Process and apparatus for recovering lactide from a gas containing lactide

Abstract

The present application relates to the field of lactide preparation, in particular to a method and device for solidifying and collecting lactide from lactide-containing gas. The method comprises: lactide-containing gas and solvent-containing liquid are contacted in an ejector; wherein the solvent-containing liquid is used as working fluid to generate vacuum in the ejector, so that the lactide-containing gas is sucked into the ejector as injection fluid to contact the solvent, solidify the lactide and form mixed slurry. By using the method of the present application to solidify and collect lactide, the yield and lactide quality can be greatly improved, and the production cost can be reduced.

Description

Technical Field

[0001] This invention relates to the field of preparation of lactide compounds, and more specifically to a method and apparatus for solidifying and collecting lactide from a gas containing lactide. Background Technology

[0002] Polylactic acid (PLA) materials have a wide range of applications due to their excellent mechanical properties, barrier properties, biodegradability, and compatibility. For example, polyglycolic acid (PGA) is a chemically simple, fully biodegradable material that hydrolyzes in the human body or natural environment, ultimately degrading into water and carbon dioxide. Its superior mechanical properties, barrier properties, biodegradability, and compatibility have led to its widespread use in biomedical fields. PGA can be obtained through direct glycolic acid condensation polymerization or glycolide ring-opening polymerization. The former involves higher reaction temperatures and the production of water, while PGA has poor thermal stability, resulting in more side reactions during condensation and making it difficult to obtain high molecular weight PGA. Therefore, the industrial process currently primarily uses glycolide ring-opening polymerization. Ring-opening polymerization requires high purity of the glycolide monomer, especially since trace amounts of water and acid in glycolide significantly inhibit polymerization. Therefore, preparing qualified glycolide monomers is crucial for preparing qualified PGA.

[0003] Lactic acid (LA) is generally prepared by depolymerizing the corresponding oligomers. For example, glycolide is typically obtained by depolymerizing polyglycolic acid (PGA) oligomers under high temperature and high vacuum conditions. The depolymerization of PGA at high temperatures involves a very complex reaction network. In addition to glycolide, the product contains a large number of byproducts and entrainments, such as water, carbon dioxide, glycolic acid, PGA pyrolysis fragments, and coking products. Therefore, crude glycolide requires rigorous purification and refining. The glycolide obtained from depolymerization under high vacuum is in the gas phase. Typically, a heated pipeline is used to transport the gas phase, and then a tube-and-shell condenser is used to condense the glycolide to a molten state and collect it in an insulated buffer tank. Because both gaseous and molten glycolide gradually polymerize, polymers gradually form in low-flow-rate regions, such as at the boundary layer of pipe walls, leading to blockages in pipelines, condensers, and even buffer tanks, severely affecting product quality and production efficiency.

[0004] One existing method uses an empty tower and a gas-liquid co-flow design for the main condenser. In order to ensure that the gaseous glycolide has sufficient residence time to contact the washing liquid, the equipment must be large enough to reduce the gas velocity, resulting in low efficiency.

[0005] The second existing method involves adding an inert high-boiling-point solvent during the depolymerization process to co-distill it with glycolide, thereby avoiding the risk of glycolide vapor clogging pipelines and condensers. However, this introduces new separation problems and does not offer any significant advantages in terms of glycolide quality and yield. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low quality of lactide, low production efficiency, high cost and easy clogging of the device in the prior art, and to provide a method and device for solidifying and collecting lactide from a gas containing lactide. This method has the advantages of high collection efficiency, low cost and high quality of lactide product.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for solidifying and collecting lactide from a lactide-containing gas, the method comprising: contacting the lactide-containing gas and a solvent-containing liquid in an ejector; wherein the solvent-containing liquid, as a working fluid, generates a vacuum in the ejector, such that the lactide-containing gas, as an ejector fluid, is drawn into the ejector and contacts the solvent to solidify the lactide, forming a mixed slurry.

