Method for simultaneously cleaning multiple containers

Abstract

The invention provides a method for cleaning a plurality of containers at the same time, the containers are provided with openings, reaction residues including polylactic acid oligomers are attached to the inner walls of the containers, and the method comprises the steps that cleaning solvents are added into the containers respectively; connecting each container with a condensation reflux device; setting a preset cooling circulation temperature for condensation, heating the plurality of containers, and maintaining preset heating time to obtain a mixed solution dissolved with reaction residual substances; and the mixed liquid is removed from all the containers, and all the cleaned containers are obtained. According to the method, the cleaning mode is simple, cost is low, efficiency is high, and the multiple containers can be cleaned at the same time.

Description

[0001] This application is filed on November 03, 2022 , application number is 202211372631.7, invention name is at the same time Method for cleaning multiple reaction vessels for preparing lactide A divisional application for a patent application. Technical Field

[0002] The present disclosure relates to the field of biodegradable polymer materials, and in particular to a method for cleaning multiple containers at the same time. Background Art

[0003] Medical lactide is an important raw material for the synthesis of medical polylactic acid. Medical polylactic acid has very good biocompatibility and good mechanical properties. Its degradation products are carbon dioxide and water. It is a safe and environmentally friendly medical material. Medical polylactic acid has a wide range of applications in surgical sutures, bone fixation materials, drug release, tissue engineering scaffolds and other fields.

[0004] There are two main methods for synthesizing polylactic acid. The first is to obtain polylactic acid through condensation reaction, and the other is to obtain polylactic acid through ring-opening polymerization of lactide. Because the water in the reaction product of the first method is difficult to remove, the molecular weight of the polylactic acid obtained is relatively low. At present, the second method is generally used at home and abroad, firstly obtaining pure lactide through polycondensation and cracking of lactic acid, and then obtaining medical polylactic acid through ring-opening polymerization of lactide.

[0005] The commonly used method for preparing lactide is a two-step method, in which lactic acid is first directly polycondensed to obtain low molecular weight polylactic acid, and then cracked at a higher temperature to generate lactide. When preparing medical-grade lactide on a small scale, a flask is usually used as a reaction container. The residual substances of the reaction are basically polylactic acid (i.e., polylactic acid oligomers) that cannot be cracked into lactide. The viscosity is high at high temperature, which makes it difficult to pour out and there are operational safety risks. After cooling, it solidifies and cannot be poured out. Directly treating the flask as hazardous waste has the problems of waste of resources and high cost. Summary of the invention

[0006] The present disclosure is made in view of the above-mentioned prior art conditions, and its purpose is to provide a method for cleaning multiple reaction containers for preparing lactide at the same time, which has a simple cleaning method, low cost and high efficiency, and a cleaning solvent for cleaning reaction containers for preparing lactide.

[0007] To this end, the first aspect of the present disclosure provides a method for simultaneously cleaning multiple reaction containers for preparing lactide, which comprises the following steps: preparing a cleaning solvent, wherein the cleaning solvent is a potassium hydroxide solution with a concentration of 0.1 mol / L to 1 mol / L; adding the cleaning solvent into each reaction container, wherein the ratio of the volume of the cleaning solvent in each reaction container (in L) to the mass of the reaction residual substance in each reaction container (in kg) is not less than 1; respectively arranging a reflux condenser at the opening of each reaction container, and connecting each reflux condenser in series to a condenser; turning on the condenser and setting a predetermined cooling cycle temperature for condensation, heating the multiple reaction containers until the cleaning solvent inside each reaction container reaches a predetermined heating temperature, and maintaining a predetermined heating time to obtain a mixed solution in which the reaction residual substance is dissolved, wherein the predetermined heating temperature is not less than 150°C; removing the reflux condenser from the opening of each reaction container, removing the mixed solution from the reaction container, and obtaining a cleaned reaction container.

[0008] In the first aspect of the present disclosure, by using potassium hydroxide solution as a cleaning solvent and configuring the concentration of the potassium hydroxide solution to be 0.1 mol / L to 1 mol / L, the reaction residue can be caused to dissolve in the alkaline cleaning solvent, thereby improving the cleaning effect of the reaction container; by configuring the ratio of the volume (in L) of the cleaning solvent in each reaction container to the mass (in kg) of the reaction residue in each reaction container to be not less than 1, it is conducive to the reaction residue and the cleaning solvent to fully react, thereby facilitating the dissolution of the reaction residue; by arranging a reflux condenser at the opening of each reaction container, the vapor of the cleaning solvent that is subsequently evaporated by heat can re-enter the reaction container through condensation reflux to participate in the reaction, and each reflux condenser is connected in series with a condenser, so that when the reaction container is cleaned, it is convenient to simultaneously condense and reflux the reactants in multiple reaction containers, thereby facilitating the cleaning efficiency of the reaction container and the equipment utilization rate; by configuring the predetermined heating temperature to be not less than 150° C., the dissolution rate and solubility of the reaction residue in the cleaning solvent can be increased, thereby improving the cleaning effect of the reaction container. Thus, a method for cleaning a plurality of reaction vessels for preparing lactide at the same time can be provided, which has a simple cleaning method, low cost and high efficiency.

[0009] In the method involved in the first aspect of the present disclosure, optionally, the predetermined heating temperature is 150° C. to 160° C., and the predetermined heating time is 6 h to 24 h. In this case, it is beneficial for the reaction residual substance to fully react with the cleaning solvent, thereby facilitating the reaction residual substance to fully dissolve in the cleaning solvent, thereby improving the cleaning effect of the reaction container.

[0010] In the method involved in the first aspect of the present disclosure, the plurality of reaction vessels may be heated simultaneously by oil bath heating. In this case, by placing the reaction vessels in thermal oil, the bottom area of ​​the reaction vessels may be evenly heated, thereby facilitating the reaction residual substances to be fully dissolved in the cleaning solvent, thereby improving the cleaning effect of the reaction vessels.

