Purification method of L-lactide
A purification method and lactide technology, applied in the direction of organic chemistry and the like, can solve the problems of large solvent consumption and low yield of the final product, and achieve the effect of low consumption of organic solvent and high yield
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[0056] In one embodiment, the preparation method of described L-lactide crude product comprises the following steps:
[0057] Mix L-lactic acid aqueous solution and catalyst, remove free water at 100-130℃ and normal pressure, then react at 140-160℃ and 20-40kPa for 1-2h, and then react at 170-190℃ and 5-15kPa for 2 -4h, reaching the end point of prepolymerization to generate oligomers;
[0058] Next, under the conditions of 220-240° C. and below 1 kPa, the oligomer is cracked and cyclized to generate L-lactide, which is distilled for 2-4 hours to obtain crude L-lactide.
[0059] Optionally, the catalyst is stannous octoate.
[0060] Optionally, the concentration of L-lactic acid in the L-lactic acid aqueous solution is 85-95 wt%.
[0061] Optionally, the weight ratio of the L-lactic acid aqueous solution to the catalyst is 800:(6-7).
[0062] In the present invention, the purity of the crude L-lactide can be 95.5-99.0%, which can be obtained by gas chromatography. Wherein,...
Embodiment 1
[0091] The present embodiment provides a kind of preparation method of L-lactide crude product, and the steps are as follows:
[0092] Step 1, adding 800g L-lactic acid aqueous solution with a concentration of 90wt% L-lactic acid to the 1000mL there-necked flask, adding 6.5g stannous octoate (catalyst) to the above-mentioned there-necked flask, stirring mechanically under an inert atmosphere, at a temperature of 130°C and free water under normal pressure. After that, the temperature was raised to 150°C, the pressure was reduced to 30KPa, and the reaction was carried out at a temperature of 150°C and a vacuum condition of 30KPa for 2 hours, then the temperature was raised to 180°C, and the pressure was reduced to 10KPa. At the end, oligomers are formed.
[0093] Step 2, Step 1 After generating oligomers, the temperature is raised to 230°C, the pressure is reduced to below 1kpa, and under vacuum conditions of 230°C and below 1kpa, the oligomers are cracked and cyclized, L-lacti...
Embodiment 2
[0096] The present embodiment provides a kind of purification method of L-lactide, and the steps are as follows:
[0097] Step 1: Prepare a sodium hydroxide absolute ethanol solution with a sodium hydroxide concentration of 0.1 wt% as a mixed solution for later use.
[0098] Step 2, take 80g of L-lactide crude product prepared in Example 1, add it to 160g of the mixed solution prepared in step 1 above, stir under an inert atmosphere, be warming up to 50 ° C, until the L-lactide crude product is completely dissolved in the mixed solution.
[0099]In step 3, the temperature of the solution obtained in step 2 is naturally returned to room temperature, and after crystallization for 1 hour, the crystallization is continued at 5° C. for 2 hours to obtain a solid-liquid mixture. The above solid-liquid mixture was suction filtered, and the obtained filter cake was washed once with 40 g of absolute ethanol and dried in vacuum to obtain 54.7 g of purified L-lactide with a yield of 68.3...
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