point higher than that of the solvent in the cyclic ester waste liquid, and more preferably an alcohol with C4 or more.

[0060] In a further preferred embodiment, the mass ratio of the extractant to the material to be purified is 0.2 to 2, preferably 1 to 2, and the extraction temperature is 40 to 80°C, preferably 60 to 80°C.

[0061] For example, the mass ratio of the extractant to the material to be purified is 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8 or 2, and the extraction temperature is 40℃, 50℃, 60℃, 70℃ or 80℃.

[0062] Preferably, in the purification process: when extraction separation is used, the obtained water is treated to remove the extractant and optionally recycled to a process of mixing waste liquid with water and / or water vapor; and / or, when membrane separation is used, the obtained water is optionally directly recycled to a process of mixing waste liquid with water and / or water vapor.

[0063] The method for removing the extractant can be any method disclosed in the existing technology and is not limited here. For example, it can be removed by separation, rotary evaporation, distillation and other methods.

[0064] In a further preferred embodiment, the solvent is removed after the extraction process, preferably by rotary evaporation.

[0065] In a preferred embodiment, the cyclic ester precursor optionally contains an organic acid-alcohol ester.

[0066] In a further preferred embodiment, the content of organic acid alcohol ester in the cyclic ester precursor is less than 2000 ppm, preferably less than 1000 ppm.

[0067] The organic acid alcohol esters mentioned above are generated by the esterification reaction of cyclic ester precursors with solvents, including ethyl hydroxyacetate, n-propyl hydroxyacetate, ethyl hydroxypropionate, n-propyl hydroxypropionate, etc.

[0068] The cyclic ester precursor obtained by this invention can be recycled into the synthesis of cyclic esters.

[0069] A second objective of this invention is to provide a recycling system for refined cyclic ester waste liquid, preferably used for the recycling method described in one objective of this invention. The recycling system includes a mixing unit, a solvent recovery unit, and a hydrolysis unit.

[0070] In a preferred embodiment, the mixing unit is a mixer; and / or, the solvent recovery unit is a solvent recovery tower; and / or, the hydrolysis unit is a hydrolysis reactor.

[0071] In a preferred embodiment, the mixer is provided with a waste liquid inlet, a water and / or steam inlet, and a mixed material outlet.

[0072] In a preferred embodiment, the solvent recovery unit is a solvent recovery tower.

[0073] In a further preferred embodiment, a material inlet is provided in the middle of the solvent recovery tower, a light component outlet is provided at the top of the tower, and a distillate outlet is provided at the bottom of the tower.

[0074] The light component exiting from the top of the column is an azeotropic mixture of water and solvent, while the distillate from the bottom of the column is a mixture of water and cyclic ester oligomers.

[0075] In a further preferred embodiment, the distillate outlet of the solvent recovery tower is connected to the hydrolysis unit, preferably to the top of the hydrolysis reactor.

[0076] In a preferred embodiment, the gas phase fraction of the solvent recovery tower feed is 0.1 to 0.9; and / or, the tower bottom temperature is 40 to 100°C; and / or, the operating pressure is 10 to 100 kPa(a); and / or, the theoretical number of plates is 5 to 40.

[0077] In a further preferred embodiment, the gas phase fraction of the solvent recovery tower feed is 0.3 to 0.6; and / or, the tower bottom temperature is 60 to 95°C; and / or, the operating pressure is 30 to 80 kPa(a); and / or, the theoretical number of plates is 10 to 25.

[0078] In a further preferred embodiment, the solvent recovery tower is a plate tower or a packed tower, preferably a packed tower.

[0079] In a preferred embodiment, the system further includes a dehydration unit, preferably disposed between the solvent recovery unit and the mixing unit.

[0080] In a further preferred embodiment, the dehydration unit is provided with an inlet for the material to be dehydrated, a solvent outlet, and an optional water outlet.

[0081] In a further preferred embodiment, the inlet of the material to be dehydrated is connected to the light component outlet of the solvent recovery tower, and the solvent outlet recovers the solvent, preferably the solvent is recycled back to the cyclic ester refining process, for example, the solvent outlet is connected to the cyclic ester refining unit; the optional water outlet is optionally connected to the water and / or steam inlet of the mixing unit.