[0011] In the method according to the first aspect of the present disclosure, optionally, the number of the plurality of reaction containers is 2 to 4. In this case, 2 to 4 reaction containers can be cleaned at the same time.

[0012] In the method involved in the first aspect of the present disclosure, optionally, the predetermined cooling cycle temperature is not higher than 0° C. In this case, when the cleaning solvent is heated and evaporated and rises to the reflux condenser, by setting the predetermined cooling cycle temperature to not higher than 0° C., the condensation reflux effect of the vapor of the cleaning solvent can be improved, whereby the vapor of the cleaning solvent can form droplets after being cooled and re-enter the reaction container, thereby improving the cleaning efficiency and cleaning effect of the reaction container.

[0013] In the method involved in the first aspect of the present disclosure, optionally, the reflux condenser is a serpentine reflux condenser. In this case, when the cleaning solvent is heated and evaporated and rises to the serpentine reflux condenser, the cleaning solvent vapor is cooled by contacting the serpentine reflux condenser and can form small droplets in the serpentine reflux condenser and gradually gather to form droplets and finally fall and re-enter the reaction vessel, which is conducive to increasing the reflux amount of the cleaning solvent vapor, thereby improving the cleaning efficiency and cleaning effect of the reaction vessel.

[0014] In the method involved in the first aspect of the present disclosure, optionally, the reaction vessel is selected from one of a conical flask, a two-necked flask or a three-necked flask, and the types of the reaction vessels are the same or different. Thus, a cleaning solvent can be added to the reaction vessel, and a reflux condenser is arranged at the opening of the reaction vessel, so that the reaction vessel can be easily cleaned.

[0015] In the method involved in the first aspect of the present disclosure, optionally, after obtaining the mixed solution, the mixed solution is removed from the reaction container while it is hot. In this case, by removing the mixed solution from the reaction container while it is hot, the possibility of incomplete cleaning caused by precipitation of reaction residual substances in the mixed solution due to the decrease in the temperature of the mixed solution can be effectively reduced. In other words, it can be helpful to improve the cleaning effect of the reaction container.

[0016] In the method involved in the first aspect of the present disclosure, optionally, the method of obtaining the mass of the reaction residual substance includes the following steps: weighing the reaction container to obtain the mass of the reaction container before preparing lactide; weighing the reaction container containing the reaction residual substance to obtain the total mass after preparing lactide; and subtracting the mass of the reaction container from the total mass to obtain the mass of the reaction residual substance. In this case, by obtaining the mass of the reaction residual substance, it is easy to determine the volume of the cleaning solvent added to the reaction container.

[0017] The second aspect of the present disclosure provides a cleaning solvent for cleaning a reaction vessel for preparing lactide, the reaction vessel having an opening and an inner wall with reaction residues left after preparing lactide, the reaction residues including polylactic acid oligomers, the cleaning solvent being a potassium hydroxide solution, and the concentration of the cleaning solvent being 0.1 mol / L to 1 mol / L, the ratio of the volume of the cleaning solvent (in L) to the mass of the reaction residues in the reaction vessel (in kg) being not less than 1; when the reaction vessel is cleaned with the cleaning solvent, a reflux condenser is provided at the opening of the reaction vessel for condensation, the reaction vessel is heated until the cleaning solvent inside the reaction vessel reaches a predetermined heating temperature, and the predetermined heating time is maintained to obtain a mixed solution in which the reaction residues are dissolved, the mixed solution is removed from the reaction vessel, and the cleaned reaction vessel is obtained, wherein the predetermined heating temperature is not less than 150°C. In the second aspect of the present disclosure, by cleaning the reaction vessel with the cleaning solvent, a cleaned reaction vessel can be obtained.

[0018] According to the present disclosure, a method for cleaning a plurality of reaction containers for preparing lactide at the same time, which has a simple cleaning method, low cost and high efficiency, and a cleaning solvent for cleaning the reaction containers for preparing lactide can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart showing the preparation of lactide to which examples of the present disclosure relate.

[0020] Figure 2 1 is a flow chart showing a method for simultaneously cleaning a plurality of reaction vessels for preparing lactide according to an example of the present disclosure.

[0021] Figure 3 Schematic diagram showing a condensation reflux device according to an example of the present disclosure.

[0022] Description of reference numerals:

[0023] 1 ... reaction container, 2 ... condensation reflux device, 20 ... reflux condenser, 21 ... channel, 22 ... fourth opening, 30 ... condenser. DETAILED DESCRIPTION

[0024] All references cited in this disclosure are incorporated by reference in their entirety as if fully set forth. Unless otherwise defined, technical and scientific terms used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0025] Hereinafter, the preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, the same symbols are assigned to the same components, and repeated descriptions are omitted. In addition, the accompanying drawings are only schematic diagrams, and the ratio of the dimensions of the components or the shapes of the components may be different from the actual ones.

[0026] It should be noted that the terms "including" and "having" and any variations thereof in the present invention, such as a process, method, system, product or device that includes or has a series of steps or units, are not necessarily limited to those steps or units clearly listed, but may include or have other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0027] The first aspect of the present disclosure relates to a method for simultaneously cleaning a plurality of reaction vessels for preparing lactide. The cleaning method of the present disclosure is simple in cleaning manner, low in cost and high in efficiency, and the method for simultaneously cleaning a plurality of reaction vessels for preparing lactide of the present disclosure can clean the reaction vessels without reaction residual substances attached. The method for simultaneously cleaning a plurality of reaction vessels for preparing lactide of the present disclosure can be referred to as a "cleaning method", and can also be referred to as a method for cleaning a reaction vessel for preparing lactide, a method for cleaning a reaction vessel, a method for simultaneously cleaning a plurality of polylactic acid polymerization reaction devices, etc.

