Production device and process for synthesizing propiolactone based on homogeneous and heterogeneous complex catalysis
By combining homogeneous and heterogeneous catalysts in the lactide production unit, and utilizing multi-layer mesh plates and staged heating, the problem of the difficulty in vaporizing volatile components was solved, achieving efficient lactide production and improving purity and yield.
Patent Information
- Application Number
- CN202610626811.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-08
- Publication Date
- 2026-07-14
AI Technical Summary
In existing lactide production equipment, homogeneous catalysts make it difficult for volatile components to vaporize, affecting the catalytic depolymerization effect and lactide purity. Furthermore, existing equipment is difficult to match with heterogeneous catalytic processes.
The production device using a composite catalyst of homogeneous and heterogeneous phases includes a dehydration polycondensation reactor, a pyrolysis reactor, a condenser, and a negative pressure conveying pump. The pyrolysis reactor is equipped with multiple layers of mesh plates and a heterogeneous catalyst to promote the vaporization of volatile components, which are then rapidly discharged through staged heating and negative pressure conveying.
It improves the reaction efficiency of lactic acid oligomers, enhances the purity and yield of lactide, avoids catalyst loss and product entrainment, and ensures efficient conversion and purification.
Smart Images
Figure CN122377374A_ABST
Abstract
Description
Technical Field
[0001] This invention specifically relates to a production apparatus and process for synthesizing lactide based on homogeneous and heterogeneous composite catalysis, and pertains to the field of lactide preparation technology. Background Technology
[0002] Lactide, a key precursor of polylactic acid (PLA), is widely used in biodegradable materials, biomedical materials, and 3D printing materials. Existing lactide production equipment mainly consists of a multi-stage dehydration polycondensation reactor, a fixed-bed pyrolysis reactor, and a condenser. The crucial depolymerization reaction takes place in the fixed-bed pyrolysis reactor. The polymerization and depolymerization of lactic acid oligomers is a reversible dynamic equilibrium reaction, requiring a catalyst to promote the reaction towards depolymerization. Traditional depolymerization catalysts primarily use stannous octoate, a homogeneous catalyst suitable for pyrolysis reactors with falling film evaporators. However, homogeneous catalysts lack the core catalyst to induce the vaporization of volatile components in lactic acid oligomers. This affects the catalytic depolymerization effect and can lead to incomplete removal of volatile components from the depolymerization system, impacting the purity of the lactide. Introducing heterogeneous catalysts into depolymerization reactions can enhance the transfer of products to the gas phase. However, existing reaction equipment is difficult to match such heterogeneous catalytic processes. Therefore, it is necessary to develop a production device and process for synthesizing lactide based on a composite catalytic synthesis of homogeneous and heterogeneous catalysts. Summary of the Invention
[0003] To address the problems in the background art, this invention discloses a production apparatus and process for synthesizing lactide based on a homogeneous and heterogeneous composite catalytic process. The objective is: 1. Promotes the rapid vaporization of volatile components and removes them from the depolymerization reaction system.
[0004] 2. Enhance the overall reaction efficiency of lactic acid oligomers.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: A production apparatus for synthesizing lactide based on homogeneous and heterogeneous composite catalysis includes a dehydration polycondensation reactor, a peristaltic pump, a pyrolysis reactor, a condenser, a finished product tank, and a negative pressure transfer pump connected in sequence. The dehydration polycondensation reactor is equipped with a homogeneous catalyst addition pipe. The pyrolysis reactor includes a tank body with upper and lower mesh plates dividing the tank body into an upper chamber, a middle chamber, and a lower chamber. The upper chamber is connected to the condenser, and a distributor is installed within the upper chamber, with its inlet end connected to the outlet end of the dehydration polycondensation reactor. A heater and a heterogeneous catalyst are installed within the middle chamber.
[0006] Further improve the technical solution: A waste liquid tank is installed below the tank body, and the lower cavity of the tank body is connected to the waste liquid tank.
[0007] Further improvements to the technical solution: The heater is an electric heating tube or a heat transfer oil heating coil.
[0008] Further improvements to the technical solution: The solid materials include zeolite, molecular sieve, activated carbon, ceramsite, metal-organic framework, and covalent organic framework.
[0009] Further improvements to the technical solution: The homogeneous catalyst includes stannous octoate, stannous chloride, and creatinine.
[0010] Further improve the technical solution: the particle size of the solid material is between 2 and 20 mesh.
