Method for cleaning high-temperature depolymerization reactor and application thereof

Abstract

The invention discloses a method for cleaning a high-temperature depolymerization reactor and application thereof, and the method comprises the following steps: (1) after the high-temperature depolymerization reaction is finished and a reaction product is discharged, introducing a cleaning agent into the depolymerization reactor, and stirring to obtain a mixed solution; (2) guiding the mixed solution out of the depolymerization reactor and cooling the mixed solution to obtain a liquid-solid two-phase mixture; and (3) carrying out solid-liquid separation on the liquid-solid two-phase mixture to obtain discharged solid-phase residues and a recycled cleaning agent. Residues are left on the inner wall of the depolymerization reactor, and the residues comprise at least one of coke and cyclic ester polymers; the cleaning agent is selected from at least one of C10-C30 long-chain alkyl alcohol, polyalkylene ether glycol and polyalkyl glycol. The method can be particularly used for cleaning a depolymerization reactor body, kettle cleaning is carried out under the operation condition of the depolymerization reactor, and the possibility that a reaction kettle sealing piece and the like are damaged due to repeated disassembly is reduced.

Description

Technical Field

[0001] This invention relates to the cleaning of reactors, and more particularly to the cleaning of high-temperature depolymerization reactors. Background Technology

[0002] In recent years, polymer materials such as polylactic acid and polyglycolic acid have been widely used in the pharmaceutical, agricultural, and food industries due to their good biodegradability and biocompatibility. The production methods of these polymers all involve reacting raw materials through condensation and depolymerization reactions to obtain cyclic esters, and then performing ring-opening polymerization of the cyclic esters to obtain the corresponding polymers.

[0003] To induce depolymerization of oligomers to form cyclic esters, the depolymerization reaction is carried out under high temperature and high vacuum. However, the high temperature process can lead to side reactions of the oligomers, producing high molecular weight polymers and coke within the system. Since these byproducts have high melting points, they cannot be directly discharged from the reactor. Therefore, factories typically treat the reactor by cooling it down and manually removing the coke. Summary of the Invention

[0004] To overcome the problems existing in the prior art, the present invention provides a method for cleaning a high-temperature depolymerization reactor and its application. The method can be used in particular for cleaning the depolymerization reactor itself. It performs reactor cleaning under the operating conditions of the depolymerization reactor, reducing the possibility of damage to reactor seals and other components caused by repeated disassembly. While reducing manual operation costs, it also reduces energy consumption and safety hazards.

[0005] One of the objectives of this invention is to provide a method for cleaning a high-temperature depolymerization reactor, comprising: (1) after the high-temperature depolymerization reaction is completed and the reaction products are discharged, (without cooling the depolymerization reactor or under the reaction conditions of the depolymerization reactor or under the reaction temperature and reaction pressure of the depolymerization reactor) introducing a cleaning agent into the depolymerization reactor and stirring to obtain a mixture; (2) exporting the mixture from the depolymerization reactor and cooling the mixture to obtain a liquid-solid two-phase mixture; (3) performing solid-liquid separation on the liquid-solid two-phase mixture to obtain discharged solid residue and recovered cleaning agent.

[0006] The depolymerization reactor is a bulk depolymerization reactor, where a bulk reaction takes place. Preferably, the depolymerization reactor is the reaction in which oligomers depolymerize to form cyclic esters (e.g., glycolide and / or lactide) during the production of cyclic esters (e.g., glycolide and / or lactide). While the oligomers undergo depolymerization to form cyclic esters in the depolymerization reactor, side reactions also occur, generating polymers with higher degrees of polymerization, and even producing coke. These byproducts, due to their high viscosity, cannot be discharged from the polymerization reactor and accumulate in the depolymerization reactor, with most adhering to the reactor walls and agitator after the reaction is complete.

[0007] In a preferred embodiment, the temperature of the depolymerization reactor in step (1) is 180–300°C, for example, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, or 300°C; and the pressure of the depolymerization reactor in step (1) is 0.1–10 kPa, for example, 0.1 kPa, 0.5 kPa, 1 kPa, 2 kPa, 4 kPa, 6 kPa, 8 kPa, or 10 kPa.

[0008] In a further preferred embodiment, when the depolymerization reaction in the depolymerization reactor is for the formation of glycolide, the temperature of the depolymerization reactor is 210–300°C and the pressure is 0.2–10 kPa; or, when the depolymerization reaction in the depolymerization reactor is for the formation of lactide, the temperature of the depolymerization reactor is 180–300°C and the pressure is 0.1–10 kPa.