[0028] The reaction container without reactive residual substances attached thereto obtained by cleaning by the cleaning method disclosed herein can be recovered and reused. For example, the cleaned reaction container can be used in a laboratory or used again to prepare lactide. The cleaning method disclosed herein can also be used to clean a polylactic acid polymerization reaction device. In other words, the cleaning method disclosed herein can be used to clean a container having polylactic acid oligomers.

[0029] Hereinafter, the method for cleaning a plurality of reaction vessels for preparing lactide according to the first aspect of the present disclosure will be described in conjunction with the accompanying drawings.

[0030] Figure 1 is a flow chart showing the preparation of lactide to which examples of the present disclosure relate.

[0031] In this embodiment, the preparation of lactide may include: preparing a lactic acid raw material (step S11); preparing an oxide of an amphoteric metal as a catalyst (step S12); adding the catalyst to the lactic acid raw material, and polymerizing the lactic acid raw material to obtain a polylactic acid oligomer (step S13); cracking the polylactic acid oligomer to obtain lactide (step S14) (see Figure 1 ). The order of step S11 and step S12 is not particular, for example, step S11 can be performed first and then step S12, or step S12 can be performed first and then step S11, or step S11 and step S12 can be performed simultaneously. In this case, in step S14, polylactic acid oligomers are usually not completely cleaved into lactide, and polylactic acid oligomers that cannot be cleaved into lactide and catalysts may adhere to the inner wall of the reaction container after cooling and solidification and are difficult to pour out directly, resulting in the reaction container cannot be reused. The substance attached to the inner wall of the reaction container is called reaction residual substance. That is, the reaction residual substance may include polylactic acid oligomers.

[0032] It should be noted that the reaction vessel for preparing lactide disclosed in the present invention can be used to prepare lactide not only by the above method, but also by other methods that may produce polylactic acid oligomers.

[0033] Figure 2 1 is a flow chart showing a method for simultaneously cleaning a plurality of reaction vessels for preparing lactide according to an example of the present disclosure.

[0034] In this embodiment, the method for simultaneously cleaning multiple reaction vessels for preparing lactide may include: preparing a cleaning solvent (step S100); adding the cleaning solvent into each reaction vessel respectively (step S200); setting a reflux condenser at the opening of the reaction vessel, and connecting the reflux condensers in series to a condenser (step S300); turning on the condenser and setting a predetermined cooling cycle temperature for condensation, heating the reaction vessel until the cleaning solvent reaches a predetermined heating temperature, and maintaining a predetermined heating time to obtain a mixed solution in which reaction residual substances are dissolved (step S400); removing the mixed solution from the reaction vessel to obtain a cleaned reaction vessel (step S500).

[0035] In this case, the reaction residue is dissolved in the cleaning solvent, and then the mixed solution containing the reaction residue is removed, thereby cleaning the reaction container for preparing lactide; in step S200, by adding the cleaning solvent into each reaction container respectively, a plurality of reaction containers for preparing lactide can be cleaned at the same time; in step S300, by providing a reflux condenser at the opening of the reaction container and connecting the reflux condenser in series with a condenser, it is convenient to simultaneously provide condensation reflux treatment for the reactants in a plurality of reaction containers, which is beneficial to improving the cleaning efficiency of the reaction container and the utilization rate of the equipment; in step S400, by heating the reaction container until the cleaning solvent reaches a predetermined heating temperature and maintaining the predetermined heating time, the dissolution rate and solubility of the reaction residue in the cleaning solvent can be increased, thereby improving the cleaning effect of the reaction container.

[0036] In the present disclosure, the reaction vessel for preparing lactide may be simply referred to as the reaction vessel, and the reflux condenser may be simply referred to as the condenser.

[0037] In some examples, in step S100, the cleaning solvent may be a potassium hydroxide solution. In some examples, the concentration of the potassium hydroxide solution may be 0.1 mol / L to 1 mol / L. For example, the concentration of the potassium hydroxide solution may be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L. In this case, by using the potassium hydroxide solution as the cleaning solvent and configuring the concentration of the potassium hydroxide solution to 0.1 mol / L to 1 mol / L, the reaction residual substances can be caused to dissolve in the alkaline cleaning solvent, thereby improving the cleaning effect of the reaction container.

[0038] In some examples

[0039] , the cleaning solvent can be used to clean the container for preparing lactide in the laboratory. In some examples, the cleaning solvent can also be used to clean other containers with polylactic acid oligomers.

[0040] In some examples, in step S200, the cleaning solvent may be added to each reaction container respectively, thereby being able to clean multiple reaction containers.

[0041] In some examples, in step S200, the ratio of the volume (in L) of the cleaning solvent in each reaction container to the mass (in kg) of the reaction residue in each reaction container may be no less than 1. In other words, the volume mass ratio of the cleaning solvent to the reaction residue may be no less than 1L:1kg. In this case, it is beneficial for the reaction residue to fully react with the cleaning solvent, thereby facilitating the dissolution of the reaction residue. It is understandable that when the reaction container is cleaned, the more the amount of cleaning solvent, the more fully the reaction container can be cleaned. In the present disclosure, by cooperating with a specific cleaning solvent through a condensing device, the reaction container can be cleaned when the volume mass ratio of the cleaning solvent to the reaction residue is no less than 1L:1kg, thereby reducing the cleaning cost.

[0042] In some examples, in step S200, the volume mass ratio of the cleaning solvent to the reaction residual substance can be 1L:1kg, 1.5L:1kg, 2L:1kg, 2.5L:1kg, 3L:1kg, 3.5L:1kg, 4L:1kg, 4.5L:1kg, or 5L:1kg.

