Technological process for synthesizing high-purity L-lactide
By controlling the temperature and negative pressure conditions in the reactor and combining with the catalyst, high purity L-lactide is prepared, which solves the problems of high energy consumption, high cost and low optical purity in the prior art, and realizes high purity lactide low-cost production supports the development of the polylactic acid industry.
Patent Information
- Application Number
- CN202411288499.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-13
- Publication Date
- 2024-12-20
AI Technical Summary
Domestic L-lactide synthesis technology has problems such as low yield, high cost and low optical purity, which has led to the limited development of the polylactic acid industry.
Using a new process flow, by adding L-lactic acid and catalyst to the reactor, controlling the temperature and negative pressure conditions, carrying out dehydration and negative pressure reactions to prepare high-purity L-lactide, catalysts such as creatinine, zinc oxide, and octanoic acid Stannous can improve catalytic efficiency.
The optical purity of crude L-lactide is achieved to reach 99.6%, reducing production costs, simple process and low energy consumption, and is suitable for large-scale applications.
Smart Images
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Abstract
Description
[Technical field]
[0001] The present invention belongs to the field of polymer material synthesis and relates to a method for synthesizing L-lactide. The present invention provides a process for synthesizing high-purity L-lactide. Lactide is the most important polymerization monomer for producing polylactic acid, and its chemical purity, optical purity and production cost determine the quality and economy of downstream polylactic acid products. [Background technology]
[0002] Domestic L-lactide synthesis technology generally has the problems of low yield, high cost and low optical purity. The optical purity of L-lactide determines the performance of ring-opening polymerization polylactic acid. Solving the problem of L-lactide synthesis process is the premise of expanding the polylactic acid industry. In recent years, due to the rapid development of my country's polylactic acid industry, the market demand for L-lactide, the core raw material for the production of polylactic acid, has continued to rise. However, due to technical and cost issues, the production of L-lactide in China is still blank. L-lactide is a cyclic ester used as an intermediate product for the production of polylactic acid and is a monomer required for the synthesis of high molar mass polylactic acid. Due to its expensive and time-consuming synthesis process, the cost of this dimer in the market is very high.
[0003] Patent CN1951933A discloses a method for preparing lactide, which belongs to the field of polymer material manufacturing. The method is characterized in that the method includes the following steps: a. Lactic acid oligomers are prepared using L-lactic acid as raw material; b. The prepared lactic acid oligomers are placed in a reaction vessel for reaction, and the reaction conditions are controlled as follows: the pressure is normal pressure, and the temperature is heated to 150-250°C; c. After the reaction, an inert gas at 200-500°C is introduced into the reactor to take out the reaction product in the reactor and cool it to 80-150°C for collection, and the collected mixture is purified to obtain lactide. Patent CN116041674A discloses a lactide polymerization process, including feeding, polymerization, devolatilization, granulation, packaging and other processes. In order to ensure the stability of the polymerization process and the stability of product performance, a multi-stage treatment method is used in both the polymerization stage and the devolatilization stage. However, the traditional preparation process has problems such as high energy consumption, high cost, and low optical purity.
[0004] The process flow for synthesizing high-purity L-lactide provided by the present invention is simple, has low energy consumption, low cost, and is easy to apply on a large scale. The optical purity of the crude L-lactide prepared by the present invention can reach 99.6%, thereby providing a new process for producing L-lactide. [Summary of the invention]
[0005] [Technical issues to be solved]
[0006] The purpose of the present invention is to provide a new process for preparing high-purity L-lactide, in order to solve the problems of high energy consumption, high cost, low optical purity, etc. in the field of synthesizing L-lactide. The present invention can overcome these disadvantages, and the synthesis process is simple. The optical purity of the crude L-lactide prepared by the present invention can reach 99.6%, the raw materials are cheap and easy to obtain, and the production cost is greatly reduced.
[0007] [Technical solution]
[0008] 1. (1) Prepare a reactor, add 500 g of L-lactic acid into the reactor, stir at 100 to 400 rpm, heat at 90 to 150° C., dehydrate under negative pressure for 1 to 4 h, obtain dehydrated lactic acid, and store the obtained dehydrated lactic acid in a desiccator.
[0009] (2) 80-150 g of dehydrated lactic acid is placed in a reaction kettle, 0.9-1.5 g of a catalyst is added, the heating temperature is 100-180° C., the stirring condition is 100-400 rpm, the vacuum degree is -0.5-0.1 MPa, and the negative pressure reaction is carried out for 3-8 hours to obtain L-lactide.
[0010] The water content of the L-lactic acid is 1% to 20%
[0011] The catalyst can be creatinine, zinc oxide, or stannous octoate, which can effectively improve the catalytic efficiency and the rate of converting dehydrated lactic acid into L-lactide.