[0009] In a preferred embodiment, the depolymerization reactor is a depolymerization vessel.

[0010] In a further preferred embodiment, residue remains on the inner wall of the depolymerization reactor, the residue comprising at least one of coke and cyclic ester polymers, wherein the cyclic ester polymers refer to cyclic ester oligomers and / or cyclic ester polymers, the cyclic ester oligomers refer to 3-15 polymers of cyclic esters, and the cyclic ester polymers refer to polymers of 16 or more cyclic esters.

[0011] In a preferred embodiment, the cleaning agent is selected from at least one of C10-C30 long-chain alkyl alcohols, polyalkylene ether glycols, and polyalkyl glycols, preferably a combination of at least one of polyalkylene ether glycols and polyalkyl glycols with at least one of C10-C30 long-chain alkyl alcohols.

[0012] In a further preferred embodiment, the long-chain alkyl alcohol is a C12-C20 alkyl alcohol, preferably at least one selected from dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol, and eicosyl alcohol; and / or, the polyalkylene ether glycol is selected from at least one selected from polytrimethylene ether glycol, polytetramethylene ether glycol, and polypentamethylene ether glycol; and / or, the polyalkyl glycol is selected from polyC2-C6 alkyl glycols, preferably at least one selected from polyethylene glycol, polypropylene glycol, and polybutanediol.

[0013] In a further preferred embodiment, when the cleaning agent is selected from a combination of at least one of polyalkylene ether glycols and polyalkyl glycols with at least one of C10-C30 long-chain alkyl alcohols, the weight ratio of at least one of the polyalkylene ether glycols and polyalkyl glycols to at least one of the C10-C30 long-chain alkyl alcohols is 1:(0.1-10), preferably 1:(0.5-5), for example 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10.

[0014] After extensive experimental research, the inventors discovered that when the above combination method is used, not only is the cleaning time greatly shortened, but the residue removal rate and the purity of the recovered cleaning agent are also improved.

[0015] In a preferred embodiment, in step (1), the stirring is carried out for 0.5 to 10 hours, preferably 1 to 6 hours.

[0016] For example, in step (1), the stirring is carried out for 0.5h, 1h, 2h, 4h, 6h, 8h or 10h.

[0017] In a preferred embodiment, in step (1), the cleaning agent is directly added to the depolymerization reactor or sprayed evenly onto the inner wall of the depolymerization reactor through a nozzle.

[0018] In a further preferred embodiment, the cleaning agent is introduced to 2 / 5 to 4 / 5 of the volume of the depolymerization reactor, for example, 2 / 5, 1 / 2, 3 / 5, 2 / 3, 3 / 4, or 4 / 5.

[0019] In a preferred embodiment, in step (2), the final cooling temperature is (T m +5℃)~150℃, where T m This is the melting point of the cleaning agent.

[0020] The mixture forms a liquid-solid two-phase mixture after cooling.

[0021] In a further preferred embodiment, when the cleaning agent is a combination of two or more types, the T of the cleaning agent... m Based on the high melting point.

[0022] When the cleaning agent contains two or more components, the melting point of the cleaning agent with the higher melting point shall be denoted as T. m .

[0023] In a preferred embodiment, the solid-liquid separation in step (3) is performed using a centrifuge.

[0024] In a preferred embodiment, the recycled cleaning agent in step (3) is either stored or partially discharged and partially recycled back to step (1) as a cleaning agent, or entirely recycled back to step (1) as a cleaning agent.

[0025] In this invention, the depolymerization reactor does not need to be cooled after the reaction; the cleaning agent is directly introduced into it, thus saving the cooling time of the depolymerization reactor. Simultaneously, since the cooling temperature in step (2) is relatively high, the cleaning agent in step (3) is also at a relatively high temperature; recycling it back to the depolymerization reactor reduces the heating time. The method of this invention does not require energy-intensive and complex processing methods such as distillation or rectification.

[0026] A second objective of this invention is to provide a system for cleaning a depolymerization reactor, preferably for carrying out the method described in one objective of this invention. The system includes a depolymerization reactor, a cleaning agent delivery pipeline disposed on the depolymerization reactor, and a cleaning agent recovery unit. The cleaning agent recovery unit includes a cooling-filtration combined device, or includes a cooler and a solid-liquid separation device connected in sequence by pipelines.

[0027] The cleaning agent delivery pipeline is installed on the depolymerization reactor and is used to deliver the cleaning agent to the depolymerization reactor.