[0043] In some examples, the method of obtaining the mass of the reaction residue may include the following steps: weighing the reaction container before the reaction (i.e., before preparing lactide) to obtain the mass of the reaction container; weighing the reaction container containing the reaction residue after the reaction (i.e., after preparing lactide and pouring out the lactide in the container) to obtain the total mass; subtracting the mass of the reaction container from the total mass to obtain the mass of the reaction residue. In this case, the mass of the reaction residue can be obtained, thereby determining the volume of the cleaning solvent added to the reaction container.

[0044] In some examples, in step S200, preferably, the number of reaction containers may be 2 to 4. For example, the number of reaction containers may be 2, 3, or 4. In this case, 2 to 4 reaction containers can be cleaned at the same time, thereby improving the cleaning efficiency.

[0045] In some examples, in step S200, the reaction vessel can be selected from one of a conical flask, a double-necked flask or a three-necked flask, and the types of each reaction vessel can be the same or different. Thus, it is convenient to add a cleaning solvent to the reaction vessel, and a reflux condenser is set at the opening of the reaction vessel, so that the reaction vessel can be easily cleaned. Of course, other containers with reaction residual substances can also be cleaned by the cleaning method disclosed in the present invention. Here, only several containers commonly used in experiments are listed for exemplary illustration, which should not be understood as limiting. For example, in the process of preparing lactide, it is usually necessary to add different types of reactants to the reaction vessel, so a three-necked flask is generally used as a reaction vessel for preparing lactide.

[0046] In some examples, in step S300, a reflux condenser can be respectively arranged at the opening of each reaction container. In this case, when the reaction container is subsequently heated, the vapor of the cleaning solvent evaporated by heat can re-enter the reaction container to participate in the reaction by condensation reflux, thereby saving the amount of cleaning solvent, and the reaction container can be cleaned by using a predetermined proportion of cleaning solvent, and the cost of cleaning the reaction container can also be reduced.

[0047] In some examples, the connection mode of each reflux condenser can be set to be connected in series. Among them, the reflux condenser after series connection can be connected to a condenser. In this case, when the reaction vessel is cleaned, a condenser can provide the condensate required for condensation reflux to multiple reaction vessels at the same time, which can improve the efficiency of cleaning multiple reaction vessels while also improving the equipment utilization rate of the condenser. In other words, by configuring a condenser, multiple reaction vessels can be cleaned at the same time.

[0048] In some examples, the reflux condenser may have a channel for the vapor of the cleaning solvent to move between the inner wall of its outer contour and the outer wall of the inner tube. In this case, by allowing the condensate to flow in the inner tube, it is possible to help reduce the temperature of the space in the channel. When the vapor of the cleaning solvent enters the channel with a lower temperature, it is possible to help the vapor of the cleaning solvent condense into small droplets when it is cooled and further condense on the outer wall of the inner tube and the inner wall of the outer contour of the reflux condenser to form droplets and fall into the reaction vessel, which is conducive to increasing the reflux amount of the cleaning solvent vapor, thereby improving the cleaning efficiency and cleaning effect of the reaction vessel. In some examples, in step S300, the reflux condenser may be a serpentine reflux condenser. In this case, the inner tube of the serpentine reflux condenser is in the shape of a snake-shaped coil. The serpentine inner tube has a larger surface area exposed to the space in the channel. When the condensate flows through the inner tube, it can help to quickly reduce the temperature of the space in the channel. Furthermore, when the vapor of the cleaning solvent enters the channel with a lower temperature and condenses into small droplets when it is cold, the small droplets will gradually gather on the outer wall of the inner tube with a lower temperature to form droplets. When the droplets gather to a certain amount, they will slide down along the outer wall of the serpentine inner tube under the action of their own gravity and continuously gather droplets in the process of sliding down to form a liquid flow, and finally flow downward into the reaction vessel, which is conducive to increasing the reflux speed and reflux amount of the cleaning solvent vapor, thereby improving the cleaning efficiency and cleaning effect of the reaction container.

[0049] Figure 3 Schematic diagram showing a condensation reflux device 2 according to an example of the present disclosure. Figure 3In the embodiment, the reaction container 1, the condensation reflux device 2 and the cooperation between the two are exemplarily described by taking the multiple reaction containers 1 as four three-necked flasks and the reflux condenser 20 as a serpentine reflux condenser as an example, and Figure 3 The arrows in the figure schematically indicate the moving direction of the condensate.

[0050] In such Figure 3 In the example shown, each reflux condenser 20 can be disposed at one of the openings (e.g. Figure 3 The reflux condenser 20 can be connected in series with the condenser 30 through a connecting pipe. When heating, the other openings of the three-necked flask that are not connected to the reflux condenser 20 can be in a closed state. At this time, the vapor of the cleaning solvent can be guided to move from the opening connected to the reflux condenser 20 and enter the reflux condenser 20; the end of the reflux condenser 20 that is relatively far away from the three-necked flask has an opening (hereinafter referred to as the fourth opening 22). When cleaning the reaction container 1, the reflux condenser 20 can be connected to the condenser 30 through the fourth opening 22. It is connected to the outside world. When the cleaning solvent moves upward due to heating and evaporation, even if the vapor of the cleaning solvent cannot be completely condensed and refluxed in the channel 21 of the reflux condenser 20, the vapor of the cleaning solvent can escape to the outside world from the fourth opening 22, thereby being conducive to the air pressure in the reaction vessel 1 and the reflux condenser 20 being in a balanced state with the external air pressure and effectively inhibiting the reaction vessel 1 and the reflux condenser 20 from rupturing due to excessive internal air pressure, thereby improving the safety of the cleaning process.