[0082] Preferably, when an azeotropic distillation column is used, an azeotropic agent removal unit is provided between its optional water outlet and the mixing unit; and / or, when an extraction column is used, an extractant removal unit is provided between its optional water outlet and the mixing unit; and / or, when a membrane separator is used, its optional water outlet is directly connected to the mixing unit.

[0083] In a preferred embodiment, the dehydration unit employs one or more combinations of an azeotropic distillation column, a membrane separator, an extraction column, and an adsorption device.

[0084] In a preferred embodiment, the system further includes a purification unit, which is preferably connected to a hydrolysis unit and a mixing unit (and preferably also to a monomer synthesis unit).

[0085] In a further preferred embodiment, the purification unit includes an inlet for the material to be purified, an outlet for the purified cyclic ester precursor, and an optional outlet for purified water.

[0086] In a further preferred embodiment, the inlet of the material to be purified is connected to the hydrolysis unit, preferably to the bottom of the hydrolysis reactor; the purified cyclic ester precursor outlet recovers the cyclic ester precursor and recycles it back to the cyclic ester synthesis process, for example, the purified cyclic ester precursor outlet is connected to the cyclic ester synthesis unit; the purified water outlet is optionally connected to the water and / or steam inlet of the mixing unit.

[0087] Preferably, when a membrane separator is used for purification, its optional purified water outlet is directly connected to the water and / or steam inlet of the mixing unit; and / or, when an extraction tower is used for purification, an extractant removal unit is provided between its optional purified water outlet and the water and / or steam inlet of the mixing unit.

[0088] In a preferred embodiment, a supplementary water inlet is further provided on the hydrolysis unit (preferably a hydrolysis reactor).

[0089] In a preferred embodiment, the purification unit employs one or more combinations of membrane separators and extraction towers.

[0090] A third objective of this invention is to provide the application of the method described in one objective of this invention or the system described in another objective of this invention in the synthesis of cyclic esters.

[0091] The fourth objective of this invention is to provide a system for synthesizing cyclic esters, comprising a cyclic ester synthesis unit, a cyclic ester purification unit, and the recycling system described in the second objective of this invention; wherein the recycling system comprises a mixing unit, a solvent recovery unit, and a hydrolysis unit.

[0092] In a preferred embodiment, the cyclic ester synthesis unit is a synthesis reactor; and / or, the cyclic ester refining unit includes a recrystallization vessel and a solid-liquid separation device; and / or, the mixing unit is a mixer; and / or, the solvent recovery unit is a solvent recovery tower; and / or, the hydrolysis unit is a hydrolysis vessel.

[0093] In a preferred embodiment, the mixer is provided with a waste liquid inlet, a water and / or steam inlet, and a mixed material outlet.

[0094] In a preferred embodiment, the solvent recovery unit is a solvent recovery tower.

[0095] In a further preferred embodiment, a material inlet is provided in the middle of the solvent recovery tower, a light component outlet is provided at the top of the tower, and a distillate outlet is provided at the bottom of the tower.

[0096] The light component exiting from the top of the column is an azeotropic mixture of water and solvent, while the distillate from the bottom of the column is a mixture of water and cyclic ester oligomers.

[0097] In a further preferred embodiment, the distillate outlet of the solvent recovery tower is connected to the hydrolysis unit, preferably to the top of the hydrolysis reactor.

[0098] In a preferred embodiment, the gas phase fraction of the solvent recovery tower feed is 0.1 to 0.9; and / or, the tower bottom temperature is 40 to 100°C; and / or, the operating pressure is 10 to 100 kPa(a); and / or, the theoretical number of plates is 5 to 40.

[0099] In a further preferred embodiment, the gas phase fraction of the solvent recovery tower feed is 0.3 to 0.6; and / or, the tower bottom temperature is 60 to 95°C; and / or, the operating pressure is 30 to 80 kPa(a); and / or, the theoretical number of plates is 10 to 25.

[0100] In a further preferred embodiment, the solvent recovery tower is a plate tower or a packed tower, preferably a packed tower.

[0101] In a preferred embodiment, the recycling system further includes a dehydration unit.

[0102] In a further preferred embodiment, the dehydration unit is provided with an inlet for the material to be dehydrated, a solvent outlet, and an optional water outlet.

[0103] In a further preferred embodiment, the inlet of the material to be dehydrated is connected to the light component outlet of the solvent recovery tower, and the solvent outlet is connected to the cyclic ester refining unit; the optional water outlet is connected to the water and / or steam inlet of the mixing unit.