[0028] In a preferred embodiment, the depolymerization reactor is a depolymerization vessel.

[0029] In a preferred embodiment, the solid-liquid separator is a centrifuge.

[0030] In a preferred embodiment, the discharge end of the depolymerization reactor is connected to the inlet end of the cooler or the cooling-filtration combined device via a pipeline.

[0031] In a preferred embodiment, the centrifuge includes a liquid discharge end and a solid discharge end, and a solid discharge pipeline is provided on the solid discharge end.

[0032] In a preferred embodiment, the system further includes a cleaning agent recovery tank connected to the liquid phase outlet of the centrifuge.

[0033] In a further preferred embodiment, the cleaning agent storage tank is further connected to the depolymerization reactor via a pipeline for recycling the centrifuged recovered cleaning agent back to the depolymerization reactor.

[0034] In a further preferred embodiment, a cleaning agent discharge pipeline is further provided on the cleaning agent storage tank.

[0035] 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 the second objective of this invention in cleaning depolymerization reactors, especially in cleaning bulk depolymerization reactors.

[0036] 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.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The method described in this invention reduces the operation time and eliminates labor costs while ensuring the residue removal rate of the reactor;

[0039] (2) The cleaning solvent of the method described in this invention is not discharged or is discharged in small quantities, which reduces the amount of cleaning agent used and reduces the generation of waste.

[0040] (3) The method described in this invention performs reactor cleaning under the operating conditions of the depolymerization reaction, which reduces the possibility of damage to reactor seals and other components caused by repeated disassembly.

[0041] (4) 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

[0042] Figure 1 A flowchart of the system described in this invention is shown.

[0043] 1 represents the cleaning agent delivery pipeline; 2 represents the depolymerization reactor; 3 represents the mixed liquid delivery pipeline; 4 represents the cooler; 5 represents the liquid-solid two-phase mixture delivery pipeline; 6 represents the solid-liquid separator (e.g., centrifuge); 7 represents the depolymerization residue outlet; 8 represents the recycled cleaning agent delivery pipeline; 9 represents the recycled cleaning agent storage tank; 10 represents the recycled cleaning agent delivery pipeline; 11 represents the recycled cleaning agent delivery pump; 12 represents the recycled cleaning agent circulation pipeline; and 13 represents the recycled cleaning agent discharge pipeline. Detailed Implementation

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The "residue removal rate of the depolymerization reactor" in the examples was obtained as follows:

[0049]

[0050] Example 1

[0051] In the glycolide production process, the depolymerization reactor operates at a temperature of 280℃ and a pressure of 5 kPa. After the reaction is stopped, hexadecyl alcohol is directly pumped into the reactor to two-thirds full using a cleaning agent transfer pump. The depolymerization reactor agitator is then activated and maintained for 4 hours before being discharged into a cooling reactor. The cleaning solution is slowly cooled to 55℃ in the cooling reactor, then pressurized by a pump and sent to a horizontal screw centrifuge for solid-liquid separation. The solid residue is discharged on-site, while the recovered cleaning agent is discharged into a solvent storage tank. The purity of the recovered cleaning agent in the solvent storage tank is tested and found to be 99%, allowing for direct reuse.

[0052] The above cleaning method takes 21 hours, and the residue removal rate of the depolymerization reactor is 98.6%.

[0053] Example 2

[0054] In the glycolide production process, the depolymerization reactor operates at a temperature of 260℃ and a pressure of 0.2 kPa. After the reaction is stopped, PEG400 is directly pumped into the reactor to two-thirds full using a cleaning agent transfer pump. The depolymerization reactor agitator is then activated, and the mixture is maintained for 6 hours before being discharged into a cooling reactor. The cleaning solution is slowly cooled to 150℃ in the cooling reactor, then pressurized by a pump and sent to a vertical centrifuge for solid-liquid separation. The solid residue is discharged on-site, while the recovered cleaning agent is discharged into a solvent storage tank. The purity of the recovered cleaning agent in the solvent storage tank is tested and found to be 90%. A portion is discharged, while the remainder is mixed with fresh PEG400 and reused.

[0055] The above cleaning method takes 17 hours, and the residue removal rate of the depolymerization reactor is 98.9%.