[0051] In some examples, in step 400, the predetermined cooling cycle temperature may be set to be no higher than 0°C. For example, the predetermined cooling cycle temperature may be 0°C, -1°C, -2°C, -3°C, -4°C, or -5°C, etc. In this case, when the cleaning solvent is heated and evaporated and rises to the reflux condenser, by setting the predetermined cooling cycle temperature to be no higher than 0°C, the condensation reflux effect of the vapor of the cleaning solvent can be improved, thereby increasing the reflux amount of the vapor of the cleaning solvent.

[0052] In some examples, the reaction vessel for preparing lactide can also be cleaned without using a condenser reflux tube. In this case, since the cleaning solvent will evaporate and dissipate due to heating, during the cleaning process, more cleaning solvent can be added to the reaction vessel or the cleaning solvent can be added to the reaction vessel multiple times to keep an appropriate amount of cleaning solvent in the reaction vessel at all times, so that the reaction vessel can be cleaned.

[0053] In some examples, a single reaction vessel may also be cleaned by the cleaning method disclosed herein. In this case, by providing a reflux condenser at the opening of the reaction vessel, the vapor of the cleaning solvent subsequently evaporated by heat can re-enter the reaction vessel to participate in the reaction through condensation reflux.

[0054] In some examples, more than 4 reaction vessels can also be cleaned at the same time by the cleaning method disclosed in the present invention. For example, the number of reaction vessels cleaned at the same time can be 5. Since the temperature of the condensate in the reflux condenser rises as the condensate moves in the condenser, when the condensate flows through a relatively backward condenser, such as the 5th condenser, the condensate with a temperature rise in the condenser may not be able to achieve the desired condensation effect of the vapor of the cleaning solvent in the 5th reaction vessel, resulting in part of the vapor of the cleaning solvent passing through the condenser and dissipating, affecting the cleaning effect of the reaction vessel. In this case, when more than 4 reaction vessels need to be cleaned, the condensation reflux effect of the vapor of the cleaning solvent can be improved by setting a lower cooling cycle temperature. For example, the cooling cycle temperature can be set to -5°C. Thus, the condensation reflux effect of the vapor of the cleaning solvent can be improved, thereby improving the cleaning efficiency and cleaning effect of the reaction vessel.

[0055] In some examples, in step S400, the predetermined heating temperature may be configured to be not less than 150°C. For example, the predetermined heating temperature may be 150°C, 160°C, 170°C, 180°C, or 190°C, etc. In some examples, preferably, the predetermined heating temperature may be 150°C to 160°C. In some examples, the predetermined heating time may be 6h to 24h. For example, the predetermined heating time may be 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h. In this case, by setting a specific heating temperature and heating time, it is possible to facilitate the reaction residual material to fully react with the cleaning solvent, thereby facilitating the reaction residual material to fully dissolve in the cleaning solvent, thereby improving the cleaning effect of the reaction container. However, the examples disclosed herein are not limited thereto. In other examples, the predetermined heating temperature may also be configured to be less than 150°C, and the cleaning effect may be improved by extending the predetermined heating time. For example, the predetermined heating temperature may be 140°C, and the predetermined heating time may be 48h.

[0056] In some examples, in step S400, multiple reaction vessels may be heated simultaneously by oil bath heating. In this case, by placing the reaction vessels in thermal oil, the bottom area of ​​the reaction vessels may be evenly heated, thereby facilitating the reaction residual substances to be fully dissolved in the cleaning solvent, thereby improving the cleaning effect of the reaction vessels.

[0057] In some examples, in step S500, after the reaction residual substances are fully dissolved in the cleaning solvent, the condenser tube can be removed from the opening of the reaction container, and then the mixed liquid in the reaction container can be poured out.

[0058] In some examples, in step S500, the mixed solution can be removed from the reaction container while it is hot. In this case, by removing the mixed solution from the reaction container while it is hot, the possibility of incomplete cleaning caused by precipitation of reaction residual substances in the mixed solution due to the decrease in the temperature of the mixed solution can be effectively reduced, thereby facilitating the improvement of the cleaning effect of the reaction container.

[0059] In some examples, in step S500, after the mixed solution is removed from the reaction container, the reaction container may be cleaned multiple times with water, thereby improving the cleanliness of the interior of the reaction container.

[0060] In summary, in the first aspect of the present disclosure, a method for cleaning multiple reaction containers for preparing lactide at the same time can be provided, which has a simple cleaning method, low cost and high efficiency, and the removal rate of reaction residual substances in the reaction containers obtained by cleaning is 100%. The reaction containers after cleaning have no reaction residual substances attached and can be recovered and reused (for example, they can be used in the laboratory and can also be used again for preparing lactide).

[0061] The second aspect of the present disclosure relates to a cleaning solvent for cleaning a reaction vessel for preparing lactide. In the second aspect of the present disclosure, by using the cleaning solvent to clean the reaction vessel, a cleaned reaction vessel can be obtained. The cleaning solvent involved in the second aspect of the present disclosure is consistent with the cleaning solvent in the cleaning method of the first aspect of the present disclosure. The specific description of the cleaning solvent can refer to the description of the cleaning solvent in the cleaning method above, which will not be repeated here.

[0062] When the reaction vessel with reaction residual substances is cleaned using the cleaning solvent involved in the second aspect of the present disclosure, the cleaning method involved in the first aspect of the present disclosure can be used for cleaning. Specifically, a reflux condenser can be set at the opening of the reaction vessel for condensation, the reaction vessel is heated until the cleaning solvent inside the reaction vessel reaches a predetermined heating temperature, and the predetermined heating time is maintained to obtain a mixed solution in which the reaction residual substances are dissolved, and the mixed solution is removed from the reaction vessel to obtain a cleaned reaction vessel, wherein the predetermined heating temperature is not less than 150°C. The various parameters, proportions and settings therein can refer to the description of the cleaning method above, and will not be repeated here.