[0011] A process for producing lactide includes the following steps: S1: Lactic acid raw materials are polycondensed through a dehydration polycondensation reactor to generate lactic acid oligomers; S2: Lactic acid oligomers are depolymerized in a pyrolysis reactor to generate lactide; The solid material in the cavity of the pyrolysis reactor is divided into three layers: the upper layer has a size of 2-5 mesh and is heated at 180-200℃; the middle layer has a size of 5-10 mesh and is heated at 190-220℃; and the lower layer has a size of 10-20 mesh and is heated at 200-240℃. After the lactic acid oligomers and homogeneous catalyst enter the cavity through a distributor, they come into full contact with the solid material. Under the action of heating, negative pressure, and heterogeneous catalyst, the volatile components in the lactic acid oligomers first vaporize and are then discharged from the production unit by a negative pressure pump. Under the combined catalysis of the homogeneous and heterogeneous catalysts, the lactic acid oligomers undergo a depolymerization reaction to generate lactide vapor, which is then cooled in a condenser to obtain the finished lactide product.
[0012] Further improvement of the technical solution: In S1, L-lactic acid with a purity of 98.5% is selected as raw material, added to the dehydration polycondensation reactor and stirred, and then 1% stannous octoate is added to the dehydration polycondensation reactor as a homogeneous catalyst; under the conditions of 120-160℃ and vacuum degree of 80-85kPa, dehydration polycondensation is carried out for 10 hours to generate lactic acid oligomers with a degree of polymerization of 8-12. The water generated during the reaction is discharged from the production device through a negative pressure conveying pump.
[0013] Further improve the technical solution: In S2, after continuous production for 2 hours, stop the machine, use the weighing method to calculate the crude yield of lactide, and detect the optical purity of lactide.
[0014] After implementing the above technical solution, compared with the prior art, the present invention can produce the following beneficial effects: 1. The present invention sets a heterogeneous catalyst (solid material) in the pyrolysis reaction vessel. The pore structure in the solid material provides vaporization nuclei for the volatile components in the lactic acid oligomer. These nuclei can induce the formation and growth of bubbles during the heating process, reduce the environmental pressure when bubbles are formed, help the product to transfer to the gas phase, promote the rapid vaporization of the volatile components, and thus discharge the volatile components from the depolymerization reaction system.
[0015] 2. This invention combines the advantages of both homogeneous and heterogeneous catalysts. Homogeneous catalysts can promote the depolymerization of lactic acid oligomers in the liquid phase, while heterogeneous catalysts provide a vaporization interface to promote the rapid vaporization of volatile components. The synergistic effect of the two enhances the overall reaction efficiency of lactic acid oligomers.
[0016] 3. This invention divides the pyrolysis reactor into three chambers, effectively separating waste liquid residue, heterogeneous catalyst, and gaseous products in the upper chamber, thus avoiding catalyst loss and product entrainment.
[0017] 4. The present invention ensures efficient conversion of the product through staged heating, while reducing the high-temperature process of the lactide produced in the bottom layer, thus avoiding racemization caused by high temperature.
[0018] 5. The particle size of the solid material increases layer by layer from top to bottom, which can prolong the movement process of lactic acid oligomers, increase the reaction time, and avoid gas-liquid entrainment. Attached Figure Description
[0019] Figure 1 The diagram shown is a schematic diagram of the overall structure of this lactide preparation apparatus.
[0020] Figure 2 The diagram shown is a schematic of the structure of a pyrolysis reactor.
[0021] In the diagram: 1. Dehydration condensation reaction vessel; 1.1. Homogeneous catalyst addition pipe; 2. Peristaltic pump; 3. Pyrolysis reaction vessel; 3.1. Upper mesh plate; 3.2. Lower mesh plate; 3.3. Distributor; 3.4. Heater; 3.5. Heterogeneous catalyst; 4. Condenser; 5. Finished product tank; 6. Negative pressure transfer pump; 7. Waste liquid tank. Detailed Implementation
[0022] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely for explaining the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. It should be noted that in the description of the present invention, terms such as "front," "rear," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is merely for ease of description and does not indicate or imply that the device or element must have a specific orientation and positional relationship, and therefore should not be construed as a limitation of the present invention. It should also be noted that in the description of the present invention, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.
