A negative pressure material conveying system for synthesizing lactide

Abstract

This invention provides a negative pressure material conveying system for the synthesis of lactide, relating to the field of chemical technology. The negative pressure material conveying system includes a multi-stage dehydration polycondensation reactor, a fixed-bed pyrolysis reactor, and a condenser. The condenser is connected to a vacuum pump, and the negative pressure generated by the vacuum pump is used for material conveying between the multi-stage dehydration polycondensation reactor, the fixed-bed pyrolysis reactor, and the condenser. A flow valve is installed between the dehydration polycondensation reactor and the fixed-bed pyrolysis reactor. This negative pressure material conveying system eliminates the need for a conveying pump in the pipeline, fundamentally solving the problems of easy clogging of conveying pumps, inability to control the material conveying volume, and the inability of pump conveying systems to continuously supply material under negative pressure. This negative pressure material conveying system enables continuous production of lactide and solves the problem of crystallization caused by material remaining in the conveying pipeline for a long time.

Description

Technical Field

[0001] This utility model is specifically a negative pressure material conveying system for synthesizing lactide, and relates to the field of chemical technology. Background Technology

[0002] D- and L-lactide are characterized by their renewability and biocompatibility. As a key precursor of polylactic acid (PLA), lactide is widely used in biodegradable materials, biomedical materials, 3D printing materials and other fields.

[0003] Lactide is prepared from lactic acid through dehydration condensation, oligomer depolymerization, and purification processes. The oligomer depolymerization reaction must be carried out under negative pressure. (See attached diagram.) Figure 1 Existing lactide production equipment mainly includes a stage I dehydration polycondensation reactor 1, a stage II dehydration polycondensation reactor 2, a fixed-bed pyrolysis reactor 3, and a condenser 4. A vacuum pump 5 is connected to the fixed-bed pyrolysis reactor 3, which provides a negative pressure reaction environment. To ensure the vacuum level of the fixed-bed pyrolysis reactor 3, an intermittent production method is adopted. The transfer of liquid materials between the stage I dehydration polycondensation reactor 1, the stage II dehydration polycondensation reactor 2, and the fixed-bed pyrolysis reactor 3 is achieved by a transfer pump 6. After feeding is completed, valve 7 is closed to ensure the vacuum level within the fixed-bed pyrolysis reactor 3. Existing lactide production equipment mainly has the following problems:

[0004] 1. A small amount of material entering the conveying pipeline will crystallize due to cooling. The crystallized material will block the conveying pump, causing the pump to be unable to convey materials normally.

[0005] 2. Due to the negative pressure at the output end, the conveying pump cannot control the amount of material conveyed;

[0006] 3. Unable to supply materials continuously, thus preventing continuous production. Utility Model Content

[0007] To overcome the shortcomings of the prior art, this utility model discloses a negative pressure material conveying system for synthesizing lactide, adopting the following technical solution:

[0008] A negative pressure material conveying system for synthesizing lactide includes a multi-stage dehydration polycondensation reactor, a fixed-bed pyrolysis reactor, and a condenser; the condenser is connected to a vacuum pump, and the negative pressure generated by the vacuum pump is used for conveying materials between the multi-stage dehydration polycondensation reactor, the fixed-bed pyrolysis reactor, and the condenser; a flow valve is installed between the dehydration polycondensation reactor and the fixed-bed pyrolysis reactor.

[0009] Further improvement to the technical solution: A vacuum tank is connected between the condenser and the vacuum pump.

[0010] Further improvements to the technical solution: The dehydration polycondensation reaction tank is equipped with 2-4 stages.

[0011] Further improved technical solution: The dehydration polycondensation reactor includes a stage I dehydration polycondensation reactor and a stage II dehydration polycondensation reactor, and the flow valve is set between the stage II dehydration polycondensation reactor and the fixed bed pyrolysis reactor; a negative pressure port is set at the upper part of the stage II dehydration polycondensation reactor, and the negative pressure port is connected to a vacuum pump.

[0012] Further improvements to the technical solution: A valve K1 is connected in series between the negative pressure port and the vacuum pump; a valve K2 is connected in series between the stage II dehydration polycondensation reactor and the fixed-bed pyrolysis reactor; and a valve K3 is connected in series between the stage I dehydration polycondensation reactor and the stage II dehydration polycondensation reactor.