[0008] A second aspect of the present invention provides a system for solidifying and collecting lactide from a gas containing lactide. The system includes: an injection unit with a liquid inlet for introducing a solvent-containing liquid as a working fluid, a gas inlet for introducing the lactide-containing gas as an ejector fluid, and a mixed fluid outlet for discharging a mixed fluid formed by mixing the working fluid and the ejector fluid; and a degassing unit, comprising, from bottom to top: a suspension collection zone, a gas phase collection zone, and a packing zone; wherein the suspension collection zone receives the mixed fluid from the injection unit to form a suspension, and the gas phase in the suspension escapes to the gas phase collection zone and then collects from the gas phase. The output is sent to the packing zone for purification via the packing material; the suspension treatment unit includes a first circulation pipeline that recycles at least a portion of the suspension back to the spray unit as a solvent; a second circulation pipeline that sends the suspension to a solid-liquid separation device for separation to obtain a liquid phase and lactide solids, and recycles the obtained liquid phase back to the spray unit; the first and second circulation pipelines are connected in parallel at the suspension outlet of the degassing unit; the second circulation pipeline also includes a first branch that transports the separated solvent to the degassing unit for spraying the gas phase accumulation zone and a second branch that transports the separated liquid phase to the degassing unit for spraying the packing zone.

[0009] A third aspect of the present invention provides a method for collecting and solidifying lactide from a lactide-containing gas, the method being carried out in the system described in the second aspect of the present invention, comprising: (1) a solvent-containing liquid being fed into an injection unit through a liquid inlet of an injection unit, and a vacuum being drawn so that the lactide-containing gas is drawn into the injection unit through a gas inlet and comes into contact with the solvent, and the mixed slurry formed by contact solidification of the lactide is injected into a degassing unit through a mixed fluid outlet of the injection unit; (2) the mixed fluid is collected in a suspension collection zone of the degassing unit to form a suspension, wherein the gas phase in the suspension is... Escape to the gas phase accumulation zone, optionally pass through solvent spray, and then output from the gas phase accumulation zone to the packing zone, where it is purified by the packing to form tail gas. Optionally, the packing is sprayed with solvent. After degassing, the suspension is sent to the suspension treatment unit. (3) In the suspension treatment unit, the suspension is divided into at least two parts. One part of the suspension undergoes solid-liquid separation to obtain lactide solid wet material and liquid phase. After the liquid phase is extracted, solvent is added to form a mixed liquid phase. The mixed liquid phase is mixed with another part of the suspension and then circulated back to the spraying unit as a solvent-containing liquid.

[0010] Through the above technical solution, the present invention has the following advantages:

[0011] By employing the method of this invention to solidify and collect lactide, the yield and quality of lactide can be greatly improved, while reducing production costs. Compared to the traditional spray curing method, this invention eliminates the condensation process of lactide, removing the potential risk of molten lactide self-polymerizing and clogging the condenser and conveying pipelines. The process is simple, the equipment is basic, the energy consumption is low, and it features long-term stable operation. Furthermore, the processing efficiency is greatly improved, and the product yield and quality are also higher.

[0012] The device of the present invention, by coupling the injection unit, degassing unit and suspension unit through various pipelines, can greatly improve the yield and quality of lactide products and reduce production costs. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a system and process for solidifying and recovering lactide from a gas containing lactide, according to a preferred embodiment of the present invention.

[0014] Explanation of reference numerals in the attached figures

[0015] 1-Dyslexyl alcohol vapor; 2-Heat medium inlet; 3-Heat medium outlet; 4-First circulating solvent stream; 5-Ejector, 5-1 Suction pipe, 5-2 Nozzle chamber, 5-3 Mixing section, 5-4 Ejector outlet; 6-Stirred vessel, 6-1 Agitator, 6-2 Anti-vortex device; 7-Inner vessel spiral nozzle; 8-Refrigerant inlet; 9-Refrigerant outlet; 10-Circulating pump; 11-Solid-liquid separator; 12-Crude ylexyl alcohol product; 13-Recovery system solvent; 14-1 First cooler; 14-2 Second cooler; 15-Recovery solvent inlet; 16-Third circulating solvent stream; 17-Second circulating solvent stream; 18-Tail gas outlet; 19-Tail gas scrubbing tower; 19-1 Packing layer; 19-2 Demister; 20-1 First static mixer; 20-2 Second static mixer; 21-Three-way regulating valve; 22-Reflux stream; 23-Solid-liquid separation stream. Detailed Implementation

[0016] 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.