[0056] Example 3

[0057] In the lactide production process, the depolymerization reactor operates at a temperature of 300℃ and a pressure of 10kPa. After the reaction is stopped, polytrimethylene ether glycol (ECOPROLH2000) is directly pumped into the reactor to two-thirds full using a cleaning agent delivery pump. The depolymerization reactor agitator is then activated, and the mixture is maintained for 3 hours before being discharged into a combined precipitation / filtration device. The cleaning solution is slowly cooled in the combined device for 20 hours (final cooling temperature 100℃), followed by direct solid-liquid separation. The solid residue is discharged on-site, while the recovered cleaning agent is discharged into a solvent storage tank. The purity of the recovered cleaning agent in the solvent storage tank is tested and found to be 95%, allowing for direct reuse.

[0058] The above cleaning method takes 23 hours, and the residue removal rate of the depolymerization reactor is 98.3%.

[0059] Example 4

[0060] In the lactide production process, the depolymerization reactor operates at a temperature of 240℃ and a pressure of 0.1 kPa. After the reaction is stopped, a cleaning solvent is pumped into the reactor. The reactor's top end cap is equipped with a nozzle, which sprays PEG300 onto the reactor wall to two-thirds of its height. The depolymerization reactor agitator is then activated, and the solution is maintained for 2 hours before being discharged into a cooling reactor. The cleaning solution is slowly cooled to 130℃ in the cooling reactor, then pressurized by a pump and sent to a plate and frame filter press for solid-liquid separation. The solid residue is discharged on-site, while the recovered cleaning solvent is stored in a solvent storage tank. The purity of the recovered cleaning solvent in the solvent storage tank is 92%, allowing for direct reuse.

[0061] The above cleaning method takes 13 hours, and the residue removal rate of the depolymerization reactor is 98.1%.

[0062] Example 5

[0063] In the glycolide production process, the depolymerization reactor operates at a temperature of 250℃ and a pressure of 10 kPa. After the reaction is stopped, a cleaning solvent is pumped into the reactor. The reactor's top end cap is equipped with a nozzle that sprays eicosanol onto the reactor wall to two-thirds of its height. The depolymerization reactor agitator is then activated, and the solution is maintained for 3 hours before being discharged into a cooling reactor. The cleaning solution is slowly cooled to 70℃ in the cooling reactor, then pressurized by a pump and sent to a vertical centrifuge for solid-liquid separation. The solid residue is discharged on-site, while the recovered cleaning solvent is stored in a solvent storage tank. The purity of the recovered cleaning solvent in the solvent storage tank is 98%, allowing for direct reuse.

[0064] The above cleaning method takes 17 hours, and the residue removal rate of the depolymerization reactor is 98.5%.

[0065] Example 6

[0066] In the lactide production process, the depolymerization reactor operates at a temperature of 240℃ and a pressure of 0.1 kPa. After the reaction is stopped, a cleaning solvent is pumped into the reactor. The reactor's top end cap is equipped with a nozzle that sprays octadecyl alcohol and PEG300 (with a weight ratio of 1:0.5) onto the reactor wall until it reaches two-thirds full. The depolymerization reactor agitator is then activated, and the mixture is maintained for 2 hours before being discharged into a cooling reactor. The cleaning solution is slowly cooled to 130℃ in the cooling reactor, then pressurized by a pump and sent to a plate and frame filter press for solid-liquid separation. The solid residue is discharged on-site, and the recovered cleaning solvent is discharged into a solvent storage tank. The purity of the recovered cleaning solvent in the solvent storage tank is tested and found to be 93%, allowing for direct reuse.

[0067] The above cleaning method takes 12 hours, and the residue removal rate of the depolymerization reactor is 99.3%.

[0068] Example 7

[0069] In the glycolide production process, the depolymerization reactor operates at a temperature of 280℃ and a pressure of 5 kPa. After the reaction is stopped, hexadecyl alcohol and polytrimethylene ether glycol (ECOPROLH2000) (with a weight ratio of 1:5) are directly pumped into the reactor through a cleaning agent transfer pump until it reaches two-thirds of the tank's capacity. The depolymerization reactor agitator is then activated, and the mixture is maintained for 4 hours before being discharged into a cooling reactor. The cleaning solution is slowly cooled to 55℃ in the cooling reactor, then pressurized by a pump and sent to a horizontal screw centrifuge for solid-liquid separation. The solid residue is discharged on-site, and the recovered cleaning agent is discharged into a solvent storage tank. The purity of the recovered cleaning agent in the solvent storage tank is tested and found to be 99.5%, allowing for direct reuse.

[0070] The above cleaning method takes 19 hours, and the residue removal rate of the depolymerization reactor is 99.5%.