[0104] In a preferred embodiment, the dehydration unit employs one or more combinations of an azeotropic distillation column, a membrane separator, an extraction column, and an adsorption device.

[0105] In a preferred embodiment, the recycling system further includes a purification unit.

[0106] In a further preferred embodiment, the purification unit includes an inlet for the material to be purified, an outlet for the purified cyclic ester precursor, and an optional outlet for purified water.

[0107] In a further preferred embodiment, the inlet of the material to be purified is connected to the hydrolysis unit, preferably to the bottom of the hydrolysis reactor; the outlet of the purified cyclic ester precursor is connected to the cyclic ester synthesis unit; and the outlet of the purified water is connected to the water and / or steam inlet of the mixing unit.

[0108] In a preferred embodiment, a supplementary water inlet is further provided on the hydrolysis unit (preferably a hydrolysis reactor).

[0109] In a preferred embodiment, the cyclic ester synthesis unit is connected to the purification unit of the recovery system; and / or, the cyclic ester refining unit (especially its recrystallization vessel) is connected to the dehydration unit of the recovery system.

[0110] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; 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. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0111] Compared with the prior art, the present invention has the following beneficial effects:

[0112] (1) The method of the present invention also realizes the recycling of cyclic ester precursors through hydrolysis, under the condition of solvent recycling precursors;

[0113] (2) The method described in this invention does not generate any waste liquid, and all materials formed can be returned to the corresponding process for reuse.

[0114] (3) The method described in this invention is simple to operate, easy to implement, and can be applied on a large scale in industrial applications. Attached Figure Description

[0115] Figure 1A schematic diagram of the system for synthesizing cyclic esters according to the present invention is shown.

[0116] exist Figure 1 In the diagram, 1 represents the fresh cyclic ester precursor feed line, 2 represents the cyclic ester synthesis unit, 3 represents the crude cyclic ester conveying line, 4 represents the cyclic ester refining unit, 5 represents the waste liquid conveying line, 6 represents the pure cyclic ester conveying line, 7 represents the fresh steam and / or water conveying line, 8 represents the mixer, 9 represents the solvent and water mixture conveying line, 10 represents the solvent recovery tower, 11 represents the light component conveying line at the top of the tower, 12 represents the dehydration unit, 13 represents water recycling line one, 14 represents the solvent recycling line, 15 represents the distillate conveying line from the bottom of the tower, 16 represents the fresh deionized water feed line, 17 represents the hydrolysis reactor, 18 represents the post-hydrolysis material conveying line, 19 represents the purification unit, 20 represents water recycling line two, and 21 represents the cyclic ester precursor recycling line.

[0117] Fresh cyclic ester precursors (organic acid feedstocks) and recycled cyclic ester precursors (organic acid feedstocks) pass through cyclic ester synthesis unit 2 to obtain crude cyclic esters, which then enter cyclic ester refining unit 4. The high-purity cyclic esters obtained from cyclic ester refining unit 4 are sent to the subsequent biodegradable plastics synthesis unit. Another stream of solvent containing oligomers, along with fresh steam and / or water 7 and recycled water 13 / 20, is mixed in mixer 8 and then enters solvent recovery tower 10. The light component at the top of the tower is an azeotrope of solvent and water, while the distillate from the bottom of the tower is a mixture of oligomers and water. The azeotrope of solvent and water passes through dehydration unit 12 to separate water and solvent. The resulting water is recycled to mixer 8, and the dried solvent is recycled to cyclic ester refining unit 4. The mixture of oligomer and water undergoes a hydrolysis reaction in hydrolysis reactor 17. To ensure the mass ratio of water to oligomer, fresh water is added through pipeline 16. The hydrolysis product is an aqueous solution of cyclic ester precursor (organic acid). The high-purity cyclic ester precursor (organic acid) is recycled to cyclic ester synthesis unit 2 through purification unit 19, and the separated water is recycled to mixer 8. Detailed Implementation

[0118] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0119] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0120] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0121] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0122]

Example 1

[0123] In this Example 1, the cyclic ester is lactide.