[0023] Reference Figure 1 and Figure 2 This embodiment provides a production apparatus for synthesizing lactide based on a homogeneous and heterogeneous composite catalytic process, comprising a dehydration polycondensation reactor 1, a pyrolysis reactor 3, a condenser 4, a finished product tank 5, and a negative pressure transfer pump 6 connected in sequence.
[0024] The dehydration polycondensation reactor 1 is existing technology, used for dehydrating and polycondensing lactic acid raw materials to generate lactic acid oligomers. In this invention, the dehydration polycondensation reactor 1 is equipped with a homogeneous catalyst addition pipe 1.1, which is used to add a homogeneous catalyst, such as a stannous octoate solution, into the reactor 1. This is equivalent to adding a homogeneous catalyst that facilitates the depolymerization of the lactic acid oligomers beforehand.
[0025] The pyrolysis reaction vessel 3 includes a vessel body, in which an upper mesh plate 3.1 and a lower mesh plate 3.2 are horizontally arranged. The upper mesh plate 3.1 and the lower mesh plate 3.2 divide the interior of the vessel body into an upper cavity, a middle cavity and a lower cavity from top to bottom.
[0026] The upper chamber is connected to the condenser 4 via a U-shaped tube, used to transport the lactide vapor generated by pyrolysis to the condenser 4 for cooling. A distributor 3.3 is installed in the upper chamber; the distributor 3.3 can be a spray head or a distribution plate. The inlet end of the distributor 3.3 is connected to the outlet end of the dehydration polycondensation reactor 1 via an inlet pipe. A peristaltic pump 2 is installed on the inlet pipe, used to quantitatively deliver the mixed solution of lactic acid oligomer and stannous octoate from the dehydration polycondensation reactor 1 to the distributor 3.3, and then evenly distribute it into the middle chamber.
[0027] A heterogeneous catalyst 3.5 is filled within the cavity, and a heater 3.4 is provided. The heterogeneous catalyst 3.5 is a solid material, such as zeolite, molecular sieve, activated carbon, ceramsite, metal-organic framework, or covalent organic framework. These solid materials have numerous micropores, which act as vaporization nuclei, promoting the rapid vaporization of volatile components (lactic acid monomers, lactic acid dimers, and cyclic lactic acid dimers) in the lactic acid oligomers, allowing them to exit the depolymerization reaction system earlier. The heater 3.4 can be an electric heating tube or a heat transfer oil heating coil. The heater 3.4 surrounds the inside or outside of the cavity and provides the temperature required for the depolymerization reaction (typically 170-250°C).
[0028] To create a stable pyrolysis environment within the cavity, both the upper mesh plate 3.1 and the lower mesh plate 3.2 are high-temperature resistant porous plates. The particle size of the heterogeneous catalyst 3.5 is larger than the pore size of the upper mesh plate 3.1, and the pore size of the upper mesh plate 3.1 is larger than the pore size of the lower mesh plate 3.2. The lower mesh plate 3.2 supports the heterogeneous catalyst 3.5 and allows unreacted liquid residue to drip into the lower cavity. Thus, by controlling the flow rate of the peristaltic pump 2, the mixed solution of lactic acid oligomer and stannous octoate, after entering the cavity through the distributor 3.3, can fill the cavity and reach dynamic equilibrium.
[0029] The solid material within the cavity is divided into three layers, each spaced 0-5 cm apart. Each layer contains an independent heater 3.4. The upper layer has a particle size of 2-5 mesh, and its heater 3.4 is set to a heating temperature of 180-200℃. The middle layer has a particle size of 5-10 mesh, and its heater 3.4 is set to a heating temperature of 190-220℃. The lower layer has a particle size of 10-20 mesh, and its heater 3.4 is set to a heating temperature of 200-240℃. During operation, the liquid mixture of lactic acid oligomers and stannous octoate moves downwards under gravity. Because the particle size of the solid material increases progressively from top to bottom, the falling velocity of the mixed solution is impeded by the solid material. This prolongs the depolymerization reaction process and prevents gas-liquid entrainment. Furthermore, the solid material acts as a solid catalyst, effectively promoting the depolymerization reaction. Furthermore, because the heating temperature increases layer by layer from top to bottom, it ensures efficient product conversion while reducing the high-temperature process of the lower layer of lactide, thus avoiding racemization caused by high temperatures. Experiments have shown that existing pyrolysis reactors with falling film evaporators typically achieve single-batch yields between 40% and 70%. However, this lactide preparation device combines the dual functions of homogeneous and heterogeneous catalysts. While the lactic acid oligomers flow slowly downwards, it does not impede the upward movement of gas, effectively improving the overall reaction efficiency of the lactic acid oligomers, achieving a single-batch yield of approximately 95%.