[0013] After implementing the above technical solution, the beneficial effects of this utility model compared to the prior art are:

[0014] 1. This negative pressure material conveying system does not require the installation of conveying pumps and valves on the conveying pipeline, which fundamentally solves the problems of easy blockage of conveying pumps and valves and the inability of conveying pumps to control the amount of material conveyed;

[0015] 2. This negative pressure material conveying system solves the problem that pump conveying systems cannot continuously supply materials under negative pressure, enabling continuous production;

[0016] 3. Because it is a continuous production process, there is a continuous flow of material in the conveying pipeline and flow valve, which solves the problem of crystallization caused by the material being stuck in the conveying pipeline and flow valve for a long time. Attached Figure Description

[0017] Appendix Figure 1 The diagram shows a schematic of the pump delivery system in the existing lactide production process.

[0018] Appendix Figure 2 The diagram shown is a structural schematic of this negative pressure material conveying system.

[0019] In the attached diagram: 1. Stage I dehydration polycondensation reactor; 2. Stage II dehydration polycondensation reactor; 3. Fixed bed pyrolysis reactor; 4. Condenser; 5. Vacuum pump; 6. Transfer pump; 7. Valve; 8. Flow valve; 9. Vacuum tank. Detailed Implementation

[0020] The preferred embodiments of this utility model are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of this utility model and are not intended to limit the scope of protection of this utility model. It should be noted that in the description of this utility model, 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 this utility model. It should also be noted that in the description of this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" 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 this utility model according to the specific circumstances.

[0021] A negative pressure material conveying system for the synthesis of lactide, relating to the field of chemical technology, is disclosed. It primarily addresses problems in existing technologies, such as frequent blockages in conveying pumps due to material crystallization and the inability to control the material conveying rate. The composition and working principle of this negative pressure material conveying system are described in detail below.

[0022] See attached document Figure 2 The lactide production equipment mainly includes a multi-stage dehydration polycondensation reactor, a fixed-bed pyrolysis reactor 3, and a condenser 4. The dehydration polycondensation reactor dehydrates the raw material (lactic acid) and polycondenses it into low-molecular-weight polylactic acid through heating and catalysis. The fixed-bed pyrolysis reactor 3 heats and catalyzes the polylactic acid to generate gaseous lactide. The condenser 4 condenses the lactide vapor to obtain lactide crystals. Depending on the design requirements, the dehydration polycondensation reactor can be multi-stage. In this embodiment, it has two stages: a stage I dehydration polycondensation reactor 1 and a stage II dehydration polycondensation reactor 2. The raw material (lactic acid) sequentially enters the stage I dehydration polycondensation reactor 1 and the stage II dehydration polycondensation reactor 2 for the polycondensation reaction. The upper half of the first-stage dehydration polycondensation reactor 1 contains air, while the lower half contains a mixture of lactic acid and polylactic acid; the upper half of the second-stage dehydration polycondensation reactor 2 contains gaseous reactants, while the lower half mainly contains a polylactic acid solution.

[0023] To address the problems in the background technology, this negative pressure material conveying system has a vacuum pump 5 connected to the condenser 4. The negative pressure generated by the vacuum pump 5 is used for conveying materials between the first-stage dehydration polycondensation reactor 1, the second-stage dehydration polycondensation reactor 2, the fixed-bed pyrolysis reactor 3, and the condenser 4.

[0024] Specifically, a vacuum tank 9 is connected between the condenser 4 and the vacuum pump 5. The vacuum tank 9 has a large volume, which helps maintain a constant negative pressure. A negative pressure port is set at the top of the stage II dehydration polycondensation reactor 2, which is connected to the vacuum tank 9 through a pipe. Its function is to use negative pressure to draw lactic acid and polylactic acid from the stage I dehydration polycondensation reactor 1 into the stage II dehydration polycondensation reactor 2 to continue the polycondensation reaction. The depolymerization reaction in the fixed-bed pyrolysis reactor 3 needs to be carried out under a negative pressure environment with a vacuum degree ≤10mmHg. This negative pressure material conveying system, while ensuring the depolymerization reaction of oligomers, uses negative pressure to transport the polylactic acid generated in the stage II dehydration polycondensation reactor 2 to the fixed-bed pyrolysis reactor 3 for depolymerization reaction. Finally, the generated lactide vapor is drawn into the condenser 4 for condensation, realizing pump-free material conveying.