[0017] The present invention provides a method for collecting and solidifying lactide from a lactide-containing gas. The method includes: contacting the lactide-containing gas and a solvent-containing liquid in an ejector; wherein the solvent-containing liquid acts as a working fluid to create a vacuum in the ejector, so that the lactide-containing gas is drawn into the ejector as an entraining fluid and contacts the solvent to solidify the lactide, forming a mixed slurry.

[0018] By using the method of the present invention to solidify and collect lactones, the yield and quality of lactones can be greatly improved, and production costs can be reduced.

[0019] According to a preferred embodiment of the present invention, the method further includes: separating a portion of the mixed slurry formed after contact to obtain a solid wet material of lactide and a liquid phase, wherein the liquid phase is mixed with another portion and then circulated back to the ejector as the working fluid, wherein the flow rate ratio of one portion of the mixed slurry to the flow rate of the other portion of the mixed slurry is 0.02-0.2. By adopting the aforementioned preferred scheme, the yield and quality of lactide can be further improved, and the production cost can be reduced.

[0020] According to a preferred embodiment of the present invention, the solid mass in the mixed slurry accounts for 1-5% of the total mass.

[0021] According to a preferred embodiment of the present invention, the mixed slurry formed after contact also needs to be degassed. The degassed treatment includes: the gas phase escaping from the surface of the mixed slurry is purified by passing it through a packing material to form tail gas.

[0022] According to a preferred embodiment of the present invention, a solvent-containing liquid is used to spray the gas phase escaping from the surface of the mixed slurry, and the spray liquid is transferred into the mixed slurry.

[0023] According to a preferred embodiment of the present invention, the filler is sprayed with a solvent-containing liquid, and the sprayed liquid is transferred into the mixed slurry.

[0024] According to a preferred embodiment of the present invention, at least a portion of the mixed slurry formed after contact is separated to obtain a wet solid material of lactide and a liquid phase. A portion of the obtained liquid phase is extracted, replenished with fresh solvent, and then mixed with another portion of the mixed slurry before being recycled back to the ejector as the working fluid. By adopting the aforementioned preferred scheme, the yield and quality of lactide can be further improved, and production costs can be reduced.

[0025] According to a preferred embodiment of the present invention, the ratio of the volumetric flow rate of the extracted solvent to the volumetric flow rate of the total solvent (the solvent injected into the injector) is 0.01-0.2.

[0026] According to a preferred embodiment of the present invention, the volume ratio of the replenished fresh solvent to the extracted liquid phase is 0.8-1.5.

[0027] According to a preferred embodiment of the present invention, the operating conditions of the injector include: the temperature of the gas phase inlet wall of the injector needs to be controlled above the boiling point of the lactone, preferably 180-240°C, and more preferably 210-230°C.

[0028] According to a preferred embodiment of the present invention, the operating conditions of the injector include: the ejector chamber pressure of the injector is 1200-9000 PaA, preferably 1500-5000 PaA.

[0029] According to a preferred embodiment of the present invention, the operating conditions of the injector include: the temperature of the solvent-containing liquid introduced into the injector is -15-15°C, preferably -10-5°C.

[0030] In this invention, there are no special requirements for the type of solvent used, and the usual choices in the art are generally used. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the solvent contains at least one of ester solvents, alcohol solvents, ketone solvents, alkane solvents, ether solvents and water.

[0031] According to a preferred embodiment of the present invention, the solvent contains at least one of C3-C5 ester solvents, C2-C5 alcohol solvents, C3-C5 ketone solvents, C3-C6 alkane solvents, and water.

[0032] According to a preferred embodiment of the present invention, the solvent is at least one of methyl glycolate, ethyl acetate, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, isobutanol, acetone, n-hexane, cyclohexane, pentane, petroleum ether, and water.