[0030] A drain port is provided at the bottom of the lower chamber, and a waste liquid tank 7 is provided below the tank body. The drain port is connected to the waste liquid tank 7, which is used to collect unreacted lactic acid oligomers and high-boiling-point residues.
[0031] Condensing tank 4 is existing technology. In this embodiment, condensing tank 4 adopts a coil-type condenser, with its inlet connected to the outlet at the top of the upper chamber and its outlet connected to the finished product tank 5. The function of condensing tank 4 is to condense lactide vapor and collect it in the finished product tank 5.
[0032] A negative pressure transfer pump 6 is connected to the finished product tank 5. The negative pressure transfer pump 6 has two functions: first, to establish a negative pressure (e.g., 1-10 kPa) in the pyrolysis reaction tank 3, reduce the boiling point of lactide, and promote the vaporization of volatile components in lactic acid oligomers; second, to realize the transfer of lactide between the pyrolysis reaction tank 3, the condenser tank 4, and the finished product tank 5.
[0033] A lactide production process applied to the above-mentioned lactide production unit includes the following steps: S1: Lactic acid raw materials are subjected to polycondensation treatment in a dehydration polycondensation reactor to generate lactic acid oligomers. L-lactic acid with a purity of 98.5% was selected as the raw material and added to the dehydration polycondensation reactor 1 under stirring. Then, 1% stannous octoate was added to the dehydration polycondensation reactor 1 as a homogeneous catalyst. The negative pressure transfer pump 6 was started to put the entire production unit under negative pressure. Dehydration polycondensation was carried out for 10 hours at a temperature of 120-160℃ and a vacuum degree of 80-85kPa to generate lactic acid oligomers with a degree of polymerization of 8-12. The water generated during the reaction was discharged from the production unit through the negative pressure transfer pump 6.
[0034] S2: Lactic acid oligomers are depolymerized in a pyrolysis reactor to produce lactide. Turn on the heaters 3.4 of each layer of the pyrolysis reactor 3, and simultaneously turn on the negative pressure delivery pump 6 to maintain the vacuum degree inside the entire device at 99-100 kPa. Turn on the peristaltic pump 2 to pump the lactic acid oligomer with a degree of polymerization of about 10 and the homogeneous catalyst (stannous octoate) from the dehydration polycondensation reactor 1 into the pyrolysis reactor 3, and evenly spray them into the central cavity of the pyrolysis reactor 3 through the distributor 3.3.
[0035] After the lactic acid oligomers and homogeneous catalyst enter the central cavity, they come into full contact with the solid material (activated carbon). The volatile components in the lactic acid oligomers (lactic acid monomers, lactic acid dimers, and lactic acid cyclic dimers) first vaporize under heating, negative pressure, and the action of the heterogeneous catalyst 3.5, and are then discharged from the depolymerization reaction system by the negative pressure pump 6. The principle is that the volatile components have low boiling points and low condensation points. As long as the cooling temperature of the condenser 4 is well controlled, the volatile components will not condense, but will be discharged from the production unit in a gaseous state via the negative pressure pump 6.
[0036] Then, under the combined catalysis of heating, negative pressure, homogeneous catalyst, and heterogeneous catalyst, lactic acid oligomers undergo depolymerization to generate lactide vapor. The catalytic principle of the heterogeneous catalyst is that the solid material (activated carbon) also provides a vaporization nucleus for the vaporization of lactide, which helps the product transfer to the gas phase, thereby promoting the rapid depolymerization of lactic acid oligomers.
[0037] After lactide vapor enters the upper chamber, it is transported under negative pressure into the condenser 4 and condensed into liquid, eventually flowing into the finished product tank 5. Unreacted liquid residue passes through the lower mesh plate 3.2 into the lower chamber and is eventually discharged into the waste liquid tank 7.
[0038] Table 1 shows the crude yield, chemical purity, and optical purity data of the products obtained under different reaction conditions.