[0071] Comparative Example 1

[0072] In the glycolide production process, the depolymerization reactor operates at a temperature of 280℃ and a pressure of 5 kPa. After the reaction is stopped, heating must be discontinued and the pressure restored to normal. Once the reactor temperature has cooled to room temperature, 5% alkali solution is added to two-thirds of the reactor's volume. The stirrer is then turned on, and the reactor is soaked for 10 hours before being drained. Any remaining residue in the reactor is manually removed.

[0073] The above cleaning method takes 60 hours and achieves a 98% removal rate of residue from the depolymerization reactor.

[0074] 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 of cleaning a high temperature depolymerization reactor, comprising: (1) after the high-temperature depolymerization reaction is completed and the reaction product is discharged, a cleaning agent is introduced into the depolymerization reactor, stirred to obtain a mixed solution; (2) the mixed solution is guided out of the depolymerization reactor and the mixed solution is cooled to obtain a liquid-solid two-phase mixture; (3) the liquid-solid two-phase mixture is subjected to solid-liquid separation to obtain a solid-phase residue for discharge and a recovered cleaning agent.

2. The method of claim 1, wherein, The temperature of the depolymerization reactor in step (1) is 180-300°C, and the pressure is 0.1-10 kPa; Preferably, when the depolymerization reaction in the depolymerization reactor is a reaction for generating glycolide, the temperature of the depolymerization reactor is 210-300°C, and the pressure is 0.2-10 kPa; Preferably, when the depolymerization reaction in the depolymerization reactor is a reaction for generating lactide, the temperature of the depolymerization reactor is 180-300°C, and the pressure is 0.1-10 kPa.

3. The method of claim 1, wherein, Residues are left on the inner wall of the depolymerization reactor, and the residues include at least one of coke and a cyclic ester polymer.

4. The method of claim 1, wherein, The cleaning agent is selected from at least one of a long-chain alkyl alcohol with a carbon number of C10-C30, a polyalkylene ether glycol, and a polyalkyl glycol; Preferably, the long-chain alkyl alcohol is a C12-C20 alkyl alcohol, and is preferably at least one of dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol, and eicosyl alcohol; and / or, the polyalkylene ether glycol is at least one of polytrimethylene ether glycol, polytetramethylene ether glycol, and poly-pentamethylene ether glycol; and / or, the polyalkyl glycol is at least one of a poly-C2-C6 alkyl glycol, and is preferably at least one of polyethylene glycol, polypropylene glycol, and polybutylene glycol.

5. The method of claim 1, wherein, In step (2), the cooling final temperature is (T m + 5°C) to 150°C, where T m is the melting point of the cleaning agent.

6. The method according to any one of claims 1-5, wherein, The solid-liquid separation in step (3) is performed using a centrifuge; and / or, The recovered cleaning agent in step (3) is stored, or part of the recovered cleaning agent is discharged and part of the recovered cleaning agent is recycled to step (1) as a cleaning agent, or all of the recovered cleaning agent is recycled to step (1) as a cleaning agent.

7. A system for cleaning a depolymerization reactor, preferably for performing the method according to any one of claims 1-6, the system comprising a depolymerization reactor, a cleaning agent delivery pipeline arranged on the depolymerization reactor, and a cleaning agent recovery unit, the cleaning agent recovery unit comprising a cooling-filtering two-in-one device, or comprising a cooler and a solid-liquid separation device connected in sequence through pipelines.

8. The system according to claim 7, wherein, The depolymerization reactor is a depolymerization kettle; and / or, The solid-liquid separator is a centrifuge.

9. The system according to claim 8, wherein, The centrifuge comprises a liquid phase discharge end and a solid phase discharge end, and a solid phase discharge pipeline is arranged on the solid phase discharge end; and / or, The discharge end of the depolymerization reactor is connected to the feed end of the cooler or the cooling-filtering two-in-one device through a pipeline.

10. The system of claim 8 or 9, characterized in that, The system further comprises a recovered cleaning agent storage tank connected to the liquid phase discharge end of the centrifuge; Preferably, the cleaning agent storage tank is further connected to the depolymerization reactor through a pipeline, for recycling the recovered cleaning agent after centrifugation to the depolymerization reactor. More preferably, a cleaning agent discharge pipeline is further arranged on the cleaning agent storage tank.

11. Use of the method according to any one of claims 1 to 6 or of the system according to any one of claims 7 to 10 for cleaning a depolymerization reactor, in particular for cleaning a bulk depolymerization reactor.

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