[0012] [Beneficial Effects]
[0013] Lactide is the most important polymerization monomer in the production of polylactic acid. Its chemical purity, optical purity and production cost determine the quality and economy of downstream polylactic acid products. Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:
[0014] (1) The process flow of the technology of the present invention is simple, energy consumption is low, cost is low, and it is easy to apply on a large scale.
[0015] (2) The crude L-lactide prepared by the present invention has high optical purity.
Brief Description of the Drawings
[0016] Figure 1 This is a process flow chart for synthesizing L-lactide.
[0017] Figure 2 HPLC chart of L-lactide prepared after implementing the embodiment. [Specific implementation method]
[0018] Embodiment 1:
[0019] (1) Prepare a reaction kettle in advance, weigh 150 g of L-lactic acid into the reaction kettle, stir at 100 to 400 rpm, heat at 100° C., and dehydrate under negative pressure for 2 h to obtain dehydrated lactic acid, which is then stored in a desiccator.
[0020] (2) Weigh 90 g of dehydrated lactic acid into a clean reactor, add 0.9-1.5 g of catalyst, heat to 120° C., stir at 100-400 rpm, and react under negative pressure for 3 h to obtain L-lactide.
[0021] (3) Weigh a certain amount of L-lactide into a small glass bottle and dissolve it in ethanol:methanol at a volume ratio of 1:0.8 to 1:1.2 to determine the optical purity of L-lactide.
[0022] Embodiment 2:
[0023] (1) Prepare a reaction kettle in advance, weigh 200 g of L-lactic acid into the reaction kettle, stir at 100 to 400 rpm, heat at 110° C., and dehydrate under negative pressure for 2 h to obtain dehydrated lactic acid, which is then stored in a desiccator.
[0024] (2) Weigh 120 g of dehydrated lactic acid into a clean reactor, add 0.9-1.5 g of catalyst, heat to 130° C., stir at 100-400 rpm, and react under negative pressure for 4 h to obtain L-lactide.
[0025] (3) Weigh a certain amount of L-lactide into a small glass bottle and dissolve it in ethanol:methanol at a volume ratio of 1:0.8 to 1:1.2 to determine the optical purity of L-lactide.
[0026] Embodiment 3:
[0027] (1) Prepare a reaction kettle in advance, weigh 300 g of L-lactic acid in the reaction kettle, stir at 100-400 rpm, heat at 90° C., and dehydrate under negative pressure for 2 h to obtain dehydrated lactic acid, which is then stored in a desiccator.
[0028] (2) Weigh 150 g of dehydrated lactic acid into a clean reactor, add 0.9-1.5 g of catalyst, heat to 140° C., stir at 100-400 rpm, and react under negative pressure for 4 h to obtain L-lactide.
[0029] (3) Weigh a certain amount of L-lactide into a small glass bottle and dissolve it in ethanol:methanol at a volume ratio of 1:0.8 to 1:1.2 to determine the optical purity of L-lactide.
Claims
1. A process for synthesizing high-purity L-lactide, comprising the following steps: 1) Prepare a reaction kettle in advance, weigh 150g of L-lactic acid in the reaction kettle, stir at 100-400rpm, heat at 90-150°C, dehydrate under negative pressure for 1-4h to obtain dehydrated lactic acid, and store the obtained dehydrated lactic acid in a desiccator; 2) Weigh 90 g of dehydrated lactic acid into a clean reactor, add 0.9-1.5 g of catalyst, heat to 100-180° C., stir at 100-400 rpm, and vacuum at -0.5-0.1 MPa. React under negative pressure for 3-8 h to obtain L-lactide.
2. A process for synthesizing high-purity L-lactide according to claim 1, characterized in that: The water content of the L-lactic acid is 1% to 20%.
3. A process for synthesizing high-purity L-lactide according to claim 1, characterized in that: The dehydration temperature in step 1) is 90-150°C, and the reaction temperature in step 2) is 100-180°C.
4. A process for synthesizing high-purity L-lactide according to claim 1, characterized in that: The catalyst can be creatinine, zinc oxide, or stannous octoate, which can effectively improve the catalytic efficiency and the rate of converting dehydrated lactic acid into L-lactide.
5. A process for synthesizing high-purity L-lactide as described in claims 1-4, characterized in that: Take L-lactic acid as raw material, heat to 90-150°C, dehydrate under low pressure for 1-4h to obtain dehydrated lactic acid; take 80-150g of dehydrated lactic acid in a reactor, add 0.9-1.5g of catalyst, heat to 100-180°C, react under negative pressure for 3-8h to obtain L-lactide. The process flow for synthesizing high-purity L-lactide provided by the present invention has low energy consumption, cheap and easy-to-obtain raw materials, simple synthesis process, and greatly reduces production costs. The optical purity of L-lactide prepared by the present invention can reach 99.6%.