[0033] The method of the present invention is applicable to the solidification and collection of various lactides. According to a preferred embodiment of the present invention, the lactide is at least one of glycolide, L-lactide and D,L-lactide, preferably glycolide.

[0034] like Figure 1 As shown, this invention provides a system for solidifying and collecting lactide from a gas containing lactide. The system includes: an injection unit with a liquid inlet for introducing a solvent-containing liquid as a working fluid, a gas inlet for introducing the lactide-containing gas as an ejector fluid, and a mixed fluid outlet for discharging a mixture of the working fluid and the ejector fluid; and a degassing unit, comprising, from bottom to top: a suspension collection zone, a gas phase collection zone, and a packing zone; wherein the suspension collection zone receives the mixed fluid from the injection unit to form a suspension, and the gas phase in the suspension escapes to the gas phase collection zone, and is then discharged from the gas phase collection zone to the packing zone. The material zone is purified using packing material. The suspension treatment unit includes a first circulation pipeline that recycles at least a portion of the suspension back to the spray unit as a solvent; a second circulation pipeline that sends the suspension to a solid-liquid separation device for separation to obtain a liquid phase and lactide solid wet material, and the obtained liquid phase is then recycled back to the spray unit. The first and second circulation pipelines are connected in parallel at the suspension outlet and liquid inlet of the degassing unit. The second circulation pipeline also includes a first branch that transports the separated solvent to the degassing unit for spraying the gas phase accumulation zone and a second branch that transports the separated liquid phase to the degassing unit for spraying the packing area.

[0035] The device of the present invention, by coupling the injection unit, degassing unit and suspension unit through various pipelines, can greatly improve the yield and quality of lactide products and reduce production costs.

[0036] According to a preferred embodiment of the present invention, the liquid phase outlet pipeline after separation on the second circulation pipeline is provided with a solvent extraction outlet and a fresh solvent replenishment outlet in sequence, and a mixer is provided after the fresh solvent replenishment outlet.

[0037] According to a preferred embodiment of the present invention, a mixer is provided on the discharge pipeline after the first circulation pipeline and the second circulation pipeline are combined.

[0038] According to a preferred embodiment of the present invention, the spraying unit includes at least one liquid injector, or multiple units, such as 2, 3, 4, 5, etc. The present invention does not make any special requirements in this regard.

[0039] According to a preferred embodiment of the present invention, the injection unit is provided with a heat exchange channel, through which a heating medium is introduced to heat the raw material.

[0040] According to a preferred embodiment of the present invention, the suspension collection area of ​​the degassing unit is provided with a disturbance device, such as a stirring device.

[0041] According to a preferred embodiment of the present invention, a defoaming device is provided above the packing area of ​​the degassing unit.

[0042] According to a preferred embodiment of the present invention, heat exchange devices are provided on the solvent feed pipe of the spraying unit and the liquid phase outlet pipe of the solid-liquid separation device of the suspension treatment unit, respectively, for cooling the solvent-containing liquid raw material before entering the spraying unit and for cooling the material after the liquid phase for separation is mixed with the replenished fresh solvent.

[0043] According to a preferred embodiment of the present invention, an anti-vortex device is provided at the outlet of the suspension collection area.

[0044] This invention provides a method for solidifying and collecting lactide from a gas containing lactide, the method being carried out in the system described above, comprising:

[0045] (1) The solvent-containing liquid is fed into the spraying unit through the liquid inlet of the spraying unit. A vacuum is drawn so that the gas containing lactide is drawn into the spraying unit through the gas inlet and comes into contact with the solvent. The mixed slurry formed by the contact curing of lactide is injected into the degassing unit through the mixed fluid outlet of the spraying unit.

[0046] (2) The mixed fluids are collected in the suspension collection area of ​​the degassing unit to form a suspension. The gas phase in the suspension escapes to the gas phase collection area. Optionally, after being sprayed with solvent, it is output from the gas phase collection area to the packing area. The packing is purified to form tail gas. Optionally, the packing is sprayed with solvent. After degassing, the suspension is sent to the suspension treatment unit.