[0124] An ethanol solution containing oligomers with a mass flow rate of 800 kg / h from the cyclic ester refining unit, along with 0.8 MPa (g) water vapor with a mass flow rate of 400 kg / h, is mixed and then fed into a solvent recovery tower. The solvent recovery tower has a feed vapor fraction of 0.52, 11 theoretical plates, an operating pressure of 70 kPa, a reboiler temperature of 94°C, a reboiler heat load of 319 kW, and an ethanol content of 100 ppm. The aqueous ethanol at the top of the tower is dehydrated by azeotropic distillation using benzene as the azeotropic agent at a benzene-to-ethanol mass ratio of 0.5. The azeotropic distillation tower has 20 theoretical plates, an operating pressure of 115 kPa, and a reboiler temperature of 82°C. The ethanol obtained from the reboiler is recycled to the cyclic ester refining unit, and the separated water is recycled to the mixer inlet after the azeotropic agent is removed by liquid-liquid separation.

[0125] The distillate from the solvent recovery tower was added to a hydrolysis reactor along with an appropriate amount of deionized water under a nitrogen atmosphere to hydrolyze the oligomers. The mass ratio of oligomers to water was 5:1. The operating temperature of the hydrolysis reactor was 110℃, and the operating pressure was 300 kPa(a). After 2 hours of reaction, the hydrolysis rate of the oligomers reached 70%. The product was then purified and reused using a commercially available pervaporation membrane made of molecular sieve with a pore size of 4.1 Å. The recycled organic acid contained 700 ppm of ethyl hydroxyl or ethyl propionate, and the separated water was recycled to the mixer inlet.

[0126]

Example 2

[0127] In this Example 2, the cyclic ester is glycolide.

[0128] A solution of n-propanol containing oligomers, with a mass flow rate of 800 kg / h from the cyclic ester refining unit, is mixed with 0.8 MPa (g) water vapor at a mass flow rate of 200 kg / h and then fed into a solvent recovery tower. The solvent recovery tower has a feed gas phase fraction of 0.23, 16 theoretical plates, an operating pressure of 40 kPa (a), a reboiler temperature of 81℃, a reboiler heat load of 736 kW, and a reboiler n-propanol content of 30 ppm. The aqueous n-propanol at the top of the tower is purified using a commercially available pervaporation membrane (molecular sieve with a pore size of 4.0 Å) and recycled back to the cyclic ester refining unit. The separated water is recycled to the mixer inlet.

[0129] The distillate from the solvent recovery tower was added to a hydrolysis reactor along with an appropriate amount of deionized water under a nitrogen atmosphere to hydrolyze the oligomers. The mass ratio of oligomers to water was 7:1. The operating temperature of the hydrolysis reactor was 100℃, and the operating pressure was 400 kPa(a). After 3 hours of reaction, the hydrolysis rate of the oligomers reached 86%. The oligomers were then extracted and purified for reuse. The extractant used was n-octanol, with a mass ratio of n-octanol to hydrated oligomers of 1.6. The extraction temperature was 70℃. The reused organic acid contained 200 ppm of n-propyl glycolate or n-propyl hydroxypropionate. The separated water, after being separated to remove the extractant, was recycled back to the inlet of the hydrolysis reactor.

[0130]

Example 3

[0131] In this Example 3, the cyclic ester is caprolactone.

[0132] An isopropanol solution containing oligomers, with a mass flow rate of 800 kg / h from the cyclic ester refining unit, is mixed with 0.8 MPa (g) water vapor at a mass flow rate of 100 kg / h and then fed into a solvent recovery tower. The feed vapor fraction of the solvent recovery tower is 0.13, the theoretical number of plates is 23, the operating pressure of the tower is 10 kPa, the reboiler temperature is 61°C, the reboiler heat load is 390 kW, and the isopropanol content in the reboiler is 20 ppm. The aqueous isopropanol at the top of the tower is recycled through extractive distillation. Ethylene glycol is used as the extractant, with a mass ratio of ethylene glycol to aqueous isopropanol of 2. The extractive distillation tower has 25 theoretical plates, an operating pressure of 150 kPa, and a reboiler temperature of 98°C. The isopropanol obtained from the bottom of the column is recycled to the cyclic ester purification unit. The separated water is recycled to the mixer inlet after the extractant is removed by distillation. The distillation column has 20 theoretical plates, the operating pressure of the column is 110 kPa(a), and the bottom temperature of the column is 197℃.