[0063] In summary, in the second aspect of the present disclosure, a cleaning solvent for cleaning a reaction vessel for preparing lactide can be provided. After cleaning, the reaction vessel has no reaction residue attached and can be recovered and reused (for example, it can be used in a laboratory and can also be used again to prepare lactide).

[0064] Hereinafter, the cleaning method provided by the present disclosure is described in detail with reference to the embodiments and comparative examples, but they should not be construed as limiting the protection scope of the present disclosure.

[0065] [Example]

[0066] First, before preparing lactide, the reaction container is weighed to obtain the mass of the reaction container.

[0067] Secondly, prepare lactide, the specific steps are as follows: prepare lactic acid raw material; prepare amphoteric metal oxide as a catalyst; add the lactic acid raw material and the catalyst to a reaction container, and polymerize the lactic acid raw material to obtain polylactic acid oligomers; crack the polylactic acid oligomers to obtain lactide.

[0068] Next, the prepared lactide is removed from the reaction container, and the reaction container containing the reaction residue is weighed to obtain the total mass, and the mass of the reaction container is subtracted from the total mass to obtain the mass of the reaction residue.

[0069] Next, according to Table 1, the cleaning solvents of Examples 1 to 12 are configured.

[0070] Then, the cleaning solvent was added into the reaction container according to the ratio shown in Table 1.

[0071] Then, a reflux condenser is respectively set at the opening of the reaction container of each embodiment of Example 1 to Example 7, and the reflux condenser is connected to the condenser; a reflux condenser is respectively set at the opening of the four reaction containers of each embodiment of Example 8 to Example 12, and the reflux condensers are connected in series and connected to the condenser.

[0072] Next, according to Table 1, the condenser is turned on and a predetermined cooling cycle temperature is set for condensation, and multiple reaction containers are heated until the cleaning solvent inside each reaction container reaches a predetermined heating temperature, and the predetermined heating time is maintained to obtain a mixed solution in which reaction residual substances are dissolved.

[0073] Finally, the reflux condenser was removed from the opening of each reaction container, and the mixed liquid was removed from the reaction container to obtain the cleaned reaction containers of Example 1 to Example 12.

[0074] Table 1

[0075]

[0076] [Comparative Example]

[0077] First, before preparing lactide, the reaction container is weighed using an electronic scale to obtain the mass of the reaction container.

[0078] Secondly, prepare lactide, the specific steps are as follows: prepare lactic acid raw material; prepare amphoteric metal oxide as a catalyst; add the lactic acid raw material and the catalyst to a reaction container, and polymerize the lactic acid raw material to obtain polylactic acid oligomers; crack the polylactic acid oligomers to obtain lactide.

[0079] Next, the prepared lactide is removed from the reaction container, and the reaction container containing the reaction residue is weighed using an electronic scale to obtain the total mass, and the mass of the reaction container is subtracted from the total mass to obtain the mass of the reaction residue.

[0080] Next, according to Table 2, the cleaning solvents of Comparative Examples 1 to 27 were prepared.

[0081] Then, according to Table 2, the cleaning solvent is added to each reaction container at a ratio of not less than 1 between the volume of the cleaning solvent in each reaction container (in L) and the mass of the reaction residual substance in the reaction container (in kg).

[0082] Then, a reflux condenser is respectively set at the opening of the reaction container of each comparison example 1 to comparison example 6 and comparison example 11 to comparison example 27, and the reflux condenser is connected to the condenser; a reflux condenser is respectively set at the opening of the four reaction containers of each comparison example 7 to comparison example 10, and the reflux condensers are connected in series and then connected to the condenser.

[0083] Next, turn on the condenser and set the predetermined cooling cycle temperature according to Table 2 for condensation; according to Table 2, heat the multiple reaction containers until the cleaning solvent inside each reaction container reaches a predetermined heating temperature (the predetermined heating temperature is room temperature, which means that the reaction container is placed in a room temperature environment of 25°C), and maintain the predetermined heating time to obtain a mixed solution in which the reaction residual substances are dissolved.

[0084] Finally, the reflux condenser was removed from the opening of each reaction container, and the mixed liquid was removed from the reaction container to obtain the cleaned reaction containers of Comparative Examples 1 to 27.

[0085] Table 2

[0086]

[0087] When performing the above operations, the reflux conditions of the cleaning solvent in the condensation reflux pipe of each embodiment (Example 1 to Example 12) and each comparative example (Comparative Example 1 to Comparative Example 27) are observed and recorded. In the embodiments and comparative examples in which the number of cleaning containers is 4, observing the reflux conditions of the cleaning solvent refers to observing the reflux conditions of the cleaning solvent in the condensation reflux pipe that is located at the last position among the 4 series-connected condensation reflux pipes. Among them, full reflux means that only about 1 / 3 of the lower part of the condensation reflux pipe is observed to have condensed droplets in the event of cold during the cleaning process, a large amount of reflux means that only about 2 / 3 of the lower part of the condensation reflux pipe is observed to have condensed droplets in the event of cold during the cleaning process, and a small amount of reflux means that all areas of the condensation reflux pipe are observed to have condensed droplets in the event of cold during the cleaning process. The recorded results are shown in Table 3. The removal rate of the reaction residual substances in the reaction container after cleaning is calculated as follows: the reaction container after cleaning in each embodiment and each comparative example is weighed using an electronic scale to obtain the total mass after cleaning, and the removal rate of the reaction residual substances is calculated based on the weighing result, and the results are shown in Table 3. The calculation formula of the removal rate of the reaction residual substances is: removal rate = (mass of the reaction residual substances - mass of the reaction residual substances after cleaning) / mass of the reaction residual substances × 100%. When calculating the removal rate of the reaction residual substances in each embodiment and each comparative example in which the number of cleaning containers is 4, the average value of the removal rates of the reaction residual substances in the 4 reaction containers is taken as the removal rate of the reaction residual substances in each embodiment and each comparative example.