[0047] (3) In the suspension treatment unit, the suspension is divided into at least two parts. One part of the suspension is subjected to solid-liquid separation to obtain lactide solid wet material and liquid phase. After the liquid phase is extracted, solvent is added to form a mixed liquid phase. The mixed liquid phase is mixed with another part of the suspension and then circulated back to the spray unit as a solvent-containing liquid.

[0048] According to a preferred embodiment of the present invention, 1-25 wt% of the mixed liquid phase is used as a solvent to spray the gas phase in the gas phase accumulation zone of the degassing unit, and 1-25 wt% is used as a solvent to spray the packing material in the packing zone of the degassing unit; the remaining mixed liquid phase is mixed with another portion of the suspension and then circulated back to the spraying unit as a solvent-containing liquid. By adopting the aforementioned preferred scheme, the yield and quality of lactide can be further improved, and the production cost can be reduced.

[0049] The flow rate of a portion of the suspension generally depends on the lamination condensation flow rate and the solid content control of the suspension. According to a preferred embodiment of the present invention, the flow rate ratio of one portion of the suspension to the other portion is 0.02-0.2. By adopting the aforementioned preferred scheme, the yield and quality of lamination can be further improved, and production costs can be reduced.

[0050] The present invention will be described in detail below through embodiments.

[0051] Example 1

[0052] See appendix Figure 1 Isopropanol was selected as the working solvent, and glycolide was collected in a stirred tank with dimensions of DN1000*2200 at an initial liquid level of 50% (liquid level 0 was the tangent to the lower end cap of the stirred tank). Two parallel plate filters were used to separate the solids, with a single filter cavity volume of approximately 0.43 m³. 3 Initially, the system contains approximately 1115 kg of isopropanol. The first stream of circulating solvent 4 enters the nozzle chamber 5-2 of the ejector. Under the action of the nozzle, the solvent's kinetic energy increases, its pressure decreases, creating a vacuum. This allows the upstream glycolide vapor 1 to enter the ejector's suction pipe 5-1 through a heated pipeline. The jacket temperature on the inner surface of the suction pipe is controlled at 210°C, the solvent inlet temperature of the ejector is controlled at -10°C, and the solvent flow rate is adjusted to 37.8 m³ / s. 3 The flow rate is 48.2 kg / h, with a pressure of 0.45 MPa and an ejector pressure controlled at approximately 1.5 kPa (abs). The temperature of the glycolide vapor from the upstream depolymerization reactor is 164.6℃. The two components mix vigorously in the mixing section 5-3 of the ejector. Under the action of the solvent, the glycolide vapor 1 disperses into small bubbles while simultaneously condensing into fine particles and releasing heat of phase transition. It then enters the stirred tank 6 from the ejector outlet 5-4 along with the solvent. Some non-condensable gases escape from the liquid surface inside the tank, while others disperse as bubbles within the tank. During this process, some soluble impurities in the glycolide are washed away by the solvent.

[0053] The mixing vessel 6 is equipped with a stirrer 6-1 and a baffle (not included). Figure 1(As shown in the diagram), and to maintain turbulent flow by suspending the glycolide particles inside the reactor. Because the liquid level fluctuates greatly inside the reactor, particles easily adhere to the outer surface of the injector, the gas phase reactor wall, and the stirring shaft. A second circulating solvent 16 is set up, and an in-reactor nozzle 7 is selected, with a flow rate of 0.3m. 3 A flow rate of / h is used to perform 360° washing of the gas phase space to prevent particle accumulation.

[0054] After escaping from the liquid surface in the reactor, the exhaust gas flows upwards into the exhaust gas scrubbing tower 19. The tower contains a packing layer 19-1 with relatively large void sizes, using corrugated perforated plates to structure the packing. A third stream of circulating solvent 17 is used at a flow rate of 0.3 m... 3 The packing layer is sprayed with a flow rate of / h, and the exhaust gas is washed and then sent to the downstream treatment system through demister 19-2. The pressure inside the stirred tank is generally maintained at atmospheric pressure.