[0133] The distillate from the solvent recovery tower was added to a hydrolysis reactor along with an appropriate amount of deionized water under a nitrogen atmosphere to hydrolyze the oligomers. The mass ratio of oligomers to water was 9:1. The operating temperature of the hydrolysis reactor was 90℃, and the operating pressure was 200 kPa(a). After 1.5 hours of reaction, the hydrolysis rate of the oligomers reached 85%. The product was then purified and reused using a commercially available pervaporation membrane made of molecular sieve with a pore size of 4.0 Å. The recycled organic acid contained 150 ppm of isopropyl glycolate or isopropyl hydroxypropionate, and the separated water was recycled to the mixer inlet.

[0134]

Example 4

[0135] In this Example 3, the cyclic ester is lactide.

[0136] An oligomer-containing n-butanol solution with a mass flow rate of 800 kg / h from the cyclic ester refining unit, along with 0.8 MPa (g) water vapor at a mass flow rate of 500 kg / h, is mixed and then fed into a solvent recovery tower. The solvent recovery tower has a feed gas phase fraction of 0.43, 13 theoretical plates, an operating pressure of 50 kPa, a reboiler temperature of 86°C, a reboiler heat load of 675 kW, and a reboiler isopropanol content of 80 ppm. The aqueous isopropanol at the top of the tower is purified using a commercially available pervaporation membrane (molecular sieve with a pore size of 4.0 Å) and recycled back to the cyclic ester refining unit. The separated water is recycled to the mixer inlet.

[0137] The distillate from the solvent recovery tower was added to a hydrolysis reactor along with an appropriate amount of deionized water under a nitrogen atmosphere to hydrolyze the oligomers. The mass ratio of oligomers to water was 4:1. The operating temperature of the hydrolysis reactor was 120℃, and the operating pressure was 150 kPa(a). After 1 hour of reaction, the hydrolysis rate of the oligomers reached 66%. The oligomers were then extracted and purified for reuse. The extractant used was n-butanol, with a mass ratio of n-butanol to hydrated oligomers of 1.6, and the extraction temperature was 70℃. The reused organic acid contained 600 ppm of n-butyl glycolate or n-butyl hydroxypropionate. The separated water, after being separated to remove the extractant, was recycled back to the inlet of the hydrolysis reactor.

[0138]

Example 5

[0139] In this Example 5, the cyclic ester is lactide.

[0140] An ethanol solution containing oligomers with a mass flow rate of 800 kg / h from the cyclic ester refining unit, mixed with water at a mass flow rate of 400 kg / h, enters a solvent recovery tower. The solvent recovery tower has a feed gas phase fraction of 0, a theoretical plate number of 11, an operating pressure of 70 kPa(a), a reboiler temperature of 94°C, a reboiler heat load of 591 kW, and an ethanol content of 110 ppm. The aqueous ethanol at the top of the tower is dehydrated by azeotropic distillation using benzene as the azeotropic agent at a benzene-to-ethanol mass ratio of 0.5. The azeotropic distillation tower has a theoretical plate number of 20, an operating pressure of 115 kPa, and a reboiler temperature of 82°C. The ethanol obtained from the reboiler is recycled to the cyclic ester refining unit, and the separated water, after azeotropic agent removal via liquid-liquid separation, is recycled to the mixer inlet.

[0141] The distillate from the solvent recovery tower was added to a hydrolysis reactor along with an appropriate amount of deionized water under a nitrogen atmosphere to hydrolyze the oligomers. The mass ratio of oligomers to water was 5:1. The operating temperature of the hydrolysis reactor was 110℃, and the operating pressure was 300 kPa(a). After 2 hours of reaction, the hydrolysis rate of the oligomers reached 70%. The product was then purified and reused using a commercially available pervaporation membrane made of molecular sieve with a pore size of 4.1 Å. The recycled organic acid contained 800 ppm of ethyl hydroxyacetate or ethyl hydroxypropionate, and the separated water was recycled to the mixer inlet.

[0142] Comparative Example 1

[0143] In Comparative Example 1, the cyclic ester is lactide.

[0144] An ethanol solution containing oligomers with a mass flow rate of 800 kg / h from the cyclic ester refining unit enters the solvent recovery tower. The theoretical number of trays is 11, the operating pressure of the tower is 40 kPa(a), the temperature of the tower bottom is 108℃, the heat load of the tower bottom is 354 kW, and the ethanol content in the tower bottom is 4.76%. The aqueous ethanol at the top of the tower is recycled back to the cyclic ester refining unit.