[0088] It should be noted that, in the embodiments, comparative examples, and the above-mentioned measurement processes of the present disclosure, unless otherwise specified, the reagents and instruments used are all commercially available products.

[0089] Table 3

[0090] Reflux of cleaning solvent Removal rate of reaction residual substances (%) Example 1 All reflux 100 Example 2 All reflux 100 Example 3 All reflux 100 Example 4 All reflux 100 Example 5 All reflux 100 Example 6 All reflux 100 Example 7 All reflux 100 Example 8 All reflux 100 Example 9 All reflux 100 Example 10 All reflux 100 Embodiment 11 All reflux 100 Example 12 All reflux 100 Comparative Example 1 \ 2 Comparative Example 2 All reflux 74 Comparative Example 3 All reflux 91 Comparative Example 4 A large amount of reflux 96 Comparative Example 5 All reflux 82 Comparative Example 6 A large amount of reflux 92 Comparative Example 7 All reflux 67 Comparative Example 8 All reflux 88 Comparative Example 9 A large amount of reflux 85 Comparative Example 10 Small amount of reflux 77 Comparative Example 11 All reflux 55 Comparative Example 12 A large amount of reflux 41 Comparative Example 13 \ 2 Comparative Example 14 All reflux 30 Comparative Example 15 All reflux 86 Comparative Example 16 A large amount of reflux 72 Comparative Example 17 \ 0 Comparative Example 18 All reflux 2 Comparative Example 19 \ 5 Comparative Example 20 A large amount of reflux 24 Comparative Example 21 Small amount of reflux 16 Comparative Example 22 \ 10 Comparative Example 23 A large amount of reflux 67 Comparative Example 24 Small amount of reflux 35 Comparative Example 25 \ 11 Comparative Example 26 A large amount of reflux 70 Comparative Example 27 Small amount of reflux 43

[0091] It can be seen from Table 3 that the removal rate of the reaction residual substances in each embodiment (embodiment 1 to embodiment 12) is 100%.

[0092] Particularly, in a preferred embodiment, the predetermined heating time of Example 5, Example 6, Example 7, Example 11, and Example 12 is 6 hours, and the removal rate of the reaction residual substances is 100%.

[0093] In particular, in the preferred embodiment, four reaction containers can be cleaned simultaneously in Examples 8 to 12, and the removal rate of reaction residual substances is 100%.

[0094] The removal rate of the reaction residual substances in the reaction container cleaned by Example 3 is 100%. The main reason is that when a single reaction container is cleaned, under the condition of a predetermined heating temperature of 170°C, the vapor of the cleaning solvent can be completely refluxed in the condensation reflux tube, and after a predetermined heating time of 12h, the reaction residual substances can be completely dissolved in a 0.1mol / L potassium hydroxide solution.

[0095] The removal rate of the reaction residues in the reaction container cleaned in Example 4 is 100%. The main reason is that although the dissolution rate of the reaction residues in 1 mol / L potassium hydroxide solution at the predetermined heating temperature of 140°C is lower than that at the predetermined heating temperature of 150°C, the reaction residues can be completely dissolved after the predetermined heating time of 12 hours.

[0096] The removal rate of the reaction residues in the reaction container cleaned in Comparative Example 1 is only 2%, mainly because the predetermined heating temperature is low. At room temperature (25° C.), the solubility of the reaction residues in 0.1 mol / L potassium hydroxide solution is very low.

[0097] The removal rates of the reaction residues in the reaction containers cleaned by Comparative Examples 2 and 3 were 74% and 91%, respectively. The main reason was that the predetermined heating temperature was low. Under the predetermined heating temperature conditions of 130°C and 140°C, the dissolution rate of the reaction residues in 0.1 mol / L potassium hydroxide solution was low. After a predetermined heating time of 24 hours, the reaction residues could not be completely dissolved.

[0098] The removal rate of the reaction residue in the reaction container cleaned by Comparative Example 4 is 96%. The main reason is that the predetermined heating temperature is low. Under the predetermined heating temperature condition of 130°C, the dissolution rate of the reaction residue in 1 mol / L potassium hydroxide solution is low. After 24 hours of the predetermined heating time, the reaction residue cannot be completely dissolved.

[0099] The removal rates of the reaction residues in the reaction containers cleaned by Comparative Examples 5 and 6 are 82% and 92%, respectively. The main reason is that the predetermined heating temperature is relatively high. Under the predetermined heating temperature condition of 180°C, the cleaning solvent in the reaction container evaporates quickly, and a large amount of cleaning solvent vapor is generated in a short time, which cannot be fully refluxed in the condensation reflux pipe but only a small amount can be refluxed, thereby reducing the amount of cleaning solvent in the reaction container and not being sufficient to completely dissolve the reaction residues.

[0100] The removal rates of the reaction residual substances in the reaction containers cleaned by Comparative Examples 7 and 8 were 67% and 88%, respectively. The main reason was that the predetermined heating temperature was low. Under the predetermined heating temperature conditions of 130°C and 140°C, the degradation rate of the reaction residual substances in 0.1 mol / L potassium hydroxide solution was low. After a predetermined heating time of 24 hours, the reaction residual substances could not be completely dissolved.