[0055] The suspension in the stirred tank 6 is circulated by the circulating pump 10, and the flow rates of the return stream 22 and the solid-liquid separation stream 23 are controlled separately by the three-way regulating valve 21. The flow rate of stream 23 is 0.2 times that of stream 22. When the liquid level increases to 50.46%, the solid content in the suspension reaches approximately 1%.

[0056] After the suspension stream 23 enters the solid-liquid separator 11, glycolide particles are removed. Most of the separated solvent is reused, while the remaining portion is sent to the solvent recovery system at a low flow rate of 67.9 L / h. Under continuous steady-state operation, the rate at which solid particles are retained on the filter is approximately equal to the glycolide solidification rate, meaning the solid content in the stirred tank remains relatively stable. A solvent recovery replenishment port is installed after the solvent outlet 13, with a replenishment-to-recovery ratio of 1. During long-term operation, the solvent lost during filter switching discharge is replenished by a one-time, short-term addition to maintain a stable liquid level. After pre-mixing in the static mixer 20-1, the two streams enter the first cooler 14-1 for initial solvent cooling. Then, they merge with the return stream 22 and are mixed in the second mixer 20-2. Finally, the diluted suspension is cooled to the process temperature of -10°C in the second cooler 14-2. The second cooler 14-2 is a shell-and-tube heat exchanger with tubes running on the process side. Both the second static mixer 20-2 and the second static mixer are installed vertically, and the material flows from top to bottom to prevent blockage.

[0057] Because the ejector is very close to the upstream depolymerization reactor, the glycolide vapor does not pass through intermediate equipment such as condensers and receiving tanks, resulting in a short residence time and few side reactions. Using this method, the crude glycolide product obtained has a purity of 98% and a total acid value of 96 μmol / g. Inspection of the ejector's gas phase inlet revealed no obvious adherence of glycolide to the inner surface of the suction pipe.

[0058] Example 2

[0059] Maintaining the operating conditions of the upstream depolymerization reactor unchanged, the apparatus and method described in Example 1 were used. The temperature of the jacket on the inner surface of the suction pipe was controlled at 230°C, the solvent inlet temperature of the ejector was controlled at 5°C, and the solvent flow rate was adjusted to 48.6 m³ / s. 3 The flow rate was 39.3 kg / h, with a pressure of 0.33 MPa and an ejector pressure controlled at approximately 5.0 kPa (abs). The temperature of the glycolide vapor from the upstream depolymerization reactor was 197.5℃. The flow rate of stream 23 was 0.02 times that of stream 22. When the liquid level increased to 52.39%, the solid content of the suspension reached approximately 5%.

[0060] The second circulating solvent 16 was at 0.25m 3 The gas phase space is washed 360° at a flow rate of / h, and the third circulating solvent 17 is adjusted to 0.25m 3 The packing layer was sprayed with a flow rate of 13.8 L / h. The circulating solvent was replaced with fresh solvent at a flow rate of 13.8 L / h. Using the above method, the crude glycolide product was obtained with a purity of 96.8% and a total acid value of 145 μmol / g. Inspection of the gas phase inlet of the injector revealed no obvious adhesion of glycolide to the inner surface of the suction pipe.

[0061] Example 3

[0062] Maintaining the operating conditions of the upstream depolymerization reactor unchanged, the apparatus and method described in Example 1 were used. The temperature of the jacket on the inner surface of the suction pipe was controlled at 220°C, the solvent inlet temperature of the ejector was controlled at 0°C, and the solvent flow rate was adjusted to 43.1 m³ / s. 3 The flow rate was 42.7 kg / h, with a pressure of 0.41 MPa and an ejector pressure controlled at approximately 3.5 kPa (abs). The temperature of the glycolide vapor from the upstream depolymerization reactor was 186.9 °C. The flow rate of stream 23 was 0.053 times that of stream 22. When the liquid level increased to 51.16%, the solid content of the suspension reached approximately 2.5%.

[0063] The second branch circulating solvent 16 is set at 0.32m. 3 The gas phase space is washed 360° at a flow rate of / h, and the solvent 17 in the third branch is adjusted to 0.32m 3 The packing layer was sprayed with a flow rate of 30 L / h. The circulating solvent was then replaced with fresh solvent at a flow rate of 30 L / h. Using this method, the crude glycolide product obtained had a purity of 97.9% and a total acid value of 115 μmol / g. Inspection of the gas phase inlet of the injector revealed no obvious adhesion of glycolide to the inner surface of the suction pipe.