[0145] The solvent recovery tower bottom liquid and an appropriate amount of deionized water were added to a hydrolysis reactor to carry out oligomer hydrolysis under a nitrogen atmosphere. The mass ratio of oligomers to water was 5:1. The operating temperature of the hydrolysis reactor was 110℃, and the operating pressure was 300 kPa(a). After 2 hours of reaction, the hydrolysis rate of the oligomers reached 50%. The product was purified and reused using a commercially available pervaporation membrane made of molecular sieve with a pore size of 4.1 Å. The recycled organic acid contained ethyl hydroxyacetate or ethyl hydroxypropionate at a concentration of 5000 ppm. The separated water was recycled to the mixer inlet.

[0146] The solvent recovery tower has a high bottom temperature when using the above separation method. Oligomers will undergo polymerization at the bottom of the tower to form high molecular weight polymers, which will block the pipeline. At the same time, the hydrolysis conditions of high molecular weight polymers are more stringent, which leads to a decrease in the hydrolysis rate of polymers under the same hydrolysis conditions. Finally, the high ethanol content in the bottom liquid of the tower results in the generation of a large amount of ethyl hydroxyacetate or ethyl hydroxypropionate during the hydrolysis process.

[0147] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for recycling and treating refined cyclic ester waste liquid, wherein the waste liquid contains cyclic ester oligomers and solvents, the method comprising: The waste liquid is mixed with water and / or steam, then the solvent is removed, and finally hydrolyzed to obtain a cyclic ester precursor; the cyclic ester is selected from at least one of glycolide, lactide, and caprolactone, and the solvent is selected from at least one of ethanol, n-propanol, isopropanol, n-butanol, and n-octanol; the solvent removal is carried out in a solvent recovery tower, and the tower bottom temperature is 40~100°C.

2. The recycling method according to claim 1, characterized in that, The waste liquid comes from the cyclic ester refining process.

3. The recycling method according to claim 1, characterized in that, The waste liquid comes from the recrystallization process of cyclic esters.

4. The recycling method according to claim 1, characterized in that, The oligomer is selected from at least one of the dimers to icosomers of cyclic esters.

5. The recycling method according to claim 1, characterized in that, The weight ratio of the waste liquid to the water and / or water vapor is (0.1~20):

1.

6. The recycling method according to claim 1, characterized in that, The weight ratio of the waste liquid to the water and / or water vapor is (1~10):

1.

7. The recycling method according to claim 1, characterized in that, The gas phase fraction of the feed to the solvent recovery tower is 0 to 0.9; and / or the operating pressure is 10 to 100 kPa(a); and / or the number of theoretical plates is 5 to 40.

8. The recycling method according to claim 7, characterized in that, The solvent and a portion of the water mixture in the waste liquid are removed from the solvent recovery tower, and then dehydrated after solvent removal to obtain the recovered solvent; and / or, The distillate from the bottom of the solvent recovery tower is subjected to the hydrolysis treatment.

9. The recycling method according to claim 8, characterized in that, The solvent content in the distillate from the bottom of the tower is below 500 ppm.

10. The recycling method according to claim 8, characterized in that, The solvent content in the distillate from the bottom of the tower is below 100 ppm.

11. The recycling method according to claim 8, characterized in that, The dehydration process employs one or more of the following methods: azeotropic distillation, extractive distillation, membrane separation, and adsorption.

12. The recycling method according to claim 11, characterized in that, When azeotropic distillation is used for dehydration, an azeotropic agent and the material to be dehydrated are used in an azeotropic distillation column for dehydration. The azeotropic agent is selected from solvents that can form a ternary azeotrope with water and a solvent; or... When extractive distillation is used, the extractant and the material to be dehydrated are dehydrated in an extraction tower, wherein the extractant is selected from at least one of alcohol solvents, ionic liquids, and ester solvents; or, When membrane separation and dehydration are used, a pervaporation membrane is employed; or, When using adsorption for dehydration, molecular sieve adsorption is employed.

13. The recycling method according to claim 12, characterized in that, The azeotropic agent is selected from at least one of benzene, toluene, ethyl acetate, and chloroform; or, The mass ratio of the extractant to the material to be dehydrated is 0.2 to 2, the operating pressure of the extraction tower is 150 to 800 kPa, the top temperature of the tower is 78 to 200°C, and the number of theoretical plates is 10 to 30.