[0025] In order to control the amount of material conveyed and to maintain the negative pressure in the fixed bed pyrolysis reactor 3, a flow valve 8 is installed between the stage II dehydration polycondensation reactor 2 and the fixed bed pyrolysis reactor 3. The function of the flow valve 8 is to control the amount of material conveyed by adjusting the opening of the throat.

[0026] Although a negative pressure exists within the Stage II dehydration polycondensation reactor 2, it is insufficient to draw material from the Stage I dehydration polycondensation reactor 1 into it. Therefore, valve K1 is connected in series between the negative pressure port and the vacuum tank 9; valve K2 is connected in series between the Stage II dehydration polycondensation reactor 2 and the fixed-bed pyrolysis reactor 3; and valve K3 is connected in series between the Stage I dehydration polycondensation reactor 1 and the Stage II dehydration polycondensation reactor 2. Under normal production conditions, valve K1 is closed and valve K2 is opened. Under the negative pressure within the fixed-bed pyrolysis reactor 3, polylactic acid from the Stage II dehydration polycondensation reactor 2 is drawn into the fixed-bed pyrolysis reactor 3 for depolymerization. When it is necessary to draw material from the Stage I dehydration polycondensation reactor 1 into the Stage II dehydration polycondensation reactor 2, valve K2 is closed and valve K1 is opened simultaneously, using the negative pressure to draw material from the Stage I dehydration polycondensation reactor 1 into the Stage II dehydration polycondensation reactor 2. Under normal circumstances, valve K3 is always open and is used to balance the pressure between stage I dehydration polycondensation reactor 1 and stage II dehydration polycondensation reactor 2.

[0027] Comparison Appendix Figure 1 As can be seen, this negative pressure material conveying system eliminates the need for conveying pumps and valves in the conveying pipeline, fundamentally solving the problems of easy clogging of conveying pumps and valves, and the inability of conveying pumps to control the material conveying volume. More importantly, this negative pressure material conveying system solves the problem of pump conveying systems being unable to continuously supply materials under negative pressure, enabling continuous production.

[0028] It is also worth noting that, depending on the design requirements, the dehydration polycondensation reactor can be set up with 2-4 stages. Because it is a continuous production process, material is constantly flowing through the conveying pipeline, so the material will not crystallize due to prolonged stagnation in the conveying pipeline.

[0029] 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 utility model should be included within the protection scope of this utility model.

Claims

1. A negative pressure material conveying system for synthesizing lactide, comprising a multi-stage dehydration polycondensation reactor, a fixed-bed pyrolysis reactor, and a condenser, characterized in that: The condenser is connected to a vacuum pump, and the negative pressure generated by the vacuum pump is used to transport materials between the multi-stage dehydration polycondensation reactor, the fixed-bed pyrolysis reactor, and the condenser. A flow valve is installed between the dehydration polycondensation reactor and the fixed-bed pyrolysis reactor.

2. The negative pressure material conveying system for synthesizing lactide as described in claim 1, characterized in that: A vacuum tank is connected between the condenser and the vacuum pump.

3. The negative pressure material conveying system for synthesizing lactide as described in claim 1, characterized in that: The dehydration polycondensation reactor is equipped with 2-4 stages.

4. The negative pressure material conveying system for synthesizing lactide as described in claim 1, characterized in that: The dehydration polycondensation reactor includes a stage I dehydration polycondensation reactor and a stage II dehydration polycondensation reactor. The flow valve is located between the stage II dehydration polycondensation reactor and the fixed-bed pyrolysis reactor. A negative pressure port is provided at the top of the stage II dehydration polycondensation reactor and is connected to a vacuum pump.

5. The negative pressure material conveying system for synthesizing lactide as described in claim 4, characterized in that: A valve K1 is connected in series between the negative pressure port and the vacuum pump; a valve K2 is connected in series between the stage II dehydration polycondensation reactor and the fixed bed pyrolysis reactor; and a valve K3 is connected in series between the stage I dehydration polycondensation reactor and the stage II dehydration polycondensation reactor.

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