[0064] Example 4

[0065] Similar to Example 1, except that the flow rate of stream 23 is 0.014 times that of stream 22.

[0066] The crude glycolide product obtained had a purity of 94.5% and a total acid value of 167 μmol / g. Inspection of the gas phase inlet of the injector revealed some glycolide adhering to the inner surface of the suction tube.

[0067] Example 5

[0068] Same as Example 1, except that the solvent inlet temperature of the injector is controlled at 15°C.

[0069] The crude glycolide product obtained had a purity of 94.1% and a total acid value of 175 μmol / g. Inspection of the gas phase inlet of the injector revealed some glycolide adhering to the inner surface of the suction tube.

[0070] Example 6

[0071] Same as Example 1, except that fresh solvent is not used to replace the circulating solvent.

[0072] The crude glycolide product obtained had a purity of 94.3% and a total acid value of 198 μmol / g. Inspection of the gas phase inlet of the injector revealed some glycolide adhering to the inner surface of the suction tube.

[0073] Example 7

[0074] Same as Example 1, except that the glycolide vapor is replaced with L-lactide vapor.

[0075] The crude glycolide product obtained had a purity of 97.1% and a total acid value of 118 μmol / g. Inspection of the gas phase inlet of the injector revealed no obvious adhesion of glycolide to the inner surface of the suction tube.

[0076] 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 of solidifying and collecting lactide from a lactide-containing gas, characterized in that, The method includes: contacting a gas containing lactone and a liquid containing a solvent in an injector; In this process, a solvent-containing liquid acts as the working fluid, creating a vacuum within the injector. This allows a gas containing lactide to be drawn into the injector as the ejector fluid, where it comes into contact with the solvent and solidifies the lactide, forming a mixed slurry.

2. The method of claim 1, wherein, The method further includes: separating a portion of the mixed slurry formed after contact to obtain a wet solid material of lactide and a liquid phase; preferably, the liquid phase is mixed with the other portion and then circulated back to the ejector as the working fluid, wherein the flow rate ratio of one portion of the mixed slurry to the flow rate of the other portion of the mixed slurry is 0.02-0.2; preferably, The solids in the mixed slurry account for 1-5% of the total mass.

3. The method according to claim 1 or 2, wherein, The mixed slurry formed after contact also needs to undergo degassing treatment, which includes: purifying the gas phase escaping from the surface of the mixed slurry through a packing material to form tail gas; preferably... The vapor phase escaping from the surface of the mixed slurry is sprayed with a solvent-containing liquid, and the sprayed liquid is transferred into the mixed slurry; and / or The filler is sprayed with a solvent-containing liquid, and the sprayed liquid is transferred into the mixed slurry.

4. The method according to any one of claims 1-3, wherein, The mixed slurry formed after contact is at least partially separated to obtain a wet solid material of lactide and a liquid phase. A portion of the obtained liquid phase is extracted, replenished with fresh solvent, mixed with another portion of the mixed slurry, and then circulated back to the ejector as the working fluid. Preferably, The ratio of the volumetric flow rate of the extracted solvent to the volumetric flow rate of the total solvent is 0.01-0.2; and / or The ratio of the volume of fresh solvent added to the volume of the extracted liquid phase is 0.8-1.

5.

5. The method according to any one of claims 1-4, wherein, The operating conditions of the injector include: The gas inlet wall temperature of the injector needs to be controlled above the boiling point of the lactone, preferably 180-240℃, more preferably 210-230℃; and / or The ejector chamber pressure is 1200-9000 PaA, preferably 1500-5000 PaA; and / or The temperature of the solvent-containing liquid introduced into the injector is -15-15°C, preferably -10-5°C.