[0039]
[0040] After 2 hours of continuous production, the machine was stopped. The crude lactide yield was calculated by weighing, and the optical purity of the lactide was determined by high-performance liquid chromatography (HPLC). For the detection, a CHIRALCEL OJ-3 chiral column was used with a hexane / ethanol (90 / 10) mobile phase, the column temperature was controlled at 35℃, and the detection wavelength was 223 nm. The crude lactide in the finished product tank was analyzed to determine its optical purity. A Venusil MP C18 column was used with a water / acetonitrile (90 / 10) 2% H3PO4 mobile phase, the column temperature was controlled at 35℃, and the detection wavelength was 210 nm. The crude lactide in the finished product tank was analyzed to determine its chemical purity.
[0041] It is worth noting that the content not described in detail in the above embodiments is prior art. It is also worth noting that any additions, subtractions, substitutions, and improvements made by those skilled in the art based on the structure and principles of this invention should be included within the scope of protection of this invention.
Claims
1. A production apparatus for synthesizing lactide based on homogeneous and heterogeneous composite catalysis, characterized in that: The system includes a dehydration polycondensation reactor, a peristaltic pump, a pyrolysis reactor, a condenser, a finished product tank, and a negative pressure transfer pump connected in sequence. The dehydration polycondensation reactor is equipped with a homogeneous catalyst addition pipe. The pyrolysis reactor includes a tank body with upper and lower mesh plates inside, which divide the tank body into an upper chamber, a middle chamber, and a lower chamber. The upper chamber is connected to the condenser and a distributor is installed in the upper chamber. The liquid inlet of the distributor is connected to the liquid outlet of the dehydration polycondensation reactor. A heater and a heterogeneous catalyst are installed in the middle chamber.
2. The production apparatus for synthesizing lactide based on homogeneous and heterogeneous composite catalysis as described in claim 1, characterized in that: A waste liquid tank is installed at the bottom of the tank body, and the lower cavity of the tank body is connected to the waste liquid tank.
3. The production apparatus for synthesizing lactide based on homogeneous and heterogeneous composite catalysis as described in claim 1, characterized in that: The heater is an electric heating element or a heat transfer oil heating coil.
4. The production apparatus for synthesizing lactide based on homogeneous and heterogeneous composite catalysis as described in claim 1, characterized in that: The homogeneous catalysis includes stannous octoate, stannous chloride, and creatinine.
5. The production apparatus for synthesizing lactide based on homogeneous and heterogeneous composite catalysis as described in claim 1, characterized in that: The solid materials include zeolite, molecular sieve, activated carbon, ceramsite, metal-organic framework, and covalent organic framework.
6. The production apparatus for synthesizing lactide based on homogeneous and heterogeneous composite catalysis as described in claim 1, characterized in that: The particle size of the solid material is between 2 and 20 mesh.
7. A lactide production process applied to the production apparatus according to any one of claims 1-6, characterized in that: Includes the following steps: S1: Lactic acid raw materials are polycondensed through a dehydration polycondensation reactor to generate lactic acid oligomers; S2: Lactic acid oligomers are depolymerized in a pyrolysis reactor to generate lactide; The solid material in the cavity of the pyrolysis reactor is divided into three layers: the upper layer has a size of 2-5 mesh and is heated at 180-200℃; the middle layer has a size of 5-10 mesh and is heated at 190-220℃; and the lower layer has a size of 10-20 mesh and is heated at 200-240℃. After the lactic acid oligomers and homogeneous catalyst enter the cavity through a distributor, they come into full contact with the solid material. Under the action of heating, negative pressure, and heterogeneous catalyst, the volatile components in the lactic acid oligomers first vaporize and are then discharged from the production unit by a negative pressure pump. Under the combined catalysis of the homogeneous and heterogeneous catalysts, the lactic acid oligomers undergo a depolymerization reaction to generate lactide vapor, which is then cooled in a condenser to obtain the finished lactide product.
8. The lactide production process as described in claim 8, characterized in that: In S1, L-lactic acid with a purity of 98.5% is selected as raw material and added to a dehydration polycondensation reactor for stirring. Then, 1% stannous octoate is added to the dehydration polycondensation reactor as a homogeneous catalyst. The dehydration polycondensation is carried out for 10 hours at a temperature of 120-160℃ and a vacuum degree of 80-85kPa to generate lactic acid oligomers with a degree of polymerization of 8-12. The water generated during the reaction is discharged from the production device through a negative pressure pump.
9. The lactide production process as described in claim 8, characterized in that: In S2, after 2 hours of continuous production, the machine was stopped. The crude yield of lactide was calculated by weighing, and the optical purity of lactide was tested.