[0101] The removal rates of the reaction residues in the reaction containers cleaned by Comparative Examples 9 and 10 are 85% and 77%, respectively. The main reason is that the predetermined heating temperature is high and the number of reaction containers to be cleaned is large. Under the predetermined heating temperature conditions of 170°C and 180°C, the cleaning solvent in the reaction container evaporates quickly, and the condensate will heat up after entering the series-connected condensation reflux pipe due to the heat transfer from the vapor of the cleaning solvent. The heated condensate will have a weakened condensation effect on the cleaning solvent after entering the condensation reflux pipe at the rear of the series. As a result, a large amount of cleaning solvent vapor generated in a short time cannot be fully refluxed in the series-connected condensation reflux pipe but only a small amount can be refluxed, thereby reducing the amount of cleaning solvent in the reaction container and not being sufficient to completely dissolve the reaction residues.

[0102] The removal rate of the residual substances in the reaction container cleaned by Comparative Example 11 is 55%. The main reason is that the concentration of the potassium hydroxide solution used as the cleaning solvent is relatively low. Under the predetermined heating temperature condition of 150°C, the solubility of the reaction residual substances in the 0.01 mol / L potassium hydroxide solution is relatively low and is not sufficient to completely dissolve the reaction residual substances.

[0103] The removal rate of residual substances in the reaction container cleaned by Comparative Example 15 is 86%. The main reason is that the hydrochloric acid solution used as the cleaning solvent has a poor effect in dissolving the reaction residual substances. Under the predetermined heating temperature condition of 150°C, the solubility of the reaction residual substances in 0.1 mol / L hydrochloric acid solution is relatively low and is not sufficient to completely dissolve the reaction residual substances.

[0104] The removal rates of residual substances in the reaction containers cleaned by Comparative Examples 20, 23 and 26 are 24%, 67% and 70%, respectively. The main reason is that the potassium hydroxide ethanol solution, dichloromethane and chloroform used as cleaning solvents are less effective in dissolving the reaction residual substances. Under the predetermined heating temperature of 100°C, the dissolution rate of the reaction residual substances in 0.1 mol / L potassium hydroxide ethanol solution, dichloromethane and chloroform is low. After a predetermined heating time of 24 hours, the reaction residual substances cannot be completely dissolved.

[0105] The removal rates of residual substances in the reaction containers cleaned by Comparative Examples 21, 24 and 27 are 16%, 35% and 43%, respectively. The main reason is that potassium hydroxide ethanol solution, dichloromethane and chloroform are relatively volatile. Potassium hydroxide ethanol solution, dichloromethane and chloroform, which are cleaning solvents, evaporate quickly under the predetermined heating temperature condition of 150°C. A large amount of cleaning solvent vapor is generated in a short time, but cannot be fully refluxed in the condensation reflux pipe, and only a small amount can be refluxed, thereby reducing the amount of cleaning solvent in the reaction container and not being sufficient to completely dissolve the reaction residual substances.

[0106] In summary, no reaction residue remains in the reaction container for preparing lactide cleaned in each embodiment (Example 1 to Example 12), the cleaning method is simple, and in Examples 8 to Example 12, multiple reaction containers for preparing lactide can be cleaned at the same time, with high efficiency. In contrast, the method for cleaning the reaction container for preparing lactide in each comparative example (Comparative Example 1 to Comparative Example 27) cannot simultaneously achieve the effect of the method for cleaning the reaction container for preparing lactide in the above-mentioned embodiments (Example 1 to Example 12).

[0107] Although the present disclosure is specifically described above in conjunction with the accompanying drawings and examples, it is to be understood that the above description does not limit the present disclosure in any form. Those skilled in the art may modify and change the present disclosure as needed without departing from the essential spirit and scope of the present disclosure, and these modifications and changes all fall within the scope of the present disclosure.

Claims

1. A method for cleaning multiple containers simultaneously, characterized in that: The container has an opening and an inner wall of which is attached a reaction residual substance including a polylactic acid oligomer. The method comprises: Adding a cleaning solvent into each container respectively, wherein the cleaning solvent is a potassium hydroxide solution with a concentration of 0.1 mol / L to 1 mol / L, and the volume mass ratio of the cleaning solvent added to each container to the reaction residual substance in each container is not less than 1L:1kg; Connecting each container to a condensation reflux device, wherein a reflux condenser is respectively arranged at the opening of each container, and the reflux condenser has a channel for the vapor of the cleaning solvent to move between the inner wall of the outer contour and the outer wall of the inner tube; Setting a predetermined cooling cycle temperature for condensation, heating the multiple containers, and maintaining a predetermined heating time to obtain a mixed solution in which the reaction residual substance is dissolved, wherein the vapor of the cleaning solvent evaporated by heat re-enters each container to participate in the reaction by condensation reflux; The mixed liquid is removed from each container to obtain each cleaned container.

2. The method according to claim 1, characterized in that After the mixed solution was removed from each container, each container was rinsed multiple times with water.

3. The method according to claim 1, characterized in that The predetermined heating temperature for heating the plurality of containers is not less than 150°C.

4. The method according to claim 3, characterized in that The predetermined heating temperature is 150° C. to 160° C., and the predetermined heating time is 6 h to 24 h.

5. The method according to claim 1, characterized in that The predetermined heating temperature for heating the plurality of containers is 140° C., and the predetermined heating time is 48 hours.

6. The method according to claim 1, characterized in that The condensation reflux device comprises a condenser, and each reflux condenser is connected in series to the condenser.

7. The method according to claim 1 or 6, characterized in that: One end of the reflux condenser relatively far from the container has an opening. During heating, the reflux condenser is communicated with the outside through the opening of the reflux condenser.

8. The method according to claim 1, characterized in that: The predetermined cooling cycle temperature is not higher than 0°C.

9. The method according to claim 1 or 8, characterized in that: When more than 4 containers are cleaned, the predetermined cooling cycle temperature is set to -5°C.

10. The method according to claim 1, characterized in that After the reaction residual material is fully dissolved in the cleaning solvent, the mixed solution is removed from each container while it is hot.

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