6. The method according to any one of claims 1-5, wherein, The solvent contains at least one of ester solvents, alcohol solvents, ketone solvents, alkane solvents, ether solvents, and water. More preferably, the solvent contains at least one of C3-C5 ester solvents, C2-C5 alcohol solvents, C3-C5 ketone solvents, C3-C6 alkane solvents, and water. More preferably, the solvent is at least one of methyl glycolate, ethyl acetate, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, isobutanol, acetone, n-hexane, cyclohexane, pentane, petroleum ether, and water; and / or The lactide is at least one of glycolide, L-lactide, and D,L-lactide, preferably glycolide.

7. A system for solidifying and collecting lactide from a gas containing lactide, characterized in that, The system includes: The injection unit is provided with a liquid inlet for introducing a solvent-containing liquid as the working fluid, a gas inlet for introducing a lactone-containing gas as the ejector fluid, and a mixed fluid outlet for outputting a mixed fluid after the working fluid and the ejector fluid are mixed. The degassing unit, from bottom to top, includes: a suspension collection zone, a gas phase collection zone, and a packing zone; wherein, the suspension collection zone is used to receive the mixed fluid from the jetting unit to form a suspension, the gas phase in the suspension escapes to the gas phase collection zone, and then is output from the gas phase collection zone to the packing zone, where it is purified by the packing. The suspension treatment unit includes a first circulation pipeline that recycles at least a portion of the suspension back to the spray unit as a solvent; a second circulation pipeline that sends the suspension into a solid-liquid separation device for separation to obtain a liquid phase and a lactone solid wet material, and recycles the obtained liquid phase back to the spray unit; the first and second circulation pipelines are connected in parallel at the suspension outlet and liquid inlet of the degassing unit; the second circulation pipeline also includes a first branch that transports the separated solvent to the degassing unit for spraying the gas phase accumulation zone and a second branch that transports the separated liquid phase to the degassing unit for spraying the packing zone.

8. The system according to claim 7, wherein, The second circulation pipeline has a solvent extraction port and a fresh solvent replenishment port sequentially installed on the liquid phase outlet pipeline after separation.

9. The system according to claim 7 or 8, wherein, The injection unit includes at least one liquid injector; and / or The suspension collection area of ​​the degassing unit is equipped with a disturbance device; and / or A defoaming device is provided above the packing area of ​​the degassing unit; and / or Heat exchange devices are provided on the solvent feed pipe of the spraying unit and the liquid phase outlet pipe of the solid-liquid separation device of the suspension treatment unit.

10. A method for solidifying and collecting lactide from a gas containing lactide, characterized in that, The method is performed in the system described in any one of claims 7-9, and includes: (1) The solvent-containing liquid is fed into the spraying unit through the liquid inlet of the spraying unit. A vacuum is drawn so that the gas containing lactide is drawn into the spraying unit through the gas inlet and comes into contact with the solvent. The mixed slurry formed by the contact curing of lactide is injected into the degassing unit through the mixed fluid outlet of the spraying unit. (2) The mixed fluids are collected in the suspension collection area of ​​the degassing unit to form a suspension. The gas phase in the suspension escapes to the gas phase collection area. Optionally, after being sprayed with solvent, it is output from the gas phase collection area to the packing area. The packing is purified to form tail gas. Optionally, the packing is sprayed with solvent. After degassing, the suspension is sent to the suspension treatment unit. (3) In the suspension treatment unit, the suspension is divided into at least two parts, wherein, A portion of the suspension undergoes solid-liquid separation to obtain a wet solid material of lactide and a liquid phase. The liquid phase is partially extracted, and then solvent is added to form a mixed liquid phase. A portion of this mixed liquid phase is mixed with another portion of the suspension and recycled back to the spray unit as a solvent-containing liquid. Preferably, 1-25 wt% of the mixed liquid phase is used as a solvent to spray the gas phase in the gas phase accumulation zone of the degassing unit, and 1-25 wt% is used as a solvent to spray the packing in the packing zone of the degassing unit; the remaining mixed liquid phase is mixed with another part of the suspension and then circulated back to the spraying unit as a solvent-containing liquid; preferably, the flow rate ratio of one part of the suspension to the flow rate of the other part of the suspension is 0.02-0.2.

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