14. The recycling method according to claim 12, characterized in that, The mass ratio of the azeotropic agent to the material to be dehydrated is 0.1~2, the operating pressure of the azeotropic distillation column is 110~800kPa, the bottom temperature is 78~200°C, and the number of theoretical plates is 10~30.

15. The recycling method according to any one of claims 1 to 14, characterized in that, The material after solvent removal is subjected to hydrolysis treatment, wherein the weight ratio of water to oligomers in the material after solvent removal is 1~20.

16. The recycling method according to claim 15, characterized in that, The material after solvent removal is subjected to hydrolysis treatment, wherein the weight ratio of water to oligomers in the material after solvent removal is 3~10.

17. The recycling method according to claim 15, characterized in that, The hydrolysis is performed at a temperature of 60-150°C and / or at a pressure of 120-600 kPa(a) and / or for a time of 0.5-5 h.

18. The recycling method according to claim 15, characterized in that, The hydrolysis is carried out under a protective atmosphere.

19. The recycling method according to claim 16, characterized in that, The cyclic ester precursor is purified after the hydrolysis.

20. The recycling method according to claim 19, characterized in that, The purification process is carried out using one or more combinations of membrane separation and extraction separation.

21. The recycling method according to claim 19, characterized in that, When membrane separation and purification are used, the membrane is a pervaporation membrane; or, When extraction separation and purification is used, the extractant and the material to be purified are processed in an extraction tower, wherein the extractant is selected from at least one of alcohol solvents, ionic liquids, and ether solvents.

22. The recycling method according to claim 21, characterized in that, The mass ratio of the extractant to the material to be purified is 0.2 to 2, and the extraction temperature is 40 to 80°C.

23. A system for recovering and treating refined cyclic ester waste liquid, used for the recovery and treatment method according to any one of claims 1 to 22, the system comprising a mixing unit, a solvent recovery unit, and a hydrolysis unit; the mixing unit is a mixer, provided with a waste liquid inlet, a water and / or steam inlet, and a mixed material outlet; the solvent recovery unit is a solvent recovery tower, provided with a material inlet in the middle, a light component outlet at the top, and a distillate outlet at the bottom; the distillate outlet of the solvent recovery tower is connected to the hydrolysis unit.

24. The recycling system according to claim 23, characterized in that, The hydrolysis unit is a hydrolysis reactor.

25. The recycling system according to claim 24, characterized in that, The distillate outlet of the solvent recovery tower is connected to the top of the hydrolysis vessel; and / or, A supplemental water inlet is further provided on the hydrolysis unit.

26. The recycling system according to claim 23, characterized in that, The system further includes a dehydration unit; and / or, The system further includes a purification unit.

27. The recycling system according to claim 26, characterized in that, The dehydration unit employs one or more combinations of azeotropic distillation columns, membrane separators, extraction columns, and adsorption devices; and / or, The purification unit employs one or more combinations of membrane separators and extraction towers.

28. The recycling system according to claim 26, characterized in that, The dehydration unit is provided with an inlet for the material to be dehydrated, a solvent outlet, and an optional water outlet; And / or, The purification unit includes an inlet for the material to be purified, an outlet for the purified cyclic ester precursor, and an optional outlet for purified water.

29. The recycling system according to claim 28, characterized in that, The inlet of the material to be dehydrated is connected to the light component outlet of the solvent recovery tower, and the solvent outlet recovers the solvent; the optional water outlet is optionally connected to the water and / or steam inlet of the mixing unit. And / or, The inlet of the material to be purified is connected to the hydrolysis unit; the outlet of the purified cyclic ester precursor recovers the cyclic ester precursor and recycles it back into the cyclic ester synthesis process; the outlet of the purified water is connected to the water and / or steam inlet of the mixing unit.

30. The application of the recycling method according to any one of claims 1 to 22 or the recycling system according to any one of claims 23 to 29 in the synthesis of cyclic esters.

31. A system for synthesizing cyclic esters, comprising a cyclic ester synthesis unit, a cyclic ester purification unit, and a recycling system as described in any one of claims 23 to 29.

32. The system according to claim 31, characterized in that, The cyclic ester synthesis unit is a synthesis reactor; and / or, the cyclic ester refining unit includes a recrystallization vessel and a solid-liquid separation device.

33. The system according to claim 31, characterized in that, The cyclic ester synthesis unit is connected to the purification unit of the recycling system; and / or, the cyclic ester refining unit is connected to the dehydration unit of the recycling system.

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